Electrical Discharge Machining

INTRODUCTION

Electrical Discharge Machining (EDM) is a controlled metal removal process that is used to remove metal by means of electric spark erosion. The English scientist Priestley first reported the erosive effect of electrical discharges in 1770.In this process, an electric spark is used as the cutting tool to cut the work piece to produce finished part. The metal removal process is performed by applying an electrical discharge of pulsed, high frequency alternating current or direct current through the electrode to the workpiece.The electrode location is controlled by the machine and is positioned so as not to contact the workpiece.A precise controlled space is maintained, allowing the spark to discharge its current from the electrode to the work piece through an insulated dielectric fluid of oil or water. This removes tiny particles of metal from the work piece.

EDM PROCESS

With the EDM process, both the work piece material and the electrode material must be conductors of electricity. The EDM process can be used in two different ways:


Figure.1

1. CONVENTIONAL EDM
In the EDM process, an electric spark is used to cut the workpiece, which takes the shape opposite to that of the cutting tool or electrode. The electrode and work piece are submerged in dielectric fluid, which is generally light lubricating oil. This dielectric fluid should be a non conductor (or poor conductor) of electricity. A servo mechanism maintains a gap of about 0.01 to 0.02 mm between the electrode and workpiece, preventing them from contacting each other.



Figure.2


2. WIRE-CUT EDM
The wire-cut EDM is discharge machine that uses CNC movement to produce the desired contour or shape. It does not require a special shaped electrode; instead it uses continuous traveling vertical wire under tension as the electrode. The electrode or cutting wire can be made of brass, copper or any other electrically conductive materials ranging in diameter from0.04 to 0.41 mm.The paths the wire follows is computer controlled along two axes (XY) contour, cutting a narrow slot through the work piece. This controlled movement is continuous and simultaneous in increments of 0.001 mm.Any contour may be cut to high degree of accuracy and is repeatable for any number of successive parts.The dielectric fluid maintains the proper conductivity between the wire and the work piece, and assists in reducing the heat caused by the spark.




Figure.3



Figure.4
DIELECTRIC FLUIDS
During the EDM process the work piece and electrode are submerged in the dielectric oil, which is an electrical insulator that helps to control the arc discharge. The dielectric oil that provides a means of flushing is pumped through the arc gap. This removes suspended particles of work piece material and electrode from the work cavity, insulates against premature discharging and helps to cool the electrode and work piece.

FLUSHING
One of the most important factors in a successful EDM operation is removal of the particles (chips) from the working gap. Flushing these particles out of the gap between the work piece and the electrode are very important to prevent them from forming bridges that cause short circuits. These arcs can burn holes in the work piece and in the electrode.EDMs have a built-in power adaptive control system that increases the pulse spacing as soon as this happens and reduces or shuts off the power supply.

IMPROVEMENT OF EDM PERFORMANCE

Rough machining gives poor surface finish due to micro cracks and pores, also finish machining gives better finish but in that case material removal rate(MRR) or machining speed is very less. Hence various monitoring and control systems were suggested such as continuous gap monitoring system, servo and pulse adaptive control system, knowledge based control system etc.It is very difficult to achieve higher cutting speed and better surface finish simultaneously. Hence it is considered as multi criteria optimization problem. Classical approach suggested by Fisher and Yates is inefficient because it considers one factor only at a time.Taguchi method also can optimize one factor either MRR or surface finish (SF) at a time. Hence it is supplemented with various supportive techniques such as fuzzy logic, grey relational analysis, two-phase parameter design, artificial neural network (ANN) and various combination methods.
Wire Electric Discharge Machining (WEDM) process is one of the important non traditional machining processes. It is used to machine hard materials, complex shapes and contours which are difficult by conventional methods. Particle swarm optimization (PSO) and Memetic algorithm (MA) based optimization procedures have been developed to optimize machining parameters viz.machining speed, pulse on time, pulse off time and peak current by using two response equations for material removal rate and surface roughness. The objective function considered for optimization is maximization of material removal rate and minimization of surface roughness. The objective function is solved by taking combined objective function (weight age given 50% to MRR and 50% to SR) i.e. minimization of MRR and SR.The output results of these two algorithms are compared.




Gap monitoring system identifies major gap states and thus differentiates between normal spark and harmful spark. The gap voltage and current signal have been modelled and analyzed mathematically by DDS (data dependent system).Radio and high frequency monitoring detects high frequency signal on the gap voltage. It can also provide pulse control to machine power generator.
Adaptive control for EDM adjusts the machine parameters such as servo settings, pulse off time, flushing rate etc as per the requirements so as to achieve optimal process performance i.e. maximum MRR and minimum tool wear ratio and desired integrity.
EDM fuzzy logic servo control system is capable of monitoring the gap states. Conventional EDM servo control systems, due to the lack of precise information of gap states (such as gap open, normal and harmful discharges etc) are unable to provide any action for avoiding the harmful acing. Servo feed and fuzzy logic strategy together encounters all measured gap parameters and thus makes the system capable to respond to all monitored gap signals in order to avoid arc damage and improve machining rate and work piece quality.
These monitoring and control system were not only complicated bit also costly and hence many times not economically feasible. Hence an experimental approach for parameter design was suggested.
Evaluation of machining performance in EDM is based on performance characteristics such as MRR, SR, electrode wear rate (EWR) and spark gap (SP) often called as uncontrollable factors. Various machining parameters such as peak voltage, pulse on time, pulse off time, peak current spark gap set voltage, wire feed rate, and wire tension over which an operator has sufficient control are referred as controllable parameters.

1. FUZZY LOGIC

Fuzzy model was developed with input parameters like tool-work piece combinations, tool area, tool wear, peak current and output parameters such as off time(microseconds),spark gap(mm) and servo sensitivity(milli volt/sec).Information obtained from the experimental model was,MRR is inversely proportional to quality. Increasing current (Ip) increases MRR but increases depth of heat affected zones. For finishing operation, productivity is determined by required surface finish, also for finish machining pulse recurrence frequency can be increased but it increases total and unit energy consumption. Setting off tool wear is sufficient as it determines accuracy and economy of operation and tool consumption. Higher off time decreases machining efficiency while too short off time prevents complete de-ionization of previously formed discharge channel causing abnormal discharges, which adversely affect tool wear, accuracy and surface finish. Hence optimum off time should be maintained. For optimum efficiency spark gap should be constant.
A fuzzy logic unit comprises of a fuzzifier, membership functions, a fizzy rule base, an inference engine and defuzzifier.First the fuzzyfier uses membership functions to fuzzyfy the signal to noise ratios. Next the inference engine performs fuzzy reasoning on fuzzy rules to generate a fuzzy value. Finally the defuzzifier converts the fuzzy value into a multi-response performance index. In the experiment two inputs X1(EWR) and X2(MRR) are given and one output (MRPI) i.e.Y is worked out.




Figure.5

Fig. Structure of the two input one output fuzzy logic unit.
X1=S/N ratio of first quality characteristic.
X2=S/N ratio of second quality characteristic.
Y=multi response performance index (MRPI)
Then MRPI for different levels of parameter is calculated. Larger the MRPI smaller is the variance. Based on ANOVA results it has been found out that work piece polarity; discharge current and open discharge voltage are significant parameters affecting multiple performance characteristics. The levels of these parameters are optimized. Experimental result shows and confirms that EWR is decreased from 29.9% to 20.7% and MRR is increased from 0.00159 to 0.00383 gm/min.










2. GREY RELATIONAL ANALYSIS

It can also be considered as one of approaches for solving the problem of multiple responses in EDM.A higher value of grey relational grade means that the corresponding process parameter is closer to the optimal value. Thus optimization of the complicated multiple process responses can be converted into optimization of a single grey relational grade.C.L.Lin, J.L.Lin and T.C.Ko carried out experimentation on SKD 11 alloy steel (12 mm diameter) using L-9 orthogonal array to optimize MRR, EWR and SR.The mathematical treatment is given out to calculate grey relational value Xi (k) for EWR, SR and MRR.Grey relational coefficient is then worked out. Averaging all grey relational coefficients, grey relational grade (yi) is obtained.
A higher value of grey relational grade represents a stronger relational degree between the reference sequence and the given sequence. Also the higher value of the grey relational grade indicates the closeness of process parameters closer to the optimum level. Calculations using grey relational analysis are simpler, straight forward than fuzzy based Taguchi method for optimizing the EDM process with multiple process responses.

3. TWO PHASE PARAMETER DESIGN

Two phase parameters designed strategy using Taguchi technique develops a robust high speed and high quality EDM process. A system with dynamic characteristics is no longer suitably designed using the conventional Taguchi approach, which is based on static characteristic. In actual practice the energy transmission of any system does not happen as designed or intended as there may be noise factors disturbing the system. The reality of the system therefore consists of non linear effects between input and output. Hence two phase parameter strategy with double signals for process optimization was proposed.




Figure.6


The result of the two phase dynamic experiment shows that the factor pulse on time, low voltage electric current high voltage sparking current have maximum influence on EDM process robustness. The factor pulse on time and low voltage electric current are controlling factors for EDM machining speed. The final product dimension can be further adjusted to the desired dimension using the second ideal function model. This method is simple, effective and efficient in developing a robust, high speed and high quality machining process.

4. ARTIFICIAL NEURAL NETWORK (ANN)

ANN can also model the multi objective optimization problem. ANN is a logical structure in which multiple processing elements communicate with each other through the interconnections between the processors. A feed forward back propagation learning algorithm that uses a gradient search technique to minimize the mean square deviation between the actual output and the desired output patterns is used to solve multi criteria problem.Dr.Bhattacharya carried out an experimental investigation of two response parameter i.e. cutting speed, surface roughness on Electra supercut-734 with titanium aluminide alloy as a work piece material.
The experimental results are first used to train the neural network. For training the network in cumulative learning; the delta weights are accumulated and the weights are adjusted until a complete set of input and output pairs are presented to the network. ANN model is then tested and varied for its performance by using training data. Initially three levels of six different input parameters (Ton, Toff, SP, Wt, SV, flow rate of dielectric fluid) which are then increased up to five for generating more number of optimum points, so as to give 15625 different combinations and hence the use of ANN model is highly justified as it is not feasible to carry out 15625 experiments. ANN gives important combinations to be worked out and further optimizes the system.

5. COMBINATION METHODS

Combination of EDM and ball burnishing machining (BBM) for surface improvement by modifying the micro structure of the machined surface (i.e.minimise surface roughness) eliminates micro cracks and pores. In this arrangement two ZnCr2 balls of 5 mm diameters attached with tool applies force to form a deformation layer and ultimately produces reinforced surfaces. Improved surface roughness ratio (ISRR) is then calculated as



(SRedm—SRedm+bbm)*100
ISRR= _____________________ %
SRedm
Where SRedm+bbm=Surface roughness obtained by combining EDM&BBM
SRedm=Surface roughness obtained by conventional EDM (micrometer Ra)
Thus combination of EDM&BBM is a feasible process for obtaining fine finishing and surface modifications. This method is found to be effective for eliminating the micro cracks and pores caused during machining.

MATHEMATICAL MODEL OF WEDM

(A). RESPONSE EQUATION FOR MRR

MRR=1.6184-0.0404{[(A-1.375)2 /0.01]-(8/12)}-0.0138(B-20)-0.0465{[(D-3.5)2/0.25]-(8/12)} ---- (1)
It is evident from the above response equation for MRR that out of four input operating parameters considered only three parameters namely machining speed, pulse on time and peak current are significant in MRR.

(B). RESPONSE EQUATION FOR SURFACE ROUGHNESS

Ra= 1.6592+0.687[A-1.375][1-4.07(D-3.5)-0.0061[C-20]+0.0374[((D-3.5)2-(8/12--------- (2)
It is evident that from the above equation out of four operating parameters considered only three parameters viz. machining speed, pulse off time and peak current are significant in surface roughness.

(C). COMBINED OBJECTIVE FUNCTION (COF)

COF= [WF1*Ra/Ra*]-[WF2*MRR/MRR*] -------- (3)
Where WF1=weight age factor 1=0.5
WF2=weight age factor 2=0.5
Ra*=2, surface roughness limitation in micro meter.
Ra*=2, MRR limitation in mm3/min.
The COF considered for optimization are maximization of MRR and minimization of surface roughness.

6. PARTICLE SWARM OPTIMIZATION (PSO)
PSO was developed by Dr.Eberhart and Dr.Kennedy in 1995.PSO is initialized with a group of random particles and then searches for optima by updating generations. In every iteration each particle is updated by following two “best” values. The first one is the best solution (fitness) it has achieved so far. This value is called pbest.Another best value that is tracked by the particle swarm optimizer is the best value, obtained so far by any particle in the population. This best value is a global best called gbest.When a particle takes a part of the populations its topological neighbours,the best value is a local best and is called lbest.After finding the two best values, the particle updates its velocity and position with following equation (a)&(b).
V[ ]=C1*rand( )*(pbest[ ]-present[ ])+C2*rand( )*(gbest[ ]*(gbest[ ]-present[ ]) ------ (a)
Present [ ] =persent [ ] +V [ ] ------ (b)
V [ ] is the particle velocity.
Persent [ ] is the current particle (solution).
Rand ( ) is a random number between 0&1.
C1, C2 are velocity factors.
Velocity values for C1=2.25, C2=3.25




Figure.7

6.1. IMPLEMENTATION OF PARTICLE SWARM ALGORITHM

The four WEDM parameters such as machining speed, pulse on time, pulse off time and peak current are considered as particle. The four particles are initialized using the following formulae.
Machining speed (A) =A min-{(A max-A min)*ran (0-1)}
Pulse on time (B) =B min + {(B max –B min)*ran (0-1)}
Pulse off time(C) =C min+ {(C max-C min)*ran (0-1)}
Peak current (D) =D min+ {(D max-D min)*ran (0-1)}
After initializing each particle in the first iteration, MRR, SR is calculated. Then pbest &gbest are chosen in the first iteration. In the second iteration each particle of the first iteration are updated using velocity formula (a) & (b).Then pbest & gbest are chosen in the second iteration. This process is continued in all iteration.

7. MEMETIC ALGORITHM (MA)

The combination of local search operators with a global search technique has provided very good results in certain optimization problems. The resulting algorithm from such an approach is termed as memetic algorithm. Particle swarm optimizer (global search) &simulated annealing (local search) are combined. The memetic approach takes the concept of evolution. It combined with an element of local search. PSO employs the basic operational steps of population initialization, updating the particles position by acceleration. An additional component of the algorithm is the notion that each individual can be readily improved upon.





Figure.8

7.1. SIMULATED ANNEALING

It is a point by point method. The algorithm begins with an initial point and a high temperature T.A second point is created at random in the vicinity of the initial point and the difference in the function values (E) at these two points is calculated. If the second point has small function value, otherwise point is accepted with the probability exp {-∆E/T}.This completes one iteration of the simulated annealing procedure. In the next generation another point is created at random in the neighborhood of the current point & the metropolis algorithm is used to accept or reject the point. The algorithm is terminated when a sufficiently small temperature is obtained or a small enough change in function values is found.

7.2. IMPLEMENTATION OF MEMETIC ALGORITHM

The four WEDM parameters are initiated the initial population as explained in PSO.MRR, Ra&COF are calculated using the formulae (1), (2) & (3) respectively and algorithm explained in simulated annealing. Then pbest&gbest values were chosen using PSO algorithm. In the second iteration each particle of first iteration is updated using velocity formulae (a) & (b).Then MRR, Ra, COF are calculated using SA.Then pbest, gbest values are chosen. Thus the entire iteration is continued with the same procedure.



RESULT AND DISCUSSION

PSO technique produces maximum combined objective function value at initial iteration and minimum COF value in the subsequent iterations. MA produces varying COF value in the initial stages &middle stages. At the end of the iterations MA produces better results i.e. minimum COF values.



Figure.9


Figure.10

CONCLUSION
Taguchi method which is supplemented with various supportive techniques minimizes the complexities involved in setting the process parameters so as to satisfy multi objective optimization for maximum MRR&minimum SR and power consumption simultaneously. PSO and MA based procedures used to optimize WEDM parameters viz. machining speed, pulse on time, pulse off time and peak current by taking COF.From the test analysis, it is evident that PSO technique yields better results than MA.This optimization process is easy to use and very simple to implement and efficient in handling COF.















REFERENCES

Journal: MANUFACTURING TECHNOLOGY TODAY (MTT)
CMTI, A NICMAP Publication, Volume 3, July 2004. (pp 11-21).
Books: 1. R.K.Jain, “Production Technology”, Khanna Publishers.
2. HMT Production Technology, Tata McGraw-Hill.
3. Steve Krar& Arthur Gill, “Exploring Advanced Manufacturing
Technology”, Industrial Press Inc.
Websites: www.charmillesus.com
www.makino.com

ELECTRIC DRIVES

INTRODUCTION



Machining time per work piece represents one of the most important parameters in the area of manufacturing technology with respect to attainable productivity and is the sum of cutting and non-cutting time for a specific work piece. One way to improve productivity is to reduce both these time parameters. The non-cutting times mainly comprises the time required for positioning and tool changes. Clearly increasing the positioning speed and acceleration of the machining tool by properly designing the drive, decrease non-cutting time and increase in productivity can be achieved. In a general machine tool the feed rate during machining is appropriate. During other movements the feed rate is high. In the Electro Mechanical drive system discussed here the feed unit is equipped with 2 motors one (brake motor) for rapid advance &other (standard motor) for slow feed as shown in fig .1b.It is designed in such a way that movement at feed rate is restricted to cutting length while all idle distance are traveled at rapid traverse rate.

The fine boring machine consist of bed, table, lead, screw, brake motor, slow feed motor & two spindle one at each side of the fine boring machine as shown in fig 1b.



FIGURE. (1b)

The main functions of table drive are the following (fig 1a):

1. Job that is fixed on table is moved from left to right fast called as rapid advance (RA).
2. Boring using right spindle take place slowly (SF).
3. Table is moved from right to left fast (Rapid Return-RR).
4. Boring take place left spindle slowly (SF).
5. Ttable brought to home position fast (RR).






FIGURE (1a)


CONCEPT OF ELECTRIC DRIVE

In many of the industrial applications an electric motor is the most important component. A complete production unit consists of primarily of three basic components; an electric motor, an energy transmitting drive and the working (or driven) machine.

An electric motor is source of motive power. An energy-transmitting device delivers power from electric motor to the driven machine (or the load) it usually consists of shaft, belt, chain, rope, etc. A working machine is the driven machine that performs the required production process. Examples of working machines are lathes, centrifugal pumps, drilling machines, boring machines, etc. An electric motor together with its control equipment and energy-transmitting device forms an electric drive. An electric drive together with its working machine constitutes an electric drive system. A ceiling fan motor with its speed regulator but without blades is an example of electric drive. Other examples of electric drives are: - a food mixer without food to be processed, a motor and Conveyer belt without any material on its belt. Some examples of electric drive systems are: a ceiling fan motor with regulator and also with blades, a food mixer with food to be processed, a motor and conveyer belt with material on its belt and so on.





Figure shows an electric drive system. The electric drive, consisting of electric motor, its power controller and energy-transmitting shaft

BORING

Boring is a machining process in which internal surfaces of revolution are generalized with a single point cutting tool. The term `boring` is applicable to enlarging an existing drilled or cored hole and it also includes machining of blind holes, holes with contoured bores and bores with steps, under cuts, etc.

FINE BORING MACHINE

Fine boring machines are precision boring machines built to machine components requiring high degree of accuracy and surface finish. The boring spindle, which is the heart of these machines, can be of a ball, roller bearing, hydrostatic, or air bearing type. On these machines, diamond tools can be use to achieve high degree of accuracy and surface finish.


ELECTRO MECHANICAL DRIVE SYSTEM FOR FINE BORING MACHINE

OPERATION OF DRIVE SYSTEM

The total drive system consists of a brake motor, slow feed motor, lead screw, guide ways and table. Brake motor is meant for rapid feed rate when table travels the idle distance. When the table has moved the idle distance, the brake motor will be switched off. Slow feed motor will be switched on. The table moves slowly. The sequence of operations is controlled by limit switches. The operations controlled by limit switches are explained below (refer fig.1c).



1, 2, 3, 4-LIMIT SWITCHES
FIGURE (1c)
First brake motor is switched on and Rapid table movement follows. Spindle motor is also on. Limit switch 1 is on. When the table moves left to right and meets limit switch by trip dog brake motor stops. Slow feed motor is on. Table is under slow feed job facing right side spindle. Limit switch 2 is on. When the t able moves and meets limit switch 2 slow feed motors is off. Spindle also off.

Next brake motor is switched on in the reverse direction. Table under rapid rate. Limit switch 3 is on. When table moving towards left touches limit switches 3 and brake motor stops. Slow feed motor is on. Table is under slow feed and job facing the left spindle. When table meets limit switch 4, slow feed is off. Brake motor is on. Table comes to home position. This is the cycle of events that tables placed in a fine boring machine drive system under operation.

GEAR ARRANGEMENT

The gear box is designed for transmitting power from brake motor to lead screw via sun and planet gear during rapid advance and transmitting power from slow feed motor to lead screw via change gear, bevel gears and sun & planet gear during slow feed. By varying the change gears during slow feed as many as 45 feeds can be obtained.



FIGURE (2a)
First when the brake motor rotates it transmits power to gear A. From gear A it is transmitted to B (spur gear) .The speed reduces. From B it is transmitted to gear C (sun gear) &C to D (planet gear) D to 9, 9 to 10 and 10 to 8. From 8 power is transmitted to lead screw 12 via 10A and 11 as shown in figure.





FIGURE (2b)



FIGURE (2c)
Now the lead screw rotates at rapid feed rate. When the lead screw rotates table gets linear motion and moves towards the spindle. When it reaches near the spindle, the brake motor is switched off and slow feed motor is switched on. The power is transmitted from standard motor (slow feed motor) to change gear 1. From spur gear 1 power is transmitted to spur gear 2 and speed is reduced considerably. Again the speed is reduced by transmitting via gears 3,4,5 and 6.Bevel gears 7 is fixed at the other side of spur gear. From bevel gear 7 power is transmitted to bevel gear 8 in perpendicular direction. From, bevel gear 8 power is transmitted through sun and planet gears C, D, 9, 10 and 10A, level to lead screw 12 and table gets slow feed.


CALCULATION OF RAPID FEED

The rapid rate is got from Brake Motor rotating at 1500 rpm. The power is transmitted from brake Motor to lead screw 12 via C, D, 9, 10A, 11 as shown in fig. 2.

From fig. 2 the gear ratio for rapid rate
= (ZA / ZB) * (ZC / ZD) * (Z9 / Z10) * (Z10A / Z11)

This is calculated as follows:

The gear ratio = (26/51)*(20/13)*(13/22)*(22/53)
= 0.192378

Pitch of screw = 8
No. of start = 2

Multiply the gear ratio by 1500, rpm of brake motor and pitch of lead screw thread and no. of start, we get rapid rate
= 0.192378*1500*8*2 mm/min
= 4617 mm/min
= 4.6 m/min
So the rapid rate at which the table will be moving is 4.6 m/min. During rapid rate only the brake motor will be switched on. The slow feed motor will be switched off. So there will be no power transmission to the gears meant for slow feed.


CALCULATION OF SLOW FEED

Slow feeds obtained from slow feed motor. Power is first transmitted from slow feed motor to gear 8 via, gears 1,2,3,4,5,6,7(ref fig 2). From gear 8 power is transmitted through sun and planet gears CD, 9, 10 then from 10 to 10A and 11 &12 leads screw.
The speed ratio after passing through sun and planet gear is got from table1. The type of planetary gearing as shown in fig3 is compound planetary drive with two sun wheels. From the table1, for the present application, drive no.2 is selected.

Among the fixed ratio drive possibilities,

The transmission ratio I = (rpm of driver /rpm of driven). Is got as
= Z10ZD/ (Z10ZD-ZCZ9)
(Refer drive no.2 in table 1& fig 2&3)

ZC = 20, Z10 = 22, ZD =13, Z9 =13

The speed ratio after passing through planet gear is
=22*13/ (22*13-20*13)
= 286/26 =1:11



Table 1 Fixed ratio drive possibilities (Compound planetary drive with two sun gears-fig 3)

Drive No. 1 2 3 4 5 6
Fixed Member 1 1 2 2 4 4
Driver 2 4 1 4 1 2
Driven 4 2 4 1 2 1
Transmission ratio I
=(Rpm of driver/rpm of driven) 1=(ZCZD/
Z10ZD) Z10ZD/(Z10ZD-ZCZ9) 1-(Z10ZD)/ZCZ9) (ZCZ9)/
(ZCZ9-Z10ZD) (Z10ZD)/
(ZCZD) (ZCZ9)/
(Z10ZD)



The speed is reduces 11 times after passing through sun and planet gear CD 9 &10.we can get as many as 45 feed rate using change gears and with and without reductor.

The gear ratio for slow feed can be obtained from fig.2 as
(Z1/Z2)*(Z3/Z4)*(Z5/Z6)*(Z7/Z8)*(1/11)
(The speed ratio after passing through sun and planet gear) *(Z10A/Z11)

In this (Z7/Z8)*(1/11)*(Z10A/Z11) is common for all 45 feeds.

They are (30/47)*(1/11)*(22/53)*(Z5/Z6)

Are change gears, which will be changed each time, when different feeds required. The different change gears starting from
(15/67) 0 (54/29) are shown in table 2.

As per table 2, first 15 feeds are obtained with gear pair.

Z1/Z2 = 41/41, Z3/Z4 = 41/41
Z5/Z6 change gears

By varying change gear we can get first 15 speeds.
For example the feed rate 129 mm/min is obtained from
(41/41)*(41/41)*(15/67)*(30/47)*(1/11)*(22/53)*1500

(Rpm of slow feed motor)*8 (pitch of the lead screw)*2(no of start -double start)
= 129 mm/min

Next 15 feed rates are obtained by putting
Z1/Z2 = 18/64, Z3/Z4 = 15/67

Z5/Z6 change gears

By varying change gears we can get next 15 feeds. For example the feed rate 8 mm/min.is obtained from
(18/64)*(15/67)*(15/67)*(30/47)*(1/11)*(22/53)

For example the feed rate 36mm/min is obtained from
=8 mm/min
Table 2 Different Slow Feeds

Change Gear 5 Change Gear 6 Slow Feed MM/Min
Number of Teeth Z5 Number of Teeth Z6 Z5 / Z6 Range without Reductor and with 41/41*41/41 Range with Reductor 18/64 with gear pair
15*67 41*41
15 67 15/67 129 8 36
18 64 18/64 162 10 45
22 60 22/60 212 13 59
26 57 26/57 263 16 74
29 54 29/54 310 19 87
32 51 32/51 363 23 102
35 48 35/48 421 26 118
37 45 37/45 475 29 133
41 41 41/41 578 36 162
43 39 43/39 637 40 180
45 37 45/37 703 44 200
48 35 48/35 792 49 222
51 32 51/32 921 57 259
54 29 54/29 1076 67 302


Next 15 feed rates are obtained by keeping
Z1/Z2 = 18/64, Z3/Z4=41/41

Z5/Z6 change gears

By varying change gears we can get next 15 feed rates.

For example the feed rate 36 mm/min is obtained from
(18/64)*(41/41)*(15/67)*(30/47)*(1/11)*(22/53)*1500*8*2
=36 mm/min
CYCLE TIME OF FEED

The cycle times of doing the five operations are calculated as follows. The job selected is shown in fig 4. The component taken for the boring is the cylinder of one type of I.C. engine. The bore 500.05 is made on fine boring machine. The cylinder is having a length of 70 mm.

Cutting speed = 90 m/min for material cast iron and cutter carbide tip




Figure 4


Details of the component bored in fine boring machine

Material: cast iron
Component name: cylinder for I.C Engine
All dimensions are in mm

Cutting speed = (DN/1000)
= 90 m/min

Dia of bore D = 50 mm

N = (90*1000)/ (*50)
= 600 rpm.

Feed rate for fine boring 0.05 mm/rev. (normal feed for fine boring operation)

Feed /min = 600*0.05
= 30 mm/min

Bore length = 70 mm

Machining time = (70/30)*60
= 140 secs.

Rapid rate = 4600 mm/min
Rapid travel = 300 mm

Time for rapid travel = (300/4600)*60
= 4 sec.

Time for feed

Table from home position to right = 4secs
Right side boring = 140 secs
Right to left = 8 secs
Left side boring = 140 secs
Left to home position = 4 secs
Total = 296 secs
Cycle time for fine boring using Electro Mechanical Drive System = 296 secs

COST OF DRIVE SYSTEM

1. Raw material cost Rs. 47530
2. Bought out Rs. 28150
3. Imported Rs. 3295
4. Sub contract Rs. 1960

Labour cost

5. Manufacturing Rs. 1, 02160
6. Assembly cost Rs. 25520
7. Pattern cost Rs. 25000

Production cost =1+5+6+7 = 200210

Factory cost Rs. 200210

Cost price 10% added Rs. 220231 (200210+20021)

Bought out + imported + sub contract = 33405

Total cost Rs. 253636


Cost of Electro Mechanical Drive System = Rs. 2, 53,636







CONCLUSION


The electro mechanical drive system is designed to operate at rapid feed rate of 4.6 m/min and 45 m/min slow feeds. Since the non-cutting time is reduced considerably the over all cycle time is reduced. So the productivity is increased. The cost of drive system is justifiable. For stepped drive this is the best drive. The only the advantage is that the gear changing is little tiresome when change in feed rate is required unlike step less drive where speed changing is very easy. This same design can be tried in other special purpose and other machine tools also.

























REFERENCE



1. Dr.P.S.Bimbhra, Power Electronics text book, Khanna Publishers
(2003), Pg-460
2. R.Henry Xavier and Dr K.V.Thyagarajan, Manufacturing Technology Today, volume-3, August 2004, Page No-13 to 17.
3. T.P.S.Iyer, Production Technology,HMT Publication Ltd,New Delhi

Effect of elevated piston temperature on combustion chamber deposit growth

ABSTRACT
Combustion chamber deposits are found in all internal combustion engines. When fuel and air burn inside an internal combustion engine, deposits form on the walls inside the cylinder. The factors influencing deposit formation are changes in fuel composition, coolant temperatures, engine speed and load, and spark timing. One way to discourage deposit formation is to prevent condensation. Raising the wall temperature prevent condensation. With increased wall temperature, hydrocarbon condensation tendencies decreases and thus deposit formation is reduced.
In these attempts is made to investigate the effects of wall temperature on deposit growth, without the use of ceramic coatings on the combustion chamber surfaces. Also methods for monitoring combustion chamber deposit growth as a function of metal wall temperature are described. In this, a composite piston design was developed to control and monitor surface temperature. The design incorporated ceramic wafers of varying thickness encapsulated between a metal cap and piston top. The cap was fitted with surface-mounted thermocouples to measure wall temperatures. An accelerated test cycle was used to accumulate deposits. There is a description of methodology employed in raising the wall temperature and monitoring deposit growth. After stabilization of deposit growth a physical and chemical analysis of deposits from different locations were also conducted.










INTRODUCTION
Combustion chamber deposits are recognized as a major contributor to the deterioration of SI engine performance . Their build-up leads to reduced air mass flow rates, increased charge emissions, and increased tendency for knock. The primary mechanism of formation of fuel deposits is condensation of the high boiling point components, such as aromatics, and their carbonization while in the liquid phase. The amount of air mixed with the fuel has been found to be critical to the deposit growth in engines. Therefore, oxidative fuel pyrolysis better describes the mechanism of deposit formation. With increased wall temperature, hydrocarbon condensation tendencies decrease, and therefore deposit formation is reduced. Deposits on hot surfaces, such as the exhaust valve of the spark plug, are primarily composed of oil-based inorganic compounds. Deposit growth in the end gas region, the region with the coolest surfaces, is typically higher than in any other portion of the combustion chamber, end chamber deposits also have lower oxygen and higher carbon content than elsewhere in the combustion chamber.
The purpose of this experiment is to investigate the effects of wall temperature on deposit growth, without the use of ceramic coatings on the combustion chamber surfaces. This study monitors in -situ combustion chamber deposit growth, as a function of metal wall temperature, and attempts to determine the critical wall temperature for no growth a composite piston design was developed to control and monitor surface temperature. The design incorporated ceramic wafers of varying thickness encapsulated between a metal cap and piston top. The cap was fitted with surface-mounted thermocouples to measure wall temperatures. An accelerated test cycle was used to accumulate deposits. This also contains the methodology employed in raising the wall temperature and monitoring deposit growth.







COMBUSTION CHAMBER DEPOSITS
Combustion chamber deposits are found in essentially all internal combustion engines. Their influence can be seen in many aspects of engine performance. Deposits form on all engine surfaces that are in contact with fuel or fuel air mixture at any point in the cycle. The mechanism by which these deposits form from fuel are not well understood .the effect of deposit include increased engine NO emissions, octane requirement increase and changes in flame speed and thermal efficiency.
The factors influencing deposit formation are changes in fuel composition, coolant temperatures, engine speed and load, and spark timing. These factors affect the rate of deposit formation and removal and the structure of deposits. To create a deposit control strategy needed is the magnitude and direction of these various effects over a wide range of fuel types and engine conditions.

The chemical and thermo physical properties deposits depend on fuel and oil composition, wall temperature, engine operating conditions, and engine design. The carbon to hydrogen (C/H) ration of the deposits indicates the relative proportion of fuel and oil contribution to the deposits. A low carbon to hydrogen ratio indicates deposit constituents are mostly oil based, and originate from oil cracking on the wall. A high carbon to hydrogen ratio indicates the deposits are primarily fuel derived. In general, deposits collected from engines that operate under normal conditions are primarily fuel derived.
OCTANE REQUIREMENT INCREASE
The actual octane requirement of a vehicle is called octane number requirement. A new engine require a fuel of octane number 6-9 lower than the same engine running for a long time. This octane requirement increase is due to the formation of a mixture of organic and inorganic deposits resulting from fuel and the lubricant. When using unleaded fuel two-thirds of the octane requirement is caused by deposit accumulation in the end gas region.
EFFECT OF COMBUSTION CHAMBER DEPOSITS
The effect of combustion chamber deposits include octane requirement increases, decreased volumetric efficiency, increased thermal efficiency due to insulation of the cylinder, combustion chamber deposit interference(CCDI) and combustion chamber flaking.


As deposits build up on the combustion chamber surfaces, the minimum fuel octane number needed to avoid engine knock increases. In modern engines this increase is approximately 4 to 5 octane numbers on average as the deposits build up to their equilibrium thickness. Combustion chamber deposit interference is the result of physical contact between deposits on the piston top and cylinder head. Combustion chamber deposit flaking causes low compression pressures due to improper sealing of the valves.
EXPERIMENTAL SETUP AND PROCEDURE
THE ENGINE CONFIGURATION
The investigation was performed using a Waukesha, single cylinder, split head, variable compression ratio, Cooperative Fuel Research (CFR) engine. Engine motoring and loading was handled by a General Electric DC dynamometer with 20 hp motoring and 35 hp absorbing capacity. The CFR’s intake manifold was modified to incorporate a throttle body in order to regulate engine load. An active magnetic pickup, mounted in close proximity to the dynamometer shaft, was used to measure engine speed. The dynamometer was controlled with a Dyne Systems DYN-LOC IV controller

The fuel delivery system was converted from the standard CFR system to a modern electronic fuel injection setup which was comprised of an automotive fuel fitter and pump, along with a Bosch fuel injector and pressure regulator. The fuel injector was installed in the in take manifold where the CFR injector was normally fitted. The ignition system consisted of a single pole, ignition coil and a TFI module that was used to trigger coil discharge. A fuel/spark controller was developed to control timing of the fuel injector and initiate coil discharge so as to achieve desired fuel flow rate and spark timing.

Engine oil and water jacket cooling was provided by tube type heat exchangers. The jacket water consisted of a mixture of approximately 80 percent water and 20 percent ethylene glycol. Engine oil temperature and jacket water temperatures were measured with K-type thermocouples. During testing, oil temperature in the crankcase sump was maintained at 90± 20 ºC. The jacket water temperature stabilized to 100 ºC in 15 minutes after starting the engine.

Air flow was measured with an ASME 5/8 inch metering orifice with flange mounted pressure taps. Fuel flow rate was measured with a calibrated burette Cylinder pressure was measured with a water cooled piezoelectric transducer mounted in the knock sensor hole of he head. The transducer was cleaned and covered with high temperature silicone RTV.
CONTROL AND MEASUREMENT OF PISTON SURFACE TEMPERATURES
Deposit growth was investigated on the top surface of the piston, which typically accounts for two-thirds of the deposit growth in the combustion chamber.A composite piston design was developed to control and monitor surface temperature. The design incorporated a ceramic wafer between an added iron cap and the standard iron piston top. The ceramic wafer was fabricated from a glass/ceramic material with low conductivity of 1.38 W/m. ºC, and high compression strength of 344 Mpa, and excellent machinability. The wafer measured 76.2mm in diameter, and 1.0, 2.0, or 3.0 mm in thickness. By varying the thickness of the ceramic wafer, the surface temperature of the cap could be increased from its baseline value. Predictions ware generated through a one-dimensional heat transfer analysis of the composite piston design, based on an assumed transient heat flux on its combustion surface.


A series of caps was machined from ferromagnetic iron, with each cap having a matching pocket to a seat a given ceramic wafer. For all caps, the distance between the top surface and its pocket was maintained at 4 mm for structural support. The cap was secured to the standard piston by countersunk fasteners. The CFR cast iron piston was used because its material closely matched the piston cap material. Since the iron piston has four compression rings and only one oil ring, the connecting rod oil jet, which is normally used for cooling the piston’s underside, was sealed off to avoid excess oil consumption in the combustion chamber.



Surface-mounted thermocouples were mounted flush with the cap surface to allow monitoring of its temperature during engine operation. Four constantan wires were affixed to the cap at 36.5 mm radially from the iron wire. The J-type thermocouple wire used was 24 gauge and has a peak temperature range of 700 ºC. The wires were fitted in the cap through counter-bored and counter sunk holes. The wires were bonded to the cap by welding the wire end into the countersunk holes.
TRANSMISSION OF ELECTRICAL SIGNALS-
Due to the harsh environment of high accelerations and temperatures, the piston assembly was meticulously wired to insure electrical continuity between the cap’s thermocouples and the connecting road. Augat electrical connectors which forming good electrical contact with 24-gage copper wire, were placed in the piston top to serve as an electrical socket for the thermocouple wires. Standard 26-gauge copper wire, which was secured to the connector with silver solder, was used to continue transmission of the electric signals. An RTD was placed next to a protruding Augat connector on the piston’s underside to establish the reference junction temperature. The RTD and all wires were bonded to the piston with epoxy.


A stainless steel band was used to provide a path between the piston and the connecting rod. The band was mechanically secured to the piston’s skirt and the connecting rod. Finely stranded copper wires were guided along the band’s outside surface and held with high-strength RTV and segmented high-strength heat shrink tubing. After passing under two aluminum plates which were fastened to the connecting rod’s shank, the wires were eventually routed to the end cap of the connecting rod. In order to establish electrical continuity of the thermocouple signals from the end cap of the connecting rod to an external data acquisition system, a mechanical telemetry linkage system was designed. The system works on the concept of classical four bar linkage. The longest possible wire life was achieved by minimizing angular deflection and by maximizing the transmission angle between adjoining linkage members. This reduced bending of wires at linkage joints, thus promoting longer wire life.
TEST PROCEDURE
A transient test cycle, appropriate for a single-cylinder engine, was designed for the test The test schedule was broken down into four and one half hour test cycles, followed by engine cool down to ambient temperature. Within each test cycle, a repeated fifteen minute test segment was conducted. One and one half minutes were spent at idle, thirteen minutes at low load, and one half minute at a high load. At the beginning of each test, the engine was warmed up at 800 rpm for twenty minutes.


The four and one half hour test cycle was repeated as many times as needed for establishing well defined growth patterns. For each four and one half hour test cycle, fast response, pressure and temperature data were recorded every half hour during the 1800 rpm segment. Additional measurements included airflow, oil and cooling water temperatures, exhaust temperature, and intake pressure. Fuel consumption measurements were documented periodically during testing.

At the end of testing with a given cap, the cylinder head was removed, and the deposit thickness on the head, valves, bore, ports and piston were recorded. Deposits were removed from the cylinder head, valves and ports. Then the valves were lapped and the engine was reassembled for further testing. All piston configurations were tested with a base premium unleaded fuel without reformer bottoms. The 3 mm cap test was repeated with the unleaded fuel doped with reformer bottoms.
IN-SITU MONITORING OF DEPOSIT GROWTH
A technique for in-situ monitoring of deposit growth is through measurement of local surface temperature using thermocouples affixed to the combustion surface. As deposits build up on the surface and form an insulation barrier, heat flow is reduced from the combustion gases to the wall. The restriction in heat flow reduces the wall’s surface temperature which is measured by the surface-mounted thermocouple. The rate of change of wall surface temperature is thus indicative of the rate of deposit growth. The surface temperature has been found to decrease almost linearly until deposit growth has stabilized, from then on, the surface temperature remains relatively constant.



Temperature gradients and stabilized growth periods have been found to be greatly influenced by the fuel’s hydrocarbon structure. Fuels with aromatic hydrocarbons, toluene and xylene, measured higher surface temperature gradients, during the first three hours of testing, than fuels containing paraffins, like iso-octane. The higher the boiling point of aromatic components, the faster the deposit growth, and the lower the measured wall temperature

Initially the baseline cap was run for a 42 hour deposit growth test. Recorded temperature histories exhibited two distinct temperature discontinuities at the 10th and 22nd hour. The first temperature discontinuity was due to the thermocouple wires and connectors being coated with a carbonaceous film, as a result of combustion gases penetrating into crevices of the contact surface between piston and cap. The gap was seated with a thin layer of high temperature RTV applied on the lower surface of the cap. The second temperature discontinuity was associated with vibration in the flat head fasteners. This was corrected by the use of flat head lock washers with the fasteners. After this, the first 12hours of the baseline test were repeated.

Regional differences in the measured rate of temperature decay are attributed to differences in deposit composition and thermal properties at the different locations. There is an accelerated deposit build-up in the regions surrounding thermocouples 3 and 4 (under the intake valve). The differences are driven by regional variations in wall surface temperature and changes in the C/H composition of deposits. The surface-averaged wall temperature of the baseline cap decreased linearly over time, at a rate of 0.38oC/hr.

EFFECT OF ELEVATED PISTON TEMPERATURE ON DEPOSIT GROWTH
TEST USING UNLEADED FUEL
Caps insulated with a1, 2 and 3 mm ceramic wafer were tested with the base unleaded fuel without reformer bottoms. An overall test period of 18hours was used to define deposit growth patterns. Local and averaged surface temperature histories of the insulated caps are compared with those of the baseline cap. Insulating the piston cap raised the initial temperature of the surface from an average of 215 ºC to 317 ºC for 3 mm cap .Elevating the initial temperature of the cap reduced the rate of decay with time, from –0.38 ºC/hr (baseline) to 0.02 ºC/hr for the last 11hours of the test with the 3mm insulated cap. This shows an overall decrease in deposit growth with elevated piston temperature

The discontinuity in the surface temperature gradients of the 3mm cap is that light engine knock was experienced after 6hour of testing with the unleaded fuel without additives. Spark timing was then retarded by three crank angle degrees to eliminate knock, and the test was continued. A thermocouple histories in the 3mm insulated cap shows surface temperatures to decrease at a rapid rate, particularly in the end gas region of thermocouples 2 & 3, between the second and sixth hour. This decrease indicates accelerated early deposit growth, with the largest concentration in the end gas region. Deposit growth causes an increase in gas temperature, which leads to knock. The high thermal stresses crated by the knocking condition cause deposit flaking, or random removal of deposits. Once flaking occurred, deposit accumulation on the exposed surfaces was retarded. A deposit film remained on the cap’s surface leads to periodic reoccurrence of knock and flaking, this shows the observed fluctuations in surface temperature after the sixth hour of testing.

There is a slightly positive slopes for the recorded temperature change at locations 2 and 3. This is attributed to , an inability to take data during the first one hour of testing, when a relatively large deposit accumulation occur at those locations, and difficulties during the first four-and-a- half hour test cycle. Data with the second test cycle establish negative (or close to zero) slopes. A little deposit growth is experienced with the 2 mm insulated cap, by an average rate of temperature decay of 0.06 ºC/hr. With further increase in cap insulation, the mean temperature gradient during the last seven hours of testing was –0.02 ºC/hr, indicating negligible deposit growth with the 3mm insulated cap. An average wall temperature of 320 ºC identifies a critical point above which the base unleaded fuel does not form deposits.

Results through in-situ monitoring of deposits using unleaded fuel yielded a critical surface temperature of 3200C.
TESTS USING FUELS WITH REFORMER BOTTOMS
Reformer bottoms are large hydrocarbon molecules which have poor oxidation characteristics, and thus enhance deposit growth rate. This is also affected by potential changes in the thermal properties of fuel deposits.

Testing with the reformer bottoms fuel was conducted for only eleven hours. The average wall temperatures for the reformer bottoms test were compiled from thermocouples 1 and 3.No knock occurred during testing of the 3 mm insulated cap with the reformer bottoms fuel. The linear decay in the average temperature of the piston surface (at a rate of 0.350 C/hr) shows a steady deposit growth. Reformer bottoms can promote deposit growth under operating conditions at which no deposits are formed with the base fuel.


The wall surface temperature for the reformer bottoms test was approximately 8 ºC lower than that for the base fuel test, after one hour of testing. This difference can be accounted for by a 4 o C lower inducted air temperature for the reformer bottoms test. The other differences are a result of differences in thermal properties of deposits from the two fuels. The deposit layer from the reformer bottoms fuel experiences a lower temperature swing during the cycle, and a lower peak surface temperature, this also leads to a lower mean wall temperature and thus increased deposit growth. The deposit growth is effectively controlled by the temperature at the deposit surface. The temperature difference (5 0C) between the peak temperatures at the gas-exposed surface of deposits from unleaded fuels with and without reformer patterns, shows differences in deposit growth patterns.
TEST ANALYSIS OF DEPOSITS
PHYSICAL ANALYSIS
A physical analysis of deposits is important in fully characterizing deposit growth patterns. At the end of each test schedule, overall observations were made concerning the color and texture of deposits in each of the four cap quadrants. In addition deposit thickness measurements were made with a Titan ZDM-1 microscope. This information was useful in correlating deposit growth and change in wall restricted within a square region defined by the thermocouple locations. The exact locations on the cap surface where deposit thickness measurements were taken.



Deposit thickness measurements are taken for various caps. At the baseline 12 hour test deposits in cap regions 1, 2, and 4 appeared as dark down in color with a sooty texture, while region 3 deposits had a lighter shade of brown and a crusty texture. After 18 hours of testing, the 1 mm insulated cap was covered with a deposit coating of a lighter shade of brown. In regions 1 & 4, deposits were observed to be denser and more sooty than those in regions 2 & 3, the regions 2 & 3 had a gritty texture. Compared to the 1 mm insulated cap which collected an average deposit thickness of 6.28 m, the 2mm cap had a reduced deposit growth (1.83 µm on average), particularly in region 2 where no deposits had accumulated . The deposits on the remaining three quadrants of the cap had a light- brown metallic color with a gritty texture. The 3mm cap exhibited almost negligible deposit accumulation after 18 hours of testing. In regions 3 & 4, the cap surface seen under a rough and gritty texture whereas regions 1 & 2 were covered by a thin, smooth, brownish white deposit film.





The exhaust valve maintained a white color in all cases, at the end of each test with the unleaded fuel (without reformer bottoms).The intake valve color changed from a dark brown to a light gray as the piston surface temperature increased. At the end of the 3 mm insulated cap test, the exhaust valve had a clear evidence of deposit flaking. This is due to high surface temperature as well as engine knock.

The average deposit thickness was found to decrease at 3.38 µm per millimeter of ceramic insulation. Low temperature regions, such as under the intake valve, were not always found to be covered under the thickest deposit coating. Thicker deposits accumulated on the cap for the longer test period. After 42 hours more deposits were found under the intake valve (region 3). Deposit flaking under the intake valve, where there is a tendency for large accumulation of deposits, resulted in removal of excessive deposit build-up with a long test period.

After 11 hours of testing with the reformer bottoms fuel, the 3mm cap accumulated a deposit layer with an average thickness of 0.47 µm, 55% more than the layer accumulated after testing the unleaded fuel without additives for 18 hours. Aside from the poor oxidation properties of the reformer bottoms, the differences in these growth patterns are attributed to differences in thermal properties of the two types of deposits. Deposits from the reformer bottoms fuel were primarily centered in regions 3 & 4, as well as the edges of regions 1 & 2. They were identified with a dark brown color, and a rough, sooty texture. The intake valve from the reformer bottoms test accumulated a dark brown deposit layer. The exhaust valve appeared to maintain a light brown appearance. Deposit flaking was not found on this component.

Insulating the piston cap had a noticeable impact on deposit characteristics. The deposits were found to progress from a dark brown color with a sooty texture ( baseline cap ) to light-brown pigment with a gritty texture (3 mm cap ) Deposit growth on the cylinder head, showed similar trends. Deposits on the 3 mm insulated cap from the reformer bottoms fuel test exhibited comparable characteristics to those formed on the baseline cap using unleaded fuel without reformer bottoms.
CHEMICAL ANALYSIS
A carbon to hydrogen (C/H) ratio analysis indicate the relative proportion of fuel and oil in the deposits, as well as the mechanism of deposit formation. The analysis reveals that deposits in the end gas region have the highest fuel content, as a result of deposition of unburned hydrocarbon products on the end gas region surfaces. The region between the spark plug and the intake valve has lower fuel content than the end gas region, and higher oil content. Since the former region runs approximately 16 ºC hotter than the latter region, this behavior can be attributed to fuel vaporization on the higher temperature surfaces. The deposits collected near the cap’s edge in the end gas region present the highest oil content. Excess oil on the cylinder liner accumulates on the latter region of cap during the piston’s travel.



Mole fraction of carbon and hydrogen in the deposits collected under the exhaust valve portion of the end gas region (region 2) for each cap configuration tested with unleaded fuel without additives, shows an increase in the concentration of carbon within the deposits. The C/H ratio decreases with increased surface temperature. As wall surface temperature elevate, more oil contributes to deposits. A decreasing C/H ratio with increasing wall temperature indicates that deposit growth primarily originates from oil cracking on the wall. Deposits collected on high temperature, combustion chamber walls were composed mostly of inorganic compounds, such as those preset in engine lubrication. Deposits collected on cooler surfaces have been composed primarily of carbon.
CORRELATION OF TEMPERATURE DECAY AND DEPOSIT GROWTH
An analysis was performed that, measured changes in temperature over a given test period were normalized with respect to the measured deposit thickness at the corresponding location. The all four thermocouple locations were considered for the base unleaded fuel tests with the baseline metal cap (for 12 hours) and the 1mm insulated cap (for 18 hours). For all except one case, there appears to be a strong correlation between measured temperature decay and associated deposit thickness.
The effective conductivity of the deposits collected at a given location is nearly constant during the accumulation period. This holds true as long as there is no drastic change in local composition of deposits while increasing piston operating temperature. For the case of the 1mm cap, the region between the spark plug and the intake valve (region 4) progressively accumulated deposits of lower fuel content and higher oil content, with increasing piston temperatures.

DEPOSIT CONTROL
When fuel and air burn inside an internal combustion engine, deposits form on the walls inside the cylinder. Deposits form on all engine surfaces that are in contact with fuel or fuel-air mixture at any point in the cycle. These deposits have significant effects. The deposit layer on the cylinder wall prevents the coolant that runs through the engine from bringing down the temperature inside the cylinder. Due to the increased temperatures, parts of the fuel-air mixture may ignite before the flame front reaches them, causing the engine to knock. Another effect of the raised temperatures is increased production of pollutants such as nitrogen oxides inside the engine cylinder. One way to discourage deposit formation is to prevent condensation. Raising the wall temperature prevent condensation. With increased wall temperature, hydrocarbon condensation tendencies decreases and thus deposit formation is reduced. Deposits on hot surfaces such as exhaust valves or ceramic of the spark plug are composed of oil based inorganic compounds. Deposit growth in the end gas region (region with coolest surfaces) is typically higher than in any other portion of combustion chamber.
Disadvantage of increasing wall temperature is that, if defects the overall goal of keeping cylinder temperatures down.

CONCLUSION
Combustion chamber deposits are found in essentially all internal combustion engines. When fuel and air burn inside an internal combustion engine, deposits form on the walls inside the cylinder. Factors that influencing deposit formation are changes in fuel composition, coolant temperatures, engine speed and load, and spark timing. These affect the rate of deposit formation and removal and the structure of the deposits. Deposits form on all engine surfaces that are in contact with fuel or fuel-air mixture at any point in the cycle. These deposits have significant effects. The deposit layer on the cylinder wall prevents the coolant that runs through the engine from bringing down the temperature inside the cylinder. Due to the increased temperatures, parts of the fuel-air mixture may ignite before the flame front reaches them, causing the engine to knock. Another effect of the raised temperatures is increased production of pollutants such as nitrogen oxides inside the engine cylinder.
One way to avoid deposit formation is to prevent condensation. Raising the wall temperature prevent condensation. With increased wall temperature, hydrocarbon condensation tendencies decreases and thus deposit formation is reduced. The unleaded fuel would not condense into a carbonaceous film once a critical wall temperature is reached. Reformer bottoms yielded a 55 percentage increase in deposit thickness compared to base unleaded fuel. This difference was due to poor oxidation properties of reformer bottoms. Elevating wall temperature increases the carbon to hydrogen ratio in the composition of deposits. Deposits in the end gas region are mostly fuel derived.
Disadvantage of increasing wall temperature is that, if defects the overall goal of keeping cylinder temperatures down.




REFERENCES
 Christopher Forssen o’Brien , “ Combustion chamber deposit research.”
 Energy laboratory research And related activities at the MIT , “ Inside engine cylinders; cleaner walls for lower emissions, higher efficiency”
 Chevron U S A , “Gasoline vehicles deposit control.”
 The engineering society for advancing mobility land sea air and space, “Effect of elevated piston temperature on combustion chamber deposit growth ” SAE Technical paper series ,940948,1994

CAMLESS ENGINE

INTRODUCTION

The cam has been an integral part of the IC engine from its invention. The cam controls the “breathing channels” of the IC engines, that is, the valves through which the fuel air mixture (in SI engines) or air (in CI engines) is supplied and exhaust driven out. Besieged by demands for better fuel economy, more power, and less pollution, motor engineers around the world are pursuing a radical “camless” design that promises to deliver the internal – combustion engine’s biggest efficiency improvement in years. The aim of all this effort is liberation from a constraint that has handcuffed performance since the birth of the internal-combustion engine more than a century ago. Camless engine technology is soon to be a reality for commercial vehicles. In the camless valve train, the valve motion is controlled directly by a valve actuator – there’s no camshaft or connecting mechanisms .Precise electrohydraulic camless valve train controls the valve operations, opening, closing etc. The seminar looks at the working of the electrohydraulic camless engine, its general features and benefits over conventional engines. The engines powering today’s vehicles, whether they burn gasoline or diesel fuel, rely on a system of valves to admit fuel and air to the cylinders and let exhaust gases escape after combustion. Rotating steel camshafts with precision-machined egg-shaped lobes, or cams, are the hard-tooled “brains” of the system. They push open the valves at the proper time and guide their closure, typically through an arrangement of pushrods, rocker arms, and other hardware. Stiff springs return the valves to their closed position. In an overhead-camshaft engine, a chain or belt driven by the crankshaft turns one or two camshafts located atop the cylinder head.
A single overhead camshaft (SOHC) design uses one camshaft to move rockers that open both inlet and exhaust valves. The double overhead camshaft (DOHC), or twin-cam, setup does away with the rockers and devotes one camshaft to the inlet valves and the other to the exhaust valves.

Such valve trains, as they are known, are complicated but reliable. Yet they have the major disadvantage of inflexibility. Valve timing, valve lift, and event duration are all fixed values specific to the camshaft design. Like a very simple software program that contains only one set of instruction, the cams always open and close the valves at the same precise moment in each cylinder’s constantly repeated cycle of fuel-air intake, compression, combustion, and exhaust. They do so regardless of whether the engine id idling or spinning at maximum rpm. As a result, engine designers can achieve optimum performance at only one speed. An engine designed for impressive high-rpm power may be a wimp at low rpm, and vice versa.
Some automakers have tried to get around that limitation with mechanisms that “phase”, or shift, the rotational position of the camshafts as rpm varies, Honda uses a system called VTEC. At faster engine speeds, it hydraulically brings extra sets of cam lobes and rockers into play to help the motor breathe more deeply and make more power. Clever as they are, these schemes are limited by their reliance on hard-metal parts of fixed geometry, and thus can only approximate the benefits of a dream long held by mechanical engineers: infinite variation of the timing, lift, and duration of valve openings to get the best performance across the whole rpm range.
The camless engine would be the latest in a series of changes that have made internal –combustion engines increasingly clean, efficient, and responsive to the driver’s right foot. The camless valve train, which eliminates the mechanical linkage by using a separate controller/actuator to move the valves, allows the optimization of the exhaust and intake valve timing, motion, and activation for individual valve. Various studies have shown that a camless valve train can alleviate many of engine design tradeoffs by supplying extra degrees of freedom to the overall power train system.



WORKING OF PUSH ROD ENGINE

Pushrod engines have been installed in cars since the dawn of the horseless carriage. A pushrod is exactly what its name implies. It is a rod that goes from the camshaft to the top of the cylinder head which push open the valves for the passage of fuel air mixture and exhaust gases. Each cylinder of a pushrod engine has one arm (rocker arm) that operates the valves to bring the fuel air mixture and another arm to control the valve that lets exhaust gas escape after the engine fires. There are several valve train arrangements for a pushrod.

Crankshaft
Crankshaft is the engine component from which the power is taken. It receives the power from the connecting rods in the designated sequence for onward transmission to the clutch and subsequently to the wheels. The crankshaft assembly includes the crankshaft and bearings, the flywheel, vibration damper, sprocket or gear to drive camshaft and oil seals at the front and rear.

Camshaft
The camshaft provides a means of actuating the opening and controlling the period before closing, both for the inlet as well as the exhaust valves, it also provides a drive for the ignition distributor and the mechanical fuel pump.

The camshaft consists of a number of cams at suitable angular positions for operating the valves at approximate timings relative to the piston movement and in the sequence according to the selected firing order. There are two lobes on the camshaft for each cylinder of the engine; one to operate the intake valve and the other to operate the exhaust valve.
Working

When the crank shat turn the cam shaft the cam lobs come up under the valve lifter and cause the lifter to move upwards. The upward push is carried by the pushrods through the rocker arm. The rocker arm is pushed by the pushrod, the other end moves down. This pushes down on the valve stem and cause it to move down thus opening the port. When the cam lobe moves out from under the valve lifter, the valve spring pulls the valve back upon its seat. At the same time stem pushes up on the rocker arm, forcing it to rock back. This pushes the push rods and the valve lifter down, thus closing the valve. The figure-1,2 shows cam-valve arrangement in conventional engines



Figure-1 Figure-2
Single cam and valve conventional valve train mechanism

Since the timing of the engine is dependent on the shape of the cam lobes and the rotational velocity of the camshaft, engineers must make decisions early in the automobile development process that affect the engine’s performance. The resulting design represents a compromise between fuel efficiency and engine power. Since maximum efficiency and maximum power require unique timing characteristics, the cam design must compromise between the two extremes.
This compromise is a prime consideration when consumers purchase automobiles. Some individuals value power and lean toward the purchase of a high performance sports car or towing capable trucks, while others value fuel economy and vehicles that will provide more miles per gallon.
Recognizing this compromise, automobile manufacturers have been attempting to provide vehicles capable of cylinder deactivation, variable valve timing (VVT), or variable camshaft timing (VCT). These new designs are mostly mechanical in nature. Although they do provide an increased level of sophistication, most are still limited to discrete valve timing changes over a limited range.

AN OVERVIEW OF CAMLESS ENGINE

To eliminate the cam, camshaft and other connected mechanisms, the
Camless engine makes use of three vital components – the sensors, the electronic control unit and the actuator



Mainly five sensors are used in connection with the valve operation. One for sensing the speed of the engine, one for sensing the load on the engine, exhaust gas sensor, valve position sensor and current sensor. The sensors will send signals to the electronic control unit.

The electronic control unit consists of a microprocessor, which is provided with a software algorithm. The microprocessor issues signals to the solid-state circuitry based on this algorithm, which in turn controls the actuator, to function according to the requirements.
Camless valve train

In the past, electro hydraulic camless systems were created primarily as research tools permitting quick simulation of a wide variety of cam profiles. For example, systems with precise modulation of a hydraulic actuator position in order to obtain a desired engine valve lift versus time characteristic, thus simulating the output of different camshafts. In such systems the issue of energy consumption is often unimportant. The system described here has been conceived for use in production engines. It was, therefore, very important to minimize the hydraulic energy consumption.

Hydraulic pendulum

The Electro hydraulic Camless Valve train, (ECV) provides continuously variable control of engine valve timing, lift, and velocity. It uses neither cams nor springs. It exploits the elastic properties of a compressed hydraulic fluid, which, acting as a liquid spring, accelerates and decelerates each engine valve during its opening and closing motions. This is the principle of the hydraulic pendulum. Like a mechanical pendulum," the hydraulic pendulum involves conversion of potential energy into kinetic energy and, then, back into potential energy with minimal energy loss". During acceleration, potential energy of the fluid is converted into kinetic energy of the valve. During deceleration, the energy of the valve motion is returned to the fluid. This takes place both during valve opening and closing. Recuperation of kinetic energy is the key to the low energy consumption of this system.. Figure 7 illustrates the hydraulic pendulum concept. The system incorporates high and low-pressure reservoirs. A small double-acting piston is fixed to the top of the engine valve that rides in a sleeve. The volume above the piston can be connected either to a high- or a low-pressure source. The volume below the piston is constantly connected to the high-pressure source. The pressure area above the piston is significantly larger than the pressure area below the piston. The engine valve opening is controlled by a high-pressure solenoid valve that is open during the engine valve acceleration and closed during deceleration. Opening and closing of a low-pressure solenoid valve controls the valve closing. The system also includes high and low-pressure check valves.

Figure 7. Hydraulic Pendulum.

During the valve opening, the high-pressure solenoid valve is open, and the net pressure force pushing on the double-acting piston accelerates the engine valve downward. When the solenoid valve closes, pressure above the piston drops, and the piston decelerates pushing the fluid from the lower volume back into the high-pressure reservoir. Low-pressure fluid flowing through the low-pressure check valve fills the volume above the piston during deceleration. When the downward motion of the valve stops, the check valve closes, and the engine valve remains locked in open position. The process of the valve closing is similar, in principle, to that of the valve opening. The low-pressure solenoid valve opens, the pressure above the piston drops to the level in the low pressure reservoir, and the net pressure force acting on the piston accelerates the engine valve upward. Then the solenoid valve closes, pressure above the piston rises, and the piston decelerates pushing the fluid from the volume above it through the high-pressure check valve back into the high-pressure reservoir. The hydraulic pendulum is a spring less system. Figure 8 shows idealized graphs of acceleration, velocity and valve lift versus time for the hydraulic pendulum system. Thanks to the absence of springs, the valve moves with constant acceleration and deceleration. This permits to perform the required valve motion with much smaller net driving force, than in systems which use springs. The advantage is further amplified by the fact that in the spring less system the engine valve is the only moving mechanical mass. To minimize the constant driving force in the hydraulic pendulum the opening and closing accelerations and decelerations must be equal (symmetric pendulum).

Figure 8. Dynamic characteristics of hydraulic pendulum.

Valve opening and closing

A more detailed step-by-step illustration of the valve opening and closing process is given in Figure 9. It is a six-step diagram, and in each step an analogy to a mechanical pendulum is shown. In Step 1 the opening (high-pressure) solenoid valve is opened, and the high-pressure fluid enters the volume above the valve piston. The pressure above and below the piston become equal, but, because of the difference in the pressure areas, the constant net hydraulic force is directed downward. It opens the valve and accelerates it in the direction of opening. The other solenoid valve and the two check valves remain closed. In Step 2 the opening solenoid valve closes and the pressure above the piston drops, but the engine valve continues its downward movement due to its momentum. The low-pressure check valve opens and the volume above the piston is filled with the low-pressure fluid. The downward motion of the piston pumps the high-pressure fluid from the volume below the piston back into the high-pressure rail. This recovers some of the energy that was previously spent to accelerate the valve. The ratio of the high and low-pressures is selected so, that the net pressure force is directed upward and the valve decelerates until it exhausts its kinetic energy and its motion stops. At this point, the opening check valve closes, and the fluid above the piston is trapped. This prevents the return motion of the piston, and the engine valve remains fixed in its open position trapped by hydraulic pressures on both sides of the piston. This situation is illustrated in Step 3, which is the open dwell position. The engine valve remains in the open dwell position as long as necessary. Step 4 illustrates the beginning of the valve closing. The closing (low-pressure) solenoid valve opens and connects the volume above the piston with the low-pressure rail. The net pressure force is directed upward and the engine valve accelerates in the direction of closing, pumping the fluid from the upper volume back into the low-pressure reservoir. The other solenoid valve and both check valves remain closed during acceleration. In Step 5 the closing solenoid valve closes and the upper volume is disconnected from the low-pressure rail, but the engine valve continues its upward motion due to its momentum. Rising pressure in the upper volume opens the high-pressure check valve that connects this volume with the high-pressure reservoir. The upward motion of the valve piston pumps the fluid from the volume above the piston into the high-pressure reservoir, while the increasing volume below the piston is filled with fluid from the same reservoir. Since the change of volume below the piston is only a fraction of that above the piston, the net flow of the fluid is into the high-pressure reservoir. Again, as it was the case during the valve opening, energy recovery takes place. Thus, in this system the energy recovery takes place twice each valve event. When the valve exhausts its kinetic energy, its motion stops, and the check valve closes. Ideally, this should always coincide with the valve seating on its seat. This, however, is difficult to accomplish. A more practical solution is to bring the valve to a complete stop a fraction of a millimeter before it reaches the valve seat and then, briefly open the closing solenoid valve again. This again connects the upper volume with the however, is difficult to accomplish. A more practical solution is to bring the valve to a complete stop a fraction of a millimeter before it reaches the valve seat and then, briefly open the closing solenoid valve again. This again connects the upper volume with the low-pressure reservoir, and the high pressure in the lower volume brings the valve to its fully closed position. Step 6 illustrates the valve seating. After that, the closing solenoid valve is deactivated again. For the rest of the cycle both solenoid valves and both check valves are closed, the pressure above the valve piston is equal to the pressure in the low-pressure reservoir, and the high pressure below the piston keeps the engine valve firmly closed.



Valve motion control

Varying the activation timing of both solenoids varies the timing of the engine valve opening and closing. This, of course, also vanes the valve event duration. Valve lift can be controlled by varying the duration of the solenoid voltage pulse. Changing the high pressure permits control of the valve acceleration, velocity, and travel time. The valve can be deactivated during engine operation by simply deactivating the pair of solenoids which control it. Deactivation can last any number of cycles and be as short, as one cycle.
Increasing the number of valves in each cylinder does not require a corresponding increase in the number of solenoid valves. The same pair of solenoid valves, which controls a single valve, can also control several valves running in-parallel. Thus, in a four-valve engine a pair of solenoid valves operates two synchronously running intake valves, and another pair runs the two exhaust valves.

UNEQUAL LIFT MODIFIER - In a four-valve engine an actuator set consisting of two solenoid valves and two check valves controls the operation of a pair of intake or a pair of exhaust valves. Solenoids and check valves are connected to a common control chamber serving both valves (Figure 10). In a four-cylinder engine there is a total of eight control chambers connected to eight pairs of valves. For each pair, the volumes below the hydraulic pistons are connected to the high pressure reservoir via a device called the lift modifier. In a neutral position the modifier does not affect the motion of the valves, and activation of the solenoid valves moves both engine valves in unison
.
Figure 10. Paired valves with unequal lift control.

To enhance the ability to vary the intake air motion in the engine cylinder, it is often desirable to have unequal lift of the two intake valves, or even to keep one of the two valves closed while the other opens. In some cases it may also be used for paired exhaust valves. The lift modifier is then used to restrict the opening of one the paired valves. The modifier is shown schematically in Figure 11 as a Rotating rod with its axis of rotation perpendicular to the plane of the drawing. The rod is installed in the cylinder head between the two intake valves. A cutout in the rod forms a communication chamber connected to the volumes below the hydraulic pistons of both intake valves. The communication chamber is always connected to the high pressure reservoir. In the case A the modifier is in the neutral position, and both valves operate in unison. In the case B the modifier rod is shown turned 90 degrees clockwise. The exit of oil from the volume below the hydraulic piston in the valve No. 1 is blocked and the valve cannot move in the direction of opening. However, the entry of oil into the volume below the hydraulic piston is permitted by a one-way valve installed in the modifier rod. This guarantees that, whenever deactivation takes place, the valve No. 1 will close and remain closed, while the valve No.2 continues its normal operation. If the modifier rod is turned 90 degrees counter-clockwise (from the position shown in the case A), the valve No.2 is deactivated, while the valve No. 1 would continue normal operation. In the case C the lift of one of the valves is reduced relative to the second one. The rod is turned a smaller angle so that the exit of oil from the valve No. 1 into the communication chamber is not completely blocked, but the flow is significantly throttled. As a result, the motion of the valve No. 1 is slowed down and its lift is less than that of the valve No.2. Varying the angular position of the modifier rod 26 varies the degree of oil throttling, thus varying the lift of the valve No. 1.

Figure 11. Unequal lift control.

DESIGN APPROACH FOR CAMLESS ENGINE

The camless engine was created on the basis of an existing four-cylinder, four-valve engine. The original cylinder head with all the valves, springs, camshafts, etc. was replaced by a new cylinder head assembly fully integrated with the camless valvetrain. The camshaft drive was eliminated, and a belt-driven hydraulic pump was added. There was no need for lubrication, and the access for engine oil from the engine block to the cylinder head was closed off. No other changes to the engine have been made.

Cylinder head

Two cross sections of the cylinder head are shown in Figure 12. The aluminum casting is within the original confines and contains all hydraulic passages connecting the system components. The high- and low-pressure hydraulic reservoirs are integrated into the casting. The reservoirs and the passages occupy the upper levels of the cylinder head and are part of the hydraulic system. The hydraulic fluid is completely separated from the engine oil system. A finite element analysis was used to assure the cylinder head integrity for fluid pressures of up to 9 MPa. The lower level of the head contains the engine coolant.

Figure 12. Cross sections of cylinder head.

Figure 13. Cylinder head with cover removed.

The engine valves, the check valves and the modifiers are completely buried in the body of the head. The solenoid valves are installed on the top of the cylinder head and are kept in their proper locations by a cylinder head cover. Hydraulic and electric connections leading to the hydraulic pump and the electronic controller, respectively, are at the back end of the cylinder head. The height of the head assembly is approximately 50 mm lower than the height of the base engine head. Figure 13 is a photograph of the head on the engine with the head cover removed. 27

COMPONENTS OF CAMLESS ENGINE

Main components of a camless engine are-Engine valve, solenoid valve, high pressure pump, low pressure pump, cool down accumulator, etc.

Engine valve – A cross section of the engine valve assembly is shown in Figure 14. The valve piston is attached to the top of the valve, and both the valve and the piston can slide inside a sleeve. The sleeve openings above and below the valve piston allow the hydraulic fluid to enter and exit. A seal in the lower part of the sleeve prevents leakage of fluid into the intake or exhaust port. A leak-off (not shown) unloads the seal from excessive pressure, which otherwise increases friction. There is a tight hydraulic clearance between the valve and the sleeve. However, the clearance between the sleeve and the cylinder head is relatively large, which improves the centering of the valve in its seat Circulation of hydraulic fluid through the chambers above and below the valve piston cools and lubricates the valve. All the forces acting on the valve are directed along its axis. Absence of side forces reduces stresses, friction and wear.

Figure 14. Engine valve
Solenoid valve – Figure 15 shows a cross section of the solenoid valve. The solenoid has conically shaped magnetic poles. This reduces the air gap at a given stroke. The normally-closed valve is hydraulically balanced during its movement. Only a slight unbalance exists in the fully-open and the fully-closed positions. A strong spring is needed to obtain quick closing time and low leakage between activations. The hydraulic energy loss is the greatest during the closing of either the high- or the low-pressure solenoid, because it occurs during the highest piston velocity. Thus, the faster the solenoid closure, the better the energy recovery. The valve lift and the seat diameter are selected to minimize the hydraulic loss with a large volume of fluid delivered during each opening. Both high-pressure and low-pressure solenoid valves are of the same design.

Figure 15. Solenoid valve.

Lift modifier - The design of the lift modifier permits a simultaneous hydraulic control of a group of modifiers with a single pulse-width modulated solenoid-valve that adjusts the pressure in a control gallery.

Hydraulic system

A diagram of the hydraulic system is shown in Figure 16. An engine-driven variable-displacement pump automatically adjusts its output to maintain the required pressure. The high-pressure and the low-pressure reservoirs are connected to all corresponding locations serving the high- and the low-pressure solenoids and the check valves.

Figure 16. Hydraulic System.

High pressure pump: the quantity of fluid delivered by the high pressure pump with the actual needs of the system at various engine speeds and loads is critical to assuring low energy consumption. To conserve the mechanical power needed to drive the pump, its hydraulic output should closely match the needs. A variable displacement, high efficiency, axial plunger-type pump was initially selected for that reason. Taking into account the prohibitively high cost of such pump for automotive applications, a low-cost variable capacity pump was conceived. A cross section of the pump is shown in Figure 17. The pump has a single eccentric-driven plunger and a single normally-open solenoid valve. During each down stroke of the plunger the solenoid valve is open, and the plunger barrel is filled with hydraulic fluid from the low pressure branch of the system. During the upstroke of the plunger, the fluid is pushed back into the low pressure branch, as long as the solenoid valve remains open. Closing the solenoid valve causes the plunger to pump the fluid through a check valve into the high pressure branch of the system. Varying the duration of the solenoid voltage pulse varies the quantity of the high-pressure fluid delivered by the pump during each revolution.

Figure 17. High pressure pump.

Low pressure pump - A small electrically driven pump picks up oil from the sump and delivers it to the inlet of the main pump. Only a small quantity of oil is required to compensate for the leakage through the leak-off passage, and to assure an adequate inlet pressure for the main pump. Any excess oil pumped by the small pump returns to the sump through a low-pressure regulator. A check valve 1 assures that the inlet to the main pump is not subjected to pressure fluctuations that occur in the low-pressure reservoir.

Cool down accumulator - The system also includes a cool-down accumulator that, during normal operation, is fully charged with oil under the same pressure as in the inlet to the main pump. When the engine stops running, the oil in both the high- and the low-pressure branches cools off and shrinks. As the system pressure drops, the accumulator discharges oil into the system, thus compensating for the shrinkage and preventing formation of pockets of oil vapor. The high-pressure branch is fed from the accumulator through a check valve 2 that is installed in-parallel to the main pump. The low-pressure branch is fed through an orifice that is installed in-parallel to the check valve 1. The orifice is small enough to prevent pressure wave propagation through it during each engine cycle, but sufficient to permit slow flow of oil from the accumulator to the reservoir. In some applications, the orifice can be incorporated directly in the check valve. After the oil in the system has cooled off, the accumulator maintains the system at above atmospheric pressure by continuously replenishing the oil that slowly leaks out through the leak-off passage. When the engine is restarted, the accumulator is recharged again. If the engine is not restarted for a very long time, as it is the case when a vehicle is left in a long-term parking, the accumulator will eventually become fully discharged. In that case, the pressure in the accumulator drops to an unacceptable level, and a pressure sensor, that monitors the accumulator pressure, sends a signal to the engine control system which reactivates the electric pump for a short period of time to recharge the accumulator. This process can be repeated many times, thus maintaining the system under a low level of pressure until the engine is restarted. After the engine restarts it takes less than one revolution of the main pump to restore the high pressure. Operating the hydraulic system in a closed loop contributes to low energy consumption. The amount of hydraulic power consumed by the system is determined by the flow of fluid from the high- to the low-pressure reservoir times the pressure differential between the outlet from and the inlet to the high pressure pump. A small loss is also associated with leakage. There are good reasons to use high hydraulic pressure in the system, one of them being the need to maintain a high value of the bulk modulus of the oil. In a closed-loop system the pressure in the low-pressure reservoir can also be quite high, although lower than in the high-pressure reservoir (thus the pressure in the low-pressure rail is low only in relative terms). Hence, the system can operate with very high hydraulic pressure, and yet the energy consumption remains modest due to a relatively low pressure differential. The ratio of high pressure to low pressure must be sufficiently higher than the ratios of the pressure areas above and below the valve piston to assure reliable engine valve closure.

TESTING AND DEVELOPMENT

The development of the camless valve train is a gradual process, involving design, testing, evaluation, and redesign of various components and subsystems. The initial laboratory testing was conducted with a single-valve test installation and was intended to verify the ability of the system to operate reliably and repeatable at wide range of speeds and valve lifts and event durations. Figure 18 illustrates a 9 mm valve lift obtained in a test fixture at a given crank angle duration and 1500, 4000 and 8000 engine rpm. The high pressure was selected to assure a sufficiently fast motion of the valves at the maximum engine speed. As the speed is reduced the lift profile becomes trapezoidal with progressively steeper slopes. Testing and development of a system with two intake or two exhaust valves running in parallel was dedicated primarily to developing independent lift control for each individual valve. Since the two valves are controlled by the same pair of solenoids, the nominal lift of both valves is determined by the solenoid voltage-pulse duration. The action of the lift modifier is superimposed over the solenoid action and permits an independent and continuously variable reduction of lift for either of the paired valves, while the other valve remains at the computer controlled lift. Figure 19 shows the traces of two hydraulically-paired valves with maximum lift set to 4 mm. The valves are operated in the near synchronous mode (bottom), or with a small reduction of one of the lifts (middle), or with a nearly deactivated lift (top).

Figure 18. Lift traces of engine valve.

Figure 19. Traces of unequally set lifts.
A substantial amount of work was devoted to obtaining a quiet seating of engine valves. The previously described hydraulic pendulum was capable of producing the quiet seating only with a high precious of lift control and low cycle-to-cycle lift variability. However, a small deviation from a finely-tuned low-noise operation resulted in a noisy operation. As a practical solution, a hydraulic snubbing action was introduced. The snubbing takes place in the last 0.2 - 0.4 mm of closing and reduces the sensitivity to seating control parameters with minimum interference with hydraulic energy recovery (Figure 20). This keeps the valve seating velocity at 0.1 m/s or less.

Figure 20. Quiet seating control.

At the time of preparation of this paper only a limited amount of engine dynamometer testing has been conducted on a firing engine. Figure 21 shows part-load pressure-volume diagrams obtained with conventional and late intake valve closing. At 1500 rpm and 4 bar IMEP the engine ran essentially unthrottled. A number of system improvements are planned for the near future. The cylinder head structure will be reinforced to handle higher hydraulic pressures. This will allow to minimize the effect of air content in the fluid on the bulk modulus. The pressures in both the high- and the low-pressure reservoirs will be increased by equal amounts in order not to increase the hydraulic energy consumption. The control chamber volume will be minimized, and the performance of the hydraulic pendulum optimized to increase the hydraulic energy efficiency. Solenoid and driver circuit optimization is also planned.

Figure 21. Pressure-Volume Diagram.

ADVANTAGES OF CAMLESS ENGINE

` Electro hydraulic camless valve train offers a continuously variable and independent control of all aspects of valve motion. This is a significant advancement over the conventional mechanical valve train. It brings about a system that allows independent scheduling of valve lift, valve open duration, and placement of the event in the engine cycle, thus creating an engine with a totally uncompromised operation. Additionally, the ECV system is capable of controlling the valve velocity, perform selective valve deactivation, and vary the activation frequency. It also offers advantages in packaging. Freedom to optimize all parameters of valve motion for each engine operating condition without compromise is expected to result in better fuel economy, higher torque and power, improved idle stability, lower exhaust emissions and a number of other benefits and possibilities. Camless engines have a number of advantages over conventional engines.
In a conventional engine, the camshaft controls intake and exhaust valves. Valve timing, valve lift, and event duration are all fixed values specific to the camshaft design. The cams always open and close the valves at the same precise moment in each cylinder’s constantly repeated cycle of fuel-air intake, compression, combustion, and exhaust. They do so regardless of whether the engine is idling or spinning at maximum rpm. As a result, engine designers can achieve optimum performance at only one speed. Thus, the camshaft limits engine performance in that timing, lift, and duration cannot be varied.
But in a cam less engine, any engine valve can be opened at any time to any lift position and held for any duration, optimizing engine performance. The valve timing and lift is controlled 100 percent by a microprocessor, which means lift and duration can be changed almost infinitely to suit changing loads and driving 0conditions. The promise is less pollution, better fuel economy and performance.
Another potential benefit is the cam less engine’s fuel savings. Compared to conventional ones, the cam less design can provide a fuel economy of almost 7- 10% by proper and efficient controlling of the valve lifting and valve timing. The implementation of camless design will result in considerable reduction in the engine size and weight. This is achieved by the elimination of conventional camshafts, cams and other mechanical linkages. The elimination of the conventional camshafts, cams and other mechanical linkages in the camless design will result in increased power output.
The better breathing that a camless valve train promotes at low engine speeds can yield 10% to 15% more torque. Camless engines can slash nitrogen oxide, or NOx, pollution by about 30% by trapping some of the exhaust gases in the cylinders before they can escape. Substantially reduced exhaust gas HC emissions during cold start and warm-up operation.
The combustion process can be optimized by changing the composition of the cylinder charge by varying the intake valve opening and exhaust valve-closing timing as a function of load and speed. Under full load conditions the maximum volumetric efficiency is increased by optimized timing for intake valve. Another potential benefit is the elimination of external EGR. The EGR system is used to reduce or NOx emissions. This is achieved by diluting the intake charge with exhaust gas. Due to the absence of oxygen exhaust gas itself will not burn; it lowers the combustion temperature thereby reducing the information of NOx. In the camless design there is no need of external EGR. The intake charge can be diluted by trapping some exhaust gas inside the engine cylinder by the earlier closing of the exhaust valve. For this purpose extra sensors are to be placed in the exhaust manifold to detect the presence of NOx in the exhaust gas.
The most intriguing prospect is momentarily shutting off individual engine cylinders by stopping their fuel supply and cracking open their valves to spoil the compression. It’s a way to save fuel when an engine is running under a light load. The electronics are so fast that it should be able to selectively shut off cylinders in a way that will be imperceptible to the driver.



























CONCLUSIONS


1. An electro hydraulic camless valve train was developed for a camless engine. Initial development confirmed its functional ability to control the valve timing, lift, velocity, and event duration, as well as to perform selectively variable deactivation in a four-valve multicylinder engine.
2. The system employs the hydraulic pendulum principle, which contributes to low hydraulic energy consumption.
3. The electro hydraulic valve train is integral with the cylinder head, which lowers the head height and improves the engine packaging.
4. Review of the benefits expected from a camless engine points to substantial improvements in performance, fuel economy, and emissions over and above what is achievable in engines with camshaft-based valve trains.
5. The development of a camless engine with an electro hydraulic valve train described in this report is only a first step towards a complete engine optimization. Further research and development are needed to take full advantage of this system exceptional flexibility.












BIBLIOGRAPHY
• Michael M.Schechter and Michael B.Levin “Camless Engine”
SAE paper 960581
• P. Kreuter, P. Heuser, and M. Schebitz, "Strategies to Impove SI-Engine Performance by Means of Variable Intake Lift, Timing and Duration", SAE paper 920449.
• K. Hatano, k. Lida, H. Higashi, and S. Murata, “Development of a New Multi-Mode Variable Valve Timing Engine”,SAE paper930878
• J-C. Lee, C-W. Lee, and J. Nitkiewitz, “The Application of a Lost Motion VVT System to a DOHC SI Engine”,SAE paper 950816
• John B. Heywood, “Internal combustion engine fundamentals”
• William H. crouse. “Automotive mechanics.”
• John Steven Brader ,A Thesis on Development of a Piezoelectric Controlled Hydraulic Actuator for a Camless Engine
• mwww.machinedesign.com
• www.halfbakery.com
• www.deiselnet.com
• www.greendieseltechnology.co
• www.me.sc.edu

ABSTRACT

An engine with an electro hydraulic camless valve train, capable of total valve motion control, has many advantages other than the conventional engine. The system uses neither cam nor springs, which reduces the engine height and weight Hydraulic forces both open and closes the valves. During valve acceleration, potential energy of compressed fluid is converted into kinetic energy of the valve. During deceleration, the energy of valve motion is returned to the fluid. The System offers a continuously variable and independent control of virtually all parameters of valve motion .This permits optimization of valve events for each operating condition without any compromise.