MARATHWADA MITRAMANDAL’S COLLGE OF ENGINEERINGKARVENAGAR, PUNE 411052

Welfare of Masses

SEMINAR

On

CRANKLESS ENGINEBy

HOLKAR GAURAV PANDURANG Under the Guidance

Of

Prof. L.R.BHANDARKAR

Toward the fulfillment of Third Year Mechanical Engineering, Semester-I

Of

University of Pune

Academic Year 2010-11

MARATHWADA MITRAMANDAL’S COLLGE OF ENGINEERINGKARVENAGAR, PUNE 411052

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CERTIFICATE

This is to certify that Holkar Gaurav Pandurang Roll No. TM-140. A student of T.E. (Mechanical Engineering Department) Batch 2010-11, has satisfactorily completed a seminar report on “Crankless Engine” under the guidance of Prof. L.R.Bhandarkar towards the partial fulfillmeent of the Third Year Mechanical Engineering, Semester I of the Pune University.

Prof. L.R.Bhandarkar Prof Mrs R.R.Desai

(Seminar Guide) (Examiner) (HOD)

Date:-

Place

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ACKNOWLEDGEMENT

I take up the opportunity to express our gratitude towards all those who have been

instrumental in the completion of this seminar.

I am extremely thankful to the seminar guide Prof. L.R.Bhandarkar for his precious

guidance and encouragement throughout the development of the seminar.

I also express our sincere thanks to Mrs. R. R. Desai, Head of Department and also the

staff of Mechanical Department.

Holkar Gaurav PandurangTE (Mechanical)Roll No. TM-140

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ContentsTopic Page No1.Introduction 6 2.Basic Engine Components 72.1 Engine Components 73.Need of work 83.1 Inability to utilize entire gas force 83.1A Inertia Forces 93.2Unbalanced Forces on the Engine components 10 3.2A Side Thurst 11 4.Cam Engine 12 4.1Construction 14 4.2Cam Design 155.Introduction To Revetec Engine 17 5.1 Prototype engines 18 6.Advantages 19 7.Drawbacks 208.Future Scope 20 9.Conclucions 21 10.References 22

Figure IndexFigure Page No

2.1 Cross Section of a single cylinder Engine 83.1 Forces on piston 103.2Crank moment for various positions of piston 113.3Inertia forces on connecting rod 123.4Effect of Inertia forces on crank moment 124.1Proposed modified cam engine 144.2Cam Profile Design 17 4.3Torque Lever on the Cam 185.1Cam driven Revetec Engine 185.2Rotating Parts of a Revetec engine 19

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Abstract:

The conventional engine that we have been using for over a century

suffers from certain inherent drawbacks. These shortfalls are a major reason why these

engines operate on very low thermal efficiencies (typically 30 %). In the present

scenario, it is of prime importance that the efficiency of these engines is improved upon

to give better fuel economy with lower emissions. However there is limited scope for

development of the engine in its present configuration, since the drawbacks that these

engines suffer from, are resulting from the mechanism these engines use to transfer

force and motion.

In this seminar, an attempt as been made to point out these drawbacks

and a modification has been suggested, which has the potential to solve these drawbacks

and much more, provided that extensive research and development goes into the

optimization of the proposed design.

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Chapter 1

INTRODUCTIONThe distinctive feature of our civilization today, one that makes it different from all

others, is the fact that we are capable of sustained generation and wide use of mechanical

power.

One of the major reasons for our rapid development has been due to improvements

in transportation. While power from man’s muscles and that from animals were harnessed

before, the boost to development came when man learnt the art to convert energy from one

form to other. [1]

The machine which does this job of energy conversion is called an Engine. Normally

most of the engines convert thermal energy into mechanical energy and hence they are

called ‘Heat Engines’. The heat engine basically converts the chemical energy of fuel into

thermal energy by a process called combustion and utilizes this thermal energy to do

useful work.

Heat engines can be broadly classified as

Internal Combustion Engines (I. C. Engines)

External Combustion Engines (E. C Engines)

Internal or External combustion engines are classified by the fact that in I. C. engines,

combustion takes place inside the engine while in E. C. Engines the combustion takes

place outside the engine and only the heat energy developed by the combustion process is

utilized in the engine.

The use of E. C. Engines in transportation is questionable since they require bulky

apparatus and operate on much lower thermal efficiencies than the I. C. Engines. As a

result,

I. C. Engines are widely used for motive applications.

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Chapter2

BASIC ENGINE COMPONENTS AND NOMENCLATUREEven though the reciprocating internal combustion engine looks quite simple,

they are highly complex machines. There are hundreds of components which have to

perform satisfactorily to produce power.

2.1 ENGINE COMPONENTS

A cross-section of the single cylinder spark ignition engine with overhead

valves is shown in fig. 3. The major components of the engine and their functions are

briefly described below.[1,2]

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Fig. 2.1 CROSS-SECTION OF A SINGLE CYLINDER ENGINE Chapter 3

NEED OF WORK

3.1 INABILITY TO UTILISE THE ENTIRE GAS FORCE

The first and most important drawback of the conventional engine is

the fact that it cannot utilize the entire pressure generated by the combustion of fuel and

convert it into usable work. This is inherent to the I.C. Engine mainly because the

mechanism that the conventional engine uses (viz. single slider crank chain I.C.

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Engine mechanism) is itself inefficient in converting the reciprocating motion of the

piston to the rotary motion of the crankshaft.

As we see in fig 4. a, the crank moment obtained by the connecting

rod at TDC is necessarily nil as the connecting rod and the crank arms are in line with

each other and there is no effective moment arm. As the piston moves away from TDC,

a very small crank moment is obtained (fig 4. b). This moment is not enough to

efficiently transfer motion to the crank. As we move further down the stroke the crank

moment increases, however it is not substantial until 30 deg ATDC and reaches its

maximum value only after 40% of the piston stroke is completed, i.e. at about 60 deg

ATDC (fig 4. c) and then drops at a rapid rate which mirrors its rise. Thus it is very

evident that the (combustion characteristics of the fuel) has nothing to do with the

mechanism by which power is transmitted from the piston to the drive line, in a

conventional engine.[3,4,6]

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FIG. 3.1 FORCES ON THE PISTON

A)INERTIA FORCES

The con rod gives rise to considerable inertia forces. The path of

motion of the connecting rod is not along or about the cylinder axis, but it pulsates on

either side of it. The weight of the con rod is also not uniformly distributed, but

concentrated at its ends. The con rod has to be robust rigid and tough to withstand the

effects of these unbalanced forces and also to transmit the high compressive stresses at

the start of the expansion stroke.[4]

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The large inertia forces due to the mass of the con rod and the

components of the other forces due to the angularity of the con rod causes increase in

piston side thrust and also loads the bearings heavily(fig. 9). This causes increased

friction losses and reduces thermal efficiency and also increases noise and vibration in

the engine.

(a) (b) (c)

FIG. 3.2CRANK MOMENT FOR VARIOUS POSITIONS OF THE PISTON

3.2 Unbalanced Forces on the Engine Components

A) SIDE THRUST

The connecting rod (con rod) is one of the components of the engine

that is a major source of unbalanced forces in the engine. In fig 4.a we can see that at

TDC or BDC, the con rod is in line with the crank and the entire gas force is

transmitted along the axis of the con rod. Hence this would not give any effective

moment arm to the crank and would only load the bearings.

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However at any other position of the piston, the angularity of the

connecting rod causes it to press the piston against the cylinder wall and the cylinder

wall to react against the piston. This is called piston side thrust.[3,6]

FIG. 3.3 INERTIA FORCES ON THE CONNECTING ROD

The unbalanced inertia forces due to the various reciprocating and

pulsating engine components has to be overcome by the engine to produce any usable

power. If these forces were reduced or eliminated, more gas force can be converted into

usable power which would be available at the driveline. Even though the inertia forces

assist to some extent in the expansion and the compression stroke, but it eats away a

major chunk of the gas-pressure moment in the initial and crucial stage of the

expansion stroke

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FIG. 3.4 EFFECT OF INERTIA FORCES ON CRANK MOMENT

B) FORCES DUE TO OTHER FACTORS

To accommodate the entire assembly and also to damp some of the

vibrations caused due to the reciprocating parts, the engine block becomes tough, heavy

and bulky. As a result the weight of the engine further increases and power to weight

ratio of the engine is considerably lowered. This further increase the load on the drive

and ultimately lesser tractive force is available to the driver.

Thus we can see that due to various drawbacks in the configuration of the basic

conventional engine, about 15% of the power generated by the engine is lost as frictional

losses. Also about 25% of the usable heat is lost to the exhaust because the engine is not

able to convert the gas force into usable work

4) THE CAM ENGINE:In this seminar, a design modification of the motion transfer

is suggested. It consists of the following basic changes,

1) Remove inefficient engine components i.e. the crank arm

and the connecting rod.

2) Replace the components by a cam of suitable profile.

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FIG. 4.1 PROPOSED MODIFIED ENGINE

4.1 CONSTRUCTION

The engine would consist of a bilobed cam mounted on the splined

crankshaft. In this case, the piston would act as the follower and is provided with a

roller bearing with the inner race fixed to the piston assembly and the outer race fixed

to roll on the cam profile (fig. 11).

Since heavy engine components like the connection rod and the crank

arm has been eliminated, lot of the engine weight has already been reduced. Further

reduction in weight can bed brought about by reducing or eliminating the piston skirts

and also by drilling holes on the cam.

We have seen how insufficient the conventional engine is in

converting the gas forces into usable force. The movement if the piston in a

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conventional engine is the function of crank rotation. However since the piston is acting

as the follower in the modified engine, we can control the displacement, velocity and

acceleration of the piston by controlling the cam profile.

In the conventional engine, one of the major hurdles facing the of

force was the fact that mechanical advantage is obtained at around 60 deg. ATDC, i.e.

after the piston has covered about 40% of its travel, thus losing valuable cylinder

pressure. This problem is overcome using the cam of suitable profile which would give

maximum mechanical advantage at around 20 deg ATDC (i.e. app. 10 % of the piston

travel). The cam profile is also customized to give maximum torque lever over a greater

no. of degrees of rotation which transfers the torque to the output shaft more efficiently

over the entire operating range.

One thing that has to be considered in the modified design is that, the

cranking distance is determined by the length from the point of contact of the bearing

with the cam to the centre of the output shaft. The cam can be designed to provide the

same max torque lever as that of the conventional engine over a larger no. of degrees of

rotation.

Another drawback of the conventional engine, we have seen is that

the piston displacement, velocity and acceleration is a function of crank position.

However this is a major drawback as the motion of the piston should compliment the

rate of expansion of the burnt gases so as to fully utilize the potentially available gas

force without shock and vibration. However in case of the cam engine we can

customize the piston acceleration and alter it to suit a particular fuel and / or torque

application, so as to attain better control over the combustion.

It is also seen that the force ‘Ps’ generated due to the angularity of the

con rod causes side thrust on the piston during major part of the stoke. This increases

wear and thus lubrication requirement of the assembly. In the cam engine the piston rod

is made integral to the piston and two roller bearings are mounted on either side of it.

Since the gas force is transmitted along the axis of the piston rod to the roller bearings.

For the entire stoke, side thrust is considerable reduced. Some side thrust, however, will

still be present due to the reaction from the bearings. But this is much lesser than what

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exists in a conventional engine. This eliminates the need for large piston skirts as in the

case of conventional engine.

Also since the side thrust is reduced the effective gas force available at

the lever arm is increased and more torque is generated on the output shaft. This result

in more power and increase in the thermal efficiency of the engine.

Eliminating the connecting rod gives the cam engine two major

advantages over the conventional engine.

a. The con. Rod is an irregularly reciprocating member and gives rise to

unbalanced inertia forces which reduces the effective crank movement (fig.)

available to the crank and also increases friction losses by inducing piston side

thrust. Due to its pulsating motion causes vibration in the engine.

b. To have optimum mechanical advantage the length of the con. Rod is usually

kept 4 times the length of the crank arm. (n=l/r=4). This increases the size f

the engine and hence its weight. In the cam engine the same mechanical

advantage is provided by the cam in a much smaller space. Hence the cam

engine would be much smaller in sixe than a comparable conventional engine.

The weight of the cam is comparable to the weight of the crank arm with

the balancing weight. Hence there would not be much change in the overall weight of

the engine due to the cam. Since the cam engine has fewer moving parts than the

conventional engine, friction losses would be substantially reduced. Since parts like the

gudgeon pin and the crank pin are eliminated, there are no friction losses due to these

parts.

4.2CAM DESIGN

The cam for the model was designed to simulate the same

piston motion as that of the conventional engine for the purpose of

comparing and analyzing the two configurations. The variation of piston

displacement with respect to crank rotation is given in the graph. (fig.4.2),.

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4.2)Cam Profile Design

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(a) (b)

FIG.4.3 TORQUE LEVER ON THE CAM

Of course the cam provides lesser and lesser torque lever as the piston

advances in its stroke but cylinder pressure also decreases as the stroke advances. The

basic advantage of the cam engine is that we can make the cam give the maximum

mechanical advantage when there is maximum gas pressure in the cylinder. Thus we

can get more power output from the engine with the same quantity of fuel burnt. This

would also help in keeping the idle speed of the engine lower.[6]

5)Introduction to Revetec Engine

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5.1)Cam Driven Revetec Engine

Revetec Engine consists of Two counter rotating “Tribolate”(three lobbed) cams geared

together,so both cams contribute to forward motion.Two bearings run along the profile of the

cam(four bearing in all) stay in contact with cam at all the time.The bearings are mounted on the

underside of the two interconnected pistons which maintain the bearing to Trilobe clearance

through the stroke.

5.2)Rotating parts in a Revetec Engine

The two cams rotate and raise the piston with a scissor-like action to the bearings. Once at the

top of the stroke the air/fuel mixture is fired. The expanded gas then forces the bearings down

the ramps of the cams spreading them apart ending the stroke. The point of maximum

mechanical advantage or transfer is around 20-30deg ATDC (when the piston moves

approximately 10% of its travel) making the most of the high cylinder pressure.

This compares to a conventional engine that reaches maximum mechanical advantage around

60-70deg ATDC. (after the piston has moved through just over 40% of its travel, losing

approximately half of the cylinder pressure).

The effective cranking distance is determined by the length from the point of bearing contact to

the centre of the output shaft (not the stroke). A conventional engine's turning distance is half of

the piston stroke. The piston acceleration throughout the stroke is controlled by the cam “grind”

which can be altered to suit a wide variety of fuels, torque requirements and/or rev range. The

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piston assembly slides rigidly through the block via an oil pressure fed guiding system

eliminating piston to cylinder-bore contact.

This reduces wear and lubrication requirements in the cylinder, and also reduces piston side

shock making ceramic technology suitable.

One module can either comprise of two trilobate cams and either two, or four pistons in an “X”

configuration.

The counter rotation is performed by a reverse gear set at a 1:3 ratio shaft providing two strokes

of a piston to 360 degrees of output shaft rotation. The same as a conventional engine.

5.1) Prototype Engines

X4v2 Prototype - 2.4litre (2007- Current)

The X4v2 is the current prototype under development and based on the X4v1

engine design. The X4v2 prototype engine was designed, machined,

assembled and running by the end of 2007. The engine completed tests on the

dynamometer, and was fitted and trialled in the GTM trike. The engine was

independently tested by Orbital Australia and achieved a top BSFC figure

207g/(kW-h) or 39.5% efficiency.

Applications: The advantages of Revetec’s engine technology can be applied to most

internal and external combustion engines for use in motor vehicles, trucks, buses, motorcycles,

pumps and generators, light aircraft engines, diesel and marine engines.

6) ADVANTAGES

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On comparing with the conventional engine the cam engine has the

following advantages.[5]

Approximately one half the size and weight of a conventional engine (for similar

applications) combined with improved output substantially increases

power/weight

and torque/weight ratio.

Fewer moving and total components. As a result of fewer components, more

easily manufactured than conventional engines.

Identical cylinder head assembly (“top end”) to conventional engines. Most

existing head technology can be either adapted or utilized.

Flexible design - can be four-stroke, two-stroke, petrol, diesel or gas, natural of

forced aspiration.

Eliminated irregularly reciprocating components such as connecting rods.

7)Drawbacks

Developing the optimum cam profile would require extensive testing and

research.

The cam follower mechanism may suffer from the jump phenomenon at high

speeds. However it can be over come by using two pistons in an opposed

cylinder configuration.

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The engine would suffer from balancing problems as the cam is not a

symmetrical member. This can be overcome by mounting a counter-rotating

balancer shaft on the output shaft.

8)Conclusions:

1.Many alternative internal combustion engine designs are proposed

every year. However a very few of them are developed commercially. Most designs

would require substantial development and manufacturing investment to enable them to

fully realize their advantages.

2.However automobile manufacturers prefer to invest on the tried and

tested technology of the conventional engine that is well known and well provided for

in the automotive sphere – design, manufacturing investment to use and disposal.

3.However recent restriction on emissions and the looming shortage of

fossil fuel has forced manufacturers to look for alternative technology that would give

more power, more efficiency and more mileage.

4.The S.I. Engine has been developed for more then a century and

carries a vast knowledge base with it. The CAM Engine can use this extensive

development to enhance its performance even further. It can use the advancements in

ignition control, air-fuel mixture preparation control etc. It still needs a lot of

development, but its basic configuration provides a promising answer to a lot of

questions.

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9)Future Scope

C.F.D. analysis and F.E.M. analysis could be done on the engine

components to obtain optimum design of the components. The cam profile can be

perfected upon by model testing and PRO-E analysis. I have simulated the motion of

the piston with the model to show that motion transfer is possible. Further I would like

to modify an actual engine to the proposed configuration to actually visualize its effects

and feasibility.

10)References

1. FUNDAMENTALS OF INTERNAL COMBUSTION ENGINE by PAUL

W GILL, JAMES H SMITH, EUGENE J ZIURYS,FOURTH ED,

OXFORD & IBH PUB., p: p- 1.1 – 1.6

2. INTERNAL COMBUSTION ENGINE by V GANESHAN

SECOND ED, TATA MCGRAW HILL PUB, p: p- 1-6, 19,397,495,606

3. www.Revetec.com

4. www. Matra et Alpine.com/Q&A/revetec engine (ENTRY DATED 26-02-

2006)

5. ALTERNATIVE ENGINE TECHNOLOGY by C F TAYLOR

p: p- 5-6,153

6. COMBUSTION ENGINES by P M HELDT, p:p- 29,34,38-39,123

7. AUTOMOTIVE ENGINES by S SRINIVASAN, FIRST ED,THIRD

REPRINT

TATA MCGRAW HILL PUB, Page No. 13

8. THEORY OF MACHINES by R S KHURMI, J K GUPTA

REV. MULTICOLOUR ED, S CHAND PUB, p: p- 523-525, 530, 780-

782,799-800

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9. DESIGN AND SIMULATION OF FOURSTROKE ENGINE by GORDON

P BLAIR

Page No. 484

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