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Transcript of Crankless Engine
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
1
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
2
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
3
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
4
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.
5
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.
6
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]
7
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.
8
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]
9
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]
10
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.
11
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
12
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.
13
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
15
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),.
16
4.2)Cam Profile Design
17
(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
18
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
19
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
20
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.
21
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.
22
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
23
9. DESIGN AND SIMULATION OF FOURSTROKE ENGINE by GORDON
P BLAIR
Page No. 484
24