WALCHAND INSTITUTE OF TECHNOLOGY.

SEMINAR

ON

“SCOTCH YOKE TECHNOLOGY ENGINE”

SUBMITTED BY

DOSHI VISHAL JAIN KALPESHMob:-9967192620 Mob:-9975431436Email:-vishlalu@gmail.com

DEPARTMENT OF MECHANICAL ENGINEERING SOLAPUR

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CERTIFICATE

This is to certify that Mr. Abhijeet V. Wagh, student of

B.E Automobile Engg. Of Roll No. 4044 has successfully

completed the Seminar report on “SCOTCH YOKE

TECHNOLOGY ENGINE”

In the fulfillment of Bachelors Degree in Automobile

Engineering of “Shivaji University, Kolhapur” during academic

year of 2007-2008.

Prof. S .D .Yadav Prof. D. G. Thombare

Automobile Department. Head of Department

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ACKNOWLEDGEMENT

I would like to take this opportunity to express my honor, respect, deep gratitude and

genuine regard to my guide Prof. S. D Yadav and head of department Prof. D. G Thombare for

giving me all guidance required for my seminar apart from being a constant source of inspiration

and motivation. It was indeed my privilege to have worked under them.

Last but not the least, the backbone of my success and confidence lies solely on the

blessing of my parents.

ABHIJEET V. WAGH

(BE Automobile Engg)

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ABSTRACT

Scotch yoke is an inversion of double slider crank chain. The scotch yoke mechanism

can be used in an engine to convert the reciprocating motion of piston into the rotary motion of

the crankshaft. The engine thus build is called as a Scotch Yoke Technology Engine or simply a

‘SYTech Engine’.

Added to their cost effectiveness and simplicity, the SYTech engines have many

advantages. Their width can be kept small. The short engine block and low engine height

provide the greatest freedom for the design of drag efficient bonnet styling and effective crust

zones, even in small vehicles. The absence of unbalanced inertia forces and moments with

SYTech engines reduces the need for expensive measures to reduce cabin noise and vibrations.

SYTech engines run more quietly and smoothly for mainly three reasons: firstly, the

engines are perfectly balanced with no free inertia forces or moments, secondly, the mechanical

piston noise is very low and finally, the peak to peak variation of the output torque are much

lower under all important operating conditions.

NOx is the exhaust gas component, which is most difficult to reduce. The sinusoidal

motion of SYTech engine piston can provide up to 30% NOx reduction with no increase in

specific fuel consumption.

SYTech crank mechanism can be applied to diesel and S.I., two stroke and four stroke

engines.

The SYTech Engine is tested in ‘dynamometer durability test’ by Collins Motor

Corporation (CMC), Melbourne, Australia. The engine is also tested in the Australian concept

family car ‘aXcessaustralia II’ during many kilometers of road running under day-to-day traffic

conditions.

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The Scotch Yoke Mechanism:

The Scotch Yoke mechanism is an inversion of the Double slider crank chain. It can be

used for converting reciprocating motion into rotary motion. Figure 1 shows the schematic

arrangement of the mechanism.

Fig.1 Schematic arrangement of Scotch yoke mechanism

Here, link 1 is fixed. When the link 4 (slider) reciprocates, link 2 (crank ) rotates about

B as centre.

This principle is used in an I.C. engine to convert reciprocating motion of the piston into

rotary motion of the crank. The engine is called as a scotch Yoke Technology engine or a

‘SYTech engine.’

CONSTRUCTION AND WORKING OF SYTECH ENGINES:

A SYTech crank mechanism replaces the arrangement of connecting roods, gudgeon pins

and pistons in conventional engines with a rigid assembly of two pistons and two connecting

rods and a bearing block (figure 2).

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Link1 1

Link2

Link3

Link 4 (Frame)

Fig.2 Fundamental components of SYTech engine mechanism

The crankpin rotates within the bearing block, which slides up and down between the

parallel surfaces formed by the bases of the two connecting rods. The crankshaft is conventional.

The piston and connecting rod assembly oscillates along the cylinder axis in a simple harmonic

or sinusoidal motion. Hence, the bearing block mounted on the crankpin traverses a circular

path around the crankshaft axis causing rotation of the crankshaft.

The bearing surfaces between the bearing block and the base of the connecting rod are

called as ‘linear slider bearings’. They operate like a combination of a hydrodynamic and a

hydrostatic bearing. The bearings are highly loaded only at times of high relative bearing speeds

(0,180, 360, 5400 crank angle). The load equals zero or is very low during the times, when the

relative motion slows down and changes direction (90, 270, 450, 6300). Under the low speed

condition, the bearing act like hydrostatic bearings with decreasing bearing clearance, but

increasing load carrying capability. At high sliding speed, an oil wedge builds up causing the

hydrodynamic action of the bearing. As figure 3 shows, the horizontally opposed cylinder

layout ensures that the load on each linear bearing is negative for 50% of the engines operating

cycle. Negative forces open up the bearing clearance, supporting the supply of new oil into the

gap between bearing plates.

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Fig.3 The linear bearing load and relative sliding speed at 5000 rpm

All moving components in the SYTech crank arrangement conduct either a rotational or a

perfectly sinusoidal linear motion. Hence, inertia forces of a higher order do not exist for a

symmetrical crank layout, the first order, inertia forces balance each other. For engines with

four and more cylinders, the horizontal distance between the cranks causes an inertial moment

around the vertical axis of the engine. Because this moment is of first order, it can be perfectly

balanced by balance weights, which rotate only with engine speed. Only the balance shaft,

which turns in the direction opposite to the engine revolution, has to exist physically as a

separate shaft. The balance weights rotating with the crankshaft can be directly attached to it

(figure 4)

Fig.4 Perfect balance with only one balance shaft

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SIMPLE HARMONIC PISTON MOTION:

The difference in piston motion of conventional and of SYTech engines can be described

by the following equation for piston position, speed and acceleration.

Piston position, speed and acceleration for the conventional and the SYTech engines are

identical in their first order term, which is the only term for sinusoidal piston motion. The

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higher order parts of the equations describe the more complicated motion in conventional

engines.

Figure 5 shows the different piston positions for the point of time when the combustion

has been completed. At this time, when most of the chemical energy contained in the fuel

mixture has been converted into gas pressure and temperature, the piston of the engine with

sinusoidal piston motion is, at 6000 rpm, still located 1.5 mm closer to TDC than the piston with

a conventional crank mechanism. At 1000 rpm, the difference is nearly 1mm. this means that

the conventional piston has already done more than 20% of it’s travel with less than the

theoretically available gas pressure action upon it.

Fig.5 Piston position as a function of time after TDC at 1000 and 6000 rpm

With the exception of TDC and BDC, the combustion chamber volume with sinusoidal

piston motion is smaller than the volume with a normal crankshaft and connecting rod for any

given crank angle during the whole expansion stroke. The difference in combustion chamber

volume between both crank mechanisms is shown in figure 6.

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Fig.6 Difference in combustion chamber volume between normal and sinusoidal piston

motion

Assuming identical cylinder pressure at each piston position, which means identical

IMEP, for both engine types, the pressure curves as a function of crank position are shown in

figure 7.

Fig.7 Cylinder pressure for identical IMEP

From the figure it is clear that the peak pressure is lower in SYTech engines, but the

pressure during most of the expansion strake is higher, resulting in a higher torques output and

less peak stresses in the pistons, usually, for the same torque output, the SYTech engine needs

less fuel.

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VALVE TIMING:

The piston of an engine with sinusoidal piston motion is at every crank angle located

closer to the TDC position than the piston of a conventional engine. Only exactly at TDC and

BDC is this difference zero. The acceleration shows the biggest differences at the extreme

positions, while the differences in piston position and speed between sinusoidal and normal

piston motion are largest at around 900 crank angle. Therefore, valve events close to the extreme

positions are not significantly influenced by the type of crank mechanism. The differences are,

however, relatively large for the events of inlet valve closure and exhaust valve opening, which

take place further away from the extreme positions. Table 1 shows these differences for the

examples of a SYTech engine and an equivalent conventional engine. The ratio of connecting rod

length to crank radius for the conventional comparison engine is 3.49.

Table 1: Valve timing and piston motion

IVC:600 ABCD IVO:20 BTDC

EVO:500 BBDC EVC:160 ATDC

2500

rpm

Piston position

mm

Piston speed

m/s

Piston accel.

m/s2

SYTech/Conventional SYTech/Conventional SYTech/Conventional

IVO -0.02/ -0.03 0.34/ 0.44 2570/ 3300

IVC -56.25/ -60.34 8.50/ 7.24 -1290/ -1650

EVO -61.60/ -64.80 -7.52/ -6.10 -1650/ -1770

EVC -1.45/ -1.86 -2.71/ -3.45 2470/ 3100

Identical geometrical compression and expansion ratios for an engine achieved when the

inlet valve closes and the exhaust valve opens at the same piston position, not at the same crank

angel. Table 2 shows the shift of the valve event angles for identical piston positions, for

example of a SYTech engine.

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Table 2: Valve timing for identical geometrical compression and expansion ratios for

normal and for sinusoidal piston motion

Valve timing

(conventional

engine)

Piston position(below

TDC)

(both engine types)

Valve timing

(SYTech engine)

IVO 20 before TDC 0.03 mm 20 before TDC

IVC 600 after BDC 60.34 mm 520 after BDC

EVO 500 before BDC 64.80 mm 430 before BDC

EVC 160 after TDC 1.86 mm 180 after TDC

A significant change is only required for the closing angle of the inlet valve and the

opening angle of the exhaust valve. The inlet valve of a SYTech engine has to close earlier, the

exhaust valve to open later

IGNITION / INJECTION TIMING:

The ignition angle or, in the case of Diesel engines, the injection timing needs

adjustment too. This is especially important at high engine speeds, when the ignition delay

requires an earlier angle for the best efficiency. If the start of the combustion is not retarded for

the sinusoidal piston motion, a higher cylinder pressure peak would occur than in a conventional

engine, because more chemical energy is converted close to the top position of the piston.

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ADVANTAGES TO APPLY A SYTECH CRANK MECHANISM:

There are several areas, where SYTech engines are superior to engines with conventional

crank mechanisms –

1. Inertia forces and moments –

Sinusoidal piston motion means sinusoidal piston speed and acceleration. As

shown in figure 8, the maximum deceleration at TDC, in the 2.2-liter SYTech engine is

around 20% lower than that in the equivalent displacement conventional engine.

Fig.8 Piston acceleration VS crank angle at 6000 rpm

From figure it is clear that conventional engines are designed to withstand very

high inertia forces around TDC with the inertia forces at BDC being much lower. In

SYTech engines, the peaks are equal at TDC and BDC.

In SYTech engines, a single balance shaft, running only at engine speed, can be

used to eliminate all free inertia forces and moments, 50% of the inertia force created by

the piston and connecting rod oscillation is balanced by counter weights on the

crankshaft, arranged opposite to crankpin. The other 50% is balanced by weights on the

balance shaft. Thus, the use of single balance shaft instead of two as in conventional

engines, reduce mechanical losses and noise in SYTech engines.

2. Improved Engine Torque Uniformity -

Even in perfectly balanced engines, inertia influences and the intermittent

combusting cycles cause the engine torque to be delivered with a high degree of non-

unifomity. Torque peaks occur with the firing stroke, negative peaks with the

compression stroke of each cylinder. But the arrangement in SYTech engines with two

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opposing pistons being rigidly connected to each other causes the output torque to be

more uniform under all important operating conditions.

Fig.10 Variations in torque at part load and full load

At part load, the example in figure 10 shows that the peak to peak variations of

the engine torque are reduced by 170 Nm or 44% in the SYTech engine, while at the

same speed of 3000rpm under full load conditions, the reduction is 228 Nm at 37%. The

more uniform development of the produced torques puts less stress onto all components

of the drive train and can reduce gear rattle in the transmission. Also, it leads to a more

uniform engine speed, which has the positive side effect, that all auxiliaries are exposed

to less engine speed variations during each revolution and a harmonic balancer in the

crankshaft pulley might not be necessary to protect the belts and auxiliary components

from torsional vibrations of the crankshaft.

3. Noise and vibration -

The engine is one of the main sources of noise and vibration both within and

outside the cabin of a motor vehicle. Engine noise originates mainly from free inertia

forces and moments and their harmonics and from higher frequency combustion and

mechanical impact noise. It is transmitted into the cabin of the vehicle by air, the vehicle

structure and other components. Resonances and interferences then determine the

general noise level at low frequencies. The second order cabin noise level is often used

as a measure for the acoustical quality of a vehicle, because it is especially in 4-cylinder

cars, predominant and representative for the overall noise impression. Figure 11 shows

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this noise level during ‘wide open throttle’ accelerations for cars with conventional

engines and for a car with a SYTech engine.

Fig.11 cabin noise during WOT accelerations in second gear

The SYTech engine showed the lowest noise level over the whole engine speed

range.

Vibration test results measured on an engine dynamometer with acceleration

sensors mounted on the generator bracket of the conventional and the SYTech engine

demonstrate the smooth operation of the SYTech engine. The reduction in vibration

amplitudes is significant at all speeds and over the whole load range.

SYTech engines run more quietly and smoothly for mainly three reasons: firstly,

the engines are perfectly balanced with no free inertia forces or moments, secondly, the

mechanical piston noise is very low and finally, the peak to peak variations of the output

torque are much lower under all important operating conditions.

4. Fuel Consumption and Emissions –

Combustion simulations for Diesel as well as S.I. engines indicated that the

sinusoidal piston motion of SYTech engines has a positive influence on the level of NOx

emissions. For the comparison of the SYTech and the conventional engine, the ignition

timing was adjusted in two different ways as shown in figure 13.

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Fig.13 Test results for CMC422 SYTech engine and equivalent conventional

engine

For the ‘low bsfc’ condition, a reduction in specific fuel consumption occurs over

the whole range with about the same NOx emissions under low loads and a considerable

NOx reduction at higher part load. With the setting to ‘Low NOx’ emissions levels an

average of 30% reduction of NOx emissions could be achieved. This reduction is due to

a longer well time around TDC of the pistons of SYTech engine resulting in more time

being available for the combustion.

For HC and Co, the direct influence of the type of piston motion on the emission

levels has not yet been clearly established. If a difference exists the longer dwell time

should lead to a more complete combustion, thus HC as well as co levels will show small

reductions.

5. Mechanical efficiency –

SYTech engines require fewer bearings than conventional engines. The additional

linear bearings are compensated by the reduced number of main and big end bearings

and by the elimination of gudgeon pins. This leads to lower overall frictional losses.

The lower piston side forces cause less friction between pistons and cylinders, which

further reduces mechanical losses of the engine. Thus, the mechanical efficiency of

SYTech engine is greater than that of a conventional engine as shown in figure 14.

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Fig.14 Mechanical engine efficiency

6. Engine Size –

With their horizontally opposed cylinder layout, SYTech engines have the low

height of conventional engines. More than 150 mm height difference can be achieved for

a 2 litre engine. Also, the connecting rods of SYTech engines are rigidly connected to the

pistons and do not move vertical to the piston motion. They can therefore be designed

very short without any increase in piston side force, which occurs with shorter

connecting rods in conventional engines. With shorter connecting rods, the engine width

is reduced approximately by 62 mm. The savings in engine heights and width allow a

much lower hood line with potential advantages on the drag coefficient.

7. Manufacturing costs –

Figure 15 shows the percentage of total manufacturing costs of different engine

components for a conventional and a SYTech engine. From the figure, it is clear that the

manufacturing cost of a SYTech engine is less than that of a conventional engine. This is

because the higher production cost of the SYTech connecting rods is offset by savings

from a reduced number of main and big end bearings, the elimination of gudgeon pins

and simplest crankcase and crankshaft designs.

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Fig.15 Manufacturing cost difference between a conventional and SYTech engine

8. Safety –

With the application of SYTech engines, a variety of safety advantages are

achieved in ranged to ‘active’ safety, which helps to prevent accidents to happen, and in

regard to ‘passive’ safety, which helps to protect the passengers of motor vehicles in case

an accident does happen.

Active safety:

The low centre of gravity of SYTech engines, which is situated close to the level

of the crankshaft above the road, reduces the roll moment during cornering and makes

driving through sharp bends safer.

Passive safety:

The short and flat engine allows the design of larger crush zones even in very

small vehicles. Because the engine is so flat, it can slide under the passenger cabin in

case of a frontal impact.

THE SYTECH ENGINE IN THE NEW AXCESSAUSTRALIA HYBRID CAR:

The Australian concept car 'aXcessaustralia II' is a serial hybrid car of the so-called 'New

Generation Hybrids'. Its internal combustion engine drives an electrical power generator. The

wheels are driven by the electrical traction motor only, which receives its energy from a

combination of batteries, capacitors and the electrical power generator. In a drive train, which

consists of a combustion engine, a generator, a traction motor, two different systems for

electrical energy storage and the necessary electronics to apply the most fuel efficient power

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strategy, all components require an extremely high degree of weight optimization to avoid

offsetting the fuel savings achieved with the system by an increased overall vehicle weight.

They also need to be extremely efficient in themselves.

SYTech engine contributes its share of weight savings by being lighter than comparable

conventional combustion engines and by allowing further secondary weight savings in other

vehicle components. All SYTech engines are perfectly balanced and therefore require much less

effort to isolate the vehicle cabin from engine originated noise and vibrations. The output torque

is more uniform under all important operating conditions allowing a lighter drive train than

required for conventional piston engines. The small size of SYTech engines makes them

especially suitable for the more complex packaging requirements in a hybrid car. The low

weight of the engine itself and the lower mass of components and material required to meet the

NVH requirements help to overcome the inherent weight disadvantage of a complex hybrid

system.

APPLICATIONS OF SYTECH ENGINE:

SYTech engines can be used instead of conventional engines in most applications. The

compact layout makes them suitable for very small city cars, where the provision of a sufficient

crush zone is a problem, and for hybrid cars, where the overall size of the electrical components

and of the combustion engine is even more critical. The smoothness of Scotch Yoke engines

makes them applicable in the luxury car segment, where the advantages in NVH are important

and in high performance cars the superior power density allows to package engines with more

cylinders or higher capacity into the available space. The very good NVH levels allow the

design of larger than usual capacity 4 cylinder engines, which would be especially interesting for

vans and similar vehicles, where less noise dampening measures are applied to keep costs down.

The reduced engine width and the much lower engine vibrations together with a low weight

make the CMC Scotch Yoke engine an ideal motor for motorbikes. The small cross section, low

weight and low vibrations of CMC’s Scotch Yoke engines are important for small piston engine

aircraft and also for small boats. Mobile power generators and combined engine/compressor

designs are further applications, where the compact SYTech engines with their reduced

vibrations and NOx emissions and their improved efficiency can make an important difference.

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Conclusion

SYTech engines are smaller, lighter and less noisy. They do not require as much effort

and expense for vibration and noise control and emit less NOx than conventional engines. Their

mechanical efficiency is better, especially at high engine speeds, and they enable a reduction in

vehicle manufacturing costs.

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References

1. Dr.Hans. G. Rosenkranz, “ Simple harmonic piston motion of CMCR’s SYTech engines,

influence on design operation”, 10th International Pacific Conference on Automotive

Technology, Melbourne, May 1999.

2. Dr.Hans. G. Rosenkranz, “What’s different in SYTech engines?”, CMC Research house,

Melbourne, April 2000.

3. Dr.Hans. G. Rosenkranz, “Why change to CMC Scotch Yoke engine

technology?”,Melbourne, September 1998

4. Richard P. Gabler, Harry C. Watson, “Experimental investigation of the CMC Scotch Yoke

engine linear bearing lubrication system”, SAE Paper 971393, November 1999

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