sem engine report

8/10/2019 Sem Engine Report

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The design of the power system started with the selection of the wheels using the Quality Function

Development (QFD) approach. Considerations were given to rolling resistance, availability and cost. Based on

this a wheel rim diameter of 17 inches was selected.

Based on the track details given, average speed to be achieved by the car to successfully complete the

competition was obtained to be 25 kmph. Considering the acceleration, deceleration, cornering times and draglosses, the top speed was decided to be limited to 40 kmph.

The following formula was used to calculate the resisting force acting on the car, using which power was

calculated :

( )

where the symbols have their usual meaning. It is to be noted that the above formula gives the power required

to maintain the vehicle speed only and to accelerate the vehicle, additional power is to be applied on the car.

It was seen from the graph that at 40 kmph, power of 4 kW is required to maintain the speed. Based on this,

another QFD matrix was developed for the engine selection. Various parameters considered were mileage, type

of transmission, weight, cost, availability and power. As this was the first time the team was competing in Urban

Concept category, Continuous Variable Transmission (CVT) was given preference over geared transmission to

reduce complexities. A 110 cc TVS Jupiter engine, with peak power of 6 kW was selected based on this analysis.

An engine simulation software, Ricardo Wave, was used to obtain the power generated by the engine at various

RPMs. Engine torque peaked at 8 N-m at 5500 RPM, whereas maximum power of 6kW was obtained at 7500

RPM. Considering the drive train efficiency, a peak power of 4.9 kW is transmitted to the wheel. At all times, the

torque delivered to the wheel has to be greater than the resisting torque for the vehicle to accelerate. To

accomplish this, transmission ratio of 1 : 14 was selected. At all the velocities, it was observed from the graph

that the power delivered by the engine was exceeding the power required by about 600 W on an average,

whereas only about 300 W was needed to accelerate the vehicle further. We are planning to reduce the volume

of the cylinder to 90 cc to reduce this excess power.

The flow of power from the combustion chamber to the wheel is as follows – Combustion chamber, crankshaft,

centrifugal clutch, CVT, chain drive, axle, wheel. Since the vehicle is expected to take the turns at moderately

low speeds, it was decided not to add a differential.

Centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with the

driving shaft nested inside the driven shaft. The input of the clutch is connected to theengine crankshaft while the output drives the CVT. As engine revolutions per minute increase and

reaches a certain speed, weighted arms in the clutch swing outward due to centrifugal force and force

the clutch to engage. The idle speed of the engine is normally around 1,800 RPM and the clutch starts

to engage around 2,000 rpm and will lock up around 2,600 rpm.

Due to the large distance involved between the CVT shaft and the axle, a chain drive with a velocity ratio of 14 :

1 was selected.



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0 2000 4000 6000 8000 10000

P o w e r R e q u i r e d

( W )

RPM

Without Reduction

Power Required

Power Delivered

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0 100 200 300 400 500 600 700

P o w e r ( W )

Wheel RPM

With Reduction

Power Delivered Power Required



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T o r q u e ( N - m )

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Without Reduction

Torque Required

Torque Delivered

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T o r q u e ( N - m )

RPM

With Reduction

Torque Required

Torque Delivered

sem engine report

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