(SEM VII) THEORY EXAMINATION 2017-18 AUTOMOBILE ENGINEERING

SECTION A

(Short answers – explained clearly)

1. Why is a clutch necessary in the transmission system of an automobile?

A clutch is necessary in an automobile to connect and disconnect the engine power from the transmission system smoothly. When the vehicle is starting or changing gears, the clutch temporarily disconnects the engine from the gearbox, allowing smooth gear engagement without shock or damage. It also helps the vehicle stop without stalling the engine and enables smooth acceleration.

2. What is meant by fading of vehicle brakes?

Brake fading is the reduction in braking efficiency when brakes are applied continuously or repeatedly for a long time. It mainly occurs due to overheating of brake components, which reduces friction between brake linings and drum or disc. As a result, the stopping distance increases, making braking less effective and unsafe.

SECTION B

(Medium answers – conceptual explanation)

3. State and explain the principle of Ackermann steering mechanism.

The Ackermann steering mechanism is designed to ensure that all wheels of a vehicle roll without slipping while turning. According to this principle, during a turn, the inner front wheel must turn through a larger angle than the outer front wheel. This arrangement allows the wheels to follow different circular paths with a common center, reducing tire wear and improving steering efficiency.

4. Give a brief description of torsion bar and stabilizer bar.

A torsion bar is a type of suspension spring that works on the principle of twisting. One end of the bar is fixed to the chassis, while the other end is connected to the wheel. When the wheel moves up and down, the bar twists and provides suspension action.
A stabilizer bar, also known as an anti-roll bar, connects the left and right wheels of a vehicle. It reduces body roll during cornering by distributing load evenly, improving vehicle stability and passenger comfort.

SECTION C

(Long answers – detailed explanation)

5. What are synchronizers? Explain their utility in transmission.

Synchronizers are devices used in modern gearboxes to enable smooth gear shifting without grinding noise. They work by equalizing the speed of the gear and the shaft before engagement. When a gear is selected, the synchronizer brings both parts to the same speed using friction before meshing. This eliminates the need for double declutching and makes gear shifting easier, faster, and more comfortable for the driver.

6. Compare the constructional and operational aspects of disc and drum brakes. Which is preferred and why?

Drum brakes consist of brake shoes that press outward against a rotating drum, while disc brakes use brake pads that clamp onto a rotating disc. Disc brakes have better heat dissipation, consistent braking performance, and less brake fading compared to drum brakes. Drum brakes are cheaper and provide higher braking force at low speeds but suffer from overheating.
Disc brakes are generally preferred because they offer better braking efficiency, improved safety, and lower maintenance requirements.