Subject: Automobile Engineering

Topic: Suspension, Wheels & Tires

Difficulty: High

All the parts which perform the function of isolating the automobile from the road shocks are collectively called a suspension system.
Requirements of an automobile suspension system:
i) In order to provide comfortable ride to the passengers & avoid additional stresses in the vehicle frame.
ii) The vehicle should neither bounce nor roll nor sway passengers when cornering pitch, when accelerating, braking or sudden lifting or dropping of the front wheel with respect to rear wheels. Although some of road irregularities & inequalities are absorbed by large tyres .
iii) It is necessary to provide a suspension system for reducing the shocks to passengers for comfortable ride also reduce additional stresses in the automobile frame & body.
iv) Suspension system acts as a safeguard for the occupants against road shocks & provide comfort ride.
v) Suspension system keeps the body perfectly in level while travelling over the uneven road.

Independent suspension system :
Five types of independent Suspension are in use in front axle :
i) wishbone type or parallel link type
ii) Mac Pherson strut type
iii) vertical guide type
iv) Traiting link type
v) Swnging half-axle tyte

Wish bone type Suspension: Fig:1.1 shows a diagramatic sketch of wishbone type suspension with coil spring. The use of coil spring in the front suspension of cars is now almost universal.

It consists of upper & lower wishbone arms pivoted to the frame member. These arms resemble letter 'A' of the roman alphabet due to which these are also referred to as “ A arms”. The Spring is placed in between the lower wishbone & the underside of the cross member. The vehicle weight is transmitted from the body & the cross member to the coil spring through which it goes to the lower wishbone member. A shock absorber is placed inside the coil spring & is attached to the cross- member & to lower. wishbone members.

The wishbone arms are like the chicken wishbone or letter V in shape, beause of which the system is so called. Because of this V-shape, the wishbone not only position the wheels & transmit the vehicle load to spring, but these also resist acceleration, braking & cornering forces. The upper arms are shorter in length than the lower ones. This helps to keep the wheel track constant thereby avoiding the tyre scrub thus minimising tyre wear.

Objective of suspension: -
i) To acts as a safeguard for the occupants against road shocks & provide comfort ride.
ii) to preserve the stability of vehicle in rolling, pitching, while in motion
iii) To minimize the effects of stresses due to road shock on mechanism of a vehicle & provide cushioning effect.
iv) To provide the required height to body structure as well as Bear the torque & braking reaction.
v) To keep the body perfectly in level while travelling over the uneven road.