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Suggest suitable suspension system for the following category of vehicles: (i) Passenger Car (ii) 50 Seater Luxury bus.
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(i) Passenger Car (Mac-pherson strut suspension)

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  • The Mac-pherson strut is a type of car suspension system which uses the axis of a telescopic damper as the upper steering pivot.
  • It is widely used in modern vehicles and named after Earle S. Mac-pherson, who developed the design.
  • Mac-pherson struts consist of a wishbone or a substantial compression link stabilized by a secondary link which provides a bottom mounting point for the hub or axle of the wheel. This lower arm system provides both lateral and longitudinal location of the wheel.
  • The upper part of the hub is rigidly fixed to the inner part of the strut, the outer part of which extends upwards directly to a mounting in the chassis of the vehicle.
  • The wishbone is hinged to the cross member and resists accelerating, braking and side forces.

Advantages:

  • Simple design
  • Low manufacturing cost
  • It is lighter than double wishbone type and hence unsprung weight is lower.
  • It gives maximum room in the engine compartment and hence generally used in FWD vehicles.

Disadvantages:

  • It requires substantial vertical space and a strong top mount.
  • Geometric analysis shows it cannot allow vertical movement of the wheel without some degree of either camber angle change, sideways movement, or both.
  • It is not generally considered to give as good handling as a double wishbone or multi-link suspension, because it allows the engineers less freedom to choose camber change and roll centre.
  • It tends to transmit noise and vibration from the road directly into the body shell, giving higher noise levels and a "harsh" feeling to the ride compared with double wishbones.

(ii) 50 Seater Luxury bus: (Air suspension)

  • The line diagram of air suspension system is shown in Figure. It consists of four air bags.
  • The elastic element consists of housing, diaphragm with suitable air inlet and piston group. The housing is linked with housing is linked with the frame (sprung mass). The housing contains the piston group which is linked with the unsprung mass (rear and the front axle).
  • The housing and piston group are connected by a metallic diaphragm for better sealing and to friction between the members of elastic elements.
  • Each air bag is filled with compressed air.
  • The components of air suspension system are air filter, compressor, air reservoir, relied valve, pressure regulator, solenoid valve, levelling valve and ‘T’ check valve.
  • Air compressor is mounted on vehicle frame supplies high pressure air into the reservoir. The compressor sucks the air from atmosphere through air filter.
  • The pressure in the reservoir is maintained at about $20 kg/cm^2.$
  • The compressed air in the air bags support the weight of vehicle whenever vehicle comes across the bump of the road surface, the air in the air bag compressed and absorbs the shocks.
  • Air admitted into the four air bags through two circuits. In one circuit a pressure reduced to $12 kg/cm^2$ by pressure regulator.

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  • This pressure is kept in air bag through levelling valve if the pressure in one of the bag is low, the levelling arm moves and air is admitted into low pressure air bag through inlet valve.
  • The outer circuit has air pressure of 20 kg/cm2. This circuit pressure is used for additional loading of vehicle.
  • This can be achieved by special regulator, which keeps the same distance between wheel and frame under various loads. This circuit maintain the vehicle level constant in loaded or unloaded condition.
  • For this situation, the air at 20 kg/cm2 pressure is admitted into the levelling valve through solenoid valve.
  • Also the air is quickly released by levelling valve whenever load is decreased from corresponding air bag. This lower the air bag and hence the vehicle to the proper level.
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