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2.Reduces wear on the tyre. 3.To keep the vehicle stable while in motion by providing good road holding during driving, cornering and braking. 4.Provides safe vehicle control and free of irritating vibrations. 7.2REQUIREMENTS 1.Vertical vibrations and pitching : The damper present in suspension system eliminates the vibrations caused due to striking of front wheel to a bump. However, rear wheel also experiences similar vibrations as it reaches the bump after some time and this depends on wheel base and vehicle speed. There are three possible relations of front and rear suspension frequencies. i)Front frequency higher than the rear - After the initial vibration i.e., after one or two vibrations the maximum amplitude occurs. ii)Front frequency equal to rear - The amplitude collapses throughout, though pitching Department of Mechanical EngineeringPage 177
AUTOMOTIVE ENGINEERING 10ME844 tendency still exists iii)Front frequency lesser than the rear - Practically there is no pitching tendency. So, It is-clear that in order to reduce pitching tendency of the vehicle, the (iii) condition is suitable. 2.Rolling: The centre of gravity of the vehicle will be at certain height above the ground level. A turning couple about the longitudinal axis of the vehicle will be induced during cornering because of the centrifugal force acting at C.G. and forces at tyre - road contact surface. This results in a motion called rolling. The manner in which the vehicle is sprung determines the axis about which the vehicle will roll. 3.Brake dip: When the brakes are applied, the vehicle nose has a tendency to be lowered or to dip. This in turn depends up on C.G position relative to the ground, wheel base, and other suspension characteristics 4.Unsprung weight: When the wheels hit a bump, they vibrate along with the unsprung parts which stores the vibration energy and transmit it to the sprung parts through the springs. When the weight of unsprung parts if greater, it increases energy stored due to vibrations and thus transmits greater shocks to the sprung parts. Therefore it is necessary to keep the unsprung weight as low as possible. 7.3 TYPES OF SUSPENSION PRINGS 1.Steel springs a)Leaf spring b) tapered leaf spring c) coil spring d) torsion bar 2.Rubber Spring a)compression spring b) compression - shear spring c) Steel reinforced spring d)progressive spring e) Face shear spring. 3.Air springs a)Bellow type b) piston type. 7.31Torsion bars It is a simple rod which is acting in torsion and takes stresses only. It nearly stores the same amount of energy per unit weight as that of coil spring. Torsion bar is often used with independent suspensions. Department of Mechanical EngineeringPage 178
AUTOMOTIVE ENGINEERING 10ME844 When compared with other systems, it is lighter and occupies less space. Torsion tubes may also be used instead of torsion bars. One end of torsion bar is fixed to the frame, while the other end is fixed to the end of the the wheel arm the supported in bearing. The