SHOCK ABSORBERS

SHOCK ABSORBERS

Springs alone are not satisfactory for suspension system. The ideal spring for automotive suspension would be one that would absorb road shock rapidly and then return to it normal position slowly. This is quite impossible in the case of springs, as they are by nature to oscillate. The spring mist be a compromise between flexibility and stiffness. An extremely flexible spring, or too soft, would allow too much movement, while a stiff or hard spring would give too rough a ride. However, satisfactory riding qualities are attained by using a fairly soft spring in combination with a shock absorber. For this reason spring cannot be used along, since they would give a bouncing ride and the shock absorbers smooth out his spring action. The have been many types of shock absorbers, operating on (a) friction (b) compressed air and (c) hydraulically. The most common in use in automotive at present is, and hydraulic shock. Absorber which operates on the principle that fluids are incompressible. For example, a telescopic tube, if filled partially with a fluid cannot be compressed completely. Further more, when the tube was pushed together, it would “jolt” when the air had been compressed and the top surface struck the fluid. The tube then can be compressed more smoothly, only by introducing a plate with restricted opening over the fluid. And as now the tube is compressed, the oil will slowly flow through the restricted opening, causing a more gradual slowing of the telescopic tube. The resistance to the movements of the fluid through the restricting orifices imposes a drag on spring movement, thus quickly dampening out spring oscillations.

Working of telescopic shock absorber

Construction: the telescopic or direct acting shock absorber is wound on both front and rear suspension systems. On the present day automobiles, it consists of a cylinder in which a piston is moved bup and down by a rod. The piston rod is attached to the chassis and the case of cylinder to the axle. Surrounding the cylinder is a reservoir and the upper portion of the unit is surrounded by the dust cover. The dust cover is larger in diameter than the reservoir and moves up and down around the reservoir.

Working: on a rebound stroke, the piston in the cylinder is drawn upward. The fluid above the piston passes through the holes in the lower part of the cylinder. there is not enough fluid above the piston to fill the space below the piston due to the volume occupied by the piston rod. The lower part of the cylinder is thus slightly accumized and additional fluid enters the cylinder from the reservoir. The operation of shock absorber on a rebound strike is shown in Fig.

References

1. Automobile Engineering (Vol. 1 & 2)            -           K.M.Guptha
2. Automotive Mechanics                                   -           Joseph Heitner
3. Automobile Engineering                                 -           Harbans Singh Reyd
4. Automotive Mechanics                                   -           William H. Course

On a compression stroke, the piston is forces downward in the cylinder. The fluid below the piston passes through to the upper part of the cylinder by opening piston intake compression relief. The piston rod displaces its own volume as it enters the cylinder, fluid thus displaced is forced out of the cylinder through check valve located beteeen the bottom of the cylinder and the reservoir. The fluid level is slightly compressed which does not play andy part in the operation of shock absorber.