A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Most shock absorbers are a form of dashpot (a damper which resists motion via viscous friction).
Description Pneumatic and hydraulic shock absorbers are used in conjunction with cushions and springs. An automobile shock absorber contains spring-loaded check valves and orifices to control the flow of oil through an internal piston (see below). One design consideration, when designing or choosing a shock absorber, is where that energy will go. In most shock absorbers, energy is converted to heat inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid heats up, while in air cylinders, the hot air is usually exhausted to the atmosphere. In other types of shock absorbers, such as electromagnetic types, the dissipated energy can be stored and used later. In general terms, shock absorbers help cushion vehicles on uneven roads and keep wheels in contact with the ground.
Vehicle suspension
In a vehicle, shock absorbers reduce the effect of traveling over rough ground, leading to improved ride quality and vehicle handling. While shock absorbers serve the purpose of limiting excessive suspension movement, their intended main purpose is to damp spring oscillations. Shock absorbers use valving of oil and gasses to absorb excess energy from the springs. Spring rates are chosen by the manufacturer based on the weight of the vehicle, loaded and unloaded. Some people use shocks to modify spring rates but this is not the correct use. Along with hysteresis in the tire itself, they damp the energy stored in the motion of the unsprung weight up and down. Effective wheel bounce damping may require tuning shocks to an optimal resistance. Spring-based shock absorbers commonly use coil springs or leaf springs, though torsion bars are used in torsional shocks as well. Ideal springs alone, however, are not shock absorbers, as springs only store and do not dissipate or absorb energy. Vehicles typically employ both hydraulic shock absorbers and springs or torsion bars. In this combination, "shock absorber" refers specifically to the hydraulic piston that absorbs and dissipates vibration. Now, composite suspension systems are used mainly in 2 wheelers and also leaf springs are made up of composite material in 4 wheelers.
Construction
The most common type is a hydraulic shock absorber which uses a piston with small holes mounted to a shaft, a cylindrical body and an oil-filled chamber and is constructed as a typical dashpot. A more advanced style uses an additional compressed gas section separated from the oil with a free-moving solid piston inside the cylinder or a smaller, separate cylinder in a piggy-back orientation to the main chamber. The gas filled section contains dehydrated nitrogen gas at high pressure (typically 500psi) which acts to compress the oil to prevent frothing from the dissolved/entrained air. Construction requires a balance of features for various applications such as piston design and the oil bypass galleries, hydraulic oil viscosity, cylinder diameter and compression length, gas-charge pressure and chamber size, and various mounting struts or external structural connections. As technology progresses, other types of shock absorbers have emerged: adjustable oil/air, fixed magnetic resistance and tunable eddy-current types.
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