Theoretical approaches There are several commonly used principles behind shock absorption: Hysteresis of structural material, for example the compression of rubber disks, stretching of rubber bands and cords, bending of steel springs, or twisting of torsion bars. Hysteresis is the tendency for otherwise elastic materials to rebound with less force than was required to deform them. Simple vehicles with no separate shock absorbers are damped, to some extent, by the hysteresis of their springs and frames. Dry friction as used in wheel brakes, by using disks (classically made of leather) at the pivot of a lever, with friction forced by springs. Used in early automobiles such as the Ford Model T, up through some British cars of the 1940s and on the French Citroën 2CV in the 1950s. Although now considered obsolete, an advantage of this system is its mechanical simplicity; the degree of damping can be easily adjusted by tightening or loosening the screw clamping the disks, and it can be easily rebuilt with simple hand tools. A disadvantage is that the damping force tends not to increase with the speed of the vertical motion. Solid state, tapered chain shock absorbers, using one or more tapered, axial alignment(s) of granular spheres, typically made of metals such as nitinol, in a casing. , Fluid friction, for example the flow of fluid through a narrow orifice (hydraulics), constitutes the vast majority of automotive shock absorbers. This design first appeared on Mors racing cars in 1902.Setright, L. J. K. "Dampers: Smoothing Out the Bumps", in Northey, Tom, ed. World of Automobiles (London: Orbis, 1974), Volume 5, p.490. and 1903-03-07 - Le Génie civil: "Amortisseur Mors". One advantage of this type is, by using special internal valving, the absorber may be made relatively soft to compression (allowing a soft response to a bump) and relatively stiff to extension, controlling "rebound", which is the vehicle response to energy stored in the springs; similarly, a series of valves controlled by springs can change the degree of stiffness according to the velocity of the impact or rebound. Specialized shock absorbers for racing purposes may allow the front end of a dragster to rise with minimal resistance under acceleration, then strongly resist letting it settle, thereby maintaining a desirable rearward weight distribution for enhanced traction. Compression of a gas, for example pneumatic shock absorbers, which can act like springs as the air pressure is building to resist the force on it. Enclosed gas is compressible, so equipment is less subject to shock damage. This concept was first applied in series production on Citroën cars in 1954. Today, many shock absorbers are pressurized with compressed nitrogen, to reduce the tendency for the oil to cavitate under heavy use. This causes foaming which temporarily reduces the damping ability of the unit. In very heavy duty units used for racing or off-road use, there may even be a secondary cylinder connected to the shock absorber to act as a reservoir for the oil and pressurized gas. In aircraft landing gear, air shock absorbers may be combined with hydraulic damping to reduce bounce. Such struts are called oleo struts (combining oil and air) . Inertial resistance to acceleration, the Citroën 2CV had shock absorbers that damp wheel bounce with no external moving parts. These consisted of a spring-mounted 3.5 kg (7.75 lb) iron weight inside a vertical cylinder and are similar to, yet much smaller than versions of the tuned mass dampers used on tall buildings. Composite hydropneumatic suspension combines many suspension elements in a single device: spring action, shock absorption, ride-height control, and self leveling suspension. This combines the advantages of gas compressibility and the ability of hydraulic machinery to apply force multiplication. Conventional shock absorbers can be combined with air suspension springs - an alternate way to achieve ride-height control, and self leveling suspension. In an electrorheological fluid damper, an electric field changes the viscosity of the oil. This principle allows semi-active damper applications in automotive and various industries. Magnetic field variation: a magnetorheological damper changes its fluid characteristics through an electromagnet. The effect of a shock absorber at high (sound) frequencies is usually limited by using a compressible gas as the working fluid or mounting it with rubber bushings.
Theoretical approaches There are several commonly used principles behind shock absorption: Hysteresis of structural material, for example the compression of rubber disks, stretching of rubber bands and cords, bending of steel springs, or twisting of torsion bars. Hysteresis is the tendency for otherwise elastic materials to rebound with less force than was required to deform them. Simple vehicles with no separate shock absorbers are damped, to some extent, by the hysteresis of their springs and frames. Dry friction as used in wheel brakes, by using disks (classically made of leather) at the pivot of a lever, with friction forced by springs. Used in early automobiles such as the Ford Model T, up through some British cars of the 1940s and on the French Citroën 2CV in the 1950s. Although now considered obsolete, an advantage of this system is its mechanical simplicity; the degree of damping can be easily adjusted by tightening or loosening the screw clamping the disks, and it can be easily rebuilt with simple hand tools. A disadvantage is that the damping force tends not to increase with the speed of the vertical motion. Solid state, tapered chain shock absorbers, using one or more tapered, axial alignment(s) of granular spheres, typically made of metals such as nitinol, in a casing. , Fluid friction, for example the flow of fluid through a narrow orifice (hydraulics), constitutes the vast majority of automotive shock absorbers. This design first appeared on Mors racing cars in 1902.Setright, L. J. K. "Dampers: Smoothing Out the Bumps", in Northey, Tom, ed. World of Automobiles (London: Orbis, 1974), Volume 5, p.490. and 1903-03-07 - Le Génie civil: "Amortisseur Mors". One advantage of this type is, by using special internal valving, the absorber may be made relatively soft to compression (allowing a soft response to a bump) and relatively stiff to extension, controlling "rebound", which is the vehicle response to energy stored in the springs; similarly, a series of valves controlled by springs can change the degree of stiffness according to the velocity of the impact or rebound. Specialized shock absorbers for racing purposes may allow the front end of a dragster to rise with minimal resistance under acceleration, then strongly resist letting it settle, thereby maintaining a desirable rearward weight distribution for enhanced traction. Compression of a gas, for example pneumatic shock absorbers, which can act like springs as the air pressure is building to resist the force on it. Enclosed gas is compressible, so equipment is less subject to shock damage. This concept was first applied in series production on Citroën cars in 1954. Today, many shock absorbers are pressurized with compressed nitrogen, to reduce the tendency for the oil to cavitate under heavy use. This causes foaming which temporarily reduces the damping ability of the unit. In very heavy duty units used for racing or off-road use, there may even be a secondary cylinder connected to the shock absorber to act as a reservoir for the oil and pressurized gas. In aircraft landing gear, air shock absorbers may be combined with hydraulic damping to reduce bounce. Such struts are called oleo struts (combining oil and air) . Inertial resistance to acceleration, the Citroën 2CV had shock absorbers that damp wheel bounce with no external moving parts. These consisted of a spring-mounted 3.5 kg (7.75 lb) iron weight inside a vertical cylinder and are similar to, yet much smaller than versions of the tuned mass dampers used on tall buildings. Composite hydropneumatic suspension combines many suspension elements in a single device: spring action, shock absorption, ride-height control, and self leveling suspension. This combines the advantages of gas compressibility and the ability of hydraulic machinery to apply force multiplication Conventional shock absorbers can be combined with air suspension springs - an alternate way to achieve ride-height control, and self leveling suspension. In an electrorheological fluid damper, an electric field changes the viscosity of the oil. This principle allows semi-active damper applications in automotive and various industries. Magnetic field variation: a magnetorheological damper changes its fluid characteristics through an electromagnet. The effect of a shock absorber at high (sound) frequencies is usually limited by using a compressible gas as the working fluid or mounting it with rubber bushings.