• Shock absorbers allow the use of soft springs, and at the same time it controls the rate of suspension movement in response to any bumps.
They also, with hysteresis in the tire itself, damp the motion of the unsprung weight up and down on the springiness of the tire. Since the tire is not as soft as the springs, to get effective wheel bounce, damping may require stuffer shocks than what would be ideal for the vehicle motion alone.
Pneumatic and hydraulic shock absorbers often take the form of a cylinder with a sliding piston inside. Here the cylinder must be filled with a viscous fluid, which is either hydraulic fluid or air. This fluid filled piston or cylinder combustion is then a dashpot (mechanical device or damper that resists motion via viscous friction).
Spring based shock absorbers often use coil springs or leaf springs, torsion bars can be used in torsional shocks as well. Ideal springs alone, are not shock absorbers as springs only store, they do not dissipate or absorb energy. Vehicles mostly use springs or torsion bars as well as hydraulic shock absorbers. In this combination the shock absorbers or the shocks (as we know them) is reversed specifically for the hydraulic piston that absorbs and dissipates vibration.
There are many different types of shock absorbers and some commonly used approaches to shock absorption:
• Hysteresis – the compression of rubber disks, bending of steel springs or the twisting of torsion bars.
• Dry friction – used in wheel brakes, but using disks that are made of leather, at the pivot of a lever, with friction that is forced by springs. It was used in earlier vehicles and is now considered obsolete. There was an advantage to this system, as the degree of damping could easily be adjusted by tightening or loosening the screw clamping the disks, and it could easily be rebuilt with hand tools. The disadvantage is that the damping force tends to not increase with the speed of the vertical motion.
• Fluid friction – this is the flow of fluid through a narrow opening, the hydraulics. This constitutes the vast majority of automotive shock absorbers. An advantage of this type is that by using special internal valuing the absorber can be made very soft to compression. This then allows a soft response to a bump. Then quite it is quite stiff extension, which is the vehicle response to energy stored in the springs.
Specialized shock absorbers for racing purposes can allow the front end of a dragster to rise with a little resistance under acceleration, then it strongly resists letting it settle, thereby maintaining a desirable
rearward weight distribution for enhanced traction. With some shock absorbers you can manually adjust them. Others can be adjusted by remote. But the ultimate control is provided by dynamic valve control via a computer in response to the sensors. This then gives a smooth ride and a firm suspension when it needed.
• Compression of a gas – for example pneumatic shock absorbers. These can act like springs as the air pressure builds to resist the force on it. Once the air pressure reaches the necessary maximum, air dashpots will then act.
• Magnetic effects – many hybrid automobiles now days have regenerative braking. This uses a reversed electric motor to dampen and eventually stop the motion of the vehicle.
• Inertial resistance to acceleration – some vehicles have an additional pair of rear shock absorbers that damp wheel bounce with no external moving parts. The energy is absorbed by hydraulic fluid friction, but the operation all depends on the inertia of an internal weight.
• Composite hydropneumatic devices – these combine in a single device spring that allows ride height adjustment or control.