Most conventional suspension systems use passive springs to absorb impacts and shock absorbers to control spring motions. The majority of land vehicles are suspended by steel springs, of these types:
A shock absorber smooths out a sudden shock impulse and dissipates kinetic energy. Shock absorbers are an important part of a vehicle’s suspension.
In a vehicle, it will reduce the effect of traveling over any rough ground. If there were no shock absorbers, the vehicle would just have a very bouncy ride, as energy transfers through the springs to the vehicle. This could possibly exceed the allowed range of suspension movement.
- To control excessive suspension movement without shock absorption, it will require stiffer springs. This then would give a firmer ride.
- 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 contain 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 shocks primarily absorb and dissipate vibration.
Common Approaches To Shock Absorption
- Hysteresis — the compression of rubber disks, bending of steel springs or the twisting of torsion bars.
- Dry friction — brakes using leather disks that cause friction at the pivot of a lever. It was common in earlier vehicles but is now 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. This then allows a soft response to a bump. This is quite stiff extension, which is the vehicle response to energy stored in the springs.
- Compression of 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.
“Coilover” is short for “coil spring over shock”. It consists of a shock absorber with a coil spring encircling it. The shock absorber and spring are one unit that replaces the shock absorber as a unit. Some coilovers allow adjustment of ride height and pre-load, using a simple threaded spring perch similar to a nut. More advanced adjustable coilover systems use a threaded shock body, along with an adjustable lower mount for ride height adjustment, while an adjustment knob is used to adjust damping.
The coilover style of spring is a component of the MacPherson strut suspension system, which uses a design of anti-roll bar as a longitudinal constraint.
Coilovers are different from struts or independently mounted shock absorbers.
Benefits Of Coilover Shock Absorbers
- Coilovers provide tight packaging for shocks and springs
- Assembly line installation is easier with distinct packages
- Easy replacement with aftermarket coilovers
- Aftermarket coilovers can offer many adjustments including ride height
Disadvantages Of Coilover Shock Absorbers
- ncreases shock wear due to spring side load
- Increased shock bushing wear
- More expensive to manufacture than separate shock and spring