What is Shock Absorber?
A shock absorber or damper is a mechanical or hydraulic device used to absorb and damp shock impulses. This is done by converting the kinetic energy of the shock into another form of energy (typically heat), which is then dissipated. Most shock absorbers are some sort of dashpot (a damper that resists motion by viscous friction).
Along with smoothening out bumps and vibrations, the key role of the shock absorber is to ensure that the vehicle’s tyres remain in contact with the road surface at all times, which ensures the safest control and braking response from your car.
What do shock absorbers do?
Shock absorbers essentially do two things. Shock absorbers not only control the movement of springs and suspension but also keep your tires in contact with the ground at all times. At rest or in motion, the bottom of your tires is the only part of your vehicle that comes into contact with the road.
Any time that a tyre’s contact with the ground is broken or reduced, your ability to drive, steer and brake is severely compromised.
How do shock absorbers work?
The shock absorbers dampen the movement of the springs by converting the spring’s kinetic energy into thermal (heat) energy. Shock absorbers are oil-filled cylinders. When your vehicle’s suspension moves, a piston moves up and down through the oil-filled cylinder.
Firstly, a little bit of science. Shock absorbers work by taking the kinetic energy (movement) of your suspension and converting it to thermal energy (heat) that is then dissipated into the atmosphere through the mechanism of heat exchange. But it’s nowhere near as complicated as it may sound.
As mentioned, shock absorbers are basically oil pumps. A piston is attached to the end of a piston rod and works against hydraulic fluid in the pressure tube. As the suspension travels up and down, the hydraulic fluid is forced through orifices (tiny holes) inside the piston.
Because the orifices only allow a small amount of fluid through the piston, the piston is slowed which in turn slows down spring and suspension movement.
Shock absorbers automatically adjust to road conditions because the faster the suspension moves, the more resistance they provide.
Parts of Shock absorber
- Shock Absorber Mounts: Shock absorber mounts are parts that secure shocks to the vehicle body and suspension. There is the upper and lower mount. Both of these can be of the same design, featuring an “eye into” in which a bushing and bolt are inserted.
- Shock Absorber Bush: These are located on the mountings. Usually made of rubber or urethane, bushings absorb vibrations and separate metal parts to prevent noise and wear. Bushings are among the shock absorber components that can be replaced.
- Shock Absorber Coil Spring: Some shock absorber types feature a coil spring as part of the shock absorber assembly. These are commonly known as coil-over shock absorbers or spring coil shock absorbers.
- Shock Absorber Piston and Piston rod: The shock absorber piston contains valves or openings. The working of the shock revolves around the movement of oil through these passageways.
- Shock Absorber Cylinder: This is the tube that forms the body of the shock absorber. It contains the compression oil and forms the tube inside which the shock absorber piston moves.
- Shock absorber bolts: The fasteners that hold the shock to the body of the vehicle on one end and suspension at the other end. These must be torqued to the right torque values. Under torquing can cause loose shocks that do not work as expected.
Types of Shock absorbers
Following are the different types of shock absorbers:
- Hydraulic type shock absorbers
- Double acting shock absorbers
- Single acting shock absorber
- Friction type shock absorber
- Lever type shock absorber
- Telescopic type shock absorber
1. Hydraulic Type Shock Absorber
Hydraulic type shock absorbers are now used on all passenger cars. They increase resistance to the spring action by forcing a fluid through check valves and small holes.
2. Double Acting Shock Absorber
Double-acting shock absorbers offer resistance both during compression and rebound of the springs.
3. Single Acting Shock Absorber
A single-acting shock absorber offers resistance only on the rebound.
4. Friction Type Shock Absorber
The friction-type shock absorbers have almost become obsolete due to their non-predictable damping characteristics.
5. Lever Type Shock Absorber
The lever-type shock absorber is of indirect-acting type. It is bolted to the chassis through a lever and link. As the axle moves up and down, a double piston arrangement forces the oil through a valve.
6. Telescopic Type Shock Absorber
Telescopic type shock absorber is of direct-acting type. It is mounted between the axle and the frame.
A simplified diagram of the telescopic shock absorber. Its upper eye is attached to the axle and the lower eye to the chassis frame. A two-way valve A is attached to a rod G. Another two-way valve B is connected to the lower end of cylinder C.
The fluid is in the space above and below valve A, and also in the annular space between cylinder C and tube D, which is connected to the space below valve B. The head J has a gland H. Any fluid scrapped off by the rod G is brought down into the annular space through the inclined passage.
7. Twin Tube Shock Absorber
A twin-tube shock absorber consists of an inner and outer cylinder. The inner cylinder contains oil and the piston rod is connected to the piston valve. Whereas the outer cylinder acts as a reservoir and has a low-pressure gas. The flow of oil from one chamber to another is controlled by a base valve.
As the wheel moves up and down, so does the piston rod. The piston valve and base valve confirm the compression and rebound of the absorber. They measure how fast the oil flows back and forth. Vibration and shock are similarly absorbed by low-pressure gas. This gas acts like a balloon and absorbs vibrations.
8. Mono-tube Shock Absorber
These are high-pressure gas shocks having a pressure tube. This pressure tube consists of two pistons, a dividing piston, and a working piston. The installed pistons and rods are similar in design to twin-tube shocks.
A mono-tube shock absorber is mounted upside down or right side up and will work either way. Considering its flexibility, mono-tube shocks with springs are an important component to support the weight of the vehicle.
A mono-tube shock absorber does not have a base valve. The mono-tube shock has a greater surface area and carrying capacity. These are well known because the high amount of oil helps to dissipate heat much faster and reduces fading.
9. Spool Valve
Spool valve dampers are characterized by the use of hollow cylindrical sleeves with machined-in oil passages as opposed to traditional conventional flexible discs or shims. Spool valving can be applied with monotube, twin-tube, and/or position-sensitive packaging, and is compatible with electronic control.
Primary among benefits cited in Multimatic’s 2010 patent filing is the elimination of performance ambiguity associated with flexible shims, resulting in mathematically predictable, repeatable, and robust pressure-flow characteristics.