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 Types of vehicle shock absorbers:
- Twin-tube type
- Mono tube type
- Twin-tube gas charged.
- Position sensitive damping.
- Acceleration sensitive damping.
1. Twin-tube type
It also, known as a “two-tube” shock absorber, this device consists of two nested cylindrical tubes, an inner tube that is called the “working tube” or the “pressure tube”, and an outer tube called the “reserve tube”.
At the bottom of the device on the inside is a compression valve or base valve. When the piston is forced up or down by bumps in the road, hydraulic fluid moves between different chambers via small holes or “orifices” in the piston and via the valve, converting the “shock” energy into heat which must then be dissipated.
2. Mono tube type
These are high-pressure gas shocks with only one tube, the pressure tube. Inside the pressure tube, there are two pistons: a dividing piston and a working piston. The working piston and rod are very similar to the twin-tube shock design.
The mono tube type has an inline arrangement featuring an oil chamber and a gas chamber. The piston valve generates damping forces in both the extending and contracting strokes.
Due to these characteristics, damping forces have a linear relationship to piston movement. In addition, this type is easy to tune and offers good heat dissipation. They’re often used in sport suspensions.
3. Twin-tube gas charged
Variously known as a “gas cell two-tube” or similarly-named design, this variation represented a significant advancement over the basic twin-tube form. Its overall structure is very similar to the twin-tube, but a low-pressure charge of nitrogen gas is added to the reserve tube.
The result of this alteration is a dramatic reduction in “foaming” or “aeration”, the undesirable outcome of a twin-tube overheating and failing which presents as foaming hydraulic fluid dripping out of the assembly. Twin-tube gas charged shock absorbers represent the vast majority of original modern vehicle suspensions installations.
4. Position sensitive damping
Often abbreviated simply as “PSD”, this design is another evolution of the twin-tube shock. In a PSD shock absorber, which still consists of two nested tubes and still contains nitrogen gas, a set of grooves has been added to the pressure tube.
These grooves allow the piston to move relatively freely in the middle range of travel (i.e., the most common street or highway use, called by engineers the “comfort zone”) and to move with significantly less freedom in response to shifts to more irregular surfaces when upward and downward movement of the piston starts to occur with greater intensity.
5. Acceleration sensitive damping
The next phase in shock absorber evolution was the development of a shock absorber that could sense and respond to not just situational changes from “bumpy” to “smooth” but to individual bumps in the road in a near instantaneous reaction. This was achieved through a change in the design of the compression valve, and has been termed “acceleration sensitive damping” or “ASD”.
Not only does this result in a complete disappearance of the “comfort vs. control” tradeoff, it also reduced pitch during vehicle braking and roll during turns. However, ASD shocks are usually only available as aftermarket changes to a vehicle and are only available from a limited number of manufacturers.
6. Coil over
Coilover shock absorbers are usually a kind of twin-tube gas charged shock absorber inside the helical road spring. They are common on motorcycle and scooter rear suspensions, and widely used on front and rear suspensions in cars.