Shock Absorber

What Is a Shock Absorber?

A shock absorber, also known as an industrial buffer or buffer stop, is a device used to absorb shock impulses; it can either be mechanical or hydraulic. The shock is damped by converting the shock’s kinetic energy into another form of energy, such as heat, and is then dissipated. In particular aspects of a car, shock absorbers are an integral part of the vehicle that ensures drivers’ safety. 
Despite being a relatively smaller component, it plays a very crucial role in the automotive industry and is typically hidden beneath the vehicle’s wheel arches. Unlike tires, it is not an easy task to go through the maintenance procedure regularly for the shock absorber. 

Designs and Principles

Shock absorbers are typically a two-tube design, which is connected to the frame of the vehicle. The piston is located at the bottom and the upper mount is called the piston rod. The piston rod passes through a seal and a bushing at the upper end of the pressure tube. The bushing aligns the pressure tube with the piston rod, enabling the rod to move freely inside. 

The purpose of the seal is to keep hydraulic oil inside and is typically a multi-lip design made of silicone rubber and other materials to keep contamination out. There is also a base valve (or compression valve) located at the bottom of the configuration, which controls the action of fluids in the compression cycles. The lower mounting of the shock is formed by the outside of the reserve tube.

In terms of mechanism, shock absorbers convert the kinetic energy from the movement of the suspension to thermal energy (typically heat), and is then dissipated into the atmosphere via the mechanism of heat exchange. Simply put, shock absorbers act like oil pumps, and the principles are actually not as complicated you think.

Types of Shock Absorbers

Shock absorbers come in different styles, the most common of which are outlined as follows:

Standard Twin-Tube Shock Absorbers: It is also known as the “two tube” shock absorber because it is made up of two cylindrical tubes – one is the inner tube referred to as the “pressure tube”, and the other is the outer tube called the “reserve tube”. A compression valve (or a base valve) is located at the bottom of the design. When in action, the piston moves up and down, so that the hydraulic fluid can move between different chambers through the small holes in the piston via the valve, and the shock energy is then converted into heat that is eventually dissipated. 

Gas-charged Twin-Tube Shock Absorbers: This type of shock absorber is also known as the “gas cell two tube”, which is constructed very similarly to the standard twin-tube, except that a low pressure charge of nitrogen gas is supplemented to the reserve tube. The primary function of a gas-charged twin tube is to keep the aeration of hydraulic fluid to the minimum. 

The air bubbles in the hydraulic fluid is compressed by the pressure of the nitrogen gas, preventing the air and oil from mixing and producing foam. And the main benefit of this type of absorber is the reduced aeration which provides greater control over a wide array of road conditions as opposed to the non-gas absorbers. 

Position Sensitive Damping(PSD) Shock Absorbers: This type of device is often abbreviated as the “PSD”, and is considered to be the evolution of the twin-tube shock absorber. This device is composed of two nested tubes containing nitrogen gas as well, with a set of grooves added to the working tube. These grooves provide the flexibility for the piston to move freely in “comfort zone” travel (i.e., street or highway use). 

It is also designed to cope with unstable upward and downward movement due to irregular terrains. That said, the key advantage of such innovative advancement allows PSD to be tailored to the specific makes and models of cars. In other words, you can have every application individually tuned based on parameters such as length, depth, etc. to ensure satisfactory vehicle performance and ride comfort. 

Acceleration Sensitive Damping (ASD) Shock Absorbers: ASD is another evolution following PSD. It is characterized by the capability of prompt response to “bumpy” situations in the road. Design wise, the compression is tweaked in a way to reduce pitch during vehicle braking and roll during turns. 

However, ASD is by no means as prominent as PSD because it is only designed to accommodate limited applications. Also, not every manufacturer makes this type of shock absorber. 

Coilover: You will have coilover in many types of vehicles, from standard vehicles to racing cars even. Coilover shock absorbers are often a twin-tube gas-charged design which are common in the rear suspensions of motorcycles and scooters, as well as the front and rear suspensions of automobiles.  

Mono-tube Design: This is a single tube high-pressure gas shock, also referred to as the pressure tube. You’d find two pistons inside this pressure tube, namely a dividing piston and a working piston. The working piston closely resembles the design of the twin-tube shock. A typical feature of the mono-tube shock absorber is its mounting flexibility; you can mount one upside down or right side up. 

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