Shock Absorber

What is a Shock Absorber?

A shock absorber (also industrial buffer, buffer stop) is a device that absorbs shock impulses by mechanical or hydraulic means. The shock is damped by converting the shock's kinetic energy into another form of energy, such as heat, and then dissipated. In terms of application, shock absorbers are usually an integral part of a vehicle that ensures passengers' safety and a smooth ride. 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.

Development

As with carriages and railway locomotives, automobiles in the early days adopted leaf springs as one of the core components. The key characteristic of spring entails a certain degree of damping provided by the friction among the blades. According to a study pertaining to vehicle suspension in the 1910s, helical springs were not a desirable choice to act as the mainspring because of the lack of the characteristic.

However, it was later found that the degree of damping provided by the leaf springs was very limited, and was subject to the varying conditions of the spring. Therefore, Druid forks that are suspended by coil springs were implemented for the front suspension of motorcycles in 1906. Based on a similar design, rotary friction dampers were later adopted. They were later translated to the adoption of friction disc shock absorbers in many modern automobiles today.
 

Why is it Important?

Any mechanical device that isn't stationary is susceptible to vibration. If not handled properly, it can lead to adverse consequences to the equipment and affect the performance. One way to mitigate the vibration is to adopt shock absorbers to distribute the pressure. This is one of the most common means to cope with shocks when manufacturing highly mobile mechanical carriers.

On top of this, moveable inspection equipment in the automotive industry also employs these compact yet essential units. In terms of mechanism, shock absorbers convert the kinetic energy from the suspension to thermal energy (heat) and then dissipated it into the atmosphere via a heat exchange mechanism. Let us read on to learn more about its construction.
 

Construction

Most shock absorbers have a standard two-tube design. They connect to the frame and chassis 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. It has a multi-lip design made of silicone rubber or 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.
 

Types

Shock absorbers come in different styles. Some of the common types we see these days include:
 

Standard Twin-Tube

it is called the twin-tube type because of its two-tube construction: the inner tube (pressure tube), and the outer tube (reserve tube). This is the standard configuration of most shock absorber types. A compression valve (or a base valve) is located at the bottom. 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 converted into heat and eventually dissipated.
 

Gas-charged

This type also called the gas cell two-tube, is constructed very similarly to the standard type, 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 fluid are compressed by the nitrogen gas, preventing the air and oil from mixing and foaming. The main benefit 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

This type (abbreviated as PSD) is considered the evolution of the twin-tube type. It 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 (street or highway use). 

It is designed to cope with the unstable up-and-down movement due to irregular terrains. The key advantage is its customizability. PSD allows for custom modification to fit specific vehicles. 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 is another evolution following PSD. It is characterized by the capability of prompt response to bumpy situations on the road. Design-wise, the compression is tweaked to reduce pitch during vehicle braking and roll during turns. Yet, ASD is by no means as prominent as PSD because it is only designed to accommodate limited applications. The advantage of ASD is the reduced ride harshness.
 

Coilover

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

Mono-tube

This is a single tube high-pressure gas shock, also known 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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