Shock absorber

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Miniature oil-filled Coilover shock components for scale cars. Mini Shocks.JPG
Miniature oil-filled Coilover shock components for scale cars.

A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Most shock absorbers are a form of dashpot (a damper which resists motion via viscous friction).



Pneumatic and hydraulic shock absorbers are used in conjunction with cushions and springs. An automobile shock absorber contains spring-loaded check valves and orifices to control the flow of oil through an internal piston (see below). [1]

One design consideration, when designing or choosing a shock absorber, is where that energy will go. In most shock absorbers, energy is converted to heat inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid heats up, while in air cylinders, the hot air is usually exhausted to the atmosphere. In other types of shock absorbers, such as electromagnetic types, the dissipated energy can be stored and used later. In general terms, shock absorbers help cushion vehicles on uneven roads.

Vehicle suspension

In a vehicle, shock absorbers reduce the effect of traveling over rough ground, leading to improved ride quality and vehicle handling. While shock absorbers serve the purpose of limiting excessive suspension movement, their intended main purpose is to damp spring oscillations. Shock absorbers use valving of oil and gasses to absorb excess energy from the springs. Spring rates are chosen by the manufacturer based on the weight of the vehicle, loaded and unloaded. Some people use shocks to modify spring rates but this is not the correct use. Along with hysteresis in the tire itself, they damp the energy stored in the motion of the unsprung weight up and down. Effective wheel bounce damping may require tuning shocks to an optimal resistance.

Spring-based shock absorbers commonly use coil springs or leaf springs, though torsion bars are used in torsional shocks as well. Ideal springs alone, however, are not shock absorbers, as springs only store and do not dissipate or absorb energy. Vehicles typically employ both hydraulic shock absorbers and springs or torsion bars. In this combination, "shock absorber" refers specifically to the hydraulic piston that absorbs and dissipates vibration. Now, composite suspension system are used mainly in 2 wheelers and also leaf spring are made up of composite material in 4 wheelers.


Shock absorbers are an important part of car suspension designed to increase comfort, stability and overall safety. The shock absorber, produced with precision and engineering skills, has many important features. The most common type is a hydraulic shock absorber, which usually includes a piston, a cylinder, and an oil-filled chamber. The piston is connected to the piston rod, which extends into the cylinder and divides the cylinder into two parts. One chamber is filled with hydraulic oil, while the other chamber contains compressed oil or air. When there is an accident or vibration in the vehicle, the piston moves into the cylinder, forcing the hydraulic fluid through small holes, creating resistance and dissipating energy in the form of heat. This dampens oscillations, reducing further bouncing or wobble of the car. Shock construction requires a balance of features such as piston design, fluid viscosity, and overall size of the unit to ensure performance. As technology developed, other types of shock absorbers emerged, including gas and electric shock absorbers, that provided improved control and flexibility. The design and manufacture of shock absorbers is constantly evolving due to the continuous improvement of vehicle dynamics and passenger comfort.

Early history

In common with carriages and railway locomotives, most early motor vehicles used leaf springs. One of the features of these springs was that the friction between the leaves offered a degree of damping, and in a 1912 review of vehicle suspension, the lack of this characteristic in helical springs was the reason it was "impossible" to use them as main springs. [2] However the amount of damping provided by leaf spring friction was limited and variable according to the conditions of the springs, and whether wet or dry. It also operated in both directions. Motorcycle front suspension adopted coil sprung Druid forks from about 1906, and similar designs later added rotary friction dampers, which damped both ways - but they were adjustable (e.g. 1924 Webb forks). These friction disk shock absorbers were also fitted to many cars.

One of the problems with motor cars was the large variation in sprung weight between lightly loaded and fully loaded, especially for the rear springs. When heavily loaded the springs could bottom out, and apart from fitting rubber 'bump stops', there were attempts to use heavy main springs with auxiliary springs to smooth the ride when lightly loaded, which were often called 'shock absorbers'. Realising that the spring and vehicle combination bounced with a characteristic frequency, these auxiliary springs were designed with a different period, but were not a solution to the problem that the spring rebound after striking a bump could throw you out of your seat. What was called for was damping that operated on the rebound.

Although C.L. Horock came up with a design in 1901 that had hydraulic damping, it worked in one direction only. It does not seem to have gone into production right away, whereas mechanical dampers such as the Gabriel Snubber started being fitted in the late 1900s (also the similar Stromberg Anti-Shox). These used a belt coiled inside a device such that it freely wound in under the action of a coiled spring, but met friction when drawn out. Gabriel Snubbers were fitted to an 11.9HP Arrol-Johnston car which broke the 6 hour Class B record at Brooklands in late 1912, and the Automotor journal noted that this snubber might have a great future for racing due to its light weight and easy fitment. [3]

One of the earliest hydraulic dampers to go into production was the Telesco Shock Absorber, exhibited at the 1912 Olympia Motor Show and marketed by Polyrhoe Carburettors Ltd. [3] This contained a spring inside the telescopic unit like the pure spring type 'shock absorbers' mentioned above, but also oil and an internal valve so that the oil damped in the rebound direction. The Telesco unit was fitted at the rear end of the leaf spring, in place of the rear spring to chassis mount, so that it formed part of the springing system, albeit a hydraulically damped part. [4] This layout was presumably selected as it was easy to apply to existing vehicles, but it meant the hydraulic damping was not applied to the action of the main leaf spring, but only to the action of the auxiliary spring in the unit itself.

The first production hydraulic dampers to act on the main leaf spring movement were probably those based on an original concept by Maurice Houdaille patented in 1908 and 1909. These used a lever arm which moved hydraulically damped vanes inside the unit. The main advantage over the friction disk dampers was that it would resist sudden movement but allow slow movement, whereas the rotary friction dampers tended to stick and then offer the same resistance regardless of speed of movement. There appears to have been little progress on commercialising the lever arm shock absorbers until after World War I, after which they came into widespread use, for example as standard equipment on the 1927 Ford Model A and manufactured by Houde Engineering Corporation of Buffalo, NY.

Types of vehicle shock absorbers

Diagram of the main components of a twin-tube and mono-tube shock absorber Shock Absorbers Detail.jpg
Diagram of the main components of a twin-tube and mono-tube shock absorber

Most vehicular shock absorbers are either twin-tube or mono-tube types with some variations on these themes.


Basic twin-tube

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.

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 suspension installations.

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 (i.e., on bumpy sections of roads— the stiffening gives the driver greater control of movement over the vehicle so its range on either side of the comfort zone is called the "control zone"). This advance allowed car designers to make a shock absorber tailored to specific makes and models of vehicles and to take into account a given vehicle's size and weight, its maneuverability, its horsepower, etc. in creating a correspondingly effective shock.

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.


Coilover shock absorbers are usually a kind of twin-tube gas charged shock absorber inside the helical road spring. They are common on motorcycles and scooter rear suspensions, and widely used on front and rear suspensions in cars.


Hydraulic shock absorber monotube in different operational situations:
1 ) Drive slow or adjustments open
2 ) Like "1", but extension immediately after the compression
3 ) Drive fast adjustments or closed, you can see the bubbles of depression, which can lead to the phenomenon of cavitation
4 ) Like "3", but the extension immediately after the compression
Note: The volume change caused by the stem is considered. Ammo monotubo.gif
Hydraulic shock absorber monotube in different operational situations:
1 ) Drive slow or adjustments open
2 ) Like "1", but extension immediately after the compression
3 ) Drive fast adjustments or closed, you can see the bubbles of depression, which can lead to the phenomenon of cavitation
4 ) Like "3", but the extension immediately after the compression
Note: The volume change caused by the stem is considered.
Absorber with remote-reservoir connected rigidly, compared to most shock absorbers. It uses a diaphragm instead of a membrane, and does not contain a control valve for expansion of the pneumatic chamber.
1) Sheath and gas tank
2) Stem
3) Snap rings
4) Plate bearing spring
5) Spring
6) End cap and preload adjustment
7) Cap gas, present in versions both with or without gas valve (inverted profile)
8) Mobile diaphragm
9) Pad switch (compression)
10) Wiper
11) Oil seal assembly, and shock seal
12) Negative buffer pad or limit switch (extension)
13) Piston with sliding blades and seal Ammortizzatore con serbatoio.jpg
Absorber with remote-reservoir connected rigidly, compared to most shock absorbers. It uses a diaphragm instead of a membrane, and does not contain a control valve for expansion of the pneumatic chamber.
1) Sheath and gas tank
2) Stem
3) Snap rings
4) Plate bearing spring
5) Spring
6) End cap and preload adjustment
7) Cap gas, present in versions both with or without gas valve (inverted profile)
8) Mobile diaphragm
9) Pad switch (compression)
10) Wiper
11) Oil seal assembly, and shock seal
12) Negative buffer pad or limit switch (extension)
13) Piston with sliding blades and seal

The principal design alternative to the twin-tube form has been the mono-tube shock absorber which was considered a revolutionary advancement when it appeared in the 1950s. As its name implies, the mono-tube shock, which is also a gas-pressurized shock and also comes in a coilover format, consists of only one tube, the pressure tube, though it has two pistons. These pistons are called the working piston and the dividing or floating piston, and they move in relative synchrony inside the pressure tube in response to changes in road smoothness. The two pistons also completely separate the shock's fluid and gas components. The mono-tube shock absorber is consistently a much longer overall design than the twin-tubes, making it difficult to mount in passenger cars designed for twin-tube shocks. However, unlike the twin-tubes, the mono-tube shock can be mounted either way— it does not have any directionality. [5] It also does not have a compression valve, whose role has been taken up by the dividing piston, and although it contains nitrogen gas, the gas in a mono-tube shock is under high pressure (260-360 p.s.i. or so) which can actually help it to support some of the vehicle's weight, something which no other shock absorber is designed to do. [6]

Mercedes became the first auto manufacturer to install mono-tube shocks as standard equipment on some of their cars starting in 1958. They were manufactured by Bilstein, patented the design and first appeared in 1954s. [7] Because the design was patented, no other manufacturer could use it until 1971 when the patent expired. [6]

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. [8] Spool valving can be applied with monotube, twin-tube, and/or position-sensitive packaging, and is compatible with electronic control. [9]

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. [10]

Theoretical approaches

There are several commonly used principles behind shock absorption:

Special features

Shock absorber and strut comparison

See also

Related Research Articles

<span class="mw-page-title-main">Piston</span> Machine component used to compress or contain expanding fluids in a cylinder

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder.

<span class="mw-page-title-main">Car suspension</span> Suspension system for a vehicle

Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both road holding/handling and ride quality, which are at odds with each other. The tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.

<span class="mw-page-title-main">Hydropneumatic suspension</span> Pneumatics

Hydropneumatic suspension is a type of motor vehicle suspension system, designed by Paul Magès, invented by Citroën, and fitted to Citroën cars, as well as being used under licence by other car manufacturers, notably Rolls-Royce, Bmw 5-Series e34 Touring, Maserati and Peugeot. It was also used on Berliet trucks and has been used on Mercedes-Benz cars, where it is known as Active Body Control. The Toyota Soarer UZZ32 "Limited" was fitted with a fully integrated four-wheel steering and a complex, computer-controlled hydraulic Toyota Active Control Suspension in 1991. Similar systems are also widely used on modern tanks and other large military vehicles. The suspension was referred to as fr:Suspension oléopneumatique in early literature, pointing to oil and air as its main components.

<span class="mw-page-title-main">Coilover</span> Automobile suspension device

A coilover is an automobile suspension device. The name coilover is an abbreviation of "coil-over shock absorber".

<span class="mw-page-title-main">Active Body Control</span>

Active Body Control, or ABC, is the Mercedes-Benz brand name used to describe electronically controlled hydropneumatic suspension.

A dashpot, also known as a damper, is a mechanical device that resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. It is commonly used in conjunction with a spring. The process and instrumentation diagram (P&ID) symbol for a dashpot is .

<span class="mw-page-title-main">Hydraulic brake</span> Arrangement of braking mechanism

A hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing glycol ethers or diethylene glycol, to transfer pressure from the controlling mechanism to the braking mechanism.

A motorcycle's suspension serves a dual purpose: contributing to the vehicle's handling and braking, and providing safety and comfort by keeping the vehicle's passengers comfortably isolated from road noise, bumps and vibrations.

An active suspension is a type of automotive suspension on a vehicle. It uses an onboard system to control the vertical movement of the vehicle's wheels relative to the chassis or vehicle body rather than the passive suspension provided by large springs where the movement is determined entirely by the road surface. Active suspensions are divided into two classes: real active suspensions, and adaptive or semi-active suspensions. While semi-adaptive suspensions only vary shock absorber firmness to match changing road or dynamic conditions, active suspensions use some type of actuator to raise and lower the chassis independently at each wheel.

The following outline is provided as an overview of and topical guide to automobiles:

<span class="mw-page-title-main">Gas spring</span> Type of spring

A gas spring, also known as a gas strut, is a type of spring that, unlike a typical mechanical spring that relies on elastic deformation, uses compressed gas contained within an enclosed cylinder sealed by a sliding piston to pneumatically store potential energy and withstand external force applied parallel to the direction of the piston shaft.

<span class="mw-page-title-main">Steering damper</span> Device that helps dampen your steering from side to side

Originally designed in 1966 by Leonard R Jordan Jr the steering damper, or steering stabiliser is a damping device designed to inhibit an undesirable, uncontrolled movement or oscillation of a vehicle steering mechanism, a phenomenon known in motorcycling as the death wobble. The stabilizer absorbs unwanted energy in the side to side motion allowing the forks and shocks to work properly. Many things can cause a motorcycle chassis to get upset such as slamming on brakes, rough road, and lastly improper setup. An upset chassis can be a great deal of danger for the rider often times resulting in a crash. A steering stabilizer slows those movements down resulting in the rider feeling more comfortable on the motorcycle.

A magnetorheological damper or magnetorheological shock absorber is a damper filled with magnetorheological fluid, which is controlled by a magnetic field, usually using an electromagnet. This allows the damping characteristics of the shock absorber to be continuously controlled by varying the power of the electromagnet. Fluid viscosity increases within the damper as electromagnet intensity increases. This type of shock absorber has several applications, most notably in semi-active vehicle suspensions which may adapt to road conditions, as they are monitored through sensors in the vehicle, and in prosthetic limbs.

<span class="mw-page-title-main">Vincent Rapide</span> Line of motorcycles produced by Vincent HRD

The Vincent Rapide is a line of standard motorcycles designed and built by the Vincent HRD motorcycle company at their works in Great North Road, Stevenage, Hertfordshire, England. The model debuted in 1936 and was built until 1939. Production resumed in 1946 and ended in 1955. Four major versions were built, labelled Series A through D.

A regenerative shock absorber is a type of shock absorber that converts parasitic intermittent linear motion and vibration into useful energy, such as electricity. Conventional shock absorbers simply dissipate this energy as heat.

A pipe support or pipe hanger is a designed element that transfer the load from a pipe to the supporting structures. The load includes the weight of the pipe proper, the content that the pipe carries, all the pipe fittings attached to pipe, and the pipe covering such as insulation. The four main functions of a pipe support are to anchor, guide, absorb shock, and support a specified load. Pipe supports used in high or low temperature applications may contain insulation materials. The overall design configuration of a pipe support assembly is dependent on the loading and operating conditions.

<span class="mw-page-title-main">Oleo strut</span>

An oleo strut is a pneumatic air–oil hydraulic shock absorber used on the landing gear of most large aircraft and many smaller ones. This design cushions the impacts of landing and damps out vertical oscillations.

<span class="mw-page-title-main">Friction disk shock absorber</span> Shock absorber

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<span class="mw-page-title-main">Lever arm shock absorber</span>

Lever arm shock absorbers were the first form of hydraulic shock absorber or damper used for car suspension. They appeared in the 1930s and were most commonly used in the 1950s and 1960s, but were replaced by telescopic shock absorbers in the 1970s. One of the earliest patents for a hydraulic lever arm shock absorber was awarded in 1925 to Georges de Ram, who was already an established maker of friction disk shock absorbers.

<span class="mw-page-title-main">Telescopic fork</span>

A telescopic fork is a form of motorcycle front suspension whose use is so common that it is virtually universal. The telescopic fork uses fork tubes and sliders which contain the springs and dampers.


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  3. 1 2 "Some accessories to see at Olympia", The Automotor Journal, Nov 2nd , 1912, p1284
  4. "What a Chauffeur Expects to see at Olympia", The Automotor Journal, Nov 9th 1912, p1313
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  6. 1 2 Carley, Larry (February 2008), "Monotube shocks-- don't absorb shocks, but..." (PDF), Brake and front end magazine, archived from the original (PDF) on 2014-01-02, retrieved 1 January 2014
  7. Shelton, p.24 and p.26 caption.
  8. "From F1 to Baja: Multimatic's Clever Spool-Valve Dampers Explained" . Retrieved 2017-07-19.
  9. "Damper and Awe: 6 Types of Automotive Dampers Explained - Feature" . Retrieved 2017-07-19.
  10. US 8800732 B2,Holt, Laurence J.; O'Flynn, Damian& Tomlin, Andrew,"Hydraulic damper spool valve",published 2014-08-12
  11. Setright, L. J. K. "Dampers: Smoothing Out the Bumps", in Northey, Tom, ed. World of Automobiles (London: Orbis, 1974), Volume 5, p.490.
  12. "Understanding Car Shock Absorbers | PartsHawk". Retrieved 2023-05-21.