Self-levelling suspension
Encyclopedia
Self-levelling refers to an automobile
suspension
system that maintains a constant ride height
of the vehicle above the road, regardless of load.
Many vehicle systems on a conventional vehicle are negatively affected by changes in load, including aerodynamic properties, headlights, bumpers, shock absorption from the suspension
and the vehicles performance in a collision.
There is an inherent conflict in suspension design - if the springs are soft, the car will be comfortable but dramatically affected by load. If the springs are hard, the car will be uncomfortable, but less affected by load.
Numerous manufacturers realize this conflict and have pursued different avenues to achieve both comfort and load capacity simultaneously.
In 1954, Citroën
introduced the first self-levelling rear suspension, and then in 1955 pioneered self-levelling of all four wheels, using its hydropneumatic system. Since then, millions of Citroën cars have been equipped with self-levelling as an unobtrusive, but integral design feature. The Citroën's dashboard includes a five-position lever which allows the driver to select whether the car would travel with the body in a high or low position. When the engine is turned off, the suspension slowly loses pressure until the car rests on the rubber bump stops. When the engine is restarted it rises back to its pre-selected height.
In 1966, Rolls-Royce
licensed Citroën's hydropneumatic system to fit to the rear axle of the Silver Shadow
.
Land Rover
developed a different system for the Range Rover in the early 1970s. The Range Rover was intended to be as comfortable on the road as a normal saloon car yet as capable of heavy off-road use as a traditional Land Rover
. This highlighted the contradiction in suspension design as the Range Rover used all-round long-travel coil spring
s. If these were kept soft to maintain comfort they would compress too much under a heavy payload, restricting axle travel when off-road and compromising handling. Land Rover developed a self-energising hydraulic
strut as part of the rear suspension. Of similar construction to a hydraulic shock absorber
the strut used the motion of the suspension travelling over bumps to pump itself back up to a pre-set height. It was sufficiently powerful to regain up to 85% of normal ride height with a full load over the rear axle, and had the advantage of requiring no external power source or a dedicated hydraulic system in the vehicle. The same system was applied to the Land Rover in the 1980s when these vehicles adopted the Range Rover's coil spring suspension. In the 1990s Land Rover, in pursuit of the same blend of on- and off-road ability, developed an air suspension
system that was both self-levelling and height adjustable. Originally this was in conjunction with live axle
s but it is now used with fully independent suspension
using wishbones. The original coil-springs-with-hydraulic-strut system is still used on certain models of the current Land Rover Defender.
Mercedes-Benz
, Ford, GMC, BMW
, Scania AB
, Volvo
and Jaguar
have each pursued numerous avenues to address this issue, including air suspension
and rear axle mechanical devices.
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
system that maintains a constant ride height
Ride height
Ride height is the amount of space between the base of an automobile tire and the underside of the chassis; or, more properly, to the shortest distance between a flat, level surface, and any part of a vehicle other than those parts designed to contact the ground...
of the vehicle above the road, regardless of load.
Many vehicle systems on a conventional vehicle are negatively affected by changes in load, including aerodynamic properties, headlights, bumpers, shock absorption from the suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
and the vehicles performance in a collision.
There is an inherent conflict in suspension design - if the springs are soft, the car will be comfortable but dramatically affected by load. If the springs are hard, the car will be uncomfortable, but less affected by load.
Numerous manufacturers realize this conflict and have pursued different avenues to achieve both comfort and load capacity simultaneously.
In 1954, Citroën
Citroën
Citroën is a major French automobile manufacturer, part of the PSA Peugeot Citroën group.Founded in 1919 by French industrialist André-Gustave Citroën , Citroën was the first mass-production car company outside the USA and pioneered the modern concept of creating a sales and services network that...
introduced the first self-levelling rear suspension, and then in 1955 pioneered self-levelling of all four wheels, using its hydropneumatic system. Since then, millions of Citroën cars have been equipped with self-levelling as an unobtrusive, but integral design feature. The Citroën's dashboard includes a five-position lever which allows the driver to select whether the car would travel with the body in a high or low position. When the engine is turned off, the suspension slowly loses pressure until the car rests on the rubber bump stops. When the engine is restarted it rises back to its pre-selected height.
In 1966, Rolls-Royce
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....
licensed Citroën's hydropneumatic system to fit to the rear axle of the Silver Shadow
Rolls-Royce Silver Shadow
The Rolls-Royce Silver Shadow is a luxury car that was produced in Great Britain in various forms from 1965 to 1980. It was the first Rolls-Royce to use a monocoque chassis, a response to concerns that the company was falling behind in automotive innovation....
.
Land Rover
Land Rover
Land Rover is a British car manufacturer with its headquarters in Gaydon, Warwickshire, United Kingdom which specialises in four-wheel-drive vehicles. It is owned by the Indian company Tata Motors, forming part of their Jaguar Land Rover group...
developed a different system for the Range Rover in the early 1970s. The Range Rover was intended to be as comfortable on the road as a normal saloon car yet as capable of heavy off-road use as a traditional Land Rover
Land Rover Series
The Land Rover Series I, II, and III are off-road vehicles produced by the British manufacturer Land Rover that were inspired by the US-built Willys Jeep...
. This highlighted the contradiction in suspension design as the Range Rover used all-round long-travel coil spring
Coil spring
A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces...
s. If these were kept soft to maintain comfort they would compress too much under a heavy payload, restricting axle travel when off-road and compromising handling. Land Rover developed a self-energising hydraulic
Hydraulics
Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...
strut as part of the rear suspension. Of similar construction to a hydraulic shock absorber
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
the strut used the motion of the suspension travelling over bumps to pump itself back up to a pre-set height. It was sufficiently powerful to regain up to 85% of normal ride height with a full load over the rear axle, and had the advantage of requiring no external power source or a dedicated hydraulic system in the vehicle. The same system was applied to the Land Rover in the 1980s when these vehicles adopted the Range Rover's coil spring suspension. In the 1990s Land Rover, in pursuit of the same blend of on- and off-road ability, developed an air suspension
Air suspension
Air suspension is a type of vehicle suspension powered by an engine driven or electric air pump or compressor. This pump pressurizes the air, using compressed air as a spring. Air suspension replaces conventional steel springs. If the engine is left off for an extended period, the car will settle...
system that was both self-levelling and height adjustable. Originally this was in conjunction with live axle
Live axle
A live axle, sometimes called a solid axle, is a type of beam axle suspension system that uses the driveshafts that transmit power to the wheels to connect the wheels laterally so that they move together as a unit....
s but it is now used with fully independent suspension
Independent suspension
Independent suspension is a broad term for any automobile suspension system that allows each wheel on the same axle to move vertically independently of each other. This is contrasted with a beam axle, live axle or deDion axle system in which the wheels are linked – movement on one side affects...
using wishbones. The original coil-springs-with-hydraulic-strut system is still used on certain models of the current Land Rover Defender.
Mercedes-Benz
Mercedes-Benz
Mercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...
, Ford, GMC, BMW
BMW
Bayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
, Scania AB
Scania AB
Scania Aktiebolag , commonly referred to as Scania AB or just Scania, is a major Swedish automotive industry manufacturer of commercial vehicles - specifically heavy trucks and buses...
, Volvo
Volvo
AB Volvo is a Swedish builder of commercial vehicles, including trucks, buses and construction equipment. Volvo also supplies marine and industrial drive systems, aerospace components and financial services...
and Jaguar
Jaguar (car)
Jaguar Cars Ltd, known simply as Jaguar , is a British luxury car manufacturer, headquartered in Whitley, Coventry, England. It is part of the Jaguar Land Rover business, a subsidiary of the Indian company Tata Motors....
have each pursued numerous avenues to address this issue, including air suspension
Air suspension
Air suspension is a type of vehicle suspension powered by an engine driven or electric air pump or compressor. This pump pressurizes the air, using compressed air as a spring. Air suspension replaces conventional steel springs. If the engine is left off for an extended period, the car will settle...
and rear axle mechanical devices.