Hydrolastic

Hydrolastic is a type of space-efficient automotive suspension system used in many cars produced by British Motor Corporation (BMC) and its successor companies. Invented by famous British rubber engineer Alex Moulton, and first used on the 1962 BMC project ADO16 under designer Alec Issigonis (of Mini fame), later to be launched as the Morris 1100. Description The system replaces the separate springs and dampers of a conventional suspension system with integrated, space efficient, fluid filled displacer units which are interconnected between the front and rear wheels on each side of the vehicle. Each displacer unit contains a rubber spring, and damping is achieved by the displaced fluid passing through rubber valves. The displaced fluid passes to the displacer of the paired wheel, thus providing a dynamic interaction between front and rear wheels. When a front wheel encounters a bump fluid is transferred to the corresponding rear displacer then lowers the rear wheel, hence lifting the rear, minimising pitch associated with the bump. Naturally the reverse occurs when it is a rear wheel that encounters a bump. This effect is particularly good on small cars as their shorter wheelbases are more affected by pitching. However, the key improvement over conventional suspension is that the front/rear interconnection allows the vehicle to be stiffer in roll than in pitch. Hence it is possible to design a compliant suspension - giving a comfortable ride - without suffering a penalty in terms of excessive roll when cornering. In roll, there is no transference of fluid from the displacers, and hence its internal pressure rises. The only "give" in the suspension occurs because of the inherent flexibility of the rubber springs. These are naturally stiff. In pitch, as described above, fluid is displaced front to rear, and hence the pressure in the system stays effectively the same, and thus the suspension is much more compliant. The design of the displacer units, and the way in which they are mounted means that as the suspension is compressed, the (roughly spherical) displacer deforms, and hence presents a larger area to the mounting plates. The pressure in the system is thus acting over a larger area, and hence applying additional force. This gives the suspension a sharply rising rate even in pitch, so that there is a strong tendency to return to equilibrium. Without this rising rate there would be no effective pitch resistance at all. Cars with Hydrolastic suspension do, however, have a marked tendency to squat under acceleration, and to dive under braking (and for the rear end to sag under...

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Electronic Air Suspension

Electronic Controlled Air Suspension is the name of the air suspension system installed on the Range Rover P38A, the 1995 second-generation Range Rover. It was developed in the early 1990s by the company now known as Dunlop Systems and Components Ltd in Coventry, UK. Overview The ECAS provides variable-height suspension for on- and off-road applications. The five suspension heights typically offered by ECAS are (from lowest to highest in terms of height) "Loading," "Highway," "Standard," "Off-Road," and "Off-Road Extended." Height is controlled automatically based on speed and undercarriage sensors, but a manual ride height switch allows control over the suspension by the driver. The "Loading" and "Off-Road" heights are available only at speeds typically less than 35 miles per hour (56 km/h). The "Highway" setting is not available manually; it is set when the vehicle moves at over typically 50 miles per hour (80 km/h) for over 30 seconds. Unlike a mechanical spring system (where deflection is proportional to load), height may be varied independently from the load by altering the pressure in the air springs. The air springs were designed to provide a smooth ride, with the additional ability to raise the body of the vehicle for off-road clearance and lower it for higher-speeds road driving. Mechanical springs, for which deflection is proportional to load, cannot do this; with ECAS height is largely independent of load. The developers of ECAS also designed LoadSafe, a related system to ascertain load and change in load on an LCV type vehicle fitted with air springs. Components The system comprises: a vulcanised rubber air spring at each wheel an air compressor, which is typically located in the trunk (boot) or under the bonnet a compressed air storage tank may be included for rapid "kneel", storing air at ~150psi (1000 kPa) a valve block which routes air from the storage tank to the four air springs via a series of solenoids, valves and many o-rings an ECAS computer which communicates with the car's main computer the BeCM and decides where to route air pressure a series of 6 mm air pipe which channels air throughout the system (mainly from the storage tank to the air springs via the valve block) an air drier canister containing desiccant height sensors ideally on all 4 vehicle corners based, typically, on resistive contact sensing to give an absolute height reference for each corner of the vehicle. Dunlop Systems and Components Ltd have continued to develop the products to the point where the Electronic Control Unit (ECU) is now able to fit under the vehicle...

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Hydropneumatic suspension

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 (Silver Shadow), Maserati (Quattroporte II) and Peugeot. It was also used on Berliet trucks and has more recently been used on Mercedes-Benz cars, where it is known as Active Body Control. Similar systems are also widely used on modern tanks and other large military vehicles. The suspension was referred to as oléopneumatique in early literature, pointing to oil and air as its main components. The purpose of this system is to provide a sensitive, dynamic and high-capacity suspension that offers superior ride quality on a variety of surfaces. A hydropneumatic system combines the advantages of two technological principles: Hydraulic systems use torque multiplication in an easy way, independent of the distance between the input and output, without the need for mechanical gears or levers Pneumatic systems are based on the fact that gas is compressible, so equipment is less subject to shock damage. Gas absorbs excessive force, whereas fluid in hydraulics directly transfers force The suspension system usually features both self-leveling and driver-variable ride height, to provide extra clearance in rough terrain. The principles illustrated by the successful use of hydropneumatic suspension are now used in a broad range of applications, such as aircraft oleo struts and gas filled automobile shock absorbers, first patented in the U.S. in 1934 by Cleveland Pneumatic Tool Co. This type of suspension for automobiles was inspired by the pneumatic suspension used for aircraft landing gear, which was also partly filled with oil for lubrication and to prevent gas leakage, as patented in 1933 by the same company. Other modifications followed, with design changes such as the 1960 "Double stage oleo-pneumatic shock absorber" patented by Peter Fullam John and Stephan Gyurik. High position Low position Citroën suspension sphere Challenger 2, main battle tank of the British army, uses hydropneumatic suspension for better crew comfort and increased firing accuracy Effects Hydropneumatic suspension has a number of natural advantages over steel springs, generally recognized in the auto industry. Suspension and springing technology is not generally well understood by consumers, leading to a public perception that hydropneumatics are merely "good for comfort". They also have advantages related to handling and control efficiency, solving a number of problems inherent in steel springs that suspension designers have previously struggled to eliminate. Although auto manufacturers understood the inherent advantages over steel springs, there were two problems. First, it was patented by the inventor, and second it had a perceived element of complexity, so automakers like Mercedes-Benz, British Leyland (Hydrolastic, Hydragas), and Lincoln sought to create simpler variants using a compressed air suspension. Citroën's application of the system had the disadvantage that only...

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Self-levelling suspension

Self-levelling refers to an automobile suspension system that maintains a constant ride height of the vehicle above the road, regardless of load. Purpose Nose up, tail down attitude of vehicle without self-levelling suspension Many vehicle systems on a conventional vehicle are negatively affected by the change in attitude coming from changes in load - specifically a heavy load in the rear seat or luggage compartment. This change in attitude affects aerodynamic properties, headlight aim, braking, bumpers, shock absorption from the suspension and the vehicle's performance in a collision. Most of the braking power is on the front wheels of a vehicle, which means you will have more effective braking when more weight is over the front wheels. When the rear end has a heavy load, the braking is not as effective. The weight is concentrated on the rear end of the vehicle, and the rear brakes need to do all of the work. When braking quickly in this situation, the front brakes will be easier to lock up because of the lack of weight transfer to the front of the vehicle. Self-levelling suspension lifts the rear end of the vehicle up to spread out the weight more evenly. This puts the weight back onto the front end of the vehicle, which lets the brakes do their job more effectively. 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. History In France in 1954, Citroën introduced the first self-levelling rear suspension on a production car, and then in 1955 pioneered self-levelling of all four wheels, using its hydropneumaticsystem. These cars maintain an exact height over the road when the engine is on - height control valves attached to the roll bars via linkages would open to add or drain fluid from the suspension, and when the desired height was reached the valve would automatically close due to its design. Later models would use electronic height sensors and motors so adjustment could be achieved with the engine off. This system allowed the suspension to achieve an unusually soft ride quality. Since then, millions of fairly inexpensive Citroën cars have been equipped with self-levelling as an unobtrusive, but integral design feature. The Citroën's dashboard (later console or fascia mounted controls) includes a position lever which allows the driver to select whether the car would sit with the body...

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Air suspension

Air suspension is a type of vehicle suspension powered by an electric or engine-driven air pump or compressor. This compressor pumps the air into a flexible bellows, usually made from textile-reinforced rubber. The air pressure inflates the bellows, and raises the chassis from the axle. Overview Pneumatic spring on a semitrailer Air suspension is used in place of conventional steel springs in passenger cars, and in heavy vehicle applications such as buses and trucks. It is broadly used on semi trailers and trains (primarily passenger trains). One application was on EMD's experimental Aerotrain. The purpose of air suspension is to provide a smooth, constant ride quality, but in some cases is used for sports suspension. Modern electronically controlled systems in automobiles and light trucks almost always feature self-leveling along with raising and lowering functions. Although traditionally called air bags or air bellows, the correct term is air spring (although these terms are also used to describe just the rubber bellows element with its end plates). History In 1901 an American, William W. Humphreys, patented an idea - a 'Pneumatic Spring for Vehicles'. The design consisted of a left and right air spring longitudinally channeled nearly the length of the vehicle. The channels were concaved to receive two long pneumatic cushions. Each one was closed at one end and provided with an air valve at the other end. From 1920, Frenchman George Messier provided aftermarket pneumatic suspension systems. His own 1922-1930 Messier automobiles featured a suspension "to hold the car aloft on four gas bubbles." During World War II, the U.S. developed the air suspension for heavy aircraft in order to save weight with compact construction. Air systems were also used in heavy trucks and aircraft to attain self-levelling suspension. With adjustable air pressure, the axle height was independent of vehicle load. In 1946, American William Bushnell Stout built a non-production prototype Stout Scarab that featured numerous innovations, including a four-wheel independent air suspension system. In 1954, Frenchman Paul Magès developed a functioning air/oil hydropneumatic suspension, incorporating the advantages of earlier air suspension concepts. Citroën replaced the conventional steel springs on the rear axle of their top-of-range model, the Traction Avant 15 Hydraulique. In 1955, the Citroën DS incorporated four wheel hydropneumatic suspension. This combined a very soft, comfortable suspension, with controlled movements, for sharp handling, together with a self-levelling suspension. In the U.S., General Motors built on its World War II experience with air suspension for trucks and airplanes. It introduced air suspension as standard equipment on the new 1957 Cadillac Eldorado Brougham. An "Air Dome" assembly at each wheel included sensors to compensate for uneven road surfaces and to automatically maintain the car's height.For 1958 and 1959, the system continued on the Eldorado Brougham, and was offered as an extra cost...

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Suspension lift

A suspension lift is a modification to a vehicle to raise the ride height. It is usually done for the practical purpose of improving the off road performance of SUVs or trucks and other off-road vehicles, or for cosmetic purposes. Suspension lifts can enable steeper approach, departure, and breakover angles, higher ground clearance, and helps accommodate larger wheels and tires. Due to the raised center of gravity, maximum safe operating angles can be reduced and roadholding is often significantly impaired. Truck with a suspension lift A lift kit is an aftermarket product package with the parts needed to lift a specific model of vehicle, typically with instructions and customer support. Some kits may have only critical or difficult to obtain parts, needing generic or off the shelf hardware and parts to complete the lift. Some lifts need only a few parts, like lift blocks, the spacers placed between the axles and leaf springs, and coil spring/strut spacers and extended shocks, and special driveshafts, axles, and more. More extensive lifts require many new suspension, steering, and drivetrain parts, such as replacement control arms, trailing arms, custom four-link systems, and drive shafts. These changes may be necessary because raising the vehicle's ride height can impact drive shaft length, steering geometry, and brake lines. Legality is often an issue when installing suspension lifts, as many jurisdictions have varying laws on vehicle ride height and placement of lights and bumpers. Leaf spring lift Jeep Cherokee with 2 inch Suspension lift on 31 inch BFG A/Ts, using add-a-leaf and coil spring spacers Many trucks are supported by leaf spring suspensions. Leaf springs offer exceptional articulation, a large payload and can take a substantial amount of abuse. With the correct methods they can be modified to help a vehicle carry more weight, have better articulation or to fit large oversized tires. Some vehicles may be equipped with front and rear leaf springs or just rear leaf springs with independent front suspension. Some methods of lifting are good for the rear, but not for the front, such as lifting blocks. Lifting the rear with blocks is a common way to achieve the desired height. This is done by installing a block, of the desired height of lift, in between the leaf spring and leaf spring perch and installing longer U-bolts. It is a bad method for the front primarily because of safety issues while braking. When braking, the front wheels create the majority of the braking force. The block moves this lateral force, caused by braking, higher above the axle than it did in the stock...

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Leaf spring

A leaf spring is a simple form of spring commonly used for the suspension in wheeled vehicles. Originally called a laminated or carriage spring, and sometimes referred to as a semi-elliptical spring or cart spring, it is one of the oldest forms of springing, appearing on carriages in England after 1750 and from there migrating to France and Germany.   A traditional semi-elliptical Hotchkiss leaf spring arrangement. On the left, the spring is connected to the frame through a shackle. Leaf springs front independent suspension, front-wheel-drive Alvis1928 Independent front suspension by transverse leaf spring Humber 1935 Independent front suspension by semi-elliptical springs Mercedes Benz 230 W153 1938 Leaf spring on a German locomotive built by Orenstein-Koppel and Lübecker Maschinenbau A leaf spring takes the form of a slender arc-shaped length of spring steel of rectangular cross-section. In the most common configuration, the center of the arc provides location for the axle, while loops formed at either end provide for attaching to the vehicle chassis. For very heavy vehicles, a leaf spring can be made from several leaves stacked on top of each other in several layers, often with progressively shorter leaves. Leaf springs can serve locating and to some extent damping as well as springing functions. While the interleaf friction provides a damping action, it is not well controlled and results in stiction in the motion of the suspension. For this reason, some manufacturers have used mono-leaf springs. A leaf spring can either be attached directly to the frame at both ends or attached directly at one end, usually the front, with the other end attached through a shackle, a short swinging arm. The shackle takes up the tendency of the leaf spring to elongate when compressed and thus makes for softer springiness. Some springs terminated in a concave end, called a spoon end (seldom used now), to carry a swiveling member. The leaf spring has seen a modern development in cars. The new Volvo XC90 (from 2016 year model and forward) has a transverse leaf spring in high tech composite materials, a solution that is similar to the latest Chevrolet Corvette. This means a straight leaf spring, that is tightly secured to the chassis, and the ends of the spring bolted to the wheel suspension, to allow the spring to work independently on each wheel. This means the suspension is smaller, flatter and lighter than a traditional setup. History There were a variety of leaf springs, usually employing the word "elliptical". "Elliptical" or "full elliptical" leaf springs referred to two circular arcs linked at their tips. This was joined to the frame at the top center of the upper arc,...

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