Bushing (isolator)
Encyclopedia
A bushing or rubber bushing is a type of vibration isolator
. It provides an interface between two parts, damping the energy transmitted through the bushing. A common application is in vehicle suspension
systems, where a bushing made of rubber
(or, more often, synthetic rubber
or polyurethane
) separates the faces of two metal objects while allowing a certain amount of movement. This movement allows the suspension parts to move freely, for example, when traveling over a large bump, while minimizing transmission of noise and small vibrations through to the chassis of the vehicle. A rubber bushing may also be described as a flexible mounting or antivibration mounting.
These bushings often take the form of an annular cylinder of flexible material inside a metallic casing or outer tube. They might also feature an internal crush tube which protects the bushing from being crushed by the fixings which hold it onto a threaded spigot. Many different types of bushing designs exist. An important difference compared with plain bearing
s is that the relative motion between the two connected parts is accommodated by strain in the rubber, rather than by shear or friction at the interface. Some rubber bushings, such as the D block for a sway bar
, do allow sliding at the interface between one part and the rubber.
and vibration
are transmitted. Another advantage is that they require little to no lubrication
.
Disadvantages include:
credits Walter Chrysler
as being a leader in encouraging the adoption of rubber vibration-isolating mounts. In his memoir (1956), he says that, on March 10, 1932, Chrysler called at Ford headquarters to show off a new Plymouth
model. "The most radical feature of his car was the novel suspension of its six-cylinder engine so as to cut down vibration. The engine was supported on three points and rested on rubber mounts. Noise and vibration were much less. There was still a lot of movement of the engine when idling, but under a load it settled down. Although it was a great success in the Plymouth, Henry Ford
did not like it. For no given reason, he just didn't like it, and that was that. I told Walter that I felt it was a step in the right direction, that it would smooth out all noises and would adapt itself to axles and springs and steering-gear mounts, which would stop the transfer of road noises into the body. Today rubber mounts are used on all cars. They are also found on electric-motor mounts, in refrigerators, radios, television sets—wherever mechanical noises are apparent, rubber is used to eliminate them. We can thank Walter Chrysler for a quieter way of life. Mr. Ford could have installed this new mount at once in the V‑8
, but he missed the value of it. Later Edsel
and I persuaded him. Rubber mounts are now found also in doors, hinges, windshields, fenders, spring hangers, shackles, and lamps—all with the idea of eliminating squeaks and rattles." Chrysler's novel engine-mounting method was marketed as "Floating Power
". Its basic idea soon became the conventional method throughout the automotive industry.
Vibration isolation
Vibration isolation is the process of isolating an object, such as a piece of equipment, from the source of vibrations.-Passive isolation:Passive vibration isolation systems consist essentially of a mass, spring and damper ....
. It provides an interface between two parts, damping the energy transmitted through the bushing. A common application is in vehicle 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...
systems, where a bushing made of rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
(or, more often, synthetic rubber
Synthetic rubber
Synthetic rubber is is any type of artificial elastomer, invariably a polymer. An elastomer is a material with the mechanical property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation...
or polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...
) separates the faces of two metal objects while allowing a certain amount of movement. This movement allows the suspension parts to move freely, for example, when traveling over a large bump, while minimizing transmission of noise and small vibrations through to the chassis of the vehicle. A rubber bushing may also be described as a flexible mounting or antivibration mounting.
These bushings often take the form of an annular cylinder of flexible material inside a metallic casing or outer tube. They might also feature an internal crush tube which protects the bushing from being crushed by the fixings which hold it onto a threaded spigot. Many different types of bushing designs exist. An important difference compared with plain bearing
Plain bearing
A plain bearing, also known as a plane bearing or a friction bearing is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore the journal slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole...
s is that the relative motion between the two connected parts is accommodated by strain in the rubber, rather than by shear or friction at the interface. Some rubber bushings, such as the D block for a sway bar
Sway bar
A sway bar or anti-roll bar or stabilizer bar is a part of an automobile suspension that helps reduce the roll of a vehicle that is induced by cornering or road irregularities. It connects opposite wheels together through short lever arms linked by a torsion spring...
, do allow sliding at the interface between one part and the rubber.
Advantages and disadvantages
The main advantage of a bushing, as compared to a solid connection, is less noiseNoise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
and vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
are transmitted. Another advantage is that they require little to no lubrication
Lubrication
Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load between the opposing surfaces. The interposed...
.
Disadvantages include:
- Rubber bushings can deteriorate quickly in the presence of oils (e.g., motor oilMotor oilMotor oil or engine oil is an oil used for lubrication of various internal combustion engines. The main function is to lubricate moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts.Motor oils are derived from...
, mineral oilMineral oilA mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....
) and extreme heat and cold. - The flexibility of rubber also introduces an element of play in the suspension system. This may result in camber, caster, or toe changes in the wheels of the vehicle during high-load conditions (cornering and braking), adversely affecting the vehicle's handlingCar handlingAutomobile handling and vehicle handling are descriptions of the way wheeled vehicles perform transverse to their direction of motion, particularly during cornering and swerving. It also includes their stability when moving at rest. Handling and braking are the major components of a vehicle's...
. For this reason, a popular aftermarket performance upgrade is the replacement of rubber suspension bushes with bushes made of more rigid materials, such as polyurethane. Polyurethane bushes are also available for many vehicles with the same characteristics as the manufacturers original bushes, but with greatly increased durability. This is useful on vehicles that have a reputation for wearing out standard rubber bushes, but for which harder bushings with increased harshness of ride are not wanted.
Applications
- In vehicles:
- Sway bar links and mountings
- Shock absorberShock absorberA 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:...
mountings - Double wishbone suspensionDouble wishbone suspensionIn automobiles, a double wishbone suspension is an independent suspension design using two wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control...
assemblies
- Norton CommandoNorton CommandoThe Norton Commando is a British motorcycle with an ohv pre-unit parallel twin engine, launched by the Norton Motorcycle company in 1967. Initially a nominal 750 cc displacement, actually , in 1973 it became an 850 cc, actually ....
motorcycle - In skateboards, bushings limit the motion of the trucks.
- In fastening, bushings are also used to transfer loads from a fastening to a much larger area in the underlying structure, the object being to reduce the strain on individual fibers within the underlying structure. (See also grommetGrommetthumb|right|250px|Some rubber grommets.A grommet is a ring inserted into a hole through thin material, such as fabric. Grommets are generally flared or collared on each side to keep them in place, and are often made of metal, plastic, or rubber. They may be used to prevent tearing or abrasion of...
.) - In crankshaftCrankshaftThe crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
balancing, certain high-speed inline internal combustion engines are prone to torsional vibration of their crankshafts; the straight six and straight eight engines being particularly prone to this problem due to their long crankshaft length. Although straight eight engines faded from the marketplace in the 1950s, many straight six engines have and still do feature crankshaft vibration damping utilizing rubber bushes. The 3,442 cc Jaguar XK 6-cylinder engineJaguar XK6 engineThe renowned Jaguar XK dual overhead camshaft inline 6-cylinder engine was introduced in 1949 and continued in manufacture until 1992. It was produced in five displacements for Jaguar passenger cars, with other sizes being made by Jaguar and privateers for racing...
of 1948 and most subsequent versions of the ubiquitous Jaguar XK engine used a proprietary Metalastik vibration damper to protect their crankshafts from potentially damaging torsional vibrations. To quote William Heynes, "The Metalastik damper consists of a steel plate to which is bonded, through a thick rubber disk, a malleable iron floating weight. Variations of the weight, rubber volume and mix, give these dampers a very wide field over which they can operate."
History
Charles E. SorensenCharles E. Sorensen
Charles Emil Sorensen was a Danish-American principal of the Ford Motor Company during its first four decades. Like most other managers at Ford during those decades, he did not have an official job title, but he served functionally as a patternmaker, foundry engineer, mechanical engineer,...
credits Walter Chrysler
Walter Chrysler
Walter Percy Chrysler was an American machinist, railroad mechanic and manager, automotive industry executive, Freemason, and founder of the Chrysler Corporation.- Railroad career :...
as being a leader in encouraging the adoption of rubber vibration-isolating mounts. In his memoir (1956), he says that, on March 10, 1932, Chrysler called at Ford headquarters to show off a new Plymouth
Plymouth (automobile)
Plymouth was a marque of automobile based in the United States, produced by the Chrysler Corporation and its successor DaimlerChrysler.-Origins:...
model. "The most radical feature of his car was the novel suspension of its six-cylinder engine so as to cut down vibration. The engine was supported on three points and rested on rubber mounts. Noise and vibration were much less. There was still a lot of movement of the engine when idling, but under a load it settled down. Although it was a great success in the Plymouth, Henry Ford
Henry Ford
Henry Ford was an American industrialist, the founder of the Ford Motor Company, and sponsor of the development of the assembly line technique of mass production. His introduction of the Model T automobile revolutionized transportation and American industry...
did not like it. For no given reason, he just didn't like it, and that was that. I told Walter that I felt it was a step in the right direction, that it would smooth out all noises and would adapt itself to axles and springs and steering-gear mounts, which would stop the transfer of road noises into the body. Today rubber mounts are used on all cars. They are also found on electric-motor mounts, in refrigerators, radios, television sets—wherever mechanical noises are apparent, rubber is used to eliminate them. We can thank Walter Chrysler for a quieter way of life. Mr. Ford could have installed this new mount at once in the V‑8
Ford Model B (1932)
The Model B was a Ford automobile with production starting with model year 1932 and ending with 1934. It was a much updated version of the Model A and was replaced by the 1935 Ford Model 48...
, but he missed the value of it. Later Edsel
Edsel Ford
Edsel Bryant Ford , son of Henry Ford, was born in Detroit, Michigan, USA. He was president of Ford Motor Company from 1919 until his death in 1943.-Life and career:...
and I persuaded him. Rubber mounts are now found also in doors, hinges, windshields, fenders, spring hangers, shackles, and lamps—all with the idea of eliminating squeaks and rattles." Chrysler's novel engine-mounting method was marketed as "Floating Power
Floating power
Floating Power was a technology developed in the 1920s by the United States automobile firm of Chrysler. It was a new means of attaching an engine to its chassis, with the intention of reducing vibration. Four-cylinder engines of the day started and rode rather roughly, transmitting the torque to...
". Its basic idea soon became the conventional method throughout the automotive industry.