User:Andy Dingley/My created pages/Strut suspension

Strut suspension or shock strut suspension is a form of vehicle suspension where the main suspension travel is taken up by a telescopic strut.

Earlier, and still common, suspension designs use either the bending of a leaf spring or pivoting through a hinged linkage, such as a wishbone suspension. Struts instead use a linear sliding motion, where a near-vertical strut telescopes under load. The strut combines the functions of both locating the locus of suspension travel and of controlling the suspension forces within a single device. Wishbone designs separate these tasks into location (the wishbone and pivots) and absorption (the spring and shock absorber), handled by separate components.

Telescopic shock absorbers are widely used elsewhere, especially with wishbone suspensions. The telescopic coilover design combines a coil spring and a telescopic damper in one unit. These are not necessarily strut suspensions: a strut suspension also requires that the strut remains in approximately the same position throughout its suspension travel, i.e. that it is not hinged at the inboard (body) end, and also that the wheel hub is rigidly fastened to the outboard end of the strut, such that it maintains the same angle to the strut axis. The simple coilover design usually does not meet this requirement as it is hinged at each end.

Aircraft


Strut suspensions began with aircraft landing gear. The primary requirement of landing gear is for it to absorb the large initial forces of landing. This requires long travel for both the wheels and the shock absorbing element. Early aircraft used spindly wishbones with bungees in tension. These had several drawbacks: they were fragile, they changed track and camber as the undercarriage flexed, leading to unpredictable handling, and they still had limited ability to absorb landing shocks.

As aircraft developed in the 1920s and 1930s and moved away from timber structures to aluminium, the strut suspension undercarriage became more practical. Single, stiffer element could carry the landing force and transmit it to a compact spring.

As aircraft became faster in the 1930s, there was a demand to reduce drag and achieve higher speeds. The large strut suspension performed well, but presented a lot of wind resistance. One solution, popular in the UK, was to place the suspension strut and its shock absorber entirely within the wheel.

Cars


The first car to use a strut suspension was the Stout Scarab of 1935. This suspension was patented by Frank M. Smith in 1935.

Some years earlier, Guido Fornaca of FIAT had patented a strut-like suspension. This was not a true strut suspension as, although the hub stub axle was rigidly fixed to the lower part of the strut, the upper end of the strut was hinged and pivoted through an arc.

MacPherson strut
The MacPherson strut suspension is by far the most common form of strut suspension in use, being used for the independent front suspension of a great many cars from the 1960s onwards.

Earle S. MacPherson developed his eponymous suspension for the Chevrolet Cadet of 1946. This was patented by General Motors in 1947, although the Cadet project was cancelled. The disgruntled MacPherson left for Ford, where a modified version of the strut was also patented, in 1949. Ford had the strut in production with the Ford Consul by 1951.

The original Cadet had MacPherson struts for each wheel, front and back. The much more common layout has been to use struts only for independent suspension at the front of the vehicle, with the rear using first a beam live axle for rear wheel drive, or a simple beam axle for front wheel drive. Independent suspension offers the most advantage at the front of the vehicle and the MacPherson strut easily allows the strut axis itself to form the steering kingpin swivel.

Some mass-production cars, notably the Fiat 128, have used the MacPherson strut for front and rear suspension.

The typical MacPherson strut has a telescopic shock absorber integral with the strut and a coil spring outside this to support the weight. Other forms of spring are possible though. The Porsche 911 uses torsion bars to support its front struts. The Fiat 128 uses the conventional coil springs at the front, but a transverse leaf spring at the rear.

Chapman strut
The characteristic feature of the Chapman strut is a long upright strut combining a coil spring and shock absorber, with a universal-jointed drive shaft itself forming the lower link of the suspension.