MacPherson strut

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MacPherson strut

The MacPherson strut is part of a wheel suspension on automobiles that is named after the American engineer Earle S. MacPherson and for which he received a patent in 1949. It is similar to aircraft landing gear designs . He developed his strut during the Second World War for the Chevrolet Cadet, a small car project by General Motors (GM). When the project stopped in 1947, he left GM and went to Ford . There his concept was realized.

In Europe, the MacPherson strut suspension was used on the front axle from 1950 and first in the British Ford Consul .

MacPherson strut suspension

MacPherson suspension
  • Body, frame or subframe
  • Mute; lower spring plate
  • Wheel carrier
  • simple wishbone (original patent)
  • Stabilizer arm (original patent)
  • In the modern design, the simple wishbone and the stabilizer arm have been replaced by a triangular wishbone .
  • Steering tie rod
  • The MacPherson-axis corresponds kinematically a double wishbone suspension, in which the upper wishbone by a piston and piston rod of the shock absorber was replaced formed turning and sliding joint. The shock absorber is part of the wheel guidance. In the original design, the U-shaped stabilizer arm was part of the lower wishbone. On the front axles, the steering movement is initiated via the tie rod; on rear axles, it determines the toe angle change during springs and is used to adjust the track. By eliminating the upper link, the MacPherson axle is particularly suitable for vehicles with a transversely installed motor-gearbox unit. The suspension strut is subject to bending stress and thus worsens the response of the suspension on small uneven floors, which is why the MacPherson axle is used less often in luxury vehicles.

    The wheel carrier is firmly connected to the damper cylinder. It is either welded on or screwed to it, then the camber can be adjustable. The wishbone is usually connected to the wheel carrier via a ball joint .

    In order to reduce the scrub radius , the (triangular) wishbone can be split up into two link rods that are individually linked to the wheel carrier. Because of the small distance, the two joints can be arranged slightly offset in height.

    For the suspension of the car, MacPherson arranged a coil spring around the shock absorber, which is tilted to compensate for the bending moment in the suspension strut due to the wheel load. Later there were also wheel suspensions with integrated shock absorbers, in which the spring is not located on the shock absorber (e.g. Mercedes-Benz W 201 ), then one speaks of shock absorber struts .

    The upper bearing on the fender is called the dome bearing and consists of a slightly swiveling rubber bearing, which also keeps vibrations away from the body, and a roller bearing through which the coil spring can turn with the wheel when the steering is turned.

    Similar constructions

    Spring-damper units are often imprecisely called suspension struts, but in contrast to MacPherson struts (with attached wheel carrier), they do not guide the wheel. They can be found on motorcycles, but also on older twist beam axles , for example .

    "Real" struts with steering knuckles can be found on various rear wheel suspensions:

    • In the Chapman axle , the suspension strut is combined with a wishbone (the drive shaft) and a wishbone, the pointed side of which runs diagonally forward and which at the same time guides the wheel around the vertical axis and, together with the wishbone, absorbs the longitudinal forces. This construction can be found in Lotus cars , but similarly in the Fiat 130 .
    • On the Camuffo rear axle , the suspension strut leads together with a longitudinal and two wishbones (one of which is adjustable to allow you to adjust the toe-in). This construction was designed by Sergio Camuffo and first installed in the Lancia Beta and later also in other vehicles from the Lancia (such as the Lancia Delta ), Fiat ( Fiat Croma ) and Alfa Romeo (for example in the Alfa Romeo 147 and 156 ). This concept was later adopted by other manufacturers.

    Also damper struts cause the wheel, but the spring is not sitting on the shock absorber. They were combined with leaf, torsion bar or coil springs that were connected to the wishbone and installed both at the front and at the rear. The simplest way is the combination of shock absorber strut and wheel-guiding transverse leaf spring, such as that used by DAF on the front 33 Damper struts with levers on torsion bar springs were used on the Porsche 911 until 1989 . At the rear, front-wheel drive vehicles from the Fiat group from 1969 ( 128 , Autobianchi A112 , 127 up to Fiat Elba and Seat Ibiza ) had damper struts with trapezoidal wishbones and transverse leaf springs.

    From 1925 the French manufacturer Cottin & Desgouttes used a suspension on a transverse leaf spring and a sliding joint in its "Sans Secousses". The shock absorbers were installed separately, so it was not yet a strut axle.

    Individual evidence

    1. patent GB658387 .
    2. ^ Olaf von Fersen: A century of automobile technology. Passenger cars . VDI Verlag, 1986, ISBN 3-18-400620-4 , p. 386 . : ( limited preview in Google Book search)
    3. Exploded view of an auxiliary frame with 2 handlebars