The rigid axle is a type of wheel suspension for multi-track vehicles . With it, the wheels of an axle are connected to one another via a rigid axle beam ( "axle bridge" ). The connection can be unsprung or spring-loaded. In unsprung vehicles, only one axle can be firmly connected to the vehicle body. The other axis is suspended at right angles to the direction of travel, e.g. B. with excavators, or the frame of the vehicle is designed torsionally soft. When suspended vehicles, the axle body is of leaf springs or arms - occasionally are used an central joint - out .
Rigid axles attached to wagons already existed in the middle of the 4th millennium BC. BC, the single-axle chariot with a drawbar from the 2nd millennium BC. The development of the steerable rigid axle as a turntable by the Celts and Romans falls at the turn of the times , as does the spring-mounted car body. A rigid axle was originally used for the stub axle steering , patented by Georg Lankensperger in 1816 , the newer version of which is the fist and fork axle in the commercial vehicle sector.
One differentiates between rigid axles:
- the guidance by means of leaf springs, links or a ball joint ( central joint axis ) and special transverse links ( Panhard rod , Watt linkage )
- of the drive: driven ( banjo axle ), not driven (front axle drive, trailer ),
- of the differential: Differential integrated (banjo axle), not integrated ( De-Dion axle ) - each only with driven axles
- the connection of steered wheels (usually on the front axle): fist axle, fork axle, hemispherical axle,
- the suspension: sprung, not sprung (not guided).
Rigid axles are available in the following designs:
- Until the First World War : The differential gear and the two drive shafts are attached to the vehicle body in front of the axle. The wheels are each driven by a chain. The axle hangs on longitudinal leaf springs.
- Around 1900 - De Dion axle : The differential is attached to the vehicle body and drives the wheels via two double cardan shafts. The rigid axle is curved past the differential.
- Differential gear and both drive shafts built into a hollow rigid axle ( banjo axle ).
- Drawbar, anchor or central joint axle: The hollow axle body is extended in a T-shape towards the front by a push tube, at the front end of which it is mounted on the vehicle body by means of a central joint ( ball joint ). The drive shaft leading to the differential is located in the thrust tube. It is a cardan shaft with a cardan joint that is enclosed by the central joint.
In modern, rear central articulated axles, the axle beam is designed in an omega or U-shape when viewed from above. This reduces the space required by the axle during compression on the same side and creates space for luggage, a spare wheel recess or a motor / gear unit.
- Fist or fork axles with steered rigid axles.
Advantages and disadvantages
The rigid axle as a wheel suspension is simple and robust. It can still be found today in commercial vehicles such as trucks or off-road vehicles . Almost all modern cars have independent wheel suspension on the front axle, but the rigid axle is still used as the rear axle in 22.5% of all vehicles under 3.5 t. In the NASCAR racing series, the regulations stipulate a rigid axle.
Advantages over independent suspension
- simple and robust,
- low manufacturing costs,
- flat design with non-driven axle,
- no change in camber with parallel compression,
- constant fall to the road when the superstructure is sloping,
- track stable,
- higher instantaneous center possible.
Disadvantages compared to independent suspension
- mutual influence of the wheels on one axle,
- greater unsprung mass on driven axles due to the masses of the axle body and differential gear (with integrated design),
- poor self-steering behavior on potholes when driving straight ahead,
- Space requirement between axle and sub-floor for the compression process,
- harder to tune.
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