Direction (automobile)

The direction of an Automobile or a road vehicle in general, is the whole of the bodies which makes it possible to modify the orientation of its Trajectoire and thus to take Virage S.

On a vehicle with wheels, while operating the wheel, the driver varies the Crab angle (angle between the plan of wheel and the trajectory of the wheel) of the direct wheels (or of the direct wheel). The effort thus created between the road and the tread makes turn the vehicle.

It is also by varying the differential effort between the two sides of a vehicle that one makes turn a vehicle to caterpillars.

History

The history of the direction is initially that applied to the horse-drawn vehicles: the problem arose as soon as the vehicle had more Essieu. It seems that there were carriages with four wheels without direction. The Timon articulated then made scrape the front axle.

Rigid axle

To obtain a true system of direction, the choice of only one directional wheel was made rather early but with the detriment of stability. In fact the most widespread system of direction during several centuries was that where the steering axle of the vehicle rigid and is articulated around a vertical central pivot: the “mainstay” . The system was applied to the first cars like the Clement Panhard.

Another system rather not very widespread consisted in having a vehicle articulated in its medium, each part being supported by an axle.

Broken axle (coupled wheels)

The direction with Ankle working not being satisfactory for stability in turn, the idea to disunite the rockets of the wheels was done quickly day, even for the horse-drawn vehicles. Various more or less complex modes of coupling were used.

An original system was that used on the vehicle with vapor of Amédée Bollée - father: the two direct wheels were coupled by a chain with a toothed wheel (elliptic) interdependent of the wheel.

Geometrical formalization of the direction by the diagram of Janteau rather quickly results in using a bars direction which connects rods of direction rigidly. It is of this system that all the automobile directions are derived.

4 direct wheels (4RD)

(in English: 4 wheel-steering 4WS )
Pour to improve the capacities of evolution of the traditional vehicle with 4 wheels, one imagined a system rather quickly where the four wheels would be directors and driving. Certain military tractors of the Artillerie of the First World War were thus equipped.

The 4 direct wheels can be directed in opposite direction on the same curve (radius of gyration of the reduced vehicle) or in the same direction: it is said that the vehicle “works in Crabe”. Taking into account the capacities of operation thus obtained, this system is largely widespread on some farm tractors, vehicles of public Travaux and much of vehicles of handling.

On the vehicle of tourism, when Honda proposed such a system on its Prélude in 1979, the majority of the manufacturers were ready to consider that it was a major innovation. Among the advanced advantages, that of the improvement of the Handling at high speed seemed most promising: an identical steering of the two axles allowed a side offset with a speed of lace lower than an ordinary vehicle. Some like Mazda, Toyota and Mitsubishi proposed systems 4WS controlled by hydraulics in option, but the solution of Honda remained original because entirely mechanical although adapting at the speed of the vehicle. Success was not with go because the vehicle handling was regarded as “diverting” in spite of its qualities.

The system with electronics still makes part of the options suggested by certain manufacturers on top-of-the-range vehicles or 4x4. On the other hand, gone up on vehicles of sport, some pilot of rally regard it as extremely effective. The system is interdict in Formule 1.

On the recent vehicles, the favorable effects of such a system are returned, without 4RD, with lower amplitude, by the geometry and the flexibility of the rear wheel-axle unit. One thus obtains an orientation differentiated from the aft wheels in support in a turn. This system takes according to the manufacturers various names: “directional axle”, “rear axle will multibras”, “controlled induced steering”, etc

Technology

A traditional direction with two direct wheels comprises:

the stealing and centers it wheel (or column steering ),
the steering gear box charged to transform a rotation movement of the wheel into translatory movement,
the arm of order and coupling which can be a toothed rack,
the rods ensuring the connection between the suspended part and the not suspended part of the non-stop train,
the kingpin supports of the direct wheels which turn around an axis close to the vertical.

See too

Operation of the car

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