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Steering, 1

26th November 1983
Page 50
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Page 50, 26th November 1983 — Steering, 1
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Which of the following most accurately describes the problem?

THE STEERING mechanism of a motor vehicle must enable the driver to change direction with the minimum of effort and to maintain the straight-ahead direction with ease, even when bumps are encountered at high speed. When travelling on a straight road the vehicle must not deviate from side to side causing the driver to be constantly correcting its direction, but at the same time it must allow the driver to retain a "feel" of the road. In other words the vehicle must not wander but the driver must feel he has control of the direction in which he is travelling.

The Ackermann linkage, which positions the wheels as shown in Figure 1, is the system on

which most vehicles' suspensions are based. In this, T equals track and W wheelbase. Because the rear wheels are fitted to a solid axle the centre of rotation, C, must be on a line projected from the rear axle. Dealing with the front wheels it will be seen that the inner wheel has to turn at a larger angle than the outer wheel because it is turning on a smaller circle. The difference in the front-wheel angles depends on the ratio T/W.

The main details of the system are shown in Figure 2. Each wheel is mounted on a stub axle which swivels on a kingpin fitted to a beam axle. On light vehicles, with independent front-wheel suspension, the beam axle is dispensed with and the swivel arrangement takes some other form, but the steering geometry principle remains the same.

Reverting to the beam axl the two stub axles are coon' by two track arms and a trat rod. The track arms are positioned so that two imagir lines running through them projected rearwards, meet j ahead of the rear axle.

This means that when thf track rod is fitted behind thE axle it is shorter than the distance between the two kingpin centres. If the track fitted in front of the axle, till will be longer than the dista between the swivel centres Figure 3 shows how the Ackermann layout causes tl inner wheel to turn through larger angle and Figure 4 st the steering components.

More about steering in fu articles.

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