Electric Power Steering
    (additional information)

Assignment

In this case, important areas, other than the steering gear, are summarised into one module. This concerns not only the electric motor for the power steering support (above figure at the top right). There is also an integrated sensor for the torque coming from the steering wheel. The electric steering column locking mechanism is also installed here. All in all, a very compact concentration and a substitute for the components which were previously distributed all around the engine compartment.

Function

The old one-piece steering column can still just about be recognised. On the right, the steering wheel is mounted, on the left it leads to the gear rack. In between, for safety purposes, there are two universal joints and also the sliding collar which prevents the whole functional element from penetrating into the passenger area in the event of an accident. To avoid vibrations, a Hardy disc is mounted just in front of the second universal joint.

Apart from the lever for the steering-wheel adjustment, (see above figure, below right) if one looks carefully, one can just recognise the control device behind the servo motor. It already indicates a little of the special abilities of the electric power steering, it can regulate according to the speed and, e.g., support the reset forces of the steering right up to the zero so steering angle when the vehicle is stationary. The motor itself is installed transverse to the steering column so that it can be activated through a worm-drive. Its auto-resistance is low, so that in the event of a breakdown of the engine or its control mechanism, steering is still possible, albeit with very much more effort.

Repair

The failure of the power steering while driving should not be taken lightly. Should the error repeat itself more often it can be a reason for a recall, even though the mechanical connection from the steering wheel to the tie-rods of course, remains intact. After dismantling the electric power steering you may be surprised at just how much force the electric motor can produce.

These motors e.g., those in the compact car class, can take up to 100 A and more when the steering is in its end position. Even if the voltage then drops, in larger cars it can amount to as much as 2 kW of input power. This, by the way, is the reason why some have not yet made the change over from hydraulic- to electrical systems. Thus, should you apply the full amount of energy to the motor when testing, don't be surprised if you can't stop the movement of the steering wheel.

The electric power steering is, by the way, a good example for the problems that can arise in the electrical system when peak performance is required. Still more difficult than this peak If value, is the demand for fast availability. Even though today's generators can provide a maximum of 3 kW, they don't do it in all RPM ranges. Nonetheles, the steering must also be supported, even at just above idling speed, with the same intensity and quickness.

we wish to tackle a possible mal function in a a power unit of this type, it may soon be advisable to use an oscillosscope. E.g., if in the information from the manufacturer, we find a low-voltage limit of, let's say 10,5 V, and measure this with a customary multimeter when the steering is in it's end position, we may not be able to register the actual voltage-drop at all.

E.g., one or both condensers (in the control device) may be faulty and can no longer absorb such voltage peaks. The result: The control device switches to emergency operation each time the steering reaches it's end position. Indeed, in this case, one could alternatively check the function of the condensers. If one removes the system fuse, the voltage must decrease slowly and not abruptly. 04/11