Power steering systems have become more and more widely used in the last few years, due to the increasing front axle loads of vehicles on the one hand and the trend towards vehicles with more agile steering properties
and hence direct transmission steering systems on the other. With the exception of some members of the ‘sub-compact’ class, power steering systems are optionally or automatically included as one of the standard features.
Manual steering systems are used as a basis for power steering systems, with the advantage that the mechanical connection between the steering wheel and the wheel and all the components continues to be maintained with or without the help of the auxiliary power.
The steering-wheel torque applied by the driver is detected by a measurement system located in the region of the input shaft of the steering gear or in the steering tube, and additional forces or moments are introduced into the system. This follows a characteristic curve (valve characteristic) or group of curves depending on the height of the steering-wheel torque, if another quantity, e.g. driving speed, is entered as a signal. The steering boost is thereby reduced, with the aim of achieving better road contact at higher speeds.
Hydraulic power steering systems are still the most widely used. The method of using oil under pressure to boost the servo is sophisticated and advantageous in terms of cost, space and weight. Sensitivity to movements caused by the road surface and hence the effect of torsional impacts and torsional vibrations passing into the steering wheel is also noticeably reduced, particularly with rack and pinion steering. This can be attributed to the hydraulic self-damping. It might also be the reason why it is possible to dispense with an additional steering shock absorber in most vehicles with hydraulical rack and pinion steering, whereas it is required for the same vehicles with manual steering