It supports and assists the steering process, exactly like the hydraulic power steering system does, because of it's lower installation weight however, it requires distinctly less energy, thus reducing the fuel consumption. The assistance is not generated permanently by the engine oil pressure and provides an energy-flow only then, when it's needed. This brings a saving of up to 90% e.g., on the motorway where less steering action takes place. One speaks of fuel savings of up to 0,2 liters per 100 km. Apart from that, all the power steering components are found in the vicinity of the steering and not also in the engine (hydraulic pump). An important aspect for the manufacturer: The individual components can be more easily adapted to the respective vehicle-types.
This also opens more possibilities for the constructive design of the steering. In the past, one expected the steering wheel to return to the center position automatically. It still does that, only now, it's electrically supported. Thus e.g., the caster and the steering inclination can be chosen for lower effort on the steering wheel. While these measures lead to more sensitivity, the city-mode is intended to be a practical assistance.
The introduction of electrical power steering meant that one could now actively influence the steering. Today, this is already reality in the case of the variable steering ratio. At times, the steering can be seperated from the actual steering wheel. Then (e.g., should a dangerous situation arise), the electronics can take over the steering of the wheels. In the event of the introduction of the 42-V network, the power steering could become even more interesting. In this case, even smaller electric motors could be used. The original idea was, that the steering should be completely decoupled, and that it would serve only as a sensor for the control device and that one servo-motor for each wheel, would do the steering of the front wheels. Indeed, for this to happen, legal regulations would first have to be altered. Apart from that, the steering - as opposed to maybe the braking system - is the the most difficult system to convert. One speaks of a triple-redundancy. It is simply not sufficient to duplicate everything, because then the control device still does not know, what it should actually do, and it must do something, e.g., if the electrical system collapses while driving in a curve.
Always then, when a movement of the steering wheel is detected, an electric motor engages, either through a worm-drive or a second gear-wheel, with the steering column or with the rack and pinion. The rotational direction of the motor depends on which way the steering wheel is turned. The recentering of the steering can also be supported. A further advantage is the possible steering assistance when being towed. In this case, the control device also takes the remaining battery tension into consideration.
The system requires not only the position of the steering wheel, but also information regarding the force with which the wheel is turned. A part of the steering column is thus constructed, that it twists, in itself, when steering takes place. The twist-angle is a measure of the steering torque. It is registered by the system, e.g., the same as the driving speed is. 09/11
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