Hydraulic type power steering has been known for a long time in which a hydraulic pump is driven by a belt on the shaft of the vehicle engine.
However, that type of power steering suffers from numerous drawbacks.
Numerous failures are to be observed in practice that are due to belt wear.
In addition, such a device occupies considerable axial space on the engine shaft.
It also requires the hydraulic pump to be located in an environment in which it is liable to be subjected to high levels of thermal and vibrational stress.
Electric type power steering is also known in which an electric motor meshes with the steering column.
Nevertheless, such systems require complex electronics to control the electric motor.
Also, such systems are not of satisfactory reliability: the rotor of the electric motor can become jammed, thereby also jamming the steering column of the vehicle.
To mitigate those drawbacks, proposals have already been made for hydraulically assisted steering in which the pump is driven by an electric motor.
Nevertheless, assisted steering of the above type that has been known in the past makes use of an electric motor that is overdimensioned and some such steering systems require the electric motor to be powered continuously.
Such systems also suffer from a particularly high level of power consumption (500 kW to 1.5 kW).
This gives rise to a problem of dumping heat losses generated in the motor.
To solve that problem, proposals have already been made to control rotation of the electric motor as a function of the force imparted to the steering column. In this respect, reference can be made to patent application EP A 0 741 068.
Nevertheless, such a solution requires a torque pickup (such as a torsion bar) or a rotary speed pickup to be included on the shaft of the steering column.