Motorized power steering apparatus

Claim 2

A motorized power steering apparatus for a vehicle comprising: torque sensing means (3) for generating an output signal dependent on a steering torque exerted by a driver of the vehicle; a motor (7) for generating an auxiliary steering force; and a motor control means (12) for controlling the output torque of the motor in accordance with the output voltage of the torque sensing means; chatacterised by current limiting means (60) for limiting the motor current to a current limit which decreases as the rotational speed of the engine increases and/or as the vehicle speed increases

Claim 3

A power steering apparatus as claimed in Claim 1, wherein the current limiting means comprises: an engine speed sensor (16) for generating an engine speed signal indicative of the rotational speed of the engine; reference voltage generating means responsive to the engine speed signal for generating a reference voltage indicative of a current limit corresponding to the engine speed detected by the engine speed sensor; current sensing means for generating an output voltage proportional to the motor current; detecting means for detecting that the motor current exceeds the current limit by comparing the reference voltage and the output voltage of the current sensing means; and means for preventing current from being supplied to the motor when the detecting means detects that the motor current exceeds the current limit.

Claim 4

A power steering apparatus as claimed in Claim 2, wherein: the engine speed sensor comprises means for generating an engine speed signal having a frequency proportional to the engine rotational speed; and the reference voltage generating means comprises a frequency voltage converter which generates a reference voltage which decreases as the frequency of the engine speed signal increases.

Claim 5

A power steering apparatus as claimed in Claim 1, 2 or 3 wherein the current limit means comprises: a vehicle speed sensor (15) for generating a vehicle speed signal indicative of the rotational speed of the engine; reference voltage generating means responsive to the vehicle speed signal for generating a reference voltage indicative of a current limit corresponding to the vehicle speed detected by the vehicle speed sensor; current sensing means for generating an output voltage proportional to the motor current; detecting means for detecting that the motor current exceeds the current limit by comparing the reference voltage and the output voltage of the current sensing means; and means for preventing current from being supplied to the motor when the detecting means detects that the motor current exceeds the current limit.

Claim 6

A power steering apparatus as claimed in Claim 4. wherein: the vehicle speed sensor comprises means for generating a vehicle speed signal hauing a frequency proportional to the vehicle speed; and the reference voltage generating means comprises a frequency-voltage converter which generates a reference voltage which decreases as the frequency of the vehicle speed signal increases.

Claim 7

A power steering apparatus as claimed in Claim 4 or 5, wherein: the torque sensing means comprises means for generating an output signal which is proportional to a supply voltage and the the steering torque, and the reference voltage corresponding to the vehicle speed supplied to the torque sensing means as the supply voltage.

Claim 8

A power steering apparatus as claimed in any preceeding Claim, wherein the motor control means comprises a self-excited pulse width modulation circuit with feedback from the motor for supplying the motor with drive pulses having a pulse width which is modulated by the output voltage of the torque sensing means.

Claim 9

A power steering apparatus as claimed in Claim 7, wherein the pulse width modulation circuit comprises: a bridge circuit consisting of a plurality of switching elements, the motor being connected across the bridge circuit; a capacitor and a resistor connected in parallel between the motor and ground, and a comparator having a first input terminal to which the output voltage of the torque sensing means is applied and a second input terminal connected to the junction of the comparator being supplied to a gate one of the switching elements of the bridge circuit.

Claim 10

A motorized power steering apparatus substantially as described with reference to the accompanying drawings.

Claim 11

A motorized power steering apparatus substantially as described with reference to the accompanying drawings.