Vehicle hydraulic power steering system with means for controlling the operation of a power steering pump

Claim 2

A vehicle hydraulic power steering system including a pump (9) for supplying a pressurized working fluid and a power steering unit (6) supplied with said working fluid to assist a driver's steering effort through a steering wheel (1), comprising: means (17) for detecting a steering effort applied to the steering wheel; means (19) for detecting the pressure of the working fluid supplied to said power steering unit; and control means (20) connected to said steering effort detecting means (17) and said pressure detecting means (19) for producing an output signal for actuating said pump (9) when the steering effort is applied to the steering wheel and/or the pressure of the working fluid is above a predetermined level.

Claim 3

A vehicle hydraulic power steering system as claimed in calim 1, further comprising means (26) for keeping the operation of said pump (9) for a predetermined time after a termination of the output signal of said control means (20).

Claim 4

A vehicle hydraulic power steering system as claimed in claim 1 or 2, wherein said steering effort detecting means comprises a torque sensor for sensing a torque about a steering shaft (3) connected to said steering wheel (1).

Claim 5

A vehicle hydraulic power steering system as claimed in claim 1 or 2, wherein said steering effort detecting means comprises a rotational speed sensor for sensing a speed of the rotation of the steering wheel (1).

Claim 6

A vehicle hydraulic power steering system as claimed in claim 4, wherein said rotational speed sensor (17) comprises a light coupled position transducer including a shutter disk mounted on a steering shaft (3) and a light source and light sensor pair for producing an electric pulse signal responsive to a speed of the rotation of said steering wheel (1) and a frequency to voltage converter (18) for converting said electric pulse signal into a voltage signal.

Claim 7

A vehicle hydraulic power steering system as claimed in claim 1 or 2, wherein said pressure detecting means (19) comprises a pressure transducer incorporating therein a diaphragm and a metal thin film gauge mechanically connected thereto, disposed at a working fluid inlet port of the power steering unit.

Claim 8

A vehicle hydraulic power steering system as claimed in claim 1 wherein said control meams (20) comprises: a first comparator (21) which compares an output signal of said steering effort detecting means (17) representing a steering effort with a first reference level for producing an output signal when the voltage level of said steering effort representing signal is higher than said first reference level; a second comparator (22) which compares an output signal of said pressure detecting means representing a working fluid pressure with a second reference signal for producing an output signal when the voltage level of said working fluid pressure representing signal is higher than said second reference level; a NOT circuit having an input and an output, said input of the NOT circuit being connected to an output of said second comparator (22); an AND gate having inputs and an output, said inputs of the AND gate being connected to an output of said first comparator (21) and the output of said NOT circuit; and an OR gate having inputs and an output, said inputs of the OR gate being respectively connected to said outputs of the second comparator (22) and said AND gate.

Claim 9

A vehicle hydraulic power steering system as claimed in claim 2, wherein said control means (200)comprises: a first comparator (21) which compares an output signal of said steering effort detecting means (17) representing a steering effort with a first reference level for producing an output signal when the voltage level of the said steering effort representing signal is highier than said first reference level; a second comparator (22) which compares an output signal of said pressure detecting means (19) representing a working fluid pressure with a second reference signal for producing an output signal when the voltage level of said working fluid pressure representing signal is higher than said second reference level; a NOT circuit having an input and output, said input of the NOT circuit being connected to an output of said comparator (22); an AND gate having inputs and output, said inputs of the AND gate being connected to an output of said first comparator (21) and the output of said NOT circuit; and an OR gate having inputs and an output, said inputs of the OR gate being respectively connected to said outputs of the second comparator (22) and said AND gate, and wherein said keeping means comprises a delay circuit (26) connected to said second comparator (22) for delaying a turn off time of said second comparator (22), said inputs of the NOT circuit and the OR gate being connected to an output of said delay circuit.

Claim 10

A vehicle hydraulic power steering system as claimed in claim 1, wherein said pump (9) is driven by an engine of said vehicle, and wherein an electro-magnetic clutch (16) responsive to the output signal of said control means (20) is disposed between said pump and said engine.

Claim 11

A vehicle hydraulic power steering system as claimed in claim 1, further comprising an electric motor (30) for driving said pump (9) in response to the output signal of said control means (20).