Power steering apparatus

• US 6,216,814 B1
• Filed: 06/07/1999
• Issued: 04/17/2001
• Est. Priority Date: 06/08/1998
• Status: Expired due to Fees

• Current Assignee: Koyo Seiko Co., Ltd. (Toyota Motor Corporation)
• Original Assignee: Koyo Seiko Co., Ltd. (Toyota Motor Corporation)
• Inventors: Fujita, Kazuhiko, Nakajima, Tsuyoshi
• Primary Examiner(s): Dickson, Paul N.
• Assistant Examiner(s): Lerner, Avraham H.
• Application Number:
  US09/326,671
• Time in Patent Office: 680 Days
• Field of Search: 701/41, 701/42, 701/43, 180/446, 180/417, 180/421, 180/422
• US Class Current: 180/422
• CPC Class Codes: B62D 5/065 characterised by specially adapted means for varying pressurised fluid supply based on need, e.g. on-demand, variable assist

Abstract

A power steering apparatus which generates a steering assist force by a hydraulic pressure of a pump driven by an electric motor. The apparatus includes: an electric current sensor for sensing an electric current flowing through the electric motor; and a control circuit for switching a voltage to be applied to the electric motor from a standby voltage to an assist voltage if the motor current is higher than a first threshold or if a change rate of the motor current is higher than a second threshold.

Claims

1. A power steering apparatus, comprising:

an electric motor;

a pump to be driven by the electric motor for generating a hydraulic pressure for steering assist;

an electric current sensor for sensing an electric current flowing through the electric motor; and

a control circuit which is capable of switching a control mode between a first mode in which a first voltage is applied to the electric motor when a steering operation is performed and a second mode in which a second voltage lower than the first voltage is applied to the electric motor when a steering operation is not performed;

wherein the control circuit includes means for judging (a) whether the electric current sensed by the electric current sensor is higher than a first threshold in the second mode and (b) whether a change rate of the electric current sensed by the electric current sensor is higher than a second threshold in the second mode, and the control circuit switches the control mode from the second mode to the first mode if at least one of the conditions (a) and (b) is satisfied.

2. A power steering apparatus, comprising:

an electric motor;

a pump to be driven by the electric motor for generating a hydraulic pressure for steering assist;

an electric current sensor for sensing an electric current flowing through the electric motor;

a steering operation start judging circuit for detecting start of a steering operation on the basis of a judgment that a rate of change of the electric current sensed by the electric current sensor over a period of time has exceeded a predetermined rate of change threshold; and

a control circuit for applying a standby voltage to the electric motor when a steering operation is not performed and, in response to the detection of the start of the steering operation by the steering operation start judging circuit, applying to the electric motor an assist voltage which is higher than the standby voltage.

3. A power steering apparatus as set forth in claim 2, wherein the steering operation start judging circuit detects the start of the steering operation on the basis of a judgment that at least one of the following conditions is satisfied:

the electric current sensed by the electric current sensor is higher than a predetermined electric current threshold; and

the rate of change of the electric current sensed by the electric current sensor is higher than the predetermined rate of change threshold.