Electric power steering apparatus

Abstract

An electric power steering apparatus for generating a PWM signal based on a calculated steering assist command value, PWM-controlling a motor via a motor drive circuit including switching elements, and assist-controlling a steering system that a motor relay is inserted between the motor drive circuit and the motor, comprises a steering status detecting section that detects a steering status of a steering wheel, outputs a longtime steering holding signal when detecting that the steering status is a longtime steering holding status, and outputs a normal steering signal when detecting that the steering status is a normal steering status, and a motor current control section that determines a motor current control value for controlling a motor current flowing in the motor relay in accordance with the longtime steering holding signal or the normal steering signal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This is a divisional of U.S. patent application Ser. No. 14 / 131,809, filed Mar. 11, 2014, which is a National Stage of International Application No. PCT / JP2012 / 072356 filed Sep. 3, 2012, claiming priority based on Japanese Patent Application Nos. 2012-022811 and 2012-022814 filed Feb. 6, 2012 and 2012-024209 filed Feb. 7, 2012, the contents of all of which are incorporated herein by reference in their entirety.TECHNICAL FIELD[0002]The present invention relates to an electric power steering apparatus that provides a steering system of a vehicle with an assist force generated by a brushless DC motor, and in particular to an electric power steering apparatus capable of keeping torque variations at a low level by limiting a continuous energization time of a high current flowing in an electromagnetic type motor relay that supplies a current to the brushless DC motor and controlling so as to gradually decrease the high current flowing in the mo...

AI Technical Summary

Benefits of technology

[0030]According to an electric power steering apparatus of the present invention, by limiting a continuous energization time of a high current flowing in a motor relay used in a brushless DC motor mounted on the electric power steering apparatus and controlling so as to gradually decrease the high current flowing in the motor relay, keep torque variations at a low level. In this way, it is possible to no longer have to use an expensive large capacity relay as the motor relay and use an inexpensive small capacity electromagnetic type relay as the motor relay of the electric power steering apparatus, and simultaneously it is possible to suppress an uncomfortable feeling of the steering due to a matter that the assist of the electric power steering apparatus gradually decreases.

[0031]Moreover, according to an electric power steering apparatus of the present invention, perform temperature estimation of a relay spring portion or a relay coil portion, when an estimated relay-spring-portion-temperature or an estimated relay-coil-portion-temperature becomes equal to or more than a given temperature that is a threshold, limit so as to decrease the motor current flowing in the motor relay. Further, in the case that the estimated relay-spring-portion-temperature or the estimated relay-coil-portion-temperature declines and becomes less than the given temperature, control so as to increase the motor current and recover. In this way, there is an advantage that it is possible to use an inexpensive small capacity electromagnetic type relay without using a large capacity relay.

Problems solved by technology

However, when installing the motor relay, extraneous substances attach to relay contacts, the relay contacts are covered by oxidized coating and have a loose connection, even the motor relay is excited, there is a possibility that a failure that the relay contacts become an open state occurs.

Further, in a case that the motor current detection circuit broke down, it is impossible to detect a correct motor current, and a proper current control value cannot be outputted, as a result, an inexpedience that an excessive current flows in the motor and an excessive steering assist torque is supplied, or a necessary current does not flow in the motor and a sufficient steering assist torque cannot be supplied, occurs.

However, it is often the case that the open failure of the relay contacts lack repeatability, and a failure analysis is accompanied by a difficulty.

However, in the conventional diagnosis function, it is impossible to identify which relay caused the open failure of the relay contacts.

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