JP4957039B2 - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device which can detect failure due to grounding, and has high responsiveness. <P>SOLUTION: The electric power steering device is equipped with a torque sensor for detecting a steering torque applied to a steering member (not shown in figure), and performs steering aid by driving a motor for steering aid (S26) with a PWM control (S18) at a predetermined duty ratio or less based on the steering torque (S2) detected by the torque sensor. The electric power steering device comprises: a means (S6) for detecting steering speed of the steering member; a means (S18) for determining whether or not the steering speed detected by the mean is the predetermined speed or more; and a means (S20) for increasing the predetermined duty ratio when the means determines that the steering speed is the predetermined speed or more. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention detects steering torque applied to a steering member, and drives a steering assist motor to assist steering by PWM (Pulse Width Modulation) control with a predetermined duty ratio or less based on the detected steering torque. The present invention relates to an improvement of an electric power steering device.

  An electric power steering device that drives a motor to assist steering and reduces the burden on the driver includes an input shaft that is connected to a steering member (steering wheel, steering wheel), and an output shaft that is connected to a steering wheel by a pinion, a rack, and the like. And a connecting shaft for connecting the input shaft and the output shaft, the steering sensor detects the steering torque applied to the input shaft by the torsion angle generated in the connecting shaft, and the steering assist linked to the output shaft based on the detected steering torque The motor is driven and controlled.

Some conventional electric power steering devices use a brushless motor driven by PWM control as a steering assist motor. If the motor is normal, the sum of the currents of the three phases becomes 0, and the motor A ground fault is detected by utilizing the fact that the added value does not become zero during the terminal ground fault.
In this case, in a region where the duty ratio of PWM control is a certain level or more, noise increases and the motor current cannot be detected accurately. Therefore, the brushless motor is driven only at a predetermined duty ratio or less, a ground fault is detected, and fail-safe processing is performed.

In Patent Document 1, based on the detected steering speed value, the initial duty ratio of the PWM wave at the start of the motor (at the start of steering assist) is set so that no current flows through the motor at the start, and the set initial duty is set. An electric power steering apparatus configured to start an electric motor with a PWM wave of a ratio and prevent an excessive current from flowing at the time of starting is disclosed.
JP-A-8-198124

In the above-described conventional electric power steering apparatus, the brushless motor is driven only at a predetermined duty ratio or less, so that there is a problem that the steering assist force is limited and the responsiveness is lowered accordingly.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an electric power steering apparatus that can detect a ground fault and has high responsiveness.

An electric power steering apparatus according to the present invention includes a torque sensor that detects a steering torque applied to a steering member, and is based on the steering torque detected by the torque sensor, and is used for steering assistance by PWM control with a predetermined duty ratio or less. In the electric power steering apparatus for assisting steering by driving a brushless motor driven by three phases, means for adding each phase current of the brushless motor, and whether or not the absolute value of the addition result of the means is less than a predetermined value Current determining means for determining whether or not, means for detecting the steering speed of the steering member, steering speed determining means for determining whether or not the steering speed detected by the means is equal to or higher than a predetermined speed, and the current determining means increasing There were determined to be less than the predetermined value, and wherein when the steering speed determination means is equal to or more than the predetermined speed, said predetermined duty ratio Characterized in that it comprises a means for.

According to the electric power steering apparatus according to the present invention, based on the detected steering torque, the PWM control by less than a predetermined duty ratio, steering assist to drive the brushless motor driven three-phase steering assist, each phase When it is determined that the absolute value of the current addition value is less than the predetermined value and the detected steering speed of the steering member is greater than or equal to the predetermined speed, the predetermined duty ratio is increased, so that a ground fault is detected. In addition, an electric power steering device with high responsiveness can be realized.

Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof.
FIG. 1 is a block diagram showing a main configuration of an embodiment of an electric power steering apparatus according to the present invention. In this electric power steering apparatus, the steering torque applied to a steering member (not shown) and detected by the torque sensor 11, the vehicle speed detected by the vehicle speed sensor 16, and the steering angle of the steering member detected by the steering angle sensor 12 are microscopic. It is given to a computer (hereinafter referred to as a microcomputer) 19.

A relay control signal output from the microcomputer 19 is input to the relay drive circuit 15, and the relay drive circuit 15 turns the fail-safe relay contact 15a on or off according to the relay control signal.
The microcomputer 19 refers to a torque / current table 18a in the memory 18 based on the steering torque, the vehicle speed, the steering angle, and a motor current described later, and determines a motor current command value that is a current value to be passed through the brushless motor 20, A PWM duty ratio command corresponding to the determined motor current command value is created. The created PWM duty ratio command is given to the motor drive circuit 13. The brushless motor 20 is a steering assist motor and is three-phase driven by PWM control.

The motor drive circuit 13 is applied with the output voltage of the in-vehicle battery P through the fail-safe relay contact 15a, and rotates the brushless motor 20 based on the given PWM duty ratio command.
When the brushless motor 20 rotates, the rotor position detector 14 detects the rotor position, and the motor drive circuit 13 controls the rotation of the brushless motor 20 based on the detected rotor position signal.
The three-phase currents flowing in the brushless motor 20 are detected by the motor current detection circuit 17 and given to the microcomputer 19.

Hereinafter, the operation of the electric power steering apparatus having such a configuration will be described with reference to the flowchart of FIG.
In the steering assist operation, the microcomputer 19 first reads the steering torque detected by the torque sensor 11 (S2), reads the steering angle detected by the steering angle sensor 12 (S4), and differentiates the read steering angle, A steering angular speed (steering speed) is calculated (S6). Next, the vehicle speed detected by the vehicle speed sensor 16 is read (S8).

Next, the microcomputer 19 determines the target motor current with reference to the torque / current table 18a based on the read vehicle speed (S8) and the read steering torque (S2) (S10).
In the torque / current table 18a, when the steering torque exceeds a predetermined dead zone, the target motor current increases as the steering torque increases, and when the steering torque exceeds a predetermined value, a function that saturates the target motor current is a vehicle speed. It is variably determined according to. The function is such that the ratio of the target motor current to the steering torque increases and the saturation value of the target motor current increases as the vehicle speed decreases.

  Next, the microcomputer 19 reads each phase current (motor current) from the motor current detection circuit 17 (S12) and determines whether or not the added value is substantially 0. Failure detection processing such as displaying a failure on the display device is performed (S14). If the added value is substantially 0, the difference between the determined target motor current (S10) and the read motor current (S12) is calculated, and based on the calculated difference, the target motor current is caused to flow to the brushless motor 20. A motor current command value is determined (S16).

  Next, the microcomputer 19 determines whether or not the calculated steering angular speed (steering speed) (S6) is equal to or higher than a predetermined steering angular speed (for example, 300 deg / s) (S18). The conventional PWM duty ratio with the upper limit of 90% is determined (S22). Next, a rotation direction corresponding to the determined PWM duty ratio is determined (S24), and each command signal of the determined rotation direction and PWM duty ratio is given to the motor drive circuit 13 (S26), and the process returns to another process. .

If the calculated steering angular speed (steering speed) (S6) is equal to or higher than the predetermined steering angular speed (S18), the microcomputer 19 determines a PWM duty ratio having an upper limit of 95% according to the calculated steering angular speed (S20). ).
For example, as shown in FIG. 3, the upper limit according to the steering angular velocity is increased from 90% to 95% PWM duty ratio in proportion to the steering angular velocity from 350 deg / s to 350 deg / s. When it exceeds s, the PWM duty ratio is set to be constant at 95%.
Next, the microcomputer 19 determines the rotation direction according to the determined PWM duty ratio (S20) (S24), and gives each command signal of the determined rotation direction and PWM duty ratio to the motor drive circuit 13 (S26). Return to other processing.

It is a block diagram which shows the principal part structure of embodiment of the electric power steering apparatus which concerns on this invention. It is a flowchart which shows operation | movement of embodiment of the electric power steering apparatus which concerns on this invention. It is explanatory drawing which shows the operation example of the electric power steering apparatus which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Torque sensor, 12 Steering angle sensor, 13 Motor drive circuit, 16 Vehicle speed sensor, 17 Motor current detection circuit, 18a Torque / current table, 19 Microcomputer (detection means, determination means, increase means), 20 brushless motor (motor)

Claims (1)

A torque sensor for detecting a steering torque applied to the steering member is provided, and a three-phase driven brushless motor for driving assistance is driven by PWM control with a predetermined duty ratio or less based on the steering torque detected by the torque sensor. In the electric power steering device that assists steering,
Means for adding each phase current of the brushless motor; current determining means for determining whether or not the absolute value of the addition result of the means is less than a predetermined value ; means for detecting the steering speed of the steering member; Steering speed determining means for determining whether or not the steering speed detected by the means is equal to or higher than a predetermined speed, and determining that the current determining means is less than a predetermined value, and the steering speed determining means is equal to or higher than a predetermined speed. Means for increasing the predetermined duty ratio when it is determined that there is an electric power steering device.

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