JP2600615Y2 - Electric power steering device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus, and more particularly to an improvement in motor drive.

[0002]

2. Description of the Related Art An electric power steering apparatus has been put to practical use which detects a steering torque, drives a motor with a motor drive current target value corresponding to the detected torque, and transmits a rotation of the motor to a steering mechanism to apply a steering assist force. ing.

FIG. 1 shows a circuit around a motor M, in which four transistors T1 to T4 are connected in a bridge, and the motor M is connected so as to bridge the bridge. Flywheel diodes D1 to D4 are connected in parallel to the transistors T1 to T4, respectively. Depending on the direction of the detected steering torque, a pair of transistors T1 and T4 or a transistor T2 and
The T3 pair conducts and the motor is rotated clockwise or counterclockwise. The transistors T1 to T4 are turned on by a pulse having a duty ratio corresponding to the magnitude of the detected steering torque. To enable this, the motor drive current target signal is pulse width modulated (PWM), which is provided to transistors T1 and T4 or to transistors T2 and T3. As another control method, in the case of right (left) rotation, there is a method in which the transistor T4 (T3) is turned on, and only the transistor T1 (T2) is supplied with a PWM wave according to the motor drive current target value.

[0004]

In the case of the latter motor energization control method, there is a problem that abnormal noise is generated when the steering wheel is returned, thereby deteriorating the sense of quality. The cause is considered as follows. FIG. 2 is a schematic circuit diagram of a control system of the motor M.
A resistor R for current detection is provided at the bridge portion in series with the motor M, and the detected current is amplified by the differential amplifier 4 and fed back to the differential amplifier 1. The differential amplifier 1 is inputted the target value I ₀ of the motor current, the PWM wave generating circuit 2 and generates a conduction control signal of transistor T1~T4 based on the output. When the steering wheel is returned, the steering mechanism, the motor, and the steering wheel are rotated toward the neutral point side by receiving a force from the wheel side such that the steering wheel returns to the neutral point side. On the other hand, since the driver applies resistance to the steering wheel to prevent a sudden return, the detected torque is in the opposite direction to the steering wheel return direction, and therefore, the motor is required to perform the rotational driving in the opposite direction to the actual rotation direction. Will be given.

It is assumed that the target current in this state is positive, and the transistors T2 and T3 operate. When the transistor T3 is turned on, since the rotation direction of the motor M as described above is reverse, the counter electromotive force of the motor M is V _M direction shown (negative). This current i ₁ by is determined by the counter electromotive force V _M and the internal resistance of the motor M. At this time, if the motor current target value I ₀ is smaller than i ₁ , the polarity of the motor drive voltage output from the differential amplifier 1 is inverted, and the transistors T1 and T4 are activated. Since thereby the transistor T3 is turned off, current i ₁ is zero. When the voltage applied to the motor M is reversed, the actual current detected by the resistor R becomes zero, and as a result, the transistors T2, T2
Return to the state where 3 turns on. That is, when the steering wheel is returned, the current due to the back electromotive force flows intermittently to the motor M, and a sudden change in the motor torque causes abnormal noise.

The present invention has been made to solve such a problem. The present invention uses the motor current for feedback control, sets the duty ratio of the PWM when the motor is not driven to 50%, and changes the duty ratio according to the rotation direction. The duty ratio to 50
%, And a pair of switch elements such as transistors T1 to T4 are made to conduct in a complementary manner to eliminate discontinuous motor current supply, thereby preventing generation of abnormal noise. The purpose is to do.

[0007]

An electric power steering apparatus according to the present invention comprises a plurality of pairs of switch elements connected in series through a motor by connecting a bridge-connected switch element in a bridging manner. Is driven by a PWM wave to rotate forward or reverse to obtain a steering assist force, a resistor connected in series with a motor at a bridge of the bridge, a motor current detected from the resistor, and a motor drive. A circuit for calculating a difference from the current target value, and a circuit for generating a PWM wave corresponding to the difference, wherein one of the pair of switch elements is driven by the PWM wave, and the other pair of switch elements is driven by the complementary signal wave Is driven.

[0008]

The clockwise and counterclockwise rotations of the motor are changed around the duty ratio of 50% in the state where the motor is not driven by the input of the PWM wave generating circuit. The input of the PWM wave generation circuit is the difference between the target value of the motor drive current determined from the detected torque and the feedback value (motor current detection value). Therefore, even if the current generated by the forced rotation of the motor when returning the steering wheel increases, the motor current will be suppressed by the control, and the change in the duty ratio during that time will be centered at 50% even if there is a change in the energizing direction. Therefore, the abnormal noise generation factor is eliminated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing an embodiment thereof. FIG. 3 is a block diagram showing a motor control circuit of the electric power steering device according to the present invention. A signal representing a target value of the motor drive current is supplied to the differential amplifier 1 based on a steering torque value or the like detected by a torque sensor (not shown) or the like.
The differential amplifier 1 receives a detection value of a motor current described later. The differential output of the differential amplifier 1 is input to the PWM wave generating circuit 2, and the PWM wave generating circuit 2 has a duty ratio of 50% when the output of the differential amplifier is zero, and more than 50% according to a positive value. The pulse signal Q having a duty ratio smaller than 50% according to the negative value of the duty ratio is output, and the complementary signal Q is output.

The transistors T1, T2, T3 and T4, which are switching elements, are provided between the power supply line of the voltage E and the ground line.
Bridge circuits are connected, and transistors T1, T
The motor M and the resistor R for detecting the motor current are connected in series so as to bridge the connection point 3 and the connection point between the transistors T2 and T4. Flywheel diodes D1 to D4 are connected to the transistors T1 to T4, respectively. The signal Q is connected so as to be applied to the gates of the transistors T1 and T4 via the delay circuit 3, and the signal Q is connected so as to be applied directly to the gates of the transistors T2 and T3.

The voltage across the resistor R is applied to two inputs of a differential amplifier 4, and the amplified output is input to the differential amplifier 1 as feedback information as described above. FIG. 4 shows a specific configuration of the PWM wave generating circuit 2. A pulse is obtained from the sawtooth wave generated by the sawtooth wave generating section 21 and the output of the comparator 22 having two inputs of the differential amplifier 1 output. Into a signal Q through a one-stage inverter, and a signal Q through a two-stage inverter.
And a bar. The delay circuit 3 to which the signal Q is input is constituted by a two-stage inverter. Therefore, the signal Q becomes the signal Q
This is delayed by one inverter stage from the bar, thereby preventing a short circuit due to simultaneous conduction of the transistors T1 and T3 (or T2 and T4).

Next, the motor drive by this circuit will be described with reference to FIG. When the output of the differential amplifier 1 is zero, the PWM wave generating circuit 2 outputs a duty ratio of 50 as shown in FIG.
% Signal. This signal Q is applied to transistors T1 and T4,
Since the complementary signal Q is applied to the transistors T2 and T3, the motor M does not rotate and the motor current becomes substantially zero.

FIG. 5 (b) shows the case where the motor is rotating clockwise, the duty ratio is larger than 50%, the transistors T1 and T4 are turned on while the pulse is positive, and the transistor T1 is turned on while the pulse is negative.
2, T3 turns on. Describing the current change during this time, the positive direction motor current gradually increases due to the inductance of the motor M while the transistors T1 and T4 are on. Next, when the transistors T1 and T4 turn off,
When T2 and T3 are turned on, a current flows in the reverse direction, but the energizing current decreases only in the positive direction due to the electromotive force due to the rotation of the motor due to the energization in the positive direction and the inductance of the motor. In this way, the motor current eventually becomes positive (transistor T1, motor M, transistor
T4 direction). FIG. 5 (c) shows a case where the motor rotates counterclockwise, the duty ratio becomes 50% or less, and the current flows in the negative direction contrary to the above.

[0014]

[Effect of the Invention] As described above, the output duty ratio of the PWM wave generation circuit is determined using the motor current as feedback information in the case of the present invention, so that even if there is an electromotive force due to the rotation of the motor as in returning the steering wheel, it is compensated. Motor drive is performed. In addition, the structure can be simplified, reducing costs.
And the ability to accurately detect the motor current.
Play a fruit. Is the rightward torque detected now?
Consider the case where the motor rotation is fixed. Since the motor is fixed, the motor electromotive force is zero. In addition, the target value of the motor drive current is set to a value that sets the PWM duty ratio to, for example, 60% based on the detected torque. If the motor is rotated clockwise from this state, the motor electromotive force will be positive.
(Clockwise direction) and the duty ratio of PWM changes to 70%. Conversely, when the motor is rotated counterclockwise, the motor electromotive force is in the negative direction (left rotation direction), and the PWM duty ratio is 50.
%. As described above, since the motor current is determined in such a manner as to compensate for the influence of the motor rotation, even when the steering wheel is returned, the change in the reverse rotation of the motor rotation direction is small, and generation of abnormal noise is prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a motor and a driving circuit thereof.

FIG. 2 is a circuit diagram of a conventional motor control system.

FIG. 3 is a block diagram of the device of the present invention.

FIG. 4 is a circuit diagram of a PWM wave generation circuit.

FIG. 5 is a graph showing a relationship between a PWM wave and a motor drive current.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Differential amplifier 2 PWM wave generation circuit 3 Delay circuit M Motor T1-T4 Transistor

Claims (1)

(57) [Scope of request for utility model registration] 1. A motor connected in a bridge-like manner with a bridge-connected switch element is driven forward or backward by driving a plurality of pairs of switch elements connected in series via the motor with a PWM wave. An electric power steering apparatus for obtaining a steering assist force, comprising: a resistor connected in series with a motor at a bridge portion of the bridge; a circuit for calculating a difference between a motor current detected from the resistance and a motor drive current target value; And a circuit for generating a PWM wave corresponding to the above, wherein one of the pair of switch elements is driven by the PWM wave, and the other pair of switch elements is driven by the complementary signal wave. Power steering device.