JPH0633776U - Electric power steering device - Google Patents

Abstract

(57) [Abstract] [Purpose] Abnormal noise is prevented by eliminating sudden changes in the drive current of the electric power steering motor. [Configuration] A differential amplifier 1 calculates a difference between a motor drive current target value determined by a steering torque and a detected value of the motor drive current.
Then, it is given to the PWM wave generation circuit 2 and the PWM wave of the corresponding duty ratio is generated. The duty ratio of 50% corresponds to zero output of the differential amplifier 1 and is set to be larger or smaller than that according to the positive or negative value of the output. Transistor T1, T
4 and transistors T2 and T3 are turned on by complementary PWM waves.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an electric power steering device, and more particularly to improvement of motor drive.

[0002]

[Prior art]

 An electric power steering system has been put into practical use, which detects a steering torque, drives a motor with a motor drive current target value corresponding to the detected steering torque, and transmits a motor rotation to a steering mechanism to give a steering assist force.

FIG. 1 shows a circuit around the motor M. Four transistors T1 to T4 are bridge-connected, 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, the pair of transistors T1 and T4 or the pair of transistors T2 and T3 become conductive, and the motor is rotated clockwise or counterclockwise. Also, the transistors T1 to T4 are turned on by a pulse having a duty ratio according to the detected steering torque. In order to make this possible, the signal of the motor drive current target value is pulse-width modulated (PWM), which is applied to the transistors T1 and T4 or to the transistors T2 and T3. Another control method is to turn on the transistor T4 (T3) in the case of right (left) rotation and give only the transistor T1 (T2) a PWM wave according to the target value of the motor drive current.

[0004]

[Problems to be solved by the device]

In the latter motor energization control method, there was a problem that an abnormal noise was generated when the steering wheel was returned and the quality was impaired. The cause of this is considered as follows. FIG. 2 is a schematic circuit diagram of the control system of the motor M 1. A resistor R 1 for current detection is provided in 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 target value I ₀ of the motor current is input to the differential amplifier 1, and the PWM wave generation circuit 2 generates a conduction control signal for the transistors T1 to T4 based on the output thereof. When the steering wheel is returned, the steering mechanism, the motor, and the steering wheel are rotated to the neutral point side by the force from the wheel side that causes the steering wheel to return to the neutral point side. On the other hand, the driver applies resistance to the steered wheels to prevent a sudden return, so the detected torque is in the opposite direction to the return direction of the steered wheels. The flow will be given.

It is assumed that the target current in this state is positive and the transistors T2 and T3 are activated. 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). The resulting current i ₁ is determined by the back electromotive force V _M of the motor _M and the internal resistance. At this time, when 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 reversed, and the transistors T1 and T4 are activated. This turns off the transistor T3, and the current i ₁ becomes 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 and T3 return to their original states. That is, when the steering wheel is returned, a current due to the back electromotive force of the motor M intermittently flows, and a sudden change in the motor torque caused by the current causes abnormal noise.

The present invention has been made to solve such a problem, and uses the motor current for feedback control and sets the PWM duty ratio to 50% when the motor is not driven, depending on the rotation direction. The duty ratio is changed around 50% and the pair of switch elements such as transistors T1 to T4 are complementarily turned on to prevent discontinuous motor current conduction and prevent abnormal noise. An object is to provide an electric power steering device.

[0007]

[Means for Solving the Problems]

 The electric power steering device of the present invention drives a motor in which bridge-connected switch elements are connected in a bridging manner by driving a pair of switch elements connected in series via the motor with a PWM wave. In an electric power steering device that obtains steering assist force by rotating or reversing, the resistance connected in series with the motor at the bridge portion of the bridge and the difference between the motor current detected from the resistance and the motor drive current target value are calculated. A circuit for obtaining the difference and a circuit for generating a PWM wave corresponding to the difference are provided. The pair of switch elements are driven by the PWM wave, and the pair of switch elements are driven by the complementary signal wave. It is characterized by

[0008]

[Action]

 The right rotation and the left rotation of the motor change around the duty ratio of 50% when the motor is not driven by the input of the PWM wave generation circuit. The input of the PWM wave generation circuit is the difference between the target value of the motor drive current, which is determined by the detection torque, etc., and the feedback value (motor current detection value). Therefore, even if the generated current due to the forced rotation of the motor at the time of returning the steering wheel becomes large, the motor current is suppressed by the control, and the change in duty ratio during that period is 50% even if there is a change in the energizing direction. Since it changes around the center, the cause of abnormal noise is eliminated.

[0009]

【Example】

 Hereinafter, the present invention will be described 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 apparatus of the present invention. A signal representing the target value of the motor drive current is input to the differential amplifier 1 on the basis of the value of the steering torque detected by a torque sensor (not shown), etc. The value has been entered. The differential output of the differential amplifier 1 is input to the PWM wave generation circuit 2, and the PWM wave generation circuit 2 has a duty ratio of 50% when the differential amplifier output is zero, and a duty ratio of 50% depending on the positive value. A pulse signal Q having a large duty ratio and a duty ratio smaller than 50% is output according to a negative value, and the complementary signal Q is output.

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

The voltage across the resistor R is applied to the two inputs of the differential amplifier 4, and the amplified output is input as feedback information to the differential amplifier 1 as described above. FIG. 4 shows a concrete configuration of the PWM wave generating circuit 2. The sawtooth wave generated by the sawtooth wave generator 21 and the output of the comparator 22 having two inputs of the differential amplifier 1 output are used to obtain a pulse. Is made a signal Q through a one-stage inverter, and is made a signal Q bar through a two-stage inverter. The delay circuit 3 to which the signal Q is input is composed of a two-stage inverter. Therefore, the signal Q is delayed from the signal Q by one stage of the inverter, 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 generation circuit 2 becomes a signal with a duty ratio of 50% as shown in Fig. 5 (a). Since this signal Q is given to the transistors T1 and T4, and its complementary signal Q bar is given to the transistors T2 and T3, as a result, the motor M does not rotate and the motor current becomes substantially zero.

FIG. 5 (b) shows the case of clockwise rotation of the motor, the duty ratio is greater than 50%, the transistors T1 and T4 turn on while the pulse is positive, and the transistor T2 and T4 when the pulse is negative. T3 turns on. The current change during this period will be described. While the transistors T1 and T4 are on, the positive direction motor current gradually increases due to the inductance of the motor M and the like. Transistors T1 and T4 turn off.Next, when transistors T2 and T3 turn on, a current flows in the reverse direction, but the conduction current decreases in the positive direction due to the electromotive force caused by motor rotation due to the forward conduction and the motor inductance. Stop to do it. In this way, the motor current consequently flows in the positive direction (direction of the transistor T1, the motor M, and the transistor T4) as shown by the broken line. Fig. 5 (c) shows the case of left rotation of the motor, the duty ratio is 50% or less, and the current flows in the negative direction contrary to the above.

[0014]

[Effect of device]

 As described above, since the output duty ratio of the PWM wave generation circuit is determined by using the motor current as feedback information in the case of the present invention, even if there is an electromotive force due to the motor rotation, such as when the steering wheel is returned, the motor drive can be performed. Be seen. Now, consider the case where the rightward torque is detected or the motor rotation is fixed. Since the motor is fixed, the motor electromotive force is zero. In addition, the target value for the motor drive current becomes a value that sets the duty ratio of the PWM to 60%, for example, depending on the detected torque. If the motor is rotated to the right from this state, the motor electromotive force will be in the positive direction (to the right) and the PWM duty ratio will change to 70%. Conversely, when the motor is rotated counterclockwise, the motor electromotive force is in the negative direction (counterclockwise rotation), and the PWM duty ratio changes to 50%. In this way, the motor current is determined in a manner that compensates for the influence of the motor rotation, so that even when the steering wheel is returned, the change in the reverse rotation of the motor rotation is small and abnormal noise is prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a motor and a drive 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 the relationship between PWM waves and motor drive current.

[Explanation of symbols]

 1 Differential amplifier 2 PWM wave generation circuit 3 Delay circuit M motor T1 to T4 transistor

Claims (1)

[Scope of utility model registration request] 1. A motor, in which bridge-connected switch elements are connected so as to be bridged, is driven by a PWM wave to drive a pair of switch elements connected in series via the motor to perform forward or reverse rotation. In an electric power steering apparatus for obtaining steering assist force, a resistor connected in series with a motor at a bridge portion of the bridge, a circuit for obtaining a difference between a motor current detected from the resistor and a motor drive current target value, and the difference. And a circuit for generating a PWM wave corresponding to the above, the PWM wave drives one pair of switch elements, and the complementary signal wave drives the other pair of switch elements. Power steering device.