JP2540153B2 - Motor drive - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a power steering motor drive device for driving a steering handle of a vehicle by a steering motor.

[Prior art and its problems]

(Kagorai technology) Conventional electric power steering motor drive devices
As shown in Japanese Patent Laid-Open No. 59-156863, a bridge circuit centering around a steering motor using control elements such as first, second, third, and fourth transistors which are conducted during steering in the left-right direction. Connected as. Then, at the time of right steering, the first and second transistors are made conductive at the same time based on the detection of the steering torque to allow a positive drive current to flow through the motor, and at the time of left steering, the third and fourth transistors are detected based on the detection of the steering torque.
The transistors are simultaneously turned on to supply a reverse drive current to the motor for control.

(Problems to be Solved by the Invention) In driving such a motor, when noise is superimposed on the output signal from the torque sensor, a minute driving current flows in that direction. Particularly, when the steering wheel is rotated to rotate the drive wheels in a certain direction and then the steering wheel is returned to the original position in the released state, such noise is likely to be superimposed. When the noise is superimposed, the steering motor is driven, which delays the return of the drive wheels to their original positions.

[Object of the Invention]

The present invention has been made in view of the above problems of the motor drive device, and an object of the present invention is to promptly restore the steering wheel without the influence of such noise.

[Constitution and effect of the invention]

(Means for Solving the Problems) The present invention relates to a motor drive device for an electric power steering having a torque sensor connected to a steering shaft to detect a rotational torque of the steering shaft, and a steering motor for rotating a steering wheel. , As shown in FIGS. 1 and 4, the first switching element for holding the right steering conduction,
The second switching element for right steering high speed switching is connected symmetrically to the steering motor, and the third switching element for maintaining left steering conduction and the fourth switching element for left steering high speed switching are connected to the steering motor. When the absolute value output from the torque sensor exceeds the first threshold level, a bridge circuit configured symmetrically connected to each other is provided with a pulse width signal corresponding to the output level to the second or fourth switching element. The left and right steering torque detection signals from the high-speed switching control section and the torque sensor, which are given alternatively, are given as positive and negative signals, respectively, and exceed the second and third threshold values which are equal in absolute value and symmetrical in positive and negative directions. A polarity determination circuit that outputs a polarity determination signal that inverts the output when the first or third switching circuit is activated based on the output of the polarity determination circuit. It is characterized in that it has a conduction holding control unit for alternatively conducting element.

(Operation) According to the present invention having such a feature, the output from the torque sensor is given to the high speed switching controller.
When the absolute value of the output of the torque sensor exceeds the first threshold level, the high speed switching controller outputs a signal having a pulse width corresponding to the output level. The polarity determination circuit uses the left and right steering torque detection signals from the torque sensor as positive and negative torque signals, and the level is positive and negative symmetrically.
When the change exceeds the third threshold level, the polarity determination output is inverted. Therefore, when the output from the torque sensor exceeds the first threshold value and further exceeds the second threshold value, high speed switching is performed and the steering motor is driven. When the absolute value of the signal from the torque sensor exceeds the first threshold value and the current value becomes less than or equal to the third threshold value, the steering motor is driven in the reversed direction. When the signal from the torque sensor is near 0, the steering motor is not driven even if its absolute value fluctuates within the first threshold value.

(Effect of the invention) Therefore, according to the present invention, when the driver rotates the steering wheel, the torque sensor output above a certain level is transmitted to the high-speed switching control unit and the continuity holding control unit. The motor can be driven to rotate the steered wheels. However, even if a small level signal is generated in the torque sensor due to the inclination or unevenness of the ground such as when the steering wheel is not operated after steering, if the signal is not transmitted to the switching element if it is below the threshold level, the motor load torque is reduced. It does not occur, and the effect that the steering wheel can be returned quickly can be obtained.

[Explanation of Examples]

(Structure of Embodiment) FIG. 2 is a schematic view of a power steering mechanism to which the present invention is applied, and FIG. 1 is a block diagram showing an entire structure of a motor drive circuit thereof. In FIG. 2, a steering wheel 1 is connected with a torque sensor 2 and a transmission mechanism 3 for transmitting a steering force from the steering wheel 1.
The torque sensor 2 detects the lateral torque of the steering wheel 1, and its output is given to the motor drive circuit 4. The motor drive circuit 4 is connected to the battery 5 of the vehicle, and controls the steering motor 6 which is driven in the left-right direction in response to the torque signal in the left-right direction given from the torque sensor 2, and together with the transmission mechanism 3. The steered wheels 7 are rotated in the left-right direction by a predetermined angle.

Next, the configuration of the motor drive circuit 4 will be described with reference to FIG. In this figure, the torque detection signal from the torque sensor 2 is a signal of a level corresponding to the torque that becomes positive when rotating to the right and becomes negative when rotating to the left, and the output is entirely output via the input terminal 11. Wave rectification circuit 12 and polarity determination circuit 13
Be transmitted to. The full-wave rectifier circuit 12 full-wave rectifies the input signal and supplies it to the voltage comparison circuit 14. The polarity determination circuit 13 determines the positive or negative polarity of the output obtained from the torque sensor with a certain hysteresis. Further, the motor drive circuit 4 is provided with an oscillating circuit 15 which oscillates a square wave having a constant frequency, for example, 20 KHz, and its output is an integrating circuit 16
And DC-DC converter 17. The integrating circuit 16 integrates this square wave signal and converts it into a triangular wave, and supplies the output to the voltage comparing circuit 14 as a reference voltage. Since the voltage comparison circuit 14 compares the output of the full-wave rectification circuit 12 with a triangular wave on which a direct current component of a constant voltage is superimposed as a reference voltage, it outputs the level change of the torque sensor 2 as a pulse signal whose duty changes. , Its output is given to the drive logic circuit 18. The drive logic circuit 18 is also supplied with the polarity determination output of the polarity determination circuit 13. The drive logic circuit 18 is an AND circuit 18a,
18b, and selectively applies a pulse width modulated signal obtained from the voltage comparison circuit 14 to the + side lower FET driver 19 or the − side lower FET driver 20 based on the positive or negative polarity determination output. Is. The polarity judgment circuit 13 selectively supplies signals to the AND circuits 18a and 18b and the photocouplers 21 and 22 based on the positive or partial polarity judgment. The outputs of the photocouplers 21 and 22 are + side upper FET drivers 23 and −, respectively.
Given to the side upper FET driver 24. FET driver
Reference numerals 23 and 24 drive the right and left upper FETs 25 and 26, respectively, based on the output from the photocoupler 21 or 22, and the FET drivers 19 and 20 respectively drive the right and left lower FEs.
It drives T27 and 28. Here, “upper” indicates the side closer to the power supply terminal of the motor drive circuit 4, and “lower” indicates the FET farther from the power supply terminal. FET driver 1
“+” And “−” shown in 9, 20, 23, and 24 are polarity determination circuits 13
It corresponds to the positive voltage or the negative voltage determined by.
The FETs 25 to 28 are switching elements each composed of a power MOSFET, the FETs 25 and 27 constitute first and second switching elements which conduct when steering in the right direction, and the FETs 2 and 28 are arranged in the left and right directions. It constitutes third and fourth switching elements that are conducted during steering. These FETs are connected in a bridge circuit, and the steering motor 6 is connected in the middle between them through terminals 4a and 4b. Where DC-
DC converter 17, polarity determination circuit 13 and photo coupler 2
The 1,22, + side and-side upper FET drivers 23,24 are conduction holding sections for selectively conducting the first or third switching element based on the detection of the left and right steering torques obtained from the torque sensor 2. Make up 29. Also, full-wave rectification circuit 12, voltage comparison circuit 14, square-wave oscillation circuit 15, integration circuit 16 and drive logic circuit 18, + side and-side lower FET drivers 19, 20
Is a high-speed switching control unit 30 that selectively supplies a signal having a pulse width corresponding to the output level of the torque sensor 2 or the control signal output unit 33 to the first or third switching element. There is.

Next, an FET bridge in which four FETs are bridge-connected and a current detection circuit will be described with reference to FIG. Here, the drains of the FETs 25 and 26 are connected to the positive terminal of the battery 5 via a relay circuit, and the source terminals thereof are FET2 respectively.
Connected to the drains of 8 and 27. Also, motor connection terminals 4a and 4b are provided at the common connection ends of FETs 25 and 28 and FETs 26 and 27, respectively.
The steering motor 6 is connected via the, and the source ends of the FETs 27 and 28 are grounded. In this figure, each FET 25-28
A surge absorbing circuit composed of a diode and a Zener diode is connected between the drain and the gate of, and a flywheel diode is connected between the drain and the source.

Next, FIG. 4 shows a polarity determination circuit 13 connected to the input terminal 11.
2 is a circuit diagram showing a detailed configuration of a voltage comparison circuit 14. In the figure, the voltage comparison circuit 14 is composed of an operational amplifier 14a and compares the rectified torque sensor signal provided from the full-wave rectification circuit 12 with the triangular wave obtained from the integration circuit 16. Here, the voltage divided by the resistor R1 and the variable resistor R2 is connected to the inverting input terminal of the operational amplifier 14a via the resistor R3. As a result, a direct current voltage of a predetermined level is added to the output of the seat distribution circuit 16, and the first threshold Vref1 which is the lowest level of voltage comparison is determined. The output from the full-wave rectifier circuit 12 is given to the non-inverting input terminal of the operational amplifier 14a. The output of the voltage comparison circuit 14 is a resistor R
It is transmitted to the drive logic circuit 18 via the voltage dividing circuit of 5, R6 and R7. Further, the polarity determination circuit 13 includes two operational amplifiers 13a,
The torque sensor signal supplied from the input terminal 11 is transmitted to the non-inverting input terminal and the inverting input terminal of the operational amplifiers 13a and 13b via the resistors R8 and R9, respectively. Then, in order to alternately operate these operational amplifiers 13a and 13b and add hysteresis, the output terminal of the operational amplifier 13a is connected to the inverting input terminal of the operational amplifier 13b via the resistor R10, and the output terminal of the operational amplifier 13b is also connected. Is connected to the inverting input terminal of the operational amplifier 13a via the resistor R11. Where resistor R1
By changing the values of 0 and R11, the absolute value with respect to the input voltage of the polarity determination circuit 13 is equal to the positive and negative symmetrical second and third values.
The threshold levels Vref2 and Vref3 can be set. The outputs of the operational amplifiers 13a and 13b are transmitted to the photocouplers 21 and 22 and the drive logic circuit 18, respectively.

(Operation of Embodiment) Next, the operation of this embodiment will be described with reference to the waveform diagrams of FIGS. First, when the power is turned on, the upper
Power is supplied to the FETs 25 and 26. The square wave oscillating circuit 15 oscillates a square wave signal of 20 KHz, for example. Here, when the driver operates the steering wheel 1 so as to rotate it to the right, a change in the torque is detected by the torque sensor 2 and given to the motor drive circuit 4. Fig. 5 (a)
When the signal from the torque sensor 2 as shown in FIG. 2 is transmitted, it is full-wave rectified by the full-wave rectifier circuit 12 as shown in FIG. Further, the square wave signal of the square wave oscillator circuit 15 is converted into a triangular wave through the integrated circuit 16 and transmitted to the voltage comparison circuit 14. FIG. 6 is a diagram showing the triangular wave applied to the inverting input terminal and the non-inverting input terminal of the voltage comparison circuit 14, the output of the full-wave rectification circuit 12, and the output waveform of the corresponding voltage comparison circuit. As described above, since the constant threshold value Vref1 is superimposed on the triangular wave supplied from the integrating circuit 16 as a DC component, the triangular wave whose signal changes in a predetermined range exceeding this level is inverted as shown in FIG. 6 (a). A full-wave rectified signal is transmitted to the non-inverting input terminal applied to the input terminal. Therefore, when the output of the full-wave rectifier circuit 12 exceeds the threshold level Vref1, a signal having a pulse width corresponding to the voltage level of the torque sensor 2 which is the output of the full-wave rectifier circuit 12 is generated from the voltage comparison circuit 14. Becomes pulse width modulated. When a + side input signal is applied from the torque sensor 2 as shown at times t _{1 to} t ₂ in FIG. 5, the polarity determination circuit 13 determines the polarity and the drive logic circuit 18 outputs an AND signal. The "H" level signal is transmitted to the circuit 18a. Therefore, through the AND circuit 18a, the + side lower F
This pulse signal is transmitted to the ET driver 19. Similarly, via the photo coupler 21, the + side upper FET driver 23
Are continuously driven. Therefore, as shown in FIGS. 5 (c) and 5 (d), the FET 25 is continuously turned on, and the FET 27 is pulse-driven. Therefore, the steering motor 6 is pulse-driven as shown in FIG.

When the driver operates the steering wheel 1 so as to rotate it to the left, the torque sensor 2 produces a negative output as shown at times t _{3 to} t ₄ . In this case, − side lower FET
The FET 26 is continuously conducted by the driver 20, and the lower FET 28 is pulse-driven by the-side upper FET driver 24. Therefore, the steering motor 6 is supplied with a current as shown in FIG. The same operation is repeated after time t ₅ .

Here, when the steering wheel is left to operate until time t ₃ after the steering wheel is operated to the right from time t ₁ to t ₂ , the steering wheel 1 is operated. Even if the user does not intentionally operate and is lightly touching the ground, a slight signal may be generated in the torque sensor 2 due to unevenness or inclination of the ground. FIG. 7 is a waveform diagram showing the range between times t ₂ and t ₃ in an enlarged manner. As shown in this figure, even when a small level signal is generated in the torque sensor ₂ from time t ₂ to time t ₃ , a signal exceeding the first threshold value Vref1 which is the direct current component that determines the minimum level of the integrating circuit If the pulse width modulation signal does not occur, the pulse width modulation signal is not output. Also polarity determination circuit
Similarly, since 13 has hysteresis by resistors R10 and R11, the positive and negative threshold values Vr shown in FIG.
The polarity inversion signal is not output unless the range exceeds ef2 and Vref3. Therefore, even if a signal within this range is generated from the torque sensor 2, one FET for maintaining conduction, for example, the FET 25 is continuously turned on as shown in the figure, but the pulse driving FET is used.
No signal is generated at 27 and no current flows through the other FETs 26 and 28. Therefore, the steering motor 6 is not energized and does not become a load on the motor. Therefore, the direction of the drive wheels can be promptly returned to the neutral position with the handle left. Without such hysteresis, the motor is driven to the left and right in response to the signal from the torque sensor 2, so that the steering return is deteriorated.

In this embodiment, the minimum level of the triangular wave is defined by superimposing a constant voltage on the integrating circuit of the voltage comparing circuit, but the integrating circuit 16 may be superposed with a DC component by another method. It goes without saying that it is good. It goes without saying that the superimposed DC voltage and the threshold levels set above and below the polarity determination circuit 13 can be set independently.

Further, this embodiment is a pair of FETs which are continuously driven and pulse driven.
However, the switching element is not limited to the FET, and a power control element such as a power transistor may be used.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a motor drive circuit according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of an electric power steering mechanism to which a motor drive device according to the present embodiment is applied, and FIG. FIG. 4 is a circuit diagram showing a configuration of a bridge circuit portion of a motor drive circuit according to an embodiment of the present invention, FIG. 4 is a circuit diagram showing configurations of a polarity determination circuit and a voltage comparison circuit according to an embodiment of the present invention, and FIG. FIG. 6 is a waveform diagram showing the waveform of each part during normal operation, FIG. 6 is a waveform diagram showing the triangular wave and the full-wave rectified signal given to the voltage comparison circuit, and pulse modulation corresponding to each, and FIG. It is a waveform diagram which expands the waveform of each part in a case in time. 1 ... Steering handle, 2 ... Torque sensor, 3
...... Transmission mechanism, 4 …… Motor drive circuit, 6 …… Steering motor, 11 …… Torque input terminal, 13a, 13b, 14a ……
Operational amplifier, 19,20,23,24 …… FET driver, 25 …… Upper FET (first switching element), 26 …… Upper FET
(Third switching element), 27 ... lower FET (second switching element), 28 ... lower FET (fourth switching element), 29 ... continuity holding control section, 30 ... high speed switching control section

Claims (1)

(57) [Claims] 1. A motor drive device for an electric power steering system, comprising: a torque sensor connected to a steering shaft to detect a rotational torque of the steering shaft; and a steering motor for rotating a steering wheel. A first switching element, a second switching element for right steering high speed switching are connected symmetrically with respect to the steering motor, and a third switching element for maintaining left steering conduction and a fourth switching for left steering high speed switching. A bridge circuit configured by connecting elements symmetrically with respect to the steering motor; and when the absolute value output from the torque sensor exceeds a first threshold level, a pulse width signal corresponding to the output level is output. A high-speed switching controller for selectively providing the second or fourth switching element; The left and right steering torque detection signals from the sensor are given as positive and negative torque signals respectively, and a polarity judgment signal that inverts the output when the absolute values exceed the positive and negative symmetrical second and third threshold values is output. Including a polarity determination circuit to
And a conduction holding control section for selectively conducting the first or third switching element based on the output of the polarity determination circuit.