JP2540149B2 - 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]

(Prior Art) A motor drive device for a conventional electric power steering is
As disclosed in Japanese Patent Laid-Open No. 59-156863, a bridge centering around a steering motor is formed by using control elements such as first, second, third and fourth transistors which are electrically connected when steering in the left and right directions. Connected as a circuit. Then, when steering to the right, the first and second transistors are simultaneously turned on based on the detection of the steering torque to allow a positive drive current to flow through the motor, and during steering to the left, the third and fourth transistors are detected based on the detection of the steering torque. Are simultaneously conducted, and a drive current in the opposite direction is supplied to the motor for control. In driving such a motor, the motor is controlled by a signal from the torque sensor and feedback based on the load is not applied.

(Problems to be Solved by the Invention) As described above, since the steering motor is controlled based on the signal from the torque sensor, if the load of the steering motor is heavy, the rotation speed of the steering motor is significantly reduced. Therefore, there is a problem that the steering torque is not stable because the steering wheel rotates rapidly if the steering wheel rotation is delayed or the load is lightened.

[Object of the Invention]

The present invention has been made in view of the problems of such a motor drive device, and it is possible to drive a steering motor with a constant torque based on the output of a torque sensor that detects the drive current of the motor and the torque of the steering wheel. Is a technical issue.

[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. , Fig. 1, Fig. 3 and Fig. 4
As shown in the figure, the first switching element for high speed right steering switching and the second switching element for maintaining right steering continuity are connected symmetrically with respect to the steering motor, and the third switching element for high speed left steering switching is connected. Element, a fourth switching element for maintaining left steering continuity, which is symmetrically connected to a steering motor, and a second or fourth bridge circuit based on detection of left and right steering torques obtained from a torque sensor. Continuity holding control section which selectively conducts the switching elements of, the first, third switching elements, and the second and fourth switching elements are selectively connected in parallel and connected in parallel. The fifth and sixth switching elements, which are driven simultaneously with the switched switching elements, and are connected in series and in parallel to the fifth and sixth switching elements, respectively. And a pair of current detecting means having a current detecting resistor for detecting a current flowing through the first, third or second and fourth switching elements, and a difference value between signals of current signals detected by the pair of current detecting means. To calculate and output as a signal with different polarity depending on the rotation direction of the motor.
Differential amplifier, a second differential amplifier for amplifying a difference between the current signal output from the first differential amplifier and the output from the torque sensor, and the second differential amplifier based on the output of the second differential amplifier. And a high-speed switching control unit that selectively applies a signal having a pulse width corresponding to the output level to the first or third switching element.

(Operation) According to the present invention having such a feature, the fifth, sixth switching elements connected in series to the steering motor for power control are connected in parallel with the first, third or second, and fourth switching elements, respectively. Since a switching element and a current detection resistor are provided and current detection is required when driving these switching elements,
The sixth switching element is closed at the same time. Then, the voltage across the switching element for power control changes according to the current flowing through the switching element. Therefore, the load current is detected as a voltage change across the current detecting resistor. Then, by differentially amplifying the current value of the motor as the load current by the first differential amplifier, it can be detected as a voltage signal that changes positively or negatively according to the rotation direction of the steering motor. The difference between this current signal and the output from the torque sensor is detected by the second differential amplifier, and PWM control is performed by the second differential amplified output to control the energization of the motor.

(Effect of the Invention) Therefore, according to the present invention, the current flowing in the motor is fed back, and the difference from the voltage from the torque sensor is given to the high-speed switching control unit to become the motor drive current. Therefore, the steering motor is driven with the torque corresponding to the output from the torque sensor. Therefore, regardless of the load, the steering motor can be driven with a torque that faithfully corresponds to the signal from the torque sensor, and the feeling of steering operation can be improved.

[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 the figure, the torque detection signal from the torque sensor 2 is a signal of a level corresponding to the torque which becomes positive when rotating to the right and becomes negative when rotating to the left, and is a signal of the second level via the input terminal 11. It is provided to the differential amplifier 12. The differential amplifier 12 is provided with an output from a first differential amplifier 13 that amplifies a difference between currents flowing through a pair of switching elements, which will be described later. The differential amplifier 12 transmits these output differences to the full-wave rectification circuit 14 and the polarity determination circuit 15. The full-wave rectifier circuit 14 full-wave rectifies the input signal and supplies it to the voltage comparison circuit 16. Further, the motor drive circuit 4 is provided with an oscillating circuit 17 for oscillating a square wave having a constant frequency, for example, 20 KHz, and its output is given to an integrating circuit 18 and a DC-DC converter 19. The integrating circuit 18 integrates this square wave signal and converts it into a triangular wave, and supplies its output to the voltage comparing circuit 16 as a reference voltage. Since the voltage comparison circuit 16 compares the output of the full-wave rectification circuit 14 with the triangular wave as a reference voltage, it outputs the level change of the differential amplifier 12 as a pulse signal whose duty changes, and its output is the drive logic circuit 20.
Given to. The drive logic circuit 20 is also supplied with the polarity determination output of the polarity determination circuit 15. The drive logic circuit 20 has AND circuits 20a and 20b, and outputs a pulse width modulated signal obtained from the voltage comparison circuit 16 based on the positive or negative polarity determination output to the + side upper FET driver 21.
Alternatively, it is selectively given to the − side upper FET driver 22. The polarity determination circuit 15 selectively gives a signal to the AND circuits 20a, 20b and the photocouplers 23, 24 by positive or negative polarity determination. The outputs of the photocouplers 23 and 24 are given to the + side lower FET driver 25 and the-side lower FET driver 26, respectively. The FET drivers 21 and 22 drive the right and left upper FETs 27 and 28, respectively.
Reference numerals 5 and 26 respectively drive the right and left lower FETs 29 and 30 based on the output from the photocoupler 23 or 24, respectively. Here, “upper” means the side closer to the power supply terminal of the motor drive circuit 4, and “lower” means the FE farther from the power supply terminal.
Shows T. Further, “+” and “−” shown in the FET drivers 21, 22, 25 and 26 correspond to the positive voltage or the negative voltage judged by the polarity judging circuit 15. The FETs 27 to 30 are switching elements each composed of a power MOSFET, and the FETs 27 and 29 are the first and second FETs that conduct when operated rightward.
The FETs 28 and 30 constitute third and fourth switching elements which are conducted when operated in the leftward direction. 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. The lower FETs 29 and 30 are respectively connected to current detection circuits 31 and 32 that detect the current when the FETs are conductive, and the outputs thereof are given to the above-mentioned differential amplifier 13. The differential amplifier 13 amplifies the output difference of these current detection signals, and supplies the output to one input end of the differential amplifier 12. Here, the DC-DC converter 19, the polarity determination circuit 15, and the photocouplers 23, 24, + side and-side lowers.
The FET drivers 25 and 26 configure a conduction holding unit 33 that selectively conducts the second or fourth switching element based on the detection of the left and right steering torques obtained from the differential amplifier 12. Full wave rectifier circuit 14, voltage comparison circuit 16, square wave oscillator circuit
17, the integrator circuit 18 and the drive logic circuit 20, the + side and-side upper FET drivers 21, 22 generate a pulse width signal corresponding to the output level of the first or third side based on the signal from the differential amplifier 12. The high-speed switching control unit 34 that selectively applies to the switching elements is configured.

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 27 and 28 are connected to the positive terminal of the battery 5 via a relay circuit, and the source terminals thereof are respectively FET3.
Connected to the drains of 0 and 29. Also, the motor connection terminals 4a, 4b are provided at the common connection ends of the FETs 27, 30 and the FETs 28, 29.
The steering motor 6 is connected via the, and the source ends of the FETs 29 and 30 are grounded. In this figure, each FET 27-30
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.

The current detection circuits 31 and 32 connected to the FETs 29 and 30 are composed of a transistor Tr1 and a resistor R1, respectively, and a transistor Tr2 and a resistor R2. The collector ends of the transistors Tr1 and Tr2 are F
The bases are connected to the drains of the ETs 29 and 30 through resistors R3 and R4 and to the voltage control input terminals of the + and − side lower FET drivers 25 and 26. Further, emitter resistors R1 and R2 having the same resistance value are respectively connected to the emitters, and further, respective emitter terminals are connected to the differential amplifier 13.

FIG. 4 is a circuit diagram showing the configuration of the differential amplifiers 12 and 13. In the figure, the differential amplifier 13 includes transistors Tr1 and Tr2.
Is formed by an operational amplifier 13a connected to the non-inverting input terminal and the inverting input terminal via resistors R5 and R6, respectively, and a feedback resistor R7 is connected to the output terminal and the inverting input terminal thereof. The differential amplifier 13 detects the forward and reverse rotations of the motor by outputting the difference between these voltages, and corresponds to the current value flowing in the steering motor 6 in the positive direction when rotating to the right and in the negative direction when rotating to the left. It outputs the signal. The output of the differential amplifier 13 is given to the inverting input terminal of the differential amplifier 12 via the resistor R8. The differential amplifier 12 is composed of an operational amplifier 12a in which the signal from the torque sensor 2 given from the input terminal 11 is connected to the non-inverting input terminal via the changeover switch 35a. A feedback resistor R9 and a capacitor C1 are connected between the output terminal and the inverting input terminal of the differential amplifier 12 to smooth the signal of the steering motor 6 which is pulse-driven and to provide its differential output to the switch 35b. The switches 35a and 35b are interlocking switches, and switch between whether the input of the high speed switching control unit 34 is the input from the torque sensor 2 or the output of the differential amplifier 12.

(Operation of Embodiment) Next, the operation of this embodiment will be described with reference to the waveform charts of FIGS. 5 and 6. Upper FE when power is turned on
Power is supplied to T27, 28. The square wave oscillator circuit 17 oscillates a square wave signal of 20 KHz, for example. Here, it is assumed that the switch 35 is switched so that the output of the differential amplifier 12 is applied to the input terminal of the full-wave rectifier circuit 14. When the driver operates the steering wheel 1, a change in the torque is detected by the torque sensor 2 and given to the motor drive circuit 4. 5 and 6 are waveform charts showing waveforms at various parts of the motor drive circuit 4. When a signal from the torque sensor 2 as shown in FIG. 5 (a) is transmitted, the output of the differential amplifier 13 is at zero level because no current is flowing through the steering motor 6 at the start of the operation. Therefore, as shown in FIGS. 5B and 5C, the output from the torque sensor 2 is directly transmitted to the full-wave rectifier circuit 14 via the differential amplifier 12. Then, as shown in FIG. 5D, the signal is full-wave rectified and given to the voltage comparison circuit 16. Further, the square wave signal of the square wave oscillating circuit 17 is converted into a triangular wave via the integrating circuit 18 and transmitted to the voltage comparing circuit 16. Therefore, the voltage comparison circuit 16 produces a signal having a pulse width corresponding to the voltage level of the torque sensor 2, and the pulse width is modulated. Here, when a + side input signal is given from the torque sensor 2 as shown from time t _{1 to} t ₂ ,
The polarity determination circuit 15 determines the polarity, and the “H” level signal is transmitted to the AND circuit 18a of the drive logic circuit 20. Therefore, this pulse signal is transmitted to the + side upper FET driver 21 via the AND circuit 20a. Similarly, the + side lower FET driver 25 is continuously driven through the photocoupler 23. Therefore, as shown in FIGS. 5 (e) and 5 (f), the FET 27 is pulse-driven and the FET 29 is continuously turned on. Therefore, as shown in FIG. 5 (i), the steering motor 6 is pulse-driven.

At the same time when driving FET 29, the + side lower FET driver
The transistor Tr1 is driven by 25. And FET29
The voltage across FET2 corresponds to the change in current flowing through FET29, so by reading the voltage change across R1
The current flowing in 9 can be detected. The current detection signal flowing through the steering motor 6 thus detected is given to the differential amplifier 13. Therefore, the fifth from the differential amplifier 13
A signal as shown in FIG. 3B is output and transmitted to the differential amplifier 12. Therefore, the output of the differential amplifier 12 is shown in FIG.
Since it changes as shown in FIG. 2 and is transmitted to the full-wave rectification circuit 14, a current corresponding to the torque level of the torque sensor 2 can be supplied to the motor.

When the output from the torque sensor 2 as shown at time t ₃ ~t ₄ is negative, the FIG. 5 in the same manner as (g), (h)
As shown in, the − side upper FET driver 22 pulse-drives the FET 28, and the − side upper FET driver 26 continuously drives the lower FET 30. Therefore, the steering motor 6 is supplied with a current as shown in FIG. Also in this case, since the transistor Tr2 is simultaneously driven when the FET 30 is driven, the voltage across the FET 30 corresponds to the change in the current flowing therethrough. Therefore, the voltage change across the resistor R2 is read by the voltage detection circuit 32 and applied to the differential amplifier 13. Therefore, a signal as shown in FIG. 5 (b) is given from the differential amplifier 13 to the differential amplifier 12, and its full-wave rectified output is transmitted to the high speed switching controller. In this way, current feedback is applied via the differential amplifier 13 according to the value of the current flowing through the motor. FIG. 6 is a waveform diagram showing the waveform of each part corresponding to the output from the torque sensor 2 which is the same as in FIG. 5 when the load is heavy. As shown in this figure, the output of the differential amplifier 13 has a larger amplitude and a higher peak value than that in the case of FIG. Therefore, when this output is smoothed by the differential amplifier 12 to obtain a differential output, a low level signal is obtained as shown in FIG. 6 (c). Then, this signal is applied to the voltage comparison circuit 16 and the FET 27 is pulse-lighted. At this time, since the load of the steering motor 6 is heavy, a current having a high peak value flows in each cycle as shown in FIG. 6 (b), but the difference from the output of the torque sensor 2 is given to the differential amplifier 13 and smoothed. Voltage comparison circuit to obtain dynamic output
The input signal provided to 16 will be small. Therefore, as shown in FIG. 6 (e), the driving time of the FET 27 is shorter than that shown in FIG. The current flowing through the steering motor by integrating this current has almost the same value as in the case shown in FIG.

Now, FIG. 7 is a diagram showing changes in the smoothed current flowing through the steering motor 6 with respect to the rotation speed of the motor.
In this figure, V _{i1 to} V _i3 are voltage values from the torque sensor 2 when the steering handle is rotated to the right, and V _{i4 to} V _i6 are the same when the steering handle is rotated to the left. It is an output voltage value from the torque sensor 2, and shows a change in the current of the steering motor 6 with respect to each voltage value V _{i1 to} V _i6 . As shown in the figure, in this embodiment, the currents of the lower FETs 29 and 30 are detected and the differential amplifiers 13 and 12 are detected.
Since the negative feedback is applied to the input voltage via the input voltage, the current value flowing through the steering motor 6 becomes constant if the voltage from the torque sensor 2 is constant as described above, and only the rotation speed of the steering motor varies depending on the load. Will be different. Since the torque of the motor obtained by the voltage from the torque sensor 2 is constant regardless of the load state, it has a constant current, that is, a constant torque characteristic, and the operating wheel can be rotated as the driver desires. If such feedback control is not performed for this,
As shown in FIG. 8, the current flowing through the steering motor and the rotational speed are in an inversely proportional relationship, and the current flowing through the steering motor 6, that is, the torque is significantly different depending on the load state even if the output from the same torque sensor is used. Become. Therefore, it is effective to perform feedback control in order to faithfully reflect the driver's will.

Note that this embodiment is a pair of FETs that are continuously driven and pulse-driven.
The current detection circuit is provided in parallel with the continuously driven FET of the bridge circuit consisting of, and the current flowing therethrough is measured.
It goes without saying that a similar current detection circuit may be connected in parallel to the ETs 27 and 28. In addition, FET as a switching element
However, a power control element such as a power transistor may be used. Further, as the switching element of the current detection circuit connected in parallel to the power control switching element, a switching element such as FET may be used in addition to the transistor shown in this embodiment. In this case as well, the current can be measured by opening and closing the switching element for controlling electric power provided at the same time.

[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 a differential amplifier and a feedback circuit, and FIG. 5 is an operation when a load of a steering motor is light. 6 is a waveform diagram showing the waveforms of the respective portions, FIG. 6 is a waveform diagram showing the waveforms of the respective portions when the load of the steering motor is heavy, and FIG. 7 is the rotation speed and current of the steering motor with respect to the input from the torque sensor of this embodiment. And FIG. 8 is a graph showing the relationship between the motor speed and the motor current when the negative feedback control according to the present invention is not performed. 1 ... Steering handle, 2 ... Torque sensor, 3
...... Transmission mechanism, 4 …… Motor drive circuit, 6 …… Steering motor, 11 …… Torque input terminal, 12,13 …… Differential amplifier, 14 …… Full wave rectification circuit, 16 …… Voltage comparison circuit, 21 , 2
2,25,26 …… FET driver, 27 …… Upper FET (first switching element), 28 …… Upper FET (third switching element), 29 …… Lower FET (second switching element), 30 ...... Lower FET (fourth switching element), 31,
32 ... Current detection circuit (current detection means), 33 ... Continuity holding control section, 34 ... High-speed switching control section, Tr1 ... Switching transistor (fifth switching element), Tr
2 ... Switching transistor (sixth switching element)

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. 1 switching element,
The second switching element for holding the right steering conduction is connected symmetrically to the steering motor, and the third switching element for high speed left steering switching and the fourth switching element for holding the left steering conduction are connected to the steering motor. A bridge circuit configured to be symmetrically connected to each other, and a conduction holding control unit that selectively conducts the second or fourth switching element based on detection of left and right steering torques obtained from the torque sensor. And a fifth switching element that is selectively connected in parallel to one of the first and third switching elements and one of the second and fourth switching elements and that is driven simultaneously with the switching elements connected in parallel. A sixth switching element, and the first, third or second and fourth switches connected in series and in parallel to the fifth and sixth switching elements, respectively. A pair of current detecting means having a current detecting resistor for detecting a current flowing through the driving element, and a difference value between the signals of the current signals detected by the pair of current detecting means is calculated, and the polarity is determined according to the rotation direction of the motor. A first differential amplifier that outputs different signals, a second differential amplifier that amplifies a difference between the current signal output from the first differential amplifier and the output from the torque sensor, 2. A high-speed switching control unit that selectively supplies a signal having a pulse width corresponding to the output level of the differential amplifier 2 to the first or third switching element. Drive.