JPH065942Y2 - 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 wheel of a vehicle by a steering motor.

[Prior art and its problems]

(Prior Art) As disclosed in Japanese Patent Laid-Open No. 59-156863, a conventional motor drive device for an electric power steering system has first, second, third, and fourth electrical connections that are conducted during steering in the left-right direction. It is connected as a bridge circuit centering around the steering motor using a control element such as a transistor. 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 in the motor, and at the time of left steering, 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, if a strong steering force is applied when the steering wheel is locked or the like, the load on the steering is large, so that an excessive current flows to the motor. If the motor is short-circuited, an excessive current will flow through the switching element. If the battery is disconnected from the battery terminals while the engine is rotating and the battery is being charged, a large voltage is generated and an excessive current flows through the motor and the switching element. In addition, since the motor is started in a cold region or the like, there is a drawback that an excessive current may flow through the motor even when the motor is started by raising the power supply voltage.

Generally, a relatively large current of, for example, about several tens of amperes is controlled by a switching element, and the
As shown in the figure, it is widely practiced to connect a current detection resistor R0 in series with a switching element such as an FET and detect a drive current based on the voltage across the resistor.

(Problems to be solved by the invention) Therefore, it is conceivable to connect a resistor in series with the steering motor, detect the current flowing through the motor by the change in the resistance value, and prevent an excessive current from flowing through the motor. However, if an attempt is made to detect the current based on the voltage change of the resistor connected in series with the switching element,
When a large current flows, a voltage drop occurs across the resistance. In a vehicle, the power supply voltage is limited to, for example, 12 V, so that when it is used to control a steering motor or the like, the voltage supplied to the load becomes low. There is also a problem that heat is generated due to a voltage drop generated in the resistor, resulting in a large power loss.

[Purpose of device]

The present invention has been made in view of the problems of such a motor drive device, and it is a technique to detect a drive current of a motor without using a series resistor without causing a voltage drop or heat generation. Subject.

[Constitution and effect of device]

(Means for Solving Problems) The present invention is a motor drive device for an electric power steering system, which includes a torque sensor connected to a steering shaft to detect a rotational torque of the steering shaft, and a steering motor for rotating the steering wheel. As shown in FIGS. 1 and 3, the first switching element for maintaining the right steering conduction and the second switching element for the right steering high speed switching are connected symmetrically with respect to the steering motor, and the left steering conduction is established. For detecting the left and right steering torques obtained from the torque sensor and a bridge circuit configured by connecting the third switching element for holding and the fourth switching element for high speed left steering switching symmetrically with respect to the steering motor. Based on a continuity holding control unit that selectively conducts the first or third switching element based on the torque sensor. A high-speed switching controller that selectively supplies a signal having a pulse width corresponding to the output level to the second or fourth switching element based on the output of the first switching element, the first switching element, the third switching element, the second switching element, and the fourth switching element. Of the switching elements, and fifth and sixth switching elements that are driven in parallel with the switching elements connected in parallel, and are connected in series 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 connected in parallel with each other. is there.

(Operation) According to the present invention having such a feature, the fifth, sixth, and sixth switching elements for power control, which are connected in series to the steering motor, are connected in parallel to each other.
The switching element and the current detection resistor are provided, and current detection is required when driving these switching elements, so the fifth and sixth switching elements are 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.

(Effect of the Invention) Therefore, according to the present invention, it is not necessary to connect the resistor in series with the steering motor and the power control switching element. Therefore, the voltage applied to the steering motor does not decrease and the power loss can be improved. Moreover, since almost no current flows through the voltage detecting resistor, no unnecessary power is consumed and power efficiency can be improved.

[Explanation of Examples]

(Structure of Embodiment) FIG. 2 is a schematic view of a power steering mechanism applied to the present invention, and FIG. 3 is a block diagram showing an overall 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 that becomes positive when rotating in the right direction and becomes negative when rotating in the left direction, and the output is entirely output via the input terminal 11. It is transmitted to the wave rectification circuit 12 and the polarity determination circuit 13. The full-wave rectifier circuit 12 full-wave rectifies the input signal and supplies it to the voltage comparison circuit 14. 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 given to an integrating circuit 16 and a DC-DC converter 17. The integrating circuit 16 integrates the 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 the triangular wave as a reference voltage, it outputs as a pulse signal with which the level change duty of the torque sensor 2 changes, and its output is given to the drive logic circuit 18. To be 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, 1
8b, and selectively applies a pulse width modulated signal obtained from the voltage comparison circuit 14 based on the positive or negative polarity determination output to the + side lower FET driver 19 or the − side lower FET driver 20. Is. In addition, the polarity determination circuit 13 determines whether the AND circuit 18a, 1a has a positive or negative polarity determination.
8b and the photocouplers 21 and 22 are selectively provided with signals. The photocouplers 21 and 22 respectively drive the + side upper FET driver 23 and the − side upper FE when driven.
The T driver 24 is driven. FET drivers 23 and 24
Is for driving the right and left upper FETs 25 and 26 based on the output from the photocoupler 21 or 22, respectively, and the FET drivers 19 and 20 are for driving the right and left lower FETs 27 and 28, respectively. Here, the "upper" indicates the side closer to the power supply terminal of the motor drive circuit 4, and the "lower" indicates the FET farther from the power supply terminal. Further, “+” and “−” shown in the FET drivers 19, 20, 23 and 24 correspond to the positive voltage or the negative voltage determined by the polarity determination circuit 13. FET25〜
28 is a switching element composed of a power MOSFET, respectively, and FETs 25 and 27 constitute first and second switching elements that conduct when operated in the right direction, and FETs 26 and 28 are operated in the left direction. It constitutes the third and fourth switching elements that conduct. The FETs are connected in a bridge circuit, and the steering motor 6 is connected in the middle between the FETs via terminals 4a and 4b. The lower FETs 27 and 28 are connected to current detection circuits 29 and 30 that detect the current when they are conductive, and the output thereof is given to an overcurrent breaker 31. The overcurrent breaker 31 cuts off the current when an excessive current flows through the steering motor 6. Both positive and negative ends of the vehicle battery 5 are connected to the power input terminals 4c and 4d via an ignition switch (not shown). Here, the DC-DC converter 17, the polarity determination circuit 13, the photocoupler 21, the + side and-side upper FET drivers 23, 24 are the first or the third based on the detection of the left and right steering torques obtained by the torque sensor.
Continuity holding unit 3 for selectively conducting the switching element of
Make up 2. Also, a full-wave rectifier circuit 12, a voltage comparison circuit 14, a square-wave oscillator circuit 15, an integrating circuit 16 and a drive logic circuit 18, a + side and-side lower FET driver 1
9 and 20 constitute a high-speed switching control unit 33 which selectively supplies a signal having a pulse width corresponding to the output level of the torque sensor 2 to the first or third switching element based on the output from the torque sensor 2.

Next, a circuit configuration of an FET bridge in which four FETs are bridge-connected 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 connected to the drains of the FETs 28 and 27, respectively. Also F
The steering motor 6 is connected to the common connection ends of the ETs 25 and 28 and the FETs 26 and 27 through motor connection terminals 4a and 4b, and the source ends of the FETs 27 and 28 are grounded. In the figure, a surge absorbing circuit composed of a diode and a Zener diode is connected between the drain and gate of each FET 25 to 28, and a flywheel diode is connected between the drain and source.

Current detection circuits 29 and 30 connected to the FETs 27 and 28
Are transistor Tr1, resistor R1 and transistor Tr2 respectively.
And resistor R2. Transistors Tr1 and Tr2
Has a collector terminal connected to the drains of the FETs 27 and 28, and a base connected to the control input terminals of the + side and-side lower FET drivers 19 and 20 through resistors R3 and R4. The emitter resistors R1 and R2 having the same resistance value are used for the emitters.
Are connected to each other, and the resistor R5 is further connected by the emitter.
They are commonly connected via R6 and given to the overcurrent breaker 31 as a current detection signal. The overcurrent breaker 31 has a resistance R
A comparator 34 formed of an operational amplifier in which a threshold value of a predetermined level is set by voltage division of 7 and R8, a diode D1 for holding an output and a resistor R9 are connected between the input and output ends thereof. The output of the comparator 34 is the resistance R10.
Is given to the transistor Tr3 via. Transistor T
r3 is a switching transistor, and its collector is connected to the main switch 35 via a relay coil X. The transistor Tr3 is always turned on when the main switch 35 is turned on, and is controlled to be turned off when the output is inverted by the signal from the comparator 34 at a predetermined threshold level or higher. Relay X is FET2
5 to 28 controls the power supply of the bridge circuit, and the power is supplied from the battery 5 via the relay contact Xa.
It is connected to the drains of ETs 25 and 26.

(Operation of Embodiment) Next, the operation of this embodiment will be described. First, since a constant voltage is applied to the base of the transistor Tr3 when the power is turned on, when the main switch 35 shown in FIG. 1 is turned on, the transistor Tr3 is turned on and the relay coil X is excited. Therefore, the normally open contact Xa of the relay X is closed, and power is supplied to the upper 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, a change in the torque is detected by the torque sensor 2 and given to the motor drive circuit 4. FIG. 4 is a waveform diagram showing the waveform of each part of the motor drive circuit 4. Fourth
When a signal from the torque sensor 2 as shown in FIG. 4A is transmitted, it is full-wave rectified by the full-wave rectification circuit 12 as shown in FIG. Further, since the square wave signal of the square wave oscillator 15 is converted into a triangular wave through the integrating circuit 16 and transmitted to the voltage comparator 14,
The voltage comparison circuit 14 produces a signal having a pulse width corresponding to the voltage level, 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 time t ₂ , the polarity determination circuit 13 determines the polarity and the AND circuit 18 a of the drive logic circuit 18 indicates “ An H "level signal is transmitted. Therefore, through the AND circuit 18a, the + side lower FET driver 1
This pulse signal is transmitted to 9. Similarly, the + side upper FET driver 23 is continuously driven through the photocoupler 21. Therefore, as shown in FIGS. 4 (c) and 4 (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. 4 (g).

When the output from the torque sensor 2 as shown at time t ₃ ~t ₄ is negative side, the same way - by the side lower FET driver 20 FET 26 is continuously conductive - side upper F
The lower FET 28 is pulse-driven by the ET driver 24. Therefore, the steering motor 6 is supplied with a current as shown in FIG. FET27,28 here
At the same time, the transistor Tr1 or Tr2 is similarly pulse-driven by the + side and-side lower FET drivers 19 and 20. Since the voltage across the FET 27 or 28 corresponds to the change in the current flowing through each FET, the current flowing through the FET 27, 28 can be detected by reading the voltage change across the resistor R1 or R2. The detected current is given to the overcurrent breaker 31.

Even if an extremely large current, for example, a large current of about 100 A, flows through the FETs ₂₅ and 27 at time t5 due to some accident, the current value is detected as a change in voltage, and the signal corresponding to this current is the overcurrent breaker. Given to 31. When the output exceeds the predetermined threshold level Verf set in the comparator 34, the transistor Tr3 is turned off by the output of the comparator 34 as shown in FIG. 4 (h). Then, the energization of the relay coil X is stopped, so that the normally open contact Xa of the relay X is opened and the power supply voltage supplied to the FETs 25 to 28 is cut off. Therefore, it is possible to prevent an accident in which an abnormal current flows to the steering motor 6 and the motor is burned or the switching FETs 25 to 28 are damaged.

In this embodiment, a pair of FETs that are continuously driven and pulse-driven are used.
A current detection circuit is provided in parallel with the pulse-driven FET of the bridge circuit composed of the above, and the current flowing therethrough is measured. However, the FET that is continuously driven is parallel to the FETs 25 and 26 in this embodiment. It goes without saying that a similar current detection circuit may be connected to the. The switching element is not limited to the FET, and 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, in addition to the transistor shown in this embodiment, F
A switching element such as ET may be used. 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 circuit diagram showing a configuration of a bridge circuit portion of a motor drive circuit according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of an electric power steering mechanism to which a motor drive device of the present invention is applied. FIG. 3 is a block diagram showing the configuration of the motor drive circuit of this embodiment, FIG. 4 is a waveform diagram showing the waveform of each part, and FIG. 5 is a conventional power control element and is inserted to measure its current. It is a circuit diagram which shows a current detection resistance. 1 ... Steering handle, 2 ... Torque sensor, 3
...... Transmission mechanism, 4 ...... Motor drive circuit, 6 ...... Steering motor, 11 ...... Torque input terminal, 19, 20, 2
3,24 ... 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, 30 ... current detection circuit, 3
1 ... Overcurrent breaker, 32 ... Continuity holding control unit, 33 ...
… High-speed switching controller, 34 …… Comparator, Tr1 ……
Switching transistor (fifth switching element), Tr2 ... Switching transistor (sixth switching element)

Claims (1)

[Scope of utility model registration request] 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 element for left steering high speed switching. A bridge circuit configured by connecting elements symmetrically with respect to the steering motor, and selectively conducting the first or third switching element based on detection of left and right steering torques obtained by the torque sensor. And a continuity holding control unit for controlling the output level based on the output from the torque sensor. And fast switching control unit to provide a pulse width of the signal selectively to the second or fourth switching element, and the first, third switching element, the second, fourth
Of the switching elements, and the fifth and sixth switching elements, which are driven in parallel with the switching elements connected in parallel, and the fifth and sixth switching elements, respectively. A pair of current detection means having a current detection resistor for detecting a current flowing through the first, third or second and fourth switching elements connected in series and connected in parallel. Motor drive device.