JPS63247165A - Motor driving device - Google Patents

Abstract

PURPOSE:To simplify structure and improve reliability by detecting the driving current of a motor using series resistances without causing voltage drop or heat generation and, when a defined current flows, lowering a current flowing in said motor. CONSTITUTION:First to fourth switching elements which conduct at the time of operating in right-left directions are formed with pairs of upper and lower FET's 25-28 respectively, while mutually connecting each of which by bridge circuits to connect a steering motor 6 via terminals 4a, 4b. And, current detecting circuits 29, 30 are connected to the lower FET's 27, 28 respectively and their outputs are given to a comparator 31. The comparator 31 gives its compared output to a delay timer 32 when a current value is above a defined value. Further, the delay timer 32 gives its output to a control signal output part 33 when the signals is continuously given for a defined time. On the other hand, the control signal output part 33 gives control signals which are gradually lowered to a voltage comparing circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [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 shown in Japanese Patent Application No. 59-156863, a conventional electric power steering motor drive device has a first motor drive device which is electrically connected during left and right steering. 2nd and 3rd. The steering motor is connected as a bridge circuit using a control element such as a fourth transistor.

When steering to the right, the first control is performed based on the detection of the steering torque.
The second transistor is made conductive at the same time to supply a positive driving current to the motor, and when steering to the left, the third transistor is turned on based on the detection of the steering torque. The fourth transistor is made conductive at the same time to flow a drive current in the opposite direction to the motor for control.

Such a motor drive has the disadvantage that when a strong steering force is applied, such as when the steering wheel is locked, the load on the steering is large and an excessive current flows through the steering motor.

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

(Problems to be Solved by the Invention) Therefore, it is conceivable to connect a resistor in series with the steering motor and detect the current flowing through the motor based on a change in the resistance value to prevent excessive current from flowing through the motor. However, if the power supply to the steering motor is immediately stopped when a predetermined overcurrent is exceeded, the steering wheel suddenly becomes heavy, which is rather inconvenient. Furthermore, if an attempt is made to detect the current flowing through the steering motor based on voltage changes in a resistor connected in series with a switching element, a voltage drop will occur across the resistor when a large current flows. In a vehicle, the power supply voltage is limited to, for example, 12V, so when used to control a steering motor or the like, there is a drawback that the voltage supplied to the load becomes low. There is also the problem that heat is generated due to the voltage drop that occurs in the resistor, resulting in increased power loss. Furthermore, if the excessive current flowing through the motor is left unattended, there is a problem in that the switching element that burns out the motor may be damaged.

[Purpose of the invention]

The present invention has been made in view of these problems with motor drive devices, and detects the drive current of the motor without using a series resistor and without causing voltage drop or heat generation, and allows a predetermined current to flow. In some cases, the technical challenge is to gradually reduce the current flowing through the motor after a certain period of time.

[Structure and effects of the invention]

(Means for Solving the Problems) The present invention provides a motor drive device for electric power steering, which includes a torque sensor connected to a steering shaft and detects its rotational torque, and a steering motor that rotates the steering wheel. , as shown in FIGS. 1, 3, and 4, a first switching element for right steering continuity maintenance and a second switching element for right steering high-speed switching are connected symmetrically to the steering motor. , a bridge circuit configured by connecting a third switching element for maintaining left steering continuity, and a fourth switching element for left steering high-speed switching symmetrically to the steering motor, and left and right steering obtained from a torque sensor. a conduction maintenance control section that selectively makes the first or third switching element conductive based on torque detection; a high-speed switching control section that selectively applies switching to the switching elements of the first to fourth switching elements; a third switching element; a second switching element; 5th and 6th switching elements that are alternatively connected in parallel to either one of the fourth switching elements and driven simultaneously with the parallel-connected switching elements;
and the fifth. The first switching elements are connected in series and in parallel to the sixth switching element, respectively. Third or second. a pair of current detection means having a current detection resistor for detecting the current flowing through the fourth switching element; a comparison means for detecting a filtered current when the output of the pair of current detection means is given and exceeds a predetermined dark value; A device characterized in that it has a delay timer that delays the output of the comparison means for a certain period of time, and a control signal output section that provides the output of the delay timer and gives a control signal that gradually decreases after a predetermined period of time to the high-speed switching control section. It is.

(Function) According to the present invention having such characteristics, the first motor for power control connected in series to the steering motor. Third or second. The fifth switching element is connected in parallel with the fourth switching element. 6th
5. Switching elements and current detection resistors 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 depending on the current flowing through the switching element.

Therefore, the load current is detected as a voltage change across the current detection resistor and is provided to the comparison means. When the load current exceeds a predetermined threshold, a control signal that gradually decreases is given to the high-speed switching control section after a certain period of time determined by a delay timer, instead of the signal from the torque sensor, to gradually reduce the motor drive current. I am trying to lower it to .

(Effects of the Invention) Therefore, according to the present invention, there is no need to connect a resistor in series with the steering motor and the switching element for power control.Therefore, the voltage applied to the steering motor does not drop and power loss is reduced. In addition, since almost no current flows through the voltage detection resistor, there is no wasted power consumption, and power efficiency can be improved.And when excessive current flows to the steering motor, Since the power supply to the steering motor is gradually reduced over a predetermined period of time, even if the steering wheel locks, the driver does not feel an unnatural operation caused by a sudden increase in load, and the steering motor is Burnout and switching element burnout can be prevented.

[Explanation of Examples]

(Configuration of Embodiment) FIG. 2 is a schematic diagram of a power steering mechanism to which the present invention is applied, and FIG. 1 is a block diagram showing the overall configuration of its motor drive circuit. In FIG. 2, a torque sensor 2 and a transmission mechanism 3 for transmitting a steering force from a steering handle 1 are connected to a steering handle 1. The torque sensor 2 detects the torque of the steering wheel 1 in the left and right direction, and its output is given to the motor drive circuit 4. The motor drive circuit 4 is connected to a battery 5 of the vehicle, and controls a steering motor 6 that drives in the left-right direction in response to a left-right torque signal given from the torque sensor 2. The steering wheel 7 is rotated by a predetermined angle in the left-right direction.

Next, the configuration of the motor drive circuit 4 will be explained with reference to FIG. In this figure, the torque detection signal from the torque sensor 2 is a signal with a level corresponding to the torque that is positive when rotating to the right and negative when rotating to the left, and the output is fully output via the input terminal 11. The signal is transmitted to the wave rectifier circuit 12 and the polarity determination circuit 13. The full-wave rectifier circuit 12 performs full-wave rectification on the input signal and supplies it to the voltage comparison circuit 14 . Further, this motor drive circuit 4 is provided with an oscillation circuit 15 that oscillates a square wave of a constant frequency, for example, 20 KHz, and the output thereof is given to an integration circuit 16 and a DC-DC converter 17.

The integrating circuit 16 integrates this square wave signal and converts it into a triangular wave, and supplies its output to the voltage comparison circuit 14 as a reference voltage.

In order to compare the output of the full-wave rectifier circuit 12 using a triangular wave as a reference voltage, the voltage comparison circuit 14 outputs the level change of the torque sensor 2 as a pulse signal whose duty changes, and the output is sent to the drive logic circuit 18. Given. The drive logic circuit 18 is also provided with the polarity determination output of the polarity determination circuit 13. The drive logic circuit 18 has AND circuits 18a and 18b, and based on the positive or negative polarity determination output, the voltage comparison circuit 14
The pulse width modulated signal obtained from the + side lower FET
It is selectively applied to the driver 19 or the negative side lower FET driver 20. Further, the polarity determination circuit 13 selectively provides signals to the AND circuits 18a, 18b and the photocouplers 21 and 22 by determining whether the polarity is positive or negative.

The outputs of photo couplers 21 and 22 are respectively positive side upper FB.
T driver 23. − side upper FET driver 24. The FET drivers 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
ET drivers 19 and 20 are lower FE on the right and left sides respectively.
This drives T27 and T28. "Appa" here
"lower" refers to the side of the motor drive circuit 4 near the power supply terminal.
indicates the FET farther from the power supply terminal. Also FE
[+J,
rj corresponds to the positive voltage or negative voltage determined by the polarity determining circuit 13. FETs 25 to 27 are switching elements each constituted by a power MOS FET, and FETs 25 to 27 constitute first and second switching elements that are conductive when operated in the right direction,
FETs 26 and 28 are the third transistors that conduct when operated to the left.
and a fourth switching element. These FETs are connected in a bridge circuit with terminal 4 in the middle.
A steering motor 6 is connected via a and 4b.

- Current detection circuits 29 and 30 are connected to the lower FETs 27 and 2B to detect the current when they are conductive, and the output thereof is given to the comparator 31. The comparator 31 provides a comparison output to the delay timer 32 when the current value obtained from the current detection circuit 29, 30 exceeds a predetermined value.

The delay timer 32 provides an output to the control signal output section 33 when a signal is continuously provided for a certain period of time. The control signal output section 33 is configured to provide a gradually decreasing control signal to the voltage comparator circuit 14 when a signal is provided from the delay timer 32 . Here, a DC-DC converter 17, a polarity determination circuit 13, a photocoupler 21,
22. + side and - side upper FET driver 23.2
Reference numeral 4 constitutes a conduction holding portion 34 that selectively conducts the first or third switching element based on the detection of left and right steering torque obtained by the torque sensor 2. Also, full wave rectifier circuit 12. Voltage comparison circuit 14. Square wave oscillation circuit 1
5. Integrating circuit 16 and drive logic circuit 18. The + side and - side lower FET drivers 19 and 20 selectively send a signal with a pulse width corresponding to the output level to the first or third switching element based on the output from the torque sensor 2 or the control signal output section 33. A high-speed switching control section 35 is configured.

Next, an FBT bridge in which four FETs are bridge-connected and a current detection circuit will be explained with reference to FIG.

Here, the drains of FETs 25 and 26 are connected to the positive end of battery 5 via a relay circuit, and the source ends thereof are connected to the drains of FETs 28 and 27, respectively.

Further, the steering motor 6 is connected to the common connection ends of the FETs 25 and 28 and the common connection ends of the FETs 26 and 27 via motor connection terminals 4a and 4b, and the source ends of the FETs 27 and 28 are grounded. In this figure, each FET25 to 2
A surge absorption circuit consisting of a diode and a Zener diode is connected between the drain and gate of 8.
A flywheel diode is connected between the sources.

Current detection circuit 29.30 connected to FET27, 28
are each composed of a transistor Tri and a resistor R1, and a transistor Tr2 and a resistor R2.

The collector end of transistor TrL Tr2 is FET27
．． The drain of 28 and the base are connected to the control input terminals of the + and - side lower FET drivers 19 and 20 via resistors R3 and R4. Emitter resistors R1 and R2 having the same resistance value are connected to the emitter, respectively, and are further commonly connected from the emitter through resistors R5 and R6 to be applied to a comparator 31 as a current detection signal.

FIG. 4 shows the comparator 31. Delay timer 32. 3 is a circuit diagram showing the configuration of a control signal output section 33 and a voltage comparison circuit 14 that changes the input voltage according to the output thereof. FIG. In this figure, the comparator 31 is an operational amplifier 3 whose one input terminal is given a threshold level Vrefl determined by the voltage division of resistors R7 and R8.
1a, and its detection output is sent to delay timer 3.
Give to 2.

The delay timer 32 has a time constant circuit formed by a resistor R9 and a capacitor CI, and its output is given to the non-inverting input terminal of an operational amplifier 32a. A voltage at a dark value level Vref2 determined by resistors RIO and R11 that divides the power supply voltage is applied to the inverting input terminal of the operational amplifier 32a, and the signal is delayed by the time until this dark value is exceeded to output the control signal. 33 and a light emitting diode D1. The control signal output section 33 has a time constant circuit consisting of a resistor R12 and a capacitor C2 to which the output from the delay timer 32 is applied, and its output terminal is connected to the inverting input terminal of the operational amplifier 33a. A voltage divided by resistors R13 and R14 is applied to the non-inverting input terminal of the operational amplifier 33a, and a feedback resistor R1 is connected between the input and output terminals.
5 is connected.

The operational amplifier 33a is an inverting amplifier, and its output is given to a voltage dividing circuit including resistors R16 and R17.

The midpoint of the resistors R16 and R17 is commonly connected to the output of the full-wave rectifier circuit 12 via the diode D2, and is connected to the non-inverting input terminal of the operational amplifier 14a of the voltage comparator circuit 14. The voltage comparator circuit 14 has an inverting input terminal connected to the integrator circuit 1.
A triangular wave signal is given from 6, and the output given from the full wave rectifier circuit 12 or the control signal output section 33 is selected and compared with the triangular wave signal. The voltage comparison circuit 14 compares these signals and provides the drive logic circuit 18 with a signal having a pulse width corresponding to the input signal.

(Operation of Example) Next, the operation of this example will be explained with reference to the waveform diagrams of FIGS. 5 and 6. When the power is turned on, the upper FE
Power is supplied to T25 and T26.

The square wave oscillation circuit 15 oscillates a square wave signal of, for example, 20 KHz. Here, when the driver operates the steering wheel 1, the change in torque is detected by the torque sensor 2 and provided to the motor drive circuit 4. 5 and 6 are waveform diagrams showing waveforms of each part of the motor drive circuit 4. FIG. When a signal from the torque sensor 2 as shown in ta+ in FIG. 5 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 15 is converted into a triangular wave via the integrating circuit 16 and is transmitted to the voltage comparison circuit 14. Further, since the operational amplifier 33a of the control signal output section 33 outputs an "H" level signal, assuming that the diode D2 is not conductive, the output of the full-wave rectifier circuit 12 is directly applied to the voltage comparator circuit 14. Therefore, the voltage comparison circuit 14 generates 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, and is pulse width modulated. Here, as shown at time t, ~t2, +
When a human input signal from the side is given, the polarity determination circuit 13
The polarity is determined by the drive logic circuit 1.
The "H" level signal is transmitted to the AND circuit 18a of 8.

Therefore, this pulse signal is transmitted to the + side lower FET driver 19 via the AND circuit 18a. Similarly, the positive side upper FET driver 23 is connected via the photocoupler 21.
is driven continuously. Therefore, as shown in FIG. 5 (C1, fdl), FET25 is continuously turned on, and FE
T27 is pulse driven. Therefore, the steering motor 6 is pulse-driven as shown in FIG. 5 (gl).

When the output from the torque sensor 2 is on the negative side as shown from time t3 to t4, similarly, the m lower FET driver 20 continuously conducts the m FETs 26, and the one-side absorber FET driver 24 causes the lower FET 28 is pulse driven. Therefore, the steering motor 6 is supplied with a current as shown in FIG. 5(g). Here FET2
When driving the pulses of 7 and 28, the + side and - side lower F at the same time.
The transistor Tri or Tr2 is similarly pulsed by the ET driver 19,20. and FET27
Since the voltage across 28 corresponds to the change in current flowing through the respective FET, the current flowing through FETs 27 and 28 can be detected by reading the voltage change across resistor R1 or R2. This detected current is the comparator 3I
is given to.

Now, as shown in FIG. 6, the handle may be locked after time t5 and a large current, for example, a large current of approximately several +A, may flow through the FETs 25 and 27. In this case, since the current value is detected as a change in voltage, a signal corresponding to the current is given to the comparator 31 as shown in FIG. 6(d). Then, after time t6 when the detection signal exceeds a predetermined threshold level Vrefl as shown in FIG. 6(e), the comparator 31 provides a comparison output to the delay timer 32. The delay timer 32 is a resistor R.
9. The control signal output unit 3 outputs the output shown in FIG. 6(f) at time t7 after the predetermined delay time TI determined by the capacitor CI has elapsed.
Give to 3. Therefore, the alarm indicator Di lights up to notify the driver of the locked state of the steering wheel. Further, if the handle continues to be locked, the capacitor C2 is gradually charged via the resistor R12, so that the terminal voltage thereof gradually increases as shown in FIG. 6fgl. This voltage change is then amplified by the inverting amplifier 33a to obtain the output shown in FIG. 12 is directly transmitted to the voltage comparison circuit 14. However, when the output of the control signal output section 33 gradually decreases as shown in FIG. It gradually decreases as shown by the solid line in Figure +a+.

In FIG. 6+al, the broken line indicates the rectified output voltage of the full-wave rectifier circuit 12. And voltage comparison circuit 1.

As shown in FIG. 6(a), the input signal to
Since it gradually decreases until t8 (T2), FET2
The pulse width of 7 becomes gradually shorter as shown in FIG. 6 tel and fdl, and the current supplied to the steering motor 6 also decreases. And the time tl when capacitor C2 is saturated
The output of the operational amplifier 33a also decreases when the resistor R1
6, the divided signal of R17 remains and the 6th
As shown in Figure (h), a constant low level voltage is directly applied to the voltage comparator circuit 14. In this manner, when the steering motor 6 is locked, the drive current is controlled to gradually decrease. Therefore, burnout of the motor and switching elements can be prevented without giving the operator a sense of discomfort.

Note that this embodiment uses a pair of continuously driven and pulse driven FETs.
A current detection circuit is provided in parallel to the pulse-driven FET of the bridge circuit consisting of the FET, and the current flowing through it is measured. It goes without saying that a similar current detection circuit may be connected to. Further, the switching element is not limited to FET, but a power control element such as a power transistor may be used. Furthermore, as the switching element of the current detection circuit connected in parallel to the power control switching element, a switching element such as an FET may be used in addition to the transistor shown in this embodiment. In this case as well, it is possible to measure the current by simultaneously opening and closing the power control switching element provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the 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 the motor drive device according to this embodiment is applied, and FIG. 3 is a block diagram showing the configuration of a motor drive circuit according to an embodiment of the present invention. A circuit diagram showing the configuration of a bridge circuit section of a motor drive circuit according to an embodiment of the present invention, FIG. 4 is a circuit diagram showing an embodiment of the comparator 9 delay timer and control signal output section, and FIG. A waveform diagram showing the waveforms of each part during operation, Figure 6 is a waveform diagram showing the waveforms of each part when the handle is locked, and Figure 7 is a conventional power control element inserted to measure its current. FIG. 3 is a circuit diagram showing a current detection resistor. 1--------Steering handle 2--Torque sensor 3-------Transmission mechanism 4--
--・Motor drive diagram I? r6------Steering motor 11---Torque input terminal 19
, 20, 23, 24---FET
Driver 25--------Upper FET (1st
(switching element) 26 ------- Atsupa FET (third switching element) 21 ----
---Lower FET (second switching element)
28---One lower FET (fourth switching element)
29° 30 --- Current detection circuit (current detection means) 31 --- Comparator 32 --- Delay timer 33--- Control signal output section
34---Conduction holding control section 35--High speed switching control section Trl--Switching transistor (fifth switching element) Tr2---
---Switching transistor (sixth switching element) Patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and one other person) Part b t8 1; IQ- Figure 7

Claims (1)

[Claims] (1) A motor drive device for electric power steering, which includes a torque sensor connected to a steering shaft and detects its rotational torque, and a steering motor that rotates the steering wheel, the first motor drive device for maintaining right steering continuity. A switching element, a second switching element for right steering high-speed switching, is connected symmetrically to the steering motor, a third switching element for maintaining left steering continuity, and a fourth switching element for left steering high-speed switching. A bridge circuit configured to be symmetrically connected to the steering motor; and conduction that selectively conducts the first or third switching element based on detection of left and right steering torque obtained by the torque sensor. a holding control section; a high-speed switching control section that selectively applies a signal having a pulse width corresponding to the output level of the torque sensor to the second or fourth switching element based on the output from the torque sensor; 3 switching element, and the second and fourth switching elements.
fifth and sixth switching elements that are alternatively connected in parallel to one of the switching elements and driven simultaneously with the parallel-connected switching elements;
, a pair of current detection means having a current detection resistor for detecting the current flowing through the first, third, second, and fourth switching elements, which are connected in series and parallel to the sixth switching element, respectively; , a comparison means that receives the outputs of the pair of current detection means and detects an overcurrent that exceeds a predetermined threshold; a delay timer that delays the output of the comparison means for a predetermined period of time; A motor drive device comprising: a control signal output section that supplies a control signal that gradually decreases thereafter to the high-speed switching control section.