JPH10167085A - Electric power steering device - Google Patents

Abstract

(57) [Problem] To provide an electric power steering device which can shut off power supply to a bridge circuit for driving an electric motor in a short time and has a small and low-power-consumption switch. A field effect transistor (FET) 20 is provided between a battery power supply 13 and a bridge circuit 5.
The control device 40 sets a gate-source threshold voltage necessary for turning on the FET 20 to a gate drive signal 40a.
By supplying to the gate G of the FET 20,
Turn on T20. As a result, the battery power 13 is supplied to the bridge circuit 5. When the control device 40 detects an overcurrent or an abnormality in the PWM operation, the control device 40
By stopping the supply of a, the FET 20 is turned off. Thereby, the power supply to the bridge circuit 5 is cut off in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for reducing the steering torque by applying electric motor power to a steering system based on the magnitude and direction of a steering operation applied to a steering wheel.

[0002]

2. Description of the Related Art FIG. 1 is a schematic structural view of an electric power steering apparatus. The electric power steering device 1 detects a steering input torque from a steering wheel 3 with a steering torque sensor 2, determines a magnitude and a direction of an output of an electric motor 6 with a control device 4 based on an output signal of the steering torque sensor 2, Motor 6 via a bridge circuit 5 for driving the motor 6
, And the power of the electric motor 6 is transmitted to the steering system 8 using the torque booster 7 to reduce the steering torque.

FIG. 2 is a circuit diagram of a conventional electric power steering apparatus. The conventional electric power steering device 1 includes a control device 4 that controls the driving of an electric motor 6 based on an output signal 2 a of a steering torque sensor 2, and an electric motor 6 based on electric motor drive signals 4 a to 4 d output from the control device 4. , A switch 10 configured by using a relay to open and close power supply to the bridge circuit 5, a current detection circuit 11 for detecting a current flowing through the bridge circuit 5, a control device 4, and the like. A constant voltage circuit 12, a battery power supply 13, a key switch (ignition switch) 14, a control system fuse 15, and an electric motor system fuse 16 are provided.

When the key switch 14 is operated in the closed state, the key switch 14 and the control system fuse 15 are operated.
, A battery power supply 13 is supplied to the constant voltage circuit 12. The constant voltage circuit 12 supplies stabilized DC power to the steering torque sensor 2 and the control device 4, respectively.

When the DC power is supplied, the control device 4 initializes each circuit portion in the control device 4 and confirms that the operation of each circuit portion is normal. An exciting current is supplied to the exciting winding 10a of the switch (relay) 10 via the drive circuit, and the switch (relay) 1
0 normally open contact 10b is closed. As a result, the battery power 13 is supplied to the bridge circuit 5 via the electric motor fuse 16 and the contact 10 b of the switch (relay) 10.

The bridge circuit 5 is constructed by connecting four power n-channel enhancement type MOS field effect transistors (hereinafter referred to as FETs) 5a to 5d in an H-type bridge. In each of the FETs 5a to 5d, an internal reverse diode (parasitic diode) having a large current capacity is formed between the drain and the source due to the structure of the FET.

The control device 4 determines the rotation direction of the electric motor 6 based on the detected output 2a of the steering torque sensor 2, and outputs a steering assist torque corresponding to the detected output 2a of the steering torque sensor 2 from the electric motor 6. As described above, the power supplied to the electric motor 6 via the bridge circuit 5 is controlled by PWM (pulse width modulation).

The current detection circuit 11 includes a low resistance for current detection and an output circuit for outputting a current value signal 11a corresponding to a voltage generated across the low resistance. Current detection circuit 1
1 may be configured using a current probe that detects a current by detecting a magnetic field generated by the current.

The control device 4 constantly monitors the operation of the electric power steering device. If a failure of the electric power steering device is detected, the control device 4 stops driving the electric motor 6 and sends a signal to the switch (relay) 10. And the power supply to the bridge circuit 5 is cut off. As an example, the control device 4 monitors the current flowing through the bridge circuit 5 based on the current value signal 11a supplied from the current detection circuit 11. When the current value signal 11a reaches a preset overcurrent value, the control device 4 cuts off the power supply to the excitation winding 10a of the switch (relay) 10. As a result, the normally open contact 10b returns to the open state, and the power supply to the bridge circuit 5 is cut off.

Further, the control device 4 controls the motor drive signal 4a.
出力 4d output time is monitored, and the duty of the PWM-modulated motor drive signals 4a〜4d (duty factor)
If the current exceeds the preset allowable range, the energization to the exciting winding 10a of the switch (relay) 10 is cut off, the normally open contact 10b is returned to the open state, and the power supply to the bridge circuit 5 is performed. Cut off.

As described above, in the conventional electric power steering apparatus 1, the switch 10 constituted by using a relay is provided between the bridge circuit 5 and the battery power supply 13 as its power supply.
When the control device 4 detects an overcurrent state or a state in which the PWM operation is not performed normally, the control device 4 opens the switch 10 to cut off the power supply to the bridge circuit 5 and the electric motor 6, so that the electric motor 6 prevents the generation of an undesired auxiliary steering force.

[0012]

However, the switch 10 constituted by using a relay has a response time of several milliseconds from the time when the power supply to the exciting winding 10a is cut off to the time when the contact 10b is released. Take it. For this reason, even if the overcurrent state or the abnormality of the PWM signal is detected, the power supply to the bridge circuit 5 cannot be immediately cut off. In particular, in the overcurrent state, it is desirable to immediately cut off the current supply in order to prevent deterioration of the characteristics of the FETs 5a to 5d.

Further, in order to generate the steering assist torque, a large current of about several tens of amps to 100 amps must be supplied to the motor 6, but a relay capable of opening and closing such a large current is large. Further, the relay for high power also supplies a large amount of power to the excitation winding 10a. For this reason, the electric power steering device 1 becomes large, and the power consumption of the control device 4 also becomes large.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and provides an electric power steering apparatus which can cut off power supply to a bridge circuit in a short time and has a small and low power consumption switch. The purpose is to do.

[0015]

In order to solve the above-mentioned problems, an electric power steering apparatus according to the present invention is characterized in that a switch is formed using a field-effect transistor.

Since the switching speed of the field-effect transistor is as high as several tens nanoseconds to several hundred nanoseconds, power supply to the bridge circuit can be cut off in a very short time. In addition, the electric power for controlling the field-effect transistor to be in the on state (conduction state) may be small, so that the power consumption of the control device can be reduced. Further, since the field-effect transistor is small in size as compared with a relay for high power, the size of the electric power steering device can be reduced. The field effect transistor forming the switch and the field effect transistor forming the bridge circuit can be made common components and modules.

The switch is constituted by connecting two field effect transistors in series, one of the field effect transistors is arranged such that its parasitic diode is directed forward with respect to the power supply, and the other is connected to the other field effect transistor. May be arranged such that the parasitic diode is in the opposite direction to the power supply.

By connecting these two field effect transistors such that their parasitic diodes are in opposite directions, even if the power supply is connected in the opposite polarity, a reverse current flows through the parasitic diodes of the field effect transistors. Can be prevented.

The field effect transistor is arranged such that one is provided between the bridge circuit and the negative terminal of the power supply and the other is provided between the bridge circuit and the positive terminal of the power supply. Thus, even if the power supply is connected in the opposite polarity and the bridge circuit including the motor is short-circuited, the overcurrent can be prevented from flowing by the parasitic diode.

The field effect transistor forming the switch and the field effect transistor forming the bridge circuit may have the same characteristics, thereby forming a bridge circuit with the field effect transistor forming the switch. It is possible to make it easier to use common components and modules with the field-effect transistor, and to reduce the size and cost of the electric power steering device.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The structure of the electric power steering device is the same as that shown in FIG. FIG. 3 is a circuit configuration diagram of the electric power steering device according to the present invention. As shown in FIG. 3, the electric power steering apparatus according to the present invention uses a power n-channel enhancement type MOS field effect transistor (hereinafter referred to as FET) 20 as a switch for opening and closing power supply to the bridge circuit 5. Make up.

The control device 40 turns on the FET 20 by supplying a gate-source threshold voltage necessary for turning on the FET 20 to the gate G of the FET 20 as a gate drive signal 40a. When the control device 40 detects an abnormal state such as an overcurrent, the gate drive signal 40a
The FET 20 is turned off by stopping the supply. FE
At T20, the switching speed is as high as several tens nanoseconds to several hundred nanoseconds, for example, so that power supply to the bridge circuit 5 can be cut off in a very short time. Also, FE
In T20, the power for controlling the ON state may be small, so that the power consumption of the control device 40 can be reduced. Further, since the FET 20 is smaller than the relay 10 for high power, the electric power steering device can be downsized.

FIG. 3 shows a configuration in which the FET 20 is interposed between the positive electrode side of the battery power supply 13 and the bridge circuit 5, but the FET 20 comprises the bridge circuit 5 and the current detection circuit 1
1 may be interposed. The FET 20 may be provided between the current detection circuit 11 and the negative side of the battery power supply 13.

FIG. 4 is a circuit diagram of another electric power steering apparatus according to the present invention. The electric power steering apparatus shown in FIG. 4 forms a switch by connecting two FETs 21 and 22 in series. One FET 21 is
The parasitic diode 21D is arranged and connected so as to be in the opposite direction (reverse polarity) with respect to the battery power supply 13. The other FET 22 is arranged and connected such that its parasitic diode 22D has a forward direction (forward polarity) with respect to the battery power supply 13. Gate drive signal 40a
Are supplied in parallel to the FETs 21 and 22.

A diode 23 is interposed between the control system fuse 15 and the constant voltage circuit 12 in the forward direction. Thereby, when the battery power supply 13 is connected to the opposite polarity,
The diode 23 prevents the supply of a voltage of the opposite polarity to the constant voltage circuit 12, so that even when the battery power supply 13 is connected to the opposite polarity, each of the circuit units 12, 4 of the control system is prevented.
0 can be protected.

Further, each FET constituting the bridge circuit 5 is constituted by the parasitic diode 22D of the other FET 22.
The flow of the current in the reverse direction is prevented through the parasitic diodes 5a to 5d (internal reverse diodes) and the parasitic diode 21D of one FET 21. Thereby, even when the battery power supply 13 is connected to the opposite polarity, it is possible to prevent the overcurrent from being supplied via the parasitic diode.

FIG. 5 is a circuit configuration diagram showing a modification of the circuit configuration shown in FIG. As shown in FIG.
21 is provided on the positive power supply side of the bridge circuit 5, and the other FE
T22 may be provided on the negative power supply side of the bridge circuit 5. The other FET 22 may be provided on the positive power supply side of the bridge circuit 5, and the one FET 21 may be provided on the negative power supply side of the bridge circuit 5. As described above, one of the field effect transistors is arranged such that its parasitic diode is directed forward with respect to the battery power supply 13, and
By arranging the other field-effect transistor such that its parasitic diode is in the opposite direction to the battery power supply 13, even when the battery power supply 13 is connected in reverse polarity, a reverse current flows through the parasitic diodes 21D and 22D. Can be prevented, and the bridge circuit 5 and the electric motor 6 can be protected.

FIG. 6 is a block diagram showing a specific example of the control device. FIG. 6 shows a configuration in which a steering rotation sensor 9 is provided in addition to the steering torque sensor 2, and the auxiliary steering force supplied from the electric motor 6 is controlled based on the steering torque and the steering speed.

The control device 40 has an input interface (I
/ F) circuit 41, A / D conversion circuit 42, microcomputer unit (hereinafter referred to as MCU) 43, gate drive circuit 44 for bridge circuit, PWM operation monitoring circuit 45, power supply control circuit 46, A gate drive circuit 47 for a switch.

Input interface (I / F) circuit 41
Converts the voltage signal 2a corresponding to the steering torque output from the steering torque sensor 2 into the steering torque signal 2b within the input voltage range of the A / D converter 42. The input interface (I / F) circuit 41 converts a voltage signal 9 a corresponding to the steering rotation speed output from the steering rotation sensor 9 into a steering rotation speed signal 9 b within the input voltage range of the A / D converter 42. . The input interface (I / F) circuit 41 converts the voltage signal 11 a according to the detected current value output from the current detection circuit 11 into a current value signal 11 b within the input voltage range of the A / D converter 42.

The A / D conversion circuit 42 includes a multiplex input type A / D converter. The A / D conversion circuit 42
The input signals (the steering torque signal 2b, the steering rotation speed signal 9b, and the current value signal 11b) specified based on the A / D conversion input specification supplied from the MCU 43 are A / D converted and M
Supply to CU43.

When power is supplied, the MCU 43 first outputs a cutoff command signal 43a. MCU43 is MCU4
When the internal initialization process is completed, the output of the cutoff command signal 43a is stopped. The MCU 43 captures (information on) the steering torque and the steering rotation speed via the A / D converter 42,
It is determined whether or not it is necessary to supply a steering assist force from the electric motor 6. When it is necessary to supply steering assist force, MC
U43 is an electric motor 6 based on the steering torque and the steering rotation speed.
And the steering assist force supplied from the electric motor 6 are obtained. The MCU 43 generates and outputs the gate drive control signals 4A to 4D based on the obtained rotation direction and the steering assist force.

The gate drive circuit 44 includes a booster circuit for generating a gate supply voltage for controlling the FET constituting the bridge circuit 5 to a conductive state, and a plurality of level shift circuits. The gate drive circuit 44 controls each FE based on the gate drive control signals 4A to 4D output from the MCU 43.
Gate voltage signals (motor drive signals) 4a to 4d are supplied to the gates of T5a to 5b.

When the motor 6 is driven to rotate in the forward direction, the FETs 5a and 5b are used. One FET
With the 5a turned on, the other FET 5b is switched by PWM to control the power supplied to the electric motor 6. When the motor 6 is driven to rotate in the reverse rotation direction, the FET 5c and the FET 5d are used. One FE
With T5c turned on, the other FET 5d is
, The power supplied to the electric motor 6 is controlled.

The PWM operation monitoring circuit 45 is provided with each FET 5a.
Based on the gate voltage signals (motor drive signals) 4a to 4d supplied to the gates to 5d, it is monitored whether or not the PWM operation of the motor 6 is normally performed. The PWM operation monitoring circuit 45 outputs the gate voltage signal 4a to the FET 5a.
If the time during which the gate voltage signal 4d is simultaneously supplied to the FET 5d and the gate voltage signal 4d exceeds a preset allowable short-circuit time, a PWM operation abnormality signal 45a is output. If the time during which the gate voltage signal 4c for the FET 5c and the gate voltage signal 4b for the FET 5b are simultaneously supplied exceeds a preset allowable short-circuit time, the PWM operation monitoring circuit 45 outputs a PWM operation abnormality signal 45a.

The PWM operation monitoring circuit 45 counts the duration of the H level of the pulse width modulated gate voltage signal (PWM signal) 4d for the FET 5d, and the duration of the H level exceeds the preset continuous conduction allowable time. If so, a PWM operation abnormality signal 45a is output. In addition, PW
The duty of the M signal (for example, the ratio between the H level and the L level) is monitored.
The M operation abnormality signal 45a may be output. P
The WM operation monitoring circuit 45 measures the H-level duration of the pulse width modulated gate voltage signal (PWM signal) 4b for the FET 5b, and if the H-level duration exceeds a preset continuous energization allowable time. , And outputs a PWM operation abnormality signal 45a.

The MCU 43 monitors the current flowing through the bridge circuit 5 based on the current value signal 11b. MCU
43 outputs a cutoff command signal 43a when the current flowing through the bridge circuit 5 exceeds a preset allowable current.

The power supply control circuit 46 is provided with a cutoff command signal 43a.
While the power supply is supplied, the output of the power supply control signal 46a is stopped. The power supply control circuit 46 outputs a PWM operation abnormality signal 45.
When a is supplied, the output of the power supply control signal 46a is stopped.

The switch gate drive circuit 47 includes a booster circuit for generating a gate supply voltage for controlling the FET 20 constituting the switch to a conductive state, and a level shift circuit. The gate drive circuit 47 includes a power supply control circuit 46
Based on the power supply control signal 46a output from the
The gate drive signal 40a is supplied to the gate 20.

With the above configuration, the control device 40 shown in FIG. 6 configures the switch when the current flowing through the bridge circuit 5 exceeds the allowable current and when the normal PWM operation is not performed. The power supply to the bridge circuit 5 can be cut off by setting the FET 20 to be cut off.

The PWM operation monitoring circuit 45 monitors the PWM operation of the electric motor 6 based on gate voltage signals (motor drive signals) 4a to 4d supplied to the gates of the FETs 5a to 5d constituting the bridge circuit 5. So MCU4
In addition to the PWM signal generation operation of No. 3, the abnormality of the PWM operation including the operation abnormality of the gate drive circuit 44 for the bridge circuit can be detected. As for the PWM operation monitoring circuit 45, the failure detecting means (failure detecting circuit) disclosed in Japanese Patent Application Laid-Open No. 7-300974 can be referred to.
The control device 40 shown in FIG. 6 from which the steering rotation speed signals 9a and 9b are removed or the steering rotation speed signals 9a and 9b set to zero may be applied to the control device 40 shown in FIGS.

The FETs 20, 21, 22 and the FETs 5a to 5d constituting the bridge circuit 5 have the same characteristics, so that the FET constituting the switch and the FET constituting the bridge circuit 5 It is possible to further simplify the common parts and modularization of the power steering device. For example, a device in which five or six identical FETs are contained in one package can be used. Can be reduced in size and cost. The above embodiment is an example of the present invention, and the present invention is not limited to the above embodiment.

[0043]

As described above, in the electric power steering apparatus according to the present invention, since the switch for opening and closing the power supply to the bridge circuit is formed using the field effect transistor, the power supply to the bridge circuit is extremely short. Can be shut off in time. Further, the electric power for controlling the field-effect transistor to be in the ON state may be small, so that the power consumption of the control device can be reduced. Further, since the field-effect transistor is small in size as compared with a relay for high power, the size of the electric power steering device can be reduced. The field effect transistor forming the switch and the field effect transistor forming the bridge circuit can be made common components and modules.

By arranging the two field effect transistors constituting the switch so that their parasitic diodes are in opposite directions to each other, even when the battery power supply is connected to the opposite polarity, the reverse current is generated by the parasitic diodes of the field effect transistors. Can be prevented from flowing, and the bridge circuit and the electric motor can be protected.

The field effect transistor is arranged such that one is provided between the bridge circuit and the negative terminal of the power supply and the other is provided between the bridge circuit and the positive terminal of the power supply. Thus, even if the power supply is connected in the opposite polarity and the bridge circuit including the motor is short-circuited, the overcurrent can be prevented from flowing by the parasitic diode.

The field effect transistor forming the switch and the field effect transistor forming the bridge circuit have the same characteristics, so that the field effect transistors of the switch and the bridge circuit have a total of 5-6. The same field-effect transistors can be used, and the manufacturing process of each of the field-effect transistors can be made the same or substantially the same. The field-effect transistors that make up the switch and the field-effect transistors that make up the bridge circuit It is possible to make it easier to use a common component and a module with the transistor, and to reduce the size and cost of the electric power steering device. Also, since each field effect transistor can be controlled at the same voltage level,
The same gate drive circuit can be used for each field effect transistor, and in this regard, the gate drive circuit can be made a common component or a module.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of an electric power steering device.

FIG. 2 is a circuit configuration diagram of a conventional electric power steering device.

FIG. 3 is a circuit configuration diagram of the electric power steering device according to the present invention.

FIG. 4 is a circuit configuration diagram of another electric power steering device according to the present invention.

FIG. 5 is a circuit configuration diagram showing a modification of the circuit configuration shown in FIG. 4;

FIG. 6 is a block diagram showing a specific example of a control device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering torque sensor, 5 ... Bridge circuit, 5a-5d ... Field effect transistor (FET), 6 ... Electric motor, 8 ... Steering system, 2
0, 21, 22,... Field-effect transistors (FETs) constituting switches, 21D, 22D, parasitic diodes (internal reverse diodes), D, drains, G, gates, S, sources.

Claims (4)

[Claims] An electric motor for applying an auxiliary torque to a steering system; a bridge circuit comprising a plurality of field effect transistors for driving the electric motor; a switch interposed between the bridge circuit and a power supply; An electric power steering device comprising a control device for controlling a switch, wherein the switch is configured using a field effect transistor. 2. The switch comprises two field-effect transistors connected in series, and one of the field-effect transistors is arranged such that a parasitic diode thereof is directed forward with respect to a power supply. 2. The electric power steering apparatus according to claim 1, wherein the other field effect transistor is arranged such that its parasitic diode is in a direction opposite to a power supply. 3. One of the field effect transistors is provided between a bridge circuit and a negative terminal of a power supply, and the other is provided between the bridge circuit and a positive terminal of the power supply. The electric power steering device according to claim 2, wherein 4. The field effect transistor forming the switch and the field effect transistor forming a bridge circuit have the same characteristics.
3. The electric power steering device according to 3.