JP3375502B2 - Electric power steering device - Google Patents

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 a steering torque by applying electric 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 diagram of an electric power steering apparatus. The electric power steering apparatus 1 detects the steering input torque from the steering wheel 3 with the steering torque sensor 2, and the controller 4 determines the magnitude and direction of the output of the electric motor 6 based on the output signal of the steering torque sensor 2. Electric motor 6 via a bridge circuit 5 for driving
Is driven 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 apparatus 1 includes a control device 4 that controls driving of the electric motor 6 based on the output signal 2a of the steering torque sensor 2, and an electric motor 6 based on electric motor drive signals 4a to 4d output from the control device 4. A bridge circuit 5 for driving the switch, a switch 10 configured by using a relay for opening and closing 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, etc. A constant voltage circuit 12 for supplying a stabilized power source, a battery power source 13, a key switch (ignition switch) 14, a control system fuse 15, and a 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
The battery power supply 13 is supplied to the constant voltage circuit 12 via the. The constant voltage circuit 12 supplies a stabilized DC power source to the steering torque sensor 2 and the control device 4, respectively.

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

The bridge circuit 5 is formed 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 connection. 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 detection output 2a of the steering torque sensor 2 and outputs a steering assist torque corresponding to the detection output 2a of the steering torque sensor 2 from the electric motor 6. As described above, the electric 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 according to the 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 the driving of the electric motor 6 and sends a signal to the switch (relay) 10. The power supply to the bridge circuit 5 is cut off, and the power supply to the bridge circuit 5 is cut off. As an example thereof, 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 energization of 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 controller 4 controls the motor drive signal 4a.
~ 4d output time is monitored, PWM-modulated motor drive signal 4a ~ 4d duty (duty factor)
If the voltage exceeds the preset allowable range, the excitation winding 10a of the switch (relay) 10 is de-energized, the normally open contact 10b is returned to the open state, and power is supplied to the bridge circuit 5. Cut off.

As described above, in the conventional electric power steering apparatus 1, the switch 10 constituted by using the relay between the bridge circuit 5 and the battery power source 13 which is the power source thereof.
When the control device 4 detects an overcurrent state or a state in which PWM operation is not normally performed, the switch 10 is opened to cut off the power supply to the bridge circuit 5 and the electric motor 6, thereby the electric motor It is possible to prevent undesired auxiliary steering force from being generated.

[0012]

However, in the switch 10 constructed by using a relay, the response time from the time when the energization to the exciting winding 10a is cut off to the opening of the contact 10b is about several milliseconds. It takes. Therefore, 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 quickly cut off the energization in order to prevent the characteristic deterioration of the FETs 5a to 5d.

Further, in order to generate the steering assist torque, it is necessary to supply a large current of several tens of amps to 100 amps to the electric 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 exciting winding 10a. Therefore, the electric power steering device 1 becomes large and the power consumption of the control device 4 also becomes large.

The present invention has been made to solve the above problems, and provides an electric power steering apparatus which is capable of cutting off the power supply to the bridge circuit in a short time and equipped with a small-sized switch with low power consumption. 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 constituted by using a field effect transistor.

Since the field effect transistor has a high switching speed of, for example, several tens of nanoseconds to several hundreds of nanoseconds, the power supply to the bridge circuit can be cut off in an extremely short time. Further, since the electric power for controlling the field effect transistor to be in the ON state (conduction state) may be small, the power consumption of the control device can be reduced. Further, since the field effect transistor is smaller than the relay for high power, the electric power steering device can be downsized. The field effect transistor forming the switch and the field effect transistor forming the bridge circuit can be made into a common component or a module.

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

By connecting the two field-effect transistors so that their parasitic diodes are in opposite directions to each other, a reverse current flows due to the parasitic diode of the field-effect transistor even if the power supply is connected in reverse polarity. Can be blocked.

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. Even if the power supply is connected in reverse polarity and the bridge circuit including the electric motor is short-circuited, the parasitic diode can prevent the overcurrent from flowing.

The field effect transistor which constitutes the switch and the field effect transistor which constitutes the bridge circuit may have the same characteristics, whereby the field effect transistor which constitutes the switch and the bridge circuit are constituted. It is possible to make it easier to form a common component with the field effect transistor or to form a module, and it is possible to reduce the size and cost of the electric power steering device.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION 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 apparatus 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 the power supply to the bridge circuit 5. I am configuring.

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

In FIG. 3, the FET 20 is provided between the positive electrode side of the battery power source 13 and the bridge circuit 5, but the FET 20 includes the bridge circuit 5 and the current detection circuit 1.
You may interpose between 1 and. The FET 20 may be provided between the current detection circuit 11 and the negative electrode side of the battery power supply 13.

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

A diode 23 is provided in the forward direction between the control system fuse 15 and the constant voltage circuit 12. As a result, when the battery power source 13 is connected in reverse polarity,
The diode 23 prevents the voltage of the reverse polarity from being supplied to the constant voltage circuit 12, and even when the battery power supply 13 is connected to the reverse polarity, the circuit units 12, 4 of the control system are connected.
0 can be protected.

Further, each FET constituting the bridge circuit 5 is composed of the parasitic diode 22D of the other FET 22.
The reverse current is prevented from flowing through the parasitic diodes 5a to 5d (internal reverse diode) and the parasitic diode 21D of the FET 21 on one side. Thereby, even when the battery power supply 13 is connected in reverse 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. 5, one FET
21 is provided on the positive power source side of the bridge circuit 5, and the other FE
T22 may be provided on the negative power source side of the bridge circuit 5. The other FET 22 may be provided on the positive power source side of the bridge circuit 5, and the one FET 21 may be provided on the negative power source side of the bridge circuit 5. In this way, one of the field effect transistors is arranged such that its parasitic diode is in the forward direction with respect to the battery power supply 13, and
By arranging the other field effect transistor so that its parasitic diode is in the opposite direction to the battery power source 13, even when the battery power source 13 is connected in the opposite 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 controller 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, And 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 a steering torque signal 2b within the input voltage range of the A / D converter 42. The input interface (I / F) circuit 41 converts the voltage signal 9a corresponding to the steering rotation speed output from the steering rotation sensor 9 into a steering rotation speed signal 9b within the input voltage range of the A / D converter 42. . The input interface (I / F) circuit 41 converts the voltage signal 11a corresponding to the detected current value output from the current detection circuit 11 into a current value signal 11b 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 (steering torque signal 2b, steering rotation speed signal 9b, current value signal 11b) designated based on the A / D conversion input designation supplied from the MCU 43 are A / D converted and M
Supply to CU43.

When the power is supplied, the MCU 43 first outputs the cutoff command signal 43a. MCU43 is MCU4
3 When the internal initialization process ends, the cutoff command signal 43a is stopped from being output. The MCU 43 takes in the steering torque and the steering rotation speed (information thereof) via the A / D converter 42,
It is determined whether or not it is necessary to supply the steering assist force from the electric motor 6. When it is necessary to supply steering assist power, MC
U43 is the 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 steering assist force.

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

When the electric motor 6 is driven to rotate in the forward rotation direction, FET5a and FET5b are used. One FET
With the 5a turned on, the other FET 5b is switching-driven by PWM to control the electric power supplied to the electric motor 6. When rotating the electric motor 6 in the reverse rotation direction, the FET 5c and the FET 5d are used. One FE
With T5c turned on, PWM the other FET5d
The electric power supplied to the electric motor 6 is controlled by switching driving at.

The PWM operation monitoring circuit 45 includes FETs 5a.
Based on the gate voltage signals (motor drive signals) 4a to 4d supplied to the gates 5d to 5d, it is monitored whether the PWM operation of the motor 6 is normally performed. The PWM operation monitoring circuit 45 uses the gate voltage signal 4a for the FET 5a.
When the time period during which the gate voltage signal 4d is simultaneously supplied to the FET 5d and the FET 5d exceeds the preset allowable short circuit time, the PWM operation abnormality signal 45a is output. The PWM operation monitoring circuit 45 outputs the PWM operation abnormality signal 45a when 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 the preset allowable short circuit time.

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

The MCU 43 monitors the current flowing through the bridge circuit 5 based on the current value signal 11b. MCU
Reference numeral 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 has a shutoff command signal 43a.
Is being supplied, the output of the power supply control signal 46a is stopped. The power supply control circuit 46 uses the 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 be in 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 FET
A gate drive signal 40a is supplied to the gate of 20.

With the above-mentioned configuration, the control device 40 shown in FIG. 6 configures a switch when the current flowing through the bridge circuit 5 exceeds the allowable current and when the normal PWM operation is not performed. It is possible to cut off the power supply to the bridge circuit 5 by turning off the FET 20 that turns on.

The PWM operation monitoring circuit 45 monitors the PWM operation of the electric motor 6 based on the gate voltage signals (motor driving signals) 4a to 4d supplied to the gates of the FETs 5a to 5d forming the bridge circuit 5. So MCU4
In addition to the PWM signal generation operation of No. 3, the abnormality of the PWM operation can be detected including the operation abnormality of the gate drive circuit 44 for the bridge circuit. Regarding the PWM operation monitoring circuit 45, it is possible to refer to the failure detecting means (failure detecting circuit) disclosed in Japanese Patent Laid-Open No. 7-300074.
The control device 40 of FIG. 6 with the steering rotation speed signals 9a and 9b removed or the steering rotation speed signals 9a and 9b of zero may be applied to the control device 40 of FIGS.

Further, the FETs 20, 21 and 22 and the FETs 5a to 5d that form the bridge circuit 5 have the same characteristics, so that the FETs that form the switch and the FETs that form the bridge circuit 5 are the same. It is possible to further facilitate common componentization and modularization of the above, and it is possible to use, for example, one in which five or six identical FETs are housed in one package, whereby an electric power steering device in a vehicle can be used. It is possible to reduce the size and cost of the product. The above-mentioned embodiment is an example of the present invention, and the present invention is not limited to the above-mentioned embodiment.

[0043]

As described above, in the electric power steering apparatus according to the present invention, the switch for opening and closing the power supply to the bridge circuit is constituted by using the field effect transistor, so that the power supply to the bridge circuit is extremely short. It can be cut off in time. Further, since the electric power for controlling the field effect transistor to be turned on may be small, the power consumption of the control device can be reduced. Further, since the field effect transistor is smaller than the relay for high power, the electric power steering device can be downsized. The field effect transistor forming the switch and the field effect transistor forming the bridge circuit can be made into a common component or a module.

By arranging the two field effect transistors forming the switch so that their parasitic diodes are in opposite directions, even if the battery power supplies are connected in opposite polarities, the reverse current is generated by the parasitic diodes of the field effect transistors. Can be blocked 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 source, and the other is provided between the bridge circuit and the positive terminal of the power source. Even if the power supply is connected in reverse polarity and the bridge circuit including the electric motor is short-circuited, the parasitic diode can prevent the overcurrent from flowing.

By making the field effect transistor forming the switch and the field effect transistor forming the bridge circuit have the same characteristics, the total number of the field effect transistors in the switch and the bridge circuit is 5 to 6. The same field effect transistor can be used, and the manufacturing steps of the field effect transistors can be the same or substantially the same, and the field effect transistor that constitutes the switch and the field effect that constitutes the bridge circuit. It is possible to make it easier to form common parts with the transistor and to form a module, and it is possible 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 respect, the gate drive circuit can be made into a common component or modularized.

[Brief description of drawings]

FIG. 1 is a schematic structural diagram 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 an electric power steering device according to the present invention.

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

5 is a circuit configuration diagram showing a modified example of the circuit configuration shown in FIG.

FIG. 6 is a block configuration 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) forming switches, 21D, 22D ... Parasitic diode (internal reverse diode), D ... Drain, G ... Gate, S ... Source.

Claims (2)

(57) [Claims] 1. A motor for applying an auxiliary torque to a steering system, a bridge circuit composed of a plurality of field effect transistors for driving the motor, a switch provided between the bridge circuit and a power source, In an electric power steering apparatus including a controller for controlling a switch, the switch has two field effect transistors connected in series.
Is photoelectrically are configured, the parasitic diode one of the field-effect transistor
Place it so that it is in the forward direction with respect to the source and
The field effect transistor has its parasitic diode coupled to the power supply.
The electric power steering device is characterized in that it is arranged in the opposite direction . 2. The field effect transistor, wherein one is provided between the bridge circuit and a negative terminal of the power source, and the other is provided between the bridge circuit and a positive terminal of the power source. The electric power steering device according to claim 1 .