JPH02106465A - Motor-driven type power steering device - Google Patents

Abstract

PURPOSE:To prevent the increase of the load time rate of a FET close to 100% and prevent the generation of motor control noise by turning OFF the first FET for normal revolution or the first FET for reverse revolution during the time when PWM signal is set OFF compulsorily for a prescribed time, synchronized with the PWM frequency. CONSTITUTION:A motor-driven power steering device has a motor driving circuit 6 constituted of an electric motor 1 for assisting the steering force and a bridge circuit consisting of four FETs 2-5, and controls the FETs 2-5 by a switching circuit 8 on the basis of the PWM signal B supplied from a PWM modulation circuit 7 and the steering direction instruction signal supplied from an instruction circuit. In this case, the PWM modulation means 7 is constituted so that the PWM signal is compulsorily set off for a prescribed time, synchronized with the PMW frequency. Further, the switching circuit 8 turns OFF two FETs 4 and 5 for reverse revolution, when the steering direction instruction signal is in the normal direction, and turns ON the second FET 3 for normal revolution and controls the first FET 2 for normal revolution on the basis of the PWM signal, and when the steering direction instruction signal is in the reverse revolution direction, two FETs 2 and 3 for normal revolution are turned OFF, and the second FET 5 for reverse revolution is turned ON, and the first FET 4 for reverse revolution is controlled on the basis of the PWM signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an electric power steering device for automobiles and the like.

Prior Art and Problems of the Invention As an electric power steering device for automobiles, etc., 4
a motor drive circuit configured with a bridge circuit consisting of two FETs; a means for outputting a steering direction command signal corresponding to the steering direction; a means for outputting a motor current command signal corresponding to the steering force; A known motor is equipped with a PWM modulation means that outputs a corresponding PWM signal, and a switching means that controls an FET of a motor drive circuit based on a motor current command signal and the PWM signal.

The motor drive circuit includes a first FE for normal rotation provided between the first terminal of the electric motor and the power supply side for assisting the steering force.
T, a second FET for normal rotation provided between the second terminal of the electric motor and the ground side.

A first FET for reversing provided between the second terminal of the electric motor and the power supply side, a second FET for reversing provided between the first terminal of the electric motor and the ground side, and connected in parallel to each of these FETs. It consists of a diode.

The switching means turns off the two reverse rotation FETs when the steering direction command signal is in the forward direction, controls on/off the two forward rotation FETs based on the PWM signal, and controls the two reverse rotation FETs when the steering direction command signal is in the reverse direction. In this case, the two forward rotation FETs are turned off, and the two reverse rotation FETs are controlled on/off based on the PWM signal.

However, in the case of such a device, depending on the magnitude of the motor current command signal, the load time rate of the FET on state (
duty factor) may become close to 100%, and in this case, the PWM frequency becomes unstable and
Motor control noise becomes a problem.

An object of the present invention is to provide an electric power steering device that solves the above problems.

Means for Solving the Problems The electric power steering device according to the present invention includes a first FET for normal rotation provided between the first terminal of the electric motor for assisting steering force and the power supply side; and a second terminal of the electric motor. a second FET for forward rotation provided between the and the ground side;
A first FET for reversing provided between the second terminal of the electric motor and the power supply side, a second FET for reversing provided between the first terminal of the electric motor and the ground side, and connected in parallel to each of these FETs. a motor drive circuit configured with a bridge circuit including a diode; a means for outputting a steering direction command signal corresponding to the steering direction; a means for outputting a motor current command signal corresponding to the steering force; P that outputs the corresponding PWM signal
In an electric power steering device comprising a WM modulation means and a switching means for controlling an FET of a motor drive circuit based on a motor current command signal and a PWM signal, the PWM modulation means generates a PWM signal in synchronization with a PWM frequency. A means for forcibly turning off the steering wheel for a predetermined period of time is provided, and when the steering direction command signal is in the forward rotation direction, the switching means turns off the two reverse rotation FETs and turns on the second forward rotation FET to switch the steering direction to the forward rotation direction. PWM the first FET
When the steering direction command signal is in the reverse direction, the two forward rotation FETs are turned off, the second reverse rotation FET is turned on, and the first reverse rotation FET is controlled using PWM control.
It is characterized by comprising means for controlling based on a signal.

Note that in this specification, the term FET is used as an abbreviation for field effect transistor.

It is desirable that the time for forcibly turning off the PWM signal is the shortest time in which the load time ratio of the FET does not approach 100%.

The working PWM signal is synchronized with the PWM frequency and is forcibly turned off for a predetermined period of time, so the first FET for forward rotation (during forward rotation) is turned off during that time.
Or the first FET for reverse rotation (at the time of reverse rotation) is turned off and the FE
The load time rate of T never approaches 100%. Therefore, the PWM frequency does not become unstable, and generation of motor control noise is prevented.

In addition, the second FET for forward rotation is always on during forward rotation, and the second FET for reverse rotation is always on during reverse rotation. The flywheel current flows through the motor through the connected diode, which causes
Since the current ripple becomes smaller and the current flowing through the motor increases, the decrease in motor current caused by forcing the load time factor of the FET to be smaller than 100% is compensated to some extent.

Embodiment Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

Figure 1 shows an outline of the main parts of the electrical circuit of an electric power steering device, namely an electric motor (1) for assisting the steering force, four FETs (2) (3) (4)
(5) A motor drive circuit (6) composed of a bridge circuit consisting of a PWM modulation circuit (7) that outputs a PWM signal corresponding to a motor current command signal A from a command circuit (not shown), Steering direction command signal and PW
FET of the motor drive circuit (6) based on the M signal
A switching circuit (8) that controls on/off of (2), (3), (4), and (5) is shown.

Although not shown, the command circuit is connected to a torque sensor that detects the input torque of the steering shaft, a vehicle speed sensor that detects the vehicle speed, and the like. The command circuit is
The direction of rotation of the motor (1), that is, the steering direction, is determined from the direction of the input torque, and the required steering assist force and the corresponding motor current value are determined based on the magnitude of the input torque and the vehicle speed. Then, a motor current command signal A corresponding to this motor current value is output to a PWM modulation circuit (7), and a steering direction command signal, that is, a forward rotation signal CI and a reverse rotation signal C2, is output to a switching circuit (8). Note that the forward rotation signal C1 is at H level (on) when the motor rotates forward, and at L level (off) when it is reversed and stopped, and the reverse rotation signal C2 is at H level when it is reversed, and at L level when it is rotated forward and stopped. Become. Further, the motor (1) is connected to an appropriate location such as an output shaft of a steering shaft or a steering gear via a speed reducer, a clutch, etc., for example.

The four FETs (2) (3) of the motor drive circuit (6)
)(4)(5) are connected as follows. That is, the source terminal (S) of the first FET for forward rotation (2) is connected to the first terminal (terminal for forward rotation (Ha)) of the motor (1), and the drain terminal (D) is connected to the power supply (BATT). The drain terminal (D) of the second FET (3) for forward rotation is the second terminal (terminal for reverse rotation) of the motor (1) (
Mb), and the source terminal (S) is grounded via a current detection resistor (9). 1st FE T for reverse rotation
The source terminal (S) of (4) is the second terminal (S) of the motor (1).
Mb), and the drain terminal (D) is connected to the power supply (BAT
T). 2nd FET for reverse rotation (5
) is connected to the first terminal (M) of the motor (1).
a), and the source terminal (S) is connected to the current detection resistor (
9). And each FET
Diodes (10), (11), (12), and (13) are connected in parallel to (2), (3), (4), and (5), respectively.

The PWM modulation circuit (7) is composed of an oscillation circuit (14), a comparison circuit (15), and a one-shot circuit (1G). The oscillation circuit (14) outputs a triangular wave signal E and a trapezoidal wave signal F as shown in FIG. ). Comparison circuit (15
), the motor current command signal A is input to the non-inverting input terminal of the comparator circuit (15), and the output signal of the comparator circuit (15), that is, the PWM signal signal base. This becomes a pulse signal that becomes H level. Then, as described later, the F E of the motor drive circuit (6) is based on this PWM signal base steering direction command signal.
T (2) (3) (4) (5) are controlled.

Assuming that there is no one-shot circuit (1B), while the motor current command signal A is greater than the peak value of the triangular wave signal E, it will not become a PWM signal signal base signal, but will always be at H level, and the load time of the FET will increase. The rate becomes 100%. When the motor current command signal A approaches the peak value of the triangular wave signal E, the load time rate approaches 100%, and the PWM
The signal layer wave number (PWM frequency) becomes unstable and motor control noise is generated. In order to prevent this, a one-shot circuit (16) is used to synchronize the PW signal with the triangular wave signal E.
The M signal is stratified and turned off for a predetermined time, and the load time rate is 1.
I try not to get close to 00%.

In the one-shot circuit (1B), the oscillation circuit (14)
After passing through the amplifier (17), the trapezoidal wave signal F from
sent to. The differentiating circuit (19) outputs a positive trigger pulse at the rising timing of the input signal, that is, the falling timing of the trapezoidal wave signal F, and a second trigger pulse at the falling timing of the input signal, that is, the rising timing of the trapezoidal wave signal. (indicated by I in Figure 2). Differential circuit (1
The output signal I of 9) is sent to the rectifier diode (20),
This diode (20) outputs only the positive trigger pulse of the signal (2) (indicated by J in FIG. 2). The output signal J of the diode (20) is passed through the two resistors (21) (22
) and sent to the base of the switching transistor (23). The collector of the transistor (23) is connected to the output terminal of the comparison circuit (15), and the emitter is grounded.

While the trigger pulse is not output from the diode (20), the transistor (23) is off, and the PWM signal layer one-shot circuit (16) is not present.
It takes a value determined by triangular wave signal E and motor current command signal A. When the trigger pulse is output from the diode (20), the transistor (23) is turned on and the transistor (23)
Since the collector of the signal is grounded, the PWM signal layer level is reached only while the trigger pulse is being output. The trigger pulse is synchronized with the falling timing of the trapezoidal wave signal F, and the falling timing of the trapezoidal wave signal F is synchronized with the falling timing of the triangular wave signal E. Therefore, regardless of the value of the motor current command signal A, that is, when the motor current command signal A is smaller than the peak value of the triangular wave signal E as shown in the first half (left side) of FIG. Even if the motor current command signal A is larger than the peak value of the triangular wave signal E, as shown on the right, at least during the time (T) during which the trigger pulse is output in synchronization with the falling timing of the triangular wave signal E. is at the PWM signal layer level, and the load time rate never approaches 100%.

The switching circuit (8) is configured as follows.

The normal rotation signal Ct from the command circuit is sent to the first NAND circuit (24
), and the reversal signal C2 is input to the second NAND circuit (25).
Enter. Also, these two NAND circuits (24)
(25) includes a PWM signal layer.

The output terminal of the first NAND circuit (24) is connected to the gate terminal (G) of the first switching FET (2B). The drain terminal (D) of the first switching FET (26) is connected to the first FET for forward rotation via the resistor (27).
It is connected to the gate terminal (G) of E T (2), and its source terminal (S) is grounded. Further, a booster circuit (28) is provided between the drain terminal (D) of the first switching FET (2B) and the first terminal (Ha) of the motor (1). The booster circuit (28) has a power supply (BAT
Diode (29) and capacitor (30) in order from the T) side.
) and a resistor (31) are provided, and this resistor (31) is grounded. Then, resistor (31) and capacitor (
30) is connected to the first terminal (Ha) of the motor (1), and the part between the capacitor (30) and the diode (29) is connected to the first switching F via the resistor (32).
It is connected to the drain terminal (D) of E T (2B).

The output terminal of the second NAND circuit (25) is connected to the gate terminal (G) of the second switching FET (33). The drain terminal (D) of the second switching FET (33) is connected to the first FET for reversal through the resistor (34).
It is connected to the gate terminal (G) of E T (4), and its source terminal (S) is grounded. Further, a booster circuit (35) similar to the above is provided between the drain terminal (D) of the second switching FET (33) and the second terminal (Mb) of the motor (1).

The normal rotation signal CI is sent to the inverter circuit (36), and the output signal of the inverter circuit (36) is sent to the two resistors (37) (
38) and sent to the base of the first switching transistor (39). The collector of the first switching transistor (39) is connected to the gate terminal (G) of the second FET (3) for normal rotation via the resistor (40), and the emitter is grounded.

The reversal signal C2 is sent to the inverter circuit (41), and the output signal of the inverter circuit (41) is sent to the two resistors (42).
(43) and sent to the base of the second switching transistor (44). The collector of the second switching transistor (44) is connected to the gate terminal (G) of the reversing brush 2 FET (5) via a resistor (45), and the emitter is grounded.

Next, the motor drive circuit (6) and the switching circuit (
The operation of 8) will be explained.

When both the forward rotation signal CI and the reverse rotation signal C2 are at L level (when stopped), the four FETs (2) (3) (4) (5) of the motor drive circuit (6) are as follows. Everything is turned off and no current flows through the motor (1).

That is, since the normal rotation signal C1 is at L level, the base voltage of the first switching transistor (39), which is inverted by the inverter circuit (3B), becomes H level, and this transistor (39) is turned on. Therefore, the gate terminal (G) of the second FET (3) for forward rotation
becomes L level, and this FET (3) is turned off. Similarly, since the reversal signal C2 is at L level, the reversal brush 2
FET (5) is also turned off. In addition, the normal rotation signal C
1 is at L level, the output signal of the first NAND circuit (24) becomes H level regardless of the PWM signal value. Therefore, the first switching FET (2B
) gate terminal (G) becomes H level, this F E
T (2B) turns on. Then, when the first switching FET (2G) is turned on, the gate terminal (G) of the first forward rotation FET (2) becomes L level, and this FET (2) is turned off. Similarly, since the reversal signal C2 is at L level, the reversal brush 1FET (
4) is also turned off.

When the forward rotation signal CI is at the H level and the reverse rotation signal C2 is at the L level (during forward rotation), the reverse rotation brush 1 F E T
(4) and reverse rotation brush 2 FET (5) are turned off, forward rotation brush 2 FET (3) is turned on, and pw
The first FET (2) for forward rotation is turned on only while the M signal is at the upper level, and a current in the forward rotation direction flows through the motor (1) only during this period.

That is, since the reversal signal C2 is at the L level, the reversing brush 1 F ET (4) and the reversing brush 2 F ET (5) are turned off, as in the case of stopping. Normal rotation signal C
Since I is at H level, the first switching transistor (3) is inverted by the inverter circuit (36).
The base voltage of transistor (39) becomes L level, and this transistor (39) is turned off. For this reason, the second F E for forward rotation
The gate terminal (G) of T (3) becomes H level, and this F E T (3) is turned on. In addition, the normal rotation signal C
Since I is at the H level, the output signal of the first NAND circuit (24) is at the H level during the PWM signal value level, but when the PWM signal value level is reached, the output signal of the first NAND circuit (24) is at the L level. become the level. While the output signal of the first NAND circuit (24), that is, the voltage of the gate terminal (G) of the first switching FET (2B) is at the H level at the PWM signal value level, the first FET for forward rotation (2
) gate terminal CG) becomes L level, and this F E
T (2) is turned off and no current flows through the motor (1). Therefore, the voltage at point N of the booster circuit (28) is approximately Ov, whereas the voltage at point N is approximately Ov.
BATT) voltage, and the capacitor (30) is charged. In this state, the PWM signal value level is reached, and the output signal of the first NAND circuit (24), that is, the gate terminal (G) voltage of the first switching FET (26) becomes L.
When the level is reached, this FET (26) is turned off, the voltage at point P rises, and the first FET (26) for forward rotation is turned off.
The gate terminal (G) of (2) becomes H level. Therefore, the first FET (2) for forward rotation is turned on, and the current in the forward rotation direction passes through the first FET (2) for forward rotation, the motor (1), and the second FET (3) for forward rotation. flows. As a result, the voltage at point K increases, and the power supply (BA
TT) voltage level is reached. At this time, the capacitor (30) is charged as described above, and the forward rotation brush 1 F E
Since the gate current of T (2) is small, the voltage at point P increases from the power supply (BATT) voltage to (power supply (BATT) voltage + charging voltage) in accordance with the rise in voltage at point K.

Therefore, the gate voltage is maintained at a sufficiently high level with respect to the source voltage of the forward rotation brush 1 FET (2),
The forward rotation brush 1 FET (2) can be kept in the on state.

Here, assuming that the load time rate of the forward rotation brush 1 FET (2) is 100%, that is, the forward rotation brush 1 FET
(2) is always on and the first switching FET (26) is always off, the charge stored in the capacitor (30) between the K point and the N point is gradually discharged, and the voltage at the K point is Since the voltage at point P cannot be maintained at a sufficiently high level, the forward rotation brush 1 FET (2) cannot be maintained in the on state. However, as mentioned above, the one-shot circuit (16) of the PWM modulation circuit (7) prohibits the load time rate from reaching nearly 100%.
Since the PWM signal B is always set to L level in synchronization with the triangular wave signal E, the first signal B is synchronized with the triangular wave signal E.
Switching FET (2B) is always turned off.

Therefore, there is no problem as mentioned above, and the forward rotation brush 1 FET is
(2) can be driven.

When the reverse rotation signal C2 is at H level and the forward rotation signal CI is at L level (during reverse rotation), the forward rotation brush 1 F E
T (2) and forward rotation brush 2 FET (3) are turned off, and reverse rotation brush 2 FET (5) is turned on.
The first FE T for reversing only while PWM signal B is at H level.
(4) is turned on, and a current in the reverse direction flows through the motor (1) only during this time.

In the case of the above embodiment, since an FET is used in the motor drive circuit (6), high-speed switching is possible. Also, during forward rotation, the forward rotation brush 2FET (3) is always on,
Since only the forward rotation brush 1 FET (2) is controlled by the PWM signal, the forward rotation brush 1 FET (2) is controlled by the PWM signal.
) is turned off, but the normal rotation brush 2 remains on.
F E T (3) and the second for reversing which is turned off.
Diode (1) connected in parallel to FET (5)
A flywheel current flows to the motor (1) through 3). Similarly, when reversing, the second reversing
FET (5) and normal rotation brush 2 which is turned off
Diode (1) connected in parallel to FET (3)
A flywheel current flows through the motor (1) through the motor (1). This reduces current ripple and reduces radio noise and motor control noise when installed in an actual vehicle. Furthermore, as the flywheel current flows, the current flowing to the motor (1) increases, and the current flowing to the forward rotation brush 1 FET (2) or the reverse rotation first FET (4) decreases. Therefore, the decrease in motor current due to forcibly reducing the load time rate to less than 100% is compensated to some extent,
Since less current flows through the FET, heat generation also decreases. In addition, since the forward rotation brush 2 FET (3) and the reverse rotation second FET (5) are always on, there is no need to switch them at high speed, and the transistors (39) (44) are used for switching these. It is used.

In the above embodiment, since the load time ratio is never 100%, simple booster circuits (28) and (35) are used, but it is also possible to use a conventional booster circuit instead. .

Effects of the Invention According to the electric power steering device of the present invention, as described above, the load time rate of the FET does not become close to 100%, and therefore the PWM frequency does not become unstable. Generation of motor control noise can be prevented.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of the main parts of an electric power steering device showing one embodiment of the present invention, and FIG. 2 is a time chart showing signals of each part shown in FIG. (1)...Electric motor, (2)...Forward rotation brush 1FE
T. (3)... 2nd FET for forward rotation, (4)... 1st FET for reverse rotation, (5)... 2nd FET for reverse rotation, (6)...
・Motor drive circuit, (7)...PWM modulation circuit, (8
)...Switching circuit, (10) (11) (1
2) (13)...Diode, (14)...Oscillation circuit, (16)...One-shot circuit. Patent applicant: Koyo Seiko Co., Ltd. Figure 2

Claims (1)

[Claims] A first FET for normal rotation provided between the first terminal of the electric motor and the power supply side for assisting steering force, and a first FET provided between the second terminal of the electric motor and the ground side. 2nd FET for forward rotation,
A first FET for reversing provided between the second terminal of the electric motor and the power supply side, a second FET for reversing provided between the first terminal of the electric motor and the ground side, and connected in parallel to each of these FETs. a motor drive circuit configured with a bridge circuit including a diode; a means for outputting a steering direction command signal corresponding to the steering direction; a means for outputting a motor current command signal corresponding to the steering force; P that outputs the corresponding PWM signal
In an electric power steering device comprising a WM modulation means and a switching means for controlling an FET of a motor drive circuit based on a motor current command signal and a PWM signal, the PWM modulation means generates a PWM signal in synchronization with a PWM frequency. A means for forcibly turning off the steering wheel for a predetermined period of time is provided, and when the steering direction command signal is in the forward rotation direction, the switching means turns off the two reverse rotation FETs and turns on the second forward rotation FET to switch the steering direction to the forward rotation direction. PWM the first FET
When the steering direction command signal is in the reverse direction, the two forward rotation FETs are turned off, the second reverse rotation FET is turned on, and the first reverse rotation FET is controlled using PWM control.
An electric power steering device characterized by comprising means for controlling based on a signal.