JP2745129B2 - Electric power steering device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric power steering device for an automobile or the like.

FIG. 4 shows a conventional electric power steering apparatus. This device consists of an electric motor (1) to assist the steering force and four power transistors (2a) (2b)
(2c) A motor drive circuit (3) constituted by a bridge circuit composed of (2d), and a key switch (5) provided between the motor drive circuit (3) and the main power supply (battery) (4); A fail relay circuit (6), a torque sensor (7) for detecting an input torque of the steering shaft, a vehicle speed sensor (8) for detecting a vehicle speed,
A control device (9) for controlling the motor (1) and the fail relay circuit (6) based on the detected torque of the torque sensor (7), the detected speed of the vehicle speed sensor (8), and the like.

The control device (9) constantly monitors the abnormality of each part of the power steering device such as the torque sensor (7), the vehicle speed sensor (8), and the motor drive circuit (3). Then, based on the detected torque of the torque sensor (7), the detected speed of the vehicle speed sensor (8), and the like, the steering force assisting amount control for controlling the steering force assisting amount of the motor (1) is performed. Fail-safe control for turning off the relay contact of the fail relay circuit (6) when detected is performed.

The motor (1) is generally driven by PWM in order to save power. The PWM signal may be realized by an analog circuit, a microcomputer, or a logic IC.

FIG. 5 shows an example of a PWM conversion circuit using an analog circuit, and FIG. 6 shows waveforms at various parts. In this circuit, a triangular wave Vb oscillated from a triangular wave oscillating circuit (comparison means for PWM) (21) is compared with a steering force assisting amount instruction signal Va by a comparator circuit (22).
When the voltage is larger than Vb, a motor control signal (PWM signal) Vc of a predetermined level is output from the comparison circuit (22). This motor control signal Vc is sent to the motor drive circuit (3).

In such a PWM modulation circuit, when the triangular wave Vb is not input to the comparison circuit (22) due to a failure of the triangular wave oscillation circuit (21), as shown in FIG.
The motor control signal Vc output from the motor becomes a DC voltage, and the steering force assist amount of the motor (1) becomes abnormally large. For this reason, a large steering force assist unexpected by the driver may occur, or the arm short circuit of the motor drive circuit (3) may occur and the power transistors (2a) (2b) (2c) (2d) may be destroyed. There is. Such a problem is not limited to the PWM modulation by the analog circuit, but may occur similarly in the case of performing the PWM modulation by the microcomputer and the case of performing the PWM modulation by employing the logic IC.

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

Means for Solving the Problems In an electric power steering device according to the present invention, an electric motor for assisting a steering force is compared with a steering force assistance amount instruction signal in an electric power steering device driven by PWM. Detecting means for detecting that the output of the comparison wave from the PWM comparison wave generating means for generating the wave has stopped, and supplying power to the electric motor when the detection means detects that the output of the comparison wave has stopped. It is characterized by having means for stopping.

Operation of the Invention When the output of the comparison wave from the PWM comparison wave generation means stops due to some abnormality, the detection is detected by the detection means. Based on this detection, the power supply to the electric motor is stopped.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows the overall schematic configuration of an electric power steering apparatus. The device comprises an electric motor (1) for assisting steering force, a motor drive circuit (3) composed of a bridge circuit composed of four power transistors (2a) (2b) (2c) (2d), Motor drive circuit (3)
Key switch (5) provided between the power supply and the main power supply (4)
And a fail relay circuit (6), a torque sensor (7) for detecting an input torque of a steering shaft, a vehicle speed sensor (8) for detecting a vehicle speed, and a torque sensor (7).
A control device (9) for controlling the motor (1) and the fail relay circuit (6) based on the detected torque of the vehicle, the detected speed of the vehicle speed sensor (8), etc. A PWM control monitoring circuit (30) for interrupting the fail relay.

Although not shown, the motor (1) is connected to an appropriate portion such as an output shaft of a steering shaft or a steering gear via a speed reducer, a clutch and the like. The torque sensor (7) includes, for example, a potentiometer that detects a torsion of a torsion bar provided between an input shaft and an output shaft of a steering shaft.

The control device (9) performs a steering force assisting amount control for calculating a steering force assisting amount of the motor (1) based on a detected torque of the torque sensor (7) and a detected speed of the vehicle speed sensor (8), and a torque sensor. (7), vehicle speed sensor (8),
A microcomputer for performing fail-safe control for turning off a relay contact of a fail relay circuit (6) when an abnormality of each part of a power steering device such as a motor drive circuit (3) is detected, and a steering force assist obtained by the microcomputer A PWM modulation circuit (20) (see FIG. 2) for obtaining a PWM output according to the amount.

FIG. 2 shows a PWM modulation circuit (20) and a PWM control monitoring circuit (30), and FIG. 3 shows waveforms of respective parts of the PWM control monitoring circuit (30).

In the PWM modulation circuit (20), the steering obtained based on the triangular wave (voltage Vb) output from the triangular wave oscillation circuit (21), the detected torque of the torque sensor (7), the detected speed of the vehicle speed sensor (8), and the like. A steering force assisting amount indicating signal (voltage Va) representing the force assisting amount is compared by a comparing circuit (22), and when the indicating signal Va is larger than the triangular wave Vb, the comparing circuit (22) outputs a motor control signal (PWM signal) of a predetermined level. ) Vc is output. This motor control signal Vc is sent to the motor drive circuit (3).

In the PWM control monitoring circuit (30), the triangular wave Vb output from the triangular wave oscillation circuit (21) and the reference voltage setting device (3
The reference voltage Vo set in 1) is sent to the comparison circuit (32). The comparison circuit (32) compares the two input voltages and outputs a voltage (pulse signal) Vd of a predetermined level when the triangular wave is higher than the reference voltage Vo.

The pulse signal Vd output from the comparison circuit (32) is sent to a falling detection circuit (36) including an inverter circuit (33), a differentiation circuit (34), and a diode (35).
The fall detection circuit (36) outputs a positive trigger pulse Ve at the fall timing of the pulse of the pulse signal Vd.

The positive trigger pulse Ve output from the fall detection circuit (36) is divided by the resistors (37) and (38), and then sent to the base of the switching transistor (39).

The collector of the switching transistor (39) is connected to the output terminal of an integrating circuit (43) composed of a resistor (41) and a capacitor (42) to which the voltage + V of the DC power supply (40) is input.
Are connected via a resistor (44). The emitter of the switching transistor (39) is grounded. When the positive trigger pulse Ve is not output from the falling detection circuit (36), the switching transistor (39) is off, and current flows from the power supply (40) to the capacitor (42) via the resistor (41). , The capacitor (42) is being charged. Therefore, in this case, the output voltage Vf of the integration circuit (43) gradually increases. When a positive trigger pulse Ve is output from the falling detection circuit (36), the switching transistor (39) is turned on, and the capacitor (4
The electric charge charged in 2) is discharged via the resistor (44) and the switching transistor (39). Therefore, in this case, the output Vf of the integration circuit (43) decreases.

When the triangular wave Vb is output from the triangular wave oscillation circuit (21), the positive trigger Ve is output at predetermined intervals from the fall detection circuit (36), so that the capacitor (42) is charged and discharged at predetermined intervals. . Therefore, the integration circuit (43) outputs an exponential function type pulse Vf having a predetermined period smaller than the voltage + V of the power supply (40).

The output Vf of the integration circuit (43) is sent to the comparison circuit (46) via the resistor (45). The comparison circuit (46) is configured so that the output voltage Vf of the integration circuit (43) inputted thereto has a predetermined threshold value.
When it is lower than Vs, it is at L level, and when the output voltage Vf of the integration circuit (43) exceeds the threshold value Vs, it outputs an H level relay stop signal. The output Vg of the comparison circuit (46) is sent to the Fell relay circuit (6) as a relay control signal. The threshold value Vs is larger than the maximum value of the exponential function type pulse Vf output from the integration circuit (43) when the triangular wave Vb is output from the triangular wave oscillation circuit (21), and the voltage + V of the power supply (40).
It is set to a smaller value.

When the triangular wave oscillation circuit (21) is outputting the triangular wave Vb, the output Vf of the integration circuit (43) is equal to or lower than the threshold value Vs, and the output Vg of the comparison circuit (46) is at the L level.
Therefore, in this case, there is no influence on the fail relay circuit (6).

Due to some abnormality, the triangular wave oscillation circuit (2
When the triangular wave Vb is no longer output from 1), the comparison circuit (3
The pulse Vd is no longer output from 2), and accordingly,
The trigger pulse Ve is not output from the falling detection circuit (36). Therefore, the switching transistor (3
9) is always off and the output Vf of the integrating circuit (43)
Rises to the voltage + v of the power supply (40). Therefore, after a lapse of a required time (time T2) from time T1 when the triangular wave Vb is no longer output, the output of the integration circuit (43) becomes larger than the threshold value Vs, and the H-level relay output signal Vg is output from the comparison circuit.
Is output. This signal Vg is sent to the fail relay circuit (6), and the contact of the fail relay is turned off.

As a result, the power supply to the motor drive circuit (3) is cut off, and the drive of the motor (1) stops. Therefore, even if the triangular wave oscillating circuit (21) does not output the triangular wave Vb, even if an abnormality occurs, a large steering force assist unexpected by the driver occurs as in the related art, or the arm of the motor driving circuit (3) does not. A short circuit occurs and the power transistor (2
a) (2b) (2c) (2d) will not be destroyed.

Effect of the Invention In the electric power steering device according to the present invention,
In an electric power steering apparatus in which an electric motor for assisting a steering force is PWM-driven, an output of a comparison wave from a PWM comparison wave generation unit that generates a comparison wave to be compared with a steering force assistance amount instruction signal is output. Since the detection means for detecting the stoppage and the means for stopping the power supply to the electric motor when the detection means detects that the output of the comparison wave has been stopped, the comparison is performed from the PWM comparison wave generation means. Even if an abnormality occurs such that the wave is no longer output, a large steering force assist unexpected by the driver occurs as in the past, or the power transistor is destroyed due to the short circuit of the arm of the motor drive circuit as in the past. Disappears.

[Brief description of the drawings]

FIGS. 1 to 3 show an embodiment of the present invention. FIG. 1 is an electric block diagram showing the overall configuration of an electric power steering device, and FIG. 2 shows a PWM modulation circuit and a PWM control monitoring circuit. FIG. 3 is a time chart showing waveforms of various parts of the PWM control monitoring circuit, FIGS. 4 to 7 show a conventional example, and FIG. 4 is an electric block showing an entire configuration of an electric power steering device. Fig. 5, Fig. 5 is an electric circuit diagram showing a PWM modulation circuit, Fig. 6 is a time chart showing waveforms of various parts of the PWM modulation circuit, and Fig. 7 is a PWM modulation circuit when a triangular wave oscillation circuit stops outputting a triangular wave. 5 is a time chart showing waveforms of respective parts of FIG. (1) ... electric motor, (3) ... motor drive circuit,
(4)… Main power supply, (6)… Fail relay circuit,
(9) Control device (20) PWM modulation circuit (21)
…… Triangular wave oscillation circuit, (22) …… Comparison circuit, (30) ……
PWM control monitoring circuit.

Claims (1)

(57) [Claims] An electric motor for assisting a steering force is a PW motor.
In an electric power steering device driven by M,
PW that generates a comparison wave that is compared with the steering force assist amount instruction signal
Detecting means for detecting that the output of the comparative wave from the comparative wave generating means for M has stopped, and means for stopping the power supply to the electric motor when the output of the comparative wave has been detected by the detecting means. An electric power steering device, comprising: