JPH02270680A - Fail-safe device for rear wheel steering actuator - Google Patents

Abstract

PURPOSE:To prevent the seizure of a relay by operating a relay for supplying the driving current into an actuator and a relay for short-circuiting the electric power source terminals of the actuator, keeping a prescribed delay time, when a trouble is generated in an actuator drive control part on a vehicle in turn. CONSTITUTION:In the normal traveling, each detection signal theta, V of a steering angle sensor and a car speed sensor is inputted into a microcomputer 21, and a rear wheel steering angle instruction value is calculated in a rear wheel steering angle instruction value calculation circuit 41, and a motor 8 is driven on the basis of the result of the calculation, and rear wheels are steered through a rack shaft, etc. by the power of the motor 8. While, if the microcomputer 21 fails, and a fail signal is outputted from a trouble detecting means 80, an always closed type relay 31 is immediately turned OFF by a relay operation control part 70, and an always opened type relay 32 is turned ON after a certain delay time by the operation of a delaying means 90, and the lines L1 and L2 connected with the motor 8 are short-circuited, and the rear wheel 1 is returned to a neutral position.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a fail-safe device for a rear wheel steering actuator in a four-wheel steering vehicle.

2. Description of the Related Art An example of the basic structure of a conventional fail-safe device for a rear wheel steering actuator is shown in FIG. That is, the rear wheel 1 is connected to the kingpin 2. It is connected to a tie rod 4 via a knuckle arm 3, and the rear wheel 1 is steered by moving the tie rod 4 in the left and right direction. 5 is a ball screw into which the tie opening/end 4 is screwed; 6 is a driven gear fixed to the ball screw 5; 7 is a drive gear meshing with the driven gear 6; and 8 is a motor for steering the rear wheels. An output shaft 8a of this motor 8 is fitted and fixed to the drive gear 7. 8b is an angular velocity detection sensor attached to the motor 8. 9 is a motor drive circuit for driving the motor 8, and this motor drive circuit 9 receives an input signal S from a rear wheel steering angle target value setting circuit (not shown) and a feedback signal F from the angular velocity detection sensor 8b. In response to this, the rotation of the motor 8 is controlled.

Furthermore, a spring 15 is interposed between a support plate 4a projecting from the middle of the tie rod 4 and a vehicle body side plate 13. A failsafe mechanism 20 is constituted by the support plate 4a, the vehicle body side plate 13, and the spring 15. This failsafe mechanism 20
are attached to the left and right rear wheels 1, respectively.

According to such a configuration, the rotational force of the motor 8 is transmitted to the ball screw 5 via the drive gear 7 and the driven gear 6, and the tie rod 4 screwed to the ball screw 5 is moved in the left-right direction. Although the rear wheels 1 can be steered by the rocking motion of the knuckle arm 3 and the king pin 2, the control system such as the motor drive circuit 9 or the rear wheel steering angle target value setting circuit may malfunction due to some reason. If this occurs and the rear wheels 1 cannot be steered, the left and right rear wheels 1 are maintained in a straight-line state by the elastic force of the spring 15.
Steering of the rear wheels 1 is prohibited, allowing the control system to function as a safety device in the event of a failure of the control system.

On the other hand, in place of the fail-safe mechanism 20 described above, for example, Japanese Patent Application Laid-open No. 146773/1983 discloses a failure detection means for a control system that controls rear wheel steering, a rear wheel steering angle detection means, and a rear wheel steering angle detection means. and a means for returning the rear wheels to the neutral position, and when the control system is malfunctioning and the steering angle is small by receiving outputs from both the detection means, the rear wheels are returned to the neutral position using the neutral position return means. A configuration is disclosed.

Furthermore, Japanese Patent Application Laid-open No. 62-206867 discloses a system that includes an actuator for rear wheel steering and a hydraulic device that assists the operation of the actuator, and also includes a rotational state detection means of an engine, a hydraulic pressure detection means of the hydraulic device, Providing means for determining an abnormality in the hydraulic system from both of the detection means,
A configuration is disclosed in which the actuator is fixed at a predetermined position when there is an abnormality in the hydraulic system.

Furthermore, Japanese Patent Application Laid-open No. 62i31878 discloses a fluid pressure actuator for steering rear wheels and a control valve means for controlling this fluid pressure actuator, and when the control valve means is in normal operation, the control valve means and the fluid pressure An example of a safety device is disclosed in which the actuator is normally connected, but the connection between the two is cut off when a failure occurs in the fluid pressure system.

Furthermore, Japanese Utility Model Publication No. 62-23173 discloses that in a configuration in which the hydraulic pressure of a hydraulic cylinder for rear wheel steering is controlled by an electromagnetic switching valve, there is a normally closed opening/closing mechanism between the electromagnetic switching valve and the hydraulic cylinder. A configuration is disclosed in which a control valve is provided, and when an abnormality occurs, the opening/closing control valve is closed to maintain the hydraulic cylinder at the operating position at that time.

Furthermore, JP-A-62-139756 provides a control circuit for determining a rear wheel steering angle in response to detection signals from a front wheel steering angle sensor and a vehicle speed sensor, and an actuator operated by the output of this control circuit. An abnormality detection section for the drive system of each sensor and actuator is provided, and when this abnormality detection section detects an abnormality, the operation of the actuator is stopped, and the rear wheel steering angle is fixed at the same steering angle as at the time of occurrence of the abnormality. A means for retaining the information is disclosed.

Furthermore, Japanese Patent Application Laid-Open No. 62-241774 discloses a structure in which a front wheel steering mechanism and a rear wheel steering mechanism are mechanically connected, and an electric control device is provided to control the steering mode in the rear wheel steering mechanism. , a failure detection means for the rear wheel steering mechanism or the electric control device; a fixing means for fixing the steering angle of the rear wheels to the steering angle at the time the failure was detected in response to the failure detection means; An example of a failure compensating device for a front and rear wheel steered vehicle is disclosed, which is provided with means for canceling the steering force transmitted from the front wheel steering mechanism to the rear wheel steering mechanism when the front wheel steering mechanism fails.

However, in the case of such a conventional fail-safe device for a rear-wheel steering vehicle, especially in the case of the configuration example shown in FIG. Since the rear wheels 1 are held in this position, if a large force is applied to the rear wheels 1 from the outside, the rear wheels 1 may be steered, resulting in a problem of impaired running stability. There is.

On the other hand, the fail-safe mechanisms described in each of the above-mentioned publications have, as basic configuration means, an actuator for rear wheel drive, failure detection means for the control system that controls the steering of the rear wheels, and a means for detecting a failure in the control system that controls the steering of the rear wheels. Since the rear wheel drive actuator is equipped with an angle detection means and the rear wheel drive actuator is set to be neutral or fixed in the event of a failure of the control system, it is mechanically complex and difficult to manufacture and assemble into a vehicle. It has points.

Therefore, the present applicant has solved the problems of such conventional fail-safe devices for rear-wheel steering vehicles, simplified the configuration, and, in addition, has made it possible to immediately control the rear wheels in the event that an abnormality occurs in the control system. For the purpose of providing a fail-safe mechanism in which the steering is stopped and the rear wheels are not subsequently steered by one external force, Japanese Patent Application No. 63-226'183 discloses
The structure shown in FIG. 5 is proposed. In the figure, 1 is a rear wheel to be steered, 2 is a king pin, and 3 is a nockle arm.The rear wheel 1 is linked to a tie rod 4 via the king pin 2, the nocle arm 3, and the second wheel arm.

5 is a ball screw to which the tie rod 4 is screwed.

6 is a driven gear fixed to the ball screw 5, 7 is a drive gear meshing with the driven gear 6, 8 is a motor as an actuator for steering the rear wheels, and the output shaft 8 of this motor 8 is
a is fitted and fixed to the drive gear 7. 8b is an angular velocity detection sensor 29 attached to the motor 8.
A motor drive circuit 30 is a controller that transmits a rear wheel steering command signal S to the motor drive circuit 9.

Motor 8 above. Motor drive circuit 9 and controller 3
o for rear wheel steering. A control system 40 is configured.

The motor drive circuit 9 receives a rear wheel steering angle command signal S calculated by the controller 30 and a feedback signal F from the angular velocity detection sensor 8b, and drives and controls the rotation of the motor 8.

Furthermore, a spring 15 is interposed between a support plate 4a projecting from the middle of the tie rod 4 and a vehicle body side plate 13. That is, this spring 15 is given an elastic force that returns the rear wheel 1 to the neutral position.

FIG. 5 is a circuit diagram showing a specific example of the control system 40,
In the figure, 21 is a microcomputer, 22 is a counter circuit, and 23 is a watchdog timer.

24 is an OR gate circuit. Further, 26 and 27 are bias resistors, 28 and 29 are transistors, 31 is a normally closed relay, 32 is a normally open relay, 33 is a power supply for driving the relay, and 34
is an interface, and this interface 34
A feedback signal F from the angular velocity detection sensor 8b of the motor 8 is input to the , which is converted into a position signal of the motor 8, and this position signal is input to the microcomputer 21. Further, the transistors 28 and 29, the normally-closed relay 31, and the normally-opened relay 32 constitute circuit means for short-circuiting the power terminal of the motor 8. Further, the counter circuit 22 and the watchdog timer 23 constitute means for detecting a failure in the control system 40.

According to this configuration, during normal rear wheel steering, the transistors 28 and 29 are off, the normally closed relay 31 remains on, and the normally open relay 32 remains off. The output of a motor drive circuit 9 is connected to an input terminal of the motor 8 via a normally closed relay 31 . At this time, the rear wheel steering angle command signal SI is manually input to the microcomputer 21, a rear wheel steering angle target value is calculated, and the calculated command signal S is transmitted to the motor drive circuit 9. 9 is a motor 8 based on the command signal S.
The driving state continues while adjusting the rotation angle.

Next, if a failure occurs in the control system 40 for some reason, for example, if an abnormality signal is output from the microcomputer 21 that constitutes the control system 40, then the output from the output terminal P of the microcomputer 21 will be The program signal is the input terminal W of the watchdog timer 23,
Therefore, the signal is not transmitted to the output terminal W of the watchdog timer 23.

The reset pulse Rs from the microcomputer 21
This reset pulse R9 is input manually to the counter circuit 2.
It is also input to the input terminal CI of No. 2 and counted by the counter circuit 22. If the number of the reset pulses R, is thicker than a preset value, the logic output "1" is output from the output terminal C1 of the counter circuit 22, and the logic output of the OR gate circuit 24 also becomes "1". , a voltage is applied to the base of the transistor 28.29 through the bias resistor 26.27, turning on the transistor 28.29.Therefore, the current of the relay drive 111Wj33 is applied to the normally closed relay 31 and the normally closed Since the normally closed type relay 32 is energized, the normally closed type relay 31 is turned off and the normally closed type relay 32 is turned on, so that the driving power from the motor drive circuit 9 is not input to the motor 8, and the rotation of the motor 8 is stopped. At the same time as the motor 8 stops, the normally open relay 32 is closed, and the power terminal of the motor 8 is short-circuited.

Further, in response to the command signal S from the microcomputer 21, the motor 8 is detected by the angular velocity detection sensor 8b.
If the rotation angle does not follow the same, it is determined that there is an abnormality in the control system 40, and the microcomputer
A logic output "1" is output from the output terminal P1 of the OR gate 24, and the logic output of the OR gate 24 also becomes "1", and at the same time, the rotation of the motor 8 is stopped based on the same operating principle as described above, and at the same time, the normally open relay 32 is closed. The power supply terminals of the motor 8 are short-circuited by this configuration. Therefore, since the output shaft 8a of the motor 8 is fixed, an effect is obtained in which the steering force is not transmitted to the rear wheels 1 thereafter.

Problems to be Solved by the Invention However, in such a conventional rear-wheel steering vehicle 7 ale safe device, 31. In order to stop energizing the motor 8 as an actuator in the event of a failure in the control system 40, the on/off operating states of the normally closed relay 31 and the normally open relay 32 are controlled, and the operating timing of both relays is controlled. Since they are very close, the relay 31.32
If the operating timing of both relays 31 and 32 is deviated due to variations in the characteristics of the There was a problem in that it could cause a burn-in phenomenon in the relay.

For example, if the control system 40 fails, the relay 31.3
Assuming that the operation timing of step 2 is off and the normally open relay 32 is turned on before the normally closed relay 31 is turned off, a large current from the power supply VD will be applied to the normally open relay 32. As a result, the normally open type relay 32 is momentarily burned out, making it impossible to operate from now on.

Therefore, the present invention solves the problems of such conventional fail-safe devices for rear-wheel steering vehicles, and enables on-off operation of both relays when a failure occurs in the control system of a vehicle that is turning. It is an object of the present invention to provide a fail-safe device for a rear wheel steering actuator that maintains normal state timing and does not cause a burn-in phenomenon of a relay.

Means for Solving the Problems In order to achieve the above object, the present invention includes an actuator that steers a rear wheel, an actuator drive unit that drives the actuator, and a drive unit that calculates a rear wheel steering angle command value to drive the actuator. an actuator drive control section that issues a rear wheel steering angle command signal to the actuator; a failure detection means that detects a failure of the actuator drive control section;
The actuator is equipped with a relay that supplies a drive current from one source, a relay that shorts the power terminal of the actuator, and a relay operation control section that controls the open/close state of each of the relays based on the signal from the failure detection means. Furthermore, the relay operation control section is provided with a delay means that prevents the relay for supplying drive current to the actuator from turning on while the relay for shorting the power supply terminal of the actuator is on.

According to this configuration, during normal rear wheel steering, the actuator drive section operates based on the rear wheel steering angle command value issued from the actuator drive control section, and as the actuator is driven, the driving force of the actuator is applied to the rear wheels. This information can be transmitted to the rear wheels to steer the rear wheels.

Next, when a failure occurs in the actuator drive control section for some reason, the failure detection means attached to the actuator drive control section detects the above failure, and this detection signal is sent to the relay operation control section. 1! of the actuator based on the action of the delay means provided in the relay operation control section. While the source terminal short-circuit relay is on, the operation of each relay is controlled so that the relay that supplies drive current to the actuator is not on. Therefore, the timing of the on/off operation state of the relay is maintained normally, and there is an effect that there is no habituation that causes a phenomenon such as burn-in of the relay.

Embodiment An embodiment of a fail-safe device for a rear wheel steering actuator according to the present invention will be described in detail below, with the same reference numerals attached to the same components as in the conventional structure.

In the configuration shown in FIG. 1, 21 is a microcomputer as an actuator drive control section, and a rear wheel steering angle command value calculation circuit that calculates a rear wheel steering angle command value δ1 from the rear wheel steering angle θ and the vehicle speed V. 41 and this rear wheel steering angle command value δ1
A current command value calculation circuit 42 is provided which calculates a current command value (1) to be passed through the motor 8 as an actuator from the current rear wheel actual steering angle δ3 obtained from a feedback means (not shown). The above current command value
l1dth Modulate) is supplied to an actuator drive unit 43, which will be described later, via a current amplifier etc.
The motor 8 is driven to rotate in forward and reverse directions.

Reference numeral 80 denotes a failure detection means for detecting that a failure has occurred in the microcomputer 21. For example, when the rear wheel steering angle command value δ6'' becomes an unexpectedly large value, it is determined that a failure has occurred. Then, the failure detection means 80
A microcomputer fail signal MF is output from.

On the other hand, numeral 43 is an actuator drive unit for rotationally driving the motor 8, which includes four high-output field effect transistors (PET) M, , M,.

M, , M, the actuator drive section 4
Lines L, , L, derived from 3 are connected to the motor 8 . Incidentally, DFI is each transistor MH.

It is a gate protection diode attached to M,,M,,M,.

■o is a power source, 44 is a Hinney's, and the power source V is.

A normally closed relay 31 is disposed between the actuator drive section 43 and the actuator drive section 43 . That is, when the coil g in the normally closed relay 31 is energized, the normally closed relay 31 is turned off.

Further, one end of the lines L, L, led out from the actuator drive unit 43 has one end connected to the power supply VD.
A normally open relay 32 connected to is disposed. That is, when the coil Qt+ in the normally open relay 32 is energized, the normally open relay 32 is turned on.

On the other hand, the microcomputer fail signal M output from the failure detection means 80 attached to the microcombi coater 21 is passed through a diode D, with one end connected to the power supply (2). ', a resistor R2 connected in series, a capacitor CI and a diode D, one end of which is grounded, to a Schmitt trigger type inverter 46. That is, diode D has the function of protecting inverter 46 from negative voltage.

70 is a relay operation control section, and the output of the inverter 46 is inputted to an inverter 47 and an inverter 51 arranged in the relay operation control section 70 via a line L3.

The Schmitt trigger type inverter mentioned above is an inverter that has two stable states, and when the input signal waveform reaches a certain level, it transitions to another stable state and becomes the output signal waveform. It has hysteresis characteristics.

On the other hand, the above-mentioned inverter 47 is connected to an inverter 48 via a diode D3+resistor R5 connected in parallel and a capacitor C8 whose one end is grounded, and the output of this inverter 48 is connected to a transistor via a bias resistor R6. Connected to the base of 5o. The emitter side of the transistor 50 is grounded, and the collector side is connected to the coil Q1 in the normally closed relay 31. The diode D mentioned above is connected in the forward direction. Note that D is a Zener diode that protects the transistor 50 from surge voltage.

The inverter 51 on the other side is connected in series to two inverters 52 and 53 via a diode D 4+ resistor R6 connected in parallel and a capacitor C3 whose one end is grounded. is connected to the base of transistor 54 via bias resistor R6. The emitter side of this transistor 54 is grounded, and the collector side is connected to the coil h in the normally open type relay 32. The diode D4 mentioned above is connected in the opposite direction. Note that D6 is a Zener diode that protects the transistor 54 from surge voltage.

Above diode D! +Resistance RS+ Capacitor C! and diode D 4+ resistor R4+ capacitor C5
This constitutes delay means 90 for the on/off operation of the relays 31, 32.

FIG. 2 shows an example of a rear wheel steering system 61, in which a worm gear 55 is fixed to the output shaft 8a of the motor 8. A worm wheel 56 meshes with the worm gear 55, and a pinion gear 577 that rotates coaxially with the worm wheel 56! ! <Fixed. 58 is a rack shaft meshed with the pinion gear 57, 59 is a knuckle arm, 60 is a king pin shaft, and ■ is a rear wheel.

The operation of the rear wheel steering actuator fail-safe device according to the present invention will be described below. That is, when the vehicle is running normally, the steering angle θ and vehicle speed V at that time are detected by a steering angle sensor and a vehicle speed sensor (not shown), and are input to the microcomputer 21. A rear wheel steering angle command value δe is calculated by the rear wheel steering angle command value calculation circuit 41.

Next, the current command value calculation circuit 42 calculates the rear wheel steering angle command value δ.
1 and the current rear wheel actual steering angle δ obtained from a return means not shown.
A predetermined current command value 11 is calculated from 3, and this current command value 1'' is supplied to a PWM current amplifier (not shown), and the PWM
A drive current whose pulse width is modulated so as to follow the actual current value I flowing through the motor 8 is outputted by the g-flow amplifier,
This drive current is transmitted from the actuator drive section 43 to the motor 2.
is applied to

When rotating the motor 8, the field effect transistors M, , M, in the actuator drive section 43 are turned on.

■ Power on by turning off M3. The drive current from transistor M, line 151. Motor 8° line L2. The current flows through the transistor M4 and the ground 100, causing the motor 8 to rotate forward, and conversely, by turning on the field effect transistors M, , M, and turning off the field effect transistors M, , M, in the actuator drive unit 43. Power supply V
The drive current from transistor M1. Line L! , motor 8. Line L L+transistor M, and ground 1
00 and the motor 8 reverses. The rotational force of this motor 2 is transmitted from a worm gear 55 to a worm wheel 56 shown in FIG. The movement of the rack shaft 58 is transmitted to the knuckle arm 59 and the rear wheel 1
can be steered.

During the above operation, when the vehicle is running normally, the microcomputer fail signal MF output from the failure detection means 80 is rLowJ, and therefore the output of the inverter 46 is rHighj.

This signal is routed through the relay operation control section 70.
The signal is input to an inverter 47 and an inverter 51 that constitute the . That is, the output of the inverter 47 is rLovJ, the output of the inverter 48 is [HighJ, and the transistor 50 is on, while the output of the inverter 51 is rLovJ.
wJ, the output of the inverter 52 is rHighJ, the output of the inverter 53 is rLowJ, and the transistor 5
4 is off.

Therefore, the power supply ■. from coil e1 and transistor 5
A closed circuit reaching 0 is formed, and the normally closed relay 31 remains on, while the coil C1 is not energized, so the normally open relay 32 remains off.

Next, due to some reason, the microcomputer 21
Assume that a failure occurs. Then, the microcomputer fail signal MP output from the failure detection means 80 attached to the microcomputer 21 becomes r)IhighJ, so the output of the inverter 46 becomes rLowJ and the output of the inverter 47 becomes "High". Therefore 1HiX
Since the current supplied from vn' passes through diode D3 connected in the forward direction without passing through resistor R5, capacitor C
7 is rapidly charged and the input side of the inverter 48 immediately becomes rHighJ. Also, the output of the inverter 48 is rL
otvj, and as a result, the transistor 50 is turned off, cutting off the current to the coil C4, and the normally closed relay 3 is turned off.
1 is off. That is, the microcomputer fail signal MF is r
"When switching from LowJ to old ghJ, relay 31 is also switched off at the same time.

On the other hand, when the microcomputer fail signal MF becomes rHighJ, the output of the inverter 46 on the other side becomes "LowJ,
When the output of the inverter 51 becomes rllighJ,
Since the current supplied from the power source V D ' does not pass through the reversely connected diode D4, but through the resistor R4, the capacitor C3 is slowly charged and therefore the inverter 5
The input side of 2 gradually becomes rHighJ.

Also, the output of the inverter 52 is rLowj, and the output of the inverter 5
3 becomes rHighJ, the transistor 54 is turned on, and the current from the power source VI) flows through the coil e.

The normally open type relay 32 is turned on.

In other words, the microcomputer fail signal MP changes from rLowJ to
When switching to hJ, the relay 32 is turned on after a certain period of time based on the action of the delay means 90, and the line L and the line L supplying the drive current to the motor 8 are short-circuited.

Next, when the microcomputer fail signal M is canceled, the microcomputer fail signal changes from [old ghJ to [LowJ
The output of the inverter 46 becomes rHigJ, and the output of the inverter 47 becomes rLovJ. Then, the electric charge stored in the capacitor C2 returns to the inverter 47 through the resistor R3, so that the input side of the inverter 48 slowly becomes rLovJ, and at the point when it falls below the threshold of the Schmitt trigger type inverter 48. The output of the inverter 48 becomes rHighJ, and the transistor 50 is turned on.Therefore, from the power supply VI) to the coil a
, and the transistor 50 is formed again, and the normally closed relay 31 gradually returns to the on state.

That is, the microcontroller signal MP changes from r HighJ to r
[, When switching to owJ, the relay 31 is turned on after a certain period of time has elapsed, and the drive current is supplied to the motor 8.

On the other hand, the microcomputer fail signal changes from rHighJ to rLovJ, and the output of the inverter 46 becomes "H+g".
hJ + When the output of the inverter 51 becomes rLowJ, the charge stored in the capacitor C3 is transferred to the diode D.
Therefore, the input side of the inverter 52 rapidly becomes rLowJ, the output of the inverter 52 becomes rHighj, the output of the inverter 53 becomes rLowJ, and the transistor 54 is immediately turned on. Therefore the power supply ■. A closed circuit is formed from the filter L to the transistor 54, and the normally open relay 32 returns to the OFF state.

That is, the microcontroller signal MF changes from rHighJ to r
Switch to LowJ. Immediately, the relay 32 is turned off, the short-circuit condition to the motor 8 is released, and the driving of the motor 8 is restarted with the relay 310 turned on.

To summarize the above operation, when the microcomputer fail signal M is input from the failure detection means 80, the normally closed relay 31 is immediately turned off, while the normally open relay 32 is immediately turned off.
is turned on after a certain delay time, and the lines L,,L! connected to the motor 8 are turned on after a certain delay time. and the failure detection means 80
When the microcomputer fail signal M from , is released, contrary to the above, the normally closed relay 31 is turned on after a certain delay time, while the normally open relay 32 is immediately turned off. The operating mode is obtained. In other words, based on the action of the delay means, while the normally open type relay 32, which is a relay for shorting the power supply terminal of the actuator, is on, the normally closed type relay, which is a relay that supplies drive current to the actuator, is turned on. The drive can be controlled so that the relay 31 does not turn on.

FIG. 3 is a time chart for specifically explaining the above operation. When the microcomputer fail signal M2 changes from rLowJ to I'FightJ at time t in the figure, the inverter 47 constituting the relay control section 70 The output of .51 becomes "HighJ", the input side of the inverter 48 immediately becomes rHighJ, and the output of the inverter 48 becomes "rLo".
The transistor 50 is turned off and the normally closed relay 31 is turned off. At this time, based on the action of the delay means 90, the input side of the inverter 52 slowly
Shifts from LovJ to rHighJ, and the inverter 52
At time t, when the threshold voltage vs is reached, the output of the inverter 52 becomes rLowJ. Therefore, the transistor 54 is turned on by the inverter 53, and '
The open type relay 32 is turned on, and as described above, the line L for supplying drive current to the motor 8 and the line L are turned on.
, and are shorted. That is, time t.

Both relays 31 and 32 are off between and time t.

Next, at time t3, the microcomputer fail signal M y becomes “Hi”.
When ghJ becomes rLowJ, the outputs of inverters 47 and 51 that constitute the relay control unit 70 both become [LowJ
At the same time, the input side of the inverter 52 immediately becomes rHi.
ghJ to rLowJ, and therefore the inverter 5
The output of the inverter 53 turns off the transistor 54, and the normally open relay 32 immediately returns to off. At this time, based on the action of the delay means 90, the input of the inverter 48 The side is gently rHigh
The output of the inverter 48 becomes rHighJ at a time t4 when it shifts from hJ to "1, owl" and becomes lower than the threshold voltage Vs of the inverter 48, and the transistor 50 is turned on, causing a normally closed relay. 31 returns to on. That is, between time t3 and time t4, both relays 31
．． 32 are both turned off.

As is clear from the above time chart, when the microcontroller fail signal M is output, a certain period of time elapses after the normally closed relay 31, which is a relay that supplies drive current to the actuator, shifts from on to off. After the elapsed time, the normally open type relay 32, which is a relay for shorting the power supply terminal of the actuator, turns on, and conversely, the microcomputer fail signal M
When F is released, the relay 31 is turned back on after a certain period of time has elapsed since the relay 32 was turned off, and the driving of the motor 8 is resumed. Therefore, the effect that a large current from the power supply VD is not applied to the coil g constituting the relay 32 can be obtained.

Effects of the Invention As explained in detail above, the fail-safe device for a rear wheel steering actuator according to the present invention includes an actuator that steers a rear wheel, an actuator drive section that drives the actuator, and a rear wheel steering angle command. an actuator drive control section that calculates a value and issues a rear wheel steering angle command signal to the actuator drive section; a failure detection means that detects a failure of the actuator drive control section; and supplies a drive current from a power source to the actuator. The relay includes a relay that shorts the power terminals of the relay and the actuator, and a relay operation control section that controls the opening and closing states of each of the relays based on the signal from the failure detection means, and further includes a relay operation control section that controls the opening and closing state of each of the relays based on the signal from the failure detection means. Since the delay means is provided so that the relay for supplying drive current to the actuator does not turn on while the relay for shorting the power supply terminal of the actuator is on, the following effects can be obtained.

That is, during normal rear wheel steering, the actuator drive section operates based on the rear wheel steering angle command value issued from the actuator drive control section, and the driving force of the actuator is transmitted to the rear wheels to steer the rear wheels. In addition, when a failure occurs in the actuator drive control section due to some reason, the failure detection means attached to the actuator drive control section detects the above failure and the detection signal is sent to the relay operation control section. and can control the operation of each of the above-mentioned relays. That is, by the action of the delay means provided in the relay operation control section, while the relay for shorting the 'i4m terminal of the actuator is on, the relay operation is controlled so that the relay that supplies the drive current to the actuator is not turned on. Therefore, the timing of the on/off operation state of the relay is maintained normally, eliminating the habit of causing burn-in of the relay, etc., and maintaining normal operation and increasing safety.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a fail-safe device for rear wheel steering according to the present invention, Fig. 2 is a schematic diagram showing the main parts of the rear wheel steering system, and Fig. 3 is a timing diagram showing the operating state of the present invention. Chart, Figure 4 is a schematic diagram showing an example of a conventional fail-safe device,
FIG. 5 is a block circuit diagram of the conventional example, and FIG. 6 is a schematic diagram showing the basic structure of the conventional fail-safe device. DESCRIPTION OF SYMBOLS 1... Rear wheel, 8... Motor, 21... Microcomputer (actuator drive control part), 31... Normally closed type relay, 32... Normally open type relay, 41st... Rear Wheel steering angle command value calculation circuit, 42... Current command value calculation circuit, 43... Actuator drive unit, 46, 47, 48. 51. 52, 53.
...Inverter, 50.54...Transistor, 55
... Worm gear, 56 ... Worm wheel, 5
7... Pinion gear, 58... Rack shaft, 59...
・Knuckle arm, 60...King pin shaft, 70...
・Relay operation control unit, 80...Failure detection means, 90・
...delay means, Figure 2, Figure 6

Claims (1)

[Claims] (1) an actuator that steers a rear wheel, an actuator drive section that drives the actuator, and an actuator drive control section that calculates a rear wheel steering angle command value and issues a rear wheel steering angle command signal to the actuator drive section; a failure detection means for detecting a failure of the actuator drive control unit; a relay for supplying a drive current from a power source to the actuator; and a relay for short-circuiting a power supply terminal of the actuator;
and a relay operation control section that controls the opening/closing state of each of the relays based on the signal from the failure detection means, and further includes a relay for short-circuiting the power supply terminal of the actuator in the relay operation control section. A fail-safe device for an actuator for rear wheel steering, characterized in that a delay means is provided to prevent a relay for supplying drive current to the actuator from being turned on while the actuator is being operated.