JPH06312668A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To set the neutral return speed of rear wheels to a desired value without any influence on a rear wheel steering performance in a rear wheel steering device adapted to return the rear wheels to the neutral steering angle by the energizing force of a neutral return spring provided on a rear wheel steering mechanism when the device is abnormal. CONSTITUTION:In a rear wheel steering device adapted to steer the rear wheels by on-off controlling transistors TR1-TR6 in a driving circuit 41 of a rear wheel steering electric motor 12 through a transistor switching circuit 56, when an abnormality detecting part 52 detects the abnormality of the device, a power switch SW1 is turned off to cut off the power supply to the driving circuit 41, and a field winding of the electric motor 12 is short-circuited according to a pulse signal output from a pulse generating part 54c in a braking control part 54 with a designated period. Accordingly, braking torque corresponding to the duty ratio of the pulse signal is generated in the electric motor 12 so that the neutral return speed of the rear wheels can be set arbitrarily according to a pulse signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle rear wheel steering control device for controlling a rear wheel steering angle according to a driving state of the vehicle,
More specifically, the present invention relates to a rear wheel steering device for a vehicle that restores the rear wheels to a neutral steering angle when an abnormality occurs in the device.

[0002]

2. Description of the Related Art Conventionally, in a rear wheel steering system of a vehicle, a target steering angle of a rear wheel is calculated based on a driving state of the vehicle such as a steering angle of a front wheel and a vehicle speed. Thus, the electric motor that is the power source of the rear wheel steering mechanism is energized and controlled.

Further, in this type of device, each part constituting the rear wheel steering device, such as a sensor for detecting various driving states of the vehicle, a control circuit for setting a target steering angle and the like according to a detection result of the sensor. If any abnormality occurs in the rear wheel, the rear wheel may be steered largely regardless of the driving state of the vehicle, which is extremely dangerous.

Therefore, conventionally, in this type of device, a neutral return spring is provided in a rear wheel steering mechanism that steers the rear wheels in response to rotation of the electric motor, and when such a system abnormality occurs, the electric motor is energized. There is one in which the rear wheels are stopped and returned to the neutral steering angle by the biasing force of the neutral return spring.

Further, in such a device in which the rear wheel steering mechanism is provided with the neutral return spring for returning the rear wheels to the neutral steering angle, the electric motor can be operated by simply stopping the energization of the electric motor when the system is abnormal. , Since it freely rotates due to the biasing force of the neutral return spring received via the rear wheel steering mechanism,
When a system abnormality occurs, the rear wheels are quickly returned to the neutral steering angle, and especially when the rear wheels are steered largely, the rear wheel steering angle suddenly changes.

For this reason, in the above-described device in which the power supply to the electric motor is stopped when the system is abnormal and the rear wheel is returned to the neutral steering angle by the urging force of the neutral return spring, the electric motor is energized when the system is abnormal. In addition to simply stopping the motor, the field winding of the electric motor is short-circuited to provide a braking force when the electric motor is rotated by the force received from the rear wheel steering mechanism side (Honda Prelude Service). Manual, Structure No. 60SS010 Issued in September 1991: See).

That is, in this device, when the rear wheel rudder angle cannot be normally controlled due to an abnormality in the control circuit or the like, the electric motor is de-energized and the neutral return spring biases the rear wheel to the neutral rudder angle. In addition, at the time of this neutral return, the field winding of the electric motor is short-circuited so that the electromotive force generated in the field winding by the rotation of the electric motor applies an electromagnetic brake to the electric motor. It prevents the wheel steering angle from changing suddenly.

[0008]

However, when a braking force is applied to the electric motor, and thus the rear wheel steering mechanism, by short-circuiting the field winding of the electric motor as described above, the braking force is controlled. Power is uniquely determined from the characteristics of the electric motor.

That is, when the electric motor is rotated by the urging force of the neutral return spring transmitted through the rear wheel steering mechanism, assuming that the input torque of the motor shaft is T1 and the rotation speed of the electric motor is ω, the field is The braking torque T2 generated by the electric motor when the winding is short-circuited can be expressed by the following equation (1), and this model is represented in the figure as shown in FIG. In this model, the response from the input torque T1 to the rotation speed ω is expressed by the following equation (2), and it is steady (during neutral return) from s → 0 to The number ω is
It is given in (3).

[0010]

[Equation 1]

However, in the above equations (1) to (3), J is the inertia of the motor rotor, KE is the induced voltage constant, KT is the torque constant, L is the inductance of the motor coil, and R is the combined value of the coil resistance and the circuit resistance. , S are Laplace operators. Then, as is clear from the above equation (3), the neutral return speed is generally determined by the biasing force of the neutral return spring and the motor characteristics.

Therefore, when the rear wheels are returned to the neutral steering angle, the field winding of the electric motor is short-circuited to suppress the neutral return speed, and the braking force is unique from the characteristics of the electric motor. It will be decided. Therefore, in the above-described conventional device, in order to set the neutral return speed of the rear wheel steering angle to a desired value, the spring constant or set load of the neutral return spring that becomes a resistance when performing the rear wheel steering is adjusted. It is necessary to change the induced voltage constant KE and the torque constant KT, which are motor characteristics, and this will affect the characteristics at the time of steering the rear wheels, which is the original purpose of the rear wheel steering system.

The present invention has been made in view of these problems. As described above, the neutral return spring is provided in the rear wheel steering mechanism, and when an abnormality occurs, the drive of the electric motor is stopped to urge the neutral return spring. As a result, in the rear wheel steering system of the vehicle in which the rear wheels are returned to the neutral steering angle, the neutral return speed by the neutral return spring can be set to a desired value without affecting the rear wheel steering characteristics. The purpose is to do.

[0014]

A rear wheel steering system according to claim 1, which has been made to achieve the above object, has a structure as shown in FIG.
As illustrated in (a), a rear wheel steering mechanism for steering the rear wheels of the vehicle, and a biasing means for applying a biasing force for returning the rear wheels to the neutral steering angle to the rear wheel steering mechanism. An electric motor for driving the rear wheel steering mechanism against the urging force of the urging means, a drive circuit for energizing the electric motor, and a steering angle of the rear wheel depending on a driving state of the vehicle. An abnormality in the rear wheel steering control unit that drives the rear wheel steering mechanism by energizing the electric motor through the drive circuit so as to achieve the target steering angle and the rear wheel steering system including the rear wheel steering control unit Abnormality detection means for detecting, and when an abnormality is detected by the abnormality detection means, power supply to the drive circuit is cut off to prohibit rear wheel steering control by the rear wheel steering control means. A rear-wheel steering device for a vehicle, comprising: During operation, the field winding of the electric motor is short-circuited to provide a braking means for applying a braking force to the rotation of the electric motor by the biasing force, and a short circuit of the field winding of the electric motor by the braking means is predetermined. And a braking control means to be executed in a cycle.

A rear wheel steering system according to a second aspect of the present invention is, as illustrated in FIG. 1B, a rear wheel steering mechanism for steering a rear wheel of a vehicle, and the rear wheel steering mechanism including the rear wheel steering mechanism. A biasing means for applying a biasing force for returning the wheels to the neutral steering angle, an electric motor for driving the rear wheel steering mechanism against the biasing force of the biasing means, and a field winding of the electric motor. An H-bridge type drive circuit composed of a large number of switching elements connected in an H-shape sandwiching the switching element and a diode for protecting the switching elements connected in parallel to each switching element, and the steering angle of the rear wheels driving the vehicle. Rear wheel steering control means for driving the rear wheel steering mechanism by turning on / off the switching element of the drive circuit to energize the electric motor so as to obtain a target steering angle according to the state, and the rear wheel steering control. Error detection of rear wheel steering system including A detecting means, and a rear wheel steering prohibiting means for prohibiting the rear wheel steering control by the rear wheel steering control means by cutting off the power supply to the drive circuit when the abnormality is detected by the abnormality detecting means. In a vehicle rear wheel steering system including the above, when the rear wheel steering prohibiting means is activated, all switching elements of the drive circuit are turned off, and a predetermined electric load is connected between power supply terminals of the drive circuit. Second braking means for applying a braking force to the rotation of the electric motor due to the urging force is provided.

[0016]

In the rear-wheel steering system according to the first aspect of the present invention configured as described above, the rear-wheel steering control means causes the rear-wheel steering angle to be a target steering angle according to the operating condition of the vehicle. By energizing the electric motor via the drive circuit, the rear wheel steering mechanism is driven, and the abnormality detecting means detects an abnormality in the rear wheel steering system including the rear wheel steering control means. When the abnormality detecting means detects an abnormality in the rear wheel steering system, the rear wheel steering prohibiting means cuts off the power supply to the drive circuit to prohibit the rear wheel steering control by the rear wheel steering control means. . Further, since the rear wheel steering mechanism is provided with the biasing means for returning the rear wheels to the neutral steering angle, when the rear wheel steering prohibiting means cuts off the power supply to the drive circuit, the electric motor is
It rotates by the urging force of the urging means input from the rear wheel steering mechanism side. As a result, the rear wheels are steered in the neutral steering angle direction by the urging force of the urging means.

When the rear wheel is returned to neutral, the braking means short-circuits the field winding of the electric motor,
A braking torque is generated in the electric motor, and the braking control means causes the braking means to execute a short-circuiting operation of the electric motor field winding in a predetermined cycle. Therefore, the steering speed (neutral return speed) when the rear wheels return to the neutral steering angle when an abnormality occurs is
It is determined by the short-circuit cycle of the electric motor field winding controlled by the braking control means and the biasing force of the biasing means.

Further, in a rear wheel steering system according to a second aspect of the invention, the rear wheel steering control means controls the steering angle of the rear wheels to be the operating state of the vehicle, as in the rear wheel steering system of the first aspect. The rear wheel steering mechanism is driven by energizing the electric motor through the drive circuit so that the target steering angle corresponding to the rear wheel steering control means including the rear wheel steering control means is provided. Detect an abnormality. When the abnormality detecting means detects an abnormality in the rear wheel steering system, the rear wheel steering prohibiting means cuts off the power supply to the drive circuit to prohibit the rear wheel steering control by the rear wheel steering control means. . Further, since the rear wheel steering mechanism is provided with an urging means for returning the rear wheels to the neutral steering angle, when the rear wheel steering prohibiting means cuts off the power supply to the drive circuit, the electric motor causes the rear wheels to operate. It rotates by the urging force of the urging means input from the steering mechanism side. As a result, the rear wheels are steered in the neutral steering angle direction by the urging force of the urging means.

On the other hand, in the rear wheel steering system according to the second aspect, the drive circuit for energizing and driving the electric motor includes:
H consisting of a large number of switching elements connected in an H-shape across the field winding of an electric motor and switching element protection diodes connected in parallel to each switching element
It is composed of a bridge type drive circuit, and when the rear wheel steering prohibiting means is activated, the second braking means turns off all the switching elements of the drive circuit and connects a predetermined electric load between the power supply terminals. As a result, braking force is applied to the rotation of the electric motor. As a result, in the present invention, the neutral return speed of the rear wheel is determined by the magnitude of this electric load (resistance value).
And the urging force of the urging means.

That is, first, in the H-bridge type driving circuit, when the electric motor is rotated from the rear wheel steering mechanism side with all the switching elements turned off and the power supply terminals thereof are short-circuited, the rotation occurs. Due to the electromotive force, a current flows through the diode provided in each switching element, and a constant braking torque is generated in the electric motor. However, in the present invention, when an abnormality occurs, the power supply terminal of the drive circuit is connected via the electric load, so the current flowing by this electric load is limited and the braking torque changes depending on the magnitude of the electric load. Therefore, in the present invention, the neutral return speed of the rear wheel is determined by the magnitude of the electric load (resistance value) and the urging force of the urging means.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 2 is a schematic configuration diagram showing the overall configuration of the rear wheel steering system of the first embodiment to which the invention according to claim 1 is applied.

As shown in FIG. 2, the rear wheel steering system of the present embodiment has a rear wheel steering mechanism 10 for steering the left and right rear wheels 2RL, 2RR of the vehicle and a rear wheel steering mechanism 10 for driving the rear wheel steering mechanism 10. Electric motor 12 consisting of a three-phase brushless motor
And a magnetic pole sensor 20 for generating three-phase pulse signals PU, PV, PW for each predetermined rotation angle of the electric motor 12, and a steering angle θr of the rear wheels 2RL, 2RR attached to the rear wheel steering mechanism 10. The rear wheel steering angle sensor 22 and the steering shaft 28 from the steering wheel 24 for steering the left and right front wheels 2FL and 2FR by the vehicle driver to the steering gear box 26 are attached to the steering shaft 28. Front wheel steering angle θ
s), a steering sensor 30 for detecting the vehicle speed Vs, a vehicle speed sensor 32 for detecting the vehicle speed Vs, and a yaw rate W generated on the vehicle body.
The yaw rate sensor 34 for detecting s and an electronic control unit (ECU) 40 for controlling the rear wheel steering angle θr based on detection signals from these sensors.

As shown in FIG. 3, the rear wheel steering mechanism 10 includes a helical gear 13 fixed to the rotating shaft of the electric motor 12, and a helical gear 14 that meshes with the helical gear 13 to decelerate and input the rotation of the electric motor 12. A worm gear 15 provided on the rotary shaft of the helical gear 14, a worm wheel 16 meshed with the worm gear 15,
The pinion gear 17 attached to the rotary shaft of the worm wheel 16 is meshed with the pinion gear 17, and the rotation of the pinion gear 17 is converted into straight movement to convert the left and right rear wheels 2RL,
Rack 18 that is transmitted to a 2RR tie rod, and rack 1
When 8 is displaced from the neutral position in the left-right direction in FIG. 3,
The neutral return spring 19 applies a biasing force to the rack 18 according to the displacement amount.

The rear wheel steering angle sensor 22 for detecting the rear wheel steering angle is attached to the rotary shaft of the worm wheel 16 and detects the rear wheel steering angle from its rotational position. Also,
Even if an external force is input from the tire during normal traveling of the vehicle, the set load of the neutral return spring 19 is set to the rear wheels 2RL, 2
A load that can hold the RR at a neutral steering angle (for example, 100 kg
f) is set.

In the rear wheel steering mechanism 10 of the present embodiment constructed as described above, when the electric motor 12 rotates, the worm gear 15 rotates via the helical gears 13 and 14. Then, the worm wheel 16 is rotated and the pinion gear 17 also rotates. The rack 18 linearly moves by the rotation of the pinion gear 17, and steers the left and right rear wheels 2RL, 2RR via tie rods. Further, at this time, the neutral return spring 19 contracts as the rack 18 moves, and applies an urging force to the rack 18. The urging force is applied from the rack 18 to the pinion gear 17 and the worm wheel 1
6, is transmitted to the electric motor 12 via the worm gear 15, the helical gear 14, and the helical gear 13.

Therefore, when the driving of the electric motor 12 is stopped while the rack 18 is displaced from the neutral position by driving the electric motor 12 (that is, the left and right rear wheels 2RL, 2RR are being steered), The urging force generated by the neutral return spring 19 causes the electric motor 12 to rotate in a direction opposite to that at the time of steering the rear wheels, so that the rack 18, and hence the left and right rear wheels 2RL, 2 are rotated.
The RR returns to the neutral steering angle.

Further, in the rear wheel steering mechanism 10 of this embodiment, the worm gear 15 is provided in the power transmission system from the electric motor 12 to the rack 18, and the rotation of the electric motor 12 is transmitted from the worm gear 15 to the worm wheel 16. Thus, since the left and right rear wheels 2RL and 2RR are steered, as shown in FIG. 4, when the rear wheels are steered by the electric motor 12 (when the rear wheels are driven from the motor side), the electric motor 12 is driven. The generated torque is efficiently transmitted to the rack 18, but when the neutral return spring 19 returns the neutral state of the rear wheel (when the motor is driven from the rear wheel side), the neutral return spring 19 is generated.
It becomes difficult for the urging force of the above to be transmitted to the electric motor 12. Therefore,
When the rear wheel is returned to the neutral position by the neutral return spring 19, the rack 18 (and thus the rear wheel steering angle) is returned to the neutral position more slowly than when the electric motor 12 steers the rear wheel. It should be noted that the configuration is made in order to reduce the holding current for holding the rear wheel steering angle at the steering angle after steering the rear wheels 2RL, 2RR by driving the electric motor 12.

Next, as shown in FIG. 5, the ECU 40 includes field windings for the U / V phase, V / W phase, and W / U phase of the electric motor 12 as drive circuits for energizing the electric motor 12. In order to drive the electric motor 12 to rotate in both directions by bidirectionally flowing electric current to each other, six transistors TR1 to TR6 connected to each other in an H-shape with each field winding interposed, and each transistor TR1 to TR6. Diode D1 connected in parallel to
-D6 well-known H type bridge type drive circuit 41
Is provided.

The positive electrode of the battery 43 is connected to the positive electrode side power supply terminal 41a of the drive circuit 41 through the power switch SW1, and the negative electrode side power supply terminal 41b.
Is connected to the ground line to which the negative electrode of the battery 43 is connected, and further, in the current path from the power switch SW1 to the positive electrode side power supply terminal 41a, a resistor R for current detection is connected.
x is provided.

The power switch SW1 is turned on when a control signal input from the outside is at a low level to enable power supply from the battery 43 to the drive circuit 41, and the control signal input from the outside is at a high level. Then, the power supply path from the battery 43 to the drive circuit 41 is cut off.

Next, the ECU 40 calculates a rear wheel steering angle command value according to the operating state of the vehicle based on the detection signals from the above-mentioned sensors, and the rear wheel steering angle becomes this command value. A pulse width modulation signal (PWM signal) for duty-controlling the energization current of the electric motor 12 and the electric motor 12
Of the rear wheel command value calculating unit 50 for generating a direction command signal indicating the rotation direction of the rear wheel, the operating states of the rear wheel command value calculating unit 50, the terminal voltages A and B of the resistor Rx, the output pulses PU and PV of the magnetic pole sensor 20 , PW and the like to determine an abnormality of the device, and if the device is normal, output an abnormality detection signal that becomes Low level, and if there is an abnormality in the device, outputs an abnormality detection signal. Based on the abnormality detection signal, when the device is normal, the electric motor 12 is driven according to the output signal from the rear wheel command value calculation unit 50, and when the device is abnormal, the driving of the electric motor 12 is stopped to stop the electric motor 12. A braking control unit 54 for braking rotation, a direction command signal from the rear wheel command value calculation unit 50, three-phase pulse signals PU, PV, PW from the magnetic pole sensor 20, a control signal Sa from the braking control unit 54, S The transistor switching circuit 56 to the transistors S1~S6 on / off in the drive circuit 41 based on the equal are provided.

Here, the rear wheel command value calculation unit 50 uses the CP
It is composed of a well-known microcomputer including U, ROM, RAM and the like. In the rear wheel command value calculation unit 50, the rear wheel steering angle command value is calculated by the command value calculation processing shown in FIG. 6 executed every 5 msec.
The direction command signal and the PWM signal are output by the motor drive processing shown in FIG. 7 that is executed each time. Hereinafter, each process executed by the rear wheel command value calculation unit 50 will be described.

As shown in FIG. 6, in the command value calculation process, first, at step 110, the steering sensor 3
0, the vehicle speed sensor 32, and the front wheel steering angle θs detected by the yaw rate sensor 34, the vehicle speed Vs, and the yaw rate W.
Then, in step 120, whether or not each of the detected values θs, Vs, and Ws is within a preset normal range, that is, whether each of the above-mentioned sensors is operating normally, is read. to decide.

When it is determined in step 120 that each of the sensors is operating normally, the process proceeds to the following step 130, and the read detection result θs,
Based on Vs and Ws, the target yaw rate Wo during turning of the vehicle
Is calculated, and in the next step 140, the rear wheel steering angle command value θr for controlling the yaw rate Ws to the target yaw rate Wo.
Calculate o.

On the other hand, at step 120, at least one of the detected values θs, Vs, and Ws is out of the preset normal range, and it is judged from the detection result that normal rear wheel steering control cannot be executed. If done, step 1
At 50, the rear wheel steering angle command value θro is updated by subtracting the current rear wheel steering angle command value θro by a predetermined amount in order to steer the rear wheels 2RL and 2RR in the neutral steering angle direction.

In this way, when the latest rear wheel steering angle command value θro is calculated in step 140 or step 150, this time the process proceeds to the following step 160, and the rear wheel steering angle command value θro obtained above, A motor rotation angle command value θmo for controlling the rear wheel steering angle θr to the rear wheel steering angle command value θro is calculated from the current rear wheel steering angle θr detected by the rear wheel steering angle sensor 22, and the process is executed. Ends once.

Next, in the motor drive processing shown in FIG. 7, first, at step 210, the current motor rotation angle θm is calculated based on the three-phase pulse signals PU, PV, PW output from the magnetic pole sensor 20. Then, in the subsequent step 220, the motor rotation angular velocity dθm is calculated. Then, in the next step 230, based on the calculated motor rotation angle θm and motor rotation angular velocity dθm, and the motor rotation angle command value θmo calculated by the command value calculation process, the motor current is calculated using the following equation (4). The command value Imo is calculated.

Imo = Kp × (θm−θmo) −Kd × dθm (4) In the equation (4), Kp is a proportional gain and Kd is a differential gain. In this way, when the motor current command value Imo is calculated in step 230, it is then determined in step 240 whether the motor rotation angle command value θmo is larger than the motor rotation angle θm. If the motor rotation angle command value θmo is larger than the motor rotation angle θm, the direction command signal output to the transistor switching circuit 56 is set to the “High” level in step 250, and conversely, the motor rotation angle command value θmo is set. Is less than the motor rotation angle θm, the direction command signal is set to the “Low” level in step 260.

Further, in the following step 270, the drive duty ratio of the transistors TR1 to TR6 is obtained based on the motor current command value Imo calculated in the above step 230, the PWM signal corresponding to this is output, and the process is once ended. . Next, the abnormality detection unit 52 is configured as a logic circuit including various logic circuits, and performs the abnormality determination of the device every 5 msec. According to the procedure shown in FIG.

That is, in the abnormality detecting section 52, first, in step 310, it is judged whether or not the voltage (BA) across the resistor Rx for current detection is within a preset normal range. Determines whether the motor current is normal. When it is determined in step 310 that the motor current is normal, in step 320, the power switch SW1 is normal depending on whether the drive circuit side voltage B of the power switch SW1 is within the normal range. To determine whether it is working.

If it is determined in step 320 that the power switch SW1 is normal, step 3
At 30, the rear wheel command value calculation unit 50, especially the CPU, operates normally by monitoring the watchdog pulse for abnormality determination that is periodically output from the CPU in the rear wheel command value calculation unit 50. Judge whether or not.

Next, when it is determined in step 330 that the rear wheel command value calculation unit 50 is operating normally, the output voltage (power supply voltage) of the battery 43 is preset in step 340. Normal range (for example, 8V-16V)
To determine whether it is inside. Furthermore, this step 3
If it is determined at 40 that the power supply voltage is normal, at step 350, the difference between the motor rotation angle θm calculated by the rear wheel command value calculation unit 50 and the motor rotation angle command value θmo is within a predetermined range. Whether or not the magnetic pole sensor 20 is normally operating is determined depending on whether or not it is inside.

When it is determined in step 350 that the magnetic pole sensor 20 is operating normally, it is determined that the device is normal, and an abnormality detection signal is output in step 360.
When the abnormality is determined in any of the above steps 310 to 350, the abnormality detection signal is set to the low level in step 370.

Next, as shown in FIG. 5, the braking control unit 54 receives the PWM signal directly from the rear wheel command value calculation unit 50 and the abnormality detection signal from the abnormality detection unit 52 to the negation circuit 54a. When the abnormality detection signal input from the abnormality detection unit 52 is at a low level (that is, when the device is normal), the transistor switching circuit 56 uses the PWM signal from the rear wheel command value calculation unit 50 as the control signal Sa. Output from the AND circuit 54b, a pulse generator 54c that generates a pulse signal Po having a frequency of 50 Hz and a duty ratio of 30% as shown in FIG. 9, a pulse signal Po from the pulse generator 54c, and an abnormality from the abnormality detector 52. When the detection signal is input and the abnormality detection signal from the abnormality detection unit 52 is at the high level (that is, when the device is abnormal), the pulse generation unit 54c outputs the power. AND circuit 54 for outputting to the transistor switching circuit 56 a scan signal Po as the control signal Sb
and d.

Therefore, in the transistor switching circuit 56,
When the abnormality detection unit 52 detects that the device is normal, the PWM signal from the rear wheel command value calculation unit 50 is input as the control signal Sa, and the control signal Sb of Low level is input. When the abnormality is detected by the abnormality detecting unit 52, the pulse signal Po from the pulse generating unit 54c is input as the control signal Sb and the control signal Sa of Low level is input. Will be entered.

The braking control unit 54 outputs the abnormality detection signal from the abnormality detection unit 52 as it is to the power switch SW1 as a control signal. Therefore, when the abnormality detection unit 52 detects an abnormality in the device, the power switch SW1 is turned off and the power supply to the drive circuit 41 is cut off.

The transistor switching circuit 56 controls the control signal S.
If b is at the low level, the rear wheel command value calculation unit 50
Based on the direction command signal from the magnetic pole sensor 20 and the three-phase pulse signals PU, PV, PW from the magnetic pole sensor 20, the combination of the transistors to be turned on is S1 in order to drive the electric motor 12 to rotate in the rotation direction corresponding to the direction command signal. ~ S3, and S4 ~ S
One of each of the six transistors is selected, and the selected transistor is turned on / off at a duty ratio according to the control signal Sa, in other words, the PWM signal from the rear wheel command value calculation unit 50. On the contrary, when the control signal Sb is at the high level, the ground side transistors TR4 to TR6 are forcibly turned off and the positive side transistors TR1 to TR3 are turned on. The transistor switching circuit 56 is composed of a logic circuit including various logic circuits, like the abnormality detecting section 52.

In the rear wheel steering system of the present embodiment constructed as described above, when no abnormality has occurred in the system, the abnormality detection section 52 outputs a low level abnormality detection signal. Therefore, in this case, the power switch SW
A low-level control signal is input to the control unit 1 via the braking control unit 54, the power switch SW1 is turned on, and the electric motor 12 can be driven via the drive circuit 41. Further, in this case, the braking control unit 5
From 4 the PWM output from the rear wheel command value calculation unit 50
Since the signal is output as it is as the control signal Sa and the control signal Sb is at the Low level and is not output, the transistor switching circuit 56 determines that the three-phase pulse signals PU, PV, PW.
Based on the control signal Sa and the direction command signal, the drive circuit 4
Each of the transistors S1 to S6 of No. 1 is turned on / off. As a result, like the conventional rear wheel steering system, the rear wheels 2RL, 2R
The steering angle of R can be optimally controlled according to the vehicle driving state such as the steering angle of the front wheels 2FL and 2FR by the vehicle driver, the vehicle speed, and the yaw rate.

On the other hand, when an abnormality occurs in the apparatus and the abnormality detecting section 52 detects that, the abnormality detecting section 5
The abnormality detection signal from 2 changes to High level. Then, the control signal input to the power switch SW1 via the braking control unit 54 also becomes High level, so that the power switch SW1 is turned off and the power supply to the drive circuit 41 is cut off. The driving of the electric motor 12 is stopped. Therefore, when an abnormality of the device is detected by the abnormality detecting section 52 while the rear wheel is being steered, the electric motor 12 is driven in the opposite direction to that when the rear wheel is steered by the biasing force generated by the neutral return spring 19. Then, the rear wheel steering angle is returned to the neutral steering angle.

By the way, when all the transistors S1 to S6 in the drive circuit 41 are turned off at the time of returning to the neutral state, the field windings of the respective phases U, V and W are opened.
As indicated by the alternate long and short dash line in FIG. 10, braking is not applied to the rotation of the electric motor 12, and the rear wheel steering angle suddenly changes. Further, for example, by turning on all the transistors S1 to S3 and turning off all the transistors S4 to S6 in the drive circuit 41, both ends of the field winding of each phase U, V, W of the electric motor 12 can be short-circuited. For example, as shown by the dotted line in FIG. 10, the rotation of the electric motor 12 can be braked, but in this case, the braking force becomes too large and it takes time for the rear wheel steering angle to return to the neutral steering angle. Takes.

However, in the present embodiment, when an abnormality occurs in the device and the abnormality detection signal from the abnormality detection section 52 becomes High level, the braking control section 54 outputs the control signal Sa to the rear wheel command value calculation section 50. Low regardless of the PWM signal output from
The pulse signal Po output from the pulse generator 54c is output as the control signal Sb to the transistor switching circuit 56, and the transistor switching circuit 56 keeps the transistors S4 to S6 in the OFF state and controls the input control. Transistor S in drive circuit 41 in response to signal Sb
Turn on / off 1 to S3.

Therefore, in the rear wheel steering system of this embodiment, each phase U, V, W of the electric motor 12 is generated when the system is abnormal.
The field winding of the electric motor 1 is short-circuited according to the pulse signal Po output from the pulse generator 54c.
As shown in FIG. 9, braking is applied to No. 2 when the pulse signal Po is at the high level, and is in the non-braking state when the pulse signal Po is at the low level. Therefore, the braking force generated in the electric motor 12 at the time of neutral return of the rear wheel steering angle is reduced by an amount corresponding to the duty ratio of the pulse signal Po as compared with the case where the field windings are continuously short-circuited.

Therefore, according to this embodiment, as shown by the solid line in FIG.
4c can be optimally set according to the duty ratio of the pulse signal Po, and by adjusting the duty ratio of the pulse signal Po, the neutral return speed can be freely changed.

As described above, after the rear wheels have returned to the neutral steering angle when an abnormality occurs in the device, the rear wheels are held at the neutral steering angle by the set load of the neutral return spring 19, so that the tire is added. The rear wheels are not steered by external force. Here, in the present embodiment, the pulse generator 54c that generates the pulse signal Po that determines the neutral return speed of the rear wheels is
A preset fixed duty ratio (30 in this embodiment)
%) Of the pulse signal Po, the pulse generation unit 5 is, for example, as shown in FIG.
4c may be configured by a one-shot multivibrator, and a pulse signal (vehicle speed signal) corresponding to the vehicle speed Vs output from the vehicle speed sensor 32 may be input to the one-shot multivibrator.

In this case, for example, the one-shot multivibrator outputs a pulse signal which becomes High level for 2.5 msec. For each input pulse, as shown in FIG. Vehicle speed 60km / h
If 20 × 637 pulse signals are output per minute, the cycle of the vehicle speed signal is 18.9 msec. When the vehicle speed is low at 15 km / h, so the duty ratio of the pulse signal Po is about 13 %, The duty ratio of the pulse signal Po is about 53% when the vehicle speed is 60 km / h, and the duty ratio of the pulse signal Po is 88% when the vehicle speed is 100 km / h.

That is, in this way, the pulse generator 54c
Is composed of a one-shot multivibrator, and a pulse signal corresponding to the vehicle speed Vs output from the vehicle speed sensor 32 is input to this, the duty ratio of the pulse signal Po increases as the vehicle speed Vs increases.

Therefore, in this case, the braking force applied to the electric motor 12 increases as the vehicle speed Vs increases,
When the vehicle is traveling at low speed, the neutral return of the rear wheels is promptly performed by weak braking, and the straight-line safety of the vehicle is secured at an early stage. Conversely, when the vehicle is traveling at high speed, the neutral return of the rear wheels is slowed by strong braking (for example, 0.1 deg / sec.) To prevent the neutral return of the rear wheels from affecting the behavior of the vehicle body.

Further, for example, as shown in FIG. 12 (a), the pulse generating section 54c inverts the input signal to the two one-shot multi-vibrators 62, 64 and one one-shot multi-vibrator 64, and inputs the inverted signal. Circuit 6
6, and each one-shot multivibrator 62, 64
And three pulse generating circuits 60 including an OR circuit 68 for summing output pulses from
And the OR circuit 70 for obtaining the sum of the output pulses from the three-phase pulse signals PU, PV, PW output from the magnetic pole sensor 20.

That is, when the pulse generator 54c is configured in this way, the pulse generators 60 output the pulse signals PU, PV, PW of the respective phases U, V, W for a predetermined time (rising and falling). For example, since a pulse signal of 50 msec.) High level is output, the pulse generator 5
From FIG. 4c, the combination of these pulse signals is shown in FIG.
The pulse signal Po shown in is output.

Therefore, in this case, when the rotation of the electric motor 12 increases, the duty ratio of the pulse signal Po increases and the braking force increases. Conversely, when the rotation of the electric motor 12 decreases, the pulse signal Po changes. The duty ratio becomes smaller and the braking force becomes smaller. Therefore, in this case, the rotation speed of the electric motor 12, and thus the neutral return speed of the rear wheels, can be made substantially constant, and the rear wheels can be reliably returned at a safe return speed and reliably. Will be able to return to.

As described above, in this embodiment, the braking control unit 54 is provided with the pulse generation unit 54c for generating the pulse signal Po for braking the electric motor 12, and when the apparatus is abnormal, this pulse signal Po is used as the control signal. Although the configuration is such that Sb is output to the transistor switching circuit 56, for example, the braking control unit 54 is configured by a microcomputer or the like, and when an abnormality occurs, the rotation angular speed of the electric motor 12 is monitored and the High / Low of the control signal Sb is set. You may make it switch. Hereinafter, the motor braking processing operation when the braking control unit 54 is configured in this way will be described with reference to the flowchart shown in FIG.

As shown in FIG. 13, in this motor braking process, first, at step 410, the current motor rotation angle θm is calculated based on the three-phase pulse signals PU, PV, PW output from the magnetic pole sensor 20. And then step 4
At 20, the motor rotation angular velocity dθm is calculated.

Then, in the next step 430, it is determined whether or not the abnormality detection signal from the abnormality detection section 52 is at a high level, that is, whether or not there is an abnormality in the device, and the abnormality detection signal is low. If there is no abnormality in the device at the level, the process proceeds to step 440, the PWM signal from the rear wheel command value calculation unit 50 is set as it is as the control signal Sa, and at the next step 450, the control signal Sb is set. Lo
Set to w level and end the process once.

On the other hand, in step 430, the abnormality detection unit 5
When the abnormality detection signal from 2 is at a high level and an abnormality has occurred in the device, the process proceeds to step 460, the control signal Sa is set at a low level, and the PWM signal is output to the transistor switching circuit 56. To stop. Then, in subsequent step 470, it is determined whether or not the motor rotation angular velocity dθm calculated in step 420 is larger than a preset reference value δ, and the motor rotation angular velocity dθm is determined to be the reference value δ.
If it is larger, the control signal Sb is set to a high level in order to suppress the motor rotation angular velocity dθm, and conversely, if the motor rotation angular velocity dθm is the reference value δθ or less, step 4
Go to 50, set the control signal Sb to Low level,
The process ends.

As described above, in the case where the braking control section 54 executes the motor braking process, if the motor rotation angular velocity dθm is larger than the reference value δ, the control signal Sb becomes Hi.
If the gh level is reached and the electric motor 12 is braked and the motor rotation angular velocity dθm is equal to or less than the reference value δ, the control signal Sb is set to the Low level and the electric motor 12 is in the non-braking state. Therefore, in this case, the rotational angular velocity dθm of the electric motor 12 is controlled to the substantially reference value δ, and the neutral return velocity of the rear wheels can be made constant. In the motor braking process, the control signal S depends on whether the motor rotation angular velocity dθm is larger than the reference value δ.
Although the High / Low of b is switched, the neutral return speed of the rear wheels can be made constant by setting the duty ratio of the control signal Sb according to the motor rotation angular speed dθm, for example.

Further, when controlling the control signal Sb so that the neutral return speed of the rear wheels becomes constant in this way, it is not always necessary to use the magnetic pole sensor 20, and for example, detection from the rear wheel steering angle sensor 22 is possible. The rear wheel steering angle change speed is calculated based on the signal, and the control signal S is set so that this value becomes a predetermined value.
b may be controlled, or the rotation speed of the electric motor 12 is detected from the current flowing through the electric motor 12,
The control signal Sb may be controlled so that the rotation speed becomes a predetermined value.

Next, in this embodiment, the NOT circuit 54a and the AND circuit 54b are provided in the braking control unit 54 in order to prohibit the input of the PWM signal to the transistor switching circuit 56 when the abnormality of the device occurs. For example, the abnormality detection signal output from the abnormality detection unit 52 is also input to the rear wheel command value calculation unit 50, and if the abnormality detection signal is at the high level on the rear wheel command value calculation unit 50 side, the PWM signal If the output is stopped, it is not necessary to provide the NOT circuit 54a and the AND circuit 54b in the braking control unit 54, and the PWM signal output from the rear wheel command value calculation unit 50 is directly used as the control signal Sa.
Can be input to the transistor switching circuit 56.

Furthermore, in the present embodiment, the electric motor 12
I used a three-phase brushless motor for
Various conventionally used electric motors, such as a DC motor, can be used for this. The rear wheel steering system to which the invention described in claim 1 is applied has been described above. Next, the rear wheel steering system to which the invention described in claim 2 is applied will be described as a second embodiment of the present invention. To do.

The overall structure of the rear wheel steering system of this embodiment is exactly the same as that of the above embodiment shown in FIG.
Since only the internal configuration of 0 is different, description of the overall configuration of the device and the like will be omitted, and only the configuration and operation of the ECU 40 will be described. First, FIG. 14 shows the internal configuration of the ECU 40 of the rear wheel steering angle device of this embodiment. As shown in FIG. 14, in the ECU 40 of the present embodiment, as in the above embodiment, an H-type bridge type including six transistors TR1 to TR6 and diodes D1 to D6 connected in parallel to the respective transistors TR1 to TR6. The drive circuit 71 of FIG. Then, similarly to the above-described embodiment, the positive electrode side power supply terminal 71a of the drive circuit 71 can be connected to the positive electrode of the battery 43 through the resistor Rx for current detection and the power switch SW2, and the negative electrode side. The power supply terminal 71b is connected to the ground line to which the negative electrode of the battery 43 is connected.

On the other hand, when the connection between the drive circuit 71 and the battery 43 is cut off, the power switch SW2 does not open the positive-side power supply terminal 71a of the drive circuit 71 as in the above embodiment, but its power source. The load Z1 whose one end is grounded is connected to the supply terminal 71a. Therefore, when the power switch SW2 is turned off to interrupt the power supply path to the drive circuit 71, the load Z1 is connected between the power supply terminals 71a and 71b of the drive circuit 71.

Further, in the ECU 40 of the present embodiment, the rear wheel command value calculation unit 80 constituted by a microcomputer as in the above embodiment, the abnormality of the device is judged, and the abnormality which becomes High level when the device is abnormal. An abnormality detection unit 82 that outputs a detection signal, and a transistor switching circuit 86 that turns on / off the transistors TR1 to TR6 of the drive circuit 71 according to the output signals from these units are provided.

Here, the rear wheel command value calculation unit 80 executes the command value calculation process and the motor drive process in the same manner as the rear wheel command value calculation unit 50 in the above-mentioned embodiment to determine the rear wheel steering angle as the vehicle operating condition. Command signal and PWM for controlling the steering angle according to
A signal is output, but when the abnormality detection signal from the abnormality detection unit 82 is input to the rear wheel command value calculation unit 80 and the abnormality detection signal is at the high level, that is, when the device has an abnormality. , The output of the PWM signal is stopped.

Further, the transistor switching circuit 86 outputs the PWM output from the rear wheel command value calculation unit 80 when the abnormality detection signal output from the abnormality detection unit 82 is at a low level and no abnormality has occurred in the device. Signal and direction command signal, and three-phase pulse signals PU and P from the magnetic pole sensor 20.
When each of the transistors TR1 to TR6 in the drive circuit 71 is turned on / off based on V and PW to drive the electric motor 12 to rotate, and the abnormality detection signal is at the high level, and an abnormality has occurred in the device. Are configured to turn off all the transistors TR1 to TR6 in the drive circuit 71.

The abnormality detecting section 82 is constructed in exactly the same manner as in the above embodiment, and makes an abnormality determination in the procedure shown in FIG. The abnormality detection signal output from the abnormality detection unit 82 is also input to the power switch SW2, and the power switch SW2 connects the battery 43 to the drive circuit 71 if the abnormality detection signal is at the low level, If the abnormality detection signal is at high level, the load Z1 is connected between the power supply terminals 71a and 71b of the drive circuit 71.

In the rear wheel steering system of the present embodiment constructed as described above, when no abnormality occurs in the system, the abnormality detection section 82 outputs a Low level abnormality detection signal. The switch SW2 connects the battery 43 to the drive circuit 71, and the rear wheel command value calculation unit 80 outputs the PWM signal and the direction command signal for driving the electric motor 12 to the transistor switching circuit 86, and the transistor switching circuit 8
6 indicates each transistor T of the drive circuit 71 in response to this signal.
Turn on / off R1 to TR6. As a result, similarly to the rear wheel steering system of the above-described embodiment, the rear wheels 2RL and 2RR are controlled to the steering angle according to the vehicle running state such as the steering angle of the front wheels 2FL and 2FR by the vehicle driver, the vehicle speed, and the yaw rate. It will be.

On the other hand, when an abnormality occurs in the device and the abnormality detection unit 82 detects the fact, the abnormality detection unit 8
Since the abnormality detection signal from 2 changes to the high level, the power switch SW2 shuts off the power supply path to the drive circuit 71, connects the load Z between the power supply terminals 71a and 71b of the drive circuit 71, and switches the transistor. The circuit 86 turns off all the transistors TR1 to TR6 in the drive circuit 71.

Therefore, when an abnormality of the device is detected by the abnormality detecting portion 82 while the rear wheels are being steered, the electric motor 1 is driven by the urging force generated by the neutral return spring 19.
2 rotates in the opposite direction to that at the time of steering the rear wheels, and the rear wheel steering angle is returned to the neutral steering angle. At this time, the electric motor 1
The field winding of each phase U, V, W of No. 2 is the diode D1 connected in parallel to the transistors S1 to S6 in the drive circuit 71.
Since the load Z is connected via D6, current flows through the load Z due to the electromotive force generated in each field winding due to the rotation of the electric motor 12, and
This current, and eventually a braking force corresponding to the magnitude of the load Z, is generated.

The reason for this is as follows.
The braking force generated by the electromotive force generated in the U and V phase field windings will be described as an example. First, when the abnormality detecting unit 82 detects an abnormality, the U and V phase field windings of the electric motor 12 are connected to the load Z via the drive circuit 71 as shown in FIG. In the drive circuit 71, since the transistors TR1, TR2, TR4, TR5 are all in the off state, the electric motor 12 is rotated by the biasing force of the neutral return spring 19 and the electric motor 12 is changed from the U phase to the V phase. If an electromotive force is generated that tries to send a current to the phase,
In accordance with the directions of the diodes D1, D2, D4, D5 connected in parallel to the respective transistors TR1, TR2, TR4, TR5, a current flows through the load Z via the diodes D2, D4 along the path i1 shown by the dotted line in FIG. On the contrary, when an electromotive force that causes a current to flow from the V-phase to the U-phase is generated in the electric motor 12, the load Z is passed through the diodes D1 and D5 along the path i2 shown by the alternate long and short dash line in FIG. Current flows through.

Here, the electromotive force generated by the rotation of the electric motor 12 is K in proportion to the rotation speed ω of the electric motor 12.
It is given by E · ω. KE is an induced voltage constant. Further, the current loop i1 formed by the diodes D1 and D4 (or the diodes D2 and D5) as described above.
The circuit impedance Zi of (or i2) is the combined value of the inductance of the U / V phase field winding, the coil resistance of the field winding, and the forward resistance of the diodes D1, D4 (or D2, D5). Is expressed as R, it is expressed by the following equation (5). In the expression (5), s is a differential operator (called Laplace operator in the field of control engineering).

Zi = Ls + R + Z (5) Therefore, the current i flowing through the U and V phase field windings is
(6), i = KEω / (Ls + R + Z) (6) The electric motor 12 has a braking torque T proportional to this current.
2 (= KT · i) occurs. KT is a torque constant. The braking torque T2 is the torque constant KT
And the above equation (6), it can be described as the following equation (7).
From equation (7), it can be seen that the braking torque can be adjusted by the magnitude (resistance value) of the load Z.

T2 = KTKEω / (Ls + R + Z) (7) As described above, in the rear wheel steering system of the present embodiment, an abnormality occurs in the system and the neutral return spring 19 causes the rear wheel to become neutral. When the steering angle is returned to, the braking torque is generated in the electric motor 12 according to the magnitude of the load Z. Therefore, according to the rear wheel steering system of the present embodiment, the braking force generated in the electric motor 12 at the time of neutral return of the rear wheel steering angle is controlled by the field winding of the electric motor 12 according to the magnitude of the load Z. It can be made smaller than the conventional device in which short-circuiting occurs continuously, and the neutral return speed of the rear wheels can be arbitrarily set according to the magnitude of the load Z.

When the load Z is used to set the neutral return speed of the rear wheels to a desired value as in the rear wheel steering system of this embodiment, the neutral return spring 19 causes the electric motor 1 to return to the neutral position.
The input torque T1 input to the rotary shaft of No. 2 can be easily calculated from the gear ratio and efficiency of each part of the rear wheel steering mechanism 10. Therefore, if the desired neutral return speed ωo is determined, the load Z
The size of can be easily set using the following equation (8). However, in the actual design, taking into consideration that the input torque T1 has an external force from the tire in addition to the force of the neutral return spring 19, the load Z should be smaller than the value obtained by the following equation (8). It is desirable to set the value.

[0083]

[Equation 2]

In this embodiment, the fixed load having a preset resistance value is used as the load Z connected to the drive circuit when an abnormality occurs. However, as shown in FIG. 16, for example, the drive circuit 91 is used. A braking control circuit 95 whose circuit resistance changes according to the electromotive force generated by the electric motor 93 is provided between the power supply terminals 91a and 91b of the electric power supply terminals 91a and 91b. You may make it control constant. Hereinafter, this braking control circuit 95
The configuration and operation of will be described in detail.

In FIG. 16, the electric motor 93 for driving the rear wheel steering mechanism 10 is composed of a DC motor, and the drive circuit 91 of the electric motor 93 is connected in an H-shape with the field winding of the DC motor interposed therebetween. 1 shows a rear wheel steering system including a transistor and a diode, and a transistor switching circuit 97
When an abnormality is detected by the abnormality detector 99, each transistor in the drive circuit 91 is turned off as in the above embodiment. Further, the power switch SW3 is similar to the power switch SW2 in the above-described embodiment, and the abnormality detection unit 9
Although the power supply path to the drive circuit 91 is cut off when an abnormality is detected in 9, the braking control circuit 9
5 is always connected between the power supply terminals 91a and 91b of the drive circuit 91 regardless of the ON / OFF state of the power switch SW3.

As shown in FIG. 16, as an example of the braking control circuit 95, the cathode is connected to the positive side power supply terminal 91a of the drive circuit 91, and the anode is supplied through the resistor Ra to the negative side power supply of the drive circuit 91. A Zener diode Da having a breakdown voltage of about 7.5 V, which is connected to the terminal 91b, and a cathode which is also the positive electrode side power supply terminal 91a of the drive circuit 91.
And the anodes are connected to resistors Re and Rf (Re = Rf
= 1 kΩ) to the negative side power supply terminal 91b of the drive circuit 91 and the Zener diode Db having a breakdown voltage of about 2V, the base is connected to the anode of the Zener diode Da via the resistor Rb, and the collector is Resistor R
NP connected to the connection point between e and the resistor Rf and having the emitter connected to the negative-side power supply terminal 91b of the drive circuit 91
An N-type transistor TRa, a base of which is connected to the collector of the transistor TRa via a resistor Rc, a collector of which is connected to a positive side power supply terminal 91a of a drive circuit 91 via a semi-fixed resistor Rd, and an emitter of which is It is composed of an NPN-type transistor TRb connected to the negative power supply terminal 91b of the drive circuit 91.

In the braking control circuit 95 thus constructed, an abnormality occurs in the device and the power switch SW
3 and the transistor in the drive circuit 91 are turned off and the electric motor 93 is rotated by the neutral return spring 19, an induced voltage according to the rotation of the electric motor 93 is applied via the diode in the drive circuit 91. .

The applied voltage Vm at this time is, as shown in FIG. 15, independent of the rotation direction of the electric motor 93.
The positive side of the drive circuit 91 becomes positive, and as shown in FIG.
A terminal voltage Va on the anode side of the Zener diode Da,
ON / OFF state of transistor TRa, transistor T
Ra collector voltage Vb, transistor TRb on /
The off state changes according to the applied voltage Vm.

Then, for example, when a voltage Vm of 5 V is applied to the braking control circuit 95 by the rotation of the electric motor 93, the transistor TRb is turned on and the resistance of the semi-fixed resistor Rd is changed as shown in FIG. A current determined by the value flows, and a braking torque proportional to this current is generated in the electric motor 93.

On the other hand, the induced voltage generated by the rotation of the electric motor 93 decreases as the rotation speed of the electric motor 93 decreases. Then, when the voltage Vm applied to the braking control circuit 95 becomes 3 V or less due to the decrease in the rotation speed of the electric motor 93, the transistor TRb is turned off as shown in FIG. As a result, when the rotation speed of the electric motor 93 decreases, the impedance of the braking control circuit 95 increases, so that the electric motor 93 is not braked and the rotation speed increases.

Therefore, in the rear wheel steering system of this embodiment, when the system is abnormal, the electric motor 93 rotates at a substantially constant rotational speed for generating an induced voltage of approximately 3 V, and the neutral return speed of the rear wheels. Can be controlled to be substantially constant. On the other hand, when the device is normal, the power switch SW3 is in the ON state, so that the voltage applied to the braking control circuit 95 is the power supply voltage 8 to 16 V in normal condition. Then, in this case, as shown in FIG.
Since Rb is turned off, the impedance of the circuit becomes high, and the electric motor 93 can be driven without consuming unnecessary current in the device.

When the device is abnormal, the electric motor 93
When the induced voltage increases to a rotational speed at which the induced voltage becomes 3 V or more, the electric motor 93 is braked and the rotation of the electric motor 93 is suppressed. Therefore, a voltage exceeding the minimum power supply voltage 8 V is applied to the braking control circuit 95. Is never applied.

As described above, in the rear wheel steering system of this embodiment, when the rear wheels are returned to the neutral position, the motor current, and thus the braking force, is determined by the semi-fixed resistor Rd in the braking control circuit 95, and the zener diode is used. The braking on / off timing is determined by the breakdown voltage of Db and the ratio of the resistors Re and Rf. Therefore, by adjusting the ratio of the resistance value of the semi-fixed resistor Rd, the breakdown voltage of the Zener diode Db, and the resistors Re and Rf, the neutral return speed of the rear wheels can be set to an arbitrary value. .

Since the Zener diode Da is for preventing the transistor TRb from being turned on to wastefully consume the power source power when the device is normal, the Zener diode Da has a current source power source. It is sufficient to use a transistor having a breakdown voltage that is lower than the base-emitter voltage of the transistor TRa with reference to the lowest value of the voltage guarantee range.

[0095]

As described above in detail, in the rear wheel steering system according to the first aspect of the present invention, the neutral return speed of the rear wheels when an abnormality occurs is determined by the short circuit period of the electric motor field winding and the biasing means. And the urging force of. Therefore, according to the present invention, by adjusting the short-circuit cycle of the electric motor field winding, the neutral return speed of the rear wheels can be set to a desired value without affecting the steering characteristics of the rear wheels. become able to.

In the rear wheel steering system according to the second aspect of the invention, the neutral return speed of the rear wheels when an abnormality occurs is determined by the electric load connecting the power supply terminal of the drive circuit and the urging force of the urging means. It is determined. Therefore, according to the present invention, the neutral return speed of the rear wheels is adjusted without affecting the steering characteristics of the rear wheels by adjusting the magnitude of the electric load that connects the power supply terminal of the drive circuit when an abnormality occurs. The desired value can be set.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of the present invention.

FIG. 2 is a schematic configuration diagram showing a configuration of an entire rear wheel steering system of the first embodiment.

FIG. 3 is an explanatory diagram showing a configuration of a rear wheel steering mechanism of the first embodiment.

FIG. 4 is an explanatory diagram showing power transmission characteristics of the rear wheel steering mechanism of the first embodiment.

FIG. 5 is an electric circuit diagram showing an internal configuration of the ECU of the first embodiment.

FIG. 6 is a flowchart showing a command value calculation process executed by a rear wheel command value calculation unit in the first embodiment.

FIG. 7 is a flowchart showing a motor drive process executed by a rear wheel command value calculation unit in the first embodiment.

FIG. 8 is a flowchart showing an abnormality detecting operation in the abnormality detecting unit of the first embodiment.

FIG. 9 is an explanatory diagram showing a pulse signal output from the pulse generator of the first embodiment.

FIG. 10 is a time chart showing changes in the steering angle of the rear wheels due to the braking control of the first embodiment.

FIG. 11 is an explanatory diagram showing a configuration and an output pulse thereof when the pulse generator is operated by an output signal from the vehicle speed sensor.

FIG. 12 is an explanatory diagram showing a configuration and its output pulse when the pulse generator is operated by an output signal from the magnetic pole sensor.

FIG. 13 is a flowchart showing an example of a processing operation when the braking control unit is configured by a microcomputer.

FIG. 14 is an electric circuit diagram showing an internal configuration of an ECU in the rear wheel steering system of the second embodiment.

FIG. 15 is an explanatory diagram illustrating a motor braking operation according to the second embodiment.

FIG. 16 is an electric circuit diagram showing another configuration example of the ECU of the second embodiment.

17 is an explanatory diagram showing the operation of the braking control circuit shown in FIG.

FIG. 18 is an explanatory diagram showing a model of a power transmission system in a conventional rear wheel steering system.

[Explanation of symbols]

2RL, 2RR ... rear wheel 10 ... rear wheel steering mechanism 1
2, 93 ... Electric motor 15 ... Worm gear 16 ... Worm wheel 1
7 ... Pinion gear 18 ... Rack 19 ... Neutral return spring 20 ... Magnetic pole sensor 22 ... Rear wheel steering angle sensor 30 ... Steering sensor
32 ... Vehicle speed sensor 34 ... Yaw rate sensor 40 ... Electronic control device (EC
U) 41, 71, 91 ... Drive circuit 43 ... Battery 50, 80 ... Rear wheel command value calculation unit 52, 82, 99 ...
Abnormality detection unit 54 ... Braking control unit 54c ... Pulse generation unit 56, 86, 97 ... Transistor switching circuit 95 ... Braking control circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B62D 137: 00

Claims (2)

[Claims] 1. A rear wheel steering mechanism for steering a rear wheel of a vehicle, a biasing means for applying a biasing force to the rear wheel steering mechanism for returning the rear wheel to a neutral steering angle, and the rear wheel steering mechanism. An electric motor for driving the wheel steering mechanism against the urging force of the urging means, a drive circuit for energizing the electric motor, and a steering angle of the rear wheel corresponding to a target steering angle according to a driving state of the vehicle. So that the electric motor is energized through the drive circuit to drive the rear wheel steering mechanism, and an abnormality that detects an abnormality in the rear wheel steering system including the rear wheel steering control means. A detecting means, and a rear wheel steering prohibiting means for prohibiting the rear wheel steering control by the rear wheel steering control means by shutting off power supply to the drive circuit when the abnormality is detected by the abnormality detecting means. In a vehicle rear wheel steering system including: And a braking means for short-circuiting the field winding of the electric motor to apply a braking force to the rotation of the electric motor due to the biasing force, and a short circuit of the field winding of the electric motor by the braking means. A rear wheel steering device for a vehicle, comprising: 2. A rear wheel steering mechanism for steering the rear wheels of a vehicle, a biasing means for applying a biasing force to the rear wheel steering mechanism for returning the rear wheels to a neutral steering angle, and the rear wheel steering mechanism. An electric motor for driving the wheel steering mechanism against the urging force of the urging means, a large number of H-shaped switching elements connected to each other across the field winding of the electric motor, and a parallel connection to each switching element. And a switching element of the drive circuit so that the steering angle of the rear wheel becomes a target steering angle according to the driving state of the vehicle. A rear wheel steering control means for energizing the electric motor to drive the rear wheel steering mechanism, an abnormality detection means for detecting an abnormality in a rear wheel steering system including the rear wheel steering control means, and the abnormality detection means. If an abnormality is detected at A rear wheel steering prohibiting unit that prohibits the rear wheel steering control by the rear wheel steering control unit by cutting off the power supply to the dynamic circuit; In operation, the switching elements of the drive circuit are all turned off, and a predetermined electric load is connected between the power supply terminals of the drive circuit to apply a braking force to the rotation of the electric motor by the biasing force. A rear wheel steering system for a vehicle, comprising: a braking means.