JP2832380B2 - Vehicle rear wheel steering system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rear wheel steering device for a vehicle. More particularly, the present invention relates to a rear wheel steering device of a vehicle having rear wheel steering means adapted to steer rear wheels in a predetermined relationship with respect to front wheels.

(Prior art)

In a vehicle, a four-wheel steering system in which the rear wheels are steered in association with the steering of the front wheels has already been put to practical use. In this four-wheel steering device, an electronic control device such as a microcomputer is used to determine the steering angle of the rear wheels in relation to the steering of the front wheels. This control device controls the turning of the rear wheels according to one or more combinations of various factors representing the running state of the vehicle, such as the vehicle speed, the turning direction of the front wheels, the turning angle of the front wheels, the steering speed, and the like. The direction, the turning angle and the like are determined and the rear wheel turning means is operated.

In the rear wheel steering device of this type, when a failure occurs in the control device, the detection unit, or the operation unit, it is dangerous if the operation of the rear wheel steering unit is continued as it is. Therefore, when a failure occurs in the rear wheel steering device, a configuration is adopted in which the failure is detected and the rear wheel is returned to the neutral position.

Conventionally, the means for returning to the neutral position provided for this purpose is:
When a failure is detected, the rear wheels are returned at a predetermined return speed. The predetermined speed is set to a relatively low value in order to avoid this problem, since a sudden return from the four-wheel steering state to the two-wheel steering state may give the driver an uncomfortable feeling. However, depending on the driving state of the vehicle, this slow return speed may not be preferable. For example,
When the rear wheels are steered in the opposite phase direction with respect to the front wheels during relatively low speed operation, if a failure is detected in this state and the rear wheels start returning to the neutral position, this If the vehicle is accelerated during this state and the steering in the same direction is performed, the rear wheels are steered in the opposite phase, although it is desirable to steer the rear wheels in the same phase. It may be in a standing state. If a failure is detected while traveling on a curved road such as a mountain road, the rear wheels start to return from a one-way steering state at a predetermined return speed. However, since the front wheels are likely to frequently change the steering direction, a state occurs in which the phase changes from the same phase to the opposite phase or vice versa in the return process.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problem that occurs in a recovery process when a failure occurs in a conventional rear wheel steering device.

A further limited object of the present invention is to provide a control device for preventing a rear wheel from being out of phase with a front wheel in a process of returning a rear wheel to a neutral position when a rear wheel steering device fails.

[Means for solving the problem]

In order to solve the above-mentioned problem, the present invention provides a return speed control that controls a neutral return means so that a speed of return of a rear wheel to a neutral position when a rear wheel steering means fails varies according to a running state of a vehicle. Means. In one aspect of the present invention, the above-described return speed control means, when the steering direction of the front wheel and the rear wheel at the time of failure detection is the same phase, the steering speed of the front wheel at the time of return is determined by the predetermined rear wheel. When the speed is lower than the predetermined return speed, the rear wheel is returned at the predetermined return speed, and when the steering speed of the front wheel is higher than the predetermined speed, the rear wheel is returned at a speed higher than the front wheel steering speed. Also,
In another aspect of the present invention, when the steering direction of the rear wheel is in phase with the steering direction of the front wheel, the return speed control means causes the rear wheel to return to the neutral position at a predetermined return speed and is in the opposite phase. In some cases, the rear wheel returns to the neutral position at a speed higher than the predetermined return speed.

(Operation)

In the present invention, in the process of returning to the neutral position of the rear wheels, by controlling the speed of the return of the rear wheels to the neutral position when the rear wheel steering means fails, the speed is changed according to the traveling state of the vehicle. It is possible to prevent an undesirable state from occurring in relation to the front wheels. For example, when the steering directions of the front wheel and the rear wheel at the time of failure detection are in phase, and when the steering speed of the front wheel at the time of return is lower than a predetermined predetermined return speed of the rear wheel, the rear wheel is moved to the predetermined return speed. When the steering speed of the front wheels is higher than the predetermined speed, if the control to return the rear wheels at a speed higher than the steering speed of the front wheels is performed, the rear wheels are compared when the steering of the front wheels is not in an opposite phase. It is possible to prevent the driver from feeling uncomfortable by returning to the neutral position at a slowly returning speed. If the steering speed of the front wheels is higher than the above-mentioned predetermined speed, an anti-phase state may occur. In this case, the return speed of the rear wheels can be increased to prevent the occurrence of the anti-phase state. Further, when the steering direction of the rear wheel is in phase with the steering direction of the front wheel, the rear wheel is returned to the neutral position at a predetermined return speed, and when the steering direction is opposite phase, the rear wheel is rotated at a speed higher than the predetermined return speed. Can be prevented from continuing for a long time also by performing control to return to the neutral position.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 and 2 are an overall configuration diagram showing an embodiment of a rear wheel steering device of a vehicle according to the present invention, and a detailed view of main parts thereof.

As shown in FIG. 1, the rear wheel steering device 3 constitutes a part of a four-wheel steering device that also turns the rear wheel in accordance with front wheel steering, and includes a rear wheel steering rod 4 and It comprises a neutral position return means 6, a servo motor 8, a clutch 10, and a control unit 12.

The rear wheel steering rod 4 extends in the vehicle width direction, and both ends thereof are connected to a pair of left and right rear wheels 18L, 18R via a pair of left and right tie rods 14L, 14R and knuckle arms 16L, 16R. The rear wheels 18L and 18R are steered by displacing the rear wheel steering rod 4 in the vehicle width direction.

The neutral position returning means 6 has a casing 22 attached to the rear wheel steering rod 4 and fixed to the vehicle body 20 as shown in detail in FIG. The spring supports 24a and 24b are loosely fitted, and these spring supports
A compression spring 26 is provided between 24a and 24b. The rear wheel steering rod 4 extends through the casing 22, and a pair of flanges 4a and 4b are formed on the rear wheel steering rod 4 at intervals, and the spring receiver 24a is formed by the flanges 4a and 4b. , 24b, and the rear wheel steering rod 4 is provided with a compression spring 26.
Always at a predetermined neutral position, that is, the rear wheels 18L, 1
8R is biased toward a position where the steering angle is zero and the vehicle is going straight. The compression spring 26 has a spring force enough to overcome the side force during cornering.

The servo motor 8 is a stepping motor, and as shown in FIG. 2, its output shaft 8a is connected to a rear wheel steering rod 4 via a reduction mechanism 28 composed of a gear train 28a and a ball screw 28b.
As shown in FIG. 1, it is operated by a control signal from the control unit 12 to control the rear wheel steering rod 4.
Can be displaced from the neutral position against the urging force of the neutral position return means 6. The output shaft 8a of the servo motor 8 has a brake for applying a brake to the rotation of the output shaft 8a.
An output shaft 8a is provided by the operation of the brake 30.
Further, the rear wheel steering rod 4 can be locked so that the rear wheel steering rod 4 can be held in a predetermined displacement state. The operation of the brake 30 is controlled by the control unit 12.

The clutch 10 includes an output shaft 8a of the servomotor 8 and a gear train 28.
When a predetermined abnormality described later occurs, the connection between the rear wheel steering rod 4 and the servomotor 8 is released, and the rear wheel steering rod 4 displaced from the neutral position is returned to the neutral position returning means 6. Is returned to the neutral position by the urging force. The operation of the clutch 10 is controlled by the control unit 12.

FIG. 4 shows the brake 30 and the clutch 10 in detail. The brake 30 has a disk 32 fixed to the output shaft 8a of the servomotor 8. The disk 32 has a plurality of concave and convex grooves extending radially on both surfaces. Further, the brake 30 includes a ring plate 34 having an uneven groove that meshes with an uneven groove on the servo motor 8 side of the disk 32, and a suction plate fixed to the casing 35 by attaching the ring plate 34 to the casing 35.
And a solenoid 38 that is made to adsorb to 36. In the OFF state where the solenoid 38 is not energized, the brake 30 freely rotates the ring plate 34 together with the disk 22, but in the ON state where the solenoid 38 is energized, the ring plate 34 engages with the disk 32. The rotation of the disk 32, that is, the rotation of the output shaft 8a of the servomotor 8, is applied to the suction plate 36 while applying the braking force.

The clutch 10 is a twin clutch provided in series, and is a clutch 10A on the upstream side, that is, the brake 30 side.
Is a normally open type, and the downstream side, that is, the gear train 28
The clutch 10B on the a side is a normally closed type.
That is, the clutch 10A is a ring plate having an uneven groove that meshes with the uneven groove on the anti-servo motor side of the disk 32.
40 and a solenoid for adsorbing the ring plate 40 to a disk 44 fixed to a rotating shaft 42 coaxial with the output shaft 8a.
In the OFF state where power is not supplied to the solenoid 46, the connection between the ring plate 40 and the disk 44 is released, while in the ON state where power is supplied to the solenoid 46, the ring plate 40 and the disk 44 are connected. They are connected by surface contact. Note that the ring plate 40 always maintains the meshing state with the disk 32. Also,
The clutch 10B is provided with a ring plate 50 splined to a hub 48 fixed to the rotating shaft 42, and abuts against the surface of the ring plate 50 on the side opposite to the servomotor to move the ring plate 50 upstream by the spring force of the spring 52. The ring plate 50 pressed by the pad 54 is provided on the opposite side of the pad 54 with the ring plate 50 interposed therebetween.
A drum 58 is provided in contact with one surface of the ring plate 50 so as to restrict the movement of the ring plate 50 toward the servomotor by a predetermined amount or more. The drum 58 is fixed to a rotating shaft 56 coaxial with the rotating shaft 42. Further, a solenoid 60 that sucks the ring plate 50 to separate the ring plate 50 from the drum 58 is used.
In the OFF state where power is not supplied to the solenoid 60, the ring plate 50 and the drum 58 are connected by surface contact, and in the ON state where power is supplied to the solenoid 60,
The connection between the ring plate 50 and the drum 58 is released.

Therefore, the rotation of the output shaft 8a due to the operation of the servomotor 8 is transmitted to the gear train 28a only when the brake 30 and the clutch 10B are in the OFF state and the clutch 10A is in the ON state. Rear wheel steering is performed in this state. In addition, as the clutch 10, a clutch
The twin clutch 10A and 10B are provided in series because, even if one of them becomes inoperable due to seizure or the like, the other is turned on or off so that the servo motor 8 and the gear train 28a and, consequently, the connection with the rear wheel steering rod 4 can be released. One normally open type and the other normally closed type require a normally open type clutch to release the above connection when power supply to both clutches 10A and 10B is stopped due to disconnection of the coupler. However, the fact that both are normally open requires both clutches to be in the ON state for power transmission in normal times, and requires extra power consumption.

The control unit 12 shown in FIG. 1 controls the operation of the servomotor 8, the brake 30, and the clutch 10. The control by the control unit 12 is performed by the rear wheel steering device 2 as shown in FIG. Since it constitutes a part of the four-wheel steering device, it is designed to perform a required four-wheel steering function.

The four-wheel steering system includes, in addition to the rear-wheel steering system 2, a front-wheel steering mechanism 70 and various sensors that transmit various information to the control unit 12 for appropriate rear-wheel steering control according to running conditions. Equipped.

The front wheel steering mechanism 70 extends in the vehicle width direction, and has a pair of left and right tie rods 72L, 72R and a knuckle arm 74 at both ends.
A clutch 78 connected to a pair of left and right front wheels 76L and 76R via L and 74R, and a steering shaft 84 provided with a pinion 80 meshing with a rack 78 at one end and a steering wheel 82 at the other end. By operating the steering wheel 82, the rack 78 is displaced in the vehicle width direction to steer the front wheels 76L and 76R.

The rear wheel steering control by the control unit 12 is performed in response to the vehicle speed. An example of changing the steering ratio (rear wheel steering angle / front wheel steering angle) according to the vehicle speed is as shown in FIG. It may be. When the control characteristics shown in the figure are given, the rear wheel steering angle with respect to the front wheel steering angle changes in the same phase direction as the vehicle speed increases, and this control is shown in FIG.

In order to perform such rear wheel turning control, the control unit 12 includes a steering wheel angle sensor 86, a vehicle speed sensor 88,
A signal from a rotary encoder 62 for detecting the rotational position of the servo motor 8 is input. The control unit 12 sets the target rear wheel steering angle based on the steering angle (ideally equal to the front wheel steering angle) and the vehicle speed. And a control signal corresponding to the required rear wheel turning amount is output to the servo motor 8. Then, while the rotary encoder 62 constantly monitors whether the servo motor 8 is properly operated, the rear wheels 18L, 18R
Is to be steered.

In the rear wheel turning control, the control system has a double configuration for fail-safe. That is, a front wheel steering angle sensor 90 is added to the steering wheel steering angle sensor 86, a second vehicle speed sensor 92 is added to the vehicle speed sensor 88, and the rear wheel is steered to the rotary encoder 62 more than the clutch 10. A rear wheel steering angle sensor 64 for detecting the mechanical displacement of the member on the rod 4 side is added. Among these three sensors, the rear wheel steering is performed only when both of the corresponding sensors detect the same value. Have been to do. Therefore, when the vehicle speed detected by the first vehicle speed sensor 88 and the vehicle speed detected by the second vehicle speed sensor 92 are different from each other in the above three sets of sensors, it means that an abnormality, that is, a failure has occurred. Rear wheel by control
18L and 18R are held at the neutral position.

For detecting various abnormalities, the control unit 12 receives ON / OFF signals from the switches 94, 96, 98, and 100, and an L terminal 102 of the alternator. Is done. Here switch 94
Is a neutral clutch switch, switch 96 is an inhibitor switch, switch 98 is a brake switch, and switch 100 is an engine switch. Here, in a vehicle equipped with a manual transmission, the neutral signal 94 outputs an OFF signal when the shift position of the manual transmission depresses the neutral or clutch pedal,
Otherwise, an ON signal is output. In a vehicle equipped with an automatic transmission, the inhibitor switch 96 outputs an ON signal when the range is in neutral (N) or parking (P), and outputs an OFF signal when the range is in the travel range. ing. The brake switch 98 outputs an ON signal when the brake pedal is depressed, and the engine switch 100 outputs an ON signal when the engine is operating.

FIG. 7 is a block diagram showing the control system.

The microprocessor 104 has a double structure of I and II, and the microprocessor 104 includes vehicle speed sensors 88, 9
2 and switches 94, 96, 98, 100 and the signal from the L terminal 102 of the alternator are input via a buffer 106, and the signals from the sensors 86, 90, 64 are input via an A / D converter 108. , A signal from the rotary encoder 62 is input via the interface 110. On the other hand, the signal generated by the microprocessor 104 is sent to the servomotor 8 via the motor drive circuit 112, sent to the brake 30 via the brake drive circuit 114, or sent to the clutch 10 via the clutch drive circuit 116. Sent out. The rear wheel turning control is started on condition that the signal from the L terminal 102 of the alternator becomes high (Hi). In the figure, reference numeral 118 denotes a battery, 120 denotes an ignition key switch, and 122 denotes a relay. When a predetermined abnormality described later occurs, the energization of the coil 126 is stopped by the operation of the relay drive circuit 124. The switching of the contact point 122 is performed, the power supply to the motor drive circuit 112 is stopped, and the warning lamp 128 is turned on. When an abnormality other than the above occurs, the microprocessor 104 controls the transistor 1
The base current flows through 30, and the warning lamp 128 lights up.

Next, abnormalities that may occur in the four-wheel steering device and their measures will be described.

In the present embodiment, a treatment corresponding to the location where the abnormality has occurred is performed, and there are the following two forms of the treatment.

Treatment Mode A (Control During First Fail Mode) This is a mode in which control of rear wheels 18L and 18R and determination of their positions are still possible. That is, when the rear wheel steering rod 4 can be returned to the neutral position by the servo motor 8, the return to the neutral position is performed by the servo motor 8. Specifically, the contents of this treatment are as follows.

After the warning lamp 128 is turned on, the rear wheel steering rod 4 is returned to the neutral position by driving the servo motor 8, and then the brake 30 is turned on.

Treatment Mode B (Control in Second Fail Mode) This is a mode in which the control of the rear wheels 18L and 18R or the position determination thereof becomes impossible. The details of this treatment are as follows.

After the warning lamp 128 is turned on, the brake 30 is turned on, the power supply to the servomotor 8 is stopped, and then the clutch 10A is turned off, the connection between the servomotor 8 and the rear wheel steering rod 4 is released, and the neutral position is set. After waiting for the rear wheel steering rod 4 to return to the neutral position by the spring force of the return means 6, (6) the clutch 10A is turned on to connect the servo motor 8 to the rear wheel steering rod 4.

In the above treatment mode B, if the operation of turning off the clutch 10A is performed rapidly, the rear wheel steering rod 4 will return to the neutral position in a short time due to the spring force of the neutral position return means 6, When such a phenomenon occurs when the front and rear wheels are in the same phase state, it is considered that the vehicle attitude is adversely affected. Therefore, in this embodiment, the neutral position of the rear wheel steering rod 4 displaced to the same phase side is considered. The operation of the clutch 10A is controlled by the control unit 12 so as to gradually return to the position. That is, as shown in FIG.
ON / OFF by intermittently repeating the clutch 10A for a predetermined time
Control to operate, as shown in FIG.
The rear wheel steering rod 4 is gradually returned to the neutral position.

In the following, abnormal modes and their setting conditions are classified into each system,
The corresponding treatment mode will be described.

Vehicle speed signal system When it is determined that an abnormality has occurred in this system, the treatment of the above-described mode A is performed.

(1) Change amount error of first vehicle speed sensor 88 In this determination, the brake switch 98 is OFF and the first vehicle speed sensor 88 detects the deceleration of | dV ₁ / dt |> a (constant). Is required. Wherein V ₁ was representative of a vehicle speed at which the first vehicle speed sensor 88 has detected. In other words, when the vehicle decelerates beyond a predetermined level even though the vehicle is not braked, it is determined that the first vehicle speed sensor 88 is abnormal.

(2) Change amount error of second vehicle speed sensor 92 This determination is made in the same manner as in the case of the first vehicle speed sensor 88 described above.
The condition is that the brake switch 98 is in the OFF state and the second vehicle speed sensor 92 detects the deceleration of | dV ₂ / dt |> a (constant). Here V ₂ represents a vehicle speed at which the second vehicle speed sensor 92 has detected.

(3) Vehicle speed mismatch error This determination is made on condition that the detection values of the first and second vehicle speed sensors 88 and 92 do not match as represented by, for example, | V ₁ −V ₂ |> b (constant). You.

In this case, since it is considered that an abnormality of at least one of the vehicle speed sensors has occurred, it is determined that the abnormality is abnormal irrespective of whether the abnormality has occurred in any of the sensors 88 and 92, and as described above, , The processing of the aspect A is performed.

(4) Simultaneous Abnormality of Both Vehicle Speed Sensors 88 and 92 This determination is based on the fact that the signal from the L terminal 102 of the alternator is high (Hi) and the first and second vehicle speed sensors 88 and 92
Is assumed to be zero (V ₁ = V ₂ = 0), in the case of a vehicle with a manual transmission, on the condition that the ON state of the neutral clutch switch 94 continues for a certain period of time, In the case of a motorized vehicle, the inhibitor switch 96
Are OFF, the engine switch 100 is ON, and the brake switch 98 is OFF for a certain period of time.

That is, despite the fact that the engine speed is attainable based on the amount of power generation and the vehicle can be considered to be traveling from the shift position, the vehicle speed of zero means that any abnormality has occurred in the sensors 88 and 92. No.

Rear wheel steering mechanism system When it is determined that an abnormality has occurred in this system,
The treatment of Embodiment B is performed.

(1) Control Deviation (Part 1) This determination is based on a mismatch between the output (EN) of the rotary encoder 62 and the output of the rear wheel steering angle sensor 64, that is, the rear wheel steering angle (θR), for example, | f (EN) −G (ΘR) |> C (constant).

(2) Control deviation (No. 2) This determination is based on the discrepancy between the target rear wheel steering angle (θr) set by the control unit 12 and the actual rear wheel steering angle (θR), for example, | θr−θR |> C ( (Constant).

(3) Rear wheel reference position error This determination is made on condition that the center reference of the rear wheel cannot be found at the start of control (at the time of initialization). Here, the initialization is performed on condition that the engine switch 100 is turned on.

DC servo motor system When it is determined that an abnormality has occurred in this system,
The treatment of Embodiment B is performed.

(1) Rotation amount error This judgment is based on the control amount and the rotation amount of the motor 8 (the encoder 62
Are not the same.

(2) Motor monitor error This judgment is made in the following cases.

  Disconnection or short circuit of motor coil.

  Disconnection or short circuit of the harness.

  Failure of the motor drive circuit 112.

Rear wheel steering angle sensor system When it is determined that an abnormality has occurred in the present system, the treatment of mode B is performed.

(1) Rotary encoder monitor error This determination is made on the condition that an error is detected in the code output from the encoder 62.

(2) Rear wheel steering angle sensor monitor error This determination is made on condition that the output of the rear wheel steering angle sensor 64 exceeds a set range.

Front wheel steering angle sensor system When it is determined that an abnormality has occurred in this system,
The treatment of aspect A is performed.

(1) Steering angle sensor monitor error This determination is made on condition that the output of the steering angle sensor 86 exceeds a set range.

(2) Front wheel steering angle sensor monitor error This determination is made on condition that the output of the front wheel steering angle sensor 90 exceeds a set range.

(3) Front Wheel Steering Angle Mismatch Error This determination is made on the condition that the difference between the output of the steering wheel steering angle sensor 86 and the output of the front wheel steering angle sensor 90 exceeds a certain value.

Incorrect disconnection operation of the electromagnetic clutch When it is determined that the disconnection operation of the clutch 10 is defective, the treatment of the embodiment A is performed.

This determination is based on the fact that the output of the rear wheel steering angle sensor 64 fluctuates by a certain value or more when the servo motor 8 is operated and the OFF signal is output to the clutches 10A and 10B, or the clutches 10A and 10B When the servo motor 8 is activated, the rear wheel steering angle sensor
The condition is that the output of 64 fluctuates more than a certain value.

Control unit system When it is determined that an abnormality has occurred in this system,
The treatment of Embodiment B is performed.

(1) RAM error This determination is made on the condition that an abnormality is found in the RAM read / write check.

(2) ROM error This determination is made on the condition that an abnormality is found in the ROM dumb sum check.

(3) FRC error This determination is made on condition that an abnormality is found in the initial check of the self-propelled counter.

(4) A / D Error This determination is made on the condition that an abnormality is recognized in the I / O check of the A / D converter 108.

Microprocessor system (1) Operation error This determination is made on condition that the operation result of the microprocessor I and the operation result of the microprocessor II do not match.

(2) Communication error This determination is made on condition that mutual communication between the microprocessors I and II is disabled.

Brake When abnormality occurs in the brake 30, the treatment of the mode B is performed. The determination of the abnormality of the brake 30 may be performed, for example, as follows.

(1) When the output shaft 8a of the motor 8 is kept locked by the brake 30.

Control is performed to rotate the servomotor 8 in a state where the brake 30 is not operated (unlocked). At this time, when there is no output from the rotary encoder 62 and the rear wheel steering angle sensor 64 (the rear wheels 18L and 18R are steered). Is not.)

(2) When the output shaft 8a of the servomotor 8 cannot be locked by the brake 30.

When the control for locking the brake 30 is performed and the braking for rotating the servo motor 8 is performed, the output of the rotary encoder 62 and the rear wheel steering angle sensor 64 is present (the rear wheels 18L and 18R are steered). .

Next, a description will be given, with reference to the flowcharts of FIGS. 9 to 11, of the above-described abnormal state and the control for fail-safe corresponding thereto. In the following description, P or S indicates a step.

Overall Control (FIG. 9) First, at step P0 in FIG. 9, system initialization is performed. At this time, at the time of the initialization, a test for a known abnormality, for example, an error check of the rear wheel reference position, an error check of the ROM, the RAM, and the like of the control unit 12 are performed.

Next, in step P1, a signal from each sensor or switch is input, and the above-described abnormality determination is sequentially performed. That is, if it is determined in step P2 that there is an abnormality in the vehicle speed signal system, if it is determined in step P3 that there is an abnormality in the front wheel steering angle sensor system, it is determined that there is an abnormality in the clutch 10 in step P4. If any one of
If one of the above conditions is satisfied, the process proceeds to step P5, and braking in the first failure mode, ie, treatment mode A described later, is performed in principle.

If all of the determinations in steps P2 to P4 are NO, an abnormality determination in steps P6 to P11 is made. This step P6 ~ P
If it is determined in step P6 that there is an abnormality in the rear wheel steering mechanism system in step P6, the servo motor 8 is determined in step P7.
If there is an abnormality in the microprocessor system in step P8, it is determined that there is an abnormality in the rear wheel steering angle sensor system in step P8, or if there is an abnormality in the control unit system in step P9. If it is determined that there is, or if it is determined that there is an abnormality in the brake 30 in step P11, the process proceeds to step P12 if it corresponds to any one of them. In this case, treatment mode B, which will be described later, that is, control in the second fail mode is performed.

When the determinations in steps P2 to P4 and steps P6 to P11 are all NO, there is no abnormality, and in this case, in step P13, normal control is performed. That is, control is performed to realize the steering ratio characteristics shown in FIG.

Treatment mode A (FIG. 10) The details of the control in step P5 are shown in FIG.

First, in step S1, the warning lamp 128 is turned on to notify the driver that an abnormality has occurred. Then
Steps S2 and S3 are determined in order to check whether the rear wheel steering control and the position determination are performed normally. That is, the determination in step S2 indicates that the rear wheel steering angle sensor 64 is normal, and the determination in step S3 indicates that the rotary encoder
If it is indicated that 62 is normal, the operation of the servo motor 8 is controlled in step S4 to gradually return the rear wheel steering rod 4 to the neutral position. Thereafter, in step S5, it is confirmed that the servo motor 8 itself is normal,
After confirming that the rear wheel steering rod 4 has actually reached the neutral position in step S6, the brake 30 is operated in step S7, and the motor 8 is turned on while the rear wheel steering rod 4 is in the neutral position. Lock the output shaft 8a. At this time, the clutch 10A remains connected, so that the rear wheel steering rod 4 applies the spring force of the neutral position return means 6, the resistance of the motor 8 via the speed reduction mechanism 28, and the braking force.
Due to the locking action of the thirty, it is firmly held in the neutral position.

On the other hand, if the determination in step S2, S3, or step S5 is NO, it is impossible to accurately return the rear wheel steering rod 4 to the neutral position by the servo motor 8, and in this case, The process proceeds to step S11 in a treatment mode B in FIG. 11 described later.

Treatment Mode B (FIG. 11) First, after turning on the warning lamp 128 in step S10,
In step S11, the brake 30 is operated to lock the output shaft 8a of the servomotor 8, and then, in step S12, the power supply to the servomotor 8 is stopped. Thus, it is possible to prevent a problem such as a runaway of the servo motor 8 from occurring.

Next, in step S13, the clutch 10A is intermittently and repeatedly turned on and off as shown in FIG. When this control is continued, the rear wheel steering rod 4 displaced from the neutral position does not return to the neutral position suddenly simply due to the spring force of the neutral position return means 6, but gradually returns to the neutral position using this spring force. As a result, it is possible to prevent a sudden change in the vehicle attitude that gives the driver or the like a sense of discomfort. However, when the steering angles of the front and rear wheels are in the opposite phase, even if the rear wheel steering rod 4 is suddenly returned to the neutral position, the vehicle posture shifts to the stable side, so that there is no particular adverse effect. If the steering wheel is operated in the opposite direction while gradually returning to the neutral position in the same phase state as described above, the rear wheels that should be in the same phase side will turn to the opposite phase side and the vehicle posture will be changed. Becomes unstable. Therefore, in this control process, step S14 is executed to determine whether or not the front wheel actual steering angle (θF) and the rear wheel actual steering angle (θR) are in opposite phases. Immediately executes step S16 and disengages clutch 10A.
In the OFF state, otherwise, steps S13 and S14 are repeated until a predetermined time elapses to gradually return to the neutral position. When a predetermined time has elapsed from the start of the ON / OFF operation of the clutch 10A in S13, the clutch 10A is turned off.
As described above, the predetermined time is set in consideration of the time required for returning to the neutral position, but when it takes time to return to the neutral position due to the degree of external force such as cornering force, etc. During that time, the possibility of turning to the opposite phase by operating the steering wheel increases, so when the predetermined time elapses,
The clutch 10A is turned off regardless of whether the return to the neutral position has been completed.

In addition, when it changes to the opposite phase by steering wheel operation,
The opposite phase is detected in step S14, and step S16
In this case, the clutch 10A is turned off, but since this operation is performed only after switching to the opposite phase, by dividing the predetermined time, the possibility of switching to the opposite phase by operating the steering wheel is reduced as much as possible. To do.

After the clutch OFF operation in step S16, step
The clutch 10A is turned off until it is confirmed by the signal from the rear wheel steering angle sensor 64 that the rear wheel steering rod 4 has returned to the neutral position in the determination of S17, and it is confirmed that the clutch 10A has returned to the neutral position. In step S18, the clutch 10A is turned on again, and thereafter, the clutch 10A is maintained in the ON state, whereby the rear wheel steering rod 4 is turned on by the spring force of the neutral position return means 6 and the locking action of the brake 30. Strongly held in neutral position.

If an abnormality occurs in the rear wheel steering angle sensor 64,
In order to prevent the connection between the rear wheel steering rod 4 and the servo motor 8 from being made at a position other than the neutral position, the clutch ON operation in step S18 is not performed, the clutch 10A is held in the OFF state, and the rear wheel steering rod 4 It is held at the neutral position by the spring force of the neutral position return means 6.

Although the above-described clutch ON / OFF operation control has been described as being performed on the normally open type clutch 10A, it may be performed on the normally closed type clutch 10B. In this case, ON / OFF as above
May be operated in reverse.

As a method for gradually returning the rear wheel steering rod 4 to the neutral position, instead of the method of intermittently turning ON / OFF the clutch 10A or 10B as described above, as shown in FIG. In addition, by gradually reducing the clutch current supplied to the clutch 10A,
The connection between the output shaft 8a of the servomotor 8 and the gear train 28a may be gradually released by sliding A. Incidentally, it is possible to gradually release the connection by gradually increasing the clutch current using the clutch 10B instead of the clutch 10A, but in consideration of the fact that the clutch is allowed to slide as intended, A method of gradually reducing the clutch current, that is, control using the clutch 10A is preferable.

In the control using the slip of the clutch, a powder clutch or the like may be used in place of the plate-type clutch as shown in FIG. 4 to perform operation control for gradually reducing the excitation transmission force. Alternatively, the return of the rear wheels to the neutral position can be controlled by a motor, and the return speed can be changed according to the running state of the vehicle.

FIG. 13 shows another embodiment of the present invention. In this embodiment, after the determination whether or not the front wheel steering direction and the rear wheel steering direction are in opposite phases in step S14, when the front wheel steering direction and the rear wheel steering direction are in phase, step S19 is performed.
To determine whether the front wheel steering speed is faster than the rear wheel steering speed. When the front wheel steering speed is higher than the rear wheel steering speed, step S16 is immediately executed to return the rear wheels to the neutral position. When the front wheel steering speed is lower than the rear wheel steering speed, the process proceeds to step S15, and the rear wheels are returned to the neutral position at a predetermined speed. In this control,
As a result of the determination in step S19, when the front wheel steering speed is higher than the rear wheel steering speed, the process does not immediately proceed to step S16, and it is possible to control the return speed of the rear wheel within a range not to be higher than the front wheel steering speed.

(Effect)

According to the present invention, in the four-wheel steering system for a vehicle, when the rear wheel is returned from the steering position to the neutral position when the failure of the rear wheel turning means is detected, the return speed is changed according to the traveling state of the vehicle. Therefore, it is possible to prevent the driver from feeling uncomfortable in relation to the steering of the front wheels until the rear wheels return to the neutral position. In particular, when returning to the neutral position of the rear wheels, by controlling the return speed of the rear wheels so that the steering direction of the rear wheels does not have the opposite phase to the steering direction of the front wheels, It is possible to smoothly return to the neutral position.

[Brief description of the drawings]

1 is an overall configuration diagram showing one embodiment of a rear wheel steering device of a vehicle according to the present invention, FIG. 2 is a detailed view of a main part of the device, and FIG. 3 is a detailed sectional view of a neutral position returning means of the device. Fig. 4 is a detailed sectional view of the brake and clutch of the device, Figs. 5 and 6 are characteristic diagrams showing an example of the operation of the four-wheel steering device, Fig. 7 is a block diagram of a control system, and Fig. 8 is a rear view. FIG. 9, FIG. 9, FIG. 11 are flowcharts showing an example of control by the control unit, FIG. 12 is a characteristic diagram showing control characteristics in the control example, and FIG. 9 is a flowchart illustrating another embodiment of the present invention. 2 ... rear wheel steering device 4 ... rear wheel steering rod 6 ... neutral position return means 8 ... servo motor 8a ... output shaft 10 ... clutch 10A ... normally open type clutch 10B ... ... normally closed type clutch 12 … Control unit 18L, 18R… Rear wheel 28… Reduction gear 28a… Gear train 28b… Ball screw 30… Brake 62… Rotary encoder 64… Rear wheel steering angle sensor

Claims (2)

(57) [Claims] 1. A rear wheel steering device having a rear wheel steering means adapted to steer a rear wheel in a predetermined relationship with respect to a front wheel, wherein the neutral wheel acts to return the rear wheel to a neutral position. Return means, failure determination means for determining the failure of the rear wheel steering means and returning the rear wheel to the neutral position by the operation of the neutral return means at the time of failure, and whether the steering directions of the front wheel and the rear wheel are in phase. Steering direction determining means for determining whether the phases are opposite to each other, and steering speed detecting means for detecting the steering speed of the front wheels are provided, and the failure determining means is provided for returning the front wheels and rear wheels to the neutral position when a failure occurs. A return speed control unit that controls the neutral return unit so that a speed changes according to a traveling state of the vehicle, wherein the return speed control unit has a steering direction of a front wheel and a rear wheel that are in phase when a failure is detected. In the case, when the front wheel When the steering speed is lower than a predetermined predetermined return speed of the rear wheel, the rear wheel is returned at the return speed.When the steering speed of the front wheel is higher than the predetermined speed, the rear wheel is lower than the steering speed of the front wheel. A rear wheel steering device, characterized in that it is means for returning at a speed that does not occur. 2. A rear steering apparatus for a vehicle having rear wheel steering means adapted to steer the rear wheels in a predetermined relationship with respect to the front wheels, wherein the neutral wheels act to return the front wheels to the neutral position. Return means, failure determination means for determining the failure of the rear wheel steering means and returning the rear wheel to the neutral position by the operation of the neutral return means at the time of failure, and whether the steering directions of the front wheel and the rear wheel are in phase. Steering direction determining means for determining whether the phases are opposite to each other, and steering speed detecting means for detecting the steering speed of the front wheels are provided, and the failure determining means is provided for returning the rear wheels to the neutral position when a failure occurs. A return speed control unit that controls the neutral return unit so that a speed changes according to a traveling state of the vehicle, wherein the return speed control unit has a steering direction of a front wheel and a rear wheel that are in phase when a failure is detected. Sometimes the rear wheel is in neutral position Means for returning the rear wheel to the neutral position at a predetermined return speed predetermined for return, and for returning the rear wheel to the neutral position at a speed higher than the predetermined return speed when the phase is reversed. A rear wheel steering device characterized by the above-mentioned.