JPH01275273A - Rear-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To perform operation stop control smoothly and certainly by feeding a rear wheel steering means with a control in order to hold the rear wheels in neutral position from two control means when the rear wheel steering control becomes imcapable. CONSTITUTION:A rear wheel steering means A is furnished, which steers the rear wheels against the action of a neutral position returning means when an actuator such as a servo motor is operated, and is controlled by a control means in accordance with the car running condition sensed by a running condition sensing means B. Therein as a control means, a No.1 control means C is furnished which emits a No.1 control means to actuate the rear wheel steering means A in accordance with the running condition detection signal and a No.2 control signal to hold the rear wheels in the neutral position when the operational control of the rear wheel steering means A becomes imcapable. Also a No.2 control means D is furnished, which is fed with a running condition detection signal and only emits the mentioned No.2 control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering device for a vehicle that steers the rear wheels according to the running condition of the vehicle.

(Prior Art) A vehicle equipped with a four-wheel steering device or the like that steers the rear wheels in response to front wheel steering requires a rear wheel steering device for steering the rear wheels. Conventionally, such rear wheel steering devices have been known to use hydraulic pressure or an electric motor as the driving source for steering the rear wheels. is disclosed, for example, in Japanese Utility Model Application Publication No. 62-25277.

When using any of the above drive sources, as described in each of the above publications, a control means for controlling these drive sources is required, and this control means controls the rear wheels according to the running condition of the vehicle. It is designed to perform control to steer the vehicle. That is, the control means performs control to operate the rear wheel steering means based on a signal from the driving state detection means that detects the driving state of the vehicle. This includes not only normal rear wheel steering control that is activated depending on the vehicle's driving condition, but also deactivation control that maintains the rear wheels in a predetermined neutral position when the rear wheel steering control becomes impossible. It is designed to be safe.

(Problem to be Solved by the Invention) When only one of the above-mentioned control means is provided, when an abnormality occurs in the control means itself and rear wheel steering control becomes impossible, the above-mentioned operation stop control is performed. This becomes difficult. On the other hand, a watch dog timer (W,
It is possible to provide a monitoring function such as D, T, etc. to take measures against runaway of the control means. However, W.
D and T are configured such that a signal is output from the control means to the external monitoring element during normal operation, and when the signal is cut off quickly, the external monitoring element forcibly issues a reset signal to the control means. Therefore, even if an abnormality occurs in the control means, if the abnormality is of a nature that does not interfere with the signal output function to the external monitoring element, W, D, T.

Therefore, no abnormality is detected. For example, in case of an abnormality such as when only the data inside the control means is destroyed, or when a part of the control means is damaged, W.
D, T, is difficult to completely detect. On the other hand, reliability is improved by providing two identical control means to perform control in a dual system, and when an abnormality occurs in one of these, the remaining one is controlled to stop operating. It is possible to achieve this.

However, providing two identical control means in this way and having each perform normal rear wheel steering control and operation stop control in the event of an abnormality requires consistency between the two control means. This makes the configuration complicated and increases the cost of the rear wheel steering device.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rear wheel steering device for a vehicle that can improve the reliability of rear wheel steering control with a simple configuration. It is.

(Means for Solving the Problems) The vehicle rear wheel steering device according to the present invention does not simply provide two identical control means to perform similar control in a dual system.
One of the control means is designed to achieve the above object by using a tM configuration that only performs operation stop control when an abnormality occurs. That is, as shown in FIG. 1, there is a rear wheel steering means for steering the rear wheels from a predetermined neutral position, a running state detecting means for detecting the running state of the vehicle, and an output signal from the running state detecting means. A first control signal is input to operate the rear wheel steering means in accordance with the running condition of the vehicle, and a first control signal is input when the rear wheel steering means is inputted and is configured to operate the rear wheel steering means in accordance with the running condition of the vehicle. a first control means for outputting a second control signal for maintaining the wheels in the neutral position to the rear wheel steering means; and an output signal from the running state detection means are input, and the second control signal is inputted to the drive state detection means; The present invention is characterized by comprising a second control means for outputting only a signal to the rear wheel steering means.

In this case, it is effective if the first control means and the second control means use different methods for determining whether or not it has become impossible to operate the rear wheel steering means according to the running state of the vehicle. be.

(Function) As shown in the above configuration, in normal times, the first control signal is output from the first control means to the rear wheel steering means based on the signal from the driving state detection means, and this causes the vehicle to rotate. Rear wheel steering control is performed according to the driving condition. On the other hand, when this rear wheel steering control becomes impossible, the first and second
A second control signal is output from the control means to the rear wheel steering means, thereby performing operation stop control, that is, control to maintain the rear wheels at a neutral position. At this time, since the second control signal from the second control means is output independently of the second control signal from the first control means, an abnormality in the first control means itself causes the first control Even if the second control signal cannot be output from the means, the operation stop control can be smoothly performed.

(Effects of the Invention) As described above, according to the present invention, since the second control means is provided and only the operation stop control is performed in a dual system,
The reliability of rear wheel steering control can be improved with a simple configuration.

The above-mentioned operation stop control is performed based only on whether or not it has become impossible to operate the rear wheel steering means according to the driving condition of the vehicle, so the determination method is
The control means may be different from the second control means, and by doing so, the configuration of the second control means can be further simplified.

(Examples) Examples of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 is an overall configuration diagram showing an embodiment of a rear wheel steering device for a vehicle according to the present invention.

As shown in FIG. 2, the rear wheel steering device 1 constitutes a part of a four-wheel steering device that also steers the rear wheels in accordance with front wheel steering, and includes a rear wheel steering means 2, A rear wheel steering angle sensor 64, a steering wheel steering angle sensor 86, a front wheel steering angle sensor 90, and a vehicle speed sensor 88, 92, which are running state detection means, a microprocessor 104, which is a first control means, and a backup circuit 132, which is a second control means. The control unit 12 has a control unit 12.

The rear wheel steering means 2 includes a rear wheel steering rod 4, a neutral position return means 6, a servo motor 8, a clutch 10, a deceleration mechanism 28, and a brake 30.

The rear wheel steering rod 4 extends in the vehicle width direction, and is connected to a pair of left and right rear wheels 18L through its both ends via a pair of left and right tie rods 14L, 14R and knuckle arms lcL, tGR.
, 18R, and when the rear wheel steering rod 4 is displaced in the vehicle width direction, the rear wheel 18L.

], 8R is steered.

The neutral position return means 6 is attached to the rear wheel steering rod 4,
As its cross section is shown in detail in FIG. 4, it has a casing 22 fixed to the vehicle body 20, and a pair of spring receivers 24a, 24b are loosely fitted into the casing 22. A compression spring 26 is arranged between 24b and 24b. The rear wheel steering rod 4 is connected to the casing 2
A pair of flanges 4a, 4b are formed at intervals on this rear wheel steering rod 4, and extend through the rear wheel steering rod 4.
b is configured to receive the spring receivers □24a and 24b, and the rear wheel steering rod 4 is always kept at a predetermined neutral position by the compression spring 26 (that is, when the rear wheels 18L and 1.8R are moving straight with zero steering angle). position). The compression spring 26 has a spring force sufficient to overcome side forces during cornering.

The servo motor 8 is a step motor, and as shown in FIG. 3, its output shaft 8a is connected to the rear wheel steering rod 4 via a speed reduction mechanism 28 consisting of a gear train 28a and a ball screw 28b. As shown in FIG. 2, the rear wheel steering rod 4 is actuated by a control signal from the control unit 12 to displace the rear wheel steering rod 4 from the neutral position against the biasing force of the neutral position return means 6. The output shaft 8a of this servo motor 8 is provided with a brake 30 that applies braking to the rotation of the output shaft 8a, and the operation of this brake 30 locks the output shaft 8a (and by extension the rear wheel steering rod 4). The rear wheel steering rod 4 can be maintained at a predetermined displacement state. This brake 30
The operation of is controlled by a control unit 12.

Clutch]0 is provided between the output shaft 8a of the servo motor 8 and the gear train 28a, and is used when a predetermined abnormality occurs, which will be described later.
Disconnect the rear wheel steering rod 4 and the servo motor 8,
Thereby, the rear wheel steering rod 4 displaced from the neutral position is returned to the neutral position by the biasing force of the neutral position return means 6. The operation of this clutch 10 is controlled by a control unit 12.

FIG. 5 is a sectional view showing the brake 30 and clutch 0 in detail.

The brake 30 is fixed to the output shaft 8a of the servo motor 8, and includes a ring plate 34 having an uneven groove that engages with an uneven groove on the servo motor 8 side of a disk 32, which has a plurality of uneven grooves extending radially on both sides. , and a solenoid 38 that attracts this ring plate 34 to a suction plate 36 fixed to a casing 35. When the solenoid 38 is in the OFF state, in which the solenoid 38 is not energized, the ring plate 34 rotates freely together with the disk 32, while the solenoid In the ON state where 38 is energized, the ring plate 3
4 is attracted to a suction plate 36 while maintaining the meshing state with the disk 32, and the rotation of the disk 32, that is, the rotation of the output shaft 8a of the servo motor 8 is braked.

The clutch 10 is a twin clutch in which two clutches are provided in series, and the clutch IOA on the upstream side (brake 30 side)
The clutch IOB on the downstream side (gear train 28a side) is a normally closed type. That is, the clutch IOA includes a ring plate 40 having an uneven groove that engages with an uneven groove on the downstream side of the disk 32, and a rotating shaft 4 that is coaxial with the output shaft 8a.
and a solenoid 46 that is attracted to a disk 44 fixedly attached to the solenoid 46.
In the FF state, the connection between the ring plate 40 and the disk 44 is released, while in the ON state, where the solenoid 46 is energized, the ring plate 40 and the disk 44 are connected by surface contact. Note that the ring plays 1 and 40 always maintain a meshing state with the disk 32. Further, the clutch IOB is connected to the rotating shaft 42
Ring plates 1 and 50 spline-coupled to a hub 48 fixedly attached to the ring plate 50, and a pad that comes into contact with the downstream surface of the ring plate 50 and presses the ring plates 1 and 50 upstream by the spring force of a spring 52. 54, and ring plates 1 and 5 are arranged to restrict movement of the ring plate 50 pressed by the pad 54 to the upstream side by more than a predetermined amount.
A drum 58 fixed to a rotary shaft 56 coaxial with the rotary shaft 42 and in contact with the upstream surface of the ring plate 1 and the ring plate 50 are sucked from the downstream side.
In the OFF state where the solenoid 60 is not energized, the ring plate 50 and the drum 58 are connected by surface contact, and in the ON state where the solenoid 60 is energized, the ring plate 50 and the drum 58 are connected. The connection with 58 can be canceled.

Therefore, the rotation of the output shaft 8a due to the operation of the servo motor 8 is caused by the brake 30 and the clutch 1. OB is OFF
In this state, the transmission is transmitted to the gear train 28a only when the clutch IOA is in the ON state, or rear wheel steering in normal times is performed in this state. In addition, as the clutch 10, clutches IOA and 1
．． The twin clutch, which has two OBs installed in series, is designed so that even if one of the OBs becomes inoperable due to seizure or the like, the other one can be turned ON or OFF to maintain the servo motor 8 and the gear train 28a. This is to enable the connection with the rear wheel steering rod 4 to be released, and the reason why one is a normally open type and the other is a normally closed type is because both clutches IOA , Normally open type clutches are required to release the above connection when power supply to the IOB is stopped, but making both clutches normally open type means that both clutches are turned off for power transmission under normal conditions.
This is because it is necessary to enter the N state, which requires additional power consumption.

As shown in FIG. 2, the control unit 12 controls the operation of the servo motor 8, the brake 30, and the clutch 10, as described above. As shown in the figure, since the rear wheel steering device 2 constitutes a part of the four-wheel steering device, it is designed to perform the required four-wheel steering function.

In addition to the rear wheel steering device 2, the four-wheel steering device includes a front wheel steering mechanism 70 and various sensors that send control unit information for appropriate rear wheel steering control according to driving conditions. There is.

The front wheel steering mechanism 70 extends in the vehicle width direction, and has both ends connected to a pair of left and right front wheels 76L, 72R via a pair of left and right tie rods 72L, 72R and knuckle arms 74L, 74R.
A rack 78 connected to 76R and a rack 78 at one end.
A steering wheel 84 is provided with a pinion 80 that meshes with the front wheel 7 and a steering wheel 82 is provided at the other end thereof, and by operating the steering wheel 82, the rack 78 is displaced in the vehicle width direction to move the front wheel 7. [iL, 76R is now being steered.

Rear wheel steering control by control I/roll unit I/12 is as follows:
This is done in response to vehicle speed, and an example of changing the steering ratio (rear wheel steering angle/front wheel steering angle) according to vehicle speed is the 6th wheel steering angle.
There are cases as shown in the figure. When the control characteristics shown in the figure are applied, the rear wheel steering angle relative to the front wheel steering angle changes in the same phase direction as the vehicle speed increases, and this situation is shown in FIG.

In order to perform such rear wheel steering control, the control unit 12 includes a steering wheel angle sensor 86 and a vehicle speed sensor 8.
8 and a rotary encoder 62 that detects the rotational position of the servo motor 8, and the control unit 12 determines the target rear wheel based on the steering angle (theoretically equal to the front wheel steering angle) and the vehicle speed. The steering angle is calculated, and a control signal corresponding to the required amount of rear wheel turning is output to the servo motor 8. The rotary encoder 62 constantly monitors whether or not the servo motor 8 is operating properly, that is, the rear wheels 18L and 18R are steered under feedback control.

In the rear wheel steering control described above, the control system has a dual configuration for fail-safe purposes.

That is, a front wheel steering angle sensor 90 is added to the steering wheel steering angle sensor 86, and a second front wheel steering angle sensor 90 is added to the vehicle speed sensor 88.
A vehicle speed sensor 92 is added to the rotary engine cog 62, and a rear wheel steering angle sensor 64 is added to the rotary engine cog 62 to detect mechanical displacement of a member closer to the rear wheel steering rod 4 than the clutch 10. In the set of sensors, rear wheel steering is performed only when both corresponding sensors detect the same value. Therefore, if 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 among the three sets of sensors, an abnormality (failure) has occurred, and a fail event will occur, which will be described later. The rear wheels 18L and 18R are kept in the neutral position by control during mote.

The control unit 12 also includes a switch 94 for detecting various abnormalities. 9B, 98, 10
An ON-OFF signal from 0 is inputted, and a signal indicating whether or not power generation is generated is inputted from the alternator terminal 102. Here, the switch 94 is a neutral clutch switch, the switch 96 is an inhibitor switch, the switch 98 is a brake switch, and the switch 100 is an engine switch. Here, the neutral switch 94
In a vehicle equipped with a manual transmission, an OFF signal is output when the shift position of the manual transmission is neutral or the clutch pedal is depressed, and an ON signal is output otherwise. 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 driving 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 in operation.

FIG. 8 is a block diagram showing the control system.

The microprocessor 104 includes a vehicle speed sensor 88°92.
The signals from switches 94.9B, 98.100 and alternator terminal 102 are buffered 1.0.
6, and signals from the steering wheel steering angle sensor 86, front wheel steering angle sensor 90, and rear wheel steering angle sensor 64 are also inputted via the buffer 106 and the A/D converter 1.08, signals are input via the interface 110. On the other hand, the signal (first control signal) generated in the microprocessor 104 is sent to the servo motor 8 via the motor drive circuit 112, and also sent to the brake 3o via the brake drive circuit 114, or to the clutch drive circuit. 116 to the clutch 1o. This rear wheel steering control is performed when the signal from the alternator terminal 102 is high (Hi).
).

In the figure, reference numeral 118 is a battery, 120 is an ignition key switch, 122 is a relay, and when a predetermined abnormality described later occurs, the microprocessor 104
A second control signal is output from the relay drive circuit 124.
energization to the coil 126 is stopped, and as a result, the contacts of the relay 122 are switched, power supply to the motor drive circuit 112 is stopped, and the warning lamp 128 is turned on. Further, when an abnormality other than the above occurs, a second control signal is output from the microprocessor 1.04, a base current flows through the transistor 130, and the warning lamp 128 lights up.

Next, an explanation will be given of an abnormality that may occur in the four-wheel steering system and how the microprocessor 1.04 handles the abnormality (operation stop control).

In this embodiment, a treatment corresponding to the location where the abnormality occurs is performed, and there are the following two modes of treatment. In any of these embodiments, the action (operation stop control) is performed by the microprocessor 1.
This is done by the signal from 04 (second control signal).

Treatment mode A (control during second fail mode) Rear wheel 18L
, 1.8R and its position determination 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 servo motor 8 is used to return the rear wheel steering rod 4 to the neutral position. Specifically, the contents of this procedure are as follows.

(1) After the warning lamp 128 lights up, (2) the rear wheel steering rod 4 is returned to the neutral position by driving the servo motor 8, and (2) the brake 30 is turned on.

Treatment mode B (control during second fail mode) Rear wheel 18L
, 18R or its position determination becomes impossible. The details of this action are as follows.

■After the warning lamp 128 lights up, ■Turn on the brake 30, ■Stop the power supply to the servo motor 8, ■Turn off the clutch IOA, and release the connection between the servo motor 8 and the rear wheel steering rod 4. (2) After waiting for the rear wheel steering rod 4 to return to the neutral position by the spring force of the neutral position return means 6, (2) turning on the clutch IOA to connect the servo motor 8 and the rear wheel steering rod 4;

In the above treatment mode B, if the operation of turning off the clutch IOA is suddenly performed, the rear wheel steering rod 4 will return to the neutral position after a short period of time due to the spring force of the neutral position return means 6. If such a phenomenon occurs when the front and rear wheels are in the same phase state, it may have a negative effect on the vehicle attitude. The operation of the clutch IOA is controlled by the control unit 12 so that the return to the neutral position is performed gradually. That is, as shown in FIG. 9, the control unit 12 performs control to repeatedly turn ON/OFF the clutch IOA for a predetermined period of time, thereby gradually turning the rear wheel steering lot 4 as shown in FIG. It is designed to return to the neutral position. In addition, the said predetermined time is set to sufficient time for the rear wheel steering lot 4 to return to a neutral position.

Hereinafter, the abnormality modes and their setting conditions will be classified into each system, and the corresponding treatment modes will be explained.

When it is determined that an abnormality has occurred in the main vehicle speed signal system, the above-mentioned mode A is taken.

(1) The actual determination of the amount of change error in the first vehicle speed sensor 88 is as follows:
The conditions are that the brake switch 98 is in the OFF state and that the first vehicle speed sensor 88 detects a deceleration of ldV, /dtl>a (constant). Here, Vj represents the vehicle speed detected by the first vehicle speed sensor 88. That is,
When the vehicle exhibits deceleration exceeding a predetermined value even though the vehicle is not braked, it is determined that the first vehicle speed sensor 88 is abnormal.

(2) The actual determination of the amount of change error in the second vehicle speed sensor 92 is as follows:
As with the first vehicle speed sensor 88, the brake switch 98 is in the OFF state, and the second vehicle speed sensor 92 detects a deceleration of l d V 2 / d t l > a (constant). is the condition.

Here, V2 represents the vehicle speed detected by the second vehicle speed sensor 92.

(3) Vehicle speed mismatch error This determination is made on the condition that the detected values of the first and second vehicle speed sensors 8g and 92 do not match, as expressed by, for example, IVl-V21>b (constant).

In this case, it is considered that an abnormality has occurred in at least one of the vehicle speed sensors.

Regardless of whether the occurrence occurs in any of the sensors 88 or 92, it is determined that there is an abnormality, and as described above, mode A is detected.
processing 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 that the first... Assuming that the outputs of the second vehicle speed sensors 8g and 92 are zero (V1=V2=0),
In a vehicle with a manual transmission, the condition is that the neutral clutch switch 94 remains ON for a certain period of time, while in a vehicle with an automatic transmission, the inhibitor switch 96 is turned OFF and the engine switch 100 is turned ON. Also, on the condition that the brake switch 98 remains OFF for a certain period of time, it is determined that both sensors 8g and 92 are abnormal at the same time.

In other words, the fact that the vehicle speed is zero even though the engine speed is at a sufficient engine speed to drive based on the amount of power generated and it can be considered that the vehicle is traveling from the shift position, it is possible that some abnormality has occurred in the sensor 88 or 92. It won't happen.

When it is determined that an abnormality has occurred in the main system of the rear wheel steering mechanism system, the action of aspect B is taken.

(1) Control Thread (Part 1) This determination is based on the 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, 1f (EN) - G( The condition is that θR)l>C (constant).

(2) Control deviation (Part 2) This determination is based on the mismatch between the target rear wheel steering angle (or) set by the control unit 12 and the actual rear wheel steering angle (θR), for example, θr−θIl>C (constant ) is required.

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

When it is determined that an abnormality has occurred in the main DC servo motor system, the measure B is taken.

(1) Rotation amount error This judgment is based on the control amount and the rotation amount of the motor 8 (encoder 62
The condition is that the detected values) do not match.

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

■Motor coil disconnection or short circuit.

■Harness disconnection or short circuit.

■Failure of motor drive circuit 2.

When it is determined that an abnormality has occurred in the main system of the rear wheel steering angle sensor system, the treatment of aspect B is performed.

<1) Low encoder monitor error actual judgment is as follows:
The condition is that an abnormality is recognized in the code output from the encoder 62.

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

When it is determined that an abnormality has occurred in the main front wheel steering angle sensor system, the treatment of mode A is performed.

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

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

(3) Front wheel steering angle mismatch error This judgment is made by the steering wheel steering angle sensor 86 and the front wheel steering angle sensor 90.
The condition is that the difference in output between the

Malfunction of disengagement of electromagnetic clutch When it is determined that the disengagement of the clutch 10 is malfunctioning, the action of mode A is taken.

This judgment is OFF for clutch IOA and IOB.
When the signal is output and the servo motor 8 is operated, the output of the rear wheel steering angle sensor 64 fluctuates by more than a certain value, or the clutch is turned ON for OA and 10B.
The condition is that the output of the rear wheel steering angle sensor 64 fluctuates by a certain value or more when the signal is output and the servo motor 8 is operated.

When it is determined that an abnormality has occurred in the main control unit system, the treatment of aspect B is performed.

(1) RAM error The condition for this judgment is that an abnormality is found in the RAM read/write check.

(2) ROM error The condition for this judgment is that an abnormality is found in the ROM dumb thumb check.

(3) FRC error The condition for this judgment is that an abnormality is found in the initial check of the self-running counter.

(4) A/D error This judgment is made on the condition that an abnormality is recognized in the I10 check of the A/D converter 108.

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

(1) The output shaft 8a of the motor 8 is
remains locked.

Control is performed to rotate the servo motor 8 with the brake 30 inactive (unlocked), and at this time, if there is no output from the rotary encoder 62 or rear wheel steering angle sensor 64 (rear wheels 18L, 18R or not) ).

(2) When it is impossible to lock the output shaft 8a of the servo motor 8 with the brake 30.

If the rotary encoder 62 and the rear wheel steering angle sensor 64 output when the brake 30 is controlled to lock and the servo motor 8 is rotated while the brake 30 is controlled to lock and the servo motor 8 is rotated. ).

Next, the above-mentioned abnormality and corresponding fail-safe control will be explained with reference to the flowcharts shown in FIGS. 10 to 12.

Note that in the following explanation, P or S indicates a step.

Overall Control (FIG. 10) First, system initialization is performed at PO in FIG. At this time, an abnormality that can be detected at the time of initialization is checked (for example, checking for errors in the rear wheel reference position, checking the ROM of the control unit 12, etc.).
, error check of RAM, etc.).

Next, signals from each sensor or switch are input at Pl, and the above-described abnormality determination is performed in sequence. That is, if there is an abnormality in the vehicle speed signal system (YES in P2), in the front wheel steering angle sensor system (YES in P3), or in the clutch 10 (YES in P4). If any one of the following applies (when the determination is YES), the process moves to P5, and treatment mode A (braking in the first fail mode), which will be described later, is performed in principle.

If all of the above judgments from P2 to P4 are No, P6 to P4
1.1 abnormality determination is made. In the judgments from P6 to P11, if there is an abnormality in the rear wheel steering mechanism system (YES in P6), if there is an abnormality in the servo motor 8 (P
7), if there is an abnormality in the rear wheel steering angle sensor system (when YES in P8), if there is an abnormality in the control unit system (YES in P9)
), if there is an abnormality in the microprocessor system (
When the brake 30 is abnormal (when the Plo determination is YES), or when there is an abnormality in the brake 30 (when the Pll determination is YES), the process moves to P12. In this case, treatment mode B (second fail mode control), which will be described later, is performed.

All the determinations of P2 to P4 and P6 to PIL are No.
When , there is no abnormality, and in this case, normal control is performed at Pl3. That is, control is performed to realize the steering ratio characteristics shown in FIG. 6.

Treatment mode A (Figure 11) Details of the control at P5 are shown in FIG. 11.

First, in Sl, turn on the warning lamp 128,
Notify the driver that an abnormality has occurred. Next, in order to check whether rear wheel steering control and its position determination are performed normally, S2. A determination in S3 is made. That is, when the rear wheel steering angle sensor 64 is normal (when the determination in S2 is YES) and the rotary encoder 62 is normal (S
3), in S4, the servo motor 8 is operated and controlled to gradually return the rear wheel steering rod 4 to the neutral position. After this, in S5, confirm that the servo motor 8 itself is normal and the determination in S5 is Y.
After confirming that the rear wheel steering rod 4 is actually in the neutral position (when the determination in S6 is YES), the brake 30 is activated in S7 and the rear wheel steering rod 4 is in the neutral position. The output shaft 8a of the motor 8 is locked in this position. At this time, the clutch IOA remains connected, and therefore the rear wheel axle lot 4
is firmly held at the neutral position by the spring force of the neutral position return means 6, the resistance of the motor 8 via the deceleration mechanism 28, and the locking action of the brake 30.

On the other hand, the above S2. If the determination in either S3 or S5 is No, the servo motor 8 turns the rear wheels F4.
This is a case in which it is impossible to accurately return to the neutral position, and in this case, the process moves to Sit in treatment mode B in FIG. 12, which will be described later.

Treatment mode B (Fig. 12) First, after lighting the warning lamp 128 in SIO, S1
1, the brake 30 is activated to lock the output shaft 8a of the servo motor 8, and then, in S12, power supply to the servo motor 8 is stopped. This causes the servo motor 8
It is possible to prevent problems such as runaway.

Next, in S13, the clutch IOA is intermittently and repeatedly operated 0N-OFF as shown in FIG. Instead of returning the vehicle to the neutral position suddenly, the spring force is used to gradually return the vehicle to the neutral position, thereby preventing a sudden change in the vehicle posture that would make the driver feel uncomfortable. However, when the steering angles of the front and rear wheels are in the opposite phase state, even if the rear wheel steering rod 4 is suddenly returned to the neutral position, the vehicle attitude will shift to the stable side, so there will be no particular adverse effect. If the steering wheel is operated in the opposite direction while the vehicle is gradually returning to the neutral position as described above in the same phase state, the rear wheels, which should normally be in the same phase, will shift to the opposite phase and the vehicle attitude will change. Because of this, it is determined in S14 whether the actual front wheel steering angle (θF) and the actual rear wheel steering angle (θR) are in opposite phases, and if they are in opposite phases (if the determination in S14 is YES). ), the clutch 10A is turned off, and in other cases (No in S14), the operation of gradually returning to the neutral position is continued. Turning on the clutch IOA in S13
When a predetermined period of time has elapsed since the start of the OFF operation (when the determination in S15 is YES), the clutch LOA is turned OFF (S
I6). As mentioned above, the above-mentioned predetermined time is set in consideration of the time required to return to the neutral position, or if it takes time to return to the neutral position due to the degree of external force such as cornering force, the predetermined time is set in consideration of the time required to return to the neutral position. Since there is a high possibility that the phase will change to the opposite phase due to steering wheel operation, the clutch IOA is turned OFF after a predetermined period of time, regardless of whether the return to the neutral position has been completed.

In addition, if the phase is reversed by operating the handle, S
Clutch 1. The OA is turned off, but since this operation is performed only after the phase changes to the opposite phase, by dividing the above-mentioned predetermined time period, it is possible to prevent the phase change from changing to the opposite phase due to handle operation as much as possible. It is.

After the clutch OFF operation at S] and B, the rear wheel steering angle sensor 64 indicates that the rear wheel steering rod 4 has returned to the neutral position.
clutch], OA is O until confirmed by a signal from
It is set to the FF state (NO in S17), and when it is confirmed that it has returned to the neutral position (YES in S17).
S) Clutch IOA is turned ON again (S], 8
), from then on, the clutch IOA is held in the ON state,
As a result, the rear wheel steering rod 4 is moved to the neutral position return means 6.
The spring force and the locking action of the brake 30 firmly maintain the neutral position.

In addition, if an abnormality occurs in the rear wheel steering angle sensor 64,
In order to prevent the rear wheel steering rod 4 from being connected to the servo motor 8 at a position other than the neutral position, the clutch O of S18 is
The N operation is not performed, the clutch 10A is held in the OFF state, and the rear wheel steering rod 4 is held in the neutral position by the spring force of the neutral position return means 6.

Note that the clutch ON-OFF operation control described above has been described as being performed for the normally open type clutch IOA, or may be performed for the normally closed type clutch IOB. In this case, the above case and O
It may be activated by reversing N/OFF.

As detailed above, as long as the microprocessor 104 is normal, when an abnormality occurs in the four-wheel steering system due to a failure or the like, the operation stop control is performed by the second control signal output from the microprocessor 104. As a result, the rear wheel steering rod 4 can be reliably returned to the neutral position and then held at this neutral position to ensure the running function as a normal two-wheel steered vehicle. The servo motor 8 is used as much as possible to return to the neutral position, while the neutral position return means 6 is used only when unavoidable. Therefore, the transient state until returning to the neutral position can be made as favorable as possible.

However, if an abnormality occurs in the microprocessor 104 itself, the above operation stop control will not be performed appropriately, so in this embodiment, as shown in FIG. A backup circuit 132 is provided. This backup circuit 132 does not perform normal rear wheel steering control like the microprocessor 104, but rather determines whether or not rear wheel steering control has become impossible and operates when it is determined that rear wheel steering control is impossible. It is designed to perform only stop control.

That is, the backup circuit 132 is provided independently of the microprocessor 104 and is connected to the vehicle speed sensors 88 and 92.
, the steering wheel steering angle sensor 86, the front wheel steering angle sensor 90, and the rear wheel steering angle sensor 64 are inputted via the buffer 106, and based on these signals, the rear wheel steering means 2 or the vehicle Monitoring is performed separately from the microprocessor 104 to determine whether or not the rear wheel steering control is operating according to the driving state, and when it is determined that the rear wheel steering control is not being performed normally, a predetermined signal is sent to the rear wheel steering means 2 control signal (
the second control signal) and the warning lamp 12.
8 is lit. The second control signal to the rear wheel steering means 2 is output to the clutch 10 via the clutch drive circuit 11B, thereby causing the clutch 10 to
The rear wheel steering rod 4 is set to FF in order to return and hold the rear wheel steering rod 4 to the neutral position.

Furthermore, the backup circuit 132 is designed to determine if the microprocessor 104 is running out of control in order to quickly discover an abnormality in the microprocessor 104.

FIG. 13a is a circuit diagram showing the contents of rear wheel steering control abnormality determination and microprocessor runaway determination for operation stop control performed by the backup circuit 132.

Rear wheel steering control abnormality determination is performed using θFISW, θF25W, θ
Hi, Lo from R3WI, θR3W2 and vehicle speed SW
The input of each of these signals is based on the 1st and 3rd signal.
This is done under the conditions shown in Figure b. That is, θFISW, θ
F25W and θR3WI are H11θR5W when the detected steering angles of the steering wheel steering angle sensor 86, front wheel steering angle sensor 90, and rear wheel steering angle sensor 64 are to the right of the center (zero steering angle), respectively.
2, when the detected steering angle of the rear wheel steering angle sensor 64 is within 0.5° from the center on each side, the Hi1 vehicle speed SW is such that the detected vehicle speed (V) of the vehicle speed sensors 88 and 92 is 40 km/h (
When the steering ratio (θS) is equal to or higher than the vehicle speed at which the steering ratio (θS) switches between the opposite phase and the same phase (see FIG. 6), a Hi signal is input, and at other times, a LO signal is input. By using the circuit shown in Figure 1te13a, high speed (■
≧40km/h) and opposite phase (θS=θR/θF≦0)
, or low speed (■≦40km/h) and same phase (θS
≧0), it is determined that the rear wheel steering control is not being performed according to the steering ratio characteristics shown in FIG. 6, and a second control signal for turning off the clutch and lighting the warning lamp is output. In addition, the rear wheel steering angle (OR) is -0.5°≦θ
When R≦+0.5°, the second control signal is not output even if other conditions are met. This means that even if normal rear wheel steering control is being performed, after the control signal (first control signal) is output, the rear wheel steering rod 4 responds to the target steering angle by driving the zarpo motor 8. Since it takes some time to move to the desired position, there is a risk that the second control signal will be output based on the opposite signals of Hj and LO near the center. It was designed to be avoided.

Microprocessor runaway determination is performed when the backup circuit sends 0.0 to the microprocessor. 1 signal is output, a corresponding output signal of the microprocessor is inputted, and it is determined whether the microprocessor is operating normally or not. When it is determined that the microprocessor is abnormal, it outputs a second control signal to reset the rear wheel steering control of the microprocessor, and also outputs a second control signal to turn off the clutch and turn on the warning lamp. Outputs a control signal.

As described in detail above, according to this embodiment, the backup circuit 132 is provided which only determines whether or not rear wheel steering control is impossible using a determination method different from that of the microprocessor 104. While rear wheel steering control and operation stop control are performed, the backup circuit 132 with a simple configuration monitors the rear wheel steering control status from an objective standpoint, and the reliability of the rear wheel steering device 1 can be easily improved. And it can be realized at low cost.

FIG. 14 is a schematic block diagram showing another embodiment, in which a backup circuit is provided in a rear wheel steering device that uses hydraulic pressure as a drive source for rear wheel steering.

That is, vehicle speed sensor 140 and steering ratio sensor 142
Based on the signal from the microprocessor 144 and the backup circuit 146, the microprocessor 144 and the backup circuit 146 independently determine whether rear wheel steering control is impossible, and if it is determined that it is impossible, each outputs a second control signal. Then, the hydraulic control solenoid of the fail-safe valve 148 provided in the rear wheel steering means is turned on, and the rear wheel steering rod (not shown) is turned on.
is returned to the neutral position, held at the neutral position, and a warning lamp 150 is turned on. Therefore, even if an abnormality occurs in the microprocessor 144 itself, the operation stop control can be performed reliably.

FIG. 15 is a circuit diagram showing details of the backup circuit 146 shown in FIG. 14.

The backup circuit 146 is configured as a dual system that receives input signals from two different vehicle speed sensors as input signals from the vehicle speed sensor 140 . Since both circuit configurations are the same, to explain one of them, the vehicle speed signal from the vehicle speed sensor 140 is waveform-shaped and then compared with a reference level Vr1 (corresponding to a vehicle speed of 40 km/h) in a comparator 152. Hi if the vehicle speed is 40km/h or more
signal is output. On the other hand, the steering ratio (θS) signal from the steering ratio sensor 142 is compared with the reference level ■r2 (θ5=0) in the comparator 154, and the steering ratio O8≦0
When this happens, a Hi signal is output.

When these 100 output signals are both Hi (that is, high speed and opposite phase) or Lo (that is, low speed and the same phase), the Hl signal (the 2 control signal) is output. This output signal is input to the timer circuit 158 and the latch circuit 160, and after a predetermined period of time has elapsed, an output is made to turn on the hydraulic control solenoid of the fail-safe valve 148 and the warning lamp 150. Timer circuit 1
The reason why the predetermined delay time is provided in accordance with No. 58 is that even when normal rear wheel steering control is performed, the delay in the operation of the rear wheel steering means in response to the control signal causes a high level in the region around zero steering ratio. , Lo There is a possibility that an erroneous determination may be made based on the opposite signal, so the erroneous determination is avoided by masking the determination for a predetermined period of time.

[Brief explanation of the drawing]

FIG. 1 is a conceptual block diagram showing the configuration of the present invention, FIG. 2 is an overall configuration diagram showing an embodiment of a vehicle rear wheel steering device according to the present invention, FIG. 3 is a partially detailed view of the device, Figure 4 is a detailed sectional view of the neutral position return means of the device, Figure 5 is a detailed sectional view of the brake and clutch of the device, and Figures 6 and 7 are a four-wheel steering system in which the device is a part of its components. FIG. 8 is a block diagram of the control system of the device; FIG. 9 is a characteristic diagram showing an example of operation stop control performed by the microprocessor of the device; 10.1.1 and 12 are flowcharts showing examples of the control, FIGS. 13a and 13b are circuit diagrams and charts showing examples of operation stop control using the backup circuit of the device, and FIG. 14 is a block diagram showing another embodiment. The schematic diagram, FIG. 15, is a circuit diagram showing a backup circuit in another embodiment. ]... Rear wheel steering device 2... Rear wheel steering means 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 104... Microprocessor (first control means) 1
32... Backup circuit (second control means) 1.8
L, 1.8R...Rear wheel 28...Deceleration mechanism 28a...Gear train 28
b... Ball screw 30... Brake 62...
Rotary encoder 64...Rear wheel steering angle sensor (driving state detection means) 86...
・Handle steering angle sensor (running state detection means) 90 ・・
・Front wheel steering angle sensor (driving state detection means) 88, 92...
・Vehicle speed sensor (driving state detection means) 144...Microprocessor 146...backup circuit only)

Claims (1)

[Scope of Claims] 1) Rear wheel steering means for steering the rear wheels from a predetermined neutral position, driving state detecting means for detecting the traveling state of the vehicle, and an output signal from the driving state detecting means being inputted. , a first for operating the rear wheel steering means according to the running condition of the vehicle;
and a second control signal for maintaining the rear wheels at the neutral position when the rear wheel steering means cannot be operated depending on the running state of the vehicle. a first control means that outputs an output signal to the rear wheel steering means; and a second control means that receives an output signal from the driving state detection means and outputs only the second control signal to the rear wheel steering means.
A rear wheel steering device for a vehicle, comprising a control means. 2) The first control means and the second control means have different methods for determining whether or not it has become impossible to operate the rear wheel steering means in accordance with the running state of the vehicle. A rear wheel steering device for a vehicle according to claim 1.