JP3065783B2 - Vehicle rear wheel steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering device for a vehicle, and more particularly, to a rear wheel steering device for a vehicle provided with an anti-skid braking system (hereinafter referred to as "ABS"). Things.

[0002]

2. Description of the Related Art A rear wheel steering apparatus is known which is configured to variably set a steering ratio of a rear wheel to a front wheel steering angle in accordance with a vehicle speed, a front wheel steering angle, or the like. (For example, JP-A-57-44568). Also, the slip state of each wheel is detected by detecting the rotation speed of each wheel during braking, and the brake hydraulic pressure for the brake device of each wheel is ensured so as to ensure the maximum frictional force between each wheel and the road surface. That is, an anti-skid braking system is known which is configured to control a braking hydraulic pressure, thereby preventing a lock or skid of a wheel that occurs at the time of sudden braking.

Here, in a rear wheel steering device of a vehicle equipped with an ABS, which controls a steering ratio of a rear wheel to a steering angle of a front wheel in accordance with a vehicle speed, control is performed by the ABS. A wheel speed sensor for detecting the rotation speed of each wheel is provided to execute the operation. The rear wheel steering device calculates the vehicle speed based on the detection signal of the wheel speed sensor, and calculates the steering angle of the rear wheel. Is generally configured to be controlled.

[0004]

As described above, in a rear wheel steering device provided with an ABS, a steering ratio of a rear wheel to a steering angle of a front wheel is controlled according to a detection signal of a wheel speed sensor. In the rear wheel steering system of the vehicle, when the ABS is activated, the wheel speed changes greatly. Therefore, it is desirable to calculate the vehicle speed in accordance with the detection signal of the wheel speed sensor and control the steering angle of the rear wheel. As described above, there is a problem that the control of the steering angle of the rear wheels cannot be performed. There has been proposed a rear wheel steering device for a vehicle configured to calculate an average vehicle speed based on the wheel speed thus obtained, and to use the average vehicle speed as a control vehicle speed to control a steering angle of a rear wheel.

However, since the average vehicle speed thus obtained is based on the past wheel speeds, when the ABS is operated and braking is applied to the wheels, the average vehicle speed always becomes a value larger than the actual vehicle speed. During operation, the average vehicle speed is used as a control vehicle speed for controlling the rear wheel steering angle, and AB
When the control vehicle speed is switched to the actual vehicle speed calculated from the wheel speed detected by the wheel speed sensor when S stops, the control vehicle speed sharply decreases, and the steering ratio of the rear wheels to the steering angle of the front wheels decreases. In the vehicle speed-sensitive rear wheel steering device, the turning ratio characteristic is set so that the rear wheel is steered more in the same phase direction as the front wheel as the vehicle speed is higher. However, there has been a problem that the in-phase amount is reduced and the running stability is reduced.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a rear wheel steering device for a vehicle including a wheel speed sensor for detecting a rotation speed of each wheel and an ABS, based on a wheel speed detected by a wheel speed sensor for a driven wheel. A vehicle speed calculating means for calculating a vehicle speed, an average vehicle speed calculating means for calculating an average vehicle speed, and an operation signal indicating an operation state are input from the ABS, and the average vehicle speed calculation is performed based on the operation signal while the ABS is operating. A rear-wheel steering device including a rear-wheel steering angle control unit that turns a rear wheel at a predetermined steering ratio with respect to a front-wheel steering angle in accordance with the average vehicle speed calculated by the means. It is an object of the present invention to provide a rear wheel steering device for a vehicle in which running stability does not decrease even when the operation of the vehicle is stopped.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to provide the rear wheel steering system until the vehicle speed calculated by the vehicle speed calculating means becomes equal to or higher than the average vehicle speed calculated by the average vehicle speed calculating means after the operation of the ABS is stopped. The angle control means is configured to turn the rear wheels at a predetermined turning ratio with respect to the steering angle of the front wheels according to the average vehicle speed calculated by the average vehicle speed calculation means. .

[0008]

According to the present invention, even after the operation of the ABS is stopped, the vehicle speed calculated by the vehicle speed calculating means is equal to or higher than the average vehicle speed calculated by the average vehicle speed calculating means.
According to the average vehicle speed calculated by the average vehicle speed calculation means, the rear wheels are steered at a predetermined steering ratio with respect to the steering angle of the front wheels. Therefore, when the operation of the ABS is stopped, the control vehicle speed suddenly decreases. As a result, it is possible to effectively prevent running stability from being impaired.

[0009]

Embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic overall configuration diagram of a vehicle including a vehicle rear wheel steering device according to an embodiment of the present invention. 1, a vehicle 1 includes left and right front wheels 2FL and 2FR connected by a front wheel steering mechanism A, and left and right rear wheels 2RL and 2RR connected by a rear wheel steering mechanism B.

[0010] Front wheel steering mechanism A, a pair of knuckle arms 3
FL, 3FR and tie rod 4FL, 4FR and tie rod 4F
And a relay rod 5F connecting the L and 4FR to each other. The front wheel steering mechanism A includes a rack (not shown) connected to a relay rod 5F and a steering shaft 7.
And a rack-and-pinion type steering mechanism C having a pinion 6 connected to the steering wheel 8.
The left and right front wheels 2FL and 2FR are steered by displacing the relay rod 5F left and right in accordance with the steering angle of the vehicle.

The rear wheel steering mechanism B includes a pair of knuckle arms 3RL, 3RR, tie rods 4FL, 4FR, and tie rods 4FL.
The relay rod 5R connects the RL and 4RR to each other, the servomotor 10 acting as a drive source for steering the left and right rear wheels 2RL and 2RR, and the drive force of the servomotor 10 for transmitting the driving force to the relay rod 5R. A transmission mechanism 11 is provided, and by rotating the servo motor 10 forward or backward, the relay rod 5R
Is displaced left and right, and the left and right rear wheels 2RL and 2RR are steered.

The rear wheel steering mechanism B is provided on the transmission mechanism 11 and is capable of releasing the connection between the servo motor 10 and the relay rod 5R.
A fail-safe mechanism is provided between the vehicle body R and the vehicle body and comprises a neutral holding means 9 having a spring 9a which constantly urges the relay rod 5R in a neutral direction. When the steering angle control of the rear wheels 2RL and 2RR is to be stopped, the clutch 12 is released and the relay rod 5R is forcibly held at the neutral position by the neutral holding means 9, thereby steering the vehicle 1 by two wheels. The vehicle is configured to be driven.

The vehicle 1 also includes a steering angle sensor 13 for detecting a steering angle of the steering wheel, an encoder 17 for detecting a rotational position of the servomotor 10 and a relay rod 5.
A rear wheel steering angle sensor 18 for detecting the displacement of R is provided. Further, a steering angle sensor 13 and a rear wheel 2 (not shown)
Detection signals are input from a wheel speed sensor for detecting the rotation speeds of RL and 2RR, an encoder 17 and a rear wheel steering angle sensor 18, and based on these detection signals, the servo motor 10
Is provided with a control unit 30 for controlling the rotation of.

The control unit 30 calculates the vehicle speed V in accordance with the rotational speeds of the wheels detected by the wheel speed sensors of the rear wheels 2RL and 2RR, which are driven wheels, and calculates the front wheel 2FL based on a predetermined steering ratio characteristic. Rear wheel 2 for 2FR
The steering ratio of RL and 2RR is calculated as a function of the calculated vehicle speed V, and the target rear wheel steering angle is calculated based on the calculated steering ratio and the steering angle detected by the steering angle sensor 13. Further, based on the target rear wheel steering angle calculated in this way, via a servo motor drive circuit (not shown),
The servomotor 10 is operated, and the rear wheels 2RL and 2RR are steered while monitoring the rotational position of the servomotor 10 detected by the encoder 17 and the displacement of the relay rod 5R detected by the rear wheel steering angle sensor 18.

FIG. 2 is a schematic overall configuration diagram showing an outline of an ABS mounted on the vehicle shown in FIG. As shown in FIG. 2, the left and right front wheels 2FL and 2FR and the left and right rear wheels 2RL and 2RR of the vehicle 1 have respective wheels 2FL, 2FR, 2RL and 2RR.
Disk rotors 23a, 23a, 2
3a, 23a and brake devices 23, 23, 23, 23 each having calipers 23b, 23b, 23b, 23b for braking the rotation of each disk rotor 23a when brake hydraulic pressure (brake fluid pressure) is supplied. Have been.

The ABS is configured to individually and variably adjust the brake hydraulic pressure for each of the brake devices 3 during a braking operation, that is, when a brake pedal is depressed.
An acceleration sensor 24 for detecting the acceleration of the vehicle 1 is provided on each of the wheels 2FL, 2FR, 2RL and 2RR, and a wheel speed sensor 25, 25, 25 for detecting the rotational speed of each wheel, that is, the wheel speed, respectively. 25, acceleration sensor 24
And wheel speed sensors 25, 25, 25, 25 for each wheel
Control unit 40 and ABS control unit 4 which receive a detection signal from and generate a control signal
Hydraulic control valve 2 that variably controls the brake hydraulic pressure supplied to each brake device 23 based on a control signal output from 0
6, 26, 26, 26, these hydraulic control valves 26, 26,
26, 26, hydraulic oil set to a predetermined pressure,
That is, a hydraulic unit (not shown) for supplying the brake fluid is provided.

The ABS control unit 40 controls the rotational speeds WFL, WF of the wheels 2FL, 2FR, 2RL and 2RR detected by the wheel speed sensors 25, 25, 25, 25.
R, WRL and WRR, a reference rotation speed Vr at which a wheel and a road surface generate an optimum braking force based on a rotation speed of a predetermined wheel, for example, a rotation speed of the slowest wheel.
Is set, and the reference rotational speed Vr and the rotational speeds WFL, WFR, WRL, WRR of the respective wheels detected by the respective wheel speed sensors 25 are set.
In order to prevent skidding or locking of each wheel, hydraulic control valves 26, 26, 26, 26
Control the braking oil pressure for each wheel.

FIG. 3 is a block diagram of a rear wheel steering device according to an embodiment of the present invention. 3, the vehicle rear wheel steering device according to the embodiment of the present invention includes a control unit 30. The control unit 30 includes a vehicle speed calculating unit 31 and an average vehicle speed calculating unit 3.
2. A vehicle speed-sensitive rear wheel steering angle calculating means 33 and a rear wheel turning means 34 are provided.

The vehicle speed calculating means 31 of the control unit 30 detects the rear wheel 2R detected by the wheel speed sensors 25, 25.
The vehicle speed VRL and the vehicle speed VRR are calculated based on the wheel speeds WRL and WRR of L and 2RR, respectively, and the higher value is selected as the vehicle speed V, and the vehicle speed signal is transmitted to the average vehicle speed calculation means 32 and the rear wheel steering. Output to the means 34. The average vehicle speed calculating means 32 calculates an average vehicle speed Vav based on the vehicle speed signal input from the vehicle speed calculating means 31 according to the following equation, and outputs the average vehicle speed signal to the rear wheel steering means 34.

Vav (n) = {(Vmax−V) × Vav (n−1) + V ² } / Vmax where Vmax is the maximum vehicle speed, Vav (n) is the average vehicle speed in the cycle, Vav (n) -1) is the average vehicle speed in the previous cycle. Control unit 3
The steering wheel angle detection signal from the steering angle sensor 13 is input to the rear wheel steering angle calculation means 33 of the ABS, and ABS
From the control unit 40, an operation signal indicating an ABS operation state for each brake device 23, a vehicle speed signal from the vehicle speed calculation means 31 and an average vehicle speed signal from the average vehicle speed calculation means 32 are input. Rear wheel steering angle calculating means 33
In accordance with an operation signal from the ABS control unit 40, while the ABS is operating, the average vehicle speed calculating means 32
And the rear wheels 2RL, 2RR with respect to the front wheels 2FL, 2FR in accordance with a predetermined steering ratio characteristic based on the average vehicle speed Vav input from the
, And further, based on the calculated steering ratio and the steering angle detected by the steering angle sensor 13,
The target rear wheel steering angle is calculated and output to the rear wheel steering means 33,
On the other hand, when the ABS is not operating, AB
After S stops operating, until the vehicle speed V input from the vehicle speed calculation means 31 becomes equal to or higher than the average vehicle speed Vav input from the average vehicle speed calculation means 32, based on the average vehicle speed Vav, in other cases, On the basis of the actual vehicle speed V input from the vehicle speed calculating means 31, a steering ratio of the rear wheels 2RL, 2RR to the front wheels 2FL, 2FR is calculated according to a predetermined steering ratio characteristic,
Further, a target rear wheel steering angle is calculated based on the calculated steering ratio and the steering wheel angle detected by the steering angle sensor 13, and is output to the rear wheel steering means 33.

Further, the target rear wheel steering angle calculated by the rear wheel steering angle calculating means 33 is input to the rear wheel steering means 34, and a detection signal of the rotational position of the servomotor 10 detected by the encoder 17 is provided. And rear wheel steering angle sensor 1
8, a detection signal of the displacement of the relay rod 5R detected by the rear wheel steering unit 8 is input, and the rear wheel steering unit 33 outputs the servo motor drive circuit 14 based on the target rear wheel steering angle input from the rear wheel steering angle calculation unit 31. While monitoring the rotational position of the servo motor 10 detected by the encoder 17 and the displacement of the relay rod 5R detected by the rear wheel steering angle sensor 18,
RL and 2RR are steered.

FIG. 4 is a flowchart for calculating the steering angles of the rear wheels 2RL and 2RR by the rear wheel steering angle calculating means 33. In FIG. 4, first, the rear wheel steering angle calculating means 33 includes:
Based on the vehicle speed V calculated by the vehicle speed calculating means 31 and the average vehicle speed based on the vehicle speed V calculated by the vehicle speed calculating means 31, based on the wheel speeds WRL, WRR of the rear wheels 2RL, 2RR detected by the wheel speed sensors 25, 25. The average vehicle speed Vav calculated by the calculation means 32 is input and the ABS
An operation signal is input from the control unit 40.

The rear wheel steering angle calculating means 33 determines whether the flag F is 1 or not. Here, the flag F is set to 1 when the ABS operates, and after the ABS operation is stopped,
When the vehicle speed V becomes equal to or higher than the average vehicle speed Vav, the value is set to 0. At the start of the determination, the value is set to 0, and thus the determination result is NO. This determination result is NO
In the case of, the rear wheel steering angle calculation means 33 further performs the AB control based on the operation signal from the ABS control unit 40.
It is determined whether S is operating.

As a result, when the result is NO, that is, when it is determined that the ABS is not operating, it is desirable to control the steering angles of the rear wheels 2RL and 2RR based on the actual vehicle speed V. The angle calculating means 33 calculates the turning ratio of the rear wheels 2RL, 2RR to the front wheels 2FL, 2FR in accordance with predetermined turning ratio characteristics based on the vehicle speed V input from the vehicle speed calculating means 31, and further calculates. Steering ratio and steering angle sensor 13
The target rear wheel steering angle is calculated based on the steering angle detected by the steering wheel and output to the rear wheel turning means 33, and the flag F
Then, the process shifts to the next cycle while maintaining the value of 0.

On the other hand, when YES, that is,
When it is determined that the ABS is operating, there is a possibility that the wheel speeds WRL and WRR may have changed significantly due to the operation of the ABS, and the rear wheels 2RL and 2RR are determined based on the actual vehicle speed V.
When the steering angle is controlled, there is a possibility that the rear wheel steering angle may not be controlled as desired. On the basis of the average vehicle speed Vav input from the calculating means 32, the steering ratio of the rear wheels 2RL, 2RR to the front wheels 2FL, 2FR is calculated in accordance with predetermined steering ratio characteristics. Based on the steering angle detected by the angle sensor 13, a target rear wheel steering angle is calculated and output to the rear wheel turning means 33, and the process proceeds to the next cycle.

In the next cycle, similarly, the rear wheel steering angle calculating means 33 first determines whether or not the flag F is "1". If the result is NO, as in the previous cycle, it is determined whether or not the ABS is operating based on the operating signal from the ABS control unit 40. On the other hand, if YES, it is determined based on the operation signal from the ABS control unit 40 whether or not the ABS operation has stopped.

As a result, when the result is NO, that is, when ABS
Is determined to be operating, there is a possibility that the wheel speeds WRL and WRR may have changed significantly due to the operation of the ABS, and the steering angles of the rear wheels 2RL and 2RR are controlled based on the actual vehicle speed V. Then, as desired, there is a possibility that the control of the rear wheel steering angle cannot be performed.
Based on the average vehicle speed Vav input from the average vehicle speed calculation means 32, the front wheels 2FL, 2FR
, The steering ratio of the rear wheels 2RL and 2RR is calculated, and based on the calculated steering ratio and the steering angle detected by the steering angle sensor 13, the target rear wheel steering angle is calculated. Output to the rudder means 33, while the flag F is kept at 1,
Move to the next cycle.

On the other hand, if YES, that is,
If it is determined that the operation of the ABS has stopped, it is unlikely that the wheel speeds WRL and WRR have changed significantly due to the operation of the ABS. It is more likely that the actual vehicle speed V will be lower than Vav. Therefore, the rear wheel steering angle calculator 33 receives the vehicle speed V input from the vehicle speed calculator 31 and inputs the vehicle speed V from the average vehicle speed calculator 32. Average vehicle speed V
It is determined whether the value is equal to or larger than av.

As a result, when the result is NO, that is, when the vehicle speed V
Is less than the average vehicle speed Vav, the actual vehicle speed is used as the control vehicle speed, and based on the actual vehicle speed V, the rear wheels 2RL, 2RR
If the steering angle of the rear wheels RL and 2RR is controlled rapidly, the in-phase amount of the rear wheels RL and 2RR with respect to the front wheels 2FL and 2FR may be reduced, and the running stability may be reduced. 33 calculates the steering ratio of the rear wheels 2RL, 2RR to the front wheels 2FL, 2FR based on the average steering speed Vav input from the average vehicle speed calculation means 32, and further calculates the steering ratio. A target rear wheel steering angle is calculated based on the steering ratio and the steering angle detected by the steering angle sensor 13, output to the rear wheel steering means 33, and while the flag F is kept at 1, the next cycle is performed. Move to

On the other hand, if YES, that is,
When the actual vehicle speed V is equal to or higher than the average vehicle speed Vav, the actual vehicle speed V is used as the control vehicle speed, and based on the actual vehicle speed V,
Even if the steering angles of the rear wheels 2RL and 2RR are controlled, there is no danger that the in-phase amount of the rear wheels RL and 2RR with respect to the front wheels 2FL and 2FR will be small and running stability will be reduced. Reference numeral 33 denotes front wheels 2FL, 2FR in accordance with predetermined turning ratio characteristics based on the vehicle speed V input from the vehicle speed calculating means 31.
, The steering ratio of the rear wheels 2RL and 2RR is calculated, and based on the calculated steering ratio and the steering angle detected by the steering angle sensor 13, the target rear wheel steering angle is calculated. Output to the steering means 33, set the flag F to 0, and proceed to the next cycle.

According to this embodiment, even if the operation of the ABS is stopped, the steering angle control of the rear wheels 2RL and 2RR based on the actual vehicle speed V is performed until the actual vehicle speed V becomes equal to or higher than the average vehicle speed Vav. When the ABS is stopped, the control vehicle speed sharply decreases, and as a result, the in-phase amount of the rear wheels RL and 2RR with respect to the front wheels 2FL and 2FR decreases, so that the vehicle travels. It is possible to effectively prevent a decrease in stability.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the invention described in the claims, which are also included in the scope of the present invention. Needless to say, For example, in the above embodiment, the wheel speed sensors WRL and WRR detected by the wheel speed sensors 25 of the left and right rear wheels 2RL and 2RR are detected by the ABS control unit 40 from the rear wheel steering angle calculating means 31 and the rear wheel steering angle calculating means 31. Although input to the wheel steering stop means 32, the detection signals of the wheel speeds WRL and WRR from the wheel speed sensors 25 and 25 of the rear wheels 2RL and 2RR are sent to the rear wheel steering angle calculation means 31 and the rear wheel steering stop means 32. May be input directly.

In the above embodiment, the control by ABS and the control of the rear wheel steering angle are performed by using the wheel speeds WRL and WRR detected by the wheel speed sensors 25 and 25 of the left and right rear wheels 2RL and 2RR. However, the detection signal of the wheel speed of the wheel speed sensor of the driven wheel may be used, and the wheel speed sensors 25, 25 of the front wheels 2FL, 2FR may be used depending on the driving type of the wheel.
The control by the ABS and the control of the rear wheel steering angle may be performed by using the wheel speeds WFL and WFR detected by the above.

[0034]

According to the present invention, there is provided a rear wheel steering device for a vehicle including a wheel speed sensor for detecting a rotation speed of each wheel and an ABS, based on a wheel speed detected by a wheel speed sensor for a driven wheel. A vehicle speed calculating means for calculating a vehicle speed, an average vehicle speed calculating means for calculating an average vehicle speed, and an operation signal indicating an operation state from the ABS, and based on the operation signal, when the ABS is in operation, the average is calculated. According to the average vehicle speed calculated by the vehicle speed calculation means, a rear wheel steering device having a rear wheel steering angle control means for turning the rear wheels at a predetermined steering ratio with respect to the front wheel steering angle. , It is possible to provide a rear wheel steering device for a vehicle in which running stability does not decrease even when the operation of the ABS is stopped.

[Brief description of the drawings]

FIG. 1 is a schematic overall configuration diagram showing a rear wheel steering device of a vehicle according to an embodiment of the present invention.

FIG. 2 is a schematic overall configuration diagram showing an outline of an anti-skid braking system mounted on the vehicle shown in FIG. 1.

FIG. 3 is a block diagram of a rear wheel steering device of the vehicle according to the embodiment of the present invention.

FIG. 4 is a flowchart for calculating a steering angle of a rear wheel by a rear wheel steering angle calculating means;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vehicle 2FL Left front wheel 2FR Left rear wheel 2RL Right front wheel 2RR Right front wheel 3FL, 3FR, 3RL, 3RR Knuckle arm 4FL, 4FR, 4RL, 4RR Tie rod 5F, 5R Relay rod 6 Pinion 7 Steering shaft 8 Handle 9 Neutral holding means 10 Servo Motor 11 Transmission mechanism 12 Clutch 13 Steering angle sensor 14 Servo motor drive circuit 17 Encoder 18 Rear wheel steering angle sensor 23 Brake device 23a Disk rotor 23b Caliber 24 Acceleration sensor 25 Wheel speed sensor 30 Control unit 31 Vehicle speed calculating means 32 Average vehicle speed calculating means 33 rear wheel steering angle calculation means 34 rear wheel steering means 40 ABS control unit

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B62D 113: 00 (56) References JP-A-3-193560 (JP, A) JP-A-4-81351 (JP, A) JP-A-3-262779 (JP, A) JP-A-62-148861 (JP, A) JP-A-63-215466 (JP, A) JP-A-1-172070 (JP, A) JP-A-57-44568 ( JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00

Claims (1)

(57) [Claims] 1. A rear wheel steering device for a vehicle, comprising: a wheel speed sensor for detecting a rotation speed of each wheel; and an anti-skid braking system, wherein a wheel speed of a driven wheel is detected based on a wheel speed detected by the wheel speed sensor. A vehicle speed calculating means for calculating a vehicle speed, an average vehicle speed calculating means for calculating an average vehicle speed,
An operation signal indicating an operation state is input from the anti-skid braking system, and based on the operation signal, while the anti-skid braking system is operating, the rear wheels according to the average vehicle speed calculated by the average vehicle speed calculation means. A rear wheel steering device having a rear wheel steering angle control means for turning the steering wheel at a predetermined steering ratio with respect to the steering angle of the front wheels, after stopping the operation of the anti-skid braking system, Until the vehicle speed calculated by the means is equal to or higher than the average vehicle speed calculated by the average vehicle speed calculation means, the rear wheel steering angle control means controls the rear wheels according to the average vehicle speed calculated by the average vehicle speed calculation means. The steering wheel of the vehicle is configured to be steered at a predetermined steering ratio with respect to the steering angle of the front wheels.