JPH0585385A - Rear wheel steering control device for four-wheel steering vehicle - Google Patents

Abstract

(57) [Abstract] [Purpose] In a four-wheel steering vehicle that controls the steering of the rear wheels by feeding back the yaw rate, to improve the turning performance and running stability of the vehicle during sudden steering. [Configuration] The microcomputer 55 includes a steering wheel steering angle sensor 51, a vehicle speed sensor 52, and a yaw rate sensor 5.
The rear wheel steering mechanism B is controlled according to the steering speed dθ / dt, the vehicle speed V and the yaw rate ωy based on the detection signal from the target rear wheel steering wheel RW1 and RW2 in the direction to suppress the yaw rate ωy. Steer to the angle θr * = K ₃ , K ₂ · K ₁ · ωy. The coefficient K ₁ increases as the vehicle speed V increases, and improves the running stability of the vehicle during medium-high speed running.
The coefficient K ₂ becomes small when the steering speed dθ / dt of the steering wheel is large, and improves the turning performance of the vehicle during sudden steering. Coefficient K ₃
Is large when the yaw rate ω y is large, and prevents deterioration of the running stability of the vehicle for ensuring the turning performance.

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 control device for a four-wheel steering vehicle which steers and controls the rear wheels according to the yaw rate of the vehicle body.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type is disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Publication No. 164374, the yaw rate of the vehicle body is detected by the yaw rate detecting means, and the detected yaw rate is fed back to the rear wheel steering mechanism to be proportional to the magnitude of the yaw rate in the direction of suppressing the yaw rate. In the rear wheel steering control device for a four-wheel steering vehicle that controls the steering of the rear wheels, steering speed detecting means for detecting the steering speed of the steering wheel is provided, and when the detected steering speed is high, the steering speed is lower than that when the steering speed is low. The gain by the feedback control means is corrected to be small so that the turning performance of the vehicle is improved when the steering wheel is steered steeply for lane change, emergency avoidance, etc. during medium and high speed traveling.

[0003]

However, in the above-mentioned conventional apparatus, although the turning performance of the vehicle is improved, the yaw rate feedback gain is lowered when the steering speed is increased, so that the steering wheel is steered. Due to the subsequent increase in the yaw rate of the vehicle body, the running stability of the vehicle may not be sufficiently controlled. The present invention has been made to address the above problems, and its purpose is to:
It is an object of the present invention to provide a rear wheel steering control device for a four-wheel steering vehicle, which is capable of maintaining good traveling stability of the vehicle while maintaining good turning performance of the vehicle.

[0004]

In order to achieve the above object, a structural feature of the present invention is a control device for electrically controlling a rear wheel steering mechanism for steering a rear wheel, the yaw rate of a vehicle body. A yaw rate detection means for detecting the yaw rate, feedback control means for feeding back the detected yaw rate to the rear wheel steering mechanism to suppress the yaw rate, and feedback control means for steering control of the rear wheel in proportion to the magnitude of the yaw rate; Steering speed detecting means for detecting the steering speed of the steering wheel,
A rear wheel steering control device for a four-wheel steering vehicle, comprising: a first gain correction means for correcting the gain by the feedback control means to be smaller when the detected steering speed is higher than when the steering speed is low; The second gain correction means is provided to largely correct the gain by the feedback control means when the detected yaw rate is high compared to when the yaw rate is low.

[0005]

In the present invention constructed as described above, the steering wheel is steered steeply for lane change, emergency avoidance, etc. at the time of traveling at middle and high speeds, and as shown in FIG. 6, first, the steering speed dθ / dt of the steering wheel. Becomes larger, the first gain correction means corrects the gain by the feedback control means to a smaller value, so that the steering amount of the rear wheels steered in the direction in which the yaw rate is suppressed becomes smaller, as in the conventional device described above.
The turning ability of the vehicle is improved. On the other hand, due to the sudden steering of the steering wheel, as shown in FIG. 6, a large yaw rate ωy continues to occur in the vehicle body, and the second gain correction means largely corrects the gain by the feedback control means. The steering amount of the rear wheel that is steered in a direction that suppresses the increase of the steering amount is increased, and the traveling stability of the vehicle is improved.

[0006]

As described above, according to the present invention, when the steering wheel is steered for lane change, emergency avoidance, etc. during middle and high speed traveling, the yaw rate is delayed with respect to the steering wheel steering. Utilizing this, the first and second gain correction means control the gains by the feedback control means with a time difference, so that good running stability of the vehicle can be secured at the same time without impairing the turning performance of the vehicle.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows an entire four-wheel steering vehicle according to the embodiment. This four-wheel steering vehicle has left and right front wheels FW1,
The front wheel steering mechanism A for steering the FW2 and the left and right rear wheels RW1,
A rear wheel steering mechanism B that steers the RW2 and a rear wheel steering mechanism B
And an electric control device C for electrically controlling the.

The front wheel steering mechanism A has a steering handle 11, and this steering handle 11 is connected to a pinion gear 13 via a steering shaft 12. This pinion gear 1
Reference numeral 3 is for engaging with the rack bar 14 and converting the rotational movement of the steering handle 11 into the reciprocating movement of the rack bar 14 for transmission. Left and right tie rods 1 on both ends of the rack bar 14.
The left and right front wheels FW1 and FW2 are steerably connected via the left and right knuckle arms 16a and 16b, and the bar 14 has left and right front wheels FW1 and FW2 depending on the axial displacement of the steering wheel 11. Steer.
A control valve 17 composed of a four-way valve is assembled in the middle of the steering shaft 12, and the valve 17 is operated by a hydraulic pump 21 driven by an engine 18 according to a steering torque acting on the steering shaft 12. It functions to supply the oil to one oil chamber of the power cylinder 22 and to discharge the hydraulic oil in the other oil chamber of the power cylinder 22 to the reservoir 23. The power cylinder 22 assists the steering of the left and right front wheels FW1 and FW2 by driving the rack bar 14 in the axial direction according to the supply and discharge of the hydraulic oil.

The rear wheel steering mechanism B has a relay rod 31 for axially displacing and steering the left and right rear wheels RW1 and RW2, like the rack bar 14. Similar to the case of the front wheel steering mechanism A, the left and right tie rods 32a, 32b and the left and right knuckle arms 33a, 3 are provided on both ends of the relay rod 31, respectively.
The left and right rear wheels RW1, RW2 are steerably connected via 3b. The relay rod 31 is axially displaceably supported by a housing 34 supported by the vehicle body, and a power cylinder 35 is formed in the housing 34. The power cylinder 35 drives the relay rod 31 in the axial direction according to the supply and discharge of hydraulic oil.
Is divided into left and right oil chambers 35b and 35c by a piston 35a fixed to the relay rod 31. Springs 36a, 36b are provided in the left and right oil chambers 35b, 35c.
Is installed so as to penetrate the relay rod 31 with the preload applied, and the spring 3
6a and 36b are relay rods 31 due to their resilience.
Is biased to the neutral position.

A spool valve 37, which constitutes a hydraulic pressure copying mechanism together with the power cylinder 35, is incorporated in the housing 34. The spool valve 37 includes a valve sleeve 37a that is housed in the housing 34 so as to be fluid-tight and slidable in the axial direction, and a valve spool 37b that is fixed to the housing 34. Depending on the displacement, the engine 18
The hydraulic oil from the hydraulic pump 38 driven by is supplied to the left oil chamber 35b of the power cylinder 35, and the hydraulic oil in the right oil chamber 35c of the cylinder 35 is discharged to the reservoir 23. When the valve sleeve 37a is displaced rightward in the drawing, the spool valve 37 supplies the hydraulic oil from the hydraulic pump 38 to the right oil chamber 35c of the power cylinder 35, and the hydraulic oil in the left oil chamber 35b of the cylinder 35. Is discharged to the reservoir 23.

A through hole 37a1 is provided at the right end portion of the valve sleeve 37a, and a lever 41 penetrates the through hole 37a1. A spherical nodal ridge 41a is provided in the middle of the lever 41, and the lever 41 engages with the inner peripheral surface of the through hole 37a1 at the outer peripheral surface of the nodal ridge 41a so as to be tiltable and slidable. ing. The lower end of the lever 41 has an annular groove 35a1 provided on the outer circumference of the piston 35a.
The upper end of the lever 41 is rotatably connected to the pin 42 so as to be rotatable and slidable in the vertical direction.

Both ends of the pin 42 enter into the support holes 34a and 34b provided in the housing 34 so as to be able to move forward and backward and not to rotate. The rack teeth 4 are provided on the outer circumference of the pin 42.
2a is formed, and a worm 44 fixed to the rotation shaft of the step motor 43 meshes with the rack tooth 42a. In this case, when the step motor 43 rotates in the positive (or negative) direction, the pin 42 is displaced rightward (or leftward).

The electric control unit C includes a steering wheel steering angle sensor 51, a vehicle speed sensor 52, a yaw rate sensor 53, and a rear wheel steering angle sensor 54. The steering wheel steering angle sensor 51 detects the steering wheel steering angle θ by measuring the rotation angle of the steering shaft 12, and outputs a detection signal representing the steering angle θ. The vehicle speed sensor 52 detects the vehicle speed V by measuring the rotation speed of an output shaft of a transmission (not shown), and outputs a detection signal representing the vehicle speed V. The yaw rate sensor 53 detects a rotational angular velocity around the vertical axis of the vehicle body, that is, a yaw rate ωy, and outputs a detection signal representing the yaw rate ωy. The rear wheel steering angle sensor 54 detects the rear wheel steering angle θr by measuring the rotation angle of the rotary shaft of the step motor 43, and outputs a detection signal representing the rear wheel steering angle θr. The steering wheel steering angle θ, the yaw rate ωy, and the rear wheel steering angle θr are positive in the right rotation direction and negative in the left rotation direction, respectively.

Each of these sensors 51 to 54 is connected to a microcomputer 55, and the computer 55.
Are the ROM 55b and CP respectively connected to the bus 55a
It consists of U55c, RAM55d and I / O55e (input / output interface). The ROM 55b stores a program corresponding to the flowchart of FIG. 2 and also stores the coefficients K ₁ , K ₂ and K ₃ in the form of a table. As shown in FIG. 3, the coefficient K ₁ is such that the vehicle speed V is a predetermined vehicle speed (about 20
It is zero when the vehicle speed V is less than or equal to Km / h) and gradually increases as the vehicle speed V increases further, and becomes constant (e.g., "0.0" at a predetermined vehicle speed (about 120 Km / h) or more).
7 ”). The coefficient K ₂ is, as shown in FIG. 4, an absolute value of the steering speed dθ / dt of the steering wheel 11 | dθ /
When dt | is less than or equal to a predetermined value (about 0.5 degree / second), it has a constant ratio (for example, “1.0”) and the same absolute value | dθ /
It gradually decreases as dt | becomes larger,
At a predetermined value (about 2.0 degrees / second) or more, the smaller constant ratio (for example, "0.5") is maintained. The coefficient K ₃ is, as shown in FIG. 5, the absolute value of the yaw rate ω y |
When ωy | is less than or equal to a predetermined value (about 15 degrees / second), the ratio is constant (for example, “1.0”) and the absolute value | ωy
| Gradually increases as | increases, and is maintained at a larger constant ratio (for example, “1.5”) above a predetermined value (about 20 degrees / second).

The CPU 55c repeatedly executes the program from the closing to the opening of an ignition switch (not shown), and the RAM 55d temporarily stores variable data necessary for executing the program. The I / O 55e exchanges signals with an external circuit. The I / O 55e is connected to the sensors 51 to 54 and the drive circuit 56.
The drive circuit 56 rotates the step motor 43 by the number of steps corresponding to the rotation control signal from the microcomputer 55, and then controls the motor 43 to maintain the position after the rotation.

Next, the operation of the embodiment configured as described above will be described. When the ignition switch (not shown) is closed, the CPU 55c starts executing the program in step 100 of FIG.
The circulation process consisting of 5 is executed. In this circulation processing, in step 101, the steering angle θ of the steering wheel, the vehicle speed V, the yaw rate ωy, and the steering angle θ of the rear wheels are read from the sensors 51 to 54.
The detection signals respectively representing r are read, and step 10
The steering speed d can be calculated by differentiating the steering angle θ by 2
θ / dt is calculated. Next, at step 103, a table in the ROM 55b is referred to based on the vehicle speed V, the absolute value | dθ / dt | of the steering speed dθ / dt and the absolute value | ωy | Value | dθ / dt |,
The respective coefficients K ₁ , K ₂ and K ₃ corresponding to │ωy│ are derived, and the target rear wheel steering angle θr * is calculated in step 104 by executing the calculation of the following equation 1.

[0017]

[Equation 1] θr * = K ₃ · K ₂ · K ₁ · ωy After calculating the target rear wheel steering angle θr *, in step 105, the target rear wheel steering angle θr * is changed to the current rear wheel steering angle θr. The steering amount θr * −θr of the left and right rear wheels RW1 and RW2 to be steered is calculated by subtracting the steering amount θr *
A rotation control signal for the step motor 43 corresponding to −θr is output to the drive circuit 56 via the I / O 55e.

The drive circuit 56 supplies a drive pulse according to the rotation control signal to the step motor 43,
3 rotates the worm 44 by an amount corresponding to the drive pulse. In this case, if the rotation control signal corresponding to the rear wheel steering amount θr * −θr is positive, the step motor 43 rotates normally, the pin 42 is displaced to the right, and the upper end of the lever 41 is moved to the lower end. Displace to the right with the part as a fulcrum. As a result, the valve sleeve 37a is displaced to the right,
The hydraulic oil from the hydraulic pump 38 is supplied to the right oil chamber 35c of the power cylinder 35, and the hydraulic oil in the left oil chamber 35b of the cylinder 35 is discharged to the reservoir 23. The left and right rear wheels RW1 and RW2 are displaced to the left and steered to the right. On the other hand, the lever 41 is displaced by the displacement of the relay rod 31 to the left.
The lower end of the valve sleeve 37a is displaced leftward with its upper end as a fulcrum, and the valve sleeve 37a is displaced leftward. Then, when the valve sleeve 37a returns to the reference position,
Since the supply and discharge of the hydraulic oil is stopped and the displacement of the relay rod 31 to the left is also stopped, the left and right rear wheels RW1, RW2
Is steered rightward from the past state by an amount corresponding to the rear wheel steering amount θr * −θr, and the steering angle θr becomes equal to the target rear wheel steering angle θr *.

If the rotation control signal corresponding to the rear wheel steering amount θr * -θr is negative, the step motor 43 rotates negatively and the pin 42 is displaced leftward. , The left and right rear wheels RW1 and RW2 are steered to the left by an amount corresponding to the rear wheel steering amount θr * −θr from the past state, and in this case also, the steering angle θr is the target rear wheel steering angle θr *.
Is equal to

As described above, the left and right rear wheels RW1 and RW2 are steered to the target rear wheel steering angle θr * (= K ₃ · K ₂ · K ₁ · ωy). (Or negative)
When the yaw rate ωy of is generated, the coefficients K ₁ , K ₂ , and K ₃ are always zero or positive, so that the rear wheels RW1 and RW2 are kept in the neutral state or the right (or left) direction, that is, the yaw rate ωy is changed. The steering wheel is steered in the restraining direction, and the steering angle θr becomes proportional to the yaw rate ωy.
This means that the steering of the left and right rear wheels RW1 and RW2 is feedback controlled according to the yaw rate ωy, and the feedback gain of the control is determined by the coefficients K ₁ , K ₂ and K ₃ .

If the steering wheel 11 is steered at a speed that is not so large and a yaw rate ωy that is not so large is generated in the vehicle body while the vehicle is traveling at a medium or high speed, in this case, both coefficients K ₂ and K ₃ are "1. Since it is "0", the steering of the left and right rear wheels RW1, RW2 is feedback-controlled according to the yaw rate ωy with a gain determined only by the coefficient K ₁ . On the other hand, since the coefficient K ₁ as the feedback gain is a positive value that gradually increases as the vehicle speed V increases, the rear wheel steering angle θr proportional to the magnitude of the yaw rate ωy increases as the vehicle speed V increases. The yaw rate generated in the vehicle body is further suppressed, and the running stability of the vehicle is improved during medium and high speed running, especially during high speed running.

On the other hand, when the steering wheel 11 is steered quickly for lane change, emergency avoidance, etc. while the vehicle is traveling at medium and high speeds, as shown in FIG. 6, first, the steering speed dθ / dt
Although the absolute value | dθ / dt | of the yaw rate increases, the generation of the yaw rate ωy is delayed and the absolute value | ωy | is initially kept at a small value. As a result, the coefficient K ₂ becomes smaller than “1.0”, but the coefficient K ₃ is maintained at “1.0”, so that the feedback gain of the yaw rate ωy becomes smaller than that in the above case, and the rear wheel steering is performed. The angle θr is corrected to be smaller. As a result, during such a sudden steering of the steering wheel 11, the turning performance of the vehicle becomes good at first.

When some time has passed since the steered steering wheel 11 was steered, a yaw rate ωy is generated and its absolute value | ωy | increases, as shown in FIG. As a result, the coefficient K ₃ previously held at "1.0" becomes larger than "1.0", and the feedback gain of the yaw rate ωy becomes larger than that in the above case. The corrected feedback gain is restored, and the rear wheel steering angle θr is corrected to the larger side (time
See t1). As a result, the yaw rate ωy generated on the vehicle body
Will be suppressed more. Further, even after the absolute value | dθ / dt | of the steering speed dθ / dt becomes small, the feedback gain is kept at a large value while the absolute value | ωy | of the yaw rate ωy is large, and the yaw rate ωy is further increased. The running stability of the vehicle that is largely suppressed and lost due to the importance of turning ability is restored in a short time, and the running stability of the vehicle becomes good.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of a four-wheel steering vehicle showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a program executed by the microcomputer of FIG.

FIG. 3 is a change characteristic graph of a coefficient K ₁ .

FIG. 4 is a change characteristic graph of coefficient K ₂ .

FIG. 5 is a change characteristic graph of the coefficient K ₃ .

FIG. 6 is a time chart showing changes in steering speed dθ / dt, yaw rate ωy, coefficients K ₂ and K _3, and rear wheel steering angle θr during sudden steering.

[Explanation of symbols]

A ... Front wheel steering mechanism, B ... Rear wheel steering mechanism, C ... Electric control device, FW1, FW2 ... Front wheels, RW1, RW2 ... Rear wheels, 5
1 ... Steering wheel steering angle sensor, 52 ... Vehicle speed sensor, 53 ...
Yaw rate sensor, 54 ... Rear wheel steering angle sensor, 55 ... Microcomputer.

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

Claims (1)

[Claims] 1. A controller for electrically controlling a rear wheel steering mechanism for steering rear wheels, comprising yaw rate detecting means for detecting a yaw rate of a vehicle body, and the detected yaw rate being fed back to the rear wheel steering mechanism. Then, feedback control means for steering control of the rear wheels in proportion to the magnitude of the yaw rate in the direction of suppressing the yaw rate, steering speed detecting means for detecting the steering speed of the steering wheel, and the detected steering speed are When the steering speed is large, the rear wheel steering control device for a four-wheel steering vehicle including the first gain correction means for correcting the gain by the feedback control means to be smaller than when the steering speed is low, the detected yaw rate is high. At this time, the gain by the feedback control means is largely corrected as compared with the case where the yaw rate is small.
A rear-wheel steering control device for a four-wheel steering vehicle, comprising: