JPH0632241A - Rear wheel steering control method for vehicle - Google Patents

Abstract

PURPOSE:To allow a large angle steering to the same phase side and the opposite phase side prohibit a large angle steering to the opposite phase side according to a running condition. CONSTITUTION:A rear wheel steering control method for a vehicle in which operating pressure oil is supplied from a hydraulic pump 3 to a hydraulic cylinder 4 via a steering angle control valve 5 to steer a rear wheel 25 by an angle corresponding to the magnitude of the operating oil pressure to the same side and the opposite phase side, the operating pressure oil which arrives from the hydraulic pump 3 at the steering control valve 5 is increased as a front wheel steering angle is increased. If the front wheel steering angle is small, the maximum steering angle of the rear wheel 25 is limited to be small and if the front steering angle is large a large angle of steering of the rear wheel 25 is allowed. If the running speed of the vehicle exceeds a preset speed, a large angle opposite-phase steering of the rear wheel 25 is prohibited and the preset speed is changed according to a friction coefficient between the wheel and a road surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle rear wheel steering control method.

[0002]

2. Description of the Related Art As a rear wheel steering system for a four-wheel steering vehicle, a hydraulic pump driven by an engine, a hydraulic cylinder capable of steering the rear wheels, and a hydraulic pump interposed between the hydraulic pump and the hydraulic cylinder are operated. Some are equipped with a steering angle control valve that can control the direction and amount of hydraulic pressure.

In this rear wheel steering system, when the steering angle of the front wheels is small, the steering angle control valve is electrically controlled by the controller. Therefore, in this case, the rear wheels are steered according to the front wheel steering angle and the vehicle speed, and can be steered by a slight angle to the in-phase side and the anti-phase side (FIG. 19). On the other hand, when the front wheels are largely steered, the steering angle control valve is mechanically controlled by the control wire. Therefore, in this case, the rear wheels are steered according to the front wheel steering angle, and the large steering angle steering is possible only on the opposite phase side.

[0004]

By the way, when a vehicle parked in parallel on the side of a wall is started, the rear wheel is steered largely to the same phase side to facilitate the operation of the vehicle, while the rear wheel is operated. If the steering wheel is steered to the opposite phase side, it may be difficult to operate the vehicle. However, in the above-mentioned conventional rear wheel steering control method, there is a problem that the rear wheels cannot be steered to the same phase side by a large steering angle, resulting in poor vehicle operability.

Further, when the front wheels are steered largely, the control cable steers the rear wheels to the opposite phase side by a large steering angle, so that the rear wheels are steered by a large steering angle even when traveling on a slippery road surface. Can be dangerous. Further, even when the vehicle is traveling on a relatively slippery road surface, there is a problem that it is not preferable to steer the rear wheels at a large steering angle opposite phase during high speed traveling.

Furthermore, since the electric motor operated by the controller and the control cable connecting the front wheel steering device and the rear wheel steering device operate the steering angle control valve separately, the configuration of the rear wheel steering device is There is also a problem that it becomes complicated and increases the production cost. The present invention has been made to solve the above problems, and enables large steering angle steering to the in-phase side and anti-phase side, and depending on the traveling situation, the large steering to the anti-phase side. It is an object of the present invention to provide a rear wheel steering control method for a vehicle, which can prohibit angular steering and further reduce the production cost of a rear wheel steering device.

[0007]

In order to achieve the above object, according to the present invention, a working fluid pressure is supplied from a fluid pressure source to a fluid pressure actuator through a control valve, and the magnitude of this working fluid pressure is adjusted. In a rear wheel steering control method for a vehicle in which the rear wheels are steered to the in-phase side and the anti-phase side by a corresponding angle, the working fluid pressure reaching the control valve from the fluid pressure source is increased according to the increase in the front wheel steering angle. When the front wheel steering angle is small, the maximum steering angle of the rear wheels is limited to a small value, while when the front wheel steering angle is large, it is possible to steer the rear wheels at a large steering angle, and the traveling speed of the vehicle is set to a predetermined value. When the speed is exceeded, the large steering angle reverse phase steering of the rear wheels is prohibited, and the rear wheels are controlled so that the set speed is changed according to the friction coefficient between the wheels and the road surface.

[0008]

According to the vehicle rear wheel steering control method of the present invention, when the front wheel steering angle is small when the vehicle is turning, the rear wheels are steered within a small steering angle range while the front wheels are largely steered. If so, the rear wheels are steered within a large steering angle range. In addition, when the traveling speed of the vehicle exceeds the set speed, the rear wheels
Steering is performed within the large steering angle range on the in-phase side and within the small steering angle range on the opposite phase side. In this case, this set speed is
Since it is determined according to the friction coefficient between the wheel and the road surface, the steering of the rear wheels is controlled according to the road surface condition.

[0009]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a vehicle rear wheel steering apparatus for carrying out a rear wheel steering control method according to the present invention. The rear wheel steering apparatus 1 is composed of a hydraulic circuit, a controller 2 and the like. This hydraulic circuit includes a hydraulic pump 3, a hydraulic cylinder 4, a steering angle control valve 5, a relief valve 6 and the like, which are connected by an oil passage.

In other words, from the hydraulic pump 3 to the oil passages 11, 1
2 extends, and these oil passages 11 and 12 are connected to the steering angle control valve 5 and the relief valve 6, respectively. Further, oil passages 13 and 1 extending from the steering angle control valve 5 and the relief valve 6 respectively.
Both 4 are connected to the reserve tank 16. Further, a pair of oil passages 18 and 19 extend from the steering angle control valve 5, and these oil passages 4 a and 4 b of the hydraulic cylinder 4 are provided.
Respectively connected to. The oil passages 11 and 13 are connected by an oil passage 21, and in the middle of the oil passage 21,
An unload valve 22 is provided.

The hydraulic cylinder 4 has an operating rod 4c extending in the vehicle width direction. The operating rod 4c is attached to each rear wheel 25 via left and right tie rods 24 and knuckle arms (not shown). It is connected. This working rod 4
c reciprocates by a distance according to the magnitude of the operating hydraulic pressure adjusted by the steering angle control valve 5 described later. Therefore, the steering angle of the rear wheel 25 increases in proportion to the increase in the operating hydraulic pressure supplied from the steering angle control valve 5 to the hydraulic cylinder 4. For example, 35.
When the working hydraulic pressure of 0 kg / cm ² is supplied, the hydraulic cylinder 4 steers the rear wheels by 0.8 degrees, and the hydraulic pressure is 90.0 kg / c.
When the hydraulic pressure of m ² is supplied, the hydraulic cylinder 4 steers the rear wheels by 5.0 degrees.

The steering angle control valve 5 has, for example, a pair of solenoids, and is operated by a controller 2 which will be described later to switch the connection between the oil passages 11, 13, 18 and 19 and to connect the oil passages 18 to each other. , 19 can be reduced. For example, at the neutral position of the steering angle control valve 5, the oil passage 11 and the oil passage 13 and the oil passage 18 and the oil passage 19 are in communication with each other. Therefore, when the steering angle control valve 5 is switched to the neutral position, the pressures in the hydraulic chambers 4a and 4b of the hydraulic cylinder 4 become equal, and the operating rod 4c is moved to the neutral position by the spring force of the return spring (not shown). Will be restored.

Further, when the position of the steering angle control valve 5 is switched and the oil passage 11 and the oil passage 18 and the oil passage 13 and the oil passage 19 respectively communicate with each other, the operating hydraulic pressure supplied from the hydraulic pump 3 is supplied. Can be guided to the first hydraulic chamber 4a of the hydraulic cylinder 4, and the hydraulic oil in the second hydraulic chamber 4b can be guided to the reserve tank 16. Therefore, in this case, the operating rod 4c of the hydraulic cylinder 4 moves forward and steers each rear wheel 25 to the right. At this time, the steering angle control valve 5 can reduce the amount of oil flowing into the oil passage 18, adjust the magnitude of the operating hydraulic pressure introduced into the first hydraulic chamber 4a, and control the steering angle of the rear wheel 25. be able to.

Further, when the position of the steering angle control valve 5 is switched and the oil passage 11 and the oil passage 19 and the oil passage 13 and the oil passage 18 respectively communicate with each other, the operating hydraulic pressure supplied from the hydraulic pump 3 is supplied. Is guided to the second hydraulic chamber 4b of the hydraulic cylinder 4, and the hydraulic oil in the first hydraulic chamber 4a is stored in the reserve tank 16
Can lead to. Therefore, in this case, the operating rod 4c of the hydraulic cylinder 4 is returned to steer each rear wheel 25 to the left. At this time, the steering angle control valve 5 can throttle the amount of oil flowing into the oil passage 19, adjust the magnitude of the operating hydraulic pressure introduced into the second hydraulic chamber 4b, and control the steering angle of the rear wheel 25. be able to.

The unload valve 22 is, for example, a normally-open type electromagnetic opening / closing valve, which is opened / closed by the controller 2. That is,
When an engine (not shown) is started, the controller 2 excites the solenoid and closes the unload valve 22 unless any abnormality is detected in the rear wheel steering system 1. The hydraulic pump 3 is driven by the engine.

The relief valve 6 is attached to the steering gear box 64 of the front wheel steering device 31, and is shown in FIG.
As shown in detail in FIG.
The valve body 36 is housed in the second space 38, and the pressure adjusting mechanism 40 is housed in the second space 38. The casing 33 is provided with an inflow port 33a and an outflow port 33b. The inflow port 33a is opened to face an oil passage 47, which will be described later, and the oil passage 12 is connected thereto. Further, the outflow port 33b is opened to face the first space 35, and the oil passage 14 is connected thereto.

The valve body 36 is provided with a valve seat 42 screwed and fixed to the casing 33, a spring seat 43 which is movable in the axial direction with respect to the casing 33, and between the spring seat 43 and the valve seat 42. A spool 44 movable in the axial direction with respect to the casing 33
And a pressure adjusting spring 45 and the like which are compressed between the spring seat 43 and the spool 44.

The valve seat 42 is provided with a screw portion 42a. The screw portion 42a is provided on the outer peripheral surface of the base end side half portion and meshes with the screw portion 33d of the casing 33. Therefore, when the valve seat 42 is rotated, the amount of insertion into the casing 33 changes, and the preload of the pressure adjusting spring 45 described later can be adjusted. The valve seat 42 is fixed with a nut 49. An O-ring 51 seals between the valve seat 42 and the casing 33.

The valve seat 42 has an inflow port 3
An oil passage 47 is formed which connects 3a and the first space 35. The oil passage 47 includes an annular groove 47a provided on the outer peripheral surface of the valve seat 42 so as to face the inflow port 33a.
A hole 47 extending in the axial direction from the front end surface of the valve seat 42.
b, and a plurality of holes 47c that penetrate the valve seat 42 in the radial direction and open the holes 47b facing the annular groove 47a. Width dimension of the annular groove 47a (valve seat 42
Is set to be larger than the diameter of the opening of the inflow port 33a. Therefore, the valve seat 4
Even when the insertion amount of 2 is changed, the annular groove 47a always faces the inflow port 33a.

A shaft 44a extending toward the spring seat 43 is integrally formed with the spool 44 that abuts the valve seat 42 and closes the oil passage 47. This axis 4
The tip of 4a is slidably inserted into a shaft hole 43a formed in the spring seat 43. Therefore, the spool 44 is relatively displaceable with respect to the spring seat 43 and is not detachable. Also, the spool 44
The notch 44b is provided in the outer peripheral part at a plurality of positions at predetermined intervals in the circumferential direction, and serves as a passage through which hydraulic oil flows.

A connecting portion 43b projecting into the second space 38 is integrally formed at the tip of the spring seat 43. A hole 43c extending in the axial direction from the tip end surface is formed in the connecting portion 43b, and the connecting portion 43b is radially penetrated, and
An elongated hole 43d communicating with the hole 43c is formed. The long hole 43d has a shape elongated in the axial direction (FIG. 3).

The pressure adjusting spring 45 is a coil spring, for example, and presses the spool 44 toward the valve seat 42 side. The pressure adjusting spring 45 is contracted between the spring seat 43 and the spool 44 and has a predetermined preload. When the pressure on the oil passage 12 side becomes larger than the preload of the pressure regulating spring 45, the oil passage 47
The hydraulic oil therein moves the spool 44 and flows into the first space, thus reducing the pressure on the oil passage 12 side. That is, the maximum value of the operating hydraulic pressure on the oil passages 12 and 11 side is determined by the pressure adjusting spring 45.

The pressure adjusting mechanism 40 is composed of a shaft 53, an eccentric shaft 54, a connecting rod (hereinafter referred to as a connecting rod) 55, and the like. A gear 57 having a relatively small diameter is attached to the shaft 53 such that the gear 57 cannot rotate relatively. Further, the shaft 53 is
Is rotatably supported at predetermined positions via bearings 58 and 59. A convex portion 53a extending in the radial direction is integrally formed at the base end of the shaft 53. The convex portion 53a
By inserting into the groove 61a of the rotary shaft 61, these rotate integrally. The rotary shaft 61 extends from the front wheel steering device 31 and rotates integrally with a pinion gear (not shown) in the steering gear box 64 when the steering wheel 63 (FIG. 1) is rotationally operated. Therefore, the shaft 53 rotates in conjunction with the steering wheel 63.

The rotation angle of the steering wheel 63 is limited to 400 degrees in both left and right directions.
Eccentric shaft 54 having an eccentric portion 54a at the center
Extend in parallel with the shaft 53, and the casing 33
Is rotatably supported at predetermined positions via bearings 66 and 67. At the position near the base end of the eccentric shaft 54,
A gear 69 having a relatively large diameter and arranged concentrically is provided. The gear 69 meshes with the gear 57 of the shaft 53. Therefore, when the shaft 53 rotates, the eccentric shaft 54 also rotates. In addition, when the steering wheel 63 is not operated,
The eccentric portion 54a is located on the shaft 53 side (state shown in FIG. 3), and when the steering wheel 63 is operated up to the maximum angle (that is, 400 degrees), the eccentric portion 54a is located on the valve body 36 side. Eccentricity (state shown in FIG. 5).

The base end of the connecting rod 55 is a bearing 71.
Is rotatably connected to the eccentric portion 54a of the eccentric shaft 54 via. Further, a cylindrical connecting piece 55a extending horizontally in a substantially T shape is integrally formed at the tip of the connecting rod 55. The tip of this connecting rod 55 is
It is inserted in the hole 43c of the connecting portion 43b of the spring seat 43, and the connecting piece 55a is arranged in the elongated hole 43d.

The relief valve 6 controls the hydraulic pressure supplied by the hydraulic pump 3 to the steering angle control valve 5 in accordance with the steering angle of the front wheels 73. That is, when the steering wheel 63 is not operated (that is, the steering wheel angle θ _H is 0 degrees), as shown in FIG.
4, the eccentric portion 54a is located on the shaft 53 side, and accordingly, the connecting rod 55 is connected to the spring seat 43.
The amount of elastic deformation of the pressure adjusting spring 45 is minimized without moving. When this amount of elastic deformation is minimum, the force of the pressure adjusting spring 45 pressing the spool 44 against the valve seat 42 is the weakest, and the relief pressure has a minimum value P1 (for example, 35.0 kg / cm ² ). Therefore, the hydraulic pump 3
The operating hydraulic pressure that reaches the steering angle control valve 5 from (that is, the maximum value of the operating hydraulic pressure of the hydraulic cylinder 4) is set to the value P1.

From this state, the steering wheel 63
Is operated, the pinion gear of the front wheel steering device 31 rotates, so that the shaft 53 of the pressure adjusting mechanism 40 rotates and the eccentric shaft 54 rotates. Therefore, the connecting piece 55a at the tip of the connecting rod 55 moves to the right side in FIG. However, since the connecting piece 55a first moves inside the elongated hole 43d, in this state, the movement of the connecting piece 55a does not affect the spring seat 43, and the spring seat 43 is pressed by the pressure adjusting spring 45. First space 35
It is located at the left end in the figure. Therefore, the relief pressure of the relief valve 6 is maintained at the value P1 for a while after the front wheel 73 is steered from the state where the steering operation is not performed, and the operating hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 is maintained. Is set to the value P1.

Further, when the steering wheel 63 is operated and the steering wheel angle θ _H reaches 230 degrees, for example,
The eccentric shaft 54 of the pressure adjusting mechanism 40 rotates to the position shown in FIG. 4, and the connecting piece 55a contacts the wall on one side defining the elongated hole 43d. Then, when the steering wheel 63 is further operated from this state, the connecting piece 55a of the connecting rod 55 moves the spring seat 43 and presses the pressure adjusting spring 45. Therefore, the pressure adjusting spring 45
The amount of elastic deformation increases and the relief pressure increases. As a result, the hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 starts to increase from the value P1.

When the steering wheel angle θ _H reaches its maximum value of 400 degrees, the eccentric portion 54a of the eccentric shaft 54 is located on the valve body 36 side and the spring seat 43 moves, as shown in FIG. Maximum distance. Therefore,
The elastic deformation amount of the pressure adjusting spring 45 becomes maximum, and the relief pressure reaches the value P2 (for example, 90.0 kg / cm ² ). As a result, the hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 is set to the maximum value P2.

On the other hand, when the steering wheel 63 is returned from this state, the eccentric shaft 54 starts to rotate in the direction opposite to the above case. Therefore, the connecting piece 55a of the connecting rod 55 moves to the left side in the figure, and accordingly, the spring seat 43 is pressed by the pressure adjusting spring 45 and moves toward the left end. As a result, the elastic deformation amount of the pressure adjusting spring 45 is reduced, and the relief pressure is also reduced. That is, the hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 decreases.

When the steering wheel 63 is returned and the steering wheel angle θ _H reaches 230 degrees, and the eccentric shaft 54 of the pressure adjusting mechanism 40 is returned to the position shown in FIG. 4, the spring seat 43 is moved to the first space. Reach the left end of 35. Therefore, the elastic deformation amount of the pressure adjusting spring 45 is minimized, the relief pressure is reduced to the minimum value P1, and the operating hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 is set to the minimum value P1.

When the steering wheel 63 is further returned from this state, the eccentric shaft 54 rotates and the connecting piece 55a of the connecting rod 55 moves further to the left. Since the spring seat 43 has already reached the left end, the connecting piece 55a moves within the elongated hole 43d. In this case, the movement of the connecting piece 55a does not affect the elastic deformation amount of the pressure adjusting spring 45, that is, the relief pressure. Therefore, the relief pressure is maintained at the value P1.

As described above, the magnitude of the hydraulic pressure supplied to the steering angle control valve 5 is adjusted by the relief valve 6 according to the steering wheel angle θ _H , that is, the steering angle of the front wheels 73. The controller 2 controls the steering angle control valve 5 as described below.
This operating oil pressure is further adjusted via to control the steering angle of the rear wheel 25. The controller 2 has a microcomputer and incorporates a storage device such as a ROM and a RAM (not shown), a central processing unit, an input / output device, a counter, and the like. On the input side of the controller 2, various sensors such as a steering wheel angle sensor 27, a vehicle speed sensor 28,
A pair of pressure sensors 29A and 29B, a road surface gradient sensor 3
0, the steering angle sensor 32, etc. are electrically connected.

The steering wheel angle sensor 27 detects the steering wheel angle θ _H based on the rotation angle of the steering shaft.
The vehicle speed sensor 28 detects the vehicle speed V based on the rotation speed of the rotating shaft of the transmission (not shown). The pair of pressure sensors 29A and 29B detect pressures P _L and P _R in the left and right pressure chambers (not shown) of the hydraulic cylinder of the front power steering mechanism, respectively. Further, the road surface gradient sensor 30 determines the road surface gradient R based on the inclination angle of the vehicle body.
detect _k . The steering angle sensor 32 recognizes the position of the operating rod 4c of the hydraulic cylinder 4 and detects the steering angle of the rear wheel 25 based on this.

The road gradient sensor 30 is not always necessary and may be omitted. In this case, the engine driving force is calculated from the engine speed and the intake air amount,
Acceleration resistance, cornering resistance, aerodynamic resistance, and rolling resistance are obtained from acceleration, lateral acceleration, vehicle speed, etc. Further, gradient resistance is obtained by subtracting each of these resistances from the engine driving force, and the road surface gradient R is obtained from this gradient resistance. Estimate _k .

The controller 2 continues to monitor the signals from the sensors 27 to 29 and the like according to the program stored in the storage device, and based on these signals, the steering angle of the rear wheel 25 suitable for the running condition of the vehicle. To calculate.

FIGS. 7 to 12 show a control procedure in which the controller 2 steers the rear wheels 25 in reverse phase for a moment during high speed traveling and then in-phase steering during low speed traveling, and for large steering angle reverse phase steering during low speed traveling. . When the ignition switch (not shown) is turned on, the controller 2 repeats this control procedure. Then, when the ignition switch is turned off, the controller 2 suspends the execution of this control procedure.

At step S101 in FIG.
The roller 2 first detects the handle angle from each sensor 27-30.
θ_H, Vehicle speed V, pressure P_L, P_R, Road slope R_kRead
After that, the process proceeds to step S102 and the steering wheel angular velocity (θ
_H) ′ And the differential pressure ΔP. Steering wheel angular velocity (θ_H) 'Is
Previously detected steering wheel angle θ_HAnd the steering wheel angle detected this time
θ_HIt can be calculated from the deviation from. In addition, the differential pressure Δ
P is each pressure P_L, P _RCan be calculated from the deviation of
It The symbol (θ_H) 'Is the steering wheel angle θ_HTime derivative of
Represents a value.

The controller 2 then proceeds to step S1.
04, the friction coefficient μ between the road surface and the wheels (hereinafter, road surface μ
Calculated). Various methods can be considered for detecting the road surface μ, but in the present embodiment, the road surface μ is calculated from the steering wheel angle θ _H , the vehicle speed V, and the differential pressure ΔP.
This will be specifically described. When the front wheels 73 are steered, the front wheels 7
Side slip angle β and cornering force F
And the road surface μ can be expressed by the following equation.

F∝β · μ Here, since the cornering force F and the differential pressure ΔP of the front power steering are in a substantially proportional relationship, the differential pressure ΔP is used instead of the cornering force F to obtain the above equation. Rewriting, the following equation is obtained. ΔP = C1 · β · μ (C1 is a constant) On the other hand, the sideslip angle β is represented by the following equation using the vehicle speed V, the steering wheel angle θ _H, and the road surface μ.

Β = C3 · V ² · θ _H / (μ + C2 · V ² ) (C2 and C3 are constants) From the above two expressions, the ratio between the differential pressure ΔP and the steering wheel angle θ _H , that is, ΔP / θ _H Can be expressed by the following equation. ΔP / θ _H = μ · C1 · C3 · V ² / (μ + C2 · V ² ) Therefore, the controller 2 calculates the road surface μ by substituting the vehicle speed V, the steering wheel angle θ _H and the differential pressure ΔP into this equation. can do.

Next, in step S106 of FIG. 7, the controller 2 obtains the in-phase steering angle coefficient K1 from the relationship with the vehicle speed V. As shown by the solid line in FIG. 13, the in-phase steering angle coefficient K1 sharply increases to some extent as the vehicle speed V increases when the vehicle speed V becomes equal to or higher than the speed V ₁ (for example, 60 km / h). It is set to converge to the maximum value.

The controller 2 then proceeds to step S10.
8, the anti-phase steering angle coefficient K2 is momentarily changed from the relationship with the vehicle speed V.
Ask for. As shown by the solid line in FIG. 14, when the vehicle speed V becomes equal to or higher than the speed V ₂ (for example, 35 km / h), the instantaneous anti-phase coefficient K2 increases sharply as the vehicle speed V increases, and then reaches a predetermined value until the predetermined vehicle speed. The value (for example, the value −1.0 × 10 ⁻² ) is maintained, and thereafter, the value gradually decreases as the vehicle speed V increases, and the value is reached when the speed V ₃ (for example, 125 km / h) is reached. It is set to 0, and is further set so as to converge to a positive predetermined value as the vehicle speed V increases.

Next, the controller 2 proceeds to step S112 of FIG. 8 to obtain the road surface gradient correction coefficient K1 'on the in-phase side. The road surface slope correction coefficient K1 ′ is obtained by associating the in-phase steering angle coefficient K1 described above with the road surface slope R _k . For example, if a vehicle is climbing a 10% slope,
As shown by the broken line in FIG. 13, the road surface gradient correction coefficient K1 ′ rapidly increases to some extent as the vehicle speed V increases after the vehicle speed V reaches the speed V ₄ (for example, 70 km / h). Later, it is set to converge to its maximum value. Further, when the vehicle is descending a slope having an inclination of 10%, as shown by a chain double-dashed line in the figure, as shown by a chain double-dashed line in the figure,
When the vehicle speed V reaches the speed V ₅ (for example, 50 km / h), the vehicle speed V starts to increase, and thereafter, it is set to converge to the maximum value.

The controller 2 then proceeds to step S1.
In step 14, the road surface gradient correction coefficient K2 'on the opposite phase side is obtained for a moment. The road surface gradient correction coefficient K2 'is obtained by associating the antiphase steering angle coefficient K2 moment mentioned above the road surface slope R _k. For example, the slope of 10% of the slope when climbing vehicle, the road surface gradient correction coefficient K2 ', as indicated by a broken line in FIG. 14, the vehicle speed V is the speed V ₂ or more, the increase in the vehicle speed V A sudden increase to a predetermined value (for example, a value of −2.0 × 10 ⁻² ) is performed, and then this value is maintained until a predetermined vehicle speed, and thereafter, the value is decreased as the vehicle speed V increases. It is set. Further, when the vehicle speed V becomes equal to or higher than the speed V _{2 as} shown by the chain double-dashed line in the figure when the vehicle is descending the slope of 10%, a predetermined value (for example, a value After being increased to −0.7 × 10 ⁻² ), this value is maintained until a predetermined vehicle speed, and thereafter, it is set to decrease as the vehicle speed V increases.

The controller 2 then proceeds to step S116.
Then, it is determined whether the steering wheel angle θ _H is larger than 230 degrees. When the steering wheel angle θ _H , that is, the steering angle of the front wheels 73 is small, it is desirable to limit the steering angle of the rear wheels 25 to a small value. On the other hand, when the front wheels 73 are steered largely, it is desirable to steer the rear wheels 25 to the opposite phase side by a large steering angle. Therefore, the subsequent processing is selected based on the magnitude of the steering wheel angle θ _H.

That is, when the steering wheel angle θ _H is 230 degrees or less, the determination result of step S116 becomes negative,
The controller 2 proceeds to step S118 to set the large steering angle value Br to the value 0, and proceeds to step S119 to set the control variable K _DR to the value 1.0. Here, the large steering angle value Br is the rear wheel steering angle δr in step S126 described later.
When calculating, the steering of the rear wheels 25 is influenced so as to be the large-steering angle antiphase steering. The large steering angle value Br is set to 0 or a negative value. Therefore, as the absolute value of the large steering angle value Br increases, the value of the rear wheel steering angle δr increases in the negative direction.

After that, the controller 2 proceeds to step S120 of FIG. 9 and corrects the in-phase steering angle coefficient K1 and the momentary anti-phase steering angle coefficient K2 in accordance with the road surface μ. Generally, it is desirable to reduce the steering angle of the rear wheels 25 when the road surface is slippery. Therefore, the in-phase steering angle coefficient K1
The momentary antiphase steering angle coefficient K2 is multiplied by the value of the road surface μ, and the road surface μ is reflected in the values of the coefficients K1 and K2.

Next, the controller 2 carries out step S122.
Then, the in-phase side steering angle value δa is calculated. This in-phase side
The rudder angle value δa is used when the rear wheel steering angle δr is calculated.
This affects the steering of the small steering angle in-phase steering.
As the in-phase side steering angle value δa increases, the rear wheel steering angle
δr increases in the positive direction. This in-phase side steering angle value δa
Is the addition of the in-phase steering angle coefficient K1 and the road surface slope correction coefficient K1 '
As a result, the steering wheel angle θ_HIt is calculated by multiplying by. Therefore,
The in-phase side steering angle value δa is the vehicle speed V, the road surface μ and the steering wheel angle.
θ_HThe road surface slope R _kClimbing
Increases with increasing direction.

Next, the controller 2 carries out step S124.
Then, the steering angle value δb for the opposite phase is calculated for a moment. This momentary opposite-phase side steering angle value δb is calculated as follows when calculating the rear wheel steering angle δr.
This affects the steering of the rear wheels 25 to be the small-steering angle antiphase steering. As the value of the steering angle value δb on the opposite phase side increases for a moment, the rear wheel steering angle δr increases in the negative direction. This momentary antiphase steering angle value δb is obtained by adding the momentary antiphase steering angle coefficient K2 and the road surface slope correction coefficient K2 ′ to the steering wheel angular velocity (θ _H ) ′.
It is calculated by multiplying by. Therefore, for the moment, the steering angle value δb on the opposite phase side
Increases as the road surface μ and the steering wheel angular velocity (θ _H ) ′ increase, and decreases as the road surface gradient R _k increases in the ascending direction.

After this, the controller 2 proceeds to step S1.
In step 26, the rear wheel steering angle δr is calculated. Rear wheel steering angle δ
r is obtained by dividing the predetermined value ρ from the addition result of the large steering angle value Br, the in-phase side steering angle value δa, and the momentary opposite-phase side steering angle value δb. Here, the predetermined value ρ is a steering gear ratio of the front wheel steering device 31, and is stored in the storage device of the controller 2 in advance.

The controller 2 then proceeds to step S1.
In step 28, the steering angle control valve 5 is operated to steer the rear wheels 25. The controller 2 operates the steering angle control valve 5 according to the value of the rear wheel steering angle δr. That is, when the rear wheel steering angle δr is a positive value, the rear wheels 25 are steered to the same phase side, and when the rear wheel steering angle δr is a negative value, the rear wheels 25 are steered to the opposite phase side. Further, the steering angle of the rear wheels 25 is increased or decreased in proportion to the magnitude of the absolute value of the rear wheel steering angle δr.

Now, the large steering angle value Br is determined by step S118.
The steering wheel angle θ _H and the steering wheel angular velocity (θ _H ) ′ are small, and the in-phase side steering angle value δa and the instantaneous anti-phase side steering angle value δb are small absolute values. Therefore, the absolute value of the rear wheel steering angle δr is small, and therefore the rear wheels 25 are not steered at a large steering angle.

In this case, as described above, when the steering wheel angle θ _H is 230 degrees or less, the working oil pressure reaching the steering angle control valve 5 from the hydraulic pump 3 is the value P1 by the action of the relief valve 6. Is set to. Therefore, the maximum steering angle of the rear wheels 25 is limited to 0.8 degrees on both the in-phase side and the anti-phase side (FIG. 6). Further, in step S128, the controller 2 performs feedback control of the steering angle control valve 5 based on the signal from the steering angle sensor 32, and steers the rear wheels 25.

Then, the controller 2 returns to step S101 in FIG. 7 and repeatedly executes this routine.
On the other hand, in step S116, the steering wheel angle θ _H is 2
If it exceeds 30 degrees, the result of this determination is affirmative,
The controller 2 proceeds to step S132 in FIG.

In step S132, the road surface μ has a value of 0.4.
Is greater than or equal to. This road surface μ is 0.4
If it is larger than this, it is considered that the vehicle is traveling on a relatively slippery road surface, and the large steering angle antiphase steering of the rear wheels 25 is allowed up to a relatively high speed. On the other hand, the road surface μ is 0.
When it is 4 or less, it is considered that the vehicle is traveling on a relatively slippery road surface, and the large steering angle antiphase steering of the rear wheels 25 is limited from a relatively low speed.

Therefore, if the determination result of step S132 is affirmative, the controller 2 proceeds to step S133 to set the upper limit speed V _U to 35 km / h and the lower limit speed V _L to 30 km / h. In addition, step S13
When the determination result of 2 is negative, the controller 2 proceeds to step S134 and sets the upper limit speed V _U to 25 km / h.
The lower limit speed V _L is set to a speed of 20 km / h.

After that, the controller 2 proceeds to step S1.
In step 35, it is determined whether the vehicle speed V is higher than the upper limit speed V _U. When the vehicle speed V is equal to or lower than the upper limit speed V _U , the control variable K _DR is set to the value 1.0 and the large steering angle value Br is set.
On the other hand, when the vehicle speed V exceeds the upper limit speed V _U , the control variable K _DR is set to a small value to decrease the absolute value of the large steering angle value Br.

That is, when the determination result of step S135 is negative, the controller 2 proceeds to step S136 and determines whether or not the control variable K _DR is set to the value 1.0. Then, when the control variable K _DR is already set to the value 1.0, the process proceeds to step S144 of FIG. 11 without executing steps S138 and S140. When the control variable K _DR is set to a value other than 1.0 in step S136, the process proceeds to step S138, and it is determined whether the vehicle speed V is equal to or higher than the lower limit speed _VL . The control variable K _DR is set in step S152 described later.
Is set to a value other than 1.0.

If the determination result in step S138 is negative, the controller 2 proceeds to step S140 and sets the control variable K _DR to the value 1.0, and then proceeds to step S144.
Proceed to. If the determination result is affirmative, the process proceeds to step S144 while holding the value of the control variable K _DR without executing step S140. In this case, the control variable K _DR has a value of 0 or more and 1 or less.

The controller 2 executes the above-mentioned step S1.
By executing S140 from S36, when the vehicle speed V exceeds the upper limit speed V _U , when the vehicle speed V starts to decrease and reaches the lower limit speed V _L , the control variable K
_DR is increased to a value of 1.0. On the other hand, step S
At 135, the vehicle speed V exceeds the upper limit speed V _U ,
If the determination result is affirmative, the controller 2 proceeds to step S152 in FIG. In step S152, the controller 2 divides the integration result of the time constant B and the calculation cycle INT by the control variable K _DR . After that, the controller 2 proceeds to step S154 and controls the control variable K _DR.
Is less than the value 0. If this determination result is affirmative, step S156 is executed to set the control variable K _DR to the value 0, and then the process proceeds to step S144. If the determination result is negative, step S156 is executed. No, the process proceeds to step S144.

[0062] That is, the controller 2, by executing the S156 from step S152 described above, when the vehicle speed V has exceeded the upper limit speed V _U, gradually with decreasing the control variable K _DR, the control variable K _DR is After the value becomes 0 or less, the value is held at 0. On the other hand, as described above, the controller 2 executes steps S136 to S140 to increase the value of the control variable K _DR . That is, the speed at which the control variable K _DR is decreased (upper speed V _U ) and the speed at which it is increased (lower speed V _L ) are set to different speeds, so-called hysteresis is generated, and the control variable K _DR is short. It prevents big changes.

The time constant B and the value of the calculation cycle INT are stored in the storage device of the controller 2 in advance.
After setting the control variable K _DR according to the vehicle speed V, the controller 2 proceeds to step S144 to calculate the large steering angle value Br. The large steering angle value Br is obtained by calculating the product of the deviation of the steering wheel angle θ _H from 230 degrees, the large steering angle coefficient K _B, and the control variable K _DR, and further multiplying this product by the value −1. Here, the value -1 is multiplied because the large steering angle value Br is a variable indicating the steering angle on the opposite phase side, and therefore the large steering angle value Br becomes a negative value.

The large steering angle coefficient K _B is a predetermined value stored in the storage device of the controller 2 in advance. After that, the controller 2 proceeds to step S120 of FIG. 9 to correct each coefficient K1 and K2, and then executes steps S122 and S124 to obtain the in-phase side steering angle value δa and the instantaneous opposite-phase side steering angle value δb. calculate. Then, step S126
The rear wheel steering angle δr is calculated at
According to the above, the steering angle control valve 5 is operated to steer the rear wheels 25 (step S128).

FIG. 15 shows the steering characteristics of the rear wheels 25. When the controller 2 repeatedly executes this control routine and, for example, the vehicle changes lanes while traveling at high speed, the value of the rear wheel steering angle δr increases to the minus side and then immediately increases to the plus side. . Therefore, as indicated by the solid line in the figure, the rear wheels 25 are steered by the small steering angle opposite phase for a moment and then are steered by the small steering angle in-phase.

Further, when the vehicle turns while traveling at a low speed, the value of the rear wheel steering angle δr greatly increases to the minus side. Therefore, as indicated by the chain double-dashed line in the figure, the rear wheels 25 are steered by the large steering angle opposite phase. Further, the vehicle speed V is the upper limit speed V _U
When it exceeds, as described above, the control variable K _DR that influences the large steering angle value Br gradually decreases, and the rear wheel steering angle δr does not suddenly change. Therefore, when the rear wheel 25 is being steered by the large steering angle reverse phase, the rear wheel 25 is gradually returned to the straight traveling state.

The vehicle turns and the steering wheel angle θ _H is 2
When it exceeds 30 degrees, as described above, the relief pressure of the relief valve 6 increases in accordance with the increase of the steering wheel angle θ _H , and the working hydraulic pressure that reaches the steering angle control valve 5 from the hydraulic pump 3 changes. Therefore, the rear wheel 25 can be steered within the range shown in FIG. 6, and within this range, the rear wheel 25 is steered according to the calculated rear wheel steering angle δr.

In the control method of this embodiment, the controller 2 sets the value of the control variable K _DR to each step S13.
6 to 140 and S152 to 156 are executed, the method for determining the control variable K _DR is not limited to this. For example, the control variable K _DR is directly determined from the relationship with the vehicle speed V. Is also good. This method will be described in detail with reference to FIG. FIG. 16 conceptually shows the relationship between the vehicle speed V and the control variable K _DR . When the vehicle speed V is increasing, this vehicle speed V is the upper limit speed V _U (that is, 35 km / when the road surface μ> 0.4).
When h and the road surface μ ≦ 0.4, 25 km / h), the control variable K _DR is changed from the value 1.0 to the value 0. Further, when the vehicle speed V decreases, when the vehicle speed V reaches the lower limit speed _VL (that is, 30 km / h when the road surface μ> 0.4, 20 km / h when the road surface μ ≦ 0.4), The control variable K _DR is changed from the value 0 to the value 1.0.

In addition, in the control method of this embodiment,
Execute step S132 and the road surface μ is larger than 0.4
Whether or not the upper limit speed is determined according to the result of this determination
Degree V _UAnd lower limit speed V_LBy changing the set value of
Speed V_U, V_LFrom the relationship between the vehicle speed and the vehicle speed V_DRDecided
Control variable K_DRAs a way to determine
It is not limited to this. For example, continuous depending on the road surface μ
The speed limit Vc that changes to
Control variable K from the relationship with vehicle speed_DRAs a way to determine
good.

This method will be described with reference to FIG.
If the determination result of step S116 of FIG. 8 is affirmative, the controller 2 proceeds to step S172 of FIG. 17, and obtains the speed limit Vc from the relationship with the road surface μ. FIG.
Indicates the relationship between the road surface μ and the speed limit Vc. The speed limit Vc is 2 when the road surface μ is smaller than 0.2.
It is set to 5km / h. Then, the limit vehicle speed Vc also increases in accordance with the increase of the road surface μ, and when the road surface μ reaches the value 0.6, the speed limit Vc is set to the maximum value of 35 km / h. After this, regardless of the increase in the road surface μ, the speed limit Vc
Is maintained at 35 km / h.

After obtaining the speed limit Vc, the controller 2
Advances to step S174, and it is determined whether the vehicle speed V is higher than the speed limit Vc. If the determination result is affirmative, the process proceeds to step S152 in FIG. 12, and the control variable K _DR is set in the same manner as the above case. On the other hand, if the determination result is negative, the controller 2 proceeds to step S1.
Proceeding to 76, it is determined whether the control variable K _DR is set to the value 1.0.

If the result of this determination is affirmative,
The controller 2 does not execute steps S178 and S180, and therefore the control variable K _DR remains the value 1.0 and proceeds to step S144 in FIG. On the other hand, step S
If the determination result of 176 is negative, step S178.
Then, it is determined whether the vehicle speed V is higher than the speed (Vc-5). And, when this determination result is negative,
After executing step S180 to set the control variable K _DR to a value of 1.0, the process proceeds to step S144, and when the determination result is affirmative, the step S180 is not executed and therefore the value of the control variable K _DR is set. Step S without change
Proceed to 144.

In this method, the control variable K _DR can be finely set according to the road surface μ.

[0074]

As described above, according to the vehicle rear wheel steering control method of the present invention, the working fluid pressure reaching the control valve from the fluid pressure source is increased in accordance with the increase in the front wheel steering angle. When the front wheel steering angle is small, the maximum steering angle of the rear wheels is limited to a small value, while when the front wheel steering angle is large, it is possible to steer the rear wheel at a large steering angle. If it exceeds, the large steering angle reverse phase steering of the rear wheels is prohibited and this set speed is changed according to the friction coefficient between the wheels and the road surface. The steering angle can be steered, and the operability of the vehicle is improved. Further, the maximum steering angle of the rear wheels is determined according to the steering angle of the front wheels, and the large steering angle steering to the opposite phase is prohibited according to the traveling situation, so that the safety can be improved. Further, there is an excellent effect that productivity can be improved by simplifying the rear wheel steering device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a vehicle rear wheel steering system in which a method according to the present invention is implemented.

2 is a cross-sectional view of the relief valve of FIG.

3 is a cross-sectional view of the pressure adjusting mechanism of FIG.

Figure 4 shows the operation of the pressure regulating mechanism of FIG. 3, the steering wheel angle theta _H
It is sectional drawing in the state which reached | attained 230 degrees.

Figure 5 illustrates the operation of the pressure regulating mechanism of FIG. 3, the steering wheel angle theta _H
FIG. 4 is a cross-sectional view in a state where the angle reaches 400 degrees.

FIG. 6 is a steering characteristic diagram of the rear wheel steering system of FIG.

7 is a flowchart showing a part of a rear wheel steering control routine executed by the controller of FIG.

8 is a flowchart showing a part of a rear wheel steering control routine executed by the controller of FIG. 1 and continuing from FIG.

9 is a flowchart showing a part of a rear wheel steering control routine executed by the controller of FIG. 1 and continuing from FIG.

10 is a flowchart showing a part of a rear wheel steering control routine executed by the controller of FIG. 1 and continuing from FIG.

11 is a flowchart showing a part of a rear wheel steering control routine executed by the controller of FIG. 1 and continuing from FIG.

12 is a flowchart showing a part of a rear wheel steering control routine executed by the controller of FIG. 1, and is a flowchart continued from FIG.

FIG. 13 is a conceptual diagram showing a relationship between a vehicle speed V and an in-phase steering angle coefficient K1 and a road surface gradient correction coefficient K1 ′.

FIG. 14 is a conceptual diagram showing a relationship between a vehicle speed V and an instantaneous antiphase steering angle coefficient K2 and a road surface slope correction coefficient K2 ′.

FIG. 15 is a diagram showing a change over time of a rear wheel steering angle.

FIG. 16 is a diagram showing a relationship between a vehicle speed V and a control variable K _DR .

FIG. 17 is a flowchart showing another method of FIG. 10.

FIG. 18 is a diagram showing a relationship between a road surface μ and a speed limit Vc.

FIG. 19 is a steering characteristic diagram of a conventional rear wheel steering control method.

[Explanation of symbols]

 1 Rear Wheel Steering Device 2 Controller 3 Hydraulic Pump 4 Hydraulic Cylinder 5 Steering Angle Control Valve 6 Relief Valve 25 Rear Wheel 31 Front Wheel Steering Device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B62D 133: 00

Claims (1)

[Claims] 1. A working fluid pressure is supplied from a fluid pressure source to a fluid pressure actuator via a control valve, and the rear wheels are steered to the in-phase side and the anti-phase side by an angle corresponding to the magnitude of this working fluid pressure. In the rear wheel steering control method of a vehicle, the working fluid pressure reaching the control valve from the fluid pressure source is increased according to the increase of the front wheel steering angle, and when the front wheel steering angle is small, the maximum steering angle of the rear wheel is reduced. On the other hand, if the front wheel steering angle is large, the rear wheel can be steered at a large steering angle.
When the traveling speed of the vehicle exceeds a predetermined set speed, the large steering angle reverse phase steering of the rear wheels is prohibited, and this set speed is
A rear wheel steering control method for a vehicle, characterized by changing the friction coefficient between a wheel and a road surface.