JP2848138B2 - Vehicle rear wheel steering control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As a rear wheel steering device of a four-wheel steering vehicle, a hydraulic pump driven by an engine, a hydraulic cylinder capable of steering rear wheels, and a hydraulic pump and a hydraulic cylinder are interposed between the hydraulic pump and the hydraulic cylinder. Some include a steering angle control valve capable of controlling the direction and amount of hydraulic pressure.

In this rear wheel steering device, when the steering angle of the front wheels is small, the steering angle control valve is electrically controlled by a 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 in the same phase and in the opposite phase (FIG. 19). On the other hand, when the front wheels are largely steered, the steering angle control valve is mechanically controlled by a control wire. Therefore, in this case, the rear wheels are steered according to the front wheel steering angle, and the large steering angle can be steered only in the opposite phase.

[0004]

By the way, when a vehicle which is parked in parallel at the wall is started, the operation of the vehicle is facilitated by largely steering the rear wheels in the same phase, while the rear wheels are easily operated. If the steering wheel is largely steered to the opposite phase, the operation of the vehicle may be rather difficult. However, the conventional rear wheel steering control method described above has a problem in that the rear wheels cannot be steered by a large steering angle in the same phase, and the vehicle operability is poor.

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

Further, since the electric motor operated by the controller and the control cable connecting the front wheel steering device and the rear wheel steering device separately operate the steering angle control valve, the structure of the rear wheel steering device is reduced. There was also a problem that it became complicated and increased the production cost. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and enables large steering angle steering to the same phase side and the opposite phase side, and also sets the large steering angle to the opposite phase side depending on the driving situation. It is another object of the present invention to provide a method of controlling rear wheel steering of a vehicle, which can inhibit angle steering and reduce the production cost of a rear wheel steering device.

[0007]

According to the present invention, a working fluid pressure is supplied from a fluid pressure source through a control valve to a fluid pressure actuator, and the magnitude of the working fluid pressure is reduced. In a rear wheel steering control method for a vehicle in which a rear wheel is steered to a same phase side and a reverse phase side by a corresponding angle, a working fluid pressure reaching a control valve from a fluid pressure source is increased in accordance with an increase in a front wheel steering angle. When the front wheel steering angle is small, the maximum steering angle of the rear wheel is limited to a small value. On the other hand, when the front wheel steering angle is large, the large steering angle of the rear wheel is enabled. When the speed is exceeded, large-angle steering of the rear wheels in reverse phase is prohibited, and the rear wheels are controlled such that the set speed is changed according to the friction coefficient between the wheels and the road surface.

[0008]

According to the 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. In this case, the rear wheels are steered within a large steering angle range. When the traveling speed of the vehicle exceeds the set speed, the rear wheels
Steering is performed within the range of a large steering angle on the same phase side, and within a range of a small steering angle on the opposite phase side. In this case, the 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]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of a rear wheel steering device for a vehicle that implements a rear wheel steering control method according to the present invention. The rear wheel steering device 1 includes 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.

That is, the hydraulic pump 3 sends the oil passages 11, 1
The oil passages 11 and 12 are connected to the steering angle control valve 5 and the relief valve 6, respectively. Oil passages 13, 1 extending from the steering angle control valve 5 and the relief valve 6, respectively.
4 are both 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.
Connected to each other. The oil passages 11 and 13 are connected by an oil passage 21.
An unload valve 22 is provided.

The hydraulic cylinder 4 has an operating rod 4c extending in the vehicle width direction, and the operating rod 4c is attached to each rear wheel 25 via left and right tie rods 24 and a knuckle arm (not shown). Are linked. This operating rod 4
c reciprocates by a distance corresponding to the magnitude of the operating oil 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 oil pressure supplied from the steering angle control valve 5 to the hydraulic cylinder 4. For example, 35.
When the operating oil pressure of 0 kg / cm ² is supplied, the hydraulic cylinder 4 steers the rear wheels by 0.8 degrees,
When the hydraulic pressure of m ² is supplied, the hydraulic cylinder 4 to steer the rear wheels only 5.0 degrees.

The steering angle control valve 5 has, for example, a pair of solenoids, and is operated by a controller 2 described later to switch the connection between the oil paths 11, 13, 18, and 19, and to connect the oil paths 18 , 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 respectively connected. 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 a return spring (not shown). Is restored.

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 communicate with each other, the operating hydraulic pressure supplied from the hydraulic pump 3 is applied. 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 and controls the steering angle of the rear wheel 25 by adjusting the magnitude of the operating oil pressure guided into the first hydraulic chamber 4a. 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 To the second hydraulic chamber 4b of the hydraulic cylinder 4 and the hydraulic oil in the first hydraulic chamber 4a
Can be led to. Therefore, in this case, the operating rod 4c of the hydraulic cylinder 4 moves backward, and each rear wheel 25 is steered to the left. At this time, the steering angle control valve 5 can reduce the amount of oil flowing into the oil passage 19, and controls the steering angle of the rear wheel 25 by adjusting the magnitude of the operating oil pressure guided into the second hydraulic chamber 4b. be able to.

The unload valve 22 is, for example, a normally-open solenoid valve which is opened and 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 the rear wheel steering device 1 detects any abnormality. The hydraulic pump 3 is driven by an engine.

The relief valve 6 is attached to a steering gear box 64 of the front wheel steering device 31, and is shown in FIG.
As shown in detail in FIG.
And a pressure adjusting mechanism 40 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 opens to an oil passage 47 to be described later, and the oil passage 12 is connected. The outflow port 33b opens to face the first space 35, and the oil passage 14 is connected.

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

The valve seat 42 is provided with a thread 42a. The screw portion 42 a is provided on the outer peripheral surface of the base-side half portion, and meshes with the screw portion 33 d of the casing 33. Therefore, when the valve seat 42 is rotated, the insertion amount 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. The space between the valve seat 42 and the casing 33 is sealed by an O-ring 51.

The valve seat 42 has an inflow port 3
An oil passage 47 that connects the first space 35 to the first space 35 is formed. 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 distal end surface of the valve seat 42
b and a plurality of holes 47c which penetrate the valve seat 42 in the radial direction and open the hole 47b facing the annular groove 47a. Width of annular groove 47a (valve seat 42)
Is set larger than the diameter of the opening of the inflow port 33a. Therefore, the valve seat 4
This annular groove 47a always faces the inflow port 33a even when the amount of insertion of the second groove 2 is changed.

A shaft 44a extending toward the spring seat 43 is formed integrally with a spool 44 which abuts on the valve seat 42 to close 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 can be displaced relative to the spring seat 43 and cannot fall off. Also, the spool 44
Are provided with a plurality of notches 44b at a plurality of locations at predetermined intervals in the circumferential direction, thereby forming a passage through which hydraulic oil flows.

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

The pressure adjusting spring 45 is, for example, a coil spring and presses the spool 44 toward the valve seat 42. 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
Hydraulic oil inside 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 working oil pressure on the oil passages 12 and 11 is determined by the pressure adjusting spring 45.

The pressure adjusting mechanism 40 includes a shaft 53, an eccentric shaft 54, a connecting rod (hereinafter, referred to as a connecting rod) 55, and the like. A relatively small-diameter gear 57 is attached to the shaft 53 so as not to rotate relatively. The shaft 53 is connected to the casing 33.
Are rotatably supported at predetermined positions via bearings 58 and 59. At the base end of the shaft 53, a convex portion 53a extending in the radial direction is integrally formed.
Are inserted into the groove 61a of the rotating shaft 61, thereby integrally rotating. The rotation 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 rotated. 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 the left and right directions.
Eccentric shaft 54 having an eccentric portion 54a at the center
Extends in parallel with the shaft 53, and the casing 33
Are rotatably supported at predetermined positions via bearings 66 and 67. At a position near the base end of the eccentric shaft 54,
A relatively large-diameter gear 69 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 the state where the steering wheel 63 is not operated,
The eccentric portion 54a is located on the shaft 53 side (the state shown in FIG. 3), and when the steering wheel 63 is operated to the maximum angle (ie, 400 degrees), the eccentric portion 54a is located on the valve body 36 side. It is eccentric (the state shown in FIG. 5).

The connecting rod 55 has a bearing 71
Is connected to the eccentric portion 54a of the eccentric shaft 54 via the. 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
The connecting piece 55a is inserted into the hole 43c of the connecting portion 43b of the spring seat 43, and the connecting piece 55a is arranged in the long hole 43d.

The relief valve 6 controls the operating oil pressure supplied by the hydraulic pump 3 to the steering angle control valve 5 according to the steering angle of the front wheel 73. In other words, a state where the steering wheel 63 is not operated (i.e., steering wheel angle theta _H is 0 degrees), as shown in FIG. 3, adjustment eccentric shaft 5 of the pressure mechanism 40
4, the eccentric portion 54a is located on the shaft 53 side, and therefore, the connecting rod 55 is connected to the spring seat 43.
Without moving, the elastic deformation amount of the pressure adjusting spring 45 is minimized. When the amount of elastic deformation is minimum, the force by which the pressure adjusting spring 45 presses the spool 44 against the valve seat 42 is the weakest, and the relief pressure is the minimum value P1 (for example, 35.0 kg / cm ² ). Therefore, the hydraulic pump 3
The operating oil pressure that reaches the steering angle control valve 5 from above (ie, the maximum value of the operating oil pressure of the hydraulic cylinder 4) is set to a 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 is rotated, and the eccentric shaft 54 is rotated. Accordingly, the connecting piece 55a at the tip of the connecting rod 55 moves to the right in FIG. However, since the connecting piece 55a first moves in 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 regulating spring 45. First space 35
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 starts being 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 provided. Is set to the value P1.

Further, when the steering wheel 63 is operated and the steering wheel angle θ _H reaches, for example, 230 degrees,
The eccentric shaft 54 of the pressure adjusting mechanism 40 rotates to the position shown in FIG. 4, and the connecting piece 55a contacts one wall 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 and contracts the pressure adjusting spring 45. Therefore, the pressure regulating spring 45
Increases the amount of elastic deformation and the relief pressure. Accordingly, the operating oil 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 54 a of the eccentric shaft 54 is located on the valve body 36 side as shown in FIG. The distance becomes the maximum. Therefore,
The amount of elastic deformation of the pressure adjusting spring 45 becomes maximum, and the relief pressure reaches a value P2 (for example, 90.0 kg / cm ² ). Thus, the operating oil 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 opposite direction to the above case. Accordingly, the connecting piece 55a of the connecting rod 55 moves to the left in the drawing, and accordingly, the spring seat 43 is pressed by the pressure adjusting spring 45 and moves toward the left end. As a result, the amount of elastic deformation of the pressure adjusting spring 45 decreases, and the relief pressure also decreases. That is, the operating oil 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. Accordingly, the amount of elastic deformation of the pressure adjusting spring 45 becomes minimum, the relief pressure decreases to the minimum value P1, and the operating oil 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 further moves to the left. Since the spring seat 43 has already reached the left end, the connecting piece 55a moves in the long hole 43d. In this case, the movement of the connecting piece 55a does not affect the amount of elastic deformation 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 operating oil 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 wheel 73. The controller 2 includes a steering angle control valve 5 as described below.
The operating oil pressure is further adjusted through the control of the steering wheel 25 to control the steering angle of the rear wheel 25. The controller 2 includes a microcomputer, and includes 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. 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 and the like 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 a vehicle speed V based on the rotation speed of a rotation shaft of a transmission (not shown). The pair of pressure sensors 29A and 29B detect the 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 detects the road surface gradient R based on the vehicle body inclination angle.
_{Find 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 surface gradient sensor 30 is not always necessary and may be omitted. In this case, the engine driving force is determined 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, and the like. Further, a slope resistance is obtained by subtracting each of these resistances from the engine driving force. _{It is sufficient} to estimate _k .

The controller 2 continuously monitors signals from the sensors 27 to 29 and the like according to a program stored in the storage device, and, based on these signals, a steering angle of the rear wheel 25 suitable for a running state of the vehicle. Is calculated.

FIGS. 7 to 12 show a control procedure in which the controller 2 controls the rear wheels 25 to reversely phase-shift the rear wheels 25 for a moment during high-speed traveling and then performs the same-phase steering during low-speed traveling. . When an ignition switch (not shown) is turned on, the controller 2 repeatedly executes this control procedure. When the ignition switch is turned off, the controller 2 stops executing this control procedure.

In step S101 of FIG.
The roller 2 is first provided with a steering wheel angle from each of the sensors 27 to 30.
θ_H, Vehicle speed V, pressure P_L, P_R, Road surface gradient R_kRead
After that, the process proceeds to step S102, in which the steering angular velocity (θ
_H) ′ And the differential pressure ΔP. Handle angular velocity (θ_H) '
Handle angle θ detected last time_HAnd the handle angle detected this time
θ_HCan be calculated from the deviation from The differential pressure Δ
P is each pressure P_L, P _RCan be calculated from the deviation of
You. Note that the symbol (θ_H) 'Is the handle angle θ_HTime derivative of
Represents a value.

Then, the controller 2 proceeds to step S1
04, the coefficient of friction μ between the road surface and the wheels (hereinafter referred to as the road surface μ
Is calculated). Various methods can be considered for detecting the road surface μ. In this 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
3 and the cornering force F generated at 3
And the road surface μ can be expressed by the following equation.

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

Β = C 3 · V ² · θ _H / (μ + C 2 · V ² ) (C 2 and C 3 are constants) From the above two equations, 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, when the vehicle speed V becomes equal to or higher than the speed V ₁ (for example, 60 km / h), the in-phase steering angle coefficient K1 increases to some extent with the increase in the vehicle speed V, and thereafter, It is set to converge to the maximum value.

Then, the controller 2 proceeds to step S10
8 and the instantaneous anti-phase steering angle coefficient K2
Ask for. As shown by a 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 antiphase coefficient K2 increases rapidly with the increase in the vehicle speed V, and then reaches a predetermined value until the predetermined vehicle speed is reached. (E.g., the value -1.0 * 10 ^<-2 >), and thereafter, gradually decreases as the vehicle speed V increases, and reaches a value at the time when the speed V ₃ (e.g., 125 km / h) is reached. 0 and further converges to a positive predetermined value in accordance with the increase in the vehicle speed V.

Next, the controller 2 proceeds to step S112 in FIG. 8, and obtains a road surface gradient correction coefficient K1 'on the same phase side. The road surface gradient correction coefficient K1 'is obtained by associating the in-phase steering angle coefficient K1 mentioned above the road surface slope R _k. For example, if the vehicle is climbing a 10% slope,
The road surface gradient correction coefficient K1 ', as indicated by a broken line in FIG. 13, the speed V ₄ the vehicle speed V (e.g., 70 km / h) somewhat increases rapidly with the increase of the vehicle speed V from after reaching this Later, it is set to converge to the maximum value. Also, when the vehicle is descending on a 10% slope, as shown by the two-dot chain line in the figure, as shown by the two-dot chain line in the figure,
Velocity V ₅ vehicle speed V (e.g., 50 km / h) starts to increase upon reaching, after this, it is set to converge to the maximum value.

Then, the controller 2 proceeds to step S1
Proceeding to 14, the momentary road surface gradient correction coefficient K2 'on the opposite phase side is obtained. 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 After that, the value rapidly increases to a predetermined value (for example, the value -2.0 × 10 ^-2 ), and then maintains this value until the predetermined vehicle speed, and thereafter, decreases as the vehicle speed V increases. Is set. Further, the slope 10% gradient when the vehicle is off, as shown by two-dot chain line, when the vehicle speed V is the speed V ₂ or more, the predetermined value with an increase in vehicle speed V (for example, a value After increasing 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
To determine whether the steering wheel angle θ _H is greater than 230 degrees. When the steering wheel angle θ _H , that is, the steering angle of the front wheel 73 is small, it is desirable to limit the steering angle of the rear wheel 25 to a small value. On the other hand, when the front wheel 73 is steered largely, it is desirable to steer the rear wheel 25 to the opposite phase by a large steering angle. Therefore, based on the magnitude of the steering wheel angle theta _H, selects the subsequent processing.

That is, when the steering wheel angle θ _H is equal to or smaller than 230 degrees, the determination result of step S116 is negative, and
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 _KDR to the value 1.0. Here, the large steering angle value Br is determined by the rear wheel steering angle δr in step S126 described later.
Is calculated so that the steering of the rear wheels 25 is changed to a 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.

Thereafter, the controller 2 proceeds to step S120 in FIG. 9, and corrects the in-phase steering angle coefficient K1 and the momentary anti-phase steering angle coefficient K2 according to the road surface μ. Generally, when the road surface is slippery, it is desirable to reduce the steering angle of the rear wheel 25. Therefore, the in-phase steering angle coefficient K1
And the momentary antiphase steering angle coefficient K2 is multiplied by the value of the road surface μ to reflect the road surface μ in the values of the coefficients K1 and K2.

Next, the controller 2 proceeds to step S122.
To calculate the in-phase side steering angle value δa. When calculating the rear wheel steering angle δr, the in-phase side steering angle value δa has an effect such that the steering of the rear wheels 25 becomes a small steering angle in-phase steering. As the value of the in-phase side steering angle value δa increases, the rear wheel steering angle δr
Increases in the positive direction. The in-phase side steering angle value δa is the addition result of the same phase steering angle coefficient K1 road surface gradient correction coefficient K1 ', obtained by multiplying the steering wheel angle theta _H. Thus, the same phase side steering angle value δa is increased with an increase in vehicle speed V, the road surface μ and the steering wheel angle theta _H, also decreases in accordance with an increase in the climbing direction of the road gradient R _k.

Next, the controller 2 proceeds to step S124.
And momentarily calculates the anti-phase side steering angle value δb. This momentary anti-phase side steering angle value δb has an effect such that when the rear wheel steering angle δr is calculated, the steering of the rear wheel 25 becomes small steering angle anti-phase steering. With this momentary increase in the value of the anti-phase side steering angle value δb,
The rear wheel steering angle δr increases in the negative direction. The momentary anti-phase side steering angle value δb is obtained by multiplying the result of addition of the momentary anti-phase steering angle coefficient K2 and the road surface gradient correction coefficient K2 ′ by the steering wheel angular velocity (θ _H ) ′. Therefore, the momentary anti-phase side steering angle value δb instantaneously increases as the road surface μ and the steering wheel angular velocity (θ _H ) ′ increase,
Also, Ru <br/> be increased according to the increase in the climbing direction of the road gradient R _k.

Thereafter, the controller 2 proceeds to step S1
Proceeding to 26, the rear wheel steering angle δr is calculated. Rear wheel steering angle δ
r is obtained by dividing a predetermined value ρ from the addition result of the large steering angle value Br, the same-phase side steering angle value δa, and the momentarily 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.

Then, the controller 2 proceeds to step S1
The program proceeds to 28, where the steering angle control valve 5 is operated to steer the rear wheel 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, and when the rear wheel steering angle δr is a negative value, the rear wheels 25 are steered to the opposite phase. Further, the steering angle of the rear wheel 25 is increased or decreased in proportion to the absolute value of the rear wheel steering angle δr.

Now, the large steering angle value Br is calculated in 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 instantaneously 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 wheel 25 is not steered by 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 by the action of the relief valve 6 is equal to the value P1. Is set to Therefore, the maximum steering angle of the rear wheel 25 is limited to 0.8 degrees on the same phase side and the opposite phase side (FIG. 6). In step S128, the controller 2 performs feedback control of the steering angle control valve 5 based on a signal from the steering angle sensor 32, and steers the rear wheel 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 becomes 2
If the angle exceeds 30 degrees, the result of this determination is affirmative,
The controller 2 proceeds to Step S132 of FIG.

In step S132, the road surface μ has a value of 0.4.
It is determined whether it is greater than. This road μ has a value of 0.4
If it is larger, it is considered that the vehicle is traveling on a relatively slippery road surface, and the large steering angle anti-phase steering of the rear wheels 25 is allowed to a relatively high speed. On the other hand, when the road surface μ is 0.
In the case of 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 restricted from a relatively low speed.

[0057] Therefore, if the decision in Step S132 is affirmative, the controller 2 proceeds to step S133, the upper limit speed V _U to the speed 35km / h, respectively set the lower limit speed V _L to a speed 30 km / h. Step S13
If the second determination result is negative, the controller 2 proceeds to step S134, the upper limit speed V _U to the speed 25km / h,
The lower limit speed _VL is set to a speed of 20 km / h.

Thereafter, the controller 2 proceeds to step S1
Proceeds to 35, the vehicle speed V is determined whether greater than the upper limit speed V _U. When the vehicle speed V is less than the upper limit speed V _U is the control variable K _DR to set to a value 1.0 large steering angle value Br
While increasing the absolute value of, in the case where the vehicle speed V exceeds the upper limit speed V _U decreases the absolute value of the large steering angle value Br by setting the control variable K _DR to a small value.

That is, when the result of the determination in step S135 is negative, the controller 2 proceeds to S136 and determines whether or not the control variable _KDR is set to a value of 1.0. If the control variable K _DR has already been set to the value 1.0, the process proceeds to step S144 in FIG. 11 without executing steps S138 and S140. If the control variable _KDR 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 . Note that the control variable K _DR is determined in step S152 described later.
Is set to a value other than the value 1.0.

If the decision result in the step S138 is negative, the controller 2 proceeds to a step S140, sets the control variable _KDR to a value of 1.0, and then proceeds to a step S144.
Proceed to. Further, when the determination result is positive, without executing Step S140, the process proceeds to step S144 while maintaining the value of the control variable K _DR. 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-described step S1
36 from the By executing S140, in a case where the vehicle speed V exceeds the upper limit speed V _U, the vehicle speed V starts decreasing, and, when reaching 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
In 135, the vehicle speed V has exceeded 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 . Thereafter, the controller 2 proceeds to step S154, where the control variable K _DR
Is smaller than the value 0. If the 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. 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 kept 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 _KDR . That is, the speed at which the control variable K _DR is decreased (upper limit speed V _U ) and the speed at which the control variable K _DR is increased (lower limit speed V _L ) are set to different speeds, so-called hysteresis is generated, and the control variable K _DR is set at a short cycle. Prevents significant changes.

The value of the time constant B and the value of the calculation period INT are stored in the storage device of the controller 2 in advance.
After setting the control variable _KDR according to the vehicle speed V, the controller 2 proceeds to step S144 to calculate the large steering angle value Br. Large steering angle value Br has a deviation from 230 degrees of the steering wheel angle theta _H, and large steering angle coefficient K _B, obtains the product of the control variable K _DR, obtained by multiplying the addition value -1 to the product. 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 is a negative value.

[0064] Incidentally, the large steering angle coefficient K _B, is a predetermined value stored in advance in the controller 2 storage. Thereafter, the controller 2 proceeds to step S120 in FIG. 9 and corrects the coefficients K1 and K2. Then, the controller 2 executes steps S122 and S124 to determine the same-phase side steering angle value δa and the momentarily opposite-phase side steering angle value δb. calculate. Then, step S126
Calculates the rear wheel steering angle δr, and calculates the rear wheel steering angle δr
The steering wheel 5 is steered by operating the steering angle control valve 5 in response to (step S128).

FIG. 15 shows the steering characteristics of the rear wheels 25. The controller 2 repeatedly executes this control routine. For example, when the vehicle performs a lane change during high-speed running, the value of the rear wheel steering angle δr increases to a negative side and then immediately increases to a positive side. . Accordingly, as shown by the solid line in the figure, the rear wheel 25 is subjected to the small steering angle reverse phase steering for a moment and then the small steering angle in-phase steering.

When the vehicle turns while traveling at low speed, the value of the rear wheel steering angle δr greatly increases to the minus side. Therefore, as shown by the two-dot chain line in the figure, the rear wheels 25 are steered by a large steering angle in reverse phase. Further, when the vehicle speed V is the upper limit speed V _U
If it exceeds, as described above, the control variable K _DR affecting the large steering angle value Br decreases gradually and the rear wheel steering angle δr is not changed abruptly. Therefore, when the rear wheel 25 is being steered by a large steering angle in reverse phase, the rear wheel 25 is gradually returned to the straight traveling state.

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

In the control method of the present embodiment, the controller 2 determines the value of the control variable _KDR in each step S13.
6-140, was determined by performing the S152～156, not limited to this as a method of determining the control variable K _DR, for example, to determine the direct control variable K _DR from the relationship between 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 _KDR . When the vehicle speed V is increasing, the vehicle speed V becomes equal to the upper limit speed V _U (that is, 35 km / V when the road surface μ> 0.4.
h, 25 km / h when μ ≦ 0.4), the control variable K _DR is changed from 1.0 to 0. When the vehicle speed V decreases, when the vehicle speed V reaches the lower limit speed V _L (that is, 30 km / h when the road surface μ> 0.4, and 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 the control method of the present embodiment,
Execute step S132 to make the road surface μ larger than 0.4
Is determined, and the upper limit speed is determined according to the result of this determination.
Degree V _UAnd lower limit speed V_LChange the setting of
Speed V_U, V_LControl variable K from the relationship between_DRDecide
Control variable K_DRThis is a way to determine
It is not limited to this. For example, continuous according to the road surface μ
Is set, and the speed limit Vc
From the relationship with vehicle speed, control variable K_DRAs a way to determine
good.

This method will be described with reference to FIG.
If the determination result in step S116 in FIG. 8 is affirmative, the controller 2 proceeds to step S172 in 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 the value 0.2.
Set to 5 km / h. Then, the vehicle speed limit Vc 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. Thereafter, regardless of the increase in the road surface μ, the speed limit Vc
Is maintained at 35 km / h.

After determining the speed limit Vc, the controller 2
Proceeds to step S174, and determines whether or not 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 _KDR is set in the same manner as in the above-described case. On the other hand, if the result of this determination is negative, the controller 2 proceeds to step S1.
Proceeding to 76, it is determined whether the control variable _KDR is set to a value of 1.0.

If the result of this determination is affirmative,
The controller 2 does not execute steps S178 and S180, and therefore proceeds to step S144 in FIG. 11 with the control variable K _DR remaining at the value of 1.0. On the other hand, step S
If the decision result in 176 is negative, step S178
To determine whether the vehicle speed V is higher than the speed (Vc-5). When the result of this determination is negative,
After executing step S180 to set the control variable K _DR to the value 1.0, the process proceeds to step S144. When the determination result is affirmative, step S180 is not executed, and therefore, the value of the control variable K _DR is changed. 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 method for controlling the rear wheel steering of a vehicle according to 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 wheel is limited to a small value. On the other hand, when the front wheel steering angle is large, the rear wheel can be steered at a large steering angle. When the vehicle speed exceeds the maximum value, the rear wheel large steering angle anti-phase steering is prohibited, and the set speed is changed in accordance with the friction coefficient between the wheel and the road surface. The steering angle can be steered, and the operability of the vehicle is improved. In addition, the maximum steering angle of the rear wheel is determined according to the steering angle of the front wheel, and the large steering angle steering to the opposite phase is prohibited according to the traveling situation, so that 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 the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a vehicle rear wheel steering device in which a method according to the present invention is performed.

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

FIG. 3 is a sectional view of the pressure adjusting mechanism of FIG. 2;

Figure 4 shows the operation of the pressure regulating mechanism of FIG. 3, the steering wheel angle theta _H
Is a cross-sectional view in a state where has reached 230 degrees.

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

FIG. 6 is a steering characteristic diagram of the rear wheel steering device of FIG. 1;

FIG. 7 is a flowchart showing a part of a rear wheel steering control routine executed by the controller of FIG. 1;

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. 7;

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. 8;

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. 8;

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. 10;

FIG. 12 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;

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 anti-phase steering angle coefficient K2 and a road surface slope correction coefficient K2 ′.

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

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

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

FIG. 18 is a diagram illustrating 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]

 Reference Signs List 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

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification symbol FI B62D 133: 00 (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 6/00 B62D 7/14

Claims (1)

(57) [Claims] An operating fluid pressure is supplied from a fluid pressure source via a control valve to a fluid pressure actuator, and the rear wheels are steered to the same phase and opposite phase by an angle corresponding to the magnitude of the working fluid pressure. In the vehicle rear wheel steering control method, 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, and when the front wheel steering angle is small, the maximum steering angle of the rear wheel is reduced. On the other hand, when 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 wheel steering angle anti-phase steering of the rear wheels is prohibited, and the set speed is
A rear wheel steering control method for a vehicle, wherein the method is changed according to a friction coefficient between a wheel and a road surface.