JPH0585384A - Electrical control unit for rear wheel steering gear - Google Patents

Abstract

PURPOSE:To make the steering performance of a vehicle desirable by providing a correcting means for adding the correction quantity, corresponding to the steered direction of rear wheels and also the dead zone of hydraulic copy mechanism, to the target steering angle to correct a steering control signal. CONSTITUTION:A microcomputer 55 computes the angle of rotation according to a yaw rate based on a detection signal from a yaw rate sensor 53 so as to rotate a step motor 43 into this angle of rotation. This rotation is transmitted to hydraulic copy mechanism, formed of a lever 41, a spool valve 37 and a power cylinder 35, through a pin 42, so that lateral rear wheels RW1, RW2 are steered into the target steering angle corresponding to this angle of rotation. In this case, the correction value, set to be positive or negative in the grade corresponding to a dead zone in the vicinity of the neutral state of the spool valve 37 on the basis of the steering wheel steering angle detected by a steering wheel steering angle sensor 51, is added to the target angle of rotation so as to prevent the influence of the dead zone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system having a hydraulic copying mechanism for maintaining a rear wheel in a neutral position in a neutral state and driving the rear wheel by being driven by an electric actuator. The present invention relates to an electric control device for a rear wheel steering device that electrically controls a rear wheel steering device.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type is disclosed in, for example, Japanese Patent Laid-Open No.
-212667, a target steering angle is determined according to a vehicle running state such as a yaw rate, a steering wheel steering angle, and a vehicle speed, and a steering control signal representing the steering angle is output to the electric actuator. Then, the rear wheels are steered to the target steering angle.

[0003]

However, in the above-mentioned conventional apparatus, the hydraulic copying mechanism has a dead zone portion in the vicinity of the neutral state in order to suppress the impact noise due to the oil hammer and the vibration of the hydraulic fluid. However, even if the steering control signal indicating the target steering angle is given to the electric actuator and the hydraulic copying mechanism is driven by the electric actuator, the rear wheel is not accurately steered to the target steering angle due to the dead zone. Alternatively, there is a problem in that there is a delay in steering the rear wheels near the neutral position. The present invention has been made to solve the above problems, and an object of the present invention is to provide a rear wheel steering device that corrects the dead zone to steer the rear wheels accurately and responsively to a target steering angle. It is to provide an electric control device for.

[0004]

In order to achieve the above object, the structural features of the present invention include an electric actuator driven in response to an input control signal, and a rear wheel in a neutral position in a neutral position. It is also applied to a rear wheel steering device that is equipped with a hydraulic profile mechanism that is driven by an electric actuator to steer the rear wheels, determines a target steering angle, and outputs a steering control signal representing the steering angle to the electric actuator. In an electric control device for a rear wheel steering device including steering control means for steering the rear wheels to the same steering angle, a target steering amount corresponding to a steering direction of the rear wheels and a dead zone of a hydraulic copying mechanism is controlled. The correction means is provided to correct the steering control signal by adding it to the angle.

[0005]

In the present invention configured as described above, the steering control is performed by adding the correction amount corresponding to the steering direction of the rear wheels and the correction amount corresponding to the dead zone of the hydraulic pressure copying mechanism to the target steering angle. Since the signal is corrected, the influence of the dead zone near the neutral state of the hydraulic copying mechanism is canceled by the correction, and the rear wheels are accurately steered to the target steering angle, and the steering of the rear wheels near the neutral position is delayed. Therefore, the maneuverability of the vehicle is improved.

[0006]

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

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

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

On the other hand, a spool valve 37, which constitutes a hydraulic pressure copying mechanism together with the power cylinder 35, is incorporated in the upper portion of the housing 34. This spool valve 3
Reference numeral 7 denotes a valve sleeve 37a housed in the housing 34 so as to be fluid-tight and slidable in the axial direction, and a valve spool 37b fixed to the housing 34. To supply the hydraulic oil from the hydraulic pump 38 driven by the engine 18 to the left oil chamber 35b of the power cylinder 35,
The hydraulic oil in the right oil chamber 35c of the cylinder 35 is stored in the reservoir 2
Discharge to 3. When the valve sleeve 37a is displaced to the right in the figure, the spool valve 37 moves to the hydraulic pump 38.
The hydraulic oil from the is supplied to the right oil chamber 35c of the power cylinder 35, and the hydraulic oil in the left oil chamber 35b of the cylinder 35 is discharged to the reservoir 23. Further, the spool valve 37 functioning in this manner is such that the valve sleeve 37a and the valve spool 37b are underlapped,
It is in a neutral state, and shock noise due to oil hammer and vibration of hydraulic oil are alleviated. That is, the spool valve 37 has a dead zone of a predetermined width in the neutral state.

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

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

The electric control unit C includes a steering wheel steering angle sensor 51, a vehicle speed sensor 52, a yaw rate sensor 53, and a motor rotation angle sensor 54. The steering wheel steering angle sensor 51 detects the steering wheel steering angle θ by measuring the rotation angle of the steering shaft 12 from the reference position, and the steering angle θ is detected.
The detection signal indicating is output. The steering angle θ of the steering wheel is positive in the right rotation direction of the steering wheel 11 (left and right front wheels FW1, FW2) and negative in the left rotation direction. The vehicle speed sensor 52 detects the vehicle speed V by measuring the rotation speed of an output shaft of a transmission (not shown), and outputs a detection signal representing the vehicle speed V. The yaw rate sensor 53 detects a rotational angular velocity around the vertical axis of the vehicle body, that is, a yaw rate ωy, and outputs a detection signal representing the yaw rate ωy. The yaw rate ωy is also positive in the right rotation direction and negative in the left rotation direction. Motor rotation angle sensor 5
Reference numeral 4 detects the rotation angle of the rotation shaft of the step motor 43 from the reference position, and outputs the rotation angle as a detection signal representing the motor rotation angle θr. The motor rotation angle θr is proportional to the steering angles of the left and right rear wheels RW1 and RW2, and the forward rotation direction of the step motor 43 (the left and right rear wheels RW1 and RW2).
Corresponding to the right steering direction) and the negative rotation direction (corresponding to the left steering direction of the left and right rear wheels RW1, RW2) are negative.

Each of these sensors 51 to 54 is connected to a microcomputer 55, and the computer 55
Are the ROM 55b and CP respectively connected to the bus 55a
It consists of U55c, RAM55d and I / O55e (input / output interface). The ROM 55b stores a program corresponding to the flowchart of FIG. 2 and also stores the coefficients K ₁ and K ₂ in the form of a table. Coefficient K ₁
As shown in FIG. 3, with a zero at the low vehicle speed range (predetermined vehicle speed V ₀ or less), in the medium vehicle speed region (exceeds a predetermined vehicle speed V ₀₎ gradually increases, in the high vehicle speed region Is maintained at a large positive predetermined value. Coefficient K ₂
4 is zero in the low vehicle speed range (predetermined vehicle speed V ₀ or lower) and is in the middle and high vehicle speed range (predetermined vehicle speed V ₀ ) as shown in FIG.
₍₀ or more) is maintained at a positive predetermined value. This predetermined value is a control amount corresponding to ½ of the width of the dead zone in the neutral state of the spool valve 37 in the hydraulic copying mechanism. To be precise, the control amount is converted into the rotation amount of the step motor 43. It is the value.

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

Next, the operation of the embodiment configured as described above will be described. When the ignition switch (not shown) is closed, the CPU 55c starts executing the program in step 100 of FIG.
The circulation process consisting of 4 is repeatedly executed. In this circulation processing, in step 101, detection signals representing the steering wheel steering angle θ, the vehicle speed V, the yaw rate ωy, and the motor rotation angle θr are read from the sensors 51 to 54, and in step 102, the ROM 55b is read based on the vehicle speed V. With reference to the table in the table, each coefficient K ₁ corresponding to the vehicle speed V,
K ₂ is derived, and in step 103, the target rotation angle θr * of the step motor 43 corresponding to the target steering angle of the left and right rear wheels RW1 and RW2 is calculated by executing the calculation of the following formula 1.

[0016]

[Equation 1] θr * = K ₁ · ωy + K ₂ · sign [θ] In the above Equation 1, the function sign [θ] becomes “1” when θ is positive and “−1” when it is negative. , Θ is “0”, it becomes “0”.

After calculating the target rotation angle θr *, step 1
At 04, by subtracting the current motor rotation angle θr of the step motor 43 from the target rotation angle θr *, the rotation amount θr * −θr of the motor 43 to be calculated is calculated,
The rotation control signal for the step motor 43 corresponding to the rotation amount θr * −θr is sent to the drive circuit 5 via the I / O 55e.
6 is output. The drive circuit 56 supplies a drive pulse according to the rotation control signal to the step motor 43, and the motor 43 rotates the worm 44 by an amount corresponding to the drive pulse, that is, rotates the worm 44 to a target rotation angle θr *. .. Due to the rotation of the worm 44, the left and right rear wheels RW are operated by the action of the hydraulic pressure copying mechanism including the pin 42, the lever 41, the spool valve 37, the power cylinder 35, and the like.
1 and RW2 are steered to a target steering angle corresponding to the target rotation angle θr *.

Next, the process of steering the left and right rear wheels RW1 and RW2 from the neutral position to the left and right will be described in detail with reference to FIG. When the steering wheel 11 is steered to the right at time t1 while the vehicle is traveling straight, the steering angle θ of the steering wheel gradually increases from “0” to the positive direction at time t1.
After a slight delay, the yaw rate ωy gradually increases from “0” in the positive direction at time t2. As a result, from time t1 to time t2, the target rotation angle θr * calculated in step 103 has a value equal to the coefficient K ₂ . As a result, the step motor 43 rotates forward by an amount corresponding to the coefficient K ₂ , the pin 42 is displaced rightward from the neutral position, and the upper end of the lever 41 is displaced rightward with its lower end serving as a fulcrum. Therefore, the valve sleeve 37a is also displaced rightward. In this case, the coefficient K ₂ is set to a value corresponding to half the width of the dead zone of the spool valve 37, so that the valve sleeve 37a is only displaced to the end of the dead zone, and the valve 37 causes the power cylinder 35 to move. The supply / drainage of hydraulic oil to and from is not controlled, and the left and right rear wheels RW1 and RW2 are in a neutral state, that is, the rear wheel steering angle is maintained at "0".

In this state, after the time t2, the yaw rate ωy becomes a positive value, so the target rotation angle θr * calculated in the above step 103 becomes the value K ₁ · ωy + K ₂ . As a result, the step motor 43 causes the target rotation angle θr *
Rotate to (= K ₁ · ωy + K ₂ ), pin 42, lever 41
The upper end of the valve sleeve 37a and the valve sleeve 37a are further displaced rightward from the above state by an amount corresponding to the rotation angle K ₁ · ωy.
Therefore, in this case, since the valve sleeve 37a is displaced to the right by removing the dead zone, the hydraulic oil from the hydraulic pump 38 is supplied to the right oil chamber 35c of the power cylinder 35 and the left oil of the cylinder 35 is also supplied. The hydraulic oil in the chamber 35b is discharged to the reservoir 23, the relay rod 31 is displaced leftward, and the left and right rear wheels RW1, RW2 are steered rightward. As a result, immediately from time t2,
The left and right rear wheels RW1 and RW2 start to be steered. On the other hand, the lever 41 is displaced by the displacement of the relay rod 31 to the left.
The lower end of the valve sleeve 37a is displaced leftward with its upper end as a fulcrum, and the valve sleeve 37a is displaced leftward. Then, when the valve sleeve 37a returns to the position before the time t2 (the boundary position of the dead zone), the supply and discharge of the hydraulic oil is stopped and the leftward displacement of the relay rod 31 is also stopped. , RW2 are steered to a position corresponding to the rotation angle K ₁ · ωy of the step motor 43.

Further, even when the steering wheel 11 is steered to the left from the neutral position, the valve sleeve 3 is operated according to the steering of the steering wheel 11 before the yaw is generated in the vehicle body.
7a is displaced by an amount corresponding to the dead zone. However,
In this case, since the steering angle θ of the steering wheel is negative and the target rotation angle θr * becomes the value −K ₂ , the step motor 43 rotates in the negative direction opposite to the above case, and the pin 42 and the lever 41 are rotated.
And the valve sleeve 37a are displaced leftward. Then, when yaw occurs in the vehicle body, the step motor 43 further rotates in the negative direction from the position by the rotation angle K ₁ ωy (<0), and the left and right rear wheels RW1, RW2 move leftward at the same time as the yaw occurs. As the steering is started, the steering is performed to a position corresponding to the rotation angle K ₁ · ωy.

As a result of such steering control, as shown in FIG. 5, the influence of the dead zone in the vicinity of the neutral state of the spool valve 37 in the hydraulic pressure copying mechanism is canceled, and the left and right rear wheels RW.
1 and RW2 are steered with good responsiveness to the occurrence of yaw of the vehicle body due to the steering of the steering wheel 11, and are accurately steered to the target steering angle corresponding to the rotation angle K ₁ ωy. Good maneuverability. Incidentally, the broken line of the rear wheel steering angle in FIG. 5 shows the change state of the steering angle of the left and right rear wheels RW1 and RW2 in the conventional device that does not consider the dead zone.

(Modification) Next, a modification of the above embodiment will be described. In this modified example, the left and right rear wheels RW1, R according to the yaw rate ωy at the time of traveling at medium and high speeds in the above embodiment.
In addition to the steering control of W2, the left and right rear wheels RW1 and RW2 are changed to the left and right front wheels FW1 according to the steering angle θ of the steering wheel at low speed.
The present invention is applied to a four-wheel steering vehicle in which steering is performed in a reverse phase with respect to FW2.

The vehicle according to this modification is structurally the same as that of the above-described embodiment shown in FIG. 1, but the ROM 55b in this case is replaced by the flowchart of FIG. 6 instead of the flowchart of FIG. The program corresponding to is stored,
In addition to the coefficient K ₁ of the above embodiment, the coefficient K ₃ is stored in the form of a table, and the coefficient K _{2 of the} above embodiment is stored.
Instead of this, the coefficient K ₄ is stored in the form of a table. The coefficient K ₃ is, as shown in FIG. 7, a low vehicle speed region (predetermined vehicle speed V
It becomes negative at _{1 to} V ₀ ) and becomes zero at other times. As shown in FIG. 8, the coefficient K ₄ is obtained by making the predetermined value of the above embodiment negative in the low vehicle speed region (predetermined vehicle speed V _{1 to} V ₀ ), and also in the medium and high vehicle speed region (predetermined vehicle speed V ₀ or more). ), The predetermined value is the same as in the above embodiment.

Next, the operation of this modification will be described. Also in this modification, when the ignition switch (not shown) is closed, the CPU 55c starts executing the program in step 200 of FIG. 6, and repeatedly executes the circulation process including steps 201 to 204, thereby Steering control is applied to the rear wheels RW1 and RW2. In this case, the processing of steps 201 and 204 is the same as the processing of steps 101 and 104 of the above-mentioned embodiment, and the difference is that
The points are that the coefficients K ₃ and K ₄ are derived together with the coefficient K _{1 in} step 202, and that the target rotation angle θr * is calculated by executing the calculation of the following equation 2 in step 203.

[0025]

[Equation 2] θr * = K ₃ · θ + K ₁ · ωy + K ₄ · sign · [θ] In this way, the target rotation angle θr * is determined, and the left and right rear wheels are set to the steering angle corresponding to the rotation angle θr *. RW1,
RW2 result is steered, since the time of medium and high speed traveling coefficient K ₃ is "0", the target rotational angle [theta] r * is the same as in the above embodiment, the left and right rear wheels RW1, RW2 is similar to the above examples Steering is controlled by.

On the other hand, when traveling at a low speed, the coefficient K ₁ is "0".
At the same time, since the coefficients K ₃ and K ₄ are negative, when the steering handle 11 is steered in the right (or left) direction to the steering angle θ, the step motor 43 rotates negative (or positive). , The magnitude of the rotation angle is equal to the value | K ₃ · θ + K ₄ |. As a result, the valve sleeve 37a is displaced in the left (or right) direction to a position corresponding to an amount obtained by adding a correction amount of 1/2 of the dead zone width of the spool valve 37 to the rotation angle | K ₃ · θ | The influence of the dead zone of the valve 37 is canceled, and the left and right rear wheels RW1 and RW2 correspond to the left (or right) direction, that is, the rotation angle | K ₃ · θ | in the opposite phase with respect to the left and right front wheels FW1 and FW2. Steer to the target steering angle. As a result, even when the left and right rear wheels RW1 and RW2 are steered in opposite phases to the left and right front wheels FW1 and FW2, the rear wheels RW1 and RW2 are steered with good responsiveness to the steering of the steering wheel 11. And the rotation angle K ₃
Since the target steering angle corresponding to θ is accurately steered, the steerability of the vehicle is improved.

[Brief description of drawings]

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

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

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

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

FIG. 5 is a time chart showing changes in steering wheel steering angle θ, yaw rate ωy, target rotation angle θr *, and rear wheel steering angle.

FIG. 6 is a flowchart showing a program executed by a microcomputer according to a modified example of the embodiment.

FIG. 7 is a change characteristic graph of a coefficient K _{3 according to} the modification.

FIG. 8 is a change characteristic graph of a coefficient K _{4 according to} the modification.

[Explanation of symbols]

A ... Front wheel steering device, B ... Rear wheel steering device, C ... Electric control device, FW1, FW2 ... Front wheels, RW1, RW2 ... Rear wheels, 3
5 ... Power cylinder, 37 ... Spool valve, 41 ... Lever, 42 ... Pin, 43 ... Step motor, 51 ... Steering angle sensor, 52 ... Vehicle speed sensor, 53 ... Yaw rate sensor, 54 ... Rotation angle sensor, 55 ... Microcomputer ..

Claims (1)

[Claims] 1. An electric actuator driven according to an input control signal, and a hydraulic copying mechanism for maintaining the rear wheel in a neutral position in a neutral state and driving the electric actuator to steer the rear wheel. A rear wheel steering system which is applied to a rear wheel steering device and which has steering control means for determining a target steering angle and outputting a steering control signal representing the steering angle to the electric actuator to control the rear wheels to the same steering angle. In the electric control device for the apparatus, there is provided a correction means for correcting the steering control signal by adding a correction amount corresponding to the steering direction of the rear wheels and corresponding to the dead zone of the hydraulic pressure copying mechanism to the target steering angle. An electric control device for a rear wheel steering device characterized in that: