JPH06336172A - Vehicle steering system - Google Patents

Abstract

(57) [Summary] [Purpose] To accurately judge that a wheel has exceeded the cornering limit, and to accurately steer the wheel when it exceeds the cornering limit. [Configuration] The microcomputer 47 includes the sensors 41 to 41.
The vehicle lateral acceleration G _Y , yaw rate γ, vehicle speed u, steering wheel steering angle θ _H , front wheel control steering angle δ _F, and rear wheel control steering angle δ _R are input respectively based on the detected values. The slip angles α and the cornering forces F of the front and rear wheels are calculated respectively, and each cornering force F is partially differentiated by each slip angle α. When the partial differential value is negative, each wheel has a cornering limit. Determine that it has been exceeded. When one wheel exceeds the cornering limit, the vehicle attitude is changed so that the slip angle of the same wheel becomes the limit slip angle, and the other wheel is adjusted according to the difference between the slip angle and the limit slip angle. Steering control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system for electrically steering and controlling wheels, and more particularly to a vehicle steering system for steering control of front wheels or rear wheels so that front and rear wheels do not exceed cornering limits. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type has been disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Laid-Open No. 2-116355, when the time differential value of the side force of the front wheel (or the rear wheel) and the time differential value of the self-aligning torque have different signs, the front wheel (or the rear wheel) is Rear wheel (or front wheel) by a predetermined amount determined based on the judgment that the cornering limit has been reached
The steering wheel is steered to prevent the front wheels (or rear wheels) from exceeding the cornering limit.

[0003]

However, the cornering limit of the wheel is originally defined as the state of the wheel in which the cornering force begins to decrease as the slip angle increases. Determines the cornering limit of the wheel irrespective of the slip angle of the wheel, it cannot accurately determine the cornering limit of the wheel. For example, when returning a wheel to a neutral position, side force may decrease and self-aligning torque may increase even if the wheel has not reached its cornering limit. Misjudged. Further, in the above-mentioned conventional device, if the wheel exceeds the cornering limit, the wheel is always corrected and steered by a fixed amount regardless of the extent of the cornering limit. Not steered.

The present invention has been made to solve the above problems, and an object thereof is to accurately determine that a wheel has exceeded a cornering limit and to appropriately perform steering of the wheel at the time of the determination. It is to provide a steering device for a vehicle.

[0005]

In order to achieve the above object, the structural features of the present invention include a first slip angle detecting means for detecting a slip angle of a front wheel and a first slip angle detecting means for detecting a cornering force of a front wheel. Cornering force detecting means, first differentiating means for differentiating the detected cornering force of the front wheel by the detected slip angle of the front wheel to calculate a first differential value, and second detecting means for detecting the slip angle of the rear wheel. Slip angle detection means, second cornering force detection means for detecting the rear wheel cornering force, and the detected rear wheel cornering force are differentiated by the detected rear wheel slip angle to obtain a second differential value. A second differentiating means for calculating, and a first differentiating means according to a difference between the detected slip angle of the rear wheel and the limit slip angle of the rear wheel when the calculated second differential value is negative. A first control means for outputting a control signal to the first actuator to steer the front wheels in a direction in which the slip angle decreases in accordance with the difference; and the detected first differential value when the calculated first differential value is negative. A second control signal corresponding to the difference between the slip angle of the front wheel and the limit slip angle of the front wheel is output to the second actuator to steer the rear wheels in a direction in which the slip angle decreases in accordance with the difference. Two
The control means is provided.

[0006]

In the present invention constructed as described above, the first
And the second differentiating means differentiates the detected cornering forces of the front and rear wheels by the slip angles of the detected front and rear wheels, respectively, and when the differential value of one of the wheels is negative, the first and second controls are performed. According to the difference between the slip angle of one of the wheels and the limit slip angle, the means steer-controls the other wheel in such a direction that the slip angle decreases in accordance with the difference. That is, when one of the front wheels or the rear wheels exceeds the cornering limit, the posture of the vehicle is changed by steering control of the other wheel, and the slip angle of the wheel on the side exceeding the cornering limit is changed to the same limit. Can be controlled within.

[0007]

As can be understood from the above explanation of the operation,
According to the present invention, since the cornering limit of the wheel is determined based on the value obtained by differentiating the cornering force of the wheel by the slip angle, the same determination is accurately performed. Further, since the first and second control means steer-control the other wheel in accordance with the difference between the slip angle of the wheel on the side exceeding the cornering limit and the limit slip angle, the steering amount of the other wheel can be accurately controlled. Become.

[0008]

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 vehicle according to the embodiment. This vehicle includes a front wheel steering mechanism A that steers the front wheels FW1 and FW2, a rear wheel steering mechanism B that steers the rear wheels RW1 and RW2, and an electric control device C that electrically controls both steering mechanisms A and B. I have it.

The front wheel steering mechanism A includes a housing 11 formed in a cylindrical shape and supported by a vehicle body (not shown) so as to be axially displaceable. A rack bar 12 is axially displaceable in the housing 11. Supported by. The rack bar 12 includes a pinion 13 that meshes with the bar 12 in the housing 11, and a steering shaft 14 that includes an intermediate shaft 14a (allowing a slight bending of the steering shaft 14) connected to the pinion 13 at the lower end. The front wheels FW1 and F2 are connected to the steering wheel 15 via the tie rods 16a and 16b and the knuckle arms 17a and 17b at both ends thereof.
W2 is steerably connected. A power cylinder 18 is integrally formed in the housing 11, the piston of the cylinder 18 is fixed to the rack bar 12, and the left and right oil chambers partitioned by the piston are respectively provided in the control valve 21 assembled in the housing 11. It is connected. The control valve 21 controls the supply of hydraulic oil from the hydraulic pump 22 to one oil chamber of the power cylinder 18 and the discharge of hydraulic oil from the other oil chamber to the reservoir 23 according to the steering torque acting on the steering shaft 14. .

A piston rod of a hydraulic cylinder 25 is connected to the housing 11 via a bracket 24, and the cylinder 25 drives the housing 11 in the axial direction according to the supply and discharge of hydraulic oil to the left and right oil chambers. Hydraulic cylinder 2
The left and right oil chambers 5 are connected to the hydraulic pump 22 and the reservoir 23 via electromagnetic switching valves 26, respectively.
The electromagnetic switching valve 26 includes a solenoid 26a, which is set to a first state (a central position in the drawing) when a voltage is not applied to the solenoid 26a so that the hydraulic pump 22 and the reservoir 23 communicate with the left and right oil chambers of the hydraulic cylinder 25. Prohibit The solenoid switching valve 26 is a solenoid 26.
When a positive voltage is applied to a, the hydraulic pump 22 is set to the second state (left position in the drawing) to supply hydraulic oil to the left oil chamber of the hydraulic cylinder 25, and from the right oil chamber of the cylinder 25 to the reservoir 23. Allowing hydraulic oil to be discharged and at the time of applying a negative voltage to the solenoid 26a is in the third state (right position in the drawing).
Is set to allow the supply of hydraulic oil from the hydraulic pump 22 to the right oil chamber of the hydraulic cylinder 25 and the discharge of hydraulic oil from the left oil chamber of the hydraulic cylinder 25 to the reservoir 23.

The rear wheel steering mechanism B is provided with a housing 31 formed in a cylindrical shape and supported by the vehicle body, and a relay rod 32 is supported in the housing 31 so as to be axially displaceable. The relay rod 32 has tie rods 33a, 33b and knuckle arms 34a, 34b at both ends thereof connected to the rear wheels RW1, RW2 in a steerable manner.
A power cylinder 35 is integrally formed in the housing 31, and the piston of the cylinder 35 is fixed to the relay rod 32. The left and right oil chambers of the power cylinder 35 partitioned by the piston are electromagnetic switching valves 36.
And a hydraulic pump 22 and a reservoir 23, respectively. The electromagnetic switching valve 36 is the solenoid 3
6a, which is set to the first state (the central position in the drawing) when the voltage is not applied to the solenoid 36a, and prohibits the hydraulic pump 22 and the reservoir 23 from communicating with the left and right oil chambers of the power cylinder 35. Further, the electromagnetic switching valve 36 is set to the second state (the right position in the drawing) when the positive voltage is applied to the solenoid 36a, and supplies the hydraulic oil from the hydraulic pump 22 to the right oil chamber of the power cylinder 35 and the cylinder 35. The hydraulic oil is allowed to drain from the left oil chamber to the reservoir 23, and is set to the third state (the left position in the drawing) when a negative voltage is applied to prevent the hydraulic oil from being discharged from the hydraulic pump 22 to the left oil chamber of the cylinder 35. The supply and discharge of the hydraulic oil from the right oil chamber of the cylinder 35 to the reservoir 23 are allowed.

The electric control unit C detects a lateral acceleration sensor 41 for detecting a lateral acceleration G _Y of the vehicle, a yaw rate sensor 42 for detecting a yaw rate γ of the vehicle, a vehicle speed sensor 43 for detecting a vehicle speed u, and a steering wheel steering angle θ _H. And a front wheel control steering angle sensor 45.
And a rear wheel control steering angle sensor 46. The front wheel control rudder angle sensor 45 detects the amount of displacement of the piston rod of the hydraulic cylinder 25 from the reference position to determine the front wheel FW.
1, the control steering angle δ _F of FW2 is detected. The rear wheel control rudder angle sensor 46 detects the amount of displacement of the relay rod 32 from the reference position, whereby the rear wheels RW1 and RW2 are detected.
The control rudder angle δ _R is detected. Each of the detected values G _Y , γ, θ _H , δ _F , δ _R is represented by a positive value in the left direction and a negative value in the right direction.

Each of these sensors 41 to 46 is connected to a microcomputer 47. The microcomputer 47 is a ROM commonly connected to the bus 47a.
47b, CPU 47c, RAM 47d and I / O (input / output interface circuit) 47e. ROM47
b stores a program corresponding to the flowcharts of FIGS. 2 to 4, and the front wheel FW1, as shown in FIG.
The characteristics of the cornering force of FW2 with respect to the slip angle (α- _FF characteristics) and the rear wheel RW as shown in FIG. 6 (B).
Stored respectively 1, characteristic for the slip angle of the cornering force RW2 data representing the (alpha-F _R characteristics) as a table. The CPU 47c executes the program, and the RAM 47d temporarily stores the variables necessary for executing the program. Further, a part of the RAM is configured to be non-volatile, and a characteristic (α-H characteristic) with respect to a slip angle of a partial differential value obtained by partially differentiating a cornering force as shown in FIG. The data represented is the table for the front wheels FW1, FW2 and the rear wheels RW1,
Each is stored as a table for RW2. I
In addition to the sensors 41 to 46, differential amplifiers 48a and 48b are connected to / O47e. Differential amplifier 4
8a is a positive input (+) D / built in the I / O 47e.
An analog control signal representing the front wheel control steering angle δ _F from the A converter is input, and a detection signal representing the front wheel control steering angle δ _F from the front wheel control steering angle sensor 45 is input at the negative side input (-). Then, the steering of the front wheels FW1 and FW2 is feedback-controlled. The differential amplifier 48b has an I / O4 at the positive side input (+).
Rear wheel control steering angle δ _R from the D / A converter built in 7e
Input the analog control signal that indicates
At (-), the rear wheel control rudder angle δ from the rear wheel control rudder angle sensor 46
A detection signal representing _R is input to feedback control steering of the rear wheels RW1 and RW2.

Next, the operation of the embodiment configured as described above will be described. When the ignition switch is turned on,
The CPU 47c starts the execution of the program in step 100 of FIG. 2, and after the initialization processing of step 102, repeatedly executes the processing of steps 104 to 118.

At step 104, each sensor 41-46
From the lateral acceleration G _Y , the yaw rate γ, the vehicle speed u, the steering wheel steering angle θ _H , the front wheel control steering angle δ _F, and the rear wheel control steering angle δ _R , respectively. To calculate.

[0016]

[Formula 1] β = ∫ (G _Y / u−γ) dt In this embodiment, the slip angle β of the vehicle is calculated by the formula 1 as described above, but 1 is used instead of the integral calculation. The slip angle β may be calculated by the next-delay pseudo-integral calculation. Alternatively, the slip angle β of the vehicle may be measured.

Next, at step 108, the slip angles α _F of the front wheels FW1 and FW2 and the rear wheels RW are calculated by the following equations 2 and 3.
The slip angle α _R of 1, RW2 is calculated (see FIG. 5).

[0018]

[Formula 2] α _F = β + aγ / u−Nθ _H −δ _F

[0019]

Equation 3] Incidentally _{α R = β-bγ / u} -δ R, in the number 2,3, a is a fixed value provided in advance to represent the distance between the front wheel axle and the center of gravity, b is a rear wheel axle It is a preset fixed value that represents the distance from the center of gravity, and N is a preset fixed value that represents the steering gear ratio.

Next, at step 110, the cornering force F _F of FW1 and FW2 and the cornering force F _R of the rear wheels RW1 and RW2 are calculated by the following equations 4 and 5.

[0021]

[Equation 4]

[0022]

[Equation 5]

In the equations 4 and 5, M is a predetermined fixed value that represents the vehicle weight, and I is a predetermined fixed value that represents the yaw moment of inertia of the vehicle.

In the processing of steps 108 and 110, the previously calculated slip angles α _F and α _R and the cornering forces F _F and F _R are also stored in the RAM 47d. At 112, the previously calculated slip angles α _F (n-1), α _R (n-1) and the cornering forces F _F (n-1), F _R (n-1) and the slip angles α _F ( n), α _R (n) and cornering force F _F (n), F
Partial differential values H _F (α _F ) and H _R (α _R ) obtained by partially differentiating the cornering forces F _F and F _R by slip angles α _F and α _R , respectively, according to the following equations 6 and 7 using _R (n) To calculate.

[0025]

[Equation 6]

[0026]

[Equation 7]

Next, in step 114, the calculated slip angles α _F and α _R and partial differential values H _F (α _F ) and H _R (α _R )
Is used to correct the data in each table provided in the nonvolatile portion of the RAM 47d.

Here, the physical meanings of the equations 4 to 7 will be explained. In a wheel, as shown in FIGS. 6A and 6B, the absolute value | α | of the slip angle α is the limit. Until reaching the slip angle α ₀₁ , the front wheels FW1, FW2 and the rear wheels R
The cornering forces F _F and F _R of W1 and RW2 increase as the absolute value | α | increases. When the absolute value | α | exceeds the limit slip angle α ₀₁ , the cornering force F decreases as the absolute value | α | increases. The cornering limit of the wheel is defined when the absolute value | α | is equal to the limit slip angle α ₀₁ . Therefore, by partially differentiating the cornering force F by the slip angle α, the partial differential value H (α) becomes a range in which the absolute value | α | of the slip angle α is smaller than the limit slip angle α ₀₁ as shown in FIG. Is a positive value, and the same absolute value | α | is a negative value in a range larger than the limit slip angle α ₀₁ . Thus, when the absolute value | α | exceeds the limit slip angle α ₀₁ , the wheels are steered by the amount exceeding this limit and the absolute value | α | of the slip angle α becomes the limit slip angle α _{01.
If it is set to 01} , the wheel will generate the maximum cornering force F _MAX . The "front wheel steering control routine" and the "rear wheel steering control routine" in steps 116 and 118 using this theory will be described below.

The CPU 47c is a "front wheel steering control routine".
Is started in step 200 of FIG.
At 02, it is determined whether the calculated partial differential value H _R (α _R ) for the rear wheels RW1 and RW2 is less than “0”. In this case, if the rear wheels RW1 and RW2 have not reached the cornering limit and the partial differential value H _R (α _R ) is “0” or more, it is determined to be “NO” in step 202 and the program is transferred to step 210. Proceed. In step 210, the target front wheel control steering angle δ _F * is set to “0”, and in step 212, a control signal representing the target front wheel control steering angle δ _F * is output to the differential amplifier 48a via the I / O 47e. Then, in step 214, this "front wheel steering control routine" ends.

The differential amplifier 48a compares the front wheel control steering angle [delta] _F detected by the target front-wheel control steering angle [delta] _F * and the front wheel control steering angle sensor 45 which is the output, the electromagnetic switching based on the comparison result The front wheels FW1 and FW2 are steered by controlling the valve 26. In this case, if the target front wheel control steering angle δ _F * and the detected front wheel control steering angle δ _F are equal, the differential amplifier 48a releases the voltage applied to the solenoid 26a to cause the electromagnetic switching valve 26 to move to the first state ( It is set to the central position in the drawing), and the supply and discharge of hydraulic oil to and from the hydraulic cylinder 25 is stopped to drive the housing 11. If the target front wheel control rudder angle δ _F * is larger than the detected front wheel control rudder angle δ _F , the differential amplifier 48a sets the electromagnetic switching valve 26 to the second state (left position in the figure) by applying a positive voltage to the solenoid 26a. Then, the hydraulic oil from the hydraulic pump 22 is supplied to the left oil chamber of the hydraulic cylinder 25, and the hydraulic oil from the right oil chamber of the cylinder 25 is discharged to the reservoir 23 to drive the housing 11 to the right. As a result, the rack bar 12 is displaced rightward together with the housing 11, and the front wheels FW1 and FW2 are steered leftward (forward direction). Further, the target front wheel control rudder angle δ _F * is the detected front wheel control rudder angle δ
If it is smaller than _F , the differential amplifier 48a causes the solenoid 26
Electromagnetic switching valve 2 by applying a negative voltage to a
6 is set to the third state (right position in the drawing), and the hydraulic cylinder 2
The hydraulic oil from the hydraulic pump 22 is supplied to the right oil chamber 5 and the hydraulic oil from the left oil chamber of the cylinder 25 is discharged to the reservoir 23 to drive the housing 11 leftward. As a result, the rack bar 12 is displaced leftward together with the housing 11, and the front wheels FW1 and FW2 are moved rightward (negative direction).
Steered to. Therefore, the front wheels FW1 and FW2 are corrected and steered to the target front wheel control steering angle δ _F *.
The control steering angles of W1 and FW2 are controlled to "0".

On the other hand, if the calculated partial differential value H _R (α _R ) is less than “0”, it is determined to be “YES” in step 202 and the program proceeds to steps 204 to 208. In step 204, the difference Δα _R between the limit slip angle α ₀₁ and the current rear wheel slip angle α _R is calculated by the following equation 8 (see FIG. 6B).

[0032]

Δα _R = α ₀₁ −α _{R In} step 206, the vehicle attitude is changed and the rear wheel R
A change amount ΔF _F of the cornering force F _F of the front wheels FW1 and FW2 necessary to reduce the slip angle α _R of W1 and RW2 by the difference Δα _R is calculated using the following formula 9.

[0033]

[Equation 9]

In the above equation 9, s is a Laplace operator.
In step 208, the ROM corresponding to FIG.
The cornering force F _F corresponding to the current slip angle α _F of the front wheels FW1 and FW2 is derived by referring to the table in the table, and the change ΔF _F is added to the cornering force F _F to obtain the front wheels FW1 and FW2. The cornering force F _F + ΔF _F is calculated, the slip angle α _F 'corresponding to the cornering force F _F + ΔF _F is derived again by referring to the same table, and the slip angle derived from the current slip angle α _{F is} derived. target front wheel control steering angle by subtracting the alpha _F '[delta]
Calculate _F *.

[0035] After calculation of the target front wheel control steering angle [delta] _F *, a control signal indicating the steering angle [delta] _F * at step 212 I / O47
output to the differential amplifier 48a via e, and step 21
At "4", this "front wheel steering control routine" ends. As a result, the front wheels FW1 and FW2 are corrected and steered to the target front wheel control steering angle δ _F * as described above, and the posture of the vehicle is adjusted to the front wheel F.
The target front wheel control steering angle δ _F * of W1 and FW2 is changed. Therefore, the slip angle α _R of the rear wheels RW1, RW2
Becomes the limit slip angle α ₀₁ , the rear wheels RW1 and RW2 generate the maximum cornering force F _R, and the slip angle α _F of the front wheels FW1 and FW2 is inevitably kept below the limit slip α ₀₁ . The vehicle will be able to make a stable turn and fully exhibit its turning ability.

Next, the "rear wheel steering control routine" will be described. The CPU 47c starts the execution of the "rear wheel steering control routine" at step 300 of FIG.
In step 2, it is determined whether the calculated partial differential value H _F (α _F ) for the front wheels FW1 and FW2 is less than “0”. In this case, if the front wheels FW1 and FW2 have not reached the cornering limit and the partial differential value H _F (α _F ) is “0” or more, it is determined to be “NO” in step 302 and the program proceeds to step 310. . In step 310, the target rear wheel control steering angle δ _R * is set to “0”, and in step 312, a control signal representing the target rear wheel control steering angle δ _R * is sent to the differential amplifier 48b via the I / O 47e. After outputting, the "rear wheel steering control routine" is ended in step 314.

The differential amplifier 48b controls the electromagnetic switching valve 36 based on the output target rear wheel control steering angle δ _R * and the rear wheel control steering angle δ _R detected by the rear wheel control steering angle sensor 46. The same control is performed as in the case of the front wheels FW1 and FW2. Electromagnetic switching valve 36 and power cylinder 35
The electromagnetic switching valve 26 and the hydraulic cylinder 2 described above
5, the rear wheels RW1 and RW2 are steered to the target rear wheel control steering angle δ _R * (= 0), that is, the neutral state.
However, in this case, the rear wheels RW1 and RW2 are steered left and right due to the axial displacement of the relay rod 32.

On the other hand, if the calculated partial differential value H _F (α _F ) is less than “0”, it is determined to be “YES” in step 302 and the program proceeds to steps 304 to 308. In step 304, the difference Δα _F between the limit slip angle α ₀₁ and the current front wheel slip angle α _F is calculated by the following equation 10.
Is calculated (see FIG. 6 (A)).

[0039]

[Formula 10] Δα _F = α ₀₁ −α _{F In} step 306, the vehicle attitude is changed to change the front wheel F
The change amount ΔF _R of the cornering force F _R of the rear wheels RW1 and RW2 necessary to reduce the slip angle α _F of W1 and FW2 by the difference Δα _F is calculated using the following formula 11.

[0040]

[Equation 11]

In the above equation 11, s is a Laplace operator. At step 308, R corresponding to FIG.
Referring to the table in the OM, the current rear wheels RW1, RW2
The slip angle α to derive the cornering force F _R corresponding to _R, the variation [Delta] F _R in the cornering force F _R
Is calculated to calculate the cornering force F _R + ΔF _R required for the rear wheels RW1 and RW2, and the same table is referred to again to derive the slip angle α _R 'corresponding to the same cornering force F _R + ΔF _R. from the slip angle alpha _R by subtracting the slip angle alpha _R 'described above derived to calculate the target rear-wheel control steering angle [delta] _R * of.

Next, in step 312, a control signal representing the target rear wheel control steering angle δ _R * is output to the differential amplifier 48b via the I / O 47e, and in step 314, this "rear wheel steering control routine" is executed. Ends. As a result, the rear wheels RW
1 and RW2 are corrected and steered to the target rear wheel control steering angle δ _R * as described above, and the posture of the vehicle is changed by the target rear wheel control steering angle δ _R * of the rear wheels RW1 and RW2. Therefore, the slip angle α _F of the front wheels FW1 and FW2 is equal to the limit slip angle α _F.
01 , the front wheels FW1 and FW2 generate the maximum cornering force F _F, and the slip angle α _R of the rear wheels RW1 and RW2 is necessarily kept within the limit slip α _01, so that the vehicle is stable and stable. You will be able to make full turns with your turning ability.

As can be understood from the above description of the operation, according to the above embodiment, the front wheels FW1 and FW2 and the rear wheels RW.
1 and RW2 cornering forces F _F and F _R are partially differentiated by slip angles α _F and α _R. Values H _F (α _F ) and H _R (α _R ) are determined according to the positive / negative of each wheel FW1, FW2, RW1, RW2. Since the cornering limit is determined, the same determination can be made accurately.
Further, when the front wheels FW1, FW2 exceed the cornering limit, the vehicle attitude is changed to change the slip angle α _F of the front wheels FW1, FW2 by the limit slip angle α _01.
Since W1 and RW2 are steered, the steering amounts of the rear wheels RW1 and RW2 are accurate. Further, when the rear wheels RW1 and RW2 exceed the cornering limit, the vehicle attitude is changed to change the slip angle α _R of the rear wheels RW1 and RW2 to the limit slip angle α.
_{Since the} front wheels FW1 and FW2 are steered by the amount that becomes ₀₁ , the steering amounts of the front wheels FW1 and FW2 are accurate.

(Other Embodiments) Next, in the embodiment configured as described above, the front wheels FW1 and FW2 or the rear wheels RW.
Another embodiment of the present invention will be described in which, when 1 and RW2 exceed the cornering limit, the wheels on the side of the cornering limit are also corrected and steered. The other embodiment is also configured as shown in FIG.
The only difference is that a program corresponding to the flowcharts of FIGS. 8 and 9 is stored in the OM 47b instead of the program corresponding to the flowcharts of FIGS.

Also in this other embodiment, when the ignition switch is turned on, the CPU 47c executes the program of FIG. 2 and, after the processing of steps 102 to 114,
In step 116, the "front wheel steering control routine" corresponding to the flowchart of FIG. 8 is executed, and in step 118, the "rear wheel steering control routine" corresponding to the flowchart of FIG. 9 is executed.

First, the front wheels FW1 and FW2 are also rear wheels RW1,
The case where the RW2 is not in the vicinity of the cornering limit and is in the normal steering state will be described. "Front wheel steering control routine"
Is shown in detail in FIG. 8, and the CPU 47c starts its execution in step 200, and determines in step 220 whether or not the partial differential value H _F (α _F ) is “0” or more. In this case, since the front wheels FW1 and FW2 are in the normal steering state, the partial differential value H _F (α _F ) is positive. Therefore, in step 220, it is determined to be “YES”, and in step 222, the front wheel _F that does not include the front wheel control steering angle δ _F is calculated by the following equation 12.
Calculate the slip angle ε _F of W1 and FW2.

[0047]

For Equation 12] ε _F = α _F + δ _F meaning of this number 12, previously with minor description.
If the front wheels FW1 and FW2 are steered to the left (positive direction) as shown in FIG. 5, the slip angles α _F of the front wheels FW1 and FW2 are negative values. On the other hand, in this case, the front wheels FW
1 and FW2 have reached the cornering force limit, the front wheels FW1 and FW2 should be steered to the right in order to reduce the absolute value | α _F | of the slip angle α _F. At this time, the front wheel control steering angle δ _F has a negative value. Therefore, the slip angle ε _F is a negative value whose absolute value | ε _F | is larger than the absolute value | α _F | of the slip angle α _F by the absolute value | δ _F | of the front wheel control steering angle δ _F. As a result, the slip angle ε _F indicates the slip angle of the front wheels FW1 and FW2 when the front wheels FW1 and FW2 are not steered. Of course, the front wheel control rudder angle δ _F
Is 0, both slip angles ε _F and α _F have the same value. Further, when the front wheels FW1 and FW2 are steered to the right (negative direction), both the slip angle α _F and the front wheel control steering angle δ _F are values of “0” or more, and the slip angle ε _F is the front wheel FW1, The slip angles of the front wheels FW1 and FW2 when the steering control of the FW2 is not performed are shown.

After the processing of step 222, step 2
At 24, the partial differential value H _F (ε _F ) is derived by referring to the table in the RAM 47d based on the absolute value | ε _F | of the slip angle ε _F , and at step 226, the partial differential value H
It is determined whether or not _F (ε _F ) is “0” or more. Since the front wheels FW1 and FW2 are now in the normal steering state, the partial differential value H _F (ε _F ) is positive. Therefore, in step 226, the determination is “YES” and the program proceeds to step 228. In step 228, the target front wheel control steering angle δ
Set _F * to "0".

Then, the above-mentioned steps 202 to 212.
Execute the process consisting of. In this case, the rear wheels RW1, RW
Since 2 is also in the normal steering state, the partial differential value H _R (α _R ) is positive. Therefore, it is determined to be “NO” in step 202, and the control signal representing the target front wheel control steering angle δ _F * set to “0” in step 212 is output to the operational amplifier 48a via the I / O 47e. . As a result, the front wheels FW
The control rudder angle δ _F of 1 and FW2 is maintained at “0”.

Next, the "rear wheel steering control routine" will be described. Even in this "rear wheel steering control routine",
The CPU 47d starts its execution in step 300 of FIG. 9, and determines in step 320 whether the partial differential value H _R (α _R ) is “0” or more. Also in this case, the rear wheels RW1,
Since RW2 is in a normal steering state, the partial differential value H _R (α _R )
Is positive. Therefore, in step 320, "YE
It is determined that S ", calculates the slip angle epsilon _R of wheels RW1, RW2 after that does not include the rear wheel control steering angle [delta] _R by the following equation 13 at step 322.

[0051]

Ε _R = α _R + δ _R Next, in step 324, the absolute value of the slip angle ε _R |
The partial differential value H _R (ε _R ) is calculated by referring to the table in the RAM 47d based on ε _R |, and step 326
At, it is determined whether the partial differential value H _R (ε _R ) is “0” or more. Since the front wheels FW1 and FW2 are now in the normal steering state, the partial differential value H _R (ε _R ) is positive. Therefore, in step 326, the determination is “YES” and the program proceeds to step 328. In step 328, the target rear wheel control steering angle δ _R * is set to “0”, and the above-described step 30 is performed.
The process consisting of 2-312 is executed. In this case, since the partial differential value H _F (ε _F ) is also positive, “N
“O”, and at step 312, the control signal representing the target rear wheel control steering angle δ _R * set to “0” is set to I / O 47.
It outputs to the operational amplifier 48b via e. This allows
The control steering angle δ _R of the rear wheels RW1 and RW2 is maintained at “0”.

Next, the front wheels FW1 and FW2 or the rear wheels RW.
A case will be described in which 1 and RW2 are steered to the cornering limit. Front wheels FW1 and FW2 are rear wheels RW1 and RW
If the cornering limit is exceeded before 2, the partial differential value H _F (α _F ) calculated by the process of step 112 is first calculated.
Is smaller than “0”. Therefore, step 220
In step 230, the program is determined to be “NO”.
Proceed to. In step 230, the corrected steering angle Δδ _F is calculated by the following equation 14.

[0053]

Equation 14] _{Δδ F = | α F | -α} 01 this correction steering angle .DELTA..delta _F, as shown in FIG. 7, the absolute value of the slip angle α _F | α _F | exceeds a limit slip angle alpha ₀₁ Represents quantity. Next, at step 232, the slip angle α _F
Is positive. In this case, the slip angle α
_{If F} is positive, it is determined to be "YES" in step 232, and the target front wheel control steering angle δ _F * is calculated in step 234 by the following Expression 15.

[0054]

## EQU15 ## δ _F * = δ _F + Δδ _{F If} the slip angle α _F is not positive, step 232
It is determined to be “NO” in step 236, and in step 236, the following expression 1
The target front wheel control rudder angle δ _F * is calculated from 6.

[0055]

## EQU16 ## δ _F * = δ _F −Δδ _F After the processing of these steps 234 and 236, step 2
At 02, similarly to the above, it is determined whether the partial differential value H _R (α _R ) is less than “0”. In this case, the rear wheels RW1, RW2
Has not reached the cornering limit, so step 20
It is determined to be "NO" in step 2, the control signal representing the target front wheel control steering angle δ _F * is output to the differential amplifier 48a in step 212, and this "front wheel steering control routine" is ended in step 234. . As a result, when the front wheels FW1 and FW2 are steered to the right (negative direction) and the slip angle α _F is positive, the front wheels FW1 and FW2 decrease the absolute value | α _F | of the slip α _F to the left. Steering is performed in the positive direction to the limit slip angle α ₀₁ . If the front wheels FW1 and FW2 are steered to the left (positive direction) and the slip angle α _F is negative, the front wheels FW1 and FW2 have the absolute value of the slip α _F | α _F
The limit slip angle α ₀₁ to the right (negative direction) that decreases |
Steered up to. As a result, the front wheels FW1 and FW2 are corrected and steered to the angle at which the maximum cornering force is generated.

Even if the partial differential value H _F (α _F ) is “0” or more, if the partial differential value H _F (ε _F ) corresponding to the slip angle ε _F is not “0” or more, step “YE in 220
Based on the determination of “S” and “NO” in step 226, the program proceeds to steps 230-236. Also in this case, the target front wheel control steering angle δ _F * is calculated by the processing of steps 230 to 236, and the front wheels FW1 and FW2 are steering-controlled to the calculated target front wheel control steering angle δ _F * by the processing of step 212. The front wheels FW1 and FW2 are corrected and steered to an angle at which the maximum cornering force is generated.

On the other hand, in the "rear wheel steering control routine" of FIG. 9, since the partial differential values H _R (α _R ) and H _R (ε _R ) are both positive, the above-mentioned steps 320 to 328 are executed. After the same process, it is determined to be “YES” in step 302 and the processes of steps 304 to 312 are performed. As a result, the rear wheels RW1 and RW2 are steered so that the slip angle α _F of the front wheels FW1 and FW2 becomes the limit slip angle α ₀₁ . Thus, when the front wheels FW1, FW2 exceed the cornering limit, the front wheels FW1, FW2 and the rear wheels RW
The rear wheels RW1 and RW calculated by the processing of step 306 by correcting and steering the first and second RW2 simultaneously.
Even if the change amount ΔF _R of the cornering force F _R of 2 includes some error, the slip angle α _F of the front wheels FW1 and FW2 is reliably controlled to the limit slip angle α ₀₁ .

Further, the front wheels FW1 and FW2 and the rear wheels R
During the correction steering of W1 and RW2, the partial differential value H _F (α _F ) is “0”.
As described above, in step 220, as described above, "Y
ES "and the program is executed in steps 222 to 226.
Proceed to. In this case, the partial differential value H corresponding to the slip angle ε _F when the front wheels FW1 and FW2 calculated by the processing of steps 222 and 224 are not steered
_{When F} (ε _F ) becomes equal to or greater than “0”, the determination in step 226 is “YES”.
The correction steering of the front wheels FW1 and FW2 is stopped by the processing of 2,212. On the other hand, in this case, in the "rear wheel steering control routine" of FIG.
It is determined to be “ES”, and the process of step 312 is executed without executing the processes of steps 304 to 308. At this time, since the partial differential value H _R (α _R ) is positive, the rear wheels RW1 and RW are processed by the processing of step 328 described above.
Since the target rear wheel control steering angle δ _R * of 2 is set to “0”, the correction steering of the rear wheels RW1 and RW2 is also stopped.

Next, the rear wheels RW1 and RW2 become the front wheels FW1.
Explaining the case where the cornering limit is exceeded before FW2, in this case, the partial differential value H _R (α _R ) calculated in step 112 becomes negative. Therefore, in step 320 of the "rear wheel steering control routine" of FIG. 9, "NO" is determined and the program proceeds to step 330. In step 330, the corrected steering angle Δδ is calculated by the following equation 17.
Calculate _R.

[0060]

Equation 17] _{Δδ R = | α R | -α} 01 Next, the processing of step 332-336, the target rear-wheel control steering angle shown in following equation 18, if positive slip angle alpha _R is [delta] _R * If the slip angle α _R is not positive, the target rear wheel control rudder angle δ _R * shown in Formula 19 below is calculated.

[0061]

[Formula 18] δ _R * = δ _R + Δδ _R

[0062]

Equation 19] δ _R * = δ _R -Δδ _R In this case, since the front wheels FW1, FW2 does not reach the cornering limit, determines a "NO" in step 302, the target front-wheel control steering at step 312 The control signal representing the angle δ _F * is output to the differential amplifier 48b, and step 31
At "4", the "rear wheel steering control routine" ends. Therefore, if the rear wheels RW1 and RW2 are steered to the right (negative direction) and the slip angle α _R is positive, the rear wheels RW
1 and RW2 are steered to the limit slip angle α ₀₁ in the left direction (forward direction) to decrease the absolute value | α _R | of the slip α _R. If the rear wheels RW1, RW2 are steered to the left (positive direction) and the slip angle α _R is negative, the rear wheels RW1, R
W2 is steered to the limit slip angle α ₀₁ in the right direction (negative direction) to decrease the absolute value | α _R | of the slip α _R. As a result, the rear wheels RW1 and RW2 are corrected and steered to an angle at which the maximum cornering force is generated.

Even if the partial differential value H _R (α _R ) is "0" or more, if the partial differential value H _R (ε _R ) corresponding to the slip angle ε _R is not "0" or more, step “YE at 320
Based on the determination of “S” and “NO” in step 326, the program proceeds to steps 330-336. Also in this case, the target rear wheel control steering angle δ _R * is calculated by the processing of steps 330 to 336, and the steering control is performed by the rear wheels RW1 and RW2 to the calculated target rear wheel control steering angle δ _R * by the processing of step 312. As a result, the rear wheels RW1 and RW2 are corrected and steered to an angle at which the maximum cornering force is generated.

On the other hand, at this time, in the "front wheel steering control routine" of FIG. 8, since the partial differential value H _F (α _F ) is positive, the above-mentioned processing of steps 220 to 228 is performed. Then, in step 202, it is determined to be "YES" and the processes of steps 204 to 212 are performed. As a result, the rear wheels RW1 and RW2 are steered so that the slip angle α _F of the front wheels FW1 and FW2 becomes the limit slip angle α ₀₁ . Thus, even when the rear wheels RW1, RW2 exceed the cornering limit, the rear wheels RW1, RW2 and the front wheel F
By simultaneously correcting and steering W1 and FW2, the front wheels FW1 and FW2 calculated by the process of step 206 are calculated.
Even if the change amount ΔF _F of the cornering force F _F of W2 includes some error, the slip angle α _R of the rear wheels RW1 and RW2 is reliably set to the limit slip angle α ₀₁ .

Further, the rear wheels RW1 and RW2 and the front wheels F
During the correction steering of W1 and FW2, the partial differential value H _R (α _R ) is “0”.
As described above, in step 320, as described above, "Y
ES "and the program is executed in steps 322 to 326.
Proceed to. In this case, the partial differential value H corresponding to the slip angle ε _F when the rear wheels RW1 and RW2 calculated by the processing of steps 322 and 324 are not steering-controlled.
_{When F} (ε _F ) becomes equal to or greater than “0”, the determination in step 326 is “YES”.
The correction steering of the rear wheels RW1 and RW2 is stopped by the processing of 2 and 312. On the other hand, in this case, in the "front wheel steering control routine" of FIG.
It is determined to be “ES”, and the process of step 212 is executed without executing the processes of steps 204 to 208. At this time, since the partial differential value H _F (α _F ) is positive, the front wheels FW1 and FW2 are processed by the processing of step 228 described above.
Since the target front wheel control steering angle δ _F * is set to “0”, the correction steering of the front wheels FW1 and FW2 is also stopped.

[Brief description of drawings]

FIG. 1 is an overall schematic view of a vehicle showing an embodiment of the present invention.

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

FIG. 3 is a detailed flowchart of a front wheel steering control routine of FIG.

FIG. 4 is a detailed flowchart of a rear wheel steering control routine of FIG.

FIG. 5 is an explanatory diagram for explaining directions such as a front wheel steering angle, a rear wheel steering angle, a yaw rate, and a slip angle.

FIG. 6 (A) is a characteristic diagram showing the relationship between the front wheel cornering force F _{F and} the slip angle α _F , and FIG. 6 (B) is a characteristic diagram showing the relationship between the rear wheel cornering force F _{R and} the slip angle α _R. Is.

FIG. 7 is a characteristic diagram showing a relationship of a partial differential value H obtained by partially differentiating the cornering force F with a slip angle α with respect to the slip angle α.

FIG. 8 is a detailed flowchart of a front wheel steering control routine according to another embodiment of the present invention.

FIG. 9 is a detailed flowchart of a rear wheel steering control routine according to another embodiment of the present invention.

[Explanation of symbols]

FW1, FW2 ... front wheels, RW1, RW2 ... rear wheels, A ... front wheel steering mechanism, B ... rear wheel steering mechanism, C ... electric control device, 1
1, 31 ... Housing, 12 ... Rack bar, 15 ... Steering handle, 25 ... Hydraulic cylinder, 26, 36 ... Electromagnetic switching valve, 32 ... Relay rod, 35 ... Power cylinder, 41 ... Lateral acceleration sensor, 42 ... Yaw rate sensor,
43 ... Vehicle speed sensor, 44 ... Steering wheel steering angle sensor, 45 ...
Front wheel control rudder angle sensor, 46 ... Rear wheel control rudder angle sensor, 47
… Microcomputer.

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

Claims (1)

[Claims] 1. A front wheel steering mechanism that has an electrically controlled first actuator for steering front wheels by the operation of the first actuator, and a second actuator that has an electrically controlled second actuator. In a vehicle steering system including a rear wheel steering mechanism that steers rear wheels by operation, a first slip angle detecting means for detecting a slip angle of a front wheel, and a first cornering force detecting means for detecting a cornering force of a front wheel. First differentiation means for calculating a first differential value by differentiating the detected cornering force of the front wheel by the detected slip angle of the front wheel, and second slip angle detection means for detecting a slip angle of the rear wheel A second cornering force detecting means for detecting the cornering force of the rear wheel, and the detected cornering force of the rear wheel as described above. Second differentiating means for calculating a second differential value by differentiating with the slip angle of the rear wheel that has been taken out; when the calculated second differential value is negative, the slip angle of the rear wheel detected and the rear wheel First control means for outputting to the first actuator a first control signal corresponding to a difference from the limit slip angle to control the front wheels in a direction in which the slip angle decreases according to the difference; When the first differential value is negative, a second control signal corresponding to the difference between the detected slip angle of the front wheel and the limit slip angle of the front wheel is output to the second actuator, and the slip angle of the rear wheel is equal to the difference. And a second control means for performing steering control in a decreasing direction according to the above.