JPH0781600A - Steering control device for vehicle - Google Patents

Abstract

PURPOSE:To improve the steering stability by generating the canceling moment in the opposite direction to cancel the yaw moment generated from the longitudinal forces of a vehicle to be inputted in wheels when a vehicle passes a puddle or a bump on the road surface through the control of the steering angle by a steering angle changing mechanism. CONSTITUTION:Longitudinal forces FFL, FFR to be inputted in the right and left front wheels from the output value fFL, fFR of a longitudinal force detector such as load cells mounted on the suspension of the front right and left wheels are calculated (S1, S2), the steering angle deltaR of the rear wheels is calculated by considering the normal control part deltaRO for the rear wheel to generate the canceling moment (S3, S4), and the hydraulic control signals CS1, CS2 to be given to a cylinder for steering the rear wheels to obtain the steering angle deltaR of the rear wheels are outputted until being matched with the real steering angle deltaRR to obtain the canceling moment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering control device capable of controlling a steering angle changing amount of a front wheel and / or a rear wheel of a vehicle by a steering angle changing device provided on the wheel, and more particularly, to a steering angle changing device. The steering input by the steering wheel is suitable for a four-wheel steering (hereinafter also simply referred to as 4WS) vehicle or the like in which the steering angle change amount of the wheel is individually variable.

[0002]

The basic purpose of four-wheel steering is to improve the steering characteristics of a vehicle. Specifically, in today's four-wheel steering vehicles, when the steering wheel is steered to steer the front wheels that are steered wheels at low speeds, the rear wheels are steered in the opposite direction to the front wheels, so-called reverse-phase steering. The stability is improved by so-called in-phase steering in which the rear wheels are steered in the same direction as the front wheels when traveling at high speed. Further, in order to enhance the effect of the four-wheel steering, not only the rear wheels which are non-steering wheels but also the front wheels which are steered wheels are provided with a steering angle changing mechanism by the control means such as the electronic / hydraulic pressure, and the whole vehicle is provided. There is also a proposal to totally improve the steering characteristics of the.

An example of such a four-wheel steering system, especially a steering control system for the rear wheels, is "Improvement of steering stability by phase inversion control of rear wheels" (Preprint, No. 891968, Japan Society of Automotive Engineers, 19 (19)).
89)) This steering control device controls the steering angle of the rear wheel to be controlled based on the vehicle speed and the steering angle of the steering wheel. On the other hand, steering control devices described in Japanese Patent Application Laid-Open Nos. 1-172070 and 1-132472 are also proposed. The steering control devices described in these publications detect or calculate the left and right imbalances of the forces applied to the wheels and acting rearward of the vehicle from the brake hydraulic pressure during braking, and the left and right unbalance of the vehicle rearward input is detected. The steering angle of the rear wheels to be controlled is controlled based on the balance.

[0004]

By the way, when either one of the left and right wheels intrudes into the water film road surface while the vehicle is traveling, or when only one wheel passes over a road surface having a step or a protrusion, the vehicle Tries to turn carelessly and its behavior becomes unstable. This is because the force applied to the wheels in the front-rear direction of the vehicle differs between the left and right wheels, that is, on the left and right sides of the vehicle.
A yaw moment is generated around a vertical axis that passes through the center of the vehicle. Specifically, an input directed toward the rear of the vehicle acts on one wheel that specifically enters the road surface of the water film or passes through the road protrusion, and this rear input causes the vehicle to move around the vertical axis passing through the center of the vehicle. A yaw moment having a magnitude obtained by multiplying the input by the vertical distance from the vehicle center is generated. In such a situation, the driver does not turn carelessly while steering the front wheels, which are steered wheels, so that the driver can delicately steer the steering wheel to obtain the side force that cancels the yaw moment. Have to be controlled.

With respect to such an imbalance of the vehicle front-rear direction input, in the steering control device described in the above-mentioned "Improvement of steering stability by phase inversion control of rear wheels", the vehicle speed and the steering angle by the steering wheel are changed. Since the steering angle of the wheel to be controlled is set and controlled based only on
There is no control effect on the yaw moment resulting from the imbalance of the longitudinal input.

Further, in the steering control device described in the above-mentioned JP-A-1-172070 and JP-A-1-132472, the left and right imbalance of the vehicle rear input is detected or calculated from the brake working hydraulic pressure during braking. It is possible to obtain the control effect on the yaw moment generated by the left-right unbalance of the vehicle rear input during the braking, but there is no control effect when the vehicle is not braking.

The present invention has been developed in view of these problems, and generates a moment in the opposite direction with respect to the yaw moment generated by the imbalance of the forces input to the wheels and acting in the longitudinal direction of the vehicle. By doing so, it is an object of the present invention to provide a vehicle steering control device capable of improving steering stability under the above-mentioned situation.

[0008]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above problems, and as a result, have obtained the following findings and developed the present invention. That is, in order to reduce the yaw moment resulting from the imbalance of the forces acting in the front-rear direction of the vehicle by using the steering angle changing mechanism provided in a four-wheel steering vehicle, a moment around the yaw moment is generated. We focused on the fact that it is possible. At this time, it is important to detect the force that is input to the wheels and acts in the vehicle front-rear direction. For example, a detector such as a load cell is attached to a link or arm that extends in the vehicle front-rear direction and that constitutes a suspension link. From the output value from the detector, the force acting on the link or arm, that is, the force acting in the vehicle front-rear direction can be detected. Then, the yaw moment acting on the vehicle is calculated from the deviation between the left and right wheels of this force, and the steering angle of the wheel to be controlled required to generate a moment that cancels this yaw moment is calculated. It was found that steering stability can be improved by changing and controlling the angle.

The vehicle steering control apparatus of the present invention, as shown in the conceptual diagram of FIG. 1, includes a longitudinal force detecting means for detecting a longitudinal force input to each of the left and right wheels of the vehicle and acting in the longitudinal direction of the vehicle. A steering angle changing means for changing the steering angle of either or both of the front wheels and the rear wheels, and the longitudinal force based on the deviation of the longitudinal force between the left and right wheels of the vehicle detected by the longitudinal force detecting means. And a steering angle control means for controlling the steering angle change amount of the steering angle change means necessary to generate a vehicle moment in the opposite direction to the vehicle yaw moment caused by the deviation.

[0010]

In the vehicle steering control device of the present invention, as shown in the conceptual diagram of FIG. 1, either or both of the front wheels and the rear wheels of the vehicle can be changed by the steering angle changing means. From the output of a load cell or the like attached to a link or an arm extending in the vehicle front-rear direction that constitutes the link, the front-rear force that is input to each of the left and right wheels of the vehicle by the front-rear force detection means and that acts in the vehicle front-rear direction is detected.
By the steering angle control means, the steering angle change amount of the steering angle change means necessary to generate a vehicle moment in the opposite direction to the vehicle yaw moment generated by the deviation of the front and rear forces of the left and right wheels of the vehicle is set by the steering angle control means. It was decided to control based on the deviation of the longitudinal force between the wheels.

[0011]

2 to 5 show one embodiment in which the vehicle steering control device of the present invention is applied to a four-wheel steering vehicle capable of steering the rear wheels. Here, it is assumed that the basic steering characteristic improvement control contents in the four-wheel steering vehicle as described above are well known, and only the control for disturbance, that is, the longitudinal force in the vehicle longitudinal direction input to the wheels will be described in detail.

First, FIG. 2 briefly shows the overall structure of a four-wheel steering vehicle. In the figure, 10FL and 10FR are left and right front wheels, and 10RL and 10RR are left and right rear wheels. Each of the wheels 10FL to 10RR is rotatably supported by at least a hub carrier that is swingably supported in the horizontal direction with respect to the vehicle. Of these, the front wheels 10FL, 10
For FR, tie rod 1 between both hub carriers
It is connected to the rack shaft of the rack and pinion type steering gear device 14 via 2. A pinion (not shown) connected to the steering shaft 16 meshes with the rack shaft, and the front wheel can be mechanically steered by rotating the steering wheel 15.

Further, reference numeral 2 in the figure indicates rear wheel steering mounted on the vehicle.
A rudder device is shown. In this rear wheel steering system 2, the rear wheels 10R
For both L and 10RR, both hub carriers are
The steering shaft 20 for steering the rear wheels is connected via the saddle 18.
It The steering shaft 20 is a double-rod double-acting system for steering the rear wheels.
It functions as the piston rod of the Linda 22,
The inside of the cylinder 22 for steering the rear wheels is a fixed piston integrated with the steering shaft 20.
Divided into left and right cylinder chambers 26L, 26R
Oil supplied to these cylinder chambers 26L, 26R
The steering shaft 20 is stroked according to the amount. In addition, each system
The same elasticity coefficient and the same elasticity are used in the binder chambers 26L and 26R.
A spring 28 with a length is installed inside each
When the hydraulic pressure to the chambers 26L and 26R is released, the piston
24 is moved to the center of the cylinder 22 and centered
Then, the rear wheels 10RL and 10RR are returned to the moderate position.
It Further, each cylinder chamber of the rear wheel steering cylinder 22.
26L and 26R include hydraulic ports sucked from the reservoir 34.
The hydraulic oil of a predetermined pressure from the pump 30 cuts the control valve 32 and
It is supplied through the off valve 36. Specifically, hydraulic pump
30 is connected to the pump port P of the control valve 32,
The return port R of the control valve 32 is connected to the reservoir 34.
On the other hand, one output port S of the cutoff valve 36₁But
It is connected to one cylinder chamber 26L of the cylinder 22,
The other output port S of the cutoff valve 36 ₂Is a cylinder
22 is connected to the other cylinder chamber 26R for further control
The two output ports A and B of the valve 32 are cutoff valves, respectively.
36 two input ports N₁, N₂Individually connected to
There is. The hydraulic pump 30 is mounted on, for example, a vehicle.
Operation in the reservoir 34, driven by rotation by the engine
The oil is discharged and supplied to the control valve 32. In addition, this
Among them, the hydraulic pump 32 and the reservoir 34 are the rack ann
Illustration shown in parallel with Dopinion type steering gear device
It may also be used as a power steering mechanism.

The cutoff valve 36 is a 4-port 2-position electromagnetic directional control valve having a function as a so-called fail-safe valve. In FIG. 2, a return spring 62 is arranged on the right side of the cutoff valve 36, and an electromagnetic solenoid 63 arranged on the left side is excited by a control signal CF from a controller described later. is there. Therefore, in the normal state in which the electromagnetic solenoid 63 is not excited, the position is the right switching position in FIG. 2, and in this state both input ports N of the cutoff valve 36 are
₁ and N _{2, that} is, both output ports A and B of the control valve 32 are in communication with each other, the output oil pressure of the control valve 32 is returned as it is, and both output ports S ₁ and S _{2 of the} cutoff valve 36, that is, Both cylinder chambers 26 of the cylinder 22
When L and 26R are in communication, both cylinder chambers 26L and
Both cylinder chambers 26 by the spring 28 in 26R
The hydraulic pressures in L and 26R are balanced so that the steering shaft 20 is centered, and the rear wheels 10RL and 10RR are in a straight traveling state, that is, in a non-steering state. Therefore, in a state where the control signal CF is not output, fail safe (defective compensation) ) Is done. The spring 28 has an elastic coefficient that does not easily deform due to the cornering force generated on the wheel during normal turning.

On the other hand, when the electromagnetic solenoid 63 of the cutoff valve 36 is excited by the control signal CF from the controller, the cutoff valve 36 resists the elastic force of the return spring 62 and is moved to the left switching position in FIG. Is switched to. In this state, one input port N ₁ of the cutoff valve 36 is in communication with the _one output port S _1, and the other input port N ₂ is in communication with the other output port S ₂ , so that the control valve One output port A of 32 is communicated with the left cylinder chamber 26L of the cylinder 22, and at the same time, the other output port B of the control valve 32 is communicated with the right cylinder chamber 26R of the cylinder 22.

On the other hand, the control valve 32 is composed of a 4-port 3-position, spring center type electromagnetic directional control valve having two input / output ports, as can be understood from the above, and is shown in FIG. electromagnetic solenoid 60a of the left is excited by the control signal CS ₁ from the controller to be described later, the electromagnetic solenoid 60b of the right is excited by the control signal CS ₂ from the controller. Here, in a state where both electromagnetic solenoids 60a and 60b of the control valve 32 are not excited, the elastic forces of the return springs 61a and 61b on both sides of FIG. 2 are balanced and the control valve 32 is at the central switching position.
In this state, the pump port P and the return port R of the control valve 32 are in communication with each other, and the output ports A and B are in cutoff states. Therefore, in this state, the hydraulic pump 3
The discharge hydraulic pressure of 2 is returned to the reservoir 34 as it is, and when the cut-off valve 36 is in the operating state, the internal hydraulic pressures of the left and right cylinder chambers 26L and 26R of the cylinder 22 are respectively contained and the holding mode is set.

From this state, when the electromagnetic solenoid 60a on the left side of FIG. 2 is excited by the control signal CS ₁ of the controller, the control valve 32 is actuated against the elastic force of the return spring 61b on the right side of the figure. It becomes the left switching position in the figure,
In this state, the pump port P of the control valve 32 and one output port A are in communication with each other, and the return port R and the other output port B are in communication with each other. Therefore, in this state, when the cut-off valve 36 is in the operating state, the discharge pressure from the hydraulic pump 30 supplies the operating oil to the left cylinder chamber 26L of the cylinder 22 and the piston 24 of the steering shaft 20.
Is moved to the right in FIG. 2, and as a result, the right cylinder chamber 26R
Since the hydraulic oil inside is returned to the reservoir 34, the rear wheels 10
RL and 10RR are in the left cut mode.

On the other hand, the control signal CS ₂ of the controller
When the electromagnetic solenoid 60b on the right side of FIG. 2 is excited by this, the control valve 32 becomes the right switching position in the figure against the elastic force of the return spring 61a on the left side of the figure, and in this state the control valve 32 The pump port P and the other output port B are in communication with each other, and the return port R and one output port A are in communication with each other. Therefore, in this state, when the cut-off valve 36 is in the operating state, the discharge pressure from the hydraulic pump 30 supplies the operating oil to the right cylinder chamber 26R of the cylinder 22 so that the piston 24 of the steering shaft 20 moves as shown in FIG. Since the hydraulic fluid in the left cylinder chamber 26L is returned to the reservoir 34 as a result of being moved to the left, the rear wheel 10R
L and 10RR are in the right cut mode.

As will be described later in detail with respect to the controller, the steering shaft 16 of the vehicle is provided with a steering angle sensor 8 for detecting the steering angle θ of the steering wheel 15. Depending on the size of the angle θ and for example the steering wheel 1
A steering angle detection signal, which is a voltage signal that is positive when turning 5 to the right and negative when turning to the left, is output to the controller 3. Further, the vehicle is provided with a vehicle speed sensor 6 for detecting a vehicle front-rear direction speed (vehicle speed) V. The vehicle speed sensor 6 detects a positive voltage when the vehicle travels forward and a negative voltage signal when the vehicle travels backward. The vehicle speed detection signal is output to the controller 3.

Further, the steering shaft 2 for the rear wheels 10RL, 10RR
In the vicinity of 0, the rear wheel 10R from the position of the steering shaft 20
A rear wheel steering angle sensor 9 for detecting the actual rear wheel steering angle δ _RR of L, 10RR is provided. The rear wheel steering angle sensor 9 is adapted to detect the actual rear wheel steering angle δ _RR from the middle position of the rear left and right wheels 10RL, 10RR and to adjust the rear wheels 10RL, 10RR.
Outputs to the controller 3 an actual rear wheel steering angle detection signal composed of a voltage signal that is positive when the vehicle is turned to the left and negative when the vehicle is turned to the right.

The front left and right wheels 10FL and 10FR are
Front-rear force detectors 4FL and 4FR for detecting front-rear force input to each wheel and acting in the front-rear direction of the vehicle are provided. The front-rear force detectors 4FL, 4FR constitute the multi-link suspensions 5FL, 5FR of the front left and right wheels 10FL, 10FR as detailed in FIG. 3, and are arranged in the front-rear direction or slightly in the front-rear direction of the vehicle. It is composed of load cells attached to the tension rods 7FL, 7FR, etc., and is input to the front left and right wheels 10FL, 10FR transmitted in the axial direction of the tension rods 7FL, 7FR via tires, road wheels, hub knuckles, etc. ,
A voltage signal that is detected as longitudinal forces F _FL and F _{FR in} the longitudinal direction of the vehicle and that is positive when inputting to the rear of the vehicle and negative when inputting to the front of the vehicle according to the magnitude of these longitudinal forces F _FL and F _FR. And outputs a front-back force detection signal consisting of The output values of the detection signals from the longitudinal force detectors 4FL and 4FR are referred to as f _FL and f _FR , respectively.

The controller 3 has at least an A / D
It is provided with a microcomputer having an input interface circuit having a conversion function, a central processing unit (CPU), a storage device (ROM, RAM), an output interface circuit having a D / A conversion function, and the like. Although the detailed contents of the four-wheel steering control for improving the steering characteristic at the time of normal cornering by the controller 3 will not be described in detail here, the vehicle speed detection value from the vehicle speed sensor 6 and the steering angle obtained from the steering angle sensor 8 are described. Detection value, steering angular velocity detection value,
By steering the front wheels with the steering wheel 15 and rear-wheel steering in the same phase in accordance with the detected steering angular acceleration value, the steering characteristics are controlled to be changed to the weak understeer direction in the low speed range of the vehicle to improve the turning performance. In the high speed range, the steering characteristics are changed and controlled to be strengthened in the understeer direction to improve the stability of the vehicle at the time of turning, changing lanes, etc. and improving the convergence of cornering. Furthermore, when a fast steering input is given mainly in the low speed range, the rear wheels are momentarily reverse-phase steered immediately after the start of steering,
It is also possible to improve the running stability during cornering by improving the yaw rate rise necessary for turning to improve the response to steering, that is, the turning performance, and then performing the in-phase steering of the rear wheels. It is possible. The calculation of the steering angle change amount in the normal rear wheel steering control is performed by the microcomputer in the controller 3.
It is performed according to an individual program not shown,
The rear wheel steering control amount δ _RO is stored in the storage device.

On the other hand, in the four-wheel steering system of this embodiment, the rear wheel steering system 2, the controller 3, the longitudinal force detector 4F.
L, 4FR, etc. are used to improve the unstable vehicle behavior caused by the imbalance of the longitudinal force input to the wheels and acting in the longitudinal direction of the vehicle in addition to the artificial driving force and braking force. The specific calculation and control are performed by the microcomputer in the controller 3. Before that, the principle of control of the longitudinal force imbalance according to this embodiment will be described.

First, as shown in FIG. 7a, one of the left and right wheels of the vehicle, for example, the front left wheel 10FL in the figure, attempts to enter a thick water pool of water film or pass through road surface projections or steps. In this case, it is assumed that the other wheel, that is, the front right wheel 10FR in FIG. 10A is traveling on a smooth paved road surface, and the large front-rear force F _FL due to the rotation of the wheel acts only on the front left wheel 10FL. On the other hand, the longitudinal force F _FR to the front right wheel is almost "0". Here, the center of the vehicle is the front left and right wheels 10F
A vehicle that occurs around a vertical axis passing through the center of the vehicle from the left-right deviation (F _FL −F _FR ) of the front-rear force input to the front left and right wheels 10FL and 10FR, assuming that the vehicle exists at the center of the tread T of the L and 10FR. The yaw moment M is represented by the following equation 1. The vehicle yaw moment M is positive on the left side (counterclockwise) of the vertical axis passing through the center of the vehicle and negative on the right side (clockwise) of the vertical axis.

M = T · (F _FL −F _FR ) / 2 (1) Therefore, the yaw inertia I is calculated by the vehicle yaw moment M.
For vehicles of the same type, the following 2
The yaw angular acceleration α represented by the equation is generated. α = M / I = T · (F _FL −F _FR ) / 2I (2) Due to the yaw angular acceleration α due to the vehicle yaw moment M, the vehicle acts on the angular acceleration α as shown in FIG. 7b. Try to rotate in the direction. Therefore, in a conventional vehicle, the driver delicately steers the steering wheel to apply a side force to the steered wheels, thereby generating a vehicle moment that cancels the yaw moment due to the left-right deviation of the longitudinal force, and Although the stability is as described above, the theoretical left-right deviation of the longitudinal force disappears after passing through the water pool, road protrusion, and step, so steering of the steering wheel reverses the vehicle at that moment. It could also cause you to turn to. This is because the driver steers while feeling the slight variations in the self-aligning torque and lateral acceleration of the steering wheel. When the yaw moment appears in a simple first-order lag system as is known, driving It means that the person must steer the steering wheel so as to be almost synchronized with it.

Conversely, if the lateral deviation of the longitudinal force can be detected or calculated, the vehicle yaw moment M based on the lateral deviation of the longitudinal force can be calculated. Therefore, a vehicle moment (hereinafter referred to as a cancel moment) M that cancels this vehicle yaw moment M
It is possible to generate _R by steering the rear wheels. Here, the cancellation moment M _R is the vehicle yaw moment M
Is equal to, the canceling moment M _R is the side force S _R generated on each of the rear left and right wheels due to the rear wheel steering,
The following three expressions are established for the vehicle front-rear direction distance L _R from the vehicle center to the rear left and right wheels.

M _R = S _R · 2 · L _R = M (3) The side force S _R is expressed by the following four equations with respect to the rear wheel steering angle δ _R and the rear wheel cornering power Cp _R. It As known, the rear wheel cornering power Cp _R is a constant determined by tire characteristics and vehicle characteristics under conditions where wheel load fluctuations and slip angles are small.

S _R = δ _R · Cp _R (4) Therefore, the canceling moment M is obtained by substituting Equation 4 into Equation 3.
_{The following} five equations regarding _R are obtained. M _R = δ _R · Cp _R · 2 · L _R = M (5) By substituting the above equation 1 into these 5 equations, the rear wheel steering angle δ
_{The following} six formulas regarding _R are obtained.

Δ _R = T · (F _FL −F _FR ) / (2 · (2 · Cp _R · L _R )) ... (6) Of which, the front wheel tread T and the rear wheel cornering power C
p _R, since the vehicle longitudinal distance L _R to the rear right and left wheels from the vehicle center is constant, the left and right front wheels 10FL, front-rear force F _FL acting on 10FR, steering angle of the rear wheels if it is possible to obtain F _FR δ _R can be calculated. However, the longitudinal force detectors 4FL and 4FR such as the load cell shown in FIG. 3 are attached to, for example, the tension rods 7FL and 7FR, and are offset from the wheel center and the axial direction of the tension rod is not necessarily the same as that of the vehicle. Due to the fact that they do not coincide with each other in the front-rear direction, the front-rear force detectors 4FL, 4FR cannot directly detect the front-rear forces F _FL , F _FR that act on the wheel center and generate the vehicle yaw moment M. is there. Therefore, in this embodiment,
The correlation between the output value f from the front / rear force detector such as the load cell and the front / rear force F acting on the wheel center was obtained by an actual vehicle experiment, and this was mapped as shown in the characteristic diagram of FIG. Front and rear force detectors 4FL, 4FR
The front and rear forces F _FL and F _FR can be directly obtained from the output values f _FL and f _{FR of} .

Further, in controlling the rear wheel steering angle δ _R , the rear wheel steering angle control amount δ _RO for improving the normal steering characteristics is taken into consideration. Therefore, the actual rear wheel steering angle δ _R follows the following equation 7 in which the control component δ _RO represented by the function of the vehicle speed V and the front wheel steering angle θ is taken into consideration. δ _R = T · (F _FL −F _FR ) / (2 · (2 · Cp _R · L _R )) + δ _RO ………… (7) The normal rear wheel steering angle control component δ _RO is, for example, the primary The steady-state yaw rate gain represented by the delay system is satisfied and is appropriately multiplied by the feedback gain K, which is represented by the following equation (8). Here, τ and t are functions of the vehicle speed V, and the feedback gain K may be a function of the vehicle speed V. θ is the steering angle of the steering wheel. For details of the rear wheel steering angle control amount δ _RO , refer to, for example, Japanese Patent Application Laid-Open No. 2-106469 previously proposed by the present applicant.

Δ _RO / θ = K (1 + τS) / (1 + TS) (8) The arithmetic control processing based on the principle of the rear wheel steering control is performed according to the processing program stored in the microcomputer of the controller. Be seen. This program is executed at every predetermined time ΔT (for example, 10 mse
c. every) is processed by the timer interrupt.

First, in step S1, the load cell etc.
Force output from front and rear force detectors 4FL and 4FR
Value f_FL, F_FRRead in. Next, in step S2,
Front-back force output value f read in step S1 _FL, F_FR
From the characteristic diagram shown in FIG. 4 by using the front left and right wheels 10F
The longitudinal force F acting on the wheel center of L and 10FR_FL, F
_FRTo calculate.

Next, in step S3, the storage device is
For normal steering characteristic improvement control stored in
Latest rear wheel steering control amount δ_RORead in. Next step
And the rear wheel steering angle δ is calculated based on the equation (7)._R
To calculate. Next, in step S5, the rear wheel operation is performed.
Real rear wheel steering angle δ from the steering angle sensor 9 _RRRead in.

Next, in step S6, it is determined whether or not the rear wheel steering angle δ _R matches the actual rear wheel steering angle δ _{RR. If} they match, the process proceeds to step S7. If not, the process proceeds to step S8. In the step S7, it is judged that the rear wheel steering control is unnecessary or the necessary rear wheel steering control is completed, and the output of the control signal CS ₁ or CS ₂ from the controller 3 is stopped to return to the main program. To do.

On the other hand, in step S8, the control signal CS ₁ or CS ₂ for achieving the rear wheel steering angle δ _R obtained in step S4 is formed. Next, in step S9, the control signal CS ₁ or CS ₂ formed in step S4 is output to the control valve 32, and the process returns to the main program.

Next, the operation of the steering control system of this embodiment will be described. Here, the piston 24 of the rear wheel steering cylinder 22 is a spring 28 in both cylinder chambers 26L and 26R.
A description will be given from the state of being centered at the center position by. First, assuming that the vehicle is traveling straight on a flat paved road surface while the cutoff valve 36 is ON, the front left and right wheels 10FL and 10FR are almost always driven by the rotation of the tire at the vehicle speed. since extremely small longitudinal force F _FL evenly, F _FR (≒ 0) is acting, two front left and right wheels 10FL, front-rear force detector 4FL such as a load cell provided in 10FR, each longitudinal force from 4FR F _FL , F _FR , output values f _FL , f _FR are output. Therefore, the longitudinal force detector 4 such as the load cell read in step S1 is read.
Based on the output values f _FL , f _FR from the _FL , 4 _FR , in the step S2, both front-back forces F _FL ,
Calculating a F _FR but both longitudinal force F _FL, left and right deviations of F _FR (F
_FL- F _FR ) becomes almost zero, and the steering angle of the steering wheel 15 is zero or almost zero. Therefore, the rear wheel steering angle control amount δ _RO, which is performed by improving the normal steering characteristics, is also zero or almost zero. When the rear wheel steering angle δ _R calculated by the equation 7 performed in step S4 is zero or almost zero, and the rear wheel steering angle δ _R matches the actual rear wheel steering angle δ _RR in step S6. is without a control signal CS ₁ or CS ₂ is output by the step S7, and a control signal CS ₁ or CS ₂ is also approximately zero is outputted are formed in the step S8, S9 even if not, the control valve 32 is It is held in the central switching position, whereby the hydraulic oil due to the discharge pressure from the hydraulic pump 30 is returned to the reservoir 34 as it is, and the piston 24 of the rear wheel steering cylinder 22 is set to the middle position. Is centered state is maintained normal constant-speed straight running state is maintained in position.

From this state, as shown in FIG.
If only the left wheel 10FL enters a water pool with a thick water film
Or if you try to pass a bump or step on the road surface,
The impact of the wheels colliding with those obstacles and the rotation of the tires
The front left wheel 10FL is
Front-rear force F toward the rear of the vehicle_FLActs, which causes
Front / rear force detector such as a load cell provided on the left wheel 10FL
4FL is this front-back force F_FLOutput value f according to the size of_FLTo
Output. On the other hand, the longitudinal force F acting on the front right wheel 10FR_FR
Since it is still extremely small, it is installed on the front right wheel 10FR.
The front / rear force detector 4FR for the loaded load cell is
_FROutput value f according to the size of_FRIs output. Where the above
Both front and rear force detectors 4FL and 4F read in step S1
Output value f of R_FL, F_FRBased on
Front / rear force F between the left and right front wheels 10FL, 10FR_FL，
F_FRA corresponding deviation occurs in. Therefore, steering
This longitudinal force is applied to the vehicle without steering the wheel 15.
Deviation of (F_FL-F_FR) According to the formula 1
Ment M and yaw angular acceleration α according to equation 2
To do. However, in step S4, the normal rear wheel operation is performed.
Rudder control component δ_RRWhen the yaw moment M is
Canceling moment M_RPositive value for generating
Rear wheel steering angle δ_RIs calculated, and this positive value of the rear wheel steering angle δ
_RIn order to achieve the above, the rear left and right wheels 10RL, 1
Control signal CS for left-turning 0RR ₁Is the step
The control formed in step S8 and output in step S9
Signal CS ₁The control valve 32 is switched to the left switching position.
The hydraulic oil that accompanies the discharge pressure of the hydraulic pump 30 is steered to the rear wheels.
Since it is supplied to the left cylinder chamber 26L of the working cylinder 22,
The piston 24 is moved to the right in FIG.
The shaft 20 is moved to the right and the rear left and right wheels 10RL, 10RR
Is cut left around the kingpin axis (not shown). this
The rear wheel steering is the actual rear wheel steering angle read in step S5.
δ_RRAnd rear wheel steering angle δ _RUntil and match in step S6
Continuing, it is determined in step S6 that they match.
If it is determined that the control signal CS₁
Since the output of the control valve 32 is stopped, the control valve 32 switches the central switching.
Position of the rear wheel steering cylinder 22
The hydraulic pressure in the rear chambers 26L and 26R is sealed in the state immediately before
The rear wheel steering angle δ_R(Or after the fact
Wheel steering angle δ_RR) Is maintained. This makes the driver special
Without steering the steering wheel 15
The traveling condition is maintained.

At this time, when the driver turns the steering wheel 15 to the right before or immediately after the driver enters the water pool or passes through the projection or the step, the normal rear wheel steering angle control component δ _RO described above. Occurs, but the step S
The rear wheel steering angle control amount δ _RO read in step 3 becomes a negative value in the in-phase steering and acts in a direction of canceling the vehicle yaw moment M, and further, in the step S4.
Since the rear wheel steering angle δ _R calculated by the equation 7 calculated by the equation becomes a value smaller by the rear wheel steering angle control amount δ _RO , the rear wheel steering angle δ _R can be achieved by the series of processing programs. For example, since the magnitude of the canceling moment M _R generated in the entire vehicle coincides with the vehicle yaw moment M and cancels it, the straight traveling state of the vehicle is maintained as in the case where the steering wheel 15 is not steered. The normal rear wheel steering angle control amount δ _RO becomes a positive value in the reverse phase steering at low speed, and is calculated in step S4 7
The rear wheel steering angle δ _R becomes larger by that amount, but the front-rear force F _FL acting on the front left wheel 10FL is small when entering a water pool or passing through a projection or a step when traveling at low speed, Further, in such a case, since the steering angle of the steering wheel 15 given by the driver is very small, the normal rear wheel steering angle control amount δ _RO is also very small and instantaneous, so the whole The vehicle canceling moment M _R itself is small, and the behavior of the vehicle cannot be made unstable.

Moreover, even when the thickness of the water film in the water pool changes and the longitudinal force F _FL acting on the front left wheel 10FL changes, the rear wheel set by the feedback control performed in steps S1 to S9. Since the steering angle δ _R follows the change in the longitudinal force F _FL , the straight traveling state of the vehicle is maintained even in such a case. When the water passes through the water pool, the protrusion, or the step in this way, the longitudinal forces F _FL and F _FR acting on the front left and right wheels 10FL and 10FR again return to an extremely small and almost equal state. In order to return the wheels 10RL and 10RR to the moderate state, that is, the straight traveling state, the rear wheel steering angle δ _R is set to substantially zero in steps S1 to S4, and the rear left and right wheels are set until the rear wheel steering angle δ _R is reached. In order to turn 10RL and 10RR to the right, the control signal CS ₂ is formed and output in steps S8 to S9, and when the actual steering angle δ _RR becomes almost zero, which is the rear wheel steering angle δ _R , steps S6 to S7. The output of the control signal CS ₂ is stopped by the rear left / right wheels 10RL, 10R.
R is returned to the normal state, that is, the straight traveling state.

In the above, when the front right wheel 10FR passes through a pool of water, a protrusion, or a step, the wheels to be controlled are reversed left and right, and the vehicle yaw moment M, the canceling moment M _R , and the rear wheel steering angle δ _R. , Real rear wheel steering angle δ
The sign of _RR , is reversed, and the control signal CS ₁ is the control signal C.
The control signal CS ₂ is changed to the control signal CS ₁ at S ₂ , and the actual control condition of the vehicle is substantially the same as the above.

Further, during the turning of the vehicle or during the transition to the turning, the normal rear-wheel steering control amount δ _RO is only added as in the case where the driver steers the steering wheel 15. The control for canceling the vehicle yaw moment due to the unbalance of the longitudinal force is almost the same as the above. Also, the cornering force generated during turning is
Except when the turning radius is logically very small, the difference between the inside and outside wheels of the turn, that is, the left and right wheels, is small, so the left-right deviation of the longitudinal force to the vehicle, which is the component, is also small. The impact is small.

In the straight running, when the front wheels are the driving wheels and acceleration / deceleration is performed by the accelerator pedal operation or braking is performed by the brake pedal operation, the brake is applied between the left and right wheels. As long as the characteristics and the tire characteristics are not significantly different, the same front-rear force acts on the front left and right wheels, so that no vehicle yaw moment is generated and no rear wheel steering control is executed.

In other words, when there is a large difference in the braking characteristics and tire characteristics between the left and right wheels, there is a deviation in the longitudinal force between the front and left wheels, or there is a difference in the road surface friction coefficient between the left and right wheels. Even when a front-rear force deviation occurs between the left and right front wheels in split μ roads, on rough terrain traveling with wheel bouncing and vehicle rolling motion, the rear-wheel steering control allows The vehicle's behavior can be stabilized by effectively generating a canceling moment that cancels the vehicle yaw moment due to left-right deviation.

In this embodiment, the load cell is attached to the tension rod which constitutes the suspension as the front-back force detector, but a strain gauge is used instead of this, or a change in the rotational force of the load wheel is detected. It is possible to take appropriate measures such as Also,
In the present embodiment, the control target is the method of detecting the front-rear force with the front left and right wheels and controlling the steering angle of the rear wheel. However, for example, the front-rear force is detected with the front left and right wheels and the steering angle of the front wheel is controlled. The combination of front-rear force detection and steering control target wheels is required for the vehicle, such that front-rear force is detected by each of the front-rear and left-right wheels, and the steering angle of the front-rear wheels is controlled by an appropriately set distribution ratio. It should be properly selected according to the characteristics.

Further, in the present embodiment, a detector which is simply a vehicle speed sensor is used to detect the longitudinal speed of the vehicle.
If it is difficult to detect the vehicle speed with a high resolution, the pseudo vehicle speed is calculated and set from the wheel speed obtained with the existing wheel speed sensor, or the vehicle acceleration obtained from the acceleration sensor is integrated over time and used. It is also possible. Of course, it is also possible to combine auxiliary functions and configurations for performing normal four-wheel steering, which is performed to improve the steering characteristics during turning, or it is possible not to combine these at all.

[0046]

As described above, according to the vehicle steering control apparatus of the present invention, it is necessary to generate the vehicle moment around the opposite side to the vehicle yaw moment caused by the deviation of the longitudinal forces of the left and right wheels of the vehicle. Since the steering angle changing amount of the steering angle changing means is controlled by the steering angle control means based on the deviation of the longitudinal force between the left and right wheels, the vehicle yaw moment is reduced or offset, and the driver The behavior of the vehicle does not become unstable even if the steering wheel is not delicately steered.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a vehicle steering control device of the invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of a four-wheel steering vehicle equipped with the vehicle steering control device of the invention.

3 is an explanatory diagram of a detector for detecting a longitudinal force in the vehicle front-rear direction which is input to the front left and right wheels in the four-wheel steering vehicle of FIG.

FIG. 4 is a characteristic diagram of an output value from the longitudinal force detector of FIG. 3 and longitudinal force.

5 is a flowchart of a rear wheel steering control for stabilizing the vehicle behavior due to an unbalance of longitudinal forces, which is performed by the vehicle steering control device of FIG.

FIG. 6 is an explanatory diagram of a vehicle behavior control effect by the rear wheel steering control of FIG. 5.

FIG. 7 is an explanatory diagram of a vehicle behavior when the rear wheel steering control of FIG. 5 is not performed.

[Explanation of symbols]

 2 is a rear wheel steering device 3 is a controller 4FL, 4FR is a front / rear force detector 5FL, 5FR is a front multi-link suspension 6 is a vehicle speed sensor 7FL, 7FR is a tension rod 8 is a steering angle sensor 9 is a rear wheel steering angle sensor 10FL to 10RR Is a wheel 12 is a tie rod 14 is a steering gear device 15 is a steering wheel 16 is a steering shaft 18 is a tie rod 20 is a steering shaft 22 is a rear wheel steering cylinder 24 is a piston 26L, 26R is a cylinder chamber 28 is a spring 30 is a hydraulic pump 32 Control valve 34 is reservoir 36 is cut-off valve

Claims (1)

[Claims] 1. A front / rear force detecting means for detecting a front / rear force applied to each of left and right wheels of a vehicle and acting in a vehicle front-rear direction, and a steering angle change for changing a steering angle of one or both of a front wheel and a rear wheel. And the vehicle yaw moment generated by the deviation of the longitudinal force based on the deviation of the longitudinal force between the left and right wheels of the vehicle detected by the longitudinal force detecting means. A steering control device for a vehicle, comprising: a steering angle control means for controlling a steering angle change amount of the steering angle change means.