JPH0277360A - Rear-wheel steering control device for vehicle - Google Patents

Abstract

PURPOSE:To improve stability and responsiveness of a vehicle by steering the rear wheels according to the optimum feedback gain calculated by a basic gain determined depending on the stability and responsiveness of a vehicle from the relation between slip angles of front and rear wheels and a steering angle and a vehicle state decision value showing the state of the vehicle and a driver's will. CONSTITUTION:A steering speed signal and a car velocity signal are input to vehicle state decision means II11 to decide the state of the vehicle and the present state of a driver's steering will from the above signals and output a vehicle state decision value. On the other hand, basic gain generating means II12 decides the basic gain depending on the stability and responsiveness of the vehicle. Optimum gain calculating means II13 calculates the feedback gain most suitable for the present vehicle state according to the basic gain and the vehicle state decision value to be output as the optimum gain. Steering amount calculating means 11 calculates the rear wheel steering amount by multiplying the behavior variation of a vehicle from a behavior sensor I3 by the optimum gain to be output as a control signal. Rear wheel steering actuator means III controls the rear wheels to be steered according to the control signal.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a rear wheel steering device for a vehicle. More specifically, the present invention relates to a rear wheel steering device for a vehicle. The present invention relates to a rear wheel steering device for a vehicle that achieves both stability and responsiveness of the vehicle through control.

<Prior art> In general, the dynamic performance and steering stability of a vehicle are determined by the vehicle's yaw rate (rotational angular velocity occurring at the center of gravity when viewed from above) or lateral acceleration (vehicle progress at the vehicle's center of gravity) in response to the driver's steering input. The relationship between direction (acceleration in a direction perpendicular to direction) is an important factor.

In addition, the vehicle is not affected by external disturbances such as crosswinds or road friction coefficients, and is able to move quickly in response to steering inputs, and maintains stability such that when driving straight, its course follows the driver's will. The ideal is.

By the way, Japanese Unexamined Patent Application Publication No. 1987-1987 describes a device for controlling the sideslip angle of a vehicle using a state observation device, with the aim of giving the vehicle stability and responsiveness as described above. ing. As shown in Figure 2, this device detects the front and rear wheel steering signals, vehicle speed signals, vehicle weight signals, and vehicle yaw rate or lateral acceleration signals, and inputs these detection signals to the condition observation device. The vehicle sideslip angle β is estimated based on a vehicle model between the front and rear wheel steering angles stored in advance and the vehicle yaw rate or lateral acceleration, and the vehicle sideslip angle β estimated by this condition observation device is used as the predetermined target vehicle sideslip angle. β. A control signal is generated to steer wheels other than the steered wheels so that the deviation becomes zero.

However, since the purpose of this conventional technology is to control the sideslip angle of the vehicle, the tire slip angle (sideslip angle), which is the basis of vehicle motion, is not directly controlled. It is not possible to control vehicle motion to the maximum extent possible.

Here, the tire slip angle and the sideslip angle of the vehicle will be explained using FIG. 3. The sideslip angle of a vehicle is the angle formed by the longitudinal direction of the vehicle and the direction of travel of the vehicle, and has conventionally been used as a value for evaluating vehicle motion. The tire slip angle is the angle between the direction in which the tire is cut and the direction in which the vehicle is traveling at that tire position, and has different values for each of the four tires. In particular, for the front and rear wheels, the product of the vehicle's yaw rate and the distance from the center of gravity of the front and rear wheels in the longitudinal direction of the vehicle is added to the vehicle's sideslip angle, and since the steering angles of the front and rear wheels are different, Conventionally, the evaluation quantity has been the sideslip angle of the vehicle, which is measured using a special measuring device (such as a lateral speedometer) mounted on the vehicle.

Further, in the above control method, even if the driver operates the steering wheel quickly in order to make the vehicle turn quickly, the driver's intention is not reflected in the movement of the vehicle.

That is, even if the driver steers the vehicle sufficiently to cause the vehicle to move, the sideslip angle and yaw rate of the vehicle occur with a delay, so there is a tendency to over-steering.

Furthermore, since the state observation device includes an integrator, control may not be achieved due to accumulation of errors due to integral deviation. In order to perform this calculation, a digital computer with very high computing power is required, which makes the system large-scale and difficult to install in a vehicle.

The above problem arises from controlling the sideslip angle of the vehicle. Therefore, the inventor of the present invention secured higher vehicle stability and responsiveness by using the steering wheel steering speed as a criterion for changing the gain and by making the control objective the optimum control of the tire slip angle itself. We focused on what we could do and devised the present invention.

<Object of the Invention> The present invention provides optimal auxiliary steering by providing a steering system with control that has a high ability to modify vehicle behavior in response to crosswinds, disturbances, etc., and improves the responsiveness of changes in vehicle behavior to steering input. The purpose is to make it possible.

<Summary of the Invention> As shown in FIG. 1, a rear wheel steering control device for a vehicle according to the present invention is a rear wheel steering control device for controlling a rear wheel steering amount of a vehicle, and includes a steering speed control device that detects at least a steering speed of a steering wheel. a sensor means ■ comprising a sensor ■, a vehicle speed sensor I2 that detects the vehicle speed, and a behavior sensor ■3 that detects the amount of behavior of the vehicle; a rear wheel steering actuator means ■ that steers the rear wheels; and at least the detection a vehicle state determining means (2) that determines the current state of the vehicle state and the driver's steering intention based on the signal corresponding to the steering speed and the signal corresponding to the vehicle speed, and outputs a vehicle state determination value; A term consisting of the front wheel slip angle and the front wheel steering angle, a term consisting of the rear wheel slip angle and the rear wheel steering angle, a term consisting of the rear wheel steering angle, and a weighting coefficient applied to the above three terms. a basic gain generating means lt that calculates a state feedback gain corresponding to a weighting coefficient of the evaluation function based on the evaluation function; control gain calculating means (1) comprising: optimum gain calculating means (2) for calculating the optimum gain by distributing the optimum gain accordingly; and a steering control means (2) comprising a steering amount calculation means (2) which is used as a control signal for the rear wheel steering actuator means.

The operation and effects of the present invention having such structural features will be explained.

Steering speed sensor 1. In the step, the steering speed at the steering wheel is converted into a signal corresponding to the steering speed.

Further, the vehicle speed sensor (2) converts the vehicle speed into a signal corresponding to the vehicle speed. Similarly, behavior sensor I.

In the step, the amount of change in behavior of the vehicle is converted into a signal corresponding to the amount of change. In the steering control means (2) which inputs the signals output from the steering speed sensor (1), the vehicle speed sensor (2), and the behavior sensor (13), first, the steering Means for determining vehicle status using speed signals, vehicle speed signals, etc.■
, and determines the state of the vehicle and the current state of the driver's steering intention based on the signal, and outputs a vehicle state determination value.

On the other hand, the basic gain generation means (■) has three terms consisting of the vehicle's front wheel slip angle, front wheel actual steering angle, rear wheel slip angle, rear wheel actual steering angle, and rear wheel steering angle, and these three terms. The basic gain calculated based on the evaluation function consisting of the weighting coefficient and the weighting coefficient applied to the basic gain is output. This basic gain is determined in accordance with the stability and responsiveness of the vehicle from the previously known relationship between the tire slip angles of the front and rear wheels of the vehicle and the steering angles of the front and rear wheels.

Then, the optimum gain calculation means 11+s calculates the basic gain from the basic gain generation means I[It and the vehicle state judgment value from the vehicle state judgment means U11, that is, the required degree of stability and responsiveness of the vehicle. , calculates the feedback gain most suitable for the current vehicle condition, and outputs it as the optimal gain.

The steering amount calculating means 2 calculates the rear wheel steering amount by multiplying and adding the amount of change in vehicle behavior from the behavior sensor I by the optimum gain from the optimum gain calculating means 1113, and outputs the result as a control signal. The rear wheel steering actuator means (2) controls the steering of the rear wheels based on the control signal.

The present invention is based on a basic gain determined according to the stability and responsiveness of the vehicle based on the relationship between the slip angle of the front and rear wheels and the steering angle, and a vehicle state judgment value that represents the vehicle state and the driver's steering intention. Steering the rear wheels based on the optimal feedback gain. In other words, the optimum rear wheel steering control angle is determined by detecting the amount of vehicle behavior instantaneously, and by providing the optimum gain depending on the required degree of vehicle stability and responsiveness, an instantaneous state feedback control system for the vehicle state is constructed. Therefore, by switching the state feedback coefficient to the optimal value for the vehicle that the driver is steering depending on the steering speed and vehicle speed, it is possible to perform optimal front and rear wheel slip angle control for the driver's steering. In turn, it becomes possible to improve the stability and responsiveness of the vehicle.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 4 shows a schematic diagram of an embodiment of the present invention.

The sensor means detects the steering angle δ of the steering wheel S by the driver.
A steering speed sensor 1 detects the angular velocity 8' and outputs the angular velocity 8'.
．． , a vehicle speed sensor that is attached to the output shaft of the vehicle's transmission and detects and outputs the vehicle speed u0; and a yaw rate sensor 13+ that detects the rotational angular velocity around the center of gravity of the vehicle.
and a lateral acceleration sensor I3□ which measures the acceleration y in the left-right translational direction of the vehicle.The output signals from each of the sensors are input to the steering control means H, which will be described later. In this embodiment, a sensor that directly detects the steering speed of the steering wheel is used, but the steering wheel angular speed 3 can also be obtained by differentiating the input steering wheel angle δ in a microcomputer 200, which will be described later.

The steering control means (2) consists of a control gain calculation means (2) and a steering amount calculation means (2).

The control gain calculation means (1) calculates a signal corresponding to the steering angular velocity outputted from the steering speed sensor 11 and a vehicle speed U outputted from the vehicle speed sensor I2.

an input section 201 that takes in a signal corresponding to , an arithmetic processing section 202 that determines the state of the vehicle and calculates an optimal gain based on the steering angular velocity signal and vehicle speed signal obtained by the input section 201; The arithmetic processing unit 202
a storage unit 203 that stores the calculation method; and an output unit 20 that outputs the optimal gain selected by the calculation processing unit 202.
4, and is configured by a microcomputer 200.

The functions performed by the microcomputer 200 will be explained in detail based on FIG.

Initialize with Pl when the ignition key is turned on. In this initialization routine, the states of various sensors are detected, abnormalities are checked, and initial values are set. When the initialization routine Pi ends, a signal corresponding to the steering angular velocity 8 is read from the steering speed sensor 11 (P2). This value of the read steering angular velocity and a preset value when the steering angular velocity is small (for example, l 6 l < L = 15 de
g/sec) When W1=0 and the steering angular velocity is large (1 sen〉δt = 50 deg/see) W,
= 1, and the coefficient W1 is calculated from an increasing function that continuously connects them (P3).

Next, a signal corresponding to the vehicle speed u0 is read from the vehicle speed sensor 2 (P4). Then, the value of this vehicle speed and a preset value when the vehicle speed is small (for example, uO<u, = 40k
m/H) Wz = 1, and when the vehicle speed is large (u
o > u z = 120 km/H) W2=
0, and a decreasing function that continuously connects them,
A coefficient W2 is calculated (P5).

After that, a coefficient M for determining the current state of the vehicle and the steering state of the driver is calculated (P6). This coefficient M is M=
It is determined by the formula W, ・W2.

Then, according to the obtained coefficient M, the optimum gains G1 and G2 that match the current vehicle condition and the driver's steering intention are determined.
, G1, and G4 are calculated using the following formula (Pl).

G+= (I M) XGto+MXCt, where cto and c++ each have a coefficient M of M=O1M
The optimum gain is shown when =1, and i represents 1 to 4, respectively.

This state feedback gain Ct. , G is the optimal control gain determined based on the optimal regulator theory,
It is determined by the following principle.

Vehicle with weight m, yaw moment of inertia) Iz (4-wheel steering vehicle)
The equation of motion with two degrees of freedom in one direction and the horizontal direction is expressed as follows.

m−v=2 (Fr+F,,) (1
) I z−r=2 (ar−Ft−41,+Fr)
(2) F, = −Cr・βf
(3) F, = -c, ar (4)
uOny=v-cos(ψ) +uolsin(ψ)#v+u
0・ψ (7)ψ=r
(8) However, the above symbols are as follows.

af: Distance a between the front axle and the center of gravity of the vehicle, , : Distance between the rear axle and the center of gravity of the vehicle c, : Cornering power of the front wheels of the vehicle cF: Cornering power of the rear wheels of the vehicle Fri vehicle ff Cornering force of one wheel F., Cornering force y of the rear wheels of the two vehicles: Lateral displacement of the vehicle ■ = Lateral speed ψ of the vehicle: Yaw angle r of the vehicle: Yaw rate β of the vehicle: Slip angle βr of the front wheels = Slip angle δ of the rear wheels, :Front wheel steering angle of the vehicle δ7 Rear wheel steering angle command value of the two vehicles uo zVehicle speed Tr Actual rear wheel steering angle of the two vehicles Also, considering the delay of the actual steering angle with respect to the rear wheel steering angle command, it is expressed by the following formula. It will be done.

6, (S) = Gd(S)・δ, (S) However, S represents a Laplace operator.

Here, Gd(S) is an expression indicating the delay of the actual rear wheel steering system, and is a Laplace calculation that describes delays such as a -order delay system, a second order delay system, and dead time.

Considering all these conditions and focusing only on the lateral and yaw motions of the vehicle, the above equation can be written in the form of the following state equation.

x=A−x+b, −δ, +b, ·δ.

However, x = (y, 糺ψ, small, Tr)Now, when considering the motion of the vehicle, when the vehicle speed is high, it is generally possible to improve the stability of the vehicle by giving priority to the lateral motion over the yaw motion. Furthermore, when the vehicle speed is slow, the responsiveness of the vehicle can be improved by generating yaw motion with priority over lateral motion.

By the way, in order to generate lateral motion of the vehicle with priority over motion in the yaw direction, the slip angle of the vehicle must be greater than the yaw rate, but if the lateral motion is too rapid relative to the steering angle, If the slip angle of the tires is increased to provide speed, that is, to provide a vehicle sideslip angle, the vehicle will lack stability. Furthermore, in order to increase the responsiveness of the vehicle to the driver's steering, it is better to generate the tire slip angle in proportion to the steering wheel angle.

Therefore, in this embodiment, the above-mentioned disadvantage is eliminated by controlling the tire slip angle to increase in proportion to the steering wheel angle of the vehicle, and the tire slip angle of the front wheels and the tire slip of the rear wheels are adjusted according to the vehicle speed. The stability and responsiveness of the vehicle are improved by changing the angle ratio.

That is, assuming that the purpose of control is to control the slip angles of the front and rear wheels of the vehicle, the evaluation function J for controlling the rear wheels is described as follows.

J=J"'(f" (af kl'6f)"10g
・(β,-kt-L)"+h・δ,")cttHere,
This corresponds to the first term of the above-mentioned evaluation function J (af kl・δ
, ) is an evaluation term for giving the front wheel slip angle in proportion to the front wheel steering angle, and controls the front wheel slip angle so that it becomes βt/δf−””k1. Similarly, the second term (β, - to □・δ, ,) is an evaluation term for giving the rear wheel slip angle in proportion to the actual steering angle of the rear wheels, and β, /6. = to,
The slip angle of the rear wheels is controlled so that

By using this evaluation function, the rear wheels of the vehicle are controlled at an optimal steering angle according to the state of the vehicle, taking into account the delay of the rear wheel steering mechanism.

To determine the rear wheel steering gain from this evaluation function, the gain can be determined by assuming the front wheel steering angle to be a step input and applying the optimal regulator theory.

A method to solve this problem is, for example, Proceedings of the Society of Instrument and Control Engineers, ``Design of model-following servo controllers for linear multivariable systems, J'' (vol. 1B-1, f18-14.1982).
).

By the way, when controlling a vehicle using the above control theory,
The control effect changes depending on the weights r, g, and h of the evaluation function J. That is, when the weights f and g are increased, the slip angles of the front and rear wheels are controlled to be as small as possible, which is effective in stabilizing the vehicle against external disturbances. On the other hand, when the weight h is increased, the amount of energy (steering amount) for steering the rear wheels is controlled to be smaller, and thereby the energy constraints of the control amount in an actual vehicle can be replaced by the equation.

By the way, from the above-mentioned equations (5,) and (6), the slip angles of the front and rear wheels change depending on the vehicle speed. From the above equation and Figure 3, if the same amount of steering angle is given regardless of the vehicle speed, and if the turning radius of the vehicle is constant, the centrifugal force applied to the vehicle will increase as the vehicle speed increases, and the above equation ( Due to the relationships 5) and (6), the slip angle of the tire increases. On the other hand, when the vehicle speed is low, the centrifugal force applied to the vehicle is small, and the amount of tire slip angle is small. In actual vehicle motion, the magnitude of centrifugal force changes depending on the vehicle speed due to the oversteer and understeer characteristics of the vehicle, and because the generation of lateral force with respect to the tire slip angle deviates from the linear range. , it may be impossible to turn on concentric circles, but the tendency of movement is according to the above linear form (1
) to (8) can be roughly described.

Taking these things into account, we created a system that gives priority to yaw motion over lateral motion when the vehicle speed is slow, and gives priority to lateral motion over yaw motion when the vehicle speed is high. To achieve the above objective, the weight f is increased and the weight g is decreased when the vehicle speed is slow or the steering speed is high, and the weights r and g are increased when the vehicle speed is high or the steering speed is slow. You can take action by doing so.

Furthermore, since the driver often wants to move the vehicle quickly when the steering speed is high, the evaluation function is set to increase the weight to satisfy this desire.

That is, the gain G1° given by program P6,
ci+ corresponds to the gain when the vehicle speed is very high and the steering speed is slow, and the gain when the vehicle speed is low and the steering speed is very fast, and these gains change the weights f and g of the above evaluation function, respectively. When increased, or the weight f
This corresponds to when g is made large and g is made small.

Next, gain G1 (i=1
~4) is output to the coefficient setter 210.211.212.213 (P8).

After executing this program P8, the execution flow returns to program P2 and repeats this.

The storage unit 203 stores the above-mentioned information (D6+% 6t, u+,
In addition to uz, the optimal gain value G when the coefficient M is 0,
. ,G2゜,G,. , G4°, optimal gain values Gll, Ct+, Gel, 041 when the coefficient M is 1, and programs P1 to P8 are stored.

Steering amount calculation means ■2 is 4 coefficient setters 210.211
．． 212, 213, and two first-order lag filters 214.
215, an integrating circuit 216, and three adders 217.2.
It consists of 18.219.

The -order lag filter 214 outputs a signal representing a pseudo yaw angle ψ corresponding to the yaw angle ψ from the signal representing the yaw rate. Further, the -order lag filter 215 outputs a signal corresponding to the lateral acceleration y, and the integrating circuit 216 integrates the signal representing the simulated lateral velocity y to output the simulated lateral displacement y. The functions and effects of these -order lag filters 214 and 215 will be described below.

As shown in FIG. 6(a), generally, in order to obtain the yaw angle ψ from the yaw rate ↓ or the lateral velocity 9 from the lateral acceleration y, the signal passes through an integrating circuit 101. However, a steady deviation may occur in the yaw angle ψ and the lateral velocity 9 due to the influence of some noise generated in the yaw rate sensor Iz+ and the lateral acceleration sensor 3□. Therefore, by providing a bypass filter 102 having an effect as shown in FIG. 6(b) after the integrating circuit 101, it is possible to eliminate the steady-state deviation. By the way, Figure 6 (b
) can be equivalently replaced by a first-order lag filter 103 and a coefficient setter 104 as shown in FIG. 6(C).

Therefore, in this embodiment, the integration circuit 101 and the bypass filter 102 are replaced with a first-order lag filter 103 and a coefficient setter 104 to provide the above-mentioned effect.

The coefficient setter 210 sets the yaw rate feedback gain G1, the coefficient setter 211 sets the yaw angle feedback gain G2, the coefficient setter 212 sets the lateral velocity feedback gain G, and the coefficient setter 213 sets the lateral displacement feedback gain G4. Power. The adder 217 adds the outputs of the coefficient setters 210 and 218, the outputs of the coefficient setters 212 and 213, and the outputs of the adders 217 and 218, and outputs the result as a control signal δ corresponding to the angle.

The rear wheel actuator means (2) converts the signal output from the steering control means (2) into a rear wheel steering angle, and is comprised of a drive means (2), a hydraulic assist mechanism (2), and a rear wheel steering mechanism (2).

Driving means 1 includes an amplifier 310 and a stepping motor 3
It consists of 11.

The amplifier 310 inputs a steering control signal output from the steering control means (2), that is, a signal corresponding to the rear wheel turning angle, converts it into an actuator drive signal, and outputs it to the stepping motor 311. Based on this, as will be described later, the servo valve 324 is driven and controlled, and the rod 334 is driven left and right via a gear box 335.

Hydraulic assist mechanism 2 is driven by a hydraulic pump 321, a relief valve 322 for keeping the hydraulic pressure at a constant pressure, an accumulator 323 for suppressing fluctuations in the hydraulic pressure caused by the hydraulic pump 321, and a stepping motor 311 to maintain the hydraulic pressure. A servo valve 324 that determines the direction of oil supply to the piston 336, an oil supply path 325 for supplying hydraulic pressure to the hydraulic piston 336, and a collection of oil discharged from the hydraulic piston 336 and leaked oil from the relief valve 322. The hydraulic assist mechanism consists of an oil recovery path 326 and an oil tank 327 that stores oil used in this hydraulic assist mechanism.

Rear wheel steering mechanism■, rear wheel 331, knuckle 332,
Knuckle arm 333, rod 334, gear box 3
35, and a hydraulic piston 336.

The rear wheel 331 is rotatably supported by the vehicle body by a knuckle 332, and a knuckle arm 333 is connected by a rod 334 and a hydraulic piston 336.

Further, the stepping motor 311 is controlled by a signal corresponding to the rear wheel steering angle from the amplifier 310, and drives the servo valve 324 and drives the rod 334 left and right via the gear box 335. These mechanisms cause the stepping motor 311 to move the rod 334 left and right in response to the signal from the amplifier 310, and also to move the rod 334 left and right in response to the signal from the amplifier 310.
25 is supplied to the chamber of the hydraulic piston 336 by moving the servo valve 324, and the other chamber is communicated with the oil tank 327 through the oil recovery passage 326.
By driving the hydraulic piston 336 and assisting the force applied to the stepping motor 311, it becomes possible to steer the rear wheel 331 left and right.

The front wheel steering mechanism (2) consists of a front wheel 41, a steering linkage 42, a rod 43, a rack 44, and a pinion 45.
These steering linkages 42 are connected by a rod 43 and a rack 44. With these mechanisms, the front wheel 41 is connected to the handle S.
By steering the wheel, the pinion 45 rotates, and the rack 44 converts the rotation of the pinion 45 into linear motion to move the rod 43 left and right, and the front wheels 41 are steered left and right via the steering linkage 42.

The functions and effects of the present invention having the above configuration are as follows.

The steering speed sensor I detects the steering speed of the steering wheel S,
The yaw rate sensor L+, which belongs to the behavior sensor ■3, includes the vehicle's yaw rate, and the lateral acceleration sensor ■3! detects the acceleration y in the left and right translational directions of the vehicle.

A signal corresponding to the steering angular velocity δ and a signal corresponding to the vehicle speed u0 are input to the input section 201 of the control gain calculating means (1).

On the other hand, in the steering amount calculating means (2), a signal corresponding to the yaw rate ↓, a signal representing the pseudo yaw angle ψ is passed through the −th order lag filter 214, and a signal corresponding to the lateral acceleration y is passed through the first order lag filter 215 to the pseudo lateral velocity. The signal is divided into a signal representing y and a signal representing pseudo lateral displacement y via the integrating circuit 216.

The input section 201 of the aforementioned control gain calculation means (1) determines the state of the vehicle based on the input.

In other words, coefficients W that continuously change between 0 and 1 correspond to the driver's evaluation value of whether the vehicle speed u0 is large or small, or whether the steering angular velocity 8 is large or small.
, ,W, and determine the state as follows.

(1) If vehicle speed u6 is large, stability is improved.

(II) If the vehicle speed u0 is not large, follow the following rules.

(I[[) If the steering angular velocity 1x is large, the responsiveness will be increased.

(IV) If the steering angular velocity 131 is small, stability is improved.

Here, improving responsiveness means creating an optimal tire slip angle for the front and rear wheels in response to steering wheel steering, and thereby giving priority to lateral motion over yaw motion when the vehicle speed is high. When the vehicle speed is slow, the yaw motion is optimally controlled to avoid obstacles, such as a quick lane change to avoid obstacles, and to quickly change course when the vehicle is steered. Increasing the stability of a vehicle means reducing the tire slip angles of the front and rear wheels and achieving a movement that quickly returns to its original state in response to lateral movement or yaw movement. This indicates that the vehicle will quickly maintain its course in the event of a disturbance such as a crosswind.

The logic from (1) to (IV) above is executed here by the calculation of coefficient M=W, xWt, and the coefficient M, that is, the contribution index is determined. Optimal gain values G, ~G4 are determined according to this coefficient M.

GIG, G2°, G20, G40 corresponding to coefficient M=0
, Gll corresponding to coefficient M=1, cz+, G33, G
4. is stored in the storage unit 203 in advance, and the optimum gain value is calculated by the calculation processing unit 202.

Then, these calculated optimal gain values, that is, the optimal gain output G5 (i=1 to 4) from the output section 204 of the control gain calculation means (1) are calculated by the four coefficients of the steering amount calculation means (2). 210.211, y, gives the optimal gain to y.

The adder 219 of the steering amount calculation means ■2 multiplies the above yaw rate signal ↓ and the optimum gain ratio to produce a signal G1 ↓.
, the signal G2・ψ is the product of the pseudo yaw angle signal ψ and the optimal gain Gt, the signal G3・y is the product of the pseudo lateral displacement signal y and the optimal gain G, and the pseudo lateral displacement The signal G4 is the sum of the signal y and the optimal gain G4.
By adding y, the feedback signal G1・
↓+G2・ψ+G3・y 10 G 4・y is output to the rear wheel actuator means ■.

The driving means (■1) receives a steering control signal δ from the steering amount calculating means (■2), =G, ·ψ10G, ·ψ10G, ·)l+G4·y
This drives the hydraulic assist mechanism (2) and operates the rear wheel steering mechanism (2) to perform predetermined steering control.

That is, in this embodiment, by controlling the tire slip angles of the front and rear wheels of the vehicle, when the vehicle speed is relatively slow and the steering speed of the steering wheel is high, the slip angles of the front and rear wheels are controlled to be large, thereby improving the responsiveness of the vehicle. When the vehicle speed is relatively high and the steering speed of the steering wheel is relatively low, the slip angles of the front and rear wheels are controlled to be small to improve the stability of the vehicle.

Through these operations, when the driver turns the steering wheel quickly, the rear wheels are steered to improve responsiveness to the steering wheel, assuming that the driver wants to turn the vehicle quickly, and when the driver is not turning the steering wheel at all, the rear wheels are steered to improve responsiveness to the steering wheel. Since the rear wheels are steered to improve vehicle stability based on the driver's judgment that the driver does not want to change the vehicle's situation, it is possible to provide a highly stable vehicle in the face of external disturbances such as crosswinds and ruts. Become. In other words, it is possible to achieve both optimum vehicle responsiveness and stability depending on the vehicle condition and the driver's will.

In addition, when determining the vehicle's optimal state feedback coefficient, it is possible to set the coefficient in advance by taking into account the response characteristics of rear wheel steering, which prevents a decrease in steering stability due to a delay in the response of the vehicle's rear wheels. It is possible to prevent this from happening, and the steering stability can be further improved.

<Modified Example> Although not described in the above embodiment, the signals taken into the vehicle state determining means (■) for determining the state of the vehicle include not only the steering wheel angular velocity signal and the vehicle speed signal but also the behavior amount signal generated from the behavior sensor (■3). It is also possible to take in signals generated from an external environmental condition sensor, such as the condition of the road surface or the like.

For example, when the behavior amount signal from the behavior sensor ■ is taken in, a coefficient W is set in addition to the coefficient W, , Wt, and when the behavior change is extremely large, the coefficient W3 is set to 0, and when the behavior change is small, the coefficient W3 is set. = 1, the coefficient W3 is determined by continuously interpolating this interval, and the calculation method of the coefficient M is set as M-work W1, W2, W3.

As a result, it is possible to follow conditions where the behavior changes significantly, such as when the tire grip force decreases or changes in vehicle motion due to changes in the payload.
The stability and responsiveness of the vehicle can be further improved.

Similarly, if the signal from the road sensor is added to the vehicle condition determining means, the coefficient W4 can be calculated when the road surface is slippery (for example, when the friction coefficient μ between the road surface and the tires is μ<0.3). When W4=0 and the road surface condition is good (μ>0.
8) This can be handled by setting W, = 1, determining a coefficient W4 by continuously interpolating between them, and multiplying this W4 by the coefficient M.

In addition, it is possible to similarly take in various signals to the vehicle state determination means.

Further, in the above embodiment, the steering control method of the present invention is applied to the rear wheel steering device of the vehicle, but it is also possible to apply the steering control method to the front and rear wheel steering devices of the vehicle.

In this case, a front wheel auxiliary steering mechanism is added to the front wheel steering mechanism to steer the front wheels according to signals from the computer, and the gain G5 obtained by the control gain calculation means described in the embodiment is for the front wheels. There are two types, one for the front wheels and one for the rear wheels, and the gain can be easily calculated by adding only the term of the steering angle of the front wheels to the evaluation function that determines the gain. In this case, the coefficient M
− Front and rear wheel gains corresponding to 〇 and coefficient M=1
The gains of the front wheels and rear wheels corresponding to are stored in advance in the storage unit 203 of the control gain calculating means (2), and the respective optimum gains for the front and rear wheels are calculated by the calculation processing unit 202. These computed optimal gains are output to the control signal computing means (2), and the feedback signal computed as a result operates the front wheel auxiliary steering mechanism and the rear wheel steering mechanism to perform predetermined steering control. This makes it possible to directly control the tire slip angle of the front wheels as well.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of the rear wheel steering control device according to the present invention, and FIG.
The figure is a schematic diagram of a conventional steering control device, FIG. 3 is a diagram showing the relationship between the steering angle of the front and rear wheels and the tire slip angle, and FIG. 4 is a schematic diagram of a specific embodiment of the rear wheel steering device according to the present invention. , 51st
The figure is a flowchart of a microcomputer, and FIG. 6 is a principle diagram of a first-order lag filter used in an embodiment of the present invention. I...Sensor means, ■,...Steering speed sensor, I2...Vehicle speed sensor, ■,...State detection sensor, I4...Behavior sensor, ■...Steering control means, ■,... ...Control gain calculation means, ■, ...Vehicle condition determination means, ■1□...Basic gain generation means, Ls...Gain change means, ■2...Steering amount calculation means, ■... rear wheel actuator means

Claims (1)

[Scope of Claims] A rear wheel steering control device that controls a rear wheel steering amount of a vehicle, which includes at least a steering speed sensor that detects a steering speed of a steering wheel, a vehicle speed sensor that detects a vehicle speed, and a behavior amount of a vehicle. a sensor means comprising a behavior sensor; a rear wheel steering actuator means for steering the rear wheels; and at least a signal corresponding to the detected steering speed and a signal corresponding to the vehicle speed. A vehicle state determination means that determines the current state of the vehicle and outputs a vehicle state determination value, a term that includes a front wheel slip angle and a front wheel steering angle, and a term that includes a rear wheel slip angle and a rear wheel steering angle. basic gain generating means for calculating a state feedback gain corresponding to the weighting coefficient of the evaluation function based on an evaluation function consisting of a term consisting of a term consisting of a rear wheel steering angle, and a weighting coefficient applied to the three terms; control gain calculation means comprising an optimum gain calculation means for calculating an optimum gain by distributing the state feedback gain according to the state of the vehicle and a vehicle state judgment value representing the steering intention of the driver; a steering control means comprising a steering amount calculation means which multiplies the calculated behavior signal by the calculated optimum gain and adds the result to a control signal for the rear wheel steering actuator means; A rear wheel steering control device for a vehicle, which performs optimal control according to vehicle conditions and a driver's steering intention.