JPH037675A - Four-wheel steering device - Google Patents

Abstract

PURPOSE:To have optimum control of rear wheels in compliance with changing situation by setting appropriately the rule and the membership function such as output abut the rear wheel steering angle and inputs to a fuzzy controller about the steering angle, steering speed, car speed, etc. CONSTITUTION:In a fuzzy controller 10 the membership functions are set for the front wheel steering angle sensed by a sensor 11, the car speed and sideways acceleration sensed by front wheel steering speed sensors 13, 14 with the aid of a differentiating device 12, and further is set a membership function for the optimum rear wheel steering angle to be fed to a rear wheel steering controller 15. Inputs of these values are taken in, and a fuzzy inference due to MIN- MAX computing regulation, for ex., is executed according to these membership functions and the rules set appropriately, and optimum rear wheel steering angle signal is fed to the rear wheel steering controller 15 for steering the rear wheels 3. This embodies a four-wheel steering which better suits the human feelings.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention By instantaneously and optimally controlling the steering angle of the rear wheels using fuzzy control, an optimal four-wheel steering system that more closely matches human senses is realized.

Background of the invention The present invention relates to a steering system for a four-wheeled vehicle.

Conventional four-wheel steering systems for automobiles include one mechanical type and one electronically controlled type. However, mechanical four-wheel steering systems have the problem that the steering angle of the rear wheels is uniquely determined by the steering angle of the front wheels, regardless of the vehicle speed, and therefore it is not possible to obtain a steering feeling that is suitable for various situations. In addition, with electronically controlled systems, the steering angle of the rear wheels is determined by the steering angle of the front wheels, vehicle speed, lateral acceleration of the vehicle body, etc., so it can be adjusted to more situations than with mechanical systems. The problem is that the wheel steering speed, control delay, etc. do not match human senses.

SUMMARY OF THE INVENTION The present invention provides a four-wheel steering system that is compatible with human senses.

The four-wheel steering device according to the present invention includes a steering angle sensor that detects the steering angle of the front wheels, a turning speed detection means that detects the turning speed of the front wheels, a vehicle speed sensor that measures the vehicle speed, and a rear wheel that controls the steering drive of the rear wheels. The steering controller and the detected steering angle, steering speed, and vehicle speed are input, and inference is made according to the membership function of these inputs, the membership function of the rear wheel steering angle, and a predetermined rule. It is characterized by comprising a fuzzy controller that calculates the rear wheel steering angle to be given to the controller.

According to this invention, by appropriately determining the membership functions and rules for the fuzzy controller and its output, the rear wheels can be optimally controlled in response to changes in the situation. It allows four-wheel steering to be more in line with human sensibilities, allowing for instantaneous response to changing situations. This effect can be obtained.

Furthermore, it is preferable to provide a lateral acceleration sensor for detecting lateral acceleration of the vehicle body. In this case, the detected steering angle, steering speed, vehicle speed, and lateral acceleration are human-powered, and a membership function of these inputs, a membership function of the rear wheel steering angle, and a predetermined rule are used to create the fuzzy controller. The system is configured to perform inference based on the desired rear wheel steering angle and calculate the rear wheel steering angle to be given to the rear wheel steering controller.

As a result, when the vehicle body skids, the rear wheels can be optimally steered to stabilize the vehicle body.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows an embodiment of the present invention, showing the configuration of a four-wheel steering system applied to the body of an automobile, and FIG. 2 is a block diagram showing only its electrical configuration. It is a diagram.

Front wheels 2. front and rear of the vehicle body 1, respectively. Two rear wheels 3 are provided. The two front wheels 2 are simultaneously steered by a front wheel steering device including a handle 4.

The two rear wheels 3 are simultaneously subjected to steering drive control by a rear wheel steering controller 15 controlled by a fuzzy controller 10.

The input devices of the fuzzy controller 10 include a steering angle sensor 11. Differentiator 12. There is a vehicle speed sensor 13 and a lateral acceleration sensor]4. The steering angle sensor 11 detects the steering angle θ caused by the steering wheel 4. Differentiator 12 differentiates a signal representing steering angle θ to detect steering speed θ. The vehicle speed sensor 13 detects the speed (vehicle speed) of the vehicle. The lateral acceleration sensor 14 detects the lateral acceleration a of the vehicle body 1 by installing an accelerometer that uses the current inertia force in the lateral direction.

These detected steering angle θ, steering speed θ, vehicle speed V, and lateral acceleration a are given to the fuzzy controller I roller 10. When the fuzzy controller 10 is of a digital type, these detected physical quantities θ, θ, v
, a are converted into digital signals and given to the fuzzy controller. Differentiator 12 can also be implemented by software.

The fuzzy controller 10 executes fuzzy inference or fuzzy calculation, and is called a fuzzy computer, fuzzy inference device, fuzzy inference calculation device, or the like. This is a dedicated device (regardless of analog or digital type) for fuzzy inference (for example, "Nikkei, Electronics J 1
(See Nikkei McGraw-Hill, July 27, 1987, pp. 148-152), but also by a binary type computer, processor, etc., programmed to perform fuzzy inference. Not even.

In the fuzzy controller 10, FIGS. 3a, 31D, 3c, and 3 are provided for the input front wheel steering angle θ, front wheel turning speed θ, vehicle speed V, and lateral acceleration a of the vehicle body.
A membership function as shown in Figure d is set. In FIG. 3a, the front wheel steering angle θ is positive when steering to the right. In FIG. 3C, a negative vehicle speed V means moving backward. In Fig. 3d, the lateral acceleration a of the vehicle body assumes that the acceleration in the right direction is positive. FIG. 4 shows the optimum rear wheel steering angle ψ given from the fuzzy controller 10 to the rear wheel steering controller 15.
shows the membership function of , with steering to the right set to positive.

In Figures 3a-3d and Figure 4.

NL is a large negative value, and NM is a medium negative value.

NS represents a small negative value, ZR represents approximately zero, PS represents a small positive value, PM represents a medium positive value, and PL represents a large positive value.

Fuzzy controller] 0 is input θ, θ, ■ and a
and according to the membership function described above and appropriately set rules, e.g. M I If-MAX
Fuzzy inference based on calculation rules is executed to output a signal representing the optimal rear wheel steering angle ψ. Although various rules can be set, an example of a rule when the lateral acceleration a is not considered is shown below. This is called the If, then rule. The basic idea of this rule is as follows.

At low speeds, the rear wheels are steered in the opposite phase to the front wheels to enable tight turning, and at high speeds, the rear wheels are steered in the same phase as the front wheels for stable cornering and lane changes. Further, when the front wheel turning speed θ is high when driving at high speed, the rear wheels are steered in the same phase to a larger extent to emphasize sharpness to the driver.

Ifθ=ZR, θ−ZR, v=PSthe
nψ−ZR1rθ=PM, θ−PM, v−PS
thenψ−NMrθ=PM, θ−PM, v=
PM thenψ=ZRfθ−PM, θ−PM,
v-PL thenψ-psfθ=PL, θ
= P L , v = P S thenψ−N
Lfθ=NL, θ−NL, v−PS the
nψ−PLfθ=ps, θ−PL, v=
P L thenψ=psfθ=ps, θ=
P S , v = P L thenψ−ZRr
θ −PM, θ −NM, v=Ps
thenψ=NSfθ=PM, θ−PM,
v-NS thenψ-NM1fθ-ZR, θ-Z
R, v = Z Rthenψ = ZR As mentioned above, it is not necessary to consider the lateral acceleration a, but in order to keep the car body stable against side skidding, the lateral acceleration a can also be added to the elements of fuzzy inference. preferable. That is, when the vehicle body skids relative to the road surface due to sudden steering, etc., the lateral acceleration of the vehicle body becomes unstable. Therefore, when the vehicle body skids, the vehicle body can be stabilized by optimally steering the rear wheels. An example of a rule in this case is as follows.

lfθ=ZR, θ=ZR, v=Ps, a=ZRthen
ψ=ZR 1fθ=PM, θ=PM, v=Ps, a=PSt
h e nψ−NM Ifθ=PM, θ=PM v=PM a=PM
thenψ=ZR 1rθ−PM, θ=PM, v=PL, a=PLth
enψPS 1rθ−PL, e=PL, v−PS, a=PSthen
ψ−NL 1fθ=NL, 0−PL, v=PS, a−
NSthenψ−PL Ifθ=ps, θ=PL, v=PL, a−
PLthenψ=PS lfθ-ps, θ=PS, v-PL, a=
Psthenψ−ZR 1fθ=PM, θ−NM, v−PS a−PS
thenψ−NS If'θ=PM, e=PM, v=NS, a
=Nst h e nψ−NM Ifθ=ZR,θ= Z R,v = Z R,a =
It is also possible to perform fuzzy inference not only according to the ZRthenψ-ZR MI N-MAX operation rule but also according to other operation rules. Further, the membership function is not limited to the triangular shape as shown in FIGS. 3a to 3d and FIG. 4, but may be of any shape. Furthermore, membership functions and rules can be changed or modified as appropriate depending on control results and the like.

[Brief explanation of the drawing]

Fig. 1 shows the configuration of the four-wheel steering system, Fig. 2 is a block diagram showing its electrical configuration, and Figs. 3a, 3b, 3C, and 3d show the front wheel steering angle, the front Graph showing the membership function of wheel turning speed 1 vehicle speed and lateral acceleration of the vehicle body. FIG. 4 is a graph showing the membership function of the optimum rear wheel steering angle. 1... Vehicle body 2... Front wheel. 3... Rear wheel. 10... Fuzzy controller 11... Steering angle sensor 12... Differentiator 13... Vehicle speed sensor 14... Lateral acceleration sensor. 15...Rear wheel steering controller. that's all

Claims (2)

[Claims] (1) A steering angle sensor that detects the steering angle of the front wheels, a steering speed detection means that detects the steering speed of the front wheels, a vehicle speed sensor that measures the vehicle speed, a rear wheel steering controller that controls the steering drive of the rear wheels, and a steering angle sensor that detects the steering angle of the front wheels. The steering angle, steering speed, and vehicle speed are input, and inference is made according to the membership function of these inputs, the membership function of the rear wheel steering angle, and predetermined rules, and the rear wheel steering controller is given the rear wheel steering controller. A four-wheel steering device equipped with a fuzzy controller that calculates the steering angle. (2) Furthermore, it is equipped with a lateral acceleration sensor that detects the lateral acceleration of the vehicle body, and the fuzzy controller receives the detected steering angle, steering speed, vehicle speed, and lateral acceleration as input, and calculates the membership function of these inputs and the rear wheel steering. The four-wheel steering system according to claim 1, wherein the rear wheel steering angle to be given to the rear wheel steering controller is calculated by performing inference according to an angle membership function and a predetermined rule.