JPH05201344A - Rear wheel steering angle control device - Google Patents

Abstract

(57) Abstract: OBJECTIVE The rear wheel steering angle [delta] _r based on the front wheel steering angle [delta] _f, rear-wheel steering angle to front wheel steering angle [delta] _f the vehicle turning initially [delta] _r
In the device that controls the response of the vehicle to be delayed, the turning characteristic of the vehicle is always made appropriate by changing the degree of the response delay based on the parameter related to the vehicle turning. [Configuration] Target rear wheel steering angle δ _r is (1-e ^{−t / T} ) · k · δ
_The actuator drive circuit 52, which is determined as _f (however, T: time constant, k: steering angle ratio), and various sensors 30, 32
And a fuzzy controller 50 that determines the time constant T using fuzzy inference based on the front wheel steering angle δ _f , the vehicle speed V, and the steering speed v _sw . Furthermore, the fuzzy rule thereof is that the time constant T is set to a larger front wheel steering angle δ _{f and a} larger vehicle speed V,
Further, the larger the steering speed v _sw , the larger the determination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering angle control device for controlling a steering angle of a rear wheel based on a steering angle of a front wheel of a vehicle. The present invention relates to a rear wheel steering angle control device of a type that controls a rear wheel steering angle so that a response is delayed.

[0002]

2. Description of the Related Art A rear wheel steering angle control device for controlling a rear wheel steering angle based on a front wheel steering angle is already known. This is generally
As described in Japanese Patent Application Laid-Open No. 62-146783, (a) front wheel steering angle acquisition means for acquiring the steering angle of the front wheels of the vehicle,
(b) Target rear-wheel steering angle determining means for determining the target value of the rear-wheel steering angle based on the obtained front-wheel steering angle, (c) rear-wheel actuator for changing the rear-wheel steering angle, and (d) determination. Actuator drive means for driving the rear wheel actuator so that the desired target rear wheel steering angle is realized.

The following type of rear wheel steering angle control device already exists. This is a form in which the target rear wheel rudder angle determining means determines the target value of the rear wheel rudder angle based on the acquired front wheel rudder angle so that the response of the rear wheel rudder angle to the front wheel rudder angle is delayed. Is.

In a conventional example of the rear wheel steering angle control device of this type, the target rear wheel steering angle determining means determines the target value of the rear wheel steering angle based on the acquired front wheel steering angle. And the direction is the same, and there is a first-order delay in the response of the rear wheel steering angle to the front wheel steering angle at the beginning of turning of the vehicle. Specifically, at the start of turning (that is, from the straight traveling state, Δ _r = (1−e ^{−t / T} ) · k · δ _f , with the elapsed time t = 0 at the start of transition to the turning state) where δ _f : front wheel steering angle δ _r : rear wheel steering angle T: The target rear wheel steering angle δ _r is determined by using the formula of time constant k: steering angle ratio.

[0005]

In this conventional rear wheel steering angle control device, since the rear wheels are deflected in the same direction as the front wheels with a later delay, the yaw rate of the vehicle body when the steering wheel is steered by the driver is reduced. The responsiveness is improved, the direction of the vehicle body is changed sharply, and so-called turning performance is improved. However, when the rear wheels are deflected later than the front wheels, the response of the lateral acceleration of the vehicle body to steering is lower than that when the rear wheels are deflected simultaneously with the front wheels (without response delay), and the lane change characteristics are reduced. descend.

As described above, changing the rear wheels after the front wheels delays the lateral acceleration response at the expense of improving the yaw rate response. However, in some cases, the yaw rate response is sacrificed. However, it may be desirable to improve the lateral acceleration response. However, in the conventional rear wheel steering angle control device, since the time constant T is fixed, the lateral acceleration responsiveness is inevitably lowered in any case, and the desired vehicle turning characteristic may not be realized. There was a problem.

Under these circumstances, the present invention has been made to solve the problem by varying the extent to which the response of the rear wheel steering angle to the front wheel steering angle is delayed.

[0008]

In order to solve this problem, the gist of the present invention is, as shown in FIG. 1, (a) front wheel steering angle acquisition means 1 for acquiring the steering angle of the front wheels of a vehicle; b) Target rear wheel rudder angle determining means 2 for deciding the target value of the rear wheel rudder angle based on the acquired front wheel rudder angle so that the response of the rear wheel rudder angle to the front wheel rudder angle is delayed. ) Rear wheel steering angle control including a rear wheel actuator 3 for changing the rear wheel steering angle, and (d) actuator driving means 4 for driving the rear wheel actuator 3 so that the determined target rear wheel steering angle is realized. The apparatus is provided with the steering angle response delay control means 5 for changing the degree of the response delay of the rear wheel steering angle based on the parameter relating to the vehicle turning.

In one mode of the "target rear wheel rudder angle determining means 2 and the rudder angle response delay control means 5" in the present invention, the target rear wheel rudder angle determining means 1 determines the rear wheel rudder angle relative to the front wheel rudder angle. Determine the target rear wheel steering angle so that there is a first-order delay in the response,
Specifically, δ _r = (1-e ^{−t / T} ) · k · δ _f (where k: steering angle ratio) is used to set the target rear wheel steering angle δ.
_{In addition} to determining _r , the steering angle response delay control means 5 changes the time constant T in the equation based on a parameter relating to vehicle turning.

In addition, the "parameter relating to vehicle turning"
For example, at least one of the front wheel steering angle, the vehicle speed, and the steering speed can be selected.

Another aspect of the "target rear wheel rudder angle determination means 2" in the present invention is that the rear wheel rudder with respect to the front wheel rudder angle is limited only to the beginning of the vehicle turning (that is, the transition process from the straight traveling state to the turning state). It may cause a delay in the response of the corner,
Not only at the beginning of the vehicle turning, but also during the transition process from one steady turning state to another steady turning state for reducing the turning radius of the vehicle, the response of the rear wheel steering angle to the front wheel steering angle is delayed. You can also

[0012]

In the rear-wheel steering angle control device according to the present invention, the degree of the response delay of the rear-wheel steering angle with respect to the front-wheel steering angle is changed based on the parameter relating to the vehicle turning. It is properly controlled not only in relation to the angle but also in relation to the parameter related to vehicle turning.

For example, when the front wheel steering angle, the vehicle speed, and the steering speed are selected as parameters relating to vehicle turning,
The degree of the response delay of the rear wheel steering angle with respect to the front wheel steering angle is properly controlled in relation to the front wheel steering angle, the vehicle speed and the steering speed, respectively, and as a result, the turning characteristics of the vehicle are changed to the front wheel steering angle, the vehicle speed and the steering speed, respectively. It will be a match.

[0014]

As described above, according to the present invention, the degree of the response delay of the rear wheel steering angle with respect to the front wheel steering angle is made variable and is appropriately controlled in relation to the parameter relating to vehicle turning. Regardless of the above, the effect that the vehicle turning characteristic becomes desirable can be obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A rear wheel steering angle control device according to an embodiment of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 2, the present rear wheel steering angle control device includes a steering wheel 10
It is provided in a vehicle in which the steering angle δ _f of the left and right front wheels 12 changes according to the steering angle of the vehicle.

The rear wheel steering angle control device comprises a rear wheel actuator 26 for changing the steering angle δ _r of the left and right rear wheels 22. Further, a front wheel steering angle sensor 30 for detecting the front wheel steering angle δ _f , a vehicle speed sensor 32 for detecting the vehicle speed V, and the like are also provided.

The rear wheel steering angle control device further includes a fuzzy controller 50 and an actuator drive circuit 52. The front wheel steering angle sensor 30 and the vehicle speed sensor 32 are connected to the input section of the fuzzy controller 50, and the input section of the actuator drive circuit 52 is connected to the output section thereof. The rear wheel actuator 26 is connected to the output portion of the actuator drive circuit 52. The front wheel steering angle sensor 30 and the input section of the fuzzy controller 50 are further connected to each other via a steering speed calculation circuit 60. The steering speed calculation circuit 60 calculates the steering speed v _sw of the steering wheel 10 as a time differential value of the front wheel steering angle δ _f supplied from the front wheel steering angle sensor 30, and supplies it to the fuzzy controller 50. .

The rear wheel steering angle control device controls the target value of the rear wheel steering angle δ _{r in} order to control the actual value of the rear wheel steering angle δ _r so that the direction of the vehicle body is the traveling direction as much as possible. δ _r = (1−e ^{−t / T} ) · k · δ _f . Here, “k” is the steering angle ratio, “δ _f ” is the actual value of the front wheel steering angle, “t” is the elapsed time,
"T" means each time constant.

The steering angle ratio k is a variable value which is determined so as to increase from negative to positive as the vehicle speed V increases from zero. Therefore, the rear wheel steering angle is controlled in the opposite direction (in the opposite phase) to the front wheel steering angle in the low speed traveling state, and is controlled in the same direction (in the same phase) as the front wheel steering angle in the high speed traveling state.

The fuzzy controller 50 includes a CPU and R
It is mainly composed of a computer including an OM, a RAM and a bus, and has a steering speed v _sw ,
Based on the front wheel steering angle δ _f and the vehicle speed V, the time constant T as a consequent part variable is determined using fuzzy reasoning. Therefore, the fuzzy controller 50 is
In the OM, (a) a fuzzy reasoning program (not shown) and (b) a plurality of membership functions corresponding to each of the front wheel steering angle δ _f , the vehicle speed V, the steering speed v _sw and the time constant T (Fig. 3, Fig. 3). 4, graphed in FIG. 5 and FIG. 6 respectively), and (c) defuzzification rule (graphed in FIG. 7) for converting the calculated value by fuzzy inference of the time constant T into an actual physical value, ( d) Memorizing a plurality of fuzzy rules (shown in the table below).

[0021]

[Table 1]

As is clear from this table, an example of the fuzzy rule this time is if v _sw = PS and δ _f = NL and V = NL th
It is represented by en T = NM.

The fuzzy inference program is well known and is not indispensable for understanding the present invention, so it will be briefly described. That is, as described in the document “Fuzzy Control (published on July 20, 1989, first edition, 5th edition, Nikkan Kogyo Shimbun)”, first, based on each given value of the antecedent variable, a plurality of fuzzy The goodness of fit ω _i is calculated for each rule in turn, and then the inference result (defined by each goodness of fit ω _i and the membership function of the time constant T) is calculated for each fuzzy rule. The inference result of the whole fuzzy rule, that is, the fuzzy value of the time constant T as the consequent part variable is calculated by using the centroid method or the area method. Then, the fuzzy value is converted into an actual physical value according to the defuzzification rule of FIG.

The fuzzy label of each antecedent variable will be described. Regarding the front wheel steering angle δ _f , as shown in FIG.
"NL", "NM", "NS", "ZR", "PS",
Seven fuzzy labels "PM" and "PL" are prepared. Correspondence between the front wheel steering angle [delta] _f and fuzzy labels, as the front wheel steering angle [delta] _f is increased from 0, are assumed to fuzzy label changes toward the "PL" from the "NL". As for the vehicle speed V, as shown in FIG. 4, seven fuzzy labels are prepared according to the case of the front wheel steering angle δ _f . For the steering speed v _sw, see FIG.
As shown in FIG. 3, three fuzzy labels “ZR”, “PS” and “PS” are prepared. Steering speed v
The correspondence between _sw and fuzzy label is that steering speed v _sw is 0
It is supposed that the fuzzy label changes from "ZR" to "PS" as the number increases. As for the time constant T, as shown in FIG. 6, seven fuzzy labels are prepared according to the case of the front wheel steering angle δ _f , and the correspondence between the time constant T and the fuzzy label is that the time constant T is The fuzzy label is supposed to change from "NL" to "PL" as it increases from zero.

The plurality of fuzzy rules are designed based on the following idea. That is, first, as conceptually shown in the graph of FIG. 8, the fuzzy rule is designed so that the time constant T increases as the front wheel steering angle δ _f increases. That is, in the state in which the rear wheel steering angle [delta] _r is in the front wheel steering angle [delta] _f the same phase, in a region front wheel steering angle [delta] _f is small, the time constant T is small, the rear wheel steering angle to front wheel steering angle [delta] _f [delta] _r The response delay of the
_{When r} becomes sensitive and the lateral acceleration response of the vehicle to steering is improved, on the other hand, in a region where the front wheel steering angle δ _f is large, the time constant T becomes large and the rear wheel steering angle δ _{f with} respect to the front wheel steering angle δ _f .
_The fuzzy rule is designed so that the response delay of _r becomes high, the rear wheel steering angle δ _r becomes insensitive, and the yaw rate response of the vehicle to steering is improved.

Specifically, this is described in the above table (hereinafter,
It is expressed as follows in the fuzzy rule table). That is, for example, the fuzzy label of the steering speed v _sw is “PS” (hereinafter, simply referred to as the steering speed v _sw
Is "PS". The same applies to other parameters) and when the vehicle speed V is "ZR",
As the front wheel steering angle δ _f increases from 0, the time constant T becomes “N
It is expressed as increasing in order of "S", "ZR", "PS" and "PM".

Further, as shown conceptually by the graph in FIG. 8, the fuzzy rule is designed so that the time constant T increases as the vehicle speed V increases. That is, when the rear wheel steering angle δ _r is in the same phase as the front wheel steering angle δ _f , the time constant T becomes small in the low speed traveling state, and the rear wheel steering angle δ _r
Becomes more sensitive and the lateral acceleration response of the vehicle is improved. On the other hand, in a high-speed running state, the time constant T becomes large, the rear wheel steering angle δ _r becomes insensitive, and the yaw rate response of the vehicle improves. So fuzzy rules are designed.

This is specifically expressed in the fuzzy rule table as follows, for example. That is, for example, when the steering speed v _sw is “PS” and the front wheel steering angle δ _f is “ZR”, the time constant T becomes “NS”, “ZR” as the vehicle speed V increases from 0. ], "P
It is expressed as increasing sequentially to "S" and "PM".

Further, the plurality of fuzzy rules are designed so that the time constant T increases as the steering speed v _sw increases, as conceptually shown in the graph of FIG. That is, when the rear wheel steering angle δ _r is in the same phase as the front wheel steering angle δ _f , the time constant T becomes small in a region where the steering speed v _sw is small (a region where the steering wheel 10 is gently operated). The rear wheel steering angle δ _r becomes sensitive and the lateral acceleration responsiveness of the vehicle is improved. On the other hand, in a region where the steering speed v _sw is large (a region where the steering wheel 10 is quickly operated), the time constant T becomes large. , Rear wheel steering angle δ _r
The fuzzy rule is designed to make the vehicle insensitive and improve the yaw rate response of the vehicle.

This is expressed in the fuzzy rule table as follows, for example. That is, the front wheel steering angle δ
_{When f} is "NM" and the vehicle speed V is "NS", the time constant T increases in the order of "NM", "NS" and "ZR" as the steering speed δv _sw increases from 0. It is expressed as doing.

The actuator drive circuit 52 is also mainly composed of a computer, and its ROM has a structure shown in FIG.
Various programs including the target rear wheel steering angle determination program represented by the flowchart of 0 are stored.

In the target rear wheel steering angle determination program, first, in step S1 (hereinafter simply referred to as S1; the same applies to other steps), the front wheel steering angle δ _f supplied from the fuzzy controller 50 is set. Based on
It is determined whether turning of the vehicle has started. If not, the process returns to S1, and if so, the process proceeds to S2.

In S2, the fuzzy controller 5
The latest time constant T is read from 0, and subsequently, the value of the elapsed time t is set to 0 in S3.

Thereafter, in S4 and S5, the current front wheel steering angle δ _f and the vehicle speed V are read from the fuzzy controller 50, respectively, and in S6, the current value of the steering angle ratio k is based on the vehicle speed V, and the current value is calculated as described above. That is, as the vehicle speed V increases from 0, the steering angle ratio k is calculated according to the relationship increasing from negative to positive.

Subsequently, at S7, the current value of the elapsed time t (currently 0), the current value of the steering angle ratio k, and the front wheel steering angle δ _f.
The target rear wheel steering angle δ _r is calculated based on the current value of Specifically, the target rear wheel steering angle δ _r is calculated by substituting each of these values into the formula δ _r = (1−e ^{−t / T} ) · k · δ _f . Since the value of the elapsed time t is 0 and the value of (1-e ^{−t / T} ) is 0 this time, the target rear wheel steering angle δ _r is 0 in the end.

After that, in S8, the elapsed time t is increased by a minute time Δt, and in S9, the front wheel steering angle δ.
Based on _f , it is determined whether the vehicle is still in a turning state. If this is the case this time, the determination is yes, the process returns to S4 and the steps from S4 onward are executed again.

When the execution of the steps S4 and below is repeated many times, the elapsed time t increases and the value of (1-e- ^{t / T} ) also increases from 0 and approaches 1; In the period sufficiently close to 0, that is, at the beginning of turning, the rear wheel steering angle δ _r
The value when there is no response delay, i.e., is determined smaller than k · [delta] _f, after all, the rear wheel steering angle to front wheel steering angle [delta] _f [delta]
There will be a delay in the response of _r .

If the execution of the steps from S4 onward is further repeated, the elapsed time t becomes further longer, and (1-e
The value of ^{-t / T} ) is close to 1 sufficiently. After that, the above equation is eventually equivalent to the equation of δ _r = k · δ _f , and the rear wheel steering angle δ with _respect to the front wheel steering angle δ _f .
There will be no delay in _r response.

As is apparent from the above description, in the present embodiment, the time constant T is made variable so that it is properly controlled in relation to the front wheel steering angle δ _f , the vehicle speed V and the steering speed v _SW . Therefore, the extent of the response delay of the rear wheel steering angle δ _r becomes appropriate in the relationship with the front wheel steering angle δ _f, etc., and by extension, the turning characteristic of the vehicle becomes appropriate in the relationship with the front wheel steering angle δ _f, etc. The effect is obtained.

As is apparent from the above description, in the present embodiment, the front wheel steering angle sensor 30 constitutes one aspect of the "front wheel steering angle acquisition means" of the present invention, and the actuator drive circuit 52 shown in FIG. The part that executes the target rear wheel rudder angle determination program of (1) constitutes one aspect of "target rear wheel rudder angle determination means", and the determined target rear wheel rudder angle δ _{r of} the actuator drive circuit 52 is realized. The portion that drives the rear-wheel actuator 26 is "actuator driving means".
That is, the fuzzy controller 50 cooperates with the front wheel steering angle sensor 30, the vehicle speed sensor 32, and the steering speed calculation circuit 60 to form one aspect of the "steering angle response delay control means".

In addition, since the steering angle response delay control means in this embodiment is of a type that determines the degree of rear wheel steering angle response delay using fuzzy reasoning, it is vaguely sensuous to the designer. The requirement can be reflected relatively easily in the characteristic of the fuzzy reasoning, that is, the degree of the response delay of the rear wheel steering angle, and the effect of being able to design the fuzzy reasoning relatively easily and accurately is also obtained. .. The parameters to be tuned in the fuzzy inference are the membership functions and the fuzzy rules, because they can correspond to human words relatively easily. However, the steering angle response delay control means in the present invention may be of a type that determines the degree of the response delay of the rear wheel steering angle by another method.

Besides this, the present invention can be carried out in variously modified and improved modes based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief description of drawings]

FIG. 1 is a block diagram conceptually showing the structure of the present invention.

FIG. 2 is a system diagram showing a rear wheel steering angle control device according to an embodiment of the present invention.

FIG. 3 is a graph showing a plurality of membership functions prepared in relation to the front wheel steering angle δ _f in the fuzzy controller in FIG.

4 is a graph showing a plurality of membership functions prepared in relation to a vehicle speed V in the fuzzy controller in FIG.

5 is a graph showing a plurality of membership functions prepared in relation to the steering speed v _sw in the fuzzy controller in FIG.

6 is a graph showing a plurality of membership functions prepared in relation to the time constant T in the fuzzy controller in FIG.

7 is a fuzzy controller shown in FIG.
It is a graph which shows the rule for defuzzifying a fuzzy inference value.

FIG. 8 is a graph for explaining characteristics of a plurality of fuzzy rules used by the fuzzy controller in FIG.

9 is a graph for explaining characteristics of a plurality of fuzzy rules used by the fuzzy controller in FIG.

10 is a flowchart showing a target rear wheel steering angle determination program used by the actuator drive circuit in FIG.

[Explanation of symbols]

 10 Steering Wheel 26 Rear Wheel Actuator 30 Front Wheel Steering Angle Sensor 32 Vehicle Speed Sensor 50 Fuzzy Controller 52 Actuator Drive Circuit 60 Steering Speed Calculation Circuit

Claims (1)

[Claims] 1. Front wheel steering angle acquisition means for acquiring a steering angle of a front wheel of a vehicle, and a target value of a steering angle of a rear wheel of the vehicle based on the acquired front wheel steering angle, a rear wheel steering for the front wheel steering angle. Target rear wheel steering angle determining means for determining a delay in angular response, a rear wheel actuator for changing the rear wheel steering angle, and the rear for achieving the determined target rear wheel steering angle. In a rear wheel steering angle control device including actuator driving means for driving a wheel actuator, steering angle response delay control means for changing a degree of response delay of the rear wheel steering angle is provided based on a parameter relating to vehicle turning. A rear wheel steering angle control device characterized by.