JP2626226B2 - Four-wheel steering control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention has a rear wheel steering mechanism and is a front-wheel drive vehicle (FF vehicle).
And a four-wheel steering control device applied to a vehicle such as a rear-wheel drive vehicle (FR vehicle).

(Prior Art) Conventionally, as a four-wheel steering control device, for example,
A device described in -71761 is known, in which the front and rear wheel rotation speed difference is used as drive slip information, and the steering angle ratio of the front and rear wheels is changed to a stable side based on the front and rear wheel rotation speed difference. A technique for preventing the vehicle from being over-steered or under-steered based on driving slip is disclosed.

Further, as an improvement technique of the above-mentioned conventional device, Japanese Patent Application Laid-Open
A device described in Japanese Patent Publication No. 166664 is known. In this publication, the change rate of the front and rear wheel rotation speed difference is simply taken as road surface u information, and when the change rate of the front and rear wheel rotation speed difference is large, the steering based on the drive slip is performed. There is disclosed a technology for improving steering stability on a rough road or a low u road by prohibiting a change in the angle ratio.

(Problems to be Solved by the Invention) However, the above-described conventional device is a device that, when a driving slip occurs, performs change correction control of the steering angle ratio regardless of the magnitude of the driving slip. Is not taken into account at all, for example, depending on the tire characteristics, although a slip ratio of around 0.05 may generate the maximum lateral force, it is simply considered that drive slip has occurred, and the steering angle ratio is corrected. This unnecessarily lowers the turning limit of the vehicle.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. In a four-wheel steering control device having a rear-wheel steering mechanism, a turning limit of a vehicle is increased as much as possible, and a rear-wheel steering in a nonlinear region of tire characteristics is performed. It is an object to perform control appropriately.

(Means for Solving the Problems) In order to solve the above problems, the four-wheel steering control device of the present invention has a rear wheel turning mechanism a capable of turning the rear wheels, and performs rear wheel rotation in relation to the steering state of the front wheels. In a four-wheel steering control device in which a steering amount is determined, a driving slip detecting means b for detecting a slip state of a driving wheel, a lateral force characteristic with respect to a driving slip of a tire on which the driving wheel is mounted, that is, driving from a non-slip state. The lateral force increases with the increase of the wheel slip and increases to a maximum, and thereafter, the tire lateral force characteristic setting means c for setting the tire lateral force characteristic which decreases with the increase of the drive wheel slip, and the detected drive slip is set. Steering angle ratio calculating means d for calculating the steering angle ratio of the front and rear wheels in accordance with the tire lateral force determined based on the tire lateral force characteristics, and rear wheel rotation by multiplying the calculated steering angle ratio by the front wheel steering angle. Rudder Wheel steering control means e after that steering control of the rear wheels decide
And.

(Operation) At the time of turning in which a driving wheel slip occurs, the steering angle ratio calculating means d detects the driving slip detected by the driving slip detecting means b and the tire lateral force characteristic set by the tire lateral force characteristic setting means c. The steering angle ratio of the front and rear wheels is calculated according to the tire lateral force obtained based on the above. Then, in the rear wheel turning control means e, the rear wheel turning amount is determined by multiplying the front wheel turning angle by the steering angle ratio calculated by the steering angle ratio calculating means d, and the rear wheels are turned.

Therefore, instead of simply determining the steering angle ratio between the front and rear wheels due to the occurrence of the drive slip, the tire lateral force characteristic with respect to the drive slip, that is, the lateral force increases from the non-slip state to the drive wheel slip and increases to the maximum. Thereafter, since the steering angle ratio of the front and rear wheels is determined according to the tire lateral force required based on the characteristic that decreases with the rise of the drive wheel slip, the optimal amount for the lateral force maximum point and nonlinearity of the tire characteristic The rear wheels are steered.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

 First, the configuration will be described.

FIG. 2 is an overall view showing the four-wheel steering control device according to the first embodiment of the present invention.

The four-wheel steering control device of the first embodiment is applied to a front-wheel-drive vehicle, where 1, 2 are front wheels, 3, 4 are rear wheels, 5 is a steering wheel, 6 is a steering angle sensor, 7 is a transmission, and 8 is an engine. , 9
Is a controller, 10 is a rear wheel steering actuator (rear wheel steering mechanism), 11 is a front left wheel speed sensor, 12 is a front right wheel speed sensor,
13 is a left rear wheel speed sensor, 14 is a right rear wheel speed sensor, and 15 is a vehicle speed sensor.

The controller 9 controls each of the sensors 5, 11, 12, 13, 14, (1
5) Input the sensor signal from
Wheel speed information, calculates a rear-wheel steering amount [delta] _r based on the (vehicle speed information), and outputs a drive command the rear wheel steering amount [delta] _r is obtained in the rear wheel steering actuator 10.

The controller 9 calculates a steering angle ratio K (S) based on the calculated driving slip ratio S and a preset tire lateral force characteristic map, and calculates the steering angle ratio K (S) and the front wheel steering. There is a rear wheel turning control unit (rear wheel turning control means) for obtaining a rear wheel turning amount δ _r by multiplication of the angle δ _f . Incidentally, the front wheel steering angle [delta] _f is the steering angle θ is a value obtained by dividing the vehicle-specific steering gear ratio N, the controller 9
Is calculated within.

The lateral force characteristic map of the tire is set in the form of a table having a non-linear characteristic or an arithmetic expression based on experimental data obtained from individual tires mounted on the driving wheels.

 Next, the operation will be described.

FIG. 3 is a flowchart showing the flow of the rear wheel steering control operation performed by the controller 9, and each step will be described below.

In step 30, each steering θ and each wheel speed N _FL , N _FR , N _RL , N
_RR is read.

In step 31, the drive slip ratio S is calculated based on the wheel speeds N _FL , N _FR , N _RL , N _RR .

The equation for calculating the drive slip ratio S is as follows when the rear wheel speed, which is the driven wheel, is approximated to the vehicle speed.

N _F = 1/2 (N _FL + N _FR ) N _R = 1/2 (N _RL + N _RR ) In step 32, the fixed characteristic or tire slip βt
(For example, the characteristics described in the step frame), the tire lateral force characteristics f (S) are set. In this embodiment, βf (front wheel side slip angle) described later corresponds to the tire side slip angle βt.

In step 33, the steering angle ratio K (S) is calculated by the following equation based on the tire lateral force characteristic f (S) set in step 32 and the vehicle-specific constant A.

 The constant A is given by the following equation.

a; front-centroid distance b; rear-centroid distance between Cf; wheel cornering power Cr; the rear wheel cornering power step 34, the rear rotary by the multiplication of the steering angle ratio K (S) and the front wheel turning angle [delta] _f The steering amount δ _r (= K (S) · δ _f ) is determined.

 Next, the lateral force characteristics of the tire will be described.

FIG. 4 shows tire characteristics (lateral force characteristics and driving force characteristics with respect to the driving slip ratio S).

It can be seen from FIG. 4 that all the characteristics depend on the driving slip ratio S. Of these, when focusing on the lateral force characteristics, the lateral force immediately decreases as the driving slip ratio S increases. Instead, the lateral force is maximum when the drive slip ratio S is around 0.05 regardless of the tire side slip angle βt, and decreases after that.

However, the above-mentioned prior art is a control for correcting the steering angle ratio in accordance with the degree of occurrence of the driving slip, and does not consider this lateral force maximum point at all.

Therefore, when this conventional device is applied to a front-wheel drive vehicle and the rear wheel steering amount is corrected in the opposite phase from the point in time when the front wheel drive slip occurs even a little, understeer is prevented.
Unnecessarily lowering the turning limit.

In contrast, in the present embodiment, focusing on the driving slip ratio dependency of tire lateral force, but so as to determine a rear-wheel steering amount [delta] _r by K (S) · δ _f, the physical meaning Will be described with reference to the analysis model shown in FIG.

First, in the case of 4WS, the yaw moment m of the vehicle is represented by the following equation.

m = a · Cf · βf−b · Cr · βr (1) βf; front wheel side slip angle βr; rear wheel side slip angle Here, the front wheel cornering power Cf changes according to the drive slip ratio S. Cf as function
If f (S) is set, the effective amount of the rudder (the change in the yaw moment m of the vehicle with respect to the change in the steering angle θ) is _{However, δ r = K · δ f} βf = δ f + β- (a / R) βr = δ r + β + (b / R) β; a steering angle ratio; vehicle gravity center point sideslip angle R; turning radius K.

Here, the effectiveness of the rudder Does not depend on the drive slip ratio S.

Solving the above equations (1) and (2) using the steering angle ratio K as a function K (S) of the drive slip ratio S, However, Becomes

Therefore, (Step 33).

That is, it is understood that the steering angle ratio K (S) may be determined based on the tire lateral force characteristic f (S) with respect to the driving slip ratio S.

As described above, in the four-wheel steering control device of the embodiment, the drive slip dependence f (S) of the tire lateral force is obtained.
And a device for determining the steering angle ratio K (S) of the front and rear wheels based on the lateral force characteristic f (S) with respect to the driving slip ratio S of the tire. The rear wheels 3 and 4 are steered by the optimum amount for the non-linearity, so that the turning limit of the vehicle can be raised as much as possible, and the rear wheel steering control in the non-linear region of the tire characteristics is accurately performed. Can be done.

 Next, a second embodiment will be described.

The device of the first embodiment is set as K (0) = 0 in the above equation (5), that is, when the drive slip ratio S is zero, the steering angle ratio K
As is clear from the fact that (S) is set to zero, the rear wheel is not steered when the drive slip ratio S is zero (2WS), and only when a drive slip occurs, the rear wheel is changed according to the drive slip ratio S. This is an example of turning the steering wheel.

On the other hand, in the second embodiment, the rear wheels 3 and 4 are basically steered at a steering angle ratio K (V) corresponding to the vehicle speed V. This is an example in which the steering amount of the rear wheels 3 and 4 is corrected by the steering amount based on the steering angle ratio K (S).

The configuration of the device of the second embodiment is the same as the configuration shown in FIG.

The controller 9 determines the main rear wheel turning amount δ _r1 from the main steering angle ratio K (V) calculated based on the vehicle speed V, and based on the driving slip ratio S and the tire lateral force characteristic f (S). Rear wheel turning control which determines the corrected rear wheel turning amount δ _r2 from the corrected steering angle ratio K (S) calculated in the above, and obtains the total rear wheel turning amount δ _r by the sum of both rear wheel turning amounts δ _r1 and δ _r2. (Rear wheel steering control means).

 Next, the operation will be described.

FIG. 6 is a flowchart showing the flow of the rear wheel steering control operation performed by the controller 9, and each step will be described below.

In step 60, the steering θ, the vehicle speed V, and the wheel speeds N _FL , N
_FR , _NRL , and _NRR are read.

In step 61, the main steering angle ratio K (V) is determined according to the vehicle speed V.

That is the ratio of the rear wheel steering amount [delta] _r with respect to the front wheel steering angle [delta] _f the main steering ratio K (V), as shown in FIG. 7, and as is the low-speed large after reverse phase wheel steering amount The higher the vehicle speed, the larger the in-phase rear wheel steering amount, and the ratio is smoothly changed from the opposite phase to the same phase as the vehicle speed V increases.

In step 62, the main steering angle ratio K (V) and the front wheel turning angle δ _f
Accordingly, the main rear wheel steering amount _δr1 is determined by the following equation.

δ _r1 = · K (V) δ _{f In} step 63, similarly to step 31, the respective wheel speeds N _FL ,
The drive slip ratio S is calculated based on N _FR , N _RL , and N _RR .

In step 64, similarly to step 32, the tire lateral force characteristic f (S) based on the fixed characteristic or the characteristic (for example, the characteristic described in the step frame) according to the tire slip angle βt (= βf) is set. .

In step 65, similarly to step 33, the corrected steering angle ratio K (S) is calculated based on the tire lateral force characteristic f (S) set in step 64 and the vehicle-specific constant A.

In step 66, the corrected steering angle ratio K (S) and the front wheel turning angle δ
_f , the corrected wheel turning amount δ _r2 (= K (S) · δ
_f ) is determined.

In step 67, the total rear wheel steering amount [delta] _r is determined by the following equation which is the sum of the primary rear wheel steering amount [delta] _r1 and corrected rear wheel turning amount [delta] _r2.

δ _r = δ _r1 + δ _r2 Therefore, in the second embodiment, the vehicle turning limit can be raised as much as possible at the time of the acceleration turning in which the driving slip occurs, as in the first embodiment, and the tire can be raised. The rear wheel steering control can be accurately performed in the non-linear region of the characteristic. In addition, at the time of turning without driving slip, the rear wheel steering amount is given according to the vehicle speed V by δ _r = δ _r1. In addition, it is possible to achieve both turning performance in a low-speed turning range and stability in a high-speed turning range.

Although the embodiments have been described with reference to the drawings, the specific configuration is not limited to the embodiments.

For example, in the embodiment, an example in which the present invention is applied to an FF vehicle is shown, but the present invention may be applied to an FR vehicle.

However, in the case of FF vehicles, the rear wheel steering amount and the corrected rear wheel steering amount are given to the opposite phase side to prevent strong understeering based on drive slip, whereas in the case of FR vehicles, A rear wheel turning amount and a corrected rear wheel turning amount are given to the in-phase side in order to prevent a strong oversteer caused by the driving slip.

Further, in the embodiment, the example in which the drive slip ratio is used as the control information for checking the drive slip state is shown, but the difference between the front and rear wheel rotational speeds and the drive slip ratio may be used as the drive slip information.

(Effects of the Invention) As described above, according to the present invention, a four-wheeled vehicle having a rear-wheel steering mechanism capable of steering the rear wheels, and in which the rear-wheel steering amount is determined in relation to the steering state of the front wheels. In the steering control device, a driving slip detecting means for detecting a slip state of the driving wheel, and a lateral force characteristic with respect to a driving slip of a tire on which the driving wheel is mounted, that is, a lateral force with a rise of the driving wheel slip from a non-slip state. Tire lateral force characteristic setting means for setting a tire lateral force characteristic that increases to a maximum and thereafter decreases as the drive wheel slip increases, and a tire lateral force characteristic determined based on the detected drive slip and the set tire lateral force characteristic. Steering angle ratio calculating means for calculating the steering angle ratio of the front and rear wheels in accordance with the lateral force of the tire, and determining the amount of rear wheel steering by multiplying the calculated steering angle ratio by the front wheel steering angle to steer the rear wheels. Rear wheel steering to control Control means, the rear wheels are steered by an optimum amount for the lateral force maximum point and the non-linearity of the tire characteristics when a drive slip occurs, and the turning limit of the vehicle can be raised as much as possible. Thus, an effect is obtained that the rear wheel steering control can be accurately performed in the non-linear region of the tire characteristics.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram showing a four-wheel steering control device of the present invention, FIG. 2 is an overall view showing a four-wheel steering control device of a first embodiment, and FIG. 3 is a four-wheel steering control of the first embodiment. FIG. 4 is a flow chart showing a flow of a rear wheel steering control operation performed by a controller of the apparatus, FIG. 4 is a characteristic diagram of lateral force and driving force with respect to a driving slip ratio, FIG. 5 is an analysis model diagram of a four-wheel steering vehicle, FIG.
FIG. 7 is a flowchart showing the flow of a rear wheel turning control operation performed by the controller of the four-wheel steering control device according to the second embodiment. FIG. 7 is a main steering angle ratio characteristic diagram corresponding to the vehicle speed. a rear wheel turning mechanism b drive slip detecting means c tire lateral force characteristic setting means d steering angle ratio calculating means e rear wheel turning control means

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B62D 113: 00 137: 00

Claims (1)

(57) [Claims] A four-wheel steering control device having a rear wheel steering mechanism capable of steering a rear wheel and determining a rear wheel steering amount in relation to a front wheel steering state. Slip detecting means and a lateral force characteristic with respect to the drive slip of the tire on which the drive wheel is mounted, that is, the lateral force increases from the non-slip state with the increase of the drive wheel slip and becomes maximum, and thereafter, the drive wheel slip increases. Tire lateral force characteristic setting means for setting a tire lateral force characteristic to be decreased, and a steering angle ratio between the front and rear wheels according to a tire lateral force obtained based on the detected drive slip and the set tire lateral force characteristic. Steering angle ratio calculating means for calculating, and rear wheel turning control means for determining the amount of rear wheel turning by multiplying the calculated steering angle ratio by the front wheel turning angle to control turning of the rear wheels. Featured four wheels Rudder control unit.