JP2630609B2 - Control method of driving force distribution and rear wheel steering angle of four-wheel drive, four-wheel steering vehicle - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a driving force distribution and a rear wheel steering angle of a four-wheel drive, four-wheel steering vehicle.

2. Description of the Related Art Conventionally, in a vehicle, a rear wheel steering device that provides a steering angle to the rear wheel in the same direction as the front wheel, that is, a direction to increase the understeer tendency, in accordance with steering of the front wheel to improve stability during traveling is conventionally known. It is more known (see, for example, JP-A-62-31566).

It is known from Japanese Patent Application Laid-Open No. 62-50230 that in a four-wheel drive vehicle, the driving force distribution ratio between the front wheel side and the rear wheel side affects straight running stability. A device that improves the turning performance of the vehicle body by increasing the distribution of the driving force to the rear wheels in accordance with the steering angle of the steering wheel has already been developed and has been filed in Japanese Patent Application No. 61-144478.

Problems to be Solved by the Invention Equipped with a device (hereinafter, referred to as a torque split control device) that improves the turning performance at the time of steering by controlling the distribution of the driving force to the front and rear wheels as described above. Providing a conventionally known rear wheel steering device in a wheel drive vehicle as described above can achieve a target characteristic by mutually interfering and canceling out the effects of torque split control and rear wheel steering control. May not be.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control method capable of sufficiently exhibiting the advantages of both torque split control and rear wheel steering control.

Means for Solving the Problems The present invention relates to a four-wheel-drive vehicle equipped with the torque split control device and the rear wheel steering device as described above, wherein the actual lateral acceleration detected by the front wheel steering lateral G sensor and the front wheel steering Virtual lateral acceleration calculated from angle and vehicle speed If the set range -ε to ε is greater than or less than, the difference And the correction control of the distribution of the driving force to the front and rear wheels and the steering angle of the rear wheel according to the total driving force at that time.

Action From the above, In the case of, it is determined that the vehicle has a tendency to spin, and the front wheel driving force distribution is corrected to be large, and the steering angle of the rear wheels in the understeer direction (in-phase direction) is corrected to be large. In this case, the total driving force is large. If so, the front wheel drive force distribution is further increased and the degree of increase in the understeer steering angle of the rear wheels is reduced to reduce the degree.If the total drive force is small, the degree of increase in the front wheel drive force distribution is reduced and the rear wheel The understeering direction steering angle is further increased.

In this case, it is determined that the vehicle is in a drift state, and the rear wheel driving force distribution is corrected to be large, and the understeer steering angle of the rear wheels is reduced. If the total driving force is small, reduce the degree of increase in the rear wheel driving force distribution and further increase the rear wheel understeering direction steering angle. Correction control is performed to greatly reduce the amount.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a steering handle, 2 denotes a front wheel, and a known front wheel steering mechanism from the steering handle 1 to the front wheel 2 has a control valve 3 that operates in accordance with a steering torque. A known hydraulic power cylinder device including a power cylinder 5 having left and right oil chambers into which the discharge hydraulic pressure of the oil pump 4 is selectively introduced is provided.

Numeral 6 is a steering force detection system comprising left and right oil pressure sensors 7a and 7b for detecting the oil pressures in the left and right oil chambers of the power cylinder 5 and an operational amplifying device 8 for calculating the difference between the oil pressure signals of the oil pressure sensors, that is, the steering assist force. The steering force signal of the steering force detection device 6 is input to the rear wheel steering control unit 9. Reference numeral 10 denotes a vehicle speed sensor. A vehicle speed signal of the vehicle speed sensor 10 is also input to the rear wheel steering control unit 9, and the rear wheel steering control unit 9 is set in advance based on the steering force signal and the vehicle speed signal. A rear wheel steering angle target value is determined based on a steering force-rear wheel steering angle characteristic using the vehicle speed as a parameter, and an output signal is issued to a rear wheel steering actuator 11 such as a motor to output a rear wheel 14.
Is turned according to the target value. 12 is an electromagnetic clutch, 13 is a rear wheel steering mechanism including a speed reduction mechanism, a link mechanism, etc., 15 is a rear wheel steering angle sensor for detecting a rear wheel steering angle, and a rear wheel steering angle signal of the rear wheel steering angle sensor 15 Is input to the rear-wheel steering control unit 9 and is feedback-controlled by this.

Reference numeral 16 denotes an output shaft of a power unit composed of an engine, a transmission, and the like (not shown). The torque of the output shaft 16 is transmitted to a front drive shaft 18 and a rear drive shaft 19 via a center differential device 17, respectively. The wheels 14 are driven.

Reference numeral 20 denotes a torque distribution control mechanism. In the illustrated embodiment, an example using a hydraulic clutch is shown. That is, the torque distribution control mechanism 20 is a hub that is directly connected to the front drive shaft 18 and rotates.
20a and a case 20b which is decelerated and rotated via a gear mechanism by the rear drive shaft 19, and is constituted by a multi-plate hydraulic clutch. When the hydraulic pressure supplied to the clutch is zero, the clutch torque of the clutch is zero. Therefore, the front-rear torque distribution ratio (50: 5
The torque is distributed in the range of 0 to 70:30).

As the hydraulic pressure supplied to the clutch increases, the hub 20
A clutch torque corresponding to the oil pressure is generated due to a rotation difference between a and the case 20b, and the clutch torque is applied to the case 20b on the low rotation side, so that the torque distribution of the rear drive shaft 19 increases as the oil pressure increases. Then, the torque distribution of the front drive shaft 18 decreases.

Therefore, the hydraulic pressure source 22 is controlled by the duty solenoid valve 21.
By controlling the hydraulic pressure supplied to the clutch, the distribution of the driving force to the front and rear wheels can be freely changed and controlled.

Reference numeral 23 denotes a torque split control unit. The control unit 23 includes a front wheel steering angle signal of a front wheel steering angle sensor 24 for detecting a front wheel steering angle, a vehicle speed signal of the vehicle speed sensor 10, and an engine speed for detecting an engine speed. An engine speed signal from the sensor 25 and an accelerator opening signal from an accelerator opening sensor 26 for detecting the accelerator opening are input, and a drive force distribution target value for the front and rear wheels is determined based on the front wheel steering angle and the vehicle speed. Calculate the engine output torque from the number and the accelerator opening, determine the hydraulic pressure to be supplied to the torque distribution control mechanism 20 from the engine output torque and the driving force distribution target value, issue an output signal to the duty solenoid valve 21, and determine Torque distribution control mechanism for hydraulic pressure according to value
The driving force is supplied to the motor 20 and is subjected to feedback control based on signals from the front, rear, left, and right wheel rotation speed sensors 27 so that the driving force is distributed according to a target value.

In general, in a four-wheel drive vehicle, when the driving force distribution on the front wheel side is large, the vehicle tends to understeer and the straight running stability is improved, and when the driving force distribution on the rear wheel side is large, the understeering tendency decreases and the steering speed decreases. It is conventionally known that the turning performance of the front wheel is improved.Therefore, the front wheel side driving force distribution is set to a large value such as a front / rear driving force distribution ratio of 60:40 by the center differential device 17, and during steering, The front wheel steering angle-driving force distribution ratio characteristics using the vehicle speed as a parameter, for example, based on the characteristics shown by the solid line in FIG. 3, in the steering angle range where the front wheel steering angle is relatively small, the rear wheel driving force distribution is increased. By performing such control as to gradually decrease the driving force distribution on the rear wheel side in the steering angle range where the front wheel steering angle is relatively large,
It is possible to satisfy all the demands of improving straight running stability, improving turning performance during steering in a small turning angle range, and improving stability during steering in a large turning range.

In a four-wheel drive vehicle in which the rear wheel steering control and the torque split control are performed as described above, even if the turning property is improved by reducing the understeer tendency by the torque split control during steering, depending on the vehicle speed, depending on the vehicle speed. By the steering control, the rear wheel is steered in the same direction as the front wheel (in-phase steering), that is, steered in the understeer direction, and both effects may cancel each other. In such a case, if the turning angle of the rear wheels in the understeer direction by the rear wheel steering control is significantly reduced, the above-described problem can be solved. However, if the vehicle is spinning at that time, the spin is prevented by the rear wheel steering. Since the effect is almost eliminated, there is a problem that the possibility of spin generation is increased.

Therefore, the steering controller 29 determines whether the front wheel steering angle δf and the vehicle speed V
Virtual lateral acceleration from (Where l is a wheelbase and A is a stability factor.) The information of the actual lateral acceleration actually generated in the vehicle body detected by the lateral G sensor 28 and the virtual lateral acceleration detected by the following equation. And the difference between the two Is greater than a set value ε Determines that the vehicle has a tendency to spin, and controls the torque split control to reduce the rear wheel drive power distribution from the basic drive power distribution characteristic shown by the solid line and increase the source wheel drive power distribution as shown by the dotted line in FIG. 3, for example. A command is issued to the unit 23 to reduce the turning performance, and based on the characteristic that the steering angle of the rear wheel is increased toward the understeer side (in-phase side) as shown by the dotted line from the basic steering angle characteristic shown by the solid line in FIG. A command is issued to the rear-wheel steering control unit 9 to control the vehicle, thereby preventing the vehicle from falling into spin due to an increase in the rear wheel slip angle and generation of a yaw moment in the direction of suppressing spin accompanying the increase. .

If it is determined that the vehicle is in a drift state, the controller 29 issues a command to the torque split control unit 23 so as to increase the rear wheel driving force distribution as indicated by the chain line tightening in FIG. By issuing a command to decrease the steering angle in the understeer direction of the rear wheel to the rear wheel steering control unit 9 as shown by the chain line in FIG.

However, the influence of the above-described distribution of the driving force and the steering of the rear wheels on the steering characteristics of the vehicle varies depending on the magnitude of the total driving force, and is shown in FIG.

That is, the larger the total driving force, the smaller the margin of the frictional force of each wheel, the smaller the difference in the driving force distribution, the more the lateral force can be adjusted, and the greater the influence of the driving force distribution on the steering characteristics, Conversely, when the total driving force is small, the margin of the frictional force of each wheel is large, and the width in which the steering characteristic of the vehicle can be changed by correcting the driving force distribution becomes very narrow.

On the other hand, the degree of influence of the rear wheel steering on the steering characteristics decreases as the total driving force increases. This is because if the total driving force is large, the margin of the rear wheel frictional force is small, so that even if the slip angle is increased, the lateral force is easily saturated.

Therefore, in the present invention, the torque splitting control unit 23 obtains the total driving force from each information of the axle opening and the engine speed, and inputs this to the controller 29,
The controller 29 is If the total driving force is large, the rear wheel driving force distribution as shown by the dotted line in FIG. 3 is further reduced to increase the front wheel driving force distribution, and the understeer as shown by the dotted line in FIG. Direction to reduce the rear wheel steering angle,
Mainly prevent the vehicle body spin by increasing the front wheel drive power distribution, When the total driving force is small, the distribution of the rear wheel driving force as shown by the dotted line in FIG. 3 is made closer to the characteristic shown by the solid line to reduce the front wheel driving force distribution, and the rear wheel shown by the dotted line in FIG. Modify the steering angle to increase further in the understeer direction,
The body spin is prevented mainly by rear wheel steering.

In the case where the total driving force is large, the distribution of the rear wheel driving force is further increased to reduce the distribution of the front wheel driving force as shown by the chain line in FIG. 3, and the rear wheel steering angle shown by the chain line in FIG. To improve the turning performance mainly by reducing the front wheel drive power distribution, In the case where the total driving force is small, the distribution of the rear wheel driving force indicated by the chain line in FIG. 3 is corrected so as to approach the characteristic indicated by the solid line, and the rear wheel steering angle in the understeer direction indicated by the chain line in FIG. 4 is further reduced. Then, the turning performance is improved mainly by rear wheel steering.

That is, in the present invention, as shown in the flowchart of FIG. 2 and the correction characteristic example diagram of FIG. 5, the longitudinal driving force distribution and the rear wheel steering angle are calculated by calculating the actual lateral acceleration of the vehicle and the virtual lateral acceleration obtained by calculation. By performing the feedback control based on the difference and the total driving force at that time, the respective functions of the torque split control and the rear wheel steering control can be efficiently and sufficiently exerted, and the stability can be significantly improved. .

Advantageous Effects of the Invention As described above, according to the present invention, by associating the rear wheel steering control and the torque split control, the vehicle with the rear wheel steering control can sufficiently exhibit the excellent kinetic performance provided by the torque split control. In addition to accurately maintaining the function of improving the stability of the, you can use both of these functions efficiently,
This can bring a great effect in practical use.

[Brief description of the drawings]

FIG. 1 is an explanatory plan view showing an embodiment of the present invention, FIG. 2 is a flowchart showing an example of a control mode in the present invention,
FIG. 3 is an explanatory diagram of a rear wheel driving force distribution characteristic, FIG. 4 is an explanatory diagram of a rear wheel steering angle characteristic, and FIG. 5 is a difference between the actual lateral acceleration and the virtual lateral acceleration of the vehicle and the front and rear wheel driving force based on the total driving force. FIG. 6 is a diagram showing an example of the distribution and the correction characteristics of the rear wheel steering angle, and FIG. 6 is a diagram for explaining that the degree of influence on the driving force distribution and the steering characteristics of the rear wheel steering changes depending on the total driving force. DESCRIPTION OF SYMBOLS 1 ... Steering handle, 2 ... Front wheel, 6 ... Steering force detection device, 9 ... Control unit for rear wheel steering, 10
…… Vehicle speed sensor, 11 …… Rear wheel steering actuator, 14
... Rear wheel, 15 ... Rear wheel steering angle sensor, 20 ... Torque distribution control mechanism, 23 ... Control unit for torque split, 24 ... Front wheel steering angle sensor, 25 ... Engine speed sensor, 26 ... Accelerator opening sensor, 28 Horizontal G sensor, 29
……controller.

Claims (1)

(57) [Claims] 1. A four-wheel drive vehicle equipped with a device for variably controlling the distribution of driving force to front and rear wheels based on a front wheel steering angle and a vehicle speed, wherein the rear wheels are steered in the same direction as the front wheels during front wheel steering. Equipped with a device for controlling the rear wheel steering angle,
If the difference between the actual lateral acceleration detected by the lateral G sensor at the time of front wheel steering and the virtual lateral acceleration calculated by the front wheel steering angle and the vehicle speed is greater than or less than a certain set value range, Driving of a four-wheel drive or four-wheel steering vehicle, wherein the driving force distribution to the front and rear wheels and the rear wheel steering angle are modified and controlled according to the difference between the lateral acceleration and the virtual lateral acceleration and the total driving force at that time. Control method of power distribution and rear wheel steering angle.