JPH0687342A - Driving force distributing device for four wheel drive - Google Patents

Abstract

PURPOSE:To prevent a tight corner braking phenomenon by controlling the engaging force of a clutch so as to coincide the actual yaw rate to a target yaw rate only when car speed is judged a standard car speed or higher. CONSTITUTION:A driving force distributing device for four-wheel drive vehicle has a clutch 3 for limiting the differential rotation of front.and rear wheels by an increase in fastening force and increasing the distribution of the driving force to the front wheel. The device also has a car speed detecting means 4 for detecting car speed; a steering angle detecting means 5 for detecting steering angle; and a yaw rate detecting means 6 for detecting actual yaw rate, and a target yaw rate is determined by a target yaw rate setting means 7 on the basis of the detected car speed and steering angle. Further, it is judged whether the car speed is a determined standard car speed or more, and only when the car speed is judged the standard car speed or more, a driving force distribution control means 9 controls the engaging force of the clutch 3 to coincide the actual raw rate to the target yaw rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive force distribution device for a four-wheel drive vehicle having a clutch for changing the distribution ratio of drive force to the front and rear wheels by limiting the differential between the front and rear wheels, and more particularly to an actual yaw rate. The present invention relates to a driving force distribution device capable of controlling the clutch engagement force so that the value of s is equal to the target yaw rate.

[0002]

2. Description of the Related Art In a four-wheel drive vehicle in which the distribution ratio of the driving force to the front and rear wheels can be changed, the slip of the wheels can be prevented by controlling the distribution of the driving force so as to suppress the rotational speed difference between the front and rear wheels. If so, power performance can be improved. Further, if the distribution ratio of the driving force to the front and rear wheels is changed, the lateral force generated at the front wheels and the rear wheels also changes, so the steer characteristic also changes. Therefore, conventionally, the target yaw rate during turning is set based on the vehicle speed, the steering angle, the stability factor, etc., and the distribution of the driving force to the front and rear wheels is not limited to the actual yaw rate as well as the rotational speed difference between the front and rear wheels. A device for controlling so as to match the target yaw rate has been developed, and an invention of this kind is disclosed in Japanese Patent Laid-Open No. 61-229616, Japanese Patent Laid-Open No. 62-99213 or Japanese Patent Laid-Open No. 62-198522. It is listed.

[0003]

The so-called yaw rate follow-up control for controlling the distribution of the driving force so that the actual yaw rate matches the target yaw rate is the drive distribution according to the yaw rate deviation obtained from the difference between the actual yaw rate and the target yaw rate. Generally, this is done by engaging a clutch for. For example, when it is detected that the actual yaw rate is higher than the target yaw rate, it is necessary to correct the steer characteristic to an understeer tendency, so the engagement force of the clutch is increased. Further, when the clutch engagement force is increased in this way, the distribution of the driving force to the front wheels increases, and at the same time, the differential rotation of the front and rear wheels is limited.

Therefore, in the conventional general yaw rate follow-up control described above, the clutch engagement force is increased in order to correct the steer characteristic to an understeer tendency when traveling at a low speed in a tight corner, that is, at a low speed turning with a large steering angle. In some cases, the so-called tight corner braking phenomenon occurs because the differential rotation based on the inner ring difference between the front and rear wheels is limited.
Driving performance may be impaired.

The target yaw rate for the yaw rate follow-up control is determined by the vehicle speed, the steering angle, the stability factor, and the wheelbase. Even if the stability factor can be corrected according to the vehicle speed, the vehicle speed or Since the wheel speed is obtained by counting the output pulses from the magnetically sensitive elements and optical means, the vehicle speed detection accuracy deteriorates at extremely low vehicle speeds.
There was a risk that the target yaw rate would go wrong and a tight corner braking phenomenon would occur.

The present invention has been made in view of the above circumstances, and when performing yaw rate follow-up control involving differential limitation of front and rear wheels, drive distribution of a four-wheel drive vehicle capable of preventing a tight corner braking phenomenon. The purpose is to provide a device.

[0007]

The present invention is characterized in that it has the structure shown in FIG. 1 in order to achieve the above object. That is, the present invention relates to a driving force distribution device for a four-wheel drive vehicle, which includes a clutch 3 that restricts differential rotation of the front and rear wheels 1 and 2 by increasing the fastening force and increases the distribution of the driving force to the front wheels. Vehicle speed detection means 4 for detecting the steering angle, steering angle detection means 5 for detecting the steering angle, yaw rate detection means 6 for detecting the actual yaw rate, and target yaw rate setting means for obtaining a target yaw rate based on the detected vehicle speed and steering angle. 7, vehicle speed determination means 8 for determining whether or not the vehicle speed is equal to or higher than a predetermined reference vehicle speed, and the actual yaw rate is made to match the target yaw rate only when it is determined that the vehicle speed is equal to or higher than the reference vehicle speed. The driving force distribution control means 9 for controlling the engagement force of the clutch 3 is provided.

[0008]

In the device of the present invention, by increasing the engagement force of the clutch 3, the differential rotation between the front wheels 1 and the rear wheels 2 is limited, and the distribution ratio of the driving force to the front wheels 1 is increased. The engagement force of the clutch 3 is basically the driving force distribution control means 9 so that the actual yaw rate matches the target yaw rate.
Controlled by. That is, the target yaw rate setting means 7 sets the target yaw rate based on the vehicle speed detected by the vehicle speed detection means 4 and the steering angle detected by the steering angle detection means 5. The target yaw rate is compared with the actual yaw rate detected by the yaw rate detecting means 6, and the driving force distribution control means 9 changes the engagement force of the clutch 3 so that the difference is eliminated, that is, the actual yaw rate matches the target yaw rate. Control. On the other hand, the detected vehicle speed is judged by the vehicle speed judging means 8 to be equal to or higher than the reference vehicle speed. As a result, if the vehicle speed is slower than the reference vehicle speed, the driving force distribution control means 9 does not control the engagement force of the clutch 3. Therefore, if the vehicle speed at the time of turning with a large steering angle is low, the differential restriction between the front and rear wheels is not particularly actively performed, so that the tight corner braking phenomenon is prevented.

[0009]

EXAMPLES The present invention will now be described based on examples. FIG. 2 is a schematic view showing an embodiment of the present invention,
The four-wheel drive transfer 10 to be controlled is provided on the output side of the automatic transmission 12 connected to the engine 11. This transfer 10 distributes the driving force to the rear wheel side and the front wheel side by a planetary gear type center differential 13, and a drive shaft 14 which is an output shaft of an automatic transmission 12 is connected to a carrier 15. The ring gear 16 is connected to the rear propeller shaft 18 via the output shaft 17. On the other hand, sun gear 19
Is connected to a drive sprocket 20, and transmits a driving force to a front propeller shaft 23 via a chain 21 and a driven sprocket 22 wound around the drive sprocket 20. Also, the carrier 15 and the sun gear 19
A differential limiting clutch 24 is provided between the control unit and the differential limiting clutch 24, and the distribution ratio of the driving force to the front wheels is increased by increasing the engaging hydraulic pressure, that is, by increasing the torque capacity. .

As a device for controlling the hydraulic pressure to the differential limiting clutch 24, a hydraulic control device 25 mainly composed of a linear solenoid valve and a four-wheel drive electronic control device (4WD-ECU) 26 are provided. There is. The electronic control unit 26 mainly includes a central processing unit (CPU), memories (ROM, RAM), and an input / output interface.
Includes a steering angle sensor 27, a yaw rate sensor 28, a wheel speed sensor 29 provided for each wheel, a lateral acceleration (lateral G) sensor 30, and a longitudinal acceleration (longitudinal G) sensor 31.
The signal from each sensor is input. Then, the electronic control unit 26 determines the target yaw rate at the time of turning based on these input parameters, and controls the hydraulic pressure to the differential limiting clutch 24 so that the deviation between the target yaw rate and the actual yaw rate becomes small. Has become.

FIG. 3 shows a control routine for so-called yaw rate follow-up control for controlling the hydraulic pressure of the limited slip differential clutch 24 so that the actual yaw rate matches the target yaw rate. In FIG. 3, in step 1, the actual steering angle δ obtained from the steering angle, the speed v of each wheel, the yaw rate γ, the longitudinal G
x and lateral Gy are read, then in step 2, the vehicle speed (vehicle speed) V is estimated from the wheel speed v, and the rotation speed N of each wheel is obtained. In step 3, the front wheel rotation speed N _F and the rear wheel rotation speed N _R are calculated as the average rotation speeds of the left and right wheels (N _F = (N _FL + N _FR ) / 2, N _R = (N _RL +
N _RR ) / 2). The number of rotations N of the obtained front and rear wheels
_{From F} and N _R , the absolute value ΔN _FR of the rotational speed difference between the front and rear wheels is obtained (step 4). Next, in step 5, the target yaw rate γ ₀ is calculated. This is determined by the coefficient K _{1 (v)} corresponding to the vehicle speed V and the steering angle δ. The coefficient K _{1 (v)} is generally calculated from the vehicle speed V, the wheel base L, and the stability factor K _{h by} the formula K _{1 (v)} = V / {L (1 + K _h · V ² )}. The coefficient K _{1 (v)} may be a coefficient corrected according to the acceleration, the friction coefficient μ of the road surface, or the like.
Further, while the target yaw rate γ ₀ shows a response similar to that of the steering angle δ, the actual yaw rate γ is an element of second-order lag, so the target yaw rate γ ₀ is corrected by a first-order lag (γ ₀ / (1
+ Ts)) may be applied. Here, T is a time constant, which is a predetermined constant value or a variable that increases according to the vehicle speed. Also, s is a Laplace operator. By making such a correction, it is possible to reduce the control error during the turning transition.

Based on the target yaw rate γ ₀ and the actual yaw rate γ thus obtained, their deviation Δγ
(= Γ (γ ₀ −γ)) is calculated in step 6. Here, as the deviation Δγ, the target yaw rate γ ₀ and the actual yaw rate γ
The product of the difference between and the actual yaw rate γ is taken for the following reason. That is, the yaw rate is a directional parameter, and the deviation Δγ also shows a drift-out tendency and a spin (oversteer) tendency as positive (+) or negative (-).
Therefore, if the product is taken as described above, it will be a positive value when there is a drift-out tendency, and the spin tendency will be the opposite, regardless of whether the vehicle is turning left or right. Is negative when.

Next, in step 7, it is judged whether the vehicle speed V exceeds a predetermined reference vehicle speed V0. This reference vehicle speed V0 is a low vehicle speed that may cause a tight corner braking phenomenon during turning with differential limitation. If the actual vehicle speed V is higher than this reference vehicle speed V0, proceed to step 8. , Rotational speed difference between front and rear wheels ΔN _FR
The differential limiting clutch pressure P (ΔNFR) based on the above is corrected based on the yaw rate deviation Δγ, and the corrected pressure is set as the differential limiting clutch pressure P _CD .

That is, the vehicle provided with the transfer 10 shown in FIG. 2 is a four-wheel drive vehicle based on the rear wheel drive, and the distribution ratio of the drive force to the front wheel side is increased by increasing the differential limitation. Therefore, if there is a tendency to drift out, it is necessary to increase the distribution ratio of the driving force to the rear wheel side to correct it to the spin side. Conversely, if there is a tendency to spin, drive to the front wheel side. It is necessary to increase the force distribution ratio and correct it to the drift-out side. Therefore, as shown in FIG. 4, the correction coefficient K _{2 (Δγ)} corresponding to the deviation Δγ is set to a value smaller than “1” when Δγ is large in the plus direction, and is large when Δγ is large in the minus direction. Is set to a value larger than "1".

On the other hand, the engagement oil pressure P (ΔNFR) of the differential limiting clutch 24 based on the rotational speed difference ΔN _FR between the front and rear wheels is, as shown in FIG.
Although higher as _RF increase, the actual yaw rate γ in cornering
When the deviation Δγ occurs between the target yaw rate γ ₀ and the target yaw rate γ ₀ , the correction coefficient K _{2 (Δ
γ)} is applied for correction (step 8), and the value is supplied to the limited slip differential clutch 24 as the actual engagement hydraulic pressure P _CD . The relationship between the actual engagement hydraulic pressure P _CD and the rotation speed difference ΔN _FR between the front and rear wheels is shown in FIG. 6 when the deviation Δγ is expressed as a parameter.

When the vehicle speed V is equal to or lower than the reference vehicle speed V0 (when the result of the determination in step 7 is "no"), the process proceeds to step 9 to stop the yaw rate follow-up control. That is, the pressure value P (ΔNFR) based on the rotational speed difference ΔN _FR between the front and rear wheels is directly used as the differential limiting clutch pressure P _CD . Therefore, in this case, even if the yaw rate deviation Δγ takes a negative value, the correction coefficient K _{2 (Δγ) having a} value larger than “1” described above.
However, since it is not multiplied by the pressure value P (ΔNFR) based on the rotational speed difference ΔN _FR , the differential limiting clutch pressure P _CD is suppressed low, and as a result, the braking phenomenon occurs even in a tight corner where the steering angle δ is large. Does not occur.

As a general tendency, the stronger the drift-out characteristic is, the better the stability is. Therefore, when the yaw rate sensor or the steering angle sensor fails and the yaw rate follow-up control cannot be performed, It is preferable to adopt the map shown in FIG. 7 as a map for obtaining the pressure value P (ΔNFR) based on the rotation speed difference ΔN _FR of the front and rear wheels.
FIG 7 is a pressure value P (delta corresponding to the rotational speed difference .DELTA.N _FR
NFR) is set to a higher pressure than that in the normal state (map shown in FIG. 5), and therefore, in the case of failure,
By adopting the map of, the differential limitation becomes stronger, the tendency of drifting out becomes stronger, and the stability of the vehicle increases.

The present invention is not limited to the above embodiment, and when the vehicle speed is equal to or lower than the predetermined vehicle speed, the engagement hydraulic pressure P _CD of the differential limiting clutch 24 is set to "0". Good. Further, in the above embodiment, the distribution of the driving force to the front and rear wheels is performed by the planetary gear type transfer, and the differential limitation thereof is performed by the clutch to change the distribution ratio of the driving force. The present invention is not limited to this embodiment, and the point is that the distribution ratio of the driving force to the front and rear wheels may be changed according to the engagement pressure of the clutch.

[0019]

As is apparent from the above description, according to the present invention, the differential limitation between the front and rear wheels is weakened at a low vehicle speed,
Or, because it is canceled, it is possible to prevent the tight corner braking phenomenon when turning at a large steering angle, and when the vehicle speed is a predetermined value or more, the clutch pressure is increased or decreased to perform yaw rate follow-up control, which is good. It is possible to maintain excellent steering characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a block diagram schematically showing an embodiment of the present invention.

FIG. 3 is a flowchart showing a control routine of an engagement hydraulic pressure of a limited slip differential clutch.

FIG. 4 is a diagram showing a correction coefficient based on a yaw rate deviation.

FIG. 5 is a map showing an engagement hydraulic pressure of a limited slip differential clutch based on a difference in rotation speed between front and rear wheels.

FIG. 6 is a diagram showing the relationship between the rotational speed difference between the front and rear wheels and the actual engagement hydraulic pressure of the limited slip differential clutch, using the yaw rate deviation as a parameter.

FIG. 7 is a map showing the engagement hydraulic pressure of the differential limiting clutch based on the rotational speed difference between the front and rear wheels used when the sensor fails.

[Explanation of symbols]

 1 Front Wheel 2 Rear Wheel 3 Clutch 4 Vehicle Speed Detecting Means 5 Steering Angle Detecting Means 6 Yaw Rate Detecting Means 7 Target Yaw Rate Setting Means 8 Vehicle Speed Judging Means 9 Driving Force Distribution Control Means

Claims (1)

[Claims] 1. A vehicle speed for detecting a vehicle speed in a driving force distribution device for a four-wheel drive vehicle, comprising: a clutch for limiting differential rotation of front and rear wheels and increasing distribution of driving force to front wheels by increasing fastening force. The detection means, the steering angle detection means for detecting the steering angle, the yaw rate detection means for detecting the actual yaw rate, the target yaw rate setting means for obtaining the target yaw rate based on the detected vehicle speed and the steering angle, and the vehicle speed are predetermined. Vehicle speed determining means for determining whether or not the vehicle speed is equal to or higher than the reference vehicle speed,
A four-wheel drive system comprising: a drive force distribution control means for controlling the engagement force of the clutch so that the actual yaw rate matches the target yaw rate only when it is determined that the vehicle speed is equal to or higher than the reference vehicle speed. Driving force distribution device for driving vehicles.