JP2745992B2 - Driving force distribution device for four-wheel drive vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle capable of changing a distribution ratio of driving force to front and rear wheels, and more particularly to an apparatus for controlling a clutch engagement force for changing a distribution ratio of driving force. It is.

[0002]

2. Description of the Related Art Driving force and lateral force generated by a tire of a vehicle vary depending on a friction coefficient μ of a road surface, torque applied to a tire, and the like. Basically, it has better power performance and running stability than two-wheel drive vehicles because it is handled by tires. However, the coefficient of friction μ between the tire and the road surface
Is not always the same for all four wheels, and therefore, for example, the driving force of the front wheels or the rear wheels may become relatively excessive and slip may occur on the wheels. In such a case, the excellent power performance and stability of the four-wheel drive vehicle cannot be exhibited, so the distribution of the driving force to the front and rear wheels is changed to reduce the driving force of the slipping wheel, and All are designed to generate sufficient driving force.

On the other hand, the lateral force (cornering force) generated by the tire decreases due to an increase in the driving force (braking force) of the tire. When the tire has a large slip, the friction circle of the tire decreases and the driving force and the lateral force decrease. And decrease. Therefore, if the driving force applied to the rear wheel is large, the lateral force generated at the rear wheel at the time of turning is small, indicating an oversteer tendency (spin tendency), and if the driving force applied to the front wheel is large, the lateral force of the front wheel at the time of turning is Shows a tendency to understeer (drift-out tendency).

[0004] As described above, the manner of distributing the driving force to the front and rear wheels in a four-wheel drive vehicle greatly affects the power performance, running stability, and steering characteristics.
In the device described in Japanese Patent Publication No. 030, the clutch engagement force for changing the distribution of the driving force to the front and rear wheels is controlled based on the slip state of the wheels and the yawing state of the vehicle. Specifically, in the device described in this publication, the first clutch engagement force is determined so that the wheel slip detection value becomes the target value, and the second clutch engagement force is determined so that the yawing state matches the target value. Further, the sum of these clutch engagement forces is obtained, and the clutch engagement force is controlled based on the obtained value.

Therefore, according to this conventional device, for example, in a four-wheel drive vehicle in which a part of the driving force given from the engine to the rear wheel is distributed to the front wheel, the rear wheel slips during turning and the rear wheel slips. When the lateral force is lost and the steer characteristics tend to be oversteer with the loss of the lateral force, the second clutch engagement force due to the increased yaw is added to the first clutch engagement force due to the detection of the slip state, Because the clutch engagement force as the sum is achieved,
The distribution of the driving force to the front wheels is increased, the rear wheels are prevented from slipping, and the tendency to oversteer is corrected.

[0006]

The control of the clutch engagement force based on the yawing state of the vehicle is performed by calculating the target yaw rate using the steering angle and the vehicle speed as parameters, detecting the actual yaw rate by the yaw rate sensor, and determining the target yaw rate and the actual yaw rate. Since the deviation from the yaw rate and the calculation of the clutch engagement force based on the deviation are performed, if the steering angle sensor, the yaw rate sensor, or the calculation function related to the yaw rate control fails, the clutch engagement force based on the yaw rate can be controlled. Disappears. In such a case, in the above-described conventional apparatus, the control of the clutch engagement force is performed only by the rotation speed difference between the front and rear wheels even if the yaw rate occurs, and thus, for example, when traveling on a low μ road having a small road surface friction coefficient. Even if yawing occurs in the vehicle, control of the clutch engagement force based on the yawing, that is, distribution control of the driving force, cannot be performed. That is, in the above-described conventional apparatus, when the control of the clutch engagement force based on the yaw rate is not performed, even if an excessive yaw rate occurs, the driving force for suppressing the yaw rate cannot be distributed, so that the stability of the vehicle is reduced, or There is a possibility that the stability inherent in the four-wheel drive vehicle cannot be exhibited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended for driving a four-wheel drive vehicle capable of ensuring vehicle stability even when control of clutch engagement force based on yaw rate is stopped. It is an object to provide a force distribution device.

[0008]

According to the present invention, in order to achieve the above-mentioned object, the configuration shown in FIG. 1 is adopted. That is, the present invention provides a front wheel 1 and a rear wheel 2
And a clutch 3 that changes the distribution of the driving force to the front wheel 1 and the rear wheel 2 with a predetermined control gain based on the rotational speed difference between the front wheel 1 and the rear wheel 2. At the same time, in the driving force distribution device for a four-wheel drive vehicle that controls the engagement force of the clutch 3 so that the actual yaw rate matches the target yaw rate, the control of the engagement force of the clutch 3 based on the actual yaw rate and the target yaw rate is stopped. A yaw rate control stop detecting means 4 for detecting, and a control gain changing means for increasing the control gain when the yaw rate control stop detecting means 4 detects that the control of the clutch engagement force based on the actual yaw rate and the target yaw rate has been stopped. 5 using the control gain set by the control gain changing means 5 and the rotational speed difference between the front wheel 1 and the rear wheel 2. And it is characterized in that a clutch control means 6 for controlling the engagement force of the switch 3.

[0009]

The coupling force of the clutch according to the present invention is usually
The control is performed based on the rotational speed difference between the front and rear wheels and the deviation between the target yaw rate and the actual yaw rate. That is, as the difference between the rotational speeds of the front and rear wheels increases, the clutch engagement force is controlled with a predetermined control gain so as to increase, and the clutch engagement force is controlled so that the actual yaw rate matches the target yaw rate. On the other hand, if the control of the clutch engagement force based on the yaw rate is stopped due to a sensor failure, etc.,
The suspension of this control is detected by the yaw rate control suspension detecting means 4. In that case, the control gain changing means 5 increases the control gain of the clutch engagement force based on the rotational speed difference between the front and rear wheels, and the clutch control means 6 uses the increased control gain to control the clutch control means 6 based on the rotational speed difference between the front and rear wheels. The engagement force of the clutch 3 is controlled. Therefore, when the clutch engagement force cannot be controlled so that the actual yaw rate matches the target yaw rate, the clutch engagement force is controlled to be higher, so that the oversteer characteristic is suppressed as the steering characteristic, and as a result, the vehicle stability is reduced. Is improved.

[0010]

Next, the present invention will be described based on embodiments. FIG. 2 is a schematic diagram showing one embodiment of the present invention,
The four-wheel drive transfer 10 to be controlled is provided on the output side of an automatic transmission 12 connected to an engine 11. The transfer 10 distributes driving force to a rear wheel side and a front wheel side by a center differential 13 of a planetary gear type. A drive shaft 14 which is an output shaft of the automatic transmission 12 is connected to a carrier 15. A ring gear 16 is connected to a rear propeller shaft 18 via an output shaft 17. In contrast, sun gear 19
Are connected to a drive sprocket 20 and transmit a driving force to a front propeller shaft 23 via a chain 21 and a driven sprocket 22 wound around the drive sprocket 20. Carrier 15 and sun gear 19
And a differential limiting clutch 24 is provided between them, and by increasing the engagement hydraulic pressure, that is, by increasing the torque capacity, the distribution ratio of the driving force to the front wheels is increased. .

As a device for controlling the hydraulic pressure applied 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. I have. The electronic control unit 26 is mainly composed of 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.
And other signals from each sensor. Then, the electronic control unit 26 feedback-controls the hydraulic pressure of the differential limiting clutch 24 with a predetermined control gain based on the rotational speed difference between the front and rear wheels among these input parameters,
Further, a target yaw rate is obtained from the steering angle, the vehicle speed, and the like, and the hydraulic pressure for the differential limiting clutch 24 is controlled so that the deviation between the target yaw rate and the actual yaw rate is reduced.

FIG. 3 shows an example of a control routine for controlling the hydraulic pressure of the differential limiting clutch 24, which is executed by the electronic control unit 26. First, in step 1, the actual steering angle δ obtained from the steering angle is calculated. Wheel speed v, yaw rate γ, front and rear G
x and the lateral Gy are read, and then in step 2, the vehicle speed (vehicle speed) V is estimated from the wheel speed v, and the rotational speed N of each wheel is obtained. In addition Step 3, the front wheel speed N _F and the rear wheel rotational speed N and _R, the average rotational speed of the respective left and right wheels _{(N F = (N FL +} N FR) / 2, N R = (N RL +
N _RR ) / 2). Obtained rotation speed N of front and rear wheels
_F, from N _R, the absolute value .DELTA.N _FR of the rotational speed difference of the front and rear wheels (Step 4). Next, at step 5, a target yaw rate γ ₀ is determined. This is obtained from the coefficient K _{1 (v)} corresponding to the vehicle speed V and the steering angle δ. In general, the coefficient K _{1 (v)} is calculated from the vehicle speed V, the wheel base L and the stability factor K _h by the following equation _: K _{1 (v)} = V / {L (1 + K _h · V ² )}. Note that the coefficient K _{1 (v)} may be a coefficient corrected according to the acceleration, the friction coefficient μ of the road surface, and the like.

On the basis of the target yaw rate γ ₀ and the actual yaw rate γ thus determined, a 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
Is multiplied by the actual yaw rate γ for the following reason. That is, the yaw rate is a directional parameter, and the deviation Δγ also indicates the understeer tendency and the oversteer tendency with positive (+) and negative (−) signs. Regardless of whether the vehicle is turning left or right, a positive value is obtained when the vehicle is understeering, and a negative value is displayed when the vehicle is oversteering.

Next, at step 7, it is determined whether or not the yaw rate can be controlled. Specifically, the failure is determined by an ordinary method such as whether or not a signal from a yaw rate sensor or a steering angle sensor is input. When the determination result is “No”, that is, when the yaw rate can be controlled, the engagement hydraulic pressure based on the rotational speed difference ΔN _FR between the front and rear wheels is corrected based on the yaw rate deviation Δγ to take into account the steering characteristics. It performs the control of 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 rear-wheel drive, and the distribution ratio of the driving force to the front wheels increases by increasing the differential restriction. Therefore, when there is an understeer tendency, it is necessary to increase the distribution ratio of the driving force to the rear wheel side and correct it to the oversteer side, and conversely, when there is an oversteer tendency, It is necessary to increase the distribution ratio of the driving force to compensate for the understeer. Therefore, the correction coefficient K _{2 (Δγ)} according to the deviation Δγ is “1” when Δγ is large in the positive direction as shown in FIG.
It is set to a smaller value, and if it is larger in the negative direction, it is set to a value larger than "1".

On the other hand, the engagement hydraulic pressure of the differential limiting clutch 24 based on the rotational speed difference ΔN _FR between the front and rear wheels is feedback-controlled with a predetermined control gain, and an example of the engagement hydraulic pressure P 1 (ΔNFR) in a normal state is illustrated. This is as shown in FIG. That engagement oil pressure P1 (ΔNFR) is increased controlled based on the rotational speed difference .DELTA.N _FR of the front and rear wheels.

If a yaw rate deviation Δγ occurs during normal operation in which yaw rate control is possible, the differential limiting clutch 26 is controlled taking this into account. That is, the rotational speed difference ΔN _FR between the front and rear wheels
Hydraulic pressure P1 (ΔNFR) obtained from FIG.
A, by multiplying the correction coefficient K _{2 ([Delta] [gamma])} obtained from FIG. 3 in accordance with the yaw rate deviation [Delta] [gamma], setting all determine the engagement pressure P _CD (step 8). Engaging pressure P _CD which is obtained in this manner
Is schematically shown in accordance with the sign of the yaw rate deviation Δγ, as shown in FIG.

[0018] That is, if the oversteering tendency, the engagement pressure P _CD is higher is set, therefore since the lateral force of the rear wheel driving force is lowered in the rear wheels becomes large, oversteer suppression . Further, if the understeer tendency Conversely, the engagement pressure P _CD, the rotational speed difference between the front and rear wheels ΔN
_{Since the} pressure is set lower than the pressure determined based on the _FR , the driving force applied to the rear wheels increases and the lateral force decreases, thereby suppressing the tendency of understeer.

On the other hand, if the judgment result of step 7 is "yes"
In other words, if the yaw rate cannot be controlled,
The process proceeds to step 9, defining the engaging pressure P _CD based on only the rotational speed difference .DELTA.N _RF of the front and rear wheels. The control gain in that case is
Yes is made larger than the control gain in the normal, it is shown in Figure 5 (B) if shown the engagement hydraulic pressure P2 (ΔNFR) corresponding to the rotational speed difference .DELTA.N _FR of the front and rear wheels. In step 9, employing a pressure P2 (ΔNFR) determined based on (B) of FIG. 5 as an engagement pressure P _CD differential limiting clutch 26. Therefore, in the state where the control of the yaw rate is stopped, the distribution of the driving force to the front wheels is increased as compared with the normal state, and the driving force to be applied to the rear wheels is reduced, so that the oversteer tendency is suppressed or the understeer tendency is reduced. And, as a result, the stability of the vehicle is improved.

In the present invention, the control gain of the clutch engagement force when the yaw rate control is stopped need not be a single type, but a plurality of types of control gains are set according to the state of the vehicle. You may. 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 is limited by the clutch to change the distribution ratio of the driving force. The present invention is not limited to the above-described embodiment, but may be configured to change the distribution ratio of the driving force to the front and rear wheels according to the clutch engagement pressure. The comparison between the target yaw rate and the actual yaw rate may be performed by taking the ratio between the two and not by multiplying the difference between the two by the actual yaw rate value. Anything may be used as long as it can be compared so that it can be grasped.

[0021]

As is apparent from the above description, according to the present invention, when the distribution of the driving force to the front and rear wheels cannot be controlled based on the yaw rate, the clutch based on the rotational speed difference between the front and rear wheels cannot be obtained. Since the control gain of the fastening force is increased to reduce the distribution of the driving force to the rear wheels, even when the yaw is generated on a low μ road or the like, the vehicle behaves so as to suppress the yaw. The stability of the vehicle can be improved.

[Brief description of the drawings]

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

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

FIG. 3 is a flowchart illustrating a control routine of an engagement hydraulic pressure of a differential limiting clutch.

FIG. 4 is a diagram illustrating a relationship between a deviation between a target yaw rate and an actual yaw rate and a hydraulic pressure correction coefficient.

FIGS. 5A and 5B are diagrams showing a relationship between a rotational speed difference between front and rear wheels and an engagement hydraulic pressure of a differential limiting clutch, wherein FIG. 5A is a diagram in a normal state, and FIG. FIG. 5 is a diagram in which the control gain is increased when there is no control gain.

FIG. 6 is a diagram showing a relationship between a difference in rotation speed between front and rear wheels and an actual engagement hydraulic pressure of a differential limiting clutch when a deviation between a target yaw rate and an actual yaw rate occurs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Front wheel 2 Rear wheel 3 Clutch 4 Yaw rate control suspension detecting means 5 Control gain changing means 6 Clutch controlling means

Claims (1)

(57) [Claims] A clutch for changing a distribution of a driving force between a front wheel and a rear wheel in accordance with the engagement force, and a predetermined control of the engagement force of the clutch based on a rotational speed difference between the front wheel and the rear wheel. A driving force distribution device for a four-wheel drive vehicle that controls the engagement force of the clutch such that the actual yaw rate matches the target yaw rate, while controlling the engagement force of the clutch based on the actual yaw rate and the target yaw rate. Control stop detecting means for detecting the stop of the control, and a control gain change for increasing the control gain when the yaw rate control stop detecting means detects that the control of the clutch engagement force based on the actual yaw rate and the target yaw rate has been stopped. Means and a control gain set by the control gain changing means, based on a rotational speed difference between the front wheels and the rear wheels. It driving force distribution device for a four wheel drive vehicle, characterized in that a clutch control means for controlling the engagement force of the switch.