Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2002-02-06
2003-05-13
Cuchlinski, Jr., William A (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C280S012130, C180S197000
Reexamination Certificate
active
06564139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for controlling a four-wheel drive vehicle, which can implement optimum controls even when an on-board traction control device operates so that driving force transmitted to a road surface is limited.
2. Description of the Related Art
In recent years, a traction control device is equipped on automotive vehicles which controls engine outputs and braking forces so as to prevent driving wheels from slipping in order to thereby secure acceleration, steering stability and vehicle behavior stability when the automotive vehicle starts from stand still conditions.
In a case where the traction control device like this is equipped on a four-wheel drive vehicle, there may occur unfavorable conditions to the vehicle in which a vehicle behavior control device interferes with controls by a power distribution control device equipped on the four-wheel drive vehicle. For eliminating these problems, Japanese Patent Unexamined Publication No. Sho. 61-37541 discloses the four-wheel drive vehicle in which a four-wheel drive is forcibly shifted to a two-wheel drive when a slip control operation is activated.
On the other hand, Japanese Patent Unexamined Publication No. Hei. 1-266049 discloses a technology in which a limited slip differential function is stopped to provide for a so-called locked-up four-wheel drive when there occurs an acceleration slip. Namely, the acceleration slip suppression effect results from stopping the limited slip differential function.
However, with the former prior art, the four-wheel drive is shifted to the two-wheel drive at the same time as the slip control operation is activated. This may lead to a possibility that the drivability of the vehicle is remarkably deteriorated. In addition, there is caused a problem that the driver is forced to feel large physical disorders when there occurs a drastic change in vehicle characteristics that would result when the four-wheel drive is shifted to the two-wheel drive.
In addition, with the latter prior art, slips on the four wheels are rather promoted, leading to a risk that a sufficient traction performance cannot be secured.
SUMMARY OF THE INVENTION
The present invention was made in view of these situations. An object of the present invention is to provide an apparatus and a method for controlling a four-wheel drive vehicle which can continue to implement optimal limited slip differential controls without unnecessarily interfering with the traction control to maintain a superior drivability without making the driver feel the physical disorder, and to ensure that the stability of the vehicle can be improved by properly controlling slips on the four wheels.
With a view to attaining the object, according to a first aspect of the invention, there is provide a control apparatus for a four-wheel drive vehicle comprising:
a traction control unit for controlling a driving force when there occurs a wheel slip on a wheel;
a transfer device with a limited slip differential unit for limiting a differential rotational action between front and rear wheels for distributing said driving force transmitted thereto between the front and rear wheel sides; and
a limited slip differential control unit for setting a limited slip differential force by the limited slip differential unit,
wherein the limited slip differential control unit compensates for the limited slip differential force by said limited slip differential control unit in such a manner that the limited slip differential force is increased when there occurs a wheel slip exceeding a predetermined value at least either one of front left and right wheels or rear left and right wheels.
According to a second aspect of the invention, there is provided the control apparatus for the four-wheel drive vehicle as set forth in the first aspect of the invention, wherein the limited slip differential control unit sets the limited slip differential force according to at least either one of the driving force inputted into the transfer device or the difference in the number of rotations between the front and rear wheels.
According to a third aspect of the invention, there is provided the control apparatus for the four-wheel drive vehicle as set forth in the first or second aspect of the invention, wherein the limited slip differential control unit implements the increasing compensation of the limited slip differential force at the time of running at a low speed.
According to a fourth aspect of the invention, there is provided the control apparatus for the four-wheel drive vehicle as set forth in any of the first to third aspects of the invention, wherein the limited slip differential control unit implements the increasing compensation of the limited slip differential force according to at least a steering angle.
According to a fifth aspect of the invention, there is provided the control apparatus for the four-wheel drive vehicle as set forth in any of the first to fourth aspects of the invention, wherein the limited slip differential control unit implements the increasing compensation of the limited slip differential force according to at least a vehicle speed.
According to a sixth aspect of the invention, there is provided the control apparatus for the four-wheel drive vehicle as set forth in the fifth aspect of the invention, wherein the increasing compensation according to the vehicle speed is implemented when the steering angle is small.
According to a seventh aspect of the invention, there is provided the control apparatus for the four-wheel drive vehicle as set forth in any of the first to sixth aspects of the invention, wherein the traction control unit operates so that the driving force transmitted to a road surface is limited only when there occurs a wheel slip exceeding the predetermined value at least either one of the front left and right wheels or the rear left and right wheels.
Namely, with the control apparatus for the four-wheel drive vehicle according to the first aspect of the invention, the limited slip differential unit limits the differential rotation between the front and rear wheels with the limited slip differential force set by the limited slip differential control unit, and the transfer device distributes the driving force from the power source between the front and rear wheel for driving the vehicle. In addition, the traction control unit controls the driving force when there occurs a wheel slip on the wheel. Here, the limited slip differential control unit compensates for the limited slip differential force that is to be set by the limited slip differential control unit such that the limited slip differential force is increased when there occurs the wheel slip exceeding the predetermined value at least either one of the front left and right wheels or the rear left and right wheels. Consequently, in case there occurs the wheel slip exceeding the predetermined value at least either one of the front left and right wheels or the rear left and right wheels (for example, the wheel slip that occurs due to the difference in friction coefficient between the left and right wheels of the vehicle and the road surface, respectively, in normal driving conditions), the traction control unit is activated to control to suppress the driving force transmitted to the road surface, and the limited slip differential control unit is activated to increase the limited slip differential force for limiting the differential action between the front and rear wheels. Therefore, stable driving can be provided. Thus, the limited slip differential control unit operates properly when there occurs the wheel slip either one of on the left or right wheels and continues to implement the optimal limited slip differential control without necessarily interfering with the traction control. Therefore, it is possible to maintain the superior drivability without making the driver feel the physical disorder. In addition, the limited slip differential control unit can properly suppress wheel slips on the four
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