Motor vehicles – Having four wheels driven – With differential means for driving two wheel sets at...
Reexamination Certificate
2001-02-28
2003-06-10
DePumpo, Daniel G. (Department: 3611)
Motor vehicles
Having four wheels driven
With differential means for driving two wheel sets at...
C180S197000, C701S089000
Reexamination Certificate
active
06575261
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive-force distribution controller and a control method for a four-wheel-drive vehicle, and more particularly to a drive-force distribution controller and a control method for a four-wheel-drive vehicle in order to avoid a tight-corner braking phenomenon and a slip state when the vehicle turns.
2. Description of the Related Art
In a four-wheel-drive vehicle, it is known that a braking application acts on front and rear wheels due to a difference of a traveling distance therebetween when the vehicle travels on a corner whose radius is small in a case that a differential between front and rear wheel is restricted, i.e., a tight-corner braking phenomenon happens, whereby it cause to deteriorate a steering feeling in general.
To avoid this tight-corner braking phenomenon, that described in Japanese Patent Publication (Kokai) No. 8-2278 has been proposed, for example. In this related art, a differential speed between an outer front wheel and an inner rear wheel is calculated when the vehicle travels on the corner. In a case that the calculated differential speed is larger than a preset differential speed in a turning radius where the tight-corner braking phenomenon happens, it is judged that the tight-corner braking phenomenon happens, the differential between the front and rear wheel can be accepted by decreasing an engagement force in a differential restricting clutch of a torque distribution unit.
However, in the aforementioned art, when any one of the driving wheels travels on a low &mgr; road, e.g., when any one of the driving wheel works in a rut in which water ponds, that wheel may slip. In such a situation, the tight-corner braking phenomenon is detected accidentally, so that the differential between the front and rear wheels may be accepted momentarily.
Further, in a case that the vehicle launches from the low &mgr; road, e.g., a deep-snow road or a dirt road, it is generated frequently that any one of the driving wheels slips. In the front-wheel drive base four-wheel drive vehicle, one of the front wheels facilitates to slip to give a large drive force to the front wheels, for example. In this case, the tight-corner braking phenomenon is detected accidentally in the aforementioned art, so that the differential between the front and rear wheels may be accepted momentarily. Thus, in a case the differential between the front and rear wheel is accepted momentarily, a required drive force is not obtained substantially. As a result it may be generated that the vehicle gets free from the rut when traveling on the low &mgr; road, or that the vehicle threatens to launch smoothly when launching on the low &mgr; road.
Furthermore, the controller described in Japanese Patent Publication (Kokai) No. 11-1129 is proposed to prevent the tight-corner braking phenomenon when turning at an extremely low speed and to slip. In that controller, a wheel speed difference between the front and rear wheel is calculated based upon a wheel speed of each of the four wheels, an operated steering angle and yaw rate, and the engagement force in the differential restricting clutch of the torque distribution unit is based upon that wheel speed difference. Consequently, the tight-corner braking phenomenon is prevented when the vehicle turns at the extremely low speed, and the slipping is also prevented. In the aforementioned controller, a yaw rate sensor is however required, so that the control operation becomes complex.
Further, the aforementioned controller is of the type for controlling the wheel speed difference between the front and rear wheels, in a case that one of the driving wheels slips, the slipping may not be detected. In such a situation, the required drive force is not obtained substantially, so that it may be generated that the vehicle gets free from the rut when traveling on the low &mgr; road, or that the vehicle threatens to launch smoothly when launching on the low &mgr; road.
To solve the aforementioned problem, an object of the present invention is to provides a torque distribution controller of a four-wheel drive vehicle which is capable of preventing a generation of a tight-corner braking phenomenon and preventing slipping in one of the driving wheels infallibly.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a drive-force distribution controller for a four-wheel-drive vehicle having a torque distribution unit configured to distribute an output torque transmitted from a prime motor to a first set of wheels to a second set of wheels includes a first judging device for judging which of the first set of wheels is an inner wheel with respect to a turning of the four-wheel-drive vehicle, a second judging device for judging whether the turning of the four-wheel-drive vehicle is a tight turn, a third judging device for judging whether the inner wheel is slipping, a fourth judging device for judging whether an outer wheel of the first set of wheels is slipping, and a controller for controlling the torque distribution unit. The second judging device judges that the four-wheel-drive vehicle is engaged in a tight turn if the turning has a turning radius smaller than a predetermined value. The controller decreases the output torque to the second set of wheels if the second judging device judges that the four-wheel-drive vehicle is engaged in a tight turn and if the third and fourth judging devices judge that the first set of wheels are not slipping.
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patent: 4921065 (1990-05-01), Hamada et al.
patent: 4966250 (1990-10-01), Imaseki
patent: 5497333 (1996-03-01), Sasaki
patent: 5701247 (1997-12-01), Sasaki
patent: 5850616 (1998-12-01), Matsuno et al.
patent: 5894904 (1999-04-01), Yakou et al.
patent: 6145614 (2000-11-01), Kimura et al.
patent: 6205391 (2001-03-01), Ghoneim et al.
patent: 8-2278 (1996-01-01), None
patent: 11-1129 (1999-01-01), None
Ido Yusaku
Mori Yutaka
Shigeta Ryohei
Takahashi Yoshio
DePumpo Daniel G.
Toyoda Koki Kabushiki Kaisha
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