Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1998-03-17
2001-03-27
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S038000, C280S005500
Reexamination Certificate
active
06208920
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a tire contact load control system for increasing the road wheel contact pressure on the road surface as needed by actuating an actuator interposed between the sprung mass and the unsprung mass of the vehicle at a certain acceleration.
BACKGROUND OF THE INVENTION
The gripping force F of a tire can be given by the product of the frictional coefficient &mgr; between the tire and the road surface and the vertical contact load W acting on the tire contact surface (F=&mgr;W). In other words, the tire contact load which plays an important role in the handling of the vehicle is proportional to the magnitude of the tire contact load for a given road condition.
In a known active wheel suspension system, a linear actuator which can be actively extended and retracted is typically installed between the vehicle body and each road wheel so that the distribution of tire contact load may be distributed to the four different road wheels according to a prescribed control mode. For instance, U.S. Pat. No. 4,625,993 issued Dec. 2, 1986 to Williams et al. discloses an active wheel suspension system which controls the stroke of the hydraulic actuator provided with each road wheel so that the attitude of the vehicle body may be properly controlled when the vehicle is travelling. When the vehicle is travelling straight ahead, the tires are made to follow the irregular contour of the road surface so that the gravitational center of the sprung mass may be controlled or may stay at a relatively fixed height. When the vehicle is accelerating or decelerating, the load distribution between the front axle and the rear axle is appropriately changed so that the pitching movement of the vehicle may be controlled. When the vehicle is turning a curve, the load distribution between the right and left wheels is appropriately changed so that the rolling movement of the vehicle may be controlled.
According to such a conventional active wheel suspension system, the weight of the vehicle body was simply distributed between the different road wheels, and the sum of the contact pressures of the four road wheels was essentially constant. Therefore, such an active wheel suspension system was not able to increase the overall traction or braking force of the vehicle.
It is known that the maximum gripping force which optimizes the braking force and the traction force can be achieved when the slip ratio of the wheel is at a certain value. The slip ratio is given as a ratio of the difference between the circumferential speed of the tire and the vehicle speed to the vehicle speed. The ABS (antilock brake system) is based on this concept, and is now widely used in motor vehicles. However, the ABS system is not able to change the gripping force of the tire, and typically intermittently release the brake to avoid excessive slipping. In other words, the capability of the ABS system to reduce the braking distance of the vehicle is limited by the given traction force. It is therefore desirable if the gripping force itself can be increased in view of further reducing the braking distance.
The road gripping force of a tire is important also when accelerating a vehicle. When a vehicle is excessively accelerated for a given road condition, the tires start slipping, and not only is a desired acceleration prevented from being achieved, but also the lateral stability of the vehicle may be lost. By noting this problem, it has been proposed to control the traction force of each driven wheel so that the slip ratio of the wheel may be kept within a limit, and a maximum available traction may be obtained at all times. The traction control system is designed to carry out such a control action. However, the conventional traction control system is not able to increase the magnitude of the available traction, and simply reduces the torque transmitted to the wheels so as to prevent the slip ratio from exceeding a prescribed limit.
The frictional coefficient of the road surface for the tires may not be even, and the right and left wheels may travel over road surfaces of different frictional coefficients. This may be called as a split &mgr; road surface. When a brake is applied to a vehicle travelling over such a road surface, the vehicle tends to swerve from a straight course, and may even go into a spin. To avoid such condition from occurring, an ABS system normally controls the braking force of each wheel so that the braking force of each of the wheels would not exceed that of the wheel experiencing the smallest frictional coefficient (see Japanese patent laid open publication No. 2-220958). This is beneficial in maintaining the lateral stability of the vehicle, but increases the braking distance of the vehicle. The same problem arises when an attempt is made to accelerate a vehicle traveling over a split &mgr; road surface.
BRIEF SUMMARY OF THE INVENTION
With the foregoing limitations and disadvantages of the known systems in mind, the inventors have recognized that when a linear actuator interposed between a wheel and a vehicle body is either extended or retracted at a certain acceleration, a corresponding inertia force is produced in the sprung mass and the unsprung mass. The reaction of such an inertia force may be used to increase the contact load of the road wheel or the gripping force of the tire. Therefore, when this concept is applied to a traction control system, it is possible to increase the magnitude of the available traction. In particular, an optimum result can be achieved if the contact load of the wheel encountering a smallest frictional coefficient is increased. The same principle may also be applied in controlling the traction or the braking force of the vehicle traveling over a split &mgr; road surface.
In view of such problems of the prior art and the recognition by the inventors, a primary object of the present invention is to provide a vehicle tire contact load control system which can selectively increase the tire contact load of each road wheel.
A second object of the present invention is to provide a vehicle tire contact load control system which can increase the gripping force of each road wheel for a given road condition.
A third object of the present invention is to provide a vehicle tire contact load control system which can increase the traction or the braking force for each road wheel for a given road condition.
A fourth object of the present invention is to provide a vehicle tire contact load control system which can improve the handling of a vehicle making a turn.
A fifth object of the present invention is to provide a vehicle tire contact load control system which can allow a vehicle to accelerate or decelerating on a split &mgr; road surface in a stable manner.
According to the present invention, such objects can be accomplished by providing a vehicle tire contact load control system, comprising: a wheel suspension system for supporting an unsprung mass including a wheel to a sprung mass including a vehicle body; an active actuator interposed between the unsprung mass and the sprung mass; and a controller for extending the actuator at a prescribed acceleration so as to selectively apply an additional contact load to the wheel. The extended actuator may be retracted at such a time when the tire contact load is not so critical. Preferably, one of the actuators is provided for each of a plurality of wheels, and the controller is adapted to extend at least one of the actuators at a prescribed acceleration without retracting any one of the remaining actuators.
Thus, the tire contact load of each wheel can be increased at will and independently from the other wheels so that the gripping force available to each wheel can be increased as required by appropriately operating the corresponding actuator.
This can be advantageously utilized for improving the braking performance of the vehicle by reducing the braking distance or the distance over which the vehicle has to travel before coming to a stop. In particular, the present invention allows the braking force for the
Izawa Masaki
Oshida Kei
Shibue Hideaki
Shimizu Yasuo
Blackman William D.
Carrier Joseph P.
Carrier Blackman & Associates P.C.
Honda Giken Kogyo Kabushiki Kaisha
Nguyen Tan
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