Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1998-05-22
2001-04-24
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C280S005513, C280S005504
Reexamination Certificate
active
06223108
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 gripping force 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.
It is well known that the handling of a vehicle is severely impaired when a road wheel thereof is locked up when braking. In particular, on a road surface such as a frozen road surface and a gravel road surface which could significantly reduce the gripping force of the tire, it is important to apply as large a braking force to the wheel as possible, but, without locking the wheel. The antilock brake system (ABS) makes use of this principle, and is widely used in road vehicles now on the market. According to this system, by noting the relationship between the tire slip ratio (&lgr;=(V
v
−V
w
)/V
v
: the ratio of the difference between the vehicle speed V
v
and the tire speed V
w
to the vehicle speed V
v
) and the tire grip force F, the slip ratio is kept within a limit typically by intermittently releasing the brake so as to avoid excessive slipping and to provide a high gripping force at all times. However, the ABS system is not able to change the gripping force of the tire. In other words, the capability of the ABS system to reduce the braking distance of the vehicle is limited by the given road gripping 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 a desired acceleration is 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 was 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.
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 brake control system or a traction control system, it is possible to reduce the braking distance or to increase the magnitude of the available traction. In particular, the inventors have recognized that an optimum result can be achieved if the contact load of the wheel is increased when the slip ratio of the wheel is about to exceed a threshold level beyond which the tire grip force starts diminishing.
BRIEF SUMMARY OF THE INVENTION
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 a 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 a 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 maximize the braking or the traction force of a vehicle on a given road surface.
A fourth 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 low-&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; means for computing a slip ratio of a wheel; and a controller for extending the actuator at a prescribed acceleration so as to selectively apply an additional contact load to the wheel when a slip ratio computed by the computing means has exceeded a prescribed value. The extended actuator may be retracted at such a time when the tire contact load is not so critical.
Thus, the tire grip force can be increased for the given road condition, and the braking force or the traction force available to the wheel can be increased. The prescribed value may be selected at a level which is preferably below the level from which the tire grip force starts diminishing. In particular, it is preferable to select the prescribed value at the level at which the tire grip force takes a maximum value. In case of a tire contact load control during braking in a vehicle equipped with an antilock brake system, it is preferable to set the prescribed value lower than the reference value at which the antilock brake system is activated. Thus, the additional brake force which is made available by increasing the tire contact load can be fully utilized, and the antilock brake system can take over the brake control only after the maximum braking force has been used so that the overall braking distance may be minimized.
Because the road condition could significantly change the tire grip force available to the tire, it is preferable to determine the road condition, for instance by analyzing the tire noise or the road noise, and to properly estimate the critical slip ratio at which the contract load control should be started for an optimum result.
REFERENCES:
patent: 4625993 (1986-12-01), Williams et al.
patent: 4729580 (1988-03-01), Buma et al.
patent: 5297646 (1994-03-01), Yamamura et al.
patent: 5322319 (1994-06-01), Tanaka et al.
patent: 5590898 (1997-01-01), Williams et al.
patent: 5718446 (1998-02-01), Fuchida
patent: 5892139 (1999-04-01), Miyazaki
patent: 5927426 (1999-07-01), Hall et al.
Izawa Masaki
Oshida Kei
Shibue Hideaki
Blackman William D.
Carrier Joseph P.
Carrier Blackman & Associates P.C.
Honda Giken Kogyo Kabushiki Kaisha
Nguyen Tan
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