Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
1999-07-08
2001-07-24
Chin, Gary (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S080000, C303S150000, C073S009000
Reexamination Certificate
active
06266600
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to an antilock braking device for precluding the locking of the wheels of a vehicle on sudden application of the brake and a road surface friction sensor and a road surface friction coefficient detector which can be used as components of the antilock braking device.
2. Technical Background
The conventional antilock braking device for cars or other vehicles generally employs a system such that the braking action is automatically controlled according to the chassis speed and wheel speed in such a manner that the slip ratio will fall within a definite range (see, for example, Japanese Patent Publication No. 30585/1984 and Japanese laid-open Patent Application KOKAI No. 61354/1985). The relationship between road surface friction coefficient and slip ratio is variable according to the texture of the road surface and, for this reason, the above system does not always provide the maximum braking force, depending on the condition of the road surface, and; in such cases, does not insure the minimum braking distance. Furthermore, because the chassis speed value used is an approximate value estimated from the wheel speed, the precision of slip ratio control is not sufficiently high. In order to ascertain the exact chassis speed, one has to rely on complicated devices such as a ground relative speed sensor (for example, Japanese laid-open Patent Application No. 64861/1988) or chassis deceleration sensor (for example, Japanese laid-open Patent Application No. 170157/1988).
In the conventional antilock braking device described in Japanese laid-open Patent Application No. 25169/1988, the road surface friction torque acting on the wheel (tire torque) is calculated from the wheel angular acceleration and brake fluid pressure values and the beginning of a fall in tire torque during the elevation of brake fluid pressure is utilized as one of the criteria for ascertaining the condition immediately preceding a wheel lock. However, since the tire torque is indirectly calculated from the wheel angular acceleration and brake fluid pressure, the above system does not take care of indefinite constants such as the moment of inertia of the wheels, the braking efficiency of the brake and so on, thus presenting problems in terms of the accuracy of data. There also is the problem that since the distance from the wheel to the road surface varies according to the deceleration of the chassis, depending on the pneumatic pressure of the tires and the weight of the chassis, the road surface friction force and the tire torque are not necessarily maintained in a fixed ratio.
It is an object of this invention to provide an antilock braking device free from the above-mentioned disadvantages of the conventional device.
It is another object to provide a road surface frictional force sensor and a road surface friction coefficient detector which can be used as components of an antilock braking device.
SUMMARY OF THE INVENTION
A first antilock braking device according to this invention includes a brake control means adapted to cyclically perform an operational series which comprises sensing the road surface frictional force, increasing the brake fluid pressure while the road surface frictional force is increasing in response to the elevation of brake fluid pressure, decreasing the brake fluid pressure when the road surface frictional force declines despite elevation of the brake fluid pressure, and increasing the brake fluid pressure again when the road surface frictional force decreases in response to a fall-off of brake fluid pressure. The road surface frictional force is determinable from measured values of the strain on a vehicle structure in the vicinity of the wheel of the vehicle. Herein the phrase “a vehicle structure in the vicinity of the wheel of a vehicle” refers to a knuckle of a suspension, an axle housing or the like.
A second antilock braking device according to this invention includes a brake control means adapted to cyclically perform an operational series which comprises detecting the coefficient of road surface friction, increasing the brake fluid pressure while the road surface friction coefficient is increasing in response to the elevation of brake fluid pressure, relieving or releasing the brake fluid pressure as the velocity of gain i.e., rate of increase in road surface friction coefficient falls below a set value and increasing the brake fluid pressure again after the road surface friction co-efficient has declined below a set value. The road surface friction coefficient value used in this second antilock braking device can be calculated from the road surface frictional force value and the vertical load value obtainable from measured values of the strain on a vehicle structure in the vicinity of the wheel.
The relationship between wheel-road surface slip ratio and road surface friction coefficient can be represented by curves such as shown in FIG.
1
. On the ordinary road surface, this relation can be expressed by a curve having a peak as shown at C
1
. On an extraordinary road surface, such as a snow-clad road surface, the relation may be represented by a curve without a peak as shown at C
2
. Not only the presence or absence of a peak but also the height of the peak and the magnitude of the slip ratio corresponding to the peak vary with the condition of the road surface and the chassis speed. On the other hand, as represented by curve C
3
, the cornering force (lateral drag) decreases continuously in response to an increase in slip ratio. Therefore, as far as trackless vehicles such as automobiles are concerned, in order to obtain the maximum braking force without sacrificing the cornering force, it is ideal to apply the brake in the neighborhood of P
1
or P
2
on curve C
1
or C
2
as the case may be.
Let it be supposed that the vehicle is running on a road surface such that the relation between road surface friction coefficient and slip ratio can be represented by the curve Cl shown in FIG.
1
. It should be understood that the road surface friction force is approximately proportional to the road surface friction coefficient. Under these conditions, the first antilock braking device according to this invention functions as follows. First, as sudden braking is applied by depressing the brake pedal or manipulating the brake lever, the brake fluid pressure increases. While the detected road surface frictional force value continues to rise, the brake fluid pressure is increased consistently to apply the brake with an increasing force. This phase corresponds to the segment to the left of P
1
on the curve Cl shown in FIG.
1
. As the brake fluid pressure is increased to apply the brake more forcefully, the slip ratio increases to approach the point P
1
of maximum road surface friction coefficient. As the brake fluid pressure is further increased, the point P
1
is passed over in due course. Beyond P
1
, locking of the wheels begins to occur as the road surface frictional force begins to decline in response to the elevation of brake fluid pressure. When the road surface friction sensor output decreases in this manner, the brake fluid pressure is decreased to relieve the brake action. Therefore, locking of the wheels is prevented. As the road surface frictional force decreases in response to a decline in brake fluid pressure, the brake fluid pressure is increased again. As the result of this action, as long as the vehicle runs on a road surface which can be represented by a curve with a peak in regard to the road surface friction coefficient-slip ratio relation, the locking of the wheels can be prevented irrespective of road condition and, moreover, braking action making the most of road surface frictional force can be realized.
The frictional force which acts between each wheel of the vehicle and the road surface is dynamically equivalent to the braking force applied by the wheel on the chassis. Therefore, strains and stresses proportional to the road surface frictional force are generated in all given positions of the struct
Chin Gary
Japan Electronics Industry Ltd.
Jordan and Hamburg LLP
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