Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
1998-02-12
2001-01-23
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S070000, C701S075000, C701S079000, C303S138000, C303S139000, C303S167000, C303S176000, C303S126000, C188S18100R, C188S18100R
Reexamination Certificate
active
06178370
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to brake control systems, and more particularly to a deceleration based antiskid brake controller.
BACKGROUND OF THE INVENTION
Antiskid brake controllers have been in widespread use for many years. In the simplest sense, an antiskid brake controller compares the speed of a vehicle (e.g., automobile, aircraft, etc.) derived from a wheel speed sensor to the vehicle speed derived from a secondary or reference source. If the wheel is determined to be skidding an excessive amount, then brake pressure applied to the wheel is released and the wheel is allowed to spin back up to the appropriate speed.
A fundamental problem associated with virtually all antiskid brake controllers relates to determining an appropriate amount of skidding. Two types of controllers which are generally known utilize different techniques. The first type of antiskid controller is deceleration based. In short, the deceleration based controller differentiates the wheel speed to determine how fast the wheel speed is changing. If the wheel decelerates too quickly, there is said to be excessive skidding and the controller reduces the amount of pressure transmitted to the brakes.
A second type of antiskid controller relies on a model of the mu-slip curve which describes the tire-to-road surface friction characteristics. The difference between the wheel velocity and the vehicle velocity is referred to as the slip velocity. The slip velocity is compared with a predefined set point on the mu-slip curve in order to achieve a desired amount of skidding.
Antiskid controllers which are based on the mu-slip curve are oftentimes computationally complex and require multiple sensors for measuring wheel speed, vehicle speed, etc. Consequently, deceleration based antiskid controllers may be preferred as a simpler approach. However, deceleration based antiskid controllers in the past have not been sufficiently adaptive to adjust to varying tire/surface conditions (e.g., wet or icy conditions) insofar as determining an acceptable amount of skidding. Failure to adjust for varying conditions can result in the antiskid controller prematurely releasing brake pressure and/or failing to adequately control excessive skidding.
In view of the aforementioned problems associated with conventional antiskid brake controllers, there is a strong need in the art for a controller which is adaptive to handle changing tire/surface conditions. In addition, there is a strong need for such a controller which is not computationally intensive and which does not require multiple sensors, etc.
SUMMARY OF THE INVENTION
In an exemplary preferred embodiment, the antiskid brake controller of the present invention utilizes measured wheel speed in order to provide brake control for a vehicle such as an aircraft. The measured wheel speed is differentiated to determine the deceleration of the wheel, and the controller then compares the deceleration to a predefined deceleration threshold. If the wheel decelerates faster than the deceleration threshold, the controller reduces the command pressure provided to the brakes by a scaling factor. As the wheel begins to decelerate at a rate less than the deceleration threshold, the command pressure is increased until full command pressure is otherwise applied. The rate at which the controller reduces command pressure preferably is greater than the rate at which the controller otherwise increases command pressure. As a result, brake pressure may be decreased more quickly so as to avoid excessive skidding while at the same time brake pressure is increased more slowly so as to provide for smoother braking. The controller is capable of operating based only on measured wheel speed, thus additional sensors are not necessary. The wheel speed signal may be generated by an optical encoder, for example, located at the wheel itself.
The controller modifies the deceleration threshold based on the ability of the wheel to hold the requested brake pressure without excessive skidding. In the exemplary embodiment, the brake controller compares the wheel deceleration to a range including the deceleration threshold. If the wheel deceleration falls below the range, thus indicating the onset of excessive skidding, the value of the deceleration threshold is decreased. On the other hand, if the wheel deceleration goes beyond the range so as to indicate that the wheel can handle additional braking, the value of the deceleration threshold is increased. Preferably, the rate at which the controller decreases the deceleration threshold is greater than the rate at which the controller increases the deceleration threshold.
The brake controller also provides for increasing the deceleration threshold based on the detection of higher vehicle speeds. More specifically, the deceleration threshold is increased by a scaling factor at wheel speeds exceeding a predefined threshold. It has been found that a wheel typically can hold more deceleration at higher wheel speeds. Thus, for high speeds the value of the deceleration threshold is increased to provide for additional brake pressure applied to the wheel.
In addition, the brake controller includes protection against instantaneous wheel lock up. Specifically, the brake controller compares the estimated vehicle velocity with the measured wheel speed. In the event wheel lock up were to occur during a braking operation, pressure to the brake is released and the controller is reset.
According to one particular embodiment of the invention, an antiskid brake controller is provided for controlling a braking operation of a wheel of a vehicle based on a wheel speed signal provided by a wheel speed sensor coupled to the wheel. The controller includes means for estimating a deceleration of the wheel based on the wheel speed signal provided by the wheel speed sensor; comparison means for comparing the estimated deceleration of the wheel with a predefined deceleration threshold; and output means for providing a control signal for adjusting a brake force applied to the wheel based on the comparison, the control signal functioning to decrease the brake force applied to the wheel at a rate which is greater than a rate a which the control signal increases the brake force applied to the wheel.
According to another aspect of the invention, an antiskid brake controller is provided for controlling a braking operation of a wheel of a vehicle. The controller includes means for estimating a deceleration of the wheel based on the wheel speed signal provided by the wheel speed sensor; adaptive deceleration threshold means for providing a deceleration threshold which varies in accordance with a prescribed criteria; comparison means for comparing the estimated deceleration of the wheel with the deceleration threshold; and output means for providing a control signal for adjusting a brake force applied to the wheel based on the comparison.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
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Louis-Jacques Jacques H.
Renner , Otto, Boisselle & Sklar, LLP
The B. F. Goodrich Company
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