Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
1999-05-28
2001-04-03
Zanelli, Michael J. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C303S183000, C303S191000
Reexamination Certificate
active
06212461
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process and apparatus for determining whether the driver of a vehicle is effecting “hard” braking of the vehicle. This practice is useful in computer-controlled vehicle braking and traction control systems and in vehicle stability enhancement systems involving yaw rate measurements or estimations.
BACKGROUND OF THE INVENTION
Automotive vehicles have been produced with computer-controlled brake systems that modulate brake force during stops to provide anti-lock brake (ABS) control and/or that modulate brake force during vehicle acceleration to provide positive acceleration traction control (TCS). Recently, more comprehensive computer-based vehicle brake control systems have been developed that provide additional chassis control under braking or positive acceleration conditions. Such systems are described, e.g., in U.S. Pat. Nos. 5,720,533 and 5,746,486, both entitled “Brake Control System” and assigned to the assignee of this invention. These systems seek to control, among other parameters, the yaw rate of the vehicle.
The computer in the chassis control systems described in these patents uses signals from a variety of sensors such as wheel speed sensors, steering wheel angle sensor, brake switch sensor, brake pedal extended travel sensor, master brake cylinder pressure sensor, yaw rate sensor and a lateral accelerometer. For further development of such control systems, it is desirable and/or necessary to provide algorithms or computer-controlled processes for eliminating some of such sensors or for detecting faults in their operation.
For example, a process has been developed that permits vehicle yaw control based on an estimated yaw rate rather than the output of a yaw rate sensor. This practice is described in U.S. Ser. No. 09/080,372, entitled “Vehicle Yaw Control Based on Yaw Rate Estimate” and assigned to the assignee of this invention. While this yaw rate estimate practice can eliminate the use of a yaw rate sensor, it does use the output of a brake pedal travel sensor to measure the extent of driver braking. Such a sensor is expensive compared to a marginal increase in on-board computer processing capacity and, furthermore, the sensor is subject to failure.
Accordingly, it is an object of this invention to provide a process for determining whether a brake pedal travel sensor is faulty or for eliminating the need for input from such a sensor, especially in making computer-based estimates of vehicle yaw rate.
SUMMARY OF THE INVENTION
This invention is typically applicable in automotive vehicles incorporating a computer-based antilock brake system (ABS) or a traction control system (TCS) in combination with vehicle yaw control. It is applicable in such systems in which at least two of the vehicle wheels, i.e., the front wheels or the rear wheels, are undriven. In vehicle control systems of this type, the micro-processor-based controller receives data from wheel speed sensors and a brake off/on switch, among other possible data sources, in the course of its control of brake actuators for each wheel. In many such control systems, it also necessary to employ a brake pedal travel sensor so that the controller receives more data concerning whether the driver is pressing heavily on the brake pedal and has thus effected a hard brake condition.
Reliance upon a brake pedal travel sensor, or extended brake switch as it is sometimes called, presents three possible disadvantages. Such a switch adds expense and it may not work properly. Finally, the hydraulic brake pressure obtained from a fully-actuated brake is constant and independent of road surface conditions. This means that a 300 psi brake pressure on a dry surface that might not corrupt the wheel speed of an undriven wheel, might cause a wheel lock-up on ice and result in a bad yaw rate estimation. Therefore, one setting of the extended brake switch travel is not adequate for the yaw rate estimation.
This invention provides a method of determining a hard brake condition and, therefore, provides a substitute for a brake pedal travel sensor. In an alternative embodiment, the invention also provides a means for determining the effectiveness of such a sensor. In accordance with the method, the speed (i.e., velocity in, e.g., meters per second) of the undriven wheels is measured using available wheel speed sensors. This data, utilized over a suitable number of controller processing cycles, is used to calculate the average acceleration of the undriven wheels. Data from all wheel sensors may be used to determine values of instantaneous vehicle velocity. The velocities of the undriven wheels (e.g., the right and left rear wheels in a front wheel drive vehicle) at a time of interest and the corresponding vehicle velocity are used to calculate slip values of the undriven wheels.
The average acceleration (appropriately, deceleration) of the undriven wheels and the slip values are compared with predetermined threshold values for these parameters. If the average deceleration and/or the respective slip values (determined at, e.g., successive 0.010 second increments) exceed the corresponding threshold deceleration and slip values throughout a suitable comparison period (for example, 0.25 second), a hard braking condition is affirmed. On the other hand, when such calculated values do not exceed the respective threshold values during a like comparison period, it is concluded that a hard braking condition does not exist.
In a preferred embodiment of the invention, data indicating that the ABS is actuated or data from a brake on/off switch can be used to bypass entry into this controller process.
The above described process was illustrated as replacing a brake pedal travel sensor but it could also be used to confirm a signal, positive or negative, from such a sensor.
Other objects and advantages of the invention will become apparent from a description of a preferred embodiment which follows. In the description, reference will be had to the drawings which are described in the following section of this specification.
REFERENCES:
patent: 5480221 (1996-01-01), Morita et al.
patent: 5720533 (1998-02-01), Pastor et al.
patent: 5746486 (1998-05-01), Paul et al.
Ghoneim Youssef Ahmed
Sidlosky David Michael
General Motors Corporation
Grove George A.
Zanelli Michael J.
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