Brakes – Operators – Electric and mechanical
Reexamination Certificate
1998-12-22
2001-04-10
Schwartz, Christopher P. (Department: 3613)
Brakes
Operators
Electric and mechanical
C188S158000, C192S219400
Reexamination Certificate
active
06213259
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrically powered parking brake and particularly to a method and system for controlling and operating a parking brake using an automatic adjustment feature and current limiting for determining brake cable tension.
BACKGROUND
Almost all vehicles have a parking brake mechanism, and most of these vehicles have a hand lever or foot activated lever for actuating the parking brake mechanism. Typically, these levers are attached to a cable that causes displacement of the cable and operation of the attached parking brake mechanism. There is a need to provide an electrically actuated cable mechanism that operates reliably with a minimum number of parts and has a low cost, so that manual lever actuated mechanisms may be replaced or easily selectively replaced.
It is known in the art to provide electric motor-driven brake systems. Examples of conventional technology in the motor-driven brake systems art are described in U.S. Pat. Nos. 4,795,002 to Burgei et al.; 4,865,165 to Taig; 5,590,744 to Belmond; 4,281,736 to Lizzio; 4,629,043 to Matsuo et al; 4,561,527 to Nakamoto et al; 5,180,038 to Arnold et al.; 5,485,764 to Sugimoto et al; and 5,542,513 to Reyes.
U.S. Pat. No. 5,485,764 to Sugimoto et al. describes a parking brake system for a vehicle that includes a unidirectional connecting member, such as a ratchet, that interconnects a brake operating member for manual operation of the parking brake and an automatic drive source for operating the parking brake. The device of Sugimoto suggests use of motor torque in brake application, but does not provide details by which use of motor torque can be economically measured.
U.S. Pat. No. 5,542,513 to Reyes describes an automatic parking brake that includes a second solenoid that activates the solenoid for the starter motor to engage a gear to activate the parking brake through the ignition switch. In addition, Reyes describes use of a mechanical tensioning limit device for controlling the tension of parking brake application. A problem with the use of tension limit switch in the cable, as described, is that this approach introduces unnecessary cost and complexity.
Prior art relating to setting travel using travel limit switches is ineffective, as the correct released state is not a fixed position, but a specified residual tension. It is also known to provide a mechanical tension limit feature for applying brakes, but no prior art exists in conjunction with these systems to control the released position of the brakes.
It is thus clear that conventional electrically powered parking brake systems lack effective controls for applying and releasing the brake and that these existing systems are relatively complex and costly. There is a need in this art for an electrically powered parking brake system that is reliable, self-adjusting in a relatively simple and reliable manner, cost-effective, uses a simple screw and drive tube assembly, and does not rely on additional mechanical activation, such as spring, or a complicated device or system for tension control and operation. There is a further need for a control system for an electrically powered parking brake system that produces a repeatable output within a relatively narrow range, in a manner sufficient to guarantee a level of braking, but not great enough to cause damage to associated components or require that the components be over-designed. There is a further need for a control system that relies upon a reliable and economical method and system for controlling the application of a parking brake, such as by use of motor current draw, which is proportional to output torque and sufficiently independent of other variables.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the problems of the prior art by providing a vehicle electrically powered parking brake that is automatically self-adjusting.
It is a further object of the present invention to provide a vehicle electrically powered parking brake that uses a mechanism that is not easily reversible, such as a screw mechanism, for engagement.
It is a further object of the present invention to provide a vehicle electrically powered parking brake that allows brake modulation for application during movement of the vehicle is in motion.
It is a further object of the present invention to provide a vehicle electrically powered parking brake that provides simple and effective controls for apply and release.
It is a further object of the present invention to provide a vehicle electrically powered parking brake that is simple, reliable, and inexpensive.
It is a further object of the present invention to provide a vehicle electrically powered parking brake that employs a high speed electric motor and a reaction conduit system.
It is a further object of the present invention to provide a control system utilizing a reliable and economical system variable for determining the cable tension for brake application. It is a further object of the present invention to provide a control system that utilizes motor current draw for reliable and economic brake application.
It is a further object of the present invention to provide an electrically powered parking brake system that operates in conjunction with a conduit reaction system.
It is a further object of the present invention to provide an electrically powered parking brake system that is easily installable in a vehicle.
The present invention solves the problems associated with conventional vehicle electrically powered parking brake designs and methods of operation by providing an electrically powered parking brake system that employs a high speed electric motor and use of a mechanism that is not easily reversible, such as a screw mechanism, in conjunction with a reaction conduit system. An example of a reaction conduit system that provides a force sufficient to engage the parking brake (e.g., to cause a brake pad to contact a brake drum or disc) is disclosed in U.S. Pat. No. 5,086,662, which is hereby incorporated by reference. Conduit reaction systems are also available commercially on motor vehicles.
The system of an embodiment of the present invention comprises an electric motor/gear train assembly having a line screw that is operatively connected to a drive tube. One end of a wire rope or strand is connected to the drive tube and the other end to the aforementioned reaction conduit system. The electric motor assembly is attached to a strut wherein the drive tube is free to move within the strut. The strut is attached to a vehicle at any expedient location.
In an embodiment of the present invention, an electronic control module that has an electrical connection to the electric motor controls operation of the electric motor and, in turn, movement of the drive tube. Moving the position of the drive tube either increases or decreases tension upon a wire rope or strand cable. When applying the parking brake, the tension within the strand is determined by monitoring the applied current of the electric motor. The parking brake is released by reversing the electric motor a defined distance (irrespective of the applied brake position) using an electronic positioning feature, such as a Hall Effect sensor and a magnetic pickup wheel.
Using the system of an embodiment of the present invention in combination with a conduit reaction cable system serves several purposes, including the following: 1) the present invention permits use of a commercially available and cost-effective electric motor of a small size; 2) the present invention reduces by a factor of two the reduction gearing necessary to take advantage of the motor characteristics and reduces by a factor of two the additional travel (and resulting length) of the mechanism required to provide the slack for installation during vehicle manufacture; 3) the present invention reduces from two to one the number of holes through the vehicle floor-pan or platform that are needed to locate the mechanism within the vehicle cabin, thereby reducing weatherproofing expenses; and 4) the present
Hanson John
Mercer Daniel R.
Dura Automotive Systems Inc.
Porter Wright Morris & Arthur
Schwartz Christopher P.
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