Brakes – Wheel – Positive lock
Reexamination Certificate
1999-05-24
2001-06-26
Oberleitner, Robert J. (Department: 3613)
Brakes
Wheel
Positive lock
C188S031000, C180S273000
Reexamination Certificate
active
06250433
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to parking brakes for mobile vehicles and, more particularly, to parking brake systems designed to prevent parking brake engagement at speeds higher than a selected engagement-speed range.
BACKGROUND OF THE INVENTION
Parking brakes of many different kinds have long been used on a wide variety of vehicles, including on, among others, a wide variety of work vehicles. One example of prior devices is disclosed in U.S. Pat. No. 5,551,523 and is usable in a skid-steer loader. In some cases it is desirable that parking brakes not be engageable at vehicle speeds above some predetermined level—that is, that the braking effect they provide only be available in a predetermined speed range of zero up to the predetermined level. This range is referred to herein as the “engagement-speed range.” If a parking brake system, like some, is unable to prevent parking brake engagement when the vehicle is moving at high speeds, brake engagement at such high speeds can cause major component failures because components of the parking brake are unable to absorb the high levels of kinetic energy that high speeds involve. The result can be breakage of brake parts and the consequent need for repairs.
There is a clear need for improvement in parking brake devices which cannot be engaged at speeds above a predetermined level—i.e., which can only be engaged at or below a given speed. There is a need for improved vehicle parking brake systems which are rendered unable to engage at high speeds—i.e., beyond those for which parking brake engagement is desirable. Parking brake systems, particularly systems with advanced capabilities, can tend to be complicated and, therefore, expensive. There is a need for an improved parking brake which is simple and economical in construction but still has the capability of being unable to fully engage at high speeds.
SUMMARY OF THE INVENTION
The present invention is an improved parking brake for vehicles of various kinds. Generally speaking, the parking brake of this invention operates by the interaction of a rotatable plate and a longitudinally movable pin which is movable into and out of engagement with openings in the plate. The nature of the structure as set forth below, and the method involved, form the present invention and result in a parking brake system overcoming problems and shortcomings of the prior art.
There is provided a work vehicle comprising a vehicle support structure with a plurality of wheels. A hydraulic lift assembly is mounted on the vehicle support structure with an attachment coupled to the hydraulic lift. The attachment can be a variety of tools such as a bucket, a backhoe arm, a cold scrapper, a jack hammer or any other type of attachment conventionally and typically coupled to a work vehicle. The work vehicle is also provided with a plate rotatable about an axis and coupled to at least one of the vehicle wheels, with the plate including a portion defining at least one opening radially spaced from the axis. The plate may also have a plurality of openings evenly spaced in the plate. A pin including an end movably supported and mounted on the vehicle support structure relative to the plate to engage the opening to restrict the plate and the wheel coupled to the plate from rotating, wherein one of the portion and the pin end include an angled surface with respect to the pin which prevents the pin from engaging the plate when the velocity of the opening relative to the pin exceeds a predetermined limit. The pin is biased to an extended position and a pin-retraction mechanism is mounted on the vehicle support structure and operatively connected to the pin for moving the pin from the extended position to a retracted position. The predetermined limit corresponds to a vehicle speed of no more than two (2) miles per hour with the preferred range between 1 and 1.5 miles per hour.
More specifically, the rotatable plate, which defines a plate axis and is operatively connected to a turning member of the vehicle such that plate rotation is related to vehicle speed —i.e., faster vehicle speed means faster plate rotation, has at least one pin-receiving opening therethrough, and preferably a plurality of such openings. The pin-receiving opening or openings are radially spaced from the plate axis along an axially concentric circle, i.e., such that each opening is radially equidistant from a plate axis. The openings are evenly spaced along such circle.
The aforementioned pin has a longitudinal pin axis and is deployed such that the pin axis is transverse to the plate at the opening circle. The pin is axially movable between a retracted position spaced from the plate and an extended position through one of the plate openings. When the pin is in the retracted position, the plate is free to rotate, and when the pin is in the extended position, the engagement with a plate opening prevents plate rotation—i.e., the parking brake is engaged to prevent movement.
Each pin-receiving opening in the rotatable plate is bounded by an edge, the edge including a leading edge and a trailing edge, sometimes referred to as leading edge and trailing edge portions. The pin, which is preferably deployed so that its axis is perpendicular to the plate, has a distal end at least a portion of which is a deflecting surface angled with respect to the pin axis. More specifically, the deflecting surface is angled such that contact thereon by the trailing edges (of the plate openings) during plate rotation will cam the pin back toward the retracted position. When such contact and resulting cam action occur, brake engagement is avoided because the pin cannot be fully inserted into a plate opening.
The pin and its deflecting surface, and the plate and its openings, are positioned and arranged such that, when the rotatable plate has rotational velocity above a predetermined threshold, the pin is prevented from moving fully into one of the openings by virtue of the aforementioned interaction of the leading edges with the deflecting surface. When the rotational velocity of the rotatable plate falls below a predetermined threshold, then movement of the pin toward its extended position allows the pin to enter one of the openings before the trailing edge of the opening can contact the deflecting surface on the distal end of the pin.
In highly preferred embodiments, the deflecting surface is a chamfer on the distal end of the pin. The chamfer is preferably at an angle to the pin axis of from 15 to 85 degrees, and most preferably at an angle of from 30 to 60 degrees. The chamfer has a first dimension parallel to the pin axis. Such chamfer dimension sets the axial length of pin movement which must occur before contact of a trailing edge with the pin. If trailing edge contact is with the chamfer, rotation of the plate will serve to cam the pin toward its retracted position and prevent full pin insertion into an opening. Another embodiment of the present invention has the angled deflecting surface on the open edge, with the pin having a constant diameter at the distal end. It is also possible to have both the edge of the opening and the distal end of the pin having an angled deflecting surface to cause the camming action.
The apparatus of this invention includes a biasing structure for biasing the pin to its extended position and a pin-retraction mechanism for moving the pin from its extended position to its retracted position. The biasing structure determines the speed of the axial movement of the pin toward its extended position. Not only are the pin and its deflecting surface, and the plate and its openings positioned and arranged to provide the critical aforementioned camming action above certain speeds, but the biasing structure is selected for that purpose as well. That is, it is selected such that when vehicle speed is above a predetermined velocity, rotation of the plate will be at a rotational velocity such that pin speed will move the pin a distance less than the first dimension (i.e., the axially parallel dimension of the preferred chamf
Chimalakonda Sastry P.
Sealine Ronald L.
Werner Ronald H.
Case Corporation
Foley & Lardner
Oberleitner Robert J.
Rodriguez Pamela J.
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