Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
2000-01-26
2002-05-28
Schwartz, Christopher P. (Department: 3613)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S908000, C277S436000, C277S437000, C092S068000, C188S15300R
Reexamination Certificate
active
06394462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to disc brake systems for vehicles, and in particular to a seal for engagement with the push rod of a disc brake actuator to prevent unwanted contaminants from entering the disc brake mechanism.
2. Description of the Prior Art
The use of disc brakes is becoming more and more common in the trucking industry to control the brakes of heavy-duty vehicles and their trailers. Foundation disc brakes on trucks and trailers are generally operated using separately manufactured brake actuators which are mated to the disc brake systems. The internal operating mechanisms of foundation disc brake systems have become increasingly more precise. Foreign material and contaminants such as dirt, moisture, or other elements can reduce the useful life of a disc brake if allowed to enter the internal mechanism. These materials can cause rust or corrosion of the sensitive disc brake mechanism, potentially resulting in jamming or other hazardous failures of the disc brakes. It is therefore important that the disc brakes be securely sealed to their corresponding brake actuators in order to avoid such contamination.
A typical service brake actuator is characterized by a closed housing which contains a movable diaphragm stretched across the inside. One side of the diaphragm moves a slidable push rod which extends out of the housing for attachment to the disc brake system of the vehicle. On the other side of the diaphragm a sealed chamber is formed within the housing. An opening is provided in this chamber for connection to a pneumatic (air) pressure source usually provided by an air compressor on board the vehicle. The brakes of the vehicle can be applied by introducing sufficient pneumatic pressure into the sealed chamber to act against the service brake diaphragm which moves the push rod out. A small return spring is ordinarily provided inside the service brake housing around the push rod to urge it to retract when the air pressure behind the diaphragm is reduced.
The disc brake system is typically attached directly to the bottom of the service brake actuator so that as the push rod extends out of the actuator, it extends into the disc brake mechanism. An annular rubberized bead is typically provided on the outer mating surface of the disc brake mechanism for engagement with the service brake actuator. This bead forms a seal between the disc brake system and the service brake actuator to prevent foreign material from entering the disc brake system. In operation, the outer end of the push rod engages a caliper arm on the disc brake. When the vehicle operator presses on the brake pedal, air pressure is applied to the service brake actuator causing the rod to push out. The rod then engages the arm and pushes against it. As the arm is pushed, it causes the disc brake calipers to push frictional pads against the wheel rotor or disc which slows or stops the moving vehicle. Releasing the brake pedal removes air pressure from the service brake actuator causing the push rod to retract, thereby disengaging the arm and releasing the disc brakes.
While the vehicle is operating, air pressure is being constantly applied to and removed from the sealed chamber in the upper portion of the service brake housing to operate the brakes of the vehicle. The application and removal of air pressure causes the diaphragm inside the housing to move back and forth, moving the push rod in and out. In order for the diaphragm to be able to expand, the air in the lower portion of the service brake housing is allowed to escape to the outside. Then, in order for the diaphragm to contract, air is allowed to enter this area.
Typical service brake housing assemblies include a plurality of air holes in the lower housing to allow air to enter and exit this region as the diaphragm moves back and forth. The unfortunate effect of this action is to allow dirt, water, oil, debris, and other unwanted materials to enter the service brake housing from the outside through the air holes. Transmission of this material to the sensitive disc brake mechanism could lead to failures of the disc brakes thereby shortening their useful life.
The use of O-rings to provide sealing engagement around a brake actuator push rod is well known. However, the use of such O-rings has generally been limited to providing a seal to maintain pressurization inside one of the brake actuator chambers, as in U.S. Pat. No. 5,937,733. In order to maintain the seal, the '733 patent relies on an external pivot on the push rod, since the push rod articulates (wobbles) as it extends through its stroke. The dust shield of U.S. Pat. No. 5,002,164 does not completely seal around the push rod, but acts as a guide for the push rod as it articulates through its stroke.
The invention of U.S. Pat. No. 5,320,026 employs a rubber dust guard in the form of a tubular bellows deployed in the upper housing of an emergency spring brake actuator to prevent particulate matter which enters the housing from passing beyond the main spring into the actuator tube where it might affect the sliding rod. However, this dust guard is not designed for use on a service brake actuator where the push rod articulates through its stroke. Moreover, the accordion shape of this dust guard includes numerous corners and elbows, each of which is subject to constant movement and stress which lead to failures and leaks allowing contaminants to find their way to the push rod. The frequency of such failures would be increased in a service brake actuator because of the higher frequency of use, and because the service brake accordion dust guard would have to completely collapse every time the service brake is used, requiring that it be made of a thinner material which would tolerate less stress.
It is therefore desirable to provide a reliable, long-lasting seal for engagement with the push rod of a service brake actuator which prevents contaminants and foreign material brought in through breather holes in the actuator from being transmitted along the push rod to the sensitive internal mechanisms of an attached disc brake.
SUMMARY OF THE INVENTION
The present invention overcomes the drawbacks of existing dust shields and allows a service brake actuator to enjoy the benefits of having breather holes in its housing while preventing any contaminants brought into the housing through such holes from being transmitted to an attached disc brake mechanism by providing a highly reliable, long-lasting removable attachment to the lower service brake housing that provides sealing engagement with the housing and with the push rod as it moves in and out of the housing. The attachment of the present invention is a molded piece in the form of a tubular insert made of a slightly deformable material which fits into the central opening in the lower service brake housing through which the push rod extends. The tubular insert is hollow in order to allow the push rod to pass through it. The insert includes an outer annular flange which fits over the outside of the housing wall at the opening, and an inner annular flange which fits over the inside of the housing wall at the opening. Each of these flanges is made of a deformable material having elastic or rubber properties in order to provide a seal between the tubular insert and the housing wall. The insert also includes a collar adjacent to the inner flange for supporting an insertable bushing that is made of more durable material than the insert itself. The bushing fits into the inside of the collar and provides support for at least one annular seal or O-ring. The annular seal provides a seal against the push rod as it slides in and out of the tubular insert. Additional annular seals may be provided in the bushing for multiple seals with the push rod. An annular extension or brush is also provided at the distal end of the collar for snug, slidable engagement with the push rod.
The collar extensions and the annular O-ring seal(s) around the push rod prevent dirt, debris, moisture or other foreign materials from b
Constantinides Savvas K.
Smith Ted D
Kramer Devon
Miller Mark D.
Schwartz Christopher P.
TSE Brakes, Inc.
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