Expansible chamber devices – With fluid purifying means
Reexamination Certificate
1999-11-19
2002-05-21
Ryznic, John E. (Department: 3745)
Expansible chamber devices
With fluid purifying means
C092S13000R
Reexamination Certificate
active
06389954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to spring brake systems for heavy duty vehicles, and in particular to a removable, breathable filter plug for attachment to the service brake housing or emergency brake housing of a spring brake actuator which prevents moisture and unwanted contaminants from entering the actuator, while allowing air to pass into and out of the housing during normal use.
2. Description of the Prior Art
Spring brake actuators are widely used in the trucking industry to control the brakes of heavy-duty vehicles and their trailers. There are two basic types of spring brake actuators, service brake actuators, and emergency brake actuators. These actuators can be deployed as separate assemblies, or combined into a single dual assembly including both a service brake and an emergency brake actuator. A service brake actuator is operator controlled and is used for slowing or stopping a moving vehicle. An emergency or parking brake actuator is typically held off with air pressure while the vehicle is in use, but automatically engages (thereby applying the brakes) when air pressure is removed, such as when the vehicle is turned off or if there is a failure in the vehicle air system.
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 brakes 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.
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 must be allowed to escape to the outside. Then, in order for the diaphragm to contract, air must be 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.
A typical emergency brake actuator is attached in axial alignment with or made a part of the service brake assembly. The emergency brake is a separate closed housing which contains a heavy main compression spring and a second movable diaphragm creating a second sealed chamber. The emergency brake diaphragm is also attached to or directly associated with the slidable central push rod of the service brake. The second sealed chamber is formed inside the emergency brake housing on one side of the diaphragm, and the heavy main compression spring is deployed on the opposite side. As with the service brake, the sealed chamber of the emergency brake is connected to the on-board pneumatic source of the vehicle. As long as sufficient air pressure is provided to the sealed chamber, the diaphragm in the emergency brake will remain fully expanded thereby compressing (caging) the main spring. However, should air pressure fall, or should there be a leak in the sealed chamber, the diaphragm will be unable to hold the main compression spring in place. When this occurs, either slowly or quickly, the main compression spring will expand causing the push rod to be extended out thereby applying the brakes of the vehicle.
Under normal conditions, when the vehicle is parked, the air pressure to the emergency brake is removed causing the main compression spring to apply the brakes. As the emergency brake is engaged and disengaged, air pressure is introduced and removed from the sealed chamber in the lower portion of the emergency brake housing, causing the diaphragm inside the housing to move back and forth. In order for the diaphragm to expand and compress the main spring, the air in the upper portion of the housing around the spring must be allowed to escape to the outside. Then, in order for the diaphragm to contract and release the main spring, air must be allowed to enter the area of the upper housing around the spring.
Typical emergency brake housing assemblies also include a plurality of air holes in the upper housing in the vicinity of the main spring to allow air to enter and exit this region as the diaphragm moves back and forth. The unfortunate effect of this action is the same as in the service brake housing, allowing dirt, water, oil, debris, and other unwanted materials to enter the emergency brake housing from the outside through the air holes.
Several inadequate or cumbersome solutions have been advanced to respond to this problem. The inventions of U.S. Pat. Nos. 4,508,018 and 5,671,654 describe a sealed internal breathing system which utilizes a tubular structure connecting between the service brake housing and the emergency brake housing. Air is transmitted between the two sealed housings through the tubular structure, so that no outside air is ever needed. However, the use of such a tube requires specially designed housings for both the spring brake and emergency brake making it difficult and costly to manufacture.
The invention of U.S. Pat. No. 5,320,026 employs a rubber dust guard in the upper housing between the power spring and the housing wall to prevent particulate matter from passing beyond the spring into the actuator tube where it might affect the sliding rod. However, this invention does not prevent foreign matter from entering the upper chamber in the first place through the air openings. Thus, foreign material can collect around the power spring potentially affecting operation of the brake.
The inventions of U.S. Pat. Nos. 5,372,059 and 5,722,311 use a pair of valves: a first one-way valve allows air to enter the area around the main spring only from the sealed chamber in the spring brake housing; another other one-way valve only allows air to escape from this area to the outside. A similar approach is taught in U.S. Pat. No. 5,873,297 which employs a double check valve in the housing, and a separate valve in the upper housing diaphragm for communication between the sealed chamber and the area around the main spring. Each of these inventions requires cumbersome specially designed emergency brake housing structures including at least one opening(s) in the spring brake diaphragm, together with the use of no less than two separate valves, leaving such systems vulnerable to several different kinds of failures which could be costly and difficult to repair.
The invention of U.S. Pat. No. 5,836,233 describes a spring brake actuator which employs breather holes located on the cylindrical side walls of the upper housing such that when the main spring is compressed or caged, the diaphragm covers the holes. However, when uncaged, these unfiltered breather holes are exposed to the atmosphere, allowing foreign material to enter the housing. A check valve is also provided in a cap attached to the upper housing.
The invention of U.S. Pat. No. 5,937,733 describes a spring brake actuator having a filter integrated into the emergency brake housing. A series of vent openings, valves, seals and internal conduits allow air to escape from both the service and emergency brake housings through this filter. A
Constantinides Savvas K.
Smith Ted D
Miller Mark D.
Ryznic John E.
TSE Brakes, Inc.
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