Breather filter for sealed spring brake actuators

A brake actuator assembly includes a housing defining a spring chamber. A spring is disposed in the spring chamber, the spring being biased toward an extended position and movable against the bias toward a caged position. A release assembly is provided for selectively moving and retaining the spring against the bias toward the caged position, the release assembly comprising a hollow release bolt having a fluid passage passing therethrough by which fluid passage the spring chamber is in fluid communication with an environment surrounding the housing. A filter is disposed within the fluid passage in the hollow release bolt for filtering fluid passing through the fluid passage.

FIELD OF THE INVENTION

The present invention relates generally to spring brake actuators for vehicles and particularly diaphragm- or piston-style spring brake actuators.

BACKGROUND OF THE INVENTION

An air brake system for a vehicle such as a bus, truck or the like typically includes a brake actuator assembly which is actuated by means of an actuator assembly operated by the selective application of a fluid such as compressed air. Conventional air brake actuators typically have both a service brake actuator for actuating the brakes under normal driving conditions by the application of compressed air and an emergency or spring brake actuator which causes actuation of the brakes when air pressure has been released. The spring brake actuator can be used as a parking brake or emergency brake in the event that the air pressure system fails. The spring brake actuator includes a compression spring which forces application of the brake when fluid or air pressure is either released or lost. Typically, the spring brake actuator is disposed in tandem with the service brake actuator.

The service chamber which houses the service break actuator is typically divided into two chambers by a diaphragm. Depressing the brake pedal during normal driving operation introduces compressed air or fluid into one of the chambers of the service brake actuator which, acting against the diaphragm, causes a service brake push rod in the opposite chamber to be extended and the brakes to be applied with an application force proportional to the air pressure in the service brake actuator.

Like the service chamber, the spring brake actuator is typically divided into two chambers, a pressurized chamber and a non-pressurized chamber, separated by a rubber diaphragm and pressure plate, with the spring in the non-pressurized chamber acting between an end wall of the spring brake housing and the pressure plate. When compressed air or fluid is introduced to the pressurized chamber, air or fluid pressure acting against the diaphragm and pressure plate compresses the spring in the non-pressurized chamber.

In the event of a loss of air or fluid pressure or an intentional exhaustion of air or fluid from the spring brake actuator, the spring brake will be mechanically activated by the force of the compression spring acting on the spring brake actuator rod which, in turn, acts upon the brake push rod to apply the brakes. Thus, the spring brake portion serves both as a parking brake and an emergency brake. Because the force generated by the compression spring is quite large, it can be dangerous to service the spring brake if the spring has not been properly restrained. For safety purposes during servicing, some spring brake actuators include a release bolt and nut assembly that can be adjusted to retain the spring in a fixed and safe position during surfacing of the brake.

When air or fluid pressure is released from the spring brake actuator, the spring and diaphragm extend significantly, expanding the volume of the spring brake actuator non-pressurized chamber containing the spring. A pressure vacuum is then created in the chamber by the expanding volume of the non-pressurized chamber, so means must be provided to allow air to enter into the expanded volume of the non-pressurized chamber from the outside environment. Conversely, when the spring is retracted, and the volume of the non-pressurized chamber contracts, means must be provided for evacuating air from the chamber.

In many prior brake actuators, the chamber containing the spring is simply open to the outside environment and atmosphere through ports or vents in the chamber housing. However, this allows dirt, salt, moisture and other unwanted material and contaminants from the environment outside the brake chamber to enter that chamber through the ports. Some prior art brake designs have used complex arrangements of valves and fluid conduits to permit fluid flow to the spring brake chamber from other chambers in the brake actuator assembly. These arrangements require extra components and complex machining of the components. Other prior art brake actuators have used external filters placed over the vent holes and attached to the outside of the brake actuator housing to prevent contaminants from entering the brake chambers. However, external filters require additional space, components, machining and assembly effort.

Prior art brake actuators include U.S. Pat. No. 5,937,773 which discloses a spring brake actuator with an internal breathing conduit made up of a series of complicated weep holes in the spring brake housing, the spring brake actuator rod and the sleeve of the push rod. This series of weep or vent holes fluidly connects the unpressurized chambers of the brake with the outside environment. The fluid which enters and exits the brake actuator through the external vent hole passes through a filter assembly that attaches to the exterior of the spring brake housing and covers the external vent hole filtering fluid passing in and out of the spring brake.

U.S. Pat. No. 5,632,192 issued to Plantan et al. discloses a spring brake actuator which includes an indicator system incorporated into a release tool therefor. The indicator provides an indication of when the release tool has is fully released. The release tool is of the type wherein a threaded member does not extend outwardly of the actuator during caging of the power spring. The indicator is biased outwardly of the actuator when the release bolt has even partially caged the power spring. It is only when release bolt is fully released that the indicator is pulled inwardly. Thus, an observer has a visual indication of when the power spring caging mechanism has been fully released. However, this reference does not disclose any type of filter or vent system at all.

U.S. Pat. Nos. 5,263,403 and 5,311,809 issued to Choinski et al. disclose a brake actuator having a non-pressurized spring brake chamber and a non-pressurizing service brake chamber fluidly interconnected by a breather tube mounted on the outside of the brake actuator housing.

U.S. Pat. No. 4,890,540 issued to Mullins discloses a brake actuating unit having a housing with a pair of vent holes wherein the lower vent hole is left completely open to the outside environment without a cap or filter while only the upper vent hole is sealed to prevent contaminants from entering the housing.

U.S. Pat. No. 3,896,706 issued to Newstead discloses a brake unit having vent holes in the brake housing of the non-pressurized chamber that are covered by external filters that are attached to the outside of the brake housing.

U.S. Pat. No. 5,123,330 issued to Roether et al, U.S. Pat. No. 4,283,992 issued to Wilson and U.S. Pat. No. 4,259,895 issued to Owens all disclose assemblies having filters for outside air located within or adjacent to actuating cylinders.

All of the prior art references listed above suffer from a number of disadvantages, including the fact that complex filter designs are employed, that additional holes are required to be created in the housing, and/or that unsatisfactory filtering of contaminants is achieved.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a brake actuator assembly which permits air flow in and out of the actuator brake housing.

Another object of the present invention is to provide a brake actuator assembly having the above characteristics and which filters out unwanted contaminants from entering the actuator brake housing.

A further object of the present invention is to provide a brake actuator assembly having the above characteristics and which does not employ a complex filter design.

Still another object of the present invention is to provide a brake actuator assembly having the above characteristics and which does not require that additional holes be created in the housing.

Yet a further object of the present invention is to provide a brake actuator assembly having the above characteristics and which achieves satisfactory filtering of contaminants.

These and other objects of the present invention are achieved by provision of a brake actuator assembly including a housing defining a spring chamber. A spring is disposed in the spring chamber, the spring being biased toward an extended position and movable against the bias toward a caged position. A release assembly is provided for selectively moving and retaining the spring against the bias toward the caged position, the release assembly comprising a hollow release bolt having a fluid passage passing therethrough by which fluid passage the spring chamber is in fluid communication with an environment surrounding the housing. A filter is disposed within the fluid passage in the hollow release bolt for filtering fluid passing through the fluid passage. Preferably, the spring chamber is substantially air-tight except for the fluid passage in the hollow release bolt.

In certain embodiments, the release assembly comprises threads provided on an outer surface of the hollow release bolt, which threads cooperate with threads provided on an inner surface of a nut. In these cases, the spring is preferably moved and retained toward the caged position when the hollow release bolt is rotated with respect to the nut. In certain of these embodiments, the nut is fixedly mounted to the housing.

In certain embodiments, an indicator mechanism is provided which indicates whether the spring has been moved and retained toward the caged position. In certain of these embodiments, the indicator mechanism indicates to what extent the spring has been moved and retained toward the caged position. In certain embodiments, the indicator mechanism comprises threads provided on an outer surface of the hollow release bolt, which threads cooperate with threads provided on an inner surface of a nut. In certain of these embodiments, the nut is fixedly mounted to the housing. In certain embodiments, the hollow release bolt extends out beyond the housing when the spring has been moved and retained toward the caged position. In certain of these embodiments, an extent to which the hollow release bolt extends out beyond the housing indicates an extent to which the spring has been moved and retained toward the caged position.

The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

An exemplary embodiment of a brake actuator assembly in accordance with the invention is shown in FIG.1. The brake actuator assembly includes a brake housing10, which is formed of two portions, a spring break chamber or first proximal portion12and a second distal portion14. The first proximal portion defines an aperture16in the proximal end of the housing10while the second distal portion defines an aperture18in the distal end of the housing10. A sleeve20is slideably located at least partially within housing10and can move reciprocally from a retracted position within the housing to extended position outside the housing. A diaphragm22is attached between the sleeve20and the housing10. In the disclosed embodiment, the diaphragm's outer periphery24is attached to the housing10where the first housing portion12and the second housing portion14meet. In the embodiment shown inFIG. 1, the diaphragm's inner periphery26is attached near the proximal end of sleeve20with spring retraction plate28which forms an assembly that moves with sleeve20as the sleeve reciprocates between a retracted (proximal) and extended (distal) position.

Within sleeve20is a release bolt40with one end that extends at least partially outside housing10through aperture16and second end to which collar42is attached. Release bolt40is hollow and has a channel therein at least partially defining a fluid passage44between the environment outside the brake housing10and the brake chamber45inside the brake housing10. Inside the release bolt40and located in the fluid passage44is a filter element46for filtering contaminants from fluid that passes through the fluid passage44.

The exterior or outer surface of release bolt40is at least partially threaded and is at least partially engaged with a nut48that is fixedly attached to the first housing portion12and at least partially defines the first aperture16. The interior of inner surface of nut48is threaded to mate with the exterior threads on release bolt40. Due to the mating threads of release bolt40and nut48, the position of release bolt40relative to first housing portion12can be adjusted by simply rotating release bolt40.

Collar42includes a fluid passage50to at least partially define a fluid path that allows fluid to pass by or through collar42(best seen in FIG.7), as more fully described below. Collar42can also include a nylon bearing surface on the face of the collar that comes in contact with sleeve20and release plate28to reduce friction between the parts during rotation of the release bolt40.

A spring chamber30is at least partially defined by the first housing portion12, the diaphragm22and the spring release plate28. Typically, the spring chamber30is unpressurized and houses a power spring34. The spring34is located between the inner wall36of the housing's first proximal section12and the spring retraction plate28. The brake chamber45is at least partially defined by distal housing portion14and the diaphragm/spring retraction plate/sleeve assembly. Typically, brake chamber45is pressurized by fluid pressure, in this embodiment by compressed air. When fluid is forced into the brake chamber45, the fluid pushes the spring retraction plate/diaphragm/sleeve assembly in a distal direction to a retracted position within the brake housing10(as more fully described below). As the spring retraction plate/diaphragm/sleeve assembly moves to the retracted position, spring34is compressed and the volume defined by the spring chamber30decreases while the volume of the brake chamber45increases.

As the volume of the spring chamber30decreases, fluid in the first chamber is forced out of the first chamber through an opening38in the spring retraction plate/diaphragm/sleeve assembly (as best seen in FIG.6), as more fully described below. The fluid being forced out of the spring chamber30travels through opening38and down inside sleeve20between sleeve20and a release bolt40. The fluid then passes through the fluid passage50which is at least partially defined by collar42and exits housing10by passing through fluid passage44and out through filter element46. Preferably, chamber45is substantially air-tight with respect to the environment outside brake housing10except for fluid passage44.

Alternatively, when pressure in the brake chamber45decreases and spring34expands, the volume defined by the spring chamber30increases while the volume of the brake chamber45decreases. As the volume in spring chamber30increases the fluid or air pressure in the chamber decreases and a vacuum is created. This vacuum effect causes fluid (i.e., air) from the environment outside the brake housing10to be drawn in through the fluid passage44in release bolt40, through filter element46, through fluid passage50in collar42, between release bolt40and sleeve20, through opening38and into first chamber30(as best seen in FIG.6).

Those skilled in the art will recognize there are various other fluid paths that could be conceived connecting spring chamber30with the environment outside the brake housing10that include the use of a filter element with in the release bolt40.

A better understanding of the fluid flow through filter46can be gained by reviewing the other figures. WhileFIG. 1illustrates the situation when brake chamber45is fully pressurized, spring34is fully compressed and sleeve20is in its most retracted position within housing10(i.e., release bolt40is in a fully disengaged position),FIG. 2discloses the situation when the pressure in the brake chamber45is reduced, permitting spring34to partially expand, forcing sleeve20in a distal direction to a partially extended position. As pressure in brake chamber45is reduced the diaphragm22moves distally, decreasing the volume of brake chamber45and increasing the volume of spring chamber30. The increasing volume of brake chamber45creates a vacuum, drawing fluid such as ambient air from outside housing10. The arrows inFIG. 2show the path of the fluid drawn in from outside housing10. First, the fluid is drawn into release bolt40, through filter element46. As the fluid is drawn through the release bolt40, filter element46filters out any unwanted contaminants such as dirt, grease, moisture or any other undesirable material not wanted within the brake chambers. After passing through the filter46and fluid passage44in the release bolt40, the fluid passes through fluid passage50, in or around collar42, and travels between sleeve20and release bolt40until is passes through opening38into the spring chamber30. As the diaphragm22continues to move distally the volume in spring chamber30continues to expand and continues to draw in more fluid. This flow of fluid is seen even more clearly in FIG.6.

FIG. 3illustrates the situation when the pressure in the brake chamber45has been completely released or loss, permitting spring34to fully expand, and forcing sleeve20in a distal direction to a fully extended position outside housing10. Diaphragm22is in its most distal position minimizing the volume of brake chamber45and maximizing the volume of spring chamber30. The increased volume of spring chamber30is filled with ambient air from outside housing10. The arrows inFIG. 3show the path of the fluid drawn in from outside housing10. Again the fluid, such as ambient air is drawn into release bolt40, through filter element46. As the fluid, or ambient air is drawn through the release bolt40, filter element46filters out any unwanted contaminants such as dirt, grease, moisture or any other undesirable material not wanted within the brake chambers. After passing through the filter46and fluid passage44in the release bolt44, the fluid passes through fluid passage50, in or around collar42, and through opening38into the spring chamber30. The situation shown inFIG. 3would occur, for example, when the spring brake is actuated or in an emergency brake situation when air pressure is lost in brake chamber45.

FIG. 4shows the situation where the release bolt40is in a partially engaged position and with the spring34partially caged by the release bolt40. More specifically, release bolt40has been rotated within fixed nut48causing release bolt40to move in a proximal direction and to further extend outside housing10. As release bolt40is rotated and moved in a proximal direction collar42acts upon the spring retraction plate/diaphragm/sleeve assembly to move it in a proximal direction, thereby compressing spring34. As spring34is compressed the volume of the spring chamber30decreases, fluid in the spring chamber30is forced out of the spring chamber through opening38in the spring retraction plate28. The fluid being force out of the first chamber travels through opening38, through fluid passage50in collar42inside sleeve20and exits housing10by passing through fluid passage44and out through filter element46of release bolt40. The arrows inFIG. 4show the path of the fluid from inside spring chamber30to outside housing10. As the release bolt40continues its rotation and continues to further extend out of housing10the volume of spring chamber30continues to be reduced further forcing air or fluid out of the spring chamber30.

It should be noted that the extension of release bolt40outside of housing10when spring34is being caged provides a mechanism whereby it can be easily visually determined whether spring34has been partially or fully caged by release bolt40. Moreover, as should be understood by those skilled in the art, the extent to which release bolt40extends out of housing40indicates the extent to which spring34has been caged thereby.

FIG. 5shows release bolt40completely extended from housing10and completely compressing and caging spring34. The volume of spring chamber30is at its minimum. Any increase in the volume of spring chamber30due to movement of the diaphragm will require additional air or fluid to enter into the spring chamber30.

FIG. 6shows an enlarged detailed view of one embodiment of opening38in the spring retraction plate28and fluid passage50in collar42. The arrows show the fluid path through these passages as fluid is being drawn into spring chamber32, as would be the case with the situation described above with respect to FIG.2. The fluid flow would be reversed if fluid were being expelled from spring chamber32.

FIG. 7shows an enlarged detailed view of one embodiment of collar42and fluid passage50.FIG. 7shows a collar with only a single groove defining a single fluid passage. Those skilled in the art recognize that collar42could have any number of grooves or channel arrangements that would permit fluid flow around or through collar42.

The present invention, therefore, provides a brake actuator assembly which permits air flow in and out of the actuator brake housing, which filters out unwanted contaminants from entering the actuator brake housing, which does not employ a complex filter design, which does not require that additional holes be created in the housing, and which achieves satisfactory filtering of contaminants.

For example, the present invention could easily be adapted by one having ordinary skill in the art for use with substantially any brake actuator assembly which includes a release bolt, such as the brake actuator assembly disclosed in U.S. Pat. No. 5,632,192 to Plantan et al.