Patent Description:
The parking brake portion of the spring brake actuator will often include an aperture permitting access to the spring brake chamber in order to permit manual release of the parking brake. Internal components may degrade over time from fluids and other contaminants that enter the housing through such apertures. In order to address this issue, some spring brake actuators employ vent holes to permit contaminants to escape from the housing. However, these vent holes often become a source of contaminant entry and may become clogged. Other spring brake actuators attempt to seal apertures in the housing to prevent contaminants from entering the housing. These latter spring brake actuators frequently employ a dust plug that is inserted in the aperture when the aperture is not in use. Conventional dust plugs, however, are frequently discarded by vehicle operators and maintenance personnel following removal of the dust plug during regular maintenance. These dust plugs can be difficult to reinstall. Further, if an individual does reinstall the dust plug, the dust plug is often installed incorrectly. Conventional dust plugs are also subject to displacement by vibration during normal vehicle operation. Document <CIT> discloses a sealing assembly for a spring brake actuator with a cap arranged on a plug, the cap being held on a curved portion of an outer wall of the plug. Accordingly, those skilled in the art continue with research and development efforts in the field of spring brake actuator designs and means to seal spring brake actuators.

In accordance with one embodiment, a sealing assembly for a spring brake actuator comprises a plug, a one-way valve and a cap. The plug comprises a circular planar section having a central opening and at least two orifices arranged outside an outer diameter of the central opening. The plug includes a first set of segments on a first surface of the circular planar section arranged to fit within an inner diameter of a port of the spring brake actuator, a second set of segments on the first surface of the circular planar section arranged to fit outside an outer diameter of the port of the spring brake actuator, an elastomeric piece affixed between the first set of segments and the second set of segments for sealing against an inner surface of the port, a third set of segments on a second surface of the circular planar section arranged to receive a cap and a fourth set of segments arranged around the outer circumference of the circular planar section defining the length of the plug, each of the fourth set of segments having a curved portion at one end and a protrusion at an opposite end. The one-way valve fits in the central opening for providing one-way air flow through the at least two orifices. The cap has arms sized to extend around the third set of segments and snap onto the first surface of the circular planar section, wherein the cap forms a chamber when mated with the plug.

In another embodiment, a spring brake actuator for an air brake system comprises a housing defining a spring brake chamber, an aperture in the spring brake chamber of the housing and a port affixed to the spring brake chamber of the housing for providing access to the aperture. The port has a smooth inner surface and a groove on an outer surface. A sealing assembly is installed on the port. The sealing assembly comprises a plug, a one-way valve and a cap. The plug includes a circular planar section having a central opening and at least two orifices around outside an outer diameter of the central opening. The plug includes a first set of segments on a first surface of the circular planar section arranged to fit within an inner diameter of a port, a second set of segments on the first surface of the circular planar section arranged to fit outside an outer diameter of the port, an elastomeric piece molded to the first set of segments for sealing against the smooth inner surface of the port, a third set of segments on a second surface of the circular planar section arranged to receive a cap and a fourth set of segments arranged around the outer circumference of the circular planar section defining the length of the plug, each of the fourth set of segments having a curved portion at one end and a protrusion at an opposite end for fitting within the groove of the port. The one-way valve fits in the central opening for providing one-way air flow through the at least two orifices. The cap has arms sized to extend around the third set of segments and snap onto the first surface of the circular planar section, wherein the cap forms a chamber when mated with the plug.

In another embodiment, a method of operating a spring brake actuator comprises installing a sealing assembly to a port of the spring brake chamber of a spring brake actuator. The sealing assembly comprises a one-way valve for providing one-way air flow. The method comprises setting the spring brake actuator at zero stroke, wherein the sealing assembly maintains about two psi of air in the spring brake chamber. The method further comprises setting the spring brake actuator at normal stroke, wherein the sealing assembly exhausts air from the spring brake chamber through the one-way valve to maintain about zero psi in the spring brake chamber.

Referring to <FIG>, a spring brake actuator <NUM> having a housing <NUM> that defines a spring brake chamber is shown. The parking brake chamber (not shown) of the parking brake portion receives a pneumatic input to compress a power spring (not shown) located in the spring brake chamber, thereby holding the parking brakes in the unparked position. This spring brake chamber is sealed to prevent moisture and contaminants from entering. However, air trapped in the spring brake chamber when the power spring is released must be allowed to be vented to ensure proper operation of the parking brakes. In addition, the power spring inside the spring brake chamber must be accessed to be caged if maintenance is needed to be completed on the spring brake actuator or accompanying brake system. Therefore, access through the housing <NUM> must be present for this purpose as well.

The housing <NUM> defining the spring brake chamber of a parking brake section of the spring brake actuator <NUM> is generally a metallic material, such as aluminum or steel. The housing <NUM> includes an aperture <NUM> that is used as an access point for a tool used in caging the power spring located inside the housing <NUM>. The aperture <NUM> also serves to release air from the spring brake chamber.

Port <NUM> is affixed to the housing <NUM> and surrounds the aperture <NUM>. The port <NUM> may be the same metallic material as the housing <NUM> or it may be a different metallic material. The port <NUM> includes a smooth inner surface and a groove <NUM> around an outer circumference of the port <NUM>. The port <NUM> may be welded to the housing <NUM> or otherwise staked. No machining of the port <NUM> is required after welding to the housing <NUM>.

The housing <NUM> may also include a post <NUM> affixed to the housing <NUM>. The post <NUM> may be a metallic material or other material.

Sealing assembly <NUM> is an example of a simple to install assembly that seals the housing <NUM> against moisture and contaminants while allowing pressurized air from the spring brake chamber to vent to atmosphere. The sealing assembly <NUM> is depicted as disengaged from the port <NUM>.

The sealing assembly <NUM> includes a plug <NUM> and a cap <NUM>. The cap <NUM> may have a tether <NUM>. In order to keep the sealing assembly <NUM> near the housing <NUM> when disengaged, the tether <NUM> affixes to the post <NUM> by sliding the tether <NUM> over the post <NUM>. The aperture <NUM> can then be accessed by a technician with the proper tools without interference from the sealing assembly <NUM>. The sealing assembly <NUM> will not be misplaced while it remains affixed to the post <NUM>.

<FIG> depicts an enlarged cross-section in a first view of the plug <NUM> of the sealing assembly <NUM>.

The plug <NUM> comprises a circular planar section <NUM>. The circular planar section <NUM> has a central opening <NUM>. The circular planar section <NUM> also includes at least two orifices <NUM> arranged outside the outer diameter of the central opening <NUM>. The diameter of the at least two orifices <NUM> is less than the diameter of the central opening <NUM>.

The plug <NUM> includes a first set of segments <NUM> extending outward from a first surface of the circular planar section <NUM>. The first set of segments <NUM> are arranged axially outside the location of the at least two orifices <NUM>.

The plug <NUM> includes a second set of segments <NUM> arranged near the outer circumference of the first surface of the circular planar section <NUM>. The second set of segments <NUM> are approximately the same length as the first set of segments <NUM>.

The plug <NUM> includes a third set of segments <NUM> arranged around the outer circumference of a second surface of the circular planar section <NUM>, opposite the first surface. The third set of segments <NUM> extend outward from the circular planar section <NUM>.

<FIG> depicts an enlarged cross-section in a view of the plug <NUM> of the sealing assembly <NUM> arranged ninety degrees from the view shown in <FIG>.

The plug <NUM> includes a fourth set of segments <NUM> arranged around the outer circumference of the circular planar section <NUM>. The fourth set of segments <NUM> define the full length of the plug <NUM> and are elastically deformable. The fourth set of segments <NUM> include a protrusion <NUM> at the end extending from the first surface and a curved portion <NUM> extending from the second surface. The fourth set of segments <NUM> may include a living hinge such that when the curved portion <NUM> is pressed inward, the protrusion <NUM> moves outward.

<FIG> depicts a cross-section in a first view of the spring brake actuator <NUM> having the sealing assembly <NUM> as installed on the port <NUM>.

The first set of segments <NUM> of the plug <NUM> extend partially into an inner diameter of the port <NUM> when the sealing assembly <NUM> is installed on the port <NUM>. The second set of segments <NUM> are arranged to partially surround the outer diameter of the port <NUM> when the sealing assembly <NUM> is installed.

The plug <NUM> includes an elastomeric piece <NUM> affixed between the first set of segments <NUM> and the second set of segments <NUM>. The elastomeric piece <NUM> may be overmolded directly to the first set of segments <NUM>. The elastomeric piece <NUM> is shaped to be fully within the inner diameter of the port <NUM> when the sealing assembly <NUM> is installed. The elastomeric piece <NUM> will seal against the smooth inner surface of the port <NUM>. The elastomeric piece <NUM> may be of silicon, rubber or other material having similar flexibility. The elastomeric piece <NUM> may be molded to include ribs along its outer diameter to improve the seal against the inner surface of the port <NUM>. No additional seals, such as O-rings found on prior art spring brake actuators dust plugs, are required.

The sealing assembly <NUM> includes a one-way valve <NUM>. The one-way valve <NUM> is frictionally fit in the central opening <NUM> of the circular planar section <NUM>. The one-way valve <NUM> is designed to cover the at least two orifices <NUM> when in the at rest position. The one-way valve <NUM> may be an umbrella valve. The one-way valve <NUM> may be made of a silicone or similar material. The one-way valve <NUM> allows air to flow through the at least two orifices <NUM> out of the spring brake chamber when the pressure in the spring brake chamber is between about one psi and about three psi. The shape and structure of the one-way valve <NUM> may be adjusted to provide different opening pressures (crack pressures).

The sealing assembly <NUM> includes the cap <NUM>. The cap includes a planar section <NUM> and arms <NUM> arranged to surround the third set of segments <NUM> of the plug <NUM>. Arms <NUM> of the cap <NUM> are shaped to facilitate snap fitting the cap <NUM> to plug <NUM>. A chamber <NUM> is formed between the circular planar section <NUM> and the cap <NUM> when the cap <NUM> is snap-fit onto the plug <NUM>. Air escapes the chamber <NUM> to atmosphere around the planar section <NUM> of cap <NUM> when the one-way valve <NUM> is open.

The cap <NUM> may also include the tether <NUM>. The tether <NUM> extends from the cap <NUM> across the body of the actuator housing <NUM> to the post <NUM>. An aperture <NUM> on the distal end of the tether <NUM> fits over the post <NUM>. When the sealing assembly <NUM> is uninstalled, it can be pivoted around the post <NUM>.

The material of the plug <NUM> and the cap <NUM> may be the same elastically deformable material, such as nylon or ABS plastic. The material selected should be stable with exposure to ultraviolet light and impact resistant. Alternatively, the plug <NUM> may be a glass filled plastic to improve the ability to withstand the overmolding process. The plug <NUM> and the cap <NUM> are assembled together easily by snapping the cap <NUM> over the plug <NUM> prior to the sealing assembly <NUM> being installed on the port <NUM>. Once snapped together, the cap <NUM> will not need to be unsnapped from the plug <NUM>. The assembly of the cap <NUM> to the plug <NUM> could also be accomplished by including living hinges as part of the arms <NUM> of the cap <NUM>.

<FIG> depicts a cross-section of the sealing assembly <NUM> as installed on the port <NUM> in a second view, approximately ninety degrees from the first view of <FIG>.

Ridges <NUM> on the planar section <NUM> of the cap <NUM> abut the one-way valve <NUM> and assist in holding the one-way valve <NUM> in the central opening <NUM> when installed.

The curved portion <NUM> and protrusion <NUM> of the fourth set of segments <NUM> facilitate the attachment and removal of the sealing assembly <NUM> from the port <NUM>. The fourth set of segments <NUM> affix to the groove <NUM> on the outer diameter of the port <NUM>, such as by the protrusion <NUM> snap fitting into the groove <NUM>. The sealing assembly <NUM> is held onto the port <NUM> by this feature throughout the operation of the actuator. The sealing assembly <NUM> can easily be released by pressing inward on curved portion <NUM>, which in turn will release the protrusion <NUM> from the groove <NUM>. The sealing assembly <NUM> is reusable for multiple installations onto the spring brake actuator <NUM>.

No special tools are required to insert the one-way valve <NUM> into the plug <NUM> and to assemble the cap <NUM> to the plug <NUM>. No special tools are required to install the sealing assembly <NUM> onto the port <NUM>. The sealing assembly <NUM> remains on port <NUM> throughout normal operation of the actuator and is impervious to debris or rust. The spring brake actuator <NUM> is now easily serviceable. No additional machining process is required for the port <NUM> before or after welding or staking to the housing <NUM>, since no threads are required.

Therefore, a sealing assembly for a spring brake actuator comprises a plug, a one-way valve and a cap. The plug comprises a circular planar section having a central opening and at least two orifices arranged outside an outer diameter of the central opening. The plug includes a first set of segments on a first surface of the circular planar section arranged to fit within an inner diameter of a port of the spring brake actuator, a second set of segments on the first surface of the circular planar section arranged to fit outside an outer diameter of the port of the spring brake actuator, an elastomeric piece affixed between the first set of segments and the second set of segments for sealing against an inner surface of the port, a third set of segments on a second surface of the circular planar section arranged to receive a cap and a fourth set of segments arranged around the outer circumference of the circular planar section defining the length of the plug, each of the fourth set of segments having a curved portion at one end and a protrusion at an opposite end. The one-way valve fits in the central opening for providing one-way air flow through the at least two orifices. The cap has arms sized to extend around the third set of segments and snap onto the first surface of the circular planar section, wherein the cap forms a chamber when mated with the plug.

Therefore, a spring brake actuator for an air brake system comprises a housing defining a spring brake chamber, an aperture in the spring brake chamber of the housing and a port affixed to the spring brake chamber of the housing for providing access to the aperture. The port has a smooth inner surface and a groove on an outer surface. A sealing assembly is installed on the port. The sealing assembly comprises a plug, a one-way valve and a cap. The plug includes a circular planar section having a central opening and at least two orifices around outside an outer diameter of the central opening. The plug includes a first set of segments on a first surface of the circular planar section arranged to fit within an inner diameter of a port, a second set of segments on the first surface of the circular planar section arranged to fit outside an outer diameter of the port, an elastomeric piece molded to the first set of segments for sealing against the smooth inner surface of the port, a third set of segments on a second surface of the circular planar section arranged to receive a cap and a fourth set of segments arranged around the outer circumference of the circular planar section defining the length of the plug, each of the fourth set of segments having a curved portion at one end and a protrusion at an opposite end for fitting within the groove of the port. The one-way valve fits in the central opening for providing one-way air flow through the at least two orifices. The cap has arms sized to extend around the third set of segments and snap onto the first surface of the circular planar section, wherein the cap forms a chamber when mated with the plug.

When a spring brake actuator is assembled, some pressurized air remains in the spring brake chamber. During operation of the prior art spring brake actuators, normally approximately zero pounds per square inch (psi) of pressure in the parking brake section is present at zero stroke of the actuator rod (when the vehicle is parked). At the normal parking stroke, which is about <NUM> inches, a vacuum would form of about three psi. The presence of the vacuum equates to a reduction in available force to park of about ninety pounds force (Ibf). Spring brake actuators are required to continue to apply a force throughout the full stroke of the actuator rod with a recommended SAE tolerance band of <NUM> lbf. At full stroke, the vacuum in the spring brake chamber could be about nine psi. This negative pressure equates to about <NUM> Ibf loss in parking force when using a Type <NUM> (<NUM> cubic inch volume) parking brake chamber, which is almost the entire tolerance band. Some prior art spring brake actuators make up for this reduction in force by using a larger power spring in order to maintain the required force output through the entire stroke. In the present spring brake actuator, zero psi is not desired in the spring brake chamber at zero stroke.

<FIG> discloses a method <NUM> of operating the spring brake actuator <NUM> having the present inventive sealing assembly <NUM>. At full stroke with the present one-way valve <NUM> in operation, a lower pressure vacuum would be formed that would not detrimentally affect the force output of the parking brake spring. Prior art one-way valves used in spring brake actuators do not have a minimum opening pressure (crack pressure) and tend to exhaust all of the pressure from the spring brake chamber.

In step <NUM>, the sealing assembly <NUM> is installed on the port <NUM>. In step <NUM>, the spring brake actuator <NUM> is set to zero stroke. In step <NUM>, the inventive sealing assembly <NUM> maintains a small positive pressure of about two psi in the spring brake chamber at zero stroke. Then, throughout the stroke of the spring brake actuator, the vacuum pressure created in the spring brake chamber will be reduced from prior art spring brake actuators.

In step <NUM>, the spring brake actuator <NUM> is set to a normal stroke, such as a standard parking stroke of about <NUM>". In step <NUM>, the sealing assembly <NUM> maintains about zero pressure in the spring brake chamber. At zero pressure, there is no reduction in force output of the spring brake actuator <NUM>. Zero pressure is possible at normal stroke because of the initial opening pressure setting of the one-way valve <NUM>, which does not exhaust all of the pressure out of the spring brake chamber at zero stroke.

In step <NUM>, the spring brake actuator is set to a full stroke. In step <NUM>, the sealing assembly maintains a vacuum of about <NUM> psi, causing a reduction in available force of about <NUM> lbf. However, this is a <NUM> lbf improvement over prior art spring brake actuators. The remaining tolerance band for operation of the spring brake actuator is then <NUM> lbf, and not <NUM> lbf as in the prior art spring brake actuators. The size and material of the power spring used in this inventive spring brake actuator assembly can be lighter weight since there is less expected force output loss.

Another advantage of the sealing assembly <NUM> is if there is a leak in the spring brake chamber, the positive chamber pressure enabled by the sealing assembly <NUM> will tend to expel any contaminants rather than draw them into the spring brake chamber.

Therefore, a method of operating a spring brake actuator comprises installing a sealing assembly to a port of the spring brake chamber of a spring brake actuator. The sealing assembly comprises a one-way valve for providing one-way air flow. The method comprises setting the spring brake actuator at zero stroke, wherein the sealing assembly maintains about two psi of air in the spring brake chamber. The method further comprises setting the spring brake actuator at normal stroke, wherein the sealing assembly exhausts air from the spring brake chamber through the one-way valve to maintain about zero psi in the spring brake chamber.

Claim 1:
A sealing assembly (<NUM>) for a spring brake actuator (<NUM>) comprising:
a plug (<NUM>), the plug (<NUM>) comprising
a circular planar section (<NUM>) having a central opening (<NUM>) and at least two orifices (<NUM>) arranged outside an outer diameter of the central opening (<NUM>);
a first set of segments (<NUM>) on a first surface of the circular planar section (<NUM>) arranged to fit within an inner diameter of a port (<NUM>) of the spring brake actuator (<NUM>);
a second set of segments (<NUM>) on the first surface of the circular planar section (<NUM>) arranged to fit outside an outer diameter of the port (<NUM>) of the spring brake actuator (<NUM>);
an elastomeric piece (<NUM>) affixed between the first set of segments (<NUM>) and the second set of segments (<NUM>) for sealing against an inner surface of the port (<NUM>);
a third set of segments (<NUM>) on a second surface of the circular planar section (<NUM>) arranged to receive a cap (<NUM>); and
a fourth set of segments (<NUM>) arranged around the outer circumference of the circular planar section (<NUM>) defining the length of the plug (<NUM>); each of the fourth set of segments (<NUM>) having a curved portion (<NUM>) at one end and a protrusion (<NUM>) at an opposite end;
and
a one-way valve (<NUM>) fit in the central opening (<NUM>) for providing one way air flow through the at least two orifices (<NUM>); and
the cap (<NUM>), the cap (<NUM>) having arms (<NUM>) sized to extend around the third set of segments (<NUM>) and snap onto the first surface of the circular planar section (<NUM>), wherein the cap (<NUM>) forms a chamber (<NUM>) when mated with the plug (<NUM>).