Seal assembly for a spring brake actuator

Abstract

A seal assembly for mounting on a port of a spring brake actuator includes a plug, a check valve, and a cap. The plug receives the check valve for providing one-way air flow through the bore and maintaining about two psi in the spring brake chamber at zero stroke. An elastomeric member is secured to a first set of sections of the plug to seal against an inner surface of the port. The cap has arms sized to extend around a third set of sections of the plug and snap on the plug. A fourth set of sections of the plug elastically deform so the seal assembly can be easily mounted and unmounted from the port.

Description

[0001] BACKGROUND

[0002] The present application relates to a sealing assembly for a spring brake actuator. Spring brake actuators are used in commercial vehicle air brake systems. Each air brake system can include at least two spring brake actuators mounted on opposite wheel ends. A common type of spring brake actuator has a housing that defines a service brake portion having a service brake chamber and a parking brake portion having a parking brake chamber and a spring brake chamber. For service braking, compressed air is selectively introduced into the service brake chamber to move a piston, push an actuator lever, and thereby operate the service brake system. In the parking brake chamber, introduction of compressed air moves a second piston that compresses a power spring and allows the actuator lever to retract into the housing, thereby setting the vehicle parking brake. The spring brake actuator sets the vehicle parking brake by bleeding compressed air from the parking brake chamber upon a driver request, thereby allowing the power spring located in the spring brake chamber to extend. The spring brake actuator can also be set automatically when compressed air above a predetermined pressure is no longer provided to the parking brake chamber.

[0003] The parking brake portion of a spring brake actuator will often include an aperture that allows access to the spring brake chamber in order to allow for manual release of the parking brake. Over time, internal components can deteriorate from fluids and other contaminants that enter the housing through such apertures. To address this problem, some spring brake actuators employ a breather hole to allow contaminants to escape from the housing. However, these breather holes often become a source of contaminant ingress and can become clogged. Other spring brake actuators attempt to seal the aperture in the housing to prevent contaminant ingress into the housing. These latter spring brake actuators often use a dust plug that is inserted into the aperture when the aperture is not in use. However, conventional dust plugs are often removed by vehicle operators and maintenance personnel during routine maintenance and discarded after the dust plug is removed. These dust plugs can be difficult to reinstall. Furthermore, if an individual does reinstall the dust plug, the dust plug is often installed incorrectly. Conventional dust plugs can also become dislodged due to vibration during normal vehicle operation. Accordingly, those skilled in the art continue with research and development efforts in the field of spring brake actuator design and devices that seal spring brake actuators. SUMMARY

[0004] According to one embodiment, a seal assembly for a spring brake actuator includes a plug, a check valve, and a cover. The plug includes a circular planar portion having a central opening and at least two holes disposed outside an outer diameter of the central opening. The plug includes a first set of segments on a first surface of the circular planar portion 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 portion arranged to fit outside an outer diameter of the port of the spring brake actuator; an elastomer piece secured 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 portion arranged to receive the cover; and a fourth set of segments arranged around an outer circumference of the circular planar portion defining a length of the plug, each of the fourth set of segments having a bend at one end and a protrusion at an opposite end. The check valve is fitted in the central opening to provide one-way air flow through the at least two holes. The cover has an arm sized to extend around the third set of segments and snap onto the first surface of the circular planar portion, wherein the cover forms a chamber when mated with the plug.

[0005] In another embodiment, a spring brake actuator for an air brake system includes a housing defining a spring brake chamber, a bore in the spring brake chamber of the housing, and a port secured to the spring brake chamber of the housing for providing access to the bore. The port has a smooth inner surface and a groove on an outer surface. A seal assembly is mounted on the port. The seal assembly includes a plug, a check valve, and a cover. The plug includes a circular planar portion having a central opening and at least two holes around an outer diameter of the central opening. The plug includes a first set of segments on a first surface of the circular planar portion arranged to fit within an inner diameter of the port; a second set of segments on the first surface of the circular planar portion arranged to fit outside an outer diameter of the port; an elastomer piece molded onto 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 portion arranged to receive the cover; and a fourth set of segments arranged around an outer circumference of the circular planar portion defining a length of the plug, each of the fourth set of segments having a bend at one end and a protrusion at an opposite end for fitting within the groove of the port. The check valve is fitted in the central opening to provide one-way air flow through the at least two holes. The cover has an arm sized to extend around the third set of segments and snap onto the first surface of the circular planar portion, wherein the cover forms a chamber when mated with the plug.

[0006] In another embodiment, a method of operating a spring brake actuator includes installing a seal assembly to a port of a spring brake chamber of the spring brake actuator. The seal assembly includes a check valve for providing one-way air flow. The method includes setting the spring brake actuator to zero stroke, where the seal assembly holds about two psi of air in the spring brake chamber. The method also includes setting the spring brake actuator to normal stroke, where the seal assembly vents air from the spring brake chamber through the check valve to hold about zero psi in the spring brake chamber. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a schematic view of a portion of a spring brake actuator having the seal assembly of the present invention.

[0008] Figure 2A and Figure 2B are each a cross-section of a plug as part of the seal assembly of the present invention.

[0009] Figure 3A and Figure 3B are each a cross-section of the seal assembly of the present invention having a plug as in Figure 2A and Figure 2B installed on a spring brake actuator.

[0010] Figure 4 is a method of operating a spring brake actuator having the seal assembly of the present invention. DETAILED DESCRIPTION

[0011] Referring to Figure 1 , a spring brake actuator 10 is shown having a housing 12 that defines a spring brake chamber. A park brake portion of the park brake chamber (not shown) receives pneumatic input to compress a power spring (not shown) located in the spring brake chamber to hold the park brake in a non-park position. This spring brake chamber is sealed to prevent moisture and contaminants from entering. However, it is necessary to vent air that becomes trapped in the spring brake chamber when the power spring is released to ensure proper operation of the park brake. In addition, if maintenance is required on the spring brake actuator or the accompanying brake system, it is necessary to access the power spring inside the spring brake chamber to secure it. Therefore, an access port through the housing 12 must also exist for this purpose.

[0012] The housing 12 that defines the spring brake chamber of the park brake portion of the spring brake actuator 10 is typically a metal material, such as aluminum or steel. The housing 12 includes an aperture 14 that serves as an entry point for a tool used to secure the power spring located inside the housing 12. The aperture 14 also serves to vent air from the spring brake chamber.

[0013] Port 16 is secured to housing 12 and surrounds opening 14. Port 16 may be made of the same metal as housing 12, or it may be made of a different metal. Port 16 includes a smooth inner surface and a groove 18 surrounding the outer circumference of port 16. Port 16 may be welded to housing 12 or otherwise riveted. No machining is required on port 16 after welding to housing 12.

[0014] The housing 12 may also include a post 20 fixed to the housing 12. The post 20 may be made of metal or other materials.

[0015] The sealing assembly 30 is an example of a simple assembly to install, its sealed housing 12 preventing moisture and contaminants while allowing pressurized air from the spring brake chamber to escape into the atmosphere. The sealing assembly 30 is depicted as detached from port 16.

[0016] The sealing assembly 30 includes a plug 32 and a cap 34. The cap 34 may have a fastener 36. To keep the sealing assembly 30 close to the housing 12 when disengaged, the fastener 36 is attached to the post 20 by sliding it onto the post 20. A technician can then access the orifice 14 with appropriate tools without disturbing the sealing assembly 30. The sealing assembly 30 will not be misplaced while it remains attached to the post 20.

[0017] Figure 2A An enlarged cross-section of the plug 32 of the sealing assembly 30 is depicted in a first view.

[0018] The plug 32 includes a circular planar portion 38. The circular planar portion 38 has a central opening 62. The circular planar portion 38 also includes at least two holes 54 disposed outside the outer diameter of the central opening 62. The diameter of the at least two holes 54 is smaller than the diameter of the central opening 62.

[0019] The plug 32 includes a first set of segments 40 extending outward from a first surface of a circular planar portion 38. The first set of segments 40 are axially arranged outside the positions of at least two holes 54.

[0020] The stopper 32 includes a second set of segments 42, which are arranged near the outer circumference of the first surface of the circular planar portion 38. The length of the second set of segments 42 is approximately the same as the length of the first set of segments 40.

[0021] The stopper 32 includes a third set of segments 46 arranged around the outer circumference of the second surface of the circular planar portion 38, which is opposite to the first surface. The third set of segments 46 extends outward from the circular planar portion 38.

[0022] Figure 2B An enlarged cross-section of the plug 32 of the sealing assembly 30 is depicted in the view, which is arranged in relation to... Figure 2AThe view shown in the middle is rotated ninety degrees.

[0023] The plug 32 includes a fourth set of segments 66 disposed around the outer circumference of the circular planar portion 38. The fourth set of segments 66 define the full length of the plug 32 and are elastically deformable. The fourth set of segments 66 include a protrusion 68 at an end extending from the first surface and a curved portion 70 extending from the second surface. The fourth set of segments 66 can include a living hinge such that when the curved portion 70 is pressed inward, the protrusion 68 moves outward.

[0024] Figure 3A A cross-section in a first view of the spring brake actuator 10 with the sealing assembly 30 mounted on the port 16 is depicted.

[0025] The first set of segments 40 of the plug 32 partially extend into the inner diameter of the port 16 when the sealing assembly 30 is mounted on the port 16. The second set of segments 42 are disposed to partially surround the outer diameter of the port 16 when the sealing assembly 30 is mounted.

[0026] The plug 32 includes an elastomeric piece 44 fixed between the first set of segments 40 and the second set of segments 42. The elastomeric piece 44 can be overmolded directly to the first set of segments 40. The elastomeric piece 44 is shaped to sit entirely within the inner diameter of the port 16 when the sealing assembly 30 is mounted. The elastomeric piece 44 seals against the smooth inner surface of the port 16. The elastomeric piece 44 can be silicone, rubber, or other material with similar flexibility. The elastomeric piece 44 can be molded to include ribs along its outer diameter to improve the seal against the inner surface of the port 16. No additional seal, such as an O-ring found on prior art spring brake actuator dust plugs, is needed.

[0027] The sealing assembly 30 includes a one-way valve 48. The one-way valve 48 is friction fit in the central opening 62 of the circular planar portion 38. The one-way valve 48 is designed to cover at least two of the holes 54 when in a resting position. The one-way valve 48 can be an umbrella valve. The one-way valve 48 can be made of silicone or similar material. The one-way valve 48 allows air to flow out of the spring brake chamber through the at least two holes 54 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 48 can be adjusted to provide different cracking pressures.

[0028] The sealing assembly 30 includes a cap 34. The cap includes a planar portion 60 and arms 50 disposed around the third set of segments 46 of the plug 32. The arms 50 of the cap 34 are shaped to facilitate snap fitting the cap 34 to the plug 32. When the cap 34 is snap fitted to the plug 32, a chamber 52 is formed between the circular planar portion 38 and the cap 34. When the one-way valve 48 is open, air escapes from the chamber 52 to the atmosphere around the planar portion 60 of the cap 34.

[0029] The cover 34 can also include a tether 36. The tether 36 extends from the cover 34 across the body of the actuator housing 12 to the post 20. A hole 64 on the distal end of the tether 36 fits over the post 20. When the seal assembly 30 is not installed, it can pivot about the post 20.

[0030] The material of the plug 32 and the cover 34 can be the same resiliently deformable material, such as nylon or ABS plastic. The material chosen should be stable when exposed to ultraviolet light and resistant to impact. Alternatively, the plug 32 can be a glass-filled plastic to improve its ability to withstand the overmolding process. The plug 32 and the cover 34 are easily assembled together by snapping the cover 34 onto the plug 32 before the seal assembly 30 is installed onto the port 16. Once snapped together, the cover 34 will not need to be unsnapped from the plug 32. Assembly of the cover 34 to the plug 32 can also be accomplished by including a living hinge as part of the arm 50 of the cover 34.

[0031] Figure 3B A cross section of the seal assembly 30 installed on the port 16 is depicted in the second view, approximately 90 degrees from the first view of Figure 3A

[0032] The ridge 56 on the planar portion 60 of the cover 34 abuts the check valve 48 and helps to keep the check valve 48 centered in the central opening 62 when installed.

[0033] The curved portion 70 and the protrusion 68 of the fourth set of segments 66 facilitate attachment and removal of the seal assembly 30 from the port 16. The fourth set of segments 66 are secured to the groove 18 on the outer diameter of the port 16, such as by a snap fit of the protrusion 68 into the groove 18. The seal assembly 30 is retained on the port 16 throughout the operation of the actuator by this feature. The seal assembly 30 can be easily released by pressing inward on the curved portion 70, which in turn releases the protrusion 68 from the groove 18. The seal assembly 30 is reusable to be installed onto the spring brake actuator 10 multiple times.

[0034] No special tools are required to insert the check valve 48 into the plug 32 and to assemble the cover 34 to the plug 32. No special tools are required to install the seal assembly 30 onto the port 16. The seal assembly 30 is retained on the port 16 throughout the normal operation of the actuator and is not subject to debris or corrosion. The spring brake actuator 10 is now easily serviceable. Because no threads are required, no additional machining process is required to the port 16 before or after welding or riveting to the housing 12.

[0035] ​Therefore, a sealing assembly for a spring brake actuator includes a plug, a one-way valve, and a cap. The plug includes a circular planar portion having a central opening and at least two orifices arranged outside the outer diameter of the central opening. The plug includes a first set of sections on a first surface of the circular planar portion arranged to fit within the inner diameter of a port of the spring brake actuator; a second set of sections on the first surface of the circular planar portion arranged to fit outside the outer diameter of the port of the spring brake actuator; an elastomeric element fixed between the first and second sets of sections for sealing an abutment against an inner surface of the port; a third set of sections on the second surface of the circular planar portion arranged to receive the cap; and a fourth set of sections arranged around the outer circumference of the circular planar portion defining the length of the plug, each of the fourth set of sections having a curved portion at one end and a protrusion at an opposite end. The one-way valve is fitted into the central opening to provide unidirectional airflow through at least two orifices. The cap has an arm sized to extend around the third set of sections and snap onto the first surface of the circular planar portion, wherein the cap forms a chamber when mated with the plug.

[0036] Therefore, a spring brake actuator for an air braking system includes a housing defining a spring brake chamber, an aperture in the spring brake chamber of the housing, and a port fixed to the housing to provide access to the aperture. The port has a smooth inner surface and grooves on an outer surface. A sealing assembly is mounted on the port. The sealing assembly includes a plug, a one-way valve, and a cap. The plug includes a circular planar portion having a central opening and at least two apertures surrounding the outer diameter of the central opening. The plug includes a first set of sections on a first surface of the circular planar portion arranged to fit within the inner diameter of the port; a second set of sections on the first surface of the circular planar portion arranged to fit outside the outer diameter of the port; an elastomeric element molded onto the first set of sections for sealing against the smooth inner surface of the port; a third set of sections on the second surface of the circular planar portion arranged to receive the cap; and a fourth set of sections arranged around the outer circumference of the circular planar portion, the fourth set of sections defining the length of the plug, each of the fourth set of sections having a curved portion at one end and a protrusion at the opposite end for fitting into a groove in the port. A one-way valve is fitted into a central opening to provide unidirectional airflow through at least two orifices. The cap has an arm sized to extend around a third set of sections and snap onto the first surface of a circular planar portion, wherein the cap forms a chamber when mated with a stopper.

[0037] When the spring brake actuator is assembled, some pressurized air remains in the spring brake chamber. During operation of prior art spring brake actuators, there is typically about zero pounds per square inch (psi) of pressure in the park brake portion at zero travel of the actuator rod (when the vehicle is parked). During a normal park travel of about 1.25 inches, a vacuum of about three psi is created. The presence of the vacuum equates to a reduction of about ninety pounds force (Ibf) of available park force. Spring brake actuators need to consistently apply force throughout the travel of the actuator rod, with a recommended SAE tolerance band of 300 Ibf. At full travel, the vacuum in the spring brake chamber can be about nine psi. This negative pressure equates to about a 270 Ibf loss of park force when using a 30 type (30 cubic inch volume) park brake chamber, which is almost the entire tolerance band. Some prior art spring brake actuators compensate for this loss of force by using a larger power spring in order to maintain the required force output throughout the travel. In the present spring brake actuator, zero psi is not expected in the spring brake chamber at zero travel.

[0038] Figure 4 A method 80 of operating a spring brake actuator 10 having the sealing assembly 30 of the present invention is disclosed. At full travel in operation of the present invention one-way valve 48, a lower pressure vacuum will be created, which does not adversely affect the force output of the park brake spring. Prior art one-way valves used in spring brake actuators do not have a minimum opening pressure (crack pressure) and tend to bleed all pressure from the spring brake chamber.

[0039] In step 82, the sealing assembly 30 is installed on the end 16. In step 84, the spring brake actuator 10 is set to zero travel. In step 86, the sealing assembly 30 of the present invention maintains about two psi of small positive pressure in the spring brake chamber at zero travel. Then, throughout the travel of the spring brake actuator, the vacuum pressure created in the spring brake chamber will be reduced from prior art spring brake actuators.

[0040] In step 88, the spring brake actuator 10 is set to normal travel, such as a standard park travel of about 1.25 v. In step 90, the sealing assembly 30 maintains about zero pressure in the spring brake chamber. With zero pressure, there is no reduction in the force output of the spring brake actuator 10. Zero pressure is possible at normal travel because of the initial opening pressure setting of the one-way valve 48, which does not bleed all pressure from the spring brake chamber at zero travel.

[0041] In step 92, the spring brake actuator is set to full stroke. In step 94, the seal assembly maintains a vacuum of about 6 psi, resulting in a reduction of available force of about 180 Ibf. However, this is an improvement of 90 Ibf over the prior art spring brake actuator. The remaining tolerance band for spring brake actuator operation is then 120 Ibf, as opposed to 30 Ibf in the prior art spring brake actuator. The power spring used in the spring brake actuator assembly of the present invention can be sized and materialized to be lighter, as there is less expected loss of force output.

[0042] Another advantage of the seal assembly 30 is that if there is a leak in the spring brake chamber, the positive chamber pressure achieved by the seal assembly 30 will tend to expel any contaminants rather than draw them into the spring brake chamber.

[0043] Accordingly, a method of operating a spring brake actuator includes installing a seal assembly to a port of a spring brake chamber of the spring brake actuator. The seal assembly includes a one-way valve for providing one-way air flow. The method includes setting the spring brake actuator to zero stroke, wherein the seal assembly maintains about two psi of air in the spring brake chamber. The method also includes setting the spring brake actuator to normal stroke, wherein the seal assembly expels air from the spring brake chamber through the one-way valve to maintain about zero psi in the spring brake chamber.

[0044] While the application has been illustrated by a description of example procedures and system components, and while the various procedures and components have been described in considerable detail, it is not the intention that the application be limited or restricted to the specific details set forth. Additional modifications will readily occur to those skilled in the art. The application in its broader aspects is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. Accordingly, departures can be made from such details without departing from the spirit or scope of applicant's general inventive concept.

Claims

1. A seal assembly for a spring brake actuator, comprising: a plug, the plug comprising a circular planar portion having a central opening and at least two holes arranged outside an outer diameter of the central opening; a first set of segments on a first surface of the circular planar portion 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 portion arranged to fit outside an outer diameter of the port of the spring brake actuator; an elastomeric piece secured 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 portion arranged to receive a cap; and a fourth set of segments arranged around an outer circumference of the circular planar portion, the fourth set of segments defining a length of the plug, each of the fourth set of segments having a bend at one end and a protrusion at an opposite end; and a one-way valve fitted in the central opening for providing one-way air flow through the at least two holes; and a cap having an arm sized to extend around the third set of segments and snap onto the first surface of the circular planar portion, wherein the cap forms a chamber when mated with the plug.

2. The seal assembly of claim 1, wherein, the cap further comprising a tether having a hole for attaching to a post on the spring brake actuator.

3. The seal assembly of claim 1, wherein, the cap further comprising a ridge on an inner surface that abuts the one-way valve when the cap is mounted on the plug.

4. The seal assembly of claim 1, wherein, the seal assembly allows air in the chamber to communicate with the atmosphere.

5. The seal assembly of claim 1, wherein, the one-way valve is an umbrella valve.

6. The seal assembly of claim 1, wherein, the elastomeric piece is a silicone material overmolded to the first set of segments of the plug.

7. The seal assembly of claim 6, wherein, the elastomeric piece is molded to include ribs on an outer diameter of the elastomeric piece to seal against the inner surface of the port.

8. The seal assembly of claim 1, wherein, the plug and the cap are constructed of the same elastically deformable material.

9. The seal assembly of claim 1, wherein the fourth set of segments elastically deform to fit over the outer diameter of the port when pressed at the bend and the protrusions snap into grooves on an outer surface of the port when mounted on the port.

10. A spring brake actuator for an air brake system, comprising: a housing defining a spring brake chamber; a hole in the spring brake chamber of the housing; a port secured to the spring brake chamber of the housing for providing access to the hole, the port having a smooth inner surface and a groove on an outer surface; a seal assembly mounted on the port, the seal assembly comprising: a plug, the plug comprising a circular planar portion having a central opening and at least two holes arranged outside an outer diameter of the central opening; a first set of segments on a first surface of the circular planar portion arranged to fit within an inner diameter of the port; a second set of segments on the first surface of the circular planar portion arranged to fit outside an outer diameter of the port and secured to the groove 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 portion arranged to receive a cap; a fourth set of segments arranged around the outer circumference of the circular planar portion 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 a groove of the plug; a one-way valve fitted within the central opening for providing one-way air flow through the at least two holes; and a cover having an arm sized to extend around the third set of segments and snap onto the first surface of the circular planar portion, wherein the cover forms a chamber when mated with the plug.

11. The spring brake actuator of claim 10, wherein, The port is riveted to the housing.

12. The spring brake actuator of claim 10, wherein, The cover further includes a tether and the housing further includes a post for receiving a distal end of the tether.

13. The spring brake actuator of claim 10, wherein the one-way valve maintains two pounds of positive pressure per square inch in the spring brake chamber in response to a spring brake actuator at zero stroke.

14. The spring brake actuator of claim 10, wherein, The plug and cover are made of a resiliently deformable material, while the housing and port are of a metallic material.

15. A method of operating a spring brake actuator, comprising: installing a seal assembly to a port of a spring brake chamber of a spring brake actuator; wherein the seal assembly includes a one-way valve therein for providing one-way air flow; setting the spring brake actuator at zero stroke, wherein the seal assembly maintains two psi of air in the spring brake chamber; setting the spring brake actuator at normal stroke, wherein the seal assembly expels air from the spring brake chamber through the one-way valve to maintain zero psi in the spring brake chamber; and fitting the one-way valve within a central opening of a plug of the seal assembly, the plug including: a circular planar portion having a central opening and at least two holes arranged outside an outer diameter of the central opening; a first set of segments on a first surface of the circular planar portion arranged to fit within an inner diameter of the port; a second set of segments on the first surface of the circular planar portion arranged to fit outside an outer diameter of the port and secured to a groove of the port; an elastomeric piece molded onto the first set of segments for sealing against a smooth inner surface of the port; a third set of segments on a second surface of the circular planar portion arranged to receive a cover; a fourth set of segments arranged around the outer circumference of the circular planar portion 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 a groove of the plug; and a cover having an arm sized to extend around the third set of segments and snap onto the first surface of the circular planar portion, wherein the cover forms a chamber when mated with the plug.

16. The method of claim 15, further comprising: setting the spring brake actuator at full stroke, wherein the seal assembly maintains negative six psi of air in the spring brake chamber.

17. The method of claim 15, wherein the amount of pressure maintained by the seal assembly is adjusted by varying a structure of the one-way valve.

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