BACKGROUND OF THE INVENTION This Application relates to an improved release tool for a spring brake actuator that cages the power spring of the brake actuator with little or no axial movement outwardly of the actuator housing.

Spring brake actuators are utilized on modern heavy vehicles to actuate a brake when the vehicle is parked, or when a portion of the vehicle brake system

fails. In either situation, a powerful spring expands to move a mechanical rod that actuates the brake actuator. This actuation will sometimes occur while the vehicle is on the road. An operator of the vehicle will then need to cage the spring such that the vehicle may be moved. Servicing of a spring brake actuator and, in particular, servicing of the parking side (where the power spring is located), is not recommended. Even so, in the event that one does attempt to open the parking side, the spring must be caged by a mechanical element prior to any such opening. The power spring is also typically caged when the actuator is removed, installed or when the vehicle is towed.

Thus, release tools have typically been provided in the parking side of a spring brake actuator. The release tools have typically been a bolt that is received within a piston that holds the power spring. When the bolt is turned it pulls the power spring piston toward an outer end of the housing, holding or "caging" the spring. The bolt has typically moved axially outwardly of the housing as it is turned. Thus, in prior art spring brake actuators, the release bolt typically extends axially outwardly from an outer end of the brake actuator housing when the power spring is fully caged.

While this type of release bolt has proven successful, in many applications, there may not be sufficient axial room for the release bolt to extend axially from the brake actuator. Thus, there are desirable benefits to providing a release bolt that does not extend axially away from the actuator when the power spring is caged. The prior art has not successfully provided an arrangement to achieve the goal of allowing reliable caging of the power spring, while at the same time not requiring additional axial clearance at the outer end of the spring brake actuator chamber.

SUMMARY OF THE INVENTION In a disclosed embodiment of this invention, a spring brake actuator is provided with a release tool that extends little or not at all axially outwardly beyond its initial position as it cages the power spring. In preferred embodiments of this invention, a release bolt has a head accessible from outside the brake actuator housing. The bolt engages an internal threaded nut. Turning the head of the bolt moves the nut axially. The nut engages and moves a spring piston. The spring piston is thus pulled axially toward an outer end of the brake housing, caging the power spring. The bolt head does not move axially away from the brake actuator head during this movement, and thus additional axial space outwardly of the brake actuator is not necessary. In other preferred features, the nut is initially maintained by a spring at a location such that it is aligned with an initial thread on the bolt. When an operator begins to turn the bolt, the nut is immediately engaged by the thread and begins to be withdrawn toward the outer end of the housing. On the other hand, since the nut is initially not actually engaged with the thread, should an operator begin to turn the

bolt in the wrong direction, the nut will not be driven away from the outer end of the brake actuator. In this way, the present invention insures that there is not movement of the nut in a direction that would impede the normal operation of the brake actuator. In another feature of this invention, the nut has an outer periphery that matches the profile of an inner bore in the piston. The nut may slide within this inner bore during normal operation of the brake.

In one embodiment, a spring biases the nut towards the bolt. Before the nut contacts the spring piston, this spring will bias the nut and bolt slightly axially outwardly. The bolt extends a small distance away from the outer portion of the brake actuator housing. An observer seeing this bolt head spaced slightly axially outwardly from the housing will know that the brake actuator is uncaged. In this embodiment, when the operator begins to turn the bolt, the nut eventually contacts a flange on the spring piston, begins to cage the power spring and takes up the clearance. Initially after this contact, the spring force which is biasing the nut outwardly is first overcome, such that the bolt head does move inwardly from the power spring is completely caged before the outward position discussed above. An observer seeing the bolt head in this position will recognize that the power spring is partially or fully caged. Most preferably, a snap ring on the bolt abuts the inner side of the housing when the bolt is moved outwardly by the spring to its outer position. This snap ring defines a stop limiting outward movement of the bolt.

In other features, an O-ring is positioned on an outer peripheral surface of the bolt at a position such that it provides a seal with the outer housing, and during movement of the bolt as described above. This O-ring in conjunction with the

spring at an inner end of the bolt provides a centering force to stabilize the bolt and dampen the effect of vibrations on the bolt.

In other embodiments, the bolt may be utilized without the small spring. In this embodiment, the bolt does not pop up when uncaged, and the nut is received on threads at all times. Other operational aspects of this embodiment are similar to those discussed above.

Further, in other features, the invention includes a hollow push rod that receives a portion of the length of the bolt and the nut. In this way, the length of the release bolt does not increase the overall length of the brake actuator. Rather a portion of the length of the release bolt may extend axially inwardly beyond the power spring and into the push rod to reduce the required outer envelope size for the brake actuator.

In other features, the invention may be utilized on either piston or diaphragm brakes. In a method of operating a spring brake actuator to cage a power spring according to the present invention, a bolt is received within a threaded nut. The nut is received within a portion of a spring piston such that when the bolt is turned the nut engages the spring piston and draws it toward an outer end of the brake housing head. The method includes the steps of turning the release bolt head, thereby turning the nut until the nut engages the spring piston. The method further envisions continued turning of the head such that the nut begins to move the spring piston until the spring is fully caged.

With the inventive type of release bolt described above, one issue that does arise is that it is somewhat difficult to identify when the release bolt is fully

released. If the release bolt does not fully release the power spring, then the brake cannot extend to its maximum effective stroke. This would be undesirable. For that reason, further embodiments of the present invention provide a structure visible from outside of the brake that provides an indication of whether the release bolt has been fully released.

In one embodiment, a pop-up indicator is included into the release bolt that extends outwardly of the brake if the power spring has not been fully released. The pop-up indicator is preferably formed of a bright color such that it may be easily visible. A worker seeing the pop-up indicator would know that the brake has not been fully released.

In a further preferred embodiment, the release bolt itself has two threaded portions, with the threads extending in opposing directions. An inner threaded portion is received in the nut as described above. An outer threaded portion, which is formed integrally with the inner threaded portion, is threadably received in an outer nut. When one turns this release bolt the outer threaded portion moves in the outer nut and the bolt extends outwardly of the brake, pulling the inner portion, and the nut, outwardly. At the same time, the inner threaded portion will be turning in its release nut, which then moves upwardly. Thus, the release nut is being moved relative to the push rod and power spring by both threaded portions. In this way, the outer portion will extend outwardly of the brake housing, but only for a relatively small amount. The observer of this brake will be able to identify whether the brake has been fully released by looking to see whether the release bolt is moved inwardly against the outer surface of the brake housing. If so, then one knows the brake has been fully released.

These and other features of the present invention can be best understood from the following specification and drawings, of which the following is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partially cross-sectional view of a spring brake actuator incorporating the present invention.

Figure 2 is a cross-sectional view along line 2-2 as shown in Figure 1. Figure 3 is a cross-sectional view of the spring brake actuator moving towards the actuated position. Figure 4 shows the spring brake actuator of Figure 1 with the spring caged.

Figure 5 shows a second embodiment release bolt. Figure 6A shows a third embodiment brake actuator. Figure 6B shows the embodiment of Figure 6A having moved to a different operational position. Figure 6C shows the embodiment of Figure 6A having moved to yet another operational position.

Figure 7 shows another embodiment brake in a first condition. Figure 8 shows the Figure 7 embodiment in a subsequent position. Figure 9 shows yet another subsequent position. Figure 10 shows yet another subsequent position.

Figure 11 shows yet another embodiment of the release tool of this invention. Figure 12 shows the Figure 11 embodiment in an extended position. Figure 13 shows the Figure 11 embodiment in its caged position. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Figure 1 shows a spring brake actuator 20. The structure of the spring brake actuator other than that relating to the release tool mechanism is as known in the art. Thus, a detailed description of all components of the brake actuator will not be included. As is known, a spring brake actuator includes a central housing body 22, typically referred to as a flange case that connects an outer brake housing member 24, sometimes known as a head to an inner brake housing 26, sometimes known as a service chamber. Within the head is a power spring 28. Spring 28 selectively engages a brake through the yoke 27 upon certain conditions, as known. A chamber 30 is defined beneath a diaphragm 32. When pressurized air is received within chamber 30, diaphragm 32 moves upwardly compressing the spring 28. In that condition, a push rod 34 associated with the diaphragm 32 is also moved upwardly. In this position, the spring 28 is not actuated, and the push rod 34 is not forced downwardly. The parking side of the brake actuator thus does not move the yoke 27 to actuate the brake. When the parking brakes are turned on, or if there is some failure in the system, then spring 28 expands, forcing the push rod 34 downwardly to move the yoke 27 outwardly.

The spring 28 is received on a spring piston 36. A release bolt 38 extends through the brake housing 24. An O-ring seal 39 provides an air-tight seal between bolt 38 and the housing portion 24. A threaded bolt portion 40 extends from the bolt head 41. A nut 42 is received on the bolt 38 at an inner end of the housing 24. The nut 42 is received within a bore 44 in the piston 36. Spring 46 biases the nut 42 to a position such that the threads within the nut 42 are aligned with the beginning thread 48 of the threaded portion 40. The portion 49 below thread 48 is not threaded. Thus, should the bolt head 41 be turned in a first direction, the

thread 48 will be engaged on threads 42, and the nut will begin to be drawn upwardly on the threaded portion 40. On the other hand, should the head 41 be turned in the opposed direction, the nut 42 will not be drawn onto the thread 48 and the nut 42 will not be moving onto the threaded portion 40. As also shown in Figure 1, the small spring 46 has biased the bolt head 41 to a position such that there is a slight clearance 70 between the bolt head 41 and the housing 44. A snap ring 64 prevents further outward movement of the bolt 38. The spring 46 biases the nut 42 and hence the bolt 38 outwardly to this position. An observer of the clearance 70 will know that the power spring 28 remains uncaged in a brake actuator 20.

As shown in Figure 2, the bore portion 44 has an inner periphery that corresponds to the outer periphery of the nut 42. In this illustration the nut and bore are both shown as being hexagonal, although other cross sections may well come within the scope of this invention. As also shown, a lower unthreaded portion 49 of the bolt 38 is received within a bore 52 of the nut 42. Bore 52 is threaded.

As shown in Figure 3, when the spring 28 expands it moves the piston 36 downwardly along with the push rod 34. This movement does not affect the release tool since the nut 42 slides in bore 44. That is, as the spring 28 moves from the position shown in Figure 1 to the position shown in Figure 3, the nut 42 merely slides within the bore 44. As shown in Figure 3, it is possible to design a long spring which will keep clearance 70 during this movement. The observer will know that the power spring 28 remains uncaged.

In some instances, when the brake actuator is in the expanded position, an operator would like to capture or cage the power spring 38 mechanically from outside of the brake actuator 20. The prior art has typically provided a release bolt which is turned to move a mechanical member within the housing to capture the spring 28.

As shown in Figure 4, tool 60 may begin to turn the head 41 of the bolt 38. Upon initially tuming the bolt 38, the nut 42 will be engaged on the threads of the threaded portion 40. Continued tuming of the head 41 will cause the nut 42 to move axially upwardly along the threaded portion 40. Eventually, the nut 42 contacts a flange 62 at an outer end of the piston 36.

At that time, continued tuming of the bolt head 41 causes the nut 42 to move the piston 36. This movement captures or cages the spring 28. As the nut initially contacts flange 62, the first movement that occurs is the movement of the bolt head 41 inwardly towards the housing 24. After the nut 42 contacts flange 62, the force of the spring 46 no longer biases the nut outwardly. Rather, as the nut turns, the nut and bolt move inwardly to eliminate clearance 70. Upon further tightening, the nut 42 begins to draw the flange 62, piston 36, and hence spring 28 to the caged position such as shown in Figure 4. Thus, an observer seeing there is no longer a clearance 70 would recognize that the power spring is partially or fully caged. Figure 5 shows another embodiment actuator 80. In actuator 80, there is no small spring. The spring piston 82 includes a bore 84 as in the previous embodiment. A nut 86 rides along a bolt 88. Upon tuming of the bolt 88, the nut 86 moves axially within the bore 84 as in the above embodiment. There are threads 90 along the length of the bolt 88, and the nut 86 is always received on the threads

90 in a preferred embodiment. Flange 92 extends inwardly from the piston 82. As the bolt 88 is turned, the nut 86 moves and eventually contacts the flange 92. Continued tuming of the bolt head 88 cages the spring as in the previous

embodiment. The brake actuators shown in Figures 1-5 utilize diaphragms as their actuating member in the spring chamber. The embodiment 80 shown in Figure 6A-6B disclose a piston type brake actuator. Other features of a embodiment

80 are also shown in a Figure 6A-6C embodiment. It should be understood that the features generally shown for the release tool in Figures 6A-6C would also find benefits in diaphragm brakes. Moreover, the release tools shown in Figures 1-5 may also find benefits in piston brakes.

As shown in Figure 6A, a piston brake 80 incorporates a housing member 82 that is connected to a central housing 84, as with a clip 86 or other known connection. A power spring 88 biases a piston 90 outwardly. Piston 90 moves with a push rod 92 to actuate a yoke as in the previous embodiments. Push rod 92 is formed with a bore 94, and a bolt 96 extends downwardly into bore 94. A nut 98

is biased upwardly by a small spring 99 as in the prior embodiment. As shown, bolt 96 is thus spaced by a small amount 97 from the outer housing 82, again to provide an indication to an observer that the power spring is not caged. In this embodiment, since the bolt 96 extends into the push rod 92, brake actuator 80 may be of a relatively smaller axial outer envelope size than if the push rod 92 were

solid. A portion of the bolt length is thus taken up by having it extend into the hollow push rod 92. As shown, the push rod 92 extends through an opening 100

in the central housing 84. In the position shown in Figure 6A, the power spring 88 is compressed by air pressure in the chamber beneath the piston 90.

As shown in Figure 6B, the power spring 88 has now expanded to drive the piston 90 against the center housing 84. The push rod 92 extends through the opening 100, and the yoke is actuated as is known. As also shown, the nut 98 is slightly spaced from the flange 102 in this position. The clearance 97 remains in this position, and the dimensions are preferably selected such that the piston 90 bottoms out on the housing 84 before the flange 102 contacts the nut 98 and overcomes the small force of the spring 99. Thus, an observer will also be able to tell that the power spring 88 remains uncaged in this position.

As shown in Figure 6C, the bolt 96 has now been turned to move the nut 98 and cage the piston 90 and power spring 88. Although the hollow push rod concept has been illustrated with the small retum spring embodiment as discussed above, it should be understood that the embodiment shown in Figure 5 wherein there is no spring could also be combined with this hollow push rod embodiment.

In a method of caging a brake actuator according to the present invention, one initially provides a brake actuator with a threaded release tool that may be turned to cage a power spring without moving the tool axially away from the housing member. In a preferred embodiment, the method includes the steps of providing such a release tool which threadably engages a nut, with the nut moving axially when turned by the release bolt to cage the power spring. The method further includes the steps of beginning to turn the release bolt to move the nut and cage the power spring.

With the above described release tool, it may be difficult to identify whether the brake is fully released from outside of the brake. Thus, embodiments of the invention having indication stmcture which is visible from outside of the brake have also been developed. A first embodiment 110 is illustrated in Figure 7. A push rod 112 receives a nut 114 as in above-described embodiment. A spring piston 116 provides a stop for the nut 114 as in the above embodiment. A cap 118 is received on a pop-up indicator rod 120. A spring 124 reacts off of the release bolt 123 at a ledge portion 122. Spring 124 forces a head 126 of the indicator 120 outwardly of the brake housing. The head 126 is preferably formed of a bright color. An observer seeing the bright head will know that the brake is not fully released. As an example, in Figure 7, the brake is shown fully caged. Thus, the head 126 can move relative to the bolt 123 and the ledge 122.

As shown in Figure 8, the release nut 114 has been moved downwardly, but has not yet fully released the spring. Thus, the spring is not able to extend to its full stroke. It would be desirable to provide an indication that the operator has not yet fully released the brake. As shown in this figure, the spring 124 continues to bias head 126 outwardly of the brake.

As shown in Figure 9, the release nut 114 has been moved further and has now fully released the brake. The release nut 114 has now abutted cap 118, and pulled cap 118 inwardly. This in turn pulls the rod 120 and head 126 against the force of the spring 124. As shown, the head 126 is no longer extending outwardly of the cap. An observer will now know that the brake has been fully released.

As shown in Figure 10, since the nut 114 has fully released the brake, the spring may extend to its full stroke. Again, the head 126 does not extend outwardly of the brake in this condition.

Figure 11 shows another embodiment 140 having a release bolt 142. Release bolt 142 turns an inner release nut 144, which moves within a push rod 146 in a manner such as described with the above embodiments. Release bolt 142 also has an outer nut 148. Release bolt 142 has two integral threaded portions 150 and 152. The threads on portions 150 and 152 extend in opposed directions. The threads on portion 150 turn within outer nut 148 and the threads on portion 152 turn within inner nut 144.

In the position shown in Figure 11, the release bolt 142 has fully released the brake. Note that the release bolt 142 does not extend at all outwardly of the housing.

As shown in Figure 12, in this location, the push rod 146 can extend under the influence of a power spring 154 to its full extent. Again, the bolt 142 does not extend outwardly of the housing, and an observer will be able to see that the brake has been fully released.

When one wishes to cage the power spring, one turns the bolt head 142. The thread 152 turns within nut 144, and the nut 144 advances along thread 152 as in the previous embodiments. However, at the same time, the thread 150 is tuming within the outer nut 148, and thus the thread 150 is moving outwardly of the housing. As the thread 150 moves so does the bolt 142, and hence the nut 144. Thus, in essence, when one turns the nut 142, the thread 150 does cause the bolt 142 to move outwardly of the housing. However, there is an amplification of the

caging of the nut 144 due to the second thread 152. For that reason, the bolt 142 need only move outwardly of the housing a relatively small amount such as shown in Figure 13 to achieve full caging of the power spring.

Although preferred embodiments of this invention have been disclosed, a

worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the tme scope and content of this invention.