Non-pressure plate stone shield with energy absorbing lugs, and pushrod shield for welded clevis

A fluid pressure operable actuator includes a housing, with an end wall, and a pushrod projecting through an opening in the end wall for reciprocation upon service pressure application or release. A shield, configured as an annulus, is disposed on the pushrod to restrict contamination of an interior chamber of the actuator housing through a gap existing between an edge of the opening and a pushrod outer surface. To facilitate connecting the shield and the pushrod together, the annulus has a slit with an enlarged void at a radially outer end of the slit. This enlarged void engages an outer pushrod surface as the shield and the pushrod are joined.

BACKGROUND OF THE INVENTION

1. Field of the Invention

A dust or stone shield of the type forming the subject matter of this invention is designed to surround the pushrod of a fluid operated service brake actuator to operate as a barrier to block entry of contaminants into the actuator housing.

2. Description of Related Art

Dust or stone shields of the type noted are designed to surround pushrods of fluid operated service brake actuators. Typically, this sort of shield operates as a barrier to block entry of contaminants that might otherwise pass from outside an actuator housing, through a gap between a pushrod outer circumference and a pushrod opening in an actuator wall, and into an interior of the actuator housing, such as a chamber providing for expansion and contraction of a service brake pressure volume. In such an arrangement, the shield commonly has an inner diameter surrounding the articulating pushrod at the very location at which side loading of the pushrod occurs. For most rigid shields, shield inner diameters have been accepted as load bearing interfaces. In such a construction, if the inner diameter of a shield is compromised by side loading, the shield may no longer operate effectively.

Conventional pushrod dust or stone shields for chambers with threaded pushrods lack slits or slices in them. When such a shield is to be used with a welded clevis, it is not possible to drop the shield over the end of the pushrod. To address this issue, some shields now used with welded devises have slits or slices to facilitate fitting the shields over respective pushrods. Single-slit designs have been the accepted standard, regardless of assembly difficulty and part stress.

U.S. Pat. No. 6,354,187 to Plantan et al. concerns a known arrangement in which an annular damping stone shield has a slit allowing assembly around a pushrod. An annular groove in the stone shield circumscribes the push rod opening and allows the shield to absorb lateral forces when the push rod is operated during braking.

U.S. Pat. No. 6,729,224 to Roy discloses various configurations of an annular ring surrounding a pushrod when assembled. In one such configuration, the ring has end surfaces that are angled relative to the shaft opening axis of the ring. The angled end surfaces are configured so that the return spring can bias the slit opening in a closed position to create a seal, thereby preventing contaminants from entering the brake chamber.

SUMMARY OF THE INVENTION

A fluid pressure operable actuator according to the invention includes an actuator housing having an end wall, and a pushrod projecting through an opening in the end wall for reciprocation upon service pressure application or release. A shield, configured as an annulus, is disposed on the pushrod to restrict contamination of an interior chamber of the actuator housing through a gap existing between an edge of the opening and a pushrod outer surface. To facilitate connecting the shield and the pushrod together, the annulus has a slit with an enlarged void at a radially outer end of the slit that engages an outer pushrod surface as the shield and the pushrod are joined. In each of the particularly disclosed embodiments, the enlarged void is defined by angled surfaces diverging from one end of the slit at approximately a right angle.

The shield is constrained against movement relative to the end wall. Constraint of the shield in this way is provided by either a cover secured to the end wall or a spring that biases the shield against the end wall. In the latter case, the shield may actually define a seat for one end of the spring.

In one arrangement, the shield includes a plurality of lugs that receive, absorb, and dissipate lateral pushrod loading. Preferably, at least some of the lugs include voids defined near tips of the lugs. The energy-absorbing lugs, integral with the shield, provide advantageous load mitigation. More precisely, in normal air operated service brake application, the pushrod moves in a linear direction to apply or release the brake. As a secondary consequence of actuation, however, the pushrod also moves laterally. This lateral movement can be detrimental to both the housing and the shield used to protect the housing interior. The pushrod can degrade the structural integrity of the housing, the shield, or both the housing and the shield when contact occurs, and can itself be damaged as well by excessive side loading. Side loading imposed by the pushrod, here, is removed from the inner diameter of the shield, and, instead, is absorbed, dissipated, or partly absorbed and partly dissipated by the lugs, which form part of the shield circumferential exterior.

The shield may include a surface that positions the shield within the opening in the end wall; such a surface can be either the surface of a single central flange surrounding a central opening in the shield or a surface of an outer flange disposed concentrically with an inner flange surrounding the central shield opening.

In another disclosed arrangement, only the radial slit and void arrangement mentioned is included, and the special energy absorbing features helping the shield receive, absorb, or dissipate side-to-side pushrod loading are not provided. This arrangement still facilitates assembly, and is usable across product lines to commonize parts and improve end user product quality. Both arrangements are highly visible to end users, producing directly recognizable improvements that should enhance customer satisfaction.

DETAILED DESCRIPTION OF THE INVENTION

The first embodiment described is a dust or stone shield for an unpressurized brake actuator chamber. In this embodiment, a pushrod, with a yoke that connects to a slack adjuster or another brake assembly element, extends through an opening in an actuator housing end wall, and a new and improved shield assembly, having a floating deformable shield with a plurality of energy absorbing lugs, is retained in an oversized cover within the unpressurized brake actuator chamber. Lugs on the shield have curved voids near their tips to improve the ability of the shield to absorb energy when the pushrod moves in a radial direction during operation.

The shield is formed as an annulus, and has a radial slit extending from its outer diameter to a central inner opening encompassing the pushrod after the shield is installed. Angular surfaces extend from the outer end of the slit and intersect the perimeter of the shield to create an angular void in the shield at the slit outer terminus. When pressed radially against the pushrod during assembly, the angular void allows the shield to be circumferentially deformed as the pushrod travels along the slit toward the inner opening of the shield. The floating shield is retained within a cover that allows at least radial movement (floating), inside of the cover, within the actuator housing. An advantageous combination of the shaped energy absorbing lugs and the angular voids eases assembly of the shield onto the pushrod and permits the floating mentioned.

Part of the first embodiment of the invention may be seen in the partially cut away view ofFIG. 1.FIG. 1shows the interior of a non-pressure brake actuator housing20secured, via mounting bolts or other such fasteners22, to a vehicle utilizing an air brake system having the housing20. The brake actuator housing20forms part of an overall brake actuating unit generally configured have a construction similar to that forming the subject matter of either U.S. Pat. No. 6,729,224 to Roy or U.S. Pat. No. 6,354,187 to Plantan et al. mentioned above. The disclosures of both the Roy ('224) patent and the Plantan et al. ('187) patent referred to are incorporated herein by reference in their entireties as non-essential subject matter.

Ventilation openings24provide for communication between the interior of the actuator housing20and the atmosphere48at the exterior of the housing20. The actuator includes a pushrod26with a yoke, a clevis, or some other connection28(referred to hereafter as “yoke” for simplicity) secured to its end. Air or, possibly, hydraulic fluid could be used to displace the pushrod during operation. As illustrated, the yoke28has a generally U-shaped configuration, including legs30joined together by way of a central connecting section32. Openings34in the legs30are used to connect the yoke28to the slack adjuster of a drum or disc brake assembly or to some other brake operating element.

The actuator housing20shown includes a circumferential wall36, having the ventilation openings24, and an end wall38. The pushrod26projects through an approximately central opening40in the end wall38, as best shown inFIG. 2, for axial reciprocation produced by supply of pressurized air or other fluid to and exhaust of pressurized air or other fluid from a service brake pressure volume (not shown). A shield42operates as a barrier, preventing entry of contaminants that, otherwise, might pass from the exterior of the housing20, through a gap44between a pushrod outer surface and the edge46of the central pushrod opening in the end wall38, and into an interior chamber56, vented by the openings24to the atmosphere48, providing for expansion and contraction of the service brake pressure volume. The shield42is a floating, deformable element provided with a plurality of energy absorbing lugs50, and is retained in an oversized cover52, held by a spring (not shown) against a surface54. The cover52may also be welded or otherwise secured to the surface54, which, as shown inFIG. 3, is a surface of the end wall38delimiting the non-pressurized interior chamber56. In this embodiment, the shield42is to be assembled on the pushrod26before the cover52is secured to the end wall surface54. Together, the shield42and the cover52constitute an overall shield assembly.

The shield42according to the first embodiment of the invention is best shown inFIG. 4, which illustrates each of the energy absorbing lugs50of the shield42as having a curved void58near its tip. Fewer than all of the lugs50, of course, could be associated with respective voids. Each of the voids58shown includes an arcuate, inwardly bowed central section57interconnecting a pair of enlarged terminal ends59. The voids58improve the ability of the shield42to absorb energy when the pushrod26happens to be displaced in a radial direction during operation. The voids58are sized and positioned so that a maximum displacement of the shield, limited by way of clearances78and82to be described, will not permit contamination of the interior chamber56through the voids58.

The shield42also has a radial slit60extending from its outer circumference to a central inner pushrod-receiving opening62that encompasses the pushrod26when the shield is installed. At the radially outer end of the slit60, angular surfaces64extend from the slit and form part of the shield perimeter, creating an angular void66in the shield at the radially outer end of the slit60. Each of the surfaces64is oriented at an acute angle relative to a central line bisecting the void66, such that the surfaces64are oriented at roughly 65°-115° relative to each other. Angles outside of the range noted are also acceptable. One preferred design has the surfaces64oriented at an acute angle of about 80°, while another preferred design has the surfaces64oriented at an angle of about 70°.

The slit60and the void66combine to define a roughly “Y-” shaped opening or cutout in the shield42. When the angular surfaces64of the void66press radially against the pushrod exterior during assembly, these surfaces64cause the shield to be circumferentially deformed as the shield42is twisted and the pushrod26is displaced along the slit60towards the central inner opening62. A combination of the slit60and the void66engages the pushrod outer surface more broadly than a slit alone, without such a void or cutout, so that a shield having the Y-shaped cutout mentioned requires less effort to assemble, due to the broad opening, than a shield lacking the void or cutout. A slit having such a cutout also does not require the same degree of slit expansion, thereby protecting the strength and integrity of the shield itself. The shield42preferably has an enlarged thickness around the opening62to form a flange61enhancing stiffness and structural integrity of the shield.

In another configuration, shown inFIG. 11, a radial slit60′ extends from the enlarged angular void66′ at the outer circumference of the shield42′ beyond the central inner pushrod-receiving opening62′. An end67′ of the slit60′ distal the angular void66′ is defined by an opening having a thickness slightly larger than that of the slit60′ itself. In all other aspects, the shield42′ shown inFIG. 11is the same as the shield42shown inFIG. 4.

The oversized cover52, visible inFIG. 5, may include three concentric flanges. These three flanges include a circumferentially outer, radially extending, annular mounting flange70, a circumferentially inner, radially extending, annular retention flange72, and an axially extending, annular connection flange74, which joins together the mounting and retention flanges70and72.FIG. 3shows the shield42and the cover52, collectively constituting the overall shield assembly, in a mounted condition on the housing end wall38. In this mounted condition, an annular underside76of the mounting flange70is welded or otherwise retained on the surface54of the end wall38, a small axial clearance78is defined between an annular underside80of the retention flange72and a side surface81of the shield42, and circumferential clearances82are defined between an annular underside84of the connection flange74and the tips of the energy absorbing lugs50.

By way of the two-piece shield assembly illustrated inFIGS. 1-3, a floating, deformable shield42, with a plurality of energy absorbing lugs50, is retained within the non-pressurized chamber56, in an advantageous manner, between the cover52and the surface54of the end wall38. The shield42is retained within the cover52in a way that allows radial movement (floating) inside of the cover through the clearances82and, to a lesser extent, axial movement (floating) inside of the cover through the clearance78. The angular void66at the radially outer end of the slit60and the energy absorbing lugs50provide for both easy assembly of the shield42onto the pushrod26and ready deformation of the shield42to the limited extent necessary during use.

The shield assembly described thus prevents contamination of the chamber56by debris that could otherwise pass from the exterior of the housing20through the gap44and, simultaneously, accommodates articulation of the pushrod26. The energy absorbing lugs50of the shield42receive, absorb, and help to dissipate side-to-side loading on the pushrod26, thereby improving shielding integrity. By relieving the inner shield opening62of forces imposed by pushrod side-to-side loading, the shield42retains integrity at its inner diameter, keeping the shielding function intact. The energy absorbing lugs, of course, will collapse on themselves if loading on the pushrod increases articulation to a greater degree.

A shield according to the first embodiment of the invention thus has the dual effect of providing the chamber56with internal shielding and accommodating side-to-side loading imposed by articulation of the pushrod26. The energy absorbing feature provided by the illustrated voids58, of course, could be accomplished by other void geometries. Additional integral parts produced by over-molding further features to absorb side loading could also be used, although an over-molding process would be more expensive and not necessarily as robust. Although the shield42is preferably a molded nylon part to be assembled onto an existing pushrod assembly, medium to high durometer rubber or another appropriate material could alternatively be used.

While the first embodiment of the invention is described in connection with certain overall brake actuating unit configurations, energy absorbing features such as those disclosed could be incorporated into any product in which energy diversion is desirable.

FIGS. 6-10illustrate several variations of a second embodiment of the invention, which has a radial slit and void arrangement similar to that described above but which does not include any special energy absorbing lugs, curved voids, or other features helping the shield receive, absorb, or dissipate side-to-side pushrod loading. Elements of the second embodiment that are essentially the same as or analogous to those described in connection with the first embodiment are identified by the same reference numbers increased by one hundred. Thus,FIG. 6illustrates a brake actuator pushrod126, with a yoke128secured to its end. A shield142, preferably having an enlarged thickness forming a flange161around its central inner opening162, is also shown inFIG. 6. In addition to enhancing stiffness and structural integrity, the flange161can perform a positioning function to be described.

FIG. 7, which is a plan view of the shield142of the second embodiment, shows that the shield142also has a radial slit160extending from its outer circumference to a central inner opening162, which is to encompass the pushrod126when the shield is installed. At the radially outer end of the slit160, angular surfaces164extend from the slit and form part of the shield perimeter, creating an angular void166in the shield at the radially outer end of the slit160. As in the first embodiment, each surface164in the second embodiment is oriented at an acute angle relative to a central line bisecting the void166, such that the surfaces164are oriented at roughly 65°-115° relative to each other. Once again, this range is not to be considered limiting, and angles outside of the range noted are also acceptable. Once again, moreover, the slit160and the void166combine to define a roughly “Y-” shaped opening, so that when the angular surfaces164of the void166press radially against the pushrod exterior during assembly, the surfaces164cause the shield to be circumferentially deformed as the shield142is twisted and the pushrod126is displaced along the slit160towards the central inner opening162. Displacement of the pushrod126in this way will occur upon movement of the shield142relative to the pushrod126in the direction of arrow127inFIG. 6.

While the first embodiment utilizes a cover52to retain the shield42in position, the second embodiment does not require such a cover. Instead, in the second embodiment, the shield142is permitted to move axially along the outer surface of the pushrod126. When in use, as shown inFIG. 9, the shield142of the second embodiment serves as a spring seat for one end of a service brake piston return spring190. The return spring190, at its second, opposite end, is secured to a service brake piston head192(FIGS. 6,9, and10) by way of an anchor194.

Although it is not shown inFIGS. 6,9, and10for reasons of clarity, a non-pressure actuator housing similar to the housing20of the first embodiment receives the service brake piston head192for movement within the housing. A configuration including the piston head192and the return spring190could also be used in connection with the arrangement illustrated inFIGS. 1 and 2. The pushrod126of the second embodiment projects for axial reciprocation through an approximately central opening in an actuator housing end wall in the same way that the pushrod26of the first embodiment projects through the end wall38. In use, the return spring190operates to bias the shield142into contact with the brake actuator housing end wall. A centering flange196, shown inFIGS. 8,9, and10as formed on the shield142concentrically with the stiffness enhancing flange161, is designed for reception in the end wall opening through which the pushrod126projects so that a surface198of the flange196assures correct shield positioning. If desired, a single, somewhat thicker stiffness enhancing flange161, such as that shown inFIG. 6, may perform both the shield stiffness enhancing function and the shield positioning function.

A pushrod stone or dust shield according to the invention, again, will be made of nylon or equivalent material, and will be split for ease in installation. The split, in each embodiment described, will include an approximately 90° degree lead-in feature to help open the shield for sliding over the push rod. The shield does not actually seal the actuator in an airtight manner, and allows lateral pushrod motion. The shield of the second embodiment of the cover of the first embodiment also assists in keeping the return spring centered with respect to the pushrod.

Advantages of all arrangements according to the invention include ease in assembly, lower part weight, and improved reliability. In each arrangement, the lead-in feature of the shield slice assists an installer when deforming the shield to fit around the pushrod.

The Y-shaped void or cutout described enables the shield to engage the pushrod with a broad opening for assembly, and enables the shield to slide onto the pushrod with less expansion of the slit. While a Y-shaped cutout is described and illustrated, the cutout could have a U-shaped profile, a part-spherical profile, a square profile, or any other profile that would also provide improved assembly by expanding the radial terminus of a slit in the shield. As mentioned, medium to high durometer rubber could be used as the shield material, although care would have to be taken to ensure part integrity across the required temperature range.