Patent Publication Number: US-2023144321-A1

Title: Piston assembly formed of interlocking piston members

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 63/263,830 filed Nov. 10, 2021, the disclosure of which is incorporated by reference as if fully set forth in detail herein. 
    
    
     FIELD 
     The present disclosure relates to a piston assembly, such as that used in an automotive shock absorber, that is formed of interlocking piston members. 
     BACKGROUND 
     It is known in the field of automotive shock absorbers to form a piston for the shock absorber from multiple piston members, where each piston member is formed of compacted powdered metal. It is known to form a series of relatively short cylindrical projections and relatively shallow cylindrical holes on the abutting surfaces of the piston members that mate with one another to control both the orientation of one piston member relative to the other, as well as to provide a modicum of frictional engagement that tends to resist the separation of the piston members from one another. This configuration, however, has several drawbacks. 
     For example, the piston members must be sintered while resting on an axial end surface of the piston member rather than on the short cylindrical projections as the relatively small diameter projections have a propensity to break off if the piston member is sintered while resting on the short cylindrical projections. Sintering the piston member while it rests on its axial end surface may not be desirable in situations where that surface could become damaged during the sintering operation. Additionally, the retention force that is provided through the mating of relatively short cylindrical projections with relatively shallow cylindrical holes is relatively small and relatively inconsistent. 
     Accordingly, there remains a need in the art for a multi-piece compacted powered metal piston assembly that employs a more robust locking system for securing adjacent compacted powdered metal components to one another. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, the present disclosure provides a piston assembly that includes a pair of piston members. Each of the piston members has a central hub, an outer rim, a plurality of vent apertures and a set of locking features. The central hub defines a rod aperture. The outer rim is disposed concentrically about the central hub. The vent apertures are disposed radially between the outer rim and the central hub. The set of locking features includes a plurality of projections and a plurality of recesses. The projections extend from an axial end surface of the central hub and are spaced apart from one another about the rod aperture. Each of the projections is formed along a projection axis that extends radially from a center axis along which the rod aperture is formed. Each of the projections intersects the rod aperture. Each of the projections has a pair of opposite side walls and an end wall that connects the side walls to one another on a side of the projection that is opposite the rod aperture. The recesses extend through the axial end surface and into of the central hub and are spaced apart from one another about the rod aperture. Each of the recesses is formed along a recess axis that extends radially from the center axis. Each of the recesses intersects the rod aperture. Each of the recesses has a pair of opposite side walls and an end wall that connects the side walls of the recess to one another on a side of the recess that is opposite the rod aperture. The projections on each piston member are received into and are frictionally engaged with a corresponding one of the recesses that is formed on the other piston member to thereby secure the piston members to one another. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG.  1    is a perspective view of an exemplary piston assembly constructed in accordance with the teachings of the present disclosure; 
         FIG.  2    is an exploded perspective view of the piston assembly of  FIG.  1    showing a pair of mating piston members; 
         FIG.  3    is a top plan view of a portion of the piston assembly of  FIG.  1    illustrating one of the piston members in more detail; 
         FIG.  4    is an enlarged portion of  FIG.  3    illustrating a projection of a set of locking features; 
         FIG.  5    is a section view taken along the line  5 - 5  of  FIG.  4   ; 
         FIG.  6    is a section view taken along the line  6 - 6  of  FIG.  5   ; 
         FIG.  7    is an enlarged portion of  FIG.  3    illustrating a recess of the set of locking features; 
         FIG.  8    is a section view taken along the line  8 - 8  of  FIG.  7   ; and 
         FIG.  9    is a section view taken along the line  9 - 9  of  FIG.  8   . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     With reference to  FIGS.  1  and  2   , a piston assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10 . The piston assembly  10  includes first and second piston members  12  and  14 , respectively, that are each formed of a compacted powdered metal material. In the example provided, the first and second piston members  12  and  14  are identical in their configuration and as such, only the first piston member  12  will be discussed in detail. In view of this similarity, reference numerals used to identify elements or features of the first piston member  12  will also be used herein in references to those elements or features on the second piston member  14 . It will be appreciated that the first and second piston members  12  and  14  need not be configured in an identical manner, and that the piston assembly  10  could include more than two piston members. 
     With reference to  FIGS.  2  and  3   , the first piston member  12  can be generally shaped as a right cylindrical plynth and can define a central hub  20 , an outer rim  22 , a plurality of vent apertures  24 , and set of locking features  26 . The central hub  20  can define a rod aperture  30  that is configured to receive a rod (not shown) therethrough. The outer rim  22  is disposed concentrically about the central hub  20 . The outside diametrical surface  36  of the outer rim  22  is cylindrically shaped in the example provided, but could optionally be configured in a contoured manner to engage a circumferentially extending seal (not shown). The vent apertures  24  are disposed about the circumference of the first piston member  12  in a desired manner, such as concentrically about the central hub  20 . The configuration of the vent apertures  24  is not germane to this discussion and as such, a detailed description of the vent apertures  24  will not be provided herein. In brief, the vent apertures  24  are configured to aid in the flow of fluid through the piston assembly  10 . 
     The set of locking features  26  includes a plurality of projections  40  and a plurality of recesses  42  that are formed on the central hub  20  and intersect the rod aperture  30 . The projections  40  are spaced apart from one another about the central hub  20  and extend from an axial end surface  50  of the central hub  20 . The recesses  42  are spaced apart from one another about the central hub  20  and extend into the central hub  20  from the axial end surface  50  of the central hub  20 . In the example provided, the quantity of recesses  42  is equal to the quantity of projections  40  and each of the recesses  42  is disposed between an adjacent pair of the projections  40 . It will be appreciated, however, that that the quantities of the projections  40  and the recesses  42  can be different from one another. It will also be appreciated that the projections  40  and/or the recesses  42  need not be disposed about the central hub  20  in a symmetric manner, which may be desirable in a situation where the first and second piston members  12  and  14  must be assembled to one another in a single orientation. 
     With reference to  FIGS.  3  through  6   , in a cross-section of a projection  40  taken perpendicular to the center axis  54  of the rod aperture  30 , the projection  40  can be formed symmetrically about a projection axis  56  that extends radially from the center axis  54  of the rod aperture  30  and can be shaped as a portion of a stadium, a discorectangle or obround. More specifically, the cross-sectional shape of the projection  40  can have a pair of sidewalls  60  and an end wall  62  that joins the sidewalls  60  to one another. In the plane of the cross-section, which is specifically shown in  FIG.  6   , the sidewalls  60  are depicted as parallel lines that are also parallel to the projection axis  56 , while the end wall  62  would be depicted as being a half-circle that joins the sidewalls  60  together. In practice, the sidewalls  60  and the end wall  62  could be formed with draft (i.e., taper) to permit them to be more easily released from the tooling (not shown) that is employed to form the first piston member  12 . 
     In the example shown, the radially inner end of the projection  40  conforms to the diameter of the rod aperture  30 , but it will be appreciated that the radially inner end of the projection  40  can be formed differently. For example, the radially inner end of the projection  40  could be formed as a portion of a right frustum or cone whose axis is coincident with the center axis  54  of the rod aperture  30  and which diverges from the center axis  54  with increasing distance from the axial end surface  50  of the central hub  20 . Configuration in this manner may be desirable to provide a modicum of clearance between the radially inner ends of the projections  40  and the rod (not shown) that is fitted through the rod aperture  30 . A first fillet radius can be used where the sidewalls  60  and end wall  62  of each projection  40  intersects the axial end surface  50  of the central hub  20 . A second fillet radius, or alternately a chamfer, can be used where the sidewalls  60  and end wall  62  intersect the end face  66  of their associated projection  40 . 
     With reference to  FIGS.  2  and  3   , each of the recesses  42  can be configured to matingly receive a corresponding one of the projections  40  (i.e., the projections  40  formed on the second piston member  14 ) in a desired manner (i.e., with a desired engineering fit). For example, the recesses  42  can be configured to receive the projections  40  in an interference fit. The engineering fit that is employed between the recesses  42  and the projections  40  could be dependent in part on the process that is employed to form the piston assembly  10 . In this regard, the first and second piston members  12  and  14  could be assembled to one another in a “green” condition (i.e., prior to sintering), with the intention that the first and second piston members  12  and  14  fuse together during the sintering operation. A brazing compound (not shown) could optionally be employed (e.g., on the abutting axial end surfaces  50  of the central hubs  20  of the first and second piston members  12  and  14 , and/or on the sets of locking features  26 ) to secure (or further secure) the first and second piston members  12  and  14  to one another. In the particular example provided, the first and second piston members  12  and  14  undergo sintering before being assembled to one another. 
     With reference to  FIGS.  3  and  7  through  9   , in a cross-section of a recess  42  taken perpendicular to the center axis  54  of the rod aperture  30 , the recess  42  can be formed symmetrically about a recess axis  76  that extends radially from the center axis  54  of the rod aperture  30  and can be shaped as a portion of a stadium, a discorectangle or obround. More specifically, the cross-sectional shape of the recess  42  can have a pair of parallel sidewalls  80  and an end wall  82 . In the plane of the cross-section, the sidewalls  80  are depicted as parallel lines that are also parallel to the recess axis  76 , while the end wall  82  is depicted as a half-circle that joins the sidewalls  80  to one another. In practice, the sidewalls  80  and the end wall  82  could be formed with draft (i.e., taper) to permit them to be more easily released from the tooling (not shown) that is employed to form the first piston member  12 . 
     In the example shown, the radially inner end of the recess  42  conforms to the diameter of the rod aperture  30 . A third fillet radius can be used where the sidewalls  80  and end wall  82  of each projection  40  intersects the axial end face  86  of their associated recess  42 . A fourth fillet radius, or alternately a chamfer, can be used where the sidewalls  80  and end wall  82  intersect the axial end surface  50  of the central hub  20 . 
     With reference to  FIGS.  2  and  3   , the projections  40  and recesses  42  of the set of locking features  26  on the first piston member  12  can be aligned to the recesses  42  and projections  40 , respectively, on the second piston member  14 . Optionally, one or more features on the first and second piston members  12  and  14  can be employed to orient them about the center axis  54  of the rod aperture  30  to thereby provide the desired alignment of the two sets of locking features  26 . Features employed to orient the first and second piston members  12  and  14  to one another could comprise existing features formed thereon, such as the configuration of the vent apertures  24 , and/or could comprise one or more features that are solely used to orient an associated one of the first and second piston members  12  and  14 . Also optionally, one or more features could also be formed into each of the first and second piston members  12  and  14  to permit automated inspection (i.e., via a camera) of the first and second piston members  12  and  14  prior to their assembly to one another. In the example provided, a feature  100  that is formed as a dimple in the end face  66  of one of the projections  40 . The feature  100  is employed in an automated inspection operation to verify the placement of the feature  100  in a desired orientation (or optionally, one of a plurality of desired orientations), which ensures that the projections  40  and recesses  42  are disposed in correct orientations. 
     With the projections  40  and the recesses  42  on the first piston member  12  being aligned to the recesses  42  and the projections  40  on the second piston member  14 , the first and second piston members  12  and  14  can be pressed together along an axis that is coincident with the center axes  54  of the rod apertures  30  formed through the first and second piston members  12  and  14 . When pressed together, the sidewalls  60  on the projections  40  on one of the first and second piston members  12  and  14  engage the corresponding sidewalls  80  of the recesses  42  on the other one of the first and second piston members  12  and  14 , and vice versa. Optionally, the end walls  62  and  82  can also engage one another. If the first and second piston members  12  and  14  had not been sintered prior to their assembly to one another, the assembly can be sintered to complete the piston assembly  10 . 
     The locking features  26  are advantageous over the prior art because the first and second piston members  12  and  14  are able to be sintered while resting on the protrusions  40 . Consequently, the risk of an external surface of the first and second piston members  12  and  14  becoming damaged during the sintering process is greatly reduced. Additionally, the configuration of the locking features  26  permit the first piston member  12  to be assembled to the second piston member  14  in numerous positions, rendering the orienting step of the assembly process somewhat easier and contributing to a lower scrap rate due to an error in the orientation between the first and second piston members  12  and  14 . Also additionally, the retention force that is provided by the locking features  26  is much more consistent than that of the prior art, and can be configured to be significantly higher than that which is provided by the prior art. In the example provided, the retention force provided by the locking features  26  is approximately three times that which was provided by the prior art. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.