Abstract:
A hydraulic tensioner is described. The hydraulic tensioner hasincludes an inlet portion which defines a pressurized fluid inlet. The hydraulic tensioner also hasincludes a housing defining a chamber which is coupled to the inlet portion. A band check valve separates the pressurized fluid inlet from the chamber, and a piston slideably engages the housing. An automobile having a driving shaft and a driven shaft may include such a hydraulic tensioner. A method of manufacturing athe hydraulic tensioner is also disclosed.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims an invention which was disclosed in Provisional Application No. 60/749,832, filed Dec. 13, 2005, entitled “HYDRAULIC TENSIONER WITH A BAND TYPE CHECK VALVE”. The benefit under 35 USC § 119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention pertains to the field of hydraulic tensioners. More particularly, the invention pertains to a hydraulic tensioner with a band type check valve. 
         [0004]    2. Description of Related Art 
         [0005]    In automobiles, hydraulic tensioners may be applied to a timing system or an auxiliary drive (e.g. oil pump) system. A hydraulic tensioner generally includes a housing, a piston slideably engaging the housing biased in a protruding direction by a spring, and a fluid chamber defined by the piston and the housing. During operation of the tensioner, external force from a chain or belt is imparted on the distal end of the piston. The force on the distal end is balanced by the tensioner spring load and hydraulic pressure in the chamber. Over time, the volume of the chamber may increase as the piston slides away from the housing, creating a need for more hydraulic fluid to fill the chamber. Hydraulic fluid may also need to be replenished in the chamber as fluid leaks out of the chamber. 
         [0006]    There is a need in the art for a hydraulic tensioner with a low-cost check valve to facilitate replenishing the hydraulic fluid within the chamber, which is also simple to manufacture and reliable. 
       SUMMARY OF THE INVENTION 
       [0007]    A hydraulic tensioner includes an inlet portion which defines a pressurized fluid inlet, a housing defining a chamber which is coupled to the inlet portion, a band check valve (also known as a band valve or a band type check valve) separating the pressurized fluid inlet from the chamber, and a piston slideably engaging the housing. 
         [0008]    A method of manufacturing the hydraulic tensioner is also described. In this method, a chamber is drilled in a housing and a hydraulic fluid inlet is drilled in an inlet portion. A band valve guide area is formed on the inlet portion. An exit hole is drilled through the band valve guide area to be in communication with the hydraulic fluid inlet and the band check valve is coupled to the band valve guide area such that the band check valve covers the exit hole and acts as a check valve between the hydraulic fluid inlet and the chamber. 
         [0009]    A hydraulic tensioner in another embodiment includes an inlet portion having an interior and an exterior, the inlet portion defining a pressurized fluid inlet on the interior, a band valve guide area with at least one groove on the exterior, and an exit hole between the band valve guide area and the pressurized fluid inlet. The hydraulic tensioner also includes a band check valve sprung to restrict its diameter coupled to the band valve guide area of the inlet portion exterior such that the band check valve covers the exit hole. The hydraulic tensioner also includes a housing defining a chamber in an axial direction which is open to a first end of the housing, an inlet coupling hole in a radial direction which is coupled to the chamber and is sized to receive the inlet portion such that the band check valve separates the pressurized fluid inlet from the chamber and such that the band check valve may be flexed outward by hydraulic pressure to allow fluid from the pressurized fluid inlet to enter the chamber. The hydraulic tensioner further includes a piston slideably engaging the housing and hydraulically coupled to the chamber, and a spring biasing the piston away from the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates a hydraulic tensioner providing tension to a timing chain in an embodiment of the present invention. 
           [0011]      FIG. 2  illustrates an exploded view of a hydraulic tensioner having a band-type check valve in an embodiment of the present invention. 
           [0012]      FIG. 3  illustrates the hydraulic tensioner of  FIG. 2  assembled and in cross-section. 
           [0013]      FIG. 4  illustrates a cross-section of a hydraulic tensioner in another embodiment of the present invention. 
           [0014]      FIG. 5  partially illustrates the hydraulic tensioner of  FIG. 4 . 
           [0015]      FIG. 6  illustrates a cross-section of  FIG. 4  along lines  6 - 6  of  FIG. 5 . 
           [0016]      FIG. 7  illustrates a cross-section of a hydraulic tensioner in yet another embodiment of the present invention. 
           [0017]      FIG. 8A  illustrates a band check valve in an embodiment of the present invention. 
           [0018]      FIG. 8B  illustrates a band check valve in another embodiment of the present invention. 
           [0019]      FIG. 8C  illustrates a band check valve in yet another embodiment of the present invention. 
           [0020]      FIG. 8D  illustrates a band check valve in another embodiment of the present invention. 
           [0021]      FIG. 8E  illustrates a band check valve in another embodiment of the present invention. 
           [0022]      FIG. 9  partially illustrates a hydraulic tensioner where the band check valve curls inward in an embodiment of the present invention. 
           [0023]      FIG. 10  partially illustrates a hydraulic tensioner where the band check valves curls outward in an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 1  schematically illustrates a hydraulic tensioner  22 . A hydraulic tensioner  22  provides tension to a timing chain  24 , which couples a driving shaft  26  to a driven shaft  28  via sprockets  30 ,  32 . Although a chain and sprocket system is shown in this figure, hydraulic tensioners may alternatively be used with a pulley and belt system. Similarly, additional shafts may be coupled to the driving and driven shafts  26 ,  28  by the belt or chain  24 . For simplicity, only two shafts are shown in this figure. The hydraulic tensioner  22  has an inlet portion  34  which is coupled to pressurized hydraulic fluid  36 , such as pressurized engine oil. The hydraulic tensioner  22  also includes a housing  38  which is coupled to the inlet portion  34 . The inlet portion  34  may be a separate part from the housing  38 , or it may be integral to the housing  38 . A piston  40  slideably engages the housing  38 , and may be biased away from the housing  38  by hydraulic pressure within the housing  38  as well as a mechanical spring force provided by a spring  42 . Spring  42  is coupled between housing  38  and the piston  40  and is chosen to push these two elements apart. A tensioner shoe or tensioner guide  44  may be coupled to the piston  40  to provide an interface between the hydraulic tensioner  22  and the timing chain  24 . 
         [0025]      FIG. 2  illustrates an exploded view of a hydraulic tensioner  22  in an embodiment of the present invention. The inlet portion  34  in this embodiment includes a band valve guide area  46  which has been turned or formed to have a smaller diameter than the diameter of the inlet portion  34 . Inlet portion  34  also defines an inlet  48  which may be coupled to the pressurized hydraulic fluid (not shown in this view). The inlet  48  runs through the interior of the inlet portion  34  at least as far as the band valve guide area  46 . At least one inlet exit hole  50  is formed in the band valve guide area  46 , the inlet exit hole  50  being coupled to the inlet  48 . In this embodiment, the inlet portion  34  is separate from the housing  38 , but in others, the inlet portion  34  could be integral to the housing  38 . In one embodiment, seals  41  (see  FIG. 3 ), such as o-rings, are located between the inlet portion  34  and the housing  38 . A band style check valve  52  may be installed over the band valve guide area  46  to cover the inlet exit hole  50 . In a preferred embodiment, the band check valve  52  is annular. In the embodiment shown in  FIG. 2 , the band check valve  52  is illustrated as encircling less than 360 degrees of the band valve guide area  46 , but in other embodiments band check valves covering 360 degrees or more may be desirable. Example embodiments of band check valves and their attachment to the band valve guide area  46  of the inlet portion  34  will be discussed in further detail with regard to FIGS.  5  and  8 A- 8 E. The band check valve  52  is positioned and/or sized to cover the inlet exit hole  50 . The band check valve  52  in this embodiment is sprung in an inwards direction to be biased against the band valve guide area  46  of the inlet portion  34 . 
         [0026]    After the band check valve  52  has been attached to the inlet portion  34 , the inlet portion  34  may be inserted into an inlet coupling hole  54  defined by the housing  38 . The inlet portion  34  may be coupled to the housing  38  by a snap ring or a retaining clip (not shown). Alternatively, the inlet portion  34  may be threaded, passed through the housing  38 , and attached in place with a fastener, such as a nut. Another method of attaching the inlet portion  34  to the housing  38  is pressing the inlet portion  34  into place. Other methods of attaching the inlet portion  34  to the housing  38  will be obvious to those skilled in the art, including embodiments where the inlet portion  34  is integral to the housing  38 . The housing  38  also defines a chamber  56  which passes axially through the housing  38  at least as far as the inlet coupling hole  54 . In this embodiment, a piston  40  may be slideably engaged on the outside of the chamber  56  end of the housing  38 . A spring  42  is installed between the piston  40  and the housing  38 . When the hydraulic pressure in the inlet  48  exceeds the hydraulic pressure in the chamber  56  plus the spring force of the band check valve  52 , the band check valve  52  moves away from the inlet exit hole  50 , allowing pressurized hydraulic fluid to fill the chamber  56 . As pressure in the chamber  56  increases, the band check valve  52  returns to a sealing position where the inlet exit hole  50  is covered and not in fluid communication with the chamber  56 . 
         [0027]      FIGS. 3-7  illustrate different embodiments of hydraulic tensioners with a band type check valve.  FIG. 3  illustrates the hydraulic tensioner  22  shown in  FIGS. 1-2  assembled and in cross-section. This view is useful for seeing the fluid paths within the hydraulic tensioner  22 , as well as for discussing some of the manufacturing techniques and advantages involved with producing a hydraulic tensioner with a band type check valve. A drill bit may be used to bore the inlet hole  48  into the inlet portion  34 . The inlet portion  34  may be sized so that a tapered portion  58  of the inlet hole  48 , from the tip of a drill bit, may extend into the inlet portion  34  without interfering with the inlet exit hole  50 . The inlet exit hole  50  may be bored all the way through the inlet portion  34 , since the band check valve  52  may be sized to cover both ends of the exit hole  50 . Although exit hole  50  is illustrated as being perpendicular to the inlet  48 , in other embodiments, the exit hole  50  may be non-perpendicular, provided the exit hole  50  still falls within the band valve guide area  46  of the inlet portion  34 . Similarly, the chamber hole  56  may be bored into the housing  38  with a drill bit. The housing  38  may be sized so that a tapered portion  60  of the chamber  56 , from the tip of a drill bit, may extend into the housing  38  without interfering with the inlet coupling hole  54 . 
         [0028]    Pressurized fluid (not shown in this view) starts in the inlet  48  and may pass through the inlet exit hole  50  and the band check valve  52  into the chamber  56  as described above. The hydraulic pressure within the chamber  56 , coupled with the spring force provided by the spring  42  biases the piston  40  away from the housing  38  (In the negative X-axis direction in this view). It should be noted that, for simplicity, the illustrated clearances between the parts in the figures of this specification have been expanded so that the individual parts may be seen. 
         [0029]      FIG. 4  illustrates another embodiment of a hydraulic tensioner  122  in cross-section. This embodiment is similar to the embodiment of  FIG. 3  insofar as the operation and construction of the inlet portion  134 , the band check valve  152 , and the chamber  156 . The piston  162  in this embodiment, however, is different. In this embodiment, the piston  162  is slideably engaged with the housing  138  on the interior of the housing  138 , and the spring  142  is consequently located within the chamber  156 . The chamber  156  may be provided with a lip  143  in this embodiment to keep the spring  142  from contacting the band check valve. This embodiment offers a more simple piston  162 , which may just be a rod cut to length, rather than the more complex piston of  FIG. 3 . Both the embodiments of  FIGS. 3 and 4  benefit from the simple manufacturing process made possible by the integration of a band type check valve  152 . 
         [0030]      FIG. 5  partially illustrates the hydraulic tensioner  122  shown in  FIG. 4 . The housing and the piston have been removed in this view, leaving only the inlet portion  134  and band check valve  152  assembly described above. A cross section along lines  6 - 6  of  FIG. 5  is shown in  FIG. 6 .  FIG. 6  is a cross-sectional view of the hydraulic tensioner  122  in  FIG. 4 , rotated back so that the positive Y-axis is pointing up. This view in  FIG. 6  illustrates the band check valve  152  as it pertains to the inlet exit hole  150 . In the embodiment of  FIG. 6 , the band check valve  152  wraps more than 360 degrees around the band valve guide area  146  where the exit hole  150  is located. 
         [0031]      FIG. 7  illustrates a further embodiment of a hydraulic tensioner  222  in cross-section. This embodiment is similar to the embodiment of  FIG. 4 , but the housing defines a well area  264  around part of the piston  262  where it exits the housing  238 . A natural leak path is present between the housing  238  and the piston  262 . The addition of well area  264  allows the capture of leakage oil from the hydraulic tensioner  222 , thereby helping to prevent air from entering the tensioner when the internal tensioner pressure is lower than the surrounding pressure. This may occur when the piston is rapidly extending. The well area  264  may be formed by using a larger drill bit on the piston end of the housing  238 . The embodiment of  FIG. 7  also illustrates an alternative manufacturing technique which may be used to make the chamber  256  within the housing  238 . In previous embodiments, the chamber  56 ,  156  is shown as being drilled into one end of the housing  38 ,  138  while not exiting the other end of the housing  38 ,  138 . In this embodiment, the chamber hole  256  is drilled all the way through the housing  238 . A plug  266 , such as a ball bearing, may be press-fit into the end of the chamber  256  opposite the piston  262  to seal the chamber  256 . This may offer manufacturing advantages in situations where it is quicker and/or less expensive to cut pieces of pre-drilled housing and plug them versus having to precision drill one side of the chamber while not exiting the other side. 
         [0032]    For simplicity, the band check valve  52  and inlet portion  34  are schematically illustrated by themselves in  FIGS. 8A-8E . The band check valves shown in  FIGS. 8A-8E  may be used in any of the embodiments of the hydraulic tensioners discussed herein.  FIG. 8A  illustrates an embodiment of a band check valve  52 A which wraps more than 360 degrees around the band valve guide area  46  where the exit hole  50  is located. With a greater-than-360-degree band check valve  52 A, the orientation of the band check valve  52 A is not important. In fact, this type of band check valve  52 A may rotate during operation without affecting its operation. 
         [0033]      FIG. 8B  illustrates an embodiment of a band check valve  52 B which is coupled to the band valve guide area  46  of the inlet portion  34  by a solder or weld  68 . Since the orientation of welded band check valve  52 B is fixed, a band check valve of 360 degrees or less may be used. 
         [0034]      FIG. 8C  illustrates an embodiment of a band check valve  52 C which makes use of a slightly different band valve guide area  46  on the inlet portion  34  than has been described to this point. In this embodiment, a flat portion  70  may be milled or formed onto the band valve guide area  46  of the inlet portion  34 . A band check valve  52 C of less than 360 degrees may be formed to have a flat side which corresponds to the flat portion  70 . While this embodiment adds additional steps to the manufacture of the band valve guide area  46 , it may offer advantages for easier installation of the check valve than the embodiments shown in  FIGS. 8A-8B , since the band check valve  52 C may be sized so that it just needs to be snapped into place. 
         [0035]      FIG. 8D  illustrates an embodiment of a band check valve  52 D which offers a possible advantage over the embodiment of  FIG. 8C  while still allowing for easier installation of the band check valve  52 D. The band check valve  52 D is provided with a tab  72  which may be fit into the unused exit hole  74 . Recalling the discussion regarding the formation of exit hole  50  above, it should be noted that an extra or unused exit hole  74  may be formed with a single drilling operation while making the main exit hole  50 . The tab  72  on the band check valve  52 D orients the band check valve  52 D without needing to change the configuration of the band valve guide area  46  of the inlet portion  34 . The tab  72  is less wide than the band check valve  52 D where it covers the exit hole  50 . 
         [0036]      FIG. 8E  illustrates another embodiment of a band check valve  52 E. In this embodiment, the unused exit hole  74  is enlarged by an additional drilling process to allow for a full-width tab  76  to be bent into the band check valve. This bend in the band check valve  52 E may be snapped in to engage the extra exit hole  74 . 
         [0037]      FIG. 9  illustrates an embodiment of an inlet portion  334  with a band valve guide area  346  which defines an exit hole  350  coupled to the inlet hole  348 . Embodiments of hydraulic tensioners with this structure have been discussed above with regard to a band check valve  352 . In this case, the band check valve  352  is spring biased so that it is trying to curl up, and will therefore exert an inward force onto the band valve guide area  346  of the inlet portion  334  where the exit hole  350  comes through. 
         [0038]    It has been discovered experimentally that debris may build up over time between the band check valve  352  and the band valve guide area  346 . This build-up of debris may cause a leakage problem, by preventing the band check valve from sealing properly. To alleviate this issue, one or more grooves  378  may be formed in the band valve guide area  346  of the inlet portion  334  underneath where the band check valve  352  makes contact. The grooves  378  may act as places for debris to gather while also helping to create a known and/or more reliable pop-off or release pressure of the band check valve  352 . The grooves  378  may also be used to reduce the surface adhesion of a clean band check valve  352  so that a lighter weight band check valve  352  may possibly be used, although it is not necessary to use a lighter band check valve material with a textured or grooved band valve guide area. As an alternative to grooves  378 , the band valve guide area  346  of the inlet portion  334  may be roughened, scratched, or otherwise textured to provide a similar benefit to grooves  378 . The grooved or textured surface may also be designed as a known leak path. A known leak path can also act to flush debris away from the backside of the band check valve  352 . 
         [0039]    Up to this point, all hydraulic tensioner embodiments have shown band check valves which tend to curl in upon themselves. It is also possible to have embodiments where the band check valves tend to curl outwards.  FIG. 10  illustrates this type of alternative embodiment for a hydraulic tensioner  422 . This hydraulic tensioner includes a housing  480  which includes a pressurized oil inlet  482  which enters radially as opposed to the axial entrance in previous embodiments. The inlet portion  434  is integral with the housing  480  in this embodiment. The housing  480  defines a chamber  484  which slideably engages a piston  486 . The piston  486  is biased away from the housing  480  by spring  488  and the hydraulic pressure in the chamber  484 . A band valve guide area  490 , such as an annular recessed area may be formed around all or part of the circumference of the chamber  484 . A band style check valve  492  may be installed in the band valve guide area  490 , the band check valve  492  in this case being sprung outward to seal off the inlet  482 . 
         [0040]    When the hydraulic pressure in the inlet  482  exceeds the hydraulic pressure in the chamber  484  plus the spring force of the band check valve  492 , the band check valve  492  moves away from the inlet  482  hole, allowing pressurized hydraulic fluid to fill the chamber  484 . As pressure in the chamber  484  increases, the band check valve  492  returns to a sealing position where the inlet  482  hole is covered and not in fluid communication with the chamber  484 . As discussed before with other embodiments, the band check valve  492  may be greater than, equal-to, or less than 360 degrees, and may or may not contain tabs, bends, or welds to align it within the band valve guide area  490 . The embodiment of  FIG. 10  is also illustrated with annular grooves  494 , which operate similarly to the grooves  378  discussed with regard to the hydraulic tensioner of  FIG. 9 . The grooves  494  are not necessary in a hydraulic tensioner having a band style check valve, but can be used to improve the pop-off and sealing performance, and/or provide a known leak path, as discussed above. 
         [0041]    In a method of the present invention, a hydraulic tensioner is manufactured by drilling a chamber into a housing, drilling a hydraulic fluid inlet in an inlet portion, forming a band valve guide area on the inlet portion, drilling an exit hole through the band valve guide area to be in communication with the hydraulic fluid inlet, and coupling a band check valve to the band valve guide area such that the band check valve may cover the exit hole and act as a check valve between the hydraulic fluid inlet and the chamber. 
         [0042]    Accordingly, it is to be understood that the embodiments described herein are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.