Abstract:
Provided, is a simple-structured tensioner that can. favorably expel the air that has entered an oil pressure chamber, while enabling a reduction in size in the axial direction, and in processing and assembling workload. The tensioner  10  includes a relief mechanism made up of a relief hole  22  and a disc-like orifice member  60.  A first main surface  61  of the orifice member  60  is provided with an outer circumferential annular groove  61   a  formed along an outer peripheral edge and a communication groove  61   b  that extends from a central portion of the first main surface  61  to the outer circumferential annular groove  61   a,  The orifice member  60  has a plurality of notches  63  arranged along a circumferential direction in the outer peripheral edge of the orifice member  60.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a tensioner that applies appropriate tension to a running chain, belt, or the like. 
         [0003]    2. Description of the Related Art 
         [0004]    It has been common practice to use a tensioner for maintaining appropriate tension in a chain or the like. For example, a known chain guide mechanism, which slidably guides a transmission chain, such as an endless roller chain passing over respective sprockets of a crankshaft and of a cam shaft inside an engine room, uses a tensioner to bias a tensioner lever in order to maintain appropriate tension of the chain or the like. 
         [0005]    The known tensioner includes a housing having a plunger bore open toward a front side, a plunger slidably inserted in the plunger bore, and a coil spring that biases the plunger toward the front side. In such a tensioner, oil is supplied to an oil pressure chamber formed between the plunger bore and the plunger, so that the plunger is biased toward the front side by the oil in the oil pressure chamber. As the plunger reciprocates, the oil flows through the small gap between the plunger and the plunger bore and the flow resistance provides the damping effect of slowing down the reciprocal movement of the plunger. 
         [0006]    It has been known to provide a relief mechanism for discharging the oil inside, the oil pressure chamber to the outside of the plunger when the oil pressure in the oil pressure chamber builds up, so as to maintain the oil pressure of the oil pressure chamber at an appropriate level. In one form of the relief mechanism, as shown in  FIG. 8 , it is known to provide a relief hole  122  in the plunger  120  to connect the inside and outside of the plunger  120 , and to dispose an orifice member  160  inside the plunger  120 . 
         [0007]    A helical groove  161   b  is formed on an outer circumferential surface of the orifice member  160 . The orifice member  160  is press-fitted into a plunger hole  123 , and the gap between the inner circumferential surface of the plunger hole  123  and the groove  161   b  is used to adjust the amount of oil to be discharged from the relief hole  122 . 
         [0008]    In this example shown in  FIG. 8 , however, since the orifice member  160  is installed inside the plunger hole  123  by press-fitting, the length in the front to back direction (axial direction) of the orifice member  160  needs to be set large so as to secure a press-fitting allowance for the orifice member  160 , and the outer diameter of the orifice member  160  and the inner diameter of the plunger hole  123  must be formed with high precision. Moreover, because of the possibility of deformation of the plunger  120  caused by the press-fitting or the orifice member  160 , a polishing process is necessary after the assembly. Furthermore, the press-fitting process causes various other problems such as the need for providing press-fitting equipment. 
         [0009]    As one possible solution to the problems described above, it has been proposed to provide a disc-like orifice member  160  with an oil groove (not shown) in a first main surface  161  thereof facing a plunger bottom  121  side, such as to be fixedly pressed against the plunger bottom  121  by a coil spring  140  as shown in  FIG. 9  (see, for example, Japanese Patent Application Laid-open No. 2003-194164). 
         [0010]    In the tensioner of Japanese Patent Application Laid-open No. 2003-194164, when the oil pressure in the oil pressure chamber  111  rises, the oil O inside the oil pressure chamber  111  is discharged to the outside of the plunger  120 , traveling through the gap between the outer circumferential surface of the orifice member  160  and the inner circumferential surface of the plunger hole  123 , the oil groove in the first main surface  161 , and the relief hole  122 . 
         [0011]    This relief mechanism described in Japanese Patent Application Laid-open No. 2003-194164 also serves as a degassing mechanism for expelling the air A that has entered the oil pressure chamber  111  to the outside of the oil pressure chamber  111 . More specifically, the air A that has entered the oil pressure chamber  111  is discharged to the outside of the plunger  120 , traveling through the gap between the outer circumferential surface of the orifice member  160  and the inner circumferential surface of the plunger hole  123 , the oil groove in the first main surface  161 , and the relief hole  122 , similarly to the oil O. 
       SUMMARY OF THE INVENTION 
       [0012]    However, in the tensioner of Japanese Patent Application Laid-open No. 2003-194164 the orifice member  160  is fixed by being pressed against the plunger bottom  121  with the coil spring  140 , because of which the gap between the inner circumferential surface of the plunger hole  123  and the outer circumferential surface of the orifice member  160  may sometimes become uneven in the circumferential direction as shown in  FIG. 10A . When the portion R where the gap is small is located on an upper side in the direction of gravitational force where the trapped air A accumulates as shown in  FIG. 9 , the trapped air A can hardly be released toward the first main surface  161  of the orifice member  160 . 
         [0013]    As a possible solution to the problem described above, a notch  163  may be formed to the outer peripheral edge of the orifice member  160  in a portion located on the upper side in the direction of gravitational force as shown in  FIG. 10B , so as to allow the trapped air A to be released more easily toward the first main surface  161  of the orifice member  160 . 
         [0014]    In this case, however, the orifice member  160  must be assembled into the plunger hole  123  such that the notch  163  will be located on the upper side in the direction of gravitational, force, which, leads to the problem of increased, assembling workload. Another problem is that this solution, is not applicable to a tensioner of the type in which the plunger  120  is set inside the plunger bore of the housing  130  in a freely rotatable state. 
         [0015]    An object of the present invention is to solve these problems and to provide a simple-structured tensioner that can favorably expel the air that has entered an oil pressure chamber, while enabling a reduction in size and production workload. 
         [0016]    The present invention provides a tensioner, including a cylindrical plunger having a plunger bottom on a front end; a housing having a plunger bore that is open toward a front side and accommodates the plunger; a coil spring that is accommodated in an oil pressure chamber formed between the plunger bore and a rear end of the plunger such as to foe able to freely expand and contract and that biases the plunger toward the front side; and a relief mechanism that, releases oil inside the oil pressure chamber to outside of the plunger when oil pressure in the oil pressure chamber rises. The relief mechanism is made up of a relief hole that is open in a central portion on an inner surface of the plunger bottom and connects inside and outside of the plunger, and a disc-like orifice member disposed on the inner surface of the plunger bottom. The orifice member is biased toward the plunger bottom, by the coil spring and includes a first main surface disposed on the plunger bottom and a second main surface opposite from the first main surface. The first main surface is provided with an outer circumferential annular groove formed along an outer peripheral edge of the first main surface and a communication groove that extends from a central portion of the first main surface to the outer circumferential annular groove. The orifice member has a plurality of notches arranged along a circumferential direction in an outer peripheral edge of the orifice member. The problems described above are thereby solved. 
         [0017]    According to one aspect of the present invention, the first main surface of the orifice member disposed on the plunger bottom is provided with an outer circumferential annular groove formed along an outer peripheral edge and a communication groove that extends from a central portion of the first main surface to the outer circumferential annular groove, and the orifice member further has notches in an outer peripheral edge thereof. When the oil pressure in the oil pressure chamber builds up, the oil in the oil pressure chamber is discharged to the outside of the plunger through the notches, outer circumferential annular groove, and communication groove of the orifice member, and through the relief hole of the plunger, to maintain the oil pressure of the oil pressure chamber at an appropriate level. That the orifice member does not require a press-fitting process to be installed not only enables the orifice member to be made smaller and its production, workload to be reduced, but also provides the following effects. 
         [0018]    That is, because a plurality of notches are formed in the circumferential direction along the outer peripheral edge of the orifice member, the air that may be trapped and accumulate on an upper side in the direction of gravitational force can be released toward the first main surface through one of the plurality of notches. Therefore, the positions of the notches need not be taken into consideration when assembling the orifice member, so that the assembling workload can be reduced. Also, the orifice member can be applied to a tensioner of the type in which the plunger is set inside the plunger bore of the housing in a freely rotatable state. 
         [0019]    According to another aspect of the present invention, the plurality of notches are equally spaced along the outer peripheral edge of the orifice member, so that the degassing function is stably achieved irrespective of the orientation of the orifice member inside the plunger hole. 
         [0020]    According to yet another aspect of the present invention, the second main surface is provided with a second outer circumferential annular groove formed along an outer peripheral edge of the second main surface, and a second communication groove that extends from a central portion of the second main surface to the second outer circumferential annular groove. When the orifice member is assembled into the plunger hole, there is no need to consider which side of the orifice member should be on top, so that the assembling, workload, can be further reduced. The length of the oil flow passage can be easily adjusted by using a plurality of orifice members laid upon one another. 
         [0021]    According to a further aspect of the present invention, a second disc-like orifice member is disposed between the inner surface of the plunger bottom and the orifice member, and the second orifice member includes, in a central portion thereof, a through hole which extends from a first, main surface opposite the plunger bottom through a second main surface opposite the orifice member. The through hole of the second orifice member has a diameter smaller than that of the relief hole. The amount, of oil to be discharged can thus be favorably adjusted with a simple structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a cross-sectional view illustrating a tensioner according to a first embodiment of the present invention; 
           [0023]      FIG. 2  is a perspective view illustrating an orifice member assembled into the tensioner shown in  FIG. 1 ; 
           [0024]      FIG. 3  is a plan view illustrating the orifice member assembled into the tensioner shown in  FIG. 1 ; 
           [0025]      FIG. 4  is a perspective view illustrating a variation example of the orifice member; 
           [0026]      FIG. 5  is a plan view illustrating the: orifice member shown in  FIG. 4 ; 
           [0027]      FIG. 6  is a cross-sectional view illustrating a tensioner according to a second embodiment of the present invention; 
           [0028]      FIG. 7  is a perspective view illustrating a second orifice member assembled into the tensioner shown in  FIG. 6 ; 
           [0029]      FIG. 8  is a cross-sectional view illustrating an example of a tensioner for reference; 
           [0030]      FIG. 9  is a cross-sectional view illustrating a conventional tensioner; and 
           [0031]      FIGS. 10A and 10B  are reference diagrams for describing a gap between the orifice member and the plunger bore. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    A tensioner  10  according to a first embodiment of the present invention will be described with reference to the drawings. 
         [0033]    First, the tensioner  10  of this embodiment is incorporated in a chain transmission used in a timing system or the like of a car engine. The tensioner is attached to an engine block to apply appropriate tension to the slack side of a transmission chain passing over a plurality of sprockets via a tensioner lever to reduce vibration during the drive. 
         [0034]    The tensioner  10  includes, as shown in  FIG. 1 , a cylindrical plunger  20  having a plunger bottom  21  at a front end, a housing  30  having a plunger bore  31  for accommodating the plunger  20 , a coil spring  40  accommodated in an oil pressure chamber  1  formed between the plunger bore  31  and the rear end of the plunger  20  such as to be able to freely expand and contract and to bias the plunger  20  toward a front side, a check valve  50  that prevents the oil from flowing out from the oil pressure chamber  11  while allowing the oil to flow into the oil pressure chamber  11 , and a relief mechanism that releases the oil inside the oil pressure chamber  11  to the outside of the plunger  20  when the oil pressure in the oil pressure chamber  11  rises. 
         [0035]    Hereinafter, various constituent elements of the tensioner  10  will be described with reference to the drawings. 
         [0036]    The plunger  20  is made of metal such as iron or the like and inserted in the plunger bore  31  such as to be able to move back and forth in the front to back direction, as shown in  FIG. 1 . A relief hole  22  is formed in the plunger bottom  21  such as to open in a central portion of the inner surface of the plunger bottom  21 . The plunger  20  has a plunger hole  23  open toward the rear side. 
         [0037]    The housing  30  is made of aluminum alloy or synthetic resin and the like and includes, as shown in  FIG. 1 , the cylindrical plunger bore  31  open toward the front side, and an oil supply hole  32  for supplying oil into the oil pressure chamber  11  from the outside of the housing  30 . 
         [0038]    The coil spring  40  has one end abutting on an orifice member  60  to be described later and the other end arranged in contact with the bottom of the plunger bore  31 , as shown in  FIG. 1 . 
         [0039]    The check valve  50  is disposed between the oil pressure chamber  1  and the oil supply hole  32  as shown in  FIG. 1 , and allows the oil to flow in from the outside of the housing  30  through the oil supply hole  32  into the oil pressure chamber  11 , and prevents the oil from flowing out from the oil pressure chamber  11  through the oil supply hole  32 . 
         [0040]    The relief mechanism is made up of the relief hole  22  that connects inside and outside of the plunger  20 , and the orifice member  60  disposed on the inner surface of the plunger bottom  21 , as shown in  FIG. 1 . The orifice member  60  is biased toward the front side by the coil spring  40  so that it is pressed against the inner surface of the plunger bottom  21  and fixedly held there. 
         [0041]    The orifice member  60  is made of metal such as iron or the like or synthetic resin and the like in a disc-like shape, and has a first main surface  61  that is disposed in contact with the inner surface of the plunger bottom  21 , and a second main surface  62  on the opposite side from the first main surface  61 . The disc-like orifice member  60  has an outer diameter, that is slightly smaller than the inner diameter of the plunger hole  23 . 
         [0042]    The first main surface  61  is provided with a first outer circumferential annular groove  61   a  formed along an outer peripheral edge of the first main surface  61  and a first communication groove  61   b  that extends from a central portion of the first main surface  61  to the first outer circumferential annular groove  61   a,  a shown in  FIGS. 2 and 3 . 
         [0043]    The second main surface  62  is provided with a second outer circumferential annular groove  62   a  formed along an outer peripheral edge of the second main surface  62  and a second communication groove  62   b  that extends from a central portion of the second main surface  62  to the second outer circumferential annular groove  62   a.    
         [0044]    In this embodiment, as shown in  FIGS. 2 and 3 , the communication grooves  61   b  and  62   b  are formed in the main surfaces  61  and  62  in a substantially spiral shape. 
         [0045]    However, the communication grooves  61   b  and  62   b  may have any specific shapes as long as they extend from a central portion of the main surfaces  61  and  62  to the outer circumferential annular grooves  61   a  and  62   a.  For example, as shown in  FIGS. 4 and 5 , the communication grooves  61   b  and  62   b  may extend straight along the radial direction from the central portion of the main surfaces  61  and  62  to the outer circumferential annular grooves  61   a  and  62   a.    
         [0046]    A plurality of circumferentially equally spaced notches  63  are formed along the outer peripheral edge of the orifice member  60 , as shown in  FIGS. 2 and 3 . These notches  63  extend from the first main surface  61  through the second main surface  62  to communicate with the first outer circumferential annular groove  61   a  and the second outer circumferential annular groove  62   a.    
         [0047]    In the tensioner  10  of this embodiment thus configured, when the oil pressure in the oil pressure chamber  11  rises, the oil inside the oil pressure chamber  11  is discharged to the outside of the plunger  20 , traveling successively through the notches  63 , first outer circumferential annular groove  61   a,  and first, communication groove  61   b  of the orifice member  60 , and through the relief hole  22  of the plunger  20 . 
         [0048]    When air enters the oil pressure chamber  11 , the air is discharged to the outside of the plunger  20  similarly, traveling successively through the notches  63 , first outer circumferential annular groove  61   a,  and first communication groove  61   b  of the orifice member  60 , and through the relief hole  22  of the plunger  20 . 
         [0049]    Next, a tensioner  10  according to a second embodiment of the present, invention will be described with reference to  FIGS. 6 and 7 . The second embodiment is, in part, exactly the same as the previously described first embodiment, and therefore its configurations will not be described except for the differences. 
         [0050]    In the tensioner  10  of the second embodiment, as shown, in  FIG. 6 , a second disc-like orifice member  70  is disposed, between the inner surface of the plunger bottom  21  and the orifice member  60 . 
         [0051]    The second orifice member  170  includes, in a central portion thereof, a through hole  73  which extends from a first main surface  71  opposite the plunger bottom  21  through a second main surface  72  opposite the orifice member  60 , as shown in  FIGS. 6 and 7 . The through hole  73  of the second orifice member  70  is designed to have a diameter that is smaller than that of the relief hole  22 . 
         [0052]    While the embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments and may be carried out with various design changes without departing from the scope of the present invention set forth in the claims. 
         [0053]    For example, various configurations of the embodiments described above may be freely combined to form other tensioners. 
         [0054]    While the tensioner was described as a component to be incorporated in a timing system of a car engine in the embodiments above, the purpose of use of the tensioner is not limited to this specific application. 
         [0055]    Also, while the tensioner was described as a component that applies tension to a transmission chain with a tensioner lever in the embodiments above, the plunger can directly guide the transmission chain, slidably with a distal end thereof to apply tension to the transmission chain. 
         [0056]    The tensioner may not necessarily be applied to a transmission mechanism with a transmission chain but can also foe used for similar transmission mechanisms that use belts, ropes and the like, and can be applied in a variety of industrial fields where it is required to apply tension to an elongated component. 
         [0057]    While the housing accommodating the plunger is described as the component known as a housing that, is attached to an engine block or the like in the embodiments described above, the housing is not limited to the specific form described above and may be a cylindrical component known as a sleeve inserted into a body hole formed in the engine body. 
         [0058]    While the outer circumferential annular grooves and communication grooves are formed on both first and second main surfaces of the orifice member in the embodiments described above, the outer circumferential annular groove and communication groove may be formed only on the first main surface. 
         [0059]    Optionally, two or more orifice members, or the second orifice member, may be disposed one upon another in the front to back direction.