Abstract:
To provide a simple-structured tensioner capable of minimizing an increase in production cost, and avoiding performance degradation of its check valve resulting from a buildup of oil pressure inside an oil pressure chamber, while securing good assemblability of the check valve. A check valve  50  is provided in the tensioner  10  in which a ball seat  52  is fixedly set to a housing  30  or a plunger  20  and has a retainer receiving recess  52 b for setting a retainer  53  on one side facing an oil pressure chamber  11.

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]    In the prior art, using a tensioner to maintain tension in a chain, etc. appropriate has been common practice. For example, a known chain guide mechanism uses a tensioner to urge a tensioner lever for slidably guiding an endless transmission chain passed over respective sprockets of a crankshaft and cam shafts inside an engine room, so as to maintain tension in the chain, etc. appropriate. 
         [0005]    One known tensioner used in such a chain guide mechanism includes, as shown in  FIGS. 5 and 6 , a housing  530  having a plunger bore  531  that is opened to a front side, a plunger  520  slidably inserted in the plunger bore  531 , and biasing unit  540  that urges the plunger  520  toward the front side (see, for example, Japanese Patent Application Laid-open Nos. 2009-192031, 2006-144958, and 2008-95850). 
         [0006]    In such a tensioner, oil is supplied to an oil pressure chamber  511  formed between the plunger bore  531  and the plunger  520 , so that the plunger  520  is biased toward the front side by the oil in the oil pressure chamber  511 . As the plunger  520  reciprocates, oil flows through the small gap between the plunger  520  and the plunger bore  531 , and the flow resistance exerts a damping effect of slowing down the reciprocal movement of the plunger  520 . 
         [0007]    In such a tensioner, a check valve  550  is provided for preventing the oil from flowing out from the oil pressure chamber  511  while allowing the oil to flow into the oil pressure chamber  511 . The check valve  550  includes a check ball  551 , a ball seat  552  having a ball seat part for the check ball  551  to sit on, and a retainer  553  that restricts the movement of the check ball  551 . 
       SUMMARY OF THE INVENTION 
       [0008]    Such a tensioner, however, may sometimes be subjected to an excessive load resulting from an engine failure or the like, in which case the oil pressure inside the oil pressure chamber  511  may rise significantly. In a tensioner such as the one described in Japanese Patent Application Laid-open No. 2009-192031 and shown in  FIG. 5 , the ball seat  552  is press-fitted in a seat receiving recess  555   a  that is formed in a side face on a rear side of the ball guide  555  that is fixedly set in the housing  530  (i.e., opposite side of the ball guide  555  from the side facing the oil pressure chamber  511 ). In such a case, when a buildup of oil pressure inside the oil pressure chamber  511  occurs, the ball seat  552  may be displaced in a manner such as the ball seat  552  coming out of the seat receiving recess  555   a  due to the increased oil pressure inside the oil pressure chamber  511 , for example, which may lead to performance degradation of the check valve  550 . 
         [0009]    A possible measure for preventing such displacement of the ball seat  552  may be to form the inner diameter of the seat receiving recess  555   a  and the outer diameter of the ball seat  552  with a higher degree of precision so as to increase the strength with which the ball seat  552  fits in the seat receiving recess  555   a,  i.e., to increase the force of the seat receiving recess  555   a  retaining the ball seat  552 . This, however, would require formation of the seat receiving recess  555   a  and ball seat  552  with a high degree of precision and therefore leads to the problem of increased production cost. 
         [0010]    Another possible measure would be to fixedly set the ball seat  552 A in the housing  530  by press-fitting, as in the check valve  550 A incorporated in the tensioners of Japanese Patent Application Laid-open Nos. 2006-144958 and 2008-95850 shown in  FIG. 6 , with a retainer  553 A having a flange that makes contact with the housing  530  and being fitted with one end of the ball seat  552 A facing the oil pressure chamber  511 . This way, displacement of the ball seat  552 A or retainer  553 A that may result from a buildup of oil pressure inside the oil pressure chamber  511  can be prevented. However, in this case, when assembling the tensioner, the ball seat  552 A would have to be press-fitted to the housing  530  before the check ball  551 A is set on the ball seat  552 A, and the retainer  553 A is fitted to the ball seat  552 A after that, which all have to be done in a constricted space inside the housing  530 . Thus the assemblability of the tensioner would be greatly compromised. In the case with the check valve  550 A having the structure described above, there is a limitation on the position where the check valve  550 A can be installed inside the tensioner. For example, the check valve  550 A could not be set at a middle position inside the plunger hole  521 . 
         [0011]    When the ball seat  552 B and retainer  553 B are in contact with the plunger  520  or the like on the opposite side from the oil pressure chamber  511  as in the check valve  550 B of another type incorporated in the tensioners of Japanese Patent Application Laid-open Nos. 2006-144958 and 2008-95850 shown in  FIG. 6 , the displacement of the ball seat  552 B or retainer  553 B resulting from the buildup of oil pressure inside the oil pressure chamber  511  may be prevented. However, this only applies to cases where the check valve  550 B is set to a specific position inside the tensioner. 
         [0012]    Also, with a further increase in engine output in future, the load input conditions of the tensioner are expected to become harsher. Therefore, a reliable check valve  550  that can withstand an excessive input is more and more sought after. 
         [0013]    The present invention solves these problems and it is an object of the invention to provide a simple-structured tensioner capable of minimizing an increase in production cost, and avoiding performance degradation of its check valve resulting from a buildup of oil pressure inside an oil pressure chamber, while securing good assemblability of the check valve. 
         [0014]    The present invention solves the problems described above by providing a tensioner that includes: a plunger having a plunger hole that is opened to a rear side; a housing having a plunger bore that is opened to a front side for accommodating the plunger; biasing unit accommodated inside an oil pressure chamber formed between the plunger bore and a rear end of the plunger such as to be able to expand and contract and to urge the plunger toward the front side; and a check valve that allows oil to flow into the oil pressure chamber and prevents the oil from flowing out from the oil pressure chamber. The check valve includes a check ball, a ball seat having a ball seat part for the check ball to sit on, and a retainer that restricts movement of the check ball. The ball seat is fixed to either the housing or the plunger, and the ball seat has a retainer receiving recess for setting the retainer on one side facing the oil pressure chamber. 
         [0015]    According to one aspect of the present invention, the ball seat is fixedly set to the housing or the plunger, and has a retainer receiving recess for setting a retainer on one side facing an oil pressure chamber. When the tensioner is subjected to an excessive load and the oil pressure inside the oil pressure chamber rises, the ball seat and the retainer are reliably prevented from being displaced, and thus performance degradation of the check valve is prevented with a simple structure. 
         [0016]    Since the retainer receiving recess is formed in the ball seat, the check ball and the retainer can be assembled to the ball seat and thus the check valve can be in one piece, which allows handling of the check valve as a single unit during assembly of the tensioner and enables the assembling work to be achieved easily. 
         [0017]    Displacement of the retainer and others that may occur by a buildup of oil pressure inside the oil pressure chamber can be prevented irrespective of the strength with which the retainer fits in the retainer receiving recess, and therefore the machining precision requirements for the retainer and retainer receiving recess can be kept low. 
         [0018]    According to another aspect of the present invention, an inner spring that is in contact with the retainer and urges the retainer toward the ball seat is set radially inside the coil spring that is set inside the oil pressure chamber and urges the plunger toward the front side. The inner spring is set this way by making efficient use of the space radially inside of the coil spring, whereby the retainer can be installed stably relative to the ball seat. Also, since the retainer need not be fixedly attached to the ball seat by press-fitting or the like, the degree of design freedom of the check valve is increased. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a cross-sectional view illustrating a tensioner according to a first embodiment of the present invention; 
           [0020]      FIG. 2  is a perspective view illustrating a check valve assembled into the tensioner shown in  FIG. 1 ; 
           [0021]      FIG. 3  is an exploded perspective view of the check valve; 
           [0022]      FIG. 4  is a cross-sectional view illustrating a tensioner according to a second embodiment of the present invention; 
           [0023]      FIG. 5  is a cross-sectional view illustrating a conventional tensioner; and 
           [0024]      FIG. 6  is a cross-sectional view illustrating another conventional tensioner. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    A tensioner  10  according to a first embodiment of the present invention will be described with reference to the drawings. 
         [0026]    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 passed over a plurality of sprockets via a tensioner lever to reduce vibration during the drive. 
         [0027]    The tensioner  10  includes, as shown in  FIG. 1 , a plunger  20  having a plunger hole  21  that is opened to a rear side, a housing  30  having a plunger bore  31  for accommodating the plunger  20 , a coil spring  40  that is biasing unit accommodated inside an oil pressure chamber  11  formed between the plunger bore  31  and the rear end of the plunger  20  such as to be able to expand and contract and to urge the plunger  20  toward a front side, and a check valve  50  that allows the oil to flow into the oil pressure chamber  11  and prevents the oil from flowing out from the oil pressure chamber  11 . 
         [0028]    Hereinafter, various constituent elements of the tensioner  10  will be described with reference to the drawings. 
         [0029]    The plunger  20  is made of metal such as iron or the like and inserted in the plunger bore  31  such as to move back and forth in the front to back direction, as shown in  FIG. 1 . 
         [0030]    The housing  30  is made of aluminum alloy, synthetic resin or the like, and includes, as shown in  FIG. 1 , the cylindrical plunger bore  31  that is opened to the front side, a cylindrical valve accommodating hole  32  formed continuously on the rear side of the plunger bore  31  and having a smaller diameter than that of the plunger bore  31 , and an oil supply hole  33  that extends through an outer wall of the housing  30  all the way into the valve accommodating hole  32 . This oil supply hole  33  functions as a part that supplies oil from the outside of the housing  30  into the oil pressure chamber  11 . 
         [0031]    The coil spring  40  has one end abutting on the bottom of the plunger hole  21  (front side portion of the plunger  20 ) and the other end arranged in contact with the bottom of the plunger bore  31 . 
         [0032]    As shown in  FIG. 1 , the check valve  50  allows the oil to flow in from the outside of the housing  30  through the oil supply hole  33  into the oil pressure chamber  11 , and prevents the oil from flowing out from the oil pressure chamber  11  through the oil supply hole  33 . As shown in  FIG. 1 , the check valve is disposed inside the valve accommodating hole  32 . 
         [0033]    As shown in  FIGS. 1 to 3 , the check valve  50  is made up of a spherical check ball  51 , a ball seat  52  having a check ball holding part  52   a  that is opened to the side facing the oil pressure chamber  11  (front side in this embodiment), a retainer  53  that restricts the movement of the check ball  51 , and a ball spring  54  disposed between the check ball  51  and the retainer  53 . These components of the check valve  50  are made of metal or the like. 
         [0034]    The ball seat  52  is press-fitted into the valve accommodating hole  32  of the housing  30  and thus fixed to the housing  30 , as shown in  FIG. 1 . The ball seat  52  may be fixed to the housing  30  by other means than press-fitting. The ball seat  52  includes, as shown in  FIGS. 1 to 3 , the check ball holding part  52   a,  a retainer receiving recess  52   b  formed continuously on the front side of the check ball holding part  52   a,  and an oil hole  52   c  that extends from the check ball holding part  52   a  to the rear side of the ball seat  52 . 
         [0035]    The retainer receiving recess  52   b  has a larger diameter than that of the check ball holding part  52   a  as shown in  FIG. 1 , while the oil hole  52   c  has a smaller diameter than that of the check ball holding part  52   a.  The step between the check ball holding part  52   a  and the oil hole  52   c  (bottom of the check ball holding part  52   a ) functions as a ball seat part  52   d  for the check ball  51  to sit on in annular tight contact therewith. 
         [0036]    The retainer  53  is press-fitted in the retainer receiving recess  52   b,  as shown in  FIG. 1 . As shown in  FIGS. 1 to 3 , the retainer  53  has a plurality of oil holes  53   a  that extend through in the front to back direction, and a spring support part  53   b  that protrudes from the rear face of a top plate of the retainer  53  toward the rear side. 
         [0037]    The ball spring  54  is arranged to fit around the spring support part  53   b  as shown in  FIG. 1  and urges the check ball  51  toward the ball seat part  52   d.  This ball spring  54  is not an essential constituent element and may not be needed depending on the embodiment. 
         [0038]    Next, a tensioner  10  according to a second embodiment of the present invention will be described with reference to  FIG. 4 . The second embodiment is, in part, exactly the same as the previously described first embodiment. Therefore, the configuration will not be described again except for different features. 
         [0039]    In the tensioner  10  of the second embodiment, as shown in  FIG. 4 , the check valve  50  is set inside the plunger hole  21 . Therefore, the internal space formed between the housing  30  and the plunger  20  is divided into the oil pressure chamber  11  on the rear side and an oil reservoir chamber  12  on the front side. 
         [0040]    The plunger  20  includes a connection/adjustment groove  22  formed in an outer circumferential surface thereof, and a through hole  23  for supplying oil from the connection/adjustment groove  22  into the oil reservoir chamber  12 . The housing  30  includes an oil supply hole (not shown) that extends through the outer wall of the housing  30  all the way into the valve accommodating hole  32 . These connection/adjustment groove  22 , through hole  23 , and oil supply hole (not shown) function as an oil supply part that supplies oil from the outside of the housing  30  into the oil reservoir chamber  12 . The connection/adjustment groove  22  may be formed at least in one of the outer circumferential surface of the plunger  20  and an inner circumferential surface of the plunger bore  31 . The oil supply part for supplying oil from the outside of the housing  30  into the oil reservoir chamber  12  is not limited to the specific form described above. 
         [0041]    Moreover, in the tensioner  10  of the second embodiment, as shown in  FIG. 4 , the inner spring  41  pressing the retainer  53  toward the ball seat  52  and being in contact with the retainer  53  is set radially inside the coil spring  40 . The inner spring  41  has one end in contact with the retainer  53  and the other end in contact with the bottom of the plunger bore  31 . 
         [0042]    In the tensioner  10  of the second embodiment, as shown in  FIG. 4 , a step  24  is formed in an inner wall portion of the plunger hole  21 , and this step  24  restricts the movement of the ball seat  52  toward the front side. With this step  24 , the check valve  50  is prevented from moving toward the front side due to the urging forces of the coil spring  40  and inner spring  41 . 
         [0043]    While the ball seat  52  is fixed to the plunger  20  in the manner described above in the embodiment, the ball seat  52  can be fixed to the plunger  20  by any other means, such as press-fitting the ball seat  52  into the plunger hole  21 . 
         [0044]    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. 
         [0045]    For example, various configurations of the embodiments described above may be freely combined to form other tensioners. 
         [0046]    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. 
         [0047]    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. 
         [0048]    The tensioner may not necessarily be applied to a transmission mechanism with a transmission chain but can also be 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. 
         [0049]    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 housing. 
         [0050]    While the retainer is press-fitted into the retainer receiving recess formed on one side of the ball seat facing the oil pressure chamber in the embodiments described above, installation of the retainer is not limited to the manner described above, and the retainer may simply be set inside the retainer receiving recess, when there is provided an inner spring, etc.