Abstract:
Provided is a simple-structured tensioner that can reduce processing and assembling workload as well as increase the degree of design freedom. A tensioner  10  includes an oil supply hole  33  formed in a sleeve bottom  32  and a check valve  50  disposed on a front face of the sleeve bottom  32 . The check valve  50  includes a check ball  51  and a retainer  52 . The sleeve bottom  32  includes a ball seat  34  which protrudes in a cylindrical shape toward the front side integrally with and continuously from the edge of the oil supply hole  33  and on which the check ball  51  is seated.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a tensioner that provides 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  510  used in such a chain guide mechanism includes, as shown schematically in  FIG. 4 , a tensioner body  520  having a body hole  521  that is open on one side, a plunger  540  slidably inserted in the body hole  521 , and a biasing unit  560  that biases the plunger  540  toward a front side (see, for example, Japanese Patent Application Laid-open No. 2009-002495). 
         [0006]    In such a tensioner  510 , oil is supplied to an oil pressure chamber  511  formed between the body hole  521  and the plunger  540 , so that the plunger  540  is biased toward the front side by the oil in the oil pressure chamber  511 . As the plunger  540  reciprocates, the oil flows through the small gap between the plunger  540  and the body hole  521 , and the flow resistance provides the damping effect of slowing down the reciprocal movement of the plunger  540 . A check valve  550  (schematically shown as a check ball alone) is disposed in the body hole  521 . The check valve  550  allows the oil to flow in from the outside into the oil pressure chamber  511 , and prevents the oil from flowing out from an oil supply hole  522 . 
         [0007]    One problem with the tensioner  510  is that, since the tensioner body  520  is a die-cast product made of cast iron or aluminum alloy, the body hole  521  in which the plunger  540  slides needs to be subjected to film formation by coating, or smoothing, or machining and the like, in order to achieve surface precision and durability for the purpose of preventing wear and seizure of the plunger  540 . When the tensioner body  520  and the plunger  540  are made from different materials, there will be a difference in the degree of thermal deformation, and this difference in thermal deformation may adversely affect the sliding properties or damping characteristics of the plunger  540  relative to the tensioner body  520 . 
         [0008]    It has been proposed to use a metal sleeve, which is a separate component, to be interposed between the inner circumferential surface of the body hole and the outer circumferential surface of the plunger so as to allow selection of material for the tensioner body and to achieve a certain degree of design freedom with respect to the treatment of the inner circumferential surface of the body hole (see, for example, Japanese Patent Application. Laid-open No. 2002-206603). 
         [0009]    In this tensioner described in Japanese Patent Application Laid-open No. 2002-206603, a hole is formed in the tensioner body with a smaller diameter than that of the body hole to be used as a part for setting a check valve in position. 
         [0010]    In some designs of use that are adopted in recent years, the tensioner body is not attached to an engine block but instead a sleeve is directly attached to the engine block. In such a case, a check valve  650  should desirably be accommodated also inside a sleeve  630  as shown in an example for reference of  FIG. 5  to facilitate the work of attaching the tensioner to the engine block. 
         [0011]    In the tensioner  610  shown in  FIG. 5 , a counterbore is formed in the front face of the sleeve bottom  632  to provide a sleeve recess  632   a,  and a ball seat  653  on which a check ball  651  is seated is disposed in this sleeve recess  632   a.  The check ball  651  is seated at the front end of the ball seat  653 . The movement of the check ball  651  is restricted by disposing a retainer  652  on the front side of the check ball  651 . 
       SUMMARY OF THE INVENTION 
       [0012]    In the tensioner  610  shown in  FIG. 5 , however, there is a risk that, if there is formed a gap between the sleeve recess  632   a  and the ball seat  653 , the oil may leak out from the gap. The problem is that, the respective seal surfaces of the sleeve recess  632   a  and the ball seat  653  (more specifically, the bottom face of the sleeve recess  632   a  and the lower face of the ball seat  653 ) must be formed highly precisely. 
         [0013]    The ball seat  653  must be pressed toward the rear side by a biasing unit  660  (coil spring  660  in the example shown in  FIG. 5 ) because if the ball seat  653  moves up from the sleeve recess  632   a,  there will be formed a gap between the sleeve recess  632   a  and the ball seat  653 . As a result, the degree of design freedom is compromised and the assembling work of the tensioner  610  is made more difficult. There is also a possibility of a gap being formed between the sleeve recess  632   a  and the ball seat  653  if the coil spring  660  loses some of its spring force due to elongation of the chain or by some other factors. 
         [0014]    The present invention is directed at solving these problems and it is an object of the invention to provide a simple-structured tensioner that can reduce the processing and assembling workload as well as increase the degree of design freedom. 
         [0015]    The present invention solves the problems described above by providing a tensioner including: a sleeve having a sleeve bottom on a rear side; a plunger inserted in the sleeve so as to be able to move forward and backward along an axial direction of the sleeve; and a biasing unit that is accommodated so as to be able to expand and contract inside an oil pressure chamber formed between a rear end of the sleeve and a rear end of the plunger and that biases the plunger toward a front side. An oil supply hole is formed in the sleeve bottom. A check valve for preventing oil from flowing out from the oil supply hole is disposed on a front face of the sleeve bottom. The check valve includes a check ball, and a retainer disposed on the front face of the sleeve bottom and restricting movement of the check ball. The sleeve bottom includes a ball seat which protrudes in a cylindrical shape toward the front side integrally with and continuously from an edge of the oil supply hole and on which the check ball is seated. 
         [0016]    According to one aspect of the present invention, the sleeve bottom includes a ball seat which protrudes in a cylindrical shape toward the front side integrally with and continuously from an edge of the oil supply hole and on which the check ball is seated. Thereby, the number of component parts is reduced and the operation workload associated with the assembling work is reduced. In addition, since the risk of oil leakage through between the sleeve and the ball seat can be eliminated, the degree of precision required in the formation of various constituent elements is lowered. Also, since there is no need to consider the possibility of the ball seat being lifted up, a biasing unit for pressing the ball seat against the sleeve bottom is not necessary, and accordingly the degree of design freedom can be increased. 
         [0017]    The ball seat is formed in the sleeve bottom that has a smaller thickness, and protrudes in a cylindrical shape toward the front side integrally with and continuously from an edge of the oil supply hole. Therefore, the ball seat can be formed by a drawing process, and so the production workload can be reduced. 
         [0018]    The check valve is disposed inside the sleeve, so that, after the plunger and check valve have been installed in the sleeve, these components can be handled as one unit. Therefore, the operation workload associated with the attachment work even when the sleeve is directly attached to the engine block or the like can be reduced. 
         [0019]    According to another aspect of the present invention, a tapered portion with its diameter increasing from the front side toward the rear side is formed on the rear side of the oil supply hole, so that the oil can be smoothly supplied from the outside into the oil supply hole. When the ball seat is formed by a drawing process, such a tapered portion can be formed on the rear side of the oil supply hole without performing any additional process, so that an increase in the production workload can be avoided. 
         [0020]    According to another aspect of the present invention, the ball seat and the skirt decrease in diameter from the front side toward the rear side. Therefore, in assembling the tensioner, the check ball and the retainer can be retained to the sleeve by fitting the retainer onto the ball seat after disposing the check ball on the ball seat, and thus the plunger, coil spring, and others can be assembled easily into the sleeve. 
         [0021]    According to another aspect of the present invention, the skirt includes a plurality of circumferentially arranged slits extending from a rear end of the skirt toward the front side. As the slits allow the skirt of the retainer to be radially elastically expanded, the retainer can be fitted onto the ball seat easily. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is an illustrative diagram showing a timing system in which a tensioner according to one embodiment of the present invention is incorporated; 
           [0023]      FIG. 2  is a cross-sectional view illustrating the tensioner; 
           [0024]      FIG. 3  is a cross-sectional perspective view illustrating the rear end of a sleeve; 
           [0025]      FIG. 4  is a cross-sectional view illustrating a conventional tensioner; and 
           [0026]      FIG. 5  is a cross-sectional view illustrating an example of a tensioner for reference. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    A tensioner  10  according to one embodiment of the present invention will be described with reference to the drawings. 
         [0028]    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. As shown in  FIG. 1 , the tensioner is attached to an engine block (not shown) to apply appropriate tension to the slack side of a transmission chain CH passing over a plurality of sprockets S 1  to S 3  via a tensioner lever G to reduce vibration during the drive. 
         [0029]    The tensioner  10  includes, as shown in  FIG. 1  to  FIG. 3 , a tensioner body  20  having a body hole  21 , a sleeve  30  inserted in the body hole  21 , a plunger  40  inserted in the sleeve  30  so as to be able to move forward and backward along the axial direction of the sleeve  30 , a check valve  50 , and a coil spring  60  as a biasing unit that is accommodated so as to be able to expand and contract inside an oil pressure chamber  11  formed between the rear end of the sleeve  30  and the rear end of the plunger  40  and that biases the plunger  40  toward a front side (protruding side). 
         [0030]    Hereinafter, various constituent elements of the tensioner  10  will be described with reference to the drawings. 
         [0031]    The tensioner body  20  is made from an aluminum alloy, synthetic resin, and the like, and includes, as shown in  FIG. 1 , the body hole  21  that is open, on one (front) end, an oil supply hole  22  that extends through an outer wall of the tensioner body  20  to the body hole  21 , and a mounting part  23  having a mounting hole for a bolt or the like to be passed through to secure the tensioner body  20  to an engine block. 
         [0032]    The sleeve  30  is made from a metal such as iron or the like and includes the cylindrical sleeve body  31 , and a sleeve bottom  32  formed integrally at the rear end of the sleeve body  31 , as shown in  FIG. 2  and  FIG. 3 . 
         [0033]    As shown in  FIG. 2  and  FIG. 3 , an oil supply hole  33  is formed in the sleeve bottom  32  for supplying oil into the oil pressure chamber  11  from the outside. This oil supply hole  33  communicates with the oil supply hole  22  of the tensioner body  20  with the sleeve  30  being disposed in the tensioner body  20 . 
         [0034]    In the sleeve bottom  32  is also formed, as shown in  FIG. 2  and  FIG. 3 , a ball seat  34  protruding in a cylindrical shape toward the front side integrally with and continuously from the edge of the oil supply hole  33 . This ball seat  34  functions as a seat for the check ball  51  of a check valve  50  which will sit on the front end thereof. The ball seat  34  is formed by a drawing process wherein the sleeve bottom  32  is pressed from the rear face toward the front face, and as a result of this drawing process, a tapered portion  33   a  with its diameter increasing from the front side toward the rear side is formed on the rear side of the oil supply hole  33 . The ball seat  34  decreases in diameter from the front side toward the rear side. 
         [0035]    The plunger  40  is made from a metal such as iron or the like and has a plunger hole  41  inside, which is open on the rear side as shown in  FIG. 2  and  FIG. 3 . 
         [0036]    The check valve  50  allows the oil to flow in from the outside through the oil supply holes  22  and  33  into the oil pressure chamber  11 , and prevents the oil from flowing out from the oil supply holes  22  and  33 . As shown in  FIG. 2  and  FIG. 3 , the check valve is disposed on the front face of the sleeve bottom  32 . 
         [0037]    As shown in  FIG. 2  and  FIG. 3 , the check valve  50  is made up of a spherical check ball  51  that is seated on the front end of the ball seat  34  to be capable of tightly contacting therewith, a retainer  52  attached on the front face of the sleeve bottom  32  to restrict the movement of the check ball  51 , and a ball spring (not shown) disposed between the check ball  51  and the retainer  52 . The ball spring (not shown) is provided to bias the check ball  51  toward the ball seat  34 , but the ball spring (not shown) may not necessarily be provided. The check ball  51  and the retainer  52  are made of metal. 
         [0038]    The retainer  52  includes, as shown in  FIG. 2  and  FIG. 3 , a substantially disc-like top  52   a  disposed on the front side of the check ball  51 , a skirt  52   b  extending vertically downward toward the rear side from the peripheral edge of the top  52   a  and arranged on the radially outer side of the ball seat  34 , and a plurality of flanges  52   c  extending radially outward from the rear end of the skirt  52   b.  The skirt  52   b  decreases in diameter from the front side toward the rear side, and includes a plurality of circumferentially arranged slits  52   d  extending from the rear end toward the front side (front end) of the skirt  52   b.    
         [0039]    The coil spring  60  is disposed such that its front end is in contact with the bottom of the plunger hole  41  of the plunger  40  while its rear end is in contact with the front face of the flanges  52   c  of the retainer  52 , and configured to bias the plunger  40  toward the front side, as shown in  FIG. 2  and  FIG. 3 . 
         [0040]    While the coil spring  60  is disposed such that its rear end is in contact with the flanges  52   c  of the retainer  52  in this embodiment, the way how the rear end of the coil spring  60  is disposed is not limited to the example described above. For example, the rear end of the coil spring  60  may be disposed on the radially outer side of the flanges  52   c  without making contact therewith. 
         [0041]    While 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. 
         [0042]    For example, 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. 
         [0043]    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. 
         [0044]    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. 
         [0045]    In the embodiment described above, the sleeve is disposed inside the tensioner body that is attached to a part in the surroundings of the tensioner such as an engine block or the like. Instead, the sleeve may be directly attached to the engine block or the like.