Abstract:
Provided is a simple-structured tensioner that can reduce processing and assembling workload and maintain the tensioner performance constant, as well as store a sufficient amount of oil. The tensioner includes a plunger  20 , a housing  30 , an inner sleeve  40 , a check valve  50 , and a biasing unit  60 . The inner sleeve  40  includes a cylindrical body  41  having an inner part that serves as an oil reservoir chamber  13 , a sleeve bottom  42  formed at one end of the cylindrical body  41 , an oil hole  43  formed in the sleeve bottom  42 , and a ball seat  44  which protrudes in a cylindrical shape toward an oil pressure chamber  12  integrally with and continuously from an edge of the oil hole  43  and on which a 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, for example, as shown schematically in  FIG. 6 , a housing  530  having a cylindrical plunger bore  531  that is open on a front side, a cylindrical plunger  520  slidably inserted in the plunger bore  531 , and a biasing unit that biases the plunger  520  toward the front side. The biasing unit is formed by a coil spring  560  accommodated inside a plunger hole  521  of the cylindrical plunger  520  and compressed between the plunger and the housing bottom  532 . 
         [0006]    Oil is supplied from an oil supply hole  533  formed in the housing  530 , so that an oil pressure chamber  512  formed between the plunger bore  531  and the plunger  520  is filled with the oil, which oil biases the plunger  520  toward the front side. A check valve  550  (schematically shown only as a check ball) prevents the oil from flowing out from the oil supply hole  533 . As the plunger  520  reciprocates, the oil flows through the small gap between the plunger  520  and the plunger bore  531 , and the flow resistance provides the damping effect of slowing down the reciprocal movement of the plunger  520 . 
         [0007]    In such a known tensioner  510 , when let stand for a long time after the oil supply is stopped (in the case with an engine, after the engine is stopped), there is a time lag before the oil is supplied immediately after the next start-up, and as no oil is replenished but the oil in the oil pressure chamber  512  only leaks out when the plunger  520  moves back and forth, there occurs a shortage of oil in the oil pressure chamber  512 . Because of this shortage of oil, the damping force of the oil does not act on the plunger  520 , which sometimes may lead to vibration and abnormal noise of the timing chain, or damage on the timing chain. 
         [0008]    Therefore, a tensioner is known, such as the tensioner  610  of Japanese Patent Application Laid-open No. 2008-215553 shown in FIG. 7, which is designed to have an oil reservoir chamber  613  inside the plunger  620  to supply oil into the oil pressure chamber  612  from the oil reservoir chamber  613 . A constant amount of oil is retained in the oil reservoir chamber  613  such as not to leak out, so that, even immediately after the start-up after a long stop, the oil remaining in the oil reservoir chamber  613  is supplied to the oil pressure chamber  612 , to maintain the damping force of oil for the plunger  620 , reduce vibration and prevent damage of the chain. 
         [0009]    In the tensioner  610  shown in  FIG. 7 , an inner sleeve  640  is disposed inside the plunger hole  621  on the rear side, so that an internal space formed between the housing  630  and the plunger  620  is divided by the inner sleeve  640  into the oil pressure chamber  612  on the front side and the oil reservoir chamber  613  on the rear side. A check valve  650  is disposed on one side of the inner sleeve  640  facing the oil pressure chamber  612  for preventing the oil from flowing reversely from the oil pressure chamber  612  into the oil reservoir chamber  613 , so that a constant amount of oil is retained in the oil reservoir chamber  613  without leakage, and even immediately after the start-up after a long stop, the oil remaining in the oil reservoir chamber  613  is supplied to the oil pressure chamber  612 . 
         [0010]    In this tensioner  610 , a cylindrical ball seat  644  on which a check ball  651  is seated is press-fitted to the front end of the inner sleeve  640  that faces the oil pressure chamber  612 . As a result, unlike the case where the ball seat  644  is fixed to the inner sleeve  640  with the use of a biasing force of a coil spring  660 , the inner sleeve  640  and the check valve  650  can be assembled together easily. 
       SUMMARY OF THE INVENTION 
       [0011]    In the tensioner  610  described in Japanese Patent Application Laid-open No. 2008-215553, the stroke of the check ball  651  varies depending on the protruding length L of the ball seat  644  from the front end of the inner sleeve  640 , as shown in  FIG. 7 . This protruding length L must therefore be controlled precisely. However, the problem is that controlling this protruding length L precisely is difficult when the ball seat  644  is press-fitted to the inner sleeve  640 . 
         [0012]    In order to firmly attach the ball seat  644  to the inner sleeve  640 , an amount of insertion S by which the ball seat  644  is inserted into the inner sleeve  640  needs to be at least a certain amount. This leads to another problem that, if a sufficient amount of insertion S is secured, the space inside the oil reservoir chamber  613  will be reduced by that amount. 
         [0013]    Since the ball seat  644  is press-fitted to the inner sleeve  640 , the ball seat  644  and the inner sleeve  640  must be designed to have a large thickness to ensure their strength, which leads to another problem that the available space inside the oil reservoir chamber  613  is compromised. 
         [0014]    The ball seat  644  may be displaced from its set position relative to the inner sleeve  640 , or come off of the inner sleeve  640  when a high pressure is applied from the oil reservoir chamber  613  to the ball seat  644 . Hence another problem that the tensioner  610  may not be fit for use in a car engine where such a high pressure may be input. 
         [0015]    When the inner sleeve  640  and the ball seat  644  are made from different materials, there will be a difference in the degree of thermal deformation, and this difference in thermal deformation may result in a misalignment between the inner sleeve  640  and the ball seat  644  and change the tensioner performance. 
         [0016]    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 and maintain the tensioner performance constant, as well as store a sufficient amount of oil. 
         [0017]    The present invention solves the problems described above by providing a tensioner including: a plunger having a plunger hole that is open on a rear side; a housing having a plunger bore that is open on a front side and accommodates the plunger; an inner sleeve disposed inside the plunger hole and dividing an internal space formed between the housing and the plunger into an oil pressure chamber and an oil reservoir chamber; a check valve disposed inside the plunger hole and preventing oil from flowing reversely from the oil pressure chamber into the oil reservoir chamber; and a biasing unit that biases the plunger toward the front side. The check valve includes a check ball. The inner sleeve includes a cylindrical body having an inner part that serves as the oil reservoir chamber, a sleeve bottom formed at one end of the cylindrical body, an oil hole formed in the sleeve bottom, and a ball seat which protrudes in a cylindrical shape toward the oil pressure chamber integrally with and continuously from an edge of the oil hole and on which the check ball is seated. 
         [0018]    According to one aspect of the present invention, the inner sleeve includes a ball seat protruding in a cylindrical shape toward the oil pressure chamber integrally with and continuously from the edge of the oil hole. By forming the cylindrical body and the ball seat integrally, the number of components and assembling workload can be reduced. Moreover, since the protruding length of the ball seat from the distal end of the cylindrical body can be readily controlled with high precision, variations in the stroke of the check ball for each tensioner can be prevented. Also, even when a high pressure is applied to the ball seat or when the temperature inside the car engine is high, the ball seat can be prevented from being displaced from or come off of the cylindrical body, so that the tensioner performance can be maintained constant. 
         [0019]    Moreover, since the cylindrical body and the ball seat are formed integrally, the length of an overlapping portion between the cylindrical body and the ball seat in the front to back direction can be reduced as compared to when the ball seat is press-fitted to the inner sleeve, and also, the inner sleeve can foe designed thinner. Accordingly, the oil reservoir chamber can have a larger space to store more oil. 
         [0020]    The ball seat is formed in the sleeve bottom that has a smaller thickness, and protrudes in a cylindrical shape toward the oil pressure chamber integrally with and continuously from the edge of the oil hole. Therefore, the ball seat can be formed by a drawing process, and so the production workload can be reduced. 
         [0021]    According to another aspect of the present invention, the oil hole includes, on one side close to the oil reservoir chamber, a diameter-reduced portion with a diameter thereof decreasing from the side close to the oil reservoir chamber toward the oil pressure chamber. Thus the oil can be smoothly supplied from the oil reservoir chamber into the oil pressure chamber. When the ball seat is formed by a drawing process, such a diameter-reduced portion can be formed on one side of the oil hole facing the oil reservoir chamber without performing any additional process, so that an increase in the production workload can be avoided. 
         [0022]    According to another aspect of the present invention, the housing includes a housing oil supply hole for supplying oil to the oil reservoir chamber. Therefore, also in tensioners designed to have an oil reservoir chamber on the rear side of the oil pressure chamber, the oil can be supplied smoothly from the outside of the tensioner into the oil reservoir chamber. 
         [0023]    According to another, aspect of the present invention, a connection/adjustment indentation is formed at least in one of an outer circumferential surface of the plunger and an inner circumferential surface of the plunger bore. The housing includes a housing oil supply hole for supplying oil to the connection/adjustment indentation. The plunger includes a plunger oil supply hole for supplying oil from the connection/adjustment indentation into the plunger hole. The inner sleeve includes a sleeve oil supply hole that connects the plunger oil supply hole with the oil reservoir chamber. Therefore, also in tensioners designed to have an oil reservoir chamber on the front side of the oil pressure chamber, the oil can be supplied smoothly from the outside of the tensioner into the oil reservoir chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a cross-sectional view illustrating a tensioner according to a first embodiment of the present invention; 
           [0025]      FIG. 2  is a perspective view illustrating an inner sleeve with a check valve mounted therein; 
           [0026]      FIG. 3  is a perspective view illustrating the inner sleeve; 
           [0027]      FIG. 4  is an illustrative diagram for explaining various dimensions of the inner sleeve; 
           [0028]      FIG. 5  is a cross-sectional view illustrating a tensioner according to a second embodiment of the present invention; 
           [0029]      FIG. 6  is a cross-sectional view schematically illustrating a conventional tensioner; and 
           [0030]      FIG. 7  is a cross-sectional view illustrating another conventional tensioner. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    A tensioner  10  according to a first embodiment of the present invention will be described with reference to the drawings. 
         [0032]    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. 
         [0033]    The tensioner  10  includes, as shown in  FIG. 1 , a plunger  20  having a plunger hole  21  that is open on a rear side, a housing  30  having a plunger bore  31  that is open on a front side and accommodates the plunger  20 , an inner sleeve  40  slidably set inside the plunger hole  21 , a check valve  50  disposed inside the plunger hole  21 , and a coil spring  60  as a biasing unit disposed inside the plunger hole  21  to bias the plunger  20  toward the front side. 
         [0034]    The housing  30  includes, as shown in  FIG. 1 , the plunger bore  31 , a housing bottom  32  formed on the rear side, and a housing oil supply hole  33  formed in the housing bottom  32  to supply oil from the outside into an oil reservoir chamber  13 . 
         [0035]    The inner sleeve  40  is made from a metal such as iron or the like and includes, as shown in  FIG. 1 , a cylindrical body  41 , the inside of which functions as the oil reservoir chamber  13 , a sleeve bottom  42  formed at the front end of the cylindrical body  41 , an oil hole  43  formed in the sleeve bottom  42 , and a ball seat  44  protruding in a cylindrical shape toward the front side (toward the oil pressure chamber  12 ) integrally with and continuously from the edge of the oil hole  43 . 
         [0036]    The ball seat  44  functions as a seat for a check ball  51  to sit on the front side thereof. The ball seat  44  is formed by a drawing process wherein the sleeve bottom  42  is pressed from the rear face toward the front face, and as a result of this drawing process, a diameter-reduced portion  43   a  is formed on the rear side of the oil hole  43  (on the side close to the oil reservoir chamber  13 ) as shown in  FIG. 1 , the diameter-reduced portion  43   a  having a diameter decreasing from the rear side toward the front side. The cylindrical body  41  and the sleeve bottom  42  may also be formed by a drawing process. 
         [0037]    The inner sleeve  40  is set inside the plunger hole  21 , with the sleeve bottom  42  oriented toward the front side, as shown in  FIG. 1 . The inner sleeve  40  is biased toward the rear side by the coil spring  60  arranged between the plunger bottom  22  and the sleeve bottom  42 , so that the rear end of the cylindrical body  41  is in contact with the front face of the housing bottom  32 . An internal space  11  formed between the housing  30  and the plunger  20  is divided by the inner sleeve  40  into the oil pressure chamber  12  on the front side and the oil reservoir chamber  13  on the rear side. 
         [0038]    The check valve  50  allows the oil to flow in from the oil reservoir chamber  13  into the oil pressure chamber  12 , and prevents the oil from flowing reversely from the oil pressure chamber  12  into the oil reservoir chamber  13 . As shown in  FIG. 1 , the check valve is disposed on the front side of the sleeve bottom  42 . 
         [0039]    As shown in  FIG. 1 , the check valve  50  is made up of a spherical check ball  51  that is seated on the front end of the ball seat  44  to be capable of tightly contacting therewith, a retainer  52  that restricts the movement of the check ball  51 , and a ball spring  53  disposed between the check ball  51  and the retainer  52  for biasing the check ball  51  toward the rear side (toward the ball seat  44 ). The ball spring  53  is not an essential constituent element and may not be needed depending on the embodiment. 
         [0040]    The retainer  52  includes, as shown in  FIG. 1  and  FIG. 2 , 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 fitted on the radially outer side of the ball seat  44 , and a flange  52   c  extending radially outward from the rear end of the skirt  52   b.  The skirt  52   b  and the flange  52   c  include a plurality of circumferentially arranged slits extending in a front to back direction. 
         [0041]    The coil spring  60  is accommodated in the oil pressure chamber  12  so as to freely expand and contract as shown in  FIG. 1 , more specifically the coil spring  60  is disposed between the rear face of the plunger bottom  22  and the front side of the sleeve bottom  42  (front face of the flange  52   c  of the retainer  52 ). 
         [0042]    In the tensioner  10  of this embodiment, the inner sleeve  40  includes a ball seat  44  protruding in a cylindrical shape toward the oil pressure chamber  12  integrally with and continuously from the edge of the sleeve bottom  42 . Therefore, as shown in  FIG. 4 , the protruding length L of the ball seat  44  from the distal end of the cylindrical body  41  can be readily controlled with high precision, which helps prevent the stroke of the check ball  51  from varying for each tensioner  10 . 
         [0043]    Moreover, since the cylindrical body  41  and the ball seat  44  are formed integrally, the length S of an overlapping portion between the cylindrical body  41  and the ball seat  44  in the front to back direction can be reduced as compared to when the ball seat  644  is pressed into the inner sleeve  640  as shown in  FIG. 4 . Accordingly, the oil reservoir chamber  13  can have a larger space that is increased by the difference P and can store more oil. 
         [0044]    Next, a tensioner  10  according to a second embodiment of the present invention will be described with reference to  FIG. 5 . The second embodiment is, in part, exactly the same as the previously described first embodiment. Therefore, the configuration other than different features will not be described again. 
         [0045]    In the tensioner  10  of the second embodiment, as shown in  FIG. 5 , the inner sleeve  40  is disposed inside the plunger hole  21  such that, the sleeve bottom  42  is oriented toward the rear side. 
         [0046]    The inner sleeve  40  is biased toward the front side by the coil spring  60  arranged between the sleeve bottom  42  and the housing bottom  32 , so that the front end of the cylindrical body  41  is in contact with the rear face of the plunger bottom  22 . 
         [0047]    All internal space  11  formed between the housing  30  and the plunger  20  is divided by the inner sleeve  40  into the oil pressure chamber  12  on the rear side and the oil reservoir chamber  13  on the front side. 
         [0048]    The check valve  50  is disposed on the rear side of the sleeve bottom  42 . 
         [0049]    In the second embodiment, various passages described below are formed to supply oil from the outside of the housing  30  into the oil reservoir chamber  13 . 
         [0050]    The plunger  20  includes, as shown in  FIG. 5 , a connection/adjustment indentation  23  formed in the outer circumferential surface thereof so as to extend all around or over a circumferential part thereof, and a plunger oil supply hole  24  extending from the outer circumferential surface through to the inner circumferential surface so as to supply the oil from the connection/adjustment indentation  23  into the plunger hole  21 . 
         [0051]    The housing  30  includes a housing oil supply hole  33  extending from the outside of the housing  30  through to the plunger bore  31  to supply oil from the outside to the connection/adjustment indentation  23 . 
         [0052]    The inner sleeve  40  includes a sleeve oil supply hole  45  that connects the oil reservoir chamber  13  with the plunger oil supply hole  24 . This sleeve oily supply hole  45  is formed by a small-diameter part  45   a  on the outer circumference of the cylindrical body  41  and a plurality of cut-out portions  45   b  at the front end of the cylindrical body  41 . 
         [0053]    The sleeve oil supply hole  45  may have any specific design as long as it connects the oil reservoir chamber  13  with the plunger oil supply hole  24 . For example, it may be a hole extending through the cylindrical body  41  from the inner circumferential surface to the outer circumferential surface thereof. 
         [0054]    While the connection/adjustment indentation  23  is formed in the outer circumferential surface of the plunger  20  in the description above, this connection/adjustment indentation  23  may be formed on at least one of the outer circumferential surface of the plunger  20  and the inner circumferential surface of the plunger bore  31 . 
         [0055]    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. 
         [0056]    For example, various configurations of several embodiments described above may be freely combined to form other tensioners. 
         [0057]    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. 
         [0058]    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. 
         [0059]    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. 
         [0060]    While the housing accommodating the plunger is described as the component known as a tensioner body 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 tensioner body.