Abstract:
In a hydraulic tensioner, an oil pressure control recess, at a proximal end of a cylindrical, plunger-receiving hole, receives from an oil supply, and also receives oil which oozes past a check valve and an inner sleeve inside the plunger, thereby returning the oil, which would leak to the outside in a conventional hydraulic tensioner, to the interior of the plunger.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a tensioner for applying tension to a chain or belt used as a transmission medium for transmitting power between a crankshaft and a camshaft in the timing system of an internal combustion engine.  
       BACKGROUND OF THE INVENTION  
       [0002]     As shown in  FIG. 5 , a conventional hydraulic tensioner  500  comprises a plunger  510  having a hollow portion  511  with a closed end  511   b , and open toward the inside of the tensioner. The plunger  510  fits into a cylindrical hole  520  in a tensioner housing  520 , and is extensible and retractable in the tensioner housing so that it can maintain engagement with a timing chain. An oil passage  522  allows oil, supplied under pressure from an oil source, to communicate with the cylindrical hole  521 . A check valve block  530 , which is slidably fitted into the cylindrical inner surface  511   a  of hollow portion  511 , allows oil to flow toward the closed end  511   b  of the plunger  510 . A spring  540 , interposed between the check valve block  530  and the closed end  511   b , biases the plunger forward, and at the same time holds the check valve block against a sleeve  550 , which is seated on an end portion  523   a  of a hole  523  in the plunger. Hole  523  has a diameter d2 which is smaller than the diameter d1 of the cylindrical hole  521 . The check valve block  530  is thus held at a fixed position in the tensioner housing  520  although it is slidable relative to the inner circumferential surface  511   a  of the plunger  510 .  
         [0003]     In the conventional hydraulic tensioner  500 , the oil passage  522  communicates with an internal space IA of the inner sleeve  550 , which functions as an oil reservoir. The oil fills a high pressure chamber HA between the closed end  511   b  of the hollow portion  511 , and the check valve block  530 , from the inside of the inner sleeve  550 , through the check valve block  530 . The plunger  510  is always pressed toward the timing chain by the biasing force of the spring  540 , to apply chain tension to the chain.  
         [0004]     When the plunger  510  is pushed back into the tensioner housing by an impact applied to the plunger through the timing chain, oil in the high pressure chamber HA is discharged through an oil discharge passage  526 , which connects the cylindrical hole  521 , to the outside of the tensioner housing  520 . The oil flows through gaps between the outer circumferential surfaces of the check valve block  530  and inner sleeve  550 , and the inner circumferential surface  511   a  of the plunger, thereby absorbing, and reducing the effect of, the impact force.  
         [0005]     The conventional hydraulic tensioner  500  is disclosed at page 1, and shown in FIG. 1, of Japanese Patent No. 3054068. Secondary machining is required to The conventional tensioner must be subjected to secondary machining to form the oil discharge passage  526 , and fine secondary machining to form an oil supply opening  551 , which provides for fluid communication between the oil passage  522  and the interior of the inner sleeve  550 . The requirement for secondary machining resulted in a significant increase in the time and cost for manufacturing the conventional tensioner. Another problem encountered in the operation of the tensioner was that oil tended to adhere to and clog the oil discharge passage  526  and the oil supply opening  551 , especially after the tensioner was in use for a long period of time. The clogging of these passages can result in unstable operating conditions, that cannot be easily remedied.  
         [0006]     Another problem with the conventional tensioner was that a significant amount of oil was consumed as a result of discharge through passage  526  when impact forces were encountered. Thus, the engine oil pump was required to have sufficient power to supply oil to the tensioner under varying conditions. Moreover, when the engine is stopped, the engine oil pump also stops, but the discharge of oil from the tensioner cannot be avoided. Under such conditions, the amount of oil in the tensioner body  520  tends to be inadequate when the engine is restarted, and the tensioner cannot properly accommodate impact forces applied through the timing chain until the interior of the tensioner is re-charged with oil. Accordingly, wobbling of the timing chain occurs as the engine is started, producing noise known as a “wobbling sound.” 
         [0007]     The objects of the invention are to solve the problems of the conventional hydraulic tensioner; to provide a hydraulic tensioner which is simpler in construction, and can be manufactured in a shorter time and at a lower cost; to suppress the consumption of oil by the tensioner; to achieve stable application of tension; and to eliminate wobbling sounds in the timing transmission medium upon starting of an engine.  
       SUMMARY OF THE INVENTION  
       [0008]     The hydraulic tensioner according to the invention comprises a tensioner housing having a cylindrical hole and a hollow plunger having a closed end and a cylindrical interior circumferential surface. The plunger fits slidably in the cylindrical hole and is open toward the inside of the tensioner housing. The plunger projects from the housing and is engageable with a timing transmission medium. An oil passage extends from the exterior of the housing and communicates with an interior space within the cylindrical hole in the interior of the housing, for delivering oil under pressure from an oil supply. A check valve block, fits slidably within the plunger, and allows oil to flow into the part of interior of the plunger on the side of the check valve block adjacent the closed end of the plunger. A spring, disposed in compression between the closed end of the plunger and the check valve block, biases the plunger in the projecting direction. An inner sleeve, seated on a proximal end portion of the cylindrical hole and engaged with the check valve block, holds the check valve block at a fixed position in the tensioner housing. The inner sleeve fits slidably in the plunger. A gap exists between the check valve block and the inner circumferential surface of the plunger, and another gap exists between the inner sleeve and the inner circumferential surface of the plunger. An oil pressure control recess is formed at a proximal end of the cylindrical hole of the tensioner housing adjacent the seated end of the inner sleeve. This oil pressure control recess is in communication with the cylindrical hole, the oil passage and the gaps. In operation of the tensioner, oil oozing through the gaps from the interior of the plunger is returned, along with oil supplied through the oil passage, to the interior of the plunger through the check valve block.  
         [0009]     The oil pressure control recess circulates oil which oozes under high pressure through the gaps from the space within the plunger adjacent the closed end thereof. The pressure control recess can be simultaneously molded or cast together with the cylindrical hole in the housing. The use of the pressure control recess allows realization of a simpler tensioner construction, without the need for secondary machining or cutting of the tensioner housing or of an inner sleeve as in the conventional case. Thus the manufacturing man-hour and manufacturing costs can be significantly reduced. Moreover, clogging of oil, which tends to occur in a conventional hydraulic tensioner, can be avoided and stable application of tension over a long period of time can be attained.  
         [0010]     The provision for return of oil from the interior of the plunger to the oil pressure control recess, reduces the consumption of oil remarkably. Moreover, the tensioner allows for a reduction of the discharge capacity of the engine oil pump.  
         [0011]     The tensioner construction ensures that sufficient oil is present in the tensioner even upon engine start-up. Accordingly impact forces exerted by the timing transmission medium are absorbed immediately, and wobbling sounds are suppressed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a cross-sectional view of a hydraulic tensioner in accordance with a first embodiment of the invention;  
         [0013]      FIG. 2  is a cross-sectional view taken on plane X-X in  FIG. 1 ;  
         [0014]      FIG. 3  is a cross-sectional view of a hydraulic tensioner in accordance with a second embodiment of the invention;  
         [0015]      FIG. 4  is a cross-sectional view of a hydraulic tensioner in accordance with a third embodiment of the invention; and  
         [0016]      FIG. 5  is a cross-sectional view of a conventional hydraulic tensioner. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     The tensioner housing used in accordance with the invention may be composed of any of a variety of materials including plastics, i.e., a synthetic resin, aluminum, and cast iron. In a case of a tensioner housing made of plastics, for example, the oil pressure control recess can be molded during injection molding of the tensioner housing without the need for additional cutting or machining. In the case of cast iron or aluminum tensioner housing, the oil pressure control recess can also be simultaneously molded during the casting of the tensioner housing, without additional cutting or machining.  
         [0018]     The oil pressure control recess, which is formed in the tensioner housing make take any of a wide variety of forms provided that they can return oil under high pressure from the inside of the plunger to the oil passage while communicating with the proximal end the cylindrical hole and the oil passage. The recess may take any shape or size allowed by the tensioner housing.  
         [0019]     The hydraulic tensioner  100  shown in  FIG. 1  comprises a hollow plunger  110  having a closed end  111  and open toward the inside of the tensioner. A housing  120  has a cylindrical hole  121 . The plunger is retractable in the cylindrical hole, and extensible toward a timing chain (not shown). An oil passage  122  allows oil, supplied under pressure by an engine oil pump (not shown) to communicate with the cylindrical hole  121 . A check valve block  130 , which allows the oil to flow toward the closed end of the plunger, is disposed within the hollow portion  111  of the plunger, and fits slidably with respect to the inner circumferential surface of the plunger. A spring  140 , which is in compression between the check valve block  130  and the closed end  111   b  of the plunger, biases the plunger  110  forward. An inner sleeve  150  seats on a proximal end portion  123   a  of the cylindrical hole, holding the check valve block  130  at a fixed position in the tensioner housing  120  while being slidable with respect to the inner circumferential surface  111   a  of the plunger  110 . The oil supplied from the engine oil pump flows into the internal space IA of the inner sleeve  150  through the oil passage  122  in the tensioner housing  120 . The space  1 A serves as an oil reservoir. While part of the oil in space  1 A flows through the check valve to fill the high pressure chamber HA, defined between the closed end  111   b  of the plunger  110  and the check valve block  130 , the plunger  110  is biased in the protruding direction toward the timing chain by spring  140  inside the plunger  110 .  
         [0020]     The outer circumferential surface  112   a  of the plunger  110  and the cylindrical hole  121  of the tensioner housing  120  have coaxial circumferential surfaces, and the plunger  110  is retractable and extensible with respect to the cylindrical hole  121  of the tensioner housing  120 . The inner circumferential surface  111   a  of the plunger  110 , the check valve block  130  and the inner sleeve  150  also have coaxial circumferential surfaces, and the check valve block  130  and the inner sleeve  150  fit slidably with respect to the inner circumferential surface  111   a  of the plunger  110 .  
         [0021]     The valve block  130  causes oil, supplied under pressure through the oil passage  122  to the interior of the inner sleeve  150 , to flow into the space defined between the check valve block and the closed end  111   b  of the plunger. The check valve mechanism comprises a check ball  131  disposed in the path of the oil, a ball seat  132 , engageable by the ball, a spring  133 , which urges the check ball  131  into contact with the seat  132 , and a retainer  134 , which holds the spring  133 , and maintains the ball in close proximity to the seat. The retainer is provided with an oil port  134   a.    
         [0022]     The inner sleeve  150  is seated on a proximal end portion  123   a  of an inner sleeve retaining hole  123 , which has a diameter d2, smaller than the diameter d1 of the cylindrical hole  121 . The inner sleeve  150  is held straight by the inner sleeve retaining hole  123  to ensure smooth sliding of the plunger  110 .  
         [0023]     Next, the oil pressure control recess  124 , which is an important feature of the embodiment shown in  FIG. 1 , is formed simultaneously with the cylindrical hole  121  when the cylindrical hole is molded. The oil pressure control recess  124  is formed so that it provides communication between the proximal end  121   a  of the cylindrical hole  121  and the oil passage  122 , and is adapted to return, to the oil passage  122 , oil which oozes under high pressure from the space between the check valve block  130  and the closed end  111  of the plunger. This oil flows through the gaps between the inner circumferential surface  111   a  of the plunger  110 , and the check valve block, and inner sleeve, respectively.  
         [0024]     As shown in  FIGS. 1 and 2 , the oil pressure control recess  124  comprises an oil pressure control region  124   a  having a diameter d3 smaller than the hole diameter d2 of the inner sleeve retaining hole  123 . The oil pressure control recess also has a region  124   b  for returning oil which oozes under high pressure from the space between  111   b  of the plunger  110  and the check valve block. This oil returns to the oil pressure control region  124   a  via a gap between the inner circumferential surface  111   a  of the plunger  110  and the inner sleeve  150 . Thus the returning oil flows into the oil pressure control region together with oil flowing under pressure through the oil passage  122 .  
         [0025]     The oil pressure control recess  124 , which comprising both the oil pressure control region  124   a  and the region  124   b , can be molded or cast simultaneously with the cylindrical hole  121  and the inner sleeve retaining hole  123  when the tensioner housing  120  is formed. Additional machining and cutting are not needed.  
         [0026]     The oil passage  122  extends in a direction perpendicular to the central axis the cylindrical hole  121 .  
         [0027]     Since the oil pressure control recess  124  returns the oil under high pressure from the closed end of plunger  110  toward the oil passage  122 , consumption of oil in the tensioner housing  120  is remarkably lower than the oil consumption experienced with the conventional hydraulic tensioner  500  ( FIG. 5 ), which discharges oil to the outside of the tensioner housing. Furthermore, the discharge capacity requirement of the engine oil pump is significantly reduced, since a sufficient amount of oil in the tensioner housing  120  is ensured, even upon restarting of the engine. Consequently, impact forces exerted by the timing chain upon engine start-up are taken up immediately by the tensioner, and the wobbling sounds, which occur when an ordinary tensioner is used, are suppressed.  
         [0028]     The tensioner  100  depicted in  FIGS. 1 and 2  is structurally simple, and can be produced at reduced cost, utilizing fewer man-hours. Because of its lower manufacturing cost, its ability to reduce oil consumption, and its ability to apply tension in a stable manner and eliminate wobbling sounds on engine start-up, the tensioner is highly advantageous.  
         [0029]     The alternative embodiment of the invention, shown in  FIG. 3 , is similar in many respects to the embodiment shown in  FIGS. 1 and 2 . The tensioner  200  comprises a hollow plunger  210  having a closed end  211  and open toward the inside of the tensioner. A housing  220  has a cylindrical hole  221 . The plunger is retractable in the cylindrical hole, and extensible toward a timing chain (not shown). An oil passage  222  allows oil, supplied under pressure by an engine oil pump (not shown) to communicate with the cylindrical hole  221 . A check valve block  230 , which allows the oil to flow toward the closed end of the plunger, is disposed within the hollow portion  211  of the plunger, and fits slidably with respect to the inner circumferential surface of the plunger. A spring  240 , which is in compression between the check valve block  230  and the closed end  211   b  of the plunger, biases the plunger  210  forward. An inner sleeve  250  seats on a proximal end portion  223   a  of the cylindrical hole, holding the check valve block  230  at a fixed position in the tensioner housing  220 , while being slidable with respect to the inner circumferential surface  211   a  of the plunger  210 . The oil supplied from the engine oil pump flows into the internal space IA of the inner sleeve  250  through the oil passage  222  in the tensioner housing  220 . The space  1 A serves as an oil reservoir. While part of the oil in space  1 A flows through the check valve to fill the high pressure chamber HA, defined between the closed end  211   b  of the plunger  210  and the check valve block  230 , the plunger  210  is biased in the protruding direction toward the timing chain by spring  240  inside the plunger  210 .  
         [0030]     The outer circumferential surface  212   a  of the plunger  210  and the cylindrical hole  221  of the tensioner housing  220  have coaxial circumferential surfaces, and the plunger  210  is retractable and extensible with respect to the cylindrical hole  221  of the tensioner housing  220 . The inner circumferential surface  211   a  of the plunger  210 , the check valve block  230  and the inner sleeve  250  also have coaxial circumferential surfaces, and the check valve block  230  and the inner sleeve  250  fit slidably with respect to the inner circumferential surface  211   a  of the plunger  210 .  
         [0031]     The valve block  230  causes oil, supplied under pressure through the oil passage  222  to the interior of the inner sleeve  250 , to flow into the space defined between the check valve block and the closed end  211   b  of the plunger. The check valve mechanism comprises a check ball  231  disposed in the path of the oil, a ball seat  232 , engageable by the ball, a spring  233 , which urges the check ball  231  into contact with the seat  232 , and a retainer  234 , which holds the spring  233 , and maintains the ball in close proximity to the seat. The retainer is provided with an oil port  234   a.    
         [0032]     The inner sleeve  250  is seated on a proximal end portion  223   a  of an inner sleeve retaining hole  223 , which has a diameter d2, smaller than the diameter d1 of the cylindrical hole  221 . The inner sleeve  250  is held straight by the inner sleeve retaining hole  223  to ensure smooth sliding of the plunger  210 .  
         [0033]     The oil pressure control recess  224  in this embodiment is simultaneously molded together with the cylindrical hole  221 . The oil pressure control recess  224  communicates with the proximal end  221   a  of cylindrical hole  221 , and also with the oil passage  222 . The recess  224  returns oil, which oozes under high pressure from the closed end portion of the plunger  210  via the gaps between the inner circumferential surface  211   a  of the plunger  210  and the outer circumferential surfaces of the check valve block  230  and the inner sleeve  250 , to the portion of the interior of the tensioner housing which communicates directly with oil passage  222 .  
         [0034]     The oil pressure control recess  224  comprises an oil pressure control region  224   a  having a diameter d3 smaller than the diameter d2 of the inner sleeve retaining hole  223 . The recess  224  also comprises a region  224   b  for returning the oil, which oozes from the closed end of the plunger  210  to the oil pressure control region  224   a  via the gaps surrounding the check valve block and the inner sleeve.  
         [0035]     The oil pressure control recess  224 , comprising regions  224   a  and  224   b  can be simultaneously formed with the cylindrical hole  221  and the inner sleeve retaining hole  223  when the tensioner housing  220  is cast or molded, eliminating the need for additional machining and cutting.  
         [0036]     The oil passage  222  is different from passage  122  in the first embodiment in that passage  222  is inclined toward region  224   b  with respect to the central axis of the cylindrical hole  221  so that oil flowing from region  224   b  into the oil pressure control region  224   a , is biased. The embodiment of  FIG. 3  has all of the advantages of the embodiment of  FIGS. 1 and 2 .  
         [0037]     The hydraulic tensioner  300  shown in  FIG. 1  comprises a hollow plunger  310  having a closed end  311  and open toward the inside of the tensioner. A housing  320  has a cylindrical hole  321 . The plunger is retractable in the cylindrical hole, and extensible toward a timing chain (not shown). An oil passage  322  allows oil, supplied under pressure by an engine oil pump (not shown) to communicate with the cylindrical hole  321 . A check valve block  330 , which allows the oil to flow toward the closed end of the plunger, is disposed within the hollow portion  311  of the plunger, and fits slidably with respect to the inner circumferential surface of the plunger. A spring  340 , which is in compression between the check valve block  330  and the closed end  311   b  of the plunger, biases the plunger  310  forward. An inner sleeve  350  seats on a proximal end portion  323   a  of the cylindrical hole, holding the check valve block  330  at a fixed position in the tensioner housing  320  while being slidable with respect to the inner circumferential surface  311   a  of the plunger  310 . The oil supplied from the engine oil pump flows into the internal space IA of the inner sleeve  350  through the oil passage  322  in the tensioner housing  320 . The space  1 A serves as an oil reservoir. While part of the oil in space  1 A flows through the check valve to fill the high pressure chamber HA, defined between the closed end  311   b  of the plunger  310  and the check valve block  330 , the plunger  310  is biased in the protruding direction toward the timing chain by spring  340  inside the plunger  310 .  
         [0038]     The outer circumferential surface  312   a  of the plunger  310  and the cylindrical hole  321  of the tensioner housing  320  have coaxial circumferential surfaces, and the plunger  310  is retractable and extensible with respect to the cylindrical hole  321  of the tensioner housing  320 . The inner circumferential surface  311   a  of the plunger  310 , the check valve block  330  and the inner sleeve  350  also have coaxial circumferential surfaces, and the check valve block  330  and the inner sleeve  350  fit slidably with respect to the inner circumferential surface  311   a  of the plunger  310 .  
         [0039]     The valve block  330  causes oil, supplied under pressure through the oil passage  322  to the interior of the inner sleeve  350 , to flow into the space defined between the check valve block and the closed end  311   b  of the plunger. The check valve mechanism comprises a check ball  331  disposed in the path of the oil, a ball seat  332 , engageable by the ball, a spring  333 , which urges the check ball  331  into contact with the seat  332 , and a retainer  334 , which holds the spring  333 , and maintains the ball in close proximity to the seat. The retainer is provided with an oil port  334   a.    
         [0040]     The inner sleeve  350  is seated on a proximal end portion  323   a  of an inner sleeve retaining hole  323 , which has a diameter d2, smaller than the diameter d1 of the cylindrical hole  321 . The inner sleeve  350  is held straight by the inner sleeve retaining hole  323  to ensure smooth sliding of the plunger  310 .  
         [0041]     An oil pressure control recess  324  is simultaneously molded together with the cylindrical hole  321 . The pressure control recess  324  communicates with the proximal end  321   a  of the cylindrical hole  321  and the oil passage  322 . The oil pressure control region  324   a  has a diameter d3 smaller than than the diameter d2 of the inner sleeve retaining hole  323 , and can be simultaneously molded together with the hole  321  and the inner sleeve retaining hole  323  when the tensioner housing  320  is cast or molded, without the need for additional machining or cutting.  
         [0042]     In this case, the oil passage  322  is different from the previously described embodiments. The passage  322  is inclined toward to the oil pressure control recess  324  with respect to the central axis of the cylindrical hole  321 , and extends to the cylindrical pressure control recess  324 , meeting the control recess  324  directly, so that there is no region corresponding to regions  124   b  and  224   b  in the first two embodiments. The proximal end  323   a  of hole  323  is interposed by a short distance into passage  322 . Thus, oil, which oozes under high pressure via the gaps surrounding the plunger  310  and the inner sleeve  350 , is returned directly to a part of the passage  322  which is adjacent the pressure control region  324   a , and from there to the pressure control region.  
         [0043]     This embodiment has all of the advantages of the previously described embodiments. That is, the discharge capacity of the engine oil pump can significantly reduced, sufficient oil is ensured in the tensioner housing at engine start-up, and impact forces exerted on the plunger by the timing chain are taken up immediately upon starting of the engine, and wobbling sounds, are suppressed.  
         [0044]     In addition, as in the case of the embodiments of  FIGS. 1-3 , the tensioner of  FIG. 4  can contribute to reduced oil consumption