Abstract:
A chain tensioner for use on a chain drive system is disclosed which has a housing open at both ends. Into the housing, a cartridge is inserted, the cartridge having including a body with a cylinder within and a piston. A retention system is provided to substantially prevent the body of the cartridge from moving with respect to the housing. Such a retention system, in one embodiment, includes a lip at a first end of the body and a groove on a second end of the body. The lip serves as a stop to prevent the body of the cartridge from moving axially beyond the stop in one direction. A clip is interlocked into the groove on the second end of the body of the cartridge to prevent movement in the opposite direction.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present development pertains to chain tensioners used in chain drive systems. 
         [0003]    2. Background Art 
         [0004]    It is known in the prior art to drive auxiliary components of an engine system by a chain or belt driven off of a crankshaft or other driving sprocket. To accommodate slack in the chain due to momentary changes in torque requirements of the various components and changes in system tension due to stretching of the chain with aging, it is known to provide a chain tensioner to take up the slack. Consequently, a relatively constant tension in the chain is maintained regardless of operating condition and/or state of wear of the chain. 
         [0005]    One type of chain tensioner cartridge  1  is shown in  FIG. 1  which has a cartridge body  2  having a hollow cylinder within and a piston  3  which can move axially in the cylinder. Cartridge  1  is intended to be mounted proximate a belt drive system on an internal combustion engine or other energy conversion unit. To engage with such an energy conversion unit, external threads  4  are provided on the outer surface of cartridge  1  which engage with a threaded housing mounted on the energy conversion unit (not shown). Cartridge body  2  remains fixed with respect to the energy conversion unit. The length of chain tensioner  1  is determined by the position of piston  3  with respect to cartridge body  3 . A spring  5  applies a force on piston  3 . Additionally, hydraulic pressure acts on piston  3  when oil passage  6  is supplied a pressurized fluid supply, typically from an engine&#39;s lubricant supply. Oil passage  6  is coupled to a cavity  7  between cartridge body  2  and piston  3  via a check valve  8 . The mechanical spring force and the hydraulic force are balanced against a chain  9  riding against piston  3 . When there is slack, the forces push piston  3  upward which causes a bow in chain  9  riding on piston  3  and thus the slack is taken up. When there is an increased tension in chain  9  due to, for example, a rapidly changing engine speed, the force that chain  9  exerts on piston  3  causes piston  3  to retreat into cartridge body  2  to establish a new equilibrium of forces, i.e., the force of the chain balances spring and hydraulic forces. In  FIG. 1 , chain  9  rides directly on piston  3 . This is one alternative. In many applications, piston  3  presses directly against a tensioning arm, which presses into the chain. Or, in other applications, a shoe is applied to piston  3  with the chain riding on the shoe. 
         [0006]    Cartridge  2  mounts into a threaded housing on an energy conversion unit by engaging with threads  4 . In some applications, finding space to package the mating thread set presents a challenge. Furthermore, with such a design, there must be space to rotate the cartridge  2  with respect to the energy conversion unit both during an initial build and during repair and replacement operations. There is a cost associated with machining threads on the outer surface of cartridge  2  and the mating internal threads on the power conversion unit. An alternative mounting system obviating the need for a threaded connection is desired. 
       SUMMARY 
       [0007]    A chain tensioner is disclosed which has a housing open at both ends. Into the housing, a cartridge is inserted having a lip extending outwardly at a first end and a groove on a second end. The lip serves as an axial stop to prevent the cartridge from moving beyond the lip in a first direction. A clip is interlocked into the groove on the second end of the cartridge. With the clip installed, the cartridge is fixed in the housing such that it is substantially prevented from moving axially with respect to the housing or moving only an amount of a clearance in the system. 
         [0008]    The cartridge includes a body having a cylinder inside and a piston within the cylinder. It is the body portion of the cartridge that has the lip and the groove for the clip. The body doesn&#39;t move with respect to the housing. However, the piston is able to freely move within the cylinder inside the body. 
         [0009]    The piston is forced partially out of the cylinder, i.e., lengthening of the cartridge, under a spring force and/or hydraulic pressure. In one embodiment, a spring is installed in the cartridge forcing the piston in a direction to lengthen the cartridge. In another embodiment, an oil passageway through the housing fluidly connects an engine oil system to a cavity adjacent to the piston. When the chain tensioner is installed on an engine and supplied pressurized oil from the engine, the piston is forced in a direction which lengthens the cartridge. When the cartridge lengthens, the piston or a shoe coupled to the piston pushes on a chain of a drive system to increase tension in the chain drive. When the cartridge shortens, the tension in the chain drive is decreased. 
         [0010]    In one embodiment, a shoe for riding on the chain is affixed to the piston near the first end. In another embodiment, the body of the chain tensioner has tabs near the second end for engaging with a shoe, the shoe having arms to interlock with tabs extending outwardly from the housing. In yet another embodiment, a first shoe is affixed to the piston and a second shoe engages with tabs on the housing. In such an embodiment, the chain tensioner has shoes on both ends. 
         [0011]    Also disclosed is a method to assemble a chain tensioner, which includes inserting a chain tensioner cartridge into a housing. The cartridge has a lip extending outwardly at a first end of the cartridge and a groove in the cartridge at a second end of the cartridge. The method also includes sliding a clip into the groove to secure the cartridge within the housing. In one embodiment, a housing of the chain tensioner has tabs extending outwardly proximate the second end. An outer periphery of a clip engages with a groove in a shoe prior to being assembled with the housing and cartridge. An inner portion of the clip engages with the groove on the cartridge and arms on the shoe interlock with the tabs on the housing substantially simultaneously during assembly of the shoe and clip. 
         [0012]    A chain tensioner is also disclosed which has a housing defining a cylinder, a chain tensioner cartridge installed in the cylinder, and a retention system coupled to a body of the chain tensioner cartridge wherein the retention system substantially prevents movement of the body of the cartridge with respect to the housing. In one embodiment, the retention system includes a lip on one end of the body, a groove in the other end of the body, and a clip engaged with the groove. 
         [0013]    An advantage of the disclosed chain tensioner is that by restraining the cartridge body by lip on one end and a clip at the other end, no threads on the cartridge body are necessary thereby limiting machining operations, reducing cost, and simplifying installation of the cartridge in the housing. 
         [0014]    Because the cartridge is restrained in one direction by the lip and in the other direction by a clip, the cartridge body is prevented from moving in an axial direction. Such restraint is possible by providing a cartridge body which is open at both ends. Due to dynamic conditions during operation, the tension in the chain may change more rapidly than the piston can accommodate, in which case the cartridge body moves upward with respect to housing when tension is low and downward when tension is high. Such vertical oscillations may cause damage to the housing and the cartridge body thereby reducing the chain and chain tensioner&#39;s operating life and may cause noise and vibration. Because the disclosed cartridge retention system secures the cartridge from moving in either axial direction, such vertical oscillations are prevented, thereby preventing premature failure of the chain tensioner system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross-sectional view of a chain tensioner according to the prior art; 
           [0016]      FIG. 2  is a front view of a portion of a partially-assembled internal combustion engine illustrating a chain tensioner in accordance with an embodiment of the present disclosure; 
           [0017]      FIG. 3  is a detail drawing of a portion of a chain tensioner such as shown in  FIG. 2 ; 
           [0018]      FIG. 4  is a cross section of a chain tensioner such as shown in  FIG. 2 ; 
           [0019]      FIG. 5  is a front view of a portion of a partially-assembled internal combustion engine shown in a more assembled condition than  FIG. 2 ; 
           [0020]      FIG. 6  is cross section of a detail of a chain tensioner with a shoe assembled on the clip end of chain tensioner such as shown in  FIG. 2 ; 
           [0021]      FIG. 7  is cross-sectional top view of a shoe with a clip engaged according to an embodiment of the present disclosure; and 
           [0022]      FIG. 8  is a front view of shoe and clip of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0024]    A view of a partially-assembled internal-combustion engine  10  is shown in  FIG. 2 . A first cam sprocket  12  and a second cam sprocket  14  are coupled together by a chain  16 . Chain  16  rides on a first shoe  18 . A chain tensioner  20  has a second shoe  22  on which chain  16  also rides. As will be describe in more detail below, first shoe  18  does not move against chain  16  and as such, does not adjust chain tension. Instead, shoe  18  acts as a chain guide. Shoe  18  causes chain  16  to bow out a small amount so that chain  16  must ride on shoe  18 . This prevents resonant frequencies being set up in the chain. Within chain tensioner  20  is a piston-cylinder arrangement (not shown here, but discussed below in regard to  FIG. 4 ) which is coupled to the engine&#39;s pressurized lubrication system. By virtue of pressurized oil acting on the piston, second shoe  22  exerts an upward force on chain  16 . It is the action of second shoe  22  that modifies the chain tension in the system. 
         [0025]    In  FIG. 3 , a chain tensioner cartridge  24 , which is a portion of chain tensioner  20 , is shown. Body  26  defines a hydraulic cylinder within which piston  28  may slide. At one end of piston  28 , a shoe  30  is affixed. Shoe  30  may be integrally formed or attached to piston  28  in any manner known to one skilled in the art. A portion of chain  16  is proximate shoe  30 . Shoe  30  provides a wear surface for chain  16  to ride upon in operation. In an alternative embodiment discussed below, piston  28  is not coupled to a shoe, in which case chain  16  rides on piston  28 . Cartridge  24  is slipped into a housing (shown as element  42  in  FIG. 2 ) to form chain tensioner  20 . So that cartridge  24  moves minimally, or not at all, with respect to the housing, a lip  32  is provided at one end of body  26  of cartridge  24 . The outside dimensions of lip  32  and the inside dimensions of the housing are such that lip  32  cannot enter the housing. Lip  32  serves as a stop in a first axial direction for relative motion between the housing and body  26  (such stopping function is apparent in  FIG. 4 ). To prevent relative motion in a second axial direction with respect to the housing, a groove  34  is formed in body  26  of cartridge  24  into which a clip  36  is inserted. To facilitate assembly of the cartridge into the housing, clip  36  is uninstalled to allow cartridge  24  to slide into the housing. Then, clip  36  is engaged into groove  34 . The outside dimensions of clip  36  are such that clip  36  serves as a stop to prevent movement of cartridge  24  with respect to the housing in the second axial direction (illustrated in  FIG. 4 ). 
         [0026]    In  FIG. 4 , a cross section of chain tensioner  20  is shown having a housing  42  in which cartridge  24  is installed. Body  26  of cartridge  24  is held in place by lip  32  and clip  36  fitting into groove  34 . Oil is supplied to chain tensioner  20  via an oil passage  44  through housing  42 . In one embodiment, housing  42  is integrally cast with a component of engine  10  thereby ensuring housing  42  is affixed to engine  10  in a desired orientation. Alternatively, housing  42  is attached to engine  10  by bolts, a bracket, or any other manner known to one skilled in the art. Oil passage  44  is coupled to the pressurized oil supply within engine  10 . Without departing from the spirit of the disclosure, any other pressurized fluid may be supplied to chain tensioner  20  from other sources. Oil passage  44  leads to an annular oil cavity  46  between housing  42  and cartridge  24 . Pressure in annular oil cavity  46  is maintained between housing  42  and body  26  of cartridge  24  by O-rings  38  and  40 , which are fitted into grooves in the outside surface of body  26 . Body  26  forms a hydraulic cylinder  48  within which a piston  50  can slide. Piston  50  is acted upon by a spring  52  and by hydraulic pressure: oil from cavity  46  going through radial passageways  54  and then past a check ball  56  into internal cavity  58 . Pressurized oil in internal cavity  58  acts upon a resilient member  60  affixed to piston  50 . Piston  50  can move relative to body  26 , with O-ring (or other type of seal)  61  to prevent oil leakage between piston  50  and body  26 . In the embodiment shown in  FIG. 4 , an oil passage  62  passes through the top of piston  50  and through shoe  30 . (The view shown in  FIG. 4  is rotated 90 degrees with respect to the view shown in  FIG. 3 ; thus, the arms of the shoe are not visible in this cross-sectional view). The oil through passage  62  provides lubrication for the interface between the shoe  30  and the chain (not shown). 
         [0027]    As shown in  FIG. 2 , chain tensioner  20  includes second shoe  22  and is interlocked with first shoe  18  and is disposed between two portions of chain  16 . An alternative chain configuration is shown in  FIG. 5  in which partially-assembled, V-configured engine  10  is shown in a different stage of assembly than that shown in  FIG. 2 . Both  FIGS. 2 and 5  show the engine without the front cover installed. Chain  70  follows a serpentine path and engages with: cam sprockets  72  and  74 ; driving sprocket  75  coupled to the engine&#39;s crankshaft; chain guides  76 ,  78 , and  80 ; and tensioner arm  82 . A housing of chain tensioner  84  is affixed to engine  10 . A piston  86  of chain tensioner  84  presses against tensioner arm  82  during engine operation (under lubricating oil pressure). Tensioner arm is affixed to engine  10  at one location  88 , a pivot point. Thus, when piston  86  of chain tensioner  84  causes tensioner arm  82  to rotate about pivot point  88 , tensioner arm  82  applies appropriate tension in chain  70 . Chain  16 , which is shown in more detail in  FIG. 2 , is partially shown in  FIG. 5 .  FIG. 5  shoes two chains  16 ; one chain provided on each bank of V-configured engine  10 . 
         [0028]    In  FIG. 6  a detail of the lower portion of cartridge  24  is shown in cross section. Cartridge  24  is contained within housing  42  and sealed by O-ring  40 . Clip  36  inserted into groove  34  is wider than the cylindrical opening in housing  42  preventing upward movement of cartridge  24  with respect to housing  42 . Arms  90  and  92  of shoe  18  interlock with tabs  94  and  96  of housing  42 . In the embodiment shown in  FIG. 6 , interlocking tabs/arms are shown diametrically opposed to each other. In another embodiment, a single tab extending around about half of the circumference is provided. These are non-limiting examples; any known method to lock shoe  18  to body  42  can be employed. In  FIG. 6 , clip  36  is a separate piece from shoe  18 . Clip  36  may be integrally formed with shoe  18 , according to one alternative. 
         [0029]    In  FIG. 7 , a top view of shoe  18  is shown in cross section with clip  36 . Shoe  18  has tabs  98  and  100 . Clip  36  is partially retained by tabs  98  and  100  which are part of shoe  18 . This is also shown in an alternate view in  FIG. 8  in which clip  36  slides under tabs  98  and  100  which extend from inner walls of shoe  18 . But because tabs  98  and  100  don&#39;t extend down to meet the horizontal surface of shoe  18 , this provides a groove into which clip  36  can be slid. Tabs  98  and  100 , in one embodiment, engage with mating detents (not shown) in the outside surface of housing  42  (shown in at least  FIGS. 4 and 6 ). In  FIGS. 7 and 8 , clip  36  can be removed from shoe  18 . In an alternate embodiment, clip  36  can be affixed to shoe  18  by adhesives or mechanical connectors in any known manner. 
         [0030]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The present disclosure, although described as applied to an internal combustion engine, can be applied to any known chain drive system in which chain tensioning is desired. The present disclosure applies to systems that act on the piston by spring force only, hydraulic force only, combined spring/hydraulic, and another manner known to one skilled in the art. Depending on the application, the piston acts on a chain tensioner arm, the piston acts on the chain directly, and the piston is affixed to a shoe which acts on the chain. Also depending on the application, the stationary end of the chain tensioner acts as a chain guide and may be provided with a shoe. In other applications, the stationary end does not contact the chain. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.