BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a chain guide having a guide shoe that slidably guides a chain, and a reinforcing unit that reinforces the guide shoe. 
         [0003]    2. Description of the Related Art 
         [0004]    It has been common practice to use a chain guide having a guide shoe that slidably guides a running chain to stabilize a chain running between sprockets and to keep an appropriate chain tension. As a system that uses this chain guide, for example, an engine timing system is known, wherein an endless timing chain runs over sprockets of a crankshaft and cam shafts inside an engine room. A chain guide is used to guide this endless timing chain passing over a drive sprocket of the crankshaft and a pair of driven sprockets of the cam shafts inside the engine room. 
         [0005]    Guide rails of chain guides used in such known timing systems should preferably be made of a low-friction, high wear-resistance material, and therefore a guide entirely made of a low-friction resin material is known. On the other hand, the chain guide needs to have certain levels of strength, rigidity, and durability to be able to withstand the tension or vibration of the chain and to guide the chain stably. If the chain guide is made solely of a resin material, it needs to have a larger material thickness to achieve necessary strength, rigidity, and durability, and will end up occupying a larger space inside the engine room. Therefore, some known chain guides have their guide rail made of a low-friction resin material and reinforced with a material with high strength, rigidity, and durability such as metal, so as to reduce the occupying space while securing necessary strength, rigidity, and durability of the chain guide as a whole. 
         [0006]    One of such known chain guides is formed by a guide shoe that slidably guides a running chain and a plate that reinforces the guide shoe along the guide longitudinal direction. The guide shoe has a plate holding part in the form of a slit-like groove, into which the plate can be inserted from a lower side thereof, on the backside of the guide rail. With the plate having high rigidity and durability being inserted into the plate holding part from below, the occupying space of the chain guide is reduced, while necessary strength, rigidity, and durability are secured as a whole (see Japanese Patent Application Laid-open No. 2015-025535). 
       SUMMARY OF THE INVENTION 
       [0007]    According to Japanese Patent Application Laid-open No. 2015-025535, the chain guide has mounting holes for mounting shafts to pass through, which are used to attach the chain guide to an object of interest such as an engine block. Tubular parts are formed by burring at the edge of the mounting holes such as to protrude in the guide width direction. Therefore, the inner surface of the mounting hole and the mounting shaft make contact with each other in an increased area along the width direction, so that the chain guide is unlikely to incline relative to its proper orientation and capable of allowing stable running of the chain. Moreover, with the inner surface of the mounting hole and the mounting shaft making contact with each other in a wider area, they are less susceptible to load concentration, and less likely to suffer wear or damage on the inner surface of the mounting hole and on the mounting shaft. 
         [0008]    However, while the tubular parts provide the effects described above in the chain guide described in Japanese Patent Application Laid-open No. 2015-025535, there is another problem that connecting portions between a flat part of the plate that can be warped largely and the tubular parts (base portions of the tubular parts) are more susceptible to concentration of internal stress generated inside the plate due to the force applied to the plate during the running of the chain, because of which the durability of the plate is compromised. Another problem is that since the tubular parts of the plate are formed by burring, certain limitations are imposed on the dimensional setting of the tubular parts in the guide width direction, and also the production cost of the plate is high. 
         [0009]    The present invention solves these problems, its object being to provide a chain guide that allows for stable running of a chain, suffers less wear or damage on the inner surface of mounting holes or on mounting shafts, and improves the durability without causing an increase in production cost. 
         [0010]    The present invention solves the problems described above by providing a chain guide including a guide shoe that slidably guides a chain, and a reinforcing unit that reinforces the guide shoe, wherein the guide shoe includes a guide rail extending along a guide longitudinal direction, and a unit holding part that accommodates the reinforcing unit inserted thereinto from a backside of the guide rail, and the reinforcing unit includes a plate having a plate through hole extending through the plate in a guide width direction, and a spacer having a spacer through hole extending through the spacer in the guide width direction. The plate and the spacer are aligned in the guide width direction, so that the plate through hole and the spacer through hole are continuous in the guide width direction, and are disposed in the unit holding part. 
         [0011]    According to one aspect of the present invention, the plate and spacer are aligned in the guide width direction, so that the plate through hole and spacer through hole are continuous in the guide width direction, and are disposed in the unit holding part. The mounting shaft used for attaching the chain guide to an object of interest such as an engine block makes contact with the inner surface of mounting holes (plate through hole and spacer through hole) over a longer area in the guide width direction, so that the chain guide is less likely to be inclined relative to its proper orientation and can thus allow for stable running of the chain. Moreover, with the inner surface of the mounting holes and the mounting shaft making contact with each other in a wider area, the chain guide does not suffer a concentrated load, which results in less wear or damage on the inner surface of the mounting holes and on the mounting shaft, as well as provides the following effects: 
         [0012]    Namely, with the spacer provided separately from the plate, the mounting hole for inserting the mounting shaft is formed so that the length in the guide width direction of the mounting hole for inserting the mounting shaft can be freely adjusted by changing the size of the spacer in the guide width direction. 
         [0013]    Since there is no need to form a tubular part that protrudes in the guide width direction to the plate, the production cost of the plate can be reduced. Moreover, the connecting portion between the flat part and the tubular part of the plate is prevented from suffering concentration of internal stress that is generated inside the plate due to the force applied to the plate during the running of the chain, and thus the plate can have improved durability. 
         [0014]    According to another aspect of the present invention, the spacer is disposed in the unit holding part with a spacer locking portion formed on the guide shoe and the plate sandwiching the spacer in the guide width direction, and part of the spacer makes protrusion/recess engagement with the plate in the guide width direction. Thus the spacer disposed inside the unit holding part can be prevented from coming off from the backside of the guide rail with a simple structure. Attachment of the reinforcing unit to the guide shoe only requires a simple operation of inserting the reinforcing unit into the unit holding part after fitting the spacer to the plate to make protrusion/recess engagement therewith. 
         [0015]    According to another aspect of the present invention, the spacer includes a tubular body in which the spacer through hole is formed, and a flange formed at one end of the tubular body, and the flange formed on the spacer is disposed in the unit holding part with the spacer locking portion and the plate sandwiching the flange in the guide width direction. This way, the size of the tubular body can be freely set in the guide width direction, so that the length of the mounting hole for inserting the mounting shaft can be adjusted freely in the guide width direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is an illustrative diagram showing a chain guide that is one embodiment of the present invention; 
           [0017]      FIG. 2  is an illustrative diagram showing the chain guide viewed from the opposite side from that of  FIG. 1 ; 
           [0018]      FIG. 3  is an illustrative diagram showing the chain guide viewed from below; and 
           [0019]      FIG. 4  is a plan view showing a plate and spacers that form a reinforcing unit. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    A chain guide  10  according to one embodiment of the present invention will be hereinafter described with reference to the drawings. 
         [0021]    The chain guide  10  according to one embodiment of the present invention is used as part of a timing system equipped inside an engine room and fixed to an engine block, which is an object of interest, to slidably guide a chain running over sprockets. 
         [0022]    The chain guide  10  includes, as shown in  FIG. 1  to  FIG. 3 , a guide shoe  20  that slidably guides the running chain along a guide longitudinal direction, and a reinforcing unit  30  that is removably attached to the guide shoe  20  and reinforces the guide shoe  20 . 
         [0023]    The guide shoe  20  has a guide rail  21  that guides the chain along the guide longitudinal direction on the upper side facing the chain, as shown in  FIGS. 1 and 2 . 
         [0024]    The guide shoe  20  also has a unit holding part  22  in the form of a slit-like groove for accommodating the reinforcing unit  30  inserted thereinto from the backside of the guide rail  21  (underside of the guide shoe  20 , in the direction of arrow in  FIGS. 1 and 2 ). 
         [0025]    The reinforcing unit  30  is formed by a plate  40  having plate through holes  41  extending through in the guide width direction, and two spacers  50  each having a spacer through hole  53  extending through in the guide width direction, as shown in  FIGS. 3 and 4 . 
         [0026]    The plate through holes  41  are formed in the plate  40  at two positions distanced from each other in the guide longitudinal direction as shown in  FIG. 1 . The plate  40  and spacers  50  are aligned in the guide width direction, so that the plate through holes  41  and spacer through holes  53  are continuous in the guide width direction, and are disposed in the unit holding part  22 , as shown in  FIG. 3 . The plate through holes  41  and spacer through holes  53  arranged to be continuous in the guide width direction function as mounting holes for inserting mounting shafts that are used for attaching the chain guide  10  to an engine block. The spacers  50  are disposed on the side facing the engine block, and function as parts that will be in contact with the engine block when the chain guide  10  is attached to the engine block. 
         [0027]    The plate  40  includes, as shown in  FIG. 4 , the two plate through holes  41  mentioned above, annular recesses  42  formed by recessing the edge of the plate through holes  41  on one side of the plate  40  facing the spacers  50 , and annular protrusions  43  formed by projecting the edge of the plate through holes  41  on the other side of the plate  40 . These annular recesses  42  and annular protrusions  43  can be formed at one time by a pressing process performed to the edges of the plate through holes  41  from one side of the plate  40  facing the spacers  50  to the other side. 
         [0028]    Each spacer  50  includes, as shown in  FIGS. 3 and 4 , a cylindrical tubular body  51  in which the spacer through hole  53  is formed, a flange  52  formed at one end of the tubular body  51 , and an annular boss  54  formed by projecting the edge of the spacer through hole  53  on one side facing the plate  40 . With the reinforcing unit  30  being disposed in the unit holding part  22 , each annular boss  54  is received in the annular recess  42  of the plate  40 . 
         [0029]    The reinforcing unit  30  is attached to the guide shoe  20  as follows: the spacers  50  are set in the plate  40  such that the annular bosses  54  of the spacers  50  fit in the annular recesses  42  of the plate  40 , as shown in  FIG. 4 , after which the plate  40  and spacers  50  are inserted into the unit holding part  22  of the guide shoe  20  from the underside. 
         [0030]    When the reinforcing unit  30  is inserted into the unit holding part  22 , the plate  40  is restricted from moving to both sides in the guide longitudinal direction, both sides in the guide width direction, and upward in the guide height direction, by the peripheral walls of the unit holding part  22 , and also prevented from coming out of the underside of the guide shoe  20  by locking pawls  24  formed to the guide shoe  20 . 
         [0031]    When the reinforcing unit  30  is inserted into the unit holding part  22 , the spacers  50  are restricted from moving to both sides in the guide width direction as the flanges  52  are sandwiched in the guide width direction between the spacer locking portions  23  formed to the guide shoe  20  and the plate  40 . The spacers  50  are restricted from moving to both sides in the guide longitudinal direction, and upward in the guide height direction by the peripheral walls of the unit holding part  22 , and also prevented from coming out of the underside of the guide shoe  20  by engagement between the annular bosses  54  of the spacers  50  and the annular recesses  42  of the plate  40 . 
         [0032]    While one embodiment of the present invention have been described in detail, the present invention is not limited to the above-described embodiment and may be carried out with various design changes without departing from the scope of the present invention set forth in the claims. 
         [0033]    For example, while the chain guide was described as a component to be incorporated in a timing system of an engine in the embodiment above, the chain guide can be applied to various other equipment other than this. 
         [0034]    The chain tensioner may not necessarily be applied to a chain transmission mechanism but also used for similar transmission mechanisms that use belts, ropes and the like, and can be applied in a variety of industrial fields. 
         [0035]    For example, the material of the guide shoe may be selected from known suitable materials in accordance with various conditions such as elasticity, friction resistance, rigidity, durability, formability, cost, and so on. Synthetic resin materials are particularly suitable. 
         [0036]    The material of the plate and spacers that form the reinforcing unit may be selected from, for instance, metal materials, as appropriate, in accordance with various conditions such as rigidity, durability, formability, cost, and so on. 
         [0037]    While the chain guide is configured as a fixed guide fixedly attached to the engine block in the embodiment described above, the chain guide may be configured as a pivotal guide pivotally supported inside the engine room. If the chain guide is configured as a pivotal guide, there need be only one mounting hole in the plate for passing the mounting shaft and the like for attaching the chain guide to an object of interest such as an engine block. More specifically, the plate may have one plate through hole, and one spacer. 
         [0038]    In the embodiment described above, the spacer is prevented from coming out of the underside of the guide shoe by engagement between the annular bosses formed on the spacers and the annular recesses formed in the plate. To prevent the spacer from coming out of the underside of the guide shoe, the spacer only needs to partly make protrusion/recess engagement with the plate in the guide width direction. For example, a recess formed in the spacer may make engagement with a protrusion on the plate. Alternatively, the spacer may not necessarily have a protruded part on the side facing the plate and the spacer on the side facing the plate may entirely make engagement with an annular recess in the plate.
A chain guide is provided that allows for stable running of a chain, causes less wear or damage on the inner surface of mounting holes or on mounting shafts, and improves the durability without increasing production cost. The guide shoe includes a guide rail and a unit holding part that accommodates a reinforcing unit inserted thereinto from the backside of the guide rail. The reinforcing unit includes a plate and a spacer. The plate and spacer are aligned in a guide width direction, so that a plate through hole and a spacer through hole are continuous in the guide width direction, and are disposed in the unit holding part 22.