Abstract:
An object is to provide a guide shoe having a simple structure and suppressing a significant shift in pitch line while reducing friction losses and preventing possible noise. In a guide shoe having a shoe surface on which a traveling chain is guided, the shoe surface includes a plate guide surface which is formed on an upstream side of the shoe surface in a shoe longitudinal direction and on which only chain plates are slidably guided, a guiding protruding portion which is formed on a downstream side of the plate guide surface and on which only a chain roller or a chain bush is guided, and a continuously transitioning protruding portion that smoothly connects the plate guide surface and the guiding protruding surface together. Plate escaping portions are formed on opposite sides across the guiding protruding portion in a shoe width direction to avoid contact with the chain plates.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a guide shoe with a shoe surface on which a traveling chain is guided. 
     2. Description of the Related Art 
     A chain guide is conventionally known which is assembled in a timing system in an engine room in an automobile to guide a chain traveling between sprockets to properly maintain chain tension. Such a chain guide includes a guide shoe with a shoe surface and a base member that supports the guide shoe along a guide longitudinal direction. 
     Various shoe surface aspects of such a guide shoe are well known. For example, in the known aspects, a chain plate end surface is slidably guided along a shoe surface shaped like a flat surface or a chain roller is rolled and guided by a guiding protruding portion formed on the shoe surface. 
     However, in the former guide shoe, the sliding of the chain plate end surface on the shoe surface disadvantageously causes an increase in chain traveling resistance, promoting sliding friction of the guide shoe. In the latter guide shoe, the chain roller intermittently collides against an upstream end of the guiding protruding portion, and the collision disadvantageously causes noise and increases friction losses. 
     Thus, in order to solve the above-described problem, the present applicant has proposed a guide shoe in which a shoe surface includes a plate guide surface which is formed on an upstream side of the shoe surface in the shoe longitudinal direction and on which only the chain plate is slidably guided, a guiding protruding portion which is formed on a downstream side of the plate guide surface and on which only the chain roller is guided, and a continuously transitioning protruding portion that smoothly connects the plate guide surface and the guiding protruding portion together such that slidable guiding of the chain plate on the chain plate can be smoothly shifted, by the continuously transitioning protruding portion, to rolling guidance of the chain roller by the guiding protruding portion, with a possible excessive collision between the chain roller and the guiding protruding portion avoided (see Japanese Patent Application Laid-open No. H10-184828). 
     In the guide shoe described in Japanese Patent Application Laid-open No. H10-184828, the height dimension of the guiding protruding portion from the shoe surface is designed to enable avoidance of contact of the chain plate end surface with the shoe surface when the chain roller is guided by the guiding protruding portion. However, in view of possible wear of the guiding protruding portion, possible dimensional errors in chain components, and the like, the height dimension of the guiding protruding portion needs to be equal to or larger than a design value. As a result, a pitch line of the chain traveling on the guide shoe is disadvantageously significantly shifted upward at the guiding protruding portion. 
     Thus, the present invention is intended to solve such a problem. An object of the present invention is to provide a guide shoe having a simple structure and suppressing a significant shift in pitch line while reducing friction losses and preventing possible noise. 
     SUMMARY OF THE INVENTION 
     In order to accomplish the object, the present invention provides a guide shoe having a shoe surface on which a traveling chain is guided, wherein the shoe surface includes a plate guide surface which is formed on an upstream side of the shoe surface in a shoe longitudinal direction and on which only chain plates are slidably guided, a guiding protruding portion which is formed on a downstream side of the plate guide surface and on which only a chain roller or a chain bush is guided, and a continuously transitioning protruding portion that smoothly connects the plate guide surface and the guiding protruding surface together, and plate escaping portions are formed on opposite sides across the guiding protruding portion in a shoe width direction to avoid contact with the chain plates. 
     In an aspect of the present invention, the shoe surface includes the plate guide surface which is formed on the upstream side of the shoe surface in the shoe longitudinal direction and on which only the chain plate is slidably guided, the guiding protruding portion which is formed on the downstream side of the plate guide surface and on which only the chain roller or a chain bush is guided, and the continuously transitioning protruding portion that smoothly connects the plate guide surface and the guiding protruding surface together, and the plate escaping portions are formed on the opposite sides across the guiding protruding portion in the shoe width direction to avoid contact with the chain plate. Thus, even when the height dimension of the guiding protruding portion is designed to be small, the contact of the chain plate end surface with the shoe surface can be reliably avoided during guidance by the guiding protruding portion. Consequently, the simple structure is used to allow a significant shift in pitch line to be suppressed while reducing friction losses and preventing possible noise. 
     In another aspect of the present invention, an upstream end of the plate escaping portion is formed downstream of an upstream end of the guiding protruding portion at a distance from the upstream end, with the distance being equal to or more than double of a chain pitch. Thus, in an area from the upstream end of the guiding protruding portion to an upstream end of the plate escaping portion, at least two chain rollers or chain bushes can be kept lying on the guiding protruding portion. Therefore, stable chain traveling can be achieved. 
     In another aspect of the present invention, at least an upstream end of the continuously transitioning protruding portion is formed like a taper so as to increase in width from an upstream side toward a downstream side. Thus, even if the traveling chain is slightly deflected in the shoe width direction, the chain roller can be smoothly guided onto the continuously transitioning protruding portion. 
     In another aspect of the present invention, outer plate guide wall portions are each formed on an outer side of the corresponding plate escaping portion in the shoe width direction to face an outer side surface of an outer plate of the chain plates to guide the chain. Thus, not only is a guide function performed by the guiding protruding portion positioned between inner side surfaces of an inner plate but also the chain can be guided from the outer side surface side of the outer plate. Consequently, the traveling chain can be reliably prevented from being tilted in the shoe width direction, further reducing friction losses. 
     In another aspect of the present invention, a groove-like outer plate contact avoiding portion is formed in the plate guide surface to avoid contact with only the outer plate of the chain plates. This enables not only a reduction in the number of chain plates contacting the plate guide surface, allowing friction losses to be reduced, but also a reduction in the mass of the guide shoe. 
     In another aspect of the present invention, a groove-like inner plate contact avoiding portion is formed in the plate guide surface to avoid contact with only the inner plate of the chain plates. This enables not only a reduction in the number of chain plates contacting the plate guide surface, allowing friction losses to be reduced, but also a reduction in the mass of the guide shoe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a use aspect of a guide shoe according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view depicting the guide shoe according to the first embodiment; 
         FIG. 3  is a diagram illustrating the guide shoe of the first embodiment as viewed in a lateral direction; 
         FIG. 4  is a top view depicting the guide shoe of the first embodiment; 
         FIG. 5  is a diagram depicting the guide shoe of the first embodiment as viewed at a position B in  FIG. 3 ; 
         FIG. 6  is a diagram depicting a guide shoe of a second embodiment as viewed at the position B in  FIG. 3 ; 
         FIG. 7  is a diagram depicting a guide shoe of a third embodiment as viewed at a position A in  FIG. 3 ; and 
         FIG. 8  is a diagram depicting a guide shoe of a fourth embodiment as viewed at the position A in  FIG. 3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A guide shoe  100  according to a first embodiment of the present invention will be described below based on  FIGS. 1 to 5 . 
     As depicted in  FIG. 1 , the guide shoe  100 , supported by a metallic base member E fixed to an engine block (not depicted in the drawings) with the guide shoe  100  attached thereto, is assembled in a timing system installed in an engine room. The guide shoe  100  guides a chain CH configured as a roller chain traveling among sprockets S 1  to S 3  to properly maintain chain tension. Specifically, as depicted in  FIG. 1 , the guide shoe  100  guides the chain CH wound around the sprockets S 1  to S 3  provided over a crank shaft and a cam shaft to stabilize the traveling of the chain CH, while properly maintaining the tension of the chain CH. In the present embodiment, the guide shoe  100  is configured as a guide shoe for a fixed guide fixedly installed in the engine room. However, the guide shoe  100  may be configured as a guide shoe for a pivoting guide G that is pivotally supported by a shaft in the engine room and pressed toward the chain CH by a tensioner T as depicted in  FIG. 1 . 
     The guide shoe  100  is formed of a synthetic resin material and has a shoe surface  110  that faces the engine room and that extends in a chain traveling direction. Guide wall portions  160  are formed on outer sides of the shoe surface  110  in a shoe width direction. A side wall portion  170  is formed outside one of the guide wall portions  160 . The above-described guide wall portions  160  and side wall portion  170  may be omitted from a partial area or the entire area in a shoe longitudinal direction as needed. 
     As depicted in  FIGS. 2 to 4 , the shoe surface  110  of the guide shoe  100  includes a plate guide surface  120  formed on an upstream side (chain entry side) of the shoe surface  110  in the shoe longitudinal direction and on which only chain plates PLP and RLP of the chain CH are slidably guided, a guiding protruding portion  130  formed on a downstream side of the plate guide surface  120  and on which only a chain roller R is guided, and a continuously transitioning protruding portion  140  that connects the plate guide surface  120  and the guiding protruding portion  130  together. Plate relief portions  150  are formed on opposite sides across the guiding protruding portion  130  in a shoe width direction to avoid contact with the chain plates PLP and RLP. 
     As depicted in  FIGS. 2 to 4 , the plate guide surface  120  is flat. 
     As depicted in  FIGS. 2, 4, and 5 , the guiding protruding portion  130  is formed in the center of the shoe surface  110  in the shoe width direction and extends along the shoe longitudinal direction. 
     As depicted in  FIGS. 2 to 4 , the continuously transitioning protruding portion  140  is inclined so as to smoothly connect the plate guide surface  120  and the guiding protruding portion  130  together. As depicted in  FIG. 4 , at least an upstream end of the continuously transitioning protruding portion  140  is formed like a taper so as to increase in width from the upstream side toward the downstream side. 
     As depicted in  FIGS. 3 to 5 , the plate escaping portions  150  are formed like recess grooves on opposite sides across the guiding protruding portion  130  in the shoe width direction by recessing the shoe surface  110 , and extend along the shoe longitudinal direction. An upstream end of each of the plate escaping portions  150  is formed downstream of an upstream end of the guiding protruding portion  130  at a distance from the upstream end that is equal to or more than double of a chain pitch. That is, as depicted in  FIG. 3 , a distance L from the upstream end of the guiding protruding portion  130  to the upstream end of the plate escaping portions  150  is set equal to or more than the double of the chain pitch. 
     Next, a guide shoe  200  according to a second embodiment will be described based on  FIG. 6 . The second embodiment is exactly the same as the above-described first embodiment except for a part of the configuration. Thus, reference numbers in the 100s in the specification and drawings that relate to the second embodiment are replaced with reference numerals in the 200s, and description of the components other than those which are different from the corresponding components of the first embodiment is omitted. 
     First, in the above-described first embodiment, when the chain CH travels on the guiding protruding portion  130 , the guiding protruding portion  130  positioned between inner side surfaces of laterally opposite inner plates RLP functions to guide the chain CH in the shoe width direction as depicted in  FIG. 5 . 
     In contrast, in the second embodiment, outer plate guide wall portions  280  are each formed outside the corresponding plate escaping portion  250  and lies opposite to an outer side surface of an outer plate PLP of the chain plates to guide the chain as depicted in  FIG. 6 . Consequently, not only is the guide function performed by the guiding protruding portion  230  but the outer plate guide wall portions  280  allows the chain CH to be guided in the shoe width direction. 
     Now, a guide shoe  300  according to a third embodiment will be described based on  FIG. 7 . The third embodiment is exactly the same as the above-described first embodiment except for a part of the configuration. Thus, reference numbers in the 100s in the specification and drawings that relate to the third embodiment are replaced with reference numerals in the 300s, and description of the components other than those which are different from the corresponding components of the first embodiment is omitted. 
     In the guide shoe  300  of the third embodiment, outer plate contact avoiding portions  390  are each formed like a recess groove in a plate guide surface  320  so as to avoid contact with only the outer plate PLP as depicted in  FIG. 7 . In the example depicted in  FIG. 7 , the outer plate contact avoiding portion  390  is formed like a recess groove, but the specific aspect of the outer plate contact avoiding portion  390  is not limited to this. For example, the outer plate contact avoiding portion  390  may be formed like a through groove penetrating the guide shoe from a front surface (shoe surface) to a back surface thereof. 
     The outer plate contact avoiding portion  390  is formed to extend from the middle of the plate guide surface  320  in the shoe longitudinal direction. Thus, the plate guide surface  320  is contacted first by both the inner plates RLP and the outer plates PLP of the chain CH, but then the plate guide surface  320  is contacted only by the inner plates RLP. Subsequently, a continuously transitioning protruding portion  340  and a guiding protruding portion  330  are contacted by only the chain roller R. The formation position of the outer plate contact avoiding portion  390  in the plate guide surface  320  in the shoe longitudinal direction is not limited to the above-described position. 
     Next, a guide shoe  400  according to a fourth embodiment will be described based on  FIG. 8 . The fourth embodiment is exactly the same as the above-described first embodiment except for a part of the configuration. Thus, reference numbers in the 100s in the specification and drawings that relate to the fourth embodiment are replaced with reference numerals in the 400s, and description of the components other than those which are different from the corresponding components of the first embodiment is omitted. 
     In the guide shoe  400  of the fourth embodiment, an inner plate contact avoiding portion  491  is recessed in a plate guide surface  420  so as to avoid contact with only the inner plates RLP as depicted in  FIG. 8 . In the example depicted in  FIG. 8 , the inner plate contact avoiding portion  491  is formed like a recess groove, but the specific aspect of the inner plate contact avoiding portion  491  is not limited to this. For example, the inner plate contact avoiding portion  491  may be formed like a through groove penetrating the guide shoe from a front surface (shoe surface) to a back surface thereof. 
     The inner plate contact avoiding portion  491  is formed to extend from the middle of the plate guide surface  420  in the shoe longitudinal direction. Thus, the plate guide surface  420  is contacted first by both the inner plates RLP and the outer plates PLP of the chain CH and then by only the outer plates PLP. 
     Subsequently, a continuously transitioning protruding portion  440  and a guiding protruding portion  430  are contacted by only the chain roller R. The formation position of the inner plate contact avoiding portion  491  in the plate guide surface  420  in the shoe longitudinal direction is not limited to the above-described position. 
     The embodiments of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments, and various changes may be made to the design without departing from the present invention recited in the claims. 
     For example, in the above description of the embodiments, the chain traveling on the guide shoe is the roller chain. However, the guide shoe of the present invention may be used to guide a bush chain corresponding to the roller chain from which the chain roller is omitted. In this case, instead of the chain roller, a chain bush climbs on the guiding protruding portion. 
     In the above description of the embodiments, the plate escaping portions on the opposite sides across the guiding protruding portion are formed like recess grooves by recessing the shoe surface. However, the plate escaping portions have any specific aspect as long as the plate escaping portions enable avoidance of the contact between the guide shoe and the chain plates when the chain travels on the guiding protruding portion. For example, the plate escaping portion may be formed like a through groove that penetrates the guide shoe from the front surface (shoe surface) to the back surface thereof. Alternatively, the material portion of the guide shoe may be removed from the opposite sides across the guiding protruding portion, that is, a shoe longitudinal direction interval including only the guiding protruding portion may be provided. 
     In the above description of the embodiments, the upstream end of the plate escaping portion is formed downstream of the upstream end of the guiding protruding portion at a distance from the upstream end that is equal to or more than double of the chain pitch. However, the formation position of the plate escaping portions is not limited to this. Any formation position may be used as long as the plate escaping portion is formed laterally to the guiding protruding portion. 
     A well-known appropriate material may be selected for the guide shoe according to conditions such as frictional resistance, rigidity, durability, moldability, and costs. In particular, a synthetic resin material is preferable. 
     A well-known appropriate metallic material may be selected for a base material according to conditions such as rigidity, durability, moldability, and costs. 
     The guide shoe and the base member may be integrated together. The guide shoe may be configured by optionally combining configurations of the above-described plurality of embodiments. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           100 ,  200 ,  300 ,  400  . . . Guide shoe 
           110  . . . Shoe surface 
           120 ,  320 ,  420  . . . Plate guide surface 
           130 ,  230  . . . Guiding protruding portion 
           140  Continuously transitioning protruding portion 
           150 ,  250  Plate escaping portion 
           160  Guide wall portion 
           170 ,  270 ,  370 ,  470  Side wall portion 
           280  Outer plate guide wall portion 
           390  Outer plate contact avoiding portion 
           491  Inner plate contact avoiding portion 
         B Base member 
         CH Chain 
         PLP Outer plate (chain plate) 
         RLP Inner plate (chain plate) 
         R Chain roller 
         B Chain bush 
         P Coupling pin 
         E Base member 
         T Tensioner 
         G Pivoting guide 
         S 1  to S 3  Sprocket