Patent Publication Number: US-7901269-B2

Title: Grinding apparatus for a pin for use in power transmission chain and manufacture method of a pin for use in power transmission chain

Description:
This application is a Divisional of application Ser. No. 11/663,839, filed on Mar. 27, 2007 now U.S. Pat. No. 7,607,969 and for which priority is claimed under 35 U.S.C. §120. This application claims priority to Application No. 2004-30423 filed in Japan on Oct. 19, 2004 and Application No. 2004-315848 filed on Oct. 29, 2004 under 35 U.S.C. §119, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an apparatus for=grinding a pin for use in power transmission chain and a manufacture method of the pin for use in power transmission chain. 
     BACKGROUND ART 
     In a continuously variable transmission for use in automotive vehicles (see, for example, Japanese Unexamined Utility Model Publication No. H3-84459) for example, a pair of conical pulleys (sheaves)  51 ,  52  are mounted to a driving shaft  50  shown in  FIG. 10 . One  51  of the conical pulleys is capable of being axially moved by a cylinder piston unit  53 . The width of a groove defined between the conical pulley pair  51 ,  52  may be increased or decreased by such a movement of the pulley. A belt-like power transmission chain  56  is entrained between the conical pulley pair  51 ,  52 . The groove width is increased or decreased whereby the power transmission chain  56  is moved toward the center of the conical pulleys  51 ,  52  or pushed toward outer sides of the pulleys, as making sliding contact with conical surfaces  51   a ,  52   a  of the conical pulleys  51 ,  52 . 
     The power transmission chain  56  is formed by bendably interconnecting unit members into an endless belt form by means of load pins  55  (pins for use in power transmission chain), the unit member having a structure wherein thin plates called link plates  54  are overlapped on one another. The load pin  55  is formed by machining opposite ends of a flat-plate member in conformity to the conical surfaces  51   a ,  52   a  of the pulleys  51 ,  52 . The load pin is adapted to make contact with the conical surfaces  51   a ,  52   a  of the pulleys  51 ,  52  at the opposite end faces thereof when the power transmission chain  56  is entrained between the conical pulley pair  51 ,  52 . The power transmission chain  56  is adapted to transmit power by way of frictional force based on the contact between the load pins and the conical surfaces. 
     All the load pins  55  must be finished in an exact length and must have the opposite end faces finished in predetermined configurations. Therefore, the load pin  55  is subjected to a grinding process using a grinding wheel.  FIG. 11  schematically shows the locations of members involved in the grinding process.  FIG. 11(   a ) is a plan view and  FIG. 11(   b ) is a side view. The grinding process is performed as follows. First, a bundle of load pins  55  are retained on a support portion  58  by means of a jig  57 . In this state, one end face of each load pin is ground by a grinding wheel  59 . Subsequently, the bundle is turned over and the other end face of each load pin is ground. 
     DISCLOSURE OF THE INVENTION 
     However, it takes a long time to grind all the opposite end faces of a large number of load pins constituting the whole length of chain. 
     In view of the foregoing problem, the present invention is directed to the reduction of time taken by the grinding process in the manufacture of the pins for use in the power transmission chain. 
     According to the invention, a grinding apparatus a for a pin for use in power transmission chain comprises: a grinding wheel portion which is a rotary member rotating about an axis parallel to a Z-direction provided that three directions orthogonal to one another are defined as an X-direction, a Y-direction and the Z-direction, and which includes a pair of grinding surfaces at an outer circumferential area thereof for simultaneously grinding opposite end faces of a pin for use in power transmission chain as a grinding subject; and a carrier which supports the pin for use in power transmission chain in parallel to the Z-direction as allowing the opposite end faces of the pin to project therefrom, and which moves the pin for use in power transmission chain relative to the grinding surfaces on an X-Y plane, thereby passing the pin for use in power transmission chain through space between the pair of rotated grinding surfaces. 
     The grinding apparatus of the above constitution simultaneously grinds the opposite end faces of the pin for use in power transmission chain by means of the rotating grinding surfaces. Thus, the time taken by the grinding process may be reduced as compared with a case where one end face is ground at a time. 
     According to another aspect of the invention, a grinding apparatus for a pin for use in power transmission chain comprises: a grinding wheel portion which is a rotary member rotated about a first axis parallel to a Z-direction provided that three directions orthogonal to one another are defined as an X-direction, a Y-direction and the Z-direction, and which includes a pair of grinding surfaces at an outer circumferential area thereof for simultaneously grinding opposite end faces of a pin for use in power transmission chain as a grinding subject; and a carrier which supports the pin for use in power transmission chain in parallel to the Z-direction as allowing the opposite end faces of the pin to project therefrom, and which rotates about a second axis extending in parallel to the first axis and spaced away therefrom on an X-Y plane, thereby passing the pin for use in power transmission chain through space between the pair of rotating grinding surfaces. 
     The grinding apparatus of the above constitution simultaneously grinds the opposite end faces of the pin for use in power transmission chain by means of the rotating grinding surfaces. Furthermore, the formation of a centrally protruded configuration on the respective opposite end faces of the pin may be accomplished by rotating the carrier, the centrally protruded configuration depending upon a radius defined between the second axis and the pin for use in power transmission chain. 
     In the above grinding apparatus, the grinding wheel portion is shaped like a disc and the grinding surfaces thereof are defined by axially opposite walls of a circumferential groove formed in an outer periphery of the grinding wheel portion. 
     In this case, both of the grinding surfaces belong to a single grinding wheel and hence, grinding precisions may be easily achieved. 
     The above grinding apparatus may also have a constitution wherein the grinding wheel portion is shaped like a disc and the grinding surfaces thereof are defined by axially opposite walls of a circumferential groove formed by cutting inwardly an outer periphery of the grinding wheel portion and are conically inclined. 
     Furthermore, the grinding wheel portion may comprise a pair of grinding wheels having the same configuration and opposing each other as defining a predetermined gap between the grinding surfaces thereof. 
     The carrier may also be a disc-like member formed with notches at an outer periphery thereof at regular space intervals. 
     According to the invention, a manufacture method of a pin for use in power transmission chain comprises a procedure for grinding opposite end faces of a pin for use in power transmission chain, wherein a grinding wheel portion including a pair of grinding surfaces at an outer circumferential area thereof for simultaneously grinding the opposite end faces is rotated about an axis parallel to a Z-direction provided that three directions orthogonal to one another are defined as an X-direction, a Y-direction and the Z-direction while a carrier supports the pin in parallel to the Z-direction as allowing the opposite end faces of the pin to project from the carrier, and wherein the carrier moves the pin for use in power transmission chain relative to the grinding surfaces on an X-Y plane thereby passing the pin for use in power transmission chain through space between the pair of rotated grinding surfaces. 
     The above manufacture method permits the opposite end faces of the pin for use in power transmission chain to be simultaneously ground by the rotated grinding surfaces. 
     According to another aspect of the invention, a manufacture method of a pin for use in power transmission chain comprises a procedure for grinding opposite end faces of a pin for use in power transmission chain, wherein a grinding wheel portion including a pair of grinding surfaces at an outer circumferential area thereof for simultaneously grinding the opposite end faces is rotated about a first axis parallel to a Z-direction provided that three directions orthogonal to one another are defined as an X-direction, a Y-direction and the Z-direction, while a carrier supports the pin in parallel to the Z-direction as allowing the opposite end faces of the pin to project from the carrier, and wherein the carrier is rotated about a second axis extending in parallel to the first axis and spaced away therefrom on an X-Y plane whereby the pin for use in power transmission chain is passed through space between the pair of rotated grinding surfaces. 
     The above manufacture method permits the opposite end faces of the pin for use in power transmission chain to be simultaneously ground by the rotated grinding surfaces. Furthermore, the formation of a centrally protruded configuration on the respective opposite end faces of the pin may be accomplished by rotating the carrier, the centrally protruded configuration depending upon a radius defined between the second axis and the pin for use in power transmission chain. 
     The above manufacture method may also have a constitution wherein the carrier, normally rotated at a high speed, is rotated at a low speed only when the pin for use in power transmission chain is passed through space between the grinding surfaces. 
     In the manufacture method, it is also possible to perform an infeed grinding process in which the grinding wheel portion is moved to the carrier for cutting. 
     The manufacture method may also have a constitution wherein the pin for use in power transmission chain is passed through space between the pair of grinding surfaces as vertically moved. 
     According to still another aspect of the invention, a grinding apparatus for a pin for use in power transmission chain comprises: a grinding wheel portion which is a rotary member including a pair of grinding surfaces at an outer circumferential area thereof for simultaneously grinding opposite end faces of a pin for use in power transmission chain as a grinding subject; and a carrier which includes a pin retainer for retaining the pin in parallel to a rotary axis of the grinding wheel portion as allowing the opposite end faces of the pin to project from the pin retainer, and which is rotated about an axis parallel to the rotary axis of the grinding wheel portion thereby passing the pin retained by the pin retainer through space between the pair of rotated grinding surfaces, the pin retainer including: a pin retaining surface against which a side surface of the pin is pressed and which extends in parallel to the rotary axis of the grinding wheel portion and intersects a direction of grinding the opposite end faces of the pin; and an elastically deformable holder member cooperating with the pin retaining surface to removably clamp the pin for use in power transmission chain pressed against the pin retaining surface. 
     In the grinding apparatus of the above constitution, the opposite end faces of the pin for use in power transmission chain are simultaneously ground by means of the pair of rotated grinding surfaces. Therefore, the time taken by the grinding process may be reduced as compared with the case where one end face is ground at a time. 
     Furthermore, the pin is retained with its side surface pressed against the pin retaining surface intersecting the grinding direction, so that a most of the grinding resistance exerted on the pin in conjunction with the grinding of the opposite end faces may be received by the pin retaining surface. Therefore, the pin need not to be clamped firmly and may be retained by means of a relatively simple constitution to clamp the pin between the pin retaining surface and the elastically deformable holder member. This constitution permits the pin to be easily mounted or dismounted without taking a complicated procedure. 
     It is preferred in the above grinding apparatus that the pin retaining surface is in contact with only opposite end portions of the pin for use in power transmission chain. 
     In this case, the pin is supported at two points of the opposite ends thereof and hence, the free play and the like of the pin may be suppressed. Thus, the pin may be retained in a stable position. 
     According to the above grinding apparatus, the pin retainer may be formed at place where a part of a periphery of the carrier is cut away. 
     The grinding apparatus may also have a constitution wherein a step portion continuously extending from the pin retaining surface to a step surface raised therefrom is formed and the pin for use in power transmission chain is pressed against the step portion. In this case, the positioning of the pin for use in power transmission chain may be accomplished by pressing the pin against the step portion. 
     The grinding apparatus may also have a constitution wherein the holder member is a leaf spring, a proximal end of which is fixed to the step surface and a distal end of which opposes the pin retaining surface via a gap therebetween. It is preferred that the gap is slightly smaller than a clamp dimension of the pin for use in power transmission chain clamped in the gap. This constitution provides for a proper elastic deformation of the holder member. 
     According to still another aspect of the invention, a manufacture method of a pin for use in power transmission chain using the above grinding apparatus for a pin for use in power transmission chain comprises a procedure for grinding the opposite end faces of the pin for use in power transmission chain, wherein the grinding wheel portion is rotated, 
     wherein the pin for use in power transmission chain is clamped between the pin retaining surface and the holder member of the pin retainer so as to be retained in parallel to the rotary axis of the grinding wheel portion as projecting the opposite end faces thereof from the carrier, and wherein the carrier is rotated thereby passing the pin through space between the pair of rotated grinding surfaces. 
     The above manufacture method permits the opposite end faces of the pin for use in power transmission chain to be simultaneously ground by the rotated grinding surfaces. The method not only ensures that the pin is positively retained during the grinding process but also provides easy mounting/dismounting of the pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view schematically showing an outward appearance of a grinding apparatus for a pin for use in power transmission chain according to a first embodiment of the invention; 
         FIG. 2  is a group of fragmentary enlarged views showing a carrier and a grinding wheel of the grinding apparatus shown in  FIG. 1 ; 
         FIG. 3  is a perspective view showing a post-grinding load pin; 
         FIG. 4  is a diagram showing the carrier of  FIG. 2  and an end face of a load pin as viewed in a Z-direction; 
         FIG. 5  is a front view schematically showing an outward appearance of another grinding apparatus for a pin for use in power transmission chain, which includes a carrier of a different constitution; 
         FIG. 6  is a front view schematically showing an outward appearance of a grinding apparatus for pin for use in power transmission chain according to a second embodiment of the invention; 
         FIG. 7  is a fragmentary enlarged view showing a carrier and a grinding wheel of the grinding apparatus of  FIG. 6 ; 
         FIG. 8  is a horizontal sectional view of an essential part including a center line CL 1  in  FIG. 7 ; 
         FIG. 9  is an enlarged perspective view showing a pin retainer; 
         FIG. 10  is a diagram showing a power transmission chain entrained about a conical pulley of a driving shaft; and 
         FIG. 11  is a group of diagrams showing, in plan view and side view, the locations of members involved in a conventional grinding process of the load pin. 
     
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
     Referring to the accompanying drawings, the following description will be made on a grinding apparatus for a pin for use in power transmission chain according to a first embodiment of the invention and a procedure for grinding opposite end faces of the pin in a manufacture method of the pin for use in power transmission chain. 
       FIG. 1  is a plan view schematically showing an outward appearance of the grinding apparatus for a pin for use in power transmission chain. The explanation of the pin for use in power transmission chain is omitted because the description has already been made on FIG.  6 (sic). 
     The horizontal, vertical and depth-wise directions mutually intersecting at right angles in  FIG. 1  are defined as X-direction, Y-direction and Z-direction, respectively. A grinding apparatus  100  includes: a base  1 ; a carrier support  2  mounted to the base  1 ; a disc-like carrier  3  supported by the carrier support  2  in a manner to be rotatable about an axis  3   z  parallel to the Z-direction; a grinding wheel support  4  mounted to the base  1  in a manner to be movable in parallel to the X-direction; a grinding wheel  5  as a disc-like rotary member supported by the grinding wheel support  4  in a manner to be rotatable about an axis  5   z  parallel to the Z-direction; dresser supports  6 ,  7  mounted to the grinding wheel support  4  in a manner to be movable in parallel to the X-direction and the Y-direction, respectively; and a dresser  8  supported by the dresser supports  6 ,  7 . 
     The carrier  3  and the grinding wheel  5  are each driven into a counterclockwise rotation by means of an unillustrated motor. The rotational speed of the carrier  3  is not constant. The carrier  3  may be rotated at two rotational speeds (high speed and low speed). The dresser  8  is also driven into rotation by means of an unillustrated motor. While the grinding wheel  5  and the dresser  8  are rotated, the dresser supports  6 ,  7  are moved to bring the dresser  8  into contact against the grinding wheel  5 , whereby the grinding wheel  5  may be machined into a desired configuration. A standard position of the dresser  8  is on a center line CL 1  extending in the X-direction and intersecting the axis  5   z  of the grinding wheel  5 . 
     Now referring to  FIG. 2 , a detailed description is made on the carrier  3  and the grinding wheel  5  constituting an essential part of the grinding apparatus for a pin for use in power transmission chain according to the invention. 
       FIG. 2(   a ) is a fragmentary enlarged view of the carrier  3  and the grinding wheel  5  shown in  FIG. 1 . The axis  3   z  of the carrier  3  and the axis  5   z  of the grinding wheel  5  are on the same center line CL 1  extending in the X-direction.  FIG. 2(   b ) is a horizontal sectional view including the center line CL 1  in  FIG. 2(   a ). The carrier  3  is circumferentially formed with pockets  3   a  at regular space intervals. A load pin  55  (a pin for use in power transmission chain) is mounted in the pocket by using an unillustrated jig. The load pin  55  mounted in the pocket  3   a  of the carrier  3  is supported in parallel to the Z-direction as projecting its opposite end faces from the carrier  3 . 
     On the other hand, the grinding wheel  5  is formed with a circumferential groove  5   a  in the vicinity of an outer periphery thereof. The circumferential groove is formed by cutting inwardly the outer periphery of the grinding wheel in a manner to define a trapezoidal sectional shape as shown in the figure. Axially opposite walls (Z, −Z directions) of the circumferential groove  5   a  constitute grinding surfaces  5   b  conically inclined. These grinding surfaces oppose each other in the Z-direction to define symmetric configurations. Referring to  FIG. 2(   b ), a portion of the grinding surface  5   b , which is responsible for grinding the load pin  55 , is so finished as to have a curvature radius R 1 . The curvature radius R 1  as well as an inclination of the grinding surface  5   b  and a Z-wise distance between the grinding surfaces  5   b  are so defined as to provide correct dimensions and configuration of the post-grinding load pin  55 . A radius of rotation R 2  as viewed from the axis  3   z  of the carrier  3  is defined by a distance between the axis of the carrier and the center of the load pin  55 . 
     In a state where the grinding wheel  5  is rotated at a constant speed, the load pin  55  is ground by being passed through space between the pair of grinding surfaces  5   b  of the grinding wheel by means of the rotated carrier  3 . In this process, the carrier  3  is rotated at the low speed to feed the next load pin  55  into space between the grinding surfaces  5   b  and to move the load pin through an angular range α where the load pin is actually ground by the grinding surfaces  5   b . Otherwise, the carrier  3  is rotated at the high speed. As moved through the angular range α, the load pin  55  has its opposite end faces  55   a  simultaneously ground by the rotated grinding surfaces  5   b.    
       FIG. 3  is a perspective view showing post-grinding configurations of the upper and lower end faces of the load pin  55  shown in  FIG. 2(   b ). The figure shows the X-, Y- and Z-directions on assumption that the load pin  55  is in the position shown in  FIG. 2(   b ). In the figure, the upper end face  55   a  is inclined downward to the right and the lower end face  55   a  is inclined upward to the right because of the inclinations of the grinding surfaces  5   b  ( FIG. 2(   b )). Because of the configuration of the grinding surface  5   b  (such as the curvature radius R 1 ), the end face  55   a  has a centrally protruded configuration having a mean curvature radius R 1 ′ with respect to a longitudinal direction thereof. 
     On the other hand,  FIG. 4  shows the carrier  3  of  FIG. 2  and the end face  55   a  of the load pin  55  as viewed in the Z-direction. Because of the rotation of the carrier  3 , any post-grinding contour line on the end face  55   a  as viewed in the Z-direction defines a concentric circle having a radius R 2 ′ on average. The radius R 2 ′ depends upon the radius of rotation R 2  of the pin. In a case where R 2  is in the range of 50 to 300 mm, for example, R 2 ′ is about five times as great as R 2 . As shown in  FIG. 3 , therefore, the end face  55   a  defines a three-dimensional curved surface having the curvature radius R 1 ′ with respect to the longitudinal direction and the curvature radius R 2 ′ (average value) with respect to a traverse direction. A quantity of central protrusion d defined by the curvature radius R 2 ′ is on the order of 1 μm when R 2  is 150 mm, for example. Such a centrally protruded configuration contributes to the decrease of contact resistance between the load pin  55  and the conical pulleys  51 ,  52  (see  FIG. 10 ). A relation between R 2  and the quantity of central protrusion is such that the quantity of central protrusion is increased with the decrease of R 2  or the quantity of central protrusion is decreased with the increase of R 2 . 
     In this manner, the opposite end faces  55   a  of the load pin  55  are simultaneously ground by the rotated grinding surfaces  5   b . Furthermore, the opposite end faces  55   a  of the pin are ground into the centrally protruded configurations based on the radius R 2  because of the rotation of the carrier  3 , the radius R 2  defined between the axis  3   z  of the carrier and the load pin  55 . Thus, the centrally protruded configurations contributing to the decrease of contact resistance are simultaneously formed on the opposite end faces. Accordingly, the time taken by the grinding process may be reduced as compared with the conventional process wherein one end face is ground at a time. What is more, the load pin  55  may have its opposite end faces  55   a  ground at a time, without re-mounting the load pin to the carrier. Thus, the opposite end faces of the load pin may be ground with high precisions because the grinding process does not involve errors associated with the re-mounting of the pin. 
     According to the above embodiment, both of the grinding surfaces  5   b  belong to a single grinding wheel  5  so that the dimensional precisions of the circumferential groove  5   a  may be easily achieved. This facilitates the grinding of the load pin  55  with high precisions. It is noted, however, an alternative constitution may also be made, for example, wherein a pair of grinding wheels having the same constitution including the grinding surface  5   b  are prepared and are combined with each other in a manner that the respective grinding surfaces  5   b  thereof oppose each other via a predetermined gap therebetween. Thus, the grinding wheels as a whole may constitute a “grinding wheel portion” in the mode shown in  FIG. 2(   b ). 
     The grinding process according to the embodiment is a through process (one-step finishing process) wherein the carrier  3  being rotated is passed through space between a pair of grinding surfaces  5   b  of the grinding wheel  5  rotated as fixed to place with respect to the X-direction. Alternatively, an infeed grinding process may also be adopted wherein the grinding wheel  5  is moved to the carrier  3  by slidably moving the grinding wheel support  4 , so as to cut inwardly with respect to the carrier. 
     The above embodiment illustrates the constitution wherein the carrier  3  is rotated as retaining the load pins  55 . As shown in  FIG. 5 , an alternative constitution may also be made wherein a conveyor-type carrier  10  is provided for vertical conveyance of the pins between upper and lower pulleys  9  and wherein the load pins mounted to the carrier  10  in parallel to the Z-direction are vertically moved to be passed through space between the grinding surface pair  5   b . In this case, the aforesaid R 2  is practically infinite and hence, the end face  55   a  is ground into a configuration which is free from the central protrusion with respect to the transverse direction. Any other constitution may also be made so long as the load pin and the grinding surfaces are moved relative to each other on an X-Y plane for allowing the load pin to pass through space between the grinding surfaces. An end-face configuration having an arbitrary curvature radius R 2 ′ may be obtained by changing the path of the above relative movement. 
     Now referring to the accompanying drawings, description is made on a grinding apparatus for a pin for use in power transmission chain according to a second embodiment of the invention and on a procedure of grinding the opposite end faces of the pin in a manufacture method of the pin for use in power transmission chain. 
       FIG. 6  is a front view schematically showing an outward appearance of a grinding apparatus for a pin for use in power transmission chain. A difference from the first embodiment consists in the mode of the carrier  3 . The carrier  3  according to the second embodiment is configured such that a disc-like member is formed with notches at an outer periphery thereof at regular space intervals. The carrier  3  is supported by the carrier support  2  in a manner to be rotatable about the axis  3   z  parallel to the Z-direction. 
     Next, referring to  FIG. 7  to  FIG. 9 , a detailed description is made on the carrier  3  and the grinding wheel  5  constituting the essential part of the grinding apparatus for a pin for use in transmission power chain according to the invention. 
       FIG. 7  is a fragmentary enlarged view showing the carrier  3  and the grinding wheel  5  shown in  FIG. 6 . The axis  3   z  of the carrier  3  and the axis  5   z  of the grinding wheel  5  are on the same center line CL 1  extending in the X-direction.  FIG. 8  is a horizontal sectional view of the essential part including the center line CL 1  in  FIG. 7 . The carrier  3  includes eight pin retainers  30  which are circumferentially arranged with equal spacing and are each formed by cutting away a part of the periphery of the carrier. The load pins  55  (pins for use in power transmission chain) are retained on the carrier. The load pin  55  is retained by the pin retainer  30  in parallel to the Z-direction (axis  5   z ) as projecting its opposite end faces from the carrier  3 . 
     The circumferential groove  5   a  and the grinding surfaces  5   b  of the grinding wheel  5  are constituted the same way as in the first embodiment. As shown in  FIG. 7 , the radius of rotation R 2  as viewed from the axis  3   z  of the carrier  3  is defined by the distance between the axis of the carrier and the center of the load pin  55 . 
       FIG. 9  is an enlarged perspective view showing the pin retainer  30 . The pin retainer  30  includes: a pin retaining surface  31  extended along a radial line of the carrier  3  and in parallel to the axis  3   z  (axis  5   z ); and a plate-like holder member  33  fixed to a step surface  32  raised relative to the pin retaining surface  31 . The load pin  55  is positioned as pressed against the pin retaining surface  31  and a step portion  32   a  at its side surfaces, the step portion  32   a  continuously extending from the pin retaining surface  31  to the step surface  32 . The load pin  55  is clamped between the pin retaining surface  31  and the holder member  33  so as to be retained in parallel to the Z-direction as projecting its opposite end faces from the carrier  3 . 
     The holder member  33  is a leaf spring formed from a spring steel and having a shape shown in the figure, for example. The holder member  33  has one-end portion thereof clamped between shims  34 ,  35  and secured to the step surface  32  with bolts  36 , the one-end portion substantially accounting for one half of the member. The other-end portion of the holder member is projected from the step surface  32 , thus defining a projecting portion  33   a . The projecting portion  33   a  is designed to oppose the pin retaining surface  31  via a gap slightly smaller than an outer peripheral width of the load pin  55 , the gap determined in a state where the load pin  55  is not clamped between the projecting portion and the pin retaining surface. Since the holder member  33  is the leaf spring, the projecting portion  33   a  thereof is adapted for a proper elastic deformation. Hence, the load pin  55  may be properly clamped by way of an elastic force arising from the elastic deformation of the holder member holding the load pin  55 . Thus, the load pin  55  is retained by the pin retainer  30  in a manner to be readily mounted or removed therefrom. 
     A recess  37  is formed between a pair of pin retaining surfaces  31 , so that a side surface (X-Z surface) of the load pin  55  is in contact against the pin retaining surfaces  31  at only two portions near the opposite ends of the pin. In this case, the load pin  55  is retained at two points spaced away from each other in the Z-direction and hence, the load pin may be retained in a stable position and besides, the free play and the like of the load pin  55  in the retained position may be minimized. Furthermore, a contact area between the pin retaining surface  31  and the load pin  31  is decreased so that the load pin  55  may encounter less resistance when mounted or removed. This further facilitates the mounting or dismounting of the load pin  55 . 
     The load pin is ground as follows. In a state where the grinding wheel  5  is rotated at a constant speed, the carrier  3  is rotated for passing the load pin  55  through space between the grinding-surface pair  5   b . In this process, the rotational speed of the grinding wheel  5  is set to a relatively high speed, whereas the rotational speed of the carrier  3  is set to a speed lower than that of the grinding wheel  5 . 
     In the grinding wheel  5 , the load pin  55  is passed through space between the grinding-surface pair- 5   b  in an angular range γ shown in  FIG. 7 . On the other hand, the carrier  3  passes the load pin  55  through space between the grinding-surface pair  5   b , as rotated through an angular range P. The pin retaining surface  31  of the pin retainer  30 , as moved through the angular range β, is never oriented in parallel to a grinding direction (direction of force applied by grinding) of the grinding surface  5   b  in the angular range γ or is constantly oriented to intersect the grinding direction. 
     The load pin  55 , as moved through the above angular range β, has its opposite end faces  55   a  simultaneously ground by the rotated grinding surfaces  5   b . The post-grinding configurations of the upper and lower end faces of the load pin  55  are the same as those of the first embodiment, as shown in  FIG. 3 . 
     In this manner, the opposite end faces  55   a  of the load pin  55  are simultaneously ground by the rotated grinding surfaces  5   b , while the carrier  3  is rotated for simultaneously forming the centrally protruded configurations, contributing to the decrease of contact resistance, on the opposite end faces. 
     Furthermore, the load pin  55  is retained with its side surface pressed against the pin retaining surface  31  intersecting in the grinding direction of the grinding surfaces  5   b , so that the most of the grinding resistance exerted on the load pin  55  in conjunction with the grinding of the opposite end faces  55   a  may be received by the pin retaining surface  31 . Therefore, the load pin  55  need not to be clamped as firmly as in the conventional method but may be retained by means of a relatively simple constitution to clamp the load pin between the pin retaining surface  31  and the elastically deformable holder member  33 . This constitution permits the load pin to be easily mounted or dismounted without taking a complicated procedure. 
     The invention may achieve the reduction of the time taken by the grinding operation because the apparatus is adapted for simultaneous grinding of the opposite end faces  55   a  of the load pin  55  and also permits the load pin to be easily mounted or dismounted without taking the complicated procedure. 
     In the above grinding apparatus, it may be contemplated, for example, to replace the pin retainer  30  for retaining the load pin  55  with a hydraulic chuck such that the load pin  55  may be firmly retained in an easy-to-mount or remove manner and that the load pins  55  may be automatically supplied. However, if such a hydraulic chuck mechanism is mounted to the carrier  3 , the hydraulic chuck must be mounted in a limited space or the rotatable carrier  3  must be equipped with auxiliary machinery including hydraulic piping and the like. Hence, the grinding apparatus as a whole has an extremely complicated arrangement and besides, is increased in cost. 
     In contrast, the grinding apparatus according to the embodiment permits the load pin  55  to be removably retained by way of the relatively simple constitution. Therefore, the grinding apparatus may be readily redesigned for automatically supplying the load pins to the carrier  3  without employing the complicated mechanism. 
     While the foregoing embodiments employ the leaf spring as the holder member  33 , any material that is elastically deformable and is capable of removably clamping the load pin  55  may be used. For instance, a resin material or the like may be employed. In addition, the configuration of the holder member  33  is not limited to the plate shape and may have any configuration adapted for removably clamping the load pin  55 .