Outer ring, drawn cup needle roller bearing, drawn cup needle roller bearing structured body, piston pin supporting structure of engine, crankshaft supporting structure of engine, and 2-cycle engine

The straightness and parallelism of a track surface on which rollers roll are measured within a range “L2” as a range for measuring the straightness and parallelism. The range “L2” is a range such that L2≧0.8×L when a roller length is “L”. When the dimension from the corner P of the flange on the inner diameter side to the starting point of the range “L2” is “L1”, the dimension “L1” is ranged such that 0.8 mm≦L1≦2 mm. In this range, the straightness of the track surface of the outer ring in the axial direction is not more than 0.008 mm and the parallelism thereof is not more than 0.015 mm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a outer ring press fitted in a housing and having a track surface on its inner diameter surface, a drawn cup needle roller bearing, a drawn cup needle roller bearing structured body, a piston pin supporting structure of an engine, a crankshaft supporting structure of an engine, and a 2-cycle engine comprising the above outer ring.

2. Description of the Background Art

A 2-cycle engine having small capacity is used in a utility engine of a bush cutter and the like. A technique regarding the 2-cycle engine is disclosed in Japanese Unexamined Patent Publication No. 7-332371.

FIG. 14is a longitudinal sectional view showing a 2-cycle engine in which roller bearings are used at the small end part and large end part of a connecting rod con-rod). Referring toFIG. 14, the 2-cycle engine comprises a crankshaft83outputting rotary motion, a piston85moving in a linear line back and forth, and a con-rod84connecting the crankshaft83to the piston85and converting the linear reciprocating motion to the rotary motion. The crankshaft83rotates around a rotation center shaft90and keeps a rotation balance with a balance weight91.

The mixed gas of gasoline and lubricant oil is sent from an inlet87to a crank chamber82and then led to a combustion chamber89arranged at the upper part of a cylinder81according to the vertical motion of the piston85. The exhaust gas is discharged from an exhaust hole88.

The con-rod84comprises a large end part93at the lower part of a linear rod and a small end part94at the upper part thereof. The crankshaft83is rotatably supported at the large end part93of the con-rod84through a roller bearing86mounted in an inner diameter hole, and a piston pin92connecting the piston85to the con-rod84is rotatably supported by a roller bearing86mounted in an inner diameter hole.

As the roller bearings86mounted in the inner diameter holes provided at the small end part and the large end part of the con-rod84to support the piston pin92and the crankshaft83, a drawn cup needle roller bearing that can receive high load in spite of its small projected area and highly rigid is used. Here, the drawn cup needle roller bearing comprises a outer ring formed of a steel plate processed by drawing, a plurality of rollers and a retainer. The retainer comprises pockets for holding the rollers and the interval of the rollers is retained by a column part positioned between the pockets.

Here, one manufacturing method of the retainer contained in the above drawn cup needle roller bearing will be briefly described hereinafter. First, a band steel that is the material of the retainer is punched out to form a pocket having a size in which the roller can be held. Then, it is pressed into a V-shaped form in section at a pressing step. Then, it is cut to the circumferential length of the retainer, and the cut band steel is bent into a cylindrical shape and the end faces of the bent band steel are connected by welding and the like. Then, it is heat treated, whereby the retainer is completed.

Here, when the band steel is pressed so that its sectional configuration becomes V shape, since its height in the diameter direction can be largely ensured, the following effect is provided.FIGS. 15A and 15Bare sectional views showing the cut band steel in the diameter direction after the pressing process before and after it is bent into the cylindrical shape. Since the interval of column parts106on the side of an inner diameter surface112before a retainer104is bent into the cylindrical shape (FIG. 15A) becomes small after the retainer104is bent into the cylindrical shape (FIG. 15B), a roller103held in the pocket is prevented from falling off toward the side of the inner diameter surface112. In this case, the roller103may be prevented from escaping toward the side of an outer diameter surface111by providing a roller escape preventing part at the column part106on the side of the outer diameter surface111.

In addition,FIG. 16is a view showing a state in which the retainer104retaining the roller103is incorporated in a outer ring102and a shaft101. By performing the pressing process so that its sectional configuration becomes V shape, the roller103can be guided in the vicinity of a PCD (Pitch Circle Diameter)105in which the roller103can roll most stably when guided.

In addition, a retainer of a roller bearing having the same configuration as that of the retainer manufactured by the above steps is disclosed in Japanese Unexamined Patent Publication No. 2005-98368.

A description will be made of a method for measuring the precision of the outer ring102contained in the above drawn cup needle roller bearing hereinafter. The outer ring102has a track surface on which the roller rolls, at its cylindrical inner diameter surface119. Regarding the track surface of the outer ring102, since it is necessary that the roller can roll stably, high dimensional precision is required.

When the precision of the track surface of the outer ring102in which the high dimensional precision is required is measured, a variation in thickness dimension in the circumferential direction, that is, a variation in thickness of the cylindrical part of the outer ring102has been measured.FIG. 17is a view showing a state when the variation in thickness of the cylindrical part of the outer ring102is measured in this case. Referring toFIG. 17, the outer ring102has a track surface on which the roller rolls, on the side of the inner diameter surface119of its cylindrical part116. Here, the variation in thickness of the cylindrical part116is measured such that while an outer diameter surface118is pressed with a reference member117at the position shown by an arrow X or Y inFIG. 17and the corresponding inner diameter surface119is pressed with a gauge terminal, the outer ring102is rotated.

In addition, a drawn cup needle roller bearing comprising a outer ring having a track surface on its inner diameter surface, in which a thickness difference is provided at a cylindrical part is disclosed in Japanese Unexamined Patent Publication No. 2002-235753.

According to the method of measuring the precision of the above outer ring contained in the drawn cup needle roller bearing, when the thickness of the cylindrical part is measured, the variation in thickness of the cylindrical part116, that is, a difference in thickness in the circumferential direction is measured. However, this is not necessarily optimal as a precision parameter for evaluating whether the roller can roll stably. Especially, since the cylindrical part116of the outer ring102is relatively thin, and it could be deformed at a heat treatment and the like, it is necessary to measure the configuration after press fitted.

In this case, while the outer ring is press fitted in an inner diameter hole provided in a reference ring having a reference surface for parallelism and the like, the generatrix configuration of the inner diameter surface of the outer ring is measured and this is to be set to the precision parameter. However, when the generatrix configuration is set to the precision parameter as it is, since the generatrix configuration is measured including a part other than the surface on which the roller rolls, it cannot be correctly evaluated whether the roller can roll stably or not.

Meanwhile, among the above manufacturing steps of the retainer, at the pocket punching-out step, the blade of a punch is pressed against the material of the retainer along a pocket configuration to punch out the pocket. In this case, a sheared surface and a fractured surface are generated in the side wall surface of the pocket, that is, the side wall surface of the column part positioned between the pockets. The sheared surface is a smooth surface punched out with the edge of the blade of the punch and the like. Meanwhile, the fractured surface is a coarse surface fractured by the material pressed and punched out with the blade edge.

Here, when the pocket is punched out from the side that becomes the inner diameter surface when the retainer is bent into the cylindrical shape at the pocket punching-out step, the fractured surface is positioned in the side wall surface of the column part on the side of the outer diameter surface.

FIG. 18is a sectional view showing the retainer104in the diameter direction in this case.FIG. 19is a sectional view showing the retainer104in the axial direction in this case. InFIG. 19, the part shown by a dotted line designates the roller103retained in the pocket of the retainer104, and a dashed line designates the PCD105. Referring toFIGS. 18 and 19, when the pocket is punched out from the direction shown by an arrow Z in the drawing that becomes the inner diameter surface112, a sheared surface108is positioned on the side of the inner diameter surface112of a side wall surface110, and a fractured surface109is positioned on the side of the outer diameter surface111of the side wall surface110. Here, since the retainer104is pressed into the V shape, when it retains the roller103, the fractured surface109is positioned at the center part of the side wall surface110in the vicinity of the PCD105and the sheared surface108is positioned at the end of the side wall surface110in the vicinity of the PCD105.

A configuration curve114of the side wall surface110at the PCD105in this case is shown inFIG. 20together with an outline113of the roller103. Referring toFIG. 20, in the side wall surface110, the center part is the fractured surface109and the end is the sheared surface108. In this case, the configuration line114is recessed at the center part with respect to the outline113, so that the roller103is in contact with the sheared surface108at the end of the side wall surface110when guided.

However, since the end of the roller103is chamfered and the end of the side wall surface110does not follow the outline113of the roller103, the roller cannot be appropriately in contact with it, so that the roller103cannot be guided stably.

In the drawn cup needle roller bearing comprising the above retainer and outer ring, the roller cannot roll stably. In addition, when the above drawn cup needle roller bearing is used in a piston pin supporting structure of an engine and the like, the roller is skewed and seizing could be generated.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a outer ring and drawn cup needle roller bearing in which the roller can roll stably.

It is another object of the present invention to provide a drawn cup needle roller bearing and a drawn cup needle roller bearing structured body in which a roller can roll stably.

It is still another object of the present invention to provide a piston pin supporting structure of an engine, a crankshaft supporting structure of an engine and a 2-cycle engine in which an anti-seizing property is improved.

A outer ring according to the present invention comprises a track surface on the side of an inner diameter. Here, when the outer ring is press fitted in a reference ring having an inner diameter hole in which the outer ring is to be press fitted, the straightness of the track surface of the outer ring in the axial direction is not more than 0.008 mm, and the parallelism based on the inner diameter surface or outer diameter surface of the reference ring is not more than 0.015 mm.

According to the above constitution, while the outer ring is press fitted in the inner diameter hole provided in the reference ring, the track surface on which the roller rolls can be provided so as to be straight and parallel. Thus, the rolling surface of the roller and the track surface of the outer ring positioned on the inner diameter surface can be in contact with each other appropriately at the time of rolling, so that the roller can roll stably. Here, the straightness is a difference between a maximum thickness and a minimum thickness of the track surface of the outer ring in the axial direction when it is press fitted in the reference ring, and the parallelism is a degree of parallelism between the inner diameter surface of the reference ring serving as the reference surface and the track surface of the outer ring. In addition, when the inner diameter surface and the outer diameter surface of the reference ring are coaxially provided, the outer diameter surface of the reference ring can be the reference surface of the parallelism.

According to still another aspect of the present invention, a drawn cup needle roller bearing comprises the above outer ring and a plurality of rollers. Thus, since the roller can roll stably in the drawn cup needle roller bearing comprising the above outer ring, the anti-seizing property and the like can be improved.

According to the present invention, while the outer ring is press fitted in an inner diameter hole provided in a reference ring, the track surface on which the roller rolls can be provided so as to be straight and parallel. Thus, since the rolling surface of the roller and the track surface of the outer ring positioned on the inner diameter surface can be appropriately in contact with each other at the time of rolling, the roller can roll stably.

In addition, since the roller can roll stably in the drawn cup needle roller bearing comprising the above outer ring, the anti-seizing property and the like can be improved.

A drawn cup needle roller bearing according to the present invention comprises a plurality of rollers, a outer ring having a track surface in its inner diameter side, and a retainer retaining the rollers. When the outer ring is press fitted in a reference ring having an inner diameter hole in which the outer ring is to be press fitted, the straightness of the track surface of the above-described outer ring in the axial direction is not more than 0.008 mm, and the parallelism based on the inner diameter surface or outer diameter surface of the reference ring is not more than 0.015 mm. The retainer comprises a pair of annular parts, and column parts connecting the pair of annular parts so as to form pockets for housing the rollers. Here, the side wall surface of the column part comprises a sheared surface provided when the pocket is formed by a punching blade, and a fractured surface fractured by a material pressed by the punching blade. The above-described roller is guided by the sheared surface.

According to the above constitution, in the retainer contained in the drawn cup needle roller bearing, the roller can be guided by the smooth sheared surface along the roller outline positioned at the center part in the side wall surface of the column part. In addition, according to the outer ring contained in the drawn cup needle roller bearing, while the outer ring is press fitted in the inner diameter hole of a reference ring, the track surface on which the roller rolls can be provided so as to be straight and parallel. Thus, the roller rolling surface and the track surface positioned on the inner diameter surface of the outer ring can be appropriately in contact with each other at the time of rolling.

In the drawn cup needle roller bearing containing the above retainer and the outer ring, the roller can roll stably. Here, the straightness is a difference between a maximum thickness and a minimum thickness of the track surface of the outer ring in the axial direction when it is press fitted in the reference ring, and the parallelism is a degree of parallelism between the inner diameter surface of the reference ring serving as the reference surface and the track surface of the outer ring. In addition, when the inner diameter surface and the outer diameter surface of the reference ring are coaxially provided, the outer diameter surface of the reference ring can be the reference surface of the parallelism.

Preferably, the column part has a configuration in which its center part is recessed toward the inner side of the diameter direction, the sheared surface is positioned on the outer side of the diameter direction and the fractured surface is positioned on the inner side of the diameter direction. Thus, the sheared surface can be positioned in the vicinity of the PCD, so that the roller can be guided stably.

More preferably, the length of the sheared surface that guides the roller in the axial direction is not less than 60% of the length of the roller in the axial direction. Thus, in the retainer contained in the drawn cup needle roller bearing, the guiding surface for guiding the roller stably can be largely ensured, so that the roller can roll more stably.

According to the present invention, in the retainer contained in the drawn cup needle roller bearing, the roller can be guided by the smooth sheared surface along the roller outline positioned at the center part in the side wall surface of the column part. In addition, according to the outer ring contained in the drawn cup needle roller bearing, while the outer ring is press fitted in the inner diameter hole of a reference ring, the track surface on which the roller rolls can be provided so as to be straight and parallel. Thus, the roller rolling surface and the track surface positioned on the inner diameter surface of the outer ring can be appropriately in contact with each other at the time of rolling.

As a result, the roller can roll stably in the drawn cup needle roller bearing and the drawn cup needle roller bearing structured body.

A piston pin supporting structure of an engine according to the present invention comprises a con-rod converting linear reciprocating motion to rotary motion and having an inner diameter hole at a small end part, a piston pin connecting the con-rod and a piston through the inner diameter hole, and a drawn cup needle roller bearing press fitted in the inner diameter hole and supporting the piston pin. The above drawn cup needle roller bearing comprises a outer ring, a plurality of rollers, and a retainer retaining the rollers. When the outer ring is press fitted in a reference ring having an inner diameter hole in which the outer ring is to be press fitted, the straightness of the track surface of the above-described outer ring in the axial direction is not more than 0.008 mm, and the parallelism based on the inner diameter surface or outer diameter surface of the reference ring is not more than 0.015 mm. The retainer comprises a pair of annular parts, and column parts connecting the pair of annular parts so as to form pockets for housing the rollers. Here, the side wall surface of the column part comprises a sheared surface provided when the pocket is formed by a punching blade, and a fractured surface fractured by a material pressed by the punching blade. The above-described roller is guided by the sheared surface.

According to the above constitution, in the retainer contained in the drawn cup needle roller bearing, the roller can be guided by the smooth sheared surface along the roller outline positioned at the center part in the side wall surface of the column part. In addition, according to the outer ring contained in the drawn cup needle roller bearing, while the outer ring is press fitted in the inner diameter hole provided at the small end part of the con-rod, the track surface on which the roller rolls can be provided so as to be straight and parallel. Thus, the roller rolling surface and the track surface positioned on the inner diameter surface of the outer ring can be appropriately in contact with each other at the time of rolling.

In the drawn cup needle roller bearing containing the above retainer and the outer ring, the roller can roll stably. Therefore, the piston pin supporting structure of the engine comprising the above drawn cup needle roller bearing can improve its anti-seizing property. Here, the straightness is a difference between a maximum thickness and a minimum thickness of the track surface of the outer ring in the axial direction when it is press fitted in the reference ring, and parallelism is a degree of parallelism between the inner diameter surface of the reference ring serving as the reference surface and the track surface of the outer ring. In addition, when the inner diameter surface and the outer diameter surface of the reference ring are coaxially provided, the outer diameter surface of the reference ring can be the reference surface of the parallelism.

According to another aspect of the present invention, a crankshaft supporting structure of an engine comprises a con-rod converting linear reciprocating motion to rotary motion and having an inner diameter hole at a large end part, a crankshaft connected to the large end part of the con-rod through the inner diameter hole and outputting the rotary motion, and a drawn cup needle roller bearing press fitted in the inner diameter hole and supporting the crankshaft. The above drawn cup needle roller bearing comprises a outer ring, a plurality of rollers, and a retainer retaining the rollers. When the outer ring is press fitted in a reference ring having an inner diameter hole in which the outer ring is to be press fitted, the straightness of the track surface of the above-described outer ring in the axial direction is not more than 0.008 mm, and the parallelism based on the inner diameter surface or outer diameter surface of the reference ring is not more than 0.015 mm. The retainer comprises a pair of annular parts, and column parts connecting the pair of annular parts so as to form pockets for housing the rollers. Here, the side wall surface of the column part comprises a sheared surface provided when the pocket is formed by a punching blade, and a fractured surface fractured by a material pressed by the punching blade. The above-described roller is guided by the sheared surface.

According to the above constitution, similar to the above, in the retainer contained in the drawn cup needle roller bearing, the roller can be guided by the smooth sheared surface along the roller outline positioned at the center part in the side wall surface of the column part. In addition, according to the outer ring contained in the drawn cup needle roller bearing, while the outer ring is press fitted in the inner diameter hole provided at the large end part of the con-rod, the track surface on which the roller rolls can be provided so as to be straight and parallel. Thus, the roller rolling surface and the track surface positioned on the inner diameter surface of the outer ring can be appropriately in contact with each other at the time of rolling.

In the drawn cup needle roller bearing containing the above retainer and the outer ring, the roller can roll stably. Therefore, the crankshaft supporting structure of the engine comprising the above drawn cup needle roller bearing can improve its anti-seizing property.

According to still another aspect of the present invention, a 2-cycle engine comprises any piston pin supporting structure of the engine described above.

According to still another aspect of the present invention, a 2-cycle engine comprises any crankshaft supporting structure of the engine described above.

According to the above constitution, the 2-cycle engine can improve its anti-seizing property.

According to the present invention, in the retainer contained in the drawn cup needle roller bearing, the roller can be guided by the smooth sheared surface along the roller outline positioned at the center part in the side wall surface of the column part. In addition, according to the outer ring contained in the drawn cup needle roller bearing, while it is press fitted in the inner diameter hole provided at the small end part of the con-rod, the track surface on which the roller rolls can be provided so as to be straight and parallel. Thus, the roller rolling surface and the track surface positioned on the inner diameter surface of the outer ring can be appropriately in contact with each other at the time of rolling.

In the drawn cup needle roller bearing containing the above retainer and the outer ring, the roller can roll stably. Therefore, the piston pin supporting structure of the engine comprising the above drawn cup needle roller bearing can improve its anti-seizing property. Similarly, the crankshaft supporting structure of the engine comprising the above drawn cup needle roller bearing can improve its anti-seizing property.

In addition, with the above piston pin supporting structure of the engine or the crankshaft supporting structure of the engine, the 2-cycle engine can improve its anti-seizing property.

According to another aspect of the present invention, a drawn cup needle roller bearing structured body comprises a housing having an inner diameter hole, and a drawn cup needle roller bearing comprising a plurality of rollers, a outer ring having a track surface in its inner diameter side, and a retainer and press fitted in the inner diameter hole of the housing. Here, the retainer in the above drawn cup needle roller bearing comprises a pair of annular parts, and column parts connecting the pair of annular parts so as to form pockets for housing the rollers. The above column part has a configuration in which its center part is recessed toward the inner side of the diameter direction. Here, the side wall surface of the column part comprises a sheared surface provided when the pocket is formed by a punching blade on the outer side of its diameter direction, and a fractured surface fractured by a material pressed by the punching blade on the inner side of its diameter direction. Here, when the outer ring is press fitted in a reference ring having an inner diameter hole in which the outer ring is press fitted, the straightness of the track surface of the outer ring in the axial direction is not more than 0.008 mm, and the parallelism based on the inner diameter surface or outer diameter surface of the reference ring is not more than 0.015 mm.

Since the drawn cup needle roller bearing structured body comprises the drawn cup needle roller bearing comprising the retainer and the outer ring in which the roller can roll stably, the roller can be prevented from being skewed and the anti-seizing property can be improved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference to the drawings hereinafter.FIG. 1is a sectional view showing a part of a shell type bearing structured body11in which a drawn cup needle roller bearing comprising a outer ring is press fitted. Referring toFIG. 1, the drawn cup needle roller bearing structured body11comprises a housing12comprising an inner diameter hole13, and a drawn cup needle roller bearing21. The drawn cup needle roller bearing21comprises a outer ring22formed of a steel plate through a drawing process and the like, a plurality of rollers23, a retainer24retaining the plurality of rollers23. Here, in order to prevent the rollers23and the retainer24from moving in the axial direction, the outer ring22comprises a flange29bent toward the inner side of the diameter direction. The retainer24comprises a pair of annular parts positioned at both end faces of the outer ring22, and a column part connecting the pair of annular parts so as to form a pocket for housing each roller and having a configuration in which its center part is bent toward the inner side of the diameter direction.

The drawn cup needle roller bearing21is press fitted in the inner diameter hole13provided in the housing12so that an outer diameter surface25of the outer ring22abuts on an inner diameter surface14of the inner diameter hole13. In addition, a rolling surface27of the roller23is in contact with an inner diameter surface26of the outer ring22and the drawn cup needle roller bearing21supports a rotation shaft (not shown) inserted into its inner diameter side.

Here, a manufacturing method of the retainer24among components of the drawn cup needle roller bearing21will be described.

FIG. 2is a flowchart showing manufacturing steps of the retainer24of the drawn cup needle roller bearing21according to one embodiment of the present invention.FIGS. 3A to 3Eare schematic view showing representative steps in the steps shown inFIG. 2. The manufacturing method of the retainer24will be described with reference toFIGS. 2andFIGS. 3A to 3E.

First, a steel plate as the material of the retainer24in a state of a band steel (FIG. 3A) is punched out to form the pocket for holding the roller23at a pocket punching-out step (FIG. 3B). The pocket punching-out step is performed using a punch having a punching blade in such a manner that the blade edge of the punch is pressed along a pocket configuration and punches it out. Here, the pocket is punched out from the direction that becomes the outer diameter surface when the band steel is bent into a cylindrical shape at a subsequent bending step.

Thus, in the finally manufactured retainer, the side wall surface of the column part on the side of an outer diameter surface is a sheared surface and the side wall surface of the column part on the side of an inner diameter surface is a fractured surface.

Then, the band steel in which the pockets are punched out is pressed so that its sectional configuration becomes V shape at a pressing step (FIG. 3C). Here, the V shape means that a step difference between the center part and the annular part of the band steel is provided in the diameter direction when the band steel having the pockets is bent into the cylindrical shape. This pressing step is performed by pressing a press against the band steel from the side that becomes the outer diameter surface to the side that becomes the inner diameter surface later. Thus, at the pressing step, the center part is recessed from the annular part in the column part in the diameter direction.

Then, the band steel is cut to a circumferential length of the retainer24at a cutting step. Then, the cut band steel is bent into the cylindrical configuration along the inner diameter surface of the outer ring22at a bending step (FIG. 3D). Then, both end surfaces are connected by welding and the like at a welding step (FIG. 3E). Then, a heat treatment such as soft-nitriding or carburized quenching is performed, whereby the retainer24is completed.

In addition, the plurality of rollers23are incorporated in the pockets of the retainer24manufactured by the above method, and the retainer24comprising the rollers23is incorporated in the outer ring22, whereby the drawn cup needle roller bearing21is manufactured.

FIG. 4is a sectional view showing the retainer24manufactured by the above method in the axial direction. InFIG. 4, a part designated by a dotted line shows the roller23retained in the pocket of the retainer24, and a dashed line shows a PCD24f. In addition, a configuration curve32of a side wall surface24ein the PCD24fin this case is shown inFIG. 5together with an outline31of the roller23.

Referring toFIGS. 4 and 5, a column part24bhas been pressed so that its sectional configuration becomes V shape toward the side of an inner diameter surface24hat the above pressing step. Therefore, the center part of the column part24bis positioned on the side of the inner diameter surface24hwith respect to an annular part24a.

In addition, since the pocket has been punched out with the blade of the punch pressed from the side of an outer diameter surface24gat the above pocket punching-out step, in a side wall surface24eof the column part24b, a sheared surface24cis positioned on the side of the outer diameter surface24gand a fractured surface24dis positioned on the side of the inner diameter surface24h. Therefore, at the PCD24f, the sheared surface24con the side of the outer diameter surface24gis positioned at the center part of the side wall surface24eand the fractured surface24don the side of the inner diameter surface24his positioned at the end of the side wall surface24e.

Here, the configuration curve32of the sheared surface24cpositioned at the center part of the side wall surface24eis smooth and follows the outline31of the roller23. Thus, the center part of the roller23and the center part of the side wall surface24ecan be appropriately in contact with each other, so that the roller23can be stably guided.

In addition, it is preferable that the length of the sheared surface24cfor guiding the roller23in the axial direction is not less than 60% of the length of the roller23in the axial direction. Here, to implement the length of the sheared surface24cthat is not less than 60% of the roller, the above pressing step is performed such that the length of the sheared surface24con the PCD24fmay become 60% of the roller or more. More specifically, the band steel is pressed into the V shape in the diameter direction in such a manner that the dimension “A” inFIG. 4, that is, the dimension of the sheared surface24don the side of one annular part24aon the PCD24fmay become not more than 20% of the dimension “B” that is the length of the pocket in the axial direction. InFIG. 5, the smooth configuration along the outline31positioned at the center part of the configuration curve32is not less than 60% of the roller length.

Thus, the sheared surface24cthat is appropriately in contact with the roller can be increased, so that the motion of the roller can be controlled and the roller23can be stably guided.

A method for measuring the degree of straightness and parallelism of the track surface of the outer ring will be described hereinafter. First, a description will be made of an apparatus for measuring the straightness and parallelism of the track surface.FIG. 6is a schematic view showing a configuration measuring apparatus41for measuring the straightness and parallelism of the outer ring. Referring toFIG. 6, the configuration measuring apparatus41for measuring the outer ring comprises a reference ring42having an inner diameter hole45, a probe43for measuring the generatrix configuration of the inner diameter surface of the outer ring press fitted in the inner diameter hole43, and an outer diameter surface49or an inner diameter surface46of the reference ring42in the axial direction, and probe moving means44for moving the probe43in the axial direction to scan them.

The reference ring42is cylindrical and has the inner diameter hole45in which the outer ring can be press fitted. In addition, the inner diameter surface46of the inner diameter hole45and the outer diameter surface49of the reference ring42are concentrically provided, so that either surface becomes a reference surface in measuring the parallelism to the track surface of the press fitted outer ring.

The probe43comprises a head47for measuring the generatrix configuration of the object to be measured by touching the object, and an arm48connecting the head47and the probe moving means44.

The probe moving means44comprises moving means for moving the probe43so that the probe43scans the inner diameter surface of the outer ring press fitted in the reference ring42, and moving means for moving the probe43so that the probe43scans the outer diameter surface49or the inner diameter surface46of the reference ring42. The probe43can be moved by the probe moving means in the axial direction, that is, the lateral direction inFIG. 6, and it can be moved in the vertical direction inFIG. 6while it is being moved in the axial direction. That is, even when the object to be measured is inclined, since the movement in the lateral direction is not prevented, the probe43can be moved along the configuration of the object to be measured.

A description will be made of a method for measuring the straightness and parallelism of the track surface of the outer ring using the above configuration measuring apparatus41hereinafter. In addition, although the outer ring in which the flange is bent toward the inner side of the diameter direction at one end is used as the outer ring whose straightness is measured here, the same can be applied to a case where a outer ring is measured in which flanges are bent toward the inner side of the diameter direction on both ends like the outer ring22contained in the above drawn cup needle roller bearing21.

First, the outer ring is press fitted in the inner diameter hole45of the reference ring42.FIG. 7is a sectional view in the axial direction, showing a state in which an outer ring36in which the flange is bent at one end is press fitted. Referring toFIG. 7, the outer ring36is press fitted so that an outer diameter surface37of the outer ring36and an inner diameter surface46of the inner diameter hole45are in contact with each other.

Then, the generatrix configuration of the outer diameter surface49of the reference ring42is measured.FIG. 8is a sectional view in the axial direction, showing the reference ring42when the generatrix configuration of the outer diameter surface49is measured. Referring toFIG. 8, the reference ring42is inclined at a certain angle. Thus, the generatrix configurations of the surface of a flange40of the outer ring36on the inner diameter side and an inner diameter surface38of a cylindrical part can be measured.

Then, the head47is brought to be in contact with the outer diameter surface49of the reference ring42, and the probe43is moved in the direction shown by an arrow C. Thus, the generatrix configuration of the outer diameter surface49of the reference ring42that is the reference surface is measured. In addition, in this case, the generatrix configuration of the inner diameter surface46of the inner diameter hole45that is the reference surface may be measured. For example, the generatrix configuration of the inner diameter surface46at the part shown by “D” inFIG. 8may be measured. Thus, even when the generatrix configuration of the outer diameter surface49cannot be measured, the generatrix configuration of the inner diameter surface46is measured as the reference surface in measuring the parallelism.

Then, the generatrix configuration of the inner diameter surface38of the press fitted outer ring36is measured.FIG. 9is a sectional view showing the reference ring42in the axial direction when the generatrix configuration of the inner diameter surface38of the outer ring36is measured. In addition, inFIG. 9, the part shown by a dotted line designates a roller35incorporated in the outer ring36. Referring toFIG. 9, while the reference ring42in which the outer ring36is press fitted is inclined at a certain angle, the head47is brought to be in contact with the inner diameter surface of the flange40of the outer ring36. Thus, a corner P of the flange40on the inner diameter side can be a starting point to measure the generatrix configuration in the axial direction. In addition, since the reference ring42is inclined at a certain angle, even when the head47and the arm48are perpendicularly connected as shown in the drawing, the head47can be easily in contact with the surface in the vicinity of a bent part39that is a crossing part between the flange40and the inner diameter surface38.

Then, the head47is moved in the direction of the arrow “C” to measure the generatrix configuration of the inner diameter surface38of the outer ring36. According to the generatrix configuration of the inner diameter surface38, since the generatrix configuration is measured from the inner diameter surface of the flange42to the open end of the outer ring36, the measured generatrix configuration of the inner diameter surface38includes a part in which the roller35is not in contact with the outer ring36.

Thus, in the inner diameter surface38of the outer ring36, the straightness and parallelism are measured within a range “L2” inFIG. 9as a range for measuring the straightness and parallelism of the track surface in which the roller35rolls. The range “L2” is a range such that L2≧0.8×L when the roller length is “L”. When the range having the predetermined length or more is defined as “L2”, the straightness and parallelism to be measured can be high in reliability. In addition, when the dimension from the corner P of the flange40on the inner diameter side to the starting point of the range “L2” is “L1”, the dimension “L1” is ranged such that 0.8 mm≦L1≦2 mm. The region “L1” corresponds to the part in which the roller35and the outer ring36are not in contact with each other in general.

FIG. 10is a sectional view showing the reference ring42in which the outer ring36is press fitted when the reference ring42is cut in the diameter direction. Referring toFIG. 10, the generatrix configuration of the inner diameter surface38is measured in four directions that are symmetric laterally and vertically as shown by arrows E, F, G and H. Thus, the straightness and parallelism can be measured with high precision. In addition, when the precision is to be higher, the measurement may be performed in directions more than the above 4 directions.

FIG. 11shows a schematic view showing the generatrix configurations measured as described above. Referring toFIG. 11, the horizontal axis designates the dimension in the axial direction and the vertical axis designates measured generatrix configurations. Based on the generatrix configuration51of the outer diameter surface49of the reference ring42serving as the reference surface, the straightness and parallelism are measured from the generatrix configuration53within the range “L2” in the inner diameter surface38excluding the generatrix configuration52within the range “L1”. That is, as the straightness, a difference between a maximum value and a minimum value of the generatrix configuration53is to be found, and as the parallelism, the degree of parallelism between the generatrix configuration51and the generatrix configuration53is to be found. Thus, the track surface on which the roller rolls is provided so as to be straight and parallel.

A test for confirming an anti-seizing property was performed for drawn cup needle roller bearings comprising outer rings having different values in straightness and parallelism. In addition, the configuration measurement is made by an outline measuring machine (CV3000 produced by Mitutoyo corporation).

The test conditions are as follows. The result of this test is shown in Table 1.

Operation pattern: full throttle

Operation time: two hours or until seizing is generated

Referring to Table 1, according to a conventional sample 1, seizing was generated in three drawn cup needle roller bearings out of ten. According to a conventional sample 2, seizing was generated in four drawn cup needle roller bearings out of ten. According to a conventional sample 3, seizing was generated in seven drawn cup needle roller bearings out of ten. Meanwhile, according to a sample in this embodiment, seizing was not generated in all of ten drawn cup needle roller bearings.

Therefore, when the parallelism is not more than 0.010 mm and the straightness is not more than 0.008 mm, the roller can roll stably and the seizing can be prevented.

In addition, a drawn cup needle roller bearing containing the retainer in which the sheared surface is not less than 60% of the roller length shown inFIG. 5as an embodiment 2, a drawn cup needle roller bearing containing a retainer in which a sheared surface shown as the configuration curve33inFIG. 12is 50% of a roller length as a sample A, and a drawn cup needle roller bearing containing the conventional retainer as a conventional sample 4 are used in a con-rod and a test for confirming the anti-seizing property was performed for them.

The test condition is the same as the above. The result of this test is shown in Table 2.

Table 2 shows the result of the above test. Referring to Table 2, according to the conventional sample 4, seizing was generated in eight drawn cup needle roller bearings out of ten. According to the sample A, seizing was generated in six drawn cup needle roller bearings out of ten. Meanwhile, according to the sample in the embodiment 2, seizing was not generated in all of ten drawn cup needle roller bearings.

Therefore, when the length of the sheared surface in the axial direction is not less than 60% of the roller length, there is no seizing generated, so that the length of the sheared surface in the axial direction needs to be at least 60%.

As described above, a piston pin supporting structure of an engine or a crankshaft supporting structure of an engine comprising the drawn cup needle roller bearing containing the retainer and the outer ring described above can improve their anti-seizing property. In addition, a 2-cycle engine comprising the above piston pin supporting structure of the engine or the above crankshaft supporting structure of the engine can improve its anti-seizing property.

Although the entire reference ring is inclined when the straightness and parallelism of the track surface of the outer ring are measured in the above embodiment, the present invention is not limited to this. For example, a structure in which a head of a probe is formed into a slanting configuration so that the head of the probe can abut on the corner of a flange on the inner diameter side without inclining the reference ring may be employed.

In addition, although the generatrix configuration of the outer diameter surface of the reference ring or the inner diameter surface of the outer ring are measured with the head of the probe touched in the above embodiment, the present invention is not limited to this. For example, the generatrix configuration of the outer diameter surface of the reference ring and the like may be measured by a laser and the like without any contact between them.

As one example of the drawn cup needle roller bearing structured body comprising the above drawn cup needle roller bearing, there is a 2-cycle engine having the drawn cup needle roller bearing comprising the above outer ring.FIG. 13is a schematic sectional view showing the essential part of the 2-cycle engine.

Referring toFIG. 13, a 2-cycle engine410comprises a piston (not shown) moving in a straight line back and forth by combustion of mixed gas, a crankshaft440outputting rotary motion, a con-rod420connecting the piston and the crankshaft and converting linear reciprocating motion to the rotary motion, and a drawn cup needle roller bearing press fitted in the large end part or the small end part of the con-rod420and supporting the crankshaft440or a piston pin430. The piston is connected to the small end part of the con-rod420by the piston pin430through the drawn cup needle roller bearing450. In addition, the crankshaft440is connected to the large end part of the con-rod420through the drawn cup needle roller bearing460.

The drawn cup needle roller bearing450supporting the piston pin430is press fitted in an inner diameter hole provided in the small end part of the con-rod420, whereby the piston pin supporting structure of the 2-cycle engine410is formed. Similarly, the drawn cup needle roller bearing460supporting the crankshaft440is press fitted in an inner diameter hole provided in the large end part of the con-rod420, whereby the crankshaft supporting structure of the 2-cycle engine410is formed.

The drawn cup needle roller bearing450comprises the above outer ring470, a plurality of rollers480, and a retainer490retaining the rollers480. In addition, the drawn cup needle roller bearing460has the same constitution as that of the drawn cup needle roller bearing450although their sizes are different such that it comprises an outer ring, a plurality of rollers and a retainer. Here, since the track surface of the above outer ring has the straightness of 0.008 mm or less and parallelism of 0.015 mm or less when the outer ring is press fitted in the reference ring, the rollers48′ can roll stably. Therefore, the anti-seizing property can be improved at the large end part and the small end part of the con-rod.

Thus, there is provided the 2-cycle engine having the large end part and the small end part of the con-rod in which the anti-seizing property is improved.

In addition, although the drawn cup needle roller bearing comprises the retainer in the above embodiment, the present invention is not limited to this. For example, the bearing may be a full-type roller bearing.

Furthermore, although the entire reference ring is inclined when the straightness and parallelism of the track surface are measured in the above embodiment, the present invention is not limited to this. For example, a structure in which a head of a probe is formed into a slanting configuration such that the head of the probe can abut on the corner of a flange on the inner diameter side without inclining the reference ring may be employed.

In addition, although the generatrix configuration of the outer diameter surface of the reference ring or the inner diameter surface of the outer ring are measured with the head of the probe touched in the above embodiment, the present invention is not limited to this. For example, the generatrix configuration of the outer diameter surface of the reference ring and the like may be measured by a laser and the like without any contact between them.

In addition, although the con-rod having the inner diameter holes in the small end part and the large end part is used as the housing in the drawn cup needle roller bearing structured body in the above embodiment, the present invention is not limited to this. For example, another member having an inner diameter hole in which the drawn cup needle roller bearing can be press fitted may be used.

Although the embodiments of the present invention have been described with reference to the drawings in the above, the present invention is not limited to the above-illustrated embodiments. Various kinds of modifications and variations may be added to the illustrated embodiments within the same or equal scope of the present invention. Since the roller can roll stably in the outer ring and the drawn cup needle roller bearing according to the present invention, they can be effectively used as an outer ring in which the anti-seizing property is improved and the drawn cup needle roller bearing comprising such outer ring.

In addition, since the roller can roll stably in the drawn cup needle roller bearing according to the present invention and the drawn cup needle roller bearing structured body comprising such drawn cup needle roller bearing, they can be used in the con-rod of the 2-cycle engine in which the anti-seizing property is improved.

Furthermore, since the piston pin supporting structure of the engine, the crankshaft supporting structure of the engine, and the 2-cycle engine according to the present invention comprise the drawn cup needle roller bearing in which the roller can roll stably, they can be effectively used as a piston pin supporting structure of an engine, a crankshaft supporting structure of an engine, and a 2-cycle engine the crankshaft supporting structure in which the anti-seizing property is improved.