Bearing

A bearing comprising:

• an inner ring case;
• an outer ring case disposed around the inner ring case;
• a plurality of first rollers adapted to roll between an outer periphery of the inner ring case and an inner periphery of the outer ring case;
• and
• a plurality of second rollers each disposed between adjacent first rollers, each of the second rollers being smaller in diameter than each of the first rollers and having a longer axial length along a rotation axis than each of the first rollers, wherein
• the outer ring case includes an annular guide groove, the guide groove housing an end of each of the plurality of second rollers, with the rotation axis of each of the second rollers being perpendicular to a radial direction and a circumferential direction of the bearing,
• a groove width representing a length of the guide groove along the radial direction of the bearing is greater than a diameter of each of the second rollers, and
• a first radius representing a distance from a bearing axis to an inner wall face of the guide groove that is a radially outermost wall face of the guide groove in the radial direction of the bearing is smaller than a distance from the bearing axis to an axial center of the first roller plus a radius of the second roller, wherein
• the guide groove houses only one of a plurality of the ends of each of the second rollers, wherein a distance from the bearing axis center to the axial center of the first roller equals to a distance from the bearing axis center to the outer periphery of the inner ring case plus a radius of the first roller, and
• the outer ring case includes a hole to allow insertion of the second rollers into the guide groove from outside the outer ring case.

A bearing comprising:

• an inner ring case;
• an outer ring case disposed around the inner ring case;
• a plurality of first rollers adapted to roll between an outer periphery of the inner ring case and an inner periphery of the outer ring case;
• and
• a plurality of second rollers each disposed between adjacent first rollers, each of the second rollers being smaller in diameter than each of the first rollers and having a longer axial length along a rotation axis than each of the first rollers, wherein
• the outer ring case includes an annular guide groove, the guide groove housing an end of each of the plurality of second rollers, with the rotation axis of each of the second rollers being perpendicular to a radial direction and a circumferential direction of the bearing,
• a groove width representing a length of the guide groove along the radial direction of the bearing is greater than a diameter of each of the second rollers, and
• a first radius representing a distance from a bearing axis to an inner wall face of the guide groove that is a radially outermost wall face of the guide groove in the radial direction of the bearing is smaller than a distance from the bearing axis to an axial center of the first roller plus a radius of the second roller, wherein
• when a radius of each of the second rollers is “b”, the radius “b” satisfies the following formula:
• L2+(R2+H)2−2L(R2+H))/2(a+L−R2−H)<b≤(a+R2)cos(π/n)−(H+R2)
• wherein “a” is a radius of each of the first rollers, L is a distance between a contact point where the first rollers contact each other and the bearing axis and wherein L=√((R2+a)2−a2), R2 is a distance from the bearing axis to the outer periphery of the inner ring case, H is a distance between the outer periphery of the inner ring case and an inner periphery of the guide groove, and “n” is a number of second rollers,
• wherein
• a distance from the bearing axis center to the axial center of the first roller equals to a distance from the bearing axis center to the outer periphery of the inner ring case plus a radius of the first roller, and
• the outer ring case includes a hole to allow insertion of the second rollers into the guide groove from outside the outer ring case.