Shifting mechanism

A shifting mechanism, comprising:

• a shift sleeve that is arranged around a rotary shaft to be rotated integrally with the rotary shaft;
• a shift fork that reciprocates in an axial direction of the rotary shaft;
• and
• an engagement groove that is formed entirely on an outer circumference of the shift sleeve,
• a pair of cutouts formed on a bottom of the engagement groove,
• wherein the shift sleeve is reciprocated in the axial direction by the shift fork but allowed to rotate relatively to the shift fork,
• the shift fork comprises
• an arcuate fork section that is fitted onto the shift sleeve, and
• at least a pair of engagement ridges formed on an inner circumference of both ends of the fork section, each of which is engaged with the engagement groove,
• an angle toward the shift fork between:
• a line drawn between one end of the fork section and a rotational center of the shift sleeve;
• and a line drawn between the other end of the fork section and the rotational center of the shift sleeve, is a reflex angle,
• a first diameter of the shift sleeve between a predetermined site of the bottom of the engagement groove within the cutout and a symmetrical site across the rotational center is shorter than a second diameter of the shift sleeve between predetermined sites of the bottom of the engagement groove where the cutout is not formed, and
• a straight-line distance between the engagement ridges formed on both ends of the fork section is longer than the first diameter but shorter than the second diameter.