The gear-shifting type of meshing sleeve is usually used with helical gear transmission. Because the gears are often engaged, the noise and dynamic load are reduced, and the strength and service life of the gears are improved. The engagement sleeve is divided into the inner tooth engagement sleeve and the outer tooth engagement sleeve. Depending on the arrangement of the structure, if the inner space of the gear pair allows, the inner tooth engagement type is adopted to reduce the axial size. Combined with the sleeve shift structure is simple, but can not completely eliminate the impact of shifting, at present in the low-demand gear often used.