The use of synchro gear shift can ensure that the gear shift is not impact, so that the strength of the gear can be fully exerted, while ensuring rapid, noise-free, easy to operate, reducing the shift time, thus, the acceleration, economy and driving safety of the vehicle are improved. In addition, this type is also beneficial to the realization of automatic control. Its disadvantages are complex structure, high manufacturing accuracy, increased axial size, copper synchronous ring short service life. At present, synchronizer is widely used in all kinds of transmission.