The difference between helical bevel gear and hypoid bevel gear

Helical bevel gears and quasi-hyperboloid bevel gears are the main driving modes of automobile main reducers. What's the difference?
Helical bevel gears as shown in figure 2 (a), the main, driven gear axes intersect in one point, Angle can be arbitrary, but in most of the automobile drive axle, the main reducer gear pair with 90 ° Angle of vertical arrangement. Because of the influence of the tooth face overlap, more than there are at least two pairs of tooth mesh at the same time, as a result, the spiral bevel gear can bear larger load, together with its tooth not to nod in the whole tooth meshing at the same time, but gradually from one end of the tooth row to the other end, making the work is smooth, even at high speed, noise and vibration is very small.
Hypoid gear as shown in figure 2 (b), the main, driven gear axis of disjoint and space of the cross, the space also use 90 ° Angle more crossing Angle different surface vertical way. The active gear shaft has an upward or downward offset relative to the driven gear shaft (appropriately called the upper or lower offset). When the offset is large enough, a gear shaft is passed by the other shaft. So you can in each gear bearing on either side of the size compact, to strengthen the support stiffness, guarantee the tooth meshing correctly, so as to improve gear life is good, it is suitable for the type of drive axle.
Fellowship with due to the axis of the gear pair of helical bevel gears and make the winner and driven gear equal helix Angle is different, the axis of the hypoid gear pair migration makes the driving gear helix Angle is greater than the driven gear spiral Angle. Therefore, the method of the quasi-hyperboloid bevel gear pair is equal, but the end surface modulus is unequal (the end face modulus of the active gear is greater than that of the driving gear). This makes the driving gear of the quasi-double-sided bevel gear has a larger diameter and better strength and stiffness than the corresponding helical bevel gear drive. In addition, due to the large diameter and spiral Angle of the driving gear of the hypoid bevel gear drive, the contact stress of the tooth surface is reduced and the life span is increased.
But the transmission comparison hour, the driving gear of the quasi-double-sided bevel gear is too large for the driving gear of spiral bevel gear, and the helical bevel gears is more reasonable.