Spiral bevel gear

A spiral bevel gear is a bevel gear with helical teeth.


A spiral bevel gear set should always be replaced in pairs i.e. both the left hand and right hand gears should be replaced together since the gears are manufactured and lapped in pairs.


A right hand spiral bevel gear is one in which the outer half of a tooth is inclined in the clockwise direction from the axial plane through the midpoint of the tooth as viewed by an observer looking at the face of the gear.


A left hand spiral bevel gear is one in which the outer half of a tooth is inclined in the counterclockwise direction from the axial plane through the midpoint of the tooth as viewed by an observer looking at the face of the gear.


A hypoid is a type of spiral bevel gear whose axis does not intersect with the axis of the meshing gear.
The spiral angle in a spiral bevel gear is the angle between the tooth trace and an element of the pitch cone, and corresponds to the helix angle in helical teeth.


In older automotive designs, hypoid gears were typically used in rear-drive automobile drivetrains, but modern designs have tended to substitute spiral bevel gears to increase driving efficiency.


For practical purposes, it is often impossible to replace low efficiency hypoid gears with more efficient spiral bevel gears in automotive use because the spiral bevel gear would need a much larger diameter to transmit the same torque.