About Spiral Bevel Gears and Its Comparison With Hypoid Gears

Spiral bevel gears are gears with helical teeth. These gears are used in the differential of a vehicle where the drive’s direction must be turned at an angle of 90 degrees from the drive shaft to drive the wheels. The helical design facilitates less vibration and noise in comparison to the traditional spur-cut gears with straight teeth.

As the Spiral bevel gears are lapped and manufactured in pairs, it is advised that one should replace them in pairs, i.e., both the left hand and the right hand gear should be replaced together when either gets damaged.

A right hand gear is the one in which the external half of a tooth is inclined from the axial plane via the midpoint of the tooth in the clockwise direction. This is based on the observation of a person who looked at the gear’s face. On the other hand, the left hand gear is one whose tooth’s outer half is inclined in the anticlockwise direction from the axial plane and through a tooth’s midpoint. However, it is to be noted that both the right and left hand designations are applied similarly to other types of gears such as the hypoid, oblique tooth face, and many other.

Hypoid is a kind of gear whose axis does not intersects with the meshing gear’s axis. The shape of a hyploid is a revolved hyperboloid, while the spiral bevel are conical. A hypoid places the pinion off-axis to the ring gear. This allows the pinion to be larger in diameter, thus having more contact area.

The pinion and gear are always of opposite hand in a hypoid gear. It incorporates some sliding and can be considered as the midway between a worm and straight-cut gear. A hypoid gear requires special oils to ensure smooth sliding action under extreme conditions between the teeth.

Comparison between Spiral Bevel and Hypoid Gears

Although hypoid gears operate more quietly, they also have some sliding action which reduces their mechanical efficiency. Earlier, hypoid were used in rear-drive automobile drivetrains, but their modern designs have made them a neat substitute of the spiral bevel.

A hypoid is still common in trucks due to the capability of trucks in transmitting higher torque. However, one cannot replace hypoid with the spiral bevel gears in automotive because the latter requires a much larger diameter in comparison to the former one to transmit the requisite torque.

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