Bevel gears connect intersecting axes and come in several types. The
pitch surface of bevel gears is a cone. They are useful when the
direction of a shaft's rotation needs to be changed. Using gears of
differing numbers of teeth can change the speed of rotation. They are
usually mounted on shafts that are 90 degrees apart, but can be designed
to work at other angles as well. Bevel gears permit minor adjustment during assembly and allow for some displacement due to deflection under operating loads without concentrating the load on the end of the tooth. For reliable performance, they must be pinned to shaft with a dowel or taper pin. Bevel gear sets consist of two gears of different pitch diameter that yield ratios greater than 1:1.
Types of bevel gears
The bevel gears can be of varied types and the types are known by the teeth of the gears. Different varieties are:
- Straight Bevel Gears:
In straight bevel gears teeth have no helix angles. They either have equal size gears with 90 degrees shaft angle or a shaft angle other than 90 degrees. Straight bevel angle can also be with one gear flat with a pitch angle of 90 degrees. In straight when each tooth engages it impacts the corresponding tooth and simply curving the gear teeth can solve the problem.
- Spiral Bevel Gears:
Spiral bevel gears have spiral angles, which gives performance improvements. The contact between the teeth starts at one end of the gear and then spreads across the whole tooth. In both the bevel types of gears the shaft must be perpendicular to each other and must be in the same plane.
- Hypoid Bevel Gears:
The Hypoid bevel gears can engage with the axes in different planes. This is used in many car differentials. The ring gear of the differential and the input pinion gear are both hypoid. This allows input pinion to be mounted lower than the axis of the ring gear. Hypoid gears are stronger, operate more quietly and can be used for higher reduction ratios. They also have sliding action along the teeth, potentially reducing efficiency.
- Angular Bevel Gears:
These are bevel gears whose shafts are set at an angle other than 90 degrees. They are useful when the direction of a shaft's rotation needs to be changed. These gears permit minor adjustment of gears during assembly and allow for some displacement due to deflection under operating loads without concentrating the load on the end of the tooth.
A good example of bevel gears is seen as the main mechanism for a hand drill. As the handle of the drill is turned in a vertical direction, the bevel gears change the rotation of the chuck to a horizontal rotation. The bevel gears in a hand drill have the added advantage of increasing the speed of rotation of the chuck and this makes it possible to drill a range of materials. They are important components on all current rotorcraft drive system.
The bevel gears find its application in
- Locomotives
- Marine applications
- Automobiles
- Printing presses
- Cooling towers
- Power plants
- Steel plants
- Defence and
- Railway track inspection machine
