Types of Gears

1-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. Using gears of differing numbers of teeth can change the speed of rotation.

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. For reliable performance, Gears must be pinned to shaft with a dowel or taper pin.

The bevel gears find its application in locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, defence and also in railway track inspection machine. They are important components on all current rotorcraft drive system.

2-Bevel Gears

They 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.

These 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, Gears 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

The teeth on bevel gears can be straight, spiral or bevel. 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 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. 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.

Applications

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. The bevel gears find its application in locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, defence and also in railway track inspection machine. They are important components on all current rotorcraft drive system.

Spiral bevel gears are important components on all current rotorcraft drive systems. These components are required to operate at high speeds, high loads, and for an extremely large number of load cycles. In this application, spiral bevel gears are used to redirect the shaft from the horizontal gas turbine engine to the vertical rotor.

3-Crown Wheel and Pinion

A crown wheel is a wheel with cogs or teeth set at right angles to its plane and the pinion is a small cogwheel that meshes with the crown wheel. Crown wheel and pinion have excellent heat distortion control, high strength, wear resistance property and noiseless and vibration free operation. They are made of fine-grained steel billet.

The pinion thread is specially made on the thread grinder to ensure proper fitting. Tooth contact of a crown pinion is inspected on a Gleason machine at regular intervals of time for uniform hardness and adequate case depth. They are checked thoroughly for high spots because this ensures premature failure and noise-free operation. The crown wheel & pinion are paired and checked for centralized tooth bearing and desired proximity. An elliptoid contact pattern is ensured between the crown wheel and pinion.

In a machine, when any torque is applied to the drive unit, the tendency is for the crown wheel and pinion to be forced into or out of mesh by the sliding contact. The amount of pre-load on the bearings determines how much torque can be transmitted without allowing end float, which cause the meshing of the gears to become incorrect.

Application

Crown wheel & pinion are used widely in automotive industries. They are one of the most stress prone parts of a vehicle. They are used in automobiles to maintain forward motion. To maintain forward motion both output drive shaft sides covers are removed and the pinion and crown wheel are swapped completely with differential.

4-Crown Wheel

A crown wheel is a wheel with cogs or teeth set at right angles to its plane. The internal diameter of a crown wheel is ground by holding the component in pitch like chucks to ensure accuracy of the finished gear.

As a result of the development of "flat" crown wheels it has become possible to construct a special gearbox. IHC has used these new gearwheels to produce a prototype of a continuously variable speed gearbox.

Applications

Crown wheels are used in motorcycle automotive gearboxes. It is also used in mechanical clocks. The clock consists of a crown wheel, rotated by a falling weight, whose teeth drive the pallets of a verge backward and forward. This verge is connected to an arm with a hammer on the end that struck the bell.

5-Differential Gears

Differential gears link two shafts with a covering, forcing the total of the rotational angles of the shafts to be the same as the rotational angles of the covering. Arrangement of the system is done in such a way that one axle turns faster than the other.

When a differential gear is meshed with the other gear then the highly efficient torque is applied from the differential side gears to the axle shaft. When torque level decreases then the gear separating forces also decreases allowing the axle shaft to rotate independently. Differential gears can add or subtract the movement of two inputs. In practical terms, they will turn the number of revolutions proportional to the movements of both inputs. They are used to convert the lengthwise flow of power from the engine through the clutches, transmissions, and propeller shafts into a right-angle direction. This change allows the engine power to turn the wheels.

In the differential gears there are two coaxial gears, the pinions and the turntable. Pinions are mounted on intermediate shafts and these shafts are connected to a fixed carrier called the turntable. The differential gears are lubricated with a fluid that absorbs heat and increases the life and performance of the gears as well as the wheel. Regular driving subjects the fluid to high heat that breaks the fluid at a later stage. This results in the contact of two metals, which eventually increases the heat and prevents the gear from turning the car's wheel. So, the fluid should be properly checked in regular intervals.

Types of Differential Gears:

There are two designs of differential gears, hypoid and spiral.

a)Spiral Differential:In spiral differential the pinion gears contacts the ring gears at its centerline.

b)Hypoid Gear: In the hypoid the pinion gear contacts the ring gear below the centerline. The size of pinion gear in hypoid differential is much smaller and the contact ratio is high, comparatively hypoid differential is much stronger than the spiral differential.

Applications

Differential gears in automobiles are the most common application of these gears. When the car is moving in a straight line, there is no movement of the differential gear with respect to its axis but when the car takes a turn then these gears help two wheels of the car to rotate differentially with respect to each other. When one wheel is stationary then the counterpart wheel rotates at twice of its expected speed.

6-External Gear

These are the most often used and the simplest gear system with cylindrical gears with straight teeth parallel to the axis. They are used for transmitting rotary motion between parallel shafts. When a smaller gear called the pinion, drives the larger gear called the wheel, also having external teeth, the corresponding driving and driven shafts rotate in opposite direction. The two gear surfaces come into contact once and so they are noisy at high speed.

External gears are generated with a tool moving forward towards the component axis. Internal gear cutter with very small diameter and few teeth is used for the production of external gear. External gears are widely used in various industrial sectors like coal industry, mining, steel plant, paper industry, and many more.