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Types Of Gears [Classification of Gears] and Gear Trains

In this article, you will learn what is gear and how it works, types of gears and different types of gear trains.

Gears and Types of Gears

When there’s a gear problem everything can come to stop because of this it’s important for you to understand how gears work in order to keep them working in their associated equipment operating.

Gear can be defined as a toothed wheel can be engaged in another toothed wheel in order to transmit energy that gives the change of speed and direction of motion. It is widely used in mechanical devices. The teeth of the gear are generally carved on wheels, cylinders or cones.

Types of gears

Many devices that we use in our day to day life have their own working principle. The tooth and wheel of gear are working parts of all types of gears. The different types of gears are used to complete the transfer of energy in different ways and different directions.

A gear is a component within a transmission device that transmits the rotational force to another gear or device. Gear is different from a pulley in that a gear is a round wheel which has teeth that mesh with other gear teeth. Allowing the force to be fully transferred without slippage.

Depending on their construction and arrangement, geared devices can transmit forces at different speeds, torques, or in a different direction, from the power source.

The most common situation is for a gear to mesh with another gear. To overcome the problem of slippage as in belt drives, gears are used which produce positive drive with uniform angular velocity.

Read also: Gear Terminology: Basic Terms Used In Gear

Types of Gears

Following are the different types of gears:

  1. Parallel gears
    1. Spur Gears
    2. Helical Gears
    3. Double Helical or Herringbone Gears.
  2. Perpendicular axis gears
    1. Nonintersection perpendicular axis
    2. Intersection perpendicular axis gear
  3. Intersecting gears
    1. Spiral gears
    2. Bevel Gears
  4. Non-intersecting and Non-Parallel gears.
    1. Worm Gears
  5. Rack and Pinion gears

Gears or toothed wheel may be classified according to the axes of the two shaft between which the motion is to the transmitted. The types of gears to be determined based on the application in which they are to be used.

1. Parallel Axis Gears

In this type of gearing, the axis of both the gears tends to be Parallel to each other. The types of gears that come under this system is gears are:

  1. Spur Gears
  2. Helical Gears
  3. Double Helical or Herringbone Gears.

Application of Parallel Axis Gears

Some typical application areas of spur and helical are automobile gearboxes, industrial gearboxes, etc. Some of the application areas of herringbone gears are in the gearboxes used for steel rolling mills, etc.

2. Perpendicular Axis Gears

In this type of gearing the axis of the gears tend to be perpendicular to each other. There are two in this type of gearing too. they are:

  1. Nonintersection perpendicular axis
  2. Intersection perpendicular axis gear

1. Nonintersection Perpendicular Axis

In this type, the two perpendicular axes of the gearing do not intersect each other. The two types of gearing that fall into this category are Worm Gear and hypoid Gear.

Some typical applications of the worm gears are in the passenger lifts used in the buildings. Another typical application of the Hypoid gear is in the rear axle of the busses, lorries and heavy vehicles.

2. Intersection Perpendicular Axis Gear

In this type, the perpendicular axis of the gears tends to intersect at a certain point. The types of gears that fall under are the straight Bevel Gear, spiral bevel Gears, and Gears. some typical application of straight bevel gear is the differential mechanism in the automobile.

Read also: What Is Gear Ratio And How To Calculate Gear Ratio

Classification of Gears

The different types of gears are classified as follows:

  1. Spur gear: for parallel axes shafts
  2. Helical gears: For both parallel and non-parallel and non-intersecting axes shafts.
  3. Spiral gears: For non-parallel and intersecting axes shaft.
  4. Bevel gears: For intersecting axes shaft
  5. Worm gear: For non-parallel and non-coplanar axes shaft
  6. Rack and pinion: For converting rotary motion into linear motion

1. Spur Gear

The spur gear is the most common and simplest type of gear. It is generally used for transmission of rotary motion between parallel shaft. The spur gear is the best option for gears except when speed, loads, and ratios direct towards other options.

types of gears: spur gear

They have straight teeth and are mounted on parallel shafts. Their general form is a cylinder or disk. The teeth project radially, and with these “straight-cut gears”. When two spur gears different sizes mesh together, the larger gear is called a wheel and the smaller gear is called a pinion.

In a simple gear train of two spur gears, the input motion and force are applied to the driver gear. The driver gear rotates the driven gear without slipping.

Read also: Chain Drives and Types Of Chains

2. Helical Gears

Helical gears offer a refinement over spur gears. The teeth of a helical gear are not parallel to the axis of rotation but are set at a helix angle. Helical gears can be meshed in a parallel or crossed orientation.

Helical gear: types of gear

Along with parallel helical gear, each pair of teeth first contacts one point on the one side of the gear wheel. A moving curve of contact increases gradually against the teeth face to a maximum then come back until the teeth reach contact at one point on the opposite side.

Because of angled teeth of helical gear they reduce the noise and stress in the gears, most of the gears in your car are helical. The use of helical gears is indicated when the application involves high speeds, large power transmission, or where no noise is important.

3. Bevel Gears

Bevel gears have teeth cut on a cone instead of a cylinder blank. they are used in pairs to transmit rotary motion and torque where the bevel gear shaft are at right angles (90 degrees) to each other. When two bevel gear has their axes at right angles and is equal sizes, they are called mitre gears.

bevel gear

Bevel gear transmits power between two intersecting shafts at any angle or non-intersecting shaft. they are classified as straight and spiral tooth bevel and hypoid gears. These are gears cut from conical blanks and connect intersecting shaft axes.

The connecting shaft is generally at 90°and sometimes one shaft drives a bevel gear which is mounted on a through the shaft resulting in two output shafts. The point of intersection of the shaft is called the apex and the teeth if the two gears converge at the apex.

Read also: Transmission Of Power By Rope Drive and [Types of Ropes]

4. Rack and Pinion

A rack and pinion is a pair of gears which convert rotational motion into linear motion and vice versa. A circular gear called “the pinion” engages teeth on a linear “gear” bar called “the rack”.

Rack and pinion

Rotational motion applied to the pinion will cause the rack to move to the side, up to the limit of its travel. The diameter of the gear determines the speed that the rack moves as the pinion turns.

A rack and pinion are commonly found in the steering mechanism of cars or other wheeled, steered vehicles. In a rack railway, the rotation of a pinion mounted on a locomotive or a railcar engages a rack between the rails and pulls a train along a steep slope, machine tools such as lathe machine, drilling machine, planning machine.

5. Hypoid Gear

Hypoid gear looks like the spiral bevel gear in some respects. For example, hypoid gears are shaped like spiral bevel gears and high points are used on cross axis shafts like bevel gear sets are.

Hypoid gear

But unlike bevel gear sets the shafts of hypoid gears do not line up with each other they’re offset. This offset allows hypoid pinions to have as few as five teeth in a high ratio gear set while the various types of bevel gears typically don’t have less than 10 teeth on opinion

The smaller number of teeth on a hypoid pinion means that larger ratios can be obtained with a hypoid gear set than with a bevel gear set of the same dimensions.

6. Worm and Worm Wheel

The arrangement of gears shown in the image is called a worm and worm wheel. The two elements called the worm screw and worm wheel.

A gear which has one tooth is called a worm wheel. The tooth in the form of a screw thread is called worm screw. The worm wheel is a helical gear with teeth inclined so that they can engage with the thread-like worm.

Worm and worm wheel

This wheel transmits torque and rotary motion through a right angle. The worm can easily turn the gear, but the gear cannot turn the worm. This is because of the angle on the worm is so shallow that the gear tries to spin it. Worm mechanisms are very quiet running.

It is used to transmit power between the driving shaft having their axes at right angles and non-coplanar as shown in fig. Worm gears are used in machine tools when large gear reductions are needed.

It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater. This feature is useful for machines such as conveyor systems, in which the locking feature can act as a brake for the conveyor when the motor is not turning.

Types of Gear Trains

A gear train is a mechanical system formed by mounting gears on a frame. As mentioned above, when two or more gears mesh together to transmit power from one shaft to another such arrangement is called a gear set or a gear train.

Sometimes two or more gears are made to mesh with each other to transmit power from one shaft to another such a combination is called “gear train of the wheel”.

Also, each gear is generally attached to a shaft often gears that are meshed together will be of different sizes in this case the smaller gear is referred to as the pinion and the larger one is simply referred to as the gear.

Following are the different types of gear trains:

  1. Simple gear train
  2. Compound gear trains
  3. Reverted gear trains
  4. Epicyclic gear trains

1. Simple Gear Trains

In these types of gear trains, the distance between the two wheels is great the motion from one wheel to another is transmitted by providing one or more intermediate wheels as shown in the figure.

simple gear train

When the number of intermediate wheels is odd, the motion of driver and follower is like as shown in the figure. If the number of intermediate wheels is even the motion of the follower will be in the opposite direction of the driver as shown in the figure.

2. Compound Gear Train

In compound gear train, each intermediate shaft has two wheels fixed to it. These wheels have the same speed. One wheel gears with the drier and the other wheel gears with the follower attached to the next shaft.

3. Reverted Gear Trains

reverted gear train

When the axes of the first and last wheels are co-axial the train is known as “reverted gear trains” as shown fig. Since the motion of the first and last wheel is alike, therefore a compound wheel is provided. Since the distance between the centres of the shaft 1 and 2 as well as 3 and 4 is the same.

An epicyclic gear train, the axes of the shaft, over which the gears are mounted, move relative to a fixed axis. A simple epicyclic or planetary gear train is shown the figure.

Epicyclic gear train

Here wheel A and arm C have a common axis at O1 about which they can rotate. The wheel B meshes with wheel A and has its axis on the arm at O2, about which the wheel B can rotate. If wheel A is fixed and the arm is rotated, the train becomes an “epicyclic gear train”.

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About Saif M

Saif M. is a Mechanical Engineer by profession. He completed his engineering studies in 2014 and is currently working in a large firm as Mechanical Engineer. He is also an author and editor at www.theengineerspost.com

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