Gear is a toothed cylindrical or roller-shaped element of a machine that meshes with another toothed cylindrical element to transmit power from one shaft to another. In order to change the direction of the driving and driven shafts or to obtain different torque and speed ratios, it is primarily used.
Others include belt drives, chain drives, rope drives, etc. for power transmission., but the main advantage of the gear system is that there is almost negligible or no slippage between the driver and the driven member. Wherever there is a short distance between the axis driving and the driven shaft, such as in a bicycle, motorcycle, car, etc., gears are typically used.
Table of Contents
What Is Gear?
A gear is a rotating, circular machine part with teeth that mesh with another toothed component to transmit torque. The teeth may be cut or, in the case of a cogwheel or gearwheel, inserted. A cog is another colloquial term for gear. The fact that gear teeth prevent slippage is one of their benefits.
Unevenly spaced teeth are cut around cylindrical or conical surfaces to form a gear, a type of machine component. They are used to transfer rotation and forces from the driveshaft to the driven shaft by interlocking two of these components.
Involute, cycloid, and trochoid gears are the three shapes under which gears can be categorized. Additionally, they can be divided into three groups based on how the shafts are positioned: parallel shaft gears, intersecting shaft gears, and non-parallel and non-intersecting shaft gears. The use of gears dates back to ancient Greece in B.C., according to the long history of gears. in the writing of Archimedes.
Principle Of Gear
The fundamental tenet of thermodynamics, also known as the law of conservation or the first law of thermodynamics, is that energy cannot be created or destroyed. It is conservative, to be sure. It is capable of changing its form. We are aware that power (P = TV) is a function of the torque (force in rotary motion) and speed of the shaft. As a result, the driven shaft speed decreases per rotation of the driving shaft when a small gear is connected to the driving shaft and a larger gear to the driven shaft.
Knowing that power is conservative, we can say that the ratio of the driving gear to the driven gear—or, alternatively, the ratio of the driving shaft velocity to the driven shaft velocity—determines how much torque the driven shaft will produce. As a result, we can get different torque and speed combinations for the driven member by using different gear designs.
Why Use Gears?
To transfer rotation from one axis to another, gears are a very helpful transmission mechanism. As was already mentioned, gears can be used to modify a shaft’s output speed. Let’s say you have a motor that spins at 100 revolutions per minute and you only want it to spin at 50 revolutions per minute.
So that the output shaft rotates at half the engine speed, the speed can be lowered (while also increasing the torque) using a gear system. Because of their ability to control a shaft’s movement with greater precision and discretion, gears are frequently used in high load applications. The majority of pulley systems lack this advantage, which gears do.
Parts Of A Gear
When you first begin working with gears, you should be familiar with the terms listed below. Both the pressure angle and the diametrical pitch must match for the gears to mesh.
- Axis: The axis of revolution of the gear, where the shaft passes through
- Teeth: The rough faces that protrude from the gear’s circumference and are used to drive rotation in other gears Any gear must have an integer for its tooth count. Only when the teeth of a gear mesh and have the same profile do they transmit rotation.
- Pitch Circle: the elliptical region that designates the gear’s “size.” Two gears that mesh together require tangential pitch circles in order for them to mesh. The pitch circle would be the circumference of the two disks if there were two friction-driven disks instead of two gears.
- Pitch Diameter: The working diameter of the gear, also known as the pitch diameter, is referred to., the diameter of the pitch circle. The pitch diameter can be used to determine the distance between two gears: The separation between the two axes is equal to the sum of the two pitch diameters divided by two.
- Diametral Pitch: the proportion between the pitch diameter and tooth count. To mesh, two gears need to have the same diametrical pitch.
- Circular Pitch: the distance, as measured along the pitch circle, between a point on one tooth and the same point on the neighboring tooth. (so that the length is the length of the arc rather than a line).
- Module: The circular pitch is simply divided by pi to form the gear module. Because it is a rational number, this value is much simpler to work with than the circular pitch.
- Pressure Angle: The angle formed between the pitch circle’s radius line and the tooth’s tangent line at the point where the pitch circle intersects a tooth is known as the pressure angle of a gear. The common print angles are 14.5 degrees, 20 degrees, and 25 degrees. The distribution of force and the tooth’s contact with the gears are both influenced by the pressure angle. For meshing, the contact angle between two gears must be the same.
Different Types Of Gear
There are a wide variety of gear types, including:
- Spur Gear.
- Helical Gear.
- Gear Rack.
- Bevel Gear.
- Spiral Bevel Gear.
- Screw Gear.
- Double Helical Gear
- Herringbone Gear
- Hypoid Gear
- Miter Gear.
- Worm Gear.
- Internal gear
To achieve the required force transmission in mechanical designs, a precise understanding of the differences between gear types is required.
Even after selecting a general type, it’s crucial to take dimensions (such as module, teeth per module, helix angle, face width, etc.) into account.), the standard of precision grade, need for teeth grinding, and/or heat treating, allowable torque, and efficiency, etc.
1. Spur Gear
One of the most common varieties of precision cylindrical gears is the spur gear. These gears have a straightforward layout of parallel, straight teeth that are spaced evenly around the circumference of a cylinder body with a central bore that fits over a shaft.
In many variations, the gear is machined with a hub that thickens the gear body around the bore without changing the gear face. A splined or keyed shaft can accommodate the spur gear by broaching the central bore.
By transferring motion and power from one shaft to another through a series of mated gears, spur gears are used in mechanical applications to multiply torque or change the speed of a device.
In a mechanical setup, spur gears are used to transmit motion and power from one shaft to another. This transference can change the speed at which machinery operates, increase torque, and enable precise control of positioning systems. Because of their design, they can operate at lower speeds or in noise-sensitive environments.
2. Helical Gear
A cylindrical gear with a slanted tooth trace is called a helical gear. They have a higher contact ratio than spur gears, perform better in terms of quietness and reduced vibration, and can transmit significant amounts of force. The helix hand of a pair of helical gears is the opposite, but the helix angle is the same.
A lot of the same applications can be used for helical gears and spur gears, two of the most popular gear types. Helical gears have some significant advantages over spur gears despite being more complex and expensive to manufacture.
A helical gear has teeth that are shaped like a helix and are positioned at an angle to the gear’s axis. As a result, the teeth can gradually mesh, beginning with point contact and moving toward line contact as the engagement progresses.
Less noise is one of the most obvious advantages of helical gears over spur gears, especially at medium- to high speeds. Additionally, the load on each tooth is reduced in helical gears because multiple teeth are always in mesh. Vibrations, shock loads, and wear are decreased as a result of a smoother transition of forces from one tooth to the next.
3. Gear Rack
A gear rack is a structure with uniformly spaced teeth of the same size and shape that runs along a flat surface or a straight rod. A gear rack is a cylindrical gear with an infinite pitch cylinder radius. It transforms rotary motion into linear motion by meshing with a cylindrical gear pinion.
Gear racks can be broadly divided into straight tooth racks and helical tooth racks, but both have straight tooth lines. It is possible to join gear racks end to end by milling the ends of the gear racks.
4. Bevel Gear
A bevel gear is a rotating machine part with teeth used to transmit mechanical energy or shaft power between shafts that are intersecting, either perpendicularly or at an angle. As a result, the shaft power’s axis of rotation changes. In addition to performing this task, bevel gears can also change the torque while having the opposite impact on the angular speed.
Consider a bevel gear as a cone that has been cut off at the top. Teeth that interlock with other gears using its own set of teeth are milled into the side of the gear. The gear that transmits shaft power is referred to as the driver gear, and the gear that receives power is referred to as the driven gear.
In order to create a mechanical advantage, the driver and driven gears typically have different numbers of teeth. While the mechanical advantage is the ratio of the output torque to the input torque, the gear ratio is the relationship between the number of teeth on the driver’s gear and the driver gear.
5. Spiral Bevel Gear
Gears with curved tooth lines have a spiral bevel. They outperform straight bevel gears in terms of efficiency, strength, vibration, and noise thanks to the higher tooth contact ratio. They are harder to produce, though, on the other hand.
Additionally, the curved teeth generate thrust forces in the axial direction. The gear with zero twisting angles is known as zero bevel gear and is part of the spiral bevel gears.
6. Screw Gear
A pair of identical hand helical gears with a twist angle of 45 degrees mounted on non-parallel, non-intersecting shafts are known as screw gears. They have a low load carrying capacity and are not appropriate for large power transmission because the tooth contact is a point.
When using screw gears, it is important to consider lubrication because power is transmitted by the sliding of the tooth surfaces. Regarding the arrangements of various teeth, there are no limitations.
7. Double Helical Gear
Double helical gears are a type of helical gear in which two helical faces are arranged side by side, separated by a space. The helix angles on each face are identical but in opposition to one another.
A double-helical gear set can have even more tooth overlap and operate more smoothly while eliminating thrust loads. In enclosed gear drives, double helical gears are frequently used as the helical gear.
8. Herringbone Gear
Despite not having a gap between the two helical faces, herringbone gears are very similar to double-helical gears. When compared to comparable double helical gears, herringbone gears are typically smaller and are best used in high shock and vibration applications. Due to its expensive and challenging manufacturing process, herringbone gearing is not used very frequently.
9. Hypoid Gear
While spiral bevel gears resemble hypoid gears in appearance, the latter work on shafts that do not intersect. The shafts are supported by the bearings at either end of the shaft in the hybrid arrangement because the pinion is positioned on a different plane than the gear.
10. Miter Gear
With a speed ratio of 1, miter gears are beveled gears. They are utilized to switch the power transmission’s direction while maintaining the same speed. There are straight and spiral miter gears. Since spiral miter gears produce thrust force in the axial direction, it is necessary to take thrust bearings into consideration when using them.
An angular miter gear is a type of miter gear that has a shaft angle other than the standard 90 degrees.
11. Worm Gear
A worm gear is made up of a worm, which is a gear with a screw-like cutout on a shaft, a worm wheel, which is mounted next to it, and both of these gears on separate shafts. There are other shapes besides cylindrical ones for worms and worm wheels. The contact ratio can be increased with the hourglass type, but production is more challenging.
Reduced friction is necessary because the gear surfaces slide against one another. Because of this, soft material is typically used for the worm wheel and hard material for the worm. Despite the sliding contact’s low efficiency, the rotation is quiet and sputter-free. A self-locking feature is created when the worm’s lead angle is small.
12. Internal Gear
When used in conjunction with external gears, internal gears have teeth carved out of the interior of cylinders or cones. Planetary gear drives and gear-type shaft couplings are the primary applications for internal gears. Due to issues with trimming, trochoid interference, and involute interference, the number of teeth that can be different between internal and external gears is constrained.
When there are only one or two external gears in the mesh, the rotational directions of the internal and external gears are opposite.
Advantages Of Gear
- In addition to offering a wider range of speed and torque for the same input power than a chain system, gear drives also produce less noise and friction loss.
- Since the gear has a positive drive, a high velocity ratio can be achieved with little room.
- Higher loads can be lifted because gears have strong mechanical properties.
- For the transmission of heavy HF, gears are used.
- They are used for transmitting motion over small centre distance of shafts
- They serve as a means of transmitting torque as well as for significant speed reduction.
- Because only lubrication is needed for gears, less maintenance is needed.
- We can transfer motion between intersecting shafts that are not parallel by using gear systems.
- Its velocity ratio stays constant because they are used for positive drive.
- They have long life, so the gear system is very compact
Disadvantages Of Gears
- For high velocities, they are not appropriate.
- They are inadequate for long-distance motion transmission.
- In the event of excessive loading, some parts of the machine may sustain permanent damage due to the engagement of toothed gear wheels.
- They are not adaptable.
- Noise is produced during gear operation.
