Gear and Gear Trains

Contents

Define the term Gear 1

List Advantages and Disadvantage of the Gear 2

Classify the Toothed Wheels (Gears) 3

Recall different terms used in the Gears 4

State the Law of Gearing 6

Define the following terms i. Cycloidal Teeth Profile ii. Involute Teeth Profile 8

Describe the following terms: i. Line of Action ii. Length of Path of Contact iii. Arc of Contact iv. Contact Ratio 9

Define the term Interference 11

Recall the Methods to Prevent Interference 12

Recall the minimum number of teeth to prevent interference 13

Recall the effect of Variation in Centre Distance 14

Recall the Terminology used in Helical Gears 16

Recall the Shaft Angle in Spiral Gears 17

Describe the following i. velocity Ratio and Centre distance For Spiral and Helical Gears ii Forces and efficiency for Spiral and Helical Gears 18

Recall the Terminology used in Worm Gear 19

Describe the Velocity Ratio and Center distance for Worm Gear 20

Recall and calculate the Efficiency of Worm Gear 21

Classify Gear Trains 23

Describe the following Gear Trains: i. Simple Gear Train ii. Compound Gear Train iii. Reverted Gear Train iv. Epicyclic Gear Train v. Sun and Planet Gear Train 24

Define the term Gear

In mechanical engineering, a gear refers to a rotating machine component that consists of a toothed wheel or cylinder that meshes with another toothed component, thereby transmitting torque or rotational force between them. The two meshing gears may be of different sizes or may be of the same size, with the number of teeth on each gear determining the gear ratio.

Gears are widely used in various machines and mechanisms to transmit power or motion between two or more rotating shafts. They can be used to increase or decrease the speed of a rotating shaft, to change the direction of motion, or to transmit torque to a different location. Gears can be found in a wide range of applications, from simple machines like bicycles and wristwatches to complex machinery like automobiles, ships, and aircraft. They are often used in combination with other mechanical components like pulleys, belts, and chains to achieve a desired mechanical output.

List Advantages and Disadvantage of the Gear

Gears are mechanical elements that transmit power between two rotating shafts through a meshing process. They are used in many different mechanical systems for power transmission and are available in a wide variety of sizes, shapes, and materials.

Advantages of Gears:

1. Transmit power efficiently: Gears are an efficient way to transmit power between two rotating shafts, with very little loss of power during the transfer.
2. High accuracy: Gears can be very accurate, and can transmit motion with precision, which is essential in many mechanical systems.
3. Speed reduction and increase: Gears can be used to reduce or increase the speed of a rotating shaft, which can be useful in many mechanical systems where speed reduction or increase is required.
4. Large range of sizes: Gears are available in a wide variety of sizes and shapes, and can be made from many different materials to suit the requirements of different mechanical systems.

Disadvantages of Gears:

1. Noise and Vibration: Gears can generate noise and vibration during operation, which can be undesirable in some mechanical systems.
2. Wear and tear: Gears can experience wear and tear over time, which can lead to decreased efficiency and the need for replacement or maintenance.
3. Design Complexity: The design of a gear system can be complex, and it requires careful consideration to ensure that the gears mesh correctly, transmit power efficiently, and operate with a long service life.
4. Cost: The cost of gears can vary depending on the size, material, and precision required. Some gears can be quite expensive to manufacture and install, making them less desirable in some applications.

Classify the Toothed Wheels (Gears)

The classification of toothed wheels or gears is based on different factors such as the configuration of the teeth, size, shape, and application. Here are the classifications of toothed wheels:

1. According to the Configuration of Teeth:

• Spur Gear: It has straight teeth that are parallel to the gear axis. It is the simplest and most commonly used gear type.
• Helical Gear: It has teeth that are inclined at an angle to the gear axis. It provides smooth and quiet operation and is widely used in heavy machinery.
• Bevel Gear: It has teeth that are inclined at an angle to the gear axis and used to transmit power between intersecting shafts.
• Spiral Bevel Gear: It has teeth that are curved and inclined at an angle to the gear axis. It provides smooth and quiet operation at high speeds.
• Worm Gear: It has a worm or screw-like tooth that meshes with a worm wheel or a gear with a large diameter. It provides high reduction ratios and is used in heavy machinery.
• Rack and Pinion: It has a gear with teeth that mesh with a flat toothed bar or rack. It converts rotary motion into linear motion and vice versa.

2. According to the Size:

• Small Gears: They have a diameter of less than 250 mm and are used in light machinery.
• Medium Gears: They have a diameter of 250 mm to 1500mm and are used in medium-sized machinery.
• Large Gears: They have a diameter of more than 1500mm and are used in heavy machinery.

1. According to the Shape:

• External Gear: It has teeth on the outer surface of the wheel and is used to mesh with an internal gear.
• Internal Gear: It has teeth on the inner surface of the wheel and is used to mesh with an external gear.
• Crown Gear: It is a type of bevel gear with teeth that are perpendicular to the gear axis.
• Rack Gear: It is a type of gear with teeth that are cut into a straight toothed bar or rack.

1. According to the Application:

• Speed Reduction Gears: They are used to reduce the speed of the input shaft to the output shaft.
• Speed Increasing Gears: They are used to increase the speed of the input shaft to the output shaft.
• Differential Gears: They are used to transmit power to the wheels of a vehicle while allowing them to rotate at different speeds during cornering.
• Idler Gears: They are used to transmit power between two gears without changing the direction of rotation.
• Gear Train: It is a combination of gears arranged in a series to transmit power from one shaft to another.

Recall different terms used in the Gears

Gears are an essential component in many mechanical systems. They are used to transmit power and motion from one shaft to another, change the speed or direction of rotation, and modify the amount of torque applied to a system. Gears come in many shapes, sizes, and configurations, and there are several terms used to describe their various parts and functions.

1. Pitch Circle: The pitch circle is an imaginary circle that passes through the point where the teeth of two meshing gears meet. The pitch circle diameter is used to calculate the gear ratio and to determine the spacing and size of the gear teeth.
2. Pitch Diameter: The pitch diameter is the distance between the centre of the gear and the pitch circle. It is used to calculate the gear ratio and to determine the tooth size and spacing.
3. Module: The module is a measure of the size of the gear teeth. It is defined as the ratio of the pitch circle diameter to the number of teeth on the gear. The module is used to determine the size of the gear teeth and to ensure that two gears mesh correctly.
4. Teeth: The teeth are the protruding parts of a gear that mesh with the teeth of another gear to transmit power and motion. The number, size, and shape of the teeth are critical to the proper functioning of the gear.
5. Face: The face of a gear is the surface of the gear tooth that comes into contact with the teeth of another gear. The shape and curvature of the gear face affect the transmission of power and motion between the gears.
6. Pressure Angle: The pressure angle is the angle between the tooth face and a line perpendicular to the pitch circle. It determines the force applied to the gear teeth and affects the efficiency of the gear system.
7. Helix Angle: The helix angle is the angle between the gear tooth and the axis of the gear. It is used in helical gears, which have angled teeth that provide a smoother and more efficient transmission of power and motion.
8. Backlash: Backlash is the amount of clearance between two gears when they are meshed together. It is important to maintain a small amount of backlash to prevent the gears from jamming or binding.

By understanding and recalling these different terms used in gears, individuals can effectively design, manufacture, and maintain gear systems that meet the required specifications and functions.

State the Law of Gearing

The Law of Gearing is a fundamental principle in the field of mechanical engineering that governs the relationship between the size and number of teeth on two gears that are meshed together. This law states that the ratio of the rotational speeds of two gears is equal to the inverse ratio of their diameters. In other words, the larger the diameter of a gear, the slower it will rotate compared to a smaller gear with the same number of teeth.

The Law of Gearing can be expressed mathematically using the following equation:

N₁/D₁ = N₂/D₂

Where N₁ and N₂ are the rotational speeds of the two gears, and D₁ and D₂ are their diameters. This equation can be rearranged to solve for any of the four variables.

The Law of Gearing is a critical concept in gear design and analysis, as it allows engineers to determine the required gear sizes and tooth counts to achieve a specific gear ratio. By using this law, engineers can also calculate the speed and torque of a system based on the input and output gear sizes and speeds.

It is important to note that the Law of Gearing assumes that the gears are perfectly rigid and there is no slippage or loss of power during the transmission of motion. In practice, there will always be some degree of friction and inefficiency in a gear system, which must be taken into account during the design and analysis process.

Overall, understanding and applying the Law of Gearing is essential for the design, operation, and maintenance of gear systems in a wide range of mechanical applications, including automotive, aerospace, manufacturing, and robotics.

Describe the Velocity of the Sliding Teeth
In a gear system, the teeth of two meshing gears slide past each other as the gears rotate. The velocity of the sliding teeth is an important factor in gear design and analysis, as it can affect the efficiency, wear, and noise of the gear system.

The sliding velocity of the teeth is the relative velocity between two meshing gear teeth at the point where they are in contact. This velocity can be calculated using the following formula:

V = (π × D × RPM) / (60 × Z)

Where V is the sliding velocity of the teeth in meters per second (m/s), D is the pitch diameter of the gear in meters (m), RPM is the rotational speed of the gear in revolutions per minute (RPM), and Z is the number of teeth on the gear.

The sliding velocity of the teeth is a function of the diameter and rotational speed of the gear and the number of teeth on the gear. A gear with a larger diameter or slower rotational speed will have a lower sliding velocity compared to a gear with a smaller diameter or faster rotational speed. A gear with more teeth will also have a lower sliding velocity compared to a gear with fewer teeth.

High sliding velocities can lead to increased wear and noise in the gear system, as well as decreased efficiency. To minimize sliding velocities, designers can use gears with larger diameters or fewer teeth, or they can reduce the rotational speed of the gears. Lubrication can also be used to reduce friction and wear between the sliding teeth.

In summary, the sliding velocity of the teeth is an important factor in gear design and analysis, as it affects the efficiency, wear, and noise of the gear system. By understanding and controlling the sliding velocity of the teeth, designers can optimize the performance and lifespan of gear systems in a wide range of mechanical applications.

Define the following terms i. Cycloidal Teeth Profile ii. Involute Teeth Profile

i. Cycloidal Teeth Profile

A cycloidal teeth profile is a type of gear tooth profile that is characterized by its smooth curves and constant angular velocity. In this profile, the shape of the tooth is defined by a curve known as a cycloid, which is created by the path of a point on the circumference of a circle as it rolls along a straight line.

Cycloidal teeth profiles have a number of advantages over other tooth profiles, including their high efficiency, low noise, and smooth operation. They are commonly used in high-speed and high-torque applications, such as in gearboxes for industrial machinery, automobiles, and robotics.

ii. Involute Teeth Profile

An involute teeth profile is another type of gear tooth profile that is commonly used in mechanical engineering. In this profile, the shape of the tooth is defined by an involute curve, which is a curve that is formed by unwinding a taut string from a circle. The involute curve is then used to generate the shape of the gear tooth.

Involute teeth profiles have a number of advantages over other tooth profiles, including their ease of manufacture, high efficiency, and tolerance to manufacturing errors. They are commonly used in a wide range of mechanical applications, including automotive transmissions, machine tools, and industrial equipment.

One key advantage of involute teeth profiles is that they can be easily replicated, allowing for the mass production of gears with consistent tooth profiles. They are also highly customizable, as the shape of the involute curve can be adjusted to optimize the gear’s performance for a specific application.

In summary, a cycloidal teeth profile is defined by a smooth curve known as a cycloid, while an involute teeth profile is defined by an involute curve formed by unwinding a taut string from a circle. Each profile has its own advantages and is commonly used in a variety of mechanical applications.

Describe the following terms: i. Line of Action ii. Length of Path of Contact iii. Arc of Contact iv. Contact Ratio

i. Line of Action

The line of action is an imaginary line that runs tangent to the pitch circles of two meshing gears. It is an important concept in gear design and analysis, as it determines the force and torque transmission between the gears.

When two gears are meshed together, the teeth of one gear engage with the teeth of the other gear. This contact between the teeth creates a force that causes the gears to rotate. The force is transmitted along the line of action, which is the line that is tangent to both pitch circles at the point where the teeth are in contact.

The line of action is important in gear design, as it determines the pitch point, which is the point where the pitch circles intersect. The pitch point is the point of maximum force transmission between the gears, and it is used to calculate the gear ratios and other design parameters.

The line of action is also important in analyzing the forces and stresses within the gear system. The forces acting on the gears can be resolved into components along and perpendicular to the line of action. The force along the line of action is known as the tangential force, and it is responsible for the rotational motion of the gears. The force perpendicular to the line of action is known as the radial force, and it is responsible for the axial load on the gears.

In summary, the line of action is an imaginary line that runs tangent to the pitch circles of two meshing gears. It determines the force and torque transmission between the gears, and it is used to calculate the gear ratios and other design parameters. The line of action is also important in analyzing the forces and stresses within the gear system.

ii. Length of Path of Contact

The length of path of contact is the distance along which the teeth of two gears remain in contact as they roll past each other. It is an important parameter in gear design, as it determines the load capacity and durability of the gear system.

The length of path of contact is influenced by a number of factors, including the tooth profile, the pressure angle, and the number of teeth on the gears. In general, a longer path of contact is desirable, as it distributes the load over a larger area and reduces the stresses on the gear teeth.

iii. Arc of Contact

The arc of contact is the portion of the pitch circle of a gear that is in contact with the teeth of its mating gear. It is an important parameter in gear design, as it determines the load capacity and durability of the gear system.

The arc of contact is influenced by a number of factors, including the tooth profile, the pressure angle, and the number of teeth on the gears. In general, a larger arc of contact is desirable, as it distributes the load over a larger area and reduces the stresses on the gear teeth.

iv. Contact Ratio

The contact ratio is a measure of the average number of teeth that are in contact between two meshing gears. It is an important parameter in gear design, as it affects the smoothness and efficiency of the gear system.

The contact ratio is influenced by a number of factors, including the tooth profile, the pressure angle, and the number of teeth on the gears. In general, a higher contact ratio is desirable, as it results in a smoother and more efficient gear system.

A contact ratio of 1 means that each tooth on the driving gear contacts one tooth on the driven gear for a full revolution. A contact ratio greater than 1 means that each tooth on the driving gear contacts multiple teeth on the driven gear during a full revolution. A contact ratio less than 1 means that there are periods of time during the revolution when no teeth are in contact between the gears.

In summary, the length of path of contact is the distance along which the teeth of two gears remain in contact, the arc of contact is the portion of the pitch circle that is in contact with the teeth of its mating gear, and the contact ratio is a measure of the average number of teeth that are in contact between two meshing gears. All of these parameters are important in gear design, as they affect the load capacity, durability, smoothness, and efficiency of the gear system.

Define the term Interference

Interference in gears is a phenomenon that occurs when the tooth thickness of two meshing gears is not designed properly, resulting in teeth touching each other at points other than the pitch point. This can cause noise, vibration, and damage to the gear teeth.

Interference occurs when the tooth thickness of one gear is greater than the space between the teeth of the mating gear. In such cases, the teeth will touch each other before the pitch point and continue to touch each other after the pitch point. This results in the teeth being in contact for a longer duration than they should be, leading to higher stresses, wear, and potentially tooth breakage.

Interference can be avoided in gear design by ensuring that the tooth thickness of each gear is less than the space between the teeth of the mating gear. This can be achieved by careful selection of the gear module, pressure angle, and tooth profile. For example, gears with a smaller pressure angle and a higher number of teeth are less likely to experience interference.

In some cases, interference may be deliberately introduced into a gear design to achieve certain functional requirements. For example, in high-performance racing applications, interference can be used to create a preloaded gear system that can handle higher torque and reduce backlash.

In summary, interference is a phenomenon that occurs when the tooth thickness of two meshing gears is not designed properly, resulting in teeth touching each other at points other than the pitch point. It can cause noise, vibration, and damage to the gear teeth. Interference can be avoided in gear design by ensuring that the tooth thickness of each gear is less than the space between the teeth of the mating gear.

Recall the Methods to Prevent Interference

Interference in gears can lead to noise, vibration, and damage to the teeth. Therefore, it is important to prevent interference in gear design. There are several methods to prevent interference, including:

1. Proper Gear Design: One of the most effective ways to prevent interference is to ensure proper gear design. This includes selecting appropriate gear parameters such as the module, pressure angle, and tooth profile. The gear design should be such that the tooth thickness of each gear is less than the space between the teeth of the mating gear.
2. Backlash Adjustment: Backlash is the clearance between the teeth of two gears in mesh. Adjusting the backlash can help prevent interference. Backlash can be increased or decreased depending on the requirements of the system.
3. Reducing Tooth Thickness: Another method to prevent interference is to reduce the tooth thickness of the gears. This can be achieved by using a smaller module or pressure angle. However, reducing tooth thickness can also lead to reduced tooth strength and increased wear.
4. Increasing the Number of Teeth: Increasing the number of teeth on the gears can also help prevent interference. Gears with a higher number of teeth have smaller tooth thickness, which reduces the chances of interference.
5. Modifying Tooth Profile: Modifying the tooth profile can also help prevent interference. For example, using a modified profile like a tip relief or root relief can help reduce the likelihood of interference.

In summary, preventing interference in gear systems is essential for reliable and efficient operation. Proper gear design, adjusting backlash, reducing tooth thickness, increasing the number of teeth, and modifying the tooth profile are some of the methods that can be used to prevent interference. Gear designers need to carefully consider these factors when designing a gear system to ensure proper functioning and prevent interference.

Recall the minimum number of teeth to prevent interference

The minimum number of teeth required to prevent interference in a gear system depends on the pressure angle and the tooth profile used. In general, a gear pair should have a minimum of 17 teeth to prevent interference for a pressure angle of 20 degrees and an involute tooth profile. For other pressure angles and tooth profiles, the minimum number of teeth required may be higher.

If the number of teeth in a gear pair is less than the minimum required, the gear system is likely to experience interference, which can lead to noise, vibration, and damage to the gear teeth. Interference occurs when the teeth of the gear system touch each other before the pitch point, resulting in high stresses, wear, and potentially tooth breakage.

It is important to note that while a minimum number of teeth can prevent interference, a higher number of teeth can improve the performance and durability of the gear system. Higher tooth counts distribute the load more evenly, reducing wear and improving load-carrying capacity. Therefore, gear designers should aim for a tooth count that is not just the minimum but also meets the functional requirements of the system.

In summary, the minimum number of teeth required to prevent interference in a gear system is generally 17 teeth for a pressure angle of 20 degrees and an involute tooth profile. For other pressure angles and tooth profiles, the minimum number of teeth required may be higher. However, it is important to note that a higher tooth count can improve the performance and durability of the gear system.

Recall the effect of Variation in Centre Distance

Centre distance is the distance between the axes of two gears in mesh. Variation in centre distance can have a significant effect on the operation and performance of a gear system. Some of the effects of variation in centre distance are:

1. Gear Ratio: Centre distance has a direct effect on the gear ratio of a gear system. The gear ratio is the ratio of the number of teeth between the driving and driven gears. If the centre distance is increased, the gear ratio will decrease, and if the centre distance is decreased, the gear ratio will increase.
2. Contact Ratio: Contact ratio is the ratio of the length of the path of contact to the circular pitch. Variation in centre distance can affect the contact ratio of a gear system. If the centre distance is increased, the contact ratio will decrease, and if the centre distance is decreased, the contact ratio will increase.
3. Tooth Loading: Variation in centre distance can also affect the distribution of the load on the gear teeth. If the centre distance is increased, the load will be distributed over a smaller number of teeth, resulting in higher tooth stresses. Similarly, if the centre distance is decreased, the load will be distributed over a larger number of teeth, resulting in lower tooth stresses.
4. Backlash: Backlash is the clearance between the teeth of two gears in mesh. Variation in center distance can affect the backlash of a gear system. If the centre distance is increased, the backlash will increase, and if the centre distance is decreased, the backlash will decrease.
5. Noise and Vibration: Variation in center distance can also affect the noise and vibration levels in a gear system. If the centre distance is not uniform, the gears will experience varying levels of tooth loading, which can lead to noise and vibration.

In summary, variation in center distance can have a significant effect on the operation and performance of a gear system. It can affect the gear ratio, contact ratio, tooth loading, backlash, and noise and vibration levels. Gear designers should carefully consider the center distance when designing a gear system to ensure proper functioning and optimal performance.

Recall the comparison between Involute and Cycloidal Teeth

Involute and cycloidal teeth are two types of tooth profiles commonly used in gear design. Both types of teeth have unique characteristics that make them suitable for different types of gear applications. Here are some key differences between involute and cycloidal teeth:

1. Profile Shape: The shape of the involute tooth profile is a curve that follows a mathematical function. On the other hand, the shape of the cycloidal tooth profile is a curve that is generated by a rolling circle.
2. Manufacturing: Involute gears are relatively easy to manufacture using modern CNC machines. Cycloidal gears, on the other hand, are more difficult to manufacture due to the complex shape of the tooth profile.
3. Tooth Strength: Involute teeth have a higher tooth strength compared to cycloidal teeth. This is because the involute tooth profile distributes the load more evenly along the tooth surface, resulting in lower stress concentrations.
4. Noise: Cycloidal teeth produce less noise compared to involute teeth due to their smoother tooth engagement. This makes them suitable for high-speed and precision gear applications.
5. Contact Ratio: Cycloidal gears have a higher contact ratio compared to involute gears. This means that the teeth stay in contact for a longer period, resulting in a smoother gear operation and longer gear life.

In summary, both involute and cycloidal teeth have unique characteristics that make them suitable for different types of gear applications. Involute teeth are easy to manufacture, have high tooth strength, but can be noisy. Cycloidal teeth are more difficult to manufacture, produce less noise, and have a higher contact ratio. Gear designers should consider these differences when selecting the appropriate tooth profile for their gear application.

Recall the Terminology used in Helical Gears

Helical gears are a type of gears that have teeth that are cut at an angle to the axis of rotation. This results in a gradual engagement of the teeth, which makes them ideal for high-speed and high-load applications. Here are some common terminologies used in helical gears:

1. Lead: The lead is the axial distance that the gear travels in one revolution.
2. Helix Angle: The helix angle is the angle between the tooth helix and the gear axis.
3. Pressure Angle: The pressure angle is the angle between the line of action and a tangent to the pitch circle at the point of contact.
4. Addendum: The addendum is the radial distance from the pitch circle to the top of the tooth.
5. Dedendum: The dedendum is the radial distance from the pitch circle to the bottom of the tooth.
6. Whole Depth: The whole depth is the radial distance between the addendum and the dedendum.
7. Transverse Module: The transverse module is the ratio of the pitch diameter to the number of teeth in the gear.
8. Normal Module: The normal module is the ratio of the pitch diameter to the cosine of the helix angle.
9. Axial Pitch: The axial pitch is the distance between corresponding points on adjacent teeth measured along the axis.
10. Face Width: The face width is the axial length of the tooth in the axial direction.

In summary, helical gears have teeth that are cut at an angle to the axis of rotation, and they have unique terminologies that describe their geometrical features. These terminologies include lead, helix angle, pressure angle, addendum, dedendum, whole depth, transverse module, normal module, axial pitch, and face width. Gear designers should be familiar with these terminologies to design and manufacture helical gears that meet the specific requirements of their applications.

Recall the Shaft Angle in Spiral Gears

Spiral gears are a type of helical gears in which the teeth are cut in a spiral pattern. Unlike straight-cut helical gears, the teeth of spiral gears gradually engage, which results in a smoother and quieter operation. Spiral gears are commonly used in automotive differentials and other high-torque applications.

In spiral gears, the shaft angle is the angle between the axis of the driving shaft and the axis of the driven shaft. The shaft angle is an important parameter in spiral gear design because it affects the load distribution among the teeth and the tooth contact pattern. The shaft angle can be either parallel or crossed.

In parallel spiral gears, the shaft angle is 0 degrees, which means that the axes of the driving and driven shafts are parallel to each other. Parallel spiral gears are commonly used in applications where the axes of the driving and driven shafts are fixed, such as automotive differentials.

In crossed spiral gears, the shaft angle is greater than 0 degrees, which means that the axes of the driving and driven shafts are not parallel to each other. Crossed spiral gears are commonly used in applications where the axes of the driving and driven shafts are not fixed, such as in printing presses and rolling mills.

The shaft angle in spiral gears is an important design parameter that affects the performance and reliability of the gear system. Gear designers should carefully consider the shaft angle and other design parameters to ensure that the gear system meets the specific requirements of the application.

Describe the following i. velocity Ratio and Centre distance For Spiral and Helical Gears ii Forces and efficiency for Spiral and Helical Gears

i. Velocity Ratio and Centre Distance for Spiral and Helical Gears

Velocity ratio is the ratio of the speed of the driving gear to the speed of the driven gear in a gear system. In spiral and helical gears, the velocity ratio is determined by the number of teeth on each gear and the gear ratio. The centre distance is the distance between the centres of the driving and driven gears in a gear system.

In spiral and helical gears, the centre distance and velocity ratio are related. As the centre distance between the gears increases, the velocity ratio decreases. Conversely, as the centre distance decreases, the velocity ratio increases. Therefore, in spiral and helical gears, the designer must consider both the centre distance and the gear ratio to achieve the desired velocity ratio.

ii. Forces and Efficiency for Spiral and Helical Gears

In spiral and helical gears, the forces acting on the teeth of the gears are primarily radial and tangential. The radial forces are directed towards the centre of the gear, while the tangential forces are directed parallel to the gear’s axis. The forces acting on the gears depend on the applied torque, the gear ratio, and the geometry of the gears, including the number of teeth, the pressure angle, and the tooth profile.

The efficiency of a gear system is the ratio of the output power to the input power of the system. In spiral and helical gears, the efficiency of the gear system is influenced by several factors, including the design of the gears, the manufacturing tolerances, and the operating conditions of the gear system. In general, spiral and helical gears are more efficient than straight-cut gears because they have better load-carrying capacity and smoother operation.

Spiral gears have a higher load-carrying capacity than helical gears because they have more teeth in contact at any given time. However, spiral gears are more difficult to manufacture and are more expensive than helical gears. Helical gears are more commonly used in industry because they are easier to manufacture and have a lower cost.

Recall the Terminology used in Worm Gear

A worm gear is a type of gear used in power transmission systems where a worm meshes with a gear to transmit torque and rotational motion. The following are some of the common terminologies used in worm gears:

1. Worm: The worm is the cylindrical screw-like component with a helical thread that meshes with the teeth of the gear. It is the driving component of the worm gear system.
2. Gear: The gear is the component that meshes with the threads of the worm. It is the driven component of the worm gear system.
3. Lead Angle: The lead angle is the angle between the helix of the worm and the axis of the worm gear. The lead angle determines the speed and efficiency of the worm gear system.
4. Pitch Diameter: The pitch diameter is the diameter of the gear measured at the point where it meshes with the worm.
5. Centre Distance: The centre distance is the distance between the axis of the worm and the axis of the gear.
6. Contact Ratio: The contact ratio is the ratio of the length of the path of contact to the pitch of the worm gear. It is a measure of the amount of contact between the worm and the gear.
7. Efficiency: The efficiency of a worm gear system is the ratio of the output power to the input power. The efficiency is influenced by several factors, including the lead angle, the number of teeth on the gear, and the materials used for the worm and gear.

Understanding these terminologies is crucial for designing and analyzing worm gear systems.

Describe the Velocity Ratio and Center distance for Worm Gear

The velocity ratio (VR) of a worm gear is the ratio of the speed of the worm to the speed of the gear. It can be calculated by dividing the number of teeth on the gear by the number of threads on the worm. For example, if the gear has 40 teeth and the worm has 2 threads, then the velocity ratio would be 20:1.

The center distance is the distance between the axis of the worm and the axis of the gear. It is an essential parameter in the design of worm gears, as it determines the tooth profile, gear size, and efficiency of the gear system. The center distance is typically chosen based on the required speed reduction, the size of the gear system, and the desired gear ratio.

The center distance also influences the contact ratio between the worm and the gear. In general, a larger center distance leads to a higher contact ratio, which improves the load-carrying capacity and wear resistance of the gear system. However, a larger center distance also results in a more significant axial thrust and higher power losses due to the increased sliding friction.

Therefore, the selection of the center distance is a trade-off between the contact ratio, axial thrust, and efficiency of the worm gear system. Designers typically use empirical formulas and computer simulations to optimize the center distance for a given application.

Recall and calculate the Efficiency of Worm Gear

The efficiency of a worm gear refers to the ratio of the output power to the input power, expressed as a percentage. It is an essential parameter in the design and operation of worm gear systems, as it determines the power losses and energy consumption of the system.

The efficiency of a worm gear depends on several factors, including the lead angle of the worm, the number of threads on the worm, the coefficient of friction between the worm and gear, and the center distance between the worm and gear.

The efficiency of a worm gear can be calculated using the following formula:

Efficiency = (π * (1 – λ) / (2 * tanφ)) * 100%

where λ is the lead angle of the worm, and φ is the pressure angle of the worm gear. The lead angle is the angle between the axial direction of the worm and a plane perpendicular to the axis of the worm gear. The pressure angle is the angle between the line of action of the teeth and the tangent to the pitch circle of the worm gear.

The coefficient of friction between the worm and gear depends on the materials, lubrication, and operating conditions of the gear system. In general, lower coefficients of friction result in higher efficiency, while higher coefficients of friction result in lower efficiency.

The center distance between the worm and gear also influences the efficiency of the gear system. As the center distance increases, the sliding friction between the worm and gear also increases, leading to higher power losses and lower efficiency.

In practice, the efficiency of a worm gear is typically in the range of 50% to 90%, depending on the design and operating conditions of the system. Designers can optimize the efficiency of the gear system by selecting suitable materials, lubricants, and operating conditions, as well as by optimising the lead angle, pressure angle, and center distance of the worm gear.

Define the term Gear Trains

Gear trains are mechanisms consisting of two or more gears that are connected and work together to transmit motion and power between rotating shafts. The gears in a gear train can be arranged in various configurations, depending on the requirements of the particular application. The basic types of gear trains include simple gear trains, compound gear trains, and epicyclic gear trains.

In a simple gear train, two or more gears are arranged in a straight line and transmit power from one shaft to another. A compound gear train, on the other hand, includes multiple shafts and at least one intermediate gear between the input and output shafts. Finally, an epicyclic gear train, also known as a planetary gear train, consists of one or more planet gears that rotate around a central sun gear, and is often used in situations where high gear ratios are required in a compact space.

Gear trains are commonly used in a variety of machinery, including automobiles, bicycles, and industrial machinery, to transmit power and motion between rotating shafts at different speeds and torque levels. The design and arrangement of gear trains can have a significant impact on the overall efficiency and performance of the system, and careful consideration of gear train parameters such as gear ratio, center distance, and tooth profile is essential in optimizing the design for a particular application.

Classify Gear Trains

Gear trains can be classified into three main types: simple, compound, and epicyclic. The classification is based on the number and arrangement of gears in the train.

1. Simple Gear Train:

A simple gear train is the most basic type of gear train, consisting of two or more gears connected in series. The input and output shafts of a simple gear train are parallel and rotate in the same direction. This type of gear train is used when a fixed gear ratio is required, and can also be used to change the direction of rotation of the output shaft.

1. Compound Gear Train:

A compound gear train is a type of gear train that has more than two gears and at least one of these gears is an idler gear. An idler gear is a gear that is placed between the driver and driven gears, and its purpose is to change the direction of rotation of the output shaft. Compound gear trains are used when a large change in the gear ratio is required.

1. Epicyclic Gear Train:

An epicyclic gear train, also known as a planetary gear train, consists of one or more planet gears that revolve around a sun gear. The planet gears are mounted on a carrier, which in turn rotates around the sun gear. Epicyclic gear trains are used when a high gear ratio is required in a compact space. They are often found in automatic transmissions, robotics, and other applications where a high gear ratio and precise control are necessary.

In addition to these three main types, gear trains can also be classified by their specific arrangements, such as parallel shaft gear trains, intersecting shaft gear trains, and non-parallel and non-intersecting shaft gear trains. The choice of gear train type and arrangement depends on the specific application requirements, such as the desired gear ratio, space limitations, and power and torque requirements.

Describe the following Gear Trains: i. Simple Gear Train ii. Compound Gear Train iii. Reverted Gear Train iv. Epicyclic Gear Train v. Sun and Planet Gear Train

i. Simple Gear Train: A simple gear train consists of two gears, where one gear is driving the other, and the two gears are mounted on parallel shafts. The speed ratio of the gears in the train is determined by the ratio of the number of teeth on each gear. The output shaft speed can be calculated by dividing the input shaft speed by the gear ratio. Simple gear trains are commonly used in applications where a constant speed reduction or increase is required, such as in clocks, watches, and speedometers.

ii. Compound Gear Train: A compound gear train consists of more than two gears, where two or more gears are mounted on the same or different shafts. In a compound gear train, the output of one pair of gears serves as the input to another pair of gears, resulting in a higher gear ratio than what can be achieved with a simple gear train. Compound gear trains are often used in applications where a large change in speed is required, such as in automotive transmissions, heavy machinery, and machine tools.

In a compound gear train, there are two types of arrangements: series and parallel. In a series arrangement, the gears are mounted in a line, with the output of one gear serving as the input to the next gear. In a parallel arrangement, two or more gears are mounted on separate shafts and mesh with a common gear. The output shaft is typically connected to the common gear.

Compound gear trains can have various configurations, such as the epicyclic gear train or planetary gear train, which is a type of compound gear train with one or more gears rotating around a central gear. This arrangement can provide high gear ratios in a compact design and is often used in automatic transmissions, bicycles, and wind turbines.

iii. Reverted Gear Train: A reverted gear train is a type of compound gear train where two or more shafts are connected to each other in a specific way. In this gear train, the input shaft and the output shaft are parallel to each other, and they rotate in opposite directions. The input shaft is connected to a large gear, which meshes with a small gear on a second shaft. The second shaft also has a large gear that meshes with a small gear on the output shaft. The small gears are usually idlers, and their size is determined by the center distance between the input and output shafts.

The advantage of the reverted gear train is that it allows for a compact design, with the input and output shafts in a parallel orientation, and it also provides a large gear ratio without the need for excessively large gears. However, the disadvantage is that it is less efficient than a simple gear train because of the extra gears that are added to the system. The extra gears introduce more friction and potential for misalignment, which can reduce the overall efficiency of the system.

Reverted gear trains are commonly used in applications where a high gear ratio is required, but space is limited, such as in machine tools, robotics, and conveyor systems.

iv. Epicyclic Gear Train: An epicyclic gear train, also known as a planetary gear train, consists of three elements: a sun gear, a planet carrier, and two or more planet gears. The sun gear is positioned at the center and surrounded by planet gears that mesh with the sun gear and the internal teeth of the ring gear. The planet gears rotate around their own axis and the carrier rotates around the sun gear. The ratio of the input speed to the output speed depends on the number of teeth on the sun gear, planet gears, and ring gear, and the arrangement of the gears in the system. The epicyclic gear train finds applications in automatic transmissions, power tools, and robotics.

v. Sun and Planet Gear Train: A sun and planet gear train, also known as an annular gear train, consists of a central sun gear that meshes with three or more planet gears. The planet gears are mounted on a carrier and mesh with an internally toothed annular ring gear. As the planet gears rotate, they revolve around the sun gear, which remains stationary. The speed ratio in a sun and planet gear train depends on the number of teeth on the sun gear, planet gears, and annular gear, and the arrangement of the gears in the system. The sun and planet gear train is used in watches, clocks, and other precision instruments.