## What is power transmission?

It is defined as the energy transfer from one location to another location. The energy will start moving from the energy generation source to the energy applied position to obtain the work output. From this method, a large amount of electric energy moves from the power station to various electrical substations.

## What are power transmission elements?

The elements used for the transfer of electric power can be termed power transmission elements. Each element has its own function like some elements are used to hold the machine components, some elements are used to transmit power, and others are used as supporting elements.

## What are the types of power transmission elements?

For the transmission of power from one system to another there are various methods that are mentioned below:

• Mechanical Transmission
• Electric Transmission
• Hydraulic Transmission
• Pneumatic Transmission

The discussion of the types of power transmission is shown below:

## Mechanical Transmission

Mechanical transmission involves the transfer of energy with the help of machine elements. The energy is supplied to the system to obtain the required work output. The elements or drives which come under this category are gear drives, turbo vortex drive, belt drive, chain drive, wheel drive, electric drive, etc.

### Gear Drives

This type of drive provides the exact value of the velocity ratio. Gears are used for the transmission of large power. Various types of gear drives can be given as,

• Based on the axes location of the shafts, the gear is classified into parallel shaft, non-intersecting shaft, intersecting shaft, and non-parallel shafts. Examples of these gears are spur gear, helical gear, bevel gear, skew bevel gears, spiral gears.
• Based on the peripheral velocity, the gears are divided into three types gear which are low, medium and, high-velocity gears.
• Based on the gearing type, the gears are divided into external, internal, rack, and pinion gears.
• Based on the teeth position, the gears are classified as straight, inclined and curved.

### Spur Gear

The spur gears are connected by a parallel shaft and also a non-coplanar shaft. The spur gear tooth is parallel to the wheel axis. They consist of two gears, namely, gear and pinion. It is the basic type of gear. The application of spur gears is speed reducers, gear pumps, transmissions, etc.

### Other Gears

• The bevel gears are joined by the coplanar shafts, intersecting shafts, and non-parallel shafts.
• The helical gears having inclined teeth are connected to parallel shafts.
• The helical bevel gear consists of inclined teeth.
• The skew bevel gear has non-intersecting shafts as well as non-coplanar shafts.

The spur gears can be shown as,

Here, the larger size gear driver is called gear and the smaller driven gear is the pinion gear.

The circular pitch of the gear can be expressed as,

${P}_{c}=\frac{\mathrm{\pi D}}{T}$

Here, D is the diameters of pinion or gear, T is the teeth of pinion or gear.

The module of the gear can be written as,

$m=\frac{D}{T}$

### Rack and Pinion Gear

In this gear arrangement, the rack gear is a linear type of gear, and the pinion gear is circular. Here, the rotational motion changes into linear motion. When the pinion drives rotationally, then the rack starts driven translatory action and vice versa. These types of gears can be used in rack railways, actuators, steerings, etc.

The rack and pinion gear can be shown as,

### Turbo Vortex Drive

This type of gear has a large value power transmission ratio. These drives have compact designs. They are used for the motion between two axes having vertical spaces. But they provide one-way power transmission, and they have very low efficiency.

### Belt Drive

These type of drives uses belt and pulley arrangement for the power transmission. The belts are usually tensioned on both drives, namely driven and driver gear wheels. A large distance separates the two gears. They also absorb vibration and are simply designed drives. The types of belt drives are open, fast, and lose cone pulley, cross, jockey pulley belt drives.

The belt drives can be shown as,

### Chain Drive

The chain drive consists of chains (tooth-shaped) and sprockets. And the chain consists of links that are interconnected by pin joints. The chain usually moves over the driver and driven gears. Applications of these gear drives are bicycles and bikes.

The chain drives can be shown as,

### Wheel Drive

This type of drive has an extra number of gears. They are arranged to form gear trains. In this type of drive, more than two gears combine each other, and they transmit power. The types of wheel drives are simple, epicyclic, compound and reverted gear trains.

The gear train can be shown as,

## Electric Transmission

In this type of transmission, electric drives convert the electrical form of energy into the mechanical form of energy. Electrical drives are generally used in vehicles. They produce negligible noise while in operation. They are precisely controlled drives and have high precision as they use servo motors.

## Hydraulic Transmission

The hydraulic transmission uses fluids to transmit power. In this type of transmission, the variable displacement pump transforms the hydraulic motor changes the mechanical form of energy into pressure energy. Then with the help of a motor, the pressure energy is changed into mechanical energy. It is the fluid energy that is converted to work.

The diagram of the hydraulic transmission can be shown as,

## Pneumatic Transmission

It transmits power with the help of compressed air. The piston compresses the air. This compressed air is utilized to obtain the required work. The efficiency of the pneumatic system is higher. The application of pneumatic transmission systems is pneumatic rammer, spray painting, forming operations, jigs, and fixtures, etc. They consist of pneumatic cylinders, actuators, controllers, air compressors, control valves distributors, etc.

## Other Power Transmission Elements

### Couplings

Couplings join two shafts for the transmission of torque. Types of couplings are rigid and flexible type couplings. Flexible couplings are suitable for the misalignment of two shafts. Rigid couplings need more accurate and precise alignments of shafts.

### Power Screws

Power screws are used to change the rotational type of motion into translational motion. Power screws have high mechanical advantages. The power screws like lead screws are widely used in screw jack, steering mechanisms, machine slides etc. They are not preferable for high-power transmission.

### Brakes

Brakes are applied for the deceleration of the vehicles. The brakes provide resistance to the moving elements to stop their motion. The energy absorbed by the brakes during the application of the brake is lost in the form of heat. Types of brakes are hydraulic, mechanical, electrical, shoe, band, disc, regulating, drum brakes, etc.

### Clutches

Clutches usually engage the moving elements and then disengage them. They transmit the power between two rotating shafts, which are moving at different velocities. Clutch helps to move the driver as well as driven elements. Types of clutches are positive, frictional, closing, hydraulic, pneumatic, dry, opening, wet, mechanical, electromagnetic, etc.

### Pulleys

Pulley consists of belt, wheel, rope, chain, etc. Pulleys are generally used to transmit motion or power. Pulleys are used to lift or place any object. The applications of pulleys are construction, cargo lift mechanism, wells, theatre system and, elevators.

## Advantages of Power Transmission Elements

• Gear drives are simple, compact, long life, safe and positive types of drives. They provide a constant velocity ratio.
• Chain drives provide higher efficiency, a large velocity ratio, high power transmission, long life, positive drives.
• Belt drives are more flexible, less noisy, less costly.
• With the help of power transmission elements, the rotational motion is converted into a linear type of motion.
• Transmission elements vary the rotational speeds.

## Disadvantages of Power Transmission Elements

• Gear drives are not compatible with transmission at high velocity. The maintenance cost is high. It produces noise.
• Chain drives have a higher cost than other belt drives.
• Belt drives are not considered as positive drives. They have less life, more space and, large axial forces.
• Turbo-vortex drives have low efficiency, large axial force and single way transmission.

## Common Mistakes

• It is a misconception that the spur gears can be used between two shafts separated by a long distance. They can be used for short distance separation between shafts.
• It is a misconception that the turbo vortex drive is a two-way transmission drive as it can be used only for power transmission.
• Sometimes, students get confused that the belts have high power transmission efficiency. But belts have low transmission power.
• Students get confused that the pneumatic transmission devices are noiseless. But at the exhaust, they produce a lot of noise.
• It is a misconception that gears can be used for large velocities. But it is not true as the gears are not suitable for large speeds.
• Students get confused between pneumatic and hydraulics transmission safety comparison. Hydraulic transmission is safer as compared to pneumatic power transmission.
• Students get confused that the pinion is not the gear, but the pinion is also a type of gear.

## Context and Applications

The topic of power transmission elements is significant in many professional exams, graduation courses, post-graduation, Ph.D. level, and others. For example:

• Bachelor of Technology in Mechanical Engineering
• Bachelor of Technology in Automobile Engineering
• Diploma in Mechanical Engineering
• Master of Technology in Mechanical Engineering
• Master of Technology in Automobile Engineering
• Ph.D. in Mechanical Engineering
• PhD in Automobile Engineering
• Gears
• Hydraulic power transmitting devices
• Pneumatic device
• Belts and pulley
• Chains
• Mechanical transmission
• Electrical transmission
• Power transmission
• Mechanical drives

## Practice Problems

Q1: Which of the following is true for skew bevel gears?

(a) non-intersecting

(b) Non-parallel

(c) Non-coplanar

(d) Non-parallel and non-coplanar

Correct option: (d)

Explanation: The skew bevel gears are explained as the sort of gears that connects pair of non-parallel as well as non-coplanar shafts.

Q2: Which type of gear is used in the actuators?

(a) Rack and pinion

(b) Spur gear

(c) Helical gear

(d) Bevel gear

Correct option: (a)

Explanation: The actuator is expressed as the device which is applied to the machine to provide movements. The gears which are most widely used in actuators are Rack and pinion.

Q3: The diameter of the driver gear is 100 mm and the teeth on that gear is 20. Find module of the gear.

(a) 15 mm

(b) 12 mm

(c) 5 mm

(d) 8 mm

Correct option: (c)

Explanation:

The relation for finding module is given by,

Q4: If the module of the gear is 8 mm and the number of teeth is 3. What is the pitch circle diameter of the gear?

(a) 30.98 mm

(b) 24 mm

(c) 20.67 mm

(d) 16.78 mm

Correct option: (b)

Explanation:

The relation for finding pitch circle diameter is given by,

Q5: In which type of transmission does the pressure into the mechanical form of energy?

(a) Pneumatic transmission

(b) Mechanical transmission

(c) Electric transmission

(d) Hydraulic transmission

Correct option: (d)

Explanation: The hydraulic transmission is useful in controlling the speed of the machine, dynamic braking, and overload protection. In hydraulic transmission, the pressure is transformed into the mechanical form of energy.

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### Design of Power Transmission Elements and Power Transmission Systems

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