What are clutches?

The clutch is described as a machine element used to connect or disconnect two shafts together to transmit torque or power. The clutch works on the principles of friction. The clutch is commonly used in automobiles to transfer power from the driving shaft to the driven shaft.

Functions of clutch

Following are the various functions of clutch:

• Starting and warming up the engine.
• Helps in engaging of first gear to start moving the vehicle from rest.
• For easy shifting of gear without damage.
• To stop the vehicle without turning off the engine.
• To allow loads to the engine without shock or jerk.

Types of clutch

Following are the two types of clutch:

• Positive clutches
• Friction clutches

Positive clutch

In a positive clutch, a pair of clutch exteriors interlock to produce rigid joints. It is a low-cost, compact device that transfers rotating motion without slip or heat generation. The diagrammatical representation of the positive clutch is shown as:

Following are the types of positive clutch:

• Square jaw type
• Spiral jaw type

Friction clutch

In friction clutch, the engagement and disengagement of the clutch are done by using frictional force. Friction clutches have better performance as compared to positive clutches. It is used in almost all automobiles.

Following are the major types of frictional clutches:

• Single plate clutch
• Multi-plate clutch
• Cone clutch
• Centrifugal clutch

Single plate clutch

In a single plate clutch, one friction plate is connected to the driving shaft, and another friction plate is connected to the pressure plate and can slide over a driven shaft. The pressure plate is connected to a spring that applies an axial force to the other frictional pate. Torque or power is transmitted from one shaft to another when they come in physical contact.

It has a low torque transmitting capacity. Less heat is generated during the working; therefore, it does not require any cooling medium. It is also called dry clutches.

The diagrammatical representation of the single plate clutch is shown as:

Multi-plate clutch

In the multi-plate clutch, multiple frictional plates work similarly to the single-plate clutch. The multiple friction plates have more area of contact that directly increases the torque transmitting capacity of the clutch.

Due to more friction plates, the multi-plate clutch heats up quickly, and it requires some cooling medium. Hence, it is also termed a wet-type clutch.

The diagrammatical representation of the multi-plate clutch is shown as:

Cone clutch

The cone clutch has two drums; one is attached to the driving shaft and has an interior frictional surface, while the other drum is mounted over a driven shaft and has an outer frictional surface. When the clutch is engaged, both drums come in contact and rotate together.

The cone clutch can transmit a higher amount of torque as compared to a single plate clutch. The cone angle plays a vital role in providing axial force, and its range is between 12 to 15 degrees.

The diagrammatical representation of cone clutch is shown as:

Centrifugal clutch

The centrifugal clutch is that whose working depends on centrifugal force. It is also termed an automatic clutch because it does not require any pedal.

In the centrifugal clutch, a hub containing multiple shoes via spring is connected with an engine crankshaft, and each shoe has an outer frictional surface. These shoes come in contact with the drum at a certain speed and transmit power to it.

The diagrammatical representation of centrifugal clutch is shown as:

Brake

A brake is a mechanical component used to decelerate the moving vehicle leading it to stop by applying frictional force. The brake converts the kinetic energy of the vehicle into heat form and dissipates in nature.

Types of brakes

Following are the major types of brakes:

• Mechanical brake
• Hydraulic brake
• Air and vacuum brakes

Mechanical brake

In a mechanical brake, the machine is decelerated by using a friction material against the motion. Friction-based brake generates heat and slight noise. Mechanical brakes are broadly used in various machines, automobiles, and others. The mechanical brake is further classified as:

• Drum brake
• Disk brake

Drum brake

In the drum brake, the driving wheel is attached to the drum, and frictional brake shoes are used to contact the rotating drum for braking operation. When a brake pedal is applied, a cam is used to lift the brake shoes at the drum opposite to their pivoted ends, and a retaining spring is used to bring the brake shoes back to their initial position after releasing the brake pedal.

The diagrammatical representation of drum brake is shown as:

Disk brake

In disk brake, a high-grade cast iron disc is mounted with the wheel. The disk is also connected with a disk caliper having a pair of high friction material pads. When the pedal is pressed, the friction material pads of the caliper hold the disk and release, when the pedal is released. It is primarily used in braking techniques in automobiles nowadays.

The various types of friction materials are used in caliper pads based on their friction coefficient. High coefficient pads supply high frictional force.

The diagrammatical representation of disk brake is shown as:

Hydraulic brake

The hydraulic brake works on Pascal's law. In hydraulic brakes, brake fluids are used to operate the braking mechanism. The pedal force is transmitted to the wheel brake by using incompressible pressurized fluid. Hydraulic brakes are widely used in heavy equipment or vehicles.

Air and vacuum brakes

In air brakes, compressed air is used to operate the braking system. In this system, when a braking pedal is pressed, compressed, air rotates the brake cam that pushes a brake shoe over a drum. It is also commonly used in heavy vehicles like trucks, trains, and others.

While in a vacuum brake system, braking action is produced by creating a vacuum on the side of the piston. In this system, a vacuum is present on both sides of the piston, and when a brake paddle presses, atmospheric pressure is applied on one side of the piston and, pushing it on another side creates a braking effect.

Couplings

A coupling is described as a mechanical device that is used to join two shafts. The primary purpose of coupling is to combine two rotating pieces of machinery while allowing some end movement.

The diagrammatical representation of couplings is shown as:

Classification of couplings

Following is the classification of couplings:

• Rigid couplings
• Flexible couplings

Rigid couplings

A rigid coupling is utilized to combine well-aligned shafts. It is simple and economical. Following are the various types of rigid coupling:

• Sleeve or muff coupling
• Clamp or split-muff coupling
• Flange coupling

Flexible couplings

Flexible couplings are used to transmit torque from one shaft to another when the two shafts have a lateral and angular misalignment. Following are the various types of flexible coupling:

• Bushed pin-type coupling
• Universal coupling
• Oldham coupling

Flywheels

A flywheel is described as a mechanical rotating device that collects or expands energy. It is generally made up of steel and rotates on proper bearings.

It is used in machines or automobiles as a reservoir that stores energy during excessive energy supply and releases stored energy when required.

The diagrammatical representation of the flywheel is shown as:

Functions of flywheel

Following are the main functions of flywheel:

• It absorbs energy when its speed increases, and it releases energy when its speed decreases.
• It reduces the fluctuation of speed.
• It balances the speed variations of the engine during each cycle of operation.

Application of flywheels

Following are the various applications of flywheels:

• The flywheel helps in maintaining the constant angular velocity of the engine crankshaft.
• It is used to provide continuous energy in systems where the energy source is non-continuous.
• It is used in the riveting machine to store energy from a motor.
• It is also used to orient satellite instruments.

Common Mistakes

Following are the common mistakes performed by students:

• Sometimes, students forget that clutches and brakes are working on the friction principle.
• Sometimes, students forget that the hydraulic brake works on the principle of Pascal's law.
• Sometimes, students get confused between positive clutch and couplings.
• Sometimes, students are confused about the functions of a flywheel.

Context and Applications

The topic of clutches, brakes, couplings, and flywheel is significant in various courses and professional exams of undergraduate, graduate, postgraduate, doctorate levels. For example:

• Bachelor of Technology in Mechanical Engineering
• Bachelor of Technology in Automobile Engineering
• Master of Technology in Machine Design
• Doctor of philosophy in Automobile

Related Concepts

• Torque or power transmission
• Automobile components
• Design of shaft
• Basic automobile terminologies

Practice Problems

Q1. Which of the following clutch does not require any cooling medium?

1. Single plate clutch
2. Multi-plate clutch
3. Cone clutch
4. None of these

Correct option:(a)

Explanation: During the power transmission, more heat is dissipated. The multi-plate clutch and the cone clutch require a lubrication system for cooling. Due to cooling or lubrication, the coefficient of friction will be reduced. A single plate does not require a cooling system.

Q2. Normally the range of cone angle for cone clutch is ______?

1. 15 to 20 degree
2. 4 to 15 degree
3. 5 to 10 degree
4. 12 to 15 degree

Correct option: (d)

Explanation: The suitable cone angle can be given as 12 degrees. The cone angle can vary between 12 degrees to 15 degrees. It should always be above 8 degrees.

Q3. Hydraulic brake works on which of the following law?

1. Electromagnetic law
2. Pascal's law
3. Faraday's law
4. Conservation of momentum

Correct option: (b)

Explanation: Generators work on the Electromagnetic law. Electric transformer works on the principle of Faraday's law. Rocket and jet engines work on the Conservation of momentum. But the Hydraulic brake works on Pascal's law.

Q4. Which of the following is not flexible couplings?

1. Universal couplings
2. Oldham couplings
3. Flange couplings
4. Bushed pin-type couplings

Correct option: (c)

Explanation: Universal couplings, Oldham couplings, Bushed pin-type couplings are flexible couplings. But the flange couplings are generally fixed permanently at the end of every shaft. They are not flexible couplings.

Q5. Which of the following is a function of the flywheel?

1. Reduces fluctuations
2. Increases velocity
3. Increases kinetic energy
4. Reduced kinetic energy

Correct option: (a)

Explanation: The flywheel maintains the inertia of the system. It provides constant delivery of torques. It reduces fluctuations. It provides a smooth power impulse. The kinetic energy can be stored in the flywheel.