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Last Updated on March 1, 2023 by Noaman Adenwala
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Human beings depend upon automobiles significantly for their daily transportation. Therefore, in automobiles, a lot of development is done to utilize the maximum performance. Often an Engine is termed as ‘The Heart’ of a vehicle. In an automobile, the clutch is the part that makes or breaks the relationship between an engine and a gearbox. The clutch is a member of a machine component that transmits the power from the engine to the wheels of the vehicle through the gearbox.
The clutch consists of several parts like
- Friction surface
- Diaphragm spring
- Coil spring
Among all the types of clutches, friction clutches are the most commonly used in the automotive industry. In a vehicle, the clutch paddle or clutch lever is pressed to change the gear to vary the speed.
Definition of a Clutch
In mechanical engineering, a clutch is defined as a type of device or component used by engineers to engage and disengage the transmission or the power from a driving shaft to a driven shaft. In this mechanism, the driving shaft is directly connected to an engine. The driven shaft provides the power output that is utilized by the user. Many a times clutches are used to limit the motion or amount of power transmission between two components.
Here is an animated video by Learn Engineering, that shows the working of a clutch.
Working Principle of Clutch
When two revolving frictional surfaces comes in contact with each other, they get united and start revolving at the same speed due to the frictional force between them. This is the basic principle of a clutch. The friction between these two surfaces depends on the area of the surface. It also depends on the pressure applied to them as well as the frictional material between them. The driving member of a clutch is the flywheel. It is mounted on the engines crankshaft. The driving member is a pressure plate mounted on the transmission shaft.
Some friction plates, also known as clutch plates are kept between these two members. This entire assembly is known as the clutch.
function of the Clutch
The Following are the functions of an Automotive Clutch:
- It can be disengaged. This allows the engine to run without delivering power to the transmission.
- While disengaging, it allows the driver to shift the transmission into various gears according to operating conditions.
- While engaging, the clutch slips momentarily. This provides smooth engagement and lessens the shock on gears, shafts, and other parts of an vehicle.
- While engaging, the clutch transmits the power to the wheels without slipping, in ideal condition.
Types of Clutches
In an automobile, different types of clutches are present. Numerous types of clutches are used for multiple purposes by engineers. Every type has its own advantages and disadvantages that should be addressed by engineers in order to increase the mechanical efficiency of a component.
The working principle of different types of clutches are also different in nature. The different types of the clutch are:
- Friction Clutch
- Single Plate Clutch
- Multi Plate Clutch
- Cone Clutch
- Centrifugal Clutch
- Semi-centrifugal Clutch
- Diaphragm Clutch
- Dog and Spline Clutch
- Electromagnetic Clutch
- Vacuum Clutches
- Hydraulic clutch
- Freewheel Clutch
Let’s start with the Friction Clutch.
Nowadays, most of the cars are using a basic friction clutch that mainly has some general components, that people may have heard of before. A friction clutch are used by engineers for engaging and disengaging the transmission and flywheel. It is operated through a mechanical cable or hydraulic cable that consists of a clutch plate, a pressure plate and a release bearing.
It is categorized into two main types which are as follows:
- Single Plate Clutch
- Multi Plate Clutch
Single Plate Clutch
Single plate clutch is mainly used in lightweight vehicles for transmitting torque from an engine to the input shaft. As the name suggest, it has only one plate.
This type of clutch has multiple clutch plates that are used to transmit power from the shaft of an engine to the transmission shaft of the same vehicle.
It is further divided into two sub-sections.
- Wet clutch
- Dry clutch
A clutch when operates within an oil bath then it is called a wet clutch. On the other hand, a dry clutch operates without oil.
Working Principle of Friction Clutch
In a car, disengagement occurs between the engine and gearbox by applying force over the clutch. Due to this the springs are compressed by the peddle and the pressure plate slides backward. The clutch plate has now become free to move between the flywheel and the pressure plate. Now the clutch can shift gears. The principle of clutch helps to rotate the flywheel until the engine shaft does not stop rotation.
A clutch disengages the gearbox and engine since it has been pressed by the driver. Moreover, when the clutch plate is released by the driver then the pressure plate again comes into its origin and the Clutch becomes engaged. Single plate and multiple plates works on the same principle although the difference is that a single plate clutch is used in lightweight cars whereas a multiple plate clutch is used in heavy-duty cars.
The frictional surface is assembled in such a way that if forms a cone which is why it is named as a cone clutch. Two surfaces transmit torque by utilizing the concept of friction. The engine shaft consists of a male and a female cone. It is categorized under two sections
- Internal Cone Clutch
- External Cone Clutch.
1. Cones: female cone (green), male cone (blue)
2. Shaft: the male cone is sliding on splines
3. Friction material: usually on the female cone, here on the male cone
4. Spring: brings the male cone back after using clutch control
5. Clutch control: separating both cones by pressing
6. Rotating direction: both directions of the axis are possible
Advantages of Cone Clutch
- The cone clutch is more efficient than a single plate clutch.
- In the case of a cone clutch the friction surface experiences a normal force.
Disadvantages of Cone Clutch
- The cone clutch is often inefficient to disengage the clutch.
- This situation takes place when the angle is more than 20°.
- Small wear can produce due to huge axial movement.
For engaging clutches, a Centrifugal clutch uses the concept of centrifugal force. It is operated automatically according to the speed of an engine. Thus, in a vehicle, any clutch paddle is not required for the movement of the clutch. A driver can stop as well as can start an engine without downing or upping the gear.
Working Principle of Centrifugal Clutch
This clutch includes a weight that is pivoted in a specific location. According to engine speed, centrifugal force moves up the weight and applies force on the bell crank. Due to this, the plate is pressed. After that, the plate presses the spring, which is the spring that is mainly used to press the clutch plate. Now the clutch has become engaged. The clutch remains to disengage up to a lower RPM that is near about 500rpm.
Advantages of Centrifugal Clutch
- It is automatic.
- Low initial cost and low maintenance cost.
- Less wear and tear.
- Greater control over speed.
Disadvantages of Centrifugal Clutch
- Sometimes, engines suffer from slippage in lower RPM.
- It cannot be used in a high-speed engine.
- Peak speed depends on clutch size.
For keeping in the engaged position, the semi-centrifugal clutch uses spring force along with centrifugal force. Semi-Centrifugal Clutch is made of a Clutch plate, Friction lining, lever, Pressure plate, Flywheel, and Clutch springs.
Working Principle of Semi-Centrifugal Clutch
Clutch springs and levers fix upon the pressure plate equally. At a normal speed of an engine, the clutch is designed to send a torque spring. At a normal speed and low-power transmission, there is no pressure on the pressure plate. Hence, a clutch remains engaged. At a high speed and high-power transmission, there is exerted pressure on the pressure plate and the clutch has become engaged. Less stiff springs of the clutches help to get rid of any strain for clutch operations. When the speed of the vehicle decreases or speed fell rapidly, there is no pressure on the pressure plate by levers.
Advantages of Semi-Centrifugal Clutch
- Less stiff springs of the clutches at low speed.
- There is no stain for clutch operations.
Disadvantages of Semi-Centrifugal Clutch
- At a normal speed of an engine, the clutch is designed to send a torque spring.
- Assists the torque transmission at the high-speed engine by Centrifugal force.
For engaging clutches, this type of clutch generates pressure on the pressure plate. This clutch is made of a diaphragm on the conical spring. The crown or finger-type spring is attached to the pressure plate.
Working Principle of Diaphragm Clutch
For the Diaphragm Clutch, engine power is sent to the flywheel from the crankshaft. Flywheel consists of friction lining, and the clutch is connected to the flywheel. As the pressure is applied to the pressure plate of the clutch, the clutch plate is located behind the pressure plate. The diaphragm clutch is conical in shape. The outside bearing goes to the flywheel after pressing the clutch pedal. The outside bearing presses the Diaphragm spring. The pressure plate is pushed backward by the Diaphragm spring. This pressure is disengaged by the clutch due to the removal of the pressure on the plate. The Diaphragm spring and pressure plate come back to their normal state after releasing the pressure from the clutch peddles.
Advantages of Diaphragm Clutch
- In the Diaphragm clutch, no need to release the levers as the springs function as the levers.
- The coil spring increases the pressure more than the heavy paddles so that there was no need for heavy paddles.
Disadvantages of Diaphragm Clutch
- As the clutch is a cone, the springs become stiffer, which needs more force to disengage.
- At the higher speed, the coil spring faces the distortion tendency in a transverse direction.
Dog and Spline Clutch
Dog and Spline Clutch have two parts. One is a Dog clutch and another is a Spline clutch. The Spline is also termed a Sliding sleeve. This clutch is used to connect a shaft with the gear or to lock together, the two shafts.
Working Principle of Dog and Spline Clutch
The Dog clutch consists of external teeth’s and the Spline clutch consists of internal teeth’s. The two clutches are designed to rotate with each other together at the same speed but they never slip from each other. For engaging two shafts, they have to be connected. The sliding sleeve goes backward from the splined shaft and makes no contact with each other and then the clutch will be disengaged.
Advantages of Dog and Spline Clutch
- Clutches do not slip from each other.
- Dog and Spline clutch produce a huge amount of torque.
- No friction takes place as they are locked together when rotated.
Disadvantages of Dog and Spline Clutch
- At a higher speed, it is difficult to engage or disengage the clutches.
- For disengagement and engagement, some relative motion is required.
The electromagnetic clutch is made of the following components:
Rotor is a part that connects directly to the engine shaft and helps to rotate the engine shaft and the driving shaft continuously.
Winding is attached behind the Rotor. It does not rotate. It is connected to the high-voltage DC supply which is converted into the electromagnet by winding.
Armature is attached at the front of the rotor. It is attached to the hub by bolts or rivets.
Hub is attached behind the Armature. It is attached to the driven shaft by the bolts and rotates with the shaft.
Based on the transmission of the power, friction plate insertion between the rotor and armature is done.
The supply unit consists of a battery, clutch switch, wire, etc.
Working Principle of Electromagnetic Clutch
High Voltage DC supply is supplied to the Winding using a dynamo or battery. Winding produces an electromagnetic field that allures the pressure plate and engages the clutch. For disengaging, the supply should be disconnected. The clutch is disengaged by changing the gear by driver holds. The Clutch is not engaged when the output of the dynamo is low at a low speed. There are three springs on the pressure plate to engage the clutch at low speed also.
Advantages of Electromagnetic Clutch
- The operating process is easy.
- The remote direction is used to operate a clutch as it has no requirement for linkage.
Disadvantages of Electromagnetic Clutch
- High cost.
- As the high temperature is not sustained by any electrical components, there must be a limitation on operating temperature.
Vacuum clutch is generally used in automatic transmission. It works by using an engine vacuum or release pressure on the clutch mechanism. The following are the components of Vacuum clutch:
- Non-return valve
- Vacuum Reservoir
- Vacuum Cylinder
- Inlet and Outlet
Working Principle of vacuum clutch
There is an existing vacuum in the engine manifold (Inlet) which operates the Vacuum clutch. The engine manifold is attached through a valve that is non-returnable with the Vacuum reservoir. The reservoir is attached through a valve which is solenoid-operated attached to the Vacuum cylinder. There is a switch in the gear lever. The battery operates the solenoid. The lever changes the gear when it is held by the driver and the operation of the switch is done. The pressure increases in the inlet manifold when the throttle is turned on. There is a vacuum present at all time in a reservoir.
Advantages of vacuum clutch
- It is far cheaper than other clutches.
- It allows minimum travel of the actuator.
Disadvantages of vacuum clutch
- It consists of multiple components.
- Sometimes sluggishness is found by engineers in a machine while working with it.
The working principle of the vacuum and the hydraulic clutch is almost the same. Although the significant difference between these two is that the hydraulic clutch operates through the pressure of oil while a vacuum clutch operates through a vacuum.
Working principle of Hydraulic clutch
Oil is pumped to the accumulator from the reservoir through a pump by an engineer. The connection between the accumulator and cylinder is done by a control valve. The engine of the vehicle operates the pump. A switch is used to control the valve. Apart from this, a linkage mechanism is used by engineers to establish the connection between the piston and the clutch. The driver then presses the gear lever of the vehicle and opens the switch to enable the oil flow. Due to the pressure of oil, the piston of the vehicle starts moving forward and backward which leads to the clutch engaging and disengaging.
Advantages of Hydraulic clutch
- It is far easier to push.
- Providence of an equivalent amount of fluid.
Disadvantages of Hydraulic clutch
- Sometimes, due to the use of silicon type of fluids, leakage can take place.
- It can impact the seals.
It is often called by different names such as overrunning, one-way, and spring clutch. The transmission power produced by these types of clutch mainly takes place in one direction. Freewheel Clutch is mounted by engineers behind the gearbox of an engine.
Working principle of Freewheel clutch
The hub of the freewheel clutch rotates clockwise and then the roller rises up the cams. This movement takes place due to wedging action. After this situation, the hub is followed by the outer racer. The racer rotates in the same direction and at the same speed as compared to the hub. Hub is connected to the main shaft and the outer race is connected to the output shaft by an engineer.
Advantages of freewheel clutch
- Freewheel can deliver better fuel economy.
- Less wear and tear than a manual clutch.
Disadvantages of freewheel clutch
- If engineers try to produce engine braking then the freewheel clutch is subjected to more wear.
There are a number of materials that are used for making the clutch plates. In the past asbestos was the material which was used to make the clutch plates. Nowadays the manufacturers use compound organic resin with a wire of copper facing. In the application of heavy-duty hauling or racing, typically ceramic materials are used for clutch. Now in the modern world asbestos has been classified as unreliable and are rarely used.
This type of material contains 30% to 65% of steel, iron, and copper. These clutches have high heat resistance and are hard to break. The plates are reliable but not that good for high-speed operation.
These are the common type of materials that we used the most. These materials clutches are capable of all kinds of usage in a variety of vehicles. This material contains high copper content because of which it can transfer heat effectively.
These types of clutches contain organic and inorganic materials at the same time such as glass, rubber, Kevlar, and carbon materials. In this clutch, the coefficient of friction is relatively higher which lies between 0.33 to 0.4. In most intense applications like racing cars or trucks these types of clutches are used.
A clutch is a significant component of an engine as it is capable of not only transmitting motion from one machine part to another but also has the ability to disengage and engaging the driver. The speed of rotation must be controlled by a person to maintain a safe and secure environment.
READ MORE ON CLUTCHCentrifugal Clutch
Single Plate Clutch
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