What is Clutch And How Does a Clutch Work?

If you’ve ever driven a manual shift car, then you’re probably familiar with the clutch. It’s the third pedal that you have to press in order to change gears.

However, you might not know exactly what the clutch does, especially if you’ve only driven cars with automatic transmissions. What is a clutch and why do you need one?

Because your engine is always spinning, there has to be a way for the wheels to disengage so they can stop moving. This is where the clutch comes into play. It can disengage the wheels without killing the engine.

What is a Clutch?

The car clutch is essentially an on-demand coupling: its job is to mate the engine to the manual transmission until you push down the clutch pedal to initiate a gear change.

When you push down the clutch pedal, you’re momentarily breaking this mechanical connection, cutting engine power from flowing through the transmission. When you release the pedal, the clutch once again links the engine and gearbox.

The reason cars require a clutch in the first place – indeed, why they need a transmission – is because internal combustion engines operate efficiently only in a narrow band of engine speed that’s known as the power band.

To take advantage of that powerband at different road speeds, power is routed through the different gears in your transmission. Depending on which gear is engaged, the transmission can step up or step down the engine power according to your need for speed.

Here’s the thing with a transmission, though – you don’t want to change gears while engine power is actively flowing through it, as doing so would cause your gearbox components to quickly suffer some extreme wear and tear.

To sidestep this, the engine needs to be temporarily decoupled from the transmission while you select a different gear. That’s where the clutch comes in.

What Does the Car Clutch Do?

Now, everyone knows that a car has an engine to power it, but not everyone is familiar with a clutch or how it works. This mechanism both engages and disengages your power transmission from the driving shaft to the driven shaft.

It connects rotating shafts, and there can be two or more of these under your hood. If you drive a manual transmission, the clutch is connected to both the shaft coming from the engine and the shafts that turn the wheels. While the motor is going to spin constantly, you don’t want the wheels continually spinning.

One of the rotating shafts is going to be connected to the engine or power unit, this will be the driving member, while the other rotating shaft, or driven member, provides output for work. For example, a drill has a shaft that’s driven by a motor and one that’s driven by a drill chuck.

The clutch connects the shafts so they can be engaged (spin at the same speed), slipping (spinning at different speeds), or disengaged (spinning at different speeds). Typically, you’ll find that these motions are rotary; although, linear clutches are possible.

How Does a Clutch Work in a Car?

We’ve outlined the working relationship between the clutch’s three main components, the flywheel, the clutch disc and the pressure plate. But how is it that they specifically interact?

Pressing the clutch pedal activates the release mechanism, causing the clutch to disengage.
This means that the connection between the engine and the transmission is temporarily broken.
With the clutch disengaged, the engine can spin independently of the transmission.
This separation is crucial for changing gears, as it allows the driver to select a new gear ratio without causing damage to the gearbox.
When the clutch pedal is released, the pressure plate applies force to the clutch disc, causing it to press against the flywheel.
This re-establishes the connection between the engine and the transmission, allowing power to flow seamlessly.
The friction between the clutch disc and the flywheel is crucial for a smooth engagement, and this friction is what enables the driver to control the vehicle’s speed and power.

Parts of the clutch

The modern clutch has four main components:

The Flywheel: The flywheel is a large, round metal disc connected to the engine’s crankshaft. It stores rotational energy and helps smooth out fluctuations in engine speed. Needless to say, it has a close relationship with – and direct impact – on the engine.
The Clutch Plate (Driven Plate or Clutch Disc): This is positioned between the flywheel and the pressure plate. Its main role is to create friction between the two.
The Pressure Plate: Attached to the flywheel, the pressure plate is synchronised to rotate along with the engine. Meanwhile, the clutch plate remains unconnected to both the flywheel and the pressure plate. The pressure plate is designed to firmly secure the clutch plate in position whenever the clutch pedal is engaged or raised.

Types of Clutch

Following are the different types of clutch:

Friction Clutch – Single Plate Clutch | Multi-Plate Clutch – Wet Clutch & Dry Clutch | Cone Clutch
Centrifugal clutch
Semi-centrifugal clutch
Hydraulic clutch
Conical spring clutch or Diaphragm clutch
Positive clutch or Dog and Spline Clutch
Vacuum clutch
Electromagnetic clutch

#1. Friction Clutch.

Nowadays, most of cars are using a basic friction clutch that mainly has some normal components, which people may be heard before. A friction clutch can be used by engineers in engaging and disengaging 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.

Types of Friction Clutch

It is categorized into two parts. These are as follows:

Single Plate Clutch:

A single plate clutch is mainly used in lightweight vehicles for transmitting torque from an engine to the input shaft. As per the name of this Clutch it just has a single Clutch plate.

Multi-plate Clutch:

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 divided into two subdivisions also; they are wet clutch and 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 engine and gearbox by applying force over the clutch thus the springs are compressed by the peddle, and the pressure plate slide to backward.

After this situation, the clutch plate has become free 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 are working in 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.

#2. Cone Clutch.

The frictional surface is located in this type of clutches as a cone that 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 into two sections they are Internal and External cone clutch.

Cones: female cone (green), male cone (blue)
Shaft: the male cone is sliding on splines
Friction material: usually on the female cone, here on male cone
Spring: brings the male cone back after using clutch control
Clutch control: separating both cones by pressing
Rotating direction: both directions of the axis are possible

Advantages of Cone Clutch

Here are a few advantages of Cone Clutch:

As compared to each other, the cone clutch is more efficient than a single plate clutch.
In the case of cone clutch the friction surface experience the potential of the normal force.

Disadvantages of Cone Clutch

Although there are some disadvantages of cone clutch, and here are those:

Cone clutch oftentimes 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.

#3. Centrifugal Clutch.

For engaging clutches, the 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 moving up the weight and it applies force on the bell crank. Due to this, the plate is pressed.
After that, the plate presses spring, which is the spring that 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. Lastly, the weights’ movement is controlled by Stop (H).

Advantages of Centrifugal Clutch

These are the advantages of Centrifugal Clutch:

It is automatic.
Low cost and also low maintenance cost.
Less wear and tear.
Greater control over speed.

Disadvantages of Centrifugal Clutch

Here are some disadvantages of the 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.

#4. Semi-Centrifugal Clutch.

For keeping in the engaged position, the semi-centrifugal clutch uses spring force along with the centrifugal force. Semi-Centrifugal Clutch is made of a Clutch plate, Friction lining, Levers, Pressure plate, Flywheel, and Clutch springs.

Working Principle of Semi-Centrifugal Clutch

Clutch spring and levers fix upon the pressure plate equally. At a normal speed of an engine, the clutch is designed to send 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 exert 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 the 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 torque spring.
Assists the torque transmission at the high-speed engine by Centrifugal force.

#5. Diaphragm Clutch.

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.
The flywheel consists of friction lining, and the clutch is connected with the flywheel.
As the pressure is applied to the pressure plate of the clutch, due to which, 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 of the clutch.
The outside bearing presses the Diaphragm spring. So that the pressure plate is pushed backward by the Diaphragm spring.
That pressure disengaged the clutch by removing the pressure on the plate.
The Diaphragm spring and pressure plate came back to the normal state after releasing the pressure from clutch peddles.

Advantages of Diaphragm Clutch

Here are some advantages of a Diaphragm Clutch:
In a Diaphragm clutch, no need to release 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.

#6. Dog and Spline Clutch.

Dog and Spline Clutch has two parts. One is Dog clutch and another is a Spline clutch.

The Spline is also termed as 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 and the Spline clutch consists of internal teeth.
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 made a huge amount of torque.
No friction takes place as they locked together when rotates.
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.

#7. Electromagnetic Clutch.

The electromagnetic clutch is made of things that are applied in electrical engineering.

Those are as follows:

Rotor: Rotor is the part that connects directly to the engine shaft and helps to rotate the engine shaft and the driving shaft continuously.
Winding: Winding is attached behind the Rotor. It does not rotate. It is connected with the high voltage DC supply which is converted into the electromagnet by winding.
Armature: Armature is attached at the front of the rotor. It is attached to the hub by bolts or rivets.
Hub: Hub is attached behind the Armature. It is attached to the driven shaft by the bolts and rotates with the shaft.
Friction Plate: Base on the transmission of the power friction plate insertion between rotor and armature is done.
Supply Unit: Supply unit consists of a battery, clutch switch, wire, etc.

Working Principle of Electromagnetic Clutch

High Voltage DC supply is supplied to the Winding from dynamo or battery.
Winding produces an electromagnetic field that allures the pressure plate and engages the clutch.
For disengaging, the supply should be disconnected.
For reliving the switch of the clutch gear lever is made, therefore the clutch is disengaged by changing the gear by driver holds.
The Clutch is not engaged when the output is low of the dynamo at the low speed.
There are three springs on the pressure plate to engage the clutch at the 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 of 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.

#8. Vacuum Clutch.

The vacuum clutch works through a vacuum. So, its name is Vacuum clutch.

It consists of such parts. Those are:

Switch
Non-return valve
Solenoid
Piston
Vacuum Reservoir
Vacuum Cylinder
Battery
Inlet and Outlet
vacuum clutch diagram

Working Principle of vacuum clutch

There is an existing vacuum in the engine manifold (Inlet) that operates the Vacuum clutch.
The engine manifold is attached through a valve which is non-returnable with the Vacuum reservoir.
The reservoir is attached through a valve that is solenoid-operated with 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 open the throttle. So that the non-return valve is closed, the manifold isolates the reservoir. There is a vacuum present all the 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.

#9. Hydraulic clutch.

The working principle of vacuum and the hydraulic clutch is almost the same.

Although the significant difference between those is that, the hydraulic clutch operates through the pressure of oil, on the other hand, 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 takes place by a control valve.

The engine of the vehicle operates the pump. A switch controls the valve. Apart from that, a linkage mechanism is used by engineers to establish the connection between piston and clutch.

The driver of a vehicle presses the gear lever of the vehicle and opens the switch to the valve to enable the oil flow. Due to the pressure of oil, the piston of the vehicle starts moving forward and backward that leads the clutch is 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.

#10. Freewheel Clutch.

It is often called in 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 a gearbox of an engine.

Working principle of Freewheel clutch

The hub of the aforementioned clutch rotates clockwise and then the roller rise 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 with the main shaft and the outer race is connected with the output shaft by an engineer.

Advantages of freewheel clutch

Freewheel can deliver a better fuel economy.
Less wear and tear than the manual clutch.

Disadvantages of freewheel clutch

If engineers try to produce engine breaking then the freewheel clutch is subjected to more wear.

Clutch Material

There are so many materials that have been used for making the clutch plates.

In the past asbestos was the material which was used to make the clutch plates. These days the manufacturers use compound organic resin with the wire of copper facing and they use ceramic material as well.

In the application of heavy-duty hauling or racing, typically there were used ceramic materials.

Now in the modern world asbestos has been classified as unreliable and generally these clutches are not common with the modern advanced clutches.

Semi-Metallic Materials: This type of material contains 30% to 65% of steel, iron, and copper. These clutches have high heat resistance and are hard to break and those are durable enough. The plates are reliable but not that good for high-speed operation.

Organic Materials: These are the most common type of materials that we used the most. These materials clutches are capable of all kinds of usage in a variety of vehicles such as size. This material contains high copper content because it can transfer heat effectively.

Ceramic Materials: These types of clutches contain organic and inorganic materials at the same time which include glass, rubber, Kevlar, and carbon materials. In this clutch, the coefficient of the friction is relatively high which lies between 0.33 to 0.4. In most intense applications, this type of clutch is used, like in trucks and racing cars.