Hydraulic Clutch – Overview, Parts, Working, Advantages, Disadvantages, and Applications

A clutch is an automobile device to transmit rotating motion or torque from the engine to the gearbox.
The transmission of power between the engine and the gearbox needs to be stopped temporarily under some conditions like shifting gears and some other conditions. To disconnect the engine and the gearbox temporarily a clutch is used.

Manual transmission vehicles mainly use two types of clutch, i.e., mechanical and hydraulic. If you observe old vehicles, you can see the mechanical clutches. 

Hydraulic Clutch is used in modern vehicles. Hydraulic clutches are used in manual transmission automobiles manufactured after the 90s. This clutch operates with the help of hydraulic fluid and is safe, reliable, and works smoothly compared to the mechanical clutch.

Hydraulic Clutch uses hydraulic fluid to engage and disengage the power transmission from the engine shaft to the gearbox. In a hydraulic clutch, the clutch pedal can be operated smoothly and with less effort than a mechanical clutch.

Parts Of the Hydraulic Clutch

The hydraulic clutch uses hydraulic fluid instead of a cable to engage and disengage the power transmission. There are various parts of the hydraulic clutch, which are listed below:

1. Flywheel

Flywheel is connected to the engine crankshaft. The friction lining of the clutch plate is connected to the flywheel.
Whenever the clutch pedal is pressed, the flywheel gets disconnected from the rest part of the clutch and the power transmission between the engine and the gearbox is stopped.

2. Pressure Plate

The work of the pressure plate is to press the clutch plate or friction plate against the flywheel so that power transmission can occur smoothly. There is a diaphragm spring attached to the pressure plate.
The pressure plate is used to engage and disengage the hydraulic clutch by pressing and releasing the clutch plate against the flywheel.

3. Clutch Plate Or Friction Plate

The clutch plate is a metal plate with friction lining on both sides. It is usually made of asbestos because the asbestos can control the heat produced due to friction. It is usually present in between the flywheel and pressure plate. 

4. Diaphragm Spring

The diaphragm spring is C shaped and mounted on the pressure plate. There is a release bearing with one end connected to the diaphragm spring and the other end to the clutch pedal.
The diaphragm spring is used to move the pressure plate.
 Wherever you press the clutch pedal, the release bearing will press the inner side of the diaphragm spring thus, its outer edges will move outward. As the outer edges move outward, the pressure plate connected to the outer portion of the diaphragm spring moves away from the clutch plate.

5. Release Fork

One end of the release fork is connected to the slave cylinder, and its other end connects with the release bearing.

The main function of the release fork is to push the release bearing so that it further presses the diaphragm spring and the clutch gets disengaged.

6. Master Cylinder

Master Cylinder is an essential component in working the hydraulic clutch. The master cylinder has a piston rod that is connected to the clutch pedal. The primary function of the master cylinder is to pressurize and send the hydraulic fluid towards the slave cylinder.

7. Slave Cylinder

The slave cylinder connects to the master cylinder by the hose pipe. It even has a piston rod attached to the release fork. A slave cylinder is used to push the release fork.

8. Hose pipe

The hose pipe helps to transfer the hydraulic fluid from the master cylinder to the slave cylinder.

9. Clutch Pedal 

The clutch pedal is connected to the piston rod of the master cylinder. When the clutch pedal is pressed by the driver the piston rod of the master cylinder gets pushed and hydraulic fluid is transferred to the slave cylinder.

10. Reservoir

The hydraulic fluid is stored in the reservoir. A reservoir is used to store and maintain the quantity of hydraulic fluid.

Working Of Hydraulic Clutch

The working of a hydraulic clutch is divided into two parts, i.e., engagement and disengagement. Both engagement and disengagement of the hydraulic clutch are discussed below in detail:-

1. Disengagement:-

When the driver presses the hydraulic clutch pedal, the piston rod of the master cylinder which is connected to the clutch pedal gets pushed and in turn, it pressurizes the hydraulic fluid and the hydraulic fluid moves from the master cylinder towards the slave cylinder.

The slave cylinder also has a piston rod that connects with the release fork. This release fork is connected to the release bearing present on the clutch shaft.

Whenever the pressurized hydraulic fluid enters the slave cylinder, it will act on the piston rod of the slave cylinder and push it outward. The piston rod will push the release fork and the release fork will push the release bearing.

The release bearing is connected to the diaphragm spring and presses it in the centre. 

As a result, the outer edges of the diaphragm spring will move outward and hence it will pull the pressure plate away from the clutch plate or friction plate. There will be no more pressure on the clutch plate, separating it from the flywheel. As the clutch plate is disconnected from the flywheel, the hydraulic clutch disengages and the power transmission between the engine and the gearbox stops.

2. Engagement:-

The hydraulic clutch engages when the driver releases the clutch pedal after changing the gears.
When the clutch pedal is released, the piston rod of the master cylinder moves backwards and the pressure on the hydraulic fluid of the master cylinder is released.
As the pressure on hydraulic fluid is released, the piston rod of the slave cylinder will move back and hence the release fork and release bearing will return to their original position and the diaphragm spring will return to its original shape.

When the diaphragm spring returns to its original shape, the pressure plate which moved away due to the outer movement of the diaphragm spring during disengagement will return to its original position and will again put pressure on the clutch plate and will push it towards the flywheel.

Hence, clutch plate connects with the flywheel, and thus, power transmission between the engine and the gearbox starts again.

Advantages Of Hydraulic Clutch

• The driver doesn’t have to apply much force on the clutch pedal compared to the mechanical clutch.
• It requires low maintenance.
• Hydraulic clutches are known as self-lubricating clutches. The usage of hydraulic fluid causes the components of the clutch to lubricate. Hence the parts are less prone to wear and tear. But if we talk about mechanical clutches, there is no hydraulic fluid and the cable is used to operate the clutch, so it needs lubrication and maintenance from time to time.
• The longevity of the hydraulic clutch is more in comparison to the mechanical clutch.

Disadvantages Of Hydraulic Clutch

• The hose pipe can get damaged with time.
• You need to check the level of hydraulic fluid from time to time. If the reservoirs lack hydraulic fluid, the clutch may fail to operate.
• The price of a hydraulic clutch is relatively high.
• Hydraulic clutch requires more space in automobiles. Again failure of the master or slave cylinder can cause an outflow of hydraulic fluid and may fail the clutch to operate.

Applications Of Hydraulic Clutch 

• High-performance vehicles
• Passenger cars
• Trucks
• Racing cars
• Marine applications
• Aircraft
• Military vehicles

Conclusion

A hydraulic clutch provides smooth engagement and disengagement of power transmission compared to a mechanical clutch. It even lasts longer; you don’t need to maintain it periodically. 

But its price is relatively high. Again damage to pipes, master cylinder, or slave cylinder components can cause an outflow of hydraulic fluid, malfunctioning the working clutch.

We have discussed above the components, working principle, advantages, disadvantages, and applications of hydraulic clutch and hope the information is helpful.