Hydraulic clutches are a type of clutch that utilizes liquid pressure to control power transmission, and are widely used in automobiles, construction machinery and various industrial equipment. Its core working principle is to transfer the operating force through the hydraulic system to realize the clutch friction plate engagement and separation, so as to control the power connection between the engine and the transmission system.

Hydraulic clutch basic composition

Hydraulic system: including hydraulic pumps, hydraulic tanks, pipelines, control valves and piston cylinders. The hydraulic pump is responsible for pressurizing the hydraulic oil, which is transported to the sub-pump of the clutch through the pipeline.

Clutch assembly: including pressure plate, friction plate, release bearing and so on. The friction plate is located between the pressure plate and the flywheel and is the part that actually transmits or interrupts the power.

Control Mechanism: Operated by the driver via the clutch pedal, this action is transmitted mechanically (e.g. push rod) to the main hydraulic cylinder, which in turn affects the hydraulic system.

The operating principle of the hydraulic clutch is based on the use of a fluid as a force transmission medium to ensure smooth clutch operation in the vehicle's driveline.

Basic operating principle of the hydraulic clutch

1. Depressing the clutch pedal: When the driver depresses the clutch pedal, this action is transmitted to the clutch master cylinder via a push rod.

2. Piston of the master cylinder moves: The piston of the clutch master cylinder moves to the left under the action of the push rod, and this movement results in the oil in the master cylinder and piping being pressurized, and the pressure rises.

3. Separate pump piston movement: Under the action of oil pressure, the piston of the clutch separate pump is also pushed to the left. This movement further pushes the release pedal.

4. Clutch disengagement: The release pedal drives the release bearing, which eventually disengages the clutch. In this way, the power transmission from the engine is cut off and the clutch disengagement function is realized.

The following is the detailed work flow of its hydraulic clutch:

1. Activation of the hydraulic system: When the driver depresses the clutch pedal, this action drives the piston in the master cylinder to move forward. The piston inside the master cylinder compresses the hydraulic fluid (usually brake fluid) and increases the hydraulic pressure. 

2. Pressure transfer: The high pressure hydraulic fluid is rapidly transferred through a series of pipes or hoses to the slave cylinder (or follower cylinder) located near the gearbox.

3. Separation action: In the slave cylinder, the increased hydraulic pressure pushes the piston, which in turn moves the release bearing (also known as the release fork) forward. This action presses on the clutch pressure plate, separating it from the flywheel, interrupting the power transfer from the engine to the transmission, and permitting the gears to be shifted.

4. Sealing process: When the driver releases the clutch pedal, the piston in the master cylinder returns, the oil pressure in the slave cylinder decreases, and the pressure on the release bearing decreases, thus allowing the pressure plate to reattach itself to the flywheel and the slave (friction disk), and once again transmitting power from the engine to the transmission through friction.

5. Multi-friction plate design: In some hydraulic clutch systems, the follower disc adopts multi-friction plate structure, which enhances the suction and release ability under high speed rotation and ensures the stability and efficiency of power transmission.

6. Automatic Adjustment: The characteristics of the fluid in the hydraulic system allow for consistent clutch pedal feel without the need for frequent adjustments, as the fluid automatically compensates for clearance due to wear.

7. Control and Feedback: Throughout the process, the hydraulic fluid acts as a “liquid spring” that not only transmits force, but also provides immediate feedback to ensure that the driver can feel the clutch engagement state and realize precise shift control.

Through this series of precise hydraulic operations, the hydraulic clutch realizes fast and smooth gear changes while the car is in motion, and is an indispensable part of modern automobile transmission systems.

The main advantages of the hydraulic clutch are that it provides a smoother clutch pedal feel and a stronger clutch mechanism due to the use of lightweight materials and high-pressure oil and cylinders. Since the early 1990s, most automobiles have utilized hydraulic clutch systems.