The device and principle of operation of the clutch drive

An important part of a vehicle equipped with a manual transmission is the clutch. It consists directly of the clutch (basket) of the clutch and the drive. Let us dwell in more detail on such an element as the clutch drive, which plays an important role in the overall clutch assembly. It is with its malfunction that the clutch loses its functionality. Let's analyze the drive device, its types, as well as the advantages and disadvantages of each.

Clutch drive and its types

The drive is designed for remote control of the clutch directly by the driver from the passenger compartment. Pressing the clutch pedal directly affects the pressure plate.

The following drive types are known:

• mechanical;
• hydraulic;
• electrohydraulic;
• pneumohydraulic.

The most widespread are the first two types. Trucks and buses use a pneumatic hydraulic drive. Electro-hydraulic is installed in machines with a robotic gearbox.

In some vehicles, a pneumatic or vacuum booster drive is used to facilitate control.

Mechanical drive

The mechanical or cable drive has a simple design and low cost. It is unpretentious in maintenance and consists of a minimum number of elements. The mechanical drive is installed in cars and light trucks.

The elements of a mechanical drive include:

• clutch cable;
• clutch pedal;
• clutch release fork;
• release bearing;
• adjustment mechanism.

The sheathed clutch cable is the main drive element. The clutch cable is attached to the fork and also to the pedal in the passenger compartment. At the moment of depressing the pedal by the driver, the action is transmitted through the cable to the fork and release bearing. As a result, the engine flywheel is disconnected from the transmission and, accordingly, the clutch is disengaged.

An adjusting mechanism is provided in the connection of the cable and the lever drive, which provides free travel of the clutch pedal.

The clutch pedal travel is free movement until the drive engages. The distance traveled by the pedal without much effort by the driver when pressed is free travel.

If the gear change is accompanied by noise, and at the beginning of the movement there are small jerks of the car, then it is necessary to adjust the pedal stroke.

The clutch play should be within 35-50 mm of pedal free travel. The standards for these indicators are indicated in the technical documentation of the car. Pedal travel is adjusted by changing the length of the rod with the adjusting nut.

In trucks, not a cable, but a lever mechanical drive is used.

The advantages of a mechanical drive include:

• simplicity of the device;
• low cost;
• reliability in operation.

The main disadvantage is considered to be a lower efficiency compared to a hydraulic drive.

Hydraulic clutch drive

The hydraulic drive has a more complex design. Its elements, in addition to the release bearing, fork and pedal, also include a hydraulic line, which replaces the clutch cable.

In fact, this line is similar to the hydraulic brake system and consists of the following elements:

• clutch master cylinder;
• clutch slave cylinder;
• reservoir and pipeline with brake fluid.

The device of the clutch master cylinder resembles the device of the brake master cylinder. The clutch master cylinder consists of a piston with a pusher, located one in the housing. It also includes a fluid reservoir and sealing rings.

The clutch slave cylinder, which has a design similar to the master cylinder, is additionally equipped with a valve to remove air from the system.

The mechanism of action of a hydraulic drive is the same as that of a mechanical one, only the force is transmitted with the help of the liquid in the pipeline, and not through the cable.

When the driver presses the pedal, the force is transmitted through the rod to the clutch master cylinder. Then, due to the incompressible property of the liquid, the clutch slave cylinder and the release bearing drive lever are actuated.

The following features can be distinguished as the advantages of a hydraulic drive:

• the hydraulic clutch allows the transmission of force over a considerable distance with high efficiency;
• resistance to fluid overflow in the elements of the hydraulic drive contributes to the smooth engagement of the clutch.

The main disadvantage of a hydraulic drive is a more complicated repair compared to a mechanical one. Leakage of working fluid and ingress of air into the hydraulic drive system are perhaps the most common breakdowns that the clutch master and slave cylinders can boast of.

The hydraulic drive is used in passenger cars and trucks with a tipping cab.

The nuances of clutch operation

Drivers often tend to associate unevenness and jerky movement with clutch malfunctions. This logic is wrong in most cases.

For example, a car, when changing gears from first to second, sharply decelerates. It is not the clutch itself that is to blame, but the clutch pedal position sensor. It is located behind the clutch pedal itself. Sensor malfunctions are eliminated by simple repairs, after which the clutch will again work smoothly and without jerking.

Another situation: when changing gears, the car jerks a little, and when starting off, it can stall. What could be the reason? The clutch delay valve is most often to blame. This valve provides a certain speed at which the flywheel can engage, no matter how quickly the clutch pedal is thrown. For novice drivers, this function is necessary because The clutch delay valve prevents excessive wear on the surface of the clutch disc.