How does the clutch work in the car and how to check it?

What is clutch?

The reason for the movement of the car is in its engine, more precisely, in the torque that it generates. The clutch is the transmission mechanism that is responsible for transferring this moment from the car's engine to its wheels through the gearbox.

The clutch is built into the structure of the machine between the gearbox and the motor. It consists of such details as:

• two drive discs - flywheel and clutch basket;
• one driven disk - a clutch disk with pins;
• input shaft with gear;
• secondary shaft with gear;
• release bearing;
• clutch pedal.

How does a clutch work in a car?

The driving disk - the flywheel - is rigidly mounted in the crankshaft of the engine. The clutch basket, in turn, is bolted to the flywheel. The clutch disc is pressed against the surface of the flywheel thanks to the diaphragm spring, which is equipped with a clutch basket.

When the car is started, the engine provokes rotational movements of the crankshaft and, accordingly, the flywheel. The input shaft of the gearbox is inserted through the bearing into the clutch basket, flywheel and driven disk. Rotations are not transmitted directly from the flywheel to the input shaft. To do this, there is a driven disk in the clutch design, which rotates with the shaft at the same speed and moves back and forth along it.

The position in which the gears of the primary and secondary shafts do not mesh with each other is called neutral. In this position, the vehicle can only roll if the road is sloped, but not drive. How to transfer rotation to the secondary shaft, which will indirectly set the wheels in motion? This can be done using the clutch pedal and gearbox.

Using the pedal, the driver changes the position of the disc on the shaft. It works like this: when the driver presses the clutch pedal, the release bearing presses on the diaphragm - and the clutch discs open. The input shaft in this case stops. After that, the driver moves the lever on the gearbox and turns on the speed. At this point, the input shaft gears mesh with the output shaft gears. Now the driver begins to smoothly release the clutch pedal, pressing the driven disc against the flywheel. And since the input shaft is connected to the driven disk, it also begins to rotate. Thanks to the meshing between the gears of the shafts, the rotation is transmitted to the wheels. In this way, the engine is connected to the wheels, and the car starts moving. When the car is already at full speed, you can fully release the clutch. If you add gas in this position, the engine speed will rise, and with them the speed of the car.

However, the clutch is necessary not only for the car to start and accelerate. You can't do without it when braking. To stop, you need to squeeze the clutch and gently press the brake pedal. After stopping, disengage the gear and release the clutch. At the same time, in the work of the clutch, processes occur that are the opposite of those that occurred at the beginning of the movement.

The working surface of the flywheel and clutch basket is made of metal, and that of the clutch disc is made of a special friction material. It is this material that provides disc slip and allows it to slip between the flywheel and the clutch basket when the driver holds the clutch at the start of the movement. It is thanks to the slippage of the discs that the car starts off smoothly.

When the driver abruptly releases the clutch, the basket instantly compresses the driven disk, and the engine does not have time to start the car and start moving so quickly. Therefore, the engine stalls. This often happens to novice drivers who have not yet experienced the position of the clutch pedal. And she has three main points:

• top - when the driver does not press it;
• lower - when the driver completely squeezes it out, and it rests on the floor;
• medium - working - when the driver gently releases the pedal, and the clutch disc is in contact with the flywheel.

If you throw the clutch at high speeds, then the car will start to move with slipping. And if you keep it in a half-squeezed position when the car is just starting to move, and gradually add gas, then the friction of the driven disk on the metal surface of the flywheel will be too intense. In this case, the movements of the car are accompanied by an unpleasant smell, and then they say that the clutch is “burning”. This can lead to rapid wear of the working surfaces.

What does the clutch look like and what is it?

The clutch is systematized according to several functional devices. According to the contact of passive and active elements, the following categories of nodes are distinguished:

• Hydraulic.
• Electromagnetic.
• Friction.

In the hydraulic version, the work is done by the flow of a special suspension. Similar couplings are used in automatic gearboxes.

1 – a reservoir of a hydraulic drive of coupling / the main brake cylinder; 2 - fluid supply hose; 3 - vacuum brake booster; 4 - dust cap; 5 - brake servo bracket; 6 - clutch pedal; 7 - bleed valve of the clutch master cylinder; 8 - clutch master cylinder; 9 – a nut of fastening of an arm of the main cylinder of coupling; 10 - pipeline coupling; 11 - pipeline; 12 - gasket; 13 - support; 14 - bushing; 15 - gasket; 16 – fitting for bleeding the clutch slave cylinder; 17 - clutch slave cylinder; 18 - nuts for fastening the bracket of the working cylinder; 19 - clutch housing; 20 - flexible hose coupling; 21 - flexible hose

Electromagnetic. Magnetic flux is used to drive. Installed on small vehicles.

Frictional or typical. The transfer of momentum is carried out due to the force of friction. The most popular type for cars with a manual transmission.

1.* Dimensions for reference. 2. Tightening torque of the crankcase mounting bolts 3. The clutch disengagement drive of the car must provide: 1. Clutch movement to disengage the clutch 2. Axial force on the thrust ring when the clutch is not disengaged 4. In the view A-A, the clutch and gearbox casing are not shown.

 By type of creation. In this category, the following types of coupling are distinguished:

• centrifugal;
• partially centrifugal;
• with main spring
• with peripheral spirals.

According to the number of driven shafts, there are:

• Single disk. The most common type.
• Double disk. Are established on cargo transport or buses of solid capacity.
• Multidisk. Used in motorcycles.

Drive type. According to the category of the clutch drive, they are classified into:

• Mechanical. Provide for the transfer of momentum when pressing the lever through the cable to the release fork.
• Hydraulic. They include the main and slave cylinders of the clutch, which are paired with a high pressure tube. When the pedal is pressed, the rod of the key cylinder is activated, on which the piston is located. In response, it presses on the running fluid and creates a press that is transmitted to the main cylinder.

There is also an electromagnetic type of coupling, but today it is practically not used in mechanical engineering due to expensive maintenance.

How to check the clutch function?

4 speed test. For cars with a manual transmission, there is one simple method by which you can verify that the manual transmission clutch has partially failed. The readings of the standard speedometer and tachometer of the car located on the dashboard are sufficient.

Before checking, you need to find a flat stretch of road with a smooth surface about one kilometer long. It will need to be driven by car. The clutch slip check algorithm is as follows:

• accelerate the car to fourth gear and a speed of about 60 km / h;
• then stop accelerating, take your foot off the gas pedal and let the car slow down;
• when the car starts to “choke”, or at a speed of approximately 40 km / h, sharply give gas;
• at the time of acceleration, it is necessary to carefully monitor the readings of the speedometer and tachometer.

With a good clutch, the arrows of the two indicated instruments will move to the right synchronously. That is, with an increase in engine speed, the speed of the car will also increase, the inertia will be minimal and due only to the technical characteristics of the engine (its power and weight of the car).

If the clutch discs are significantly worn out, then at the moment you press the gas pedal, there will be a sharp increase in engine speed and power, which, however, will not be transmitted to the wheels. This means that the speed will increase very slowly. This will be expressed in the fact that the arrows of the speedometer and tachometer move to the right out of sync. In addition, at the moment of a sharp increase in engine speed, a whistle will be heard from it.

Handbrake check. The presented test method can only be performed if the hand (parking) brake is properly adjusted. It should be well tuned and clearly fix the rear wheels. The clutch condition check algorithm will be as follows:

• put the car on the handbrake;
• start the engine;
• press the clutch pedal and engage third or fourth gear;
• try to move away, that is, press the gas pedal and release the clutch pedal.

If at the same time the engine jerks and stalls, then everything is in order with the clutch. If the engine runs, then there is wear on the clutch discs. Disks cannot be restored and either adjustment of their position or complete replacement of the entire set is necessary.

External signs. The serviceability of the clutch can also be indirectly judged simply when the car is moving, in particular, uphill or under load. If the clutch slips, then there is a high probability of a burning smell in the cabin, which will come from the clutch basket. Another indirect sign is the loss of the dynamic characteristics of the machine during acceleration and / or when driving uphill.

The clutch "leads". As mentioned above, the expression "leads" means that the clutch master and driven discs do not fully diverge when the pedal is depressed. As a rule, this is accompanied by problems when turning on / shifting gears in a manual transmission. At the same time, unpleasant creaking sounds and rattles are heard from the gearbox. The clutch test in this case will be performed according to the following algorithm:

• start the engine and let it idle;
• fully depress the clutch pedal;
• engage first gear.

If the gearshift lever is installed without problems in the appropriate seat, the procedure does not take much effort and is not accompanied by a rattle - which means that the clutch does not “lead”. Otherwise, there is a situation where the disc does not disengage from the flywheel, which leads to the problems described above. Please note that such a breakdown can lead to a complete failure of not only the clutch, but also lead to a malfunction of the gearbox. You can eliminate the described breakdown by pumping the hydraulics or adjusting the clutch pedal.