Car Clutch: Role, Structure, Classification and Principle

Clutch is an important mechanical structure located between the internal combustion engine and the gearbox of a car. This part has the task of transmitting or disconnecting the power from the engine crankshaft to the gearbox primary shaft smoothly, flexibly and accurately.

According to a 2022 study by the Society of Automotive Engineers (SAE), more than 80% of transmission failures originate from clutch failures. This shows the extremely important role of the clutch in the stable operation and longevity of the car's transmission system.

Car clutch consists of three main parts: the active part, the passive part and the control mechanism. The active part consists of the flywheel and the friction disc which can withstand temperatures up to 300°C. The passive part consists of the pressure plate and the high-strength clutch housing. The control mechanism with the clutch pedal, cylinder, cutting fork and spring are made of special materials such as cast iron, alloy steel, ceramic and heat-resistant rubber.

Clutches are classified according to four criteria: torque transmission method, pressure generation method, number of friction discs and control method; helping to choose the right one for each type of vehicle and usage needs.

The operating principle of this part consists of two stages: engaging and disengaging the clutch, helping to transmit power smoothly or stopping power transmission to change gears without damaging the gearbox.

To maintain the clutch, the owner should periodically check the oil, clutch pedal and friction plate, ensuring that the oil and wear parts are replaced as recommended. In addition, careful driving is also a way to prolong the life of the vehicle and avoid problems such as clutch slippage or difficult gear shifting.

And Thanh Phong Auto Learn about the role, structure and how to maintain the clutch to keep your vehicle running smoothly and durably through this article!

What is a Car Clutch? The Role of a Car Clutch

The car clutch is a mechanical part located between the engine and the gearbox, which is responsible for transmitting or disconnecting power from the engine to the gearbox smoothly and flexibly. This part helps the car start and shift gears smoothly, protects the transmission system, prolongs the life of components and improves operating efficiency.

What is the main role of the clutch in the automotive transmission system?

The clutch helps temporarily disconnect the engine and transmission for starting, smooth gear shifting, protecting the transmission, increasing component life and improving the overall operating performance of the vehicle.

• Smooth starting and shifting support: The clutch temporarily cuts power to help the vehicle start smoothly and shift smoothly, avoiding shock and gearbox wear.

According to a 2021 study by Sachs (Germany), proper clutch operation increases gearbox life by up to 30% and reduces annual maintenance costs by about 15%.

• Transmission protection: The clutch reduces sudden loads on the gearbox and engine, especially when downshifting at high speeds, thereby avoiding damage due to impact and wear.
• Longevity: A quality and well-maintained clutch can last up to 200.000 – 300.000 km, while protecting components such as the gearbox, driveshaft, etc.
• Increased operating efficiency: An efficient clutch helps the vehicle run smoothly and saves fuel. Each time the clutch is opened/closed, it consumes about 0,2 - 0,5% of fuel due to friction heat generation.

What is the structure of a car clutch?

The structure of a car clutch consists of three main parts: the active part (flywheel, friction disc), the passive part (pressure plate, clutch housing) and the control mechanism (clutch pedal, cylinder, cutting fork, spring). They are made from heat-resistant, wear-resistant materials (cast iron, steel, ceramic, rubber) to ensure stable and durable power transmission.

1. Main parts

The clutch consists of three main components: the active part, the passive part, and the control mechanism.

Initiative:

• Flywheel: A round cast iron or steel block, weighing from 5 to 15 kg, fixed to the engine crankshaft. The flywheel surface is machined smooth and flat with an accuracy of 0,01 mm to ensure good contact with the friction disc.
• Friction disc: The friction disc is located between the flywheel and the pressure plate, with a diameter of 180–430 mm, a thickness of 3–8 mm, with a steel core and two composite material coated surfaces. The spiral grooves help dissipate heat, increase grip and reduce wear. This is the key component that determines the ability to transmit power.

Passive part:

• Pressure plate: A circular steel plate, parallel and opposite to the flywheel, with the task of pressing the friction plate against the flywheel when the clutch is engaged with a force of 1.000 - 2.000 N. The pressure plate is usually made of ductile iron or high-strength steel, the surface is machined flat with an error of no more than 0,05 mm.
• Clutch housing: Is the part that covers and protects the entire clutch assembly, and is also the place to fix details such as springs and cutting forks. Clutch housings are usually cast from cast iron or aluminum alloy.

Control mechanism:

• Clutch pedal: Is the part that communicates directly with the driver, used to control the clutch through a cable or hydraulic system.
• Master/slave cylinders: These are hydraulic cylinders that transmit force from the clutch pedal to the cutting fork to engage/disengage the clutch. When the clutch is depressed, oil from the master cylinder will be pushed to the slave cylinder.
• Cutting fork: Is a lever located between the slave cylinder and the clutch bearing. When the slave cylinder pushes the cutting fork, the cutting fork will act on the bearing, pressing the pressure plate away from the friction plate, cutting off the power transmission.
• Clutch spring: Usually in the form of a spiral spring or disc spring. The spring's role is to create pressure between the pressure plate and the friction plate when the clutch is engaged.

There are also some additional parts such as clutch bearings, oil pipes, oil seals, etc.

2. Crafting Materials

Clutch parts are made from high heat and abrasion resistant materials such as cast iron, alloy steel, ceramic, kevlar or specialized rubber to ensure durability and stable performance in harsh environments.

• Flywheels are usually cast from gray cast iron or alloy steel with good heat resistance and wear resistance.
• Friction discs use materials such as asbestos, ceramic, kevlar... mixed with synthetic resin to create good friction and wear resistance.
• Pressure plates are mainly made of ductile iron or high strength steel.
• Springs are usually made of alloy steel with good elasticity and corrosion resistance.
• Bearings, seals made of alloy steel, heat-resistant rubber...

According to a 2023 study by the European Automotive Materials Institute, GG25 gray cast iron with a carbon content of 3,2-3,5% provides 35% more efficient heat dissipation than conventional cast iron. Meanwhile, 40Cr alloy steel with a hardness of 28-32 HRC provides 2,5 times more wear resistance.

How Are Car Clutches Classified?

Automobile clutches are classified according to four criteria: torque transmission method, pressure generation method, number of friction discs, and control method.

1. According to the torque transmission method

According to the torque transmission method, the clutch is divided into friction clutch, hydraulic clutch and electromagnetic clutch. Each type is suitable for different vehicle models according to the requirements of performance, durability and smoothness.

• Friction clutch: The most common type today, transmitting torque through friction between contact surfaces. There are two types:
• Dry: No lubricating oil, high power transmission efficiency but susceptible to wear and heat. Often used in passenger cars and small trucks.
• Wet: Soaked in oil, better heat dissipation, longer life, but lower power transmission efficiency. Often used for motorcycles, sports motorcycles, automatic transmissions.
• Hydraulic clutch: Transmits torque by oil movement between the pump wheel and turbine wheel. No direct frictional contact, smooth operation, suitable for automatic transmission.
• Electromagnetic clutch: Controls the transmission of power by magnetic fields, allowing for very fast and precise engagement/disengagement. This type is commonly found in hybrid vehicles or vehicles using modern electronic control.

According to statistics from the Global Automotive Parts Manufacturers Association (GAPA) in its 2022 report, friction clutches account for 78% of the global market share, hydraulic clutches 19%, and electromagnetic clutches 3%.

2. According to the method of creating pressure

According to the method of creating pressure, there are types of clutches using springs, centrifugal and hydraulic, with characteristics ranging from simple, common to precise control, suitable for both ordinary and automatic vehicles.

• Spring: Using a spring to press the friction disc against the flywheel is the simplest and most common mechanism today. The spring can be disc or cylindrical.
• Centrifugal: Uses centrifugal force to compress the friction disc when the rotation speed increases. Suitable for scooters or some models without a clutch pedal.
• Hydraulic: Creates pressure by oil pressure, more precise control, often used in automatic control systems.

3. According to the number of friction discs

According to the number of friction discs, clutches are divided into single disc, double disc and multi-disc. The more discs there are, the higher the power transmission capacity and working efficiency.

• Single disc clutch: Only one friction disc, simple structure, low cost. Suitable for cars, light trucks.
• Dual-disc clutch: Has two friction discs, increasing contact area and torque transmission. Commonly used in high-performance vehicles or medium-duty trucks.
• Multi-plate clutch: Has many alternating friction plates, usually placed in an oil environment (wet clutch), high efficiency, compact size. Commonly used in racing cars, sports cars, large displacement scooters.

4. According to control method

According to the control method, there are manual and automatic clutches, with the difference lying in the level of driver intervention and the possibility of automatic control via the ECU.

• Manual clutch: Driver controls via clutch pedal, common in manual transmission vehicles. Advantages are authentic driving feel, low cost, easy maintenance.
• Automatic clutch: No need for direct operator, the electronic system will automatically engage/disengage the clutch based on signals from the ECU. Used in automatic, semi-automatic or high-end cars.

How Car Clutch Works

The car clutch allows the torque transmission between the engine and the transmission to be connected or disconnected, allowing the car to start, change gears and stop smoothly. The operating principle consists of two main stages: engaging and disengaging the clutch, ensuring the power transmission process is flexible, smooth and protects the transmission system.

1. Basic functions

The main function of the clutch is to connect or disconnect the engine crankshaft and the transmission input shaft, thereby transmitting or disconnecting torque from the engine to the transmission system.

• When the clutch is engaged, force from the engine is transmitted through the clutch components to the gearbox gears and rotates the wheels.
• When the clutch disengages, the entire power transmission is suspended, allowing the driver to change gears or stop the vehicle without turning off the engine.

2. Clutch engagement process

When the driver releases the clutch pedal, the hydraulic or mechanical system reduces the force acting on the cutting fork, causing the pressure spring to push the pressure plate back to its original position. At this point:

• The pressure plate presses the friction disc against the flywheel.
• The flywheel, friction disc and gearbox primary shaft rotate together, torque is continuously transmitted from the engine to the gearbox.

Thanks to that, the vehicle can accelerate, move or maintain speed depending on operating conditions.

3. Clutch disengagement process

When the driver presses the clutch pedal, the force from the driver's foot is transmitted through the hydraulic or mechanical system to the cutting fork, moving the cutting bearing, acting on the pressure spring and pushing the pressure plate away from the friction plate.

The result is:

• The friction disc leaves the flywheel, torque from the engine can no longer be transmitted to the transmission.
• The transmission is temporarily isolated, allowing the driver to shift gears or stop the vehicle without damaging the gears in the transmission.

4. Role in shifting and starting

The clutch plays a vital role in both shifting gears and starting from a standstill.

• When shifting gears, disengaging the clutch helps reduce the load and disconnect the torque transmission between the engine and the gearbox, avoiding gear wear or strong impact, thereby helping to shift gears smoothly without causing jerks.
• When starting off, the driver slowly engages the clutch to gradually transfer torque from the engine to the wheels. This process helps the vehicle start smoothly, avoiding stalling or rapid wear of parts.

How to Maintain Car Clutch?

Car clutch maintenance includes regular inspection of components such as the oil, clutch pedal and friction plate, periodic replacement of oil and wear parts, and attention to driving habits to maintain performance and prolong life. Proper maintenance and use helps prevent clutch slippage, difficult gear shifting, and transmission damage.

1. Periodic check

Periodic clutch inspection includes checking the fluid level, clutch pedal travel and friction plate wear to ensure efficient operation and prevent damage.

• Clutch fluid level (for vehicles using hydraulic systems): If the fluid is low or contaminated, the force acting on the cutting fork will be weak, leading to incomplete clutch disengagement. Should be checked every 10.000 km.
• Clutch pedal travel: If the pedal is too high or too low compared to the standard, it can cause clutch slippage or difficulty shifting gears. The ideal travel is usually between 120 – 160 mm, depending on the vehicle.
• Disc wear: When the disc wears to a critical level (usually less than 2mm), the grip will be reduced, causing clutch slippage and flywheel wear. This can be detected by unusual noise, burning smell or difficulty accelerating.

2. Periodic replacement

Clutch components require periodic replacement, including oil, friction plates and other components, at mileage intervals or manufacturer recommendations.

• Clutch oil: Should be changed every 40.000 - 60.000 km or as recommended by the manufacturer to ensure stable hydraulic system operation.
• Friction disc: Depending on operating conditions and driving skills, the friction disc needs to be replaced between 80.000 - 120.000 km.
• Other parts: Cutting bearings, springs, pressure plates… can also be worn or deformed, so check carefully when replacing the friction plate to replace synchronously if necessary.

3. Note when using

Driving habits greatly affect the life of the clutch, so avoid continuously applying the clutch, releasing the clutch too quickly, holding the clutch at red lights and accelerating too much when releasing the clutch.

• Do not continuously apply the clutch: Many drivers have the habit of placing their foot on the clutch pedal when not necessary, causing the friction plate to come into contact halfway and causing slippage and rapid wear.
• Do not release the clutch too quickly when starting off: It will cause jerking, transmission shock and reduce the life of the parts.
• Avoid holding the clutch when stopping at red lights: Shift to N and release the clutch to avoid creating continuous pressure on the bearings and friction discs.
• Do not increase the throttle too much when releasing the clutch: Especially when climbing a slope, suddenly increasing the throttle can cause the friction disc to burn, slip or wear unevenly.

Driving habits affect 65% of clutch life according to a 2021 study from the European Society of Automotive Engineers (EUAE).

Replacement cycle table of parts in the car clutch system:

*Note: The above cycle is for reference only, the actual cycle depends on the conditions of use and quality of spare parts.

FAQ – Frequently Asked Questions

1. What are the signs that your car's clutch is having problems?

Some common signs include:

• Clutch pedal is heavy, sinks deeply or makes strange noises.
• Clutch feels "hot", unusually heavy to pedal.
• Car jerks when starting or shifting gears.
• Burning smell from transmission area.
• The car's clutch slipped, I increased the throttle but the speed increased slowly.

2. What causes clutch friction discs to wear out quickly?

Clutch friction discs can wear out quickly due to the following reasons:

• Regularly leave the clutch in half clutch.
• Starting off and shifting gears suddenly, shocks the clutch.
• Use the clutch to keep the vehicle stationary on a slope.
• Clutch not fully depressed when shifting gears.
• Poor quality friction disc, not suitable.

3. Do automatic cars need a clutch?

Most of automatic transmission car Modern automatic transmissions do not use a traditional clutch but instead use a torque converter. However, some automatic transmissions still use a multi-plate hydraulic clutch to do the shifting.

If you are wondering between manual and automatic transmission cars, see more articles: Should I buy a manual or automatic car??

4. What is the correct way to use the clutch to protect the gearbox?

To protect the gearbox, drivers should avoid continuously engaging the clutch, not holding the clutch at red lights, releasing the clutch slowly when starting off, and not accelerating sharply before releasing the clutch completely. These actions help reduce pressure on the friction plates and gearbox gears, prolonging the life of both systems.

To better understand the relationship between the clutch and the gearbox, how it works and common errors, refer to the article: Car gearbox – structure, classification, principles & common failures.

5. Can I replace my car clutch at home?

You should not replace your car's clutch at home without professional knowledge and specialized tools. The process of removing and installing the clutch is quite complicated and requires high precision.

Small installation errors can also cause serious consequences such as gearbox failure, car suddenly died… It is best to take your car to a reputable garage for advice and proper replacement.

6. Which address is reputable and quality for clutch inspection and maintenance?

Thanh Phong Auto is the center car repair reputable in Ho Chi Minh City, specializing in providing inspection and maintenance services and replace clutches for all vehicle lines, from popular to high-end, with professional processes, modern equipment and a team of highly skilled technicians.

Outstanding advantages of Thanh Phong Auto:

• Highly skilled technicians with extensive experience in handling clutch and transmission related problems.
• Modern equipment supports accurate diagnosis of the condition and wear level of the clutch.
• Genuine spare parts, guaranteed quality and durability.
• Professional process, transparent inspection - consultation - quotation before repair.
• Clear warranty, good after-sales service.
• Provide proper driving advice to prolong the life of the clutch and gearbox.

Hopefully, this article has helped you better understand the car clutch – an important part closely linked to the gearbox. Use and maintain it properly to keep your car running smoothly, durably and safely on every journey.