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What is the principle of a clutch, and why is a clutch needed?
Recently, we've been talking a lot about pure electric trucks, but we've also discussed traditional fuel vehicles quite a bit. In fact, there are quite a few interesting aspects in traditional fuel vehicles. For example, the engine, the transmission, and even the connecting component between the engine and the transmission: the clutch. Today, let's talk about how the clutch works.
If we were to talk about what a clutch actually does, I think almost every driver knows. The clutch is responsible for disconnecting the power connection between the engine and the transmission. But if you ask why we need to disconnect the power, I believe very few people can explain it very clearly.
As everyone knows, the drivetrain of our truck starts from the engine output, goes through the transmission to change the gear ratio, and then through the driveshaft and rear axle to the wheels, propelling the vehicle. The clutch is located between the engine and the transmission.
Everyone knows that an engine can deliver powerful performance, and once it starts running, it won't stop unless there are special external factors. Therefore, the engine needs a transmission to change the speed ratio between itself and the wheels; otherwise, if the engine tries to increase the vehicle's speed solely by its own RPM, it wouldn't be long before the engine is on the verge of being ruined.
In order to keep the engine speed within a reasonable range and avoid wasting power, the transmission must change the gear ratio by switching gears. When changing the gear ratio, the gears inside the transmission need to engage and switch. Modern transmissions are generally equipped with synchronizers, which pre-synchronize the speeds of the gears to facilitate smooth shifting.
But after all, the engine continuously outputs power. At this time, if you try to forcefully engage the gear, the gears will inevitably suffer a great impact, and there could even be gear tooth damage, while the synchronizer will also experience significant wear. Over time, the transmission simply wouldn't be able to withstand it. That’s why we need a clutch to cut off the power and protect the transmission.
In fact, the clutches we commonly use in trucks are essentially friction devices. According to the Baidu Encyclopedia entry on 'clutch': 'The clutch is located inside the flywheel housing between the engine and the transmission, and the clutch assembly is fixed to the rear surface of the flywheel with screws. The output shaft of the clutch is the input shaft of the transmission. During vehicle operation, the driver can press or release the clutch pedal as needed, temporarily disengaging or gradually engaging the engine and transmission, in order to cut off or transmit the power from the engine to the transmission. The clutch is a commonly used component in mechanical transmission, allowing the transmission system to be engaged or disengaged at any time.'
In other words, the components that are most effective are the pressure plate and the friction disc. When you press the clutch pedal, these two components separate, naturally cutting off the power transmission. When you release the clutch, these two components come together, and their friction allows the power to be transmitted to the gearbox through their connection. Of course, when you press the clutch pedal, other components like the booster pump and diaphragm spring also come into play.
Actually, the main components of a clutch are the clutch disc, clutch pressure plate, diaphragm spring, and release bearing. There’s nothing particularly special, but if you break it down in detail, there are quite a few parts.
Among them, the clutch disc and the clutch pressure plate are the friction components we commonly use. When we say the 'clutch is worn out,' it basically refers to these two parts being excessively worn, causing them to malfunction. According to the Pacific Auto Network Encyclopedia: 'The clutch friction plate is mainly made of composite materials. The main material of the friction plate is asbestos-based friction material. Some clutch discs are made of semi-metallic materials and composite fibers, while others are made of ceramic fiber materials.'
In fact, the material used to make a clutch plate ultimately depends on the purpose of the clutch and the amount of torque it needs to withstand. For example, motorcycle clutch plates are sometimes referred to as 'paper-based clutches.' Observant riders might have noticed that in the clutch component shown in the picture below, there are four axial springs (aligned in the same direction as the rotation of the axle). So, what are these four springs used for?
According to the explanation of answers to related questions in the Baidu question bank: 'The axial one presses the clutch plate, and the radial one handles torque buffering, reducing the impact at the moment the clutch engages or sudden resistance while driving, thereby protecting the engine from damage.' Doesn't that seem a bit confusing? If we apply this to the operation of a car, it becomes clearer.
We all know that when you release the clutch, it engages instantly, and at this moment, the engine is running. If the engagement is sudden and the rotational speeds of the engine and the transmission are slightly mismatched, it can cause a significant jolt. These springs are designed to mitigate those impacts. With them, not only will the driving feel much smoother, but the stress on the vehicle's transmission and engine components will also be reduced.
In addition, we can also see an object covered with fins in the picture. This is not a friction component of the clutch, but a spring, which is what we call a diaphragm spring. Its principle is somewhat like a seesaw: when we press the clutch, the center is pressed down, and the surrounding edges spring up due to the structural design, thereby causing the clutch disc and the pressure plate to separate and cut off the power.
The 'shaft' in the middle of this component is the release bearing. One end of the release bearing is fixed to the diaphragm spring, and the other end is fixed to the linkage of the clutch pedal. When the clutch is pressed, the first part to be subjected to force is the release bearing, which then applies force to the diaphragm spring, enabling the power to be disengaged and restored.
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