Why is the clutch pedal the heaviest of the three pedals in a manual transmission car?

Why is the clutch pedal the heaviest of the three pedals in a manual transmission car?

I saw a question like this: The clutch pedal is the heaviest of the three pedals in a manual transmission car, so why don't manufacturers design the clutch pedal to be lighter? In fact, this question is very simple, and we can analyze it from the following points:

Why is the clutch pedal so heavy

For a car with manual shifting, the clutch pedal is definitely the heaviest, which is related to its working principle. Do you know what you are driving when you step on the clutch? It is a huge spring.

Because the clutch is transmitted by friction, and the engine torque is so large, in order to ensure that the clutch does not slip, the clutch plate must be clamped, so there is a huge diaphragm spring on the pressure plate, which can generate a large clamping force to ensure that the clutch can normally transmit large torque without slipping. But when stepping on the clutch, the spring force must be overcome to disengage the clutch. So the clutch pedal is the heaviest.

And the accelerator pedal is very light, because they drive the throttle. The biggest resistance on the early pull throttle is the return spring, but the elastic force is extremely limited, and one toe can step on it, let alone the whole foot. Now many cars have electronic throttles, which makes the pedals lighter.

Although the brake pedal is very light to step on, that is because of the vacuum assist. If there is no assist, the brake pedal is definitely much heavier than the clutch pedal.

Why not make the clutch pedal lighter?

There are three main ways to reduce the weight of the clutch pedal:

The first is to reduce the spring force of the pressure plate, but this is obviously impractical, because the decrease in elastic force means that the clutch is not strong enough and the clutch is easy to slip.

The second is to increase the leverage ratio of the clutch pedal, because the clutch pedal itself is a lever structure, and increasing the leverage ratio can make the pedal lighter. But unfortunately, this is not practical, because the clutch pedal stroke will also increase after the leverage ratio increases, affecting driving. After all, you don't want to lift your legs when stepping on the clutch.

The third is to increase the strength of the clutch, which is achievable. For example, many heavy trucks have a force clutch. But the problem is that the torque of the truck engine can easily reach thousands of meters. In order to ensure that the clutch does not slip, the spring force is too large. There is no need to fully step on the force. It is necessary to use force. Moreover, the clutch pedal strength of a family car is acceptable to most people, so it doesn't matter if you don't step on the force.

More importantly, increasing power will increase costs. Not only will the cost of power equipment increase, but the structure of the clutch and gearbox will also change. Moreover, the resistance characteristics of the clutch pedal are different at different positions. If a constant power is simply added, the clutch will be lighter, but the pedal feedback will become very vague. If the original characteristics of the clutch are to be maintained, the cost will continue to increase, so the manufacturer might as well go directly to the automatic transmission.

Reasons for abnormal clutch weight

Some faults or minor problems can also cause the clutch to become heavier. The most common situations in daily car use are the following:

1. Damage to the clutch cable

Many manual transmissions now have hydraulic clutches, which use brake fluid to transmit power. However, the clutch of some cars uses a cable to transmit power. After some cars have been used for a long time, the friction gap between the cable and the cable wall is large, causing the cable to be clamped in the gap and increase the movement resistance. At this time, the clutch will become heavy.

2. Clutch plate wear

Clutch plate wear can also cause the clutch pedal to become heavier, which is a problem that many people are not aware of. Because the diaphragm spring of the disc is more deformed after the clutch plate is worn, it takes more force to push the diaphragm spring away when the clutch is pressed.

3. Wear of the pressure plate diaphragm spring

Wear of the pressure plate diaphragm spring will also cause the clutch to become heavier, because there are many pressure plate diaphragm springs. Under normal circumstances, when the clutch is pressed, the release bearing pushes all the diaphragms together to separate, so that the entire spring body is evenly stressed and it is easy to separate.

4. The release bearing seat has large resistance

When the clutch is pressed, the release bearing will move back and forth. Some people like to apply butter on the bearing seat when replacing the release bearing, so that the release bearing can be better lubricated when it moves. In fact, this practice is superfluous. Since the release bearing rotates very slowly and the friction between the bearing and the bearing seat is very small, it is difficult to wear even without lubrication. But after applying butter, the movement resistance of the release bearing will increase, making the clutch heavier. In particular, the clutch plate will wear off a lot of dust during use, and sticking butter will make the butter thicker and harder, which can only further increase the resistance of the release bearing movement.

Therefore, when replacing the release bearing, there is no need to apply extra butter on the bearing seat, otherwise the clutch pedal will become heavier after a period of use.