Why is the clutch pedal of a manual transmission car the heaviest of the three pedals?
I saw such a question: The clutch pedal is the heaviest of the three pedals of 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 manual transmission cars, 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 like a huge spring.
Because the clutch is transmitted by friction, and the engine torque is so large, to ensure that the clutch does not slip, the clutch pressure plate must be clamped, so there is a large 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 it can be stepped on with just one toe, let alone the whole foot. Many cars are now equipped with electronic throttles, making the accelerator pedal lighter.
Although the brake pedal is very light to step on, that is because there is vacuum assistance. If there is no assistance, 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 not practical, because the reduction 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 travel will also increase after the leverage ratio increases, affecting driving. After all, you definitely don't want to have 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 power-assisted clutches. But the problem is that the torque of the truck engine is tens of thousands of meters. In order to ensure that the clutch does not slip and cause excessive spring force, it is not necessary to fully step on the power assist, but must use the power assist. Most people can accept the clutch pedal strength of family cars, so there is no impact without power assistance.
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 you simply increase the constant power, the clutch will be lighter, but the pedal feedback will become very vague. If you want to maintain the original characteristics of the clutch, 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 heavy. The most common situations in daily car use are the following:
1. Damage to the clutch cable
Many manual transmissions today are hydraulic clutches that use brake fluid to transmit power. However, there are still some cars whose clutches use cables to transmit power. After long-term use, the friction gap between the cable and the cable wall of some cars increases, causing the cable to be clamped in the gap, increasing the movement resistance, and the clutch will become heavy at this time.
2. Wear of the clutch plate
Wear of the clutch plate can also cause the clutch pedal to become heavier, which is a problem that many people are not aware of. As the clutch plate is worn, the diaphragm spring of the clutch plate is deformed more, and more force is needed to push the diaphragm spring away when the clutch is pressed.
3. Wear of the pressure plate diaphragm spring
Wear of the disc diaphragm spring will also cause the clutch to become heavier. Because there are more diaphragm springs on the pressure plate, when the clutch is pressed under normal circumstances, the release bearing pushes all the diaphragms together to separate, so that the entire spring body is evenly stressed and 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 to the bearing seat when replacing the release bearing so that the release bearing movement can be better lubricated. 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. However, applying butter will increase the movement resistance of the release bearing and make 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 additional butter to the bearing seat, otherwise the clutch pedal will become heavier after a period of use.