The Clutch
More info on the clutch can be found HERE
How The Clutch Works
Would you like to know how the clutch works? What exactly is ‘the biting point’?
How does clutch control help you to perform all those driving maneuvers?
This page will give you a very simple explanation of how the clutch works. But don’t be fooled . . . the basic principles of the clutch actually ARE very simple really!! Let us show you how the clutch works and you’ll understand what we mean by ‘clutch control’, ‘biting point’, and ‘holding point’ . . .
You don’t need to know any of this information to learn to drive . . . many, many people have been driving very safely for years and yet they don’t have the slightest clue about how the clutch works!!
However, if you take the time to read this section over a few times and to study the diagrams, you’ll find that a basic understanding of the clutch will help you to understand the finer points of car control enormously.
So, you’re starting to learn how to drive.
You get into the driver’s seat for the first time . . .
Yep, steering wheel . . . I know what that does . . . brake pedal mmm . . . that must be to slow the car down . . . gas pedal. Yep, that’s what makes us go!
But what’s this thing on the left??
Oh no!! They put an extra pedal in the car just to frighten us and make it harder!!
Well, actually, no they didn’t. The clutch is very easy to understand and when you’ve learned what it can do for you you’ll find using it a breeze. It’s all just a matter of practice, practice, practice . . .
By the way, you only need to know the basics of what the clutch does; you don’t need to know how it actually works. I bet you can turn on your TV and watch a movie by pressing all the buttons on the remote control, right? But I bet you don’t know exactly how the remote and the TV work because you don’t need to. See what I mean?
Right, so just what does the clutch do??
Ok, well, we all know (I hope!) that the thing that makes the car ‘go’ along the road is the engine. The insides of the engine ‘spin’ around and turn all sorts of cogs and things that we don’t need to know about. The engine is connected to the car wheels by a metal ‘broom handle’ called the drive shaft. . . it’s the long yellow ‘bar’ that goes straight up and down in the diagram below.
The drive shaft is made to spin by the engine because it’s connected to it. When we press the gas pedal we put more fuel into the engine and that makes it go faster. When the engine goes faster the drive shaft goes faster, and because the drive shaft’s connected to the wheels the car goes faster. Ok so far?
Right, can you imagine what might happen if the engine was connected to the wheels all the time by the drive shaft?
How would we be able to stop the car? The engine would always want to push us along! We’d have to turn the ignition off just to stop the car. Imagine doing that at every set of traffic lights!!
So, we need a way of ‘turning off’ the engines power to the wheels so that we can stop the car when we want to, without having to actually turn off the engine.
And that’s exactly what the clutch does!!
The clutch is a very clever little device that’s fitted to the cars drive shaft. Just imagine that the drive shaft is sawn in half and the two parts can be kept apart, just like in the diagram. The two parts of the drive shaft are now only connected together by the clutch.
Ok so far, but how does this clutch thing turn off the engines power to the wheels?
Well, the clutch is actually made up of two circular discs called ‘clutch plates’. One of the clutch plates is permanently attached to the part of the drive shaft the goes into the engine. That means that this clutch plate is always spinning round along with the drive shaft. The other clutch plate is attached to the other bit of the drive shaft, the one that’s attached to the wheels. The clutch plates are made of a very hard wearing material and when they are pressed together hard there’s a lot of friction between them. In fact, when they are firmly pressed together there’s so much friction between them that they may as well not be there! It’s as though both parts of the drive shaft are connected together as before.
Just have a quick look at the diagram; you can now see the two clutch plates on the drive shaft. The engine makes the first bit of the drive shaft turn and this turns the first clutch plate. The first clutch plate is pressed very firmly against the second clutch plate and this makes the rest of the drive shaft, and the wheels, turn around.
The diagram shows how the clutch plates are when your foot is off the pedal. In other words, when you don’t press the clutch pedal the plates are pressed very firmly together. This actually happens because there are some really big strong springs that push the plates together. So, as above, when your foot is off the pedal the clutch might as well not be there!!
Ok, so what happens when we do press the clutch pedal? I wonder if you can guess!
What happens when we press the pedal is that the clutch plates are forced apart, so there’s a gap in between them. The engine keeps on turning and it turns the little bit of the drive shaft that’s connected to the engine. The clutch plate that’s attached to this first bit of the drive shaft also carries on turning. Remember? The first clutch plate is permanently attached to the first bit of the drive shaft and always spins with it.
But wait. What about the second clutch plate? The one attached to the other bit of the drive shaft? Well, there’s a gap between the two plates now so they’re not touching. So the second plate can’t spin, no matter how fast the engine is turning. Because the second plate can’t spin. Neither can the rest of the drive shaft, and if that can’t spin the wheels can’t spin!!
We’ve managed to ‘turn off’ the engines power to the wheels without turning off the ignition and actually stopping the engine. Very clever!!
So, the clutch lets us turn the engines power to the car wheels on and off, whenever we want. When the pedal is ‘up’, the full power of the engine is connected to the wheels and the clutch might as well not be there. When we press the pedal all the way down we separate the two plates so that the second one can’t spin. This turns off ALL the engines power to the wheels and the engine might as well not be there!!
But here’s the really clever part . . .
By varying how much we press down on the clutch pedal we can vary how much power from the engine is connected to the wheels.
Remember how I said that the two clutch plates are made of a hard wearing material and that there is a lot of friction between them? Well, the clutch works entirely on friction. The second clutch plate is connected, via the second half of the drive shaft, to the wheels. You can imagine that it takes quite a lot of power to turn the wheels and make the whole car move. So, when the first plate is only just touching the second one there’s not enough friction between them to make the second one move. The first plate actually spins and kind of ‘rubs’ against the second one but can’t actually make it move. Press the plates together a bit more . . . there still may not be enough friction to turn the second plate and move the whole car but the first plate still spins and rubs against the second one. Press the plates a bit more . . . a bit more . . . a bit more. Can you see that as we press the plates together the friction builds up until they both start turning?
At some point the plates will be pressed together just tight enough for the second plate to start turning, but they won’t be pressed hard enough together for the second plate to turn quite as fast as the first. Lift the clutch a bit more . . . now they’re pressed tighter together and the second plate will move a little quicker . . .
By varying how much you press the pedal you are varying how hard the two plates are pressed together and, therefore, how much of the engines power is sent to the wheels.
I can turn the engines power to the wheels all the way off (clutch down) or all the way on (clutch up). I can also vary the power to the wheels as much as I like by varying the position of the pedal, just like a volume control.
You find ‘the bite’ by lifting the pedal up very slowly until you just feel the car wanting to move. What you’ve done is actually allowed the clutch plates to press against each other enough so that the friction between them is now high enough to just make the second plate want to start turning with the first one. Simple, really!! In this diagram we would be at the 'holding point' at position 5 (the position where the clutch just holds the car still) and the biting point at about position 6 when the clutch plates would be touching just enough - by the time we allowed the clutch pedal to come up to position 10 the clutch plates would be pressed firmly together.
We hope that this introduction to how the clutch works has helped you to understand what the clutch does. All you need to do is get a picture in your mind of those two plates pressing against each other with varying clutch pressure, depending on how much you’ve pressed the pedal down.