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A lesson on clutches

After engines, it’s time to move on to some rub and grind

india Updated: Aug 28, 2009 11:33 IST
Grease Monkey

We’ve finished a long series on the number of cylinders used in engines of cars and bikes. If you’ve heard of a V18 engine or the like, do let me know. Today we’ll move a little beyond engines: the clutch.

Your engine can operate within particular limits — it cannot stay switched on below the idling speed, and it will not be able to rev itself much beyond the redline. This is due to the torque developed by an internal combustion engine, which, unlike an electric motor’s, doesn’t remain equal throughout the rev range. This explains why electric motors are unexciting compared to internal combustion engines — there is no go-faster reward, no intoxicating exhaust note if you rev the engine harder; just a smooth, electric-whine-accompanied surge all the way to the motor’s redline.

Below idle speed, the combustion engine doesn’t make enough torque to keep itself going, so there has got to be a way to keep the engine going while the car is stationary, for example. Another instance where you will want your engine to be free of the driveline is when you’re changing gears.

What does the clutch do exactly?
It engages and disengages your engine’s output and the gearbox’s input. The engine has something called a ‘flywheel’ which transfers the crankshaft’s rotation to the clutch. The clutch has one or more plates made of high-friction material. When you press the clutch pedal, springs help pull the plates apart, separating the flywheel from the gearbox.

The plates on either side are called ‘pressure plates’ as they apply pressure to the clutch plates. If anyone asks, the pressure plates are the ones with high-friction material on one side only.

Wearing the clutch thin
The clutch isn’t covered under warranty, since it undergoes wear and tear under normal usage. Revving the car a lot while starting off from a standstill or while going up a slope from a standstill can wear the clutch out quicker than usual. Use the handbrake while going uphill to conserve your clutch.

Another driving habit that can wear out the clutch quickly is ‘riding’ the clutch — the habit some drivers have of leaving their left foot on the pedal even while in gear. The pressure on the pedal might be just enough to pull the plates slightly apart so that they rub against each other. Changing gears while revving the engine (instead of getting off the throttle) will also wear the clutch out faster than normal.

Once a clutch is worn, it will slip, which means that even while a gear in engaged, the engine revs will not rise corresponding to the increase in the car’s speed. If this happens to your car or bike, do get your clutch looked at — you don’t want to get stuck in a traffic jam or a lonely road with a car that cannot move because of a clutch that has given up the ghost. Modern technology has increased clutch life with developments like ceramic clutches, but their life cannot be predicted as too many variables like driving style and conditions can affect the outcome.

Clutches that have to transfer more torque from the engine generally need more effort at the pedal because the springs have to be stronger to clamp the plates together. Hydraulics help ease the effort for truckers and drivers of sportscars, by using some of the engine’s power to help engage or disengage the clutch. Clutches are an integral part of your car — we’ll take a peek at how racecar drivers use them next week.