Tag Archive | "CVT transmission"

How CVT Gearboxes Work


Although by no means commonplace, Continuously Variable Transmissions (CVT) are beginning to appear on more and more cars. The thinking presumably is that, given the rise of hybrid and electric vehicles, they are more efficient and thus more economic.

Most CVT systems replace traditional gears with a pair of pulleys – one for the engine and one for the wheels. They are linked together by a metal belt. Because the diameter of the pulleys changes the effect is of having an infinite number of gears.

In regular gearboxes the ratios are predetermined to whatever the manufacturer requires the in-gear performance to be – longer or shorter for acceleration or economy with the engine speed rising or falling accordingly; this is what we’ve all grown up with. With CVT the ratios change which allows the engine to maintain it’s most efficient speed thus making the car more economical.

Switching a CVT ‘box from auto to manual has the effect of fixing the ratios and allowing the driver to select a gear just like a regular transmission but to the detriment of the efficiency of the car. The only real advantage of doing such a thing is to maximise engine braking when descending a steep hill but, after a couple of seconds, the on-board computer should recognise what’s happening with the descent and switch to a lower ratio anyway. With CVT it is probably best to leave it to the car.

At this point it is worth mentioning some caveats to this. On the face of it CVT gearboxes are the way to go but Motor Blogger isn’t so sure. Certainly, the way the car proceeds is at first slightly odd. Under acceleration the engine note rises and kind of stays there and, because, economy is at the helm, progress doesn’t seem a brisk as with conventional gears.

This gearbox will suit drivers who have no interest in cars. They see them as just being transport and they will require the best of economic choices. Keen drivers might not be so easily pleased and I would suggest it will be harder to prise them away from their regular choices.

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