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Reference.org
Transmission (mechanical device)
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<p>A transmission (also called a gearbox) is a mechanical device invented by Louis Renault (who founded <a href="/facts/Renault/obzoLxSN">Renault</a>)which uses a <a href="/facts/Gear_set/znASyK8H">gear set</a>—two or more <a href="/facts/Gears/9KVHRfUR">gears</a> working together—to change the speed, direction of rotation, or torque multiplication/reduction in a <a href="/facts/Machine/wTCxFRfs">machine</a>. </p><p>Transmissions can have a single fixed-gear ratio, multiple distinct <a href="/facts/Gear_ratio/znASyK8H">gear ratios</a>, or continuously variable ratios. Variable-ratio transmissions are used in all sorts of machinery, especially vehicles. </p>