A gearbox is the compartment for the part that connects the engine of a vehicle to the wheels and controls the speed at which the wheels turn (either manually or automatically); in its simplest form a gearbox is the box-like home of an automobile gear system. A gearbox carries different forms of bearings to aid adjustment of speed and movement.
The maximum working speed of most motor engines is about 3,000 R. P. M. (despite the day-by-by technical-technological advancements). The maximum speed required by the road wheels is about 700 R. P. M. The reduction in rotating speeds between the crankshaft of the engine and the road wheels is accomplished by the gearbox and the differential gearing. The difference in speeds is made variable by the gearbox (which makes speed increase or decrease among the functions performed by the gearbox). A selection of three or four ratios and a reverse are generally provided, together with a "neutral" which enables the engine and propeller shaft to be disconnected mechanically (and by so doing, creates a freewheel function of the gearbox).
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