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On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons (or turbine, in the case of a steam turbine locomotive). On a conventional, non-articulated locomotive, the driving wheels are all coupled together with side rods (also known as coupling rods); normally one pair is directly driven by the main rod (or connecting rod) which is connected to the end of the piston rod; power is transmitted to the others through the side rods. On diesel and electric locomotives, the driving wheels may be directly driven by the traction motors. Coupling rods are not usually used, and it is quite common for each axle to have its own motor. Jackshaft drive and coupling rods were used in the past (e.g. in the Swiss Crocodile locomotive) but their use is now confined to shunting locomotives. On an articulated locomotive or a duplex locomotive, driving wheels are grouped into sets which are linked together within the set. ==Diameter== Driving wheels are generally larger than leading or trailing wheels. Since a conventional steam locomotive is directly driven, one of the few ways to 'gear' a locomotive for a particular performance goal is to size the driving wheels appropriately. Freight locomotives generally had driving wheels between in diameter; dual-purpose locomotives generally between , and passenger locomotives between or so. Some long wheelbase locomotives (four or more coupled axles) were equipped with blind drivers. These were driving wheels without the usual flanges, which allowed them to negotiate tighter curves without binding. The driving wheels on express passenger locomotives have come down in diameter over the years, e.g. from on the GNR Stirling 4-2-2 of 1870 to on the SR Merchant Navy Class of 1941. This is because improvements in valve design allowed for higher piston speeds. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Driving wheel」の詳細全文を読む スポンサード リンク
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