On asteam locomotive, adriving wheel is a powered wheel which is driven by the locomotive'spistons (orturbine, in the case of asteam turbine locomotive).[1] On a conventional, non-articulated locomotive, the driving wheels are all coupled together with side rods (also known ascoupling rods); normally one pair is directly driven by themain rod (orconnecting rod) which is connected to the end of thepiston rod; power is transmitted to the others through the side rods.[2][3][4]
Ondiesel andelectric locomotives, the driving wheels may be directly driven by thetraction 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[5][6] (e.g. in theSwiss Crocodile locomotive[7]) but their use is now confined toshunter locomotives.
On anarticulated locomotive or aduplex locomotive, driving wheels are grouped into sets with wheels within each set linked together.
Driving wheels are generally larger thanleading ortrailing 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.[8] Freight locomotives generally had driving wheels between 40 and 60 inches (1,016 and 1,524 mm) in diameter; dual-purpose locomotives generally between 60 and 70 inches (1,524 and 1,778 mm), and passenger locomotives between 70 and 100 inches (1,778 and 2,540 mm) or so.
The driving wheels on express passenger locomotives have come down in diameter over the years, e.g. from 8 ft 1 in (2,464 mm) on theGNR Stirling 4-2-2 of 1870 to 6 ft 2 in (1,880 mm) on theSR Merchant Navy Class of 1941. This is because improvements in valve design allowed for higher piston speeds.
Some long-wheelbase locomotives (four or more coupled axles) were equipped withblind drivers. These were driving wheels without the usualflanges, which allowed them to negotiate tighter curves without binding.[9]
Some three-driving-axle locomotives also had flangeless wheels on the middle axle, such asEverett Railroad 11, and theNZR WH class.
On locomotives withside rods, including moststeam andjackshaft locomotives, the driving wheels have weights to balance the weight of the coupling and connecting rods.[10][11] The crescent-shaped balance weight is clearly visible in the illustrative image.
In theWhyte notation, driving wheels are designated by the middle number or numbers in the set.[12][13] TheUIC classification system counts the number of axles rather than the number of wheels and driving wheels are designated by letters rather than numbers. The suffix 'o' is used to indicate independently-powered axles.[14]
The number of driving wheels on locomotives varied quite a bit. Some early locomotives had as few as two driving wheels (one axle). The largest number of total driving wheels was 24 (twelve axles) on the2-8-8-8-2 and2-8-8-8-4 locomotives. The largest number of coupled driving wheels was 14 (seven axles) on the ill-fated AA204-14-4 locomotive.
The termdriving wheel is sometimes used to denote thedrive sprocket which moves thetrack on tracked vehicles such astanks andbulldozers.[15][16]
Many American roots artists, includingThe Byrds,Tom Rush,The Black Crowes andCowboy Junkies, have performed a song written byDavid Wiffen called "Driving Wheel", with the lyrics "I feel like some old engine/ That's lost my driving wheel."[17] These lyrics are a reference to the traditional blues song "Broke Down Engine Blues" byBlind Willie McTell, 1931.[18] It was later directly covered byBob Dylan andJohnny Winter.
Many versions of the American folk song "In the Pines" performed by artists such as Leadbelly,Mark Lanegan (onThe Winding Sheet), andNirvana (OnMTV Unplugged In New York) reference a decapitated man's head found in a driving wheel.[19] In addition, it is likely that Chuck Berry references the locomotive driving wheel in "Johnny B. Goode" when he sings, "the engineers would see him sitting in the shade / Strumming with the rhythm that the drivers made."
locomotive driving wheel ratio.