AAR type A switcher truck
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Bogie Trucks
EMD AAR Type A bogie trucks were first introduced with EMD locomotives sold in 1935; they were a success, became standard on EMD switchers into the 1970s, and were also used on various other makers locomotives. Their initial design was a collaboration between Martin Blomberg at EMD and the originating foundry General Steel Castings; see U.S. patent 2,137,074 filed 1937Jul06 then granted 1938Nov15. Intended for industrial plant and rail yard shunting duty, this bogie truck has a basic suspension system with drop equalizers, secondary leaf springs and primary coil springs, which provide adequate damping and relatively simplified maintenance; it does not have swing hangers as may be seen in higher-speed designs such as the EMD Blomberg. As of this 2019 writing, these bogie trucks remain in revenue service on operating locomotives in North America.
Wheel sets on this bogie truck are typically 56.5 inch (1.435 m) standard gauge with 40 inch (1.016 m) tread diameters; wheel base is 96 inch (2.438 m); early builds have Plain#6.500x12 journal bearings allowing 62750 Lbs (28.46 tonne) Axle GRL; later builds have APcGG#6.500x12 conical bearings allowing 70000 Lbs (31.75 tonne) Axle GRL; various gears and trac motors (EMD#D17+D27+D37+D47+D57+D77+D78...) have been used, though rebuilds typically have a 62tAxleBull~15tMotorPinion gear ratio and EMD#D78 motors; maximum stable speed is typically 45 MpHr (72 KpHr).
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