I honestly forget where I read this so forgive me. Whatever became of the locomotives that raise an unpowered axle or lower a powered axle to improve traction? The adhesion of locomotives and their immense weight has always fascinated me and this innovative solution sounded good but I wonder how it worked out in practice? Was there a scientific comparison of raising unpowered vs. lowering powered axles or did it just consist of raising the unpowered axle to put more force down on the powered axles?
The Only ones I know that can do that is the NEw GE EVO AC44C4. The Only Road that has them is the BNSF. They get the Pulling power of a DC GE44EVO but the Reliablity of an AC Traction motor System. Crews from what my scanner is saying they like them and they run them on about anything there is from General Merchandise to the Hottest Pigs. Also the Axle can only be lifted at speeds below 15 MPH.
IIRC from what I have read and heard from teh crews. The center axles can be moved to put 15% of the weight that they carry onto the outer axles but they never leave the rail. How this is done is with Air cylinders and bellcranks. However just moving that much weight is something to see.
The middle axle on BNSF’s ES44C4s can be lifted while moving, which spreads the weight out over the other two axles. The original idea was to lash these up & run them between LA & Chicago on the Transcon, the modern version of Santa Fe’s Dash 8 40BWs. From what I understand, they were successful (although can be found working every where, on all types of trains) & BNSF now owns 53 units, 6600-6652 with more on the way in 2011 (or so I’ve read). Below are a few pictures of BNSF 6613s front truck & middle axle.
The problem of adhesion in A1A-A1A locomotives was first encountered back in the day of the A1A equipped “Covered Wagon” first generation passenger diesels, where four traction motors was sufficient power to move the unit at passenger train speeds and the unpowered axle was used for weight distribution. Railroads operating such units encountered adhesion issues on steep grades particularly in wet rail situations [rain or snow] and so worked with the locomotive builders to modify the bogie’s to provide greater adhesion by reducing the load distributed via the centre unpowered axle.
Adhesion of steel wheel on steel rail is a formula of the total weight of the locomotive and the percentage of that weight applied to the rail via the powered [or driven axles in the case of steam] versus the percentage applied via unpowered axles. The exact formulas and percentages are the stuff engineers get excited over due to all the maths and rail conditions so I wont go into that.
As for the ES44C4, the following quote is from Wikipedia and may help explain how it works;
ES44C4
The ES44C4 (Evolution Series, 4400 HP, AC traction, 4 traction motors) is the newest model in the series. It is similar to the ES44AC, except that it has four traction motors instead of six. The center axle of each truck is unpowered, giving an A1A-A1A wheel arrangement. BNSF is the launch customer for this model, ordering 25 units numbered 6600-6624.[3]
A unique feature of these units is that there is a variable traction control system in their computer systems. One of the differences between an ES44AC and an ES44C4 are the air cylinders and linkages on the truck side-frames of the ES44C4; these are part of the traction control system. Every time a variabl
There is no air bag involved, in fact there isn’t an air bag on any modern US freight loco truck. I don’t know what you see but there are two extra air cylinders (they are using standard air brake cylinders) that connect to a lever tied to a rod with a bellcrank connected to a chain that puts an upward force on the journal bearing housing. The cylinders and lever are all that is visible on the side of the truck but the GE patents on the system show how it works. If you search the US patent office files you can find them.