BNSF ET44C4 Trucks and Locomotive Page February 2016 Trains Magazine

[M636C]

 

When is a brake cylinder not a brake cylinder?

 

When it is being used to adjust the weight on the axle....

 

The two "additional brake cylinders" each side on the central axle of an ES44C4 or ET44C4 (as described on the "Locomotive" page in the Feb 2016 Trains) are used to reduce the axle load on the centre axle on starting by changing the spring force on the axle. (I'm not sure of the exact method of load reduction in this case but the crank coupled to the two cylinders actuates the mechanism...)

 

But these are not "brake cylinders" in this application because they don't operate as part of the brake system, although they could be fitted as brake cylinders if removed from the weight transfer system during an overhaul and refitted as brake cylinders.

 

They would best be described as "weight transfer cylinders" in this application.

 

The former Soviet railways used air cylinders to reduce the axle load on the leading and trailing trucks (and increase that on the coupled axles) of the class LV (LV = Lebedyansky design built at Voroshilovgrad) 2-10-2 built in the 1950s by changing the fulcrum of the equalising beams that shared the loads between the coupled and leading and trailing axles. These were also brake cylinders in a different application. The same mechanism was applied to the larger and heavier Chinese QJ class (at least initially). I don't know if this equipment is fitted to any QJ locomotives in the USA, or if the idea was abandoned before those locomotives were built.

 

Does anybody share my view on this?

 

M636C

[Wizlish]

M636C

The two "additional brake cylinders" each side on the central axle of an ES44C4 or ET44C4 (as described on the "Locomotive" page in the Feb 2016 Trains) are used to reduce the axle load on the centre axle on starting by changing the spring force on the axle. (I'm not sure of the exact method of load reduction in this case but the crank coupled to the two cylinders actuates the mechanism...) But these are not "brake cylinders" in this application because they don't operate as part of the brake system, although they could be fitted as brake cylinders if removed from the weight transfer system during an overhaul and refitted as brake cylinders.

Here is a pretty clear picture of the arrangement as applied to a Hi-Ad truck:

and the explanation of how it works is perhaps best started with reference to one of the applicable patents (20100175581 A1), which can be downloaded and perused here:

http://www.google.com/patents/US20100175581

Note that they cover both the use of 'compliant members' to lift the axleboxes, and a chain to lift the center of the axle.  The two cylinders acting on the lever are to equalize the 'pull' on the central shaft, in part to allow it lateral excursion as the center axle moves on curves. 

Note the emphasis on rapid release of the 'lift' on brake application or when wheelslide is detected.

Interestingly, although the patent goes into considerable detail about the actuators and their operation, it does not claim that ordinary brake cylinders could either be used or adapted to this service to reduce the number and variability of parts to be stocked -- as I agree is the case with the design as produced.  However, there is little to no likelihood that either cylinder location could be used for brake rigging to the center axle, if that was being suggested.  (There may also be specific optimizations to the cylinder structure or valves that make them unsuitable as one-to-one replacements with actual brake cylinders, even though they share many common parts - someone like buslist with more experience than I have can look at the drawing of the cylinder and decide if it reflects current air-brake practice.)

As noted, this system is different from a 'traction increaser' like Miller's that throws extra weight or load on the frame, or that pushes down on powered axles (e.g. with steam cylinders) to increase their load in some more direct fashion.  The patent discussion, I think correctly, goes into why unloading idler axles is a better approach.

 

 

(Just in case anyone wonders, this approach won't work on the P4s because they delete the 'end' traction motors that overhang (the ones inboard, adjacent to the tank) and any attempt to control traction by lifting that axle would fail in a number of ways...So presumably it's the advantage of the radial=steering truck (and more granular individual-inverter axle control) that will reduce slip propensity when appropriate.  Presumably they will have timed autosanding, the equivalent of modulated excitation, etc.

Also BTW: the HTCR-6 trucks are in testing...)

[M636C]

Wizlish,

Thanks for the patent.

While I can normally follow such things, this one seems obscure.

I understand the variable stiffness springs and the cylinders, crank and chain.

But it looks to me as though the centre chain is all that lifts the axle.

If not what have I missed?

M636C

[Wizlish]

M636C

But it looks to me as though the centre chain is all that lifts the axle. If not what have I missed?

It looked to me as if they were hedging their bets a bit.  Part of the discussion and drawing (4B, I think, without reopening the patent) involves the rotating shaft lifting 'compliant means' on the individual axleboxes, while the diagram that shows the 'chain' carefully ignores how the 'far' end of the chain actually connects to the axle.  Presumably there would be a clevis or yoke to something like the axle end of a traction-motor frame (running on machined parts of an idler axle corresponding to the TM support areas on an axle with a bull gear installed) but I do not know for sure.  I do think it makes better sense, given much of the discussion in the patent, to lift the idler axle at the center than by the tops of the axleboxes.  (I came across a reference that seemed to indicate a witness could see 'daylight' under the idler at times, but I found that hard to believe...)

I looked but could not find good pictures of the method the actual C4 trucks use.  I feel certain there are pictures, and that there will be more and better ones soon, and I look forward to seeing what the actual arrangement turns out to be.

[M636C]

For some time now GE DC motors have used roller suspension bearings so I assume that the AC motors do too, even though they are lighter.

So a roller bearing suspension tube attached at the end of the chain sounds likely.

M636C