Note that there is a ‘packaging’ formula for most diesel-electric locomotives: pivoted trucks (or span-bolster assemblies) somewhere near the quarter points of the bed frame, engine in the middle of the span, large fuel tank suspended between frame and rails. The first thing that happens with an articulated locomotive is that you lose the cantilever benefits of pivots at the quarter points where the frame bears on the articulated truck. You also will probably have to have a specialized bolster with two separate pivot locations, appropriate seals or bulkheads at each end of the separate unit, more need to balance components between the units if they are not absolutely common to each “end”, etc. (My understanding is that it is more difficult to accompli***raction-motor cooling in a C truck articulated this way, for a variety of reasons).
I looked at articulated locomotives rather carefully in the early 1970s, and there are some other concerns. If you ‘standardize’ on a single design of carbody module for a given class of locomotive, you automatically have two cabs on the completed locomotive, or none if you go with boosters (which I have never particularly liked in high horsepowers) You have no capability of using the articulated underframes for other purposes – not that you’d have much re-use for the single long bed frame either, but it’s cheaper and gives a more rigid bed for the ancillaries. The weight-packaging problem is the real issue: it’s almost impossible to get the weight properly balanced between the full truck on the end and the half-truck in the middle without cutting into allowable cab room, or increasing forward cantilever length (which has implications on tracking and equalization for the end trucks). My personal observation was that very careful extended side-bolster support for the middle truck was also necessary, but this might have been ‘overkill’ in design since my interest was in high-speed power at the t
By the way, weren’t the Milwaukee’s Bi-Polar electrics a double articulated locomotive in three sections, with the center cab and driving units on either end?
Note that the ‘cab’ at each end is in unit with the hood. Each eight-wheel truck is rigidly attached to its respective end unit, with the 1-B truck allowed to swing with a centering device. There are ‘ball-and-socket’ joints between the truck frames, and my understanding is that all buff and draft forces go entirely through the underframe. The center “box” is carried entirely by the adjacent carbodies (and has, or had, the train-heat boiler etc. in it)
This really makes the locomotive more like two semipermanently-coupled 1-B+D units rather than an ‘articulated’ locomotive in the classical sense (which would involve the center unit being carried by pins or mountings on the trucks or on span bolsters, not on the adjacent carbodies). Of course, since the undercarriage IS fully articulated, I consider an EP-2 an articulated locomotive with ‘somewhat unusual carbody structure’.
Perhaps interestingly, look at this locomotive, on the same site as the bipolar picture:
This illustrates a rather interesting variant of a ‘span-bolster’ idea – these are full span frames, complete with ‘front porches’, and a shorter center-cab carbody.
To get back to the CC200 and its centre truck, it struck me that there might be some vertical travel on the pivot, perhaps with a concentric coil spring to allow vertical translation as well as tilting to occupy all that space allowed.
The Japanese had some locomotives of this general type, with air bag secondary suspension on the centre truck which was deflated to increase adhesion on the driven trucks on track where higher loads were acceptable. This was presumably able to account for vertical curves with pressure relief valves.
I was thinking exactly the same thing – hey, just like an HO-scale lead truck…
The only thing is that I don’t see any telltale spring silhouette in the picture, and I’d think a spring of the required diameter and strength would ‘show’. Of course, the spring arrangement might easily be carried inside the carbody, with only the shaft of the pivot extending through a collar or bearing…
The B-B-B locomotives are generally regarded as much easier on curves than the equivalent C-C, and no worse than than a B-B. The centre truck doesn’t have to do anything other than hold up the centre of the unit. The two end trucks do all the guiding, and the centre truck can just follow the track. The suspension is designed to allow free lateral movement, and shouldn’t apply any excess lateral force to the rails. They have been very successful in Europe, in Switzerland and Italy particularly (although the Italians also have a large number of articulated B-B-B locomotives as well as more recent rigid units).
Regarding the comparison of B-B-B being easier on curves than a C-C, does that include C-C’s with radial steering?
One other point of interest. If this mid-truck concept works for locomotives, why not use it on freight cars to increase load limit above the current 286k/soon to be 315k limit? Frankly, with the advent of radial steering in three axle trucks, I would think the three axle truck would be the way to go for increasing load limits on freight cars. Then again, with standardization, it is probably cheaper to go 2-2-2 using run of the mill three piece trucks than to go with the hassles of radial steering components.
Since the 286K/315K issue is primarily related to covered hoppers, I don’t think that the idea of a mid-frame truck is a practical solution since most covered hoppers empty from the bottom. Also, since freight car trucks are not actually attached to the frame, it might be too expensive to consider a mid-frame truck since lateral-play devices and other such hardware would have to be considered.
Good points. My thoughts were that a mid-frame supporting truck on an 86’ boxcar would increase the load limit from the current 180,000 lbs (286,000 lb gross) to around 300,000 lbs (at 429,000 lb gross). Or take a plastic pellet hopper and add the mid frame truck (between unloading chutes) to allow it to carry grain at up to 350,000 lbs payload. This assumes that the weight bearing characteristics are equalized among the three trucks. I’m not sure if that is possible.