I was reading the Wikipedia article about Rail Diesel Cars in which it states that these cars are powered by two diesel engines, each of which drives an axle through a hydraulic torque converter. My question, why not use a conventional diesel electric power-train to power RDCs? Among the RDC’s precursors were CN’s pioneering rail cars of 1923-1930, which were powered by 185 hp diesels mounted directly above the drive axle and traction motor. From what I’ve read, these early railcars were a resounding success and encouraged further diesel development and eventual replacement of steam. No mention anywhere of problems with the diesel electric configuration. I’m thinking that maybe the electric generator was too bulky, using up room that could have been occupied by fare paying riders.
I asked a similar question to an officer of Alstom several years ago. And his answer was that there are some in Europe. But, nothing like that has met the approval or acceptance because of US standards. I think it would be great for an MU to come to the end of the wire, a diesel hook up front or rear and feed an electric service to the MU’s exactly like from the wire or third rail. But the problem might also be the need to produce enough power to feed ten or 12 car lengths of motors when needed. I am sure there are many engineering problems which have to be considered and it not be just like a plug in power pack.
Inquiring minds want to know. I long wondered the same thing, why were the RDC’s, and their SPV2000 attempted successors diesel-hydraulic instead of diesel electric, so thank you for starting this thread, and hopefully an expert will give us a correct and easy to understand answer.
May we expand this? My commuting vehicle, along with my bicycle, is NJ Transit’s Riverline. What’s its diesel type power, and the handful of other recent North American diesel railcar operations?
And what about Colorado Railcar? What was, or is, since I think some of their cars still operate in Florida or Texas, its power?
As usual, I can’t resist to promote my yacht, it’s straight air with a diesel backup.
The mechanical drive is a much simpler arrangment.
It’s pretty well suited to a self propelled car since you can get a decent match between engine output and car propulsion requirments with the torque converter.
$$$$$$$$$$$$$$$$$!
That’s why. The mechanical drive was way cheaper and I believe it used existing truck/bus parts for the expensive bits. Since they were in an application where there was a good service life, why not just pocket the money? Electric drive still made sense for heavier duty or extreme service life. It is the same thinking behind Gensets.
The downfall of the RDC was the SPV. The space age electronics and engineering failed on the rails. Thus Budd lost big on it.
I expect that the “decent match” gave Budd reason to void any warranty if an RDC was used to draw an unpowered car.
The New Haven RDC-based Roger Williams had traction motors, to allow continued operation into Grand Central Terminal on the third rail, with diesels shut down. I think it was still primarily diesel-hydraulic, though.
You have an unlimited supply of Other Peoples Money? - the investment in infrastructure and additional equipment is not justified on its own. The cop outs that it’s “modern’” (hardly); environmentally friendly (not really) or more efficient (hardly) won’t fly with the folks paying the operating costs.
The NH solution was a unique fix on an old headache in NYC’s buried R/W which worked rather well. Don’t try applying that on a larger scale unless all your utopian dreamers want to cough up some serious $$$$ to benefit a relatively small group.
A little diesel engine that runs a generator and traction motor is that much more expensive than that same diesel powering a hydraulic torque converter?
the hydraulic pumps and motors are so much more reliable today than even 5 years ago. Note how much construction / mining equipment uses them instead of electric motors except for very large units. Most operators seem to like the hydraulic types better. Isn’t a torque converter just a hydraulic type motor ?
At the very least a torque converter is a term that helps fool me into thinking the person using it knows more about engines than I do.
That’s interesting…you just used it yourself.
Not knowing what it means would never stop me from using it in conversation, after all I’m a trains.com contributor with a reputation to uphold.
Just google “torque converter”…read for five minutes and voila… you’re there.
I would opine that the torque converter option works well for things like RDCs because it is commonly built for that level application. Large truck automatic transmissions handle similar loads on an everyday basis. And for that reason, the parts and service are easily available.
I’m not sure that suitably sized traction motors are as common.
The Europeans have applied the principle to “full scale” locomotives with some success. OTOH, SP and Rio Grande experimented with Diesel-hydraulics and decided they didn’t fit the bill.
What’s suitably sized for a traction motor? I’m a long time jolly trolley boy, and I would think that streetcars, subways or at least electric multiple unit railroad coaches have suitably sized traction motors. What’s wrong with those size motors that they couldn’t go into a diesel electric railcar?
Yes. More parts plus a control system.
It’s why automobiles (up until very recently) have had mechanical transmissions and not electrical ones.
No, and it will pay you to read up on why the two are different, and then work backward to see why torque converter drive from truck diesels is such a good idea for underfloor railcar drive. (While hydrostatics, for example, for railcars and locomotives meets with far, far less satisfaction…)
It may also be useful to look at how diesel-hydraulics (the successful ones imho all involving torque converters or fluid couplings of some kind) have been built for locomotive applications, most notably the Krauss-Maffei Amerika-Loks, and where the detail design succeeded and failed.
Note that one of the so-far-underdiscussed points about the RDC vs. typical EMC-style ‘doodlebugs’ is the idea that very little of the ‘floor area’ of the car needs to be taken up with machinery. Aside from the complication of diesel-electric drive, you’d need to carry the main generator or alternator and all the switchgear under the car, and arrange to keep it out of the weather and at least nominally accessible for service. But assume that you’re going to have to ‘get out and get under’ when any of the complex stuff gets deranged… for example, when the main generator flashes over.
Now look at the effect of having even streetcar motors nose-suspended on the drive axles vs. a simple Spicer-style drive and Cardan shaft. Lots of mass down low, acting laterallly on the track. Lots of unsprung mass to hammer the track vertically… and the resulting shock, for example, making carbon from brush wear bounce up to short commutator segments. Contemporary motors and control technology were far from ‘sealed power’!
The real issue with the SPV2000 was that it had horsepower-to-weight that really required all four axles to be driven… which was no particular technical problem (IIRC Metro-North in fact had the kits on hand to do
I had thought that a powered RDC or two could haul an unpowered trailer, but apparently not - see:
http://en.wikipedia.org/wiki/Budd_Rail_Diesel_Car#Variants
Evidently there was only ever a single unpowered RDC trailer built - see:
http://en.wikipedia.org/wiki/New_South_Wales_1100_class_railcar#Construction
“BRB 1181 was the only Budd Rail Diesel Car in the world built as trailer.”
- Paul North.