dumpsterman I see your point of having to shop the whole engine which is actually two engines in one. as you pointed out that three engines are the typical train but at full throttle isn't the limits of the knuckle exceeded? and with the current reliability of todays engines I don't think the failure rate would be that high. did you consider my theory of the one engine of a two-engine locomotive providing electrical current to both sets of traction motors if that is possible or would that be too complicated technology? it seems that fuel reduction is the main purpose today and the gensets seem to use that technology wouldn't that work for road units as well? are we at the limits of locomotive size and horsepower?
I see your point of having to shop the whole engine which is actually two engines in one. as you pointed out that three engines are the typical train but at full throttle isn't the limits of the knuckle exceeded? and with the current reliability of todays engines I don't think the failure rate would be that high. did you consider my theory of the one engine of a two-engine locomotive providing electrical current to both sets of traction motors if that is possible or would that be too complicated technology? it seems that fuel reduction is the main purpose today and the gensets seem to use that technology wouldn't that work for road units as well? are we at the limits of locomotive size and horsepower?
Genset locomotives do allow a single engine to power both trucks. There are some Genset designs on the market that are aimed at use in road freight operations in addition to switching work.:
http://www.progressrail.com/repowered-locomotives-PR43C.asp
However, my understanding is that the Genset combination is most efficient in locomotives that spend a lot of time operating in part load conditions ,i.e. yard switching where full throttle is not often applied. in the case of a 4300-4400 AC drive road unit where the prime mover (the Diesel powerplant itself) spends a lot of time operating at high RPM's a single engine is more efficient..
As far as limits in locomotive size, bigger units would require a lot of expensive rebuilding of track, roadbed and clearences.
The railroad industry in North America finds 4300-4400 HP per unit fit current train operating practices and provide efficient fuel consumption..
as far as the future, time will tell..
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
The mathematics of reliability engineering are against a multi-engine road locomotive (which usually needs most of its horsepower). Two engines on the same underframe are "serial" components, that is, you need both to make the whole, so to speak. If one engine has a reliability of 90% (it is available for work 90% of the time), two engines will have a reliability of 90% times 90% or 81%. Union Pacific learned this with the famous "twin diesel" EMD, Alco and GE units of the 1960s and 1970s. when one of two diesel engines failed ... the whole locomotive ended up being shopped. Southern Pacific learned the same lesson with the twin-engine Krauss-Maffei diesel-hydraulics.
If we're talking about yard units (which seldom need full power), the reliability math would say that a 3 engine Gensets switcher would have a reliability of 72% (90% cubed), but the 2nd and 3rd engines aren't needed much as on a road unit. Multi-engine yard units are different animals, they exist to minimize exhaust emissions, making full power like a road unit is not as critical.
On the other hand, the single-engine math also points out why the 6000hp units of the 1990s with one engine each were essentially flops. A pair of 6000hp units were intended to replace three 4000hp units, but the reliability of the extremely-complex 6000hp units resulted in per-unit reliability so low that a pair of 6000hp was riskier than a triplet of 4000hp. If one of two 6000hp units died, a train would be dead except in very-low grade or flat territory (the train would likely stall), whereas if a triplet of three 4000hp units lost a single unit, they usually could make it to terminal but at a lower speed.
You might ask "Why are modern airliners frequently 2 jet engined replacing older jets with 3 or even 4 jet engines?" The answer is in the inherent reliability of such newer 2-engine jet aircraft. The planes and their pair of advanced jet engines are significantly more reliable than the previous equipment.
I have always been curious if any builder or railroad has expressed interest in a dual engine locomotive such as the DD40 etc? in the day unit reduction was a big selling point and the large horsepower race was to run one locomotive on trailer trains or whatever. didn't conrail order the SD 80macs for that purpose? but then run as a pair if one unit failed then too much loss of horsepower/traction would leave the train stranded. I have thought of a design similar to this one but have taken it further. could it be possible to build a dual-engine locomotive with 2 12v710 engines rated at 3150hp each on a heavy c-c or d-d truck and that the engine operate as two locomotives in one? is it possible to divert the electrical current to both sets of tractions motors if one engine failed? same as a mother/slug setup. my theory is that 2 of these dual-engine locomotives would have sufficient horsepower/traction to handle the typical train. under low horsepower/traction needs each engine would alternate its running time and under full horsepower/traction demands both engines would run. would this be possible and does it make any sense?
Where's the dynamic brake fan?
What you have there is a DD75Ace...
Not likely but EMD did test a prototype 4 axle truck back in the 80's that while not desigend for AC traction motors, was articulated and self steering, IINM...
A 4 axle fixed wheelbase truck provides more stress on curved track than carriers are likely to tolerate.
Never too old to have a happy childhood!
Those trucks won't work right -- HTCR radial steering works with steered axles to either side of a fixed one. B steered trucks can use their center pin location as a reference. But four steered axles aren't going to do well. You'd be better off with four B trucks and span bolsters if you need that many axles.
Not sure about those outward-facing traction motors on the inner truck ends...
Good Day,
My imagination at work…………..Presenting today is the EMD SD75ACe. The original SD70ACe drawing was created by Michael Eby. The drawing was modified and painted by me.
Did I ever mention...........I like the MKT railroad. I saw the “Katy” F3’s and GP7’s often in the 60’s.
Maybe it should be a SHD75ACe............Special Heavy Duty.
H--Heavy
Regards,
Swafford
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