I’ve always wondered how a diesel loco can move such great tonnages without stripping the teeth off the motor shaft also just how the gear is attached to the motor?? how does it all work together has baffeled me since the mid-50’s. Is there a book on this that doesn’t get all big worded and thecnological but just puts it into the average persons language? new to this site I think I’m in the right area to post this question.
A mechanical engineer had to properly calculate the stress loads involved, what type and strength steel could handle that load, and what it’s service life would be. Lets give a round for all the engineers out there…
Adrianspeeder
That sounds to me like a biased answer. [;)] [8D]
Hmmm, you wouldn’t be an engineering student, would you? (Like I didn’t know [:D] )
Well I’m going to say a little something here that was explained to me. One of the reasons why locomotives are able to haul great tonnages in a single load is because of resistance. There is virtully very little friction of the steel wheel on the steel rail. Also the contact surface of a locomotive’s wheel on rail is only three inches, therefor there is almost no rolling resistance.
In the most simplistic of terms there is a Diesel engine driving electric generators which provide power to electric (traction) motors that, in turn, pass through a transmission and finally power to the wheels. This “thumb nail sketch” is teally too brief for more than clearing up any mistaken notions that the “drive train” is from the Diesel engine to the wheels. Happy rails [swg]
When you think about it a locomotive like a dash 8 -40B rated @ 4000hp puts 1000 hp to each traction motor under full load. That is quite a load on the pinion gear teeth. Sometimes they do break and then you really have problems.
Lower friction between the locomotive’s wheels and the rail is bad. The friction between the locomotive and the rail is what allows the locomotive to move the train.
But Sara, the less resistance the cars have to have them roll easier also hurts the locos that would like to have a high contact force to get the train moving. Hence the use of antiwheelslip controls and sand.
Adrianspeeder
I think your question is about the traction motor gearing, in particular the pinion gear on the motor shaft.
The first step is to find out the maximum torque the motor can produce. This is what you need to design to. The pinion is fit onto the shaft with an interference fit. That is, the inner diameter of the gear is less than the outside the diamter of the shaft so that there is constant pressure between the gear and the shaft. The total area of contact between the two determines the amount of force that can be transmitted before it slips.
The size and shape of the gear teeth determines how many teeth are in contact at a time and what the contact stresses will be. The gears can be case hardened or induction hardened to improve the overall strength and wear characteristics.
Finally, the lubrication system needs to designed. The lubricant has to be able to minimize tooth wear which would cause severe vibration.
The basic design on an EMD traction motor has actually changed little over the years, even as maximum torque has increased. The design has been tweaked to allow for higher forces, though. Most notably, the tooth design changed with the advent of the SD50s, allowing an increas in the number of gear teeth in contact at a time, although they are smaller teeth.
And, the lubrication has gotten better over the years. In the early years, an asphalt based compound was used (“crater”). Specially formulated greases replace
Ah… oops. Let’s not confuse rolling resistance and drag with tractive effort here! Sara is dealing with rolling resistance, and is quite correct that one of the reasons that rail transport is so successful is the very low rolling resistance of a steel wheel on a steel rail, combined with the very low friction in the journals (roller bearing journals have very low friction at all times; the older type had a moderately high static friction, but much the same friction as a roller bearing once they were moving).
Adrian, you’re talking about tractive effort. What is wanted here is a reasonably high resistance to sliding between the wheel and the rail and, curiously, this is quite compatible with low rolling resistance. Once a wheel really starts to slip, though – whether it is because of trying to put too much tractive effort through an axle or because the brakes are applied too hard – you go from static friction (high) to sliding friction (low) and the sliding will just keep going unless you reduce the tractive effort applied (wheel slip controls, brake release) or increase the sliding friction (sand).
So if we look at the whole picture, low sliding friction is good in the truck jour
Got all of that st[paul?[:O]
I remember reading something about NYC discovering in one case one axle of a C truck (probably the middle) was spinning merrily along at over 100 mph as its brothers ran at track speed, like they should. Obviously from the days before wheel slip technologies were applied.
I am sure you know this, but for those who do not, force and torque are not interchangeable.
[:)]
Thanks to all for the information I now understand how this is possible.
This is a good thread.
So can we have more info on the “crater compound”?
Adrianspeeder
Torque can rightly be thought of as “rotational force”.
From what I remember, it some sort of petroleum goo - sort for like tar or other refinery bottoms. What I REALLY remember is that the stuff was a mess, and if you got any on your work boots, you’d leave a messy trail all over the place.
My vote for the most interesting but not often discussed aspect of a Diesel-electric locomotive is the air cooling of the traction motors.
No transmission is 100 percent efficient, the losses in a transmission generate heat, and that heat has to go someplace. Even hydraulic transmissions are not 100 percent efficient — people pulling boats or house trailers often have to add transmission oil coolers to their rigs or risk burning up the transmission.
The electric drive is generally regarded as more rugged than hydraulic drive, but that ruggedness depends on cooling the generator and especially the traction motors, which are squeezed into the tight spaces between the wheels. My understanding is that traction motors are air-cooled – liquid cooling would present all kinds of complications. That air cooling depends on blowing a lot of air into the traction motor housings.
I have the impression that early generation Diesels (F’s and Geeps) had traction motor blowers for each traction motor, but later generation units had a centralized blower run off the main engine shaft and a system of blower ducts to get the air to the motors. I suppose the details of these systems varied between manufacturers as well – didn’t U-boats have a mechanical radiator fan while EMDs pretty much used electric fans?
Cooling air for traction motors and main generators.
The early GPs and Fs did have separate motor driven blowers, powered from the aux alternator (same as what powers engine cooling fans). I can’t remember if it was one per motor or per truck…
Later, starting with the GP30, EMD used a single blower, shaft driven from the “rear” of the diesel engine (which is at the front of the locomotive). The air was carried back to the rear truck through a duct on top of the fireman’s side walkway. (They put a matching duct on the engr’s side of the GP30 for styling - it wasn’t functional)
GE started out with a single shaft driven blower that pumped air into a plenum that was the space between the underframe I beams and the top and bottom cover plates.
All of these arrangement were satisfactory, but none were optimum as most of the time too much cooling air was being supplied. For example, in N8 at 12 mph, you need lots of cooling, but at 50 mph, very little. Since these are sizable blowers (>100 HP on a six axle at N8 engine speed), it was a big waste of fuel.
GE’s solution that began with the Dash 8s was to go to a front an rear motor driven blower with a “cycle skipper” to allow the motor to run and 1/4 or 1/2 speed. EMD used a mechanical vane arrangement to choke off the air flow into the blower.