Diesel-Electric v Diesel-Mechanical MU

[moonrakerz]

Really interesting thread !!!

 

[LE Greys]

I presume you don't drive a car? From the gearchange point of view a first generation DMU is easy, no clutch. Basically it's open the throttle, wait until the revs reach a certain point (marked "change up" on the rev counter, to make it nice and simple), close the throttle, wait a few seconds for the revs to die down, select the next gear, wait a second or two, open the throttle and so on and so on. The only skill is to time the changes right to get a smooth change, but it's more about not rushing than anything. To stop just leave it in top gear and then knock it into neutral as it comes to a stop. Simples. The real skill in driving first generation DMUs is the vacume brake.

Not cars, but I have driven steam locos. There, it depends on the type of reverser you're using, but to lengthen or shorten the cut-off, you can leave the regulator where it is (fully open sometimes) if you have a steam or screw reverser. With pole reversers, you have to close the regulator, otherwise the pole can do strange things (it's hard enough to shift as it is), but you then just open it again. When drifting, stick it in mid gear with the regulator mostly closed (just open a bit to prevent a vacuum in the cylinders). It's actually possible to drive entirely on the reverser with the regulator wide open, but I've never tried it.

From the few times I've tried to drive cars, it gets very confusing. Internal combustion seems to work the whole thing backwards, you can't just drop a gear to save power. It's a bit like a pole reverser, but not quite.

 

[strange6]

Hmm, fascinating. I have noticed the much smoother upchange on modern units (and buses) and remember how clunky the 101s could be sometimes, but I honestly had no idea that the driver would have to decide when to change gear and control the throttle. They must have been a lot harder to drive, and I take my hat off to them.

Quite often that clunking sound was due to the driver not leting the engine revs drop down enough before he changed gear. If done too often, mechanical bits would begin to break. It was a real art driving these things smoothly and properly.

 

[RobShipway]

So Chris would you say that it is like going from driving a manual 5 geared car (First Generation DMU) to a semi - automatic Honda Civic as I have now which I can either place in automatic mode or push the gear lever up to go up the gears or down to go down the 6 gears that my car has on it?

 

[notadriver]

The gear changing operation is totally transparent to the driver Robbies. Driving a train is nothing like driving a car.

 

[seagull]

From the gearchange point of view a first generation DMU is easy, no clutch. Basically it's open the throttle, wait until the revs reach a certain point (marked "change up" on the rev counter, to make it nice and simple), close the throttle, wait a few seconds for the revs to die down, select the next gear, wait a second or two, open the throttle and so on and so on.

Yes indeed it appears easy enough. But I do remember one or two historical trips from Manchester Picc to Sheffield (Hope Valley line) where a three car 101 (i.e only two powered cars, front and rear) had been used, or, worse still, a 'Power-Trailer' 2-car 101, instead of the more normal 'Power Twin' 101.

Then, when ascending one of the steep climbs on that route - revs max out, close throttle to let revs drop, change gear, only by the time the driver's done that, the speed's dropped drastically so that the gear change works but nearly stalls the engine... so back to square one again...

Yes, drivers of modern units don't know how lucky they have it - although having said that, it must have been a lot less boring driving the old DMUs.

 

[Smudger105e]

Don't think the 60s even have WSP.

Correct, no WSP (ABS to the layman!) on class 60's