From: rap@tcom.stc.co.uk (Richard Porter)
Newsgroups: rec.railroad
Subject: Re: Diesel-Electric vs. Diesel-hydraulic
Date: 16 Apr 92 13:59:28 GMT
Reply-To: rap@tcom.stc.co.uk (Richard Porter)
Organization: BNR Europe Limited

In article <92106.142557FPU08@DMSWWU1A.BITNET> FPU08@DMSWWU1A.BITNET
(Ruediger Gaensfuss) writes:

>In article <92106.113829LMASSONN@ESOC.BITNET>, Dr. Lutz Massonne
><LMASSONN@ESOC.BITNET> says:

>>Maybe the feeling was that Diesel-Electric with its additional power
>>consumption due to the conversion mechanic-electric was applicable only
>>for large traction power, whereas the typical European trains are
>>shorter than e.g. in the US or in Russia.

>Diesel-hydaulics have had much better realtionship power - weight than
>diesel-electrics. So it has nothing to do with shorter trains in Europe.
>Remember: the most powerfull diesel engine in the world was (still is?)
>the German V320 001, a diesel-hydraulic.

This was to their disadvantage in the UK. Whilst the Western Region went
its own independent way (true to the traditions of the Great Western Railway)
and ordered diesel hydraulics under the 1955 Modernisation Plan, the other
regions of BR opted for diesel-electrics. BR later decided to standardise on
electric transmission and scrapped all its hydraulic locos.

One of the arguments against the hydraulics was their light weight which
meant that they were less able to cope with unfitted (with brakes) wagons
than the big, heavy English Electric and Brush/Sulzer type 4s (later classes
40, 44-46).

The first BR diesel-hydraulics, the North British D600s, were not successful.
The later D800s (class 42/43) were a direct development of the DB V200s and
had either Maybach or MAN engines. These 2,000 h.p. machines had a lot of
teething problems, most of which had been overcome by the time they were
prematurely scrapped.

The later 2,700 H.P. "Westerns" (Class 52) were of C-C configuration like the
V300 but with a less obvious visual similarity to the German parent. They were
not the most powerful locos on BR - the Deltics had 3,300 h.p. on board, but
the Westerns could knock spots off the opposition when it came to pulling
power - a massive 72,000 lbf only recently exceeded by the EMD Class 59s.

The big advantage with hydraulic transmission is that you can put full power
down from a standstill whereas this is not possible with electric transmission
(the current would be too great for the generator and traction motors).
Consequently a Western could beat a Deltic up to 40 m.p.h. after which the
superior power of the Napier Deltic engines began to show.

Another advantage is that all the axles on one bogie are geared together
so the wheels do not slip until all four or all six let go at once. Diesel-
electrics normally have separate traction motors for each powered axle, and
until fairly recent advances in technology if one wheelset lost grip you had
to reduce power on the whole lot.

One poster asked for an explanation of hydraulic transmission. Basically it
is similar to an automatic car with the engine driving a gearbox via a torque
converter, and cardan shafts to link the gearbox to the bogies (trucks).
Some designs dispensed with the gearbox (except for reversing) and used
multi-stage torque converters. The Voith transmissions in the Class 52 had
three torque converters covering different speed ranges. Only one at a time
would be filled with fluid and providing transmission.

Ironically BR has gone back to hydraulic transmissions (Voith to boot!) for
its new generation of diesel multiple units. The Rolls-Royce powered dmus
with hydraulic transmission (Cl. 127???) were amongst the most successful
of the Modernisation Plan dmus, and I think some survive as parcels units.

Richard