I recently spent some time in Teignmouth and had occasion to take a FGW train
to/from Exeter. I don't know what models FGW uses - the set going to Exeter was
definitely an older 2 car set, the return trip was still two car but much newer.

I thought most modern trains were diesel electric. That is, the diesel ran at
constant speed power an genset, which in turn provided electricity to drive
electric motors.

What seemed strange to me was that the engineer raised the RPM of the diesel
prior to leaving every station - almost as if he were engaging a clutch. Was the
the diesel directly driving the train?

On Sat, 09 Jul 2011 08:55:17 -0600, Robert Neville
wrote:

I recently spent some time in Teignmouth and had occasion to take a FGW train
to/from Exeter. I don't know what models FGW uses - the set going to Exeter was
definitely an older 2 car set, the return trip was still two car but much newer.

I thought most modern trains were diesel electric. That is, the diesel ran at
constant speed power an genset, which in turn provided electricity to drive
electric motors.

What seemed strange to me was that the engineer raised the RPM of the diesel
prior to leaving every station - almost as if he were engaging a clutch. Was the
the diesel directly driving the train?

I don't know much about trains, but does the speed of the diesel
engine not increase when more power is needed, as when accelerating
from a standing start? Ordinary physics suggests more energy would be
needed at that stage.

In message , at 08:55:17 on
Sat, 9 Jul 2011, Robert Neville remarked:
I recently spent some time in Teignmouth and had occasion to take a FGW train
to/from Exeter. I don't know what models FGW uses - the set going to Exeter was
definitely an older 2 car set, the return trip was still two car but much newer.

I thought most modern trains were diesel electric. That is, the diesel ran at
constant speed power an genset,

Not at constant speed. It will run at a speed necessary to generate the
amount of power (electricity) demanded by the driver...

which in turn provided electricity to drive
electric motors.

What seemed strange to me was that the engineer raised the RPM of the diesel
prior to leaving every station - almost as if he were engaging a clutch. Was the
the diesel directly driving the train?

....which will be higher (more revs) when the train is starting from
rest.
--
Roland Perry

Robert Neville wrote:
I recently spent some time in Teignmouth and had occasion to take a
FGW train
to/from Exeter. I don't know what models FGW uses - the set going to
Exeter was
definitely an older 2 car set, the return trip was still two car but
much newer.

I thought most modern trains were diesel electric. That is, the diesel
ran at
constant speed power an genset, which in turn provided electricity to
drive
electric motors.

What seemed strange to me was that the engineer raised the RPM of the
diesel
prior to leaving every station - almost as if he were engaging a
clutch. Was the
the diesel directly driving the train?

This is normal for diesel electrics. The driver (engineer indeed! - this
is not the US) does nothing other than open the throttle, but the train
doesn't move until the generator is producing enough power for the
motors to start turning. It is possible to avoid the time lag by being
able to vary the generator excitation rate, but it is probably not
considered worth while to fit this for a general-purpose DMU.

Eric

Roland Perry wrote:

Not at constant speed. It will run at a speed necessary to generate the
amount of power (electricity) demanded by the driver..

Ah... Just hadn't noticed that before.

Eric wrote:

This is normal for diesel electrics.

Thank you...

"Robert Neville" wrote in message
...
I recently spent some time in Teignmouth and had occasion to take a FGW
train
to/from Exeter. I don't know what models FGW uses - the set going to
Exeter was
definitely an older 2 car set, the return trip was still two car but much
newer.

I thought most modern trains were diesel electric. That is, the diesel ran
at
constant speed power an genset, which in turn provided electricity to
drive
electric motors.

None of FGW's 2 car DMUs are diesel electric - I'm sure the only diesel
electric units (ie DEMUs) in use in GB are the Voyagers and Meridians.

The latest new small DMUs (the 172s used by LO and Chiltern) aren't diesel
electric either, and have surprisingly gone back to mechanical gearboxes
following the widespread use of hydraulic gearboxes...

Paul S

"Paul Scott" wrote:
None of FGW's 2 car DMUs are diesel electric - I'm sure the only diesel
electric units (ie DEMUs) in use in GB are the Voyagers and Meridians.

The latest new small DMUs (the 172s used by LO and Chiltern) aren't diesel
electric either, and have surprisingly gone back to mechanical gearboxes
following the widespread use of hydraulic gearboxes...


Why surprisingly?

The six-speed mechanical gearboxes have much lower power losses than a
two-speed hydraulic transmission using a torque converter. This leads
to significantly improved fuel consumption and lower CO2 emissions.

"Bruce" wrote in message
...
"Paul Scott" wrote:
None of FGW's 2 car DMUs are diesel electric - I'm sure the only diesel
electric units (ie DEMUs) in use in GB are the Voyagers and Meridians.

The latest new small DMUs (the 172s used by LO and Chiltern) aren't diesel
electric either, and have surprisingly gone back to mechanical gearboxes
following the widespread use of hydraulic gearboxes...

Why surprisingly?

The six-speed mechanical gearboxes have much lower power losses than a
two-speed hydraulic transmission using a torque converter. This leads
to significantly improved fuel consumption and lower CO2 emissions.

I'm not surprised myself - but there seem to be many critics who keep
suggesting it'll never work, usually based on what happened about 40 years
go...

Paul S

"Paul Scott" wrote:
"Bruce" wrote in message
.. .
"Paul Scott" wrote:
None of FGW's 2 car DMUs are diesel electric - I'm sure the only diesel
electric units (ie DEMUs) in use in GB are the Voyagers and Meridians.

The latest new small DMUs (the 172s used by LO and Chiltern) aren't diesel
electric either, and have surprisingly gone back to mechanical gearboxes
following the widespread use of hydraulic gearboxes...

Why surprisingly?

The six-speed mechanical gearboxes have much lower power losses than a
two-speed hydraulic transmission using a torque converter. This leads
to significantly improved fuel consumption and lower CO2 emissions.

I'm not surprised myself - but there seem to be many critics who keep
suggesting it'll never work, usually based on what happened about 40 years
go...


.... while their sucking their teeth, sighing and shaking their heads
theatrically as though they know something that they don't.

The motor industry has steadily been abandoning its torque converter
gearboxes over the past decade in the quest for better fuel economy
and lower CO2 emissions. The railway industry needs to catch up.