Thanks for the explanation of how diesel-electric locomotives operate
Robert.
The MotorWeek TV show this week here in Maryland (USA) showed a car which
will go into production soon. It uses the same approach as diesel-electric
locomotives.
The first model will have an electric motor on each rear wheel. For larger
cars/vehicles planned for the future, an electric motor will be placed on
the front wheels or additional wheels as needed.
Regards, Stan Doore
----- Original Message -----
From: "Robert H. Bushnell" <[EMAIL PROTECTED]>
To: "U.S. Metric Association" <[email protected]>
Sent: Friday, March 10, 2006 2:59 PM
Subject: [USMA:36239] diesel electric propulsion
2006 March 10
In the matter of propulsion with diesel engines, the design was made
optimum
more than 60 years ago. A railroad locomotive has a diesel engine (often
more than one) which drives a generator which drives electric motors which
drive the propulsion wheels with fixed gears (no gear shift). The
generator
and the motors are each compounded to allow maxumum power at any speed.
The
generator and the motors are a matched set. A compound motor has both a
shunt field winding and a series field winding. The design of the number
of
wire turns (the windings) in each of these fields and the number of turns
in
the armature (the moving part of the motor) is motor engineering at its
best. The design gives maximum power transfer without controls in the
electric circuit. The throttle (the injector stroke) on the diesel engine
is the only control. Railroad diesel engines are never turned off so
there
is a way to stop generation. (I would open the shunt field so the engine
could idle with no generation.)
To start a train from zero speed the diesel engine can throttle up to
maximum power while the train is still hardly movimg. The compounding in
both the generator and the motors gives high efficiency at this low speed.
The compound windings give high efficiency at any speed so the throttle
can
be left wide open at any speed.
For ship propulsion, the design may be different. For a screw propellor,
power and efficiency change with speed of the shaft rotation and the speed
of the ship. I have been told that the design of ship screws is more an
art
than an engineering matter. So, screw performance is found by experiment.
Given this measured performance, the motor compound can be designed.
Robert H Bushnell PhD PE
