Quote:
Originally Posted by Shepherd777
We have decided that the new truck will be electromotive power. A Cummins diesel engine powering a generator powering hub motors. No tranny or differential...
...It would allow the diesel to run at a constant speed, except when going down hill, where it would idle.
The mechanical losses from a 13 speed transmission and a monster size differential churning all that oil with those monster gears are not very efficient.
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I will start by stating that I have no direct experience with the mechanical efficiencies of heavy truck transmissions. Having said that, I would imagine that everything is fairly relative, meaning that from a % loss standpoint shouldn't a car's drivetrain be roughly the same efficiency as a heavy truck?
What you are proposing to do would be similar to what GM does with the Volt when it is running in it's "Range Extending" mode (gasoline engine running a generator to drive the electric motor once the main battery is depleted). The generator runs at fairly steady speed to generate the power required to drive the vehicle.
One thing the Volt does, however, is directly couple the engine to the drive wheels through a simple transmission linkage at higher speeds. This is because there's a lot of loss involved in converting mechanical energy into electrical energy and then back into mechanical energy again.
I would think your concept would work really well if you were able to couple it with a transmission and differential gearing that allowed a 1:1 transmission ratio while cruising to minimize losses. This way the electric motors could be used around town and geting up to speed, and once on the highway with the cruise control set the engine could couple directly to the wheels for maximum efficiency.
As another poster commented, I don't think the diesel locomotives use electric propultion for its efficiency, but more for the low end torque characteristics of the electric motor, getting a train moving from rest. Some large ships have used this method as well, but many that do have done it to adapt rotatable "pods" that house the drive motor and propeller. These pods are directable, allowing the ship to steer based on the direction of the propeller's thrust, making navigation in tight spaces much easier. There's a slight efficiency payback with not having to steer by dragging a rudder through the propeller's wake as well.
Absolutely brilliant work, by the way!