Sooner or later I am going to get into an accident from watching that thing.

I noticed there is a mode whereby the engine is driving the electric motor and the drive train, while at the same time the electric motor is driving the drive train, and battery is idle!

What does this mean? If there is only one shaft coming out of the electric motor, and since torque is a scalar value, this can't be meaningful. It can't be driven and driving at the same time. If the electric motor is a two-shaft system (one for generator one for driver) then why would the system waste mechanical energy from the engine by converting it to electricity and back again?

What am I missing?

 

You are aware there are two electric motors? One ~70kW and one ~40kW right?

Much of the time, if not MOST of the time, the engine will run at an optimum RPM no matter the wheel speed of the vehicle. Thus, the engine will spin the 40kW motor in generator mode, and that electricity is sent to the 70kW motor to change the speed at the wheels. The battery does not need to do any work. The diagram in the car is over-simplified.

And yes, spinning the ICE at optimum or nearly optimum RPM and converting the power to electricity and using electricity to spin the wheels is more efficient than a direct ICE drive of the wheels.

Every single train locomotive post WWII has been a "hybrid-electric" design, and works just this way. Only recently have we put 50 year old technology into cars!!!
-John

 

I guess that means a two-shaft design, one being driven and the other driving. I knew there were two electric motors, one called "Generator Motor" and one called "Tractor Motor" and was wondering why they used two instead of one. Is supporting this power flow configuration the reason?
Is it? There has to be some loss in there, but if true, why have any connection to between the ICE and the drive train at all?
I thought they did that not for efficiency, but because of the engineering problems associated with building a gearbox that can rotate by 90 degrees the massive amount of energy needed to get a train moving.

Thanks for your answers -- it sounds like you are really into this.

 

I think that is the most important point.

I thought in Diesel-Electric locomotives, the Diesel engine drives the generators, and only the generators, and never directly drives the wheels. The reason is that the electric motors have far, far better low end torque, and that is required to get the freight train moving.

BTW, GE is looking at actually making a hybrid locomotive. The biggest problem, is that Diesel-Electric locomotives, are AC, not DC. There is no practical way to store AC. So, converting from AC to DC is a rather major engineering challenge.

 

It's hard to imagine the advantaqe of a battery in a diesel locomotive. They predominantly run at high constant speed and already have a very efficient diesel cycle. Maybe for switch engines??

 

It just so happens.... that I recently visited the U.P.R.R. museum in Council Bluffs, IA. A very nicely done FREE museum in old town that covers 3 ( or 4? ) floors of an old brick building... would take more than 2 hours to see everything... best FREE museum I've seen in a long time.
Two shots of relative interest... let me know if you can't read the text.
The Locomotives do have regen braking too, not shown in the pictures.





-John

 

The text is hard to make out, but the diagram is abundantly clear. The batteries are simply put in-line on the power bus and there is nothing new in the drive train.

I suppose the overall system is more efficient at acceleration because the diesel engine will be most inefficient at low RPM/high torque settings. Odd that they don't mention regenerative braking, perhaps they don't have it.

 

A couple of quick clarifications here. Early diesel-electric locomotives were all-DC. Generator driven, DC traction motors. In the 60's when solid-state electronics were sufficiently developed to withstand the demands of a railroad application, diesel-electrics gradually shifted over to using an alternator, with rectified current still driving a DC traction motor. In the 80's, straight-AC diesel-electrics began to come onto the scene as again the technology maturation allowed for equipment that could stand up to the rigors of railroading. So we now have alternator-equipped locomotives driving AC traction motors, which have their advantages in power and traction. You can literally take an AC locomotive and hold a train stopped on a grade with the throttle, much like you would hold a car with an automatic transmission with slight power. On a DC locomotive, you'd burn up the traction motors doing that. Even on the AC locomotives, however, the generated AC is rectified into DC for purposes of throttle control, then inverted back into AC to drive the traction motors. Remember that with AC motors, speed is a function of current frequency, not voltage.

Most of the new locomotive purchases these days goes to AC locomotives, but there is still a market for DC locomotives as well. Regenerative braking, known as dynamic braking, has been in use since the earliest diesel-electrics but the energy is just wasted by dissipating it through a series of resistance grids cooled with huge fans. A giant toaster, in effect. The new GE hybrid locomotive is an attempt to store at least a little of that lost energy.

There are also hybrid switching locomotives around that are for all practical purposes, battery powered units with a small diesel "trickle charger" onboard. Small being relative, here. Nonetheless, they are designed for use in yards where a lot of stop and go, back and forth switching occurs. The diesel generator is able to keep up with the overall demands of charging because of the idle time. One of these locomotives, commonly known as "Green Goats", would not last on a road train as its battery power would get depleted quickly and the diesel charger not able to keep up.

Another newer diesel-electric technology being used is what is referred to as "Genset" locomotives. These are really nothing more than a diesel-electric that uses one or more stationary generator-type of engines, and in the case of multiple engines, starts and stops the 2nd and 3rd engines as power is needed, much like a displacement-on-demand system. The diesels in these are typically variants of existing truck engines and as such are emissions controlled. The idea behind the Gensets is low fuel use, low emissions, and commonality of parts.