Why aren’t more DMUs built as DEMUs?

[supervc-10]

An electric 'transmission' is kind of the way that the BMW i3 REX and the Chevy Volt (aka Vauxhall Ampera) operate, although the latter does have a mechanical link from the engine to the wheels which kicks in at certain speeds. The difference is that those vehicles have a buffer in the form of a battery, which can take in charge when braking. It also means that they have a relatively small petrol motor- I believe the i3's engine is basically out of a scooter.

The Toyota Hybrid system is also kind of an electric 'transmission'. It's very weird, yet also very simple and very effective. It uses a planetary gearset with 3 inputs and one output. The petrol engine and two motors make up the inputs, the output of course goes to the wheels. I tried to find a good explainer on YouTube, without luck. But basically the outer ring gear is an input and the output, and it's connected to one of the motors. The planets are connected to the petrol engine, and the sun is connected to the other motor. When in EV mode, the ring motor is the only one running. When running on petrol, the two motors operate at different speeds with one 'powering' the other to vary the speed of the wheels. As I said, very weird!

A battery hybrid 'tri-mode' train could be very interesting. Wonder how the 756s will turn out!

 

[apk55]

For car makers there is probably a lot of sense going along the electric transmission or serial hybrid route. The same car could be sold as both pure electric or hybrid version. Many versions might come with only a tiny engine and there would be little reason to have an engine that can drive the car continuously at more than 70MPH as instant acceleration would be available from using the battery pack.