Time was when many thought two gears was adequate. GM made two speed automatics for many years. Later Honda used the Hondamatic, a manually operated two speed with torque converter which appeared in many cars and fewer bikes. I’ve got a vague memory of being on two speed buses. But the two speed was abandoned years ago, wasn’t it?
Voith are a German company who make a wide variety of things. Amongst these are hydrodynamic transmissions for rail use. In the 2000s Voith were approached by a customer who wanted to build a powerful locomotive and wanted a hydrodynamic transmission for it. Voith got to work. Just as they were done the customer had a change of plan and said “nein, danke”. What to do, after all that effort? Why, get into the loco business of course and so it was done. Voith designed a small shunter using their existing transmission and the Maxima, the most powerful single-engined diesel loco built.
Here we see one.
Yes it is from the New Brutalist school of industrial design, isn’t it? Looks like it’s designed to move really big things without much regard for being able to slip easily through the air.
Anyway, the Maxima had two speeds. Not two gears mind, two speeds. It had only one gear. How so? When starting the one gear was driven by a torque converter which provided lots of torque at the expense of efficiency. At higher speeds the torque converter is drained and a fluid coupling is filled. The coupling drives exactly the same gear but as it slips less so the overall effect is of a higher speed.
You want to know how this setup copes with starting something really, really heavy, don’t you? Of course you do. Here we go with , according to the author, three thousand-odd tonnes.
There are in-cab videos of these and until boredom set in I watched a speedometer taking an unconscionably long time to drag itself to 30 kmh with occasional breaks to watch the revs inch up from about 880, one rpm at a time.
So there you have it. How to get two speeds from one gear and put them to hard work.
The Maxima sadly was a commercial failure and not all of the 30 or so made were sold. Voith switched to repair work and later announced the closure of the factory.