A blast from the past #3

Two speed supercharging.

There is, as the popular saying would have it, nothing new under the sun. So when I read a press release from Antonov Automotive Technologies proclaiming 2-speed superchargers the way forward I recalled that the idea has been tried on piston-engined aircraft. In aviation the idea was to maintain performance at altitude so as the aeroplane climbed the pilot would select a gear to speed up the supercharger. It was a crude but reasonably effective way to compensate for the thinning of the air.

A supercharger is an air pump and while different types have different characteristics but, broadly speaking, the faster it runs the more air it moves. Antonov’s idea is to run the supercharger relatively faster at low engine rpm to boost low-speed torque without blowing the engine up at high speed. They don’t say this, of course, but that is what it amounts to. The behaviour of the supercharger should be fully automated and imperceptible when driving. The goal is to allow vehicle manufacturers to use smaller engines that are more economical.

I’m not sure how plausible their claims are. Superchargers are not the most efficient means of increasing performance. I’m not convinced by anyone who claims that superchargers don’t have the heat issues of turbochargers. Anyone who has used a bicycle pump knows that compressing air makes it hot, the air isn’t particularly bothered how it gets compressed. Two-speed supercharging is an interesting idea but I wonder when engineering fashion will swing back towards big, engines in low states of tune combined with high gearing – the sort of thing seen with the BMW 525e and Renault 5TS.