Question at 21min22sec mark in this just posted Talking Cars episode - "Are hybrid engines designed differently than traditional internal combustion engines? Does the on/off cycle of a hybrid engine affect its longevity?" - short answer provided is no. PS - they love the new Supra unless you need to install a child seat.
They’re just regular engines with some tuned to run on the Atkinson cycle for better fuel economy. Beefier starter motors (usually one of the electric motors) help reduce wear and tear by spinning the engine up to a higher rpm (closer to idle) than a regular car’s starter motor. Based on the Gen 2 Prius, my understanding is that it’s spun to almost 1,000rpm instead of a typical 100rpm thus the constant stop/start is less of an issue than a regular car.
The primary reason why you’ll never hear the traditional starter motor “whining chatter” when the Prius ICE or so kicks into life. It just comes online, and often you’re already moving from a standstill before the engine comes online. I’ve often wondered if other drivers are ever puzzled by the lack of a traditional starter motor sound when (occasionally) a totally silent Prius engine suddenly bursts to life as it moves off with heavy acceleration. It’s one of the most amazing things that delights me about the Prius II - or indeed, any Prius. iPhone 6s +
