From where to where are you driving?!
Roughly along which route?
Lots of stuff to see... But you need to be a bit more precise in places and time, I'm afraid...
Speyer & Sinsheim have some nice technical museums. Vienna has a nice technical museum, too.
Lucerne hosts the Swiss museum of transport, Dubendorf the Swiss air force Museum, not clear whether Switzerland is an option or not? (Since you seem to think about Friedrichshafen).
The Aero Exhibition at Friedrichshafen in April is quite awesome, but only a few days from April 17-April 20...
Stuttgart (Porsche, Mercedes), Ingolstadt (Audi) and Munich (BMW) have a host of automobile museums...
And so forth.