I am kind of an inventor and always come up with problems that need answers. Let me think.....

Variable speed transmission (line Nuvici bike hub)
This would be very important when trying to make a good electric vehical.

One way Clutch
There are sprag and clicker type couplings. Sprag is hard to manufacture and the clicker style (bicycle hub type) are noisy and wear out. Come up with a new way and you are a millionaire

High speed cutting of thin wall tube without making burr on the end. (low cost)

Heat recovery system for internal combustion engine. (steam or likewise)

Effecient pnumatic motor design (compressed air energy recovery system)

Automated gray water recovery system

Flywheel energy storage device

Automated MIG weld torch cleaner (all on the market are crap, million dollar idea)

Temporary house stairs that can be folded up and meet safety standards (used when building houses)

Cable recoil system that does not use a spring, recoil is on a rotating shaft. (like used on a rowing machine)

Windmill blade automatic blade pitch system (low or no electricity).

Automatic automotive block heater connection (just drive up to house and plugs in automatically and cycles on only when cold out)

Shaft speed differential (different design but same idea as automotive axel differential)

IC engine valve lift control mechanism (valve lift controlled engine instead of throttle plate) (Mercedes has a model) (investigate "jake brake" in diesel engines)

I will think of more...............................