We all know that a lot of energy is wasted by the throttle valve in a gasoline engine. We also know that diesel engines are more efficient because they do not have throttle valves. And we know that air flows through the throttle valve.
Somebody had the idea to make use of the lost energy by replacing the throttle valve with a turbine connected to a generator, and controlling the generator load through the gas pedal to control the air flow to the engine. See patent #5,394,848 for the details. Go to
Google to see the patent.
At the bottom of the page is a list of 23 other patents that build on this patent. This patent is expired, so anybody can build, use, or sell anything in it.
The only real problem is the range of pressure drops and flow rates make it impractical to completely replace the throttle valve with a turbine. Other than that, the basic concept is valid.