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Variable supercharging as throttle

 Throttle an engine by varying the boost pressure from a supercharger
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Inspired by my CVT supercharger drive idea (in the Car: Engine: Supercharger section).

The throttle vane in a petrol engine exists to control the mass of air that the engine can suck in (fishbone me now if I'm wrong) and superchargers exist to increase the mass of air that can be taken into a cylinder by pressurising the intake air. At part throttle the supercharger will be sucking in air, compressing it and then ramming it straight into a partly closed throttle vane, wasting some of the pressure that has been generated. Instead of generating pressure only to waste it, why not charge the engine with exactly the right mass of air for that throttle position and engine speed by varying the speed of the supercharger and do away with the throttle vane completely.

The supercharger would have to be of the positive displacement type (twin-screw etc.) as a centrifugal supercharger provides an uninterrupted pathway for the intake air which would make it difficult to control the engine. It could be driven either by a CVT or an electric motor, whichever works out best for efficiency/reliability.

—squigbobble, May 26 2005

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       Feasible, I think.
—5th Earth, May 26 2005
   

       Now this one I have to think about. Mainly the "why" part. Interesting idea, though.
—justaguy, May 27 2005
   

       Sounds feasible, with the possible advantage of having an unimpeded airflow at "full throttle" i.e. no throttle butterfly in the airstream.   

       Some sort of fail-safe mechanism would be required though. Conventional throttles have springs that will return the butterfly to a closed position should a cable snap etc. This idea needs a device that prevents things from just going faster and faster in the event of a malfunction.
—Texticle, May 27 2005
   

       The 2005 Buick Park Avenue Ultra is just one of the many supercharged street vehicles available without a ginormous through-the-hood blower. The setup you describe is used on race cars, yes, but they produce about 35lbs of boost through a combination of cold ram air and mechanical compression. Most production superchargers live quietly under the hood and make between 5-10lbs. Very hard to blow an engine at those levels.
—justaguy, May 27 2005
   

       This is somewhat related to my vacuum-powered alternator, in that when an engine is supposed to be powered down, drawing the air through a turbine and extracting energy from it would actually improve efficiency even beyond the free energy the turbine would provide.
—supercat, May 27 2005
   

       Pa've, Jaguar seem to quite like the supercharger, on their XKR for instance. It's still very much a production item.   

       Long live the hotrod, indeed. Why shouldn't it run on hydrogen with an IC engine?
—david_scothern, May 27 2005
   

       /Another big problem with a super stack poking through the hood is that in most states, that's not street legal./   

       Luckily the rest of the world is a big place.
—Texticle, May 29 2005
   

       If you control this 'charger through a CVT, what's to prevent a control-lag induced oscillation? The engine won't react instantly to inputs (inertia, you know), but then it speeds up in response to the charger, which is now blowing harder, and harder, so you back off, and it goes slower, and sloooowwweeer. A great device for people who can't settle on a throttle setting. Every drive would be a foot-stomping thrill!
—elhigh, Jun 03 2005
   

       I had a similar idea myself. One thing you should note is that if there is a lower pressure on the output side of the supercharger, the power needed to drive it is negative, ie you put power back into the engine. It might even be enough to make up for the lower efficiency of the lower compression required for a supercharger.   

       Oh, elhigh   

       I read about a study on lag with different types of supercharger. A turbo took something 150 cycles (300 revolutions) of the engine to develop full boost. A centrifugal supercharger took 17, and a positive displacement supercharger? Just 4. As you can see lag wouldn't be an issue with the right type of supercharger.   

       The electric throttle seems to work ok, I see no reason why a small CVT has to have a longer delay than an electric throttle.
—BLSTIC, May 19 2008
   


 

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