prins@cornell.UUCP (Jan Prins) (01/09/85)
Phil Ngai suggests electronically controlled valve actuation could be even more exciting than breakerless ignition! But why settle for "programmable" cams -- when you could have dynamic valve timing. Increase lift and duration with rpm and throttle position and your lightweight idlemaster economotor might become a nasty 125 hp/liter screamer at high revs. But how could you make electromechanical valves work? Do you open conventional valves with solenoids? The current requirements would be impossible. Desmo- dromic actuation (push to open, pull to close) would be preferable -- the valves would be much easier to open without a stiff spring, and the resultant decrease in forces would allow the valves themselves to be much smaller and lighter. Still, to accelerate a valve over 10mm in 40 degrees of crank revolution at 7200 rpm (specs suitably blue-sky, to fit pipe-dreams) will require enormous forces. Can it be done? Moreover, you may need to control the opening/closing rate, to capitalize on all the gas flow quirks that the cam people know all about, not to mention the proper operation at TDC overlap while staying out of the pistons way. That brings up another difficulty. One program/transducer/whatever error, just one, in those hundreds of events per second, and your motor will be dining on valves. Maybe those messy chains, inflexible cams, funky followers and stiff springs aren't so bad after all... But it can't hurt to dream! Uh, except when you have work to do. cornell!prins
markmo@tekig.UUCP (Mark Morland) (01/11/85)
--------
British Leyland tested a modified TR7 engine with solenoid
operated valves about 4 years ago. Powerful solenoids with
a 1mm stroke operated the valves through 8:1 ratio rocker
arms.
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Box 500 MS 39-353, Beaverton OR 97077mikey@trsvax.UUCP (01/11/85)
I read in one of the hot rod type magazines that someone already built an engine that had pseudo adjustable cams. I can't remember where I read it, but I seem to remember something that it used an adjustable fulcrum for the rocker, and it was hydrolic controlled for lift. Sounded like what Honda uses in the Night Hawk for the self-adjusting valves. mikey at trsvax
rs55611@ihuxk.UUCP (Robert E. Schleicher) (01/16/85)
In the discussion on electronic valve control, someone mentioned desmodromic (sp?) valve operation, where there are no valve springs, and there is both positive opening and closing of the valves. An early example of this principle (perhaps the first) was in Mercedes-Benz Grand Prix cars in the late 30's, perhpas in the Auto-Unions of the same year. The M-B racing engine of the late 30's has become a legendary engine, being recognized in the recent Car and Driver as one of the 10 besrt engines of all time (in terms of technical advances, influence, importance, etc.) BTW, some of the others on this list include: - Model T Ford engine - 1920's Alfa Romeo inline 6 (first real use of overhead cam) - 1932 Flathead Ford V-8 - 30's M-B Grand Prix engine (for dominance of racing for several years) - Jaguar XK series DOHC six - VW flat 4 - Porsche 911 flat 6 - Chevy small-block V-8 (introduced 1955) - MB engine from 1910 or so - one I can't remember Bob Schleicher ihuxk!rs55611