A maintenance NIGHTMARE and not useful for independent valve control. I remember an article several years ago about a computer controlled valve system. The limiting factor was the weight of the valves. The solenoids could not control even ceramic valves at anything over about 2000 rpm.

 

The good news? It is being worked on, and we will eventually have this technology. I just hope we get it before we go fuel cell electric!

 

Sort of. It's more a matter of having an engine achieve one goal, i.e. max power or max economy or min emissions, at various engine speeds instead of only at one engine speed.

First, the designer determines the goal of power, economy or low emissions, or a certain balance. Every design is "perfect" for one parameter at one specific RPM. Variable valve timing spreads out that "sweet spot" so it occurs across a broader RPM range. You get the relatively restrictive valve openings that are best for low speeds when the engine is running slowly. As RPMs rise, valve opening and duration is extended to give the better breathing an engine needs at higher revs.

It's typically used to increase power without sacrificing mileage or emissions. But I imagine it could be used to maximize economy, too.

As for the FEH, you make a good point that it's already tuned for efficiency. I think it may also have something to do with the CVT nature of the drive system. CVTs of all types are good at keeping an ICE running at a certain speed and I'm sure Ford has our vehicles programmed to keep the FEH within a relatively efficient RPM range.

 

I wouldn't go so far as to say a nightmare. Once you got the hang of it was not that hard and the system was very stable for an all mechanical system. With one and two cylinder engines and two valves per cylinder, the amount of work was limited.

The Ducati system came into being because of the valve spring technology limits and the tendency for valve float at higher rpm. Back in the day, many engines floated valves at 6000 to 7000 rpm and Ducatis were able to rev to above 9000.

The system could easily be adapted to varible valve timing if you converted it to a two cam system instead of one came and put variable timing on the intake came. However, it seems there is little or no interest in mechanical systems these days.

 

To give us something specific for comparison, I'm attaching some pages from the Toyota Camry Hybrid's "New Car Features Guide." Page EG-3 compares the 2.4-L hybrid's "Atkinson" with the non-hybrid's "Otto" engines. You'll see that Toyota's VVT is on the intake valves only, and varies intake valve timing over a 30-degree range in the hybrid versus 43-degree range in the non-hybrid. Note that the hybrid intake valves are open for fully 280 degrees, compared with 248 degrees for the non-hybrid. In both cases, the exhaust valves are open for 228 degrees.

Stan