AutoSpeed Variable Valve Article The ability to fully control the duration as well as phase angle means the engine can breath fully. Taken to its logical conclusion, the engine would not need a throttle plate. In effect, the absence of pumping losses combined with the ability to tune for any operating range. Literally, the engine could on the fly switch from Atkinson for efficiency to Otto for high power or any operating mode in between. Our Prius has a very efficient engine but it takes this kind of variable valve technology to take the next step. Then add the ability to operate at a lower block temperature, the 80 MPG range Al Gore's team envisioned in the 1990s becomes practical. Bob Wilson
Why bother with the camshaft at all, the efficiency of hydraulic systems and the timing of microprocessor control would mean that you could use the power steering pump to do it and then you could really have it as you like for maximum power or efficiency or engine braking, whatever you wanted. I suppose the reason is that it would need a new engine design specifically for it.
Hi Bob, Pumping losses would not be eliminated. But due to the aerodynamics of a new-technology valve could greatly reduce pumping losses. And also since there is only one restriction in the flow, and that restriction is tuned to the mass flow rate and speed of the flow, the aerodynamics could be greatly improved. Aren't people also working on aerodynamic plunger throttle valves? Something like a tear-drop shape tha fits into a reduced, or expanded diameter valve body? Then the tear-drop portion is operated in the axial direction ? This would be a neat retrofit for the Prius or any other car.
I don't know about the throttle valve but I read Toyota's paper on their variable valve technology. In Toyota's version, they have compound curve insert that slips between the valve stem and cam shaft. Phase angle is handled by the current system and then inserting or withdraw changes the duration. Regardless of which system is used, these advanced valve systems promise significant efficiency improvements. Bob Wilson
Large stationary "prime mover" engines are also being equipped with similar technology. R&D principles and most important R&D programmes Dresser Waukesha - APG1000 As most prime movers operate at constant speed, the efficiency gains are enormous. Per cylinder fuel, valve, and timing control all provide for impressive gains in lifetime operating efficiency
reason they dont use valvematic in prius is that prius engine is already optimized to run at certain rpm's, so it is waste of money (according to toyota head engineers i spoke to).
This is pretty interesting. Would you mind starting a thread over in the Gen II Technical section with more details? There are definitely times when it would be nice to have the option for more ICE power with complete disregard on the impact on fuel economy. Gen II Prius Technical Discussion - PriusChat Forums
The inertia of the volume/pressure of fluid required to QUICKLY lift and then release valves does not allow the use of hydraulics at typical high engine RPMs. "Air" maybe.
But there is also the ATF pressure pump and even the engine lub oil pump. While these are both going the way of real-time volume pumping variability either could still be used if not for the inertia issue.
"..the absence of pumping losses.." This I don't get. On the intake stroke the piston is working against atmospheric pressure in the crankcast so to eliminate pumping losses the intake side must also be at atmospheric pressure during the entire intake stroke. If you do that then on the compression stroke you must allow reverse flow until the cylinder volume is correct for an equivalent low throttle opening. Now, except for 4 cylinder engines, you would either be compressing air within the intake manifold/chamber or "exhausting" it back out the air intake filter. So in any case work is being done, moving an air volume in and then OUT, so where is the gain...?? "..the engine would not need a throttle plate.." Except for 4 cylinder engines....How so..?
Fiat is using a rather advanced design to eliminate the throttle plate, and use a single cam instead of dual. Inside the 2012 Fiat 500 Engine | Fiat 500 USA There are some cool diagrams showing the available valve timings. This is true, but even the prius and leaf have hydraulic brakes as well as electronic. If there is an engine there is availability of hydrolics. Fully electric valves are available as well and could completely eliminate the need for any cam shaft. I think mazda is using electronic intake valves on the skyactiv family of engines but using traditional valve driven ones for exhaust valves.
On a 4 cylinder engine two pistons are going up while the other two pistons are 180 deg out of phase and going down. Crankcase volume remains essentially constant. With no throttle plate, the air is being moved through open passages so little work is required to move the air. With a throttle plate, the engine must supply the power to move the air through the restriction caused by the partially closed throttle plate.
Poking around on Wikipedia, I came across this blurb. Another way to view the pumping losses of the throttle plate, is that the vacuum created with throttle partially open pulls up on the pistons during the intake stroke. Don't think many practice it, but I've heard of using a burn and coast/glide to reduce pumping losses while hypermiling. Same as pulse and glide, but the pulse is at wide open throttle.
