OK, engineers, mathematicians, scientists & resident gearheads.... 'What?' do you see???
Warning! My cabin fever has already set in, since Doc's 'sentence' is to last until Spring.... 'Parole date' is April 9th....
Take Care; Behave; "Don't Shoot!" (and)
A cam increasing the stroke but also the thrust angle. I see more drag and moving parts. A better solution than increasing the stroke length is changing the head volume.
Does it really increase the stroke, or does it just raise the piston position at TDC, I'm just throwing this question out without having tried to go through the geometry of it.
Thought maybe Vern was suggesting a supercharger, but had an engineering friend tell me it "reminded (him) of a mechanical heart pump." One of my gearhead friends said "Honda does have a variable stroke engine design."
Take Care; Behave; "Don't Shoot!" (and)
I'm with Vern on this. Lots more moving parts and drag. Maybe I'm dense, but wouldn't it be easier and better to just design an engine with a longer stroke to begin with? What's the advantage (real or perceived) with this set-up?
That engine is an Infinity design. It is planned for production in the near future. The length of the stroke doesnít change, only the compression ratio. The idea is to enable a very high CR under light load conditions, which provides a significant increase in efficiency, therefore fuel economy. At high loads, or wide open throttle the CR is reduced to avoid spark knock.
To help visualize, imagine the stroke is say, 3 inches. The system shown is capable of moving that 3 inch working range up and down the bore, so points for TDC and BDC are not fixed.
You can expect to see more of the same, meaning exotic engine designs over the next few years and decades as the lovers of internal combustion engines refuse to give up without a fight.
Weíve already seen turbos, belt driven blowers, direct fuel injection, overhead cams, 4 valves per cylinder and other technologies become mainstream in the last few years. These last gasp efforts to improve fuel efficiency of the ICE will help to ensure gasoline remains available for many decades to come. Good news for the old car hobbyist.
Found the link. Read all about it.
Itís interesting to me that a lot of the improvements in the piston ICE were developed just prior to, during and just after WWII for aircraft engines. Then it stopped, thanks to the jet engine. If the jet engine had not arrived I suspect something like this variable CR engine might have been developed here in the U.S.
I concede, all pistons are raised. At frame 8, at the top of stroke for cylinders 2 and 3, the rod is not completely vertical. On frame 31, again with 2 and 3 pistons at the top of the stroke, the rod is vertical. The thrust angle cannot be the same for both positions since the pivot point is above the crank for all pistons on frame 29. My thinking was that the hypotenuse (thrust angle) was different at the top and bottom of the stroke.
Changes to the working range of the fixed stroke inevitably do change the rod angle with this design.
The effect of rod angularity and resulting friction is well known and engine designs have taken this into account for decades utilizing crankshafts offset relative to the bore centerline. The idea is to reduce the angle on the expansion stroke, where the friction would be highest. This increases the thrust angle on the compression stroke and exhaust stroke but cylinder pressure is a small fraction of that on the expansion stroke so the offset is worthwhile.
Waukesha has been making variable compression engines since the 1930's to test octane ratings in fuels. They're commonly called "knock engines". New from the factory, with installation and all the instrumentation, they run around $500K.
I see them in action nearly every day in the work that I do.
In this case, it's the head that moves....thereby changing the cylinder volume and compression.
Iíve heard of those engines. $500K huh? A bargain Iím sure.
Iím dying to know the mechanism that allows for moving the head while running. Are they OHC? If so is the cam driven by a chain or do they use a shaft and bevel drive? I can picture a splined shaft that can slide through one of the bevel gears, though I suspect they use something completely different.
Can you get some pics?
Gary: Lot's of hits on line on the subject. My employer scrapped one of these 20 yr's ago, it was a nice example of mechanical craftsmanship. jb Here's a brief article: http://www.runyard.org/jr/CFR/octane1.html
In the fifties a guy was in Popular Mechanics or P. Science, had a flathead Olds six. He had built a head with variable compression ratio. It had "Contra pistons" in the head with screw threads that could be operated, but I don't remember how the controls were connected. There is a site where this could be researched, with magazines back to at least the early thirties, or before. Merry Christmas, Dave in Bellingham,WA