"Well, at least Skip has figured out the the camshaft profile enters into the compression pressure equation!" The toyota and Ford hybrids have used the effect of cam timing to adjust cylinder pressure to good effect.
The Prius hybrid, which has an Atkinson cycle engine, has a mechanical 13/1 compression ratio built in, which makes great part throttle mpg, but would detonate like heck on pump gas at wide open throttle. To fix that, they use variable intake cam timing to hold the intake valve open as the piston rises on compression. Some of the air in the cylinder is allowed to blow back into the intake manifold through the still open intake valve, thus reducing peak compression pressure. If the pressure is high enough to detonate, the knock sensor tells the intake cam to retard a bit more and bleed off more cylinder pressure. This keeps cylinder pressure just below detonation at part throttle for more burn efficiency and top mpg. They consider it to be 5 cycles, 1 intake 2/3 compression / blowback, 4 power, 5 exhaust.
The down side to an Atkinson 5 cycle engine is that it must blow off so much air at wide open throttle that it can't make as much full throttle power. Thats why you only see them in a hybrid where the battery / electric motor can make up for the gas engines lack of WOT power.
The system seems to work amazingly well, my 2010 Prius does 0-60 in 10 seconds, 115 mph flat out and has AVERAGED better than 50 mpg at the speed limit (65)for the 8,000 miles I have owned the thing. I wish someone would put that type driveline in a light duty 1/2 ton pickup for the city cowboy and farmer "gofer" pickup market. I suspect the thing would make 30 mpg or better.
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Today's Featured Article - History of the Nuffield Tractor - by Anthony West. The Nuffield tractor story started in early 1945. The British government still reeling from the effects of the war on the economy, approached the Nuffield organization to see if they would design and build an "ALL NEW" British built wheeled tractor, suitable for both British and world farming.
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