Atkinson's Cycle

If you read the description of the original patent it was based on the compression stroke being shorter than the expansion/power stroke. This allows the expanded gases to expand to nearly atmospheric pressure making the most of the expansion process.

The thermodynamic process can be implemented with many mechanical linkages or even in a rotary engine. One linkage over another does not make it or not make it an Atkinson cycle (any mechanical/chemical engineer will tell you so, I'm a mechanical engineer).

The valve timing in this engine does just that: it makes the compression stroke shorter (by the time the intake valve is still open) compared to the expansion/power stroke. I would say, technically, that IS an Atkinson cycle.

 

I know you know how it works; but, due to the apparently widespread confusion I think we need to be more careful with our wording. Perhaps qualifying that with effectively shortens the compression stroke or simulates a shorter compression stroke.

 

I'm not sure what you mean. It does shorten the compression stroke. The compression stoke begins when the intake valve seals. Just because the piston is past BDC (bottom dead center) doesn't mean it's in the compression stroke yet because with the intake valve open no pressure increase can be affected.

 

I'm just saying that people Google "Atkinson cycle", go to Wikipedia, see the Atkinson engine animated GIF, see someone say shorten the compression stroke, then come to the conclusion that the 3.5 does what Wikipedia says it does.

 

Well I think trying to keep people from misinterpreting highly technical information about thermodynamic cycles on Wikipedia is a lost cause!

 

Doug007 is right.

It essentially does the same thing except you don't have those extra linkages on the piston that actually cause the piston to change the length of its stroke during its cycle.

What Toyota did was instead of using those funky linkages that you see in a traditional Atkinson cycle animations, Toyota leaves the intake valve open during the compression stroke, so some of the air fuel mixture that entered cylinder during the intake stroke is forced back out into the intake. The intake valve then closes at a later point and compression begins. So volumetrically, you have less air and fuel in the cylinder during compression vs if it was running otto cycle. In otto the intake valve closes when the piston is at BDC so as a result you have more air fuel mix in the cylinder.

 

This was what I was trying to tell you earlier, but I see others have explained the actual workings, vs the theory of the original design.

 

I hate to admit it, but I have a degree in Mechanical Engineering too. And I know internal combustion engine theory fairly well. Conventional "Otto" cycle engines don't open their intake valves at exactly 0 degrees and close them at 180 degrees of the cycle either. Nor do exhaust valves do the opposite. They have valve overlaps that vary all over the place depending on what characteristics the engineer wants the engine to have. The stroke is the stroke, no matter what the valves do. Look at a two cycle engine; No one determines the stroke or displacement by port position, that would be preposterous.

What we are dealing here is with names. And names really don't mean much. What Toyota (and probably others) have done is cleverly mimic the characteristics of original Atkinson cycle without the excess baggage. That is good. But IMO it is sort of misleading to call it an Atkinson cycle. It is an Otto cycle with an unusually long closing duration on the intake valve. By definition, an Atkinson cycle has two different length strokes. The Atkinson Cycle name appears to be more of a marketing ploy than anything to acknowledge they are doing something different, which from that viewpoint, is probably OK.

 

Well since your so smart tell me why my 09 Dodge with tow/haul has been doing just fine. Use it towing a trailer on trips, use it in mountain driving with our without towing, and the transmission is doing great.

By the way, do you own a vehicle with the tow/haul button?

 

This is not an Atkinson cycle engine....

 

If people followed that advice , none would be sold and the model would die out.

 

Not really. The Toyota engine does not employ a "true Atkinson cycle" in the form of the different stroke lengths you cite. This engine simulates (and probably very nicely) the Atkinson cycle by leaving the intake valve open for part of the compression stroke. Nevertheless, I am concerned that there may be trade-offs at the low end of the torque and HP curve, so I continue to search for dyno tests to no avail.

 

Well, obviously there's enough suckers to make the discoveries of what is bad for the rest? I was a sucker and bought a 2005... well, it had issues, but not enough to chase me away from Toyota... as I got a 2010 now, the finest Tacoma I have had!

 

@Brussell56 , @allmotorrex ,and I were having a drunken campfire discussion about this new Atkinson's cycle engine. Can't remember if we figured it out or not. Subbed for clarity

 

In the original Atkinson engine design, the crankshaft only turned once for each time the pistons went through the four cycles of intake, compression, power, and exhaust. This must have generated much more torque per displacement unit than our 2016 Atkinson 'style' engine.

 

If the ect was for towing (always has been always will be) @BlueT why would they have put it on multiple cars in the 90's early 2000's such as avalon...

 

Seemingly they could accomplish the same simulation of an Atkinson Cycle by shortening the duration of intake valve opening. Rather than leave it open until 220 degrees (or whatever it is) close it at 140 degrees, or alternatively just wait to open it until 40 degrees. Wonder why they chose the leave it open a long time route?

 

Presumably, they chose the duration based on maximizing Otto cycle power. The VVT system cannot change duration; so, that would significantly affect max power. Probably more pumping losses with shorter duration, too.

 

Electromagnetic valving will be the next big game in oil combustion engines, if oil combustion engines keep going for a while. Then you have timing and duration control of individual valves