Although I'm not sure how VVT works, I think there is more to it than that, considering Toyota uses VVT in pretty much all their engines, hybrid or not. I'd guess that the amount of valve timing adjustment made by VVT is relatively small compared with the valve timing design difference between a hybrid and non hybrid engine.

 

I'm pretty familiar with VVT Technologies such as that implemented by the pioneer of the technology (Honda - Vtec) and Ford's Variable Camshaft timing. The function of these systems can alter not only the cam timing but the effective duration of the valve's open/dwell/close phase. Durable? Check out Formula-1, very few failures involving valve train and they idle at a faster speed than our engines redline at.
So - what I'm saying is that while the basic function and principle of operation of VVT may be the same as implemented in the TCH as well as other Toyota vehicles - the programming of the ECU will determine to what degree of an impact the technology will have.

When the demand is there - you'll undoubtedly see companies coming forward with Flash Programmers that will reprogram your ECU for more power / better mileage.. It will probably be a while before we see them though..

 

So you are saying that all it takes is a theoretical software update to convert my Sienna's 3.3L V6 VVT engine into an Atkinson cycle engine?

 

Hi Andy - I hesitate to even call our engines Atkinson Cycle as the design of the original is far different (finctionally) than what the TCH has. That said - I think it's entirely within the realm of possibility with current Toyota technology.
I know for a fact that it's possible with the technology that exists today.

It's the fuel system that has me really curious right now...
I am really chomping at the bit to get a look at a Toyota cylinder head from one of these cars. I feel almost certain that they have direct injection to the combustion chamber - if not, it must be an extremely high pressure fuel system to be able to focus the spray pattern onto the intake valve.

 

Even if there were enough adjustment range to make an effective Atkinson cycle, you wouldn't get what you want. The benefit of the Atkinson is a larger expansion ratio for the max compression ratio (max compression avoiding pre det).

To reprogram your (and mine!) Seinna's VVT to an Atkinson cycle would only be reducing the compression ratio, as the expansion ratio is already at max for the bore/stroke of the cylinder. Our TCH engine is modified from the Otto version of the same engine for the crank/cylinder config to maintain the desired compression ratio at a reduced stroke while maximizing the expansion ratio at the full stroke.

Note that the modified valving increases efficiency and reduces emissions (thanks to the greater expansion ratio) at the cost of a narrower power bandwidth, and less total power. Fortunately, this is not an issue for the hybrid, with the CVT to (over-)compensate for the reduced power bandwidth, and the electric motors to (over-)compensate for the reduced HP.

-- Alan

 

You're absolutely right Alan...
Speaking of the technology - It won't be too much longer and we will see production automobiles that have no camshafts at all - the valve operation will be controlled entirely by the ECU.. Combined with the CVT transmission, we'll see displacement sizes go down and RPMs will increase - but not at the price of performance or economy.

 

Uhhhh...yeah, that was gonna be my next answer...

 

QUOTE:- I have to say that I was exceptionally disappointed when I learned that the Atkinson-Cycle engines used by both Toyota and Ford (Escape Hybrid) were not true Atkinson-Cycle in that they still have 4 distinct cycles and it takes two full revolutions of the crankshaft to complete one power cycle.
The True Atkinson Cycle engine takes 1 full revolution to accomplish all 4 strokes via it's linkage and intermediate shaft (a marvelous design).

The Engines we are dealing with here are (for all intents and purposes) standard Otto Cycle 4 stroke engines that have a special valve timing mechanism (VVT). I truly have no idea at this point how either Toyota or Ford can claim Atkinson-Cycle engine..


Probably the "modified" Atkinson-Cycle (I think this is what I've heard this design called), engine that Toyota produce has the advantage of simplicity and less moving parts to wear out.

I assume it would be possible to boost the output of the engine by closing the intake valves sooner thus upping the effective compression ratio on the combustion stroke to the maximum that premium fuel could tolerate? I'm not suggesting anyone try this it's just a hypothetical question.

 

I'm guessing that the engine cannot take advantage of a higher octane and still keep the CO2 levels at spec. That is, while the VVT could probably make excellent use of high octane for increased power, the emissions (and quite possibly the overall efficiency) would suffer. Therefore, I'm guessing the computer will not take advantage of the octane in the way a normal knock sensor controlled engine would and will keep emissions control an overriding priority over power.

-- Alan

 

I agree that it would be a Modified Atkinson Cycle engine - I just wish Toyota and Ford would call it what it really is...

In regard to maximum compression ration on premium fuel - I can speak to that one but not with the TCH. I've done a lot of work in the field of auto-racing and engine design / building. The highest compression ratio you can typically get by with in a non-ECU controlled vehicle is 10.5:1 with alloy cylinder heads and 92 Octane fuel.
Some other points of reference:
I've got a 69 Camaro-SS with 10:1 with Iron Heads and have had to reduce the timing substantially in addition to not lugging the engine in any one gear or detonation occurs.
I've also got a 70 Nova Pro-Street car with a 468 Cubic Inch Big-Block that has 12.5:1 compression. It requires 100 Octane minimum for its 605HP. I'm in the process of building a new 468 inch engine for the Nova that will have a static compression ratio of 9:1, but the GMC 6-71 Supercharger will raise that effective (dynamic) compression ratio to between 13-15:1 depending on the speed of the blower. It will be running on E85 rather than gasoline.