Are the valves completely closed or is some mixing with fresh air allowed to keep cylinder temperatures down?
How does this kind of engine save fuel?
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JHZR2
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I can see the spring analog in order to not require the rest of the valvetrain, etc to have tomove totaly dead weight. However, I was under the impression that there was a 'decompresion solenoid' valve or something to prevent the buildup of pressure... is that not the case?
My impression was that it would be similar to pumping a bicycle pump without having anything attached to the other end... the piston moves along its stroke, but without P-V work, the energy required to move it is minimal at best. Of course, it is a pumping loss then... but being that any real system isnt 100% efficient, you either have pumping losses or compression losses, which at least have some recoverable energy.
Of course I suppose this doesnt account for the change in momentum, so a spring type movement is required... So I agree with XS650, is it fresh air to perform cooling, or does the air stay in the chamber semi-permanently during the shutdown portion? Also, is the air in there metered to be 1 atmosphere of pressure at some standard point, or is there less than a full amount of air in there, so that when it is compressed to act as a spring, the compression work isnt as high as if it was a 'full combustion chamber worth' of air?
Thanks,
JMH
My impression was that it would be similar to pumping a bicycle pump without having anything attached to the other end... the piston moves along its stroke, but without P-V work, the energy required to move it is minimal at best. Of course, it is a pumping loss then... but being that any real system isnt 100% efficient, you either have pumping losses or compression losses, which at least have some recoverable energy.
Of course I suppose this doesnt account for the change in momentum, so a spring type movement is required... So I agree with XS650, is it fresh air to perform cooling, or does the air stay in the chamber semi-permanently during the shutdown portion? Also, is the air in there metered to be 1 atmosphere of pressure at some standard point, or is there less than a full amount of air in there, so that when it is compressed to act as a spring, the compression work isnt as high as if it was a 'full combustion chamber worth' of air?
Thanks,
JMH
According to Wikipedia both the intake & exhaust valves are de-activated by dropping oil pressure from the hydraulic roller lifters.
A decrease in throttle body air pumping losses are also referenced & are a factor in the fuel economy gains.
Note that this article states that only 40 hp is required to move a full sized vehicle down the highway at freeway speeds.
A decrease in throttle body air pumping losses are also referenced & are a factor in the fuel economy gains.
Note that this article states that only 40 hp is required to move a full sized vehicle down the highway at freeway speeds.
why would you need fresh air to cool? There are no combustion events, which is probably a great contributor to heat. So the coolant surrounding the cylinder is probably sufficient.
Of course, this makes me wonder about what such different temperatures at different parts of the head would do.
I don't know if an entire bank of cylinders is deactivated, or if two cylinders on each bank are deactivated.
Of course, this makes me wonder about what such different temperatures at different parts of the head would do.
I don't know if an entire bank of cylinders is deactivated, or if two cylinders on each bank are deactivated.
JHZR2
Staff member
Fresh air to cool because in the simplest sense, PV=nRT, and given that we arent working with idealities, but rather real systems, there will be heat buildup due to the compression over thousands and thousands of cycles.
I was wondering the same regarding temperature gradients at the head... perhaps this is a good reason to allow heat buildup in the cylinder, so that there is minimal variation...
JMH
I was wondering the same regarding temperature gradients at the head... perhaps this is a good reason to allow heat buildup in the cylinder, so that there is minimal variation...
JMH
You are probably right on the heat being taken care of by the coolant.
The 2006 Honda Odyssey has the cylinder deactivation. Now, this isn't exactly scientific because the model with the cylinder deactivation is 62lbs heavier than the model without. But the EPA difference between them is 25MPG without, 28MPG with. That is an 11% difference.
Truth be told, my best MPG has been 20.26MPG. However, we do 90% of our driving in the city so it doesn't surprise me.
For what it is worth, the cylinder deactivation is hardly noticeable. Then again it only seems to kick in on flat surfaces with the cruise control set at 70MPH or below. Any faster than that and it needs all 6 cylinders.
I could see it being more useful on an 8 cylinder that has a larger margin to improve in MPG. It doesn't seem to turn on very often in the 6 cylinder that is hauling around 4537lbs of weight (which is really 5000+lbs with passengers in it).
Truth be told, my best MPG has been 20.26MPG. However, we do 90% of our driving in the city so it doesn't surprise me.
For what it is worth, the cylinder deactivation is hardly noticeable. Then again it only seems to kick in on flat surfaces with the cruise control set at 70MPH or below. Any faster than that and it needs all 6 cylinders.
I could see it being more useful on an 8 cylinder that has a larger margin to improve in MPG. It doesn't seem to turn on very often in the 6 cylinder that is hauling around 4537lbs of weight (which is really 5000+lbs with passengers in it).
mechtech2,
Huh? Vacuum is produced when the throttle is restricting the intake. The cylinders are trying to draw in air and the throttle is restricting that.
If you watch a vacuum gauge, vacuum is closest to zero at WOT, and is highest when you close the throttle at high RPMs. (Not making much power.)
I may not be a mechanical engineer, but I believe I do understand what causes vacuum in an engine.
Huh? Vacuum is produced when the throttle is restricting the intake. The cylinders are trying to draw in air and the throttle is restricting that.
If you watch a vacuum gauge, vacuum is closest to zero at WOT, and is highest when you close the throttle at high RPMs. (Not making much power.)
I may not be a mechanical engineer, but I believe I do understand what causes vacuum in an engine.
I think he understands that. He just said it differently. He is looking as making power=losing power. I think.
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