OT - Cylinder Deactivation

I think every manufacturer is working on this in some way shape or form...bottom line is that it is the modernized version of the infamous 8-6-4 cylinder deactivation scheme.

The latest 2007 Tahoes and Yukons have them out...appears that it adds about 4mpg highway.

The system is of course complex...but here's my thinking:

It seems like the most difficult challenge is in "calibrating" the controls to determine when deactivation is going to start. Some people are going to want it to cut in sooner, some people are going to have power-loss at highway speeds when passing or hill climbing. (In reality I think that the inactive cylinders can come on as fast as the next intake valve and spark event...so that's pretty fast.)

However the bottom line is that it is calibrated to "feel good" and "smooth" which in my thinking means heavy on the power side.

But the root of my post here is: why bother with all the control algorithms? Just gimme a selector switch on the dash.

If I am feeling cheap, heck, I'll leave it in DEAC the whole time, even while accelerating, if I need a little extra to get by that 18wheeler, or I'm going to tow a trailer, then back to ALL.

Seems like there is a lot more economy to be gained there in my thinking, and possibly some customer satisfaction to boot. After all, when Joe Public determines what each setting will do in terms of the seat-of-pants performance, and what it does to his wallet, he/she'll select a "personalized" setting that's bound to satisfy.

Your thoughts?

Actually - the control system is pretty simple, it is the software that is complex. All that happens mechanically is that the lifters collapse on the cylinders that stop working and those cylinders are turned into air springs.

The complexity comes in shutting off the fuel injectors, changing the throttle response (pedal by wire to servo on the butterfly) - changing engine timing, shift patterns . . . bla bla bla

All of these controls already exist on the engine, they just all need new setpoints and operating parameters when running with 4 of 8 cylinders shut off.

I know a guy putting one of these motors into a '54 chevy suburban - I was surprised at how simple the wiring harness / engine control unit was and how simple the system was for turning off the valve train for the cylinders that were shut down.

I think this might actually be something that GM has done right for a change.

IIRC, Cadillac was the first to try that, back in the late 70's/early 80's? In the mid/late 80's I was doing a lot of work for Lucas, the plant was making aftermarket replacement fuel injectors. I often ate lunch with some of the staff at the in-plant cafeteria. One day the conversation was about an order for some injectors for the Caddy that shut off some cylinders. They needed a car to test them,had a hard time finding one, finally found one that an elderly Black man had. They paid him a hefty sum, & rented him a new car to use, while they did the R&D..
I think it is a good idea to run on fewer cylinders, once up to speed... the only thing I wonder about, is the long-term effects of the different thermal differences causing more wear...

I could imagine that giving an extra 4 mpg,
but what's the base mileage that one starts
with, 10, 12 mpg?

Sure some folks need a truck/car like that.

Sure, the ones on *this* board are among the
few in the world that really do, honestly.

All the ones I see driving along on the parkway
around here (and by this, I mean that more than
half the vehicles I see on my morning commute
fit the gigantic SUV profile) have about one
person in them.

Sure that one person's gonna get all touchy
feely when the jug selector goes from 8 to 6 and
all, but they still look like found a turd
in the punchbowl every time I see them at the
gas pump.

Jim

The electronic automatic selection of number of cylinders probably allows the manufacturer to count some aspects of the higher mileage into their fleet mileage toward meeting federally mandated standards. The knob on the dash almost certainly wouldn't give the manufacturer any brownee points. Charles

matt:

You and I may thing a manual switch is a good idea but try to teach somone else how to use it.

Steering wheels and brake pedals are difficult enough these days.

Motion makes an excelent point about software. Why have a bunch of junk when code will do the work.

WHAT!!!!

This coming from Jimmy K???

Well if you are going with such an outlandish idea of cutting engine cylinders out of operation, you might as well go all the way. Mechanical links and levers really aren't that good at that kind of thing.

I am surprised that the big three didn't do it the Navy Way. The SUV's would have their big, throbbing V8 or V10 and then have tweety little four cylinder motor for a 'cruise engine'. If the things are as friggin big as frigates, then they should have the propulsion system of one.

Matt, you are not like most people. Your average soccer mom is not about to push a switch for anything other than her lipstick to pop out.

Look at the horrendous problems and expense generated by electonic shift 4WD setups - yet I don't see people lining up at the dealerships demanding the good old lever sticking through the floor.

I think most people have the attitude "I don't care what's under the hood or how it works - you take care of those details - I just want the end result".

In other words, they don't even care if the cylinders deactivate or not -they just know iut's up to GM to give them a 5500lbs. SUV that gets 30 MPG. In exchange, they sacrifice their future retirement by throwing $1000 a month at the General.

I always thought of myself as a manual switch kind of guy.
I drove a sports car with a 5 speed for years.
But my current car, a Mazda 3, came with a fancy smart automatic transmission.
My wife refuses to learn to drive a stick, and so I ended up going with the slush box, but I insised on getting one with the manual shifting option, Right?

So what I find, is that current software is so good, that the damn automatic has several different shift point patterns stored in it, and it chooses which one to use, based on gas pedal position, speed, rpm, etc- and you know what? The stupid thing is usually RIGHT!

So occasionally, when I am alone in the car, on a twisty, deserted road, with the music turned up high, I manually shift- but I find 98% of the time, its just as fun to drive with it set on full auto- for instance, if I roar up a freeway on ramp, it will hold first gear til 6000rpm, then shift to second, and hold it too, making for a real zippy freeway merge. But under normal, everyday driving, it might make the same shift at 2500rpm.

My point is that even the few people who demand the control of a manual switch will find themselves hardly using it, because of how good the technology is today for predicting when to switch.

Newer 6 speed automatic transmissions have multiple shift pattern templates- sometimes as many as 6 or 10 of them- and usually, its dead nuts on.
I cant imagine that the General is that far behind- I think they probably have this thing adding and subtracting cylinders pretty much when you would do it manually.

Jim Rozen said about SUVs: "but they still look like found a turd
in the punchbowl every time I see them at the
gas pump"

Amen brother.

I don't care how many cylinders you shut off on a HUMMER (I think all caps are manditory for this vehicle), the aerodynamics and size put a pretty low ceiling on the MPG. Not that a BUMMER buyer would ever select a 4/6/8 option...

To my mind, they represent some of the worst characteristics of our society: gross consumerism, distorted values regarding form/funcion, that old "keeping up with the Joneses" competitiveness, willfull ignorance of global engergy issues, and just plain old selfishness.

Not to mention that they're useless for any real hauling or real off-roading activities, and not particularly safer than a minivan.

I have a question for the engineerine-minded here.

Since injection and ignition are now computer controlled, why couldn't the de activated cylinders be mixed up in some sequence so that the same cylinders aren't running cold?

Maybe an algorithm controlling a stochastic sequence so that the engine is at optimum balance while the distribution of deactivation maintains uniformly constant temperatures amongst cylinders.

Jimmy Scores! - Check it out, the statement is technicllay correct.

Jargon as my statement may be I am asking this seriously.

Jim - I thought that's how they did work. I know MSD ignition uses this logic for their rev limiters, I just guessed that the same thought went into this.


Andy

Jim, what you are proposing actually works in "camel mode" ala when all coolant is lost. Air is pumped every other stroke in a non-combustion event to keep things cool.

However, this is a very low-powered "limp" mode, and the emissions are wacked out because of the unexpected fresh air. The engine is trying to save itself.

Not that it couldn't be combined with the actual valve deactivation that works above.

But then you're trying to manage two technologies concurrently...a lot of variables, lot of development, and a lot of validation to make sure it works.

After some more thought on the original posting...what if I upgraded my solution to a 3-position selector..."DEAC - AUTO - ALL", or simply "DEAC - AUTO". That way the soccer mom doesn't have to ever mess with the switch if it looks too "scary"

I think I can do better than the computer, because I'm willing to tolerate some clearly underpowered moments, whereas the person signing their name on the powertrain calibration is not. And I also think there are more applications as the price of gasoline climbs up.

We can all talk about releasing a 2.5L Iron Duke powered full sized truck, but it would get laughed off the dealer lots...however, put out a 5.3L V8 that can run more or less like the 2.5 from a fuel economy standpoint...then you have something.

Really, the best application (and most willing customers) is probably for pickup trucks...when lightly loaded or hauling people only...choose DEAC, however when loaded up with sod, sand, granite, whatever...then the power can be chosen. Those guys generally seem financially conscious.

There was an interesting controversy on one of
the motorcycle forums a while ago.

The essense of it was, "where does engine
braking come from?"

There was one set of folks who claimed that
air pumping was a major contributor to engine
braking. That is, you should see a change
in the load that an engine produces on the
driving source as the throttle is opened or
closed.

The experiment was, to turn the ignition off
on a vehicle while it was decending a hill,
in gear with the motor acting as the brake.

Then see if changing the throttle position
altered the speed of the vehicle.

The short answer is, it doesn't. Pumping
losses were small in comparison to the drag
of the moving parts in the motor. There
was no change in speed as the throttle was
opened up.

Jim

Not so sure I agree, Jim. The problem with the 'test' you describe is that while the throttle position is being changed, cam timing is not.

You don't mention if the 'throttle theory' states that the load should decrease or increase as the thottle is opened - I'd like to hear what they say about that.

Without seeing some better definitions put in place, I'll wager that the engine still acts as a pretty good 'air brake' regardless of throttle position.

The 'throttle test' would suggest that if you could instantly remove the cylinder heads on deceleration you'd still see the same braking; i.e., there is no significant contribution to braking as a result of the air being compressed - it's all friction. I don't agree at all.


That experiment is hillbilly engineering at it's best.

I'll even go you one further and tell you WHY there is not a vast difference between closed and open throttle.

First off, keep in mind with spark removed the engine becomes a much different animal than when combustion is present.

With the thottle open, the engine can gulp plenty of air, and fill the cylinders 'full'. When the piston has to compress all that air, it acts as a brake. Everyone is happy.

With the throttle closed, the engine can STILL fill its cylinders pretty well. How? By robbing air from the exhaust cycle or from other cylinders. With all the valves opening and closing there is still plenty of air to be had, even if it doesn't come past the throttle plates. Again, with no combustion taking place the engine is not so fussy as to where all the air comes from or goes.

I also don't agree that the thottle position makes NO difference - I have done the 'throttle test' many times over the years and there IS indeed a difference, if not great. The difference is attributable to the differences mentioned above in how and where the engine gets its air.

Those motorcyle guys you were talking to was a bunch of dinks!

Jim Rozen said:
"The experiment was, to turn the ignition off
on a vehicle while it was decending a hill,
in gear with the motor acting as the brake.

Then see if changing the throttle position
altered the speed of the vehicle."

Virtually all carbureted street motorcycles use CV carbs which don't have a direct linkage between the throttle cable and the slide. They have a butterfly that controls the vacuum, but the slide operates independently.

If you wanted to do a more meaningful test, you could do two no-power downhill rolling timed runs: one with the slide closed, one with the slide removed and the butterfly open. Of course, that's a total PITA...

GregSY said: "With the throttle closed, the engine can STILL fill its cylinders pretty well. How? By robbing air from the exhaust cycle or from other cylinders."

Carbs are designed so that when the throttle is "closed" there is still an opening that passes enough air to draw fuel from the pilot jet. Otherwise, the motor would just shut off as if you'd stuck your palm over the intake every time you let the throttle return to idle.

Racer Al,

I am thinking more of all engines rather just just bikes; Jim's Throttle Theory deals more with engine braking for all vehicles rather than just bikes.

Regardless of a pilot jet air passage, the engine will still fill the cylinders - nature abhors a vacuum after all. Even on theworst culprit, and enigne with mechanical slides and no connection to any other cylinders (via manifolding) it will still get air from the exhaust pipe and a slight bit from the crankcase.

BTW - My ol' Triumph Bonneville has a cable attached to each slide....no CV carbs!

Many modern motorbikes do have CV carbs.

A test such as mine, done with CV carbs would
be invalid. The test was done on:



You might be able to notice the carbs lack
CV diaphragm domes - it's not *real* clear from
the photo, but they're direct slide carbs in
fact.

You also might notice there's not much way for
air to swap from one jug to the other.

The theory that engine braking would be
quite reduced if the heads (the actual discussion
at the time suggested removing the plugs) were
taken off is on point I think. Consider that
there's no air to speak of coming in during the
downstroke, so there's considerable vacuum being
created. There's a lot of force on the rod on
the downstroke, and thus a good deal of friction
between the piston and the cylinder wall.

This happens even when there's no pumping loss,
and would disappear if the plugs were removed.
I never did that particular test, partly because
I could not figure a safe way to valve the
chambers open to air on the fly.

The reason I'm bringing this all up is, how
much does one gain by shutting down half of
a V8 motor? The implications from my tests
suggest not a heck of a lot. You might be
do better by simply sticking a chunk of 2X4
under the gas pedal?

Now the other issue with the test I did is
more subtle, and somebody pointed it out at the
time: the boxer motor has both pistons rising
and falling at the same time. The volume
change in the crankcase is pretty huge by
comparision to a V8 motor. So there's the
possibilty of a lot of pumping loss in the case
if it's not handled right.

There was the suspicion that the "no change"
effect from full/closed throttle in braking
might have had something to do with that as well.

Jim

Pumping losses are caused by the bottom side of the piston pushing against atmospheric pressure air.

The lower the pressure on the top of the piston on intake, the greater the pumping losses. On a naturally aspirated engine there will always be pumping losses.

The compression braking that you feel when going downhill is actually caused by the pumpung loss due to the fact that you took your foot off the gas pedal.

The effect was greater in the old cars that didn't have the link that holds the throttle partway open when coasting against the engine as a part of the pollution control system. Many young people have never driven old cars like that.

On any engine, when there is no ignition on the power stroke the compressed air in the cylinder gives back most of the energy that it took to compress it. Without mechanical friction and heat loss the give back would be perfect.

The Jake Brake and it's like allow the Diesel to go to full compression and then pop the exhaust valve. All the energy used to compress the air in the cylinders is completely lost. The heat energy invested in the compressed air by the overdriving power supplied to the Diesel goes right out the exhaust.

PLAN n works in reverse, the engine can dissipate the same power that it makes.

Enging makers test their engines for motoring friction on a dynomometer. The dyno's generator is connected as a motor and the current at no load is comared with the current when turning the engine with no compression. Motoring frictiom goes up a bit with rotative speed but not much.