Scotty discussing drawbacks and criticisms of those silly cylinder deactivation systems the other day gave me an interesting idea. He said the uneven heating slowly distorts the cylinder bores, engine block, etc. and the oil doesn't flow right in those cylinders because they're not at operating temperature. As far as I know, a V8 is essentially a pair of Inline-4s joined at the crank and set at a 90-degree angle for balancing, along with the addition of balance shafts to run smoothly. Instead of shutting down the same 4 cylinders for cruising, why not program the PCM to alternate which 4 cylinders fire on every other rotation of the crankshaft? That would minimize the hot and cold spots that develop, and ensure the cylinders are used relatively evenly. The only issue I could really see popping up with this is the possible introduction of nuisance vibrations, since the firing may not be even at times. I agree that these systems are silly, don't drive a V8 if you don't like bad MPG, but government MPG regulations can't be argued with.
, why not program the PCM to alternate which 4 cylinders fire on every other rotation of the crankshaft?
I think that would dramatically increase cost and complexity. That means you would would have to integrate AFM technology into each cylinder. If there's not enough space in the block, that means you have to redesign the whole block. Which means you have to redesign everything around the block too, and it cascades from there. Millions of bucks right.
Maybe that's what they'll have to end up doing. They tried going the quick & dirty route the 1st time we know where that led them.
Or maybe, they'll eventually drop the V8 like everyone else and go turbo V6.
That's usually what they do with pretty much everything to keep things as cheap as possible, and they don't seem to pay much attention to problems, or they deny them until it's blatant. Ford made that mistake with the Ranger based Explorer in the 1990s, trying to be cheap by using a pre-existing platform not intended for the new purpose. They to "fix" the roll- over problem by letting air out of the tires and running them at lower than normal pressure instead of just a clean sheet. They ended up doing that in the mid 2000s anyways.
The manufacturers seem to replace their engine designs around once every 10-20 years these days. I read just now that the system cuts off individual valves as well as the ignition, which I didn't know. It does sound like this would be a good idea but extremely complex to implement.
yup, it's the cause of the notorious AFM collapsed lifters.
The best way to "improve" cylinder deactivation is to disable it. (Though the best thing is not to have it in the first place.)
I won't buy vehicles with it. This was one of those random thoughts I have to fix well intentioned but poorly executed ideas. I had an idea in college for a jet engine that combined a high bypass turbofan with an afterburner from a turbojet/ low bypass turbofan with cleverly designed bypass ducts. I showed it to a professor whose expertise was aircraft structures. He sent it to a guy he knows on base. Apparently it caused quite a stir and debate, before a final person in research said the theory I had was excellent, but advanced thermodynamics doesn't support it, sadly. I did get kudos for thinking well outside of the box and off the beaten path. The idea was supposed to combine the relative fuel efficiency of a passenger jet with the available speed of a supersonic fighter.
You’re basically describing GM’s “Dynamic Fuel Management”(I think that’s what it’s called). They have it, I believe, in their 5.3 and 6.2L “EcoTec” V8’s.
It’s basically ECM programming that shuts down cylinders in sequence, depending on load. Im not an automotive engineer, so someone correct me if I’m wrong. The way I understand it is at full power, all 8 cylinders will fire. As demand drops, it will skip 1 out of 8, then 1 out of 7, then 1 out of 6, and so on. Or you can think of it that it is an 8 cylinder motor that can be functionally a 2 cylinder, 3,4,5,6, or 7 cylinder motor.
Because the deactivated cylinders are in sequence, it’s never the same cylinders that shut down, and you don’t have the same long-term wear issues as the old “Active Fuel Management” system. And since it’s mostly an ECM programming thing, you aren’t adding that much complexity.
You are right that vibrations are the issue, and that took a lot of work to get sorted. Also, it’s pretty new, so we will have to see what long term issues come up.
I believe we're discussing the same thing. What I was trying to get at, was instead of leaving the same 4 cylinders off the entire time, alternate the firing of each cylinder, so it's still functionally behaving as a 4, only the firing cylinders alternate. Doing that within a revolution or two would keep the block close to uniform in temperature. I read after what Joe mentioned about complexity, that the lifters on said engines are hydraulically disabled, sealing the cylinders. That would be quite difficult to start and stop within microseconds. https://www.carmagazine.co.uk/car-news/tech/what-is-cylinder-deactivation/
Yep. Exactly.
Looking at Range Technology that Toyotagrl mentions. Their website emphasizes that their OBD plug-ins eliminate the hesitation you get on acceleration. I imagine that’s a pretty annoying feature of current systems.
Range Tech. make products that go in between the ecu and the vehicle, so no messing with reprogramming it, and the pitfalls that go with that. I'll disabling it and the auto stop/start (yet another stupid feature). I'll be getting my unit soon for my pickup, waiting for it to get back in-stock (stupid chip shortage).
do you have a link? All I see is the dongles that plug into OBD.
@daywalker @toyotagrl @chucktobias
I don't think the point of Justin's post is "how to defeat CD".
Maybe I'm wrong, but the way I understood it was: Companies will be FORCED to consider technology such as CD in order to meet stricter regulation. How can CD be designed to work reliably?
This is what I was trying to convey, make the thing actually workable and not cause engine wear because it was poorly executed.
I don't know if that is even possible.
yeah..the "idea" is a good one, but the execution is pi$$ poor which leads to problems years/miles later.
There is a reason Toyota has not implemented CD. Plus, they will go with turbos and hybrids; I don’t think they will have to go with CD, unlike the other automakers.
Keep in mind the actual cylinder deactivation system such as GM’s AFM (or DFM, which they have moved to now) - the hardware within the engine is still there, i.e. the lifters, the cam, the lifter oil manifold assembly (LOMA), the oil pressure relief valve, the signal path to the LOMA, all those can still fail or activate/deactivate at the wrong time (if signal is corrupted or there is a glitch - gotta love GM electronics). A full proof solution would be to replace the lifters, cam, etc. with non-AFM/DFM ones and retune the ECU but that is thousands of dollars from a reputable shop or just avoid the stupid thing altogether.
Hearing lots of unhappiness from 5.3 and 6.2 owners right now about lifters. Seems like GM’s engineers are better than their manufacturers.
do you have a link? All I see is the dongles that plug into OBD.
Range Technology 22451 Pulsar LT for 2019-2022 GM 1500 5.3L/6.2L
This is what I need for my truck, but they have other units for other years.
ah ok that's for the new DFM system. Thanks.
Ouch. That's spendy.
The only way to improve the CD (AFM) system is to eliminate it and concentrate of better solutions to keep the government and the EPA happy. The way things are going, everything will have little tiny displacement engines with turbochargers that won't kick in until after the car passes the smog test.
To add and to question as well I guess. (I ain't super familiar so apologies for that) Would not throwing in more technology at CD also help it's case? My additional thought being why have none used free valve that Koenigsegg created? There isn't that many patents to get past as the concept is fairly layed out. We already control fuel in regular cars, I would like to think that controlling the air to get that microscopic adjustment on the air fuel ratio would better help efficiency right? There was a guy who made it work on his Miata though I'm forgetting the name.
