Dynamic Skip Fire for 2019 Sierra V8 Engines

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Originally Posted By: emmett442

As I understand it, there is no throttle valve: like a diesel. That way, since there is no air restriction, whichever cylinders are selected to fire are operating at peak efficiency every time they fire = less emissions and better fuel efficiency.

If that's correct, I suppose that means either they've done away with all vacuum operated equipment or they're going to use a vacuum pump to retain it.

As far as complication, it seems to me they'd be able to eliminate the throttle body and it's associated management. Not sure EXACTLY how this is implemented, but there's a chance that this could actually be a simpler (mechanically) system than what we currently have!


My BMW is like that. Does not have a throttle body. For vacuum, there are two pumps in the cylinder head. They supply vacuum to the brake booster etc, and run the crankcase at a vacuum for PCV.
 
My 135i doesn't use the throttle plate except in limp home and certain limited situations. This sounds like what BMW does plus DI fuel control.

Seems to make sense to vary all cylinders instead of select ones.
 
The BMW uses Valvetronic(tm), a continuously variable intake valve lift mechanism which as you mention performs most of the throttling in normal conditions. The GM system has no such variable lift capability and will undoubtedly use the throttle plate much more.
 
If they find the sequence and algorithm of firing/shutting off that is imperceptible to the user under all driving conditions, that could be a great system from the average driver's perspective. However, I can't even think of all the combinations of harmonic interference throughout the engine, the body and suspension vibrations.
Continuous alternation of the firing cylinders will definitely mitigate current problems with oily cylinders, fouled plugs and valves. However, they now double the number of AFM lifters vs 4/8 design, and we know how they currently do sometimes. It doubles the chance of the collapsed lifter due to so many things that it makes me not liking it twice as much as my 4/8.
 
BMW varies valve lift and duration, anywhere between .8mm to 11mm in valve lift, thats how they control idle and acceleration without a throttle body. The throttle valve is always held wide open. Now a 20% percent decrease in consumption is great, but at what cost? Idk if any BMW owners have dealt with Vanos solenoids, eccentric shaft sensors, or the valvetronic motors failing, but in every case its not very cheap to repair. And god forbid you bought one of the cars with cam bridge wear issues.... Just another thing to overcomplicate an engine, add ot its repair costs, and adds to what the tech needs to know and fix. Im guessing this will be phased out in less than ten years.
 
Despite a poor choice of name, I think (hope?)that this will be good technology. It's not exactly blazing a new trail for technology, others have done it before. What I read is that your oil change regimen will affect the system more than variable valve timing presently does. Keep the oil nice and clean, it should last....devil in the details as always.

When I read this thread, it makes me chuckle about how - if we could all be transported back in time - witnessing the birth of automatic transmissions and how would the experts at BITOG react to the notion of torque converters, valve bodies, solenoids, planetary gears.
 
This is BITOG!

Bring back-points, condensers, distributor caps, and carburetors!
 
Originally Posted By: KGMtech
When I read this thread, it makes me chuckle about how - if we could all be transported back in time - witnessing the birth of automatic transmissions and how would the experts at BITOG react to the notion of torque converters, valve bodies, solenoids, planetary gears.


I wish GM all the luck in the world to be finally successful with cylinder de-activation. But as you mentioned, we've been there before with current AFM system, and the new one is variation of it with more collapsible lifters, expanded VLOM and the software... The current system isn't great by any stretch of imagination, that's why many people take AFM out in the process of the engine re-built after its failure. How much hope there is that the new and improved DOD system will eliminate all the deficiencies of the current one and improve reliability? With added and more complex components to boot.
 
Originally Posted By: CKN
This is BITOG!

Bring back-points, condensers, distributor caps, and carburetors!




I'm quite sure many of us will not be the first in line to get hands on this very modern and exiting piece of automotive engineering, would you?
 
Originally Posted By: yugrus
Originally Posted By: CKN
This is BITOG!

Bring back-points, condensers, distributor caps, and carburetors!




I'm quite sure many of us will not be the first in line to get hands on this very modern and exiting piece of automotive engineering, would you?



AFM-for example gets a bad rap. GM sells over 40,000 units a month (Silverado/Sierra-combined) and the Internet (and it get perpetuated on this forum as well) that there are trucks lined up in to the service bay and around the block due to AFM issues. While there has been some isolated cases (and we don't have maintenance history on problem trucks) the issue is fairly isolated.

I would have no issue buying a new truck with a comprehensive warranty.
 
Originally Posted By: KGMtech
When I read this thread, it makes me chuckle about how - if we could all be transported back in time - witnessing the birth of automatic transmissions and how would the experts at BITOG react to the notion of torque converters, valve bodies, solenoids, planetary gears.


Let's see, automatics as we know them date back to what, 1950, give or take? In any large numbers. Yet what is the given typical lifespan of an automatic these days, and what was it over the years?

Most of the hard parts seem to be robust (save 4L60 sun shaft) but everything else is a wear point in 'em.
 
Quote:
...Developed by parts supplier Delphi and automotive tech company Tula, the cylinder shut-off technology has the biggest effect in larger capacity engines like V8s...

...The dynamic skip fire cylinder (DSF) deactivation system works by deciding whether to fire or skip each cylinder before its firing. If a cylinder is skipped, the intake and exhaust valves are held closed by Delphi’s cylinder deactivation hardware. The system works by controlling the car’s spark ignition, so only petrol cars are compatible. It makes independent decisions up to 32,000 times a minute…

...Scott Bailey, president and CEO of Tula said: "Every time a cylinder is ready to be fired, the system makes a dynamic decision – do we fire this cylinder or do we drive this cylinder for torque reasons?"…

...Bailey explained that this process takes place independently for each cylinder, so each one can be managed to maximise efficiency when not running at full throttle. "We don’t look at running fixed patterns [like conventional cylinder deactivation systems], so we can run anywhere from zero cylinders to 100% of the available cylinders, with any firing density between them," he added...


https://www.autocar.co.uk/car-news/industry/new-dynamic-cylinder-shut-tech-cut-co2-15-2018
 
All I know is that I'm glad that my 98 K1500 with the 5.7L only has 135,000 miles on it and that the body and interior are still nice so that I don't have to probably ever buy a new truck again. My 98 with the 7.4L only has 115,000 miles so I should be good either way.

I don't like cylinder deactivation and is why I chose a Ford Mustang GT when I was shopping performance cars a few years ago since both GM and Dodge were using it in their cars.

I tend to keep vehicles a long time and like things to be the least complicated as possible. It will interesting to see how reliable this system is long term.

Wayne
 
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