alfadriver wrote:
In reply to crankwalk:
That's for their variable compression, not variable displacement....
The link says compression and displacement. Also, there is a TURBO!
Other than the fact it can adjust its compression ratio between 8:1 for high performance and 14:1 for maximum efficiency, the Infiniti VC-T can adjust its displacement. But how does it do that? Well, it so happens that the pistons aren’t connected to the crankshaft.
In this application, Infiniti went for a pivot arm with a connection at each end. The first of the two ends is connected to the piston, while the second is connected to a second lower shaft, which is controlled by an actuator arm. While the pistons move up and down according to the crankshaft’s lobes, the actuator arm mentioned earlier is able to change the angle of the pivot arm. Are you still with me? Good.
When the actuator arm moves the pivot up, there’s less room at the top, equaling a higher compression ration. When the pivot arm is in its lowest position, the compression ratio goes down. But that’s not all there is to this engine. The second lower shaft eliminates the need for counter-rotating balance shafts as you might find on a regular internal combustion engine.
Edit: spelling
In reply to crankwalk:
Either I'm missing something here or the writer doesn't understand what "displacement" means, the piston's range of motion doesn't change (at least to any appreciable degree), only where in the bore that motion is happening.
In reply to crankwalk:
The volume of the compressed area changed, yes. But the displacement does not.
alfadriver wrote:
In reply to crankwalk:
The volume of the compressed area changed, yes. But the displacement does not.
OT:
Just for my clarification, isn't Infiniti's system of changing compression ratio changing the length of the stroke of the piston to make a smaller area to compress? Isn't that like the opposite of a "stroker" motor and in turn lowering the displacement? Just trying to wrap my head around it.
In reply to crankwalk:
In theory they could, but it would be such a small change that the effective displacement change would be almost nothing.
But I would wonder if the mechanism can operate that fast.
alfadriver wrote:
In reply to crankwalk:
In theory they could, but it would be such a small change that the effective displacement change would be almost nothing.
But I would wonder if the mechanism can operate that fast.
In my head (speculation) how they would use it would be high compression cruising around with vacuum then when boost is detected, the fulcrum drops the compression ratio for more aggressive boost and timing. I don't thing it would have to move "that" fast.
Knurled
MegaDork
10/25/16 7:31 p.m.
alfadriver wrote:
Funny how many of you think the idea of variable displacement is a terrible idea. It's really a good one- you can see and measure the fuel economy benefits. For the rolling AFM, I measured close to 10% FE improvement, especially in the city.
The problem are the problems.... If all of those can be fixed, it would really mean that the large NA engines will come back.
That is great and all, but in the real world, AFM engines seem to get worse economy because it trains the driver to kick the throttle open when it drops into four cylinder mode.
At least, on Da Boss's Suburban, when we eliminated DoD, real world as-measured fuel economy did not change, but the truck drove a hell of a lot better.
And this WAS one of the engines we had to work with where the dealership wanted to replace the engine. Just the lifters got replaced and it still works just fine, good oil pressure, no oil consumption. Doesn't make sense to me why they'd want to do a whole engine rather than lifters, I'd think the lifters would be more labor-hours and there isn't all that much profit on parts sold... and at the dealership I was at, labor rate went up as labor hours per job went up.
I've heard that if you stay with synthetic oil every 5k and change the little filter in the oil galley every few years the system lasts just fine.
I'd still rather tune it out when new or do a conversion...
In reply to Knurled:
"Trains" the driver? Seems like someone doesn't like it, and tries to drive around it. Which isn't hard to do- just like the skip shift in GM cars.
AFM plus 6spd auto plus 6000# Suburban= FAIL.
I deleted that crap and mileage didn't change on top of actually being able to drive it properly. It never could find the right gear/mode/situation to be in all the time. If it wasn't hunting for gears, it couldn't decide if it needed to be in 8 or 4 Cyl mode. Engineers need to get out of the flatlands and drive some mountains and they think they are so smart....
Ranger50 wrote:
AFM plus 6spd auto plus 6000# Suburban= FAIL.
I deleted that crap and mileage didn't change on top of actually being able to drive it properly. It never could find the right gear/mode/situation to be in all the time. If it wasn't hunting for gears, it couldn't decide if it needed to be in 8 or 4 Cyl mode. Engineers need to get out of the flatlands and drive some mountains and they think they are so smart....
They claim the "mileage savings" on the fleet fuel economy mandates from the feds. This is not much different than the VW crap.
In reply to bentwrench:
At least GM is trying to run the AFM in the field. Big difference.
In reply to alfadriver:
FiatChrysler has been in their hemis. Works way better than gm's idea. It's seamless and even with the 8spds don't hunt as bad for the right gear or mode to be in.
alfadriver wrote:
In reply to bentwrench:
At least GM is trying to run the AFM in the field. Big difference.
My point is they know it doesn't work and are still producing/selling it and customers are getting stuck with the fallout, because GM can't remove it without loosing cred with the feds.
In reply to bentwrench:
Which isn't nearly the same as intentionally cheating the system. Not sure how you can think they are equivalent. GM does a bad job isn't cheating- it's just doing a bad job.
Shareef
New Reader
12/23/19 4:04 p.m.
I've been told by my Chevy tech that gm knows this afm /DOD system is E36 M3ty but since it's happening on vehicles over the 100k mark(usually) that they wiggle their way out of it due to most warranties being exhausted. Also, by not taking responsibility, it does not affect the data of numbers showing that this is an issue. Recalling this issue would 'Break' Chevy and they know it. Also, if your arm/dod vehicle is under warranty, authorized techs are being instructed to 'nit-pick' and find any and all reasons to void the warranty, for instance, if you've ever had any work done by a non-authorized party, welp! Warranty Voided. Every changed your own oil, warranty voided!
My 07 truck has it. I decided to leave it in there but adjust it some. GM had it kicking out above 6% throttle input and at speeds below 20 mph. It was pretty annoying having it switch between V4 and V8 constantly. I adjusted it to kick out above 20% throttle and at speeds below 50 mph. It's much less intrusive now. Now it stay off around town but once it engages, it takes more throttle to kick it off so it's not constantly switching between V4 and V8.
The truck just turned over 200k so I guess I won the durability test.
Shareef said:
I've been told by my Chevy tech that gm knows this afm /DOD system is E36 M3ty but since it's happening on vehicles over the 100k mark(usually) that they wiggle their way out of it due to most warranties being exhausted. Also, by not taking responsibility, it does not affect the data of numbers showing that this is an issue. Recalling this issue would 'Break' Chevy and they know it. Also, if your arm/dod vehicle is under warranty, authorized techs are being instructed to 'nit-pick' and find any and all reasons to void the warranty, for instance, if you've ever had any work done by a non-authorized party, welp! Warranty Voided
If the majority of failures happen outside of warranty, then why should they be all that concerned? It's outside of the period where they are responsible for it.
They aren't selling new trucks to people who keep them for ten years. They also aren't selling new trucks to people who bought them used.
It's the same theory as extended oil service intervals and "lifetime" fluids. It's great if you're a three-years-and-out new car buyer/leaser, not so good if you're in it for the long haul.
Mine is doing great after I shut it off at 35k miles and now at almost 150k....
In reply to Shareef :
Join the class action lawsuit.
84FSP
SuperDork
12/25/19 9:52 a.m.
It wasn't terrible to convert the AFM back to normal when I turned an L76 into an LS2. It was lifters, lifter cups, valley cover, and oil pan.
84FSP said:
It wasn't terrible to convert the AFM back to normal when I turned an L76 into an LS2. It was lifters, lifter cups, valley cover, and oil pan.
Plus head gaskets and balancer bolt.
