Another Kill Switch Idea

[jeff88]

So I was wondering if this was possible and what it would take to do it...

I was thinking about having a kill switch (either a button or put it into neutral, more on that in the next paragraph), which will kill all, but one of the cylinders. When at a light I can hit the switch, which will kill 3 cylinders, but leave one on. When the light turns green, the other 3 cylinders will come on when I step on the gas, either all at once, or individually as needed (like a certain RPM count turns another one on, then the next, then the last). If I can make it to my destination without turning the other cylinders on then great, if not then I have the power of the cylinders to get me up to speed, but they won't be used if I don't need them.

For the neutral kill switch, I am thinking it would need at least two inputs. The first is obviously the transmission in neutral, but the second is RPM speed. If I am at speed and RPMs are say 1500, then it will not kill the engine, but at lets say 900 or less RPMs then it will work.

My question is: is this possible?, how do I do it?, and would it save me fuel in the long run (i.e. does the load of one cylinder powering the whole car without the "help" of the other 3 cylinders negate the savings of the other 3 cylinders being off?

Thanks for your help and insight!
Jeff

[wmjinman]

I'm not the knowledgeable, experienced mechanic by any stretch of the imagination, so this is just idle brainstorming because I like your thinking.

First, I guess you'd want to be killing the injectors instead of the spark - otherwise you'd be pumping raw fuel through the engine & out the exhaust.

Second, I kinda doubt it would even keep running on only one cylinder. When my 4-cylinder Swift had 2 dead cylinders, it barely ran - and when the mechanic pulled the power to the injector to either of the "live" cylinders, it would die almost immediately.

Third, I suspect you'd have to figure out some way to hold the valves open on the deactivated cylinders, or else the one remaining running cylinder would just be powering 3 "air compressors" doing nothing but sapping a bunch of energy. It's far beyond me to even imagine how the valve holding open thing would work, but I think the cars that actually can deactivate cylinders do something like that.

[redpoint5]

Originally Posted by jeff88

would it save me fuel in the long run (i.e. does the load of one cylinder powering the whole car without the "help" of the other 3 cylinders negate the savings of the other 3 cylinders being off?
Jeff

Neat idea, but not practical. Modern cars attempt maintain a set rpm while idling, and deactivating cylinders that are normally running will just make for a rough idle and either not save any fuel, or such a minuscule amount as to not be worth the hassle and rough idle.

You will also get misfire codes since the computer thinks the engine is running, but isn't detecting combustion events.

[Frank Lee]

In addition to ^, it won't run unless it also gets a heavier flywheel.

[Diesel_Dave]

You have several issues.

First, if the valves are still active on the de-actived cylinders, then you're going to have pretty much the same friction & pumping work to overcome as you did when firing on all cylinders. You might gain a little efficiency by running the one cylinder at a high load factor, but probably not much.

Second, if you didn't deactivate the valves, it's going to wreak havoc on the AFR control because the O2 sensor will see all the fresh air from the non-firing cylinders and massively over-fuel the firing cylinders.

Third is the mechanical balancing issue. Like Frank said, a single cylinder engine needs a massive flywheel to have enough retained momentum to complete the compression stroke.

[jeff88]

Ok so it sounds like I came up with another unicorn idea. What if I ran the same setup, but killed all the cylinders. The 'key' to reactivate them would either be putting it in 'D' or putting in in 'D' and pressing the accelerator. Then they would all go back on like normal. Or is this no different then a normal kill switch?

Would it need a heavier flywheel if it only ran one cylinder in neutral and all of them in drive?

Going back to wmjinman's point, how do the modern deactivated engines hold the valves open? Computer tells it to stay open, but what actually stops gravity from holding them down? Also do these vehicles have a camshaft? With yhe ability to stop the valve action I would think the nudge (excuse the improper name) on the shaft would need to be out of the way, so it doesn't force the valve down.

Thanks!
Jeff

[Frank Lee]

Pop the hood, start it, pull injector or plug wires until there is one cylinder left or it quits, whichever occurs first.

[Diesel_Dave]

Originally Posted by jeff88

Ok so it sounds like I came up with another unicorn idea. What if I ran the same setup, but killed all the cylinders. The 'key' to reactivate them would either be putting it in 'D' or putting in in 'D' and pressing the accelerator. Then they would all go back on like normal. Or is this no different then a normal kill switch?

Would it need a heavier flywheel if it only ran one cylinder in neutral and all of them in drive?

Going back to wmjinman's point, how do the modern deactivated engines hold the valves open? Computer tells it to stay open, but what actually stops gravity from holding them down? Also do these vehicles have a camshaft? With yhe ability to stop the valve action I would think the nudge (excuse the improper name) on the shaft would need to be out of the way, so it doesn't force the valve down.

Thanks!
Jeff

Google "cylinder deactivation". There's quite a bit of info out there...even wikipedia:
Variable displacement - Wikipedia, the free encyclopedia

And actually you need to keep the valves closed--not open.

And with an automatic kill switch remember that the kill switch is only halh the picture-- you still need to restart the engine. With an automatic tranny you can't bump start so that means you would have to use the starter to restart...which has other issues like wearing out the starter and draining the battery down.

[jeff88]

Originally Posted by Diesel_Dave

And actually you need to keep the valves closed--not open.

And with an automatic kill switch remember that the kill switch is only halh the picture-- you still need to restart the engine. With an automatic tranny you can't bump start so that means you would have to use the starter to restart...which has other issues like wearing out the starter and draining the battery down.

OK, so valves closed, good to know (and makes sense).

That is why I wanted to keep a cylinder on, to keep the ICE on and not have to restart it at every light I stop at. Unfortunately, it looks like that won't work.

Originally Posted by Frank Lee

Pop the hood, start it, pull injector or plug wires until there is one cylinder left or it quits, whichever occurs first.

I wouldn't even know where to begin with that! I know about cars, in theory, but in practice I am a little more amateur. That's what friends are for though!

I am also still wondering if it would need a heavier flywheel for one cylinder if I only have one cylinder on in neutral?

Thanks!

[wmjinman]

Yeah, I think it would still need the heavier flywheel. Maybe more realistic to leave TWO cylinders running & only kill the other two. May get away with keeping the stock flywheel that way. And I know my Swift would run - barely - on 2 of the 4 cylinders, but not one.

As far as "de-activating" the valves, I dunno. . . seems the cam would need to be moved away (but that would probably mess up the cam settings, etc.) or else somehow the valves moved away from the cam - - - or some sort of adjustable spacer between the valves & the cam. Maybe adjusted "down" so the cam doesn't activate the valves when the cylinders are turned off, and then "extended" again to start working again. Maybe something like a "lifter" in the old pushrod engines that has some sort of valve to allow it to "pump up" when it's time to work the valves, and "drained" when it's time to shut down the cylinders. I'd think this would have to be part of the original design of the engine - don't know how to try to retrofit an existing engine to do it.

I can't help but wondering if this would have any advantage over the simple kill switches that just shut down the fuel to the whole engine? If you wanted it to keep running, say, because it's an automatic you can't "bump-start", maybe just coast in neutral? I guess sitting at a red light for a couple minutes with the engine idling would be tedious - but even those of us with manual boxes still have to use the starter in that case.