Cylinder Deactivation on an L28?

[CybrStuff]

I've been lurking here in the forums for a while to research my options for a 240Z L28(ET/ETT?) build that I want to do someday (being a college student doesn't afford one the time, money, or space for a project of this magnitude). I hope I'm not wasting peoples' time by shooting the breeze about a car I probably won't have for three years, but I have no one else to talk to about some (hopefully) cool ideas that have come to me as I've been researching .

Anyway, being an electrical engineer, I tend to like to replace simple, mechanical systems with vastly more complex electronic ones (like going to standalone EFI instead of carbs), which brings me to my question. I've been seeing more and more cars lately that can deactivate a bank of cylinders (displacement-on-demand for GM, etc.) to save fuel while cruising, and thought it might be a cool feature to add to an electronically-controlled L28.

With a standalone EFI system (I'm eyeing Wolf3D at the moment) in conjunction with a bit of custom hardware (disabling fuel injection for three cylinders under a set throttle position), I think it would be relatively simple to set up a basic 3-cylinder deactivation system. Further, if the intake were engineered to use dual (or even individual) throttle bodies, the three deactivated cylinders could be cut off from the air supply as well, which would reduce pumping losses and improve fuel economy even more. My main concern is vibrations. I know that the new Honda V-6 with cylinder deactivation has to have an active vibration cancellation setup in its engine mounts to keep the car from shaking, but I also know that a V-6 is not an inherently smooth system like an I-6 is. I was just wondering if any of you people who actually have your L28s might have some insight into the feasibility of a setup like this. Thanks.

[technicalninja]

Welcome CybrStuff, I lurked for a while before I posted as well.

Your ideas have great merit as a theroetical challenge and research and development project, but at the end you will find the process you go through may develop you more than it helps the Z in the gas mileage department. If you successfully develop you own cylinder de-activation system I bet you will be able to land a design job at any of the major manufactors.

 

The very biggest problem you will have to overcome is being able to deactivate at least one of the valves in each cylinder you plan to deactivate.

The compression stroke on a deactivated cylinder pushes against the rotating crankshaft on every deactivation cycle. This reverse load occures (at least on an even-fire six) exactly between each power stroke which is not a good spot to lose power. The even fire (120 degrees between power strokes) engine will be getting a power stroke every 240 degrees when operating in 3 cyl mode. Suzuki (and maybe others) built a few small 3 cyl engines in the late 80s-mid 90s and these were little vibrating beasts and were not successful. I don't believe any 3 cyl are being built today but I may be wrong. I hated them when I made my living wrenching.

These cars had problems with out the extra backward push that a deactivated 6 will have. You have to address this or your 6 in deactivated mode will get worse gas mileage than if the engine were run normally.

 

Look to Honda's deactivation system for ideas. Dealing with the fuel and spark is child's play compared to dealing with the valvetrain.

Late model BMW V8s have a truely innovated design which controls lift well enough to allow the engine to have an open intake (like a deisel) with no throttle body at all. This engine would allow true cylinder deactivation with software alone. All the hard parts are already there. The BMW may have a deactivation mode, seems silly not to.

 

You will need to design motor mounts in which a ball type seat rests on a silicone "pillow" in a spherical housing. If the engine is a high power unit these mounts will need to be made strong. The tranny mount may need to be addressed as well.

 

Idle quality will be vastly improved if you run a very heavy flywheel and it might be benificial to have the additional weight added at very specific spots around the perimeter of the flywheel (I'd guess the spots would be at 120 degree locations). Performance would not appreciate this heaver peice.

 

For evenly spaced power strokes you will need to isolate either the first or last three cylinders. This makes controling the throttles some what easier to develop. I would look to Porsche flat six stuff for your intake.

 

And finally what could you expect to save over the life of the car in fuel cost

if you developed a truly efficient system?

 

Allowing-

A well tuned hi-performace Z should be able to hit 25 MPG normally

Your system realizes 25% improvement in fuel mileage overall (may be overly optimistic).

Fuel averages 2.50 a gallon for the duration of the "test" (this also may be overly optimistic)

In 100,000 miles you will save $2000.

As long as the system has ZERO maintenace cost and never breaks down.

 

On the bright side: After gaining all the abilities you will need for this project you will be a hot commodity in the engine control design engineer field and be able to afford a new BMW 6 or 7 series. This will cause you to use the Datsun only for special events and you may have a hard time putting 100,000 miles on it anyway so " Your actual savings may be less"

 

Theoretical discuss is great. It is the beginning of each new technological "breakthrough" we humans have experienced. It is what drives expansion. Try to never let it die within you, even when a crusty old-timer like me brings up reasons why something should not be attempted,-even if the reasons are good. Sooner or later you'll think up something that no one else has.

I would not waste a significant amount of time on a project like this as the economical benefits are not high enough for me but it is a complete valid project just for its technical merit.

 

Welcome to the board

Rick

[CybrStuff]

Your ideas have great merit as a theroetical challenge and research and development project, but at the end you will find the process you go through may develop you more than it helps the Z in the gas mileage department.

 

I'm aware that the complexity of a system like this is probably far greater than the fuel economy that I would gain by using such a system, but I'm always game for a technical challenge when it's not horribly impractical. Also, I have to do something to distinguish myself from all the other fine vehicles around here.

 

The very biggest problem you will have to overcome is being able to deactivate at least one of the valves in each cylinder you plan to deactivate.

The compression stroke on a deactivated cylinder pushes against the rotating crankshaft on every deactivation cycle. This reverse load occures (at least on an even-fire six) exactly between each power stroke which is not a good spot to lose power. The even fire (120 degrees between power strokes) engine will be getting a power stroke every 240 degrees when operating in 3 cyl mode. Suzuki (and maybe others) built a few small 3 cyl engines in the late 80s-mid 90s and these were little vibrating beasts and were not successful. I don't believe any 3 cyl are being built today but I may be wrong. I hated them when I made my living wrenching.

These cars had problems with out the extra backward push that a deactivated 6 will have. You have to address this or your 6 in deactivated mode will get worse gas mileage than if the engine were run normally.

 

I have to say that I've done a lot of searching online and this is the first time I really understood how the valves played in all of this (looking back, it makes me feel rather foolish ). Thanks for that. Back to the research!

[HeatRaveR]

Perhaps do some research on forums of cars that have such a system and see how each company made theirs work. I'm thinking, if you were truly ambitious and design a some sort of universal retrofit you could even start your own business out of it. ^^ Hmm, I wonder if it'd be easier to retrofit to hybrid or retrofit to cylinder-deactivation.

[CybrStuff]

I've been thinking about this, trying to figure out the easiest way to actuate a valve deactivation system. It seems that the companies that have done this so far have used a special lifter that can be activated or deactivated by hydraulically actuating a pin inside the lifter. This seems beyond my fabrication abilities. However, I was thinking that maybe I could hook up a system that works similarly to Honda's VTEC. By making a two-piece rocker, I might be able to set it up such that a pin, which would connect the two pieces to allow normal operation, could be removed to allow cylinder deactivation. Any thoughts?

[Tony D]

Check out Lance Nist's webiste from Pantera Specialists.

The controller he uses is also capable of driving electrohydraulic valve actuators.

 

Yeah, that's right, no camshaft...

 

If you want to go into some REAL neat stuff, Lance is the guy you want to talk to... Wish I had a link right handy, but the EFI system he sells can be combined with another ECU and you can have electrohydraulic valve actuation, and totally sequential fuel and spark control...

 

"Cam Profile" totally programmable for throttle position, rpm, acceleration rate.... Muahahahahaha!

 

How's that for complex engineering options. I think you will like what you have to see there!

 

"Lance Nist, Pantera Specialists, Santa Ana California"

 

Should work on a Google...

[AK-Z]

I to think that it has some merit. The new dodge charger has such a system. It uses a V8 that only uses 4 cylinders for fuel economy using many variables ( throttle position, acceleration, speed) to calculate when to disable/enable the other 4 cylinders.

 

But the I don't think it would be as applicable for a line six, because of only using 3 of the 6 cylinders I would imagine some vibration and crankshaft problems down the line.

[AK-Z]

Sorry I didn't read the whole thing before I typed the reply earlier.

[CybrStuff]

Check out Lance Nist's webiste from Pantera Specialists.

The controller he uses is also capable of driving electrohydraulic valve actuators.

 

Yeah' date=' that's right, no camshaft...[/quote']

 

Yeah, I've heard about this. Unfortunately, from what research I've done, the valve actuators are quite expensive and/or hard to come by (they haven't really hit the aftermarket mainstream yet). Also, a control system for such a setup is extraordinarily complicated (think about all the variables to optimize!). It is a very cool idea though, and is definitely worth examining again. Thanks!

 

Edit: spelling and some inaccurate information

[technicalninja]

Well, you post got me to thinking: If I was to attempt this what would be the easiest setup?

I'd start with a P90a head which already has hydros and I would build 6 "special" lifters. I believe the best valve position would be intake closed and exhaust open at during a complete 4 cycle "event". I have done no research but it seems to me that you would not want any wierd dynamic pulses from the deactivated cylinders getting back in to the intake as it would disrupt normal flow to the other cylinders. This leaves the exhaust valve as the only place to perform the compression bleed off. My intake lifters would allow collapse during deactivation to the point that the cam could rotate a full 360 degrees with out contacting the rocker. The ehaust lifter would extend enough during deactivation to keep the valve off the seat at all times. Expected problems with intake side- rocker falling off valve tip and lifter causing complete upper end failure when it gets into the other valves. Some form of bracket/spring may be able to address this problem. Exhaust side- Clearance issues around TDC between piston and valve and valve seal to retainer clearance at max cam lift. The P90 head has the highest valve position of any of the heads and may allow clearance with out putting valve pockets in the piston. The location of the L-series lifter would make plumbing easy as you would just drill from the outside into the lifter "bore". You would need a high pressure hydralic system, some sort of electro-hydralic actuator, and a proper controller.

 

And you may have issues that you did not expect: I recently took a customer core engine apart to scavenge usable parts. This engine had approx 60,000 miles on a "full" rebuild by a less than perfect shop. The customer drove this engine for quite awhile with two badly burned exhaust valves and the bores that had the bad valves were destroyed. It would have require a .040 cut (1.0 mm) just to clean them up. The other four bores were fine and could have been refreshed with just a set of rings. Fuel and spark were not cut off in this case but compression sure was. Having your front 3 cylinders wear at different rates that the back three will lead to reliability issues down the road. This could be solved by also plumbing the front 3 for a second system and alternate front to rear on some time based formula.

 

You posted about someone else's actuators being expensive.

If I was seriously thinking about doing this to any engine that didn't originally have such a system I would buget $50,000 and be happy if I ended up with just 1 functional system. Basically having the project at the point it could be used to model a final design for production. This is parts and machine work buget only. I would be doing all of the work myself. Having something like this done by a competent design and manufactoring company would be incredibley expensive.

 

One final note: We all feel foolish at some time so don't feel bad about posting your questions. Just recently I was helping a friend put a spoiler on and we needed to "machine" a screw mounting surface bore in a part with the location being down a long curved "wing" section. After 30 minutes messing with the tools I had (die grinder,Dremel, variety of drills) we were headed to the local Home Depot to purchase a Dremel flex shaft kit when my 15 year old son took one look at our problem and said "why don't you take the bit out of the Dremel, put the bit through your hole, reattach the Dremel on the outside of the part and use the back side of the bit to grind your flat spot?" My friend and I just looked at each other for a few seconds and I said "damn- from the mouths of babes- wish you'd said that about 30 minutes ago". It worked absolutely perfect. Bryan (my son) sure makes me proud at times. It was still a "newbie" who saw through a problem that had two "supposedly intelligent" techs stumped .

Sometimes even the most experienced people make "foolish" mistakes or don't understand a system as well as they thought. Welcome to the club. This is the best way to learn. When a bit of knowledge cost you money, blood, or "face" you will remember it better. least-wise I do.

 

Reading a column on the Honda Odyssey in GRM it appears that Honda's system is good for about a 10% increase in fuel economy and the system requires the interior sound system to broadcast "anti-noise" during operation to mask excess noise from the rattling vibrating 3 cyl .

Seems pretty complicated for 10% increase to me. Also looks like a drivability nightmare for the Honda techs some time down the road.

 

Good luck

Rick

[CybrStuff]

I'd start with a P90a head which already has hydros and I would build 6 "special" lifters. I believe the best valve position would be intake closed and exhaust open at during a complete 4 cycle "event".

The only problem I would see with this is that the main reason for deactivating valves at all is to keep the compressed charge in the deactivated cylinders to act as something like an "air spring" (I think I stole that term from somewhere where I was doing research, but I don't remember where) for the crankshaft to push against in between power strokes in the three active cylinders.

 

I have done no research but it seems to me that you would not want any wierd dynamic pulses from the deactivated cylinders getting back in to the intake as it would disrupt normal flow to the other cylinders.

I understand this concern, but I was already considering running separate intakes for the two banks (either one per bank or maybe even individual). Instead of having to disable both intake and exhaust valves to maintain charge pressure in the cylinder, a bit of clever timing would allow the exhaust side to remain closed after a power stroke and then just keep the throttle body(ies) closed so that even though the intake valves are doing their thing, charge pressure is maintained.

 

Thanks again for a well-thought-out reply. It's fun to talk about this stuff, even if I'll never have the budget or skills to pull it off.

[Tony D]

I have signed a confidentiality agreement regarding something in the last post.

Please open your minds about the air spring and think how you could harness that to your advantage...

The patent should be up for sale soon...

[CybrStuff]

I have signed a confidentiality agreement regarding something in the last post.

Please open your minds about the air spring and think how you could harness that to your advantage...

The patent should be up for sale soon...

Sounds like a mystery wrapped in an enigma to me. Can we play charades and try to guess the answer?