Displacement on Demand? Could this be done in a lexus?
09-10-06, 02:49 PM
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Displacement on Demand? Could this be done in a lexus?
Enabled by GM's powerful electronic powertrain controls, Active Fuel Management saves fuel by using only half of the engine's cylinders during most normal driving conditions. When loads are light, the control system automatically closes both intake and exhaust valves for half of the cylinders, cutting off their air and fuel supply. The fuel supply resumes and the valves are reopened to provide all-cylinder operation when the driver needs it for quick acceleration or for hauling heavy loads.
The V-8 engine always starts on eight cylinders, and in the case of the V-6 engine, six cylinders. But once the vehicle has accelerated to speed, the engine control module activates Active Fuel Management, providing improved fuel economy through a relatively inexpensive change in displacement to meet the vehicle load requirements.
The V-8 engine always starts on eight cylinders, and in the case of the V-6 engine, six cylinders. But once the vehicle has accelerated to speed, the engine control module activates Active Fuel Management, providing improved fuel economy through a relatively inexpensive change in displacement to meet the vehicle load requirements.
Any input?
09-10-06, 05:37 PM
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the valves are mechanical, you dont want fuel/air getting sucked into the cylinder without being ignited, besides your not really saving fuel if its still getting sucked in. The behavior of the injectors would have to be altered. Perhaps on a vvti engine the one of the cam profiles could be modified to keep some of the valves closed. Of course the ECU would have to be moddifed as well to change the conditions for the alternate profile to be engaged. Im not as knowledgable about toyotas design as hondas vtec design, but i belive the same basic priciples apply.
I am not sure how GM accoplishes this task, but i would assume its a similar a variable valve technology.
I am not sure how GM accoplishes this task, but i would assume its a similar a variable valve technology.
09-10-06, 05:43 PM
#3
its possible, the way that it works is that the cyls just dont fire. by having the valves closed at all times when the cyl is not working creates vacuum and pressure in the cyl and thus would make it work more and need more fuel to run without the firing pistons which for our motors is not big enough of an increase to bother. By only cutting off two cyls its not really going to save you much gas, taking an 8 cyl down to 4 now thats a different story.
the long and short of it, yes it can be done, but really would it be worth the extra 2 miles per tank and lag when switching cyls on and off....? IMO i dont think so
the long and short of it, yes it can be done, but really would it be worth the extra 2 miles per tank and lag when switching cyls on and off....? IMO i dont think so
09-10-06, 06:59 PM
#4
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fuel is not "sucked" in through injectors... injectors are fired via an electronic signal fron the ECU or fuel computer which tells them to releas fuel. the valves would still be opening and closing because the camshaft would not be changed. however, when a particulr non firing cylinder is on an intake stroke, the air will still be pulled in, durring the compression stroke, nothing would happen, and the exhaust stroke would simply push the air that was brought in back out. all you would need to do is manipulate the ECU to not fire two or four injectors when not under full throttle or a particular set RPM.
its quite simple, but would only be benneficial when cutting 4 of the 8 cylinders on the 400 as stated above... wouldnt really help us 6cyl guys.
its quite simple, but would only be benneficial when cutting 4 of the 8 cylinders on the 400 as stated above... wouldnt really help us 6cyl guys.
09-11-06, 09:04 AM
#5
Yeah, I need to stand on the pedal as it is already to get my SC3 moving. I would think the mechanicals would be simple enough, but the ECU programming would be a bit more complicated to get it performing correctly. GM had this out in early 1980 on their Caddy V8s calling it the V4-6-8. Worked as described, but the lag was pretty bad. Had a little display showing how many cylinders were firing. So you don't neet VVT-i or anything of that sort to have displacement on demand.
09-11-06, 04:35 PM
#6
TOked i totally forgot about the caddies, decent car but never worked right and it didnt save fuel like they thought back then...now its a different story. Kudos for remembering that. Still the best way for gas mileage is keeping the whole car in good shape, clean, and opening up the airways to let it breathe better.
09-11-06, 09:41 PM
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the 4-6-8, that has been the topic of many laughs over the years. I didnt bring it up because it sucked. it was an excellent idea though. problem with either design is that the pistions still move, more friction, power is lost in moving the pistons of the deactivated cylinders.
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09-11-06, 11:51 PM
#8
its possible, the way that it works is that the cyls just dont fire. by having the valves closed at all times when the cyl is not working creates vacuum and pressure in the cyl and thus would make it work more and need more fuel to run without the firing pistons which for our motors is not big enough of an increase to bother. By only cutting off two cyls its not really going to save you much gas, taking an 8 cyl down to 4 now thats a different story.
the long and short of it, yes it can be done, but really would it be worth the extra 2 miles per tank and lag when switching cyls on and off....? IMO i dont think so
the long and short of it, yes it can be done, but really would it be worth the extra 2 miles per tank and lag when switching cyls on and off....? IMO i dont think so
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