Controlling VVTi

[JustenGT8]

So before dropping the VVTi 1UZ in i want to test the feasibility of running the inlet cam advance facility with my SM2. Apparently it won't do this closed loop (as an SM4 would), but theoretically you should be able run it open loop in a similar fashion to an EBC...i think?

Basically it's just a solenoid control of oil flow, with more flow = more advance. I have a free 2D PWM output i could configure to control these solenoids....say based on RPM and MAP? (i'd be interested to hear if anyone knows what the main inputs the factory ECU takes to determine cam advance?).

So just like an EBC, you would vary the solenoid duty until you get the desired cam advance. This is where i hit a major snag, without a cam position sensor how will i know can position? Could maybe set up a 'scope to measure the output of the cam position sensors and work it out from there? Could likely work out full scale (full retard and full advance) and just assume it's linear.

Once we now that relationship it's just a matter of setting up the PWM table to give the duty (advance) you want at what points in the table. Some dyno time involved but i'm not looking for closed loop perfection, just some coarse utilisation of cam advance to take what advantage this control might give....it would have to be better than leaving it locked at full retard?

Educated thoughts

[dumbass]

ditch the sm2 and get an sm4 or maybe a link
the time u stuff around would be cheaper to get new ecu
the pwm might change much faster than u can adjust it sometimes
there might also be slight variance in cam timing with oil pressure changes
thats y u need a refereence

[JustenGT8]

Yeah i hadn't considered oil pressure changes and think that skittles it. Oil pressure is all over the place at the track and i think even a closed loop setup would struggle a bit.

Fixed/manual advance it will be then. 25psi will make up for any VVTi advantage i miss out on

[dumbass]

just run anti lag that will cure all your low down problems

[knightrous]

Could always just use it as VVT with specific ON/OFF points tuned via some AUX ouputs

[thechuckster]

Without Cam position sensor, is not worth it. You'd be guessing where the cam is.

Oil pressure shouldn't be an issue if the system is tracking cam position? In any case, the spool valve that controls oil supply to the cam positioner will bleed off any excess pressure. the thing to watch out for would be low pressure (particularly at startup) and/or (possibly - happy to be wrong here) running an oiling system from a non-VVTi motor on a VVTi setup.

You could run it as a dumb VVT system (on or off) like the 4AGEs with VVTi (silvertop?) - 100% duty fully advanced, 0% duty for fully retarded?

[JustenGT8]

That was the idea with the oscilloscope Chuckster, to get some idea of duty cycle versus cam position....viscosity changes, effecting oil pressure likely mean this would be so varibale as to be pretty useles though i agree.

Yes in closed loop the oil pressure change is far less an issue (partly the point of closed loop i guess) but in the track situtaion where oil pressure is changing a lot, it might casue some issues for the closed loop system to keep up? Dunno, depends how quickly it can bleed oil pressure etc. Just an aside.

Yes i was thinking last night the simple on/off may still be worth persuing...try and take it a step further using the PMW 2d table so for example, no advance when cruising off boost? Also, try and soften the advance/retard rates by increasing solenoide duty more gradually, rather than 0 and 100% ?

Does anyone know the max advance of the 20V engine? I believe the UZ is as much as 30 deg, which would feel almost Vtec like if you just used on/off.

BTW, the engine is a full VVTi 1UZ so no mechanical system issues to worry about, just how/if to bother controlling it.

[knightrous]

IIRC, the 4AGE 20V have 30 degree advance using the VVT.

[JustenGT8]

That's good to know it's in the same league...anyone know the switch point or parameters used to trigger the switch point? I assume rpm would be a major one but also MAP, Throttle position, road speed perhaps? I can factor in 2 and would guess rpm and MAP are the likely ones i'd use?

Try and configure the table on theory and do 3 dyno runs. Fully retarded, Fully advanced and rough VVT and see what we get?

[trdee]

silvertop is AFM so it can't be MAP. IIRC it is a function of TPS and RPM.

even as an on/off system VVT is definitely worth the effort man. makes a MASSIVE difference (on 4As anyway)

edit; justen maybe try seeking some advice from a tuner who has some experience with VVT to see how they get it working? In my mind I cant see you being able to use constantly variable VVT without some sort of feedback loop, but someone with real world experience might know some tricks and workarounds etc..

[JustenGT8]

Yeah Vito, next step is a chat to my tuner...who has done Toyota VVTi on Steve's 2GR AE86. He's a Autronic guru too which will help. I just want it as clear in my head as possible 1st.

[George]

Why not run stock computer for VVTi? Then you would only worry about splitting sensors' signals into two computers

[MR22ZZ]

might also be worth dropping Neil Trama a line, he's had plenty of experience with VVTi and VVTLi systems.
And he's local to you...

[JustenGT8]

Can't say i know Neil? which w'shop?

I thought about running a stock ECU to control the VVTi stuff but rare as rocking horse shit and a royal PITA to achieve neatly.

Now another source informs me the UZ VVTi could adavnce the cam as much as 50 deg? That's excessive for a simple on/off so would need to limit the advance mechanism so how...damn.

[George]

Do you mean VVTI ECU's are rare? Or info about them? Maybe consider buying one from Yahoo Auctions Japan?