VVTi Cam change info req!

[mph]

Anyone know exactly how the ECU switches the cams? I know the changeover is done using oil pressure, but I'm presuming that the ECU has some pin out signal level that changes.

Reason: Hedley was remapping the car this morning. Whatever we do, we loose a bucket load of torque when the ECU decides to switch cams, so I want the unichip to handle it instead - hence need to know what to trap to do it.

[Anonymous]

From Big Green Book: VVT ssytem controls the intake valve timing properly in response to driving condition. ECM controls OCV(Oil control valve) to make the intake valve timing properly and oil pressure controlled with OCV is supplied to the VVT controller and then VVT controller changes relative position between the camshaft and crankshaft.
Two wires from OCV go in 24 E5 ( OCV+) and 23 E5 ( OCV-) of ECM. With a Oscilloscope connected to OCV+ and OCV- terminals, it's possible inspect the OCV functionality ( a waveform that is lengthned as engine speed becomes higher). I hope it is useful.

[Tem]

Anyone know exactly how the ECU switches the cams?

Huh...you have a 2ZZ..?  s:? :? s:?  

1ZZ doesn't switch cams, it only changes the timing.

And in short, Maurizio was saying that it's controlled by PWM  s8) s8)

[mph]

1ZZ, Tem. Matters not exactly what's inside, just the end result. However, how *do* you change valve timing if not by changing the cam?

[markiii]

I beleive you right.

You could have completely motorised valves, and hence infinite valve timing by compuer. This isn't that sophicticated though.

there are multiple cams IMHO with the same lift pattern and different timing.

I'll bring the manuals tommorow and we can drink beer and investigate  :-) :-) :-)

[SteveJ]

there are multiple cams IMHO with the same lift pattern and different timing.

Glad you said IMHO - there are only 2 cams - the VVT adjusts the timing by advancing or retarding the pulley. VVTL is another ball game that I need to get my head around - Adam it's about time you got the 2ZZ manual.

[markiii]

care to explain how you advance or retard a pulley?

[aaronjb]

The Nissan VG30DETT engine had a similar VVT system on the intake cams which was (again) oil pressure operated.

AFAIK it worked by having the cam pulley essentially indirectly connected to the cam itself, pumping oil pressure in/out of the cam pulley hub (the centre section had a big spring and oil chamber in it, and another sealed bit..) moved the cam pulley around on the end of the cam by a number of degrees, thus offsetting the cam timing - on the VG30DETT it was an on/off variation, no middle ground.

Really hard to describe, now I try and do it!
[edit: Unless you're Steve, in which case it's really easy to explain  s:D s:D  And that sounds exactly like the way the VG system worked - and would explain the presence of that giant spring (the return mechanism in the VG's on/off system)]

I'm guessing the 1ZZ-FE system works in a similar way..

[SteveJ]

care to explain how you advance or retard a pulley?

The oil is pushed (under pressure) into the centre of the pulley where it acts on a piston that connects the inner and outer parts of the pulley together. The oil pressure dictates the position of the piston, and hence the relative position of the cam and the cam-belt.

Simple. (well relatively anyway  s;) s;)  )

[markiii]

except you mean chain  :-) :-) :-)

[Peter Laborne]

An interesting read:

 m http://www.billzilla.org/vvtvtec3.htm m

[Anonymous]

As stated above the 1ZZ only has 2cams with one lobe/valve.  The VVT-i(variable valve timing intelligent)is just the pully on the intake cam which retards or advances the cam.  Basically like you do with adjustable vernier pullies but it is continuasly adjustable by the ECU and adjusts itself on the fly and not manually on a dyno like with the normal pullies.  Maurizio posted how it works with oil pressure.

The 2ZZ has 2cams with 2 lobes/valve which are used for the VVL(variable valve lift)to change cam profile at 6000rpm while it also has VVTi on the intake cam.

Same for the new honda K20A.

[Tem]

However, how *do* you change valve timing if not by changing the cam?

Changing the cam phase. And since there are a zillion different positions, you can't possibly have a different cam for all anyway. It's not just on/off, like the lift in 2ZZ.

Think of it this way. The chain and cam don't have a solid connection, but instead the VVT-i controller is inbetween. The controller has the ability to change the phase between the cam and chain.

You could have completely motorised valves, and hence infinite valve timing by compuer. This isn't that sophicticated though.

The valves in F1 engines are controlled by pressurized air, would that be sophisticated enough?  s;) s;)  Good side is you can make them work just the way you want at any time.