[Diy_efi] Continuous VVT system

[Alexei Pavlov]

Hi all,

I'm rebuilding an Alfa Romeo 2L 4cyl inline engine of a
75 Twin Spark car. The engine (designed mid-80 years) has
a binary on/off variable valve timing (VVT) device on the intake
camshaft. The VVT device is electrically controled by a Motronic ECU.

I'm trying to modify the VVT system to get a continuous angular
cam positionning on intake and exhaust camshafts (as all 4cyl AR
engines this is a twin cam one).

Has someone already done this kind of systems ?

The principle of the original system is as follows:
An electric activator pushes a button which allows engine oil
entering a chamber, in which oil pressure pushes another piece that
shifts the cam timing.
The shifter is located on the front of camshaft. It's driven by
the engine chain, it drives the camshaft.
The angular shift is 0 or 15 cam (30 crank) degrees.

Modern continuous VVT systems (like Toyota/Lexus ones) often use
the same principle, but can control the cam position in a continuous
way. A slight mod of the Alfa VVT should allow me doing the same.

An additional ECU that controls VVT will contain maps with cam shifts
as function of load and RPM.

I'm planning to use electro-magnetic sensors to get the current
angular position of camshafts collected on the cams. I think oil
vapors will prevent me from using opto sensors.

As the oil pressure depends on the RPM I'll have to do some kind
of PID control loop to mantain a constant angular shift at all RPMs. 

All fresh ideas are welcome.

I'll be on vacations next week but will wait for replies and read them
after the New Year.

And welcome to all coming back to the diy-efi :-)

Thank you,
Alexei
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