Ahhh, now i get it, I think. So the accumulator wouldn't just be helping VVT operation, it would also be assisting with maintaining all engine oil pressure, which would probably reduce slapping of the chain on the tensioners, due to more consistent oil pressure in the tensioners during changes in VVT?
Yes. If Alfa chose to fit an oil pressure relief valve that operates at 6 bar, I hope it's because pressures can exceed that. Pressure is going to be highest when cold starting. So if one can prevent the oil pressure relief valve from lowering the oil "PUMP" pressure, by utilizing that excessive "Oil gallery back - pressure" to fill the V.V.T. system, it's a win, win situation. The back pressure from the galleries and the inertia of cold oil is there regardless. But at the end of the galleries, feeding the tensioners, main bearings and con rods, the pressure will be suppressed. Particularly if someone is continually "blipping the throttle; a nasty habit some garages have, even when the engine is cold. One must remember the V.V.T system requires oil to advance the camshafts and oil to retard them. So sixteen voids are being filled when someone hits the throttle on tick over, and sixteen are being filled when they release it. If engine oil pressure is not enough to sustain this, as well as maintain tensioner pressure; and main bearings et all, then the voids will be dragging down the main gallery oil pressure.
The accumulator has to maintain the charge, at main gallery oil pressure when the engine is switched off. When the engine is running, oil temperature will reduce viscosity, so inertia will also be lower. But regardless, the oil pressure at the other side of the cylinder head non return valves will always be higher because, the feed to the V.V.T. suffers less inertia - larger diameter pluming and it is "Tee-ed" from the outlet of the oil cooler, at the point the oil normally enters the block. Engine Oil pressure switch actually.
The demand of the V.V.T. system is wholly dependent upon driver technique and can be considerable; neglecting cruise control. If the driver is enthusiastic the way he works the throttle and gearbox, the demand is greatest.The demand is much much less when cruising as the E.C.U. should invoke small adjustments to advance/retard due to small changes in engine load depending upon the road conditions, i.e. undulating terrain.
I contend, the modifications Alfa Romeo made to this engine when adding V.V.T. geometry, results in oil starvation. The Accumulator is intended to maintain the oil pressure at the V.V.T. such that the advance/retard mechanism can respond better to the E.C.U. demands for change. The charge it needs to hold has to be sufficiently large enough to fill the voids completely, several times over, whilst holding the cylinder head valves closed and allowing the main engine oil pump to service the bearings and tensioners. This is not as difficult as it sounds as oil pressure will rise with increase in engine revs. And if the driver has dropped a cog or two, it will respond much more quickly, and the Accumulator will continually be replenished.
Do not forget, regardless of adopting this method or maintaining what is currently in place, when the V.V.T. is set, there is no oil oil demand. Small changes in advance/ retard and it will probably be difficult to see any main gallery oil pressure reduction. This will only happen if the car is driven by a robot, or on cruise control. But that's not the reason most people by Alfa Romeos. Researching this issue shows how out of step Alfa is will so many other car manufacturers.