Variable Valve Timing (Variocam) System

"VARIOCAM" INLET CAMSHAFT ADJUSTMENT
VarioCam, a feature that adjusts setting of the inlet camshaft at 1,500 rpm* and 5,500 rpm, respectively, has a particularly important impact on engine output, excellent torque and favorable exhaust gas composition.

At engine speeds below 1,500 rpm, a small overlap of the inlet valve to exhaust valve lift curves is achieved.

One particular benefit of this system is that the hydrocarbon contents (HO contents) in the exhaust ahead of the catalytic converter are particularly low.

As soon as the engine exceeds the 1,500 rpm threshold*, the inlet camshaft is readjusted by approx. 7.5 deg. (i.e. approx. 15 deg. when measured at the crankshaft).

Adjustment towards greater overlap of the inlet and exhaust valve lift curves results in an increase of engine torque by up to 8 Nm.

At engine speeds above 5,500 rpm, the inlet camshaft is readjusted back to the basic timing (as at idle). This is due to the twin-scroll bypass intake system. Retarded closing of the inlet valves provides for an extended flow of the air drawn in into the cylinder, thus producing a supercharging effect since the flow is not interrupted. This improves the cylinder charge and produces an increase of output by approx. 4 kW.

* As the engine oil temperature increases, the value of 1,500 rpm is increased to 2,000 rpm (at oil approx. 120 ° C) and approx. 2,800 rpm (at oil approx. 130 ° C).




E = Inlet camshaft Basic setting
A = Exhaust camshaft Torque setting

The chain between both camshafts allows the chain tensioner to raise and lower the chain links between the camshafts.

The basic selling (shown in black) at engine speeds below 1,500 rpm and above 5,500 rpm occupies the upper position: the inlet camshaft is set to "small overlap' (retarded inlet start)~

If the chain tensioner is lowered due to hydraulic action (shown in red), timing is advanced and larger overlaps between "exhaust valve closes' and "inlet valve opens" result.