Description And Operation
The intake and exhaust camshafts are made of steel.
- Intake camshaft (1)
- Exhaust camshaft (2)
Both intake camshafts have a tone ring (1) for the camshaft position sensor, a specific cam (2) to activate the high pressure fuel pump and at the end the oil vapor separator (3).
The right bank exhaust cam also has a tone ring (1) for the camshaft position sensor. In addition, the end of the camshaft (drive pulley side) has a hexagonal marking to connect it to the additional oil pump.
In the left bank exhaust camshaft, in addition to the tone wheel (1) for the camshaft position sensor, there is a drive for the vacuum pump placed at the end of the camshaft itself (drive belt side).
The intake valves are in steel and have been subjected to a hardening heat treatment and then to a tempering to increase its hardness.
Because of the high mechanical and thermal stress, the central part of the valve stem has been made in hollow sections with an internal diameter of about 2.9 mm. The hollow section allows improved efficiency in dispersing the heat, allowing the maximum reachable temperatures to be limited.
Differentiating from the intake valve, the exhaust valves have to resist higher temperatures and are also subjected to the corrosive effect of exhaust gases. For this reason, the valve head has been made in a different steel alloy from the stem. The exhaust valve head is produced in a special alloy, high in nickel and chrome, called Nimonic.
The exhaust valves' internal stem cavity is filled with 60% sodium. Sodium in liquid stage moves inside the valve cavity during high alternating motion, transferring part of the high heat from the valve head to the stem (and from there to the cylinder head via the guide valve). This way, the valve temperature goes down to about 70-100°C.
The opening and closing of the intake and exhaust valves happens thanks to the hydraulic tappets that allow the camshaft thrust to "unload" on the valve stem. The left bank tappets cannot be deactivated because the cylinder deactivation system is only on the right bank.
- Exhaust rocker arm (1).
- Intake rocker arm (2).
- Exhaust valve guide (3).
- Hydraulic tappet (exhaust side) (4).
- Hydraulic tappet (intake side) (5).
- Intake valve guide (6).
- Exhaust valve (7).
- Intake valve (8).
Variable Valve Timing (VVT) allows for optimizing cylinder filling by adapting the opening and closing angles of the valves according to the engine's operating point. Optimizing the filling coefficient allows benefits in terms of performance, consumption and emissions. There are phasers on the intake and exhaust cams on both bearings that allow both powertrain control modules to adopt the best phasing.
- Right intake phaser (1)
- Right exhaust phaser (2)
- Left intake phaser (1)
- Left exhaust phaser (2)