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Structure
The aluminium cylinder block is fitted with cast iron cylinder liners. Four cast iron crankshaft bearings are fitted to the aluminium crankcase at the casting stage. Major design changes to the aluminium cylinder head include enhanced combustion chambers and inlet ducts, which increase power output and torque, while lowering exhaust emissions.
The new inlet manifold, in composite material, comprises six ducts of equal length. These are mounted on an aluminium distributor attached to the cylinder heads in the centre of the V. The distributor comprises 12 ducts, each with a variable cross-sectional area, and each feeding a single valve.
This layout optimises the flow into the cylinders.
The position of the electronic throttle is precisely controlled by the computer in response to a large number of parameters, including accelerator pedal position, coolant temperature and incoming air temperature.
Rotating assembly
Improved fuel consumption and lower vibration have been achieved through extensive design studies seeking to reduce friction and to make parts lighter.
The forged steel crankshaft includes five precision-ground case-hardened bearing sections. The bearing grooves and journals are rolled in sections. In contrast to traditional rolling techniques, this process hardens the metal without distorting the crankshaft, thereby improving stress resistance.
The forged steel connecting rods feature integral oil channels for cylinder lubrication and cooling.
The pistons are 40 g lighter than those in the previous version. The flat piston tops are raised slightly in the centre, with rebates to provide valve clearance.
A “flexible” engine flywheel reduces engine vibration at high speeds. The flywheel consists of a cast friction ring on the clutch side and a sheet metal damping mechanism on the engine side.
Valve gear
The four camshafts act directly on hydraulic tappets that automatically take up any play in the system.
A phase shifter, or variable-timing camshaft, adjusts the timing of the valve gear for optimum flow into the cylinder.
For example, during acceleration at low engine speeds, valve lead and lag take place earlier.The inlet camshafts are moved between two possible positions by means of a double helical ramp controlled by the oil pressure. The engine computer controls the oil intake through an electrovalve, in accordance with engine speed, engine load and oil temperature. The camshaft position is monitored by an angular position sensor.
Injection and ignition
The engine is controlled by a Bosch ME 7.4 engine control system driving the sequential injection system and coil-per-plug ignition. The new multi-jet injectors are fed from two rails with no fuel return. The fuel circuit includes a surge damper to eliminate noise and variations in pressure.
Exhaust and emission control
A pre-catalyst is mounted at the outlet of each exhaust manifold, with oxygen sensors fitted at the inlet and outlet.
The sensors analyse the oxygen content of the exhaust gas and transmit the information to the engine control system, which then adjusts the fuel / air ratio accordingly. The main catalytic converter completes the pollution control system, ensuring emission levels compliant with the Euro 4 standard.
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