The engine uses a valve timing mechanism with intake and exhaust overhead camshafts, the cams of which act on the valves through roller levers with hydraulic compensators.
The camshafts in each engine cylinder head are driven by a roller chain from the crankshaft sprocket. Camshafts have a mechanism for changing the angle of the initial position (turn) – the Bi-Vanos system, which leads to a change in the valve opening phase, depending on the engine load at the moment.
The gas distribution mechanism includes, in addition to the cylinder head with camshafts and the Bi-Vanos system, intake and exhaust valves, valve guides, valve springs with fastening parts, hydraulic lifters, camshaft drive chains with tension parts.
The chain tension is regulated by an automatic tensioner with a hydraulic damping mechanism. The camshaft and crankshaft sprockets are mounted on segment keys and fixed with bolts.
A feature of the design of the engine is the Valvetronic system, which allows you to change the height of the intake valves when adjusting the engine power. The principle of the system is shown in figure 5.12, its design is shown in figure 5.13.
Camshafts
The camshafts are five-bearing, rotate in plain bearings. Drive chain sprockets are mounted on the camshafts.
Axial movement of the camshaft:
- nominal - 0.065 - 0.150 mm;
- the maximum allowable is 0.25 mm.
Radial runout of shaft journals for engine models during its assembly, not more than 0.040–0.074 mm. The limit value in operation is 0.1 mm.
Thrust bearing width 14.100–14.143 mm.
The clearance between the shaft journals and their bearings is 0.040–0.082 mm.
Eccentric shaft (1) Valvetronic system has an axial clearance of 0.100–0.200 mm.
Camshaft drive
The camshaft drive is shown in Figure 5.14 (cylinders 1–4) and in Figure 5.15 (cylinders 5–8).
System «DOPPEL VANOS»
System «Doppel VANOS» («D-Vanos») is designed to change the valve timing of the engine depending on the engine speed and load, by changing the angular position of the intake and exhaust camshafts (pic. 5.16).
The rotation of the camshafts is carried out by supplying oil under pressure to the actuator of the system. This allows you to get the optimal time to open the intake and exhaust valves, in relation to idling, torque characteristics and fuel consumption. ECU-KSUD controls the flow of oil to the executive (regulating) mechanism through a solenoid valve for each camshaft.