Cylinder Head

Cylinder Head







The cylinder head and camshaft mount is one joined component and is identical for the Cayenne S and Cayenne Turbo.

Technical data, valve drive










To ensure efficient gas exchange and valve lift control, the camshaft mount is -> length: 9 mm higher on the intake side compared to the outlet side. This arrangement meant that is was possible to optimise the inlet port.







The cooling system was designed in such a way that high-temperature parts are optimally cooled.

The cylinder head is made of AlSi7Mg.

Oil supply in the cylinder head







Camshaft control with valve lift control (VarioCam Plus)

The requirements imposed on engine design with regard to customer requests for higher performance combined with improved driving comfort, compliance with statutory emission limits and reduced fuel consumption give rise to conflicting design criteria.







The development of the VarioCam Plus was therefore based on the idea of producing a variable engine, which can be optimised for maximum performance and also for regular driving in city traffic or on secondary roads.

A control system for the intake camshaft to vary the opening and closing times in combination with a valve lift system is necessary.

Camshaft control

Camshaft control on the intake camshaft is based on the principle of a vane controller. The DME control unit determines the current position of the camshaft in relation to the crankshaft (actual angle) on the basis of the speed sensor signal and the Hall sensor signal. The position control in the control unit receives the desired nominal angle via the programmed map values (speed, load, engine temperature). A regulator in the DME control unit activates a solenoid hydraulic valve according to the desired adjustment when there is a difference between the target angle and actual angle. The adjustment angle is -> adjustment value: 50° in relation to the crankshaft (-> adjustment value: 25° in relation to the camshaft).

Vane controller

The vane controller consists essentially of the stator ( -A- ), which is fixed on the crankshaft via the sprocket, the rotor ( -B- ), which is fixed on the camshaft, the inserted vanes and two lids. The sprocket is fitted to the outer diameter of the stator. It is interlocked with the crankshaft via the chain drive. The rotor is screwed securely to the camshaft. Rotation is possible between the rotor and stator (inner mounting of the controller). The rotation is limited by the vanes inserted in the rotor and by the stops on the stator. The vanes also divide the recesses on the stator into two separate chambers.







These chambers can be filled with oil via oil bores and oil ducts in the rotor. To guarantee secure sealing, small springs are installed between the vanes and rotor. The chambers are each sealed off at the sides with a lid fixed to the sprocket. The controller is locked at a stop (retarded). To do this, a spring-loaded pin in the retarding device of the controller moves into a bore in the lid. An interlocked connection between the stator and the rotor is created for the engine's starting process. This locking prevents noises during the period before oil pressure is produced.

Function

Two chambers, which act in different directions of flow, are fitted in the controller. Filling of one chamber turns the rotor with respect to the stator. The rotor and thus also the camshaft can be turned back into the original position by filling the other chamber. The oil of the non-pressurised chamber flows back into the crank chamber via the solenoid hydraulic valve. If the oil supply and the oil return are interrupted at the solenoid hydraulic valve (centre position of the valve) during the filling of a chamber, the controller remains at the position just assumed. The chambers lose oil through leakage so that the controller leaves its position. The solenoid hydraulic valve is controlled correspondingly by the control unit, and the controller returns to the desired position.







Solenoid hydraulic valve










The solenoid hydraulic valve is designed as a 4-way proportional valve, which connects one of the two control lines ( -A/B- ) to the oil pressure supply line ( -P- ) depending on the control unit specification and opens the other line so that the oil can flow into the crank chamber ( -T-line- ). If the A-line is pressurised with oil, the controller will change direction to advance the valve timing. If the B-line is pressurised with oil, the controller will change direction to retard the valve timing. Both control lines are closed in the centre position. The camshaft is held in the desired position. In addition, any intermediate position between the three switch positions described above can be set via the control unit. Therefore, it is possible not only to move the adjustment position very quickly but also to move it very slowly in the case of slight deviations of the valve from the central position. In this way, the solenoid hydraulic valve defines the adjustment direction and speed of the controller.







Scavenging concept

A scavenging restrictor is fitted on the end of the control pressure line to keep the switching time to a minimum during valve lift control. This scavenging restrictor is used to bleed the line and reduce switching time.







Check valve







The camshaft requires a high drive torque at times due to the valve actuation, but the camshaft continues rotating unaided at other times (alternating torques). If a check valve is inserted into the P-line and the solenoid hydraulic valve is energised, for example (adjustment in direction of advanced valve timing), the controller automatically intakes oil via the feed line, the solenoid hydraulic valve and the check valve for an advancing camshaft. If the camshaft then tries to lag due to the high drive torque, the check valve closes and the oil cannot escape. The camshaft is driven by the oil cushion of the sprocket during this time, as with a freewheel. The advancing and lagging phases of the camshafts repeat so that the camshaft automatically shifts to advanced valve timing in stages. As the principle described above only functions with well-sealed adjustment control systems and low-friction valve drives, oil pressure is required. To ensure that an extremely large oil pump is not required, the principle described above is taken advantage of when the engine is hot and at a low oil pressure through the use of the check valve. The check valve serves to increase the adjustment speed at low oil pressures.