Each of the two cylinder heads houses two camshafts, one for the opening of the inlet valves and one for the opening of the exhaust valves.The camshafts are supported by four bearings fitted on the cylinder head. The camshaft for the left cylinder head is also supported by another bearing due to the connection with the shaft used for activating the high pressure fuel pump; the front (timing side) bearing also carries out the task of controlling the camshaft thrust.Each of the four camshafts is connected by the respective "continuous" type phase transformer.
Components
CamshaftsThe four camshafts are made from cast iron with a superficial treatment of the cams.The active part of the cams is produced with a profile with a 250 degree angle for the inlet valves and 254 degree angle for the exhaust valves; the valve lift is 11 mm for both the inlet valves and the exhaust valves.The phase transformers are fitted on the front of the camshafts and there are ports for supplying the oil to the phase transformer actuators.
1. Oil supply ports for phase transformer actuators2. Threaded port3. Phase transformer actuator position reference4. Seal housing5. Shoulder surface6. Cams7. BearingsRocker arms and tappetsThe rocker arm is the type with a finger and roller; this system makes it possible to minimize the loss in output due to the operation of the rocker arms by the camshaft in as far as the relative movement between the cam and roller is a rolling movement and not a sliding movement as is the case in other systems.
1. Roller2. Valve rocker arm contact3. Tappet rocker arm contact
The tappets are the hydraulic type and continuously ensure the correct operating contact between the components controlling the valve lift; the tappets for the exhaust valves (1) and inlet valves (2) are different heights and should not be mixed up, the diameter of both tappets, on the other hand, is the same.
Variable timing system
The continuous variable timing system controls and alters the timing diagram in relation to the different operating conditions to ensure optimum engine behaviour in terms of an increase in performance and reduction in consumption and emissions.Basically the advantages should not be seen in terms of a simple increase in the maximum torque and maximum power, but as a gain in powerfulness, fullness and prompt responsiveness throughout the entire engine operating speed and load range.There are four transformers for this engine, one for each camshaft; they are capable of altering the cam angle during the operation of the engine based on the usage conditions. There are therefore four control solenoid valves, through which the engine management control unit regulates the flow of oil inside the actuator compartments to allow the rotation of the camshafts in relation to the gears controlled by the secondary timing chains.The phase transformers allows the continuous rotation of the camshafts at 50 degrees.The engine management control unit determines and controls the position of the cam through sensors on the camshafts and the crankshaft.
The actuator consists of a stator rotated by the ring gear which it forms one piece with controlled by the secondary timing chain and a rotor connected directly to the camshaft which can move in relation to the actual stator. The rotor and stator may become offset by sending oil which, flowing through ducts controlled by the solenoid valve operated by the control unit, fills the compartments between the internal profiles of the actual stator and the rotor. This produces the rotation in both directions depending on the "distribution of the oil" by the control unit by means of the solenoid control valve (1).
The solenoid valve is made up of a needle cursor that is moved in three different poisitions through the electromagnetic induction of a solenoid; in this way each of the two types of compartment for the transformer may be placed in contact either with the oil supply duct or the drainage duct depending on the rotation. Obviously, in order to allow the movement, when one compartment is in contact with a duct, the other should be in contact with the other duct and viceversa, to allow the flow of oil; the different positions of the cursor lead to three distinct situations:1) the oil flows into the red compartment and out of the other (blue) so that the camshaft is offset in an anti-clockwise direction;2) the oil flows into the blue compartment and out of the other (red) so that the camshaft is offset in a clockwise direction;3) the oil in the two compartments is stopped so that the position between the stator and the rotor is maintained. In this situation the position of the solenoid needle ensures that the two types of transformer compartments are insulated and are not in contact with either the supply duct or the oil drainage duct.With the engine idling, both camshafts are in the "default" or "basic fitting" position which is maintained thanks to an internal pin that locks the rotation of the shaft (rotor) in relation to the timing gear (stator) in the basic position. In this situation the exhaust camshafts are completely advanced and the inlet camshafts completely delayed and remain like this during starting; this timing configuration guarantees the minimum crossover between the inlet and exhaust valves.The pins that lock the camshafts in the basic position ensure that they are in the correct position on starting and that there is no noise due to the uncontrolled rotation of the rotor in relation to the stator. To allow the movement of the phase transformer a certain operating pressure must be reached in order to release the pin locking the transformer in the basic position and allowing movement.Depending on the engine position, it is possible from the basic position to control the advance of the inlet camshafts and the delay of the exhaust camshafts within a maximum rotation range of 50 degrees for each shaft; what is of fundamental importance is that this system makes it possible to control all the intermediate positions for the shafts within the above mentioned range so that the best engine working conditions can be produced for all speed and load conditions.Variable valve timing actuator
1. Stator2. Rotor3. Vanes4. Spring5. FlywheelThe above diagram shows the stator with the ring gear and the rotor with the camshaft. The rotor is the vane type with ports that supply the compartments on either side of each of the four vanes; a fifth vane acts as a lock-up locking the actuator in the normal fitting position.The lock-up is only released when the oil that passes through a port pushes the lock-up (pin) vane towards the edge of the stator reaches the operating pressure releasing the rotor from the stator. A spring guarantees the pre-loading of the rotation between the rotor and the stator cover.The housing for the camshaft with the oil arrival ports can be seen below; a second set of openings is found inside the main shaft port where the shaft fixing bolt is found.The two sets of ports supply the compartments on either side of the four vanes separately.
Timing diagram variationThanks to the intervention of the phase transformers, the timing diagram can be altered; in particular, the opening advance for the inlet valves can move inside the area defined by the line A and the line A'', whilst the closing delay for the exhaust valves can move inside the area definied by the line B and the line B''.
A. Inlet shaft basic fitting position (completely delayed)B. Exhaust shaft basic fitting position (completely advanced)A''. Maximum rotation in relation to inlet shaft positionB’. Maximum rotation in relation to exhaust shaft positionThe action of the phase transformers is therefore principally understood as controlling the opening advance of the inlet valves and the closing delay of the exhaust valves. Obviously the variation in the opening advance of the inlet valves also produces a variation in their closing point in the same way as the variation in the closing delay of the exhaust valves also produces a variation in the opening point.The maps used for the management of the timing diagram are a compromise between the opening advance and closing delay for both the inle and exhaust valves in terms of ensuring optimum consumption, performance and emissions.
