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Home >> Volvo >> 2006 >> S60 2.5T AWD L5-2.5L Turbo VIN 59 B5254T2 >> Repair and Diagnosis >> Engine, Cooling and Exhaust >> Engine >> Timing Components >> Variable Valve Timing >> Variable Valve Timing Actuator >> Description and Operation >> Camshaft Control (CVVT)

Camshaft Control (CVVT)



Camshaft Control (CVVT)







When the camshaft is set at the factory, it is aligned with the position of the crankshaft. The position of the camshaft in relation to the crankshaft is designated the camshaft 0 position.

During camshaft control (CVVT) the camshaft 0 position is offset. The value of the 0 position offset is called the cam timing. The cam timing is 0 degrees if the camshaft is not being controlled.

By controlling the cam timing (the camshaft is deployed from its 0 position) the performance of the engine is increased, the idle speed quality is improved and the emissions are reduced.

In order to detect the cam timing, the engine control module (ECM) uses the signals from the engine speed (RPM) sensor (the position of the crankshaft) and from the camshaft position (CMP) sensor (the position of the camshaft). By comparing these two signals, the control module is able to determine the cam timing (the number of degrees the camshaft is from its 0 position).

There are diagnostic for this function. See also Camshaft diagnostics (CVVT).

Camshaft cam timing






The camshaft (A) is divided into four flanks per revolution of the camshaft (flanks 1-4). The angle between flanks 1-2 = 103 degrees, flanks 2-3 = 90 degrees, flanks 3-4 = 90 degrees and flanks 4-1 = 77 degrees. The angle between the flanks is different, allowing the control module to determine which flank it is detecting and therefore determine which combustion cycle the cylinders are in.

The crankshaft has four reference positions, one for each camshaft flank. The camshaft turns at half the speed of the crankshaft. This means that two reference positions are detected for each turn of the crankshaft. Therefore two engine revolutions are required to detect all flanks on the camshaft. For example (may vary between different engine variants): flank 1 at 0 degrees, flank 2 at 206 degrees, flank 3 at 386 degrees and flank 4 at 576 degrees (flanks 3 and 4 are detected during the second engine revolution).

The reference positions of the crankshaft coincide exactly with each camshaft flank if the camshaft cam timing is 0 degrees. If the cam timing deviates from 0 degrees, i.e. the flanks deviate from the reference positions of the crankshaft, the control module calculates the number of crankshaft degrees by which the flank is deviating.

The control module detects the reference positions for the camshaft flanks using the signal from the engine speed (RPM) sensor.

Example:
If camshaft flank 1 is detected at 10 degrees from the crankshaft reference position for flank 1 (0 degrees +10 degrees), the cam timing is 10 degrees. If the cam timing is the same (10 degrees), flank 2 is detected at 216 degrees (206 degrees + 10 degrees), flank 3 at 396 degrees (386 degrees + 10 degrees), and flank 4 at 586 degrees (576 degrees + 10 degrees). The cam timing can be positive (+) or negative (-) depending on whether the flank is detected before or after the different reference positions for the crankshaft.

The engine control module (ECM) controls the camshaft reset valve smoothly in order to regulate the camshaft cam timing. The valve controls the flow of engine oil to the continuous variable valve timing (CVVT) unit which is affected by the oil pressure that builds up. Also see Design.


Control







Control takes place as follows when deploying the camshaft:
1. Oil is forced from the engine lubricating system to the intake port on the reset valve
2. The engine control module (ECM) grounds the valve, the position of the piston in the valve changes and the oil is guided to the continuous variable valve timing (CVVT) unit chamber (A1) via the duct (A2) in the camshaft
3. The continuous variable valve timing (CVVT) unit hub is pressed backwards by the oil pressure. The continuous variable valve timing (CVVT) unit then rotates the hub and the carriers are joined by twisted splines
4. The oil flows to the engine oil pan via the outer ducts on the hub and the reset valve's return hose.

Control takes place as follows when returning the camshaft:
1. Oil is forced from the engine lubricating system to the intake port on the reset valve
2. The engine control module (ECM) breaks the ground connection for the valve. The piston in the valve is then pressed back by a spring. The oil flows to the continuous variable valve timing (CVVT) unit chamber (B1) via a duct (B2) in the camshaft
3. The hub of the continuous variable valve timing (CVVT) unit is forced forward by the oil pressure that is created. The continuous variable valve timing (CVVT) unit will rotate back to the nondeployed position
4. The oil flows to the engine oil pan via the center duct on the hub and the reset valve's return duct.

The above takes place very quickly. The engine control module (ECM) controls the deployment and return of the reset valve continually at high frequency. This results in rapid and exact control.

The extent of camshaft control (the change of cam timing) varies depending on the engine variant and the model year.
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