Camshaft Control (CVVT)
When the camshaft (A) is set at the factory, it is aligned with the position of the crankshaft (B). The position of the camshaft in relation to the crankshaft is designated the camshaft 0 position . During camshaft (CVVT) control, the 0 position of the camshaft is advanced so that the opening and closing of the intake valves can be changed to relative to the camshaft. By controlling the camshaft (the camshaft is regulated from its 0 position) the performance of the engine is increased, the idle speed quality is improved and the emissions are reduced.
There are diagnostics for this function. See also: CAMSHAFT DIAGNOSTICS (CVVT)
Camshaft position detection
In order to detect the position of the camshaft in relation to the crankshaft, 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). The control module uses these two signals to determine the position of the camshaft in relation to the position of the crankshaft.
Both the intake camshaft and exhaust camshaft have a camshaft position sensor. Cylinder detection on start up (the operating cycle of each cylinder) is improved by using a camshaft position sensor on the intake camshaft and exhaust camshaft.
The following description applies to the intake camshaft.
Detecting the camshaft flanks
The camshaft is divided into five flanks per camshaft revolution (flanks 1-5). The flanks are detected by the camshaft position (CMP) sensor. Its signal is affected by the shape of the camshaft rotor. See also: CAMSHAFT POSITION (CMP) SENSOR
Because the teeth on the camshaft pulse wheel are differently designed the control module can determine the position of the camshaft using the camshaft position (CMP) sensor signal. The control module is able to establish which combustion cycle the cylinders are in.
Detecting the reference positions of the camshaft
The crankshaft has five reference positions, one for each camshaft flank. The reference positions are predetermined points on the flywheel. The reference positions are detected using the signal from the engine speed (RPM) sensor. See also: ENGINE SPEED (RPM) SENSOR
The camshaft rotates at half the speed of the crankshaft. Two engine revolutions are required to detect all five camshaft flanks:
The positions on the flywheel are designated °CA (Crank angle). 0°CA = Top dead center cylinder 1.
Detecting the position of the camshaft in relation to the position of the crankshaft
Each camshaft flank aligns with pre-defined positions on the crankshaft when the camshaft is in its 0 position. These positions on the crankshaft are called flank reference positions. Each flank is 33°CA before top dead center (BTDC) when the camshaft is in its 0 position (camshaft not deployed), see D1-D5 in illustration.
A: Engine speed (RPM) sensor signal.
B: Camshaft position (CMP) sensor signal, intake. From high to low signal when the teeth on the camshaft pulley leave the camshaft position (CMP) sensor.
C: Low engine speed (RPM) sensor signal because of the holes in the flywheel/carrier plate.
1: Top dead center (TDC) cylinder 1, 0°CA (84°CA after hole "C " in the flywheel/carrier plate).
2: Top dead center (TDC) cylinder 2, 144°CA.
4: Top dead center (TDC) cylinder 4, 288°CA.
5: Top dead center (TDC) cylinder 5, 432°CA.
3: Top dead center (TDC) cylinder 3, 576°CA.
Regulating the camshaft position
To control the intake camshaft the engine control module (ECM) regulates the infinitely variable camshaft reset valve. 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. This allows the CVVT unit to change the position of the camshaft. Also, see "Control, CVVT unit " below and CAMSHAFT RESET VALVE (CONTINUOUS VARIABLE VALVE TIMING (CVVT))
When controlling the camshaft position (the engine control module (ECM) controls the camshaft), detection of the camshaft flanks will be offset from the reference positions on the crankshaft. Angles D1-D5 shown in the illustration will increase when the camshaft is controlled.
HINT: The exhaust camshaft signals are the same as those of the intake camshaft. However, the exhaust camshaft flanks are 318°CA before the intake camshaft flanks.
The engine control module (ECM) is then able to calculate the °CA (crankshaft degrees from top dead center (TDC)) that the intake valve opens and the exhaust valve closes for each cylinder. This is because the opening and closing angles are fixed and predefined in relation to the camshaft flanks.
The camshaft position relative to the crankshaft position can be read in VIDA (Volvo scan tool).
Control, CVVT unit
HINT: The illustration is a view of the CVVT unit from the side and from the rear.
1: Timing belt pulley
2: Lock pin with spring
3: Rotor
4: Rotor wings
A1: Chamber A
B1: Chamber B
The continuous variable valve timing (CVVT) unit allows the position of the camshaft to be adjusted relative to the crankshaft.
The camshaft is secured to the rotor (3). The rotor (and with it the camshaft) rotates in relation to the timing belt pulley (1) within set angles.
When the camshaft is in its 0 position, the timing belt pulley and the rotor are locked together by the lock pin (2). A spring-loaded lock pin slides into a hole on the inside of the end of the timing belt pulley to secure it.
Camshaft reset valve
5: Piston with slits
6: Return spring
A: Channel leading to chamber A1 in the CVVT unit
B: Channel leading to chamber B1 in the CVVT unit
C: Channel for oil (pressure)
D: Channel for oil (return)
The camshaft reset valve controls the oil flow to the continuous variable valve timing (CVVT) unit. The engine control module (ECM) uses a pulse width modulation (PWM) signal to control the valve. See also: CAMSHAFT RESET VALVE (CONTINUOUS VARIABLE VALVE TIMING (CVVT))
Control takes place as follows when deploying the camshaft
HINT: The illustration is a view of the CVVT unit from the side and from the rear.
- The oil is forced from the engine lubrication system (C)
- The valve is grounded by the engine control module (ECM). The oil flows via the slits in the piston (5) to the oil channel (A) in the camshaft
- The oil flows via oil channels in the camshaft to the top of the lock pin (2). If the camshaft is in its 0 position, the lock pin will be forced in by the oil pressure and the rotor releases from the timing belt pulley
- The chamber (A1) fills with oil. The oil pressure will rotate the rotor (3)
- The oil in the chamber (B1) will be forced out of the chamber by the rotation of the rotor. The oil flows to the engine oil pan via the camshaft, channel (D) and the valve.
Control takes place as follows when returning the camshaft
HINT: The illustration is a view of the CVVT unit from the side and from the rear.
- The oil is forced from the engine lubrication system (C)
- The engine control module (ECM) breaks the ground connection for the valve. The piston (5) in the valve springs back (6) and the oil flows via the piston slits in the valve to the oil channel (B) in the camshaft
- The chamber (B1) fills with oil. The oil pressure in the chamber will rotate the rotor
- The rotor (4) reaches its limit position and the lock pin slides into a hole on the inside of the front end of the camshaft pulley
- The oil in the chamber (A1) will be forced out of the chamber by the rotation of the rotor. The oil flows to the engine oil pan via the camshaft, channel (D) and the valve.
The reset valve is controlled by the engine control module (ECM) at high frequency. The frequency changes for deployment and return. This ensures rapid and precise control. The extent of camshaft control (change in the camshaft radial position) varies depending on the engine variant.