Camshaft Position Detection
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.
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.
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 degree CA (Crank angle). 0 degree 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 degree CA before top dead center (BTDC) when the camshaft is in its 0 position (camshaft not deployed), see illustration (D1-D5).
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 degree CA (84 degree CA after hole "C" in the flywheel/carrier plate).
2: Top dead center (TDC) cylinder 2, 144 degree CA.
4: Top dead center (TDC) cylinder 4, 288 degree CA.
5: Top dead center (TDC) cylinder 5, 432 degree CA.
3: Top dead center (TDC) cylinder 3, 576 degree 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.
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 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 degree CA before the intake camshaft flanks.
The engine control module (ECM) is then able to calculate the degree 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 Vehicle Information and Diagnostics Application (VIDA).