Camshaft Position Sensor: Description and Operation

CAMSHAFT POSITION (CMP) SENSOR

The camshaft position (CMP) sensor is a hall ignition control (IC) type sensor. The sensor is true power on (TPO) at power up, which means it is capable of recognizing whether it is in front of a tooth or a notch at power up, and to set its output accordingly. The sensor is a high technology product that integrates a self calibrating system that compensates for environmental changes, such as temperature and air gap. The sensor is composed of a magneto-electronic module that generates a magnetic signal and transforms it into a digital signal. The sensor operates in 2 functional modes. The first mode is the static functional mode. This mode is valid at sensor power up. In this mode, the sensor behaves like a simple DC hall IC switch with 2 fixed switching points. The static functional mode is active during the first 10 mechanical edges of the reluctor wheel and as long as the signal frequency is lower than 1.2 Hertz, plus or minus 0.5 Hertz, with the one tooth reluctor wheel. When the signal frequency exceeds the previous mentioned limit, the sensor switches to the second functional mode, the self-calibrating functional mode. This mode enables the sensor to reach high angular position accuracy, which is not possible to achieve in the static functional mode. In the self-calibrating mode, the sensor acts as a field induction sensor, which is more accurate at higher engine RPM. The sensor switches from self-calibrating mode to static functional mode when the signal frequency becomes lower than 0.3 Hertz, plus or minus 0.1 Hertz, with the 1-tooth reluctor wheel. When the sensor switches back from self-calibrating mode to the TPO mode, a pulse of short duration is generated on the sensor output signal. The pulse may occur on the low signal state or on the high signal state.

The CMP sensor wiring consists of a 12-volt reference circuit, a low reference circuit, and a signal circuit. The CMP sensors work in conjunction with a 1-tooth reluctor wheel on the exhaust CMP actuators. The CMP sensors work in conjunction with an 8-tooth reluctor wheel on the intake CMP actuators. As each tooth on the reluctor wheel passes the CMP sensor it sends a digital signal, which is an image of the wheel, to the engine control module (ECM). The ECM processes this information to determine the exact position of the camshafts, and to determine the optimum ignition and injection points of the engine.