Advanced Automotive Fault Diagnosis
Inductive crankshaft and
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LÔØI NOÙI ÑAÀU, ledklok
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- Figure 4.4
- Figure 4.6
| 4.2.4 Inductive crankshaft and
camshaft sensor waveform The inductive type crank and cam sensors work in the same way. A single tooth, or toothed wheel, induces a voltage into a winding in the sensor. The cam sensor provides engine position information as well as which cylinder is on which stroke (Figure 4.7). The crank sensor pro- vides engine speed. It also provides engine posi- tion in many cases by use of a ‘missing’ tooth. In this particular waveform (Figure 4.8) we can evaluate the output voltage from the crank Figure 4.4 Air vane output voltage Figure 4.5 Hot wire air mass meter (Source: Bosch Press) Oscilloscope diagnostics 43 sensor. The voltage will differ between manufac- turers and it also increases with engine speed. The waveform will be an alternating voltage signal. The gap in the picture is due to the ‘missing tooth’ in the flywheel or reluctor and is used as a reference for the ECU to determine the engine’s position. Some systems use two reference points per revolution. The camshaft sensor is sometimes referred to as the cylinder identification (CID) sensor or a ‘phase’ sensor and is used as a reference to time sequential fuel injection. This particular type of sensor generates its own signal and therefore does not require a voltage Figure 4.6 Air mass meter waveform Figure 4.7 Crank sensor in position near the engine flywheel Figure 4.8 Crank and cam sensor output signals 44 Advanced automotive fault diagnosis Figure 4.10 Decreasing voltage from the temperature sensor supply to power it. It is recognisable by its two electrical connections, with the occasional addi- tion of a coaxial shielding wire. The voltage produced by the camshaft sensor will be determined by several factors, these being the engine’s speed, the proximity of the metal rotor to the pick-up and the strength of the mag- netic field offered by the sensor. The ECU needs to see the signal when the engine is started for its reference; if absent it can alter the point at which the fuel is injected. The driver of the vehicle may not be aware that the vehicle has a problem if the CID sensor fails, as the drivability may not be affected. However, the MIL should illuminate. The characteristics of a good inductive cam- shaft sensor waveform is a sinewave that increases in magnitude as the engine speed is increased and usually provides one signal per 720° of crankshaft rotation (360° of camshaft rotation). The voltage will be approximately 0.5 V peak to peak while the engine is cranking, rising to around 2.5 V peak to peak at idle as seen in the example show. tải về 7.07 Mb. Chia sẻ với bạn bè của bạn:
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