When the external load (such as headlight, air conditioning, cooling fan and other electrical loads) is turned on, the system will increase the idle speed to compensate for the increased load and maintain the stability of the idle speed.
Knock control principle.
Introduction of knock sensor.
]Knock sensor is a kind of vibration acceleration sensor, which is installed on the engine cylinder block.
Normally, it is installed between cylinder No.2 and 3, which is good for knock balance of engine.
ECM makes use of the vibration frequency signal outputted by the sensor, through the internal filtering of ECM, and then determines whether there is a engine knock.
When the knock signal is detected, ECM corrects the ignition angle until no knock occurs.
Knock control requirements.
Vehicles are equipped with knock sensors.
Engine speed is more than 800rpm.
MAP is more than 40kpa.
Knock control mode.
Steady-state control: during the normal running of the engine, ECM collects and analyzes the sound during the combustion process of the engine through the knock sensor. After filtering, the knock is detected.
Once the knock intensity exceeds the limit, the system will quickly delay the ignition advance angle of the cylinder where the knock occurs, and eliminate the knock.
Transient control: knock is easy to occur when there is a rapid acceleration or a sharp change in engine speed.
When the system predicts the possibility of knock, it will automatically delay the ignition advance angle in order to avoid the occurrence of overrun (strong) knock.
Quick delay ignition angle: after the knock is detected, according to the different engine speed, system will quickly delay the ignition advance angle, and returns to normal in the next 2, 3 seconds.
Adaptive adjustment of ignition angle: due to manufacturing error and wear after long-term use (because belt, toothed belt pulley and cam have effects on phase angle), there are differences or changes in the engine.
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