Knock Sensor; Electric Throttle Body - Chery QQ6 Service Manual

5. Knock Sensor

5.1 Function of the sensor:
The knock sensor provides ECU with knock signal. When the engine generates knock, ECU
will control to gradually reduce ignition advance angle to eliminate the knock; when no knock
occurs during certain strokes, ECU will gradually increase ignition advance angle to enable the
engine to obtain max. torque.
5.2 Principle of the sensor:
Knock sensor is a kind of vibrating acceleration sensor and is assembled on cylinder block.
Either single or multiple can be installed. The sense organ of the sensor is a piezoelectric element.
The vibration of cylinder block is transferred to piezoelectric crystal by mass block inside of sensor.
The piezoelectricity crystalloid gets pressure from mass block vibration, producing voltage on two
polar and transferring vibration signals to voltage signal and output it. See the following frequency
response characteristic curve. Because the frequency of knock vibration signal is much higher than
the normal engine vibration signal, the ECU can separate the signal into knock signal and non-knock
signal.
5.3 Attentions
Knock sensor has a hole in the middle, through which it is fastened on the cylinder by a M8 bolt.
For the aluminum alloy block, using long bolt with 30 mm; for the casting iron, using 25mm bolt.
The tightening torque is 20± 5Nm. The installation position should ensure that the sensor is liable to
receive vibration signals from all cylinders. Decide the optimal installation position of knock sensor
through modal analysis to the engine body. Generally, for a 4-cylinder engine, the knock sensor is
installed between 2# cylinder and 3# cylinder; for a 3-cylinder engine, it is installed at the center of
2# cylinder. Do not let liquid such as engine oil, coolant, brake fluid and water etc. contact the sensor
long. Use of gasket of any type is not allowed in installation. The sensor must cling to the cylinder
tightly through its metal surface. During wiring of sensor signal cables, do not make the signal
cables resonate; otherwise, they may break. Be sure to prevent turning on of high voltage between 1#
and 2# pins of the sensor; otherwise, damage to the piezoelectric element may occur.
5.4 Effects and judgment method
Failure effects: poor acceleration etc.
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Reasons for general failures: long time contact of liquid such as engine oil, coolant, brake fluid
and water etc. with the sensor, which may corrode the sensor.
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Maintenance precautions: (see installation attentions)
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Simple measurement method: (remove the joint) put digital multimeter at ohm shift, and contact
the No. 1, No. 2 and No. 3 pin with its two meter pens. The resistance value should be more
than 1MΩ¸ under normal temperature. Leave the digital multimeter at millivolt shift, and tap
around the sensor using little hammer, there should be voltage signal output.

6. Electric Throttle Body

6.1 Function: