Chery QQ6 (S21) / S12LHD. Manual — part 199
5. Remove the four fixing bolts of electronic throttle body.
Pull out the connector and take out the electronic throttle body.
6. Use a screwdriver to press down the fixed clip of the injection
nozzle connector and then pull out the connector.
7. Use a screwdriver to press down the fixed clip of the knock
sensor connector and then pull out the connector.
8. The water temperature sensor is behind the thermostat seat.
9. Pull out the connector of the ignition primary coil by hand.
10. Pull out the connector of the engine tachogenerator by hand.
Chapter Two Principle of Electronic Fuel Injection System
I. Overhaul of System Components
1. Intake Air Temperature Pressure Sensor
1.1 Function of the sensor:
Detect air intake pressure and temperature in air intake manifold, which will be provided to
ECU as main load signal of engine; ECU will calculate injection pulse-width based on this signal.
1.2 Principle of the sensor:
Intake air temperature pressure sensor is a sensor that integrates an intake air pressure sensor
and an intake air temperature sensor. Absolute pressure sensor element of intake manifold is
composed of a silicon chip. A pressure diaphragm is etched on the silicon chip. On the pressure
diaphragm, there are 4 piezo-resistances, which serve as strain sensors and constitute a Wheatstone
bridge. In addition to this pressure diaphragm, a signal processing circuit is also integrated on the
silicon chip. The silicon chip and a metal housing constitute a closed reference, where the absolute
pressure of the gas inside approaches to zero. Thus, a micro-electronic mechanical system is
formed. The active face of the silicon chip stands a pressure close to zero, while its back face stands
the pending measuring intake manifold absolute pressure introduced by a connecting pipe. The
thickness of the silicon chip is merely several mm, so the absolute pressure change in intake manifold
will bring mechanical deformation to the silicon chip. The 4 piezo-resistances will accordingly
deform and their resistances also change. The voltage signal in linear relation to the pressure is
formed after process by the signal processing circuit on the silicon chip. The intake temperature
sensor element is a negative temperature coefficient (NTC) resistance, which will change with the
intake temperature. This sensor sends out a voltage indicating the intake temperature change to the
controller.
Cross-section view for sensor of air absolute pressure and temperature in intake manifold
1 Gasket 2 Stainless Steel Sleeve 3 PCB Board 4 Sensing Element 5 Housing 6 Pressure Bracket 7 Soldering 8
Bonded With Bonding Agent
进气压力温度传感
器
Intake air temperature
pressure sensor
1.3 Parameters of technical features
This sensor is designed to be mounted on the plane of auto engine intake manifold. The
pressure connecting pipe together with the temperature sensor protrudes inside the intake manifold
and an O gasket is used to enable atmosphere-proof.
If it is mounted on an auto through an appropriate method (picks up pressure from the intake
manifold and the pressure connecting pipe tilts down etc.), it can be ensured that no condensed water
will be formed on the pressure-sensitive element.
Drilling and fixing on the intake manifold must be carried out according to the supply drawing
so as to ensure a long seal and a good tolerance to fretting by agent.
The reliable contact of electric connection of a joint will mainly be affected by the joints of
components and parts, and it is also in relation to the material quality and dimensional precision of
the joint fitted with it on the harness.
1.4 Failure effects and judgment method
l Failure effects: spark extinction and poor idling etc.
l General Failure Reason:
1. Abnormal high voltage or inverse strong current occur during working;
2. The vacuum element is damaged during maintenance.
l Maintenance precautions: during maintenance, impinge using high pressure gas toward the
vacuum element is prohibited; when replacing the sensor after a failure is found, remember to
check if output voltage and current of the generator is normal.
l Simple measurement method:
1.4.1 Temperature sensor:
With the joint removed, turn the digital multimeter to Ohm shift, and then connect the two
meter pens respectively to 1# and 2# pins of the sensor; At 20
, the rated resistance should be 2.5
℃
kΩ±5%, and the other corresponding resistances can be measured out from the characteristic curve
in above chart. Analogue method can also be used when measuring, i.e., use an electric drier to blow
the sensor (be careful not to be too close to the sensor), and then observe the change of the sensor
resistance. At this point, the sensor resistance should fall.
1.4.2 Pressure sensor:
With the joint connected, turn the digital multimeter to DC Voltage shift, and then connect the
black pen to ground while the red pen respectively to 3# and 4# pins. Under idle speed state, 3# pin
should have a 5V reference voltage while the voltage on 4# pin should be around 1.3V (the actual
value depends on the model); Under no load state, when opening the throttle slowly, the voltage on
4# pin may change little; when opening the throttle rapidly, the voltage on 4# pin may reach around
4V instantly (the actual value depends on the model) and then fall to around 1.5V (the actual value
depends on the model).
2. Tachogenerator of Engine
2.1 Function of the sensor:
As one of the uppermost sensors of engine, the tachogenerator of engine provides ECU with rev
signal, acceleration signal and crank angle signal etc. of engine. ECU will calculate injection
pulse-width, injection time and ignition timing through these signals and provide the instruments
with rev signal of engine.
2.2 Principle of the sensor:
The inductive tachogenerator work together with pulse disc, it is used in ignition system
without distributor providing engine speed and crank shaft top dead center information.
Inductive tachogenerator is made up of a permanent magnet and coil outside of magnet.
Pulse disc is a tooth disc with 60 teeth originally but there are two teeth opening. Pulse disc is
assembled on crank shaft and rotate with crankshaft. When the tooth tip passes through closely the
end of the inductive engine tachogenerator, the pulse disc made of the ferromagnetic material will
cut the line of magnetic force of the permanent magnet in the inductive engine tachogenerator to
generate inductive voltage in the coil as engine speed signal output.
Tachogenerator
1. Shielded wire 2. Permanent magnet
3. Housing of sensor 4. Installation bracket
5. Soft magnet core 6. Coil
7. Air gap 8. 60-2 gear ring
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