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Chery QQ6 (S21) / S12LHD. Manual - part 244

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

2.3 Parameters of technical features

Value

Item

Min.

Typical

Max.

Unit

Resistance under a room temperature of

20°

774

860

946

Inductance

310

370

430

Output voltage at a crankshaft

revolution of 416rpm

>1650

2.4 Installation attentions:
l For the inductive tachogenerator, it is permitted to take out from its pack before it is assembled

to the auto or testing device right away.

l Inductive tachogenerator is assembled by press in method but not hammer tapping.
l Partly micro-encapsulated bolt M6´12 for fixing of the inductive engine tachogenerator is

recommended.

l The tightening torque is 8±2Nm.
l Gas clearance between inductive tachogenerator and pulse disc tip is 0.8-1.2mm.

Dimension d (see the figure below): 4.7mm.

2.5 Failure effects and judgment method:

Failure effects: start failure etc.

l General cause of the failure: man induced failure.
l Maintenance precautions: during maintenance, the tachogenerator should be installed by using

press-in method instead of hammering method.

l Simple measurement method:

1. With the joint removed, turn the digital multimeter to Ohm shift, and then connect the two

meter pens respectively to 2# and 3# pins; At 20

, the rated resistance should be 860Ω±10%.

℃

2. With the joint connected, turn the digital multimeter to AC Voltage shift, and then connect the

two meter pens respectively to 2# and 3# pins of the sensor; start the engine and voltage output

should be present at this point. (Inspection with vehicle oscilloscope is recommended).

Oscillogram in Test

f t

cho
g

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