Chery A18. Manual — part 7

WORKING PRINCIPLE

This system is capable of controlling the actual tested air-fuel ratio under all engine speeds to
stay close to the equivalent proportion of the chemical reaction, so as to protect the catalyst
package and subsequently reduce the discharge of pollution. The oxygen sensor analyses the
oxygen content of the discharge gas using real-time principle and makes it possible for the
ECU to control the amount of injecting fuel to correct the air-fuel ratio. The fuel with a
pressure of about 3.5 bars is directly injected into the air intake manifold near the throttle
valve.

The fuel injectors of all cylinders are utilizing a sequential phase angle control method
according to the intake sequence and the opening time of the air intake valves; the injection
destinations are stored in the ECU map, and can vary autonomously according to the engine
speeds and intake air pressures. The application of sensors in the system is a basic strategy
used to correct the engine under all operating conditions. The system is implementing an
induction type of electrical discharge ignition, where the power source module in the ECU
controls the ignition timing. The ignition advance angle is calculated according to the engine
compression ratio and intake air volume. The idling speed is maintained at stable condition
through controlling the opening of the branch-connection pipe by a step motor and also
through the changing of the ignition points.

Other than capable of obtaining the input signals and controlling the output components, the
system has also equipped with various other functions. These functions include the following:

- When self-diagnose that the sensor is faulty, adopt the restoration strategic control.

- Restoration of the self-regulating mixed concentration engine and variances in spare parts.

- Exchange data with the diagnostic tester.

The idling speed of the engine and the amount of CO in the air discharged must not be
manually adjusted.

ELECTRONIC CONTROL UNIT

The ECU is located on the left of engine firewall. The ECU handles various signals from the
sensors and controls the actuator so as to achieve the best possible operating condition. Many
extra functions are added as compared with the previous model. While by the usage of a
custom-made circuit board that can achieve many special functions, the integrated functions
are enhanced so that the structure has considerably reduced in size and become much more
compact.

The hard wares in the ECU are as follows:

-16 bit CPU single chip

- 8KB RAM (2KB IRAM + 6KB ERAM)

- 2MB FLASH EPROM (12V programming voltage)

- 2KB SERIAL EEPROM

- 16 CHANNELS 10 MODULES/NO. (A/D) CONVERTER

- 4PWM OUTPUT

- CAN MODULE (CAN2.0B)

The ECU software structure is divided into two parts for data processing:

-The “Application” part obtained the measurement of engineering parameter through sensors

to calculate the control parameters of the fuel injectors, ignition coils and idling speed step
motor for controlling the engine starting.

-The “Basic” part is collecting the data from the sensors and converts it into engineering data.

After that it controls the actuator through the calculated parameter generated by the
“application” software, and manages the self-diagnostic programs of the various sensors and
actuators. In addition, it can also communicate with the externally connected diagnostic
tester through the use of “K” serial cable.

The operating system is capable of ensuring the accurate management of the matters related
with time (such as the management of definite and delay timing) and angles (related to the
engine rotation sequence). This type of management is integrated in the software and
calculated according to the precise priority to ensure the optimization management of the
engine even at its high-speed condition. This type of “modular structure” design allows the
possibility of achieving all kinds of flexibility control and in the mean time not tampering the
overall characteristic of the system.

The following data are transmitted into the ECU:

- Battery voltage

- Absolute pressure sensor in the air intake manifold

- Top dead center

- Throttle valve opening angle position

- Air intake temperature

- Engine coolant temperature

- Air conditioning operation

- Signal from oxygen sensor

- Knock sensor for the accelerator meter on top of the engine crankshaft housing

The air intake efficiency is obtained by calculating through the processing of absolute
pressure, air intake temperature, engine speed, throttle valve position and other signals, and
help to determine the air intake quantity of the cylinder. The inbuilt power supply module in
the ECU is controlling the following functions:

- To control the injected fuel quantity through the control of opening timing of the fuel
injector

- Idling speed step motor

- Ignition coils of the 4 high voltage outputs

- Check valve for recirculation the gaseous fuel on top of the air intake manifold (carbon
canister)

- Temporary turnoff of the air condition compressor

- Dual speed cooling fan for the engine

- Overheating alarm light in the coolant of the engine

- Malfunction alarm light

Other than these major functions, ECU also controls:

- All the self-diagnostic strategy related to input sensors and output actuators

- Wrong signals restoration strategy works on basically effective input signals

WORKING PRINCIPLE OF ELECTRONIC FUEL INJECTION

CONTROL AND ACTUATORS

※ Intake Pressure and Intake Air Temperature

Sensor

Purpose: detects manifold absolute pressure from
0.1~0.2bar and intake air temperature, provides engine
with load information.

Composition and principle: this sensor is composed
of two different sensors (i.e. manifold absolute
pressure sensor and intake temperature sensor), and is
installed above pressurizer.

Pressure-sensitive element inside intake pressure
sensor detects pressure signal on intake manifold for
injection pulse width control of EFI system. This
sensor also serves as the substitute of load signal
sensor.

Intake air temperature sensing element is a resistor
of negative temperature coefficient (NTC), which is
similar to water temperature sensor with resistance
value decreasing with the increasing of intake air
temperature. And engine ECU monitors the variation
of intake air temperature via a comparison circuit
inside.

Failure diagnosis: The electronic device next to
intake pressure sensor detects sensor circuit troubles
such as open circuit, short circuit and sensor damages,
etc. In case ECU detects any sensor output signal that
goes beyond output characteristic curve, the sensor is
diagnosed as failed by ECU. For example: when
intake pressure is higher than upper limit or lower than
lower limit, ECU detects sensor failure (in case that
intake pressure is lower than lower limit when starting,
ECU is able to recognize the starting condition), and
the engine fault indicating lamp goes on. Under this
condition the engine works in failure mode.

Installation: to be installed on pressurizer.

Circuit diagram of manifold absolute
pressure and intake air temperature sensor

Pins:

1# is grounded (connecting ECU 17#);

2#

outputs

temperature

signal

(connecting ECU 40#);

3# connects with standard 5V power
source (connecting ECU 33#);

4# outputs pressure signal (connecting
ECU 37#).

Manifold

absolute

pressure and intake air

temperature sensor

TMAP