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#);

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

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