User's Manual

LAUNCH X-431Tool User’s Manual
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3) In braking system: vehicle speed, wheel
speed, deceleration, sliding rate, braking
pedal force, braking pedal position sensors,
etc.
4) In steering control system: steering, vehicle
acceleration, vehicle speed sensors, etc.
5) In suspension system: vehicle speed,
vehicle height, steering angle, throttle
position, braking force sensors, etc.
6) In A/C system: external temperature,
internal temperature, sunshine, coolant
temperature, refrigerant pressure and
humidity sensors, etc.
7) In instrument, alarm and diagnosis systems:
remaining fuel, coolant temperature, oil
pressure, oil status, intake air pressure,
windshield washer fluid level, battery liquid
level, door lock, braking fluid level sensors.
ECU
The electronic control unit is composed of input
circuit, A/D converter, SMC, output circuit, etc.
See Fig 6-2.
Fig 6-2
1- Sensor 4- A/D converter 7- SMC
2- Analog signal 5- output circuit 8- Digital signal
3- Input circuit 6- Actuator 9- ROM/RAM
1) Input circuit: digital signal from sensor will
enter the CPU directly. However, the
analogue signal will be treated in the A/D
converter before getting into CPU. The
input circuit filters out the noise, converts
sine wave into rectangular wave and then
into electrical parameter.
2) A/D converter: it converts the analogue
signal from the sensor into digital signal.
Then the digital signal can get into SMC.
3) SMC: it consists of I/O interface, CPU,
RAM/ROM, etc. The received digital signal
is computed here with the pre-programmed
parameters from ROM. The computed
result is transmitted through I/O interface to
the output circuit, and then to the
corresponding actuators.
The data in ROM is written by manufacturer
and will not be lost when power is off.
However, the data in RAM will be lost when
power is off.
4) Output circuit: it is to amplify the signal from
SMC. The weak current from SMC is not
able to activate the actuator. So it has to be
amplified.
Actuator
Actuator is to convert the electrical signal into
force or displacement. The popular actuators
are listed below:
1) Solenoid valve: This actuator is to convert
electrical signal into linear movement. Two
types of solenoid valves are used in the
vehicle. One is directly driven with linkage,
e.g. the magnetic switch of starter motor.
The other is for controlling pressure and
flow by transferring the movement to
relevant valves. For example, in engine
intake air control, electronically controlled
automatic transmission, suspension control,
etc.
2) Motor: DC motor is the most popular
actuator used in automobile. It can be
divided into two types according to its use.
One is rotated by power, e.g. windshield
wiper, seat adjuster, etc. The other is used
in servo mechanism. In this situation,
external force makes the rotor rotate
around the stator, e.g. the servo motor for