09-9
ENGINE CONTROL SYSTEM
RODIUS 2005.07
0452-01
2. FUEL SYSTEM
The function of the fuel metering system is to deliver the correct amount of fuel to the engine
under all operating conditions.
The fuel is delivered to the engine by the individual fuel injectors mounted into the intake
manifold near each cylinder.
The main fuel control sensors are the Mass Air Flow (MAF) sensor and the oxygen (O2)
sensors.
The MAF sensor monitors the mass flow of the air being drawn into the engine.
An electrically heated element is mounted in the intake air stream, where it is cooled by the
flow of incoming air.
Engine Control Module (ECM) modulates the flow of heating current to maintain the
temperature
differential between the heated film and the intake air at a constant level. The amount o
f
heating current required to maintain the temperature thus provides an index for the mass ai
r
flow.
This concept automatically compensates for variations in air density, as this is one of the
factors that determines the amount of warmth that the surrounding air absorbs from the heated
element. MAF sensor is located between the air filter and the throttle valve.
Under high fuel demands, the MAF sensor reads a high mass flow condition, such as wide
open throttle.
The ECM uses this information to enrich the mixture, thus increasing the fuel injector on?time,
to provide the correct amount of fuel. When decelerating, the mass flow decreases.
This mass flow change is sensed by the MAF sensor and read by the ECM, which then
decreases the fuel injector on?time due to the low fuel demand conditions.
The O2 sensors are located in the exhaust pipe before catalytic converter.
The O2 sensors indicate to the ECM the amount of oxygen in the exhaust gas, and the ECM
changes the air/fuel ratio to the engine by controlling the fuel injectors.
The best air/fuel ratio to minimize exhaust emissions is 14.7 to 1, which allows the catalytic
converter to operate most efficiently. Because of the constant measuring and adjusting of the
air/fuel ratio, the fuel injection system is called a “closed loop” system.
The ECM uses voltage inputs from several sensors to determine how much fuel to provide to
the engine.
The fuel is delivered under one of several conditions, called ‘‘modes”.
0-7
BRAKS SYSTEM
RODIUS 2005.07
4830-01
4) Master Cylinder
The brake master cylinder is designed to
convert the force from the brake maste
r
cylinder to the high hydraulic pressure. The
brake system uses the tandem type master
cylinder with in-line 2 pistons.
The in-line 2 pistons generate the hydraulic
pressure. The piston cup on the piston keeps
the sealing conditions in cylinder and
prevents the oil leaks. The hydraulic
pressure generated by the primary piston is
delivered to the front wheels, and the
hydraulic pressure generated by the
secondary piston is delivered to the rea
r
wheels.
5) Brake Booster
The brake booster is a power assist device for brake system. It relieves the pedal depressing
force by using the pressure difference between the vacuum pressure generated by vacuum
pump in intake manifold and the atmospheric pressure.
▶Pressure distribution at working
When depressing the brake pedal, the push
rod (1) in booster pushes the poppet (2) and
valve plunger (3). The poppet (2) pushes the
power piston seat (5) resulting in closing the
vacuum valve (9). The chamber (A) and (B)
in power cylinder are isolated and the valve
plunger (3) is separated from the poppet (2).
And then the air valve (6) opens and ai
r
flows into the chamber (B) through filter.
Then, the power piston (5) pushes the
master cylinder push rod (7) to assist the
brake operation.
▶Pressure distribution after working
When releasing the brake pedal, the valve
plunger (3) returns back to the original
position by return spring (4) and the air valve
(6) closes. At this time, the vacuum valve (9)
opens and the pressure difference between
chamber (A) and (B) in power cylinder is
eliminated. Accordingly, the power piston (5)
returns back to original position by the
reaction of master cylinder (10) and the
diaphragm return spring (8).
