Computers and Control Systems: Description and Operation
SFI SYSTEM
System Circuit
The SFI system is composed of three basic sub-systems: Fuel, Air Induction and Electronic Control Systems.
Fuel System
Fuel is supplied under constant pressure to the SFI injectors by an electric fuel pump. The injectors inject a metered quantity of fuel into the intake manifold in accordance with signals from the ECM (Engine Control Module).
Air Induction System
The air induction system provides sufficient air for engine operation.
Electronic Control System
The CAMRY 3VZ-FE engine is equipped with a TOYOTA Computer Controlled System (TCCS) which centrally controls the SFI, ESA, AC, Diagnosis systems etc. by means of an Engine Control Module (ECM-formerly SFI computer) employing a microcomputer. By means of the ECM, the controls the following functions:
1. Sequential Multiport Fuel Injection (SFI)
The ECM receives signals from various sensors indicating changing engine operation conditions such as:
Intake air volume
Intake air temperature
Engine coolant temperature Engine rpm
Acceleration/deceleration
Exhaust oxygen content etc.
The signals are utilized by the ECM to determine the injection duration necessary for an optimum air-fuel ratio.
2. Electronic Spark Advance (ESA)
The ECU is programmed with data for optimum ignition timing under any and all operating conditions. Using data provided by sensors which monitor various engine functions (rpm, engine coolant temperature, etc.), the microcomputer (ECM) triggers the spark at precisely the right instant.
3. Idle AIR Control (IAC)
The ECM is programmed with target idling speed values to respond to different engine conditions (Engine coolant temperature, air conditioning ON/OFF etc.). Sensors transmit signals to the ECM which control the flow of air through the by-pass of the throttle valve and adjust idle speed to the target value.
4. Diagnosis
The ECM detects any malfunctions and abnormalties in the sensor network and lights a Malfunction Indicator Lamp on the combination meter. At the same time, the trouble is identified and a diagnostic trouble code is recorded by the ECM. The diagnostic trouble code can be read by the number of blinks of the Malfunction Indicator Lamp when terminals TE1 and E1 are connected.
5. Fail-Safe Function
In the event of the sensor malfunctioning, a back-up circuit will take over to provide minimal driveability, and the Malfunction Indicator Lamp will illuminate.
Operation Fuel System
Fuel is pumped up by the fuel pump, flows through the fuel filter and is distributed to each injector and cold start injector at a set pressure maintained by the pressure regulator. The fuel pressure regulator adjusts the pressure of the fuel from the fuel line (high pressure side) to a pressure 284 kPa (2.9 kgf/cm2, 41 psi) higher than the pressure inside the intake manifold, and excess fuel is returned to the fuel tank through the return pipe. When the engine is hot. the fuel pressure is increased to control percolation in the fuel system and improve restartability and idling stability. The pulsation damper absorbs the slight fluctuations in fuel pressure caused by fuel injector from the injector. The injectors operate on input of injection signals from the ECM and inject fuel into the intake manifold. The cold start injector operates when starting at low engine coolant temperature or at normal temperature ranges, injecting fuel into the air intake chamber to improve startability.
Air Induction System
Air filtered through the air cleaner passes through the volume air flow meter and the amount flowing to the air intake chamber is determined according to the throttle valve opening in the throttle body and the engine rpm. The volume air flow meter measures the intake air flow by the opening of the measuring plate in response to the volume of intake air to the engine. Located in the throttle body is the throttle valve, which regulates the volume of intake air to the engine. Intake air controlled by the throttle valve opening is distributed from the air intake chamber to the manifold of each cylinder and is drawn into the combustion chamber. At low temperatures the IAC valve opens and the air flows through the IAC valve and the throttle body, into the air intake chamber. During engine warning up, even if the throttle valve is completely closed, air flows to the air intake chamber, thereby increasing the idle speed (first idle operation). The air intake chamber prevents pulsation of the intake air, reduces the influence on the volume air flow meter and increases the accuracy of the measurement of the intake air volume. It also prevents intake air interference in each cylinder.
Electronic Control System
The control system consists of sensors which detect various engine conditions, and a ECM which determines the injection volume (timing) based on the signals from the sensors. The various sensors detect the intake air volume, engine rpm, oxygen density in the exhaust gas, engine coolant temperature, intake air temperature and atmospheric pressure etc. and convert the information into an electrical signal which is sent to the ECM. Based on these signals, the ECM calculates the optimum ignition timing for the current conditions and operates the injectors. The ECM not only controls the fuel injection timing, but also the self diagnostic function which records the occurrence of a malfunction, ignition timing control, idle rpm control, fuel pressure control and fuel pump control.