Contents: Fuel system ↓ Electronic control system ↓
The fuel injection system consists of three main subsystems: fuel supply, air supply and electronic control.
Fuel system
Fuel at a constant pressure difference (284 kPa) is supplied by the fuel pump through the filter to the injectors, which inject fuel into the intake manifold pipes directly in front of the intake valves. The amount of fuel supplied is determined by the duration of the control pulse, which is set in accordance with the signal from the electronic control unit.
The fuel pressure regulator maintains a constant difference between the fuel pressure before the working injector and the air pressure in the intake manifold. In this case, the amount of fuel supplied is clearly determined by the open state of the injector. Regulation is carried out by bypassing part of the fuel into the tank through the valve and the fuel return line.
Air supply system The air supply system ensures that the required amount of air is supplied to the intake valves.
The amount of air entering the engine is determined by the throttle valve opening angle and the engine crankshaft speed. The air flow passes the air filter, the throttle valve body channel and enters the upper part of the intake manifold, from where it is distributed through separate pipes to the engine cylinders.
At low coolant temperatures, the idle speed control valve opens and some air enters the upper part of the intake manifold through the bypass passage in addition to the air passing through the throttle valve. Thus, as the engine warms up, even with the throttle valve fully closed, air enters the upper part of the intake manifold, which leads to an increase in engine speed (1st stage idle speed control). -
[The publication is taken from the website: toyotaman.ru]
The upper part of the intake manifold reduces air flow pulsations (functions as a receiver or resonator), and also prevents the work of some cylinders from overlapping with others.
Electronic control system
The 3S-FE, 3S-GE, 4A-FE and 7A-FE engines are equipped with an electronic control system from TOYOTA, which controls fuel injection, ignition timing, diagnostics, etc. using an electronic control unit. Using the electronic control unit, the fuel injection control system performs the following functions:
1. Fuel injection control. The electronic control unit receives signals from various sensors that record changes in the engine operating condition. In particular, the sensors record:
- absolute pressure in the intake manifold,
- air intake temperature,
- coolant temperature,
- engine crankshaft speed,
- throttle opening angle,
- oxygen content in exhaust gases, etc.
These signals are processed in the electronic control unit, which generates an output signal for the fuel injection duration, ensuring the optimum excess air ratio for the current engine operating conditions.
2. Control of ignition timing angle.
The electronic control unit memory stores the values of the optimal ignition advance angle for all possible engine operating modes. Using signals from various sensors that monitor engine operating conditions (crankshaft speed, coolant temperature, etc), the electronic control unit generates impulses that control the neoplasm at strictly defined moments in time.
3. Idle speed control system.
The electronic control unit memory stores data on the optimum idle speed, which corresponds to various conditions (for example, coolant temperature, air conditioning on/off, etc.). The sensors transmit signals to the electronic control unit, which controls the air flow through the bypass channel (bypassing the throttle valve) and regulates the idle speed in accordance with the set value.
4. Diagnostics.
The electronic control unit warns of a malfunction or abnormal operation via the "CHECK" indicator displayed on the instrument panel. The malfunction is identified as a diagnostic code, which is stored by the electronic control unit. The diagnostic code can be decoded by the number of blinks of the indicator light when contacts TE1 and E1 are shorted. Diagnostic codes are discussed below.
5. Function "Fail-Safe" ("Get home").
In case of failure of any sensor, an emergency operating mode is provided (to get to the nearest service station). At the same time, the "CHECK" indicator light on the instrument panel lights up.
6. Lean Burn system developed by TOYOTA for the 4A-FE engine.
This system provides optimal values for various engine operating conditions: fuel injection moment, fuel dose, ignition timing, etc. using negative feedback on the mixture composition when operating in the lean mixture range. That is, with mixture compositions leaner than the stoichiometric ratio. As a result, the vehicle's fuel efficiency improves without deteriorating the engine's performance properties (in particular, its responsiveness) In addition, lean combustion produces less nitrogen oxides (NO) in the exhaust gases.