Control system
To ensure the supply of fuel to the engine cylinders at the right time and in the right amount, the control system for this process must be able to perform a number of separate functions. The brain of this system is the ECU electronic control module (on-board computer) based on an 8-bit processor. The module consists of a CPU (data processing unit), memory devices and data input/output ports. Based on the basic data stored in the computer's memory, and taking into account the real signals coming from various sensors, the module calculates the correct fuel mixture, which the engine may require.
Electronic control module (ECU)
The main, first, task of the module is to control the process of fuel supply to the engine. Compliance with the exact match of the supplied fuel to the needs of the engine reduces the level of harmful gases in the exhaust to a minimum, and maintains efficiency at a maximum. The ECU can only control the fuel injectors by energizing them. Since the fuel pressure in the injector is kept constant and the size of the injector is unchanged, the exact amount of fuel supplied to the combustion chamber is controlled by the duration of the injection and its timing.
The module stores in memory the values of standard injection durations for various engine speeds and pressures in the vacuum manifold. The value of the injection duration read from the memory is specified by signals from various sensors. Other control system features include:
- Engine start control: The fuel mixture must be varied according to different operating modes. For example, at the time of start-up, the mixture should be enriched. Therefore, the injection duration read from the computer memory is specified by signals about the position of the starter, engine speed, coolant temperature, which ensures the supply of additional fuel at the time of engine start.
- Fuel pump control: When the engine speed falls below a certain limit, the power supply to the fuel pump is interrupted, which stops fuel injection from the injectors.
- Fuel cut function: During braking, near full throttle, and when the engine speed exceeds 900 rpm, the power supply to the injectors is interrupted, which increases the efficiency of the engine. The fuel cut function is also activated when the engine speed exceeds the maximum safe value (red line). This occurs regardless of the position of the throttle valve.
- Security System: A dedicated business continuity system monitors all sensors and the correct operation of the ECU. It ensures safe driving, even if several sensors fail at the same time or ECU malfunctions. In case of failure of the ECU itself, all control signals are replaced with a fixed set so that the car can safely reach the parking lot. When this function is enabled, the driving performance of the machine is significantly reduced.
Crank angle sensor
The ignition distributor and its sensors are structurally designed as a single module in order to reduce size and weight. It consists of two rotors - BMT (TDC) and CIL (SUd - and two sensors for each of them. The rotors are connected to the camshaft and rotate with it as one unit. The CYL sensor measures the position of cylinder #1 as the starting point of the sequence, and the TDC sensor determines the ignition timing of each cylinder. The TDC sensor also measures the engine speed, which determines the initial fuel injection duration. After that, the duration of the injection is specified for specific driving conditions.
Manifold pressure sensor (MAP sensor)
The sensor converts the measured manifold air pressure into an electrical voltage signal that is sent to the ECU. This data, along with ignition angle sensor data, is used to read the original fuel injection duration from the ECU memory.
Atmospheric pressure sensor (RA sensor)
Like the MAP sensor, this sensor converts the measured barometric pressure into a voltage signal that is sent to the ECU. This signal is used to adjust the initial injection duration with the atmospheric pressure difference compensation circuit.
Coolant temperature sensor (TW sensor)
This sensor measures fluctuations in coolant temperature using a temperature sensor (ter-mistor). The signal from this sensor is used by the ECU to refine the original injection duration. The resistance of the thermistor decreases with increasing coolant temperature.
Intake air temperature sensor (TA sensor)
This sensor is also a thermistor placed in the intake manifold. It works like a liquid temperature sensor, but with less heat capacity for faster response. The data from this sensor is also used to refine the injection duration in order to compensate for changes in driving conditions.
Throttle Angle Sensor
This sensor is essentially a variable resistor. It works as follows. The rotor shaft is connected to the axis of the throttle valve. Therefore, with the movement of the throttle valve, the resistance of this connection changes, which causes a change in the voltage output signal sent to the ECU.
Oxygen sensor
The oxygen sensor, by measuring the oxygen content in the exhaust gases, maintains the air-fuel mixture ratio. During operation, the ECU receives signals from this sensor and accordingly changes the duration of fuel injection. The oxygen sensor is located in the exhaust manifold or in the exhaust pipe before the catalytic converter.
The sensor is made in the form of a glass of zirconium. The inner and outer surface of the glass is coated with a layer of platinum, forming platinum electrodes. The inner surface of the glass opens into the outer atmosphere, and the outer surface is blown by the flow of exhaust gases.
When there is a difference in oxygen content between the inside and outside of the sensor, a voltage is induced across the platinum electrodes. The principle of operation of this device is that when the electrode is heated above a certain temperature, the induced voltage tends to change sharply if the stoichiometric proportion in the air-fuel mixture is exceeded.
Idle mixture adjustment sensor (IMA sensor)
This sensor is located in the control box and its purpose is to maintain the correct mixture ratio at idle. This sensor does not need to be adjusted.
Starter switch
When starting the engine, the air-fuel mixture must be rich. During starter operation, the ECU receives the starter switch position and increases the amount of fuel injected according to engine temperature. After turning off the starter, the amount of injected fuel is gradually reduced.