The control device in the system is an electronic control unit (ECU). The amount of fuel supplied by the injectors is controlled by an electrical impulse signal from the ECU. The electronic unit monitors data on the state of the engine, calculates the need for fuel and determines the required duration of fuel supply by injectors (pulse duration - duty cycle). To increase the amount of fuel supplied, the ECU increases the pulse duration, and to reduce the fuel supply, it shortens it. In addition, in accordance with the embedded algorithm, the ECU controls the operation of the electric motor of the fan of the engine cooling system and the electromagnetic clutch for turning on the air conditioning compressor, performs the function of self-diagnostics of the system elements and notifies the driver of any malfunctions.
In the event of failure of individual sensors and actuators, the ECU includes emergency modes that ensure engine performance.
The ECU has the ability to evaluate the results of its calculations and commands, remember the modes of recent operation and act in accordance with them. «self-learning», or ECU adaptation, is a continuous process, but the corresponding settings are stored in the RAM of the electronic unit until the first power off of the ECU.
The engine management system, along with the electronic control unit, includes sensors, actuators, connectors and fuses.
The amount of fuel supplied is determined by the state of the engine, i.e. its mode of operation. These modes are provided by the ECU and are described below.
When the crankshaft of the engine begins to scroll with the starter, the first pulse from the crankshaft position sensor causes a pulse from the ECU to turn on all the injectors at once, which allows you to accelerate the start of the engine.
Initial fuel injection occurs each time the engine is started. The duration of the injection pulse depends on the temperature. On a cold engine, the injection pulse increases to increase the amount of fuel; on a warm engine, the pulse duration decreases. After the initial injection, the ECU switches to the appropriate injector control mode.
Start mode. When the ignition is turned on, the ECU turns on the relay for the electric fuel pump, which creates pressure in the fuel supply line to the fuel rail.
The ECU checks the signal from the coolant temperature sensor and determines the amount of fuel and air required for starting.
When the engine crankshaft starts to crank, the ECU generates a phased pulse to turn on the injectors, the duration of which depends on the signals from the coolant temperature sensor. On a cold engine, the pulse duration is longer (to increase the amount of fuel supplied), and on warm - less.
Enrichment mode when accelerating. The ECU monitors abrupt changes in the position of the throttle pedal (Throttle pedal position sensor signal), as well as the signal from the mass air flow sensor and provides an additional amount of fuel by increasing the duration of the injection pulse. Acceleration rich mode is only used for transient fuel control (when moving the throttle pedal).
Fuel cut-off mode during engine braking. When braking with the engine in gear and clutch engaged, the ECU may completely shut off the fuel injection pulses for short periods of time. Turning off and on the fuel supply in this mode occurs when certain conditions are created for the coolant temperature, crankshaft speed, vehicle speed and throttle opening angle.
Supply voltage compensation. When the supply voltage drops, the ignition system may produce a weak spark, and the mechanical movement of the nozzle opening may take longer. The ECU compensates for this by increasing the energy storage time in the ignition module and the duration of the injection pulse.
Accordingly, with increasing battery voltage (or voltage in the vehicle's on-board network) The ECU reduces the energy storage time in the ignition module and the duration of the injection.
Fuel cut off mode. When the engine is stopped (off ignition) fuel is not supplied by the nozzle, thus eliminating spontaneous ignition of the mixture in an overheated engine. In addition, pulses to open the injectors are not given if the ECU does not receive «support» pulses from the crankshaft position sensor, i.e. this means the engine is not running.
The fuel supply is also cut off when the maximum permissible engine speed is exceeded to protect the engine from operating at unacceptably high speeds.
Electronic control unit (ECU) located on the left side of the engine compartment on a bracket mounted on the battery mounting shelf, and is the control center of the electronic engine management system. The electronic unit is connected by electrical wires to all sensors of the system. Receiving information from them, the block performs calculations in accordance with the parameters and control algorithm stored in the memory of a programmable read-only memory device (PROM), and controls the executive devices of the system. The program variant recorded in the PROM memory is indicated by the number assigned to this ECU modification.
The control unit detects a malfunction, identifies and stores its code, even if the failure is unstable and disappears (e.g. due to poor contact). The signal lamp for a malfunction of the engine management system in the instrument cluster goes out 10 s after the failure of the unit is restored.
After repair, the fault code stored in the memory of the control unit must be erased. To do this, turn off the power supply of the unit for 10 s (remove the fuse for the power supply circuit of the electronic control unit or disconnect the wire from the terminal «minus» battery).
The unit supplies 5 and 12 V direct current to various sensors and switches of the control system. Since the electrical resistance of the power circuits is high, the test lamp connected to the system outputs does not light up. To determine the supply voltage at the computer terminals, a voltmeter with an internal resistance of at least 10 MΩ should be used.
The ECU has the following types of memory:
- programmable read only memory (PROM);
- random access memory (RAM);
- electrically reprogrammable memory (ERPZU).
Programmable Read Only Memory (PROM). It contains a general program, which contains a sequence of working commands (control algorithms) and various calibration information. This information is control data for injection, ignition, idle, and other parameters that depend on vehicle weight, engine type and power, transmission ratios, and other factors. PROM is also called a calibration memory. The contents of the PROM cannot be changed after programming. This memory does not need power to save the information recorded in it, which is not erased when the power is turned off, i.e. this memory is non-volatile.
Random access memory (RAM). This «notebook» ECU. The ECU microprocessor uses it to temporarily store measured parameters for calculations and intermediate information. The microprocessor can enter data into it or read them out as necessary.
The RAM chip is mounted on the PCB of the ECU. This memory is volatile and requires an uninterruptible power supply to maintain. When the power supply is interrupted, the diagnostic trouble codes and calculated data contained in the RAM are erased.
electrically reprogrammable memory (ERPZU). Used for temporary storage of car anti-theft system passwords (immobilizer). The password codes received by the ECU from the immobilizer control unit are compared with the codes stored in the EEPROM, as a result of which the engine start is allowed or prohibited.
The EEPROM records vehicle operating parameters such as total vehicle mileage, total fuel consumption, and engine operating time.
ERPZU also registers some violations of the engine and car:
- operating time of the engine with overheating;
- engine operating time on low-octane fuel;
- engine operation time exceeding the maximum allowable speed;
- engine operation time with misfires of the air-fuel mixture, the presence of which is indicated by the warning light for exceeding the permissible level of toxicity of exhaust gases;
- engine operation time with a faulty knock sensor;
- engine operation time with a faulty oxygen concentration sensor;
- the time of movement of the car with excess of the maximum permitted speed during the break-in period;
- vehicle movement time with a faulty speed sensor;
- number of battery disconnections with the ignition switch on.
EEPROM is a non-volatile memory, it can store information without powering the ECU.
The ECU is not repairable and should be replaced if it fails.
Diagnostic connector, located on the left under the instrument panel next to the hood latch handle, is used to communicate with the computer. A scanning device is connected to the diagnostic connector to read error information stored in the ECU memory, to check sensors and actuators in real time, to control actuators and reprogram the ECU.
crankshaft position sensor inductive type is designed to synchronize the operation of the electronic control unit with the TDC of the pistons of the 1st and 4th cylinders and the angular position of the crankshaft. The sensor is installed at the rear of the engine.
The sensor holder is a special bracket on the rear crankshaft oil seal.
The sensor drive is mounted on the rear flange of the crankshaft. As the crankshaft rotates, magnetic marks on the outer circumference of the disk change the magnetic field of the sensor, inducing AC voltage pulses. The control unit determines the crankshaft speed from the sensor signals and sends pulses to the injectors. If the sensor fails, the engine cannot be started.
Camshaft Position Sensors (phase sensors) inductive type are used to organize phased fuel injection in accordance with the order of operation of the cylinders. The signals from the intake and exhaust camshaft sensors are also used by the controller to control the change in valve timing depending on the engine operating mode. If a malfunction occurs in the circuit of any of the sensors, the controller stores its code in its memory and turns on the signal lamp.
The Chevrolet Aveo engine has two coolant temperature sensors. One sensor is installed at the bottom of the right tank of the radiator of the engine cooling system...
...the second sensor is located in the water distributor housing and serves as a sensor for the coolant overheat warning light in the instrument cluster.
Both sensors are identical in design and are a thermistor (resistor whose resistance changes inversely with temperature). Low coolant temperature (-40°C) thermistor resistance is about 100 kΩ, when the temperature rises (up to +130°C) decreases to 70 ohms.
The electronic unit feeds the temperature sensor circuit with constant «pivotal» voltage. The sensor signal voltage is maximum on a cold engine and decreases as it warms up. Based on the voltage value, the electronic unit determines the engine temperature and takes it into account when calculating the injection and ignition control parameters. If the sensor fails or there are violations in its connection circuit, the ECU sets the fault code and remembers it.
Combined mass flow and intake air temperature sensor installed in the air hose between the air filter and the throttle assembly. The principle of operation of the mass air flow sensor is based on maintaining a constant temperature of the resistors (the higher the airflow rate, the more current is needed to maintain the temperature of the resistor). The principle of operation of the intake air temperature sensor is similar to that of the coolant temperature sensor. Depending on the readings of these sensors, the ECU adjusts the amount of fuel injected into the cylinder to obtain the optimal working mixture.
Absolute pressure sensor (fuel pulsation compensator removed for clarity) installed on the intake pipe. The output voltage of the sensor changes in accordance with the pressure in the intake pipe: from maximum (at wide open throttle) to the minimum (with damper closed). When the engine is not running, the control unit determines the atmospheric pressure from the sensor voltage and adapts the injection control parameters to the specific height above sea level. The atmospheric pressure values stored in the memory are updated periodically when the vehicle is in steady motion and during full throttle opening.
Throttle position sensor (removed for clarity) installed in the electric drive housing on the throttle assembly.
When the throttle is turned (from impact on the control pedal), the voltage at the output of the sensor changes. When the throttle is closed, it is lower than 2.5 V. When the throttle opens, the voltage at the sensor output rises, when the throttle is fully open, it should be more than 4 V.
By monitoring the output voltage of the sensor, the controller adjusts the fuel supply depending on the throttle opening angle (those. at the request of the driver).
The throttle position sensor does not require adjustment, as the control unit senses idling (those. full throttle closing) as a zero point.
Control oxygen sensor used in a feedback injection system and installed in the exhaust manifold. To correct the calculations of the duration of the injection pulses, information is used on the presence of oxygen in the exhaust gases, this information is provided by the control oxygen concentration sensor. The oxygen contained in the exhaust gases reacts with the sensor, creating a potential difference at the sensor output.
Information from the sensor enters the control unit in the form of low and high level signals. When the signal is high (about 4.2V) sensor at the inlet to the collector, the control unit receives information about the high oxygen content. Low signal (about 2.2V) this sensor indicates a low oxygen content in the exhaust gases.
Constantly monitoring the voltage of the sensor signals, the control unit adjusts the amount of fuel injected by the injectors. With a high level of the sensor signal at the inlet to the collector (lean air-fuel mixture) the amount of fuel supplied increases, with a low signal level (rich mixture) - decreases. If the level of the sensor signal at the output of the converter does not correspond to the values allowed in this mode of operation, the control unit identifies a malfunction of the collector.
Diagnostic oxygen sensor installed in the exhaust pipe after the converter, it works on the same principle as the control sensor. The output characteristics of the sensor at the outlet of the collector are different: a high oxygen content corresponds to a low level signal (about 0.1 V), and low oxygen content - a high level signal (about 0.9 V). The signal generated by the diagnostic oxygen concentration sensor indicates the presence of oxygen in the exhaust gases after the converter. If the converter is working properly, the readings of the diagnostic sensor will differ significantly from the readings of the control sensor.
Knock sensor attached to the top of the cylinder block in the areas between the 2nd and 3rd cylinders and picks up abnormal vibrations (detonation strikes) in the engine.
The sensing element of the knock sensor is a piezoelectric plate. During detonation, voltage pulses are generated at the output of the sensor, which increase with increasing intensity of detonation impacts. The controller, based on a sensor signal, regulates the ignition timing to eliminate detonation fuel flashes.