Layout of components in the engine compartment of the C240 and C320 models
1 - Knock sensor (KS) 1 (On the right side of the engine); 2 - Knock sensor (KS) 2 (On the left side of the engine); 3 - Throttle Position Sensor (TPS); 4 - EGR vacuum transmitter; 5 - Intake manifold configuration switch valve; 6 - Oil temperature/quality/level sensor
Fuel is sucked from the fuel tank by an electric fuel pump and supplied through a fuel filter to the fuel distribution line. The pressure regulator maintains the pressure in the fuel system equal to 3.2–3.6 atm.
The fuel is injected pulsed into the intake manifold, located directly in front of the engine intake valves, via electrically controlled injectors. The engine control unit sequentially controls the injectors in accordance with the ignition sequence, regulates the injection time and thus the amount of fuel injected.
The air required to form the fuel mixture is sucked into the engine through the air filter and passes through the throttle valve and the intake manifold to the intake valves. The amount of air sucked in is regulated by the throttle valve, which is moved by a stepper motor controlled by the engine control unit. In compressor engines, the sucked air is compressed by a compressor driven by a V-belt transmission. The compressed air is then cooled in the charge air cooler and fed to the engine to form the fuel mixture.
The volume of air sucked in is determined by the air volume meter. The meter is located in the air intake duct. The meter housing contains a thin, electrically heated sensor plate, cooled by the flow of sucked air. The electric current that heats the plate is regulated by the control system in such a way as to maintain the temperature of the plate constant. If, for example, the amount of air sucked in increases, the temperature of the heated plate begins to decrease. At the same time, the magnitude of the electric current immediately increases in order to maintain the temperature of the plate unchanged. Fluctuations in the electric current of the plate indicate to the engine control unit its load state, which allows the amount of fuel injected to be correctly determined.
The engine control unit is located in the electronics box, on the left, near the brake fluid reservoir or directly on the engine. The control unit determines the optimal ignition time, injection moment and the amount of fuel injected. At the same time, the operation of the control unit is coordinated with other systems of the car, for example, with the gearbox control or anti-theft system.
Information from other sensors and control voltages supplied to the actuators ensure optimal engine operation in any situation. If some sensors fail, the control unit switches to the emergency program mode to prevent possible engine damage and ensure further movement of the vehicle. In this case, the engine runs unevenly and tends to stall when the gas is increased.
Sensors and actuators of the injection system
The crankshaft position sensor is screwed into the cylinder block near the flywheel. It transmits information about the engine speed and the TDC position of the piston of the first cylinder to the control unit.
The camshaft position sensor is located at the end of the cylinder head cover. Together with the crankshaft position sensor, it transmits information about the TDC of the piston of the first cylinder to the control unit. It serves to synchronize the ignition timing and ignition sequence.
The throttle actuator consists of an electric motor and two potentiometers. It regulates the position of the throttle valve. This ensures a stable idle speed, regardless of the connection of additional consumers, such as the power steering or air conditioning compressor.
The throttle potentiometer is located in the throttle actuator and reports the current throttle angle to the control unit. The second potentiometer reports the base value to the control unit and generates a backup signal when the throttle potentiometer fails.
The gas pedal sensor is located in the driver's footwell area directly on the gas pedal axis. It provides the control unit with information about the pedal position. For safety reasons, an additional signal is taken from the pedal sensor, as well as from the throttle potentiometer.
The coolant temperature sensor is located in the thermostat housing. It is a resistor with a negative temperature coefficient, the resistance of which decreases with increasing temperature.
The intake air temperature sensor is also an NTC resistor.
The fuel tank ventilation system consists of an adsorber and an electromagnetic valve. The adsorber accumulates fuel vapors formed as a result of heating the fuel. When the engine is running, the vapors are sucked out of the adsorber and fed into the combustion chambers of the engine.
Lambda probes (oxygen sensors) measure the oxygen content in the exhaust gases before and after the catalytic converter and transmit the corresponding signals to the engine control unit. One lambda probe is located before and the other after the catalytic converter.
The knock sensor is screwed into the cylinder block, next to the guide tube. It prevents the dangerous shock combustion of the fuel mixture. Thanks to this, the ignition timing can be kept at the detonation limit, which ensures efficient use of the combustion energy of the fuel and thus reduces fuel consumption.