In a 2.0-liter engine, fuel is injected simultaneously by two injectors every crankshaft revolution. In other engines, injection occurs sequentially, in accordance with the firing order of the cylinders.
The air sucked in by the engine passes through the air filter, the throttle body and then is directed to the intake valves.
Fig. 5.37. Mass air flow sensor: 1 – plate
The required amount of fuel to be injected is determined based on the mass of air entering the engine and measured by the mass air flow sensor (HFM). The mass air flow sensor has a sensitive heated plate 1 (Fig. 5.37) cooled by the air passing through it. To maintain a constant temperature of the plate, the current value changes according to the mass of air being sucked in. The engine control unit determines the required amount of fuel to be injected based on the current value received from the mass air flow sensor.
The electronic control unit, receiving signals from various sensors and controls, ensures optimal engine operation depending on driving conditions. If one of the sensors is damaged, the control unit switches to emergency mode to prevent engine damage and ensure the vehicle's movement to the nearest auto repair shop. In this mode, the engine operates unstably and may stop when the accelerator pedal is pressed more.
Elements of the engine management system
The crankshaft position sensor is mounted on the cylinder block near the flywheel ring gear. It informs the control unit of the position and rotation speed of the crankshaft.
The camshaft position sensor is located on the cylinder head and indicates the current position of the camshaft.
The throttle position sensor transmits a signal about its angular position.
The idle switch informs the control unit about the throttle position when the engine is idling. In this case, the full load switch signals that the throttle valve is in the position corresponding to the operation of the engine at full load.
The coolant temperature sensor is a resistor whose resistance decreases as the coolant temperature increases.
The intake air temperature sensor is designed similarly to the coolant temperature sensor.
Fuel vapors from the fuel tank are captured by an absorber with an electromagnetic valve. Activated carbon accumulates fuel vapors, which, when the engine is running, as a result of the formation of a vacuum in the intake manifold, enter the cylinders, where they are burned.
(Article was borrowed from the website: mercedesman.ru)
Oxygen concentration sensor (lambda probe) is necessary for the correct operation of the catalytic converter, it sends a signal to the control unit about the amount of oxygen in the exhaust gases, as a result of which the control unit changes the fuel supply.
The idle speed control valve of the crankshaft regulates the amount of air entering the throttle bypass. As a result, a constant speed of rotation of the crankshaft is ensured, regardless of the number of connected consumers, such as, for example, a power steering pump or an air conditioning compressor.
Knock sensor (except for 2.0 l engine manufactured before 04.1996.) designed to determine the optimal ignition timing angle.
Camshaft Adjustment Device (except for 2.0L engines manufactured before 04.1996 and V6 engines). As a result of the action of the electrohydraulic actuator after the command of the control unit, the intake camshaft is rearranged relative to the chain drive. When rearranging in the "retard" direction, the engine operation at idle speed becomes softer, and accordingly, when the engine is running at a high crankshaft speed, the power increases. At low and medium crankshaft speeds, with early closing of the intake valves, the filling of the cylinders is improved, resulting in an increase in torque.
The use of a so-called resonant intake pipe on in-line 6-cylinder engines, which changes the length of the intake tract to the cylinders depending on the crankshaft speed, improves the torque characteristics.
Electronic control system Motronic ME, used on V6 and V8 engines
The Motronic ME system is an advanced HFM system. The fuel injectors, like those in the HFM system, operate sequentially in accordance with the cylinder firing order. The main difference is that the throttle valve is controlled by an actuator, which in turn regulates the crankshaft speed at idle. The accelerator pedal in this system has an electronic connection with the engine control unit. An electronic sensor monitors the pedal position. The throttle valve is controlled by the control unit using a servomotor. The accelerator pedal control system has a built-in system that ensures that the vehicle speed is maintained at a constant level.