"brain" injection system and the ignition system connected to it is the control unit. It is located in the electronic unit on the left rear in the engine compartment (in a space that can also be called a casing). If a turbocharger is installed, then the height sensor is also located there, i.e. a device that regulates the boost pressure when driving at high altitude, for example, in the mountains. In the car itself, the control unit is recognized by the black housing, because it is covered with a lid. under cover (1) electronic unit is the electronic control unit.
1 Electronic unit
2 Expansion tank cap
3 Brake fluid reservoir
4 Expansion tank of the cooling system
5 Collector
6 Oil dipstick
7 ABS control unit
8 Glass washer reservoir
9 Power steering pump reservoir
The control unit receives the following information via the multi-pin plug.
- From the starter terminal 50 about the beginning and end of the starting process.
- The potentiometer on the throttle gives the instantaneous throttle position.
- The hall sensor of the ignition system, among other things, provides information on the engine speed. The lambda probe in the catalytic converter informs about the content of residual oxygen in the exhaust gases. The air mass meter determines the amount of incoming air.
Turbocharged engines have an intake air temperature sensor that continuously informs the control unit of the intake air temperature.
The coolant temperature sensor is located in the coolant pipe behind the cylinder head and provides the control unit with information about the current coolant temperature.
The knock sensor or two knock sensors are screwed into the cylinder block. They regulate knock combustion and adjust the ignition timing accordingly.
Thanks to the constant input of the above data on the speed, load and temperature of the engine, the control unit determines the duration of the injection, i.e. the opening time of the injectors and accurately doses the amount of injected fuel. The so-called ranges are built into the control unit (Database), which cover all possible engine operating conditions and, based on them, accurately select the optimal fuel doses and ignition timing. When the temperature of the incoming air or coolant changes, the necessary adjustments are made.
Before a short description of the operation of individual parts, we briefly mention the general principles of the system under various operating conditions.
At "cold" startup (starting a cold engine)
Thanks to the presence of the throttle control unit, additional air enters the engine, because. The coolant temperature sensor tells the control unit that that the engine is cold. The injectors open for a longer time and inject more fuel (rich mixture).
When warming up
The control unit is informed about the gradual heating of the coolant. The built-in idle speed control valve closes. and the duration of the opening of the injectors returns to the nominal value.
At idle
The control unit recognizes the idle speed. This is reported by a potentiometer on the throttle valve of the throttle control unit to the air mass meter of the control unit ("main"). With a decrease in the number of revolutions, the ignition timing changes. More air can flow through the throttle control unit, which increases the amount of fuel injected.
During normal engine operation
The position of the throttle valve and the data of the air mass meter on the flowing air amount determine the duration of the opening of the injectors and. next, the operation of the engine.
Now we can talk in more detail about the details of the system already mentioned above.
Throttle control unit
This device contains various parts. The first is the throttle valve. Through the throttle lever and cable, the eye is connected to the pedal "gas". The figure shows the position of the throttle valve with the air duct removed (hose). In accordance with the regulation filed "gas", the cross section of the opening for the flow of the working mixture increases or decreases. When fully loaded, it opens completely. For some engines (usually smaller in size), the throttle valve works on the same principle, however, the installation methods are different.
Throttle assembly
1 throttle lever
2 Plug socket
3 Throttle control unit
4 throttle valve (closed)
Throttle connections
1 Connector socket for plug
2 Throttle lever
The throttle valve potentiometer is installed in the control unit. He "is following" throttle position under all conditions and reports this to the control unit. From the information received, the stabilization of the idle mode, shutdown when coasting and enrichment in full load mode are determined.
The idle speed stabilization valve equalizes the idle speed when the steering wheel is turned to maximum, when the air conditioner is turned on, or when the automatic transmission is installed, when additional air can flow behind the throttle valve. This extra air is monitored by the air mass meter so that more fuel can be delivered to the engine. The engine can run a little faster so that the additional engine power required to operate the power steering, air conditioning or automatic transmission is compensated.
Fuel pressure control
Fuel pressure control (1) usually located in front of the fuel distributor and regulates the pressure of the fuel supplied to the injectors. Because it is connected by a hose (2) with the throttle body, it is controlled by the vacuum in the intake manifold.
With increasing vacuum (e.g. at idle), the pressure is kept low. As the engine speed increases, the vacuum decreases. This means that the fuel pressure is increased by the regulator.
Injectors
With each revolution of the crankshaft, fuel is injected into the intake port ahead of the intake valve (or valves) of the corresponding cylinder. The opening of the injector is determined by the electronic control unit.
Intake air temperature sensor
It is only installed on turbocharged engines. The sensor reports the temperature of the pressurized air coming from the turbocharger, which is processed in the control unit. This compensates for the temperature increase from the supercharger.
Coolant temperature sensor
The coolant temperature determines many engine functions, such as cold start richness, warm-up, acceleration, and coast-down fuel cut-off. The temperature is supplied to the control unit as a resistance value. This determines the correct injection duration, which is correspondingly extended when the engine is cold.
Air mass meter
Air mass meter (1) together with connector (2) located next to the air filter.
With a turbocharged engine, the flow meter is not visible, because it is located inside the air filter housing. In the flow of incoming air there is a small plate, which is heated by an electric current. If the amount of incoming air is increased, the plate is cooled accordingly. This cooling causes a change in electrical resistance, which is reported to the control unit.
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