Accelerator pedal position sensor
TDI engines do not have an accelerator cable. Information about the position of the accelerator pedal is transmitted to the control unit by a potentiometer. To prevent the control unit from making wrong decisions (for example, due to a defect, the unit believes that the pedal is in position «Full throttle»), the brake pedal is connected to an additional brake light switch that prevents the control unit from recognizing the information «Full throttle» when braking. The same goes for the clutch pedal.
Engine speed and TDC sensor
This inductive sensor is located under the oil filter flange on the crankcase and reads the number of revolutions from the slip ring on the crankshaft. The slip ring has 4 grooves, each corresponding to TDC (see illustration 10.0a).
Needle lift sensor in the nozzle of cylinder No. 3.
This sensor tells the control unit the exact start of injection at the current moment (see illustration 10.0b).
Intake air temperature sensor, intake manifold temperature, coolant temperature and fuel temperature
These sensors are located in the air volume flow meter, in the air guide pipe, in the coolant outlet pipe and in the injection pump itself (see illustration 10.0c).
Air volume flow meter
Information about the amount of air taken in is necessary for the control unit to calculate the fuel required for injection. The intake air volume is measured as follows. The valve shutter of the air volume flow meter deviates depending on the incoming air quantity. This gate movement is recorded as a change in resistance (potentiometer) and is recognized by the control unit as the value of the electric current (see illustration 10.0g).
Intake air mass flow meter
This sensor is installed on vehicles manufactured since the end of 1993, as well as on vehicles with automatic transmission. It performs the same function as the air mass meter it replaces, but the measurement is performed differently. The film installed in the path of air movement is heated. The incoming air, depending on its mass, to some extent cools this film. The resistance of the film changes and the control unit again receives an electrical signal of a certain value.
Intake manifold pressure sensor
This sensor is located at the rear of the engine compartment on the right side and is connected by a hose to the charge air cooler (intercooler). For vehicles with an automatic transmission and for vehicles with a manual transmission from the end of 1993, this sensor is an element of the control unit. The specified sensor is responsible for information about the boost air pressure and regulation of the injection volume.
Condensate level sensor in the fuel filter
This sensor is not installed on vehicles with automatic transmission. Cars with a manual transmission were equipped with this sensor until the end of 1993. (see illustration 10.0d).
Boost pressure valve
The boost pressure is controlled by a solenoid valve that opens the pressure reducing valve. For older vehicles, in the rear of the engine compartment at the rear. For vehicles with an automatic transmission, as well as for vehicles with a manual transmission from the end of 1993, it is located on the right in front of the engine compartment.
EGR valve
The exhaust gas recirculation valve, together with an oxidizing catalytic converter, ensures that the content of harmful substances in the exhaust gas is within the limits of existing standards and requirements. In contrast to the 55 kW diesel engine with swirl chamber injection, in which the exhaust gas recirculation is carried out according to the principle «intake-exhaust», for TDI engines, intermediate exhaust gas values can be generated by means of recirculation.
Preheating device
The injection system control unit controls the preheater depending on the engine temperature.
10.0 Scheme of operation of the control unit of the power supply system for TDI diesel engines. Arrows show incoming and outgoing information
1 - accelerator pedal
2 - engine speed and TDC
3 - start of injection
4 - temperature of intake air, coolant and fuel
5 - boost pressure
6 - boost air temperature
7 - air flow meter
8 - electronic control unit
9 - other information
10 - EGR valve
11 - start of injection
13 - position of the control spool
14 - injection volume
15 - candle glow control
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