Page 342 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Bosch common rail diesel injection system
coolant temperature, accelerator pedal position etc. Thus it is clear that the functioning of all electronically
controlled fuel control systems depends on the inputs from different types of sensors. The ECU (Electronic Control
Unit) receives these signals from sensors and after manipulation and calculations sends outputs to vary the
injection timing, fuel quantity, ignition timing etc. It also controls systems like the fuel injection pump, idle speed
control unit, particulate trap regenerator (in a diesel engine), coolant supply etc. Thus any engine management
system consists of the following main units: sensor, signal conditioner, analogue to digital converter, electronic
control unit, output signal, driver and actuator. There will be more than one input and also more than one output
which will be involved in controlling the engine at any given instant. We will look at different kinds of sensors that
are normally used along with their measuring principle. For clarity, the discussion is divided depending on the
parameter that is measured and applicable sensors in under each category.
3 Position displacement and speed sensing
Position displacement and speed sensing are very important in the engine management system. For such
sensing inductive, hall effect, potentiometric, electro optical, differential transformer and strain gauge sensors are
extensively used for these applications particularly in automobiles and engine laboratories.
Types of Sensors used
1 Mass air flow (MAF) rate
2 Exhaust gas oxygen concentration (possibly heated)
3 Throttle plate angular position
4 Crankshaft angular position/RPM
5 Coolant temperature
6 Intake air temperature
7 Manifold absolute pressure (MAP)
8 Differential exhaust gas pressure
9 Vehicle speed
10 Transmission gear selector position
Computer-Process Interface to implement process control, the computer must collect data from and transmit
signals to the production process
Components required to implement the interface
1 Sensors to measure continuous and discrete process variables
2 Actuators to drive continuous and discrete process parameters
3 Devices for ADC and DAC
4 I/O devices for discrete data
Computer Process Control System

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CITS : Automotive - Mechanic Diesel - Lesson 104 - 107 CITS : Automotive - Mechanic Diesel - Lesson 104 - 107