Process Control

Subjects:

  • Control technology
  • Process control based on operating conditions

Control technology:
The ECU measures, controls and regulates the processes. The ECU gets information from sensors. A sensor converts a change in a physical quantity into an electrical signal. This sensor information enters the ECU via the input. Possible input signals come from:

  • speed sensor;
  • temperature sensor;
  • load (underpressure) sensor;
  • oxygen sensor.

The information that comes in does not have to lead directly to an action. The control of the actuator can only be adjusted when a measured value deviates from the desired value. The ECU then has a “regulating” function. Yes/no decisions are made by means of the pre-programmed computer program (ROM / Flash memory).

Process control in an ECU

To measure: the sensor measures a physical quantity and converts it into an electrical signal. This measured value (X) is sent to the controller. The measured value does not have to lead directly to an action; think of a constant temperature.

Send: the controller (ECU) controls an actuator. There is no feedback from a sensor, so the ECU does not follow the process. A fault in the process is therefore not always recognized. An example of the control is the manual operation of the horn (W); the ECU controls the horn (Y) when operating the switch. There is no monitoring function on the horn, which means that faults (Z) are not recognized.

Arrange for: the controller can process a manual command (W) or a measured sensor value (X) into an actuator control. The actuator provides a change in the process; think of the injection time, for example. More injection means a richer mixture. The oxygen content is measured by the lambda sensor and transmits this measured value (X) to the controller. When an unforeseen fault is present (eg a blockage in an injector), this gives a change (Z) to the process. This deviation is also measured by the sensor, so that the controller can adjust the process by means of the actuator control.

Process control based on operating conditions:
The engine management system of an internal combustion engine must burn the mixture optimally under all operating conditions. Determining the mixture composition and the ignition timing are crucial for guaranteeing the exhaust gas composition (emission), economy and achieving the desired power.

Each operating condition has its own control technology:

  • Cold start: mixture is rich and ignition late;
  • Warm start: the mixture is less rich than at the cold start;
  • Cold idle: mixture is rich and idle speed is increased;
  • Warm idle: mixture is less rich at lower idle speed;
  • Part load: mixture stoichiometric, speed range between 1500 and 4000 rpm, ignition timing is predefined, lambda control is active;
  • Full load: mixture is enriched, load and speed are high;
  • Acceleration: mixture rich, ignition late;
  • Deceleration: mixture poor, ignition early.
Process Control Flowchart
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