- Practice · 6 marks
Sensors, actuators and ECU
Short answer
The ECU reads sensors like MAF, throttle position, coolant temperature, and oxygen sensor, processes signals with microprocessor and maps, and drives actuators such as fuel injectors, ignition coil, and idle air control. Closed-loop lambda feedback maintains stoichiometric mixture.
What is an electronic control unit (ECU)? With a block diagram, explain how sensors, ECU and actuators work together. Give examples of four sensors and three actuators used in an engine.
The ECU is the on-board computer of the engine. It reads inputs from sensors, calculates the best output from stored maps and controls the actuators.
SENSORS ---> [ Input ]
MAF, TPS, [ circuits] -> [Microprocessor + memory] -> [Output drivers]
CTS, O2, (ADC, (ROM maps, RAM) -> ACTUATORS
crank, knock filters) injectors, ignition
coil, idle valve, EGR
<---- CAN bus / diagnostic ---->
Working
- Sensors convert physical quantities (temperature, air flow, speed, position) into electrical signals.
- The ECU changes analogue signals into digital using an A/D converter and compares with stored 3D maps.
- It calculates injection pulse width, ignition timing and idle speed, and sends signals to power transistors (drivers).
- Actuators carry out the action. Oxygen sensor feedback gives closed-loop correction.
- The ECU stores fault codes (DTC) for diagnosis through the OBD port.
Examples
| Type | Device | Function |
|---|---|---|
| Sensor | Mass air flow (MAF) | Measures intake air mass |
| Sensor | Throttle position (TPS) | Driver's demand |
| Sensor | Coolant temperature (CTS/NTC) | Warm-up enrichment |
| Sensor | Crankshaft position (Hall/inductive) | Speed and timing |
| Sensor | Oxygen (lambda) | Mixture feedback |
| Actuator | Fuel injector (solenoid) | Delivers fuel |
| Actuator | Ignition coil | Spark |
| Actuator | Idle air control / electronic throttle, EGR valve | Idle speed, NOx control |
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Engine management system and ADAS · Automotive Technology, chapter 11
- Phases of combustion in a CI engine · Automotive Technology, chapter 3
- Engine displacement, compression ratio and power · Automotive Technology, chapter 1
- Air flow and fuel flow of an SI engine · Automotive Technology, chapter 2
- Two-stroke versus four-stroke engines · Automotive Technology, chapter 1
- Valve timing diagram of four-stroke engine · Internal Combustion Engines, chapter 4
- How the Internet and Web work together · Web Technology, chapter 1
- PID control operation with block diagram · Embedded System, chapter 7 · asked 4×
- Closed loop control system block diagram explained · Control Systems, chapter 1 · asked 4×