Transcript Transducers
3. Transducers Automotive – Engine Performance Transducers Topics covered in this presentation: Active and Passive Sensors Common Sensor Types and Their Operation ClassAct SRS enabled. 3. Transducers Automotive – Engine Performance Transducers A sensor (transducer) changes a condition into an electrical signal. Sensor may be active or passive. Next > 3. Transducers Automotive – Engine Performance Active Sensors Two wire device. Generates own voltage signal. Voltage signal Voltage signal connects to ECU input. ECU processes input signal into digital information. Active sensor Trigger wheel 2 wire output ECU operates outputs, depending upon digital information received. Example - inductive/magnetic pickup. Next > 3. Transducers Automotive – Engine Performance Passive Sensors Three wire device. Supplied with voltage from ECU. Sensor supply voltage Internal resistance Internal resistance changes with a change in conditions. +5V 5V 0V Sensor Corresponding output voltage change is measured by ECU. 0V Output voltage Example - throttle position sensor. Next > 3. Transducers Automotive – Engine Performance Question 1 The main distinction between an active and a passive sensor is that an active sensor generates its own voltage, a passive sensor must be supplied with a voltage. Is this true or false? Answer True or False. 3. Transducers Automotive – Engine Performance Question 2 The electronic control unit (ECU) has to convert all analogue signals to digital before processing them. Is this true or false? Answer True or False. 3. Transducers Automotive – Engine Performance Passive Sensors Two wire device. Current limiting resistor Supplied with voltage from ECU via resistor. Internal resistance changes with a change in conditions. Corresponding output voltage change is measured by ECU. Example - coolant temperature sensor. +V 5V Sensor V W 0V Internal resistance Output voltage Next > 3. Transducers Automotive – Engine Performance Passive Sensors Switch must be either open or closed. Supplied with voltage from ECU via resistor. Current limiting resistor +12V 12V 0V Switch Switch open, ECU measures 12V. Switch closed, ECU measures 0V. Example - brake pedal switch. 0V Output voltage Next > 3. Transducers Automotive – Engine Performance Question 3 The diagram shows a brake pedal switch and its connections to the ECU. What voltage will the ECU measure when the switch is closed? A) 12V +12V B) 6V Switch C) 5V 0V D) 0V 3. Transducers Automotive – Engine Performance Sensor Types Most common types: Intake Air Temperature (IAT). Manifold Absolute Pressure (MAP). Engine Coolant Temperature (ECT). Oxygen (O2). Mass Air Flow (MAF). Throttle Position (TPS). Crankshaft Position (CKP). Camshaft Position. Vehicle Speed (VSS). EGR Position. Brake Switch. Oil Level Switch. Knock. Next > 3. Transducers Automotive – Engine Performance Oxygen Sensor (O2) Wires to ECU Located in exhaust downpipe. Measures oxygen content in exhaust gas and atmosphere. Produces output voltage corresponding to difference in oxygen levels. Heating element Sensor element 0 volts = high oxygen content in exhaust gas. 1.4 volts = low oxygen content. Protective cap with gas intake slots V 0.7V 0.3 - 0.7 volts = ideal oxygen content. 0.3V Heating element speeds up sensor operation from cold. Rich Lean 14.7:1 Air/fuel ratio Next > 3. Transducers Automotive – Engine Performance Question 4 What is an IDEAL voltage for an oxygen sensor, located in the exhaust downpipe, to produce? A) 0V B) 0.5V C) 1.4V D) 5.0V 3. Transducers Automotive – Engine Performance Engine Coolant / Intake Air Temp Sensors ECT located in coolant. IAT located in incoming air. Reference voltage +V V W 0V Engine coolant temperature sensor Resistance and voltage changes with temperature Sensor resistance changes with temperature change. Resistance change causes voltage change at ECU input. ECU measures voltage to determine temperature. Next > 3. Transducers Automotive – Engine Performance Question 5 The ECU measures the change in current, in the resistive sensor, to monitor the intake air temperature. Is this true or false? Answer True or False. 3. Transducers Automotive – Engine Performance Throttle Position Sensor (TPS) Variable resistor (potentiometer), fixed to the throttle valve. Resistance changes with throttle position. Reference voltage +5V 5V TPS 0V 0V Output voltage ECU supplies sensor with voltage. Sensor output voltage changes with throttle position. ECU measures voltage to determine throttle position. Next > 3. Transducers Automotive – Engine Performance Mass Airflow Sensor (MAF) Mounted before the throttle valve on EFI engines. Measures mass of air entering engine. Contains ‘hot wire’ which is heated by current flow. Output to ECU Airflow cools hot wire, changing current flow. Air in Electronics module outputs signal to ECU corresponding to current change. Change in current is proportional to airflow into engine. Electronics module Next > 3. Transducers Automotive – Engine Performance Crankshaft/Camshaft/Vehicle Speed Sensor Mounted next to trigger wheel with small air gap. Sensor (inductive/magnetic pickup) contains magnet and coil. Movement of tooth towards sensor disrupts magnetic field and produces voltage in coil. Inductive/ magnetic pickup Output voltage Trigger wheel Movement of tooth away from sensor disrupts magnetic field and produces opposite polarity voltage. Output frequency is determined by trigger wheel speed. Next > 3. Transducers Automotive – Engine Performance Inductive pulse generators produce a voltage to create a trigger signal • AC current is produced • + voltage • 0 voltage • - voltage • The trigger point is normally at 0 voltage Hillier 3. Transducers Automotive – Engine Performance Hall Effect V - NO POTENTIAL DIFFERENCE + 3. Transducers Automotive – Engine Performance Hall Effect V Magnetic field deflects the electron flow through the Hall chip, causing a potential difference to appear across the chip. + N S 3. Transducers Automotive – Engine Performance Hall effect Magnet Halls chip C A Rotor Vane Halls chip B D • Current flow from A to B • Current flows from C to D (trigger current) • Current flows from A to B • With halls effect the current is turned on and off only to produce a square wave 3. Transducers Automotive – Engine Performance Low Oil/Brake Fluid Level Sensor Oil level switch located in sump. 12V Lamp off ABS, ECU monitoring point Brake fluid switch located in reservoir. Switch open when fluid level normal, lamp is off. 12V Switch open Fluid level okay Lamp on Switch closed Fluid level low Switch closed when fluid level low, lamp is on. Next > 3. Transducers Automotive – Engine Performance Knock Sensor Mounted on the engine. Detects vibrations that indicate abnormal combustion (knock). Output voltage +V Produces output voltage proportional to knock strength. Uses Piezo Crystal. 0V Knock sensor ECU retards ignition when abnormal combustion is detected. Next > 3. Transducers Automotive – Engine Performance Question 7 What does a knock sensor detect? A) Gas concentration B) Abnormal combustion C) Wheel movement D) Gas level 3. Transducers Automotive – Engine Performance Summary You should be aware of: Active and Passive Sensors Common Sensor Types and Their Operation End >