Download 2 Sensors File - Totton College

3. Transducers
Automotive – Engine Performance
Transducers
Topics covered in this presentation:
 Active and Passive Sensors
 Common Sensor Types and
Their Operation
3. Transducers
Automotive – Engine Performance
Transducers
A sensor (transducer) changes a condition into an electrical signal.
Sensor may be active or passive.
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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.
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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.
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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
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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
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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
Make a list of as many sensors as you can.
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.
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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
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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.
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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, 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.
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Throttle position switch
3. Transducers
Automotive – Engine Performance
1.Switch type, which have contacts for both idle
and full throttle positions but no other
information.
Throttle position switch
3. Transducers
Automotive – Engine Performance
• Potentiometer type, give the ECU accurate
information on the throttle position because it gives
a signal for all throttle positions.
3. Transducers
Automotive – Engine Performance
Describe the 2 ways that the throttle is
controlled.
1. By cable that links the throttle body to the
accelerator pedal.
2. “Fly by wire” where the ECU operates the
throttle valve in relation to the driver’s
accelerator pedal position.
3. Transducers
Air flow meter.
Automotive – Engine Performance
Engine load is sensed by the engine
load sensor – e.g. air flow meter
Air cleaner
Air drawn into
intake system
Engine load is dictated by the position of the
throttle butterfly – i.e. driver demands
Automotive – Engine Performance
3. Transducers
Air Flow Meter
3. Transducers
Automotive – Engine Performance
EFI components - input signal
flow sensor
Vane type air
Oscilloscope is better!!
Earth
terminal
--v
Signal terminal
Supply voltage
terminal
ECU
Automotive – Engine Performance
3. Transducers
Air Flow Meter
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
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Automotive – Engine Performance
3. Transducers
Hot wire metering.
Automotive – Engine Performance
3. Transducers
Air Mass Meter
3. Transducers
Automotive – Engine Performance
Pressure/vacuum
sensing
• This system
uses a manifold
absolute pressure (MAP)
sensor to measure the
manifold depression.
Manifold depression is
created by the pumping
actions of the pistons. The
MAP sensor measures the
manifold pressure in the inlet
manifold which changes with
the engine’s load and throttle
position. The MAP sensor
consists of a diaphragm and a
piezoelectric circuit.
Automotive – Engine Performance
Manifold
3. Transducers
Absolute Pressure Sensor (Map)
Automotive – Engine Performance
3. Transducers
• When is manifold depression at its highest?
• At idle speed, when the throttle plate is fully
closed
• When is manifold depression at its lowest?
• At full throttle, when there is no restriction
to the air flowing into the cylinders.
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.
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Automotive – Engine Performance
3. Transducers
Positive
voltage
Negative
voltage
• Crank Angle Sensor gives
information on the speed and
position of the crankshaft to
the ECU to control ignition
timing, and injection
sequencing. The control unit
can then trigger the ignition,
and injection, to suit operating
conditions.
Automotive – Engine Performance
3. Transducers
• The camshaft position
sensor provides
definitive positional
information because the
camshaft only rotates
once per engine cycle.
3. Transducers
Automotive – Engine Performance
Question 6
A vehicle speed sensor produces a signal whose frequency is
proportional to the speed of the vehicle. Is this true or false?
Answer True or False.
3. Transducers
Automotive – Engine Performance
Knock Sensor
Mounted on the engine.
Detects vibrations that
indicate abnormal
combustion (knock).
Output
voltage
+V
0V
Produces output
voltage proportional
to knock strength.
Knock
sensor
ECU retards ignition
when abnormal
combustion is detected.
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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
Automotive – Engine Performance
3. Transducers
Lambda sensor
• What information
does this sensor
give to the ECU?
• It detects left-over
oxygen in the
exhaust gas, and
sends the data to
the control unit.
What does the ECU do with the information from this
sensor?
The control unit uses it to fine-tune the pulse it sends to
the fuel injectors.
3. Transducers
Automotive – Engine Performance
Summary
You should be aware of:
 Active and Passive Sensors
 Common Sensor Types
and Their Operation
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