The document summarizes sensors and actuators used in automotive control systems. It describes several common sensors that measure important engine variables like mass air flow, crankshaft position, throttle position, and temperature. It provides details on how sensors like the airflow sensor, crankshaft position sensor, throttle angle sensor, and coolant temperature sensor operate. The document also discusses actuators used to control engine inputs and mentions fuel injectors as an example.

1. Module 2
Sensors and Actuators

2. SYLLABUS
 Sensors and Actuators: Introduction to sensors and transducers-Types-Air
flow rate sensor, Engine crankshaft angular position senor, Engine speed sensor,
Timing sensor, Throttle angle sensor, Pressure sensor, Temperature sensors,
Pressure sensor-Flow sensor, Exhaust gas oxygen sensors, Knock Sensor,
Engine torque sensors, Automotive engine control actuators, Exhaust gas
recirculation actuator.

3. INTRODUCTION
 In any control system, sensors provide measurements of important plant
variables in a format suitable for the digital microcontroller.
 Similarly, actuators are electrically operated devices that regulate inputs to the
plant that directly controls its output.
 For example, as we shall see, fuel injectors are electrically driven actuators that
regulate the flow of fuel into an engine for engine control applications.

4. AUTOMOTIVE CONTROL SYSTEM APPLICATIONS
OF SENSORS AND ACTUATORS

5. VARIABLES TO BE MEASURED
THE SUPERSET OF VARIABLES SENSED IN ENGINE CONTROL
INCLUDES THE FOLLOWING
1. mass airflow (MAF) rate
2. exhaust gas oxygen concentration
3. throttle plate angular position
4. crankshaft angular position/RPM
5. camshaft angular position
6. coolant temperature
7. intake air temperature
8. ambient air pressure
9. ambient air temperature
10. manifold absolute pressure (MAP)
11. differential exhaust gas pressure (relative
to ambient)
12. vehicle speed
13. transmission gear selector position
14. actual transmission gear, and
15. various pressures.

6. These switches include the following:
1. air conditioner clutch engaged
2. brake on/off
3. wide open throttle
4. closed throttle, and
5. transmission gear selection.

7. AIRFLOW RATE SENSOR

8. • The concept of such an airflow sensor is based upon the variation in resistance of
the two terminal sensing element with temperature.
•A current is passed through the sensing element supplying power to it, thereby
raising its temperature and changing its resistance.
•When this heated sensing element is placed in a moving air stream (or other
flowing gas), heat is removed from the sensing element as a function of the mass
flow rate of the air passing the element as well as the temperature difference
between the moving air and the sensing element.
•For a constant supply current (i.e., heating rate), the temperature at the element
changes in proportion to the heat removed by the moving air stream, thereby
producing a change in its resistance.
•A convenient model for the sensing element resistance (RSE) at temperature (T) is
given by

9. The mass flow rate of the moving air stream is measured via a measurement of the
change in resistance.

10.  In the bridge circuit, three resistors (R1, R2, and R3) are connected as depicted in Figure
6.2 along with a resistive sensing element denoted RSE(T).
 This sensing element consists of a thin film of conducting (e.g., Ni) or semiconducting
material that is deposited on an insulating substrate.
 The voltages V1 and V2 (depicted in Figure 6.2) are connected to the inputs of a
relatively high-gain differential amplifier.
 The output voltage of this amplifier vo is connected to the bridge (as shown in Figure
6.2) and provides the electrical excitation for the bridge.
 This voltage is given by
where G is the amplifier voltage gain

11.  In this bridge circuit, only that sensing element is placed in the moving air stream whose
mass flow rate is to be measured.
 The other three resistances are mounted such that they are at the same ambient
temperature (Ta) as regards the moving air.
 The combination bridge circuit and differential amplifier form a closed-loop in which
the temperature difference ∆T between the sensing element and the ambient air
temperature remains fixed independent of Ta (which for an automobile can vary by more
than 100 C).
 We discuss the circuit operation first and then explain the compensation for variation in
Ta.

14. ENGINE CRANKSHAFT ANGULAR POSITION
SENSOR

15.  The measurement of crankshaft angular position or RPM in
engine control involves principles applicable to rotating shafts.
 In this context, envisioning the engine from the rear is helpful.
 A significant component is the flywheel, a circular steel disk
connected to and rotating with the crankshaft. The flywheel
mark, a designated point on the flywheel, is crucial.
 A reference line is defined as the line through the crankshaft
axis and a point on the engine block (b). In this discussion, the
reference line is considered horizontal.
 Crankshaft angular position is the angle between the reference
line and the line through the axis and the flywheel mark,
illustrating the fundamental principles of measuring rotating
shafts in engine control.

16.  Imagine that the flywheel is rotated so that the mark is directly on
the reference line.
 This is an angular position of zero degrees. For our purposes,
assume that this angular position corresponds to the No. 1
cylinder at TDC (top dead center) on either intake or power
strokes.
 As the crankshaft rotates, this angle increases from zero to 360 in
one revolution.
 However, one full engine cycle from intake through exhaust
requires two complete revolutions of the crankshaft; that is, one
complete engine cycle corresponds to the crankshaft angular
position going from zero to 720.
 During each cycle, it is important to measure the crankshaft
position relative to the reference for each cycle in each cylinder.
 This information is used by the electronic engine controller to set
ignition timing and, in most cases, to set the fuel injector pulse
timing.

17. THROTTLE ANGLE SENSOR

20.  Consider now a resistive material formed in a segment of a circle
of radius r as depicted in Figure 6.19. Let the radial dimension
and the thickness of the material be uniform and small compared
to the circumferential distance along the arc (ra). A movable
metallic contact that pivots about the center of the circular arc
makes contact with the resistive material at an angle a (measured
from a line through the center and the grounded end of the
resistive material). The opposite end of the material (at an angle
amax) is connected to a constant voltage Vs. A structure such as
that depicted in Figure 6.19 is known as a rotary potentiometer
(or just as a potentiometer). Let the total resistance from the end
of the material which is connected to Vs be denoted Rp and the
resistance from the movable contact to ground at any angle a be
denoted R(a). With the assumptions of uniform geometry given
above, this resistance varies linearly with arc length ra. Thus, the
resistance R(a) can be shown to be given by

22. TEMPERATURE SENSORS
 Temperature (T) is an important parameter throughout the automotive system.
 In the operation of an electronic fuel control system it is vital to know the
temperature of the coolant, the temperature of the inlet air, and the temperature
of the exhaust gas oxygen sensor (a sensor to be discussed in the next section).
 Several sensor configurations are available for measuring these temperatures,
but we can illustrate the basic operation of most of the temperature sensors by
explaining the operation of a typical coolant sensor.
 The temperature sensor for any given application is designed to meet the
expected temperature range.
 For example, a coolant, temperature sensor experiences far lower temperatures
than a sensor exposed to exhaust gases.

23. TYPICAL COOLANT SENSOR
 A typical coolant sensor, shown in Figure 6.20, consists of a
thermistor mounted in a housing that is designed to be
inserted in the coolant stream. This housing is typically
threaded such that it seals the assembly against coolant
leakage. A thermistor is a two-terminal semiconductor
whose resistance varies inversely with its temperature. The
theory of operation is based upon the influence of
temperature on the charge carrier concentrations which, in
turn, depend upon the difference in energy between the

25. The terminal voltage VT is input to the digital engine control system (e.g., via an A/D
converter) where RT is computed from VT. Then, temperature is obtained using the model
for RT(T) given above or another model (e.g., polynomial).