Automotive electronicsAutomotive electronics

Use of electronics in automobileUse of electronics in automobile• To improve fuel economyTo improve fuel economy• To reduce exhaust emissionTo reduce exhaust emission

Current trend in Current trend in automobileautomobile

1. Electronic engine control for minimizing exhaust emissions and maximizing fuel economy

2. Instrumentation for measuring vehicle performance parameters and for diagnosis of on-board system malfunctions

3. Driveline control4. Vehicle motion control5. Safety and convenience6. Entertainment/communication/navigation

AUTOMOBILE PHYSICAL CONFIGURATION

These systems include the following:1. Engine2. Drivetrain (transmission, differential, axle)3. Suspension4. Steering5. Brakes6. Instrumentation7. Electrical/electronic8. Motion control9. Safety10. Comfort/convenience11. Entertainment/communication/navigation

ENGINE

Engine blockEngine block

Cylinder Head

The 4-Stroke Cycle

Engine operationEngine operation

ENGINE CONTROL

Intake Manifold andFuel Metering

Spark PlugConfiguration

Schematic of theIgnition Circuit

Spark Pulse Generation

SUSPENSION

Shock AbsorberAssembly

STEERING SYSTEM

Engine terms

PowerPower is a measurement of an engine’s ability toperform useful work. Brake power, which ismeasured with an engine dynamometer, is the actual power developed by the engine minus losses due to internal friction.BSFCBSFC is a measurement of an engine’s fuel economy. It is the ratio of fuel flow to the brake power output of the engine

BSFC = rf/pb

TorqueEngine torque is the twisting action produced on the crankshaft by the cylinder pressure pushing on the piston during the power stroke.

Volumetric Efficiency Volumetric efficiency actually describes how well the

engine functions as an air pump, drawing air and fuel into the various cylinders. It depends on various engine design parameters such as piston size, piston stroke, and number of cylinders and is strongly influenced by camshaft design.

Thermal EfficiencyThermal efficiency expresses the mechanical energy that is delivered to the vehicle relative to the energy content of the fuel.

CalibrationThe definition of engine calibration is the setting of the air/fuel ratio and ignition timing for the engine.

ELECTRONIC ENGINE CONTROL

Inputs to Controllers1.Throttle position sensor

(TPS)2. Mass air flow rate (MAF)3. Engine temperature

(coolant temperature) (CT)

4. Engine speed (RPM) and angular position

5. Exhaust gas recirculation (EGR) valve position

6. Exhaust gas oxygen (EGO) concentration Outputs from

Outputs from Controllers

1. Fuel metering control

2. Ignition control3. Ignition timing4. Exhaust gas

recirculation control

Electronic Distributor lessIgnition System

Sensors and Sensors and actuatorsactuators

Sensors:Sensors: S Sensors provide measurements of important plant variables in a format suitable for the digital microcontroller.Ex:Throttle position sensor (TPS), directly regulates the air flow into the engine, thereby controlling output power.Autuators:Actuators are electrically operated devices that regulate inputs to the plant that directly control its output.Ex: Fuel injectors are electrically driven actuators that regulate the flow of fuel into an engine for engine control applications.

TYPES OF TYPES OF SENSORSSENSORS

• 1. Mass air flow (MAF) rate• 2. Exhaust gas oxygen concentration

(possibly heated)• 3. Throttle plate angular position• 4. Crankshaft angular position/RPM• 5. Coolant temperature• 6. Intake air temperature• 7. Manifold absolute pressure (MAP)• 8. Differential exhaust gas pressure• 9. Vehicle speed• 10. Transmission gear selector position

AIR FLOW RATE SENSOR

In the MAF, the hot-wire, or sensing, element is replaced by a hot-film structure (Thermister) mounted on a substrate. On the air inlet side is mounted a honeycomb flow straightener that “smooths” the air flow.

The film element is electrically heated to a constant temperature above that of the inlet air.

The Wheatstone bridge consists of three fixed resistors R1, R2, and R3 and a hot-film element having resistance RHW. With no air flow the resistors R1, R2, and R3 are chosen such that voltage va and vb are equal (i.e., the bridge is said to be balanced).

As air flows across the hot film, heat is carried away from the film by the moving air. The amount of heat carried away varies in proportion to the mass flow rate of the air. The heat lost by the film to the air tends to cause the resistance of the film to vary, which un balances the bridge circuit, thereby producing an input voltage to the amplifier

The output of the amplifier is connected to the bridge circuit and provides the power for this circuit. The amplified voltage changes the resistance in such a way as to maintain a fixed hot-film temperature relative to the inlet temperature.

• voltage-to-frequency (v/f ) converter is used to convert the analog voltage in to digital signal This circuit is a variable-frequency oscillator whose frequency f is proportional to the input voltage (in this case, the amplifier output voltage).

• The variable-frequency output voltage (vf ) is applied through an electronic gate, which is essentially an electrically operated switch. Control circuitry (also part of the sensor solid-state electronics) repeatedly closes the switch for a fixed interval t. Then it opens it for another fixed interval. During the first interval the variable-frequency signal from the v/f circuit is connected to the binary counter (BC)

B=ftB = BC countf = frequency of v/ft = duration of closure of electronic gate

• After the engine controller reads the count, the BC is reset to zero to be

ready for the next sample

Indirect Measurement of Mass Air Flow (speed-

density method)This method computes an estimate of mass air flow from measurements of manifold absolute pressure (MAP), RPM, and inlet air temperature.

Strain Gauge MAP SensorManifold pressure applied to the diaphragm causes it to deflect. The resistance of the sensing resistors changes in proportion to the applied manifold pressure by a phenomenon that is known as piezoresistivity.

The resistors in the strain gauge MAP sensor are connected in a wheatstone bridge circuit. Output voltage of the circuit varies as the resistance varies in response to manifold pressure variations.

ENGINE CRANKSHAFT ANGULAR POSITION

SENSOR

Crankshaft angular position is an important

variable in automotive control systems, particularly

for controlling ignition timing and fuel injection

timing.

The crankshaft angular position is the angle between the reference line and the mark on the flywheel .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). As the crankshaft rotates, this angle increases from zero to 360° in one revolution.

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 with reference to TDC for 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.

TYPESTYPES

• MECHANICALMECHANICALMagnetic Reluctance Position SensorHall-Effect Position Sensor

• OPTICALOPTICALOptical Crankshaft Position Sensor

MAGNETIC RELUCTANCE POSITION SENSOR• In the magnetic reluctance position sensor, a coil

wrapped around the magnet senses the changing intensity of the magnetic field as the tabs of a ferrous disk pass between the poles of the magnet.

• The voltage generated by the magnetic reluctance position sensor is determined by the strength of the magnetic flux. When a tab on the steel disk passes through the gap, the flow of the magnetic flux changes significantly.

• The reluctance of a magnetic circuit is inversely proportional to the magnetic permeability of the material along the path. The magnetic permeability of steel is a few thousand times larger than air; therefore, the reluctance of steel is much lower than air.

• Note that when one of the tabs of the steel disk is located between the pole pieces of the magnet, a large part of the gap between the pole pieces is filled by the steel. Since the steel has a lower reluctance than air, the “flow” of magnetic flux increases to a relatively large value.

• when a tab is not between the magnet pole pieces, the gap is filled by air only. This creates a high-reluctance circuit for which the magnetic flux is relatively small. Thus, the magnitude of the magnetic flux that “flows” through the magnetic circuit depends on the position of the tab, which, in turn, depends on the crankshaft angular position.

Output Voltage Waveform From The Magnetic Reluctance Position Sensor Coil

The voltage induced in the sensing coil varies with the rate of change of the magnetic flux. When the tab is centered between the poles of the magnet, thevoltage is zero because the flux is not changing

coil voltage, Vo, begins to increase from zero as a tab begins to pass between the pole pieces, reaches a maximum, then falls to zero when the tab is exactly between the pole pieces . (Note that although the value of magnetic flux is maximum at this point, the rate of change of magnetic flux is zero; therefore, the induced voltage in the sensing coil is zero.) Then it increases with the opposite polarity, reaches a maximum, and falls to zero as the tab passes out of the gap between the pole pieces

Disadvantages:Disadvantages: Lack of output when the engine isn’t

running.

Hall-Effect Position SensorThe Hall element is a thin slab of semiconductor material that is placed between the magnets so it can sense the magnetic flux variations as the tab passes. A constant current is passed through the semiconductor in one direction, and a voltage is Generated that varies with the strength of the magnetic flux. This effect—the generation of a voltage that is dependent on a magnetic field—is called the Hall effect.

Vo is proportional to the magnetic flux density, it reaches maximum when any of the tabs is symmetrically located between the magnet pole pieces (corresponding to TDC of a cylinder).

.

Advantages: Hall-effect sensor produces the same output voltage waveform regardless of engine speed, the engine timing can be set when the engine is not running

Waveform of Hall Element Output Voltage for Position

Sensor

Shielded-Field SensorWhen one of the tabs passes between the magnet and the sensor element, the lowreluctance of the tab and disk provides a path for the magnetic flux thatbypasses the Hall-effect sensor element, and the sensor output drops to nearzero. The waveform is just opposite to hall effect sensor.

Optical Crankshaft Position Sensor

In the optical crankshaft position sensor, adisk coupled to the crankshaft has holes to pass light between the LED and the phototransistor. An output pulse is generated as each hole passes the LED.

The hole in the disk allows transmission of light through the light pipes from the light-emitting diode (LED) source to the phototransistor used as a light sensor. Light would not be transmitted from source to sensor when there is no hole because the solid disk blocks the light.

Advantages:• It can sense position without the

engine running and that the pulse amplitude is constant with variation in speed.

Disadvantages:• optical sensors must be protected

from dirt and oil; otherwise, it will not work properly.

Throttle Angle Sensor

The throttle plate is linked mechanically to the accelerator pedal. When the driver depresses the accelerator pedal, this linkage causes the throttle plate angle to increase, allowing more air to enter the engine and thereby increasing engine power.

• The voltage at the contact point of the movable contact is proportional to the angle (a) from the ground contact to the movable contact. Thus,

v(a) =kawhere v(a) is the voltage at the contact point k is a constant a is the angle of the contact point from the ground connection

Disadvantages:• For digital engine control, the voltage v(a)

must be converted to digital format using an analog-to-digital converter.

Exhaust Gas Oxygen Sensor(lambda sensor)

• The amount of oxygen in the exhaust gas is used as an indirect measurement of the air/fuel ratio.

λ = air/fuel air/fuel at stoichiometry

λ =1(air/fuel at stoichiometry)λ >1(air–fuel mixture is too lean)λ <1(air–fuel mixture is too rich)

TypesTypes

Based on the use of active oxides of two types of materials.

• Zirconium dioxide (ZrO2)• Titanium dioxide (TiO2).

The zirconium dioxide EGO sensor useszirconium dioxide sandwiched betweentwo platinum electrodes. One electrode is exposed to exhaust gas and theother is exposed to normal air for reference.

The inside electrode is exposed to air, and the outside electrode is exposed to exhaust gas through a porous protective overcoat.

• An ion is an electrically charged atom. Oxygen ions have two excess electrons and each electron has a negative charge; thus, oxygen ions are negatively charged. The ZrO2 has a tendency to attract the oxygen ions, which accumulate on the ZrO2 surface just inside the platinum electrodes.

• The platinum plate on the air reference side of the ZrO2 is exposed to a much higher Concentration of oxygen ions than the exhaust gas side.

• The polarity of this voltage is positive on the exhaust gas side and negative on the air reference side of the ZrO2. The magnitude of this voltage depends on the concentration of oxygen in the exhaust gas and on the sensor temperature.

• The quantity of oxygen in the exhaust gas is represented by the oxygen partial pressure

• Rich mixture varies over the range of 10-16 to 10-32 of atmospheric pressure and lean mixture is roughly 10-2 atmosphere

• Rich mixture -low oxygen concentration and higher EGO sensor output(1V)

• lean mixture-exhaust gas oxygen concentration is relatively high and low EGO sensor output voltage(0.1V)

Desirable EGO Characteristics1. Abrupt change in voltage at

stoichiometry2. Rapid switching of output voltage in

response to exhaust gas oxygen changes3. Large difference in sensor output voltage

between rich and lean mixture conditions4. Stable voltages with respect to exhaust

temperature

Switching Characteristics

Temperature affects switching times and output voltage

Hysteresis is the difference in the switchingpoint of the output voltage with respect tostoichiometry as a mixture passes from lean to rich, as contrasted to a mixture that passes from rich to lean.

The sensor output doesn’t change at exactly the same point for increasing air/fuel ratio as for decreasing air/fuel ratio. This phenomenon is called hysteresis.

Typical Voltage Switching Characteristics of EGO Sensor

The switching times are roughly 0.1 second at 350°C, whereas at 800°C they are about 0.05 second.

The EGO sensor should not be used for control at temperatures below about 300°C because the difference between rich and lean voltages decreases rapidly with temperature in this region.

Heated EGO Sensors

• This sensor is electrically heated from start-up until it yields an output signal of sufficient magnitude to be useful in closed-loop control.

• Electrical power from the car battery is applied at start-up, which quickly warms the sensor to usable temperatures.

• This heating potentially shortens the time interval until closed-loop operation is possible, thereby minimizing the time during warm-up that the air/fuel ratio deviates from stoichiometry and correspondingly reduces undesirable exhaust gas emissions.

Knock Sensors

This sensor is employed in closed-loop ignition timing to prevent undesirable knock

• Rapid rise in cylinder pressure during combustion.

• Excessive spark advance.Some engine knock sensors use rods within a magnetic field to detect the presence of knock. Other use vibration sensitive crystals or semiconductors

• Magnetostriction is a phenomenon whereby the magnetic properties of a material depend on stress (due to an applied force). When sensing knock, the magnetostrictive rods, which are in a magnetic field, change the flux field in the coil due to knock-induced forces. This change in flux produces a voltage change in the coil. This voltage is used to sense excessive knock

Surprise test-1Surprise test-11.What is the primary purpose of fuel

control?a. to minimize fuel economyb. to eliminate exhaust emissionsc. to optimize catalytic converter efficiencyd. to maximize engine torque

2.What does exhaust gas recirculation do?a. improves fuel economyb. reduces NOx emissionc. increases engine torqued. provides air for the catalytic converter

3.The Hall effect is a. the resonance of a long, narrow corridorb. the flow of air through the intake manifold c. zero crossing error in camshaft position

measurementsd. a phenomenon occurring in semiconductor

materials in which a voltage is generated that is proportional to the strength of a magnetic field

4.The resistance of a thermistora. varies inversely with temperatureb. varies directly with temperaturec. is always 100,000ohmsd. none of the above

5.Piezoresistivity isa. a property of certain semiconductors in

which resistivity varies with strainb. a resistance property of insulatorsc. metal bonding padsd. an Italian resistor

6.What engine quantities are measured to determine spark advance for an electronic ignition system?

a. manifold pressure, RPM, and temperatureb. coolant temperature and mass air flowc. manifold position and crankshaft positiond. none of the above

7.Brake power of an engine isa. the power required to decelerate the carb. an electronic system for stopping the carc. the difference between indicated power

and power losses in the engined. none of the above

8.Which of the following are examples of a plant?

a. automotive drivetrainb. high-temperature ovenc. an airplane navigation systemd. all of the above

9.What does signal processing do?a. converts a mechanical input to an electrical

outputb. converts an electrical input to a mechanical

outputc. reduces the effects of noise and other

disturbances on the measured quantityd. all of the above10.The air–fuel ratio isa. the rate at which combustible products enter

the engineb. the ratio of the mass of air to the mass of fuel in

a cylinder before ignitionc. the ratio of gasoline to air in the exhaust piped. intake air and fuel velocity ratio

ActuatorsActuators

• An actuator is a device that receives an electrical input (e.g., from the engine controller) and produces a mechanical or thermal (or other)

output. Examples

Electric motors, solenoids, and piezoelectric force generators.

Schematic Drawing of a Solenoid

When a current passes through the coil, a magnetic field is created that tends to pull the movable element toward the steel frame. When the magnetic field, which is proportional to the current, is sufficient to Overcome the force at the spring holding the movable element, then it begins to move toward the frame. As this element moves, the size of the gap is reduced, causing an increase in the strength of the magnetic field. This increase causes the movable element to accelerate toward the frame until it reaches the stop.

This abrupt motion of the movable element is essentially in the form of a mechanical switching action such that the solenoid tends to be either in its rest position (as held by the spring) or against the mechanical stop.AdvantagesSimple and inexpensive.ApplicationsFuel injectors and EGR valves.

Schematic Drawing of Fuel Injector

Pulse Mode Fuel Control Signal to Fuel Injector

EGR Actuator Control

Stepper motor throttle actuatorStepper motor throttle actuator