Transcript Electronics and Computer Systems Fundamentals

Electronics and Computer
Systems Fundamentals
Chapter 45
© 2012 Delmar, Cengage Learning
Objectives
• Describe the operation of various
semiconductors
• Understand how computers operate
• Explain the operation of various types of
sensors and actuators
• Compare the different types of computer
memory
• Summarize the various guidelines of on-board
diagnostics
© 2012 Delmar, Cengage Learning
Introduction
• Electronics is the science of using small
amounts of electricity to control larger amounts
– All laws of basic electricity apply
• Emphasis of this chapter is the operation of:
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Semiconductors
Computers
Sensors
Actuators
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Semiconductors
• Can be a conductor or insulator
– Crystalline structure
• Doping
– Small amount of impurity added to crystal
• Circuit can pass through
• N-type: five or more electrons in outer valence ring
• P-type: three electrons in outer valence ring
• Electrons flow from negative to positive
– Semiconductors are designed to handle a limited
amount of current
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© 2012 Delmar, Cengage Learning
Diodes
• One-way electrical check valve
– P-type and N-type crystals placed back-to-back
• P-N junction
– Allows current to pass when voltage greater than
0.5 to 0.7 volt
• Forward bias diodes allow current to flow
• P-N junction empty: current flow stops
• Clamping diode
– Installed parallel to coil
– Provides an alternate electrical path
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Transistors
• Turn electrical circuits on and off
– Controlled by another electrical circuit
• Semiconductor crystal layers
– Emitter, base, and collector
• Bipolar transistors
– Used in automobiles
– Polarities: electrons and holes
• Electrical current
– Cannot move across transistor layers unless
voltage applied to base
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Transistors (cont'd.)
• Biases
– Forward bias: allowing current to flow
– Reverse bias: voltage removed from base
• Transistor never shuts off
– Current flows from base or collector
– Can regulate at 10,000 times per minute
• Zener diode
– Crystals are more heavily doped
– Halt current below a certain voltage
– Controls backwash or double bounce of voltage
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Electronic Instrument Displays
• Light emitting diodes
– Crystal glows when current flows through it
• Use more power than other display types
• Less power than ordinary bulbs
• Liquid crystal displays
– Liquid and glass with conductive coating
• Light can pass through when voltage is applied
• Vacuum fluorescent displays
– Glass tubes filled with argon or neon gas
• Current causes tube to glow
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Automotive Computer Systems and
Parts of a Computer System
• Integrated circuit
– Complete miniature electric circuit
• Chip
– Tiny sandwiched silicon wafers of P-type or Ntype material
– As many as 30,000 transistors placed on a chip
• Main parts to computer systems
– Computer
– Sensors
– Actuators
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On-Board Computer
• Functions
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Gather input
Make decisions and process information
Store information
Take action by way of output command
• Hardware and software
– Items that make up a computer system
• Computer electrical control
– Ground and logic side switching
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Information Processing
• Logic circuits: turn signals into output or store
them in computer memory
– Sensor information may be digital or analog
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Computer Memory and
Communication Rate
• Microprocessor reads and writes to memory
– Temporary information: stored in random access
memory (RAM)
• Volatile: erased when ignition turned off
– Read-only memory (ROM): permanently
programmed into chip during manufacturing
– Programmable read-only memory (PROM):
specific program for one function of vehicle
• Time between one crystal pulse
– One bit of information is transmitted (i.e., baud
rate)
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Sensors, Actuators, and
Types of Sensors
• Sensors monitor engine functions
– Modify voltage signals that return to computer
• Actuator
– Electronic or magnetic relay
• Transducer
– Converts energy from one form to another
• Types of sensors
– Variable resistors and variable DC frequency
– Variable voltage generators and switches
– Variable AC voltage/frequency generators
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Thermistors and Voltage
Dividers
• Thermistor
– Variable resistor made from semiconductor
material
• Resistance changes with temperature
• Voltage dividers
– Variable resistors that produce variable DC
voltage signal
– Potentiometer: three-terminal variable resistor
• Measures linear or rotary motion
– Rheostat: carries current
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Piezoelectric and Piezoresistive
Sensors
• Piezoelectric crystals: develop voltage on their
surface when pressure applied
– Used as switches for measuring pressure in
engine oil, power steering, or air-conditioning
• Piezoresistive sensor: used in MAP sensors
– Silicon diaphragm sealed to a quartz plate
– Doping creates four resistances around edges of
diaphragm
– Pressure deflected from diaphragm
– Causes a change in resistance of resistors
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Heated Resistive Sensors and
Variable DC Frequency Sensors
• Heated resistive sensor
– Monitors the amount of air taken into the engine
– Computer applies current to maintain wire
temperature
– From the current, the computer calculates
amount of airflow into engine
• Frequency sensors
– Used for same things
– Produce digital signal
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Voltage Generators
• Voltage generating sensors
– Have no reference voltage but create their own
– Variable AC voltage generator
• Magnetic pickup generates an AC analog signal
– Pulse generators
• Signal generators
– Oxygen sensor
• Variable CD voltage generator
– Knock sensor
• Piezoelectric crystal senses vibration and creates
voltage signal
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Wheatstone Bridges and
Switches
• Wheatstone bridges
– Two simple series circuits connected in parallel
across battery power on its way to ground
– Used by a hot wire MAF sensor
• Switches
– Switch-to-power
– Switch-to-ground
– Hall-effect
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Types of Actuators
• Act upon processed signals received from the
computer
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Solenoids
DC motors
Relays
Switches
Control Modules
• Output drivers: supply actuators with ground
– Without ground the actuator does not work
• Quad driver: controls up to four transistors
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Solenoid Actuators and
Relay Actuators
• Solenoid: magnetic switch
– Uses for solenoids
• Fuel injectors
• Electronic transmissions
• EGR vacuum control
• Relay actuators
– Trigger operation of high-current load devices
– Normally open relay: open until energized
– Computer controls ground side of relay
• Current can pass through when grounded
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Motor Actuators and
Actuator Switches/Modules
• Motor actuator
– Example: idle speed control motor
– Types of idle motors
• Fuel injection with idle air control motor
• Actuator switches/modules
– Example: ignition module
– Other modules control the operation of cruise
control and the air-conditioning compressor
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Adaptive Strategy
• Keep alive memory (KAM)
– Computer maintains power to RAM when ignition
switch is off
• Keeps information as long as battery connected
• Computer compensates for wear and aging
• Adaptive fuel trim
– Varies fuel system to operate at correct ratio
• Short-term fuel trim: short-term correction in airfuel mixture during closed loop
• Long-term fuel trim: makes long-term corrections
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Knock Sensor
• Computer advances timing until engine knocks
– Retards the timing until knock goes away
• Searches for best timing settings
– Rpm, load, temperature, and fuel
– Stores the best setting in memory
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Electronic Throttle Control/
Drive-By-Wire
• Electronic throttle control
– Module receives accelerator pedal position signal
• Controls electric motor attached to throttle plate
• Inputs include how fast pedal depressed or
released
– Provides better drivability, fuel economy, and
lower emissions
– Cruise control may be part of the system
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On-Board Diagnostics and
Diagnostic Trouble Codes
• On-board diagnostics
– Computer has diagnostic capabilities
• Universal data link connector (DLC) for reading
trouble codes
• Universal generic scan tool
• Diagnostic trouble codes
– Universal diagnostic trouble codes (DTC)
• Stored in computer’s non-volatile RAM
• Battery supplies power to computer for memory
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Computer Self-Diagnostics
• Computers diagnose the majority of electronic
system faults
– MIL comes on while car is running: fault code is
stored
– Hard faults: present and stored in memory during
self-test
– Intermittent fault code: only occurs occasionally
for a short time and is not present in the system
at the time of the fault test
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Multiplexing
• Average vehicle has 16 electronic control units
– Multiplexing (MUX) allows control modules to
communicate
• Twisted pair wiring
– Reduces interference from other circuits
• Protocol
– Language used by modules to communicate
– Gateway module allows communication from
slower to faster modules
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Network Sizes and Types and
CAN Systems
• Networks
– Wide area network (WAN)
– Local area network (LAN)
– Controller area network (CAN)
• CAN systems
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Messages: diagnostic mode and normal mode
Manufacturers use different CAN system designs
Topology describes the physical network makeup
CAN chip manages information transfer
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Supplemental Data Bus
Networks
• Provide additional support to main bus network
– Media-oriented system transport (MOST)
• Connects audio and video components
• Lowers manufacturing costs
• Minimizes wiring harnesses
– System information carried by fiber optics
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Capable of higher speeds than ordinary networks
Plastic or glass fibers
Transmits light waves free of electrical noise
Light signals transmitted between LED,
photodiode, and transceiver
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Telematics and
Wireless Networks
• Telematics blends computers and wireless
communications
– Example: General Motors OnStar
• Wireless networks transmit without wires
– Tire pressure information monitor
– Bluetooth™: wireless personal area network
• Allows communication between modules using
standard radio transmissions
– DSRC: dedicated short range communications
• Links vehicles to each other and roadside access
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