Electronics and Computer Systems Fundamentals Chapter 45

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

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: Semiconductors Computers Sensors Actuators

Semiconductors Can be a conductor or insulator Doping 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

Diodes One-way electrical check valve P-N junction Clamping diode 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

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

Transistors (cont'd.) Biases Transistor never shuts off Zener diode 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

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

Automotive Computer Systems and Parts of a Computer System Integrated circuit Complete miniature electric circuit Chip Tiny sandwiched silicon wafers of P-type or N-type material As many as 30,000 transistors placed on a chip Main parts to computer systems Computer Sensors Actuators

On-Board Computer Functions Hardware and software 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

Information Processing Logic circuits: turn signals into output or store them in computer memory Sensor information may be digital or analog

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)

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

Thermistors and Voltage Dividers 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

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

Heated Resistive Sensors and Variable DC Frequency Sensors 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

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

Wheatstone Bridges and Switches 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

Types of Actuators Act upon processed signals received from the computer 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

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

Motor Actuators and Actuator Switches/Modules 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

Adaptive Strategy Keep alive memory (KAM) Adaptive fuel trim 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 air-fuel mixture during closed loop Long-term fuel trim: makes long-term corrections

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

Electronic Throttle Control/ Drive-By-Wire 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

On-Board Diagnostics and Diagnostic Trouble Codes 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

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

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

Network Sizes and Types and CAN Systems Wide area network (WAN) Local area network (LAN) Controller area network (CAN) CAN systems Messages: diagnostic mode and normal mode Manufacturers use different CAN system designs Topology describes the physical network makeup CAN chip manages information transfer

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 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

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