Chapter 17 Computer System Fundamentals

Contents Cybernetics Computer advantages Digital electronics Integrated circuits Computer signals Computer system operation Sensors Computers Actuators

Computer Complex electronic device that will produce programmed electrical output signals after receiving specific electrical input signals Computers monitor and control all major systems of a modern vehicle

Cybernetics Study of how electrical-mechanical devices can duplicate the action of the human body Comparing the human body to a computer system is an easy way to explain this subject

Cybernetics

The Nervous System Uses chemical-electrical signals to control the body If you touch a sharp needle, nerve cells in your finger “fire” and send a signal through a strand of nerve cells in your hand, up your arm, and into your brain Nerve cells in your finger are comparable to a sensor, or input device, in a computer system

The Brain Uses billions of cells interconnected by linking cells called neurons When the brain “thinks”, minute electrical impulses travel from neuron to neuron Cells in the brain can be either charged (on) or not charged (off)

The Brain By connecting all the brain cells, the brain can decide what to do in each situation Computers produce logical outputs in a similar fashion

The Reflex Action Specific brain cells are activated by the needle prick (pain) signal, and a reflex output is produced The brain sends a signal to your arm to pull back This is similar to the action of an actuator, or output device, in a car’s computer system

Computer Advantages There are several reasons that computers are being used in modern vehicles Computers can provide several advantages

Computer Advantages Fewer moving parts to wear and go out of calibration Reduced fuel consumption Lower emissions Increased engine power Reduced vehicle weight

Computer Advantages On-board diagnostics Increased driver convenience Improved passenger safety Compensation for component wear

Digital Electronics Field of study dealing with the ways a computer uses on-off signals to produce “artificial intelligence”

Binary Numbering System Uses only two numbers, zero and one Key to how computers operate Zero (0) and one (1) can be arranged in different sequences to represent other numbers, letters, words, an input, an output, or a condition

Binary Numbering System To use the binary system, a computer turns switches (transistors) on or off Off represents zero On represents one

Binary Numbering System

Binary Numbering System Binary numbers can be converted into decimal (base ten) numbers

Binary Language A single zero or a one is called a bit Four bits make a nibble Eight bits make a byte or word

Gating Circuits Gate Common gate types: electronic circuit that produces a specific output voltage for given input voltages Common gate types: NOT AND NAND OR NOR

NOT Gate

AND Gate

NAND Gate

OR Gate

NOR Gate

Shows what the output of a gate will be with different inputs Truth Table Shows what the output of a gate will be with different inputs

“Thinking” with Gates If an AND gate is compared to two switches wired in series, both switches must be on to activate the starter motor

Using Gates Logic gates can be connected together to form super-complex circuits Millions of gates can be interconnected to produce thousands of programmed outputs from numerous inputs This is how a computer works, or thinks

Integrated Circuits Electronic circuits that have been reduced in size and etched on the surface of tiny semiconductor chips

Integrated Circuit Different semiconductor substances are deposited on a silicon chip and then etched to produce resistors, diodes, and transistors Metal conductors on the top of the chip connect these various electronic components to form the circuit Wire leads allow for input and output connections

Integrated Circuit Wire leads connect the chip to the metal pins. The pins plug into or are soldered to other parts of the circuit.

Integrated Circuit A digital IC uses logic gates. An analog IC increases output strength or alters output.

IC Construction The circuit has been photographically reduced in size, etched on a silicon chip, and placed in a protective plastic case

Computer Signals Computer signal voltage variation over short periods of time specific arrangement of pulses or waves used to carry data, or information Computer signals can be digital or analog

On-off signal like that is produced by a rapidly flipping switch Digital Signal On-off signal like that is produced by a rapidly flipping switch

A digital waveform as seen on an oscilloscope Digital Signal A digital waveform as seen on an oscilloscope

Gradually changes in strength like the output from a dimming switch Analog Signal Gradually changes in strength like the output from a dimming switch

An analog waveform as seen on an oscilloscope Analog Signal An analog waveform as seen on an oscilloscope

Scoping a Magnetic Sensor

Electrical Waveforms

Signal Frequency How fast a signal changes over time High-frequency signal short pulse width Low-frequency signal long pulse width

Measured in cycles per second (hertz) Signal Frequency Measured in cycles per second (hertz)

Voltage level present in the waveform Signal Amplitude Voltage level present in the waveform

Percentage of on-time compared to total cycle time Duty Cycle Percentage of on-time compared to total cycle time

Computer System Operation There are three stages of computer system operation: input processing and storage output

Inputs and Outputs

Computer System Block Diagram Service manual drawing that shows how the sensors, the actuators, and the computer interact Useful when trying to find out what types of sensors are used and what conditions are controlled

Computer System Block Diagram Fig 18

Sensors Most vehicle sensors, or transducers, change a physical condition into an electrical signal Transduce: to change from one form to another

Sensor Locations Sensors can be found almost anywhere on a vehicle: on the engine on or in the transmission or transaxle in the exhaust system on the wheel hubs on and in the fuel tank on the suspension in the trunk

Some of the sensors located on the engine and transaxle Sensor Locations Some of the sensors located on the engine and transaxle

Sensor Classifications Sensors can be classified into two general categories: active sensors passive sensors

Active Sensor Produces its own voltage signal internally The signal is fed to the computer for analysis Shielded wire may be used to block induced voltage and interference in the signal wire(s)

Active Sensor

Passive Sensor Variable resistance sensor Voltage is fed to the sensor from the computer Sensor resistance varies with changes in a condition temperature, pressure, motion, etc. As sensor resistance changes, the voltage signal sent back to the computer changes

Passive Sensor

Types of Sensors

Variable Resistor Sensor Changes its resistance with a change in condition temperature, pressure, etc. Throttle position and temperature sensors are variable resistance sensors

Switching Sensor Opens or closes the sensor circuit to provide an electrical signal Used to detect almost any condition Produces a digital signal Transmission pressure switches are switching sensors

Magnetic Sensor Also called a permanent magnet (PM) generator Uses part movement and induced current to produce a signal Produces an analog signal Used to monitor speed or part rotation Vehicle speed and wheel speed sensors are often magnetic sensors

Hall-Effect Sensor Uses a special semiconductor chip to sense part movement and speed Produces a digital signal Applications: crankshaft position sensors camshaft position sensors distributor pickup devices

Uses a semiconductor chip that reacts to magnetic fields Hall-Effect Sensor Uses a semiconductor chip that reacts to magnetic fields

A reverse-biased photodiode conducts current when exposed to light Optical Sensor A reverse-biased photodiode conducts current when exposed to light

Optical Sensor Uses light-emitting diodes and photo diodes to produce a digital signal Used to sense part rotation and speed Used in some distributors and as speed sensors mounted outside the speedometer

Piezoelectric Sensor Generates voltage from a physical shock or motion An internal crystal produces a voltage signal proportional to the amount of vibration detected Used to sense abnormal engine vibration caused by engine knock knock sensor

Piezoelectric Sensor

Solar Sensor Converts sunlight directly into an electrical signal Made of a semiconductor material that converts photons into direct current

Solar Sensor

Direction Sensor Detects the polarity of a moving magnet Signals which direction a part is rotating Used in some computer-controlled steering systems

Reference Voltage Applied to a passive sensor by the computer 5 volts on most vehicles The computer steps down battery voltage so that a smooth, constant supply of dc voltage is fed to the sensor The sensor changes its internal resistance to alter the reference voltage

Sensor Types Common sensors used in late-model vehicles: Intake air temperature sensor (IAT) measures the temperature of intake air as it enters the intake manifold Engine coolant temperature sensor (ECT) measures the temperature of engine coolant

Sensor Types Oxygen sensors Manifold absolute pressure sensor (MAP) measure the amount of oxygen in the engine’s exhaust gases Manifold absolute pressure sensor (MAP) measures pressure inside the intake manifold Barometric pressure sensor (BARO) measures the outside air pressure

Sensor Types Throttle position sensor (TP) Engine speed sensor measures the opening angle of the throttle valves to detect driver power demand Engine speed sensor measures engine rpm Crankshaft position sensor (CKP) measures crankshaft position and speed

Sensor Types Camshaft position sensor (CMP) Mass airflow sensor (MAF) measures camshaft position and rotation Mass airflow sensor (MAF) measures the amount of intake air flowing into the engine Knock sensor (KS) detects engine pinging, preignition, or detonation

Sensor Types Transaxle/transmission sensor Brake switch checks transaxle or transmission gear selection Brake switch detects brake pedal application Wheel speed sensor measures wheel rotational speed for anti-lock brake and traction control application

Sensor Types Oil level sensor EGR sensor Impact sensors measures the amount of oil in the engine oil pan EGR sensor measures the position of the exhaust gas recirculation valve pintle Impact sensors detect a collision

Sensor Types Vehicle speed sensor (VSS) Fuel tank pressure sensor measures the vehicle’s road speed Fuel tank pressure sensor measures fuel tank pressure as part of some evaporative emission control systems Battery temperature sensor monitors battery temperature so the computer can adjust charging system output as needed

Circuit Sensing Involves using the computer itself to monitor component and circuit operation Computer monitors current flow through various circuits to diagnose: fuel injectors ignition coil action computer operation

Computers The term computer refers to any electronic circuit configuration that can use multiple inputs to determine outputs

Computer Names Automobile manufacturers have many names for their computers: central processing unit (CPU) electronic control unit (ECU) electronic control module (ECM) engine control module (ECM) (Continued)

Computer Names electronic control assembly (ECA) powertrain control module (PCM) vehicle control module (VCM) microprocessor logic module

Computer Types Several types of computers can be used in a car The most common types are: Vehicle control module coordinates engine, transmission, traction control, and anti-lock brake functions Powertrain control module monitors and controls the engine and transmission

Computer Types Engine control module Anti-lock brake module controls engine management functions Anti-lock brake module controls anti-lock brake operation Instrumentation module operates the digital dash display

Computer Types Ignition module Suspension system module controls ignition functions, such as timing Suspension system module controls ride stiffness or shock absorber action Climate control module controls the operation of the heating, ventilation, and air conditioning systems

Computer Types Air bag module High-power module Body module controls the vehicle’s air bag system High-power module Controls current or processes output signals from a few sensors and the main computer Body module coordinates body functions, such as lighting, radio, driver’s information center, electronic compass, etc.

Computers may be located almost anywhere on the vehicle Computer Locations Computers may be located almost anywhere on the vehicle

Computer Construction Computers are composed of printed circuit boards, integrated circuits, capacitors, resistors, transistors, and other electronic components

Parts of a Computer A computer can be divided into 11 basic parts: voltage regulator amplifiers conditioners buffer microprocessor memory clock output drivers circuit board harness connector computer housing

Parts of a Computer

Voltage Regulator Provides a reduced voltage for the components in the computer and sensors Provides a smooth dc voltage that does not vary and is free of any spikes (abrupt changes in voltage)

Computer Amplifier Strengthens various signals when inside the computer amplifier might increase the voltage signal from the oxygen sensor, which is less than one volt Allows a low voltage signal to be used by the circuits in the computer

Input Conditioner Also called a converter or interface Alters the input signals from some sensors Modifies incoming data so that it can be utilized by the computer Converts analog signals to digital signals

Output Conditioner Also called a converter or interface Changes output signals from digital to analog Allows the operation of actuators Protects the computer processor from high current

Buffer Serves as a temporary storage area for data Protects internal components from improper data controls the rate of data flow Built into the input conditioner

Microprocessor Integrated circuit capable of analyzing data and calculating appropriate outputs Uses the binary number system to make decisions, comparisons, or calculations Compares input signals to memory data to decide what the outputs should be for maximum efficiency

Computer Data Flow The interaction between the different computers in a vehicle's computer network is referred to as multiplexing

Computer Memory Uses gates that are capable of storing data as voltage charges ICs inside the memory chips will hold the data until needed by the microprocessor

RAM Random access memory Stores information or data temporarily Data is erased if battery power is removed

ROM Read only memory Stores permanent data that cannot be removed from memory Contains calibration tables and lookup tables for the general vehicle make and model

PROM Programmable read only memory Contains permanent data that is more specific than the data stored in ROM engine and transaxle specifications, vehicle weight, and tire size are specifics found in the PROM May be replaced or reprogrammed to upgrade vehicle operation

EPROM Erasable programmable read only memory Can be changed, usually by the manufacturer using special equipment Used for storing odometer readings on an electronic dash display

EEPROM Electrically erasable programmable read only memory Can be altered by the technician in the field Allows the manufacturer to change operating parameters if a performance or driveability problem is discovered

Other Memories Flash erasable programmable read only memory (FEPROM) similar to EEPROMs in all respects Keep alive memory (KAM) memory chip that allows the computer to have an adaptive strategy stores calibration information that enhances vehicle operation as parts wear

Output Drivers Control current flow through the actuators When energized by the computer, drivers ground the actuator circuits, providing actuator operation

Processor-Memory Bus Pathway by which sections of a computer communicate Microprocessor controls this flow of data writes data about vehicle operation into memory and reads data about how the vehicle should operate from memory

Multiple Sensor Inputs Computer system uses inputs from more than one sensor to make most control decisions Fuel injection example: engine coolant temperature sensor signals a cold engine computer would use both speed and temperature signals to increase injector pulse width to enrich the mixture for cold engine operation

Multiple Sensor Inputs

Computer Network Series of computers that control different systems but work together to improve overall vehicle efficiency Shares wires, input signals, and output signals Computers exchange data from sensors to prevent duplication of parts and to reduce wiring

Actuators Devices that allow the computer to do work and alter the operation of other components Actuators may be found anywhere on the modern automobile

Actuator Classifications Actuators can be grouped into the following categories: solenoid relay servo motor display device control module

Actuator Classifications

Actuator Operation When the computer turns on an actuator, it normally provides the device with a ground circuit Current can then operate the actuator

Actuator Operation

Solenoid Operation Computer grounds the solenoid circuit Current flows through the solenoid winding A magnetic field moves the plunger mounted in the solenoid windings Plunger movement is used to operate a device fuel injectors, vacuum valves, door locks, etc.

Solenoid Operation (Automatic Door Locks)

Relay Operation Computer grounds the relay coil windings Low current flows through the relay windings Relay coil field will then pull the mechanical contacts closed, allowing high current to flow to the load

Relay Operation

Servo Motor Operation Computer can ground the motor circuit, turning the motor on and off or reversing motor rotation as needed Some servo motors are simply reversible dc motors these motors turn a threaded mechanism to produce controlled movement of a part

Specific coils can be energized to attract and stop the armature Servo Motor Operation Specific coils can be energized to attract and stop the armature

Specific Actuators Common actuators used on modern vehicles include: Fuel injector solenoid valve that controls fuel flow Fuel pump electric motor-driven pump

Specific Actuators Idle air solenoid Idle speed motor EGR solenoids controls airflow into the engine to control idle speed Idle speed motor reversible dc motor that opens and closes the throttle valve to control idle speed EGR solenoids open and close small ports to control exhaust gas flow back into the engine

Specific Actuators Canister purge solenoids Door lock motors control vacuum flow to draw fuel vapors from the fuel tank into the engine for burning Door lock motors solenoids that move latch mechanisms to lock or unlock the doors Electric seat motors reversible dc motors that move the seat into the desired position

Specific Actuators Ignition coil Ignition module changes low voltage into high voltage, which operates the spark plugs Ignition module uses computer signals to control the operation of the ignition coils