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8/7/2019 Computer Fundamentals (Toyota)

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TOYOTA COURSE 852: ENGINE CONTROL SYSTEMS 1

Chapter 11

Automotive Fuel and Emission Control Systems

Computer Fundamentals


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Chapter 11 Computer Fundamentals


Computer Control Modern automotive control systems consist of a network of electronic

sensors, actuators, and computer modules designed to regulate thepowertrain and vehicle support systems.

The powertrain control module (PCM) is the heart of this system. Automotive computers use voltage to send and receive information.

Voltage is electrical pressure and does not flow through circuits, butvoltage can be used as a signal. A computer converts input informationor data into voltage signal combinations that represent number

combinations. A computer processes the input voltage signals it receives bycomputing what they represent, and then delivering the data incomputed or processed form.


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The Four Basic Computer Functions The operation of every computer can be divided into four basic

functions. Input

Each sensor transmits its information in the form of voltagesignals.

Processing Input voltage signals received by a computer are processed

through a series of electronic logic circuits maintained in itsprogrammed instructions. These logic circuits change the inputvoltage signals, or data, into output voltage signals orcommands.


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The Four Basic Computer Functions (continued) Storage

Computers have two types of memory: permanent andtemporary. Permanent memory is called read-only memory(ROM) because the computer can only read the contents. Thisdata is retained even when power to the computer is shut off.Part of the ROM is built into the computer, and the rest islocated in an IC chip called a programmable read-only memory(PROM) or calibration assembly.

Temporary memory is called random-access memory (RAM)because the microprocessor can write or store new data into itas directed by the computer program, as well as read the dataalready in it. Automotive computers use two types of RAM

memory: volatile and nonvolatile. Volatile RAM memory is lost whenever the ignition is turned off.However, a type of volatile RAM called keep-alive memory(KAM) can be wired directly to battery power.

Nonvolatile RAM memory can retain its information even whenthe battery is disconnected.


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The Four Basic Computer Functions (continued) Output

After the computer has processed the input signals, it sendsvoltage signals or commands to other devices in the system,such as system actuators. An actuator is an electrical ormechanical device that converts electrical energy into amechanical action, such as adjusting engine idle speed,altering suspension height, or regulating fuel metering.


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Digital Computers In a digital computer, the voltage signal or processing function is a

simple high/low, yes/no, on/off signal. The digital signal voltage islimited to two voltage levels: high voltage and low voltage.

The signal is called digital because the on and off signals areprocessed by the computer as the digits or numbers 0 and 1. Thenumber system containing only these two digits is called the binarysystem.

A digital computer changes the analog input signals (voltage) to digitalbits (binary digits) of information through an analog-to-digital (AD)converter circuit.

Parts of a computer Central Processing Unit (CPU). The microprocessor is the central

processing unit of a computer. Computer memory Computer programs


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Digital Computers (continued) Clock rates and timing

The microprocessor must have some way of knowing when onesignal ends and another begins. That is the job of a crystaloscillator called a clock generator.

C C


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Reference Voltage Vehicle computers apply a 5-volt reference voltage to the following

sensors: Throttle position (TP) sensor Manifold absolute pressure (MAP) sensor Barometric pressure (BARO) sensor Fuel tank pressure (TFP) sensor

This reference voltage is commonly referred to as the V-ref.


9/20TOYOTA COURSE 852: ENGINE CONTROL SYSTEMS 9

Computer FundamentalsComputer Fundamentals

The Big Seven:

Inputs that indicate engineoperating conditions



Basic Information the PCM

needs:

Basic Information the PCM

needs:

Airflow Coolant Temperature

Engine Speed/ Crank Position Camshaft Position

Exhaust Oxygen Content

Intake Air Temperature

Throttle Position



Basic Inputs:Basic Inputs:

Major Inputs:

Engine Speed Airflow

Correction Inputs (fuel trim):

CMP

CTS

IAT 02S

TPS



Major Outputs:Major Outputs:

Injector Pulse Width

Ignition Spark Output

Idle Speed Control

Long Term Fuel Trim Correction



BASIC AIR INDUCTION SYSTEMBASIC AIR INDUCTION SYSTEM



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BASIC FUEL INJECTION SYSTEMBASIC FUEL INJECTION SYSTEM



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BASIC IGNITION SYSTEMBASIC IGNITION SYSTEM


BASIC ELECTRONIC ENGINEBASIC ELECTRONIC ENGINE


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BASIC ELECTRONIC ENGINECONTROL SYSTEM

BASIC ELECTRONIC ENGINECONTROL SYSTEM



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INPUTSINPUTS



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ECM PROCESSING FUNCTIONECM PROCESSING FUNCTION



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OUTPUT ACTUATORS AND DEVICESOUTPUT ACTUATORS AND DEVICES




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CHAPTER SUMMARY

1. The Society of Automotive Engineers (SAE) standard J-1930 specifies thatthe term powertrain control module (PCM) be used for the computer thatcontrols the engine and transmission in a vehicle.

2. The four basic computer functions include input, processing, storage, andoutput.

3. Read-only memory (ROM) can be programmable (PROM), erasable(EPROM), or electrically erasable (EEPROM).

4. Computer input sensors include engine speed (RPM), MAP, MAF, ECT,

O2S, TP, and VS.

5. A computer can only turn a device on or turn a device off, but it can do theoperation very rapidly.