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OBJECTIVES

OBJECTIVES. After studying Chapter 11, the reader will be able to: Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic Systems Diagnosis). Explain the purpose and function of onboard computers.

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OBJECTIVES

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  1. OBJECTIVES After studying Chapter 11, the reader will be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic Systems Diagnosis). • Explain the purpose and function of onboard computers. • List the various parts of an automotive computer. • List five input sensors. • List four devices controlled by the computer (output devices).

  2. COMPUTER CONTROL • Modern automotive control systems consist of a network of electronic sensors, actuators, and computer modules designed to regulate the powertrain and vehicle support systems. • The powertrain control module (PCM) is the heart of this system. • It coordinates engine and transmission operation, processes data, maintains communications, and makes the control decisions needed to keep the vehicle operating.

  3. THE FOUR BASIC COMPUTER FUNCTIONS • The operation of every computer can be divided into four basic functions. • Input • Processing • Storage • Output FIGURE 11-1 All computer systems perform four basic functions: input, processing, storage, and output.

  4. THE FOUR BASIC COMPUTER FUNCTIONS FIGURE 11-2 A potentiometer uses a movable contact to vary resistance and send an analog voltage right to the PCM.

  5. 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 is limited to two voltage levels: high voltage and low voltage. FIGURE 11-3 Many electronic components are used to construct a typical vehicle computer. Notice the quantity of chips, resistors, and capacitors used in this General Motors computer.

  6. DIGITAL COMPUTERSParts of a Computer • The software consists of the programs and logic functions stored in the computer’s circuitry. • The hardware is the mechanical and electronic parts of a computer. • Central Processing Unit (CPU). • Computer Memory.

  7. DIGITAL COMPUTERSComputer Programs • By operating a vehicle on a dynamometer and manually adjusting the variable factors such as speed, load, and spark timing, it is possible to determine the optimum output settings for the best driveability, economy, and emission control. • This is called engine mapping. FIGURE 11-4 Typical ignition timing map developed from testing and used by the vehicle computer to provide the optimum ignition timing for all engine speeds and load combinations.

  8. DIGITAL COMPUTERSComputer Programs FIGURE 11-5 A replaceable PROM used in a General Motors computer. Notice that the sealed access panel has been removed to gain access.

  9. DIGITAL COMPUTERSClock Rates and Timing • The microprocessor receives sensor input voltage signals, processes them by using information from other memory units, and then sends voltage signals to the appropriate actuators. FIGURE 11-6 The clock generator produces a series of pulses that are used by the microprocessor and other components to stay in step with each other at a steady rate.

  10. DIGITAL COMPUTERSComputer Speeds • Not all computers operate at the same speed; some are faster than others. • The speed at which a computer operates is specified by the cycle time, or clock speed, required to perform certain measurements. • Cycle time or clock speed is measured in megahertz (4.7 MHz, 8.0 MHz, 15 MHz, 18 MHz, etc.).

  11. DIGITAL COMPUTERSBaud Rate • The computer transmits bits of a serial data stream at precise intervals. • The computer’s processing speed is called the baud rate, or bits per second.

  12. DIGITAL COMPUTERSControl Module Locations • The onboard automotive computer has many names. • It may be called an electronic control unit (ECU), electronic control module (ECM), electronic control assembly (ECA), or a controller, depending on the manufacturer and the computer application. FIGURE 11-7 This powertrain control module (PCM) is located under the hood on this Chevrolet pickup truck.

  13. DIGITAL COMPUTERSControl Module Locations FIGURE 11-8 This PCM on a Chrysler vehicle can only be seen by hoisting the vehicle because it is located next to the radiator, and in the airflow to help keep it cool.

  14. COMPUTER INPUT SENSORS • The vehicle computer uses the signals (voltage levels) from the following engine sensors: • Engine speed (RPM or revolutions per minute) sensor. • MAP (manifold absolute pressure) sensor. • MAF (mass airflow) sensor. • ECT (engine coolant temperature) sensor. • O2S (oxygen sensor). • TP (throttle position) sensor. • VS (vehicle speed) sensor. • Knock sensor.

  15. COMPUTER OUTPUTS • A vehicle computer can do just two things. • Turn a device on. • Turn a device off. • Typical output devices include the following. • Fuel injectors. • Ignition timing. • Transmission shifting. • Idle speed control. • Evaporative emission control solenoids.

  16. FUEL CONTROL SYSTEM OPERATING MODES • A computer-controlled fuel metering system can be selective. • Depending on the computer program, it may have different operating modes. • The onboard computer does not have to respond to data from all of its sensors, nor does it have to respond to the data in the same way each time. • Under specified conditions, it may ignore sensor input. • Or, it may respond in different ways to the same input signal, based on inputs from other sensors. • Most current control systems have two operating modes: open and closed loop.

  17. SUMMARY • The Society of Automotive Engineers (SAE) standard J-1930 specifies that the term powertrain control module (PCM) be used for the computer that controls the engine and transmission in a vehicle. • The four basic computer functions include input, processing, storage, and output. • Read-only memory (ROM) can be programmable (PROM), erasable (EPROM), or electrically erasable (EEPROM). • Computer input sensors include engine speed (RPM), MAP, MAF, ECT, O2S, TP, and VS. • A computer can only turn a device on or turn a device off, but it can do the operation very rapidly.

  18. REVIEW QUETSIONS • What part of the vehicle computer is considered to be the brain? • What is the difference between volatile and nonvolatile RAM? • List four input sensors. • List four output devices.

  19. CHAPTER QUIZ • What unit of electricity is used as a signal for a computer? • Volt • Ohm • Ampere • Watt

  20. CHAPTER QUIZ • What unit of electricity is used as a signal for a computer? • Volt • Ohm • Ampere • Watt

  21. CHAPTER QUIZ 2. The four basic computer functions include _____. • Writing, processing, printing, and remembering • Input, processing, storage, and output • Data gathering, processing, output, and evaluation • Sensing, calculating, actuating, and processing

  22. CHAPTER QUIZ 2. The four basic computer functions include _____. • Writing, processing, printing, and remembering • Input, processing, storage, and output • Data gathering, processing, output, and evaluation • Sensing, calculating, actuating, and processing

  23. CHAPTER QUIZ 3. All OBD II vehicles use what type of read-only memory? • ROM • PROM • EPROM • EEPROM

  24. CHAPTER QUIZ 3. All OBD II vehicles use what type of read-only memory? • ROM • PROM • EPROM • EEPROM

  25. CHAPTER QUIZ 4. The “brain” of the computer is the _____. • PROM • RAM • CPU • AD converter

  26. CHAPTER QUIZ 4. The “brain” of the computer is the _____. • PROM • RAM • CPU • AD converter

  27. CHAPTER QUIZ 5. Computer processing speed is measured in _____. • Baud rate • Clock speed (Hz) • Voltage • Bytes

  28. CHAPTER QUIZ 5. Computer processing speed is measured in _____. • Baud rate • Clock speed (Hz) • Voltage • Bytes

  29. CHAPTER QUIZ • Which item is a computer input sensor? • RPM • Throttle position angle • Engine coolant temperature • All of the above

  30. CHAPTER QUIZ • Which item is a computer input sensor? • RPM • Throttle position angle • Engine coolant temperature • All of the above

  31. CHAPTER QUIZ 7. Which item is a computer output device? • Fuel injector • Transmission shift solenoid • Evaporative emission control solenoid • All of the above

  32. CHAPTER QUIZ 7. Which item is a computer output device? • Fuel injector • Transmission shift solenoid • Evaporative emission control solenoid • All of the above

  33. CHAPTER QUIZ 8. The SAE term for the vehicle computer is _____. • PCM • ECM • ECA • Controller

  34. CHAPTER QUIZ 8. The SAE term for the vehicle computer is _____. • PCM • ECM • ECA • Controller

  35. CHAPTER QUIZ 9. What two things can a vehicle computer actually perform (output)? • Store and process information • Turn something on or turn something off • Calculate and vary temperature • Control fuel and timing only

  36. CHAPTER QUIZ 9. What two things can a vehicle computer actually perform (output)? • Store and process information • Turn something on or turn something off • Calculate and vary temperature • Control fuel and timing only

  37. CHAPTER QUIZ 10. Analog signals from sensors are changed to digital signals for processing by the computer through which type of circuit? • Digital • Analog • AD converter • PROM

  38. CHAPTER QUIZ 10. Analog signals from sensors are changed to digital signals for processing by the computer through which type of circuit? • Digital • Analog • AD converter • PROM

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