chap31 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 31, the reader should be able to: • Prepare for ASE Electrical/Electronic Systems • • • • (A6) certification test content area “A” (General Electrical/Electronic System Diagnosis) Define electricity Explain the units of electrical measurement Discuss the relationship among volts, amperes, and ohms Explain how magnetism is used in automotive applications Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: ammeter • amperes • atom • bound electrons concentric rings • conductors • conventional theory • coulomb • current electrical potential • electricity • electrochemistry • electrons • electron theory • elements • electromotive force (EMF) free electrons • insulators • ion neutral charge • neutrons • nucleus ohmmeter • ohms Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: peltier effect • photoelectricity • piezoelectricity • positive temperature coefficient (PTC) • potentiometer • protons resistance • resistors • rheostat semiconductors • shells • static electricity thermocouple • thermoelectricity valence shell • volt • voltmeter watt Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The electrical system is one of the most important systems in a vehicle today Every year, more and more components and systems use electricity Technicians who really know and understand automotive electrical and electronic systems will be in great demand Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRICITY Our universe is composed of matter, anything that has mass and  occupies space. All matter is made from slightly over 100  individual components called elements The smallest particle that an element can be broken into and still  retain the properties of that element is known as an atom Figure 31–1 In an atom (left), electrons orbit protons in the nucleus just as planets orbit the sun in our solar system (right) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Electricity is the movement of electrons from one atom to another.  The dense center of each atom is called the nucleus. The nucleus  contains protons, which have positive charge, and neutrons,  electrically neutral (no charge) Electrons surround the nucleus in orbits. Each atom contains an  equal number of electrons and protons Because the number of negative­charged electrons is balanced with  the same number of positive­charged protons, an atom has a neutral  charge (no charge) NOTE: As an example of relative sizes of parts of an atom, consider that  if an atom were magnified so that the nucleus were the size of the period at  the end of this sentence, the whole atom would be bigger than a house Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Positive and Negative Charges  Parts of the atom have different  charges. Orbiting electrons are negatively charged, protons  positively charged. Positive charges are indicated by the “plus” sign  (+), and negative charges by the “minus” sign () These same + and  signs are used to identify parts of an electrical circuit.  Neutrons have no charge at all.  They are neutral Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 31–2 The nucleus of an atom has a positive () charge and the surrounding electrons have a negative () charge ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 In a normal, or balanced, atom, the number of negative particles  equals the number of positive particles. The number of neutrons  varies according to the type of atom Figure 31–3 This figure shows a balanced atom Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 An ordinary magnet has two ends, or poles. One end is the south  pole, and the other the north pole If the opposite poles of the magnets are brought close to each other,  south to north, the magnets will snap together because unlike poles  attract each other If two magnets are brought close to each other with like poles  together (south to south or north to north), the magnets will push  each other apart. This is because like poles repel each other Figure 31–4 Unlike charges attract and like charges repel Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 10 Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 31–20 A display at the Henry Ford Museum in Dearborn, Michigan, that includes a handcranked generator and a series of light bulbs This figure shows a young man attempting to light as many bulbs as possible The crank gets harder to turn as more bulbs light because it requires more power to produce the necessary watts of electricity Watts A watt is the electrical  unit for power, the capacity to  do work. Named for Scottish  inventor, James Watt (1736– 1819) The symbol for power is P. Electrical power is calculated as  amperes times volts: P (power) = I (amperes)  E (volts) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 29 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SOURCES OF ELECTRICIY There are several sources of electrical energy, but only a few of them are  used in automotive electrical systems Friction When certain different materials are rubbed together, the  friction causes electrons to be transferred from one to the other.  Both materials become electrically charged These charges are not in motion but stay on the surface where they  were deposited. Because the charges are stationary, or static, this  type of voltage is called static electricity Vehicle tires rolling on pavement often create static electricity that  interferes with radio reception 30 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Heat  When pieces of two metals are joined together at both ends  and one junction is heated, current passes through the metals. Only  millionths of an ampere, but enough to use in a temperature­ measuring device called a thermocouple.  Figure 31–21 Electron flow is produced by heating the connection of two different metals Some engine temperature  sensors operate in this  manner This form of voltage is  called thermoelectricity 31 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 In 1823, German physicist Thomas Johann Seebeck discovered that  voltage was developed in a loop containing two dissimilar metals,  provided the junctions were maintained at different temperatures A decade later, French scientist Jean Charles Peltier found electrons  moving through a solid can carry heat from one side of the material  to the other side. This effect is called the Peltier effect A Peltier effect device is often used in portable coolers to keep food  items cool if the current flows in one direction and to keep items  warm if the current flows in reverse 32 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Light  In 1839, Edmond Becquerel noticed that shining a beam of  sunlight over two different liquids developed electric current When certain metals are exposed to light, some light energy is  transferred to free electrons of the metal. This excess energy breaks  electrons loose from the metal. They can be collected and made to  flow in a conductor Photoelectricity is  widely used in light­ measuring devices  such as photographic  exposure meters and  automatic headlamp  dimmers Figure 31–22 Electron flow is produced by light striking a light-sensitive material Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 33 Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Pressure  The first demonstration of a connection between  macroscopic piezoelectric phenomena and crystallographic structure  was published in 1880 by Pierre and Jacques Curie.  When  subjected to pressure, certain crystals, such as quartz, develop a  potential difference, or voltage, on the crystal faces. This current is  used in phonograph pickups, crystal microphones, underwater  hydrophones, and certain stethoscopes.  The voltage created is called piezoelectricity Some automobile engine control sensors, such as the knock sensor (KS), use piezoelectricity to create voltage or to vary resistance and control a computer input signal Figure 31–23 Electron flow is produced by pressure on certain crystals Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 34 Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Chemistry Two different materials (usually metals) placed in a  conducting and reactive chemical solution create a difference in  potential, or voltage, between them. This principle is called  electrochemistry and is the basis of the automotive battery Conductors and Resistance  All conductors have some resistance  to current flow. Several principles of conductors and their resistance  include the following: If the conductor length is doubled, its resistance doubles   This is why battery cables are designed as short as possible If the conductor diameter is increased, resistance is reduced   This is the reason starter motor cables are larger in diameter  than other wiring in the vehicle See Chapter 7 for further details on wiring sizes 35 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 As the temperature increases, the resistance of the  conductor also increases  This is the reason for installing heat  shields on some starter motors. The shield helps protect the  conductors (copper wiring inside the starter) from excessive  engine heat and reduces resistance of starter circuits. Because  a conductor increases in resistance with increased temperature,  the conductor is called a positive temperature coefficient  (PTC) resistor Materials used in the conductor have an impact on its  resistance  Silver has the lowest resistance of any conductor,  but is expensive. Copper is the next lowest in resistance and it  is reasonably priced See the following chart for a comparison of materials 36 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 CONDUCTION CHART Starting with the best… Silver Copper Gold Aluminum Tungsten Zinc Brass (copper and zinc) Platinum Iron 10 Nickel 11 Tin 12 Steel 13 Lead See this chart on Page 323 of your textbook.  37 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Resistors Resistance is opposition to current flow. Resistors  represent an electrical load, or resistance, to current flow Figure 31–24 This figure shows a resistor color code interpretation Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 38 Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Most electrical and electronic devices use resistors of specific  values to limit and control the flow of current Resistors can be made from carbon or from other materials that  restrict the flow of electricity and are available in various sizes and  resistance values Most resistors have a series of painted color bands around them.  These color bands are coded to indicate the degree of resistance Figure 31–25 This figure shows a typical carbon resistor Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 39 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Variable Resistors  Two types of mechanically operated variable  resistors are used in automotive applications. A potentiometer is a  three­terminal variable resistor where the majority of the current  flow travels through the resistance of the unit and a wiper contact  provides a variable voltage output.  Figure 31–26 A three-wire variable resistor is called a potentiometer Potentiometers are most commonly used as throttle position (TP)  sensors on computer­equipped engines Continued 40 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Another type of mechanically operated variable resistor is the  rheostat. A rheostat is a two­terminal unit in which all of the  current flows through the movable arm. A rheostat is commonly  used for a dash light dimmer control Figure 31–27 A two-wire variable resistor is called a rheostat Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 41 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Electricity is movement of electrons from one atom to another Automotive electricity uses the conventional theory of current  flow (electricity flows from positive to negative) The ampere is the measure of the amount of current flow Voltage is the unit of electrical pressure The ohm is the unit of electrical resistance Sources of electricity include: friction, heat, light, pressure, and  chemical Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 42 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 43 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458