Automotive Electronic Circuits

SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.QUESTIONS REGARDING THIS DOCUMENT: (412) 772-8512 FAX: (412) 776-0243TO PLACE A DOCUMENT ORDER; (412) 776-4970 FAX: (412) 776-0790http:\\Copyright 1995 Society of Automotive Engineers, Inc.3.Definitions—For general definitions, see SAE J1113-1.4.Test Equipment—The test apparatus shall consist of the following:4.1Signal Source—Any signal source and power amplifier capable of supplying approximately 50 W ofmodulated or unmodulated power to develop the immunity levels specified in the test plan shall be used, provided the following requirements are met:a.Residual FM shall be less than 10 Hzb.Frequency resolution shall be less than 100 Hzc.Harmonics and spurious outputs shall not be more than −20 dB when referred to the fundamentalpower4.2RF Voltmeter—An RF voltmeter capable of measuring 100 V up to 10 MHz.4.3In-Line directional coupler with an RF wattmeter capable of measuring 50 W up to the maximum frequency inuse.4.4Field Strength Meter—A RF field strength meter capable of measuring 200 V/m up to 200 MHz.4.5Strip line—An example construction of a strip line is shown in Appendix A.5.Test SetupCAUTION—Hazardous voltages and fields exist on and near the strip line when the equipment is energized.Test personnel should ensure that no one is in the test chamber during a test.5.1Test setup should be as shown in Figures 1 and 2.The DUT is installed next to and parallel to the strip line. The distance between the closest edges of the driven conductor and the DUT shall be 200 mm (+20 −0 mm).The distance from any peripheral device to the closest edge of the driven conductor shall be at least 200 mm. 5.2The DUT wire harness should be placed in a nonconductive fixture in the center of the strip line, parallel to itsmajor axis, supported midway between the plates. Note that the primary function of the fixture is to lock the positions of the harness and DUT to ensure the most repeatable results and should be constructed with this in mind. This non-conductive fixture shall be constructed of material with a very low dielectric constant (e.g., polystyrene or equivalent εR≤ 1.4). The length of the harness section under the active conductor shall be at least 1.5 m. Deviations of the height above the ground plane are only permitted near the DUT or the peripheral device. Peripheral devices are to be bonded to the ground plane, if possible.When peripheral devices are used for operating or monitoring the DUT, they should be the original vehicle devices, if possible. The original peripheral devices are placed on the ground plane, and electrically/ mechanically bonded to it as in the vehicle application.The power supply shall be equipped with an adequate filter to prevent overloading the front end regulator by induced RF current. The impedance of this filter, as seen from the DUT, shall correspond to the vehicle power supply system impedance as close as possible.FIGURE 1—STRIP LINE TEST CONFIGURA TIONFIGURE 2—TEST SETUP FOR A STRIP LINEThe remaining peripheral devices can be installed in one of three ways depending on their size and inherent RF immunity.a.Outside of the shielded testing chamberb.Shielded and filtered, in the shielded testing chamberc.In the case of exclusively passive periphery (resistors, capacitors, coils, ferrites, mechanical switches,etc.) or radiation resistant periphery, unshielded and unfiltered in the shielded testing chamber Lines fed through the wall of the shielded testing chamber shall be equipped with adequate RF filters at the wall. This prevents these lines from emitting significant radiation outside of the testing chamber, and possibly influencing the external measuring system, or causing other interference.5.3When a DUT or peripheral device with a metal housing used for the measurement are electrically connecteddirectly to the vehicle mass (by screws, rivets, etc.), they shall be bonded to the ground plane by a low inductance connection.When the DUT or peripheral is not electrically connected directly to the vehicle mass, they shall be placed on an insulating support. This insulating support shall be constructed of material with a low dielectric constant(e.g., foamed polystyrene or equivalent 1 ≤εR≤ 1.4) and shall have the same height as the insulating supporton which the wire harness is installed.6.Test Procedure—Three test configurations are feasible; exposure of the wiring harness alone, exposure of theDUT alone, or exposure of both the harness and DUT together.6.1Exposure of Wiring Harness Alone—This is the most commonly used test configuration permitting thewidest frequency range of testing. The RF fields induced in the harness couple into the DUT using the harness wiring as 'antennas' for the received signal. When the strip line is used above the frequency where the wavelength of the wave is less than twice the length of the strip line, the length of cable is sufficiently long to ensure that the field is 'integrated' or 'averaged' along the cable thus producing the effect of maintaining a uniform field where, in fact, it is no longer uniform.6.2Exposure of the DUT Alone—When it is desired to determine DUT immunity directly, the DUT may be placedbetween the driven portion of the strip line and the ground plane with the attached cable harness exiting at 90 degrees to the main axis of the strip line to minimize induction into the wiring harness. Care must be taken to ensure that the physical size of the DUT does not exceed 1/3 of the height between the driven element and the ground plane of the strip line as this may distort the test field.NOTE—Caution must be exercised not to exceed the frequency at which the wavelength exceeds twice the length of the strip line during this type of test as the moving peaks and nodes of the field under the stripline above this frequency may place the DUT in fields which are either much lower or much higher thaninstruments indicate, possibly producing erroneous test results. This requires special agreementbetween the users.6.3Exposure of both the DUT and its Wiring Harness—Both the DUT and its harness may be exposedsimultaneously to the field of the strip line if the provisions of the previous paragraph are taken into account.NOTE—This requires special agreement between the users.6.4Fields should be generated as required in the test plan. The field level is determined using the informationgathered from the directional coupler and power meters in accordance with the method outlined in Appendix A.For calibration purposes, at frequencies of 100 kHz or below, E v can be measured by using an RF voltmeter connected across the elements of the line. For calculation of the field under the strip line, see Appendix A. 6.5The strip line shall be excited in accordance with the frequency and modulation information supplied inJ1113-1.7.Test Severity Levels7.1 A full description and discussion of the Function Performance Status Classification including Test SeverityLevels are given in SAE J1113-1 Appendix A. Please review it prior to using the suggested Test Severity Levels presented in Appendix B.8.Notes and Special Considerations8.1For most designs of a strip line, the field strength is uniform (±2 dB) along its length up to approximately200MHz. Above 200 MHz, the uniformity degrades. The field will vary along the length of the strip line as the frequency increases. These characteristics must be considered when determining how to set up the field strength at higher frequencies.8.2Limit the size of the DUT to no more than 1/3 of the space between the active conductor and the ground plane.If this parameter is exceeded, the test field will be perturbed resulting in a stronger field than that indicated by the measured forward power.8.3Since the RF field is not fully contained, the test must be performed in a shielded room with the generating andmonitoring equipment outside the room. Energy radiated from the strip line into the shielded room will create standing wave patterns which may affect the net field strength about the test object and/or cable harness.These standing waves will be quite noticeable at frequencies where the shielded room dimensions support a cavity resonance.This effect can be reduced significantly by installing RF absorbing panels between the strip line and the walls.These panels absorb the energy radiated from the strip line (especially at frequencies where the wavelength of the frequency is more than twice the length of the strip line) and therefore reduce the influence of any reflections from the walls of the shielded room and dampen the cavity resonance effects.PREPARED BY THE SAE EMI STANDARDS AND TEST METHODS COMMITTEEAPPENDIX A(INFORMATIVE)STRIP LINE TEST THEORYA.1 A strip line sets up a region of uniform electric and magnetic fields between the ground plane and a drivenelement suspended above the ground plane. The primary usage of the strip line is to expose at least 1.5 m of the wire harness feeding the Device Under Test (DUT) to RF fields. (See Figure 1.)Because the wire harness typically is oriented longitudinally along the length of the strip line, both the E and H fields are coupled into the wire harness. (See Figure A1.)FIGURE A1—E AND H FIELD DISTRIBUTION IN A STRIP LINEThe equations for this coupling for a 377 Ω field are shown as follows:(Eq. A1)(Eq. A2)(Eq. A3)Vi 2πfhL µH ()=Vi 2πfhLx µE 377--------- =Vi E -----2h πL λ------ sin =where:Vi = Voltage Induced in lineL = Length of linef = Frequencyh = Height of harness above ground planeH = Magnetic FieldE = Electric FieldIn practice, the fields generated will be uniform only for frequencies for which the wavelength is much longer than the strip line length (i.e., the wavelength is at least two (2) times the length of the strip line). The use of a straight length of cable or harness within the strip line is required to integrate fields above the frequencies where the length of the wave is much less than the length of the harness exposed to the fields. It is also recommended that the test be performed using the actual harness, where practical, connected to the actual loads at each end. Several different lengths of harness may be used to more fully characterize the system behavior to EMI.A.2Strip Line Construction—The construction of a strip line is shown in Figures A2, A3, A4, and A5. The Ldimension shall be at least 2 m. The ratio of W to h determines the characteristic impedance according to Equation A4:(Eq. A4)where:W is the Strip line active conductor widthh is the Strip line active conductor height above the ground planeπ is approximately equal to 3.14159Given a specific example with:strip line width—W = 0.740 m.strip line height—h = 0.15 m.Equation A1 gives an impedance of Z = 50.125 Ω.NOTE—See M.V . Schneider, "Micro Striplines for Microwave Integrated Circuits," Systems Technical Journal48 #5, May-June 1969.Typical strip line fixtures are constructed to be either 50 Ω or 90 Ω with W/h equal to 5 and 1.75 respectively.Termination may be either a matched resistive load or by a tapered matching section terminated in a 50 Ωcoaxial resistive load. A resistive load can be constructed of carbon resistors, conductive strips, thick film on a ceramic substrate, etc., such that it matches the characteristic impedance of the strip line minimizing the standing waves. Both ends of the strip line should be 'tuned' using a network analyzer or time domain reflectometer to ensure a reasonably smooth match between test section of the strip line and the feed and termination points.Z 120x πW h ----- 2.420.44x h W ----- –1h W -----–6++-------------------------------------------------------------------------------------------for W/h 1.>=FIGURE A2—DIMENSIONS FOR A 50 Ω STRIP LINEFIGURE A3—FEED POINT DETAILSFIGURE A4—RESISTOR CARD TERMINATIONFIGURE A5—THICK FILM RESISTOR TERMINATIONIf the strip line is set up carefully so as to minimize reflections and maintain the system VSWR at less than or equal to 1.4:1, then only the forward power into the directional coupler needs to be measured to determine field strength. A sample calculation of strip line impedance and a plot of the field strength is shown in Figure A6. The presence of a normal wiring harness placed in the Strip line for test will not significantly alter the performance of the Strip line.NOTE—It is also necessary to measure the VSWR of the strip line with any large DUT in place.As an alternative to direct measurement of the impressed field, a calibration with an empty strip line (no harness or DUT) based upon the RMS value of the field can provide field information which will be valid for all modulations and will not be influenced by reflections from a harness or a DUT.FIGURE A6—STRIP LINE FIELD VERSUS NET POWERAPPENDIX B(NORMATIVE)TEST SIGNAL SPECIFICATIONS AND RECOMMENDED TEST LEVELSB.1Unless otherwise required in the equipment specification or approved plan, the test signals shall be setupaccording to the guidelines in SAE J1113-1. The theory of the operation of the strip line is contained in Appendix A.The suggested minimum and maximum severity levels are given in Figure B1. Testing at other levels may be chosen based on agreement between the customer and the supplier.FIGURE B1—SUGGESTED TEST LEVELSAPPENDIX C(INFORMATIVE)STRIP LINE FIELD CALCULATIONC.1The field under the driven element of the strip line is determined by measuring the forward power into thedirectional coupler and determining the field by using Equation C1:(Eq. C1)where:P is the RF power into the 50 Ω line feeding the strip lineZ is the Characteristic impedance of strip line (see Appendix A.)h is the height of active conductor above ground planeAn example of the field plot that would result from the example of a 50 Ω line is shown in Figure A6.NOTE—As a check, the strip line field below 100 kHz may be found by using Equation C2:(Eq. C2)where:E v is the Field strengthh is the height of active conductor above ground planeV rf is the RF Voltmeter reading across the septum-ground plane gapA small RF field probe may be used to verify the calculated calibration curve between the RF power into the strip line and the field in the uniform field region at frequencies below which the wavelength is less than twice the length of the strip line. The position of the field probe shall be as close as possible to the middle of the empty strip line (no harness or DUT in place) and referenced to the longitudinal and transverse axes under the strip line.Typically, the strip line field is measured only by the first method (Equation C1), which is valid over the entire frequency range. The second method (Equation C2) is only used as a check against the first.E v PxZ h --------------Volts meter ⁄=E v V rf h ------=Rationale—This SAE Recommended Practice provides a convenient method for testing automotive electronic modules and harnesses with easy access into and out of the physical test area. It is particularly suitable for small and medium size electronic components which would be difficult or impossible to test in either a Strip line or TEM cell fixture.Relationship of SAE Standard to ISO Standard—This SAE Recommended Practice is aligned with ISO Standards. The SAE through the EMI and EMR Standards Committees has been an active participant in the development of these International standards.Application—This procedure covers the recommended testing techniques for the determination of electric field immunity of an automotive electronic device. This technique uses a strip line 2 from 10 kHz to 200 MHz and is limited to exposing the harnesses (and/or devices) which have a maximum height of equal to or less than 1/3 the strip line height.This method is being replaced by the Tri-plate Line (SAE J1113-25) which is considered to be a superior test method. It will be retained for historical purposes for a period of 5 years where upon it will be considered to be withdrawn.Reference Section—For general references, see SAE J1113-1.SAE J1113-1—Electromagnetic Compatibility Measurement Procedures and Limits for Vehicle Components (Except Aircraft) (60 Hz to 18 GHz)SAE J1113-25—Electromagnetic Compatibility Measurement Procedure for Vehicle Components—Immunity to Radiated Electromagnetic Fields, 10 kHz to 500 MHz—Tri-Plate Line MethodM.V. Schneider, "Micro Striplines for Microwave Integrated Circuits," Systems Technical Journal 48 #5, May-June 1969Clayton R. Paul, "Literal Solutions for the Time-Domain Response of a Two-Conductor Transmission Line Excited by an Incident Electromagnetic Field," IEEE Transactions on Electromagnetic CompatibilityMay 1995, Volume 37, Number 2, IEMCAE (ISSN 0018-9375)Developed by the SAE EMI Standards and Test Methods Committee2.Strip line in this document refers to a giant version of an unbalanced parallel plate 'micro strip line' with a single driven plate above a groundplane. See Figure 1 for a physical description of this configuration.。

三极管复合管的四种类型英文回答：Types of Transistor Hybrid Circuits.Transistor hybrid circuits, also known as hybrid integrated circuits, are electronic circuits that combine transistors with other discrete components such as resistors, capacitors, and inductors. These circuits are often used in applications where the performance requirements cannot be met by either transistors ordiscrete components alone.There are four main types of transistor hybrid circuits:Thin-film hybrids: These circuits are fabricated on a thin film of insulating material, such as ceramic or glass. The transistors and other components are deposited on the substrate using a variety of techniques, such as evaporation, sputtering, or electroplating. Thin-filmhybrids offer a number of advantages, including small size, high reliability, and excellent electrical performance.Thick-film hybrids: These circuits are fabricated on a thick film of insulating material, such as alumina or epoxy. The transistors and other components are mounted on the substrate using a variety of techniques, such as solder, epoxy, or wire bonding. Thick-film hybrids offer a numberof advantages, including low cost, high reliability, and good electrical performance.Multi-chip hybrids: These circuits are fabricatedusing multiple chips, which are interconnected using wiresor other conductive materials. The chips can be ofdifferent types, such as transistors, resistors, capacitors, or inductors. Multi-chip hybrids offer a number of advantages, including high performance, small size, and low cost.MCM hybrids: These circuits are fabricated on a multi-chip module (MCM), which is a small, high-density circuit board. The MCM is typically made of a ceramic or metalsubstrate, and the transistors and other components are mounted on the substrate using a variety of techniques, such as solder, epoxy, or wire bonding. MCM hybrids offer a number of advantages, including small size, highreliability, and excellent electrical performance.Transistor hybrid circuits are used in a wide variety of applications, including:Automotive electronics: Transistor hybrid circuits are used in a variety of automotive applications, such as engine control modules, anti-lock brake systems, and airbag controllers.Consumer electronics: Transistor hybrid circuits are used in a variety of consumer electronics products, such as televisions, radios, and DVD players.Industrial electronics: Transistor hybrid circuits are used in a variety of industrial applications, such as programmable logic controllers, process controllers, and power supplies.Military electronics: Transistor hybrid circuits are used in a variety of military applications, such as radar systems, communications systems, and guidance systems.中文回答：三极管复合管的四种类型。

电子信息工程专业主要课程简介1G10125 电路分析学分：4.0 Circuit Analysis预修课程：高等数学，大学物理内容简介：本课程的任务主要是讨论线性、集中参数、非时变电路的基本理论与一般分析方法，使学生掌握电路分析的基本概念、基本原理和基本方法，提高分析电路的思维能力与计算能力，以便为学习后续课程奠定必要的基础。

推荐教材：《电路分析》，胡翔骏、黄金玉，高等教育出版社，2001年主要参考书：《电路》（第四版），邱关源，高等教育出版社，1999年，“九五”重点教材1G10447 信号与系统学分：4.0 Signal & System预修课程：电路分析、工程数学内容简介：信号与系统是通信和电子信息类专业的核心基础课，其中的概念和分析方法广泛应用于通信、自动控制、信号与信息处理、电路与系统等领域。

本课程中通过信号分解、连续系统时域分析、频域分析、复频域分析和离散系统时域分析、变换域分析方法的学习，培养思维能力，为后续课程打下必要的理论基础。

推荐教材：《信号与系统教程》，燕庆明，高等教育出版社，2004年主要参考书：《信号与系统》，郑君里，高等教育出版社，2000年1G10295模拟电子技术学分：4.0 Analog Electronic Technology预修课程：高等数学、电路分析内容简介：模拟电子技术是电子信息工程专业最主要的专业基础课之一，主要讲授晶体二极管、晶体三极管和场效应管的基本原理和工作特性，重点分析放大器的工作原理，使学生能充分理解基本放大器、多级放大器、负反馈放大器和低频功率放大器的交流和直流特性及其简单应用，并在其基础上了解集成运算放大器的结构，着重掌握集成运算放大器的各种应用。

对于直流稳压电源主要了解其组成和各部分功能及典型电路。

模拟集成电路应用主要讲解常用模拟集成电路，如NE555的各种应用。

推荐教材：《模拟电子技术》，邬国扬等编，西安电子科技大学出版社，2002年主要参考书：《电子技术基础模拟部分》（第四版），康华光等编，高等教育出版社，1999年1G10335数字电子技术学分：3.0 Digital Electronic Technology预修课程：高等数学、电路分析、模拟电子技术内容简介：数字电子技术是电子信息工程专业最主要的专业基础课之一，首先讲授逻辑代数和门电路，使学生掌握基本逻辑代数的运算和基本门电路组成结构。

附录1:英文文献AUTO ELECTRIC APPLIANCES1、Starting SystemAutomobile engines are not self-starts. In order to start them, the engine crankshaft must be turned over. To do this, the starter motor receives electrical power form the storage battery. The starter motor then converts this energy into mechanical energy, which it transmits through the drive mechanism to the engine’s fly wheel.The starter motor draws a great deal of electrical current from the battery. A large starter motor might require 300 to 400 amperes of current. This current flows through the heavy gauge cables that connect the battery to the starter.The drive controls the flow of this current using the starting switch. However, if the cables were routed from the battery to the starting switch and then on to the starter motor, the voltage drop caused b resistance in the cables would be too great. To avoid this problem, the system is designed with two connected circuits: the starter circuit and the control circuit.1.1 The starting safety switchThe starting safety switch is also called a neutral start switch. It is a normally open switch that prevents the starting system from opening when the automobile’s transmission is in gear. If the car has no starting safety switch, it is possible to spin the engine with the transmission in gear. This will make the car lurch forward or backward which could be dangerous. Safety switches or interlock devices are used with all automatic transmissions and on many late-model cars with manual transmissions. The safety switch can be an electrical switch that opens the control circuit if the car is in gear. It can also be a mechanical interlock device that will not let the ignition switch turn to start if the car is in the gear.1.2 Magnetic Switch (Relays and Solenoids)A magnetic switch in the starting system allows the control circuit to open and close the starter circuit. The switch can be a:(1)Relay which uses the electromagnetic field of a coil to attract an armature and close the contact points.(2)Solenoid which uses the electromagnetic field of a coil to pull a plunger into the coil and close the contact points. The plunger’s movement can also be used to do a mechanical job, such as shifting the starter motor gear in a solenoid-actuated drive.1.3 Starter MotorThe starter motor converts electrical energy from the battery into mechanical energy to turn the engine. It does this through the interaction of magnetic fields. When current flowsthrough a conductor, a magnetic field is formed around the conductor. If the conductor is placed in another magnetic field, the two fields will be weakened at one side and strengthened at the other side. An automotive starter motor has many conductors and uses a lot of current to create enough rotational force to crank the engine.The armature is the collection of conductors that will spin to crank the engine. The starter drive gear is mounted on the armature shaft. The pole pieces are the stationary magnetic fields. The motor housing encloses the armature and pole pieces, holds the bearings that support the armature shaft, and provides the terminals for connecting the motor to the rest of the staring system.2.I gniting SystemThe ignition system on an internal combustion engine provides the spark that ignites the combustible air/fuel mixture in the combustion chamber. The spark consists of an electric are produced by applying a high voltage across the electrodes of a spark plug. This spark must occur near the end of the compression stroke, as the position approaches top dead center (TDC). The cylinders must fire in the proper order and at a precise instant, depending on engine speed, load and temperature conditions.A spark plug consists of a pair of electrodes called the center and ground electrodes, separated by a gap. A spark is produced by applying a high voltage (from approximately 6 KV to 40 KV) between the center electrode and ground. Once the arc is started, a much lower voltage is required to sustain the arc to ignite the air/fuel mixture.The ignition system is divided into two circuits: the primary and the secondary. The primary circuit is the low-voltage side of the system and controls the secondary circuit, which is the high-voltage side of the system.The following are the basic parts of the primary ignition circuit:(1)Battery and/or alternator. Supplies the low voltage (12V) used to operate the primary circuit.(2)Ignition switch. Key-operated switch used to feed battery voltage to the primary circuit.(3)Primary wires. Low voltage wires used to connect the electrical components of the primary circuit.(4)Ignition coil primary winding. Current flow through the coil produces an electromagnetic field, which is used to induce a high voltage in the secondary coil.(5)Electronic control unit. Contains a switching transistor controlled by a speed sensor and is used to open and close the primary circuit.(6)Speed sensor, or pickup. Produces a pulsating voltage that signals the generation of an ignition spark.The following are the basic parts of a secondary ignition circuit:(1)Ignition coil secondary winding. Has a high voltage (40,000 V or more) induced in it each time the primary magnetic field collapses.(2)Coil wire. Heavily insulated wire that feeds high voltage from the ignition coil to distributor cap.(3)Distributor rotor. Operates in conjunction with the distributor cap to distribute the high voltage from the ignition coil to the individual spark plug wires in the firing order.(4)Distributor cap. Insulated cap that transfers high voltage from the distributor rotor to spark plug wires.(5)Spark plug wire. Heavily insulated wire that carries high voltage from the distributor to the spark plugs.(6)Spark plug. Provides the air gap within the combustion chamber for the high voltage to arc across, thus igniting the air/fuel mixture.３.Lighting CircuitThe lighting system in a typical automobile includes the headlight, parking lights, direction-signal lights, side marker, stoplights, tail lights, and interior lights.3.1 Main Lighting SwitchThe main lighting switch (sometimes called the headlight switch) is the heart of the lighting systems. It controls the headlights, parking lights, side marker lights, taillights, license plate light, instrument panel lights, and interior lights.Individual switches are provided for special purpose lights such as directional signals, hazard warning flashers, back up lights, and courtesy lights. The main lighting switch may be of either the “push-pull” or “push-pull with rotary contact” types. A typical switch will have three positions: off, parking, and headlamps. Some switches also contain a rheostat to control the brightness of the instrument panel lights. The rheostat is operated by rotating the control knob, separating it from the push-pull action of the main lighting switch.When the main lighting switch completes the circuit to the headlamps, the low beam lights the way for city driving and for use when meeting oncoming traffic on the highway. When the dimmer switch is actuated, the single filament headlamps go “on”, along with the high beam of the two filamentheadlamps. The next actuation of the dimmer switch returns the headlight system to low beams only on the two filament lamps. Some cars are equipped with and electronic headlight dimming device, which automatically switches the headlights from high beam to low in response to light from an approaching vehicle or light from the taillight of a vehicle being overtaken. The dimmer switch in the automatic headlamp dimming system is a special override type. It is located in the steering column as part of a combination dimmer, horn, and turn signal switch. The override action occurs when a slight pull toward the driver on the switch lever providers high beam headlights regardless of the amount of light on the sensor-amplifier.For some years there has been discussion about the advantages of a polarized headlight system. Such a system comprises headlights which produce polarized light in a particular plane. The windscreens of all cars would be fitted with polarizing glass, which would be oriented so that glare from an approaching vehicle would be essentially eliminated, while the forward vision would still be kept at the present levels. The advantages the system appear attractive, but the practical problems of making the transition are very great, since it would not be practical to convert all existing vehicles to this type of lighting. Also, any benefits would only be marginal because glare itself is not a frequent cause of accidents. However, many cars now have refracting or colored glass to cut down on glare.3.2 Directional Signal SwitchThe directional signal switch is installed just below the hub of the steering wheel. A manually controlled lever projecting from the switch permits the driver to signal the direction in which he wants to turn. Moving the switch handle down will light the “turn signal” lamps on the left front and left rear of the car, signaling a left turn. Moving the switch upward will light the turn signal lamps on the right (front and rear), signaling a right turn. With the s witch in a position to signal a turn, lights are alternately turned “on” and “off” by a turn signal flasher. Incorporated in the directional signal switch is a “lane change switch mechanism”. This feature provides the driver the opportunity tosignal a lane change by holding the turn lever against a dent, then releasing it so cancel the signal immediately after the maneuver is completed.3.3 Stoplight SwitchIn order to signal a stop, a brake pedal operated “stoplight switch” is provided to operate the vehicle’s stop lamps. In addition to lighting the conventional rear lights, the switch also operates the center high-mounted stop lamp, which became mandatory on later models. Cruise control equipped vehicles may also utilize a vacuum release valve. In this case, both the vacuum release valve and the stoplight switch are actuated by movement of the brake pedal.。