《电子工程师手册》学习资料（英文版）ch106 Vehicular Systems.pdf_大学文库

106 Vehicular Systems 106.1 Introduction Design Considerations 106.3 Land Transportation Classifications 106.4 Propulsion inda sue boehmer 106.5 Microprocessor Controls 106.6 Monitoring and Diagnostics 106.1 Introduction Vehicular systems have evolved and incorporated advances from many other fields of technology over the past decade. Instrumentation and controls for the various modes(aircraft, marine vessels, cars, trucks, buses, and rail vehicles)resemble each other more every year. Technology from one mode of transportation used to be of little interest to practitioners of any other mode. a technology historian might notice similarities among the nctions of airport beacons, lighthouses, traffic lights, and railroad signals, but the specialists in each field had little to say to each other. This is no longer the case. Computers, microprocessor controls, electronics, GPS, and advanced networking and radio technologies are being applied in all forms of passenger and freight transportation,from aviation to marine, highway, and rail transport. The vehicles are now considered in context with an entire system within a particular mode, which is increasingly viewed as part of an overall transportation environment encompassing more than one mode Although"multimodal"is a term that was coined by policy makers to facilitate equitable distribution funding among transportation modes and to facilitate interfaces among them, it applies equally well to the supporting technologies of the original modes. All modes now utilize microprocessor controls in their sub- systems. With microprocessor control has come additional diagnostic capability and the use of system level intelligence, linking all intelligent subsystems and analog sensors and controls. Propulsion of vehicles now varies by mode less than it used to. Because of microprocessors, propulsion can be controlled more precisely, allowing vehicles to use non-traditional energy sources and to switch from one source to another easily, even automat- cally. We do not yet have the ideal multimodal vehicle, capable of navigating, either automatically or by a driver/operator, through air, in water, on roads, and on rails, but technology is no longer a limiting factor. We ye not yet achieved the best balance among modes so that the most appropriate mode is utilized for passenger or freight transportation, but the tools exist to make those decisions possible. (This section deals primarily with land transportation. See the index for aviation and maritime applications. 106.2 Design Considerations If design could begin with a clean slate, the first step would be to decide which mode of transportation and which power source is best suited for the application, based on geography, priority of the passenger or cargo to be transported, energy efficiency, safety, cost per mile, and other factors. However, this is not really possible because the factors relating to funding sources and existing infrastructure often outweigh any technical c 2000 by CRC Press LLC

© 2000 by CRC Press LLC 106 Vehicular Systems 106.1 Introduction 106.2 Design Considerations 106.3 Land Transportation Classifications 106.4 Propulsion 106.5 Microprocessor Controls 106.6 Monitoring and Diagnostics 106.1 Introduction Vehicular systems have evolved and incorporated advances from many other fields of technology over the past decade. Instrumentation and controls for the various modes (aircraft, marine vessels, cars, trucks, buses, and rail vehicles) resemble each other more every year. Technology from one mode of transportation used to be of little interest to practitioners of any other mode. A technology historian might notice similarities among the functions of airport beacons, lighthouses, traffic lights, and railroad signals, but the specialists in each field had little to say to each other. This is no longer the case. Computers, microprocessor controls, electronics, GPS, and advanced networking and radio technologies are being applied in all forms of passenger and freight transportation, from aviation to marine, highway, and rail transport. The vehicles are now considered in context with an entire system within a particular mode, which is increasingly viewed as part of an overall transportation environment encompassing more than one mode. Although “multimodal” is a term that was coined by policy makers to facilitate equitable distribution of funding among transportation modes and to facilitate interfaces among them, it applies equally well to the supporting technologies of the original modes. All modes now utilize microprocessor controls in their subsystems. With microprocessor control has come additional diagnostic capability and the use of system level intelligence, linking all intelligent subsystems and analog sensors and controls. Propulsion of vehicles now varies by mode less than it used to. Because of microprocessors, propulsion can be controlled more precisely, allowing vehicles to use non-traditional energy sources and to switch from one source to another easily, even automatically. We do not yet have the ideal multimodal vehicle, capable of navigating, either automatically or by a driver/operator, through air, in water, on roads, and on rails, but technology is no longer a limiting factor. We have not yet achieved the best balance among modes so that the most appropriate mode is utilized for passenger or freight transportation, but the tools exist to make those decisions possible. (This section deals primarily with land transportation. See the index for aviation and maritime applications.) 106.2 Design Considerations If design could begin with a clean slate, the first step would be to decide which mode of transportation and which power source is best suited for the application, based on geography, priority of the passenger or cargo to be transported, energy efficiency, safety, cost per mile, and other factors. However, this is not really possible because the factors relating to funding sources and existing infrastructure often outweigh any technical considerations. Linda Sue Boehmer LSB Technology

© 2000 by CRC Press LLC Railroads, rail transit, buses, vans, and automobiles each have their own operating environments, although they are increasingly considered part of a system rather than simply as independent vehicles. Many of the underlying technologies are utilized across modal boundaries, but the basics of design remain highly dependent on mode. Electrical systems are widely used in automobiles and trucks today and electronic systems currently make up about 10% of the value of a car. Electronic systems are currently used to control the engine, transmission, steering, braking, suspension, and traction. Many autos incorporate an integrated computer system for controlling the functions mentioned. In addition, electronic systems are used to display information such as speed and engine conditions. ROAD ENGINE George B. Selden Patented November 5, 1895 #549,160 n excerpt from George Selden’s patent application: Be it known that I, George B. Selden, a citizen of the United States, residing in Rochester in the county of Monroe, in the state of New York, have invented an improved Road Engine, of which the following is a specification, reference being had to the accompanying drawings. The object of my invention is the production of a safe, simple, and cheap road-locomotive light in weight, easy to control and possessed of sufficient power to overcome any ordinary inclination. Perhaps one of the most famous patent lawsuits surrounded this patent applied for in 1879 by Selden, who was more of a patent attorney than an inventor. He sold the patent to Col. Allen Pope in 1899 who began to enforce the patent and won judgments against several car manufacturers—except one. They were forced to pay royalties on all vehicles they produced. Henry Ford called the patent preposterous claiming that it didn’t cover his vehicles that he had invented first. He refused to pay royalties and won a ruling in his favor in 1911, after millions had been paid out by his competitors. (Copyright © 1995, DewRay Products, Inc. Used with permission.) A

ir bag inflation units use sensors and electronic controls to insure proper inflation within milliseconds after As antilock brakes, active suspensions, and other computer-dependent technologies are fully utilized, elec- tronic systems may constitute more than 20% of the value of a car. Much of the added computing power will be used for new technology for smart cars and smart roads, or ITs(intelligent transportation systems). The erm refers to a varied assortment of electronics that provide real-time information on accidents, congestion, routing, and roadside services to drivers and traffic controllers. ITS encompass devices that would make vehicles more autonomous: collision-avoidance systems and lane-tracking technology that alert drivers to impending disaster or allow a car to drive itself. ITS also includes interfaces between personal traffic and mass transpor tation, particularly when rail traffic mixes with cars and at rail crossings, whether or not such crossings are protected by gates. Railroads and mass transit vehicles have many of the same internal subsystems as cars do, and also additional subsystems, for which cars may soon have analogous functions. The electrical and electronic systems and controls account for 15 to 30%of the cost of the vehicle udio an systems include propulsion, braking, power conditioning, communication,passenger information (audio and visual), heating/air conditioning, door control, speed control, and monitoring and diagnostics. All of these subsystems interact with each other and many also interact with subsystems external to the vehicle Some of the initial design considerations for vehicles include: will the vehicle interface with an existing fleet? will the vehicle operate independently or as part of a consist, or both What are the physical requirements, including dimensions, number of passengers(seated vs standing)? Is the system(or portions of it)elevated, in tunnels, at grade, underground? will the vehicles mix with or cross other types of traffic? Are ambient conditions exceptionally hot, cold, or dangerous? How closely must one vehicle(or consist) follow another and how fast must they be capable of traveling? Where, how often, and for how long will they stop? To what degree will the vehicles be automated; how much control will a human operator(and/or other crew)have and under what conditions? What kind of power is available, how will it be collected, and can energy generated during electric braking be returned to the power system? How will system and subsystem failures be handled, what kind of failures are acceptable, and to wha degree(or for how long) will they be tolerated? How often and with what degree of expertise will the vehicles be serviced? 106.3 Land Transportation Classifications Among land transportation vehicles, there are more subdivisions than the lay person might expect. In general, distinctions are based on vehicle size, weight, speed, and passenger or cargo capacity. Cars, trucks, mini-vans, vans, sport utility vehicles, etc are familiar terms. There is some variation among them relative to the electronics embedded in the systems and the options available to the driver. The same is true for railroads, rail transit, and mass transit, although the distinctions among classifications are important to the manufacturers and operators of the equipment. The classifications include railroad, commuter rail, heavy rail, light rail, street car, trolley bus, bus, paratransit, and"people mover" or monorail 106.4 Propulsion By 1910 electric automobiles were commonplace. Nevertheless, they were replaced by gasoline-fueled automobiles by 1920 because electric cars operated at lower top speeds and over shorter ranges without recharging than gasol cars could achieve. However, the availability of electric motive power remained a critical factor in the developme f cities. Since the mid-1970s, when the electric vehicle reemerged as an appealing transportation option, many have recognized the potential of electric fleet vans. An electric vehicle uses electric energy storage, electric controls, and electric propulsion devices. Because the vans use batteries to drive their electric motors, they are well suited e 2000 by CRC Press LLC

© 2000 by CRC Press LLC Air bag inflation units use sensors and electronic controls to insure proper inflation within milliseconds after a collision. As antilock brakes, active suspensions, and other computer-dependent technologies are fully utilized, electronic systems may constitute more than 20% of the value of a car. Much of the added computing power will be used for new technology for smart cars and smart roads, or ITS (intelligent transportation systems). The term refers to a varied assortment of electronics that provide real-time information on accidents, congestion, routing, and roadside services to drivers and traffic controllers. ITS encompass devices that would make vehicles more autonomous: collision-avoidance systems and lane-tracking technology that alert drivers to impending disaster or allow a car to drive itself. ITS also includes interfaces between personal traffic and mass transportation, particularly when rail traffic mixes with cars and at rail crossings, whether or not such crossings are protected by gates. Railroads and mass transit vehicles have many of the same internal subsystems as cars do, and also additional subsystems, for which cars may soon have analogous functions. The electrical and electronic systems and controls account for 15 to 30% of the cost of the vehicle. The major vehicle subsystems include propulsion, braking, power conditioning, communication, passenger information (audio and visual), heating/air conditioning, door control, speed control, and monitoring and diagnostics. All of these subsystems interact with each other and many also interact with subsystems external to the vehicle. Some of the initial design considerations for vehicles include: • Will the vehicle interface with an existing fleet? • Will the vehicle operate independently or as part of a consist, or both? • What are the physical requirements, including dimensions, number of passengers (seated vs. standing)? Is the system (or portions of it) elevated, in tunnels, at grade, underground? Will the vehicles mix with or cross other types of traffic? Are ambient conditions exceptionally hot, cold, or dangerous? • How closely must one vehicle (or consist) follow another and how fast must they be capable of traveling? Where, how often, and for how long will they stop? • To what degree will the vehicles be automated; how much control will a human operator (and/or other crew) have and under what conditions? • What kind of power is available, how will it be collected, and can energy generated during electric braking be returned to the power system? • How will system and subsystem failures be handled, what kind of failures are acceptable, and to what degree (or for how long) will they be tolerated? How often and with what degree of expertise will the vehicles be serviced? 106.3 Land Transportation Classifications Among land transportation vehicles, there are more subdivisions than the lay person might expect. In general, distinctions are based on vehicle size, weight, speed, and passenger or cargo capacity. Cars, trucks, mini-vans, vans, sport utility vehicles, etc. are familiar terms. There is some variation among them relative to the electronics embedded in the systems and the options available to the driver. The same is true for railroads, rail transit, and mass transit, although the distinctions among classifications are important to the manufacturers and operators of the equipment. The classifications include railroad, commuter rail, heavy rail, light rail, street car, trolley bus, bus, paratransit, and “people mover” or monorail. 106.4 Propulsion By 1910 electric automobiles were commonplace. Nevertheless, they were replaced by gasoline-fueled automobiles by 1920 because electric cars operated at lower top speeds and over shorter ranges without recharging than gasoline cars could achieve. However, the availability of electric motive power remained a critical factor in the development of cities. Since the mid-1970s, when the electric vehicle reemerged as an appealing transportation option, many have recognized the potential of electric fleet vans.An electric vehicle uses electric energy storage, electric controls, and electric propulsion devices. Because the vans use batteries to drive their electric motors, they are well suited

to the short routes and regular schedules followed by vans in a company fleet. One such fleet van, the general Motors Griffon, is produced in England. Because the vans can be recharged regularly at night, they offer electric utilities a new off-peak demand. At the same time, electric vehicles run cleanly and burn no gasoline Increasing the distance an electric vehicle can travel on a single charge is the most significant factor expanding the market for electric vans. The 60-mile(97-km)range of the Griffon makes it a replacement late for about 600,000 commercial fleet vehicles now operating in the United States. If advanced batteries doubled the range of a van to 120 miles, the potential market for these vehicles could top 2 million. A variety of electric cars has been introduced over the years, but none have enjoyed general use. Products of combustion gradually were recognized as major air pollutants and fuels have been acknowledged as non-renewable resources, so alternatives have been sought with increasing diligence Today, electric motors are used more widely for rail vehicles than for cars, vans, or buses, although this is slowly changing(see above). Electric motors as a back-up mode for buses are becoming more common in certain areas where air pollution is considered a serious problem and in portions of systems, such as North American tunnels, where fumes from internal combustion can be hazardous. Power distribution for rail vehicles ranges from three phase ac, at various voltages(usually collected from overhead wires), to several different dc voltages(usually collected from a"third rail"). Until recently(within the past 5 years in the U.S. ), most electric traction motors utilized dc power. Today, most traction motors in new vehicles use ac power. Various techniques are used to cool the motors, depending on the operating environment. Collected power is conditioned continuously(see power"converters"and"inverters")to meet the motors' requirements and the power requirements of other vehicle systems, and also is stored to power critical on-board systems if power is lost. Traction motors also are used for braking, which generates power that can be reconditioned and returned to the power system to power other vehicles or returned to the power grid. Power that cannot be returned or d elsewhere in the system is converted into heat by banks of large braking resistors. Electric braking supplemented by mechanical braking systems which can be actuated pneumatically, hydraulically, and/ electrically. Coordination of propulsion and braking efforts, especially when traction surfaces are slippery, is an important design point. Microprocessor controls have allowed optimization of automotive internal combustion processes to econo- mize on fuel and minimize air pollution. Alternative fuels, such as natural gas, are becoming more common because the combustion process can be managed more uniformly, responsively, and safely than ever before Diesel electric locomotives have become the propulsion vehicle of choice for long haul freight railroads. icroprocessors control the combustion process which produces electricity to power electric motors when ac power is not available, such as on long sections of rail that are not yet electrified. Dual mode buses utilize internal combustion when operating on the streets, but switch to electric power in tunnels. Dual mode rail vehicles or streetcars collect power from an overhead catenary or third rail, but can switch to battery power when they are not operating in electrified areas Improvements in battery technology(cost, life, power density, weight, and maintenance requirements)and solar power as a supplementary or primary source will improve the acceptance of alternatives to internal ombustion and direct electric power. 106.5 Microprocessor Controls All major vehicle subsystems and many minor ones are now microprocessor-controlled. Embedded micropro cessors replace banks of relays and mechanical switches to perform functions on the vehicle and also to control microprocessors handling different functions and coordinating analog and digital input and output sigla e functions that did not exist prior to the advent of microprocessors. Some major vehicle subsystems have sev Intelligent subsystems exchange information within a vehicle, among vehicles in a consist, and between the vehicle and its external environment. This information is exchanged through increasingly sophisticated net- works, which may or may not use traditional wiring. There may also be a separate network or layers of erro checking to handle safety-critical data. A human vehicle operator typically has status indicators, alarms, and controls. These have changed dr cally with the advances in microprocessor-controlled subsystems. The "glass cockpit" and"fly by wire" technic e 2000 by CRC Press LLC

© 2000 by CRC Press LLC to the short routes and regular schedules followed by vans in a company fleet. One such fleet van, the General Motors Griffon, is produced in England. Because the vans can be recharged regularly at night, they offer electric utilities a new off-peak demand. At the same time, electric vehicles run cleanly and burn no gasoline. Increasing the distance an electric vehicle can travel on a single charge is the most significant factor in expanding the market for electric vans. The 60-mile (97-km) range of the Griffon makes it a replacement candidate for about 600,000 commercial fleet vehicles now operating in the United States. If advanced batteries doubled the range of a van to 120 miles, the potential market for these vehicles could top 2 million. A variety of electric cars has been introduced over the years, but none have enjoyed general use. Products of combustion gradually were recognized as major air pollutants and fuels have been acknowledged as non-renewable resources, so alternatives have been sought with increasing diligence. Today, electric motors are used more widely for rail vehicles than for cars, vans, or buses, although this is slowly changing (see above). Electric motors as a back-up mode for buses are becoming more common in certain areas where air pollution is considered a serious problem and in portions of systems, such as North American tunnels, where fumes from internal combustion can be hazardous. Power distribution for rail vehicles ranges from three phase ac, at various voltages (usually collected from overhead wires), to several different dc voltages (usually collected from a “third rail”). Until recently (within the past 5 years in the U.S.), most electric traction motors utilized dc power. Today, most traction motors in new vehicles use ac power. Various techniques are used to cool the motors, depending on the operating environment. Collected power is conditioned continuously (see power “converters” and “inverters”) to meet the motors’ requirements and the power requirements of other vehicle systems, and also is stored to power critical on-board systems if power is lost. Traction motors also are used for braking, which generates power that can be reconditioned and returned to the power system to power other vehicles or returned to the power grid. Power that cannot be returned or used elsewhere in the system is converted into heat by banks of large braking resistors. Electric braking is supplemented by mechanical braking systems which can be actuated pneumatically, hydraulically, and/or electrically. Coordination of propulsion and braking efforts, especially when traction surfaces are slippery, is an important design point. Microprocessor controls have allowed optimization of automotive internal combustion processes to economize on fuel and minimize air pollution. Alternative fuels, such as natural gas, are becoming more common because the combustion process can be managed more uniformly, responsively, and safely than ever before. Diesel electric locomotives have become the propulsion vehicle of choice for long haul freight railroads. Microprocessors control the combustion process which produces electricity to power electric motors when ac power is not available, such as on long sections of rail that are not yet electrified. Dual mode buses utilize internal combustion when operating on the streets, but switch to electric power in tunnels. Dual mode rail vehicles or streetcars collect power from an overhead catenary or third rail, but can switch to battery power when they are not operating in electrified areas. Improvements in battery technology (cost, life, power density, weight, and maintenance requirements) and solar power as a supplementary or primary source will improve the acceptance of alternatives to internal combustion and direct electric power. 106.5 Microprocessor Controls All major vehicle subsystems and many minor ones are now microprocessor-controlled. Embedded microprocessors replace banks of relays and mechanical switches to perform functions on the vehicle and also to control functions that did not exist prior to the advent of microprocessors. Some major vehicle subsystems have several microprocessors handling different functions and coordinating analog and digital input and output signals. Intelligent subsystems exchange information within a vehicle, among vehicles in a consist, and between the vehicle and its external environment. This information is exchanged through increasingly sophisticated networks, which may or may not use traditional wiring. There may also be a separate network or layers of errorchecking to handle safety-critical data. A human vehicle operator typically has status indicators, alarms, and controls. These have changed dramatically with the advances in microprocessor-controlled subsystems. The “glass cockpit” and “fly by wire” techniques

© 2000 by CRC Press LLC developed for aviation generally transition to cars and trains as they are service-proven and as their cost decreases. A driver or train operator once had a few lights, a gauge or two, a throttle of some sort, and a brake handle or pedal. For vehicles that are not automated but are partially automated or allow manual operation at times, a human operator today is confronted by a dense array of dials, buttons, data and CCTV screens, LCD panels, microphones, and annunciators (audio and visual) of various types. In some cases there is far more information than an operator can use. In others, there is duplication between the old, analog indicators and controls and new, digital or “soft” controls on a touch screen. There has been some resistance to technology advances, based on the perception that electronics are not as reliable as electromechanical devices (such as relays) and on a concern that they will be more complicated to troubleshoot and maintain than electro-mechanical and analog equipment. POWER APPLYING MECHANISM Otto Zachow and William Besserdich Patented December 29, 1908 #907,940 n excerpt from Otto Zachow and William Besserdich’s patent application: Our invention relates to new and useful improvements in power-applying mechanism and more particularly to that class adapted to be used in connection with motor-propelled vehicles, such as automobiles, or the like, and our object is to provide a mechanism of this class whereby the power may be applied to both the front and rear axles. Early in this century, Otto Zachow and his friend, William Besserdich, had the idea of making all four wheels of their vehicle turn, when they slid into a ravine and got stuck. Out of frustration the four-wheel drive mechanism was invented. At the beginning of World War I, they sold about 50 trucks equipped with the mechanism to Great Britain. When the United States entered the war, Zachow and Besserdich sold 3,750 trucks to the U.S. Army. Today, four-wheel drive is available on a wide range of vehicles from small sport utilities to luxury imports. (Copyright © 1995, DewRay Products, Inc. Used with permission.) A

106.6 Monitoring and Diagnostics A great advantage of microprocessor-controlled systems is the degree to which they can be self-diagnosing. Each intelligent subsystem has internal self-diagnostics which include routines to perform initial tests on power p, update checks for"hot startup and continuous checking to assure that inputs and outputs are within expected ranges. Internal self-diagnostics are also capable of performing self-tests on request. When fault nditions are noted, typically there are internal resets to allow for inaccurate data, with faults being logged after a certain number of occurrences or duration of a fault condition The basis of any monitoring and diagnostics system is the underlying maintenance philosophy. Micropro- cessor controls make it possible to capture any combination of information from the intelligent subsystems. Information can then be processed and presented in a variety of ways, along with data from analog sensors which are not part of any intelligent system. Information of interest includes operating status and existing or historical fault information. Events"may include faults and also other expected actions that may or may not be considered faults. Historical information can include faults, events, and the status of parameters of interest associated with the fault. The amount of information that can be captured is limited only by the amount of memory provided and the speed at which it can be transferred. Typically, some(or all) of the memory is in a form that will allow the fault data to be preserved after power is lost or vehicles are shut down between operating periods. Decisions on which information to capture, how often to sample, and how many samples to preserve are ideally based on what will be most valuable for troubleshooting existing faults and predicting future failures. rough understanding of each intelligent subsystem is needed in addition to an understanding of the environment in which it operates, including the other subsystems with which it interacts. It is also important to know what level of skill will be applied to interpreting the saved information. If the level of skill will be low, ome degree of artificial intelligence can be designed into the diagnostics to guide a maintenance technician through the troubleshooting process. The information needed to be collected is influenced by the target audience. The most detailed internal subsystem information is primarily used by engineers or specialized technicians to troubleshoot detailed failures or fine tune operation. A subset of less detailed information is used by maintenance staff to determine which components or sub-modules to replace or repair. A further subset of that information is used by a gener troubleshooting staff to determine which subsystem is malfunctioning or which higher level modules to replace in even smaller subset of operating status information and only a few major faults are needed by the operator, with a selection of that data being useful to a central control or maintenance dispatching facility if real time links are available. A variety of techniques are being used to present this information to the target audience(s) in ways and at times that are most appropriate Event recorders"similar to the ones required on passenger airliners, capturing selected parameters, quired by the FRA for railroads and are under consideration by industry standards groups for other me Defining Terms Active suspension: An electronically controlled suspension system for maintaining level suspension of a Consist: Two or more vehicles coupled together in a train. The vehicles may be identical or they may each lack a major subsystem(such as propulsion), whose functions may be handled by another vehicle in the consist. Dual mode: Vehicles that are designed to switch manually or automatically from one type of propulsion to another, for instance from internal combustion Electric braking: Use of traction motor to slow the Electric vehicle: Vehicle using electric energy storage, Traction motor: Electric motor that provides motive power to move vehicle Ctric propulsion devices controls, and elec Related Topics 66.2 Motors.82.1 Practical Microprocessors e 2000 by CRC Press LLC

© 2000 by CRC Press LLC 106.6 Monitoring and Diagnostics A great advantage of microprocessor-controlled systems is the degree to which they can be self-diagnosing. Each intelligent subsystem has internal self-diagnostics which include routines to perform initial tests on powerup, update checks for “hot” startup and continuous checking to assure that inputs and outputs are within expected ranges. Internal self-diagnostics are also capable of performing self-tests on request. When fault conditions are noted, typically there are internal resets to allow for inaccurate data, with faults being logged after a certain number of occurrences or duration of a fault condition. The basis of any monitoring and diagnostics system is the underlying maintenance philosophy. Microprocessor controls make it possible to capture any combination of information from the intelligent subsystems. Information can then be processed and presented in a variety of ways, along with data from analog sensors which are not part of any intelligent system. Information of interest includes operating status and existing or historical fault information. “Events” may include faults and also other expected actions that may or may not be considered faults. Historical information can include faults, events, and the status of parameters of interest associated with the fault. The amount of information that can be captured is limited only by the amount of memory provided and the speed at which it can be transferred. Typically, some (or all) of the memory is in a form that will allow the fault data to be preserved after power is lost or vehicles are shut down between operating periods. Decisions on which information to capture, how often to sample, and how many samples to preserve are ideally based on what will be most valuable for troubleshooting existing faults and predicting future failures. A thorough understanding of each intelligent subsystem is needed in addition to an understanding of the environment in which it operates, including the other subsystems with which it interacts. It is also important to know what level of skill will be applied to interpreting the saved information. If the level of skill will be low, some degree of artificial intelligence can be designed into the diagnostics to guide a maintenance technician through the troubleshooting process. The information needed to be collected is influenced by the target audience. The most detailed internal subsystem information is primarily used by engineers or specialized technicians to troubleshoot detailed failures or fine tune operation. A subset of less detailed information is used by maintenance staff to determine which components or sub-modules to replace or repair. A further subset of that information is used by a general troubleshooting staff to determine which subsystem is malfunctioning or which higher level modules to replace. An even smaller subset of operating status information and only a few major faults are needed by the operator, with a selection of that data being useful to a central control or maintenance dispatching facility if real time links are available. A variety of techniques are being used to present this information to the target audience(s) in ways and at times that are most appropriate. “Event recorders” similar to the ones required on passenger airliners, capturing selected parameters, are now required by the FRA for railroads and are under consideration by industry standards groups for other modes. Defining Terms Active suspension: An electronically controlled suspension system for maintaining level suspension of a vehicle. Consist: Two or more vehicles coupled together in a train. The vehicles may be identical or they may each lack a major subsystem (such as propulsion), whose functions may be handled by another vehicle in the consist. Dual mode: Vehicles that are designed to switch manually or automatically from one type of propulsion to another, for instance from internal combustion to electric. Electric braking: Use of traction motor to slow the vehicle. Electric vehicle: Vehicle using electric energy storage, electric controls, and electric propulsion devices. Traction motor: Electric motor that provides motive power to move vehicles. Related Topics 66.2 Motors • 82.1 Practical Microprocessors