BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The invention relates to electrical circuit protection systems and more particularly to a fail safe circuit interruption system for motor vehicles employing thermal optical fault detection.  
         [0003]     2. Description of the Problem  
         [0004]     Wiring for carrying electrical current is subject to overcurrent conditions which may be the result of short circuits or of excessive loads being connected into a circuit including the wiring. Conventionally, protection is provided by positioning a fuse or circuit breaker in the circuit. A fuse tends to be stable even in high ambient temperature conditions and responds quickly and completely when it functions. Fuses are highly reliable, but must be replaced after a circuit opening event. Circuit breakers typically come in one of two types, magnetic and thermal. The magnetic systems are the more reliable, but tend to be bulky and are not cost effective for motor vehicle applications. Thermal breakers are the type familiar to most users but tend to be vulnerable to ambient heat and are further vulnerable to mechanical failure. Circuit breakers can be reset after use and have been favored for use in trucks for that reason.  
         [0005]     Circuit breakers used in motor vehicle applications have proven less reliable than desired. Automotive and truck applications are frequently hostile or difficult environments. Circuit breakers are often located in the engine compartment under the motor vehicle hood where they are subjected to overheating from sources other than electrical wiring. Another favored location for circuit breakers is under or in the motor vehicle&#39;s dash, which, while less hostile than the engine compartment can suffer from poor ventilation. The dash is more vulnerable to damage in case of failure of the breakers than are components located under the hood.  
         [0006]     An overloaded circuit can generate an amount of heat exceeding what the wiring, insulation covering the wiring, or the environment of use can tolerate. Failure of the wiring or damage to the circuit components may be indicated by an excursion of the wire&#39;s temperature above a threshold temperature. It may also be indicated by a prolonged period above a second, lower temperature. The potential for failure may also be indicated by an upward spike in wire temperature, even if the wire&#39;s temperature has yet to exceed any of the thresholds. Temperature spikes may be associated with a circuit fault or short circuit.  
       SUMMARY OF THE INVENTION  
       [0007]     According to the invention there is provided an electrical power system for a motor vehicle. The electrical system comprises a plurality of electrical loads, electrical conductors connected to the plurality of electrical loads to form a circuits, circuit interruption devices connected into the electrical conductors and responsive to cutoff signals for opening the respective circuits, at least a first infrared optical sensor disposed with respect to an electrical conductor for measuring the temperature thereof and generating a signal proportional to the temperature, and a body computer or equivalent data processing device coupled to receive the proportional signal and responsive thereto for generating a cutoff signal for application to the circuit interruption device. The body computer is programmed to generate the cutoff signal if the proportional signal indicates that the temperature has exceeded a never exceed temperature, if the proportional signal indicates a rapid upward change in temperature, or if the temperature of the electrical conductor exceeds a predetermined threshold for longer that a minimum time period, the predetermined threshold being lower than the never exceed temperature.  
         [0008]     Additional effects, features and advantages will be apparent in the written description that follows.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0010]      FIG. 1  is a perspective view of a tractor and trailer combination with which the present invention can be practiced;  
         [0011]      FIG. 2  is a block diagram of a vehicle controller area network used in a preferred embodiment;  
         [0012]      FIG. 3  is a high level circuit schematic of an electronic gauge controller, an electrical system controller and a plurality of lamps energized under the control of the electrical system controller;  
         [0013]      FIGS. 4A  and B are schematics of implementations of the invention utilizing FET switching and relay switching, respectively;  
         [0014]      FIG. 5  is a block diagram of a modular light switch unit incorporating a thermal sensor; and  
         [0015]      FIG. 6  is a high level flow chart illustrating response of the system to fault indicating events. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  illustrates in a perspective view a truck  10  comprising a combination of a tractor  12  and a trailer  14 . Tractor  12  includes the conventional major systems of a vehicle, including an engine, a starter system for the engine, brakes, a transmission and various lamps. Tractor  12  and trailer  14  mount several exterior lamps by which the vehicle provides light for its driver to see by and means to be seen, particularly at night, by others. On the front of tractor  12  are headlights  16 , front corner turn signal lamps  17 , and fog lamps  18 . Several identification lights  21  are installed on the roof of tractor  12 . A lamp box  19  installed on the rear end of tractor  12  carries additional turn signal lights, reverse lights and brake lights. As is common, the forward and tail end turn signal lights have a hazard function and can be cycled on and off together (generally the forward pair together and then the tail end pair together) to provide warning to passing motorists. A pair of electrically activated horns  22  are installed on the roof of tractor  12 . Trailer  14  also carries various lights, including tail end brake and turn signal lamps (not shown), as well as identification lights  23  which may be positioned any where on the trailer, but are commonly found on upper and lower edges of the trailer. All of the various lamps are electrified by delivery of current to the lamps by electrical wires and may be taken as exemplary of the various systems of truck  10  which require electrical power. The invention will be explained with reference to lighting systems, its preferred application, but those skilled in the art will appreciate its general applicability to other vehicle electrical systems.  
         [0017]     Referring now to  FIG. 2 , tractor  12  includes a network  11  based on an electrical system controller (ESC)  30  and including first and second shielded, twisted pair busses  60 ,  160  over which data communications between ESC  30  and other controllers occur. Busses  60  and  160  conform to the SAE J1939 standard with bus  60  being a public bus and bus  160  being proprietary. ESC  30  executes the programming used to implement the preferred embodiment of the invention. Among other vocational controllers and sensor interface modules which may be connected to public bus  60  are an automatic transmission controller  50 , an engine controller  20  and an anti-lock brake system  120 . A thermal sensor data transmitter  132  is connected for communication with ESC  30  over private bus  160 . Busses  60  and  160 , along with the various nodes attached thereto form controller area networks (CAN).  
         [0018]     Active vehicle components are typically controlled by one of a group of autonomous, vocational controllers. However, most lamps are powered directly from ESC  30 , which includes a number of power field effect transistors (FETs) for that purpose. A switch set  42  for the lamps is attached to electrical gauge controller (EGC)  40 , which communicates requests to illuminate lamps to ESC  30  over bus  60 . A panel display including a plurality of warning LEDs  44  is connected to and under the control of EGC  40 . ESC  30  additionally drives horn transducers  36  mounted in the horns  22  on top of tractor  12 . ESC  30  includes a programmable computer including conventional memory (both volatile and non-volatile) and the capability for program execution (CPU  31 , see  FIG. 3 ).  
         [0019]      FIG. 3  is a high level circuit schematic of EGC  40 , ESC  30 , and a plurality of lamps energized under the control of the ESC as configured for a preferred embodiment of the invention. ESC  30  is a programmable body systems computer used to control many vehicle electrical system functions. In the past, many of these functions were controlled by switches, relays and other independently wired and powered devices. ESC  30  is based on a microprocessor  31  which executes programs and which controls switching of a plurality of power FETs used to actuate vehicle exterior lights and the horn. EGC  40  communicates with ESC  30  over an SAE J1939 data link (bus  60 ) and CAN controllers  43  (for EGC  40 ) and  143  for ESC  30 . EGC  40  includes a microprocessor  41  but is of limited capability and typically characterized by fixed programming. EGC  40  handles switch  45  inputs providing manual control over headlights and enablement of the headlights  16 . Another source of switch inputs may by provided by a switch pack  38  which is connected to microprocessor over an SAE J1708 bus and controller  39  or through switches associated with brake pedals, turn signal levers and other similar systems.  
         [0020]     ESC  30  communicates with a sensor controller  240  over private J1939 bus  160 , implemented using a twisted pair of wires and CAN controllers  243  and  343  for sensor controller  240  and ESC  30 , respectively. Sensor controller  240  includes a microprocessor  241  and an analog to digital conversion unit  243 . A plurality of thermal sensors are connected to analog to digital conversion unit  243 , which passes the data to microprocessor  241 . The thermal sensors are positioned as illustrated in  FIGS. 5 and 6  to monitor the temperature of electrical power conducting wires connecting various lamps to the FETs of ESC  30 .  
         [0021]     Microprocessor  31  can apply activation signals to all of various lamps  37 ,  38 ,  61 ,  48 ,  43 ,  64 ,  45  and  46 , as well as to a horn coil  36 . In the case of headlights  16 , this may also involve pulling high a headlight enable line by instruction to EGC  40 . Microprocessor  31  is connected to provide an activation signal to a horn power FET  51  which in turn drives a horn coil  36 . Another signal line from microprocessor  31  is connected to drive a park light FET  52  which in turn drives park/tail/marker light bulbs  37 , a license plate ID and mirror light bulbs  38 . Yet another signal line from microprocessor  31  drives a low beam FET  53 , which in turn drives filaments in headlight bulbs  41  and  48 . Low beam FET  53  and park light FET  52  further require an input on the headlight enable line to operate. Still another pin on microprocessor  31  controls a high beam FET  54  which drives high beam filaments in bulbs  41  and  42 . Lastly, a set of four pins on microprocessor  31  are used to control the turn signal lights at each corner of the vehicle. Four FETs  55 ,  56 ,  57  and  58  are connected to receive the signals and, in turn, to power bulbs  43 ,  44 ,  45 , and  46  mounted in turn signal fixtures at the four corners of the vehicle. FETs  55 ,  56 ,  57  and  58  can be activated together or separately to provide turn indications and emergency flasher operation.  
         [0022]      FIG. 4A  exemplifies one way of providing thermal sensing and circuit breaker functions. FET  456 , intended to be representative of any one of the power switching FETs of ESC  30 , provides electrical power on command of the ESC  30  through a wire  404  connected to a lamp  445 . Disposed adjacent to wire  404  is an infrared thermal sensor  402  which generates a signal proportional to the temperature of wire  404 . The proportional signal is monitored by sensor control  240 , which in turn supplies the data over private bus  160  to ESC  30 . Responsive to the temperature of the wire, ESC  30  can interrupt the circuit including FET  456 , wire  404  and lamp  445  by opening, i.e. interrupting, FET  456 . Here the cutoff signal would be removal of the gate signal to the FET  456 .  
         [0023]      FIG. 4B  illustrates application of the invention to a relay system. Here a relay  450  provides power from a vehicle battery  452  to a load  458  along a lead  460  between the relay and the load upon closure of relay switch  454 . Relay  480  is controlled by the state of the signal on load  456  connected between a control input of the relay  450  and a relay driver output terminal on ESC  30 . Sensor  402  still operates to sense the temperature of wire  460 , with the output of the sensor being applied to ESC  30 .  
         [0024]     It is not necessary to have an CAN bus based electrical control system to implement the invention on all or part of a vehicle.  FIG. 5  exemplifies a modular system providing thermal sensing and circuit interruption functions from a connector interface  511 . Connector interface is supplied power from the vehicle power cable  507  and distributes it to standard vehicle wiring  501  which may be bundled into a vehicle harness. Power is selectively applied to wires  510  by a series of circuit disrupting devices  503 A-H (e.g. relays, FETs, etc.). The temperature of each wire is monitored using an infrared thermal scanner  509  with rotational sweep. The readings taken by scanner  509  are supplied to a circuit interruption microcontroller or programmable logic array  505  which can selectively activate the desired circuit disrupting device  503 A-H by a cutoff signal, the character of which depends upon the type of device. The circuit disrupting devices  503 A-H may function as circuit switch elements under the control of another device. Here the cutoff signal sinks the actuation signal.  
         [0025]      FIG. 6  is a high level flow chart illustrating the three tests implemented by programming of an ESC  30  or of interruption control logic 505. All of the tests are based on current temperature measurements, which are periodically checked (step  602 ). At step  604  the current measured temperature is compared with a first, never exceed threshold. If this temperature is exceeded the circuit is interrupted (step  612 ). If the never exceed temperature is not exceeded a time versus temperature analysis is done (step  606 ). This may be quite simple, for example, each of the last  12  measurements has exceeded a second, lower threshold. If yes, the circuit is interrupted (step  612 ). Finally, short circuits may be indicated by sudden increases in temperature. This may be indicated by the temperature&#39;s change over time (step  608 ) or by a large delta T over successive periods, even if the never exceed temperature has not yet been broached. Again, a positive indication (step  610 ) results in the circuit being opened. Additional circuit interruption protocols may be implemented.  
         [0026]     The invention provides a compact circuit protection system largely immune to nuisance trips and providing reset capability.  
         [0027]     While the invention is shown in only two of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.
Electrical circuits are interrupted in response to temperature transients of the electrical conductors of the circuit. Temperature excursions are sensed using a thermo optical device. The circuit interruption device may be the same element as the circuit switching element.