BACKGROUND OF THE INVENTION
1. Technical Field
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.
2. Description of the Problem
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.
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'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.
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'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'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
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.
Additional effects, features and advantages will be apparent in the written description that follows.
BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 is a perspective view of a tractor and trailer combination with which the present invention can be practiced;
FIG. 2 is a block diagram of a vehicle controller area network used in a preferred embodiment;
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;
FIGS. 4A and B are schematics of implementations of the invention utilizing FET switching and relay switching, respectively;
FIG. 5 is a block diagram of a modular light switch unit incorporating a thermal sensor; and
FIG. 6 is a high level flow chart illustrating response of the system to fault indicating events.
DETAILED DESCRIPTION OF THE INVENTION
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.
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).
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).
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.
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.
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.
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.
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.
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 503A-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 503A-H by a cutoff signal, the character of which depends upon the type of device. The circuit disrupting devices 503A-H may function as circuit switch elements under the control of another device. Here the cutoff signal sinks the actuation signal.
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'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.
The invention provides a compact circuit protection system largely immune to nuisance trips and providing reset capability.
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.
Patent Application
20060044727
