Abstract:
A programmed microprocessor has a learning mode of operation wherein data to and from a circuit coupled to a wiring harness in a vehicle is stored by the microprocessor. After the learning mode is completed, removal of the circuit does not cause an error condition because appropriate data is supplied instead by the microprocessor. A sleep mode of operation prevents the microprocessor from interfering with the operation of the circuit when the circuit and the microprocessor are coupled to the wiring harness.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the control network in a light duty motor vehicle, such as a van, minivan, or sport utility vehicle, and, in particular, to a shunt for emulating a removed front seat. 
     Modern automobiles are endowed with a plurality of computers and sensors to provide convenience and safety for drivers and passengers. These computers are distributed throughout the vehicle communicate with each other via one or more networks. For example, a computer controlling the instrument panel may sense that the vehicle is moving rapidly enough to lock the doors and will signal the appropriate computer that it is time to lock the doors. 
     Some of the computers provide protection and safety for the driver and passenger. A computer determines, for example, whether the seat belt has been fastened, whether or not there is a person in the passenger seat, and the weight of the person in the passenger seat. Each of these parameters or measurements is performed by sensors located in or near the seat. 
     The amount of data that is generated and communicated is greater for a passenger&#39;s seat than for a driver&#39;s seat. If a driver inserts a key into the ignition, then the appropriate air bags will be enabled and the seat belt will be checked for being buckled. However, the presence of mass or a live body in the passenger seat is ambiguous. The passenger side air bag should only be activated if there is a person in the passenger seat and only if that person has a height and weight greater than certain minimums. Hence, the number and sophistication of sensors in the passenger&#39;s seat are usually greater than those for the driver&#39;s seat. 
     Typically, sensors, and sometimes their network interfaces, are built into the seat itself and coupled to other computers within the vehicle. If a front seat is removed, the absence of the sensors will be noted by other computers in the vehicle and error signals (visual and audible) will be generated as long as the sensors are missing. One must do something to suppress the error signals without compromising the safety of the vehicle. 
     Driver side sensors can be transferred to a new seat or passive devices can be added to emulate the driver&#39;s seat to prevent detecting false errors. For the driver&#39;s seat, the typical OEM (original equipment manufacturer) sensors are the seat belt buckle, air bag sensor, and seat position. These sensors can usually be replaced by passive networks of resistors and/or capacitors to suppress the vehicle warning system. The passive network can often be contained in a small module that plugs into the OEM wiring harness ending at the driver&#39;s seat. 
     The passenger seat, on the other hand, typically has sensors for the seat belt, air bag, adult passenger detection, and weight sensor. The first two sensors are coupled to computers under the seat, while the last two sensors are coupled by network to other computers. The first two sensors can be replaced with passive networks but the last two cannot. The data stream from the passenger sensor and weight sensor must represent occupancy as if the seat were still in place. The problem is further complicated by the fact that some manufacturers uniquely identify each seat with a code that also must be received on a regular basis by other computers in one or more networks. That is, not only must the data be present but it must be present on the correct network at the correct time and preceded by the correct identification code. 
     For aftermarket outfitters modifying light duty motor vehicles, the problem of removing a front passenger seat, or otherwise removing sensors from a vehicle, is compounded by a lack of information from an OEM, generally because of concern for product liability in a judicial system where outcome can be very unpredictable. 
     In digital systems, binary data can only represent one of three things: data, an address, or an instruction. This is the information that is carried on a serial data bus or network as used in modern vehicles. The binary data is sent along the serial bus in a format specified by one organization or another. The J1850 standard is from the Society of Automotive Engineers (SAE). Another standard is ISO9141. Control signals are not on the serial bus, at least not directly. Control information can be passed along a network as an instruction to be executed but the wire, the physical bus itself, cannot also be a control line. Conversely, a control line is not a data bus. Collectively, control lines, lines supplying power or ground, and data buses are referred to as the “wiring harness” of a vehicle. 
     As used herein, no distinction is made among the terms “computer,” “microprocessor,” and “microcontroller.” Similarly, a microprocessor can be a single integrated circuit or a “chip set,” having plural integrated circuits. Microprocessors are produced in a variety of capabilities and one of ordinary skill in the art can readily choose an appropriate device. Most manufacturers produce guides for choosing a device. 
     In view of the foregoing, it is therefore an object of the invention to provide a shunt for emulating circuitry that has been disconnected from the wiring harness of a light duty motor vehicle. 
     Another object of the invention is to provide a shunt that can emulate a circuit even when the meaning of signals within the circuit is not understood. 
     A further object of the invention is to provide a shunt that can be programmed in the vehicle for which it is to be used. 
     Another object of the invention is to provide a shunt that can adapt to identification or other unique codes circulating in a vehicle control system. 
     A further object of the invention is to provide a shunt that can be left coupled in parallel with the circuit it is to replace without interfering with the operation of that circuit. 
     SUMMARY OF THE INVENTION 
     The foregoing objects are achieved in this invention in which a programmed microprocessor has a learning mode of operation wherein data to and from a circuit coupled to a wiring harness in a vehicle is stored by the microprocessor. After the learning mode is completed, removal of the circuit does not cause an error condition because appropriate data is supplied instead by the microprocessor. A sleep mode of operation prevents the microprocessor from interfering with the operation of the circuit when the circuit and the microprocessor are coupled to the wiring harness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a portion of the wiring harness in a light duty motor vehicle, including a shunt constructed in accordance with the invention; 
         FIG. 2  is a block diagram illustrating a shunt constructed in accordance with a preferred embodiment of the invention; 
         FIG. 3  is a wiring diagram of a Y-harness used for coupling the shunt to the wiring harness of a vehicle; 
         FIG. 4  is a wiring diagram of the seat harness used to couple the seat modules to the Y-harness; 
         FIG. 5  is a wiring diagram of the “learning” harness used to couple the seat harness to the Y-harness and switch the shunt into learning mode; and 
         FIG. 6  is a block diagram of the connections of the harness segments during learn mode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates the front end of a light duty motor vehicle, such as a minivan, and a portion of the wiring harness in such a vehicle. Harness  11  includes supplemental restraint system (SRS-air bag) module  12  and weight sensing module  14 . Weight sensing module  14  is located under front seat  15  and is coupled to several force sensors, such as sensors  17  and  18 . By interpreting the signals from the force sensors, module  14  can determine the weight of the mass resting on front seat  15 . 
     Occupant detection system  21  typically includes capacitive sensors located in the back of seat  15  and is coupled to wiring harness  11  by module  23 . Wiring harness  11  includes various connectors that separate the harness into segments to facilitate assembly or repair. In accordance with one aspect of the invention, the segment between the seat and the SRS module is replaced with a section of harness including two segments,  25  and  26 . Segment  27  couples shunt  28  to wiring harness  11 . 
       FIG. 2  illustrates a shunt constructed in accordance with a preferred embodiment of the invention. Connector  31  couples microprocessor  32  to segment  27  ( FIG. 1 ). As described in the Background, some portions of the OEM system can be emulated with passive components. Circuit  41  replaces the buckle switch. Circuit  41  includes a switch in the event that it becomes necessary to indicate a closed buckle. For example, if the front passenger area is modified to accommodate a wheelchair or other device for carrying a person of limited mobility. Circuit  42  emulates an airbag sensor (indicates the presence of a seat to the SRS controller). Circuit  43  represents other circuits that can be emulated with passive components. 
     In accordance with the invention, microprocessor  32  is coupled to the network portion of harness  11  ( FIG. 1 ) by transceiver  33 . Microprocessor  32  also has control or sense lines coupled to harness  11 . As illustrated in  FIG. 2 , serial bus  45  is a two wire bus, shown as a twisted pair of wires. The serial bus can be a single wire instead. 
     Circuit  44  is a ground loop or short that exists in the OEM harness and is used by microprocessor  32  as an indication that a seat is installed. In this case, microprocessor enters a sleep mode and the electronics in the passenger seat modules operate normally. There is no possibility of interference from shunt  28 . This provides a significant advantage for the vehicle owner because the vehicle can be reconfigured at will to suit the passengers by installing or removing the seat and connecting or disconnecting the wiring harness. For wiring harnesses in other make or model vehicles, a direct connection to ground could be utilized instead if there is no existing loop. 
     When the ignition is turned on, SRS module  12  sends out a code, an initiation request, to the passenger seat. Assuming that weight sensor module  14  is addressed, module  14  responds with a serial number, which is checked by SRS module  12 . SRS module  12  then sends an initiation request to occupant detection module  23 , which responds with a serial number. Assuming that the serial numbers are correct, SRS module  12  then enters a loop in which weight and occupant data are repeatedly requested from and sent by the appropriate module. This process is performed in a Honda Odyssey minivan for model year 2006. Other makes, models, or years could have a different sequence. The serial numbers are not revealed by the OEM. Thus, the number of possibilities that must be accommodated is significant. 
     In accordance with the invention, microprocessor  32  enters a “learn” mode in which the microprocessor monitors data bus  45  and memorizes the signals and the responses to the various signals. If the seat is empty and the correct response is learned, such is usually sufficient. The standards for the serial bus define the components (e.g. header, address, data, checksum) of a message, simplifying the learning process somewhat. That is, the microprocessor knows (is programmed) where to look for content in the data stream and does not memorize or store needless or repetitious data. 
     During the learning process, various conditions can be imposed; e.g. the front passenger seat is left empty, an adult sits in the seat, a small person sits in the seat, or a bag of goods is placed on the front passenger seat. The various conditions, depending upon year, make, and model of the vehicle, may not be necessary. Imposing various conditions provides reassurance during the development of a shunt that the system is learning correctly even if the meaning of the signals is not known. It is another advantage of the invention that the meaning of the signals need not be known. The shunt merely provides a sufficient response to obviate a false positive in the error detection software of an OEM module. The meaning of that response need not be known. 
       FIG. 3  is a wiring diagram of the Y-harness used for coupling the shunt to the wiring harness of a vehicle. Connectors  51  and  52  couple the Y-harness to harness  11  ( FIG. 1 ). Connector  54  couples the Y-harness to shunt  28  ( FIG. 1 ). Connector  53  connects to connector  56  ( FIG. 4 ) or  61  ( FIG. 5 ). The harness illustrated in  FIG. 4  couples to seat  15  by means of connectors  57  and  58 . The harness illustrated in  FIG. 5  couples to seat harness  26  by means of connectors  62  and  56 . 
       FIG. 5  illustrates the “learning” harness that is connected between the harness of  FIG. 4  and the Y-harness illustrated in  FIG. 3 . The connections for the learning mode are illustrated in  FIG. 6 . In  FIG. 4 , pin  21  (BRN) is an intermittent ground. If a seat is connected, this ground is detected by the shunt and microprocessor  32  ( FIG. 2 ) enters a sleep mode. In learning mode, the intermittent ground is switched from one pin to another pin when passed to the shunt. Pins  21  in connectors  61  and  62  are not connected. Pin  23  in connector  61  is grounded. Thus, the shunt is active and in learning mode. 
     During learn mode, signals on a single wire serial bus, pin  16  (GRN/ORN), are monitored as described above for twisted pair  45  ( FIG. 2 ). Learn mode is completed when the responses to all commands have been stored. When learn mode is completed, intermittent supply line  24  is activated, supplying current to light emitting diode  65  through resistor  66 . This signals the installer that the shunt is ready for use. The installer removes harness  60  and connects connector  56  ( FIG. 4 ) to connector  53  ( FIG. 3 ). 
     When the shunt learns the codes necessary to emulate the OEM data, the learning mode ends. The duration of the learning mode depends upon how long it takes for the OEM module to send and receive the required data among OEM modules  12 ,  14 , and  23  and the time it takes for microprocessor  32  to store that date in memory. For example, if the ignition is turned on and simply left on, the shunt will end learning mode in approximately 30-40 seconds and turn on LED  65 . 
     The invention thus provides a shunt for emulating circuitry that has been disconnected from the wiring harness of a light duty motor vehicle. The shunt can emulate the circuit even when the meaning of the signals is not understood. The shunt can be programmed in the vehicle for which it is to be used and adapt to identification or other unique codes circulating in networks of the vehicle. The shunt can be left coupled in parallel with the circuit it is to replace without interfering with the operation of that circuit. 
     Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, although described in the context of a front passenger seat, a shunt can be used to emulate any circuit coupled to a network in a vehicle, such as but not limited to, circuits associated with other seating, doors, tailgates, sliding roof panels, or lift gates. A “sleep” mode is any mode of operation in which the microprocessor is prevented from providing signals to the network when a “sleep” signal is sent to the microprocessor. Whether such mode is effected as sleep, power down, enable/disable, masking interrupts, or other means is immaterial. The action need not be taken at the microprocessor. For example, transceiver  33  could be disabled instead.