Abstract:
A data transmission system for external use with a controller area network is installed on a motor vehicle undergoing high intensity electromagnetic interference susceptibility testing. The data transmission system includes a fiber optic cable extending from the immediate vicinity of the truck to a site relatively remote to the truck and out of the effective area of the artificially generated electromagnetic interference. An optical/electrical coupler in close proximity to the motor vehicle is connected to the vehicle controller area network to convert messages occurring on the network to optical signals. The connection is provided by an electrical cable constructed of a twisted pair of wires. The optical/electrical coupler is also connected to an end of the fiber optic cable in the vicinity of the truck. A remote data processing device is attached to the remote end of the fiber optic cable by an interface card installed in the remote data processing device. The interface card converts optical signals to controller area network compatible electrical signals for evaluation.

Description:
REFERENCE TO PRIOR APPLICATION 
     The present application is a continuation in part of Provisional Application No. 60/122,991 for CAN/J1939 Telemetry Probe for EMI Susceptibility Testing filed Mar. 5, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to vehicle communications networks and more particularly relates to providing a system and method for testing such networks for electromagnetic. interference (EMI) susceptibility 
     2. Description of the Prior Art 
     Contemporary designs for the control and management of vehicle components increasingly rely on methods derived from computer networking. Digital data is exchanged between component controllers over a common physical layer, such as a twisted shielded pair of wires. Intelligible communication between two or more device controllers among a greater plurality of devices, all occurring over the common physical layer, depends upon the communicating devices being able to discriminate among messages they receive and respond to those messages directed to them. Such methods are well known in the art and are part of the standards which the Society of Automotive Engineers (SAE) has published and continues to publish as part of the SAE J1939 protocol. 
     The J1939 protocol provides an open protocol and a definition of the performance requirements of the medium of the physical layer, but also allows for development of proprietary protocols. The SAE J1939 protocol is a specialized application of a controlled area network (CAN) and may be readily implemented utilizing commercial integrated circuits such as the C167 Integrated Circuit from Stemens of Germany. 
     The CAN protocol is an ISO standard (ISO 11898) for serial data communication, particularly aimed at automotive applications. The CAN standard includes a physical layer (including the data bus) and a data-link layer, which define a few different message types, arbitration rules for bus access and methods for fault detection and fault confinement. The physical layer uses differential transmission on a twisted pair wire bus. A non-destructive bitwise arbitration is used to control access to the bus. Messages are small, at most eight bytes, and are protected by checksum error detection. Each message carries a numeric value which controls its priority on the bus and typically also serves as an identification of the contents of the message. CAN offers an error handling scheme that results in retransmission of messages when they are not properly received. CAN also provides means for removing faulty nodes from the bus. CAN further adds the capability of supporting what are termed “higher layer protocols” for standardizing startup procedures including bit rate setting, distributing addresses among participating nodes or kinds of messages, determining the layout of the messages and routines for error handling on the system level. 
     Digital data communications over serial data paths are an effective technique for reducing the number of dedicated communication paths between the numerous switches, sensors, devices and gauges installed on the vehicles. Multiplexing the signals to and from local controllers and switches promises greater physical simplicity through displacing much of the vehicle wiring harness, reducing manufacturing costs, facilitating vehicle electrical load management, and enhancing system reliability. However, such systems are not immune to electromagnetic interference (“EMI”). The physical layer of the communication network is, in effect, an antenna, which converts electromagnetic radiation into electrical signals on the physical layer. These signals can combine with data pulses in ways that change the values of the data pulses. Changing a single data point (bit) in a data package makes the data package useless to the intended destination, and may even prevent the destination from decoding the signal at all. 
     The design of vehicles, and of particular interest here, trucks, requires consideration of the EMI susceptibility of the vehicle&#39;s communication system. Testing of such systems, as part of the design and development of trucks, is carried out in an intense EMI environment with the truck mounted on rollers so that EMI susceptibility may be determined during operation of the vehicle. The testing environment provides a roller bed for the truck, with the roller bed possibly disposed on a turntable. An EMI source is aimed at the truck. In effect, an objective of the testing is to make the vehicle&#39;s communication network as inefficient an antenna as possible. The specifications for the testing are set forth in the SAE Standard J551, parts 11, 12 and 13. 
     During testing a datalink or telemetry probe is connected into a data bus diagnostic port on the truck, and may be positioned in the truck cab under the steering column. The datalink runs from the port to a location away from the truck, where it is connected to monitoring equipment. These data links have typically been constructed of a twisted pair cable. The external data link is severely limited in length, in large part because the cable acts as an extension of the antenna formed by the physical layer of the truck&#39;s network. Because the external cable changes the dimension and length of the antenna, it also changes the susceptibility of the combined system. This can result in additional errors to messages transmitted on the truck&#39;s CAN network, or, under some circumstances, it can result in fewer errors than would otherwise occur. In either case the test results are suspect. 
     Because the external link acts as an antenna itself, or as an extension of the antenna formed by the physical layer of the truck&#39;s data network, the external data link distorts the conditions of the test. More accurate direct measurements can be obtained if the affects of the external data link are minimized. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a reliable controller area network communication link in an EMI intensive environment. 
     It is another object of the invention to provide a test data link into an electrical data communications system which minimizes changes to the EMI susceptibility of a vehicle communications system. 
     It is a still further object of the invention to provide a CAN based repeater able to simulate a portion of a CAN network. 
     It is yet another object of the invention to provide extension of the CAN network to a remote location during EMI susceptibility testing. 
     It is still another object of the invention to provide qualification of a optical interconnection to an electrical controller area network. 
     According to the invention there is provided a data transmission system for external use with a controller area network installed on a motor vehicle undergoing high intensity electromagnetic interference susceptibility testing. The data transmission system includes a fiber optic cable extending from the immediate vicinity of the truck to a site relatively remote to the truck and out of the effective area of the artificially generated electromagnetic interference. An optical/electrical coupler in close proximity to the motor vehicle is connected to the vehicle controller area network to convert messages occurring on the network to optical signals. The connection is provided by an electrical cable constructed of a twisted pair of wires. The optical/electrical coupler is also connected to an end of the fiber optic cable in the vicinity of the truck. A remote data processing device is attached to the remote end of the fiber optic cable by an interface card installed in the remote data processing device. The interface card converts optical signals to controller area network compatible electrical signals for evaluation. 
     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 an illustration of a vehicle electrical system in a perspective, partial cutaway view of a truck; 
     FIG. 2 is a high level block diagram of the invention; 
     FIG. 3 is a state diagram illustrating the control sequence for the system of the invention; 
     FIG. 4 is a detailed block diagram of an optical electric coupler used with the system of the invention; 
     FIG. 5 is a plan view of an optical electrical coupler connected and a test regimen topography; and 
     FIGS. 6A-6C is a detailed circuit schematic of one channel of the optical electric coupler of FIGS.  4  and  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a perspective view of a vehicle  13  and of an electrical control system  10  installed on the vehicle. Vehicle electrical system  10  comprises a twisted pair (either shielded or unshielded) cable operating as a serial data bus  18 . Collectively, bus  18  and the various nodes attached thereto form a controller area network (CAN). 
     Active vehicle components are typically controlled by one of a group of autonomous, vocational controllers, which include a gauge cluster  14 , an engine controller  2 , 0 , a transmission controller  16 , an auxiliary instrument and switch bank  12 , and an antilock brake system (ABS) controller  22 , all of which are nodes on bus  18 . The autonomous controllers include local data processing and programming and are typically supplied by the manufacturer of the controlled component. Bus  18  is a twisted pair cable constructed in accordance with SAE standard J1939 and is externally accessible via a diagnostic port  36 . Diagnostic port  36  is typically located under the steering column inside the cab of vehicle  13 , but may be located elsewhere. 
     In many applications, the autonomous controllers handle many functions locally, utilizing data received over bus  18  from other controllers. Some CAN networks may include an Electrical System Controller (ESC)  30 , in which case they report data to ESC  30  and receive operational requests from ESC  30 . When present, ESC  30  manages a number of vocational controllers connected to bus  18  as nodes and disposed on vehicle  13 . ESC  30  also executes a load management program which oversees the total load imposed on the vehicle electrical system and power train by various accessories installed on the vehicle. 
     The loads imposed on vehicle  13  systems controlled by electrical control system  30  are usually electrical loads, however, they may include electronically controlled engagement of mechanical devices to the power train of vehicle  13 . Gear selection in an automatic transmission would be an example of such a system. Other electrically controlled nonelectrical loads can include control of a clutch for an air conditioning compressor, or actuation of pumps driven by the vehicle drive train. The load management program can, depending on power demands by components, request increased power output from the engine through engine controller  20 . 
     Gauge cluster  14 , transmission controller  16  and engine controller  20  can all communicate with ESC  30 , which then monitors inputs received from the auxiliary instrument and switch bank  12  over the serial communication link in harness  18 . ESC  30  may be programmed to override the normal response characteristics of the gauge cluster  14 , transmission controller  16  and engine controller  20 , should electrical and mechanical loads exceed the capacity of the vehicle, should requests conflict with one another, and under other circumstances. 
     Bus  18 , being either a shielded or unshielded twisted pair of wires, can function as an antenna and thus is vulnerable to electromagnetic interference (EMI). Digital data is unlike digitally transmitted voice or music in being relatively vulnerable to electromagnetic interference. Digitally transmitted uncompressed music and voice is relatively immune to EMI because changing a few bits in the stream of digital data does not change enough of the data stream to effect human perception of its auditory reproduction. However, in the typical eight byte message used on a CAN, the change of a single bit destroys the usefulness of the message. Excessive error rates, defined as the increased frequency of messages having any error, particularly where they relate to the critical automotive or truck functions, can be controlled to some extent by a physical disposition of bus  18 , or by the substitution of more expensive shielded cable for unshielded cable. 
     Accordingly, vehicle  13  development preferably includes testing for EMI susceptibility of the CAN network including bus  18  and the nodes attached thereto. Evaluation of the network is done by accessing the network through diagnostic port  36  while exposing the vehicle  13  to EMI. A transmitting antenna  38 , positioned externally to the vehicle  13 , transmits electromagnetic radiation toward vehicle  13  during testing. The effects of the radiation on network communications are then monitored. 
     In the prior art, a J1939 compliant cable would be stretched from port  36  to a remote diagnostic computer  44 . J1939 cables, being shielded or unshielded twisted wire pairs, are typically electrically indistinguishable from the cable used on the vehicle as bus  18 . Thus the diagnostic cable functions as an antenna in the same manner as the vehicle mounted bus  18 . The effect can distort the results of testing, either by introducing additional message errors to the network or by reducing the number of errors which are occurring. The effect can be expected to be dependent on the frequencies of the EMI interference since the change introduced to the network cable is one akin to changing the geometry and dimensions of an antenna. The susceptibility of an antenna is a function of electromagnetic frequency. The system of the present invention utilizes an optical link  42  to extend the physical layer of the CAN network to a remote diagnostic computer  44 . The physical layer extension includes diagnostic port  36 , a short shielded twisted wire pair  39 , and a CAN compatible optical coupler unit  40 . Wire pair  39  usually connects diagnostic port  36  to coupler unit  40 , however, under some circumstances the wire pair is used as a feedback loop into coupler unit  40  for diagnostic purposes. Personal computer  44  is coupled to the data link by a CAN compatible optical/electrical network interface card as described below. 
     FIG. 2 illustrates a possible topography of the physical layer extension to a vehicle CAN  50  including twisted pair cable  39 , optical electrical coupler  40  and optical link  42 . Optical link  42  is connected to an adaptor card/remote bus controller  46  connected into an ISA, PCI, or PCMIA bus  48  expansion slot in a personal computer  44  programmed to operate as a diagnostic tool. Personal computer  44  is otherwise conventional stored program computer having a memory  52 , a central processing unit  54  and a display adaptor  56 . Cable  39 B indicates connection of cable  39  in a feedback loop for qualification of optical link  42  and coupler  40 . 
     Computer  44  implements various states illustrated by the state diagram of FIG.  3 . The system operates in two modes, standby  60  and data collecting  62 . There is of course the non-operational “OFF” mode  64 , where the test regimen installed on computer  44  is not operating. On transition from off mode  64  to standby mode  60 , various hardware interfaces are initialized. In standby mode  60  no data is collected from CAN bus  18 . From standby mode  60  the system can return to off mode  64 , or it can move to data collecting mode  62 . 
     Within standby mode  60  interactions are allowed with an operator through a conventional graphical user interface program written to one of the Windows application program interfaces and conventionally implemented through peripheral devices (e.g. CRTs, keyboards, pucks (not shown)) attached to computer  44 . The user may interact with system configuration, specification of descriptive information that is stored for each test, instructing the computer to move to collecting mode  62  (i.e. starting a new test), handling the results from previous tests, and instructing the system to move to off mode  64 . Configuration information, which may be entered during standby mode  60 , includes data required to specify the CAN interface hardware characteristics, including for example, interrupt number and input/output address. In addition, default thresholds for error detection rates, default values for moving window periods for error rate calculations and default information for general annotations must be entered. 
     All configuration information is stored in configuration initialization files used on instrument initialization. An initialization file is used on transition from off mode  64  to standby mode  62 . At that time available memory and hard drive space are checked to confirm sufficient computer  44  resources to carry out the test. Inadequate resources does not prevent test operation but does cause issuance of a warning to the user. The configuration file(s) is(are) read to establish the initial configuration, subject to user changes. 
     Within the data collecting mode  62  the system collects data from the CAN bus  18 . Personal computer  44  provides near real time display of the results of the test in progress, including the results for particular and overall error monitoring, message transfer rates, the current status of CAN bus  18  and any change in bus  18  status. User interactions are allowed relating to control of transition of the system from collection mode  62  to standby mode  60 , modifications of thresholds used to detect error rates, the control of error detection latches and to permit annotation of a test in progress, including: (1) notes about the test; (2) control of the event counter; and (3) notation of input field strength and frequency. 
     Additionally, there is a test transmit mode  66  which may be active within collecting mode  62 . Test transmit mode  66  supports transmission of a user specified message list at a user specified interval. This provides the system with the ability to qualify itself for both transmitting and receiving messages in the high EMI environment. This operational mode also allows the user to issue requests to particular CAN nodes during vehicle tests to cause the node to receive and transmit during the test. 
     The test regimen implemented by computer  44  includes the use of CAN bus error detection of several types. Explanation of the test regimens is aided by explanation of some operations of CAN  50 . Every transmitted message on CAN  50  includes a 16 bit Cyclic Redundancy Check (CRC) code. The CRC is computed by the transmitting node and is generated from the message content. The test process accumulates the number of CRC errors which occur during the collection mode  62 . The accumulation count may be executed by computer  44 &#39;s CAN interface and may be aggregated with other errors. Other error mode detection regimens exist, such as bit stuffing. Detection of a bit stuffing error results in CAN resynchronization. 
     There are certain predefined bit values that must be transmitted in certain locations of any CAN message. If a receiving node detects an invalid bit at one of these positions a Format error is flagged by the receiver. The number of format errors occurring during collection mode  62  is tabulated for comparison to a limit. Another error type monitored is the acknowledge (ACK) error which is flagged by a transmitting node. In addition, the actual bit level is monitored during collecting mode. 
     Bit stuffing has already been mentioned. The bit stuffing protocol requires that whenever five consecutive bit levels of like polarity have transmitted, a transmitter automatically injects (stuffs) a bit of opposite polarity into the bit stream. Receivers automatically delete such bits before processing messages. A receiving node that detects six consecutive bits of the same value flags a stuff error. The occurrence of such errors is monitored. Error performance data about the CAN bus  18  is aggregated in the form of either loss of synchronization or a low message rate. 
     The test data displayed includes: time; event counter; message error rates; message success rates; bus state (active/passive/off); zero error count to non-zero error count transitions; current pass/fail status for each observed error rate; latched pass/fail status and the ability to reset pass/fail latches. 
     FIG. 4 is a block diagram of the major functional blocks of the optical-electrical coupler  40  and remote bus controller  46  used in implementing the present invention. The system of the present invention allows a CAN bus to be extended to a remote location, here the location of personal computer  44 , without effecting the results of EMI susceptibility testing of the CAN bus. A field unit, provided by optical to electrical coupler  40 , must be operable in close proximity to vehicle  13 , and is preferably located within 2 meters of diagnostic port  36 . Optical-electrical coupler  40  is typically coupled to CAN bus  18  via a CAN compatible, twisted pair cable  39  connected between a J1939 stub connector  70  and diagnostic port  36 . Internally optical-electrical coupler  40  comprises a J1939 transceiver  72  for converting CAN messages to a pulse sequence for actuating light emitting diodes (part of fiber transceiver  74 ). The LEDs and photosensitive elements of fiber transceiver  74  are positioned in a fiber optic connector  76  for coupling light pulses onto a fiber optic link  42 . The two way transmission of data may extend out to 40 meters, with 35 meters being exposed to the EMI intense environment, without bit timing problems. Greater one way transmission lengths are possible. Optical-electrical coupler is shielded  78  against EMI and is preferably electrically independent of the vehicle  13 . 
     Fiber optic link  42  is connected at one end to fiber optic connector  76  on optical electrical connector  40  and at its other end to a fiber optic connector on a remote bus controller card  46  installed in a convention personal computer. The remote bus controller card  46  has a fiber transceiver  82  directly connected to fiber optic connector  80 . Fiber transceiver  82  communicates with a CAN controller unit  84  which in turn communicates over any selected standard, contemporary PC bus including an ISA bus, a PCI bus, or a PCMCIA bus. 
     FIG. 5 illustrates the interconnection topography of two fiber optic transceiver channels  104  and  154  contained within an optical electrical connector  40 . In the test topography two independent remote bus controllers  184  and  194 , which are preferably installed on independent test bed personal computers, but which may be installed on the same personal computer. Remote bus controller  184  is connected by a fiber optic link  174  to receive signals transmitted by LED  110 A, or to transmit signals to photosensitive receiving element  112 A, in a fiber optic connector  170 . Remote bus controller  194  is similarly connected by a fiber optic link  164  to an fiber optic connector  76 , which in turn includes a transmitting element  112  and a receiving element  110  in connector  70 . Signals may be transmitted or received over fiber optic link  164 . Channels  154  and  104  are electrically connected a J1939 compliant twisted pair cable  144 . Optical signals applied to either channel  154  or channel  104  are passed by the receiving channel as electrical signals over cable  144  to the non-receiving channel for retransmission as optical signals. Thus complete testing of the unit is possible. The differentiated channels also have the ability to receive their own messages and to verify circuitry from controllers out to the linkages. The possibility of false indications of correct operation are thus limited. 
     FIG. 6 is a detailed circuit schematic for a preferred embodiment of optical-electrical coupler  40 , illustrating one fiber optic channel  104  and a power supply  90 . A second fiber optic channel is deleted for the sake of clarity. Electrical isolation of coupler  40  from the power system of the CAN network being monitored is conventionally provided by a power supply section  88  using six commercial 1.5 volt batteries connected in series as a pack  90 . Coupler  40  is actuable by a simple hard switch  92  connected in series with the battery pack  90 . A five volt supply  100  is supported by pack  90  via a regulator section  102  from the maximum raw 9.0 volt supply supported by a fresh pack  90 . An “ON” indication is provided by illumination of a green LED  94  mounted in the exterior shielding  78  of the coupler  40 . This occurs when the positive output voltage on “channel 2” is sufficiently high. A low power indication is supplied by illumination of a red LED  96 , which is located in a sense section  98 . LED  96  passes current in response to a drop of voltage of the raw supply voltage to below a minimum required level. 
     A fiber optic channel transceiver section  104  includes J1939 stub connector  70 . Transceiver section  104  includes a LED  110  and a photosensitive element  112 . The circuitry is conventional for changing the format of the messages from or to CAN standards. 
     The invention provide a reliable controller area network communication link to a remote location in an EMI intensive environment. The communication link, being optical, does not affect the EMI susceptibility of an electrical communications system undergoing testing. The link itself is readily qualified for use in a particular EMI environment. 
     While the invention is shown in only one 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.