1. Field of the Invention:
The present invention relates to a system for multiplexed communications on vehicles and particularly relates to providing non-specialized remote interface modules from which may be invoked specialized functionality by an electronic system controller. The remote interface modules operate specific vehicle systems under the direction of an electronic system controller communicating with the remote interface module over a multiplexed communication system. The electronic system controller is programmable to implement, in sequence, certain states on the remote interface module(s). The present invention further relates to a method for installing the programming on electronic system controllers.
2. Description of the Prior Art:
Multiplexed communications involve data transmission interconnections which interleave nonsynchronous digital signals into a single serial signal. Multiplexed communication systems also provide the reverse function (demultiplexing) of dividing the single signal into multiple, nonsynchronous digital signals. Applied to motor vehicles, multiplexed serial communication paths are seen as an effective technique for reducing the number of dedicated communication paths between the numerous switches, sensors, device and gauges installed on the vehicles. With each increase in the number and variety of accessories and functions installed on each vehicle, the benefits of using a single, multiplexed serial communication link for passing instructions to and receiving information from vehicle devices as diverse as running lights and rear axle temperature sensors becomes greater. Multiplexing the signals to and from vehicle systems promises greater physical simplicity through displacing much of the vehicle wiring harness, the reduction of manufacturing costs, the enabling of vehicle electrical load management, and the enhancement of system reliability. The development by the Society of Automotive Engineers of the J1939 series of standards for multiplexed communications testifies to the progress in the application of multiplexed communications to vehicles. Standards have been or are being developed relating the communication path, transmission collision detection, diagnostic ports and data protocols, among other topics.
A multiplexed serial communications system can link several remote digital controllers positioned around a vehicle with an electrical system controller (ESC) for two way communication. Remote digital controllers are addressable, allowing them to respond to signals intended for them initialize particular functions. They may also include programming that allows the device to react to local conditions as well as condition indicating signals provided the controller. The ESC may pass requests and instructions received for operations of certain devices, addressed to the correct remote controller, in a fashion to condition the timing and duration of the responses to requests to better manage overall vehicle electrical load.
U.S. Pat. No. 4,809,177 to Windle, et al., which is assigned to the assignee of this patent, relates to a multiplexed communications system in which a central controller organizes signals to various vocational controllers distributed about a vehicle. The distributed controllers included internal data processing capability and programming. Among the controllers were engine, cab and chassis controllers. The environment of Windle et al. is a limited multiplexing environment, where much operational responsibility is distributed to the controllers.
Windle et al. teach a controller constructed according to a single design suitable for use both as a chassis controller and a cab controller. The chassis controller handles the engine brakes, the ignition, the air conditioning compressor and some external lights while the cab controller handled other external lights, the air conditioning compressor, the windshield wiper motor, among other functions. The dual purpose controller is a microprocessor based system running stored programs in local memory. The controller is adapted to handle one or the other of the differing sets of functions by being reprogrammed and by applying different inputs to the device. Reprogramming involved overwriting non-volatile memory or replacing programmable read only memory units. Windle et al. recognized that if a controller could be constructed in accordance with a single design for different vocations, benefits would be gained in terms of inventory costs and manufacturing costs, and anticipated improvements in reliability. However, Windle et al. did not attempt to extend the idea of single design controller outside of an environment where the requirements on the controller could be fully anticipated nor did they attempt to remove specialized programming from the distributed controllers.
The extension of the idea of applying a generic controller to differing vocations is greatly complicated where the chassis manufacturer may not know the functions to which a controller will be put. Remote controllers are more readily applied to vehicles where the accessories to be installed on the vehicle are fairly standardized, even if numerous, than they are to commercial vehicles where the vehicle's required vocations are less predictable. This is especially true where a manufacturer provides a chassis and the purchaser adds extensive functionality. A number of examples of this situation come readily to mind, for example, coach builders of luxury busses, fire trucks and ambulances all place highly specialized requirements on a vehicle's electrical system which may, or may not, be known to the chassis manufacturer. In some cases these requirements may even be unique to a particular vehicle. Still, it is desirable for a coach builder to be able to adapt a serial communication system for the functionality of its bodies and to be able to specify accessory functionality without the need to hardwire that functionality into the vehicle.
Substantial economies of scale could be gained from using a standardized component for several vocations on commercial vehicles. The ability to support such a device would also simplify assembly and allow for smaller parts inventories, as partially achieved by Windle et al. Were remote controllers truly multi-application ready, greater differentiation in vehicles would also be obtainable.