This invention relates generally to multiplexed D.C. electrical systems. More specifically, the invention relates to the multiplexing of electrical voltage to electrical loads in automotive vehicles, such as trucks and highway tractors.
Known automotive electrical technology includes proposals for various forms of multiplex systems. These systems have a number of documented advantages. One of the principal advantages is a reduction in the aggregate amount of wiring in a vehicle. Another advantage is that the current capacities of switching devices which control the flow of power to associated electrical loads can be significantly reduced in comparison to a non-multiplex system where the switching devices must be able to carry the full load current of their associated loads. Similar current-rating reductions can be made in many of the electrical connectors. State-of-the-art multiplex systems incorporate electronic control circuitry, often microprocessor-based, for performing the multiplex control functions. The added expense of such control circuitry is justified by advantages, such as those just mentioned. Corollary benefits of D.C. multiplex systems may include improved diagnostics, better reliability, and longer useful lives for electrical components.
Evolution of automotive electrical systems has resulted in increased voltage power supplies. The old 6-volt system has been essentially obsoleted in favor of today's prevailing 12-volt system. The ever-increasing use of electrical devices in vehicles imposes further demands on prevailing system voltage, and obsolescense of the 12-volt system is a real possibility in the future.
Fundamental principles of electric power distribution recognize that for a given wattage, increased efficiencies can be obtained by delivery of that power at higher voltage. While it is generally true that most electrical load devices can be designed for any given system voltage, the adaptation of certain types of electrical load devices for higher voltage operation may be accompanied by certain adverse consequences on them. One load device which may be adversely affected is the incandescent lamp which is designed for automotive vehicle usage. While it is certainly possible to fabricate a 24-volt continuous D.C. incandescent lamp, concerns have been expressed about the ability of the filament to attain life expectancies comparable to those of existing 12-volt lamp filaments. Because of the extensive use of incandescent lamps in automotive vehicles, particularly trucks and highway tractors, such concerns must be addressed in order to take advantage of the benefits of both higher voltage and multiplex systems in these vehicles.
One aspect of the present invention relates to a novel electrical system for adapting 6 and/or 12-volt D.C. incandescent lamps for use in a 24-volt D.C. electrical system so that the established life expectancies for such lamps can be anticipated in an automotive vehicle lighting system operated from such an increased voltage supply.
Another aspect of the invention relates to a multiplex system for multiplexing a given D.C. supply voltage to an electrical load whose continuous D.C. voltage rating is at most essentially one-half that of the supply. As applied to an automotive vehicle electrical lighting system, the invention adapts existing 6 and/or 12-volt D.C. incandescent lamps to a 24-volt D.C. supply in a manner which enables various standard signaling functions to be performed in novel and unique ways.
One series of embodiments of the invention is of a "two-wire" type system; another series, of a "three-wire" type system. The embodiments are disclosed in a highway tractor lighting system to perform running (park/tail/marker) light, stop (brake) light, turn signal, marker interrupt, and hazard warning functions. A single lamp, or single lamp load, can be used to perform these signaling functions because they are prioritized according to a pre-assigned priority.
Within the generic principles of the invention, further, and more specific, inventive features are found in the particular circuit embodiments which will be described in detail. Although the particular circuit embodiments illustrated in the several drawing figures are of electrical lighting systems, principles of the invention extend to certain electrical systems other than electrical lighting systems.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.