The present invention relates to locomotive headlight assemblies and more particularly to a headlight assembly that includes a controller that determines which of several current paths through a resistive control switch has been selected and controls light intensity as a function of the selected current path.
A locomotive requires one or more large headlights in order to illuminate a track in front of a train for warning and safety purposes. Most locomotive headlight systems have been designed so that the headlight or headlights can be driven with different currents to generate light with two or three different intensities. For instance, when on an open track in the country, the headlights may be driven with a very high intensity to provide warning far in front of the locomotive that a train is approaching while locomotives used in a city or in a work yard may be driven at a medium or low intensity.
Most known locomotive headlight system configurations include one or more incandescent-type headlights linked to a power source through a control switch where the control switch is controllable to adjust current applied to the headlight thereby controlling headlight light intensity. For instance, in at least some cases the control switch will include three current paths between an input node linked to the source and an output node linked to the headlight. Each path has a different resistance value which affects the amount of current that passes through that path when the control switch selects the path.
Several problems exist with headlight systems like those described above. First, when a locomotive headlight fails, the headlight has to be replaced prior to using the locomotive. While replacement is typically a relatively simple process, sometimes replacement headlights may not be readily available resulting in locomotive down time (i.e., a locomotive cannot be used when a headlight malfunctions). Trains only generate revenue when they are running and therefore any down time is extremely costly.
Second, incandescent type locomotive headlights require a large amount of power and therefore are relatively costly to drive when compared to other types of headlights.
Third, electrical systems in locomotives vary appreciably and the variance affects the amount of current delivered to headlights in different locomotive setups. For instance, in many cases two or more locomotives may be linked together at the front of a train and, in many cases, any one of the linked locomotives may be used to drive and control the headlights at the front of the train. For example, where first, second and third locomotives are linked at the front of a train, each of the three locomotives will have its own power source and electrical system and any one of the locomotives may be used to drive and control the front headlights. Here, while the power sources on each of the three locomotives will have similar output, often times the outputs vary somewhat so that current delivered at any of the selectable output levels may vary somewhat. For instance, when a control switch selects the high light intensity, depending on the source output level, the high intensity currents may be different thus resulting in different headlight intensities.
Exacerbating the intensity control problem, the total resistive drop between driving source and headlight(s) depends on which power source is used to drive the headlights. For instance, in the case of three linked locomotives, where the first locomotive source is used to drive a headlight, current from the first source only has to pass through the first locomotive's electrical system. Where the second locomotive source is used to drive the headlight, current from the second source has to pass through the first and second locomotive electrical systems and the resistive drop is greater. Where the third locomotive source is used to drive the headlight, current from the third source has to pass through the first, second and third locomotive electrical systems and the resistive drop is even greater. The different resistive drops affect the output light intensities.
One solution suggested for solving the problems described above has been to provide LED based locomotive headlight assemblies. As known in the art LED headlights typically last far longer than incandescent type headlights and use less power. In addition, a controller can be provided for an LED headlight to precisely control the amount of current provided to the LEDs that comprise the headlight and therefore to control the intensity of the headlight. These controllers can be used to adjust headlight intensity to be high, medium or low.
While it would be useful to replace incandescent type headlights with LED based headlights in locomotives, one impediment to such use is that a headlight control system for switching between high, medium and lower intensities is required. Ideally the existing resistive control switch could be employed so that additional components are not required. Unfortunately, existing resistive control switches simply rely on changes in current through a switch to adjust headlight intensity. Because the current levels used for incandescent lights are far greater than currents required to drive LEDs, existing resistive control switches alone cannot be used to drive an LED headlight.
Another solution would be to install a completely different headlight control system that can deliver intensity command signals to a headlight. While this solution would work, this solution is likely cost prohibitive as it would require additional hardware and installation time.