Abstract:
A method and apparatus for automatically responding to headlamp radiation from oncoming vehicles to down-switch beam patterns in a tri-beam headlamp system in an automotive vehicle. A mid-beam sensor is provided to detect only that headlamp radiation from oncoming vehicles present within the defined high intensity projection areas of the mid-beam pattern and functions in conjunction with a conventional automatic dimmer sensor and a unique control circuit to achieve appropriate and automatic down-switching.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to the field of automotive headlamp systems and more specifically to the area of automatic control for such systems in order to down-switch the beam patterns and prevent interfering glare to oncoming drivers. 
     2. Description of the Prior Art 
     In U.S. Pat. Nos. 3,373,311 and 3,894,227 inventions are disclosed which provide &#34;tri-beam&#34; headlighting systems of low, mid and high beam patterns controlled by various manually actuated switches to obtain the appropriate selection. 
     Low-beam headlamps are designed to provide adequate illumination for a vehicle operator without producing unacceptable glare for operators of opposing or oncoming vehicles. The low-beams are directed so that the high intensity projection areas of its beam patterns are directed sightly down and to the right for countries of the world which utilize right hand traffic patterns. In left hand traffic patterns, the low-beams are aimed down and slightly to the left. (For the remainder of this discussion right hand traffic patterns will be assumed.) With the use of low-beams, the left lane, the mid foreground and the right lane, beyond approximately 150 feet, are not intensely lighted. On the other hand, high-beam patterns are generally directed so as to cover much wider horizontal and vertical angles that will cause glare in the eyes of drivers of oncoming vehicles even on straight roads. 
     The mid-beam concept, although first disclosed several years ago, provides more usable light directed to the right edge of the driving lane without causing increased glare to opposing drivers, while on straight roads. However, the mid-beam concept has not been adopted by the industry. It is believed this reluctance to adopt such an improvement in headlighting systems is based upon the fact that when a mid-beam system is utilized, there are still those instances when the mid-beams have to be down-switched to the low-beams in order to prevent glare from interfering with the vision of the oncoming driver. For instance, when the road geometry varies (curves and hills) or the lamps are misaimed so that they could cause the high intensity projection areas of the mid-beam pattern to be directly aimed at opposing drivers, down-switching of the lights is required. Taking into consideration the aforementioned patents it is believed that such systems of manually down-switching from mid to low-beams by a vehicle operator would require the operator to have a sophisticated understanding of the system concepts in order to appreciate the necessity of when to manually down-switch the beams. It is clearly evident that a manually controlled mid-beam system is not practical, since it has not been adopted by the industry. Applicants have appreciated that it would be desirable to have an automatic headlamp control system, but such control systems presently available for high-beam down-switching will not function for a &#34;tri-beam&#34; headlighting system. U.S. Pat. Nos. 3,177,397; 4,599,544; and 4,645,975 are typical of such high-beam control systems. 
     SUMMARY OF THE INVENTION 
     Applicants have invented a unique system which automatically determines the appropriateness of down-switching from either the high to mid, high to low, or mid to low beams without the need for manual intercession by the vehicle operator. By providing a conventional high-beam sensor, a mid-beam sensor which is uniquely configured to sense the presence of oncoming vehicles in the mid-beam pattern projection area and a unique control circuit, the automatic down-switching is achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isocandella diagram showing candle power contours of the high intensity portion of a mid-beam pattern. 
     FIG. 2 illustrates a preferred geometric relationship between a headlamp that generates a mid-beam pattern and an associated mid-beam sensor. 
     FIG. 3 is a schematic representation of a mid-beam sensor such as is shown in FIG. 2. 
     FIG. 3A is a plan view of a mask employed in the sensor shown in FIG. 3. 
     FIG. 4 is a schematic representation of a second embodiment of a sensor such as is shown in FIG. 2. 
     FIG. 4A is a plan view of a detector array employed in the sensor shown in FIG. 4. 
     FIG. 5 is a schematic of a control circuit employed to provide the automatic down-switching of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The isocandella diagram shown in FIG. 1 is a gross plot of the high intensity pattern as projected by a mid-beam headlamp system. The diagram illustrates the high intensity beam pattern over a projection area above and below a horizontal reference line, as well as left and right of a vertical center line coincident with the center line of the vehicle. The designated angled lines on the diagram represent the perspective view of the right edge of the right lane, the road center line, the left edge of the left lane and the path of the eyes of an opposing driver, as it would appear when viewed from the vantage point of the left, outboard headlamp. It can seen from the diagram in FIG. 1 that one highest intensity (5,000-20,000 cp) illumination area for the mid-beam light projection is below the horizontal reference when referenced to the left of the vehicle center line and well below the path of opposing driver&#39;s eyes. Also, the mid-beam pattern provides another highest intensity illumination area both above and below the horizontal reference to illuminate the right edge of the right lane, when referenced to the right of the vehicle center line. 
     By concentrating on the center of the diagram as depicting the distant horizon on a flat straight road, it can be seen that the normal areas of projection by the mid-beam pattern would not cause irritating glare to be present in the eyes of an opposing driver. However if one imagines that the road curves off to the right, or that the center portion is a hill crest below the horizontal reference, the high intensity illumination pattern will intersect the line designated as the path of an opposing driver&#39;s eyes. In those instances, it is necessary to down-switch the beam to the low-beam pattern. 
     In the present invention, it is intended that, in normal use, the mid-beam headlamp will be on and that a mid-beam light sensor be provided which senses the presence of headlamps from only those oncoming vehicles that enter into the projection areas of the mid-beam pattern. When the mid-beam light sensor detects the presence of opposing headlamps in the projection areas of the mid-beam pattern, the mid-beam is automatically turned off. When this sensor no longer detects opposing headlamps, the mid-beam is turned back on. 
     Since the mid-beam pattern provides such a highly tuned radiation beam pattern, it is essential that the mid-beam headlamps be properly aligned in the vehicle so as not to cause excessive glare in the eyes of the opposing drivers. It is therefore preferable that the sensor be positioned on the vehicle so that its optical axis is parallel and closely aligned to the axis of the mid-beam headlamp. That configuration is shown in FIG. 2 where the sensor 10 and the headlamp 20 are shown as respective having optical axes S and M parallelly configured. If the sensor 10 and the headlamp 20 are provided with a fixed and rigid interconnection mounting, the system will still function even if there is an occurrence of misaiming of the mid-beam headlamp. In the event of misaiming, the system will continue to function to protect the eyes of oncoming drivers by down-switching the beam patterns when the oncoming headlamps of those vehicles are sensed within the mid-beam pattern projection area. 
     FIG. 3 illustrates a first embodiment of a mid-beam headlamp sensor 10 in which a forward field lens 14 is aligned along the optical axis S extending through the sensor 10. A mask 12 (detailed in FIG. 3A) is shown as being in the focal plane of an object lens 14 and contains an aperture 11 at the focal plane which outlines the inverted mid-beam pattern as shown in FIG. 1. A focusing lens 17 is positioned behind the mask 12 so as to focus any light passing through the aperture 11 onto a photodetector 15. Photodetector 15 is shown as being at the focal point of the lens 17 and mounted on a substrate 16. When this sensor 10 is mounted so that its optical axis S is aligned with the optical axis M of the mid-beam headlamp 20, light from the headlamps of oncoming vehicles will pass through the mask only when the location of the oncoming headlamps coincides with the mid-beam pattern projection area. 
     FIG. 4 illustrates a second embodiment of mid-beam headlamp sensor 10&#39;. In sensor 10&#39;, an object lens 14&#39; has an optical axis S&#39; and a detector 15&#39;. In this case, the detector 15&#39; is a photocell array 11&#39; (detailed in FIG. 4A) disposed on the focal plane of lens 14&#39;; and the array 11&#39; is configured as the inverted image of the mid-beam pattern shown in FIG. 1. The detector 15&#39; located at the focal plane of the lens 14&#39;; functions in a manner similar to the photodetector 15 shown in FIGS. 3 and 3A. The advantage of a sensor such as shown in FIG. 4 is that less optical elements are required, while continuing to achieve appropriate detection of oncoming headlamps solely within the mid-beam pattern projection area. In addition, it is envisioned that circuitry may be combined with the sensor shown in FIG. 4 to distinguish between opposing headlamps and other light sources which might be sensed and inappropriately cause the mid-beam headlamps to be down-switched. 
     FIG. 5 is an electrical circuit diagram illustrating a preferred embodiment of implementing the present invention. In that diagram, four headlamps 20, 22, 40 and 42 are selectively energized by an electrical energy source (Battery B-2) through current drivers D L , D M  or D H , via a control circuit 100. The headlamps 40 and 42 are designated as containing only the high-beam filaments; and the lamps 20 and 22 are shown as each containing both low-beam and mid-beam filaments. 0f course, other configurations such as arc lamps or separate lamps for high, mid and low beams could also be controlled in a manner using principals similar to those disclosed herein. 
     In FIG. 5, a high-beam sensor 30, with a lens 34, is shown and is assumed to be a conventional high-beam sensor which detects light radiation forward of the vehicle in a wide range that is at least as great as the high-beam pattern projection area. In any event the range of light detection of the sensor 30 overlaps the mid-beam pattern projection area. The detection of oncoming vehicle headlamps within the sensing area of high-beam sensor 30 is provided as a voltage signal on line A which is also connected to control circuit 100. 
     A mid-beam sensor 10 may be either of the sensors previously discussed with regard to FIGS. 3 and 4 and is configured to only sense light present in the mid-beam projection area and produced by oncoming vehicles within that limited detection area. Upon detecting light, the sensor 10 provides a voltage output on line B which is connected to the control circuit 100. 
     A battery B-1 is shown as providing logic level energy to the control circuit 100 via a headlamp switch SW-1. The headlamp switch SW-1 is shown as having three manually selected switch position settings including &#34;Off&#34;, &#34;Mid/Low&#34; and &#34;High&#34;. 
     The control circuit 100 contains various logic elements configured to provide output signals on the L, M or H lines to corresponding current driver devices D L , D M  or D H  in response to the manually set position of SW-1 and the ON or OFF state of sensors 10 and 30 when the light levels detected by those sensors are above predetermined thresholds sufficient to trigger associated logic elements. 
     The following Truth Table reflects the function of the control circuit 100 based upon the variables of the setting of switch SW-1, the state of high-beam sensor 30 and the state of mid-beam sensor 10. 
     
         ______________________________________TRUTH TABLE   HI-SENSOR  MID-SENSORSW-1    30         10          LIGHTS ON______________________________________HIGH    OFF        OFF         HIGH/MID/LOWHIGH    ON         OFF         MID/LOWHIGH    ON         ON          LOWMID/LOW --         OFF         MID/LOWMID/LOW --         ON          LOW______________________________________ 
    
     In the first instance when the switch SW-1 is set to its High position, the vehicle operator expects the filaments in high-beam lamps 40 and 42 to be energized along with the mid-beam filaments and low-beam filaments in lamps 20 and 22, to provide maximum light output from the vehicle headlighting system. If no oncoming vehicles are sensed by either the high-beam sensor 30 or the mid-beam sensor 10, the AND gate 102 receives a relatively high (logic &#34;1&#34;) level on line C and a relatively high (logic &#34;1&#34;) level from inverter 110. The AND gate 102 therefore outputs a relatively high (logic &#34;1&#34;) level on line H to bias the current driver D H  ON. With driver D H  in an ON (conducting state) the high-beam filaments of headlamps 40 and 42 are energized. Likewise, a direct connection on line C through diode 126 is made to bias the low-beam current driver D L  ON. With the current driver D L  in its ON state, the low-beam filaments in lamps 20 and 22 are thereby energized. The absence of detected light by both high-beam sensor 30 and mid-beam sensor 10 (logic &#34;0&#34;) causes the output of AND gate 106 to be at a low level (logic &#34;0&#34;). The output of AND gate 106 is inverted to a relatively high (logic &#34;1&#34;) level by inverter 116. The output of inverter 116 (logic &#34;1&#34;) is passed by diode 124 and causes the current driver D M  to be biased ON. With current driver D M  in an ON state, the mid-beam filaments in lamps 20 and 22 are also energized. 
     In the second instance, with the switch SW-1 still set in the High position, an assumption is made that the high-beam sensor 30 detects an oncoming vehicle and the mid-beam sensor 10 does not indicate such a detection. In that case, the change in signal on line A does not affect the relatively low (logic &#34;0&#34;) output state of AND gate 106 and the mid-beam current driver D M  continues to be biased ON. However, the inverter 110 inverts the relatively high (logic &#34;1&#34;) signal from sensor 30 to provide a relatively low (logic &#34;0&#34;) output signal to an input terminal of AND gate 102. That combination of input signals to AND gate 102 causes the output of AND gate 102 to be switched to a relatively low (logic &#34;0&#34;) signal. That low signal is carried by line H to thereby bias the current driver D H  to an OFF state. With current driver D H  in an OFF state, the high-beam filaments in lamps 40 and 42 are deenergized. The high-beams remain deenergized until the sensor 30 ceases to detect the presence of oncoming vehicle lamps in its field of view. 
     In the third instance, where the mid-beam sensor 10 also detects the presence of oncoming vehicle headlamps within its mid-beam pattern projection area field of view, both the sensor 10 and the sensor 30 provide relatively high (logic &#34;1&#34;) signal levels on lines A and B. This change from the preceding instance will cause the AND gate 106 to change state and provide a relatively high (logic &#34;1&#34;) level output, since all three input levels are at a relatively high (logic &#34;1&#34;) state. The high (logic &#34;1&#34;) output level of 106 is inverted by inverter 116 to a relatively low (logic &#34;0&#34;) level which biases the driver D M  to its OFF state. In that instance, the mid-beam filaments in lamps 20 and 22 are also extinguished, leaving only the low-beam filaments energized. The mid-beam filaments remain extinguished until the detector 10 no long senses the presence of oncoming vehicle headlamps in its field of view. 
     In the fourth instance, where the switch SW-1 is manually set to the Mid/Low position, the high-beam filaments in lamps 40 and 42 are not energized and detection of oncoming headlamps by the high-beam sensor 30 have no effect on the circuit. However, assuming that no oncoming headlamps are detected by the mid-beam sensor 10, all three inputs to the AND gate 104 are at a relatively high (logic &#34;1&#34;) level and the output of the AND gate 104 is at a relatively high (logic &#34;1&#34;) level. This high level output of AND gate 104 is communicated through diode 122 to bias the current driver D M  to an ON state and thereby cause the mid-beam filaments in lamps 20 and 22 to be energized. The low-beam filaments in lamps 20 and 22 are maintained in an energized condition by the current driver D L  that is biased to its ON state via diode 128 and switch SW-1. 
     In the event the mid-beam sensor 10 detects the presence of oncoming headlamps within its limited field of view, the voltage signal produced on line B is inverted by inverter 114 to provide a relatively low (logic &#34;0&#34;) level input to the AND gate 104. Consequently, the AND gate 104 switches to a relatively low output state and the current driver D M  is biased to its OFF state, thereby extinguishing the mid-beam filaments and leaving only the low-beam filaments to be energized. 
     It makes previously proposed &#34;tri-beam&#34; headlighting systems more acceptable since it can be seen from the foregoing description that the present invention provides an automated system for down-switching beam patterns to avoid producing glare in the eyes of drivers of oncoming vehicles. 
     It will be apparent that many modifications and variations may be implemented without departing from the scope of the novel concept of this invention. Therefore, it is intended by the appended claims to cover all such modifications and variations which fall within the true spirit and scope of the invention.