WO2000041008A1 - Visibility sensor system - Google Patents

Abstract

A fog sensing system is disclosed having a sensor enclosure (226'') having a light source (52) and a light detector (56) therein. The sensor enclosure (226'') has an opening with a filter (308) thereover. The sensor enclosure (226'') is particularly suited for applications on an automotive vehicle. As the automotive vehicle travels, air rushing by an opening in the enclosure creates a low pressure within the enclosure (226'') so that air is drawn through the filter (308) and over the light source (52) and the detector (56). The moving clean air continuously washes over the light source (52) and detector (56) so that dirt or other contaminants are not built up on the detector (56) and light source (52).

Description

VISIBILITY SENSOR SYSTEM

BACKGROUND OF THE INVENTION

The present invention relates generally to a sensor system to detect visibility and, more specifically, to a visibility sensor system particularly suited for automotive applications.

Reduced visibility on highways due to fog or blowing dust has often been the cause of tragic traffic accidents. Fog, especially m mountainous regions, has a tendency to build up m patchy dense pockets. At highway speeds, m particular, a driver may suddenly find himself withm one of these patchy dense fog pockets .

The ability to adequately warn drivers of dense fog is highly desirable. If adequate warning is provided to drivers, drivers may then reduce their speed based on the density of the fog. Adequate warnings will reduce loss of life.

Several optical and non-optical methods for determining the presence of fog are known. Most, however, are not suitable for highway visibility sensors. There are several optical systems that may be used. Radar and lidar systems are used to gather general weather data. Such systems are too expensive, bulky, insensitive and difficult to use on a highway.

Closed circuit television has limited use for visibility detection, but it cannot function at night and requires monitoring by an operator. Airports commonly use transmissometers . Transmissometers measure the transmission of a light beam traveling a given path. Transmissometers are very expensive and require considerable maintenance and thus are not suitable to detect patchy highway fog. Coulter counters are often used m clean room monitoring. Coulter counters are very expensive and have high maintenance and power consumption requirements.

Non-optical devices such as triboelectπc current sensors depend on the flow of gas rubbing against an electrode. Fog, however, frequently occurs m quiet atmospheric conditions. Spark discharge sensors require sensor electrodes to continually be kept clean and thus maintenance costs are prohibitive. A dosimeter-type particle density measurement device does not provide real-time data.

Another optical device for measuring fog is a nephelometer . Known nephelometers have expensive optical systems and are very large m size. The optical system requires constant maintenance to clean the windows through which the optics are directed.

In certain situations, it may be desirable for the vehicle to have a visibility detection system associated therewith. It would likely be cost prohibitive to provide highway visibility detection systems across the country. Therefore, it is desirable to provide a visibility sensor system associated with the vehicle. The output of the visibility sensor may be used to signal the driver as to the amount of visibility.

On ships, it is difficult to determine visibility due to lack of background for comparison. For ships, it may also be desirable to locate a visibility sensor on the ship.

It would therefore be desirable to provide a visibility sensor system that overcomes the drawbacks of the prior art. Particularly, it would be desirable to provide a visibility sensor system that is inexpensive, has low maintenance, and is reliable to endure the conditions experienced on a highway.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved visibility detection system. More specifically, it is an object of the invention to provide a visibility detection system suitable for incorporation on an automotive vehicle.

According to one embodiment of the invention, a detector includes a housing having a first hollow opening and a second hollow opening. A first light source is fixed within the housing and directs light through the first hollow opening to a sample volume outside the housing. A first light detector receives light reflected from the sample volume through the second hollow opening. A controller is coupled to the first light source and the first detector. The controller determines an output indicative of visibility from the light received by the first light detector .

In another embodiment of the invention, a fog sensing system is disclosed having a sensor enclosure having a light source and a light detector therein. The sensor enclosure has an opening with a filter thereover. The sensor enclosure is particularly suited for applications on an automotive vehicle. As the automotive vehicle travels air rushing by an opening m the enclosure creates a low pressure withm the enclosure so that air is drawn through the filter and over the light source and the detector. The moving clean air continuously washes over the light source and detector so that dirt or other contaminants are not built up on the detector.

In another embodiment of the visibility sensor system, a display may be coupled to the controller to warn drivers of the existence of fog ahead. The display may also indicate a safe driving speed through the fog.

In yet another embodiment of the invention, a means for compensating for the deterioration of the first detector may be included. To compensate for the deterioration of the first detector, a second light source may be placed adjacent to the first detector and illuminate the first detector with a predetermined amount of light. The controller then calculates the deterioration of the first detector m its visibility calculation. In another aspect of the invention, a means for determining deterioration of the first light source may be concluded. The means for compensating for deterioration of the first light source includes a second detector located adjacent to the first light source. The second detector would provide feedback to the controller as to the deterioration of the light source. The controller would then compensate for any deterioration of the first light source m its calculation for visibility.

In yet another embodiment of the invention, a method for detecting visibility comprises the steps of illuminating a sample volume of air from a first hollow opening within a housing using a first light source, detecting the amount of light scattering from the volume of air with a first detector that receives light through a second hollow opening and calculating a visibility factor based upon the light scattering from the fog particles m the volume of air.

In one aspect of the method for calculating visibility, the calculation may take into consideration deterioration of the first detector and the first light source .

In still another embodiment of the invention, a removable sensor head comprises a sensor enclosure defining a first optical port and a second optical port. A first circuit board is coupled to the sensor enclosure. A first connector is coupled to the first circuit board. A light source is coupled to the first circuit board, which positions the light source withm the first optical port. A second circuit board is coupled to the sensor enclosure. A second connector coupled to the second circuit board. A light detector is coupled to the second circuit board. The second circuit board positions the light detector with the second optical port A calibration memory is coupled to the second circuit board.

In a further embodiment of the invention, a visibility sensor assembly has a housing having a sensor head opening. A removable sensor head assembly is removably coupled to the housing withm the sensor head opening. The sensor head assembly has a sensor enclosure and a connector. An electronics module is coupled to the sensor head through the connector.

In yet another embodiment, a ram sensor is provided, which is configured to close one or more shutters that cover the first and second openings. This has the advantage of minimizing the entry of contaminants .

In yet another embodiment, a sensor enclosure is provided which is configured to produce an airflow therethrough such that contaminants are swept through the enclosure. This has the advantage of minimizing the contamination of the light source and/or light detector.

In yet another embodiment, the sensor output may be used to automatically turn on the fog lights when fog or reduced visibility is sensed and turn off the fog lights when visibility improves. One advantage to providing a removable sensor head is that the maintenance costs are reduced because the sensor head may be easily replaced.

One advantage of the present invention is that no optics or windows are required within the hollow openings through which light is transmitted and received. This eliminates a major problem for optical sensor systems. That is, eliminating the persistent need for cleaning of the optics or windows .

Another advantage of the present invention is that short periodic onsite inspections for calibration are not required. The sensor system provides a means for compensating for the deterioration of a detector and light source. The sensor system also can provide a self check and report the results to a central monitoring station.

Another advantage of the present invention is that a variety of communication options may be supported. For example, communication to a display from the sensing device may be provided not only by hard wire but also through fiber optics or a wireless RF link.

Yet another advantage of the present invention is that the system operates using a significantly less amount of energy compared to that of other known fog detection systems. The sample rate for determining fog may be changed depending on whether the conditions around the sensor are changing to make fog more likely. If the conditions are such that fog is likely (fog prediction) , the sample rate may be increased. Power use is thereby minimized.

Yet another advantage is that fog prediction may be used to open and close shutters over detector and light source ports.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent from the following detailed description which should be read m conjunction with the drawings m which:

Figure 1 is a diagrammatic view of a highway warning system employing a visibility sensor according to the present invention;

Figure 2 is a diagrammatic of a visibility sensor head according to the present invention;

Figure 3 is a diagrammatic view of an alternative embodiment of a visibility sensor;

Figure 4 is a flow chart a method for operating a visibility sensor system to conserve energy;

Figure 5 is a partial cutaway elevational view of a removable sensor head according to the invention;

Figure 6 is a bottom view of the removable sensor head of Figure 5; Figure 7 is a side elevational view of a removable sensor and electronic module mounted withm a housing;

Figure 8 is a bottom view of the visibility sensor system of Figure 7 ;

Figure 9 is a forward looking elevational view of an external rear view mirror housing of a car having a visibility detection system located therein;

Figure 10 is a top elevational view of the rear view mirror housing with visibility detection system of Figure 9;

Figure 11 is a side view of an automotive vehicle having a visibility detection system mounted thereto;

Figure 12 is a side view of an automotive vehicle having a visibility detection system mounted m an alternative manner to that of Figure 11;

Figure 13 is a cross-sectional view of an alternative sensor head housing;

Figure 14 is a side cross-sectional view similar to that of Figure 13 having sensor located m a different orientation;

Figure 15 is a timing diagram view illustrating a synchronous detection feature to identify precipitation according to the invention; Figure 16 is a simplified, perspective view of a vehicle having a visibility sensor/fog lamp combination embodiment according to the invention;

Figure 17 is a simplified front view of a preferred visibility sensor/fog lamp combination embodiment according to the present invention;

Figure 18 is a side view, partially m section, of the embodiment shown m Figure 17;

Figure 19 is a simplified front view of an alternate, preferred visibility sensor/fog lamp combination embodiment m accordance with the present invention;

Figure 20 is a simplified side view, partially m section, of the embodiment shown m Figure 19;

Figure 21 is a simplified bottom view of yet another preferred visibility sensor/fog lamp combination embodiment accordance with the present invention;

Figure 22 is a simplified side view, partially m section, of the embodiment shown Figure 21;

Figure 23 is a simplified front view of still yet another preferred, visibility sensor/fog lamp combination embodiment m accordance with the present invention; Figure 24 is a simplified side view, partially m section, of the embodiment illustrated Figure 23;

Figures 25A and 25B are partial cutaway views of an alternative fog sensor according to the present invention;

Figures 26A and 26B are partial cutaway views of yet another embodiment of a fog sensor according to the prevent invention;

Figure 27 is a cross-sectional view of a fog sensor mounted on a vehicle with a fog lamp;

Figure 28 is a cross-sectional view of a sensor housing having a removable portion;

Figure 29 is a front elevational view having a fog sensor mounted m the grill of an automotive vehicle ;

Figure 30 is a schematic view of a fog sensing system incorporated into the grill of an automotive vehicle; and

Figure 31, is a side view of an automotive vehicle having various sensor locations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, like reference numerals are used to identify identical components m the various views. Although the invention will be illustrated m terms of a fog detection visibility sensor, it will be appreciated that this invention may be used with other visibility applications such as detection of blowing dust. In addition the visibility sensor may be used for remote weather stations, airports and m maritime applications such as near a lighthouse .

Referring now to Figure 1, a highway visibility detection system 10 has a visibility sensor unit 12, a warning display 14 and a central controller 16. Visibility sensor unit 12 is preferably placed at eye level of a vehicle operator 18 m an automotive vehicle 20. Visibility sensor unit 12, warning display 14 and central controller 16 may all be linked through a communications network. A communication network, for example, may be cellular phone, RF, cable, or optical fiber. As shown, each of visibility sensor unit 12, warning display 14 and central controller 16 has an antenna 22 which may be used for RF or cellular communication between each.

Upon detection of reduced visibility by visibility sensor unit 12, an indication as to the distance of visibility may be displayed on warning display 14. Also, a suggested vehicle speed may also be displayed on warning display 14.

Central controller 16 may be part of an intelligent transportation system (ITS) . The central controller 16 may be a manned controller which may perform a number of functions such as initiating self-tests for the sensor unit 12 or sending a maintenance crew to service the sensor in the ever.: of contamination .

Referring now to Figure 2, visibility se sor unit 12 preferably has most of its components sealed within a housing 24. Several visibility sensor units may be coupled within one housing 24. The operation of the system is generally controlled by a micro controller 26. A sensor head 28 is coupled tc and controlled by micro controller 26. Sensor head 28 transmits light to a sample volume 30 and provides micro controller 26 an indication of the amoun: of light reflected from fog particles in a sample volume 30 below sensor head 28. A memory 32 is used to store various information and is coupled to micro controller 26. Memory 32 is preferably nonvolatile memory.

Memory 32, for example, may contain a conversion factor for converting the amount of light received by sensor head 28 to a visibility distance. Memory 32 may also store service and calibration data, security codes, the serial number of the system, and visibility data history .

Various sensors for sensing the atmospheric conditions around the housing 24 of visibility sensor system 12 are coupled to micro controller 26. Such sensors may include an atmosphere pressure sensor 34, one or more precipitation sensors 35, a temperature sensor 36 and a humidity sensor 38.

Micro controller 26 may also be coupled to a communications link 40 that allows micro controller 26 to communicate with a central controller 16. Although atmospheric pressure sensor 34 has been shown coupled directly to micro controller 26, atmospheric pressure sensor 34 may be coupled directly to central controller 16. In such a case, atmospheric pressure data would be provided through communications link 40 to micro controller 26. Micro controller 26 may be used to calculate the safe speed based upon the visibility detected by the sensor head 28. The calculation of a safe speed may be done at a central controller.

Communications link 40 may be one of a number of types of communications links that may be used to link micro controller 26 to central controller 16. Because the detector system may be used in a variety of locations and conditions, flexibility for various types of communications is required. Communications link 40 may, for example, be cellular telephone link, an RF link, a fixed cable link, or optical fiber link. Communications link 40 may be used to couple to a warning display (shown as 14 of Figure 1) on the highway.

Sensor head 28 has a first optical port 42 and a second optical port 44. First optical port 42 has a first optical axis 46 and second optical port 44 has a second optical axis 48. First optical axis 46 coincides with the longitudinal axis of first optical port 42. Likewise, the second optical axis 48 coincides with the longitudinal axis of second optical port 44. An angle 50 between first optical axis 46 and

Second optical axis 48 may be about 150( .

In some applications the first optical port could coincide with the second optical port. In such a case, no the ports would share the same longitudinal

Recessed withm first optical port 42 is a first light source 52. First light source 52 is preferably mounted m an end of first optical port 42.

First light source 52 is preferably an infrared light emitting diode having a relatively narrow beam width.

First light source 52 may, for example, have a total beam width of 10( . Light from first light source 52 emerges from first optical port 42 at a first hollow opening 54. The cone of diverging light from first light source 52 illuminates a sample volume 30 outside first optical port 42.

Second optical port 44 has a first detector

56 located m an end thereof. First detector 56 is sensitive to the wave length of light scattered from the sample volume 30. First detector 56 may have a small surface area such as a five square millimeter surface area. Light is reflected from particles m sample volume 30 into a second hollow opening 58. A light filter 60 may be interposed m the optical path between sample volume 30 and first detector 56. Filter 60 is provided to filter ambient light from first detector 56. First detector 56 provides an output to micro controller 26 through a low noise amplifier 62 corresponding to the amount of light reflected from particles m sample volume 30. In one constructed embodiment, both second optical port 44 and first optical port 42 were constructed of .5 inch diameter by 3.5 inch tube.

A test light source 64 may be provided m second optical port 44. Test light source 64 is also preferably an infrared LED. Test light source 64 preferably has a relatively wide beam width of approximately 80( so that light may be directed into second optical port 44 to first detector 56. Test light source 64 is coupled to micro controller 26.

Micro controller 26 controls the operation of test light source 64. Test light source 64 is used during self testing and self calibration as will be further described below.

A compensation detector 66 is coupled with first optical port 42. Compensation detector 66 may have a smaller area such as a 1.5 square millimeter detection area. Compensation detector 66 is coupled to micro controller 26 through a low noise amplifier 68, compensation detector 66 provides feedback to micro controller 26 as to the operation of first light source 52 during self test and self calibration.

A heater 70 is coupled adjacent to first light source 52 and first detector 56 to prevent condensation on the optical surfaces. Heater 70 may be a tungsten wire or thermoplastic element. Heater 70 may, for example, maintain a differential temperature of roughly 5( C between the optical surfaces and ambient temperature to prevent condensation. A thermistor 72 may be coupled adjacent to the heater 70 to provide feedback to micro controller 26 so that the functioning of heater 70 may be monitored.

An insect repellant 74 may be placed side or adjacent to first optical port 42 and second optical port 44. Insect repellant 74 may be a variety of insect repellant means. Insect repellant may, for example, be a chemical known to be poisonous or repellant to the insects of the area into whicn the highway visibility detector system will be placed.

A power source 76 is used to power the highway visibility detection system 10. Highway visibility detection system 10 is flexible m the sense that it may operate from a variety of sources of power. Power source 76 may, for example, be a solar cell coupled to storage batteries. The power source may also be batteries or be coupled directly to a fixed power line.

Precipitation sensor 35 may comprise a conventional ram sensor or a conventional snow sensor.

Such sensors are known, for example, as described m

K. Mori, et al . "An Intermittent Wiper System with a

Raindrop Sensor," SAE Technical Paper Series, SAE,

September 23-26, 1985, hereby incorporated by reference.

Referring now to Figure 3, an alternative embodiment for first optical port 42 and second optical port 44 is shown. In this embodiment, first optical axis 46 and second optical axis 48 are not aligned with the longitudinal axis of first optical port 42 and second optical port 44. First optical axis 46 and second optical axis 48 also preferably have an angle of about 150( between them. The embodiment of Figure 3 Operates m the same manner as that of Figure 2.

One method for operating a highway visibility detector system of the present invention would be to continuously operate the system so as to constantly provide feedback to the central control and to a warning display or several displays. Operating a fog detection system continuously, nowever, is unnecessary and consumes power unnecessarily.

Referring now to Figure 4, based upon atmospheric conditions, the potential for fog can be predicted. From meteorology, a saturation surface, which is sometimes called the maximum vapor pressure surface, can be defined m three-dimensional space defined by temperature, humidity and pressure or two dimensional surface defined by temperature and humidity. Fog occurs when the saturation surface is reached. In order to conserve energy or open and close shutters as described below, micro controller 26 performs the following operations. First the atmospheric pressure is measured m step 80. In step 82 the humidity is measured. In step 84 the temperature is measured. Each of the atmospheric pressure, humidity and temperature conditions are preferably measured outside the housing of the highway visibility detector system. From the condition measured steps 80 through 84, step 86 determines the distance from the saturation surface. In step 88, the distance from the saturation surface is compared with the previous distance from the saturation surface to determine the speed that the saturation surface is being approached. In step 90, the time to reach the saturation surface is estimated. In step 92, the sample rate is changed so that the micro controller will turn on to determine visibility at a higher rate if the saturation surface is being approached. One method for setting the sample rate may be that if the estimated time to reach saturation is below 3 hours, then the micro controller will turn on at a rate twice as fast as the normal operation mode. For example, this faster rate may be twice an hour. As the estimated time goes lower, the sample rate can be further increased. By increasing the time of sample only when the saturation surface is being approached, energy is conserved. After executing step 92, step 80 is re-executed and the next sample period determined by the micro controller.

In this manner, the highway visibility detector system 10 does not operate needlessly. Thus, energy is conserved.

In operation, during visibility sampling, the first light source illuminates a sample volume 30 beneath housing 24. Fog or dust particles cause light to be scattered from the sample volume 30 into first detector 56. The amount of light scattered will be dependent upon the particle size and/or the number of particles of the contaminants withm the sample volume 30. The light scattered from the sample volume has a direct correlation to the visibility present around the highway visibility detector. Date acquisition may be taken once or preferably sampled a number of times to statistically ensure satisfactory results. The received voltage level corresponding to the amount of illumination on the first detector 56 may be converted by a micro controller 26 into a visibility. Micro controller 26 may also convert the visibility into a safe speed for the roadway. The safe speed may be calculated or looked up m a table stored m memory 32.

The sensor system also has the ability to self calibrate. During manufacturing, a light scattering calibration object may be positioned m the sample volume. The micro controller, when commanded, can save the measurement and determine a correction factor to be stored m the non-volatile memory. The connection factor will be used to correct subsequent visibility measurements. Calibration may easily be done at the manufacturer and easily confirmed when installed m the field.

Referring now to Figures 5 and 6, m certain implementations of the invention it may be desirable to have a sensor head 100 that is easily removable and replaceable. In such a manner, servicing time of the visibility sensor would be reduced. A sensor enclosure 102 defines first optical port 42 and second optical port 44. A center wall 104 separates first optical port 42 from second optical port 44. End pieces 106 and 108 of each port 42 and 44 opposite center wall 104 have end pieces 106 and 108 respectively. Eacn end piece 106 and 108 are respectively used to secure circuit boards 110 and 112 thereto. Sensor enclosure 102 of removable sensor head 100 has a bottom surface 120 that has first hollow opening 54 and second hollow opening 58 similar to that described above.

Circuit board 110 is also used to secure light source 52. Circuit board 110 may also be used to secure a connector 113 which is used to supply power to light source 52. Connector 113 may be one of a variety of types of connectors including being a male or female end of a snap m or screw type connector. Connector 113 should allow easy connection and disconnection to facilitate removal of removable sensor head 100. A plurality of wires 117 may be used to couple light source 52 to a power source or microcontroller.

Circuit board 112 is secured to photo detector 56. Photo detector 56 is preferably coupled to infrared filter 60 as described above. Circuit board 112 preferably has an amplifier 62 mounted thereto. By mounting amplifier 62 to circuit coard 112, noise transmission through connecting wire 118 is reduced. Circuit board 112 also preferably has a calibration memory 116 coupled thereto. Functionally, calibration memory 116 may be part of memory 32 snown Figure 2. By locating calibration memory 116 on circuit board 112, the calibrations associated wit the removable sensor head 100 are also removed. When a replacement sensor head 100 is coupled to the visibility sensor system, micro controller 26 uses the information stored m calibration memory 116 to generate the required results.

Commercially, photo detectors are often packaged together with an amplifier 62. A wire or a plurality of wires 118 are used to couple connector 114 to the remaining circuitry of the visibility sensor.

Referring now to Figure 6, first hollow opening 54 and second hollow opening 58 withm bottom surface 120 are preferably oval shape. The oval shape has been found to be beneficial m providing a high signal to noise ratio for the fog detection system, as well as providing the least signal deterioration due to contamination of the surface of first light source 52.

A shutter 122 shown on second hollow opening

58 may be used to cover second hollow opening 58 to prevent contamination of photo detector 56. Of course, a second shutter may also be incorporated m a similar manner over first hollow opening 54 to prevent contamination of light source 52. Shutter 122 is preferably a simple solenoid operated device. Shutter 122 may be switch operated, operated manually or automatically operated. One manner for automatically operating shutter 122 is to estimate the likelihood of fog with respect to the approachment of a saturation surface as described above . As the saturation surface is approached, shutter 122 may be opened. To prevent shutter 122 from opening m a car wash, the system may be coupled to a sensor m the transmission of the vehicle that senses whether the vehicle is m neutral, park or the engine is stopped. Commonly vehicles are placed m neutral when being washed m a car wash. This prevents soap film from fouling the sensors.

To reiterate, one of the problems of conventional fog sensors for automotive applications involves keeping the sensor "window" surface clean.

Most of the conventional sensor system attempts for an automotive application fail because of this problem.

As described above, and m accordance with the present invention, an inventive sensor enclosure configuration eliminates a sensor "window", and further, optionally employs means, such as one or more shutters, for covering the "wmdowless" openings during no- fog conditions. Such shutters are only opened when, as described above, a fog prediction algorithm indicates that fog is likely. Also as described above, the shutters may be closed during, for example, car washing, or when the car is parked. This mode of operation minimizes contamination when the visibility sensor functionality is not needed. The foregoing approach may be implemented by including means for generating a closure signal, which is applied to the shutters, when a closure condition exists. The closure condition may be one condition selected from the group consisting of a condition where a transmission of an automotive vehicle is a neutral condition, a condition where the transmission is m a parked condition, and a condition where an engine of the vehicle is stopped. In addition, it should be understood that the presence of fog is unlikely during ram or snow. Accordingly, m one embodiment, precipitation sensor 35, such as a ram sensor or a snow sensor, is provided which generates an output signal. The output signal, m one embodiment, may be directed to microcomputer 26, which m turn is configured to generate the closure signal. The closure signal is then applied to one or both of the shutters 122 (Figure 2 and Figure 6) to cause them to close and cover the first and second openings. In an alternative embodiment, an output of sensor 35 may be used directly (i.e., not directed through microcomputer 26) to close shutters 122 to thereby cover openings 54 and 58. As is well known, ram sensor 35 may comprise a piezo-electric plate which produces a voltage when a pressure is applied.

An alternative embodiment of the inventive system of detecting ram or snow involves analyzing the light scattering characteristic of ram and/or snow (relative to the light scattering characteristic of fog) . To fully appreciate this aspect of the mvention, a description of a synchronous detection technique used m accordance with the present invention will be briefly described.

Referring to Figure 15, the top trace thereof represents the ON and OFF control signals generated by microcontroller 26 indicative of the ON and OFF states of light source 52. Further, photodetector 56 is configured to generate a signal having a magnitude corresponding to the intensity of the received light. Therefore, when light source 52 is OFF, photodetector 56 generates an output signal having a magnitude corresponding to the intensity of only the amoient light. When light source 52 is ON, however, photodetector 56 generates an output signal having a magnitude corresponding to the intensity cf a combination of the ambient light, and the light scattered from sample volume 30 from light source 52.

Referring now to the middle trace m Figure 15, microcontroller 26 internally generates a sealer or multiplier parameter which alternates m polarity, m synchronous registry with the ON/OFF states of light source 52. That is, when light source 52 is ON, the multiplier is "+1" , while when the light source 52 is OFF, the multiplier is "-1".

In operation, the sealer is used to filter out the effect of ambient light (bias component) . Referring now to the bottom trace of Figure 15, during a first time slot when light source 52 is ON, the multiplier is "+1" . The output of photodetector 56 is multiplied or scaled by the multiplier parameter

(middle trace) . Therefore, the output of detector 56 is maintained m a positive polarity state, and is represented diagrammatically as the combination of ALi, and SL_X . During the next time slot, when light source 52 is OFF, the multiplier is "-1". During this time slot, the output of detector 56 corresponds solely to the ambient light. The resulting product is of a negative polarity, and is designated AL₂ m Figure 15. Over the course of a preselected interval ("time constant"), designated m the lower trace of Figure 15 as "TC" , the area under the curve is added by microcontroller 26 having due regard for the indicated polarity. The ambient light terms (i.e., ALi, AL₂, AL₃, AL₄ , . . . , AL₈ ) cancel out or, m other words, net out to "zero." Since the sealer is always "+1" when light source 52 is ON, the accumulated value resulting from the "addition" operation is a function only of the scattered light derived from sample volume 30 due to the illumination thereof by light source 52 (i.e., the sum of SL_1; SL₂, . . . , SL₄) . The magnitude of the accumulated scattered light is then correlated to predetermined data, and a measure of visibility is determined thereby. For example, the time constant TC, when used to detect fog, may be selected to be between about 10-60 seconds, and may be up to several minutes.

However, m accordance with the present invention, raindrops (or snowflakes) can be analyzed (i.e., detected) by shortening the time constant TC, which may be selected to be between about 10-20 milliseconds, up to about 100 milliseconds. Individual readings (i.e., one reading is the accumulated value over one time constant TC) compared with each, for example, over a relatively long period of time relative to the selected time constant (i.e., a detection interval) , such as one minute , if widely fluctuating, are indicative of raindrops or snowflakes. In contrast, if each of the individual readings show little variation m magnitude ( .e., smooth), then what is being detected is likely fog. Preferably, wnether a dedicated sensor 35 is used, or whether precipitation (ram or snow) is determined parametπcally by shortening the time constant as described above, preferably at least two, and most preferably at least three of such sensors 35

(or sensor head assembly 28 when precipitation is detected parametrically) are used to minimize false detections. Use of a plurality of sensors is also preferred for fog detection as well. False signals, caused by many reasons other than fog or ram (or snow) , can be significantly reduced using two sensors simultaneously. For example, sensor head 28 may be employed m both a right and a left fog lamp assembly, as shown diagrammatically Figure 16.

Referring now to Figures 7 and 8, a housing

124 is shown having a removable sensor head 100 and an electronic module 126. Electronic module 126 may have different variations. Preferably, electronic module 126 contains many of the features of Figure 2 such as a micro controller 26, a memory 32 and a communications link 40. Also m some applications electronic module contains algorithms to determine the true fog occurrence from such data provided by an atmospheric pressure sensor 34, a temperature sensor 36, a humidity sensor 38. The sensors may be coupled to each fog sensor. To reduce cost and avoid redundancy, however, one or all sensors may De located m a central location if a group of visibility sensors are used m a single system, for example, along a highway. Bottom surface 120 of removable sensor head 100 is preferably flush with bottom surface 128 of housing 124. For applications, where the visibility sensor will be mounted to a moving vehicle, providing bottom surface 120 of sensor head 100 flush with bottom surface 128 of housing 124 does not disturb the laminar flow near openings 54 and 58.

Removable sensor head 100 may be snap fit withm housing 124. A mechanical fastening device 130 may also be used to secure removable sensor head 100 withm housing 124. Mechanical fastening device 130 may, for example, be used conjunction with screws or other fasteners to secure sensor head 100 withm housing 124. The particular mechanical fastening device 130 is preferably relatively easy to disassembly and reassembly to facilitate replacement of sensor head 100.

Electronic module 126 may also be designed to be easily removed from withm housing 124. In the practical sense, sensor head 100 is more likely to be replaced or serviced. Electronic module 126 may be coupled to an external power supply through a connector 132. Connector 132 may also be used to couple electronic module 126 to a remote display 134. Display 134 may also be coupled through a central computer or host controller. Remote display 134 may be a warning signal or an audible signal Remote display 134 may provide an indication as to the distance of visibility.

Display may be a visual indicator, an audible indicator or a combination of the two. If the fog sensor is coupled to a vehicle, the visual indicator may be incorporated into an instrument panel or a heads-up display. The audible indicator may be a buzzer or be coupled to he audio system of the vehicle.

A gasket 136 may be used between removable sensor head 100 and housing 124 to prevent infiltration of moisture into housing 124. Likewise, connector 132 may be a sealed connector to prevent water from entering housing 124.

Referring now to Figure 8, a heater 138 may be coupled adjacent to first hollow opening 58 and second hollow opening 54. By placing heater 138 near openings 54 and 58, frost is prevented from building up around either opening. If frost forms on the edge of either opening, the accuracy of the detector system may be affected.

In operation, removable sensor head 100 has thus been made easy to remove and replace from housing

124. To replace removable sensor head 100, mechanical fastening device 130 releases removable sensor head

100. Connectors 113 and 114 are disconnected.

To connect a replacement sensor head, connectors 113 and 114 are connected to removable sensor head 100. Mechanical fastening device 130 is coupled to the replacement sensor head 100. The calibration data from calibration memory 116 is then communicated to micro controller 26. The calibration data was stored within calibration memory 116 during manufacture of the sensor head. Referring now to Figures 9 and 10, the removable sensor head configuration is particularly suitable for implementation with an automotive vehicle. This feature may be included as an after-market application or as original equipment. One manner for implementing a removable sensor head 100 into an automobile is to place removable sensor head 100 into a rear view mirror housing 140. Removable sensor head 100 is preferably placed behind mirror 142 and directed m a downward position. Bottom surface 120 of sensor head 110 is preferably flush with bottom 144 of rear view mirror housing 140. In this manner, the laminar flow of air around mirror housing 140 is least disturbed.

Electronic module 126 may also be incorporated withm rear view mirror housing 140. However, electronic module 126 may easily be incorporated into the interior of the automotive vehicle. By placing electronic module 126 withm the interior of the automotive vehicle, the electronics are not subjected to the harsh weather conditions and thus may increase the accuracy and life of electronic module 126.

It is desirable to include shutters 122 an automotive application. It is desirable to close shutters 122 during a car wash to prevent soap residue from building on the light detector or light source.

By providing shutters 122, the life of sensor head 100 may be increased. Shutters 122 may also be applied to a highway sign application. Referring now to Figure 11, an automotive vehicle 146 has a roof 148. A removable sensor head 100 is shown coupled near the rear end of roof 148. Sensor head 100 may be positioned to reduce wind resistance. Electronic module 126 may be placed m many areas of vehicle including withm the interior of the vehicle adjacent to display unit 134 with appropriate wiring. Display unit 134 and electronic module 126 may, for example, be mounted to a rear view mirror withm the vehicle.

Electronic module 126 may also be coupled to vehicle battery 150 which provides power for the entire detector system 10.

Sensor head 10 may be removable or fixed when included m an automotive vehicle. Sensor head 10 may, for example, be placed m the trim around the rear window of the vehicle. In such a manner, sensor head 100 becomes unobtrusive.

Referring now to Figures 12, 13 and 14, removable sensor head 100 may be detachable from automotive vehicle 146. By providing a detachable housing 152, visibility detector system 10 is particularly suited for after-market automotive applications. Detachable housing 152 preferably has magnets 150 suitable for coupling detachable housing 152 to a steel component such as roof 148 or a vehicle door 155. Removable sensor head 100 may be removed from and coupled to detachable housing 152 as described above. As is best shown in Figures 13 and 14, the housing 152 may have legs 156. Legs 156 have magnets 150 therein for attachment to the automotive vehicle.

As shown in Figure 13, sample volume 30 may be between detachable housing 152 and the exterior automotive vehicle 146.

As shown in Figure 14, sample volume 30 may be directed away from automotive vehicle 146.

For an after-market application, an automotive vehicle owner merely couples the detachable housing 152 to the outside of automotive vehicle 146.

Display device 132 and electronic module 134 may, for example, be clipped to a rear view mirror within the passenger compartment of automotive vehicle 146. Electronic module 126 may, for example, be powered through the cigar lighter of the automotive vehicle which is coupled to vehicle battery 150. One cable having a plurality of wires may be used to couple detachable housing 152 and removable sensor head 100 therein to electronic module 126.

In operation, a sensor head for an automotive vehicle may be used to activate the fog lights that are commonly found on the front of vehicles (and the rear of vehicles in Europe) . Such a system may work as follows: once the saturation detects that fog is likely, the shutters 122 are opened; if fog is detected, the fog lights of the vehicle may then be illuminated .

Figure 16 shows exemplary vehicle 20 including a first and a second combination visibility sensor/fog lamp apparatus 200. Apparatus 200, in one embodiment, is an integral unit including the functionality of the above-described visibility sensor with the illumination functionality of a conventional fog lamp assembly. As shown in Figure 16, apparatus 200 may be disposed in a front bumper fascia of vehicle 20.

The embodiments illustrated in Figures 17-18, and Figures 19-20 will be referred to hereinafter as "look-down forward" embodiments, inasmuch as the optically sensitive volume 30 is "forward" and "down" of the apparatus, relative to the direction of travel of the vehicle. Figures 17 and 18 show a first embodiment of apparatus 200, which includes a unit housing assembly 210, a lamp assembly 212, and a visibility sensor head assembly 214. As illustrated in Figure 18, apparatus 200 may include one or more electrical connections to electronic module 126, to thereby access the functionality of the electronic module 126, which is illustrated and described in connection with, for example, in Figure 2. As described above, and in the Background, a problem with conventional visibility sensors involves contamination of the light source/photo-detector and/or surfaces or structures "windows" through which the illumination light and the signal light must pass. To address this problem, and in accordance with the present invention, apparatus 200 includes an improved sensor enclosure configured for contamination reduction.

With continued reference to Figures 17 and 18, unit housing assembly 210 includes a plurality of relatively thin-walled structures 216ι, 216₂, 216₃, and

216₄. The thin-walled structures may comprise conventional and well-known materials.

Lamp assembly 212 is configured to produce illumination in response to an excitation signal, and may generally comprise conventional and well-known components and materials. Lamp assembly 212 may include a reflector 218, a bulb 220, a lens or other light transmissive material 222, and an electrical connection 224 for connecting bulb 220 to a source of electrical power such as may be controlled by microcontroller 26 (i.e., the excitation signal) and wherein the electrical power may be supplied by power source 76.

Sensor head assembly 214 includes a sensor enclosure 226 having a plurality of relatively thin- walled structures "walls" 228_1; 228₂, 228₃, and 228₄. Walls 228ι define a first optical port 230 having a first opening 232, and walls 228_ι further define a second optical port 234 having a second opening 236.

Optical port 230 is a volume bounded in-part by wall

228₂ on the top, and wall 228₄ on the right (with reference to Figure 17) , while optical port 234 is bounded in-part on the left by wall 228₄, and wall 228₂ on the top. First optical port 230 is optically isolated from second optical port 234 primarily by intervening wall 228₄. Sensor enclosure 226 further includes an exit opening 238, a first deflector 240 having a first aperture 242 and a second aperture 244, and a second deflector 246.

Light source 52, and photodetector 56 are located m respective relatively "concealed" positions withm first optical port 230, and second optical port 234. "Concealed" m this context means positions that are difficult for contaminants (such as moisture, water, dust, etc.) to reach. In the illustrated embodiment, sensor enclosure 226 and light source 52

(disposed m first optical port 230) are configured to emit a light beam through first aperture 242 and first opening 232 to illuminate sample volume 30 located outside apparatus 200. Likewise, m the illustrated embodiment, enclosure 226 and light detector 56

(disposed m second optical port 234) are configured to detect light through second aperture 244 and second opening 236. Detector 56 generates an output signal in response thereto indicative of the amount of light scattered from particles contained m the sample volume 30 (after the signal is "filtered" - -as described above to remove contributions of ambient light) . As illustrated, openings 232 and 236 are located on a first side of deflector 240, while light source 52 and photodetector 56 are located on a second side opposite the first side of deflector 240. Inasmuch as openings 232 and 236 are m direct communication with the ambient environment- -the source of contaminants- -the foregoing arrangement (i.e., use of deflectors and use of "concealed" positions) provides a barrier reducing or minimizing the entry of dust, water or other contaminants. In addition, as the vehicle 20 moves in a forward direction, respective air flows occur along the paths indicated by arrows designated 248 in the drawings. Dust, water, or other contaminants in the air will pass through the sensor enclosure 226 along the air flow path. This flow-through action reduces the likelihood that the surfaces of light source 52 and photodetector 56 will become contaminated.

In addition, by selecting a proper air flow path difference between the inside of enclosure 226 relative to the outside of enclosure 226, and, further, by selecting proper sizes for the openings 232, 236 and 238, an air pressure differential can be established.

That is, one can make the air pressure adjacent and around light source 52 and photodetector 56 higher than the pressure in the central portion of enclosure 226.

This pressure differential feature helps reduce contamination. Basic principles of aerodynamics may be used to make the above selections.

Thus, two features of the above-described configuration combine to keep the surfaces of light source 52 and photodetector 56 clean: (l)a "concealed" position feature wherein the source 52 and photodetector 56 are located in "concealed" positions

(e.g., above the apertures, and openings, through which the illumination and receiving light beams pass) ; and

(2) a pressure differential feature wherein the enclosure and deflectors and openings are configured to create suitable air paths to establish a pressure differential to thereby assist in keeping the surfaces of source 52 and detector 56 clean. With the foregoing implementation, the use of one or more shutters, such as shutters 122 in Figure 6, is optional.

Figures 19 and 20 illustrate a second preferred embodiment of the apparatus shown in Figure 17 and 18, namely apparatus 200' . Apparatus 200' is substantially similar to apparatus 200, except that apparatus 200' does not include second deflector 246, but in lieu thereof includes exit opening 238 that is positioned at a distal end of an air flow channel 250.

Apparatus 200' illustrates just one of the plurality of variations and modifications of enclosure 226 possible which are adapted to create air flow path differences to thereby establish the above-described pressure differential arrangement.

Figures 21 and 22 illustrate yet another preferred embodiment, namely apparatus 200''. Apparatus 200' ' will be referred to as a "look-down rearward" embodiment wherein the optically sensitive volume 30 is located on the "down" side or downward side of the apparatus enclosure, and looking "rearward" relative to the direction of travel of vehicle 20. Apparatus 200' ' includes unit housing 210, lamp assembly 212, and sensor head assembly 214' ' . Unit housing 210 and lamp assembly 212 may comprise structure and function as described above in connection with the embodiments illustrated in Figures 17-20. Sensor head assembly 214 ' ' includes a sensor enclosure 226'' having a plurality of walls 228_ι, 228₂, 228₃, 228₄, and 228₅, that define a first optical port having a first opening and a second optical port having a second opening, as described above in connection with apparatus 200. Enclosure 226' ' includes a deflector

240' ' having first and second apertures 242, and 244.

In the illustrated embodiment, apparatus 200'' creates an air flow path difference that establishes a pressure differential in the same manner and to the same effect as described above in connection with apparatus 200 and

200' . Figure 21 is a bottom view of Figure 22.

Figures 23 and 24 illustrate still yet another preferred embodiment of the present invention, namely apparatus 200' ' ' . Apparatus 200' ' ' includes a unit housing 210, a lamp assembly 212, and a sensor head assembly 214' ' ' . Unit housing 210, and lamp assembly 212 may comprise structure and function as described above in connection with the embodiments illustrated in Figures 17-22. Apparatus 200' ' ' may be generally cylindrical in shape, and comprise a sensor enclosure 226' ' ' that includes a first deflector 240' ' ' , and a second deflector 246' ' ' . Walls, including thin walls 256_x, and 256₂, in-part, define first optical port 232, and second optical port 236. First and second openings 232 and 236 are best shown in Figure 23. First deflector 240' ' ' includes first aperture 242 ' ' ' , and second aperture 244 ' ' ' , while second deflector 246 ' ' ' is illustrated as including third aperture 252, and fourth aperture 254. Apertures 242' ' ', and 252 are, generally, in registry, while apertures 244' ' ' and 254 are, likewise, generally in registry. The foregoing configuration permits light source 52 to generate a light beam to illuminate optically sensitive sample volume 30, while the apertures as described above permit photodetector 56 to receive light therethrough from scattered particles in the optically sensitive sample volume 30. Operation of apparatus is generally the same, in manner and effect, as described above in connection with apparatus 200.

Referring now to Figures 25A and 25B, a similar embodiment 300 to that shown in Figures 21 and 22 is illustrated. The embodiment 300 shown as Figures 25A and 25B does not have a unit housing or lamp assembly, and thus may be incorporated into various locations within the vehicle. Sensor head assembly 214' ' includes a sensor enclosure 226' ' having a plurality of walls 228_!, 228₂, 228₃, 228₄, and 228₅ that define a first optical port having a first opening and second optical port having a second opening, as described above. This embodiment is a look down rearward embodiment relative to the vehicle. Enclosure

226' ' includes a deflector 240' ' having a first and second aperture 242 and 244, respectively. A support

302 supports detector 56 within sensor enclosure 226''.

A support 304 supports light source 52 within sensor enclosure 226 ' ' .

Wall 228₃, has an air inlet 306 therethrough.

Preferably, a filter 308 is positioned over inlet 306 to prevent moisture, dust and other contaminants from entering sensor enclosure 226' ' . A shield extending from sensor enclosure 226' ' may be used to protect filter 308. Of course, two or more air inlets may be used as would be evident to those in the art . For example, one air inlet may be used adjacent to detector 56 and one adjacent to light source 52.

In operation, a portion of air flow 312 enters sensor enclosure 226' ' at opening 236 and leaves through opening 238. Another portion of air flow 312 travels through inlet 306 and through filter 308. Air thus washes over the surface of detector 56 and light source 52 to prevent contamination buildup thereon.

This allows an increase in accuracy as well as an increase in reliability of the system. In this embodiment, the air pressure differentials as mentioned above are present. Air enters inlet 306 to attempt to balance the air pressure differential within sensor enclosure 226. An optional feature of embodiment 300 is the addition of shutters 314 over openings 236 and 238. Thus, as described above, shutters 314 may be operated only when fog is likely.

Referring now to Figures 26A and 26B, another embodiment 300' ' is illustrated. In this embodiment, an angularly disposed deflector 316 is positioned within each port. Deflector 316 has a first aperture 242 and a second aperture 244 for respective light source 52 and detector 56. In this embodiment, wall 228₄ has only a single opening 232, 236 for each optical port. Thus, the flow of air under sensor enclosure 226' ' does not enter housing except through filter 308 at inlet 306. In this embodiment, the quickly rushing air

312 by opening 236 causes the inside of sensor enclosure 226' ' to be at a lower pressure than the ambient air pressure (stationary) outside the sensor enclosure 226. The air rushing by the ports is at a lower pressure than inside the sensor enclosure 226 which is at a lower pressure than the ambient pressure.

This causes air to be drawn through the sensor enclosure 226 from the relatively higher ambient pressure surrounding the enclosure in a path to the quickly rushing air beneath the sensor enclosure 226.

Thus, in this embodiment, an air curtain washes over light source 52 and detector 56.

This embodiment acts in a look down and rearward manner similar to the previous embodiment.

An optional shutter 314 may also be used to selectively close openings 236 and 232.

The quickly rushing air may be channeled by a tube 317 that may be integrally formed with sensor enclosure 226. Tube 317 defines an air channel 319 under the enclosure 226. To provide accurate fog detection, the speed of the air inside tube 317 should be the same or close to the speed of the vehicle. Also, turbulence should be minimized. In contrast as described below, the air channel may be formed as part of an automotive vehicle structure.

Referring now to Figure 27, an embodiment 300' ' is shown that is similar to embodiment 300' above. In this embodiment, however, sensor enclosure 226' ' is incorporated together with a fog lamp housing 318. Fog lamp housing 318 has a fog larp 320 disposed therein. Fog lamp housing 318 may be mounted to a bumper 322 or other front automotive support.

Sensor enclosure 226' ' has a deflector 316 therein with a single opening 236, 232 (not shown) for each optical port. Of course, one skilled m the art would recognize that the embodiment of Figures 25A and 25B may also be used.

In this embodiment, an air cnannel 324 is defined between sensor enclosure 226' ' and a portion of the automotive structure 326. The automotive structure is preferably a portion of the front end of the vehicle such as the front fascia, air dam, or a portion of the bumper. Air channel 324 increases the air flow speed by opening 236 and thus further reduces the pressure withm sensor enclosure 226' ' . In this manner, a laminar flow through air channel 324 increases the accuracy of the fog detector.

Referring now to Figure 28, a similar embodiment 300' ' ' to embodiment 300' ' is illustrated.

In this embodiment, sensor enclosure 226' ' is segmented into two pieces 328, 330. Segment 330 contains light source 52 and detector 56. So that they may easily be replaced, a snap 332 or other fastener may be used to connect first housing portion 328 with second housing portion 330.

Referring now to Figure 29, a portion of an automotive vehicle 334 is illustrated having a bumper 322 with a fog light 320 therein. Automotive vehicle 334 also has a headlight 336 and a grill 338 used for allowing air into the engine compartment of the automotive vehicle 334. A sensor enclosure 226 is incorporated into grill 338. Sensor enclosure 226' ' is preferably constructed m a similar manner to those shown above m Figures 25 and 26. A portion of grill 338 may be used to define an air channel 324 as taught m Figure 27. That is, automotive structure 326 m Figure 27 may comprise a portion of grill 338. In this manner, smooth laminar flow may be used to pass by the openings and sensor enclosure 226' ' .

Referring now to Figure 30, a fog lamp control system 346 is illustrated. In this embodiment, a portion of grill 338 is shown defining air channel

324. A sensor enclosure 226' ' is mounted to grill 338.

Sensor enclosure 226 ' ' may be similar to those shown above m Figures 25, 26 or 27. That is, sensor enclosure 226' ' may also incorporate an opening with a filter therein. The operation of fog lamp control system 346 is similar to that described m the prior figures. A light source 52 and a light detector 56 coupled to an amplifier 348 controlled by a microprocessor 350. As described above, a thermistor 352 and a heater 354 similar to those described above are also controlled by microprocessor 350. Thermistor 352 is used to monitor the operation of heater 354. Heater 354 prevents condensation buildup withm sensor enclosure 226' ' . Microprocessor 350 is illustrated as a separate component from car computer 356. However, car computer 56 and microprocessor 350 may be incorporated into a single housing or single controller. Car computer 356 controls the operation of fog lamp 320. Car computer 356 may also be coupled to a visibility indicator 358. Visibility indicator 358 may comprise a variety of indicators such as an audible indicator, a visual indicator indicating the amount of visibility, or provide a numerical reading to provide the operator of the vehicle with an indication as to the visibility as detected by the fog detector.

Microprocessor 350 is used to control the operation of the fog detector. As described above, the fog detector may also include a test infrared LED 360 and the other features shown in Figure 2.

Referring now to Figure 31, a full automotive vehicle 334 is shown having sensor enclosures 226' ' incorporated in various locations. Also, a visibility indicator 358 is incorporated within the vehicle for providing the vehicle operator with an indication as to the presence of fog. As illustrated, various locations may be chosen for a fog detector such as adjacent to a fog lamp 320, in a grill 338, or within a side rearview mirror 364. To increase the accuracy of the system, more than one location of the fog detection sensor may be used. That is, two locations on the grill may be used, adjacent to both headlights 320 may be used, both side rearview mirrors 364 may be used, or a combination of any of the locations described above. All the locations illustrated would likely not be used.

While the best mode for carrying out the present invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claim. For example, the humidity, temperature and atmospheric pressure sensors may be replaced by a wind velocity sensors if this invention were to be used to measure visibility m blowing dust.

Claims

What is claimed is: 1. An apparatus comprising: a sensor enclosure having a plurality of walls defining a first optical port having a first opening and a second optical port having a second opening, said enclosure comprising an air mlet therethrough; a deflector having first and second apertures; a light source disposed m said first optical port adjacent to said air mlet, said light source being configured to emit a light beam through said first aperture and said first opening to illuminate a sample volume located outside of said sensor enclosure; a light detector disposed m said second optical port adjacent to said second air mlet and configured to detect light through said second aperture and said second opening and generate an output signal m response thereto indicative of the amount of light scattered from particles m the sample volume; said first and second openings being located on a first side of said deflector, said light source and said light detector being located a second side opposite said first side of said deflector.

2. The apparatus of claim 1 further comprising an air filter disposed withm said first air mlet .

3. The apparatus of claim 1 wherem said enclosure further including an exit opening.

4. The apparatus of claim 3 wherem at least one of said first opening and said second opening and said exit opening have a shutter thereover.

5. The apparatus of claim 1 further comprising a shield coupled to said enclosure adjacent to said filter.

6. The apparatus of claim 1 wherem said sensor enclosure comprises a first portion and a second housing portion, said second housing portion having said light detector and said light source therein.

7. The apparatus of claim 1 further including: a lamp assembly coupled to said enclosure.

8. The apparatus of claim 1 further comprising a microcontroller configured to activate said lamp responsive to said output signal.

9. The apparatus of claim 1 wherem said apparatus is configured for installation m an automotive vehicle wherem said first and second openings lie substantially m a first plane and wherein an external airflow due to motion of said vehicle occurs generally m a direction, said sensor enclosure being configured m a look down rearward mode.

10. The apparatus of claim 9 wherem said automotive vehicle having an automotive structure, said structure and said housing defining an air channel therebetween.

11. The apparatus of claim 10 wherem said air channel is positioned m an orientation direction parallel to said direction so that a laminar airflow flows therethrough.

12. The apparatus of claim 10 wherem said automotive structure is one selected from the group of a mirror housing, a grill and a fog lamp housing.

13. The apparatus of claim 1 wherem said sensor enclosure comprises a tube defining an air channel therein adjacent to said first opening and said second openings .

14. An apparatus comprising: a sensor enclosure having a plurality of walls defining a first optical port having a first opening and a second optical port having a second opening, at least one of said walls having an air mlet therethrough; a light source disposed m said first optical port adjacent to said air mlet, said light source being configured to emit a light beam through said first opening to illuminate a sample volume located outside of said sensor enclosure; and a light detector disposed m said second optical port adjacent to said air mlet and configured to detect light said second opening and generate an output signal m response thereto indicative of the amount of light scattered from particles m the sample volume.

15. The apparatus of claim 14 further comprising a deflector having first and second apertures .

16. Tne apparatus of claim 15 wherem said first and second openings being located on a first side of said deflector, said light source and said light detector being located a second side opposite said first side of said deflector.

17. Tne apparatus of claim 14 further comprising a shutter selectively covering at least one of said first opening and said second opening.

18. The apparatus of claim 14 further comprising a first precipitation sensor configured to detect a condition selected from the group consisting of a ram condition and a snow condition and generate a closure signal m responsive thereto, said closure signal operative to cause said covering means to cover said first and second openings.

19. The apparatus of claim 18 further comprising electronic module responsive to said first output signal configured to generate a second output signal indicative of the presence of a visibility impairment .

20. The apparatus of claim 18 wherem said microcontroller is further configured to generate said closure signal when said precipitation signal is generated.

21. The apparatus of claim 14 wherem said electronic module includes a microcontroller configured to analyze said output signal and generate m response thereto a precipitation signal indicative of the presence of at least one of ram and snow.

22. The apparatus of claim 14 further comprising an air filter disposed withm said first air mlet .

23. The apparatus of claim 14 further comprising a shield coupled to said enclosure adjacent to said filter.

24. The apparatus of claim 14 wherem said sensor enclosure comprises a first portion and a second housing portion, said second housing portion having said light detector and said light source therein.

25. The apparatus of claim 14 further including: a lamp assembly coupled to sa d enclosure.

26. The apparatus of claim 14 further comprising a microcontroller configured to activate said lamp responsive to said output signal.

27. The apparatus of claim 14 wherem said apparatus is configured for installation m an automotive vehicle wherem said first and second openings lie substantially m a first plane and wherem an external airflow due to motion of said vehicle occurs generally a direction, said sensor enclosure being configured m a look down rearward mode.

28. The apparatus of claim 27 wherem said automotive vehicle having an automotive structure, said structure and said housing defining an air channel therebetween.

29. The apparatus of claim 28 wherem said air channel is positioned m an orientation direction parallel to said direction so that a laminar airflow flows therethrough.

30. The apparatus of claim 28 wherem said automotive structure is one selected from the group of a mirror housing a grill and a fog lamp housing.

31. The apparatus of claim 14 wherem said sensor enclosure comprises a tube defining an air channel therein adjacent to said first opening and said second openings .

32. A fog lamp control system for an automotive vehicle comprising: a fog 1amp ; a controller coupled to said fog lamp; a fog detector coupled to said controller, said fog detector having, a sensor enclosure having a plurality of walls defining a first optical port having a first opening and a second optical port having a second opening, at least one of said walls having an air let therethrough; a light source disposed m said first optical port adjacent to said air mlet, said light source being configured to emit a light beam through said first opening to illuminate a sample volume located outside of said sensor enclosure; and a light detector disposed said second optical port adjacent to said air mlet and configured to detect light said second opening and generate an output signal m response thereto indicative of the amount of light scattered from particles m the sample volume.

33. A fog lamp control system as recited m claim 32 wherem said fog lamp and said fog detector are coupled together.

34. A fog lamp control system as recited m claim 32 further comprising a display.

35. The apparatus of claim 32 further comprising an air filter disposed with said first air mlet .

36. The apparatus of claim 32 wherem at least one of said first opening and said second opening having a shutter thereover.

37. The apparatus of claim 32 further comprising a shield coupled to said enclosure adjacent to said filter.

38. The apparatus of claim 32 wherem said sensor enclosure comprises a first portion and a second housing portion, said second housing portion having said light detector and said light source therein.

39. The apparatus of claim 32 wherem said first and second openings lie substantially m a first plane and wherem an external airflow αue to motion of said vehicle occurs generally m a direction, said sensor enclosure being configured m a look down rearward mode .

40. The apparatus of claim 32 wherem said automotive vehicle having an automotive structure, said structure and said housing defining an air channel therebetween.

41. The apparatus of claim 40 wherem said air channel is positioned m an orientation direction parallel to said direction so that a laminar airflow flows therethrough.

42. The apparatus of claim 40 wherem said automotive structure is one selected from the group consisting of a mirror housing a grill and a fog lamp housing.

43. The apparatus of claim 32 wherem said enclosure is configured to at least partially define an air channel adjacent said first opening and said second openings .

44. A method for operating a fog detection system comprising the steps of : placing a detector on the vehicle so that air flows m a direction thereby; creating a low pressure withm a sensor enclosure; drawing air into said enclosure through an air inlet; and washing a light detector and a light source with air.

45. A method as recited in claim 44 wherein the step of washing comprises a light detector and a light source with filtered air.