Abstract:
A moisture sensing device for detecting moisture on a moisture collecting surface including an air pump for accelerating the formation of moisture on the moisture collecting surface. The moisture sensing device includes a moisture sensor that is operably positionable relative to a moisture collecting surface. The device also includes an air pump for accelerating the formation of moisture on the moisture collecting surface. A small pump can direct a flow of air over the moisture collecting surface to accelerate the formation of moisture through condensation.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a rain sensor for a windshield of a vehicle, and more specifically, the invention provides a rain sensor and a small air pump for directing a flow of air with respect to a surface sensed by the sensor.  
         BACKGROUND OF THE INVENTION  
         [0002]    When an automobile driver travels long distances through rain, the driver must continually adjust the speed of the windshield wipers because the intensity of the rain striking the windshield continually varies. Variation is caused by the natural variation in rain over time and distance, and also by man-made agents, such as passing vehicles which shower the windshield with spray.  
           [0003]    This continual adjustment can be tedious. Rain sensors have been developed in order to automate the control of windshield wipers. These sensors generally take the form of conductive sensors capacitive sensors, or optical sensors. In all types of sensors, however, the sensing of moisture is passive in that a moisture collecting surface is simply exposed to the environment. Typically, the moisture collecting surface is the windshield of the vehicle. It would be desirable to manipulate the moisture collecting surface to promote the formation of moisture in proximity to the surface sensed by the sensor before moisture actually collects on the remaining portions of the surface.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides an apparatus for actively detecting the presence of moisture on a moisture collecting surface. The apparatus includes a moisture sensor that can detect the presence of moisture on a moisture collecting surface. The moisture sensor can be a conductive moisture sensor, an optic moisture sensor, or a capacitive moisture sensor. The moisture collecting surface can be defined by at least a portion of the windshield of a vehicle. The apparatus also includes means for accelerating the formation of moisture on the moisture collecting surface adjacent to or in proximity to the portion of the surface sensed by the sensor. The means for accelerating moisture formation can be an air pump capable of directing a flow of air with respect to the moisture collecting surface. The air pump can include means for cooling the air to be directed over the moisture collecting surface. The air pump can be formed of a flexible housing having an inlet port and an outlet port and valves to control the flow of air in and out of the ports. An air pump with a flexible housing can be expanded and contracted, similar to a bellows, to draw air into the housing and discharge air out of the housing by a pulsatable member, such as a piezoelectric member. In such an embodiment, the apparatus can include means for alternating the voltage across the piezoelectric member. Accelerating the formation of moisture on the collecting surface can also be accomplished by any means capable of reducing the temperature of the collecting surface to promote condensation. The apparatus can also include a controller for controlling the operation of the air pump or cooling means.  
           [0005]    Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0007]    [0007]FIG. 1 is a cross sectional side view of an embodiment of the present invention wherein an air pump is positioned adjacent to a windshield of a vehicle;  
         [0008]    [0008]FIG. 2 a  is a cross sectional side view of an air pump according to the present invention expelling air with respect to a position of the windshield in proximity to the sensor; and  
         [0009]    [0009]FIG. 2 b  is a cross sectional side view of an air pump according to the present invention drawing air into the flexible housing or bellows. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]    The present invention provides a moisture detector for actively promoting condensation in a predefined location. The detector  10  includes a moisture sensor  12  operably positionable with respect to a moisture collection surface  14 . The moisture sensor  12  can be positioned spaced apart from the surface  14 , or mounted directly to the surface  14 , or incorporated with the surface  14  as part of the sensor  12 . For example, in a capacitive rain sensor as used on the windshield of a vehicle, the sensor can be positioned adjacent an interior surface of the windshield, and is operably positioned with respect to the exterior surface of the windshield defining the moisture collecting surface. In such an embodiment of a moisture sensor, the windshield physically separates the moisture sensor  12  and the moisture collecting surface  14 . In a conductive or resistive rain sensor, a pair of parallel conductors extend from the sensor and are positioned on the moisture collecting surface. The detector  10  can include one or more sensors selected from a group of sensors including a capacitive sensor, a resistive sensor, a conductive sensor, and an optical sensor.  
         [0011]    The active moisture detector  10  of the present invention also includes means  15  for accelerating the formation of moisture on the collecting surface  14 . The accelerating means  15  can include means operable for reducing the temperature of the collecting surface  14  to otherwise accelerate the formation of moisture through condensation. The acceleration means  15  can also include means  19  for directing a flow of air over the collecting surface. By directing a flow of air over the collecting surface, the active moisture detector  10  takes advantage of wind chill effects. Wind chill is the rate of heat loss caused by air motion. Specifically, it is the rate of units of heat carried away from a body by wind. For example, at a temperature of 0° F. and a wind speed of 30 mph, the heat loss is equivalent to −49° F. By directing a flow of air over the moisture collecting surface  14 , the active moisture detector  10  can increase the rate of heat loss experienced by the moisture collecting surface  14 . As heat is lost by the moisture collecting surface  14 , the likelihood of condensation first occurring on the moisture collecting surface  14  in proximity to or adjacent the sensor prior to collecting on other portions of the surface is increased.  
         [0012]    The air flow directing means  19  can be a pump or blower  16 . The pump  16  can include a housing or bellows  18  defined by at least one wall  20 . The housing  18  can be formed in the shape of a cone or a wedge. The wall  20  can be formed of a flexible material such as rubber or plastic. The housing  18  can include an inlet port  22  as shown in FIG. 2 b,  and an outlet port  24  as shown in FIG. 2 a.  Valves  26  and  28  respectively, can be operable to selectively open and close the inlet port  22  and outlet port  24  in response to expansion and contraction of the housing or bellows  18 . The wall  20  of the housing  18  can be joined to a drive member  30 , as shown in FIG. 1. The drive member  30  can be reciprocable or pulsatable to operably increase and decrease in the direction indicated by the arrow  32  shown in FIG. 1 for driving the flexible housing or bellows  18  to pump air out of the outlet port  24  to be directed across the moisture collecting surface  14 . The drive member  30  can be a piezoelectric member. The pump  16  can include a voltage alternator  34 . The voltage alternator  34  can apply positive and negative voltage across the peizoelectric member  30  to bring about changes in dimension of the drive member  30 .  
         [0013]    During the operation of the pump  16 , the voltage alternator  34  applies alternating positive and negative voltages across the piezoelectric member  30  causing the piezoelectric member  30  to increase and decrease in dimension. The wall  20  of the housing  18  can be connected to the piezoelectric member  30  at positions  36   a  and  36   b  as shown in FIG. 2 b.  When the piezoelectric member  30  increases in dimension, the housing  18  is stretched as the base positions  36   a  and  36   b  become further apart. The expansion of the housing  18  results in a negative pressure differential between an internal cavity  38  of the housing  18  and the ambient air. The pressure differential causes the flap valve  26  to open and allow air into the housing  18  through the inlet port  22 . When the voltage is reversed, the piezoelectric member  30  decreases in dimension. The base positions  36   c  and  36   d,  as shown in FIG. 2 a,  can move towards each other as the housing  18  contracts. The contraction of the housing  18  creates a positive pressure differential between the internal cavity  38   a  of the housing  18  and the ambient air. The flap valve  28  opens and air is driven out of the housing  18  through the outlet port  24 . In this embodiment of the invention, the pump  16  acts as a bellows.  
         [0014]    The pump  16  can also include a heat exchanger  40 . The heat exchanger  40  can be positioned in the wall  20  of the housing  18 . The heat exchanger  40  can act on the air in the internal cavity  38  to heat or cool the air. The heat exchanger  40  can be powered by an electric power source.  
         [0015]    The active moisture detector  10  can also include control means  42  for controlling the operation of the voltage alternator  34 . The control means  42  can receive a signal from the moisture sensor  12  indicating that the moisture sensor  12  has sensed the presence of moisture on the moisture collecting surface  14 . The control means  42  can then stop the operation of the voltage alternator  34  and thereby stop the operation of the pump  16 . Generally, for a moisture sensor for a windshield of a vehicle, once moisture has been detected on the exterior surface of the windshield, the windshield wipers are activated to remove the moisture. During the wiping operation, pump  16  can be disengaged.  
         [0016]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.