Abstract:
A heater system for resisting fog and ice buildup on advanced driver assistance cameras provides a chamber covering the camera lens and providing a transparent window through which the camera lens may be directed. A heating element communicates with an air gap between the lens and the transparent window and the periphery of the transparent window to provide heating of the transparent window without blocking an image received by the camera lens.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application 62/144,541 filed Apr. 8, 2015 and hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to vehicular systems for advanced driver assistance systems (ADAS) and the like and, in particular, to a heater system for allowing operation of imaging cameras outside of the vehicle during adverse weather conditions. 
       BACKGROUND OF THE INVENTION 
       [0003]    Advanced Driver Assistance Systems (ADAS), such as those that provide assistance to the driver in guiding a vehicle, may employ multiple electronic cameras positioned to monitor the environment of the vehicle. For example, an automotive surround view camera system can provide the driver with a 360-degree view of the area surrounding the vehicle using four to six cameras mounted around the vehicle facing different directions. Similar camera systems may be used for lane departure warning systems, pedestrian avoidance systems, blind spot monitors, automatic parking, and the like. 
         [0004]    The positioning of these cameras for proper function may leave them susceptible to image degradation from frost, ice, fog, and water spray. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a “lens cap” heater that may attach to the camera over the camera lens to provide a heated assembly that repels and dissipates liquid and frozen water that can degrade the images provided by the camera. In one embodiment, the assembly provides a housing having a self-contained heating element supporting a water repelling transparent window. The heater applies heat to the window area without blocking the window area by heating a small air volume in the vicinity of the window such as transfers heat to the window without blocking the lens. The heater may employ a polymer positive temperature coefficient (PTC) material that provides automatic temperature regulation simplifying control of the heater. 
         [0006]    Specifically, the invention provides a heater for an advanced driver assistance camera having a housing with a first opening sized to receive a lens of the advanced driver assistance camera therethrough into a housing volume and a second opening providing a transparent window area through which the driver assistance camera may receive an image when the lens is positioned in the housing volume. A heater element is in the housing outside of the transparent window area to heat the transparent window area by at least one of conduction and convection. 
         [0007]    It is thus a feature of at least one embodiment of the invention to provide a heater system that may work with a variety of different advanced driver assistance cameras to harden those cameras against obstructing fog and ice. 
         [0008]    The transparent window may be treated with a hydrophobic material. 
         [0009]    It is thus a feature of at least one embodiment of the invention to promote the shedding of liquid water to augment the effectiveness of the heater. 
         [0010]    The first opening may conform to a size of the lens to support the housing with respect to the camera. 
         [0011]    It is thus a feature of at least one embodiment of the invention to provide a “lens cap” type design easily installed and replaced on a camera. 
         [0012]    The heater housing may be substantially cylindrical. 
         [0013]    It is thus a feature of at least one embodiment of the invention to provide a lightweight heater assembly minimizing opportunities for water ingress. 
         [0014]    The heater element may be a flexible polymer sheet. 
         [0015]    It is thus a feature of at least one embodiment of the invention to provide a heater element that can be readily adapted to attach to various surfaces of the housing. 
         [0016]    The heater element may be attached to the housing by adhesive. 
         [0017]    It is thus a feature of at least one embodiment of the invention to provide a heater element that can be adapted to work with separately fabricated injection molded components. 
         [0018]    The heater element may be a positive temperature coefficient material. 
         [0019]    It is thus a feature of at least one embodiment of the invention to provide temperature regulation in a robust, vibration resistant form eliminating bimetallic thermostatic elements and the like. 
         [0020]    The heater may include a voltage source for applying a current through the heater element to heat the transparent window area to a temperature preventing accumulation of ice and fog. 
         [0021]    It is thus a feature of at least one embodiment of the invention to provide a heater element that may practically melt frozen water and dissipate fog. 
         [0022]    The housing may retain the lens to provide an air gap between the lens and the transparent window area exposed to the heater to heat the air in the air gap thereby conducting heat from the heater to the transparent window. 
         [0023]    It is thus a feature of at least one embodiment of the invention to avoid the need for direct heating of the camera lens to remove ice or fog from the camera lens such as may be resisted by problems of accessibility of the camera lens to heating elements and high thermal resistance of the camera lens material. 
         [0024]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a top plan view of an automobile showing example camera locations and fields of view for those cameras as used for an advanced driver assistance system; 
           [0026]      FIG. 2  is an exploded perspective view of one camera of  FIG. 1  and a lens cover heater system of the present invention; 
           [0027]      FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 2  showing the components of the lens cover heater system including a cylindrical heater element and transparent window element; 
           [0028]      FIG. 4  is an exploded perspective view of the lens cover heater system in a first embodiment having an applied heater element; and 
           [0029]      FIG. 5  is a cross-sectional view perpendicular to that of  FIG. 3  showing a second embodiment of the invention employing an overmolded positive temperature coefficient material. 
       
    
    
       [0030]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Referring now to  FIG. 1 , a vehicle  10  may provide for multiple cameras  12 , for example, CCD cameras for implementing an automotive surround view camera system each having a field of view directed away from the center of the vehicle  10  to provide for 360-degrees of imaging. These cameras  12  may be exposed to environmental contamination, for example, when mounted at positions exposed through the body of the vehicle  10  or, for example, on wing mirrors. 
         [0032]    Referring now to  FIG. 2 , the cameras  12  may provide a cylindrical lens barrel  14  supporting a lens  16  for collecting light in the production of an image. The rear base of the lens barrel  14  may attach to a camera body  18  including circuitry for processing of the received image and providing a harness assembly  20  for communicating high-speed image data from the camera  12 , for example, through a serial port communication protocol. Camera body  18  may further include mounts  19  for attaching the camera body to the vehicle  10  with the lens  16  facing outward therefrom into the environment around the vehicle  10 . 
         [0033]    Referring now to  FIGS. 2 and 3 , a lens cover heater  22  per the present invention may provide for a cylindrical sleeve  24  sized to provide an internal diameter that fits tightly over the external diameter of the lens barrel  14  so that the cylindrical sleeve  24  may slide over the lens barrel  14  to cover a proximal end of the lens barrel  14 . The cylindrical sleeve  24 , for example, may be made of a molded thermoplastic material of low heat conductivity and may desirably be opaque to provide for resistance to off-axis light. Teeth or detent surfaces  26  may extend inward from a rear lip of the cylindrical sleeve  24  to retain the sleeve in proper position with respect to a groove in the lens barrel  14 , or an adhesive or other fastening mechanism may be provided to retain the cylindrical sleeve  24  in position on the lens barrel  14 . A front base of the cylindrical sleeve  24  is covered by a disk-shaped transparent window  28  and sealed at its periphery to the cylindrical sleeve so that the lens cover heater  22  provides a sealed volume  29  in front of the lens  16  (when installed on the lens barrel  14 ) protecting the lens  16  from direct environmental contact. A portion of the disk-shaped transparent window  28  inside the cylindrical sleeve  24  (thus unobstructed) defines a transparent window area  25 . The transparent window  28  may be a transparent thermoplastic material or glass sealed to one end of the cylindrical sleeve  24  to prevent the ingress of water at the interface between the transparent window  28  and cylindrical sleeve  24 . Desirably, the transparent window  28  has a thermal resistance and thickness such as to conduct heat readily through its surface from the volume  29  to the outer surface of the transparent window  28 . In this regard, the transparent window  28  may be a thermoplastic having a thickness of less than 1/16 inch or a glass having a thickness of less than ⅛ inch. 
         [0034]    A front surface of the transparent window  28  may be treated with a hydrophobic material such as a silicone material or textured with a nanoscopic surface or coated with a similar material to repel water while remaining optically clear. 
         [0035]    Referring now to  FIG. 4 , the cylindrical sleeve  24  may provide for tubular element  32  fitting tightly against the lens barrel  14  and adhered to or in-molded with a generally planar transparent window  28 . The tubular element  32  may attach to a flexible heater band  34 , for example, which may fit against the inner wall of the tubular element  32  and which may provide an inner coating, or be formed, of a positive temperature coefficient material  36 . 
         [0036]    In one embodiment, the positive temperature coefficient material  36  may provide a flexible polymer sheet that may flex or roll to readily conform to the inner surface of the tubular element  32 . 
         [0037]    Electrodes  38  may be applied in contact with the positive temperature coefficient material  36  and may communicate with terminals  40  so that electricity (typically 12 volts) can be passed through the electrodes  38  and then through the positive temperature coefficient material  36 . The positive temperature coefficient material  36  may provide at least 0.25 watts per square inch of heater area and optionally more than two watts per square inch of heater area. The positive temperature coefficient materials  36  may be adapted to provide at least 0.75 watts per square inch of transparent window area  25  and preferably more than 1.25 watts per square inch of transparent window area. 
         [0038]    The flexible heater band  34  may, for example, be adhered to the outside or inside circumference of the tubular element  32  using an adhesive or pressure-sensitive tape or film or may be in-molded to the cylindrical element  32  during an injection molding process. 
         [0039]    A positive temperature coefficient of resistance causes the amount of electrical flow through the material to vary according to the temperature of the material, with increased electrical flow at lower temperatures and decreased electrical flow at higher temperatures. This property provides for a self-regulating temperature of the flexible heater band  34  when a substantially constant voltage source is applied across the positive temperature coefficient material  36 . Positive temperature coefficient (PTC) heaters, suitable for the present invention, are also disclosed in U.S. Pat. Nos. 4,857,711 and 4,931,627 to Leslie M. Watts hereby incorporated in their entirety by reference. Alternatively or in addition, the flexible heater band  34  may be provided with a pulse width modulated voltage providing either a constant average voltage or an average voltage that varies according to a feedback signal such as the temperature signal or the like. 
         [0040]    Electrodes  38  may be, for example, screenprinted using conductive metallic inks or vapor deposited, for example, of silver, aluminum or the like or applied as a thin decal or etched from an adhered film using integrated circuit techniques or a variety of other manufacturing processes. 
         [0041]    As positioned on the camera  12  and held on the camera  12 , for example, through detent surfaces  26  described above, the front surface of the lens  16  is spaced away from a rear surface of the transparent window  28  to provide an air volume  29  therebetween. This air volume  29  is sized to allow conduction of heat from the heater band  34  to the entire surface of the transparent window  28  over the transparent window area  25 . The heater band  34  may thus heat the transparent window area  25  by convection as well as by edgewise heat conduction through the periphery of the transparent window  28  proximate to the heater band  34 . 
         [0042]    Referring now to  FIG. 5 , in an alternative embodiment, terminals  40  may attach to a solid molded split-tube of positive temperature coefficient material  36  on opposite sides of the split so that electricity must be conducted through the circumference of the positive temperature coefficient material  36 . Positive temperature coefficient material  36  may be overmolded with an outer insulating layer  42  which also provides an insulating separator between the terminals  40  within the split. 
         [0043]    Generally inwardly directed heat generated by the positive temperature coefficient material  36  in any of these embodiments will be concentrated in the volume  29  to heat the transparent window  28 , thereby allowing the transparent window  28  to resist the buildup of fog, ice, or snow on the outer surface of that window. The hydrophobic or super hydrophobic outer surface of the window  28  will generally also shed liquid water  48  from the outer surface of the transparent window  28 . 
         [0044]    Conductive leads  44  may attach to the terminals  40  and lead to an electrical connector  46  (shown in  FIG. 2 ) that can be connected to an automotive harness to provide power thereto from a voltage source such as a car automotive system. 
         [0045]    Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. 
         [0046]    Various features of the invention are set forth in the following claims.