Abstract:
A heater for vehicular sensors is configured to pass sensing energy and thereby permit placement of the heater directly over the sensing area in the path of the sensed energy. In this way, direct heating of the sensing area is provided minimizing the energy necessary to prevent icing and improving deicing speed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. provisional filing 62/074,211 filed Nov. 3, 2014, and hereby incorporated in its entirety by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to vehicular systems and, in particular, to advanced vehicular sensing system systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Sensors for sensing pedestrians, other vehicles, and obstacles in the vicinity of the a vehicle are being developed for use with advanced systems which can control a vehicle&#39;s accelerator and braking systems to regulate the distance between the vehicle and the other object. Ultimately, such systems may also be used in providing self-guiding or self-driving vehicles. 
         [0004]    Sensors of this type, including radar, LIDAR, infrared video, visible-light video, and ultrasound, can be adversely affected by a covering of ice, sleet, or snow—materials likely to be experienced in real-world driving conditions. Placing shields or other materials in front of the sensor can also interfere with operation of the sensor. Particularly with respect to radar sensors, any conductive metal, such as electrical heater elements, placed over the radar sensor may block the radio wave propagation. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a front-face heater that may be placed over a vehicular sensing system to limit or remove the accumulation of sleet, ice, or snow. The heater employs a polymer positive temperature coefficient (PTC) material that may be configured to be transmissive to light, sound, and microwave radio frequency energy. By properly sizing and shaping the conductive heater electrodes communicating with the PTC material, interference with sensing energy from the sensor may be minimized despite the heater being placed in the way of the sensed energy. 
         [0006]    Specifically, the present invention provides a vehicular sensing system having a sensor receiving sensed energy through a window area and having a heater positioned over the sensor, the heater positioned within the window area and comprised of a resistive film communicating with metallic conductors adapted to apply current to the resistive film. The resistive film and metallic conductors are configured to be substantially transparent to the sensed energy within the heater window area. 
         [0007]    It is thus a feature of at least one embodiment of the invention to provide an energy transparent heater for automotive use that can be mounted in the path of the sensed energy to more quickly and completely melt ice, sleet, and snow accumulating in the energy path. By positioning the heater in the energy path, indirect heating of a window area such as may require additional energy and increased delay is avoided. 
         [0008]    The metallic conductors may be applied to the resistive film within the window area in an interdigitated pattern. 
         [0009]    It is thus a feature of at least one embodiment of the invention to provide for substantially uniform current flow and thus heating to the heater to eliminate hot spots, cold spots, and maximize energy efficiency. 
         [0010]    The resistive film may be a positive temperature coefficient material. 
         [0011]    It is thus a feature of at least one embodiment of the invention to provide a heater that may be largely self-regulating without the need for temperature measurement elements and thermostatic control. 
         [0012]    The sensed energy may be microwave radiation, and the metallic conductors may have dimensions tuned to reject absorption of the microwave radiation. 
         [0013]    It is thus a feature of at least one embodiment of the invention to provide the benefits of a window-located heater without degrading the microwave signal. 
         [0014]    The metallic conductors may have a vertical width of less than two millimeters and a thickness of less than 0.05 millimeters. 
         [0015]    It is thus a feature of at least one embodiment of the invention to balance the need for current distribution with a need to minimize metallic area in the path of the microwave beam such as may adsorb microwave energy. 
         [0016]    The vehicle sensor may include mounting points for mounting the vehicle sensor to a vehicle in a predetermined orientation and the metallic conductors may extend horizontally across the window area when the vehicle sensor is mounted in the vehicle. 
         [0017]    It is thus a feature of at least one embodiment of the invention to minimize diffractive effects in the horizontal plane such as may degrade the more important measurement axis of a microwave sensing system. 
         [0018]    The heater provides at least 10 watts of heat. 
         [0019]    It is thus a feature of at least one embodiment of the invention to provide sufficient heating capability for rapid deicing. 
         [0020]    In one alternative embodiment, the sensed energy may be light and the sensor may include an optically transparent substrate supporting the heater elements, and the heater elements are substantially opaque and include a set of apertures for transmission of light. 
         [0021]    It is thus a feature of at least one embodiment of the invention to provide a resistive-type heater that can work with optical sensing as well as microwave sensing. 
         [0022]    The sensor may be a camera having a light sensor and lens for focusing light on the light sensor heater element that is placed with in a focal length of the lens. 
         [0023]    It is thus a feature of at least one embodiment of the invention to minimize interference with the imaging of an imaging-type light sensor. By placing the opaque heater elements out of the focal plane, they may remain out of focus without creating image artifacts. 
         [0024]    The sensed light may be infrared light and may include a controller for alternating the application of electrical current to the heater and the sensing of energy using the sensor. 
         [0025]    It is thus a feature of at least one embodiment of the invention to permit coexistence of a heater and an infrared sensor. 
         [0026]    Alternatively, the sensed energy may be ultrasound energy, and the sensor may be an ultrasound transducer transmitting ultrasonic energy through an acoustically transparent window material, and the resistive material and metallic conductors are adhered directly to the window material. 
         [0027]    It is thus a feature of at least one embodiment of the invention to minimize blockage of ultrasound energy by reducing transitions between materials of different sound propagation properties. 
         [0028]    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 
         [0029]      FIG. 1  is a perspective view of a vehicle having a variety of different obstacle sensors; 
           [0030]      FIG. 2  is an exploded block diagram of a sensor and a front-surface heater as may be applied over the face of the sensor in the present invention; 
           [0031]      FIG. 3  is a cross-section taken along line  3 - 3  of  FIG. 2  showing construction of the front-surface heater using a thin sheet of polymer material with an overlay of conductive electrodes; 
           [0032]      FIG. 4  is a rear elevational view of the heater of  FIGS. 2 and 3  showing important dimensions with respect to promoting the transmission of sensing energy; 
           [0033]      FIG. 5  is a side elevational view of an optical sensing system when used with the present invention showing positioning of the heater within the focal plane of the camera lens; 
           [0034]      FIG. 6  is a figure similar to that of  FIG. 4  showing an alternative construction of the heater element to provide for the passage of light energy; 
           [0035]      FIG. 7  is a figure similar to that of  FIG. 5  showing an ultrasound sensing system used with the present invention; and 
           [0036]      FIG. 8  is a figure similar to  FIG. 7  showing arrangement of the heater elements. 
       
    
    
       [0037]    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 
       [0038]    Referring now to  FIGS. 1 and 2 , a vehicle  10  suitable for use with the present invention may incorporate a variety of sensing units  12  for monitoring potential obstacles in the path or vicinity of the vehicle  10 . The sensing units  12  may incorporate a sensor  15  within a housing  17 , for example, the former for receiving and sensing a sensed energy. 
         [0039]    The sensor  15  may exchange electrical signals with a sensor interface circuit  13  which in turn communicates with a vehicular computer  11 , the latter managing vehicle control tasks, for example, by controlling steering actuators  19   a , braking actuators  19   b , and engine acceleration actuators  19   c . The sensors  15  may also communicate with vehicle cockpit display systems  23  to provide information to the vehicle occupants. 
         [0040]    The housing  17  may include mounting elements  19  for mounting the housing  17  in a predetermined orientation with respect to the vehicle  10  and will generally provide sealing against environmental contamination and the like. 
         [0041]    Front facing sensing units  12   a  may provide, for example, a 77 gigahertz long range radar  14  providing 1 to 120 meters of sensing capability. Alternatively or in addition, the front facing sensing units  12   a  may include far infrared (night vision) imaging  18  sensors, providing sensing from 0.2 to 80 meters of sensing capability, normal visible-light video  20  sensors (or LIDAR  16 ), providing up to 280 meters of sensing capability, short range radar  22 , for example, using twenty-four gigahertz short range radar and providing 0.2 to 20 meters of sensitivity, and ultrasonic sensing  24  providing 0.2 to 1.5 meters of sensing range. Short-range radar and ultrasonic sensing may also be provided by side sensing units  12   b.    
         [0042]    Referring now to  FIG. 2 , each of the sensing units  12  may have a window area  26  through which the sensing unit  12  receives sensing energy  28  inward toward the vehicle  10  along a sensing axis  31 . This sensing energy  28  may be available environmentally or generated by an energy source associated with the sensing unit  12  and in certain cases being the sensor  15 . The received energy, for example, may be long- or short-range radar, infrared light, and visible spectrum light including but not limited to a laser beam, or ultrasound. 
         [0043]    The invention may provide a front-face heater  30  placed over the window area  26  between the window area  26  and sources of environmental exposure to ice, sleet, and snow. The front-face heater  30  may receive electrical power through leads  37  which provide energy to heat the front-face heater  30  to melt received sleet, ice, or snow that might otherwise block outward transmission of the sensing energy  28  or inward receiving of the sensed energy. In this regard, the front-face heater  30  may desirably have a regulated surface temperature above the melting point of ice. In one embodiment the heater may have a wattage of 15 to 20 watts. 
         [0044]    Power from the electrical leads  37  may be provided by a power control circuit  35  (for example, a solid-state switching device such as a transistor or the like) switching a DC voltage to the leads  37 , for example, based on a range of air temperature sensed by separate temperature sensors (not shown) or at periodic intervals interleaved with sensing intervals in the case of an infrared sensor where some interference may be present. The DC voltage to the leads  37  may be floating or tied to voltages used by the sensing unit  12  itself, including, for example, radiofrequency modulators and demodulation amplifiers in the case of radar. 
         [0045]    Referring now to  FIG. 3 , the front-face heater  30  may provide for a thin sheet of transparent and in some cases optically clear polymer material providing a substrate  32 . The substrate  32  is desirably water-resistant and may be treated to be water repellent and may face outward with respect to the window area  26  to provide protection of the sensing unit  12  against the environment. Alternatively, or in addition, additional energy transmissive protective housing (not shown) may be placed in front of the front-face heater  30  along the direction of propagation of the sensing energy  28 . 
         [0046]    Coated on a rear face of the clear polymer material is a PTC (positive temperature coefficient) material  33  having the property of conducting electricity with a positive temperature coefficient of resistance. A positive temperature coefficient of resistance causes the amount of electrical flow 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 PTC material  33  when a substantially constant voltage source is applied across the PTC material  33 . 
         [0047]    In one embodiment, the PTC material  33  may comprise an ethylene vinyl acetate copolymer resin, such as DuPont  265  which comprises about 28 percent vinyl acetate monomer and about 72 percent ethylene monomer modified to have a sheet resistivity of 15,000 ohms per square. To achieve this electrical characteristic, this ethylene vinyl acetate copolymer resin may be first dissolved in an aromatic hydrocarbon solvent such as naphtha, xylene, or toluene at about 80 degrees C. and let down to where twenty percent of the total weight of the solution is solids. Carbon black, such as CABOT VULCAN PF, maybe added and mixed to bring the total solid content to about 50 percent by weight. This material is then passed through a three-roll dispensing mill having a 0.1 to 1 mil nip clearance to further disperse and crush the solids. The material is further let down with about a twenty percent solids resin and solvent solution until the desired sheet resistivity is achieved. 
         [0048]    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. 
         [0049]    The rear surface of the PTC material  33  may support interdigitated electrodes  34  that apply voltage across the PTC material  33  promoting current flow through the PTC material  33  generally along the plane of its extent. Electrodes  34  may be, for example, screenprinted using conductive metallic inks or vapor deposited, for example, of 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. In one example, NazDar 9600 series ink with a twenty percent flattening paste added thereto is suitable for use in forming the electrodes  34  in one embodiment of the invention. This ink is commercially available from NazDar Inc, of Kansas, USA. The conductive electrical pattern of the electrodes  34  may be deposited on the substrate  32  in a thickness ranging between about 8 to 10 microns. 
         [0050]    Referring now to  FIG. 4 , in one example embodiment, a first electrode bus strip  36   a  of the interdigitated electrodes  34  may extend along a vertical left edge of the area of the front-face heater  30  displaced out of the path of the sensing energy  28 . A second electrode bus strip  36   b  may be positioned parallel to and opposite the bus strip  36   a  also displaced from the center of the front-face heater  30 . 
         [0051]    Extending inward, horizontally and perpendicularly to the extent of the bus strips  36  and from the bus strips  36 , may be interdigitated finger electrodes  38   a  and  38   b  each electrically communicating with an alternate respective one of the first electrode bus strip  36   a  and second electrode bus strip  36   b.    
       Radar System 
       [0052]    A typical radar sensor may provide an 80 millimeter by 80 millimeter area window area  26 . In this case the sensing unit  12  includes both a microwave transmitting and microwave receiving antenna  27 . The front face heater  30  may extend over the window area  26 . 
         [0053]    In the case of microwave radiation for use with radar, the absorption by the finger electrodes  38  may be limited by controlling their tuning as well as minimizing their size and extent. For the case of 77 gigahertz microwave radiation, the vertical thickness  44  of the finger electrodes  38  will be less than 0.2 millimeters and desirably less than 0.15 millimeters. In addition the finger electrodes  38  may have a thickness of less than 0.05 millimeters and desirably less than 0.02 millimeters. 
         [0054]    Generally, the spacing  42  between the finger electrodes  38  will be larger than the wavelength of the radar intended to be passed so as to reduce interference. Ideally, the spacing will be substantially larger than twelve millimeters for low-frequency 24 gigahertz microwave radiation and larger than three millimeters in the case of high-frequency 77 gigahertz radar and desirably a multiple of these values. Generally, the tuning will reduce the thickness  44  to a fraction of the wavelength of the microwave radiation and will set the lengths  40  not to equal an integral multiple of the wavelength. 
         [0055]    The invention also contemplates that radiofrequency trap structures (not shown) may be placed in the finger electrodes  38 , for example, by creating radiofrequency chokes using capacitive elements and distributed inductance or the like. Alternatively, shorting structures such as diodes may be used to shunt the finger electrodes  38  to minimize electrical resonance, for example, as switched synchronously with the application of a radiofrequency pulse. At the times of microwave transmission and reception, heating currents can be turned off. 
         [0056]    The orientation of the finger electrodes  34  will generally be such as to reduce diffractive effects in the desired axis of highest resolution (typically horizontal) by running the electrodes  34  in a horizontal direction. The invention contemplates that other methods of reducing interference including orienting the finger electrodes  38  according to any polarization (horizontal or vertical) of the radar signal; randomly varying finger length and spacing may also be employed. 
       Light Sensing System (Camera, LIDAR, Infrared) 
       [0057]    Referring now to  FIG. 5 , an alternative sensing unit  12 ′ may provide a camera having a light sensor  50 , for example, a charge coupled device circuit at a focal length  52  behind a lens assembly  54  projecting an image of a roadway or the like on the surface of the light sensor  50 . In this case, the heater  30  may be placed within the focal distance  57  of the lens assembly  54  in front of the lens assembly  54  to minimize its effect on the image formed on light sensor  50 . A beam stop  51  may be positioned in front of the heater  30  or behind the heater  30  to define the window area  26 . 
         [0058]    Referring also to  FIG. 6 , in this case the PTC material  33  may be laid in strips passing perpendicularly between the finger electrodes  38  to provide openings  60  therebetween revealing the transparent substrate  32  allowing light to pass therethrough without diffusion or aberration. In this way an opaque PTC material  33  may be used or PTC material  33  that is light diffusing. Desirably the size of the openings  60  will be maximized to the point where suitable heat is still generated with desirable heating uniformity and ample conductor size is provided by finger electrodes  38  for the necessary current. 
       Ultrasound System 
       [0059]    Referring now to  FIGS. 7 and 8 , the heater  30  may be also applied to an ultrasonic transducer  62  providing the sensing unit  12 ″. Here, the transducer  62  may provide, for example, a piezoelectric material  64  to which electricity may be applied by means of surface electrodes  66 . The piezoelectric material  64  may be coupled to a transmission window  68  of an ultrasound transmitting material as is generally understood in the art. In this case, the heater  30  may be adhered directly to a front or rear face of the transmission window  68 . Ideally, the combined electrodes  34 , PTC material  33  and substrate  32  has similar acoustomechanical properties to the transmission window  68  (e.g., density, modulus of elasticity, etc.) to prevent reflections at the interface. Interference with the sensing energy  28  can also result from mechanical absorption which is treated by controlling the thickness of the polymer material of the substrate  32 . The electrodes  34  and finger electrodes  38  may be applied directly to the transmission window  68  with a space-filling adhesive having similar acoustic properties to the transmission window  68  or intermediate properties between the transmission window  68  and the substrate  32 . 
         [0060]    Alternatively, the PTC material  33  and electrodes  34  may be applied directly to the transmission window  68 , the latter of which is implicitly acoustically matched to the piezoelectric material  64  at the intended excitation frequency. Sound absorbing channeling stops  51  may define an energy-receiving window area  26 . 
         [0061]    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. 
         [0062]    Various features of the invention are set forth in the following claims.