Patent Publication Number: US-11654864-B2

Title: Heating device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to EP Application No. 18213507.9, which was filed on 18 Dec. 2018. 
     TECHNICAL FIELD 
     The present disclosure relates generally to a heating device that clears condensation from a viewing window of a camera. 
     BACKGROUND 
     Typical heating devices require electrical terminals and wiring attached to a windshield or cover-glass. United States Patent Application Publication Number 2006/0171704 A1 describes a heating element for heating a transparent camera lens cover that includes electrical terminals in contact with a surface of the transparent camera lens cover. Other applications describe a heating element positioned on a lens holder, and resilient contacts used to heat a camera lens. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure proposes to solve the above mentioned problem by providing a heating device comprising a housing configured to retain a camera lens, a primary induction coil positioned proximate the housing and configured to generate a magnetic field in response to receiving electrical power from a power supply, a controller circuit in electrical contact with the primary induction coil configured to control the electrical power delivered to the primary induction coil, and a secondary induction coil overlaying the primary induction coil configured to receive the magnetic field from the primary induction coil and generate heat. The secondary induction coil is in direct contact with a windshield of a vehicle and defines a viewing window through which the camera lens views a surrounding area. The secondary induction coil heats the viewing window when the primary induction coil receives the electrical power. 
     According to other advantageous features of the present disclosure: 
     the primary induction coil surrounds an optical axis of the camera lens; 
     the controller circuit includes a low-Q resonant circuit in electrical communication with the primary induction coil; 
     a temperature of the secondary induction coil is controlled by adjusting a voltage applied to the primary induction coil; 
     a temperature of the secondary induction coil is controlled by adjusting a frequency of a signal delivered to the primary induction coil; 
     the secondary induction coil is comprised of a first layer of resistive material and a second layer of low-Curie point ferrite; 
     the secondary induction coil is located between glass layers of the windshield; 
     the secondary induction coil is located on an inner surface of the windshield; 
     the secondary induction coil is located on an outer surface of the windshield; 
     the secondary induction coil is formed of a conductive material having a greater electrical resistance relative to the primary induction coil; 
     the secondary induction coil is characterized as segmented, wherein adjoining segments are formed of materials having a different electrical conductivity from one another; 
     a distance between the primary induction coil and the secondary induction coil is in a range from 0.0 mm to 10.0 mm; 
     a number of windings on the primary induction coil is at least one; 
     a number of windings on the secondary induction coil is at least one; 
     the secondary induction coil has a thickness in a range from 1.0 μm to 1000 μm; 
     the secondary induction coil has a width in a range from 0.1 mm to 10 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is now described by way of example with reference to the accompanying drawings in which: 
         FIG.  1    is an exploded perspective view of a heating device according to an embodiment of the disclosure; 
         FIG.  2    is a section view of the heating device of  FIG.  1   ; 
         FIG.  3    is a section view of a portion of the heating device of  FIG.  2   ; 
         FIG.  4    is a schematic of the heating device of  FIG.  1    illustrating a controller circuit. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a heating device  10  for a windshield  20  and/or a cover-glass according to an embodiment of the present disclosure will be described with reference to the figures.  FIG.  1    is an exploded perspective view illustrating the heating device  10 , hereafter referred to as the device  10 . The device  10  includes a housing  12  configured to retain a camera lens  14 . The housing  12  may be formed of any material, such as a polymeric material, a ceramic, or a metal. The housing  12  may have a circular cross section or may have any other cross section, such as a rectilinear cross section. The housing  12  may include an imager  15  used to render an image of a surrounding area. The camera lens  14  defines a field-of-view  16  and an optical axis  18  as illustrated in  FIG.  1   . The housing  12  may be mounted on a front of a vehicle, on sides of a vehicle, on a rear of a vehicle, or mounted in the interior of the vehicle at a location suitable for the camera to view the area around the vehicle through the windshield  20 . In the examples illustrated herein, the housing  12  is mounted inside the vehicle with the view through the windshield  20 . 
     The device  10  also includes a primary induction coil  22  positioned proximate the housing  12  and configured to generate a magnetic field  24  in response to receiving electrical power  26  from a power supply  28 . The power supply  28  may be a direct-current (DC) power supply  28 , or may be an alternating-current (AC) power supply  28 . In the examples illustrated herein the power supply  28  is an AC power supply  28 . The primary induction coil  22  surrounds the optical axis  18  of the camera lens  14  and may also surround a portion of the housing  12 . A number of windings  30  (e.g., wires, conductive traces, etc.) on the primary induction coil  22  is at least one and are preferably wound onto a ferromagnetic core  32  (e.g. iron, ferrites, etc.). It will be appreciated that the number of windings  30  will increase with the increasing size of the area required to be heated. It will also be appreciated that the ferromagnetic core  32  may be omitted (i.e., an air core coil) depending on packaging and weight constraints. A single winding  30  (i.e. a single wire) of the primary induction coil  22  may be any diameter, and in the examples illustrated herein, preferably has the diameter in a range from 0.2 mm to 1.0 mm. The windings  30  may be formed of any electrically conductive material, such as copper alloys or aluminum alloys and may include a dielectric layer on a surface of the windings  30 . 
     The device  10  also includes a controller circuit  34  in electrical contact with the primary induction coil  22 . The power supply  28  may be separate or integral to the controller circuit  34 , and in the examples illustrated herein, the power supply  28  is integral to the controller circuit  34 . The controller circuit  34  is configured to control the electrical power  26  delivered to the primary induction coil  22 . The controller circuit  34  may include a processor (not shown) such as a microprocessor or other control circuitry such as analog and/or digital control circuitry including an application specific integrated circuit (ASIC) for processing data as should be evident to those in the art. The controller circuit  34  may include a memory (not shown), including non-volatile memory, such as electrically erasable programmable read-only memory (EEPROM) for storing one or more routines, thresholds, and captured data. The one or more routines may be executed by the processor to perform steps for determining the electrical power  26  delivered to the primary induction coil  22  based on signals received by the controller circuit  34  from the primary induction coil  22 , as described herein. 
     The device  10  also includes a secondary induction coil  36  overlaying the primary induction coil  22 . The secondary induction coil  36  is configured to receive the magnetic field  24  from the primary induction coil  22 , thereby generating heat  38 . The magnetic field  24  from the primary induction coil  22  induces an electrical current in the secondary induction coil  36 . The induced electrical current in the secondary induction coil  36  causes the secondary induction coil  36  to increase in temperature because the secondary induction coil  36  is formed of a material that has an electrical resistance. The electrical resistance of the secondary induction coil  36  resists the flow of electrical current within the secondary induction coil  36 , which generates the heat  38  (also known as Joule heating or Ohmic heating). It will be appreciated that no wire connections exist between the primary induction coil  22  and the secondary induction coil  36 . This has the technical benefit of reducing a size and complexity of the overall assembly. The secondary induction coil  36  also surrounds the optical axis  18  and is in direct contact with the windshield  20  of the vehicle. In the example illustrated in  FIG.  1   , the secondary induction coil  36  is located on an inner surface  42  of the windshield  20 . In an alternative embodiment the secondary induction coil  36  may be located on an outer surface  43  of the windshield  20 . 
     The secondary induction coil  36  defines a viewing window  40  through which the camera lens  14  views the surrounding area. That is, an inner diameter of the secondary induction coil  36 , as illustrated in  FIG.  1   , creates a “window” through which light rays may pass to the camera lens  14  and imager  15 . The secondary induction coil  36  heats the viewing window  40  and removes condensation (e.g., fog, ice, etc.) when the primary induction coil  22  receives the electrical power  26  from the controller circuit  34 . A heating rate and a maximum temperature is controlled to inhibit a thermal shock to the windshield  20 , and also to prevent an unsafe surface temperature of the windshield  20  for human contact. 
       FIG.  2    is a section view of the device  10  and illustrates an embodiment where the secondary induction coil  36  is located between glass layers  44  of the windshield  20 . A distance  46  between the primary induction coil  22  and the secondary induction coil  36  is preferably in a range from 0.0 mm to about 10.0 mm. The distance  46  primarily impacts a coupling of the primary induction coil  22  and the secondary induction coil  36 . 
     The number of windings  30  on the secondary induction coil  36  is at least one, and may be increased to achieve a specific temperature profile applied to the windshield  20 . The windings  30  on the secondary induction coil  36  may be a single flat winding  30  that may be deposited using a thick-film ink, for example. The secondary induction coil  36  as illustrated in  FIG.  2    has a thickness  48  in the range from about 1 μm to about 1000 μm. The thickness  48  may be adjusted based on the type of material comprising the secondary induction coil  36 , and based on a frequency  50  of the electrical power  26  delivered to the primary induction coil  22 . In an embodiment, the secondary induction coil  36  has a thickness  48  of 400 μm and is formed of a material with a low relative magnetic permeability (e.g., silver, aluminum, etc.). In another embodiment, the secondary induction coil  36  is formed of a material having higher relative magnetic permeability (e.g., iron) having a thickness  48  of 15 μm. The thickness  48  may also be reduced by increasing the frequency  50  of the of the electrical power  26  delivered to the primary induction coil  22 . The secondary induction coil  36  has a width  49  in a range from about 0.1 mm to 10 mm, and preferably has the width  49  of about 5 mm due to packaging constraints on the windshield  20 . It will be appreciated that the width  49  of the secondary induction coil  36  affects the heat transfer to the windshield  20 . The width  49  may be user defined depending on a desired heating profile for the windshield  20 . 
       FIG.  3    is a magnified view of a portion of the device  10  of  FIG.  1   . The secondary induction coil  36  is preferably comprised of a first layer  52  of resistive material that dissipates the power transmitted by the magnetic field  24 , and a second layer  54  of low-Curie point ferrite. When the secondary induction coil  36  reaches a Curie point temperature (e.g. approximately 90 degrees Celsius for a Mn—Zn ferrite at 8 μm-9 μm thickness  48 ), the magnetic permeability of the second layer  54  is decreased, thereby reducing the induced heating of the secondary induction coil  36 . This reduction of the induced heating of the secondary induction coil  36  changes a resonant-frequency of a control circuit  56 , the benefit of which will be described in more detail below. Preferably, the secondary induction coil  36  is formed of a conductive material having a greater electrical resistance than that of the primary induction coil  22 . The first layer  52  and the second layer  54  may also have a protective coating (not specifically shown) applied to their exposed surfaces to improve a durability of the layers. 
     Referring back to  FIG.  1   , the secondary induction coil  36  may be characterized as segmented  58 , wherein adjoining segments  58  are formed of materials having a different electrical conductivity from one another. That is, a first segment may have a relatively low electrical resistance thereby emitting a relatively low quantity of heat  38 , wherein a second segment in contact with the first segment may have a higher electrical resistance compared to the first segment, thereby emitting a larger quantity of heat  38  than the first segment. This segmentation  58  has the technical benefit of enabling a specific heating profile on the windshield  20 . For example, preferentially heating corners of a rectangular viewing window  40  where the corners are a greater length away from the optical axis  18  compared to a side of the rectangular viewing window  40  that may be closer to the optical axis  18 . It will be appreciated that other patterns of segmentation  58  are possible based on a geometry of the viewing window  40 . 
       FIG.  4    is a schematic diagram of the device  10  illustrating the controller circuit  34 . The controller circuit  34  preferably includes a low-Q resonant control circuit  56  in electrical communication with the primary induction coil  22 . A Q-factor (i.e., quality factor) of an electronic circuit is a parameter that describes the resonance behavior of a harmonic oscillator or resonator. The low-Q factor is indicative of an overdamped system that does not resonate or oscillate. The low-Q resonant control circuit  56  has the technical benefit of improved temperature control in the secondary induction coil  36 . It will be appreciated that the values of capacitors C 1  and C 2  (not specifically shown) may be selected to achieve the desired resonant-frequency to drive the secondary induction coil  36  and produce the desired heat  38 . The temperature of the secondary induction coil  36  may be controlled by adjusting a voltage  62  applied to, and/or adjusting the frequency  50  of a signal delivered to, the primary induction coil  22  through the MOSFETs M 1  and M 2  (not specifically shown) and through the power supply  28 . The controller circuit  34  is configured to monitor an impedance of the primary induction coil  22 , which is directly related to the temperature of the secondary induction coil  36 , and controls the voltage  62  and/or frequency  50  (e.g. 40 kHz) to maintain proper operation of the control circuit  56 . This method of temperature measurement has the technical benefit or eliminating a separate temperature sensor mounted to the windshield  20 .