CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of US provisional application

61/314,833 filed March 17, 2010 and hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to lighting systems and in particular to lighting systems for appliances such as refrigerators.

BACKGROUND OF THE INVENTION

[0003] Lights in a refrigerator are typically mounted to the interior walls of the refrigerator compartment. These lights may provide sufficient illumination when the refrigerator is empty, but when the shelves are filled with goods, light can be blocked and portions of the shelves cast in shadows.

[0004] One solution to this problem is the placement of lighting systems on the shelves themselves, for example on the underside of the shelves, to illuminate the contents of the shelf below, or the placement of lighting systems on the upper outer edges of the shelves to illuminate product on the upper surface of the shelf itself.

[0005] A problem with shelf-mounted lighting is getting electrical power to the lights on the shelf. Refrigerator shelves are typically adjustable in position and can be removed entirely from the refrigerator for cleaning. Releasable electrical connectors can be provided for conducting electricity to the shelves, but these connectors necessarily but undesirably break the continuous inner wall of the refrigerator with releasable connectors making cleaning the inner surface of the refrigerator more difficult. Such connectors may also present electrical conductors that must be shielded from liquid spills and the like.

[0006] One solution to this problem is described in PCT patent application WO 2009/079209 assigned to the assignee of the present invention and hereby incorporated by reference. The invention described in this application uses inductively coupled power transfer between a primary coil positioned behind the walls of the refrigerator and corresponding coils on the shelves. The primary and secondary coils may be freely separated so that the shelves may be removed and cleaned. Further, the inductive coupling eliminates any exposed conductors or breaks in the inner wall of the refrigerator. An elongated primary coil spanning multiple shelf locations may be used to provide flexibility in the arrangement of the shelves by the consumer.

SUMMARY OF THE INVENTION

[0007] The present invention employs multiple smaller primary coils each associated with a particular shelf location. In one embodiment, the use of multiple coils permits a lighter weight coil design, for example, one that can be implemented on a printed circuit board or without a ferromagnetic core. The localization of the coils at each shelf position allows a planar coil design concentrating coil turns in a limited area. Coil size may be further reduced and an iron core eliminated by employing a high-frequency electrical signal that may be synthesized to convey power between the coils for improved inductive coupling. The use of multiple coils permits individual primary coils to shut down if there is no shelf present near the primary coil, increasing energy efficiency of the refrigerator.

[0008] Specifically, one embodiment of the present invention provides a lighting system for a refrigerator of a type providing an insulated housing defining a refrigerated chamber. The lighting system includes shelves movably fitting within the housing at locations and holding light emitting diodes for illumination of the refrigerated chamber. A plurality of primary coils are attached to the insulated housing and positioned proximate to locations and secondary coils are attached to the shelves to be positioned near the primary coils when the shelves are fitted within the housing at the locations. Driving circuitry communicates with the primary coils to produce an alternating current signal at a frequency greater than twice that of line frequency and receiving circuitry attached to the shelves communicates with the secondary coils to rectify the alternating current signal and provide the same to the light emitting diodes.

[0009] It is thus a feature of at least one embodiment of the invention to provide substantially smaller and localized inductive coupling coils through the use of high frequency synthesized signals.

[0010] The primary coils and secondary coils may be planar coils having conductors confined substantially each to a single plane.

[0011] It is thus a feature of at least one embodiment of the invention to provide simple coils that may provide for good inductive coupling.

[0012] The insulated housing may have an inner nonferrous wall surrounded by thermal insulation and the primary coils may be placed between the nonferrous wall and the thermal insulation. [0013] It is thus a feature of at least one embodiment of the invention to permit the ready integration of the primary coils into the existing structure of the refrigerator without compromising its insulation.

[0014] The primary coils and secondary coils may be substantially parallel.

[0015] It is thus a feature of at least one embodiment of the invention to provide permit maximum inductive coupling between small area coils.

[0016] The primary coils and secondary coils maybe formed at least in part as traces in a printed circuit board.

[0017] It is thus a feature of at least one embodiment of the invention to provide coils that may be readily fabricated without the need for conventionally wound wire coils.

[0018] The printed circuit boards of the primary coils and secondary coils may hold the driving circuitry and the receiving circuitry respectively.

[0019] It is thus a feature of at least one embodiment of the invention to provide coupling coils that may be integrated with their associated circuitry during manufacture.

[0020] The primary coil may include a conductive metal form electrically connected to the traces on the printed circuit board.

[0021] It is thus a feature of at least one embodiment of the invention to permit an arbitrary current carrying capacity for the primary coil constructed in part from, and integrated to, a printed circuit board.

[0022] The driving circuitry may include a sensor for sensing a shelf proximate to the mounting point for disabling the driving circuitry when a shelf is not proximate to be mounting point.

[0023] It is thus a feature of at least one embodiment of the invention to provide improved energy efficiency in an inductive coupling system by partitioning the primary coil and selectively switching off some coils not associated with shelves.

[0024] The sensor may be partially formed by the primary coil for sensing an inductive load on the primary coil from the secondary coil.

[0025] It is thus a feature of at least one embodiment of the invention to eliminate the need for separate proximity sensors by employing the inductive coupling itself to sense the presence of the shelf.

[0026] The receiving circuitry may include a power regulation circuit for controlling at least one of the voltage and current provided to the light emitting diodes.

[0027] It is thus a feature of at least one embodiment of the invention to provide a controlled current to the LEDs independent of variations in the inductive coupling. [0028] The primary and secondary coils may be tuned circuits having a center frequency substantially equal to the frequency of the alternating current signal.

[0029] It is thus a feature of at least one embodiment of the invention to provide improved efficiency in the inductive coupling by employing the primary and secondary coils as part of tuned tank circuits.

[0030] 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

[0031] Fig. 1 is a phantom cutaway view of a simplified refrigerator showing the location of multiple local primary coils behind a rear wall of the refrigerator housing and the positioning of a shelf having an integrated secondary coil and lighting strips on left and right edges;

[0032] Fig. 2 is a perspective view of one shelf showing mounting points for an inductive coil per the present invention and alternative orientations of the light emitting diodes on each shelf;

[0033] Fig. 3 is an exploded diagram of a primary and secondary coil in the refrigerator housing and on the shelf respectively and showing a fitting of the primary coil between the inner refrigerator wall and the refrigerator insulation;

[0034] Fig. 4 is a block diagram of the driving and receiving circuitry used with the coils of Fig. 2 for the efficient transmission of power from the refrigerator housing to the individual shelves;

[0035] Fig. 5 is a cross-sectional view through a printed circuit board

implementing a primary coil or secondary coil and showing an optional reinforcing metal form for increasing current capacity;

[0036] Fig. 6 is a simplified circuit schematic of driving circuitry of Fig. 4; and

[0037] Fig. 7 is a figure similar to that of Fig. 6 showing the receiving circuitry.

[0038] 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

[0039] Referring now to Fig. 1, a refrigerator 10 may provide for a housing 12 having left, right, top, bottom, and rear insulated walls together defining generally an enclosed rectangular volume open at the front. A door 14 may hinge at a front edge of one side wall to provide, when closed, a refrigerated volume maintained at a desired temperature by a compressor system (not shown).

[0040] One or more shelves 16 may be placed within the volume at various mounting points 18, for example, defined by side rails. Generally, the shelves 16 may abut, at their rear edge, a rear portion of the inner wall 17 of the housing 12 and at their left and right edges, left and right portions of the inner wall of the housing 12. In one embodiment, primary coils 20 may be positioned behind the inner wall 17 of the housing 12 at each mounting point 18 along the rear of the housing 12 as shown. Alternatively, but not shown, the primary coils 20 may be positioned behind the left or right inner walls 17 of the housing 12 at each mounting point 18. A shelf 16 positioned at a given mounting point 18 holds a secondary coil 22 proximate to a particular primary coil 20. Generally the area of the primary coils and secondary coils may be relatively limited, for example, to less than 30 square inches

[0041] Referring now to Fig. 2, the shelf 16 may include an outer frame 23, for example, constructed of an opaque thermoplastic material to hide wiring and circuitry and supporting a center transparent portion 19, for example a pane of tempered glass. The outer frame 23 may provide downwardly extending support structure 21 at one or more of a rear edge of the shelves 16 or a side edge of the shelf 16 supporting the secondary coil 22 therein.

[0042] Secondary coil 22 and its associated circuitry, as will be described, may provide power to one or more light emitting diodes 36 positioned in the frame 23 to be directed upward to illuminate goods placed on the transparent portion 19 or downward to illuminate goods placed on a lower shelf (not shown). The frame 23 may include supporting structure to attach the shelf 16 to the various mounting points according to conventional design.

[0043] Referring now to Fig. 3, the primary coils 20 may be, for example, planar in configuration and formed as traces on a printed circuit board, the traces passing in a rectangular helix to form a so-called "fingerprint" or planar coil substantially within a plane of the printed circuit board. The secondary coil 22 held on the shelf 16 may be of substantially the same design as the primary coil 20 being formed on a printed circuit board as a planar coil and maybe given a similar (vertical) orientation so that the planes of the primary coil 20 and secondary coil 22 are substantially parallel. The primary coil 20 may be placed in close proximity to an outer surface of an inner wall 17 of the housing 12, such inner wall 17 which will typically be a non-ferromagnetic thermoplastic material. As such, the primary coil 20 may fit between the inner wall 17 of the housing 12 and insulating material 25 placed around this inner wall 17 without disturbing the integrity of that insulating material.

[0044] Other circuitry, to be described below, may be placed on a side of the printed circuit board opposite the side holding the coils 22 and 20. By localizing the primary coils 20 at the mounting points 18, coil turns may be concentrated near the secondary coils 22.

[0045] Referring now to Fig. 4, each primary coil 20 may receive an alternating current signal from an oscillator 24 synthesizing that signal from a DC source 26, for example, of twenty-four volts available in the refrigerator 10 from a conventional DC power supply of the type well known in the art. Generally, the frequency of oscillation will be substantially above that of line current (i.e. 60 Hz) or rectified line current (e.g. 120 Hz) and may be, for example, 350 to 700 kHz to provide for more efficient transmission. Such higher frequencies also permit filtering with smaller capacitors.

[0046] The output of the oscillator 24 may be provided to a resonant circuit formed by the inductance of the primary coil 20 and a capacitor 31 together tuned to a resonant frequency substantially equal to the fundamental frequency of the oscillator 24. The circuitry to produce the AC oscillator 24 can be placed on the same printed circuit board holding the primary coil 20. Higher frequency operation is further enhanced by elimination of a magnet core of ferromagnetic material permitting more efficient high-frequency operation by the elimination of eddy current losses.

[0047] The secondary coil 22 may also be tuned to the resonant frequency of the primary coil 20, for example, by a tuning capacitor 28 to efficiently inductively couple to the primary coil 20 thereby providing an AC signal to a rectifier 30 and filter 32 to provide DC power to a regulator 34. The regulator 34 may be, for example, a boost or buck converter that may provide a controlled voltage or current to the LEDs 36 contained on each shelf 16. [0048] The primary coil 20 may also be attached to sensing circuitry providing a shelf sensor 38 which may sense the load of secondary coil 22, for example, as an increase in voltage on primary coil 20, and may communicate with the oscillator 24 to turn the oscillator 24 off when there is no shelf present, thus conserving power. The shelf sensor 38 may periodically turn the oscillator 24 on to check for a new shelf 16 in a place adjacent to that primary coil 20.

[0049] Referring now to Fig. 5, coil conductors of the primary or secondary coil 20 or 22 may be traces 40 on a printed circuit board substrate 42, for example a glass epoxy substrate material. The traces 40 may be formed in a spiral pattern to eliminate cross over in a single dimension of the trace or may be concentric circles connected by vias and other layers of the circuit board or the like. The primary coil 20 may be provided with increased current capacity by soldering a metal wire form 44 (for example a copper wire) to the trace to be supported and constrained thereby. Components of the oscillator 24, shelf sensor 38, rectifier, 30 filter 32, and regulator 34, as well as capacitors 31 and 28 may be soldered on similar traces on the opposite side of the printed circuit board substrate 42 to provide a compact robust and integrated assembly.

[0050] Referring now to Fig. 6, transmitter circuitry 46 associated with the primary coil 20 may include a bi-stable multi-vibrator 48 (for example a 555 timer) using a capacitive/resistive network and comparators to provide a substantially 50% duty cycle waveform 49 at the desired resonant frequency to a half bridge driver 50. The half bridge driver 50 may drive transistors 52a and 52b connected at a common point to coil 20 and having their other leads connected to power and ground respectively. For this purpose, the half bridge driver 50 may provide two modified waveforms 51 (only one shown for clarity) at 180° phase difference providing a switching of the transistors 52a and 52b alternately on and off while ensuring no overlap. The resulting switched signal may be applied to a resonant circuit formed from the primary coil 20 and capacitor 31 connected in series to ground to provide a substantially sinusoidal current flow 56 at the desired frequency. A junction between the coil 20 and capacitor 31 may be monitored by a threshold-detecting amplifier 58 that may activate the reset line of the oscillator 48 turning the oscillator 48 off when voltage rises beyond a certain point indicating the absence of an adjacent shelf on the opposite side of the refrigerator to the inner wall 17.

[0051] Referring now to Fig. 7, the receiving circuitry 61 may attach to the secondary coil 22 to also provide for a parallel resonant tuned circuit by means of capacitor 28 connected across coil 22 and providing, with the inductance of secondary coil 22, a center resonant frequency substantially equal to the center resonant frequency of the circuit of primary coil 20. The resulting sinusoidal received waveform 60 may be rectified by a full wave rectifier 30 and filtered by a filter 32 comprising a shunting capacitor to provide unregulated direct current to the voltage regulator 34. A subsequent filter capacitor 62 may be provided to further filter the output of the regulator 34. The LEDs 36 are shown connected in parallel but alternatively may be connected in series and the series connected LEDs operated at a higher voltage.

[0052] It will be appreciated from the above description that the wireless power transmission system of the present invention is not limited to shelf lighting but can be used for other electronic components mounted on the shelf or to the walls of the refrigerator like sensors, fans, thermometers, and user interfaces.

[0053] When introducing elements or features of the present disclosure and the exemplary embodiments, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of such elements or features. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0054] Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being 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.