Abstract:
An electric generating unit as a substitute for a vehicle battery includes a housing including an air pressure control member to control air pressure in an inner space of the housing, at least a diaphragm unit configured to sufficiently fluidly-insulate the inner space of the housing from outside of the housing and flexibly deformable by an inertia applied by a mass unit according to an external force so as to generate electricity, wherein the mass unit is formed on the diaphragm unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to Korean Patent Application Number 10-2008-0045114 filed May 15, 2008, the entire contents of which application is incorporated herein for all purposes by this reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an electric generating unit as a substitute for a vehicle battery and, more particularly, to an electric generating unit as a substitute for a vehicle battery, which is independently provided for the operation of an electronic device for a tire pressure monitoring system (TPMS), for example, which is newly governed by laws and regulations. 
         [0004]    2. Description of Related Art 
         [0005]    In general, an automobile is equipped with electronic devices and requires power supply to drive these electronic devices. Recently, since the application of electronic devices to the automobile is rapidly increased, the quantity of electric wires for the power supply to the electronic devices is also increased. For example, a tire pressure monitoring system (TPMS) is governed by laws and regulations, and a power generating device capable of generating electrical energy by external vibration or pressure is provided to operate the TPMS. 
         [0006]      FIG. 1  is a diagram illustrating a concept of generating electricity in a conventional piezoelectric generating apparatus in accordance with a conventional art, in which a steel ball beats piezoelectric ceramics plates disposed on both sides thereof by external vibration. 
         [0007]    Referring to  FIG. 1 , piezoelectric ceramics plates  1  are disposed on both sides of a cylindrical container closed at both ends and, when a steel ball  4  beats these piezoelectric ceramics plates  1 , electricity is generated. A buffer plate  3  is attached on one sidewall of the container  8  using an adhesive  6 , and one piezoelectric ceramics plate  1  is attached to only the center of the buffer plate  3  using the adhesive  5 . Same as above, the other piezoelectric ceramics plate  1  is attached on the other sidewall of the container  8 , and thereby the piezoelectric ceramics plates  1  face each other. A protective plate  2  is fixed at the center of each of the piezoelectric ceramics plates  1  facing each other. A pipe  7  is arranged between both of the piezoelectric ceramics plates  1 , and the steel ball  4  which can roll freely is provided in the pipe  7 . 
         [0008]    The piezoelectric ceramics plate  1  is formed by joining two plate-like piezoelectric ceramics elements  1   a  and  1   b  having the same shape (same material and same thickness) with inverted polarity of the dielectric polarization. Since the piezoelectric ceramics elements  1   a  and  1   b  formed in the same manner are joined to each other, a flexural vibration is caused on the junction surface as the central point (position where it does not expand and contract). In this case, if the ceramics element  1   a  on one surface expands, the ceramics element  1   a  on the other surface contracts, and the polarities of output voltages are the same direction. The two piezoelectric ceramics elements  1   a  and  1   b  are connected in series in the electricity generation structure. 
         [0009]    When the flexural vibration is generated centering on the junction surface, both operations of expansion and contraction are performed on one piezoelectric ceramics element  1   a  or  1   b  and the generation of electricity is effectively performed without cancellation of the polarization. The current generated as electrical energy is obtained through lead wires  9 . 
         [0010]    In this case, the two piezoelectric ceramics elements  1   a  and  1   b  are stacked; however, each piezoelectric ceramics element  1   a  or  1   b  can be formed in a stacked manner. In this stacked structure, a plurality of thin piezoelectric ceramics plates (in this case, polarities of the polarization are the same) are joined and stacked, and thereby one piezoelectric ceramics element  1   a  or  1   b  is formed. 
         [0011]    The reason that the piezoelectric ceramics plate  1  is fixed to the center of the buffer plate  3  using the adhesive  5  is to prevent the vibration of the piezoelectric ceramics plate  1  from decreasing. When the piezoelectric ceramics plate  1  vibrates, a member supporting the piezoelectric ceramics plate  1  is a factor of reducing the vibration of the piezoelectric ceramics plate  1 . To remove the factor of reducing the vibration, the piezoelectric ceramics plate  1  is in a free state using the buffer plate  3 . 
         [0012]    Since a natural vibration of the piezoelectric ceramics plate  1  is maintained for a long time by using the buffer plate  3 , the efficiency of electricity generation is improved. The buffer plate  3  also absorbs the impact applied to the piezoelectric ceramics plate  1 . The protective plate  2  is made of metal, synthetic resin, or the like, and it protects the piezoelectric ceramics plate  1  from the beating of the steel ball  4 . 
         [0013]    If the piezoelectric generating apparatus is arranged under predetermined motional conditions that utilize wind, wave or human action, the steel ball  4  rolls up and down and beats the right and left piezoelectric ceramics plates  1  so as to apply impact energy by the collision. Then, the vibration is generated on the piezoelectric ceramics plates  1 , the piezoelectric ceramics plates  1  repeatedly expand and contract, and therefore the piezoelectric ceramics plates  1  generate alternating current electricity. 
         [0014]    The above-described piezoelectric generating apparatus can generate large energy with a relative small force; however, the performance is significantly reduced by high frequency vibration and, especially, abrasion occurs in the region where the steel ball beats, which affects the durability. Moreover, concave and convex portions are formed by contaminants on the inside surface of the pipe, where the steel ball moves, thus obstructing the movement of the steel ball. 
         [0015]    The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       BRIEF SUMMARY OF THE INVENTION 
       [0016]    Various aspects of the present invention are directed to provide a small-sized electric generating unit having excellent durability, in which a diaphragm including a piezoelectric element is provided to generate electricity by the action of mechanical stress using external vibration, pressure, or acoustic energy. The electric generating unit can be used as a substitute for a vehicle battery and thus used for the operation of an electronic device for a tire pressure monitoring system (TPMS), for example, disposed on the outside such as a tire, and thereby it is possible to solve the problem that the battery should be replaced periodically. 
         [0017]    In an aspect of the present invention, an electric generating unit as a substitute for a vehicle battery includes a housing including an air pressure control member to control air pressure in an inner space of the housing, at least a diaphragm unit configured to sufficiently fluidly-insulate the inner space of the housing from outside of the housing and flexibly deformable by an inertia applied by a mass unit according to an external force so as to generate electricity, wherein the mass unit is formed on the diaphragm unit. 
         [0018]    A sound absorbing plate may be formed between the diaphragm units to absorb external acoustic energy. 
         [0019]    The mass unit may be integrally formed with the diaphragm unit. 
         [0020]    The size and thickness of the mass unit may be adjusted according to resonant frequency of the diaphragm unit. 
         [0021]    The air pressure control member may include at least a vent hole formed to the housing and configured to fluidly communicate the inner space with the outside of the housing to control the air pressure in the inner space so as to prevent generation of excessive amplitude of the diaphragm unit and improve durability. 
         [0022]    In another aspect of the present invention, the electric generating unit may further include a power conversion device converting a current generated from the diaphragm unit and storing the converted current, wherein the power conversion device includes power terminals connected to the power conversion device. 
         [0023]    The diaphragm unit may include a silicon wafer being supported by a fixed wafer formed in the housing, wherein the mass unit is formed substantially on center of the silicon wafer, upper and lower electrodes provided at top of the silicon wafer, and a piezoelectric element disposed between the upper and lower electrodes and configured to generate electricity by mechanical stress occurring from the flexible deformation of the piezoelectric element. 
         [0024]    The piezoelectric element may include PZT(Pb(Ti,Zr)O3) with a Zr Tr composition ratio of approximately 52 approximately 48. 
         [0025]    The upper and lower electrodes may be made of a platinum, gold, copper, or aluminum. 
         [0026]    The fixed wafer may have hardness higher than that of the silicon wafer. 
         [0027]    The fixed wafer may be made of quartz glass or silicon material. 
         [0028]    A silicon oxide layer may be formed on upper and lower surfaces of the silicon wafer and configured to be removed after a predetermined time period of etching. 
         [0029]    An intermediate layer may be formed between the silicon oxide layer and one of the upper or lower electrode, wherein the intermediate layer is made of titanium or chrome. 
         [0030]    The mass unit may be formed by backside etching during processing of the silicon wafer. 
         [0031]    The housing may include an lower housing on which the fixed wafer and the diaphragm unit are placed, an upper housing connected to the lower housing and covering top portion of the diaphragm unit, and a power conversion device converting a current generated from the diaphragm unit and storing the converted current. 
         [0032]    The vent hole may be disposed at the lower housing. 
         [0033]    A sound absorbing plate may be formed between the diaphragm units and formed integrally with the upper housing to absorb external acoustic energy. 
         [0034]    The power conversion device may be formed integrally with the lower housing and includes power terminals connected to the power conversion device. 
         [0035]    The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a schematic diagram illustrating a concept of generating electricity in a conventional piezoelectric generating apparatus, in which a steel ball beats piezoelectric ceramics plates disposed on both sides thereof by external vibration. 
           [0037]      FIGS. 2 and 3  are schematic diagrams showing an exemplary electric generating unit as a substitute for a vehicle battery in accordance with the present invention. 
           [0038]      FIG. 4  is a schematic diagram showing an exemplary structure of a diaphragm of the electric generating unit in accordance with the present invention. 
           [0039]      FIG. 5  is a schematic diagram showing an exemplary overall structure of the electric generating unit in accordance with the present invention. 
           [0040]      FIG. 6  is a graph showing an exemplary effect of the electric generating unit in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0042]      FIGS. 2 and 3  are schematic diagrams showing an electric generating unit as a substitute for a vehicle battery in accordance with various embodiments of the present invention,  FIG. 4  is a schematic diagram showing a structure of a diaphragm of the electric generating unit in accordance with various embodiments of the present invention,  FIG. 5  is a schematic diagram showing the overall structure of the electric generating unit in accordance with various embodiments of the present invention, and  FIG. 6  is a graph showing an effect of the electric generating unit in accordance with various embodiments of the present invention. 
         [0043]    Referring to  FIGS. 2 to 6 , the electric generating unit as a substitute for a vehicle battery in accordance with various embodiments of the present invention comprises a housing  10  having a predetermined inner space therein, a fixed wafer  20  disposed on one side of the housing  10 , and a diaphragm unit  30  being in contact with the fixed wafer  20  and capable of generating electrical energy by external vibration, pressure, or acoustic energy. 
         [0044]    First, a plurality of diaphragms  30  is disposed to be spaced at a predetermined distance at the top of the fixed wafer  20 , and each of the diaphragms  30  may have a rectangular or circular shape. 
         [0045]    The diaphragm unit  30  comprises a silicon wafer  31 , which is directly in contact with the top of the fixed wafer  20  and includes a mass unit  31   a  formed integrally on the center thereof so as to adjust the resonance frequency and generate a inertia to make a flexible deformation of the diaphragm unit  30 , upper and lower electrodes  32  and  33 , through which a current flows, provided at the top of the silicon wafer  31 , and a piezoelectric element  34  disposed between the upper and lower electrodes  32  and  33  and capable of generating electricity by the action of mechanical stress of the piezoelectric element  34 . 
         [0046]    The mass unit  31   a  is formed during processing of the silicon wafer  31  by backside etching, and the size and thickness of the mass unit  31   a  can be adjusted according to a desired resonant frequency. The mass unit  31   a  may be formed into the same shape as the diaphragm unit  30 . 
         [0047]    The piezoelectric element  34  may comprise PZT(Pb(Ti,Zr)O3) with a Zr:Tr composition ratio of 52:48 that exhibits an excellent piezoelectric effect. The upper and lower electrodes  32  and  33  may be made of a platinum, gold, copper, or aluminum layer. 
         [0048]    When forming the lower electrode  33  on the silicon wafer  31 , a silicon oxide layer is formed on the surface of the silicon wafer  31 . An intermediate layer is formed to increase the adhesion between the silicon oxide layer and the lower electrode  33 , and the intermediate layer C may be made of titanium or chrome. 
         [0049]    As shown in  FIG. 4 , when forming the diaphragm unit  30 , a silicon-on-insulator (SOI) wafer bonded to a silicon oxide is used to obtain a uniform thickness. At this time, an oxide layer O is formed in the middle of the SOI wafer; however, it is removed after a sufficient etching time, thus obtaining a diaphragm having a uniform thickness. 
         [0050]    Next, the fixed wafer  20  is formed of quartz glass or silicon material having hardness higher than that of the silicon wafer  31 , and a plurality of holes  21 , through which air passes, may be formed to be spaced at a predetermined distance therein. 
         [0051]    The housing  10  comprises an upper housing  12  and a lower housing  11 , and thereby an inner space in which the fixed wafer  20  and the diaphragm unit  30  are disposed is formed. On the lower housing  1 , the fixed wafer  20  and the diaphragm unit  30  are placed, and the upper housing  12  covers the top of the diaphragm unit  30  and is connected to the lower housing  11 . 
         [0052]    Moreover, the housing  10  further includes a power conversion device  13  for converting alternating current output form the diaphragm unit  30  into direct current and storing the converted current. 
         [0053]    The power conversion device  13  may be formed integrally with or separately from the lower housing  11 , and it is formed integrally with the lower housing  11  in various embodiments of the present invention. The power conversion device  13  includes power terminals  13   a  connected thereto, and the power terminals  13   a  may be made of a copper alloy-tin plated material, brass, or bronze. 
         [0054]    The connection between the diaphragm unit  30  and the power conversion device  13  and the connection between the power conversion device  13  and the power terminals  13   a  may be made by wires  13   b.    
         [0055]    The upper housing  12  includes a sound absorbing plate  12   a  to effectively absorb external acoustic energy. The sound absorbing plate  12   a  may be formed separately and then attached to the upper housing  12  or formed integrally with the upper housing  12 , and it is formed integrally with the upper housing  12  in various embodiments of the present invention. 
         [0056]    Moreover, the lower housing  11  includes a plurality of vent holes  11   a,  spaced at a predetermined distance, to control air pressure in the inner space of the housing  10  and thus prevent excessive amplitude from being generated in the diaphragm unit  30  and improve the durability. 
         [0057]    As shown in  FIG. 5 , if the number and size of the vent holes  11   a  are appropriately adjusted, it is possible to prevent the diaphragm unit  30  from being excessively deformed by strong external vibration or acoustic energy with an appropriate pressure generated in the vent holes  11   a  by air passing through the vent holes  11   a,  thus suppressing the amplitude. 
         [0058]    Lastly, the upper housing  12  and the lower housing  11  may be bonded to each other using epoxy for semiconductor or by ultrasonic fusion. 
         [0059]    The structure and operation of the electric generating unit as a substitute for a vehicle battery in accordance with various embodiments of the present invention having the above-described construction will be described below. 
         [0060]    First, when the lower housing  11  is provided, the fixed wafer  20  is disposed on one side of the lower housing  11 . The fixed wafer  20  includes the holes  21  formed to be spaced at a predetermined distance so that air can pass therethrough. 
         [0061]    The diaphragm unit  30  is disposed at the top of the fixed wafer  20 , corresponding to the position of the hole  21 . 
         [0062]    The diaphragm unit  30  includes the silicon wafer  31 , on which the mass unit  31   a  is formed integrally on the center thereof so as to adjust the resonance frequency, and the lower electrode  33  disposed at the top of the silicon wafer  31  and made of a platinum, gold, copper, or aluminum layer. The silicon wafer  31  and the lower electrode  33  are bonded to each other using titanium or chrome. 
         [0063]    The piezoelectric element  34  of PZT is disposed on a surface of the lower electrode  33 , which is not in contact with the silicon wafer  31 , so as to generate electricity by the action of mechanical stress. The upper electrode  32  formed of the same material as the lower electrode  33  is disposed at the top of the piezoelectric element  34 . 
         [0064]    When the diaphragm unit  30  is formed at the top of the fixed wafer  20 , the upper housing  12  covering the top of the diaphragm unit  30  and including the sound absorbing plate  12   a,  formed integrally therewith and capable of effectively absorbing external acoustic energy, is connected to the lower housing  11 . 
         [0065]    Meanwhile, the power conversion device  13  capable of converting alternating current output form the diaphragm unit  30  into direct current and storing the converted current is formed integrally with the lower housing  11 . 
         [0066]    The power terminals  13   a  made of brass or bronze are connected to the power conversion device  13 , and the connection between the diaphragm unit  30  and the power conversion device  13  and the connection between the power conversion device  13  and the power terminals  13   a  are by the wires  13   b.    
         [0067]    In the above-described electric generating unit as a substitute for a vehicle battery in accordance with various embodiments of the present invention, when external vibration, pressure, or acoustic energy is delivered to the diaphragm unit  30 , the diaphragm unit  30  is elastically deformed up and down to deform the piezoelectric element  34  provided in the diaphragm unit  30 , and thereby electricity is generated between the upper and lower electrodes  32  and  33 . 
         [0068]    Moreover, as shown in  FIG. 6 , in the electric generating unit as a substitute for a vehicle battery in accordance with various embodiments of the present invention, when the (sound) pressure of acoustic energy is increased above 90 dB, the plastic deformation of the diaphragm unit  30  is prevented by the damping effect of air due to the vent holes  11   a  formed in the lower housing  11 , and thereby the amount of generated electrical energy is not increased any more. As a result, the electric generating unit as a substitute for a vehicle battery has excellent durability without the risk of damaging the diaphragm unit  30  by an excessive sound pressure. 
         [0069]    As described above, according to the electric generating unit of various embodiments of the present invention, in which a diaphragm including a piezoelectric element is provided to generate electricity by the action of mechanical stress using external vibration, pressure, or acoustic energy, it is possible to provide a small-sized electric generating unit, which can be used as a substitute for a vehicle battery and thus used for the operation of an electronic device for a tire pressure monitoring system (TPMS), for example, disposed on the outside such as a tire, and thereby it is possible to solve the problem that the battery should be replaced periodically. 
         [0070]    For convenience in explanation and accurate definition in the appended claims, the terms “upper” and “lower” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
         [0071]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.