Patent Publication Number: US-2023150465-A1

Title: Control Unit for Electromechanical Brake Systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application PCT/EP2021/069772 with an international filing date of Jul. 15, 2021 and claiming priority to co-pending Chinese Patent Application No. CN 202010686690.6 entitled “Control unit for electromechanical brake systems”, filed on Jul. 16, 2020. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the present disclosure relate to vehicle brake technology, and more particularly relate to a control unit for electromechanical brake systems. 
     BACKGROUND OF THE INVENTION 
     Existing electromechanical brake (EMB) systems mainly comprise a control unit, an electronic brake actuator, and a braking request input device (e.g., an electronic brake pedal and an EPB (electronic parking brake) switch). To perform service braking, when the driver steps on the electronic brake pedal, the electronic brake pedal simulates the non-linear tactile feedback of a pneumatic/hydraulic brake system, meanwhile detects the pedal stroke and/or pedal force, and synchronously transmits a pedal stroke signal to the control unit; the control unit parses the pedal stroke signal, identifies the driver&#39;s braking intention, and controls the electronic brake actuator to actuate the calipers to produce a corresponding brake force, thereby implementing braking. 
     In the electromechanical brake system, the braking energy comes from the mechanical energy converted from electric power, while the electric power is originated from an in-vehicle or on-board battery or generator, or from a power battery in the case of an electric vehicle. In an optional power supply architecture of the electromechanical brake system, an energy storage module is provided between the in-vehicle power supply and the electronic brake actuator so as to enhance system reliability, wherein the energy storage module, which is charged by the in-vehicle power supply, only supplies power to the electromechanical brake system, such that a voltage higher than that supplied by the in-vehicle power supply may be applied to the brake system of a vehicle (especially a commercial vehicle), and even upon failure of the in-vehicle power supply, the vehicle can still be braked to stop with the power supplied by the energy storage module. 
     Further prior art is described in U.S. Pat. No. 10,432,016 B2, Chinese patent application No. CN 107 618 496 A and international patent application WO 2019/007122 A1. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present disclosure provide an electromechanical brake system control unit integrated with an energy storage module, which simplifies system architecture and connection circuitry, and offers good performance in environment protection, heat dissipation, and electromagnetic interference resistance. Embodiments of the present application present the following technical solutions: 
     A control unit for electromechanical brake systems comprises: 
     a housing; and 
     a frame plate, a braking energy storage module and a brake system control module, which are configured in the housing, wherein the braking energy storage module and the brake system control module are respectively arranged at two opposite sides of the frame plate. 
     With the novel control unit for electromechanical brake systems it is in particular possible to simplify the system architecture and connection circuitry and to offer good performance in environment protection, heat dissipation, and electromagnetic interference resistance. 
     In at least one embodiment of the control unit for electromechanical brake systems, the braking energy storage module is fixed between the frame plate and an inner wall of the housing, and the brake system control module is fixedly connected to the frame plate or an inner wall of the housing. 
     In at least one embodiment of the control unit for electromechanical brake systems, the braking energy storage module comprises a power management circuit board; and a plurality of energy storage cells configured on the power management circuit board, the power management circuit board being fixedly connected to the frame plate. 
     In at least one embodiment of the control unit for electromechanical brake systems, a thermal pad is provided between the energy storage cells and an inner wall of the housing. 
     In at least one embodiment of the control unit for electromechanical brake systems, a thermally conductive medium and/or a shock absorbing medium are provided between the braking energy storage module and the frame plate and/or between the brake system control module and the frame plate. 
     In at least one embodiment of the control unit for electromechanical brake systems, a voltage conversion module is further provided in the housing, the voltage conversion module and the brake system control module being arranged at the same side of the frame plate. 
     In at least one embodiment of the control unit for electromechanical brake systems, the braking energy storage module is in signal or electric connection with the brake system control module and/or the voltage conversion module via a board-to-board connector, a cable, or a bus, the board-to-board connector, the cable, or the bus passing through the frame plate. 
     In at least one embodiment of the control unit for electromechanical brake systems, the bus is supported on a dielectric stand, the dielectric stand being fixed to the frame plate. 
     In at least one embodiment of the control unit for electromechanical brake systems, the control unit further comprises an input connector configured for an external power supply to input power, and an output connector configured for outputting power to an electronic brake device. 
     In at least one embodiment of the control unit for electromechanical brake systems, a plurality of support units are provided in the housing, and through-holes are provided respectively in the frame plate, the braking energy storage module, and the brake system control module, whereby the frame plate, the braking energy storage module, and the brake system control module are stacked and fastened to the support units by bolts through the through-holes. 
     The present disclosure offers the following beneficial effects: 
     According to various embodiments of the control unit for electromechanical brake systems provided by the present disclosure, the braking energy storage module and the brake system control module are arranged at the opposite sides of a same frame plate, such that the braking energy storage module and the brake system control module are compactly mounted in the housing of the control unit, which avoids process, installation, and expense issues that arise from separately mounting, and a stronger adaptability is offered with respect to the internal space of the housing, which saves the mounting space and thus reduces the size of the control unit; alternatively, the saved space is usable for mounting other components. 
     In the present disclosure, the frame plate might not only serve as a carrier for mounting the braking energy storage module and the brake system control module, but in some cases also serves as a heat dissipation medium therefor so as to enhance their heat dissipation effect. More specifically, the heat produced by the braking energy storage module and the brake system control module during operation can be conducted to the frame plate, which enhances heat dissipation (e.g., by increasing the heat dissipation area, or by conducting the heat to the housing via the frame plate, such that the heat is released to the outside via the frame plate). Compared with radiative dissipation, a faster heat dissipation rate is achieved with the frame plate as the heat dissipation medium; as a result, the braking energy storage module and the brake system control module maintain a relatively low temperature rise during operation. 
     Further, the braking energy storage module can be fixed between the frame plate and a inner wall of the housing. In this way, an additional fixing part can be eliminated for fixing the braking energy storage module in the control unit, which saves expense. 
     Further, the braking energy storage module preferably comprises a power management circuit board; and a plurality of energy storage cells configured on the power management circuit board, the power management circuit board being fixedly connected to the frame plate. The power management circuit board can be configured to warrant voltage balancing among the plurality of energy storage cells during charging and alleviate voltage imbalance among some energy storage cells; with the power management circuit board, the frame plate applies a uniform pressure on the plurality of energy storage cells, thereby effectively fixing the plurality of energy storage cells. 
     Further, preferably a thermal pad is provided between the energy storage cells and a inner wall of the housing. The thermal pad mainly might plays the following roles: first, its good heat conductivity accelerates heat conduction from the energy storage cells to the inner wall of the housing, which improves heat dissipation efficiency; second, it also offers a good elastic compressive property for absorbing vibration energy and external shock and is configured for providing elastic support for the energy storage cells, fixing the energy storage cells more securely, avoiding collision between the energy storage cells and the housing, and warranting reliability of the electrical connection between the energy storage cells and the power management circuit board; third, also thanks to its elastic compressive property, the assembly tolerance of the braking energy storage module may be compensated through compression of the thermal pad, avoiding looseness of the energy storage cells due to assembly tolerance, or deformation of the power management circuit board due to excess tightening, or damages to the weld spots of the energy storage cells. 
     Further, preferably a thermally conductive medium and/or a shock absorbing medium are provided between the braking energy storage module and the frame plate and/or between the brake system control module and the frame plate. With the thermally conductive medium arranged between the brake system control module and the frame plate, the good thermally conductive property of the thermally conductive medium accelerates heat conduction from the brake system control module to the frame plate, thereby improving heat dissipation efficiency; alternatively, with the shock absorbing medium arranged between the brake system control module and the frame plate, the shock absorbing medium may absorb vibration energy, thereby alleviating vibration impact on the brake system control module, so does the arrangement of the thermally conductive medium and/or shock absorbing medium between the braking energy storage module and the frame plate. 
     Further, preferably a voltage conversion module is further provided in the housing, the voltage conversion module and the brake system control module being fixed to the same side of the frame plate. The voltage conversion module can be configured to convert the voltage of the external power supply to a voltage adapted for operation of the brake system control module; the voltage conversion module and the brake system control module can be fixed to the same side of the frame plate; the voltage conversion module can be securely supported by the frame plate; as such, electrical connection between the voltage conversion module and the brake system control module is facilitated. 
     Further, preferably a plurality of support units are provided in the housing, and corresponding through-holes are provided respectively in the frame plate, the braking energy storage module, and the brake system control module, whereby the frame plate, the braking energy storage module, and the brake system control module are stacked and fastened to the support units by bolts through the through-holes. By fixedly stacking the frame plate, the brake system control module, and the braking energy storage module, the assembled size for the three is reduced as much as possible; the more compact architecture facilitates one-time fixing of them within the housing with the bolts, thereby facilitating assembly. 
     These characteristics and advantages of the present disclosure will be disclosed in detail in the preferred embodiments below with reference to the accompanying drawings. 
     Advantageous developments of the invention result from the claims, the description and the drawings. 
     The advantages of features and of combinations of a plurality of features mentioned at the beginning of the description only serve as examples and may be used alternatively or cumulatively without the necessity of embodiments according to the invention having to obtain these advantages. 
     The following applies with respect to the disclosure—not the scope of protection—of the original application and the patent: Further features may be taken from the drawings, in particular from the illustrated designs and the dimensions of a plurality of components with respect to one another as well as from their relative arrangement and their operative connection. The combination of features of different embodiments of the invention or of features of different claims independent of the chosen references of the claims is also possible, and it is motivated herewith. This also relates to features which are illustrated in separate drawings, or which are mentioned when describing them. These features may also be combined with features of different claims. Furthermore, it is possible that further embodiments of the invention do not have the features mentioned in the claims which, however, does not apply to the independent claims of the granted patent. 
     The number of the features mentioned in the claims and in the description is to be understood to cover this exact number and a greater number than the mentioned number without having to explicitly use the adverb “at least”. For example, if an element is mentioned, this is to be understood such that there is exactly one element or there are two elements or more elements. Additional features may be added to these features, or these features may be the only features of the respective product. 
     The reference signs contained in the claims are not limiting the extent of the matter protected by the claims. Their sole function is to make the claims easier to understand. 
     Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and the detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Hereinafter, the present disclosure will be described in further detail with reference to the accompanying drawings: 
         FIG.  1    shows an exploded view of a control unit in one embodiment of the present disclosure. 
         FIG.  2    is a sectional view of a control unit in one embodiment of the present disclosure. 
         FIG.  3    shows a view of a control unit in one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure provide a control unit for electromechanical brake system, comprising: a housing; and a frame plate, a braking energy storage module and a brake system control module, which are configured in the housing, wherein the braking energy storage module and the brake system control module are respectively placed at two opposite sides of the frame plate. The braking energy storage module and the brake system control module are compactly mounted in the housing of the control unit; such an arrangement avoids process and expense issues arising from separately mounting of the two, offers a higher adaptability to the internal space of the housing, saves the mounting space, and reduces the size of the control unit; alternatively, the saved space is usable for mounting other devices. Besides, the frame plate also serves as a heat dissipation medium for the braking energy storage module and the brake system control module so as to realize conductive heat dissipation and offer a higher heat dissipation rate; as a result, the braking energy storage module and the brake system control module still maintain a relatively low temperature rise during operation. 
     Hereinafter, the technical solutions of the embodiments of the present disclosure will be explained and illustrated with reference to the accompanying drawings. However, the embodiments are only preferred embodiments of the present disclosure, not all of them. Other embodiments derived by those skilled in the art without exercise of inventive work based on the examples in the embodiments all fall within the protection scope of the present disclosure. 
     In the present disclosure, unless otherwise explicitly provided and limited, the terms such as “mounting”, “connected”, “connection”, and “fixing” or their variables should be understood broadly, which, for example, may refer to a secured connection, a detachable connection, or an integrated connection, which may be a mechanical connection or an electrical connection, which may be a direct connection or an indirect connection via an intermediate agent, and which may further be a communication between the insides of two elements. To a person of normal skill in the art, specific meanings of the above terms in the present disclosure may be construed dependent on specific situations. 
     Referring to  FIGS.  1  and  2   , a control unit for electromechanical brake systems according to one embodiment of the present disclosure comprises a housing  100 ; and a frame plate  300 , a braking energy storage module  200 , and a brake system control module  400 , which are configured in the housing  100 ; the braking energy storage module  200  and the brake system control module  400  are arranged at two opposite sides of the frame plate  300 , respectively. The two opposite sides of the frame plate  300  herein refer to two side surfaces of the frame plate  300  in the thickness direction. With the state shown in  FIG.  2    as an example, the two opposite sides of the frame plate  300  refer to the upper surface and the lower surface of the frame plate  300 , wherein the brake system control module  400  is arranged at the upper surface of the frame plate  300 , and the braking energy storage module  200  is fixed to the lower surface of the frame plate  300 , such that the braking energy storage module  200  and the brake system control module  400  are compactly mounted in the housing  100  of the control unit, avoiding those process and expense issues caused by separately mounting of the two. The brake system control module  400  can be fixed at the upper side of the frame plate  300  or an inner wall of the housing  100 , which can be, for example, the inner side of the cover plate  600 . 
     In view that the braking energy storage module  200  and the brake system control module  400  are fixed to the same frame plate  300 , a higher adaptability is offered with respect to the internal space of the housing  100 , which saves the mounting space and reduces the size of the control unit; alternatively, the saved space is usable for mounting other devices. As shown in  FIG.  2   , the frame plate  300 , the braking energy storage module  200 , and the brake system control module  400  are stacked and fixed in the housing  100 , which enables reduction of the assembled size of the three as much as possible, thereby saving more space. 
     In this embodiment, the frame plate  300  not only serves as a carrier for mounting the braking energy storage module  200  and the brake system control module  400 , but also serves as a heat dissipation medium therefor so as to enhance heat dissipation for the braking energy storage module  200  and the brake system control module  400 . The heat produced by the braking energy storage module  200  and the brake system control module  400  during operation is conducted to the frame plate  300  via which heat is dissipated to the outside (e.g., the frame plate  300  conducts heat to the housing  100  via which the heat is released outside). Compared with radiative dissipation, a faster heat dissipation rate is achieved with the frame plate  300  as the heat dissipation medium, such that the braking energy storage module  200  and the brake system control module  400  maintain a relatively low temperature rise during operation. The frame plate  300  is preferably made of a metal material with a good thermally conductive property, such as aluminum, copper, aluminum alloy, etc.; the metal frame plate  300  has a high structural strength, such that it is not only enabled to reliably support the braking energy storage module  200  and the brake system control module  400 , but also enhances heat dissipation. 
     Hereinafter, detailed illustration will be made with respect to the assembly and connection structure and the electrical connection structure with respect to the frame plate  300 , the braking energy storage module  200 , and the brake system control module  400  in the embodiments: 
     Assembly and Connection Structure 
     Corresponding through-holes are provided respectively in the frame plate  300 , the braking energy storage module  200 , and the brake system control module  400 , whereby the frame plate  300 , the braking energy storage module  200 , and the brake system control module  400  are stacked and fastened to the support units of the housing  100  by bolts through respective through-holes. In one exemplary embodiment, referring to  FIGS.  1  and  2   , a plurality of first through-holes  310  are arranged along the perimeter of the frame plate  300 ; the brake system control module  400  comprises a control circuit board  410  and a control circuit configured on the control circuit board  410 , wherein a plurality of second through-holes  411  are arranged along the perimeter of the control circuit board  410 ; the braking energy storage module  200  comprises a power management circuit board  210  and a plurality of energy storage cells configured on the power management circuit board  210 , wherein a plurality of third through-holes  211  are arranged along the perimeter of the power management circuit board; the first through-holes  310 , the second through-holes  411 , and the third through-hole  211  are arranged in alignment with one another; an opening  110  is provided on the upper end of the housing  100 , and a plurality of support units  120  are formed by upward extension from the bottom inner wall inside the housing  100 . 
     Continued with the above depictions, to assemble them, the braking energy storage module  200 , the frame plate  300 , and the brake system control module  400  are sequentially placed into the housing  100  via the opening  110 ; the support unit  120  is supported against the lower surface of the power management circuit board  210 ; the bolts sequentially pass through the second through holes  411 , the first through holes  310 , and the third through holes  211  and are then fastened to the support unit  120 ; the frame plate  300 , the braking energy storage module  200 , and the brake system control module  400  are one-time fixed in the housing  100 , which saves assembly procedures and expense; finally, the opening  110  of the housing  100  is sealed with a cover plate  600 , wherein the cover plate and the opening  110  of the housing  100  are hermetically fitted via a sealing ring  610 . 
     The assembly and connection structure with respect to the frame plate  300 , the braking energy storage module  200 , and the brake system control module  400  is not limited to the scheme above. In other embodiments of the present disclosure, the frame plate  300  and the braking energy storage module  200  are made into one modular assembly which is then assembled with the brake system control module  400 ; or, the frame plate  300  and the brake system control module  400  are made into one modular assembly which is then assembled with the brake energy storage module  200 ; the fixing manner is not limited to the bolt connection either; in some embodiments, the fixing manner is a combination of snap-fittings and bolts, or tight pressing with other ancillary connectors, etc. 
     Electrical Connection Structure 
     The braking energy storage module  200  is in signal or electric connection with the brake system control module  400  via a bus passing through the frame plate  300 . In an exemplary embodiment, referring to  FIGS.  1  and  2   , a dielectric stand  330  and a bus avoidance hole  320  are provided on the frame plate  300 ; the bus is embedded in the dielectric stand  330 ; the bus passes through the bus avoidance hole  320  to electrically connect the control circuit board  410  and the power management circuit board  210  to thereby implement transmitting of power or signals between the control circuit board  410  and the power management circuit board  210 ; arrangement of the dielectric stand  330  protects and supports the bus and achieves a reliable electric insulation. 
     In other embodiments, the electric connection between the braking energy storage module  200  and the brake system control module  400  may also be implemented via a board-to-board connector or a cable. 
     The energy storage cells  220  in this embodiment are supercapacitors, and a plurality of supercapacitors are connected in an array on the power management circuit  210 ; the brake system control module  400  is configured to control charge and discharge of the supercapacitors; the power management circuit board  210  is configured to warrant voltage balance between the plurality of supercapacitors during charging, thereby alleviating voltage imbalance among some supercapacitors. 
     In other embodiments, the energy storage cells  220  may also be other types of capacitive elements or other devices with a power storage function. 
     In one embodiment of the present disclosure, based on the control unit described above: the brake system control module is fixed to the upper surface of the frame plate, the energy storage cells of the braking energy storage module are fixed to the lower surface of the frame plate, and the power management circuit board is partitioned from the frame plate by the energy storage cells, i.e., the energy storage cells are fixedly held between the power management circuit board and the frame plate; the scheme illustrated in this embodiment also achieves the technical effect of the preceding embodiments. 
     Referring to  FIGS.  1  and  2   , in one embodiment of the present disclosure, based on the control unit disclosed in the preceding embodiments: the braking energy storage module  200  is fixed between the frame plate  300  and an inner wall of the housing  100 , such that an additional fixing part is eliminated to fix the braking energy storage module  200  in the control unit, thereby saving expense. In an exemplary embodiment, in conjunction with the assembly and connection structure described in the preceding embodiment, the braking energy storage module  200  is installed in a top-down manner in the housing  100 ; after the assembly work is accomplished, the braking energy storage module  200  is fixedly connected between the frame plate  300  and the bottom inner wall of the housing  100 . 
     When the power management circuit board  210  is fixedly connected to the frame plate  300 , the frame plate  300  uniformly applies pressure via the power management circuit board  210  against the plurality of energy storage cells  220 , thereby effectively fixing the plurality of energy storage cells  220 . A thermal pad  700  is provided between the energy storage cells  220  and the bottom inner wall of the housing  100 ; the good thermally conductive property of the thermal pad  200  facilitates heat conduction from the energy storage cells  220  to the inner wall of the housing  100 , thereby enhancing heat dissipation efficiency; the thermal pad  700  also has a good elastic compressive property for absorbing vibration energy and buffering external impact and is configured for providing elastic support for the energy storage cells  220 , fixing the energy storage cells  220  more securely, avoiding collision between the energy storage cells  220  and the housing  110 , and warranting reliability of the electrical connection between the energy storage cells  220  and the power management circuit board  210 . 
     Also thanks to the elastic compressive property of the thermal pad  700 , the assembly tolerance of the braking energy storage module  200  is compensated by compressing the thermal pad  700  during assembly, avoiding looseness of the energy storage cells  220  due to assembly tolerance, or deformation of the power management circuit board  210  due to excess tightening. Specifically, in conjunction with the assembly and connection structure as described in the preceding embodiment, if the height of the energy storage cells  220  is lower than that of the support units  120 , the energy storage cells  220  cannot be securely held between the frame plate  300  and the bottom inner wall of the housing  100 ; if the height of the energy storage cells  220  is greater than that of the support units  120 , the power management circuit board  210  is easily deformed by being compressed by the energy storage cells  220 . With the thermal pad  700  provided between the energy storage cells  220  and the bottom inner wall of the housing  100 , the height of the support units  120  is configurable to be lower than that of the energy storage cells  220 , such that upon assembly, the energy storage cells  220  compress the thermal pad  700  to thereby neutralize the assembly tolerance (height difference) between the energy storage cells  220  and the support units  120 . 
     In some embodiments, without considering the assembly tolerance, another type of thermally conductive structure is arranged between the energy storage cells  220  and the bottom inner wall of the housing  100  to enhance heat dissipation, e.g., by filling a thermally conductive grease between the energy storage cells  220  and the bottom inner wall of the housing  100 . 
     In one embodiment of the present disclosure, based on the control unit described above: a thermally conductive medium  710 , such as a thermal pad, a thermally conductive silicon grease, a thermally conductive adhesive, etc., is arranged between the brake system control module  400  and the frame plate  300  so as to accelerate heat conduction from the brake system control module  400  to the frame plate  300  by leveraging the good thermally conductive property of the thermally conductive medium  710 , thereby enhancing heat dissipation efficiency; alternatively, a shock absorbing medium, such as silica gel, rubber, foamed plastics, etc., is further arranged between the brake system control module  400  and the frame plate  300 , which absorbs the vibration energy and thus alleviates the vibration impact on the brake system control module  400 ; in some embodiments, the thermally conductive medium and the shock absorbing medium are integrated into for example an elastic thermal pad, which is securely connected to one of the brake system control module  400  and the frame plate  300 , or securely held by the two. 
     Optionally, the thermally conductive medium and/or the shock absorbing medium are also arranged between the braking energy storage module  200  and the frame plate  300 , so as to absorb shock and/or accelerate heat dissipation with respect to the brake energy storage module  200 . 
     Referring to  FIG.  3   , in one embodiment of the present disclosure, based on the control unit described above: a voltage conversion module  500  is further provided in the housing  100 , the voltage conversion module  500  and the brake system control module  400  being fixed to the same side of the frame plate  300 . In an exemplary embodiment, the voltage conversion module  500  comprises a power circuit board  510  and a voltage conversion circuit configured on the power circuit board  510 ; the power circuit board  510  is fixed to the upper surface of the frame plate  300  using the assembly and connection structure described above, and the power circuit board  510  is in signal or electric connection with the control circuit board  410  via any one of a board-to-board connector, cable, or bus. The control unit in this embodiment further comprises an input connector  530  configured for an external power supply to input power, and an output connector  520  configured to output power to the electronic brake device; the input connector  530  and the output connector  520  are mounted on the power circuit board  510 ; the voltage conversion module  500  is configured to convert the external power supply voltage to an operating voltage adapted to the brake system control module  400 ; the voltage conversion module  500  and the brake system control module  400  are fixed to the same side of the frame plate  300 ; the voltage conversion module  500  is securely supported by the frame plate  300 ; as such, electrical connection is facilitated between the voltage conversion module  500  and the brake system control module  400 . 
     In some embodiments, the voltage conversion module  500  is in signal or electric connection with the power management circuit board  210  of the brake energy storage module  200  via one of the board-to-board connector, the cable, and the bus. 
     In other embodiments, the voltage conversion module  500  is optionally integrated to the brake system control module  400 , i.e., the control circuit and the voltage conversion circuit are both configured on the control circuit board  410 , and the power circuit board  510  and the control circuit board  410  are optionally integrated into one circuit board. 
     What have been described above are only preferred embodiments of the present disclosure; however, the protection scope of the present disclosure is not limited thereto. A person skilled in the art should understand that the present disclosure includes, but is not limited to the contents described in the drawings and the preferred embodiments. Any modifications without departing from the functions and structural principles of the present disclosure will be included within the scope of the claims. 
     Many variations and modifications may be made to the preferred embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of the present invention, as defined by the following claims.