Wireless communication system

Abstract

A wireless communication system (101) is provided with: a housing (10) formed of a conductive material; a plurality of battery packs (20) each having a surface formed of a conductive material; and a plurality of wireless communication devices (40, 30) having antennas (46, 36), the antennas being disposed in propagation paths (S1, S2) formed between the housing and the plurality of battery packs, and the plurality of wireless communication devices performing wireless communication with each other by using radio waves having a predetermined communication frequency. Each of the plurality of wireless communication devices is mainly provided with an antenna that transmits and receives a radio wave based on a polarization plane in a predetermined direction corresponding to that wireless communication device more strongly than a radio wave based on a polarization plane in any direction different from the predetermined direction. With the polarization planes in the predetermined directions, the cutoff frequencies individually defined on the basis of the lengths in the longitudinal directions of cross sections of the propagation paths in which the antennas of the plurality of wireless communication devices are individually disposed are all lower than the predetermined communication frequency.

Description

wireless communication system CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2023-176849, filed on October 12, 2023, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a wireless communication system including a plurality of wireless communication devices that perform wireless communication within a housing that houses a plurality of battery packs.

[0003] For example, one such wireless communication system includes a battery management unit including first to third wireless transceiver modules with antennas that transmit and receive radio waves polarized in the Z direction and a fourth wireless transceiver module with an antenna that transmits and receives radio waves polarized in the X direction, and a plurality of battery modules each having a wireless transceiver module that communicates with the battery management unit via radio waves using a polarization diversity system (see Patent Document 1). Patent Document 1 also describes that even if radio waves generated within a panel or container are diffusely reflected and significant interference occurs, the battery management unit includes more wireless transceiver modules that transmit and receive radio waves polarized in the Z direction, which is the direction in which the antenna receives the greatest power, than wireless transceiver modules that transmit and receive radio waves polarized in the X direction, thereby improving communication reliability. Patent Document 1 also describes that the polarization that maximizes received power is determined in advance through simulations and experiments that take diffuse reflection into account.

[0004] Patent No. 7106766

[0005] However, Patent Document 1 merely considers measures against significant interference caused by diffuse reflection of radio waves when used inside a panel or container.

[0006] Recently, there has been a study on applying wireless communication systems to battery systems that are required to be compact and have a housing made of conductive material, such as those installed in hybrid vehicles and electric vehicles. However, in the case of battery systems that are required to be compact and have a housing made of conductive material, it is difficult to improve the reliability of communication simply by considering the diffuse reflection of radio waves within the housing.

[0007] The present disclosure has been made to solve the above-mentioned problems, and its main purpose is to improve the reliability of communications in wireless communication systems, particularly in battery systems that require miniaturization, such as those installed in hybrid vehicles and electric vehicles.

[0008] Therefore, the present inventors conducted extensive research into the propagation paths of wireless communications within a battery system made of a housing made of a conductive material, which is required to be compact, and found that sufficient communication reliability cannot be achieved by simply considering the diffuse reflection of radio waves, as has been done in the past.

[0009] In particular, we discovered for the first time that, inside a housing made of conductive material, which requires miniaturization, the propagation path is extremely narrow, and that it is necessary to select a polarization plane that can propagate through the propagation path that exists inside the housing, rather than to avoid diffuse reflection of the radio waves.

[0010] Therefore, in the present disclosure, as a first means for solving the above problem, there is provided a wireless communication system comprising: a housing made of a conductive material; a plurality of battery packs arranged inside the housing and having surfaces made of a conductive material; and a plurality of wireless communication devices each having an antenna for transmitting and receiving radio waves, the antenna being arranged in a propagation path formed between the housing and the plurality of battery packs, and performing wireless communication with each other using radio waves of a predetermined communication frequency, wherein the plurality of wireless communication devices are mainly equipped with antennas that transmit and receive radio waves with a polarization plane in a predetermined direction corresponding to each of the wireless communication devices more strongly than radio waves with a polarization plane in any direction different from the predetermined direction, and the polarization plane in the predetermined direction is a polarization plane whose cutoff frequencies, each defined based on the longitudinal length of a cross section of the propagation path in which the antennas of the plurality of wireless communication devices are respectively arranged, are all lower than the predetermined communication frequency.

[0011] According to the above configuration, the housing is made of a conductive material (e.g., metal). The plurality of battery packs are disposed inside the housing, and the surfaces thereof are made of a conductive material. Therefore, the inner surfaces of the propagation paths formed between the housing and the plurality of battery packs are made of a conductive material. The plurality of wireless communication devices each have an antenna for transmitting and receiving radio waves, and the antenna is disposed in the propagation path formed between the housing and the plurality of battery packs, and wireless communication is performed between the wireless communication devices using radio waves of a predetermined communication frequency. Therefore, in wireless communication between the plurality of wireless communication devices, the propagation path can be considered similar to a wave guide for radio waves.

[0012] Here, when radio waves propagate through a waveguide, propagation loss increases for radio waves with frequencies lower than the cutoff frequency. The cutoff frequency is determined, for example, based on the width a and height b of the waveguide cross section. The cutoff frequency fv of vertically polarized waves with mode number 1 is determined by the width a and the speed of light c, as fv = c / 2a. The cutoff frequency fh of horizontally polarized waves with mode number 1 is determined by the height b and the speed of light c, as fh = c / 2b. Therefore, the present inventors have noticed that propagation loss can be suppressed by performing wireless communication using radio waves with a polarization plane in which the cutoff frequency, determined according to the length in each direction of the cross section of the propagation path in which the antenna of the wireless communication device is located, is lower than the predetermined communication frequency in the wireless communication. Furthermore, for example, if the width a of the cross section of the propagation path is greater than the height b (a > b), the cutoff frequency fv of vertically polarized waves will be lower than the cutoff frequency fh of horizontally polarized waves (fv < fh). In this case, radio waves with a vertically polarized plane tend to propagate at a lower cutoff frequency fv or higher than radio waves with a horizontally polarized plane. That is, the cutoff frequency of radio waves with a polarization plane in a predetermined direction (the polarization plane of vertically polarized waves in the above example) is determined based on the length (width a) of the cross section of the propagation path in the longitudinal direction (the width direction in the above example), and is lower than the cutoff frequency of radio waves with a polarization plane in any direction other than the predetermined direction. In this case, selecting a polarization plane in the predetermined direction makes it easier to set the cutoff frequency lower than a predetermined communication frequency in wireless communication, and setting the cutoff frequency lower than the predetermined communication frequency can suppress propagation loss.

[0013] In this regard, the multiple wireless communication devices mainly include antennas that transmit and receive radio waves polarized in a predetermined direction corresponding to each of the multiple wireless communication devices, with stronger transmission and reception strength than radio waves polarized in any direction other than the predetermined direction. Therefore, compared to a wireless communication device equipped with multiple antennas that transmit and receive radio waves polarized in multiple directions, the number of antennas included in the wireless communication device can be minimized. The polarization direction of the predetermined direction is a polarization plane whose cutoff frequency, determined based on the longitudinal length of the cross section of the propagation path in which the antennas of the multiple wireless communication devices are respectively arranged, is lower than the predetermined communication frequency. Therefore, by performing wireless communication using radio waves polarized in the predetermined direction, the cutoff frequency of each of the multiple wireless communication devices is lower than the predetermined communication frequency, thereby suppressing propagation loss. Therefore, the reliability of communication in the wireless communication system can be improved.

[0014] The second means includes a first wireless communication device and a second wireless communication device that are multiple wireless communication devices that communicate wirelessly with each other, the antenna of the first wireless communication device is arranged on a first propagation path that is the propagation path where cutoff frequencies of radio waves due to a first polarization plane and a second polarization plane that are orthogonal to each other are a first cutoff frequency and a third cutoff frequency, respectively, the antenna of the second wireless communication device is arranged on a second propagation path that is the propagation path where cutoff frequencies of radio waves due to the first polarization plane and the second polarization plane are a second cutoff frequency and a fourth cutoff frequency, respectively, the specified communication frequency is higher than the first cutoff frequency and the third cutoff frequency, higher than the second cutoff frequency, and lower than the fourth cutoff frequency, and the polarization plane in the specified direction is the first polarization plane.

[0015] According to the above configuration, the first wireless communication device and the second wireless communication device communicate wirelessly with each other. The antenna of the first wireless communication device is arranged in a first propagation path, which is the propagation path along which the cutoff frequencies of radio waves due to first and second polarization planes that are orthogonal to each other are a first cutoff frequency and a third cutoff frequency, respectively. That is, in the first propagation path, the cutoff frequency of radio waves due to the first polarization plane is the first cutoff frequency, and the cutoff frequency of radio waves due to the second polarization plane is the third cutoff frequency.

[0016] The antenna of the second wireless communication device is arranged in a second propagation path, which is the propagation path in which the cutoff frequencies of radio waves in the first polarization plane and the second polarization plane are the second cutoff frequency and the fourth cutoff frequency, respectively. That is, in the second propagation path, the cutoff frequency of radio waves in the first polarization plane is the second cutoff frequency, and the cutoff frequency of radio waves in the second polarization plane is the fourth cutoff frequency.

[0017] Here, the predetermined communication frequency is higher than the first cutoff frequency and the third cutoff frequency. Therefore, in the first propagation path, propagation loss can be suppressed regardless of whether radio waves with the first polarization plane or radio waves with the second polarization plane are used. Meanwhile, the predetermined communication frequency is higher than the second cutoff frequency and lower than the fourth cutoff frequency. Therefore, in the second propagation path, propagation loss can be suppressed when radio waves with the first polarization plane are used, but propagation loss increases when radio waves with the second polarization plane are used. In this regard, the polarization plane in the predetermined direction is the first polarization plane. Therefore, even if the multiple wireless communication devices mainly include antennas that transmit and receive radio waves with the first polarization plane, a decrease in communication reliability can be suppressed.

[0018] Specifically, as in the third aspect, the first propagation path may be configured by the inner upper surface, the inner lower surface, and a pair of inner side surfaces of the housing, with the distance between the inner upper surface and the inner lower surface being shorter than the distance between the pair of inner side surfaces; the second propagation path may be configured by the inner upper surface of the housing, the outer upper surfaces of the plurality of battery packs, and a pair of inner side surfaces of the housing, with the distance between the inner upper surface and the outer upper surface being shorter than the distance between the pair of inner side surfaces; the first polarization plane is a polarization plane of vertically polarized waves; and the second polarization plane is a polarization plane of horizontally polarized waves. With this configuration, the relationship of the second aspect can be satisfied in a configuration in which the polarization plane in the predetermined direction is the first polarization plane, i.e., the polarization plane of vertically polarized waves. Therefore, in a configuration in which the plurality of wireless communication devices mainly include antennas that transmit and receive radio waves mainly with a polarization plane of vertically polarized waves, a decrease in communication reliability can be suppressed.

[0019] A fourth means includes a first wireless communication device and a second wireless communication device that are multiple wireless communication devices that communicate wirelessly with each other, wherein the antenna of the first wireless communication device is arranged on a first propagation path that is the propagation path where cutoff frequencies of radio waves due to a first polarization plane and a second polarization plane that are orthogonal to each other are a first cutoff frequency and a third cutoff frequency, respectively, and the antenna of the second wireless communication device is arranged on a second propagation path that is the propagation path where cutoff frequencies of radio waves due to the first polarization plane and the second polarization plane are a second cutoff frequency and a fourth cutoff frequency, respectively, and the specified communication frequency is higher than the first cutoff frequency and the third cutoff frequency, lower than the second cutoff frequency, and higher than the fourth cutoff frequency, and the polarization plane in the specified direction is the second polarization plane.

[0020] According to the above configuration, the predetermined communication frequency is higher than the first cutoff frequency and the third cutoff frequency. Therefore, in the first propagation path, propagation loss can be suppressed regardless of whether radio waves with the first polarization plane or radio waves with the second polarization plane are used. Meanwhile, the predetermined communication frequency is lower than the second cutoff frequency and higher than the fourth cutoff frequency. Therefore, in the second propagation path, propagation loss increases when radio waves with the first polarization plane are used, but propagation loss can be suppressed when radio waves with the second polarization plane are used. In this regard, the polarization plane in the predetermined direction is the second polarization plane. Therefore, even if the multiple wireless communication devices are equipped with antennas that mainly transmit and receive radio waves with the second polarization plane, a decrease in communication reliability can be suppressed.

[0021] Specifically, as in the fifth aspect, the first propagation path may be configured by the inner upper surface, the inner lower surface, and a pair of inner side surfaces of the housing, the distance between the inner upper surface and the inner lower surface being shorter than the distance between the pair of inner side surfaces; the second propagation path may be configured by the inner upper surface and the inner lower surface of the housing, the outer side surfaces of the plurality of battery packs, and the inner side surface of the housing, the distance between the inner upper surface and the inner lower surface being longer than the distance between the outer side surfaces and the inner side surfaces; the first polarization plane is a polarization plane of vertically polarized waves, and the second polarization plane is a polarization plane of horizontally polarized waves. With this configuration, the relationship of the fourth aspect can be satisfied in a configuration in which the polarization plane in a predetermined direction is the second polarization plane, i.e., the polarization plane of horizontally polarized waves. Therefore, in a configuration in which the plurality of wireless communication devices mainly include antennas that transmit and receive radio waves mainly with a polarization plane of horizontally polarized waves, a decrease in communication reliability can be suppressed.

[0022] A sixth means includes a first wireless communication device and a second wireless communication device that are the plurality of wireless communication devices that communicate wirelessly with each other, wherein the antenna of the first wireless communication device is arranged on a first propagation path that is the propagation path where cutoff frequencies of radio waves due to a first polarization plane and a second polarization plane that are orthogonal to each other are a first cutoff frequency and a third cutoff frequency, respectively, and the antenna of the second wireless communication device is arranged on a second propagation path that is the propagation path where cutoff frequencies of radio waves due to the first polarization plane and the second polarization plane are a second cutoff frequency and a fourth cutoff frequency, respectively, and a predetermined propagation path that is the propagation path that causes polarization rotation in radio waves transmitted from the antenna of the first wireless communication device and the antenna of the second wireless communication device exists between the antenna of the first wireless communication device and the antenna of the second wireless communication device, and the predetermined communication frequency is higher than the first cutoff frequency and the third cutoff frequency, lower than the second cutoff frequency, and higher than the fourth cutoff frequency, and the polarization plane in the predetermined direction at the position of the antenna of the second wireless communication device is the second polarization plane.

[0023] According to the above configuration, a predetermined propagation path exists between the antenna of the first wireless communication device and the antenna of the second wireless communication device, the predetermined propagation path being the propagation path that causes polarization rotation in radio waves transmitted from the antenna of the first wireless communication device and the antenna of the second wireless communication device. In this case, for example, radio waves transmitted from the antenna of the first wireless communication device in a second polarization plane can be changed into radio waves in a first polarization plane at the position of the antenna of the second wireless communication device by being subjected to polarization rotation by the predetermined propagation path.

[0024] Here, the predetermined communication frequency is higher than the first cutoff frequency and the third cutoff frequency. Therefore, at the position of the antenna of the first wireless communication device, propagation loss can be suppressed regardless of whether radio waves with the first polarization plane or radio waves with the second polarization plane are used. On the other hand, the predetermined communication frequency is lower than the second cutoff frequency and higher than the fourth cutoff frequency. Therefore, at the position of the antenna of the second wireless communication device, propagation loss increases when radio waves with the first polarization plane are used, but propagation loss can be suppressed when radio waves with the second polarization plane are used. In this regard, at the position of the antenna of the second wireless communication device, the polarization plane in the predetermined direction is the second polarization plane. Therefore, even if the multiple wireless communication devices are equipped with antennas that transmit and receive radio waves with a polarization plane in a corresponding predetermined direction more strongly than radio waves with a polarization plane in any direction other than the predetermined direction, a decrease in communication reliability can be suppressed.

[0025] Specifically, as in the seventh means, the first propagation path is composed of the inner upper surface, inner lower surface, and a pair of inner side surfaces of the housing, and the distance between the inner upper surface and the inner lower surface is shorter than the distance between the pair of inner side surfaces; the specified propagation path includes the propagation path composed of the inner upper surface of the housing, the outer upper surfaces of the multiple battery packs, and a pair of inner side surfaces of the housing, and the distance between the inner upper surface and the outer upper surface is shorter than the distance between the pair of inner side surfaces; the second propagation path is composed of the inner upper surface and inner lower surface of the housing, the outer sides of the multiple battery packs, and the inner side surfaces of the housing, and the distance between the inner upper surface and the inner lower surface is longer than the distance between the outer side surfaces and the inner side surfaces; and at the position of the antenna of the second wireless communication device, the second polarization plane is a polarization plane of horizontal polarization. According to this configuration, in a configuration in which the polarization plane in the predetermined direction at the position of the antenna of the second wireless communication device is the second polarization plane, i.e., the polarization plane of horizontally polarized waves, the relationship of the sixth means can be satisfied. Therefore, in a configuration in which the second wireless communication device mainly includes an antenna that transmits and receives radio waves mainly with the polarization plane of horizontally polarized waves, it is possible to prevent a decrease in communication reliability.

[0026] In an eighth aspect, the plurality of wireless communication devices each include only antennas that transmit and receive radio waves polarized in a predetermined direction corresponding to the plurality of wireless communication devices, with stronger polarization than radio waves polarized in any direction other than the predetermined direction. With this configuration, it is possible to minimize the number of antennas in a wireless communication system while suppressing a decrease in communication reliability.

[0027] a ninth means is a wireless communication system comprising: a housing made of a conductive material; a plurality of battery packs arranged inside the housing and having surfaces made of a conductive material; and a first wireless communication device and a second wireless communication device, each having an antenna for transmitting and receiving radio waves, the antenna being arranged in a propagation path formed between the housing and the plurality of battery packs, which wirelessly communicate with each other using radio waves of a predetermined communication frequency, wherein the antenna of the first wireless communication device is arranged in a first propagation path, which is the propagation path in which a cutoff frequency of radio waves in a polarization plane of vertical polarization is a first cutoff frequency and a cutoff frequency of radio waves in a polarization plane of horizontal polarization is a third cutoff frequency, the first propagation path is made up of an inner upper surface, an inner lower surface, and a pair of inner side surfaces of the housing, the distance between the inner upper surface and the inner lower surface is shorter than the distance between the pair of inner side surfaces, and the antenna of the second wireless communication device is arranged in a second propagation path, which is the propagation path in which a cutoff frequency of radio waves in a polarization plane of vertical polarization is a second cutoff frequency and a cutoff frequency of radio waves in a polarization plane of horizontal polarization is a fourth cutoff frequency, the second propagation path is composed of the inner top surface of the housing, the outer top surface of the plurality of battery packs, and a pair of inner side surfaces of the housing, and the distance between the inner top surface and the outer top surface is shorter than the distance between the pair of inner side surfaces; the specified communication frequency is higher than the first cutoff frequency and the third cutoff frequency, and higher than the second cutoff frequency, and lower than the fourth cutoff frequency; and the first wireless communication device and the second wireless communication device mainly comprise antennas that transmit and receive radio waves with a polarization plane of vertical polarization more strongly than radio waves with a polarization plane of any direction other than vertical polarization.

[0028] According to the above configuration, the first wireless communication device and the second wireless communication device have antennas for transmitting and receiving radio waves, and the antennas are arranged in propagation paths formed between the housing and the plurality of battery packs, and wireless communication is performed between the first wireless communication device and the second wireless communication device using radio waves of a predetermined communication frequency. Therefore, in wireless communication between the first wireless communication device and the second wireless communication device, the propagation path can be considered to be similar to a waveguide for radio waves.

[0029] The antenna of the first wireless communication device is disposed in a first propagation path, which is the propagation path having a first cutoff frequency for radio waves in a vertically polarized wave plane and a third cutoff frequency for radio waves in a horizontally polarized wave plane. Specifically, the first propagation path is formed by an inner upper surface, an inner lower surface, and a pair of inner side surfaces of the housing, and the distance between the inner upper surface and the inner lower surface is shorter than the distance between the pair of inner side surfaces. With this configuration, the first cutoff frequency is lower than the third cutoff frequency.

[0030] Furthermore, the antenna of the second wireless communication device is disposed on a second propagation path, which is the propagation path having a second cutoff frequency for radio waves in a polarization plane of vertical polarization and a fourth cutoff frequency for radio waves in a polarization plane of horizontal polarization. Specifically, the second propagation path is formed by an inner upper surface of the housing, outer upper surfaces of the plurality of battery packs, and a pair of inner side surfaces of the housing, and the distance between the inner upper surface and the outer upper surface is shorter than the distance between the pair of inner side surfaces. With this configuration, the second cutoff frequency is lower than the fourth cutoff frequency and is lower than the first cutoff frequency.

[0031] The predetermined communication frequency is higher than the first cutoff frequency and the third cutoff frequency. Therefore, in the first propagation path, propagation loss can be suppressed regardless of whether radio waves with a vertical polarization plane or radio waves with a horizontal polarization plane are used. Meanwhile, the predetermined communication frequency is higher than the second cutoff frequency and lower than the fourth cutoff frequency. Therefore, in the second propagation path, propagation loss can be suppressed when radio waves with a vertical polarization plane are used, but propagation loss increases when radio waves with a horizontal polarization plane are used. In this regard, the first wireless communication device and the second wireless communication device mainly include antennas that transmit and receive radio waves with a vertical polarization plane more strongly than radio waves with a polarization plane other than the vertical polarization. Therefore, even when the first wireless communication device and the second wireless communication device mainly include antennas that transmit and receive radio waves with a vertical polarization plane, a decrease in communication reliability can be suppressed.

[0032] In a tenth aspect, the first wireless communication device and the second wireless communication device are provided with only antennas that transmit and receive radio waves with a vertically polarized wave plane stronger than radio waves with a polarization plane of any direction other than vertical polarization. With this configuration, it is possible to minimize the number of antennas in a wireless communication system while suppressing a decrease in communication reliability.

[0033] An eleventh means is a wireless communication system comprising: a housing made of a conductive material; a plurality of battery packs arranged inside the housing and having surfaces made of a conductive material; and a first wireless communication device and a second wireless communication device each having an antenna for transmitting and receiving radio waves, the antenna being arranged in a propagation path formed between the housing and the plurality of battery packs, and which wirelessly communicate with each other using radio waves of a predetermined communication frequency, wherein the antenna of the first wireless communication device is arranged in a first propagation path, which is the propagation path in which a cutoff frequency of radio waves in a polarization plane of vertical polarization is a first cutoff frequency and a cutoff frequency of radio waves in a polarization plane of horizontal polarization is a third cutoff frequency, the first propagation path being composed of an inner upper surface, an inner lower surface, and a pair of inner side surfaces of the housing, and the distance between the inner upper surface and the inner lower surface is shorter than the distance between the pair of inner side surfaces, the antenna of the second wireless communication device is arranged on a second propagation path, which is the propagation path in which the cutoff frequency of radio waves in the polarization plane of vertical polarization is a second cutoff frequency and the cutoff frequency of radio waves in the polarization plane of horizontal polarization is a fourth cutoff frequency; the second propagation path is composed of the inner top and bottom surfaces of the housing, the outer surfaces of the multiple battery packs, and the inner surface of the housing, and the distance between the inner top surface and the inner bottom surface is longer than the distance between the outer surface and the inner surface; the specified communication frequency is higher than the first cutoff frequency and the third cutoff frequency, lower than the second cutoff frequency, and higher than the fourth cutoff frequency; and the first wireless communication device and the second wireless communication device mainly include antennas that transmit and receive radio waves in the polarization plane of horizontal polarization more strongly than radio waves in the polarization plane of any direction other than horizontal polarization.

[0034] According to the above configuration, the antenna of the first wireless communication device is disposed in a first propagation path, which is the propagation path having a first cutoff frequency for radio waves in a polarization plane of vertical polarization and a third cutoff frequency for radio waves in a polarization plane of horizontal polarization. Specifically, the first propagation path is formed by an inner upper surface, an inner lower surface, and a pair of inner side surfaces of the housing, and the distance between the inner upper surface and the inner lower surface is shorter than the distance between the pair of inner side surfaces. With this configuration, the first cutoff frequency is lower than the third cutoff frequency.

[0035] Furthermore, the antenna of the second wireless communication device is disposed on a second propagation path, which is the propagation path in which the cutoff frequency of radio waves in a polarization plane of vertically polarized waves is a second cutoff frequency and the cutoff frequency of radio waves in a polarization plane of horizontally polarized waves is a fourth cutoff frequency. Specifically, the second propagation path is formed by the inner upper and lower surfaces of the housing, the outer surfaces of the plurality of battery packs, and the inner surface of the housing, and the distance between the inner upper surface and the inner lower surface is longer than the distance between the outer surface and the inner surface. With this configuration, the fourth cutoff frequency is lower than the second cutoff frequency.

[0036] The predetermined communication frequency is higher than the first cutoff frequency and the third cutoff frequency. Therefore, in the first propagation path, propagation loss can be suppressed regardless of whether radio waves with a vertical polarization plane or radio waves with a horizontal polarization plane are used. Meanwhile, the predetermined communication frequency is lower than the second cutoff frequency and higher than the fourth cutoff frequency. Therefore, in the second propagation path, propagation loss increases when radio waves with a vertical polarization plane are used, but propagation loss can be suppressed when radio waves with a horizontal polarization plane are used. In this regard, the first wireless communication device and the second wireless communication device mainly include antennas that transmit and receive radio waves with a horizontal polarization plane more strongly than radio waves with a polarization plane other than the horizontal polarization. Therefore, even when the first wireless communication device and the second wireless communication device mainly include antennas that transmit and receive radio waves with a horizontal polarization plane, a decrease in communication reliability can be suppressed.

[0037] In a twelfth aspect, the first wireless communication device and the second wireless communication device each include only an antenna that transmits and receives radio waves with a horizontally polarized wave plane stronger than radio waves with a polarization plane of any direction other than horizontal polarization. With this configuration, it is possible to minimize the number of antennas in a wireless communication system while suppressing a decrease in communication reliability.

[0038] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a plan view of a battery system according to a first embodiment, Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1, Fig. 3 is a cross-sectional view taken along line III-III of Fig. 1, Fig. 4 is a perspective view showing a waveguide and the lowest modes of vertically polarized waves and horizontally polarized waves, Fig. 5 is a plan view of a modified example of the battery system, Fig. 6 is a plan view of another modified example of the battery system, Fig. 7 is a plan view of a battery system according to a second embodiment, Fig. 8 is a cross-sectional view taken along line VIII-VIII of Fig. 7, and Fig. 9 is a cross-sectional view taken along line IX-IX of Fig. 7. 14 is a cross-sectional view taken along line XIV-XIV of FIG. 13; FIG. 15 is a cross-sectional view taken along line XV-XV of FIG. 13; FIG. 16 is a plan view of a modified example of the casing; FIG. 17 is a plan view of another modified example of the casing; and FIG. 18 is a plan view of another modified example of the casing. 19 is a side view of another modified example of the battery system, FIG. 20 is a plan view of another modified example of the battery system, FIG. 21 is a plan view of another modified example of the battery system, FIG. 22 is a front view of a vertically polarized antenna, FIG. 23 is a perspective view of a modified example of the vertically polarized antenna, FIG. 24 is a perspective view of another modified example of the vertically polarized antenna, FIG. 25 is a perspective view of a horizontally polarized antenna, FIG. 26 is a perspective view of a modified example of the horizontally polarized antenna, and FIG. 27 is a perspective view of a horizontally polarized antenna. FIG. 28 is a front view of another modified example of the horizontally polarized antenna, FIG. 29 is a rear view of another modified example of the horizontally polarized antenna, FIG. 30 is a rear view of another modified example of the horizontally polarized antenna, FIG. 31 is a cross-sectional view corresponding to the cross-sectional view of line XIV-XIV in FIG. 13 in another modified example of the battery system, FIG. 32 is a side view of the horizontally polarized antenna and bracket, FIG. 33 is a schematic diagram showing the mesh communication mode, and FIG. 34 is a plan view of a modified example of the housing.

[0039] Hereinafter, an embodiment embodied in a wireless communication system applied to a battery system mounted on a hybrid vehicle or an electric vehicle will be described with reference to the drawings.

[0040] [First embodiment] Fig. 1 is a plan view of a battery system 101, Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1, and Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1. Note that in Fig. 1, the top wall of a housing 10 is not shown.

[0041] The battery system 101 is mounted on a hybrid vehicle or the like. The battery system 101 has a housing 10 formed of a conductive material (conductor) such as metal, and a plurality of battery packs 20, a plurality of acquisition devices 30, and a monitoring device 40 installed within the housing 10. The acquisition devices 30 and the monitoring devices 40 constitute a battery monitoring system (wireless communication system) that monitors each battery pack 20.

[0042] In the following, three predetermined directions that are orthogonal to one another will be referred to as the "left-right direction X," the "front-rear direction Y," and the "up-down direction Z" in accordance with the drawings. However, the battery system 101 can be installed in any direction, for example, by installing the battery system 101 so that the "up-down direction Z" is set to the left-right or front-rear direction, or by installing the battery system 101 so that the "left-right direction X" is set to the front-rear direction.

[0043] The plurality of battery packs 20 are formed in a rectangular parallelepiped shape and are arranged side by side in the left-right direction X. Each battery pack 20 is, for example, an assembled battery having a plurality of battery cells (not shown) arranged in the front-rear direction Y. The plurality of battery cells are, for example, electrically connected in series or electrically connected in parallel. The surface of each battery pack 20 is made of a conductive material such as metal. Note that each battery pack 20 may mainly have one battery cell, or may have, for example, only one battery cell.

[0044] A plurality of acquisition devices 30 (second wireless communication devices, wireless communication devices) are installed for each battery pack 20. Specifically, each acquisition device 30 is installed on the outer upper surface 20u of the corresponding battery pack 20. Each acquisition device 30 has a controller, a measurement circuit, a communication unit, etc. (not shown). Each acquisition device 30 acquires battery information, which is information about the battery pack 20, from the corresponding battery pack 20. The battery information includes, for example, voltage information and temperature information of each of the plurality of battery cells in the battery pack 20, and information about the current flowing through the battery pack 20.

[0045] The monitoring device 40 (first wireless communication device, wireless communication device) is attached inside the housing 10, for example, to the left inner surface of the housing 10. The monitoring device 40 has a controller, a communication unit, etc. (not shown). The multiple acquisition devices 30 and the monitoring device 40 communicate with each other wirelessly using radio waves at a communication frequency f0 (predetermined communication frequency). The communication frequency f0 is, for example, 2.4 GHz. Through wireless communication with each acquisition device 30, the monitoring device 40 transmits acquisition commands to the acquisition devices 30 to cause them to acquire battery information, receives battery information from each acquisition device 30, and transmits equalization commands to the acquisition devices 30 to equalize the voltages of each battery cell. The monitoring device 40 is also connected to a host ECU (not shown) wirelessly or via a wired connection so as to be able to communicate with each other.

[0046] The housing 10 has a box-like shape that three-dimensionally surrounds the master antenna 46 of the monitoring device 40 and the slave antennas 36 of each acquisition device 30, which transmit and receive radio waves. However, as used herein, "surrounding three-dimensionally" means that there are surrounding objects on six sides of the surrounded object, with six directions consisting of the positive and negative sides of three mutually orthogonal directions being defined as "six directions." In other words, in this case, walls of the housing 10 are located on six sides of each antenna 46, 36. Therefore, the housing 10 may have openings such as screw holes, vents, and connector insertion holes, as well as other gaps.

[0047] A first propagation path S1, which is a propagation path for radio waves, is formed between the monitoring device 40 and the leftmost battery pack 20 (the battery pack 20 closest to the monitoring device 40). The first propagation path S1 is a passage surrounded three-dimensionally by a conductive material. Specifically, in this embodiment, the first propagation path S1 is formed by the inner upper surface 10u, the inner lower surface 10d, and the front and rear inner surfaces 10s (a pair of inner surfaces) of the housing 10. The cross-sectional dimensions of the first propagation path S1 are smallest in the vertical direction Z among the three-dimensional directions. That is, the distance between the inner upper surface 10u and the inner lower surface 10d of the housing 10 is shorter than the distance between the front and rear inner surfaces 10s.

[0048] A second propagation path S2, which is a propagation path for radio waves, is formed between the outer upper surface 20u of the battery pack 20 and the inner upper surface 10u of the housing 10. The second propagation path S2 is a passage surrounded three-dimensionally by a conductive material. Specifically, in this embodiment, the second propagation path S2 is composed of the inner upper surface 10u of the housing 10, the outer upper surfaces 20u of the multiple battery packs 20, and the front and rear inner surfaces 10s of the housing 10. The cross-sectional dimension of the second propagation path S2 is smallest in the vertical direction Z among the three-dimensional directions. In other words, the distance between the inner upper surface 10u of the housing 10 and the outer upper surface 20u of the battery pack 20 is shorter than the distance between the front and rear inner surfaces 10s of the housing 10.

[0049] The monitoring device 40 is attached within the housing 10, for example, at the upper part of the left inner surface of the housing 10, in the middle in the front-to-rear direction. The monitoring device 40 has a master antenna 46 for wireless communication with each acquisition device 30. The master antenna 46 is provided, for example, on the right side (side) of the monitoring device 40. As a result, the master antenna 46 is installed (disposed) within the first propagation path S1. Note that the height at which the monitoring device 40 is installed within the first propagation path S1 and the front-to-rear position at which the monitoring device 40 is installed are arbitrary. Furthermore, as long as the master antenna 46 is disposed within the first propagation path S1, a main body (part of the main body) of the monitoring device 40 may be disposed at the boundary between the inside and outside of the housing 10, or the main body of the monitoring device 40 may be disposed outside the housing 10 (only the master antenna 46 may be disposed within the housing 10).

[0050] Each acquisition device 30 is attached within the housing 10, for example, at a central portion in the front-to-rear direction on the outer upper surface 20u of each battery pack 20. Each acquisition device 30 has a slave antenna 36 for wireless communication with the monitoring device 40. Each slave antenna 36 is provided, for example, on the upper surface of the corresponding acquisition device 30. As a result, each slave antenna 36 is installed (disposed) within the second propagation path S2. Note that the front-to-rear positions at which each acquisition device 30 is installed within the second propagation path S2 and the left-to-right positions at which each acquisition device 30 is installed within the outer upper surface 20u of each battery pack 20 are arbitrary.

[0051] As described above, the master antenna 46 and the slave antenna 36 are disposed on the propagation paths S1 and S2 formed between the housing 10 and the plurality of battery packs 20. The inner surfaces of the propagation paths S1 and S2 are made of a conductive material. Therefore, in wireless communication between the monitoring device 40 and the plurality of acquisition devices 30, the propagation paths S1 and S2 can be considered to be similar to wave guides for radio waves.

[0052] Here, when radio waves propagate through a waveguide, radio waves with frequencies lower than the cutoff frequency do not propagate (leading to large propagation loss). As shown in Figure 4, for example, the cutoff wavelength λ is defined as shown in the following formula (1) based on the width a and height b of the cross section of the waveguide. Note that (m / 2a)^2 represents the square of (m / 2a).

[0053] λ=1 / √{(m / 2a)^2+(n / 2b)^2} (1) where m is the number of waves in the height direction (number of modes) and n is the number of waves in the width direction (number of modes). The cutoff frequency fv of vertically polarized waves is defined by the following equation (2):

[0054] fv = c / λv (2) where c is the speed of light and λv is the cutoff wavelength of vertically polarized waves. The cutoff frequency fv of vertically polarized waves is lowest when m = 1 and n = 0. The cutoff frequency fv of the lowest mode of vertically polarized waves is defined as follows by equations (1) and (2):

[0055] fv=c / 2a Similarly, the cutoff frequency fh of horizontally polarized waves is defined by the following equation (3).

[0056] fh = c / λh (3) where c is the speed of light and λh is the cutoff wavelength of horizontally polarized waves. The cutoff frequency fh of horizontally polarized waves is lowest when m = 0 and n = 1. The cutoff frequency fh of the lowest mode of this horizontally polarized wave is defined as follows by equations (1) and (3):

[0057] fh = c / 2b For example, when a = 1000 mm and b = 50 mm, the cutoff frequency of vertical polarization is fv = 150 MHz, and the cutoff frequency of horizontal polarization is fh = 3 GHz. When the communication frequency f0 = 2.4 GHz, since fv < f0, the propagation loss of vertical polarization can be suppressed. On the other hand, since f0 < fh, horizontal polarization does not propagate (the propagation loss increases). In other words, the present inventors have noticed that propagation loss can be suppressed by performing wireless communication using radio waves with a polarization plane in which the cutoff frequencies fv and fh, which are determined according to the lengths in each direction of the cross section of the propagation path in which the master antenna 46 and the slave antenna 36 are arranged, are lower than the communication frequency f0. Note that if the communication frequency f0 is lower than the cutoff frequency of the lowest mode, at least the radio waves in the lowest mode can propagate.

[0058] Furthermore, when the width a of the cross section of the propagation path is greater than the height b (a > b), the cutoff frequency fv of vertically polarized waves is lower than the cutoff frequency fh of horizontally polarized waves (fv < fh). In this case, radio waves with a vertically polarized plane of polarization are more likely to propagate at a lower cutoff frequency fv or higher than radio waves with a horizontally polarized plane of polarization. That is, the cutoff frequency fv of radio waves with a vertically polarized plane of polarization (polarization in a predetermined direction) is determined based on the width a (longitudinal length) of the cross section of the propagation path, and is lower than the cutoff frequency of radio waves with a horizontally polarized plane of polarization (polarization in any direction other than the predetermined direction) that is different from the vertically polarized wave. In this case, selecting a vertically polarized plane of polarization (polarization in a predetermined direction) makes it easier to lower the cutoff frequency fv below the communication frequency f0 in wireless communication, and by lowering the cutoff frequency fv below the communication frequency f0, propagation loss can be suppressed. Furthermore, the dimensions of the radio wave propagation path can be designed taking into consideration the above relationship between the communication frequency f0 and the cutoff frequencies fv and fh.

[0059] Therefore, the monitoring device 40 and each acquisition device 30 are mainly equipped with antennas that transmit and receive radio waves with a plane of polarization in a predetermined direction corresponding to each device more strongly than radio waves with a plane of polarization in any direction other than the predetermined direction. It is desirable that the monitoring device 40 and each acquisition device 30 are equipped with only one or more antennas that transmit and receive radio waves with a plane of polarization in a predetermined direction corresponding to each device more strongly than radio waves with a plane of polarization in any direction other than the predetermined direction.

[0060] The monitoring device 40 is primarily equipped with an antenna that primarily transmits and receives radio waves with a vertically polarized plane (transmitting and receiving stronger signals than radio waves with any other polarization plane). It is desirable that the monitoring device 40 be equipped with only one or more antennas that primarily transmit and receive radio waves with a vertically polarized plane. As shown in FIGS. 22( a) to 22(e), an antenna 55 that transmits and receives radio waves with a vertically polarized plane is mounted on a circuit board 50 that performs wireless communication. The circuit board 50 has a ground plate 51 and a power supply portion 52 that supplies power to the antenna 55. The antenna 55 is formed in a linear shape. The antenna 55 has a specific portion 55a connected to the power supply portion 52 and a specific portion 55b connected to the ground plate 51. The specific portions 55a and 55b are mounted upright relative to the circuit board 50. The state of standing with respect to the circuit board 50 includes, for example, a state perpendicular to the circuit board 50 and a state shifted by several degrees from perpendicular to the circuit board 50. A ground plate 51 is present below the specific portions 55a and 55b. As shown in FIGS. 23(a) to 23(c), the antenna 55 that transmits and receives radio waves with a vertically polarized wave plane may be formed in a plate shape. In this case, the antenna 55 also has a specific portion 55a connected to the power feeder 52. The specific portion 55a is provided in a state of standing with respect to the circuit board 50. A ground plate (not shown) is present below the specific portion 55a. As shown in FIGS. 24(a) and 24(b), the antenna 55 that transmits and receives radio waves with a vertically polarized wave plane may be a zero-order resonant antenna including a plate-shaped portion and a rod-shaped (linear) portion. In this case, the antenna 55 also has a specific portion 55a connected to the power feeder 52 and a specific portion 55b connected to the ground plate 51. The specific portion 55b is provided in an upright position relative to the circuit board 50. That is, at least one of the specific portions 55a and 55b is provided in an upright position relative to the circuit board 50. The ground plate 51 is located below the specific portions 55a and 55b.

[0061] 1 to 3 , in the first propagation path S1, the polarization plane of vertical polarization (the polarization plane in a predetermined direction) is a polarization plane in which the cutoff frequency fv, which is determined based on the length of the front-rear direction Y (longitudinal direction) of the cross section of the first propagation path S1 where the base station antenna 46 is located, is lower than the communication frequency f0. Specifically, in the first propagation path S1, the cutoff frequency of radio waves generated by the vertical polarization plane (first polarization plane) is the first cutoff frequency f1, and the cutoff frequency of radio waves generated by the horizontal polarization plane (second polarization plane orthogonal to the first polarization plane) is the third cutoff frequency f3. Here, in the cross section of the first propagation path S1, the distance between the front and rear inner surfaces 10s of the housing 10 (the length in the front-rear direction Y) is longer than the distance between the inner upper surface 10u and the inner lower surface 10d of the housing 10 (the length in the up-down direction Z). Therefore, the first cutoff frequency f1 is lower than the third cutoff frequency f3 (f1<f3). The communication frequency f0 is higher than the first cutoff frequency f1 and the third cutoff frequency f3 (f1<f3<f0).

[0062] Each acquisition device 30 is mainly equipped with an antenna that mainly transmits and receives radio waves with a vertically polarized wave plane (transmits and receives radio waves with stronger polarization than radio waves with a polarization plane in any direction other than vertical polarization). It is desirable that each acquisition device 30 is equipped with only one or more antennas that mainly transmit and receive radio waves with a vertically polarized wave plane.

[0063] In the second propagation path S2, the polarization plane of vertical polarization (the polarization plane in a predetermined direction) is a polarization plane in which a cutoff frequency fv, which is determined based on the length of the cross section of the second propagation path S2 in the front-rear direction Y (longitudinal direction) where each slave antenna 36 is arranged, is lower than the communication frequency f0. Specifically, in the second propagation path S2, the cutoff frequency of radio waves generated by the vertically polarized wave polarization plane (first polarization plane) is the second cutoff frequency f2, and the cutoff frequency of radio waves generated by the horizontally polarized wave polarization plane (second polarization plane orthogonal to the first polarization plane) is the fourth cutoff frequency f4. Here, in the cross section of the second propagation path S2, the distance between the front and rear inner surfaces 10s of the housing 10 (the length in the front-rear direction Y) is longer than the distance between the inner upper surface 10u of the housing 10 and the outer upper surfaces 20u of the multiple battery packs 20 (the length in the up-down direction Z). Therefore, the second cutoff frequency f2 is lower than the fourth cutoff frequency f4 (f2<f4). The communication frequency f0 is higher than the second cutoff frequency f2 and lower than the fourth cutoff frequency f4 (f2<f0<f4).

[0064] That is, the polarization plane in the specified direction is a polarization plane in which the cutoff frequencies f1 and f2, which are respectively determined based on the longitudinal lengths of the cross sections of the propagation paths S1 and S2 in which the parent antenna 46 and each child antenna 36 are respectively arranged, are both lower than the communication frequency f0.

[0065] The present embodiment described above in detail has the following advantages.

[0066] The monitoring device 40 and each acquisition device 30 are primarily equipped with a master antenna 46 and each slave antenna 36, ​​respectively, that transmit and receive radio waves polarized in a predetermined direction more strongly than radio waves polarized in any direction other than the predetermined direction. Therefore, compared to a case in which the monitoring device 40 and each acquisition device 30 are equipped with multiple master antennas 46 and multiple slave antennas 36 that transmit and receive radio waves polarized in multiple directions, the number of master antennas 46 and each slave antenna 36 equipped in the monitoring device 40 and each acquisition device 30 can be minimized. The polarization in the predetermined direction is a polarization whose cutoff frequency, determined based on the longitudinal length of the cross section of the propagation path S1, S2 in which the master antenna 46 and each slave antenna 36 are respectively disposed, is lower than the communication frequency f0. Therefore, when wireless communication is performed using radio waves polarized in the predetermined direction, the cutoff frequency is lower than the communication frequency f0 in both the monitoring device 40 and each acquisition device 30, thereby suppressing propagation loss. This can improve the reliability of communication in the battery system 101. In particular, when the monitoring device 40 and each acquisition device 30 are each provided with only a master antenna 46 and each slave antenna 36 that transmit and receive radio waves with a plane of polarization in a predetermined direction corresponding to the respective acquisition device 30 more strongly than radio waves with a plane of polarization in any direction different from the predetermined direction, the number of master antennas 46 and each slave antenna 36 can be reduced to the minimum required.

[0067] In the first propagation path S1, the communication frequency f0 is higher than the first cutoff frequency f1, which is the cutoff frequency of radio waves in the first polarization plane, and the third cutoff frequency f3, which is the cutoff frequency of radio waves in the second polarization plane. Therefore, in the first propagation path S1, propagation loss can be suppressed regardless of whether radio waves in the first polarization plane or the second polarization plane are used. On the other hand, in the second propagation path S2, the communication frequency f0 is higher than the second cutoff frequency f2, which is the cutoff frequency of radio waves in the first polarization plane, and lower than the fourth cutoff frequency f4, which is the cutoff frequency of radio waves in the second polarization plane. Therefore, in the second propagation path S2, propagation loss can be suppressed when radio waves in the first polarization plane are used, but propagation loss increases when radio waves in the second polarization plane are used. In this regard, the polarization plane in the predetermined direction is the first polarization plane. Therefore, even if the monitoring device 40 and each acquisition device 30 are mainly equipped with a parent antenna 46 and each child antenna 36, ​​which transmit and receive radio waves mainly in the first polarization plane, a decrease in communication reliability can be suppressed.

[0068] In a configuration in which the monitoring device 40 and each acquisition device 30 are primarily equipped with a parent antenna 46 and each child antenna 36 that transmit and receive radio waves primarily in the polarization plane of vertical polarization (first polarization plane), it is possible to prevent a decrease in communication reliability.

[0069] By wirelessly connecting the monitoring device 40 and each acquisition device 30, not only can the process of reusing the battery pack 20 be simplified compared to when the monitoring device 40 and each acquisition device 30 are connected via a wire, but the number of parts can also be reduced and the work of handling high voltage can be reduced.

[0070] The first embodiment can be modified as follows: The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be incorporated herein.

[0071] As shown in the plan view of FIG. 5 , the battery packs 20 may be formed in a rectangular parallelepiped shape and arranged side by side in the front-rear direction Y. Also, as shown in the plan view of FIG. 6 , the battery packs 20 may be formed in a rectangular parallelepiped shape and arranged side by side in the left-right direction X and the front-rear direction Y. In these cases, the first propagation path S1 and the second propagation path S2 are configured similarly to the first propagation path S1 and the second propagation path S2 of the first embodiment. The master antenna 46 is disposed on the first propagation path S1, and the slave antenna 36 is disposed on the second propagation path S2. The monitoring device 40 and each acquisition device 30 are each primarily equipped with the master antenna 46 and each slave antenna 36 that transmit and receive radio waves primarily in a vertically polarized plane (first polarization plane). Even with this configuration, the same effects as those of the first embodiment can be achieved.

[0072] Second Embodiment The following describes a second embodiment, focusing on differences from the first embodiment. In the second embodiment, each acquisition device 30 is installed on the outer surface of each battery pack 20. Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be incorporated herein.

[0073] Fig. 7 is a plan view of the battery system 101, Fig. 8 is a cross-sectional view taken along line VIII-VIII in Fig. 7, and Fig. 9 is a cross-sectional view taken along line IX-IX in Fig. 7. Note that the top wall of the housing 10 is not shown in Fig. 7.

[0074] A plurality of acquisition devices 30 (second wireless communication devices, wireless communication devices) are installed for each battery pack 20. Specifically, each acquisition device 30 is installed on the outer surface 20s of the corresponding battery pack 20.

[0075] The monitoring device 40 (first wireless communication device, wireless communication device) is arranged in the same manner as the monitoring device 40 of the first embodiment. However, in this embodiment, the base unit antenna 46 of the monitoring device 40 is different from the base unit antenna 46 of the monitoring device 40 of the first embodiment, as will be described later.

[0076] The housing 10 is the same as the housing 10 of the first embodiment. The first propagation path S1 is the same as the first propagation path S1 of the first embodiment.

[0077] A second propagation path S2, which is a propagation path for radio waves, is formed between the outer surface 20s of the battery pack 20 and the front inner surface 10s of the housing 10. The second propagation path S2 is a passage surrounded three-dimensionally by a conductive material. Specifically, in this embodiment, the second propagation path S2 is formed by the inner upper surface 10u and inner lower surface 10d of the housing 10, the front outer surface 20s of the plurality of battery packs 20, and the front inner surface 10s of the housing 10. The cross-sectional dimension of the second propagation path S2 is smallest in the front-to-rear direction Y among the three-dimensional directions. In other words, the distance between the inner upper surface 10u and inner lower surface 10d of the housing 10 is longer than the distance between the front outer surface 20s of the battery pack 20 and the front inner surface 10s of the housing 10.

[0078] Each acquisition device 30 is attached within the housing 10, for example, at the middle of the outer surface 20s of each battery pack 20 in the left-right direction X. Each slave antenna 36 is provided, for example, on the side surface of the corresponding acquisition device 30. As a result, each slave antenna 36 is installed (placed) within the second propagation path S2. Note that the vertical position at which each acquisition device 30 is installed within the second propagation path S2 and the horizontal position at which each acquisition device 30 is installed within the outer surface 20s of each battery pack 20 are arbitrary.

[0079] As described above, the master antenna 46 and the slave antenna 36 are respectively disposed on the propagation paths S1 and S2 formed between the housing 10 and the plurality of battery packs 20. In the present embodiment as well, in wireless communication between the monitoring device 40 and the plurality of acquisition devices 30, the propagation paths S1 and S2 can be considered to be similar to wave guides for radio waves.

[0080] Therefore, the monitoring device 40 and each acquisition device 30 are mainly equipped with antennas that transmit and receive radio waves with a plane of polarization in a predetermined direction corresponding to each device more strongly than radio waves with a plane of polarization in any direction other than the predetermined direction. It is desirable that the monitoring device 40 and each acquisition device 30 are equipped with only one or more antennas that transmit and receive radio waves with a plane of polarization in a predetermined direction corresponding to each device more strongly than radio waves with a plane of polarization in any direction other than the predetermined direction.

[0081] In this embodiment, the monitoring device 40 is primarily equipped with an antenna that primarily transmits and receives radio waves with a horizontally polarized plane (which transmits and receives stronger radio waves than radio waves with any other polarization plane other than horizontal polarization). It is desirable that the monitoring device 40 be equipped with only one or more antennas that primarily transmit and receive radio waves with a horizontally polarized plane. In the first propagation path S1, the cutoff frequency of radio waves with a vertically polarized plane (first polarization plane) is a first cutoff frequency f1, and the cutoff frequency of radio waves with a horizontally polarized plane (second polarization plane orthogonal to the first polarization plane) is a third cutoff frequency f3. The communication frequency f0 is higher than the first cutoff frequency f1 and the third cutoff frequency f3 (f1<f3<f0).

[0082] Each acquisition device 30 is primarily equipped with an antenna that primarily transmits and receives horizontally polarized radio waves (transmitting and receiving radio waves more strongly than radio waves polarized in any direction other than horizontal polarization). It is desirable that each acquisition device 30 be equipped with only one or more antennas that primarily transmit and receive horizontally polarized radio waves. As shown in FIGS. 25 and 26 , an antenna 65 that transmits and receives horizontally polarized radio waves is mounted on a circuit board 60 that performs wireless communication. The circuit board 60 includes a ground plate 61 and a power supply unit 62 that supplies power to the antenna 65. The antenna 65 is formed in a plate shape. The antenna 65 includes a specific portion 65a connected to the power supply unit 62 or a specific portion 65b connected to the ground plate 61. The specific portions 65a and 65b are arranged along the circuit board 60. The "along the circuit board 60" state includes, for example, a state parallel to the circuit board 60 and a state offset by several degrees from parallel to the circuit board 60. The ground plate 61 does not exist below the predetermined portions 65a and 65b.

[0083] 7 to 9 , in the second propagation path S2, the polarization plane of the horizontally polarized wave (the polarization plane in a predetermined direction) is a polarization plane in which the cutoff frequency fv, which is determined based on the length in the vertical direction Z (longitudinal direction) of the cross section of the second propagation path S2 where each slave antenna 36 is arranged, is lower than the communication frequency f0. Specifically, in the second propagation path S2, the cutoff frequency of the radio wave generated by the vertically polarized wave (first polarization plane) is the second cutoff frequency f2, and the cutoff frequency of the radio wave generated by the horizontally polarized wave (second polarization plane orthogonal to the first polarization plane) is the fourth cutoff frequency f4. Here, in the cross section of the second propagation path S2, the distance between the inner upper surface 10u and the inner lower surface 10d of the housing 10 (the length in the vertical direction Z) is longer than the distance between the front outer surface 20s of each of the plurality of battery packs 20 and the front inner surface 10s of the housing 10 (the length in the front-rear direction Y). Therefore, the fourth cutoff frequency f4 is lower than the second cutoff frequency f2 (f4<f2), and the communication frequency f0 is higher than the fourth cutoff frequency f4 and lower than the second cutoff frequency f2 (f4<f0<f2).

[0084] That is, the plane of polarization in the predetermined direction is a plane of polarization in which cutoff frequencies f1 and f4, which are respectively defined based on the longitudinal lengths of the cross sections of the propagation paths S1 and S2 in which the master antenna 46 and each slave antenna 36 are arranged, are both lower than the communication frequency f0. Furthermore, the plane of polarization in the predetermined direction is a plane of polarization in which a third cutoff frequency f3, which is defined based on the shorter length of the cross section of the first propagation path S1, is lower than the communication frequency f0.

[0085] The present embodiment described above in detail has the following advantages.

[0086] In the first propagation path S1, the communication frequency f0 is higher than the first cutoff frequency f1, which is the cutoff frequency of radio waves in the first polarization plane, and the third cutoff frequency f3, which is the cutoff frequency of radio waves in the second polarization plane. Therefore, in the first propagation path S1, propagation loss can be suppressed regardless of whether radio waves in the first polarization plane or the second polarization plane are used. On the other hand, in the second propagation path S2, the communication frequency f0 is lower than the second cutoff frequency f2, which is the cutoff frequency of radio waves in the first polarization plane, and higher than the fourth cutoff frequency f4, which is the cutoff frequency of radio waves in the second polarization plane. Therefore, in the second propagation path S2, propagation loss increases when radio waves in the first polarization plane are used, but propagation loss can be suppressed when radio waves in the second polarization plane are used. In this regard, the polarization plane in the predetermined direction is the second polarization plane. Therefore, even if each acquisition device 30 is mainly equipped with each slave antenna 36 that transmits and receives radio waves mainly in the second polarization plane, it is possible to prevent a decrease in communication reliability.

[0087] - In a configuration in which the monitoring device 40 and each acquisition device 30 are mainly equipped with a parent device antenna 46 and each child device antenna 36, ​​which transmit and receive radio waves mainly in the horizontally polarized polarization plane (second polarization plane), it is possible to prevent a decrease in communication reliability.

[0088] The second embodiment can be modified as follows: The same parts as those in the second embodiment are denoted by the same reference numerals, and the description thereof will be incorporated herein.

[0089] As shown in the plan view of FIG. 10 , acquisition devices 30 may be installed on the front outer surface 20s and the rear outer surface 20s of each battery pack 20. In this case, the first propagation path S1 and the second propagation path S2 are configured similarly to the first propagation path S1 and the second propagation path S2 of the second embodiment. Specifically, the front second propagation path S2 is configured by the inner upper surface 10u and the inner lower surface 10d of the housing 10, the front outer surface 20s of the multiple battery packs 20, and the front inner surface 10s of the housing 10. The rear second propagation path S2 is configured by the inner upper surface 10u and the inner lower surface 10d of the housing 10, the rear outer surface 20s of the multiple battery packs 20, and the rear inner surface 10s of the housing 10. The master antenna 46 is arranged on the first propagation path S1, and the slave antenna 36 is arranged on the second propagation path S2. The monitoring device 40 and each acquisition device 30 mainly include a master antenna 46 and each slave antenna 36, ​​which transmit and receive radio waves mainly in the horizontally polarized wave plane (second polarization plane). With this configuration, the same effects as those of the second embodiment can be achieved.

[0090] As shown in the plan view of FIG. 11 , the battery packs 20 may be formed in a rectangular parallelepiped shape and arranged side by side in the front-rear direction Y. Each acquisition device 30 may be installed on the right outer surface 20s of each battery pack 20. In this case, the first propagation path S1 is configured similarly to the first propagation path S1 of the second embodiment. The second propagation path S2 is configured by the inner upper surface 10u and inner lower surface 10d of the housing 10, the right outer surface 20s of the battery packs 20, and the right inner surface 10s of the housing 10. In the cross section of the second propagation path S2, the distance between the inner upper surface 10u and inner lower surface 10d of the housing 10 (length in the vertical direction Z) is longer than the distance between the right outer surface 20s of the battery packs 20 and the right inner surface 10s of the housing 10 (length in the horizontal direction X). Therefore, the fourth cutoff frequency f4 is lower than the second cutoff frequency f2 (f4<f2). The communication frequency f0 is higher than the fourth cutoff frequency f4 and lower than the second cutoff frequency f2 (f4<f0<f2). The master antenna 46 is disposed on the first propagation path S1, and the slave antenna 36 is disposed on the second propagation path S2. The monitoring device 40 and each acquisition device 30 are respectively equipped with the master antenna 46 and each slave antenna 36, ​​which transmit and receive radio waves primarily in the polarization plane of horizontal polarization (second polarization plane). This configuration can also achieve the same effects as the second embodiment.

[0091] As shown in the plan view of FIG. 12 , the battery packs 20 may be formed in a rectangular parallelepiped shape and arranged side by side in the left-right direction X and the front-back direction Y. Each acquisition device 30 may be installed on the left outer surface 20s of each battery pack 20. In this case, the first propagation path S1 is configured similarly to the first propagation path S1 of the second embodiment. The second propagation path S2 is configured by the inner upper surface 10u and the inner lower surface 10d of the housing 10 and the left and right outer surfaces 20s of the battery packs 20. In the cross section of the second propagation path S2, the distance between the inner upper surface 10u and the inner lower surface 10d of the housing 10 (length in the vertical direction Z) is longer than the distance between the left and right outer surfaces 20s of the battery packs 20 (length in the horizontal direction X). Therefore, the fourth cutoff frequency f4 is lower than the second cutoff frequency f2 (f4<f2). The communication frequency f0 is higher than the fourth cutoff frequency f4 and lower than the second cutoff frequency f2 (f4<f0<f2). The master antenna 46 is disposed on the first propagation path S1, and some of the multiple slave antennas 36 are disposed on the second propagation path S2. The monitoring device 40 and each acquisition device 30 mainly include the master antenna 46 and each slave antenna 36, ​​which transmit and receive radio waves mainly in the polarization plane of horizontal polarization (second polarization plane). Even with this configuration, it is possible to achieve the same effects as in the second embodiment.

[0092] As shown in FIGS. 27 and 28 , the monitoring device 40 may include a circuit board 60 including an antenna 65 (corresponding to the parent antenna 46) and a power supply unit 62. As shown in FIG. 27 , the power supply unit 62 may be provided on the front side of the circuit board 60, or as shown in FIG. 28 , the power supply unit 62 may be provided on the back side of the circuit board 60. The antenna 65 (circuit board 60) may be disposed at an angle with respect to the horizontal plane. In this case, the monitoring device 40 primarily transmits and receives radio waves with an obliquely polarized plane. Similarly, each acquisition device 30 primarily transmits and receives radio waves with an obliquely polarized plane. That is, as described above, the battery system 101 can be installed in any orientation. Even in this case, the monitoring device 40 and each acquisition device 30 primarily include a parent antenna 46 and each child antenna 36 that transmit and receive radio waves with a polarization plane corresponding to a respective predetermined direction more strongly than radio waves with a polarization plane other than the predetermined direction. The polarization plane in the specified direction may be a polarization plane in which the cutoff frequencies, which are determined based on the longitudinal lengths of the cross sections of the propagation paths S1 and S2 in which the parent unit antenna 46 and each child unit antenna 36 are respectively arranged, are both lower than the communication frequency f0.

[0093] 29 and 30 , the monitoring device 40 may include a circuit board 60 including an antenna 65 (corresponding to the master antenna 46) and a power supply unit 62. The antenna 65 primarily transmits and receives circularly polarized radio waves. As shown in FIG. 29 , one power supply unit 62 may be provided on the rear surface of the circuit board 60, or as shown in FIG. 30 , two power supply units 62 may be provided on the rear surface of the circuit board 60. Note that the power supply method may be electromagnetic coupling. Similarly, each acquisition device 30 includes an antenna 65 that primarily transmits and receives circularly polarized radio waves. Even in this case, the monitoring device 40 and each acquisition device 30 primarily include a master antenna 46 and each slave antenna 36 that transmit and receive radio waves polarized in a predetermined direction more strongly than radio waves polarized in any direction other than the predetermined direction. The polarization plane in the specified direction may be a polarization plane in which the cutoff frequencies, which are determined based on the longitudinal lengths of the cross sections of the propagation paths S1 and S2 in which the parent unit antenna 46 and each child unit antenna 36 are respectively arranged, are both lower than the communication frequency f0.

[0094] [Third Embodiment] The following describes the third embodiment, focusing on the differences from the second embodiment. In the third embodiment, a predetermined propagation path exists between the master antenna 46 and each slave antenna 36, ​​which is a propagation path that causes polarization rotation in the radio waves transmitted from the master antenna 46 and the slave antenna 36. Note that the same parts as in the second embodiment are denoted by the same reference numerals, and the description thereof will be incorporated herein.

[0095] Fig. 13 is a plan view of the battery system 101, Fig. 14 is a cross-sectional view taken along line XIV-XIV in Fig. 13, and Fig. 15 is a cross-sectional view taken along line XV-XV in Fig. 13. Note that the top wall of the housing 10 is not shown in Fig. 13.

[0096] The multiple acquisition devices 30 (second wireless communication device, wireless communication device) are similar to the multiple acquisition devices 30 of the second embodiment.

[0097] The monitoring device 40 (first wireless communication device, wireless communication device) is arranged in the same manner as the monitoring device 40 of the first embodiment. However, in this embodiment, the master antenna 46 of the monitoring device 40 is a master antenna 46 that takes into account the polarization rotation of radio waves, as will be described later.

[0098] The housing 10 is the same as the housing 10 of the first embodiment. The first propagation path S1 is the same as the first propagation path S1 of the second embodiment. The second propagation path S2 is the same as the second propagation path S2 of the second embodiment.

[0099] Between the master unit antenna 46 and each slave unit antenna 36, ​​there exists a predetermined propagation path that causes polarization rotation in the radio waves transmitted from the master unit antenna 46 and each slave unit antenna 36. The predetermined propagation path includes a third propagation path S3 that is configured by the inner upper surface 10u of the housing 10, the outer upper surfaces 20u of the plurality of battery packs 20, and the front and rear inner surfaces 10s (a pair of inner surfaces) of the housing 10. In the third propagation path S3, the distance between the inner upper surface 10u of the housing 10 and the outer upper surface 20u of the battery pack 20 is shorter than the distance between the front and rear inner surfaces 10s of the housing 10.

[0100] In this case, for example, radio waves transmitted from the parent device antenna 46 travel from the first propagation path S1 to the third propagation path S3 and then reach each child device antenna 36 in the second propagation path S2. At this time, for example, the radio waves transmitted from the parent device antenna 46 with the second polarization plane may be subjected to polarization rotation by the predetermined propagation path, and may be changed to radio waves with the first polarization plane at the position of the child device antenna 36.

[0101] Here, in the first propagation path S1, the communication frequency f0 is higher than the first cutoff frequency f1, which is the cutoff frequency for radio waves in the first polarization plane, and the third cutoff frequency f3, which is the cutoff frequency for radio waves in the second polarization plane. Therefore, at the location of the master antenna 46, propagation loss can be suppressed regardless of whether radio waves in the first polarization plane or the second polarization plane are used. On the other hand, in the second propagation path S2, the communication frequency f0 is lower than the second cutoff frequency f2, which is the cutoff frequency for radio waves in the first polarization plane, and higher than the fourth cutoff frequency f4, which is the cutoff frequency for radio waves in the second polarization plane. Therefore, at the location of the slave antenna 36, ​​propagation loss increases when radio waves in the first polarization plane are used, but propagation loss can be suppressed when radio waves in the second polarization plane are used.

[0102] In this regard, the direction of the plane of polarization of the radio waves transmitted by the master antenna 46 is selected so that the plane of polarization in a predetermined direction becomes the plane of polarization of horizontally polarized waves (second plane of polarization) at the position of the slave antenna 36. In other words, the monitoring device 40 mainly includes a master antenna 46 that mainly transmits and receives radio waves that become radio waves with a plane of polarization of horizontally polarized waves at the position of the slave antenna 36. It is desirable that the monitoring device 40 only includes one or more master antennas 46 that mainly transmit and receive radio waves that become radio waves with a plane of polarization of horizontally polarized waves at the position of the slave antenna 36.

[0103] Each acquisition device 30 is mainly equipped with an antenna that mainly transmits and receives radio waves with a horizontally polarized wave plane (transmits and receives radio waves with a stronger polarization plane than radio waves with a polarization plane in any direction other than horizontal polarization). It is desirable that each acquisition device 30 is equipped with only one or more antennas that mainly transmit and receive radio waves with a horizontally polarized wave plane.

[0104] The present embodiment described above in detail has the following advantages.

[0105] The plane of polarization in the predetermined direction is the second plane of polarization at the position of each slave antenna 36. Therefore, even if the monitoring device 40 and each acquisition device 30 are mainly equipped with the master antenna 46 and each slave antenna 36 that transmit and receive radio waves with a plane of polarization in a predetermined direction corresponding to each of them more strongly than radio waves with a plane of polarization in any direction other than the predetermined direction, it is possible to prevent a decrease in communication reliability.

[0106] The monitoring device 40 mainly includes a master antenna 46 that mainly transmits and receives radio waves with a horizontally polarized wave plane at the position of the slave antenna 36. Each acquisition device 30 mainly includes a slave antenna 36 that mainly transmits and receives radio waves with a horizontally polarized wave plane (second polarization plane). In this configuration, a decrease in communication reliability can be suppressed.

[0107] The first to third embodiments and their modifications can also be implemented with the following modifications. The same parts as those in the first to third embodiments are denoted by the same reference numerals, and the description thereof will be incorporated herein.

[0108] The configurations shown in FIGS. 13 to 15 can also be modified as shown in FIG. 31 . In this case, each acquisition device 30 is attached to the outer surface 20s of each battery pack 20 within the housing 10, protruding above the upper end in the vertical direction Z. As a result, the portion of each slave antenna 36 that transmits and receives radio waves is substantially located within the second propagation path S2A. Therefore, similar to the first embodiment, the monitoring device 40 and each acquisition device 30 mainly include a master antenna 46 and each slave antenna 36 that transmit and receive radio waves primarily in the polarization plane of vertical polarization (first polarization plane). In other words, the propagation path in which the master antenna 46 and each slave antenna 36 (antennas) are respectively located is the propagation path in which the portions of the master antenna 46 and each slave antenna 36 that transmit and receive radio waves are substantially located.

[0109] As shown in the plan view of FIG. 16 , the housing 10 may have a box-like shape with a corner removed (chamfered) on the left side (one side). As shown in the plan view of FIG. 17 , the housing 10 may have a box-like shape with corners removed on the left and right sides (both sides). As shown in the plan view of FIG. 18 , the housing 10 may have a box-like shape with a first section 10A and a second section 10B. The first section 10A is larger than the second section 10B. The left corner of the second section 10B (opposite the first section 10A) may be removed. Even in these cases, the monitoring device 40 and each acquisition device 30 each primarily include a master antenna 46 and each slave antenna 36 that transmit and receive radio waves polarized in a predetermined direction more strongly than radio waves polarized in any direction other than the predetermined direction. The polarization plane in the specified direction may be a polarization plane in which the cutoff frequencies, which are determined based on the longitudinal length of the cross section of the propagation path in which the parent antenna 46 and each child antenna 36 are respectively arranged, are all lower than the communication frequency f0.

[0110] The monitoring device 40 may include a circuit board 60 and a bracket 67 as shown in FIG. 32 . The circuit board 60 has an antenna 65, a ground plate 61, and a power supply unit 62 that supplies power to the antenna 65. The bracket 67 forms a third propagation path S3A around the antenna 65 (corresponding to the parent device antenna 46). The third propagation path S3A (predetermined propagation path) causes polarization rotation in the radio waves transmitted from the parent device antenna 46 and the child device antenna 36. For example, in the case of FIGS. 1 to 3 (first embodiment), the monitoring device 40 transmits radio waves with a horizontally polarized plane from the antenna 65 (parent device antenna 46), and the radio waves are polarized and rotated by the third propagation path S3A to become radio waves with a vertically polarized plane, which are then received by each acquisition device 30. Each acquisition device 30 transmits radio waves with a vertically polarized plane of polarization, and these radio waves are polarized and rotated by the third propagation path S3A to become radio waves with a horizontally polarized plane of polarization, which are received by the monitoring device 40. Also, in the case of Figures 7 to 9 (second embodiment), for example, the monitoring device 40 transmits radio waves with a vertically polarized plane of polarization from the antenna 65 (master antenna 46), and these radio waves are polarized and rotated by the third propagation path S3A to become radio waves with a horizontally polarized plane of polarization, which are received by each acquisition device 30. Each acquisition device 30 transmits radio waves with a horizontally polarized plane of polarization, and these radio waves are polarized and rotated by the third propagation path S3A to become radio waves with a vertically polarized plane of polarization, which are received by the monitoring device 40. Even in these cases, the cutoff frequencies defined based on the longitudinal lengths of the cross sections of the first propagation path S1 and the second propagation path S2 on which the antenna 46 of the monitoring device 40 and the antenna 36 of each acquisition device 30 are respectively arranged are both lower than the communication frequency f0 (predetermined communication frequency). Therefore, the same effects as those of the first and second embodiments can be achieved.

[0111] As shown in the side view of FIG. 19 , the multiple battery packs 20 may be formed in a rectangular parallelepiped shape and arranged side by side in the left-right direction X and the up-down direction Z. Note that the side walls of the housing 10 are not shown in the battery system 102 shown in FIG. 19 . The monitoring device 40 may be attached to the outer surface 20s of one of the battery packs 20, and each acquisition device 30 may be attached to the outer surface 20s of each battery pack 20. In wireless communication between the monitoring device 40 and the multiple acquisition devices 30, radio waves may pass through a fourth propagation path S4 between the first propagation path S1 and the second propagation path S2. The fourth propagation path S4 has a cross-sectional length that is short enough to affect the ease of radio wave propagation. In this case, the polarization plane of the radio waves transmitted from the master antenna 46 and each slave antenna 36 needs to be a polarization plane in which the cutoff frequency, defined based on the longitudinal length of the cross section of the fourth propagation path S4, is lower than the communication frequency f0.

[0112] As shown in the plan view of FIG. 20 , the multiple battery packs 20 may be formed in a rectangular parallelepiped shape and arranged side by side in the left-right direction X and the up-down direction Z. Note that the top wall of the housing 10 is not shown in the battery system 102 shown in FIG. 20 . The battery packs 20 are stacked two levels high and low on the right side of the housing 10. The monitoring device 40 is attached to the front outer surface of the front-right battery pack 20. In the portion with one level of battery packs 20, each acquisition device 30 is attached to the outer surface of the center of each battery pack 20 in the front-to-back direction Y. In the portion with two levels of battery packs 20, each acquisition device 30 is attached to the left outer surface of each battery pack 20. Even in this case, the monitoring device 40 and each acquisition device 30 mainly include a master antenna 46 and each slave antenna 36 that transmit and receive radio waves polarized in a predetermined direction more strongly than radio waves polarized in any direction other than the predetermined direction. The polarization plane in the specified direction may be a polarization plane in which the cutoff frequencies, which are determined based on the longitudinal lengths of the cross sections of the propagation paths S1 and S2 in which the parent unit antenna 46 and each child unit antenna 36 are respectively arranged, are both lower than the communication frequency f0.

[0113] As shown in the plan view of FIG. 21 , the multiple battery packs 20 may be formed in a rectangular parallelepiped shape and arranged side by side in the left-right direction X and the front-rear direction Y. In the battery system 103 shown in FIG. 21 , the top wall of the housing 10 is not shown. The foot space F is a space outside the housing 10 where the vehicle driver places his or her feet. The monitoring device 40 and the multiple battery packs 20 are attached to the outer upper surface 20u of the battery pack 20. During wireless communication between the monitoring device 40 and the multiple acquisition devices 30, radio waves may pass through a fourth propagation path S4 between the first propagation path S1 and the second propagation path S2. The fourth propagation path S4 has a cross-sectional length that is short enough to affect the ease of radio wave propagation. In this case, the polarization plane of the radio waves transmitted from the master antenna 46 and each slave antenna 36 needs to be a polarization plane in which the cutoff frequency, defined based on the longitudinal length of the cross section of the fourth propagation path S4, is lower than the communication frequency f0.

[0114] 31 , a monitoring device 40 (first wireless communication device) and a plurality of acquisition devices 30 (second wireless communication device) may be configured to perform mesh communication. Furthermore, the plurality of wireless communication devices arranged in the propagation path formed between the housing 10 and the plurality of battery packs 20 may be wireless communication devices used for purposes other than the monitoring device 40 and the acquisition device 30. In this case, the plurality of wireless communication devices may not be distinguished as a parent device (master) and a child device (slave).

[0115] The housing 10 may be made of a conductive material other than metal, such as conductive plastic, etc. Also, as shown in Fig. 34, the housing 10 may have an outer layer 11 made of a non-conductive material such as resin, and an inner layer 12 made of a conductive material such as metal plating.

[0116] The above-described embodiments and their modifications can be combined within the scope of possible combinations.

[0117] Furthermore, various technical matters are disclosed in the above-described embodiments and their modifications. Therefore, for example, some of the technical matters disclosed in the above-described embodiments and their modifications may be appropriately added and applied to a wireless communication system 101, 102, or 103 including a housing 10, multiple battery packs 20 disposed within the housing, and multiple wireless communication devices 40, 30 having antennas 46, 36, 55, and 65 for transmitting and receiving radio waves and performing wireless communication with each other using radio waves at a predetermined communication frequency. In this case, depending on the technical matters to be applied, an antenna other than the antenna described in the above-described embodiments and their modifications, such as an omnidirectional antenna, may be used. Furthermore, any technical matters may be appropriately combined, or specific technical matters may be appropriately excluded.

[0118] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A wireless communication system (101, 102, 103) comprising: a housing (10) made of a conductive material; a plurality of battery packs (20) arranged inside the housing and having surfaces made of a conductive material; and a plurality of wireless communication devices (40, 30) each having an antenna (46, 36, 55, 65) for transmitting and receiving radio waves, the antenna being arranged in a propagation path (S2, S1) formed between the housing and the plurality of battery packs, and performing wireless communication with each other using radio waves of a predetermined communication frequency, wherein the plurality of wireless communication devices mainly comprise antennas for transmitting and receiving radio waves with a polarization plane in a respective predetermined direction more strongly than radio waves with a polarization plane in any direction different from the predetermined direction, and the polarization plane in the predetermined direction is a polarization plane in which the cutoff frequencies, each of which is determined based on the longitudinal length of a cross section of the propagation path in which the antennas of the plurality of wireless communication devices are respectively arranged, are all lower than the predetermined communication frequency.

2. The wireless communication system according to claim 1, comprising a first wireless communication device (40) and a second wireless communication device (30) which are a plurality of wireless communication devices which wirelessly communicate with each other, the antenna (46) of the first wireless communication device being arranged on a first propagation path (S1) which is the propagation path in which the cutoff frequencies of radio waves due to a first polarization plane and a second polarization plane which are orthogonal to each other are a first cutoff frequency and a third cutoff frequency, respectively, the antenna (36) of the second wireless communication device being arranged on a second propagation path (S2) which is the propagation path in which the cutoff frequencies of radio waves due to the first polarization plane and the second polarization plane are a second cutoff frequency and a fourth cutoff frequency, respectively, the specified communication frequency being higher than the first cutoff frequency and the third cutoff frequency, and higher than the second cutoff frequency and lower than the fourth cutoff frequency, and the specified direction polarization plane being the first polarization plane.

3. The wireless communication system described in claim 2, wherein the first propagation path is composed of the inner upper surface (10u), the inner lower surface (10d), and a pair of inner side surfaces (10s) of the housing, and the distance between the inner upper surface and the inner lower surface is shorter than the distance between the pair of inner side surfaces; the second propagation path is composed of the inner upper surface of the housing, the outer upper surfaces (20u) of the multiple battery packs, and a pair of inner side surfaces of the housing, and the distance between the inner upper surface and the outer upper surface is shorter than the distance between the pair of inner side surfaces; the first polarization plane is a polarization plane of vertical polarization; and the second polarization plane is a polarization plane of horizontal polarization.

4. The wireless communication system according to claim 1, comprising a first wireless communication device (40) and a second wireless communication device (30) which are a plurality of wireless communication devices which wirelessly communicate with each other, the antenna (46) of the first wireless communication device being arranged on a first propagation path (S1) which is the propagation path in which the cutoff frequencies of radio waves due to a first polarization plane and a second polarization plane which are orthogonal to each other are a first cutoff frequency and a third cutoff frequency, respectively, the antenna (36) of the second wireless communication device being arranged on a second propagation path (S2) which is the propagation path in which the cutoff frequencies of radio waves due to the first polarization plane and the second polarization plane are a second cutoff frequency and a fourth cutoff frequency, respectively, the specified communication frequency being higher than the first cutoff frequency and the third cutoff frequency, lower than the second cutoff frequency and higher than the fourth cutoff frequency, and the polarization plane in the specified direction being the second polarization plane.

5. The wireless communication system described in claim 4, wherein the first propagation path is composed of an inner upper surface (10u), an inner lower surface (10d), and a pair of inner side surfaces (10s) of the housing, and the distance between the inner upper surface and the inner lower surface is shorter than the distance between the pair of inner side surfaces; the second propagation path is composed of an inner upper surface and an inner lower surface of the housing, outer surfaces (20s) of the multiple battery packs, and an inner side surface of the housing, and the distance between the inner upper surface and the inner lower surface is longer than the distance between the outer side surfaces and the inner side surfaces; the first polarization plane is a polarization plane of vertical polarization; and the second polarization plane is a polarization plane of horizontal polarization.

6. A radio communication system comprising a first radio communication device (40) and a second radio communication device (30) which are a plurality of radio communication devices which perform radio communication with each other, wherein the antenna (46) of the first radio communication device is disposed on a first propagation path (S1) which is the propagation path in which the cutoff frequencies of radio waves due to a first polarization plane and a second polarization plane which are orthogonal to each other are a first cutoff frequency and a third cutoff frequency, respectively, and the antenna (36) of the second radio communication device is disposed on a second propagation path (S2) which is the propagation path in which the cutoff frequencies of radio waves due to the first polarization plane and the second polarization plane are a second cutoff frequency and a fourth cutoff frequency, respectively, wherein a predetermined propagation path which is the propagation path which causes polarization rotation in radio waves transmitted from the antenna of the first radio communication device and the antenna of the second radio communication device exists between the antenna of the first radio communication device and the antenna of the second radio communication device, and the predetermined communication frequency is higher than the first cutoff frequency and the third cutoff frequency, lower than the second cutoff frequency and higher than the fourth cutoff frequency, 2. The wireless communication system according to claim 1, wherein the plane of polarization in the predetermined direction at the position of the antenna of the second wireless communication device is the second plane of polarization.

7. The wireless communication system described in claim 6, wherein the first propagation path is composed of the inner upper surface (10u), inner lower surface (10d), and a pair of inner side surfaces (10s) of the housing, and the distance between the inner upper surface and the inner lower surface is shorter than the distance between the pair of inner side surfaces; the specified propagation path includes the propagation path (S3) composed of the inner upper surface of the housing, the outer upper surface (20u) of the multiple battery packs, and a pair of inner sides of the housing, and the distance between the inner upper surface and the outer upper surface is shorter than the distance between the pair of inner side surfaces; the second propagation path is composed of the inner upper and inner lower surfaces of the housing, the outer sides (20s) of the multiple battery packs, and the inner sides of the housing, and the distance between the inner upper surface and the inner lower surface is longer than the distance between the outer sides and the inner side surfaces; and at the position of the antenna of the second wireless communication device, the second polarization plane is a polarization plane of horizontal polarization.

8. A wireless communication system according to any one of claims 1 to 7, wherein the plurality of wireless communication devices are equipped only with antennas that transmit and receive radio waves with a plane of polarization in a respective predetermined direction more strongly than radio waves with a plane of polarization in any direction other than the predetermined direction.

9. A wireless communication system (101, 102, 103) comprising: a housing (10) made of a conductive material; a plurality of battery packs (20) arranged inside the housing and having surfaces made of a conductive material; and a first wireless communication device (40) and a second wireless communication device (30) each having an antenna (46, 36, 55, 65) for transmitting and receiving radio waves, the antenna being arranged on a propagation path (S2, S1) formed between the housing and the plurality of battery packs, the first wireless communication device (40) and the second wireless communication device (30) performing wireless communication with each other by radio waves of a predetermined communication frequency, wherein the antenna (46) of the first wireless communication device is arranged on a first propagation path (S1), which is the propagation path in which a cutoff frequency of radio waves due to a polarization plane of vertical polarization is a first cutoff frequency and a cutoff frequency of radio waves due to a polarization plane of horizontal polarization is a third cutoff frequency, the first propagation path is composed of an inner upper surface (10u), an inner lower surface (10d), and a pair of inner side surfaces (10s) of the housing, and a distance between the inner upper surface and the inner lower surface is shorter than a distance between the pair of inner side surfaces; the antenna (36) of the second wireless communication device is disposed on a second propagation path (S2), which is the propagation path in which a cutoff frequency of radio waves in a polarization plane of vertical polarization is a second cutoff frequency and a cutoff frequency of radio waves in a polarization plane of horizontal polarization is a fourth cutoff frequency; the second propagation path is composed of an inner upper surface of the housing, an outer upper surface (20u) of the plurality of battery packs, and a pair of inner side surfaces of the housing, and a distance between the inner upper surface and the outer upper surface is shorter than a distance between the pair of inner side surfaces; the specified communication frequency is higher than the first cutoff frequency and the third cutoff frequency, higher than the second cutoff frequency, and lower than the fourth cutoff frequency; A wireless communication system, in which the first wireless communication device and the second wireless communication device mainly include an antenna (55) that transmits and receives radio waves with a polarization plane of vertical polarization more strongly than radio waves with a polarization plane of any direction other than vertical polarization.

10. A wireless communication system as described in claim 9, wherein the first wireless communication device and the second wireless communication device are equipped only with an antenna that transmits and receives radio waves with a vertically polarized plane more strongly than radio waves with a polarization plane of any direction other than vertical polarization.

11. A wireless communication system (101, 102, 103) comprising: a housing (10) made of a conductive material; a plurality of battery packs (20) arranged inside the housing and having surfaces made of a conductive material; and a first wireless communication device (40) and a second wireless communication device (30) which have antennas (46, 36, 55, 65) for transmitting and receiving radio waves, the antennas being arranged on propagation paths (S2, S1) formed between the housing and the plurality of battery packs, and which wirelessly communicate with each other using radio waves of a predetermined communication frequency, wherein the antenna (46) of the first wireless communication device is arranged on a first propagation path (S1), which is the propagation path in which a cutoff frequency of radio waves due to a vertically polarized wave plane is a first cutoff frequency and a cutoff frequency of radio waves due to a horizontally polarized wave plane is a third cutoff frequency; the first propagation path is composed of an inner upper surface (10u), an inner lower surface (10d), and a pair of inner side surfaces (10s) of the housing, and a distance between the inner upper surface and the inner lower surface is shorter than a distance between the pair of inner side surfaces; the antenna (36) of the second wireless communication device is disposed on a second propagation path (S2), which is the propagation path in which a cutoff frequency of radio waves in a polarization plane of vertical polarization is a second cutoff frequency and a cutoff frequency of radio waves in a polarization plane of horizontal polarization is a fourth cutoff frequency; the second propagation path is composed of the inner upper surface and the inner lower surface of the housing, outer sides (20s) of the multiple battery packs, and the inner side surface of the housing, and a distance between the inner upper surface and the inner lower surface is longer than a distance between the outer side surface and the inner side surface; the specified communication frequency is higher than the first cutoff frequency and the third cutoff frequency, lower than the second cutoff frequency, and higher than the fourth cutoff frequency; A wireless communication system, in which the first wireless communication device and the second wireless communication device are mainly equipped with an antenna (65) that transmits and receives radio waves with a polarization plane of horizontal polarization more strongly than radio waves with a polarization plane of any direction other than horizontal polarization.

12. The wireless communication system according to claim 11, wherein the first wireless communication device and the second wireless communication device are equipped only with an antenna that transmits and receives radio waves with a horizontally polarized plane stronger than radio waves with a polarized plane of any direction other than horizontal polarization.

13. A wireless communication system as described in any one of claims 3, 5 and 9, wherein the antenna (55) for transmitting and receiving radio waves with the polarization plane of the vertical polarization is provided on a circuit board (50) that performs the wireless communication, and has at least one specified part (55a, 55b) connected to a power supply part (52) that supplies power to the antenna or a ground plate (51), at least one of the specified parts is provided in an upright position relative to the circuit board, and the ground plate is present below the specified part.

14. A wireless communication system as described in any one of claims 3, 5, 7 and 11, wherein the antenna (65) for transmitting and receiving radio waves with the horizontally polarized plane of polarization is provided on a circuit board (60) that performs the wireless communication, and has a specified portion (65a, 65b) connected to a power supply portion (62) that supplies power to the antenna or a ground plate (61), the specified portion is provided along the circuit board, and the ground plate is not present below the specified portion.

15. The wireless communication system according to any one of claims 1 to 7 and 9 to 12, wherein the wireless communication system is provided in a housing made of a conductive material and mounted on a hybrid vehicle or an electric vehicle.

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