JP5845821B2 - Antenna system for tire condition detection device - Google Patents

Description

  The present invention relates to a tire state detection device that measures and displays tire air pressure and the like.

  In order to allow drivers to quickly grasp tire pressure and other abnormalities while driving a car, in recent years, by mounting a wireless sensor incorporating a pressure sensor, antenna element, etc. in the tire, the tire pressure can be reduced. Systems that allow monitoring in the driver's seat are becoming popular. In this tire pressure monitoring system (TPMS), a detection signal such as tire pressure transmitted by a wireless sensor in a tire is received by an antenna mounted on the vehicle body side, and is transmitted to a display / control device via a communication device. It is supposed to be transmitted.

In general, the antenna on the vehicle body side is attached to a tire house or the like in the vicinity of each tire. This will be described with reference to FIG.
FIG. 12 is a diagram (conventional example 1) showing a part of the configuration of a conventional tire pressure monitoring system.

  In the configuration of Conventional Example 1 shown in the figure, a wireless sensor 2 is provided in the tire 1. On the vehicle body 6 side, a wireless communication unit 4 having a vehicle-mounted antenna 3 and a transmission / reception circuit 5 is provided. The wireless communication unit 4 (particularly the vehicle-mounted antenna 3) is provided in the vicinity of the tire 1. Although not shown, the communication device (or display / control device or the like) connected to the transmission / reception circuit 5 by wire (for example, a coaxial cable) is also mounted on the vehicle. The transmission / reception circuit 5 is a circuit that realizes wireless communication via the vehicle-mounted antenna 3, and transmits any signal (data) from the vehicle-mounted antenna 3 at an arbitrary frequency, or a signal received by the vehicle-mounted antenna 3. It has a function of a general wireless transmission / reception circuit such as amplifying the signal (since it is a general one, it will not be described in detail here).

  Here, only the configuration related to one tire is shown in the figure, but the other three tires (usually, because there are four tires) have the wireless communication unit 4 in the vicinity of the tire in a similar manner. In addition, the wireless communication unit 4 and the communication device (or display / control device or the like) are connected by a coaxial cable, for example.

  Accordingly, radio signals (including tire pressure data) transmitted from the respective wireless sensors 2 in the four tires 1 are respectively received by the vehicle-mounted antenna 3 on the vehicle body side located in the vicinity thereof. Are individually transmitted to the display / control device and the like via the transmission / reception circuit 5 and the coaxial cable (not shown). Thus, in the display / control device, the state (air pressure and the like) of each of the four tires is displayed and a warning sound is emitted.

Such conventional example 1 is disclosed, for example, in Patent Document 2 as the prior art (FIG. 11).
In addition, since a steel belt is embedded on the tread side of a tire mounted on a metal wheel, communication between the wireless sensor in the tire and the antenna on the vehicle body is mainly performed on the side wall of the tire. Is done through.

  In any case, in the case of the above-described conventional example 1, four vehicle-mounted antennas 3 are necessary, and it is necessary to wire four coaxial cables, which causes a problem that it is complicated and expensive.

  For such a problem, for example, conventional techniques described in Patent Documents 1, 2, and 3 are known. In these conventional techniques, it is not necessary to wire a coaxial cable from at least each of the antennas.

First, the prior art of Patent Document 1 is referred to as Conventional Example 2.
In the prior art of Patent Document 1, a unit in which the vehicle body side antenna unit and the control processing circuit unit are integrated as shown in FIGS. 2 to 4 is formed at a substantially central portion of the vehicle body as shown in FIG. And a radiation beam having a strong directivity is radiated in four directions (the direction in which each tire is present). The vehicle body side antenna section (antenna unit) is divided into four sections as shown in FIGS. 2 to 4, and each antenna bar (monopole antenna) is arranged in each fan-shaped section, and the tire direction The directivity is given to the four directions. This saves the trouble of wiring the coaxial cable to the communication device.

Patent Documents 2 and 3 disclose a configuration in which only one vehicle-side antenna is required.
That is, first, in the prior art of Patent Document 2, the radio wave transmitted from the sensor device provided in each tire can be received with high gain by one antenna connected to the monitoring unit. This one antenna is provided on the window glass of the vehicle and has a portion extending in the vertical direction.

  In Patent Document 2, a radio wave is radiated from an antenna, and by measuring the shape and arrangement of the antenna so that the electric field strength at the position of each tire is highest, the weak radio wave transmitted from each sensor device is So that it can be received with high efficiency.

  Moreover, in the prior art of patent document 3, the tire position where each sensor apparatus was attached can be identified with one antenna. The one antenna connected to the monitoring unit via a coaxial cable has uniform directivity in a horizontal plane. The monitoring unit identifies the tire position where each sensor device is attached based on the reception intensity of the radio wave received via the antenna.

JP 2008-126805 A JP 2004-345364 A JP 2005-335654 A

  However, in the prior art disclosed in Patent Document 1, four bar antennas are prepared in order to provide directivity in the four tire directions, and further divided into four sections by a metal plate to act as a corner reflector, and its reflection Is used to direct the directivity of radio waves toward the tire.

  As described above, in Patent Document 1, four antenna bars are required, and the antenna unit is divided into four sections, and a configuration for providing directivity is required, and the structure is complicated and expensive. There is a problem of becoming.

  Further, in the prior arts of Patent Documents 2 and 3, directivity is not provided in the four tire directions. In the case of Patent Document 3, as described above, it has uniform directivity (non-directionality) in a horizontal plane. In Patent Document 2, a “λ / 2 dipole antenna” (paragraph 0045) is used, and as is well known, this has a figure-eight (e.g., front and rear two directions) directivity. .

  As is well known, in the case of having directivity in a specific direction (multiple directions are possible), better wireless communication can be performed in a specific direction than in the case of non-directivity. . This is because radio waves can be radiated strongly in a specific direction, and even weak radio waves can be easily received, and are less susceptible to noise generated in directions other than the specific direction. .

  In that sense, it is desirable to provide directivity in the four tire directions as in Patent Document 1 as compared to non-directivity as in Patent Documents 2 and 3. However, as described above, the structure of Patent Document 1 has a complicated structure and is expensive.

  An object of the present invention is to detect the state of a tire so that directivity can be given to four tire directions with one antenna and communication with a wireless sensor of each tire can be satisfactorily performed with a simple configuration. It is to provide an antenna system for a device.

  An antenna system for a tire condition detection device according to the present invention is an antenna system that is provided for each of at least four tires and includes at least four wireless sensors that detect and transmit the condition of the tires wirelessly. By providing one dipole antenna at the position of the dipole antenna so that the total length of the dipole antenna satisfies a predetermined condition, the dipole antenna has a directivity in four directions in the horizontal direction. The antenna transmits and receives radio waves to and from the at least four wireless sensors.

  By changing the wavelength λ of the radio wave in a state where the total length of the dipole antenna is fixed to an arbitrary length that satisfies the predetermined condition, the directivity angle of the main lobe corresponding to the directivity in the four directions is changed. ,change.

  According to the antenna system for a tire condition detection device of the present invention, directivity can be given to four tire directions with one antenna, and communication with the wireless sensor of each tire can be satisfactorily performed with a simple configuration. Will be able to.

It is the example of whole structure of the antenna system for tire state detection apparatuses of this example. (A), (b) is a figure which shows the directivity characteristic of the horizontal direction in the case of L = 2.0 (lambda) and L = 2.2 (lambda). (A), (b) is a figure which shows the directional characteristic of the horizontal direction in the case of L = 2.4 (lambda) and L = 2.6 (lambda). (A), (b) is a figure which shows the directional characteristic of a horizontal direction in the case of L = 2.8 (lambda) and L = 3.0 (lambda). It is a figure which shows the directional characteristic of the horizontal direction in the case of L = 3.2 (lambda). (A), (b) is a figure which shows the directivity characteristic of the horizontal direction in the case of L = 1.8 (lambda) and L = 1.6 (lambda). It is a figure which shows the directional characteristic of the horizontal direction in the case of L = 1.4 (lambda). It is a figure (the 1) shown about the directivity angle of a main lobe. It is a figure (the 2) shown about the directivity angle of a main lobe. It is a whole structural example (other example 1) of the antenna system for tire state detection apparatuses of this example. It is a whole structural example (other example 2) of the antenna system for tire state detection apparatuses of this example. (A), (b) is a figure which shows a part of structure of the conventional tire pressure monitoring system.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an overall configuration example of the antenna system for a tire condition detection device of this example.
Here, in FIG. 1, the same reference numerals are given to components that may have substantially the same configuration as the conventional example shown in FIG. First, the vehicle body 6 and each tire 1 are (of course) given the same reference numerals as in FIG. Further, as shown in the figure, the wireless sensors 2 provided in the tires 1 are also given the same reference numerals as those in FIG. That is, the configuration on each tire side may be substantially the same as the conventional one. There are four tires, and therefore there are four wireless sensors 2.

  On the other hand, the configuration on the vehicle body 6 side is different from the conventional one. That is, conventionally, a vehicle-mounted antenna 3 is provided in the vicinity of each of the wireless sensors 2. That is, four vehicle-mounted antennas 3 were provided. Further, a coaxial cable or the like for connecting each vehicle-mounted antenna 3 (wireless communication unit 4) and a communication device (or display / control device) (not shown) is provided.

  In contrast, in the configuration shown in FIG. 1, one vehicle-mounted antenna 10 is provided on the vehicle body 6 side. The vehicle-mounted antenna 10 is a dipole antenna (provided that a predetermined condition described later is satisfied). By satisfying the predetermined condition, it is configured that only one vehicle-mounted antenna 10 can perform good wireless communication with all the four wireless sensors 2. This is made possible by realizing directivity in four directions to each tire 1 (each wireless sensor 2) as shown by a dotted line in FIG. The vehicle-mounted antenna 10 is installed, for example, at a substantially central portion of the vehicle body 6 (however, the present invention is not limited to this example, and the vehicle-mounted antenna 10 may be installed at an arbitrary position of the vehicle body 6, but has directivity in the four directions. It must be in a position that corresponds to the direction to the four tires). Further, the vehicle-mounted antenna 10 is stretched in a substantially horizontal direction (a plane direction orthogonal to the direction of gravity).

  The communication device (not shown), the display device and the control device (not shown) described in FIG. 12 are omitted in FIG. The vehicle-mounted antenna 10 is connected to a transmission / reception circuit 11. The transmission / reception circuit 11 may be integrated with a communication device, a display device, a control device, or the like (not shown), or connected by a coaxial cable or the like. It may be. The function and configuration of the transmission / reception circuit 11 may be substantially the same as that of the conventional transmission / reception circuit 5, and the description thereof is omitted. In this configuration, only one antenna on the vehicle side is required, only one transmission / reception circuit is required, and no coaxial cable is required or only one is required.

  Here, as described in the prior art, the directivity in the horizontal plane direction (plane orthogonal to the gravitational direction; xy plane if the gravitational direction is the z direction) by the dipole antenna is typically the figure 8 direction. (Front-rear direction). Further, as in Patent Document 3, when the dipole antenna is stretched in a substantially vertical direction, it has uniform directivity (omnidirectionality) in a horizontal plane.

  On the other hand, the present inventor has recognized that the directivity in the four directions can be realized when the length (full length) of the dipole antenna satisfies a predetermined condition. It has been recognized that the directivity in the above four directions can be realized particularly when the relationship between the total length L of the dipole antenna and the wavelength λ of the radio wave used satisfies a predetermined condition. As will be described later, this is recognized as a result of simulation using various conditions using existing simulation software.

Here, the predetermined condition (especially, the relationship between the total length L of the dipole antenna and the wavelength λ of the radio wave to be used) may basically be anything as long as the directivity in the four directions can be realized. . However, since it will be described later, for example, the following conditions may be considered.
-The side lobe gain should be less than α dB down with respect to the main lobe.
Typically, α is set to 10. That is, the gain of the side lobe is less than 10 dB down with respect to the main lobe.

  For example, 20 dB down or 30 dB down corresponds to the above condition (less than 10 dB down), and for example, 8 dB down or 5 dB down means 10 dB down or more.

  Further, when the above condition (less than 10 dB down) is replaced with the relationship between the total length L of the dipole antenna and the wavelength λ of the radio wave to be used, the following results are obtained based on the simulation results described later.

“1.6λ ≦ L ≦ 2.2λ”
However, it is not strictly limited to this value. For example, since the simulation described later is in increments of 0.2λ, even if there are simulation results of 1.6λ, 1.4λ, 2.2λ, 2.4λ, etc., the simulation results of 1.5λ, 2.3λ There is no. Therefore, if both 1.5λ and 2.3λ satisfy the above condition (less than 10 dB down), “1.5λ ≦ L ≦ 2.3λ” may be satisfied.

Further, as desirable conditions, for example, the following conditions can be considered.
・ No side lobe occurs.
Substituting the above condition (no side lobe) into the relationship between the total length L of the dipole antenna and the wavelength λ of the radio wave to be used, the following results based on the simulation results described below.

"1.8λ ≤ L ≤ 2.0λ"
However, even in this case, the numerical values are not strictly limited. For the above-described reason, for example, “1.7λ ≦ L ≦ 2.1λ” may be satisfied.

Details will be described later.
In any case, in this method, directivity in four directions (directions of four tires) can be realized with one dipole antenna, and thus high-quality wireless communication can be realized with a simple configuration. That is, the directivity to the four tires can be realized without being complicated and expensive as in Patent Document 1. Therefore, as described above, it is difficult to be affected by noise generated in directions other than the four directions, and can be transmitted to each wireless sensor 2 even with a relatively small output, and a weak radio wave is transmitted from each wireless sensor 2. However, it can be received without problems (that is, high-quality / good wireless communication can be realized).

  The installation position of the vehicle-mounted antenna 10 is not necessarily limited to the center of the vehicle body. That is, the installation position of the vehicle-mounted antenna 10 is such that the directivity in the above four directions corresponds to the position of the four tires, and normally the vehicle body center part corresponds. It is not restricted to this example.

  Here, as is well known, a dipole antenna is generally provided with a feeding point at the center, and is λ / 4 in length from the feeding point to both ends, so the total length is λ / 2. Is. As is well known, the directivity of such a typical dipole antenna is a figure eight.

  On the other hand, as described above, the present inventor conducted the simulation using the existing simulation software, so that the directivity of the dipole antenna becomes four directions, and the conditions (dipole) We have found out the conditions concerning the antenna length; among them, the conditions for obtaining a particularly desirable directivity.

The existing simulation software is, for example, “MMAN”. “MMAN” is antenna analysis software based on the method of moments, and can analyze the characteristics of an antenna in which straight wires are combined in an arbitrary shape. “MMAN” has the following functions, for example.
-Antenna definition editor-Antenna shape display, segment division, current distribution display-Horizontal pattern, vertical pattern display and printing-Comparison of multiple results "MMAN" is introduced on the following URL site, for example.

http://n1yn.com/MMANA/MMANA.html
In addition to “MMAN”, for example, a simulation of a site with the following URL is also used.

http://www-antenna.ee.titech.ac.jp/~hira/hobby/edu/em/dipole/index-j.html
2 to 7 show simulation results (horizontal directivity characteristics).
The gain (dB) shown in FIG. 2 to FIG. 7 means a relative gain with the maximum value (absolute gain of the main lobe) as a reference “0”. Therefore, naturally, all values are below the standard (10 dB down (1/10), 20 dB down (1/100), 30 dB down (1/1000), etc.). In the figure, for example, “−10” means the 10 dB down. Others are the same.

2 to 7 show the results of simulation by changing the length L of the dipole antenna by 0.2λ within the range of 1.4λ to 3.2λ.
That is, the length L of the dipole antenna is shown as 2.0λ in FIG. 2A, 2.2λ in FIG. 2B, 2.4λ in FIG. 3A, 2.6λ in FIG. 4 (a) is 2.8λ, FIG. 4 (b) is 3.0λ, FIG. 5 is 3.2λ, FIG. 6 (a) is 1.8λ, FIG. 6 (b) is 1.6λ, and FIG. The simulation result in the case of 1.4λ is shown.

As an example, the wavelength λ of the radio wave to be used is set to 0.1224 (m) (frequency f = 2.45 GHz), but is not limited to this example.
In all of FIGS. 2 to 7, the main lobe (main beam) can be regarded as having four directions. Therefore, it cannot be said that setting the length L of the dipole antenna within the range of, for example, 1.4λ to 3.2λ is inappropriate as the application range of the present invention.

However, for the reasons described below, it is desirable to set the value within the range such as “1.6λ ≦ L ≦ 2.2λ” as described above.
That is, first, in the case of “L = 1.8λ” shown in FIG. 6A, as shown in the figure, there are only four main lobes and no side lobes (sub-beams) appear. Also, in the case of “L = 2.0λ” shown in FIG. 2A, as shown in the figure, there are only four main lobes, and side lobes hardly appear (this also shows side lobes). It shall be regarded as not present). That is, these can be regarded as suitable / optimal.

  On the other hand, for example, as shown in FIG. 6B, in the case of “L = 1.6λ”, there are four main lobes that are substantially the same as in the case of “L = 1.8λ”. Instead, a sidelobe appears. That is, in the figure, the gain (relative gain with the maximum value (absolute gain of the main lobe) as the reference “0”) is approximately 13 dB in the vertical direction (actually the longitudinal direction of the vehicle body). Side lobes appearing down.

  In FIGS. 2 to 7, 0, −10, −20, −30, etc. shown in the figure mean 10 dB down, 20 dB down, 30 dB down, etc., with the main lobe as the reference (0).

  As shown in FIG. 7, in the case of “L = 1.4λ”, there are four-direction main lobes and side lobes appear as in the case of “L = 1.6λ”. As shown in the figure, the side lobe is larger than in the case of “L = 1.6λ” (about 2 dB down).

  A problem arises when at least large side lobes as shown in FIG. 7 appear. That is, it is greatly affected by the noise of the engine or the like in the side lobe direction (the vertical direction in the figure (actually the longitudinal direction of the vehicle body)), and the wireless communication with each wireless sensor 2 is adversely affected. . In addition, the antenna output is not concentrated in the main lobe direction but is also dispersed in the side lobe direction.

  On the other hand, when the side lobe is small (approximately 13 dB down) as shown in FIG. 6B, the adverse effect of the side lobe described above is very small, and good wireless communication with each wireless sensor 2 can be realized. .

  From the above, it is difficult to be affected by noise or the like generated in directions other than the four directions, and good wireless communication with each wireless sensor 2 can be realized (a radio wave can be strongly emitted in the direction of each wireless sensor 2 and each wireless In the above example, “L = 2.0λ”, “L = 1.8λ”, “L = 1... Can be received without any problem even if a weak radio wave is transmitted from the sensor 2”. “6λ” is appropriate, but “L = 1.4λ” is considered inappropriate. As one guideline for determining such appropriate / inappropriate, the present inventor has determined, based on experience, “appropriate if the side lobe is less than 10 dB down” and “inappropriate if the side lobe is lower than 10 dB”. It is suggested that “appropriate” be a condition. However, the present invention is not limited to this example.

  In addition to the example described above, that is, in the case of 2.2λ to 3.2λ shown in FIGS. 2B to 5, if it is determined based on the above condition, only 2.2λ shown in FIG. “Appropriate”, but otherwise “inappropriate”.

  Therefore, when considering from the viewpoint that good wireless communication with each wireless sensor 2 can be realized, the total length L of the vehicle-mounted antenna 10 (dipole antenna) is in the range of “1.6λ ≦ L ≦ 2.2λ”. It is desirable. However, this is a definition according to the specific examples shown in FIGS. 2 to 7, and the condition is “the side lobe is less than 10 dB down” as described above. Accordingly, the example of FIGS. 2 to 7 is not known because it is in increments of 0.2λ. For example, in the case of 1.5λ, if “the side lobe is 10 dB down or less”, “1.5λ ≦ L ≦ 2.2λ ”.

  Further, as described above, the more desirable condition is that “no side lobe occurs”. Based on the simulation result, the total length L of the vehicle-mounted antenna 10 (dipole antenna) and the wavelength of the radio wave to be used It is considered that the relationship with λ is within the range of “1.8λ ≦ L ≦ 2.0λ”. However, depending on the simulation results for 1.7λ and 2.1λ, 1.7λ and 2.1λ may also be included in the preferred / optimal range.

  As described above, it is considered that the desirable condition (condition within the preferable / optimum range) is that there is no (or almost no) side lobe as shown in FIG. 2 (a) and FIG. 6 (a), for example. You can hesitate. In this condition, there is no condition stipulation with specific numerical values such as 10 dB down or less. For example, as one guideline, “side lobe is 30 dB down (including the case where there is no side lobe)” or the like may be used.

  Needless to say, it is necessary to configure the wireless sensors 2 for measuring and transmitting the air pressure and temperature of the tire 1 in the four directions of the main lobe.

  In this regard, it is conceivable to use the fact that the directivity angle of the main lobe changes depending on the relationship between the total length L of the vehicle-mounted antenna 10 (dipole antenna) and the wavelength λ of the radio wave used.

  For example, as shown in FIGS. 8 and 9, the directivity angle of the main lobe with respect to the front-rear direction is about 32 degrees when L = 2.0λ, and about 37 degrees when L = 1.8λ. ing. By utilizing this, the directivity angles in the four directions of the main lobe can be adjusted and controlled. For example, fine adjustment can be performed after installation.

  That is, the total length L of the vehicle-mounted antenna 10 (dipole antenna) can be changed after installation, but it is very difficult and troublesome. However, as described above, the directivity angle is determined by the relationship between the wavelength λ of the radio wave used and L. Therefore, when a vehicle-mounted antenna 10 having a certain length is used and a radio wave having a wavelength λ of L = 2.0λ is used, the directivity angle is about 32 degrees from the above. When it is desired to change (finely adjust) the directivity angle to about 37 degrees, the wavelength λ (frequency) of the radio wave to be used may be changed to one that satisfies the relationship of L = 1.8λ.

  In this way, the directivity angle can be controlled. Thus, for example, even when the wireless sensor 2 does not exist (is slightly shifted) in the four directions of the main lobe at the time of installation, the wireless sensor 2 is later moved in the four directions of the main lobe, respectively. It becomes possible to adjust so that it exists.

  In FIG. 1, the dipole antenna is installed at 90 degrees (perpendicular) with respect to the vehicle traveling direction (front-rear direction). Needless to say.

  Here, as described above, FIG. 1 shows an example of the overall configuration of the antenna system for a tire condition detection device of this example, but this is not a limitation. For example, the configuration shown in FIGS. 10 and 11 may be used as another example.

FIG. 10 is an overall configuration example (another example 1) of the antenna system for a tire condition detection device of the present example.
FIG. 11 is an overall configuration example (another example 2) of the antenna system for a tire condition detection device of the present example.

  10 and 11, each main lobe is indicated by a dotted line as in FIG. As shown in the figure, the main lobe is in four directions, in other words, a single dipole antenna (vehicle-mounted antenna 10) has directivity in four directions, and this is the same as FIG.

  Here, although the number of tires is four in the example of FIG. 1, the present invention is not limited to this example. For example, in the case of a large vehicle such as a truck, a trailer or a bus, the number of tires is often more than four. FIGS. 10 and 11 show an example of the overall configuration when the tire state detection device antenna system of the present example is applied to a vehicle having six tires.

  10 and 11 both have two front wheels and four rear wheels as shown, but in FIG. 10, two tires are arranged in parallel on the left and right of the rear wheels. On the other hand, in FIG. 11, two tires are arranged in series on each of the left and right rear wheels. This technique can be applied to such a configuration with six tires. However, as shown in the figure, in this case, the directivity in four directions is realized by one dipole antenna, which is the same as the configuration in FIG. Further, the number is not limited to six, and may be eight, ten, twelve, and the like, and therefore, it can be said that this method can be applied to a vehicle provided with at least four tires.

  Note that the above-mentioned eight configurations are, for example, not only the rear wheel tires but also the front wheel tires having two in parallel or two in series on the left and right, respectively, so that four front wheel tires and four rear wheel tires are provided. This is a total of eight configurations. That is, for example, “front wheel: parallel arrangement of two left and right. Rear wheel: parallel arrangement of two of right and left”, “front wheel: serial arrangement of two of right and left. Rear wheel: serial arrangement of two of right and left”, etc. are examples. However, the eight configurations are not limited to these examples.

  Or, for example, in the case of the ten tires described above, for example, the rear wheel tire is configured by combining FIG. 10 and FIG. 11, that is, two in parallel and two in series, a total of four on the left and right sides This is a configuration provided for each of them (therefore, there are a total of 8 rear wheels, and there are a total of 2 front wheels, one on each side). Alternatively, the number of rear wheels is eight as described above, but in the case of a configuration in which two tires 1 are arranged in parallel or in series on the left and right of the front wheel side, the total number is twelve.

  Here, basically, since the wireless sensor 2 is provided for each tire 1, in the case of a vehicle having six tires as shown in FIGS. 10 and 11, the number of wireless sensors 2 is six. Become. Similarly, when the number of tires is 8, 10, and 12, the numbers of the wireless sensors 2 are 8, 10, and 12, respectively.

Returning to the description with reference to FIGS.
In the case of the configuration of FIGS. 10 and 11, the two wireless sensors 2 are provided on the left and right sides of the rear wheel side, as described above. And since one dipole antenna (vehicle-mounted antenna 10) has directivity in four directions as shown in the figure, on the rear wheel side, one main lobe covers two wireless sensors 2. What is necessary is just to arrange. For example, a total of two wireless sensors 2 provided on each of the two tires 1 on the left rear wheel side may be arranged so as to be covered by the main lobe corresponding to the left rear wheel side. The same applies to the right rear wheel side. In other words, even in the case of such a configuration composed of six tires (six wireless sensors 2), directivity in four directions (four tire directions) in the tire direction can be realized with only one dipole antenna. Can be said.

  Needless to say, the above “four tire directions” does not mean “four tire directions”, but means four directions with one or more tires 1 (one or more wireless sensors 2) in each direction. To do.

Needless to say, the present technique is not limited to the configuration examples of FIGS. 10 and 11, and the present technique can be applied to any tire arrangement corresponding to “four directions of directivity that one dipole antenna has in the horizontal direction”.
Therefore, even when the number of tires is 8, 10, 12, etc., if the tire arrangement is such that it corresponds to “directivity in four directions that one dipole antenna has in the horizontal direction”, This method is applicable. In other words, for each main lobe in four directions, if the tire arrangement is such that one or a plurality of wireless sensors 2 are covered by the main lobe, etc., all the wireless sensors 2 can be covered as a whole. This method is applicable. However, even if this is difficult to realize, the present technique may be substantially applicable by switching the use frequency by using two or more kinds of use frequencies, for example.

  That is, as described with reference to FIGS. 8 and 9, the directivity angle can be controlled based on the relationship between the frequency used and the antenna length of the dipole antenna (vehicle-mounted antenna 10). As described in FIGS. 8 and 9, the main lobe directivity angle is switched to one of two directions of about 32 degrees and about 37 degrees by switching to one of two types of use frequencies. Means you can.

  In this case, one of the two types of use frequencies is also used as the use frequency of the wireless sensor 2. For example, if the directivity angle is about 32 degrees at the use frequency f1, and the directivity angle is about 37 degrees at the use frequency f2, the use frequency of the wireless sensor 2 in the 32 degree direction is f1. The operating frequency of the wireless sensor 2 in the 37 degree direction is f2.

  For example, the transmission / reception circuit 11 first communicates with all the wireless sensors 2 that can communicate at the use frequency f1, and then switches to the use frequency f2 to communicate with all the wireless sensors 2 that can communicate at the use frequency f2. If communication can be performed with all the wireless sensors 2 by performing communication, it can be said that the present method is substantially applicable.

As a matter of course, the above-mentioned “frequency” may be rephrased as “wavelength”, “use frequency” as “wavelength of radio wave to be used”, and the like.
In the above example, the directivity angle is switched to either one of the two angles. However, the present invention is not limited to this example, and may be switched to any one of the three angles, for example.

  As described above, in the present invention, the length of the dipole antenna satisfies the predetermined condition (for example, it is defined as the relationship between the length of the dipole antenna and the wavelength of the radio wave), and only one dipole antenna is used. It is possible to achieve directivity in the tire direction in four directions. That is, communication with the wireless sensor 2 of each tire 1 can be performed satisfactorily with a simple configuration. Furthermore, there is an advantage that the directivity can be finely adjusted by changing the frequency of the radio wave used. Thereby, for example, optimization to various vehicles can be easily performed.

DESCRIPTION OF SYMBOLS 1 Tire 2 Wireless sensor 6 Vehicle body 10 Vehicle-mounted antenna 11 Transmission / reception circuit

Claims (6)

An antenna system having at least four wireless sensors that are provided for each of at least four tires and wirelessly detect and transmit the state of the tire,
One dipole antenna is installed at any position on the vehicle,
By making the total length of the dipole antenna satisfy a predetermined condition, the dipole antenna is configured to have a directivity in four directions in the horizontal direction, and the at least four wireless sensors and radio waves are configured by the one dipole antenna. send and receive,
By changing the wavelength λ of the radio wave in a state where the total length of the dipole antenna is fixed to an arbitrary length that satisfies the predetermined condition, the directivity angle of the main lobe corresponding to the directivity in the four directions is changed. , tire condition detecting device antenna system and changes.   The predetermined condition is that, even when a side lobe occurs with respect to the main lobe corresponding to the directivity in the four directions, the gain of the side lobe is reduced by α dB with respect to the main lobe (α: any real number) The antenna system for a tire condition detection device according to claim 1, wherein the total length of the dipole antenna is set so as to be less than.   The predetermined condition is that, even when a side lobe occurs with respect to a main lobe corresponding to the directivity in the four directions, the gain of the side lobe is less than 10 dB down with respect to the main lobe. 2. The tire system for a tire condition detection device according to claim 1, wherein a total length of the dipole antenna is set. The predetermined condition is that the relationship between the total length L of the dipole antenna and the wavelength λ of the radio wave is
1.6λ ≦ L ≦ 2.2λ
The antenna system for a tire state detection device according to claim 1 or 3, wherein the antenna system is within the range of (2).   2. The tire condition detection according to claim 1, wherein the predetermined condition sets a total length of the dipole antenna so that a side lobe does not occur with respect to a main lobe corresponding to directivity in the four directions. Antenna system for equipment. The predetermined condition is that the relationship between the total length L of the dipole antenna and the wavelength λ of the radio wave is
1.8λ ≦ L ≦ 2.0λ
The antenna system for a tire state detection device according to claim 1 or 5, wherein the antenna system is within the range of (1).