JP2011109553A - Transmission antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission antenna for easily adjusting an inductance value of a coil even after the case is attached. <P>SOLUTION: The transmitting antenna 100 includes a core 3 formed of a magnetic material, a coil 4 wound around the core 3, a case 1 covering the core 3 and a coil 4, and a hollow adjusting member 10 formed of a magnetic material to cover the external circumference of the case 1. An inductance value of the coil 4 can be adjusted easily to the desired value by adjusting the position of the adjusting member 10. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a transmission antenna in which a core around which a coil is wound is housed in a case, and more particularly to a structure for adjusting the inductance value of a coil.

  For example, in a keyless entry system for a vehicle, a transmission antenna is provided at the door of the vehicle. Then, a radio wave of a predetermined frequency is transmitted from the transmitting antenna, and the door of the vehicle is unlocked or locked depending on whether or not the portable device having the built-in transmission / reception antenna is within the propagation range of the radio wave. ing. When the portable device enters the radio wave propagation range, an unlock signal is transmitted from the portable device to the receiving antenna of the vehicle, and the door is unlocked. On the other hand, when the portable device leaves the radio wave propagation range, a locking signal is transmitted from the portable device to the receiving antenna of the vehicle, and the door is locked.

  As is well known, in the transmitting antenna, when the frequency of the applied alternating current matches the resonance frequency of the resonance circuit composed of the coil and the capacitor, the current flowing through the coil becomes maximum. As the frequency of the applied current moves away from the resonance frequency, the current flowing through the coil decreases rapidly. For this reason, if the resonance frequency varies due to variations in the inductance value of the coil and the capacitance value of the capacitor, the electromotive force induced in the antenna decreases. As a result, the communication distance between the transmitting antenna and the portable device becomes short, and there arises a problem that the door unlocking / locking operation becomes unstable.

  Therefore, a method for adjusting the inductance value of the coil of the transmitting antenna and setting the resonance frequency to a desired value has been conventionally proposed. For example, Patent Documents 1-3 describe such inductance value adjusting means.

  In Patent Document 1, a coil core for an antenna including a magnetic core and a coil wound around the magnetic core is provided with a moving core disposed so as to be movable in the winding axis direction of the coil. Describes a technique for adjusting the inductance value of the coil by changing the relative position between the magnetic core and the magnetic core.

  In Patent Document 2, in a transmission antenna having a core wound with a winding, a screw constituting a small core smaller than the core, a screw is magnetically coupled to the core, and a distance between the core and the screw is determined. A technique for setting a resonance frequency by providing a distance adjusting unit to be adjusted and adjusting the screwing amount of the screw is described.

  In Patent Document 3, in a transformer including a coil wound around the outer periphery of a bobbin, a first core provided inside the bobbin and a second core provided outside the bobbin are respectively moved up and down. Thus, a technique for performing coarse adjustment and fine adjustment of mutual inductance is described.

JP 2008-181947 A Table 2003/036761 Japanese Utility Model Publication No. 62-184709

  In the adjustment method described in Patent Literatures 1 to 3, before the core around which the coil is wound is covered with the case, the inductance value of the coil is adjusted. However, in the case of the transmission antenna provided on the vehicle door as described above, even if the inductance value is adjusted so as to obtain a desired resonance frequency, if the antenna is attached to the vehicle door, the metal constituting the door The actual resonance frequency may deviate from the adjustment value due to the influence of components and the like. In this case, in the method disclosed in Patent Documents 1-3, the adjustment work of the coil inductance value must be performed again after the case is once removed, and the case must be mounted again after the work is completed.

  Therefore, an object of the present invention is to provide a transmitting antenna that can easily adjust the inductance value of a coil even after the case is attached.

  The transmitting antenna according to the present invention includes a core made of a magnetic material, a coil wound around the core, a case covering these cores and the coil, and a hollow adjustment made of a magnetic material covering the outer periphery of the case. And a member.

  If it does in this way, the inductance value of a coil will change according to the position of the adjustment member put on the perimeter of a case. For this reason, by adjusting the position of the adjustment member, the inductance value of the coil can be adjusted to a value at which a predetermined resonance frequency can be obtained without removing the case.

  In the present invention, when the signal terminal protrudes from one end side of the case, the adjustment member is preferably covered on the outer periphery on the other end side of the case. According to this, the adjustment member can be easily attached to the case from the side where the signal terminal and the lead wire connected thereto are not present.

  In this case, the capacitor that forms the resonance circuit together with the coil is preferably provided inside one end of the case. According to this, since the capacitor is arranged in the vicinity of the signal terminal, a long wiring between the capacitor and the signal terminal is unnecessary, and the manufacturing is facilitated.

  In the present invention, it is preferable that the transmission frequency when the adjustment member is not covered on the case is set to a value higher than the transmission frequency required for the antenna. The inductance value of the coil changes only in the minus (decrease) direction by adjusting the position of the adjustment member. Therefore, by setting the transmission frequency as described above, the inductance value can be easily changed to a desired value by changing the inductance value from a high value to a low value.

  In the present invention, a measurement terminal for measuring the characteristics of the antenna when the adjustment member is covered may be provided. According to this, it is possible to easily adjust the antenna characteristics by connecting a device for measuring the inductance value, resonance frequency, etc. of the coil to the measuring terminal and adjusting the position of the adjusting member while checking the measured value. it can.

  In the present invention, a positioning part for positioning the adjustment member may be provided in the case. According to this, since the adjustment member can be easily positioned on the case when the adjustment member is put on the case, the adjustment work can be performed efficiently.

  According to the transmitting antenna of the present invention, since the inductance value of the coil can be easily adjusted even after the case is mounted, the adjustment work for obtaining a desired resonance frequency can be easily performed. is there.

It is a figure which shows the antenna for transmission before mounting | wearing with an adjustment member. It is a perspective view of an adjustment member. It is a figure explaining mounting | wearing to the case of an adjustment member. It is a figure which shows the state which covered the adjustment member on the edge part of a case. It is a figure which shows the state which moved the adjustment member. It is a figure which shows the state which moved the adjustment member. It is a graph which shows the change of the inductance value of a coil by the position of an adjustment member. It is a figure explaining the adjustment principle of an inductance value. It is a figure which shows embodiment using several adjustment member. It is a figure which shows other embodiment using several adjustment member. It is a figure which shows embodiment which provided the positioning part in the case. It is a perspective view which shows the other example of an adjustment member. It is a perspective view which shows the other example of an adjustment member. It is a perspective view which shows the other example of an adjustment member. It is a figure which shows embodiment at the time of covering an adjustment member in another position.

  Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B show a transmitting antenna 100 before the adjustment member is mounted, in which FIG. 1A is a plan view with the case cut out, FIG. 1B is a side view thereof, and FIG. It is front sectional drawing in XX.

  The transmitting antenna 100 includes a case 1 and a base 2 on which the case 1 is mounted. Inside the case 1, a rod-shaped core 3 and a coil 4 wound around the core 3 are housed, and these are covered with the case 1. The case 1 is formed from a resin such as plastic. The base 2 is also formed from the same material. The core 3 is made of a magnetic material such as ferrite, and extends in the left-right direction in FIGS. The coil 4 is made of enamel-coated copper wire and is wound on the core 3 with a predetermined number of turns with a part of the tip side of the core 3 (the tip 1a side of the case 1) exposed. Yes. A tape 5 for fixing the copper wire at the start end and the end end of the coil 4 is wound around the rear end side of the core 3.

  A substrate 6 is provided adjacent to the rear end of the core 3. A capacitor 7 that constitutes a resonance circuit together with the coil 4 is mounted on the substrate 6. The capacitor 7 is a chip type capacitor here, but may be a discrete type capacitor. A pair of signal terminals 8 are connected to the substrate 6. The signal terminal 8 is held on the base 2 and protrudes from the rear end side of the case 1 (the side opposite to the front end 1a). An antenna driving signal (alternating current) is input to the signal terminal 8 from the outside. Further, the substrate 6 is provided with a pair of measurement terminals 9 for measuring the antenna characteristics. The measurement terminal 9 is connected to an LCR measurement device that measures an inductance value L, an electrostatic capacitance value C, a resistance value R, and the like, which are antenna parameters, and a frequency measurement device that measures a resonance frequency. The measurement terminal 9 passes through the case 1 and protrudes in a direction orthogonal to the signal terminal 8.

  FIG. 2 shows an example of the adjusting member 10 used in the present invention. The adjusting member 10 is made of a cylindrical magnetic body (for example, iron) having a hollow portion 10a. The hollow portion 10a is formed to have a size slightly larger than the outer shape of the case 1 in the XX cross section of FIG. Therefore, the adjustment member 10 can be fitted into the case 1 with almost no gap.

  The adjusting member 10 is fitted into the case 1 from the tip 1a side of the case 1 as shown in FIG. 3, and is put on the outer periphery of the case 1 as shown in FIG. In FIG. 4, the end surface 10 b of the adjustment member 10 is flush with the tip portion 1 a of the case 1. The position Y1 of the end face 10b of the adjustment member 10 at this time is hereinafter referred to as “reference position”.

  FIG. 5 shows a state in which the adjustment member 10 has been moved from the reference position Y1 by a distance d, and the adjustment member 10 is placed on the case 1 at the position Y2. FIG. 6 shows a state where the adjustment member 10 is further moved from the position Y2 by a distance d (from the reference position Y1 to 2d), and the adjustment member 10 is placed on the case 1 at the position Y3. 5 and 6, the adjustment member 10 surrounds a part of the core 3.

  In this way, the inductance value of the coil 4 when the position of the adjustment member 10 is changed to Y1, Y2, Y3,... Changes as shown in the graph shown in FIG. That is, the inductance value decreases as the adjustment member 10 moves away from the reference position Y1. It has been experimentally confirmed that the inductance value is minimized when the adjustment member 10 is located at the center of the coil 4 and increases as the distance from the center of the coil 4 increases.

FIG. 8 is a diagram for explaining the principle of adjusting the inductance value in the transmitting antenna. When an alternating current is passed through the coil W wound around the core K, a magnetic flux φp corresponding to the inductance value of the coil W is generated. At this time, the resonance frequency fo is L1 as the inductance value of the coil W, and C is the capacitance of a capacitor (not shown) connected in series with the coil W.
fo = 1 / 2π√ (L1 · C) (1)
It becomes. Here, as shown in FIG. 8A, when the ring-shaped magnetic body A is placed in the vicinity of the tip of the core K, the generated magnetic flux φp is linked to the magnetic body A. As a result, as shown in FIG. 8B, an induced current I is generated in the magnetic body A, and a reverse magnetic flux φq is generated based on the induced current I. This means that the coil W apparently has a negative inductance value (−L2). Then, the total sum (L1−L2) of the inductance value L1 and the inductance value −L2 becomes the actual inductance value L in the transmitting antenna. Therefore, the resonance frequency when the magnetic substance A exists is from fo in the above equation (1).
fv = 1 / 2π√ [(L1-L2) · C] (2)
To change. Further, when the position of the magnetic body A is changed in the longitudinal direction of the core K, the value of the induced current I generated in the magnetic body A changes, and the reverse magnetic flux φq also changes accordingly. It is considered that the inductance value L changes.

  From the above, when the position of the adjustment member 10 (corresponding to the magnetic body A in FIG. 8) covered on the outer periphery of the case 1 is changed in the longitudinal direction of the core 3 as in the above-described embodiment, Thus, the inductance value of the coil 4 changes. For this reason, the coil 4 can be adjusted by adjusting the position of the adjusting member 10 without removing the case 1 even when the resonance frequency needs to be adjusted after the transmitting antenna 1 is attached to the door of the vehicle, for example. The inductance value can be easily adjusted to a desired value.

  In the actual adjustment operation, the adjustment member 10 needs to be fixed at a predetermined position on the outer periphery of the case 1, so that the adjustment member 10 is fixed to the case 1 with an adhesive, for example.

  By the way, when adjustment is performed by moving the adjustment member 10 from the reference position Y1, the inductance value of the coil 4 changes only in the minus (decrease) direction. Therefore, in the present embodiment, the transmission frequency (resonance frequency) when the adjustment member 10 is not covered on the case 1 is set to a value higher than the transmission frequency (resonance frequency) required for the transmitting antenna 100. Yes. For example, if the required transmission frequency is 125 ± 3 KHz, the transmission frequency is designed to 128 ± 3 KHz in the design stage. In addition, the transmission frequency can be adjusted to 122 ± 3 KHz by the adjusting member 10. In this way, the transmission frequency can be easily adjusted to a desired value of 125 ± 3 KHz by changing the inductance value of the coil 4 from a high value to a low value in accordance with the position of the adjustment member 10.

  In the present embodiment, the transmitting antenna 100 is provided with a measuring terminal 9, and the above-described LCR measuring device, frequency measuring device, and the like can be connected to this terminal. For this reason, the characteristics of the antenna can be easily adjusted by adjusting the position of the adjustment member 10 while checking the inductance value, resonance frequency, and the like of the coil 4 with a measuring instrument.

  Moreover, in this embodiment, the adjustment member 10 is put on the outer periphery of the case 1 on the side opposite to the side from which the signal terminal 8 protrudes. For this reason, the adjustment member 10 can be easily attached to the case 1 from the distal end portion 1a side of the case 1 where the signal terminal 8 and the lead wire (not shown) connected thereto are not present.

  Further, in the present embodiment, the capacitor 7 that constitutes a resonance circuit together with the coil 4 is provided inside the case 1 on the side opposite to the tip portion 1a. For this reason, since the capacitor 7 is disposed in the vicinity of the signal terminal 8, a long wiring between the capacitor 7 and the signal terminal 8 is not required, and the manufacturing is facilitated.

  In the embodiment described above, the case where the inductance value of the coil 4 is adjusted using one adjustment member 10 is taken as an example. However, in the present invention, the adjustment of the inductance value is performed using a plurality of adjustment members 10. May be performed. FIG. 9 shows a state in which two adjustment members 10 are put on the case 1, and FIG. 10 shows a state in which three adjustment members 10 are put on the case 1. As described above, when a plurality of adjusting members 10 are used, the change in inductance value is larger than when a single adjusting member 10 is used. However, according to experiments by the inventors, it has been confirmed that the change in inductance value due to the position of the adjustment member 10 is more significant than the change in inductance value due to the number of adjustment members 10.

  As described above, since the influence on the inductance value largely depends on the position of the adjustment member 10, the length of the adjustment member 10 in the case longitudinal direction may be appropriately selected according to the case. For example, a plurality of adjusting members 10 may be used as shown in FIGS. 9 and 10, or a single adjusting member corresponding to the total length of the adjusting members 10 in FIGS. 9 and 10 may be used. It may be used.

  In the embodiment described above, an example in which the adjusting member 10 is fixed to the case 1 with an adhesive has been described. However, fixing by other means is also possible. For example, as shown in FIG. 11, a plurality of ribs (protrusions) 11 are formed at regular intervals on the outer periphery of the case 1 on the distal end portion 1 a side, and the adjustment member 10 is fitted and fixed between the ribs 11. You may do it. In this case, since the rib 11 functions as a positioning portion, the adjustment member 10 can be easily positioned on the case 1 when the adjustment member 10 is put on the case 1. As a result, the adjustment work can be performed efficiently.

  Further, the adjusting member used in the present invention is not limited to the cylindrical adjusting member 10 as shown in FIG. 2, but may be a ring-shaped adjusting member 20 as shown in FIG. Further, the shape of the adjusting member is not limited to the square shape as shown in FIGS. 2 and 12, but for example, a cylindrical adjusting member 30 as shown in FIG. 13 or a circular ring shape as shown in FIG. The adjusting member 40 may be used. In short, the shape of the adjustment member may be selected according to the shape of the case 1. The adjustment member needs to form a closed loop so as to surround the case 1.

  Further, in FIGS. 4 to 6, 9 and 10, the case where the adjustment member 10 is put on the front end side of the case 1 is taken as an example, but in principle, as shown in FIG. Even if the adjustment member 10 is put on the rear end side, the inductance value of the coil 4 can be adjusted.

  The transmitting antenna according to the present invention can be widely applied to a wireless transmission / reception system such as a location detection system and an entrance / exit management system in addition to the above-described vehicle keyless entry system.

DESCRIPTION OF SYMBOLS 1 Case 1a Tip part 3 Core 4 Coil 7 Capacitor 8 Signal terminal 9 Measurement terminal 10, 20, 30, 40 Adjustment member 10a Hollow part 11 Rib (positioning part)
100 Transmitting antenna

Claims (6)

A core made of magnetic material,
A coil wound around the core;
A case covering the core and the coil;
A hollow adjustment member made of a magnetic material, which is put on the outer periphery of the case;
A transmission antenna comprising: The transmitting antenna according to claim 1, wherein
The signal terminal protrudes from one end side of the case,
The transmitting antenna according to claim 1, wherein the adjustment member is placed on an outer periphery on the other end side of the case. The transmitting antenna according to claim 2, wherein
A transmitting antenna, wherein a capacitor constituting a resonance circuit together with the coil is provided inside one end of the case. The transmitting antenna according to claim 1, wherein
A transmission antenna, wherein a transmission frequency when the adjustment member is not covered on the case is set to a value higher than a transmission frequency required for the antenna. The transmitting antenna according to claim 1, wherein
A transmitting antenna having a measuring terminal for measuring characteristics of the antenna when the adjustment member is covered. The transmitting antenna according to claim 1, wherein
A transmitting antenna, wherein the case is provided with a positioning portion for positioning the adjustment member.

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