JP3316140B2 - In-vehicle antenna device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle-mounted antenna device for receiving FM / AM broadcasts, and more particularly, to a vehicle-mounted antenna device for extracting a signal with little signal attenuation.

[0002]

2. Description of the Related Art Generally, a principle structure as shown in FIG. 4 is employed as a basic structure of a vehicle-mounted antenna. As shown in the figure, an antenna hole b formed in a vehicle body a
In addition, a metal cylinder d for antenna ground accommodating the antenna element c is assembled from the back side of the vehicle body a. The signal received by the antenna element c is output from a signal extraction hole e formed in the antenna earth metal cylinder d.

By the way, the performance of antenna reception is as follows.
Ideally, the relationship between the received signal voltage (VO) of the antenna element c and the final extraction voltage (VE) is equal. However, stray capacitance is generated by the above-described antenna structure, and the signal is expressed by the following relational expression. Attenuation occurs. VO = VE × CE / (CS + CE) where CE is an element equivalent capacitance, and CS is a capacitance (floating capacitance) generated between the antenna element c and the antenna earth metal cylinder d.

[0004]

According to the above-mentioned relationship, in order to pursue the ideal performance of the antenna, it is required that CS be extremely small. In view of such a problem, an antenna structure as shown in FIG. 5 has been conventionally used. This corresponds to the antenna hole b formed in the vehicle body a.
Further, an insulating member cylinder d 'for housing the antenna element c and an earth metal e are assembled from the back side of the vehicle body a, and an electrode cylinder f is disposed on the inner surface of the insulating member cylinder d'. Then, a contact electrode spring g is assembled to the antenna element c, and a signal is output from the electrode cylinder f when the contact electrode spring g contacts the electrode cylinder f.

In the above configuration, since the contact electrode spring g is in contact with the electrode cylinder f, CS occurs between the electrode cylinder f and the earth metal e. Therefore, CS is reduced by reducing the outer diameter of the electrode cylinder f without changing the inner diameter of the earth metal e. Here, since CS is generally inversely proportional to the distance, the distance (between electrodes)
Is larger, CS is smaller.

In the configuration of FIG. 5 described above, there is a limit to the reduction of CS. To further reduce CS, the inner diameter of the electrode cylinder f must be further reduced, and the contact electrode spring g must be further reduced in size. Must. However, since the contact electrode spring g always moves up and down, it must be increased to have a certain strength.
In addition, the distance between the antenna element c and the electrode cylinder f must be maintained to some extent. Therefore, further miniaturization is difficult, and further reduction of CS has been difficult.

The present invention has been devised to solve the above-mentioned technical problems, and has as its object to provide a vehicle-mounted antenna device that reduces stray capacitance and improves antenna performance.

[0008]

In order to achieve the above object,
A vehicle-mounted antenna device according to the present invention has a coil-shaped or rod-shaped antenna element and an inner diameter substantially equal to or slightly larger than an outer diameter of the antenna element, and is slidably held in contact with the antenna element. The antenna element
A hot tube for transmitting the received signal at a ground bracket, which is connected to the apparatus main body is disposed so as to contact the lower surface of the body the body and the ground bracket by inserting the hot tube, the hot With the outside diameter of the tube
A substantially cylindrical earth metal having an inner diameter with a distance between the insulator, an insulator disposed on the upper surface side of the vehicle body so as to correspond to the earth metal, and screwed to an upper end of the hot tube; And a top nut.

More specifically, the inner diameter of the earth metal is 1.2 to 1.8 times the outer diameter of the hot tube.

[0010]

According to the above construction, when the vehicle-mounted antenna device according to the present invention is mounted on a vehicle body, the ground metal is disposed on the lower surface of the vehicle body, that is, on the rear side of the body, and the insulator is disposed on the upper surface of the vehicle body. The antenna device is mounted on the vehicle body by holding the body between the earth metal and the insulator, inserting a hot tube through the earth metal, and screwing a top nut from above the insulator to the hot tube.

At this time, since the inner diameter of the hot tube is substantially the same as or slightly larger than the outer diameter of the antenna element, the antenna element slides while contacting the inside of the hot tube. Therefore, no stray capacitance is generated between the antenna element and the hot tube, but instead, a stray capacitance (CS) is generated between the hot tube and the earth metal. Here, since the inside diameter of the earth metal is considerably larger than the outside diameter of the hot tube, the distance between the hot tube and the earth metal is large, so that the stray capacitance (CS)
Is greatly reduced. More specifically, the inner diameter of the earth metal is 1.5 to 1.5 times the outer diameter of the hot tube.
The stray capacitance (CS) is greatly reduced when the ratio is 1.8 times.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an overall explanatory view of the antenna device of the present invention, and FIG. 2 is a sectional explanatory view. In the figure, reference numeral 1 denotes an antenna element, reference numeral 2 denotes a hot tube, reference numeral 3 denotes a grounding metal, reference numeral 4 denotes a ground metal, reference numeral 5 denotes an insulator,
Reference numeral 6 denotes a top nut.

The antenna element 1 has an antenna length of 15
cm. A metallic conductive transmission member 1 having a spring 11 extending in a skirt shape at a plurality of locations on the circumference at a base end of the antenna element 1.
2 are integrated. The transmission member 12 is a member for transmitting a signal received by the antenna element 1 to a hot tube described later. The base end of the antenna element 1 has a rack cord 13 extending downward in the antenna axis direction.
Are connected to each other, and mesh with a motor gear (not shown) to move the antenna element up and down.

The hot tube 2 accommodates the antenna element 1 and is a cylindrical member having a total length longer than at least the antenna element 1. The hot tube has a metallic conductive cylinder 21 disposed inside, and an insulating cylinder 22 made of a rubber material or the like is integrally formed outside the cylinder 21. Further, the inner diameter of the conductive cylinder 21 is substantially the same as or slightly larger than the outer diameter of the antenna element 1. Therefore, as shown in the sectional view of FIG. 2, the antenna element 1 slides up and down while the spring 11 of the transmission member 12 contacts the inner surface of the conductive cylinder 21 of the hot tube 2. Then, the signal received by the antenna element 1 is transmitted to the hot tube 2. Although not shown, a signal extraction line is connected to the conductive cylinder 21 of the hot tube 2.
Further, a screw portion 23 is provided at an upper end portion of the hot tube 2 so that the top nut 6 can be screwed.

The earth metal fitting 3 is formed of a metal material, and is connected so as to cover a part of the entire circumference of the insulating cylinder 22 of the hot tube 2. And the earth metal fitting 3
Is provided with a screw hole 31 so that it can be attached to the vehicle body with screws, bolts and the like.

The earth metal 4 is connected to the earth metal fitting 3.
Similarly to the above, it is formed of a metallic material, and the outer shape is such that the upper part of the cylindrical member is inclined. The inner diameter of the earth metal 4 is larger than the outer diameter of the hot tube 2. This will be described in detail later. In addition, irregularities are formed on the upper peripheral edge of the earth metal 4 so that the earth metal 4 can contact the vehicle body 7 without slipping. Earth metal 4 thus formed
Are arranged such that the lower end is in contact with the grounding metal fitting 3 and the upper end is in contact with the lower side (back side) of the vehicle body 7.
The hot tube 2 is inserted through the center.

The insulator 5 is made of a hard resin such as polypropylene in order to perform a mounting function and an insulating function. Further, an insertion hole is formed in the inner peripheral side of the insulator 5 so as to penetrate along the axis, and the hot tube 2 is inserted into the insertion hole.

The components of the antenna device as described above are mounted on a vehicle body as follows. First, the hot tube 2 is inserted into an antenna insertion hole formed in the vehicle body 7, and the ground metal 4 is
That is, the ground metal 4 is disposed on the back side of the body 7 and the insulator 5 is disposed on the upper surface of the vehicle body 7.
And the insulator 5 with the body 7 sandwiched therebetween.
The antenna device is attached to the vehicle body by screwing a top nut 6 to the hot tube 2 from above the insulator 5.

At this time, as shown in FIG. 3, since the inner diameter of the hot tube 2 is substantially the same as or slightly larger than the outer diameter of the antenna element 1, the antenna element 1 comes into contact with the inside of the hot tube 2 (conductive cylinder 21). While sliding. Therefore, no stray capacitance is generated between the antenna element 1 and the hot tube 2, but instead, a stray capacitance (CS) is generated between the hot tube 2 and the earth metal 4. Here, the inner diameter of the earth metal 4 is the hot tube 2.
, The distance between the hot tube 2 and the earth metal 4 is large, so that the stray capacitance (CS) is greatly reduced.

Here, as a specific numerical value, the inner diameter of the earth metal 4 is 1.2 times the outer diameter of the hot tube 2.
When it is set to about 1.8 times, the stray capacitance (CS) is greatly reduced. Here, the inner diameter of the earth metal 4 is set to 1.5 of the outer diameter of the hot tube 2, the inner diameter of the earth metal is set to 30Φ, and the outer diameter of the hot tube 2 is set to 20Φ.
The following table shows a comparison between the prior art and the present invention.

[0021]

[Table 1]

As shown in the above table, by setting the inner diameter of the earth metal 4 to 1.5 of the outer diameter of the hot tube 2, the stray capacitance (CS) can be reduced by as much as 30 PF, and the performance of the antenna can be reduced. Can be greatly improved.

In the embodiment described above, the antenna element 1 is described using a coil antenna. However, the present invention is not limited to this, and another antenna such as a rod antenna may be used.
In addition, the antenna element 1 is described to be automatically moved up and down by the rack cord 13, but the present invention is not limited to this, and a manual antenna may be used. Furthermore, the antenna element 1 has been described as having a short overall length of about 15 cm, but is not limited thereto, and a long antenna element of 0.8 to 1 m may be used.

[0024]

As is apparent from the above description, according to the present invention, no stray capacitance is generated between the antenna element and the hot tube, and instead, the stray capacitance (CS) is set between the hot tube and the earth metal. Will occur. Since the inner diameter of the earth metal is considerably larger than the outer diameter of the hot tube, the distance between the hot tube and the earth metal is large, so that the stray capacitance (CS) is greatly reduced.

Since the diameter of the earth metal contacting the lower side of the vehicle body is increased, the contact area with the vehicle body is increased, and the stability at the time of assembly is improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a vehicle-mounted antenna device according to an embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view of the vehicle-mounted antenna device according to one embodiment of the present invention.

FIG. 3 is an explanatory top view of the antenna device.

FIG. 4 is a diagram illustrating the principle of an antenna.

FIG. 5 is an explanatory view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna element 11 Spring 12 Transmission member 13 Rack cord 2 Hot tube 21 Conductive cylinder 22 Insulated cylinder 23 Screw part 3 Grounding bracket 31 Screw hole 4 Ground metal 5 Insulator 6 Top nut 7 Body body

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-243829 (JP, A) Japanese Utility Model 7-1613 (JP, U) Japanese Utility Model 4-2107 (JP, U) Japanese Utility Model Utility Model No. 3- 3824 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01Q 1/00-1/52 H01Q 9/14

Claims (2)

(57) [Claims] 1. An in-vehicle antenna device in which an antenna capable of receiving FM / AM broadcast is extended and contracted from an antenna hole formed in a vehicle body, wherein the antenna device has a coil-shaped or rod-shaped antenna element. Having an inner diameter substantially the same as or slightly larger than the outer diameter of the antenna element, and transmitting the signal received by the antenna element by holding the antenna element in a slidable manner.
That a hot tube, and a ground metal is connected to the apparatus main body is disposed so as to contact the lower surface of the body the body and the ground bracket by inserting the hot tube,該Ho
A substantially cylindrical earth metal having an inner diameter having a distance from the outer diameter of the hot tube, an insulator disposed on the upper surface side of the vehicle body so as to correspond to the earth metal, and an upper end of the hot tube And a top nut screwed into the antenna. 2. The on-vehicle antenna device according to claim 1, wherein the inner diameter of the earth metal is 1.2 to 1.8 times the outer diameter of the hot tube.