Automobile antenna attachment device

Abstract: An automobile antenna fastening device comprises an inner fastening assembly (20A) and outer fastening assembly (20B). The inner fastening assembly includes a gland washer (40) made of an elastic material and a gland base (22), and the outer fastening assembly includes a pad (23) and fastening nut (25). An antenna is mounted on the automobile body wall (30) by clamping the automobile body wall between the outer and inner fastening assemblies, and the clamping force of the fas­ tening assemblies is maintained by the elastic deforma­ tion of the gland washer of the inner fastening assembly.

Description: The present invention relates to an automobile antenna attachment device for attaching a telescopic automobile antenna to the body of an automobile. Figures 1 through 3 show a prior art device, and in particular, Figure 1 is a cross section of an automobile antenna attachment device, wherein reference numeral 10 is an extending and retracting type automobile antenna, and 20 is an attachment device which is used to attach the antenna 10 to the automobile body wall 30. The antenna 10 is made up of a multi-stage extending and retracting type antenna element 11 which is formed by connecting a plurality of conductive pipes of different diameters so that the pipes are free to slide relative to each other. The antenna element 11 is held in a tube 12 so that the antenna element 11 can be freely inserted into or withdrawn from the tube 12. An insulating pipe 13 is connected to the upper end of the tube 12, and a first conductive pipe 14 is inserted into the insulating pipe 13 so that the inner surface of the pipe 14 is in electrical contact with the outer surface of the antenna element 11. A coaxial power supply cable 15 having a core conductor 15a is connected to the first conductive pipe 14. A second conductive pipe 16 provided for grounding purposes is mounted over the outer circumferences of the tube 12 and insulating pipe 13. The outer conductor of the coaxial power supply cable 15, i.e., the braided wire 15b used for shielding, is connected to this second conductive pipe 16. The attachment device 20 includes an inner fastening assembly 20A which is installed inside of the automobile body wall 30 and an outer fastening assembly 20B which is installed outside of the automobile body wall 30. A gland washer 21 of the inner fastening assembly 20A is provided on the insulating pipe 13 so that it sits on a flange 17 formed in the top portion of the second conductive pipe 16. A gland base 22 is provided on the insulating pipe 13 so that it sits on the gland washer 21, and its upper rim portion is in contact with the inside surface of the automobile body wall 13. As shown in Figure 2, the gland washer 21 is an annular component (with almost no elasticity) which has a circumferential wall 21a. As seen in Figure 3, the gland base 22 is a bowl-shaped component (with almost no elasticity), having a multiple number of projections 22a on its upper edge. Referring back to Figure 1, the outer fastening assembly 20B includes a pad 23 which is made of a soft plastic or soft rubber material, etc. It contacts the outside surface of the automobile body wall 30. An insulating spacer 24 of the outer fastening assembly 20B is provided on the pad 23, and a fastening nut 25 is screw-engaged with the external circumference of the upper end of the first conductive pipe 14 so that the nut 25 presses against the insulating spacer 24 and the pad 23 from above. The upper portion of the automobile antenna 10 projects outside through an antenna attachment hole which is formed in the automobile body wall 30. The upper edge of the gland base 22 of the inner fastening assembly 20A is positioned so that it contacts the inside surface of the automobile body wall 30, and the outer fastening assembly 20B is fitted over the portion of the antenna that projects outside from the antenna attachment hole. The fastening nut 25 is then screwed onto the upper end of the first conductive pipe 14 and tightened, so that the antenna 10 is securely fastened to the automobile body wall 30. Generally, it is extremely important that the automobile antenna be well grounded. Improper grounding must especially be avoided in the cases of ultra-shortwave antennas so as to ensure adequate transmitting and receiving. If grounding is improper, the standing-wave ratio (SWR) becomes poor, and this causes an output drop during transmission. This can also cause white noise during reception. In the prior art antenna attachment device shown in Figures 1 through 3, grounding is accomplished via the inner fastening assembly 20A of the attachment device 20. Specifically, the antenna 10 is grounded via the shielding braided wire 15a of the coaxial power supply cable 15, the second conductive pipe 16, the flange 17, the gland washer 21, the gland base 22 and the automobile body wall 30. If the contact between the flange 17 of the second conductive pipe 16 and the gland washer 21, the contact between the gland washer 21 and the gland base 22, and the contact between the gland base 22 and the automobile body wall 30, are not adequately maintained, improper grounding will result. The contact pressure of the abovementioned contact areas depends primarily on the tightening force of the nut 25. Accordingly, the tightening force of the fastening nut 25 is set at a value which is great enough to ensure that the contact pressure of the respective contact areas is adequately maintained when the antenna is attached to the body of the automobile. However, when the automobile antenna 10 is used over a long period of time, the contact pressure may decrease, even if the fastening nut 25 is not loosened. Thus, improper grounding will occur and the performance of the antenna will deteriorate. The inventor of the present invention studied. this problem in various phases. As a result of their studies, the inventors ascertained that this problem is caused by permanent deformation of the pad 23. The pad 23 is installed in order to ensure that the outer fastening assembly 20B is held tightly against the outside surface of the automobile body wall 30 so that rattling will not occur, and in order to prevent rain water or other type of moisture, dirt, etc., from penetrating into the interior of the automobile body via the gap between the external fastening element 20B and the automobile body wall 30. However, as mentioned above, because this pad 23 is formed from a soft plastic, rubber, etc., the properties of the pad 23 deteriorate when it is used over a long period of time, causing a permanent deformation. A device similar to that shown above is also shown in Japanese Utility Model Application Publication No. 53-29080. US-A-2470693 discloses a device for mounting an antenna on a vehicle. The device comprises two major parts adapted to fit together from either side of the wall of a vehicle via a hole in the wall. Means is provided on the outside of the vehicle to clamp the two parts of the device together. Electrical grounding is achieved via the internal part of the device which is in contact with the vehicle wall. The present invention provides a device adapted to fasten an antenna to an automobile body wall comprising: an inner fastening assembly including a first conductive element; and an outer fastening assembly including fastening means; the inner and outer fastening assemblies being adapted such that, in use, they sandwich said automobile body wall, a force for such sandwiching being applied by way of said fastening means and such that said conductive element is in electrical contact with said body wall; characterized in that: said first conductive element is a gland base and the inner fastening assembly also comprises a gland washer formed of a conductive elastic material; and said outer fastening assembly also comprises a pad formed of an elastic material; wherein when said fastening means applies said force, the gland washer and the pad are both deformed by said force, the degree to which said gland washer is deformed being greater than the degree to which the pad is deformed, and the value of contact resistance between said gland washer and said body wall is less than or equal to a predetermined value. Accordingly, an advantage of the present invention is the promise of an automobile antenna attachment device which maintains a specified contact pressure between the respective contact parts of an inner fastening element, which forms a ground path, even if the pad on the outer fastening element should show material deterioration as a result of a long-term use, so that the pad is free from permanent deformation. Thus, the automobile antenna attachment device of the present invention not only eliminates rattling, but also eliminates improper grounding. The gland washer of the inner fastening element is formed from an elastic material, and the clamping force of the fastening elements is maintained by the elastic deformation of elastic material (gland washer) so that decreases in the contact pressure acting between the respective components of the fastening elements and between these components and the automobile body wall, that is caused by the permanent deformation of the pad, can be compensated for. Thus, the clamping force of the fastening elements is maintained via the elastic deformation of elastic material from which the gland washer is made of so as to compensate for any decrease in the contact pressure acting between the respective components of the fastening elements and between the components and the automobile body wall. Accordingly, even if the pad of the outer fastening element should undergo material deterioration as a result of a long-term use and the pad shows permanent deformation, the contact pressure between the various contact components of the internal fastening element forming the ground path can be maintained at a specified contact pressure. As a result, rattling will not occur, and there is no danger of improper grounding. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figure 1 is a cross sectional view of a conventional automobile antenna attachment device; Figures 2 and 3 are perspective views of the conventional gland washer and gland base of Figure 1; Figure 4 is a cross sectional view of the structure of the automobile antenna attachment device of this invention; Figure 5 is a side view of a gland washer used in the invention; Figure 6 is a perspective view of the shape of the contact parts of the gland washer; Figures 7A and 7B are cross-sectional views illustrating deformation of the gland washer; Figure 8 is a partial cross sectional view showing the permanent deformation of the pad of this invention; and Figure 9 is a diagram which explains the relationship between contact resistance and the degree of displacement of the gland washer. Figure 4 is a cross sectional view of the structure of an automobile antenna attachment device of the present invention. Components which are the same as those shown in Figure 1 are given the same reference numerals, and accordingly a detailed description of such components will be omitted here. The inner fastening element or assembly 20A in this case includes a gland washer 40 and a gland base 22. The gland washer 40 is formed from an elastic material such as phosphor bronze, etc. and is installed in an elastically unformed state. The bottom of the gland washer 40 is locked in place in a recess formed in the flange section 18 located at the top of the conductive pipe 16. Figure 5 is a side view of the gland washer 40. The gland washer 40 is a saucer-shaped component in terms of its overall shape and has a multiple number of cut-out areas 41 formed in the periphery. Thus, a multiple number of contact parts or tongues 42 are formed in a petal-like arrangement. Figure 6 is a cut-away perspective of one of the contact tongues 42. As seen from this Figure, each contact tongue 42 has projections 42a and 42b on both sides of its outer rim, so that a good contact with the bottom of the gland base 22 is ensured. The function of the embodiment described above will be described below with appropriate reference to Figures 7A, 7B and following Figures. When the inner fastening assembly 20A and outer fastening assembly 20B are installed in their prescribed positions and the fastening nut 25 is tightened, the gland washer 40 is gradually and elastically deformed so that the contact tongues 42 formed in petal-like arrangement are caused to open outwardly. As a result, the gland washer 40 presses against the gland base 22 as illustrated in Figure 7A. In this state, the contact resistance is satisfactorily small. The relationship between the tightening force P of the fastening nut 25 and the contact resistance can be expressed by the following equation: R = 1/√P characterized in that R is the contact resistance. When the fastening nut 25 is tightened further and the gland washer 40 nears its bending limit, the gland washer 40 and gland base 22 press against each other in a more or less tight state as shown in Figure 7B (this state is illustrated in Figure 4). Noting now the tightest point of contact between the gland washer 40 and the gland base 22, if the point of displacement in the state shown in Figure 7A (initial bending) is indicated as C1, the point of displacement in the state shown in Figure 7B (final bending) as C2, and the amount of displacement constituting the difference between C1 and C2 as D, the amount of displacement D is the compensation range and can be used to maintain the contact resistance at a minimum value. Furthermore, the difference D is set within the elastic limits of the gland washer 40, so that damage due to over-tightening is prevented. The pad 23 can undergo material deterioration as a result of a long-term use so that the pad 23 is permanently deformed and compressed by a displacement amount d as shown in Figure 8. In the present embodiment, as shown in Figure 9, the gland washer 40 is designed so that D > d. Accordingly, even if the pad 23 should undergo pemanent deformation, the gland washer 40 and gland base 22 can be kept in a state of satisfactory contact under pressure, so that there is no danger of an increase in the contact resistance. Furthermore, the clamping force of the inner and outer fastening assemblies 20A and 20B is kept at the same level by the elastic deformation of the gland washer 40. Accordingly, the contact pressure between respective parts of the inner and outer fastening assemblies 20A and 20B, and the contact pressure between these assemblies and the automobile body wall 30, are maintained at a stable level. Thus, there is no danger of rattling occurring between the respective parts. Also, penetration of water via the gap between the pad 23 and the automobile body wall 30 is prevented. As described above, in the present invention, the clamping force of the fastening assemblies of an automobile antenna attachment device is kept stable and any decrease in the contact pressure acting between the respective parts of the fastening assemblies and between these assemblies and the automobile body wall is prevented by the elastic deformation of the gland washer which is made of an elastic material. Accordingly, even if the pad of the outer fastening assembly should undergo material deterioration as a result of a long-term use and shows permanent deformation, the contact pressure between the respective parts of the inner fastening assembly which constitute the ground path is maintained at a specified level or greater. As a result, in the automobile antenna attachment device of this invention, rattling or improper grounding will not result.

Claims: A device adapted to fasten an antenna to an automobile body wall (30) comprising: an inner fastening assembly (20A) including a first conductive element; and an outer fastening assembly (20B) including fastening means (25); the inner and outer fastening assemblies being adapted such that, in use, they sandwich said automobile body wall, a force for such sandwiching being applied by way of said fastening means (25) and such that said conductive element is in electrical contact with said body wall; characterized in that: said first conductive element is a gland base (22) and the inner fastening assembly also comprises a gland washer (40) formed of a conductive elastic material; and said outer fastening assembly also comprises a pad (23) formed of an elastic material; wherein when said fastening means (25) applies said force, the gland washer (40) and the pad (23) are both deformed by said force, the degree to which said gland washer is deformed being greater than the degree to which the pad is deformed, and the value of contact resistance (R) between said gland washer (40) and said body wall (30) is less than or equal to a predetermined value. A device according to claim 1, wherein said gland washer (40) is saucer shaped and has a plurality of tongues (42) which, in use, are brought into contact with said gland base (22). A device according to claim 2, wherein each of said tongues (42) is provided with projections at its outer end. A device according to claim 1, 2 or 3, wherein, in use, an insulating spacer (24), said pad, said automobile body and said gland base (22) are clamped between said fastening means (25) and said gland washer (40).

Inventors: EGASHIRA YOSHIMI, EGASHIRA, YOSHIMI
Applicants: HARADA IND CO LTD, HARADA INDUSTRY CO., LTD.
Application year: 1989
Main classification: H01Q1
IPC codes: H01Q1