Mounting Structure of a Reed Switch for an Eddy-Current Indicator

1. Field of the Invention

The present invention relates to a mounting structure of a reed switch for detecting rotation of a magnet which is provided in an eddy-current indicator such as an eddy-current speed meter or tachometer for a vehicle.

2. Description of the Prior Art

Generally, an eddy-current indicator has a magnet which is rotated in proportion to the number of rotation of wheels or an engine of a vehicle, and an induction plate which is able to pivot with crossing a magnetic flux formed by the magnet. In the eddy-current indicator, eddy-current corresponding to the rotation of the magnet is generated in the induction plate, and the eddy-current further makes the induction plate pivoted in accordance with the rotation number of the magnet, so that a speed of the vehicle or rotation number of the engine can be indicated by a pivot angle of a pointer which is mounted on the induction plate.

In the eddy-current indicators as described above, there is known one indicator having a digital display device for indicating speed or rotation number in addition to the the analog display by the pointer. The digital display device comprises a reed switch as a rotation sensor which is arranged in the vicinity of the magnet. The reed switch generates pulse having a period corresponding to the rotation number of the magnet by an on-off control of the reed switch in accordance with magnetic fields generated by the rotation of the magnet, and then the pulse is processed into the digital form.

As a structure for mounting the above-mentioned reed switch in a housing holding therein the magnet rotatably, there is known a structure shown in FIGS. 1 to 5.

In these drawings, a housing 1 is formed of a resin material integrally molded. As shown in FIG. 1, the housing 1 has a concave portion 3 having a long and narrow opening 2 at the side of the central portion of the housing 1. In the concave portion 3 of the housing 1, an assembly body 5 having a reed switch 4 is provided such that the reed switch 4 is disposed in the opening 2.

As shown in FIGS. 2 and 3, the assembly body 5 includes an insulating plate 7 (distributing plate) having copper-leaf conductive bodies 6a, 6b at the top surface thereof. A pair of terminals 8a, 8b are secured at the distributing plate 7 with rivets 9a, 9b, respectively, and therefore the terminals 8a, 8b are electrically connected to the copper-leaf conductive bodies 6a, 6b, respectively. The reed switch 4 is arranged between side arm portions 7a, 7b of the distributing plate 7. The reed switch 4 has leg portions 4a, 4b which extend toward the opposite directions. The tip parts of the leg portions 4a, 4b are formed into a hook-shape, respectively, which is engaged with each of the side arms 7a, 7b of the distributing plate 7 from the underside of the side arms 7a, 7b. In this state, the leg portions are in contact with the under surfaces of the side arms. The ends of the hook-shape tip parts of the leg portions 4a, 4b are respectively secured to the the copper-leaf conductive bodies 6a, 6b by soldering at soldering points 15a, 15b as shown in FIG. 3. Thus, the reed switch 4 is electrically connected to the copper-leaf conductive bodies 6a, 6b.

The above-mentioned assembly body 5 is mounted in the concave portion 3 of the housing 1 as shown in FIGS. 4 and 5. Then, the reed switch 4 of the assembly body 5 is accommodated in the opening 2 of the housing 1, and further the terminals 8a, 8b are secured on a wall 1a of the housing 1 with screws 10a, 10b, respectively. In this mounting state, the reed switch 4 is disposed near a magnet (not shown) which is held rotatably in the housing 1. The magnet is connected to a rotation transmission rod (not shown) which passes through a bearing lb of the housing 1. To the transmission rod, a pointer is mounted.

Incidentally, in FIGS. 1 to 5, the reference numerals 11a, 11b denote holes which are formed in the concave portion 3 of the housing 1 to contain head portions 9c, 9d of the revets 9a, 9b therein. The reference numerals 12a, 12b denote holes formed in the wall la of the housing 1 for mounting the screws 10a, 10b therein which pass through screw holes 13a, 13b formed in bending vertical portions of the terminals 8a, 8b. The reference numerals 21a, 21b are recess portions formed in both sides of the opening 2 of the concave portion 3, in which the leg portions 4a, 4b of the reed switch 4 are contained respectively so as not to directly contact with the housing 1.

In the above-mentioned structure, there is a disadvantage that when the reed switch 4 is subjected to an on-off control, vibration is caused by the operation of the reed switch and the operation vibration energy is transmitted to not only the side arms 7a, 7b of the distributing plate 7 but also the housing 1 through the leg portions 4a, 4b of the reed switch 4. This is because the leg portions 4a, 4b are in contact with the side arms 7a, 7b of the distributing plate 7 at the under side of the side arms. The transmitted vibration generates a strong resonance sound (an operation vibration sound of the reed switch) when the rotation of the magnet reaches at a certain number.

FIG. 6 shows frequency characteristics of the operation sound generated in an eddy-current indicator which does not have a reed switch at a certain car speed, and FIG. 7 shows frequency characteristics of the operation sound generated in an eddy-current indicator which has the reed switch mounted by the above-mentioned mounting structure. As apparently seen from the drawings, when the reed switch is provided, a strong resonance sound having a peak at about 4 kHz is generated, which is not seen in the case that the reed switch is not provided.

Therefore, it is an object of the present invention to provide mounting structure of a reed switch in an eddy-current indicator, which is capable of lessening an operation vibration sound generated by provision of a reed switch in the eddy-current indicator.

In order to achieve the object, a mounting structure of a reed switch in an eddy-current indicator according to the present invention, comprises a housing, a magnet rotatably provided in the housing, a pair of terminals mounted on the housing, a reed switch for detecting the number of the rotation of the magnet by generating pulse corresponding to the rotation of the magnet, the reed switch having a pair of leg portions electrically connected to the terminals, respectively, and means for preventing vibration generated in the reed switch when it is operated from being transmitted to the housing and terminals.

The vibration transmission preventing means comprises cushion members which elastically contact with the leg portions of the reed switch.

In the above-mentioned structure, the resonance sound can be prevented because the cushion members are always in elastically contact with the leg portions of the reed switch so that the operation vibration energy of the reed switch is absorbed in the cushion members, thereby the energy is not transmitted to the terminals and the housing.

The cushion members may be formed of a foam resin or a foam rubber. Further, it is possible for the housing to form a concave portion having a long and narrow opening having opposite side portions and provide the reed switch in the opening, and to provide the cushion members at the opposite side portions, respectively.

Furthermore, it is also possible to bent each of the tip portions of the leg portions into a U-shape, and then to electrically connect the end of the U-shape tip portion of the leg portion to the upper side of terminal from the underside of the terminal such that the other portion of the leg portion does not contact with the terminal with keeping a gap between the other portion and the terminal.

These and other objects, features and advantages of the present invention will be more apparent from the following description of a preferred embodiment, taken in conjunction with the accompanying drawings.

FIGS. 1 to 5 show a conventional mounting structure of a reed switch, in which FIG. 1 is a perspective view of a housing, FIG. 2 is a exploded perspective view of an assembly body, FIG. 3 is an a perspective view of the assembly body, FIG. 4 is a perspective view for explaining the mounting state of a reed switch to the housing and FIG. 5 is a cross sectional view taken along line B--B in FIG. 4,

FIG. 6 is a graph showing an operation sound characteristic of an eddy-current indicator having no reed switch,

FIG. 7 is a graph showing an operation sound characteristic of an eddy-current indicator having the conventional reed switch,

FIG. 8 shows a cross sectional view of a primary portion of an embodiment of a mounting structure of a reed switch in an eddy-current indicator according to the present invention,

FIG. 9 shows a cross sectional view of a primary portion of another embodiment of a mounting structure of a reed switch in an eddy-current indicator according to the present invention,

FIGS. 10 and 11 show a cross sectional view and a perspective view of still another embodiment according to the present invention, and

FIG. 12 is a graph showing an operation sound characteristic of an eddy-current indicator for explaining the effect in each embodiment according to the present invention.

Hereinafter, embodiments according to the present invention will be described in accordance with drawings.

FIG. 8 shows a cross sectional view of an embodiment of a mounting structure of a reed switch in an eddy-current indicator according to the present invention, and this cross sectional view is corresponding to a view taken along line A--A in FIG. 4. Other parts which are not shown in the drawing are the same as conventional one which is described in FIGS. 1 to 5, thus it is believed to be unnecessary to explain.

As shown in FIG. 8, the reed switch 4 is arranged between both side arms 7a, 7b of a distributing plate 7. The reed switch 4 has leg portions 4a, 4b which extend opposite directions on the underside of the side amrs 7a, 7b with keeping a certain space between each of the side arms and the leg portion. The tip parts of the leg portions 4a, 4b are bent into a U-shape, respectively. Only end portions of the tip parts of the leg portions 4a, 4b are respectively secured to the copper-leaf conductive bodies 6a, 6b provided on the top surface of the side amrs 7a, 7b by soldering at soldering points 15a, 15b as shown in FIG. 8. Thus, the reed switch 4 is electrically connected to the copper-leaf conductive bodies 6a, 6b.

As a result, between each of the leg portions 4a, 4b of the reed switch 4 which is secured to the distributing plate 7 as mentioned above and the under surface of each of the side arms 7a, 7b of the distributing plate 7, there is provided a suitable space G such that the leg portions 4a, 4b do not directly contact with the under surfaces of the side arms 7a, 7b.

On the bottom of each of the recesses 21a, 21b which are formed on opposite sides of a long and thin opening 2 provided in a concave portion 3 of a housing 1, a substantially plate-shaped cushion member 25a, 25b is disposed, respectively. Each of the cushion members 25a, 25b comprises for example a foam resin or a foam rubber having a substantially rectangular shape. The cushion member may be secured to the bottom of the recess with an adhesive, respectively. Then, the leg portions 4a, 4b of the reed switch 4, particularly portions thereof which constitute the spaces G with respect to the side arms 7a, 7b of the distributing plate 7, can fully and elastically contact with the surfaces of the cushion members 25a, 25b under urged state.

In the above-mentioned structure, since the cushion members 25a, 25b always contact with the portions of the leg portions 4a, 4b of the reed switch 4 elastically, an operation vibration energy generated in the reed switch 4 is absorbed in the cushion members 25a, 25b, so that the vibration energy is not transmitted to the side arms 7a, 7b of the distributing plate 7 and the housing 1, thus generation of a resonance sound can be prevented.

Particularly, since the leg portions 4a, 4b of the reed switch 4 are soldered at only the ends of the U-shaped tip parts thereof to the copper-leaf conductive bodies 6a, 6b provided on the top surfaces of the side arms 7a, 7b with keeping the certain space G between the leg portions and the side arms 7a, 7b of the distributing plate 7, a sufficient contact area can be obtained between the leg portions 4a, 4b and cushion members 25a, 25b. Therefore, the operation vibration energy of the reed switch 4 is well absorbed in the cushion members 25a, 25b before it reaches the securing portions of the leg portions 4a, 4b to the side arms 7a, 7b. As a result, the transmission of the vibration to the side arms 7a, 7b can be effectively prevented.

In the above-mentioned embodiment, the spaces G are arranged between the leg portions 4a, 4b and the under surfaces of the side arms 7a, 7b of the distributing plate 7, respectively. However, please note that the provision of these spaces are not essential to the present invention although the prevention effect for the vibration transmission may be somewhat lowered if they are not provided. However, what is the most important in this structure is to absorb the vibration generated in the leg portions 4a, 4b by the cushion members 25a, 25b.

In the embodiment shown in FIG. 8, the cushion members 25a, 25b are secured to the bottom portions of the recesses 21a, 21b, but the cushion members may be fixed on support members 26a, 26b which are mounted on the distributing plate 7 so as to elastically protrude into the opening as shown in FIG. 9. According to this embodiment of FIG. 9, the vibration can be also absorbed by the support members 26a, 26b.

Moreover, please also note that the side arms 7a, 7b of the distributing plate 7 are not essential. Namely, as shown in FIGS. 10 and 11, it is possible to provide a pair of terminals 31a, 31b which are secured to an insulating plate 30 comprising a phenol resin or the like with revets 32a, 32b. In this case, the leg portions 4a, 4b of the reed switch 4 are in engagement with bending ends 31c, 31d of the terminals 31a, 31b and are fixed by soldering at soldering sections 33a, 33b, respectively.

FIG. 12 shows an operation sound characteristic of an overcurrent-type indicator with the above-mentioned mounting structure according to the present invention, as apparently seen from the drawing, an operation vibration sound generated from the reed switch, which is represented by a dot line, is dissolved.

In summary, according to the present invention, since the cushion members are always in contact with the leg portions of the reed switch elastically, the operation vibration energy generated from the reed switch is absorbed in the cushion members, so that the vibration energy is not transmitted to a pair of the side arms and the housing, thereby the generation of a resonance sound being prevented.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.