Embodiments of the present invention relate to a liquid level detection device capable of improving a bonding strength between components, and a method of manufacturing the liquid level detection device.
Various types have been developed as a liquid level detection device, which is provided in a fuel tank for storing liquid fuel such as gasoline, and measures a liquid level of liquid fuel. For example, Patent Literature 1 discloses a liquid level detection device, which comprises a float that is vertically moved accompanying a liquid level fluctuation, a float arm that converts the vertical movement of the float into a rotational movement, a detection unit that outputs a detection signal indicating a liquid level in accordance with the rotational movement of the float arm, and a first case and a second case that contain the detection unit in a closed state.
Patent Literature 2 discloses a method of manufacturing a liquid level detection device, which manufactures a fuel level gauge for detecting a liquid level height, comprising a housing fixed to a fuel tank, and a circuit unit that is comprised of a magnetoelectric conversion element, a capacitor, and a terminal, and is embedded inside the housing. In a first molding process, a cover unit that covers the terminal with a molding material of the housing is formed. The cover unit has a positioning groove with one end in the longitudinal direction closed and the other end opened. In a connection process, a foot portion of the capacitor is inserted into the positioning groove, thereby positioning the capacitor, and the foot portion is welded to a capacitor connection part. In a second molding process, the capacitor is covered, providing an appearance of the housing.
Patent Literature 1: JP-A-2003-172653
Patent Literature 2: JP-A-2011-203022
However, in the liquid level detection device disclosed in the Patent Literature 1, the welding structure of first and second cases adopts a structure that fixes a contact surface comprising the flat surfaces of the first and second cases by melting by a laser. Such welding is difficult to grasp the state of welding, and may be insufficient in the strength of welding.
In the liquid level detection device manufactured by the method of manufacturing a liquid level detection device disclosed in the Patent Literature 2, the housing is composed of a first molded product comprising the circuit unit, and a second molded product covering the area around the first molded part. When inserting the first molded product into the second molded product, since the positioning part formed in the first molded product is not covered by the second molded product, there is a problem that a fuel soaks through a gap between the first and second molded products, and corrodes the internal circuit. When setting the second molded product in a mold, a fitting failure occurs, and a concave portion that is a positioning part is not set on a pin. This causes a problem that the production equipment is stopped, and the production efficiency is lowered.
The present invention has been made in order to solve the above problems. Accordingly, it is an object of the invention to provide a liquid level detection device capable of improving a bonding strength between components, and a method of manufacturing the liquid level detection device.
In order to achieve the above object, a liquid level detection device according to a first aspect of the invention comprises a holder that has a magnet inside, and rotates in accordance with displacement of a float floating on liquid that is a measuring object of liquid level; a main body unit that rotatably supports the holder, and has a magnetic detection element for detecting a change in a magnetic pole accompanying rotation of the magnet; and a cover that covers the holder, and prevents the holder from falling out from the main body unit by welded to the main body unit, wherein the cover is welded to the main body unit by melting a protrusion formed in the main body unit or the cover.
The protrusion may be tapered, and may have a trapezoidal cross section.
In order to achieve the above object, a liquid level detection device according to a second aspect of the invention comprises a holder that has a magnet inside, and rotates in accordance with displacement of a float floating on liquid that is a measuring object of liquid level; and a main body unit that comprises a magnetic detection element for detecting a change in a magnetic pole accompanying rotation of the magnet, a capacitor, and a terminal that is electrically connected to the magnetic detection element and the capacitor, wherein the main body unit comprises a primary molded body that is formed by insertion molding the terminal, and a secondary molded body that is formed by insertion molding the primary molded body provided with the capacitor and the magnetic detection element, the primary molded body comprises a positioning means for positioning the primary molded body at a predetermined position when molding the secondary molded body, and a first protrusion ring that is a circular protrusion surrounding the positioning means, and an apex of the first protrusion ring is welded to a part that is molded when molding the second molded body.
The positioning means may be a pin hole into which a positioning pin is inserted, and an inside slope of the first protrusion ring may be directly connected to the peripheral edge of the pin hole.
The primary molded body may have a second protrusion ring surrounding the first protrusion ring.
The first protrusion ring may have a triangular cross section.
In order to achieve the above object, a method of manufacturing a liquid level detection device according to a third aspect of the invention is a method of manufacturing a liquid level detection device comprising a holder that has a magnet inside, and rotates in accordance with displacement of a float floating on liquid that is a measuring object of liquid level; and a main body unit comprising a magnetic detection element for detecting a change in a magnetic pole accompanying rotation of the magnet, a capacitor, and a terminal that is electrically connected to the magnetic detection element and the capacitor, the method is characterized by comprising a step of molding a primary molded body by insertion molding the terminal, and a step of molding the main body unit by insertion molding the primary molded body provided with the capacitor and the magnetic detection element, wherein the primary molded body comprises a positioning means for position the primary molded body at a predetermined position when molding the main body unit, and a protrusion ring that is a circular protrusion surrounding the positioning means.
According to the embodiments of the present invention, it is possible to provide a liquid level detection device capable of improving a bonding strength between components, and a method of manufacturing the liquid level detection device.
Hereinafter, a liquid level detection device 1 according to an embodiment of the present invention will be explained with reference to the accompanying drawings.
As shown in
The float 50 is made of synthetic resin, for example, and is configured to receive buoyancy from liquid as an object of measuring a liquid level, and is floated in the liquid. The float 50 is formed substantially in a bale shape so as to stably float in the liquid.
The float arm 40 is made of a metallic wire, for example, and is interposed between the float 50 and the holder 20 thereby connecting them. The float arm 40 transmits a vertical movement of the float 50 caused liquid level fluctuations to the holder 20. The holder 20 rotates on the main body unit 10 by the force transmitted from the float arm 40.
The main body unit 10 is made of resin material such as Polyacetal. In substantially a central portion of the top of the main body unit 10 in the drawing, a cylindrical rotary support part 11 is protruded. The rotary support part 11 supports the holder 20 rotatably in a circumferential direction, when it is fit with a rotation hole 24 formed in the holder 20 described later. On the top of the main body unit 10, four welding protrusions 12 are formed so as to surround the rotary support part 11. By melting the welding protrusions 12 by laser or the like, the cover 30 is welded to the main body unit 10. The welding protrusions 12 shown in
As shown in
The holder 20, like the main body unit 10, is made of resigning material such as Polyacetal. The holder 20 is provided with an arm holding part 21 for holding the float arm 40 having a float 50 attached at the distal end thereof.
As shown in
The holder 20 has a cylindrical magnet 25 inside. The magnet 25 is previously set in a mold before the holder 20 is molded. Thereafter, the magnet 25 is fixed in the holder by injecting a resin for the holder 20 into the mold. The magnet 25 is made of neodymium ferrite, for example, and is magnetized in two poles in the embodiment. When the holder 20 is attached to the main body unit 10, the magnet in the holder 20 is arranged to face to the magnetic detection element 14 provided in the main body unit 10. Thus, the magnetic detection element 14 can detect changes in the magnetic pole of the magnet 25 accompanying the rotation of the holder 20.
A middle hole 22a of the rotary shaft 22 provided on the top of the holder 20, and a rotation hole 24 provided on the bottom of the holder 20 are each communicating to the magnet 25. Thus, it is possible to view the magnet 25 fixed in the holder 20 from outside through the middle hole 22a and the rotation hole 24. As the holder 20 is provided with the middle hole 22a and the rotation hole 24 communicating to the magnet 25, it is possible to discharge the gas generated inside during molding the main body unit 10 to the outside. Thus, it is possible to ensure sufficient contact between the magnet 25 and the holder 20.
The cover 30 is made of resigning material such as Polyacetal, like the main body unit 10 and the holder 20. As shown in
As shown in
Next, a structure of the liquid level detection device 1 will be described in detail while describing a manufacturing process of the main body unit 10 that is a component of the liquid level detection device 1 according to the embodiment.
The main body unit 10 of the liquid level detection device 1 according to the embodiment is manufactured through two times of resin molding process.
A structure of the primary molded body 60 manufactured as above will be described in detail. As shown in
As shown in
Then, a magnetic detection element 14, a capacitor 15, and a wiring cord 13 are arranged on the primary molded body 60, and electrically connected to the terminal 16 by laser welding or resistance welding. As shown in
Further, the embodiment uses the capacitor 15 with two lead wires 15a extend from a main body. As shown in
Two positioning parts 64 are formed on the top of the primary molded body 60 (the surface shown in
As shown in
As shown in
As shown in FIGS. (a) and (b), first the positioning pin 81 provided in the mold is inserted into the pin hole 67, and the primary molded body 60 is positioned and fixed. Then, the resin for the secondary molded body 70 is injected into the mold 80, and the secondary molded body 70 is formed around the primary molded body 60.
As described above, the first protrusion ring 65 and second protrusion ring 66 have triangular cross sections with a pointed apexes. Thus, the apexes of the first and second protrusion rings 65 and 66 are easily melted by the molding heat of secondary molding. Therefore, it is possible to securely execute the welding of the primary molded body 60 and the secondary molded body 70. This securely prevents the liquid to be measured from entering into the main body unit 10, and prevents corrosion of the mounted electronic components or the like.
In this way, the primary molded body 60 provided with the magnetic detection element 14 and the likes is formed by insertion molding, and the main body unit 10 shown in
The dissolving amount of the welding protrusion 12 for welding the cover 30 to the main body unit 10 is desirably a half or more of the height of the trapezoid. The dissolving amount of the welding protrusion 12 can be checked by measuring the amount of gap between the cover 30 and the main body unit 10. As described above, as a cross section of a part to be melted is formed as a tapered trapezoidal protrusion, it is possible to easily ensure the proper welding strength between the cover 30 and the main body unit 10. It is also possible to easily check whether the welding is properly executed.
Next, the holder 20 and the magnet 25 formed in the holder 20 by insertion molding will be explained.
As described above, the holder 20 is provided with a middle hole 22a that communicates to the magnet 25 so as to enable to visually recognize the magnet 25 from outside. The central axes of the rotary shaft 22 (middle hole 22a) and the magnet 25 are aligned. Therefore, the magnet 25 is formed by insertion molding, so that when the magnet 25 is viewed through the middle hole 22a, the center of the magnet 25 coincides with the center of the middle hole 22a. As shown in
As described above, since mark 25a indicated in the center of the magnet 25 can be viewed from outside through the middle hole 22a, when the mark 25a is present at the center of the middle hole 22a, it is possible to determine that the magnet 25 has been placed in an appropriate position in the holder 20. On the other hand, when the mark 25a is not present at the center of the middle hole 22a, it is possible to determine that the magnet 25 has been displaced, and the amount of displacement can also be checked. Therefore, it is possible to detect the displacement of the magnet 25 in an early stage, thereby improving the yield in the manufacturing process.
In the holder 20 in the embodiment, four magnet check holes 23 are formed separately from the middle hole 22a to enable detection of the displacement of the magnet 25 in an early stage. As shown in
The invention is not limited to the above embodiment, and may be modified and improved in various forms. In the embodiment, the main body unit 10 is provided with a protruded rotary support part 11, the holder 20 is provided with a rotation hole 24 to fit with the rotary support part 11. The main body unit 10 may be provided with a hole for rotation, and the holder 20 may be provided with a protrusion to fit in the hole. Similarly, the relationship between the holder 20 and the cover 30 is not limited to the embodiment.
In the embodiment, the terminal 16 comprises a first flat portion 16a, and a second portion 16b that is stepped down from the first portion 16a by the bent portion 19. The bending dimension of the bent portion 19 is determined by the distance between the lead wire 15a and the bottom of the capacitor 15. As shown in
In
Further, in the embodiment, an adhesive is used for bonding the capacitor 15 and the terminal 16 (the second portion 16b). A double-side tape, for example, may be used for bonding the both. The term “adhesive” used here includes an adhesive, a double-sided tape and the likes.
As shown in
The cross section of the first protrusion ring 65 and second protrusion ring 66 are not limited to a triangular shape, and may be any shape as long as the apex is tapered. Therefore, it is possible to easily melt the apex in the molding heat, and achieve secure welding of primary molded body 60 and the secondary molded body 70.
Further, as shown in
The mark 25a at the center of the magnet 25 is a circle in the embodiment. However, the mark 25a may be of any shape as long as the center position of the magnet 25 can be visually recognized. For example, the mark 25a may be a cross marked at the center of the magnet 25.
Further, as shown in
The embodiment of the invention is applied to a liquid level detection device that fixes components with a preferable strength, and a method of manufacturing the liquid level detection device.
Number | Date | Country | Kind |
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2012-218598 | Sep 2012 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2013/074057 | 9/6/2013 | WO | 00 |