Level sensor and method for manufacturing level sensor

Abstract

To provide a level sensor which is less affected by heat stress and a method for manufacturing a level sensor.SOLUTION: A level sensor 1 includes a cylindrical part 11 (a storage unit) and a hole IC 20 (a magnetic detection element) stored in the cylindrical part 11. In the cylindrical part 11, a potting agent 40 covering the entire hole IC 20 is filled. An inner surface 12a as a contact surface in contact with the potting agent 40 of the cylindrical part 11 is provided with a drain hole 18 connecting to the outside.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a level sensor and a method for manufacturing a level sensor. [Background technology]

[0002] A level sensor that detects the level of a liquid contained inside a tank is known (see, for example, Patent Document 1). The liquid level detection device (level sensor) described in Patent Document 1 includes a device body that houses a Hall element that detects magnetism, and a holder that is rotatably provided with respect to the device body and has a magnet that surrounds the Hall element. The liquid level detection device also includes a float arm whose base end is connected to the holder, and a float that is fixed to the other end of the float arm. In the liquid level detection device, the float follows the liquid level in the tank, causing the float arm to swing, and this swing causes the holder and magnet to rotate, and the Hall element detects the change in magnetic flux of the rotating magnet, thereby measuring the liquid level. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-205136 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the above-mentioned Hall element is generally fixed inside the device body in an insulated state by a potting agent filled in the device body. However, when filling the potting agent, a gap may be generated between the potting agent and the device body, or minute air bubbles may be generated in the potting agent, resulting in the formation of a void when the level sensor is completed. If a level sensor in which a void is generated is installed in a fuel tank of a vehicle, thermal stress caused by temperature changes in the tank will concentrate around the void, and cracks or the like will occur in the device body starting from the void. This may cause fuel to enter the device body, resulting in a breakdown of the level sensor. In this regard, it is possible to reduce the above-mentioned gap by lowering the viscosity of the potting agent, but in this case, the force fixing the Hall element to the device body will be reduced, and the earthquake resistance of the level sensor will be reduced. On the other hand, it is also possible to reduce the air bubbles by lengthening the degassing time for removing the air bubbles, but in this case, the manufacturing time of the level sensor will be extended and the manufacturing cost of the level sensor will increase.

[0005] An object of the present invention is to provide a level sensor that is less susceptible to the effects of thermal stress and a method for manufacturing the level sensor. [Means for solving the problem]

[0006] In order to solve the above problems and achieve the above objectives, the level sensor is provided with a storage section and a magnetic detection element stored inside the storage section, and is characterized in that the level sensor is provided with a potting material that is filled inside the storage section and covers the entire magnetic detection element, and a drainage hole that is provided on the contact surface of the storage section with the potting material and communicates with the outside. Effect of the Invention

[0007] According to the present invention, it is possible to provide a level sensor that is less susceptible to the effects of thermal stress and a method for manufacturing a level sensor. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing a level sensor according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a vertical cross-sectional view showing the level sensor before being filled with a potting agent. [Diagram 3] FIG. 4 is a vertical cross-sectional view showing the level sensor when a potting material is being filled. [Figure 4] FIG. 4 is a vertical cross-sectional view showing the level sensor after being filled with a potting agent. [Diagram 5] FIG. 11 is a vertical cross-sectional view showing a state in which a receiving jig is attached to the level sensor after filling with potting material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the level sensor 1 will be described below with reference to Figs. 1 to 5. The level sensor 1 is installed, for example, inside a fuel tank of a vehicle, and detects the level of the liquid contained inside the tank. As shown in Fig. 1, the level sensor 1 includes a lead frame assembly 10. The lead frame assembly 10 is an assembly including terminals 17 connected to an external circuit, and is contained in a sensor housing (not shown). The lead frame assembly 10 includes a tubular portion 11 (container) extending in a predetermined direction, and a box portion 14 connected to one end of the tubular portion 11. The tubular portion 11 is made of a resin material such as PPS (polyphenylene sulfide), and is formed into a cylindrical shape with a bottom, including a disk-shaped bottom wall 12 (bottom) and a side wall 13 rising from the periphery of the bottom wall 12.

[0010] The box portion 14 is formed in a substantially rectangular plate shape and extends in a direction intersecting the axial direction of the tube portion 11. The box portion 14 is formed with a plurality of recesses 15 recessed in the plate thickness direction. The recesses 15 are portions for accommodating the leads 24 and the lead frames 25 described later, and in this embodiment, a total of three recesses 15 are formed in accordance with the number of the leads 24 and the lead frames 25. The inside of the recesses 15 communicates with the inside of the tube portion 11. A protruding portion 16 protruding outward is formed on the side of the box portion 14. Three protruding portions 16 are formed in accordance with the number of the leads 24 and the lead frames 25. The inside of the protruding portion 16 communicates with the inside of the recess 15, and a terminal 17 provided on a lead wire (not shown) connected to the lead frame 25 is accommodated in the inside of the protruding portion 15. A part of the terminal 17 protrudes outward from each protruding portion 16 of the box portion 14.

[0011] As shown in FIG. 2, the tubular portion 11 is formed with a vent hole 18 that communicates in the inside and outside directions. The vent hole 18 is a hole that releases gas inside the tubular portion 11 to the outside, and opens to the inner surface 12a of the bottom wall 12, which is the contact surface with the potting material 40, and communicates with the outside. The vent hole 18 has a first hole portion 18a and a second hole portion 18b. One end of the first hole portion 18a opens to the inside of the tubular portion 11, and the other end communicates with the second hole portion 18b. One end of the second hole portion 18b is continuous with the first hole portion 18a, and the other end opens to the outside of the tubular portion 11. The inner diameter of the second hole portion 18b is formed larger than the inner diameter of the first hole portion 18a. Specifically, the inner diameter of the first hole portion 18a is set to about 1 mm from the viewpoint of preventing leakage of the potting material 40 described later, and the inner diameter of the second hole portion 18b is set to 1 mm or more. In this embodiment, the punched hole 18 is configured with the first hole portion 18a and the second hole portion 18b, but the second hole portion 18b may be omitted.

[0012] The Hall IC 20 is accommodated inside the tube portion 11. The Hall IC 20 is an electronic component including a magnetic detection element, an amplifier circuit, and the like, and includes a top surface 21, a side surface 22, and a bottom surface 23. A conductive lead 24 extending toward the box portion 14 is connected to the top surface 21 of the Hall IC 20. In this embodiment, a total of three leads 24 are provided, one for transmitting a signal to the Hall IC 20, one for grounding the Hall IC 20, and one for powering the Hall IC 20. A lead frame 25 is connected to the leads 24. The lead frame 25 is a member that electrically connects the Hall IC 20 to an external circuit, and is formed of a conductive metal plate such as stainless steel. The tube portion 11 of the lead frame assembly 10 configured in this manner is to be fitted into a mounting hole 31 of a holder 30 (both of which are only shown in FIG. 2), and the bottom wall 12 side is covered by the holder 30 due to this fitting. The holder 30 is a member that houses a magnet 32 ​​(shown only in FIG. 2) that circumferentially covers the magnetic detection element of the Hall IC 20 from the outside of the cylindrical portion 11.

[0013] The holder 30 is supported by the sensor housing (not shown) so as to be rotatable around the axis of the tube part 11. The holder 30 is connected to a float (not shown) that swings following the liquid level of the liquid to be detected, and rotates around the axis of the tube part 11 in accordance with the swing of the float. When the holder 30 rotates, the magnet 32 ​​also rotates, and the magnetic flux of the magnet 32 ​​changes due to this rotation, and the magnetic detection element detects the change in magnetic flux to measure the liquid level. As shown in FIG. 3, the entire Hall IC 20, a part of the lead 24, and a part of the lead frame 25 are fixed inside the tube part 11 in a state where they are covered with the potting material 40 filled inside the tube part 11. Specifically, the Hall IC 20 is fixed inside the tube part 11 in a state where it is spaced from the inner surface 12a of the bottom wall 12 of the tube part 11 in the axial direction of the tube part 11.

[0014] The potting material 40 is a material filled inside the cylindrical portion 11 for the purposes of protection from thermal or mechanical shock, prevention of intrusion of liquid inside the tank, insulation, etc., and is made of a resin material such as epoxy resin or urethane resin.

[0015] Next, a method for manufacturing the level sensor 1 will be described. First, as shown in FIG. 2, a lead frame assembly 10 is prepared. The lead frame assembly 10 can be molded, for example, by resin molding. In this case, the punch hole 18 may be molded in accordance with the molding of the tubular portion 11 and the box portion 14, or the punch hole 18 may be formed by a drill or the like after the molding of the tubular portion 11 and the box portion 14. However, when the punch hole 18 is molded in accordance with the molding of the tubular portion 11 and the box portion 14, a long and thin pin of about 1 mm is required as a mold for molding the first hole portion 18a. In this case, the strength of the mold is likely to decrease, and the mold is likely to be damaged by repeated use. Therefore, when the punch hole 18 is molded in accordance with the molding of the tubular portion 11 and the box portion 14, it is preferable to refrain from omitting the second hole portion 18b as described above. By not omitting the second hole portion 18b, the diameter of a part of the mold for the punch hole 18 becomes large, so that the strength of the mold can be increased.

[0016] After the lead frame assembly 10 is prepared in this manner, the Hall IC 20, the leads 24, and the lead frame 25 are placed inside the tube portion 11. Next, as shown by the white arrow in FIG. 3, the liquid (liquid) potting material 40 is filled from the opening side of the tube portion 11 toward the bottom wall 12 side. At this time, the potting material 40 flows between the bottom surface 23 of the Hall IC 20 and the inner surface 12a of the bottom wall 12 while covering the Hall IC 20 in the order of the top surface 21, the side surface 22, and the bottom surface 23 of the Hall IC 20. At this time, the air inside the tube portion 11 and gas such as bubbles generated in the potting material 40 flow toward the hole 18 while being pushed by the potting material 40. Then, these gases escape to the outside through the hole 18 as shown by the solid arrow in FIG. 3.

[0017] Then, as shown in FIGS. 4 and 5, when the potting material 40 fills the gap between the bottom surface 23 of the Hall IC 20 and the inner surface 12a of the bottom wall 12, the filling of the potting material 40 is completed. In this way, by providing the vent hole 18, the gas inside the tube portion 11 can be discharged to the outside. Therefore, the potting material 40 can be spread throughout the entire inside of the tube portion 11 without gaps even without lowering the viscosity of the potting material 40. This is particularly effective for a configuration such as the tube portion 11 of this embodiment in which the storage portion of the Hall IC 20 is elongated and gaps are likely to occur while the potting material 40 is spreading to every corner. In addition, according to this configuration, even if air bubbles are generated in the potting material 40, the air bubbles can be discharged to the outside through the vent hole 18, so that the air bubbles in the potting material 40 can be reduced without ensuring a long degassing time.

[0018] Next, the potting agent 40 is heated for a predetermined time by hot air or far infrared rays, etc., to harden the potting agent 40. This hardening fixes the Hall IC 20, the leads 24, and the lead frame 25 inside the tube portion 11. In this embodiment, since the inner diameter of the first hole portion 18a of the punch hole 18 is set to about 1 mm, the potting agent 40 itself is unlikely to leak out of the punch hole 18 due to surface tension. However, in the unlikely event that the potting agent 40 leaks out of the tube portion 11, or in order to reliably prevent such leakage, as shown in FIG. 5, a step of installing a receiving jig 50 may be provided taking into account the time it takes for the potting agent 40 to fill the entire inside of the tube portion 11. For example, as shown in FIG. 5, the receiving jig 50 may be attached to the punch hole 18 in accordance with the timing at which the potting agent 40 fills the first hole portion 18a. The receiving jig 50 includes a cylindrical sealing protrusion 51 and a flat plate-shaped main body portion 52 that supports the sealing protrusion 51.

[0019] The sealing projection 51 is configured with a diameter larger than the inner diameter of the first hole portion 18a and smaller than the inner diameter of the second hole portion 18b. With this configuration, in this embodiment, the sealing projection 51 can be inserted into the second hole portion 18b of the punched hole 18, and when inserted into the second hole portion 18b, its end face 53 abuts against the opening edge of the first hole portion 18a. In this state, the inside of the first hole portion 18a is sealed by the end face 53, thereby reliably preventing the potting material 40 from flowing out to the outside. The main body portion 52 is formed in a cylindrical shape with a diameter larger than the diameter of the sealing projection 51.

[0020] As described above, according to this embodiment, the level sensor 1 including the tubular portion 11 (accommodation portion) and the Hall IC 20 (magnetic detection element) accommodated inside the tubular portion 11 includes the potting material 40 that fills the inside of the tubular portion 11 and covers the entire Hall IC 20. The inner surface 12a of the tubular portion 11, which is the contact surface with the potting material 40, is provided with a hole 18 that communicates with the outside.

[0021] According to this configuration, the gas between the potting material 40 and the tube portion 11 can be discharged to the outside through the vent hole 18. Therefore, the potting material 40 can be spread throughout the entire inside of the tube portion 11 without gaps even without lowering the viscosity of the potting material 40. This makes it possible to suppress the generation of voids without impairing the stability of the Hall IC 20. Even if air bubbles are generated in the potting material 40, the air bubbles can be discharged to the outside through the vent hole 18, so that the generation of voids can be suppressed without ensuring a long degassing time. By suppressing the generation of voids, the effect of thermal stress on the level sensor 1 can be reduced. Therefore, it is possible to provide a level sensor 1 that is less susceptible to the effect of thermal stress. Furthermore, by forming the vent hole 18, the amount of resin required for molding the tube portion 11 can be reduced, and the manufacturing cost of the level sensor 1 can be reduced.

[0022] In this embodiment, the punch hole 18 is composed of the first hole portion 18a and the second hole portion 18b. For example, when the punch hole 18 is provided at the same time as the resin molding of the tubular portion 11, a pin-shaped mold corresponding to the shape of the punch hole 18 is required. In this case, in order to prevent the potting agent 40 from leaking to the outside, it is preferable to form the punch hole 18 with an inner diameter of about 1 mm, so that the pin-shaped mold is likely to be elongated. Due to this shape, the strength of the mold is likely to decrease, and the mold is likely to be damaged by repeated use. However, according to this embodiment, the inner diameter of the second hole portion 18b is made larger than the inner diameter of the first hole portion 18a, so that the diameter of a part of the mold for the punch hole 18 can be increased. Therefore, the strength of the mold for forming the punch hole 18 can be improved, and the durability of the mold can be improved.

[0023] In this embodiment, the vent hole 18 is formed in the bottom wall 12 (bottom) of the tubular portion 11, and the bottom wall 12 side of the tubular portion 11 is covered with the holder 30 containing the magnet 32. According to this configuration, by forming the vent hole 18 in the bottom wall 12, when the potting agent 40 is filled from the upper side of the tubular portion 11, the gas in the tubular portion 11 can be pushed toward the vent hole 18 by the potting agent 40 flowing toward the bottom wall 12 side. This makes it difficult for gas to remain in the tubular portion 11, and makes it easier to prevent the above-mentioned void from occurring. According to this configuration, the bottom wall 12 side of the tubular portion 11 is covered with the holder 30 containing the magnet 32, so that the vent hole 18 is not exposed in the tank in which the level sensor 1 is installed. Therefore, it is possible to prevent the fluid in the tank from entering the tubular portion 11 through the vent hole 18.

[0024] According to this embodiment, a level sensor 1 that is resistant to the effects of thermal stress can be manufactured by the steps of accommodating the Hall IC 20, filling the potting material 40 and evacuating the gas inside the tubular portion 11 through the hole 18, and hardening the potting material 40.

[0025] Furthermore, when manufacturing the level sensor 1, the receiving jig 50 is placed to seal the punched hole 18. Therefore, the receiving jig 50 can prevent the potting material 40 from flowing out of the tubular portion 11 through the punched hole 18.

[0026] An embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to these embodiments, and the present invention also includes design changes and the like that do not deviate from the gist of the present invention. [Explanation of symbols]

[0027] 1 Level Sensor 11 Cylinder section (housing section) 18 Punching hole 20 Hall IC (magnetic detection element) 40 Potting agent

Claims

1. A level sensor including a housing portion and a magnetic detection element housed inside the housing portion, a potting agent that is filled into the housing and covers the entire magnetic detection element; a hole provided on a contact surface of the container portion with the potting material and communicating with the outside.

2. The container is made of a resin material, The void includes a first hole portion that opens into the inside of the storage portion and a second hole portion that is continuous with the first hole portion and opens to the outside of the storage portion, 2. The level sensor according to claim 1, wherein an inner diameter of the second hole portion is larger than an inner diameter of the first hole portion.

3. the housing portion includes a bottomed cylindrical tube portion that houses the magnetic detection element, a holder that houses a magnet and that circumferentially covers the magnetic detection element from outside the cylindrical portion; 2. The level sensor according to claim 1, wherein the hole is formed in a bottom of the cylindrical portion.

4. A method for manufacturing a level sensor including a housing portion having a through hole communicating with an inside and an outside, a magnetic detection element housed inside the housing portion, and a potting agent filled inside the housing portion and in contact with the through hole, the method comprising the steps of: housing the magnetic detection element inside the housing portion; filling the inside of the container with the liquid potting agent to remove gas from the container through the vent hole; and a step of hardening the potting agent.

5. The method for manufacturing a level sensor according to claim 4, further comprising the step of installing a receiving jig that seals the inside of the hole.

Images