JP2017090313A - Liquid level detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique that suppresses adhesion of foreign matters on a liquid level detection device due to a magnetic field of a permanent magnet above a level on a side opposite to a magnetic detection element.SOLUTION: A permanent magnet 44 to be arranged in the liquid level detection device is arranged to oppose a magnetic detection element. A rear surface 44b of the permanent magnet 44 is covered with an enclosure. An opposing surface 44a of the permanent magnet 44 has a pair of magnetic polarities magnetized. The rear surface 44b of the permanent magnet 44 has at least the pair of magnetic polarities magnetized so that an opposite magnetic polarity is located on a rear side of each magnetic polarity of the opposing surface 44a. The pair of magnetic polarities of the opposing surface 44a has an element side magnetic field that passes above the opposing surface 44a from one polarity of the opposing surface 44a and heads for other polarity thereof. The at least pair of magnetic polarities of the rear surface 44b has an opposite side magnetic field that passes above the rear surface 44b from one polarity of the rear surface 44b, and heads for other polarity thereof. Magnetic flux density of the element side magnetic field is greater than that of the opposite side magnetic field.SELECTED DRAWING: Figure 5

Description

  The technology disclosed in the present specification relates to a liquid level detection device (for example, a device that detects a liquid level of fuel stored in a fuel tank of an automobile or the like) that detects a liquid level.

  Patent Document 1 discloses a liquid that includes a float that floats on fuel, an arm that converts the vertical movement of the float into a rotational motion, a permanent magnet that rotates integrally with the arm, and a magnetic detection element that detects the rotation of the permanent magnet. A surface detection device is disclosed. The permanent magnet is disposed to face the magnetic detection element. A surface of the permanent magnet other than the surface facing the magnetic detection element is covered with one end of the arm. The permanent magnet has a pair of magnetic poles arranged in the axial direction of the arm. The magnetic field of the permanent magnet passes through the magnetic detection element from one end of the permanent magnet in the axial direction of the arm, and the magnetic detection element toward the other end of the permanent magnet in the axial direction of the arm uses the magnetic field of the permanent magnet. The rotation of the permanent magnet is detected.

JP 2003-172653 A

  In the above technique, the magnetic field of the permanent magnet passes from one end of the permanent magnet in the axial direction of the arm to the other end of the permanent magnet in the axial direction of the arm while passing through the magnetic detection element. The magnet passes from one end of the magnet over the back surface on the opposite side of the magnetism detection element to the other end of the permanent magnet in the axial direction of the arm. For this reason, on the back side of the permanent magnet, the magnetic field of the permanent magnet may spread to the outside of the arm covering the magnet, and foreign matter such as metal powder may adhere to the arm. As a result, the magnetic field of the permanent magnet changes and a detection error may occur.

  In this specification, the technique which suppresses that a foreign material adheres to a liquid level detection apparatus with the magnetic field of the permanent magnet on the surface on the opposite side to a magnetic detection element is provided.

  The liquid level detection device disclosed in this specification has a float, a float attached, an arm that converts the vertical motion of the float into a rotational motion, a rotating member that holds the arm, and a fixed to the rotating member A permanent magnet, a magnetic detection element facing the permanent magnet, and a support member that rotatably supports the rotation member with respect to the magnetic detection element. The permanent magnet has a facing surface that faces the magnetic detection element. The rotating member covers the back surface located on the back side of the opposing surface of the permanent magnet. The opposing surface of the permanent magnet is magnetized by at least a pair of magnetic poles. The back surface of the permanent magnet is magnetized to at least a pair of magnetic poles so that opposite magnetic poles are located on the back sides of the magnetic poles on the opposing surface. At least a pair of magnetic poles on the opposing surface has an element-side magnetic field that passes from one pole of the opposing surface to the other pole through the opposing surface. At least one pair of magnetic poles on the back surface has an opposite magnetic field that passes from one pole on the back surface to the other pole. The magnetic detection element detects the rotation of the magnet using the element-side magnetic field. The magnetic flux density of the opposite side magnetic field is smaller than the magnetic flux density of the element side magnetic field.

  For each magnetic pole of at least a pair of magnetic poles arranged on the opposing surface, the same magnetic pole is arranged on the back surface located on the back side of the opposing surface, that is, the same magnetic pole is arranged from the opposing surface to the back surface of the permanent magnet. Then, a symmetrical magnetic field is generated between the opposing surface side and the back surface side of the permanent magnet. For this reason, if it is going to make the magnetic flux density of the permanent magnet of a back surface side small, the magnetic flux density of the permanent magnet in the magnetic detection element side will also become small. In this case, the magnetic flux density passing through the magnetic detection element is also reduced, and the detection accuracy is lowered.

  According to the configuration described above, by disposing the opposite magnetic poles on the opposed surface side and the back surface side of the permanent magnet, the magnetic flux density of the opposite magnetic field can be kept small without reducing the magnetic flux density of the element-side magnetic field. it can. According to this structure, it can suppress that an opposite side magnetic field spreads beyond the rotating member which covers the back surface of a permanent magnet. As a result, it is possible to suppress foreign matter from adhering to the liquid level detection device, particularly the rotating member, by the opposite magnetic field.

The structure of the fuel pump module of an Example is shown. The front view of the magnetic sensor unit of an Example is shown. The disassembled perspective view of the magnetic sensor unit of an Example is shown. Sectional drawing of the IV-IV cross section of FIG. 2 of an Example is shown. The trihedral figure explaining arrangement | positioning of the magnetic pole of the permanent magnet of an Example is shown. The figure for demonstrating the magnetization method of the permanent magnet of an Example is shown. Sectional drawing which represents typically the magnetic flux of the permanent magnet of an Example is shown. Sectional drawing which represents typically the magnetic flux of the permanent magnet of a comparative example is shown. The longitudinal cross-sectional view of the permanent magnet of a modification is shown. The perspective view explaining arrangement | positioning of the magnetic pole of the permanent magnet of another modification is shown.

  The main features of the embodiments described below are listed. Note that the technical elements described below are independent technical elements, and exhibit technical usefulness alone or in various combinations.

(Characteristic 1) In the liquid level detection device of the embodiment, the opposing surface of the permanent magnet may be magnetized by a pair of magnetic poles. The back surface of the permanent magnet may be magnetized by the pair of magnetic poles so that the magnetic poles opposite to the magnetic poles on the opposing surface are located. According to this configuration, the rotation of the magnet can be detected by using the magnetic field from one magnetic pole of the pair of magnetic poles on the opposing surface to the other magnetic pole using the magnetic detection element. Thereby, the structure of a liquid level detection apparatus can be simplified.

(Feature 2) In the liquid level detection device of the embodiment, the permanent magnet may have a hollow portion that is recessed on the back surface side at a position facing the magnetic detection element on the facing surface. According to this structure, the magnetic flux which passes a magnetic detection element from the position which opposes the magnetic detection element of an opposing surface can be reduced. Thereby, it can suppress that the magnetic flux which passes a magnetic detection element changes greatly by the position of a permanent magnet shifting | deviating with respect to a magnetic detection element. As a result, it is possible to suppress a detection error due to the displacement of the position of the permanent magnet with respect to the magnetic detection element.

(Characteristic 3) In the liquid level detection device of the embodiment, the hollow portion may penetrate the permanent magnet from the facing surface to the back surface. According to this configuration, it is not necessary to generate a magnetic flux that passes through the magnetic detection element from a position facing the magnetic detection element on the opposite surface. Thereby, the detection error by the position of a permanent magnet shifting | deviating with respect to a magnetic detection element can be suppressed.

  As shown in FIG. 1, the fuel pump module 10 is a unit for supplying fuel in a fuel tank 4 mounted on a vehicle such as an automobile to an internal combustion engine (not shown). The fuel pump module 10 is disposed in the fuel tank 4.

  The fuel pump module 10 includes a fuel pump unit 12 and a liquid level detection device 20. The fuel pump unit 12 is accommodated in the fuel tank 4. The fuel pump unit 12 is attached to a set plate 6 that closes the opening of the fuel tank 4. The fuel pump unit 12 sucks the fuel in the fuel tank 4 into the fuel pump unit 12, boosts the fuel, and discharges the fuel outside the fuel pump unit 12. The fuel discharged from the fuel pump unit 12 is supplied from the discharge port 14 to an internal combustion engine (not shown).

  The liquid level detection device 20 includes a float 22, an arm 24 attached to the float 22, and a magnetic sensor unit 30 that detects the rotation angle of the arm 24. The float 22 floats on the fuel in the fuel tank 4 and moves in the vertical direction according to the liquid level of the fuel. The float 22 is rotatably attached to the tip of the arm 24. The base end of the arm 24 is rotatably supported by the magnetic sensor unit 30. When the float 22 moves up and down in accordance with the fuel level in the fuel tank 4, the arm 24 swings and rotates with respect to the fuel pump unit 12. That is, the arm 24 converts the vertical movement of the float 22 into a rotational motion. The arm 24 is made of a metal having resistance to fuel, such as stainless steel, and is formed in a cylindrical rod shape.

  As shown in FIGS. 2 and 3, the magnetic sensor unit 30 supports the arm 24 rotatably with respect to the fuel pump unit 12. 2 and the subsequent drawings, the float 22 and a part of the arm 24 on the float 22 side are omitted. The magnetic sensor unit 30 includes a support member 34, a permanent magnet 44, a cover 36, a magnetic sensor 48 (see FIG. 5), and a lead wire 32.

  The support member 34 is fixed to the outer wall of the fuel pump unit 12. The support member 34 is made of resin. The support member 34 includes a main body 35, a cylindrical portion 42, an axial direction restriction portion 40, and a rotation restriction portion 60. The main body 35 has a flat plate shape. The back surface of the main body 35 is attached to the outer wall of the fuel pump unit 12. On the surface side of the main body 35, an axial direction restricting portion 40 and a cylindrical portion 42 are disposed. The cylindrical portion 42 protrudes from the surface of the main body 35. The cylindrical portion 42 has a cylindrical shape with the rotation axis X of the arm 24 as the central axis.

  The arm 24 is attached to the outer peripheral surface of the cylindrical portion 42. The arm 24 has a curved portion 24 a that is curved in a semicircular shape at the end opposite to the float 22. The arm 24 further includes a pair of facing portions 24b that face each other. The arm 24 is attached to the support member 34 by inserting the facing portion 24 b into the cylindrical portion 42. As shown in FIG. 4, in a state where the arm 24 is attached to the support member 34, the arm 24 is disposed between a pair of axial restriction portions 40 disposed at both ends of the cylindrical portion 42 in the rotation axis X direction. The As a result, the arm 24 can be prevented from being displaced in the direction of the rotation axis X.

  A pair of rotation restricting portions 60 are disposed on the right side surface of the support member 34 in FIG. The pair of rotation restricting portions 60 are arranged away from each other in the rotation direction of the arm 24.

  A cover 36 to which a permanent magnet 44 is attached is attached to the support member 34 and the arm 24. The cover 36 is disposed on the support member 34 so as to be slidable in the rotation direction of the arm 24 around the rotation axis X. As shown in FIG. 4, the cover 36 includes a cylindrical outer edge portion 38 covering the base end of the arm 24 and the outer peripheral edge of the axial direction restricting portion 40, and the axial direction restricting portion 40 and the cylindrical portion 42 opposite to the main body 35. And a disc-shaped disc portion 39 covering from the above. According to this configuration, the cover 36 can suppress the arm 24 from falling off the support member 34. The arm 24 has a notch for sandwiching the arm 24 extending from the cover 36 at the left end of the cover 36 in FIG. As a result, the arm 24 is fixed to the cover 36, and the cover 36 rotates in synchronization with the rotation of the arm 24.

  The cover 36 has a stopper member at the right end in FIG. The stopper member protrudes from the end on the support member 34 side of the cover 36 to the support member 34 side, and is disposed between the pair of rotation restricting portions 60. When the cover 36 rotates around the rotation axis X in synchronization with the rotation of the arm 24, the stopper member abuts on one of the pair of rotation restricting portions 60 and restricts the rotation of the arm 24.

  As shown in FIG. 4, the cover 36 includes a cylindrical magnet housing portion 37 on the inner peripheral side of the cylindrical portion 42. The magnet housing part 37 has a substantially cylindrical shape with the rotation axis X as the central axis. A permanent magnet 44 is fitted on the inner peripheral side of the magnet housing portion 37. The cover 36 holds the permanent magnet 44 accommodated in the magnet accommodating portion 37. The back surface 44 b of the permanent magnet 44 is covered with a cover 36.

  The support member 34 accommodates the magnetic sensor 48. The magnetic sensor 48 is disposed so as to face the facing surface 44 a (the surface on the fuel pump unit 12 side) of the permanent magnet 44. The support member 34 is fixed to the magnetic sensor 48, and the arm 24 and the cover 36 are rotatable with respect to the support member 34. For this reason, the permanent magnet 44 fixed to the cover 36 can rotate with respect to the magnetic sensor 48.

  The magnetic sensor 48 detects the rotational movement of the arm 24 and outputs an analog signal corresponding to the amount of fuel stored in the fuel tank 4 to a fuel meter (not shown) based on the detection result (see FIG. 1). ). The magnetic sensor 48 is a magnetic sensor that detects the rotation angle of the permanent magnet 44, that is, the rotation angle of the arm 24. For example, an MRE (abbreviation of Magnet Resistive Element) or a Hall IC is used. A known sensor can be used. The magnetic sensor 48 includes a magnetic detection element that detects the direction of the magnetic flux of the permanent magnet 44 or the strength of the magnetic flux. The magnetic sensor 48 is covered by the support member 34 so as not to be exposed to the outside. The magnetic sensor 48 is arranged such that the detection center is located on the rotation axis X.

  A small clearance is set between the support member 34, the arm 24, and the cover 36 in consideration of dimensional error and swelling due to fuel. For this reason, the rotation center of the permanent magnet 44 and the detection center of the magnetic sensor 48 may be slightly shifted. In this embodiment, the rotation center of the permanent magnet 44 and the detection center of the magnetic sensor 48 are arranged on the rotation axis X, that is, in a state where they are arranged at normal positions in design. Relationships are explained.

  As shown in FIG. 2, three lead wires 32 extend from the magnetic sensor 48. The three lead wires 32 are connected to the power supply line 52, the output line 54, and the ground line 56, respectively. The power supply line 52, the output line 54, and the ground line 56 pass through the set plate 6 and are connected to the fuel meter.

  Next, the configuration of the permanent magnet 44 will be described. In FIG. 5, the magnetic poles of the permanent magnet 44 are shown. The upper part of FIG. 5 is a view of the facing surface 44a on the magnetic sensor 48 side. The middle view of FIG. 5 is a side view of the permanent magnet 44. The lower part of FIG. 5 is a view as seen from the back surface 44 b opposite to the magnetic sensor 48.

  The permanent magnet 44 has an annular shape coaxial with the rotation axis X. Specifically, the permanent magnet 44 has a shape in which both ends in the diametrical direction (left and right ends in FIG. 5) are cut off in an annular shape. This is to prevent the permanent magnet 44 from rotating with respect to the rotating member 34 described later. A flat surface that prevents the permanent magnet 44 from rotating is disposed on the inner peripheral surface of the magnet housing portion 37. The permanent magnet 44 has a cylindrical hollow portion 44c with the rotation axis X as a central axis. The cavity 44c penetrates the permanent magnet 44 from the facing surface 44a to the back surface 44b.

  As shown in the upper diagram of FIG. 5, on the facing surface 44 a side, the permanent magnet 44 is magnetized by a pair of magnetic poles of N and S poles. The N-pole region N1 and the S-pole region S1 of the facing surface 44a are arranged with the rotation axis X in between, the left half of the facing surface 44a is the N-pole region N1, and the right half is the S-pole region S1. It is.

  As shown in the center diagram of FIG. 5, the N pole region N <b> 1 is in contact with the S pole region S <b> 2 on the back surface 44 b side at the center in the thickness direction of the permanent magnet 44. Similarly, the south pole region S1 is in contact with the north pole region N2 on the back surface 44b side at the center of the permanent magnet 44 in the thickness direction.

  As shown in the lower diagram of FIG. 5, the permanent magnet 44 is magnetized to a magnetic pole opposite to the magnetic pole on the opposite surface 44 a side on the back surface 44 b side. The N-pole region N2 and the S-pole region S2 on the back surface 44b are arranged with the rotation axis X in between, the left half of the back surface 44b is the S-pole region S2, and the right half is the N-pole region N2. That is, the permanent magnet 44 has four magnetized regions of two N-pole regions N1, N2 and two S-pole regions S1, S2.

  Next, a method of magnetizing the permanent magnet 44 will be described with reference to FIG. FIG. 6 shows the side of the permanent magnet 44. The permanent magnet 44 is formed in a substantially annular shape using ferrite iron oxide with a forming die before magnetization. Next, the magnetizing yoke YK is brought into contact with the opposed surface 44a of the molded intermediate part before magnetization (hereinafter, the intermediate part is also referred to as “permanent magnet 44”). In the magnetized yoke YK, a coil is disposed on the iron core. The magnetizing yoke YK is brought into contact with each of the region that becomes the N-pole region N1 and the region that becomes the S-pole region S1 after the magnetization on the facing surface 44a. And an electric current is sent through the coil of the magnetizing yoke YK. Thereby, a strong magnetic field is generated from the magnetizing yoke YK, and the permanent magnet 44 is magnetized.

  Next, the magnetic field generated by the permanent magnet 44 will be described with reference to FIG. FIG. 7 schematically shows lines of magnetic force representing a magnetic field in the vicinity of the opposing surface 44a and the back surface 44b of the permanent magnet 44. The permanent magnet 44 has a sensor-side magnetic field that passes from the N-pole region N1 to the S-pole region S1 through the opposing surface 44a on the facing surface 44a side. Further, the permanent magnet 44 has an opposite magnetic field that passes from the N-pole region N2 to the S-pole region S2 through the back surface 44b on the back surface 44b side. The permanent magnet 44 is magnetized by abutting the magnetizing yoke YK on the facing surface 44a side. For this reason, in the permanent magnet 44, the magnetic flux density of the sensor-side magnetic field generated on the facing surface 44a side can be made larger than the magnetic flux density of the opposite-side magnetic field generated on the back surface 44b side.

  According to the liquid level detection device 20 of the present embodiment, the magnetic flux density on the cover 36 side can be kept small without reducing the magnetic flux density on the magnetic sensor 48 side of the permanent magnet 44. According to this configuration, it is possible to suppress the magnetic field of the permanent magnet 44 from extending beyond the cover 36 to the outside of the liquid level detection device 20. As a result, it is possible to prevent magnetic foreign matters such as metal powder contained in the fuel from adhering to the cover 36. Accordingly, it is possible to suppress a situation in which the magnetic field of the permanent magnet 44 is disturbed by the foreign substance of the magnetic body and a detection error occurs in the liquid level detection device 20.

  Further, in the permanent magnet 100 of the comparative example having a pair of magnetic poles as shown in FIG. 8 and having the same magnetic pole from the opposing surface to the back surface, the lines of magnetic force are on the S pole side from the end 102 on the N pole side of the permanent magnet. The end 104 extends symmetrically on the magnetic sensor 48 side and the cover 36 side. For this reason, if the magnetic flux density on the cover 36 side is to be suppressed, the magnetic flux density on the magnetic sensor 48 side is also reduced. On the other hand, in the permanent magnet 44 of the present embodiment, such a situation can be avoided.

  Further, the permanent magnet 44 has a hollow portion 44 c at a position facing the magnetic sensor 48. According to this configuration, it is not necessary to generate a magnetic flux that extends from a position facing the magnetic sensor 48 and passes through the magnetic sensor 48. As a result, the magnetic flux passing through the magnetic sensor 48 can be made parallel to the facing surface 44 a of the permanent magnet 44. Thereby, when the position of the permanent magnet 44 is shifted with respect to the magnetic sensor 48, it is possible to prevent the direction of the magnetic flux passing through the magnetic sensor 48 from changing greatly. As a result of the simulation using the permanent magnet 44, if the backlash due to the clearance set in the liquid level detection device 20 is about a level, the angle detection error is 0. 0 depending on the thickness and diameter of the permanent magnet 44. It was found that the error can be suppressed to a small error of 5 ° or less. This result is the same as when the conventional permanent magnet 100 as shown in FIG. 8 is used, and the liquid level detection device 20 of the present embodiment can also suppress the detection error to be small.

  As mentioned above, although embodiment of this invention was described in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  For example, the configuration of the permanent magnet 44 is not limited to the above embodiment. FIG. 9 is a longitudinal sectional view of the modified permanent magnet 44 as seen in a cross section passing through the rotation axis X. FIG. For example, as shown in FIG. 9, the end of the cavity 44c on the back surface 44b side may be closed. Alternatively, the cavity 44c may be filled with a nonmagnetic material such as resin. Alternatively, the permanent magnet 44 may not have the hollow portion 44c.

  For example, as shown in FIG. 10, two pairs of magnetic poles may be arranged on the opposing surface 44 a and the back surface 44 b of the permanent magnet 44. Alternatively, three or more pairs of magnetic poles may be disposed on the opposing surface 44 a and the back surface 44 b of the permanent magnet 44. In this case, a plurality of magnetic sensors 48 may be arranged, and the rotation of the permanent magnet 44 may be detected by detecting the direction or strength of each pair of magnetic fluxes.

  In addition to the liquid level detection device 20 that detects the amount of fuel in the fuel tank 4, the “liquid level detection device” of the present specification is, for example, a liquid level in a water tank or a reservoir (that is, a water level or a water storage amount). It may be a liquid level detection device that detects the above.

  Further, the permanent magnet 44 is not limited to an annular shape or a disc shape, and may be a rectangular shape, a polygonal shape, or the like.

  The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

DESCRIPTION OF SYMBOLS 10: Fuel pump module 20: Liquid level detection apparatus 22: Float 24: Arm 30: Magnetic sensor unit 34: Support member 35: Main body 36: Cover 37: Magnet accommodating part 40: Axial direction control part 44: Permanent magnet 44a: Opposite Surface 44b: Back surface 44c: Cavity 48: Magnetic sensor N1: N-pole region N2: N-pole region S1: S-pole region S2: S-pole region X: Rotating axis YK: Magnetizing yoke

Claims (4)

Float,
An arm to which a float is attached and which converts the vertical movement of the float into a rotational movement;
A rotating member holding the arm;
A permanent magnet fixed to the rotating member;
A magnetic sensing element facing the permanent magnet;
A support member that rotatably supports the rotating member with respect to the magnetic detection element,
The permanent magnet has a facing surface facing the magnetic detection element,
The rotating member covers the back surface located on the back side of the facing surface of the permanent magnet,
The facing surface of the permanent magnet is magnetized to at least a pair of magnetic poles,
The back surface of the permanent magnet is magnetized to at least a pair of magnetic poles so that the opposite magnetic poles are positioned on the back side of each of the opposing surface magnetic poles,
At least a pair of magnetic poles on the opposing surface has an element-side magnetic field that passes from one pole of the opposing surface to the other pole through the opposing surface,
At least a pair of magnetic poles on the back surface has opposite magnetic fields that pass from one pole on the back surface to the other pole through the back surface,
The magnetic detection element detects the rotation of the magnet using the element side magnetic field,
The liquid level detection apparatus in which the magnetic flux density of the element side magnetic field is larger than the magnetic flux density of the opposite side magnetic field. The opposing surface of the permanent magnet is magnetized by a pair of magnetic poles,
The liquid level detection device according to claim 1, wherein the back surface of the permanent magnet is magnetized by the pair of magnetic poles so that the magnetic poles opposite to the magnetic poles of the opposing surface are located.   The liquid level detection device according to claim 1, wherein the permanent magnet has a hollow portion that is recessed on the back surface side at a position facing the magnetic detection element on the opposite surface. The liquid level detection device according to claim 3, wherein the hollow portion penetrates the permanent magnet from the facing surface to the back surface.

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