JP2887520B2 - Electromagnetic induction type rotation detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an electromagnetic induction type rotation detector, in particular, a coil wound around a core bonded to a permanent magnet, and a core having a rotation surface on a rotating surface of a rotating body. The present invention relates to an electromagnetic induction type rotation detector which is disposed so that axial end surfaces thereof face each other.

[Conventional technology]

As an electromagnetic induction type rotation detector, for example,
As disclosed in Japanese Patent No. 105847, a rotation detector in which a coil is wound around a magnetic body is known. In this publication, it is proposed that the shape of the magnetic material is formed in a truncated cone shape in order to optimize the magnetic flux density over the entire length of the magnetic material in view of the relationship between the magnetic material and the rotating body facing the magnetic material. . That is, it has a frustoconical magnetic body and a cylindrical bobbin that houses the magnetic body, and the coil winding is wound around the bobbin. Similarly, Japanese Utility Model Application Laid-open No. Sho 58-80518 proposes that the yoke to be joined to the permanent magnet, that is, the yoke is formed in a tapered shape in order to optimize the magnetic flux density over the entire length of the core. ing.

[Problems to be solved by the invention]

Cutting, cold forging and sintering are methods for manufacturing a core having a tapered portion whose cross-sectional area gradually increases in the direction of the joint with the permanent magnet from the tip, such as the core used in the above-described conventional rotation detector. is there. When a core is manufactured by cutting, the core is cut out from a round bar. However, since the cut portion is large, it takes a long time and wastes a lot of material. In the case of cold forging, it is necessary to perform a heat treatment to remove residual stress at the time of manufacturing, and the same applies to the case of cutting. When manufacturing the core by sintering,
Such heat treatment is unnecessary, and no waste of material occurs. However, in the case of sintering, since the cross-sectional area of the tapered portion is not constant, the filling rate of the material becomes non-uniform, and desired magnetic properties cannot be obtained.

Then, an object of the present invention is to provide an electromagnetic induction type rotation detector provided with a core having a tapered portion, which is easy to manufacture and does not waste material.

[Means for solving the problem]

In order to achieve the above object, the present invention includes a core having a distal end portion arranged to face a rotating body, a permanent magnet joined to a base end portion of the core, and a coil wound around the core, In the electromagnetic induction type rotation detector, the core has a tapered portion whose cross-sectional area gradually increases in the direction of the joint with the permanent magnet from the tip end, and a tapered hollow portion is formed at the axis of the tapered portion of the core. The thickness of the tapered portion is substantially uniform.

The core may be formed into the above-mentioned shape by sintering.

[Action]

In the electromagnetic induction type rotation detector configured as described above, the core around which the coil is wound has a tapered portion whose cross-sectional area gradually increases in the direction of the junction with the permanent magnet from the distal end, that is, in the direction of the proximal end, An appropriate magnetic flux density is formed. Moreover, this core is formed by, for example, sintering, has a tapered hollow portion at the axis of the tapered portion, and the thickness of the tapered portion is substantially uniform. Therefore, there is no waste in the material and it helps to reduce the weight.

Thus, a predetermined magnetic flux distribution is formed through the core by the permanent magnet, and when the rotating body disposed to face the core rotates, for example, due to the presence of the teeth formed on the outer periphery of the rotating body, the core is formed. And the air gap formed between them changes. As a result, the flux linkage to the coil changes in accordance with the rotation of the rotator, and an electromotive force is induced in the coil by the electromagnetic induction to output a pulse signal.

〔Example〕

Hereinafter, preferred embodiments of the electromagnetic induction type rotation detector of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of an electromagnetic induction type rotation detector according to the present invention, which is provided for a crank angle detection device for an internal combustion engine. That is, a rotating body (not shown) made of a magnetic material having teeth formed on a rotating surface and rotating in synchronization with an internal combustion engine (not shown).
An electromagnetic pickup 1, which is an electromagnetic induction type rotation detector, is disposed so as to face the.

The electromagnetic pickup 1 contains a core 2, a substantially columnar permanent magnet 3 joined to a base end thereof, a core 4 and a permanent magnet 3, and a coil 4 wound around a shaft containing the core 2. The bobbin 5 is turned.

The core 2 is composed of a substantially frusto-conical tapered portion 2b and a cylindrical tip 2a that is continuous with the small-diameter end. The tapered portion 2b has a tapered hollow portion 2c formed at the axis thereof. It is formed so that the thickness is substantially uniform. In this embodiment, the core 2 is formed into a shape as shown in FIG. 2 by sintering, that is, by forming fine powder of a magnetic material and baking it in a furnace. This reduces the filling rate of the magnetic material to the tapered part.
Since it is substantially equal over the entire length of 2b, predetermined magnetic characteristics are secured.

The bobbin 5 is a synthetic resin cylindrical body including a small-diameter cylindrical body 5a, a tapered portion 5b having a tapered surface, and a large-diameter cylindrical body 5c. Hollow portions having a large-diameter circular cross section are formed continuously, and the core 2 and the permanent magnet 3 are accommodated in these hollow portions, respectively. The flanges 5d and 5e are provided at the tip of the cylindrical body 5a and the large-diameter end of the taper 5b.
Are formed integrally, and the winding of the coil 4 is wound between the flanges 5d and 5e, and the insulating tape 14 is wound therearound. An annular convex portion 5f is formed on a substantially central outer surface of the large-diameter cylindrical body portion 5c of the bobbin 5, and an annular convex portion 5g is similarly formed at the tip of the cylindrical body portion 5c. Therefore, a groove 5h is formed between the two convex portions 5f and 5g. Two annular grooves 5i and 5j are formed in the convex portion 5f, and O
Rings 9 and 10 are fitted. An annular step 5k is formed at the open end of the recess 5g.
11 is installed.

The connector 6 has a pair of terminals (only one of which is indicated by 7 in the figure) formed by insert resin molding. That is, it has a flange portion 6a and a joint portion 7b, and is formed so that respective axes are substantially orthogonal to each other.
6a extends downward, and the other end serves as a connection terminal 7b at the junction 6b.
In the recess. An annular stepped concave portion 6c is formed on the joint surface (the lower surface in FIG. 1) of the flange portion 6a. The core 2, the permanent magnet 3, and the spring washer 12 are housed in the bobbin 5, and a convex portion 5 g formed at the open end of the bobbin 5 is attached to the mounting recess of the connector 6 via the O-ring 11.
6c is fitted. The joint between the projection 5g and the flange 6a is welded by a welding technique such as ultrasonic welding. In the hollow portion of the bobbin 5, the core 2 and the permanent magnet 3 are pressed by the spring washer 12 in the direction of the tapered portion 5b.

A pair of terminals (not shown) are fixed to the cylindrical body portion 5c of the bobbin 5, and the winding of the coil 4 is connected to each free end. The other end of each of the pair of terminals fixed to the cylindrical body 5c is overlapped with the extension of the terminal 7 after the bobbin 5 is joined to the flange 6a as described above, and is joined by, for example, projection welding. After joining in this manner, the insulating tape 15 is wound.

A case 8 is provided so as to surround the bobbin 5, and the end surface of the tip 2 a of the core 2 is in contact with the bottom surface. This case 8 is a bottomed cylindrical body made of metal, for example, stainless steel, and its open end 8a is caulked and locked to the projection 5f. An O-ring 13 for an oil seal is fitted in the groove 5h.

In the electromagnetic pickup 1, a tapered hollow portion 2c is formed at the axis of the tapered portion 2b of the core 2, and the tapered portion 2c is formed.
Since the thickness of 2b is substantially uniform, the material is reduced as compared with the conventional case. When the core 2 is formed by sintering, the filling rate of the material becomes substantially equal over the entire length of the tapered portion 2b, and a predetermined magnetic property can be secured. According to the experimental results, when the hollow portion 2c is about 12% of the volume of the core 2, the decrease in the maximum output voltage of the electromagnetic pickup 1 is 4%.
It was confirmed that:

As described above, the core 2 is desirably formed into the shape shown in FIG. 2 by sintering. However, even when the core 2 is formed into the shape shown in FIG. 2 by cold forging, the material can be reduced as compared with the case of cutting. Becomes

The operation of the electromagnetic pickup 1 configured as described above will be described. In FIG. 1, a predetermined magnetic flux distribution is formed in the core 2 by the permanent magnet 3. When the rotating body (not shown) rotates, the magnetic flux distribution changes each time the teeth face the tip end surface of the core 2. As a result, the amount of magnetic flux interlinking with the coil 4 changes, and the output is reversed when approaching and separating from the teeth of the rotating body. Is induced and output as a signal indicating the number of rotations.

〔The invention's effect〕

Since the present invention is configured as described above, the following effects can be obtained.

That is, in the electromagnetic induction type rotation detector of the present invention, a tapered hollow portion is formed at the axis in the tapered portion of the core,
Since the thickness of the tapered portion is substantially uniform, the number of materials can be reduced as compared with the conventional one while securing predetermined magnetic characteristics. For example, it can be manufactured easily and inexpensively by sintering.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an electromagnetic pickup according to one embodiment of the present invention, and FIG. 2 is a perspective view of a core housed in the electromagnetic pickup shown in FIG. 1. Electromagnetic pickup (electromagnetic induction type rotation detector) 2. Core, 2a Tip, 2b Tapered part, 2c Hollow part, 3. Permanent magnet, 4. Coil, 5. Bobbin, 5a… Cylinder, 5b… Taper, 5c… Cylinder, 5d, 5e… Flange, 5f, 5g… Protrusion, 6… Connector, 6a… Flange, 6b ... Junction, 7 ... Terminal, 8 ... Case, 9,10,11 ... O-ring, 12 ... Spring washer, 13 ... O-ring

Claims (1)

(57) [Claims] 1. A core having a distal end disposed opposite to a rotating body, a permanent magnet joined to a base end of the core, and a coil wound on the core, wherein the core is disposed from a distal end. In an electromagnetic induction type rotation detector having a tapered portion whose cross-sectional area gradually increases in a direction of a joint with the permanent magnet, a tapered hollow portion is formed at an axis of the tapered portion of the core, and a thickness of the tapered portion is increased. An electromagnetic induction type rotation detector characterized by having a substantially uniform shape.