JP3572396B2 - Bar magnet - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a bar-shaped magnet for forming a magnetic field, and more particularly to a bar-shaped magnet for forming a magnetic field suitable for measuring displacement.
[0002]
[Prior art]
As one type of displacement measurement method, there is a method of measuring a mutual displacement between the rod-shaped magnet and the magnetic detection element by using a rod-shaped magnet having magnetic poles at both ends and a magnetic detection element such as a Hall element, and measuring a magnetic field strength by the rod-shaped magnet. For example, Japanese Patent Laying-Open No. 6-180242 discloses an example applied to a flow rate measuring device.
[0003]
By the way, in recent years, an engine of a type that electromagnetically controls the opening and closing of an intake valve and an exhaust valve, that is, an electronically controlled intake / exhaust valve system has been put into practical use. FIG. 3 shows an electromagnetic type intake / exhaust valve used in such a system. This is an example of an exhaust valve (intake valve or exhaust valve) drive system. This example shows a mover (amateur) 1 made of a magnetic material, two electromagnets 2, 3 and a spring 4 as shown in the figure. An intake / exhaust valve 6 is attached to the drive shaft 5 of the mover 1 using an electromagnetic actuator consisting of
[0004]
When the intake / exhaust valve 6 is moved upward in the figure, that is, when the valve is closed, the electromagnet 2 is energized to attract the mover 1, and when it is moved downward, that is, when the valve is opened, the electromagnet 3 is energized. At this time, the mover 1 is attracted. At this time, the spring 4 works together with other springs (not shown) to hold the mover 1 in the neutral position when the electromagnets 2 and 3 are not energized. is there.
[0005]
In this case, it is characteristic that independent control of the valve opening timing and the valve closing timing during operation and also the control of the lift amount are possible. For this purpose, the drive position of the mover 1 is changed. It is necessary to control accurately, and for this purpose, it is necessary to correctly detect the displaced position.
Therefore, in the example of FIG. 3, as shown, a rod-shaped permanent magnet, that is, a position detecting means including a rod-shaped magnet 7 and a Hall element 8 is provided.
[0006]
Here, the rod-shaped magnet 7 is attached to the upper end in the figure opposite to the side where the intake / exhaust valve 6 of the drive shaft 5 is attached, so that the Hall element 8 faces the rod-shaped magnet 7. Therefore, the position of the bar-shaped magnet 7 with respect to the Hall element 8 changes according to the displacement of the drive shaft 5, and as a result, the strength of the magnetic field detected by the Hall element 8 changes. The position of the bar-shaped magnet 7, that is, the position of the intake / exhaust valve 6, can be detected according to the strength of the magnetic field, and the displacement can be known.
[0007]
At this time, the Hall element 8 is installed in parallel with the moving direction of the mover 1, and when the mover 1 is in the neutral position, the center of the length direction of the bar-shaped magnet 7 whose upper and lower ends are magnetic poles and the Hall element 8 Are adjusted so that the centers of the movable elements 1 coincide with each other, whereby the Hall element 8 can measure the magnetic field intensity generated in the radial direction from the rod-shaped magnet 7, the position of the movable element 1 is measured, and the displacement amount is obtained. It is possible.
[0008]
[Problems to be solved by the invention]
The above prior art does not consider the asymmetry of the magnetic field existing in the bar-shaped magnet for position detection, and has a problem in a position detection error generated with the rotation of the drive shaft.
In the electromagnetic intake / exhaust valve drive system, as described above, it is necessary to detect the position of the movable element 1 that reciprocates at high speed in order to control the intake / exhaust timing to be optimal under various operating conditions of the engine. .
[0009]
Further, in order to reduce noise and shock generated when the mover 1 collides with the upper and lower electromagnets 2, 3, speed control for reducing the collision speed, that is, variable speed control during a stroke is necessary. High-precision position measurement near the top and bottom dead center of the stroke immediately before the child 1 collides is an essential element.
Furthermore, since the acceleration at the time of collision reaches several thousand G, it is necessary to control the speed of the mover 1 to extend the life.
[0010]
By the way, in the above-described electromagnetic intake / exhaust valve drive system, during operation, the mover 1 sometimes rotates at the same time as reciprocating motion.
In this case, there is no problem when the magnetic axis of the bar-shaped magnet 7 is correctly coincident with the central axis of the bar-shaped magnet 7 in the longitudinal direction. When the rod-shaped magnet 7 is not circularly symmetric with respect to the central axis in the longitudinal direction, the magnetic field strength around the magnet changes due to the rotational movement, so that accurate measurement of the displacement cannot be performed.
[0011]
In other words, if the magnetic axis of the rod-shaped magnet is bent, the symmetry of the magnetic field with respect to the central axis in the longitudinal direction is broken, and the magnetic field changes even if the position in the longitudinal direction does not change just by rotating, The measurement error increases.
However, in the prior art, it is difficult to obtain a bar-shaped magnet whose magnetic axis does not bend and is exactly coincident with the central axis in the longitudinal direction, and therefore, a problem occurs in maintaining the detection accuracy. .
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to provide a rod-shaped magnet which is used for position detection and has sufficient detection accuracy easily with little deviation from a central axis due to bending of a magnetic axis.
[0013]
[Means for Solving the Problems]
The object is to magnetize a rod-shaped member made of a magnetic material for a permanent magnet so that both ends become magnetic poles, and then divide the magnetized rod-shaped member into two parts in a length direction to form a first member and a second member. Then, the ends of the first and second members, which have become the magnetic poles, are joined to each other so that a new magnetic pole is formed at the divided end. You.
[0014]
In the present invention, the rod-shaped magnet shown in FIG. 2 has also been studied in the process of arriving at the above means, and it has been confirmed that the object can be achieved to some extent. Before describing the embodiment of the present invention, the bar-shaped magnet of FIG. 2 will be described as a reference example.
[0015]
In the reference example of FIG. 2, after the both ends of the rod-shaped member made of a permanent magnet material are magnetized to be magnetic poles, one end and the other end of the rod-shaped member are removed, and new magnetic poles are formed at both ends that appear. First, as shown in FIG. 2A, a bar 7A made of a magnetic material for a permanent magnet is prepared.
[0016]
Here, as the magnetic material (permanent magnet material) for the permanent magnet, various alloy steels represented by tungsten steel and the like, and sintered materials such as barium-based and neodymium-based materials are used, and finally required. the length L (described later) that is formed is prepared as a rod 7A having a long dimension L ₁ by a predetermined dimension than.
[0017]
Next, as shown in FIG. 2B, the bar 7A is magnetized by applying a magnetic field in its longitudinal direction to form a bar-shaped magnet 7B.
However, at this time, even if the bar 7A is correctly magnetized in the axial direction, the magnetic axis M formed by the magnetizing bends, and as a result, as shown, the magnetized bar-shaped magnet 7B Then, it is inevitable that the end face deviates from the center axis C.
It is to be noted that this is a problem in the prior art, as described above.
[0018]
Then, as shown in FIG. 2C, when both ends 7B1 and 7B2 of the bar-shaped magnet 7B are cut off, these ends 7B1 and 7B2 are cut off to form a new end face. The newly formed portions each newly form a magnetic pole, and become a bar-shaped magnet 7 having a length L as shown in FIG. It should be noted that the length L at this time is a dimension finally required for the bar-shaped magnet 7 as described above.
[0019]
Here, looking at the magnetic axis M, as is apparent from FIG. 2B, it is bent, but coincides with the central axis C at the center point O, and moves away toward the end. Farthest at the end.
[0020]
Therefore, as shown in FIG. 2C, if both ends 7B1 and 7B2 of the bar-shaped magnet 7B are cut off, a new bar-shaped magnet 7 is formed as shown in FIG. 2D. In the magnetic poles N and S formed by the end faces, the ratio of the magnetic axis M separated from the central axis C is sufficiently small.
[0021]
Therefore, the bending of the magnetic axis at the magnetic poles N and S can be suppressed to be small by the rod-shaped magnet 7 according to this reference example. For example, the rod-shaped magnet 7 can be applied to the electromagnetic intake / exhaust valve drive system described with reference to FIG. Can be obtained.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a bar-shaped magnet according to the present invention will be described in detail with reference to the illustrated embodiments.
FIG. 1 shows an embodiment of a bar-shaped magnet according to the present invention. First, as shown in FIG. 1A, a bar 7A of a magnetic material serving as a base material of a permanent magnet is prepared, and then, FIG. As shown in Fig. 7, a magnetic field H is applied to the bar 7A in the length direction thereof to magnetize the bar 7A to obtain a bar-shaped magnet 7B.
[0023]
Here, as the magnetic material (permanent magnet material) to be the bar 7A, a samarium-cobalt permanent magnet material is used from the viewpoints of, for example, thermal stability, corrosion resistance, and high coercive force characteristics. Various alloy steels and sintered materials described in the reference example can be used.
[0024]
Next, as shown in FIG. 1 (c), the bar-shaped magnet 7B is cut off at the center in the length direction to form two bar-shaped magnets 7L and 7R each having a length of L / 2.
Here, in these rod-shaped magnets 7L and 7R, the original end faces are designated as EL and ER, respectively, and the cut faces are designated as CL and CR, respectively.
[0025]
Next, as shown in FIG. 1D, the bar-shaped magnets 7L and 7R are switched to the right and left in the figure, and the original end faces EL and ER are joined so as to face each other.
Then, the cut surfaces CL and CR of the bar magnets 7L and 7R form new magnetic poles N and S, and the bar magnet 7 having the length L is obtained.
[0026]
The bonding at this time may be performed using, for example, an epoxy-based adhesive or a cyanoacrylate-based adhesive. However, the original end faces EL and ER of these rod-shaped magnets 7L and 7R are magnetically attracted to each other with one being an N pole and the other being an S pole, so that if an appropriate holding method is adopted, There is no particular need for bonding.
[0027]
According to this embodiment, as is clear from FIG. 1D, the cut surfaces CL and CR of the bar-shaped magnet 7B whose magnetic axis M coincides with the center line C are new magnetic poles N and S. Therefore, at these magnetic poles N and S, the magnetic axis C is hardly bent.
[0028]
Therefore, according to this embodiment, the bending of the magnetic axis at the end face serving as the magnetic pole is extremely small and can be almost close to zero. As a result, for example, the present invention is applied to the electromagnetic intake / exhaust valve drive system described with reference to FIG. Thus, it is possible to easily obtain the bar-shaped magnet 7 capable of detecting the position with sufficiently high accuracy.
[0029]
【The invention's effect】
According to the present invention, the bending of the magnetic axis is small, and high-precision position detection can be easily obtained by a rod magnet that is almost zero. Can be controlled by
[Brief description of the drawings]
FIG. 1 is an explanatory view showing one embodiment of a bar-shaped magnet according to the present invention.
FIG. 2 is an explanatory view of a bar-shaped magnet serving as a reference example of the present invention.
FIG. 3 is a sectional view showing an example of an electromagnetic intake / exhaust valve drive system to which the bar-shaped magnet according to the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Mover 2, 3 Electromagnet 4 Spring 5 Drive shaft 6 Intake / exhaust valve 7 Bar-shaped magnet 7A Bar-shaped member 7B of magnetic material for permanent magnets Magnetized bar-shaped magnet 7B
7L, 7R Cut rod magnet 8 Hall element

Claims (2)

After magnetizing so that both ends of the bar-shaped member made of a magnetic material for a permanent magnet become magnetic poles, the magnetized bar-shaped member is divided into two in the length direction to form first and second members. A rod-shaped magnet, wherein the ends of the first and second members which have become the magnetic poles are joined to each other, and a new magnetic pole is formed at the divided end. In the invention according to claim 1,
A rod-shaped magnet, wherein the first and second members are divided into two parts at the longitudinal center of the magnetized rod-shaped member.

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