JP2613449B2 - Relative displacement detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relative displacement detection device that detects a relative change between a first shaft body and a second shaft body connected via a connecting body.

[Prior Art] Conventionally, after detecting a direction and an amount of change in relative angle change between a first shaft body and a second shaft body connected via a torsion bar (torsion bar) which is a continuous body. There has been proposed an apparatus configured to apply a driving force having a direction and an amount of change corresponding to a detection result of a relative angle change to a second shaft body, and an electric power steering apparatus as an application example thereof has been proposed. It has been known.

The relative displacement detecting device of the electric power steering device includes a relative angle between an input shaft to which the torque of the first shaft, that is, the steering torque is transmitted, and an output shaft connected to the second shaft, that is, the steering gear device. A sliding contact type detection device for detection is used.

The sliding contact type detecting device includes a detecting portion including a sliding contact for detecting a relative angle change between an input shaft and an output shaft and a resistance wire, a first shaft member and a second shaft member. And a take-out part constituted by a brush and a slip ring for taking out the detection result of the relative angle between the main body side.

Since the detection portion and the take-out portion are based on the sliding contact principle, the metal plating is applied to the slip ring in consideration of the safety standards of the vehicle. It was formed on a ceramic substrate having excellent characteristics to ensure thoroughness.

[Problems to be Solved by the Invention] However, since the conventional relative displacement detection device is configured as described above, it is expensive, and it is a contact type, and a brush and a resistor are compared with the non-contact type. There is a problem in that the reliability and durability are poor due to the noise and the like caused by abrasion and abrasion powder generated by the abrasion. Furthermore, since the brushes that make up the detector rotate together with the shaft, curl cords and the like are used for the output lead wires, and the winding operation is repeated. I got a point.

Therefore, the relative displacement detection device of the present invention has been made in view of the above-described problems, and has as its object to provide a non-contact type relative displacement that is relatively inexpensive and has excellent durability. A detection device is provided.

Means for Solving the Problems In order to solve the above-mentioned problems and achieve the object, a relative angle detecting device of the present invention has the following configuration, that is, a first rotatably supported pivotally supported by a housing. A shaft, a permanent magnet fixed to the first shaft, a second shaft rotatably supported by the housing and arranged to face the first shaft; A relative displacement detection device including a magnetic core fixed to the second shaft and a magnetic sensor fixed to the housing and disposed in a magnetic circuit formed by the permanent magnet and the magnetic core. The change in the magnetic flux caused by the relative displacement between the permanent magnet and the magnetic core is determined by the direction of the relative position change of the first shaft body and the second shaft body about the rotation axis and the change amount of the displacement. Go,
The detection is performed by the magnetic sensor.

Preferably, the first shaft body and the second shaft body are connected to each other via a continuous body.

Preferably, the permanent magnet has an annular shape provided on an outer peripheral surface of one of the first shaft member and the second shaft member.

Preferably, the permanent magnet is magnetized such that its magnetization direction is in the thrust direction with respect to the first shaft body, the second shaft body, and the rotation axis.

Preferably, the permanent magnet is multipolar magnetized in a radial direction with respect to a rotation axis of the first shaft body and the second shaft body.

Preferably, the permanent magnet and the magnetic sensor are interposed between the pair of magnetic cores.

Preferably, the magnetic material core has a substantially U-shaped cross section.

Preferably, the magnetic core has a protruding portion formed on an inner peripheral surface.

Preferably, the number of teeth of the magnetic core is half of the number of magnetized poles of the permanent magnet.

[Operation] A permanent magnet fixed to a first shaft rotatable with respect to the housing, and a first magnet rotatably supported by the housing and rotatably supported by the first shaft.
When a relative displacement occurs between the magnetic core fixed to the second shaft disposed opposite to the shaft, the magnet is fixed to the housing and formed by the permanent magnet and the magnetic core. The magnetic sensor disposed in the circuit serves to detect the direction of the relative position change and the amount of change in the displacement of the first shaft body and the second shaft body about the rotation axis by the magnetic sensor.

In addition, the first shaft body and the second shaft body are connected via a connecting body, and the direction of relative position change and the amount of change in displacement of the first shaft body and the second shaft body around the rotation axis are determined. , And works to detect by a magnetic sensor.

Further, the permanent magnet is formed in an annular shape provided on one of the outer peripheral surfaces of the first shaft body and the second shaft body, and the relative position change around the rotation axis of the first shaft body and the second shaft body. The direction and the amount of change in displacement act to be detected by a magnetic sensor.

In addition, the permanent magnet is magnetized in a thrust direction with respect to the rotation axis of the first shaft body and the second shaft body, and is magnetized to be the first magnet.
The magnetic sensor serves to detect the relative position change direction and the change amount of the displacement of the shaft body and the second shaft body about the rotation axis by the magnetic sensor.

In addition, the permanent magnet is magnetized in a multipolar manner in a radial direction with respect to a rotation axis of the first shaft body and the second shaft body, and is rotated around a rotation axis of the first shaft body and the second shaft body. The magnetic sensor operates to detect the direction of the relative position change and the amount of change in the displacement.

Further, the permanent magnet and the magnetic sensor are interposed between the pair of magnetic cores, and the relative position change direction and the change amount of the displacement of the first shaft body and the second shaft body around the rotation axis are expressed as: It works to detect by a magnetic sensor.

The cross-sectional shape of the magnetic core fixed to the housing is formed in a substantially U-shape, and the direction of the relative position change around the rotation axis of the shaft and the amount of change in the displacement are detected by the magnetic sensor. Work like that.

In addition, the magnetic core has a protruding portion formed on the inner peripheral surface, and serves to detect the direction of the relative position change about the rotation axis of the shaft body and the amount of change in the displacement from the protruding portion by the magnetic sensor.

Further, the magnetic core has a number of teeth that is half of the number of magnetized poles of the permanent magnet, and the direction of relative position change and the amount of change in displacement about the rotation axis of the first shaft body and the second shaft body. It works to detect by a magnetic sensor.

First Embodiment Hereinafter, an embodiment will be described in detail with reference to the drawings. FIG. 1 is a central sectional view of a relative displacement detecting device, and FIG.
The figure is a three-dimensional exploded perspective view of the relative displacement detecting device of FIG.

On both sides, the upper end of the first shaft body 1 is connected to a steering wheel or the like (not shown), and the bearing 101 of the main body 100 causes the CW direction in the clockwise direction of the arrow and the counterclockwise direction in the arrow.
It is rotatably supported in the CCW direction. A sleeve 5 is fixed to the lower end by a pin 6.

The multipolar magnetized magnet wheel 4 whose outer diameter is the inner diameter of the series 5 is fixed in a state of contacting the flange of the sleeve 5. A hole for inserting and fixing the torsion bar 3 is provided on the lower end surface of the first shaft, and the first shaft 1 and the torsion bar are fixed by a pin 12 shown by a two-dot chain line as shown in the figure. The body 3 is integrally formed. That is, the turning operation of the first shaft body 1 becomes the turning operation of the magnet wheel 4.

On the other hand, at the upper end of the second shaft 2 rotatably supported by the bearing 102 of the main body 100, a hole for inserting and fixing the above-mentioned torsion bar 3 is formed. 12, the first shaft 1 and the second shaft 2 are integrally rotated via the torsion bar 3 as shown.

The flange body 7 having the upper surface 7A is configured so as to be integrated with the second shaft body 2 by the pin 6 with respect to the second shaft body 2. On the upper surface 7A of the flange body 7, a lower tooth-shaped core 80 made of a magnetic material is provided.
The lower tooth-shaped core 80 is formed by laminating a plurality of tooth-shaped core plates, so that the magnetic flux does not get wet to the outside. Here, when only the directionality of displacement is detected, or when rough accuracy is sufficient, the above-mentioned tooth-shaped core plate does not necessarily have to be laminated, but may be composed of a single layer.

A spacer 9 made of a non-magnetic material is provided on the upper part of the lower tooth-shaped core 80. The upper and lower surfaces of the flange 9A of the spacer 9 are made of a magnetic material, and the lower tooth-shaped core 80 and the upper part are formed. A pair of rings 10 transmitting the magnetic flux of the tooth-shaped core 8
Are provided so as to sandwich the magnet wheel 4 described above.

The upper tooth-shaped core 8 is formed in the same manner as the lower tooth-shaped core 80, and is provided on the ring 10 above the spacer 9 as shown in FIG. It is something that can be done.

Further, the magnetic sensor 11 is provided at a position sandwiched between the upper tooth-shaped core 8 and the lower tooth-shaped core 80 and fixed to the main body 100. Therefore, even if the above-described tooth-shaped core and the shaft body rotate, the magnetic sensor 11 fixed to the main body 100 does not move, so that the wiring connected to the magnetic sensor 11 is not affected. .

Next, FIG. 3 is a perspective sectional view taken along the line XX of FIG.
FIG. 3 is a plan view showing a positional relationship between a magnet wheel 4 and an upper tooth-shaped core 8 and a lower tooth-shaped core 80. FIG. 3 shows a state in which the first shaft 1 and the second shaft 2 are in a neutral state, and the magnet wheel 4 faces the rotation center of the first shaft 1 as shown in FIG. There is a magnet portion 4A which is magnetized to the N pole and has a radial angle of about 30 degrees, and a magnet part 4A which is magnetized to the S pole toward the rotation center of the first shaft 1 and has a radial angle of 30 degrees. The magnet portion 4B is multipolar magnetized so that a total of 12 magnet portions 4B are arranged. Here, the magnet part is not limited to the above-described twelve parts, and the detection angle can be made finer or coarser by increasing or decreasing the number of magnetized poles, that is, changing the division angle in the circumferential radial direction. Needless to say.

On the other hand, as shown in the drawing, the upper tooth-shaped core 8 and the lower tooth-shaped core 80 each formed by laminating a plurality of plate-shaped magnetic materials form a total of six core pieces 8A. Is detected by the tip of the core piece 8A.

Next, the magnetic sensor 11 is separated from the upper toothed core 8 and the lower toothed core 80 by an angle of about 30 degrees as shown in FIG.
100, and each of the operating states is detected by a detection circuit (not shown), and one of the magnetic sensors outputs an abnormal signal at the time of breakage, and is generated according to the number of teeth of the tooth-shaped core. The pulsation of the output of the magnetic sensor 11 is corrected.

FIG. 4 shows the magnet wheel 4 of the relative change detecting device having the above configuration.
FIG. 4 (A) shows an exhibition view in which the tooth-shaped core 8 and the lower tooth-shaped core 80 are developed in the radial direction.
FIG. 4 (B) shows a state where the first shaft 1 is rotated in a counterclockwise rotation direction, and FIG. 4 (C) shows a state where the first shaft 1 is in the neutral position state. Each of the figures shows a state where the first shaft body 1 is rotated clockwise.

In FIG. 4 (A), in the neutral state where no rotational force is applied to the first shaft body 1, the magnet portions 4A and 4B of the magnet wheel 4 described above.
As a result of forming a short-circuit closed magnetic circuit indicated by a broken line at the core tip, no magnetic flux is generated in the gap existing between the corrugated core 8 and the lower tooth-shaped core 80. In other words, a magnetic sensor consisting of a magnetoresistive element (MR element) or a Hall element
No output voltage is generated at 11. Thus, the magnetic flux density of the magnet does not change with temperature changes, and the output power at the neutral position does not change as a result.

Next, in FIG. 4 (B), when the first shaft 1 is rotated in the counterclockwise CCW direction, the magnet portion 4 of the magnet wheel 4 is rotated.
As a result of the balance formed between A and 4B being lost, the magnetic flux having the polarity of the magnet portion 4A and the magnet portion 4B flows between the upper tooth-shaped core 8 and the lower tooth-shaped core 80. A voltage is generated by magnetic flux from the lower tooth-shaped core 80 toward the upper tooth-shaped core 8.

On the other hand, in FIG. 4C, when the first shaft body 1 is rotated in the clockwise CW direction, the magnet portion 4A of the magnet wheel 4 is
As a result, the magnetic flux having the polarity of the magnet portion 4A and the magnet portion 4B flows through the upper tooth-shaped core 8 and the lower tooth-shaped core 80. The upper tooth-shaped core 8 to the lower tooth-shaped core 80
Is generated. That is, the rotation direction of the first shaft body 1 can be detected as positive or negative of the voltage of the magnetic sensor 11.

Further, the output voltage of the magnetic sensor 11 is substantially proportional to the angle change of the magnet wheel 4.

FIG. 5 is a diagram showing the relationship between the output voltage of the magnetic sensor 11 and the change in the angle of the magnet wheel 4.

In FIG. 5, the first shaft 1 is CCW in the counterclockwise direction.
When rotated in the direction, the voltage rises and changes in a substantially linear manner until the side surface of the magnet portion 4A of the magnet wheel 4 reaches the magnetic sensor 11, and then the voltage waveform V value that starts to change downward on the magnet portion 4B is changed. Output.

On the other hand, when the first shaft body 1 is rotated in the clockwise CW direction, the voltage decreases substantially linearly until the side surface of the magnet portion 4A of the magnet wheel 4 reaches the magnetic sensor 11, and further the magnetic portion 4B , A voltage waveform V value that rises and changes is output.

That is, the magnetic sensor 11 can detect not only the rotation angle direction but also the rotation angle change amount.

(Description of Application Example) The relative displacement detection device having the above configuration is applicable to an electric power steering device, and an application example will be described with reference to the drawings.

FIG. 6 is a schematic configuration diagram of an electric power steering device. In FIG. 6, a handle 15 is provided above the first shaft body 1, and a lower end of the second shaft body 2 is connected to a gear device for steering. The main body 18 is formed as a portion connecting the first shaft body 1 and the second shaft body 2, and the electric motor 16 and the above-described relative displacement detecting device are provided inside the main body 18.

The control device 200 is configured by an electronic circuit such as a CPU element, and inputs a detection signal of the relative displacement detection device and controls driving of the electric motor 16. Next, the operation of the electric power steering apparatus having the above configuration will be described with reference to a flowchart. Seventh
FIG. 7 is a flow chart of the electric power steering system. In FIG. 7, when the steering wheel is rotated by the driver in step S1, the change in the angle of the magnet wheel 4 of the relative displacement detecting device in step S2 is shown. Detection is magnetic sensor 11
It is performed by As described above, since the magnetic sensor 11 can detect the rotation direction, it is determined in step S3 whether the rotation direction is the right direction, that is, whether the rotation direction is the CW direction, and if the right direction is determined, the process proceeds to step S4. Next, the above-described V value, which is the angle change amount, is detected by the magnetic sensor 11. Next, when the A value is input to the control device 200, the electric motor 16 is driven to the right in proportion to the V value. As a result, the electric motor 16 functions as a so-called power steering device. The driving of the electric motor 16 is continued in step S6 until the change in the angle of the magnetic sensor 11 becomes zero, and is stopped when the change in angle becomes zero.

On the other hand, when it is determined in step S3 that the rotation direction is the left direction, that is, the CCW direction, the process proceeds to step S7, and the magnetic sensor 11 detects the above-described V value, which is the angle change amount. Next, this V value is stored in the control device 20.
When 0 is input, the electric motor 16 is driven to the left in proportion to the V value, and the driving of the electric motor 16 is continued in step S6 until the angle change detected by the magnetic sensor 11 becomes zero. And stop when it reaches zero.

Also, the two axes of the first shaft 1 and the second shaft 2 rotate simultaneously, and the driver once stops the steering wheel operation at an arbitrary angle,
Even if the handle is further rotated in the middle, the V value has already become zero, so that the operation can be performed in the same manner as the above-described flow. Further, a storage unit for storing the current angle becomes unnecessary, and only the displacement angle can be always detected.

[Second Embodiment] Next, a second embodiment will be described with reference to the drawings. FIG. 8 is a center sectional view showing a main part of the relative displacement detecting device in a neutral state, and FIG. FIG. 9 is a plan view of the cross section of FIG. In FIG. 8, the upper tooth-shaped core 8 and the lower tooth-shaped core 80 are integrated with each other via a spacer 9 and a pair of rings 10 and fixed to the flange body 7 as shown in the figure.

The first shaft 1 that is supported by the main body 100 by a bearing (not shown) is provided integrally with the flange body 7.

On the other hand, the second shaft 2, which is rotatably opposed to the first shaft 1 and is supported by the main body 100 by a bearing (not shown), as shown in FIG. The magnet wheel 4 is fixed to a position facing the lower tooth-shaped core 80, respectively.

The magnet wheel 4 forms a short-circuited closed magnetic circuit above and below a total of 12 magnet portions magnetized to alternate polarities described later in order to form a short-circuited closed magnetic circuit shown by a two-dot chain line. As described above, the magnet portion is provided by adding one magnet portion.

The magnetic sensor 11 is provided on the main body 100 such that the detection unit is located in a gap formed by the pair of rings 10.

Next, in FIG. 9, the pair of magnet wheels 4 are fixed to the outer peripheral surface of the second shaft body 2 as shown in the figure, but the magnet wheels 4 are all magnetized to have alternate polarities in the radial direction. Twelve magnet parts are formed. The distal end 8A of the upper tooth-shaped core 8 and the lower tooth-shaped core 80 fixed to the first shaft 1 is disposed so as to be located at the boundary of the magnet portion.

In the relative displacement detecting device having the above-described configuration, the magnetic sensor 11 functions similarly to the operation described in the first embodiment.
Here, with the configuration as in the second embodiment, the assembling and disassembling work is greatly improved.

Third Embodiment Next, a third embodiment will be described with reference to the drawings. FIG. 10 is a center sectional view showing a main part in a neutral state of the relative displacement detecting device, and FIG. 11 is a plan view of a transverse section of FIG.

In FIG. 10, upper tooth-shaped core 8 and lower tooth-shaped core
As shown in the drawing, 80 is integrally fixed to the flange body 7 through the spacer 9 and a pair of rings 10.

The first shaft 1 that is supported by the main body 100 by a bearing (not shown) is provided integrally with the flange body 7.

On the other hand, the upper shaft-shaped core 8 is rotatably opposed to the first shaft 1, and is supported on the second shaft 2 by a bearing (not shown). One magnet wheel 4 is fixed at a position facing the lower tooth-shaped core 80.

The magnet wheel 4 is formed so as to form a total of 12 magnet portions which are magnetized to alternate polarities as described later in order to form a short-circuit closed magnetic circuit (not shown).

The magnetic sensor 11 is provided on the main body 100 such that the detection unit is located in a gap formed by the pair of rings 10.

Next, in FIG. 11, the magnet wheel 4 is
The magnet wheel 4 is fixed to the outer peripheral surface of the shaft body 2, and is formed with a total of twelve magnet portions which are magnetized to have alternate polarities in the radial direction. Then, the upper tooth-shaped core 8 and the lower tooth-shaped core 80 fixed to the first shaft body 1 described above.
Are arranged such that the tips 8A are staggered to form a short-circuit closed magnetic circuit.

In the relative displacement detecting device having the above-described configuration, the magnetic sensor 11 functions similarly to the operation described in the first embodiment.
Here, by configuring as in the third embodiment, the assembling and disassembling operation is greatly improved, and the cost is reduced by using only one magnet wheel 4.

Fourth Embodiment Next, a fourth embodiment will be described with reference to the drawings. FIG. 12 (a) is a partial cross-sectional view showing a main part where the relative displacement detecting device is in a neutral state, and FIG.
It is a top view of the cross section of a figure.

In both FIGS. 12 (a) and 12 (b), the upper tooth-shaped core 8 has a U-shaped cross section as shown, and the outer peripheral surface of the first shaft body 1. The main body 100 is provided so as to surround the outer peripheral surface of the multi-pole magnetized magnet wheel 4 fixed to the main body 100. In addition, a magnetic sensor 11 is also provided on the main body 100 so that the rotational displacement of the first shaft body 1 can be detected. Even in such a configuration, the direction of the rotational displacement and the displacement amount of the first shaft body 1 can be detected, but the magnetic core and the magnetic sensor are fixed to the main body 100, which is an ideal configuration.

Fifth Embodiment Finally, a fifth embodiment will be described with reference to the drawings. FIG. 13 (a) is a plan view showing a main part where the relative displacement detecting device is in a neutral state, FIG. 13 (b) is a cross-sectional view of the main part, and FIG. 13 (c) is a plan view of the whole. is there.

In FIG. 13, the upper tooth-shaped core 8 has a pair of protrusions formed inside the circumferential surface as shown, and a pair of magnet portions 40 fixed to the outer circumferential surface of the first shaft body 1 as shown in FIG. And is detected by a magnetic sensor 11 provided in the main body.

Even in such a configuration, the direction of the rotational displacement of the first shaft body 1 and the amount of the displacement can be detected.

In each of the above configuration examples, only the embodiment in which the angular displacement around the rotation axis is detected has been described. However, the magnet wheel 4 and the tooth-shaped cores 8 and 80 are formed in a straight line, and the first By being configured to be fixed to the shaft body and the second shaft body, the displacement in the axial direction, that is, the linear position may be detected.

Furthermore, the relative displacement detecting device has been described as being limited to an application example in which the relative displacement detecting device is applied to an electric power steering device. In addition, the relative displacement detecting device of the present invention can be applied to electric tools, various machine tools, home appliances, and various industrial devices. It is needless to say that is applicable.

[Effect of the Invention] As described above, the present invention can provide a non-contact type relative displacement detection device which is inexpensively configured and has excellent durability.

[Brief description of the drawings]

1 is a central sectional view of the relative displacement detecting device, FIG. 2 is a three-dimensional exploded perspective view of the relative displacement detecting device of FIG. 1, FIG. 3 is a sectional view taken along the line XX of FIG. 4A is a developed view showing a state where the first shaft body 1 is in a neutral position state, and FIG. 4B is a developed view showing a state where the first shaft body 1 is rotated in a counterclockwise rotation direction. FIG. 4 (C) is a developed view showing a state where the first shaft body 1 is rotated clockwise, and FIG. 5 is a view showing a relationship between an output voltage of the magnetic sensor 11 and an angle change of the magnet wheel 4. FIG. 6 is a schematic configuration diagram of an electric power steering device, and FIG. 7 is a flowchart of the electric power steering device. Fig. 8 is a central sectional view showing a main part in a neutral state of the relative displacement detecting device, Fig. 9 is a plan view of a transverse section of Fig. 8, and Fig. 10 is a neutral sectional view of the relative displacement detecting device. 11 is a cross-sectional plan view of FIG. 10, and FIG. 12 (a) is a portion showing a main part in which the relative displacement detecting device is in a neutral state. Sectional view, FIG. 12 (b) is a plan view of the transverse section of FIG. 12, FIG. 13 (a) is a plan view showing a main part where the relative displacement detecting device is in a neutral state, FIG. 13 (b). Fig. 13 is a sectional view of a main part, and Fig. 13 (c) is a plan view of the whole. In the drawing, 1... First shaft body, 2... 2nd shaft body, 3... Twisted rod body, 4... Magnet ring, 5. , 80 ... lower tooth shaped core, 9
... spacer, 10 ... ring, 11 ... magnetic sensor, 100
... Body, 200... Control device.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Wakazono 2-16-20 Shimura, Itabashi-ku, Tokyo Inside Copal Co., Ltd. (56) References JP-A-61-201101 (JP, A)

Claims (9)

(57) [Claims] A first shaft rotatably supported by a housing;
A permanent magnet fixed to the first shaft, a second shaft rotatably supported by the housing and arranged to face the first shaft; and a second shaft. A relative displacement detection device comprising: a magnetic core fixed to the housing; and a magnetic sensor fixed to the housing and disposed in a magnetic circuit formed by the permanent magnet and the magnetic core. The change in magnetic flux caused by the relative displacement between the permanent magnet and the magnetic core is defined as the direction of relative position change and the amount of change in displacement of the first shaft body and the second shaft body around the rotation axis. A relative displacement detecting device characterized by detecting with a sensor. 2. The relative displacement detecting device according to claim 1, wherein the first shaft body and the second shaft body are connected via a continuous body. 3. The apparatus according to claim 1, wherein the permanent magnet has an annular shape provided on an outer peripheral surface of one of the first shaft body and the second shaft body. Relative displacement detector. 4. The permanent magnet according to claim 1, wherein the permanent magnet is magnetized in a thrust direction with respect to a rotation axis of the first shaft body and the second shaft body. A relative displacement detection device according to the item. 5. The permanent magnet according to claim 1, wherein the magnetizing direction is multipolar magnetized in a radial direction with respect to a rotation axis of the first shaft body and the second shaft body. A relative displacement detection device according to the item. 6. The relative displacement detecting device according to claim 1, wherein the permanent magnet and the magnetic sensor are interposed between a pair of the magnetic cores. 7. The relative displacement detecting device according to claim 1, wherein the magnetic core has a substantially U-shaped cross section. 8. The relative displacement detecting device according to claim 1, wherein the magnetic core has a projection formed on an inner peripheral surface. 9. The relative displacement detecting device according to claim 1, wherein the number of teeth of the magnetic core is half of the number of magnetic poles of the permanent magnet.