Fluid pressure cylinder

Abstract

This improves the ease of mounting the holder and reduces the manufacturing cost of the fluid pressure cylinder. [Solution] The hydraulic cylinder 100 comprises a cylinder tube 10, a piston rod 20, a piston 30, a magnet 40 provided inside the cylinder tube 10 and reciprocating together with the piston rod 20, a cylindrical holder 71 attached to the piston rod 20 and holding the magnet 40, and a magnetic sensor 50 that detects the stroke of the piston rod 20 and the piston 30 by the magnetism of the magnet 40. The magnet 40 is provided on a part of the circumferential direction of the cylinder tube 10 so as to face the magnetic sensor 50, and the holder 71 has a plurality of holder pieces 41a, 41b formed by dividing in the circumferential direction, and the holder 71 has a notch 44a that is provided on the magnet 40 and positions the magnet 40 in the circumferential direction.

Description

Technical Field

[0001] The present invention relates to a fluid pressure cylinder.

Background Art

[0002] Patent Document 1 discloses a cylinder provided with a magnetic sensor that detects the magnetism of a magnet attached to a piston via a holder. The magnetic sensor is disposed on the outer peripheral surface of the cylinder tube of the fluid pressure cylinder and detects the stroke of the piston. The piston is provided with an extension portion formed to extend coaxially with the piston rod, and a holder and an annular magnet are attached to the outer peripheral surface of the extension portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the cylinder described in Patent Document 1, when attaching the holder to the extension portion of the piston rod, the extension portion is inserted into the insertion hole of the holder. Since the inner peripheral surface of the insertion hole of the holder and the outer peripheral surface of the extension portion are substantially the same diameter, it takes time to insert the extension portion into the holder. Further, in the cylinder described in Patent Document 1, since the magnet is annular, while there is an advantage that the magnet faces the magnetic sensor even if it rotates, the portion of the magnet that does not face the magnetic sensor does not contribute to detection. Therefore, in the cylinder described in Patent Document 1, there is room for improving the attachability of the holder and reducing the manufacturing cost.

[0005] The present invention has been made in view of the above problems, and an object thereof is to improve the attachability of the holder and reduce the manufacturing cost of the fluid pressure cylinder.

Means for Solving the Problems

[0006] The present invention relates to a fluid pressure cylinder comprising: a cylinder tube; a piston rod reciprocally mounted within the cylinder tube; a piston connected to the piston rod and slidably housed within the cylinder tube; a magnet mounted within the cylinder tube and reciprocating together with the piston rod; a cylindrical holder attached to the piston rod and holding the magnet; and a magnetic sensor that detects the stroke of the piston rod and piston by the magnetic field of the magnet. The magnet is provided on a part of the circumferential direction of the cylinder tube so as to face the magnetic sensor, and the holder has a plurality of holder pieces formed by dividing it in the circumferential direction, and the holder has a positioning part formed therein for positioning the magnet in the circumferential direction.

[0007] In this invention, since the holder is formed by dividing it in the circumferential direction, the holder can be easily attached to the piston rod by joining the divided holder pieces. Furthermore, since the magnet is provided not in an annular shape but in a part of the circumferential direction of the cylinder tube, and is positioned to face the magnetic sensor by the positioning part of the holder, the material cost of the magnet can be reduced. Thus, the ease of attaching the holder and the manufacturing cost of the fluid pressure cylinder can be reduced.

[0008] The present invention is characterized in that the holder is provided with an annular sealing member for protecting the magnet, an annular groove in which the annular sealing member is housed, and a fixing member for fixing the holder pieces together, and an insertion hole is opened in the annular groove through which the fixing member is inserted.

[0009] In this invention, since an insertion hole is opened in the annular groove, a fixing member can be provided without lengthening the holder in the axial direction.

[0010] The present invention is characterized in that the magnet is provided so as to straddle the boundary of the holder piece.

[0011] The present invention is characterized in that the holder is provided with a restricting portion that restricts the magnet from moving radially outward of the cylinder tube.

[0012] This invention prevents the magnet from being attracted to the inner surface of the cylinder tube.

[0013] The present invention is characterized in that the positioning portion is formed on at least two of the plurality of holder pieces.

[0014] This invention allows for securing space for a magnet to be installed.

[0015] The present invention is characterized in that the holder is provided with a rotation-retaining member that contacts the piston rod and restricts the rotation of the holder relative to the piston rod.

[0016] In this invention, by preventing the rotation of the holder and the magnet provided in the holder, the magnet can always be made to face the magnetic sensor, thereby improving the detection accuracy of the magnetic sensor.

[0017] The present invention is characterized in that the rotation-preventing member is provided parallel to the dividing surface of the holder piece.

[0018] In this invention, even if the holder pieces loosen in a direction that causes them to move away from each other, the contact of the rotation-preventing member with respect to the piston rod is maintained, thus maintaining the rotation-preventing effect of the rotation-preventing member. [Effects of the Invention]

[0019] According to the present invention, it is possible to improve the ease of mounting the holder and reduce the manufacturing cost of the fluid pressure cylinder. [Brief explanation of the drawing]

[0020] [Figure 1] This is a partial cross-sectional view of a fluid pressure cylinder according to an embodiment of the present invention. [Figure 2] This is an external view of a fluid pressure cylinder according to an embodiment of the present invention. [Figure 3] This is a perspective view showing the holder attached to the piston rod. [Figure 4]It is a cross-sectional view of the holder along the line IV-IV shown in FIG. 3. [Figure 5] It is a perspective view of the holder, and is shown corresponding to FIG. 3. [Figure 6] It is a perspective view of the holder as seen from the arrow VI shown in FIG. 5. [Figure 7] It is a perspective view of a holder piece showing the state where the holder is divided.

Embodiments for Carrying Out the Invention

[0021] Referring to the drawings, a hydraulic cylinder according to an embodiment of the present invention will be described. Hereinafter, a hydraulic cylinder 100 using hydraulic oil as the working fluid will be described.

[0022] First, referring to FIGS. 1 and 2, the overall configuration of the hydraulic cylinder 100 will be described.

[0023] As shown in FIG. 1, the hydraulic cylinder 100 includes a cylinder tube 10, a piston rod 20 reciprocally provided in the cylinder tube 10, a piston 30 connected to the piston rod 20 and slidably housed in the cylinder tube 10, a cylinder head 12 closing an opening at one end of the cylinder tube 10 through which the piston rod 20 is inserted, a cylinder bottom 13 closing an opening at the other end of the cylinder tube 10, a magnet 40 provided in the cylinder tube 10 and reciprocating together with the piston rod 20, a cylindrical holder 71 holding the magnet 40, and a magnetic sensor 50 for detecting the strokes of the piston rod 20 and the piston 30 by the magnetism of the magnet 40. In FIG. 1, the illustration of the magnetic sensor 50 is omitted.

[0024] ] The cylinder tube 10 is formed of a magnetic material made of steel. The cylinder head 12 is fastened to the cylinder tube 10 via, for example, a plurality of fastening members such as bolts (not shown). The cylinder bottom 13 is joined to the cylinder tube 10 by welding, for example. The rod side chamber 2 is partitioned by the cylinder tube 10, the cylinder head 12, and the piston 30, and the non-rod side chamber 3 is partitioned by the cylinder tube 10, the cylinder bottom 13, and the piston 30. A head-side port 11a is formed on the cylinder head 12 side of the cylinder tube 10 as a supply and discharge port that communicates with the rod side chamber 2. Hereafter, the axial direction of the cylinder tube 10 will be simply referred to as the "axial direction," the radial direction of the cylinder tube 10 as the "radial direction," and the circumferential direction of the cylinder tube 10 as the "circumferential direction."

[0025] The cylinder head 12 is formed in an annular shape and slidably supports the piston rod 20. The cylinder bottom 13 has a bottom-side port 13a and a passage 13b which serve as supply and discharge ports communicating with the anti-rod side chamber 3.

[0026] The piston rod 20 includes a rod body 21 slidably supported by the cylinder head 12, a piston fixing portion 22 on which the piston 30 is provided and fixed, and a tip portion 23 formed to be smaller in diameter than the piston fixing portion 22. In the piston rod 20, the rod body 21, the piston fixing portion 22, and the tip portion 23 are arranged in this order in the axial direction. Steps are formed between adjacent rod bodies 21, piston fixing portions 22, and tip portions 23. In the piston rod 20, the rod body 21 has the largest diameter, and the tip portion 23 has the smallest diameter. A male thread 22a is formed on the outer circumferential surface of the end of the piston fixing portion 22 on the tip portion 23 side. The outer diameter of the male thread 22a (specifically, the bottom of the male thread 22a) is smaller than the outer diameter of the outer circumferential surface 22b on which the male thread 22a is not formed in the piston fixing portion 22, and larger than the outer diameter of the tip portion 23 and the flange portion 23a described later.

[0027] A holder 71 for holding the magnet 40 is attached to the outer circumferential surface of the tip portion 23. In other words, the magnet 40 is attached to the piston rod 20 (tip portion 23) via the holder 71. A flange portion 23a with a larger diameter than the tip portion 23 is formed on the tip portion 23, and the flange portion 23a prevents the holder 71 from coming off. The detailed configuration of the holder 71 will be described later. The magnet 40 is a permanent magnet such as neodymium, and is provided on a part of the circumferential direction of the cylinder tube 10 so as to face the magnetic sensor 50 (see Figure 2) across the cylinder tube 10. Specifically, the magnet 40 is provided in an area smaller than half the circumference of the cylinder tube 10. When the holder 71 is attached to the tip portion 23, the holder 71 and the magnet 40 are provided so as not to contact (be attracted to) the inner circumferential surface of the cylinder tube 10. Therefore, even if the magnet 40 is provided inside the cylinder tube 10 which is made of a magnetic material, the operation of the hydraulic cylinder 100 is not hindered. Even if the magnet 40 is attracted to the inner surface of the cylinder tube 10 by magnetic force, the stroke direction of the piston rod 20 and piston 30 is perpendicular to the lines of force of the magnetic force, so it will have little effect on the stroke of the piston rod 20 and piston 30. For this reason, it is preferable that the magnet 40 is not attracted to the inner surface of the cylinder tube 10, but it is also possible that the magnet 40 is attracted to the inner surface of the cylinder tube 10.

[0028] The piston 30 is formed in an annular shape. A nut portion 35 is formed on one axial end of the piston 30 (right side in Figure 1), and a female thread 35a is formed on the inner circumferential surface of the nut portion 35. The piston 30 is attached to and connected to the piston rod 20 by screwing the female thread 35a of the nut portion 35 of the piston 30 with the male thread 22a of the piston fixing portion 22 of the piston rod 20. The piston 30 is formed to be shorter in axial length than the piston fixing portion 22, and when the piston 30 is attached to the piston rod 20, a region is formed at the tip of the piston fixing portion 22 where the piston 30 is not provided (see Figure 4). A sealing member 31 is provided on the outer circumferential surface of the piston 30. This blocks communication between the rod-side chamber 2 and the non-rod-side chamber 3 through the space between the inner circumferential surface of the cylinder tube 10 and the outer circumferential surface of the piston 30.

[0029] In such a hydraulic cylinder 100, when hydraulic fluid is supplied from a hydraulic source (working fluid pressure source) to the anti-rod side chamber 3 through the bottom side port 13a and passage 13b, the piston rod 20 and piston 30 move in a direction that reduces the rod side chamber 2, and the hydraulic cylinder 100 extends. At this time, the hydraulic fluid in the rod side chamber 2 is discharged to a tank (not shown) through the head side port 11a.

[0030] Furthermore, when hydraulic fluid is supplied from the hydraulic source to the rod-side chamber 2 through the head-side port 11a, the piston rod 20 and piston 30 move in a direction that reduces the anti-rod-side chamber 3, causing the hydraulic cylinder 100 to contract. At this time, the hydraulic fluid in the anti-rod-side chamber 3 is discharged to the tank through the bottom-side port 13a and passage 13b.

[0031] As shown in Figure 2, the magnetic sensor 50 extends axially along the cylinder tube 10 and is mounted on the outer circumferential surface of the cylinder tube 10. The magnetic sensor 50 includes a plurality of Hall elements (not shown) spaced apart in the axial direction, an electronic circuit board (not shown) on which the Hall elements are mounted, and a connector 53. The connector 53 is connected to a processing unit (not shown) that processes the detection results of the Hall elements. The magnetic sensor 50 detects the magnetism of the magnet 40 using the Hall elements and outputs the detection result to the processing unit through the connector 53, thereby detecting the stroke of the piston rod 20 and the piston 30 (for example, displacement from the initial position). The magnetic sensor 50 is attached to the outer circumferential surface of the cylinder tube 10 by a plurality of mounting parts 60 spaced apart in the axial direction, restricting the axial and radial movement of the cylinder tube 10 and preventing rotation.

[0032] Next, we will describe in detail the configuration related to the holder 71.

[0033] Figure 3 is a perspective view showing the holder 71 attached to the tip 23 of the piston rod 20, Figure 4 is a cross-sectional view of the holder 71 along the line IV-IV in Figure 3, and Figure 5 is a perspective view of the holder 71 corresponding to Figure 3. Figure 6 is a perspective view of the holder 71 as seen from arrow VI in Figure 5, and Figure 7 is a perspective view of the holder pieces 41a and 41b showing the holder 71 divided as described later. Note that the sealing member 31 provided on the piston 30 is not shown in Figures 3 and 4.

[0034] As shown in Figure 3, the holder 71 has a holder body 41 and a magnet holding part 70 that is supported by the holder body 41 and holds the magnet 40. The magnet holding part 70 is formed in a crescent shape. Two magnets 40 are embedded and fixed in the magnet holding part 70 with an axial gap between them. In this way, the magnets 40 are held in the magnet holding part 70.

[0035] As shown in Figures 3 to 7, the holder body 41 is formed in a cylindrical shape. The holder body 41 has an insertion hole 42 (see Figures 4 and 5) through which the tip 23 of the piston rod 20 is inserted, large diameter portions 43a and 43b formed at both ends in the axial direction, and a small diameter portion 44 formed between the large diameter portions 43a and 43b. An annular groove 45 is formed in the large diameter portion 43b on the flange portion 23a side of the piston rod 20, which houses a contaminant seal 80 as an annular sealing member for protecting the magnet 40. In this embodiment, the holder body 41 is formed by joining together symmetrical, halved holder pieces 41a and 41b that are divided in the circumferential direction (see Figure 7). In other words, the holder body 41 has a plurality of holder pieces 41a and 41b formed by dividing in the circumferential direction by a dividing surface 48. The holder body 41 is provided with fastening members 85 such as bolts (see Figure 6) inserted through through holes 49 formed across the holder pieces 41a and 41b, thereby fixing the holder pieces 41a and 41b to each other. In this embodiment, three through holes 49 are formed extending perpendicularly to the dividing surfaces 48 of the holder pieces 41a and 41b, two of which open into the small diameter portion 44 and one opening into the annular groove 45 (see Figures 5 and 7). As shown in Figure 4, a region where the piston 30 is not provided is formed at the tip of the piston fixing portion 22, so when attaching the holder body 41 to the tip portion 23 of the piston rod 20, the holder body 41 can be attached with an axial gap between it and the piston 30.

[0036] The inner diameter of the insertion hole 42 is formed to be approximately the same as or slightly larger than the outer diameter of the tip portion 23 of the piston rod 20, and smaller than the outer diameter of the flange portion 23a. The holder body 41 is fixed by joining the holder pieces 41a and 41b so that the tip portion 23 is inserted into the insertion hole 42. Details of how to attach the holder body 41 will be described later. The outer diameters of the large diameter portions 43a and 43b are formed to be smaller than the inner circumferential surface of the cylinder tube 10. Therefore, the holder body 41 does not come into contact with the inner circumferential surface of the cylinder tube 10. Annular claw portions 47a and 47b are formed on the outer circumferential edges of the large diameter portions 43a and 43b, respectively, projecting axially toward the small diameter portion 44.

[0037] The small-diameter portion 44 is formed concentrically with the large-diameter portions 43a and 43b. As shown in Figures 4 and 5, a planar notch 44a is formed in the small-diameter portion 44. The notch 44a is formed across the holder pieces 41a and 41b (see Figures 5 and 7), and the bottom surface of the crescent-shaped magnet holder 70 contacts the notch 44a. In this way, the magnet 40 (magnet holder 70) is provided so as to straddle the dividing surface 48, which is the boundary between the holder pieces 41a and 41b. This ensures that space is available for providing the magnet holder 70. Alternatively, the notch 44a may be formed on only one of the holder pieces 41a and 41b, and the magnet 40 (magnet holder 70) may be provided without straddling the dividing surface 48. The magnet holding portion 70 is placed on the notch portion 44a of the holder body 41, and is held by the holder body 41 by the engagement of its axial outer peripheral surfaces 70a and 70b with the annular claw portions 47a and 47b of the holder body 41, respectively. In other words, the notch portion 44a functions as a positioning portion where the magnet 40 is provided and which positions the magnet 40 in the circumferential direction, and the annular claw portions 47a and 47b function as restricting portions that restrict the magnet 40 from moving radially outward of the cylinder tube 10. The axial dimensions of the magnet holding portion 70 and the axial dimensions between the large diameter portions 43a and 43b of the holder body 41 are formed to be approximately the same, and the outer diameters of the axial outer peripheral surfaces 70a and 70b of the magnet holding portion 70 and the inner diameters of the inner peripheral surfaces of the annular claw portions 47a and 47b are formed to be approximately the same. This restricts the relative movement of the magnet holding portion 70 with respect to the holder body 41, preventing the magnet 40 from being attracted to the inner circumferential surface of the cylinder tube 10, and also positions the magnet holding portion 70 relative to the holder body 41.

[0038] The annular groove 45 is formed on the outer circumferential surface of the large-diameter portion 43b. The contaminant seal 80 is made of, for example, fluororesin and is formed in an annular shape. Part of the contaminant seal 80 is housed in the annular groove 45 and is provided on the holder body 41, sliding along the inner circumference of the cylinder tube 10 as shown in Figure 1. The contaminant seal 80 and the sealing member 31 provided on the piston 30 prevent foreign matter such as metal fragments in the hydraulic fluid from being attracted to the magnet 40. Therefore, foreign matter attracted to the magnet 40 will not slide inside the cylinder tube 10, and damage to the cylinder tube 10 is prevented. Alternatively, the annular groove 45 and the contaminant seal 80 may be provided in pairs on both sides of the magnet 40 in the axial direction. With this configuration, foreign matter such as metal fragments in the hydraulic fluid will be more reliably prevented from being attracted to the magnet 40.

[0039] The holder pieces 41a and 41b are provided with a set screw 88 (see Figures 4 and 6) which acts as a rotation-retaining member that abuts against the tip 23 of the piston rod 20 and restricts the rotation of the holder body 41 relative to the tip 23, and a screw hole 89 (see Figure 7) through which the set screw 88 is inserted. In Figures 4 and 6, the hidden set screw 88 is shown by a dotted line, and in Figure 7, the hidden screw hole 89 is shown by a dotted line. In this embodiment, one set screw 88 and one screw hole 89 are provided on each of the holder pieces 41a and 41b, and are provided parallel to the dividing surface 48 (see Figures 4, 6, and 7). In other words, the set screw 88 and the screw hole 89 are provided perpendicular to the fixing member 85. The set screw 88 is screwed into the screw hole 89 and abuts against the tip 23 of the piston rod 20.

[0040] Next, we will explain in detail how to attach the holder body 41.

[0041] To attach the holder body 41 to the tip 23 of the piston rod 20, first, the holder pieces 41a and 41b are aligned so that the tip 23 is inserted through the insertion hole 42, while the magnet holding part 70 is held by the holder pieces 41a and 41b, and the holder pieces 41a and 41b are fixed to each other by the fixing member 85. With the holder pieces 41a and 41b fixed by the fixing member 85, the holder 71 is circumferentially rotatable relative to the tip 23 of the piston rod 20. In other words, the inner diameter of the insertion hole 42 is formed so that the holder 71 is circumferentially rotatable relative to the tip 23 when the holder pieces 41a and 41b are fixed by the fixing member 85. Then, the holder 71 is rotated circumferentially to align the magnet 40 so that it faces the magnetic sensor 50 across the cylinder tube 10. After circumferential alignment, the holder 71 is prevented from rotating by inserting the two set screws 88 into the two screw holes 89 so that they contact the piston rod 20, and the magnet 40 is attached to the tip 23 of the piston rod 20. In addition, the flange 23a of the tip 23 prevents the holder 71 (holder body 41) from coming off.

[0042] Thus, in the hydraulic cylinder 100 of this embodiment, the holder 71 (holder body 41) is formed by dividing it in the circumferential direction. The divided holder pieces 41a and 41b are joined together, making it easier to attach the holder 71 to the piston rod 20 than when a tip portion 23 of approximately the same diameter is inserted through the insertion hole of an undivided holder. Furthermore, since the magnet 40 is not annular but is provided on a part of the circumferential direction of the cylinder tube 10 and is positioned to face the magnetic sensor 50 by the notch portion 44a of the holder 71, the material cost of the magnet 40 can be reduced. Therefore, the ease of attaching the holder 71 and the manufacturing cost of the hydraulic cylinder 100 can be reduced.

[0043] Furthermore, in the hydraulic cylinder 100 of this embodiment, by preventing the rotation of the holder 71 (holder body 41) and the magnet 40 provided on the holder 71, the magnet 40 can always face the magnetic sensor 50, thereby improving the detection accuracy of the magnetic sensor 50. Moreover, since the set screw 88 is provided parallel to the dividing surface 48 of the holder pieces 41a and 41b, even if the fixing member 85 loosens and the holder pieces 41a and 41b loosen in a direction that moves away from each other (perpendicular to the dividing surface 48), the set screw 88 will not move in a direction that moves away from the tip 23 of the piston rod 20 (parallel to the dividing surface 48). Therefore, the contact of the set screw 88 with respect to the piston rod 20 is maintained, and the rotation-preventing effect of the set screw 88 is maintained.

[0044] Furthermore, in the hydraulic cylinder 100 of this embodiment, an insertion hole 49 is opened in the annular groove 45 of the holder 71 (holder body 41) through which the fixing member 85 is inserted. In other words, the fixing member 85 is provided at the position where the contamination seal 80 is placed. Therefore, the fixing member 85 can be provided without making the holder 71 longer in the axial direction. Also, since the contamination seal 80 is formed in an annular shape and is provided in the annular groove 45 straddling the insertion hole 49, the sealing performance of the contamination seal 80 is not significantly affected. Note that the insertion hole 49 opening in the annular groove 45 is formed so that the fixing member 85 does not come into contact with the contamination seal 80.

[0045] According to the above embodiment, the following effects and advantages are achieved.

[0046] In the hydraulic cylinder 100, the holder 71 is formed by dividing it in the circumferential direction, so the holder 71 can be easily attached to the piston rod 20 by joining the divided holder pieces 41a and 41b. In addition, the magnet 40 is not annular but is provided on a part of the circumferential direction of the cylinder tube 10 and is positioned to face the magnetic sensor 50 by the notch 44a of the holder 71, so the material cost of the magnet 40 can be reduced. Thus, the ease of attaching the holder 71 and the manufacturing cost of the hydraulic cylinder 100 can be reduced.

[0047] Next, modifications of this embodiment will be described. The following modifications are also within the scope of the present invention, and it is possible to combine the configurations shown in the modifications with the configurations described in the above embodiments, or to combine the configurations described in the following different modifications.

[0048] <Example 1> In the above embodiment, the holder 71 is attached to the outer circumferential surface of the tip portion 23 of the piston rod 20. However, the attachment position of the holder 71 is not limited to the above, as long as it is attached to the piston rod 20 and holds the magnet 40. For example, it may be attached to the rod body 21 of the piston rod 20 (in other words, on the base end side of the piston 30). This configuration also produces the same effects as the above embodiment.

[0049] <Modification 2> In the above embodiment, the holder 71 is formed by two symmetrically shaped holder pieces 41a and 41b that are divided in the circumferential direction. However, the holder 71 is not limited to this, and may be formed by three or more circumferentially divided holder pieces, as long as at least two of the holder pieces are provided with a magnet 40 and have positioning portions such as notches 44a for positioning the magnet 40 in the circumferential direction, and each holder piece does not have to be symmetrically shaped. Even with this configuration, the same effects as in the above embodiment can be achieved.

[0050] <Variation 3> In the above embodiment, the holder 71 is provided with a set screw 88 that contacts the piston rod 20 to restrict the rotation of the holder 71 relative to the piston rod 20. However, the holder 71 may be provided with other rotation-preventing means other than the set screw 88. For example, the holder 71 may be unable to rotate circumferentially relative to the tip 23 of the piston rod 20 while the holder pieces 41a and 41b are fixed by the fixing member 85. Also, if a set screw 88 is provided, it does not have to be provided parallel to the dividing surface 48 of the holder pieces 41a and 41b.

[0051] <Modification 4> In the above embodiment, the holder 71 includes a holder body 41 and a magnet holding portion 70 supported by the holder body 41 and holding the magnet 40. However, the magnet holding portion 70 is not an essential component, and the magnet 40 may be directly held by the holder body 41. Also, the contamination seal 80 provided on the holder body 41 to protect the magnet 40 is not an essential component. Even with this configuration, the same effects as in the above embodiment can be achieved.

[0052] The configuration, operation, and effects of the embodiment of the present invention configured as described above will be summarized below.

[0053] The hydraulic cylinder 100, as a fluid pressure cylinder, comprises a cylinder tube 10, a piston rod 20 reciprocally mounted within the cylinder tube 10, a piston 30 connected to the piston rod 20 and slidably housed within the cylinder tube 10, a magnet 40 mounted within the cylinder tube 10 and reciprocating together with the piston rod 20, a cylindrical holder 71 attached to the piston rod 20 and holding the magnet 40, and a magnetic sensor 50 that detects the stroke of the piston rod 20 and the piston 30 by the magnetism of the magnet 40. The magnet 40 is mounted on a part of the circumferential direction of the cylinder tube 10 so as to face the magnetic sensor 50, and the holder 71 has a plurality of holder pieces 41a, 41b formed by dividing in the circumferential direction, and the holder 71 has a notch 44a that serves as a positioning part for positioning the magnet 40 in the circumferential direction.

[0054] In this configuration, since the holder 71 is formed by dividing it in the circumferential direction, the holder 71 can be easily attached to the piston rod 20 by joining the divided holder pieces 41a and 41b. Furthermore, since the magnet 40 is not annular but is provided on a part of the cylinder tube 10 in the circumferential direction and is positioned to face the magnetic sensor 50 by the notch 44a of the holder 71, the material cost of the magnet 40 can be reduced. Thus, the ease of attachment of the holder 71 and the manufacturing cost of the hydraulic cylinder 100 can be reduced.

[0055] Furthermore, in the hydraulic cylinder 100, the holder 71 is provided with an annular contamination seal 80 for protecting the magnet 40, an annular groove 45 in which the annular contamination seal 80 is housed, and a fixing member 85 for fixing the holder pieces 41a and 41b together. The annular groove 45 has an insertion hole 49 through which the fixing member 85 is inserted.

[0056] In this configuration, since the insertion hole 49 is opened in the annular groove 45, the fixing member 85 can be provided without lengthening the holder 71 in the axial direction.

[0057] In addition, in the hydraulic cylinder 100, the magnet 40 is positioned to straddle the boundary between the holder pieces 41a and 41b.

[0058] In addition, the hydraulic cylinder 100 is provided with claw portions 47a and 47b on the holder 71, which serve as restricting parts that restrict the magnet 40 from moving radially outward from the cylinder tube 10.

[0059] In this configuration, the magnet 40 is prevented from being attracted to the inner surface of the cylinder tube 10.

[0060] In addition, in the hydraulic cylinder 100, the notch portion 44a is formed in at least two of the multiple holder pieces 41a, 41b.

[0061] This configuration allows for space to be provided for the magnet 40.

[0062] Furthermore, in the hydraulic cylinder 100, the holder 71 is provided with a set screw 88, which acts as a rotation-stopping member that contacts the piston rod 20 and restricts the rotation of the holder 71 relative to the piston rod 20.

[0063] In this configuration, by preventing the rotation of the holder 71 and the magnet 40 provided on the holder 71, the magnet 40 can always be made to face the magnetic sensor 50, thereby improving the detection accuracy of the magnetic sensor 50.

[0064] In addition, in the hydraulic cylinder 100, the set screw 88 is provided parallel to the dividing surface 48 of the holder pieces 41a and 41b.

[0065] In this configuration, even if the holder pieces 41a and 41b loosen in a direction that moves them apart from each other, the contact of the set screw 88 with the piston rod 20 is maintained, thus maintaining the rotation-preventing effect of the set screw 88.

[0066] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of Symbols]

[0067] 10...Cylinder tube, 20...Piston rod, 30...Piston, 40...Magnet, 41a, 41b...Holder piece, 44a...Notch (positioning part), 45...Annular groove, 47a, 47b...Claw part (regulating part), 48...Dividing surface, 49...Through hole, 50...Magnetic sensor, 71...Holder, 80...Contamination seal (sealing member), 85...Fixing member, 88...Set screw (rotation stopper member), 100...Hydraulic cylinder (fluid pressure cylinder)

Claims

1. Cylinder tube and A piston rod is provided within the cylinder tube so as to be reciprocable, A piston connected to the piston rod and slidably housed within the cylinder tube, A magnet provided inside the cylinder tube and reciprocating together with the piston rod, A cylindrical holder attached to the piston rod and holding the magnet, The system includes a magnetic sensor that detects the stroke of the piston rod and the piston by the magnetic field of the magnet, The magnet is provided on a part of the circumferential direction of the cylinder tube so as to face the magnetic sensor, The holder has a plurality of holder pieces formed by dividing in the circumferential direction, A fluid pressure cylinder characterized in that the holder is provided with the magnet and has a positioning portion formed for positioning the magnet in the circumferential direction.

2. A fluid pressure cylinder according to claim 1, The holder is provided with an annular sealing member for protecting the magnet, an annular groove in which the annular sealing member is housed, and a fixing member for fixing the holder pieces together. A fluid pressure cylinder characterized in that the annular groove has an insertion hole through which the fixing member is inserted.

3. A fluid pressure cylinder according to claim 1, The fluid pressure cylinder is characterized in that the magnet is provided so as to straddle the boundary of the holder piece.

4. A fluid pressure cylinder according to claim 1, A fluid pressure cylinder characterized in that the holder is provided with a restricting portion that restricts the magnet from moving radially outward of the cylinder tube.

5. A fluid pressure cylinder according to claim 1, The positioning portion is formed on at least two of the plurality of holder pieces, characterized in that it is a fluid pressure cylinder.

6. A fluid pressure cylinder according to any one of claims 1 to 5, A fluid pressure cylinder characterized in that the holder is provided with a rotation-stopping member that contacts the piston rod and restricts the rotation of the holder relative to the piston rod.

7. A fluid pressure cylinder according to claim 6, The fluid pressure cylinder is characterized in that the rotation-stopping member is provided parallel to the dividing surface of the holder piece.

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