Fluid pressure cylinder

Abstract

To improve the durability of the magnets. [Solution] The hydraulic cylinder 100 comprises a cylinder tube 10, a piston rod 20, a piston 30 connected to the piston rod 20 and slidably housed within the cylinder tube 10, a magnet 40 provided within the cylinder tube 10 and reciprocating together with the piston rod 20, and a magnetic sensor 50 that detects the stroke of the piston rod 20 and the piston 30 by the magnetic field of the magnet 40. The piston rod 20 has a piston fixing portion 22 to which the piston 30 is connected, with a male thread 22a formed on its outer circumference, and a tip portion 23 formed to be smaller in diameter than the piston fixing portion 22. The piston 30 is attached to the piston fixing portion 22 by the female thread 35a of a nut portion 35 formed on or separately from the piston 30 screwing into the male thread of the piston fixing portion 22, and the magnet 40 is attached to the tip portion 23 of the piston rod 20.

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 magnet is attached to the outer peripheral surface of the extension portion via a holder. By fixing a nut to the tip of the extension portion, the piston and the holder are fixed.

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 piston, since a nut is fixed to the tip of the extension portion, a load acts on the magnet provided on the extension portion during attachment. Further, in the cylinder described in Patent Document 1, when an external force in the extending direction acts on the piston rod in the fully extended state, a compressive load acts on the magnet between the piston and the nut. Thus, in the cylinder described in Patent Document 1, since a load easily acts on the magnet, there is a problem with the durability of the magnet.

[0005] The present invention has been made in view of the above problems, and an object thereof is to improve the durability of the magnet.

Means for Solving the Problems

[0006] [[ID=UC0000033]] The present invention comprises 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, and a magnetic sensor that detects the stroke of the piston rod and piston by the magnetic field of the magnet. The piston rod has a piston fixing portion to which the piston is connected, with a male thread formed on its outer circumference, and a tip portion formed to a smaller diameter than the piston fixing portion. The piston is attached to the piston fixing portion by a female thread on a nut portion formed on or separately from the piston engaging with the male thread on the piston fixing portion, and the magnet is attached to the tip of the piston rod.

[0007] In this invention, the piston is attached to the piston fixing part of the piston rod by screwing together the male thread of the piston fixing part of the piston rod and the female thread of the nut part, and the magnet is attached to the tip of the piston rod. Therefore, no load is applied to the magnet when the piston rod and piston are connected, and even if an external force in the extension direction is applied to the piston rod in the fully extended state, a compressive load is unlikely to be applied to the magnet. Thus, the durability of the magnet can be improved.

[0008] The present invention relates to a fluid pressure cylinder, further comprising a holder attached to the tip of a piston rod for holding a magnet, wherein the holder is provided with a pair of sealing members located on both sides of the magnet in the axial direction of the cylinder tube and sliding along the inner circumference of the cylinder tube.

[0009] This invention prevents foreign matter in the working fluid from being attracted to the magnet.

[0010] The present invention is characterized in that, in a holder, one of the sealing members is located radially outward of the nut portion.

[0011] In this invention, since the sealing member is provided using the space radially outside the nut portion, there is no need to lengthen the piston rod in the axial direction for the sealing member, and the sealing member can be provided without sacrificing the stroke of the piston rod and piston. [Effects of the Invention]

[0012] According to the present invention, the durability of magnets can be improved. [Brief explanation of the drawing]

[0013] [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] Figure 3 shows a cross-sectional view of the holder along the line IV-IV. [Figure 5] This is a perspective view of the holder, shown in conjunction with Figure 3. [Modes for carrying out the invention]

[0014] A fluid pressure cylinder according to an embodiment of the present invention will be described with reference to the drawings. Below, a hydraulic cylinder 100 in which hydraulic oil is used as the working fluid will be described.

[0015] First, the overall configuration of the hydraulic cylinder 100 will be described with reference to Figures 1 and 2.

[0016] As shown in Figure 1, the hydraulic cylinder 100 includes 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 cylinder head 12 that closes the opening at one end of the cylinder tube 10 and through which the piston rod 20 is inserted, a cylinder bottom 13 that closes the opening at the other end of the cylinder tube 10, a magnet 40 mounted within the cylinder tube 10 and reciprocating together with the piston rod 20, a holder 71 that holds the magnet 40, and a magnetic sensor 50 that detects the stroke of the piston rod 20 and the piston 30 by the magnetic field of the magnet 40. Note that the magnetic sensor 50 is not shown in Figure 1.

[0017] 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."

[0018] 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.

[0019] The piston rod 20 has a rod body 21 that is slidably supported by the cylinder head 12, a piston fixing portion 22 provided and fixed on the outer periphery of the piston 30, and a tip portion 23 formed to have a smaller 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 provided side by side in the axial direction in this order. Step portions are formed between the adjacent rod body 21, piston fixing portion 22, and tip portion 23, respectively. In the piston rod 20, the rod body 21 has the largest diameter, and the tip portion 23 has the smallest diameter. An external thread 22a is formed on the outer peripheral surface of the end portion on the tip portion 23 side in the piston fixing portion 22. The outer diameter of the external thread 22a (specifically, the bottom of the external thread 22a) is smaller than the outer diameter of the outer peripheral surface 22b where the external thread 22a is not formed in the piston fixing portion 22, and is larger than the outer diameters of the tip portion 23 and a flange portion 23a described later.

[0020] 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) on either side of 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.

[0021] 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.

[0022] In such a hydraulic cylinder 100, when hydraulic oil is supplied from a hydraulic source (operating fluid pressure source) to the anti-rod side chamber 3 through the bottom side port 13a and the passage 13b, the piston rod 20 and the piston 30 move in a direction to reduce the rod side chamber 2, and the hydraulic cylinder 100 extends. At this time, the hydraulic oil in the rod side chamber 2 is discharged to a tank (not shown) through the head side port 11a.

[0023] Also, when hydraulic oil is supplied from the hydraulic source to the rod side chamber 2 through the head side port 11a, the piston rod 20 and the piston 30 move in a direction to reduce the anti-rod side chamber 3, and the hydraulic cylinder 100 contracts. At this time, the hydraulic oil in the anti-rod side chamber 3 is discharged to the tank through the bottom side port 13a and the passage 13b.

[0024] As shown in FIG. 2, the magnetic sensor 50 extends in the axial direction of the cylinder tube 10 and is provided on the outer peripheral surface of the cylinder tube 10. The magnetic sensor 50 includes a plurality of Hall elements (not shown) provided at intervals in the axial direction, an electronic substrate (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 outputs the detection result of detecting the magnetism of the magnet 40 by the Hall element to the processing unit through the connector 53, thereby detecting the stroke (for example, the displacement from the initial position) of the piston rod 20 and the piston 30. The magnetic sensor 50 is attached to the outer peripheral surface of the cylinder tube 10 by a plurality of attachment portions 60 provided at intervals in the axial direction, and the movement of the cylinder tube 10 in the axial direction and the radial direction is restricted, and rotation is prevented.

[0025] Next, the configuration related to the holder 71 will be described in detail.

[0026] 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. Note that the sealing member 31 provided on the piston 30 is not shown in Figures 3 and 4.

[0027] 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.

[0028] As shown in Figures 3 to 5, 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. Annular grooves 45a and 45b are formed in each of the large diameter portions 43a and 43b, respectively, which house contaminant seals 80a and 80b as sealing members. In this embodiment, the holder body 41 is formed by joining symmetrical, halved holder pieces 41a and 41b that are divided in the circumferential direction. The holder body 41 is fixed to each other by fastening members (not shown) such as bolts fastened to fastening holes 49 formed across the holder pieces 41a and 41b. 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. Therefore, 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.

[0029] The inner diameter of the insertion hole 42 is formed to be approximately the same as 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. The holder body 41 is attached to the tip portion 23 by restricting the rotation of the holder body 41 with a set screw 88 (see Figure 4), which will be described later. In addition, the flange portion 23a of the tip portion 23 prevents the holder 71 from coming off. 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. As shown in Figure 4, the large diameter portion 43a located on the piston fixing portion 22 side (piston 30 side) of the piston rod 20 is formed in a hollow shape with a hollow portion 46. The hollow portion 46 is formed continuously with the insertion hole 42 and is formed coaxially with the insertion hole 42. The inner circumferential surface of the hollow portion 46 is formed to be larger in diameter than the inner circumferential surface of the insertion hole 42, and the nut portion 35 of the piston 30 is housed in the hollow portion 46. 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.

[0030] 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 bottom surface of the crescent-shaped magnet holder portion 70 contacts the notch 44a. The magnet holder portion 70 is placed on the notch 44a of the holder body 41 and is held by the holder body 41 by the engagement of its axial outer circumferential surfaces 70a and 70b with the annular claw portions 47a and 47b of the holder body 41, respectively. The axial dimensions of the magnet holder 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 circumferential surfaces 70a and 70b of the magnet holder portion 70 and the inner diameters of the inner circumferential 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, thereby positioning the magnet holding portion 70 relative to the holder body 41.

[0031] The annular grooves 45a and 45b are formed on the outer circumferential surfaces of the large-diameter portions 43a and 43b, respectively. In other words, the annular grooves 45a and 45b are provided on both sides of the magnet 40 in the axial direction. The contaminant seals 80a and 80b are made of, for example, fluororesin and are formed in an annular shape. The contaminant seals 80a and 80b are provided on the holder body 41 with a portion of each housed in the annular grooves 45a and 45b, respectively, and slide along the inner circumference of the cylinder tube 10 as shown in Figure 1. This prevents 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. In addition, one of the annular grooves 45a and the contaminant seal 80a are located radially outward from the nut portion 35 of the piston 30. Therefore, since the contamination seal 80a is provided by utilizing the space radially outside the nut portion 35, there is no need to lengthen the piston rod 20 (specifically, the tip portion 23) in the axial direction for the purpose of the contamination seal 80a, and the contamination seal 80a can be provided without sacrificing the stroke of the piston rod 20 and the piston 30.

[0032] As shown in Figure 4, the holder pieces 41a and 41b are provided with a set screw 88, 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 (not shown) through which the set screw 88 is inserted. In Figure 4, the hidden set screw 88 is shown by a dotted line. In this embodiment, one set screw 88 and one screw hole are provided on each of the holder pieces 41a and 41b, and are provided parallel to the dividing surfaces of the holder pieces 41a and 41b, respectively. In other words, the set screw 88 and the screw hole are provided perpendicular to the fastening member. The set screw 88 is screwed into the screw hole and abuts against the tip 23 of the piston rod 20.

[0033] Here, if the piston 30 of the hydraulic cylinder 100 were not provided with a nut portion 35, and the piston 30 and holder 71 were fixed by a nut provided in place of the flange portion 23a of the tip portion 23 of the piston rod 20, then when the nut is tightened, a load would be applied to the tip portion 23 and the magnet 40. Furthermore, in this configuration, if an external force in the extension direction is applied to the piston rod 20 when the piston 30 is in its most extended state and in contact with the cylinder head 12, the piston 30 will be unable to move because it is in contact with the cylinder head 12, and a compressive load will be applied between the piston 30 and the nut. In such a configuration of the hydraulic cylinder 100, a load is easily applied to the magnet 40, which poses a problem for the durability of the magnet 40.

[0034] In contrast, in the hydraulic cylinder 100 of this embodiment, the male thread of the piston fixing portion 22 of the piston rod 20 and the female thread of the nut portion 35 of the piston 30 are screwed together, and the magnet 40 is attached to the tip portion 23 of the piston rod 20. Therefore, when the piston rod 20 and the piston 30 are connected, a load is applied to the rod body 21 and the piston fixing portion 22 of the piston rod 20 when the nut portion 35 is tightened, but no load is applied to the tip portion 23, and therefore no load is applied to the magnet 40. Furthermore, in the hydraulic cylinder 100 of this embodiment, a nut is not provided on the tip portion 23 of the piston rod 20, and only a flange portion 23a with a smaller diameter than a nut is formed to prevent the holder 71 from falling off. Therefore, even if an external force in the extension direction is applied to the piston rod 20 in the fully extended state, a compressive load is unlikely to be applied to the magnet 40. The magnet 40 is attached to the tip 23 of the piston rod 20 via the holder 71, and since it is located radially outward compared to when it is directly attached to the tip 23, the above-mentioned compressive load is less likely to act on the magnet 40. Therefore, the durability of the magnet 40 can be improved.

[0035] Furthermore, in the hydraulic cylinder 100 of this embodiment, an axial gap is formed between the piston 30 and the holder 71, so that even when the piston 30 is subjected to a load, the load is not transmitted to the holder 71.

[0036] Furthermore, in the hydraulic cylinder 100 of this embodiment, the female thread of the nut portion 35 of the piston 30 is screwed onto the male thread of the piston fixing portion 22 of the piston rod 20. This allows the female thread of the nut portion 35 to be screwed onto a larger diameter portion of the rod than would be possible if it were screwed onto the tip portion 23 of the piston rod 20.

[0037] According to the above embodiment, the following effects and advantages are achieved.

[0038] In the hydraulic cylinder 100, the male thread of the piston fixing portion 22 of the piston rod 20 and the female thread of the nut portion 35 of the piston 30 are screwed together, and the magnet 40 is attached to the tip portion 23 of the piston rod 20. Therefore, no load is applied to the magnet 40 when the piston rod 20 and the piston 30 are connected, and even if an external force in the extension direction is applied to the piston rod 20 in the fully extended state, a compressive load is unlikely to be applied to the magnet 40. Thus, the durability of the magnet 40 can be improved.

[0039] 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.

[0040] <Example 1> In the above embodiment, the hydraulic cylinder 100 includes a holder 71 attached to the tip 23 of the piston rod 20 to hold the magnet 40. However, the hydraulic cylinder 100 is not limited to the above configuration as long as the magnet 40 is attached to the tip 23 and reciprocates together with the piston rod 20. In other words, the holder 71 is not an essential component, and the magnet 40 may be directly attached to the tip 23 of the piston rod 20. 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.

[0041] <Modification 2> In the above embodiment, the holder body 41 is formed by joining together symmetrical, halved holder pieces 41a and 41b that are divided in the circumferential direction. However, the holder body 41 may be formed without being divided in the circumferential direction.

[0042] <Variation 3> In the above embodiment, in the holder body 41, one of the contamination seals 80 (contamination seal 80a) is located radially outside the nut portion 35 of the piston 30. This eliminates the need to lengthen the piston rod 20 axially for the purpose of the contamination seal 80a, and allows the contamination seal 80a to be provided without sacrificing the stroke of the piston rod 20 and the piston 30. However, in cases where the stroke of the piston rod 20 and the piston 30 can be short, the contamination seal 80a does not need to be located radially outside the nut portion 35 of the piston 30.

[0043] <Modification 4> In the above embodiment, a nut portion 35 is formed on the piston 30, and the piston 30 is attached to the piston rod 20 by screwing the female thread 35a of the nut portion 35 on the piston 30 with the male thread 22a of the piston fixing portion 22 of the piston rod 20. However, the nut portion 35 may not be formed on the piston 30, and a separate nut (a separate component) may be provided at the tip of the piston 30 as the nut portion 35. Even in this configuration, the piston 30 is attached to the piston fixing portion 22 by screwing the female thread 35a of the nut portion 35 with the male thread 22a of the piston fixing portion 22.

[0044] The configuration, operation, and effects of the embodiment of the present invention configured as described above will be summarized below.

[0045] 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, and a magnetic sensor 50 that detects the stroke of the piston rod 20 and the piston 30 by the magnetic field of the magnet 40. The piston rod 20 has a piston fixing portion 22 to which the piston 30 is connected, with a male thread 22a formed on its outer circumference, and a tip portion 23 formed to be smaller in diameter than the piston fixing portion 22. The piston 30 is attached to the piston fixing portion 22 by the female thread 35a of a nut portion 35, which is formed on the piston 30 or separately from the piston 30, screwing into the male thread of the piston fixing portion 22. The magnet 40 is attached to the tip portion 23 of the piston rod 20.

[0046] In this configuration, the piston 30 is attached to the piston fixing portion 22 of the piston rod 20 by screwing the male thread 22a of the piston fixing portion 22 of the piston rod 20 with the female thread 35a of the nut portion 35 of the piston 30, and the magnet 40 is attached to the tip portion 23 of the piston rod 20. Therefore, no load is applied to the magnet 40 when the piston rod 20 and the piston 30 are connected, and even if an external force in the extension direction is applied to the piston rod 20 in the fully extended state, a compressive load is unlikely to be applied to the magnet 40. Thus, the durability of the magnet 40 can be improved.

[0047] Furthermore, the hydraulic cylinder 100 is further equipped with a holder 71 attached to the tip 23 of the piston rod 20 to hold the magnet 40, and the holder 71 is provided with a pair of contaminant seals 80 as sealing members, which are provided on both sides of the magnet 40 in the axial direction of the cylinder tube 10 and slide along the inner circumference of the cylinder tube 10.

[0048] In this configuration, foreign matter in the working fluid is prevented from being attracted to the magnet 40.

[0049] Furthermore, in the hydraulic cylinder 100, one of the contamination seals 80 (contamination seal 80a) is located radially outward from the nut portion 35 in the holder 71.

[0050] In this configuration, the contamination seal 80a is provided by utilizing the space radially outside the nut portion 35. Therefore, it is not necessary to lengthen the piston rod 20 in the axial direction for the purpose of providing the contamination seal 80a, and the contamination seal 80a can be provided without sacrificing the stroke of the piston rod 20 and the piston 30.

[0051] 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]

[0052] 10...Cylinder tube, 20...Piston rod, 22...Piston fixing part, 23...Tip part, 30...Piston, 35...Nut part, 40...Magnet, 50...Magnetic sensor, 71...Holder, 80, 80a, 80b...Contamination seal, 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, 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 aforementioned piston rod is A piston fixing portion to which the piston is connected has male threads formed on its outer surface, It has a tip portion that is formed to be smaller in diameter than the piston fixing portion, The piston is attached to the piston fixing part by screwing the female thread of the nut portion, which is formed on the piston or separately from the piston, with the male thread of the piston fixing part. The aforementioned magnet is attached to the tip of the piston rod, characterized in that it is a fluid pressure cylinder.

2. A fluid pressure cylinder according to claim 1, The piston rod further comprises a holder attached to the tip of the piston rod for holding the magnet, A fluid pressure cylinder characterized in that the holder is provided with a pair of sealing members that are located on both sides of the magnet in the axial direction of the cylinder tube and slide along the inner circumference of the cylinder tube.

3. A fluid pressure cylinder according to claim 2, A fluid pressure cylinder characterized in that, in the holder, one of the sealing members is located radially outward of the nut portion.

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