Hydraulic valve block

Abstract

The present invention provides a hydraulic valve block that can suppress malfunctions in the operation of the hydraulic valve device even when the flow rate of the hydraulic fluid increases. [Solution] The hydraulic valve block 1 is made of cast iron and has a spool hole 12, which is a space defined by a first inner wall surface 12A through which the spool 2 is inserted and through which the spool 2 slides, and a hydraulic fluid passage 11, which is a space defined by a second inner wall surface 11B and connected to the spool hole 12. The hydraulic valve block 1 includes a quenched hardened layer 15 formed to include the first inner wall surface 12A, and a base region 14 which is the area other than the quenched hardened layer 15. The corner portion 12B, which is the part where the first inner wall surface 12A and the second inner wall surface 11B are connected, is included in the base region 14.

Description

[Technical Field]

[0001] The present disclosure relates to a hydraulic valve block. [Background Art]

[0002] A hydraulic valve device including a spool and a hydraulic valve block formed with a plurality of working oil passages is known. In the hydraulic valve device, the connection state between the working oil passages changes due to movement of the spool (see, for example, Patent Document 1). [Prior Art Literature] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2001-221349 [Summary of Invention] [Problem to be Solved by Invention]

[0004] In the hydraulic valve device, the connection state between working oil passages is switched by movement of the spool. This allows a hydraulic cylinder or the like to operate in a desired manner. When the flow rate of hydraulic oil in the hydraulic valve device increases, a malfunction may occur in the operation of the hydraulic valve device, which may result in a state where the hydraulic cylinder does not operate in the desired manner.

[0005] One object of the present disclosure is to provide a hydraulic valve block capable of suppressing the occurrence of malfunctions in the operation of a hydraulic valve device even when the flow rate of hydraulic oil increases. [Means for Solving the Problem]

[0006] The hydraulic valve block of this disclosure is made of cast iron and has a spool hole, which is a space through which a spool is inserted and through which the spool slides, defined by a first inner wall surface, and a hydraulic fluid passage, which is a space defined by a second inner wall surface and connected to the spool hole. The hydraulic valve block comprises a quenched hardened layer formed to include the first inner wall surface, and a base region which is the region other than the quenched hardened layer. The corner, which is the portion where the first inner wall surface and the second inner wall surface are connected, is included in the base region. [Effects of the Invention]

[0007] According to the above-described hydraulic valve block, malfunctions in the operation of the hydraulic valve device can be suppressed even when the flow rate of the hydraulic fluid increases. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing the structure of a hydraulic valve device. [Figure 2] Figure 2 is a schematic cross-sectional view showing an enlarged view of region II in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view showing the state after the spool has moved from the state shown in Figure 2. [Figure 4] Figure 4 is a schematic flowchart of the manufacturing method of a hydraulic valve block. [Figure 5] Figure 5 is a photograph showing the metallographic structure of the base region. [Figure 6] Figure 6 shows the results of the cavitation erosion test. [Modes for carrying out the invention]

[0009] [Summary of the Embodiment] The hydraulic valve block of this disclosure is made of cast iron and has a spool hole, which is a space through which a spool is inserted and through which the spool slides, defined by a first inner wall surface, and a hydraulic fluid passage, which is a space defined by a second inner wall surface and connected to the spool hole. The hydraulic valve block comprises a quenched hardened layer formed to include the first inner wall surface, and a base region which is the region other than the quenched hardened layer. The corner, which is the portion where the first inner wall surface and the second inner wall surface are connected, is included in the base region.

[0010] The inventors investigated the cause of malfunctions in the operation of hydraulic valve devices when the flow rate of hydraulic fluid increases. As a result, they obtained the following findings and conceived the configuration of the hydraulic valve block of this disclosure. When desired hydraulic fluid passages are connected by the movement of the spool and hydraulic fluid flows, the gap between the wall surface of the hydraulic valve block that defines the spool hole and the outer surface of the spool may become an unintended passage through which the hydraulic fluid flows. Because this gap is very small, the pressure applied to the hydraulic fluid differs greatly between inside and outside the gap. As a result, the pressure applied to the hydraulic fluid changes rapidly, the wall surface of the hydraulic valve block is worn away by cavitation erosion, and the gap with the outer surface of the spool increases. This increases the amount of hydraulic fluid flowing through this gap, causing malfunctions in the operation of the hydraulic valve device.

[0011] The inventors considered measures to suppress cavitation erosion by forming a hardened layer in the region including the wall surface of the hydraulic valve block facing the outer circumferential surface of the spool. However, if the entire wall surface of the hydraulic valve block facing the outer circumferential surface of the spool (the inner wall surface surrounding the spool hole) is hardened, there is a risk of damaging the spool when the corner portion of the hydraulic valve block, which is the part where this inner wall surface and the inner wall surface surrounding the hydraulic fluid passage are connected, comes into contact with the spool as the spool moves. Therefore, the inventors adopted a configuration in which this corner portion is not included in the hardened layer, that is, this corner portion is included in the base region.

[0012] In the hydraulic valve block of this disclosure, a hardened layer is formed so as to include a first inner wall surface that faces the outer circumferential surface of the spool and on which the spool slides. On the other hand, the corner portion of the hydraulic valve block where the first inner wall surface and the second inner wall surface surrounding the hydraulic fluid passage are connected is included in the base region, which is a region other than the hardened layer. This suppresses the occurrence of cavitation erosion on the first inner wall surface and also suppresses damage to the spool due to contact with the corner portion. Thus, the hydraulic valve block of this disclosure can suppress malfunctions in the operation of the hydraulic valve device even when the flow rate of hydraulic fluid increases.

[0013] Here, "cast iron" refers to a material (iron alloy) having a specific component composition, regardless of the manufacturing method, and specifically refers to an alloy containing 2.1% by mass or more and 6.7% by mass or less of carbon, with iron as the main component. Specifically, examples of cast iron in this application include iron alloys having the properties specified in JIS standard G5502 spheroidal graphite cast iron and G5505 CV graphite cast iron.

[0014] In the hydraulic valve block described above, the second inner wall surface may be included in the base region. This configuration limits the area in which the quenching hardened layer should be formed, thereby suppressing an increase in the manufacturing cost of the hydraulic valve block.

[0015] In the hydraulic valve block described above, the cast iron microstructure constituting the base region may include a ferrite-graphite structure in which graphite is dispersed in the ferrite phase, and a pearlite structure. The area ratio of the pearlite structure in the cross-section of the base region may be 20% or more. This configuration makes it easier to impart sufficient hardness to the quenched layer. The area ratio of the pearlite structure may be 30% or more, and even 40% or more. This makes it even easier to impart sufficient hardness to the quenched layer.

[0016] In the hydraulic valve block described above, the cast iron may be spheroidized graphite cast iron. Spheroidized graphite cast iron is particularly preferred as the cast iron constituting the hydraulic valve block of this disclosure.

[0017] In the above-mentioned hydraulic valve block, the thickness of the hardened layer may be 2 mm or less. With this configuration, it becomes easy to form a hardened layer having appropriate hardness in the hydraulic valve block. The thickness of the hardened layer is preferably 0.1 mm or more.

[0018] In the above-mentioned hydraulic valve block, the hardness of the hardened layer may be 600 HV or more. With this configuration, the occurrence of the cavitation erosion can be more reliably suppressed.

[0019] [Specific Example of Embodiment] Next, an example of a specific embodiment of the hydraulic valve block of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

[0020] First, an example of a hydraulic valve block according to the present disclosure will be described with reference to FIG. 1 and FIG. 2. FIG. 1 is a schematic cross-sectional view showing the structure of a hydraulic valve device. FIG. 2 is a schematic cross-sectional view showing an enlarged region II in FIG. 1. Referring to FIG. 1, the hydraulic valve device 100 of the present embodiment includes a hydraulic valve block 1 and a spool 2.

[0021] The hydraulic valve block 1 has a spool hole 12, a first hydraulic oil passage 11, and a second hydraulic oil passage 13. The spool hole 12 is the space through which the spool 2 is inserted. The first hydraulic oil passage 11 and the second hydraulic oil passage 13 are spaces connected to the spool hole 12. The first hydraulic oil passage 11 and the second hydraulic oil passage 13 each connect the spool hole 12 to the space outside the hydraulic valve block 1. The first hydraulic oil passage 11 is connected to the space outside the hydraulic valve block 1 at the cylinder port 11A. Hydraulic oil flows from the outside through the cylinder port 11A to the first hydraulic oil passage 11 along arrow A. The second hydraulic oil passage 13 is connected to the space outside the hydraulic valve block 1 at the drain port 13A. Hydraulic oil in the second hydraulic oil passage 13 flows out to the outside through the drain port 13A along arrow B. The hydraulic valve block 1 is made of cast iron. The cast iron constituting the hydraulic valve block 1 is not particularly limited, but in this embodiment it is spheroidized graphite cast iron.

[0022] The spool 2 has a hollow portion 21 which is a space extending along the longitudinal direction of the spool 2. The spool 2 has a first through hole 22 which extends in a direction intersecting the longitudinal direction of the spool 2 and penetrates from the hollow portion 21 to the outer surface, and a second through hole 23 which is located apart from the first through hole 22 in the longitudinal direction of the spool 2 and penetrates from the hollow portion 21 to the outer surface in a direction intersecting the longitudinal direction of the spool 2.

[0023] Referring to Figure 2, the spool hole 12 is defined by the first inner wall surface 12A. The spool hole 12 is surrounded by the first inner wall surface 12A. When the spool 2 moves longitudinally, the outer circumferential surface 25 of the spool 2 slides against the first inner wall surface 12A. The first hydraulic fluid passage 11 is defined by the second inner wall surface 11B. The first hydraulic fluid passage 11 is surrounded by the second inner wall surface 11B. The second hydraulic fluid passage 13 is defined by the third inner wall surface 13B. The second hydraulic fluid passage 13 is surrounded by the third inner wall surface 13B. The first inner wall surface 12A and the second inner wall surface 11B are connected at the first corner 12B. The first inner wall surface 12A and the third inner wall surface 13B are connected at the second corner 12C.

[0024] The hydraulic valve block 1 includes a quenched hardened layer 15 formed to include the first inner wall surface 12A, and a base region 14 which is the region other than the quenched hardened layer 15. The hydraulic valve block 1 is made of a single piece of cast iron, and a portion of it is quenched hardened to form the quenched hardened layer 15. The region of the hydraulic valve block 1 other than the quenched hardened layer 15 is the base region 14. In this embodiment, the first corner portion 12B and the second corner portion 12C are included in the base region 14. In this embodiment, the second inner wall surface 11B and the third inner wall surface 13B are included in the base region 14. The quenched hardened layer 15 has a higher hardness than the base region 14. The hardness of the quenched hardened layer 15 is, for example, 600 HV or more. The hardness of the base region 14 is, for example, 350 HV or less.

[0025] Next, the operation of the hydraulic valve device 100 of this embodiment will be described with reference to Figures 1 to 3. As shown in Figures 1 and 2, when the first hydraulic fluid passage 11 and the second hydraulic fluid passage 13 are not in communication, the hydraulic fluid that flows into the first hydraulic fluid passage 11 through the cylinder port 11A does not flow into the second hydraulic fluid passage 13. Here, when the spool 2 moves to the right in the longitudinal direction in Figure 1, as shown in Figure 3, the first hydraulic fluid passage 11 and the hollow section 21 are connected by the first through hole 22, and the hollow section 21 and the second hydraulic fluid passage 13 are connected by the second through hole 23. As a result, the first hydraulic fluid passage 11 and the second hydraulic fluid passage 13 are connected via the first through hole 22, the hollow section 21, and the second through hole 23. Consequently, as shown in Figure 1, the hydraulic fluid that flows into the first hydraulic fluid passage 11 through the cylinder port 11A along arrow A flows into the hollow section 21 along arrow D as shown in Figure 3. Subsequently, the hydraulic fluid flows into the second hydraulic fluid passage 13 along arrow E, and then flows out to the outside through the drain port 13A along arrow B, as shown in Figure 1.

[0026] At this time, as shown in Figure 3, the gap between the first inner wall surface 12A and the outer circumferential surface 25 of the spool 2 becomes an unintended passage, and the hydraulic fluid flows through this gap along arrow C. Since it is necessary for the outer circumferential surface 25 of the spool 2 to slide against the first inner wall surface 12A, it is difficult to make the gap between the first inner wall surface 12A and the outer circumferential surface 25 of the spool 2 completely zero. Because the gap between the first inner wall surface 12A and the outer circumferential surface 25 of the spool 2 is very small, the pressure applied to the hydraulic fluid differs greatly between inside and outside the gap. As a result, the pressure applied to the hydraulic fluid changes rapidly, and the first inner wall surface 12A may be worn away by cavitation erosion, potentially increasing the gap with the outer circumferential surface 25 of the spool 2. If the gap described above becomes larger, even if the spool 2 moves to the left side of Figure 1 along the longitudinal direction, changing from the state in Figure 3 to the state in Figure 2, the hydraulic fluid may flow between the first inner wall surface 12A and the outer peripheral surface 25 of the spool 2 beyond the permissible range, potentially causing malfunctions in the operation of the hydraulic valve device.

[0027] However, in the hydraulic valve block 1 of this embodiment, the hardened layer 15 is formed so as to include the first inner wall surface 12A that faces the outer circumferential surface 25 of the spool 2 and on which the spool 2 slides. On the other hand, the first corner portion 12B and the second corner portion 12C are included in the base region 14. This suppresses the occurrence of cavitation erosion on the first inner wall surface 12A and also suppresses damage to the spool 2 due to contact with the first corner portion 12B and the second corner portion 12C. As a result, the hydraulic valve block 1 of this embodiment is a hydraulic valve block that can suppress malfunctions in the operation of the hydraulic valve device 100 even when the flow rate of the hydraulic fluid is increased.

[0028] In the hydraulic valve block 1, the cast iron microstructure constituting the base region 14 may include a ferrite-graphite structure in which graphite is dispersed in the ferrite phase, and a pearlite structure. In the cross-section of the base region 14, the area ratio of the pearlite structure may be 20% or more. This makes it easier to impart sufficient hardness to the quenched hardened layer 15. The area ratio of the pearlite structure may be 30% or more, and even 40% or more.

[0029] In the hydraulic valve block 1, the thickness of the hardened layer 15 may be 2 mm or less. This makes it easier to form a hardened layer 15 with appropriate hardness on the hydraulic valve block 1. The thickness of the hardened layer 15 is preferably 0.03 mm or more, and more preferably 0.1 mm or more.

[0030] In the hydraulic valve block 1, the hardness of the quenched layer 15 may be 600 HV or higher. This makes it possible to more reliably suppress the occurrence of cavitation erosion.

[0031] Next, an example of a method for manufacturing the hydraulic valve block 1 will be described. Figure 4 is a flowchart illustrating the manufacturing method of the hydraulic valve block. Referring to Figure 4, in the manufacturing method of the hydraulic valve block 1 of this embodiment, a casting process is first carried out as step S10. In this step S10, a mold having a cavity corresponding to the shape of the hydraulic valve block 1 is prepared, and molten cast iron is filled into the cavity. After that, the molded body obtained by the solidification of the cast iron filled into the cavity is removed from the mold.

[0032] Next, a cutting process is performed as step S20. In this step S20, referring to Figures 1 and 2, cutting is performed on the first inner wall surface 12A surrounding the spool hole 12. This improves the dimensional accuracy of the spool hole 12.

[0033] Next, a laser hardening process is performed as step S30. In this step S30, laser hardening is performed on the necessary areas (areas where cavitation erosion may be a problem) of the first inner wall surface 12A that was machined in step S20. Specifically, referring to Figure 2, the hardened layer 15 is formed so as to include the first inner wall surface 12A on which the spool 2 slides, but not the first corner 12B and the second corner 12C. Laser hardening is performed by irradiating the area where the hardened layer 15 is to be formed with a laser, heating it to a temperature range above the A1 transformation point, and then rapidly cooling the heated area to a temperature range below the MS point as the laser irradiation area moves sequentially. The hydraulic valve block 1 of this embodiment can be manufactured by the above procedure. In this embodiment, the hardened layer is formed by laser hardening, but the hardened layer of this disclosure can also be formed by hardening methods other than laser hardening. [Examples]

[0034] A test piece having a test surface corresponding to the first inner wall surface 12A of the hydraulic valve block 1 of the above embodiment was prepared, and an experiment was conducted to confirm its durability against cavitation erosion. The experimental procedure was as follows.

[0035] (A) Experimental method Test specimens with a test surface were prepared by casting, and the test surface was laser-hardened. FCD700 (spheroidal graphite cast iron with a tensile strength of 700 MPa or higher) and FCV410 (CV cast iron with a tensile strength of 410 MPa or higher) were used as the cast iron for the test specimens. For comparison, test specimens without laser hardening were also prepared. Experiments were then conducted to investigate the durability of each test specimen against cavitation erosion. The experiments basically followed the procedure in accordance with JIS standard R1646, but some experimental conditions differed from the JIS standard. A counter-type magnetic vibration test apparatus was used for the experiments. The vibration frequency was 20 kHz, the amplitude was 0.05 mm, and the gap between the tip of the transducer and the test surface was 0.5 mm. The experiments were conducted in pure water at 25°C. In addition, the test specimens were cut before testing, and the microstructure of the base region (region other than the hardened layer) of the cut surface was examined using an optical microscope.

[0036] (B) Experimental results Figure 5 is a photograph showing the microstructure of the cross-section of the base region of the test specimen. Referring to Figure 5, the microstructure of the cast iron constituting the base region includes a ferrite-graphite structure 73 in which graphite 72 is dispersed in a ferrite phase 71, and a pearlite structure 75. Analysis of the region in this photograph using image processing software revealed that the area ratio of the pearlite structure 75 was 50%.

[0037] Figure 6 shows the results of the cavitation erosion test. Figure 6 shows the mass loss after 5 hours of testing for each of the following materials: FCV410 (labeled "FCV410 without hardened layer"), FCD700 (labeled "FCD700 without hardened layer"), FCV410 with a hardened layer formed on the test surface (labeled "FCV410 with hardened layer"), and FCD700 with a hardened layer formed on the test surface (labeled "FCD700 with hardened layer"). Referring to Figure 6, it can be seen that forming a hardened layer reduces the mass loss by more than 30% in the case of FCV410 and more than 45% in the case of FCD700 compared to materials without a hardened layer. This indicates that the formation of a hardened layer is very effective in suppressing cavitation erosion.

[0038] The embodiments and examples disclosed herein are illustrative in all respects and should be understood not to be restrictive in any way. The scope of the present invention is defined by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of symbols]

[0039] 1 Hydraulic valve block, 2 Spool, 11 First hydraulic oil passage, 11A Cylinder port, 11B Second inner wall surface, 12 Spool hole, 12A First inner wall surface, 12B First corner, 12C Second corner, 13 Second hydraulic oil passage, 13A Drain port, 13B Third inner wall surface, 14 Base region, 15 Hardened layer, 21 Hole, 22 First through hole, 23 Second through hole, 25 Outer surface, 71 Ferrite phase, 72 Graphite, 73 Ferrite-graphite structure, 75 Pearlite structure, 100 Hydraulic valve device.

Claims

1. A hydraulic valve block made of cast iron is formed having a spool hole, which is a space through which a spool is inserted and through which the spool slides, defined by a first inner wall surface, and a hydraulic oil passage, which is a space defined by a second inner wall surface and connected to the spool hole. The aforementioned hydraulic valve block is A quenched hardened layer formed to include the first inner wall surface, It comprises a base region which is a region other than the aforementioned quenched hardened layer, The corner portion where the first inner wall surface and the second inner wall surface are connected is included in the base region of the hydraulic valve block.

2. The hydraulic valve block according to claim 1, wherein the second inner wall surface is included in the base region.

3. The microstructure of the cast iron constituting the base region is A ferrite-graphite structure in which graphite is dispersed in the ferrite phase, Includes perlite tissue, The hydraulic valve block according to claim 1, wherein the area ratio of the pearlite structure in the cross-section of the base region is 20% or more.

4. The hydraulic valve block according to claim 1, wherein the cast iron is spheroidized graphite cast iron.

5. The hydraulic valve block according to claim 1, wherein the thickness of the quenched hardened layer is 2 mm or less.

6. The hydraulic valve block according to claim 1, wherein the hardness of the quenched hardened layer is 600 HV or more.

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