Fluid pressure rotary machine

Abstract

The present invention provides a fluid pressure rotary machine enhanced in durability, with an improvement in the structure of a movable partition mechanism. In this invention, a rotor is housed in a rotor housing hole of a body case, a pressure receiving protrusion is formed in the rotor, a fluid operation chamber on an outer peripheral side of the rotor is partitioned by the pressure receiving protrusion, a partition mechanism for partitioning the fluid operation chamber is movably mounted in a mounting hole formed in the body case, the partition mechanism has a pair of metal plates in surface contact with an inner wall surface of the mounting hole and an elastic member mounted between the pair of metal plates and fixed in a liquid-tight manner, and a pair of springs for biasing the pair of metal plates individually toward the rotor are provided.

Description

Fluid pressure rotating machinery

[0001] The present invention relates to a rotary type fluid pressure rotating machine such as a fluid pressure pump or a fluid pressure motor, and more particularly to an improved structure of a movable partition mechanism that partitions a fluid working chamber.

[0002] Well-known fluid pressure pumps for pressurizing fluids include diaphragm pumps, radial piston pumps, external gear pumps, internal gear pumps, vane pumps, swash plate axial piston pumps, and bent-axis axial piston pumps. All of the above pumps have a complex structure, are large in size, and are expensive to manufacture.

[0003] Patent Document 1 discloses a rotary type fluid pressure pump / motor in which a rotor is rotatably accommodated in a rotor accommodation chamber, a pressure-receiving protrusion is integrally formed on the rotor, a substantially cylindrical fluid working chamber with a C-shaped cross section is formed on the outer periphery of the rotor, and a movable vane mechanism that separates the fluid working chamber is provided in the main body case.

[0004] As shown in Figures 6 to 8 of Patent Document 1, the vane mechanism 4A has two movable partition members 72, 73 that abut the peripheral surface of the rotor, and springs 76, 77 that individually urge these movable partition members 72, 73 toward the rotor.

[0005] Japanese Patent Application Publication No. Hei 6-108981

[0006] In the vane mechanism 4A of Patent Document 1, in the case of a hydraulic pump, the rotor rotates at a set speed of, for example, approximately 1,000 to 3,000 revolutions per minute, and the vane mechanism 4A reciprocates once for each rotation of the rotor. Therefore, over long periods of operation of the hydraulic pump, the frictional contact surfaces on both sides of the movable partition members 72, 73 wear, the frictional contact surfaces between the movable partition members 72, 73 wear, and the wall surfaces with which the movable partition members 72, 73 contact also wear, resulting in an increase in the amount of fluid leakage. Moreover, the amount of leakage increases as the discharge pressure of the hydraulic pump increases. The object of the present invention is to provide a fluid pressure rotating machine that can be simplified, miniaturized, and inexpensively manufactured, and to provide a fluid pressure rotating machine with an improved movable partition mechanism structure and increased durability.

[0007] The fluid pressure rotary machine according to the present invention comprises a main body case, a rotor accommodating chamber with a circular cross section within the main body case, a rotor rotatably accommodated in the rotor accommodating chamber, a fluid operating chamber formed in an outer peripheral region of the rotor within the rotor accommodating chamber, a shaft member connected to the rotor and extending to the outside of the main body case, a pressure-receiving protrusion formed integrally with the rotor so as to partition the fluid operating chamber, a mounting hole with a rectangular cross section formed in a peripheral wall of the rotor accommodating chamber within the main body case and perpendicular to the peripheral wall, a partition mechanism movably mounted in the mounting hole to partition the fluid operating chamber, biasing means for elastically biasing the partition mechanism toward the rotor, and a load applied to the pressure-receiving protrusion within the fluid operating chamber. In a fluid pressure rotary machine having first and second working chambers formed on the trailing side and leading side, respectively, of the rotor rotation direction, and first and second ports formed in the main body case so as to communicate with the first and second working chambers, the partition mechanism has first and second metal plates that are in surface contact with the trailing side inner wall surface and the leading side inner wall surface, respectively, of the inner wall surfaces of the mounting hole in the rotor rotation direction, and an elastic member that is mounted between the first and second metal plates and fixed liquid-tightly to the first and second metal plates, and that allows relative movement of the first and second metal plates in directions toward and away from the rotor, and the biasing means has first and second springs that individually bias the first and second metal plates, respectively.

[0008] According to the above configuration, the partition mechanism can be mounted in the mounting hole with the elastic member of the partition mechanism in a compressed state, and in this case, the first and second metal plates maintain a tight contact with the inner wall surface of the mounting hole even during long-term operation, which virtually eliminates fluid leakage and provides excellent durability. Furthermore, because the elastic member is fixed to the first and second metal plates in a liquid-tight manner, there are no gaps between the elastic member and the first and second metal plates, so fluid leakage is also eliminated.

[0009] Furthermore, since the biasing means has first and second springs that individually bias the first and second metal plates, when the rotor rotates, the elastic deformation of the elastic member also functions to maintain the first and second metal plates in contact with the outer circumferential surface of the rotor. The provision of the elastic member allows relative movement of the first and second metal plates in the direction toward and away from the rotor while maintaining the integrity of the first and second metal plates. In this way, the structure of the partition mechanism can be improved and its durability can be increased.

[0010] The present invention can also employ the following various configurations.

[0011] In a first embodiment, the elastic member includes first laminated rubber plates fixed to the first and second metal plates in a liquid-tight manner and having a predetermined thickness.

[0012] In a second form, the elastic member is characterized by having a third metal plate mounted between the first and second metal plates, a second laminated rubber plate mounted between the first and third metal plates and fixed to the first and third metal plates in a liquid-tight manner, respectively, and having a predetermined thickness, and a third laminated rubber plate mounted between the second and third metal plates and fixed to the second and third metal plates in a liquid-tight manner, respectively, and having a predetermined thickness.

[0013] In a third embodiment, the laminated rubber plate has one or more openings penetrating through the plate in the thickness direction, and a pressure-resistant member is disposed in the opening to suppress compressive deformation of the laminated rubber plate in the thickness direction.

[0014] A fourth aspect is characterized by providing an apex seal groove formed in the circumferential center of the pressure-receiving protrusion of the rotor, an apex seal movably mounted in this apex seal groove, and a biasing member that biases this apex seal in a direction approaching the inner peripheral surface of the rotor accommodating chamber.

[0015] As a fifth aspect, a fluid pressure introduction groove communicating with the bottom of the apex seal groove is formed in a portion of the pressure-receiving protrusion of the rotor that is closer to the leading side in the rotor rotation direction than the apex seal.

[0016] In a sixth aspect, the shaft seal mechanism includes a pair of seal-mounted shaft portions integrally formed on one and the other axial ends of the rotor and having the same diameter as or a smaller diameter than the portion of the rotor other than the pressure-receiving projections, a pair of annular seal grooves formed in the circumferential surfaces of the seal-mounted shaft portions and open on their circumferential surfaces near the circumferential surfaces of the seal-mounted shaft portions, and a pair of annular seal members respectively mounted in the annular seal grooves, the pair of seal-mounted shaft portions being respectively mounted in a pair of circular sliding holes formed in the main body case. By using annular seal members similar to piston rings in an engine, the structure of the shaft seal mechanism can be simplified while ensuring sealing performance.

[0017] According to the present invention, various actions and effects can be obtained.

[0018] Fig. 2 is a cross-sectional view of a hydraulic pump according to an embodiment of the present invention. Fig. 3 is a cross-sectional view taken along line II-II in Fig. 1. Fig. 4 is a view equivalent to Fig. 1 in a state where the rotational phase angle of the rotor is changed. Fig. 5 is a plan view of a rotor according to a modified example. Fig. 6 is a cross-sectional view of a main part of a hydraulic pump according to a modified example. Fig. 7 is a cross-sectional view of an elastic member according to a modified example. Fig. 8 is a cross-sectional view of an apex seal mechanism according to a modified example.

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydraulic pump, which is a rotary type fluid pressure rotary machine according to an embodiment of the present invention, will be described below with reference to FIGS.

[0020] This hydraulic pump 1 comprises a main body case 2, a rotor accommodating chamber 3 having a circular cross section within the main body case 2, a rotor 4 rotatably accommodated in the rotor accommodating chamber 3, a fluid working chamber 5 having a predetermined thickness in the radial direction and formed in an area of ​​the rotor accommodating chamber 3 on the outer periphery of the rotor 4, a shaft member 6 that penetrates the center of the rotor 4 and extends to the outside of the main body case 2 and is attached to the rotor 4 so as not to be able to rotate relative to it, and a pressure-receiving protrusion 7 that is integrally formed with the rotor 4 so as to partition the fluid working chamber 5. The shaft member 6 is connected to an output shaft 8a of an electric motor 8 by a shaft coupling 9 and is driven to rotate together with the rotor 4 in the direction of arrow A in FIG.

[0021] The main body case 2 and the rotor 4 may be made of a metal material (e.g., aluminum alloy, magnesium alloy, SUS, brass, etc.) or a synthetic resin material (e.g., POM, PC, PEEK, etc.) A spring accommodating section 10 is integrally formed on the side of the main body case 2, and a spring accommodating chamber 10a inside the spring accommodating section 10 is closed by a closing plate 11 bolted to it.

[0022] Next, the shaft seal mechanism 12 will be described. As shown in Figure 2, the shaft seal mechanism 12 comprises a pair of seal-mounted shaft portions 4a that are integrally formed on one and the other axial ends of the rotor 4 and have the same diameter as the portion of the rotor 4 other than the pressure-receiving projections 7 (or a smaller diameter than the portion other than the pressure-receiving projections 7), a pair of annular seal grooves 13 that are formed in the circumferential vicinity of the seal-mounted shaft portions 4a and are open on the circumferential surfaces, and a pair of metallic annular seal members 14 that are respectively mounted in the annular seal grooves 13. The pair of seal-mounted shaft portions 4a are slidably mounted in a pair of circular sliding holes 15 formed in the main case 2.

[0023] The annular seal member 14 is divided at one point in the circumferential direction, similar to a piston ring in an engine, and is kept in tight contact with the wall surface of the circular sliding hole 15 by an elastic force acting in the radial direction. This shaft seal mechanism 12 can minimize the amount of pressurized oil leaking toward the end face 4b of the rotor 4. Note that instead of this annular seal member 14 and annular seal groove 13, oil seals of various structures may be used.

[0024] Next, the apex seal mechanism 16 will be described. As shown in Figure 1, the apex seal mechanism 16 includes an apex seal groove 17 formed in the circumferential center of the pressure-receiving projection 7 parallel to the axis of the rotor 4, an elongated metallic or non-metallic apex seal 18 movably mounted in the apex seal groove 17, and a biasing member 19 (e.g., a thin leaf spring) that biases the apex seal 18 in a direction approaching the inner circumferential surface of the rotor accommodating chamber 3. The apex seal mechanism 16 described above can provide a sufficient seal between the pressure-receiving projection 7 of the rotor 4 and the inner circumferential surface of the rotor accommodating chamber 3. Note that multiple apex seal mechanisms 16 may be provided.

[0025] This hydraulic pump 1 further includes a mounting hole 20 having a rectangular cross section and formed in the peripheral wall 2a of the rotor accommodating chamber 3 of the main body case 2, perpendicular to the peripheral wall 2a, over the entire length of the rotor 4 excluding the seal mounting shaft portion 4a, a partition mechanism 21 mounted in this mounting hole 20 so as to be movable toward and away from the rotor 4 and separating the fluid working chamber 5, and a biasing mechanism 22 that elastically biases this partition mechanism 21 toward the rotor 4.

[0026] The partition mechanism 21 has first and second metal plates 23, 24 that are in surface contact with the trailing side inner wall surface 20a and the leading side inner wall surface 20b of the inner wall surfaces of the mounting hole 20 in the rotor rotation direction, respectively, and an elastic member 25 that is mounted between the first and second metal plates 23, 24 and fixed to the first and second metal plates 23, 24 in a liquid-tight manner, and that allows the first and second metal plates 23, 24 to move relative to the rotor 4 in directions toward and away from the rotor 4.

[0027] The trailing side inner wall surface 20a and the leading side inner wall surface 20b are formed with seal grooves extending parallel to the axis of the rotor 4, and metallic or non-metallic seal members 29, 30 are fitted in the seal grooves.

[0028] The biasing mechanism 22 is composed of first and second springs 22a, 22b, which are compression coil springs that individually bias the first and second metal plates 23, 24, and the first and second springs 22a, 22b are accommodated in the spring accommodating chamber 10a. In this embodiment, the first and second springs 22a, 22b are coil springs with an oval cross section, but they may also be coil springs with a circular cross section or other springs (for example, disc springs).

[0029] The elastic member 25 of the partition mechanism 21 includes a third metal plate 26 mounted between the first and second metal plates 23, 24 with a gap therebetween, a laminated rubber plate 27 mounted between the first and third metal plates 23, 26 and fixed in a liquid-tight manner to the first and third metal plates 23, 26, respectively, and having a predetermined thickness (e.g., 1.0 mm to 3.0 mm), and a laminated rubber plate 28 mounted between the second and third metal plates 24, 26 and fixed in a liquid-tight manner to the second and third metal plates 24, 26, respectively, and having a predetermined thickness (e.g., 1.0 mm to 3.0 mm).

[0030] The laminated rubber plates 27, 28 and the laminated rubber plate 35 described below may be made of various rubber materials that are oil-resistant, heat-resistant, and elastic, such as natural rubber, butadiene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, isoprene rubber, butyl rubber, acrylic rubber, fluororubber, chlorosulfonated polyethylene, and urethane rubber, or other rubber materials.

[0031] The laminated rubber plates 27, 28 may be fixed to the surfaces of the first, second, and third metal plates 23, 24, and 26 by vulcanization bonding using a vulcanization adhesive, or by a strong adhesive suitable for bonding rubber materials. It is desirable to roughen the surfaces of the metal plates 23, 24, and 26 to be bonded to the laminated rubber plates 27, 28 before bonding. Because the laminated rubber plates 27, 28 have a predetermined thickness, they are elastic in the thickness direction. When installing the laminated rubber plates 27, 28 in the installation hole 20 of the partition mechanism 21, it is desirable to install the laminated rubber plates 27, 28 in a state where they are compressed and deformed by approximately 5 to 10% of their thickness. This is to prevent leakage of pressurized oil.

[0032] The hydraulic pump 1 further includes first and second working chambers 5a, 5b formed on the trailing and leading sides of the pressure-receiving projection 7 in the fluid working chamber 5, respectively, in the rotor rotation direction, and first and second ports 31, 32 formed in the main body case 2 so as to communicate with the first and second working chambers 5a, 5b, respectively. The first working chamber 5a is the suction working chamber, and the second working chamber 5b is the discharge working chamber. The first port 31 is the suction port, and the second port 32 is the discharge port. A check valve (not shown) that allows flow only in the discharge direction is installed in the second port 32.

[0033] A relief valve for setting the discharge pressure of the hydraulic pump 1 is installed downstream of the check valve in the second port 32 or in the oil passage connected to the second port 32. When the discharge pressure of the hydraulic pump 1 is high (for example, 14 MPa or higher), pressurized oil discharged from the hydraulic pump 1 may be introduced into the spring accommodating chamber 10a as shown by the two-dot chain line in Figure 1, and the biasing force of the pressurized oil may be used to bias the partition mechanism 21 toward the rotor 4. In this case, the first and second springs 22a, 22b can be made smaller.

[0034] Next, we will explain the operation and effects of the above-described hydraulic pump 1. When the rotor 4 is driven to rotate by the motor 8, unpressurized oil is drawn into the first working chamber 5a from the first port 31, and oil in the second working chamber 5b is pressurized by the pressure-receiving projection 7 and discharged from the second port 32. Then, in the second port 32, oil pressure adjusted to a set pressure by a relief valve for setting the discharge pressure is supplied to the hydraulic pressure supply destination.

[0035] The provision of an apex seal mechanism 16 seals the gap between the pressure-receiving projection 7 and the inner peripheral surface of the rotor accommodating chamber 3, thereby suppressing leakage of pressurized oil. The provision of a shaft seal mechanism 12 effectively prevents leakage of pressurized oil toward the end face 4b of the rotor 4, thereby minimizing the amount of pressurized oil leakage. Moreover, the shaft seal mechanism 12 has a simple structure, which is advantageous in terms of manufacturing costs.

[0036] In the partition mechanism 21, when the laminated rubber plates 27, 28 of the elastic member 25 are compressed and the partition mechanism 21 is installed in the installation hole 20, gaps between the first and second metal plates 23, 24 and the inner wall surfaces 20a, 20b are eliminated, minimizing the amount of pressurized oil leakage. Furthermore, since the seal members 29, 30 are installed on the inner wall surfaces 20a, 20b, leakage of pressurized oil can be prevented. Furthermore, since the laminated rubber plates 27, 28 of the elastic member 25 are fixed to the first and second metal plates 23, 24 in a liquid-tight manner by adhesive, leakage of pressurized oil does not occur.

[0037] The first and second metal plates 23, 24 are individually biased toward the rotor 4 by coil springs 22a, 22b, so that the first and second metal plates 23, 24 are always maintained in contact with the outer peripheral surface of the rotor 4, thereby fulfilling the partition function of separating the fluid operating chamber 5.

[0038] 3, when the pressure-receiving projection 7 approaches the partition mechanism 21, the elastic deformation of the laminated rubber plates 27, 28 causes the tips of the first and second metal plates 23, 24 to maintain contact with the outer circumferential surface of the rotor 4, thereby maintaining the partition function well. In this way, the elastic member 25 allows relative movement in the direction of approaching and separating from the rotor 4 while maintaining the integrity of the first and second metal plates 23, 24. In this way, the structure of the partition mechanism 21 can be improved, and its reliability and durability can be increased.

[0039] This hydraulic pump 1 is designed to rotate the rotor 4, which has a simple structure, to suck in oil and discharge pressurized oil, thereby enabling the hydraulic pump 1 to be simple in structure, compact, and inexpensive. For example, if the maximum volume of the suction working chamber 5a is 4 cc and the rotational speed of the rotor 4 is 1800 rpm, the discharge rate of the hydraulic pump 1 will be approximately 7200 cc / min.

[0040] Next, modifications of the above-described embodiment will be described. Modification 1: See Fig. 4. In the apex seal mechanism 16, a fluid pressure introduction groove 17a communicating with the bottom of the apex seal groove 17 is formed in a portion of the pressure-receiving protrusion 7 of the rotor 4 on the leading side of the apex seal 18 in the rotor rotation direction. The fluid pressure introduced from this fluid pressure introduction groove 17a to the bottom of the apex seal groove 17 can urge the apex seal 18 toward the inner circumferential surface of the rotor accommodating chamber 3. This improves the sealing performance of the apex seal mechanism 16.

[0041] Modification 2: See Figure 5. The elastic member 25A of the partition mechanism 21A is composed of a single laminated rubber plate 35 that is fixed in a liquid-tight manner to the first and second metal plates 23, 24, respectively, and has a predetermined thickness (for example, 1.0 mm to 3.0 mm). Other components that are the same as those in the previous embodiment are given the same reference numerals, and their description will be omitted. This simplifies the structure of the partition mechanism 21A.

[0042] Modification 3: See Fig. 6 The laminated rubber plate 28 has one or more openings 36 penetrating in the plate thickness direction, and a metal pressure-resistant member 37 is disposed in the openings 36 to suppress compressive deformation of the laminated rubber plate 28 in the thickness direction. The thickness of the pressure-resistant member 37 is set to approximately 90 to 95% of the thickness of the laminated rubber plate 28. When the hydraulic pressure of the pressurized oil in the second working chamber 5b (discharge working chamber) becomes high, the pressure-resistant member 37 can suppress compressive deformation of the laminated rubber plate 28 in the thickness direction. The laminated rubber plates 27, 35 may also have a similar structure.

[0043] 7 , in the apex seal mechanism 16A, a surface 18a of the apex seal 18A is provided with an inclined surface 18b on the leading side in the rotor rotation direction, which is inclined so as to be separated from the surface of the pressure-receiving protrusion 7 as it approaches the leading side. By providing this inclined surface 18b, it is possible to ensure smooth contact between the apex seal 18A and the first to third metal plates 23, 24, 26 of the partition mechanism 21.

[0044] While the above embodiment has been described using the hydraulic pump 1 as an example, the present invention can also be applied to a hydraulic motor. In this case, pressurized oil is introduced through the first port 29, received by the pressure-receiving projection 7, causing the rotor 4 to rotate, and low-pressure oil is discharged through the second port 30. The present invention can also be applied to air pumps, gas pumps, low-discharge-pressure liquid pumps, fluid quantity measuring devices, fluid distributors, and other devices in addition to hydraulic pumps and hydraulic motors. Those skilled in the art can implement the present invention in various forms with various modifications to the above embodiment and modified examples. For example, in a large fluid-pressure rotating machine, it is possible to provide multiple pressure-receiving projections and multiple sets of first and second ports.

[0045] The present invention can provide a rotary type fluid pressure rotating machine (hydraulic pump or hydraulic motor) that is simple, compact, and can be manufactured at low cost.

[0046] REFERENCE SIGNS LIST 1 Hydraulic pump 2 Main body case 3 Rotor accommodating chamber 4 Rotor 4a, 4b Seal-mounted shaft portion 5 Fluid operating chamber 5a, 5b First and second operating chambers 6 Shaft member 7 Pressure-receiving protrusion 12 Shaft seal mechanism 13 Annular seal groove 14 Annular seal member 15 Circular slide hole 16 Apex seal mechanism 17 Apex seal groove 17a Fluid pressure introduction groove 18 Apex seal 19 Biasing member 20 Mounting hole 20a Trailing-side inner wall surface 20b Leading-side inner wall surface 21 Partition mechanism 22 Biasing mechanism 23, 24, 26 First, second and third metal plates 25, 25A Elastic member 27, 28, 35 Laminated rubber plates 31, 32 First and second ports

Claims

a rotor accommodating chamber having a circular cross section within the main case, a rotor rotatably accommodated in the rotor accommodating chamber, a fluid working chamber formed in the rotor accommodating chamber in an area on the outer periphery of the rotor, a shaft member connected to the rotor and extending to the outside of the main case, a pressure-receiving protrusion formed integrally with the rotor so as to partition the fluid working chamber, a mounting hole having a rectangular cross section formed in a peripheral wall of the rotor accommodating chamber in the main case and perpendicular to the peripheral wall, a partition mechanism movably mounted in the mounting hole to partition the fluid working chamber, a biasing means for elastically biasing the partition mechanism towards the rotor, first and second working chambers formed in the fluid working chamber on the trailing side and leading side in the rotor rotation direction relative to the pressure-receiving protrusion, respectively, and first and second ports formed in the main case so as to communicate with the first and second working chambers, the partition mechanism has first and second metal plates in surface contact with the trailing side inner wall surface and the leading side inner wall surface of the inner wall surface of the mounting hole in the rotor rotation direction, respectively, and an elastic member mounted between the first and second metal plates and fixed in a liquid-tight manner to the first and second metal plates and allowing relative movement of the first and second metal plates in directions toward and away from the rotor, and the biasing means has first and second springs that individually bias the first and second metal plates, respectively.

2. A fluid pressure rotating machine according to claim 1, characterized in that said elastic member comprises a first laminated rubber plate having a predetermined thickness and fixed in a liquid-tight manner to said first and second metal plates, respectively.

3. The fluid pressure rotating machine as described in claim 1, characterized in that the elastic member comprises a third metal plate mounted between the first and second metal plates, a second laminated rubber plate mounted between the first and third metal plates and fixed in a liquid-tight manner to the first and third metal plates, respectively, and having a predetermined thickness, and a third laminated rubber plate mounted between the second and third metal plates and fixed in a liquid-tight manner to the second and third metal plates, respectively, and having a predetermined thickness.

4. A fluid pressure rotating machine as described in claim 2 or 3, characterized in that the laminated rubber plate has one or more openings penetrating in the thickness direction of the plate, and a pressure-resistant member is arranged in the opening to suppress compressive deformation of the laminated rubber plate in the thickness direction.

5. A fluid pressure rotating machine as described in any one of claims 1 to 3, characterized in that it is provided with an apex seal groove formed in the circumferential center of the pressure-receiving protrusion, an apex seal movably mounted in this apex seal groove, and a biasing member that biases this apex seal in a direction away from the axis of the rotor.

6. A fluid pressure rotating machine as described in claim 5, characterized in that a fluid pressure introduction groove communicating with the bottom of the apex seal groove is formed in the pressure-receiving protrusion of the rotor on the leading side in the rotor rotation direction relative to the apex seal.

7. A fluid pressure rotating machine as claimed in any one of claims 1 to 3, characterized in that it has a pair of seal mounting shaft portions formed integrally with one end and the other end in the axial direction of the rotor and having the same diameter as or a smaller diameter than the portion of the rotor other than the pressure-receiving protrusions, a pair of annular seal grooves formed in the circumferential vicinity of the periphery of each of the seal mounting shaft portions and open on the circumferential surface, and a pair of annular seal members respectively mounted in each of the annular seal grooves, and the pair of seal mounting shaft portions are respectively mounted in a pair of circular sliding holes formed in a main body case.

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