Gear pump

Abstract

This gear pump 100 comprises: a pinion gear 2; a ring gear 3; a housing 4 including a storage section 411 in which the pinion gear 2 and the ring gear 3 are stored; and an arrangement member 5 provided between the pinion gear 2 and the ring gear 3. Moreover, in the gear pump 100, as viewed in the extension direction of a rotary shaft 1, a communication hole 6 extending in the direction of extension of the rotary shaft 1 is formed in the storage section 411 at a position excluding the rotary shaft 1 and portions through which external teeth 21 and internal teeth 31 pass. The communication hole 6 communicates with shaft arrangement spaces 412 and 422 of the housing 4, in which the rotary shaft 1 is arranged, and with the outside of the housing 4.

Description

Gear pump

[0001] This invention relates to a gear pump, and more particularly, to a gear pump including a pinion gear and a ring gear.

[0002] Conventionally, a gear pump including a pinion gear and a ring gear is known. For example, it is disclosed in Patent Document 1.

[0003] Patent Document 1 discloses a gear pump including a pinion gear connected to a rotating shaft and having external teeth, a ring gear disposed on the outer circumference of the pinion gear and having internal teeth meshing with the external teeth, and a housing including a housing portion that houses the pinion gear and the ring gear. In the gear pump of Patent Document 1, an oil passage for discharging the oil in the shaft arrangement space of the housing where the rotating shaft is arranged to the outside is provided in a portion of the housing outside the housing portion.

[0004] Japanese Unexamined Patent Application Publication No. 2017 - 193995

[0005] As described above, in the gear pump described in Patent Document 1, an oil passage for discharging the oil in the shaft arrangement space of the housing where the rotating shaft is arranged to the outside is provided in a portion of the housing outside the housing portion. Therefore, it is necessary to secure a surplus for forming an oil passage in a portion of the housing outside the housing portion that houses the pinion gear and the ring gear. As a result, there is a problem that the housing becomes larger by the amount of surplus for the oil passage. Therefore, a gear pump capable of reducing the size of the housing is desired.

[0006] Note that the gear pump for which it is desired to reduce the size of the housing is not limited to one that pumps oil, and the same applies to one that pumps a fluid other than oil, such as a coolant. That is, in general gear pumps regardless of the type of fluid to be pumped, it is desired to reduce the size of the housing.

[0007] This invention has been made to solve the above problems, and one object of this invention is to provide a gear pump capable of reducing the size of the housing.

[0008] To achieve the above objective, a gear pump according to one aspect of this invention comprises a housing including a pinion gear connected to a rotating shaft and having external teeth formed thereon, a ring gear arranged on the outer circumference of the pinion gear and having internal teeth formed thereon that mesh with the external teeth, a housing in which the pinion gear and the ring gear are housed, a suction part communicating with the housing and drawing in fluid, and a discharge part communicating with the housing and discharging fluid, and an arrangement member arranged in the housing of the housing and provided between the pinion gear and the ring gear in a region where the meshing of the pinion gear and the ring gear is separated, wherein, when viewed in the direction in which the rotating shaft extends, a communication hole extending in the direction in which the rotating shaft extends is formed in the housing at a position excluding the part through which the external teeth and internal teeth pass and the rotating shaft, and the communication hole communicates with the axial arrangement space of the housing in which the rotating shaft is arranged and with at least one of the space outside the housing and the space between the pinion gear and the ring gear inside the housing.

[0009] In one aspect of this invention, the gear pump, as described above, has communication holes formed in the housing at positions excluding the portion through which the external and internal teeth pass and the rotating shaft, when viewed in the direction in which the rotating shaft extends. These communication holes communicate with the axial arrangement space of the housing where the rotating shaft is located, and with at least one of the spaces outside the housing and the space between the pinion gear and the ring gear inside the housing. This allows the fluid passage to be located inside the housing, and since there is no fluid passage outside the housing, the excess material on the outside of the housing can be reduced. As a result, the housing can be made smaller. Also, by reducing the excess material of the housing, the amount of material used to form the housing can be reduced, making the housing lighter. Furthermore, since there are no communication holes in the portion through which the external and internal teeth pass, interference between the communication holes and the external and internal teeth can be suppressed. Furthermore, since no connecting holes are provided in the rotating shaft within the housing, there is no need to drill holes in the rotating shaft, which is formed from a relatively hard material to ensure mechanical strength. This reduces the complexity of the machining work required to form connecting holes.

[0010] In the gear pump according to the first aspect described above, preferably, the communication hole is formed in the arrangement member. With this configuration, a communication hole for passing fluid can be placed in the arrangement member between the pinion gear and the ring gear within the housing, so that the arrangement member within the housing can be effectively utilized to provide the communication hole.

[0011] In this case, preferably, the mounting member is positioned on the opposite side of the rotation axis from the position where the pinion gear and ring gear mesh, and includes a crescent-shaped component, with the communication hole formed in the crescent. With this configuration, since the communication hole is provided in the crescent, which is positioned without rotating within the housing, it is possible to suppress the complexity of the sealing structure at the portion connecting the communication hole compared to when the communication hole is provided in the pinion gear or ring gear that rotates within the housing.

[0012] In a gear pump in which the above-mentioned arranged member includes a crescent, preferably the housing includes a first housing with a recess formed therein as a housing portion, and a second housing connected to the first housing so as to cover the housing portion of the first housing, the recess having a support surface for supporting the pinion gear and the ring gear, and the crescent is fixedly provided so as to protrude from the support surface. With this configuration, a communication hole can be provided in the crescent integrally provided with the first housing, so that the number of parts does not increase compared to when a communication hole is provided in a member provided separately from the first housing.

[0013] In this case, preferably, the second housing has a cover surface that covers the housing, and the communication hole communicates with the axial arrangement space formed in the second housing and with a drain port formed in the first housing that communicates with the outside of the housing, and a sealing member is provided between the cover surface and the crescent so that the housing and the communication hole do not communicate. With this configuration, it is possible to suppress the flow of fluid that has risen in temperature by flowing into the axial arrangement space and coming into contact with the rotating shaft into the housing through the communication hole. This makes it possible to suppress the temperature of the fluid in the housing from rising excessively. Here, in the case of a fixed-gap type gear pump, there is no concern about fluid leakage on the second housing side, so it is sufficient to seal against fluid leakage on the first housing side. On the other hand, in the case of a pressure-guaranteed type gear pump, it is preferable to seal against fluid leakage on both the first housing side and the second housing side.

[0014] In the gear pump according to the first aspect described above, preferably, the communication hole communicates with the shaft arrangement space and a drain port that communicates with the outside of the housing, and is provided for discharging the fluid in the shaft arrangement space to the outside. With this configuration, a communication hole for discharging the fluid in the shaft arrangement space can be provided within the housing's containment portion, making it possible to miniaturize the housing of the gear pump equipped with a communication hole for discharging the fluid in the shaft arrangement space.

[0015] In this case, preferably, the housing includes a first housing with a recess formed therein as a receiving portion, and a second housing connected to the first housing so as to cover the receiving portion of the first housing. The second housing has a first axial arrangement space, the first housing has a drain port, and a communication hole communicates with the first axial arrangement space and the drain port. With this configuration, the fluid in the axial arrangement space of the second housing can be discharged to the outside through the drain port provided in the first housing, so there is no need to provide a separate drain port in the second housing. Note that since the pressure outside the housing is lower than the pressure in the axial arrangement space, the fluid in the axial arrangement space is discharged to the outside from the axial arrangement space through the communication hole and the drain port.

[0016] In a gear pump configured to have a drain port in the first housing, preferably, a second shaft arrangement space is formed in the first housing, and the second shaft arrangement space and the drain port are in communication. With this configuration, both the fluid in the first shaft arrangement space of the second housing and the fluid in the second shaft arrangement space of the first housing can be discharged to the outside through the drain port provided in the first housing.

[0017] In the gear pump according to the first aspect described above, preferably, the housing includes a first housing with a recess formed therein as a housing portion, and a second housing connected to the first housing so as to cover the housing portion of the first housing. The arrangement member is positioned on the opposite side of the rotation axis from the position where the pinion gear and ring gear mesh, and includes a crescent-shaped crescent, the crescent having a pin insertion recess into which a pin that guides the second housing relative to the first housing is inserted. With this configuration, if there are multiple types of gear pumps, a pin insertion recess can be provided in the crescent within the housing portion for inserting a guiding pin to prevent the first and second housings from being assembled together if they are not the correct combination. This makes it possible to suppress the excess material of the housing compared to when the pin insertion recess is provided on the outside of the housing portion.

[0018] In this case, preferably, the pin insertion recess is located on the suction side of the crescent rather than the central part when viewed in the direction in which the rotation axis extends. With this configuration, the pin insertion recess is located on the suction side of the crescent where the liquid pressure is lower, so it is possible to suppress the inflow of high-pressure liquid into the pin insertion recess.

[0019] In a gear pump in which the above-described arrangement member includes a crescent, preferably the crescent has a tapered shape from the center toward the suction end and the discharge end when viewed in the direction in which the rotation shaft extends, and the communication hole is provided in the center of the crescent when viewed in the direction in which the rotation shaft extends. With this configuration, since the communication hole is provided in the center of the wider crescent, the machining work of forming the communication hole in the crescent can be easily carried out.

[0020] In a gear pump in which the pin insertion recess described above is formed in the crescent, preferably, the communication hole and the pin insertion recess are formed in the crescent. With this configuration, since both the communication hole and the pin insertion recess are provided in the crescent, it is possible to effectively suppress the increase in excess material of the housing compared to when either the communication hole or the pin insertion recess is provided on the outside of the housing's receiving portion.

[0021] In the gear pump according to the first aspect described above, preferably, the number of teeth of the internal teeth of the ring gear is 1.4 times or more the number of teeth of the external teeth of the pinion gear. With this configuration, there is no need to secure a large amount of excess material in the housing that would increase the diameter of the ring gear and thus the housing portion, so it is possible to suppress the increase in the size of the housing of a gear pump with a large number of teeth on the ring gear and a large ring gear diameter. In addition, when the number of teeth of the internal teeth of the ring gear is 1.4 times or more the number of teeth of the external teeth of the pinion gear, the difference between the inner diameter of the ring gear and the outer diameter of the pinion gear becomes large, so the width of the crescent positioned between the ring gear and the pinion gear also becomes larger. As a result, a communication hole can be easily formed in the crescent within the housing portion.

[0022] In the gear pump according to the first aspect described above, preferably, the center of the ring gear and the center of the housing are positioned approximately the same when viewed in the direction in which the rotating shaft extends. With this configuration, the positions of the center of the ring gear (center of the housing) and the center of the housing can be made approximately the same, so it is possible to suppress the formation of an area where the excess material on the outside of the housing becomes excessively large. This makes it possible to effectively reduce the size of the housing.

[0023] According to the present invention, as described above, the housing can be made smaller.

[0024] This is a cross-sectional view showing a gear pump according to one embodiment. This is a cross-sectional view along line II-II in Figure 1. This is a perspective view showing the crescent of a gear pump according to one embodiment. This is an enlarged cross-sectional view showing the crescent of a gear pump according to one embodiment. This is a cross-sectional view showing a gear pump according to one embodiment. This is a cross-sectional view illustrating the arrangement of the communication holes in a gear pump according to a modified example of one embodiment. This is a cross-sectional view showing a gear pump according to a first modified example of one embodiment. This is a cross-sectional view showing a gear pump according to a second modified example of one embodiment. This is a cross-sectional view showing a gear pump according to a third modified example of one embodiment. This is a perspective view showing the crescent of a gear pump according to a fourth modified example of one embodiment.

[0025] Embodiments of the present invention will be described below with reference to the drawings.

[0026] Referring to Figures 1 to 5, the configuration of a gear pump 100 according to one embodiment of the present invention will be described.

[0027] The gear pump 100 is configured to pump (pressurize) fluids. For example, the gear pump 100 is used to pump (pressurize) hydraulic fluid. Hydraulic fluids include, for example, petroleum-based hydraulic fluids and phosphate ester-based hydraulic fluids. Also, for example, the gear pump 100 is used to pump coolant.

[0028] As shown in Figure 1, the gear pump 100 comprises a rotating shaft 1, a pinion gear 2, a ring gear 3, a housing 4, and a mounting member 5. The ring gear 3 is in contact with and meshes with the pinion gear 2. In other words, the gear pump 100 is an internal gear pump.

[0029] The rotating shaft 1 is rotated by the rotation of a drive source. The drive source is, for example, an electric motor or an internal combustion engine. The rotating shaft 1 is formed in a cylindrical shape so as to extend along the rotation axis C1. One end of the rotating shaft 1 is located outside the housing 4 and connected to the drive source. The other end of the rotating shaft 1 is located inside the housing 4. In the direction in which the rotation axis C1 extends, the rotating shaft 1 is formed to be longer than the thickness of the pinion gear 2 and the ring gear 3.

[0030] The pinion gear 2 is a gear having multiple external teeth 21 along its outer circumference. The pinion gear 2 rotates around the rotation axis C1 of the rotation shaft 1. In the example shown in Figure 1, the pinion gear 2 rotates clockwise. The pinion gear 2 is positioned between one end and the other end of the rotation shaft 1 in the direction in which the rotation axis C1 extends, and is connected to the rotation shaft 1. The pinion gear 2 is rotated by the rotation of the rotation shaft 1. The pinion gear 2 has 13 external teeth 21. The pinion gear 2 is housed in the housing portion 411 of the housing 4. In other words, the pinion gear 2 is housed in the housing portion 411 such that from one end to the other end in the direction in which the rotation axis C1 extends. The pinion gear 2 is housed in the housing portion 411 so as to be rotatable around the rotation axis C1.

[0031] The ring gear 3 rotates around the rotation axis C2. The ring gear 3 is formed in an annular shape when viewed in the direction of the rotation axis C2. The ring gear 3 has multiple internal teeth 31 along its inner circumference. The ring gear 3 is positioned on the outer circumference of the pinion gear 2. The ring gear 3 has internal teeth 31 that mesh with the external teeth 21 of the pinion gear 2. The ring gear 3 is rotated by the rotation of the pinion gear 2. The ring gear 3 rotates around the rotation axis C2, which is offset from the rotation axis C1 of the pinion gear 2. In the example shown in Figure 1, the ring gear 3 rotates clockwise. The ring gear 3 has 19 internal teeth 31. That is, the number of teeth on the internal teeth 31 of the ring gear 3 is approximately 1.46 times the number of teeth on the external teeth 21 of the pinion gear 2. Here, the number of teeth of the internal teeth 31 of the ring gear 3 is 1.4 times or more the number of teeth of the external teeth 21 of the pinion gear 2, and it is preferable that the gear pump 100 is relatively large. The ring gear 3 is housed in the housing portion 411 of the housing 4. In other words, the ring gear 3 is housed in the housing portion 411 such that, in the direction in which the rotation axis C2 extends, one end of the ring gear 3 is contained within the housing portion 411. The ring gear 3 is also housed in the housing portion 411 so as to be rotatable around the rotation axis C2. Furthermore, the ring gear 3 meshes with the pinion gear 2 at the meshing position P1.

[0032] Incidentally, the gear pump 100 of this embodiment incorporates a method to enlarge the flow path within the housing 411. Specifically, the number of teeth of the internal teeth 31 is set to 1.4 times or more the number of teeth of the external teeth 21. As a result, for example, the inner diameter of the ring gear 3 becomes larger compared to the case where the number of teeth of the internal teeth 31 is set to approximately 1.3 times the number of teeth of the external teeth 21, while keeping the size of the teeth of the external teeth 21 and internal teeth 31 unchanged, i.e., when the number of teeth of the external teeth 21 is 13 and the number of teeth of the internal teeth 31 is 17. Therefore, the flow path between the pinion gear 2 and the ring gear 3 can be enlarged. Because the gear pump 100 of this embodiment incorporates this method, the outer diameter of the ring gear 3 is also larger than when the number of teeth of the internal teeth 31 is set to approximately 1.3 times the number of teeth of the external teeth 21.

[0033] The housing 4 is a casing that houses the rotating shaft 1, the pinion gear 2, the ring gear 3, and the mounting member 5. The housing 4 also has a flow path through which the fluid to be delivered passes. As shown in Figure 2, the housing 4 includes a first housing 41 and a second housing 42. The first housing 41 and the second housing 42 are arranged along the direction in which the rotating shaft 1 extends. The first housing 41 and the second housing 42 are connected to each other. The first housing 41 has a recess 411a which serves as a housing portion 411. The second housing 42 is connected to the first housing 41 so as to cover the housing portion 411 of the first housing 41. The second housing 42 has a cover surface 421 which covers the housing portion 411.

[0034] Furthermore, as shown in Figures 1 and 2, the housing 4 is provided with an intake section 43 that communicates with the housing section 411 and draws in fluid, and a discharge section 44 that communicates with the housing section 411 and discharges fluid. The intake section 43 and the discharge section 44 are formed spanning the first housing 41 and the second housing 42, respectively. In the example shown in Figure 2, the portion of the intake section 43 provided in the first housing 41 is shown with a dashed line, and the portion provided in the second housing 42 is omitted. Similarly, in the example shown in Figure 2, the portion of the discharge section 44 provided in the second housing 42 is shown with a dashed line, and the portion provided in the first housing 41 is omitted. The gear pump 100 draws in fluid from the intake section 43, pumps (pressurizes) the fluid within the housing section 411 by the rotation of the pinion gear 2 and the ring gear 3, and discharges the fluid from the discharge section 44.

[0035] Furthermore, when viewed in the direction in which the rotating shaft 1 extends, the center of the housing 4 is in approximately the same position as the rotation axis C2 of the ring gear 3. In other words, the center of the ring gear 3 and the center of the housing 4 are located in approximately the same position. This allows the center of the housing 4 to be in approximately the same position as the center of the housing portion 411 (recess 411a) that houses the ring gear 3, thus minimizing the excess material on the outside of the housing portion 411. This effectively prevents the housing 4 from becoming larger.

[0036] Furthermore, as shown in Figure 2, the first housing 41 is provided with an axial arrangement space 412 in which the rotating shaft 1 is arranged. A bearing member 412a is arranged on the outer circumference of the rotating shaft 1 in the axial arrangement space 412. The second housing 42 is provided with an axial arrangement space 422 in which the rotating shaft 1 is arranged. A bearing member 422a is arranged on the outer circumference of the rotating shaft 1 in the axial arrangement space 422. In addition, a bearing 423 that rotatably supports the rotating shaft 1 is provided in the axial arrangement space 422 of the second housing 42. Note that the axial arrangement space 412 is an example of the "second axial arrangement space" in the claims. Also, the axial arrangement space 422 is an example of the "first axial arrangement space" in the claims.

[0037] In the housing 4, the shaft arrangement spaces 412 and 422 and the housing section 411 are in communication. Therefore, the fluid in the housing section 411 flows slightly into the shaft arrangement spaces 412 and 422 and is used for lubrication of the bearing members 412a and 422a when the rotating shaft 1 rotates.

[0038] The recess 411a of the first housing 41, which serves as a housing portion 411, has a support surface 411b that supports the pinion gear 2 and the ring gear 3.

[0039] The mounting member 5 is positioned in the housing portion 411 of the housing 4. The mounting member 5 is also provided between the pinion gear 2 and the ring gear 3 in a region where the meshing of the pinion gear 2 and the ring gear 3 is separated.

[0040] The mounting member 5 is positioned on the opposite side of the position where the pinion gear 2 and ring gear 3 mesh with the rotation axis 1 (meshing position P1). Specifically, as shown in Figure 5, the mounting member 5 in this embodiment is positioned on the opposite side of the housing portion 411 from the side where the meshing position P1 is located, with reference to the center line B2 which is perpendicular to the center line B1 passing through the meshing position P1 and the rotation axis C2.

[0041] Further, the disposed member 5 includes a crescent 51 having a crescent shape. The disposed member 5 of the present embodiment is the crescent 51. The inner peripheral side surface of the crescent 51 is formed along the outer circumference of the pinion gear 2 (the arc through which the tooth tips of the external teeth 21 pass). Also, the outer peripheral side surface of the crescent 51 is formed along the inner circumference of the ring gear 3 (the arc through which the tooth tips of the internal teeth 31 pass).

[0042] Further, the crescent 51 is fixedly provided so as to project from the support surface 411b of the recess 411a as the housing portion 411. That is, the crescent 51 is integrally formed with the first housing 41 in the housing portion 411 of the first housing 41. Also, the crescent 51 has a tapered shape extending from the central portion toward each of the end portions on the suction portion 43 side and the discharge portion 44 side when viewed in the direction in which the rotation axis 1 extends. Therefore, when viewed in the direction in which the rotation axis 1 extends, the crescent 51 has a shape with the largest width at the central portion.

[0043] As shown in FIG. 5, the crescent 51 is arranged straddling the center line B1 so as to span one side (specifically, the suction portion 43 side) and the other side (specifically, the discharge portion 44 side) with respect to the meshing position P1 and the center line B1 passing through the rotation axis C2. Note that the crescent 51 may be arranged straddling the center line B2 so as to span the side on which the meshing position P1 is arranged with respect to the center line B2.

[0044] That is, as shown in FIG. 5, the crescent 51 is arranged in a region where the meshing of the pinion gear 2 and the ring gear 3 is separated on the side opposite to the side on which the meshing position P1 is arranged with respect to the center line B2. In the present embodiment, due to the increase in the inner diameter of the ring gear 3 to expand the flow path in the housing portion 411, the width of the crescent 51 is also larger than when the number of teeth of the internal teeth 31 is set to about 1.3 times the number of teeth of the external teeth 21.

[0045] In this embodiment, as shown in Figure 1, a communication hole 6 extending in the direction of the rotation shaft 1 is formed in the housing portion 411, excluding the portion through which the external teeth 21 and internal teeth 31 pass and the rotation shaft 1 itself, when viewed in the direction of the rotation shaft 1. Furthermore, as shown in Figure 2, the communication hole 6 communicates with the axial arrangement spaces 412 and 422 of the housing 4 where the rotation shaft 1 is located, and with the outside of the housing 4.

[0046] Furthermore, in this embodiment, as shown in Figure 1, the communication hole 6 is formed in the mounting member 5. Specifically, as shown in Figures 1 and 3, the communication hole 6 is formed in the crescent 51. Therefore, as shown in Figure 5, the communication hole 6 in this embodiment is formed on the side opposite to the side where the meshing position P1 is located, with reference to the center line B2. Also, the communication hole 6 is located in the central part of the crescent 51 when viewed in the direction in which the rotation axis 1 extends. In other words, the communication hole 6 is located at the position where the width of the crescent 51 is greatest. Therefore, the distance between the fluid flowing in the communication hole 6 and the fluid flowing in the housing 411 can be increased, so for example, heat exchange between the fluids can be suppressed. In other words, the liquid that is pressurized and pumped in the housing 411 can be prevented from being heated or cooled by the fluid flowing in the communication hole 6.

[0047] As described above, in this embodiment, the inner diameter of the ring gear 3 is increased in order to enlarge the flow path within the housing 411. Therefore, the width of the crescent 51 positioned between the ring gear 3 and the pinion gear 2 is larger than when the number of teeth of the internal teeth 31 is set to approximately 1.3 times the number of teeth of the external teeth 21.

[0048] Incidentally, in the present embodiment, as described above, in order to expand the flow path in the housing portion 411, the outer diameter of the ring gear 3 is increased. And the size of the housing portion 411 is set in accordance with the outer diameter of the ring gear 3. Therefore, when the ring gear 3 becomes larger, the housing portion 411 that houses the ring gear 3 also becomes larger, resulting in a problem that the housing 4 becomes larger. Thus, in order to expand the flow path in the housing portion 411 while suppressing the enlargement of the housing 4, in the present embodiment, the communication hole 6 is formed in the disposing member 5, and the surplus material in the outer portion of the housing portion 411 of the housing 4 is reduced.

[0049] As described above, by integrally forming the crescent 51 with the first housing 41, the communication hole 6 and the flow path 413 of the first housing 41 can be formed without a gap. Therefore, it is possible to effectively suppress the leakage of fluid into the recess 411a from the location where the first housing 41 and the communication hole 6 are connected.

[0050] Further, as shown in FIG. 2, the communication hole 6 communicates with the shaft arrangement space 422 formed in the second housing 42 and the drain port 415 formed in the first housing 41 and communicating with the outside of the housing 4. Also, the shaft arrangement space 412 formed in the first housing 41 and the drain port 415 communicate with each other. That is, the communication hole 6 communicates with the shaft arrangement spaces 412 and 422 and the drain port 415 that communicates with the outside of the housing 4, and is provided to discharge the fluid in the shaft arrangement spaces 412 and 422 to the outside.

[0051] As shown in Figure 2, the drain port 415 is formed on the outer surface of the first housing 41. In this embodiment, the drain port 415 is formed on the outer surface of the first housing 41 on the side opposite to the side where the housing portion 411 is formed (the upper side in Figure 2) (the lower side in Figure 2). Furthermore, the drain port 415 is positioned to overlap with the housing portion 411 in the radial direction extending from the center of the housing 4 to the outer surface. In other words, the drain port 415 is positioned to overlap with the housing portion 411 when viewed in the direction in which the rotation axis C1 extends. Also, the drain port 415 is positioned to overlap with the communication hole 6 when viewed in the direction in which the rotation axis C1 extends. Therefore, the drain port 415 is positioned closer to the center of the housing 4 than the side surface 411c of the housing portion 411.

[0052] Here, a small amount of fluid from the housing 411 flows into the shaft arrangement spaces 412 and 422. The fluid that flows into the shaft arrangement spaces 412 and 422 is used for heat dissipation and lubrication. The fluid used for heat dissipation and lubrication is discharged from the drain port 415 through the flow path including the communication hole 6. Since the pressure outside the housing 4 (the pressure of the tank and piping, which is approximately atmospheric pressure) is lower than the pressure inside the shaft arrangement spaces 412 and 422, the fluid in the shaft arrangement spaces 412 and 422 is discharged to the outside through the communication hole 6 and the drain port 415.

[0053] As shown in Figure 2, the first housing 41 has flow paths 413 and 414 formed therein for discharging fluid to the outside. Flow path 413 is formed to extend along the direction in which the rotation axis 1 extends. Flow path 413 is positioned to overlap with the housing portion 411 in the radial direction extending from the center of the housing 4 to the outer surface. In other words, flow path 413 is positioned to overlap with the housing portion 411 when viewed in the direction in which the rotation axis C1 extends. Also, flow path 413 is positioned to overlap with the communication hole 6 when viewed in the direction in which the rotation axis C1 extends. Therefore, flow path 413 is positioned closer to the center of the housing 4 than the side surface 411c of the housing portion 411. Flow path 413 is connected to the communication hole 6. Also, flow path 413 is connected to the drain port 415. Flow path 414 is formed to extend along the radial direction. Flow path 414 is connected to flow path 413. Furthermore, the inner end of the channel 414 is connected to the axial arrangement space 412. Also, the outer end of the channel 414 is closed by a plug 414a.

[0054] As shown in Figure 2, the second housing 42 has flow paths 424 and 425 formed therein for discharging fluid to the outside. Flow path 424 is formed to extend along the direction in which the rotation axis 1 extends. Flow path 424 is positioned to overlap with the housing portion 411 in the radial direction extending from the center of the housing 4 to the outer surface. In other words, flow path 424 is positioned to overlap with the housing portion 411 when viewed in the direction in which the rotation axis C1 extends. Also, flow path 424 is positioned to overlap with the communication hole 6 when viewed in the direction in which the rotation axis C1 extends. Therefore, flow path 424 is positioned closer to the center of the housing 4 than the side surface 411c of the housing portion 411. Flow path 424 is connected to the communication hole 6. Flow path 425 is formed to extend along the radial direction. Flow path 425 is connected to flow path 424. Also, the inner end of flow path 425 is connected to the axial arrangement space 422. Furthermore, the outer end of the flow path 425 is blocked by a plug 425a.

[0055] Furthermore, the pressure in the flow paths 413, 414, 424, 425 and the communication hole 6 is lower than the pressure in the shaft arrangement spaces 412, 422 and the housing section 411. Therefore, the fluid that flows into the shaft arrangement spaces 412, 422 does not return to the housing section 411, but flows into the flow paths 413, 414, 424, 425 and the communication hole 6.

[0056] The fluid channels 413, 424 and the drain port 415 are positioned closer to the center of the housing 4 than the side surface 411c of the housing 411. Therefore, when adjusting the size of the excess material on the outside of the housing 411 of the housing 4, the fluid channels 413, 424 and the drain port 415 can be prevented from hindering the adjustment. In addition, since the fluid channels 413, 424 and the drain port 415 can be positioned inside the housing 411 of the housing 4, the excess material on the outside of the housing 411 of the housing 4 can be reduced by not providing the fluid channels 413, 424 and the drain port 415 on the outside of the housing 411 of the housing 4.

[0057] Furthermore, the flow path width of the communication hole 6 is larger than the flow path widths of the flow paths 424 and 413. This allows fluid to be easily guided from the upstream flow path 424 to the communication hole 6.

[0058] Furthermore, the flow path width of the communication hole 6 is constant in the direction in which the rotating shaft 1 extends (from the upstream side to the downstream side). This allows the fluid to flow smoothly through the communication hole 6.

[0059] Furthermore, for example, the communication hole 6 is arranged to extend along the vertical direction. In other words, the gear pump 100 is arranged so that the rotating shaft 1 extends along the vertical direction. In this case, the fluid to be discharged can flow from top to bottom through the communication hole 6.

[0060] Furthermore, as shown in Figures 2 to 4, a sealing member 45 is provided between the cover surface 421 of the second housing 42 and the crescent 51 integrally provided on the first housing 41, so that the housing portion 411 and the communication hole 6 do not communicate. Here, there is a small gap (about 1 mm or less) between the cover surface 421 of the second housing 42 and the upper surface of the crescent 51 integrally provided on the first housing 41. The sealing member 45 seals this small gap. Therefore, the fluid flowing in the communication hole 6 and the fluid flowing in the housing portion 411 do not merge, but instead flow to the outside of the gear pump 100 through separate passages. For example, if the fluid is hydraulic oil, the hydraulic oil flows between the bearing members 412a, 422a and the rotating shaft 1, thereby contributing to the lubrication of the bearing members 412a, 422a when the rotating shaft 1 rotates. The hydraulic fluid that has contributed to lubrication flows to the drain port 415 through the passages 413, 414, 424, 425 and the communication hole 6, while still carrying the heat generated during the rotation of the rotating shaft 1. If the hydraulic fluid that has flowed into the communication hole 6 flows into the housing 411, the heat generated during the rotation of the rotating shaft 1 will affect the viscosity of the hydraulic fluid in the housing 411. As a result, there is a risk that the gear pump 100 may seize up. To avoid such a situation, the housing 411 and the communication hole 6 are prevented from communicating by sealing with a sealing member 45. In consideration of the aforementioned effect on the viscosity of the hydraulic fluid in the housing 411, for example, a material with low thermal conductivity may be used for the sealing member 45. For example, the sealing member 45 is made of a resin material.

[0061] As shown in Figure 3, the sealing member 45 is positioned to surround the communication hole 6 when viewed in the direction in which the rotation axis 1 extends. The sealing member 45 includes, for example, an O-ring. The sealing member 45 is made of an elastic material such as rubber. The sealing member 45 is elastically deformed by being sandwiched between the first housing 41 and the second housing 42. For example, the sealing member 45 elastically deforms from a state in which the cross-section is substantially circular to a state in which the portion that abuts the first housing 41 and the second housing 42 is linear. As a result, the sealing member 45 adheres tightly to the first housing 41 and the second housing 42. The sealing member 45 is also positioned to fit into a recess 451 formed in the crescent 51. This makes it possible to make the sealing member 45 less susceptible to fluid pressure from both the communication hole 6 side and the housing 411 side. In other words, if the sealing member 45 is not positioned in the recess 451, the sealing member 45 will be more susceptible to fluid pressure from both the housing 411 side and the communication hole 6 side. In this case, the sealing member 45 deforms in the direction of the pressure, resulting in a decrease in sealing performance. On the other hand, by positioning the sealing member 45 in the recess 451, the sealing member 45 can be made less susceptible to pressure from the fluid, thereby suppressing deformation caused by fluid pressure. Furthermore, by positioning the sealing member 45 in the recess 451, displacement of the sealing member 45 due to fluid pressure can be suppressed.

[0062] Furthermore, in this embodiment, as shown in Figures 1 and 3, the mounting member 5 (crescent 51) has a pin insertion recess 7 into which a pin 71 that guides the second housing 42 relative to the first housing 41 is inserted. In other words, the crescent 51 has a communication hole 6 and a pin insertion recess 7. The second housing 42 also has a pin insertion recess (not shown) in a position opposite to the pin insertion recess 7 of the crescent 51 into which the pin 71 is inserted. In other words, when assembling the first housing 41 and the second housing 42, the pin 71 is inserted into the pin insertion recess 7 of the first housing 41 and used to guide the correct type of second housing 42. Specifically, the first housing 41 and the second housing 42 of the same type of gear pump are provided with pin insertion recesses at corresponding positions. The positions of these pin insertion recesses differ from one another depending on the type of gear pump.

[0063] As shown in Figure 1, when viewed in the direction in which the rotation axis 1 extends, the pin insertion recess 7 is located on the suction portion 43 side of the crescent 51, rather than on the central portion. In other words, the pin insertion recess 7 is located on the suction portion 43 side, where the pressure is relatively low.

[0064] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0065] In this embodiment, as described above, a communication hole 6 extending in the direction of the rotation shaft 1 is formed in the housing portion 411, excluding the portion through which the external teeth 21 and internal teeth 31 pass and the rotation shaft 1 itself, when viewed in the direction in which the rotation shaft 1 extends. The communication hole 6 communicates with the axial arrangement spaces 412 and 422 of the housing 4 where the rotation shaft 1 is located, and with the outside of the housing 4. This allows a fluid flow path to be placed inside the housing portion 411 of the housing 4, and by not providing a fluid flow path outside the housing portion 411 of the housing 4, the excess material on the outside of the housing portion 411 of the housing 4 can be reduced. As a result, the housing 4 can be made smaller. Also, by reducing the excess material of the housing 4, the amount of material used to form the housing 4 can be reduced, and the housing 4 can be made lighter. Furthermore, since the communication hole 6 is not provided in the portion through which the external teeth 21 and internal teeth 31 pass inside the housing portion 411, interference between the communication hole 6 and the external teeth 21 and internal teeth 31 can be suppressed. Furthermore, since no communication hole 6 is provided in the rotating shaft 1 within the housing 411, there is no need to drill a hole in the rotating shaft 1, which is made of a relatively hard material to ensure mechanical strength. This makes it possible to avoid the complicated machining work required to form the communication hole 6.

[0066] Furthermore, in this embodiment, as described above, the communication hole 6 is formed in the arrangement member 5. This allows the communication hole 6, which allows fluid to pass through, to be placed in the arrangement member 5 between the pinion gear 2 and the ring gear 3 within the housing 411, thus enabling the arrangement member 5 within the housing 411 to be effectively utilized to provide the communication hole 6.

[0067] Furthermore, in this embodiment, as described above, the mounting member 5 is positioned on the opposite side of the rotation shaft 1 from the position where the pinion gear 2 and ring gear 3 mesh, and includes a crescent-shaped crescent 51, with the communication hole 6 formed in the crescent 51. As a result, since the communication hole 6 is provided in the crescent 51 which is positioned without rotating within the housing 411, it is possible to suppress the complexity of the sealing structure of the portion connecting the communication hole 6 compared to the case where the communication hole 6 is provided in the pinion gear 2 or ring gear 3 which rotates within the housing 411.

[0068] Furthermore, in this embodiment, as described above, the housing 4 includes a first housing 41 having a recess 411a formed therein as a housing portion 411, and a second housing 42 connected to the first housing 41 so as to cover the housing portion 411 of the first housing 41. The recess 411a also has a support surface 411b that supports the pinion gear 2 and the ring gear 3, and the crescent 51 is fixedly provided so as to protrude from the support surface 411b. As a result, a communication hole 6 can be provided in the crescent 51 which is integrally provided with the first housing 41, so that the number of parts does not increase compared to when a communication hole is provided in a member that is provided separately from the first housing 41.

[0069] Furthermore, in this embodiment, as described above, the second housing 42 has a cover surface 421 that covers the housing portion 411, the communication hole 6 communicates with the axial arrangement space 422 formed in the second housing 42 and the drain port 415 formed in the first housing 41 that communicates with the outside of the housing 4, and a sealing member 45 is provided between the cover surface 421 and the crescent 51 so that the housing portion 411 and the communication hole 6 do not communicate. This makes it possible to suppress the flow of fluid that has risen in temperature by flowing into the axial arrangement space 422 and coming into contact with the rotating shaft 1 into the housing portion 411 through the communication hole 6. This makes it possible to suppress the temperature of the fluid inside the housing portion 411 from rising excessively.

[0070] Furthermore, in this embodiment, as described above, the communication hole 6 communicates with the shaft arrangement spaces 412 and 422 and with the drain port 415 which communicates with the outside of the housing 4, and is provided to discharge the fluid from the shaft arrangement spaces 412 and 422 to the outside. As a result, the communication hole 6 for discharging the fluid from the shaft arrangement spaces 412 and 422 can be provided in the housing portion 411 of the housing 4, and the housing 4 of the gear pump 100 equipped with the communication hole 6 for discharging the fluid from the shaft arrangement spaces 412 and 422 can be made smaller.

[0071] Furthermore, in this embodiment, as described above, a shaft arrangement space 422 is formed in the second housing 42, and a drain port 415 is formed in the first housing 41, and the communication hole 6 communicates with both the shaft arrangement space 422 and the drain port 415. As a result, the fluid in the shaft arrangement space 422 of the second housing 42 can be discharged to the outside through the drain port 415 provided in the first housing 41, so there is no need to provide a separate drain port in the second housing 42. Note that since the pressure outside the housing 4 is lower than the pressure in the shaft arrangement space 422, the fluid in the shaft arrangement space 422 is discharged to the outside from the shaft arrangement space 422 through the communication hole 6 and the drain port 415.

[0072] Furthermore, in this embodiment, as described above, a shaft arrangement space 412 is formed in the first housing 41, and the shaft arrangement space 412 and the drain port 415 are in communication. As a result, both the fluid in the shaft arrangement space 422 of the second housing 42 and the fluid in the shaft arrangement space 412 of the first housing 41 can be discharged to the outside through the drain port 415 provided in the first housing 41.

[0073] Furthermore, in this embodiment, as described above, the mounting member 5 is positioned on the opposite side of the rotation shaft 1 from the position where the pinion gear 2 and ring gear 3 mesh, and includes a crescent-shaped crescent 51. The crescent 51 has a pin insertion recess 7 into which a pin 71 that guides the second housing 42 relative to the first housing 41 is inserted. This allows for the provision of a pin insertion recess 7 in the crescent 51 within the housing portion 411 for inserting a pin 71 that guides the first housing 41 and second housing 42 to prevent them from being assembled together if there are multiple types of gear pumps 100 and the first housing 41 and second housing 42 are not in the correct combination. This suppresses the increase in excess material of the housing 4 compared to the case where the pin insertion recess 7 is provided on the outside of the housing portion 411 of the housing 4.

[0074] Furthermore, in this embodiment, as described above, the pin insertion recess 7 is located on the suction portion 43 side of the crescent 51, rather than on the central portion, when viewed in the direction in which the rotation axis 1 extends. This ensures that the pin insertion recess 7 is located on the suction portion 43 side of the crescent 51, where the liquid pressure is lower, thereby preventing high-pressure liquid from flowing into the pin insertion recess 7.

[0075] Furthermore, in this embodiment, as described above, the crescent 51 has a tapered shape from the center towards the end on the intake portion 43 side and the end on the discharge portion 44 side when viewed in the direction in which the rotation shaft 1 extends, and the communication hole 6 is provided in the central part of the crescent 51 when viewed in the direction in which the rotation shaft 1 extends. As a result, since the communication hole 6 is provided in the central part of the wide crescent 51, the machining work of forming the communication hole 6 in the crescent 51 can be easily performed.

[0076] Furthermore, in this embodiment, as described above, the communication hole 6 and the pin insertion recess 7 are formed in the crescent 51. As a result, since both the communication hole 6 and the pin insertion recess 7 are provided in the crescent 51, it is possible to effectively suppress the increase in excess material of the housing 4 compared to the case where either the communication hole 6 or the pin insertion recess 7 is provided on the outside of the housing portion of the housing 4.

[0077] Furthermore, in this embodiment, as described above, the number of teeth of the internal teeth 31 of the ring gear 3 is 1.4 times or more the number of teeth of the external teeth 21 of the pinion gear 2. This eliminates the need to secure a large amount of excess material in the housing 4 that would increase the diameter of the ring gear 3 and thus the size of the housing 411, thus suppressing the increase in size of the housing 4 of the gear pump 100, which has a large number of teeth in the ring gear 3 and a large diameter. Also, when the number of teeth of the internal teeth 31 of the ring gear 3 is 1.4 times or more the number of teeth of the external teeth 21 of the pinion gear 2, the difference between the inner diameter of the ring gear 3 and the outer diameter of the pinion gear 2 becomes large, so the width of the crescent 51 positioned between the ring gear 3 and the pinion gear 2 also becomes larger. This makes it easy to form a communication hole in the crescent 51 within the housing 411.

[0078] Furthermore, in this embodiment, as described above, the center of the ring gear 3 and the center of the housing 4 are positioned approximately the same when viewed in the direction in which the rotating shaft 1 extends. This makes it possible to make the center of the ring gear 3 (center of the housing portion 411) and the center of the housing 4 approximately the same, thereby suppressing the formation of an area where the excess material on the outside of the housing portion 411 becomes excessively large. This makes it possible to effectively miniaturize the housing 4.

[0079] (Modifications) It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims rather than the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are further included.

[0080] For example, the above embodiment shows an example configuration in which an external gear 21 with 13 teeth and an internal gear 31 with 19 teeth are provided, but the present invention is not limited to this. In the present invention, the number of teeth of the internal gear 31 may be set to less than approximately 1.4 times the number of teeth of the external gear 21, for example, the ring gear 3 may be provided with an internal gear 31 with 17 teeth. In other words, the present invention is naturally applicable even to gear pumps that do not have measures to enlarge the flow path in the housing.

[0081] Furthermore, although the above embodiment shows an example in which the communication hole 6 is provided in the crescent 51 of the mounting member 5 (position A1 in Figure 6), the present invention is not limited to this. In the present invention, the communication hole may be provided in a position other than the crescent, within the housing portion, excluding the portion through which the external and internal teeth pass and the rotation axis, when viewed in the direction in which the rotation axis extends.

[0082] For example, as shown in Figure 6, the communication hole may be provided at position A2, which is on the outer circumference of the internal teeth 31 of the ring gear 3. In other words, as in the first modified gear pump 200 shown in Figure 7, the communication hole 6a may be provided on the outer circumference of the internal teeth 31 of the ring gear 3. In this case, the first housing 41 and the second housing 42 may each be provided with annular grooves connected to the communication hole 6a. Furthermore, sealing members may be provided between the first housing 41 and the second housing 42 and the communication hole 6a to prevent communication between the housing portion 411 and the communication hole 6a.

[0083] Furthermore, as shown in Figure 6, the communication hole may be provided at position A3, which is on the inner circumference side of the external teeth 21 of the pinion gear 2 and outside the rotating shaft 1. In other words, as in the second modified gear pump 300 shown in Figure 8, the communication hole 6b may be provided in a portion that is on the inner circumference side of the external teeth 21 of the pinion gear 2 and outside the rotating shaft 1. In this case, the first housing 41 and the second housing 42 may each be provided with an annular groove that connects to the communication hole 6b. Also, a sealing member may be provided between the first housing 41 and the second housing 42 and the communication hole 6b to prevent communication between the housing portion 411 and the communication hole 6b.

[0084] Furthermore, multiple communication holes may be formed in a single gear pump. For example, multiple communication holes may be formed in one component, such as by forming multiple communication holes 6 in the crescent 51, or multiple communication holes may be formed in each of different components, such as by forming a communication hole 6 in the crescent 51 and a communication hole 6a at position A2 (see Figure 6) on the outer circumference of the internal teeth 31 of the ring gear 3.

[0085] Furthermore, as shown in Figure 6, the communication hole may be provided at a position A4 other than the crescent 51 located between the pinion gear 2 and the ring gear 3. For example, as in the gear pump 400 of the third modification shown in Figure 9, the communication hole 6c may be provided in the support member 53 that supports the pressure-guaranteed crescent 52. In this case, the arranged member includes the crescent 52 and the support member 53. Note that the arranged member may be a member that is positioned only at position A4. Also, in Figure 5, the communication hole may be positioned on the side where the meshing position P1 is located, with respect to the center line B2.

[0086] Furthermore, in the above embodiment, an example was shown in which the communication hole 6 communicates the axial arrangement spaces 412 and 422 of the housing 4 where the rotating shaft 1 is located with the outside of the housing 4, but the present invention is not limited to this. In the present invention, the communication hole only needs to communicate with the axial arrangement spaces of the housing where the rotating shaft is located, and with at least one of the spaces outside the housing and the space between the pinion gear and the ring gear inside the housing. For example, as shown in the fourth modified example in Figure 10, a flow path 6e may be provided in the crescent 51a so as to communicate with the space between the pinion gear 2 and the ring gear 3 in the communication hole 6d. In this case, the flow path 6e connected to the communication hole 6d may communicate with the suction section 43 side. Alternatively, the flow path 6e connected to the communication hole 6d may communicate with the discharge section 44 side. Also, in this case, the communication hole 6d does not need to communicate with the outside. In the fourth modified example, if the fluid is hydraulic oil, the viscosity of the hydraulic oil in the housing 411 may or may not be considered.

[0087] Furthermore, although the above embodiment shows an example in which a pin insertion recess 7 is provided in the crescent 51 as the mounting member 5, the present invention is not limited to this. In the present invention, it is not necessary to provide a pin insertion recess in the crescent as the mounting member. For example, the pin insertion recess may be provided outside the housing portion, or the pin insertion recess itself may not be provided in the gear pump.

[0088] Furthermore, although the above embodiment shows an example of a configuration in which a communication hole 6 is provided in the center of the crescent 51, the present invention is not limited to this. In the present invention, the communication hole may be provided at a position closer to the suction part or the discharge part than the center of the crescent.

[0089] Furthermore, although the above embodiment shows an example where the communication hole 6 and the flow paths 413 and 424 of the housing 4 connected to the communication hole 6 have different flow path widths, the present invention is not limited to this. In the present invention, the communication hole and the flow paths of the housing 4 connected to the communication hole may have the same flow path width. This makes it possible to allow fluid to flow smoothly in the communication hole and the flow paths. In other words, by eliminating steps at the boundary between the communication hole and the flow paths, it is possible to allow fluid to flow smoothly.

[0090] Furthermore, although the above embodiment shows an example in which the flow path width of the communication hole 6 is constant, the present invention is not limited to this. In the present invention, the flow path width of the communication hole does not have to be constant. For example, the communication hole may be formed in a tapered shape in which the flow path width decreases from the upstream side to the downstream side. In other words, the communication hole may be formed so that the flow path width decreases from the second housing side to the drain port side. As a result, the flow path width is large on the upstream side of the communication hole, so a large amount of fluid can be introduced from the flow path. Also, as the flow path width decreases towards the downstream side of the communication hole, the flow velocity can be increased towards the outlet of the communication hole. As a result, the fluid can be discharged from the drain port quickly.

[0091] Furthermore, although the above embodiment describes an example in which the communication hole 6 extends along the vertical direction, the communication hole is not limited to this, and may extend in the direction in which the rotation axis extends. Also, the communication hole does not need to be configured as a single line as shown in Figure 2, but may, for example, have a shape in which the end on the first housing side or the second housing side branches into two. In this case, the flow path formed in the first housing or the second housing may have a shape in which it branches into two corresponding to the communication hole, or it may be a single flow path of a size that can be connected to the bifurcated communication hole. Note that the communication hole is not limited to a bifurcated shape, and may have a shape in which the end on the first housing side or the second housing side branches into two or more.

[0092] Furthermore, although the above embodiment shows an example in which a sealing member 45 is provided between the cover surface 421 of the second housing 42 and the crescent 51, the present invention is not limited to this. In the present invention, it is not necessary to provide a sealing member between the cover surface of the second housing and the crescent.

[0093] Furthermore, although the above embodiment shows an example in which the drain port 415 is formed in the first housing 41, the present invention is not limited thereto. In the present invention, the drain port may be formed in the second housing in addition to the first housing. Also, the drain port may be formed in the second housing instead of the first housing.

[0094] 1 Rotating shaft 2 Pinion gear 3 Ring gear 4 Housing 5 Arrangement member 6, 6a, 6b, 6c, 6d Communication hole 7 Pin insertion recess 21 External teeth 31 Internal teeth 41 First housing 42 Second housing 43 Intake section 44 Discharge section 45 Seal member 51, 51a Crescent 71 Pin 100, 200, 300, 400 Gear pump 411 Housing section 411a Recess 411b Support surface 412 Axis arrangement space (second axis arrangement space) 415 Drain port 421 Cover surface 422 Axis arrangement space (first axis arrangement space)

Claims

1. A pinion gear connected to a rotating shaft and having external teeth formed thereon; a ring gear disposed on the outer circumference of the pinion gear and having internal teeth formed thereon that mesh with the external teeth; a housing including a housing portion in which the pinion gear and the ring gear are housed; a suction portion communicating with the housing portion and drawing in fluid; and a discharge portion communicating with the housing portion and discharging fluid; and an arrangement member disposed in the housing portion of the housing and provided between the pinion gear and the ring gear in a region where the meshing of the pinion gear and the ring gear is separated, wherein, when viewed in the direction in which the rotating shaft extends, a communication hole extending in the direction in which the rotating shaft extends is formed in the housing portion at a position excluding the portion through which the external teeth and the internal teeth pass and the rotating shaft. A gear pump wherein the communication hole communicates with the axial arrangement space of the housing in which the rotating shaft is located, and with at least one of the spaces outside the housing and the space between the pinion gear and the ring gear inside the housing.

2. The gear pump according to claim 1, wherein the communication hole is formed in the mounting member.

3. The gear pump according to claim 2, wherein the arrangement member is positioned on the opposite side of the rotation shaft from the position where the pinion gear and the ring gear mesh, and includes a crescent-shaped component, and the communication hole is formed in the crescent.

4. The gear pump according to claim 3, wherein the housing includes a first housing having a recess formed therein as a housing portion, and a second housing connected to the first housing so as to cover the housing portion of the first housing, the recess having a support surface for supporting the pinion gear and the ring gear, and the crescent is fixedly provided so as to protrude from the support surface.

5. The gear pump according to claim 4, wherein the second housing has a cover surface that covers the housing portion, the communication hole communicates with the axial arrangement space formed in the second housing and with a drain port formed in the first housing that communicates with the outside of the housing, and a sealing member is provided between the cover surface and the crescent so that the housing portion and the communication hole do not communicate.

6. The gear pump according to claim 1, wherein the communication hole communicates with the shaft arrangement space and with a drain port communicating with the outside of the housing, and is provided for discharging fluid from the shaft arrangement space to the outside.

7. The gear pump according to claim 6, wherein the housing includes a first housing having a recess formed therein as a housing portion, and a second housing connected to the first housing so as to cover the housing portion of the first housing, the second housing having a first shaft arrangement space, the first housing having a drain port, and the communication hole communicating with the first shaft arrangement space and the drain port.

8. The gear pump according to claim 7, wherein a second shaft arrangement space is formed in the first housing, and the second shaft arrangement space and the drain port are in communication.

9. The gear pump according to claim 1, wherein the housing includes a first housing having a recess formed therein as a housing portion, and a second housing connected to the first housing so as to cover the housing portion of the first housing, the arrangement member includes a crescent having a crescent shape and positioned on the opposite side of the rotation shaft from the position in which the pinion gear and the ring gear mesh, and the crescent has a pin insertion recess into which a pin that guides the second housing relative to the first housing is inserted.

10. The gear pump according to claim 9, wherein, viewed in the direction in which the rotating shaft extends, the pin insertion recess is located on the suction side of the crescent rather than on the central side.

11. The gear pump according to any one of claims 3 to 5, wherein the crescent has a tapered shape from the central part toward the end on the suction side and the end on the discharge side when viewed in the direction in which the rotating shaft extends, and the communication hole is provided in the central part of the crescent when viewed in the direction in which the rotating shaft extends.

12. The gear pump according to claim 9, wherein the communication hole and the pin insertion recess are formed in the crescent.

13. The gear pump according to claim 1, wherein the number of teeth of the internal teeth of the ring gear is 1.4 times or more the number of teeth of the external teeth of the pinion gear.

14. The gear pump according to claim 1, wherein, when viewed in the direction in which the rotating shaft extends, the center of the ring gear and the center of the housing are located at substantially the same position.

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