Internal gear pump

Abstract

An internal gear pump (1) comprises: a gear set (7) including a pinion gear (3) and a ring gear (4); a housing (10); a fixed crescent (54); and an introduction path (8) having an inflow port (8a) communicating with a suction part (11) of the housing, and an outflow port (8b) in contact with a movement line (FL1) of the tips of teeth of the pinion gear or a movement line of the tips of teeth of the ring gear between the suction part and a discharge part (12), the introduction path (8) causing hydraulic oil, which has flowed in from the inflow port, to flow out from the outflow port to teeth grooves of the pinion gear or teeth grooves of the ring gear.

Description

Internal gear pump

[0001] The technology disclosed herein relates to an internal gear pump.

[0002] Patent Document 1 describes a conventional internal gear pump. This internal gear pump is equipped with a crescent. The crescent is located between a pinion gear and a ring gear. The external teeth of the pinion gear and the internal teeth of the ring gear each contact the crescent. The crescent of this internal gear pump is a fixed crescent that does not move toward the external teeth or the internal teeth.

[0003] The conventional internal gear pump also has a pressure transmission oil passage. The pressure transmission oil passage is formed in the ring gear side area of ​​the pinion gear side area and the ring gear side area across the crescent, and connects the discharge port to the space between the ring gear teeth. The pressure transmission oil passage flows a portion of the high-pressure hydraulic oil from the discharge port into the space between the ring gear teeth, thereby preliminarily increasing the pressure in the space between the ring gear teeth. Because the pressure difference between the discharge port pressure and the space between the ring gear teeth pressure is reduced, pressure fluctuations are suppressed when the space is opened to the discharge port. This conventional internal gear pump can reduce noise caused by pressure fluctuations.

[0004] JP 2023-183867 A

[0005] Internal gear pumps with fixed crescents are used at relatively low rotational speeds. This is because cavitation occurs at the suction section of an internal gear pump when the rotational speed is increased. Cavitation occurs when the hydraulic oil pressure at the suction section of an internal gear pump decreases due to pressure loss. The maximum rotational speed of an internal gear pump with a fixed crescent is limited to a speed below the speed at which cavitation occurs. With conventional internal gear pumps, the rotational speed at which cavitation occurs is relatively low, so the maximum rotational speed of the internal gear pump is also low.

[0006] On the other hand, there is a demand for increasing the discharge flow rate of internal gear pumps. To increase the discharge flow rate of an internal gear pump without increasing the size of the internal gear pump, it is necessary to increase the rotation speed of the internal gear pump. However, as mentioned above, the maximum rotation speed of conventional internal gear pumps is relatively low.

[0007] The technology disclosed herein increases the maximum rotation speed of an internal gear pump.

[0008] The inventors of the present invention have applied a structure that suppresses pressure drops in the suction section to an internal gear pump, thereby making it possible to increase the rotation speed of the internal gear pump while suppressing the occurrence of cavitation.

[0009] Specifically, the technology disclosed herein relates to an internal gear pump comprising: a gear set including a pinion gear having external teeth and rotated by a shaft, and a ring gear having internal teeth meshing with the external teeth, a housing having a hydraulic oil suction section and a discharge section and rotatably accommodating the gear set, a fixed crescent located at a point where the pinion gear and the ring gear no longer mesh, an inlet port communicating with the suction section, and an outlet port between the suction section and the discharge section tangent to the line of movement of the tips of the teeth of the pinion gear or the line of movement of the tips of the teeth of the ring gear, and an introduction passage for allowing hydraulic oil that has flowed in from the inlet port to flow out from the outlet port to the tooth grooves of the pinion gear or the tooth grooves of the ring gear.

[0010] In an internal gear pump, as the gear set rotates, the pinion gear and ring gear gradually disengage from each other at the suction section. As the pinion gear and ring gear disengage, hydraulic oil is sucked into the tooth grooves of the pinion gear and the ring gear. The tooth grooves are the spaces between the gear teeth. The sucked hydraulic oil is carried from the suction section to the discharge section as the gear set rotates. Then, at the discharge section, the pinion gear and ring gear, which had been separated, gradually move closer together and engage, and the hydraulic oil in the tooth grooves of the pinion gear and the ring gear is discharged through the discharge section.

[0011] The crescent contacts the tips of the teeth of the pinion gear and the ring gear between the suction and discharge portions, suppressing leakage flow and increasing the efficiency of the internal gear pump.

[0012] The internal gear pump has an inlet passage. The inlet passage includes an inlet and an outlet. The inlet is connected to the suction section. The outlet is tangent to the line of movement of the tips of the teeth of the pinion gear or the line of movement of the tips of the teeth of the ring gear between the suction section and the discharge section. The line of movement of the tips of the gear teeth corresponds to the tip circle of the gear. The tip circle is a circle connecting the tips of the gear teeth.

[0013] The outlet is in contact with the tooth grooves of the rotating pinion gear or the tooth grooves of the ring gear. The hydraulic oil not only flows into the tooth grooves of the pinion gear or the tooth grooves of the ring gear at the suction section, but can also flow into the tooth grooves of the pinion gear or the tooth grooves of the ring gear through the introduction passage. The introduction passage reduces pressure loss in the internal gear pump. The small pressure loss suppresses a drop in hydraulic oil pressure at the suction section even when the rotation speed of the internal gear pump increases. In other words, even when the rotation speed of the internal gear pump increases, the pressure of the hydraulic oil at the suction section is maintained at a relatively high pressure, suppressing the occurrence of cavitation, and allowing the maximum rotation speed of the internal gear pump to be increased.

[0014] Therefore, by operating at a high rotational speed, this internal gear pump can achieve a high discharge flow rate even while remaining compact.

[0015] The introduction passage may be formed in the crescent.

[0016] The introduction passage formed in the crescent allows the hydraulic oil to smoothly flow into the tooth grooves of the pinion gear or the tooth grooves of the ring gear.

[0017] The crescent may have a first arc wall against which the external teeth abut and a second arc wall against which the internal teeth abut, and the introduction passage may be formed by cutting away at least a portion of at least one of the first arc wall and the second arc wall.

[0018] In other words, the introduction passage is formed between the crescent and the line of movement of the pinion gear tooth tips or the line of movement of the ring gear tooth tips. The crescent, which is part of the introduction passage, suppresses the generation of vortices within the introduction passage and functions to regulate the flow of hydraulic oil flowing through the introduction passage. The introduction passage can suppress a drop in hydraulic oil pressure at the suction section without reducing the efficiency of the internal gear pump.

[0019] The crescent may extend from a first end in contact with the edge of the suction portion to a second end on the discharge portion side, and the introduction path may extend from the first end of the crescent toward the discharge portion.

[0020] Because the inlet passage extends from the first end of the crescent, hydraulic oil can easily flow from the suction port to the inlet port, and the flow resistance of the inlet passage is low. An inlet passage with low flow resistance prevents hydraulic oil pressure from decreasing at the suction port, further increasing the maximum rotation speed of the internal gear pump. Furthermore, an inlet passage with low flow resistance promotes the flow of hydraulic oil into the tooth grooves of the pinion gear or the ring gear, which is advantageous for increasing the discharge flow rate of the internal gear pump.

[0021] The introduction passage may extend from the first end to a range equal to or greater than the pitch of the gear contacting the outlet and to a midpoint between the first end and the second end of the crescent.

[0022] If the inlet passage extends too far, close to the discharge port, leakage flow increases, potentially reducing the efficiency of the internal gear pump. If the inlet passage is too short, its effectiveness in reducing pressure loss is limited. If the inlet passage extends within the range from the suction port to the midpoint of the crescent, both pump efficiency and pressure loss can be maintained. Furthermore, if the length of the inlet passage is equal to or greater than the gear pitch (i.e., the spacing between gear teeth) adjacent to the outlet, the outlet will always be in communication with the gear tooth grooves, allowing hydraulic oil to flow into the gear tooth grooves.

[0023] The housing may have a support surface that is a surface perpendicular to the shaft and that supports a side surface of the gear set, and the housing may also include a second inlet that opens to the suction portion and a second outlet that opens at least at a position on the support surface between the suction portion and the discharge portion that corresponds to a position between the tip circle and the root circle of the pinion gear or a position between the tip circle and the root circle of the ring gear, and may have a second introduction passage that allows hydraulic oil that has flowed in from the second inlet to flow out from the second outlet to the tooth grooves of the pinion gear or the tooth grooves of the ring gear. Note that the root circle is a circle connecting the roots of the gear teeth.

[0024] The second inlet passage, like the above-mentioned inlet passage (i.e., the first inlet passage), allows hydraulic oil to flow into the tooth grooves of the pinion gear or the tooth grooves of the ring gear. An internal gear pump equipped with the first inlet passage and the second inlet passage further reduces pressure loss, thereby further increasing the maximum rotation speed of the internal gear pump.

[0025] The housing may have, as the support surfaces, a first support surface that supports a first side surface of the gear set and a second support surface that faces the first support surface and supports a second side surface of the gear set, and the second introduction passage may be formed in at least one of the first support surface and the second support surface.

[0026] The second introduction passage can exert the function of suppressing a drop in the pressure of the hydraulic oil in the suction portion, regardless of whether it is formed on the first support surface or the second support surface.

[0027] The internal gear pump described above can achieve a high maximum rotation speed because the introduction passage suppresses a drop in pressure of the hydraulic oil at the suction portion.

[0028] Fig. 1 is a cross-sectional view of an internal gear pump. Fig. 2 is an exploded view of the internal gear pump. Fig. 3 shows an inlet passage. Fig. 4 is a perspective view of the inlet passage. Fig. 5 shows an inlet passage according to a modified example. Fig. 6 shows an inlet passage according to a modified example. Fig. 7 shows an inlet passage according to a modified example. Fig. 8 shows an inlet passage according to a modified example. Fig. 9 shows an inlet passage according to a modified example. Fig. 10 is a perspective view of a first inlet passage and a second inlet passage.

[0029] Hereinafter, an embodiment of an internal gear pump will be described with reference to the drawings. The internal gear pump described here is an example.

[0030] (Overall Structure of the Internal Gear Pump) Figure 1 or Figure 2 illustrates an internal gear pump 1. Figure 2 is an exploded view of the internal gear pump 1 with the front cover 6 removed from the gear housing 5. The gear housing 5 and the front cover 6 form the housing 10 of the internal gear pump 1.

[0031] The internal gear pump 1 includes a shaft 2. The shaft 2 extends in the left-right direction of the paper in Fig. 1. The tip of the shaft 2, i.e., the left end in Fig. 1, protrudes from a housing 10. The tip of the shaft 2 is connected to a prime mover (not shown). The prime mover is, for example, an electric motor.

[0032] The internal gear pump 1 includes a pinion gear 3. The pinion gear 3 is formed integrally with the shaft 2 at an intermediate position. The pinion gear 3 and the shaft 2 are coaxial. The pinion gear 3 rotates together with the shaft 2. The pinion gear 3 has external teeth 31.

[0033] The internal gear pump 1 includes a ring gear 4. The ring gear 4 meshes with a pinion gear 3. The ring gear 4 is eccentric with respect to the shaft 2. In FIG. 2, C1 denotes the rotation axis of the pinion gear 3, and C2 denotes the rotation axis of the ring gear 4. Internal teeth 41 are formed on the inner circumferential surface of the ring gear 4. In the right diagram of FIG. 2, part of the external teeth 31 of the pinion gear 3 meshes with part of the internal teeth 41 of the ring gear 4 in the region on the left side of the page.

[0034] The pinion gear 3 and the ring gear 4 form a gear set 13 of the internal gear pump 1 .

[0035] The gear housing 5 accommodates the pinion gear 3 and the ring gear 4. An inner hole 53 is formed in the gear housing 5. The base end of the shaft 2, that is, the right end in FIG.

[0036] The pinion gear 3 and the ring gear 4 are rotatably housed in a gear housing 5. The gear housing 5 has a sliding surface 51 on which the outer peripheral surface 42 of the ring gear 4 slides. The outer peripheral surface 42 of the ring gear 4 has a circular cross section. The sliding surface 51 of the gear housing 5 also has a circular cross section. The sliding surface 51 is eccentric with respect to the shaft 2.

[0037] The gear housing 5 has a first support surface 52 that is perpendicular to the sliding surface 51. The first support surface 52 is a surface that is perpendicular to the shaft 2. The sliding surface 51 and the first support surface 52 form a space 50 that accommodates the pinion gear 3 and the ring gear 4. The space 50 is open to the left side of the paper in FIG. 1 . The first side surface 32 of the pinion gear 3 and the first side surface 43 of the ring gear 4 are each supported by the first support surface 52 of the gear housing 5 and slide on the first support surface 52. The first side surface 32 of the pinion gear 3 is a surface that is perpendicular to the rotation axis C1 of the pinion gear 3 and is the side surface on the right side of the paper in FIG. 1 . The first side surface 43 of the ring gear 4 is a surface that is perpendicular to the rotation axis C2 of the ring gear 4 and is the side surface on the right side of the paper in FIG. 1 .

[0038] The front cover 6 is disposed adjacent to the gear housing 5. The front cover 6 and the gear housing 5 are fixed to each other and integrated. The front cover 6 has a second support surface 61 that contacts the gear housing 5 and closes the space 50. The second side surface 33 of the pinion gear 3 and the second side surface 44 of the ring gear 4 are each supported by and slide on the second support surface 61 of the front cover 6. The second side surface 33 of the pinion gear 3 is a surface perpendicular to the rotation axis C1 of the pinion gear 3 and is the side surface on the left side of the paper in FIG. 1. The second side surface 44 of the ring gear 4 is a surface perpendicular to the rotation axis C2 of the ring gear 4 and is the side surface on the left side of the paper in FIG. 1.

[0039] A support hole 62 through which the shaft 2 passes is formed in the front cover 6. The shaft 2 is rotatably supported by the front cover 6 and the gear housing 5 via a bearing 63 and a bearing member 64. The opening of the support hole 62 is closed by a sealing member 621.

[0040] The front cover 6 and the gear housing 5 have suction portions 11. Hydraulic oil is sucked from the suction portion 11 into a space 50 inside the housing 10. The inlet of the suction portion 11 opens to the outer peripheral surface of the front cover 6, as shown in Figure 1. The outlet of the suction portion 11 opens to the second support surface 61 of the front cover 6 and the first support surface 52 of the gear housing 5, as shown in Figures 1 and 2. The outlet of the suction portion 11 also extends circumferentially so as to follow the rotational direction of the shaft 2.

[0041] The front cover 6 and the gear housing 5 also have a discharge portion 12. Hydraulic oil is discharged from the space 50 inside the housing 10 through the discharge portion 12. The outlet of the discharge portion 12 opens to the outer peripheral surface of the gear housing 5, as shown in Figure 1. The inlet of the suction portion 11 and the outlet of the discharge portion 12 may be oriented in different directions as shown in Figure 1, or may be oriented in the same direction.

[0042] An inlet of the discharge portion 12 opens to each of the second support surface 61 of the front cover 6 and the first support surface 52 of the gear housing 5. As shown in Figure 2, the inlet of the discharge portion 12 also extends circumferentially along the rotation direction of the shaft 2 on the opposite side of the shaft 2 from the suction portion 11.

[0043] The gear housing 5 is provided with a crescent 54. The crescent 54 is disposed at a position where the pinion gear 3 and the ring gear 4 disengage from each other. The crescent 54 suppresses leakage flow from the discharge portion 12 to the suction portion 11.

[0044] The crescent 54 extends circumferentially over a predetermined angular range along the rotational direction of the shaft 2. As shown in FIG. 2 , the crescent 54 has an arc or crescent shape when viewed in the axial direction of the shaft 2. A first end 543 of the crescent 54 contacts the edge of the suction portion 11, and a second end 544 contacts the edge of the discharge portion 12. The crescent 54 also has two arc walls, a first arc wall 541 and a second arc wall 542. The first arc wall 541 and the second arc wall 542 each connect the first end 543 and the second end 544. The first arc wall 541 and the second arc wall 542 each stand on the first support surface 52 of the gear housing 5.

[0045] The tips of the external teeth 31 of the pinion gear 3 abut against the first arc wall 541 of the crescent 54. The tips of the internal teeth 41 of the ring gear 4 abut against the second arc wall 542 of the crescent 54. The first arc wall 541 and the second arc wall 542 are both fixed walls that do not move toward the external teeth 31 and the internal teeth 41.

[0046] Next, we will briefly explain the operation of the internal gear pump 1. When the shaft 2 is rotated counterclockwise by the prime mover in the right-hand diagram of Figure 2, the pinion gear 3 and the ring gear 4 each rotate in a direction from the suction port 11 to the discharge port 12 via the crescent 54.

[0047] In the suction portion 11 inside the housing 10, as the meshed external teeth 31 of the pinion gear 3 and the internal teeth 41 of the ring gear 4 separate, hydraulic oil is sucked from the suction portion 11 into between the external teeth 31 and the internal teeth 41. As the pinion gear 3 and the ring gear 4 rotate, the sucked hydraulic oil is transported from the suction portion 11 to the discharge portion 12 via the crescent 54.

[0048] In the discharge portion 12 inside the housing 10, the external teeth 31 of the pinion gear 3 and the internal teeth 41 of the ring gear 4, which had been separated, gradually approach each other and mesh together. As a result, the hydraulic oil is discharged from between the external teeth 31 and the internal teeth 41 through the discharge portion 12.

[0049] The crescent 54 contacts the tips of the teeth of the pinion gear 3 and the ring gear 4 between the suction portion 11 and the discharge portion 12, thereby suppressing leakage flow within the space 50. The crescent 54 improves the efficiency of the internal gear pump 1.

[0050] (Structure for increasing the maximum rotation speed of the inscribed gear pump) The inscribed gear pump 1 is provided with an introduction passage 8. The introduction passage 8 reduces pressure loss in the inscribed gear pump 1, thereby suppressing a drop in pressure in the suction section 11 during operation of the inscribed gear pump 1. Because the pressure drop in the suction section 11 is suppressed, the rotation speed of the inscribed gear pump 1 can be increased without causing cavitation. In other words, the introduction passage 8 makes it possible to increase the maximum rotation speed of the inscribed gear pump 1.

[0051] 2 or 3, the introduction path 8 is formed in the crescent 54. More specifically, the introduction path 8 is formed in a first arc wall 541 of the crescent 54.

[0052] As shown by the hatched portion in FIG. 4 , the introduction passage 8 is formed by removing a portion of the first arc wall 541. More specifically, the introduction passage 8 includes an inlet 8a and an outlet 8b. The inlet 8a is located at the first end 543 of the crescent 54, as indicated by the two-dot chain line in FIG. 3 or 4 , and communicates with the suction portion 11. The outlet 8b extends from the edge of the outlet of the suction portion 11 toward the discharge portion 12 along the flow line FL1 of the tooth tip of the pinion gear 3, as indicated by the two-dot chain line in FIG. 3 or 4 . During operation of the internal gear pump 1, the outlet 8b contacts the tooth grooves of the rotating pinion gear 3. The hydraulic oil that flows into the introduction passage 8 from the inlet 8a flows out from the outlet 8b into the tooth grooves of the pinion gear 3. The hydraulic oil not only flows into the tooth grooves of the pinion gear 3 and the tooth grooves of the ring gear 4 at the suction portion 11, but also can flow into the tooth grooves of the pinion gear 3 through the introduction passage 8. The introduction passage 8 reduces pressure loss in the internal gear pump 1.

[0053] Because the introduction passage 8 reduces pressure loss in the internal gear pump 1, a drop in the pressure of the hydraulic oil in the suction section 11 is suppressed even when the rotation speed of the internal gear pump 1 increases. In other words, the occurrence of cavitation is suppressed even when the rotation speed of the internal gear pump 1 increases. The rotation speed at which cavitation occurs in the internal gear pump 1 increases. As a result, the maximum rotation speed of the internal gear pump 1 increases. By operating the internal gear pump 1 at a high rotation speed, the discharge flow rate can be increased even while maintaining a small size.

[0054] Furthermore, since the introduction passage 8 is formed by cutting a portion of the first arc wall 541 of the crescent 54, the introduction passage 8 is formed between the flow line FL of the tooth tip of the pinion gear 3 and the crescent 54. The radial width of the introduction passage 8 gradually narrows with increasing distance from the inlet 8a. The introduction passage 8 allows the hydraulic oil to smoothly flow into the tooth grooves of the pinion gear 3. Furthermore, since the introduction passage 8 is partitioned by the crescent 54, the radial width of the introduction passage 8 is relatively narrow. The crescent 54 suppresses the generation of vortices within the introduction passage 8 at the location where the introduction passage 8 is formed, thereby regulating the flow of hydraulic oil flowing through the introduction passage 8. The introduction passage 8 can suppress a pressure drop in the suction section 11 without reducing the efficiency of the internal gear pump 1.

[0055] Furthermore, the inlet passage 8 extends from the first end 543 of the crescent 54 toward the discharge portion 12, and the outlet 8b also extends a long distance from the first end 543 of the crescent 54 toward the discharge portion 12. The flow resistance of the inlet passage 8 is low. The inlet passage 8 with its low flow resistance can further suppress a drop in hydraulic oil pressure in the suction portion 11. The inlet passage 8 extending in the circumferential direction makes it possible to further increase the maximum rotation speed of the internal gear pump 1. The inlet passage 8 with its low flow resistance also promotes the flow of hydraulic oil from the suction portion 4 into the tooth grooves of the pinion gear 3. This is advantageous for increasing the discharge flow rate of the internal gear pump 1.

[0056] Here, the shape of the introduction path 8 will be described in more detail. As shown in Fig. 3, the introduction path 8 may have a circumferential length (or angle θ) that extends from the suction portion 11 to a position M between the first end 543 and the second end 544 of the crescent 54 that is equal to or greater than the pitch P of the pinion gear 3 that contacts the outlet 8b. Note that the circumferential length is expressed here as an angle θ about the rotation axis C1.

[0057] If the inlet passage 8 extends too far, close to the discharge portion 12, leakage flow within the space 50 increases, which may reduce the efficiency of the internal gear pump 1. If the circumferential length of the inlet passage 8 is too short, the amount of hydraulic oil introduced through the inlet passage 8 is small, and the effect of reducing flow resistance at the suction portion 11 is poor. If the inlet passage 8 extends within the range from the suction portion 11 to the midpoint M of the crescent 54, it is possible to maintain the efficiency of the internal gear pump 1 while reducing flow resistance. Furthermore, if the length of the inlet passage 8 is equal to or greater than the pitch of the gear that contacts the outlet 8b, the outlet 8b will always be in communication with the gear tooth grooves, allowing the hydraulic oil to flow into the gear tooth grooves.

[0058] The shape of the introduction path 8 formed by removing a portion of the crescent 54 is not limited to the smooth curved shape shown in Fig. 3, but may be a planar shape that is linear when viewed along the extension direction of the shaft 2. Furthermore, the shape of the introduction path 8 may be a shape in which a plurality of curved or planar surfaces are connected in the circumferential direction.

[0059] 5, the first end 543 of the crescent 54 may be formed with a smooth curved surface, which reduces the flow resistance of the introduction channel 8.

[0060] The introduction path 8 may be formed in a portion of the height direction of the crescent 54. The height direction of the crescent 54 here refers to the direction away from the first support surface 52 of the gear housing 5, in the crescent 54 that stands upright from the first support surface 52. For example, as shown in FIG. 6A , the introduction path 81 may be formed so as to be in contact with the second support surface 61 in the height direction of the crescent 54, and may not be formed on the first support surface 52 side. Alternatively, the introduction path may be formed so as to be in contact with the first support surface 52 in the height direction of the crescent 54, and may not be formed on the second support surface 61 side. Furthermore, the introduction path may be formed in the center of the height direction of the crescent 54, and may not be in contact with the first support surface 52 or the second support surface 61.

[0061] Furthermore, as shown in FIG. 6B, a plurality of introduction paths 82 may be formed in the crescent 54, aligned in the height direction of the crescent 54.

[0062] The inlet passage is not limited to being formed on the side of the first arc-shaped wall 541 of the crescent 54. For example, as shown in Fig. 7 , the internal gear pump 1 may have an inner inlet passage 83 on the pinion gear 3 side across the crescent 54 and an outer inlet passage 84 on the ring gear 4 side across the crescent 54 by cutting each of the first arc-shaped wall 541 and the second arc-shaped wall 542 of the crescent 54. The inlet 83a of the inner inlet passage 83 is located at the first end 543, and the outlet 83b extends toward the discharge portion 12 along the flow line FL1 of the tip of the pinion gear 3. The inlet 84a of the outer inlet passage 84 is located at the first end 543, and the outlet 84b extends toward the discharge portion 12 along the flow line FL2 of the tip of the ring gear 4. The structure or shape of the inner introduction passage 83 and the structure or shape of the outer introduction passage 84 can employ the various structures or shapes described above.

[0063] Furthermore, the internal gear pump 1 may omit the inner introduction passage on the pinion gear 3 side across the crescent 54 and have only the outer introduction passage on the ring gear 4 side across the crescent 54 .

[0064] Furthermore, the introduction passage is not limited to being formed by cutting the first arc-shaped wall 541 or the second arc-shaped wall 542 of the crescent 54. For example, as shown in FIG. 8A , an introduction passage 85 may be formed inside the crescent 54. Specifically, an inlet 85a of the introduction passage 85 opens at a first end 543 of the crescent 54. The introduction passage 85 extends inside the crescent 54 from the first end 543 toward the discharge portion 12. The introduction passage 85 is connected to an outlet 85b that opens at the first arc-shaped wall 541 of the crescent 54. Because the outlet 85b opens at the first arc-shaped wall 541, it is tangent to the flow path of the tooth tips of the pinion gear 3. The introduction passage 85 allows hydraulic oil that has flowed in from the inlet 85a to flow from the outlet 85b into the tooth grooves of the pinion gear 3.

[0065] The outlet of the introduction path 85 may be opened to the second arc wall 542 instead of the first arc wall 541. The outlet of the introduction path 85 may be opened to both the first arc wall 541 and the second arc wall 542.

[0066] The crescent 54 may be formed by a plurality of members. For example, as shown in Fig. 8(b), the crescent 54 may be formed by a first crescent 545 and a second crescent 546. The number of members forming the crescent 54 is not limited to two, and may be three or more.

[0067] The first crescent 545 is located near the suction portion 11, and the second crescent 546 is located away from the suction portion 11. In the example of FIG. 8(b), the introduction passage 86 is formed by the first crescent 545. A side wall 861 of the first crescent 545 is located radially outward of the flow line FL1 of the tooth tip of the pinion gear 3. The introduction passage 86 extends from the suction portion 11 toward the discharge portion 12 between the side wall 861 and the pinion gear 3. The structure or shape of the introduction passage formed by the first crescent 545 may be any of the various structures or shapes described above.

[0068] The first crescent 545 may form an introduction path between itself and the ring gear 4 , or may form introduction paths both between itself and the pinion gear 3 and between itself and the ring gear 4 .

[0069] The first crescent 545 may not be part of the crescent 54, but may be an introduction path member for forming the introduction path 86. In this case, the first end of the crescent is the first end 543 of the crescent 546. The first end 543 of the crescent 546 is spaced apart from the edge of the outlet of the suction section 11.

[0070] The multiple members forming the crescent may be in contact with each other as shown in Fig. 8(b) or may be spaced apart. For example, in Fig. 9(a), the first crescent 545 and the second crescent 546 are spaced apart.

[0071] 9A, the introduction path 87 extends across both the side wall 861 of the first crescent 545 and the side wall 541 of the second crescent 546.

[0072] As shown in FIG. 9B , a portion of the introduction passage 88 may be formed inside the first crescent 545. Specifically, an inlet 88a of the introduction passage 881 opens at the first end 547 of the first crescent 546. The introduction passage 881 extends inside the first crescent 545 from the first end 547 toward the discharge portion 12. The introduction passage 881 is connected to an outlet 88b that opens at the second end 548 of the first crescent 545. Because the second end 548 of the first crescent 545 and the first end 543 of the second crescent 546 are spaced apart, the outlet 88b communicates with an introduction passage 882 formed by the side surface 541 of the second crescent 546. The introduction passage 882 is tangent to the flow path of the tooth tip of the pinion gear 3. The introduction passage 88, which is composed of the introduction passage 881 and the introduction passage 882, allows the hydraulic oil that has flowed in from the inlet 88a to flow into the tooth grooves of the pinion gear 3.

[0073] 10 shows an internal gear pump 1 having, as inlet passages, a first inlet passage 8 and a second inlet passage 9. The first inlet passage 8 is the same as the inlet passage 8 shown in FIG. 4. The second inlet passage 9 is formed in the gear housing 5.

[0074] The second inlet passage 9 is located radially inward of the crescent 54 and extends circumferentially adjacent to and along the first arc-shaped wall 541 of the crescent 54. The second inlet passage 9 has a groove shape recessed from the first support surface 52. The second inlet passage 9 includes an inlet 9a and an outlet 9b. The inlet 9a opens to the suction portion 11. The outlet 9b opens to the first support surface 52. The outlet 9b extends from the edge of the outlet of the suction portion 11 toward the discharge portion 12 on the first support surface 52.

[0075] The outlet 9b of the second inlet passage 9 contacts the tooth grooves of the pinion gear 3 on the first side surface 32 of the pinion gear 3. When the internal gear pump 1 is in operation, the hydraulic oil that flows into the second inlet passage 9 from the inlet 9a flows out from the outlet 9b into the tooth grooves of the pinion gear 3.

[0076] The hydraulic oil can flow into the tooth grooves of the pinion gear 3 and the tooth grooves of the ring gear 4 through the first inlet passage 8 and the second inlet passage 9. The first inlet passage 8 and the second inlet passage 9 reduce pressure loss in the internal gear pump 1, thereby contributing to an improvement in the maximum rotation speed of the internal gear pump 1.

[0077] The second introduction passage 9 may be formed adjacent to the second arc wall 542 on the radially outer side of the crescent 54. The second introduction passage 9 may also be formed on both the radially inner and outer sides of the crescent 54.

[0078] Furthermore, the second introduction passage 9 may be formed in either the first support surface 52 or the second support surface 61. The second introduction passage 9 may be formed in both the first support surface 52 and the second support surface 61.

[0079] REFERENCE SIGNS LIST 1 internal gear pump 10 housing 13 gear set 2 shaft 3 pinion gear 31 external teeth 32 first side surface (of pinion gear) 33 second side surface (of pinion gear) 4 ring gear 41 internal teeth 43 first side surface (of ring gear) 44 second side surface (of ring gear) 52 first support surface 54 crescent 541 first arc wall 542 second arc wall 543 first end 544 second end 545 first crescent 546 second crescent 547 first end 548 second end 61 second support surface 8 introduction passage 8a inlet 8b outlet 81 introduction passage 82 introduction passage 83 inner introduction passage 83a inlet 83b outlet 84 outer introduction passage 84a Inlet 84b Outlet 85 Introduction path 85a Inlet 85b Outlet 86 Introduction path 87 Introduction path 88 Introduction path 88a Inlet 88b Outlet 881 Introduction path 882 Introduction path 9 Second introduction path 9a Inlet 9b Outlet FL1 Flow line of tip of pinion gear tooth FL2 Flow line of tip of ring gear tooth

Claims

1. An internal gear pump comprising: a gear set including a pinion gear having external teeth and rotated by a shaft, and a ring gear having internal teeth that mesh with the external teeth; a housing having a hydraulic oil suction section and a discharge section and rotatably accommodating the gear set; a fixed crescent located at a point where the pinion gear and the ring gear no longer mesh; an inlet communicating with the suction section; and an outlet between the suction section and the discharge section that is tangent to the line of movement of the tips of the teeth of the pinion gear or the line of movement of the tips of the teeth of the ring gear, and an introduction passage that allows hydraulic oil that has flowed in from the inlet to flow out from the outlet to the tooth grooves of the pinion gear or the tooth grooves of the ring gear.

2. An internal gear pump according to claim 1, wherein the introduction passage is formed in the crescent.

3. An internal gear pump according to claim 2, wherein the crescent has a first arc-shaped wall against which the external teeth abut and a second arc-shaped wall against which the internal teeth abut, and the introduction passage is formed by cutting away at least a portion of at least one of the first arc-shaped wall and the second arc-shaped wall.

4. An internal gear pump according to claim 2 or 3, wherein the crescent extends from a first end in contact with the edge of the suction section to a second end on the discharge section side, and the introduction passage extends from the first end of the crescent towards the discharge section.

5. An internal gear pump according to claim 4, wherein the introduction passage extends from the first end to a position midway between the first end and the second end of the crescent, the distance being equal to or greater than the pitch of the gear in contact with the outlet.

6. An internal gear pump according to any one of claims 1 to 5, wherein the housing has a support surface that is perpendicular to the shaft and supports a side surface of the gear set, and the housing also includes a second inlet opening to the suction portion, and a second outlet opening at least at a location on the support surface between the suction portion and the discharge portion that corresponds to the gap between the tip circle and the root circle of the pinion gear or the gap between the tip circle and the root circle of the ring gear, and further includes a second introduction passage that allows hydraulic oil that has flowed in from the second inlet to flow out from the second outlet into the tooth grooves of the pinion gear or the tooth grooves of the ring gear.

7. An internal gear pump as claimed in claim 6, wherein the housing has as its support surfaces a first support surface that supports a first side surface of the gear set and a second support surface that faces the first support surface and supports a second side surface of the gear set, and the second introduction passage is formed in at least one of the first support surface and the second support surface.

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