Internal gear pump

Abstract

An internal gear pump (1) comprises: a gear set (13) that includes a pinion gear (3) and a ring gear (4); a housing (10); and a fixed crescent (54) that extends from a first end (543) to a second end (544). The housing includes an introduction path 8: that includes inflow ports (811a, 812a) that open to a suction part, and outflow ports (811b, 812b) that at least open at positions corresponding to a space between a tooth tip circle and a tooth bottom circle of the pinion gear or at positions corresponding to a space between a tooth tip circle and a tooth bottom circle of the ring gear, on support surfaces (52, 61) of the housing; and that allows hydraulic oil flowing in from the inflow ports to flow out from the outflow ports to tooth grooves of the pinion gear or tooth 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. This internal gear pump comprises: 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 portion and a discharge portion and rotatably accommodating the gear set; and a fixed crescent extending in an arc from a first end to a second end at a point where the pinion gear and the ring gear no longer mesh; wherein the housing has a support surface that is perpendicular to the shaft and supports the side of the gear set; and the housing also includes an inlet that opens to the suction portion, and an outlet that opens at least to a position on the support surface between the suction portion and the discharge portion that corresponds to between the tip circle and the root circle of the pinion gear or between the tip circle and the root circle of the ring gear, and has an introduction passage that allows the hydraulic oil that flows 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.

[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 opens to the suction portion. The outlet opens at least at a location on the support surface 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. The tip circle is a circle connecting the tips of the gear teeth, and the root circle is a circle connecting the roots of the gear teeth.

[0013] At least a portion of 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 have a groove shape recessed from the support surface of the housing, and the outlet may extend from an edge of the suction portion toward the discharge portion on the support surface.

[0016] The outlet extending from the edge of the suction portion toward the discharge portion reduces the flow resistance of the inlet passage. In addition, because the inlet passage is a groove-shaped passage recessed from the support surface, the contact area between the outlet and the tooth grooves of the pinion gear or the tooth grooves of the ring gear is large. This also reduces the flow resistance of the inlet passage. An inlet passage with low flow resistance suppresses a drop in hydraulic oil pressure at the suction portion and promotes the flow of hydraulic oil from the suction portion into the tooth grooves of the pinion gear or the tooth grooves of the ring gear. This is advantageous for further increasing the maximum rotation speed of the internal gear pump and increasing the discharge flow rate of the internal gear pump.

[0017] The introduction passage may extend from the suction portion to a position midway between the first end and the second end of the crescent, the position being equal to or greater than the pitch of the gear in contact with the outlet.

[0018] 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.

[0019] 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 extend adjacent to the first arc wall and along the first arc wall, or adjacent to the second arc wall and along the second arc wall, at least one of a radially inner position on the support surface with respect to the first arc wall and a radially outer position with respect to the second arc wall.

[0020] A groove-shaped inlet passage adjacent to the first arc wall and extending along the first arc wall, or a groove-shaped inlet passage adjacent to the second arc wall and extending along the second arc wall, has low flow resistance and is therefore highly effective in reducing pressure loss in an internal gear pump.

[0021] The width of the inner introduction passage located radially inward of the first arc wall may be equal to or less than the tooth depth of the pinion gear.

[0022] If the width of the inner guide passage is set equal to or less than the tooth depth of the pinion gear, hydraulic oil will flow efficiently from the guide passage through the inner guide passage into the tooth grooves of the pinion gear. Note that the tooth depth of a gear is the difference between the tip circle and the root circle of the gear.

[0023] The width of the outer introduction passage located radially outward from the second arc wall may be equal to or less than the tooth depth of the ring gear.

[0024] If the width of the outer introduction passage is set to be equal to or less than the tooth height of the ring gear, the hydraulic oil will flow efficiently from the introduction passage through the outer introduction passage into the tooth grooves of the ring gear.

[0025] The depth of the introduction passage may be equal to or less than the depth of the suction portion.

[0026] If the depth of the introduction passage is equal to or less than the depth of the suction portion, the flow resistance of the introduction passage is low, and a drop in the pressure of the hydraulic oil in the suction portion when the internal gear pump is operating at high rotation speeds can be suppressed.

[0027] 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 introduction passage may be formed in at least one of the first support surface and the second support surface.

[0028] Whether the introduction passage is formed on the first support surface or the second support surface, the introduction passage can exert the function of suppressing a drop in the pressure of the hydraulic oil in the suction portion.

[0029] 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.

[0030] 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 introduction path. Fig. 4 is a perspective view of the introduction path. Fig. 5 shows a VV cross-sectional view of Fig. 3. Fig. 6 shows an introduction path according to a modified example. Fig. 7 shows an introduction path according to a modified example. Fig. 8 shows an introduction path according to a modified example.

[0031] 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.

[0032] (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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The pinion gear 3 and the ring gear 4 form a gear set 13 of the internal gear pump 1 .

[0037] 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.

[0038] 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.

[0039] 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 .

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] (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.

[0053] 2, the introduction passage 8 is formed in the housing 10. More specifically, the introduction passage 8 is formed in each of the first support surface 52 of the gear housing 5 and the second support surface 61 of the front cover 6. Hereinafter, the introduction passage 8 formed in the first support surface 52 will be referred to as the first introduction passage 81, and the introduction passage 8 formed in the second support surface 61 will be referred to as the second introduction passage 82.

[0054] 3 or 4 , the first introduction passage 81 includes an inner introduction passage 811 and an outer introduction passage 812. The inner introduction passage 811 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.

[0055] As shown in Figure 4 or Figure 5(a), the inner introduction passage 811 has a groove shape recessed from the first support surface 52. The inner introduction passage 811 includes an inlet 811a and an outlet 811b. The inlet 811a opens to the suction section 11. The inner introduction passage 811 communicates with the suction section 11. The outlet 811b opens to the first support surface 52. The outlet 811b extends from the edge of the outlet of the suction section 11 toward the discharge section 12 on the first support surface 52.

[0056] As shown by the dashed line in FIG. 3 , the outer introduction passage 812 is located radially outward of the crescent 54 and extends circumferentially adjacent to and along the second arc-shaped wall 542 of the crescent 54. The shape of the outer introduction passage 812 is substantially the same as the shape of the inner introduction passage 811. Like the inner introduction passage 811, the outer introduction passage 812 also has a groove shape recessed from the first support surface 52. The outer introduction passage 812 includes an inlet 812a and an outlet 812b. The inlet 812a opens to the suction section 11. The outlet 812b opens to the first support surface 52. The outlet 812b extends from the edge of the outlet of the suction section 11 toward the discharge section 12 on the first support surface 52.

[0057] The shape of the second inlet passage 82 is substantially the same as the shape of the first inlet passage 81. As shown by the solid line in the left diagram of Fig. 2 , the second inlet passage 82 includes an inner inlet passage 821 on the inside in the radial direction across the crescent 54, and an outer inlet passage 822 on the outside. An inlet 821a of the inner inlet passage 821 opens to the suction section 11, and an outlet 821b opens to the second support surface 61. The outer inlet passage 822 is similar to the inner inlet passage 821, and an inlet 822a of the outer inlet passage 822 opens to the suction section 11, and an outlet 822b opens to the second support surface 61.

[0058] The outlets 811b, 821b of the inner introduction passages 811, 821 described above are in contact with the tooth grooves of the pinion gear 3. When the internal gear pump 1 is in operation, the hydraulic oil that flows into the inner introduction passages 811, 821 from the inlets 811a, 821a flows out from the outlets 811b, 821b into the tooth grooves of the pinion gear 3. In addition, the outlets 812b, 822b of the outer introduction passages 812, 822 are in contact with the tooth grooves of the ring gear 4. When the internal gear pump 1 is in operation, the hydraulic oil that flows into the outer introduction passages 812, 822 from the inlets 812a, 822a flows out from the outlets 812b, 822b into the tooth grooves of the ring gear 4. In this way, the hydraulic oil not only flows into the tooth grooves of the pinion gear 3 and the ring gear 4 at the suction portion 11, but also through the inner introduction passage 811 and the outer introduction passage 812. The introduction passage 8 reduces pressure loss in the internal gear pump 1.

[0059] 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.

[0060] Furthermore, the introduction path 8 has a groove shape recessed from the first support surface 52 or the second support surface 61, and the outlets 811b, 812b, 821b, or 822b extend circumferentially on the first support surface 52 or the second support surface 61. The flow resistance of the introduction path 8 is low. Furthermore, because the introduction path 8 has a groove shape recessed from the first support surface 52 or the second support surface 61, the contact areas between the outlets 811b, 821b and the tooth grooves of the pinion gear 3, and between the outlets 812b, 822b and the tooth grooves of the ring gear 4 are large. This also reduces the flow resistance of the introduction path 8. The introduction path 8 with low flow resistance can further suppress a decrease in the pressure of the hydraulic oil in the suction portion 11 and promote the flow of hydraulic oil from the suction portion 11 into the tooth grooves of the pinion gear 3 or the tooth grooves of the ring gear 4. The groove-shaped introduction passage 8 makes it possible to further increase the maximum rotation speed of the internal gear pump 1 and is advantageous in increasing the discharge flow rate of the internal gear pump 1 .

[0061] 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 811b or the pitch P of the ring gear 4 that contacts the outlet 812b. Note that the circumferential length is expressed here as an angle θ about the rotation axis C1.

[0062] 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 that flows in through the inlet passage 8 is small, and the inlet passage 8 is not effective in reducing pressure loss. 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 pressure loss. If the length of the inlet passage 8 is equal to or greater than the pitch P of the pinion gear 3 or ring gear 4, the outlet 811b or 812b always communicates with the tooth grooves of the gears 3 and 4, allowing the hydraulic oil to flow into the tooth grooves of the gears 3 and 4.

[0063] As shown in Fig. 5, the depth D of the groove-shaped introduction path 8 may be equal to or less than the depth D1 of the suction portion 11. For example, as shown in Fig. 5(a), the depth D of the introduction path 8 may be approximately half the depth D1 of the suction portion 11 (i.e., D ≒ D1 / 2). Alternatively, as shown in Fig. 5(b), the depth D of the introduction path 8 may be approximately the same as the depth D1 of the suction portion 11 (i.e., D ≒ D1).

[0064] If the depth D of the introduction passage 8 is equal to or less than the depth D1 of the suction portion 11, the flow resistance of the introduction passage 8 is low, and the decrease in pressure of the hydraulic oil in the suction portion 11 can be suppressed.

[0065] 5(a) or 5(b), the bottom surface of the introduction path 8 may be inclined so as to approach the support surfaces 52, 61 with increasing distance from the suction portion 11. Alternatively, the bottom surface of the introduction path 8 may be straight without being inclined, as shown in FIG.

[0066] In order to reduce the flow resistance of the introduction path 8, a part of the wall surface of the introduction path 8 may be formed as a curved surface, as shown in FIG. 5(d).

[0067] 3, the radial width W of the introduction passage 8 may be equal to or less than the tooth depth of the pinion gear 3 and the tooth depth of the ring gear 4. The width W of the inner introduction passage 811 in FIG. 3 is equal to or approximately equal to the tooth depth of the pinion gear 3, and the width W of the outer introduction passage 812 is equal to or approximately equal to the tooth depth of the ring gear 4.

[0068] The introduction passage 8 has the function of allowing hydraulic oil to flow into the tooth grooves of the pinion gear 3 or the tooth grooves of the ring gear 4. If the width of the inner introduction passages 811, 821 is set to be equal to or smaller than the tooth height of the pinion gear 3 and the width of the outer introduction passages 812, 822 is set to be equal to or smaller than the tooth height of the ring gear 4, hydraulic oil will flow efficiently from the introduction passage 8 into the tooth grooves of the pinion gear 3 or the tooth grooves of the ring gear 4.

[0069] The width W of the inner introduction passages 811, 821 may be narrower than the tooth depth of the pinion gear 3. The width W of the outer introduction passages 812, 822 may be narrower than the tooth depth of the ring gear 4. Furthermore, as shown in Figure 6, it is not excluded that the width W of the inner introduction passages 811, 821 exceeds the tooth depth of the pinion gear 3 and the width W of the outer introduction passages 812, 822 exceeds the tooth depth of the ring gear 4.

[0070] Furthermore, the width W of the introduction path 8 is not limited to a constant width. For example, as shown in Fig. 7 , the width W of the introduction path 8 may gradually narrow with increasing distance from the suction portion 11. Furthermore, the width W of the introduction path 8 may gradually widen with increasing distance from the suction portion 11.

[0071] The structure or shape of the inner introduction channels 811, 821 does not have to be the same as the structure or shape of the outer introduction channels 812, 822. For example, the depth D of the inner introduction channels 811, 821 may be different from the depth D of the outer introduction channels 812, 822. Furthermore, the width W of the inner introduction channels 811, 821 may be different from the width W of the outer introduction channels 812, 822.

[0072] The inscribed gear pump 1 is not limited to having both the inner inlet passages 811, 821 and the outer inlet passages 812, 822 as the inlet passages 8. The inscribed gear pump 1 may have only the inner inlet passages 811, 821 or only the outer inlet passages 812, 822.

[0073] The structure or shape of the first introduction passage 81 of the first support surface 52 and the structure or shape of the second introduction passage 82 of the second support surface 61 do not have to be the same.

[0074] Furthermore, the inlet passage 8 of the internal gear pump 1 is not limited to being formed on both the first support surface 52 and the second support surface 61. The inlet passage 8 may be only the first inlet passage 81 on the first support surface 52, or only the second inlet passage 82 on the second support surface 61.

[0075] The introduction path 8 is not limited to a groove shape recessed from the support surfaces 52, 61. For example, as shown in Fig. 8, the introduction path 8 may have a structure including an inlet 8a communicating with the suction portion 11 and an outlet 8b opening to the support surface 52, with an intermediate portion between the inlet 8a and the outlet 8b formed inside the gear housing 5 (or the front cover 6).

[0076] 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 61 second support surface 8 introduction passage 81 first introduction passage 82 second introduction passage 811 inner introduction passage 811a inlet 811b outlet 812 outer introduction passage 812a inlet 812b outlet 821 inner introduction passage 821a inlet 821b outlet 822 Outer introduction path 822a Inlet 822b Outlet

Claims

1. An internal gear pump comprising: a gear set including a pinion gear with external teeth rotated by a shaft, and a ring gear with internal teeth that mesh with the external teeth; a housing having a hydraulic oil suction section and a discharge section and rotatably housing the gear set; and a fixed crescent extending in an arc from a first end to a second end at a location where the pinion gear and the ring gear no longer mesh; wherein the housing has a support surface that is perpendicular to the shaft and supports a side of the gear set; the housing also has an inlet that opens to the suction section, and an outlet that opens at least at a location on the support surface between the suction section and the discharge section 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 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 has a groove shape recessed from the support surface of the housing, and the outlet port extends from the edge of the suction portion towards the discharge portion on the support surface.

3. An internal gear pump according to claim 2, wherein the introduction passage extends from the suction portion within a range equal to or greater than the pitch of the gear in contact with the outlet and to a position midway between the first end and the second end of the crescent.

4. An internal gear pump according to claim 2 or 3, 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 extends adjacent to and along the first arc-shaped wall, or adjacent to and along the second arc-shaped wall, at least one of a position on the support surface that is radially inward from the first arc-shaped wall and a position on the support surface that is radially outward from the second arc-shaped wall.

5. An internal gear pump according to claim 4, wherein the width of the inner introduction passage located radially inward of the first arc wall is equal to or less than the tooth depth of the pinion gear.

6. An internal gear pump according to claim 4 or 5, wherein the width of the outer introduction passage located radially outward from the second arc wall is equal to or less than the tooth depth of the ring gear.

7. The internal gear pump according to claim 2, wherein the depth of the introduction passage is equal to or less than the depth of the suction portion.

8. An internal gear pump according to any one of claims 1 to 7, wherein the housing has, 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 introduction passage is formed in at least one of the first support surface and the second support surface.

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