Internal gear pump

Abstract

To provide an internal gear pump that is excellent in quietness.SOLUTION: An internal gear pump includes: an outer gear including an inner tooth; and an inner gear including an inner tooth groove meshing with the inner tooth. The inner tooth groove includes a bottom part forming a clearance to a tip of the inner tooth while a sealed space surrounded by the inner tooth and the inner tooth groove becomes minimum. The bottom part includes a shape projecting in a direction separating from an axis of the inner gear when being viewed from a direction along the axis.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an internal gear pump. [Background technology]

[0002] Patent Document 1 discloses an internal gear pump including an inner gear and an annular outer gear that houses the inner gear. The inner gear of the internal gear pump has a plurality of external teeth on its outer circumference. The outer gear has a plurality of internal teeth on its inner circumference. An inner tooth groove is formed between two adjacent external teeth, with which the internal teeth of the outer gear mesh. The outer gear rotates as the inner gear rotates. The outer gear rotates in the same direction as the inner gear.

[0003] The inner gear and the outer gear are accommodated in a housing. The housing has an inlet port which is an inlet for a fluid, and an outlet port which is an outlet for the fluid. The inlet port and the outlet port, for example, penetrate the housing in a direction along the axis of the inner gear. The shapes of the inlet port and the outlet port when viewed from the direction along the axis of the inner gear are, for example, approximately arc shapes extending in the rotation direction of the inner gear.

[0004] In an internal gear pump, a sealed space surrounded by the internal teeth and the inner tooth grooves is formed near the end of the outlet port. When the internal teeth are positioned between the end of the outlet port and the start of the inlet port, the sealed space is at its smallest. As the inner gear and outer gear rotate, the sealed space gradually becomes larger and connects to the inlet port. As the sealed space becomes larger, negative pressure is created in the sealed space, and fluid is sucked into the sealed space from the inlet port. The fluid sucked into the inside of the internal gear is compressed as the inner gear and outer gear rotate, and is sent out to the outside of the internal gear pump. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-98730 A Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional internal gear pumps make a relatively loud noise when in operation, so there is a need to improve the quietness of internal gear pumps.

[0007] An object of the present disclosure is to provide an internal gear pump that is highly quiet. [Means for solving the problem]

[0008] The internal gear pump of the present disclosure comprises: an outer gear having internal teeth; an inner gear having an inner tooth groove that meshes with the internal teeth, the inner tooth groove has a bottom portion that forms a gap between the bottom portion and a tip portion of the inner tooth when a sealed space surrounded by the inner tooth and the inner tooth groove is minimized, When viewed in a direction along the axis of the inner gear, the bottom portion has a shape that is convex in a direction away from the axis. Effect of the Invention

[0009] The internal gear pump of the present disclosure is highly quiet. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic plan view of an internal gear pump according to an embodiment. [Diagram 2] FIG. 2 is a partially enlarged view of a portion where the internal teeth and the inner tooth grooves mesh with each other in the internal gear pump shown in FIG. [Diagram 3] FIG. 3 is a partially enlarged view of a portion where the internal teeth and the inner tooth grooves mesh with each other in the internal gear pump of the comparative example described in Test Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Description of the embodiments of the present disclosure] The inventors have investigated the causes of noise in internal gear pumps and found that one of the causes of noise is that the internal pressure in the sealed space becomes too high when the sealed space surrounded by the internal teeth and the inner tooth grooves becomes smallest.

[0012] In the conventional internal gear pump, the bottom of the inner tooth groove has a shape that is convex in a direction toward the axis of the inner gear. In addition, in the conventional internal gear pump, when the sealed space surrounded by the internal teeth and the inner tooth groove is minimized, no substantial gap is formed between the tip of the internal tooth and the bottom of the inner tooth groove, and the sealed space is divided into a first space and a second space by the tip of the internal tooth. Here, the first space is a space that is in front of the tip of the internal tooth in the rotation direction of the inner gear, and the second space is a space behind the tip of the internal tooth in the rotation direction. When the inner gear further rotates from the state where the sealed space is minimized, the second space becomes larger, so that the sealed space consisting of the first space and the second space becomes larger, but the first space becomes smaller, and the internal pressure of the first space further increases. When the internal pressure of the first space becomes too high, the first space presses the inner gear and the outer gear in a direction away from each other. As a result, the outer gear and the inner gear come into intermittent contact with each other in a distal region on the opposite side of the axis of the inner gear from the high-pressure first space, generating noise.

[0013] Based on the above findings, the inventors have completed the internal gear pump of the present disclosure.

[0014] <1> The internal gear pump of the present disclosure comprises: an outer gear having internal teeth; an inner gear having an inner tooth groove that meshes with the internal teeth, the inner tooth groove has a bottom portion that forms a gap between the bottom portion and a tip portion of the inner tooth when a sealed space surrounded by the inner tooth and the inner tooth groove is minimized, When viewed in a direction along the axis of the inner gear, the bottom portion has a shape that is convex in a direction away from the axis.

[0015] The gap between the tips of the internal teeth and the bottom of the inner tooth groove is a gap that allows fluids in two areas that sandwich the tips of the internal teeth in the sealed space to communicate with each other. Even in conventional internal gear pumps, a minute gap of about 0.1 mm or less is formed between the tips of the internal teeth and the inner tooth groove when the sealed space is at its smallest, but the gap is substantially sealed by the fluid. In other words, in conventional internal gear pumps, no substantial gap is formed between the tips of the internal teeth and the inner tooth groove when the sealed space is at its smallest.

[0016] In the internal gear pump of the present disclosure, a gap is provided between the tip of the internal tooth and the inner tooth groove, which prevents direct contact between the internal tooth and the inner tooth groove, thereby suppressing noise when the internal gear pump is driven. In addition, the sealed space is not divided into two by the internal tooth, and the internal pressure of the sealed space does not become too high. Since the internal pressure of the sealed space does not become too high, the force with which the sealed space presses the inner gear and the outer gear in a direction away from each other does not become too high. Therefore, in the distal region on the opposite side of the axis of the inner gear to the high-pressure sealed space, strong contact between the outer gear and the inner gear can be suppressed, and noise generated in the distal region can be suppressed.

[0017] By providing a shape with an outwardly convex bottom, even if a gap is formed between the tip of the internal tooth and the bottom of the inner tooth groove, the root circle virtually connecting the bottoms of the multiple inner tooth grooves does not become too small. This ensures the strength of the inner gear except for the outer teeth. In addition, the leakage distance of the fluid from the bottom of the inner tooth groove to the shaft that rotates the inner gear can be increased.

[0018] <2> the above <1> In the internal gear pump described in When viewed in a direction along the axis, the bottom portion may have an arc shape centered on the axis.

[0019] According to the above-mentioned configuration, the leakage distance from the bottom of each sealed space to the shaft of the inner gear becomes constant. Furthermore, since the bottom has an arc shape centered on the axis, the rotation of the inner gear becomes stable.

[0020] <3> the above <1> or <2> In the internal gear pump described in When viewed from a direction along the axis, the inner tooth groove includes a non-contact portion with which the inner tooth does not come into contact when the internal gear pump is driven, the non-contact portion includes the bottom portion and an arc portion connected to the bottom portion, The arc portion may have a shape that is convex in a direction away from the internal teeth.

[0021] According to the above configuration, even if the bottom portion has a shape that is convex in the direction away from the axis of the inner gear, the width of the portion of the sealed space close to the bottom portion can be easily increased, which results in a larger sealed space and prevents the internal pressure of the sealed space from becoming too high.

[0022] <4> the above <3> In the internal gear pump described in The arc portion is disposed closer to the internal teeth than the first straight line and the second straight line are, the first straight line is a straight line passing through the axis and an end point of the non-contact portion, The second straight line may be a tangent to the inner tooth space at the end point.

[0023] According to the above configuration, the sealed space can be enlarged while preventing the roots of the outer teeth of the inner gear from becoming too thin.

[0024] <5> the above <1> from <5> In the internal gear pump according to any one of the preceding claims, When viewed in a direction along the axis, the length of the gap may be more than 0.1 mm and not more than 0.5 mm.

[0025] If the length of the gap as viewed along the axis exceeds 0.1 mm, it is possible to reliably prevent the sealed space from being divided into two by the internal teeth when the sealed space is at its smallest. If the length of the gap is 0.5 mm or less, the internal gear pump will not become too large, and the internal pressure of the sealed space will not become too low when the sealed space is at its smallest.

[0026] [Details of the embodiment of the present disclosure] Specific examples of the internal gear pump of the present disclosure will be described below with reference to the drawings. The same reference numerals in the drawings indicate the same or equivalent parts. The sizes of the members shown in each drawing are expressed for the purpose of clarifying the description and do not necessarily represent the actual dimensions. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0027] <Embodiment 1> The internal gear pump 1 of this example shown in Fig. 1 includes an inner gear 2, an outer gear 4, and a housing 5. One of the features of the internal gear pump 1 of this example is the shape of the inner tooth groove 29 of the inner gear 2. Below, each component of the internal gear pump 1 will be described, and then the shape of the inner tooth groove 29 in this example will be described in detail.

[0028] <Inner and outer gear> The inner gear 2 is fitted onto the shaft 10 and rotates with the rotation of the shaft 10. The rotation direction of the inner gear 2 in Fig. 1 is clockwise. The axis of rotation of the shaft 10 coincides with the axis of rotation 2S of the inner gear 2. In Fig. 1, the axis 2S is indicated by a black dot.

[0029] The inner gear 2 is a disk-shaped gear having a plurality of external teeth 20. The external teeth 20 extend in a radial direction away from the axis 2S. An inner tooth groove 29 is formed between two external teeth 20, 20 adjacent to each other in the rotational direction of the inner gear 2. In this example, the portion from the tip of an external tooth 20 to the tip of another external tooth 20 adjacent to that external tooth 20 is the inner tooth groove 29. The tooth profile of the inner gear 2 composed of the external teeth 20 and the inner tooth groove 29 is formed by, for example, a trochoid curve or a geocloid (registered trademark) curve.

[0030] The outer gear 4 is an annular gear having a plurality of internal teeth 40. The internal teeth 40 extend in a centripetal direction toward the axis 4S. The inner gear 2 is disposed inside the outer gear 4. The outer gear 4 is fitted into a cylindrical internal space of a housing 5, which will be described later. The outer gear 4 rotates while contacting an inner peripheral surface 50 in the internal space. The rotation direction of the outer gear 4 is the same as the rotation direction of the inner gear 2. The rotation axis 4S of the outer gear 4 coincides with the central axis of the inner peripheral surface 50. The axis 4S is disposed at a position offset from the axis 2S of the inner gear 2. The axis 4S is parallel to the axis 2S. In FIG. 1, the axis 4S is indicated by a black dot.

[0031] The inner teeth 40 of the outer gear 4 mesh with the inner tooth grooves 29 of the inner gear 2. The number of the inner teeth 40 is one more than the number of the inner tooth grooves 29. Therefore, as the inner gear 2 and the outer gear 4 rotate, the position of the inner tooth groove 29 with which the inner tooth 40 meshes shifts in the opposite direction to the rotation direction of the inner gear 2 and the outer gear 4. In other words, every time the inner gear 2 makes one revolution, the inner tooth 40 meshes with another inner tooth groove 29 that is shifted in the opposite direction from the inner tooth groove 29 with which it initially meshed. In this example, the opposite direction is the counterclockwise direction. In the state in which the inner tooth 40 meshes with the inner tooth groove 29, the space surrounded by the inner tooth 40 and the inner tooth groove 29 is referred to as a sealed space 3 in this specification.

[0032] An outer tooth groove 49 is formed between two internal teeth 40, 40 adjacent to each other in the rotational direction of the outer gear 4. In this example, the outer tooth groove 49 is a portion from the tip of an internal tooth 40 to the tip of another internal tooth 40 adjacent to the internal tooth 40. The external tooth 20 of the inner gear 2 meshes with the outer tooth groove 49 of the outer gear 4. In this example, the number of outer tooth grooves 49 is one more than the number of external teeth 20. Therefore, the position of the outer tooth groove 49 with which the external tooth 20 meshes shifts in the rotational direction of the inner gear 2 and the outer gear 4. In other words, every time the inner gear 2 makes one revolution, the external tooth 20 meshes with another outer tooth groove 49 that is shifted by one in the rotational direction from the outer tooth groove 49 with which it was initially meshed.

[0033] Housing The housing 5 houses the inner gear 2 and the outer gear 4. The contour line of an inner circumferential surface 50 of the housing 5 when viewed along the axes 2S, 4S is circular. The inner diameter of the inner circumferential surface 50 is slightly larger than the outer diameter of the outer gear 4. Therefore, the outer gear 4 can rotate while the outer circumferential surface of the outer gear 4 is in contact with the inner circumferential surface 50. The rotation of the outer gear 4 is stabilized by being supported by the inner circumferential surface 50.

[0034] The housing 5 includes a first cover and a second cover, not shown. The first cover is disposed in front of the inner gear 2 and the outer gear 4 on the paper, and the second cover is disposed behind the inner gear 2 and the outer gear 4 on the paper. In this example, an inlet port 51 and an outlet port 52 are provided in the second cover. In FIG. 1, the inlet port 51 and the outlet port 52 are indicated by dashed lines. In this example, the inlet port 51 and the outlet port 52 extend in a direction along the axes 2S and 4S and penetrate the second cover.

[0035] The inlet port 51 is a flow path for introducing a fluid from the outside to the inside of the internal gear pump 1. The outlet port 52 is a flow path for discharging a fluid from the inside to the outside of the internal gear pump 1. The fluid may be a gas or a liquid. In this example, the fluid is machine oil.

[0036] The inlet port 51 and the outlet port 52, as viewed along the axis 2S, have a roughly arc shape extending in the rotational direction of the inner gear 2. The inlet port 51 and the outlet port 52 are disposed at symmetrical positions across the axis 2S. The width of the inlet port 51, as viewed along the axis 2S, becomes wider in the direction of rotation. The width of the outlet port 52, as viewed along the axis 2S, gradually becomes narrower in the direction of rotation.

[0037] The inner radii of the inlet port 51 and the outlet port 52 as viewed in a direction along the axis 2S are smaller than the radius of a root circle including a bottom 80 of an inner tooth groove 29 described later.

[0038] <Inner tooth groove shape> Before referring to the shape of the inner tooth groove 29 of the inner gear 2, an explanation will be given of the sealed space 3 surrounded by the inner teeth 40 of the outer gear 4 and the inner tooth groove 29. In this explanation, the internal gear pump 1 is likened to a clock face centered on the axis 4S, and a position in the internal gear pump 1 is identified.

[0039] When the internal teeth 40 are at the 12 o'clock position of the internal gear pump 1, the internal teeth 40 mesh with the inner tooth grooves 29, and a sealed space 3 is formed between the internal teeth 40 and the inner tooth grooves 29. As the inner gear 2 and the outer gear 4 rotate clockwise from this state, the internal teeth 40 move away from the inner tooth grooves 29. From the 2 o'clock position to the 5 o'clock position of the internal gear pump 1, the space between the internal teeth 40 and the inner tooth grooves 29 is connected to the space between another internal tooth 40 and another inner tooth groove 29. In other words, the sealed space 3 surrounded by one internal tooth 40 and one inner tooth groove 29 no longer exists. The internal teeth 40 move away from the inner tooth grooves 29 around the 6 o'clock position of the internal gear pump 1, and start to mesh with another inner tooth groove 29 again around the 7 o'clock position of the internal gear pump 1. As the inner gear 2 and the outer gear 4 further rotate, a sealed space 3 surrounded by the internal teeth 40 and the inner tooth grooves 29 begins to be formed near the 11 o'clock position of the internal gear pump 1 .

[0040] In the internal gear pump 1 of this embodiment, the sealed space 3 is smallest when the internal teeth 40 are disposed at the 12 o'clock position. That is, the volume of the sealed space 3 is smallest when the internal teeth 40 are disposed between the end of the outlet port 52 and the start of the inlet port 51. When the sealed space 3 is smallest, as shown by the dashed line in Fig. 1, a bisector that bisects the internal teeth 40 in the rotational direction of the outer gear 4 coincides with a bisector that bisects the inner tooth groove 29 in the rotational direction of the inner gear 2. Fig. 2 is a partially enlarged view for explaining the state of the internal teeth 40 and the inner tooth groove 29 when the sealed space 3 is smallest.

[0041] 2, when the volume of the sealed space 3 is at a minimum, the area of ​​the sealed space 3 as viewed from the direction along the axis 2S is also at a minimum. In the state where the sealed space 3 is at its minimum, the inner tooth groove 29 of this example has a bottom 80 that forms a gap G with the tip 40P of the internal tooth 40. The tip 40P is the intersection of the contour line of the internal tooth 40 and a bisector 40L that bisects the internal tooth 40 in the rotational direction of the outer gear 4. The gap G is a gap that allows fluid communication between two regions in the sealed space 3 that sandwich the tip 40P of the internal tooth 40.

[0042] The presence of the gap G suppresses direct contact between the internal teeth 40 and the inner tooth grooves 29, so that noise during operation of the internal gear pump 1 can be suppressed. In addition, the sealed space 3 is not divided into two by the internal teeth 40, so that the internal pressure of the sealed space 3 does not become too high. Since the internal pressure of the sealed space 3 does not become too high, the force with which the sealed space 3 presses the inner gear 2 and the outer gear 4 in a direction away from each other does not become too high. Therefore, it is possible to suppress strong contact between the outer gear 4 and the inner gear 2 in a distal region on the opposite side of the high-pressure sealed space 3 across the axis 2S of the inner gear 2, for example, near the 7 o'clock position of the internal gear pump 1 in FIG. 1. As a result, it is possible to suppress the generation of noise generated in the distal region, and thus the noise during operation of the internal gear pump can be suppressed.

[0043] The length of the gap G is, for example, more than 0.1 mm and 0.5 mm or less. The length of the gap G in this example is the shortest distance between the internal teeth 40 and the bottom 80 of the inner tooth groove 29 in a state in which the internal teeth 40 and the inner tooth groove 29 are arranged so that the sealed space 3 is minimized and the internal gear pump 1 is not driven. In a state in which the internal gear pump 1 is driven, the length of the gap G may change slightly due to the pressure of the fluid. If the length of the gap G is more than 0.1 mm, the sealed space 3 can be reliably prevented from being divided into two by the internal teeth 40. If the length of the gap G is 0.5 mm or less, the internal gear pump 1 does not become too large, and the internal pressure of the sealed space 3 when the sealed space 3 is minimized does not become too low. The lower limit of the length of the gap G may be 0.15 mm, 0.2 mm, or 0.3 mm. On the other hand, the upper limit of the length of the gap G may be 0.45 mm or 0.4 mm. The length of the gap G may be in the range of, for example, 0.15 mm to 0.5 mm, or 0.2 mm to 0.4 mm. The length of the gap G in this example is 0.3 mm.

[0044] The bottom 80 has a shape that is convex in a direction away from the axis 2S when viewed from the direction along the axis 2S of the inner gear 2. In FIG. 2, the bottom 80 has a shape that is convex upward on the paper. By having the bottom 80 have a shape that is convex outward, even if a gap G is formed between the tip 40P of the internal tooth 40 and the bottom 80 of the inner tooth groove 29, the tooth bottom circle (see the two-dot chain line) that virtually connects the bottoms of the multiple inner tooth grooves 29 does not become too small. Therefore, the strength of the part of the inner gear 2 excluding the external teeth 20 can be ensured. In addition, the leakage distance of the fluid from the bottom of the inner tooth groove 29 toward the shaft 10 that rotates the inner gear 2 can be increased.

[0045] In this example, the bottom portion 80 has an arc shape (see the two-dot chain line) centered on the axis 2S when viewed in a direction along the axis 2S. The arc of the bottom portion 80 constitutes a part of the root circle. In other words, the radius of the bottom portion 80 coincides with the radius of the root circle. The inner gear 2 having the bottom portion 80 of this shape has a geometrically regular shape, and the rotation of the inner gear 2 is stable.

[0046] When viewed in a direction along the axis 2S, the inner tooth groove 29 has a non-contact portion 8 with which the internal teeth 40 do not come into contact when the internal gear pump 1 is in operation. The non-contact portion 8 is determined by the shapes and dimensions of the inner gear 2 and the outer gear 4. The portion other than the non-contact portion 8 is a contact portion 9 that comes into contact with the internal teeth 40 at some point when the internal gear pump 1 is in operation. The non-contact portion 8 is sandwiched between two contact portions 9, 9. The non-contact portion 8 includes the bottom portion 80 described above.

[0047] The non-contact portion 8 in this example includes two arc portions 81 connected to the bottom portion 80. In this example, the non-contact portion 8 further includes two straight portions 82 connected to each of the arc portions 81. The two arc portions 81, 81 are symmetrical with respect to the bottom portion 80. The two straight portions 82, 82 are also symmetrical with respect to the bottom portion 80.

[0048] The arc portion 81 has a shape that is convex in a direction away from the internal teeth 40. The arc portion 81 and the arc-shaped bottom portion 80 are smoothly connected. In other words, no angle is formed between the arc portion 81 and the bottom portion 80. The arc portion 81 increases the width of the portion of the sealed space 3 near the bottom portion 80, and the left-right length in FIG. 2. As a result, the sealed space 3 becomes larger, and the internal pressure of the sealed space 3 is prevented from becoming too high.

[0049] In this example, the arc portion 81 is disposed closer to the internal tooth 40 than the first straight line 91 and the second straight line 92. The first straight line 91 is a straight line passing through the axis 2S and an end point 8E of the non-contact portion 8. The second straight line 92 is a tangent to the inner tooth groove 29 at the end point 8E. The end point 8E is a boundary point between the non-contact portion 8 and the contact portion 9.

[0050] The end point 8E can be identified by examining the specifications of the internal gear pump 1 or the shape and dimensions of an actual product. The end point 8E thus determined is the theoretical end point 8E. Taking into account the manufacturing error of the internal gear pump 1, the end point 8E may be a point offset 0.5 mm downward from the theoretical end point 8E. Specifically, a horizontal line including the theoretical end point 8E is drawn. The horizontal line is a line perpendicular to the vertical line connecting the axis 2S (FIG. 1) and the center of the width of the internal teeth 40. A parallel line parallel to the horizontal line is drawn at a position closer to the axis 2S than the horizontal line. The intersection of the parallel line and the inner tooth groove 29 is set as the end point 8E, and a first straight line 91 and a second straight line 92 are drawn.

[0051] By positioning the arc portion 81 closer to the internal teeth 40 than the first straight line 91 and the second straight line 92, the sealed space 3 can be enlarged while preventing the roots of the external teeth 20 of the inner gear 2 from becoming too thin.

[0052] <Test Example> In the test example, the internal gear pump 1 described in the first embodiment and the internal gear pump 100 of the comparative example shown in FIG. 3 were produced, and the volumetric efficiency and sound pressure of each internal gear pump 1,100 were measured. The volumetric efficiency is a percentage obtained by dividing the flow rate actually discharged from the internal gear pump 1,100 by the theoretical flow rate. The theoretical flow rate is the maximum flow rate of the internal gear pump 1,100 calculated from the shapes and dimensions of the inner gear 2 and the outer gear 4. The sound pressure was measured at a position 100 mm away from the surface of the internal gear pump 1,100 using a commercially available microphone device. The unit of sound pressure is decibels (dB).

[0053] The internal gear pump 100 of the comparative example includes an inner gear 2 and an outer gear 4, similar to the internal gear pump 1 of the first embodiment. The shape of the internal teeth 40 of the outer gear 4 is the same as that of the first embodiment. Meanwhile, the bottom 110 of the inner tooth groove 29 of the inner gear 2 has a shape that is convex toward the axis 2S. In this internal gear pump 100, no substantial gap is formed between the tip end 40P of the internal teeth 40 and the bottom 110 of the inner tooth groove 29.

[0054] The internal gear pump 1 of the first embodiment and the internal gear pump 100 of the comparative example differ only in the shape of the inner tooth groove 29, and this difference results in a difference in the size of the sealed space 3. The length of the gap G in the internal gear pump 1 is 0.3 mm, and the size of the sealed space 3, i.e., the area of ​​the sealed space 3 as viewed in the direction along the axis 2S, is 2.89 mm. 2 On the other hand, in the internal gear pump 100, the sealed space 3 is divided into a first space and a second space by the tip 40P of the internal teeth 40, and the size of the sealed space 3, that is, the total area of ​​the first space and the second space as viewed in the direction along the axis 2S, is 1.86 mm 2 It was.

[0055] As a result of the test, the internal gear pump 1 of the first embodiment had a volumetric efficiency of 94.0% and a sound pressure of 63.0 dB. On the other hand, the internal gear pump 100 of the comparative example had a volumetric efficiency of 94.9% and a sound pressure of 67.1 dB. From these results, it was found that the internal gear pump 1 of this example had a slightly lower volumetric efficiency than the internal gear pump 100 of the comparative example, but could significantly reduce the sound pressure. The reason for the decrease in the volumetric efficiency of the internal gear pump 1 is presumed to be that the enclosed space 3 became larger, and therefore the negative pressure in the enclosed space 3 became smaller when the enclosed space 3 communicated with the inlet port 51. [Explanation of symbols]

[0056] 1. Internal gear pump 10 Shaft 2. Inner Gear 2S axis 20 Outer teeth 29 Inner tooth groove 3 Closed space 4 Outer Gear 4S axis 40 Inner teeth 40L bisector 40P Tip 49 Outer tooth space 5. Housing 50 Inner surface 51 Inlet port 52 Outlet Port 8 Non-contact part 8E Endpoint 80 bottom 81 Arc section 82 Straight section 9 Contact Part 91 First straight line 92 Second straight line 100 Comparative internal gear pump 110 Bottom G Gap

Claims

1. an outer gear having internal teeth; an inner gear having an inner tooth groove that meshes with the internal teeth, the inner tooth groove has a bottom portion that forms a gap between the bottom portion and a tip portion of the inner tooth when a sealed space surrounded by the inner tooth and the inner tooth groove is minimized, When viewed from a direction along the axis of the inner gear, the bottom portion has a shape that is convex in a direction away from the axis. Internal gear pump.

2. The internal gear pump according to claim 1 , wherein the bottom portion has an arc shape centered on the axis when viewed along the axis.

3. When viewed from a direction along the axis, the inner tooth groove includes a non-contact portion with which the inner tooth does not come into contact when the internal gear pump is driven, the non-contact portion includes the bottom portion and an arc portion connected to the bottom portion, The internal gear pump according to claim 1 or 2, wherein the arc portion has a shape that is convex in a direction away from the internal teeth.

4. The arc portion is disposed closer to the internal teeth than the first straight line and the second straight line are, the first straight line is a straight line passing through the axis and an end point of the non-contact portion, The internal gear pump according to claim 3 , wherein the second straight line is a tangent to the inner tooth groove at the end point.

5. The internal gear pump according to claim 1 or 2, wherein a length of the gap is greater than 0.1 mm and not greater than 0.5 mm when viewed along the axis.

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