JP2024053919A - Tooth shape evaluation method of internal gear pump and tooth shape forming method - Google Patents

Abstract

To make compatible both the prevention of interference in a position other than an engagement part of an inner rotor and an outer rotor, and the suppression of oil leakage.SOLUTION: A tooth shape evaluation method includes: preparation step S1 for arranging an inner rotor 2 and an outer rotor 3 in ideal center positions; inner rotor rotation step S2 for rotating the inner rotor up until the inner rotor is engaged with the outer rotor at a lower dead point, and the outer rotor and the inner rotor have first contact points 11; and outer rotor rotation step S3 for rotating the outer rotor in a direction which is the same as a rotation direction of the inner rotor in a state in which the inner rotor is fixed in the first contact point. In the outer rotor rotation step, a state whether or not the outer rotor and the inner rotor have second contact points while an external peripheral face 3b of the outer rotor 3 contacts with an internal peripheral face 4a of a casing 4 is made to be an index of an evaluation.SELECTED DRAWING: Figure 11

Description

The present invention relates to a tooth profile evaluation method and a tooth profile formation method for an internal gear pump.

Power mechanisms such as engines are equipped with pumps to lubricate parts with oil. For example, an internal gear pump draws in and discharges oil by pumping due to the volume changes of multiple confinement areas formed when the external teeth of an inner rotor and the internal teeth of an outer rotor rotate while meshing with each other.

In such internal gear pumps, the tooth profiles of the inner and outer rotors are designed so that a specified inter-tooth gap is provided between the tooth surfaces of the inner and outer rotors. However, when the pump is actually operating, the inter-tooth gap between the inner and outer rotors may deviate from the designed value due to the dimensional accuracy of the tooth profile, and the inner and outer rotors may have contact points other than at the meshing points, preventing smooth rotation and increasing the drive torque.

In response to this problem, Patent Document 1 proposes designing the tooth profile of the outer rotor by repeatedly offsetting the tooth surface of the inner rotor significantly outward from the center of the inner rotor by an amount equivalent to the tooth gap, so that a tooth gap can be secured between the outer rotor and the inner rotor at points other than the meshing portion with the outer rotor.

Patent No. 5561287

By the way, if the gap between the teeth of the inner rotor and the outer rotor is made as narrow as possible, it is possible to prevent oil leakage. However, if the gap between the teeth is designed too narrow, the above-mentioned interference is likely to occur, and the drive torque increases. On the other hand, if the gap between the teeth is designed too wide, the above-mentioned interference is unlikely to occur, but there is a risk of increased leakage. In Patent Document 1, the offset amount at each position of the inner rotor rotation angle is set to be larger than the machining error allowed for the rotor, so that interference at positions other than the meshing portion of the inner rotor and outer rotor can be prevented even if a machining error occurs. In the tooth profile formation method such as that in Patent Document 1, there is a concern that the gap between the teeth is enlarged more than necessary, which may increase leakage, and there is a risk that two-point contact cannot be avoided.

The present invention was made in consideration of these points, and its purpose is to provide a tooth profile evaluation method and tooth profile formation method for an internal gear pump that prevents interference at positions other than the meshing portion of the inner rotor and outer rotor, preventing an increase in drive torque, and narrowing the inter-tooth gap as much as possible to suppress an increase in leakage.

To achieve the above objective, this invention takes into consideration the body clearance between the outer peripheral surface of the outer rotor and the inner peripheral surface of the casing, thereby preventing interference at positions other than the meshing area between the inner rotor and outer rotor without unnecessarily expanding the inter-tooth gap.

Specifically, in the first invention,
an inner rotor having n external teeth;
an outer rotor having n+1 internal teeth that mesh with the external teeth from an outer circumferential side;
a casing having a body clearance between the casing and the outer rotor and covering an outer periphery of the outer rotor,
An internal gear pump that transports a fluid by sucking or discharging the fluid by changing the volume of a plurality of confinement portions formed between the tooth surfaces of the inner rotor and the outer rotor when the inner rotor and the outer rotor rotate in mesh with each other,
a preparation step of arranging the inner rotor and the outer rotor at their ideal central positions;
an inner rotor rotating step of rotating the inner rotor until the inner rotor meshes with the outer rotor at a bottom dead center and the outer rotor and the inner rotor have a first contact point;
an outer rotor rotating step of rotating the outer rotor in the same direction as a rotation direction of the inner rotor while the inner rotor is fixed at the first contact point,
In the outer rotor rotating process, an index for evaluation is whether or not the outer rotor and the inner rotor have a second contact point before the outer peripheral surface of the outer rotor comes into contact with the inner peripheral surface of the casing.

The above configuration allows for an evaluation of whether the tooth profile is such that it prevents interference at positions other than the meshing points of the inner and outer rotors without unnecessarily widening the inter-tooth gap, taking into consideration that the outer rotor will move and interfere with the inner surface of the casing during actual pump operation.

In a second aspect of the present invention, in the outer rotor rotating step of the first aspect of the present invention,
If the outer rotor and the inner rotor do not have a second contact point, the tooth profiles of the outer rotor and the inner rotor are determined to be acceptable;
When the outer rotor and the inner rotor have a second contact point, the tooth profiles of the outer rotor and the inner rotor are judged to be unacceptable.

The above configuration makes it easy to determine whether the tooth profile is suitable for preventing interference at positions other than the meshing points of the inner rotor and outer rotor without unnecessarily widening the inter-tooth gap.

A third aspect of the present invention is a tooth profile forming method for an inner rotor determined to be unacceptable in the second aspect of the present invention, comprising:
a meshing process in which a direction of a tooth tip of the inner rotor is aligned with a direction of a tooth bottom of the outer rotor, and the inner rotor and the outer rotor are meshed with each other;
an outer rotor setting process for virtually expanding a radius of curvature of a curved portion at a tooth bottom of the outer rotor, the curved portion being formed by a bottom portion and curved portions located on both sides of the bottom portion, and setting a virtual curved portion that bites into the inner side of the tooth tip of the inner rotor;
and an inner rotor correcting process for cutting off the portion of the tooth tip of the inner rotor that protrudes outward beyond the imaginary curved portion.

The shape of the tooth surface of the inner rotor is designed so that the tip circle and the root circle are connected, but if the joint between the tip circle and the root circle is angular, it is thought that this will affect interference with the outer rotor. With the above configuration, the tooth profile of the inner rotor is modified based on the shape of the corner R of the bottom of the teeth of the outer rotor, so that the joint between the tip circle and the root circle is formed smoothly, and the gap between the teeth of the inner rotor and the outer rotor is not enlarged more than necessary. This makes it possible to prevent interference between the inner rotor and the outer rotor, suppressing an increase in drive torque, and preventing oil leakage at the same time.

As described above, the technology disclosed herein makes it possible to provide a tooth profile evaluation method and a tooth profile formation method for an internal gear pump that simultaneously prevents interference at positions other than the meshing portion of the inner rotor and outer rotor, suppressing an increase in drive torque, and preventing an increase in leakage.

1 is a schematic diagram showing an internal gear pump according to an embodiment of the present invention. 5A to 5C are schematic diagrams illustrating a method for producing the inner rotor. 5A to 5C are schematic diagrams illustrating a method for producing the outer rotor. 5A to 5C are partially enlarged views for explaining a method for producing the outer rotor. FIG. 4 is a schematic diagram showing a state in which the inner rotor and the outer rotor have a first contact point. 4 is a schematic diagram showing a state in which an outer rotor is in contact with an inner circumferential surface of a casing. FIG. 5 is a schematic diagram illustrating a method for modifying the tooth profile of the inner rotor. FIG. FIG. 4 is a partially enlarged view illustrating a method for modifying the tooth profile of the inner rotor. FIG. 4 is a partially enlarged view illustrating a method for modifying the tooth profile of the inner rotor. FIG. 4 is a partially enlarged view illustrating a method for modifying the tooth profile of the inner rotor. 4 is a flowchart of a tooth profile evaluation method and a tooth profile forming method for an internal gear pump. FIG. 11 is a schematic diagram illustrating the R size of the tooth profile of the inner rotor after the tooth profile has been modified. FIG. 4 is a schematic diagram showing an area affected by oil leakage.

The following describes an embodiment of the present invention with reference to the drawings.

[Gear pump configuration]
Fig. 1 is a schematic diagram showing a gear pump according to an embodiment of the present invention. As shown in Fig. 1, this gear pump is an internal gear pump 1, and includes an inner rotor 2, an outer rotor 3, and a casing 4. When the inner rotor 2 and the outer rotor 3 rotate in mesh with each other, the gear pump 1 transports a fluid such as oil by sucking in or discharging the fluid due to a change in volume of a plurality of confinement portions 5 formed between the tooth surfaces of the inner rotor 2 and the outer rotor 3.

The inner rotor 2 has n external teeth 2a on its outer circumferential surface, and a pump shaft (not shown) is inserted through the center. The external teeth 2a are formed continuously in the circumferential direction and mesh with the internal teeth 3a of the outer rotor 3. The external teeth 2a of the inner rotor 2 are formed with one less tooth than the internal teeth 3a of the outer rotor 3. In this embodiment, the inner rotor 2 has six external teeth 2a.

The outer rotor 3 has n+1 internal teeth 3a on its inner circumferential surface. In this embodiment, seven external teeth 2a are formed on the outer rotor 3. The internal teeth 3a are formed continuously in the circumferential direction and mesh with the external teeth 2a of the inner rotor 2 from the outer periphery. The outer rotor 3 is disposed eccentrically relative to the inner rotor 2. The outer rotor 3 rotates following the rotation of the inner rotor 2.

The casing 4 covers the outer periphery of the outer rotor 3. The casing 4 has a rotor accommodating space with a circular cross section, and accommodates the outer rotor 3 and the inner rotor 2 in the rotor accommodating space. The gear pump 1 has a predetermined body clearance 6 between the inner circumferential surface 4a that forms the rotor accommodating space and the outer circumferential surface 3b of the outer rotor.

[How to make an inner rotor]
Fig. 2 is a schematic diagram for explaining a method for creating an inner rotor. As shown in Fig. 2, the inner rotor 2 of this embodiment is created by a general creation method based on a trochoid curve 20. That is, first, a trochoid curve 20 serving as a base is created.

When the parameters A, B, and e are defined as follows, the coordinates (x, y) of the trochoid curve are expressed by the following equation (1) using the following parameters and an angle parameter θ.
A: The diameter of a fixed circle (base circle) centered on the center point of the inner rotor.
B: The diameter of the circle (rolling circle) that rolls on the base circumference.
e: A trochoid curve is drawn by the locus of points e away from the center of the rotating circle when the rotating circle rolls. This corresponds to the eccentricity of the outer rotor.

The tooth profile curve of the inner rotor 2 is designed by the envelope of a group of locus circles 21 centered on a point on the trochoid curve 20 obtained by the above formula (1).

When the diameter of a locus circle 21 centered on a point on the trochoid curve 20 is C, the coordinates (X, Y) of the envelope are expressed by the following equations (2) and (3), and the smaller value of ( ^X2 + ^Y2 ) in equations (2) and (3) is taken as (X, Y) to represent the tooth profile curve of the inner rotor 2. Note that the parameter K in equations (2) and (3) is expressed by equation (4).

[How to make an outer rotor]
3 is a schematic diagram for explaining a method for creating an outer rotor. As shown in FIG. 3, the outer rotor 3 of this embodiment is created by a general method for creating an outer rotor 3 for an inner rotor 2 created based on a trochoid curve 20. That is, first, a bottom circle 31 along the bottom of the outer rotor 3 is created. The diameter D of the bottom circle is expressed by the following formula (5) using the above parameters A to C and e. In the following formula (5), γ1 is an adjustment dimension set to provide an intertooth gap between the tooth profiles of the inner rotor 2 and the outer rotor 3. Using this parameter D, the bottom circle 31 expressed by the following formula (6) is created.

D = A + B + 4e - C + γ1 ... (5)
^X2 + ^Y2 =(D/2) ² ...(6)
Next, a tip circle 32 is created along the tooth tips of the outer rotor 3. The parameter PCD of the tip circle 32 is defined as PCD = A + B + γ2 using the above parameters A and B and an adjustment dimension γ2 that is set to provide an intertooth gap between the tooth surfaces of the inner rotor 2 and the outer rotor 3. Using such PCD, the tip circle 32 of the outer rotor 3 is expressed by the following formula (7). In the following formula (7), C is the diameter of the tip circle 32 of the outer rotor 3, and is the same as the diameter of the locus circle 21.

The outer rotor 3 is created by connecting the root circle 31 expressed by the above formula (6) and the tip circle 32 expressed by the above formula (7). The tooth profile of the outer rotor 3 created in this manner has an angular joint between the root circle 31 and the tip circle 32, so the joint needs to be rounded.

Figure 4 is a schematic diagram explaining how to make an outer rotor, with a partially enlarged view. The joint between the root circle 31 and the tip circle 32 of the outer rotor 3 is formed in an R-shape that follows the correction circle 33, which is a circle that circumscribes the tip circle 32 and is also a circle that is inscribed in the root circle 31.

[Tooth profile evaluation method]
It is preferable to inspect the tooth profiles of the inner rotor 2 and the outer rotor 3 formed as described above to see whether they interfere with each other at positions other than the meshing portion of the inner rotor 2 and the outer rotor 3 when they are actually meshed and rotated.

The method for evaluating the tooth profiles of the inner rotor 2 and outer rotor 3 will be explained using the flowcharts in Figures 5 to 10 and 11.

First, in the preparation step S1, the inner rotor 2 and the outer rotor 3 are each placed in their ideal central positions. The ideal central position is a state in which the center of rotation of the inner rotor 2 coincides with the center of rotation of the rotating shaft fixed to the inner rotor 2, and the center of rotation of the outer rotor 3 coincides with the center of the rotor housing space in which the outer rotor 3 is housed; this is also called the theoretical eccentric position.

Next, in the inner rotor rotation step S2, as shown in FIG. 5, the inner rotor 2 is rotated in the direction of the arrow in FIG. 5 while the outer rotor 3 is fixed, until the inner rotor 2 meshes with the outer rotor 3 at bottom dead center and the outer rotor 3 and the inner rotor 2 have a first contact point 11. Note that in FIG. 5, a predetermined inter-tooth gap 10 exists between the outer rotor 3 and the inner rotor 2 in the portion indicated by the dotted circle.

Next, in the outer rotor rotation step S3, as shown in FIG. 6, the outer rotor 3 is rotated in the same direction as the rotation direction of the inner rotor 2 (the direction of the arrow in FIG. 6) while the inner rotor 2 is fixed at the first contact point 11.

In the outer rotor rotation process S3, whether or not the outer rotor 3 and the inner rotor 2 have a second contact point before the outer peripheral surface 3b of the outer rotor 3 comes into contact with the inner peripheral surface 4a of the casing 4 can be used as an index for evaluation. For example, the outer peripheral surface 3b of the outer rotor 3 comes into contact with the inner peripheral surface 4a of the casing 4 at the position indicated by the star in Figure 6.

Specifically, in the evaluation of the tooth profile, if the outer rotor 3 and the inner rotor 2 do not have a second contact point in the judgment process S4, the tooth profiles of the outer rotor 3 and the inner rotor 2 are judged as acceptable, and the evaluation is terminated. Also, in the judgment process S4, if the outer rotor 3 and the inner rotor 2 have a second contact point, the tooth profiles of the outer rotor 3 and the inner rotor 2 are judged as unacceptable, and the tooth profile of the inner rotor 2 is corrected.

[Modification of inner rotor tooth profile]
If the evaluation step S4 determines that the rotor is unsatisfactory, the tooth profile of the inner rotor 2 is modified. First, in the meshing step S5, as shown in Fig. 7, the direction of the tooth tips 2b of the inner rotor 2 is aligned with the direction of the tooth bottoms 7a of the imaginary outer rotor 7, and the inner rotor 2 and the imaginary outer rotor 7 are meshed with each other so that they have a common line of symmetry L.

Figure 8 is an enlarged view of the X portion of Figure 7, and is an enlarged view of the joint portion 2c between the tooth tip circle and the tooth root circle of the inner rotor 2. The tooth bottom 7a of the outer rotor 7 is formed by a bottom portion 70 that is in contact with the tooth bottom circle, and curved portions 71 located on both sides of the bottom portion 70. The curved portions 71 are the joint portion between the tooth bottom circle and the tooth tip circle, and are the portions that are smoothly formed into an angular shape when the outer rotor 7 is formed. In the outer rotor setting process S6, as shown in Figure 8, the radius of curvature of the curved portion 71 is virtually enlarged at the tooth bottom 7a of the outer rotor 7, and a virtual curved portion 72 that bites into the inside of the tooth tip of the inner rotor 2 is set.

Figure 9 is an enlarged view of part X in Figure 7, similar to Figure 8. Figure 9 shows the joint 2c between the tip circle and the root circle of the inner rotor 2, and the imaginary curved portion 72 of the outer rotor 7. As shown in Figure 9, the joint 2c between the tip circle and the root circle of the inner rotor 2 is angular. This angular joint 2c protrudes outward from the imaginary curved portion 72.

In the next inner rotor correction process S7, as shown in FIG. 10, the joint portion 2c at the tip of the teeth of the inner rotor 2 that protrudes outward from the imaginary curved portion 72 is removed, and this joint portion 2c is made into a corrected joint portion 2d that follows the imaginary curved portion 72.

Using the inner rotor 2 and outer rotor 3 formed as described above, the tooth profile is evaluated again in the order of preparation process S1, inner rotor rotation process S2, and outer rotor rotation process S3.

If the outer rotor 3 and the inner rotor 2 do not have a second contact point in the second judgment step S4, the tooth profiles of the outer rotor 3 and the inner rotor 2 are judged as acceptable, and the evaluation is terminated. If the outer rotor 3 and the inner rotor 2 have a second contact point in the judgment step S4, the tooth profiles of the outer rotor 3 and the inner rotor 2 are judged as unacceptable, and the tooth profile of the inner rotor 2 is corrected again in the order of the meshing step S5, the outer rotor setting step S6, and the inner rotor correction step S7, and this is repeated until the outer rotor 3 and the inner rotor 2 no longer have a second contact point in the judgment step S4.

As shown in FIG. 12 , the R size of the tooth profile of the inner rotor 2 modified in this manner is expressed by the following formula (8) when the parameters Δb, Δt, R1, and R2 are defined as follows, and for example, in this embodiment, α = 0.0036.
Δb: the gap (body clearance 6) between the inner peripheral surface 4a of the casing 4 and the outer peripheral surface 3b of the outer rotor 3.
Δt: the gap between the tooth surface of the inner rotor 2 and the tooth surface of the outer rotor 3 (intertooth gap 10).
R1: The outer diameter of the outer rotor 3.
R2: The diameter of the circle (pitch circle 8) connecting the positions where the inter-tooth gaps 10 are formed.

As described above, the tooth profile evaluation method for an internal gear pump of this embodiment takes into account that the outer rotor 3 moves during actual pump operation, causing its outer circumferential surface 3b to interfere with the inner circumferential surface 4a of the casing 4, and can evaluate whether the tooth profile is such that it prevents interference at positions other than the meshing points of the inner rotor 2 and outer rotor 3 without unnecessarily widening the inter-tooth gap.

If the tooth gap between the inner rotor 2 and the outer rotor 3 is too wide, as shown by the diagonal lines in Figure 13, it will affect oil leakage on both sides of the circumferential direction of the confinement portion 5. However, in the tooth profile formation method of the internal gear pump of this embodiment, the tooth profile of the inner rotor 2 is modified based on the shape of the corner R of the tooth bottom of the outer rotor 3, so that the joint between the tooth tip circle and the tooth bottom circle is formed smoothly, and the tooth gap between the inner rotor 2 and the outer rotor 3 is not enlarged more than necessary. This method makes it possible to prevent interference at positions other than the meshing portion between the inner rotor 2 and the outer rotor 3, thereby preventing an increase in drive torque, and suppressing an increase in oil leakage.

The above embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or uses.

REFERENCE SIGNS LIST 1 gear pump 2 inner rotor 2a external teeth 3 outer rotor 3a external teeth 3b outer peripheral surface 4 casing 4a inner peripheral surface 5 containment portion 6 body clearance 7 imaginary outer rotor 7a tooth bottom 10 tooth gap 11 first contact point 70 bottom 71 curved portion 72 imaginary curved portion

Claims (3)

an inner rotor having n external teeth;
an outer rotor having n+1 internal teeth that mesh with the external teeth from an outer circumferential side;
a casing having a body clearance between the casing and the outer rotor and covering an outer periphery of the outer rotor,
An internal gear pump that transports a fluid by sucking or discharging the fluid by changing the volume of a plurality of confinement portions formed between the tooth surfaces of the inner rotor and the outer rotor when the inner rotor and the outer rotor rotate in mesh with each other,
a preparation step of arranging the inner rotor and the outer rotor at their ideal central positions;
an inner rotor rotating step of rotating the inner rotor until the inner rotor meshes with the outer rotor at a bottom dead center and the outer rotor and the inner rotor have a first contact point;
an outer rotor rotating step of rotating the outer rotor in the same direction as a rotation direction of the inner rotor while the inner rotor is fixed at the first contact point,
A tooth profile evaluation method for an internal gear pump, wherein whether or not the outer rotor and the inner rotor have a second contact point during the outer rotor rotation process until the outer peripheral surface of the outer rotor comes into contact with the inner peripheral surface of the casing is used as an evaluation index. In the outer rotor rotating process,
If the outer rotor and the inner rotor do not have a second contact point, the tooth profiles of the outer rotor and the inner rotor are determined to be acceptable;
2. The method for evaluating tooth profiles of an internal gear pump according to claim 1, further comprising the step of determining that the tooth profiles of the outer rotor and the inner rotor are unacceptable when the outer rotor and the inner rotor have a second contact point. 3. The tooth profile evaluation method for an internal gear pump according to claim 2, wherein the tooth profile of the inner rotor determined to be unacceptable is formed by:
a meshing process in which a direction of a tooth tip of the inner rotor is aligned with a direction of a tooth bottom of the outer rotor, and the inner rotor and the outer rotor are meshed with each other;
an outer rotor setting process for virtually expanding a radius of curvature of a curved portion at a tooth bottom of the outer rotor formed by a bottom portion and curved portions located on both sides of the bottom portion, and setting a virtual curved portion that bites into the inner side of the tooth tips of the inner rotor;
and an inner rotor correction step of cutting off any portion of the tooth tip of the inner rotor that protrudes outward beyond the imaginary curved portion.