Patent Application
20250154951
The present invention relates to a uniaxial eccentric screw pump.
A known uniaxial eccentric screw pump includes a stator having an insertion hole with its inner peripheral surface internally threaded and a rotor including an externally threaded shaft placed through the insertion hole in the stator (refer to, for example, Patent Document 1).
In the known uniaxial eccentric screw pump, the rotor and the stator have, between them, substantially the same interference value when the rotor is located in two end areas in an opening that is the cross section of the insertion hole in the stator and when the rotor is located in a middle area in the opening.
When the interference amount is sufficiently large, the rotor uses higher torque and a greater driving force to rotate.
However, the interference amount decreased to facilitate movement of the rotor can lower the sealing tightness, causing inappropriate delivery of a fluid.
One or more aspects of the present invention are directed to a uniaxial eccentric screw pump that achieves tight sealing and also reduces the driving force for rotating a rotor.
The inventors have noticed that the interference amount can be relatively small in the middle area when the interference amount is sufficient in the two end areas, and have developed a uniaxial eccentric screw pump according to one or more aspects of the present invention.
A uniaxial eccentric screw pump according to an aspect of the present invention includes a stator having an insertion hole with an inner peripheral surface being internally threaded, and a rotor including a shaft being externally threaded and placed through the insertion hole in the stator. The rotor performs eccentric rotation about a central axis of the stator. In a cross section perpendicular to the central axis, the insertion hole is an elongated hole. The rotor has a cross-sectional center displaceable in a reciprocating manner in a longitudinal direction of the insertion hole between a pair of turn positions along a center line extending in the longitudinal direction through the central axis of the stator during the eccentric rotation of the rotor. The pair of turn positions are opposite to each other in the longitudinal direction with respect to the central axis. The rotor comes in contact with the inner peripheral surface of the insertion hole in a lateral direction of the insertion hole perpendicular to the longitudinal direction. An interference amount between the rotor and the stator includes a first interference amount when the cross-sectional center is at one of the pair of turn positions and a second interference amount when the cross-sectional center is at the central axis. The first interference amount is larger than the second interference amount.
In this structure, the interference amount between the rotor and the stator is the first interference amount when the rotor is located in one of the two end areas of the insertion hole, or in other words, when the rotor has the cross-sectional center at one of the turn positions that are the limits of the reciprocation range in the insertion hole in the cross section perpendicular to the central axis of the stator. The interference amount between the rotor and the stator is the second interference amount when the rotor is located in the middle area of the insertion hole, or in other words, when the rotor has the cross-sectional center located at the central axis that is the center of the reciprocation range in the insertion hole. The first interference amount is larger than the second interference amount. In the two end areas of the insertion hole, the rotor is thus in tighter contact with the inner peripheral surface of the insertion hole and can maintain the sealing tightness. In the middle area with the smaller interference amount, the rotor uses a less driving force to rotate.
The interference amount between the rotor and the stator may decrease gradually from the first interference amount to the second interference amount with the cross-sectional center being displaced from one of the pair of turn positions toward the central axis along the center line.
When the cross-sectional center is at a point on the center line, the interference amount between the rotor and the stator may be an excess of a distance between the cross-sectional center at the point and an outer peripheral surface of the rotor in the lateral direction over a distance between the point and the inner peripheral surface of the insertion hole in the lateral direction in a natural state of the stator with no contact with the rotor.
The insertion hole may have a first hole width being a dimension of the insertion hole in the lateral direction at each of the pair of turn positions in a natural state with no contact with the rotor, and may have a second hole width being a dimension of the insertion hole in the lateral direction at the central axis in the natural state. The rotor may have a first rotor width being a dimension of the rotor in the lateral direction at the cross-sectional center at each of the pair of turn positions, and may have a second rotor width being a dimension of the rotor in the lateral direction at the cross-sectional center at the central axis. A difference of the first rotor width from the second rotor width may be greater than a difference of the first hole width from the second hole width.
The first hole width may be less than the second hole width. The first hole width may be equal to the second hole width. The first hole width may be greater than the second hole width.
When the first hole width is equal to the second hole width, the insertion hole may have a shape of a racetrack in the cross section.
The rotor may have a shape of a non-perfect circle having a longitudinal axis and a lateral axis perpendicular to each other in the cross section. When the cross-sectional center is at one of the pair of turn positions, the longitudinal axis may be parallel to the lateral direction and the lateral axis may be parallel to the longitudinal direction. When the cross-sectional center is at the central axis, the longitudinal axis may be parallel to the longitudinal direction and the lateral axis may be parallel to the lateral direction.
The rotor may be elliptical in the cross section. The rotor may be oval in the cross section. The rotor with this simple structure can be manufactured easily.
The rotor may include, in the cross section, first curves at two sides in a direction in which the lateral axis extends, and may include second curves at two ends in a direction in which the longitudinal axis extends. The first curves may have a greater curvature radius than the second curves. The rotor may be, in the cross section, asymmetric in a direction in which the longitudinal axis extends.
The stator may consist of a stator body formed from an elastic material. This structure includes fewer components and facilitates manufacture at low costs.
When the cross-sectional center is at one of the pair of turn positions, the rotor may have an outer peripheral surface in contact with the inner peripheral surface of the insertion hole in the longitudinal direction with a predetermined interference amount in the longitudinal direction.
The uniaxial eccentric screw pump according to the above aspects of the present invention achieves tight sealing and also reduces the driving force for rotating the rotor.
Embodiments of the disclosure will now be described with reference to the accompanying drawings. The terms for specific directions or positions (e.g., terms including up, down, side, and end) are used herein as appropriate to facilitate understanding of the present invention with reference to the drawings. However, such terms do not limit the technical scope of the present invention. The drawings are schematic and are not drawn to scale relative to the actual size of each component.
The casing 1, the stator 2, and the end stud 3 are tubular and coaxial. These components 1 to 3 have a central axis A1 as a common axis. The direction in which the central axis A1 extends is referred to as the axial direction. In
The casing 1 is formed from a metal material. The casing 1 includes a peripheral wall 1b defining an internal space 1a extending in the axial direction, and includes a connection tube 1c protruding radially from the peripheral wall 1b. The connection tube 1c has a basal end in the radial direction connecting with the internal space 1a through a first opening 5. The internal space 1a is open at least at the second end of the two ends. The stator 2 has an insertion hole 10 extending in the axial direction and open at the two ends. In the present embodiment, the stator 2 includes a stator body 2a defining the insertion hole 10 and an outer cylinder 2b fitted onto the stator body 2a. The outer cylinder 2b may be bonded to the stator body 2a with any method. The end stud 3 includes an internal space 3a extending in the axial direction and open at the two ends. The end stud 3 defines a second opening 6 at the second end.
The casing 1 and the end stud 3 are connected to each other with stay bolts 8. The stay bolts 8 are turned and tightened to hold the stator 2 between the casing 1 and the end stud 3 in the axial direction. The insertion hole 10 connects with the internal space 1a in the casing 1 and also with the internal space 3a in the end stud 3. The uniaxial eccentric screw pump 100 includes a flow path 7 extending from the connection tube 1c through the first opening 5, the internal space 1a in the casing 1, the insertion hole 10 in the stator 2, and the internal space 3a in the end stud 3 to the second opening 6. The connection tube 1c is connected to a tank (not shown) storing a fluid. Examples of the fluid include a viscous material such as mayonnaise. The fluid in the tank is transferred through the flow path 7 as the rotor 4 rotates.
The rotor 4 is a shaft and is received in the insertion hole 10. The insertion hole 10 has an inner peripheral surface 10a including a single or multiple internally threaded portions with an n-start thread (a two-start thread in this example). The rotor 4 has an outer peripheral surface 4a including a single or multiple externally threaded portions with an (n−1)-start thread (a single-start thread in this example). The rotor 4 is driven by a drive (not shown) located at the first end of the casing 1 to rotate eccentrically about the central axis A1.
The uniaxial eccentric screw pump 100 includes a system for transmitting a driving force from the drive to the rotor 4 for rotation. The system includes a coupling 11 connected to the output shaft of the drive, a coupling rod 12 extending from the coupling 11, and a joint head 13 connected to the coupling rod 12. These components are accommodated in the internal space 1a of the casing 1. The joint head 13 is tubular and has a surface at the first end connected to the distal end of the coupling rod 12. The joint head 13 has a surface at the second end, from which the rotor 4 extends in the axial direction toward the second end through the insertion hole 10 in the stator 2.
The joint head 13 has a central axis A2 parallel to the central axis A1 of the stator 2 and is offset from the central axis A1 by an eccentricity e in the direction perpendicular to the axial direction. The coupling rod 12 is inclined with respect to the central axes A1 and A2 in the casing 1.
The insertion hole 10 is an elongated hole in the cross section. The insertion hole 10 is longer in a longitudinal direction X in the cross section and is shorter in a lateral direction Y perpendicular to the longitudinal direction X in the cross section. In the present embodiment, the insertion hole 10 has point symmetry (180-degree rotational symmetry) about the central axis A1. The insertion hole 10 has line symmetry about a center line CX extending in the longitudinal direction X through the central axis A1, and has line symmetry about a center line CY extending in the lateral direction Y through the central axis A1.
In the cross section, the outer peripheral surface 4a of the rotor 4 is a closed loop-shaped curve, which defines the shape of the rotor 4 in the cross section. The center of the rotor 4 in the cross section is hereafter referred to as a cross-sectional center O4. The cross-sectional center O4 is offset from the central axis A2 (the center of rotation of the rotor 4) of the joint head 13 by the eccentricity e in the direction perpendicular to the axial direction. As the rotor 4 rotates eccentrically, the cross-sectional center O4 is displaced in a reciprocating manner in the longitudinal direction X between a pair of turn positions P1 and P2 along the center line CX. The pair of turn positions P1 and P2 are opposite to each other in the longitudinal direction X with respect to the central axis A1. Each of the turn positions P1 and P2 is offset from the central axis A1 by twice the eccentricity e in the longitudinal direction X.
In
During displacement of the cross-sectional center O4 from the first turn position P1 to the central axis A1, the rotor 4 rotates 90 degrees and revolves 90 degrees. The same applies to the displacement of the cross-sectional center O4 from the central axis A1 to the second turn position P2, from the second turn position P2 to the central axis A1, and from the central axis A1 to the first turn position P1. Thus, the rotor 4 rotates once while revolving once, with one round trip of the cross-sectional center O4.
In the cross section, the outer peripheral surface 4a of the rotor 4 remains in contact with the inner peripheral surface 10a of the insertion hole 10 at least in the lateral direction Y. The rotor 4 is formed from a metal material. The stator body 10 is formed from an elastic material selected as appropriate for the type of fluid to be transferred. Examples of the elastic material include nitrile rubber, fluorine rubber, ethylene-propylene rubber, styrene-butadiene rubber, silicone rubber, and fluorosilicone rubber. The rotor 4 may be formed from a material other than a metal material, such as ceramic (e.g., silicon carbide) or a resin (e.g., nylon).
The inner peripheral surface 10a of the insertion hole 10 comes in contact with the outer peripheral surface 4a of the rotor 4 with its resilience after elastically deforming away from the central axis A1 in the lateral direction Y. Thus, the outer peripheral surface 4a of the rotor 4 has, in the cross section, a dimension in the lateral direction Y exceeding the dimension of the insertion hole 10 in the lateral direction Y in a natural state with no contact with the rotor 4. The amount by which the dimension exceeds is an interference amount δ between the stator 2 and the rotor 4 (in the lateral direction Y). The interference amount δ may also be referred to as the amount of elastic deformation of the inner peripheral surface 10a in the lateral direction Y in the contact state. A larger interference amount & achieves tighter sealing of the transfer spaces 15, but increases the driving force for eccentrically rotating the rotor 4 in the contact state.
For ease of explanation of the interference amount δ, the dimensions defined below are used. A first hole width a refers to the dimension of the insertion hole 10 in the lateral direction Y at the first turn position P1 or the second turn position P2 in the natural state. More specifically, an imaginary straight line extending in the lateral direction Y through the position P1 or P2 has two points of intersection with the inner peripheral surface 10a in the cross section. The direct distance between the two points is the first hole width a of the insertion hole 10 in the natural state. A second hole width b refers to the dimension of the insertion hole 10 in the lateral direction Y at the central axis A1 in the natural state.
A rotor width refers to the dimension of the rotor 4 in the lateral direction Y at the cross-sectional center O4 in the cross section. More specifically, an imaginary straight line extending in the lateral direction Y through the cross-sectional center O4 has two points of intersection with the outer peripheral surface 4a in the cross section. The direct distance between the two points is the rotor width. For a rotor 4 with the shape of a non-perfect circle in the cross section, the rotor width varies with the position of the cross-sectional center O4 that is displaced in a reciprocating manner as the rotor 4 rotates. A first rotor width x refers to the rotor width with the cross-sectional center O4 at the first turn position P1 or the second turn position P2. A second rotor width y refers to the rotor width with the cross-sectional center O4 at the central axis A1. The first rotor width x exceeds the first hole width a. The second rotor width y exceeds the second hole width b (x>a, y>b).
When the cross-sectional center O4 is at a point on the center line CX, the interference amount δ (in the lateral direction Y) is defined as an excess (positive value) of the distance between the cross-sectional center O4 at the point and the outer peripheral surface 4a of the rotor 4 in the lateral direction Y over the distance between the point and the inner peripheral surface 10a of the insertion hole 10 in the lateral direction Y in the natural state. In this case, a first interference amount δ1 refers to the interference amount δ for when the point is at the first turn position P1 or the second turn position P2. A second interference amount δ2 refers to the interference amount δ for when the point is at the central axis A1. The first interference amount δ1 corresponds to half the excess of the first rotor width x over the first hole width a (δ1=(x−a)/2>0). The second interference amount δ2 corresponds to half the excess of the second rotor width y over the second hole width b (δ2=(y−b)/2>0).
The first interference amount δ1 is larger than the second interference amount δ2 (δ1>δ2). In other words, the difference of the first rotor width x from the second rotor width y is greater than the difference of the first hole width a from the second hole width b (x−y>a−b). The difference herein may be a positive value, zero, or a negative value. The formula x−y>a−b can be changed into δ1>δ2 using the formula δ1=(x−a)/2 and the formula δ2=(y−b)/2.
To satisfy the relationship δ1>δ2, the insertion hole 10 in the present embodiment has the shape of a racetrack (oval) in the cross section, and the rotor 4 has the shape of a non-perfect circle having the longitudinal axis and the lateral axis perpendicular to each other at the cross-sectional center O4 in the cross section. Unless otherwise specified, the shape of the insertion hole 10 refers to the closed loop-shaped profile of the inner peripheral surface 10a of the insertion hole 10 in the cross section. The shape of the rotor 4 refers to the closed loop-shaped profile of the outer peripheral surface 4a of the rotor 4 in the cross section.
The insertion hole 10 has the shape of a racetrack including a pair of straight portions 10b extending parallel to the longitudinal direction X, a first semicircular portion 10c connecting first ends of the straight portions 10b, and a second semicircular portion 10d connecting second ends of the straight portions 10b. The pair of straight portions 10b are spaced from each other by the second hole width b in the lateral direction Y.
In the present embodiment, the first turn position P1 corresponds to a connection position at which the first semicircular portion 10c is connected to each straight portion 10b in the longitudinal direction X. The first hole width a is thus equal to the second hole width b (a=b). The first semicircular portion 10c defines a half circle with the center being at the first turn position P1 and with the radius being the first hole width a (second hole width b). The same applies to the second turn position P2.
In the present embodiment, the rotor 4 has the shape of an ellipse as an example of the non-perfect circle. The ellipse is not limited to an ellipse in a geometric sense, but may also be a shape similar to such an ellipse. For example, the ellipse may include an ellipse-like polygon including multiple line segments. In this case, the line segments may be connected with smooth curves such as circular arcs. The ellipse-like shape may include any lines. For example, the shape may be a super ellipse that is a closed curve similar to an ellipse and satisfies the formula below.
Referring to
In this manner, the first hole width a is equal to the second hole width b, and the first rotor width x is greater than the second rotor width y. The first interference amount δ1 is thus larger than the second interference amount δ2. The second rotor width y (the minor diameter of the rotor 4) is greater than the interval (the second hole width b) between the pair of straight portions 10b. Thus, during displacement of the cross-sectional center O4 from the turn position P1 or P2 toward the central axis A1 in the longitudinal direction X, the interference amount δ in the lateral direction Y decreases gradually from the first interference amount δ1 to the second interference amount δ2.
For a rotor 4 with the shape of a perfect circle in the cross section, the first rotor width is equal to the second rotor width and the first interference amount is equal to the second interference amount (with the first hole width a and the second hole width b equal to each other in the present embodiment). When this comparative rotor with the perfect circle shape has a diameter equal to the major diameter of the rotor 4 in the present embodiment, the first interference amount δ1 in the present embodiment is substantially the same as with the comparative rotor and the second interference amount δ2 is smaller than with the comparative rotor. The structure in the present embodiment thus achieves substantially the same sealing tightness in the two end areas of the insertion hole 10 as with the comparative rotor, and uses a less driving force for rotating the rotor 4 in the middle area of the insertion hole 10 than with the comparative rotor. When the comparative rotor with the perfect circle shape has a diameter equal to the minor diameter of the rotor 4 in the present embodiment, the first interference amount δ1 in the present embodiment is larger than with the comparative rotor, and the second interference amount δ2 is substantially the same as with the comparative rotor. The structure in the present embodiment thus achieves substantially as easy rotation in the middle area of the insertion hole 10 as with the comparative rotor, and also achieves tighter sealing in two end areas of the insertion hole 10 than with the comparative rotor.
As described above, the uniaxial eccentric screw pump 100 according to the present embodiment achieves tight sealing and also reduces the driving force for rotating the rotor 4.
When the cross-sectional center O4 is at the first turn position P1 as shown in
The insertion hole 10 has a shape of, for example, an ellipse. The second hole width b corresponds to the minor diameter of the ellipse. The first hole width a has a less value than the second hole width b (minor diameter).
The insertion hole 10 having the first hole width a less than the second hole width b may have any shape other than an ellipse. For example, as shown in
For example, the insertion hole 10 may have a shape combining multiple circular arcs with different curvature radii. The insertion hole 10 has a shape including a pair of circular arc portions 10g curved inward toward the central axis A1 in the lateral direction, in place of a pair of straight portions of the racetrack. The pair of circular arc portions 10g are symmetric about the center line CX. Each circular arc portion 10g has line symmetry about the center line CY. The shape includes semicircular portions 10h connecting the corresponding ends of the pair of circular arc portions 10g, similarly to the semicircular portions 10c and 10d (refer to
Although the rotor 4 is elliptical in the cross section in the above embodiments, the rotor 4 may have another shape. More specifically, the rotor 4 may simply have the shape of a non-perfect circle having the major axis and the minor axis in the cross section. In this case, the rotor 4 may have line symmetry about the major axis and the minor axis in the cross section.
For example, as shown in
When the rotor 4 with the oval cross-sectional shape is located in one of the two end areas of the insertion hole 10, the rotor 4 has its semicircular portion in contact with the straight line defining the end area with a predetermined interference amount. During movement of the rotor 4 from the end area toward the middle area, the rotor 4 rotates with its longitudinal axis gradually rotating to align with the longitudinal direction X of the insertion hole 10. This gradually reduces the tightness of contact between the outer peripheral surface 4a of the rotor 4 and the inner peripheral surface 10a of the insertion hole 10 in the stator 2. When the rotor 4 is at the central axis A1, the rotor 4 has the longitudinal axis parallel to the longitudinal direction X and is least susceptible to the force from the stator 2.
The rotor 4 may have a shape combining multiple circular arcs with different curvature radii in the cross section. For example, as shown in
The rotor 4 may be asymmetric in the horizontal (longitudinal) direction about the vertical (lateral) axis in the cross section. For example, as shown in
As described above, the rotor 4 may be used in any of the structures in the first to third embodiments when the rotor 4 has the longitudinal axis and the lateral axis in the cross section and satisfies δ1>δ2. In the second embodiment, the rotor 4 may have the shape of a perfect circle in the cross section.
In the above embodiments, the casing 1 receives a fluid through the first opening 5 and discharges the fluid through the second opening 6. In some embodiments, the casing 1 may receive a fluid through the second opening 6 and discharge the fluid through the first opening 5 by rotating the rotor 4 in the reverse direction.
In the above embodiments, the stator 2 includes the outer cylinder 2b and the stator body 2a. In some embodiments, the stator 2 may include the stator body 2a without an outer cylinder as shown in
In this structure, the stator 2 (stator body 2a) is deformable radially outward and cantilevered with the tightly held portion. This simple structure facilitates manufacture at low costs. Unlike in the above embodiments, this structure eliminates an adhesive to fix the outer cylinder 2a and the stator body 2b to each other, thus eliminating concerns about, for example, the resistance of the adhesive to the fluid.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-005929 | Jan 2022 | JP | national |
| 2022-124265 | Aug 2022 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/036254 | 9/28/2022 | WO |
