Screw pump

Abstract

A screw pump (1) comprises: a plurality of screws (10, 20) that have helical teeth and rotate about respective rotation axes; and a case (30) that accommodates the plurality of screws. The plurality of screws are arranged in a state of meshing with each other. At least one screw (10, 20) from among the plurality of screws is a first screw having a shaft (14, 24) arranged so as to be coaxial with the rotation axis, and a resin screw rotor (12, 22) integrated with the shaft. At least one end (14a, 24a, 24b) of the shaft of the first screw protrudes from the resin screw rotor, and the end protruding from the resin screw rotor is configured to be capable of coming into contact with the case (30 (32, 36)).

Description

Screw pump

[0001] The present disclosure relates to a screw pump.

[0002] Conventionally, a two-axis screw pump has been known. The two-axis screw pump has a drive screw that is driven to rotate by a drive source, and a driven screw that meshes with the drive screw and is rotated along with the rotation of the drive screw. The screw pump can transfer materials with viscosities ranging from low viscosity to high viscosity as the transferred material.

[0003] Patent Document 1 discloses a two-axis screw pump. In the screw pump disclosed in Patent Document 1, the drive screw (male screw in Patent Document 1) and the driven screw (female screw in Patent Document 1) are made of an iron-based metal material.

[0004] Patent Document 2 discloses a two-axis screw pump (fuel pump in Patent Document 1). In the screw pump disclosed in Patent Document 2, the drive screw and the motor shaft of the drive motor are connected via a clutch element that is an independent part. Thereby, by manufacturing one long drive screw and cutting the drive screw according to the size (pump output) of the screw pump and attaching a clutch element to the end, the driving force of the drive motor can be transmitted to the drive screw. Thereby, it is not necessary to manufacture separate drive screws according to the size of the screw pump, and one drive screw can be used to correspond to screw pumps of various sizes.

[0005] Japanese Unexamined Patent Application Publication No. 2019-049229, Japanese Unexamined Patent Application Publication No. 2016-142269

[0006] In order to suppress the manufacturing cost of the screw pump, it is conceivable to use a resin that is a material cheaper than metal. In the screw pump disclosed in Patent Document 1, since both the drive screw and the driven screw are made of an iron-based metal material, there is room for improvement in order to suppress the manufacturing cost.

[0007] However, if both the drive screw and the driven screw (hereinafter, when referring to both the drive screw and the driven screw collectively, simply referred to as the screw) are manufactured from resin, there is a risk of voids forming inside the screw during the screw molding process. Furthermore, if warping or distortion occurs in the screw due to variations in the cooling rate of the resin during cooling, there is a risk that the screw may come into contact with the screw housing case during rotation and wear down, indicating room for improvement.

[0008] Therefore, there is a need for a screw pump that has a screw that reduces manufacturing costs and wear.

[0009] One embodiment of the screw pump according to the present disclosure comprises a plurality of screws having helical teeth having a predetermined pitch and rotating about their respective rotational axes, and a case housing the plurality of screws, wherein the plurality of screws are arranged in a meshed state with respect to each other, and at least one of the plurality of screws is a first screw having a shaft arranged to be coaxial with the rotational axis and a resin screw rotor made of resin integrated with the shaft, wherein at least one end of the shaft of the first screw protrudes from the resin screw rotor, and the end protruding from the resin screw rotor is configured to abut against the case.

[0010] The screw pump of this embodiment is configured so that thrust loads can be received at the ends of the shafts of multiple screws. Therefore, even without using dedicated bearings to receive thrust loads, the frictional force that the ends of the shafts exert on the case when the multiple screws rotate can be reduced, thereby suppressing screw wear. In addition, since the first screw has a resin screw rotor, manufacturing costs can be reduced compared to when the entire screw is made of metal.

[0011] This is a partial cross-sectional view showing a screw pump according to the first embodiment. This is a cross-sectional view showing the drive shaft of the drive screw. This is a partially disassembled cross-sectional view of the screw pump. This is a perspective view illustrating a method for removing the screw from the molding die. This is a partial cross-sectional view showing a screw pump according to the second embodiment.

[0012] The embodiments of the screw pump according to this disclosure will be described in detail below with reference to the drawings. The embodiments described below are illustrative examples for illustrating the screw pump, and the screw pump of this disclosure is not limited to these embodiments. Therefore, the screw pump according to this disclosure can be implemented in various forms without departing from its essence.

[0013] [First Embodiment] [Configuration of Screw Pump] As shown in Figures 1 to 3, the screw pump 1 of the first embodiment is a twin-screw pump having a drive screw 10 (an example of a screw) and a driven screw 20 (an example of a screw). The screw pump 1 is used to transfer (pump) coolant such as long-life coolant (LLC) used to cool automobile engines, etc. The screw pump 1 is composed of a drive screw 10, a driven screw 20, a case 30, and a drive source 40. The drive screw 10 and the driven screw 20 are housed in the case 30. The drive source 40 is partly located outside the case 30 and transmits rotational driving force to the drive screw 10.

[0014] The drive screw 10 is a screw that rotates when rotational driving force generated by the drive source 40 is transmitted to it. The drive screw 10 is composed of a drive rotor 12 (an example of a resin screw rotor) and a drive shaft 14 (an example of a shaft and a metal shaft). The drive rotor 12 and the drive shaft 14 are integrated. The drive rotor 12 is made of a low-hygroscopic resin such as polyketone (POK) or polyacetal (POM). The drive shaft 14 is made of an iron-based metal material such as carbon steel. In other words, the drive screw 10 of this embodiment is a composite screw (an example of a first screw) consisting of a resin drive rotor 12 and a metal drive shaft 14.

[0015] The drive screw 10 is formed by insert molding the drive rotor 12 so that it is coaxial with the rotation axis X of the drive shaft 14. The drive rotor 12 has helical teeth 12a with a predetermined pitch P. The helical teeth 12a of the drive rotor 12 are composed of three grooves.

[0016] At least a portion of the drive shaft 14 that is covered by the drive rotor 12 has recesses 14c or protrusions 14d formed on its outer circumferential surface. Specific examples of recesses 14c are the D-cut shown in Figure 2(a) and the multiple grooves shown in Figure 2(b). Specific examples of protrusions 14d are the multiple convex portions that project radially outward from the outer circumferential surface of the drive shaft 14, as shown in Figure 2(c). The recesses 14c and protrusions 14d have a predetermined length along the rotation axis X. By forming recesses 14c and protrusions 14d on the drive shaft 14, the drive shaft 14 and the drive rotor 12 rotate as a single unit.

[0017] The first end 14a (an example of an end) of the drive shaft 14 of the drive screw 10, which is aligned with the rotation axis X, and the second end 14b (an example of an end) on the opposite side of the first end 14a, both protrude from the drive rotor 12.

[0018] The driven screw 20 is a screw that rotates along with the rotation of the drive screw 10. The driven screw 20 is composed of a driven rotor 22 (an example of a resin screw rotor) and a driven shaft 24 (an example of a shaft and a metal shaft). The driven rotor 22 and the driven shaft 24 are integrated. The driven rotor 22 and the driven shaft 24 are made of the same material as the drive rotor 12 and the drive shaft 14. In other words, the driven screw 20 in this embodiment is also a composite material screw (an example of a first screw).

[0019] The driven screw 20 is formed by insert molding the driven rotor 22 so that it is coaxial with the rotation axis Y of the driven shaft 24. The driven rotor 22 has helical teeth 22a formed in the opposite direction to the helical direction of the helical teeth 12a of the drive rotor 12. The helical teeth 22a have the same predetermined pitch P as the helical teeth 12a of the drive rotor 12. The helical teeth 22a of the driven rotor 22 are composed of two grooves.

[0020] In the driven shaft 24, at least a portion of the part covered by the driven rotor 22 has a recess 24c or a protrusion 24d formed on its outer surface, similar to the drive shaft 14 (see Figure 2). Although Figure 2 shows cross-sections of the drive rotor 12 and drive shaft 14, the driven shaft 24 has the same cross-sectional shape.

[0021] The first end 24a (an example of an end) of the driven shaft 24 of the driven screw 20, which is aligned with the rotation axis Y, and the second end 24b (an example of an end) on the opposite side of the first end 24a, both protrude from the driven rotor 22.

[0022] The case 30 is composed of a lid 32, a main body 34, and a dispensing section 36. The main body 34 has a cylindrical shape made of metal such as aluminum alloy or resin, and houses the drive screw 10 and the driven screw 20 in its internal space. At this time, the drive screw 10 and the driven screw 20 are arranged so that their helical teeth 12a and helical teeth 22a mesh with each other.

[0023] The lid portion 32 has a plate-like shape made of a metal such as an aluminum alloy, and is joined to one end of the cylindrical main body portion 34 by adhesive or other means, thereby sealing one end of the main body portion 34. An O-ring (not shown) is placed at the joint between the main body portion 34 and the lid portion 32, thereby preventing the cooling water that has flowed into the main body portion 34 from leaking out of the joint.

[0024] An inlet 32a, which is a through-hole for allowing cooling water to flow from the outside into the internal space of the main body 34, is formed in the center of the lid portion 32. The inner surface 32b of the lid portion 32 faces the drive screw 10 and the driven screw 20. The first end 14a of the drive shaft 14 of the drive screw 10 and the first end 24a of the driven shaft 24 of the driven screw 20 are configured to be able to contact the inner surface 32b of the lid portion 32.

[0025] The discharge section 36 has a cylindrical shape made of metal such as aluminum alloy, and a discharge port 36a extends from its side for discharging cooling water to the outside. The discharge section 36 is joined to the main body 34 at the end opposite to the lid 32. Similar to the lid 32, an O-ring (not shown) is placed at the joint between the main body 34 and the discharge section 36, thereby preventing cooling water that has flowed into the main body 34 from leaking out at the joint. On the side of the discharge section 36 opposite to the main body 34, the drive motor 42 of the drive source 40 is located, sealing the end of the discharge section 36. A sealant (not shown) is placed at the joint between the drive motor 42 and the discharge section 36. This prevents cooling water circulating in the internal space of the discharge section 36 from leaking out at the joint. Furthermore, the internal space of the discharge unit 36 ​​is in communication with the internal space of the main body 34 and the internal space of the discharge port 36a, and the cooling water that flows into the main body 34 of the case 30 from the inlet 32a of the lid 32 can circulate through the internal space of the main body 34, the internal space of the discharge unit 36, and the internal space of the discharge port 36a.

[0026] In the delivery section 36, a support section 36b is positioned opposite the second end 24b of the driven shaft 24 of the driven screw 20, and is capable of contacting the second end 24b. In other words, the driven screw 20 is housed in the case 30 in a position where the driven shaft 24 is sandwiched between the inner surface 32b of the lid section 32 and the inner surface 36c of the support section 36b. At this time, although not shown in Figure 1, the length of the driven shaft 24 of the driven screw 20 is slightly shorter (for example, 0.5 mm) than the distance between the inner surface 32b of the lid section 32 and the inner surface 36c of the support section 36b. Therefore, the driven screw 20 is movable along the rotation axis Y direction within the range until the end of the driven shaft 24 contacts either the inner surface 32b or the inner surface 36c of the support section 36b.

[0027] An engaging portion 12b is positioned at the end of the helical tooth 12a on the second end 14b side of the drive shaft 14 in the drive rotor 12 of the drive screw 10. The engaging portion 12b is formed simultaneously with the molding of the helical tooth 12a of the drive rotor 12 and is part of the drive rotor 12. In other words, the engaging portion 12b is formed by insert molding, and the helical tooth 12a and the engaging portion 12b are integrally formed. In this embodiment, the second end 14b of the drive shaft 14 protrudes from the engaging portion 12b.

[0028] As shown in the cross-sectional view A-A in Figure 3 and in Figure 4, the engaging portion 12b has a cylindrical outer shape, and multiple engaging recesses 12c, which are depressions extending from the side surface (outer edge of the circle) toward the center (direction of the rotation axis X), are formed along the circumferential direction (direction of rotation) (in this embodiment, three are spaced at 120-degree intervals). The engaging recesses 12c are formed in a direction along the rotation axis X, extending from the engaging surface 12d of the engaging portion 12b to the boundary between the engaging portion 12b and the helical teeth 12a.

[0029] The drive source 40 is composed of a drive motor 42, a motor shaft 44, and an engaged portion 46. The drive motor 42 generates rotational driving force when power is supplied. The motor shaft 44 rotates due to the rotational driving force of the drive motor 42. The engaged portion 46 is attached to the motor shaft 44 on the opposite side from the drive motor 42 and rotates together with the motor shaft 44. In other words, the rotational driving force of the drive motor 42 is transmitted to the engaged portion 46 via the motor shaft 44.

[0030] As described above, the drive motor 42 of the drive source 40 is connected to the side of the case 30 opposite to the side of the delivery section 36 that is connected to the main body 34, and the drive motor 42 closes the end of the delivery section 36.

[0031] The engaged portion 46 has a cylindrical outer shape, as shown in the B-B cross-sectional view in Figure 3, and has a plurality of engaged projections 46b (three at 120-degree intervals in this embodiment) extending from the engaged surface 46a, which is the end opposite to the side attached to the motor shaft 44. The engaged projections 46b have the same shape as the engaged recesses 12c of the engaged portion 12b in a plan view (see Figure 3). In addition, a bottomed hole 46c is formed in the center of the engaged portion 46, extending from the engaged surface 46a toward the motor shaft 44, into which the second end 14b of the drive shaft 14 of the drive screw 10 fits. The bottomed hole 46c has a hole bottom surface 46d. With the engaged projection 46b of the engaged portion 46 fitted into the engaged recess 12c of the engaging portion 12b, the engaging portion 12b (drive screw 10) is configured to be movable relative to the engaged portion 46 (drive source 40) both in the circumferential direction and along the rotation axis X. In other words, the dimensions of the engaging recess 12c of the engaging portion 12b and the engaged projection 46b of the engaged portion 46 are set so that they can move both in the circumferential direction and along the rotation axis X. However, it is preferable that the gap between the engaging recess 12c and the engaged projection 46b be as small as possible, within the range in which the drive screw 10 can move smoothly along the rotation axis X when the engaged projection 46b of the engaged portion 46 is fitted into the engaging recess 12c of the engaging portion 12b.

[0032] The length of the motor shaft 44 of the drive source 40 is set such that, with the drive motor 42 joined to the delivery section 36 of the case 30, the engaged projection 46b of the engaged portion 46 fits into the engaged recess 12c of the engaged portion 12b of the drive rotor 12 of the drive screw 10. At this time, the second end 14b of the drive shaft 14 fits into the bottomed hole 46c of the engaged portion 46, with a small gap between it and the bottom surface 46d of the hole. Also, at this time, there is a larger gap between the engaged surface 12d of the engaged portion 12b and the engaged surface 46a of the engaged portion 46 than the gap between the end face of the second end 14b and the bottom surface 46d of the hole.

[0033] Thus, the drive screw 10 is housed in the case 30 in a position where the drive shaft 14 is sandwiched between the inner surface 32b of the lid portion 32 and the bottom surface 46d of the closed hole 46c of the engaged portion 46. At this time, although not shown in Figure 1, the length of the drive shaft 14 of the drive screw 10 is slightly shorter (for example, 0.5 mm) than the distance between the inner surface 32b of the lid portion 32 and the bottom surface 46d of the closed hole 46c of the engaged portion 46. For this reason, the drive screw 10 is movable along the rotation axis X direction within the range until the end of the drive shaft 14 abuts against either the inner surface 32b or the bottom surface 46d of the closed hole 46c of the engaged portion 46. The engaging portion 12b and the engaged portion 46 are configured such that even when the end face of the second end 14b of the drive shaft 14 is in contact with the bottom surface 46d of the hole, there is a gap between the engaging surface 12d of the engaging portion 12b and the engaged surface 46a of the engaged portion 46.

[0034] The screw pump 1 of this embodiment is configured such that the end face of the drive shaft 14 of the drive screw 10 and the end face of the driven shaft 24 of the driven screw 20 can receive thrust loads (loads acting in the direction along the rotational axes X and Y). The end faces of the first end 14a and second end 14b of the drive shaft 14, and the first end 24a and second end 24b of the driven shaft 24 are stronger than the resin drive rotor 12, and their diameter (area) is smaller than the diameter (area) of the drive rotor 12 and the driven rotor 22. Therefore, even without using dedicated bearings to receive thrust loads, the frictional force that the end faces of the drive shaft 14 and the end faces of the driven shaft 24 exert on the inner surface 32b of the cover portion 32, the inner surface 36c of the support portion 36b, and the bottom surface 46d of the hole of the engaged portion 46 can be reduced when the drive screw 10 and the driven screw 20 rotate, thereby suppressing wear of the drive screw 10 and the driven screw 20. Furthermore, when the drive screw 10 and driven screw 20 rotate, cooling water penetrates between the end faces of the drive shaft 14 and driven shaft 24 and their inner surfaces, forming a thin film. This further reduces friction and suppresses wear.

[0035] Furthermore, in the screw pump 1, the drive screw 10 is provided with a first end 14a protruding from the drive rotor 12, and the driven screw 20 has a first end 24a protruding from the driven rotor 22. As a result, there is a space in which the cooling water that flows into the internal space of the main body 34 from the inlet 32a of the lid 32 of the case 30 enters and spreads radially outward without resistance. Therefore, compared to a configuration in which the first ends 14a and 24a are absent (or short) and the drive rotor 12 and driven rotor 22 are in contact (close) with the lid 32, the inflow resistance when the cooling water flows in from the inlet 32a when the screw pump 1 is operated, and the flow resistance when the cooling water flows through the internal space of the main body 34 can be reduced, thereby increasing the operating efficiency of the screw pump 1.

[0036] [Operation of the Screw Pump] Next, the operation of the screw pump 1 will be described. In the screw pump 1 according to this embodiment, cooling water that flows in from the inlet 32a of the lid 32 of the case 30 is transferred from the main body 34 toward the discharge section 36 by the rotation of the drive screw 10 and the driven screw 20, and discharged from the discharge port 36a. At this time, the drive screw 10 rotates as the rotational driving force of the drive motor 42 of the drive source 40 is transmitted in the order of motor shaft 44, engaged part 46, and engaged part 12b. The driven screw 20 receives rotational driving force from the cooling water transferred by the rotation of the drive screw 10 and rotates together with the drive screw 10. This is because the drive screw 10 and the driven screw 20 are arranged in a state where the helical teeth 12a of the drive rotor 12 and the helical teeth 22a of the driven rotor 22 are meshed.

[0037] As the drive screw 10 and driven screw 20 rotate, negative pressure is generated in the internal space of the main body 34, and cooling water outside the screw pump 1 is drawn into the internal space of the main body 34 of the case 30 through the inlet 32a. The cooling water in the space between the helical teeth 12a of the drive screw 10 and the helical teeth 22a of the driven screw 20, and in the space between the helical teeth 12a and 22a and the main body 34 is then pressurized and pumped towards the discharge unit 36 ​​as the drive screw 10 and driven screw 20 rotate. The cooling water that reaches the discharge unit 36 ​​is discharged to the outside through the discharge port 36a.

[0038] [Manufacturing Method for the Drive Screw] Next, the manufacturing method for the drive screw 10 used in the screw pump 1 of this embodiment will be explained with reference to Figure 4. In this embodiment, the drive screw 10 and the driven screw 20 are manufactured by the same method, so below, only the manufacturing method for the drive screw 10 will be explained, and the manufacturing method for the driven screw 20 will be mentioned as necessary.

[0039] As described above, the drive screw 10 is manufactured by so-called insert molding, in which resin is supplied with the drive shaft 14 placed in the molding die 50 (hereinafter also simply referred to as the die) to form the drive rotor 12.

[0040] From a manufacturing cost perspective, it is preferable to form the entire drive screw, including the drive shaft, out of resin. However, when the entire drive screw is formed out of resin, the cooling rate differs between the surface and the interior of the resin as the molten resin supplied to the mold cools and hardens, with the cooling rate being slower inside the resin. As a result, sink marks may occur on the surface of the helical teeth, potentially preventing the drive screw from achieving the necessary shape and precision. Furthermore, if voids occur inside, it may also cause problems in terms of strength. Therefore, in this embodiment, an iron-based metal material is used for the drive shaft 14. This allows the heat inside the resin to be released to the outside via the drive shaft 14, making the internal cooling rate equivalent to the surface heat dissipation rate. This suppresses sink marks and voids, enabling the manufacture of a highly precise and high-strength drive screw 10.

[0041] When forming the drive rotor 12 (helical teeth 12a) by resin molding, using a mold divided into two parts may cause burrs to form on the mating surfaces of the two molds. If burrs form on the helical teeth 12a as a result of using two molds to manufacture the helical teeth 12a, the burrs may peel off due to collision with the helical teeth 22a of the driven rotor 22 or due to the flow of the cooling water, and may be mixed into the cooling water as foreign matter. Therefore, when molding the drive rotor 12, a mold divided into two parts is not usually used for the part in which the helical teeth 12a are formed, but rather one mold (first mold 51 in this embodiment) is used for molding. Therefore, in order to remove the drive screw 10 from the first mold 51 after molding the drive rotor 12, it is necessary to rotate the drive screw 10 or the first mold 51 along the helical teeth 12a.

[0042] In this embodiment, the mold 50 includes a first mold 51 that forms the spiral teeth 12a of the drive rotor 12 and a second mold 52 that forms the engaging portion 12b. The first mold 51 has a cylindrical shape, and a spiral groove 51a that becomes the spiral teeth 12a after molding is formed inside. Further, a gear 51b coaxial with the central axis of the first mold 51 is formed on the side surface of the first mold 51. The second mold 52 has an engaging groove 52a that becomes the engaging portion 12b after molding. Since the mating surface between the first mold 51 and the second mold 52 is the boundary between the spiral teeth 12a and the engaging portion 12b, even if burrs occur, there is no risk of peeling off.

[0043] In this embodiment, a jig 60 is used to take out the drive screw 10, in which the molding of the drive rotor 12 is completed, from the mold 50. As shown in FIG. 4, the jig 60 includes a gripping portion 62, a shaft portion 64, and a holding portion 66. The gripping portion 62, the shaft portion 64, and the holding portion 66 are integrated. The gripping portion 62 is the handle of the jig 60. An operator who takes out the drive screw 10 from the mold 50 operates the jig 60 with the gripping portion 62. The shaft portion 64 extends from the gripping portion 62, and the holding portion 66 is disposed at the tip thereof. The holding portion 66 has a substrate 66a and a plurality (in this embodiment, three at 120-degree intervals) of holding protrusions 66b extending from the substrate 66a to the side opposite to the shaft portion 64. The holding protrusions 66b have a cylindrical shape.

[0044] To take out the drive screw ten from the mold 50, first, the second mold 52 is removed to expose the engaging portion 12b. Then, the holding protrusions 66b of the holding portion 66 of the jig 60 are fitted into the engaging recesses 12c of the engaging portion 1 twenty b. The distance from the center of the substrate 66a of the jig 60 to the outer peripheral surface of the holding protrusion 66b is substantially equal to the distance to the innermost peripheral surface of the engaging recess 12c of the engaging portion 12b on the rotation axis X. Therefore, when the holding protrusions 66b of the holding portion 66 of the jig 60 are fitted into the engaging recesses 12c of the engaging portion 12b, the holding protrusions 66b can hold the engaging recesses 12c without moving in the circumferential direction with respect to the engaging recesses 12c.

[0045] With the engaging portion 12b held by the jig 60, a motor (not shown) having a gear formed or attached to its rotating shaft is arranged such that the gear meshes with the gear 51b of the first mold 51, and the motor is rotated to rotate the gear 51b in the direction of the arrow. As a result, the drive screw 10 held by the jig 60 does not rotate, and only the first mold 51 rotates along the spiral teeth 12a, so that the drive screw 10 can be removed from the first mold 51.

[0046] In the drive screw 10 removed from the first mold 51, the engaging portion 12b used for holding the drive screw 10 during removal is used for engagement with the engaged portion 46 of the drive source 40 without being removed by cutting or the like. Thus, in the screw pump 1 of the present embodiment, the engaging portion 12b serves both as a portion used for holding the drive screw 10 when removing it from the mold 50 and as a portion used for engagement with the engaged portion of the drive source 40. Therefore, compared with the case where separate parts are used for the holding portion and the engaging portion, there is no need to remove the engaging portion 12b from the drive screw 10 by cutting or the like and attach a part for engaging with another engaged portion 46, so that the parts cost and the assembly man-hour are reduced, and the manufacturing cost of the screw pump 1 can be suppressed.

[0047] Similar to the drive screw 10, an engaging portion is formed in the driven screw 20 during insert molding, and the engaging portion is held by the jig 60 and removed from the first mold 51. Thereafter, the driven screw 20 is obtained by removing the engaging portion by cutting or the like.

[0048] 〔Second Embodiment〕 Next, the configuration of the screw pump 1 according to the second embodiment will be described with reference to FIG. 5. In the present embodiment, the shape of the drive rotor 12 of the drive screw 10 and the shape of the driven rotor 22 of the driven screw 20 are different from those of the first embodiment. Other than that, it has the same configuration as the first embodiment. Therefore, in the description of the present embodiment, the same reference numerals are given to the portions having the same configuration as the first embodiment, and the detailed description of the same configuration is omitted.

[0049] Specifically, in the screw pump 1 of this embodiment, the number of helical teeth 12a of the drive rotor 12 of the drive screw 10 and the number of helical teeth 22a of the driven rotor 22 of the driven screw 20 are reversed. That is, the helical teeth 12a are composed of 2 teeth, and the helical teeth 22a are composed of 3 teeth.

[0050] [Modifications of the First and Second Embodiments] Next, the configuration of the screw pump 1 according to modifications of the first and second embodiments will be described. In these modifications, the material of the drive rotor 12 of the drive screw 10 is different from that of the first and second embodiments. Otherwise, it has the same configuration as the first and second embodiments. Therefore, in the description of these modifications, the same reference numerals are used for parts with the same configuration as the first and second embodiments, and detailed explanations of similar configurations are omitted.

[0051] In this modified example, the drive rotor 12 of the drive screw 10 is made of an iron-based metal material such as carbon steel. The drive rotor 12 in this modified example is an example of a metal screw rotor. In other words, the drive screw 10 in this modified example is a metal screw (an example of a second screw) consisting of a metal drive rotor 12 and a metal drive shaft 14. Therefore, an engaging portion 12b is arranged at the end of the helical teeth 12a on the second end 14b side of the drive shaft 14 of the drive screw 10 in this modified example, and by engaging with the engaged portion 46 of the drive source 40, the rotational driving force of the drive source 40 is transmitted to the drive screw 10. The shape of the screw pump 1 in this modified example is the same as in Figures 1 and 5. In addition to the drive screw 10, the driven rotor 22 of the driven screw 20 may also be made of metal. In this case, the driven rotor 22 is an example of a metal screw rotor, and the driven screw 20 is a metal screw (an example of a second screw).

[0052] [Other Embodiments] Embodiments of this disclosure may be configured as follows, in addition to the embodiments and modifications described above (those having the same function as the embodiments described above are given the same numbers and reference numerals as the embodiments described above).

[0053] (1) In the screw pump 1 of each embodiment and modification described above, cooling water was used as the liquid to be transferred, but it is not limited to this. Instead of cooling water, insulating oil such as paraffin may be transferred. In this case, it is not necessary to use a low-hygroscopic resin as the material for the drive rotor 12 and the driven rotor 22, and an inexpensive resin material that is hygroscopic, such as nylon (PA66), can be used.

[0054] (2) In the above embodiments and modifications, the engaged projection 46b and the engaged recess 12c are assumed to have the same shape in plan view, but they do not have to be the same shape as long as the drive screw 10 is configured to be movable in both the circumferential direction (rotational direction) and along the rotation axis X relative to the drive source 40.

[0055] (3) In each of the above embodiments and modifications, the number of engaged protrusions 46b of the drive source 40 and the number of engaged recesses 12c of the drive rotor 12 was three, but it may be two or fewer or four or more.

[0056] (4) Although the screw pump 1 in each of the above embodiments and modified examples had two shafts, it may be composed of three or more shafts.

[0057] (5) In the above embodiment, both the drive screw 10 and the driven screw 20 were formed by insert molding, but the driven screw 20 may be formed by a manufacturing method and material different from insert molding.

[0058] (6) In the above embodiments and modifications, the drive shaft 14 and the driven shaft 24 were made of metal, but they may be made of resin or other materials. For example, if the drive shaft 14 and the driven shaft 24 are made of resin, the resin constituting the drive shaft 14 and the driven shaft 24 may be the same resin as the resin constituting the drive rotor 12 and the driven rotor 22, or it may be a different resin. If the drive shaft 14 and the driven shaft 24 are made of resin and are made of a different resin than the drive rotor 12 and the driven rotor 22, the drive screw 10 and the driven screw 20 can be formed by two-color molding.

[0059] In the screw pump 1 described in the above embodiment, the following configuration can be envisioned.

[0060] <1> One embodiment of the screw pump (1) comprises a plurality of screws (10, 20) having helical teeth (12a, 22a) with a predetermined pitch (P) and rotating around their respective rotation axes (X, Y), and a case (30) housing the plurality of screws (10, 20), wherein the plurality of screws (10, 20) are arranged in a meshed state with each other, and at least one of the plurality of screws (10, 20) is arranged to be coaxial with the rotation axis (X, Y). The first screw (10, 20) has a shaft (14, 24) and a resin screw rotor (12, 22) made of resin that is integrated with the shaft (14, 24), and at least one end (14a, 24a) of the shaft (14, 24) of the first screw (10, 20) protrudes from the resin screw rotor (12, 22), and the end (14a, 24a) protruding from the resin screw rotor (12, 22) is configured to be able to contact the case (30).

[0061] According to this embodiment, the screw pump (1) is configured so that thrust loads can be received at both ends (14a, 14b, 24a, 24b) of the shafts (14, 24) of the multiple screws (10, 20). Therefore, even without using dedicated bearings for receiving thrust loads, the frictional force that the ends (14a, 14b, 24a, 24b) of the shafts (14, 24) exert on the case (30) when the multiple screws (10, 20) rotate can be reduced, thereby suppressing wear. In addition, since the first screw (10, 20) has a resin screw rotor (12, 22), manufacturing costs can be reduced compared to the case where the entire screw is made of metal material.

[0062] <2> In the screw pump (1) described in <1> above, it is preferable that the shaft (14, 24) is a metal shaft made of metal, and the first screw (10, 20) is composed of a resin screw rotor (12, 22) that is insert-molded into the metal shaft (14, 24).

[0063] If the shafts (14, 24) are metal shafts, the ends (14a, 14b, 24a, 24b) of the shafts (14, 24) are stronger than the resin screw rotors (12, 22), and their diameter (area) is smaller than that of the resin screw rotors (12, 22). Therefore, even without using dedicated bearings to receive thrust loads, the frictional force exerted by the ends (14a, 14b, 24a, 24b) of the metal shafts (14, 24) on the case (30) during the rotation of the first screws (10, 20) can be further reduced, thereby suppressing wear.

[0064] Furthermore, when the entire screw (10, 20) is formed from resin, the cooling rate differs between the surface and the interior of the resin as the molten resin supplied into the mold cools and hardens, with the cooling rate being slower inside the resin. As a result, sink marks and other defects may occur on the surface of the resin screw rotor (12, 22), potentially preventing the screw (10, 20) from achieving the required shape and precision. Additionally, the occurrence of voids inside the resin may pose a strength problem. Therefore, in this embodiment, an iron-based metal material is used as the metal shaft (14, 24). This allows the heat inside the resin to be released to the outside via the metal shaft (14, 24), making it possible to make the internal cooling rate equivalent to the surface heat dissipation rate. This suppresses sink marks and voids, enabling the manufacture of a first screw (10, 20) with high precision and high strength.

[0065] <3> In the screw pump (1) described in <1> or <2> above, it is preferable that at least one of the plurality of screws (10, 20) is a second screw (10, 20) having a metal shaft (14, 24) arranged to be coaxial with the rotation axis (X, Y) and a metal screw rotor (12, 22) integrated with the metal shaft (14, 24).

[0066] According to this embodiment, at least one of the multiple screws (10, 20) is a second screw (10, 20) having a metal shaft (14, 24) arranged coaxially with the rotation axis (X, Y) and a metal screw rotor (12, 22) integrated with the metal shaft (14, 24), so that the second screw (10, 20) can be manufactured with high strength.

[0067] <4> In the screw pump (1) described in <3> above, the pump further comprises a drive source (40) having an engaged portion (46) that generates rotational driving force and transmits the rotational driving force to one of the second screws (10, 20) (10), wherein the metal screw rotor (12) of the second screw (10) has an engaged portion (12b) at one end (14b) in the direction along the rotation axis (X), and it is preferable that the rotational driving force of the drive source (40) is transmitted to the second screw (10) by the engaged portion (46) of the drive source (40) engaging with the engaged portion (12b) of the metal screw rotor (12).

[0068] According to this embodiment, by engaging the engaged portion (46) of the drive source (40) with the engaged portion (12b) of the metal screw rotor (12), the rotational driving force of the drive source (40) can be reliably transmitted to the second screw (10).

[0069] <5> In the screw pump (1) described in <1> or <2> above, the shafts (14, 24) of the first screws (10, 20) preferably have recesses (14c) or protrusions (14d) on their outer circumference in order to prevent relative rotation of the resin screw rotors (12, 22) with respect to the shafts (14, 24).

[0070] According to this embodiment, the shafts (14, 24) and the resin screw rotors (12, 22) rotate together as a single unit without relative rotation.

[0071] <6> In the screw pump (1) described in <3> or <4> above, the shafts (14, 24) of the second screws (10, 20) preferably have recesses (14c) or protrusions (14d) on their outer circumference in order to prevent relative rotation of the metal screw rotors (12, 22) with respect to the shafts (14, 24).

[0072] According to this embodiment, the shafts (14, 24) and the metal screw rotors (12, 22) rotate together as a single unit without relative rotation.

[0073] This disclosure can be used in screw pumps.

[0074] 1: Screw pump, 10: Drive screw (screw, first screw, second screw), 12: Drive rotor (resin screw rotor, metal screw rotor), 12a: Helical teeth, 12b: Engaging part, 14: Drive shaft (shaft, metal shaft), 14a: First end (end), 14b: Second end (end), 20: Driven screw (screw, first screw, second screw), 22: Driven rotor (resin screw rotor, metal screw rotor), 22a: Helical teeth, 24: Driven shaft (shaft, metal shaft), 24a: First end (end), 24b: Second end (end), 30: Case, 40: Drive unit, 46: Engaged part, P: Pitch, X: Rotation axis, Y: Rotation axis

Claims

1. A screw pump comprising: a plurality of screws having helical teeth with a predetermined pitch and rotating around their respective rotational axes; and a case housing the plurality of screws, wherein the plurality of screws are arranged in a meshed state with respect to each other; and at least one of the plurality of screws is a first screw having a shaft arranged coaxially with the rotational axis and a resin screw rotor made of resin integrated with the shaft, wherein at least one end of the shaft of the first screw protrudes from the resin screw rotor, and the end protruding from the resin screw rotor is configured to abut against the case.

2. The screw pump according to claim 1, wherein the shaft is a metal shaft made of metal, and the first screw is composed of the resin screw rotor that is insert-molded into the metal shaft.

3. The screw pump according to claim 1 or 2, wherein at least one of the plurality of screws is a second screw having a metal shaft arranged coaxially with the rotation axis and a metal screw rotor integrated with the metal shaft.

4. The screw pump according to claim 3, further comprising a drive source having an engaged portion that generates a rotational driving force and transmits the rotational driving force to one of the second screws, wherein the metal screw rotor of the second screw has an engaged portion at one end in the direction along the rotation axis, and the rotational driving force of the drive source is transmitted to the second screw by the engaged portion of the drive source engaging with the engaged portion of the metal screw rotor.

5. The screw pump according to claim 1 or 2, wherein the shaft of the first screw has a recess or protrusion on its outer surface in order to prevent relative rotation of the resin screw rotor with respect to the shaft.

6. The screw pump according to claim 3 or 4, wherein the shaft of the second screw has a recess or protrusion on its outer surface in order to prevent relative rotation of the metal screw rotor with respect to the shaft.

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