Gear pump

Abstract

To provide a gear pump which can obtain proper lubrication between a casing and a gear even when a liquid for being sucked and discharged is a low-lubricity liquid such as water, and which can curb an increase in driving torque for rotatively driving the gear.SOLUTION: A casing 1 comprises a body 2 for housing both gears 12 and 13, and two covers 3 and 4 that are arranged on both the axial sides of the body 2. The body 2 and both the covers 3 and 4 are integrally provided by being secured and connected with a bolt 11. The body 2 is made of a resin material, and both the covers 3 and 4 and both the gears 12 and 13 are made of metal. The bolt 11 is made of a metallic material with a linear expansion coefficient larger than that of carbon steel and smaller than that of the resin material constituting the body 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gear pump that sucks in and discharges liquid by rotating a drive gear and a driven gear that mesh with each other, and in particular to a gear pump that is suitable for sucking in and discharging liquids with low lubricity, such as water. [Background technology]

[0002] An external gear pump, one of these types of gear pumps, houses a drive gear and a driven gear that mesh with each other inside a casing, and the rotation of these gears draws liquid into a suction passage and discharges it from a discharge passage. The casing is composed of a body that houses the drive gear and the driven gear, a front cover located on one axial side of the body, and a rear cover located on the other axial side opposite the one axial side of the body. Bolts are inserted from the outside of the rear cover, pass through the casing, and screwed onto the front cover, so that the casing, front cover, and rear cover are tightly fastened together to form an integrated unit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-233897 (Fig. 3) Summary of the Invention [Problem to be solved by the invention]

[0004] However, in such conventional gear pumps, the casing and gears are generally made of metal, so if a liquid with low lubricity, such as water, is used as the liquid to be sucked in and discharged, it is difficult to obtain good lubrication between the casing and gears. Therefore, it is conceivable to make the body constituting the casing out of a resin material, thereby reducing wear at the points where the gears slide and contact, and achieving good lubrication between the gears. However, when the body is made of resin, the linear expansion coefficient of resin is higher than that of metal, so as the temperature of the liquid being drawn in and discharged rises, the body expands, reducing the gap between the gears and the body, which creates the problem of increasing the driving torque required to rotate the gears.

[0005] The object of the present invention is to provide a gear pump that can obtain good lubrication between the casing and the gears even when the liquid being sucked in and discharged is a liquid with low lubricity, such as water, and can suppress an increase in the drive torque that rotates the gears. [Means for solving the problem]

[0006] In order to achieve this object, the present invention takes the following measures: This gear pump houses a drive gear and a driven gear that mesh with each other and can rotate freely inside a casing, and draws in and discharges liquid by the rotation of both gears.The casing is composed of a body that houses both gears and two covers that are located on either side of the body in the axial direction.The body and both covers are tightly fastened together with bolts to form a single unit.The body is made of resin, while both covers and both gears are made of metal, and the bolts are made of metal that has a linear expansion coefficient greater than that of carbon steel but smaller than that of the resin material that makes up the body. [Effects of the Invention]

[0007] As described above, the invention described in claim 1 has a casing composed of a body housing both gears and two covers disposed on either side of the body in the axial direction. The body and covers are integrally fastened together with bolts. The body is made of a resin material, while the covers and gears are made of a metal material. The bolts are made of a metal material with a linear expansion coefficient greater than that of carbon steel but less than that of the resin material constituting the body. Therefore, the resin material used for the casing body, which makes sliding contact with the gears, reduces wear. Furthermore, the bolts expand in accordance with the expansion of the body due to a rise in temperature of the liquid being drawn in or discharged. This prevents the clearance between the body and the gears from decreasing, ensuring good lubrication between the casing and the gears and suppressing an increase in the drive torque that rotates the gears. However, if the bolts were made of a metal material with a linear expansion coefficient equal to or greater than that of the resin material constituting the body, the bolts would expand more than the body due to a rise in temperature of the liquid being drawn in or discharged, widening the gap between the body and the gears and increasing the amount of liquid leaking out. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 3 is a cross-sectional view of the external gear pump taken along line BB in FIG. 2, showing one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 2 is a left side view seen from the arrow E in FIG. [Figure 4] FIG. 2 is a right side view as seen from the arrow F in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention in which the gear pump is an external gear pump will be described with reference to the drawings. 1 to 4, 1 denotes a casing, which is composed of a body 2 and two covers, a first cover 3 and a second cover 4, which are disposed on both axial sides of the body 2. The body 2 is composed of a substantially rectangular parallelepiped, block-shaped main body member 5 and a plate-like plate member 6 that abuts against one axial side of the main body member 5 and the other axial side opposite to it. The main body member 5 is made of glass fiber-reinforced polyphenylene sulfide resin (commonly known as PPS) as a resin material, and has a linear expansion coefficient of approximately 26 x 10 -6 / °C. 7 is a first through hole and 8 is a second through hole, and both through holes 7, 8 are formed through the main body member 5 at a radial distance from each other and parallel to the axial direction. As shown in Figure 2, 9 is a gear storage hole, which is formed as a recess on the other side of the main body member 5 and has a cross section shaped like a figure eight. Both through holes 7, 8 open at the bottom of the gear storage hole 9. Four bolt insertion holes 5A are formed through the main body member 5 near the four corners in the cross section.

[0010] The plate member 6 is made of the same material as the main body member 5, that is, polyphenylene sulfide resin containing glass fiber, and has a linear expansion coefficient of approximately 26×10 -6 / °C, and the gear housing hole 9 is closed. Four bolt insertion holes 6A are formed through the plate member 6 near the four corners in the cross section at the same positions as the bolt insertion holes 5A of the main body member 5. The first cover 3 is made of spheroidal graphite cast iron FCD600 as specified in the Japanese Industrial Standard JIS G5502:2022 "Spheroidal graphite cast iron products" as a metallic material, and has a linear expansion coefficient of approximately 12 x 10 -6 / °C, and then joined to one axial side surface of the main body member 5, and both through holes 7, 8 are closed.

[0011] An insertion hole 10 is formed through the first cover 3 in the axial direction, and a protrusion 10A is formed to protrude concentrically with the insertion hole 10. A recess 5A is formed concentrically with the first through hole 7 on one axial side surface of the main body member 5, and the protrusion 10A of the first cover 3 is spigot-fitted into the recess 5A, thereby connecting the first through hole 7 and the insertion hole 10 concentrically. The insertion hole 10 is formed with a larger diameter than the first through hole 7. As shown in FIG. 3, four screw holes 3A are formed through the first cover 3 near the four corners in cross section, at the same positions as the bolt insertion holes 5A and 6A. Two mounting holes 3B are formed through the first cover 3, and bolts (not shown) are inserted through them to attach the casing 1 to the mounting portion.

[0012] The second cover 4 is made of carbon steel S45C for machine structures, as specified in the Japanese Industrial Standard JIS G4051:2023 "Carbon steel for machine structures," and has a linear expansion coefficient of approximately 12 x 10 -6 / °C and joined to the other side of the plate member 6 constituting the body 2. Four bolt insertion holes 4A are formed through the second cover 4 near the four corners in the cross section at the same positions as the screw holes 3A and the bolt insertion holes 5A and 6A.

[0013] 4, four bolts 11 are arranged with their heads 11A near the four corners of the second cover 4, are inserted through the bolt insertion holes 4A, 5A, 6A from the outside of the second cover 4, and have threaded portions 11B at their tips that are screwed into the respective screw holes 3A of the first cover 3. Each bolt 11 tightly fastens the main body member 5 and plate member 6 that make up the body 2 to both covers 3 and 4, and forms an integral unit, between the head 11A and the threaded portion 11B that screws into the respective screw holes 3A of the first cover 3.

[0014] Each bolt 11 is made of austenitic stainless steel SUS304 specified in the Japanese Industrial Standard JIS G4303:2021 "Stainless Steel Bar" and has a linear expansion coefficient of approximately 17 to 18 × 10 -6 / ℃, and the linear expansion coefficient of carbon steel is 11~12 × 10 -6 / ℃, and the linear expansion coefficient of the glass fiber-reinforced polyphenylene sulfide resin that forms body 2 is 26 × 10 -6 / ℃ or less.

[0015] Reference numeral 12 denotes a drive gear and 13 denotes a driven gear, which are a pair of identically shaped gears having a plurality of meshing external teeth 12A, 13A on their outer peripheries, and are housed in the gear housing hole 9, with the tips of the external teeth 12A, 13A slidably contacting the inner circumferential surface of the gear housing hole 9, one axial side surface of each gear slidably contacting the other axial end surface of the plate member 6, and the other axial side surface opposite to the one axial side surface of each gear slidably contacting the bottom surface of the gear housing hole 9. Both gears 12, 13 are made of the same material as the second cover 4, namely, carbon steel S45C for mechanical structures, and have a linear expansion coefficient of approximately 12×10 -6 / °C, and the surface is coated with a DLC (Diamond-Like Carbon) coating. As shown in Figure 2, reference numeral 14 denotes an intake passage for drawing in liquid, which is formed in main body member 5 and connected to one radial side of gear housing hole 9. Reference numeral 15 denotes a discharge passage for discharging liquid, which is formed in main body member 5 and connected to the other radial side that is symmetrical to the one radial side to which intake passage 14 is connected, via the meshing point where both external teeth 12A, 13A of both gears 12, 13 of gear housing hole 9 mesh.

[0016] Reference numeral 16 denotes a drive shaft formed from a metal material, which engages with the drive gear 12 in the direction of rotation via a key 17, passes through the first through-hole 7 and the insertion hole 10, and its tip protrudes outward. This tip is connected to an electric motor (not shown) to rotate the drive gear 12. Reference numeral 18 denotes a bushing press-fitted into the first through-hole 7, which makes sliding contact with the drive shaft 16 to rotatably support it. Reference numeral 19 denotes a seal member provided in the insertion hole 10, which makes sliding contact with the drive shaft 16 to seal the inside of the casing 1. Reference numeral 20 denotes a ball bearing provided axially outward of the seal member 19 in the insertion hole 10, which rotatably supports the drive shaft 16. The drive shaft 16 is supported on one axial side of the drive gear 12 by the bushing 18 and ball bearing 20.

[0017] Reference numeral 21 denotes a driven shaft formed from a metal material, which engages with driven gear 13 in the rotational direction via key 22 and is inserted into second through-hole 8. Reference numeral 23 denotes a bushing press-fitted into second through-hole 8, which makes sliding contact with driven shaft 21 and supports it rotatably. Driven shaft 21 is supported by bushing 23 on one axial side of driven gear 13.

[0018] Next, the operation of this configuration will be described. When the drive gear 12 is driven to rotate in the direction of arrow C in Figure 2 by the drive shaft 16, the driven gear 13 that meshes with the drive gear 12 is driven to rotate in the direction opposite to the direction of arrow C, and the liquid on the low-pressure side flows through the intake passage 14, is sucked between the external teeth 12A of the drive gear 12 and between the external teeth 13A of the driven gear 13, is transported along the inner periphery of the gear housing hole 9 to the discharge side, and flows through the discharge passage 15 to be discharged.

[0019] When the temperature of the liquid being sucked in and discharged rises, the main body member 5 that constitutes the body 2 expands, increasing the length dimension D1 between one side surface and the bottom surface of the gear storage hole 9, but each bolt 11 also expands, increasing the length dimension D2 between the head 11A and the threaded portion 11B that screws into each screw hole 3A of the first cover 3, thereby preventing a reduction in the gap H between the bottom surface of the gear storage hole 9 and the other axial side surfaces of the gears 12 and 13.

[0020] In this operation, the casing 1 comprises a body 2 that houses both gears 12, 13 and two covers 3, 4 disposed on either side of the body 2 in the axial direction, and the body 2 and both covers 3, 4 are tightly fastened together with bolts 11 to form an integrated unit, the body 2 being made of resin, while the covers 3, 4 and both gears 12, 13 are made of metal, and the bolts 11 are made of metal with a linear expansion coefficient greater than that of carbon steel but smaller than that of the resin material that makes up the body 2. As a result, the body 2 of the casing 1 that makes sliding contact with the gears 12, 13 is made of resin to reduce wear, and the bolts 11 expand as the body 2 expands due to a rise in temperature of the liquid being drawn in and discharged. This prevents a reduction in the gap H between the bottom surface of the gear housing hole 9 formed in the main member 5 of the body 2 and the other axial side surfaces of the gears 12, 13, ensuring good lubrication between the casing 1 and the gears 12, 13 and suppressing an increase in the drive torque that rotates the gears 12, 13. Furthermore, if each bolt 11 is made of a metal material with a linear expansion coefficient equal to or greater than that of the resin material that makes up the body 2, the rise in temperature of the liquid being sucked in or discharged will cause each bolt 11 to expand more than the body 2, increasing the gap H between the body 2 and the gears 12, 13, resulting in the inconvenience of increasing the amount of leakage of the liquid being sucked in or discharged.

[0021] In addition, the surfaces of both gears 11 and 12 are coated with DLC (Diamond-Like Carbon), which reduces wear on the body 2 with which the gears 11 and 12 slide, further reducing wear and adhesion of the body 2 in sliding contact with the gears 11 and 12, and achieving even better lubrication between the body 2 and the gears 11 and 12.

[0022] In the above-described embodiment, the drive gear 12 and the driven gear 13 are identically shaped and paired with a plurality of meshing external teeth 12A, 13A on their outer peripheries. However, an internal gear pump may be used in which the drive gear is an external gear with external teeth and the driven gear is an internal gear with internal teeth that mesh internally with the external teeth and is eccentrically disposed relative to the external gear. Furthermore, although glass fiber-reinforced polyphenylene sulfide resin (commonly known as PPS) was used as the resin material for the main body member 5 and plate member 6 that make up the body 2, polyether ether ketone resin (commonly known as PEEK) or phenolic resin may also be used. Furthermore, while the drive shaft 16 and the driven shaft 21 support both gears 12, 13 on one axial side, it is of course possible for both gears 12, 13 to be supported on both axial sides. [Explanation of symbols]

[0023] 1: Casing 2: Body 3: First cover (cover) 4: Second cover (cover) 11: Bolt 12: Drive gear 13: Driven gear

Claims

[Claim 1] A gear pump in which a drive gear and a driven gear that mesh with each other are rotatably housed inside a casing, and which draws in and discharges liquid by the rotation of both gears, wherein the casing is composed of a body that houses both gears and two covers that are located on both axial sides of the body, and the body and both covers are tightly fastened together with bolts to form an integrated unit, the body being made of resin material, while both covers and both gears are made of metal material, and the bolts are made of metal material whose linear expansion coefficient is greater than that of carbon steel but smaller than that of the resin material that makes up the body.

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