Crosslinked fluororesin-coated rotor manufacturing method

A crosslinked fluororesin-coated rotor manufacturing method is a method for manufacturing an annular outer rotor of an internal gear pump including the outer rotor, and an inner rotor, a side surfaces of the outer rotor being coated with a crosslinked fluororesin, an inner peripheral surface of the outer rotor not being coated with the crosslinked fluororesin, the method including: using an outer masking jig for covering the inner peripheral surface in a state where the side surfaces of the outer rotor are exposed; coating the outer rotor with an uncrosslinked fluororesin in a state where the outer masking jig is mounted to the outer rotor; and then irradiating the fluororesin with radiation in a state where the outer masking jig is removed from the outer rotor, to crosslink the fluororesin.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on PCT/JP2019/050632 filed on Dec. 24, 2019, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a crosslinked fluororesin-coated rotor manufacturing method.

BACKGROUND ART

As an internal gear pump, a pump described in PATENT LITERATURE 1 is known. The internal gear pump of PATENT LITERATURE 1 includes an annular outer rotor, an inner rotor which rotates about a position eccentric from the center of the outer rotor on the radially inner side of the outer rotor, and a housing in which the outer rotor and the inner rotor are housed. Here, the outer rotor has an inner peripheral surface forming a plurality of internal teeth, and side surfaces orthogonal to an axial direction. In addition, the inner rotor has an outer peripheral surface forming a plurality of external teeth which mesh with the internal teeth of the outer rotor, and side surfaces orthogonal to the axial direction.

Generally, a clearance (side clearance) for permitting rotation of the outer rotor is set between each side surface of the outer rotor and the housing. If the side clearance is large, the leak amount of fluid increases, decreasing the discharge amount of the pump. Thus, it is preferable that the side clearance is small. However, if the side clearance is made excessively small, there is a problem that seizure easily occurs between each side surface of the outer rotor and the housing. Therefore, the side clearance is usually set to a size of several tens of micrometers or more.

Similarly, a clearance (side clearance) for permitting rotation of the inner rotor is also set between each side surface of the inner rotor and the housing. This side clearance is also usually set to a size of several tens of micrometers or more.

Here, the applicants of the present application have developed an internal gear pump that allows clearances of an outer rotor and an inner rotor to be set to be very small while preventing seizure of the outer rotor and the inner rotor, and have proposed a pump of PATENT LITERATURE 2 as such an internal gear pump.

In the internal gear pump of PATENT LITERATURE 2, at least one of an outer rotor, an inner rotor, and a housing is coated with a crosslinked fluororesin. Since the crosslinked fluororesin has characteristics of having a low friction coefficient and high wear resistance, if at least one of the outer rotor, the inner rotor, and the housing is coated with the crosslinked fluororesin, even when the clearances of the outer rotor and the inner rotor are set to be very small, it is possible to prevent seizure of the outer rotor and the inner rotor over a long period of time.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Solution to Problem

A crosslinked fluororesin-coated rotor manufacturing method according to an aspect of the present disclosure is a crosslinked fluororesin-coated rotor manufacturing method for manufacturing an annular outer rotor of an internal gear pump includingthe outer rotor having an inner peripheral surface forming a plurality of internal teeth, and side surfaces orthogonal to an axial direction, andan inner rotor having an outer peripheral surface forming a plurality of external teeth which mesh with the internal teeth, and configured to rotate about a position eccentric from a center of the outer rotor on a radially inner side of the outer rotor,the side surfaces of the outer rotor being coated with a crosslinked fluororesin, the inner peripheral surface of the outer rotor not being coated with the crosslinked fluororesin, the method including:using an outer masking jig for covering the inner peripheral surface in a state where the side surfaces of the outer rotor are exposed, the outer masking jig including a positioning fitting tooth portion for positioning the outer masking jig with respect to the outer rotor in a circumferential direction by fitting to the inner peripheral surface of the outer rotor;coating the outer rotor with an uncrosslinked fluororesin in a state where the outer masking jig is mounted to the outer rotor; andthen irradiating the fluororesin with radiation in a state where the outer masking jig is removed from the outer rotor, to crosslink the fluororesin.

Moreover, a crosslinked fluororesin-coated rotor manufacturing method according to an aspect of the present disclosure is a crosslinked fluororesin-coated rotor manufacturing method for manufacturing an inner rotor of an internal gear pump includingan annular outer rotor having an inner peripheral surface forming a plurality of internal teeth, andthe inner rotor having an outer peripheral surface forming a plurality of external teeth which mesh with the internal teeth, and side surfaces orthogonal to an axial direction, and configured to rotate about a position eccentric from a center of the outer rotor on a radially inner side of the outer rotor,the side surfaces of the inner rotor being coated with a crosslinked fluororesin, the outer peripheral surface of the inner rotor not being coated with the crosslinked fluororesin, the method including:using an inner masking jig for covering the outer peripheral surface in a state where the side surfaces of the inner rotor are exposed, the inner masking jig including a positioning fitting tooth portion for positioning the inner masking jig with respect to the inner rotor in a circumferential direction by fitting to the outer peripheral surface of the inner rotor;coating the inner rotor with an uncrosslinked fluororesin in a state where the inner masking jig is mounted to the inner rotor; andthen irradiating the fluororesin with radiation in a state where the inner masking jig is removed from the inner rotor, to crosslink the fluororesin.

DETAILED DESCRIPTION

Problems to be Solved by the Present Disclosure

The inventors of the present application have conducted in-house development of an internal gear pump in which at least one of an outer rotor, an inner rotor, and a housing is coated with a crosslinked fluororesin as in PATENT LITERATURE 2, and have studied mass production of a pump in which an outer rotor and an inner rotor are coated with a crosslinked fluororesin, as such an internal gear pump.

Here, when coating an outer rotor with a crosslinked fluororesin, it is considered to coat the entirety of the surface (an inner peripheral surface forming internal teeth of the outer rotor, side surfaces of the outer rotor, an outer peripheral surface of the outer rotor) of the outer rotor. In addition, when coating an inner rotor with a crosslinked fluororesin, it is considered to coat the entirety of the surface (an outer peripheral surface forming external teeth of the inner rotor, side surfaces of the inner rotor, an inner peripheral surface of the inner rotor) of the inner rotor.

However, when the entirety of the surface of the outer rotor is coated with the crosslinked fluororesin, or when the entirety of the surface of the inner rotor is coated with the crosslinked fluororesin, it is difficult to accurately manage the clearance (tip clearance) between the external teeth of the outer rotor and the internal teeth of the inner rotor, thus facing a problem that the pump performance becomes unstable.

That is, since the inner peripheral surface forming the internal teeth of the outer rotor is a curved surface having the toothed shape of the internal teeth, it is difficult to accurately manage the thickness of the crosslinked fluororesin when coating the inner peripheral surface of the outer rotor with the crosslinked fluororesin. Similarly, since the outer peripheral surface forming the external teeth of the inner rotor is also a curved surface having the toothed shape of the external teeth, it is difficult to accurately manage the thickness of the crosslinked fluororesin when coating the outer peripheral surface of the inner rotor with the crosslinked fluororesin. Therefore, the size of the tip clearance between the internal teeth on the inner periphery of the outer rotor and the external teeth on the outer periphery of the inner rotor is not stable, thus facing a problem that the pump performance becomes unstable.

Therefore, the inventors have studied not coating the inner peripheral surface of the outer rotor and the outer peripheral surface of the inner rotor when coating the outer rotor and the inner rotor with the crosslinked fluororesin, in order to stabilize the size of the tip clearance between the internal teeth on the inner periphery of the outer rotor and the external teeth on the outer periphery of the inner rotor. Specifically, the inventors have studied coating a portion of the outer rotor excluding the inner peripheral surface by attaching masking tape to the inner peripheral surface of the outer rotor when coating the surface of the outer rotor with the crosslinked fluororesin. In addition, the inventors have studied coating a portion of the inner rotor excluding the outer peripheral surface by attaching masking tape to the outer peripheral surface of the inner rotor when coating the surface of the inner rotor with the crosslinked fluororesin.

However, since the inner peripheral surface of the outer rotor is a curved surface having the toothed shape of the internal teeth, it is difficult to attach the masking tape such that the masking tape is in close contact with the inner peripheral surface of the outer rotor. Similarly, since the outer peripheral surface of the inner rotor is also a curved surface having the toothed shape of the external teeth, it is difficult to attach the masking tape such that the masking tape is in close contact with the outer peripheral surface of the inner rotor.

Therefore, an object of the present disclosure is to easily manufacture a rotor, of an internal gear pump, which can prevent seizure of the rotor over a long period of time and has stable performance.

Effects of the Present Disclosure

According to the present disclosure, it is possible to easily manufacture a rotor, of an internal gear pump, which can prevent seizure of the rotor over a long period of time and has stable performance.

Description of Embodiments of the Present Disclosure

(1) A crosslinked fluororesin-coated rotor manufacturing method according to an aspect of the present disclosure is a crosslinked fluororesin-coated rotor manufacturing method for manufacturing an annular outer rotor of an internal gear pump includingthe outer rotor having an inner peripheral surface forming a plurality of internal teeth, and side surfaces orthogonal to an axial direction, andan inner rotor having an outer peripheral surface forming a plurality of external teeth which mesh with the internal teeth, and configured to rotate about a position eccentric from a center of the outer rotor on a radially inner side of the outer rotor,the side surfaces of the outer rotor being coated with a crosslinked fluororesin, the inner peripheral surface of the outer rotor not being coated with the crosslinked fluororesin, the method including:using an outer masking jig for covering the inner peripheral surface in a state where the side surfaces of the outer rotor are exposed, the outer masking jig including a positioning fitting tooth portion for positioning the outer masking jig with respect to the outer rotor in a circumferential direction by fitting to the inner peripheral surface of the outer rotor;coating the outer rotor with an uncrosslinked fluororesin in a state where the outer masking jig is mounted to the outer rotor; andthen irradiating the fluororesin with radiation in a state where the outer masking jig is removed from the outer rotor, to crosslink the fluororesin.

When doing so, since the side surfaces of the outer rotor are coated with the crosslinked fluororesin, even when the side clearance of the outer rotor is set to be very small, it is possible to prevent seizure of the outer rotor over a long period of time.

Since the outer masking jig for covering the inner peripheral surface in a state where the side surfaces of the outer rotor are exposed is used when coating the outer rotor with the uncrosslinked fluororesin, the inner peripheral surface of the outer rotor is not coated with the fluororesin. Therefore, the size of the tip clearance between the internal teeth on the inner periphery of the outer rotor and the external teeth on the outer periphery of the inner rotor becomes stable, and the pump performance becomes stable.

Since the positioning fitting tooth portion for positioning the outer masking jig with respect to the outer rotor in the circumferential direction by fitting to the inner peripheral surface of the outer rotor is formed in the outer masking jig, the work of mounting the outer masking jig to the outer rotor is easy.

When crosslinking the uncrosslinked fluororesin by irradiating the fluororesin with radiation, the irradiation with radiation is performed in a state where the outer masking jig is removed from the outer rotor. Therefore, the radiation is prevented from being blocked by the outer masking jig, and it is possible to evenly and uniformly crosslink the fluororesin.(2) As the outer masking jig, a jig having a toothed flange which overlaps peripheral portions, along the inner peripheral surface, of the side surfaces of the outer rotor is preferably used.

When doing so, when coating the outer rotor with the uncrosslinked fluororesin, most of each side surface of the outer rotor can be exposed while assuredly covering the inner peripheral surface of the outer rotor with the toothed flange. Therefore, it is possible to coat most of each side surface of the outer rotor with the crosslinked fluororesin while preventing the inner peripheral surface of the outer rotor from being coated.(3) The toothed flange is preferably formed such that a region where the toothed flange overlaps the side surfaces of the outer rotor has a width of not greater than 0.5 mm.

When doing so, it is possible to coat almost the entirety of each side surface of the outer rotor with the crosslinked fluororesin.(4) In the case where the outer rotor has a cylindrical outer peripheral surface,both the side surfaces and the outer peripheral surface of the outer rotor can be coated with the uncrosslinked fluororesin when coating the outer rotor with the uncrosslinked fluororesin in a state where the outer masking jig is mounted to the outer rotor; andboth the fluororesin on the side surfaces and the fluororesin on the outer peripheral surface can then be crosslinked when irradiating the fluororesin with radiation in a state where the outer masking jig is removed from the outer rotor.

When doing so, since not only the side surfaces of the outer rotor but also the outer peripheral surface of the outer rotor is coated with the crosslinked fluororesin, it is possible to effectively reduce the torque for rotationally driving the outer rotor.(5) A crosslinked fluororesin-coated rotor manufacturing method according to an aspect of the present disclosure is a crosslinked fluororesin-coated rotor manufacturing method for manufacturing an inner rotor of an internal gear pump includingan annular outer rotor having an inner peripheral surface forming a plurality of internal teeth, andthe inner rotor having an outer peripheral surface forming a plurality of external teeth which mesh with the internal teeth, and side surfaces orthogonal to an axial direction, and configured to rotate about a position eccentric from a center of the outer rotor on a radially inner side of the outer rotor,the side surfaces of the inner rotor being coated with a crosslinked fluororesin, the outer peripheral surface of the inner rotor not being coated with the crosslinked fluororesin, the method including:using an inner masking jig for covering the outer peripheral surface in a state where the side surfaces of the inner rotor are exposed, the inner masking jig including a positioning fitting tooth portion for positioning the inner masking jig with respect to the inner rotor in a circumferential direction by fitting to the outer peripheral surface of the inner rotor;coating the inner rotor with an uncrosslinked fluororesin in a state where the inner masking jig is mounted to the inner rotor; andthen irradiating the fluororesin with radiation in a state where the inner masking jig is removed from the inner rotor, to crosslink the fluororesin.

When doing so, since the side surfaces of the inner rotor are coated with the crosslinked fluororesin, even when the side clearance of the inner rotor is set to be very small, it is possible to prevent seizure of the inner rotor over a long period of time.

Since the inner masking jig for covering the outer peripheral surface in a state where the side surfaces of the inner rotor are exposed is used when coating the inner rotor with the uncrosslinked fluororesin, the outer peripheral surface of the inner rotor is not coated with the fluororesin. Therefore, the size of the tip clearance between the internal teeth on the inner periphery of the outer rotor and the external teeth on the outer periphery of the inner rotor becomes stable, and the pump performance becomes stable.

Since the positioning fitting tooth portion for positioning the inner masking jig with respect to the inner rotor in the circumferential direction by fitting to the outer peripheral surface of the inner rotor is formed in the inner masking jig, the work of mounting the inner masking jig to the inner rotor is easy.

When crosslinking the uncrosslinked fluororesin by irradiating the fluororesin with radiation, the irradiation with radiation is performed in a state where the inner masking jig is removed from the inner rotor. Therefore, the radiation is prevented from being blocked by the inner masking jig, and it is possible to evenly and uniformly crosslink the fluororesin.(6) As the inner masking jig, a jig having a toothed flange which overlaps peripheral portions, along the outer peripheral surface, of the side surfaces of the inner rotor is preferably used.

When doing so, when coating the inner rotor with the uncrosslinked fluororesin, most of each side surface of the inner rotor can be exposed while assuredly covering the outer peripheral surface of the inner rotor with the toothed flange. Therefore, it is possible to coat most of each side surface of the inner rotor with the crosslinked fluororesin while preventing the outer peripheral surface of the inner rotor from being coated.(7) The toothed flange is preferably formed such that a region where the toothed flange overlaps the side surfaces of the inner rotor has a width of not greater than 0.5 mm.

When doing so, it is possible to coat almost the entirety of each side surface of the inner rotor with the crosslinked fluororesin.

Details of Embodiments of the Present Disclosure

Hereinafter, specific examples of a crosslinked fluororesin-coated rotor manufacturing method according to an embodiment of the present disclosure will be described with reference to the drawings. The present invention is not limited to these examples and is indicated by the claims, and is intended to include meaning equivalent to the claims and all modifications within the scope of the claims.

FIG.1toFIG.6show an internal gear pump in which an outer rotor1and an inner rotor2obtained by a crosslinked fluororesin-coated rotor manufacturing method according to an embodiment of the present disclosure are used. The internal gear pump includes the annular outer rotor1, the inner rotor2which is disposed on the radially inner side of the outer rotor1, and a housing3in which the outer rotor1and the inner rotor2are housed.

As shown inFIG.3, the housing3includes a housing body4which is formed in a hollow tubular shape surrounding the outer periphery of the outer rotor1, a first side component5awhich is detachably attached to one end portion in the axial direction (an end portion on the left side in the drawing) of the housing body4, and a second side component5bwhich is detachably attached to another end portion in the axial direction (an end portion on the right side in the drawing) of the housing body4.

The first side component5a, the housing body4, and the second side component5bare fixed to each other by inserting common bolts7into bolt insertion holes6formed in each component and tightening these components with the bolts7. In addition, the first side component5a, the housing body4, and the second side component5bare positioned in a direction perpendicular to the axis by inserting common knock pins9into knock pin insertion holes8formed in each component.

In the inner rotor2, a shaft hole11into which a rotation shaft10is inserted is formed. The rotation shaft10is a shaft body which rotationally drives the inner rotor2, and is connected to a rotary drive device (electric motor or the like) which is not shown. The rotation shaft10and the shaft hole11are fitted to each other such that the rotation shaft10and the inner rotor2rotate integrally. In addition to the width-across-flat fitting as shown in the drawing, spline fitting, keyway fitting, and fitting with an interference between cylindrical surfaces (shrinkage fitting or press fitting) may be adopted for fitting the rotation shaft10and the shaft hole11.

The shaft hole11of the inner rotor2is a through hole which penetrates the inner rotor2in the axial direction. The rotation shaft10is inserted into the shaft hole11so as to have a portion protruding on one side in the axial direction (the left side in the drawing) from the inner rotor2and a portion protruding on the other side in the axial direction (the right side in the drawing) from the inner rotor2. The portion, of the rotation shaft10, protruding on the one side in the axial direction from the inner rotor2is rotatably supported by a first bearing12amounted on the first side component5a, and the portion, of the rotation shaft10, protruding on the other side in the axial direction from the inner rotor2is rotatably supported by a second bearing12bmounted on the second side component5b.

As shown inFIG.4, the outer rotor1is an annular member which has a cylindrical outer peripheral surface13, an inner peripheral surface15forming a plurality of internal teeth14, and side surfaces16(seeFIG.3) orthogonal to the axial direction. The inner rotor2is a member which has an outer peripheral surface18forming a plurality of external teeth17which mesh with the internal teeth14of the outer rotor1, and side surfaces19(seeFIG.3) orthogonal to the axial direction.

The outer peripheral surface13of the outer rotor1is fitted to a cylindrical inner peripheral surface20of the housing body4with a gap therebetween, and the outer rotor1is rotatably supported by the fitting. Here, the outer rotor1is supported so as to be rotatable about a position eccentric from the center position of the inner rotor2(that is, the rotation center position of the rotation shaft10). When the inner rotor2is rotated, the outer rotor1rotates together with the inner rotor2due to the meshing of the internal teeth14and the external teeth17. The rotation direction of the inner rotor2is the clockwise direction in the drawing.

The number of internal teeth14of the outer rotor1is larger than the number of external teeth17of the inner rotor2by one. The outer peripheral surface18of the inner rotor2is a curved surface obtained as a trajectory by translating, in the axial direction, a tooth profile of the external teeth17(for example, a tooth profile in which curves that are radially outwardly curved in a convex shape and curves that are radially inwardly curved in a concave shape are alternately aligned along the circumferential direction, such as a trochoid curve or a cycloid curve). The inner peripheral surface15of the outer rotor1is also a curved surface obtained as a trajectory by translating, in the axial direction, a tooth profile of the internal teeth14(for example, a tooth profile in which curves that are radially outwardly curved in a convex shape and curves that are radially inwardly curved in a concave shape are alternately aligned along the circumferential direction, such as a trochoid curve, a cycloid curve, or an envelope curve of a tooth profile of the inner rotor2).

A plurality of chambers21(spaces for containing fluid) defined by the respective external teeth17and the respective internal teeth14are formed between the outer periphery of the inner rotor2and the inner periphery of the outer rotor1. Here, the plurality of chambers21are formed such that the volumes thereof change as the inner rotor2and the outer rotor1rotate. That is, the volume of each chamber21is maximized at an angular position at which the center of the inner rotor2and the center of the outer rotor1are farthest from each other (at the upper position in the drawing), and decreases as the chamber21comes closer to an angular position at which the center of the inner rotor2and the center of the outer rotor1are closest to each other (the lower position in the drawing). Therefore, when the inner rotor2and the outer rotor1rotate, fluid discharge action occurs on a side through which movement is made from the angular position at which the center of the inner rotor2and the center of the outer rotor1are farthest from each other to the angular position at which the center of the inner rotor2and the center of the outer rotor1are closest to each other (on the right side in the drawing), due to reduction of the volumes of the chambers21. On the other hand, fluid suction action occurs on a side through which movement is made from the angular position at which the center of the inner rotor2and the center of the outer rotor1are closest to each other to the angular position at which the center of the inner rotor2and the center of the outer rotor1are farthest from each other (on the left side in the drawing), due to gradual increase of the volumes of the chambers21.

As shown inFIG.5, the side surfaces16of the outer rotor1are a pair of flat surfaces which are formed on both sides in the axial direction of the outer rotor1so as to face opposite to each other in the axial direction. The side surfaces19of the inner rotor2are a pair of flat surfaces which are formed on both sides in the axial direction of the inner rotor2so as to face opposite to each other in the axial direction.

The side surfaces16and the outer peripheral surface13of the outer rotor1are surfaces coated with a crosslinked fluororesin22(crosslinked fluororesin surfaces). On the other hand, the inner peripheral surface15of the outer rotor1is a surface not coated with the crosslinked fluororesin22(metal surface). Here, the outer rotor1includes a sintered metal body23and a coating layer of the crosslinked fluororesin22provided so as to coat the surface of the sintered metal body23. The sintered metal body23is formed by heating a powder compact, which is obtained by compression-molding an iron-based powder material with a mold, at a high temperature equal to or lower than the melting point of the material.

The crosslinked fluororesin22is obtained by crosslinking molecules of a chain polymer forming a fluororesin, and has a low friction coefficient equivalent to that of a general fluororesin (non-crosslinked fluororesin) but has wear resistance that is much higher than that of a general fluororesin.

As the fluororesin to be crosslinked, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and the like can be adopted. As the crosslinked fluororesin22, crosslinked PTFE is preferably adopted. When crosslinked PTFE is adopted, since the crosslinked PTFE has a particularly low friction coefficient among the above fluororesins and has excellent wear resistance, almost no wear occurs, so that it is possible to effectively increase the pump efficiency.

Similarly, the side surfaces19of the inner rotor2are also surfaces coated with a crosslinked fluororesin24(crosslinked fluororesin surfaces). On the other hand, the outer peripheral surface18of the inner rotor2and the inner surface of the shaft hole11are surfaces not coated with the crosslinked fluororesin24(metal surfaces). Here, the inner rotor2includes a sintered metal body25and a coating layer of the crosslinked fluororesin24provided so as to coat the surface of the sintered metal body25.

The width dimension between the pair of the side surfaces16of the outer rotor1is equal to the width dimension between the pair of the side surfaces19of the inner rotor2. The side surface16on one side in the axial direction (the left side in the drawing) of the outer rotor1is located on the same plane as the side surface19on the one side in the axial direction (the left side in the drawing) of the inner rotor2, and the side surface16on the other side in the axial direction (the right side in the drawing) of the outer rotor1is located on the same plane as the side surface19on the other side in the axial direction (the right side in the drawing) of the inner rotor2.

The first side component5ahas a flat mating surface26which is pressed and fixed to a side surface on the one side in the axial direction of the housing body4by tightening the bolts7, and a flat sliding guide surface27which slides and guides the side surface16on the one side in the axial direction of the outer rotor1and the side surface19on the one side in the axial direction of the inner rotor2. The second side component5balso has a flat mating surface26which is pressed and fixed to a side surface on the other side in the axial direction of the housing body4by tightening the bolts7and a flat sliding guide surface27which slides and guides the side surface16on the other side in the axial direction of the outer rotor1and the side surface19on the other side in the axial direction of the inner rotor2. The sliding guide surfaces27are each a finished surface having a surface roughness of Ra 1.6 μm or less (preferably Ra 0.8 μm or less).

The gap between the side surfaces16of the outer rotor1and the housing3(that is, the difference between the width dimension between the pair of the side surfaces16of the outer rotor1and the inner width dimension between a pair of the sliding guide surfaces27, facing each other in the axial direction, of the housing3) is set so as to be not greater than 20 μm (preferably not greater than 15 μm, more preferably not greater than 10 μm). Similarly, the gap between the side surfaces19of the inner rotor2and the housing3(that is, the difference between the width dimension between the pair of the side surfaces19of the inner rotor2and the inner width dimension between the pair of the sliding guide surfaces27, facing each other in the axial direction, of the housing3) is also set so as to be not greater than 20 μm (preferably not greater than 15 μm, more preferably not greater than 10 μm).

As shown inFIG.6, a first suction port28aand a first discharge port29aare open in the first side component5a. In addition, a second suction port28band a second discharge port29bare also open in the second side component5b.

The first suction port28aand the second suction port28bare open in the same shape at symmetrical positions with the inner rotor2and the outer rotor1therebetween. Accordingly, the pressure received by the inner rotor2and the outer rotor1from fluid in the first suction port28aand the pressure received by the inner rotor2and the outer rotor1from fluid in the second suction port28bare balanced to prevent the inner rotor2and the outer rotor1from being tilted.

Similarly, the first discharge port29aand the second discharge port29bare also open in the same shape at symmetrical positions with the inner rotor2and the outer rotor1therebetween. Accordingly, the pressure received by the inner rotor2and the outer rotor1from fluid in the first discharge port29aand the pressure received by the inner rotor2and the outer rotor1from fluid in the second discharge port29bare balanced to prevent the inner rotor2and the outer rotor1from being tilted.

As shown inFIG.4andFIG.6, the first suction port28aand the second suction port28bcommunicate with each other through a communication passage30which is formed in the housing body4. In addition, as shown inFIG.2andFIG.6, the first suction port28acommunicates with a suction port31which is open on the outer surface of the first side component5a, and the first discharge port29acommunicates with a discharge port32which is open on the outer surface of the first side component5a.

A method for manufacturing the outer rotor1in which the side surfaces16and the outer peripheral surface13are coated with the crosslinked fluororesin22will be described with reference toFIG.7toFIG.9.

First, the outer rotor1before coating and an outer masking jig40are prepared. The outer masking jig40is a jig for covering the inner peripheral surface15of the outer rotor1in a state where the side surfaces16of the outer rotor1are exposed. The outer masking jig40includes a first jig40afor closing an opening on one side in the axial direction of the outer rotor1, and a second jig40bfor closing an opening on the other side in the axial direction of the outer rotor1. The first jig40aand the second jig40bare connected to each other by a bolt41inside the outer rotor1. The first jig40aand the second jig40beach have a positioning fitting tooth portion42and a toothed flange43.

The positioning fitting tooth portion42is a portion for positioning the outer rotor1in the circumferential direction by fitting to the inner peripheral surface15of the outer rotor1. The outer peripheral surface of the positioning fitting tooth portion42is a curved surface obtained as a trajectory by translating, in the axial direction, a curve having a shape obtained by offsetting the tooth profile of the internal teeth14to the radially inner side. Here, the outer peripheral surface of the positioning fitting tooth portion42is formed such that the interval between the outer peripheral surface of the positioning fitting tooth portion42and the inner peripheral surface15of the outer rotor1is not greater than 0.2 mm (preferably not greater than 0.15 mm). The axial length of the positioning fitting tooth portion42is set so as to be not greater than 2.0 mm (preferably not greater than 1.5 mm).

The toothed flange43is a portion formed so as to project radially outward from the axially outer end of the positioning fitting tooth portion42. The toothed flange43has a toothed shape corresponding to the internal teeth14such that the toothed flange43overlaps peripheral portions, along the inner peripheral surface15, of the side surfaces16of the outer rotor1. That is, the outer peripheral surface of the toothed flange43is a curved surface obtained as a trajectory by translating, in the axial direction, a curve having a shape obtained by offsetting the tooth profile of the internal teeth14to the radially outer side. The outer peripheral surface of the toothed flange43is formed such that the distance by which the outer peripheral surface of the toothed flange43protrudes from the inner peripheral surface15of the outer rotor1to the radially outer side (a width w1of a band-shaped region where the toothed flange43overlaps the side surfaces16of the outer rotor1as shown inFIG.8) is not greater than 0.5 mm (preferably not greater than 0.3 mm).

Then, the outer masking jig40is mounted to the outer rotor1before coating, and in this state, the outer rotor1is coated with an uncrosslinked fluororesin. Specifically, a dispersion liquid obtained by dispersing fine particles of the fluororesin (for example, PTFE) in water is applied to the surface of the outer rotor1to which the outer masking jig40has been mounted. The application can be performed by dipping (immersion) or spraying. Thereafter, a coating layer of the fine particles of the uncrosslinked fluororesin is formed on the surface of the outer rotor1by drying the applied dispersion liquid. At this time, both the side surfaces16and the outer peripheral surface13of the outer rotor1are coated with the fine particles of the uncrosslinked fluororesin. Thereafter, the outer masking jig40is removed from the outer rotor1, and the outer rotor1is heated to a temperature equal to or higher than the melting point of the fluororesin, thereby baking the fine particles of the uncrosslinked fluororesin with which the side surfaces16and the outer peripheral surface13of the outer rotor1have been coated, to fuse the fine particles of the fluororesin. The outer masking jig40may be removed after baking the fluororesin.

Thereafter, the fluororesin on the side surfaces16and the outer peripheral surface13of the outer rotor1is crosslinked by irradiating the outer rotor1with radiation in a state where the outer masking jig40is removed from the outer rotor1. Specifically, in a state where the outer masking jig40is removed from the outer rotor1, the outer rotor1is placed in an oxygen-free atmosphere having a predetermined high temperature, and radiation (for example, electron beam) is applied toward the surface of the outer rotor1, thereby forming covalent bonds between molecules of a chain polymer forming the fluororesin, to crosslink the molecules of the chain polymer. In addition, chemical bonds are also formed between the outer rotor1and the molecules of the chain polymer forming the fluororesin, by the radiation applied at this time, and the adhesion of the crosslinked fluororesin22becomes very high through the chemical bonds. Thereafter, if necessary, the surface of the crosslinked fluororesin22is finished by grinding or polishing.

A method for manufacturing the inner rotor2in which the side surfaces19are coated with the crosslinked fluororesin24will be described with reference toFIG.10toFIG.12.

The inner rotor2before coating, an inner masking jig50, and a shaft hole masking jig51are prepared. The inner masking jig50is a jig for covering the outer peripheral surface18of the inner rotor2in a state where the side surfaces19of the inner rotor2are exposed. The inner masking jig50includes a first jig50ato be fitted to the outer periphery of an end portion on one side in the axial direction of the inner rotor2, and a second jig50bto be fitted to the outer periphery of an end portion on the other side in the axial direction of the inner rotor2. The first jig50aand the second jig50bare connected to each other by bolts52on the radially outer side of the inner rotor2. The first jig50aand the second jig50bhave mating surfaces53in the axial direction. An annular sealing member54(seeFIG.11andFIG.12) for sealing the mating surfaces53is incorporated between the first jig50aand the second jig50b. The first jig50aand the second jig50beach have a positioning fitting tooth portion55and a toothed flange56.

The positioning fitting tooth portion55is a portion for positioning the inner rotor2in the circumferential direction by fitting to the outer peripheral surface18of the inner rotor2. The inner peripheral surface of the positioning fitting tooth portion55is a curved surface obtained as a trajectory by translating, in the axial direction, a curve having a shape obtained by offsetting the tooth profile of the external teeth17to the radially outer side. Here, the inner peripheral surface of the positioning fitting tooth portion55is formed such that the interval between the inner peripheral surface of the positioning fitting tooth portion55and the outer peripheral surface18of the inner rotor2is not greater than 0.2 mm (preferably not greater than 0.15 mm). The axial length of the positioning fitting tooth portion55is set so as to be not greater than 2.0 mm (preferably not greater than 1.5 mm).

The toothed flange56is a portion formed so as to project radially inward from the axially outer end of the positioning fitting tooth portion55. The toothed flange56has a toothed shape corresponding to the external teeth17such that the toothed flange56overlaps peripheral portions, along the outer peripheral surface18, of the side surfaces19of the inner rotor2. That is, the inner peripheral surface of the toothed flange56is a curved surface obtained as a trajectory by translating, in the axial direction, a curve having a shape obtained by offsetting the tooth profile of the external teeth17to the radially inner side. The inner peripheral surface of the toothed flange56is formed such that the distance from the outer peripheral surface18of the inner rotor2to the inner peripheral surface, of the toothed flange56, located on the radially inner side thereof (a width w2of a band-shaped region where the toothed flange56overlaps the side surfaces19of the inner rotor2as shown inFIG.11) is not greater than 0.5 mm (preferably not greater than 0.3 mm).

The shaft hole masking jig51includes a first jig51afor closing an opening on one side in the axial direction of the shaft hole11, and a second jig51bfor closing an opening on the other side in the axial direction of the shaft hole11. The first jig51aand the second jig51bare connected to each other by a bolt57inside the shaft hole11.

Then, the inner masking jig50and the shaft hole masking jig51are mounted to the inner rotor2before coating, and in this state, the inner rotor2is coated with an uncrosslinked fluororesin. Specifically, a dispersion liquid obtained by dispersing fine particles of the fluororesin (for example, PTFE) in water is applied to the surface of the inner rotor2to which the inner masking jig50and the shaft hole masking jig51have been mounted. The application can be performed by dipping (immersion) or spraying. Thereafter, a coating layer of the fine particles of the uncrosslinked fluororesin is formed on the surface of the inner rotor2by drying the applied dispersion liquid. At this time, the side surfaces19of the inner rotor2are coated with the fine particles of the uncrosslinked fluororesin. Thereafter, the inner masking jig50and the shaft hole masking jig51are removed from the inner rotor2, and the inner rotor2is heated to a temperature equal to or higher than the melting point of the fluororesin, thereby baking the fine particles of the uncrosslinked fluororesin with which the side surfaces19of the inner rotor2have been coated, to fuse the fine particles of the fluororesin. The inner masking jig50and the shaft hole masking jig51may be removed after baking the fluororesin.

Thereafter, the fluororesin on the side surfaces19of the inner rotor2is crosslinked by irradiating the inner rotor2with radiation in a state where the inner masking jig50and the shaft hole masking jig51are removed from the inner rotor2. Specifically, in a state where the inner masking jig50and the shaft hole masking jig51are removed from the inner rotor2, the inner rotor2is placed in an oxygen-free atmosphere having a predetermined high temperature, and radiation (for example, electron beam) is applied toward the surface of the inner rotor2, thereby forming covalent bonds between molecules of a chain polymer forming the fluororesin, to crosslink the molecules of the chain polymer. In addition, chemical bonds are also formed between the inner rotor2and the molecules of the chain polymer forming the fluororesin, by the radiation applied at this time, and the adhesion of the crosslinked fluororesin24becomes very high through the chemical bonds. Thereafter, if necessary, the surface of the crosslinked fluororesin24is finished by grinding or polishing.

When the outer rotor1and the inner rotor2coated with the crosslinked fluororesins22and24are manufactured as in the above embodiment, seizure of the outer rotor1and the inner rotor2can be prevented over a long period of time, and it is possible to easily manufacture the outer rotor1and the inner rotor2having stable performance.

That is, when the outer rotor1in which the side surfaces16and the outer peripheral surface13are coated with the crosslinked fluororesin22is manufactured as in the above embodiment, since the side surfaces16of the outer rotor1are coated with the crosslinked fluororesin22, even when the side clearance of the outer rotor1is set to be very small, it is possible to prevent seizure of the outer rotor1over a long period of time.

Since the outer masking jig40for covering the inner peripheral surface15in a state where the side surfaces16of the outer rotor1are exposed is used when coating the outer rotor1with the uncrosslinked fluororesin, the inner peripheral surface15of the outer rotor1is not coated with the fluororesin. Therefore, the size of the tip clearance between the internal teeth14on the inner periphery of the outer rotor1and the external teeth17on the outer periphery of the inner rotor2becomes stable, and the pump performance becomes stable.

Since the positioning fitting tooth portion42for positioning the outer masking jig40with respect to the outer rotor1in the circumferential direction by fitting to the inner peripheral surface15of the outer rotor1is formed in the outer masking jig40, the work of mounting the outer masking jig40to the outer rotor1is easy.

When crosslinking the uncrosslinked fluororesin by irradiating the fluororesin with radiation, the irradiation with radiation is performed in a state where the outer masking jig40is removed from the outer rotor1. Therefore, the radiation is prevented from being blocked by the outer masking jig40, and it is possible to evenly and uniformly crosslink the fluororesin.

Since the outer masking jig40has the toothed flange43when coating the outer rotor1with the uncrosslinked fluororesin, most of each side surface16of the outer rotor1can be exposed while assuredly covering the inner peripheral surface15of the outer rotor1. Therefore, it is possible to coat most of each side surface16of the outer rotor1with the crosslinked fluororesin22while preventing the inner peripheral surface15of the outer rotor1from being coated.

Since the toothed flange43is formed such that the region where the toothed flange43overlaps the side surfaces16of the outer rotor1has a width w1(seeFIG.8) of not greater than 0.5 mm (preferably not greater than 0.3 mm), it is possible to coat almost the entirety of each side surface16of the outer rotor1with the crosslinked fluororesin22.

Since not only the side surfaces16of the outer rotor1but also the outer peripheral surface13of the outer rotor1is coated with the crosslinked fluororesin22, it is possible to effectively reduce the torque for rotationally driving the outer rotor1.

When the inner rotor2in which the side surfaces19are coated with the crosslinked fluororesin24is manufactured as in the above embodiment, since the side surfaces19of the inner rotor2are coated with the crosslinked fluororesin24, even when the side clearance of the inner rotor2is set to be very small, it is possible to prevent seizure of the inner rotor2over a long period of time.

Since the inner masking jig50for covering the outer peripheral surface18in a state where the side surfaces19of the inner rotor2are exposed is used when coating the inner rotor2with the uncrosslinked fluororesin, the outer peripheral surface18of the inner rotor2is not coated with the fluororesin. Therefore, the size of the tip clearance between the internal teeth14on the inner periphery of the outer rotor1and the external teeth17on the outer periphery of the inner rotor2becomes stable, and the pump performance becomes stable.

Since the positioning fitting tooth portion55for positioning the inner masking jig50with respect to the inner rotor2in the circumferential direction by fitting to the outer peripheral surface18of the inner rotor2is formed in the inner masking jig50, the work of mounting the inner masking jig50to the inner rotor2is easy.

When crosslinking the uncrosslinked fluororesin by irradiating the fluororesin with radiation, the irradiation with radiation is performed in a state where the inner masking jig50is removed from the inner rotor2. Therefore, the radiation is prevented from being blocked by the inner masking jig50, and it is possible to evenly and uniformly crosslink the fluororesin.

Since the inner masking jig50has the toothed flange56, when coating the inner rotor2with the uncrosslinked fluororesin, most of each side surface19of the inner rotor2can be exposed while assuredly covering the outer peripheral surface18of the inner rotor2with the toothed flange56. Therefore, it is possible to coat most of each side surface19of the inner rotor2with the crosslinked fluororesin24while preventing the outer peripheral surface18of the inner rotor2from being coated.

Since the toothed flange56is formed such that the region where the toothed flange56overlaps the side surfaces19of the inner rotor2has a width w2(seeFIG.11) of not greater than 0.5 mm (preferably not greater than 0.3 mm), it is possible to coat almost the entirety of each side surface19of the inner rotor2with the crosslinked fluororesin24.

REFERENCE SIGNS LIST