US20180163723A1

US20180163723A1 - Electric pump

Info

Publication number: US20180163723A1
Application number: US15/822,561
Authority: US
Inventors: Toshinobu Horimatsu; Satoshi MASUKURA; Naoto Morishita
Original assignee: Mahle Filter Systems Japan Corp
Current assignee: Mahle Filter Systems Japan Corp
Priority date: 2016-12-13
Filing date: 2017-11-27
Publication date: 2018-06-14
Also published as: JP2018096269A; CN108612652A; EP3336357A1

Abstract

An electric pump includes a housing 2 configured of a housing body 3 and a cover 4, a stator 6 having a plurality of coils 15, a rotor 7 configured of an inner side outer rotor 16 and an outer side rotor body 17, a pump part 8 disposed on the inner circumferential side of the rotor 7 of an electric motor 5, side plates 11 and 12 disposed on both side surfaces of the rotor 7, an inner rotor 9, and a plurality of connecting plates 10 interposed between the outer rotor 16 and the inner rotor 9. The side plate 12 of the side plates 11 and 12 is pressed to the rotor 7 by a compression coil spring 28.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a motor integrated type and also positive displacement type pump in which an electric motor and a pump part are integrated.
In Japanese Patent Application Publication No. 2011-74843 (hereinafter is referred to as “JP 2011-74843”), Japanese Patent Application Publication No. 2012-67735 (hereinafter is referred to as “JP 2012-67735”) and Japanese Patent Application Publication No. 2012-41867 (hereinafter is referred to as “JP 2012-41867”), as a motor integrated type electric pump which is used for an oil pump for an engine and a transmission for a vehicle, for example, an electric motor has been suggested in which a pump part is disposed on the inner circumferential side of a rotor of the electric motor.
The motor integrated type electric pump disclosed in JP 2011-74843, JP 2012-67735 and JP 2012-41867 has a structure in which the rotor of the electric motor also serves as the outer rotor of the pump part of the positive displacement type pump, and an inner rotor as a pump element is eccentrically disposed on the inner circumferential side of the outer rotor with a predetermined space. This structure is common. In addition, a trochoid type or other types of pump parts are each configured of the outer rotor and the inner rotor, and by rotating the inner rotor following the rotation of the outer rotor, a predetermined pump function is exhibited using the space between the outer rotor and the inner rotor as a pump chamber.

SUMMARY OF THE INVENTION

However, in this motor integrated type electric pump, due to the particularity of the structure in which the pump part is disposed on the inner circumferential side of the rotor of the electric motor, as described in JP 2011-74843 and JP 2012-41867, it must have a structure in which housing members defining both side surfaces of the pump chamber are fastened to each other by bolts at positions largely radially separated from the center of the pump part. In this structure, it is difficult that the housing members, the outer rotor and the inner rotor are accurately brought into close contact with each other by the fastening force of the bolts unless the housing members are made thick to have high rigidity, and there are therefore concerns that the accuracy of the mating surfaces of the both side surfaces of the pump chamber is lowered and its sealing performance also deteriorates. The deterioration of pumping efficiency caused by the leakage of liquid, the partial abrasion of a sliding part and the increase of abrasion resistance, as a result, tend to occur, and, as a motor integrated type electric pump, there is still room for improvement.
The present invention was made in consideration of such a problem. An object of the present invention is to provide a motor integrated type electric pump in which by sufficiently securing the accuracy of the mating surfaces of both side surfaces of a pump chamber and its sealing performance, secondary troubles such as, in addition to the deterioration of pumping efficiency, the partial abrasion of a sliding part and the increase of abrasion resistance can be suppressed.
According to the present invention, an electric pump comprises: a housing having a sealed structure; a stator including a plurality of coils arranged circumferentially, the stator which is accommodated in the housing; a rotor disposed on the inner circumferential side of the stator; a pump part disposed on the inner circumferential side of the rotor and driven by an electric motor, the rotor which also serves as an outer rotor of the pump part and forms the electric motor with the stator; a pair of side plates disposed on both side surfaces of the rotor; and an inner rotor disposed on the inner circumferential side of the rotor eccentrically, and forming a pump chamber of the pump part with the rotor and the pair of the side plates, the inner rotor which rotates with rotation of the rotor, and is characterized in that at least one of the pair of the side plates is pressed to the rotor by an elastic member.
In this case, as to the above rotor, to achieve both of a function required for the electric motor and a function required for the pump part, it is desirable that the rotor is configured of the outer rotor forming the pump chamber of the pump part with the pair of the side plates and the inner rotor and of the rotor body provided with permanent magnets corresponding to the respective coils provided on the stator side, rotor body which is fitted on the outer circumferential side of the outer rotor. That is, it is desirable that the rotor is functionally divided.
In addition, as the pump part, a trochoid type or other types may be used if it is structurally established. However, here, the pump part is one which has, in addition to the outer rotor, the pair of the side plates and the inner rotor, plate members. One end of each of the plate members is swingably supported on the outer rotor and the other end is slidably fitted to the inner rotor, and the plate members divide the space of the pump chamber formed between the outer rotor and the inner rotor into a plurality of regions.
In addition, as a more specific structure of the housing, it is desirable that the housing is divided into two parts in the axial direction of the rotor and is configured of a housing body and a cover member, and that the outer rotor, the inner rotor and the pair of the side plates disposed on both sides of them are held so as to be pressed by the housing body and the cover member, for improving close contact property between respective members.
Moreover, when focused on the rotation performance of the rotor, it is desirable that the outer rotor is provided, at its circumferential edge portion, with a rim portion whose length is longer than that of the rotor body in the axial center direction of the rotor, and bearings are interposed in respective spaces between the inner circumferential surface of one end portion in the longitudinal direction of the rim portion and the housing body and between the inner circumferential surface of the other end portion in the longitudinal direction of the rim portion and the cover member, and that the rotor configured of the outer rotor and the rotor body is rotatably supported at both ends by the bearings.
Therefore, according to the present invention, at least one of the pair of the side plates is pressed to the rotor by the elastic force of the elastic member, and the rotor which has the inner rotor on the inner circumferential side thereof and which also serves as the outer rotor of the pump part is sandwiched between the both side plates by the elastic force. Consequently, the rotor also serving as the outer rotor of the pump part, the inner rotor and the side plates are surely brought into close contact with each other, and it is possible to stably maintain its close contact state.
According to the present invention, since the electric motor has a so-called floating structure in which at least one of the pair of the side plates forming the pump chamber is pressed to the rotor by the elastic member, it becomes possible that the pair of the side plates, the rotor also serving as the outer rotor of the pump part and the inner rotor are brought into close contact with each other, and the accuracy of the mating surfaces of the both side surfaces of the pump chamber and its sealing performance can be sufficiently secured, and thereby it is possible to suppress the deterioration of pump efficiency and the increase of partial abrasion and frictional resistance at sliding parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a specific first embodiment for implementing an electric pump according to the present invention, and is a sectional view taken along a line B-B of FIG. 2.

FIG. 2 is a sectional view take along a line A-A of FIG. 1.

FIG. 3 is a perspective exploded view when a cover of the electric pump shown in FIG. 1 and FIG. 2 is removed.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 to FIG. 3 show a specific first embodiment for implementing an electric pump according to the present invention. In particular, FIG. 1 shows a sectional view taken along a line B-B of FIG. 2 as the entire sectional view of an electric pump 1, and FIG. 2 shows a sectional view taken along a ling A-A of FIG. 1. In addition, FIG. 3 shows a perspective exploded view when a cover 4 of the electric pump 1 shown in FIG. 1 and FIG. 2 is removed.
The electric pump 1 shown in FIG. 1 to FIG. 3 is one in which an electric motor 5 and a pump part 8 mentioned below are accommodated and concentrically disposed in a circular hosing 2 sealed by a hosing body 3 and the cover 4 such that their axial center direction positions match with each other. In addition, the entire shape of the electric pump 1 including the housing 2 is formed in a substantially flat shape.
As shown in FIG. 1 and FIG. 2, the electric motor 5 is configured of a annular stator 6 occupying the outer circumferential portion of the circular internal space of the hosing 2, and of a cylindrical rotor 7 occupying the inner space on the inner side of the stator 6. In addition, the rotor 7 also serves as the outer rotor of the pump part 8 which is mentioned below. The pump part 8 is configured of the rotor 7, an inner rotor 9 arranged eccentrically on the inner circumferential side of the rotor 7 such that a predetermined space is formed, a plurality of connecting plates 10 radially interposed between the rotor 7 and the inner rotor 9, and of a pair of side plates 11 and 12 mentioned below which are disposed on both sides of the inner rotor 9.
As shown in FIG. 1 and FIG. 3, in the axial center direction of the stator 6 or the rotor 7, the housing 2 accommodating the electric motor 5 and the pump part 8 is divided into two parts, one of which is the housing body 3 and the other of which is the cover 4 as a cover member. That is, it is formed as a half-split structure. The housing body 3 and the cover 4 abut on each other and fastened and fixed by two bolts 13.
The stator 6 of the electric motor 5 has a well-known structure in which a plurality of tooth portions 14 a are arranged at equal intervals and protrude from the inner circumferential side of a ring-shaped stator core 14 made of metal, and coils 15 are wound about these respective tooth portions 14 a. Each of the coils 15 including the tooth portions 14 a forms a magnetic pole. As mentioned above, the rotor 7 of the electric motor 5 also serves as the outer rotor of the pump part 8. In the present embodiment, it has a composite structure whose function is divided by using different material between the inner circumferential side and the outer circumferential side of the rotor 7, such that a function required as the rotor of the electric motor 5 and a function required as the outer rotor of the pump part 8 are sufficiently satisfied. The rotor 7 is configured of a cylindrical outer rotor 16 having a hollow shape on its inner circumferential side and a hollow cylindrical rotor body 17 fitted to the outer circumferential side of the outer rotor 16.
The inner circumferential side outer rotor 16 is made of a single metal material. In contrast to this, the outer circumferential side rotor body 17 is formed by a steel sheet laminated body such as an electromagnetic steel sheet. Moreover, the rotor body 17 is formed, in its circumferential direction, with a plurality of slot portions 18 (the number of the slot portions 18 is the same as that of the coils 15 on the stator 6 side) formed at equal intervals and penetrating in the axial center direction, and permanent magnets 19 are inserted into these respective slot portions 18 and fixed by adhesives. In addition, as shown in FIG. 1 and FIG. 2, a fine gap corresponding to a so-called air gap is formed between each of the tooth portions 14 a on the stator 6 side and the rotor body 17.
In addition, as shown in FIG. 1, as mentioned above, the outer rotor 16 forming the rotor 7 with the rotor body 17 is formed, at its outer circumferential edge portion, with a rim portion 20 having a step whose length (a length in the axial center direction) is longer than that of the rotor body 17, and the rim portion 20 protrudes in the axial center direction from both ends of the rotor body 17. End plates 21 made of a non-magnetic material such as an aluminum plate are stacked on both end surfaces of the rotor body 17 and cover permanent magnets 19, and the rotor body 17 is press-fitted into the small diameter portion of the rim portion 20 of the outer rotor 16, and then is integrally fixed to the outer circumference of the outer rotor 16 by press-fitting a stopper ring 22. With this, at least the rotor body 17 forms the permanent magnet embedded type electric motor 5 with the stator 6.
Here, each of the end plates 21 made of a non-magnetic material is provided to suppress the lowering of output of each of the permanent magnets 19 embedded to the rotor body 17 caused by the leakage of magnetic flux. In addition, in a case where the entire rotor 7 configured of the outer rotor 16 and the rotor body 17 is formed by a steel sheet laminated body or made of other metal materials as one body, as mentioned above, it also serves as the rotor 7 of the electric motor 5 and the outer rotor 16 of the pump part 8.
As shown in FIG. 1 and FIG. 2, in the inner circumferential side of the outer rotor 16, the cylindrical inner rotor 9 whose diameter is smaller than the inner diameter of the outer rotor 16 is disposed at a position eccentric from the axial center position of the outer rotor 16 so as to be inscribed in the inner circumferential surface of the outer rotor 16, and the space between the outer rotor 16 and the inner rotor 9 becomes a pump chamber P. A plurality of slot portions 23 having square groove shapes are opened on the outer circumferential surface of the inner rotor 9. In addition, the slot portions 23 extend radially and are radially arranged on the outer circumferential surface of the inner rotor 9 at equal intervals. The connecting plates 10 as plate members, each of which is formed in a deformed vane shape, are slidably inserted into and supported on the respective slot portions 23. That is, the connecting plates 10 are inserted into and supported on the respective slot portions 23 so as to protrude from and retract to the respective slot portions 23. Each of the connecting plates 10 is formed generally in a key-hole shape in cross section, and the base portion on an inner rotor 9 side of each of the slot portions 23 is thick and the distal end portion on an outer rotor 16 side of each of the slot portions 23 is formed as a cylindrical swing shaft portion 10 a which is thinner than the base portion.
On the other hand, a plurality of cylindrical slot-shaped supporting holes 24 extending in the axial center direction are formed on the inner circumferential surface of the outer rotor 16 at equal intervals, and the swing shaft portions 10 a of the respective connecting plates 10 are swingably inserted into and supported on the respective supporting holes 24. With this, each of the connecting plates 10 can swing with the respective swing shaft portions 10 a as a rotation center, and the separation of each of the connecting portions 10 from the outer rotor 16 is prevented. In addition, each of the connecting plates 10 is set so as to protrude from and retract to a corresponding one of the slot portions 23 to the extent that the base portions do not slip out from the respective slot portions 23 of the inner rotor 9. In this way, the plurality of the connecting plates 10 are disposed between the outer rotor 16 and the inner rotor 9 so as to be crosslinked, and the pump chamber P formed between the outer rotor 16 and the inner rotor 9 is divided into a plurality of regions.
As shown in FIG. 1, a support protruding portion 3 a having a relatively large diameter is formed in the middle part of the inner bottom surface of the housing body 3, except a space R1 facing the stator 6. Similar to this, a ring-shaped support protruding portion 4a is formed in the middle part of the inner bottom surface of the cover 4, except a space R2 facing the stator 6. In addition, a ball bearing 26 as a bearing is interposed in the space between the support protruding portion 4a on a cover 4 side and one end portion in the longitudinal direction of the rim portion 20 in the outer rotor 16, and a ball bearing 25 as a bearing is interposed in the space between the support protruding potion 3 a on a housing body 3 side and the other end portion in the longitudinal direction of the rim portion 20. With this structure, the outer rotor 16, that is, the rotor 7 is rotatably axially supported at both ends by the support protruding portion 3 a on the housing body 3 side and the support protruding portion 4a on the cover 4 side.
The side plate 11 on the housing body 3 side and the side plate 12 on the cover 4 side are disposed on both side surfaces of the inner rotor 9 so as to extend to a part of the outer rotor 16. By the existence of the both side plates 11 and 12, as shown in FIG. 1, the pump chamber P formed between the outer rotor 16 and the inner rotor 9 is also isolated in the axial center direction. In this way, the positive displacement type pump part 8 is configured of the outer rotor 16, the inner rotor 9, the connecting plates 10 and the both side plates 11 and 12.
In addition, as shown in FIG. 1, a stepped shaft-like shaft member 27 which penetrates through the inner rotor 9 and the side plate 11 on the housing body 3 side is disposed extending from the support protruding portion 3 a on the housing body 3 side to the side plate 12 on the cover 4 side. This shaft member 27 rotatably supports the inner rotor 9 in the middle part in the longitudinal direction thereof. On the other hand, one end portion in the longitudinal direction of the shaft member 27 is fitted to and supported on the side plate 12 on the cover 4 side and the other end portion is fitted to and supported on the support protruding portion 3 a on the housing body 3 side. In this way, based on the shaft member 27 which is fitted to and supported on the support protruding portion 3 a on the housing body 3 side, by fitting the side plate 11 on the housing body 3 side, the inner rotor 9 and the side plate 12 on the cover 4 side, a relative position between respective members is determined.
As shown in FIG. 1, a stepped boss portion 12 a is formed on the back surface side of the side plate 12 on the cover 4 side. The boss portion 12 a is fitted to and supported on the inner circumference of the ring-shaped support protruding portion 4a on the cover 4 side so as to slide in the axial center direction. A compression coil spring 28 is disposed as an elastic member on the outer circumference at the small diameter part of the boss portion 12 a. This compression coil spring 28 is interposed between the boss portion 12 a and the inner bottom surface of the support protruding portion 4a on the cover 4 side in a compressed state. With this, the side plate 12 on the cover 4 side becomes so-called floating structure, and the side plate 12 is pressed to the inner rotor 9 and the outer rotor 16 by the elastic force of the compression coil spring 28. In other words, this structure is a state in which the inner rotor 9, the outer rotor 16 and the side plates 11 and 12 disposed on the both sides of each of the inner rotor 9 and the outer rotor 16 so as to sandwich the inner rotor 9 and the outer rotor 16 are pressed against each other so as to be brought into close contact with each other. Consequently, close contact property and also sealing performance between the inner rotor 9, the outer rotor 16 and the both side plates 11 and 12 are secured.
In addition, as shown in FIG. 1 and FIG. 2, a suction port 29 and a discharge port 30 communicating to the pump chamber P are formed on the side plate 11 on the housing body 3 side. On the other hand, concave portions 31 and 32 are formed on the side plate 12 on the cover 4 side, concave portions 31 and 32 which respectively communicate with the suction port 29 and the discharge port 30 through the slot portions 23 on the inner rotor 9 side, slot portions 23 through which the respective connecting plates 10 are inserted. The suction port 29 and the discharge port 30 are respectively connected to a suction port and a discharge port (not shown) formed on the housing body 3. In addition, annular grooves 33 are formed on the respective inner side surfaces of the both side plates 11. and 12 which face the inner rotor 9, and annular grooves 34 are formed on the respective inner side surfaces of the both side plates 11 and 12 which face the inner rotor 9, so as to surround the shaft member 27. Side clearances as fine gaps are provided between the side surface of the inner rotor 9 and each part corresponding to the suction port 29, the discharge port 30 and the annular groove 33 formed on the side plate 11 and between the side surface of the inner rotor 9 and each part corresponding to the concave portions 31 and 32 and the annular groove 34 formed on the side plate 12.
Here, in the present embodiment, a case where the electric pump 1 is an oil pump is assumed, and the annular grooves 33 and 34 formed on each of the both side plates 11 and 12 serve as spaces to store a part of oil to be pressure-fed as lubrication oil used at sliding parts between the side plate 11 and the inner rotor 9 and between the slide plate 12 and the inner rotor 9.
The suction port 29 or the discharge port 30 formed on the side plate 11 on the housing body 3 side faces the ball bearing 25 shown in, for example, FIG. 1, such that a part of the oil to be pressure-fed fills the both ball bearings 25 and 26 and the spaces R1 and R2 respectively formed on the housing body 3 side and the cover 4 side, including stator 6. With this, in addition to the both ball bearings 25 and 26, the stator 6 and the rotor 7, including each of the coils 15, are filled with the oil to be pressure-fed, and consequently, the both ball bearings 25 and 26 are lubricated and cooling of the stator 6 and the rotor 7 are performed by the oil.
In the electric pump 1 configured as above, as shown in FIG. 1 and FIG. 2, by energizing each of the coils 15 of the stator 6 forming the electric motor 1 with the rotor 7, the rotor 7 in which the permanent magnets 19 corresponding to the respective coils 15 are embedded, that is, the rotor 7 in which the rotor body 17 in which the permanent magnets 19 are embedded and the outer rotor 16 are integrated rotates, for example, in an arrow M direction that is a clockwise direction in FIG. 2, while being guided by the both ball bearings 25 and 26.
In addition, in FIG. 1, the shaft member 27 and the both side plates 11 and 12 are concentrically drawn. However, actually, as is clear from FIG. 2, the axial center of the shaft member 27 is eccentric to the axial centers of the both side plates 11 and 12 which are disposed on the both sides of the rotor 7. The both side plates 11 and 12 do not therefore rotate with the rotation of the rotor 7.
The rotation of the rotor 7 mentioned above is transmitted to the inner side inner rotor 9 through the plurality of the connecting plates 10 existing between the outer rotor 16 and the inner rotor 9. As shown in FIG. 2, the inner roto 9 rotates with the outer rotor 16 integrally. On the other hand, at the same time when the inner rotor 9 rotates with the outer rotor 16 integrally, since the axial center of the inner rotor 9 is eccentric to the axial center of the rotor 7, the inner rotor 9 itself rotates about the shaft member 27 as a rotation center, while being inscribed in the inner circumferential surface of the outer rotor 16, continuously changing its inscribed position.
In this way, the connecting plates 10 inserted into the respective slot portions 23 of the inner rotor 9 repeatedly protrude from and retract to the respective slot portion 23 while oscillating about the corresponding swing shaft portions 10 a as centers, with the rotational motion of the inner rotor 9 about the shaft member 27 as a rotation center while being inscribed in the inner circumferential surface of the outer rotor 16, and by the protrusion and retraction of each of the connecting plates 10 in the pump chamber P, a function as a so-called positive displacement type pump is exhibited.
More specifically, since the plurality of the connecting plates 10 disposed between the outer rotor 16 and the inner rotor 9 divide the pump chamber P into a plurality of regions, a process in which each of the regions, each of which is placed between adjacent connecting plates 10, passes through the substantially crescent-shaped suction port 29 shown in FIG. 2 becomes a suction process. Similar to this, a process in which each of the regions, each of which is placed between adjacent connecting plates 10, passes through the substantially crescent-shaped discharge port 30 shown in FIG. 2 becomes a discharge process. These movements are continuously repeated, and, as mentioned above, the function as a positive displacement type pump by the pump part 8 is exhibited.
In such a process in which the pump part 8 exhibits the function as a positive displacement type pump, as shown in FIG. 1, the side plate 12 on the cover 4 side is pressed to the side surfaces of the outer rotor 16 and the inner rotor 9 by the compression coil spring 28, and the outer rotor 16 and the inner rotor 9 receiving the pressing force of the side plate 12 are pressed to the side plate 11 on the housing body 3 side. This means that the both side plates 11 and 12 disposed on the both side surfaces of the outer rotor 16 and the both side surfaces of the inner rotor 9 sandwich the outer rotor 16 and the inner rotor 9 therebetween by the elastic force of the compression coil spring 28. With this, as shown in FIG. 1, even if each position at which the housing body 3 and the cover 4 are fastened and fixed by the bolts 13 is relatively largely apart from the pump part 8, since the side plates 11 and 12 are brought into close contact with the side surfaces of each of the outer rotor 16 and the inner rotor 9 as a main element of the pump part 8, sealing performance is improved with the improvement of accuracy of the mating surfaces of the both side surfaces 11 and 12. Consequently, the rotation of the outer rotor 16 and the inner rotor 9 is performed stably, and leakage of the oil from the pump chamber P is suppressed and pump efficiency is also improved.
Moreover, as mentioned above, the side clearance is set to a part of the close-contact surface of each of the side plates 11 and 12, each of which is brought into close contact with the outer rotor 16 and the inner rotor 9, and oil lubrication is performed through the oil existing at these parts. Consequently, it is possible to suppress partial abrasion at the parts and to reduce frictional resistance, and thereby the rotation of the outer rotor 16 and the inner rotor 9 is performed more stably
In addition, the rotor 7 is not rotatably supported at a part close to a rotation center position, but is rotatably supported at the both ends at the outer side part in the radial direction by the ball bearings 25 and 26. Consequently, the rotation of the rotor 7 is also performed stably, and durability of the electric pump 1 including the ball bearings 25 and 26 is also improved.
Moreover, it is not necessary to make the entire housing 2 configured of the housing body 3 and the cover 4 so as to be thick, or so as to have high rigidity and, as the electric pump 1 in which the electric motor 5 and the pump part 8 are integrated, as shown in FIG. 1, the entire housing 2 can be formed in a flat shape and can be compact.
Here, in the present embodiment, as shown in FIG. 2, although the pump part 8 with a type in which the plurality of the connecting plates 10 are disposed between the outer rotor 16 and the inner rotor 9 so as to be crosslinked has been explained as an example, the type of the pump part 8 is not limited to this, and other pump part types such as a trochoid type may be used.
In addition, in the present embodiment, as shown in FIG. 2, as to the rotor 7, it is configured of the outer rotor 16 and the rotor body 17, such that a function required for the electric motor 5 and a function required for the pump part 8 are sufficiently satisfied. However, the rotor 7 may have a structure in which the outer rotor 16 and the rotor body 17 are completely integrated by using the same material as needed.
The entire contents of Japanese Patent Application No. 2016-240780 filed on Dec. 13, 2016 are incorporated herein by reference.

Claims

1. An electric pump comprising:

a housing having a sealed structure;

a stator including a plurality of coils arranged circumferentially, the stator which is accommodated in the housing;

a rotor disposed on an inner circumferential side of the stator;

a pump part disposed on an inner circumferential side of the rotor and driven by an electric motor, the rotor which also serves as an outer rotor of the pump part and forms the electric motor with the stator;

a pair of side plates disposed on both side surfaces of the rotor; and

an inner rotor disposed on the inner circumferential side of the rotor eccentrically, and forming a pump chamber of the pump part with the rotor and the pair of the side plates, the inner rotor which rotates with rotation of the rotor,

wherein at least one of the pair of the side plates is pressed to the rotor by an elastic member.

2. The electric pump according to claim 1, wherein the rotor is configured of the outer rotor forming the pump chamber of the pump part with the pair of the side plates and the inner rotor, and of a rotor body provided with permanent magnets corresponding to the respective coils at a stator side, the rotor body which is fitted and fixed on an outer circumferential side of the outer rotor.

3. The electric pump according to claim 2, wherein the pump part comprises, in addition to the outer rotor, the pair of the side plates and the inner rotor, plate members configured to divide the pump chamber formed between the outer rotor and the inner rotor into a plurality of regions, the plate members whose respective one ends are swingably supported on the outer rotor and the respective other ends are slidably fitted to the inner rotor.

4. The electric pump according to claim 3, wherein the housing is divided into two parts in an axial center direction of the rotor, and configured of a housing body and a cover member, and

wherein the outer rotor, the inner rotor and the pair of the side plates disposed on both side surfaces of each of the outer rotor and the inner rotor are press-held by the housing body and the cover member.

5. The electric pump according to claim 4, wherein the outer rotor includes, on its outer circumferential edge portion, a rim portion whose length in the axial center direction is longer than that of the rotor body,

wherein bearings are interposed in respective spaces between an inner circumferential surface at one end portion in a longitudinal direction of the rim portion and the cover and between the inner circumferential surface at the other end portion in the longitudinal direction of the rim portion and the housing body, and

wherein the rotor configured of the outer rotor and the rotor body is rotatably supported at both ends by the bearings.