Electric fluid pump and method for manufacturing the same

Abstract

To avoid, in an electric fluid pump in which a shaft is supported only by a plain bearing disposed axially between a motor part and a pump part, interference between an inner rotor and a housing to prevent degradation of the pump performance and the generation of abnormal noise.SOLUTION: A shaft 6 connecting a rotor 22 of a motor part 2 and an inner rotor 31 of a pump part 3 is supported only by a cylindrical plain bearing 7 provided axially between the motor part 2 and the pump part 3. The axial length A of a support area provided by the plain bearing 7, a bearing clearance B (the difference between the inner diameter B1 of the plain bearing 7 and the outer diameter B2 of the shaft 6), a pump side clearance C (the difference between the axial width C1 of a pump accommodating space 55 and the axial width C2 of the inner rotor 31 of the pump part 3), and the circumscribing circle diameter D of the inner rotor 31 satisfy C>D×B / A.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an electric fluid pump and a method for manufacturing the same. [Background technology]

[0002] In recent years, vehicles such as automobiles may use an electric oil pump to supply oil to various parts of the vehicle. For example, vehicles equipped with an idling stop mechanism (a mechanism that automatically stops the engine when the vehicle is stopped) and hybrid vehicles are provided with an electric oil pump that supplies hydraulic pressure to the transmission when the engine is stopped.

[0003] The electric oil pump has a pump section having an inner rotor and an outer rotor, and a motor section that rotates the pump section, and the inner rotor of the pump section and the rotor of the motor section are connected by a shaft. By driving the motor section to rotate the rotor of the motor section, the inner rotor of the pump section, and the shaft together, oil is compressed in a pump chamber formed between the outer rotor and inner rotor of the pump section and discharged from a discharge port.

[0004] The shaft is often supported by bearings arranged at multiple locations spaced apart in the axial direction (for example, at the end on the motor side and in the axial region between the pump and motor). However, in order to reduce the size and cost of the electric oil pump, the shaft may be supported only by a sliding bearing arranged axially between the pump and motor (for example, Patent Document 1 listed below). In this case, the shaft tends to tilt more than when multiple locations on the shaft are supported by bearings. In particular, when the pump is operating, the hydraulic pressure in the pump chamber when sucking in and discharging fluid applies a radial force to the inner rotor fixed to the end of the shaft, making the shaft more likely to tilt.

[0005] For example, Patent Document 1 listed below shows a configuration in which the tooth tips of the inner rotor are curved in order to solve the problem of abnormal noise being generated when the inner rotor is tilted, due to the tooth tips of the inner rotor colliding with the tooth surface of the outer rotor. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5824391 Summary of the Invention [Problem to be solved by the invention]

[0007] If the inner rotor tilts, not only will the inner rotor and outer rotor interfere with each other, but both axial side surfaces of the inner rotor will also interfere with the housing, which may result in reduced pump performance, abnormal noise, etc. The above-mentioned Patent Document 1 discloses a means for avoiding interference between the inner rotor and outer rotor, but does not disclose any means for avoiding interference between the inner rotor and the housing.

[0008] Therefore, the present invention aims to prevent a decrease in pump performance and the generation of abnormal noise by avoiding interference between the inner rotor and the housing in an electric fluid pump in which the shaft is supported only by a sliding bearing arranged axially between the motor section and the pump section, even when a large radial force acts on the inner rotor of the pump section. [Means for solving the problem]

[0009] The present invention, which has been made to solve the above problems, provides an electric fluid pump comprising: a housing; a motor section having a stator fixed to the housing and a rotor arranged on the inner circumference of the stator; a pump section having an inner rotor and an outer rotor accommodated in a pump accommodating space formed in the housing; a shaft connecting the rotor of the motor section and the inner rotor of the pump section; and a cylindrical plain bearing provided axially between the motor section and the pump section and supporting the shaft, wherein the shaft is supported only by the plain bearing, Let A be the axial length of the support area of ​​the shaft by the sliding bearing, B be the difference between the inner diameter of the sliding bearing and the outer diameter of the shaft, C be the difference between the axial width of the pump accommodating space and the axial width of the inner rotor, and D be the circumscribing circle diameter of the inner rotor, C>D B / A To provide an electric fluid pump that satisfies the above requirements.

[0010] As described above, by having the axial length A of the support area of ​​the shaft provided by the plain bearing, the difference B between the inner diameter of the plain bearing and the outer diameter of the shaft, the difference C between the axial width of the pump accommodating space and the axial width of the pump section's inner rotor, and the circumscribing circle diameter D of the pump section's inner rotor satisfy the above relationship, an axial gap can be secured between the pump section's inner rotor and the housing, even when the shaft is tilted to its maximum extent relative to the plain bearing, and therefore interference between the inner rotor and the housing can be avoided.

[0011] By providing a seal member that slides against the outer circumferential surface of the shaft between the sliding bearing and the motor section in the axial direction, it is possible to prevent the fluid pumped by the pump section from entering the motor section. In this case, if the area of ​​the outer circumferential surface of the shaft where the seal member slides and the axial area on the pump side are made into a straight cylindrical surface and this cylindrical surface is press-fitted into the inner periphery of the inner rotor of the pump section, the shape of the shaft can be simplified and processing costs can be reduced.

[0012] The sliding bearing may be formed, for example, of a sintered oil-impregnated bearing. Effect of the Invention

[0013] As described above, according to the present invention, in an electric fluid pump in which the shaft is supported only by a sliding bearing arranged axially between the motor section and the pump section, interference between the inner rotor and the housing can be avoided, thereby preventing a decrease in pump performance and the generation of abnormal noise. [Brief description of the drawings]

[0014] [Figure 1] 1 is an axial cross-sectional view of an electric oil pump according to an embodiment of the present invention. FIG. [Diagram 2] FIG. 2 is a cross-sectional view of the pump section taken in a direction perpendicular to the axis. [Diagram 3] 2 is an enlarged cross-sectional view showing the vicinity of a pump portion of the electric oil pump of FIG. 1. [Figure 4] FIG. 13 is a diagram illustrating a schematic positional relationship when the shaft is inclined. [Diagram 5] FIG. 4 is an axial cross-sectional view of a sliding bearing and a shaft according to another embodiment. [Figure 6] FIG. 11 is an axial cross-sectional view of a sliding bearing and a shaft according to yet another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] The electric fluid pump of this embodiment is an electric oil pump that mainly supplies hydraulic pressure to the transmission while the engine is stopped. The electric oil pump draws oil from an oil reservoir at the bottom of the transmission case, and discharges the oil under pressure into the transmission, thereby ensuring the necessary hydraulic pressure and amount of lubricating oil in the transmission.

[0017] Fig. 1 shows an electric oil pump 1 of this embodiment. This electric oil pump 1 has a motor section 2, a pump section 3 driven by the motor section 2, a controller 4 that controls the motor section 2, and a housing 5 that accommodates the motor section 2, the pump section 3, and the controller 4. This electric oil pump 1 is an electromechanical integrated type with a built-in controller 4, but is not limited to this, and the electric oil pump 1 may also be a electromechanical separate type that does not have a controller. Each member or element will be described in detail below.

[0018] In the following description, the direction parallel to the axis O of the motor unit 2 is referred to as the "axial direction," and the radial direction of a circle centered on the axis O is referred to as the "radial direction" (the "inner diameter direction" and the "outer diameter direction" also refer to the inner diameter direction and the outer diameter direction of the circle). Also, the circumferential direction of the circle centered on the axis O is referred to as the "circumferential direction."

[0019] The motor unit 2 is, for example, a three-phase brushless DC motor. The motor unit 2 has a stator 21 fixed to the housing 5 and a rotor 22 arranged on the inner circumference of the stator 21. The stator 21 has a plurality of coils arranged evenly in the circumferential direction, specifically, coils corresponding to three phases, namely, U-phase, V-phase, and W-phase. The rotor 22 has a plurality of magnets arranged evenly in the circumferential direction. The stator 21 and the rotor 22 are arranged with a minute radial gap therebetween. An axial through hole is provided at the axis of the rotor 22, and the shaft 6 is fixed into the through hole by press-fitting or the like.

[0020] The pump section 3 is disposed on one axial side (right side in the figure) of the motor section 2. The pump section 3 is a rotary pump that pumps oil by rotating. As shown in FIG. 2, the pump section 3 of this embodiment is a trochoid pump having an inner rotor 31 on which a plurality of external teeth 31a are formed and an outer rotor 32 on which a plurality of internal teeth 32a are formed. The inner rotor 31 is disposed on the inner circumference of the outer rotor 32. The rotation center O1 of the inner rotor 31 coincides with the axis O of the motor section 2. The rotation center O2 of the outer rotor 32 is radially shifted from the rotation center O1 of the inner rotor 31. Some of the internal teeth 32a of the outer rotor 32 mesh with some of the external teeth 31a of the inner rotor 31. If the number of teeth of the inner rotor 31 is n, the number of teeth of the outer rotor 32 is (n+1). An outer peripheral surface 32b of the outer rotor 32 and an inner peripheral surface 51a of the housing 5 into which the outer rotor 32 fits are both cylindrical surfaces. The outer rotor 32 is rotatably disposed on the inner periphery of the housing 5 so as to be rotated in accordance with the rotation of the inner rotor 31.

[0021] The controller 4 is disposed on the other axial side of the motor unit 2 (the left side in FIG. 1). The controller 4 has a board perpendicular to the axial direction and multiple electronic components mounted on the board. These electronic components constitute a control circuit that controls the driving of the motor unit 2. Power is supplied to the controller 4 from an external power source via a connector.

[0022] The housing 5 has a central housing 51, a pump cover 52, a controller housing 53, and a controller cover 54. The central housing 51, the pump cover 52, the controller housing 53, and the controller cover 54 are integrated together by, for example, fastening with bolts. The central housing 51, the pump cover 52, the controller housing 53, and the controller cover 54 are made of a metal material that is a conductor and has good thermal conductivity, for example, an aluminum alloy, specifically, ADC12. Alternatively, one or more of the central housing 51, the pump cover 52, the controller housing 53, and the controller cover 54 may be made of another metal material (for example, an iron-based metal or a copper-based metal) or a resin.

[0023] The housing 5 is provided with a pump accommodating space 55 that accommodates the pump section 3 consisting of the inner rotor 31 and the outer rotor 32. In the illustrated example, the pump accommodating space 55 is formed by a recess formed in an end face on one axial side (the right side in FIG. 1) of the central housing 51 and a pump cover 52 that covers this recess from one axial side. The pump cover 52 is provided with a mounting surface 52a for mounting the electric oil pump 1 to a mounting target component (a transmission case in this embodiment).

[0024] The housing 5 is provided with a motor accommodating space 56 that accommodates the motor unit 2. In the illustrated example, the motor accommodating space 56 is formed by a recess formed in an end face on the other axial side (the left side in FIG. 1) of the central housing 51 and a recess formed in an end face on one axial side (the right side in FIG. 1) of the controller housing 53.

[0025] The housing 5 is provided with a controller accommodating space 57 that accommodates the controller 4. In the illustrated example, the controller accommodating space 57 is formed by a recess provided in an end face on the other axial side (left side in FIG. 1) of the controller housing 53 and a recess provided in an end face on one axial side (right side in FIG. 1) of the controller cover 54. The controller cover 54 is provided with a plurality of fins 54a for dissipating heat generated by the controller 4 to the outside.

[0026] A suction port 61 and a discharge port 62 are formed in the pump cover 52. The suction port 61 opens into a portion (suction space 33) of the space between the inner rotor 31 and the outer rotor 32 whose spatial volume expands with rotation. The discharge port 64 opens into a portion (compression space 34) of the space between the inner rotor 31 and the outer rotor 32 whose spatial volume narrows with rotation. The suction port 61 and the discharge port 62 open to the mounting surface 52a, and communicate with an oil path of the transmission when the electric oil pump 1 is attached to the transmission.

[0027] The central housing 51 is provided with a suction side counter port 63 and a discharge side counter port 64. The suction side counter port 63 opens into the suction space 33 of the pump section 3, and the discharge side counter port 64 opens into the compression space 34 of the pump section 3. The central housing 51 is provided with a communication passage 65 that communicates the suction side counter port 63 with a space 66 adjacent to the pump section 3 side of the seal member 8. By communicating the above-mentioned space 66 with the suction side counter port 63 via this communication passage 65, the oil pressure in the above-mentioned space 66 can be suppressed and oil leakage from the seal member 8 to the motor section 2 side can be prevented.

[0028] The shaft 6 connects the axis of the inner rotor 31 (pump rotor) of the pump section 3 and the axis of the rotor 22 (motor rotor) of the motor section 2. One axial end (right side in FIG. 1) of the shaft 6 is fixed to a through hole provided in the axis of the inner rotor 31 of the pump section 3. The shaft 6 and the inner rotor 31 are fixed in a state in which relative movement is completely restricted, for example, by press fitting. The other axial end (left side in FIG. 1) of the shaft 6 is fixed to a through hole provided in the axis of the rotor 22 of the motor section 2, for example, by press fitting. As a result, the shaft 6, the inner rotor 31, and the rotor 22 are able to rotate together.

[0029] The shaft 6 is rotatably supported relative to the housing 5 via a cylindrical plain bearing 7. The plain bearing 7 can be lubricated by the oil pumped by the pump section 3, and therefore can be disposed close to the pump section 3. In addition, the plain bearing 7 has a smaller radial dimension than a rolling bearing, and therefore it is easier to ensure space for providing the communication passage 65 and the like on its outer periphery, thereby increasing the degree of freedom in designing the electric oil pump 1.

[0030] Because oil can flow between the plain bearing 7 and the pump section 3 in the axial direction, oil in the pump section 3 is supplied to the sliding contact portion between the plain bearing 7 and the shaft 6. Meanwhile, a seal member 8 is disposed between the plain bearing 7 and the motor section 2 in the axial direction. The seal member 8 is fixed to the inner circumferential surface of the housing 5 and includes a seal lip that slides against the outer circumferential surface of the shaft 6. This seal member 8 prevents oil from leaking into the motor section 2.

[0031] In this embodiment, the outer circumferential surface of the shaft 6 is a straight cylindrical surface in the region that comes into sliding contact with the seal member 8 and in the axial region on the pump section 3 side (right side in the figure). In particular, in the illustrated example, the entire axial region of the outer circumferential surface of the shaft 6 is a straight cylindrical surface. By making the outer circumferential surface of the shaft 6 have a simple shape in this manner, the processing costs of the shaft 6 are reduced.

[0032] The sliding bearing 7 is made of metal or resin. In this embodiment, a sintered oil-impregnated bearing in which the internal pores of a sintered body are impregnated with oil is used as the sliding bearing 7. In this case, it is not preferable to impregnate the sintered body with a type of oil different from the oil (e.g. ATF oil) pumped by the pump section 3, as this would result in the ATF oil being mixed with the different type of oil. Therefore, it is preferable to impregnate the sintered body with the same type of oil as the oil pumped by the pump section 3.

[0033] The sliding bearing 7 is press-fitted into the inner peripheral surface of the housing 5. The sliding bearing 7 is preferably formed from a material that has a linear expansion coefficient close to that of the housing 5 and has excellent sliding properties. For example, when the housing 5 is formed from an aluminum alloy, the sliding bearing 7 is preferably formed from a copper-iron based material, for example, a material containing 50 mass% or more of copper and 35 mass% or more of iron. The sliding bearing 7 of this embodiment is formed from a sintered body made of a material containing 35 to 45 mass% of iron, 10 mass% or less of other components, and the remainder being copper. Examples of other components include tin and / or carbon. The linear expansion coefficient of this sintered body is 14.5×10 -6 [1 / ℃] and the density is 6.5 [g / cm 3 In addition, when the housing 5, particularly the central housing 51, is made of an aluminum alloy (ADC12), its linear expansion coefficient is 21×10 -6 [1 / ℃].

[0034] In the electric oil pump 1 configured as above, the shaft 6 is supported only by a sliding bearing 7 disposed axially between the motor section 2 and the pump section 3. In other words, the bearing supporting the shaft 6 is provided only axially between the motor section 2 and the pump section 3, and no bearing is provided to support other areas of the shaft 6 (for example, the axial end section). This simplifies the support structure for the shaft 6, and reduces the size, weight, and cost of the electric oil pump 1. On the other hand, since the shaft 6 is prone to tilting, there is a concern that the shaft 6 and the inner rotor 31 fixed thereto may tilt as shown by the dotted line in FIG. 3, causing the inner rotor 31 to come into contact with the housing 5.

[0035] In FIG. 3, the axial length of the support area of ​​the shaft 6 by the plain bearing 7 is referred to as "bearing length A". In this embodiment, since only one plain bearing 7 is provided, the axial dimension of the plain bearing 7 itself is the bearing length A. The difference between the inner diameter B1 of the plain bearing 7 and the outer diameter B2 of the shaft 6 is referred to as "bearing clearance B". The difference between the axial width C1 of the pump accommodating space 55 and the axial width C2 of the inner rotor 31 (= the axial width of the outer rotor 32) is referred to as "pump side clearance C". The diameter of the circumscribed circle (see the chain line in FIG. 2) of the inner rotor 31 of the pump section 3 is referred to as "inner rotor outer diameter D". Note that in FIG. 3, the inclination angle θ of the shaft 6 and the inner rotor 31, the bearing clearance B (= B1-B2), the pump side clearance C (= C1-C2), and the like are exaggerated.

[0036] If the pump side clearance C is too large, oil is likely to escape to both axial sides from the space between the inner rotor 31 and the outer rotor 32 (the suction space 33 and the compression space 34), deteriorating pump characteristics such as compression efficiency. From this viewpoint, it is preferable that the pump side clearance C is small, for example, C<60 μm.

[0037] On the other hand, if the pump side clearance C is too small, the inner rotor 31 and the outer rotor 32 may interfere with the housing 5, resulting in problems such as abnormal noise and wear of various parts, so the pump side clearance C cannot be made unnecessarily small.

[0038] 4 geometrically shows a state in which the axis of the shaft 6 is inclined at an angle θ with respect to the axis of the sliding bearing 7. In this case, the axis of the inner rotor 31 also inclines at the angle θ, and the axial width of the inner rotor 31 increases accordingly. The increase ΔC in the axial width of the inner rotor 31 at this time is expressed by the following equation. ΔC=D·sinθ ≒D tan θ (∵θ≪1) When the shaft 6 is maximally inclined with respect to the sliding bearing 7 as shown by the dotted line in FIG. 3, tan θ=B / A, and the following equation is therefore established. ΔC=D B / A

[0039] In this embodiment, the pump side clearance C is set to be larger than the increase ΔC in the axial width of the inner rotor 31 when the shaft 6 is inclined to the maximum extent. That is, the dimensions of each part are set so that the following formula is established. C>ΔC=D B / A (1) where C=C1-C2 and B=B1-B2.

[0040] By setting the dimensions of each part so as to satisfy the above formula (1), even when the shaft 6 supported by the sliding bearing 7 is inclined to the maximum extent, an axial gap can be secured between the inner rotor 31 inclined together with the shaft 6 and the side surfaces on both axial sides of the pump accommodating space 55 in the housing 5, thereby preventing interference between the outer diameter end edges of both axial side surfaces of the inner rotor 31 and the housing 5. In other words, by setting the pump side clearance C to a value as small as possible within a range that satisfies the above formula (1), it is possible to obtain an electric oil pump 1 that does not impair the pump characteristics and that can avoid problems such as abnormal noise and wear.

[0041] However, since it is unavoidable that each component has a machining tolerance, the above formula (1) must be satisfied even if the dimensions of each component vary within the machining tolerance. Therefore, the pump side clearance C must be set larger than ΔC, taking into account the machining tolerance of each component. As a result, depending on the machining tolerance of the combined components, the pump side clearance C may become relatively large (for example, 60 μm or more), resulting in a product with poor pump characteristics. Therefore, when assembling the electric oil pump 1, matching may be performed to select each component so as to satisfy the above formula (1).

[0042] Generally, it is easy to perform matching with parts that are assembled later in the assembly process. The electric oil pump 1 (particularly the pump section 3) of this embodiment is assembled in the following order: a step of press-fitting the plain bearing 7 into the inner periphery of the housing 5, a step of inserting the shaft 6 into the inner periphery of the plain bearing 7, a step of press-fitting the inner rotor 31 of the pump section 3 onto the end of the shaft 6, and a step of accommodating the inner rotor 31 and the outer rotor 32 in the pump accommodating space 55. In this way, when the plain bearing 7, shaft 6, and inner rotor 31 are assembled in this order, it is preferable to perform matching with the inner rotor 31, which is assembled last.

[0043] Specifically, the dimensions of the axial widths C2 of all the inner rotors 31 are measured in advance, and the inner rotors 31 are ranked according to the axial widths C2. Then, in the matching process, the axial length A and inner diameter B1 of the plain bearing 7 to be incorporated into one product, the outer diameter B2 of the shaft 6, the axial width C1 of the pump accommodating space 55 of the housing 5 (i.e., the axial depth of the recess on one axial side of the central housing 51), and the inner rotor outer diameter D are obtained. These dimensions can be measured in the matching process. Alternatively, the dimensions of each of the above parts may be measured in advance, and a two-dimensional barcode or the like in which the measured values ​​are embedded may be attached to each part, and the two-dimensional barcode or the like may be read in the matching process. In order to improve the accuracy of matching, it is preferable to measure the inner diameter B1 of the plain bearing 7 after it is press-fitted into the inner circumference of the housing 5.

[0044] The dimensions A, B1, B2, C1, and D of each part thus obtained are substituted into the above formula (1) to calculate the range (minimum value) of the axial width C2 of the inner rotor 31. Then, from the inner rotors 31 previously ranked, an inner rotor 31 that satisfies the above range is selected.

[0045] By performing matching as described above, it is possible to obtain an electric oil pump 1 that satisfies the above formula (1) and has a reduced pump side clearance C. Note that the parts that are ranked in advance for matching are not limited to the inner rotor 31, and may be other parts (for example, the sliding bearing 7 or the shaft 6).

[0046] In the electric oil pump 1 having the above configuration, when the motor section 2 is driven, the inner rotor 31 rotates, and the outer rotor 32 meshed with the inner rotor 31 is rotated, so that the space formed between the teeth of the inner rotor 31 and the outer rotor 32 expand and contract as the inner rotor 31 rotates. As a result, oil stored in an oil reservoir in the transmission case is sucked into the suction space 33 of the pump section 3 through the suction port 61, and oil compressed in the compression space 34 of the pump section 3 is discharged through the discharge port 62 and supplied to the transmission.

[0047] The present invention is not limited to the above embodiment. Other embodiments of the present invention will be described below, but duplicated descriptions of the same points as the above embodiment will be omitted.

[0048] In the embodiment shown in Fig. 5, the inner circumferential surface of the sliding bearing 7 is provided with smoothed portions 7b at both axial ends. Specifically, the inner circumferential surface of the sliding bearing 7 has a cylindrical portion 7a provided in the axial center and smoothed portions 7b provided continuously on both axial sides of the cylindrical portion 7a. The smoothed portions 7b gradually increase in diameter toward the axial ends of the sliding bearing 7. The smoothed portions 7b in the illustrated example have a cross-sectional shape that smoothly continues with the cylindrical portion 7a and is a convex curve (for example, a convex arc surface) that is convex toward the inner diameter side.

[0049] When the shaft 6 is tilted, the shaft 6 is brought into contact with the roughened portion 7b of the plain bearing 7, thereby making it possible to prevent contact between the shaft 6 and the edge portion of the plain bearing 7. In this embodiment, the axial width E and drop amount F of the roughened portion 7b are set so that the shaft 6 comes into contact with the roughened portion 7b of the plain bearing 7 when the shaft 6 is maximally tilted relative to the plain bearing 7 as shown by the dotted line in Fig. 5. The axial width E of the roughened portion 7b is set to, for example, 1 / 3 or more of the overall axial length of the plain bearing 7. The drop amount F of the roughened portion 7b is set to, for example, 1 / 2 or more of the bearing clearance B.

[0050] In this embodiment, with the shaft 6 inserted into the inner circumference of the sliding bearing 7, a radial load is applied to the end of the shaft 6 to incline the shaft 6 to its maximum extent relative to the sliding bearing 7, and in this state, the inclination angle θ of the shaft 6 with respect to the axis of the sliding bearing 7 is measured, and the value of B / A can be obtained from the value of the tangent tan θ (=B / A) of this inclination angle θ. Note that in the above embodiment (see FIG. 3), B / A may also be obtained in a similar manner.

[0051] 6, a plurality of (two in the illustrated example) plain bearings 7 spaced apart in the axial direction are provided between the motor section 2 and the pump section 3. In this case, the axial distance between the ends on the axially outer sides (opposite the side on which the other plain bearings 7 are provided) of the plain bearings 7 arranged at both axial ends is the bearing length A.

[0052] In the above embodiment, the shaft 6 and the inner rotor 31 of the pump section 3 are fitted together with their cylindrical surfaces, but this is not limited thereto. For example, the outer peripheral surface of the shaft 6 and the inner peripheral surface of the inner rotor 31 may be formed with an engagement portion (for example, two flat surfaces facing each other in the diameter direction) that engages with each other in the rotational direction. In this case, the outer peripheral surface of the shaft 6 and the inner peripheral surface of the inner rotor 31 may be fitted together with a gap therebetween. When the engagement portion of the shaft 6 is formed by machining such as cutting, burrs may be generated. In this case, it is preferable that the outer diameter of the region of the shaft 6 where the engagement portion is formed is smaller than the outer diameter of the region with which the seal member 9 slides. This makes it possible to prevent the seal member 9 from interfering with the burrs of the engagement portion of the shaft 6 when the seal member 9 is disposed on the outer periphery of the shaft 6.

[0053] The present invention is not limited to an electric oil pump that pumps oil under pressure, but can also be applied to an electric pump that pumps a fluid other than oil under pressure. [Explanation of symbols]

[0054] 1 Electric oil pump (electric fluid pump) 2 Motor section 3. Pump section 4. Controller 5. Housing 6 Shaft 7. Plain bearings 8 Sealing material 21 Stator 22 Rotor 31 Inner Rotor 32 Outer Rotor 51 Center housing 52 Pump cover 53 Controller housing 54 Controller cover 55 Pump housing space 56 Motor housing space 57 Controller housing space 61 Intake port 62 Discharge port 63 Intake counter port 64 Discharge counter port 65 Communication path B Bearing clearance B1 Plain bearing bore diameter B2 Shaft outer diameter C Pump side clearance C1 Axial width of pump housing space C2 Axial width of inner rotor D Circumscribed circle diameter of inner rotor

Claims

1. an electric fluid pump comprising: a housing; a motor section having a stator fixed to the housing and a rotor arranged on an inner circumference of the stator; a pump section having an inner rotor and an outer rotor accommodated in a pump accommodating space formed in the housing; a shaft connecting the rotor of the motor section and the inner rotor of the pump section; and a cylindrical plain bearing provided axially between the motor section and the pump section and supporting the shaft, wherein the shaft is supported only by the plain bearing, When the axial length of the support area of ​​the shaft by the sliding bearing is A, the difference between the inner diameter of the sliding bearing and the outer diameter of the shaft is B, the difference between the axial width of the pump accommodating space and the axial width of the inner rotor is C, and the circumscribing circle diameter of the inner rotor is D, C>D・B / A...Formula (1) Meet the electric fluid pump.

2. a seal member that is in sliding contact with an outer circumferential surface of the shaft and is provided between the sliding bearing and the motor section in the axial direction; the shaft has an outer circumferential surface including a region with which the seal member is in sliding contact and an axial region closer to the pump portion than the region with which the seal member is in sliding contact, the shaft having a straight cylindrical surface; 2. The electric fluid pump according to claim 1, wherein said cylindrical surface of said shaft is press-fitted into an inner periphery of an inner rotor of said pump portion.

3. 2. The electric fluid pump according to claim 1, wherein the sliding bearing is a sintered oil-impregnated bearing.

4. 2. The electric fluid pump according to claim 1, wherein at least one of the sliding bearing, the shaft, and the inner rotor is selected by matching so as to satisfy the formula (1).

5. A method for manufacturing an electric fluid pump comprising: a housing; a motor section having a stator fixed to the housing and a rotor arranged on an inner circumference of the stator; a pump section having an inner rotor and an outer rotor accommodated in a pump accommodating space formed in the housing; a shaft connecting the rotor of the motor section and the inner rotor of the pump section; and a cylindrical plain bearing provided axially between the motor section and the pump section and supporting the shaft, wherein the shaft is supported only by the plain bearing, Ranking at least one of the sliding bearing, the shaft, and the inner rotor according to size; When the axial length of the support region of the shaft by the sliding bearing is A, the difference between the inner diameter of the sliding bearing and the outer diameter of the shaft is B, the difference between the axial width of the pump accommodating space and the axial width of the inner rotor is C, and the circumscribing circle diameter of the inner rotor is D, from among the ranked parts, C>D.B / A and selecting the part that satisfies the above rank.

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