CN105703591B - Single-phase motor and pump using same - Google Patents

Abstract

The invention discloses a single-phase motor and a pump using the same. The motor includes a stator and a rotor rotatable relative to the stator. The stator comprises a stator magnetic core and a stator winding wound on the stator magnetic core. The stator magnetic core is provided with pole parts and a yoke part connected with the pole parts, each pole part is provided with a pole arc surface opposite to the rotor, and an air gap is formed between the pole arc surface and the rotor; each pole part has two circumferential ends, and the ratio of the distance between adjacent circumferential ends to the width of the minimum air gap between the pole arc face and the rotor is less than 2.

Description

Single-phase motor and pump using same

Technical Field

The invention relates to a single-phase motor, which is particularly suitable for application of fans, water pumps and the like.

Background

In the starting process of the traditional single-phase synchronous motor, an electromagnet of a stator generates an alternating magnetic field and drags a permanent magnet rotor to oscillate, if the rotor obtains enough kinetic energy, the oscillation amplitude of the rotor is continuously increased, and finally the rotation of the rotor is rapidly accelerated to be synchronous with the alternating magnetic field of the stator. To ensure starting, the starting point setting of the motor is typically low, resulting in the motor not being able to operate at a high efficiency operating point and therefore being inefficient. The present invention aims to provide a new type of electrical machine which is more efficient.

Disclosure of Invention

The invention provides a single-phase motor, which comprises a stator and a rotor capable of rotating relative to the stator, wherein the stator comprises a stator magnetic core and a stator winding wound on the stator magnetic core, the stator magnetic core is provided with a pole part and a yoke part connected with the pole part, each pole part is provided with a pole arc surface opposite to the rotor, and an air gap is formed between the pole arc surface and the rotor; each pole part has two circumferential ends, and the ratio of the distance between adjacent circumferential ends to the width of the minimum air gap between the pole arc face and the rotor is less than 2.

Preferably, the pole faces are concentric with the rotors so as to form primary air gaps equally spaced from the rotors, the ratio of the distance between the adjacent circumferential ends to the width of the primary air gap being less than 2.

Preferably, the pole arc surface is provided with an inward concave starting slot, so that the central line of the rotor permanent magnet pole is offset relative to the central axis of the stator pole part when the rotor is at rest.

Preferably, the stator core includes two pole portions, and two starting slots on pole arc surfaces of the two pole portions are symmetrical in a diameter direction.

Preferably, the rotor comprises at least one pair of permanent magnet poles, and the rotor operates at a constant speed of 60f/p turns/min during a steady state phase when the stator winding is connected in series with an ac power source, where f is the frequency of the ac power source and p is the number of pole pairs of the rotor.

Preferably, the motor further comprises a driving circuit and a position sensor, wherein the driving circuit is configured to electrify the stator winding according to the rotor magnetic pole position information detected by the position sensor in a preset mode, so that the rotor has a fixed starting direction each time the motor is electrified.

In another aspect, the present invention provides a pump comprising a pump housing having a pump chamber, an inlet and an outlet communicating with the pump chamber, an impeller rotatably disposed in the pump chamber, and a single-phase motor for driving the impeller, the motor comprising a stator and a permanent magnet rotor rotatable relative to the stator, the stator comprising a stator core and a stator winding wound around the stator core, the stator winding being connected in series with an ac power source such that the rotor operates at a constant speed of 60f/p turns/minute during a steady state period, wherein f is a frequency of the ac power source and p is a number of pole pairs of the permanent magnet rotor; the stator magnetic core is provided with pole parts and a yoke part connected with the pole parts, each pole part is provided with a pole arc surface opposite to the rotor, and an air gap is formed between the pole arc surfaces and the rotor; each pole portion has a circumferential end, the ratio between the distance between adjacent circumferential ends and the minimum width of the air gap being less than 2.

Preferably, the pole arc is concentric with the rotor so as to form a main air gap with equal distance with the rotor, the ratio of the distance between the circumferential ends to the width of the main air gap is less than 2, the rotor is provided with permanent magnet poles opposite to the stator pole, and the pole arc is provided with an inward concave starting slot so that the central line of the rotor permanent magnet poles is offset relative to the central line of the stator pole when the rotor is at rest.

Preferably, the number of poles of the rotor permanent magnet poles is equal to the number of the stator pole parts.

Preferably, the impeller comprises a plurality of curved blades arranged at intervals in the circumferential direction.

Drawings

FIG. 1 illustrates a pump having an embodiment in accordance with the present invention;

FIG. 2 is an axial cross-sectional view of the pump of FIG. 1;

FIG. 3 is an axial cross-sectional view of the motor rotor of the pump of FIG. 1;

FIG. 4 shows the magnets of the rotor of FIG. 3;

FIG. 5 is a radial cross-sectional view of the motor rotor of the pump of FIG. 1 at the detent shown in FIG. 3;

FIG. 6 is a plan view of a motor of the pump of FIG. 1 with parts removed;

FIG. 7 is a plan view of a stator core of the motor of FIG. 6;

FIG. 8 illustrates another implementation of an insulated wire stand for a stator of the electric machine of FIG. 6;

FIG. 9 is a schematic view of a horizontally developed insulating bobbin of the stator of the motor of FIG. 8;

FIG. 10 illustrates a pump casing cover for the pump of FIG. 1;

FIG. 11 is a view of the pump of FIG. 1 with the pump housing cover removed;

FIG. 12 is a view showing the mounting of the motor rotor of the pump of FIG. 1;

FIG. 13 is a bottom view of the base plate of the pump of FIG. 1;

FIG. 14 shows an impeller of the pump of FIG. 1; and

fig. 15 shows a dishwasher having a pump according to a preferred embodiment of the present invention.

Detailed Description

The technical solution and other advantages of the present invention will become apparent from the following detailed description of specific embodiments of the present invention, which is to be read in connection with the accompanying drawings. It is to be understood that the drawings are provided solely for the purposes of reference and illustration and are not intended as a definition of the limits of the invention. The dimensions shown in the figures are for clarity of description only and are not to be taken in a limiting sense.

Referring to fig. 1 and 2, a pump 10 according to an embodiment of the present invention includes a pump housing 14 having a pump chamber 12, an inlet 16 and an outlet 18 communicating with the pump chamber 14, an impeller 20 rotatably provided in the pump chamber 14, and a motor 22 for driving the impeller 20. The motor 22 is preferably a single phase synchronous motor and includes a stator and a rotor 26 rotatable relative to the stator. The pump provided by the invention is particularly suitable for the drainage pump of washing devices such as dish washing machines, washing machines and the like.

Referring to fig. 3 to 5, the rotor 26 includes a rotation shaft 28 and a permanent magnet 30 fixed to the rotation shaft 28. In the preferred embodiment of the invention, rotor 26 has two permanent magnets 30, the two magnets 30 forming two permanent magnet poles of opposite polarity and being secured to shaft 28 by an overmold 32. The overmold 32 includes an inner ring 34, an outer ring 36, and two end plates 38 connecting the inner ring 34 and the outer ring 36 at both axial ends. An outer ring 36 is overmolded onto the magnet 30 with its outer surface concentric with the shaft 28. The inner ring 34 is overmolded onto the spindle 28. The two magnets 30 are fixed radially between the inner ring 34 and the outer ring 36 and axially between the two end plates 38. The outer surface of the shaft 28 is provided with a concave-convex structure 39 to enhance the bonding force between the over-mold 32 and the shaft 28. Each magnet 30 circumferentially covers half of the circumference and has a radially outer surface 40, a radially inner surface 42, and two coplanar connecting surfaces 44 connecting the radially outer surface 40 and the radially inner surface 42 on either side. The radially outer surface 40 includes a cambered surface portion 46 and a flat surface portion 48 extending from both circumferential ends of the cambered surface portion 46 to the connection surface 44. The magnet 30 may be sintered from powder and the flat portion 48 may be used to position the molded magnet 30 for subsequent polishing or the like. The arcuate portion 46 of the outer surface 40 may be concentric with the radially inner surface 42, and the radially inner surfaces 42 of the two magnets 30 together define an inner bore 50 through which the shaft 28 passes. The inner ring 34 of the overmold 32 is molded between the radially inner surface 42 and the shaft 28.

Preferably, the ratio of the polar arc angle θ of each magnet 30 to 180 degrees is between 0.75 and 0.95, and more preferably between 0.9 and 0.95. The polar arc angle referred to herein refers to an included angle formed by two circumferential ends of the arc surface portion 46 of the radially outer surface 40 of the magnet and a virtual line connecting the axes of the rotating shafts 28. The two plane parts 48 of the radial outer surfaces 40 of the two magnets 30 on the same side are arranged in a coplanar manner, and the distance d1 between the two circumferential ends of the two plane parts 48 is between 2mm and 9.5 mm. The ratio of the length d2 of the two ends of the coplanar connecting surfaces 44 of the magnet 30 to the diameter d3 of the outer surface of the overmold 32 is between 0.82 and 0.95. In a preferred embodiment, the angle θ of the pole arc of the magnets 30 is greater than 166 degrees, and the distance d1 between the circumferential ends of the two coplanar planar portions 48 of the two magnets 30 is between 2mm and 2.5 mm. The axial end of the outer ring 36 of the overmold 32 has at least two circumferentially spaced locating grooves 52 that allow the two magnets 30 to be located during the process of molding the overmold 32. Each positioning groove 52 is provided at the junction of the two magnets 30 and completely covers, in the circumferential direction, the two planar portions 48 of the two magnets 30 on the same side.

Compared with the traditional arc magnet, the rotor in the embodiment has the advantages that the pole arc angle of the magnet is larger, the cogging torque of the motor can be reduced, the rotor rotates more smoothly, and the cost is lower compared with that of an annular magnet.

Referring to fig. 6 and 7, the stator has a stator core 54 and a stator winding 56 wound on the stator core 54. In the present embodiment, the stator core 54 has a bottom portion 58, two branches 60 extending from both ends of the bottom portion 58, and a pair of opposing pole portions 62 provided to the two branches 60, respectively. Preferably, the bottom portion 58 is strip-shaped, and two branches 60 extend from two ends of the bottom portion 58 in parallel, and two pole portions 62 are disposed opposite to each other at one end of the two branches 60 away from the bottom portion 58. Each pole part 62 has two side faces 64 and 65 extending from the branch 60 substantially parallel to the bottom 58 and a pole arc face 66 recessed between the two side faces 64 and 65, the outer surface of the rotor being opposite the pole arc face 66 with an air gap therebetween.

Preferably, the base 58 and the two branches 60 are formed independently of each other. The base 58 may be assembled from a stack of several sheet-like base members and the branch 60 may be assembled from a stack of several sheet-like branch members. The bottom member and the branch members are each provided with a fitting hole 68 for integrally fixing the sheet members stacked together. The two branches 60 have a protruding portion 70 extending from the end surface thereof near the bottom 58, and two corresponding recessed portions 72 are formed at the two ends of the bottom. After the base member and the branch members are assembled into an integrated lamination structure, the protruding portions 70 of the two branches 60 and the two recessed portions 72 at the two ends of the bottom portion 58 are respectively connected in a snap-fit manner, so that the whole stator core is formed in an assembled manner. It will be appreciated that alternatively, the raised portion 70 may be provided at the bottom and the recessed portion 72 may be provided at the branch. In this embodiment, the maximum width b1 of the bottom 58 is not greater than the minimum distance b2 between the two branches 60 after splicing. The maximum length b3 of the base 58 is no greater than the maximum distance b4 between the base-facing side 64 of the branch 60 and the distal-most end of the branch 60 near one end of the base (in this embodiment, the distal-most end of the boss 70). According to this configuration, the base 58 can be molded from material between the legs 60, thereby saving material and reducing product cost. Further, the maximum length b3 of the base may be greater than the distance b5 between the side 64 of the leg 60 facing the base and the end surface of the leg 60 near the end of the base.

Both side circumferential ends of the two stator pole portions 62 have circumferential end portions 74 provided to be opposed to each other. Set up fluting 75 between the relative circumference tip, fluting 75 can form great magnetic resistance, reduces the magnetic leakage. In the present embodiment, the slit 75 penetrates the two pole portions in the radial direction so that the two pole portions are separated from each other. A substantially uniform air gap is formed between the pole arc face 66 of the stator pole section 62 and the outer surface of the rotor 26. The term substantially uniform air gap as used herein refers to a uniform air gap formed between a substantial portion of the stator and a substantial portion of the rotor, with only a minor portion being a non-uniform air gap. Preferably, the pole arc surface 66 of the stator pole part is concentric with the rotating shaft, and the outer surface of the rotor pole part is concentric with the rotating shaft, so that a main air gap 76 with equal distance is formed between the pole arc surface 66 of the stator and the rotor pole part, and the concave starting groove 78 is arranged on the pole arc surface 66, so that an air gap which is different from the main air gap is formed between the starting groove 78 and the outer surface of the rotor 26. Preferably, the two starter grooves 78 on the pole arc faces of the two pole parts 62 are diametrically symmetrical and extend from the circumferential ends 74 of the pole parts. The above arrangement allows the rotor 26 to be tilted at an angle with respect to the centerline S2 of the stator pole segment 62 when at rest (stator windings not energized) to avoid start-up dead center, allowing the rotor to have a fixed starting direction per energization of the motor by the drive circuit. The center line of the rotor magnetic pole refers to a line extending in the radial direction and passing through the circumferential center of the rotor magnetic pole, and the center line of the stator pole refers to a line extending in the radial direction and passing through the circumferential center of the stator pole.

Preferably, the ratio between the distance a1 between the circumferential ends 74 of adjacent stator pole sections and the width a2 of the minimum air gap between the pole arc and the rotor (in this embodiment, the primary air gap between the pole arc and the rotor) is less than 2.

In this embodiment, the two slots 75 have uniform width and the width of the two slots is equal and parallel to the length direction of the branch 60. It will be appreciated that alternatively, the width of each slot 75 may be non-uniform, in which case the distance a1 between the two opposing circumferential ends 74 refers to the minimum width of the slot 75. The open groove 75 may be provided only on the inner surface or the outer surface of the two pole portions without penetrating the two pole portions in the radial direction, thereby forming a large magnetic resistance between the two pole portions.

The motor configuration of the embodiment can ensure that the rotor has a preset starting direction, and simultaneously reduce the cogging torque of the motor, so that the rotor rotates more smoothly.

Referring to fig. 8 and 9, the stator preferably includes a pair of stator windings 56 wound around respective insulating bobbins 80 disposed around the two legs 60 of the stator core 54. The motor is also provided with a circuit board 82 which is fixed to the insulating bobbin 80 in a direction substantially parallel to the branches 60. A thermal protector 84 is mounted on the circuit board 82, the thermal protector 84 being disposed between the circuit board 82 and the two stator windings 56 to provide protection against electrical power loss when either winding 56 is at an excessive temperature. The two stator windings 56 may be formed by winding two separate wires 86 that are disconnected and then electrically connected to each other. Each wire 86 has a respective wire inlet end 88 and wire outlet end 90, and the two windings can be formed by simultaneously winding the two wires 86, thereby effectively saving working hours. The two inlet terminals 88 of the two stator windings 56 are located at one end of the two parallel branches 60 in the length direction and are disposed on the inner layer of the windings, and the two outlet terminals 90 are located at the other end of the two parallel branches 60 in the length direction and are disposed on the outer layer of the windings. The insulating bobbin 88 includes a tubular portion 92 and end walls 94 extending outwardly from opposite ends of the tubular portion 92. A winding space 95 is formed between the radially outer surface of the tubular portion 92 and the axially opposite surfaces of the end walls 94 to accommodate the windings 56. The end walls 94 of the two insulating wire frames 88 on one side of the wire inlet end 88 are respectively provided with a wire groove 96, the two wire inlet ends 88 of the two stator windings 56 are routed to a winding space 95 on the inner side of the wire frame from the outer side of the wire frame 80 along the wire grooves 96, a partition wall 98 is arranged between the wire grooves 96 and the winding space 95 on the inner side of the wire frame, the partition wall 98 extends to the outer surface of the tubular part 92, the wire inlet end 88 is blocked by the partition wall 98 until the outer surface of the tubular part 92 enters the winding space, therefore, the wire inlet end can be separated from each layer of coils in the winding space 95, and the phenomenon that the insulating layers of the wires are scraped due to the friction contact between the. Preferably, the two outlet terminals 90 are soldered to the circuit board 82 and electrically connected to each other such that the two windings 56 are connected in series and the two inlet terminals 88 of the two windings 56 are powered by an external single phase ac power source, such that the motor is also referred to as a single phase motor. Preferably, as shown in fig. 9, the two insulating bobbins 80 are integrally formed and arranged in a long strip shape along the length direction, and after the two windings 56 are wound on the bobbins 80, the two long strip bobbins 80 are bent into a parallel arrangement and are sleeved on the two parallel branches 60 of the stator core 54. Preferably, the two incoming ends of the two windings 56 are disposed at two far ends of the two strip-shaped bobbins 80 that face away from each other or at two adjacent ends of the two strip-shaped bobbins 80 that are disposed at the middle part of the strip shape, and the winding directions of the two windings are the same, so that the two incoming ends of the two windings are disposed at the same end after the two bobbins are bent to be arranged in parallel, and magnetic fields generated by electrifying the two windings when the two windings are connected in series cannot cancel each other.

Referring to fig. 10 to 12, the pump casing 14 includes a cover 100 and a bottom plate 102 integrally mounted with the cover 100. The cover 100 is sealingly connected to the base plate 102 via a sealing ring 104. Preferably, the sealing ring 104 is positioned in a radial groove 106 formed in the base plate 102 to prevent the sealing ring 104 from being removed from the base plate 102 prior to installation of the cover 100 and the base plate 102. The cover 100 includes a top panel 108 and a side gusset 110 connecting the top panel 108 to the bottom panel 102. The inlet 16 extends generally axially outwardly from the top plate 108 and the outlet 18 extends outwardly from the side shroud 110 in a generally perpendicular axial direction. The cover 100 and the base plate 102 form a pump chamber 12 therebetween, and the impeller 20 is rotatably provided in the pump chamber 12.

A snap fit arrangement is provided between the cover 100 and the base plate 102, which may be engaged by relative circumferential movement of the base plate 102 and the cover 100. Preferably, a circumferentially extending slot 112 may be formed on the outer peripheral edge of the bottom plate 102, a circumferentially extending protrusion 113 is correspondingly formed on the outer surface of the cover 100, and the axial width of the circumferentially extending protrusion 113 is gradually reduced along the direction of inserting into the circumferentially extending slot 112. The peripheral edge of the base plate 102 is further provided with a resilient arm 114 extending obliquely upwardly, the free end of the resilient arm having a step 116 recessed relative to the arm, and the outer surface of the cover 100 being provided with a projection 118. When the cover 100 is rotated in a clockwise direction, the circumferentially extending projections 113 of the cover 100 are inserted into the circumferentially extending slots 112 of the base 102 and the tabs 118 slide over the resilient arms 114. When the circumferentially extending protrusion 113 is rotated to form a fit with the engaging groove 112, the protrusion 118 slides to the step 116 to limit the reverse rotation of the cover 100.

The base plate 102 includes a pump chamber bottom wall 122 provided with an opening 120 and a rotor housing 124 integrally extending axially outward from the opening 120. A stationary end cap 126 is mounted within the rotor housing 124 near the open end. One end of the shaft 28 passes through the end cap 126 into the pump chamber 12 and connects with the impeller 20 to drive the impeller 20 to rotate. The shaft 28 may be supported at each end by a bearing 128 disposed in the end cap 126 and a bearing 130 disposed at an end of the rotor housing 124 remote from the opening.

Preferably, the bearing 128 is mounted to the end cap 126 via a damping member 132. The bearing 128 is cylindrical and has circumferentially extending ribs 134 on its outer surface and the damping member 132 has grooves 136 on its inner surface which engage the ribs 134, the arrangement being such that concentricity of the bearing 128 and the rotor is ensured. Bearing 130 may be supported by a bearing housing 138 integrally formed with rotor housing 134, with a plurality of internal teeth 140 formed on an inner surface of bearing housing 138 to provide non-continuous contact with an outer surface of bearing 130. The above configuration can reduce vibration generated when the motor operates.

The rotor case 124 is fixed between the two stator pole portions 62, and a gap is provided between the outer surface of the rotor 26 and the rotor case 124 so that the rotor 26 can rotate relative to the rotor case 124. The rotor housing 124 has an axially extending rib 142 (shown in fig. 11) on the outer surface thereof, and the two insulating bobbins 80 together form a rib 144 (shown in fig. 6) on two adjacent sides near one end of the stator pole 62, and the two ribs 142 and 144 extend into the two slots 75 between the circumferential ends 74 of the two ends of the two poles 62, respectively, to restrict relative circumferential movement of the two poles 62 of the stator core 54. Preferably, the outer surface of the ribs 142 on the rotor housing 124 is no higher than the side 65 of the stator pole 62 away from the base 58.

Referring to fig. 11 and 13, the motor also has a motor cover 146 fixed to the pump housing 14. The motor cover 146 covers the stator winding 56 and the circuit board 82 and includes a bottom wall 148 and two side walls 150 extending from the bottom wall 148. Two side walls 150 are provided on both sides of the stator core 54. The circuit board 82 is disposed between the bottom wall 148 and the stator windings 56. In this embodiment, the motor cover 146 and the pump casing 14 are fixed to each other by a snap structure formed by a protrusion 152 on the sidewall 150 and a hook 154 extending downward from the bottom plate 102. At least one pair of positioning protrusions 156 is disposed at positions of the bottom plate 102 corresponding to the two sidewalls 150, and the sidewalls 150 are inserted between the pair of positioning protrusions 156. Preferably, the width between the pair of positioning protrusions 156 gradually decreases along the direction from the free end to the root of the protrusion 156, so that the pressure applied to the sidewall 150 gradually increases until a tight fit is formed, thereby enhancing the fixing force between the motor cover 146 and the pump housing 14 and reducing the vibration. In this embodiment, the hook 154 can also serve as the positioning protrusion 156, and it is understood that the pair of positioning protrusions 156 can also be provided separately from the hook 154. Preferably, the two positioning surfaces of the pair of positioning protrusions 156 are staggered. It is understood that more than one pair of positioning protrusions 156 may be provided on each side as shown in the drawings, or only one pair of positioning protrusions 156 may be provided, and when more than one pair of positioning protrusions 156 are provided, each pair of positioning protrusions 156 may be provided independently of the other pairs of positioning protrusions 156, or a strip-shaped protrusion 156 may be provided on the inner or outer side of the side wall such that two or more pairs of positioning protrusions 156 share the strip-shaped protrusion 156.

The applicant's chinese patent applications No. 201410404474.2 and No. 201410404755.8 are incorporated herein by reference. The motor of the embodiment of the invention can ensure that the rotor rotates directionally along the same direction every time when being started by matching with the driving circuit disclosed by any one of the two applications or other suitable driving circuits, so that the impeller driven by the rotor can adopt bent blades in the application of a fan, a water pump and the like, thereby improving the fluid efficiency of the fan, the water pump and the like. Under the condition of ensuring the same output, a smaller motor can be used, and energy is saved. The drive circuitry described above may be provided on the circuit board 82 to energize the stator windings 56 in a predetermined manner based on rotor pole position information detected by the position sensor 158 (shown in fig. 2) to ensure a fixed starting direction for the rotor each time the motor is energized. In the present embodiment, the position sensor 158 is disposed outside the rotor case 124 and covered by the motor cover 146 within an acute angle formed by a perpendicular line to the polar axis S1 and a perpendicular line to the central axis S2 (fig. 7) of the stator when the rotor is stationary.

Referring to fig. 14, the impeller 20 is fixedly connected to the rotating shaft 28 to rotate synchronously with the rotating shaft 28. The impeller 20 may be made of plastic and includes a base plate 160 and a plurality of blades 162 fixed to the base plate 160 at intervals in a circumferential direction. Preferably, the plurality of blades 162 of the impeller 20 are arcuate in shape, having two sets of long blades 164 and short blades 166, the two sets of blades being alternately circumferentially spaced about the outer periphery of the base 160. A spiral flow path 168 (shown in fig. 11) is formed between the inner wall of the pump chamber 12 and the impeller 20. The radial cross-sectional area of the flow passage 168 increases in the circumferential direction toward the outlet 18. Under the condition that the rotor has the same rotating direction every time the rotor is started, the fluid efficiency can be improved by adopting the arc-shaped blades and the spiral flow passage. A mounting post 170 is provided in the center of the base plate 160, and one end of the shaft 28 is fixed to the mounting post 170 via a bushing 172. The sleeve 172 may be made of metal. Preferably, the axial end of the mounting post 170 remote from the motor is formed as a continuous closed end surface by the mounting post 170, the sleeve 172, and the injection molded part 174 from the outside to the inside. The injection molded portion 174 is connected to the mounting post 170 via a bridge portion 176. It is understood that straight blades may be used for the impeller 20.

The pump 10 provided by the invention is particularly suitable for being used as a drainage pump of washing devices such as dishwashers, washing machines and the like. Fig. 15 shows a dishwasher 176 having a drain pump according to a preferred embodiment of the present invention, including a washing chamber 178, a water supply passage 180 supplying washing water to the washing chamber 178, a drain passage 182 draining washing water to the outside, a circulation passage 184 circulating washing water in the washing chamber 178, and a control system 188 having the drain pump 10 and a circulation pump 186. Wherein the drain pump 10 pumps the washing water in the washing chamber 178 to the drain passage 182, and the circulation pump 186 pumps the washing water in the washing chamber 178 to the circulation passage 184.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A single-phase motor comprises a stator and a rotor which can rotate relative to the stator, wherein the rotor comprises a rotating shaft and a permanent magnet fixed on the rotating shaft, the stator comprises a stator magnetic core and a pair of stator windings wound on the stator magnetic core, the stator magnetic core is provided with a bottom, two branches extending out from two ends of the bottom, and a pair of opposite pole parts arranged on the two branches respectively, the pair of winding parts are wound on the two branches respectively, each pole part is provided with a pole arc surface opposite to the rotor, and an air gap is formed between the pole arc surface and the rotor; each pole part has two circumferential ends, and the ratio of the distance between adjacent circumferential ends to the width of the minimum air gap between the pole arc face and the rotor is less than 2.

2. The single phase electric motor of claim 1, wherein said pole arcs are concentric with the rotors to form primary air gaps equally spaced from the rotors, and wherein the ratio of the distance between said adjacent circumferential ends to the width of said primary air gaps is less than 2.

3. A single phase electric motor as claimed in claim 2, wherein the rotor has permanent magnet poles opposite stator poles, and the stator poles have concave starting slots on their pole arcs, such that the rotor permanent magnet poles are offset in their centre line relative to the stator poles when the rotor is at rest.

4. The single-phase electric motor of claim 3, wherein the stator core includes two pole portions, and wherein the two starter slots on the pole arc faces of the two pole portions are diametrically symmetrical.

5. A single phase electric motor as claimed in claim 3, wherein the permanent magnets of the rotor are secured to the shaft via overmoulding, the rotor comprising at least one pair of permanent magnet poles, the rotor operating at a constant speed in the steady state phase at 60f/p turns/minute when the stator winding is connected in series with an ac power source, where f is the frequency of the ac power source and p is the number of pole pairs of the rotor.

6. The single-phase motor according to any one of claims 1 to 5, further comprising a drive circuit and a position sensor, the drive circuit being configured to energize the stator windings in a predetermined manner based on rotor magnetic pole position information detected by the position sensor, such that the rotor has a fixed starting direction each time the motor is energized.

7. A pump comprising a pump housing having a pump chamber, an inlet and an outlet communicating with the pump chamber, an impeller rotatably disposed within the pump chamber, and a single phase motor for driving the impeller, the single phase motor comprising a stator and a permanent magnet rotor rotatable relative to the stator, the stator comprising a stator core and a pair of stator windings wound around the stator core, the stator windings when connected in series with an ac power source operating at a constant speed of 60f/p turns/minute during a steady state phase, wherein f is the frequency of the ac power source and p is the number of pole pairs of the permanent magnet rotor; the stator magnetic core is provided with a bottom, two branches extending out from two ends of the bottom and a pair of opposite pole parts respectively arranged on the two branches, the pair of winding parts are respectively wound on the two branches, each pole part is provided with a pole arc surface opposite to the rotor, and an air gap is formed between the pole arc surface and the rotor; each pole portion has a circumferential end, the ratio between the distance between adjacent circumferential ends and the minimum width of the air gap being less than 2.

8. A pump according to claim 7, wherein the pole arcs are concentric with the rotor so as to form main air gaps equally spaced from the rotor, the ratio of the distance between the circumferential ends to the width of the main air gaps being less than 2, the rotor having permanent magnet poles opposite stator poles, the pole arcs being provided with inwardly-recessed starter slots so that the centre lines of the rotor permanent magnet poles are offset relative to the centre lines of the stator poles when the rotor is at rest.

9. The pump of claim 7 wherein said rotor permanent magnet poles have a number of poles equal to the number of stator pole segments.

10. A pump according to any one of claims 7 to 9, wherein the impeller comprises a plurality of curved vanes circumferentially spaced apart.