Patent Application
20150004032
The invention relates to a wet rotor pump for pumping a fluid, in particular a liquid.
Document DE 10 2005 015 213 A1 makes known a wet rotor pump. The wet rotor pump comprises a rotor, which is connected to an impeller and is disposed in a wet zone, through which a pumped fluid flows. The wet zone is separated from a dry zone, in which the stator is disposed. The wet zone is demarcated from the dry zone by means of a printed circuit board, the electric lines of which form the stator such that the printed circuit board functions simultaneously as a containment shell.
Document DE 103 03 778 A1 makes known an electrically driven pump, which comprises an electric drive motor embodied as a disk rotor. The magnetic ring of the drive motor is disposed in a region through which fluid flows.
Axial flux motors are also known per se from the related art. In an axial flux motor, the magnetic flux extends in the air gap of the motor in the axial direction, cf. DE 100 53 400 A1, for example.
The problem addressed by the invention is that of creating an improved wet rotor pump.
The problem addressed by the invention is solved by the features of claim 1. Embodiments of the invention are set forth in the dependent claims.
According to embodiments of the invention, a wet rotor pump comprising an axial flux motor is created, said wet rotor pump having an inlet line for the fluid, which said inlet line extends through the stator and the containment shell. This makes it possible to dispose the power electronics for controlling the stator in the space between the stator and the containment shell. Since this space is located in the dry zone of the wet rotor pump, water-tight encapsulation of the power electronics is not required. Due to the geometry of the wet rotor pump, a particularly compact design is made possible, since the intermediate space formed by the stator, in particular the stator teeth, and the inlet line is used to accommodate the power electronics.
According to embodiments of the invention, the power electronics are disposed on an annular printed circuit board, wherein the inlet line extends through the printed circuit board.
According to embodiments of the invention, a wet rotor pump is created, in which an inlet line for the fluid extends through the stator, the containment shell, and the bearing for the impeller. Such a geometry has the advantage, in particular, that the wet rotor pump has a particularly compact design, i.e. a low overall height, combined with high power density.
Embodiments of the invention are furthermore particularly advantageous since the bearing functions simultaneously as a seal at the transition between the suction side and the pressure side of the wet rotor pump. The losses due to leakage are minimized due to the relatively small gap widths and the low tolerances of the bearing.
According to an embodiment of the invention, the fluid enters through a central opening in the containment shell. The containment shell can form an inlet connecting piece in particular.
According to an embodiment of the invention, the stator is formed in the shape of a torus. In particular, the stator can comprise an annular stator tooth receptacle, on which stator teeth are disposed. The stator teeth can be attached to the stator tooth receptacle by means of bonding, for example.
According to an embodiment of the invention, each of the stator teeth has a receiving region for a coil. Each of the stator teeth has an enlarged cross section at the end on the air-gap side. This has the advantage that the magnetic field is approximately homogeneous in a larger region within the air gap and therefore completely encloses the rotor magnets, which are narrower in the radial direction, thereby supporting the self-centering of the impeller. In this case, “air gap” refers to the separation between the ends of the stator teeth and the rotor, even if the gap contains no air or not only air, e.g. the fluid as well.
According to an embodiment of the invention, the power electronics, which are used to control the coils of the stator, are disposed within the space circumscribed by the stator and the containment shell, as on an annular printed circuit board, for example. The overall height of the wet rotor pump can be further reduced in this manner.
According to an embodiment of the invention, the containment shell is formed by an annular disk, which extends into the air gap between the stator and the rotor and separates the dry zone of the wet rotor pump from the wet zone. The annular disk has a central opening, at which the inlet connecting piece is disposed, which said inlet connecting piece extends through the center of the stator. The bearing for the impeller is disposed at the end region of the inlet connecting piece on the disk side, through which the fluid flows into the wet zone after having flowed through the dry zone, through the inlet line. The disk and the inlet connecting piece can be formed as one piece, in particular as a plastic injection-molded part. The containment shell can be embodied, in particular, as a plastic part (e.g. made of PPS/GFK/CFK) or as a non-magnetic, metallic part.
According to an embodiment of the invention, the bearing is designed as a plain bearing, wherein a bearing bush of the plain bearing is disposed at the end region of the inlet connecting piece on the disk side, and a plain-bearing element of the plain bearing is attached to the impeller. A sliding surface of the plain-bearing element engages in the bearing bush such that radial support is provided. A further sliding surface can be provided on the bearing to provide additional unilateral axial support for absorbing the magnetic attraction force of the stator, which acts on the impeller via the rotor.
Embodiments of the invention are particularly advantageous since, due to the axial flux motor on the impeller, a magnetic attraction force is exerted in the direction toward the stator such that the impeller requires support on only one side. This simplifies the design and further reduces the required overall height of the wet rotor pump.
According to an embodiment of the invention, the plain-bearing element has passage holes in the radial direction, such as lubrication holes approximately 1 mm in size, for example, which are used to direct a very small portion of the volume flow of the fluid through the bearing in order to provide additional lubrication of said bearing.
According to an embodiment of the invention, the bearing is coated with a combination of diamond-like carbon and silicon carbide (SiC), in order to ensure a particularly long service life of the bearing.
According to an embodiment of the invention, the bearing is designed as a combination of a plain bearing and a rolling bearing, which is designed to provide axial and radial support of the impeller. The rolling bearing is used to absorb axial forces, while the plain bearing is used to absorb radial forces, wherein said plain bearing is formed with consideration for hydrodynamic aspects.
Embodiments of the invention are particularly advantageous, since strong forces can occur in the axial direction, in particular, due to the attraction of stator and rotor magnets, which said forces can result in a high amount of wear in a plain bearing. A rolling bearing, however, is characterized by low friction, primarily in the form of rolling friction, and therefore the wear on the bearing is reduced as compared to a plain bearing.
According to an embodiment of the invention, the rolling bearing is formed by bearing shells, which have running surfaces for accommodating rolling elements, and rolling elements. In this case, a first bearing shell is attached to the impeller, while a second bearing shell is attached to the containment shell. The rolling elements are located in the space circumscribed by the running surfaces of the bearing shells.
According to an embodiment of the invention, the plain bearing is formed on the impeller side by the outer jacket surface of the first bearing shell, and by the jacket surface of the containment shell. On the containment-shell side, the plain bearing is formed by the inner jacket surface of the second bearing shell and the jacket surface of the impeller.
Embodiments are particularly advantageous, since the bearing shells are part of the plain bearing and are part of the rolling bearing. Therefore, this is a hybrid bearing. This arrangement results in a bearing for a wet rotor pump that is very compact and, simultaneously, has a long service life and is robust.
In order to further increase the service life of the bearing, in an embodiment of the invention, the jacket surfaces and/or the running surfaces of the bearing shells and/or the rolling elements are coated with silicon carbide (SiC) and/or diamond-like carbon (DLC) and/or silicon-doped DLC.
According to an embodiment of the invention, the bearing is embodied as a combination of a plain bearing and a magnetic bearing, which is designed to provide radial support of the impeller. The magnetic bearing is used to absorb axial forces, while the plain bearing is used to absorb radial forces, wherein said plain bearing is formed with consideration for hydrodynamic aspects.
Embodiments of the invention are particularly advantageous, since a magnetic bearing is characterized by friction that ideally disappears, which results in a markedly longer service life of the bearing as compared to a plain bearing. In addition, the efficiency of the wet rotor pump increases due to the very low losses due to friction.
According to an embodiment of the invention, the magnetic bearing is formed by magnetic rings. In this case, a first magnetic ring is attached to the impeller, and a second magnetic ring is attached to the containment shell. The magnetization of the magnetic rings is configured such that, in the state in which said magnetic rings are installed in the wet rotor pump, these repel one another in the axial direction.
According to an embodiment of the invention, the plain bearing is formed on the impeller side by the outer jacket surface of the first magnetic ring, and by the jacket surface of the containment shell. On the containment-shell side, the plain bearing is formed by the inner jacket surface of the second magnetic ring and the jacket surface of the impeller.
Embodiments are particularly advantageous, since the magnetic rings are part of the plain bearing and are part of the magnetic bearing. Therefore, this is a hybrid bearing. This arrangement results in a bearing for a wet rotor pump that is very compact and, simultaneously, has a long service life and is robust.
In order to further increase the service life of the bearing, in an embodiment of the invention, the jacket surfaces of the magnetic rings are coated with silicon carbide (SiC) and/or diamond-like carbon (DLC) and/or silicon-doped DLC.
According to a further embodiment, the bearing is protected by a fine-strand filter to ensure that particles do not enter the bearing. As a result, the bearing is protected from damage by particles that could be carried along in the medium.
According to an embodiment of the invention, the rotor is formed by a permanent-magnet material, namely samarium cobalt (SmCo). This is advantageous for a plurality of reasons:
Samarium cobalt can be used at high temperatures without negatively affecting the retentivity of the magnetization. As a result, the fluid can have a temperature of up to 200° C., for example.
Samarium cobalt has excellent corrosion characteristics and can be directly exposed to the fluid with simple corrosion protection or without corrosion protection.
Since samarium cobalt does not need to be encapsulated in stainless steel, for example, for corrosion protection, the magnetic material can be disposed at the outermost edge of the periphery of the impeller or the drive disk, thereby permitting the permanent-magnet material to be positioned with a maximum radius.
The permanent-magnet material forming the rotor can be disposed in the form of a plurality of individual, flat permanent magnets on the periphery of the impeller or in the form of a single magnetic ring having multipolar magnetization. In particular, the magnets or the magnetic ring can be attached directly on the periphery of the impeller or can be attached to the impeller via a drive disk.
Embodiments of the invention are explained in greater detail in the following with reference to the drawings. In the drawings:
a shows a side view of a single stator tooth,
b shows a front view of the stator tooth according to
c shows a perspective view of the stator tooth according to
a shows a top view of the stator,
b shows a sectional view of the stator,
a shows a top view of an embodiment of the containment shell,
b shows a sectional view of the containment shell according to
c shows a sectional view of the bearing bush of the containment shell according to
d shows a sectional view of an embodiment of the plain-bearing element of the impeller,
a shows a top view of an embodiment of the rotor,
b shows a sectional view of the rotor according to
Elements of the following embodiments that correspond to one another or are identical are labelled with the same reference signs in each case.
The motor cover 102 is used to cover a stator 110. The stator 110 has a stator tooth receptacle 112, which has an annular shape and on which stator teeth 114 are disposed so as to form a circle. Each of the stator teeth has a receiving region 118, on which a coil is wound (see
The various coils of the stator teeth 114 are electrically connected to power electronics 120, which are used to control the coils.
In the embodiment considered here, the rotor of the axial flux motor is formed of a permanent-magnet material, which, in this case, is disposed on a ring 124 in the form of individual permanent magnets 122 (see
The permanent magnets 122 have magnetization in the axial direction such that the magnetic flux also extends in the axial direction of the wet rotor pump 100, namely between the ends 126 of the stator teeth 114 and the permanent magnets 122, across an air gap that exists between the ends 126 and the permanent magnets 122. As a result, a magnetic attraction force is exerted by the stator 110 on the permanent magnets 122 and, therefore, on an impeller 128 of the wet rotor pump 100.
A disk 130 of a containment shell 116 extends into the air gap between the ends 126 of the stator teeth 114 and the permanent magnets 122. The disk 130 has recesses 132, which accommodate the ends of the stator teeth 114 (see
The disk 130 has an axial opening, on which an inlet connecting piece 134 is disposed.
In the installed state of the wet rotor pump 100 (see
A space is circumscribed by the containment shell 116 and the stator 110, in which the power electronics can be disposed, for example on an annular printed circuit board 136, the outer radius of which is limited by the recesses 132, and the inner radius of which is limited by the wall of the inlet connecting piece 134. This printed circuit board 136 can carry the various electric and electronic components that form the power electronics 120. Since this is disposed in the dry zone of the wet rotor pump 100, special encapsulation of the power electronics 120 is not absolutely necessary.
An attachment region 138 is disposed on the inlet connecting piece 134 with axial separation from the disk 130, to which said attachment region the motor cover 102 is attached, by means of screwed connections, for example. The stator 110 is then held between the motor cover 102 and the disk 130, wherein the ends 126 of the stator teeth 114 extend into the recesses 132 and are held there in a form-fit manner, for example.
The attachment region 138 can be annular, for example, as shown in
The wet rotor pump has a first housing half 142 and a second housing half 144, by means of which the housing of the wet rotor pump 100 is formed. The housing half 142 has an opening 146 in the center thereof, which adjoins the end of the inlet connecting piece 134 on the air-gap side, thereby allowing fluid 108 to flow from the inlet connecting piece 134 through the opening 146. The disk 130 is attached to the outer side of the housing half 142, by means of screwed connections, for example, on an annular attachment region 148 of the housing half 142. In the embodiment considered here, the inlet line is therefore formed by the inlet connecting piece 134 with the bearing bush 156 disposed at the end thereof on the air-gap side.
The impeller 128 is located between these housing halves 142 and 144. The rotor is formed at the impeller 128 by virtue of the fact that the ring 124 comprising the permanent magnets 122 is connected to the impeller 128 via a drive disk 150, by means of screws 153, for example. According to an alternative embodiment, the permanent magnets 122 can also be disposed directly on the impeller 128. Furthermore, the permanent magnets 122 can be disposed between the ring 124 and the drive disk 150.
The impeller has an extension 152 for accommodating a plain-bearing element 154, which, together with a bearing bush 156, forms a plain bearing for the radial support of the impeller 128 (see
This magnetic attraction force of the stator 110 furthermore has a self-centering effect—during rotation—on the impeller 128, which reduces the load on the plain bearing.
The two housing halves 142 and 144 are connected to one another by means of screws or adhesive 158.
An outlet 160 for the fluid 108 is formed in this manner.
Embodiments of the invention are particularly advantageous since the fluid 108 flows in on the stator side and, in fact, through the stator. Furthermore, due to the axial flux motor, support for the impeller is required on only one side, without a rotor shaft, which makes it possible overall to obtain a particularly compact design having a high power density.
a shows a front view of one of the stator teeth 126 according to the embodiment shown in
The receiving region 118 of the stator tooth 114 is closed on the air-gap side by the end 126 of the stator tooth 114, which has a larger cross section than the receiving region 118. This larger cross section has the advantage that the magnetic field is widened accordingly in the air gap and is approximately homogeneous in a larger spatial region. The self-centering of the impeller 128 (see
a shows, as an example, how one of the permanent magnets 122 is disposed on the impeller relative to the stator tooth 114. The permanent magnet 122 is shorter in the radial direction than the extension of the end 126 of the stator tooth 114 in the radial direction, and therefore the stator tooth extends beyond the permanent magnet 122. The permanent magnet 122 is positioned in the center underneath the receiving region 118, for example.
The stator tooth 114 has a slot-shaped recess 162 in the upper region thereof, which is used to attach the stator tooth 114 to the stator tooth receptacle 112 (see
b shows the stator tooth 114 in a front view, and
a shows a top view of the stator 110 having the annular stator tooth receptacle 112, which has an opening in the center thereof, through which the inlet connecting piece 134 extends (see
a shows a top view of the containment shell 116, through the inlet connecting piece 134 of which the fluid can flow in. As shown in
b shows a sectional view of the containment shell 116. As shown in
A plain-bearing element 154 is attached to the extension 152 of the impeller 128 (see
The bearing bush 156 therefore accommodates the end section 164 of the plain-bearing element 154, wherein the inner side of the bearing bush 156 and the outer side of the end section 164 of the plain-bearing element 154 form the sliding surfaces of the plain bearing. The impeller 128 is thereby radially supported. The axial degree of freedom of the impeller 128 is limited by the circumferential edge 166.
That is, during operation of the axial motor, if the impeller 128 is drawn in the direction of the stator 110 by the magnetic forces that occur, the edge 166 impacts the front side of the bearing bush 156, thereby forming an abutment for absorbing this magnetic attraction force. Although the impeller 128 is therefore supported in the containment shell 116 such that said impeller has one axial degree of freedom, i.e. axial play, the axial position of the impeller 128 is defined by the magnetic attraction force during operation of the axial flux motor.
Preferably, at least one of the sliding surfaces of the plain bearing is coated with diamond-like carbon (DLC) and silicon carbide (SiC) or a combination of DLC and SiC, in order to extend the service life of the bearing.
Embodiments of the invention are particularly advantageous in which the fluid 108 is suctioned through the bearing, which also contributes to the compact design of the wet rotor pump. The plain bearing can have a very narrow gap, which is approximately 0.01 mm to 0.03 mm, for example, and is therefore also simultaneously very well sealed.
According to an embodiment of the invention, the plain-bearing element 154 can have one or more radial openings, such as lubrication holes approximately 1 mm in size, for example. By means of these openings, a very small portion of the volume flow of the fluid 108 is directed between the sliding surfaces of the bearing in order to provide additional lubrication of said bearing. This at least one opening is preferably disposed in the end section 164 of the plain-bearing element 154 and is directed toward the center.
Samarium cobalt can be used in relatively high temperatures without the retentivity being negatively affected thereby; the fluid 108 can have a temperature of up to 200° C., in particular.
Samarium cobalt has excellent corrosion characteristics and can therefore be exposed to the fluid 108 without coating and without encapsulation.
Since encapsulation of the permanent magnets 122 is not required, said permanent magnets can be positioned at a maximum distance away from the rotational axis, thereby ensuring that maximum torque and maximum motor output result for a given amount of magnetic material.
As an alternative, other materials can also be used for the permanent magnets 122, such as neodymium iron boron.
In order to operate the wet rotor pump 100, the coils of the stator teeth 114 are controlled by the power electronics such that torque acts on the impeller 128 via the rotor. The rotor then suctions the fluid 108 through the inlet connecting piece 134 and the bearing such that the fluid 108 is conveyed through the wet rotor pump 100 and exits said wet rotor pump at the outlet 160.
The rolling bearing is formed by two bearing shells 170 and 168, which have running surfaces for accommodating rolling elements 172. In this case, the lower bearing shell 168 is attached to the impeller 128, whereas the upper bearing shell 170 is attached to the containment shell. The bearing shells can be bonded, shrunk-fit or pressed onto the corresponding components, or fixedly screwed thereon. The rolling elements are located in the intermediate space between the bearing shells, which said intermediate space is circumscribed by the running surfaces of the bearing shells. If the pump is intended to be operated at high impeller speeds, the rolling bearings can be connected to one another by means of a cage in order to increase the stability of the bearing.
The plain bearing is formed by an upper plain-bearing surface 174 between the upper bearing shell 170 and the jacket surface of the impeller 128, and by a lower plain-bearing surface 176 between the lower bearing shell 168 and the containment shell 116. The plain bearing has only slight bearing play at the bearing surface 174 in particular, thereby enabling a portion of the fluid 108 to enter the rolling bearing. The penetration of the rolling bearing by the pumped fluid can provide additional lubrication of the rolling bearing.
The bearing play, which can be considered to be an annular opening, is preferably protected by a fine-strand filter 178, in order to ensure that foreign objects that can be contained in the pumped fluid are kept away from the bearing region. The fine-strand filter 178 is held in position by a clamping ring 180.
Correspondingly precise production can be utilized in order to minimize the bearing play at the plain-bearing surfaces, preferably holding said bearing play in the range below 0.1 mm. This prevents coarse particles that can be contained in the fluid 108 from entering the rolling bearing and damaging the running surfaces of the bearing shells or the rolling bearings. In addition, this narrow hydrodynamic gap functions as a sealing surface between the suction side and the pressure side of the pump, thereby ensuring that leakage effects can be prevented, which said leakage effects typically occur when the impeller is attached to a shaft in a classic manner and is not supported via the suction side.
In order to further increase the long service life of the bearing, it is possible to coat the running surfaces of the bearing shells 168 and 170 and/or the rolling elements 172 and/or the plain-bearing surfaces 174 and 176 with SiC, DLC or silicon-doped DLC. As an alternative, ceramic or plastic bearings, which can be used in aqueous media in a frictionless manner and without risk of corrosion, are also feasible.
A further difference between the wet rotor pump 200 and the wet rotor pump described with reference to
The magnetic rings 208 and 210 comprise permanent magnets, such as neodymium iron boron (NdFeB) or samarium cobalt (SmCo), and are metallically completely encapsulated in an air- and water-tight manner. The encapsulation can be implemented by laser- or friction-welding of the encapsulation components, for example. In a preferred embodiment of the encapsulation components, the encapsulation of all sides that do not face one another comprises non-magnetic metal, such as stainless steel, for example, whereas the welded-on cover plate, i.e. the two sides that face one another, comprise soft magnetic material. The magnetic flux is thereby strengthened in the region of the cover plates.
The thickness of the encapsulation can be between 1 mm and 2 mm, for example. The magnetic ring 208, which is pressed on on the impeller side, is manufactured in a manner similar to that of the lower bearing shell 168 of the wet rotor pump shown in
The magnetic rings 208 and 210 are preferably magnetized and oriented such that the repellent effect between the magnetic rings is approximately proportional to the square of the distance between the magnetic rings. In this case, the thickness of the magnetic rings 208 and 210 is preferably designed such that, in the non-operative state of the wet rotor pump 200, equilibrium sets in between the attractive force between the rotor magnets 206 and the stator teeth 212 and the repulsive force between the magnetic rings 208 and 210. As a result, in the non-operative state, an air gap of approximately 1 mm preferably forms between the lower end of the stator teeth 212 and the rotor magnets 206, while an air gap having a width of 3 mm forms between the magnetic rings 208 and 210. The magnetic field strength generated by the magnetic rings 208 and 210 is therefore stronger than the field strength between the rotor magnets 206 and the stator teeth 212.
As the speed and, therefore, the output of the wet rotor pump 200 increases, the pressure differential between the suction side and the pressure side of the wet rotor pump 200 and, therefore, the contact pressure of the impeller 202 increases upwardly, in the direction toward the suction connecting piece 218. Similarly, the contact pressure on the mutually repellent magnetic rings 208 and 210 also increases such that the air gap between the magnetic rings 208 and 210 and the air gap between the rotor magnets 206 and the stator teeth 12 is reduced. The reduction of the air gaps continues until a new equilibrium has set in between the contact pressure, the attractive force between the rotor magnets 206 and the stator teeth 212, and the repulsive force between the magnetic rings 208 and 210.
In order to prevent the rotor from being set down onto static components of the wet rotor pump 200, the performance limit of the wet rotor pump can be dimensioned such that the air gap between the rotor magnets 206 and the stator teeth 212 does not fall below a width of 0.2 mm. In addition, safety sliding surfaces 220 can be mounted on the rotor, which extend upwardly beyond the rotor magnets 206 by 0.2 mm, for example. In the event that the aforementioned performance limit is exceeded, said safety sliding surfaces can support the rotor at the containment shell 222 and prevent damage to the impeller 202 or the rotor magnets 206.
Given that the air gap between the rotor magnets 206 and the stator teeth 212 is reduced as the pressure output increases, the coupling between the rotor magnets 206 and the stator teeth 212 increases due to the increasing magnetic flux density. This effectively results in an increase in output and, therefore, to increased efficiency of the wet rotor pump 200.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2012 200 806.3 | Jan 2012 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/050814 | 1/17/2013 | WO | 00 |
