GB2182392A

GB2182392A - Electric-motor-driven centrifugal pump unit having axial flow through the motor

Info

Publication number: GB2182392A
Application number: GB08526800A
Authority: GB
Inventors: Karsten Laing
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-11-02
Filing date: 1985-10-31
Publication date: 1987-05-13
Also published as: DE3538504C2; GB8526800D0; GB2182392B; DE3538504A1

Abstract

A spherical axial bearing 6 of the impeller-motor unit 2,3 is located within the pump suction passage 1 passing through the rotor. The air gap between the rotor 3 and the stator poles 20 is part-spherical. A tube 10 defining the suction passage around the bearing pedestal 13 provides a sealing gap 11 with the tube 1a connecting the impeller 2 and rotor 3. Part-spherical sealing gaps 2c and 2e are located between the impeller 2 and the vaned pump stator 26 which directs flow to the axial pump outlet 21. The motor windings (31, Fig. 3) may be arranged radially outwardly of the rotor and contact part (34a) of the pump casing for heat transfer to the pumped liquid. <IMAGE>

Description

SPECIFICATION Electric-motor-driven pump unit having coaxial throughflow The invention refers to pumps which form with the driving motor one structural unit and in which the rotor of the electric motor forms with the impeller one shaftless revolving unit.

Pumps have become known in which the flow of delivery passes through an electric motor in parallel with the axis of rotation. The disadvantage of these pumps is based upon the fact that the diameter of the rotodynamic delivery member (as a rule an axial impeller) is predetermined by the diameter of bore of the electric motor rotor, so that the pump impeller in relation to the electric motor rotor is much too small. Pumps have aiso been described in which a rotor-impeller unit is driven on a hydrodynamic cushion. These pumps have found no entry into practice since even the smallest impurities already lead to the formation of the hydrodynamic pressure cushion failing. Furthermore the breakaway torque necessary for overcoming the stiction is as a rule so great that pumps of that kind do not run up at all without starting assistance.

Another kind of pump, socalled spherical pumps, have in the meanwhile been built in numbers running up to six digits a year. In the case of these pumps the magnetic airgap between the stator and the rotor runs along a spherical surface, and shafts and bearing bushes are omitted. The disadvantage of these pumps consists in the fact that the hydraulic thrust from the rotor is directed in the opposite direction to the magnetic thrust, but the magnetic thrust must press the rotor against a ball so that a controlled bearing is ensured. But as soon as the electrical supply is switched off, the magnetic thrust vanishes so that only the rotor thrust remains, which leads to these rotors rising from the stationary bearing ball, which may lead to destruction.A further disadvantage of all spherical pumps consists in the fact that in the case of twisting of the rotor-impeller unit about an axis of wobble the sealing gap between the rotating and the stationary parts of the pump at the same time changes in its width of gap, which leads to reduction in power and to unstable running. Furthermore with all spherical pumps the gap extending essentially axially between the pump casing becomes increasingly larger if the bearing bush experiences a reduction in size through wear.

The aim of the invention is to combine the advantages of coaxial throughflow which lies in particular in the extraordinarily simple shape of the pump casing, with the advantages of the spherical pump and at the same time to eliminate the described disadvantages of today's spherical pumps.

In accordance with the invention the rotor which forms with the stator a gap for the magnetic flux which runs along a spherical surface, is supported by a ball which is connected via a supporting member to the suction pipe of the pump casing. The suction is effected through the stator, the winding being composed of coils which over part of the circumference rest against the suction pipe. By this means an advantageous cooling of the coils is ensured. The rotor is made with a taper towards the suction side so that a magnetic axial thrust is formed which acts in the same direction as the hydraulic axial thrust.

The rotor-impeller unit therefore even after switching off the motor cannot rise from the ball so that through this measure a stable bearing is guaranteed. If delivery media containing solids are to be delivered, the invention provides for a sealing member through which the penetration of solids into the spherical magnetic flux gap is excluded. This sealing member consists in a stub tube on the suction side projecting up to the plane of rotation. In the plane of rotation in which the centre of the ball lies, the stub tube forms a narrow gas with the inner periphery of the rotor. Through this arrangement the gap between the pressure side and the suction side of the pump lies on a cylindrical surface so that bearing wear has no influence upon the gap width.Therefore with increasing wear of the bearing cap the pump experiences no reduction in power as is the case with known spherical pumps.

A further disadvantage of the spherical pumps known hitherto is based upon the fact that the flow in the spiral casing exerts radial forces upon the rotor, whereby in dependence upon the degree of throttling an oblique position of the rotor-impeller unit is caused which leads to a deterioration both of the electrical efficiency and also of the hydraulic efficiency.

Through the invention it is ensured that the discharge is effected uniformly over the circumference of the impeller so that the feared oblique position of the impeller which in extreme cases may lead to impact or to contact between rotating parts and stationary parts and thereby to serious damage to the machine, no longer arises.

In addition a further protection against penetration of particles of dirt may be achieved by there being arranged between the rotor and the pump impeller a stationary cover ring which then forms a narrow gap with a spheri cal surface arranged between the rotor and the impeller of the pump.

The invention is to be explained with the aid of the Figures: Figure 1-illustrates an axial section through a pump in accordance with the invention; Figure 2-shows a section along the line of section ll-ll in Fig. 1; and Figure 3-shows the construction of a centrifugal pump having teeth running radially.

The rotor (3) forms with the impeller (2) one unit. In the suction region (1) a tube (1a) is arranged, by which the impeller (2) is connected rigidly to the rotor (3).

The suction is effected through the tube (9) of the suction pipe, which continues into the cup (9a) which hermetically separates the pump chamber from the electric motor chamber and follows the magnetic airgap (9b). In the suction pipe (9) a further tube (10) is arranged, which exhibits in the equatorial plane (12) a collar which forms with the tube (la) a sealing gap. A further part connected to the suction pipe (9) is the bearing pedestal (13) which carries the ball (6) which is arranged to be stationary. The openings (13a) to (13c) are chosen to be of such a size that the flow of delivery experiences no significant resistance.

The impeller (2) exhibits an annular spherical region (2a) about the centre (6a) of the ball, which forms with the cover ring (9c) a gap (11a). The impeller (2) exhibits a further concentric annular region (2b) the outer periphery of which likewise runs along a spherical surface which forms a gap (2c) with a stationary distributor (26). The periphery of the wall (24) of the impeller is made spherical too and forms with the distributor (26) a gap (2e). The distributor (26) carries blades (15) which in cooperation with the blades (15a) convert the discharge angular momentum of the flow into pressure and feed the throughput flow to the discharge region (21).The wall thickness of the axially symmetrical casing (14) is of such small dimensions that a linear expansion of the connecting system of piping through the effect of heat is compensated by axial deformation of the casing (14). Adjacent to the separating wall (9a) there are teeth (20) which pass through the winding (8) and are connected together in magnetic conductivity through the yoke (20a). These teeth (20) are pressed by the annular casing (17) which engages ina groove (20b) with a shaping fit, against the separating wall (9a) whereby the separating wall (9a) which is made thin, experiences no deformation under the influence of the pressure in the pump casing (14).

The pump casing on the suction side is formed by the axially symmetrical moulded part (14a) which is crimped to the teeth (20) via recesses (20c) in the latter. The forces exerted by the connecting pipework are thereby transmitted from the casing (14) to the annular casing (17), from the latter to the crown of teeth (20) and from the latter to the pump casing (14a) on the suction side.

The winding region with the coils (8) is surrounded by a casing (16) and (16a) consisting of insulation. The two casing shells (16) and (16a) exhibite plane faces (16b) and (16c) onto which is slipped the terminal box (16d).

Fig. 2 shows a section along the line of section ll-ll in accordance with Fig. 1, the build-up of the teeth (20) being illustrated in the tooth (20d). This consists of two laminations in strips (20e) lying respectively at the outside, which have the same shape as the strip laminations (20f). Between these strip laminations there are included strips pointing radially inwards, of narrower width. The coils (8a) exhibit regions (8b) which follow the outer contour of the insulated suction pipe (9).

Between adjacent coils a copper disc (9d) is arranged as may be seen in Fig. 1, which carries the heat from the coils (8c) to the pipe (9).

Fig. 3 shows a motor-pump unit which on the pump side exhibits essentially the same construction as the pump in Fig. 1, the items carrying the same reference numbers as in the preceding Figures. As distinct from the embodiment described above, the separating wall (9a) is carried on as far as the pump flange (30). The winding (31) is constructed in a conventional way; the stator iron consists of the teeth (32) and the yoke ring (33). The cooling of the winding (31) is effected by the delivery liquid via the annular region (34a) against which the heads (31a) of the winding rest with good conductivity of the heat. The bearing bush (35) exhibits on the surface (37) remote from the bearing gap (36) a concentric spherical configuration. The spindle (38) which forms with the distributor (26) one unit, forms operationally a gap (39) which is chosen of such a width that touching of the parts rotating relatively to one another can only occur when the rotor-impeller unit (2-3) rises from the ball (6).

Claims

1. A centrifugal pump having coaxial throughflow, which forms one unit with an electric motor having a spherical gap for the magnetic flux, the rotor of the motor forming one revolving unit with the impeller of the pump and being constructed as a ring the outer surface of which lies on an imaginary spherical shell, the axial extent of the rotor being bounded by two annular surfaces of radial symmetry and the rotor-impeller unit being supported axially by a spherical bearing, characterized in that the rotor (3) surrounds the suction region (1) of the impeller (2) and that the spherical bearing is arranged with the step bearing (5) and the convex sliding partner (6) inside the suction region (1).

2. A centrifugal pump having coaxial throughflow as in Claim 1, characterized in that certain regions (8b) of the windings (8) are connected to the suction pipe (9) to provide good conductivity of heat.

3. A centrifugal pump having coaxial throughflow as in Claim 2, characterized in that certain regions (8b) of the coils of the winding (8) follow the outer jacket of the suction pipe (9).

4. A centrifugal pump having coaxial throughflow as in Claim 1, characterized in that a stub tube (10) communicating with the suction pipe (9) projects into the suction region(1) and forms with the inner periphery of the rotor (3) a narrow sealing-gap (11) which lies in the equatorial plane (12).

5. A centrifugal pump having coaxial throughflow as in Claim 1, characterized in that the convex sliding partner (6) is carried by a bearing pedestal (13) which is connected to the suctionpipe (9) and through which the flow passes and which exhibits a small crosssection with respect to the flow.

6. A centrifugal pump having coaxial throughflow as in Claim 1, characterized in that the concentrically shaped casing half (14) on the pressure side is made so thinwalled that it permits operationally a deformation through which the axial travel of the thermal expansion of the connecting pipework is compensated.

7. A centrifugal pump having coaxial throughflow as in Claim 6, characterized in that the guide members (15, 15a) connected after the impeller (2) are rigidly connected to the inner peripheral region of the pump casing.

8. A centrifugal pump having coaxial throughflow as in Claim 1 and having a crown of teeth running axially between two imaginary cylinders, characterized in that the casing (14) on the pressure side engages via a ring (17) having an inwards projecting edge (18) in grooves (20b) in the teeth (20) and introduces the axial forces into the crown of teeth (20), whereby a static function is impressed upon the latter.

9. A centrifugal pump having coaxial throughflow as in Claim 1, characterized in that the impeller (2) exhibits on the impeller wall (24) facing the suction region (21) a convex annular region (2b) which has a spherical surface concentric with the centre of the ball and which forms with a concave annular region (2b) a narrow spherical gap (2c), the im peller wall (24) further exhibiting perforations (25) in the region near the hub.

10. A centrifugal pump having coaxial throughflow as in Claim 1, characterized in that the distributor (26) carries a spindle (27) which forms a gap with the spherical region (28) at the back of the bearing bush (5).

11. A centrifugal pump having coaxial throughflow as in Claim 10, characterized in that the spherical rear region (28) is sur rounded by a annular region (29) which forms with the spindle (27) an anular gap of such width that a predetermined angle of wobble cannot be exceeded.