GB2201844A

GB2201844A - 'Canned' rotor for electric motors used with pumps

Info

Publication number: GB2201844A
Application number: GB08802366A
Authority: GB
Inventors: Desmond Ernest Hutchinson; Christopher Rodwell
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1987-02-04
Filing date: 1988-02-03
Publication date: 1988-09-07
Also published as: GB8702461D0; GB8802366D0

Abstract

An electric motor (12) for use with a pump (10) comprising a rotor (14) coaxially surrounded by a stator (26), the rotor (14) being contained within a shroud (22) so that liquid passing into the interior of the shroud (22) via a path between the drive shaft (16) and the end portion (23) of the motor (14) is prevented from reaching the stator (26). <IMAGE>

Description

Electric Motors This invention relates to electric motors.

More especially, but not exclusively, the invention relates to electric motor assemblies for us in driving pumps.

For a number of end uses where high reliability is a prerequisite (for example, power stations, submarines, plants producing hazardous chemicals, and the like) it is desirable to construct pumps which are free of rotary seals since the latter are prone to failure. Such pumps fall into two main categories: canned motor pumps and magnetic drive pumps. In known versions of the former the windings of the rotor are sealed within a metallic 'can' and a further 'can' seals the stator assembly off from the interior of the pump. In known magnetic drive pumps, a rotor driving the pump is contained within a shroud which seals off the interior of the motor against egress of liquid and the drive is provided by means of a magnetic arrangement mounted externally of the shroud and driven externally by a separate motor.

The known canned motor pumps therefore suffer from the disadvantage that they are difficult and expensive to build since the sealing cans need to be welded in place and each motor assembly has, effectively, to be built up sequentially as a one-off. The known magnetic drive pumps involve, in effect, two motors and the drive assembly occupies a relatively large amount of space, which is disadvantageous In applications where space is at a premium, for example in submarines.

It is an object of the present Invention to overcome the above disadvantages.

According to the present invention there is provided an electric motor comprising a rotor coaxially surrounded by a stator, the rotor being enclosed within sealing means and mounted on a drive shaft of the motor which extends through an end portion of the motor and the rotor being contained within a shroud which surrounds the rotor so that fluid passing into the interior of the shroud via a path between the drive shaft and said end portion of the motor is prevented by said shroud from reaching the stator.

The motor construction of the invention avoids the long drive chain of previous magnetic drive pump motors and also eliminates the need for welded cans employed by canned motors.

Two electric motors in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic partially sectioned view of a first motor and pump assembly; and Figure 2 Is a diagrammatic partially sectioned view of the second motor and pump assembly.

Referring to the drawings* which use the same numerals for like parts, the assemblies each comprise a pump 10 driven by an electric motor generally designed 12 comprising a rotor 14 (not shown in detail) connected to a drive shaft 16 mounted in bearings 18, 20 in Figure 1 and 34, 20 in Figure 2. The drive shaft 16 extends into a channel 11 of the pump 10 along which the liquid being pumped passes. The drive shaft 16 connects to a driven shaft (not shown) of the pump 10. The rotor 14 may be a squirrel cage rotor, a synchronous drive magnetic rotor, or any of the known forms of electric motor rotor employed in this field. It is to be noted that the bearings and rotor run immersed in the liquid which is being pumped.Accordingly, the coils or magnets of the rotor are sealed against ingress of the liquid, for example by means of a metal can sealingly affixed around them in a manner known.

The rotor is sealed within a shroud 22 which at a flanged end portion is sealingly affixed to the pump body 10 at 24 and to an end portion 23 of the motor at 25, through which end portion the shaft 16 extends. The end portion provides a housing for the bearings 18, 20. A motor stator 26 is mounted coaxially around the rotor 14 externally of the shroud 22. The shroud 22 prevents liquid passing into the interior of the shroud via a path between the shaft 16 and the bearings 18,.20 of the end portion 23 from reaching the stator 26. The shroud is formed of a rigid material, metallic or composite, and serves to prevent egress of the pumped liquid from within the pump and motor assembly. As illustrated in Figure 1 the stator 26 and shroud 22 are enclosed within a secondary outer containment 28 affixed to the pump body 10 and sealingly affixed to the flanged end portion of the shroud 22.The containment in effect provides a second line of defence and may only be necessary in those applications, for example nuclear power stations, where egress of fluid is potentially dangerous. This secondary containment is not possible to arrange if the pump is of the magnetic drive variety.

Since pumps are often used with sea water the shroud 22 can act as a trap for dissolved gases which are expelled from the water.

Accordingly it is often desirable to provide a vent 30 which may incorporate a suitable valve or bleed screw in order to be able to vent off any accumulated trapped gases.

The pump operates in a similar manner to the known pumps which it replaces but is very much easier to assemble than the known canned motor pumps and much smaller and less expensive than the known magnetic drive pumps.

In the assembly of Figure 1 the drive shaft runs in two sets of bearings, 18, 20 and the rotor effectively 'overhangs' the bearings, that is there are not bearings at either end of the rotor.

This has certain advantages in that the shroud 22 can be simple.

However, for certain applications, it is necessary that the rotor be mounted in bearings at either end of it as shown in Figure 2. In this case the shroud 22 carries an internal bearing housing 32 having bearings 34 supporting the shaft 16 on the non-drive side of the rotor 14. It is important to note here that the bearing 34 and its housing 32 are supported within the shroud 22. In the equivalent construction of a known canned motor pump such a non-drive side rotor bearing would need to be supported by the stator involving a considerable precision in manufacture and close tolerances, leading to greater manufacturing expenses.

Advantages of motors In accordance with the invention include simplicity of manufacture, and relative compactness.

Furthermore where a vent or the like is needed it is simply provided through the end of the shroud, which is not possible with known designs of magnetic drive motor pumps. Furthermore stator wiring can be brought out axially of the motor instead of radially as was necessary before, once again leading to simplicity of manufacture.

Also the various components can be manufactured separately and assembled easily In contrast to the series manufacturing needed for known canned motors.

Claims

1. An electric motor comprising a rotor coaxially surrounded by a stator, the rotor being enclosed within sealing means and mounted on a drive shaft of the motor which extends through an end portion of the motor and the rotor being contained within a shroud which surrounds the rotor so that fluid passing into the interior of the shroud via a path between the drive shaft and said end portion of the motor is prevented by said shroud from reaching the stator.

2. An electric motor according to Claim 1 further comprising an outer containment surrounding said stator and said shroud and sealed to said end portion of said motor and/or said shroud.

3. An electric motor according to either of the preceding claims incorporating bleed means from the interior of said shroud enabling fluid pssing into said interior to be bled from said Interior.

4. An electric motor according to Claim 3 when dependent on Claim 2 wherein said bleed means enables fluid passing into said interior to be bled from said interior to the exterior of said outer containment.

5. A motor according to any one of the preceding claims wherein said shroud carries a bearing for the end of the drive shaft remote from said end portion of the motor.

6. An electric motor according to any preceding claim in combination with a pump for pumping said fluid along a channel within the body of said pump, said shroud being sealed to said pump body and said shaft of the motor extending into said pump body.

7. An electric motor substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

8. An electric motor and pump assembly substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.