GB2293282A - Reducing cooling load in a vacuum cleaner motor - Google Patents

Abstract

The stator/rotor assembly 10 is separate from the control pack therefor and is totally enclosed. This has the advantage that the heat generated in the control pack for the stator/rotor assembly is removed from the stator/rotor assembly itself and that a sealed stator/rotor assembly can be effectively cooled by fins 14 within the transported airstream. In this way the secondary cooling systems and secondary cooling fan can be dispensed with. This permits the use of a single motor unit for wet/dry or dry machines. <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO ELECTRIC MOTORS This invention relates to electric motors and has particular reference to electric motors for use in fluid transport systems particularly for use in the transport of air and air entrained matter such as water.

Vacuum cleaning apparatus has for many years employed electric motors for the transport of a mass of air within a conduit in order to entrain dirt from a surface to be cleaned and transport it to a container or receptacle where the dirt is collected and from which the air is exhausted. In recent years there has been an increase in machines which are capable of being used in both a dry environment and a wet environment. In dry environment machines, the air is drawn into the nozzle to entrain the dirt is then passed through a filter and is exhausted by an electrically driven fan which is located in juxtaposition an electric motor which drives the fan and is arranged so that the air flow over the motor cools the motor itself.With a wet machine, however, this arrangement is not possible since the introduction of moisture internally of the motor would result in premature failure and would also constitute a considerable health hazard to the user. Accordingly, such machines have required two airways within the motorhead. One of the primary airways serves to withdraw the moist air and to provide the basic vacuum by which the machine operates and the other is provide a separate fan means and airflow for cooling the motor.

The disadvantages of such an arrangement are, firstly, the two fan approach is much more noisy and secondly, it is less efficient, since the energy required to drive the fan detracts from that available to provide the mass transport of the air through the machine in order to effect the cleaning/drying operation intended.

The heat output of a typical vacuum cleaner motor rated at perhaps a 1000 watt is fairly considerable and is divided fairly equally between the stator/rotor assembly on the one hand and the control pack for the stator/ rotor assembly on the other. The control pack may typically be a commutator for an AC driven motor, may be a brushless motor, or a slip rings for a synchronous motor. Such a motor will hereinafter be referred to as "a motor of the kind described.

Whatever format is envisaged, the heat output generated within the stator/rotor assembly and that produced by the control pack when taken together is generally too great to provide effective cooling of a totally sealed motor.

The heat generation for both the stator/rotor assembly on the one hand and the control assembly on the other can be effectively cooled by the air stream passing through the machine only if the structure is opened. This allows air within the main transported air stream to circulate within the stator pack and also around the components of the control pack whether it is of the commutator type or is a solid state device as in a brushless motor.

Attempts have been made to seal electric motors whereby the whole motor can be placed in the primary airstream so that the secondary cooling airstream for a wet and dry motor can be dispensed with. This has not met with success since in order to achieve this, a large number of compromises are necessary which result in an extremely bulky motor which increases the weight of the appliance on the one hand and reduces the available output of the machine on the other.

The development of vacuum cleaning machines and like equipment is seeking increased power and a reduction in noise, and there is a demand for a motor assembly which can be cooled by the primary airstream only and so that secondary cooling passage and associated fan arrangement can be dispensed with.

According to one aspect of the present invention there is provided an electric motor of the kind described in which the stator/rotor assembly is separate from the control pack therefor and is totally enclosed.

This has the advantage that the heat generated in the control pack for the stator/rotor assembly is removed from the stator/rotor assembly itself and that a sealed stator/rotor assembly can be effectively cooled within the transported airstream. In this way the secondary cooling systems and secondary cooling fan can be dispensed with. This in turn permits the use of a single motor unit for all types of machine and reduces the number of components required for a wet and dry machine compared with those currently on the market.

In a particular aspect of the present invention, the motor is a brushless motor. In a further aspect of the invention, the control pack may be completely remote from the environment of use of the stator/rotor assembly. In a preferred embodiment the stator/rotor assembly comprises a pair of end plates each incorporating bearings for a rotor shaft, a stator assembly intermediate said end plates and a rotor adapted to rotate on its shaft relative to the stator, the arrangement being such that the bearings for the output shaft extend through one of the said end caps and is sealed against the ingress of air and moisture.

The level of sealing may be adjusted depending upon the purpose for which the motor is to be employed. In one aspect of the invention, the bearing seals may be sealed against any fluid ingress. In another embodiment of the invention, the bearing may be sealed against liquid ingress.

In another preferred aspect of the invention, the stator pack may be finned for cooling. In this connection, our copending application No. 9403933.6 filed on 1st March 1994 the contents of which are incorporated herein by reference provides for an electric motor having a laminated stator assembly in which each lamination is shaped to define a plurality of external cooling elements which in use are contacted directly by gas surrounding the motor for cooling the motor. In a particular aspect of that invention, each of the laminations constituting the stator pack may be shaped to define an external surface having a surface area sufficient to allow adequate cooling of the stator laminate in use by contacting directly the surrounding gas. That invention seeks to obviate the requirement for a heat conducting sleeve intermediate the stator laminate and the surrounding gas.In other words the Applicants in respect of that invention have found that adequate cooling of the stator laminate in use can be achieved without use of the heat conducting sleeve as previously employed by shaving each of the laminates to provide a plurality of external cooling surfaces which define an integral cooling surface for the stator assembly. The periphery of each lamination may be generally circular or rectilinear.

In some embodiments the external surface of each lamination may be configured to define a plurality of castellations constituting the external cooling elements.

Each lamination may be generally annular in plane view and the cooling elements may be circumferentially spaced around the outer edge of said lamination. Said external cooling elements may also be rectilinear in cross-section through the longitudinal direction of the stator.

Alternatively, the external surface of each cooling element may be arcuate in cross section.

In one embodiment, each external cooling element may be generally rectangular. Each lamination may include between 4 and 20 cooling elements and in some embodiments between 8 and 16 with a typical number being 12. The external cooling elements on each lamination may be the same or different one from the others. Typically, however, the external cooling elements on each lamination are uniform and equally spaced to provide a regular cooling surface, the arrangement being such that on assembly of the individual laminations to form a lamination pack constituting a stator, the cooling elements combine to provide fins extending longitudinally of the cooling surface.The length of each cooling element in the plane of the lamination between the outer extremity of the element and the point where the element meets the body of the lamination may be between 1 to 5% of the diameter of the lamination typically about 3%.

The provision of the external cooling elements in accordance with the invention may, therefore, increase the external surface of each lamination by between 10 and 200% and typically by about 90%.

In a particular aspect of the invention, the stator laminate may comprise 10 to 50 laminations, typically about 30. The laminations may be the same or different one from the other. In one embodiment, the laminations may be identical one to another. The laminations are arranged in the laminate such that each lamination is aligned with its neighbour such that the cooling elements on each lamination are disposed in register with the cooling elements on the neighbouring laminations. The cooling elements may therefore define a plurality of circumferentially spaced ribs or fins extending in the longitudinal direction of the stator assembly with respect to the rotor. The laminations may be manufactured by techniques well known to persons skilled in the art. In particular, each lamination may be punched out on a sheet of metal material adapted to carry a magnetic field.

Such electric motor may further comprise one or more end caps each end cap may be fitted on a respective end of the stator laminate. Typically, each end cap may comprise a crown portion and a skirt portion, the skirt portion being shaped to form a tight fit around the external surface of the end of the stator laminate assembly. The laminations in the stator pack are held together preferably by crimping or welding or spot welding at the edges. The small air gap between adjacent laminations serving to dissipate and limit the generation of eddy currents within the stator pack itself.

Another aspect of the invention includes a vacuum cleaner comprising a receptacle for the collection of dirt, inlet means connected to a cleaning nozzle and adapted to communicate with said receptacle, suction means adapted to communicate with said receptacle to draw air from the inlet means through the receptacle and exhaust the same from the apparatus. Said suction means comprising a motor in accordance with the present invention, whereby the stator rotor assembly is cooled by the air flow passing therethrough.

Apparatus such as this has the advantage that it can be used in either a wet or a dry environment thus saving considerable in the cost of power head design for a range of vacuum cleaners.

Following is a description by way of example only and with reference to the accompanying informal drawings of one method of carrying the invention into effect.

Figure 1 is a third angle projection of the stator rotor assembly of a motor in accordance with the present invention.

The stator/rotor assembly comprises a housing indicated generally at 10 comprising a rear end plate 11 and a forward end plate 12. Each of the end plates are of substantially square cross-section and each carries an axial bearing supporting a central rotor shaft (not shown). Intermediate each of end caps 11 and 12 there is provided a stator pack 13 comprising a plurality of individual sheets, the edge of each of which is configured to provide a series of projections 14 to correspond with corresponding longitudinal fins towards the corner of each of end caps 11 and 12. The individual laminations of stator pack 13 are welded together to produce a laminated structure and are similarly welded to each of the end caps to form a unitary assembly.The bearing in forward end cap 12 is a through bearing and the shaft carried thereby extends through and projects forwardly of the forward face of end cap 12. The forward face of end cap 12 further carries a fan assembly 20 comprising a generally cylindrical housing 21 having a rearward face 22 with four arcuate slots 23 each slot being juxtaposed an assemblage of fins 14.

In a particular embodiment the rotor stator pack is a brushless type motor and the electronic control circuitry is disposed remote from the motor itself. The fan assembly 20 constitutes the prime mover for air flow through a vacuum cleaner and the arrangement is such that air is drawn into fan assembly 20 and is expelled from arcuate slots 23 and passes over and along fins 14 to effect a cooling action upon the stator assembly 10. The arrangement is such that the capacity of the fan and the volumetric transfer of the air is sufficient to maintain the temperature of the stator/rotor assembly at an acceptable level without injurious effect upon the bearings of the drive shaft or upon the windings on the stator.

The stator fan assembly illustrated in Figure 1 is incorporated in the head of a standard vacuum cleaner and can be employed for a wet environment as well as a dry one.

This unit has the advantage that it is readily used in both types of machines and gives the wet and dry capability to all vacuum cleaning equipment produced using such a motor. The elimination of the secondary cooling system results in a major reduction of noise and the removal of the control assembly for the stator/rotor assembly results in an increase in the compactness of the motor. Where the control assembly is a solid state device as, for example, with a brushless type motor, this can be incorporated externally of the vacuum cleaning machine itself. In one particular aspect of the invention, this may be incorporated in the plug lead or form part of the plug assembly. In this way different and interchangeable control assembly may be provided so that the same stator/motor assembly can be used over a range of applied voltages.

Another advantage of a machine of the type described above is that a brushless motor allows the speed to be optimised thereby allowing each particular machine to be "tuned" to obtain the quietest operation. The totally enclosed stator rotor assembly ensures that there is no spark, hence motors of this particular construction are safe for use in an explosive environment.

Claims (17)

1. An electric motor of the kind described in which the stator/rotor assembly is separate from the control pack therefor and is totally enclosed.

2. A motor as claimed in claim 1 when the motor is a brushless motor.

3. A motor as claimed in claim 1 or claim 2 wherein the stator/rotor assembly comprises a pair of end plates each incorporating bearings for a rotor shaft, a stator assembly intermediate said end plates and a rotor adapted to rotate on its shaft relative to the stator, the arrangement being such that the output shaft extends in a bearing through at least one of the said end caps and is sealed against the ingress of air and moisture.

4. A motor as claimed in any preceding claim wherein each bearing is sealed against fluid ingress.

5. A motor as claimed in any preceding claim wherein the stator pack is finned for cooling.

6. A motor as claimed in any preceding claim wherein the external surface of each lamination forming part of the stator pack may be configured to define a plurality of castellations constituting external cooling elements.

7. A motor as claimed in claim 6 wherein each lamination is generally annular in plain view and the cooling elements are circumferentially spaced around the outer edge of said lamination.

8. A motor as claimed in any one of claims 1 to 7 wherein the external surface of each cooling element is arcuate in cross-section.

9. A motor as claimed in any preceding claim wherein each lamination may include between 4 and 20 cooling elements.

10. A motor as claimed in claim 9 wherein each lamination may include between 8 and 16 cooling elements.

11. A motor as claimed in any preceding claim wherein the laminations serve to increase the surface area of the stator pack by between 1% and 5%.

12. A motor as claimed in any preceding claim including at least one end cap adapted to fit an end of the stator laminate.

13. A motor as claimed in claim 12 wherein each end cap comprises a crown portion and a skirt portion, the skirt portion being shaped to form a tight fit around the external surface of the end of the stator laminate assembly.

14. A motor as claimed in any preceding claim wherein the laminations in the stator pack are held together by crimping, welding or spot welding at the edges, whereby an air gap between adjacent laminations serves to dissipate and limit the generation of eddy currents within the stator pack in service.

15. A vacuum cleaner comprising a receptacle for the collection of dirt, inlet means adapted to communicate with said receptacle, suction means adapted to communicate with said receptacle and draw air from said air inlet means through the receptacle and exhaust same from the apparatus, said suction means comprising a motor in accordance with any one of claims 1 to 15 wherein the stator pack assembly is cooled by the air flow passing through the cleaner.

16. A vacuum cleaner as claimed in claim 15 having a wet and dry capability.

17. An electric motor as claimed in claim 1 and substantially as herein described with reference to and as illustrated in the accompanying drawing.