GB2444939A - A shaped member for an impeller rotor assembly - Google Patents

Abstract

A shaped member 100 for guiding air into an impeller, which may form part of a motor and fan unit for vacuum cleaner, comprises an upstream portion adjacent the impeller inlet 40, and a downstream portion adjacent the base 34 of the impeller, the downstream portion adjacent the base 34 extending away from an axis about which the member 100 rotates and substantially parallel to the base 34. The shaped member 100 may be secured to the end 30 of a shaft 28 by means of a screw thread, a snap fit, an interference fit, or locking pins, or it could be secured to a hexagonal nut. Alternatively, the member 100 could be an integral part of the impeller. The impeller may comprise blades 38 and deliver air to diffuser blades 22.

Description

A Rotor Assembly The invention relates to a rotor assembly for an

electrical machine such as an electrical S motor or generator. Particularly, but not exclusively, the invention relates to a rotor assembly for inclusion in a motor for a vacuum cleaner.

Electrical motors are widely used for many different applications. A common use is in domestic appliances. For example, in a vacuum cleaner a motor is used to drive a fan that draws dirty air in through a dirty air inlet. The dirty air passes through a separation system such as a cyclonic separator or a bag which separates dirt and dust from the airflow before the air is exhausted from the vacuum cleaner.

It is desirable for an electrical motor and fan unit to be as efficient as possible. One way of achieving this is, for example, to improve the aerodynamics of the motor and fan unit so that it is able to operate more efficiently. One area where improvements can be made is in the region of the inlet to the fan.

Conventionally, a fan impeller is attached to a rotor shaft of an electrical motor by means of a hexagonal nut. However, a hexagonal nut presents a flat face to an incoming airflow entering the inlet to the motor and fan unit. Further, because the nut is not circular in cross section, the "apparent radius" of the nut experienced by the airflow will vary as the nut rotates. Both of these effects can disturb the airflow and can result in turbulent air impinging upon the impeller of the fan. This may lead to the impeller not operating as efficiently as possible because the incoming airflow is not uniform across the whole impeller.

A prior art arrangement which attempts to reduce these effects is disclosed in JP 2001- 24 1394. This document discloses the replacement of a traditional hexagonal impeller nut by a more streamlined unit. Either a shaped nut or a plastic cap is used to help guide air into the impeller more efficiently.

It is an object of the present invention to provide a rotor assembly which has an improved aerodynamic efficiency over prior art arrangements. It is a further object of the present invention to provide a rotor assembly which, when forming part of a motor and fan unit, is able to guide an airflow into an impeller assembly more efficiently than prior an arrangements. It is another object of the present invention to provide a shaped member for a motor and fan unit which, in use, improves the aerodynamic efficiency of the unit.

According to the invention, there is provided a rotor assembly comprising a rotor shaft rotatable about an axis of rotation and an impeller mounted on the rotor shaft and having an air inlet and a base which are spaced along the axis of rotation, the rotor assembly further comprising a shaped member located between the air inlet and the base and having a smoothly curved shaped surface for guiding an airflow from the air inlet to the base, the shaped surface including an upstream portion adjacent the air inlet and a downstream portion adjacent the base, wherein the downstream portion of the shaped surface extends away from the axis of rotation in a direction which is substantially parallel to the base.

By providing such an arrangement, the airflow from the air inlet can be guided efficiently into the impeller. The smoothly curved shaped surface turns the incoming air gently through the required angle so that the majority of the airflow entering the impeller is already flowing in the correct direction. This improves the efficiency of the impeller.

Preferably, the upstream portion of the shaped surface is substantially parallel to the axis of rotation. More preferably, the upstream portion lies closer to the axis of rotation than the downstream portion. By providing such an arrangement, the disruption to the airflow entering the air inlet is reduced.

Preferably, the impeller is attached to the rotor shaft by means of an attachment member. More preferably, the shaped member forms part of the attachment member. By providing such an arrangement, only a single part is required. This reduces manufacturing and assembly costs.

Alternatively, the shaped member covers the attachment member. By providing such an arrangement, the shaped member can be connected to existing attachment members, for example, in order to retro-fit existing motors.

According to the invention, there is-also provided a shaped member for use in a rotor assembly of a motor and fan unit forming part of a vacuum cleaner, the shaped member having an axis of rotation and a smoothly curved shaped surface for guiding an airflow entering the motor and fan unit, the shaped surface having an upstream portion and a downstream portion, wherein the downstream portion of the shaped surface extends away from the axis of rotation in a direction which is substantially perpendicular to the axis of rotation.

S

By providing such an arrangement, the shaped member can be used to guide an airflow from an air inlet of a motor and fan unit into an impeller. The smoothly curved shaped surface turns the incoming air gently through the required angle so that the majority of the airflow entering the impeller is already flowing in the correct direction. This improves the efficiency of the impeller.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross section through a motor and fan unit including a rotor assembly according to the invention; Figure 2 is a cross section through a nut forming part of the rotor assembly shown in Figure l;and Figure 3 is an isometric view of the nut shown in Figure 2.

Figure 1 shows a motor and fan unit 10. The motor and fan unit 10 includes stationary front and rear casings 12, 14. The front casing 12 has an inlet 16 and an outlet 18.

Located between the front and rear casings 12, 14 is a diffuser plate 20 which includes a plurality of diffuser blades 22. The diffuser blades 22 are located adjacent the outlet 18.

This feature is not material to the invention and so will not be described any further here.

A rotor assembly 24 according to the invention is rotatably arranged in the motor and fan unit 10. The rotor assembly 24 includes a rotor 26 and a rotor shaft 28. The rotor shaft 28 has an end 30 and an axis X-X. The rotor shaft 28 is able to rotate about the axis X-X relative to the stationary front and rear casings 12, 14.

Mounted on the end 30 of the rotor shaft 28 is an impeller 32. The impeller 32 includes a base 34, a shroud 36 and a plurality of fan blades 38 located therebetween. The base 34 extends radially from the rotor shaft 28 parallel to the diffuser plate 20 and is located in a recess formed in the diffuser plate 20. The fan blades 38 extend perpendicularly from the base 34 and are curved in shape for aerodynamic efficiency. The shroud 36 delimits an axially-arranged inlet 40 to the impeller 30. The inlet 40 to the impeller 30 is co-axial with the inlet 16 formed in the front casing 12.

The impeller 30 is attached to the rotor shaft 28 by means of a nut 100. The nut 100 is shown in more detail in Figures 2 and 3. The nut 100 has a head 102 and a base 104.

The base 104 includes a blind bore 106. The blind bore 106 is arranged to receive the end 30 of the rotor shaft 28. The end 30 of the rotor shaft 18 has a screw thread which engages with a complementary receiving thread on an inner wall 108 of the blind bore 106 in order to secure the impeller 30 to the rotor shaft 28.

The nut 100 further includes a smoothly curved shaped surface 110. The shaped surface 110 comprises three regions A, B and C. This is shown in Figure 2. Region A is an upstream portion of the shaped surface 110 which is located adjacent the inlet 40 when the nut 100 is attached to the impeller 30 and rotor shaft 28. Region A also includes the head 102 and is the portion of the shaped surface 110 closest to the axis X-X of the rotor shaft 28. At the head 102 of the nut 100, the shaped surface 110 is rounded to minimise turbulence as the airflow passes the head 102 of the nut 100. Downstream of the head 102 of the nut 100, the upstream portion of the shaped surface 110 in this region lies parallel to the axis X-X of the rotor shaft 28.

Region B is located between region A and the base 104. In region B, the shaped surface of the nut 100 follows a concave profile. In other words, in region B, the shaped surface 110 is trumpet shaped and increases in diameter towards the base 104 of the nut 100. The diameter of the shaped surface 110 in region B is smoothly varying in order to guide the airflow better and prevent flow separation. Further, the profile of the shaped surface 110 is arranged so that the cross sectional area of a passageway 42 formed between the shroud 36 and the nut 100 increases between the inlet 40 and the fan blades 38. This can be seen in Figure 1 and prevents an unwanted pressure drop.

Region C is the portion of the shaped surface 110 which is furthest downstream from the inlet 40 and which is directly adjacent the base 34 of the impeller 30. Region C includes the outermost portion of the nut 100 and in this region the shaped surface 110 extends radially away from the axis X-X parallel to the base 34. In region C, the shaped surface 110 extends away from the axis X-X in a direction which is approximately perpendicular to the axis X-X. At the radially outermost part of the nut 100, the shaped surface 110 extends perpendicular to the axis X-X.

In use, when the impeller 30 is rotated, an airflow is drawn in through the inlets 16, 36 and onto the shaped surface 110 of the nut 100. The head 102 of the nut 100 is smoothly shaped to guide the incoming airflow around the nut 100 and towards the upstream portion of the shaped outer profile 110 in region A. By having an upstream portion of the shaped surface 110 which is parallel to the axis X-X of the rotor shaft 28, the airflow passes along the shaped surface 102 of the nut 100 without separating from the surface of the nut 100 and becoming turbulent. The airflow is then guided down the shaped surface 110 in region B. The convex shape of the shaped surface 110 in region B is such that the cross-sectional area of the passageway 42 located between the shaped surface and the shroud 36 increases towards the fan blades 38. This prevents an unwanted pressure drop whilst gradually turning the direction of the airflow through substantially 9QO The airflow then passes along the downstream portion of the shaped surface 110 in region C which is perpendicular to the axis X-X and parallel to the base 34. Due to the shape of the shaped surface 110 in Region C, the airflow leaving the shaped surface 110 of the nut 100 will be substantially parallel to the base 34. This results in a uniform, laminar airflow impinging upon the fan blades 38, ensuring that the impeller 30 can operate at a high efficiency. The now-uniform, laminar airflow then passes through the fan blades 38, the diffuser blades 22 and is exhausted from the motor and fan unit 10 through the outlet 18.

The invention is not limited to the detailed description given above. Variations will be apparent to the person skilled in the art. For example, the nut itself need not have a shaped profile and instead, a shaped member having a shaped surface could fit onto a standard hexagonal nut. In this case, the shaped member would cover the attachment member to provide a streamlined outer surface.

Further, other arrangements for attaching the nut to the rotor shaft could be used. For example, a snap fit, an interference fit or locking pins could be used. Alternatively, the nut could form an integral part of the impeller, and the whole unit could fit directly onto the rotor shaft.

Additionally, the base of the impeller need not be perpendicular to the axis of rotation of the rotor shaft. It may, for example, extend away at an acute or obtuse angle to the axis of rotation of the rotor shaft.

The upper portion of the shaped surface need not be exactly parallel to the axis of rotation of the rotor shaft. However, it is useful that at least a part of the upper portion of the shaped surface is shaped so that the airflow can be guided smoothly towards the lower portion of the shaped surface. What is important is that the lower portion of the shaped surface adjacent the base of the impeller assembly extends away from the axis of rotation in a direction which is substantially perpendicular to the axis of rotation so that the airflow can be guided smoothly onto the fan blades of the impeller assembly.

Claims (20)

1. A rotor assembly comprising a rotor shaft rotatable about an axis of rotation and an impeller mounted on the rotor shaft and having an air inlet and a base which are spaced along the axis of rotation, the rotor assembly further comprising a shaped member located between the air inlet and the base and having a smoothly curved shaped surface for guiding an airflow from the air inlet to the base, the shaped surface including an upstream portion adjacent the air inlet and a downstream portion adjacent the base, wherein the downstream portion of the shaped surface JO extends away from the axis of rotation in a direction which is substantially parallel to the base.

2. A rotor assembly as claimed in claim 1, wherein the downstream portion of the shaped surface extends away from the axis of rotation in a direction which is substantially perpendicular to the axis of rotation.

3. A rotor assembly as claimed in claim I or 2, wherein the upstream portion of the shaped surface is substantially parallel to the axis of rotation.

4. A rotor assembly as claimed in claim 3, wherein the upstream portion of the shaped surface lies closer to the axis of rotation than the downstream portion.

5. A rotor assembly as claimed in any one of the preceding claims, wherein the impeller is attached to the rotor shaft by means of an attachment member.

6. A rotor assembly as claimed in claim 5, wherein the shaped member forms part of the attachment member.

7. A rotor assembly as claimed in claim 5, wherein the shaped member covers the attachment member.

8. A rotor assembly as claimed in any one of the preceding claims, wherein the impeller further comprises a shroud and a plurality of fan blades, the shroud and the shaped member defining a passageway extending from the inlet to the plurality of fan blades and having a cross-sectional area which increases downstream of the inlet.

9. A rotor assembly substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.

10. A motor and fan unit including a rotor assembly as claimed in any one of claims 1 to 9.

11. A vacuum cleaner including a motor and fan unit as claimed in claim 10.

12. A shaped member for use in a rotor assembly of a motor and fan unit forming part of a vacuum cleaner, the shaped member having an axis of rotation and a smoothly curved shaped surface for guiding an airflow entering the motor and fan unit, the shaped surface having an upstream portion and a downstream portion, wherein the downstream portion of the shaped surface extends away from the axis of rotation in a direction which is substantially perpendicular to the axis of rotation.

13. A shaped member as claimed in claim 12, wherein the upstream portion of the shaped surface is substantially parallel to the axis of rotation.

14. A shaped member as claimed in claim 13, wherein the upstream portion of the shaped surface lies closer to the axis of rotation than the downstream portion.

15. A shaped member as claimed in any one of claims 12 to 14, wherein the shaped member is adapted to be attached to the rotor assembly.

16. A shaped member as claimed in claim 15, wherein the shaped member includes a threaded bore.

17. A shaped member substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.

iS. A rotor assembly for a motor and fan unit forming part of a vacuum cleaner and including the shaped member of any one of claims 12 to 17.

19. A motor and fan unit including the rotor assembly as claimed in claim 18.

20. A vacuum cleaner including the motor and fan unit as claimed in claim 19.