GB2596547A

GB2596547A - Seal for a compressor

Info

Publication number: GB2596547A
Application number: GB2009985.9A
Authority: GB
Inventors: John Collison Michael; Corralejo Anton Raul
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2020-06-30
Filing date: 2020-06-30
Publication date: 2022-01-05
Also published as: WO2022003310A1; GB202009985D0

Abstract

A compressor for use in domestic appliances, comprising an impeller (Fig. 2, 80) with a generally conical hub 82, a generally frustoconical shroud 86, a housing 78 at least partially surrounding the shroud, and a labyrinth seal 88 formed between an outer surface of the shroud and an opposing inner surface of the housing. This seal reduces the amount of fluid leaking from a flow path between the shroud and the housing, while minimising friction. The seal may extend along at least half the length of the impeller. The seal may comprise a plurality of steps, each step having a height, length, and inclination angle. The step height/length may be consistent between steps, or may vary. The step angle may be 90°, or smaller than 90°. The shroud and/or housing may be made of plastic. The impeller may be a mixed flow impeller. A fan assembly having the compressor may generate a pressure difference between inlet and outlet of about 100Pa and 1000Pa.

Description

Seal for a compressor

TECHNICAL FIELD

The present invention relates to a compressor for use in domestic appliances and to a fan assembly using a compressor.

BACKGROUND

Many domestic appliances use fluid displacement devices such as compressors, e.g., to pump water, air or cooling fluid from one place to another or to compress air in order to obtain a pressure difference. Typical examples of fluid displacement devices used in domestic appliances are pumps used in refrigerators, washing machines and dishwashers, fans or compressors used in floor and table top fans, in hair dryers and hand dryers, in ovens and for cooling computers and consumer electronics.

For example, UK patent application GB 2535223 A discloses a fan assembly comprising a body, housing a mixed flow compressor for generating an air flow and a nozzle mounted on the body for receiving and emitting the generated air. The compressor comprises an impeller housing, forming a duct with an air inlet and an air outlet, the inlet having a smaller diameter than the outlet. The impeller comprises a generally conical hub, with a plurality of impeller blades connected thereto. A generally frustoconical shroud is connected to the blade tips so as to surround the hub and the blades. The blades and the hub are integrally formed from injection moulded plastic. The shroud is produced separately and then attached to the blade tips. The hub is connected to a rotary shaft, which is drivable by an electric motor. For optimal compressor performance, it is important that all air drawn in at the inlet flows through the impeller to the outlet.

A known problem of this type of compressors is tip leakage, i.e. air flowing through the small clearance between the stationary impeller housing and the rotating blade tips of the impeller blades. The resulting pressure losses and turbulence lead to reduced performances and increased noise. In GB 2535223 A, tip leakage is reduced by the use of the shroud and by making the clearance between the rotating shroud and the stationary impeller housing as small as possible, while keeping within the boundaries set by the manufacturing tolerances defined by the impeller production process.

However, these measures for preventing tip leakage can only solve the problem to a limited extent. It is an aim of the present invention to address one or more disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

According to an aspect of the invention there is provided a compressor for use in domestic appliances. The compressor comprises an impeller, a housing and a seal. A generally conical hub defines a rotational axis of the impeller. A generally frustoconical shroud at least partially surrounds the impeller. The housing at least partially surrounds the shroud and is coaxially arranged with respect to the rotational axis of the impeller for allowing the impeller to rotate within the housing. The seal restricts the amount of fluid leaking through a flow path between the shroud and the housing, and is formed as a labyrinth seal comprising a series of matching features in an outer surface of the shroud and an opposing inner surface of the housing.

Labyrinth seals are commonly used in bearings to avoid contamination of the inner workings of the bearing system or to avoid oil leakage from one side of the bearing to the other one. They typically take the form of a series of interlocking fingers that together create a narrow and tortuous path between two bearing parts. The use of such labyrinth seals in the impeller shroud of a compressor for use in domestic appliances has, however, not been considered before. Integrating the series of matching features in the opposing surfaces of the hub and the housing obviates the installation of more complex and often unsatisfactory seals at the front and/or rear end of the impeller. Also, because the matching features are provided in the surfaces of the conical hub and housing, sealing can be provided along the full length of the hub and not just at its two ends. The non-contact nature of a labyrinth seal further helps to improve the quality of the seal without increasing friction.

Preferably, the series of matching features extends continuously along the rotational axis over at least half of a length of the impeller. For best results, the labyrinth seal may even extend continuously along the full length of the impeller. If the seal does not extend along the full length of the impeller, there may be multiple shorter labyrinth seals. For example, one may be provided closer to the inlet end of the impeller and another one closer to the outlet.

In a preferred embodiment, the series of matching features comprise a plurality of steps.

Each step may be defined by a step height measured in a direction perpendicular to the rotational axis, a step length measured in a direction parallel to the rotational axis, and a step angle between a front face and an upper surface of the step.

This kind of step labyrinth seal turns out to be very suitable for integration into the design of the device. With the conical shape of the impeller, the steps can easily be provided in the sloping walls of the shroud and the housing, without requiring any new parts to be added to the device. Performance tests of this improved device have shown that it provides an increased performance in the form of larger pressure differences and increased efficiency, while at the same time generating less noise. A step labyrinth seal can easily be integrated in the design of the device, without taking up significantly more space or adding large rotating surfaces and can be manufactured without requiring to improve on the manufacturing tolerances.

In an embodiment, the step height is substantially identical for at least two consecutive steps of the series of matching steps. Optionally, all steps have the same height, or two or more groups of adjacent steps have the same height. Alternatively, the step height varies between at least two consecutive steps of the series of matching steps. Such variations may add to the sealing performance of the step labyrinth seal and/or may better match the geometry of the impeller. Similar variations, or the absence thereof, are possible for the step length of the steps. The step angle may be about 900 for at least some of the steps. More acute angles (< 90°) may be used for at least some of the steps to further improve the sealing performance.

Especially for intended use of the compressor in domestic appliances, the shroud and/or the housing may be made of a plastic. The shroud and the housing, as well as the impeller blades, may be produced using injection moulding. Plastic parts are cheap, light weight and easy to produce with acceptable manufacturing tolerances. Alternatively, other materials are used. For example, the use of metal comes with the advantage that it can be machined with very high precision, allowing for an even smaller clearance between the rotating shroud and the stationary impeller housing.

According to a further aspect of the invention, a fan assembly is provided comprising a compressor as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a fan assembly wherein the invention may be used.

Figure 2 shows a cross section of a prior art version of a body for a fan assembly as shown in Figure 1.

Figure 3 shows a close-up of the stair step labyrinth seal used in a compressor according to the invention.

Figure 4 shows a perspective view of the shroud and the impeller.

Figure 5 shows a perspective view of the impeller housing.

Figures 6a, 6b and 6c show three variations of the labyrinth seal that may be used for the current invention.

DETAILED DESCRIPTION

Figure 1 shows a fan assembly 10 wherein the invention may be used. As will be discussed, below, the fan assembly 10 makes use of a compressor for generating an airflow and blowing an airstream into a room. Depending on what other parts are comprised in the fan assembly, the fan assembly may function as an ordinary fan, an air conditioner, an air purifier and/or a heater. It is noted that this is just one example of a domestic appliance that may use a fluid displacement device according to the invention. Other examples of devices that may do so are, hair dryers, hand dryers, cooling fans for computers and consumer electronics, ovens, refrigerators and washing machines. While the main example of a fluid displacement device described herein will be a compressor that displaces air, other fluid displacement devices according to the invention may pump fluids such as water or cooling liquids.

In overview, the fan assembly 10 comprises a body 12, a removable filter 14 mounted on the body 12, and an annular nozzle 16 mounted on the body 12. The nozzle 16 has an elongate annular shape and has an air outlet 18 for emitting a primary air flow from the fan 10 and defines a bore 19, or opening, through which air from outside of the fan assembly 10 is drawn by the air emitted from the outlet 18. The body 12 further comprises a user interface for allowing a user to control the operation of the fan 10. The user interface comprises a user-operable button 20 to enable a user to operate the fan 10. The fan 10 may also be provided with a remote-control unit for controlling the operation of the fan 10.

Figure 2 shows a cross section of a prior art version of a body 50 for a fan assembly 10 as shown in Figure 1. The main body section 50 comprises a duct 70 having a first end defining an air inlet 72 of the duct 70 and a second end located opposite to the first end and defining an air outlet 74 of the duct 70. The duct 70 is aligned within the main body section 50 so that the longitudinal axis of the duct 70 is collinear with the longitudinal axis of the body 12, and so that the air inlet 72 is located beneath the air outlet 74. The air inlet 72 is defined by an outwardly flared inlet section 76 of an impeller housing 78. The impeller housing 78 extends about an impeller 80 for drawing the primary air flow into the body 12 of the fan assembly 10.

The impeller 80 is a mixed flow impeller and comprises a generally conical hub 82, a plurality of impeller blades 84 connected to the hub 82, and a generally frustoconical shroud 86 connected to the blades 84 so as to surround the hub 82 and the blades 84. The blades 84 are preferably integral with the hub 82, which is preferably formed from a plastic material.

The shroud 86 may be produced separately from the same (or a different) material and mounted to the blade tips later. Alternatively, the shroud 86 is formed together and integral with the blades 84 and/or the hub 82, e.g., using an injection moulding process.

The impeller 80 is connected to a rotary shaft 90 extending outwardly from a motor 92 for driving the impeller 80 to rotate about a rotational axis. The rotational axis is collinear with the longitudinal axis of the duct 70. In this embodiment, the motor 92 is a DC brushless motor having a speed which is variable by the control circuit 62 in response to user selection. The maximum speed of the motor 92 is typically in the range from 1,000 to 10,000 rpm, depending on the size of the fan assembly 10 and the air flow it is expected to provide.

The motor 92 is housed within a motor housing having an upper portion 98 and a lower portion 96. The upper portion 98 of the motor housing provides an inner wall 95 of the duct 70. The impeller housing 78 surrounds the impeller 80 and the motor housing and thereby provides an outer wall of the duct 70. The walls 78, 95, together with the hub 82, thus define an annular air flow path which extends through the duct 70.

Typically, for a fan assembly as shown in Figure 2, the shroud 86 of the impeller 80 has a diameter of about 50 to 100mm at the inlet, but for other applications, or other types of fans, smaller or larger impellers 80 may be used. When using such a typical impeller 80 and a motor 92 as described above, pressure differences between the inlet 72 and the outlet 74 of the impeller 80 are usually between about 100Pa and 1000Pa. Of course, many design parameters influence the obtainable pressure difference and different applications may achieve different pressure differences. For vacuum cleaners, the generated pressure difference can easily exceed 20kPa.

In use, the airflow and pressure difference between the inlet end and the outlet end of the impeller may cause some of the air to find its way between the shroud 86 and the impeller housing 78. Attempts to reduce the tip leakage by reducing the size of the gap between the shroud 86 and the impeller housing 78 have only been partially successful. According to the invention, better results are obtained by providing a labyrinth seal 88 as, e.g., shown in the following figures.

Figure 3 shows a close-up of the stair step labyrinth seal 88 used in a compressor 80 according to the invention. It is noted that this is just a schematic and simplified presentation. For example, the rotary shaft 90, the motor 92 and the motor housing are not shown. This part of the air duct 70 is defined by the impeller housing 78 and the conical body of the impeller hub 82. In use, the impeller hub 82 rotates around its rotational axis 91, causing the impeller blades 84 to draw in air via the air inlet 72 of the duct 70. The impeller blades 84 then draw the air through the air duct 70 towards the air outlet 74, as indicated by the six block arrows. To avoid tip leakage and turbulent air around the tips of the impeller blades 84, a frustoconical shroud 86 is attached to and surrounds the impeller blades 84. The inner surface of the shroud 86 is preferably smooth to facilitate the air flow through the duct 70. The outer surface of the shroud 86 has a stair step profile that substantially matches a stair step profile in the opposing inner surface of the impeller housing 78. A narrow clearance 89 between the shroud 83 and the impeller housing is kept as narrow as possible within the engineering tolerance levels of the manufacturing and assembly process. The clearance is wide enough to avoid contact, and thus friction, between the rotating shroud 86 and the stationary impeller housing, and as narrow as possible for an optimal sealing. The two matching stair step profiles and the narrow clearance 89 together form the labyrinth seal 88. The labyrinth seal 88, because of the tortuous path and sharp corners in the clearance 89 provides for a much-improved seal compared to conventional designs wherein the opposing surfaces of the shroud 86 and the impeller housing have a smooth surface.

In this exemplary embodiment, the labyrinth seal 88 runs continuously along the full length of the shroud 86 and the impeller 80. Alternatively, the seal 88 may only extend along a portion of the impeller 80. If the seal 88 does not extend along the full length of the impeller 80, there may be multiple shorter labyrinth seals. For example, one may be provided closer to the inlet end 72 of the impeller 80 and another one closer to the outlet 74 Figure 4 shows a perspective view of the shroud 86 and the impeller 80. It clearly shows the stair step profile and the frustoconical shape of the shroud 86, as well as how the shroud 86 surrounds the impeller blades 84. Figure 5 shows a perspective view of the impeller housing 78 that, together with the shroud 86 of Figure 4 forms the labyrinth seal 88.

Figures 6a, 6b and Sc show three variations of the labyrinth seal that may be used for the current invention. Figure 6a shows a simple and regular pattern of a plurality of steps of equal height (h) and equal length (/), wherein the front face 881 and the top surface 882 of the steps are perpendicular (a r-z 90°). The top surfaces 882 are parallel to the rotational axis 91 of the impeller 80, while the front faces are 881 are perpendicular thereto. In variations of this embodiment, the height (ii) of the front face 881 and the length (/) of the step surface 882 may vary between steps or groups of adjacent steps.

In the labyrinth seal 88 of Figure 6b, the top surfaces 882 of the stair steps are, like in Figure 6a, parallel to the rotational axis 91 of the impeller 80. The front faces 881, however, make an acute angle (a < 90°) with the top surfaces 882, which will further increase the sealing effect of this labyrinth seal 88. In Figure 6c, the top surfaces 882 of the stair steps are slightly inclined with respect to the rotational axis 91, while the front faces 881 are not perpendicular to the top surfaces 882. Like in Figure 6b, the front faces 881 make an acute angle (a < 90°) with the top surfaces 882. Although, Figures 6a, 6b, and Sc all show examples of the stair step labyrinth seal wherein each step has the same shape and dimensions, other labyrinth seals used for this invention may have varying shapes and/or dimensions.

Claims

CLAIMS1. A compressor for use in domestic appliances, the compressor comprising: an impeller connected to a generally conical hub defining a rotational axis of the impeller, and a generally frustoconical shroud at least partially surrounding the impeller, a housing, at least partially surrounding the shroud and coaxially arranged with respect to the rotational axis of the impeller for allowing the impeller to rotate within the housing, a seal for preventing fluid leaking through a flow path between the shroud and the housing, wherein the seal is formed as a labyrinth seal comprising a series of matching features in an outer surface of the shroud and an opposing inner surface of the housing.
2. A compressor as claimed in claim 1, wherein the series of matching features extends continuously along the rotational axis over at least half of a length of the impeller. 15
3. A compressor as claimed in claim 1 or 2, wherein the series of matching features comprises a plurality of steps, each step being defined by a step height, measured in a direction perpendicular to the rotational axis, a step length, measured in a direction parallel to the rotational axis, and a step angle between a front face and an upper surface of the step.
4. A compressor as claimed in claim 3, wherein the step height is substantially identical for at least two consecutive steps.
5. A compressor as claimed in claim 3 or 4, wherein the step height varies between at least two consecutive steps.
6. A compressor as claimed in any of claims 3 to 5, wherein the step length is substantially identical for at least two consecutive steps. 30
7. A compressor as claimed in any of claims 3 to 6, wherein the step length varies between at least two consecutive steps.
8. A compressor as claimed in any of claims 3 to 7, wherein the step angle is about 90° for at least some of the steps.
9. A compressor as claimed in any preceding claim, wherein the step angle is smaller than 900 for at least some of the steps.
10. A compressor as claimed in any preceding claim, wherein the shroud and/or the housing are made of a plastic.
11. A compressor as claimed in any preceding claim, wherein the impeller is a mixed flow impeller.
12. A fan assembly comprising a compressor as claimed in any of the preceding claims.
13. A fan assembly as claimed in claim 12, wherein the impeller is configured to generate a pressure difference between the inlet and the outlet of the compressor of about 100Pa and 1000Pa.