GB2046360A

GB2046360A - Fluid impeller

Info

Publication number: GB2046360A
Application number: GB7911439A
Authority: GB
Original assignee: AES PLASTICS Ltd
Current assignee: AES PLASTICS Ltd
Priority date: 1979-03-31
Filing date: 1979-03-31
Publication date: 1980-11-12

Abstract

The impeller (50), e.g. for vacuum cleaners, reduces noise generating as it rotates sound mainly at frequencies above the human audible range. This is achieved by having the impeller blades (51) not all at equal angular spacings, (5A), and preferably at random angular spacings, whilst maintaining the dynamic balance of the impeller. <IMAGE>

Description

SPECIFICATION Fluid impeller The invention relates to fluid impellers, particularly for use in domestic and industrial appliances such as vacuum cleaners, air extractor fans, fan heaters and the like.

It is customary for such appliances to have an impeller comprising a plurality of blades which extend in a plane perpendicular to the axis of rotation of the impeller, either from a central boss or from one or both faces of a disc. The impeller is supported in some form of bearing and in order that undue wear and early breakdown of that bearing is avoided the impeller should be in dynamic balance as it rotates. This is usually ensured by having identical blades located on the impeller with equiangular inter-blade spacing.

However, such appliances create a certan amount of noise in use and such noise, either by self if excessive or in conjunction with other noise present in the environment in which the appliance is used, can cause distress or even -harm to any persons subjected thereto.

Itis an object of the present invention to provide an impeller which in use creates less noise, or at least less noise within the normal audible range of humans, than was customary heretofore.

The invention provides an impeller adapted to rotate about an axis substantially in dynamic balance and having a plurality of blades extending in a plane perpendicular to said axis, any two consecutive blades having an angular spacing therebetween wherein at least two of said angular spacings are different in magnitude.

In one practical embodiment of the invention no two adjacent angular spacings are equal in magnitude but in a preferred embodiment no two angular spacings are equal in magnitude.

The angular spacings may be such that the location of the blades provides that the impeller is subtantially in dynamic balance. Alternatively the mass of the impeller may be adjusted in at least one specific location therein to provide that the impeller is substantially in dynamic balance. The local mass adjustment may be provided by means of at least one weight attached to the impeller or by means of at least one enlarged or reduced mass portion of the impeller.

Prior art impellers by virtue of the equi-angular spacings of their blades, generate a high volume basic frequency sound and low volume high frequency harmonics. The pitch of the sound created is dependent upon the number of blades and the rotational speed of the impeller, and the volume of the sound is dependent upon the power output from the impeller and in consequence upon the mass of air being moved in a given time. Since reduction of the latter would defeat the primary object of the impeller, the present invention seeks to reduce the noise problem by reducing the volume of the basic frequency of the sound produced at the expense of increased high frequency harmonic sound generation.Because of the unequal angular spacing of the blades of an impeller according to the present invention the higher harmonies, associated with a large number of imaginary blades the position of some of which coincides with the position of the actual blades, are enhanced whilst the low frequency sounds are reduced. Thus with completely random angular spacing of the blades the generation of extremely high frequencies above the normal audible range of humans is increased whilst there is a reduction in the generation of the lower and audible frequencies which cause the problems associated with prior art impellers.

Embodiments of impellers according to the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is an elevation of one embodiment; Figure 2 is an elevation of a second embodiment; Figure3 is an elevation of a third embodiment; Figure 4 is an elevation of a fourth embodiment.

Figure 5 is an elevation of a fifth embodiment Figure 6 is a sectional side elevation of the embodiment of Figure 5; Figure 7 is an elevation of a sixth embodiment; and Figure 8 is a sectional side elevation of the embodiment of Figure 7.

As shown in Figure 1 an impeller denoted generally by the numeral 10 has, for simplicity, six blades 11 which extendradiallyfrom a central boss 12. the impeller 10 is adapted to rotate about a central axis 13. In this embodiment the angles denoted by 1A are equal but are different from the angles denoted by 18, the arrangement being such that the impeller 10 is in dynamic balance whilst rotating about the axis 13. In this case the impeller 10 is not greatly removed from the prior art impellers and in consequence the improvement as regards generated noise relative to such impellers to be expected from this impeller is small but not insignificant.With this embodiment two basic sound frequencies will be generated together with a barmonic frequency associated with a large number of imaginary blades and possibly some high frequency harmonies. In consequence of the overall sound level generated a greater proportion of the harmonic frequencies and a lower proportion of the lower and audible or more audible frequencies will be generated than would be the case if the blades 11 were equi-angularly spaced.

The effect is increased ifthe angle 1 B is not a low integer multiple of the angle 1A.

The impeller 20 shown in Figure 2 also has, for simplicity, six blades 21 which extend radially from a central boss 22, and the impeller 20 is adapted to rotate about a central axis 23. As in the previous embodiment the angles 2A are equal but different from the angles 2B, but in this embodiment no two adjacent angular spacings are equal whilst the impeller 20 is again in dynamic balance as it rotates about the axis 23.

The principal sound frequencies generated by this embodiment will again be two basic frequencies and a harmonic frequency as in the previous embodiment, providing a similar improvement over equiangularly blade spaced impellers as regards noise generation.

Figure 3 illustrates an impeller 30 having six blades 31 which extend from the face of a disc 32.

The impeller 30 is adapted to rotate about a central axis 33 about which the blades 31 extend radially and in this case no two angular spacings between the blaces 31 are equal. In consequence the impeller 30 is basically not in dynamic balance as it rotates about the axis 33. However, the dynamic balance may be restored by the addition of a weight of weights to the impeller 30 at a suitable location or locations. Dynamic balance may be achieved by adding a weight, equal in magnitude to that of a blade 31, to the disc 32 diametrically opposite each blade 31 and at a distance of R/from the axis 33, where R is the radius of the disc 32.However, it is possible, either mathematically or experimentally using an actual impeller mounted on a balancing machine, to determine the magnitude and location at a single weight 34 which when added to the impeller 30 restores the dynamic balance thereof.

Depending on the magnitude of the weight 34 required in any particular case it may comprise a weight of a higher density material than that of the impeller 30 and attached thereto, or it may comprise an enlargement of the disc 32. In the latter case it could be formed conveniently during the casting or machining of the impeller 30.

Alternatively, as shown in Figure 4, the dynamic balancing of the impeller 30 may be performed by removal of mass from the disc 32 at the appropriate place or places in the same way but in direct contrast with the above mentioned methods. In this case the removal of the mass may be achieved by the thinning of or the forming of holes 35 in the disc 32 during casting or machining thereof.

Further embodiments of impeller 50, 70 are shown in Figures 5 to 8, in which the angular spacings of the nine blades 51 or twelve blades 71 are chosen so as to provide impellers which are substantially in dynamic balance without the addition or subtraction of mass from the impeller. In these embodiments the blades 51,71 extend in planes perpendicular to the axes of rotation 53, 73 about which the impellers 50, 70 are adapted to rotate. However in these embodiments the blades 51,71 do not extend radially from the axes 53,73 but in each case are tangential to a circle having its centre on the relevant axis. The embodiments of Figures 5 to 8 are just two examples of arrangements of impeller according to the present invention. Many similar arrangements can be determined mathematically or empirically. In the case of the impeller 50 to angular spacings are in sequence anticlockwise beginning with the angle 5A; 30 ; 60 ; 26 ; 38 30'; 45" 30'; 34 ; 55 ; 28 ; and 430 In the case of impeller 70 the angular spacings are in sequence clockwise beginning with the angle 7A; 30 ; 25 ; 32.5 ; 27.5 ; 37.5 ; 25.5 ; 23 ; 39 ; 30 ; 30 ; 20.5 ; and 39.5o.

Claims

1. An impeller adapted to rotate about an axis substantially in dynamic balance and having a plurality of blades extending in a plane perpendicular to said axis, any two consecutive blades having an angular spacing therebetween wherein at least two of said angular spacings are different in magnitude.

2. An impeller according to claim 1,wherein no two adjacent angular spacings are equal in magnitude.

3. An impeller according to claim 2 wherein no two angular spacings are equal in magnitude.

4. An impeller according to any preceding claim wherein the angular spacings are such that the location of the blades provides that the impeller is substantially in dynamic balance.

5. An impeller according to any one of claims 1 to 3 wherein the mass of the impeller is adjusted at at least one specific location therein to provide that the impeller is substantially in dynamic balance.

6. An impeller according to claim 5 wherein said local mass adjustment is provided by means of at least one weight attached to said impeller.

7. An impeller according to claim 5 wherein said local mass adjustment is provided by means of at least one enlarged mass portion of said impeller.

8. An impeller according to claim 5 wherein said local mass adjustment is provided by means of at least one reduced portion of said impeller.

9. An impeller substantially as hereinbefore described with reference to and as illustrated in any one of Figures 1 to 4, Figures 5 and 6 or Figures 7 and 8 of the accompanying drawings.