GB2296943A

GB2296943A - Injection moulded radial flow fan wheel

Info

Publication number: GB2296943A
Application number: GB9425791A
Authority: GB
Inventors: Huw Walters
Original assignee: Valeo Climate Control Ltd
Current assignee: Valeo Climate Control Ltd
Priority date: 1994-12-21
Filing date: 1994-12-21
Publication date: 1996-07-17
Anticipated expiration: 2014-12-21
Also published as: FR2730015B1; FR2730015A1; GB9425791D0; GB2296943B

Abstract

An injection-moulded radial flow fan wheel (1) has plural axially-extending blades (2), each of which has a radially outer portion (46) formed in the cavity part (see Fig.5) of a moulding tool and a second radially-inner portion (43) formed in the punch part (see Fig.6) of a moulding tool. The outer portion (46) tapers downwards axially from one end of the fan to the other and the inner portion (43) tapers down from the other end of the fan to the one end of the fan. A point at which the inner (43) and outer portions (46) have the same thickness is located in a region of maximum radial air flow.

Description

RADIAL FLOW FAN WHEEL The present invention relates to a radial flow fan wheel and to a method of making such a fan wheel.

Radial flow fan wheels are well known in the art. Radial flow fan wheels generally comprise plural elongate fan blades disposed around a pitch circle and extending axially to define a right circular cylinder. Air is induced into an open end of the cylinder defined by the fan blades and is expelled radially as the fan rotates. To achieve this effect each blade is angled somewhat with respect to the direction of rotation of the blade.

The fan blades may be connected together at each end by respective annular members and plural radial members extend from an axial hub, for accepting a drive shaft, to both of the annular members. Alternatively the hub may be connected to one annular member only, and via a connecting member which extends all around the hub and the inner periphery of the fan.

For efficient operation, the fan blade outlet - ie, the spacing between the blades in a circumferential direction should be as large as possible, to provide minimum impedance to air flow. However it is also necessary to make the blades mechanically strong, which implies the converse requirement of increased blade thickness, in turn reducing the blade outlet.

The basic structure of a radial flow fan wheel lends itself to manufacture from plastics. Manufacture is frequently by injection moulding.

A known radial flow fan wheel is injection moulded using a two-part moulding tool having a cavity part and a punch part.

The known wheel is made using a tool having a cavity part which has a smooth circular-cylindrical form. The punch part of the tool is cylindrical and has peripherally open slots extending axially, for receiving and moulding the material of the blades.

Thus the blades are formed in the punch part of the tool and have an outer peripheral portion delimited by the wall of the cavity part of the tool.

This known fan wheel, which has 44 blades, is used as the basis for the present invention. It has a number of problems.

During the moulding process the fit of the punch part of the tool into the cavity may not provide a perfect seal therebetween, which means that the plastics moulding material may extend circumferentially from the outer periphery of one or more blades in the form of a thin arcuate flash portion.

This flash portion may close or at least restrict the peripheral opening between two blades. The weight of the flash would unbalance the fan and the closure or restriction of the- gap between the peripheral portions of two blades would undesirably restrict the air flow. As a result, after-treatment of the fan is necessary to remove any flash.

As the outer peripheral portion of each blades is formed at the interface with the circular wall portion of the cavity part of the tool, there are likely to occur sharp discontinuities between the part of the blade moulded on the punch part of the tool, and the peripheral portion. The sharp tips of the blades leads to undesirable noise, which is also a symptom of lost efficiency.

An annular member, hereinafter referred to as a tie ring, is formed during the moulding process to support the otherwise-free axial end portion of each of the blades. In the known fan wheel, the tie ring has a relatively large axial extent, which is necessary to provide sufficient support for the blades.

It is accordingly an object of the present invention to at least partially mitigate the above-mentioned problems. It is a further object of the present invention to provide an improved radial flow fan wheel.

In other known injection moulded fan wheels the cavity part of the tool has plural axial slots open to the internal periphery thereof for forming an outer portion of the fan blades, and having corresponding externally-open slots on the punch part of the tool for moulding thereon the inner portion of the blades. In operation, the tool is assembled with the punch part inside the cavity part with the slots aligned, and moulding material is injected. After the moulding material has solidified, the punch part of the tool is withdrawn and the fan wheel is removed, either by sliding it axially from the cavity part of the tool, or by sliding it axially off the punch part of the tool.

In practice, fan wheels moulded in this way have disadvantages due to the moulding technique. Specifically each slot on the cavity part of the tool has a slight inward taper longitudinally inwards from the tool opening and each slot on the punch part has an oppositely directed longitudinal taper, to allow the completed fan wheel to be slid, respectively out of the cavity and off the punch part of the tool. As a result, each blade has a radially-outer portion which is thick at one end of the fan and relatively thin at the other end of the fan, and a radially-inner portion which is thin at the one end of the fan and relatively thick at the other end of the fan. The transition between the thick and thin portions takes the form of a step in the radial-direction along each blade.

At one end of the fan, moving radially outward along each blade, there will be a step down at the transition between a thick radially-inner portion and a thin radially-outer portion. At the other end of the fan there will be a step up, at the transition between a thin radially-inner portion and a thick radial-outer portion. Each of these steps causes a disturbance to airflow passing from inside the fan to the outside of the fan. Under normal conditions, the effect of the inwards step (which occurs on both side of each fan blade) may give rise to turbulence. Where the step is an upward step, the effect is to constrict the airflow. The overall reduction in efficiency of the fan is herein referred to as tool-mismatch.

A further problem of this technique is that, for ease of release from the cavity part of the tool, the blade tips are normally relatively sharp.

This second technique does however have the advantage that the above-mentioned tie ring can have a reduced axial extent without leading to weakness.

According to a first aspect of the present invention, there is provided an injection-moulded radial flow fan wheel having plural axially-extending blades disposed about an axis for producing radial flow which varies along the axial blade length, each blade having a radially outer portion formed using the cavity part of a moulding tool and a second radially inner portion formed in the punch part of the moulding tool, when the outer portion, at the interface with the inner portion, tapers downwards axially from one end of the fan to the other, and the inner portion, at the interface with the outer portion, tapering down from the said other end of the fan to the said one end of the fan, and wherein a point at which the inner and outer portions have the same thickness at the interface therebetween is located in a region of maximum radial airflow.

Preferably each blade is a generally concavo-convex member having a first convex surface and a second concave surface with a radiussed inner transition surface portion, the blades being disposed on a pitch circle centred at the axis of the fan and the fan blades are aligned on the circle such that a radius of the pitch circle passing through a point on the radially-inner periphery of the fan blade, at which point the inner periphery of the fan blade is perpendicular to the said radius, does not intersect the concave surface.

Advantageously the thickness of each blade reduces towards the blade tip, to provide a generally aerofoil section.

Conveniently each of the concave and convex surfaces is defined by a respective arc of a respective circle.

According to a second aspect of the present invention, there is provided a radial flow fan wheel having plural axially-extending blades, each blade being a generally concavo-convex member having a first convex surface and a second concave surface with a radiussed inner transition surface portion, the blades being disposed on a pitch circle centred at the axis of the fan and the fan blades are aligned on the circle such that a radius of the pitch circle passing through a point on the radially-inner periphery of the fan blade, at which point the inner periphery of the fan blade is perpendicular to the said radius, does not intersect the concave surface wherein the thickness of each blade reduces towards the blade tip, to provide a generally aerofoil section.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a view along the axis of an embodiment of a fan wheel of the invention taken from the induction end; Figure 2 is a side elevation of the fan wheel of Figure 1; Figure 3 is a cross-sectional view of the fan wheel of Figure 1, taken along the lines III-III'; Figure 4 is a transverse cross-sectional view of one of the blades of Figure 1; Figure 5 shows a cross-section through the cavity part of a first mould tool; Figure 6 shows a cross-section through the punch-part of the first mould tool; Figure 7 shows a transverse cross-section through a blade made using the tool of Figures 5 and 6; Figure 8 shows a cross-section through a cavity part of a second mould tool; Figure 9 shows a cross-section through the punch part of the second mould tool;; Figure 10 shows a transverse cross-section through a blade made with the second mould tool, at a first end of the blade; Figure 11 shows a transverse cross-section of the blade shown in Figure 10, at the other end of the blade; Figure 12 is a diagrammatic axial cross-section through a fan blade along the interface between the radially inner and radially outer portions; and Figure 13 is a view similar to Figure 12 but showing a fan blade in accordance with the invention.

In the figures like reference numerals indicate like parts.

Referring to Figures 1, 2 and 3, a radial flow fan wheel 1 has plural elongate blades 2, forty four in number in the example shown in Figure 1, the plural blades being disposed on a pitch circle about a central hub member 3. At a first axial end, the blades are connected together by a tie ring member 4, as will most clearly be seen from Figure 3. The tie ring member 4 is an annular, generally planar member, and the plane of the tie ring member lies within the axial extent of the hub member 3.

A support member 5 extends radially and axially from the axial mid point of the hub member 3 to the second axial end of the blades, the end remote from the tie ring member 4. As will most clearly be seen in Figure 3 the support member 5 in cross section describes a generally S-shape. The support member 5 0 extends 360 about the hub member 3 to define a generally inverted (as shown) bowl member. Within the bowl member defined by support member 5, plural reinforcing ribs 6 extend from the outer periphery of the hub member 3 to the inner periphery of the support member 5.As shown in Figure 1 in the embodiment there are eight reinforcing ribs 6 disposed symmetrically about the hub member 3, so that the angular spacing between the centre lines of each two adjacent rib members is 450. The hub member defines an axially disposed central hole 7 for a drive shaft, not shown.

The shape of a blade 2 will now be described with respect to Figure 4: The blade 2 is a generally concavo-convex member having a first convex surface 41 and a second concave surface 42. An axially inner portion 43 of the blade 2, the portion joining the surfaces 41 and 42 is radiussed. The blade 2 is disposed such that a first fan radius 400 intersects the blade member 2, entering at the inner portion 43 and passing out through the convex surface 41 without passing through the concave surface 42. The point of intersection of the radius 400 with the inner portion 43 is spaced at a radial distance rl from the centre of symmetry of the fan.

In the previously discussed known fan wheels, the radius passing through the inner peripheral portion of each blade passes out through the concave surface, before reentering the blade. This known form of blade has a "cupping effect" on the air, which is disadvantageous over the presently described fan wheel.

The convex surface 41 is defined by the arc of a circle having radius R2, and a centre 44 defined by the intersection of a fan radius r3 and a line 401 parallel to first fan radius 400 and spaced from the first fan radius 400 by a distance dl. The concave surface 42 is defined by an arc of a further circle, having radius R4, and a centre 45. The position of the centre 45 is defined by the intersection of a further fan radius r5 and a line 402 parallel to first fan radius 400, and spaced from first fan radius by a distance d2.

The blade member 2 has a radially outermost surface portion 46 which is radiussed and the radially outermost surface portion 46 is connected to the convex surface portion 41 by a first transition surface portion 47, and to the concave surface portion 42 by a second transition surface portion 48. The first transition surface portion 47 is an arc of a circle having a radius R6, and a centre 49 defined by the intersection of a yet another fan radius r7 and a line 404 parallel to, and spaced by a spacing d3 spaced from the first fan radius 400. The second transition surface portion 48 is sharply radiussed.

In the embodiment the following relationships apply: R2 > d2 > R4 > dl > d3 > R6.

r7 > r5 > r3 > rl > R2.

The above-described embodiment of a radial flow fan wheel is advantageous over the prior art by providing a thinned-down blade tip which has a generally aerofoil section. This is advantageous in that air flow restriction is reduced as the passage between each pair of blades is less constricted.

Moreover by incorporating radii in place of the sharp corners and edges of prior art fan wheels, air noise is reduced.

As previously discussed, injection moulded radial flow fan wheels may be formed with the fan blades entirely on the punch part of a moulding tool. Referring to Figure 5, the cavity part of a first mould tool consists of a body 50 defining a circular-cylindrical cavity 51. The cavity has substantially smooth walls for cooperation with a corresponding punch-part.

Referring to Figure 6, a punch part of the first mould tool consists of a cylindrical body 60 which has a number of axially extending slots 61, of which only one is shown for clarity. Each of the slots 61 is open at the periphery of the body 60 and communicates with mould-material injection openings (not shown).

In operation the punch part 60 is inserted into cavity 51 and the fan wheel is formed by injection of moulding material into the mould. The fan blades are formed in the slots 61, conforming to the shape of the slot and delimited at their outer periphery by the inner wall of cavity part 51.

Referring to Figure 7 a blade 70 has a first concave surface portion 71, a radially-inner transition surface portion 72 and a convex surface portion 73. Each of these surface portions 71, 72 and 73 is formed by interaction between the mould material and the wall or walls of the slot in the punch part 60. The blade 70 also has a radially outer surface 74 which is formed by conformity of the moulding material with the inner wall of the cavity portion 51.

It will be noted from Figure 7 that the angles between the radially outer surface 74 and the adjacent surfaces 71 and 73 are relatively sharp. Specifically, there tends to be formed at these angles discontinuities which, in operation, create noise and lead to fan losses. It is a disadvantage of use of a mould tool arrangement as shown in Figure 5 and 6 that radiussing is not possible between the radially outer surface portion 73 and the concave or convex surface portions 71 and 73. It is a further disadvantage that unless the clearance between punch part 60 and the walls of cavity 51 is extremely small, moulding material will flow into the spacing between the punch and the cavity wall to form so-called "flash".

Referring now to Figures 8 and 9, a second moulding tool will now be described: Figure 8 shows the cavity part of a mould tool which consists of a body 18 having a wall defining a cavity 81. The wall of the cavity 81 is generally circular but contains plural slots 82, of which one only is shown for clarity. Each slot 82 is shaped to form a radially outer portion of a blade of a radial flow fan wheel. Turning to Figure 9, the punch part of the tool consists of a punch member 90 which is of generally cylindrical form but which has plural axially-disposed slots 91, in the same way as the slot 61 in punch member 60 described with respect to Figure 6. The slots 91 do not extend so far radially into the punch member 90 as do slots 61 on punch member 60.

In operation the punch part 90 of the tool is inserted into cavity 81 with each slot 91 aligned with a corresponding slot 82. Each facing pair of slots 82 and 91 is then used for forming a respective blade of the radial flow fan wheel.

Moulding material is then injected into the mould and flows into the respective slot pairs so as to form a complete radial flow fan wheel having plural blades disposed about a central axis.

To empty the mould, the punch part 90 is extracted from the cavity part 81. To enable the moulded product to be released from the two parts of the mould, relative movement between the moulded product and the parts of the tool takes place in two directions. Firstly, the product is moved relative to the punch part in a first direction, and secondly the product is moved relative to the cavity part in a second opposite direction.Although it is desirable from the point of view of the fan performance, for the fan blades to be of uniform thickness along their axial length, it is however a requirement of the moulding process as described that the portion of each blade moulded in slot 91 has a first direction of taper along its axial length, to allow removal of the punch part from the product and that the portion of each blade moulded in slot 82 has a taper in the opposite direction, to allow removal of the product from cavity 81. This is shown diagrammatically in Figure 12.

Referring to Figure 12, which is a section through a blade along the interface between the cavity-moulded portion and the punch-moulded portion, 121 shows the end face of the radially-outer portion of the blade, that portion moulded in slot 82. As shown in Figure 12, the width of the outer portion 121 which corresponds to the blade thickness, is at its greatest at the top of the blade. The axially-extending walls 122 and 123 of the outer portion taper towards the bottom end of the blade 124. This arrangement allows the completed fan to be drawn up out of the cavity part of the tool in the direction shown by arrow A.

On the other hand the radially-inner portion 125 of each blade, that portion moulded in slots 91 of the punch part of the tool has a greatest thickness at the bottom of the blade 124 and has side walls 126, 127 which taper inwardly towards the top of the blade. This arrangement allows the completed fan wheel to be moved downwards in direction B from the punch part of the tool 90.

Figure 12 is a view taken from the centre of the fan radially outwardly. It will therefore be seen that as air in the top part of the fan moves outwardly along the blades, it will experience a discontinuity or step outwards. By contrast in the lower half of the blade air moving outwardly will reach an inner step at the interface between the inner and outer blades halves. The view of Figure 12 is highly exaggerated, but it will be understood by one skilled in the art that the best flow conditions will be in the region 128 along the axial length of the blade, where the step, in either direction, is relatively small. The worst conditions will arise towards the two axial ends of each blade, as will be seen in Figures 10 and 11.Figure 10 shows a cross-section at the top of a blade, having an outer portion 100 and an inner portion 101, and Figure 11 shows a cross-section of the blade at the bottom.

Referring once again to Figure 3, it will be seen that the support member 5 is relatively remote from the fan blades 2 at the hub-end, and is relatively close to the blades towards the blade end of the support member. The disposition of the support member 5 means that the passageway to the bottom of the blades is relatively constricted, whereas the passageway for air to the top of the blades is relatively open. Thus, in the fan shown in Figure 3, the greatest air flow is to be expected at the axial top (as shown in Figure 3) of the fan.

Accordingly the blade thickness transition region 128 is advantageously situated towards the top of the blade, rather than in the centre of the blade as shown in Figure 12. This effect could be achieved by altering the so-called draught angle of the taper of the fan blades. However, it is preferred to achieve the effect by increasing the thickness of the inner portion of each blade, as shown in Figure 13.

Referring to Figure 13, the transition region 128 of Figure 12 has moved up towards the top of the blade. This allows for the minimum disturbance to radially outward airflow along the blade surfaces.

Although the above-described embodiment of a radial flow fan wheel has 44 blades, where acoustic conditions are very important, it is preferable to substitute a prime number of blades. Thus for example 43 blades could be provided. This is because a prime number of blades provides the least favourable conditions for acoustic resonances to occur. Such resonances may occur for a number of reasons, but are especially likely where drive from a DC electric motor. Such motors have segmented commutators which cause torque variations which can give rise to acoustic excitation of the blades. Other measures such as resilient mountings, and modification of mounting arms may also be required to reduce transmission of acoustic vibrations from the fan arrangement to the surrounding structure.

With careful moulding, a radial flow fan wheel according to the invention can be self-balancing. In other words, an adequately balanced fan can be produced straight from the mould, without the need for after treatment. The moulding technique described permits the blades to be secured in their thickest regions to the hub member and the ring member. By contrast, known wheels have blades so secured in their thinner regions.

Claims

CLAIMS:

1. An injection-moulded radial flow fan wheel having plural axially-extending blades disposed about an axis for producing radial flow which varies along the axial blade length, each blade having a radially outer portion formed using the cavity part of a moulding tool and a second radially inner portion formed in the punch part of the moulding tool, when the outer portion, at the interface with the inner portion, tapers downwards axially from one end of the fan to the other, and the inner portion, at the interface with the outer portion, tapering down from the said other end of the fan to the said one end of the fan, and wherein a point at which the inner and outer portions have the same thickness at the interface therebetween is located in a region of maximum radial airflow.

2. An injection moulded radial flow fan wheel as claimed in claim 1 wherein each blade is a generally concavo-convex member having a first convex surface and a second concave surface with a radiussed inner transition surface portion, the blades being disposed on a pitch circle centred at the axis of the fan and the fan blades are aligned on the circle such that a radius of the pitch circle passing through a point on the radially-inner periphery of the fan blade, at which point the inner periphery of the fan blade is perpendicular to the said radius, does not intersect the concave surface,

3. An injection moulded radial flow fan wheel as claimed in claim 2 wherein the thickness of each blade reduces towards the blade tip, to provide a generally aerofoil section.

4. An injection moulded radial flow fan wheel as claimed in claim 1 or claim 2 wherein each of the concave and convex surfaces is defined by a respective arc of a respective circle.

5. An injection moulded radial flow fan wheel as claimed in any preceding claim wherein there is provided a prime number of blades.

6. A radial flow fan wheel having plural axially-extending blades, each blade being a generally concavo-convex member having a first convex surface and a second concave surface with a radiussed inner transition surface portion, the blades being disposed on a pitch circle centred at the axis of the fan and the fan blades are aligned on the circle such that a radius of the pitch circle passing through a point on the radially-inner periphery of the fan blade, at which point the inner periphery of the fan blade is perpendicular to the said radius, does not intersect the concave surface wherein the thickness of each blade reduces towards the blade tip, to provide a generally aerofoil section.

7. A radial flow fan wheel constructed and arranged substantially as herein described with reference to and as shown in the accompanying drawings.