EP1462658B1 - Radial fan - Google Patents

Abstract

The radial fan has a housing (1,2) with an axial fan wheel (3) and an air inlet (4) and air exit (5) with a floor area (6) and base surface (7) and wheel for spiral movement of the air. The wheel has a cover plate and a cover disc. The pressure area (8) is in an axial direction to a base surface and wheel covers have a pipe shaped cover edge.

Description

The invention relates to a radial fan with a housing and an air inlet arranged axially therein, an air outlet, a radially and axially expanding pressure chamber and a hollow cylindrical pot region for inserting a wheel.

Generic radial fans are used to suck in air and other gas such as methane or an air-gas mixture from a working environment and further promote, with both the flow velocity and the pressure of the pumped medium increases.

A major concern with such blowers is to improve the performance curve and adapt it to the desired application. There is also a great need for such radial fans, which at the same time develop a low noise at the highest possible specific air performance curve, since such radial fans are often used in places where noise is perceived as unpleasant. Various measures are in place Prior art has been proposed to improve the performance curve while reducing the noise level of fans. Thus, radial fans are known in which for this purpose, for example, between the tongue of the housing and the impeller, a wedge gap is provided on the tongue, whereby the running noise is substantially reduced.

There are various tongue shapes are known, which are also intended to reduce the running noise, especially when the blades of the blower past the tongue, the so-called rotary sound to reduce.

In the US 6,224,335 B1 discloses a blower for car air conditioners, in which a pressure chamber around a motor enclosing, designed as a pot of the blower area both axially and radially expanded towards the air outlet. The impeller is formed with a cover plate and a support disc, which is partially sunk into the pot and the outer part of the motor at a distance enclosing the outside. Both the impeller and the motor are surrounded by a housing, wherein the pot forming part of the housing is used in particular for receiving the motor, and in which extends in a small upper area in addition the lowest part of the support disc.

From the DE 100 17 808 A1 a radial fan is known, which has in the pressure chamber a guide for guiding the air flow in the pressure chamber towards the air outlet. This allows a higher specific air power. Also, the noise is reduced. With regard to further necessary increases in efficiency and increasingly stringent requirements in the area of noise development, however, this arrangement can still be improved.

It is therefore an object of the present invention to provide a radial blower which, by suitable measures in relation to the known radial blowers, has all the properties, e.g. the lowering of the noise level with a good efficiency, having improvements.

This object is achieved by the provision of a radial blower according to independent claim 1. Further advantageous embodiments, aspects and Details of the present invention will become apparent from the dependent claims, the description and the accompanying drawings.

The invention is directed to a radial blower having a housing and a wheel disposed axially therein, the housing having an axial air inlet, an air outlet, a bottom portion having a bottom reference surface orthogonal to the axis and a helical pressure chamber radially extending around the wheel extending to extends to the air outlet; and the wheel has a cover plate facing the air inlet and a support disk; characterized in that the spiral pressure space widens in the radial direction from the axis as well as in the axial direction towards the air outlet, the axial extension extending over at least 180 ° of the spiral circumference; and in the bottom portion in the axial direction beyond the bottom reference surface, a hollow cylindrical pot portion is sunk into which the wheel is inserted so that an inner side of the support disk of the wheel is flush with the ground reference surface, wherein in the housing a tongue is arranged substantially extends in the circumferential direction in the pressure chamber, and formed by the tongue leading edge in lateral projection over its course forms different angles with the bottom reference surface of the blower.

Several aspects characterize the basic, inventive wheel blower. On the one hand, this is the flush termination of the air outlet openings of the impeller with the so-called ground reference surface. This is generally defined as the area of the floor, if it had no recesses in the form of the hollow cylindrical pot and (optionally) the pressure chamber extension. The air taken in by the wheel during operation can thus enter the airspace directly without having to overcome an obstacle. On the other hand, this arrangement prevents excess air ejected from the wheel from getting underneath the wheel support plate, which would reduce the efficiency of air delivery.

Another aspect of the invention is to shape-optimize the pressure chamber that expands to the air outlet opening. In the prior art, spiraling pressure chambers are known which extend in the radial direction, i. Remove from the wheel, extend to the air outlet.

An additional expansion of the pressure chamber in allows a larger volume flow at the same differential pressure. Due to the special arrangement of the wheel in the hollow cylindrical pot and the pressure chamber extensions, an optimal transfer of air from the wheel into the pressure chamber is possible with the result of a high specific air flow.

In the sense of the present invention, the axis of rotation of the wheel or the imaginary center of rotation of the air in the spiral-shaped pressure chamber is to be understood as "axle" or "axially".

The bottom reference surface is an imaginary surface which would be the interior surface of the housing if the bottom did not have recesses such as the hollow cylindrical pot and / or the axial extension of the pressure space. The floor reference surface will be used as a reference surface to describe various elements of the radial fan of the present invention. The radial direction in the sense of the present invention is a direction extending radially away from the axis.

The axial direction is a direction parallel to the axis in one of two possible directions.

Tangential directions in the sense of the present invention are those which represent tangents of an imaginary or actual circumference.

Advantageously, the wheel is inserted into the hollow cylindrical pot area, that between the circumference of the support disc, which is completely sunk in the pot area, and the side wall of the pot area a smallest possible space is available, the width of which results from precision movements of the wheel during rotary operation.

Other features of an improved radial blower efficiency can be added in further developments of the invention to further improve by synergistic effects, the performance curve of the blower thus obtained.

The pressure chamber expands more advantageously in the axial direction beyond the bottom reference surface. In this way, the pressure chamber extension comes next to the hollow cylindrical Pot area lying as both extend in the same axial direction. The pressure chamber is delimited in the radial extension region by a wall which defines the ground boundary surface. Alternatively or additionally, the pressure chamber can also expand in the axial direction into the lid region of the housing.

Advantageously, the wheel has blades which have an arrow-shaped blade outer edge at the wheel circumference. As a result of this design of the blade outer edge, which may have, for example, the outermost point (blade tip) approximately in its center, the air conveyed by the blades is expelled at an angle which prevents a synchronous impact of the entire air front on the housing wall and thus the operating noise is reduced.

In addition, it may be advantageous for the blade outer edges of the blade to protrude in the radial direction beyond the circumference of the wheel cover disk and / or the wheel carrier disk.

In a preferred embodiment, the blades are backwardly curved with respect to the operating direction of rotation of the wheel so as to allow efficient air ejection from the blade clearances of the wheel.

The exit angle, which forms a tangent at the outer edge with a tangent at the circumference of the wheel at the point of the outer edge, is preferably ≦ 35 °, for example 25-30 ° and in a particularly preferred embodiment 22 °.

The entrance angle, which forms a tangent to an inner edge of the blade with a tangent to the circumference of the wheel at the point of the inner edge, is preferably 17-35 °, in particular, this initial angle can be 24 °.

In addition or as an alternative to the rearward orientation of the blades, they may be bent in an S-shape (the wheel or the air inlet) when viewed from above, wherein the exit angle is then preferably approximately 90 ° and the air output is increased with lower efficiency.

All blades of a wheel can have the same length and thus begin or end at circumferences with respect to the axis of rotation of the wheel, which for all blades are the same size. In a further preferred embodiment, alternately shorter and longer blades are arranged in the wheel, wherein the outer edges are all on the same circumference and the inner edges of the blades are radially offset from each other.

Another aspect of the invention is that in the housing, the tongue is arranged, which extends in the circumferential direction in the pressure chamber substantially, and formed by the tongue leading edge forms in lateral projection over its course different angles with the bottom reference plane of the blower. In other words, projecting from the housing wall, a tongue between the area in which the wheel rotates, and the air outlet, radially to the wheel into the housing in order to dissipate the airflow in the pressure chamber through the air outlet can, without too much of the Let the air get carried away again by the spinning wheel. Such a tongue basically serves to separate the pressure space from the rest of the housing space, i. the area of the housing in which there is a pressure which is lower than that at the end of the pressure chamber in front of the air outlet. The tongue should prevent a short-circuit flow. By this measure, moreover, the funnel shape of the pressure chamber is completed and the air power is additionally increased. The resulting from the different angles of the leading edge non-linear course of this leading edge is a particularly favorable form in terms of efficiency and noise reduction of the present invention. In this case, the tongue at the opposite wall of the air inlet has a minimum and in the area of the air outlet a maximum height, so that, which is extremely important for the effect, has a sloping ramp.

The tongue would best fulfill its task of preventing a short circuit flow if it were placed as close to the wheel as possible. As a result, however, the disadvantage of an enormous noise development would have to be accepted. Therefore, it is generally endeavored to design the tongue so that the lowest possible or optimized noise development is achieved with the best possible prevention of the short-circuit flux.

Here, the inventors have found that the use of steps and plateaus, even in combination, in the leading edge is particularly advantageous. It is therefore preferred that the leading edge in lateral projection forms at least one stage, in which over an area of the leading edge of the angle with the ground reference surface is substantially 90 °.

It is also preferred that the leading edge in lateral projection forms at least one plateau in which the angle with the ground reference surface is substantially 0 ° over a region of the leading edge.

When combining the two features results in a projection in the leading edge, which has an almost rectangular tip. In typical radial blowers with a wheel diameter of e.g. 12 cm, the vertical area of the leading edge may be e.g. have a height of 4 mm, while the plateau extends about 12 mm above the ground reference surface over a length of approximately 18 mm. The oblique region of the leading edge, measured from its beginning on the ground reference plane to the step, may e.g. 20 mm, while the height from the plateau to the upper end of the leading edge is e.g. 16 mm can be.

It is also possible to arrange several steps and plateaus to a stair structure at the leading edge.

It is also particularly advantageous if the leading edge has a bump, in particular in combination with certain Radausprägungen. Thus, it is preferred that the wheel has blades which have an arrow-shaped blade edge on the wheel periphery (see above) and the blade tip on the blade outer edge does not have the same orthogonal (measured in the orthogonal direction) distance to the ground reference plane as a tip of the leading edge bead. The relative arrangement of the blade tip and the hump offset to each other contributes to an additional noise reduction. In particular, it is preferred that the hump or the corner of the step are at a height that make up about two thirds of the height of the blades, measured from the support disk to the cover disk.

It may also be advantageous if the inclination of the outer edge of the blades of the wheel with the leading edge forms an angle greater than 0 °, ie the two do not run parallel to each other. This may apply either with respect to each tangent pair of points on the outer edge and points on the leading edge at the same orthogonal distance to the ground reference surface or for average slope lines from the outer edge and the leading edge, either as a whole or over partial areas, for example up to the hump and from the hump to the upper edge or from the wheel carrier to the blade tip and from the blade tip to the wheel cover disk.

Another measure for improving the flow efficiency is that the housing has a lid and on the lid an air guide ramp is arranged, which causes a stepless transition between the cover and the air outlet. Therefore, the air-guiding ramp is preferably arranged in the region of the cover which lies directly at the air outlet. Such a configuration is particularly useful when the entire opening of the air outlet is in the housing and otherwise an edge caused by the frame of the opening would be unavoidable. In embodiments in which the air outlet between the housing and cover is divided or the lid has approximately the same size as the other part and can therefore be spoken of two housing halves, such a Leitrampe is not absolutely necessary.

Advantageously, the cover disk of the wheel has an axially arranged air intake opening and the cover disk on the wheel of the air intake opening is bulged in the axial direction of the housing and on the circumference of the air inlet, a U-shaped profile is provided with which the edge of the air intake opening is sealingly engaged , By this arrangement of the cover of the wheel and air inlet, an unintentionally strong side stream of air can be prevented by this otherwise existing gap between the wheel and the air inlet.

The radial fan may further comprise in the pressure chamber a guide for guiding an air flow in the pressure chamber to the air outlet. The guide may, for example, have at least one Ausleitwulst and an inlet bead. The Ausleitwulst is disposed on at least one housing wall between the air outlet (or its opening) and the air inlet. By this Ausleitwulst the air flow is prevented from being at least partially re-absorbed by the circulating fan wheel in the pressure chamber area of the air inlet.

The run-in bead begins in certain embodiments at the inner radius of the Ausleitwulstes and follows radially outwardly substantially a ideal flow stream. As a result, the sucked air in the blower housing is passed not only through the blades of the impeller, but also through corresponding flow lines to the free pressure space, without any mixing with already compressed sucked air takes place. The inlet bead can have a lowest height in the area of the air inlet and a maximum height in the area of the air outlet.

It can be particularly advantageous if the air inlet bead has a spatially curved guide surface over its course. As a result, the sucked medium is forwarded streamlined.

In embodiments with a lid in which the radial fan according to the invention is equipped with a two-part housing, in which the housing is divided in a plane parallel to the plane of rotation and the housing peripheral wall is disposed substantially over its entire width at one of these parts, it can be particularly favorable be that the inlet bead and the Ausleitwulst are arranged as a substantially one-piece elevation on the designed as a substantially flat lid part of the housing.

Preferably, the bottom of the hollow cylindrical pot has a bevelled, inclined or curved shape, so that the depression in the axis region is smaller. The curvature of the bottom of the pot improves the stability of the housing in this area.

The radial fan according to the invention is preferably used in composite systems, which consist of other, interacting components in addition to the radial fan. Here are pneumatic composite systems in which the control is pneumatic by vacuum, electrical interconnected systems in which, in the case of a gas burner, a probe measures the exhaust gas and a computer calculates and electrically controls the gas supply; and mass flow systems in which the air mass and gas mass are measured and controlled by computer.

Fig. 1

eine perspektivische Darstellung eines erfindungsgemäßen Gehäuses mit Blick auf dessen Inneres und die Luftauslass;

Fig. 2

eine Draufsicht auf das erfindungsgemäße Gehäuse von Fig. 1;

Fig. 3

eine perspektivische Ansicht auf den Deckel des Gehäuses mit Leiteinrichtung und Leitrampe;

Fig. 4a

eine Querschnittsansicht durch ein Gehäuse mit darin betriebsbereit eingesetztem Rad;

Fig.

4b eine Querschnittsansicht durch ein Gehäuse mit darin betriebsbereit eingesetztem Rad und Zungenausbildung

Fig. 5

ein Rad mit seinen Schaufeln in Draufsicht ohne Deckscheibe, und

Fig. 6

ein Rad gemäß einer anderen Ausführungsform mit seinen Schaufeln in Draufsicht ohne Deckscheibe.

In the following the invention will be explained in more detail with reference to the figures based on embodiments. In the figures show:

Fig. 1

a perspective view of a housing according to the invention with a view of the interior and the air outlet;

Fig. 2

a plan view of the inventive housing of Fig. 1 ;

Fig. 3

a perspective view of the lid of the housing with guide and Leitrampe;

Fig. 4a

a cross-sectional view through a housing with inserted therein ready wheel;

FIG.

FIG. 4b is a cross-sectional view through a housing with the wheel and tongue formation inserted therein ready for use. FIG

Fig. 5

a wheel with its shovels in plan view without cover disk, and

Fig. 6

a wheel according to another embodiment with its blades in plan view without cover plate.

In Fig. 1 the housing 1 of a radial fan is shown in a perspective plan view of the interior. The radial blower has a lid 2 which can be placed on the housing (FIG. Fig. 3 ) and an impeller 3 on. The bottom portion 6 of the housing 1 is surrounded by spiral pressure space 8. The pressure chamber 8 has its greatest width in the radial direction at an air outlet 5 and narrows in a spiral manner on the circumference of the bottom portion 6 from the air outlet 5 away. The bottom portion 6 is in addition to the pressure chamber 8 from the bottom reference surface 7 and a relative to the bottom reference surface 7 depressed hollow cylindrical pot portion 9, which serves the partial inclusion of the wheel 3. Opening 22 in the axis of the bottom portion 6 serves to carry out a drive axle (not shown) for rotating the wheel 3.

Also recessed relative to the bottom reference surface 7, that extends in the axial direction beyond this, the pressure chamber 8 has an axial extension, which over the entire or substantially entire region of the pressure chamber 8, especially where there is also a radial extension of the pressure chamber 8 in the spiral extends. As a result, larger pressure chambers can be achieved without increasing the blower dimensions in the radial direction, which improve the performance characteristic of the radial blower due to their improved air intake.

The wheel blower according to the invention is further provided with a tongue 18. This tongue 18 extends substantially in the circumferential direction in the pressure chamber 8 inside. The tongue 18 has a leading edge 20, which has a continuous non-linear curve, wherein portions of the leading edge 20 have different slopes. Thus, the leading edge 20 includes sections of their course with the bottom reference surface 7 of the fan different angles. The tongue 18 has a minimum height on the wall opposite the air inlet 4 and a maximum height in the area of the air outlet 5. For example, the extension can have a projection or one or more steps 21 approximately in the middle of its leading edge 20 as the expression of the different angles.

A circumferential on one side 25 of the housing 1 groove 26 serves to receive an O-ring seal for sealing of the housing 1 and cover 2 to each other.

Fig. 2 shows the housing 1 of an embodiment of the radial fan according to the invention the Fig. 1 in plan view. The same elements are identified by the same reference numerals, so that their separate description is omitted. In this illustration, the pressure chamber 8 can be clearly seen over its entire spiral length and it is also apparent that the axially oriented pressure chamber extension (ie beyond the bottom reference surface in the bottom 6 recessed) substantially over the entire length of the pressure chamber 8, preferably extends over more than 180 ° of the pressure chamber circumference.

Fig. 3 shows a lid 2 for use with the housing 1 of Fig. 1 and 2 , Air inlet 4 serves for the suction of air through the wheel. A ramp 27 is arranged so that it can bridge the distance of the upper edge of the side wall 25 of the housing 1 from the opening of the air outlet 5 without edges (see. Fig. 1 ). In this way turbulence and / or backwater can be avoided at this edge. In other embodiments of the present invention, such an edge may be avoided other than by way of ramp 27.

In the FIGS. 4a and FIG. 4b shows in section both the housing 1 and the cover 2, as well as the wheel 3 and the position of the tongue to the blade geometry. The pressure chamber 8, which extends spirally radially around the wheel 3 arranged around over the larger part of the housing is in the left and in the right area of the Fig. 4a to recognize. Extending over the bottom reference surface 7 extends an axial extension 8a of the air space 8, which at the beginning of the air space 8 (facing away from the outlet opening 5) is still narrow and flat and then in the course of the circulation around the housing 2 both in the context of the radial pressure chamber extension as widened and deepened by the axial extension (see right section of the Fig. 4a ). The housing 1 final cover 2 may be designed in a special way to meet a mounting requirements and to avoid other resonant vibrations. As a result of the requirement, at least three threaded bores can be provided on the cover 2 'in the area of the inlet opening. In order that the geometry of the cover 2 'created by the required accumulation of material for the screw-in depth does not lead to problems in the production of the cover or in the pressure chamber to a negative influence on the flow conditions, the material thickening in a circumferential, inwardly opening groove 31' is formed , so that a kind of labyrinth seal is created. As a result, on the one hand, the possibility of a substantially symmetrical stress distribution in the lid during manufacture and on the other hand, an additional seal against the inlet opening. In this design, the lid may have a shape in the manner of a plate, resulting in an additional radial extension for the pressure chamber.

The wheel 3 consists except from the cover plate 11 and the support plate 12 from blades 13 and a hub 23. The support plate 12 is aligned, as clearly visible in the figure, on its inner side 12a with the bottom reference surface 7 of the pot area 9. It is as possible small distance between the periphery 15 of the support plate 12 and inner wall 10 of the hollow cylindrical pot 9 sought to minimize air turbulence and air inlet in the air space formed between the support plate 12 and the bottom of the hollow cylindrical pot area 9. The blades 13 are curved backwards. The blades 13 are tapered at their outer end arrow-shaped and protrude with a tip 17 beyond the diameter of the support disks out. The tip 17 in preferred embodiments of the invention is not at the same height above the bottom reference surface 7 as in FIG Fig. 1 represented projection 21 or its tip.

As shown in Fig. 4b, the tongue 18 rises from the bottom reference surface 7 at a predetermined angle, so that the tongue edge extends to a height of 2/3 of the exit width of the wheel is substantially rectilinear. This first section extends over a distance of about 20 to 40 mm, depending on the diameter of the wheel. At this first section includes a substantially vertical step whose height is about 1/3 of the outlet width. This stage is followed by a substantially horizontal tongue portion, which is in a predetermined ratio to the exit width, here about 1.5 X exit width. The last section of the tongue rises relatively steeply.

The inner edges 19 of the blades 13 are preferably obliquely inclined to a vertical of the support plate 12, preferably at an angle between 80 and 60 °, for example, as shown here, 76 °. The hub 23 has an axle channel 24, which is arranged axially above the opening 22 and serves to receive a drive shaft.

A U-shaped profile 31 is arranged in the cover 2 on the circumference of the air inlet 4, in which a bulged inner edge 11 b of the cover plate 11 engages so that a labyrinth seal is formed, which is to minimize a shunt of air from the pressure chamber 8 back to the air inlet 4 ,

As can be seen from the drawing, the bottom of the hollow-cylindrical pot region 9 is arched to improve the stability. In this way, it is additionally achieved that the surface area receives a reduced vibration capability and the resonance vibrations are reduced. The cavity formed between the support plate 12 and the bottom in the region of the axis can be kept small, whereby pressure losses are avoided.

Fig. 5 shows in plan view a wheel 3 according to an embodiment of the present invention. Shown is the support plate 11 with circumference 15 and blades 13 and hub 23. The blades are directed in the direction of movement backwards and protrude at their outer edges 16 beyond the circumference 15. In the middle remains a free area to suck in air with little friction. A voltage applied to a blade 13 tangent T1 intersects at the same point on the outer edge circumference of the blades adjacent tangent T2 at an angle β2, which is preferably less than 35 °, for example between 25 ° and 30 °.

Fig. 6 shows a further embodiment of a wheel 3 according to the present invention.
A tangent T3, which adjoins the inner edge 19 on the blade 13, intersects a tangent T4 at the same point on the radius of the inner edges at an angle β1 which in preferred embodiments is between 17 ° and 35 ° (cf. Fig. 6 ).

The arrangement of the elements is similar to that in Fig. 5 so that their further description is omitted. In addition to the widely inwardly extending blades 13, further outboard, shorter blades 14 are arranged in the wheel 3, which improve the air flow between the individual blades 13.

The present invention provides a radial fan for conveying air or gas mixtures, for example, for heating heaters of building heating, in which is improved by a synergistic combination of features, the performance over prior art fan shapes. Nevertheless, the fan according to the invention has a simple structure, which consists of a number of components, which corresponds to that of blowers of the prior art. The positive effects are achieved by designing the features and their skillful placement and relative arrangement.

Claims (19)

1. A radial fan comprising a casing (1, 2) and a fan wheel (3) arranged axially therein, the casing comprising an air intake (4) arranged axially, an air exhaust (5), a bottom area (6) having a bottom reference surface (7) and a spiral compression space provided radially around the wheel which extends to the air exhaust while expanding in radial direction as well as in axial direction towards the air exhaust (5);
   the wheel (3) comprising a cover disc (11) facing the air intake (4) and a support disc (12);
   wherein an axial and radial enlargement is formed at the casing extending over at least 180° of the spiral circumference, characterized in that
   a hollow cylindrical cup section (9) is recessed in the bottom area (6) in axial direction beyond the bottom reference surface (7), into which cup section the wheel (3) is inserted in such a manner that the inner side (12a) of the support disc (12) of the wheel (3) is flush with the bottom reference surface (7),
   wherein a tongue (18) is arranged inside the casing (1) extending substantially in circumferential direction into the compression space (8), and a leading edge (20) formed by the tongue (18) in a side projection along its extension forms different angles with the bottom reference surface (7).
2. The radial fan according to claim 1, characterized in that the compression space (8) is expanded in axial direction beyond the bottom reference surface (7).
3. The radial fan according to claim 1 or 2, characterized in that the casing has a cover (2), and that the compression space (8) is expanded in axial direction into the cover (2).
4. The radial fan according to one of claims 1 to 3, characterized in that the wheel (3) comprises blades (13, 14) having an arrow-shaped outer blade edge (16) at the circumference (15) of the wheel.
5. The radial fan according to claim 4, characterized in that the outer blade edges (16) of the blades (13, 14) extend in radial direction beyond the circumference (15) of the cover disc (11) and the support disc (12) of the wheel.
6. The radial fan according to claim 4 or 5, characterized in that the blades (13) are curved backward with respect to the direction of rotation of the wheel (3) during operation.
7. The radial fan according to claim 4, characterized in that the angle of emersion (β2) which a tangent (T1) at the outer edge (16) of the blade (13, 14) forms with a tangent (T2) at the circumference (15) of the wheel (3) at the point of the outer edge (16) is smaller than or equal to 35°.
8. The radial fan according to one of claims 4 to 7, characterized in that the entering angle (β1) which a tangent (T3) at an inner edge (18) of the blade (13, 14) forms with a tangent (T4) at the circumference of the wheel (3) at the point of the inner edge (18) is 17-35°.
9. The radial fan according to one of claims 4 to 8, characterized in that at least a part of the blades (13, 14) is curved in an S-shape in top plan view, having an angle of emersion (β2) smaller than or equal to 90°.
10. The radial fan according to one of claims 4 to 9, characterized in that shorter (14) and longer (13) blades are alternately arranged on the wheel (3).
11. The radial fan according to claim 1, characterized in that the leading edge (20) in a side projection forms at least one step in which over a portion of the leading edge (20) the angle with the bottom reference surface (7) is substantially 0°.
12. The radial fan according to claim 1 or 11, characterized in that the leading edge (20) in a side projection forms at least one plateau in which over a portion of the leading edge (20) the angle with the bottom reference surface (7) is substantially 90°.
13. The radial fan according to one of claims 11 or 12, characterized in that the vertical part of the leading edge has a height of 4 mm, the plateau extends over a length of about 18 mm about 12 mm above the bottom reference surface, the inclined part of the leading edge is 20 mm, measured from its beginning on the bottom reference surface to the step, and the height from the plateau to the top end of the leading edge is 16 mm, for example, all measures referring to an exiting width from the wheel of about 12 mm.
14. The radial fan according to claim 1, characterized in that the leading edge (20) comprises a projection (21).
15. The radial fan according to claim 14, characterized in that the wheel (3) comprises blades (13, 14) which have an arrow-shaped outer blade edge (16) at the circumference (15) of the wheel, and that the tip (17) of the blade at the outer blade edge (16) does not have the same orthogonal distance to the bottom reference surface (7) as the tip of the projection (21) of the leading edge (20).
16. The radial fan according to one of the preceding claims, characterized in that the housing has a cover (2), wherein an air guiding ramp (25) is arranged on the cover (2) providing for a continuous transition between the cover (2) and the air exhaust (5).
17. The radial fan according to one of the preceding claims, characterized in that the cover disc of the wheel comprises an axially arranged air intake port (3a), the cover disc (3) bulging in axial direction at the edge (3b) of the air intake port of the casing and a U-shaped section (31) being provided at the circumference of the air intake (4) which is in sealing engagement with the edge (3b) of the air intake port (3a).
18. The radial fan according to one of the preceding claims, characterized in that the bottom of the hollow cylindrical cup section (9) has a form differing from a flat plane, for example inclined, corrugated or cambered.
19. The radial fan according to one of the preceding claims, characterized in that the wheel comprises bores in the support disc (12) in the area of the hub for generating negative pressure behind the support disc.

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