EP1747378B1 - Fan arrangement - Google Patents

Abstract

A fan arrangement has an electric motor (18) that serves to drive a fan wheel (26; 170) and that has an internal stator (44) and an external rotor (22), with which latter the fan wheel is drivingly connected. Arranged on a circuit board (17) are components (11) that are coolable, at least in part, by an air flow (13) generated during operation by that fan wheel (26; 170). Associated with the fan wheel is an air-directing element (100) that is mounted on the circuit board (17) separately from the electric motor (18) so that, in operation, a cooling air flow (13) is generated which emerges from the fan arrangement (16) between the circuit board (17) and air-directing element (100).

Description

The invention relates to a fan assembly in the manner of a mini fan. Such fans are also referred to as small or micro fan. A fan assembly with the features of the preamble of claim 1 is for example from the US-A-2003/0048084 known.

• die Lüfter der ebm-papst-Serie 250 Abmessungen von 8 x 25 x 25 mm,
• die der ebm-papst-Serie 400F Abmessungen von 10 x 40 x 40 mm,
• die der ebm-papst-Serie 400 von 20 x 40 x 40 mm, und
• die der ebm-papst-Serie 600 von 25,4 x 60 x 60 mm.

Mini fans have very small dimensions. For example

• the fans of the ebm-papst series 250 dimensions of 8 x 25 x 25 mm,
• the ebm-papst 400F series dimensions of 10 x 40 x 40 mm,
• that of the ebm-papst 400 series of 20 x 40 x 40 mm, and
• that of the ebm-papst 600 series of 25.4 x 60 x 60 mm.

The power consumption of such fans is 0.4 ... 0.6 W for the 250 series, 0.7 ... 0.9 W for the 400F series, and 0.9 for the 400 and 600 series. 1.6 W. Its typical weight ranges from 4 to 35 grams.

Electronic devices are now being provided with more and more functions and installed in smaller and smaller cases. This causes an increase in the heat loss in the electronic circuit of such a device. A particular problem arises from the fact that in such a circuit individual elements become particularly hot, e.g. Power semiconductors, microprocessors, resistors, with which a motor current is measured, etc. These particularly hot elements generate on the PCB so-called hot spots, a term borrowed from geology. For example, Iceland has many hot springs and geysers, so many hot spots.

The cooling of such hot spots by means of conventional equipment fans is inefficient because equipment fans, as e.g. used in computers to produce a relatively diffuse air flow, which dissipates enough heat from the housing, but does not allow targeted cooling of individual hot spots.

It is therefore an object of the invention to provide a new fan assembly, which is particularly suitable for targeted cooling on a circuit board or the like.

According to the invention, this object is achieved by the subject matter of claim 1. Such a fan assembly can be placed directly on a circuit board where the greatest heat loss is generated. The brushless control or regulation of the electric motor of such a fan assembly can be done by means of switching elements, which are integrated into the electronics on the circuit board to be cooled. These switching elements can also change the speed of such a fan assembly depending on the temperature, so that the speed increases with increasing temperature.

Particularly advantageous that such a fan assembly allows a very low height, since their storage unit and the inner stator of their electric motor similar to an electronic component can be mounted directly on the circuit board and soldered, and since the air guide ring can be mounted as a separate unit on the circuit board, so that in fact the circuit board is a component of the fan and its height reduced accordingly. This allows the use of higher fan wheels and thus the increase in air performance.

When the assembly operations are completed, the fan can be mounted and secured against removal. This also makes it possible to mount the fan wheel, which is very sensitive to such mini fans, at a time when its damage is largely ruled out.

By appropriate design of the air guide, the exiting cooling air can be directed either targeted to certain components, or the air can escape uniformly in all directions and cool all the surrounding components evenly. Here are many variations.

To provide high cooling performance, the shape of its fan blades is in addition to the speed of such a mini fan of great importance. The number of blades, their angle of attack to the hub, and the blade radius are important variables. If an axial fan is used, good results are achieved by using approximately trapezoidal fan blades. Also a radiused

Blade curvature in the radial direction may be advantageous.

A radial fan has special advantages for applications on printed circuit boards. The fan blades are preferably embedded in an upper and a lower air guide plate, resulting in an optimal air flow. The air guide plates cause the characteristic as a diagonal fan and have corresponding cross-sectional profiles.

In such a case, it may be advantageous to attach a stationary air guide plate to the printed circuit board in order to reach even further hot spots on the printed circuit board. However, there will also be cases in which such an air guide plate can be dispensed with, namely when only heat sources which are in the immediate vicinity of such a mini-fan must be cooled.

Fig. 1

eine Draufsicht auf eine Leiterplatte 17, bei der an einer Stelle mit besonders hoher Wärmeentwicklung eine Lüfteranordnung 16 zur lokalen Wärmeabfuhr angeordnet ist,

Fig. 2

einen Schnitt durch eine Leiterplatte und durch den Innenstator eines Minilüfters, der an dieser Leiterplatte befestigt werden soll, in stark vergrößertem Maßstab,

Fig. 3

eine nochmals vergrößerte Darstellung einer Einzelheit III der Fig. 2,

Fig. 4

eine erste Alternative eines Schnitts, gesehen längs der Linie IV-IV der Fig. 2,

Fig. 5

eine zweite Alternative des Schnitts IV-IV,

Fig. 6

eine Darstellung analog Fig. 2, bei welcher die Leiterplatte und der Innenstator mechanisch und elektrisch miteinander verbunden sind,

Fig. 7

eine Darstellung analog Fig. 6, wobei zusätzlich der zum Innenstator gehörende Rotor (und das mit diesem verbundene Lüfterrad) vor der Montage dargestellt sind,

Fig. 8

eine Darstellung analog Fig. 7, aber nach der Verheiratung von Innenstator und Rotor,

Fig. 9

eine Darstellung analog Fig. 8, welche die Leiterplatte, den auf dieser befestigten Lüfter, und einen Luftleitring zeigt, letzteren vor seiner Montage auf der Leiterplatte, wobei er links im Schnitt und rechts ungeschnitten dargestellt ist,

Fig. 10

eine Darstellung analog Fig. 9, aber nach der Montage des Luftleitrings auf der Leiterplatte,

Fig. 11

eine Variante, bei der der Luftleitring auf der Leiterplatte montiert wurde, bevor der Rotor montiert wird; diese Variante kann in vielen Fällen sehr vorteilhaft sein,

Fig. 12

die Anordnung nach Fig. 10 nach ihrer Montage im Gehäuse eines elektrischen Geräts,

Fig. 13

eine raumbildliche, stark schematisierte Darstellung des Lüfterrotors für den Motor der Fig. 10,

Fig. 14

die Abwicklung eines Lüfterflügels 26 der Fig. 13,

Fig. 15

einen Radialschnitt durch einen Flügel 26 des Rotors der Fig. 13,

Fig. 16

eine schematische Darstellung zur Erläuterung der Fig. 17, und

Fig. 17

eine raumbildliche Darstellung eines Rotors, wie er bei der Lüfteranordnung nach Fig. 12 bevorzugt verwendet werden kann.

Further details and advantageous developments of the invention will become apparent from the following described and illustrated in the drawings, in no way as a limitation of the invention to be understood embodiments, and from the dependent claims. It shows:

Fig. 1

a top view of a printed circuit board 17, in which a fan assembly 16 is arranged for local heat dissipation at a location with particularly high heat generation,

Fig. 2

a section through a printed circuit board and through the inner stator of a mini fan, which is to be attached to this circuit board, on a greatly enlarged scale,

Fig. 3

a further enlarged view of a detail III of Fig. 2 .

Fig. 4

a first alternative of a section, seen along the line IV-IV of the Fig. 2 .

Fig. 5

a second alternative of section IV-IV,

Fig. 6

a representation analog Fig. 2 in which the circuit board and the inner stator are mechanically and electrically connected to each other,

Fig. 7

a representation analog Fig. 6 additionally showing the rotor belonging to the inside stator (and the fan wheel connected to it) before assembly,

Fig. 8

a representation analog Fig. 7 but after the marriage of inner stator and rotor,

Fig. 9

a representation analog Fig. 8 showing the printed circuit board, the fan mounted thereon, and an air guide ring, the latter before being mounted on the printed circuit board, being left uncut on the left and uncut on the right,

Fig. 10

a representation analog Fig. 9 but after mounting the air guide on the PCB,

Fig. 11

a variant in which the air guide ring was mounted on the circuit board before the rotor is mounted; this variant can be very beneficial in many cases,

Fig. 12

the arrangement after Fig. 10 after being mounted in the housing of an electrical appliance,

Fig. 13

a spatial, highly schematic representation of the fan rotor for the engine of Fig. 10 .

Fig. 14

the settlement of a fan blade 26 of the Fig. 13 .

Fig. 15

a radial section through a wing 26 of the rotor Fig. 13 .

Fig. 16

a schematic representation for explaining the Fig. 17 , and

Fig. 17

a three-dimensional view of a rotor, as in the fan assembly after Fig. 12 preferably can be used.

Fig. 1 shows a plan view of a circuit board 17, on which various electronic components are arranged. In the upper half there are components 11 which generate a lot of heat during operation and thus a hot spot. Approximately in the center of this hot spot is a fan assembly 16 of the type as described in more detail below with examples. The fan assembly 16 causes a targeted cooling of the components 11, since it generates a uniform air flow 13 in all directions. she is in Fig. 1 shown only schematically. Preferred embodiments will be apparent from the following figures.

It should be noted that the air flow 13 can also be targeted to individual components, and that in sectors where little cooling air is needed, the air flow can be reduced accordingly. In Fig. 1 For example, this would be the sector between 4 o'clock and 5 o'clock, and between 8 and 9 o'clock, where the density of the components 11 is relatively low and consequently less heat must be dissipated. This control of the air flows is possible, for example, by blending, or in many other ways. For this reference is made to technical literature.

The mini-fan 16 is driven by an external rotor motor 18 (FIG. Fig. 8 ), and Fig. 2 shows the circuit board 17 to which the stator 44 of the motor 18 is attached.

According to Fig. 7 and 8th the motor 18 has an outer rotor 22 with a rotor bell 24, on whose outer circumference fan blades 26 are provided, which are also referred to as fan blades. In the rotor bell 24 is a magnetic yoke 27 made of soft iron, and on the inside there is a radially magnetized rotor magnet 28 (FIG. Fig. 8 ), which can be magnetized, for example, four-pole. The outer diameter D ( Fig. 7 ) of the outer rotor 22 may be, for example, in the range of about 14 to about 35 mm. Of course, the use of the invention is not excluded even with larger engines, but this area is the main field of application.

The rotor bell 24 has in its center a hub 30, in which a correspondingly shaped upper shaft end 32 of a rotor shaft 34 is secured by heat-conducting plastic tips or the like, the lower, free shaft end is denoted by 35. The diameter of the end 35 decreases downwards.

For radial mounting of the shaft 34 is a sliding bearing 36, which is preferably designed as a double sintered bearing. Alternatively, to achieve particularly high lifetimes, a bearing with bearings possible. - The sliding bearing 36 is fixed in a bearing tube 38 by pressing. The bearing tube 38 is preferably made of steel, brass, or other suitable material. The use of a plastic is not excluded. The bearing tube 38 is provided with a radial projection in the form of a flange 39, which extends approximately perpendicular to the axis of rotation 41 of the rotor 22 in this example. On the outside of the bearing tube 38 of the inner stator 44 of the motor 20 is fixed, preferably by pressing, cf. Fig. 2 ,

The sintered bearing 36 has a bulbous portion 42 having a diameter which corresponds approximately to the diameter of a cylindrical portion of the inner side 40 of the bearing tube 38 and is dimensioned so that a tight fit results during assembly.

As in Fig. 2 This allows a reliable bearing of the shaft 34 and a correspondingly long running time of the motor 20, even at the high rotational speeds of these mini-fans, often in the range of 6000 to 9000 U / min lie.

The stator 44 has in the usual way a laminated core 45 which is encapsulated with a bobbin 46, on which a winding 47 is wound. Alternatively to the design shown here with salient poles, the stator 44 could be e.g. Also be designed as Klauenpolstator.

The shaft 34 has at its free end portion 35 an annular groove 58 which in Fig. 7 is shown and are locked into the after mounting elastic locking hooks 60, see. Fig. 8 , These hooks 60 have a smaller axial extent than the annular groove 58, and their function is to secure the rotor 22 against unintentional withdrawal.

The elastic latching hooks 60 are not against the shaft 34 at any point. They are formed in one piece with a cover 62 and are located on a lubricant depot 64, at the bottom of which there is a recess 66 in which a track 68 (see FIG. Fig. 7 ) of the shaft 34 rotates. Recess 66 and track 68 together form a thrust bearing for the shaft 34th

As Fig. 2 is particularly clear, the bearing tube 38 has in its upper portion a hollow cylindrical portion 42, and this extends downwards in the manner of a hollow truncated cone 70, which merges into an approximately cylindrical portion 71 below, in which annular grooves 72, 73 with an approximately semicircular cross-section are incorporated, cf. Fig. 3 , Downwardly, the cylindrical portion 71 widens in the manner of a hollow truncated cone 74. On its outer side, the bearing tube 38 has a cylindrical portion 75 at the top, onto which the inner stator 44 is pressed, cf. Fig. 2 , And the section 75 via a shoulder 76 in the top of the flange 39. This forms during assembly a stop for the bobbin 46, see. Fig. 2 ,

The underside 77 of the flange 39, in turn, merges into a cylindrical section 78 on the outside of the bearing tube 38. This section 78 has a larger diameter than the section 75, and it continues in the cylindrical outer side 79 of the latch cover 62, so that bearing tube 38 and latch cover 62 together form a cylindrical outer side, according to Fig. 2 and 6 is adapted to be pressed into a cylindrical opening 80 of the circuit board 17.

This allows easy installation, but requires that according to Fig. 2 an axial force F is generated on the bobbin 46 in the downward direction, ie the assembly in the opening 80 must be made before the rotor 62 is mounted. The invention makes this possible without problems, ie, first according to Fig. 2 the part with the inner stator 44 is pressed in the direction of an arrow 82 in the opening 80, and then, at a later date, according to Fig. 7 and 8th the engine completed by inserting the rotor 22.

As Fig. 3 shows, the detent cover 62 has on its outer side 83 Rastwülste 84, 85, which are visible only in this enlarged view. When the detent cover 62 is press-fitted into the opening 71, the beads 84, 85 form a slight detent and simultaneously provide an excellent seal, so that no lubricant can drain from the depot 64. The elastic plastic used for the lid 62 is so heat resistant that it is not damaged in a solder bath as it passes through it.

In the bobbin 46 four wire pins 88 are fixed at uniform intervals of 90 °, to which the terminals 90 of the winding 47 are connected. This usually includes two phases, namely a drive winding and a sensor winding. To carry out the pins 88, the flange 39 either has the shape Fig. 4 with four radial grooves 92, or the square shape 39 'according to Fig. 5 , The circuit board 17 has corresponding holes 94 into which these wire pins 88 are inserted during assembly and then soldered to a solder 96 in the solder bath, wherein the solder 96 rises due to capillary action through the hole 94 upwards and also the winding terminal 90 with the Pin 88 soldered. This solder 96 then simultaneously represents the electrical and a mechanical connection of the inner stator 44 with the printed circuit board 17. This simple type of attachment is possible because such a mini fan only has a weight of eg 20 g.

The hub 30 has its in Fig. 7 lower end an undercut 112, which hurls the lubricant to the outside. The bearing tube 38 also has an undercut 114 at its upper end on the inside, which prevents lubricant from leaking out of it when the fan 16 is inclined. For this reason, the gap 116 between the bearing tube 38 and rotor 22 is very narrow and dimensioned in the manner of a capillary gap to prevent the escape of lubricant. The lubricant thrown outwardly from the undercut 112 flows down the inner wall 46 of the bearing tube 38 down to the sintered bearing 36 and through this further down into the reservoir 64. In this way one achieves that in the reservoir 64 and its recess 66 is constantly a sufficient supply of lubricant.

Assembly

According to Fig. 2 and 6 First, the cylindrical part 71, 79 of the bearing tube 38 is pressed into the opening 80 of the circuit board 17, whereby the image in accordance with Fig. 6 and 7 results. In this state, the circuit board 17 is soldered in the usual manner in a solder bath. (The components 11 are in the Fig. 2 ff. not shown.)

Subsequently, according to Fig. 7 and 8th the rotor 22 is married to the inner stator 44, according to Fig. 8 the safety members 60 are first deflected outwardly and then snap into the annular groove 58 of the rotor shaft 34 and thus prevent the rotor 22 can be withdrawn again. To avoid friction losses, the safety members 60 are not against the annular groove 58 at. This increases the efficiency of such a small or micro motor.

During transport, you can transport the rotors 22 separately and install only in place, where you have previously fill appropriate lubricant in the depot 64, 66. Likewise, a transport with mounted rotors 22 is possible.

Since the magnet 28, as in Fig. 10 shown, with respect to the axial direction of the motor 20 is not arranged symmetrically to the stator plates 45, but offset relative to these upward, acts on the rotor 22, a magnetic force in the downward direction, and this presses the tip 68 into the recess 66 and prevents rattling of the rotor during vibrations.

Following assembly, the fan 16 is tested in the usual way. The commutation can e.g. by means of the induced voltage, for which a corresponding sensor winding is provided, or one uses a semiconductor sensor which detects the position of the rotor 22.

As in Fig. 9 is shown, an air guide member 110 is provided according to Figure 10 is mounted around the fan 16 to improve its efficiency. you refers to this member as Luftleitdüse 100, or as an air nozzle, or as the outer casing of the fan.

It has an upper, annular flange 102, which is provided with an annular groove 104 for a sealing ring 106. Further, it has a lower flange 108 which, as shown, is inclined upwardly at an angle ∂ (delta), e.g. at 7 °. The annular flanges 104, 108 are interconnected by a tubular portion whose lower part 117 is cylindrical and whose upper part 118 has the shape of a hollow truncated cone which widens upwards. This shape creates a venturi effect and improves fan performance.

At the lower flange 108 three spacers 120 are provided, as well as three latching hooks 122nd Fig. 9 shows only two spacers 120 and two latching hooks 122 because of the partially cut representation.

According to Fig. 10 the air guide member 100 is hooked by means of its latching hooks 122 in corresponding recesses 124 of the circuit board 17, wherein the spacer members 120 are inserted with lower, pin-shaped portions 121 of smaller diameter in corresponding recesses 123 of the circuit board 17 and the air guide member 100 at a predetermined distance L ( Fig. 10 ) from the circuit board 17. This type of attachment is very simple and reliable.

As Fig. 10 In operation, air is sucked along the arrows 126 in the vertical direction during operation and then blown out between the circuit board 17 and the lower flange 108 in an approximately horizontal direction (arrows 127), in all directions, ie all surrounding components 11 (FIG. Fig. 1 ) are cooled in the same way.

As an alternative, according to Fig. 11 After installation of the inner stator 44 on the circuit board 17, first the air guide ring 100 are mounted in the manner described, and only then mounted the rotor 22. The advantage is that in this case the rotor 22 is not damaged during assembly of the air guide ring 100 can be. In such small and micro fans, the rotor 22 is due to its extremely thin shaft 34 and its small size, which is reminiscent of a toy, especially sensitive and must be handled carefully and like a raw egg. at Fig. 11 In this case, the rotor 22 is inserted through the opening of the air guide ring 100, which serves as a guide.

Fig. 12 shows the arrangement according to Fig. 10 after installation in an electronic device 130. The flange 102 is in this case with its sealing ring 106 against the in Fig. 12 upper housing wall 132, which has an air inlet opening 134 in the middle, which is the same size as the upper opening of the air guide 100th

On the wall 132, a protective grid 136 is engaged, which is provided with a plurality of openings 138. Under the protective grille 136, a dust filter 139 may still be located, e.g. to prevent the ingress of sand or animals. The path of the sucked air is indicated at 140. If necessary, it can also exit the device 130 laterally through corresponding openings.

The Fig. 13 to 15 show a preferred form of the fan blades 26 for an axial fan as shown in FIG Fig. 13 is shown. In addition to the speed of the fan and the number of its wings, their angle of attack relative to the hub and the vane radius and the axial length of the wings and their geometry have great importance, especially in such small fans.

Fig. 13 shows the direction of rotation 141. The fan blades 26 extend axially over the entire axial length of the rotor 22nd Fig. 13 shows for comparison with dashed lines the "normal" shape of such wings. In the present case, seen in the direction of rotation rear part 142 of the normal wing 26 is not present, so that there is an approximately trapezoidal wing shape. The reason for this deviating from the "normal shape" shape of the wings 26 is that thereby the lateral outflow of the extracted air, as shown in Fig. 13 at 127 is facilitated, that is, the pressure build-up in the lateral direction is improved. With the "normal" blade geometry, only a small pressure build-up in the lateral direction and consequently only a small flow of cooling air to the printed circuit board 17 would be obtained.

If the extension of a wing 26 is described along the outside of the rotor 22 with x ₁ , and the extension of the wing along its outer circumference with x ₂ , as in Figure 13 x1> x2, ie x1 represents the base of a trapezoid. Figure 14 shows such a wing in development. The leading edge is denoted by 144 and the rear edge by 146. The direction of rotation 141 is also entered.

Fig. 15 shows a section, seen along the line XV-XV of Fig. 14 , It can be seen that the wings 26 are also curved, seen in a radial section, and have a radius of curvature R. R preferably has a value that is ≤x ₁ . The convex side 145 of the wings 26 faces the air inlet side 126. Although the curvature R causes a slight reduction in the pressure build-up, but the radial outflow of air (arrows 127 of the Fig. 13 ) is thereby improved. This curvature (radius R) favorably promotes the pressure build-up in the area of the air guide ring 100.

Fig. 16 schematically shows a radial fan wheel 160 which rotates in a clockwise direction, as indicated by the arrow 141. From the outer rotor 22 is a radial fan blade 162, which is curved forward, and its radially outer portion encloses with the periphery 164 of the fan wheel 160 an angle α ₁ (alpha1), which is greater than 90 °.

For comparison, in Fig. 16 also a radial fan blade 166 is shown, which is curved backwards, ie its radially outer portion encloses with the periphery 164 an angle α ₂ (alpha2), which is smaller than 90 °.

Blades 162, which are curved forward, achieve a greater deflection of the flow, ie a greater energy conversion into moving air. However, you need them with a volute casing and must first build up pressure through a diffuser, which is downstream of such an impeller with blades 162.

In contrast, generates a fan 160 with backward curved blades 166 the pressure already in the fan, so that can be dispensed with a volute casing and a diffuser, which means a great simplification in fans for the cooling of printed circuit boards and allows air flow in all directions.

Fig. 17 shows a preferred embodiment of such a radial fan 170 with backward curved blades 166, in which therefore the convex side rotates forward, so here a volute casing and a diffuser can be omitted. Again, an air guide 100 is used with advantage, as in Fig. 9 however, only part 108 is needed and sections 102 and 118 may be omitted.

The fan wheel 170 has an upper air guide plate 172 with a curved cross-section, whose preferred cross-sectional shape corresponds approximately to the sector of an ellipse. Furthermore, the fan wheel 170 has a lower air guide plate 174, which, viewed in cross-section, runs approximately parallel to the upper plate 172. Both plates extend to the air inlet opening 134, wherein the upper edge of the plate 172 is arranged very close to the edge of the opening 134.

The fan blades 166 are embedded in the region of the outlet between the plates 172, 174 in the manner shown and curved backwards, cf. Fig. 17 , ie the pressure build-up already takes place here in the fan.

Around the fan wheel 170, a stationary air guide plate 108 is preferably arranged, which is aligned with the outer edge of the upper air guide plate 172 and together with the circuit board 17 forms an air passageway, which widens slightly towards the outside. In this way, one can generate a targeted air flow, so that even more distant components 11 can be cooled. If all components 11 to be cooled are in the vicinity of the fan, it may be possible to dispense with the stationary air guide plate 108. This is just as fastened as the air guide member 100 of the first embodiment, ie with the same latching hooks and spacers, which is why they will not be described again. Again, the assembly of the air guide actuator 108 is extremely simple.

Naturally, many modifications and modifications are possible within the scope of the present invention.

Claims (22)

1. Fan arrangement having an electric motor (18) which serves to drive a fan wheel (26; 170) and has an inner stator (44) and an outer rotor (22), with which latter the fan wheel (26; 170) is in driving connection; also having a printed circuit board (17) on which there are disposed components (11) which can be cooled, at least partly, by a flow of air (13) generated by the fan wheel (26; 170) in the course of operation,
   characterised by an air-guiding member (100) which is associated with the fan wheel (26; 170) and is fastened separately to the printed circuit board (17) by the electric motor (18), so that a flow of cooling air (13), which emerges from the fan arrangement (16) between the printed circuit board (17) and the air-guiding member (100), is generated in the course of operation.
2. Fan arrangement according to claim 1, in which the air-guiding member (100) has, on its side that faces away from the printed circuit board (17), an aperture (117, 118) which makes it possible (Fig. 11) to fit the fan wheel (26; 170) and outer rotor (22) through the said aperture (117, 118) after the air-guiding member (100) has been fitted to the printed circuit board (17).
3. Fan arrangement according to claim 1 or 2, whose electric motor (18) has a rotor shaft (34) which is mounted in a bearing arrangement (36), said bearing arrangement (36, 60, 66) being constructed in such a way that, after being fitted, the rotor shaft (34) is secured against being withdrawn from the bearing arrangement.
4. Fan arrangement according to claim 3, in which the bearing arrangement (36, 60, 66) has at least one radially deflectable, stationary safety member (60) which is constructed for engagement in an annular groove (58) in the rotor shaft (34).
5. Fan arrangement according to one of the preceding claims, in which the air-guiding member (100) has a portion (108) which combines with the printed circuit board (17) to form an air exit (127) which widens in the radial direction.
6. Fan arrangement according to one of the preceding claims, in which the air-guiding member (100) narrows region-wise, starting from the air entry side (126), after the manner of a venturi nozzle (118, 117).
7. Fan arrangement according to one of the preceding claims, in which the air-guiding member (100) is connected to the printed circuit board (17) via at least one latching member (122).
8. Fan arrangement according to claim 7, in which the at least one latching member (122) is arranged on the air-guiding member (100) and is constructed for latching connection with an associated clearance (124) in the printed circuit board (17).
9. Fan arrangement according to claim 7 or 8, in which the at least one latching member is constructed as a resilient latching hook (122).
10. Fan arrangement according to one of the preceding claims, in which spacing members (120), which determine the size of the air exit (127), are provided between the air-guiding member (100) and the printed circuit board (17).
11. Fan arrangement according to claim 10, in which the spacing members (120) are connected to the air-guiding member (100).
12. Fan arrangement according to claim 11, in which the spacing members (120) are constructed in one piece with the air-guiding member (100).
13. Fan arrangement according to one of the preceding claims, in which a sealing arrangement (106) is provided on the air-guiding member (100) in the region of the air entry (126).
14. Fan arrangement according to one of the preceding claims, in which the fan wheel is constructed as an axial fan wheel (26).
15. Fan arrangement according to claim 14, in which the axial fan wheel has trapezoidal fan blades (26) in which the extension (x₁) in the region of the radially inner portion (22) is greater than the extension (x₂) in the region of the outer periphery.
16. Fan arrangement according to claim 15, in which the fan blades (26) have a curvature (R), referred to a radial section, in which the convex side faces towards the air entry side (126).
17. Fan arrangement according to claim 16, in which the radius (R) of curvature is smaller than, or equal to, the extension (x₁) of a fan blade (26) on the radially inner side of the latter.
18. Fan arrangement according to one of claims 1 to 13, in which the fan wheel is constructed as a radial fan wheel (170).
19. Fan arrangement according to claim 18, in which the radial fan wheel (170) has vanes (166) which are curved rearwards.
20. Fan arrangement according to claim 19, in which a vane (166) follows, in the region of its outer end, a path in the radial direction which forms an angle (α₂) with a tangent on the outer periphery of the fan wheel (170) at that point, which angle is smaller than 90°.
21. Fan arrangement according to one of the preceding claims, in which the vanes (166) are arranged between two air-guiding bodies (172, 174) which combine to form a curved air-guiding duct which extends from an axial inlet to a radial outlet.
22. Fan arrangement according to claim 21, in which the vanes (166) are arranged in the region of the radial outlet of the air-guiding bodies (172, 174).

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