EP2122182B1 - Ventilator wheel, system and transmission line - Google Patents

Description

The invention relates to a fan, a system and a transmission series.

The DE 1 253 402 B discloses a noise reduction device on multi-bladed radial fans for ventilating electrical machines. The fan blades are arranged irregularly according to a method described in more detail in the document, so that there are no adjacent pairs of fan blades which enclose the same angle.

From the WO 91/02165 A a fan is known at the central hub fan blades are arranged at regular intervals. The fan blades have a different curvature, so that their ends have irregular intervals.

From the US 5,478,201 A a suction nozzle and an impeller for a fan with regularly arranged wings is known. The suction nozzle has an elliptical cross section in a plane in which the axis of rotation of the fan is located. The impeller is sheathed and has a similar elliptical cross-section as the suction nozzle. The impeller is dimensioned such that after assembly of the fan, the sheath covers the stationary suction and rotates around it.

From the GB 2 090 338 A is a fan with regularly arranged fan blades known. The fan has an inverted shell surrounding a hollow stump. The hollow stump is connected to the shell by a set of oblique airfoils, the axial extent of the airfoils corresponding to the axial extent of the shell.

From the US 1 447 915 A and the US 1 447 916 A Fans with regularly arranged blades are known. The fans consist of a radially outwardly open fan wheel, wherein a radially outwardly open annular air outlet opening is formed, which extends over the outer edges of the blades and rotates with the fan.

From the WO 97/09535 A discloses a radial impeller with regularly arranged fan blades, wherein the fan blades open in the radial direction are mounted between a front and a rear plate. The fan blades are configured to extend radially farther outward on one of the two plates than on the other plate.

From the US 3,285,502 a fan is known which has a plurality of unevenly spaced fan blades, wherein the center of gravity of the fan wheel is located in the axis of rotation.

From the EP 0 757 181 A2 an axial fan is known, in which the fan blades are arranged radially between a hub and a circumferential ring, wherein each adjacent fan blades have different distances from one another.

The invention is therefore the object of developing a fan, so that the environmental impact is reduced.

According to the invention the object is achieved in the fan according to the features indicated in claim 1, in the system according to the features specified in claim 9 and in the transmission series according to the features indicated in claim 12.

Important features of the invention of a fan wheel are that a first fan blade has a first angular distance to a first circumferentially adjacent fan blade and the first fan blade has a second angular distance to a second fan blade adjacent in the opposite direction, wherein the first angular distance is smaller than the second angular distance , Alternatively, the sequence in the circumferential direction of the angular intervals of a respective wing to the next adjacent in the circumferential direction Fan blades at least two different types of angular distance values. Thus, a simple embodiment is specified in which the fan blades are not necessarily arranged regularly. The advantage here is that the fan blades produce periodic excitations whose main frequency component is lower than would be the case if all angular distances were equal. In particular, the frequency component is at most half that of a regular arrangement of the fan blades.

In an advantageous embodiment, each air duct is limited by at least fan blades, an air guide ring and / or a base body, wherein the cross section of the air channel has a minimum in the course from inside to outside. Thus, air ducts are formed with a nozzle effect. These nozzles advantageously cause a directed flow of cooling air.

In an advantageous development, the minimum of the cross section of the air duct is effected by a minimum of the distance between the base body and the air guide ring, in particular by a minimum of the distance between the sectional figures of the body with an axial plane on the one hand and the air guide ring with the axial plane on the other. The fan wheel advantageously comprises a main body, fan blades and an air guide ring, wherein the base body has a frustoconical region and form at least two fan blades, a segment of the frusto-conical region and a segment of the air guide a radially extending air channel whose cross-section has a minimum in the radial course. The advantage here is that the fan is easily manufacturable, since the geometric properties of the air duct, in particular the nozzle shape, with the boundary surfaces of air guide ring and body is easy to manufacture and controllable. In addition, the main body of the fan is occupied in addition to its holding function with a Luftleitfunktion. As a result, parts can be saved.

In an advantageous embodiment, the cross section of the air guide ring is convex on its inner side and concave on its outer side, in particular shaped such that the wall thickness is substantially constant. The consistency of the wall thickness depends on the manufacturing tolerances of the production technology and on the speeds at which the fan is used. The outer shape of the air guide thus follows substantially the inner shape of the air guide ring, and it is an advantageous form of the air guide at formed at the same time low material usage. The advantage here is that for the air guide little material must be used, so that its moment of inertia is minimized.

In an advantageous development, the base body has a frustoconical region and the air guide ring is concentrically inscribed in a mathematical cone such that the air guide touches the mathematical cone in a first and a second axial region and in a third axial region between air guide ring and the mathematical cone a minimum distance is provided, wherein the third axial region is arranged between the first axial region and the second axial region, and at least two fan blades, a segment of the frusto-conical region and a segment of the air guide ring form an outwardly extending air channel. The advantage here is that the constructional and manufacturing technology easy to handle geometric shapes, a nozzle-like air duct is available.

In an advantageous development, at least two different types of air ducts are formed on a fan. Preferably, each air channel is characterized by a geometric size, and the sequence of the geometric size of the air ducts is an irregular sequence in one revolution of the fan. More preferably, the geometric size of each air duct is the angle between the limiting fan blades or the angle of a limiting fan blade a fan-fixed reference direction. Alternatively, the geometric size of each air duct is the angular position of the center of gravity or the center plane of the air duct or the angle of an excellent direction of the air duct to a fan-fixed reference direction. Thus, simple geometric characteristics are given, which are heranziehbar to form a fan according to the invention.

In an advantageous development, the center of gravity formed by all the fan blades is in the center of the fan. The advantage here is that with reduced noise pollution additional loads on the bearings and the material can be avoided by imbalance.

In an advantageous development, the maximum axial extent of the fan blades is greater than the maximum axial extent of the air guide ring.

In an advantageous development, the maximum axial extent of the fan blades is more than twice as large as the maximum axial extent of the air guide ring. The advantage here is that a radial or laterally oblique discharge of the cooling air is made possible. Thus, the fan is used in various transmissions or in general systems with fan.

In an advantageous development, the maximum radial extent of the fan blades is greater than the minimum radial extent of the air guide ring. The advantage here is that large air outlets are formed, can be conducted through the cooling air to the housing to be cooled.

In an advantageous development, the fan blades on the suction side are axially retracted up to a radius, in particular by more than one third of the maximum axial extent of the fan blades. The advantage here is that at a small distance from the fan, a fan cover can be placed, wherein at the intake ports or air inlets generated by the fan blades noise can be reduced.

In an advantageous development, each fan blade on a plane of symmetry, in which preferably the axis of rotation of the fan is. Thus, a rotationally invariable fan wheel is formed in a simple manner, and cooling air always flows in the same direction through the air channels.

In an advantageous development, the radial extent of the base body is smaller than the outer diameter of the fan wheel, in particular at least fifteen percent smaller than the inner diameter of the air guide ring. Thus, advantageous geometric conditions are formed, in which the cooling air can flow particularly effective.

In an advantageous development, the air ducts each form an air outlet, which comprises a radially aligned and an axially aligned portion. Thus, the fan on different transmissions, especially directly in front of a housing wall or on a Kegelradtopf operable.

Important features of the invention of a system, in particular a transmission, are that a fan with a fan with fan blades and a fan cover is included, wherein the fan as described above according to the invention asugebildet and wherein the fan cover surrounds the fan at least partially and the fan cover a Area having axial air inlets, wherein the fan blades in a first portion of the range with axial air inlets have a constant distance from the fan cover and in a second portion of the range with axial air inlets, the distance of the fan blades of the fan cover is greater than the constant distance in the first portion is, in particular, more than twice as large. Thus, particularly advantageous flow conditions are achieved, and the noise on a fan cover by passing fan blades is reduced.

In an advantageous development, the fan blades extend radially beyond the region with axial air inlets. Thus, the cooling air is particularly advantageous sucked.

In an advantageous development, the fan wheel is arranged on a shaft of the transmission, in particular of the driving shaft. Thus, a separate motor for the drive of the fan is dispensable.

Important features of the invention of a transmission series with variants, each comprising a fan with fan and at least one gear stage are that a fan wherein the fan as described above according to the invention asugebildet and that the fan in a first variant on the driving shaft of a bevel gear is mounted and that the fan wheel is mounted in a second variant on the driving shaft of a spur gear. In the first variant, air is preferably radially passable through air ducts and, in the second variant, air is directed through the air ducts at an angle to the radial direction and at an angle to the axial direction, in particular in an axial plane of the fan wheel obliquely to the axis of the fan wheel. The advantage here is that the variety of parts is reduced in a transmission series, and that the possible variations for the fan assembly is increased.

In an advantageous development, a housing wall of the transmission partially covers the air outlet of the air ducts in the first variant, in particular the axially oriented partial region of the air outlet. Thus, advantageously, the cooling air in the radial direction can be conducted around the transmission housing. It is thus causes a good cooling performance.

Further advantages emerge from the subclaims.

• Figur 1 eine Ansicht eines Lüfterrads von vorn,
• Figur 2 eine Ansicht des Lüfterrads aus Figur 1 von hinten,
• Figur 3 eine Draufsicht auf die Vorderseite des Lüfterrads aus Figur 1,
• Figur 4 den Schnitt des Lüfterrads entlang einer in Figur 3 mit A-A bezeichneten Axialebene,
• Figur 5 eine Ansicht eines Getriebes mit montiertem Lüfter
• Figur 6 eine Seitenansicht des Getriebes aus Figur 5 mit aufgeschnittener Lüfterhaube und aufgeschnittenem Lüfterrad.

The invention will now be explained in more detail with reference to figures:
It shows

• FIG. 1 a view of a fan from the front,
• FIG. 2 a view of the fan from FIG. 1 from behind,
• FIG. 3 a plan view of the front of the fan from FIG. 1 .
• FIG. 4 the section of the fan along an in FIG. 3 Axial plane labeled AA,
• FIG. 5 a view of a gearbox with mounted fan
• FIG. 6 a side view of the transmission FIG. 5 with cut fan cover and cut fan wheel.

FIG. 1 shows a fan for a fan of a transmission. The fan wheel comprises at least one main body 10 with a hub 13, fan blades 11 and an air guide ring 12.

The fan is intended for mounting on a shaft of a gearbox. For this purpose, the hub 13 is placed on the shaft for frictional connection with the same.

The fan wheel is driven by the shaft. The shaft thus drives the fan blades 11, thereby producing an approximately radially or obliquely outwardly directed air flow. This direction of the air flow is independent of the direction of rotation of the fan wheel, since each fan blade 11 has a plane of symmetry in which the axis of rotation of the fan wheel is located.

The main body 10, the air guide ring 12 and two adjacent fan blades 11 form air channels, is passed through the air flow.

FIG. 2 shows the back of the fan FIG. 1 , A support ring 20 of the main body 10 and the support edges 21 of each fan 11 are in a common plane. Thus, an operation of the fan is close to the housing wall of a transmission feasible, the plane described is aligned parallel to the housing wall of the transmission and arranged at a small distance to this.

The fan with body, fan blades and guide ring is preferably made in one piece, in particular as a casting of aluminum or plastic, wherein in the case of use of plastic particularly preferably the plastic to avoid electrostatic charge is formed electrically conductive.

In an alternative embodiment, the fan is made of steel.

Form in mounted position - as in FIG. 2 illustrated - the radial boundary edges 22, the outer boundary edge 23 of the air guide ring 12 and the housing wall an opening through which the air flow is passed in radially outward. The air guide ring 12 thus does not extend over the entire axial length of the fan and in particular the fan blades 11th

FIG. 3 shows a top view of the front of the fan after FIG. 1 , On the main body 10, the fan blades 11 are mounted, wherein the fan blades 11 each have a plane of symmetry, which contains the axis of rotation of the fan. The fan blades 11 are thus substantially, that is, apart from inclinations of the surfaces of the fan blades 11, perpendicular to an annular, truncated cone-shaped portion 35 of the body 10th

Each fan blade 11 is arranged with respect to a fan-fixed reference direction 36 each at an angle w1. The fan blades 11 are irregularly arranged: In particular, the difference amounts of each two angles w1 can not be represented as an integer multiple of a basic amount. Thus, resonance excitations are reduced by the fan blades 11, in particular, the frequency of the resonance excitations is reduced.

In an advantageous embodiment, the fan is mounted on a gear shaft and the number of fan blades and the number of teeth of the gear shaft of the gear shaft have no common divider. Particularly preferably, the number of fan blades and the number of teeth of each gear of the transmission has no common divider. Thus, resonance effects are advantageously reduced.

In an alternative embodiment, the fan wheel on a mirror symmetry plane, in which preferably the axis of rotation of the fan wheel is included.

The outer diameter of the main body 10 in FIG. 3 is much smaller than the outer diameter of the fan selected. Preferably, the outer diameter of the base body 10 is two-thirds of the outer diameter of the fan and thus of the air guide ring 12, and more preferably, the outer diameter of the base body 10 relative to the inner diameter of the air guide ring 12 is reduced by ten to twenty percent. Thus, favorable flow conditions for the fan can be achieved.

The air guide ring 12 is composed of a first guide ring 33 and a second guide ring 34, which are each designed to be annular and frusto-conical. The opening angle of the second guide ring 34 is selected larger than the opening angle of the first guide ring 33.

In each case, a first fan blade 31, a second fan blade 32, a segment 30 of the frusto-conical region 35 of the base body 10 and a segment 37 of the air guide ring 12 enclosed by the two fan blades 31, 32 form an air channel through which air flows during operation.

Each of these air ducts formed in this way has an opening angle or angular distance w2, ie the angle between the delimiting fan blades 31, 32, ie between two nearest neighbors, and an angle w3 of the center plane of the air duct with respect to a reference direction 36. The opening angle w2 results thus in each case from the difference of the angle w1 to the limiting fan blades 31, 32. The angle w3 differs in the example according to the FIG. 3 from the angles w1 to the limiting fan blades 31, 32 each by a constant, that is independent of the number of fan blades, amount. The sequence of opening angles w2 and the sequence of angles w3 defines an irregular sequence of numbers. In the case of asymmetrical formations of the air ducts and / or fan blades, the relationships of the angles w1, w2, w3 with each other change corresponding. In particular, for defining the angles, instead of the center planes mentioned, excellent directions, for example, directions of edges of the fan blades, are usable.

FIG. 4 shows a sectional view taken along in FIG FIG. 4 with AA designated axial plane.

The fan blades 11 have approximately rectangular recesses 40, so that the fan blades 11 in operation at a first area in the FIG. 4 from the top to be mounted fan cover at a shorter distance than in a second area. This second area contains air inlets for the air supply to the fan wheel, and by the recess 40 periodic vibration excitations at the air inlets are avoided by a Vorbeistreichen the fan blades 10 in close proximity.

The main body 10 comprises at least one hub 13 for non-positive connection of the impeller on a shaft and a frusto-conical portion 35. This frusto-conical portion 35 forms with the first guide ring 33 and the second guide ring 34 a nozzle-shaped air passage, wherein the nozzle-like constriction is approximately at the minimum Distance m is formed by air guide ring 12 and body 12. This minimum distance m causes a minimum cross-section of the air channel delimited by a segment of the air guide ring 12, a segment of the frusto-conical region 35 and two adjacent fan blades 11, this cross section being assumed to be approximately at the same position as the minimum distance. The exact position of the minimum cross section with respect to the minimum distance depends on the specific configuration of the cross section of the air guide ring 12 and the frusto-conical region.

The air guide ring 12 is formed at least from a first guide ring 33 and a second guide ring 34, wherein the opening angle of the frusto-conical first guide ring 33 is smaller than the opening angle of the frusto-conical second guide ring 34. First guide ring 33 and second guide ring 34 are connected along a concentric ring. The design of the opening angle of the guide rings 33, 34 is such that the air guide ring 12 can be inscribed in a conical surface 42, wherein the conical surface 42 touches the air guide ring 12 at two concentric cutting circles 43, 44, the conical surface 42 but not the interior of the air guide ring 12 cuts. The air guide ring 12 thus has an axial cross section, whose outer contour is concave.

Accordingly, in order to form a constant wall thickness, a convex surface is formed on the inner side of the air guide ring 12 facing the shaft, where convex the property that the connecting line of two points on the inside of the air guide ring 12 always runs at least partially inside the air guide ring 12.

The inner contour of the cross section of the air guide ring 12 is thus curved with opposite signs as the outer contour of the cross section of the frusto-conical portion 35, in particular its radial outlet. Both contours are thus convex, with the convexities facing each other.

From the described design of first guide ring 33 and second guide ring 34 results in a constriction and a minimum distance m, which causes a nozzle effect in the associated air duct.

In alternative exemplary embodiments, the inside of the air guide ring is convex, but not described by two connected truncated cones, but by, for example, a parabolic or a circular arc-shaped cross-sectional contour. Even in these cases, a resulting cross-sectional constriction causes a nozzle effect with which an air flow can be conducted.

The air guide ring 12 does not extend axially over the entire length of the fan, in particular the fan blades 11. Rather, the second guide ring 34 terminates at an axial distance from the plane defined by the support ring 20. In this way, a radial opening 41 is formed for the air ducts through which - in the assembled state - air in the radial direction along the housing wall of the transmission can be conducted.

FIG. 5 shows a gear 50 with mounted fan 57. A fan cover 51 surrounds the fan. For illustration is in FIG. 5 only one half of the fan cowl 51 is shown.

The hub 13 of the fan wheel sits on an intermediate part 54 and is non-positively connected thereto, wherein the intermediate part 54 in turn is arranged on a shaft 53 of the transmission and is at least positively connected thereto. The shaft 53 is the driving shaft of the transmission 50.

The fan cover 51 has an annular area with air inlets 55, through which the fan draws air. The axial orientation of the fan blades 11 causes, regardless of the direction of rotation is sucked in the same axial direction. Thus, the suction side of the fan is clearly defined as the side through which the air flows. The air ducts have an opening through which air therefore exits independently of the direction of rotation. Thus, an air outlet is formed.

The diameter of the area with air inlets 55 is equal to the inner diameter of the first guide ring 33.

The fan blades 11 strip past the air inlets 55 during a rotational movement. To reduce noise, the fan blades 11 each have a recess 40, so that only a portion of the area of the air inlets 55 is swept by the fan blades 11 at a small distance, while another, radially further inboard portion is covered at a greater distance. The radial extent of the radially further inner subregion is greater than the radial extent of the radially outer subregion. Thus whistling sounds are reduced.

FIG. 6 shows the fan FIG. 5 in a side view. The fan wheel is mounted above a bevel gear pot 61.

By fan blades 11 air is moved, which are passed through the frusto-conical portion 35 and the first guide ring 33 and the second guide ring 34 on air outlets 56.

Between the fan cover 51 and the first guide ring 33, a gap 60 is provided. As by comparison with FIG. 4 it can be seen, the recess 40 of the fan blades 11 in the axial direction is about twice as long as the axial extent of the gap 60th

The provided along the radial boundary edge 22 of the fan blades 11 withdrawal of the second guide ring 34 allows mounting of the fan on a shaft which protrudes from a side wall of the transmission 50. This is the case, for example, with spur gears. In this case, the fan is mounted directly in front of this side wall, and the moving of the fan blades 11 air flows radially outwards and thus along the housing wall. The housing wall covers a portion of the air outlet of the air ducts, namely that portion which is axially aligned, the surface normal is thus arranged parallel to the shaft axis. Thus, when mounted in front of a housing wall in FIG. 6 created by a Kegelradtopf 61 distance of the fan from the housing of the transmission 50, because the air is directed in this case radially outward. As a result, a compact dimensions of the transmission with fan can be achieved.

By using a fan in different variants of transmissions, a series is formed in whose variants, such components that form the fan, in particular the fan, are uniformly used. Thus, the variety of parts of the series is reduced.

LIST OF REFERENCE NUMBERS

• 10 basic body
• 11 fan blades
• 12 air guide ring
• 13 hub
• 20 support ring
• 21 bearing edge
• 22 radial boundary edge
• 23 outer boundary edge
• 30 segment
• 31 first fan blade
• 32 second fan blades
• 33 first guide ring
• 34 second guide ring
• 35 frustoconical area
• 36 Reference direction
• 37 segment
• w1, w2, w3 angles
• m minimum distance
• 40 recovery
• 41 radial opening
• 42 conical jacket
• 43, 44 cutting circle
• 50 gears
• 51 Fan cover
• 52 frames
• 53 wave
• 54 intermediate part
• 55 air inlets
• 56 air outlets
• 57 fans
• 60 space
• 61 bevel gear pot

Claims (13)

1. A fan impeller with fan blades (11, 31, 32),
   wherein
   a number n >2 of non-regularly arranged fan blades (11, 31, 32) is provided, and wherein the fan blades (11, 31, 32) are formed identically, wherein a number of air ducts is provided which are limited in each case by at least the fan blades (11, 31, 32), an air guide ring (12) and a base body (10),
   characterised in that
   the fan blades (11, 31, 32) are axially set back as far as a radius on the intake side and in that the maximum axial extent of the fan blades (11, 31, 32) is greater than the maximum axial extent of the air guide ring (12), and
   in that the air ducts in each case form an air exit which comprises a radially oriented and an axially oriented partial region.
2. A fan impeller according to the preceding claim,
   characterised in that
   the cross-section of the air guide ring (12) is shaped convexly on its inside and is shaped concavely on its outside such that the wall thickness of the air guide ring (12) is substantially constant.
3. A fan impeller according to at least one of the preceding claims,
   wherein
   the base body (10) has a frustoconical region (35) and the air guide ring (12) can be inscribed concentrically in a mathematical cone such that the air guide ring (12) contacts the mathematical cone in a first and a second axial region, and in a third axial region a minimum distance is provided between the air guide ring (12) and the mathematical cone,
   wherein the third axial region is arranged between the first axial region and the second axial region,
   and at least two fan blades (11, 31, 32) in each case, a segment (30) of the frustoconical region (35) and a segment (37) of the air guide ring (12) form an air duct running radially or obliquely outwards.
4. A fan impeller according to at least one of the preceding claims,
   characterised in that
   at least two different types of air ducts are formed on a fan impeller.
5. A fan impeller according to at least one of the preceding claims,
   characterised in that
   each air duct can be described by a geometric variable,
   and the sequence of the geometric variable of the air ducts upon revolution of the fan (57) represents an irregular sequence,
   and/or in that
   the geometric variable of each air duct is the angle between the delimiting fan blades (11, 31, 32) or the angle of a delimiting fan blade (11, 31, 32) relative to a reference direction (36) which is fixed relative to the fan.
6. A fan impeller according to Claim 5,
   characterised in that
   the geometric variable of each air duct is the angular position of the centre of gravity or of the central plane of the air duct or the angle of a marked direction of the air duct relative to a reference direction (36) which is fixed relative to the fan.
7. A fan impeller according to at least one of the preceding claims,
   characterised in that
   the maximum axial extent of the fan blades (11, 31, 32) is more than twice as great as the maximum axial extent of the air guide ring (12),
   and/or in that
   the fan blades (11, 31, 32) on the intake side are axially set back as far as a radius by more than one third of the maximum axial turnout of the fan blades (11, 31, 32).
8. A fan impeller according to at least one of the preceding claims,
   characterised in that
   the radial extent of the base body (10) is smaller than the external diameter of the fan impeller, in particular at least fifteen percent smaller than the internal diameter of the air guide ring (12).
9. A system, in particular transmission (50),
   comprising a fan (57) having
   a fan impeller with fan blades (11, 31, 32)
   and a fan cowl (51)
   characterised in that
   the fan impeller is formed according to one of the preceding claims,
   the fan cowl at least partially surrounds the fan impeller
   and the fan cowl (51) has a region with axial air inlets (55),
   the fan blades (11, 31, 32) in a first partial region of the region with axial air inlets (55) being at a constant distance from the fan cowl (51),
   and in a second partial region of the region with axial air inlets (55) the distance of the fan blades (11, 31, 32) from the fan cowl (51) being greater than the constant distance in the first partial region, in particular more than twice as great,
   and/or in that
   the fan blades (11, 31, 32) extend radially beyond the region with axial air inlets (55).
10. A system according to Claim 9,
    characterised in that
    the system is a transmission (50), with the fan impeller being arranged on a shaft (53) of the transmission (50), in particular the input shaft (53).
11. A system according to Claim 10,
    characterised in that
    the number of the fan blades (11, 31, 32) and the tooth number of the gear wheel of the input shaft do not have a common divisor,
    and/or in that
    the number of the fan blades (11, 31, 32) and the tooth number of each gear wheel of the transmission do not have a common divisor.
12. A transmission series,
    with variants which comprise in each case a fan (57) with fan impeller and at least one gear stage,
    characterised in that
    a fan impeller according to one of Claims 1 to 8 is formed,
    in that the fan impeller in a first variant is mounted on the input shaft (53) of a bevel-gear stage
    and in that the fan impeller in a second variant is mounted on the input shaft (53) of a spur-gear stage.
13. A transmission series according to Claim 12, characterised in that
    in the first variant air can be guided radially through air ducts
    and in the second variant air can be guided through the air ducts at an angle to the radial direction and at an angle to the axial direction, in particular in an axial plane of the fan impeller obliquely to the axis of the fan impeller,
    and/or in that
    in the first variant a housing wall of the transmission (50) partially covers the air exit of the air ducts, in particular the axially oriented partial region of the air exit.

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