GB2116642A

GB2116642A - Axial fan

Info

Publication number: GB2116642A
Application number: GB08306978A
Authority: GB
Inventors: Kurt Hauser; Rolf Hartmann
Original assignee: Behr GmbH and Co KG
Current assignee: Mahle Behr GmbH and Co KG
Priority date: 1982-03-15
Filing date: 1983-03-14
Publication date: 1983-09-28
Also published as: GB2116642B; FR2523210A1; GB8306978D0; FR2523210B1; IT1194156B; IT8320003A1; IT8320003A0

Abstract

The fan is suitable for the radiator 2 of a water cooled internal combustion engine 3 and comprises hub 8 with blades 10 and a surrounding air conducting means 4 which increases in diameter from the inlet of the blades to the outlet, the peripheral contour 12 of the blades corresponding to the internal surface 13 of the air conducting means 4. The latter may be a stationary structure, as shown, or may be attached to blades 10 to rotate therewith. <IMAGE>

Description

SPECIFICATION Axial fan, in particular for the radiator of a water cooled internal combustion engine This invention relates to an axial fan, in particular for the radiator of a water cooled internal combustion engine for commercial vehicles, comprising a hub with fan blades and an air conducting device surrounding the hub with blades and increasing in width in the direction towards the outlet region.

Axial fans of this type are known (DE-AS 2,411,225). Cooling fans of this type are generally required to overcome a very high pressure loss, in other words they are severely throttled. Thus most of the cooling fans of the commercial vehicles available on the market today operate within a range of from T=0.07 to 0.15, where T is the so called throttle coefficient, which is calculated from the ratio of the dynamic pressure, based on the annular surface of the impellor wheel, divided by the total increase in pressure, which in turn is composed of the dynamic pressure and the static pressure. Where throttling is so severe, that is to say where the counter pressure is high and the volumetric air flow therefore low, the flow separates from the hub.The flow is not a pure axial flow in the region of the fan wheel but a so called semi-axial flow in which the air is carried obliquely outwards even when no combustion engine is arranged behind the fan. Known fans of this type therefore produce a relatively high noise level which may be slightly reduced if the edge of the fans increases in width towards the outlet.

It is an object of the present invention to enable the noise level to be even further reduced without altering the whole construction.

The invention consists in that the increase in width of the air conducting device already begins in the region of the inlet edge of the fan blades and that the external contour of the fan blades is adapted to the internal contour of the air conducting device. This arrangement results in a marked reduction in noise level at the operating point of the fan without impairing the efficiency of the fan.

The axial length of the air conducting device is advantageously at least equal to 40% of the axial length of the fan blades at their external diameter although it is preferably even greater. In one advantageous embodiment, the air conducting device may be provided with a portion of increasing width in a form resembling a circular arc extending, in the direction towards the outlet, into a conical diffuser part. This design produces good results as regards noise level and efficiency of ventilation.

This concept provides two advantageous possibilities for the constructional aspect of the air conducting device. Firstly, the device may quite simply be formed as a fixed fan border surrounding the rotating fan blades, although it may also form part of the fan wheel composed of hub and fan blades, and form a baffle ring attached to the ends of the fan blades. This measure results in a marked reduction in noise level compared with those constructions in which the fan wheel is provided with an outer ring rotating with it. (DE-OS 2,826,697).

It is advantageous if the inlet edge of the baffle ring projects axially above the inlet edge of the blades against the direction of flow and forms an axially directed ring portion. It is particularly advantageous to make use of this ring portion so that a stationary nozzle not taking part in the rotation extends into the inlet opening formed by the inlet edge of the baffle ring, because in that case the air entering the gap between the nozzle and the rotating baffle ring in the direction of flow stabilizes the main flow. A further improvement may be achieved if the inlet nozzle increases in width in the form of an arc in the direction offlowfrom its smallest cross section.

In that case, the gap flow and main flow are carried tangentially towards the rotating baffle ring which widens in the direction of air flow and the flow is encouraged to adhere to the portion of increasing width. Lastly, the noise level and efficiency of the fan action may be further improved if the inlet nozzle also embraces the rotating baffle ring on the outside.

The air in the gap is thereby deflected through 180 and is throttled accordingly so that the air gap losses are only slight. This results not only in an improvement in efficiency but also in a lowering of the noise level.

It is further advantageous to attach to the hub, in the region of the outlet edge of the fan blades, a disc having a diameter at least 30% greater than the diameter of the hub. This arrangement prevents the formation of ring vortices which are caused by the separation of air flow at the hub and hence also prevents ventilation losses. If the hub is cylindrical, a new stationary ring vortex forms between the external surface of the hub and the disc, and this vortex causes the flow to behave as if the hub were conical.

The desired semi-axial flow is thus stabilized without an alteration in the type of structure. The stationary ring vortex is produced only once, during the starting process, and therefore consumes only little energy, in contrast to vortices which separate. It has been shown that a cooling fan constructed as described above has a substantially smoother characteristic curve than conventional fans and its operational efficiency is improved by about 10%. The disc according to the invention may, of course, also be provided in the case of an axial fan wheel having a disc shaped hub and blades riveted thereto. The desired stabilization of flow is also obtained in that case.

It is advantageous if the disc is in the form of an annular disc mounted on the hub; this annular disc may be conical and may form part of the generatrix of a cone having its tip situated infront of the rear edge of the hub, viewed in the direction of flow.

According to a further feature of the invention, this annular disc may constitute a part for the attachment of the fan blades, in which case it is advantageous to attach the fan blades rigidly to the annular disc which in turn has an attachment flange by which it is screwed to the hub.

In particular in axial fan wheels having radially extending cooling ribs provided at the leading end face of a hydraulic friction clutch forming the hub, a further advantageous possibility of stabilizing the flow and hence avoiding ventilation losses exists if the annular disc is associated with a baffle surface in the region of the leading end face of the hub, which baffle surface is so adapted to the external contour of the hub and to the position of the annular disc that separation of flow at the circumference of the hub is prevented.This may be achieved very simply and effectively in fan wheels having cooling ribs at the end face of the hub if the baffle surface in the form of a conical front ring is attached by an internal attachment flange in the outer region of the leading edges of the cooling ribs, and the front ring then extends from this inner flange in the form of an approximately circular arc into the conical ring portion of the front ring. By this arrangement, the incident flow, which initially is only deflected radially outwards between the cooling ribs and is then deflected semi-axially to the rear annular disc by the action of the fan blades, is pressed agains. the external contour of the hub before it encounters the rear annular disc. A vortex of air separating from the circumference of the hub is thus completely avoided.

Embodiments of the novel axial fan are described below by way of example with reference to the drawings, in which: Fig. 1 is a schematic section through an axial fan constructed according to the invention for the radiator of a water cooled internal combustion engine, Fig. 2 is an enlarged view of the contour of increasing width of the border and the external contour of a fan blade, Fig. 3 is a graph representing the variation in noise level in the region of the operating point of the fan, Fig. 4 is a schematic longitudinal section through an axial fan constructed according to the invention for the radiator of a water cooled internal combustion engine, Fig. 5 is an enlarged view of the region of the outer edges of the fan blades with the rotating baffle ring and the inlet nozzle situated infront of the ring, Fig. 6 is a view of the axial fan wheel in the direction of arrow 11 but with the inlet nozzle omitted, and Fig. 7 is a longitudinal section through another embodiment of a fan wheel according to the invention connected with a hydraulic friction clutch and having cooling ribs at the end face and an inlet baffle ring at the end face.

In Fig. 1, a fan border 4 provided as air conducting device is connected in known manner, by way of an elastic sleeve 5, to the connecting edge 1 of a radiator 2 for a water cooled internal combustion engine 3. The fan border 4 is held in position by a web or arm 6 or the like which is firmly attached to the internal combustion engine 3. This arrangement enables the movement of the radiator 2, which is generally suspended to the underframe, to be balanced by the movement of the internal combustion engine 3 which is elastically mounted inside the vehicle. The hub 8 of the fan wheel 9 equipped with fan blades 10 is mounted on a shaft 7 (indicated schematically) driven by the internal combustion engine 3.If the airflow provided by the movement of the vehicle is not sufficient, these fan blades are intended to provide for sufficient flow of air over the radiator 2 in the direction of the arrows 11. In such forms of fan wheels 9, the powerful throttling effect produces a semi-axial discharge flow in the direction of the arrows 1 la, which according to the invention is improved by the fact that the increase in width of the fan border in the direction of flow already begins in the region of the inlet edge of the fan blade and that the external contour 12 of each fan blade 10 is adapted to the internal contour 13 of the fan border 4, as shown clearly in Fig. 2. It has been found that this arrangement provides particularly advantageous noise level values compared with those obtained when the fan border does not increase in width.The graphic representation in Fig. 3, which is purely qualitative, shows that when airflow is produced, the noise level A of an axial fan equipped according to the invention, measured in the region of the operating point Bp, is much lowerthan the corresponding noise level B of a conventional fan and that it reaches its minimum somewhere near the operating point.One particularly advantageous embodiment has the following dimensions: DZA=750 mm DsA=724 mm DZE=696 mm Dose=680 mm R=70 mm a=35' =35 a=10 mm The proportion of Lz to Ls must not be less than 0.4, as shown in the example, and is advantageously substantially greater Fig. 2 clearly shows that the increase in the width of the fan border 4 already begins near the inlet edge 10 a of the fan blades 10, namely only an axial length a behind this edge, and that the external contour 12 of the fan blades 10 conforms to the internal contour 13 of this fan border 4 over the greater part of the axial length Lz of the fan border 4.For reasons of strength and facility of transport, the edge 10b atthe end of each fan blade 10, near the outlet edge thereof, preferably takes a purely axial course.

In the example illustrated in Fig. 2, the fan border 4 comprises a short, cylindrical portion of length a, a portion 4a in the form of a circuluar arc of radius R extending over the angle os, and a conical diffuser portion 4b with which the portion 4a merges at the outlet end although this portion 4a in the form of a circular arc may also extend over the whole axial depth of the border.

In Figs. 4to 6, an axial fan wheel 9 having axial fan blades 10 uniformly distributed over the circumference of a hub 8 and projecting radially from the hub in the conventional manner is situated behind the connecting edge 1 of a radiator 2 for a water cooled internal combustion engine 3. When the fan wheel 9 is set in motion, the fan blades 10 produce an air flow through the radiator 2 in the direction of the arrows 11. The powerful throttling produced in axial fans of this construction results in a semi-axial discharge flow through the fan wheel 9 in the direction of the arrows 11 a. This outflow is improved by the attachment of a baffle ring 20 acting as air conducting device to the outer ends 1 0c of the fan blades 10.This baffle ring 20 rotates with the fan blades 10; it consists of a cylindrical portion 20a of axial length A and a portion 20b in the form of a circular arc of radius R extending over an angle ex. As indicated in broken lines, this portion 20b in the form of a circular arc may also be combined with an adjacent diffuser portion 20c. In that case, the edge 10b extending in a purely axial direction at the end of the fan blade 10 is omitted, as indicated by the broken line. The edge 10d formed at the end may also take the course 10d' indicated in broken line in Fig. 5.

In front of the cylindrical portion 20a of the baffle ring 20 is an inlet nozzle 21 which is sealed against the edge 1 by an elastic lip 1 a and, in the embodiment illustrated, it diminishes in width in the direction of flow 11 up to a certain cross section situated behind the inlet edge 20' of the baffle ring 20, and from there on it increases in width in such a manner that the end region 21 a is approximately parallel to the end region of the circular arc portion 20b of the baffle ring 20 and preferably lies on the same cone generatrix as this portion.The inlet nozzle 21 also has a cylindrical portion 21 b which surrounds the cylindrical portion 20a of the baffle ring 20 on the outside thereof so that an annular gap 22 is formed between the two cylindrical parts 21 and 20a, followed by a 1800 deflection, so that the air stream in the gap is powerfully throttled, a factor which is particularly advantageous in reducing noise. The inlet nozzle 21 is firmly attached to the motor 3 or some other fixed part by an arm 26. The baffle ring 20 therefore rotates with its cylindrical part 20a within the annular region of the substantially U-shaped inlet nozzle 21.

It would, of course, conceivably be possible to produce this inlet nozzle 21 without its cylindrical portion 21b butforthe reasons mentioned above, the embodiment illustrated here is more advantageous from the point of view of air flow and noise reduction. This applies even if the baffle ring 20 is not provided with the cylindrical part 20a illustrated here but only comprises the part 20b in the form of the circular arc and optionally the conical part 20c.

Fig. 7 illustrates an advantageous embodiment of a variation of an axial fan wheel according to the invention, in which the hub 8 forms part of the external housing of a hydraulic friction clutch which is well known and therefore not described in detail here. It substantially comprises a friction disc 30 driven by a shaft (not shown) and closely surrounded by a housing with cover 31. The hub is set into rotation by the friction of a liquid contained in the space between the disc 30 and the housing, the rotation depending upon the degree of filling. This hub is equipped with fan blades 10 which, in the example illustrated, are rigidly attached to a conical annular disc 40 which serves to conduct the air flow near the hub in the direction of the arrows 1 1a as well as serving as means for the attachment of the fan blades 10.The annular disc 40 has an internal attachment flange 40a by which it is connected to the hub 8 by the screw 32.

The hub 8 comprises several radially extending cooling ribs 33 at its leading end face 8. These ribs 33 overlap an axial region 34 of the hub 8. In the radially outer region 33a of the cooling ribs 33, a front ring 35 forming a baffle surface is screwed by its internal attachment flange 35a to correspondingly formed portions of the cooling ribs 33 and is thereby rigidly attached to the leading edges 33b of the ribs. From its substantially radial attachment flange 35a, the front ring 35 extends into a region 35b in the form of a circular arc which merges into the conical ring portion 35c whose trailing edge 35d is situated behind the leading edges 10a of the fan blades 10, viewed in the direction of air flow.The internal surface of the front ring 35 is somewhat inclined to the conical surface of the annular disc 40 but is substantially parallel thereto so that the air flowing in at the region of the cooling ribs 33 in the direction of the arrows lie is deflected between the front ring 35 and the contour of the hub towards the conical front surface of the annular disc 40.

The formation of seperating vortices on the external surface of the hub is thereby avoided, so that the air current produced by the cover 31 of the clutch housing with its cooling ribs flows unhindered into the region of the fan blades 10. The flow then continues outwards in a semi-axial direction and is then guided by the baffle ring 20 as in the embodiment illustrated in Fig. 4. All the advantages of the clutch and of Figs. 1 and 2 or 4 and 5 are thus preserved. In addition, the formation of vortices at the hub can be avoided. In fan wheels of the type illustrated in Fig. 7, where the hub serves at the same time as the housing of a hydraulic friction clutch, optimum cooling of this clutch is also achieved since the air flowing in the direction of the arrows 1 a can be effectively carried over the cooling ribs 33 and the housing cover 31.

Claims

1. Axial fan, suitable for the radiator of a water cooled internal combustion engine of a commercial vehicle, comprising a hub with fan blades and a surrounding air conducting means which increases in width towards the outlet, wherein the increase in width of the air conducting means begins in the region of the inlet edges of the fan blades and the peripheral contour of the fan blades is adapted to the internal surface of the air conducting means.

2. Axial fan according to claim 1, charcterised in that the internal surface of the air conducting means is in the form of or is similar in form to a circular arc.

3. Axial fan according to claim 1 or claim 2, characterised in that the axial length of the air conducting means is at least 40% of the axial length of the fan blades in their peripheral regions.

4. Axial fan according to any of Claims 1 to 3, characterised in that the air conducting means comprises a portion of increasing width having a form resembling a circular are followed, in the direction of the outlet end, by a conical diffuser portion.

5. Axial fan according to any of Claims 1 to 4, charcaterised in that the fan blades have an axially extending outer edge in the region of their outlet end.

6. Axial fan according to any of Claims 1 to 5, characterised in that the air conducting means is in the form of a stationary fan housing within which the fan blades rotate.

7. Axial fan according to Claim 1, characterised in that the air conducting means forms part of the fan rotor composed of the hub and fan blades and constitutes a baffle ring rigidly connected to the ends of the fan blades.

8. Axial fan according to Claim 7, characterised in that the inlet edge of the baffle ring projects axially above the blade inlet edge against the direction of airflow and forms an axially directed ring portion.

9. Axial fan according to Claim 8, characterised in that the ring portion is cylindrical.

10. Axial fan according to any of Claims 7 to 9, characterised in that a fixed nozzle extends into the inlet opening formed by the inlet edge of the baffle ring.

11. Axial fan according to any of Claims 7 to 10, characterised in that the inlet nozzle extending into the baffle ring increases arcuatiy in width in the direction of airflowfrom a smallest cross section which is preferably situated behind the inlet edge of the baffle ring.

12. Axial fan according to any of Claims 7 to 11, characterised in that the inlet nozzle arranged in front of the baffle ring also projects above the baffle ring on the outside.

13. Axial fan according to any of Claims 7 to 12, characterised in that the part of the inlet nozzle projecting above the baffle ring on the outside is parallel to the cylindrical part of the baffle ring and also extends in the axial direction so that an annular gap is formed, followed by a deflection through 180 .

14. Axial fan according to Claim 1, cherecterised in that an annular disc having a diameter at least 30% greater than the hub diameter is mounted on the hub in the region of the outlet edge of the fan blades.

15. Axial fan according to Claim 14, characterised in that the annular disc is conical and forms part of the generatrix of a cone the tip of which is situated in front of the rear edge of the hub, viewed in the direction of airflow.

16. Axial fan according to Claims 14 and 15, characterised in that the annular disc is designed as a part of the attachment of the fan blades and has an attachment flange by means of which it is bolted to the hub.

17. Axial fan according to any of Claims 14 to 16, characterised in that the annular disc is associated with a baffle surface in the form of a conical front ring which is situated in the region of the leading end of the hub and is so adapted to the external contour of the hub and the position of the annular disc that the air flow will not become detached at the circumference of the hub.

18. Axial fan according to Claim 17, comprising radial cooling ribs provided at the leading end of a hydraulic friction clutch forming the hub, characterised in that the front ring is attached to the outer region of the leading edges of the cooling ribs by an inner attachment flange and extends from there through a region in the form of a circular arc into the conical ring portion.