PROTECTIVE GRILLE WITH IMPROVED EFFICIENCY AND NOISE CHARACTERISTICS

Abstract

A protective grille for a fan has a web structure which comprises radial webs spaced apart in a circumferential direction and coaxial circumferential webs spaced apart in a radial direction. The protective grille has at least a radial outer region and a central region around a central axis of the protective grille. An envelope surface spanned by the radial outer region and the central region is of convexly curved form in the radial outer region and is of flat form, parallel to a radial plane of the protective grille, in the central region.

Claims

1. A protective grille comprising attachment means for placement on a fan, and a grille web structure, which in the circumferential direction has spaced apart radial webs and in the radial direction has spaced-apart axial circumferential webs, wherein the protective grille at least has a radially outer region and a central region about a central axis of the protective grille, an envelope surface spanning from the radial outer region and the central region configured convexly curved in the radial outer region and planar in the central region, parallel to a radial plane of the protective grille, and the circumferential webs are each placed in a radial direction at a radial distance r to the axial center of the protective grille and each has a varied angular position vis-à-vis an axial plane of the protective grille.

2. The protective grille as specified in claim 1, wherein, the protective grille is configured to be rotationally symmetric and the central region in the radial direction directly adjoins the radial outer region; and the convexly curved envelope surface of the radial outer region makes a smooth transition into the planar configured central region.

3. The protective grille as specified in claim 1, wherein the radial webs and/or the circumferential webs have a rectangular cross section with a height H and a wall thickness B, the ratio of which is set at H/B≧3.

4. The protective grill as specified in claim 1, wherein the angular position of the circumferential webs in dependence on their distance r to the axial central axis of the protective grille varies in relation to a maximum distance R of an outermost circumferential web to the axial central axis of the protective grille and with a distance ratio r/R=1.0, an angular placement is provided of 50-70°, with a distance ratio r/R=0.85, an angular placement of 30-50°, with a distance ratio r/R=0.70 an angular displacement of 20-30° and/or with a distance ratio r/R≦0.55 an angular placement of 0-20° is provided vis-à-vis an axial plane of the protective grille.

5. The protective grille as specified in claim 1, wherein the convex curved envelope surface region in a radial outer region in a lateral cross section determines a partially elliptical contour which has a ratio of a radial length a of the outer region to a radius c of the protective grille of a/c>0.25.

6. The protective grille as specified in claim 1, wherein the convex curved envelope surface in the radial outer region in a lateral cross section determines a partially elliptical contour, which has a ratio of an axial height b of the protective grille to a radius c of the protective grille of b/c>0.02.

7. The protective grille as specified in claim 1, wherein the convex curved envelope surface in the radial outer region in a lateral cross section determines a partially elliptical contour, which has a ratio of an axial height b of the protective grille to a radius c of the protective grille in a range of 0.025≦b/c≦1.

8. The protective grille as specified in claim 1, wherein the radial webs extend out radially and/or axially over an outermost circumferential web and form an outer edge of the protective grille.

9. The protective grille as specified in claim 1, wherein the number of radial webs in the radially outer region is greater than in the central region.

10. The protective grille as specified in claim 1, wherein the number of radial webs provided in a central region is reduced in the direction of an axial center of the protective grille.

11. The protective grille as specified in claim 1, wherein the radial webs in an axial cross section have a curved shape.

12. A fan with a protective grille as specified in claim 1.

Description

DRAWINGS

[0016] FIG. 1: a perspective view of a protective grille

[0017] FIG. 2: a side view of the protective grille from FIG. 1

[0018] FIG. 3: a side sectional view of the protective grille from FIG. 1

[0019] FIG. 4: a lateral depiction of a part of the envelope surface of the protective grille

[0020] FIG. 5: a lateral depiction of a part of the envelope surface of the protective grille

[0021] FIG. 6: a characteristic curve comparison of the static efficiency of a fan; and

[0022] FIG. 7: a characteristic curve comparison of the noise characteristic of a fan.

[0023] In the figures, identical reference symbols apply to identical components.

DESCRIPTION

[0024] FIG. 1 is an embodiment of a rotationally symmetric protective grille 1 in a perspective view. Protective grille 1 has a grille web structure, formed from radial webs 2 that run spaced apart, intersecting in the circumferential direction, and coaxial circumferential webs 3 that run spaced apart in a radial direction. The radial webs 3 extend radially and axially out over the outermost circumferential web 3 and form an outer edge, running radially in the circumferential direction. On this radial outer edge of protective grille 1, in a single piece four attachment webs 4 are configured, each spaced apart in the circumferential direction at 90 degree angles. The attachment webs 4 are themselves partly formed from radial webs 2.

[0025] FIG. 2 shows protective grille 1 from FIG. 1 in a side view. Protective grille 1 has a circumferential radial outer region A and a central region Z around a central axis M. An imaginary envelope surface imaginary spanned from radial outer region A to central region Z is convexly curved in radial outer region A and planar and level in central region Z, so that central region Z extends parallel to a radial plane X of protective grille 1. Central region Z in the radial, inwards direction directly adjoins radial outer region A. The transition is thus a smooth one.

[0026] In radial outer region A, the number of radial webs 2 is greater than in central region Z. This is implemented by having radial webs 2 extend to differing lengths in the radial inwards direction and some of them not reaching the radially interior circumferential webs 2. Thus the mesh width in the clear within the grille web structure is greater in central region Z, with the flow resistance simultaneously being lowered thereby.

[0027] The plurality of circumferential webs 3 is situated in the radial direction of protective grille 1 each at a radial distance r to the axial center of protective grille 1. For example in FIG. 2 an interval r of the fifth of seven circumferential webs 3 is distinguished based on the central axis M. The distance of radially outermost circumferential web 3 is designated by R. Depending on their distance r to axial central axis M, circumferential webs 3 have a varying angular placement vis-à-vis an axial plane of protective grille 1, wherein in the embodiment shown, with a distance ratio r/R=1.0, (outermost circumferential web) an angular placement is set of α=60°, with a distance ratio r/R=0.85, an angular placement of β=40°, with a distance ratio r/R=0.70 an angular displacement of 30° and/or with a distance ratio r/R 0.55 in central region Z an angular placement δ of less than 20° is set vis-à-vis an axial plane of protective grille 1.

[0028] Combining the view of FIGS. 2 and 4, the convex curved envelope surface of protective grille 1 can be specified in greater detail. In radial outer region A, the convex curved envelope surface in a lateral cross section determines a partially elliptical contour 5, the ratio of the radial length a of radial outer region A of which to radius c of protective grille 1 assumes an example value of about 0.55 in the embodiment shown. Regarding the ratio of the axial height b of protective grille 1 to radius c, in the embodiment shown, an example value of 0.35 is determined. As an example, FIG. 5 shows an alternative embodiment of a partially elliptical contour 5 of the envelope surface with a more pronounced convex arching of radial outer region A and a/c ratios of over 0.6 and b/c of over 0.4.

[0029] FIG. 3 is a lateral sectional depiction of the protective grille from FIG. 1 with a cut through a radial web 2. Well perceived is the angular placement of circumferential webs 3. Additionally shown is the thin-walled design of radial webs 2 and circumferential webs 3, wherein the wall thickness B and height H were characterized with the aid of radial webs 2. However, this is correspondingly applicable to the circumferential webs 3. In the cross section both the radial webs 2 and the circumferential webs 3 are right-angled ones. The ratio of wall thickness B to height H is at a value of 5 in the embodiment shown. The thin-walled design of webs 2, 3 is made possible by the shape of protective grille 1.

[0030] FIGS. 6 and 7 show diagrams of characteristic line comparisons of the static overall efficiency (FIG. 6) and the sound characteristics (FIG. 7) at various volume flows through protective grille 1 of FIG. 1 and through traditional planar protective grilles. The characteristic curves of disclosure-specific protective grille 1 are designed by 100, and those of the traditional protective grilles by 200. The fan employed is always the same one. According to FIG. 6, the static overall efficiency of disclosure-specific protective grille 1 at a volume flow of 400 m.sup.3 per hour continues to rise strongly, and thereby generates a difference of over 2%, which is maintained up to the maximum volume flow. The difference in the noise characteristic is also shown starting at a volume flow of 400 m.sup.3 per hour, with disclosure-specific protective grille 1 quieter at maximum volume flow by over 4 dBA than traditional protective grilles. The values measured for disclosure-specific protective grille 1 are on a level with values of fan operation with no protective grille at all.

[0031] The disclosure is not limited in its implementation to the preferred embodiments indicated above. Rather, a plurality of variants is conceivable, which also makes use of the depicted solution even with embodiments that are of fundamentally different types. For example, adjoining circumferential webs can also have an identical angular placement. Additionally, the surfaces of webs of the protective grille directed against the flow direction can have a further adapted shape, for example a rounded-off one.