DE2815680A1 - FLEXIBLE FAN WHEEL - Google Patents

Description

The invention relates to a flexible fan wheel according to the preamble of patent claim 1.

Cooling fans or fans for motor vehicles are in the Usually coupled directly to the internal combustion engine of the vehicle, so that the speed of the fan wheel with the Speed of the internal combustion engine increases. At higher speeds of the internal combustion engine is consequently from the fan wheel a correspondingly higher amount of air is sucked through the radiator, so that the internal combustion engine is often cooled too much, resulting in a considerable reduction in their efficiency and an increase in the fuel consumption of the Internal combustion engine leads.

Furthermore, if the speed of the fan wheel is too high, there are strong and annoying noises, and also consumes a

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Such a cooling fan has excessive power at high speeds.
5

To remedy these difficulties has already been proposed been to produce the impeller from plastic with a certain elasticity. By suitable choice of the elastic Plastic material for the manufacture of the fan wheel is A desired deformation is achieved at higher speeds of the fan wheel, but without optimum operating properties be achieved. In addition, these conventional fan wheels often have unfavorable effects, if in the design or manufacture of the impeller blades minor mistakes are made.

The invention is based on the object of designing a fan wheel of the generic type in such a way that those described above Disadvantages are largely avoided. When the impeller according to the invention, the configuration of the At higher speeds of the fan wheel, blades inevitably change in an optimal way to achieve approximately ideal operating behavior To achieve the impeller without, however, the strength of the blades drops below the required level.

The stated object is achieved according to the invention by the features in the characterizing part of patent claim 1.

Further advantages and features of the invention emerge from the subclaims and the following description of a Embodiment with reference to the drawings. Show it:

Figure 1 is a partial front view of a

ner preferred embodiment of the

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finding;

Figure 2 vector diagrams of the flow in the radial

inner and radially outer area of the wing according to Figure 1;

FIG. 3 shows a representation similar to FIG. 1 for the

'Purification by centrifugal force he

sufficient bending of a suitable section of the wing according to Figure 1;

FIG. 4 shows a sectional view according to B-B in FIG.

gur 3 to explain the by the Zen

moment exerted by the trifugal force on the wing;

FIG. 5 shows a sectional illustration similar to FIG

according to B-B in Figure 3 to explain the

due to the pressure differences on the top and bottom of the wing generated bend;

Figure 6 is a diagram showing the deformation of a

conventional wing shows;

FIG. 7 shows a representation similar to FIG. 1

conventional wing showing the positions of deformation measuring elements with

the help of which the measuring points of the diagram according to FIG. 6 were determined; and

Figure 3 is a diagram that depends on the

- speed controls the air throughput for a

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Convenient and one according to the invention

Fan wheel shows. 5

In Figure 1, a blower wheel is shown in part. This includes a hub 10, on the integrally numerous radial Wings 11 are formed which are made of a conventional plastic material with suitable elasticity. Everyone Wing 11 is at its foot, i.e. near the hub 10, with a recess or recess 12 which is located on the rear edge of the wing 11.

The radial component of the velocity of the flow that occurs when the fan wheel rotates in the direction of an arrow B ' in Figure 1 due to the action of centrifugal forces and pressure differences on both sides of the wing 11 on the The air masses that arise are approximately the same on the inner and outer circumference, i.e. on the foot and head, of the wing 11. Of the Wing 11 is usually designed and shaped in this way.

The circumferential components of the flow velocities at the radially more inward and radially more outward locations of the vane 11 are proportional to the radius of the vane 11; the circumferential component of the flow velocity is thus greater radially further outside than radially further inside. This is shown in FIG. FIG. 2 applies to the same radius beam of the wing and has the same radial flow component on the inner circumference and on the outer circumference of the wing for both vector diagrams. It is assumed that the vector of the radial flow _{component is V 1} and that the vectors of the circumferential components on the inner circumference and on the outer circumference are v "and v ^, respectively, where v" is less than v_. is. The vector resulting in each case from V ₁ and V ₂ or V ₁ and v. Is

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V «or V ₁ ; with the circumferential direction, V ₁ encloses the angle S ₁ and with the circumferential direction V "encloses the angle S ₇ . The direction of flow near the outer circumference is indicated in FIG. 1 by streamline A and the direction of flow near the inner circumference is indicated by streamline C. It can be seen that an area not used for conveying air is present radially inside the streamline C and which does not contribute to the cooling of the internal combustion engine (not shown).

In the following, the bending of the flexible portion of the wing 11 due to centrifugal force will be referred to explained on Figure 3. In Figure 3:

P is the center of gravity of the flexible section, M is the mass of the flexible section, F is the centrifugal force acting on the mass M when the fan wheel rotates, Fx the circumferential component of the centrifugal force F.

The above parameters directly influence the bending of the fan wheel. Furthermore, in Figure 3: 25th

Fy is the radial component of the centrifugal force F.

The above size does not directly affect the deflection of the fan wheel.

The centrifugal force F acting at the center of gravity P of the wing 11 is broken down into Fx and Fy. The circumferential component Fx acting at the center of gravity P of the wing 11 is broken down into a component F ₁ , which runs perpendicular to the chord of the wing 11 (see FIG. 4), and a component F ₂ which is parallel to the

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Tendon runs.

It is assumed that the flexible portion of the wing 11 is articulated at a pivot point S and the bend takes place around a straight line running through this point. For the at

S. S pivot point S acting moment M then applies M = L χ F ,, where L means the distance between the articulation point S and the center of gravity P. The equation above describes one of the Main influencing variables for the curvature of the wing.

The angle of attack of the wing 11 is ß _f and the angle of attack of the wing 11 is ro (see Figure 5). FIG. 5 also shows the pressure distribution on the upper side and the lower side of the wing 11, specifically for the profile according to the section BB in FIG. 3, the forces resulting from the pressure distribution being shown by arrows. It goes without saying that there is an overpressure on the underside of the wing 11 and that there is a negative pressure on the upper side of the wing 11, which results from the principle on which the blower is based.

The center of the acting pressure forces is M ₁ . This center point is placed so that it is at least closer to the rear edge of the wing 11 than the articulation point S. Assuming that the center M ₁ and the articulation point S are _{separated from each other by the distance L 1} , the following applies to the moment T around the articulation point S due to the compressive forces: T _M = L ₁ XA (P ₁ - P ₂ )

Therein mean:

P ₁ pressure on the underside of the wing 11, P ₂ pressure on the top of the wing 11,

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A area.

The moment T given by the above equation is the other main influencing variable for the bending of the wing 11. The sum of the moments M n and T _7, ie the moment (M _g + T) around the pivot point S, is essentially for the bending of the wing 11 responsible. Since in a conventional wing 11 without a recess 12, as shown in Figure 7, the (fictitious) pivot point S is closer to the trailing edge of the wing than in a wing with a recess, the distances L ₁ and L between the conventional wing Articulation point S and the center of gravity P (see Figure 4) or the articulation point S and the center point M-. (see Figure 5) relatively small. In the conventional wing without recess, the moment (M _q + T) around the articulation point S is therefore significantly less than in the wing 11 with recess 12, so that there is no significant bending.

If the deformation in the root area 13 of a conventional wing, as shown in Figure 7, is measured, gives a course of the deformation, as shown in FIG. 6. For the measurement results shown in FIG were over the depth L., of the foot area 13 of the wing 11 five strain gauges were attached at equal intervals, and the impeller was set at 1000 rpm, 2000 rpm, 3000 rpm and Rotated 4000 rpm. In FIG. 6, the positions of the deformation measuring elements are on the abscissa and the positions on the ordinate Deformation applied. The greatest deformation occurs at position 2 in FIG. The stress distribution that is results from the deformation or accompanies it, delimits the area within which the recess 12 are formed can, in the following way. FIG. 1 shows the measured stress distribution for the wing shown in FIG

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represented by curve A ¹ .

Starting from the specified mechanical power of an internal combustion engine, its thermal power is calculated and then the required cooling capacity is determined in order to determine the air throughput to be delivered by the cooling fan at a certain level Set speeds. Finally, the outside diameter of the impeller, the angle of attack of the blades, the Depth of the wings and the like set according to the required air flow. It must also be used when dimensioning The necessary strength of the fan wheel, taking into account the speed, temperature, etc., can be guaranteed.

For example, in a particular motor vehicle, the maximum load on the fan wheel at 6000 rpm and a temperature of 80 ° C. Then when calculating the Shape of a wing without a recess taking into account its thickness, the strength for 8000 rpm and a temperature of 80 ° C, there is a difference of 8000 rpm - 6000 rpm = 2000 rpm for the speeds. Accordingly, the recess 12 of the wing can be dimensioned proportionally to the speed difference of 2000 rpm.

As a result, however, the location of the recess and the depth of the wing are not yet fixed. The location of the recess will be determined so that the recess is between the hub and the streamline C (see Figure 1), so that a flexible Wing 11 is obtained without its delivery rate being reduced. To also especially at low speeds To bring about no reduction in the delivery rate, the border of the recess preferably follows the streamline C at low speeds.

Since the deformation is greatest in a conventional wing

- 11 -

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is in position 2 (see Figures 6 and 7), it goes without saying that the greatest strength is in the area near the leading edge of the Wing is required.

If the maximum speed of the fan wheel without recess on which the design is based is N = 8000 rpm and the highest Operating speed have been set at N = 6000 rpm, the maximum strength P and the required operational strength P are determined taking into account the sash weight, the Centrifugal force and the radius are calculated in a known manner as follows:

P = Kmgr ( 2 TTN ) ²

⁶⁰

P = Kmgr ( 2 7T'N ) ²

Therein mean:

K safety factor,

g acceleration due to gravity,

m sash weight,

r radius of the center of gravity of the wing.

As the ratio of the maximum strength to the operational strength surrendered:

For the assumed numerical values, 40 ° of the cross-sectional area can thus be are consumed for the recess. If it is assumed that the cross-sectional area of the basic profile without a recess in the foot area of the wing K and that the Querschnxttsflache of the wing profile with recess in the foot area K, the depth of the recess is determined so

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that the relationship

S-

equal to the value,) ^L is. A wing, the recess of which has been defined in the above manner, has maximum flexibility without sacrificing required strength. 10

The depth of the recess is thus determined taking into account the remaining cross-sectional area from the cross-sectional area of the basic profile in the foot area.

Essential features of the recess are thus that they are large Allow flexibility, is located in the area that does not contribute to the air flow, and sufficient strength of the wing guaranteed.

In Figure 8 is the effect of the impeller according to the invention shown. In FIG. 8, the curve OD applies to a fan wheel with rigid blades, whereas the curve OE applies to a fan wheel with flexible wings according to the invention applies. In the hatched area r delimited by the curve OD and the curve OE is, the air throughput is reduced due to the recess 12 in the fan wheel according to the invention. The curve OF gives the required air flow again. It can be seen that the curve OE follows the curve OF on its safer side.

The flexible impeller according to the invention thus has a cylindrical one Hub and several radially extending wings, which are made of plastic with a certain elasticity and are formed integrally with the hub. At the trailing edge of each wing there is a recess that runs along it the line of flow closest to the hub and preferably

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according to the difference between the maximum strength and the required operational strength of the wing the formation of the recess is dimensioned.

It is understood that numerous changes and modifications to the embodiment described above are within the scope of FIG Invention are possible, which should therefore not be limited by the above description of an embodiment.

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Claims (11)

■ * ■ D IdT Γ * Patent attorneys: IEDTKE - DÜHLING - 3VlNNE - ijRUPE Dipl.-lng. H. Tiedtke Dipl.-Chem. G. Bühling Dipl.-Ing. R. Chins 281568Q Dipl.-Ing. P. Grupe Bavariaring 4, P.O. Box 20 24 8000 Munich 2 Tel .: (0 89) 53 96 53 Telex: 5-24845 tipat cable: Germaniapatent Munich 11. April 1978 B 8833 / case W-1028 Claims M. Fan wheel with a cylindrical hub and several radially extending blades, at least the blades made of plastic with a certain elasticity, characterized by a recess (12) on the rear edge of each vane (11) at its radially inner end, the recess along the line of flow closest to the hub (10) runs. 2. Fan wheel according to claim 1, characterized in that that the wings (11) and the hub (10) are integral are trained. 3. Fan wheel according to claim 1 or 2, characterized in that the depth of the recess (12) is determined is by the ratio of the cross-sectional area of the foot region (13) of the wing (11) in the basic profile before the Formation of the recess for the cross-sectional area of the foot area of the wing after the formation of the recess made equal to the ratio of the maximum strength to the required operational strength of the wing without a recess will. 90981 3/0659 Dresdner Bank (Munich) Account 3939 844 Postscheck (Munich) Account 670-43-804 2815 - 2 - B 8833 4. Fan wheel according to claim 1 or 2, characterized in that the recess (12) is proportional to Difference between the maximum value and the required operating value of the wing is formed without a recess. 9098 13/0659