Impeller for a fluid energy machine

Abstract

In an impeller for a fluid energy machine with a hub and a plurality of rotor blades which are mounted on the hub and around which a medium may flow through the fluid energy machine and which form a blade duct between two neighboring rotor blades with a blade duct length which extends in the axial direction of the impeller, wherein each rotor blade is connected to the hub via a first transition region with a first curvature and via a second transition region with a second curvature and with a straight conical blade duct bottom of the blade duct formed between the first transition region and the second transition region.

Claims

1. An impeller for a fluid energy machine, with a hub (2) having an axis of rotation (D) and a plurality of rotor blades (3) which are provided on the hub (2) and around which a medium flowing through the fluid energy machine may flow and wherein a blade duct (12) is formed between two neighboring rotor blades (3) with a blade duct length (SL) which extends in the axial direction of the impeller (1), each rotor blade (3) being connected with the hub (2) via a first transition region (6) with a first curvature (K1) and via a second transition region (7) with a second curvature (K2), the impeller having a blade duct bottom (13) of the blade duct (12) between the first transition region (6) and the second transition region (7) which is at least in sections formed with different rates of inclination with respect to the axis D of the hub (2) wherein, in an axial cross-sectional view, the blade duct bottom (13) is formed to extend axially along an essentially straight line defining a surface (F) which is inclined relative to an axial hub tangent plane (NT) at an angle (), wherein an intersection point (S) between the surface (F) and the hub tangent plane (NT) defines a total length (GL) of the surface (F) which extends in the circumferential direction of the hub (2) with a diameter increasing from the intersection point S toward the end of the length (GL), that is the beginning of a transition section (9).

2. The impeller according to claim 1, wherein, with the impeller (1) configured in the form of a compressor wheel, the angle () at the wheel exit (11), or with the impeller (1) configured in the form of a turbine wheel, the angle () at the wheel entrance exhibits a value ranging between 0.5 and 10.

3. The impeller according to claim 1 wherein, with the impeller (1) configured in the form of a compressor wheel, the total axial length (GL) of the surface (F) at least at the wheel exit (11), or, with the impeller (1) configured in the form of a turbine wheel, the total length (GL) of the surface (F) at least at the wheel entrance exhibits a value ranging between 1 mm and half of the distance between two neighboring rotor blades (3).

4. The impeller according to claim 1, wherein the total length (GL) of the surface (F) is formed continuously decreasing in the direction of the wheel entrance if the impeller (1) is configured in the form of a compressor wheel, or if the impeller (1) is configured in the form of a turbine wheel, is formed continuously decreasing in the direction of the wheel exit (11).

5. The impeller according to claim 4, wherein the total length (GL) has a value of 0 mm at approximately 35% of the total length of the rotor blade (3) if the impeller (1) is configured in the form of a compressor wheel starting from the wheel exit (11) in the direction of the wheel entrance or, if the impeller (1) is configured in the form of a turbine wheel starting from the wheel entrance in the direction of the wheel exit (11).

6. The impeller according to claim 1, wherein the angle () is continuously decreasing if the impeller (1) is configured in the form of a compressor wheel starting from the wheel exit (11) in the direction of the wheel entrance or if the impeller (1) is configured in the form of a turbine wheel starting from the wheel entrance in the direction of the wheel exit (11).

7. The impeller according to claim 1, wherein the angle () at approximately 35% of the total length of the rotor blade (3) has a value of 0 if the impeller (1) is configured in the form of a compressor wheel starting from the wheel exit (11) in the direction of the wheel entrance or if the impeller (1) is configured in the form of a turbine wheel starting from the wheel entrance in the direction of the wheel exit (11).

8. The impeller according to claim 1, wherein the first transition region (6) is formed different from the second transition region (7).

9. The impeller according to claim 1, wherein the impeller (1) is essentially made from an aluminum alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a perspective view of a compressor wheel according to the state of the art indicating the stress distribution prevailing during operation,

(2) FIG. 2 is a schematic representation of a section of a development of a cross-section at the wheel exit of an impeller according to the state of the art,

(3) FIG. 3 shows a section of a schematic representation of a development of an inventive impeller at the impeller exit,

(4) FIG. 4 shows a diagram of a stress curve upon the change of a transition region of the impeller with corresponding sections of an impeller in a perspective representation and the respective existing stress distribution, and

(5) FIG. 5 is a schematic representation of a detailed view of a machined transition region of an impeller according to the state of the art.

DESCRIPTION OF THE INVENTION IN COMPARISON WITH A PRIOR ART ARRANGEMENT

(6) FIG. 1 shows an impeller 1 in the form of a compressor wheel for a compressor (not shown in detail), in particular a radial compressor, of an exhaust gas turbocharger (not shown in detail) for a combustion engine (not shown in detail). The compressor is arranged on the fresh air intake side of the combustion engine, where essentially fresh air is compressed by the compressor wheel 1.

(7) The compressor wheel 1 comprises a hub 2 as well as a plurality of rotor blades 3 which are fixedly connected with the hub 2. The hub 2 comprises a mounting opening (not shown in detail) by means of which the compressor wheel 1 is to be arranged on a shaft (not shown in detail) of the exhaust gas turbocharger and is non-rotatably connected to the shaft so that the compressor wheel 1 may be driven via the shaft by a turbine wheel (not shown in detail) of a turbine (not shown in detail) of the exhaust gas turbocharger to compress air. The rotor blades 3 and the hub 2 are formed integrally with each other. Between two neighboring rotor blades 3, a blade duct 12 is formed. The blade duct 12 has a blade duct length SL which extends in the axial direction of the impeller 1.

(8) FIG. 2 is a schematic view of a section of a development of a cross-section at the wheel exit 11 of the compressor wheel 1 according to the state of the art. The rotor blades 3 which are formed jointly with the hub 2 have both a suction side 4 and a pressure side 5 and are provided with a first transition region 6 on the pressure side as well as a second transition region 7 at the suction side 4. The first transition region 6 as well as the second transition region 7 are formed on a hub surface 8 of the hub 2 so that the joint areas extend both over a certain circumference of the hub 2 as well as over an axial extension of the hub 2. For the general description of the transition region 6, 7 it may be mentioned that the transition regions 6, 7 are characterized in that it forms a smooth connection between the rotor blade 3 and the hub 2. This means in other words, that, by means of the transition region 6, 7, discontinuities such as e.g. edge-like transitions in the connection area between hub 2 and rotor blade 3 are eliminated.

(9) Extending over the circumference of the hub 2, the first transition region 6 has a first curvature K1 with a first radius of curvature R1 and the second transition region 7 has a second curvature K2 with a second radius of curvature R2, wherein the second radius of curvature R2 is smaller than the first radius of curvature R1. However, the first radius of curvature R1 could also be formed corresponding to the second radius of curvature R2, or the first radius of curvature R1 could be smaller than the radius of curvature R2. This is dependent on the inclination of the rotor blade 3 relative to the hub 2. The first curvature K1 as well as the second curvature K2 could also comprise not only one radius but several radii merging into each other, so that in a section transversely to an axis of rotation D the first curvature K1 or the second curvature K2, respectively, is formed curved following any curve function.

(10) In their axial extension, the radius of curvature R1 and the radius of curvature R2 of the first transition region 6 or of the second transition region 7, respectively, are uniform or variable. In the state of the art, the first transition region 6 and the second transition region 7 have an essentially circular-segmented shape.

(11) An inventive impeller 1 is herein configured e.g. in the form of a compressor wheel according to FIG. 3. Here, a first section 9 of the first transition region 6 of the rotor blade 3, which is arranged opposite the second transition region 7 of the neighboring rotor blade 3, is defined by an endpoint TP of the first curvature K1. This means that the first transition region 6 has a first curvature (R1) up to the end curve 14 along the blade duct 12 over the entire blade duct length SL.

(12) Similarly, a second end 10 of the second transition region 7 of the rotor blade 3 is defined by the lowest point TP of the second curvature K2. This means that the second transition region 7 has a second end curve 15 along the blade duct 12 over the entire blade duct length SL, wherein the first end curve 14 and the second end curve 15 are positioned adjacent to each other, and the blade duct bottom 13 is formed between the first end curve 14 and the second end curve 15 extending both axially and in the circumferential direction of the hub 2.

(13) Between the first transition region 6 and the second transition region 7 of the neighboring rotor blades 3 and thus between the first end curve 14 and the second end curve 15, the blade duct bottom 13 is formed variable in the circumferential direction as well as at least partially in the axial direction of the blade duct 12.

(14) In this exemplary embodiment, the blade duct bottom 13 is variably formed so that the blade duct bottom 13 adapts smoothly to an essentially planar surface F starting from the first end curve 14. This surface F is inclined at an angle relative to a hub tangent plane NT. In other words, the surface F is inclined in the representation of FIG. 3 clockwise towards the axis of rotation D starting from the first end 9 of the first transition region 6.

(15) A section line S between the hub tangent plane NT and the surface F defines the total length GL of the surface F in the circumferential direction. This means that the angle depends on the total length GL. The blade duct bottom 13 starting from the second end curve 15 could also be made to provide for a smooth transition to the surface F. This means that the surface F would then be inclined counterclockwise starting from the second transition region 7 towards the axis of rotation D. This means in other words that the actually formed blade duct bottom 13 need not be truly plane but may be defined by means of this surface F. Thus, the surface F could also be seen as a virtual surface F which, starting from the section line S may virtually extend along the blade duct bottom 13 at the angle over the total length GL.

(16) The total length GL of the surface F again is a function of the distance of two neighboring rotor blades 3. The distance of two neighboring rotor blades 3 corresponds to the blade duct width in the circumferential direction and is the distance which, when viewed clockwise, is formed between the first end curve 14 and the second end curve 15.

(17) FIG. 4 is a diagram which shows stress conditions in a compressor wheel, wherein the total length GL and the angle are varied. Starting from the compressor wheel 1 shown in Fig. a), which has no variably formed blade duct bottom 13, a significant stress reduction can be achieved with an increasing total length GL and an increasing angle .

(18) It was found to be particularly advantageous as shown in FIG. 4 b), that the total length GL should not be less than a minimum length of 1 mm and the angle should not have a value smaller than 0.5 in order to achieve stress reduction. For the sake of clarity, the reference numerals in the figures are limited to the absolute minimum.

(19) In the inventive impeller 1 in the form of a compressor wheel according to FIG. 4 e), a highest point or a highest curve of the blade duct bottom 13, respectively, does not necessarily correspond with the first end curve 14, relating to a distance between the axis of rotation D and the blade duct bottom 13. The reason for this is that depending on the embodiment of the impeller 1 as well as its load distribution or load cycle, respectively, and the max load or the resulting stress, respectively, an adequately adapted design of the blade duct bottom 13 is required.

(20) The first transition region 6 extending in the axial direction of the hub 2 is formed essentially constant with the first curvature K1, wherein the surface F of the blade duct bottom 13 in respect to the total length GL as well as to the angle starting from a wheel entrance (not shown in detail) towards the wheel exit 11 increases.

(21) During operation of the compressor wheel 1, the intake air sucked in flows into the compressor wheel 1 via the wheel entrance (not shown in detail), then flows around the rotor blades 3 while being accelerated and, via the wheel exit 11 into an essentially diffusor-like duct (not shown in detail) where the air pressure increases.

(22) In the flow direction of the air, i.e. starting from the wheel entrance towards the wheel exit 11, the loads and thus the stresses in the first transition region 6 and in the second transition region 7 increase, with the higher stresses occurring in particular in the first transition region 6 because it is formed in the pressure region. In order to achieve a particularly long service life of the compressor wheel 1, e.g. the first transition region 6, exhibits the constant radius of curvature R1 starting from the wheel entrance over an extension of approx. 65% of the total length of the rotor blades 3.

(23) The surface F, starting from approx. 65% of the total length of the rotor blade 3 is formed continuously increasing from a value of the total length GL of 0 mm as well as from a value of the angle of 0, wherein the value of the total length GL increases to approx. half the distance between two neighboring rotor blades 3 and the value of the angle increases to approx. 10 at the wheel exit 11. Thus, the first transition region 6 comprises a surface F which in combination with the radial extension of the first transition region 6 is formed as a ramp-like area at the wheel exit 11.

(24) This keeps the stresses low. The stresses increase in the first transition region 6 from the wheel entrance towards the wheel exit 11, because the blade duct bottom 13 in the area of the first transition region 6 is adapted to the increasing loads and the resulting stresses.

(25) With this design of the blade duct bottom 13, which is adaptable to the relevant demand an efficient material utilization for the embodiment of the compressor wheel 1 is achieved, so that a very low weight as well as very low costs together with a very long service life can be realized. In the compressor wheel 1, the blade duct bottom 13 is therefore formed different in areas where high loads and thus high stresses exist, from areas where lower loads or stresses, respectively, exist. Thus, prevention, in particular of crack formation in the transition region 6, which leads to a premature failure of the compressor wheel 1, is realized.

(26) Herein, an impeller 1 is described by way of example whose blade duct bottom 13 is variably formed in the area of the first transition region 6 on the suction side 4 of the rotor blade 3. It is also possible that the blade duct bottom 13 in the area of the second transition region is variably formed in the area of the second transition region 7 on the pressure side 5 of the rotor blade 3. The blade duct bottom 13 in the area of the first transition region 6 or in the area of the second transition region 7, respectively, is to be adapted to the inclination of the rotor blade 3 relative to the hub 2. With an inclination of the rotor blade 3 in the direction of the suction side 4, for example, in particular the blade duct bottom 13 is to be variably and adequately formed in the area of the second transition region 5. Or more advantageously, the blade duct bottom 13 both in the area of the first transition region 4 and in the area of the second transition region 5 with an essentially non-inclined rotor blade 3 is to be variably formed.

(27) It should be noted that the configuration of an impeller 1 has been described by way of example for an impeller in the form of a compressor wheel, although a turbine wheel may be configured correspondingly as well. However, the area of the wheel entrance of the turbine wheel has to be designed according to the area of the wheel exit of the compressor wheel in this case, because higher stresses occur in the turbine wheel at the wheel entrance.

(28) The impeller 1 may be manufactured both by means of a milling method and by means of a casting method. If it is intended to produce a curvature K which differs from a circular section, i.e. to produce an ellipse section-like form of the curvature K, this is done according to the state of the art by a milling method through adjoining different radii Rx. As a consequence, at least when microscopically viewed, the surface of the curvature K is not smooth but exhibits peaks 16, as shown in FIG. 5. In particular for the application as a compressor impeller for an exhaust gas turbocharger of a combustion engine of a passenger vehicle, the inventive impeller 1 is particularly suited, because very high stress reductions and thus a significantly improved service life may be achieved without additional manufacturing cost expenditure.

(29) The impeller 1 may be made in particular e.g. from the material Inconel 713C, Inconel 718, MAR246 or TiAl.