WO2012139874A1

WO2012139874A1 - Compressor wheel and method for introducing internal stresses into a compressor wheel

Info

Publication number: WO2012139874A1
Application number: PCT/EP2012/055283
Authority: WO
Inventors: Stefan Reuter; Igor Makarenko
Original assignee: Continental Automotive Gmbh
Priority date: 2011-04-11
Filing date: 2012-04-10
Publication date: 2012-10-18
Also published as: DE102011079254A1

Abstract

The invention relates to a compressor wheel for an exhaust-gas turbocharger, which compressor wheel has a hub (1) with a hub bore (6) arranged centrally therein, a vane (2) which adjoins the hub (1) to the outside in the radial direction and which forms a wheel rear part (3), and compressor blades (4) arranged on the vane (2) and on the hub (1). Internal stresses are introduced into the material of the compressor wheel in the region of the hub (1) and/or in the region of the wheel rear part (3) and/or in the transition regions of the compressor blades to the hub (1) and vanes (2). The invention also relates to alternative methods for introducing said internal stresses into a compressor wheel for an exhaust-gas turbocharger.

Description

description

Compressor wheel and method for introducing residual stresses in a compressor wheel

The invention relates to a compressor wheel with inherent stresses and various methods for introducing residual stresses in a compressor wheel of an exhaust gas turbocharger.

Exhaust gas turbochargers serve to improve the efficiency of an internal combustion engine and thus to increase its performance. For this purpose, the exhaust gas turbocharger has a turbine with a turbine wheel and a compressor with a compressor wheel, wherein the two wheels are arranged on a common shaft. The turbine wheel is in this case driven via an exhaust gas mass flow of a connected internal combustion engine and in turn drives the compressor wheel. The compressor compresses fresh air sucked in and feeds it to the internal combustion engine. The common shaft is mounted in a bearing housing of the turbocharger. Furthermore, the turbine wheel of the turbine is arranged in a turbine housing and the compressor wheel of the compressor in a compressor housing.

Such an exhaust gas turbocharger has to fulfill various requirements during operation on the internal combustion engine or a connected engine. One of these requirements is to accommodate the high temperatures that may arise, for example, due to the hot exhaust gas mass flow in the turbocharger housing.

The usual construction of an exhaust-gas turbocharger thereby provides individual housings which each consist of a material adapted to the prevailing temperature there. In this case, the compressor housing is usually made of aluminum, while the bearing housing is made of gray cast iron, wherein the bearing housing can also be designed to be water cooled. The turbine housing In general, due to the high temperatures prevailing in this area, it is made of materials with a high nickel content. Due to the adapted, different materials for the individual housing, these housings are designed as separate parts which are connected to one another and must also be sealed against each other.

Due to the high rotational speeds that occur during operation of an exhaust ^¬ turbocharger, and the concomitant high centrifugal force that is made of aluminum or an aluminum alloy, preferably made of AI 2618 existing

Compressor wheel of an exhaust gas turbocharger during a vehicle ^¬ life very heavily loaded. To avoid fatigue fractures (bursting) of the compressor wheel, the design of the

Compressor wheel adapted to the speeds occurring and the associated loads. Based on material-specific properties and resulting centrifugal forces, which are determined using the finite element method (FEM method), in particular the wheel back, the blade geometry and the hub contour of the compressor wheel are constructed and designed such that the compressor wheel the loads occurring during operation Stands up. Measures to increase the stability of the compressor wheel but are regularly connected to Ma ^¬ terialverstärkungen and thus an increase in the total mass and thus the moment of inertia of the rotating parts of the ex ^¬ gas turbocharger and thus worsen the response of the turbocharger. The required construction ^¬ partial strength of a compressor wheel of an exhaust gas turbocharger is therefore in conflict with the requirement for the lowest possible moment of inertia of the running tool.

The object of the invention is to improve the component strength of an exhaust gas turbocharger without an increase in the mass moment of inertia ^¬ .

This object is achieved by a compressor wheel with the features specified in claim 1 and by the various methods of claims 3, 5 and 6. The compressor wheel for an exhaust-gas turbocharger has a hub with a hub bore centrally arranged therein, a wing adjoining the hub radially outward, having a wheel back, and compressor blades arranged on the wing and the hub. In this case, the compressor wheel is characterized in that internal stresses are introduced in the material of the compressor wheel, in the region of the hub and / or in the region of the wheel back and / or in transition regions between hub, blades and the blades characterized by blade connection radii.

The advantages of a compressor wheel with the given at ^¬ features of claim 1 are that calculations by the targeted introduction of residual stresses, particularly Druckeigenspan-, the component strength of the compressor wheel and thus also of the whole turbocharger is increased significantly. This advantageously makes it possible to design the contour of the wheel back and / or the contour of the hub of the compressor wheel, slimmer, without sacrificing strength. As a result, the mass of the component and thus the mass moment of inertia can be significantly reduced. This in turn improves the dynamics and responsiveness of the compressor wheel drive. In addition, the torque to be transmitted during dynamic operation is reduced by the reduction of the mass moment of inertia ^¬ . This increases the maximum possible

Compressor wheel size.

Another advantage of a compressor wheel with the features specified in claim 1 is that its life is increased.

In an advantageous embodiment, the compressor wheel is characterized in that the residual stresses in the area of the hub which is subjected to the greatest load in the operation of the compressor wheel due to centrifugal force loads and / or in the operation of the

Compressor wheel is the most heavily loaded area of the wheel back due to centrifugal force loads and / or the centrifugal forces which are most pronounced during operation of the compressor wheel. loaded areas of Schaufelanbindungsradien are introduced locally.

The particular advantages of a compressor, in which the residual stresses are introduced into these areas of the compressor wheel, are that a solidification of the material is present selectively in the regions in which in operation of the compressor impeller locally the highest mechanical Bean ^¬ spruchungen and thus tensions and / or strains occur and in which the initiation of fatigue fracture often occurs.

The introduction of the residual stresses, in particular the residual compressive stresses, in the compressor wheel is preferably carried out by means of the alternative or combined methods which can be used in claims 3, 5 and 6.

One of the methods for introducing the internal stresses, in a compressor wheel of the aforementioned expression, in particular for the ge ^¬ targeted introduction of residual stresses in the most heavily loaded in the operation of the compressor by centrifugal forces area of the hub, the Radrücken and the blade connection radii is characterized by a defined Overload and deformation of the most heavily loaded by centrifugal force areas of the hub, the Radrücken and Schaufelanbindungsradien by applying the

Compressor wheel with a defined overload speed, which is greater than the maximum operating speed for which the compressor is designed. The working speed is the maximum speed that must endure the running gear of a turbocharger in the intended operation in the long term, without being damaged. The overload speed is a certain amount beyond the working speed, so far that the desired residual stress generating, permanent deformations occur in the said areas, but still no destruction or undesired damage to the compressor wheel occurs. Thus, the maximum overload speed is limited by the so-called burst speed at which the Breaking strength of the material is achieved and the compressor wheel is destroyed. In the conventional for the compressor wheel Al alloys Berstdrehzahl is in a range between 1.3 to 1.7 times the allowable working speed.

In a further continued expression of the aforementioned method for introducing the residual stresses in a compressor wheel according to the aforementioned expression, the admission of the

Compressor wheel with the overload speed, in the course of an already performed process step in the production, in particular before, during or after the balancing ^¬ process of the compressor wheel done.

The aforementioned method has the advantage that residual stresses in all relevant areas can be introduced virtually simultaneously in one process step. Also, this method can be particularly easily integrated into existing processes of Her ^¬ positioning process, such as the balancing process of the compressor wheel in which this must also be set in rotation. The device and ver ^¬ technical technical overhead is kept low.

Another alternative method for introducing the internal stresses, in the region of the hub of a compressor wheel according to the aforementioned expression, is characterized by the following steps:

Closing a first end region of the hub bore with a first cover, on which a first cylindrical extension is provided, which extends into the hub bore and which rests sufficiently tight against an inner surface of the hub bore,

Closing a second end region of the bore with a second cover, on which a second cylindrical projection is provided, which extends into the hub bore and which rests sufficiently tight against an inner surface of the hub bore, - wherein the axial length of the two cylindrical extensions is set such that a portion of the hub bore is not covered by the projections used in the hub bore cylindrical projections,

- Introducing a pressure medium in the hub bore under pressure, through an opening provided in the first lid and

- Defined increase in the pressure in the hub bore, so far that in the uncovered region of the hub bore a defined deformation and associated residual stresses in the hub are caused.

Sufficient tightness or closing of the cylindrical extensions of the covers means that tightness against the escape of the pressure medium used in each case must be ensured to the extent that the pressure required for the deformation in the hub bore can be built up with reasonable effort. As a pressure medium is especially oil, especially hydraulic oil, but it can also other suitable liquids and possibly also gases are used.

This method has the advantage that targeted internal stresses can be introduced into the compressor wheel only in the region of the hub. Due to the highly precise controllability or controllability with simultaneous accurate detection of the pressure and its changes, another advantage of this method is that the desired deformations in the interior of the hub bore can be introduced very precisely defined.

Another alternative method for introducing the egg internal stresses, in a compressor wheel according to the above expression, is characterized by a defined upper ^¬ surface deformation in the regions of the hub and / or the Radrückens and or the areas of the blade connection radii. This is done in a Rollierverfahren using a controlled under contact pressure over the respective areas of

Compressor wheel guided reel body. By way of example, the roller body can be guided over the respective regions of the compressor wheel with the aid of a combination of program-controlled or regulated movement axes with a specific contact pressure. In this case, at least the surface solidifies these areas and achieved an increase in the overall resilience.

The advantage of this method is to be seen in the fact that the spatial positioning of the solidification areas, in which the residual stresses are introduced, can be done very precisely. Furthermore, this method has a high degree of flexibility with respect to different workpiece geometries.

The abovementioned methods for introducing residual stresses into a compressor wheel can be used both alternatively and in combination, as a supplement to one another.

Further details of the subject matter and the method of the invention can be taken from the figures and from their subsequent explanation.

Show it:

FIG. 1A shows a simplified sketch of a longitudinal section illustration of a partial region of a compressor wheel for an exhaust-gas turbocharger,

Figure 1B shows a three-dimensionally illustrated ^¬ segment-section of a compressor wheel with spaced compressor blades,

Figure 2 is a simplified diagram illustrating a

Method or the associated device for introducing residual stresses in the hub region of a compressor wheel for an exhaust gas turbocharger and Figure 3 is a diagram illustrating a method for introducing residual compressive stresses in a compressor wheel for an exhaust gas turbocharger by applying an overload speed

Figure 4 is a diagram illustrating the course of the mechanical residual stress in the compressor wheel as a function of the mechanical strain in the prior art and in the invention.

Functional and naming identical objects and details are indicated in the figures throughout with the same reference numerals. Figure 1A shows a simplified sketch of a longitudinal ^¬ sectional view of a portion (half) of a

Compressor wheel for an exhaust gas turbocharger of a motor vehicle. The illustrated compressor wheel has a hub 1 and a wing 2 connected to the hub and extending radially outward. Furthermore, the blade 2 of the compressor wheel forms a wheel back 3 on the compressor wheel rear side. Furthermore, the compressor wheel is equipped with compressor blades 4, of which in the figure 1, the sectional view corresponding to only a single can be seen. Further illustrated in FIG. 1A is the region B1 of the hub 1 and the region B2 of the wheel back 3 in which the internal stresses are introduced into the material.

The compressor blades in FIG. 1B, which show a segmental section of the compressor wheel in a spatial representation, are easier to recognize. The compressor blades 4 are over

Fillets, so-called blade connecting radii 12 connected to the hub 1 and the wing 2. The blade connection radii 12 simultaneously represent the regions B3 in which internal stresses are likewise introduced in the material.

In operation, the compressor wheel is rotatable about a rotation axis 5. The compressor wheel is rotationally symmetrical with respect to this axis of rotation. constructed metric and has in its central, extending in the axial direction area, a continuous, centrally arranged hub bore 6, which is cylindrically ^¬ forms.

By this hub bore 6 a shaft not shown in the figure 1 is guided in operation, the gas turbocharger extends through the bearing housing of the turbocharger through into the turbine housing from ^¬, in which a turbine wheel is arranged arrival, which is also mounted on the shaft (not shown) .

The design or the Radrückenkontur, blade geometry and Radnabenkontur the compressor wheel is determined by the yield point of the material of the compressor wheel, for example, aluminum material or aluminum alloys, in particular AL 2816 can be used. According to the ahead ^¬ invention, the yield strength of the aluminum material is increased signifi- cantly by introducing compressive stresses. Investigations have shown that the highest mechanical stresses and strains occur locally during operation of the compressor wheel in the region of the hub 1, the blade attachment radii 12 and in the region of the wheel back 3. These areas are indicated in FIGS. 1 and 2 by the reference symbols Bl, B2 and B3.

The following table proves the presence of a correlation of peripheral speed u _v with the mechanical stress ORadnabe in the hub 1 and the mechanical stress ö _Ra press in Radrücken 3:

By a targeted introduction of compressive residual stresses in the areas Bl and / or B2 and / or B3 of the compressor wheel, the Component strength of the compressor wheel can be significantly increased. Due to this increased component strength, the Radrü ^¬ cken contour and the hub contour of the compressor wheel can be constructed slimmer without sacrificing strength. This saves advantageously material and the Mas ^¬ senträgheitsmoment of the compressor wheel is reduced, the dynamics and the response of the drive of the compressor wheel improves and extends the life of the compressor wheel. FIG. 2 shows a simplified sketch to illustrate a device for carrying out a method for introducing compressive residual stresses into the hub region Bl of a compressor wheel for an exhaust gas turbocharger into which the

Compressor is used. By means of the device shown in FIG. 2, internal compressive stresses are introduced into the region Bl of the hub 1 of the compressor wheel which is subjected to the greatest load during operation.

The compressor wheel used in the device for introducing compressive residual stresses has, in addition to the aforementioned hub 1 connected to the hub, in the radial outward extending wings 2, at the back of the wing 2 a Radrücken 3, 4 blades and in its central region a cylindrical hub bore 6 on. The compressor wheel is rotationally symmetrical and can be rotated about an axis of rotation 5 during operation.

The device for introducing compressive residual stresses contains a first cover 7 and a second cover 8. The first cover 7 is provided for closing the first end region of the bore 6 provided in FIG. 2 on the left side. The second cover 8 is provided for closing the second end region of the bore 6 provided in FIG. 2 on the right-hand side.

In the first cover 7, an opening 9 is provided, through which a pressure medium for increasing the pressure prevailing in the hub bore 6 pressure can be introduced. This is in the figure 2 by illustrates the arrow p (t). The pressure medium is transported by means of a connecting line, not shown, to the opening 9. On the first cover 7, a first cylindrical extension 10 is provided, which extends into the bore 6, wherein the outer surface of the cylindrical extension to the inner shell of the hub 1 sufficiently tightly connects that introduced through the opening 9 in the bore 6 pressure medium not through a gap between the cylindrical extension 10 and the hub 1 can escape again.

On the second cover 8, a second cylindrical extension 11 is provided, which also extends into the bore 6, in turn, the outer surface of the cylindrical extension 11 to the inner shell of the hub 1 sufficiently tightly connected. Consequently, the introduced through the opening 9 in the bore 6 pressure medium can not escape through a gap between the cylindrical extension 11 and the hub 1 again.

The axial length of the two cylindrical extensions 10 and 11 is set such that a portion of the inner shell of the hub 1 remains free when inserted into the bore 6 cylindrical extensions. As can be seen in FIG. 2, this free region is the area B1 of the compressor wheel lying in the region of the hub 1, in which locally high component stresses and strains occur during operation of the compressor wheel. In the corresponding method wherein due to this high pressure in the range Bl of the compressor wheel local permanent deformation is established using the apparatus of high pressure into the hub bore 6 shown in Figure 2, caused ^¬ and thereby be introduced compressive residual stresses. This serves to reduce the mean mechanical stress during operation, which reduces the load on the compressor wheel during operation. By introducing the compressive residual stresses in the compressor wheel are in operation due to the Centrifugal load occurring tensile stresses of the component reduced.

An advantage of the method practicable with the aid of the apparatus sketched in FIG. 2 is that this method is well suited to be used in mass production of

Compressor wheels to find application.

The introduction of residual stresses, in particular compressive stresses, in the region of the wheel back 3 denoted by B2 in FIG. 1 can be achieved, for example, by means of a

Rolling process using roll bodies, which are rolled using a programmable arrangement of controlled / controlled axes of motion, as for example, an indutrial robot, while exerting a high pressure over this range. The resulting deformations of the material in this area bring the desired Eigenspannugen in the material with it. Such a method can also be carried out in an advantageous manner within the scope of the production of the compressor wheel. The method of rolling can also be applied to the area B2 in the area of the hub bore 6 and the area of the blade attachment radii 12, B3. For introducing residual compressive stresses in the

Shovel connection radii in the rolling method, for example, an industrial robot assembly can be used, which makes it possible to follow the contour of the Schaufelanbindungsradien 12 during the rolling.

Furthermore, residual compressive stresses in the areas B1, B2 and B3 can be realized by applying the compressor wheel with an overload speed no. A possible speed curve of the compressor wheel when using this method is shown in the speed diagram in Figure 3. The congestion is no speed to the difference value _D n higher than the maximum speed allowed in operation ΠΜΑΧ of the exhaust turbo supercharger ^¬. By the operation of the compressor wheel in Überla ^¬ processing speed range it comes to plastic deformation in the areas of Bl, B2 and B3, the residual compressive stresses in the areas rich Bl, B2 and B3 and thus causes a lower mechanical mean voltage during operation. The reduction of the mechanical mean voltage leads to an increase in the life of the compressor wheel.

The overload speed no can for example be realized during the already required balancing process in the production process. 4 shows a diagram for illustrating the course of the mechanical stress σ in the compressor wheel as a function of the mechanical strain ε on the one hand in a compressor wheel according to the prior art and on the other hand in a

Compressor wheel according to the invention. Here, in the upper left part of the diagram of the course of the stress-strain curve according to the prior art, that is shown with a compressor introduced without residual stresses, and with a center voltage o ^~ _m, i. The subsequent curve (characterized by the surrounding oval) reflects the plastic deformation when introducing the internal stresses.

In the lower part of the diagram is the profile of the chip-voltage-strain curve for a compressor according to the He ^¬ invention, ie with introduced in the compressor and a residual stresses Mittelspannug o _m represented 2r. From this curve ^¬ course of Figure 4 it can be seen that by the introduction of residual compressive stresses in a compressor wheel, via local plasticization of the material, tensile stresses of

Compressor in operation, which are due to the centrifugal load, are reduced. By the introduction of compressive stresses in the center voltage of operation is o ^~ _m, i on o _m, 2 at the same voltage amplitude o ^~ _a reduced.

Claims

claims

A compressor wheel for an exhaust-gas turbocharger, which has a hub (1) with a hub bore (6) arranged centrally therein, a wing (2) radially outwardly adjoining the hub (1), a wheel back (3) and on the wing (FIG. 2) and the hub (1) arranged compressor blades (4), characterized in that in the material of the compressor wheel, in the region of the hub (1) and / or in the region of the Radrücken (3) and / or in by Schaufelanbindungsradien ( 12) marked transition areas between the hub (1), wings (2) and the blades (4), residual stresses are introduced.

2. Verdicheterrad according to claim 1, characterized in that the residual stresses in the operation of the compressor wheel through

Centrifugal loads on the most heavily loaded area (Bl) of the hub (1) and / or in the operation of the compressor wheel by centrifugal loads most heavily loaded area (B2) of the Radrücken (3) and / or in the operation of the compressor wheel by centrifugal stresses most heavily loaded Regions (B3) of the Schaufelanbindungsradien (12) are introduced locally.

3. Method for introducing the residual stresses, in a

Compressor wheel according to claim 2, characterized by a defined overloading and deformation of the strongest by centrifugal force loaded areas of the hub (1), the Radrücken (3) and the Schaufelanbindungsradien (12) by acting on the compressor wheel with a defined overload speed (nu), the larger is the maximum working speed (n _Max ) _r for which the compressor wheel is designed.

4. The method of claim 3, for introducing the internal stresses in a compressor wheel according to claim 2, characterized in that the loading of the compressor wheel with the Überl- speed (nu), takes place in the course of a balancing process of the compressor wheel.

5. The method for introducing the residual stresses in the region of the hub (1) of a compressor according to claim 1 or 2, ge ^¬ characterized by the steps of:

- Closing a first end portion of the hub bore (6) with a first lid (7) on which a first cylindrical

Extension (10) is provided, which extends into the hub bore (6) and which is sufficiently tight against an inner surface of the hub bore (6),

- Closing a second end portion of the bore (6) with a second cover (8) on which a second cylindrical

Extension (11) is provided, which extends into the hub bore (6) and which fits tightly against an inner surface of the hub bore (6),

- Wherein the axial length of the two cylindrical extensions (10,11) is set such that a portion of the

Hub bore (6) is not covered by the extensions (10, 11) when the cylindrical projections (10, 11) are inserted into the hub bore (6),

- introducing a pressure medium into the hub bore (6) under pressure, through an opening (9) provided in the first cover (7) and

- Defined increase in the pressure in the hub bore (6), so far that in the uncovered region of the hub bore (6) a defined deformation and associated inherent stresses in the region of the hub (1) are caused.

6. Method for introducing the residual stresses, in a

Compressor wheel according to claim 1 or 2, characterized by a defined surface deformation in the areas of the hub (1) and / or the Radrücken (3) and or the areas of Schaufelanbindungsradien (12) in a Rollierverfahren using a controlled under contact pressure over the respective areas the compressor wheel guided roller body.