Rotor assembly for an exhaust gas turbocharger

Abstract

In a rotor assembly for an exhaust gas turbocharger including a turbine wheel and a compressor wheel mounted on a common shaft for joint rotation wherein the turbine wheel consist of a metal aluminide or of a high-temperature resistant titanium alloy, the turbine wheel and the compressor wheel are disposed on the shaft in spaced relationship by way of a bearing sleeve via which the turbien wheel and the compressor wheel are axially firmly engaged by axial clamping structures associated with the common shaft.

Description

This is a Continuation-In-Part Application of pending International patent application PCT/EP2008/001996 filed Mar. 13, 2008 and claiming the priority of German patent application 10 2007 012 641.9 filed Mar. 10, 2007.

BACKGROUND OF THE INVENTION

The invention relates to a rotor assembly for an exhaust gas turbocharger including a compressor wheel and a turbine wheel mounted on a common shaft, wherein the turbine wheel consists of a metal aluminide or a high temperature-resistant titanium alloy.

DE 10 2005 015 947 B3 discloses a method for the connection of a first component of a metal aluminide or a high-melting Ti alloy with a second component of steel, wherein the connection is produced by a friction welding process. The two components can be joined in a positive manner by means of a nickel-containing intermediate piece. The presence of two joints is characteristic for the connection. This method serves especially for the production of a rotor assembly of an exhaust gas turbocharger, which comprises a turbine wheel consisting of aluminide or of a high-melting Ti alloy and a shaft of steel.

The advantage of a turbine wheel of a metal aluminide or a high-melting Ti alloy resides in a lower weight and, consequently, a reduction of the moment of inertia of the turbine wheel, whereby the response-behavior of an exhaust gas turbocharger is considerably to be improved.

It is the object of the present invention to provide a rotor assembly which comprises a reliable connection between a turbine wheel of a metal aluminide or a high-melting Ti alloy and a shaft of steel even at high temperature and high rotational speeds of the rotor assembly.

SUMMARY OF THE INVENTION

In a rotor assembly for an exhaust gas turbocharger including a turbine wheel and a compressor wheel mounted on a common shaft for joint rotation wherein the turbine wheel consist of a metal aluminide or of a high-temperature resistant titanium alloy, the turbine wheel and the compressor wheel are disposed on the shaft in spaced relationship by way of a bearing sleeve via which the turbien wheel and the compressor wheel are axially firmly engaged by axial clamping structures associated with the common shaft.

Due to the rotationally fixed connection between the turbine wheel and the compressor wheel via the shaft of the rotor assembly and a shaft sleeve disposed between the turbine wheel and the compressor wheel, an exhaust gas turbocharger having a reduced moment of inertia and thus an improved response behavior with high operational safety can be realized.

In one arrangement, the rotationally fixed connection can be made by means of at least one tensioning element arranged at one end of the shaft. A positive connection is thereby either provided between the other end of the shaft and the turbine wheel, or the other end comprises a further tensioning element for providing the axial engagement. Alternatively, the other end itself may be used to form a tensioning element. A secure positive connection between the compressor wheel and the turbine wheel can thus advantageously established by axial engagement which is not affected by the centrifugal forces and the high temperatures to which the turbine wheel is objected during high speed operation of the turbocharger.

The invention will become more readily apparent from the following description thereof on the basis of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in a longitudinal sectional view, a first embodiment of a rotor assembly according to the invention,

FIG. 2 shows a second embodiment of the rotor assembly wherein the turbine wheel of the rotor assembly comprises an integral elongated collar,

FIG. 3 shows a third embodiment of the rotor assembly in a third version, wherein the turbine wheel comprises a positive connection with a bearing sleeve,

FIG. 4 shows a fourth embodiment of the rotor assembly, wherein the turbine wheel comprises an insulating sleeve and an insulating disk, and

FIG. 5 shows a fifth embodiment of the rotor assembly in, wherein the shaft is positively installed in the turbine wheel in a positive manner.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the figures, the same or functionally equal components are provided with the same reference numerals.

FIG. 1 shows a first embodiment of the rotor assembly 1 in a longitudinal sectional view. The rotor assembly 1 comprises a compressor wheel 2 for taking in and compressing combustion air, a turbine wheel 3 for the expansion of exhaust gas and a shaft 4 with a rotational axis 5 connecting the compressor wheel 2 with the turbine wheel 3 in a rotationally fixed manner.

The rotor assembly 1 is provided especially for an exhaust gas turbocharger, which comprises a housing receiving the rotor assembly 1 in a rotatable manner. The housing comprises an air guide section, an exhaust gas guide section and a bearing section. The compressor wheel 2 is disposed in the air guide section, the turbine wheel 3 is disposed in the exhaust guide section, and the shaft 4 is rotatably supported in the bearing section.

The exhaust gas turbocharger serves for increasing the performance of an internal combustion engine. The internal combustion engine usually has an combustion air intake duct, and an exhaust gas line, wherein the air guide section is arranged in the intake duct and the exhaust guide section in the exhaust gas line. During the operation of the internal combustion engine, the turbine wheel 3 is rotated by the exhaust gas of the internal combustion engine, and the compressor wheel 2 is rotated by means of the shaft 4, so that it takes in combustion air and compresses it.

The turbine wheel 3 is made of a metal aluminide or a high-temperature resistant titanium aluminum alloy. The advantage of these materials is, in addition to a low heat expansion, is their favorable strength-density ratio, that is, they have a high strength with a low density. The mass of the turbine wheel 3 is reduced by about half compared to a turbine wheel 3 consisting of for example the usual material Inconel 713 C. The moment of inertia of the mass of the rotor assembly 1, which characterizes the response behavior of the exhaust gas turbocharger, can thus be reduced considerably. The turbine wheel 3 as shown in FIG. 1 has an axial opening 6 which extends fully through the turbine wheel 3 and in which the shaft 4 is received. Due to the opening 6, there are essentially no radial and centrifugal forces, which occur during operation of the exhaust gas turbocharger and which may lead, depending on their size, to deformation and finally to breakage of the turbine wheel 3, effective between the shaft and the turbine wheel 3 via the surface delimiting the opening 6 at its circumference.

If the turbine wheel 3 were made of a usual material (e.g. Inconel 713 C), it would have a relatively low durability during operation with the arrangement according to the invention, as, due to the large mass the tensions occurring as a result of the centrifugal forces at the opening 6 would be so large, that the strength of the usual material would be too low for a continuous operation. The centrifugal forces need to be accommodated in the radial direction and, at the same time, torsional forces need to be transmitted in the tangential direction, which are so high that, with a turbine wheel 3 made of a usual material, the operation of the exhaust gas turbocharger would result in early material failure of the rotor assembly 1.

The shaft 4 is accommodated in the opening 6, and the turbine wheel 3 is arranged adjacent an end head 7 of the shaft 4 and is connected to the shaft 4 for example by a press-fit. The press-fit already constitutes a form of the positive connection, as the connection between the shaft 4 and the turbine wheel 3 is effected by means of frictional forces.

The compressor wheel 2 is positioned at an end 8 of the shaft 4 opposite the first end head 7. A sleeve 10 is arranged on the shaft 4 between the turbine wheel 3 and the compressor wheel 2, which sleeve forms a low-friction bearing of the shaft 4 in the bearing section.

The shaft 4 comprises a tensioning element 9 arranged at the second end 8 for the rotationally fixed connection of the turbine wheel 3 with the compressor wheel 2, wherein an axial force transmission is provided by means of a tensioning element 9.

The shaft 4 includes the end head 7 in the shape of a nut, so that the first end 7 represents a tensioning engagement element which may also be in the form of a nut threaded onto the shaft 4. By the action of a force provided by the tensioning element 9, the rotationally fixed connection between the turbine wheel 3, the shaft 4, the sleeve 10 and the compressor wheel 2 can be established, whereby the connecting forces extend mostly in axial direction of the shaft 4.

The sleeve 10 is in the form of a hollow cylinder and has a reinforcement at its end facing the turbine wheel 3, in which an annular first recess 11 is arranged at the circumference of the sleeve 10. The recess 11 serves especially for the reception of sealing elements.

In a second version of the exhaust gas turbocharger according to FIG. 2, the turbine wheel 3 includes an axial collar 13 extending from its end face 12, wherein the annular first recess 11 is arranged. The sleeve 10 comprises a simple cylindrical structure without reinforcement.

It is an advantage of the second embodiment that the sleeve 10 has a small wall thickness W, so that only a small expansion of the sleeve 10 during the operation of the rotor assembly 1 as a result of heat generation can be expected during operation even at high rotational speed of the rotor assembly 1. Additionally, temperature stresses at the collar 13 are smaller, so that an improved centering of the turbine wheel 3 on the shaft 4 is achieved.

In a further embodiment, an annular carrier 14 in the form of a ring carrier with a U-profile is positioned in the first annular recess 11, the manufacture of which can be integrated into a manufacture process for the turbine wheel 3, for example by a casting method. This ring carrier 14 is provided for the reduction of wear and consists of a corresponding material, for example ceramics.

For ensuring the operation of the exhaust gas turbocharger, the rotor assembly 1 needs to be balanced as well as possible, which can be achieved by maintaining the radial position of the turbine wheel 3, the shaft 4, the compressor wheel 2 and the sleeve 10. The corresponding centering may be obtained by a feature of a third embodiment as shown in FIG. 3. The turbine wheel 3 comprises a centering collar 15 at its collar 13, by means of which the sleeve can be accurately fixed radially with respect to the turbine wheel 3. The sleeve 10 includes at its end facing the centering collar 15 a recess 16, in which the centering collar 15 is accommodated.

As the bearing locations in the bearing section have to be kept as cool as possible, the heat transport from the turbine wheel 3 to the shaft 4 or to the sleeve 10 has to be limited. For reducing the heat transport from the turbine wheel 3 to the sleeve 10, an air gap 19 is provided between a first surface 17 of the centering collar 15 facing away from the of the turbine wheel 3 and a second surface 18 of the second recess facing the turbine wheel 3.

In a further embodiment, the end of the sleeve 10 facing the compressor wheel 2 is firmly connected to a bearing collar 25 of the compressor wheel 2.

In a fourth version according to FIG. 4, an insulating sleeve 20 in the shape of a hollow cylinder is arranged in, the opening 6 extending along the rotational axis 5 for the heat insulation and/or centering. The insulating sleeve 20 is connected to the turbine wheel 3 in rotationally fixed manner by a press-fit. The shaft 4 is accommodated in the insulating sleeve 20.

The arrangement of an annular insulating disk 21 between the collar 13 and the sleeve 10 provides for further thermal decoupling of the hot turbine wheel 3 and the sleeve 10 particularly with a suitable choice of materials. The heat transfer between the turbine wheel 3 and the bearing locations in the bearing section to be kept cool can thereby be kept low. As the rotor assembly 1 according to the invention is suitable for a ball or air suspension in the exhaust gas turbocharger, the cooling of the bearing locations is especially important with a ball or air suspension bearings of the rotor assembly 1 due to very small bearing gaps.

In a fifth version according to FIG. 5, a positive connection is provided between the turbine wheel 3 and the shaft 4. The shaft 4 comprises a thread 22 at its first end 7, wherein the shaft 4 is preferably a tension bolt. The opening 6 is formed only partially extending through the turbine wheel 3 starting from the collar 13 in the direction of the rotational axis 5. A mating thread 24 for the positive connection of the turbine wheel 3 to the shaft 4 is provided at the third end 23 of the opening 6 arranged opposite the collar 13.

With the firm axial engagement between the turbine wheel 3 and the compressor wheel 2 via the sleeve 10 which also forms a bearing structure for the rotor assembly 1 the high temperatures and the high centrifugal forces to which the turbine wheel is subjected at high speeds do not affect the engagement between the turbine wheel and the compressor wheel via the sleeve 10.

Claims

1. A rotor assembly for an exhaust gas turbocharger, comprising a shaft (4) rotatable about an axis of rotation (5), a turbine wheel (3) mounted on the shaft (11) for the expansion of a first gaseous medium, and a compressor wheel (2) mounted on the shaft (4) for the compression of a second gaseous medium, and the turbine wheel (3) consisting of a metal aluminide, or of a high-temperature resistant titanium alloy and being rotationally fixed with respect to the compressor wheel (2) by means of the shaft (4), and the turbine wheel (3) having an axial opening (6) at least partially extending through the turbine wheel (3) and receiving the shaft (4) with a rotationally fixed connection between the turbine wheel (3) and the shaft (4) and a sleeve (10) disposed around the shaft (4) and arranged between the turbine wheel (3) and the compressor wheel (2) in firm axial engagement with the turbine wheel (3) and the compressor wheel (2).

2. The rotor assembly according to claim 1, wherein the shaft (4) has a first end (7) firmly engaged with the turbine wheel (3) and a second end (8) provided with tensioning means (9) for axially engaging the compressor wheel (2) with the turbine wheel (3) via the intermediate sleeve (10).

3. Rotor assembly according to claim 2, wherein the shaft (4) extends fully through the compressor wheel (3) and the tensioning means is a nut (9) threaded onto the shaft (4) for axially engaging the turbine wheel (3) and the compressor wheel (2) via the bearing sleeve (10).

4. The rotor assembly according to claim 1, wherein the turbine wheel (3) comprises a collar (13) at an end face (12) of the wheel (12), provided with an annular first groove (11) for receiving sealing elements.

5. The rotor assembly according to claim 4, wherein an annular carrier (14) is disposed in the annular groove (11).

6. The rotor assembly according to claim 1, wherein a centering collar (15) is provided at an end face (12) of the turbine wheel (3) for engaging the sleeve (10).

7. The rotor assembly according to claim 6, wherein the centering collar (15) and the sleeve (10) are firmly connected to each another.

8. The rotor assembly according to claim 6, wherein an air gap is provided between a first surface (17) of the centering collar (15) facing away from the end face (12) of the turbine wheel (3) and a second surface (18) of the sleeve (10) facing the end face (12) of the turbine wheel (3).

9. The rotor assembly according to claim 6, wherein an insulation sleeve (20) is arranged in the axial opening (6) between the turbine wheel (3) and the shaft (4).

10. The rotor assembly according to claim 6, wherein an insulating disk (21) is provided between a collar (13) of the turbine wheel (3) and the sleeve (10).

11. The rotor assembly according to claim 6, wherein the compressor wheel (2) is provided with a bearing collar (25) which is positively connected to an end of the sleeve (10) facing the bearing collar (25) for engagement with the compressor wheel (2).