DE102016211807A1 - Turbocharger for an internal combustion engine - Google Patents

Abstract

The invention relates to a turbocharger (1) for an internal combustion engine, comprising - a bearing housing (41), - a rotor shaft (14) on which a turbine wheel (12) and a compressor wheel (13) can be arranged in a rotationally fixed manner; and - at least one radial bearing (42), by means of which the rotor shaft (14) is rotatably mounted in the bearing housing (41), wherein - the radial bearing (42) has a bearing bushing (421) surrounding the rotor shaft (14), - Bearing bush (421) has a first material (422); and - between the rotor shaft (14) and the bearing bush (421) a layer of a second material (423) is arranged, wherein the first material (422) and the layer of the second material (423) each have different thermal expansion coefficients.

Description

The invention relates to a turbocharger for an internal combustion engine.

Exhaust gas turbochargers are increasingly used to increase performance in automotive internal combustion engines. This is happening more and more often with the aim of reducing the internal combustion engine with the same or even increased performance in size and weight while reducing consumption and thus the CO2 emissions, in view of increasingly stringent legal requirements in this regard. The operating principle is to use the energy contained in the exhaust gas flow to increase a pressure in an intake tract of the internal combustion engine and thus to effect a better filling of a combustion chamber of the internal combustion engine with air-oxygen. Thus, more fuel, such as gasoline or diesel, per combustion process can be implemented, so the performance of the engine can be increased.

For this purpose, the exhaust gas turbocharger has an exhaust gas turbine arranged in the exhaust tract of the internal combustion engine, a fresh air compressor arranged in the intake tract and a rotor bearing arranged therebetween. The exhaust gas turbine has a turbine housing and a turbine runner, which is arranged therein and driven by the exhaust gas mass flow. The fresh air compressor has a compressor housing and a compressor impeller arranged therein, which builds up a boost pressure. The turbine runner and the compressor runner are arranged on the opposite ends of a common shaft, the so-called rotor shaft, rotatably and thus form the so-called turbocharger rotor. The rotor shaft extends axially between the turbine runner and the compressor runner through the rotor bearing arranged between the exhaust gas turbine and the fresh air compressor and is radially and axially rotatably mounted therein, with respect to the rotor shaft axis. According to this construction, the turbine runner driven by the exhaust gas mass flow drives the compressor runner via the rotor shaft, whereby the pressure in the intake tract of the internal combustion engine, based on the fresh air mass flow behind the fresh air compressor, is increased and thereby a better filling of the combustion space with air oxygen is effected.

The storage system of exhaust gas turbochargers of smaller combustion engines must withstand increasing loads. For example, for inertia reduction reduced diameter of the turbine and / or compressor and associated high speeds of the rotor shaft and increasingly thinner engine oils, which reduce the friction power of the drive and thus losses, new challenges for the storage system. In addition, the carrying capacity and thus the robustness of the storage system for the application in modern cars limits set. Requirements for maximum storage robustness and a design suitable for large-scale production require an optimal compromise in the design of the storage system under the boundary conditions of varying operating conditions, manufacturing tolerances and feasibility.

An object of the invention is to provide a storage concept for a turbocharger, which contributes to an efficient operation of a turbocharger.

A turbocharger for an internal combustion engine is disclosed, which has a bearing housing and a rotor shaft on which a turbine wheel and a compressor wheel can be arranged in a rotationally fixed manner. The turbocharger has at least one radial bearing, by means of which the rotor shaft is rotatably mounted in the bearing housing. The radial bearing has a bushing that surrounds the rotor shaft. The bearing bush has a first material. Between the rotor shaft and the bearing bush, a layer of a second material is arranged, wherein the first and the second material each have different thermal expansion coefficients.

The bearing bush is, for example, a plain bearing bush. The bushing is disposed between the bearing housing, such as a part of the bearing housing, and the rotor shaft. Typically, the radial bearing is designed as oil-filled floating bush bearing. Between the rotor shaft rotating during operation and the bearing housing, the rotating bushing absorbs the radial forces occurring, such as imbalance forces. At the inner diameter of the bearing bush to the rotor shaft towards this is an inner bearing gap and the outer diameter of the bush to the bearing housing out an outer bearing gap is formed. The two gaps are filled at least during operation with oil to form lubricating films.

In addition to a basic design of the radial bearing, the bearing gaps represent parameters for achieving the load capacity in order to be able to absorb imbalance and rigid body forces, for example. These are essentially influenced by manufacturing tolerances. In addition, the bearing gaps change due to the different thermal expansions of the corresponding bearing components, in particular the bearing bush, during operation. Exemplary bearing gaps are in the range of a few hundredths of a millimeter, whereby the change of a gap from a few thousandths of a millimeter can already have a significant influence on the bearing system.

Thus, with increasing oil temperature (and thus the component temperature of the bearing bush and shaft), the viscosity of the oil decreases, which would reduce the bearing capacity of the bearing system. Furthermore, it was recognized that the thermal expansion of the bearing bush at high (oil) temperatures leads to a reduction of the outer bearing gap and an enlargement of the inner bearing gap. Accordingly, the bearing capacity of the radial bearing at the inner gap would deteriorate while improving at the outer gap.

By providing the location of the second material, efficient operation of the turbocharger is contributed. The position can be arranged for example on the rotor shaft or the bearing bush. It is also conceivable that two such layers are provided, one on the bush and one on the rotor shaft. The location of the second material means, for example, a layer, coating or other material accumulation. The position of the second material has, for example, a sliding surface which, depending on the arrangement, slides either in the bearing bush or around the rotor shaft. The arrangement between the bushing and the shaft means that in the following order, a shaft material of the shaft, the second material and the first material of the bushing are arranged one above the other, such as layer-like. In other words, in a radial direction with respect to the rotor shaft, a material transfer from the shaft material to the second and the first material takes place.

By exploiting the different thermal coefficients of the bearing components, the bearing clearance of the radial bearing can be advantageously changed during operation. By combining the first and second material with different thermal expansion coefficients, the inner and outer bearing gaps can be positively influenced during operation. In particular, can be achieved by appropriate choice of the first and second material that the inner gap does not increase or not significantly increased in operation at elevated temperatures, while the outer gap decreases in operation.

As a result, at high temperatures of the bearing components, the load bearing capacity on the outer side of the bush facing away from the shaft can be improved, while the load bearing capacity on the shaft-facing side of the bushing is not or not significantly reduced in comparison to conventional bearing systems.

It should be noted that a thermal expansion coefficient of a shaft material of the rotor shaft is typically very small.

By the term material is meant, for example, a substance, a material, a raw material or a composite material. It may be a pure material, such as copper, but also an alloy, such as brass act. A material differs from another material in its thermal conductivity coefficient.

Furthermore, when the engine or oil is cold, a further bearing gap can be realized in comparison to the operating state with high temperatures. Furthermore, acoustic impairments, for example due to the excitation of the so-called Sub2, due to the suppressed or at least reduced increase of the internal game can be avoided or reduced. Sub2 is understood to mean the translatory rigid body mod, which is excited due to instabilities in the inner lubricating (bearing) gap. This vibration is transmitted to the outside via the outer bearing gap and can be heard there as a constant tone, for example.

By means of the turbocharger described it is also not mandatory or only partially necessary to adapt the bearing gaps by Lagerpieleinengungen, such as by a suitable choice of manufacturing tolerances, to improve the carrying capacity and / or acoustic properties of the radial bearing in a given design. Furthermore, it is not absolutely necessary, for example, to reduce occurring forces by reducing imbalances and / or adaptations of the compressor and / or turbine wheel. The adaptation of the wheels would have limitations in the design of the compressor or turbine wheels and thus also in terms of a thermodynamic design. Adjustments of the bearing clearance or tolerances of the bearing components would require increased production costs and production costs.

Furthermore, it is not absolutely necessary to reduce the imbalance of the compressor or turbine wheel, which would also require increased costs. Furthermore, it is not absolutely necessary to make increased demands on lubricating oils, which could, for example, run counter to customer requirements. Finally, it is not absolutely necessary to fundamentally optimize the radial bearing design, for example to provide wider bushes and / or slide bearing surfaces. All the above-described measures would always be a compromise of different objectives, with the adaptation of one element or component negatively affecting another property. For example, an increase in the carrying capacity due to larger wings leads to disadvantages with respect to the overall structure, the frictional power or the acoustics of the turbocharger.

According to one embodiment, the bearing bush on the position of the second material. With In other words, the position of the second material is arranged directly on the bushing. Thus, the layer is part of the bush, which has two materials with different thermal expansion coefficients. The bearing bush is thus constructed in two parts. As a result, for example, the inner bearing gap between the rotor shaft and the position of the other material is formed. The bushing has approximately an outer ring with the first material and an inner ring with the second material. This allows the advantages and functions described above.

According to one embodiment, the layer of the second material has a separate coating. In particular, the layer on the side facing the shaft is provided with the additional sliding layer for sliding on the shaft. By means of the sliding layer dry running properties of the bearing bush can be improved. The lubricious coating is, for example, a layer of DLC (English = diamond-like carbon), chemically nickel, chromium or Teflon.

According to a further embodiment, the rotor shaft has the position of the second material. In other words, the situation is arranged directly on the rotor shaft. The position is thus part of the rotor shaft. Thus, the socket is made in one piece from the first material. In this embodiment, the inner bearing gap between the socket and the position of the second material is formed. For example, the heat conduction coefficients are selected such that a thermal expansion of the shaft is increased by means of the position of the second material, as a result of which the inner bearing gap does not increase or does not increase significantly. This embodiment also allows the aforementioned advantages and functions.

According to one embodiment, a separate coating is applied to the layer of the second material. In particular, the position on the side facing the bush is provided with the additional sliding layer for sliding. By means of the sliding layer dry running properties can be improved. The slide coating is analogous to above, for example, a layer of DLC, chemically nickel, chromium or Teflon. For example, the entire layer of the second material need not be provided with the coating, but only individual regions can be cost-effectively coated.

According to a further embodiment, the second material has a lower coefficient of thermal expansion than the bushing material. This contributes to the functions and advantages described above.

According to a further embodiment, the shaft material is steel material. The steel material typically has a very low thermal expansion coefficient. This is especially necessary to be able to absorb the high forces acting on the shaft.

According to a further embodiment, the bushing material is brass.

According to a further embodiment, the further material is aluminum.

Further advantages and functions are disclosed in the following detailed description of exemplary embodiments.

The embodiments are described below with the aid of the appended figures. Similar or equivalent elements are provided across the figures with the same reference numerals.

In the figures show:

1 a schematic sectional view of a turbocharger,

2 an embodiment of a radial bearing of the turbocharger in a schematic cross-sectional view and

3 a further embodiment of a radial bearing of the turbocharger in a schematic cross-sectional view.

1 schematically shows an exemplary exhaust gas turbocharger 1 in sectional view, of an exhaust gas turbine 20 , a fresh air compressor 30 and a runner camp 40 includes. The exhaust gas turbine 20 is with a wastegate valve 29 equipped and an exhaust gas mass flow AM is indicated by arrows. The fresh air compressor 30 has a thrust recirculation valve 39 on and a fresh air mass flow FM is also indicated by arrows. A so-called turbocharger rotor 10 the exhaust gas turbocharger 1 has a turbine runner 12 (also called turbine wheel), a compressor impeller 13 (also called compressor wheel) and a rotor shaft 14 on (also called wave). The turbocharger rotor 10 rotates in operation around a rotor axis of rotation 15 the rotor shaft 14 , The rotor axis of rotation 15 and at the same time the turbocharger axle 2 (also called longitudinal axis) are represented by the drawn center line and indicate the axial orientation of the exhaust gas turbocharger 1 , The turbocharger rotor 10 is with his runner shaft 14 by means of two radial bearings 42 and a thrust washer 43 stored. Both the radial bearings 42 as well as the thrust washer 43 be over Oil supply channels 44 an oil connection 45 supplied with lubricant.

In general, a common exhaust gas turbocharger has 1 , as in 1 shown, a multi-part construction. Here, a turbine housing can be arranged in the exhaust tract of the internal combustion engine 21 , A can be arranged in the intake tract of the internal combustion engine compressor housing 31 and between turbine housing 21 and compressor housing 31 a bearing housing 41 with respect to the common turbocharger axis 2 arranged side by side and connected to each other montagetechnisch.

Another unit of the exhaust gas turbocharger 1 represents the turbocharger rotor 10 representing the rotor shaft 14 that in the turbine housing 21 arranged turbine wheel 12 with an impeller blading 121 and in the compressor housing 31 arranged compressor impeller 13 with an impeller blading 131 having. The turbine wheel 12 and the compressor impeller 13 are on the opposite ends of the common rotor shaft 14 arranged and rotatably connected with this. The rotor shaft 14 extends in the direction of the turbocharger axis 2 axially through the bearing housing 41 and is in this axially and radially about its longitudinal axis, the rotor axis of rotation 15 , rotatably mounted, wherein the rotor axis of rotation 15 in the turbocharger axis 2 lies, so coincides with this.

The bearing housing 41 is axial between the turbine housing 21 and the compressor housing 31 arranged. In the bearing housing 41 is the rotor shaft 14 of the turbocharger rotor 10 and the required bearing arrangement for axial bearing and for pivotal mounting of the rotor shaft 14 added.

The bearing assembly is usually made of two axially spaced radial bearings 42 for rotary bearing and a thrust washer 43 to support in operation on the rotor shaft 14 acting axial forces. The bearings can be designed as plain bearings, as rolling bearings or magnetic bearings. Furthermore, there is the possibility of the combination of axial bearing and pivot bearing, for example in rolling bearings. The summary of the bearing components to a compact storage unit, also referred to as a storage cartridge, can be applied here.

For lubrication and oil supply of the bearing components are in the bearing housing 41 Oil supply channels 44 provided, via an oil connection 45 with an external oil supply (not shown) in connection and lead to the bearing components to be supplied.

On the, the fresh air compressor 30 facing side of the bearing housing 41 is a compressor housing connection flange 47 provided on which the compressor housing 31 on the bearing housing 41 connected.

On the, the exhaust gas turbine 20 facing side of the bearing housing 41 is a turbine housing flange 46 provided on which the turbine housing 21 on the bearing housing 41 connected. Furthermore, on this side of the bearing housing 41 between turbine housing 21 and bearing housing 41 a so-called heat shield 48 arranged, which is the turbine housing 21 facing housing wall of the bearing housing 41 as well as the bearing components in the bearing housing 41 covers and so against the high exhaust gas temperatures in the exhaust gas turbine 20 shields.

Further details of the turbocharger 1 are not explained in detail. It should be mentioned at this point that the turbocharger 1 is exemplary nature and can also be otherwise configured.

2 and 3 show exemplary embodiments of a radial bearing 42 of the turbocharger 1 in schematic cross-sectional views.

2 shows the rotor shaft 14 with corresponding rotor axis of rotation 15 , Furthermore, a part of the bearing housing 41 to recognize. The radial bearing 42 has a radial bearing bush 421 on that between the rotor shaft 14 and the bearing housing 41 is arranged. The bearing bush 421 is designed as a floating plain bearing bush. The bearing bush 421 has a two-part construction of two different materials with different coefficients of thermal conductivity. In an outer, the rotor shaft 14 remote area has the bearing bush 421 a first material 422 at which directly arranged a layer of a second material 423 is arranged, which is the rotor shaft 14 assigned and facing. In other words, the bearing bush 421 from two ring-like, interconnected material layers or layers 422 and 423 educated.

Between the first material 422 and the bearing housing 41 is an outer bearing gap 424 formed while between the location of the second material 423 the bearing bush 421 and the rotor shaft 14 an inner bearing gap 425 is trained.

The rotor shaft 14 is made of a steel material or a steel material as a shaft material. The first material 422 For example, brass (CuZn) and the location of the second material 423 consists in the embodiment of aluminum. The thermal expansion coefficient of the position of the other material 423 is less than that of the first material 422 , For example, the bushing is formed of a brass tube which is filled with aluminum to form the ply of the second material 423 filled and then processed by manufacturing technology.

The bearing bush 421 surrounds the rotor shaft 14 such that the location of the second material 425 around the shaft 14 can slide.

By means of the radial bearing described above, the advantages and functions mentioned above can be achieved. In particular, due to the combination of two different materials with different coefficients of thermal expansion is achieved that the outer region of the bearing bush 421 , like the first material 422 , in operation due to the heat in the radial direction 16 expands. This will cause the outer bearing gap 424 reduced. The reduction of the outer bearing gap 424 causes an increase in the bearing capacity of the radial bearing 42 , The location of the other material 423 expands compared to the first material 422 less strong in the radial direction 16 out, so that the inner bearing gap 425 not enlarged at all or significantly less. For example, an increase in play of the bearing bush 421 in operation by 15% compared to a conventional bearing assembly without additional second material 423 be reduced.

3 shows a further embodiment of the radial bearing 42 To achieve the advantages and functions described above. In the embodiment according to 3 is the location of the second material 423 not part of the bearing bush 421 but part of the rotor shaft 14 , For example, the location of the second material 423 as a coating on the rotor shaft 14 applied. Thus, the inner bearing gap is formed 425 between the bearing bush 421 and the location of the other material 423 out. Again, the thermal expansion coefficients are chosen differently analogous to above, so that the inner bearing gap 425 advantageously does not increase significantly during operation. For example, the increase in play in the inner bearing gap 425 be halved compared to a conventional storage.

The radial bearings described 42 According to the embodiments are particularly inexpensive to implement. For example, the turbocharger can be 1 produce significantly cheaper than compared to a turbocharger, the bearing gaps and tolerances of the bearing components manufacturing technology, for example, by higher production and manufacturing specifications are set. If the tolerances on the basis of the requirement already represent the possible production limits, the radial bearing concepts described make it possible to use a specific radial bearing design.

It should be noted that instead of two radial bearings 42 also only a radial bearing 42 is conceivable. It is also conceivable that the radial bearings 42 connected via a connecting portion and thus formed in one piece. Important is the additional material layer, which is either part of the wave 14 or the socket 421 is.

Claims (9)

Turbocharger ( 1 ) for an internal combustion engine, comprising - a bearing housing ( 41 ), - a rotor shaft ( 14 ) on which a turbine wheel ( 12 ) and a compressor wheel ( 13 ) are rotatably arranged; and at least one radial bearing ( 42 ), by means of which the rotor shaft ( 14 ) in the bearing housing ( 41 ) is rotatably mounted, wherein - the radial bearing ( 42 ) a bearing bush ( 421 ), which the rotor shaft ( 14 ), - the bearing bush ( 421 ) a first material ( 422 ) having; and between the rotor shaft ( 14 ) and the bearing bush ( 421 ) a layer of a second material ( 423 ), the first material ( 422 ) and the location of the second material ( 423 ) each have different thermal expansion coefficients. Turbocharger ( 1 ) according to claim 1, wherein the bearing bush ( 421 ) the position of the second material ( 423 ) having. Turbocharger ( 1 ) according to claim 2, wherein the position of the second material ( 423 ) has a separate coating. Turbocharger ( 1 ) according to claim 1, wherein the rotor shaft ( 14 ) the position of the second material ( 423 ) having. Turbocharger ( 1 ) according to claim 4, wherein the position of the second material ( 423 ) a separate coating is applied. Turbocharger ( 1 ) according to one of the preceding claims, wherein the position of the second material ( 423 ) has a lower thermal expansion coefficient than the first material ( 422 ) having. Turbocharger ( 1 ) according to one of the preceding claims, wherein a shaft material of the rotor shaft ( 14 ) is a steel material. Turbocharger ( 1 ) according to any one of the preceding claims, wherein the first material ( 422 ) Is brass. Turbocharger ( 1 ) according to any one of the preceding claims, wherein the second material ( 423 ) Is aluminum.

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