DE102016211807B4 - Turbocharger for an internal combustion engine - Google Patents

Abstract

The invention relates to a turbocharger (1) for an internal combustion engine, which has 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). which the rotor shaft (14) is rotatably mounted in the bearing housing (41). The radial bearing (42) has a bearing bush (421) which has a first material (422) and surrounds the rotor shaft (14). A layer of a second material (423) is arranged between the rotor shaft (14) and the bearing bush (421), the first material (422) and the layer of the second material (423) each having different thermal expansion coefficients and the second material (423) is provided with an applied anti-friction coating.

Description

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

Exhaust gas turbochargers are increasingly being used to increase the performance of motor vehicle internal combustion engines. This is happening more and more often with the aim of reducing the size and weight of the internal combustion engine while maintaining the same or even increased performance and at the same time reducing consumption and thus CO2 emissions in view of increasingly strict 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 better fill a combustion chamber of the internal combustion engine with air-oxygen. This means that more fuel, such as gasoline or diesel, can be converted per combustion process, i.e. the performance of the internal combustion 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 in between. The exhaust gas turbine has a turbine housing and a turbine impeller arranged therein that is driven by the exhaust gas mass flow. The fresh air compressor has a compressor housing and a compressor impeller arranged therein that builds up a boost pressure. The turbine impeller and the compressor impeller are arranged in a rotationally fixed manner on the opposite ends of a common shaft, the so-called rotor shaft, and thus form the so-called turbocharger rotor. The rotor shaft extends axially between the turbine impeller and the compressor impeller through the rotor bearing arranged between the exhaust gas turbine and the fresh air compressor and is radially and axially rotatably mounted in this with respect to the rotor shaft axis. According to this design, the turbine impeller driven by the exhaust gas mass flow drives the compressor impeller via the rotor shaft, thereby increasing the pressure in the intake tract of the combustion engine, relative to the fresh air mass flow behind the fresh air compressor, and thus improving the filling of the combustion chamber with atmospheric oxygen.

The bearing system of exhaust gas turbochargers in combustion engines that are becoming smaller must be able to withstand increasing loads. For example, reduced diameters of the turbine and/or compressor wheel to reduce inertia and the associated high speeds of the rotor shaft as well as increasingly thinner engine oils, which reduce the frictional power of the drive and thus losses, represent new challenges for the bearing system. In addition, the load capacity and thus the robustness are There are limits to the storage system for use in modern cars. Requirements for maximum bearing robustness and a design suitable for large-scale production require an optimal compromise in the design of the bearing system under the constraints of varying operating conditions, manufacturing tolerances and feasibility.

From document DE 10 2012 207 660 A1 For example, a shaft arrangement for a turbocharger is known, with a rotatably mounted turbocharger shaft and at least one bearing arrangement for rotatably supporting the turbocharger shaft, at least one bearing element of the bearing arrangement being coated at least in sections with an amorphous carbon coating.

The publication further discloses DE 10 2010 046 596 A1 an exhaust gas turbocharger, which comprises a shaft with a bearing part connected to the shaft in a rotationally fixed manner and at least one bearing element which surrounds the bearing part on the outer circumference at least in some areas and via which the shaft is rotatably mounted. The bearing part is made of a material which has a higher coefficient of thermal expansion in the radial direction of the shaft than a material from which the bearing element is made.

Further versions of floating bushing bearings for a turbocharger are, for example, in the publications JP S57-76316 A and DE 690 04 849 T2 explained.

One object on which the invention is based is to provide a bearing concept for a turbocharger, which contributes to the 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 bearing bush that surrounds the rotor shaft. The bearing bush has a first material. A layer of a second material is arranged between the rotor shaft and the bearing bush, the first and second materials each having different coefficients of thermal expansion. The layer of the second material is either arranged on the bearing bush and is provided with a separate anti-friction coating applied to the side facing the rotor shaft, or the layer of the second material is arranged on the rotor shaft and is provided with a separate one on the bearing Anti-slip coating applied on the side facing the socket.

Typically, the radial bearing of a turbocharger is designed as an oil-flooded floating bush bearing. The bearing bushing is arranged between part of the bearing housing and the rotor shaft. Between the rotor shaft, which rotates during operation, and the bearing housing, the rotating bearing bush absorbs the radial forces that occur, such as unbalance forces. For this purpose, an inner bearing gap is formed on the inner diameter of such a bearing bush towards the rotor shaft and an outer bearing gap is formed on the outer diameter of the bush towards the bearing housing. The two gaps are filled with oil, at least during operation, 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 unbalance and rigid body forces. These are essentially influenced by manufacturing tolerances. In addition, the bearing gaps change during operation due to the different thermal expansions of the corresponding bearing components, in particular the bearing bush. Examples of bearing gaps are in the range of a few hundredths of a millimeter, although changing a gap of just a few thousandths of a millimeter can have a significant impact on the bearing system.

As the oil temperature increases (and thus the component temperature of the bearing bush and shaft), the viscosity of the oil decreases, which would reduce the load-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 in the outer bearing gap and an increase in the inner bearing gap. Accordingly, the bearing capacity of the radial bearing would deteriorate at the inner gap while it improves at the outer gap.

Providing the layer of the second material contributes to efficient operation of the turbocharger. The layer of the second material is arranged either on the rotor shaft or on the bearing bush. It is also conceivable that two such layers are provided, one on the bearing bush and one on the rotor shaft. The layer of the second material has a sliding surface which, depending on the arrangement, slides either in the bearing bush or around the rotor shaft. Arranging the second material between the bearing bush and the rotor shaft means that a shaft material of the shaft, the second material and the first material of the bush are arranged one above the other, for example in layers, in the following order. In other words, a material transition from the shaft material to the second and first materials takes place in a radial direction with respect to the rotor shaft.

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

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

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

The term material is understood to mean, for example, a substance, a material, a raw material or a composite material. This can be a pure material, such as copper, but also an alloy, such as brass. A material differs from another material by its thermal conductivity coefficient.

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

By means of the turbocharger according to the invention described, it is also not absolutely necessary or only partially necessary to adapt the bearing gap by reducing bearing play, for example by suitable selection of manufacturing tolerances, in order to improve the load-bearing capacity and/or acoustic properties of the To improve radial bearings for a given design. Furthermore, for example, it is not absolutely necessary to reduce the forces that occur by reducing imbalances and/or adjusting the compressor and/or turbine wheel. Adapting the wheels would have limitations in the design of the compressor or turbine wheels and thus also in terms of thermodynamic design. Adjustments to the bearing clearance or tolerances of the bearing components would result in increased production costs and manufacturing costs.

Furthermore, it is not absolutely necessary to reduce the unbalance of the compressor or turbine wheel, which would also result in increased costs. Furthermore, it is not absolutely necessary to place 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 bushings and/or plain bearing surfaces. All of the measures described above would always represent a compromise between different goals, with the adjustment of one element or component negatively affecting another property. For example, increasing the load capacity through larger wings leads to disadvantages in terms of the overall structure, the frictional performance or the acoustics of the turbocharger.

According to the first embodiment of the turbocharger according to the invention, the layer of the second material is arranged directly on the bearing bush. Thus, the layer of the second material is part of the bearing bushing, which has two materials with different coefficients of thermal expansion. The bearing bush is therefore constructed in two parts. This creates, for example, the inner bearing gap between the rotor shaft and the layer of the second material. The bearing bush has approximately an outer ring with the first material and an inner ring with the second material. This enables the advantages and functions described above.

According to the invention, the layer of the second material has a separate coating. The layer of the second material on the side facing the rotor shaft is provided with the additional sliding layer for sliding on the shaft. Using the sliding layer, the dry running properties of the bearing bush can be improved. The anti-friction coating is, for example, a layer of DLC (diamond like carbon), chemical nickel, chrome or Teflon.

According to the second alternative embodiment, the layer of the second material is arranged directly on the rotor shaft. The position of the second material is therefore part of the rotor shaft. The bearing bush is therefore made in one piece from the first material. In this embodiment, the inner bearing gap is formed between the bearing bush and the layer of the second material. For example, the thermal conductivity coefficients are selected so that thermal expansion of the rotor shaft is virtually increased by means of the layer of the second material, as a result of which the inner bearing gap does not increase or does not increase significantly. This configuration also enables the aforementioned advantages and functions.

According to the invention, a separate coating is also applied to the layer of the second material in the aforementioned second alternative embodiment. The layer of the second material is provided with the additional sliding layer for sliding on the side facing the socket. The sliding layer improves the dry running properties of the bearing. Analogous to the above, the anti-friction coating is, for example, a layer of DLC, chemical nickel, chrome or Teflon. For example, the entire layer of the second material does not have to be provided with the coating, but rather only individual areas can be coated cost-effectively.

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

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

According to a further embodiment, the bearing bush material is brass.

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

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

The exemplary embodiments are described below with the help of the attached figures. Elements that are similar or have the same effect are provided with the same reference numerals across the figures.

• 1 eine schematische Schnittansicht eines Turboladers,
• 2 ein Ausführungsbeispiel eines Radiallagers des Turboladers in einer schematischen Querschnittsansicht und
• 3 ein weiteres Ausführungsbeispiel eines Radiallagers des Turboladers in einer schematischen Querschnittsansicht.

Show in the figures:

• 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 exemplary embodiment of a radial bearing of the turbocharger in a schematic cross-sectional view.

1 shows schematically an exemplary exhaust gas turbocharger 1 in a sectional view, which includes an exhaust gas turbine 20, a fresh air compressor 30 and a rotor bearing 40. The exhaust gas turbine 20 is equipped with a wastegate valve 29 and an exhaust gas mass flow AM is indicated by arrows. The fresh air compressor 30 has a push-air recirculation valve 39 and a fresh air mass flow FM is also indicated by arrows. A so-called turbocharger rotor 10 of the exhaust gas turbocharger 1 has a turbine impeller 12 (also referred to as a turbine wheel), a compressor impeller 13 (also referred to as a compressor wheel) and a rotor shaft 14 (also referred to as a shaft). During operation, the turbocharger rotor 10 rotates about a rotor rotation axis 15 of the rotor shaft 14. The rotor rotation axis 15 and at the same time the turbocharger axis 2 (also referred to as the longitudinal axis) are represented by the center line and characterize the axial orientation of the exhaust gas turbocharger 1. The turbocharger rotor 10 is with its rotor shaft 14 stored by means of two radial bearings 42 and an axial bearing disk 43. Both the radial bearings 42 and the axial bearing disk 43 are supplied with lubricant via oil supply channels 44 of an oil connection 45.

As a rule, a common exhaust gas turbocharger 1, as in 1 shown, a multi-part structure. A turbine housing 21 which can be arranged in the exhaust tract of the internal combustion engine, a compressor housing 31 which can be arranged in the intake tract of the internal combustion engine and a bearing housing 41 between the turbine housing 21 and the compressor housing 31 with respect to the common turbocharger axle 2 are arranged next to one another and connected to one another in terms of assembly technology.

Another structural unit of the exhaust gas turbocharger 1 is the turbocharger rotor 10, which has the rotor shaft 14, the turbine impeller 12 arranged in the turbine housing 21 with impeller blades 121, and the compressor impeller 13 arranged in the compressor housing 31 with impeller blades 131. The turbine impeller 12 and the compressor impeller 13 are arranged on the opposite ends of the common rotor shaft 14 and are connected to it in a rotationally fixed manner. The rotor shaft 14 extends axially in the direction of the turbocharger axis 2 through the bearing housing 41 and is rotatably mounted therein axially and radially about its longitudinal axis, the rotor rotation axis 15, wherein the rotor rotation axis 15 lies in the turbocharger axis 2, i.e. coincides with it.

The bearing housing 41 is arranged axially between the turbine housing 21 and the compressor housing 31. The rotor shaft 14 of the turbocharger rotor 10 as well as the bearing arrangement required for axial bearing and rotational bearing of the rotor shaft 14 are accommodated in the bearing housing 41.

The bearing arrangement usually consists of two radial bearings 42 arranged at an axial distance from one another for rotational bearing and an axial bearing disk 43 for supporting axial forces acting on the rotor shaft 14 during operation. The bearings can be designed as plain bearings, rolling bearings or magnetic bearings. There is also the possibility of combining axial bearings and rotary bearings, for example in rolling bearings. Combining the storage components into a compact storage unit, also known as a storage cartridge, can also be used here. For lubrication and oil supply of the bearing components, oil supply channels 44 are provided in the bearing housing 41, which are connected to an external oil supply (not shown) via an oil connection 45 and lead to the bearing components to be supplied.

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

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

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

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

2 shows the rotor shaft 14 with the corresponding rotor axis of rotation 15. Furthermore, part of the Bearing housing 41 can be seen. The radial bearing 42 has a radial bearing bushing 421 which is arranged between the rotor shaft 14 and the bearing housing 41. The bearing bush 421 is designed as a floating plain bearing bush. According to the first alternative embodiment of the turbocharger, the bearing bush 421 has a two-part structure made of two different materials with different thermal conductivity coefficients. In an outer area facing away from the rotor shaft 14, the bearing bush 421 has a first material 422, on which a layer of a second material 423 is arranged directly, which is assigned and faces the rotor shaft 14. In other words, the bearing bush 421 is formed from two ring-like, interconnected material layers or layers 422 and 423.

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

The rotor shaft 14 is made of a steel material or a steel material as a shaft material. The first material 422 is, for example, brass (CuZn) and the layer of the second material 423 consists of aluminum in the exemplary embodiment. The coefficient of thermal expansion of the layer of the further material 423 is lower than that of the first material 422. For example, the bushing is formed from a brass tube, which is filled with aluminum to form the layer of the second material 423 and then processed for production.

The bearing bush 421 surrounds the rotor shaft 14 in such a way that the layer of the second material 425 can slide around the shaft 14.

The advantages and functions mentioned can be achieved using the radial bearing described. In particular, due to the combination of two different materials with different thermal expansion coefficients, the outer region of the bearing bush 421, such as the first material 422, expands in the radial direction 16 during operation due to the heat. This reduces the outer bearing gap 424. The reduction of the outer bearing gap 424 causes an increase in the load-bearing capacity of the radial bearing 42. The position of the further material 423 expands less in the radial direction 16 compared to the first material 422, so that the inner bearing gap 425 is not enlarged at all or is enlarged to a significantly lesser extent . For example, an increase in play of the bearing bush 421 during operation can be reduced by 15% compared to a conventional bearing arrangement without additional second material 423.

3 shows a further exemplary embodiment of the radial bearing 42 according to the invention in order to achieve the advantages and functions described above. In the exemplary embodiment according to 3 The position of the second material 423 is not part of the bearing bush 421, but, according to the second alternative embodiment of the turbocharger according to the invention, part of the rotor shaft 14. For example, the position of the second material 423 is applied as a layer to the rotor shaft 14. The inner bearing gap 425 is thus formed between the bearing bush 421 and the layer of the second material 423. Again, the thermal expansion coefficients are chosen differently, analogous to above, so that the inner bearing gap 425 is advantageously not significantly enlarged during operation. For example, the increase in play in the inner bearing gap 425 can be halved compared to conventional bearings.

The described radial bearings 42 according to the exemplary embodiments can be implemented particularly cost-effectively. For example, the turbocharger 1 can be manufactured significantly more cost-effectively than in comparison to a turbocharger, with the bearing gaps and tolerances of the bearing components being adjusted in terms of production technology, for example through higher production and manufacturing specifications. If the tolerances based on the requirement already represent the possible production limits, the radial bearing concepts described enable the use of a specific radial bearing design.

It should be noted that instead of two radial bearings 42, only one radial bearing 42 is also conceivable. It is also conceivable that the radial bearings 42 are connected via a connecting section and are therefore formed in one piece. What is important is the additional layer of a second material, which is either part of the shaft 14 or part of the bushing 421.

Claims (5)

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 bush (421) which surrounds the rotor shaft (14), - the Bearing bushing (421) has a first material (422); and - a layer of a second material (423) is arranged between the rotor shaft (14) and the bearing bush (421), the first material (422) and the layer of the second material (423) each having different thermal expansion coefficients, characterized in that - that the position of the second material (423) is arranged on the bearing bush (421) and is provided with a separate anti-friction coating applied to the side facing the rotor shaft (14) or - that the position of the second material (423) on the rotor shaft (14 ) is arranged and is provided with a separate anti-friction coating applied to the side facing the bearing bush (421). Turbocharger (1). Claim 1 , wherein the layer of the second material (423) has a lower coefficient of thermal expansion than the first material (422). 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 one of the Claims 1 until 3 , where the first material (422) is brass. Turbocharger (1) according to one of the Claims 1 until 3 , where the second material (423) is aluminum.

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