Exhaust turbocharger featuring a high-temperature steel material

Description

[0001] The invention relates to an exhaust gas turbocharger comprising a steel material for high-temperature applications, in particular a steel material suitable for use at high temperatures up to over 1000°C.

[0002] The development of new technologies and the refinement of corresponding devices and processes toward greater performance and efficiency while simultaneously reducing resource consumption are often accompanied by increased demands on the materials used in terms of strength, temperature resistance, corrosion resistance, and machinability. Furthermore, price naturally also plays a significant role in industrial applications.

[0003] Vehicle construction, and in particular the development of the combustion engines used in it, has traditionally been subject to such a technological challenge, which places ever higher demands on it.

[0004] To reduce fuel consumption and pollutant emissions while maintaining or even increasing the performance of the combustion engine, small-displacement engine concepts, so-called downsizing concepts, are increasingly being used. These concepts are equipped with exhaust gas turbochargers to increase performance. In particular, the high exhaust temperatures of up to over 1000°C that prevail in gasoline combustion engines pose a significant challenge for the materials used in the exhaust turbine. There is a trend toward further increasing operating temperatures in order to utilize the thermal energy generated during combustion more efficiently. Furthermore, there is also a trend in gasoline combustion engines toward lean operation with a lambda value close to 1, which further increases exhaust gas temperatures. The thermal load on the materials used in the exhaust system, including the turbocharger, is therefore increasing.

[0005] The operating principle of an exhaust gas turbocharger is to use the energy contained in the exhaust gas flow to increase the pressure in the intake tract of the combustion engine and thus ensure a better filling of the combustion chamber with atmospheric oxygen and thus be able to convert more fuel, petrol or diesel, per combustion process, thus increasing the performance of the combustion engine.

[0006] For this purpose, the exhaust gas turbocharger has an exhaust turbine arranged in the exhaust tract of the combustion engine, a fresh air compressor arranged in the intake tract and a rotor bearing arranged between them. The exhaust turbine has a turbine housing and a turbine impeller arranged therein, driven by the exhaust gas mass flow. The fresh air compressor has a compressor housing and a compressor impeller arranged therein, which builds up 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 turbine and the fresh air compressor, and is rotatably mounted therein, radially and axially 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, whereby the pressure in the intake tract of the combustion engine, relative to the fresh air mass flow behind the fresh air compressor, is increased and thus a better filling of the combustion chamber with atmospheric oxygen is achieved.

[0007] Furthermore, a device is usually provided in the turbine housing to influence the exhaust gas mass flow onto the turbine impeller. There are essentially two different devices that can be provided optionally. One is a so-called wastegate valve, the other is a so-called variable turbine geometry (VTG).

[0008] If necessary, the exhaust gas mass flow can be directed past the turbine impeller directly into the exhaust tract downstream of the exhaust turbine via a wastegate valve, while the variable turbine geometry can be used to influence the direction and quantity of the exhaust gas mass flow hitting the turbine impeller.

[0009] Depending on the engine speed and exhaust gas mass flow of the combustion engine and the load requirements, the wastegate valve or the variable turbine geometry is adjusted so that the speed of the turbine and compressor impeller as well as the pressure ratio, especially at the exhaust gas turbine, can be kept within the desired operating range of the exhaust gas turbocharger.

[0010] As already mentioned, in order to utilize the thermal energy generated during combustion in the internal combustion engine with greater efficiency through the exhaust gas turbocharger, the exhaust temperatures are kept as high as possible. The hot exhaust gases flowing through the turbine housing subject it and the components arranged in the exhaust mass flow to alternating thermal stresses with temperatures of up to 1000°C. Furthermore, there is a requirement for high strength and dimensional stability of the components while keeping the weight as low as possible, thus reducing material usage.

[0011] In order to meet these high requirements, steel materials with a mostly partially austenitic structure and in particular a high nickel content of up to 40% have been used so far.

[0012] Such materials include, for example, cast steel materials with the abbreviation 1.4848 (GX40CrNiSi25-20) and 1.4849 (GX40NiCrSiNb38-19).

[0013] The material 1.4848 is characterized by the following material composition: 0.3-0.5% C; 1.0-2.5% Si; max. 2.0% Mn; max. 0.04% P; max. 0.03% S; 24.0-27.0% Cr; max. 0.5% Mo; 19.0-22.0% Ni; balance Fe.

[0014] The material 1.4849 has the following material composition: 0.3-0.5% C; 1.0-2.5% Si; max. 2.0% Mn; max. 0.03% S; 18.0-21.0% Cr; max. 0.5% Mo; 36.0-39.0% Ni; 1.2-1.8% Nb; balance Fe.

[0015] The high nickel content increases the strength and durability of the materials, especially at operating temperatures up to 1050°C. However, nickel is a relatively expensive material, which is why more cost-effective alternatives are being sought.

[0016] Another high-temperature material with a very low nickel content, which is particularly used in pressure and steam boiler construction, as well as in aerospace engineering and turbine construction, is 1.4923 (X22CrMoV12-1). It has the following composition: 0.18-0.24% C; 11.0-12.5% ​​Cr; 0.3-0.8% Ni; 0.8-1.2% V; balance Fe. In this material, the vanadium content and the increased molybdenum addition increase the creep elongation and creep rupture strength. However, the strength values ​​drop significantly at temperatures above 500°C, which significantly limits its use for exhaust turbine casings, as described above.

[0017] In addition, WO 2010 / 036533 A2, WO 2017 / 194282 A1 and WO 2018 / 036757 A1 disclose exhaust gas turbochargers made of steel materials for high-temperature applications.

[0018] The present invention is therefore based on the object of specifying an exhaust gas turbocharger comprising steel material for high-temperature applications, which is characterized by low material costs, i.e. in particular with a low nickel content of the material, in a temperature range up to over 1050°C by sufficient strength and creep rupture strength for use in conjunction with internal combustion engines.

[0019] This object is achieved by an exhaust gas turbocharger having the features according to patent claim 1. Advantageous embodiments and further developments, which can be used individually or, provided they are not mutually exclusive alternatives, in combination with one another, are the subject of the dependent claims.

[0020] According to the invention, an exhaust gas turbocharger is disclosed with a turbine housing having a receiving area for a turbine impeller of the exhaust gas turbocharger arranged centrally to a turbine housing axis and at least one turbine spiral channel tapering in a helical manner towards the receiving area for the turbine impeller, wherein a wastegate valve with a spindle arm and a flap plate arranged thereon, or a variable exhaust gas guide device with bearing disks and guide vanes is arranged in the turbine housing, wherein at least one of the components: turbine housing, spindle arm and flap plate, or bearing disks and guide vanes, comprises a steel material for high-temperature applications, the material composition of which, in addition to iron and Fe, consists of the following alloying components in quantities within the specified limits in weight percent: Carbon, C: 0.4-0.5%; silicon, Si: 1.25-1.75%; manganese, Mn: 3.0-12.0%; chromium, Cr: 19.5-20.5%; nickel, Ni: 5.0-6.0%; niobium, Nb: 1.00-1.5% and optionally additionally contains at least one of the other alloying components in proportions up to a maximum of the specified amounts in percent by weight: tungsten, W: up to 0.6%; vanadium, V: up to 0.12%; copper, Cu: up to 0.25%; cobalt, Co: up to 1.0%; sulfur, S: up to 0.03% and phosphorus, P: up to 0.04%, as well as unavoidable impurities in proportions that are negligible with regard to the material properties.

[0021] In a further embodiment of the steel material used in the exhaust gas turbocharger according to the invention, at least one of the proportions of the alloying components silicon and manganese can be narrowed down, so that at least one of these components is added at least in quantities within the following limits in weight percent: Silicon, Si: 1.35-1.65%; Manganese, Mn: 7.0-12.0%.

[0022] In particular, the amount of manganese can be further limited to a proportion of 9.0 - 12%.

[0023] This allows the desired material properties to be achieved at a higher level with greater reliability.

[0024] In the alloy compositions listed above, the material properties achieved are primarily due to the increased proportions of manganese, chromium, and niobium, combined with a moderate addition of nickel, compared to known steel materials for high-temperature applications. This alloy is characterized by high high-temperature strength combined with corrosion resistance, particularly in the aggressive, hot exhaust gases of a combustion engine.

[0025] Furthermore, in order to achieve certain properties, the material composition according to the invention can be supplemented by adding at least one of the further alloying components mentioned, in proportions up to a maximum of the respective specified amounts in weight percent: Tungsten, W: up to 0.6%; vanadium, V: up to 0.12%; copper, Cu: up to 0.25%; cobalt, Co: up to 1.0%; sulfur, S: up to 0.03%; and phosphorus, P: up to 0.04%.

[0026] This means that at least one of these elements is definitely added in a measurable amount, but up to the specified limit. However, two, three, four, five, or all of these elements can also be added in different combinations, but each only in an amount up to the specified limit.

[0027] Depending on the combination, this can have a positive influence on various secondary material properties of the alloy, such as machinability, weldability, castability, etc.

[0028] In a further refined embodiment, the steel material used in the exhaust gas turbocharger according to the invention is characterized in that it contains at least one of the above-mentioned further alloying constituents added to the alloy in proportions of at least the stated amounts in percent by weight: Tungsten, W: at least 0.3%; vanadium, V: at least 0.06%; copper, Cu: at least 0.1%; cobalt, Co: at least 0.5%; sulfur, S: at least 0.013%; and phosphorus, P: at least 0.02%.

[0029] In combination with the previously defined upper limits of the addition quantities of the other alloying components, this results in a quantity range: for tungsten, W: between 0.3 to 0.6%; for vanadium, V: between 0.06 to 0.12%; for copper, Cu: between 0.1 to 0.25%; for cobalt, Co: between 0.5 to 1.0%; for sulfur, S: between 0.013 to 0.03% and for phosphorus, P: between 0.02 to 0.04%.

[0030] The steel material contains at least one of these additional elements in an amount within the specified range. However, the steel material can also contain two, three, four, five, or all of the additional elements mentioned in amounts within the specified limits.

[0031] The high manganese content and the other alloying components contribute to a further improvement in the desired material properties, particularly by causing a progressive transformation of ferrite into austenite at elevated material temperatures. Furthermore, corrosion resistance is increased.

[0032] A further feature of the steel material used in the exhaust gas turbocharger according to the invention is characterized by the steel material having a completely austenitic structure. This leads to a significant reduction in the formation of sigma phases in the material structure and contributes to achieving and stabilizing the desired material properties.

[0033] With the specified material composition of the steel material used in the exhaust gas turbocharger according to the invention, the material properties required for use in turbine housings for exhaust gas turbochargers with regard to the minimum yield strength, the tensile strength and the corrosion resistance are achieved, while at the same time the nickel content is significantly reduced compared to previously used high-temperature materials and thus material costs are reduced.

[0034] This is achieved, among other things, by ensuring that the alloy components are matched to one another in composition and quantity and, if necessary, defined within narrow limits so that a high proportion of austenitic structure is formed, ideally up to 100%.

[0035] The exhaust gas turbocharger according to the invention comprises a turbine housing with a receiving area for a turbine impeller of the exhaust gas turbocharger arranged centrally to a turbine housing axis and at least one exhaust gas spiral duct tapering in a helical manner towards the receiving area for the turbine impeller. A wastegate valve with a spindle arm and a flap plate arranged thereon, or a variable exhaust gas guide device (VTG) with bearing disks and guide vanes, is arranged in the turbine housing. This essentially corresponds to an arrangement as already described in the introduction. The exhaust gas turbocharger according to the invention is characterized in that at least one of the components: turbine housing, spindle arm and flap plate, or bearing disks and guide vanes, comprises a steel material according to the invention with an alloy composition as described in one of the previously described embodiments.

[0036] A corresponding exhaust gas turbocharger is characterized by an extended service life and increased operational reliability. This is achieved through the optimized material properties of the components, particularly with regard to high-temperature strength, while simultaneously being cheaper than conventional components made of high-alloy nickel alloys.

[0037] The features and combinations of features of the embodiments of the subject matter according to the invention mentioned above in the description are to be used individually, in part or in whole, also in mutual combination or mutual supplementation, in further development of the subject matter according to the invention, unless they are alternatively applicable or even mutually exclusive, without departing from the scope of the invention as defined in the claims.

[0038] Corresponding designs of exhaust gas turbochargers according to the invention are explained in more detail with the help of the figures, in which: Figure 1 shows a schematically simplified representation of an exhaust gas turbocharger with wastegate valve, in half section, and Figure 2 shows a three-dimensional representation of an exhaust gas turbocharger with variable exhaust gas guide device, in quarter section. Parts with the same function and designation are marked with the same reference symbols throughout the figures.

[0039] The figure shows the basic structure of an exhaust gas turbocharger 1 with a wastegate valve, as already roughly described in the introduction, in a schematically simplified half-sectional view.

[0040] As a rule, a conventional exhaust gas turbocharger 1, as shown in the Figures 1 and 2shown, has a multi-part structure. A turbine housing 20, which can be arranged in the exhaust tract of the internal combustion engine, a compressor housing 30, which can be arranged in the intake tract of the internal combustion engine, and a bearing housing 40 between the turbine housing 20 and the compressor housing 30 are arranged one behind the other on a common turbocharger axis 2 and are connected to one another by assembly. A further structural unit of the exhaust gas turbocharger 1 is the turbocharger rotor 10, which has a rotor shaft 14, a turbine impeller 12 arranged in the turbine housing 20, and a compressor impeller 13 arranged in the compressor housing 30. 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 through the bearing housing 40 in the direction of the turbocharger axis 2 and is rotatably mounted therein axially and radially about its longitudinal axis, the rotor rotation axis 15. The rotor rotation axis 15 lies in the turbocharger axis 2, thus coinciding with it. The turbine housing axis 2a also lies in line with the rotor rotation axis 15 and the turbocharger axis 2. The exhaust gas mass flow AM through the turbine housing 20 and the fresh air mass flow FM through the compressor housing 30 are each represented by corresponding arrows.

[0041] The turbine housing 20 has one, in other embodiments possibly also several, turbine spiral ducts 22, a so-called exhaust gas duct, arranged in a ring around the turbocharger axis 2 and the receiving area of ​​the turbine impeller 12, tapering in a helical manner towards the receiving area and the turbine impeller 12. This exhaust gas duct has a tangentially outwardly directed exhaust gas supply duct 23 with a manifold connection piece 24 for connection to an exhaust manifold (not shown) of an internal combustion engine, through which the exhaust gas mass flow AM flows into the respective exhaust gas duct. The exhaust gas duct further has an annular gap opening extending at least over part of the inner circumference, the so-called exhaust gas inlet gap 25, which extends at least partially radially towards the turbine impeller 12 and through which the exhaust gas mass flow AM flows onto the turbine impeller 12.

[0042] The turbine housing 20 further comprises an exhaust gas discharge channel 26, which extends from the axial end of the turbine impeller 12 toward the turbocharger axis 2 and has an exhaust connection piece 27 for connection to the exhaust system (not shown) of the internal combustion engine. The exhaust gas mass flow AM exiting the turbine impeller 12 is discharged into the exhaust system of the internal combustion engine via this exhaust gas discharge channel 26. The steel material SWst according to the invention, from which the turbine housing 20 is made, is symbolized by the cross-hatching.

[0043] A wastegate valve 29 connects the exhaust gas supply channel 23 upstream of the turbine runner 12 in the flow direction of the exhaust gas mass flow AM with the exhaust gas discharge channel 26 downstream of the turbine runner 12 in the flow direction of the exhaust gas mass flow AM via a wastegate channel 291 in the turbine housing 20. The wastegate valve 29 can be opened or closed via a closing device. This closing device has a spindle arm 292 rotatably mounted in the turbine housing 20, on which a flap plate 293 is arranged. In this example, both the spindle arm 292 and the flap plate 293 are made of the steel material SWst according to the invention. By actuating the spindle arm 292 by means of an external actuator (not shown), the flap plate 293 is placed sealingly on the valve seat 294 of the wastegate channel 291 or lifted off from it to close or open the wastegate valve 29.

[0044] Figure 2shows a design of an exhaust gas turbocharger 1 with an exhaust gas guide device, here a variable turbine geometry 50, also referred to as VTG for short. The basic structure of the exhaust gas turbocharger 1 with turbine housing 20, compressor housing 30, bearing housing 40 and the turbocharger rotor 10 is essentially the same as in Figure 1shown exhaust gas turbocharger 1. However, instead of a wastegate valve, a VTG 50 is provided here. This essentially consists of two annular bearing disks 51, 52, which are arranged at a specific distance from one another in the annular gap-shaped transition region between the turbine spiral duct 22 and the turbine impeller 12 and thus form the exhaust gas inlet gap 25. Between the bearing disks 51, 52, a plurality of guide vanes are arranged in the exhaust gas inlet gap 25, distributed over the circumference of the exhaust gas inlet gap. These guide vanes are rotatably mounted in at least one of the bearing disks, and their rotational position can be adjusted by means of an actuating mechanism 55 arranged on the rear side of this bearing disk and an external actuator (not shown). In this embodiment, both the turbine housing 20 and the bearing disks 51, 52 and the guide vanes 53 are made of the steel material SWst according to the invention.

Claims

1. Exhaust-gas turbocharger (1) having a turbine housing (21) with a receiving region, arranged centrally with respect to a turbine housing axis (2a), for a turbine impeller (12) of the exhaust-gas turbocharger (1) and with at least one turbine spiral duct (22) which tapers in a helical shape towards the receiving region for the turbine impeller (12), wherein, in the turbine housing, there is arranged a wastegate valve with a spindle arm and a flap plate arranged thereon or a variable exhaust-gas guiding device with bearing discs and guide vanes, characterized in that at least one of the components: turbine housing, spindle arm and flap plate, or bearing discs and guide vanes, has a steel material (21a) for high-temperature applications, the material composition of which, in addition to iron, Fe, consists of the following alloy constituents in amounts within the stated limits in percent by weight: carbon, C: 0.4-0.5%; silicon, Si: 1.25-1.75%; manganese, Mn: 3.0-12.0%; chromium, Cr: 19.5-20.5%; nickel, Ni: 5.0-6.0%; niobium, Nb: 1.00-1.5%, and optionally additionally comprises at least one of the further alloy constituents in proportions up to at most the stated amounts in percent by weight: tungsten, W: up to 0.6%; vanadium, V: up to 0.12%; copper, Cu: up to 0.25%; cobalt, Co: up to 1.0%; sulfur, S: up to 0.03% and phosphorus, P: up to 0.04%, and has unavoidable impurities in proportions which are negligible with regard to the material properties.

2. Exhaust-gas turbocharger according to Claim 1, characterized in that the steel material has at least one of the stated alloy constituents at least in amounts within the following limits in percent by weight: silicon, Si: 1.35-1.65%; manganese, Mn: 7.0-12.0%, in particular 9.0-12%.

3. Exhaust-gas turbocharger according to Claim 1 or 2, characterized in that the steel material comprises at least one of the further alloy constituents in proportions up to the maximum stated amount in percent by weight.

4. Exhaust-gas turbocharger according to Claim 1 or 2, characterized in that the steel material comprises the at least one of the further alloy constituents in proportions of in each case at least the stated amounts in percent by weight: tungsten, W: at least 0.3%; vanadium, V: at least 0.06%; copper, Cu: at least 0.1%; cobalt, Co: at least 0.5%; sulfur, S: at least 0.013% and phosphorus, P: at least 0.02%.

5. Exhaust-gas turbocharger according to any of the preceding claims, characterized in that the steel material has a completely austenitic structure.