Exhaust-gas-turbine casing

[0001] The invention relates to the field of turbochargers operated by exhaust gas.

[0002] It relates to a turbine casing according to the preamble of patent claim 1, an exhaust-gas turbine having such a turbine casing, and a turbocharger having such an exhaust-gas turbine.

[0003] Exhaust-gas turbochargers are used for increasing the output of internal combustion engines. They comprise an exhaust-gas turbine, driven by the exhaust gases of the internal combustion engine, and a compressor for compressing the fresh air fed to the internal combustion engine. In this case, the turbine wheel and compressor wheel are as a rule arranged on a common shaft. In the bottom output range up to a few megawatts, turbochargers with a turbine wheel subjected to radial flow and an internal bearing arrangement of the shaft are mainly used.

[0004] In the case of uncooled exhaust-gas turbochargers, in which the gas-conducting passages are not cooled, the exhaust-gas temperature at the turbine inlet is higher, as a result of which the thermal efficiency of the machine and the output delivered to the air compressor per exhaust-gas quantity increases.

[0005] The uncooled outer turbine casing, the gas-inlet casing, which during operation has a temperature of 650° C. for example, is usually fastened directly on the bearing casing, which at 150° C., for example, is substantially cooler. Within certain ranges of application, the bearing casing, in contrast to the gas-conducting passages, is cooled to said temperature.

[0006] To fasten the turbine casing on the bearing casing, straps or what are referred to as profile-clamp or V-band connections are used in conventional exhaust-gas turbines. In order to achieve as high an efficiency as possible, the air gap between the turbine blades and the turbine casing is to be kept as small as possible. However, this means that this casing wall and the turbine wheel are always centered relative to one another, in particular during operation under full load and with corresponding thermal loading of all parts. Since the centering seating of the turbine casing relative to the bearing casing sometimes widens radially as a result of the high temperature difference between the bearing casing and the turbine casing, the turbine casing may become offset relative to the bearing casing and in particular relative to the turbine shaft mounted therein, i.e. the turbine casing is no longer centered in the radial direction relative to the shaft and the turbine wheel arranged thereon. Such an offset, which can be additionally aided by external actions of force, leads to the tips of the turbine blades touching the casing wall of the turbine casing, to corresponding wear or defects and, associated therewith, to considerable losses in efficiency of the exhaust-gas turbine.

[0007] EP 0 118 051 shows how an offset of the hotter component can be avoided by means of groove/tongue connections which are arranged in a star shape and are movable in the radial direction.

[0008] This conventional, relatively costly solution approach, in which the production process, in addition to pure turning operations, also includes milling operations, only permits a restricted number of different casing positions on account of the discrete number of groove/tongue connections. With 3, 6 or 12 evenly distributed lugs or grooves, changes in position of the outer turbine casing relative to the bearing casing of 120°, 60° or 30° can be achieved. However, a solution approach in which the position of the outer turbine casing relative to the bearing casing can be set in an essentially infinitely variable manner is desirable.

[0009] The object of the invention is consequently to improve the casing of an exhaust-gas turbine in such a way that the exhaust-gas turbine has a higher efficiency due to improved centering of the turbine casing relative to the shaft mounted in the bearing casing, with at the same time the greatest possible flexibility with regard to the positioning of the outer parts of the turbine casing relative to the bearing casing.

[0010] According to the invention, this object is achieved with the characterizing features of patent claim 1.

[0011] The advantages of the invention are to be seen in the fact that, due to the radially or axially unidirectional centering lugs with corresponding grooves, in each case at least one of the connections between the bearing casing and the centering ring and respectively the centering ring and the gas-inlet casing is not positive-locking, as a result of which any desired positioning of the gas-inlet casing relative to the bearing casing is made possible.

[0012] This type of centering is suitable for all the current types of connection between bearing casing and gas-inlet casing, since, according to the invention, the centering is effected by components in the interior of the turbine casing in the supporting region of the gas-inlet casing on the bearing casing.

[0013] Further advantages follow from the dependent claims.

[0022] The exhaust-gas turbocharger mainly comprises an exhaust-gas turbine, shown schematically as a radial-flow turbine in FIG. 1, and a compressor (not shown). The exhaust-gas turbine mainly comprises a casing and a turbine wheel 6 rotatably arranged therein. The casing comprises a radially outer, spiral gas-inlet casing 1, a gas-outlet-side casing wall 8, and a bearing casing 4. The turbine wheel 6 with its moving blades 61 is arranged on a shaft 3 rotatably mounted by means of bearings 31. On the compressor side, a compressor wheel (likewise not shown) is arranged on the shaft.

[0023] The gas-inlet casing merges downstream into an intake passage 7 for the exhaust gases of an internal combustion engine (likewise not shown) connected to the exhaust-gas turbocharger. The intake passage is defined by the gas-outlet-side casing wall 8 and by the gas-inlet casing 1 and bearing casing 4.

[0024] A nozzle ring for the flow deflection can be arranged in the intake passage 7 between gas-inlet casing and bearing casing and the gas-outlet-side casing wall.

[0025] In the embodiment shown, the gas-inlet casing 1 is connected to the bearing casing 4 by means of straps 51, the straps, fastened to the gas-inlet casing by means of screws 52, allowing certain movements of the gas-inlet casing 1 relative to the bearing casing 4 in the radial direction. In the stationary state of the exhaust-gas turbine, when gas-inlet casing and bearing casing are cold, the gas-inlet casing rests with the support 11 on the support 41 of the bearing casing and is thereby centered relative to the shaft 3 and the turbine wheel 6 arranged thereon. In the supporting region, a centering ring 2 is arranged radially between the two casing parts. As shown in FIG. 2, the centering ring has a plurality of centering lugs 21, for example 5 to 7 centering lugs 21, which engage in corresponding centering grooves in one of the casing parts. The centering lugs are arranged so as to be distributed over the entire circumference of the centering ring and may be arranged radially inward, radially outward or in an axially oriented manner.

[0026] In the first exemplary embodiment, the centering lugs are directed radially outwards and the corresponding grooves are incorporated in the gas-inlet casing 1. FIG. 3 shows an enlarged detail of the centering ring 2 with a centering lug 21 which engages in the groove 12 of the gas-inlet casing. In the operating state of the exhaust-gas turbine, the centering ring 2 is frictionally connected to the bearing casing 4 by being pressed in place on the radially inner bearing casing 4 with the side remote from the lugs and grooves.

[0027] In the operating state of the exhaust-gas turbine, the gas-inlet casing heats up to a greater degree than the centering ring and to a much greater degree than the bearing casing. The pressing ensures that the centering ring is not released from the bearing casing. The centering ring therefore remains centered relative to the bearing casing even in the operating state. The gas-inlet casing, which heats up to a very much higher degree compared with the bearing casing and therefore threatens to lose the centering seating on the bearing casing due to heat-induced expansions in the radial direction, remains centered relative to the bearing casing by means of the radial guidance of the centering lugs in the grooves.

[0028] In this case, the pressing may be effected via a cone. That side 23 of the centering ring which is remote from the centering lugs and the opposite surface of the bearing casing are beveled in a cone shape. The cone angle, i.e. the angle between the surface 23 and the axis of the shaft 3, is advantageously selected in such a way that the centering ring, when the casing connection is released, is automatically released again from the bearing casing and the conical press fit therefore has no self-locking. This is the case at a cone angle within the range of 15°–30°.

[0029] The pressing can also be achieved by only one of the two opposite sides being beveled in a cone shape, that is to say either that side of the centering ring which is remote from the centering lugs or the opposite surface of the bearing casing, whereas the other side is of cylindrical shape.

[0030] FIG. 4 shows a correspondingly enlarged detail of the second exemplary embodiment, in which the centering lugs 21 are directed radially inward and the corresponding grooves 42 are incorporated in the bearing casing 4. The centering ring 2 is pressed into the gas-inlet casing 1 with the radially outer side remote from the lugs and the grooves.

[0031] The further figures show, in an enlarged manner, how the centering ring is fitted between gas-inlet casing and bearing casing.

[0032] FIGS. 5 to 7 show the first exemplary embodiment with grooves 12 indorporated in the gas-inlet casing 1 and centering lugs 21 directed radially outward. When the gas-inlet casing 1 is being fitted on the bearing casing 4, the centering ring 2, according to FIG. 5, is inserted between the casing parts in the axial direction. In the process, the radially outer centering lugs 21 are to be aligned with the grooves 12 in the gas-inlet casing. The orientation of the centering ring relative to the bearing casing may be selected in any desired manner, thereby also resulting in correspondingly free positioning of the gas-inlet casing relative to the bearing casing. The two casing parts are then pushed against one another in the axial direction by means of strap 51 and screw 52 until corresponding axial stops 43 and 13 touch one another. In the process, the centering ring 2 is pushed onto the bearing casing 4 and pressed against it. Owing to the cone-shaped profile, a radial press fit which is simple to realize is obtained.

[0033] FIG. 7 shows a slightly modified variant of the first exemplary embodiment in which the cone points in the other axial direction. Accordingly, the centering ring 2, during assembly, is not inserted axially between the two casing parts, but is pushed in from the compressor side. When the two casing parts are being screwed tight, the centering ring 2 is pushed by the straps 51 onto the cone of the bearing casing and is firmly pressed thereon.

[0034] FIG. 8 shows the second embodiment with grooves 42 incorporated in the bearing casing 4 and centering lugs 21 directed radially inward. When the gas-inlet casing 1 is being fitted on the bearing casing 4, the centering ring 2 is again inserted between the casing parts in the axial direction. In the process, the radially inner centering lugs 21 are to be aligned with the grooves 42 in the bearing casing. The orientation of the centering ring relative to the gas-inlet casing may be selected in any desired manner, thereby also resulting in correspondingly free positioning of the gas-inlet casing relative to the bearing casing. The two casing parts are then pushed against one another in the axial direction by means of strap 51 and screw 52 until the corresponding axial stops 43 and 13 touch one another. In the process, the centering ring 2 is pushed into the gas-inlet casing 1 and pressed in place. Owing to the cone-shaped profile, a radial press fit which is simple to realize is obtained. In the second embodiment shown of the turbine casing according to the invention, a centering ring which heats up to a considerable degree is advantageously used. The heated centering ring expands together with the likewise hot gas-inlet casing and remains centered owing to the pressing relative to the gas-inlet casing. The centering ring and the gas-inlet casing remain centered relative to the bearing casing due to the radial guidance of the centering lugs in the grooves of the bearing casing.

[0035] Despite the positive-locking connection between centering ring and the casing part provided with the grooves, the position of the gas-inlet casing relative to the bearing casing can be set in an infinitely variable manner, since there is merely a frictional press connection between the centering ring and the other casing part, but no positive-locking connection.

[0036] Instead of centering lugs, the centering ring may also have corresponding grooves. The lugs are then arranged in the bearing casing or in the gas-inlet casing.

[0037] Instead of a one-piece centering ring, a plurality of centering-ring segments, for example three centering-ring segments, may be joined together to form a centering ring. The centering-ring segments are hooked together at the ends in the radial or axial direction. The centering ring, suitable in particular for large turbines and subdivided into a plurality of segments, can be produced more cost-effectively and is simpler to fit.

• [0038] 1 Gas-inlet casing
• [0039] 11 Support
• [0040] 12 Centering grooves
• [0041] 13 Axial stop
• [0042] 2 Centering ring
• [0043] 21 Centering lugs
• [0044] 23 Pressure surface
• [0045] 3 Shaft
• [0046] 31 Inner bearing
• [0047] 4 Bearing casing
• [0048] 41 Support
• [0049] 42 Centering grooves
• [0050] 43 Axial stop
• [0051] 51 Strap
• [0052] 52 Fastening means
• [0053] 6 Turbine wheel
• [0054] 61 Blades
• [0055] 7 Intake passage
• [0056] 6 Gas-outlet-side casing wall