A turbocharger (1) with variable turbine geometry (VTG) having a guide grate (18) which surrounds a turbine wheel (4) radially at the outside, which has an adjusting ring (5) operatively connected to the guide blades (7) via associated blade levers (20) which are fastened to blade shafts (8) at one of the ends thereof. Each blade lever (20) has a lever head (23) which can be placed in engagement with an associated engagement recess (24), which has a base wall (26), of the adjusting ring (5), and which has a stop (25) at least for setting the minimum throughflow through the nozzle cross sections formed by the guide blades (7). The stop is a first support point (25) on the base wall (26), wherein, in the minimum throughflow position, the lever head (23) makes contact, via a wall surface (27) facing toward the base wall (26), with said first support point.

The invention relates to an exhaust-gas turbocharger.

A turbocharger of said type is known from EP 1 564 380 A1. To prevent weakening of the adjusting ring, said document proposes that a stop be provided which is integrally connected to the adjusting ring and which is composed of a web, the width of which may be varied or which may be provided with an adjustable headless screw. Said design duly yields, to a certain extent, the facility of an adjustable stop, but a stop constructed in this way would barely be feasible in practice because the spatial conditions would impede the insertion of a headless screw, which would moreover necessitate the provision of an internal thread in the integral stop part, and furthermore a locking facility for the headless screw would have to be provided in order to be able fix the position which has been set. This involves a high level of outlay owing to the extremely restricted spatial conditions in reality, and is therefore undesirable.

However, in the known turbocharger, as a result of the integral formation of the stop on the adjusting ring, it is possible only with relatively high outlay, if at all, to rework the projection of the stop after the assembly of the guide grate, for example if a correction of the end positions of the guide grate must be performed.

It is therefore an object of the present invention to provide a turbocharger, which turbocharger permits a simplification of the assembly of the guide grate or guide apparatus, wherein at least a simple and precise setting of the minimum throughflow should be possible by means of the guide apparatus alone.

According to the invention, it is consequently possible for the guide blade position in the cartridge or the guide grate to be realized by means of an inner stop between the adjusting ring and the blade lever or blade lever head. It is thereby possible for in each case one stop to be provided for the smallest blade position and preferably the largest blade position, without the need for additional components.

FIG. 1illustrates a turbocharger1according to the invention which has a turbine housing2and a compressor housing3which is connected to said turbine housing via a bearing housing19. The housings2,3and19are arranged along an axis of rotation R. The turbine housing2is shown partially in section in order to illustrate the arrangement of a blade bearing ring6as part of a radially outer guide grate18which has a multiplicity of guide blades7which are distributed over the circumference and which have pivot shafts or blade shafts8. In this way, nozzle cross sections are formed which, depending on the position of the guide blades7, become larger or smaller and supply a greater or lesser amount of the exhaust gas of an engine, which is supplied via a supply duct9and discharged via a central connecting piece10, to the turbine wheel4which is mounted in the center on the axis of rotation R, in order, by means of the turbine wheel4, to drive a compressor wheel17which is seated on the same shaft.

To control the movement or the position of the guide blades7, an actuating device11is provided. Said actuating device may be of any desired form, but a preferred embodiment has a control housing12which controls the control movement of a plunger rod14fastened thereto in order to transmit the movement thereof to an adjusting ring5situated behind the blade bearing ring6, said movement being converted into a slight rotational movement of said adjusting ring. Between the blade bearing ring6and an annular part15of the turbine housing2there is formed a free space13for the guide blades7. To be able to safeguard said free space13, the blade bearing ring6has integrally formed spacers16. In the example, three spacers16are arranged on the circumference of the blade bearing ring6at angular intervals of in each case 120°. It is however possible in principle for more or fewer such spacers16to be provided.

FIG. 2shows a plan view of the guide grate18according to the invention, the blade bearing ring6, the guide blades7with the blade shafts8thereof, the adjusting ring5and the blade levers20with the lever heads23thereof, wherein in each case two blade levers20with lever heads23have been illustrated by way of example and representatively of all other arrangements. The detail denoted inFIG. 2by the letter “X” is reproduced inFIGS. 3 to 5in different guide blade positions in each case. Accordingly, in each case only one cutout of the guide grate18is illustrated.

FIG. 3shows an intermediate position STMof the guide blades7.FIG. 3shows that the substantially semi-circular lever head23has a wall surface27which points toward a base surface26of the engagement recess24. In the intermediate blade position STMshown inFIG. 3, there is play S between said wall surface27and the base wall26, as can be seen in detail from the illustration ofFIG. 3.

By contrast,FIG. 4shows the closed position STGof the guide blades7. Here, in the illustration selected inFIG. 4, the blade lever20pivots with its lever head23through an angle α, which may be approximately 25°, to the left. In said position, the play S decreases to a value 0, as indicated inFIG. 4. In said position, the wall surface27bears against a first support point25of the base wall26, such that the support point25forms the stop (in this case the minimum stop).

InFIG. 5, which shows the open blade position STO, the blade lever20pivots about the central point M8of the blade shaft8through an angle β to the right, and contact occurs at a second support point28which is likewise situated on the base wall26and with which the wall surface27makes contact in said position as a maximum stop.

The two support points25and28are arranged symmetrically with respect to a radius line R which runs through the central point M8of the blade shaft8and which extends from the central point M18of the guide grate18. In the intermediate blade position illustrated inFIG. 3, the radius line R corresponds to the longitudinal central line of the blade lever20.

Said arrangement yields in particular the advantage that a defined stop can be formed both for the minimum position and also for the maximum position without the need for additional components to be manufactured and assembled. Each blade lever has its end stop at the inner stop with respect to the adjusting ring at a maximum but also equal angle deflection. As explained on the basis ofFIGS. 3 to 5, the operating principle is the same both for the minimum stop and also for the maximum stop. Here, both end positions have the advantage that the guide blades come to rest in a very precise end position.

For the maximum stop, this means a very precise inner circle at the blade ends, which is important in particular for variable turbine geometry exhaust-gas turbochargers which are used for spark-ignition engines.

The solution according to the invention yields, for the minimum stop, a very precise, uniform duct formation with a correspondingly precise throughput characteristic value, which in turn is important for diesel engines.

Furthermore, as stated, the design according to the invention yields the advantage that at least one component, and therefore a number of machining processes on the blade bearing ring, and the associated assembly of such an additional component, can be eliminated. This yields not only a simplification of the design for the same technical effectiveness but also a cost advantage.

In addition to the above written disclosure of the invention, reference is hereby explicitly made to the diagrammatic disclosure thereof inFIGS. 1 to 5.

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