BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a flap device for opening and closing a wastegate duct in a turbine housing of a turbocharger. The invention furthermore relates to a turbocharger for an internal combustion engine and to a method.

Exhaust-gas turbochargers are being increasingly used to increase power in motor-vehicle internal combustion engines. More and more frequently, this is done with the aim of reducing the overall size and weight of the internal combustion engine for the same power or even increased power and, at the same time, of reducing consumption and thus CO2emissions, with regard to ever stricter legal requirements in this respect. The principle of action consists in using the energy contained in the exhaust-gas flow to increase a pressure in an intake tract of the internal combustion engine and thus to bring about better filling of a combustion chamber of the internal combustion engine with atmospheric oxygen. In this way, more fuel, such as gasoline or diesel, can be converted in each combustion process, i.e. the power of the internal combustion engine can be increased.

To this end, 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 rotor arranged therein, which is driven by the exhaust-gas mass flow. The fresh-air compressor has a compressor housing and a compressor rotor arranged therein, which builds up a boost pressure. The turbine rotor and the compressor rotor are arranged for conjoint rotation on the opposite ends of a common shaft, referred to as the rotor shaft, and thus form what is referred to as the turbocharger rotor. The rotor shaft extends axially between the turbine rotor and compressor rotor through the rotor bearing arranged between the exhaust-gas turbine and fresh-air compressor, and is provided in said rotor bearing with rotary support in the radial and axial directions in relation to the rotor shaft axis. According to this construction, the turbine rotor driven by the exhaust-gas mass flow drives the compressor rotor via the rotor shaft, thereby increasing the pressure in the intake tract of the internal combustion engine, based on the fresh-air mass flow downstream of the fresh-air compressor, and thereby ensures better filling of the combustion chamber with atmospheric oxygen.

In exhaust-gas turbochargers, the speed and power of the turbine are frequently regulated in that a wastegate valve is opened and closed in a regulated manner in order to conduct a part of the exhaust gas past the turbine via a wastegate duct. This wastegate valve typically has a flap device and usually consists of several parts.

SUMMARY OF THE INVENTION

One object underlying the invention is to specify a concept for a flap device of a turbocharger, said flap device allowing efficient sealing of the wastegate duct and at the same time being able to be operated particularly quietly.

A flap device for opening and closing a wastegate duct in a turbine housing of a turbocharger is disclosed. The flap device has a lever element having a through-bore in which a cylindrical bushing is arranged. Also provided is a flap having a pin, said flap being arranged on the lever element such that the pin passes through the bushing. Also provided is a cover disk which is arranged on an opposite side from the flap and has an opening through which the pin of the flap passes. The flap is riveted to the lever element by means of the pin.

The flap device can be referred to as part of a wastegate valve, which represents a bypass valve device on a turbine side of a turbocharger. The flap is for example a flap plate, which is designed and configured to rest on a wastegate valve seat. Integrally formed on the flap plate or on the flap is the pin. The pin is arranged on a side of the flap that faces the lever, and extends substantially normally from the flap through the through-bore of the lever element. The flap having the pin can also be referred to as a rivet.

The lever element is for example part of a rotatable spindle which can be actuated in a known manner via an actuator. As a result, the flap is actuable between a closed position, in which it rests on a valve seat in order to seal off the wastegate duct, and an open position, in which the wastegate duct is at least partially cleared. The lever element is arranged in the region of the through-bore between the cover disk and the flap, or that side of the flap that faces the lever element. The bushing is arranged between the pin and the through-bore, or an inner wall of the through-bore. During riveting, that part of the pin that protrudes through the cover disk is riveted, such that a form-fitting connection between the pin and the cover disk is achieved. The lever element is then enclosed between the cover disk and the flap.

In principle, axial and radial clearances are necessary in flap devices in order to compensate manufacturing tolerances and/or deformations during operation of a turbocharger, for instance thermally induced deformations, and to be able to reliably close and open the wastegate duct. However, the provision of the bushing makes it possible, in contrast to arrangements without a bushing, to provide very small clearances, for instance axial and radial clearances, before the riveting process. As a result, although a necessary clearance for operation can be ensured, this clearance can also be designed to be small enough for the flap device to be particularly quiet. Furthermore, an axial clearance, for instance between the flap or the flap plate and the lever element and/or between the lever element and the cover disk, can also be formed in a particularly small and exact manner.

This also favors the abovementioned advantages. In contrast thereto, in the case of a riveting process without a bushing, particularly large clearances would be necessary, since riveting typically tends to be an imprecise and crude manufacturing process. Here and below, an axial direction means a direction which extends parallel to a bore axis of the through-bore. A radial direction relates to a radial direction perpendicular to the bore axis.

A further advantage is that it is possible to dispense with welding the pin to the cover disk. In this way, costs can be saved compared with riveting, for instance on account of complexity and the materials used, without it being necessary to dispense with the small gap dimensions, however. Furthermore, it has been found that the weld is susceptible to rupturing during operation of the turbocharger.

According to one configuration, the through-bore, the bushing and the pin are dimensioned with respect to one another such that, before riveting, a radial clearance is formed between the bushing and through-bore and between the bushing and pin. After riveting, the pin expands radially in the region of the bushing such that it partially or completely fills the bushing. The bushing itself is substantially not radially expanded by the riveting process. This contributes toward it being possible to keep the clearance between the bushing and lever element small and exact from the very start. In other words, a radial clearance which is as described above but is designed in a particularly exact and small manner remains at least between the bushing and lever element. The radial clearance is for example 50 to 100 μm.

According to a further configuration, the cover disk rests on the bushing. As a result, the axial clearance between the components can be embodied in a smaller and exact manner. Among other things, this is because the cover disk is supported on the bushing during the forming process and the rivet, for instance the pin, has been axially released from the bushing during the riveting process.

According to a further configuration, the cover disk and the bushing are formed in one piece. This contributes toward easier assembly since there are fewer components. Furthermore, the cover disk rests in a more precise position.

According to a further configuration, the bushing has at least one groove, which is arranged preferably at the outer periphery of the bushing and extends in the axial direction of the bushing, and into which a spring sheet has been introduced such that a radial clamping force of the spring sheet acts between the through-bore and the bushing. In other words, the spring sheet allows a radial spring action between the lever element and the bushing. The term. “introduce” is understood to mean for example plugging in, inserting or arranging forming a form-fit. The spring sheet may have been prebent. The spring sheet protrudes radially and/or axially from the bushing at least in part. This type of force fit ensures that the parts no longer lie loosely one in the other. Noise such as the initially mentioned clattering is avoided or reduced particularly efficiently. Alternatively, it is also possible for there to be several grooves and, corresponding thereto, several spring sheets. Preferably, at least three spring sheets or more are provided. The groove may also be referred to as a slot. The spring sheet (s) nevertheless allow clearance and deformation compensation during the operation of the flap device.

According to a further configuration, the spring sheet is formed and/or has been introduced into the groove such that said spring sheet protrudes at at least one axial end of the bushing with regard to an axial direction of extension of the bushing in a mounted state before riveting, and an axial clamping force of the spring sheet acts with regard to the axial direction of extension after riveting.

For example, the spring sheet is formed in a diamond-shaped, trapezoidal or similar manner. The spring sheet is thus clamped with regard to the axial direction of extension in the riveted state. For example, the spring sheet is clamped between the cover disk and the flap plate or between the cover disk and the bushing itself. This contributes particularly well to the avoidance or suppression of noise, as described above. Analogously to above, there is clearance and deformation compensation. Alternatively, the spring sheet can protrude at both opposite axial ends of the bushing.

Depending on the configuration, the groove can extend continuously in the entire axial direction of extension of the bushing or only partially.

Furthermore, a turbocharger for an internal combustion engine is disclosed. The turbocharger has a bearing housing, in which a rotor shaft is mounted in a rotatable manner. Also provided is a turbine wheel, which is arranged for conjoint rotation on the rotor shaft. The turbocharger has a turbine housing, which is mechanically secured in the bearing housing. The turbocharger also has a wastegate duct, which is formed in the turbine housing. Finally, a flap device according to one of the above-described configurations is provided, which is designed to open and close the wastegate duct.

The turbocharger allows substantially the abovementioned advantages and functions.

Furthermore, a method for producing a flap device according to one of the above-described configurations is described. The method has the following steps of:providing a lever element having a through-bore;introducing a bushing into the through-bore in the lever element;providing a flap having a pin;arranging the flap on the lever element such that the pin passes through the bushing;placing a cover disk on an opposite side from the flap such that the pin projects through an opening in the cover disk;riveting the flap to the lever element by means of the projecting pin.

The method allows substantially the abovementioned advantages and functions. The abovementioned features and functions also apply to the described method.

According to one configuration, after the flap has been arranged on the lever element, a respective radial clearance is formed between the pin and the bushing and between the bushing and the through-bore. As a result, during the riveting of the pin, the pin is expanded within the bushing and fills the bushing. The bushing itself is substantially not radially expanded by the riveting process. As a result, the advantages and functions mentioned at the beginning are made possible.

According to a further configuration, the bushing has at least one groove. Before the bushing is introduced into the through-bore, a spring sheet is introduced into the groove and the bushing is introduced into the through-bore together with the spring sheet, such that a radial clamping force acts between the through-bore and the bushing. For example, the spring sheet is bent by the exertion of a force against the bushing such that the bushing can be pushed into the through-bore together with the spring sheet. If the force on the spring sheet is then removed, the spring sheet can expand within the clearance between the bore and bushing. This contributes toward the parts no longer lying loosely one in the other and noise such as clattering is avoided or considerably reduced.

According to a further configuration, the spring sheet is formed and/or has been introduced into the groove such that before riveting the spring sheet protrudes at least partially at an axial end of the bushing, and during riveting the spring sheet is axially clamped and an axial clamping force of the spring sheet acts with regard to an axial direction of extension of the bushing. As a result, the advantages and functions mentioned at the beginning are made possible.

Optionally, the spring sheet(s) can also have been prebent or preformed in a step before they are introduced into the grooves.

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

The exemplary embodiment is described in the following text with the aid of the appended figures. Elements that are of identical type or act identically are provided with the same reference signs throughout the figures.

