The invention is within the field of mechanical engineering and can be used with particular advantage in automotive engineering. More specifically, the invention relates to an exhaust-gas turbocharger.
To increase the utilization of the fuel and to boost power and ensure economical and environmentally friendly operation, many modern internal combustion engines have an exhaust-gas turbocharger. A turbocharger of this kind has, in the exhaust gas flow of the internal combustion engine, a turbine that can be driven by this exhaust gas flow and a compressor, which is arranged in the induced gas flow and which compresses the induced air fed to the internal combustion engine. The exhaust-gas turbine and the compressor are connected to one another by means of a shaft, with the result that the turbine drives the compressor wheel.
For improved control of the exhaust gas flow, a wastegate opening is provided from the exhaust side of the internal combustion engine, in the region of the turbine, which wastegate opening provides a bypass channel for the exhaust gas flow and can be closed in a controlled manner by means of a wastegate flap. Depending on the operating conditions, the exhaust gas flow can thereby be fed in whole or in part to the turbine of the turbocharger. Control of the wastegate flap is usually accomplished mechanically by means of a control rod, which can be driven by an actuator. By means of a lever, the control rod usually drives a wastegate spindle or wastegate shaft, on which the wastegate flap is secured within the turbocharger device.
An important requirement of the wastegate system is that the wastegate flap can be closed and held closed reliably against the exhaust gas pressure. Compliance with this requirement depends essentially on the balance of forces acting on the wastegate flap. Said wastegate flap is acted upon, on the one hand, by the exhaust gas pressure and, on the other hand, by the contact pressure provided by the torque of the shaft. For reliable and firm closing of the flap, it is necessary that the force acting on the flap via the shaft is greater than the exhaust-gas force. To increase the contact force, either the chosen driving lever of the wastegate shaft outside the turbine casing can be particularly large and/or the chosen distance between the wastegate flap and the axis of rotation can be as small as possible.
Accordingly, it is the underlying object of the present invention to configure an exhaust-gas turbocharger of the type stated at the outset in such a way that the contact pressure on the wastegate flap becomes as large as possible.
The object is achieved by means of the features of the invention in accordance with patent claim 1.
Accordingly, the invention relates to an exhaust-gas turbocharger for an internal combustion engine, having a turbine, having a compressor wheel, which is connected to said turbine by means of a shaft, and having a wastegate device, which wastegate device has a wastegate actuator, has a wastegate drive shaft rotatable about an axis of rotation, and has a flap, which is fastened to said drive shaft and which is pivotable about the axis of rotation and which has a covering surface for potentially opening up and closing off a wastegate opening, wherein the wastegate flap and the wastegate opening that can be closed off by means of said wastegate flap are designed in such a way that the distance between the center of area of the covering surface, which covers the wastegate opening, of the wastegate flap and the axis of rotation is smaller than the radius of a circular surface of equal surface area.
The contact pressure of the wastegate flap on the wastegate opening or on the sealing edge of the opening depends on the average distance between the sealing edge of the wastegate flap forming the boundary edge of the covering surface and the axis of rotation. This quantity can be described by the position of the center of area relative to the axis of rotation. For example, the center of area of the covering surface of the wastegate flap can move closer to the axis of rotation if the covering surface is extended in length parallel to the axis of rotation and compressed transversely to the axis of rotation, starting from a constant size of the covering surface. Given a constant size of the opening or covering surface, the contact pressure of the wastegate flap on the wastegate opening can therefore be increased by means of the stated shaping of the covering surface.
A particularly advantageous possibility here is to provide for the wastegate flap and the wastegate opening that can be closed by said flap to be designed in such a way that the minimum distance between the covering surface and the axis of rotation is as small as possible.
In the case of a circular configuration of the covering surface of the wastegate flap, this is advantageously spaced apart from the axis of rotation to such an extent that the minimum distance between the covering surface and the axis of rotation corresponds to the magnitude of a tolerance, with the result that, even when the tolerance is fully exhausted, the entire covering surface is on one side of the axis of rotation and the wastegate opening can be fully opened when the wastegate flap is swung open.
The invention can furthermore advantageously provide for the covering surface to have at least one straight edge, which is, in particular, parallel to the axis of rotation or encloses with the latter an angle which is less than 10 degrees. Such an edge can form the covering-surface lateral edge facing the axis of rotation, for example, or can form the side facing away from the axis of rotation.
It is also advantageously possible to provide for the covering surface to have at least two straight edges, wherein the two edges are, in particular, parallel to one another or enclose between them an angle which is less than 10 degrees.
The covering surface can be irregularly shaped but bounded by straight lines or irregularly shaped and bounded by irregular lines. For example, it can have an edge on the side facing the axis of rotation which is substantially parallel to the axis of rotation and a parallel edge on the covering-surface side facing away from the axis of rotation. If the covering surface has an edge which is straight and parallel to the axis of rotation on its side facing the axis of rotation, then, according to plan, this edge should be spaced apart from the axis of rotation by at least the tolerance spacing.
The covering surface can be of triangular, rectangular, trapezoidal, elliptical or diamond shape. In the case of an elliptical or diamond shape, this should be extended parallel to the axis of rotation and compressed perpendicularly thereto. For example, the covering surface can be of mirror-symmetrical configuration relative to an axis perpendicular to the axis of rotation. The corresponding sealing surface at the wastegate opening should then have a corresponding shape in each case.
Provision can furthermore advantageously be made for the sealing surface of the flap, said sealing surface surrounding the covering surface, to be flat and parallel to the plane of the sealing surface.
This makes possible secure and reliable sealing of the covering flap under the influence of the contact force, even against a gas pressure.
Another advantageous embodiment of the invention envisages that the sealing surface of the flap, said sealing surface surrounding the covering surface, slopes relative to the covering surface.
If the sealing surface slopes relative to the covering surface at the covering surface, centering of the wastegate flap on the wastegate opening can be achieved by means of the transverse forces which act during the closure of the flap, and therefore better sealing and hence better efficiency of the exhaust-gas turbocharger can be achieved. In this case, all the regions of the sealing surface around the covering surface can either all have the same slope toward the inside of the covering surface or all have the same slope outward away from the covering surface.
The invention can also advantageously be configured in such a way that the sealing surface of the flap, said sealing surface surrounding the covering surface, is of conical or spherical-cap-shaped design. A conical or spherical-cap configuration of the sealing surface around the covering surface allows particularly efficient sealing and centering of the wastegate flap in the wastegate opening.
Provision can furthermore advantageously be made for the covering surface to have a projection which extends into the wastegate opening during closure. The provision of such a projection facilitates guidance of the flow during the opening of the flap and the configuration of a free channel when the wastegate flap is open.
Provision can furthermore advantageously be made for the thickness of the projection to increase with increasing distance from the axis of rotation, starting from the region of the wastegate flap which is closest to the axis of rotation. By means of such a configuration of the projection on the wastegate flap, it is ensured that the projection does not constitute an obstruction at the edge of the wastegate opening in that region of the wastegate flap which is close to the axis of rotation, especially at the beginning of the opening movement or at the end of the closing movement.
In the following part of the document, the invention is illustrated in figures of a drawing by means of illustrative embodiments and then explained. In the drawing:
Arranged in the exhaust duct 1b is a turbine 2, which is driven by the expelled exhaust gases. This is connected by means of a shaft 3 to a compressor wheel 4. During the operation of the turbocharger device, the compressor wheel 4 is driven in such a way that it additionally compresses the air drawn in through the intake duct 1a, with the result that compressed intake air is available for the combustion process and more fuel can be added to it per cylinder stroke, thus allowing the engine torque to be increased.
A throttle valve 1c for controlling the intake air, an air filter (not shown) ahead of the compressor wheel, as well as an air flow meter ahead of the compressor wheel and a charge air cooler downstream of the compressor wheel are provided in the intake duct 1a. Also worth mentioning is the possible arrangement of a catalytic converter in the exhaust duct 1b downstream of the turbine 2.
In the pressure-charged mode, the throttle valve 1c is fully open.
Regulation of pressure charging is possible by releasing some of the exhaust gas mass flow on the turbine side through the “wastegate” 10 with a wastegate opening, thereby opening a bypass duct which makes it possible to guide some of the exhaust gases past the turbine 2.
The control rod of the actuator 5 is denoted by 5a. As elements, as can be seen in
The section line A-A, along which a cross section is shown in the lower part of
The force relationships between the forces acting on the wastegate flap 8 are illustrated in
For this purpose, as can easily be seen in
A corresponding configuration of projections 24a, 24c can also be found in
In the end, an increased contact pressure of the wastegate flaps and hence better sealing behavior of the wastegate valve and therefore better efficiency of the exhaust-gas turbocharger and of the combustion engine can be achieved with the flap shapes shown and explained above.
Number | Date | Country | Kind |
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10 2015 212 381.2 | Jul 2015 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/062546 | 6/2/2016 | WO | 00 |