Exhaust gas routing section for an exhaust gas turbocharger and method for operating an exhaust gas turbocharger

Abstract

Exhaust gas routing section for an exhaust gas turbocharger, comprising a first spiral channel (4) and a second spiral channel (5) for the flow of gas to a turbine wheel rotatably mounted in the flowable exhaust gas routing section, wherein a flow opening (10) is provided between the first spiral channel (4) and the second spiral channel (5), which is designed to bring about a flow of exhaust gas from the first spiral channel (4) into the second spiral channel (5) and vice versa, and wherein the flow opening (10) has a movable cover element (9') for opening or closing the flow opening (10), wherein the cover element (9') is designed to allow a first flow cross-section (11) of the flow opening (10) to be released in a degressive manner, characterized in that, in order to bring about the degressive opening of the first flow cross-section (11), the cover element (9') is designed to have a pot-shaped outer contour (12), and wherein the cover element (9') has a base plate (13) exhibitswhich accommodates an element body (15) on a first plate surface (14), and wherein a body base cross-section (KQ) of the element body (15) as well as a plate cross-section (PQ) of the base plate (13) are oval, wherein the element body (15) has a groove (28) with a width (BR) which extends over its circumference along a transverse axis (26) over the top surface (23), wherein, for the secure sealing of the first spiral channel (4) and the second spiral channel (5) in the first position, a second channel wall (29) of the flow opening (10) opposite a first channel wall (19) of the flow opening (10) has a projection (30) that is complementary to the groove (28).

Description

[0001] The invention relates to an exhaust gas guide section for an exhaust gas turbocharger of the type specified in the preamble of patent claim 1. Furthermore, the invention relates to a method for operating an exhaust gas turbocharger.

[0002] Exhaust gas guide sections for exhaust gas turbochargers, which have a control device for controlling a fluid flowing through the exhaust gas guide section, generally exhaust gas, are known. The control device is provided for opening and closing a bypass channel in the flow-through exhaust gas guide section to bypass a turbine wheel of the exhaust gas guide section, which is rotatably arranged in a wheel chamber of the exhaust gas guide section. It has a cover element for opening and closing a flow cross-section of the bypass channel. With the aid of such a control device, it is possible to completely or partially bypass the turbine wheel at certain operating points of the exhaust gas turbocharger, in particular at operating points with large flow volumes, thus enabling efficient operation of the exhaust gas turbocharger.The efficient operation of the exhaust gas turbocharger depends on a specific opening characteristic of the control device, which must be adapted to the requirements of an internal combustion engine connected to the exhaust gas turbocharger.

[0003] For example, German Patent Application DE 198 24 913 A1 discloses an exhaust gas guide section for an exhaust gas turbocharger with a control device whose opening characteristic exhibits a progressive progression. Depending on the travel of a cover element of the control device, starting from a closed position, the opening cross-section of a bypass channel of the exhaust gas guide section increases progressively, in particular exponentially, as the travel increases. This results in a progressive opening characteristic that is suitable for the described application.

[0004] Likewise, the published patent application WO 2010 / 039596 A2 discloses an exhaust gas guide section for an exhaust gas turbocharger with a control device whose cover element has a progressive opening characteristic starting from a closed position of the cover element.

[0005] The published patent application WO 2005 / 073536 A1 discloses an exhaust gas guide section for an exhaust gas turbocharger with a control device whose cover element has a degressive opening characteristic starting from a closed position of the cover element.

[0006] From the published patent application US 2014 / 0072412 A1, a plate-shaped cover element of a control device for an exhaust gas guide section of an exhaust gas turbocharger is known, which has a groove that is designed to be complementary to a dividing wall of two spiral channels of the exhaust gas guide section.

[0007] The object of the present invention is to provide an improved exhaust gas guide section for an exhaust gas turbocharger. A further object is to specify a method for operating an exhaust gas turbocharger.

[0008] This object is achieved according to the invention with an exhaust gas guide section for an exhaust gas turbocharger having the features of claim 1. The further object is achieved according to the invention with a method for operating an exhaust gas turbocharger having the features of claim 11. Advantageous embodiments with expedient and non-trivial further developments of the invention are specified in the dependent claims.

[0009] According to the invention, an exhaust gas guide section for an exhaust gas turbocharger comprises a first spiral duct and a second spiral duct for flow to a turbine wheel rotatably mounted in the flow-through exhaust gas guide section. A flow opening is provided between the first spiral duct and the second spiral duct, which is designed to cause exhaust gas to flow from the first spiral duct into the second spiral duct and vice versa. The flow opening has a movable cover element for opening or closing the flow opening.The cover element is designed to be degressively releasable over a first flow cross-section of the through-flow opening, wherein in order to bring about the degressive opening of the first flow cross-section the cover element is designed to have a pot-shaped outer contour, and wherein the cover element has a base plate which receives an element body on a first plate surface, and wherein a body base cross-section of the element body and also a plate cross-section of the base plate are oval, wherein the element body has a groove with a width which is designed to extend over its circumference along a transverse axis over the cover surface, wherein for the secure sealing of the first spiral channel and the second spiral channel in the first position a second channel wall of the through-flow opening opposite a first channel wall of the through-flow opening has an elevation designed to be complementary to the groove.It has proven advantageous to gradually open the first flow cross-section, starting from a closed position of the cover element, to create overflow from the first spiral channel into the second spiral channel. The advantage of this gradually opening is improved controllability of the exhaust gas turbocharger, which is associated with improved turbocharger responsiveness. Furthermore, the gradually opening offers improved coordination options with other possible flow cross-sections that can be opened, for example, the flow cross-section of a bypass channel.

[0010] A further advantage of the possibility of overflow from the first spiral channel into the second spiral channel with the aid of the cover element is the provision of the exhaust gas guide section, which has the first spiral channel and the second spiral channel each in the form of a conventional partial spiral channel, such that the spiral channel wraps around a longitudinal axis of the exhaust gas guide section by only 180°, with a wrap of 360°. This allows for a smaller and more compact exhaust gas guide section to be formed.

[0011] To achieve a degressive opening characteristic, the cover element has a pot-shaped outer contour. This outer contour makes it easy to create a relatively large flow cross-section at the very beginning of the opening, starting from the closed position of the cover element, which increases degressively over a certain travel of the cover element.

[0012] The cover element is designed to be at least partially received in a wall of the exhaust gas guide section. This ensures that no outflow into the bypass channel occurs when the cover element is in the closed position. Furthermore, particularly when the cover element is designed as a cover element, it can be ensured that, for example, the second flow cross-section is opened before the first flow cross-section, provided this is required for the corresponding operation of the internal combustion engine.

[0013] In one embodiment of the exhaust gas guide section according to the invention, the exhaust gas guide section has a cover element for opening and closing a bypass channel of the exhaust gas guide section. The bypass channel is provided in the flow-through exhaust gas guide section to bypass the turbine wheel and has a second flow cross-section. The advantage is the possibility of guiding exhaust gas not only from one spiral channel to the other and vice versa, but also the exhaust gas can be guided past the turbine wheel, particularly in medium and high load and speed ranges of an internal combustion engine that is mechanically and thermodynamically connected to the exhaust gas turbocharger. This leads to a further increase in the achievable efficiency during operation of the exhaust gas turbocharger.

[0014] In a further embodiment of the exhaust gas guide section according to the invention, the cover element is designed to be able to gradually open the second flow cross-section, starting from a closed position into an intermediate position. As with flow over the turbine wheel, it has been shown that a gradually opening of the second flow cross-section during so-called flow around or bypassing is advantageous for the supply of air to the turbine wheel. It is not absolutely necessary for the second flow cross-section to be opened completely, i.e. gradually starting from the closed position into a second position in which the second flow cross-section is completely open. This provides the advantage of improved controllability of the first flow cross-section and the second flow cross-section.

[0015] A significant advantage of combining the degressive opening of the first flow cross-section and the second flow cross-section is that, during operation with the internal combustion engine, the valve opening duration of an exhaust valve of the internal combustion engine can be advantageously extended. This allows, on the one hand, a charge exchange phase of the internal combustion engine to be extended for improved scavenging.

[0016] Preferably, the cover element or the covering element is movable with the aid of a control device. A self-regulating cover element could also be designed, which opens or closes automatically with the aid of applied pressures in the spiral channels. However, control of the cover element with the aid of the control device is preferable, since this allows the pressure ratio at the turbine wheel to be actively influenced. Particularly preferably, the control device of the cover element corresponds to the control device of the cover element. Thus, the cover element and the covering element can be moved with a single control device, which enables a compact design of the exhaust gas turbocharger. A further advantage is cost-effective production of the exhaust gas turbocharger due to a smaller number of components.

[0017] In a preferred embodiment, a movement of the cover element triggers a movement of the cover element. Thus, a movement of the cover element can specifically influence the opening of the first flow cross-section and the second flow cross-section. In other words, this means that the movement of the cover element can be represented as a function of the movement of the cover element. This leads to simplified control of the two flow cross-sections, for example, with computer-controlled control of the flow cross-sections.

[0018] To further enhance the compact design of the exhaust gas turbocharger, the cover element corresponds to the cover element. In other words, this means that both the first flow cross-section and the second flow cross-section can be opened and closed with a single element. This not only results in a compact design but also in cost-effective production of the exhaust gas turbocharger, as the number of parts in the unit is reduced.

[0019] In a further embodiment, the cover element and / or the cover element has a first element section and a second element section along its longitudinal axis, wherein, to achieve a degressive opening characteristic, a first angle of inclination of a first outer surface of the first element section is greater than a second angle of inclination of a second outer surface of the second element section, wherein the second element section is arranged opposite a second channel wall. The degressive opening characteristic can be achieved in a simple manner using the two element sections. The cover element and / or the cover element is easy to manufacture.

[0020] To seal the first flow cross-section or the second flow cross-section in the closed position of the cover element and / or the cover element, the cover element has an annular surface that is designed to bear against a channel wall of the exhaust gas guide section. Furthermore, it is advantageous if the ring of the cover element is located in the bypass channel. This makes it easier to open the cover element with the aid of the exhaust gas flowing through the bypass channel.

[0021] In a further embodiment of the exhaust gas guide section according to the invention, the cover element and / or the cover element are mounted on a lever arm of the control device, which can be pivoted about a rotational axis. Due to the possible rotational movement, relatively low activation forces are required to move the corresponding element.

[0022] In a further embodiment of the exhaust gas guide section according to the invention, the cover element is designed to open the first flow cross-section after the second flow cross-section has been at least partially opened. The advantage is that overflow from the first spiral channel and the second spiral channel is only possible if the bypass channel is already open. This makes it possible to prevent knocking of the internal combustion engine due to excessive exhaust gas backpressure at the turbine wheel. At the same time, a possible backflow of overflowing exhaust gas into the spiral channel is prevented, the cylinders thermodynamically connected to it being in an intake and / or combustion phase of a cycle of the internal combustion engine. In other words, their exhaust valve(s) are closed, while the exhaust valve(s) of the cylinders connected to the other spiral channel are open.

[0023] The second aspect of the invention relates to a method for operating an exhaust gas turbocharger with a flow-through exhaust gas guide section, wherein a bypass channel is formed in the exhaust gas guide section for bypassing a turbine wheel rotatably received in the exhaust gas guide section. The bypass channel has a second flow cross-section, which can be opened and closed with the aid of a cover element. The second flow cross-section is opened gradually starting from a closed position of the cover element, in which the second flow cross-section is completely closed. The exhaust gas guide section is designed according to one of claims 1 to 10.

[0024] With the aid of the method according to the invention, in particular in conjunction with the features of subclaims 12 to 15, it is possible to achieve particularly efficient operation of the exhaust gas turbocharger in conjunction with the internal combustion engine. The method according to the invention allows operation of the internal combustion engine with longer opening times of the exhaust valve of the internal combustion engine. As a result, a charge cycle of the internal combustion engine can be improved due to a possible reduction in exhaust backpressure with a view to reducing so-called exhaust work. Due to the possibility of using longer opening times of the exhaust valve of the internal combustion engine with improved efficiency of the internal combustion engine, an internal combustion engine with reduced consumption and thus emissions can be provided. Furthermore, the tendency of the internal combustion engine to knock is significantly reduced.

[0025] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Identical or functionally equivalent elements are assigned identical reference numerals. They show: Fig. 1 in a perspective view a section along a first sectional plane through an exhaust gas guide section for an exhaust gas turbocharger according to the prior art, Fig. 2 the exhaust gas duct section according to Fig. 1 with the control device in a second position, Fig. 3 in a perspective view a section along a second sectional plane through the exhaust gas guide section according to. Fig. 1 with the control device in the first position, Fig. 4 the exhaust gas duct section acc. Fig. 3 with the control device in a second position, Fig. 5 an sA diagram of an opening characteristic of an exhaust gas turbocharger according to the invention, Fig. 6 shows a perspective view of a cover element of the exhaust gas guide section according to the invention, Fig. 7 in a perspective view the cover element of the exhaust gas guide section in a variant, Fig. 8 in a perspective view the cover element of the exhaust gas guide section in a variant, Fig. 9 in a perspective view the cover element of the exhaust gas guide section in a variant, Fig. 10 in a perspective view the cover element of the exhaust gas guide section in a variant, and Fig. 11 shows a schematic representation of the cover element of the exhaust gas guide section according to the prior art.

[0026] A according to Fig. 1 formed through-flow exhaust gas guide section 1 of an exhaust gas turbocharger 2 according to the prior art, comprises an inlet channel 3 for the entry of a fluid flow into the exhaust gas guide section 1, generally exhaust gas from an internal combustion engine 7, a first spiral channel 4 and a second spiral channel 5 downstream of the inlet channel 3 for conditioning the flow, and an outlet channel (not shown in detail) downstream of the spiral channels 4, 5, through which the exhaust gas can escape from the exhaust gas guide section 1 in a targeted manner. Between the spiral channels 4, 5 and the outlet channel, a wheel chamber (not shown in detail) is formed, in which a turbine wheel (not shown in detail) is rotatably received.

[0027] The exhaust gas guide section 1 is connected to an exhaust manifold 6 of the internal combustion engine 7, so that the exhaust gas of the internal combustion engine 7 can enter the spiral channels 4, 5 via the inlet channel 3 in order to act on the turbine wheel.

[0028] To adapt the operating behavior of the exhaust gas turbocharger 2 to the fluid flow of the internal combustion engine, and thus to the internal combustion engine, a control device 8 for separating and connecting the first spiral channel 4 and the second spiral channel 5 is arranged in the exhaust gas guide section 1. To separate and connect the two spiral channels 4, 5, a cover element 9' of the control device 8 is arranged in a flow opening 10, which is designed so that fluid can flow through the two spiral channels 4, 5.

[0029] In a first position, the closed position of the cover element 9', as shown in Fig. As shown in Figure 1, the two spiral channels 4, 5 can be flowed through completely separately from one another, with the flow opening 10 being completely closed by means of the cover element 9'. The exhaust gas of the internal combustion engine flows through the two spiral channels 4, 5, with a first part of the exhaust gas flowing through the first spiral channel 4 and a second part of the exhaust gas flowing through the second spiral channel 5.

[0030] In a second position of the cover element 9', as shown in Fig. 2, the flow opening 10 is fully open, and exhaust gas can flow from the first spiral channel 4 into the second spiral channel 5 and vice versa. This means that exhaust gas can flow from one spiral channel 4; 5 into the other spiral channel 5; 4 via the flow opening 10, which has a first flow cross-section 11.

[0031] The cover element 9' can be positioned in further intermediate positions between the first position and the second position, so that the first flow cross-section 11 can be adapted to a corresponding need to achieve the best possible efficiency of the exhaust gas turbocharger 2 in accordance with the amount of exhaust gas flowing through. It has been found that a degressive opening of the first flow cross-section 11, starting from the first position, thus starting from the completely closed first flow cross-section 11, towards the second position, thus towards a completely open first flow cross-section 11, is advantageous. In other words, the cover element 9' is designed to bring about a degressive opening of the first flow cross-section 11. This means that the control device 8 has a degressive opening characteristic for opening the first flow cross-section 11.

[0032] To achieve the degressive opening of the first flow cross-section 11, the cover element 9' is designed with a pot-shaped outer contour 12. It has a base plate 13, which receives an element body 15 on a first plate surface 14. A movement device 17 of the control device 8 is fixed to the base plate 13 on a second plate surface 16 facing away from the element body 15.

[0033] The element body 15 has a body base cross-section KQ that is smaller than a plate cross-section PQ of the first plate surface 14. This forms an annular surface 18 that completely surrounds the element body 15. This annular surface 18 serves, on the one hand, to support the cover element 9' against a first channel wall 19 of the flow opening 10 and, on the other hand, to serve as a sealing surface for sealing the two spiral channels 4, 5 in the first position of the cover element 9'.

[0034] To achieve the degressive opening characteristic, the element body 15 has two element sections, a first element section 20 and a second element section 21, which are arranged in series along a longitudinal axis 22 of the element body 15. The first element section 20 is firmly connected to the base plate 13 and arranged between the second element section 21 and the base plate 13. The second element section 21 is also firmly connected to the first element section 20. The second element section 21 has a cover surface 23 of the cover element 9', which is designed to face away from the first element section 20.

[0035] The cover element 9' in a basic representation shows Fig. 11. The first element section 20 and the second element section 21 essentially have outer surfaces 24, 25 that extend from the base plate 13 toward the cover surface 23 in the direction of the longitudinal axis 22. A first angle of inclination α1 of the first outer surface 24 of the first element section 20 is greater than a second angle of inclination α2 of the second outer surface 25 of the second element section 21.

[0036] In a variant of the cover element 9 or the cover element 9' according to the Fig. 1 to 4, 6, where only Fig. 6 shows a cover element 9' of an exhaust gas guide section 1 according to the invention, both the body base cross-section KQ and the plate cross-section PQ are oval. The element body 15 has a groove 28 with a width BR, which extends over its circumference along the transverse axis 26 over the cover surface 23. To ensure secure sealing of the first spiral channel 4 and the second spiral channel 5 in the first position, a second channel wall 29 opposite the first channel wall 19 has a raised portion 30 complementary to the groove.

[0037] In a variant acc. Fig. 7, the cover surface 23 of the cover element 9' is flat. In each variant according to the Fig. 8 and Fig. 9, the cover element 9' has a circular cross-section. In the variant according to Fig. 8, the second element section 21 is designed in the form of a cone, whereas in the variant according to Fig. 9 is shaped like a spherical layer.

[0038] The Fig. The variant of the cover element 9' shown in Fig. 10 also has a pot-shaped outer contour 12, wherein the cover surface 23 is rectangular, whereby the outer contour 12 of the second element section 21 in the area of ​​the cover surface 23 has a greater gradient that differs from the remaining area of ​​the second element section 21.

[0039] Furthermore, a bypass channel 31 is provided in the flow-through exhaust gas guide section 1 for bypassing the wheel chamber in the exhaust gas guide section 1. The bypass channel 31 has an inlet opening 32 with a second flow cross-section 33, wherein the inlet opening 32 can be completely or partially closed or completely or partially opened by means of the control device 8 or the cover element 9.

[0040] The cover element 9 of the control device 8, which corresponds to the cover element 9', is rotatably received in the bypass channel 31, and thus in the exhaust gas guide section 1, wherein the cover element 9 is pivotable about a rotation axis 34 of the cover element 9 in the bypass channel 31 and is thus mounted in the exhaust gas guide section 1. In other words, the cover element 9 is accommodated so that it can perform a pivoting movement in the exhaust gas guide section 1, wherein the second flow cross-section 33 of the inlet opening 32 can be adjusted by means of the pivoting movement.

[0041] With the help of the cover element 9, a wide opening area, see. Fig. 4, a predominantly degressive opening of the second flow cross-section 33 can be achieved. Thus, until the first flow cross-section 11 is fully opened, only a small amount of exhaust gas can be diverted via the second flow cross-section 33 into the bypass channel 31. When the first flow cross-section 11 is fully open, the second flow cross-section 33 is also fully open, allowing overflow from the first spiral channel 4 into the second spiral channel 5 and vice versa, and simultaneously allowing exhaust gas to be blown off past the turbine wheel.

[0042] To enable the cover element 9 and thus the control device 8 to move, a cylindrical opening 35 is formed in the exhaust gas guide section 1, in which a shaft 36 with a second longitudinal axis 37 of the control device 8 is rotatably received. A lever arm 38 arranged between the shaft 36 and the cover element 9 serves to connect the cover element 9 to the shaft 36, so that the cover element 9 can be pivoted by rotating the shaft 36.

[0043] Fig.5 shows an sA diagram, where s denotes a standardized adjustment path of the cover element 9 or the cover element 9', and AF denotes a free flow cross-section of the flow cross-sections 11, 33 standardized as a function of the adjustment path s. The adjustment path s is a function of an opening angle of the cover element 9 or the cover element 9', since the cover element 9' corresponds to the cover element 9. The opening angle with a value of 0° corresponds to the closed position of the cover element 9 or the cover element 9'.

[0044] A first line A represents the first flow cross-section 11 over the adjustment path s of the cover element 9' according to the exemplary embodiment. A second line B represents the free second flow cross-section 33, which can be changed with the aid of the cover element 9. A third line C represents, in a variant, the free first flow area 11. The lines A, B, C describe an opening characteristic of the control device 8.

[0045] According to the first line A and the third line C, the control device 8 has a degressive opening characteristic with respect to the first flow cross-section 11. In other words, this means that the first flow cross-section 11 is opened degressively starting from a closed position of the cover element 9', in which the first flow cross-section 11 is completely closed.

[0046] According to the course of line B, the control device 8 has a degressive opening characteristic with respect to the second flow cross-section 33. In other words, this means that the second flow cross-section 33 is also opened degressively starting from a closed position of the cover element 9, in which the second flow cross-section 33 is completely closed.

[0047] In the variant according to line C, the first flow cross-section 11 is only opened when the second flow cross-section 33 is already partially open. Preferably, the first flow cross-section 11 is opened at an opening angle of approximately 5° of the cover element 9. Particularly preferably, the opening angle is in an interval of 0° to 3°.

[0048] In order to prevent exhaust gas from overflowing from the first spiral channel 4 into the second spiral channel 5 and vice versa when the first flow cross-section 11 is opened according to the line A, the first flow cross-section 11 is smaller than the second flow cross-section 33 up to an adjustment path s1 of the cover element 9. If the first flow cross-section 11 is opened according to the line C, the first flow cross-section 11 is to be designed smaller than the second flow cross-section 33 up to an adjustment path s1'.

Claims

[1] Exhaust gas guide section for an exhaust gas turbocharger, with a first spiral channel (4) and a second spiral channel (5) for the flow to a turbine wheel rotatably received in the through-flow exhaust gas guide section, wherein a through-flow opening (10) is provided between the first spiral channel (4) and the second spiral channel (5), which is designed to bring about an overflow of exhaust gas from the first spiral channel (4) into the second spiral channel (5) and vice versa, and wherein the through-flow opening (10) has a movable cover element (9') for opening or closing the through-flow opening (10), wherein the cover element (9') is designed to have a first flow cross-section (11) of the through-flow opening (10) degressively releasable, characterized byin that, in order to bring about the degressive opening of the first flow cross-section (11), the cover element (9') is designed to have a pot-shaped outer contour (12), and wherein the cover element (9') has a base plate (13) which receives an element body (15) on a first plate surface (14), and wherein a body base cross-section (KQ) of the element body (15) as well as a plate cross-section (PQ) of the base plate (13) are oval, wherein the element body (15) has a groove (28) with a width (BR) which extends over its circumference along a transverse axis (26) over the cover surface (23), wherein for the secure sealing of the first spiral channel (4) and the second spiral channel (5) in the first position, a second channel wall (29) of the flow opening (10) opposite a first channel wall (19) of the flow opening (10) has a has a raised portion (30) complementary to the groove (28). [2] Exhaust gas guide section according to claim 1, characterized by in that the exhaust gas guide section has a cover element (9) for opening and closing a bypass channel (31) of the exhaust gas guide section (1), wherein the bypass channel (31) is provided in the through-flow exhaust gas guide section (1) for bypassing the turbine wheel, and wherein the bypass channel (31) has a second flow cross-section (33). [3] Exhaust gas guide section according to claim 2, characterized by that the second flow cross-section (33) can be released degressively with the aid of the cover element (9), at least starting from a closed position into an intermediate position. [4] Exhaust gas guide section according to one of the preceding claims, characterized by that a control device (8) is formed in the exhaust gas guide section (1) for moving the cover element (9') and / or the cover element (9). [5] Exhaust gas guide section according to one of claims 2 to 4, characterized bythat a movement of the cover element (9') triggers a movement of the cover element (9). [6] Exhaust gas guide section according to one of claims 2 to 5, characterized by that the cover element (9') corresponds to the cover element (9). [7] Exhaust gas guide section according to one of claims 2 to 6, characterized by in that the cover element (9) and / or the cover element (9') has a first element section (20) and a second element section (21) along its longitudinal axis (22), wherein, in order to bring about a degressive opening characteristic, a first angle of inclination (α1) of a first outer surface (24) of the first element section (20) is greater than a second angle of inclination (α2) of a second outer surface (25) of the second element section (21), wherein the second element section (21) is arranged opposite the second channel wall (29). [8] Exhaust gas guide section according to one of claims 2 to 7, characterized bythat the cover element (9) and / or the cover element (9') has an annular surface (18) which is designed to be supported on the channel wall (19) of the exhaust gas guide section (1). [9] Exhaust gas guide section according to one of claims 2 to 8, characterized by that the cover element (9) and / or the cover element (9') is received on a lever arm (38) of the control device (8), which is pivotable about a rotation axis (34). [10] Exhaust gas guide section according to one of claims 2 to 9, characterized by that the cover element (9') is designed to open the flow opening (10) after the second flow cross-section (33) has been at least partially opened. [11] Method for operating an exhaust gas turbocharger, with a flow-through exhaust gas guide section (1) with a first spiral channel (4) and a second spiral channel (5) for the flow against a turbine wheel rotatably received in the exhaust gas guide section (1), wherein a flow opening (10) is provided between the first spiral channel (4) and the second spiral channel (5), which is designed to bring about an overflow of exhaust gas from the first spiral channel (4) into the second spiral channel (5) and vice versa, and wherein the flow opening (10) has a movable cover element (9') for opening or closing the flow opening (10), wherein a first flow cross-section (11) of the flow opening (10) is opened degressively starting from a closed position of the cover element (9'), characterized by that the exhaust gas guide section (1) is designed according to one of claims 1 to 10. [12] Method according to claim 11, characterized byin that a bypass channel (31) for bypassing the turbine wheel is formed in the exhaust gas guide section (1), and wherein the bypass channel (31) has a second flow cross-section (33), and wherein the second flow cross-section (33) is opened with the aid of a cover element (9) starting from a closed position of the cover element (9). [13] Method according to claim 12, characterized by that the second flow cross-section (33) is opened degressively. [14] Method according to claim 12 or 13, characterized by that the first flow cross-section (11) up to a travel s1, s1' of the cover element (9') is smaller than the second flow cross-section (33) of the bypass channel (31). [15] Method according to one of claims 12 to 14, characterized by that the first flow cross-section (11) is opened after the second flow cross-section (33).

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