EP2375000B2 - Shaft seal - Google Patents

Description

technical field

The invention relates to the field of turbomachines, in particular exhaust gas turbochargers subjected to exhaust gases from internal combustion engines.

It relates to a shaft seal of such a turbomachine.

State of the art

To increase the performance of an internal combustion engine, exhaust gas turbochargers are used as standard today, with a turbine in the exhaust gas tract of the internal combustion engine and with a compressor upstream of the internal combustion engine, which is connected to the turbine via a common shaft. When an internal combustion engine is charged using an exhaust gas turbocharger, the filling quantity and thus the fuel mixture in the cylinders is increased, resulting in a noticeable increase in engine performance. Optionally, the energy contained in the exhaust gas of a combustion engine can be converted into electrical or mechanical energy using a power turbine. In this case, instead of a compressor, as with the exhaust gas turbocharger, a generator or a mechanical consumer is connected to the turbine shaft.

A standard exhaust gas turbocharger consists of a rotor consisting of a shaft, a compressor wheel and a turbine wheel, a bearing for the shaft, flow-guiding housing parts (compressor housing or turbine housing) and the bearing housing.

Due to the high process pressure in the flow area on the turbine and compressor side, the shaft of the exhaust gas turbocharger must be sealed off from the cavity of the bearing housing with a suitable sealing concept. The internal pressure in the cavity of the bearing housing is usually equal to atmospheric pressure. The gas pressure in the flow channel on the compressor or turbine side, on the other hand, depends on the current operating point of the exhaust gas turbocharger and is above the pressure in the cavity of the bearing housing at most operating points. In certain cases, however, a negative pressure is also to be expected, e.g. in partial load operation or at standstill.

Out of DE 20 25 125 a turbine-side shaft seal of an exhaust gas turbocharger is known, which consists of a simple oil collecting chamber on the turbine side of the radial bearing and a piston ring with a sealing effect between the shaft and the bearing housing. The bearing oil escaping axially from the radial bearing sprays onto the rotating shaft shoulder, which is offset outwards and is flung into the oil collection chamber by centrifugal forces. The bearing oil thrown off in this way then flows downwards within the oil collection chamber under the force of gravity and back into the oil circuit for bearing lubrication.

Piston rings made of metal, for example gray cast iron, are used as standard to reduce gas leakage from the flow channel through the rear wheel space of the turbine into the cavity of the bearing housing. The piston ring, which is under tension, is braced in a radial groove with an axial stop shoulder in the bearing housing. As a counterpart to the piston ring, the rotating shaft is provided with a radial groove, with the piston ring being trapped axially within this groove and covering it radially. Due to the differential pressure between the exhaust gas pressure and the pressure inside the bearing housing, the piston ring is axially displaced in the direction of the existing pressure gradient within the groove until it stops. Due to the axial contact of the piston ring on one of the inner surfaces of the groove, it grinds in and seals the bearing housing plenum relative to the exhaust gas flow. To improve the sealing effect, two or more piston rings can also be used, as is the case in CH 661 964 A5 , U.S. 3,180,568 , U.S. 4,196,910 or EP 1 860 299 is revealed. These documents show how the sealing effect against the hot exhaust gases can be increased by the additional use of sealing air or venting of the space between the two piston rings, thereby completely preventing the exhaust gases from escaping into the bearing housing.

Out of DE 37 37 932 A1 a shaft seal on the turbine side of an exhaust gas turbocharger is known, in which the oil drains from the radial bearing between the bearing point and the two piston rings. To improve oil tightness, an additional centrifugal disc is used instead of a simple axial shaft shoulder. The amount of undesired bearing oil hitting the area of the piston ring groove can thus be significantly reduced. The same is done in the shaft seals according to U.S. 4,268,229 such as DE 30 21 349 the oil drain between the radial bearing and the adjacent piston ring, with the oil drain always consisting of one chamber. In addition, the cavity between the two piston rings is connected to the cavity of the bearing housing by means of an additional connecting channel and vented to atmospheric pressure. The resulting pressure difference across the left-hand piston ring is thus suppressed, so that the piston ring primarily assumes an oil-tight but not hot-gas-tight function. Thus, only the right-hand piston ring takes over the sealing between the pressurized flow channel and the cavity of the bearing housing. These design variants result in two separate outlets for the media oil (from the radial bearing) and exhaust gas (from the flow channel), with the outlets being separated by a piston ring. The lubricating oil escaping from the radial bearing may spray axially into the piston ring area the gas seal and, in the worst case, floods the entire piston ring groove. The gas pressure in the flow channel of a compressor or turbine is usually greater than the internal pressure in the turbocharger bearing housing. A positive pressure difference (pressure in the flow channel is higher than in the cavity of the bearing housing) means that the resulting gas leakage blows through the piston ring seal and the bearing oil that has accidentally penetrated the piston ring area is transported back into the oil collection chamber of the bearing housing.

The in tries to counteract this DE 10 2004 055 429 B3 described sealing device for a lubricated bearing of a rotor shaft, which seals a bearing housing of an exhaust gas turbocharger against a supplied lubricant in the axial direction. A first seal in the form of a gap, a labyrinth or a piston ring and a second seal in the form of a narrow gap or a labyrinth are provided on the rotor shaft, which between them enclose an oil drain channel which extends annularly around the circumference of the rotor shaft and which is drained by means of a housing-side oil drain groove and a shaft-side oil drain groove arranged in the same position as the axis. In the oil drain channel there is a ring-shaped sealing web which protrudes in the radial direction of the rotor shaft with one end freely into the ring-shaped oil drain channel and represents a barrier acting in the axial direction for lubricant penetrating the oil drain channel and radially covers the gap of the second seal.

Out of DE 43 30 380 A1 an exhaust gas turbocharger is known, which consists of a two-part bearing housing, in which oil is sprayed onto the surface of the second part from a first part for cooling.

With all of the turbine-side shaft sealing concepts described, there is a risk under certain circumstances that hot gases from the rear wheel space of the exhaust gas turbine will escape through the piston ring seal, and the bearing oil remaining in the piston ring area and the oil drain grooves will burn locally, causing severe coking on the shaft seal and the associated wear. The risk of coking increases with increasing exhaust gas temperature and increased gas leakage through the piston rings as well as poor component cooling. Active cooling of this sealing section is decisive for the operational reliability of the shaft seal.

Out of DE 197 13 415 A1 an exhaust gas turbocharger is known which has an annular sealing plate as oil splash protection in the area of an axial bearing in the back of the compressor wheel.

Out of US2005/0188694 A1 an exhaust gas turbocharger is known, which has an oil suction pipe in the area of the shaft seal in the back of the compressor wheel between two piston rings, through which the zone between the two piston rings is cleaned of any penetrating oil by means of a vacuum pump.

Out of U.S. 4,523,763 an exhaust gas turbocharger is known which has a labyrinth seal in the area of the shaft seal in the back of the compressor wheel, which is intended to prevent oil from the lubrication circuit from getting into the working chamber of the compressor.

Summary of the Invention

The object of the present invention is to create a shaft seal for a turbomachine shaft mounted in a bearing housing, in which the drainage behavior of the lubricating oil can be improved and the risk of coking of the piston ring seal can be minimized by active cooling of the sealing part.

The shaft seal according to the invention of a turbomachine shaft mounted in a bearing housing between a cavity in the bearing housing and a rear wheel space of an impeller of the turbomachine comprises a plurality of seals. A first, impeller-side seal, which can be designed, for example, in the form of at least one piston ring, and a second, bearing-side seal, which can be designed, for example, in the form of a sealing gap between the bearing housing and the shaft. An oil drainage chamber is arranged between the impeller-side seal and the bearing-side seal, which is delimited by a third, middle seal, which is designed, for example, in the form of a sealing gap between the bearing housing and the shaft. According to the invention, a gas outlet chamber is also arranged between the third seal and the first impeller-side seal. According to the invention, the third seal cleanly separates the two media, oil from the oil drain chamber, from the gas from the gas outlet chamber, which minimizes the risk of coking in the oil drain chamber, since the two media do not meet within the same collection chamber. Both media are discharged separately from each other through the third seal through at least two drainage channels laterally into the bearing housing plenum. The shaft seal according to the invention is also actively cooled by at least one obliquely aligned splash oil device, with no splash oil getting into the drain chambers. The shaft seal is designed in such a way that as much splashing oil as possible keeps the material temperatures of the bearing housing and the optional insert and the piston rings installed in it low and prevents the oil from coking in the various drain chambers.

Optionally, that area of the bearing housing which is part of the shaft seal designed according to the invention can be designed as an insert. The insert piece can be easily replaced in the event of operational wear or removed from the bearing housing for a short period of time, for example for cleaning purposes. In addition, a material with the highest possible thermal conductivity is to be selected as the material for this insert.

Optionally, that area of the shaft which is part of the shaft seal designed according to the invention and forms the oil drain chamber and the gas outlet chamber with its contour together with the bearing housing can be designed as a sleeve-shaped attachment rotating with the shaft. This attachment can be shrunk onto the shaft, screwed on or connected to the shaft in some other way in a positive and/or non-positive manner. The attachment is optionally made of a material that has improved thermal conductivity or an increased insulating effect compared to the material of the shaft. In this way, potential oil coking in the oil drain grooves can be prevented.

Brief description of the drawings

Fig. 1

eine teilweise aufgeschnittene Ansicht eines Abgasturboladers gemäss dem Stand der Technik mit einem Radialverdichter und einer Radialturbine,

Fig. 2

einen entlang der Welle geführten Schnitt durch eine erfindungsgemäss ausgebildete, turbinenseitige Wellenabdichtung eines Abgasturboladers nach Fig. 1,

Fig. 3

eine Ansicht von unten auf ein Gehäuseteil einer zweiten Ausführungsform der Wellenabdichtung nach Fig. 2,

Fig. 4

einen entlang IV-IV geführten Schnitt durch das Gehäuseteil nach Fig. 3, und

Fig. 5

die Wellenabdichtung gemäss Fig. 2 mit einem auf der Welle aufgeschrumpften Aufsatz.

The shaft seal according to the invention is explained in detail below with reference to drawings. while showing

1

a partially cutaway view of an exhaust gas turbocharger according to the prior art with a radial compressor and a radial turbine,

2

1 shows a section along the shaft through a turbine-side shaft seal of an exhaust gas turbocharger designed according to the invention 1 ,

3

a bottom view of a housing part of a second embodiment of the shaft seal 2 ,

4

a section through the housing part along IV-IV 3 , and

figure 5

the shaft seal according to 2 with an attachment shrunk onto the shaft.

way of carrying out the invention

1 shows an exhaust gas turbocharger according to the prior art with a radial compressor 90 and a radial turbine 10. The housing of the exhaust gas turbocharger shown is shown partially cut away in order to be able to see the rotor with the compressor wheel 91, the shaft 20 and the turbine wheel 11. The air flow from the air inlet 92 via the compressor wheel 91 to the air outlet 93 and the gas flow from the gas inlet 12 via the turbine wheel 11 to the gas outlet 13 are indicated with bold arrows. The shaft 20 is rotatably mounted in the bearing housing 30, usually by means of two radial bearings and at least one axial bearing.

2 shows an enlarged view of an exhaust gas turbocharger or a power turbine in the area of the radial bearing 34 on the turbine side. On the turbine side of this wheel bearing, i.e. to the right of it in the illustration, the shaft seal designed according to the invention is arranged, which separates the cavity 50 in the bearing housing from the wheel rear space 15 of the turbine wheel 11. In the illustrated embodiment of the shaft seal designed according to the invention, the bearing housing includes an insert 31 (sealing sleeve) in the area of the shaft seal, which is implemented as a separate component. The insert piece 31 is ring-shaped and includes a radially outer oil drainage channel 52 for the splash oil thrown radially outwards from the radial bearing 34 and discharged laterally. The insert is sprayed directly or indirectly with spray oil and is thereby actively cooled. The spray oil is directed onto the components to be cooled by the oil spray device 61 . The oil spray is supplied through the oil duct 60 in the turbine-side bearing flange 62. In the embodiment shown, the oil spray device 61 is designed and aligned as a bore in such a way that the oil spray hits the inner contour 63 in the area of the bearing housing 30 and the insert piece in the area of the oil drainage channel 52 wetted. The splash oil and the oil from the bearing 34 and oil drain channel 51 cool the insert and the piston rings, seals and drain chambers located therein extensively and coking is largely prevented. To increase the cooling effect on the piston rings and discharge chambers, the insert piece 31 is optionally made from a material with the highest possible thermal conductivity. Furthermore, the components of the shaft seal 31, 30, 41, 42 can be separated from the hot turbine rear wall 11 and wheel rear space 15 by an additional heat plate 70. The heat plate 70 is arranged in the area of the wheel rear space 15 between the hot turbine rear wall 11 and the insert 31 of the shaft seal. Optionally, the heat plate rests on the insert piece 31 with a bearing surface 71 in the radially inner area. This heat plate 70 additionally reduces the material temperatures in the area of the insert 31 and the piston rings 41, 42, which in turn minimizes the tendency to form coking. The oil drainage channel 52 is delimited in the axial direction by a radially extended sealing plate 32 which in turn is itself cooled by the oil in the drainage channel 51 . The insert also includes recesses for receiving two series-arranged piston rings 41 and 42, which are known per se and whose mode of operation is described above in the prior art. In the radially inner area, the insert further comprises an oil drainage chamber 53, a separate gas outlet chamber 55 for gas leakage from the two piston rings 41 and 42 and a sealing web 33 which separates the oil drainage chamber 53 and the gas outlet chamber 55 from one another.

The oil drainage channel 51 between the radial bearing 34 and the sealing plate 32 forms the first main drainage channel for the bearing oil emerging from the radial bearing. The sealing plate 32 forms a first radial web 21 of the shaft 20 with a radially opposite first web Sealing gap 43, due to which penetration of the bearing oil from the oil drainage channel 51 into the oil drainage chamber 53 is minimized. The rotating shaft contour of the oil discharge chamber 53 is provided with a discharge groove that is offset radially inward, resulting in two splash edges to the left and right of this groove within the oil discharge chamber 53 . The oil thrown through the splash edges into the radially outer region of the oil drain chamber 53 formed by the groove in the insert piece 31 flows downwards within the oil drain chamber 53 along the contour of the insert piece 31 due to gravity. So that the bearing oil can be fed back from the oil drain chamber 53 into the oil circuit for bearing lubrication, the oil drain chamber 53 has at least one oil drain channel 54 in the lower region.

The insert piece 31 of the shaft seal designed according to the invention is characterized by a gas outlet chamber 55 which is arranged next to the oil drain chamber 53 and is separated from the oil drain chamber 53 by a circumferential sealing web 33 . The annular gas outlet chamber 55 is used for collecting the hot gas flowing through the piston rings 41 and 42 . The sealing web 33 forms a second radial sealing gap 44 with a radially opposite second web 22 of the shaft 20. The sealing gap 44 cleanly separates the two media oil from the oil drain chamber 53 from the gas from the gas outlet chamber 55. The gas collected in the gas outlet chamber 55 is in turn transferred through at least one separate gas discharge channel 56 within the insert piece 31 and separately from the oil discharge channel 54 into the common volume of the cavity 50 in the bearing housing. The intentional separation of the two drains is intended to prevent the two media from mixing in the area of the oil drain chamber 53, thereby reducing the risk of coking in the sealing compound. In addition, the major part of the bearing oil escaping from the radial bearing 34 is discharged to the outside through the large oil drainage channel 51 and the first sealing point 43 and is kept away from the piston ring section via the oil drainage channel 52 .

Optionally, the outlets of the at least one oil drainage channel 54 and of the gas drainage channel 56 are offset in the circumferential direction, as shown in FIG 3 and 4 is shown. 3 shows a view from below of the insert 31 without shaft and adjacent housing parts. The openings of the two oil drain channels 54 and of the gas drain channel 56, which lead out of the insert at the bottom, are offset axially and in particular in the circumferential direction. 4 shows the outflow channels and the radially inwardly protruding sealing plate 32 and in the area of the gas outflow channel 56 the radially inwardly protruding sealing web 33 in the section along IV-IV. The offset channel outlets result in greater strength of the insert.

In the illustrated embodiment, the seals 43 and 44 are designed as radial sealing gaps. Optionally, these seals can be supplemented or replaced with piston ring seals or other sealing elements.

Optionally, the bearing housing can be designed without a separate insert piece in the area of the shaft seal designed according to the invention. In this case, the corresponding grooves, sealing plates and sealing webs are embedded directly in the bearing housing. Compared to the one-piece variant without a separate insert piece, the embodiment described in detail with a separate insert piece has the advantage that the insert piece can be made of a material with good thermal conductivity (e.g. Ck45) for the purpose of cooling the sealing part and is therefore independent of the bearing housing material used (e.g. GGG -40). Furthermore, an insert can be easily replaced in the event of operational wear or can be removed from the bearing housing for a short period of time, for example for cleaning purposes.

Optionally, according to figure 5 the rotating shaft contour of the turbine in the area of the shaft seal designed according to the invention can be implemented by a sleeve-shaped attachment 81 . The attachment 81 is shrunk onto a seat 82 on the shaft and an edge formed on the shaft serves as an axial stop 83 for the attachment. The attachment and the shaft seat are to be designed in such a way that the heat dissipation is maximized via the oil cooling and the heat input via the shrink fit on the wave is minimized. The attachment is therefore to be made of a material with good thermal conductivity. By cooling the attachment, the oil drain channels are also cooled, which in turn minimizes the risk of coking in the drain brackets 53 and 55. Optionally, the attachment 81 can also be fixed to the shaft in a non-positive and/or positive manner in a different way, for example by means of a screw connection (thread) between the attachment and the shaft.

In the illustrated embodiment, the shaft seal comprises two piston rings 41 and 42. Alternatively, only one piston ring can be provided, or further piston rings can be provided in the area or at other points of the shaft seal.

The embodiment shown and described in detail shows the shaft seal designed according to the invention on the turbine side of an exhaust gas turbocharger or a power turbine. Of course, the shaft seal designed according to the invention can also be used analogously on the compressor side of an exhaust gas turbocharger, or in any other turbomachine.

Reference List

10

turbine

11

turbine wheel

12

gas inlet

13

gas leak

15

rear wheel space of the impeller

20

Wave

21, 22

sealing bar

30

bearing housing

31

Bearing housing insert

32

sealing plate

33

sealing bar

34

radial bearing

41, 42

piston ring

43, 44

radial sealing gap

50

cavity in the bearing housing

51, 52

oil drain channel

53

oil drain chamber

54

oil drain channel

55

gas exit chamber

56

gas discharge channel

60

oil channel

61

oil spray device

62

Turbine side bearing flange

63

Inner contour of the bearing housing

70

heat sheet

71

support point

81

Attachment rotating with the shaft

82

shaft fit

83

axial stop

90

compressor

91

compressor wheel

92

air intake

93

air leakage

Claims (13)

1. Shaft seal of a shaft (20), supported in a bearing housing (30), of a turbomachine between a cavity (50) in the bearing housing (30) and a wheel back space (15) of a rotating wheel (11) of the turbomachine, comprising a rotating wheel-side seal (41, 42) between the bearing housing (30, 31) and the shaft (20, 21) and also a bearing-side seal (43) between the bearing housing (30, 31) and the shaft (20, 21), wherein between the rotating wheel-side seal and the bearing-side seal provision is made for an oil outlet chamber (53), characterized in that

   the oil outlet chamber (53) is delimited by a third seal (44) between the bearing housing (30, 31) and the shaft (20, 22), and in that a gas discharge chamber (55) is arranged between the third seal and the rotating wheel-side seal, and

   an oil drain channel (52) is let into the bearing housing radially outside the oil outlet chamber (53), wherein at least one oil splashing device (61) is arranged in the region of the oil drain channel (52), with which oil splashing device the region of the oil drain channel can be splashed with oil, wherein the oil outlet chamber (53) and the gas discharge chamber (55) each comprise at least one separate outlet passage (54, 56).
2. Shaft seal according to claim 1, wherein the rotating wheel-side seal is designed in the form of at least one piston ring (41, 42).
3. Shaft seal according to claim 1 or 2, wherein the bearing-side seal is designed in the form of a sealing gap (43).
4. Shaft seal according to any of claims 1 to 3, wherein the third seal is designed in the form of a sealing gap (44).
5. Shaft seal according to claims 1 to 4, wherein inside the wheel back space (15), a heat shield (70) protects the shaft seal from the hot turbine back wall (11).
6. Shaft seal according to any of claims 1 to 5, wherein the bearing housing, in the region of the shaft seal, comprises an insert piece (31), into which recesses are let in, forming the oil outlet chamber (53) and also the gas discharge chamber (55).
7. Shaft seal according to any of claims 1 to 6, wherein the at least one outlet passage (54) of the oil outlet chamber (53) and the at least one outlet passage (56) of the gas discharge chamber (55) lead separately from each other into the cavity (50) in the bearing housing (30).
8. Shaft seal according to claim 7, wherein the at least one outlet passage (54) of the oil outlet chamber (53) and the at least one outlet passage (56) of the gas discharge chamber (55) lead into the cavity (50) in the bearing housing (30) in an offset manner in the circumferential direction.
9. Shaft seal according to any of claims 1 to 8, wherein the shaft, in the region of the shaft seal, comprises an attachment (81) which has a contour which together with the bearing housing forms the oil outlet chamber (53) and also the gas discharge chamber (55).
10. Shaft seal according to claim 9, wherein the attachment (81) is produced from a material which compared with the material of the shaft has higher heat conductivity.
11. Turbomachine, comprising at least one rotating wheel (11) arranged on a shaft (20), and also a bearing housing (30) in which the shaft (20) is rotatably supported, wherein a shaft seal according to any of claims 1 to 9 is arranged between the bearing housing (30) and the shaft (20).
12. Exhaust gas turbocharger or power turbine, comprising at least one turbine rotating wheel (11) which is arranged on a shaft (20), and also a bearing housing (30) in which the shaft (20) is rotatably supported, wherein a shaft seal according to any of claims 1 to 9 is arranged between the bearing housing (30) and the shaft (20).
13. Exhaust gas turbocharger, comprising at least one compressor rotating wheel (11) which is arranged on a shaft (20), and also a bearing housing (30) in which the shaft (20) is rotatably supported, wherein a shaft seal according to any of claims 1 to 9 is arranged between the bearing housing (30) and the shaft (20).

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