EP2743460B1 - Shaft seal - Google Patents

Description

Technical area

The invention relates to the field of turbomachines, in particular the exhaust gas turbochargers acted upon by exhaust gases from internal combustion engines.
It relates to a shaft seal of such a turbomachine.

State of the art

For the increase in performance of an internal combustion engine today exhaust gas turbochargers are used by default, with a turbine in the exhaust system of the internal combustion engine and with the internal combustion engine upstream compressor, which is connected to the turbine via a common shaft. With the charging of an internal combustion engine by means of an exhaust gas turbocharger, the filling quantity and thus the fuel mixture in the cylinders is increased, and from this a considerable increase in power for the engine is obtained. Optionally, the energy bound in the exhaust gas of an internal combustion engine can be converted by means of a power turbine into electrical or mechanical energy. In this case, instead of a compressor as in the exhaust gas turbocharger, a generator or a mechanical load is connected to the turbine shaft.

As standard, an exhaust gas turbocharger is composed 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 turbine as well as on the compressor side flow region, the shaft of the exhaust gas turbocharger with respect to the cavity of the bearing housing with an appropriate sealing concept is sealed. The internal pressure in the cavity of the bearing housing usually corresponds to the atmospheric pressure. The gas pressure in the flow channel of the compressor or turbine side, however, depends on the current operating point of the exhaust gas turbocharger and is in most Operating points above the pressure in the cavity of the bearing housing. In certain cases, however, is also to be expected with a negative pressure, for example, in partial load operation or at a standstill.

Out DE 20 25 125 a turbine-side shaft seal of an exhaust gas turbocharger is known, which is composed of a simple oil catch chamber on the turbine side of the radial bearing and a piston ring with sealing action between the shaft and the bearing housing. The bearing oil exiting axially from the radial bearing sprays onto the outwardly offset and rotating shaft shoulder and is thrown by centrifugal forces into the oil-collecting chamber. The bearing oil thus thrown off then flows downwards in accordance with gravity within the oil catching chamber and then back into the oil circuit of the bearing lubrication.

To reduce the gas leakage from the flow channel through the Radrückraum the turbine in the cavity of the bearing housing piston rings made of metal, such as gray cast iron, are used by default. The live piston ring is clamped 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, wherein the piston ring is axially caught within this groove and this covers radially. Due to the differential pressure between the exhaust 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 to stop. Due to the axial support of the piston ring on one of the Nutinnenfläche this grinds and seals the Lagergehäuseplenum relative to the exhaust flow. To improve the sealing effect and two or more piston rings can be used, as in CH 661 964 A5 . US 3,180,568 . US 4,196,910 or EP 1 860 299 is disclosed. In these documents is shown how the sealing effect compared to the hot exhaust gases can be increased by the additional use of air blocking respectively venting the space between the two piston rings and thereby escape of the exhaust gases can be completely prevented in the bearing housing.

Out DE 37 37 932 A1 is a turbine-side shaft seal of an exhaust gas turbocharger known, in which the oil drain from the radial bearing between the bearing and the two piston rings takes place. In this case, an additional centrifugal disc is used to improve the oil seal instead of a simple axial shaft shoulder. The amount of impinging in the range of Kolbenringnut unwanted bearing oil can thus be significantly reduced. Analog occurs in the shaft seals according to US 4,268,229 such as DE 30 21 349 the oil drain between the radial bearing and the adjacent piston ring, the oil drain always consists of a chamber. In addition, the cavity between the two piston rings is connected by means of an additional connecting channel with the cavity of the bearing housing and vented to ambient atmospheric pressure. The resulting pressure difference across the left piston ring is thereby prevented, so that the piston ring predominantly assumes an oil-sealing but not hot gas sealing function. Thus, only the right piston ring takes over the seal between the pressurized flow channel and the cavity of the bearing housing. These design variants therefore result in two separate processes for the media oil (from radial bearings) and exhaust gas (from the flow channel) whereby the processes are separated by a piston ring. The lubricating oil emerging from the radial bearing may inject axially into the piston ring region of the gas seal and, in the worst case, flood the entire piston ring groove. Usually, the gas pressure in the flow channel of a compressor or turbine is greater than the internal pressure in the bearing housing of the turbocharger. Thus, a positive pressure difference (pressure in the flow channel is higher than in the cavity of the bearing housing) with the result that adjusting gas leakage blows through the piston ring seal and the unintentionally penetrated into the piston ring area bearing oil transported back into the oil collection chamber of the bearing housing.

To counteract that in 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. On the rotor shaft, 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, which between them include an annularly around the circumference of the rotor shaft extending oil drain channel, which by means of a housing side Ölablaufnut and arranged in a coaxial position shaft side Ölablaufnut is constructed. In the oil drain passage in the radial direction of the rotor shaft is provided with one end freely projecting into the annular oil drain channel annular sealing ridge, which acts in the axial direction barrier for in represents the oil drain passage penetrating lubricant and radially overlaps the gap of the second seal.

In all described Wellenabdichtkonzepten there is a risk under certain circumstances that hot gases escape from the Radrückraum the exhaust gas turbine through the piston ring seal, and burns the remaining in the piston ring area and Ölablaufnuten bearing oil locally and thereby causes a strong coking the shaft seal and 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. Thus, an active cooling of this seal section is crucial for the reliability of the shaft seal. EP2375000 discloses a shaft seal between the bearing housing and the shaft of a fluid machine comprising an impeller-side seal and a bearing-side seal, wherein between the impeller-side seal and the bearing-side seal, an oil drain chamber is provided, which is bounded by a third seal between the bearing housing and the shaft. Between the third seal and the impeller-side seal, a gas outlet chamber is arranged, wherein the construction is actively cooled by at least one oil spill hole in the region of the oil spill, whereby a coking of the shaft seal can be prevented. The third seal separates the oil from the oil drain chamber from the gas from the gas outlet chamber. Optionally, the shaft-side part of the seal is formed by an attachment on the shaft.

Brief description of the invention

The present invention has for its object to provide an improved shaft seal mounted in a bearing housing shaft of a turbomachine in which the risk of coking the piston ring seal can be minimized by improved heat dissipation from the seal section.

In a generic shaft seal mounted in a bearing housing shaft of a turbomachine between a cavity in the bearing housing and a Radrückraum an impeller of the turbomachine with a seated on the shaft essay, comprising an impeller-side seal in shape at least one piston ring between the bearing housing and the attachment and a bearing-side seal in the form of a sealing gap between the bearing housing and the attachment, wherein between the impeller-side seal and the bearing-side seal an oil drain chamber is provided, the oil drain chamber of a third seal in the form of a sealing gap between the bearing housing and the attachment is limited, and that between the third seal and the impeller-side seal, a gas outlet chamber is arranged, and wherein the attachment has a contour which forms the oil drain chamber and the gas outlet chamber together with the bearing housing and at least one groove for receiving the at least According to the invention, the seat of the attachment on the shaft is subdivided into two axially spaced, radially force-transferable support regions to the shaft, which are designed such that they allow a transmission of force in the radial direction union, wherein the one, the impeller side disposed of the two bearing areas, is arranged axially in the region of one of the at least one piston ring of the impeller-side seal. By the two short seats at the respective ends of the essay (shaft seal bushing) instead of a long, continuous seat, the contact surface between the shaft and bearing cap and thus the heat input from the impeller can be reduced by the shaft, advantageously between the two axially spaced, radial kraftübertragunsfähigen support areas the essay on the shaft is formed with a cavity filled with air.

Due to the arrangement of the impeller-side seat directly in the region of the piston ring, centrifugal force-induced deformations can be kept low.

Optionally, an oil drainage channel is embedded in the bearing housing radially outside the oil drainage chamber and at least one oil injection hole is arranged in the bearing housing, with which the oil drainage channel can be charged with oil, wherein the oil drainage channel extends in the axial direction beyond the at least one piston ring of the impeller-side seal.

As a result, a high proportion of the heat in the storage area can be dissipated directly radially outside the piston rings via the lubricating oil.

Advantageously, in this case, the oil drainage channel is inclined in the axial direction to the impeller-side seal towards the axis, so that the oil guided on the bearing side into the oil drainage channel flows in the axial direction towards the impeller side due to gravity. Optionally, the piston rings of the impeller-side seal are exposed directly to a cooling medium (blocking air). This prevents the penetration of hot gases from the rear space of the impeller into the bearing gap.

Optionally, the attachment (shaft seal bushing) can be extended by the function of a torsion damper, this can be achieved by a slight pressure on the bearing side seat, as well as a strong compression on the impeller side seat. Where the pressure on the front seat must be designed according to the damping requirements. Additionally or alternatively, a friction element may be introduced in the seat, such as a Teflon tape, thereby relative movements of the shaft can be utilized in torsional vibrations to further increase the Dämpfungsmass.

Optionally, that region of the bearing housing which is part of the shaft seal formed according to the invention may be formed as an insert. The insert can be easily replaced during operational wear or removed but for cleaning purposes for a short time from the bearing housing. In addition, to choose as the material for this insert a material with the highest possible heat conduction property.

Brief description of the drawings

Fig. 1

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

Fig. 2

einen entlang der Welle geführten Schnitt durch eine turbinenseitige Wellenabdichtung eines Abgasturboladers gemäss dem Stand der Technik,

Fig. 3

einen entlang der Welle geführten Schnitt durch eine turbinenseitige Wellenabdichtung eines Abgasturboladers gemäss dem Stand der Technik mit einem Aufsatz auf der Welle,

Fig. 4

einen entlang der Welle geführten Schnitt durch eine erfindungsgemässe, turbinenseitige Wellenabdichtung eines Abgasturboladers.

Hereinafter, the shaft seal according to the invention will be explained in detail with reference to drawings. It shows

Fig. 1

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

Fig. 2

a guided along the shaft section through a turbine-side shaft seal of a turbocharger according to the prior art,

Fig. 3

a guided along the shaft section through a turbine-side shaft seal of a turbocharger according to the prior art with a cap on the shaft,

Fig. 4

a guided along the shaft section through an inventive, turbine-side shaft seal of an exhaust gas turbocharger.

Way to carry out the invention

Fig. 1 shows an exhaust gas turbocharger according to the prior art with a centrifugal compressor 70 and an axial turbine 10. The housing of the exhaust gas turbocharger shown is shown partially cut away to see the rotor with the compressor 71, the shaft 20 and the turbine wheel 11 can. The air flow from the air inlet 72 to the compressor 71 is indicated by a thick arrow. On the turbine side, the hot exhaust gas is passed through the gas inlet 12 via the turbine wheel 11 to the gas outlet 13. The shaft 20 is rotatably mounted in the bearing housing 30, usually by means of two radial bearings and at least one thrust bearing.

Fig. 2 shows a shaft seal according to the prior art, which separates the cavity 50 in the bearing housing from the Radraum 15 of a turbine wheel 11. In this case, the bearing housing in the region of the shaft seal comprises an insert piece 31 (sealing bushing), which is realized as a separate component. The insert 31 is ring-shaped and comprises a radially outer oil drainage channel 52 for the projecting radially outward from the radial bearing 34 and laterally discharged spray oil. The insert is sprayed directly or indirectly with spray oil and thereby actively cooled. The spray oil is passed through the oil injection hole 61 on the components to be cooled. The supply of spray oil is carried by the oil passage 60 in the bearing housing 30. The oil injection hole 61 is designed and aligned such that the spray oil in the region of the bearing housing 30 meets the inner contour 63 and wets the insert in the oil drain groove 52. By the spray oil and the oil from the storage 34 and oil drain 51, the insert and the piston rings, seals and drain chambers therein are cooled and largely prevented coking. To increase the cooling effect on the piston rings and drain chambers, the insert 31 is preferably made of a material with the highest possible heat-conducting property. The oil drainage channel 52 is bounded in the axial direction by a radially extended sealing plate 32, which in turn is itself cooled by the oil in the outlet channel 51. The insert further comprises recesses for receiving two series-arranged piston rings 41 and 42. The insert further comprises in the radially inner region an oil drain chamber 53, a separate gas outlet chamber 55 for the gas leakage from the two piston rings 41 and 42 and a sealing ridge 33 which separates the oil drain chamber 53 and the gas outlet chamber 55 from each other.

The oil drainage channel 51 between the radial bearing 34 and the sealing plate 32 forms the first main drainage channel of the bearing oil emerging from the radial bearing. The sealing plate 32 forms with a radially opposite first web 21 of the shaft 20 has a first radial sealing gap 43, due to which penetration of the bearing oil from the oil drainage channel 51 is minimized in the oil drain chamber 53. The rotating wave contour of the oil drain chamber 53 is provided with a radially inwardly offset drainage groove, resulting in two drainage edges left and right of this groove within the oil drain chamber 53. The thrown by the Abspritzkanten in the formed by the groove in the insert 31, radially outer region of the oil drain chamber 53 thrown oil flows due to gravity within the oil drain chamber 53 along the contour of the insert 31 down. Thus, the bearing oil from the oil drain chamber 53 can be returned to the oil circuit of the bearing lubrication, the oil drain chamber 53 at the bottom of at least one oil drain passage 54.

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

Fig. 3 indicates the shaft seal Fig. 2 (For the sake of clarity, only the opposite Fig. 2 additional features provided with reference numerals), in which the rotating shaft contour of the turbine in the shaft seal is performed by a sleeve-shaped attachment 81. The attachment 81 is shrunk onto a long seat 82 on the shaft and an edge formed on the shaft serves the attachment 81 as an axial stop 83.

Fig. 4 illustrates the development of the shaft seal according to the invention Fig. 3 , The bearing housing, the attachment and the shaft seat are designed such that the heat emission via the oil cooling maximizes and the heat input is minimized over the support area to the shaft. The article is advantageously made of a good heat conducting material.

According to the invention, the attachment 81 bears on the shaft 20 with two short seats. Between the bearing-side seat 821 and the impeller-side seat 822 extends an air-filled cavity 85, which serves as an insulating layer between the attachment and the shaft. In the axial direction, the attachment abuts against the shaft with an axial stop 83. In the illustrated embodiment, the annular cap 81 has four outboard grooves. The two bearing-side grooves together with corresponding grooves in the insert 31 of the bearing housing the above-described, known from the prior art oil drain chamber 53 and gas outlet chamber 55. The two impeller-side grooves of the essay serve to receive two piston rings 41 and 42, which the impeller-side seal form the shaft seal. The two piston rings abut against the insert 31 of the bearing housing. The insert 31 of the bearing housing has an oil drain groove 52, which allows the supply of lubricating oil in a region radially outside of the attachment. According to the invention, the oil drainage channel extends in the axial direction over at least one of the piston rings 41 and 42, so that the cooling of the impeller-side seal can be ensured by means of lubricating oil. The oil drain groove 52 has an inclination to the axis, so that the introduced into the oil drainage lubricating oil can flow due to gravity to the impeller side of the oil drainage channel along. The bearing housing 30 and the insert 31 are in this case designed such that a drainage possibility for the lubricating oil is provided in the lower region with respect to gravity. In the figure, the oil flow is shown with thin, dark arrows. Advantageously, to cool the shaft seal lubricating oil from the storage area, in the concrete example from the supply to the radial bearing used.

In the illustrated embodiment, the shaft seal has a sealing air supply. It is shown with small white arrows, compressed air from the compressor side (or supplied externally) via a sealing air duct in the bearing housing 30 in the bearing gap impeller side of the impeller-side piston ring seal out. The sealing air serves to directly cool the seal on the one hand, on the other hand, it prevents hot gas can penetrate from the wheel back 15 of the impeller in the sealing gap.

Optionally, the attachment (shaft seal bushing) can be extended by the function of a torsion damper, this can be achieved by a slight pressure on the bearing-side seat 821, as well as a strong compression on the impeller-side seat 822. The pressure on the bearing side seat must be designed according to the damping requirements. Additionally or alternatively, a vibration-damping friction element 86 can be introduced into the seat, such as a Teflon tape, as a result, in torsional vibrations relative movements can be exploited on the shaft to further increase the Dämpfungsmass.

Optionally, the bearing housing may be formed in the region of the shaft seal designed according to the invention without a separate insert piece. 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, the embodiment described in detail with a separate insert piece 31 has the advantage that the insert piece 31 can be made of a material with good thermal conductivity (eg Ck45) for the purpose of cooling the seal portion and thus is independent of the bearing housing material used ( eg GGG-40). Further, an insert is easy to replace in case of operational wear or remove it for cleaning purposes for a short time from the bearing housing.

In the illustrated embodiment, the shaft seal comprises two piston rings 41 and 42. Alternatively, only one piston ring may be provided, or further piston rings may be provided in the region or other locations of the shaft seal.

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

LIST OF REFERENCE NUMBERS

10

turbine

11

turbine

12

gas inlet

13

gas outlet

15

Radraum of the impeller

20

wave

21, 22

sealing land

30

bearing housing

31

Insert of the bearing housing

32

sealing plate

33

sealing land

34

radial bearings

35

Supply line for cooling medium (blocking air)

39

hood cover

41, 42

piston ring

43, 44

radial sealing gap

50

Cavity in the bearing housing

51, 52

Oil drainage channel

53

Oil drain chamber

54

Oil drain passage

55

Gas outlet chamber

56

Gas discharge channel

60

oil passage

61

Oil injection hole

62

Lagerflansch

63

inner contour

70

compressor

71

compressor

72

air inlet

81

With the shaft co-rotating attachment

821, 822

shaft seat

83

axial stop

85

cavity

86

vibration damping element

Claims (10)

1. Shaft seal of a shaft (20), mounted in a bearing housing (30), of a turbomachine, between a cavity (50) in the bearing housing (30) and an impeller backspace (15) of an impeller (11) of the turbomachine, having a crown (81) seated on the shaft, comprising an impeller-side seal in the form of at least one piston ring (41, 42) between the bearing housing (30, 31) and the crown (81), and a bearing-side seal in the form of a sealing gap (43) between the bearing housing (30, 31) and the crown (81), wherein an oil discharge chamber (53) is provided between the impeller-side seal and the bearing-side seal, wherein the oil discharge chamber (53) is bounded by a third seal in the form of a sealing gap (44) between the bearing housing (30, 31) and the crown (81), wherein a gas outlet chamber (55) is arranged between the third seal and the impeller-side seal, and wherein the crown (81) has a contour which, together with the bearing housing, forms the oil discharge chamber (53) and the gas outlet chamber (55), and at least one groove for receiving the at least one piston ring (41, 42), characterized in that the seat of the crown (81) on the shaft is divided into two axially separate, radially force-transmitting contact regions (821, 822), wherein that one (822) of the two contact regions which is arranged on the impeller side is arranged axially in the region of one of the at least one piston rings (41, 42) of the impeller-side seal.
2. Shaft seal according to Claim 1, wherein a cavity (85) bounded by the shaft (20) and the crown (81) is formed axially between the two contact regions (821, 822).
3. Shaft seal according to Claim 1 or 2, wherein an oil discharge channel (52) is introduced into the bearing housing (30, 31) radially outside the oil discharge chamber (53), and at least one oil injection bore (61) is arranged in the bearing housing (30) and serves to charge the oil discharge channel with oil, wherein the oil discharge channel extends in the axial direction past the at least one piston ring (41, 42) of the impeller-side seal.
4. Shaft seal according to Claim 3, wherein the oil discharge channel (52) is inclined with respect to the axis, in the axial direction towards the impeller-side seal, such that gravity causes the oil guided into the oil discharge channel on the bearing side to flow in the axial direction towards the impeller side.
5. Shaft seal according to one of Claims 1 to 5, wherein, in the case of the bearing-side one of the two contact regions (822), a vibration-damping element (86) is arranged between the shaft (20) and the crown (81).
6. Shaft seal according to one of Claims 1 to 5, wherein the bearing housing comprises, in the region of the shaft seal, an insert (31) into which are introduced cutouts which form the oil discharge chamber (53) and the gas outlet chamber (55).
7. Shaft seal according to one of Claims 1 to 6, wherein the crown (81) is made of a material having greater thermal conductivity than the material of the shaft.
8. Shaft seal according to one of Claims 1 to 7, wherein in the bearing housing (30, 31) there is arranged a supply line for introducing a gaseous coolant into the gap region between the bearing housing (30, 31) and the crown (81), wherein the supply line opens on the impeller side of the impeller-side seal into the gap between the bearing housing (30, 31) and the crown (81).
9. Turbomachine, comprising at least one impeller (11) arranged on a shaft (20), and a bearing housing (30) in which the shaft (20) is rotatably mounted, wherein a shaft seal according to one of Claims 1 to 8 is arranged between the bearing housing (30) and the shaft (20).
10. Exhaust-gas turbocharger or power turbine, comprising at least one turbine impeller (11) arranged on a shaft (20), and a bearing housing (30) in which the shaft (20) is rotatably mounted, wherein a shaft seal according to one of Claims 1 to 8 is arranged between the bearing housing (30) and the shaft (20).

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