Hot gas valve

Abstract

A hot gas valve has a housing, in which a gas duct is formed with an inlet and an outlet, and a valve device for controlling the fluid flow through the gas duct. The housing has at least one cooling duct for liquid cooling of the housing, wherein the gas duct is shielded with respect to the housing by means of a thermal shield, which consists of a material which has a greater thermal stability than the material of which the housing consists. The valve device has a closure body situated in the gas duct, which closure body is held on a valve shaft mounted in the housing by means of at least one bearing. The bearing may consists of a material having good thermal conductivity. The valve shaft is sealed by an elastomer shaft sealing ring on the side of the bearing facing away from the gas duct.

Claims

1. A hot gas valve, comprising: a housing, in which a gas duct comprising an inlet and an outlet is formed, and a valve device for controlling flow of a fluid through the gas duct; wherein the housing has at least one cooling duct for liquid cooling of the housing; wherein the gas duct is shielded with respect to the housing by means of a thermal shield; wherein the valve device has a closure body situated in the gas duct, which closure body is held on a valve shaft that is mounted in the housing by means of at least one bearing; and wherein a thermally insulating sleeve is attached to the valve shaft and is sealed by an elastomer shaft sealing ring on a side of the bearing facing away from the gas duct, wherein the valve shaft is thermally insulated from the elastomer shaft sealing ring by means of the thermally insulating sleeve where the thermally insulating sleeve is disposed between the valve shaft and the elastomer shaft sealing ring.

2. The hot gas valve according to claim 1, wherein the material of which the bearing consists has a lower coefficient of thermal expansion than the material of which the valve shaft consists.

3. The hot gas valve according to claim 1, wherein the valve shaft and/or the closure body consists of a material having a thermal conductivity less than 120 W/(m.Math.K).

4. The hot gas valve according to claim 3, wherein the valve shaft and/or the closure body consists of steel.

5. The hot gas valve according to claim 4, wherein the valve shaft and/or the closure body consists of steel containing nickel and/or chromium.

6. The hot gas valve according to claim 1, wherein the bearing is received in the housing by means of a press fit.

7. The hot gas valve according to claim 1, wherein the valve shaft is thermally insulated from the shaft sealing ring by means of the thermally insulating sleeve comprising polyimide.

8. The hot gas valve according to claim 1, wherein the at least one cooling duct extends in the housing in the region of the bearing.

9. The hot gas valve according to claim 8, wherein the at least one cooling duct at least partially surrounds the bearing.

10. The hot gas valve according to claim 8, wherein the valve shaft is mounted in the housing on both sides of the gas duct respectively by means of a bearing, and the at least one cooling duct in the region of both bearings are connected with one another by an overflow pipe.

11. The hot gas valve according to claim 10, wherein an inlet line for the at least one cooling duct is arranged on a side of the housing at which a drive for the valve is received.

12. The hot gas valve according to claim 1, wherein at least one air gap is provided between the thermal shield and the housing.

13. The hot gas valve according to claim 1, wherein the thermal shield is formed by a wall surrounding the gas duct, which wall extends through a passage in the housing.

14. The hot gas valve according to claim 13, wherein the wall surrounding the gas duct is received in a central contact region of the passage, wherein the wall next to the contact region is surrounded by an annular gap on both sides.

15. The hot gas valve according to claim 1, wherein the valve shaft is surrounded by a sleeve in a section situated between the closure body and the bearing.

16. The hot gas valve according to claim 15, wherein in a section of the sleeve an air gap is arranged between the valve shaft and the sleeve.

17. The hot gas valve according to claim 1, wherein an air gap is provided between closure body and valve shaft at least in one region.

18. The hot gas valve according to claim 1, wherein at the inlet and at the outlet of the gas duct respectively a flange connection is provided with a seal of a thermally insulating material.

19. The hot gas valve according to claim 18, wherein the thermally insulating material of the seal comprises mica or phyllosilicate.

20. The hot gas valve according to claim 1, wherein thermal shield consists of a material which has a greater thermal resilience than the material of which the housing consists.

21. The hot gas valve according to claim 1, wherein the thermal shield consists of steel and the housing consists of aluminum.

22. The hot gas valve according to claim 1, wherein the at least one bearing consists of graphite, ceramic or copper.

23. The hot gas valve according to claim 1, wherein the material of which the at least one bearing consists has a thermal conductivity of more than 120 W/(m.Math.K).

24. A hot gas valve, comprising: a housing, in which a gas duct comprising an inlet and an outlet is formed, and a valve device for controlling flow of a fluid through the gas duct; wherein the housing has at least one cooling duct for liquid cooling of the housing; wherein the gas duct is shielded with respect to the housing by means of a thermal shield; wherein the valve device has a closure body situated in the gas duct, which closure body is held on a valve shaft that is mounted in the housing by means of at least one bearing; and wherein a thermally insulating sleeve is attached to the valve shaft and is sealed by an elastomer shaft sealing ring on a side of the bearing facing away from the gas duct, wherein the valve shaft is thermally insulated from the elastomer shaft sealing ring by means of the thermally insulating sleeve where the thermally insulating sleeve is disposed between the valve shaft and the elastomer shaft sealing ring; and wherein the at least one bearing consists of graphite, copper or ceramic and has a thermal conductivity of more than 120 W/(m.Math.K).

25. The hot gas valve according to claim 24, wherein the thermally insulating sleeve comprises polyimide.

26. A hot gas valve, comprising: a housing, in which a gas duct comprising an inlet and an outlet is formed, and a valve device for controlling flow of a fluid through the gas duct; wherein the housing has at least one cooling duct for liquid cooling of the housing; wherein the gas duct is shielded with respect to the housing by means of a thermal shield; wherein the valve device has a closure body situated in the gas duct, which closure body is held on a valve shaft that is mounted in the housing by means of at least one bearing; and wherein the valve shaft is sealed by an elastomer shaft sealing ring on a side of the bearing facing away from the gas duct, wherein the valve shaft is thermally insulated from the elastomer shaft sealing ring by means of a thermally insulating sleeve comprising polyimide; and wherein the at least one bearing consists of graphite, ceramic or copper and has a thermal conductivity of more than 120 W/(m.Math.K).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings illustrate an embodiment of the invention.

(2) FIG. 1 is a perspective overall view of an embodiment of a hot gas valve in the form of an EEGR flap valve;

(3) FIG. 2 is a longitudinal section through the hot gas valve according to FIG. 1;

(4) FIG. 3 is a section through the housing along the line III-III according to FIG. 2;

(5) FIG. 4 is a section through the housing transversely to the exhaust gas direction; and

(6) FIG. 5 is an enlarged detail V of the section according to FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) In FIG. 1 is an embodiment of a hot gas valve illustrated in perspective and is designated as a whole by the number 10. The hot gas valve 10 is an exhaust gas valve, namely an EGR valve, which is constructed as an EEGR valve (electrically operated exhaust gas return valve).

(8) The hot gas valve 10 has a housing 12, at the upper end of which an electromotive or electromagnetic drive 14 is received. In the lower region of the housing 12 a gas duct 20 is formed, which is able to be connected to an exhaust gas pipe by means of a flange 26 on the inlet side and is able to be connected on the opposite side, likewise by means of a flange, to the exhaust gas return. The flow direction of the exhaust gas is indicated by the arrows 16, 18. A valve device, designated as a whole by number 22, which is constructed as a flap valve and has a closure body 24 in the form of a flap, is situated in the gas duct 20. The closure body 24 is held on a valve shaft 42, which is pivotable by means of the drive 14, in order to control the passage of gas through the gas duct 20.

(9) In the region between the gas duct 20 and the drive 14, a cooling duct is situated, with an inlet connecting piece 28 into which coolant is able to be fed in the direction of the arrow 29. On the other side of the gas duct 20, i.e. on the side of the gas duct 20 facing away from the drive 14, a cooling duct is likewise situated for cooling the housing 12, at which an outlet connecting piece 30 is provided for the coolant return flow according to arrow 31. The cooling in the upper region and in the lower region are connected with one another via an overflow pipe 32, so that the cooling of the housing 12 can take place on both sides of the gas duct 20 by means of a single cooling water connection at the inlet connecting piece 28 and at the outlet connecting piece 30. In this case, the inlet connecting piece 28 is preferably situated in the region between gas duct 20 and drive 14, in order to enable a particularly intensive cooling in this region, so that the drive 14 can be advantageously accommodated in a plastic housing.

(10) The housing 12 preferably consists of a light metal alloy, in particular an aluminum alloy, and can be produced for instance by pressure die casting. Through a special construction, it is ensured that despite the high thermal load by the exhaust gas flow, a housing 12, consisting for instance of an aluminum alloy, is also sufficiently thermally stable and that in addition the drive is only exposed to a minor thermal load. Therefore, the actuator or servomotor received for example in the drive 14 is not excessively loaded thermally, and furthermore the housing of the drive 14 can advantageously consist of plastic.

(11) The various measures which lead to the thermal relief of the housing 12 and to the thermal decoupling of the drive 14 are described in further detail below.

(12) According to FIG. 2, the valve shaft 42 is mounted within the housing 12 on both sides of the gas duct 20 respectively by means of a bearing 44 or respectively 48. A cooling duct 40 is provided in the housing 12, consisting of an aluminum alloy, in the immediate vicinity of the respective bearing 44, 48, through which cooling duct the respective bearing 44, 48 is respectively partially surrounded. The bearings 44, 48 preferably consist of graphite and therefore contribute to an effective heat dissipation from the valve shaft 42 directly to the cooling ducts 40.

(13) As can be seen in further detail from FIG. 3, the cooling duct 40 surrounds the associated bearing 44 in a U-shaped manner, wherein on one side the outlet connecting piece 30 for the cooling water is connected and on the other side the overflow pipe 32 for connection with the cooling ducts 40 on the other housing side, facing the drive 14, is connected. The cooling ducts 40 can be produced during the production of the housing 12 by pressure die casting with the use of cores. The remaining opening in the cooling duct 40 is preferably closed respectively by a plug 35 according to FIG. 3 or respectively 34 in the other cooling duct according to FIG. 1.

(14) As can be further seen from FIG. 2, the gas duct 20 extends transversely through an opening of the housing 12 and is surrounded by a cylindrical wall 52 of steel. The wall 52 extends through a passage in the housing 12 and forms a shield which prevents the hot exhaust gas situated in the gas duct 20 from coming directly in contact with the housing 12. The wall 52 extends continuously from the inlet 63 up to the outlet 64. The cylindrical wall 52 has a central annular contact region 55, in which it is secured at the housing opening. An annular gap 53 or respectively 54 extends on both sides of the contact region 55, whereby a good thermal insulation is produced with respect to the housing 12. The wall 52, consisting of steel, acts as a thermal shield with respect to the housing 12.

(15) It can be further seen from FIG. 2 how the flap closure body 24 is fastened on the valve shaft 42. The closure body 24 is fastened on the valve shaft 42 in a central region and in two marginal regions. Gaps 62 extend therebetween, as can be clearly seen from the enlarged illustration according to FIG. 5, which surround the valve shaft 42 as annular gap. This results in a reduced contact surface between valve shaft 42 and the closure body 24, by which the heat transmission from the flap, exposed to the hot exhaust gases which flow through the gas duct 20 in the direction of the arrows 16, 18, to the valve shaft 42 is reduced. In this way, in particular the heat transmission to the drive 14 is reduced, which is connected with the valve shaft 42 via a coupling 38.

(16) In the region of the respective lead-through of the valve shaft 42 through the wall 52 of the gas duct 20, the valve shaft 42 is surrounded respectively by a sleeve 56 or respectively 58, which sits on the valve shaft 42. Between the sleeve 58 and the wall 52 or respectively the housing 12 a narrow gap is situated, which enables the rotary movement of the valve shaft 42, as can be seen more precisely from the enlarged illustration according to FIG. 5. The sleeve 58 consists of steel. It has at its end facing the bearing 48 a collar or flange-shaped extension extending in circumferential direction of the sleeve 58, which collar or flange-shaped extension acts as a labyrinth seal and deflects a gas flow, entering in axial direction through the gap between sleeve 58 and wall 52, in radial direction away from the bearing 48 and towards the housing 12, so that a direct contact of the bearing 48 with hot exhaust gas is prevented. At its end facing the closure body 24, the sleeve 58 lies tightly against the closure body 24, in order to prevent a direct contact of the valve shaft 42 with hot exhaust gas. The sleeve 56 is constructed and arranged in an identical manner to the sleeve 58. An annular gap 57 or respectively 59 is situated between the sleeve 56, 58 and the valve shaft 42. Through these gaps 57, 59 the heat transmission from the hot gas to the valve shaft 42 is further reduced.

(17) On the side of the bearings 44, 48, consisting of graphite, facing away from the gas duct 20, sealing ring 46 or respectively 50 is arranged. On the valve shaft 42 respectively a sleeve 47 or respectively 51 is arranged, which thermally insulates the valve shaft 42 to the respective shaft sealing ring 46, 50. The sleeves 47 or respectively 51 preferably consist of a thermally insulating material, such as polyimide for instance, and therefore contribute to the thermal separation of valve sealing ring 46, 50 and valve shaft 42. The sleeves 47, 51 constructed with a flange-shaped extension or collar serve as labyrinth seals with respect to exhaust gas from the gas duct 20 and prevent exhaust gas, which has arrived through the gap between valve shaft 42 and bearing 44, 48, from coming in contact on a direct path with the respective shaft sealing ring 46, 50. If a bearing 44, 48 were ever to come loose in its press fit to the housing 12, the sleeve 47 or 51 prevents the respective bearing 44 or 48 from an axial displacement.

(18) The temperatures which occur in the region of the sealing rings 46, 50 were able to be reduced to approximately 180 C. and are thereby so small that sealing rings of EPDM are not damaged. With the hot gas valve 10, therefore, an extremely small external leakage can be achieved.

(19) The leakage which occurs at the bearing gap between bearing 44, 48 and valve shaft 42 in the direction of the respective valve sealing ring 46, 50, is reduced during operation by increasing temperatures in the region of the bearings 44, 48, because the coefficient of thermal expansion of the bearing 44, 48 of graphite with approximately 5.Math.106 1/K is substantially less than the coefficient of thermal expansion of the valve shaft 42 of steel, which lies in the range of approximately 17.Math.106 1/K to 18106 1/K (at 650 C.). Thereby, the valve shaft 42 expands with increasing temperatures during operation more intensively than the bearing 44, 48. The higher the temperature is, the smaller is the bearing gap.

(20) The two housing surfaces at the inlet 63 and at the outlet 64 of the gas duct 20 are constructed in a flange shape and are provided respectively with a flange seal 60 or respectively 61, configured in an annular shape, of a thermally insulating material, such as for instance mica or phyllosilicate. Therefore, the heat transmission from the exhaust gas pipe, screwed on the flange 26 on the inlet side, to the housing 12 is reduced.

(21) As a whole, through the described measures the heat transmission to the housing is reduced so intensively that it can consist, thermally totally unproblematically, of an aluminum alloy. At the same time, the heat transmission from the housing and from the valve shaft 42 to the drive 14, being flange-connected on the housing 12 and being fastened according to FIG. 2 by way of screws 36, is reduced such that the drive 14 can be received in a plastic housing and such that the sensitive components of an electromotive or electromagnetic drive along with electronic components are in no way thermally impaired.

LIST OF REFERENCE NUMBERS

(22) 10 hot gas valve 12 housing 14 drive 16 flow direction 18 flow direction 20 gas duct 22 valve device 24 closure body 26 flange 28 inlet connecting piece 29 coolant fluid direction 30 outlet connecting piece 31 coolant fluid direction 32 overflow pipe 34 plug 35 plug 36 screws 38 coupling 40 cooling duct 42 valve shaft 44 bearing 46 shaft sealing ring 47 sleeve 48 bearing 50 shaft sealing ring 51 sleeve 52 wall 53 annular gap 54 annular gap 55 contact region 56 sleeve 57 annular gap 58 sleeve 59 annular gap 60 flange seal 61 flange seal 62 air gap 63 inlet 64 outlet