초록 ▼

During engine braking of a turbocharged internal combustion engine, the exhaust gas pressure increases and this is used to pressurize the seals between the turbocharger shaft and the bearing housing so as to prevent oil leakage into the compressor housing. Immediately after engine braking, stored ex

During engine braking of a turbocharged internal combustion engine, the exhaust gas pressure increases and this is used to pressurize the seals between the turbocharger shaft and the bearing housing so as to prevent oil leakage into the compressor housing. Immediately after engine braking, stored exhaust gas pressure is used to pressurize the seals at the turbine end so as to prevent oil leakage into the turbine housing. In an alternative arrangement the exhaust gas is used to generate a reduced pressure in the bearing housing to increase the pressure gradient across the seals.

대표청구항 ▼

1. An engine braking method for an internal combustion engine having an air intake path and an exhaust gas path, a turbocharger comprising a turbine in the exhaust gas path and a compressor in the intake path, the turbine comprising a turbine wheel rotatably disposed in a turbine housing, the compre

1. An engine braking method for an internal combustion engine having an air intake path and an exhaust gas path, a turbocharger comprising a turbine in the exhaust gas path and a compressor in the intake path, the turbine comprising a turbine wheel rotatably disposed in a turbine housing, the compressor comprising a compressor impeller rotatably disposed in a compressor housing, the turbine wheel and compressor impeller being connected by a turbocharger shaft, a bearing housing disposed between the compressor and turbine for housing a bearing assembly to support the turbocharger shaft in rotation, at least one first seal between a compressor end of the shaft and the bearing housing, the method comprising: operating the engine in an engine braking mode by activating an exhaust gas brake to impede the flow of exhaust gas in the exhaust gas path when the engine throttle is closed, thereby generating an exhaust gas back-pressure in the exhaust gas path; diverting at least a portion of the exhaust gas during engine braking mode from the exhaust gas path in order to increase the pressure gradient across the at least one first seal in the direction from the bearing housing to the compressor housing. 2. An engine braking method according to claim 1, wherein the diverted exhaust gas is directed to a location between the at least one first seal and the compressor housing so as to raise the pressure in that location. 3. An engine braking method according to claim 2, wherein the exhaust gas is diverted through a passage in the turbocharger that emerges to a side of the at least one first seal that is closest to the compressor. 4. An engine braking method according to claim 3, wherein the passage is disposed, at least in part, through the bearing housing. 5. An engine braking method according to claim 1, wherein the diverted exhaust gas passes through a passage in the turbocharger that emerges so as to direct exhaust gas at a back face of the compressor wheel. 6. An engine braking method according to claim 1, wherein the at least one first seal is disposed in a bore in a compressor back plate and the diverted exhaust gas is directed through a passage in the back plate. 7. An engine braking method according to claim 1, wherein the at least one first seal comprises at least one pair of axially spaced first seals and the diverted exhaust gas is directed to a space between the at least one pair of axially spaced first seals so as to raise the pressure between the seals. 8. An engine braking method according to claim 1, further comprising using an exhaust brake valve in the exhaust gas path to apply the exhaust gas brake. 9. An engine braking method according to claim 1, further comprising using a variable geometry turbine to apply the exhaust gas brake, by moving a movable member of the turbine to reduce the size of an inlet passageway of the turbine so as to restrict the exhaust gas flow through the turbine and create the back-pressure. 10. An engine braking method according to claim 1, wherein the exhaust gas is diverted to a bleed path during engine braking mode, at least some of the gas being stored temporarily in a plenum chamber in the bleed path and being permitted to flow out the plenum chamber immediately after operation of the engine in engine braking mode. 11. An engine braking method according to claim 10, further comprising closing the bleed path upstream of the plenum chamber when the engine is not being operated in engine braking mode. 12. An engine braking method according to claim 1, further comprising deactivating the exhaust gas brake at the end of operating the engine in an engine braking mode, and diverting exhaust gas to a location between at least one second seal disposed between a turbine end of the shaft and the bearing housing so as to increase the pressure gradient across that seal in the direction from the bearing housing to the turbine housing. 13. An engine braking method according to claim 1, wherein the pressure gradient is increased by delivering the diverted exhaust gas into a conduit in fluid communication with the bearing housing, the exhaust gas being passed through a jet pump arrangement so as to effect a decrease in pressure in the conduit, in the pressure in the engine crankcase and therefore in the bearing housing of the turbocharger. 14. An engine braking method according to claim 13, wherein the conduit is connected downstream of a crankcase ventilation port of the engine. 15. An engine braking system comprising: an internal combustion engine with an air intake path and an exhaust gas path; a turbocharger comprising a compressor for delivering pressurised air to the air intake path and a turbine for receipt of the exhaust gas from the engine, the turbine comprising a turbine wheel rotatably disposed in a turbine housing, the compressor comprising a compressor impeller rotatably disposed in a compressor housing, the turbine wheel and compressor impeller being connected by a turbocharger shaft, a bearing housing disposed between the compressor and turbine for housing a bearing assembly to support the turbocharger shaft in rotation, at least one first seal between the shaft and a compressor end of the bearing housing; an exhaust gas brake in the exhaust gas path and operable to effect engine braking, an exhaust gas bleed path extending from the exhaust gas path to a location between the at least one first seal and the compressor housing for diverting at least a portion of the exhaust gas from the exhaust gas path during engine braking. 16. An engine braking system according to claim 15, further comprising a valve in the exhaust gas bleed path operable to open or close the exhaust bleed path. 17. An engine braking system according to claim 15, wherein the exhaust gas bleed path is in fluid communication with a passage in the turbocharger that emerges at said location between the at least one first seal and the compressor housing. 18. An engine braking system according to claim 17, wherein the passage is disposed, at least in part, through the bearing housing. 19. An engine braking system according to claim 17, wherein there is provided a compressor back plate between the compressor wheel and an interior of the bearing housing, the at least one first seal being disposed in a bore in the compressor back plate, the passage being defined at least in part in the back plate. 20. An engine braking system according to claim 15, wherein the exhaust gas bleed path is in fluid communication with a passage in the turbocharger that is configured to direct exhaust gas at a back face of the compressor wheel, which back face faces the bearing housing. 21. An engine braking system, according to claim 15, wherein the at least one first seal comprises at least one pair of axially spaced first seals, the exhaust bleed gas path extending to a space between the axially spaced first seals. 22. An engine braking system according to claim 15, wherein the exhaust gas brake is an exhaust brake valve in the exhaust gas path downstream of the turbine wheel. 23. An engine braking system according to claim 15, wherein the exhaust gas brake is a variable geometry turbine having an exhaust gas inlet passageway defined between a movable member and a facing wall, the movable member being movable towards and away from said facing wall so as to vary the size of the inlet passageway. 24. An engine braking system according to claim 15, wherein there is provided a plenum chamber in the exhaust gas bleed path, the chamber being configured for the temporary storage of exhaust gas. 25. An engine braking system according to claim 15, further comprising at least second one seal between a turbine end of the shaft and the bearing housing, the exhaust gas bleed path also extending to a location between the at least one second seal and the turbine housing. 26. An engine braking system according to claim 25, wherein the exhaust bleed path is in fluid communication with a passage in the turbocharger that emerges at said location between the at least one second seal and the turbine housing. 27. A powered vehicle having an engine braking system according to claim 15. 28. A method for reducing oil leakage in a turbocharger comprising a compressor for delivering pressurised air to an air intake path of an internal combustion engine, and a turbine for receipt of the exhaust gas from the engine, the turbine comprising a turbine wheel rotatably disposed in a turbine housing, the compressor comprising a compressor impeller rotatably disposed in a compressor housing, the turbine wheel and compressor impeller being connected by a turbocharger shaft, a bearing housing disposed between the compressor and turbine for housing a bearing assembly to support the turbocharger shaft in rotation, at least one first seal between a compressor end of the shaft and the bearing housing, activating an exhaust gas brake to impede the flow of exhaust gas into the turbine and diverting at least a portion of the impeded exhaust gas flow in order to increase the pressure gradient across the at least one first seal in the direction from the bearing housing to the compressor housing.