Scroll structure of turbine housing
The flow-through characteristics of twin exhaust gas scroll passages of a turbine are made equal to each other. A tongue which partitions the scroll portions into outer peripheral portions and inner peripheral portions includes a front-side tongue and a rear-side tongue that respectively close the two exhaust gas passages at the outer peripheral portion. The inner sides of the front-side tongue and the rear-side tongue, and the minimal outflow width portions of the front-side passage and the rear-side passage, respectively, are formed substantially parallel to each other at a downstream end of the outer peripheral portion.
1. A scroll structure of a turbine housing of a twin scroll turbocharger comprising:
a scroll portion that introduces an exhaust gas to a turbine rotor,
wherein the scroll portion includes two exhaust gas passages including a front-side scroll passage and a rear-side scroll passage, which are partitioned by a partition wall parallel to a flow direction of the exhaust gas in the scroll passages,
the partition wall is inclined with respect to a plane perpendicular to a turbine shaft,
a tongue, which partitions the scroll portion into an outer peripheral portion and an inner peripheral portion in a direction perpendicular to the flow direction of the exhaust gas,
the tongue including a front-side tongue and a rear-side tongue associated with said front-side and rear-side scroll passages, respectively, at the outer peripheral portion,
wherein the inner side of the front-side tongue is formed substantially parallel to a minimal outflow width portion of the front-side scroll passage and the inner side of the rear-side tongue is formed substantially parallel to a minimal outflow width portion of the rear-side scroll passage at a downstream end of the outer peripheral portion of the scroll portion, and
wherein a part of an outer side of the front-side tongue is cut away to form a cut portion of the front-side tongue, and wherein a build-up portion is formed on the inner side of the front-side tongue at a position corresponding to the cut portion on the outer side thereof said build-up portion increasing the thickness of the front-side tongue by at least the thickness of the part of the outer side which is cut away.
2. The scroll structure of the turbine housing according to claim 1 ,
wherein an angle formed between the inner sides of the front-side tongue and the rear-side tongue and the minimal outflow width portions of the front-side passage and the rear-side passage, respectively, as viewed in cross-section from the downstream end of the outer peripheral portion is in the range of −10° to +10°.
3. The scroll structure of the turbine housing according to claim 2 ,
wherein the front-side passage and the rear-side passage are formed to be substantially symmetrical with respect to the partition wall as viewed in cross-section from the downstream end of the outer peripheral portion.
4. The scroll structure of the turbine housing according to claim 3 ,
wherein a portion of the rear-side tongue closest to a rear wall surface of said rear-side passage extends downstream further than a portion of the rear-side tongue closest to a partition wall surface of said rear-side passage.
5. The scroll structure of the turbine housing according to claim 2 ,
wherein a portion of the rear-side tongue closest to a rear wall surface of said rear-side passage extends downstream further than a portion of the rear-side tongue closest to a partition wall surface of said rear-side passage.
6. The scroll structure of the turbine housing according to claim 1 ,
wherein the front-side passage and the rear-side passage are formed to be substantially symmetrical with respect to the partition wall.
7. The scroll structure of the turbine housing according to claim 6 ,
wherein a portion of the rear-side tongue closest to a rear wall surface of said rear-side passage extends downstream further than a portion of the rear-side tongue closest to a partition wall surface of said rear-side passage.
8. The scroll structure of the turbine housing according to claim 1 ,
wherein a portion of the rear-side tongue closest to a rear wall surface of said rear-side passage extends downstream in the direction of gas flow further than a portion of said rear-side tongue closest to a partition wall surface of said rear-side passage.
9. The scroll structure of the turbine housing according to claim 1 ,
wherein a portion of the front-side tongue closest to a front wall surface of said front-side passage extends downstream in the direction of gas flow further than a portion of the front-side tongue closest to the partition wall surface of said front-side passage.