Scroll portion structure for radial turbine or diagonal flow turbine
In a scroll structure for a radial turbine configured such that a turbine rotor 02 is rotationally driven by causing exhaust gas to flow from a spiral scroll portion 4 formed in a turbine housing 1 toward a rotor blade 3 of the scroll portion 4 in a radial direction, and act on the rotor blade 3 , then flow out in an axial direction, a heat radiation space portion is formed in a shroud portion 11 between the turbine housing 1 and a turbine chamber provided with the rotor blade 3.
1. A scroll structure for a radial turbine or a diagonal flow turbine configured such that a turbine rotor is rotationally driven by causing exhaust gas to flow from a spiral scroll portion formed in a turbine housing toward a rotor blade of the scroll portion in a radial direction, act on the rotor blade, and then flow out in an axial direction, comprising
a shroud portion formed between
the scroll portion and a turbine chamber wall covering the rotor blade in a radial cross section of the radial turbine, and a concave space formed as a heat radiation portion over the entire circumference of the shroud, wherein
a radial cross-sectional shape of the scroll portion in which the exhaust gas flows in a direction orthogonal to a line joining a tongue portion separating a flow path, which leads to the scroll portion, from a rotor blade side flow path, which leads to the rotor blade, to an axis of the scroll portion is defined by:
an outer peripheral wall;
a front wall which has one end portion connecting with one end portion of the outer peripheral wall;
a rear wall which has one end portion connecting with another end portion of the outer peripheral wall;
an inner peripheral wall which has one end portion connecting with another end portion of the rear wall, the inner peripheral wall extending inwardly and obliquely from the other end portion of the rear wall toward the front wall in the radial direction; and
the tongue portion which extends from another end portion of the inner peripheral wall to the front wall, and
a dimension B in the axial direction between the front wall and the rear wall is smaller than a dimension A in the radial direction between the outer peripheral wall and the tongue portion.
2. The scroll structure for a radial turbine or a diagonal turbine according to claim 1 ,
wherein the radial cross-sectional shape of the scroll portion is configured such that a scroll width ratio A/B between the dimension A in the radial direction and the dimension B in an axial direction of the turbine axis satisfies 1<A/B≦2.
3. The scroll structure for a radial turbine or a diagonal flow turbine according to claim 1 , wherein an inclined portion in an exhaust gas flow direction of the tongue portion is formed into a shape along a logarithmic spiral.