Abstract:
There is provided a variable capacity turbine that is capable of suppressing separation from an outer peripheral face of an involute dividing wall at an inlet portion of an outer scroll, enhancing performance, and increasing a flow rate. The variable capacity turbine includes: a turbine housing having an involuted scroll formed therein; a turbine wheel rotatably provided on an inner periphery side of the scroll; the involute dividing wall mounted on the turbine housing to divide the scroll into an inner scroll and the outer scroll; and a flow regulating valve for opening and closing an introducing port formed at an inlet end of the outer scroll. The inlet portion of the outer scroll is formed to have a continuous and gentle throttle flow path from an upstream side to a downstream side.

Description:
TECHNICAL FIELD 
     The present invention relates to a variable capacity turbine having a function of changing a flow characteristic. 
     BACKGROUND ART 
     There are known techniques as disclosed in Patent Literatures 1 and 2, for example, as a variable capacity turbine suitable for use as a turbine of a turbocharger which mainly includes the turbine and a compressor and in which exhaust gas (fluid) from an engine (internal combustion engine) rotates the turbine to thereby rotate the compressor to send atmosphere as high-pressure air into the engine. 
     CITATION LIST 
     Patent Literature 
     
         
         {PTL 1} Japanese Unexamined Patent Application, Publication No. Hei10-8977 
         {PTL 2} Japanese Unexamined Patent Application, Publication No. 2000-110572 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the variable capacity turbines disclosed in Patent Literatures 1 and 2, a flow path sectional area at an inlet portion of an outer scroll increases on a way from an upstream side to a downstream side, which reduces a flow velocity of the exhaust gas, causes separation from an outer peripheral face of an involute dividing wall for separating the outer scroll and the inner scroll from each other, and reduces performance and a flow rate. 
     The present invention has been made with the above circumstances in view and it is an object of the present invention to provide a variable capacity turbine in which separation from an outer peripheral face of an involute dividing wall at an inlet portion of an outer scroll can be suppressed, performance can be enhanced, and a flow rate can be increased. 
     Solution to Problem 
     To achieve the above object, the present invention employs the following means. 
     A variable capacity turbine according to a first aspect of the present invention includes: a turbine housing having an involuted scroll formed therein; a turbine wheel rotatably provided on an inner periphery side of the scroll; an involute dividing wall mounted on the turbine housing to divide the scroll into an inner scroll and an outer scroll; and a flow regulating valve for opening and closing an introducing port formed at an inlet end of the outer scroll. An inlet portion of the outer scroll is formed to have a continuous and gentle throttle flow path from an upstream side to a downstream side. 
     According to the variable capacity turbine of the first aspect of the present invention, the flow path at the inlet portion of the outer scroll is the continuous throttle flow path from the upstream side to the downstream side. In other words, the inner peripheral face of the outer scroll at the inlet portion of the outer scroll and/or the outer peripheral face of the involute dividing wall are/is formed so that a flow path sectional area gradually reduces, which facilitates acceleration of the exhaust gas at the inlet portion of the outer scroll, suppresses separation from the outer peripheral face of the upstream tip end portion of the involute dividing wall, enhances performance, and increases a flow rate thereof. 
     In the variable capacity turbine according to the first aspect of the present invention, preferably, an inner peripheral surface of the flow control valve is a flat face and the flow control valve is formed so that the flat face and a central axis of an inlet flange forming an inlet portion of the turbine housing become substantially parallel with each other when the valve is fully open. 
     According to this variable capacity turbine, the flow control valve is formed so that an angle formed by the flat face positioned on the inner periphery side of the flow control valve and the central axis of the inlet flange is substantially parallel with each other, which reduces a turning angle of a fluid passing through the introducing port to thereby further suppress separation from the outer peripheral face of the upstream tip end portion of the involute dividing wall, further enhance performance, and further increase the flow rate. 
     In the variable capacity turbine according to the first aspect of the present invention, preferably, the flow regulating valve is formed to move parallel between positions at times when the flow rate is high and low so that the turning angle of the fluid passing through the introducing port is maintained constant at any of times when the flow rate is low, the flow rate is high, the flow rate shifts from a low rate to a high rate, and the flow rate shifts from the high rate to the low rate. 
     According to this variable capacity turbine, the turning angle of the fluid passing through the introducing port is maintained constant at any of times when the flow rate is low, the flow rate is high, the flow rate shifts from the low rate to the high rate, and the flow rate shifts from the high rate to the low rate, which further suppresses separation from the outer peripheral face of the upstream tip end portion of the involute dividing wall, further enhances performance, and further increases the flow rate. 
     A variable capacity turbine according to a second aspect of the present invention includes: a turbine housing having an involuted scroll formed therein; a turbine wheel rotatably provided on an inner periphery side of the scroll; an involute dividing wall mounted on the turbine housing to divide the scroll into an inner scroll and an outer scroll; and a flow regulating valve for opening and closing an introducing port formed at an inlet end of the outer scroll. An inner peripheral surface of the flow control valve is a flat face and the flow control valve is formed so that the flat face and a central axis of an inlet flange forming an inlet portion of the turbine housing become substantially parallel with each other when the valve is fully open. 
     According to the variable capacity turbine of the second aspect of the present invention, the flow control valve is formed so that an angle formed by the flat face positioned on the inner periphery side of the flow control valve and the central axis of the inlet flange is substantially parallel when the valve is fully open, which reduces a turning angle of a fluid passing through the introducing port to thereby further suppress separation from the outer peripheral face of the upstream tip end portion of the involute dividing wall, further enhance performance, and further increase the flow rate. 
     A variable capacity turbine according to a third aspect of the present invention includes: a turbine housing having an involuted scroll formed therein; a turbine wheel rotatably provided on an inner periphery side of the scroll; an involute dividing wall mounted on the turbine housing to divide the scroll into an inner scroll and an outer scroll; and a flow regulating valve for opening and closing an introducing port formed at an inlet end of the outer scroll. The flow regulating valve is formed to move parallel between positions at times when the flow rate is high and low so that a turning angle of a fluid passing through the introducing port is maintained constant at any of times when the flow rate is low, the flow rate is high, the flow rate shifts from a low rate to a high rate, and the flow rate shifts from the high rate to the low rate. 
     According to the variable capacity turbine of the third aspect of the present invention, the turning angle of the fluid passing through the introducing port is maintained constant at any of times when the flow rate is low, the flow rate is high, the flow rate shifts from the low rate to the high rate, and the flow rate shifts from the high rate to the low rate, which further suppresses separation from the outer peripheral face of the upstream tip end portion of the involute dividing wall, further enhances performance, and further increases the flow rate. 
     A turbocharger according to a fourth aspect of the present invention includes a variable capacity turbine with a reduced loss due to separation and satisfactory performance. 
     According to the turbocharger of the fourth aspect of the present invention, it is possible to enhance performance of the whole apparatus. 
     Advantageous Effects of Invention 
     With the variable capacity turbine according to the present invention, separation from the outer peripheral face of the involute dividing wall at the inlet portion of the outer scroll can be suppressed, performance can be enhanced, and the flow rate can be increased. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view perpendicular to an axis of a variable capacity turbine when a flow rate is low, according to a first embodiment of the present invention. 
         FIG. 2  is a sectional view perpendicular to the axis of the variable capacity turbine when the flow rate is high, according to the first embodiment of the present invention. 
         FIG. 3  is a diagram for explaining a characteristic portion of the variable capacity turbine according to the first embodiment of the present invention. 
         FIG. 4  is a sectional view perpendicular to an axis of a variable capacity turbine when a flow rate is high, according to a second embodiment of the present invention. 
         FIG. 5  is a sectional view perpendicular to an axis of a variable capacity turbine according to a third embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A first embodiment of a variable capacity turbine according to the present invention will be described below with reference to  FIGS. 1 to 3 . 
       FIG. 1  is a sectional view perpendicular to an axis of the variable capacity turbine when a flow rate is low according to the present embodiment,  FIG. 2  is a sectional view perpendicular to the axis of the variable capacity turbine when a flow rate is high according to the present embodiment, and  FIG. 3  is a diagram for explaining a characteristic portion of the variable capacity turbine according to the present embodiment. 
     As shown in  FIGS. 1 and 2 , the variable capacity turbine  1  according to the present embodiment is mainly formed of a turbine housing  3  in which an involuted scroll  2  is formed, and a turbine wheel  4  rotatably provided on an inner periphery side of the scroll  2 . 
     The scroll  2  includes an inner scroll  5  formed inside in a radial direction (on the inner periphery side) and an outer scroll  6  formed outside in the radial direction (on an outer periphery side), i.e., formed to surround a radial outside of the inner scroll  5 . The inner scroll  5  and the outer scroll  6  are divided (separated) by an involute dividing wall  7  and the involute dividing wall  7  is formed (mounted) in the turbine housing  3  so that the outer scroll  6  has a larger capacity than the inner scroll  5 . The involute dividing wall  7  is formed of a tongue-shaped first dividing wall  8  and a plate-shaped second dividing wall  9 . In the second dividing wall  9 , there is formed a plurality of communication holes  10  which introduces from the outer scroll  6  to the inner scroll  5  exhaust gas (fluid) introduced into the outer scroll  6  when the flow rate is high. 
     The turbine housing  3  is adjacent to a compressor housing (not shown) and mounted on a bearing housing (not shown) which is mounted on the compressor housing, and has an exhaust gas introducing port  11  and an exhaust gas discharge port (not shown). On an upstream side (on the exhaust gas introducing port  11  side) of the first dividing wall  8 , the turbine housing  3  is provided with a flow control valve  12 . The flow control valve  12  is mainly formed of a plate-shaped member formed so that a flat face formed on an inner periphery side of a downstream tip end portion comes in contact with (overlaps) a flat face (flat slope) formed on an outer periphery side of an upstream tip end portion of the first dividing wall  8 . The flow control valve  12  is turned by turning means (not shown) about a turning shaft  13  positioned on the exhaust gas introducing port  11  side and provided (mounted) onto the turbine housing  3  to switch between a position for closing (fully closing) an introducing port  14  (see  FIG. 2 ) of the outer scroll  6  shown in  FIG. 1  and a position for opening (fully opening) the introducing port  14  of the outer scroll  6  shown in  FIG. 2 . In  FIGS. 1 and 2 , a reference numeral  15  designates a cover closing an opening portion of the turbine housing  3 , a reference numeral  16  designates a bolt for fixing the cover  15  to the turbine housing  3 , and a reference numeral  17  designates a built-up portion covering a tip end portion of the bolt  16 . 
     The outer scroll  6  of the variable capacity turbine  1  according to the present embodiment is formed so as to have a continuous throttle flow path from an upstream side to a downstream side at the inlet portion, i.e., so that a flow path sectional area at the inlet portion follows a track shown in a solid line in  FIG. 3 , for example. In other words, the outer scroll  6  of the variable capacity turbine  1  according to the present embodiment is formed so that a sectional area (see ( 1 ) in  FIG. 3 ) of a flow path surrounded with the tip end on the downstream inner periphery side of the flow control valve  12 , an outer peripheral face of the first dividing wall  8 , and an inner peripheral face of the turbine housing  3  is larger than a sectional area (see ( 2 ) in  FIG. 3 ) of a flow path surrounded with an inner peripheral face of the built-up portion  17 , the outer peripheral face of the first dividing wall  8 , and the inner peripheral face of the turbine housing  3 , that the sectional area (see ( 2 ) in  FIG. 3 ) of the flow path surrounded with the inner peripheral face of the built-up portion  17 , the outer peripheral face of the first dividing wall  8 , and the inner peripheral face of the turbine housing  3  is larger than a sectional area (see ( 3 ) to ( 6 ) in  FIG. 3 ) of a flow path surrounded with the outer peripheral face of the first dividing wall  8  and the inner peripheral face of the turbine housing  3 , and that the sectional area of the flow path surrounded with the outer peripheral face of the first dividing wall  8  and the inner peripheral face of the turbine housing  3  gradually (gently) reduces from the upstream side to the downstream side (see ( 3 ) to ( 6 ) in  FIG. 3 ). 
     ( 1 ) to ( 6 ) in  FIG. 3  respectively correspond to six broken lines (broken lines drawn in directions orthogonal to a central axis of the outer scroll  6 ) shown in  FIG. 2 , ( 1 ) in  FIG. 3  corresponds to the broken line positioned most upstream in  FIG. 2 , and ( 6 ) in  FIG. 3  corresponds to the broken line positioned most downstream in  FIG. 2 . 
     A 0  in  FIG. 3  indicates a sectional area of a flow path along the broken line positioned most upstream in  FIG. 2  and A in  FIG. 3  indicates a sectional area of a flow path along each of the broken lines in  FIG. 2 . 
     In the variable capacity turbine  1  according to the present embodiment, a flow path at the inlet portion of the outer scroll  6  is formed as the continuous throttle flow path from the upstream side to the downstream side. In other words, the inner peripheral face of the outer scroll  6  at the inlet portion of the outer scroll  6  and/or the outer peripheral face of the first dividing wall  8  are/is formed so that the flow path sectional area gradually reduces, which facilitates acceleration of the exhaust gas at the inlet portion of the outer scroll  6 , suppresses separation from the outer peripheral face of the upstream tip end portion of the first dividing wall  8 , enhances performance, and increases the flow rate. 
     A variable capacity turbine according to a second embodiment of the present invention will be described with reference to  FIG. 4 .  FIG. 4  is a sectional view perpendicular to an axis of the variable capacity turbine when a flow rate is high, according to the present embodiment. 
     The variable capacity turbine  21  according to the present embodiment is different from the turbine of the first embodiment in that the turbine  21  has a turbine housing  22  instead of the turbine housing  3 . Because the other components are similar to those of the first embodiment described above, description thereof will not be repeated. 
     As shown in  FIG. 4 , the turbine housing  22  according to the present embodiment is formed so that an angle α formed by a line  40  connecting the upstream tip end and a downstream tip end of the first dividing wall  8  and a central axis  23  of an inlet flange  22   a  forming an inlet portion of the turbine housing  22  is in a range of 35° to 50° when the flow rate is high (i.e., when the flow control valve  12  is in the position for opening (fully opening) the introducing port  14  of the outer scroll  6 ). In other words, the turbine housing  22  according to the present embodiment is formed so that a flat face  12   a  positioned on an inner periphery side of the flow control valve  12  and the central axis  23  of the inlet flange  22   a  becomes substantially parallel with each other when the flow control valve  12  is fully open. 
     Inside the inlet flange  22   a , the exhaust gas introducing port  11  is formed. 
     In the variable capacity turbine  21  according to the present embodiment, a flow path at the inlet portion of the outer scroll  6  is formed as the continuous throttle flow path from the upstream side to the downstream side. In other words, the inner peripheral face of the outer scroll  6  at the inlet portion of the outer scroll  6  and/or the outer peripheral face of the first dividing wall  8  are/is formed so that the flow path sectional area gradually reduces, which facilitates acceleration of the exhaust gas at the inlet portion of the outer scroll  6 , suppresses separation from the outer peripheral face of the upstream tip end portion of the first dividing wall  8 , enhances performance, and increases the flow rate. 
     Moreover, the inlet flange  22   a  is disposed so that the angle α formed by the line  40  connecting the upstream tip end and the downstream tip end of the first dividing wall  8  and the central axis  23  of the inlet flange  22   a  forming the inlet portion of the turbine housing  22  is smaller than that of the first embodiment described above and a turning angle of the exhaust gas passing through the introducing port  14  is smaller than that of the first embodiment described above, which further suppresses separation from the outer peripheral face of the upstream tip end portion of the first dividing wall  8 , further enhances performance, and further increases the flow rate. 
     A variable capacity turbine according to a third embodiment of the present invention will be described with reference to  FIG. 5 .  FIG. 5  is a sectional view perpendicular to an axis of the variable capacity turbine according to the present embodiment. 
     A variable capacity turbine  31  according to the present embodiment is different from the turbine of the first embodiment described above in that the turbine  31  has a flow control valve  32  instead of the flow control valve  12 . Because other components are similar to those of the first embodiment described above, description thereof will not be repeated. 
     As shown in  FIG. 5 , the flow control valve  32  according to the present embodiment is formed to move parallel between a high flow rate position shown in a solid line in  FIG. 5  (i.e., when the flow control valve  32  is in a position for opening (fully opening) the introducing port  14  of the outer scroll  6 ) and a low flow rate position shown in a two-dot chain line in  FIG. 5  (i.e., when the flow control valve  32  is in a position for closing (fully closing) the introducing port  14  of the outer scroll  6 ). In other words, the flow control valve  32  according to the present embodiment is formed to be opened and closed with a flat face  32   a  positioned on an inner periphery side of the flow control valve  32  and the central axis  23  of an inlet flange  3   a  forming the inlet portion of the turbine housing  3  maintained at a certain angle with respect to each other. 
     Inside the inlet flange  3   a , the exhaust gas introducing port  11  is formed. 
     In the variable capacity turbine  31  according to the present embodiment, a flow path at the inlet portion of the outer scroll  6  is formed as the continuous throttle flow path from the upstream side to the downstream side. In other words, the inner peripheral face of the outer scroll  6  at the inlet portion of the outer scroll  6  and/or the outer peripheral face of the first dividing wall  8  are/is formed so that the flow path sectional area gradually reduces, which facilitates acceleration of the exhaust gas at the inlet portion of the outer scroll  6 , suppresses separation from the outer peripheral face of the upstream tip end portion of the first dividing wall  8 , enhances performance, and increases the flow rate. 
     Moreover, a turning angle of the exhaust gas passing through the introducing port  14  is constantly maintained at any of times when the flow rate is low, when the flow rate is high, when the flow rate shifts from the low rate to the high rate, and when the flow rate shifts from the high rate to the low rate, which further suppresses separation from the outer peripheral face of the upstream tip end portion of the first dividing wall  8 , further enhances performance, and further increases the flow rate. 
     The present invention is not limited to the embodiments described above but may be carried out while being modified or changed suitably as necessary without departing from the scope of the technical idea of the present invention. 
     For example, in the second embodiment shown in  FIG. 4 , it is possible to employ the flow control valve  32  according to the third embodiment shown in  FIG. 5  instead of the flow control valve  12 . 
     Moreover, although the turbine, in which a gently curved recessed portion  8   a  (see  FIG. 1 ) is formed in the outer peripheral face of the first dividing wall  8  in order to mitigate abrupt reduction in the flow path sectional area due to the built-up portion  17 , has been described as a concrete example in the embodiments described above, the inner peripheral face of the turbine housing  3  may be recessed instead of recessing the outer peripheral face of the first dividing wall  8 , so that the flow path at the inlet portion of the outer scroll  6  becomes a continuous and gentle throttle flow path from the upstream side to the downstream side. 
     REFERENCE SIGNS LIST 
     
         
           1  variable capacity turbine 
           2  scroll 
           3  turbine housing 
           4  turbine wheel 
           5  inner scroll 
           6  outer scroll 
           7  involute dividing wall 
           12  flow control valve 
           12   a  flat face 
           14  introducing port 
           21  variable capacity turbine 
           22  turbine housing 
           22   a  inlet flange 
           23  central axis 
           31  variable capacity turbine 
           32  flow control valve