Variable nozzle unit and turbocharger of the variable geometry system

Abstract

Variable nozzle unit (101) with which a flow passage area for exhaust gas is supplied to the side of a turbine impeller (29) in a turbocharger (1) by the variable geometry system, the variable nozzle unit (101) comprising: a first base ring (47) which is arranged concentrically with the turbine impeller (29) in a turbine housing (27) in the turbocharger (1) of the variable geometry system; a second base ring (103) which is integrally present with the first base ring (47) at a position that is separated from the first base ring (47) in an axial direction of the turbine impeller (29) and faces the first base ring (47); a plurality of variable nozzles (61) arranged in a circumferential direction between an outer surface (47f) of the first base ring (47) and a front surface (103f) of the second base ring (103) such that they surround the turbine impeller (29), and which can be rotated in an opening direction and a closing direction about an axial center parallel to an axial center (C) of the turbine impeller (29) within a previously defined rotation range; and a connecting mechanism (67) for synchronously rotating the plurality of variable nozzles (61) in the opening direction and the closing direction within the rotation range, wherein a rear edge (61t) of each variable nozzle (61) projects in a radial direction with respect to an inner edge (103fe) of the front surface (103f) of at least the first base ring (47) or the second base ring (103) when the respective variable nozzle (61) rotates towards an end of the side in the opening direction in the rotation range, characterized in that the second base ring (103) has a cylindrical cover section (105) that covers leading edges (33a) of a plurality of turbine blades (33) on the turbine impeller (29), and that an annular indentation (113) on the side of the front surface (103f) of the second base ring (103) is formed such that the rear edge of each variable nozzle (61) projects inwards in the radial direction with respect to the inner edge (103fe) of the front surface (103f) of the second base ring (103) when the respective variable nozzle (61) rotates towards the end of the side of the opening direction in the rotation range.

Description

Technical area

[0001] The present invention relates to a variable nozzle unit and a turbocharger of the variable geometry system, in which a flow passage area (an inlet opening area) for exhaust gas supplied to a turbine wheel side in the turbocharger of the variable geometry system is regulated. A variable nozzle unit having the preamble features of claim 1 is known, for example, from DE 10 2008 000 724 A1. A similar variable nozzle unit is known from EP 1 574 673 A1. Technical background

[0002] In recent years, various types of variable nozzle units have been developed, such as those found in variable geometry turbochargers. Patent Documents 1 to 3 disclose a variable nozzle unit that conforms to conventional technology. A specific structure of the same is described below.

[0003] A first base ring is arranged concentrically with a turbine runner in a turbine housing. A second base ring is provided integrally with the first base ring at a position separated from the first base ring in an axial direction of the turbine runner. Further, a plurality of variable nozzles are arranged between a front surface of the first base ring and a front surface of the second base ring. The variable nozzles of the plurality are arranged at equal intervals in a circumferential direction so as to surround the turbine runner. Each variable nozzle can be rotated in an opening direction and a closing direction about an axial center parallel to an axial center of the turbine runner within a predetermined rotation range. A communication chamber is formed on a side of a surface opposite to the front surface of the first base ring.A connecting mechanism is arranged in the connecting chamber. The connecting mechanism rotates the plurality of variable nozzles synchronously in the opening direction or the closing direction within the rotation range. When the plurality of variable nozzles rotate synchronously in the opening direction, a flow passage area (an inlet opening area) for exhaust gas supplied to the turbine runner side becomes larger. Conversely, when the plurality of variable nozzles rotate synchronously in the closing direction, the flow passage area for the exhaust gas becomes smaller. List of citationsPatent documents Patent document 1: JP 2010- 65 591 A Patent document 2: JP 2009- 243 431 A Patent document 3: JP 2009- 243 300 A Summary of the inventionTechnical problem

[0004] When a variable geometry turbocharger is used in a supercharged engine system, the following two characteristics (performance parameters) are required to improve the fuel consumption of a supercharged engine. The first characteristic is improving turbine efficiency in a low-flow region where the engine speed is low and the exhaust gas flow velocity is low (turbine efficiency in a low-speed region), and the second characteristic is increasing turbine capacity in a high-flow region where the engine speed is high and the exhaust gas flow velocity is high (turbine capacity in a high-speed region).

[0005] However, improving turbine efficiency in the low flow velocity region comes at the expense of turbine capacity in the high flow velocity region and vice versa, and achieving both characteristics has proven problematic.

[0006] The present invention therefore aims to provide a variable nozzle unit and a turbocharger of the variable geometry system with which improvement of the turbine efficiency in the low flow velocity range and increase of the turbine capacity in the high flow velocity range can be achieved. Solution to the problem

[0007] One aspect of the present invention is a variable nozzle unit having the features of claim 1.

[0008] It should be noted that in the specification and claims of the present application, the meaning of "to be arranged" includes indirect arrangement via another element in addition to direct arrangement, and the meaning of "to be present" includes indirect presence via another element in addition to direct presence. Furthermore, the "trailing edge" refers to a downstream end in a flow direction of exhaust gas. Advantageous effects of the invention

[0009] According to the present invention, the variable nozzle unit and the turbocharger of the variable geometry system can be provided, with which improvement of the turbine efficiency in the low flow velocity region and increase of the turbine capacity in the high flow velocity region can be achieved. Short description of the drawings [ Fig. 1] Fig. 1 is an enlarged view of a section I marked with arrows in Fig. 3. [ Fig. 2] Fig. 2 is an enlarged sectional view taken along a line II-II in Fig. 3. [ Fig. 3] Fig. 3 is an enlarged view of a section III marked with arrows in Fig. 7. [ Fig. 4] Fig. Figure 4 is a view showing the major part of a variable nozzle unit. [ Fig. 5] Fig. 5(a) is a view showing a nozzle ring in the variable nozzle unit, and Fig. 5(b) is a sectional view taken along a line VB-VB in Fig. 5(a). [ Fig. 6] Fig. 6(a) is a view showing a support ring in the variable nozzle unit, and Fig. 6(b) is a sectional view taken along a line VIB-VIB in Fig. 6(a). [ Fig. 7] Fig. Figure 7 is a front sectional view of a variable geometry turbocharger. [ Fig. 8] Fig. Fig. 8 is a view illustrating a characteristic portion of an embodiment of the present invention and is the Fig. 1 corresponding view. [ Fig. 9] Fig. 9(a) is a schematic partial sectional view of a turbocharger of the variable geometry system according to a conventional example, and Fig. 9(b) is a sectional view taken along a line IXB-IXB in Fig. 9(a). [ Fig. 10] Fig. 10(a) is a schematic partial sectional view of a turbocharger of the variable geometry system according to a comparative example, and Fig. 10(b) is a sectional view taken along a line XB-XB in Fig. 10(a). [ Fig. 11] Fig. 11 is a graph showing performance test results of the variable geometry system turbocharger according to the conventional example and the variable geometry system turbocharger according to the comparative example. Description of an embodimentNew findings

[0010] First, new findings that serve as the basis of the present invention are explained.

[0011] Fig. 9(a) and Fig. 9(b) shows a variable geometry system turbocharger 200 according to a conventional example. Fig. 10(a) and Fig. 10(b) shows a variable geometry system turbocharger 300 according to a comparative example. In the variable geometry system turbocharger 200 according to the conventional example, although each variable nozzle 261 rotates in any direction, a rear edge 261t of each variable nozzle 261 does not protrude from an inner edge 247fe of a front surface 247f of a first base ring 247 and an inner edge 257fe of a front surface 257f of a second base ring 257. In contrast, in the variable geometry system turbocharger 300 according to the comparative example, when each variable nozzle 361 is rotated in an opening direction, a rear edge 361t of each variable nozzle 361 protrudes inward in a radial direction with respect to an inner edge 357fe of a front surface 357f of a second base ring 357. Fig. 9(b), a solid line indicates the variable nozzle 261 located at one end of a side in the opening direction in a rotation range, and a broken line indicates the variable nozzle 261 located at the end of a side in the closing direction in the rotation range. Likewise, in Fig. 10(b), a solid line indicates the variable nozzle 361 located at one end of a side in the opening direction in the rotation range, and a broken line indicates the variable nozzle 361 located at one end of a side in the closing direction in the rotation range. It should be noted that the reference numerals 227, 229, 237, 299 in Fig. 9(a) denote a turbine housing, a turbine impeller, a turbine scroll flow channel, and a seal ring of the variable geometry system turbocharger 200, respectively. Likewise, reference numerals 327, 329, 337, 399 in Fig. 10(a) a turbine housing, a turbine impeller, a turbine scroll flow channel, and a seal ring, respectively, of the turbocharger 300 of the variable geometry system.

[0012] Fig. Figure 11 shows performance test results of the variable geometry turbocharger 200 and the variable geometry turbocharger 300. Fig. Figure 11 shows a relationship between the flow rate of gas (the flow rate of test gas) flowing through the turbines of the two turbochargers and the turbine efficiency. Note that the flow rate is corrected using a known formula that uses the temperature and pressure of the turbine inlet.

[0013] In the turbocharger 300 of the variable geometry system according to the comparative example, as shown in Fig. 11, the turbine efficiency in a low flow velocity region is maintained at the same value as that of the turbocharger 200 of the variable geometry system according to the conventional example, and a flow velocity in a high flow velocity region increases more than that of the turbocharger 200 of the variable geometry system according to the conventional example.That is, if each variable nozzle is configured such that the rear edge of the respective variable nozzle protrudes inward in the radial direction with respect to the inner edge of the front surface of the second base ring when the respective variable nozzle rotates to the end of one side in the opening direction in the rotation range, this leads to the realization that sufficient turbine efficiency can be maintained in the low flow velocity range while increasing a flow velocity of exhaust gas in the high flow velocity range.It is concluded that the increase in the flow velocity of the exhaust gas is caused by the fact that a position of an inlet opening (an apparent inlet opening) T is shifted to an upstream side in a flow direction of the gas and that an area of ​​the inlet opening T (an apparent inlet opening area) is increased in the high flow velocity region. Furthermore, in the case where each variable nozzle is configured such that the rear edge of the respective variable nozzle protrudes inward in the radial direction with respect to the inner edge of the front surface of the first base ring when the respective variable nozzle rotates toward the end of one side in the opening direction in the rotation region, it can be concluded that a similar phenomenon occurs.

[0014] It should be noted that in the drawings, “R” means right-facing and “L” means left-facing.

[0015] Fig. Figure 7 shows a variable geometry turbocharger 1. The variable geometry turbocharger 1 supercharges (compresses) air supplied to an engine using energy from the engine's exhaust gas (not shown).

[0016] The variable geometry system turbocharger 1 includes a bearing housing 3. A radial bearing 5 and a pair of thrust bearings 7 are provided in the bearing housing 3. Furthermore, a rotor shaft (a turbine shaft) 9 extending in a horizontal direction is rotatably mounted on the plurality of bearings 5, 7. That is, the rotor shaft 9 can be rotated in the bearing housing 3 via the plurality of bearings 5, 7.

[0017] A compressor housing 11 is located on a right side of the bearing housing 3. In the compressor housing 11, a compressor impeller 13 is rotatably disposed around its axial center C (i.e., an axial center of the rotor shaft 9). The compressor impeller 13 compresses the air by rotation utilizing centrifugal force. Furthermore, the compressor impeller 13 includes a compressor wheel (a compressor disk) 15 integrally coupled to a right end of the rotor shaft 9, and a plurality of compressor vanes 17 arranged on an outer peripheral surface of the compressor wheel 15 at equal intervals in a circumferential direction.

[0018] An air inlet 19 for introducing air is formed on an inlet side (an upstream side in a flow direction of air) of the compressor impeller 13 in the compressor housing 11. The air inlet 19 is connected to an air filter (not shown) that purifies the air. Furthermore, an annular diffuser flow channel 21 that increases a pressure of the compressed air is formed on an outlet side (a downstream side in the flow direction of air) of the compressor impeller 13 between the bearing housing 3 and the compressor housing 11. Furthermore, a spiral compressor scroll flow channel 23 is formed inside the compressor housing 11. The compressor scroll flow channel 23 communicates with the diffuser flow channel 21.An air outlet 25 for discharging the compressed air is formed at a corresponding position of the compressor housing 11, and the air outlet 25 communicates with the compressor scroll flow passage 23 and is connected to an intake manifold (not shown) of the engine.

[0019] A turbine housing 27 is located, as in Fig. 3 and Fig. 7, on a left side of the bearing housing 3. In the turbine housing 27, a turbine runner 29 is rotatably disposed around the axial center C (an axial center of the turbine runner 29, that is, the axial center of the rotor shaft 9). The turbine runner 29 generates a rotational force (torque) using pressure energy of the exhaust gas. The turbine runner 29 includes a turbine wheel (a turbine disk) 31 integrally disposed at a left end of the rotor shaft 9, and a plurality of turbine blades 33 arranged on an outer peripheral surface of the turbine wheel 31 at equal intervals in a circumferential direction. At this time, front ends 33a of the plurality of turbine blades 33 are covered with a cover wall 27s of the turbine housing 27.

[0020] A gas inlet 35 for introducing exhaust gas is formed at a corresponding position of the turbine housing 27. The gas inlet 35 is connected to an exhaust manifold (not shown) of the engine. A spiral turbine scroll flow channel 37 is formed on an inlet side (an upstream side in a flow direction of the exhaust gas) of the turbine runner 29 inside the turbine housing 27. The turbine scroll flow channel 37 communicates with the gas inlet 35. Further, a gas outlet 39 for discharging the exhaust gas is formed on an outlet side (a downstream side in the flow direction of the exhaust gas) of the turbine runner 29 in the turbine housing 27. The gas outlet 39 is connected to an exhaust gas purification device (not shown) that purifies the exhaust gas.

[0021] Note that a heat shield plate 41 is located on a surface on the left side of the bearing housing 3. The heat shield plate 41 is formed in a ring shape and shields heat from the turbine impeller 29 side. An annular tension member 43, such as a leaf spring or a wave spring washer, is located between the surface on the left side of the bearing housing 3 and an outer peripheral edge (an outer peripheral end) of the heat shield plate 41.

[0022] The variable geometry system turbocharger 1 is provided with a variable nozzle unit 45 that regulates a flow passage area (an area of ​​the inlet port T, hereinafter referred to as an inlet port area) for the exhaust gas supplied to the turbine impeller 29 side.

[0023] The structure of the variable nozzle unit 45 is explained below. In the turbine housing 27, as shown in Fig. 1 and 3 to 5(b), a first nozzle ring 47 is arranged as a first base ring concentrically with the turbine impeller 29. A plurality of bearing holes 49 are formed in the first nozzle ring 47 at equal intervals in a circumferential direction. The bearing holes 49 are formed to pass through the first nozzle ring 47. Furthermore, an inner peripheral edge (an inner peripheral end) of the first nozzle ring 47 is fitted onto the outer peripheral edge (a shoulder of the outer peripheral edge side) of the heat shield plate 41.

[0024] A plurality of guide claws 51 are integrally formed on a surface on the right side of the first nozzle ring 47. The plurality of guide claws 51 are located outside in a radial direction of the bearing hole 49 and are radially spaced from each other in a circumferential direction of the first nozzle ring 47. Each guide claw 51 has a guide groove 53 with a U-shaped cross section on a front side (outer side in the radial direction). A convex coupling portion 55 is formed on the inner peripheral edge (the inner peripheral surface side) of the right side surface of the first nozzle ring 47. The convex coupling portion 55 is formed in a ring shape and protrudes to the right (one side in the axial direction). The convex coupling portion 55 is shaped in this way and thus couples a lower end of the plurality of guide claws 51.

[0025] A second nozzle ring 57 as a second base ring is located, as in Fig. 1 to 4, at a position separated from the first nozzle ring 47 in the horizontal direction (an axial direction of the turbine runner 29) and faces the first nozzle ring 47. The second nozzle ring 57 is integrally and concentrically arranged with the first nozzle ring 47 via a plurality (three or more) coupling bolts 59 aligned in a circumferential direction of the second nozzle ring 57. Here, the plurality of coupling bolts 59 define a gap between a front surface (a left-side surface) 47f of the first nozzle ring 47 and a front surface (a right-side surface) 57f of the second nozzle ring 57.

[0026] A plurality of variable nozzles 61 are, as in Fig. 1 to 3, arranged between the front surface 47f of the first nozzle ring 47 and the front surface 57f of the second nozzle ring 57. The plurality of variable nozzles 61 are arranged at equal intervals in the circumferential direction so as to surround the turbine runner 29. Each variable nozzle 61 can be rotated in an opening direction and a closing direction about an axial center parallel to the axial center C of the turbine runner 29 within a predetermined rotation range. A nozzle shaft 63 is integrally formed on a surface on the right side (a side surface on one side in the axial direction) of each variable nozzle 61. Each nozzle shaft 63 is rotatably supported via the corresponding bearing hole 49 of the first nozzle ring 47. Here, the variable nozzle 61 shown with a solid line is located in Fig. 2 at one end of the opening direction side in a rotation range, and the variable nozzle 61 shown with a broken line is located at one end of the closing direction side in the rotation range. Note that each variable nozzle 61 includes a nozzle shaft 63. However, another nozzle shaft (not shown) may be integrally formed on a surface on the left side (a side surface of the other side in the axial direction) of each variable nozzle 61, and each other nozzle shaft may be rotatably supported via a different bearing hole (not shown) of the second nozzle ring 57. Furthermore, the pitches of the variable nozzles 61 are constant in the circumferential direction. However, these pitches may not be constant depending on a shape of each variable nozzle 61, etc. The same applies to the bearing holes 49.

[0027] An annular connecting chamber 65 is formed on a right side (a side of the surface opposite the front surface 47f) of the first nozzle ring 47. A connecting mechanism 67 for synchronously rotating the plurality of variable nozzles 61 in the opening direction or the closing direction is located in the connecting chamber 65. The connecting mechanism 67 is coupled to the nozzle shafts 63 of the plurality of variable nozzles 61.

[0028] A concrete structure of the connecting mechanism 67 is explained below. A drive ring 69 is, as shown in Fig. 1, Fig. 3 and Fig. 4, the drive ring 69 is rotatably guided in a positive direction or an opposite direction (the opening direction or the closing direction) around the axial center C (an axial center of the first nozzle ring 47) of the turbine impeller 29 by the guide groove 53 of each guide claw 51. The drive ring 69 rotates in the positive direction or the opposite direction by driving a rotary actuator 71 such as an electric motor or a vacuum cylinder. Furthermore, a concave engaging portion (an engaging portion) 73 is formed at regular intervals in an inner edge of the drive ring 69. The concave engaging portion 73 is recessed outward in a radial direction of the drive ring 69. The number of concave engaging portions 73 corresponds to that of the variable nozzles 61.A concave engaging portion (another engaging portion) 75 is formed at a corresponding position of the inner edge of the drive ring 69. Similar to the concave engaging portion 73, the concave engaging portion 75 is also recessed outward in the radial direction of the drive ring 69. Furthermore, a lower end of a synchronizing link (a nozzle link) 77 is integrally coupled to the nozzle shaft 63 of each variable nozzle 61. A front end of each synchronizing link 77 is engaged with a corresponding concave engaging portion 73 of the drive ring 69. Note that the drive ring 69 is rotatably guided in the positive direction and the reverse direction by the guide groove 53.Instead, as shown in Patent Documents 2 and 3, the drive ring 69 may be rotatably guided in the positive direction and the reverse direction by a guide ring (not shown) located on the surface opposite to the front surface 47f of the first nozzle ring 47. Furthermore, the pitches of the concave engagement portions 73 are set according to the pitches of the variable nozzles 61. That is, by arranging the variable nozzles 61 at equal intervals, the concave engagement portions 73 are also arranged at equal intervals. However, when the pitches of the variable nozzles 61 change, the pitches of the concave engagement portions 73 also change according to the respective positions of the variable nozzles 61.

[0029] A drive shaft 79 is arranged via a bushing 81 at a portion on the left side of the bearing housing 3. The drive shaft 79 is rotatably arranged around the axial center parallel to the axial center of the turbine runner 29. A right end (one end) of the drive shaft 79 is connected to the rotary actuator 71 via a power transmission mechanism 83. Further, a lower end of a drive link 85 is integrally coupled to a left end (another end) of the drive shaft 79. A front end of the drive link 85 is engaged with another concave engaging portion (another engaging portion) 75 of the drive ring 69.

[0030] An inner peripheral edge of the support ring 87 is, as in Fig. 1, Fig. 3, Fig. 4, Fig. 6(a) and Fig. 6(b), the support ring 87 is integrally connected to the right-side surface (the surface opposite the front surface 47f) of the first nozzle ring 47 via right ends (ends on one side) of the plurality of coupling bolts 59. An outer diameter of the support ring 87 is larger than that of the first nozzle ring 47. A plurality of connecting parts 89 are integrally formed with the support ring 87 on an inner peripheral surface of the support ring 87. Each connecting part 89 projects inward in a radial direction of the support ring 87 and is spaced from the other end in a circumferential direction. Each connecting part 89 is integrally connected to the right-side surface of the first nozzle ring 47. An insertion hole 91 for inserting a left end of the coupling bolt 59 is formed in each connecting part 89. The insertion hole 91 passes through the connecting part 89.An outer peripheral edge of the support ring 87 is attached to the bearing housing 3 in a state where it is enclosed in cooperation with the turbine housing 27. The outer peripheral edge of the support ring 87 is attached to the bearing housing 3, and thereby the variable nozzle unit 45 is arranged in the turbine housing 27.

[0031] A receiving shoulder 93 as a concave receiving portion receiving a portion on the side of the inner circumference of the second nozzle ring 57 is, as shown in Fig. 1 and Fig. 3, is formed in the turbine housing 27. The receiving shoulder 93 is formed in a ring shape and is located on the inlet side of the turbine runner 29. An annular clearance 95 is formed between an inner wall surface (an inner peripheral surface) of the receiving shoulder 93 of the turbine housing 27 and an inner peripheral surface of the second nozzle ring 57. Further, a circumferential groove 97 is formed in an inner peripheral surface of the receiving shoulder 93. A plurality of seal rings 99 are located between the circumferential groove 97 of the receiving shoulder 93 and the inner peripheral surface of the second nozzle ring 57. The seal ring 99 serves as a sealing member that prevents the exhaust gas from leaking to the clearance 95 via a left side (a side of the surface opposite to the front surface 57f) of the second nozzle ring 57.It should be noted that an annular concave receiving portion (not shown) which receives the entire second nozzle ring 57 may be formed instead of the receiving shoulder 93.

[0032] When each variable nozzle 61 rotates toward the end of the side in the opening direction in the rotation range, each rear edge 61t of the respective variable nozzle 61 protrudes inward in the radial direction with respect to an inner edge 57fe of the front surface 57f of the second nozzle ring 57. When each variable nozzle 61 rotates toward the end of the side in the opening direction in the rotation range, the rear edge 61t of the respective variable nozzle 61 is closer to the inner side in the radial direction than an inner peripheral edge 93e of the receiving shoulder 93 (ie, an outer peripheral edge 27se of the cover wall 27s). It should be noted that the rear edge 61t of each variable nozzle 61 may be located closer to the outside in the radial direction than the inner peripheral edge 93e of the receiving shoulder 93 when the respective variable nozzle 61 rotates as described above.

[0033] The effect and one effect are explained below.

[0034] Exhaust gas introduced via the gas inlet 35 flows from the inlet side via the turbine scroll flow passage 37 to the outlet side of the turbine impeller 29, and thereby, rotational force (torque) can be generated using the pressure energy of the exhaust gas to rotate the rotor shaft 9 and the compressor impeller 13 integrally with the turbine impeller 29. As a result, air introduced via the air inlet 19 can be compressed and discharged from the air outlet 25 via the diffuser flow passage 21 and the compressor scroll flow passage 23, and thus the air supplied to the engine can be supercharged (compressed).

[0035] When the variable geometry turbocharger 1 is operating, when the engine speed is low and the exhaust gas flow rate is in a low flow rate range, the drive ring 69 rotates in the opposite direction (the closing direction) by driving the rotary actuator 71. When the drive ring 69 rotates in the opposite direction, the plurality of synchronous links 77 pivot in the opposite direction, and the plurality of variable nozzles 61 synchronously rotate in the closing direction (the opposite direction). As a result, the flow passage area (the inlet opening area) of the exhaust gas supplied to the turbine runner 29 side becomes smaller, and the exhaust gas flow rate increases. Accordingly, a sufficient capacity of the turbine runner 29 can be ensured.On the other hand, when the engine speed is high and the flow velocity of the exhaust gas is in a high flow velocity range, the drive ring 69 rotates in the positive direction (the opening direction) by driving the rotary actuator 71. When the drive ring 69 rotates in the positive direction, the plurality of synchronous links 77 are pivoted in the positive direction, and the plurality of variable nozzles 61 rotate synchronously in the opening direction (the positive direction). As a result, the flow passage area for the exhaust gas supplied to the turbine runner 29 side becomes larger, and an amount of the exhaust gas supplied to the turbine runner 29 side increases. As a result, the rotating force of the turbine runner 29 can be sufficiently and stably generated regardless of the flow velocity of the exhaust gas.

[0036] When each variable nozzle 61 rotates toward the end of the opening direction side in the rotation range, the rear edge 61e of the respective variable nozzle 61 protrudes inward in the radial direction with respect to the inner edge 57fe of the front surface 57f of the second nozzle ring 57. From the above findings, in this case, the exhaust gas flow velocity in the high flow velocity region can be increased more than before. That is, when the turbocharger 1 is operated by the variable geometry system, sufficient turbine efficiency can be maintained in the low flow velocity region, and the exhaust gas flow velocity can be increased in the high flow velocity region.

[0037] Accordingly, it is possible to sufficiently improve the fuel consumption of the engine and at the same time achieve improvement of the turbine efficiency in the low flow velocity region and increase of the turbine capacity in the high flow velocity region. Embodiment

[0038] An embodiment of the present invention will be described with reference to Fig. 8. It should be noted that in the drawings, "R" means right-facing and "L" means left-facing.

[0039] A turbocharger of the variable geometry system of the embodiment is as shown in Fig. 8, instead of the variable nozzle unit 45 (see Fig. 1) is provided with a variable nozzle unit 101. Furthermore, the variable nozzle unit 101 has a structure similar to that of the variable nozzle unit 45. Accordingly, only a portion of the structure of the variable nozzle unit 101 that differs from the variable nozzle unit 45 and a structure around the portion will be explained. It should be noted that in Fig. 8 of the plurality of components in the variable nozzle unit 101, components corresponding to components in the variable nozzle unit 45 are given the same reference numerals.

[0040] A second nozzle ring 103 as a second base ring is located at a position separated from the first nozzle ring in the horizontal direction (the axial direction of the turbine impeller 29) and faces the first nozzle ring 47. The second nozzle ring 103 is integrally and concentrically arranged with the first nozzle ring 47 via the plurality of coupling bolts 59 aligned in a circumferential direction of the second nozzle ring 103. Furthermore, the second nozzle ring 103 has a cylindrical cover portion 105 that covers the leading edges 33a of the plurality of turbine blades 33.

[0041] A receiving recess 107 as an annular concave receiving portion that receives the cover portion 105 is formed inside the turbine housing 27. The receiving recess 107 is formed in a ring shape and is located outside in the radial direction of the turbine impeller 29. Further, a circumferential groove 109 is formed in an outer peripheral surface of the cover portion 105. A plurality of seal rings 111 are located between the circumferential groove 109 and an inner wall surface (an inner peripheral surface) of the receiving recess 107. The seal ring 111 serves as a sealing member that prevents exhaust gas from leaking from a left side (a side of a surface opposite the front surface 103f) of the second nozzle ring 103.

[0042] A notch (circumferential groove) 113 is formed on the front surface 103f side of the second nozzle ring 103. The notch (circumferential groove) 113 is formed in a ring shape so that the rear edge 61t of each variable nozzle 61 protrudes inward with respect to an inner edge 103fe of the front surface 103f of the second nozzle ring 103 when the respective variable nozzle 61 is rotated toward the end of the opening direction side in the rotation range.

[0043] Accordingly, this embodiment also achieves the action and effect as mentioned above because the annular notch 113 is provided.

[0044] List of reference symbols: 1 - turbocharger; 3 - bearing housing; 5 - radial bearing; 7 - thrust bearing; 9 - rotor shaft (turbine shaft); 11 - compressor housing; 13 - compressor impeller; 15 - compressor wheel (compressor disk); 17 - compressor blade; 19 - air inlet; 21 - diffuser flow channel; 23 - compressor scroll flow channel; 25 - air outlet; 27 - turbine housing; 29 - turbine impeller; 31 - turbine wheel (turbine disk); 33 - turbine blade; 33a - front end (leading edge); 35 - gas inlet; 37 - turbine scroll flow channel; 39 - gas outlet; 41 - heat shield plate; 43 - clamping element; 45 - variable nozzle unit; 47 - first nozzle ring (first base ring); 47f - front surface (outer surface); 49 - bearing hole; 51 - guide claw; 53 - guide groove; 55 - coupling portion; 57 - second nozzle ring (second base ring); 59 - coupling pin; 61 - variable nozzle; 61t - trailing edge; 63 - nozzle shaft; 65 - connecting chamber; 67 - connecting mechanism; 69 - drive ring; 71 - rotary actuator;73, 75 - engagement portion; 77 - synchronizer link (nozzle link); 79 - drive shaft; 81 - bushing; 83 - power transmission mechanism; 85 - drive link; 87 - support ring; 89 - connecting part; 91 - insertion hole; 93 - receiving step; 95 - gap; 97 - circumferential groove; 99 - seal ring; 101 - variable nozzle unit; 103 - second nozzle ring (second base ring); 103f - front surface; 103fe - inner edge; 105 - cover portion; 107 - receiving step; 109 - circumferential groove; 111 - seal ring; 113 - notch (circumferential groove); C - axial center;

Claims

[1] A variable nozzle unit (101) for regulating a flow passage area for exhaust gas supplied to the side of a turbine impeller (29) in a turbocharger (1) by the variable geometry system, the variable nozzle unit (101) comprising: a first base ring (47) arranged concentrically with the turbine impeller (29) in a turbine housing (27) in the turbocharger (1) of the variable geometry system; a second base ring (103) provided integrally with the first base ring (47) at a position separated from the first base ring (47) in an axial direction of the turbine impeller (29) and facing the first base ring (47); a plurality of variable nozzles (61) arranged between an outer surface (47f) of the first base ring (47) and a front surface (103f) of the second base ring (103) in a circumferential direction so as to surround the turbine runner (29), and which can be rotated in an opening direction and a closing direction about an axial center parallel to an axial center (C) of the turbine runner (29) within a predetermined rotation range; and a link mechanism (67) for synchronously rotating the plurality of variable nozzles (61) in the opening direction and the closing direction within the rotation range, wherein a rear edge (61t) of each variable nozzle (61) protrudes in a radial direction with respect to an inner edge (103fe) of the front surface (103f) of at least one of the first base ring (47) and the second base ring (103) when the respective variable nozzle (61) rotates toward one end of the side in the opening direction in the rotation range, characterized by , that the second base ring (103) has a cylindrical cover portion (105) covering leading edges (33a) of a plurality of turbine blades (33) on the turbine runner (29), and an annular notch (113) is formed on the front surface (103f) side of the second base ring (103) such that the rear edge of each variable nozzle (61) protrudes inward in the radial direction with respect to the inner edge (103fe) of the front surface (103f) of the second base ring (103) when the respective variable nozzle (61) rotates toward the end of the opening direction side in the rotation range. [2] A variable geometry system turbocharger (1) which supercharges air supplied to an engine side by utilizing energy from exhaust gas from the engine, the variable geometry system turbocharger (1) being provided with a variable nozzle unit (101) according to claim 1.

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