阅读说明：本技术 具有可变喷嘴模块的涡轮增压器，包括用以轴向地定位该模块的弹性热屏蔽组件 (Turbocharger with variable nozzle module comprising an elastic heat shield assembly to axially position the module ) 是由 V.米卡内克 M.普罗蒂瓦 L.科瓦罗瓦 于 2019-12-10 设计创作，主要内容包括：本发明涉及具有可变喷嘴模块的涡轮增压器,包括用以轴向地定位该模块的弹性热屏蔽组件。一种涡轮增压器包括可变喷嘴模块,该可变喷嘴模块具有支撑涡轮机喷嘴中的一排可变叶片的喷嘴环。隔热罩和弹簧组件安置于在涡轮增压器的涡轮机轮、喷嘴环和中心轴承壳体之间界定的空间中。隔热罩和弹簧组件包括分立地形成的隔热罩部件和弹簧部件,这两个部件被配置为环形非平坦的盘状件。隔热罩和弹簧在它们的径向内周边区域和径向外周边区域处彼此接触,但在那些周边区域之间被间隔开,由此在它们之间产生封闭的死空间。相对于具有单个罩或具有双罩且它们之间没有死空间的布置,死空间可以显著地降低弹簧的最大温度。(The invention relates to a turbocharger with a variable nozzle module including an elastomeric heat shield assembly to axially position the module. A turbocharger includes a variable nozzle module having a nozzle ring that supports a row of variable vanes in a turbine nozzle. The heat shroud and spring assembly are disposed in a space defined between a turbine wheel, a nozzle ring, and a central bearing housing of a turbocharger. The heat shield and spring assembly includes a separately formed heat shield component and spring component configured as an annular non-flat disk. The heat shield and the spring are in contact with each other at their radially inner and outer peripheral regions, but are spaced between those peripheral regions, thereby creating a closed dead space therebetween. The dead space can significantly reduce the maximum temperature of the spring relative to an arrangement with a single cover or with double covers without dead space between them.)

1. A turbocharger having a variable nozzle turbine, the turbocharger comprising:

a turbine assembly including a turbine housing and a turbine wheel mounted in the turbine housing and connected to a rotatable shaft for rotation therewith, the turbine housing defining a chamber for receiving exhaust gas and for supplying the exhaust gas to the turbine wheel, the turbine assembly defining a nozzle leading from the chamber generally radially inwardly to the turbine wheel;

a compressor assembly including a compressor housing and a compressor wheel mounted in the compressor housing and connected to the rotatable shaft for rotation therewith;

a center housing connected between the compressor housing and the turbine housing, the center housing defining a radial reference surface facing radially outward and an axial reference surface facing axially toward the turbine wheel; and

a variable nozzle module connected between the center housing and the turbine housing and comprising an assembly of a generally annular nozzle ring and a row of rotatable vanes spaced circumferentially about the nozzle ring and disposed in the nozzle for regulating exhaust gas flow to the turbine wheel, wherein the nozzle ring defines at its radially inner periphery: a radial reference surface facing radially inward and opposite the radial reference surface of the center housing; and an axial reference surface axially facing away from the turbine wheel; and

an insert defining a nozzle portion axially spaced from the nozzle ring such that the vanes extend between the nozzle ring and the nozzle portion, a plurality of spacers being connected between the nozzle ring and the nozzle portion of the insert; and

a heat shield and spring assembly disposed in a space defined between the radially inner periphery of the nozzle ring, the turbine wheel and the center housing, the heat shield and spring assembly comprising a heat shield and a spring formed as two separate pieces, the heat shield comprising an annular non-flat disc, and the spring comprising an annular non-flat disc, the heat shield and the spring abutting each other at radially outer and inner peripheral regions thereof and being spaced apart on an intermediate region between the radially inner and outer peripheral regions so as to define a dead space between the heat shield and the spring that is sealed from exhaust gas surrounding the heat shield and spring assembly.

2. The turbocharger of claim 1, wherein the heat shroud is in contact with the axial reference surface of the nozzle ring at a radially outer peripheral region thereof and the springs are in contact with the axial reference surface of the center housing at a radially inner peripheral region thereof, and wherein the heat shroud and spring assembly is axially compressed between the axial reference surface of the nozzle ring and the axial reference surface of the center housing so as to axially position the nozzle ring relative to the center housing.

3. The turbocharger of claim 2, further comprising a locator disposed between and in contact with the radial reference surfaces of the nozzle ring and the center housing to radially locate the nozzle ring relative to the center housing.

4. The turbocharger of claim 1, wherein the heat shield is constructed of a first material and the spring is constructed of a second material different from the first material.

5. The turbocharger of claim 1, wherein the turbine housing defines an axial bore through which exhaust gas is discharged from the turbine wheel, and the insert further includes a tubular portion received into the axial bore of the turbine housing, the nozzle portion extending generally radially outwardly from one end of the tubular portion.

6. The turbocharger of claim 1, wherein the radially outer peripheral region of the heat shield extends radially inward to a first bend at which the heat shield angles radially inward and axially toward the turbine wheel to a second bend at which the heat shield bends to extend substantially radially inward to a third bend at which the heat shield angles radially inward and axially toward the center housing.

7. The turbocharger of claim 6, wherein the spring is closer to planar than the heat shield, thereby forming the dead space between the spring and the heat shield.

Technical Field

The present application relates generally to turbochargers for internal combustion engines and more particularly to exhaust driven turbochargers having a variable turbine nozzle that includes variable vanes for regulating exhaust flow to a turbine wheel.

Background

Exhaust gas driven turbochargers are devices used in conjunction with internal combustion engines to increase the power output of the engine by compressing air that is delivered to the intake of the engine to be mixed with fuel and combusted in the engine. The turbocharger includes a compressor wheel mounted on one end of a shaft in a compressor housing and a turbine wheel mounted on the other end of the shaft in a turbine housing. Typically, the turbine housing is formed separately from the compressor housing, and there is a center housing connected between the turbine housing and the compressor housing for housing bearings for the shaft. The turbine housing defines a generally annular chamber that surrounds the turbine wheel and receives exhaust gas from the engine. The turbine assembly includes a nozzle leading from the chamber into the turbine wheel. Exhaust gas flows from the chamber through the nozzle to the turbine wheel, and the turbine wheel is driven by the exhaust gas. Thus, the turbine extracts power from the exhaust gas and drives the compressor. The compressor receives ambient air through an inlet of the compressor housing, and this air is compressed by the compressor wheel and then discharged from the housing to the engine air intake.

One of the challenges in improving engine performance using a turbocharger is achieving a desired amount of engine power output throughout the entire engine operating range of the engine. It has been found that this objective is often not readily attainable using fixed geometry turbochargers, and variable geometry turbochargers have therefore been developed with the objective of: a greater degree of control over the amount of boost provided by the turbocharger is provided. One type of variable geometry turbocharger is the Variable Nozzle Turbocharger (VNT), which includes a row of variable vanes in a turbine nozzle. The vanes are pivotally mounted in the nozzle and are connected to a mechanism that enables the set angle of the vanes to be changed. Changing the setting angle of the vanes has the effect of changing the effective flow area in the turbine nozzle and thus the flow of exhaust gas to the turbine wheel can be regulated by controlling the vane position. In this way, the power output of the turbine may be adjusted, which allows the engine power output to be controlled to a greater extent than is generally possible using a fixed geometry turbocharger.

The applicant is the owner of a number of patents relating to turbochargers having a variable nozzle mechanism in the form of a module (cartridge) comprising a pre-assembled unit mounted into the turbocharger between a turbine housing and a center housing. The module includes: a nozzle ring forming one wall of the nozzle and supporting a row of variable vanes within the nozzle; and an insert connected to the nozzle ring by spacers and forming opposite walls of the nozzle, the vanes extending between the nozzle ring and the insert.

The challenges with such modular type variable nozzles are: properly positioning the module both radially and axially with respect to the turbine wheel and ensuring that the module remains properly positioned for the life of the turbocharger. The high temperature environment in which the variable nozzle module must operate causes thermal deformation of various components of the turbine and variable nozzle, and may also cause creep and/or plasticization of some components exposed to the highest temperatures. In particular, components that axially bias the module to remain in the correct axial position, such as the coil springs between the turbine wheel and the center housing, may be susceptible to such detrimental effects caused by extreme temperatures. In particular, the spring loses its ability to apply a suitable axial biasing force to the module, thereby moving the module from its correct position.

The present application relates to methods of mitigating problems such as creep and/or plasticization of springs and other components within turbochargers having variable nozzle assemblies.

Disclosure of Invention

The present disclosure relates to a turbocharger having a variable turbine nozzle in the form of a module as mentioned. In accordance with one embodiment of the invention described herein, a turbocharger of this type includes a nozzle ring having a radially inner periphery defining a radial reference surface facing radially inwardly and opposite a radial reference surface of a center housing. The nozzle ring also defines an axial reference surface facing axially away from the turbine wheel. An insert defining a nozzle portion is axially spaced from the nozzle ring such that the vanes extend between the nozzle ring and the nozzle portion, and a plurality of spacers are connected between the nozzle portion of the insert and the nozzle ring. The turbocharger also includes a heat shield and spring assembly disposed in a space defined between the radially inner periphery of the nozzle ring, the turbine wheel, and the center housing. The heat shield and spring assembly includes a heat shield and a spring formed as two separate pieces, the heat shield including an annular non-flat disc, and the spring including an annular non-flat disc. The heat shield and the spring abut each other at their radially outer and inner peripheral regions and are spaced apart on an intermediate region between said radially inner and outer peripheral regions so as to define a dead space between the heat shield and the spring that is sealed from the exhaust gas surrounding the heat shield and spring assembly.

Computer thermal analysis of an embodiment of a turbocharger according to the present invention shows that the temperature of the spring is significantly reduced relative to prior art shroud arrangements, not only is there no dead space for the single shroud design, but also the double shroud assembly is free of dead space between the two shrouds.

In one embodiment, the heat shroud contacts the axial reference surface of the nozzle ring at a radially outer peripheral region thereof, and the spring contacts the axial reference surface of the center housing at a radially inner peripheral region thereof. The heat shroud and spring assembly is axially compressed between an axial reference surface of the nozzle ring and an axial reference surface of the center housing to axially position the nozzle ring relative to the center housing.

A turbocharger according to embodiments of the invention may further comprise a locator disposed between and in contact with the radial reference surfaces of the nozzle ring and the center housing to radially locate the nozzle ring relative to the center housing.

In some embodiments, the heat shield may be constructed from a first material and the spring may be constructed from a second material different from the first material. However, in other embodiments, the heat shield and the spring may be constructed of the same material.

Drawings

Having thus described the disclosure in general terms, reference will now be made to the accompanying drawing(s), which are not necessarily drawn to scale, and wherein:

FIG. 1 is an axial cross-sectional view of a turbocharger according to an embodiment of the present invention;

FIG. 2 is an enlarged portion of FIG. 1;

FIG. 2A is similar to FIG. 2 but shows an alternative embodiment of the invention; and

FIG. 3 is a graph illustrating a comparison of finite element thermal analysis results for a turbocharger according to an embodiment of the present invention and a turbocharger that does not include the heat shield and spring assembly of the present invention.

Detailed Description

The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. As used herein, terms such as "axial," "radial," and "circumferential" are with respect to the axis of rotation of the turbocharger.

A turbocharger 10 according to one embodiment of the invention is shown in axial cross-sectional view in fig. 1. The turbocharger includes a compressor 12 having a compressor wheel or impeller 14 mounted on one end of a rotatable shaft 18 in a compressor housing 16. The shaft is supported in bearings 19 mounted in a center housing 20 of the turbocharger. The shaft 18 is rotated by a turbine wheel 22 mounted on the other end of the shaft 18 spaced from the compressor wheel, thereby rotatably driving the compressor wheel, which compresses air drawn in through the compressor inlet and delivers the compressed air into a volute 21 from which it is then fed to the intake of an internal combustion engine (not shown) for improved engine performance.

The turbocharger also includes a turbine housing 24 that houses the turbine wheel 22. The turbine housing defines a generally annular chamber 26 which surrounds the turbine wheel and receives exhaust gas from the internal combustion engine for driving the turbine wheel. Exhaust gas is directed generally radially inwardly from the chamber 26 through a turbine nozzle 28 to the turbine wheel 22. As the exhaust gas flows through the passages between the vanes 30 of the turbine wheel, the gas expands to a lower pressure and the gas discharged from the wheel exits the turbine housing through the generally axial holes 32 therein.

The turbine nozzle 28 is a variable nozzle for varying the cross-sectional flow area through the nozzle in order to regulate the flow into the turbine wheel. The nozzle includes a plurality of vanes 34 spaced circumferentially around the nozzle. Each vane is attached to a pin 36 which passes through an aperture in a generally annular nozzle ring 38 which is mounted coaxially with respect to the turbine wheel 22. Each pin 36 is rotatable about its axis within an associated bore in the nozzle ring so that the vanes can be rotated about the axis for changing the setting angle of the vanes. The nozzle ring 38 forms one wall of the flow passage of the nozzle 28. Each of the pins 36 has a vane arm 40 attached to one end thereof that projects outwardly from the nozzle ring 38 and is engaged by a generally annular unison ring 42 (also referred to herein as an actuator ring) that is rotatable about its axis and coaxial with the nozzle ring 38. An actuator (not shown) is connected to the unison ring 42 for rotating it about its axis. As the unison ring is rotated, the vane arms 40 are rotated to rotate the pins 36 about their axes, thereby rotating the vanes 34 to adjust the vane setting angle and thereby change the cross-sectional flow area through the nozzle 28.

The variable vane mechanism is provided in the form of a module (cartridge) 50 that is installable into and removable from the turbocharger as a unit. The module 50 includes the nozzle ring 38, vanes 34, pins 36, vane arms 40, and unison ring 42. The module further includes an insert 52 having: a tubular portion 54 sealingly received into the bore 32 of the turbine housing; and a nozzle portion 56 extending generally radially outwardly from one end of the tubular portion 54, the nozzle portion 56 being axially spaced from the nozzle ring 38 such that the vanes 34 extend between the nozzle ring 38 and the nozzle portion 56. The radially outer surface of the tubular portion 54 has at least one circumferential groove in which at least one sealing ring 58 is retained for sealingly engaging the inner surface of the bore 32. Advantageously, the outer diameter of the tubular portion 54 of the insert is slightly less than the inner diameter of the bore 32, such that a slight gap is defined therebetween and only the sealing ring(s) 58 are in contact with the inner surface of the bore 32. Additionally, there is a gap between the nozzle portion 56 and the adjacent end of the turbine housing at the end of the bore 32. In this manner, the insert 52 is mechanically separated and thermally isolated from the turbine housing 24.

A plurality of spacers 60 are connected between the nozzle portion 56 of the insert 52 and the nozzle ring 38 for securing the nozzle ring to the insert and maintaining a desired axial spacing between the nozzle portion of the insert and the nozzle ring. Each spacer passes through a hole in the nozzle portion 56 and has an enlarged head on a side of the nozzle portion 56 facing away from the nozzle 28. Each spacer also has a pair of enlarged shoulders axially spaced along the length of the spacer such that one shoulder abuts an opposite side of the nozzle portion 56 and the other shoulder abuts a facing surface of the nozzle ring 38, thereby setting the axial spacing between the nozzle ring and nozzle portion. An end portion of each spacer passes through a hole in the nozzle ring 38, and a distal end portion of the end portion is upset to form an enlarged head to capture the nozzle ring. Advantageously, the spacers are formed of a material having good high temperature mechanical properties and relatively low thermal conductivity, such that the nozzle ring 38 and the insert 52 are effectively thermally isolated from each other.

Referring to fig. 2, at the radially inner periphery of the nozzle ring 38, the nozzle ring defines two surfaces that serve as reference surfaces to set the axial and radial position of the nozzle ring (and thus the entire module 50): the radial reference surface NRS is defined to face radially inward, and the axial reference surface NAS is defined to face axially away from the turbine wheel 22 and toward the center housing 20. Similarly, the central housing 20 defines two reference surfaces: the radial reference surface CRS is defined as the radial reference surface NRS that faces radially outward toward the nozzle ring (and is radially spaced therefrom), and the axial reference surface CAS is defined as the axial reference surface CAS that faces axially toward the turbine wheel 22.

In the illustrated embodiment, radial positioning of the nozzle ring 38 is accomplished by a locator 100 comprising a ring having a C-shaped cross-section in the axial-radial plane. The retainer has two radially spaced apart legs extending axially with radially extending webs connected therebetween, thus forming a C-shaped cross-section. The radially outer legs 102 engage a radial reference surface NRS of the nozzle ring and the radially inner legs 104 engage a radial reference surface CRS of the center housing, thereby radially positioning the nozzle ring 38 relative to the center housing 20. The positioner 100 is configured to be flexible and resilient so for that purpose it may be constructed of a suitable metal having material properties suitable for operation in the high temperature environment of a turbocharger turbine, where engine exhaust temperatures may reach or exceed 950 ℃.

In the prior art, axial and radial positioning of the nozzle ring 38 within the turbocharger has been accomplished in various ways. One approach that applicants and others have taken is to axially position the nozzle ring using an annular disc-shaped heat shield or heat shroud disposed between the center housing 20 and the nozzle ring 38 and to shield the center housing from the extremely high temperature exhaust gas passing through the nozzle and the turbine wheel, and to radially position the nozzle ring using a positioner adjacent to the heat shield, such as described in commonly owned U.S. patent No. 7,559,199 (the entire disclosure of which is hereby incorporated herein by reference). Applicants' experience is that this approach works as long as the engine exhaust temperature does not exceed about 950 ℃. However, current engine development is moving towards engine exhaust temperatures as high as 1050 ℃. Using the same material for the heat shield and the locator as has been used in the past, the applicants have found that higher exhaust temperatures cause creep and plasticization of the heat shield and/or the locator whereby they lose their ability to hold the nozzle ring in the correct position. This causes wheel friction.

In accordance with the present invention, conventional materials used in the past can still be used for the heat shield and the retainer while avoiding creep and plasticizing problems that plague prior art turbocharger designs. As shown in fig. 2, the present invention employs a heat shroud and spring assembly disposed in the space defined between the radially inner periphery of the nozzle ring, the turbine wheel and the center housing. The assembly includes a heat shield 80 and a spring 90. The heat shield 80 comprises an annular disk-shaped piece having a series of bends such that the piece is non-flat, the shape increasing the stiffness of the heat shield under axial compressive loads. At the radially outer periphery of the heat shroud, the turbine-facing axial facing surface of the heat shroud contacts the axial reference surface NAS of the nozzle ring 38. Similar to the heat shield, the spring 90 comprises an annular disc-shaped piece having a series of bends such that the piece is non-flat for increased axial stiffness.

At the radially outer periphery of the spring, the axially facing surface of the spring facing the turbine is in contact with the opposite surface of the heat shield 80 facing away from the turbine. At the radially inner periphery of the spring, the axially facing surface of the spring facing towards the turbine is in contact with the opposite surface of the heat shield facing away from the turbine, and the axially facing surface of the spring facing away from the turbine is in contact with the axial reference surface CAS of the center housing 20. The heat shroud and spring assembly is axially compressed between the axial reference surface NAS of the nozzle and the axial reference surface CAS of the center housing, thereby axially positioning the nozzle ring relative to the center housing. The primary function of the spring 90 is to bias the nozzle ring 38 in an axial direction (to the right in FIG. 2), while the primary function of the heat shield 80 is to shield the spring and other components from the high temperature environment of the turbine nozzle.

Thus, at both their radially outer and inner peripheral regions, the heat shield 80 and the spring 90 are in contact with each other. However, between those contact areas, the heat shield and the spring are axially spaced apart, thereby creating a dead space DS within the assembly. The dead space is sealed from the exhaust gas surrounding the assembly. In the present description and in the appended claims, the term "dead space" means that the fluid within the space DS is substantially stagnant, so that the convective heat transfer on the inner surface of the wall of the dead space is negligible, or in other words, the fluid cannot be made to pass through (enter and then exit) the dead space. Despite this definition, the term "dead space" does not exclude the possibility of a small opening into the space, since in practice an absolutely airtight sealing of the space is not possible; in practice, unexpected leakage paths are always possible, especially in view of thermal deformations that may occur, which may allow fluid pressure communication between the inside and the outside of the dead space. However, as used herein, "dead space" means that any such opening into the dead space does not result in any significant fluid movement within the dead space.

According to one embodiment of the invention as shown in FIG. 2, the radially outer peripheral region of the heat shield 80 extends radially inward to a first bend B1 where the heat shield angles radially inward and axially toward the turbine wheel 22 to a second bend B2 where the heat shield bends to extend substantially radially inward to a third bend B3 where the heat shield angles radially inward and axially toward the center housing 20 to a fourth bend B4 where the heat shield bends to extend radially inward with the radially inner peripheral region of the heat shield radially inward of the fourth bend. The spring 90 has a generally similar shape, including the same series of bends as the heat shield, but closer to planar than the heat shield, thereby creating a dead space between the spring and the heat shield.

An alternative embodiment is shown in fig. 2A. The spring 90 is the same as in the previous embodiment, but the heat shield 80' has a different shape than the previous embodiment. Specifically, heat shield 80' has bends B1-B3, but it lacks fourth bend B4, so the heat shield extends substantially linearly from the third bend radially inward and axially toward the center housing. The radially inner end of the heat shield 80' contacts the spring 90 to substantially seal the dead space DS.

Finite element analysis (transient thermal analysis and structural analysis) has been performed on a turbomachine generally in accordance with fig. 1 and 2 to evaluate the impact of the new heat shield and spring assembly. The analysis imposes four consecutive cycles of operation, in each of which the engine exhaust temperature ramps up from 150 ℃ to 1020 ℃ over a period of about 10 seconds, remains at this elevated temperature for approximately 460 seconds, then ramps down to 300 ℃ in about 10 seconds, and ramps down further to 150 ℃ in about 144 seconds, immediately followed by the next identical operation cycle starting again. Three configurations were analyzed: configuration #1 employs a single spring or cover (i.e., corresponding to spring 90 without additional heat shield 80); configuration #2 employs a heat shield and spring assembly with no dead space between them (i.e., the heat shield and spring are in contact over their entire surface); configuration # 3 employs a heat shield and spring assembly with dead space generally as shown in fig. 2.

FIG. 3 is a graph of the results of a finite element analysis of these three configurations. The vertical axis represents the temperature of the spring 80 at its outer diameter (outer diameter), and the horizontal axis represents time in seconds. Fig. 3 depicts a response to the third and fourth duty cycles as described above. For configuration #1 with a single cover (i.e., only one spring but no separate heat shield), the spring OD temperature reached a maximum of about 869 ℃. For configuration #2 with two covers (spring and heat shield) and no dead space (i.e. in contact over their entire surface), the maximum spring OD temperature is 833 ℃. For configuration # 3 with two covers (spring and heat shield) and with dead space, generally corresponding to the arrangement in fig. 2, the maximum spring OD temperature is 750 ℃. Thus, a design according to an embodiment of the present invention achieves a temperature reduction of about 120 ℃ at the spring OD, which is approximately the hottest position of the spring.

While the creep and plasticization problems mentioned with respect to prior art springs can potentially be mitigated by making the springs from special materials that are made to tolerate extremely high temperatures, such materials are relatively expensive. The present invention provides an alternative solution to this problem, making it possible to use less expensive conventional materials for the heat shield, spring and locator components. Alternatively, if special high temperature resistant materials are used for the springs and other components, the present invention may enable the assembly to operate at higher exhaust temperatures without experiencing creep and plasticizing problems.

Modifications and other embodiments of the inventions described herein will be apparent to those skilled in the art based upon this disclosure. Certain terminology is used herein for the purpose of description and not of limitation. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.