Variable nozzle turbine having a device for radially positioning a variable nozzle barrel

Abstract

The present invention relates to a turbocharger having a variable nozzle turbine formed by pivotable blades supported by a nozzle ring, the turbocharger comprising a locator which is radially elastically deformable and is arranged between a radially outwardly facing surface of the center housing and an opposing surface of the nozzle ring for radially locating the nozzle ring relative to the center housing. At least one vent is defined in the radially outermost surface of the locator or in the surface of the nozzle ring to allow pressure communication between spaces on axially opposite sides of the locator.

Description

Technical Field

[0001] The present disclosure relates to a turbocharger having a variable nozzle turbine in which movable vanes are provided in the nozzle of the turbine for regulating the exhaust gas flow into the turbine. Background Art

[0002] An exhaust-driven turbocharger is a device used in conjunction with an internal combustion engine for increasing the power output of the engine by compressing air, which is delivered to the air intake of the engine to mix with fuel and burn in the engine. A 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 also another central housing connected between the turbine housing and the compressor housing for containing 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 to 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 the inlet of the compressor housing, and the air is compressed by the compressor wheel and then discharged from the housing to the engine air intake.

[0003] One of the challenges of boosting engine performance with a turbocharger is to achieve the desired amount of engine power output throughout the entire operating range of the engine. It has been found that this cannot usually be easily achieved with a fixed geometry turbocharger, and therefore, variable geometry turbochargers have been developed with the goal of providing a greater degree of control over the amount of boost provided by the turbocharger. One type of variable geometry turbocharger is a variable nozzle turbocharger (VNT), which includes a variable vane array in the turbine nozzle. The vanes are pivotally mounted in the nozzle and are connected to a mechanism that enables the mounting angle of the vanes to be varied. Changing the mounting angle of the vanes has the effect of changing the effective flow area in the turbine nozzle, and therefore, the exhaust gas flow to the turbine wheel can be adjusted by controlling the vane position. In this way, the power output of the turbine can be adjusted, which allows the engine power output to be controlled to a greater extent than is usually possible with a fixed geometry turbocharger.

[0004] The variable vane mechanism is relatively complex and therefore presents challenges in terms of assembly of the turbocharger. Furthermore, the mechanism is positioned between the turbine housing, which gets quite hot because it is exposed to the exhaust gas, and the center housing, which is much cooler than the turbine housing. The variable vane mechanism is therefore subject to high temperatures and to thermal stresses due to the mentioned temperature gradients. All of these factors present challenges for radially centering the variable vane mechanism so that it is substantially concentric with the turbine wheel. Summary of the invention

[0005] The present disclosure describes embodiments of a turbocharger of the variable nozzle turbine type mentioned above having an advantageous positioner arrangement for radially positioning the nozzle ring relative to a central housing containing the turbocharger bearings. According to a first embodiment, a turbocharger having a variable nozzle turbine comprises:

[0006] a turbine 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 and an axially extending bore, the chamber surrounding the turbine wheel for receiving exhaust gas, the exhaust gas being discharged through the axially extending bore after passing through the turbine wheel;

[0007] a nozzle opening generally radially inwardly from the chamber toward the turbine wheel;

[0008] a compressor including a compressor housing and a compressor wheel mounted in the compressor housing and connected to the rotatable shaft for rotation therewith;

[0009] a center housing connected between the compressor housing and the turbine housing and having a nose portion adjacent the turbine wheel, the nose portion defining a first surface facing generally radially outwardly and a second surface facing generally axially toward the turbine wheel;

[0010] a generally annular nozzle ring having a first face and an opposed second face, the first face comprising one wall of the nozzle and axially spaced from an opposed wall of the nozzle, and an array of vanes, the vanes being circumferentially spaced about the nozzle ring and disposed in the nozzle, the vanes being rotatably mounted to the nozzle ring such that the mounting angle of the vanes can be varied for adjusting exhaust gas flow to the turbine wheel, the nozzle ring defining a generally radially inwardly facing third surface adjacent an inner diameter of the turbine wheel, the third surface being spaced from and opposed to the first surface of the center housing;

[0011] a spring heat shroud resiliently axially compressible, the spring heat shroud having a radially outer peripheral portion in contact with a portion of the second face of the nozzle ring and having a radially inner peripheral portion in contact with the second surface of the center housing facing the turbine wheel, the spring heat shroud being axially compressed between the nozzle ring and the center housing; and

[0012] a retainer including a metal ring, the retainer being disposed between the first surface of the center housing and an opposite third surface of the nozzle ring and being used to radially position the nozzle ring relative to the center housing, the retainer being radially compressible in an elastically deformable manner, the retainer having a radially outermost surface and a radially innermost surface, the radially innermost surface of the retainer contacting the first surface of the center housing, and the radially outermost surface of the retainer contacting the third surface of the nozzle ring;

[0013] wherein at least one of the radially outermost surface of the positioner and the third surface of the nozzle ring defines at least one vent, the vent comprising a radially extending recess in the surface, the at least one vent providing fluid pressure communication between spaces on axially opposite sides of the positioner.

[0014] In some embodiments described herein, there are a plurality of said vents spaced circumferentially around the perimeter of said positioner.

[0015] According to one embodiment, the vent is defined in the third surface of the nozzle ring.

[0016] According to another embodiment, the vent is defined in the radially outermost surface of the positioner. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Having generally described the present disclosure, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and in which:

[0018] Figure 1 is an axial end view of a turbocharger according to an embodiment of the present invention;

[0019] Figure 2 is along Figure 1 A cross-sectional view of line 2-2 in FIG.

[0020] Figure 3 is a perspective view of a variable nozzle assembly for a turbocharger according to an embodiment of the prior art;

[0021] Figure 4 is based on Figure 3A partial axial cross-sectional view of a turbocharger of a prior art embodiment;

[0022] Figure 5 is a perspective view of a variable nozzle assembly of a turbocharger according to a first embodiment of the present invention;

[0023] Figure 6 is based on Figure 5 A partial axial cross-sectional view of a turbocharger of an embodiment of; and

[0024] Figure 7 is a perspective view of a vent positioner according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present disclosure will now be described in more detail with reference to the above-mentioned drawings, which depict some but not all embodiments of the inventions to which the present disclosure relates. These inventions may be implemented in a variety of forms (including forms not explicitly described herein) and should not be construed as being limited to the specific exemplary embodiments described herein. In the following description, similar reference numerals refer to similar elements throughout the entire text.

[0026] The present invention relates to a turbocharger comprising a variable nozzle turbine (VNT), wherein the variable nozzle comprises an array of pivotable vanes mounted on a nozzle ring. Figure 1 and Figure 2 A VNT turbocharger 10 of the type to which the present invention relates is shown. The turbocharger includes a compressor wheel or impeller 14 mounted on one end of a rotatable shaft 18 and disposed in a compressor housing 16. The shaft is supported in bearings 19 mounted in a central housing 20 of the turbocharger. The shaft 18 is rotated by a turbine wheel 22 mounted on the other end of the shaft 18 opposite the compressor wheel, thereby rotatably driving the compressor wheel, which compresses air drawn in through the compressor inlet and delivers the compressed air to the intake of an internal combustion engine (not shown) for use in improving the performance of the engine.

[0027] The turbocharger also includes a turbine housing 24 that houses a turbine wheel 22. The turbine housing defines a generally annular chamber 26 that surrounds the turbine wheel and receives exhaust gas from the internal combustion engine for driving the turbine wheel. Exhaust gas is directed generally radially inward from the chamber 26 through a turbine nozzle 28 to the turbine wheel 22. As the exhaust gas flows through passages between the blades of the turbine wheel, the gas expands to a lower pressure, and the gas discharged from the wheel exits the turbine housing through a generally axial hole 32 in the turbine housing.

[0028] The turbine nozzle 28 is a variable nozzle for varying the cross-sectional flow area and flow direction through the nozzle in order to regulate the flow into the turbine wheel. Figure 2 and Figure 3 , the variable nozzle includes a plurality of vanes 34 spaced circumferentially around the nozzle. Each vane is attached to a pin 36 that passes through an orifice in a generally annular nozzle ring 38 that is mounted coaxially relative to the turbine wheel 22. Each pin 36 is rotatable about its axis for rotating the attached vane. 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 that is attached to one end of the pin that protrudes from the nozzle ring 38 and is engaged by a generally annular unison ring 42 (also referred to 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 to rotate the unison ring 42 about its axis. When the unison ring is rotated, the vane arm 40 is rotated to cause the pin 36 to rotate about its axis, thereby rotating the vane 34 to change the cross-sectional flow area and flow direction through the nozzle 28.

[0029] In the turbocharger 10, the variable vane mechanism is provided in the form of a cartridge 50, which can be installed into and removed from the turbocharger as a unit. The cartridge 50 includes a nozzle ring 38, vanes 34, pins 36, vane arms 40, and a unison ring 42. The cartridge also includes an insert 52 having a tubular portion 54 and a nozzle portion 56, the tubular portion 54 being sealingly received in the portion 32a of the bore 32 of the turbine housing, the nozzle portion 56 extending generally radially outward from one end of the tubular portion 54, the nozzle portion 56 being axially spaced from the nozzle ring 38 so 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 one or more axially spaced circumferential grooves, and a sealing ring is retained in each of the circumferential grooves for sealingly engaging the inner surface of the bore portion 32a.

[0030] A plurality of spacers (not shown) are connected between the nozzle ring 38 and the nozzle portion 56 of the insert 52 for securing the nozzle ring to the insert and maintaining a desired axial spacing between the nozzle ring 38 and the nozzle portion 56. Advantageously, the spacers are formed of a material having good high temperature mechanical properties and relatively low thermal conductivity, such as stainless steel (e.g., 310 grade stainless steel), etc., so that the nozzle ring 38 and the insert 52 are effectively thermally decoupled from each other.

[0031] Figure 3 and Figure 4A cartridge 50 is shown in accordance with an embodiment that does not include features of the present invention. The cartridge also includes a metal locator ring 80 that is retained between the nozzle ring 38 and the center housing 20 when the cartridge is mounted to the center housing. The locator ring 80 can have a C-shaped cross-section as shown, or alternatively can have an S-shaped cross-section and be formed to be radially compressible in an elastically resilient manner between the nozzle ring and the center housing. The locator has a radially innermost surface that engages a radially outwardly facing surface of the center housing 20 to establish substantial concentricity between the center housing and the locator ring. The radially outermost surface of the locator ring 80 engages a radially inwardly facing locating surface 39 ( Figure 4 ), so as to radially position the nozzle ring substantially concentric with the locator ring, and thereby concentric with the center housing. In this way, concentricity of the nozzle ring 38 relative to the center housing (and thereby relative to the turbine wheel 22) is established.

[0032] The turbocharger 10 also includes a spring heat shield 90 formed of a high temperature resistant metal sheet. The radially inner peripheral portion of the spring heat shield contacts the axially facing surface of the center housing facing the turbine wheel 22, and the radially outer peripheral portion of the spring heat shield contacts the axially facing surface of the nozzle ring 38 facing the center housing. The spring heat shield is axially compressed between the center housing and the nozzle ring and is used to press against the insert 52 (at the nozzle ring 38) on the nozzle ring 38. Figure 4 The spring heat shield also acts as a heat shield between the turbine and the center housing.

[0033] The turbocharger 10 according to the prior art having a variable nozzle barrel 50 positioned by a C-shaped retainer ring 80 has proven to be an advantageous construction, but further improvements are still sought. In particular, improvements are sought with respect to the retainers for the nozzle ring 38. Referring now to Figure 4To explain one disadvantage of the positioner 80. The total pressure of the exhaust gas in the turbine housing chamber 26 is P1T. Most of the exhaust gas flows through the variable nozzle 28 to the turbine wheel 22. However, a small part of the exhaust gas leaks into the VNT chamber where the unison ring 42 and the blade arms are located; the pressure in this VNT chamber is represented by P1, which is significantly lower than P1T. There is also a small leakage flow from the nozzle 28 through the periphery of the turbine wheel 22 to the shroud / wheel cavity; the pressure in the shroud / wheel cavity is represented by P3, which is a portion of P1T depending on the installation angle of the blades 34. Generally, P3 is less than P1. Because the entire outer periphery of the positioner contacts the cylindrical surface 39 of the nozzle ring, and the entire inner periphery of the positioner contacts the cylindrical surface of the center housing 20, the positioner / shield cavity disposed between the positioner 80 and the spring heat shield 90 is sealed. Similarly, the spring heat shield 90 is in full contact with the center housing and with the nozzle ring. Therefore, the pressure P2 in the positioner / shield cavity is controlled by a small leakage flow either through the positioner or through the heat shield, and therefore P2 is lower than P3. As a result, there is a negative pressure differential across the spring heat shield that is in one direction (in Figure 4 The present invention aims to reduce or eliminate this negative pressure difference on the spring heat shield.

[0034] In this regard, Figure 5 and Figure 6 A first embodiment of the present invention is described in FIG. Figure 5 A modified variable nozzle cartridge 150 is shown which is substantially similar to the corresponding cartridge 50 of the prior art described above. However, the modified cartridge includes a "vented" nozzle ring 138 which is different from the nozzle ring 38 of the prior art cartridge. In particular, the radially inwardly facing surface of the nozzle ring (see Figure 4 The surface 39 in the nozzle ring defines at least one vent V, which includes a radially outwardly extending recess in the generally cylindrical surface of the nozzle ring, the surface of the nozzle ring being contacted by the radially outermost surface of the locator 80. There may be multiple such vents; in the illustrated embodiment, there are three vents V circumferentially spaced around the periphery of the locator 80, but the present invention is not limited to any particular number of vents. Exhaust gas can pass through the vent to the locator / shield cavity, with the result that the pressure P2 in the locator / shield cavity is substantially the same as the pressure P1 in the VNT cavity. As a result, the pressure P2 in the locator / shield cavity is higher than the pressure P3 in the shroud / wheel cavity. Therefore, there is a positive pressure differential across the spring thermal shield 90, which enhances the biasing force on the nozzle ring 138.

[0035] Figure 7 A second embodiment of the present invention is depicted in FIG. Instead of using the ventilation nozzle ring in the previous embodiment, the ventilation nozzle ring can be replaced by using a ventilation nozzle ring such as Figure 7 A similar result may be obtained by using the vented retainer 180 shown in FIG. 1 . The vented retainer includes at least one vent V comprising a radially inwardly extending recess in a generally cylindrical outermost surface of the retainer that contacts the nozzle ring. There may be a plurality of circumferentially spaced vents as in the illustrated embodiment. Because the retainer includes the vent, the surface of the nozzle ring that engages the retainer may be cylindrical rather than vented. However, it is also possible to use both a vented nozzle ring and a vented retainer, each defining at least one of the vents described.

[0036] Based on this disclosure, those skilled in the art will recognize that modifications and other embodiments of the invention described herein may be made without departing from the creative concept described herein. The specific terms used herein are used for illustrative purposes rather than for limiting purposes. Therefore, the present invention should not be limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims.

Claims

1. A turbocharger having a variable nozzle turbine, include: a turbine 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 and an axially extending bore, the chamber surrounding the turbine wheel for receiving exhaust gas, the exhaust gas being discharged through the axially extending bore after passing through the turbine wheel; a nozzle opening generally radially inwardly from the chamber toward the turbine wheel; a compressor 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 and having a nose portion adjacent the turbine wheel, the nose portion defining a first surface facing generally radially outwardly and a second surface facing generally axially toward the turbine wheel; a generally annular nozzle ring having a first face and an opposed second face, the first face comprising one wall of the nozzle and axially spaced from an opposed wall of the nozzle, and an array of vanes, the vanes being circumferentially spaced about the nozzle ring and disposed in the nozzle, the vanes being rotatably mounted to the nozzle ring such that the mounting angle of the vanes can be varied for adjusting exhaust gas flow to the turbine wheel, the nozzle ring defining a generally radially inwardly facing third surface adjacent an inner diameter of the turbine wheel, the third surface being spaced from and opposed to the first surface of the center housing; a spring heat shield resiliently axially compressible, the spring heat shield having a radially outer peripheral portion in contact with a portion of the second face of the nozzle ring and having a radially inner peripheral portion in contact with a second surface of the center housing facing the turbine wheel, the spring heat shield being axially compressed between the nozzle ring and the center housing; as well as a retainer including a metal ring, the retainer being disposed between the first surface of the center housing and an opposite third surface of the nozzle ring and being used to radially position the nozzle ring relative to the center housing, the retainer being radially compressible in an elastically deformable manner, the retainer having a radially outermost surface and a radially innermost surface, the radially innermost surface of the retainer contacting the first surface of the center housing, and the radially outermost surface of the retainer contacting the third surface of the nozzle ring; wherein at least one of the radially outermost surface of the positioner and the third surface of the nozzle ring defines at least one vent, the vent comprising a radially extending recess in the surface, the at least one vent providing fluid pressure communication between spaces on axially opposite sides of the positioner.

2. The turbocharger according to claim 1, in, There are a plurality of said vents spaced circumferentially around the periphery of said positioner.

3. The turbocharger according to claim 2, in, The vent is defined in the third surface of the nozzle ring.

4. The turbocharger according to claim 2, in, The vent is defined in the radially outermost surface of the retainer.

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