Patent Application
20080193281
The present disclosure relates to turbochargers having an array of variable vanes in the turbine nozzle for regulating exhaust gas flow into the turbine.
An exhaust gas-driven turbocharger is a device used in conjunction with an internal combustion engine for increasing the power output of the engine by compressing the air that is delivered to the engine's air intake to be mixed with fuel and burned in the engine. A turbocharger comprises 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 and compressor housings for containing bearings for the shaft. The turbine housing defines a generally annular chamber that surrounds the turbine wheel and that receives exhaust gas from the engine. The turbine assembly includes a nozzle that leads from the chamber into the turbine wheel. The exhaust gas flows from the chamber through the nozzle to the turbine wheel and the turbine wheel is driven by the exhaust gas. The turbine thus extracts power from the exhaust gas and drives the compressor. The compressor receives ambient air through an inlet of the compressor housing and the air is compressed by the compressor wheel and is then discharged from the housing to the engine air intake.
One of the challenges in boosting engine performance with a turbocharger is achieving a desired amount of engine power output throughout the entire operating range of the engine. It has been found that this objective is often not readily attainable with a fixed-geometry turbocharger, and hence variable-geometry turbochargers have been developed with the objective of providing a greater degree of control over the amount of boost provided by the turbocharger. One type of variable-geometry turbocharger is the variable-nozzle turbocharger (VNT), which includes an array of variable vanes in the turbine nozzle. The vanes are pivotally mounted in the nozzle and are connected to a mechanism that enables the setting angles of the vanes to be varied. Changing the setting angles 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 positions. In this manner, the power output of the turbine can be regulated, which allows engine power output to be controlled to a greater extent than is generally possible with a fixed-geometry turbocharger.
The variable vane mechanism is relatively complicated and thus presents a challenge in terms of assembly of the turbocharger. Furthermore, the mechanism is located between the turbine housing, which gets quite hot because of its exposure to exhaust gases, and the center housing, which is at a much lower temperature than the turbine housing. Accordingly, the variable vane mechanism is subject to thermal stresses because of this temperature gradient.
To address these issues, the assignee of the present application has developed a variable nozzle “cartridge” design that simplifies the manufacture and assembly of the variable-vane mechanism, as described in co-pending commonly assigned International Patent Application PCT/US05/37622. The cartridge is connected between the center housing and the turbine housing and comprises an assembly of a generally annular nozzle ring and an array of vanes circumferentially spaced about the nozzle ring and disposed in the nozzle such that exhaust gas flows between the vanes to the turbine wheel, each vane being rotatably mounted to the nozzle ring and connected to a rotatable actuator ring such that rotation of the actuator ring rotates the vanes for regulating exhaust gas flow to the turbine wheel. The cartridge includes an insert having a tubular portion sealingly received into the bore of the turbine housing and having a nozzle portion extending generally radially out from one end of the tubular portion, the nozzle portion being axially spaced from the nozzle ring such that the vanes extend between the nozzle ring and the nozzle portion. A plurality of spacers are connected between the nozzle portion of the insert and the nozzle ring for securing the nozzle ring to the insert and maintaining an axial spacing between the nozzle portion of the insert and the nozzle ring.
While the cartridge design generally achieves the objective of simplifying the manufacture and assembly of the variable-vane mechanism, it presents its own challenges. In particular, it is important for the insert and the nozzle ring to be substantially coaxial or concentric with each other, but achieving such concentricity in practice can be difficult. The objective can be achieved by manufacturing all of the component parts of the cartridge with very small dimensional tolerances, but this increases the manufacturing cost considerably.
The present disclosure concerns a method for manufacturing a variable-vane mechanism for a turbine of a turbocharger as generally described above, which aids in achieving the desired concentricity between the insert and nozzle ring in a way that allows relatively large tolerances to be used for the component parts. In this manner, the manufacturing cost can be kept relatively low while still attaining a small tolerance on concentricity. In accordance with one aspect of the present disclosure, a method for manufacturing a variable-vane mechanism for a variable-geometry turbine of a turbocharger comprises the steps of:
In one embodiment, opposite ends of the spacers project beyond outer faces of the nozzle ring and the insert, and step (f) comprises welding the opposite ends of the spacers to the outer faces. Various welding techniques can be employed, including but not limited to laser welding, plasma welding, and electric (arc) welding.
In one embodiment, step (e) comprises engaging a radially inwardly facing surface of the insert with a radially outwardly facing first surface of the fixture, and engaging a radially inwardly facing surface of the nozzle ring with a radially outwardly facing second surface of the fixture. For example, the surface of the insert can comprise the radially inner surface of the tubular portion of the insert, which advantageously can be a circular cylindrical surface. The surface of the nozzle ring can comprise a circular cylindrical locating surface of the nozzle ring that is used for radially locating the nozzle ring within the turbocharger.
The method makes it possible to employ relatively low-precision processes for forming the holes in the nozzle ring and insert and for manufacturing the spacers. Although the nozzle ring and insert each must have a locating surface that is formed with relatively precise dimensions, such surfaces are easily formed, such as by machining on a lathe or the like. Accordingly, the method further simplifies the manufacture of the variable-vane cartridge with precise relative positioning of the nozzle ring and insert.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
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.
One embodiment of a portion of a turbocharger 10 to which the method of the invention can be applied is illustrated in exploded perspective views in
The turbocharger also includes a turbine housing 24 that houses the turbine wheel 22. The turbine housing defines a generally annular chamber 26 that surrounds the turbine wheel and that receives exhaust gas from the internal combustion engine for driving the turbine wheel. The exhaust gas is directed from the chamber 26 generally radially inwardly through a turbine nozzle 28 to the turbine wheel 22. As the exhaust gas flows through the passages between the blades 30 of the turbine wheel, the gas is expanded to a lower pressure, and the gas discharged from the wheel exits the turbine housing through a generally axial bore 32 therein.
The turbine nozzle 28 is a variable nozzle for varying the cross-sectional flow area and flow direction through the nozzle so as to regulate flow into the turbine wheel. The nozzle includes a plurality of vanes 34 that are circumferentially spaced about the nozzle. Each vane is affixed to a pin 36 that passes through an aperture in a generally annular nozzle ring 38 that is mounted coaxially with respect 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 affixed to an end of the pin that protrudes out 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 that is coaxial with the nozzle ring 38. An actuator (not shown) is connected to the unison ring 42 for rotating it about its axis. When the unison ring is rotated, the vane arms 40 are rotated to cause the pins 36 to rotate about their axes, thereby rotating the vanes 34 so as to vary the cross-sectional flow area and flow direction through the nozzle 28.
In the turbocharger 10, the variable vane mechanism is provided in the form of a cartridge 50 that is installable into and removable from the turbocharger as a unit. The cartridge 50 comprises the nozzle ring 38, vanes 34, pins 36, vane arms 40, and unison ring 42. The cartridge further comprises an insert 52 (shown in isolated perspective view in
A plurality of spacers 62 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 the desired axial spacing between the nozzle ring 38 and the nozzle portion 56. Each spacer 62 passes through a hole 112 (
The variable-vane cartridge 50 also comprises a generally annular support ring 64 whose radially outer periphery is captured between the turbine housing 24 and the center housing 20 when these housings are bolted together. A radially inner periphery of the support ring 64 engages a surface of the nozzle ring 38 that faces toward the insert 52. The engagement between the support ring 64 and the nozzle ring 38 preferably is along a full 360° circumference of the nozzle ring so as to substantially seal the interface between the support ring and the nozzle ring. The support ring 64 also assists the spacers 62 in restraining the nozzle ring with respect to axial movement in the direction toward the insert 52. Advantageously, the support ring 64 has a radially inner surface facing toward a radially outer surface of the nozzle ring 38, and the support ring surface is slightly greater in diameter than the nozzle ring surface such that there is a radial gap between these surfaces. This gap accommodates radial displacement of the nozzle ring surface relative to the opposing support ring surface, such as may occur through differential thermal growth or other causes.
The cartridge 50 further comprises a locator ring 80 that is captively retained between the nozzle ring 38 and the center housing 20 when the cartridge is installed onto the center housing. The locator ring 80 has a radially inner surface that engages a radially outwardly facing surface of the center housing 20 so as to establish substantial concentricity between the center housing and locator ring. The radially outer surface of the locator ring 80 engages a radially inwardly facing locating surface 39 (
The present invention is concerned with a method for achieving the desired substantially concentric relationship between the insert 52 and the nozzle ring 38. Specifically, it is desired for the radially inner surface 55 (
In accordance with the present invention, an alternative manufacturing method is employed that allows the spacers 62 and corresponding holes in the nozzle ring 38 and insert 52 to be machined to a low precision. With reference to
Thus, when the fixture 100 is inserted into the cartridge assembly 50, the nozzle ring's locating surface 39 will be substantially concentric with the inner surface 55 of the insert, as shown in
As illustrated in
However, by using the fixture 100, concentricity between the nozzle ring and insert is established independently of the holes 110, 112, via engagement of the nozzle ring and insert with the surfaces 102, 104 of the fixture as previously described. Next, as shown in
In the above-described embodiment, the fixture 100 establishes radial positioning between the nozzle ring 38 and the insert 52, but the axial positioning therebetween is established by the spacers 62, and specifically by the shoulders 62s (
With reference to
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. For example, the method as shown and described above entails first assembling the nozzle ring 38 with the insert 52 using the spacers 62, and then engaging the resulting cartridge assembly with the locating fixture 100. Alternatively, however, it is possible to (1) engage one of the nozzle ring and insert with the fixture, then (2) insert the spacers into the holes in the part on the fixture, and then (3) insert the spacers into the holes in the other of the nozzle ring and insert while engaging the other part with the fixture; steps (1) and (2) may be reversed in order as well. Furthermore, various locating surfaces of various configurations and orientations can be provided on the nozzle ring and insert for engagement with the fixture. 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. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
