Patent Application
20070122267
The present invention relates generally to exhaust gas-driven turbochargers, and relates more particularly to exhaust gas-driven turbochargers having a variable turbine nozzle of the axially sliding piston type for varying the size of the nozzle that leads into the turbine wheel so as to regulate flow into the turbine wheel.
Regulation of the exhaust gas flow through the turbine of an exhaust gas-driven turbocharger provides known operational advantages in terms of improved ability to control the amount of boost delivered by the turbocharger to the associated internal combustion engine. The regulation of exhaust gas flow is accomplished by incorporating variable geometry into the nozzle that leads into the turbine wheel. By varying the size of the nozzle flow area, the flow into the turbine wheel can be regulated, thereby regulating the overall boost provided by the turbocharger's compressor.
Variable-geometry nozzles for turbochargers generally fall into two main categories: variable-vane nozzles, and sliding-piston nozzles. Vanes are often included in the turbine nozzle for directing the exhaust gas into the turbine in an advantageous direction. Typically a row of circumferentially spaced vanes extend axially across the nozzle. Exhaust gas from a chamber surrounding the turbine wheel flows generally radially inwardly through passages between the vanes, and the vanes turn the flow to direct the flow in a desired direction into the turbine wheel. In a variable-vane nozzle, the vanes are rotatable about their axes to vary the angle at which the vanes are set, thereby varying the flow area of the passages between the vanes.
In the sliding-piston type of nozzle, the nozzle may also include vanes, but the vanes are fixed in position. Variation of the nozzle flow area is accomplished by an axially sliding piston that slides in a bore in the turbine housing. The piston is tubular and is located just radially inwardly of the nozzle. Axial movement of the piston is effective to vary the axial extent of the nozzle leading into the turbine wheel, thus varying the “throat area” at the turbine wheel inlet. When vanes are included in the nozzle, the piston can slide adjacent to radially inner (i.e., trailing) edges of the vanes; alternatively, the piston and vanes can overlap in the radial direction and the piston can include slots for receiving at least a portion of the vanes as the piston is slid axially to adjust the nozzle.
There are times during the operation of a turbocharger when it is desired to pass as much flow through the turbine housing as possible. For example, it may be desirable to minimize the backpressure felt by the engine during certain operating conditions, and this is accomplished by reducing the flow restriction downstream of the engine as much as possible. In a sliding piston-type variable turbine nozzle, the downstream flow restriction is reduced by fully opening the piston to maximize the throat area at the turbine wheel inlet. However, in some cases, even fully opening the piston may not allow as much flow to pass as may be desired.
The present invention addresses the above needs and achieves other advantages, by providing a turbine housing assembly for a variable-nozzle turbocharger, in which an integrated bypass feature is arranged in the turbine housing assembly for allowing a proportion of exhaust gas to pass from the turbine housing chamber through a bypass passage without passing through the turbine wheel or the bore in the turbine housing. In one embodiment of the invention, the turbine housing assembly includes a tubular piston disposed in the bore of the turbine housing and axially slidable between a closed position and an open position for blocking the nozzle by an amount dependent on axial positioning of the piston so as to regulate flow into the turbine wheel. A bypass control member is disposed in the turbine housing and is slidable between a no-bypass position closing the bypass passage and a bypass position opening the bypass passage. The bypass member preferably is biased by a biasing device toward the no-bypass position. The piston is structured and arranged to slide relative to the bypass control member for a part of a full stroke of the piston from the closed position toward the open position thereof, and then to engage the bypass control member and cause the bypass control member to slide together with the piston as the piston further slides toward the open position thereof such that the bypass control member is moved toward the bypass position.
The bypass control member in one embodiment is generally ring-shaped or annular and concentrically surrounds the piston, and the piston includes a radially outwardly extending portion that is spaced from the bypass control member when the piston is in the closed position and that engages the bypass control member when the piston is slid toward the open position to cause the bypass control member to slide with the piston. The radially outwardly extending portion of the piston can comprise a flange extending from an upstream end of the piston.
The turbine housing in one embodiment defines a guide space adjacent the bypass passage and the bypass control member includes a cylindrical portion that slides within the guide space. The bypass control member includes a flange portion extending radially inwardly from the cylindrical portion and positioned to be engaged by the radially outwardly extending portion of the piston. A compression spring can be disposed between the flange portion of the bypass control device and a portion of the turbine housing for biasing the bypass control member toward the no-bypass position.
Actuation of the piston can be accomplished in various ways, such as by mechanical linkage connected with the piston and operated by a suitable actuator. Alternatively, in one embodiment of the invention, the piston includes a cylindrical portion and the turbine housing defines an annular space that receives the cylindrical portion of the piston for guiding the piston's axial sliding movement. Seals for sealing the piston are disposed between radially outer and radially inner surfaces of the cylindrical portion of the piston and corresponding opposing surfaces of the annular space. The turbine housing defines a fluid passage extending through the turbine housing and connected with the annular space for communicating fluid to the annular space such that a fluid pressure differential applied through the fluid passage to the annular space causes a force to be exerted on the piston to move the piston axially relative to the turbine housing. A compression spring can be arranged in the turbine housing for biasing the piston in opposition to the fluid pressure differential.
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.
The turbine housing 32 defines an axial bore 38 in which the turbine wheel resides at an upstream end of the bore. The exhaust gas that has flowed through the wheel is discharged through a downstream end of the bore 38.
A piston 40 is mounted in the bore 38 of the turbine housing such that the piston is axially slidable relative to the turbine housing. The piston is tubular in configuration. The piston is disposed between the nozzle 36 and the turbine wheel, and is movable to various axial positions for regulating the size of the nozzle flow area through which exhaust gas can flow from the chamber 34 to the turbine wheel. The piston 40 is received within the bore 38 and is slidable relative to the turbine housing. An array of circumferentially spaced vanes 42 is mounted on a heat shield 44 mounted between the turbine housing 32 and center housing 22 proximate the turbine wheel. The vanes 42 are positioned to extend partway across the axial extent of the nozzle 36. In a closed position of the piston 40, an upstream end of the piston is abutting or closely proximate to the vanes 42 as shown in
The turbine housing assembly 20 includes an integrated bypass for allowing some exhaust gas to bypass the turbine wheel and turbine housing bore 38. More particularly, the turbine housing defines a bypass passage 50 for allowing a portion of exhaust gas to flow from the chamber 34 through the bypass passage 50 without passing through the turbine wheel or turbine housing bore. A bypass control member 52 is disposed in the turbine housing and is slidable between a no-bypass position closing the bypass passage (
The piston 40 has a radially outwardly projecting flange 56 at its upstream end. The flange 56 is arranged to abut the bypass control member 52 when the piston 40 has moved to a partially open position, as depicted in
The piston 40 is able to move even farther in the downstream direction. With further movement of the piston 40 toward its fully open position, the bypass control member 52 begins to move along with the piston 40 such that the bypass passage 50 begins to be opened.
The piston can be actuated in various ways. For example, a mechanical linkage (not shown) can be connected with the piston and operated by a suitable actuator (not shown). Alternatively, in one embodiment of the invention as illustrated, the actuation of the piston 40 in the opening direction is accomplished using fluid pressure differential that acts on the piston. More specifically, the piston 40 is axially slidable within an annular cavity or guide space 60 defined by the turbine housing. The piston is sealed within the guide space 60 by a sealing arrangement. In one embodiment, the sealing arrangement can comprise an outer seal 62 arranged between a radially outer surface of the piston and a radially outer wall of the guide space 60, and an inner seal 64 arranged between a radially inner surface of the piston and a radially inner wall of the guide space 60. A fluid passage 66 is defined in the turbine housing and connects with the portion of the guide space 60 sealed by the seals 62, 64. Exertion of a differential fluid pressure through the passage 66 causes fluid pressure to act on the piston 40 for axially moving the piston. In the illustrated embodiment, exertion of a vacuum through the passage 66 moves the piston toward the open position.
A compression spring 68 is arranged to exert a force on the piston 40 tending to move the position to its closed position. The spring 68 is compressed between an upstream-facing surface 70 of the turbine housing 32 and a radially outward projection 72 on the piston. The projection 72 can comprise a snap ring mounted in a groove in the outer surface of the piston. The spring 68 thus acts on the piston in an opposite direction to that of the fluid pressure when vacuum is exerted on the space 60. When enough vacuum is exerted to overcome the spring force on the piston, the piston moves toward the open position. Various partially open piston positions can be achieved by suitably regulating the degree of vacuum exerted on the space 60 so that the spring force and fluid force balance each other at different points along the full piston stroke.
It is also possible to configure the turbine housing and piston so that a fluid pressure differential causes the piston to close, while a compression spring urges the piston toward the open position.
In operation, at low engine speeds and low throttle settings the piston 40 typically is in its closed position as in
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. 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.
