Turbocharger with axial turbine stage

A turbocharger is disclosed for use with an engine. The turbocharger may include a housing at least partially defining a compressor shroud and a turbine shroud. The turbine shroud may form a volute having an inlet configured to receive exhaust from an exhaust manifold of the engine in a tangential direction. The volute may also include an axial channel disposed downstream of the inlet. The turbocharger may also include a turbine wheel disposed within the turbine shroud that may be configured to receive exhaust from the axial channel. The turbocharger may also include a compressor wheel disposed within the compressor shroud, and a shaft connecting the turbine wheel to the compressor wheel. The turbocharger may also include a nozzle ring disposed within the axial channel at a location upstream of the turbine wheel.

TECHNICAL FIELD

The present disclosure is directed to a turbocharger and, more particularly, to turbocharger with an axial turbine stage.

BACKGROUND

A turbocharged air induction system includes a turbocharger that compresses air flowing into the engine, thereby forcing more air into an associated combustion chamber. The increased supply of air allows for increased fueling, which may result in increased power. A turbocharged engine typically produces more power than the same engine without turbocharging.

An exemplary turbocharger is described in U.S. Patent Publication No. 2011/0252790 to Lotterman et al. that published on Oct. 20, 2011. The '790 publication describes a turbocharger having an axial turbine with a spiraling volute passageway. The axial turbine receives a circumferential exhaust gas stream that drives a turbine wheel around an axis of rotation. The spiraling passageway accelerates the speed of the gas stream to supersonic speeds. The exhaust gas stream may have both an axial component and a circumferential component, and is ultimately released from the turbine in an axial direction.

Although the turbocharger of Lotterman et al, may provide accelerated airflow through the turbine, it may still be less than optimal. In particular, the turbocharger of Lotterman et al. directs a non-uniform and poorly guided axial flow through the turbine wheel for wide operating conditions. This poorly guided non-uniform flow may create high energy losses, reduced aerodynamic efficiencies, and increased mechanical or vibrational stresses (or strains) on the turbine during operation due to flow misalignment (high incidence) with the blades of the turbine at wide operating conditions. Also, the axial turbine stage shown in Lotterman et al. is a high reaction stage, which may lead to supersonic flows with higher aerodynamic losses (passage and secondary flows) in blade passages, as compared to low reaction stages at similar turbine stage loading conditions.

The disclosed turbocharger is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a turbocharger for use with an engine. The turbocharger may include a housing at least partially defining a compressor shroud and a turbine shroud. The turbine shroud may form a volute having an inlet configured to receive exhaust from an exhaust manifold of the engine in a tangential direction. The volute may also include an axial channel disposed downstream of the inlet. The turbocharger may also include a turbine wheel disposed within the turbine shroud that may be configured to receive exhaust from the axial channel. The turbocharger may also include a compressor wheel disposed within the compressor shroud, and a shaft connecting the turbine wheel to the compressor wheel. The turbocharger may also include a nozzle ring disposed within the axial channel at a location upstream of the turbine wheel.

In another aspect, the present disclosure is directed to a method of handling exhaust from an engine. The method may include receiving exhaust from an exhaust manifold of the engine at a volute inlet of a turbine in a tangential direction, and directing exhaust from the volute inlet through an axial channel. The method may also include directing exhaust from the axial channel through a nozzle ring, and directing exhaust from the nozzle ring through a turbine wheel to drive a compressor wheel connected to the turbine wheel by a shaft.

DETAILED DESCRIPTION

FIG. 1illustrates a power system10having a power source12, an air induction system14, and an exhaust system16. For the purposes of this disclosure, power source12is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that power source12may be any other type of combustion engine such as, for example, a two or four-stroke gasoline or gaseous fuel-powered engine. Air induction system14may be configured to direct air or a mixture of air, fuel, and exhaust (such as in an EGR driven system) into power source12for combustion. Exhaust system16may be configured to direct combustion exhaust from power source12to the atmosphere.

Power source12may include an engine block18that at least partially defines a plurality of cylinders20. A piston (not shown) may be slidably disposed within each cylinder to reciprocate between a top-dead-center position and a bottom-dead-center position, and a cylinder head (not shown) may be associated with each cylinder20. Each cylinder20, piston, and cylinder head may together at least partially define a combustion chamber. In the illustrated embodiment, power source12includes twelve cylinders20arranged in a V-configuration (i.e., a configuration having first and second banks or rows of cylinders20). However, it is contemplated that power source12may include a greater or lesser number of cylinders20and that cylinders20may be arranged in an inline configuration, in an opposing-piston configuration, or in another configuration, if desired.

Air induction system14may include, among other things, at least one compressor28that may embody a fixed geometry compressor, a variable geometry compressor, or any other type of compressor configured to receive air and compress the air to a desired pressure level. Compressor28may direct air to one or more intake manifolds30associated with power source12. It should be noted that air induction system14may include multiple compressors28arranged in a serial configuration, a parallel configuration, or combination serial/parallel configuration, as desired.

Exhaust system16may include, among other things, an exhaust manifold17connected to one or both of the banks of cylinders20. Exhaust system16may also include at least one turbine32driven by the exhaust from exhaust manifold17to rotate the compressor(s) of air induction system14. It should be noted that compressor28and turbine32may together form a turbocharger34. Turbine32may embody a fixed geometry turbine, a variable geometry turbine, or any other type of turbine configured to receive exhaust and convert potential energy in the exhaust to a mechanical rotation. After exiting turbine32, the exhaust may be discharged to the atmosphere through an aftertreatment system36that may include, for example, a hydrocarbon closer, a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and/or any other treatment device known in the art, if desired. It should be noted that exhaust system16may include multiple turbines32arranged in a serial configuration, a parallel configuration, or combination serial/parallel configuration.

As illustrated inFIG. 2, turbocharger34may include a center housing35at least partially defining compressor and turbine shrouds38,40configured to house corresponding compressor and turbine wheels42,44that are connected to each other via a common shaft46. Compressor shroud38may include an axially-oriented inlet48located at a first axial end49of turbocharger34, and a tangentially-oriented outlet volute50located between first axial end49and a second axial end51of turbocharger34. Turbine shroud40may include a volute52located between outlet volute50and second axial end51of turbocharger34. Turbine shroud40may be configured to receive exhaust flow in a tangential direction T at a volute inlet54(shown only inFIG. 3). Volute52may direct the exhaust flow in three directions—tangential (around a rotation axis X), radial (along a radius of the volute), and axial (along rotation axis X)—toward and through an axial channel55. Axial channel55may be disposed between an annular tongue56and a coaxial inner annular surface58. A nozzle ring59may be disposed within axial channel55and be configured to accelerate exhaust gas flowing through axial channel55.

For purposes of this disclosure, a height H of axial channel55may refer to a radial distance between annular tongue56and inner annular surface58. A tongue length may refer to a distance between an end of tongue56and nozzle ring59along rotation axis X. A tongue-to-height ratio TR may be defined as the ratio of tongue length L to height H (TR=L/H). In the disclosed embodiment, TR may be about 0.8 to 1.6.

As compressor wheel42is rotated, air may be drawn axially in to turbocharger34via inlet48, toward a center of compressor wheel42. Blades60of compressor wheel42may then push the air tangentially outward, via outlet volute50, in a spiraling fashion into an air induction manifold of power system10(referring toFIG. 1). Similarly, as exhaust from exhaust system16is directed tangentially, radially, and axially inward toward turbine wheel44, the exhaust may push against blades62of turbine wheel44, causing turbine wheel44to rotate and drive compressor wheel42via shaft46. After passing through turbine wheel44, the exhaust may exit axially outward through a turbine outlet64located at second axial end51of turbocharger34into the atmosphere via aftertreatment system36(shown only inFIG. 1). Compressor and turbine wheels42,44may embody conventional wheels, with any number and configuration of blades60,62radially disposed on corresponding wheel bases.

Referring toFIGS. 2 and 3, volute52may have a generally spiral shape and an interior surface68. A diameter of interior surface68may be larger than a diameter of annular tongue56at most portions of volute52. The difference in the diameters of interior surface68and annular tongue56may be greatest at locations closest to volute inlet54, and gradually decrease so as to converge to about zero as interior surface68winds inward tangentially with respect to rotation axis X. Annular tongue56and interior surface68may converge at a curved transition portion72. Volute52may have distinct cross-sectional areas A and corresponding radii R (referring toFIG. 2) at different azimuth angles about the turbine wheel centerline (rotation axis X). An area-to-radius ratio (A/R)imay be about 100-140 mm at an inlet flange73(shown only inFIG. 3) of the volute52. The area-to-radius ratio (A/R) may expand to (A/R)0(about 110-150 mm) at a position corresponding to a 0 degree azimuth angle. The position corresponding to the 0 degree azimuth angle may represent a plane that is parallel to a face of inlet flange73, and also intersects a center74of volute52that is disposed along rotation axis X. The area-to-radius ratio (A/R) may decrease linearly as the azimuth angle is increased about rotation axis X. That is, the area-to-radius ratio (A/R) may decrease as volute52winds tangentially inward about rotation axis X until a final (A/R)360(about 10-40 mm) is reached at a position corresponding to a 360 degree azimuth angle that substantially converges with the 0 degree azimuth angle. The control of the area-to-radius ratio (A/R) may allow for a uniform flow into nozzle ring59. Additionally, volute52may ingest purely tangential flow, and convert it to a flow additionally having axial and radial components, but maintain an about 45-75 degree tangential component through axial channel55upstream of nozzle ring59.

Referring toFIG. 3, volute52, nozzle ring59, and turbine wheel44may be located coaxially along rotation axis X. Volute52and nozzle ring59may be stationary, while turbine wheel44may rotate with respect to rotation axis X. Nozzle ring59may be generally ring-shaped and may include an inner annular hub76and an outer annular flange78. A plurality of three-dimensional vanes80may be disposed between annular hub76and outer annular flange78to direct and accelerate exhaust flow from volute52toward blades62of turbine wheel44. Each vane80may include a trailing edge82located close to turbine wheel44, and a leading edge84located away from turbine wheel44. Turbine wheel44may be generally disc-shaped and include an annular hub86. Blades62may extend outward in three dimensions from annular hub86. Each blade62may have a trailing edge88that is close to turbine outlet64, and a leading edge90that is away from turbine outlet64.

As shown inFIG. 4, vane chord length Lvmay refer to a straight line distance between trailing and leading edges82,84at any radial location. A vane spacing Svmay refer to a straight line distance between adjacent trailing edges82of vanes80(e.g., a spacing of vanes80may refer to a straight line distance between trailing edges82of adjacent vanes80) at any radial location. A vane solidity ratio SRvmay be defined as a ratio of the chord length Lvto the spacing Sv(SRv=Lv/Sv) at any radial location. A blade chord length Lbmay refer to a straight line distance between trailing and leading edges88,90at any radial location. A blade spacing Sbmay refer to a straight line distance between adjacent trailing edges88of blades62(e.g., a spacing of blades62may refer to a straight line distance between trailing edges88of adjacent blades62) at any radial location. A blade solidity ratio SRbmay be defined as a ratio of the chord length Lbto the spacing Sb(SRb=Lb/Sb) at any radial location. Vane inlet and outlet angles αvi, αvomay refer to angles between tangents to a camber line of vane80at leading and trailing edges84,82, and a turbine axial direction. The vane turning angle Δα may be defined as a difference between inlet vane angle αviand outlet vane angle αvo(Δα−αvi−αvo). The angle of vanes80with respect to the axial direction may increase from leading edge84toward trailing edge82. Blade inlet and outlet angles θbi, θbomay refer to angles between tangents to a camber line of blades62at leading and trailing edges90,88, and the turbine axial direction. The blade turning angle Δθ may be defined as a difference between inlet blade angle θbiand outlet blade angle θbo(Δθ=θbi−θbo).

The disclosed geometries of nozzle ring59and turbine wheel44(including vanes80and blades62) have been selected to take advantage of the tangential flow and flow uniformity exiting volute50. For example, because of the significant tangential flow entering nozzle ring59, vanes80and blades62may be designed to have a low solidity ratio. In this arrangement, SRvmay be about 0.9 to 1.35 at a vane midspan, while SRbmay be about 1.1 to 1.5 at a blade midspan. A maximum vane turning angle |Δα| may be about 60 degrees at annular hub76, while a maximum blade turning angle |Δθ| may be about 135 degrees at annular hub86. That is, vane turning angle |Δα| may be equal to or lesser than about 60 degrees at annular hub76, while blade turning angle |Δθ| may be equal to or lesser than about 135 degrees at annular hub86. In this arrangement, nozzle ring59may have a hub-to-flange ratio (i.e., ratio of inner annular hub76to outer annular flange78) of about 0.55-0.77. Similarly, turbine wheel44may have a hub-to-tip ratio (i.e., ratio of annular hub86to an outer end of blades62) of about 0.55-0.77. Referring toFIGS. 2 and 4, a centroid92of volute52may be radially and axially off-center from leading edge84of vane80. This off-centering of the centroid92may provide enough space to improve burst-containment features of turbine shroud40.

A degree of reaction of a turbine stage may be defined as the ratio of energy transfer by the change in static head to the total energy transfer in turbine wheel44. A turbine stage of turbine32may have a degree of reaction of about 0.5 at the design point (peak performance) operating condition.

INDUSTRIAL APPLICABILITY

The disclosed turbocharger may be implemented into any power system application where charged air induction is utilized. Specifically, use of volute52to provide a uniform tangential flow through nozzle ring59may result in overall lower aerodynamic losses and, thus, improved performance and efficiency of turbine32. The uniform and well guided flow exiting volute52and nozzle ring59may result in more uniform loading of nozzle ring59and turbine wheel44at wide operating conditions. This may help to reduce cyclic loading on turbine wheel44, extending the useful life of turbine wheel44at wide operating conditions. Because exhaust flow may be substantially uniform and well guided as to each blade62, mechanical and vibrational losses attributable to misaligned exhaust flow and turbine blade geometry may be significantly reduced. The tangential flow exiting volute52and work split up by nozzle ring59and turbine wheel44may improve turbine stage reaction, and lead to lower aerodynamic losses (such as passage, supersonic, and secondary flows) in blade passages as compared to higher reaction stages at similar turbine stage loading conditions. To accommodate the significant tangential flow within axial channel55, nozzle ring59and turbine wheel44may have low solidity and, thus, fewer vanes and blades. The reduction in vanes and blades may equate to a reduction in material costs. Further, as exhaust flow enters volute50between axial ends of turbocharger34, the thrust loads of compressor28and turbine32may oppose each other. As a result, the net force may be reduced on thrust bearings of the turbocharger, reducing mechanical losses.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed turbocharger. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed turbocharger. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.