Turbine efficiency tailoring

A turbomachinery apparatus. A turbine is provided with a retainer having a bore step element for turbine wheel retention, and with an aperture manifesting a tailored diameter less than the trim diameter of the turbine, thereby to permit customization of the turbine efficiency characteristic. Various configurations of turbine retainers, with tailored diameter apertures, are disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates generally to turbomachinery, particularly turbocharged internal combustion engines, and specifically relates to a turbine housing for improving the turbine efficiency characteristic.

2. Background Art

It is known in the general art of internal combustion engines to provide some system of turbocharging, whereby a turbine harnesses energy from exhaust gases to power a compressor. The compressor is then used to increase engine performance, typically by boosting the pressure of air supplied to the engine.

Nearly as important as engine performance is the need for cleaner exhausts. Most internal combustion engines are subject to regulations governing pollutant levels in engine emissions. “Stationary sources” such as internal combustion engine powered generators and the like, as well as motor vehicles, are required to maintain emissions of certain pollutants, such as CO and NOX, below legal limits. Pollution control, however, ideally is accomplished while compromising engine performance as little as possible.

One mode of reducing the emissions of internal combustion engines—regardless of whether the engine is turbocharged, but frequently when it is—is through exhaust gas recirculation (EGR). EGR involves the return to the engine's intake manifold of some portion of the engine exhaust. Exhaust gases are diverted from the exhaust manifold through a duct or conduit for delivery to the intake manifold, thereby allowing exhaust to be introduced to the combustion cycle, so that oxygen content is reduced, which in turn reduces the high combustion temperature that contributes to excessive NOXformation.

With the introduction of EGR systems on, for example, heavy-duty diesel engines, the desired turbine efficiency characteristic does not conform to conventional turbomachinery performance. Simply accepting classical turbomachinery turbine efficiency characteristic when using applicants' VNT™ brand of variable nozzle turbine turbocharger EGR System causes several effects, including: (1) Unacceptably high fuel consumption at certain engine operating speeds; (2) Unacceptably high turbocharger speed (i.e., turbocharger speeds which exceed acceptable limits using known production materials and processes); and (3) An inability to drive the EGR at all desires engine operating points.

Further, with the use of EGR systems in use on a heavy-duty diesel engine, the turbocharger “match” to the engine results in unusual turbocharger turbine wheel matching. In some instances, for example, the traditional or conventional wheel contour is removed from the design. This unusual machining of the turbine wheel may result in an increased difficulty in retaining the turbine wheel in the event the turbine wheel separates from the turbocharger shaft. In such an event, the turbine wheel will exit the turbine housing gas outlet at a substantially higher velocity and energy than in a similar circumstance with current turbocharger assembly designs.

Against the foregoing background, the present invention was developed. The turbine housing is modified to retain the wheel and to tailor the turbocharger turbine efficiency, thus addressing the deficiencies noted above. The scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUT THE INVENTION)

The present invention relates to turbines, particularly but not necessarily turbines used in turbocharged engines. The apparatus of the invention may find beneficial use in connection with Exhaust Gas Recirculation (EGR) systems used with diesel-fueled power plants, including but not limited to the engines of large motor vehicles. By modifying according to this invention the turbine wheel retainment design, the turbine efficiency characteristic can be tailored to meet specialized needs, and turbine wheel retention is promoted. Accordingly, the present invention ameliorates wheel retention and turbine efficiency characteristic problems attributable to the use of EGR systems in conjunction with turbines. The problems are addressed with inventive modification of the turbine housing. The present invention, as further characterized and disclosed hereafter, includes such modifications.

As known in the art, a turbine work is directly proportional to turbine efficiency, mass flow, ratio of pressure across the turbine and inlet temperature. Shaft, or rotor speed is the product of turbine work applied to a directly driven compressor. VNT turbine rotor speed can be altered by tailoring the turbine's efficiency at the turbine wheel exit via the exit configuration shape and size. The impact of the change in efficiency is used to match compressor and VNT characteristics to meet engine air system requirements. The sizing of the exit feature may be limited by resulting engine performance parameters in addition to turbomachinery speed control, i.e., fuel consumption or possibly engine pressure ratios.

By defining a shaped and sized step-bore in the turbine housing, at the turbine wheel exit, the turbine efficiency characteristic can be selectively tailored to improve turbine efficiency behavior, thereby enhancing VNT turbocharger EGR systems performance. Succinctly stated, the provision of a step-bore reduces the turbine efficiency, resulting in a favorable increase in turbine inlet pressure. The increased inlet pressure promotes the flow of exhaust gas from the engine's exhaust manifold into the engine's intake manifold. This beneficial turbocharger behavior is accomplished, according to the invention, at a reduced turbocharger speed than would be attainable with a typical turbomachinery turbine efficiency characteristic. Despite the comparatively reduced turbocharger speed, performance is not compromised; so the inventive apparatus may be fashioned from currently existing production materials, and known processes for VNT turbocharger systems are applicable. Furthermore, lowered turbine efficiency provides the capacity to drive a larger quantity of EGR flow into the engine intake manifold than would be possible with conventional turbine housing designs.

Attention is invited toFIG. 1, showing one embodiment of the apparatus of the invention. The turbine10features a turbine housing12that is manufactured generally in accordance with the known art, except as further explained hereinafter. The turbine housing12substantially surrounds and defines a turbine bore14for receiving a turbine wheel (not shown inFIG. 1) rotatable upon a turbine shaft according generally to convention. In one possible embodiment, the inlet side of the housing12may be provided with a port16permitting the placement of the turbine wheel into the bore14during turbine assembly. After the installation of the turbine wheel, the port16is closed and secured by, for example, the bolted attachment of a turbocharger center housing rotating assembly (not shown).

With continued reference toFIG. 1, it is noted that the turbine housing12features and defines a turbine tip diameter DTIPthat ordinarily corresponds approximately to the maximum tip diameter of the turbine wheel, according with known art. Also defined is the turbine housing trim diameter DTRIMwhich varies among different turbine housing models, but corresponds generally to a functional diameter of the turbine wheel, there being a very close clearance between the circumference of the wheel and the housing trim wall17defining the trim diameter DTRIM. In some embodiments of the present invention, the turbine tip diameter DTIPmay be only slightly larger than the trim diameter DTRIM.

“Downstream” within the bore12is the turbine diffuser or exducer18, a conduit via which gas is exhausted from the turbine assembly. The diameter DEXis important in making an appropriate mechanical joint for the coupling and size required for the exhaust system. Notably, the invention has practical use in turbines employing generally cylindrical exducers, such as depicted inFIGS. 1,4,5,6, and8, as well as turbines having flared or conical exducers, such as those seen inFIGS. 3 and 7.

Implementation of turbine efficiency tailoring is accomplished by, among other things, affecting the gas flow into and through the exducer18. Referring toFIG. 1, this may be achieved by the provision of a “step” in the bore14, whereby the diameter of the exducer18is abruptly reduced for an abbreviated portion of its axial length. For example, in the embodiment ofFIG. 1, there is provided a separately produced step bore ring20that is insertable through the exducer18and into the bore14. As seen inFIGS. 2A and 2B, the step bore ring20is a rigid annulus having an exterior diameter substantially equal to the exducer diameter DEXso as to be snuggly received into the throat of the exducer18, concentrically about the axis of the bore14, as seen inFIG. 1. The step bore ring20may be there fixed in position by threaded bolts21or other suitable fastening means or integrated into the casting of the turbine housing.

Notably, the step bore ring20defines an aperture22therein, preferably concentric with the ring's outer circumference, having a selected tailored diameter d (FIGS. 2A and 2B). Tailored diameter d is preferably and nearly always less than the exducer diameter DEX, and is smaller than the turbine housing trim diameter DTRIM. The step defined in the bore14by the step bore ring20thus is configured so that the normal smooth flow of the gas exiting the turbine wheel is disturbed, by constricted passage through the aperture22of the ring20, near the turbine wheel exit. The tailored diameter d is between about 80 percent and 100 percent of the DTRIM. The precise ratio between d and DTRIMis selected and determined to obtain the desired tailoring. The ratio between the tailored diameter d and the housing trim diameter DTRIMaffects the turbine efficiency characteristic. The performance tailoring of the turbine stage is associated with the impact of the downstream orifice tailored diameter d on DTRIM(inFIG. 1, for example).

The “step bore” resulting from the aperture22can be tailored such that the turbine efficiency can be matched to provide a similar efficiency characteristic to that which is desirable for VNT brand turbocharger EGR systems

FIG. 9is a graph showing relative impact of sizing of a fixed configuration d diameter with respect to a fixed trim diameter in terms of turbine pressure ratio and turbine efficiency. Modulating turbine efficiency via fixed d diameter sizing for a VNT turbine stage is a means by which turbomachinery speed can be modified or matched to meet a specific set of engine conditions. The efficiency impact of the orifice diameter varies with size and operating pressure ratio. Performance characteristics of various configuration d diameter shapes will be variable based on the basic shape of the orifice.

Reference is made toFIG. 3, illustrating a preferred embodiment of the invention. The embodiment ofFIG. 3is very similar in many respects to the embodiment ofFIG. 1, except that the step bore ring24is cast in place integrally with the housing12. A turbine wheel30is shown mounted in the turbine bore14. In this “fixed geometry” embodiment of the invention, a ring24cast integrally with the housing12provides the step25in the bore. The ring24thus is a permanent extension of the cast housing, and is integrally associated therewith at the time of housing manufacture. This cast feature is generally annular, but molded within the housing bore14as shown in the figure. The circular aperture in cast ring24defines the tailored diameter d. It is noted inFIG. 3that the exducer18is not cylindrical, but is a conical diffuser with an ever-increasing exducer diameter proceeding toward the turbine exhaust. The addition of the conical diffuser assists in fine-tuning the tailoring of the turbine performance.

In the embodiment ofFIG. 3, the bore step feature is provided by the ring24preferably cast integrally with the housing12. Alternatively, the retainer ring24may be manufactured separately, and then inserted into and secured within the turbine bore14, as suggested byFIGS. 1,2A and2B, and4. The bore step25is defined by the edge of the aperture in the ring24, which aperture has diameter d. The diameter d is the tailored diameter selected for turbine efficiency, and in any event is less than the trim diameter DTRIM. The turbine gases, of course, flow through the aperture in the ring24, but the aperture is too small to admit passage of the turbine wheel30.

FIG. 5illustrates how an insertable retainer ring24, similar to the embodiment seen inFIG. 4, may offer apparatus adaptability. An insertable ring24may be disposed within the turbine bore and secured at one or more different axial locations.FIG. 5shows the retainer ring24secured (for example with bolts directed radially through the ring and into the housing) at an axially forward position. However, since the retainer ring24is removably insertable, its axial position also is selectively adjustable. As suggested by the phantom lines inFIG. 5, the retainer ring can be disengaged from an axially forward position, slipped to any second, rearward, location, and there again temporarily fixed in place. This adjustment, which may be incrementally or infinitely variable depending upon the mode of connecting the ring24to the housing, permits the retainment and tailoring features of a single turbine apparatus10to be customized to particular uses. By this adjustability of the ring location, the axial position, and effect, of the reduced tailored diameter d defined by the ring can be regulated and selected for optimum turbine efficiency. The location of the retainer step25likewise is adjustable (e.g., to accommodate a turbine wheel30of different axial length).

The axial movement of the ring may be guided by two or more circumferentially arrayed longitudinal guides29,29′, which may be integral extensions of the housing12protruding from the turbine bore walls. Guides29,29′ also prevent radial shifting of the ring24about the central axis of the apparatus. Removably insertable retainer rings24can be removed and re-installed for maintenance or replacement.

Still another alternative embodiment of the invention is shown inFIGS. 6 and 6A. Retainer and tailoring advantages are provided by a plurality of profiled protrusions33,33′ cast integrally with the housing12. The profiled protrusions could be variably rotated about an axis resulting in a variable tailoring of the turbine efficiency. The radial array of convex protrusions33,33′ extend radially inward into the throat of the bore14, and preferably are uniformly spaced around the bore's circumferential perimeter, as seen inFIG. 6A. As indicated in the figures, especiallyFIG. 6A, effective tailored diameter d is defined approximately by the average “height” of diametrically opposite protrusions. The protrusions33,33′ may have any of a variety of profiles or shapes. One preferred profile is depicted inFIGS. 6 and 6A, where each protrusion has a somewhat oval or “tear drop” footprint and an airfoil axial profile. Any of wide variety of shapes and profiles are suitable to the function of the invention, although smooth, aerodynamic profiles such as those seen in the figures are preferred.

Alternatively, the protrusions33,33′ may be more rectilinear or vane-like in form than those shown.FIGS. 7 and 7Adepict an alternative embodiment with a plurality of uniformly spaced rectilinear protrusions33,33′ (eight protrusions in the embodiment ofFIGS. 7 and 7A.) As seen in the figures, the protrusions may have, for example, a low axial profile, each protrusion33featuring a quadrilateral axial section with a leading “face” perpendicular to the turbine axis, and a trailing face defined by an acute angle that allows the trailing face to merge smoothly into the inside wall of the exducer18. Again, the effective tailored diameter d is determined using the approximate average radial extension of the protrusions.

In any embodiment featuring an arrayed plurality of protrusions33,33′, the longitudinal axes of the protrusions, while preferably being mutually parallel, may be canted or angled in relation to the axis of the turbine, to foster “de-swirling” of the exhaust gas as it exits the turbine wheel30. The number of protrusions33,33′ also is selectable, and may number, for example, between three and eight (eight in the embodiments ofFIGS. 6 and 7).

Yet another embodiment of the invention is shown inFIGS. 8 and 8A. This embodiment of the invention permits the use of an adjustable bore step within a conical, as opposed to cylindrical, exducer. In this embodiment, a segmented ring27has a variable diameter, so as to expand or contract according to need corresponding to the oblique annular face of the conical exducer18. The ring segments31,31′ can vary in number, the plurality numbering at least three (four shown inFIGS. 8 and 8A) and up, for example, eight or ten.

The embodiment ofFIGS. 8 and 8Athus shares some of the features and advantages of the embodiments seen inFIG. 5, except that in addition to being selectively adjustable in axial position within the housing12, the effective diameter of the step ring27can be adjusted, as can the effective tailored diameter d defined by the aperture in the ring27. To increase the tailored diameter d, the uniformly spaced segments31,31′ are shifted radially outward, thus increasing the size of circumferential gaps that separate adjacent segments. Likewise, when the ring27is moved to a forward position in the exducer, the diameter d is reduced by reducing the gaps between adjacent segments of the ring27.

The ring segments31,31′ manifest wedge-shaped longitudinal profiles, as seen inFIG. 8A, and thus can shift simultaneously axially and radially by riding along the annular chamfer35in the bore. The ring segments are arrayed so as to always define a segmented annulus, and secured at one or more different axial locations.FIG. 8shows the segments of the retainer ring27secured (for example with bolts directed radially through the ring and into the housing) at an axially forward position. However, since the retainer ring27is movably insertable, its axial position also is selectively adjustable. As suggested by the phantom lines inFIG. 8, the retainer ring27can be disengaged from an axially forward position, slipped to any second, rearward, location, and there again temporarily fixed in place. Due to the changed diameter of the exducer18in which the ring27is disposed, the ring27tailored diameter d likewise is modified. This adjustment permits the retainment and tailoring features of a single turbine apparatus10to be customized to particular uses. By this adjustability of the ring location, the axial position and size, and effect, of the reduced tailored diameter d defined by the ring can be regulated and selected for optimum turbine efficiency. The location of the retainer step25likewise is adjustable (e.g., to accommodate a turbine wheel30of different axial length).

As with the embodiment ofFIG. 5, the axial movement of the ring27may be guided by two or more circumferentially arrayed longitudinal guides (not shown inFIG. 8) which may be integral extensions of the housing12protruding from the turbine bore walls.

The apparatus of the invention provides, therefore, a step bore25in all embodiments that serves to retain the turbine wheel30against improper displacement toward the rear of the turbine housing12. The retainer, typically an annular ring with or without customized protrusions, permits a tailored diameter d in relation to the trim diameter TTRIMto optimize the turbine efficiency characteristic.

By designing, shaping and sizing a “step bore” in the turbine housing, near the turbine wheel exit, the turbine efficiency characteristic can be modified or tailored, resulting in a turbine efficiency behavior which is more favorable to the performance of the variable nozzle turbine turbocharger EGR system according to the present invention. In effect, the step bore25reduces the turbine efficiency, which results in an increased turbine inlet pressure, which promotes the flow of exhaust gas from the engine's exhaust manifold into the engine intake manifold. This behavior is accomplished at a lower turbocharger speed than would be achievable with an ordinary turbomachinery turbine efficiency characteristic.