Patent Application
20060067829
1. Field of the Invention (Technical Field)
The present invention relates to a high-efficiency turborcharger compressor wheel comprising titanium, a titanium alloy, or a combination thereof, the wheel having a high degree of blade backsweep and thereby providing stable operation over a wide range of flow conditions.
2. Description of Related Art
Turbochargers for gasoline and diesel internal combustion engines are known in the art for pressurizing or boosting the intake air stream, or mixed air and exhaust stream, that is routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing.
The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor wheel or impeller mounted onto an opposite end of the shaft. Thus, rotary action of the turbine also causes the air compressor wheel to spin within a compressor housing of the turbocharger that is separate from the turbine housing. The spinning action of the air compressor wheel causes intake air, or mixed intake air and exhaust, to enter the compressor housing and to be pressurized or boosted to a desired amount before it is mixed with fuel and combusted within the engine combustion chambers.
The blades of the compressor wheel are designed to draw a fluid; such as air or mixed air and exhaust, axially into the compressor housing, to boost or pressurize the fluid by the centrifugal acceleration of the wheel, and to discharge the pressurized fluid, generally in a radially outward direction. Typically, the pressurized fluid is discharged into a volute chamber forming a part of the compressor housing.
The design of the blades of the compressor wheel has a significant impact on functionality. For many applications, it is desirable that the compressor wheel provide stable operation over a wide flow range, from surge, which places a low limit on low flow operation, to choke, which places a limit on high flow operation. The need for stable operation over a wide flow range is becoming increasingly important because of designs that have been increasing engine speed, torque, and boost level, the latter being the result of more stringent emission regulations. Additionally, the design of the blades of the compressor wheel affects compressor thermodynamic efficiency, with high thermodynamic efficiency leading to lower engine fuel consumption and reduced emissions.
Compressor wheels with backswept blades are known in the art. However, conventional aluminum compressor wheels have blades with a backsweep angle of less than 40°, and typically less than approximately 20° for high pressure applications. The material stress limitations of aluminum and aluminum alloy compressor wheels limits the degree of feasible backsweep of compressor wheels that operate at high speeds. The blade thickness in aluminum and aluminum alloy blades generally increases with backsweep, given that high backsweep typically causes high stresses, particularly near the wheel outlet, or exducer, area. At any backsweep angle of greater than approximately 40°, and typically greater than approximately 20°, the required blade thickness for operation at high speeds is too thick to provide for efficient operation.
Although compressor wheels or blades made of titanium or titanium alloys are known in the art as disclosed in U.S. Pat. No. 6,588,485, No. 6,629,556, No. 6,663,347, and No. 6,754,954, the prior art does not provide for compressor wheels or blades comprising a high degree of blade backsweep greater than approximately 40°.
There is thus a need for high-speed compressor wheels with blades with a particularly high degree of backsweep, which can provide high efficiency operation over a wide flow range. It is against this need that the invention is made.
In one embodiment, the present invention provides a compressor wheel for a turbocharger, the compressor wheel made of titanium or titanium alloys and having a plurality of blades symmetrically arrayed about a hub, each blade comprising a leading edge, a shroud edge, and a trailing edge, wherein the blade angle varies from the leading edge to the trailing edge with an average blade angle at the trailing edge of at least approximately 50°. In another embodiment, the average blade angle at the trailing edge is at least approximately 55°, and in still another embodiment, at least approximately 60°. In yet another embodiment, the blade angle continuously varies from the leading edge to the trailing edge.
The plurality of blades in the compressor wheel typically includes, but is not limited to, approximately 8 to 18 blades. In another embodiment, the compressor wheel comprises a splittered wheel, wherein certain blades, such as every other blade, are partial blades, and the remaining blades are full blades.
In one embodiment, the diameter of the compressor wheel is less than approximately 90 mm and the maximum thickness of each blade is less than approximately 0.145 inches. In this and other embodiments, the compressor wheel is preferably a high pressure compressor wheel, providing a boost relative to atmospheric pressure of at least approximately 4 to 1, and preferably at least approximately 4.4 to 1. In this and other embodiments, the compressor wheel is preferably a high speed compressor wheel designed to operate at tip speeds of at least approximately 1,900 feet per second while providing acceptable mechanical stress limits to provide a suitable low cycle fatigue.
In one embodiment of the present invention, the blade angle of the shroud streamline at the leading edge is greater than the blade angle of the shroud streamline at the trailing edge. In another embodiment, the blade angle of the shroud line at one or more intermediate points between the leading edge and the trailing edge is less than the blade angle of the shroud streamline at either the leading edge or the trailing edge.
The compressor wheel and blades are preferably made of titanium (Ti), a titanium alloy, or a combination thereof. Suitable titanium alloys provide high stress limits that provide acceptable low cycle fatigue, and such alloys are known to those skilled in the art. In one embodiment, for example, the titanium alloy contains approximately 90% Ti by weight, less than approximately 10% of aluminum and/or vanadium, and less than approximately 1% each of other elements, such as, for example, iron and/or oxygen. However, other titanium alloys may be employed with this invention.
One advantage of the present invention is that with Ti or Ti alloys it is possible to design the compressor wheel to stress levels or limits that allow the compressor wheel to operate at high pressure levels or high tip speeds, or both, without mechanical stress limits. In general, this permits the blade thickness to be substantially decreased in comparison to what is effectively possible using aluminum and other metals or alloys with lower stress limits, and further permits the design and fabrication of a compressor wheel that provides for high pressure levels and high tip speeds required by modern combustion engine turbocharger systems.
Therefore, another embodiment of the present invention provides for a method to provide stable flow over a range of engine operating conditions to reach high engine speeds, torques, and boost levels, the method comprising providing a compressor wheel for a turbocharger, the compressor wheel comprising a plurality of blades made of a metal comprising titanium, the blades symmetrically arrayed about a hub, each blade comprising a leading edge, a shroud edge, and a trailing edge, and wherein an angle of each blade varies from the leading edge to the trailing edge with an average blade angle at the trailing edge of at least approximately 50°, and operating the compressor wheel to provide a stable flow over the range of engine operating conditions that is greater than a range of engine operating conditions to which blades having an average blade angle at the trailing edge of less than approximately 50°, and even less than 40° are applied. The method may further comprise operating the compressor wheel to provide a boost relative to atmospheric pressure of at least approximately 4 to 1 and may further comprise operating the compressor wheel at a tip speed of at least approximately 1,900 feet per second.
Other objects, advantages and novel features, and further 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.
The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings:
An embodiment of the present invention provides a high efficiency compressor wheel with highly backswept blades, such that the wheel provides optimal engine efficiency over a wide operating range. The compressor wheel is made of titanium, which provides for an acceptably thin blade thickness while providing a backsweep of more than 50°. The features of the compressor blade shape design improve the aerodynamic flow characteristics within the compressor wheel's flow channels. The improvement in flow characteristics provides more stable flow at low flows, and further allows the compressor to operate at higher choke flows than is possible with conventionally designed compressors, such as aluminum or aluminum alloy compressor wheels with a backsweep of less than 40°. The ability to provide stable operation at both lower and higher flows allows a compressor to provide stable flow over a wider range of engine operating conditions, thereby accommodating higher engine speeds, torques and boost levels. The improvement in internal flow characteristics also reduces efficiency losses, such as incidence loss, associated with flow separation and recirculation, which results in improved compressor efficiency.
Conventional aluminum or aluminum alloy compressor wheels with backswept blades have a backsweep of less than about 40°, and in most instances of less than about 20° for high pressure applications. Conventional aluminum or aluminum alloy compressor wheels 10 are shown in
The blades 22 of compressor wheel 20, and generally any blades of compressor wheels, have a defined thickness and a defined blade angle at each point along the blade.
With respect to blade thickness,
The blade angle at any point may be defined by the formula:
Blade Angle=r*dθ/dM
where r is the radius, d represents a first derivative, θ is the polar angle with respect to an arbitrary datum, and M is meridianal distance from the blade leading edge to the trailing edge along a the streamline.
The “backsweep” is defined as the blade angle at the trailing edge, such as at trailing edge 28. Graphically, this may be depicted by reference to
In a preferred embodiment, the invention makes use of the improved material properties of titanium or titanium alloys. Heretofore, blade shape designs which were fabricated from either cast or forged aluminum alloys were considerably constrained due to material stress limitations of aluminum. With respect to prior art titanium compressor wheels, those wheels had, for example, thinner blade thicknesses due to the higher stress limits of titanium, but were not otherwise designed or fabricated to provide improved efficiency, and did not employ the blade shape designs of the present invention. The design constraints are considerably less severe for blades fabricated from either cast or forged titanium or titanium alloys, in large part because of the considerable higher stress limits of titanium and titanium alloys, as compared to aluminum or aluminum alloys, for a given predicted life/duty cycle. Even considering the increased density of titanium compared to aluminum, key design features that can be achieved with titanium and titanium alloys include, but are not limited to, a significant increase in impeller blade backsweep or backward curvature, the use of non-radial blade elements in the leading edge and/or inducer section of the wheel, and the use of blades with reduced blade thickness. Increased backsweep reduces the wheel exit Mach number and reduces aerodynamic blade loading. These improve flow stability, delay the onset of surge, and therefore increase flow range. By providing blades which incorporate non-radial blade elements, it is possible to minimize flow losses associated with the incidence angle at the leading edge of the blades, which contributes to increased flow range and efficiency. The ability to design blades with reduced thickness also allows for larger inducer throat size and reduces mixing losses at the wheel exit, thus increasing choke flow capacity and improving efficiency.
Therefore, although
The invention is further illustrated by
As is shown in
With respect to the fabrication of the compressor wheel, the blades or the blades and other parts of the compressor wheel are preferably made of titanium (Ti), a titanium alloy, or a combination of titanium for some parts of the compressor wheel and a titanium alloy for other parts. Suitable titanium alloys provide high stress limits that provide acceptable low cycle fatigue, and such alloys are known to those skilled in the art. In one embodiment, for example, the titanium alloy contains approximately 90% Ti by weight, less than approximately 10% of aluminum and/or vanadium, and less than approximately 1% each of other elements, such as, for example, iron or oxygen. However, other titanium alloys may be employed with this invention.
Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference.
This application claims the benefit of the filing of U.S. Provisional Patent Application Ser. No. 60/612,706, entitled “Backswept Titanium Turbocharger Compressor Wheel”, filed on Sep. 24, 2004, and the specification of that application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60612706 | Sep 2004 | US |
