Patent Application
20190178151
The present disclosure relates to centrifugal compressors, such as used in turbochargers, and more particularly relates to centrifugal compressors in which the effective inlet area or diameter can be adjusted for different operating conditions.
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 air intake of the engine 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 yet another 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 an 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.
Turbochargers typically employ a compressor wheel of the centrifugal (also known as “radial”) type because centrifugal compressors can achieve relatively high pressure ratios in a compact arrangement. Intake air for the compressor is received in a generally axial direction at an inducer portion of the centrifugal compressor wheel and is discharged in a generally radial direction at an exducer portion of the wheel. The compressed air from the wheel is delivered to a volute, and from the volute the air is supplied to the intake of an internal combustion engine.
The operating range of the compressor is an important aspect of the overall performance of the turbocharger. The operating range is generally delimited by a surge line and a choke line on an operating map for the compressor. The compressor map is typically presented as pressure ratio (discharge pressure Pout divided by inlet pressure Pin) on the vertical axis, versus corrected mass flow rate on the horizontal axis. The choke line on the compressor map is located at high flow rates and represents the locus of maximum mass-flow-rate points over a range of pressure ratios; that is, for a given point on the choke line, it is not possible to increase the flow rate while maintaining the same pressure ratio because a choked-flow condition occurs in the compressor.
The surge line is located at low flow rates and represents the locus of minimum mass-flow-rate points without surge, over a range of pressure ratios; that is, for a given point on the surge line, reducing the flow rate without changing the pressure ratio, or increasing the pressure ratio without changing the flow rate, would lead to surge occurring. Surge is a flow instability that typically occurs when the compressor blade incidence angles become so large that substantial flow separation arises on the compressor blades. Pressure fluctuation and flow reversal can happen during surge.
In a turbocharger for an internal combustion engine, compressor surge may occur when the engine is operating at high load or torque and low engine speed, or when the engine is operating at a low speed and there is a high level of exhaust gas recirculation (EGR). Surge can also arise when an engine is suddenly decelerated from a high-speed condition. Expanding the surge-free operation range of a compressor to lower flow rates is a goal often sought in compressor design.
Applicant is owner of a number of pending patent applications directed to a turbocharger compressor having an inlet-adjustment mechanism for adjusting the size of the inlet flow area into the compressor, such as U.S. patent applicant Ser. No. 15/446,054 filed on Mar. 1, 2017, which claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 62/324,488 filed on Apr. 19, 2017, the entire disclosures of said applications being hereby incorporated herein by reference. The inlet-adjustment mechanisms described in said applications are effective for shifting the compressor surge line to lower flow rates.
The present disclosure describes mechanisms and methods for a centrifugal compressor that can enable the surge line for the compressor to selectively be shifted to the left (i.e., surge is delayed to a lower flow rate at a given pressure ratio) while optimizing compressor performance. One embodiment described herein comprises a turbocharger having the following features:
In accordance with one embodiment, L≥G, where G is an axial clearance between the exducer portion of the compressor wheel and the compressor housing.
In one embodiment of the invention, each of the blades has an arcuate shape. Each of the blades is pivotable about a pivot pin, and the blades are engaged with a rotatable unison ring that surrounds the orifice, rotation of the unison ring in one direction about an axis thereof causing the blades to pivot to the closed position of the inlet-adjustment mechanism, rotation of the unison ring in an opposite direction causing the blades to pivot to the open position.
In accordance with one embodiment, the orifice in the closed position of the inlet-adjustment mechanism is circular.
In accordance with another embodiment, the orifice in the closed position of the inlet-adjustment mechanism is non-circular. For example, the orifice in the closed position of the inlet-adjustment mechanism can be elliptical.
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.
In the present disclosure, the term “orifice” means “opening” without regard to the shape of the opening. Thus, an “orifice” can be circular or non-circular. Additionally, when the blades of the inlet-adjustment mechanism are described as moving “radially” inwardly or outwardly, the term “radially” does not preclude some non-radial component of movement of the blades (for example, the blades may occupy a plane that is angled slightly with respect to the rotational axis of the compressor, such that when the blades move radially inwardly and outwardly, they also move with a small axial component of motion).
A turbocharger 10 in accordance with one embodiment of the invention is illustrated in axial end view in
The turbine wheel 22 is disposed within a turbine housing 24 that defines an annular chamber 26 for receiving exhaust gases from an internal combustion engine (not shown). The turbine housing also defines a nozzle 28 for directing exhaust gases from the chamber 26 generally radially inwardly to the turbine wheel 22. The exhaust gases are expanded as they pass through the turbine wheel, and rotatably drive the turbine wheel, which in turn rotatably drives the compressor wheel 14 as already noted.
With reference to
The compressor housing 16 defines a shroud surface 16s that is closely adjacent to the radially outer tips of the compressor blades. The shroud surface defines a curved contour that is generally parallel to the contour of the compressor wheel.
In accordance with the invention, the compressor of the turbocharger includes an inlet-adjustment mechanism 100 disposed in the air inlet 17 of the compressor housing. The inlet-adjustment mechanism comprises a ring-shaped assembly and is disposed in an annular space defined between the compressor housing 16 and the separate inlet duct member 16d. The inlet-adjustment mechanism is operable for adjusting an effective diameter of the air inlet into the compressor wheel. As such, the inlet-adjustment mechanism is movable between an open position and a closed position, and can be configured to be adjusted to various points intermediate between said positions.
With reference now to
As shown in
In an alternative embodiment (not shown), instead of a cartridge form of inlet-adjustment mechanism, the inlet-adjustment mechanism can comprise a non-cartridge assembly in which the pins 104 for the blades 102 are secured in the compressor housing 16 and/or the inlet duct member 16d. Stated differently, the end plate 105 becomes an integral portion of the compressor housing 16 and the other end plate 107 becomes an integral portion of the inlet duct member 16d.
The range of pivotal movement of the blades is sufficient that the blades can be pivoted radially outwardly (by rotation of the unison ring in one direction, clockwise in
The blades can also be pivoted radially inwardly (by rotation of the unison ring in the opposite direction, counterclockwise in
As previously described, the blades 102 are actuated to pivot between their open and closed positions by the unison ring 106 that is rotatable about the center axis of the air inlet. Referring now to
As noted, the inlet-adjustment mechanism 100 enables adjustment of the effective size or diameter of the inlet into the compressor wheel 14. As illustrated in
At low flow rates (e.g., low engine speeds), the inlet-adjustment mechanism 100 can be placed in the intermediate or closed position of
At intermediate and high flow rates, the inlet-adjustment mechanism 100 can be opened as in
In accordance with the present invention, performance of the compressor can be optimized through selection of certain geometric characteristics or parameters of the inlet-adjustment mechanism 100. With reference to
In accordance with the invention, performance of the compressor can be optimized by ensuring that the orifice flow area when the inlet-adjustment mechanism is closed, ARc, is greater than 28% of the flow area of the air inlet at the compressor inducer inlet 17i. A practical maximum upper limit on ARc is 95% of the inducer inlet flow area. Thus,
0.28*π*(F/2)2<ARc<0.95*π*(F/2)2.
More preferably, the upper limit on ARc is 90% of the inducer inlet flow area, and still more preferably 85% of the inducer inlet flow area.
Furthermore, in accordance with the invention, the axial spacing L between the orifice minimum area location (where AR is defined) and the leading edge of the compressor wheel inducer is not greater than 40% of the compressor exducer diameter D, or
L≤0.4*D.
The axial spacing L preferably is not less than the exducer-compressor housing clearance G, or
L≥G.
Accordingly, G≤L≤0.4*D.
Preferably, L can be in a range between 5% and 35% of exducer diameter D, more preferably between 5% and 30% of D, and still more preferably between 5% and 25% of D, even more preferably between 5% and 20% of D, and most preferably between 5% and 15% of D.
With reference to
Applicant has found that compressor operating range (between the choke line at high flow rates and the surge line at low flow rates) can be widened or expanded by using an inlet-adjustment mechanism such as the type of mechanism described herein. The mechanism is effective to shift the surge line to lower flow rates, thereby expanding the useful operating range. Additionally, the compressor efficiency at what would be near-surge operating conditions (typically low flow rate and moderate to high pressure ratio), for a compressor without an inlet-adjustment mechanism, can be improved by using the inlet-adjustment mechanism to restrict the orifice going into the compressor. However, Applicant has found that the gain in efficiency can be partially or completely lost if the inlet-adjustment mechanism is not designed properly. Applicant has found that the parameters described herein are important in designing the inlet-adjustment mechanism so as to provide the greatest benefit in terms of range extension and efficiency improvement at near-surge conditions.
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, although the illustrated embodiment employs three blades 102, the invention is not limited to any particular number of blades. The invention can be practiced with as few as two blades, or as many as 12 blades or more. 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.
