Method and system for controlling a variable geometry compressor

Abstract

The present invention relates to methods and systems for controlling a variable geometry compressor. Specifically disclosed is a method for controlling a VG mechanism of a compressor, which uses a predetermined VG set point map, the predetermined VG set point map including an optimal VG set point for the VG mechanism based on at least one predetermined optimization criterion. The VG mechanism has at least three different set points ranging between a minimum flow area set point and a maximum flow area set point. The location of the operating point of the compressor on its compressor map is determined. Based on the location of the operating point, the VG set point map is consulted and the optimal VG set point is determined. A prediction scheme may be included to take into account the time lag of the response of the VG mechanism.

Description

Technical Field

[0001] The present disclosure relates to compressors, such as for use in turbochargers (which broadly include exhaust-driven turbochargers, electric motor-driven or assisted electric turbochargers, and superchargers), and more particularly to compressors having variable geometry mechanisms that can be adjusted for regulating flow through the compressor. Background Art

[0002] An exhaust-driven turbocharger is a device used in conjunction with an internal combustion engine for increasing the power output of the engine by compressing air delivered to the engine intake for mixing with fuel and burning in the engine. A turbocharger includes 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 another central housing connected between the turbine housing and the compressor housing for accommodating bearings for the shaft. The turbine housing defines a generally annular chamber that surrounds the turbine wheel and receives exhaust gas from the engine. The turbine assembly includes a nozzle that leads from the chamber to the turbine wheel. 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 the inlet of the compressor housing, and the air is compressed by the compressor wheel and then discharged from the housing to the engine intake.

[0003] The operating range of the compressor is an important aspect of the overall performance of a turbocharger. The operating range is roughly defined by the surge line and the choke line on an operating map for the compressor. A compressor map is usually presented as a pressure ratio (discharge pressure) on the vertical axis. Pout Divide by the inlet pressure Pin ) versus corrected mass flow on the horizontal axis. The throttling line on the compressor diagram is located at high flows and represents the locus of maximum mass flow points over a range of pressure ratios; that is, for a given point on the throttling line, it is not possible to increase the flow while maintaining the same pressure ratio because a throttling condition occurs in the compressor.

[0004] The surge line is located at low flows and represents the locus of minimum mass flow points without surge over a range of pressure ratios; that is, for a given point on the surge line, decreasing the flow without changing the pressure ratio, or increasing the pressure ratio without changing the flow, will cause surge to occur. Surge is a flow instability that typically occurs when the compressor blade incidence angle becomes so large that substantial flow separation occurs over the compressor blades. Pressure fluctuations and flow reversals occur during surge.

[0005] In a turbocharger for an internal combustion engine, compressor surge can occur when the engine is operating at high load or torque and low engine speed, or when the engine is operating at low speed and there is a high level of exhaust gas recirculation (EGR). Surge can also occur when the engine is suddenly decelerated from a high speed. Extending the compressor's surge-free operating range at lower flows is a goal often sought in compressor design.

[0006] One solution for shifting the surge line of a centrifugal compressor to the left (i.e., surge is delayed to a lower flow at a given pressure ratio) and shifting the throttle line to the right (i.e., throttling is increased to a higher flow at a given pressure ratio) is to employ a variable geometry (VG) mechanism in the compressor inlet. The variable geometry mechanism is adjustable between a maximum flow area position and a minimum flow area position. By adjusting the VG mechanism to the minimum flow area position, the surge line can be shifted to a lower flow. Applicant is the owner of co-pending applications disclosing various mechanisms of this type, see, e.g., Application Nos. 14 / 537,339; 14 / 532,278; 14 / 642,825; 14 / 573,603; and 14 / 551,218; the entire disclosures of said applications (hereinafter referred to as "co-owned applications") are hereby incorporated by reference herein. The VG mechanism can also be positioned downstream of the compressor and similar results achieved. Summary of the invention

[0007] The present disclosure describes a method and system for controlling a variable geometry mechanism of a compressor. The VG mechanism is positioned so that the fluid passing through the VG mechanism also passes through the compressor and is compressed by the compressor. The VG mechanism can be adjusted over a range of different set points to adjust the effective flow area of ​​the fluid passing through the VG mechanism and through the compressor, and the VG mechanism can be adjusted between a minimum flow area set point and a maximum flow area set point, and can be adjusted to at least one intermediate flow area set point between the minimum flow area set point and the maximum flow area set point. According to one embodiment described herein, the method includes the following steps:

[0008] predetermining a VG set point map, the VG set point map including optimal VG set points over a range of compressor pressure ratios and over a range of compressor corrected flows, each VG set point corresponding to a unique operating point position of the compressor on the compressor map and being optimized based on at least one predetermined optimization criterion for the compressor;

[0009] locating an operating point of the compressor on a compressor map;

[0010] consulting a VG set point map based on the position of the operating point to determine an optimum VG set point for the VG mechanism; and

[0011] Adjust the VG mechanism to the optimal VG setting point.

[0012] In some embodiments of the invention, at least some of the VG setpoints in the VG setpoint map are optimized based on compressor efficiency as a predetermined optimization criterion.

[0013] Alternatively, the VG setpoint in a first region of the compressor map may be optimized based on a first optimization criterion, and the VG setpoint in a second region of the compressor map may be optimized based on a second optimization criterion.

[0014] In one embodiment, the first optimization criterion includes compressor efficiency. Regardless of whether the first optimization criterion includes efficiency, the second optimization criterion may include compressor flow stability.

[0015] The method may further include employing a prediction scheme to predict the location of the operating point on the compressor map taking into account the time lag required to adjust the VG mechanism to the new VG set point.

[0016] In one embodiment, the VG mechanism is infinitely adjustable between a minimum flow area set point and a maximum flow area set point, and the predetermined VG set point map is configured to accommodate such infinite adjustability.

[0017] In another embodiment, the VG mechanism is adjustable to only a plurality of discrete VG set points, and the predetermined VG set point map is configured to accommodate such discrete adjustability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Having thus generally described the invention, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and in which:

[0019] Figure 1 is a diagrammatic depiction of a first embodiment of a compressor having a VG mechanism, wherein the VG mechanism is located upstream of the compressor;

[0020] Figure 1Ais a diagrammatic depiction of a second embodiment of a compressor having a VG mechanism, wherein the VG mechanism is located downstream of the compressor;

[0021] Figure 2 is an exemplary VG mechanism flow characteristic, which shows the relationship between the effective flow area of ​​the mechanism and the location of the mechanism;

[0022] Figure 3 is a graphical depiction of compressor map changes under VG operation showing corrected flow on the horizontal axis versus compressor pressure ratio on the vertical axis and including a dashed line where the VG mechanism is set in a minimum area position, a solid line where the VG mechanism is set in a maximum area position, and a series of intermediate dashed lines illustrating various intermediate positions between the minimum and maximum positions (of which there may be an infinite number, making the VG mechanism continuously variable);

[0023] Figure 4 is another embodiment of a compressor map in the form of discrete points in an array, on which a minimum VG position line and a maximum VG position line have been placed;

[0024] Figure 4A is a compressor map according to another embodiment, the compressor map being divided into two regions, the two regions employing different optimization criteria in deriving an optimal VG set point in each region;

[0025] Figure 5 Shows the corresponding Figure 4 An array of optimal VG set-point locations for discrete points on the graph in;

[0026] Figure 6 is a diagrammatic illustration of one embodiment of an engine control unit (ECU) that sends a VG set point to an actuator that actuates a VG mechanism;

[0027] Figure 7 is a diagrammatic illustration of another embodiment of an engine control unit (ECU) that sends a VG set point to an actuator that actuates a VG mechanism;

[0028] Figure 8 A typical compressor diagram is depicted and illustrates how the surge line can be shifted to a lower flow by adjusting the VG mechanism. DETAILED DESCRIPTION

[0029] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the inventions are shown. Indeed, the 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. Throughout, like reference numerals refer to like elements.

[0030] Figure 1 One configuration of a variable geometry (VG) compressor 10 is represented to which the present invention may be applied. Air is supplied to the compressor 20 through an inlet duct or conduit 22. Air that has been pressurized by the compressor is discharged through a discharge conduit 24. Located upstream of the compressor (e.g., in the inlet conduit 22) is a VG mechanism 100 that is operable to regulate flow into the compressor. The present invention is not limited to any particular type of VG mechanism. Any VG mechanism that is effective for producing a selectively variable degree of restriction through the effective flow area of ​​the mechanism may be used for the purposes of the present invention. As a non-limiting example of a VG mechanism that may be employed, the inlet adjustment mechanism disclosed in the commonly owned application referenced above may be used.

[0031] The VG mechanism is connected to a suitable actuator 26 that provides actuating force for adjusting the position of the VG mechanism. The actuator may be an electric motor, such as a stepper motor, a pneumatic actuator, a hydraulic actuator, or any other suitable type of device capable of adjusting the position of the VG mechanism.

[0032] Figure 1A A second configuration of a variable geometry compressor 10' is illustrated to which the present invention may be applied. The compressor 10' includes the same or similar components as in prior compressor configurations, except that the VG mechanism 100 is located downstream of the compressor, such as in the discharge conduit 24.

[0033] The present invention relates to a method and system for adjusting the position of a VG mechanism for any operating point on a compressor map. The main purpose of such adjustment of the VG mechanism is to avoid compressor surge by effectively delaying surge to a lower flow. As is well known to those skilled in the art, a compressor map plots the compressor pressure ratio on the vertical axis and the corrected flow on the horizontal axis. Figure 8A typical compressor diagram for a compressor, such as that typically used in a turbocharger, is shown. As shown, a constant wheel speed line can be plotted on the diagram, and an island of compressor efficiency can also be placed on the diagram. The surge line is an important aspect of compressor performance. As previously mentioned, surge is a flow instability that occurs, typically at low flows, when the compressor blade incidence angle becomes so large that substantial flow separation occurs over the compressor blades. Pressure fluctuations and flow reversals occur during surge. The surge line represents the locus of minimum mass flow points without surge over a range of pressure ratios; that is, for a given point on the surge line, decreasing the flow without changing the pressure ratio, or increasing the pressure ratio without changing the flow, will cause surge to occur.

[0034] As described in applicant's commonly owned applications, the surge line can be shifted to lower flows by using a VG mechanism to reduce the effective flow area through which fluid is delivered to the compressor wheel. Figure 1 In the compressor shown in FIG. 1 , the reduction in flow area achieved by the VG mechanism 100 results in an increase in flow velocity near the leading edge of the compressor blades, thereby reducing the blade incidence angle and thus preventing flow separation and instability. As an example, when the VG mechanism flow area is reduced from its maximum area A max Reduced to its minimum area A min hour, Figure 8 The surge line on the graph of may be shifted to the left as shown.

[0035] According to the invention, for each possible operating point on the compressor map (defined by the pressure ratio and the corrected flow at that point), the optimal position of the VG mechanism is predetermined based on an optimization criterion (or criteria). Figure 3 A compressor diagram is shown on which a series of lines are plotted. The solid line is for the case where the VG mechanism is set in a position having a maximum flow area, and the line is the locus of operating points at which the selected optimization criterion is optimized. Thus, for any point on the solid line, if the pressure ratio and the corrected flow rate are held constant and the VG mechanism is adjusted to a flow area less than the maximum value, the optimization criterion will be rejected (i.e., it will not be optimized). Likewise, for any point on the dashed line, if the pressure ratio and the corrected flow rate are held constant and the VG mechanism is adjusted to a flow area greater than the minimum value, the optimization criterion will be rejected.

[0036] It will also be appreciated, therefore, that if the VG mechanism is adjustable to a range (possibly an infinite number if the mechanism is infinitely adjustable or continuously adjustable in its range) of intermediate positions between the minimum area position and the maximum area position, then Figure 3There will be a series of lines on the characteristic line diagram of , intermediate between the solid line and the dashed line, and those lines are represented by the dotted lines. Thus, this series of lines from the maximum position to the minimum position can form a predetermined set of optimal positions for the VG mechanism for all possible operating points on the compressor map.

[0037] According to the present invention, the predetermined set of optimal VG positions may take various forms. Figure 3 represents one possible form of having predetermined optimal VG positions which may be stored in the memory of the controller of the VG mechanism in any of a variety of ways, such as a table lookup format, curve fitting, etc. Figure 4 and Figure 5 Another possible form that the predetermined set of optimal VG positions may take is illustrated. Figure 4 The compressor map space is illustrated, on which an array of discrete operating points has been predetermined. There are 12 index positions along the horizontal or X axis (representing corrected flow), and there are 9 index positions along the vertical or Y axis (representing pressure ratio). Of course, for the purpose of providing a drawing of the present invention, this example is simplified. In actual practice, the array will most likely have a much larger number of X and Y index positions. Figure 4 , the optimum position of the line is shown at which the VG mechanism should be set to the minimum area position, and likewise for the maximum area position. For the purpose of explaining the invention, actual values ​​have been assigned to the VG set points, wherein the minimum area set point is defined as 0 and the maximum area set point is defined as 100.

[0038] Then, Figure 5 A table or array of predetermined optimal VG set points (i.e., flow area values) for all 108 (12×9) points on the graph is shown, where a suitable interpolation scheme can be used for points that fall between the minimum and maximum value lines. Each VG set point in the table represents a VG position that optimizes a particular optimization criterion for that point. Compressor efficiency can be the optimization criterion, or other criteria can be used in addition to or in place of efficiency.

[0039] It is not necessary to use the same optimization criterion for all points on the compressor map. For example, the map can be divided into two or more regions, and in each region a region-specific optimization criterion can be used. Figure 4A As shown in , for example, a region (in Figure 4AIn one region (at higher flows in the figure), compressor efficiency may be used as the optimization criterion, while another region (at lower flows) may use compressor flow stability as the optimization criterion. It is also within the scope of the invention to use a combination of multiple criteria combined in a predetermined manner for a given point on the graph. For example, for a point on the characteristic line graph, the VG set point may be optimized based on a combination of compressor efficiency and flow stability quantified in an appropriate manner. When multiple criteria are used, these criteria may each have a different weight (e.g., efficiency has a weight of 40% and flow stability has a weight of 60%).

[0040] Regardless of the specific form in which a set of optimal VG positions or set points are represented and stored in the memory of the controller, the present invention relates to methods and systems in which: the location of the current operating point of the compressor on the compressor map is ascertained; an optimal VG set point is determined for the operating point based on at least one optimization criterion; and an actuator of the VG mechanism is commanded to adjust the VG mechanism to the optimal set point. According to the present invention, the optimized VG set points are predetermined for the entire compressor map, and the resulting VG set point map is stored for use in regulating the VG mechanism.

[0041] Implementation of the control scheme described above may be accomplished in various ways. Figure 6 The overall architecture of a system for adjusting a VG mechanism by controlling an actuator 26 of the VG mechanism is illustrated. The actuator 26 communicates with a control unit 40, which may be an engine control unit (ECU) as shown, or may be a separate control unit that can communicate with the ECU. The control unit includes a processor 50, such as a microprocessor, and includes a memory 60, such as a non-volatile ROM, PROM, EPROM, or EEPROM memory, and an interface for communicating with other devices in the system. The memory may be programmed with control instructions (e.g., in hardware and / or firmware and / or software) that are executed by the processor 50 for implementing the functions of the control unit.

[0042] In an embodiment, the ECU may receive inputs from various engine sensors and turbocharger sensors and control various engine and turbocharger actuators. Engine sensors may be placed at various points in the engine to measure or otherwise determine corresponding engine parameters. Examples of engine sensors may include throttle position sensors, air temperature sensors, engine revolutions per minute (RPM) sensors, engine load sensors, accelerator pedal position sensors, and / or others. Engine actuators may include various relays, solenoids, ignition coils, or other electrically operable devices that can be used to control corresponding engine parameters. Turbocharger sensors may include sensors for measuring the following: turbocharger speed, compressor inlet pressure, compressor exhaust pressure, compressor correction flow, and other parameters.

[0043] In such Figure 6 In the exemplary embodiment shown in , the ECU 40 may include an anti-surge control module for adjusting the position of the VG mechanism. The anti-surge control module may be any device, such as a device or circuit specifically implemented in hardware, software, or a combination of hardware and software, which is configured to perform the corresponding functions of the anti-surge control module as described herein. In some embodiments, the anti-surge control module may be configured to enhance the ECU capabilities in terms of surge prevention (by identifying engine conditions under which action is to be taken for anti-surge activities) and in terms of taking or directing actions regarding anti-surge activities (for example, via the actuator 26 that controls the VG mechanism). Thus, in an exemplary embodiment, the anti-surge control module may simply provide additional functionality to the ECU 40. However, in some embodiments, the anti-surge control module may be a unit separate from the ECU (i.e., Figure 6 The control unit 40 shown in FIG. 4 may not include an ECU, but may communicate with the ECU).

[0044] The memory device 60 may include, for example, volatile and / or non-volatile memory. The memory device 60 may be configured to store information, data, applications, modules, instructions, etc., so that the device can implement various functions according to exemplary embodiments of the present invention. For example, the memory device 60 may be configured to buffer input data for processing by the processor 50. Additionally or alternatively, the memory device 60 may be configured to store instructions corresponding to applications for execution by the processor of the control unit 40.

[0045] As mentioned above, the processor 50 may be a processor of an ECU, or a coprocessor or processor of a separate anti-surge control module. The processor may be implemented in many different ways. For example, the processor may be implemented as a processing element, a coprocessor, a controller, or various other processing devices or apparatuses including integrated circuits, such as, for example, ASICs (Application Specific Integrated Circuits), FPGAs (Field Programmable Gate Arrays), hardware accelerators, and the like. In an exemplary embodiment, the processor may be configured to execute instructions stored in a memory device 60 or otherwise accessible to the processor. In this way, whether constructed by hardware or software methods or by a combination thereof, the processor may represent an entity capable of performing operations according to an embodiment of the present invention when constructed accordingly. Thus, for example, when the processor is implemented as an ASIC, FPGA, and the like, the processor may be specially constructed hardware for performing the operations described herein. Alternatively, as another example, when the processor is implemented as an executor of software instructions, these instructions may specifically configure the processor (if not used for a specific configuration provided by the instructions, the processor may otherwise be a general-purpose processing element) to perform the algorithms and / or operations described herein. However, in some cases, the processor 50 may be a processor of a particular device (e.g., an ECU) that is adapted to employ embodiments of the present invention by further configuring the processor 50 according to instructions for performing the algorithms and / or operations described herein (e.g., by adding an anti-surge control module).

[0046] The memory 60 of the control unit stores a compressor map comprising a set of predetermined optimal VG set points over the entire operating envelope of the compressor. Figure 6 , a diagram for a 3-position VG mechanism is shown; that is, the VG mechanism can be adjusted to only three positions: minimum flow area, intermediate flow area, and maximum flow area. Thus, the diagram depicts three regions, which represent the VG set points for each region. The VG mechanism is set in the minimum flow area position in the region of lowest flow, in the intermediate position in the region of intermediate flow, and in the maximum position in the region of highest flow. However, alternatively, the diagram may be composed of Figure 3 of the type illustrated, or may be such as that represented by Figure 4 The graph is shown in Figure 1. The graph may be stored in any of a variety of forms, such as a lookup table, a polynomial curve fit line, or any other suitable form. The control unit 40 receives the compressor correction flow W c And pressure ratio PR (or based on input from other engine and turbocharger sensors to calculate compressor corrected flow W c And pressure ratio PR). The flow and pressure ratio may be continuously sensed or calculated from suitable sensors, and the sensed or calculated values ​​may be sent to the control unit (e.g., at regular time step intervals, such as every 0.1 seconds or other appropriately selected intervals). The control unit uses these sensed parameters to decide what position the VG mechanism should be in, as further described below.

[0047] Reference now Figure 7 , describes another embodiment of the present invention that can compensate for the time lag associated with adjusting the VG mechanism. More specifically, assume that the operating point moves rapidly on the compressor map, as may occur, for example, when the driver's foot suddenly releases the accelerator pedal at a high engine speed. In this case, at a given point along the movement path of the operating point on the map, if the sensed pressure ratio and flow at that given time point are used to determine the optimal VG set point as described above, then by the time the actuator is able to move the VG mechanism to the set point position, the operating point will have moved to a different point on the map. The derived VG set point may not be appropriate for that point on the map. Therefore, in some embodiments of the present invention, a prediction scheme may be employed to predict where the operating point will be when the VG mechanism is actually adjusted to the new position. For example, if Figure 7 As shown in , for each of the sensed pressure ratio and the sensed corrected flow, a Kalman filter is employed to predict the pressure ratio and flow at the moment when the VG mechanism reaches a new adjusted position. The Kalman filter receives the instantaneous time corresponding to each sample of the pressure ratio and flow, and based on the observed behavior of these time-varying parameters, the Kalman filter predicts the values ​​that will apply when the VG mechanism reaches its adjusted position. The VG set point is then determined based on the predicted pressure ratio and the predicted flow. Figure 7 In , the diagram is for a VG mechanism that can be infinitely adjusted, but the diagram can be of any type and for any type of VG mechanism.

[0048] From the foregoing description of certain embodiments of the present invention, it will be appreciated that the control method according to the present invention is suitable for either discretely variable or infinitely variable VG mechanisms. Discretely variable VG mechanisms with as few as 3 set point positions (minimum area, intermediate area, and maximum area) can be used in the present invention. Alternatively, VG mechanisms with a greater number of set points or VG mechanisms with a substantially infinite number (or at least a very large number) of possible set point positions may also be used. It is only necessary to construct the VG set point diagram and control logic accordingly depending on which type of VG mechanism is employed. When a discrete variable VG mechanism is employed, the method and system according to the present invention can advantageously include hysteresis when adjusting the VG set point so as to avoid oscillatory behavior of the mechanism when the compressor operating point falls on or approaches the boundary between one VG set point and an adjacent VG set point.

[0049] Many modifications and other embodiments of the inventions set forth herein will come to mind to those skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing description and the associated drawings. For example, in the described embodiments, the location of the compressor operating point on the compressor map is determined based on the pressure ratio and the corrected flow. However, alternatively, the operating point location may be determined in other ways (e.g., using turbocharger speed and flow), as is known in the art. It will be understood, therefore, that these inventions are not 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.

Claims

1. A method for controlling a variable geometry mechanism of a compressor, the VG mechanism being positioned so that a fluid passing through the VG mechanism also passes through the compressor and is compressed by the compressor, the VG mechanism being adjustable to adjust an effective flow area of ​​the fluid passing through the VG mechanism and through the compressor, the VG mechanism being adjustable between a minimum flow area set point and a maximum flow area set point, and being adjustable to at least one intermediate flow area set point between the minimum flow area set point and the maximum flow area set point, the method comprising: predetermining a VG set point map, the VG set point map comprising optimal VG set points over a range of compressor pressure ratios and over a range of compressor corrected flows, each VG set point corresponding to a unique operating point position of the compressor on the compressor map and being optimized based on at least one predetermined optimization criterion for the compressor; determining a location of an operating point of the compressor on the compressor map; consulting the VG set point map based on the position of the operating point to determine an optimum VG set point for the VG mechanism; as well as adjusting the VG mechanism to the optimal VG set point, Therein, the VG setpoint in a first region of the compressor map is optimized based on a first optimization criterion, and the VG setpoint in a second region of the compressor map is optimized based on a second optimization criterion.

2. The method according to claim 1, wherein: At least some of the VG setpoints in the VG setpoint map are optimized based on compressor efficiency as a predetermined optimization criterion.

3. The method according to claim 1, wherein: The first optimization criterion includes compressor efficiency.

4. The method according to claim 1, wherein: The second optimization criterion includes compressor flow stability.

5. The method according to claim 1, further comprising: Taking into account the time lag required to adjust the VG mechanism to a new VG set point, a prediction scheme is employed to predict where the operating point will be on the compressor map when the VG mechanism reaches the new VG set point.

6. The method according to claim 1, wherein: The VG mechanism is infinitely adjustable between the minimum flow area set point and the maximum flow area set point, and the predetermined VG set point map is configured to accommodate such infinite adjustability.

7. The method according to claim 1, wherein: The VG mechanism is adjustable to only a plurality of discrete VG set points, and the predetermined VG set point map is configured to accommodate such discrete adjustability.

8. The method according to claim 7, further comprising the steps of: Hysteresis is included in adjusting the VG set point.

9. A computer program product comprising computer executable program code instructions to cause a compressor to perform the steps of the method according to any one of claims 1 to 8, the compressor comprising a variable geometry mechanism connected to an actuator, a sensor for determining the compressor pressure ratio and flow, and a control unit.

10. A computer-readable storage medium having stored thereon the computer program product according to claim 9.

Images