Patent Publication Number: US-10774676-B2

Title: Systems and methods for a variable inlet compressor

Description:
FIELD 
     The present description relates generally to methods and systems for adjusting airflow entering a compressor. 
     BACKGROUND/SUMMARY 
     A turbocharger may be provided in an engine to increase engine torque or power output density. The turbocharger may include an exhaust-driven turbine coupled to a compressor via a drive shaft. The compressor may be fluidly coupled to an air intake manifold in the engine that delivers air to a plurality of engine cylinders. Exhaust flow from one or more engine cylinders may be directed to a turbine wheel, causing the turbine to rotate about a fixed axis. The rotational motion of the turbine drives an impeller (e.g., wheel) of the compressor, which compresses air into the air intake manifold to increase boost pressure during select engine operating conditions. 
     Compressor efficiency influences overall engine performance and fuel consumption. For example, lower compressor efficiency may result in slow engine transient response and higher fuel consumption for both steady-state and transient engine operation. At lighter engine loads, when compressor efficiency is reduced, there may be increased turbocharger lag during a tip-in. Additionally, compressor surge limits may restrict boost pressure rise at low engine speeds. 
     Compressors are prone to surge during events that lead to an increased pressure ratio across the compressor or decreased mass flow into the compressor. For example, when an operator rapidly tips-out an accelerator pedal, air flow into the compressor inlet decreases, reducing the forward flow through the compressor while the compressor is still at a high pressure ratio. This may lead to pressure accumulation at an outlet end of the compressor, driving air in a reverse direction that may degrade components of the compressor. Thus, extending a margin to surge may increase a range of conditions through which compressor operation remains stable. 
     Turbocharger compressors may be adapted with a mechanism to relieve pressure at the compressor outlet, in particular for turbochargers coupled to diesel engines. Larger turbochargers may be used to provide high boost pressures for diesel engine operation. However, the benefits of high boost pressure supplied by the turbocharger compressor may be offset by a higher likelihood of compressor surge. Thus, turbocharger compressors for diesel engine applications may be configured to reduce a likelihood of surge occurring by providing a path for flow recirculation. For example, the compressor may include a bleed valve that vents intake pressure to atmosphere or, alternatively, the compressor may comprise a ported shroud. The ported shroud may be a passage within an inner casing of the compressor inlet that allows air to flow in a reverse direction through the compressor, returning compressed air from the compressor outlet to the compressor inlet to lower the pressure ratio and increase mass flow into the compressor. While the ported shroud effectively reduces a likelihood of compressor surge, the presence of the ported shroud may also adversely affect compressor efficiency, especially at low compressor speeds. 
     Various approaches have been developed to address the issue of compressor efficiency at low mass flow rate, including combining a mechanism for reducing compressor outlet pressure with a device for controlling flow into the compressor inlet. One example approach is shown by Pekari et al. in U.S. Pat. No. 4,403,912. Therein, an engine compressor with an air bleed valve and variable guide vanes is disclosed. The bleed valve is opened to vent pressure in the compressor to maintain stable compressor operation, the opening and closing of the valve adjusted by an actuator that also controls a position of the variable guide vanes. The variable guide vanes are at a specified attitude during initial engine operation with the bleed valve fully open. The actuator adjusts the bleed valve as the engine accelerates until the bleed valve is in a fully closed position, after which continued actuation actuates the guide vanes to an attitude to enable maximum compressor operation. 
     However, the inventors herein have recognized potential issues with such systems. As one example, the positioning of the guide vanes relative to the compressor inlet in the system of U.S. Pat. No. 4,403,912 may not control a flow area of the inlet sufficiently to elicit a rapid and effective response to changes in compressor stability. Furthermore, the actuation of the guide vanes only after the bleed valve is fully closed may limit flow control through the compressor and result in reduced compressor efficiency. 
     In one example, the issues described above may be addressed by a system for a compressor, comprising: a casing forming a recirculation passage surrounding an inlet conduit; an active casing treatment surrounding the inlet conduit and configured to selectively control gas flow through the recirculation passage; an impeller; a volute; and an adjustable device positioned in the inlet conduit upstream of the impeller, at least partially overlapping with a plane of the volute, configured to selectively reduce an effective size of the impeller. In this way, by including the adjustable device at a position that selectively reduces an effective size of the impeller, a flow range of the compressor may be increased at lower compressor pressure ratios and mass flows while compressor efficiency is increased. Furthermore, by selectively enabling the gas flow through the recirculation passage, the flow range of the compressor may be increased at higher compressor pressure ratios and mass flows while avoiding compressor efficiency penalties at lower compressor pressure ratios and mass flows. 
     As one example, a bleed port may fluidically couple the inlet conduit to the recirculation passage downstream of a leading edge of the impeller, and a recirculation port may fluidically couple the inlet conduit to the recirculation passage upstream of the adjustable device. A valve positioned at one of the bleed port and the recirculation port may enable the recirculation passage to be selectively blocked. For example, adjusting the valve to a closed position may block the gas flow through the recirculation passage while adjusting the valve to an open position may enable gas flow through the recirculation passage. As another example, the adjustable device may include a plurality of adjacently arranged vanes forming a ring about a central axis of the compressor, an actuation plate coupled to an actuator, and a plurality of handles connecting the plurality of vanes to the actuation plate. Interior edges of the vanes of the adjustable device may form a flow passage through the adjustable device that is aligned along the central axis, each of the vanes being rotatable about an actuation axis arranged radially to the central axis. The vanes may be rotatable between an open position having a larger radius flow passage and a closed position having a smaller radius flow passage via the actuator, the actuation plate, and the handles. In this way, the adjustable device and the valve may be independently adjusted to rapidly vary the effective size of the impeller and gas flow through the recirculation passage, respectively, resulting in a wide compressor flow range and high compressor efficiency. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic depiction of an example vehicle system. 
         FIGS. 2A-2B  show a cut-away view of a first example of a turbocharger compressor including a casing treatment and a variable inlet device positioned in an inlet conduit of the compressor. 
         FIGS. 3A-3B  show a first example of a variable inlet device for a turbocharger compressor in open and closed positions. 
         FIGS. 4A-4B  show a cut-away view of a second example of a turbocharger compressor including a casing treatment and a variable inlet device positioned in an inlet conduit of the compressor. 
         FIGS. 5A-5C  show a second example of a variable inlet device for a turbocharger compressor in open and closed positions. 
         FIG. 6  shows a flow chart of an example method for controlling a position of a variable inlet device. 
         FIG. 7  shows a flow chart of an example method for controlling an opening of a port of a casing treatment. 
         FIG. 8  shows an engine load and engine speed map for controlling a variable inlet device and an active casing treatment of a compressor. 
         FIG. 9  shows a flow chart of an example method for coordinating control of a variable inlet device and an active casing treatment of a compressor, such as via a common actuator. 
         FIG. 10  shows an example compressor map of a compressor having a variable inlet device and an active casing treatment that may be independently actuated. 
         FIG. 11  shows an example compressor map of a compressor having a variable inlet device and an active casing treatment that are actuated via a single actuation system. 
         FIG. 12  shows a prophetic example timeline for independently adjusting a position of a variable inlet device and a position of an active casing treatment of a compressor based on engine operating conditions. 
         FIG. 13  shows a prophetic example timeline for simultaneously adjusting a position of a variable inlet device and a position of an active casing treatment of a compressor based on engine operating conditions. 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems and methods for a turbocharger compressor having a variable inlet and a casing treatment. The compressor may be positioned in an intake passage of an engine, such as the engine system shown in  FIG. 1 . The compressor may include an outer casing with an inlet conduit (e.g., intake passage) and an impeller (e.g., compressor wheel) disposed downstream in the inlet conduit. The impeller may include one or more blades and is rotatable about a central axis of the compressor. As shown in  FIGS. 2A-2B  and  FIGS. 4A-4B , a variable inlet device (VID) may be disposed within the inlet conduit of the compressor upstream of the impeller in order to vary an inlet radius (or diameter) of the impeller. The VID may be adjustable between an open position (as shown in  FIGS. 2B, 3B, 4B, and 5C ) and a closed position (as shown in  FIGS. 2A, 3A, 4A, and 5A ). In one example, the VID includes vanes that are rotatable along an axis of actuation to vary the effective radius (or diameter) of the VID, as shown in  FIGS. 2A-3B . In another example, the VID includes vanes that are moved radially in and out along an actuation axis to vary the radius, as shown in  FIGS. 4A-5C . Further, the VID may be used in conjunction with an active casing treatment adapted to adjust recirculation flow between a recirculation port and a bleed port disposed in a wall of the inlet conduit. As shown in  FIGS. 4A-5C , in some examples, the VID and the active casing treatment may be controlled by a single actuation system based on engine speed and load conditions, such as according to the example method of  FIG. 9 . In other examples, such as shown in  FIGS. 2A and 2B , the VID and the active casing treatment may be controlled independently based on engine speed and load conditions, such as according to the example methods of  FIGS. 6 and 7 . An example engine speed and load map is shown in  FIG. 8 , and example compressor maps are shown in  FIGS. 10 and 11 . Furthermore, example timelines illustrating control of the VID and the active casing treatment based on engine operating conditions are shown in  FIGS. 12 and 13 . By including both a VID and an active casing treatment that are controlled based on operating conditions, the compressor efficiency may be increased and a surge margin extended at low engine speeds and loads, increasing fuel economy, while the compressor efficiency is also increased at high engine speeds and loads, increasing engine power. 
     Turbocharger compressor operating conditions will be referred to throughout the following detailed description and may be clarified in conjunction with a compressor map illustrated in  FIG. 10  that shows a mass flow rate through the compressor as a function of a pressure ratio across the compressor. A surge limit delineates a lower limit air flow for compressor operation while a choke limit defines an upper limit air flow. For example, dashed line  1004  represents a lower limit boundary that is the surge limit, and an upper limit boundary, indicated by dashed line  1006 , represents the choke limit. Compressor surge may occur during low compressor flow conditions, such as rapid engine unloading events, during which a turbine driving the compressor continues to spin at a relatively high speed, pressurizing the air downstream of the compressor. This leads to a high pressure zone at the outlet of the compressor, driving a reversal in the air flow direction that may cause degradation of the turbocharger. Compressor operation may include a trade-off between avoiding surge and operating with high efficiency. Approaches to extend the surge margin (e.g., move the surge line to the left) may allow additional operation in high efficiency regions without experiencing surge. 
     Operation beyond the upper limit of compressor pressure ratio relative to mass flow (e.g. in a region to the right of dashed line  1006  defined by relatively high compressor mass flow and relatively low pressure ratio) results in turbocharger choke. Choke may occur during transient overspeed events where, for example, an increase in engine load subjects the turbocharger to flow beyond a tolerance of the turbocharger. The rotational speed of the turbine driving the compressor may be higher than a maximum design speed of the turbocharger. Repeated instances of turbocharger choke may also cause degradation of the turbocharger and/or limit engine torque. 
     Before further description of the approaches to reduce compressor surge while maintaining or increasing compressor efficiency is provided, an example platform is described, herein the form of a vehicle including an engine, in which the turbocharger of the present disclosure may be installed. Turning now to  FIG. 1 , an example embodiment of a cylinder  14  of an internal combustion engine  10 , which may be included in a vehicle  5 . Engine  10  may be controlled at least partially by a control system, including a controller  12 , and by input from a vehicle operator  130  via an input device  132 . In this example, input device  132  includes an accelerator pedal and a pedal position sensor  134  for generating a proportional pedal position signal PP. Cylinder (herein, also “combustion chamber”)  14  of engine  10  may include combustion chamber walls  136  with a piston  138  positioned therein. Piston  138  may be coupled to a crankshaft  140  so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft  140  may be coupled to at least one vehicle wheel  55  via a transmission  54 , as further described below. Further, a starter motor (not shown) may be coupled to crankshaft  140  via a flywheel to enable a starting operation of engine  10 . 
     In some examples, vehicle  5  may be a hybrid vehicle with multiple sources of torque available to one or more vehicle wheels  55 . In other examples, vehicle  5  is a conventional vehicle with only an engine or an electric vehicle with only an electric machine(s). In the example shown, vehicle  5  includes engine  10  and an electric machine  52 . Electric machine  52  may be a motor or a motor/generator. Crankshaft  140  of engine  10  and electric machine  52  are connected via transmission  54  to vehicle wheels  55  when one or more clutches  56  are engaged. In the depicted example, a first clutch  56  is provided between crankshaft  140  and electric machine  52 , and a second clutch  56  is provided between electric machine  52  and transmission  54 . Controller  12  may send a signal to an actuator of each clutch  56  to engage or disengage the clutch, so as to connect or disconnect crankshaft  140  from electric machine  52  and the components connected thereto, and/or connect or disconnect electric machine  52  from transmission  54  and the components connected thereto. Transmission  54  may be a gearbox, a planetary gear system, or another type of transmission. 
     The powertrain may be configured in various manners including as a parallel, a series, or a series-parallel hybrid vehicle. In electric vehicle embodiments, a system battery  58  may be a traction battery that delivers electrical power to electric machine  52  to provide torque to vehicle wheels  55 . In some embodiments, electric machine  52  may also be operated as a generator to provide electrical power to charge system battery  58 , for example, during a braking operation. It will be appreciated that in other embodiments, including non-electric vehicle embodiments, system battery  58  may be a typical starting, lighting, ignition (SLI) battery coupled to an alternator. 
     Cylinder  14  of engine  10  can receive intake air via a series of intake air passages  142 ,  144 , and  146 . Intake air passage  146  can communicate with other cylinders of engine  10  in addition to cylinder  14 . In some examples, one or more of the intake passages may include a boosting device, such as a turbocharger or a supercharger. For example,  FIG. 1  shows engine  10  configured with a turbocharger, including a compressor  174  arranged between intake passages  142  and  144  and an exhaust turbine  176  arranged along an exhaust passage  148 . Compressor  174  may be at least partially powered by exhaust turbine  176  via a shaft  180  when the boosting device is configured as a turbocharger. In some examples, exhaust turbine  176  may be a variable geometry turbine (VGT) where turbine geometry is actively varied by actuating turbine vanes as a function of engine speed and other operating conditions. In one example, the turbine vanes may be coupled to an annular ring, and the ring may be rotated to adjust a position of the turbine vanes. In another example, one or more of the turbine vanes may be pivoted individually or pivoted in plurality. As an example, adjusting the position of the turbine vanes may adjust a cross sectional opening (or area) of exhaust turbine  176 . However, in other examples, such as when engine  10  is provided with a supercharger, compressor  174  may be powered by mechanical input from a motor or the engine and exhaust turbine  176  may be optionally omitted. 
     A throttle  162  including a throttle plate  164  may be provided in the engine intake passages for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle  162  may be positioned downstream of compressor  174 , as shown in  FIG. 1 , or may be alternatively provided upstream of compressor  174 . A throttle position sensor may be provided to measure a position of throttle plate  164 . 
     Exhaust passage  148  can receive exhaust gases from other cylinders of engine  10  in addition to cylinder  14 . An exhaust gas sensor  128  is shown coupled to exhaust passage  148  upstream of an emission control device  178 . Exhaust gas sensor  128  may be selected from among various suitable sensors for providing an indication of exhaust gas air/fuel ratio (AFR), such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), a NOx, a HC, or a CO sensor, for example. Emission control device  178  may be a three-way catalyst, a NOx trap, various other emission control devices, or combinations thereof. 
     Exhaust gas recirculation (EGR) may be provided to the engine via a high pressure EGR system  83 , delivering exhaust gas from a zone of higher pressure in exhaust passage  148 , upstream of turbine  176 , to a zone of lower pressure in intake air passage  146 , downstream of compressor  174  and throttle  162 , via an EGR passage  81 . In other examples (not shown in  FIG. 1 ), low pressure EGR may additionally or alternatively be provided via a low pressure EGR system, coupling a region of exhaust passage  148  between turbine  176  and emission control device  178  to intake air passage  142 . 
     An amount EGR provided to intake passage  146  may be varied by controller  12  via an EGR valve  80 . For example, controller  12  may adjust a position of EGR valve  80  to adjust the amount of exhaust gas flowing through EGR passage  81 . EGR valve  80  may be adjusted between a fully closed position, in which exhaust gas flow through EGR passage  81  is blocked, and a fully open position in which exhaust gas flow through the EGR passage is enabled. As an example, EGR valve  80  may be continuously variable between the fully closed position and the fully open position. As such, the controller may increase a degree of opening of EGR valve  80  to increase an amount of EGR provided to intake passage  146  and decrease the degree of opening of EGR valve  80  to decrease the amount of EGR provided to intake passage  146 . EGR may be cooled via passing through EGR cooler  85  within EGR passage  81 . EGR cooler  85  may reject heat from the EGR gases to engine coolant, for example. 
     Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture within cylinder  14 . Thus, it may be desirable to measure or estimate the EGR mass flow. EGR sensors may be arranged within EGR passage  81  and may provide an indication of one or more of mass flow, pressure, and temperature of the exhaust gas, for example. Each cylinder of engine  10  may include one or more intake valves and one or more exhaust valves. For example, cylinder  14  is shown including at least one intake poppet valve  150  and at least one exhaust poppet valve  156  located at an upper region of cylinder  14 . In some examples, each cylinder of engine  10 , including cylinder  14 , may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder. Intake valve  150  may be controlled by controller  12  via an actuator  152 . Similarly, exhaust valve  156  may be controlled by controller  12  via an actuator  154 . The positions of intake valve  150  and exhaust valve  156  may be determined by respective valve position sensors (not shown). 
     During some conditions, controller  12  may vary the signals provided to actuators  152  and  154  to control the opening and closing of the respective intake and exhaust valves. The valve actuators may be of an electric valve actuation type, a cam actuation type, or a combination thereof. The intake and exhaust valve timing may be controlled concurrently, or any of a possibility of variable intake cam timing, variable exhaust cam timing, dual independent variable cam timing, or fixed cam timing may be used. Each cam actuation system may include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and/or variable valve lift (VVL) systems that may be operated by controller  12  to vary valve operation. For example, cylinder  14  may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation, including CPS and/or VCT. In other examples, the intake and exhaust valves may be controlled by a common valve actuator (or actuation system) or a variable valve timing actuator (or actuation system). 
     Cylinder  14  can have a compression ratio, which is a ratio of volumes when piston  138  is at bottom dead center (BDC) to top dead center (TDC). In one example, the compression ratio is in the range of 9:1 to 10:1. However, in some examples, such as where different fuels are used, the compression ratio may be increased. This may happen, for example, when higher octane fuels or fuels with higher latent enthalpy of vaporization are used. The compression ratio may also be increased if direct injection is used due to its effect on engine knock. 
     In some examples, each cylinder of engine  10  may include a spark plug  192  for initiating combustion. An ignition system  190  can provide an ignition spark to combustion chamber  14  via spark plug  192  in response to a spark advance signal SA from controller  12 , under select operating modes. A timing of signal SA may be adjusted based on engine operating conditions and driver torque demand. For example, spark may be provided at maximum brake torque (MBT) timing to maximize engine power and efficiency. Controller  12  may input engine operating conditions, including engine speed, engine load, and exhaust gas AFR, into a look-up table and output the corresponding MBT timing for the input engine operating conditions. 
     In some examples, each cylinder of engine  10  may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, cylinder  14  is shown including a fuel injector  166 . Fuel injector  166  may be configured to deliver fuel received from a fuel system  8 . Fuel system  8  may include one or more fuel tanks, fuel pumps, and fuel rails. Fuel injector  166  is shown coupled directly to cylinder  14  for injecting fuel directly therein in proportion to the pulse width of a signal FPW received from controller  12  via an electronic driver  168 . In this manner, fuel injector  166  provides what is known as direct injection (hereafter also referred to as “DI”) of fuel into cylinder  14 . While  FIG. 1  shows fuel injector  166  positioned to one side of cylinder  14 , fuel injector  166  may alternatively be located overhead of the piston, such as near the position of spark plug  192 . Such a position may increase mixing and combustion when operating the engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to increase mixing. Fuel may be delivered to fuel injector  166  from a fuel tank of fuel system  8  via a high pressure fuel pump and a fuel rail. Further, the fuel tank may have a pressure transducer providing a signal to controller  12 . 
     In an alternate example, fuel injector  166  may be arranged in intake passage  146  rather than coupled directly to cylinder  14  in a configuration that provides what is known as port injection of fuel (hereafter also referred to as “PFI”) into an intake port upstream of cylinder  14 . In yet other examples, cylinder  14  may include multiple injectors, which may be configured as direct fuel injectors, port fuel injectors, or a combination thereof. As such, it should be appreciated that the fuel systems described herein should not be limited by the particular fuel injector configurations described herein by way of example. 
     Fuel injector  166  may be configured to receive different fuels from fuel system  8  in varying relative amounts as a fuel mixture and further configured to inject this fuel mixture directly into cylinder  14 . Further, fuel may be delivered to cylinder  14  during different strokes of a single cycle of the cylinder. For example, directly injected fuel may be delivered at least partially during a previous exhaust stroke, during an intake stroke, and/or during a compression stroke. As such, for a single combustion event, one or multiple injections of fuel may be performed per cycle. The multiple injections may be performed during the compression stroke, intake stroke, or any appropriate combination thereof in what is referred to as split fuel injection. 
     Fuel tanks in fuel system  8  may hold fuels of different fuel types, such as fuels with different fuel qualities and different fuel compositions. The differences may include different alcohol contents, different water contents, different octane numbers, different heats of vaporization, different fuel blends, and/or combinations thereof, etc. One example of fuels with different heats of vaporization includes gasoline as a first fuel type with a lower heat of vaporization and ethanol as a second fuel type with a greater heat of vaporization. In another example, the engine may use gasoline as a first fuel type and an alcohol-containing fuel blend, such as E85 (which is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline), as a second fuel type. Other feasible substances include water, methanol, a mixture of ethanol and water, a mixture of water and methanol, a mixture of alcohols, etc. In still another example, both fuels may be alcohol blends with varying alcohol compositions, wherein the first fuel type may be a gasoline alcohol blend with a lower concentration of alcohol, such as Eli) (which is approximately 10% ethanol), while the second fuel type may be a gasoline alcohol blend with a greater concentration of alcohol, such as E85 (which is approximately 85% ethanol). Additionally, the first and second fuels may also differ in other fuel qualities, such as a difference in temperature, viscosity, octane number, etc. In still another example, fuel tanks in fuel system  8  may hold diesel fuel. Moreover, fuel characteristics of one or both fuel tanks may vary frequently, for example, due to day to day variations in tank refilling. 
     Controller  12  is shown in  FIG. 1  as a microcomputer, including a microprocessor unit  106 , input/output ports  108 , an electronic storage medium for executable programs (e.g., executable instructions) and calibration values shown as non-transitory read-only memory chip  110  in this particular example, random access memory  112 , keep alive memory  114 , and a data bus. Controller  12  may receive various signals from sensors coupled to engine  10 , including the signals previously discussed and additionally including a measurement of inducted mass air flow (MAF) from a mass air flow sensor  122 ; an engine coolant temperature (ECT) from a temperature sensor  116  coupled to a cooling sleeve  118 ; an exhaust gas pressure from a pressure sensor  158  coupled to exhaust passage  148  upstream of turbine  176 ; a profile ignition pickup signal (PIP) from a Hall effect sensor  120  (or other type) coupled to crankshaft  140 ; throttle position (TP) from the throttle position sensor; signal EGO from exhaust gas sensor  128 , which may be used by controller  12  to determine the AFR of the exhaust gas; and an absolute manifold pressure signal (MAP) from a MAP sensor  124 . An engine speed signal, RPM, may be generated by controller  12  from signal PIP. The manifold pressure signal MAP from MAP sensor  124  may be used to provide an indication of vacuum or pressure in the intake manifold. Controller  12  may infer an engine temperature based on the engine coolant temperature. 
     Controller  12  receives signals from the various sensors of  FIG. 1  and employs the various actuators of  FIG. 1  to adjust engine operation based on the received signals and instructions stored on a memory of the controller. For example, upon receiving signals from various sensors, the engine controller may send control signals to an actuator to alter the position of a variable inlet device (VID) of the compressor  174  and/or to an actuator of an active casing treatment arranged along an inlet conduit of the compressor  174  (as explained further below with reference to  FIGS. 6, 7, and 9 ). For example, the controller may send an electronic signal to an actuator of the VID to adjust the VID from an open to a closed position or a closed to an open position in response to a current engine speed and engine load relative to a surge threshold of the compressor. In other examples, positions of the VID and the casing treatment may be adjusted simultaneously by a single actuator in response to engine conditions. 
     As described above,  FIG. 1  shows only one cylinder of a multi-cylinder engine. As such, each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), spark plug, etc. It will be appreciated that engine  10  may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each of these cylinders can include some or all of the various components described and depicted by  FIG. 1  with reference to cylinder  14 . 
       FIGS. 2A-2B  show a cut-away view of a first example of a compressor  202  of a turbocharger including an active casing treatment (ACT) and a variable inlet device (VID)  240  positioned in an inlet conduit (e.g., intake passage) of the compressor  202 . In one example, compressor  202  may be compressor  174  of  FIG. 1 . A turbine, such as turbine  176  shown in  FIG. 1 , may be rotationally coupled to compressor  202  via a shaft  204 . Specifically, the turbine converts the energy of the exhaust gas into rotational energy for rotating shaft  204  connected to an impeller  206 . Impeller  206  may also be referred to herein as a compressor wheel. Compressor  202  includes impeller  206 , diffusers  208 , volutes (e.g., compressor chambers)  210 , an active casing treatment  212 , and casing  214 . The rotation of impeller  206  draws gas into compressor  202  through a compressor inlet  216  of casing  214 . As non-limiting examples, the gas may include air from an intake passage, exhaust gas (such as when using external exhaust gas recirculation), an air/fuel mix (such as from a fuel vapor canister or the engine crankcase), and combinations thereof. Gas flows from compressor inlet  216  and is accelerated by impeller  206  before flowing through diffuser  208  into volute  210 . Diffuser  208  and volute  210  decelerate the gas, causing an increase in pressure in volute  210 . Gas under pressure may flow from volute  210  to the intake manifold. 
     Elements in compressor  202  may be described relative to the direction of the gas flow path through compressor  202 . An element substantially in the direction of gas flow relative to a reference point is downstream from the reference point. An element substantially opposite the direction of gas flow relative to a reference point is upstream from the reference point. For example, compressor inlet  216  is upstream from impeller  206 , which is upstream from diffuser  208 . Diffuser  208  is downstream from impeller  206 , which is downstream from compressor inlet  216 . 
     Impeller  206  includes a hub  218  and a plurality of blades, including a full blade  220  and a splitter blade  222 . Impeller  206  can also include full blade  220  without splitter blade  222 . Full blade  220  and splitter blade  222  are attached to hub  218 . The edge of full blade  220  that is most upstream in compressor  202  is the leading edge of full blade  220 . Similarly, splitter blade  222  includes a leading edge at the most upstream portion of splitter  222 . The leading edge of full blade  220  is upstream of splitter blade  222 . Impeller  206  further includes an axis of rotation  224 , which is aligned with an axis of rotation for drive shaft  204  and a turbine hub of the turbine (not shown). The axis of rotation  224  is substantially parallel with the flow of gas at the compressor inlet  216  and substantially perpendicular to the flow of gas at the diffuser  208 . The axis of rotation  224  may also be referred to herein as a central axis of the compressor  202 . 
     Casing  214  includes compressor inlet  216 , an intake passage (also referred to herein as an inlet conduit)  226 , recirculation passages  228  (only one of which is labeled), recirculation ports  230  (only one of which is labeled), and bleed ports  232  (only one of which is labeled). Impeller  206  is contained in intake passage  226 . Each bleed port  232  is downstream of the leading edge of full blade  220  and upstream of the leading edge of splitter blade  222 . Each recirculation port  230  is downstream of compressor inlet  216  and upstream of impeller  206 . Recirculation ports  230  are configured to enable gas to flow between recirculation passages  228  and intake passage  226 . 
     Active casing treatment  212  is configured to control gas flow through compressor  202 . Specifically, active casing treatment  212 , controlled by a controller (e.g., controller  12  shown in  FIG. 1 ), may selectively control the flow of gas through each recirculation passage  228  (which may also be referred to as a casing treatment cavity). For example, during high pressure ratio and low mass flow conditions, active casing treatment  212  may enable gas to flow from intake passage  226 , through bleed port  232  into recirculation passage  228 , and back into intake passage  226 , in the direction of arrows  233  shown in  FIG. 2B . Thus, the flow of gas striking the leading edge of full blade  220  may be greater than without bleed port  232 . The additional flow of gas may enable the turbocharger compressor to operate with a smaller flow of gas through the compressor before surge occurs (e.g., by increasing a surge margin). 
     Intake passage  226  may be substantially cylindrical. Recirculation passage  228  may be substantially annular since it is external to and surrounds intake passage  226 . The ports connecting intake passage  226  and recirculation passage  228 , such as recirculation port  230  and bleed port  232 , may each be implemented with various means. For example, the ports may be constructed as one or more holes formed in a wall  207  of (e.g., a wall forming) the intake passage  226 . In one example, the wall  207  may be part of the casing  214 . As another example, the ports may be constructed as one or more slots extending around the circumference of the intake passage and through a wall of casing that forms the intake passage. The ports may have a uniform or non-uniform width along the length of the port from intake passage  226  to recirculation passage  228 . Each port may have a centerline extending along the length of the port from intake passage  226  to recirculation passage  228 . The centerline may be normal to the axis of rotation  224  of impeller  206 , or the centerline may have a non-zero slope when compared to the axis of rotation of impeller  206 . 
     Active casing treatment  212  may be implemented in many ways. For example, a slidable casing sleeve may be fitted in the recirculation passage to selectively block the flow of gas through recirculation port  230  and/or bleed port  232 . The casing sleeve may include one or more holes and/or one or more slots that align with recirculation port  230  and/or bleed port  232  depending on the position of the casing sleeve. In another example, as shown in  FIGS. 2A and 2B , a slidable valve may be used to selectively block the flow of gas through recirculation passage  228 . For example, a slidable valve  234   a  may be used to open and close each recirculation passage  228  at recirculation port  230 . In an alternative example, a slidable valve  234   b  may be included to open and close each recirculation passage  228  at bleed port  232  instead of slidable valve  234   a . In still another example, slidable valve  234   b  may be positioned within intake passage  226  instead of within recirculation passage  228 , as shown. The positioning of the slidable valve (e.g., at recirculation port  230  or at bleed port  232 , within recirculation passage  228  or within intake passage  226 ) may be selected based on manufacturing constraints, such as packaging constraints. During conditions under which the slidable valve is closed, as further described herein, an efficiency of the compressor may be marginally increased by closing active casing treatment  212  at bleed port  232  (e.g., via slidable valve  234   b ) compared with closing active casing treatment  212  at recirculation port  230  (e.g., via slidable valve  234   a ). As an illustrative example, for a same compressor mass flow rate and speed, the efficiency may be approximately 0.700 when active casing treatment  212  is closed via slidable valve  234   b  and approximately 0.695 when closed via slidable valve  234   a . Similarly, the efficiency may be further marginally increased when slidable valve is positioned within intake passage  226  instead of within recirculation passage  228 . 
       FIG. 2A  shows slidable valve  234   a  positioned so that recirculation port  230  is closed (or slidable valve  234   b  is positioned so that bleed port  232  is closed), thereby preventing airflow to intake passage  226  from recirculation passage  228 . The positioning of slidable valve  234   a  shown in  FIG. 2A  may be referred to herein as a closed position.  FIG. 2B  shows slidable valve  234   a  positioned so that recirculation port  230  is open (or slidable valve  234   b  is positioned so that bleed port  232  is open), thereby enabling airflow to intake passage  226  from recirculation passage  228 , as indicated by arrows  233 . The positioning of slidable valve  234   a  shown in  FIG. 2B  may be referred to herein as an open position. In this way, the active casing treatment  212  may be adjusted so that air flows through recirculation passage  228  under select operating conditions, as will be further described with respect to  FIGS. 7 and 9 . Slidable valve  234   a  (or slidable valve  234   b ) may be moved between the open and closed positions via an actuator  209 , which may be communicatively coupled to a controller (e.g., controller  12  of  FIG. 1 ). Actuator  209  may be electrically or hydraulically actuated and may include an integrated position sensor  209   a . For example, the integrated position sensor  209   a  may supply a position feedback signal  209   b  representative of actuator position, and thus the position of slidable valve  234   a  (or slidable valve  234   b ), to the controller. When the position feedback signal  209   b  indicates that slidable valve  234   a  (or slidable valve  234   b ) has reached the commanded position, the controller may de-energize the actuator  209 , for example. 
     In an alternative example, active casing treatment  212  may be adjusted based on a pressure differential across compressor inlet  216  and an intake manifold downstream of the compressor. In yet another alternative example, active casing treatment  212  may be adjusted based on a pressure differential across the intake manifold and the turbine inlet. In still another alternative example, active casing treatment  212  may be adjusted based on engine load and engine speed conditions (e.g., a current operating speed and load of the engine) in relation to a surge threshold. It will be understood that the examples presented herein are explanatory in nature and the active casing treatment  212  may be adjusted based on other parameters. 
     As shown in  FIGS. 2A-2B , VID  240  is positioned within intake passage  226  immediately upstream of the impeller  206 , such that no other components may be placed between VID  240  and impeller  206 . In one example, immediately upstream of the impeller refers to VID  240  being positioned upstream of impeller  206  at a distance that is within 25% of a length between bleed port  232  and recirculation port  230 . For example, bleed port  232  and recirculation port  230  may be spaced apart by a first length (e.g., 50 mm) and VID  240  may be spaced away from the leading edge of impeller  206  by a second length (e.g., 10 mm), thus VID  240  may be spaced from impeller  206  by a distance that is within 25% (e.g., 20%) of the length separating the bleed port from the recirculation port. In another example, additionally or alternatively, immediately upstream of the impeller refers to VID  240  being positioned upstream of impeller  206  at a distance that is substantially smaller than a diameter of intake passage  226 , such as less than one fifth of the diameter of intake passage  226 . In still another example, additionally or alternatively, immediately upstream of the impeller refers to VID  240  being positioned proximate to impeller  206  at a distance in a range of 2 to 10 millimeters from the leading edge of impeller  206 . Furthermore, a plane of VID  240  may at least partially overlap with a plane of volutes  210 . For example, as explained in more detail below, VID  240  may include a plurality of vanes, such as vane  241 , and when the vanes are closed (as shown in  FIG. 2A ), the downstream surface of the vanes (e.g., the second surface  246  facing impeller  206 ) may form a plane  260  that intersects the volutes. An outlet end  203  of the VID  240  is arranged upstream of the bleed port  232 , and an inlet end  205  is arranged downstream of recirculation port  230 . The VID  240  spans around an inner circumference of the intake passage  226  and is arranged adjacent to an interior surface of wall  207  of the intake passage  226 . For example, an outer diameter of VID  240  may be approximately equal to an inner diameter of intake passage  226  such that an outer perimeter of VID  240  is in face-sharing contact with the interior surface of wall  207 . VID  240  includes a plurality of vanes (or blades)  241 , each vane  241  coupled to an actuation plate  215  via a pivoting pin and an actuation arm  219 . The number of vanes may vary, such as a number in a range from 2 to 15. Each vane  241  has a first surface  244  and a second surface  246 , the first surface  244  and the second surface  246  separated by a thickness of the vane and parallel to each other. Each vane  241  also has a length and a width, the width increasing along the length of the vane radially outward, as illustrated with respect to  FIG. 3A . 
       FIG. 2A  shows a first schematic  200  with the VID adjusted (e.g., actuated) into a closed position, as will be further described below with reference to  FIG. 3A , while  FIG. 2B  shows a second schematic  225  with the VID adjusted (e.g., actuated) into an open position, as will be further described below with reference to  FIG. 3B . When VID  240  is in the closed position shown in  FIG. 2A , the first surface  244  is an upstream surface and the second surface  246  is a downstream surface. The first surface  244  and the second surface  246  of each vane  241  are both substantially perpendicular to the central axis of the compressor  224  as well as a direction of gas flow at compressor inlet  216 . When VID  240  is in the open position shown in  FIG. 2B , the first surface  244  and the second surface  246  of each vane  241  are both substantially parallel to the central axis of the compressor  224  as well as the direction of gas flow at compressor inlet  216 . Furthermore, in the open position, the first surface  244  and the second surface  246  are rotated 90 degrees relative to when in the closed position. VID  240  may be actuated between the open position and the closed position via the actuation plate  215  and an actuator  223 . Actuator  223  may be a motor, for example, that is communicatively coupled to the controller such that a command signal from the controller results in actuator  223  adjusting the position of vanes  241  via actuation plate  215 . Actuator  223  may be electrically or hydraulically actuated and may include an integrated position sensor. For example, the integrated position sensor may supply a position feedback signal representative of actuator position, and thus the position of vanes  241 , to the controller. When the position feedback signal indicates that vanes  241  have reached the commanded position, the controller may de-energize the actuator  223 , for example. 
     Under lighter load conditions, VID  240  may be actuated into the closed position by the controller via actuator  223  and actuation plate  215 , as shown in  FIG. 2A . In the closed position, airflow in front of the leading edge of full blade  220  is blocked. For example, with VID  240  in the closed position, the diameter of intake passage  226  immediately upstream of impeller  206  is restricted, with VID  240  positioned in a smaller radius (e.g., small trim) condition. The outer perimeter of the impeller (e.g., outer edges adjacent to casing  214 ) does not interact with the air flow, effectively reducing a size of impeller  206 . For example, VID  240  may block airflow to 20-40% of impeller  206  when in the closed position. As used herein, the outer perimeter of the impeller refers to the 20-40% of the impeller that is blocked by VID  240  in the small trim condition, while a central portion of the impeller, including hub  218 , remains unblocked. As a result, a performance of compressor  202  resembles that of a smaller compressor, and compressor efficiency at low compressor speeds and mass flows is increased. In some examples, active casing treatment  212  may be simultaneously adjusted into a position that prevents airflow through recirculation passage  228 , such as by actuating slidable valve  234   a  to the closed position, further increasing the compressor efficiency compared to when VID  240  and slidable valve  234   a  are kept in the open position. However, in other examples, VID  240  and active casing treatment  212  may be adjusted at different timings. In still other examples, VID  240  and active casing treatment  212  may be actuated using a single actuation system, as will be described with respect to  FIGS. 4A-4B . 
     For higher engine loads, the VID  240  is actuated to the open position via actuator  223  and actuation plate  215 , as shown in  FIG. 2B . For example, actuator  223  may be an electronic or hydraulic motor, which may rotate actuation plate  215  and in turn drive VID  240  to close or open via rotation of each actuation arm  219 . In the open position, airflow to impeller  206  is unrestricted, with VID  240  positioned in a larger radius (e.g., large trim) condition, enabling higher engine power or torque. In some examples, when VID  240  is opened, active casing treatment  212  may be simultaneously adjusted so that airflow through recirculation passage  228  is enabled (e.g., slidable valve  234   a  is actuated to the open position), as shown in  FIG. 2B . By enabling air to flow through recirculation passage  228 , a surge margin of the compressor is extended. However, in other examples, VID  240  and active casing treatment  212  may be adjusted at different timings. By including both of VID  240  and active casing treatment  212  and adjusting their positions based on operating conditions, compressor  202  may be operated at a wide flow range with a high efficiency and an extended surge margin, decreasing fuel consumption and increasing engine power. 
       FIGS. 3A-3B  show details of VID  240  shown in  FIGS. 2A-2B . Specifically,  FIG. 3A  shows an angled front view  300  of the VID  240  in the closed position, and  FIG. 3B  shows an angled front view  320  of the VID  240  in the open position. Components of  FIGS. 3A-3B  that are the same as components in  FIGS. 2A-2B  are numbered the same and may not be reintroduced. 
     As shown in  FIGS. 3A-3B , VID  240  includes a plurality of adjacently arranged vanes  241  in a ring around a central axis of VID  240 , which may be collinear with a central axis of a compressor, such as axis of rotation  224  shown in  FIGS. 2A-2B . Inlet end  205  of VID  240 , shown going into the page in views  300  and  320 , is formed by actuation plate  215 . Outlet end  203  of VID  240 , shown coming out of the page in views  300  and  320 , is formed by interior edges  309  of vanes  241 . Gas (e.g., intake air) flowing through a passage in which the VID  240  is positioned (such as the inlet conduits or intake passages shown in  FIGS. 2A-2B ) contacts the interior edges  309  as it passes through the VID  240 . To transition VID  240  between the closed position ( FIG. 3A ) and the open position ( FIG. 3B ), each vane  241  is rotated about an actuation axis  313  via the corresponding actuation arm  219 . Each actuation axis  313  is arranged radially from the central axis of the compressor. 
     In the closed position shown in  FIG. 3A , the interior edges  309  of vanes  241  form a continuous ring with an inner diameter  343 , which serves as a flow passage through VID  240 . The edges of vanes  241  may have a tapered shape that allows the adjacent vanes  241  to overlap to reduce the leakage flow through the vanes. With first surface  244  and second surface  246  of each vane  241  positioned perpendicular to the direction of airflow, vanes  241  restrict airflow through VID  240 , and a diameter of outlet end  203  is equal to inner diameter  343  in the closed position. Inner diameter  343  may be equal to 60-80% of an outer diameter of VID  240 , which may be approximately equal to an inner diameter of an intake passage in which VID is positioned (e.g., intake passage  226  shown in  FIGS. 2A and 2B ). When VID  240  is in the open position and first surface  244  and second surface  246  of each vane  241  are positioned parallel to the direction of airflow, the ring formed by vanes  241  (indicated by dashed line  310  in  FIG. 3B ) is no longer continuous. In the open position, vanes  241  restrict airflow through VID  240  to a lesser extent, and the diameter of outlet end  203  is substantially equal to an inner diameter  345  of actuation plate  215 , which is greater than inner diameter  343 . 
     The VID may alternatively be adapted to shift radially in and out of the intake passage of the compressor to adjust an effective flow area of the compressor inlet.  FIGS. 4A-4B  show a cut-away view of a second example of a compressor  402  of a turbocharger including an ACT and a VID  440  positioned in an inlet conduit (e.g., intake passage) of the compressor  402 . In one example, compressor  402  may be compressor  174  of  FIG. 1 . A turbine, such as turbine  176  shown in  FIG. 1 , may be rotationally coupled to compressor  402  via a shaft  404 . Specifically, the turbine converts the energy of the exhaust gas into rotational energy for rotating shaft  404  connected to an impeller  406 . Impeller  406  may also be referred to herein as a compressor wheel. Compressor  402  includes impeller  406 , diffusers  408 , volutes (e.g., compressor chambers)  410 , an active casing treatment  412 , and casing  414 . The rotation of impeller  406  draws gas into compressor  402  through a compressor inlet  416  of casing  414 . As non-limiting examples, the gas may include air from an intake passage, exhaust gas (such as when using external exhaust gas recirculation), an air/fuel mixture, and combinations thereof. Gas flows from compressor inlet  416  and is accelerated by impeller  406  before flowing through diffuser  408  into volute  410 . Diffuser  408  and volute  410  decelerate the gas, causing an increase in pressure in volute  410 . Gas under pressure may flow from volute  410  to the intake manifold. 
     Elements in compressor  402  may be described relative to the direction of the gas flow path through compressor  402 . An element substantially in the direction of gas flow relative to a reference point is downstream from the reference point. An element substantially opposite the direction of gas flow relative to a reference point is upstream from the reference point. For example, compressor inlet  416  is upstream from impeller  406 , which is upstream from diffuser  408 . Diffuser  408  is downstream from impeller  406 , which is downstream from compressor inlet  416 . 
     Impeller  406  includes a hub  418  and a plurality of blades, including a full blade  420  and a splitter blade  422 . Impeller  406  can also include full blade  420  without splitter blade  422 . Full blade  420  and splitter blade  422  are attached to hub  418 . The edge of full blade  420  that is most upstream in compressor  402  is the leading edge of full blade  420 . Similarly, splitter blade  422  includes a leading edge at the most upstream portion of splitter blade  422 . The leading edge of full blade  420  is upstream of splitter blade  422 . Impeller  406  further includes an axis of rotation  424 , which is aligned with an axis of rotation for drive shaft  404  and a turbine hub of the turbine (not shown). The axis of rotation  424  is substantially parallel with the flow of gas at the compressor inlet  416  and substantially perpendicular to the flow of gas at the diffuser  408 . The axis of rotation  424  may also be referred to herein as a central axis of the compressor  402 . 
     Casing  414  includes compressor inlet  416 , an intake passage (also referred to herein as an inlet conduit)  426 , recirculation passages  428  (only one of which is labeled), recirculation ports  430  (only one of which is labeled), and bleed ports  432  (only one of which is labeled). Impeller  406  is contained in intake passage  426 . Each bleed port  432  is downstream of the leading edge of full blade  420  and downstream or upstream of the leading edge of splitter blade  422 . Each recirculation port  430  is downstream of compressor inlet  416  and upstream of impeller  406 . Recirculation ports  430  are configured to enable gas to flow between recirculation passages  428  and intake passage  426 . 
     Active casing treatment  412  is configured to control gas flow through compressor  402 . Specifically, active casing treatment  412 , controlled by a controller (e.g., controller  12  shown in  FIG. 1 ), may selectively control the flow of gas through each recirculation passage  428  (which may also be referred to as a casing treatment cavity). For example, during high pressure ratio and low mass flow conditions, active casing treatment  412  may enable gas to flow from intake passage  426 , through bleed port  432  into recirculation passage  428 , and back into intake passage  426 , in the direction of arrows  433  shown in  FIG. 4B . Thus, the flow of gas striking the leading edge of full blade  420  may be greater than without bleed port  432 . The additional flow of gas may enable the turbocharger compressor to operate with a smaller flow of gas through the compressor before surge occurs (e.g., by increasing a surge margin). 
     Intake passage  426  may be substantially cylindrical. Recirculation passage  428  may be substantially annular since it is external to and surrounds intake passage  426 . The ports connecting intake passage  426  and recirculation passage  428 , such as recirculation port  430  and bleed port  432 , may each be implemented with various means. For example, the ports may be constructed as one or more holes formed in a wall  407  of (e.g., a wall forming) the intake passage  426 . In one example, the wall  407  may be part of the casing  414 . As another example, the ports may be constructed as one or more slots extending around the circumference of the intake passage and through a wall of casing that forms the intake passage. The ports may have a uniform or non-uniform width along the length of the port from intake passage  426  to recirculation passage  428 . Each port may have a centerline extending along the length of the port from intake passage  426  to recirculation passage  428 . The centerline may be normal to the axis of rotation  424  of impeller  406 , or the centerline may have a non-zero slope when compared to the normal to the axis of rotation of impeller  406 . 
     Active casing treatment  412  and VID  440  may be adjusted using a suitable actuator. As shown in  FIGS. 4A and 4B , airflow through both active casing treatment  412  and VID  440  is controlled by a single actuation system  435 , as will be further described with respect to  FIGS. 5A-5C . A common actuator  423 , which may be a motor, for example, adjusts a position of a unison ring  415  via a shaft  425 . Unison ring  415  may be driven electronically or hydraulically by common actuator  423 . Unison ring  415  includes a plurality of valves  434 , a number of valves  434  corresponding to a number of recirculation passages  428 , and a plurality of slots (not visible in  FIGS. 4A and 4B ), a number of slots corresponding to a number of vanes  441  of VID  440 . Each vane  441  is coupled to a slot of unison ring  415  via an arm  419  and a pin  421 .  FIG. 4A  shows a first schematic  400  with the VID adjusted (e.g., actuated) into a closed position and airflow through each recirculation passage  428  blocked by valves  434  of unison ring  415 , as will be further described below with reference to  FIG. 5A , while  FIG. 4B  shows a second schematic  450  with the VID adjusted (e.g., actuated) into an open position and airflow through each recirculation passage  428  enabled, as will be further described below with reference to  FIG. 5C . 
     Common actuator  423  may include an integrated position sensor. For example, the integrated position sensor may supply a position feedback signal representative of actuator position, and thus the position of vanes  441  and valves  434 , to the controller. Because vanes  441  and valves  434  are actuated together via the common actuator  423  and the unison ring  415 , a single feedback signal may be used to determine that both of the vanes  441  and the valves  434  are moving as commanded. When the position feedback signal indicates that vanes  441  and valves  434  have reached the commanded position, the controller may de-energize the common actuator  423 , for example. 
     As shown in  FIGS. 4A-4B , VID  440  is positioned within intake passage  426  immediately upstream of the impeller  406 , such that no other components may be placed between VID  440  and impeller  406 . In one example, immediately upstream of the impeller refers to VID  440  being positioned upstream of impeller  406  at a distance that is within 25% of a length between bleed port  432  and recirculation port  430 . In another example, additionally or alternatively, immediately upstream of the impeller refers to VID  440  being positioned upstream of impeller  406  at a distance that is substantially smaller than a diameter of intake passage  426 , such as less than one fifth of the diameter of intake passage  426 . In still another example, additionally or alternatively, immediately upstream of the impeller refers to VID  440  being positioned proximate to impeller  406  at a distance in a range of 2 to 10 millimeters from the leading edge of impeller  406 . Furthermore, a plane of VID  440  may at least partially overlap with a plane of volutes  410 . An outlet end  403  of the VID  440  is arranged upstream of the bleed port  432 , and an inlet end  405  is arranged downstream of recirculation port  430 . The number of vanes  441  may vary, such as a number in a range from 2 to 15. Each vane  441  has a first surface  444  and a second surface  446 , the first surface  444  and the second surface  446  separated by a thickness of the vane and parallel to each other. The first surface  444  is an upstream, inlet surface of each vane  441 , and the second surface  446  is a downstream, outlet surface of each vane. The first surface  444  and the second surface  446  of each vane  441  are substantially perpendicular to the central axis of the compressor  424  and the direction of gas flow at compressor inlet  416 . Each vane  441  also has a length and a width, the width increasing along the length of the vane radially outward, as illustrated with respect to  FIG. 4A . 
     Under lighter load conditions, VID  440  may be actuated into the closed position by the controller via actuator  423  rotating unison ring  415  to a first position shown in  FIG. 4A  and further described with respect to  FIG. 5A . When VID  440  is in the closed position, vanes  441  protrude into intake passage  426  via a cavity  413  within active casing treatment  412 . Vanes  441  may be positioned adjacent to inner wall  407  such that no air flows between vanes  441  and inner wall  407 . In some examples, vanes  441  may extend into cavity  413  to reduce air leakage into cavity when in the closed position. In the closed position, airflow in front of the leading edge of full blade  420  is blocked. For example, with VID  440  in the closed position, the diameter of intake passage  426  immediately upstream of impeller  406  is restricted, with VID  440  positioned in a smaller radius (e.g., small trim) condition. The perimeter of the impeller (e.g., outer edges adjacent to casing  414 ) does not interact with the air flow, effectively reducing a size of impeller  406 . For example, VID  440  may block airflow to 20-40% of impeller  406  when in the closed position, the blocking occurring at the outer 20-40% of the impeller and not the center of the impeller. As a result, compressor efficiency at low compressor speeds and mass flows is increased. At the same time, the rotation of unison ring  415  to the first, closed position places valves  434  such that airflow is prevented through each recirculation passage  428 , further increasing the compressor efficiency compared to when VID  440  is closed and active casing treatment  412  is open (e.g., recirculation passage  428  is open). Active casing treatment  412  may be referred to herein as in a closed position when airflow through each recirculation passage  428  is blocked by valves  434 , such as shown in  FIG. 4A . 
     For higher engine loads, VID  440  is actuated to the open position by the controller via actuator  423  rotating unison ring  415  to a second position shown in  FIG. 4B  and further described with respect to  FIG. 5C  (a number of intermediate positions may exist between the first position and the second position, such as will be described with respect to  FIG. 5B ). The rotation of unison ring  415  retracts vanes  441  into cavity  413  such that vanes  441  no longer protrude into intake passage  426  and are positioned within walls of active casing treatment  412 . In the open position, airflow to impeller  406  is unrestricted, with VID  440  positioned in a larger radius (e.g., large trim) condition, enabling higher engine power or torque. For example, interior edges  409  of vanes  441  may be flush with inner wall  407 . At the same time, the rotation of unison ring  415  to the second, open position rotates valves  434  out of each recirculation passage  428  such that airflow through the recirculation passages is enabled, extending a surge margin of compressor  402  compared to when airflow through the recirculation passages is blocked. (Valves  434  are not visible in the view of  FIG. 4B , as they have been rotated out of the plane of second schematic  450 .) Active casing treatment  412  may be referred to herein as in an open position when airflow through each recirculation passage  428  is enabled, such as shown in  FIG. 4B . 
     By including both of VID  440  and active casing treatment  412  under control of a common actuator  423 , compressor  402  may be operated at a wide flow range with a high efficiency and an extended surge margin, decreasing fuel consumption and increasing engine power. In this way, active casing treatment  412  and VID  440  may be simultaneously adjusted so that air flows through recirculation passage  428  under select operating conditions and impeller  406  has a reduced effective size under other operating conditions, as will be further described with respect to  FIG. 9 . As an example, active casing treatment  412  and VID  440  may be simultaneously adjusted based on a pressure differential across compressor inlet  416  and an intake manifold downstream of the compressor. In another example, active casing treatment  412  and VID  440  may be simultaneously adjusted based on a pressure differential across the intake manifold and the compressor inlet. In still another example, active casing treatment  412  and VID  440  may be simultaneously adjusted based on engine load and engine speed conditions (e.g., a current operating speed and load of the engine) in relation to a surge thresholds. It will be understood that the examples presented herein are explanatory in nature and other examples are possible. Furthermore, by using the common actuation system, only one position sensor is needed to determine whether each of the VID and active casing treatment are moving into commanded positions as expected. 
       FIGS. 5A-5C  show details of VID  440  and unison ring  415  of  FIGS. 4A-4B . Specifically,  FIG. 5A  shows a front view  500  of VID  440  and active casing treatment  412  in the closed position,  FIG. 5B  shows a front view  510  of VID  440  and active casing treatment  412  in an intermediate position, and  FIG. 5C  shows a front view  520  of VID  440  and active casing treatment  412  in the open position. Components of  FIGS. 5A-5C  that are the same as components in  FIGS. 4A-4B  are numbered the same and may not be reintroduced. 
     As shown in  FIGS. 5A-5B , VID  440  includes a plurality of adjacently arranged vanes  441  in a ring around a central axis of VID  440 , which may be collinear with a central axis of a compressor, such as axis of rotation  424  shown in  FIGS. 4A-4B . Inlet end  405  of VID  440  is shown going into the page in views  500 ,  510 , and  520 , and outlet end  403  of VID  440  is shown coming out of the page in views  500 ,  510 , and  520 . Gas (e.g., intake air) flowing through a passage in which the VID  440  is positioned (such as the inlet conduits or intake passages shown in  FIGS. 4A-4B ) contacts the interior edges  409  as it passes through the VID  440 . Thus, interior edges  409  form a flow passage through VID  440 . 
     In the closed position shown in  FIG. 5A , the interior edges  409  of vanes  441  form a continuous ring with an inner diameter  543 . Inner diameter  543  may be equal to 60-80% of an inner diameter of an intake passage in which VID  440  is positioned (e.g., intake passage  426  shown in  FIGS. 4A and 4B ) when VID  440  is in the open position. The interior edges  409  of the vanes  441  may have a tapered shape so that adjacent vanes  411  may overlap to avoid leakage. To transition VID  440  and active casing treatment  412  between the closed position ( FIG. 5A ) and the open position ( FIG. 5C ), each vane  441  of VID  440  is retracted into cavity  413  by rotating unison ring  415  via common actuator  423  and shaft  425 . For example, common actuator  423  may be a stepper motor that laterally moves shaft  425 . The lateral movement of shaft  425  rotates unison ring  415 . As unison ring  415  is rotated, slots  417  move with respect to arm  419  and pin  421  of each vane  441 , which may be translatable in a radial direction. As a result, pin  421  slides along slot  417 , pulling vane  441  radially outward to increase inner diameter  543 . For example, as shown in  FIG. 5B , when VID  440  and active casing treatment  412  are in the intermediate position, vanes  441  are partially retracted into cavity  413 . At the same time, the rotation of unison ring  415  moves valves  434  such that recirculation passages  428  are partially opened. Note that while two recirculation passages  428  (and two corresponding valves  434 ) are shown, any number of recirculation passages are possible, which may be symmetrically or asymmetrically distributed about the central axis of the compressor. When VID  440  is in the open position and vanes  441  are fully retracted into cavity  413 , inner diameter  543  is at a maximum, which is equal to a diameter of inner wall  407 , as shown in  FIG. 5C . When active casing treatment  412  is in the open position, valves  434  no longer overlap or obstruct recirculation passages  428 , as also shown in  FIG. 5C . 
     In some examples, the intermediate position shown in  FIG. 5B  may be transitory, and VID  440  and active casing treatment  412  may be operated in only the open (e.g., fully open) and the closed (e.g., fully closed) positions. In other examples, VID  440  and active casing treatment  412  may be continuously variable between the fully open and fully closed positions, with a controller selecting a position of the unison ring that will result in a desired partially open position based on operating conditions. 
       FIGS. 2A-5C  show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example. 
     Turning to  FIG. 6 , a flow chart of an example method  600  for controlling operation (e.g., controlling a position) of a variable inlet device positioned in an inlet conduit of a turbocharger compressor is shown. Specifically, the variable inlet device (VID) may be VID  240  shown in  FIGS. 3A-3B  and may be included in an engine system, such as the system of engine  10  shown in  FIG. 1 . The VID may be positioned in an inlet conduit of a compressor, upstream of an impeller, such as shown in  FIGS. 2A-2B . As also shown in  FIGS. 2A-2B , in some examples, the compressor may additionally include a casing treatment including a recirculation passage. Instructions for carrying out method  600  and the rest of the methods included herein may be executed by a controller (e.g., controller  12  shown in  FIG. 1 ) based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference to  FIG. 1 . The controller may employ engine actuators of the engine system (e.g., EGR valve  80  of  FIG. 1 ) to adjust engine operation according to the methods described below. For example, the controller may employ an actuator of the VID (e.g., actuator  223  shown in  FIGS. 2A and 2B ) to adjust the VID between an open position (as shown in  FIGS. 2B and 3B ) and a closed position (as shown in  FIGS. 2A and 3A ). 
     Method  600  begins at  602  and includes estimating and/or measuring engine operating conditions. Engine operating conditions may include engine speed, engine load, engine temperature (such as inferred from an engine coolant temperature measured by an engine coolant temperature sensor), mass air flow (e.g., as measured by a MAF sensor, such as MAF sensor  122  of  FIG. 1 ), intake manifold pressure (e.g., as measured by a MAP sensor, such as MAP sensor  124  of  FIG. 1 ), a pressure differential across a compressor, a mass air flow rate through the compressor, a speed of the compressor, a position of the VID, exhaust pressure (e.g., as measured by exhaust pressure sensor  158 ), etc. The operating conditions may be measured or inferred based on available data. 
     At  604 , method  600  includes determining whether the engine is operating below a threshold. Operating below the threshold may include a current (e.g., currently determined) engine speed and engine load being below the threshold. In one example, the threshold may be a pre-set threshold stored in a map or look-up table in a memory of the controller. Turning briefly to  FIG. 8 , an example map  800  of engine load (vertical axis) vs. engine speed (horizontal axis) is shown. Map  800  includes an operational boundary line  802 . All of the possible engine speed and engine load operational points of the engine may be contained within the axes and operational boundary line  802 . The map  800  also includes a surge threshold  804 . When the engine is operating at an engine speed and engine load point that falls below, or to the left of, the surge threshold  804 , such as in a first area  806 , the likelihood of compressor surge may be increased relative to when the engine is operating at an engine speed and engine load point that falls above, or to the right of, the surge threshold  804 , such as in a second area  808 . 
     In the second area  808  of engine map  800 , a threshold  805  divides the second area  808  into a high load region  808   a  and a low load region  808   b . The high load region  808   a  is to the right of the threshold  805  and comprises engine loads and speeds higher than those defined by the threshold  805 . Peak torque engine operation is included in high load region  808   a , and the VID and the active casing treatment may be adjusted to provide increased flow through the compressor to enable the peak torque engine operation as well as surge mitigation. In the low load region  808   b , engine loads and speeds are lower than those defined by the threshold  805  and may correspond to idling or cruising operations of the vehicle. Thus, in this region, a capacity for peak torque engine operation is not needed, and the VIC and the active casing treatment may be adjusted into positions to decrease mass flow into the compressor while increasing compressor efficiency and therefore engine fuel economy. 
     Additionally or alternatively, the controller may refer to a map or look-up table of compressor conditions, such as the differential pressure across the compressor and/or the mass air flow through the compressor to compare the operating conditions of the compressor to the surge threshold. An example of such a compressor map  1000  in shown in  FIG. 10 . 
     The horizontal axis of compressor map  1000  represents a mass flow rate of the compressor, with values increasing from left to right, while the vertical axis represents a pressure ratio across the compressor (e.g., an output pressure divided by an input pressure), with values increasing from bottom to top. Compressor map  1000  includes a plurality of compressor speed lines  1002 , a surge limit  1004 , and a choke limit  1006 . The surge limit  1004  represents where the compressor operation may lose stability and exhibit surge behavior, ranging from whoosh noise to violent oscillations of flow. Choke limit  1006  represents the highest possible mass flow rate at a given pressure ratio. An area between the surge limit  1004  and the choke limit  1006  represents a region of stable compressor operation, which may correspond to the second area  808  of the engine map  800  of  FIG. 8 . 
     A first threshold  1008  may separate a first compressor map region  1010  of low mass flow and low pressure ratios within the region of stable operation from regions of compressor map  1000  of compressor operation at higher mass flows and higher pressure ratios. The compressor operation at higher mass flows and higher pressure ratios may be further subdivided into a second compressor map region  1012 , a third compressor map region  1013 , and a fourth compressor map region  1014 . Boundaries between each of the first, second, third, and fourth compressor map regions  1010 ,  1012 ,  1013 , and  1014 , respectively, may be defined by adjustments in the VID and active casing treatment positioning to accommodate compressor operation, as will be further described herein. 
     The first threshold  1008  may correspond to the threshold  805  of engine map  800  of  FIG. 8 . A second threshold  1011  may at least partially separate the second compressor map region  1012  and the third compressor map region  1013 . A fourth compressor map region  1014 , corresponding to a peak efficiency region, may be positioned between the second compressor map region  1012  and the third compressor map region  1013  and may be separated from the second compressor map region  1012  by the second threshold  1011 . Compressor operation in the first compressor map region  1010  may represent driving conditions where peak torque operation of the engine is not demanded and conversely, operation in one of the second compressor map region  1012 , the third compressor map region  1013 , and the fourth compressor map region  1014  may include peak torque engine operation. The second compressor map region  1012 , the third compressor map region  1013 , and the fourth compressor map region  1014  will be further described with respect to  FIG. 7 . 
     Returning to  FIG. 6 , if the engine is operating below the threshold (e.g., the current engine speed and load operating point is in the low load region  808   b  shown in map  800  and/or to the left of first threshold  1008  in compressor map  1000  of  FIG. 10 ), method  600  continues to  606  and includes maintaining the VID closed. Because the engine is already operating below the threshold, which corresponds to operation with the VID closed, it is expected that the VID will already be in the closed position. The closed position of the VID is shown in  FIGS. 2A and 3A , as described above. As explained above with reference to  FIGS. 2A and 3A , in the closed position, interior edges of the VID reduce a diameter of the intake passage immediately upstream of the impeller. 
     At  608 , method  600  includes determining if the engine operation is approaching the threshold. The engine operation approaching the threshold may indicate that a transition from operation below the threshold to operation above the threshold is expected. As one example, the controller may input the compressor mass flow rate, compressor speed, and compressor pressure ratio into one or more look-up tables, algorithms, or maps (such as compressor map  1000  of  FIG. 10 ) to determine a real-time estimation of a distance from the threshold (e.g., first threshold  1008 ). Additionally or alternatively, as another example, the controller may input the engine speed and load into one or more look-up tables, algorithms, or maps (such as engine map  800  of  FIG. 8 ) to determine the real-time estimation of the distance from the threshold (e.g., threshold  805 ). It may be determined that the engine operation is approaching the threshold in response to the distance from the threshold being within a predetermined amount and/or the distance from the threshold decreasing at greater than a threshold rate, for example. 
     If the engine operation is not approaching the threshold, a transition across the threshold is not expected, and method  600  may return to  606  to continue maintaining the VID closed. If the engine operation is approaching the threshold, method  600  proceeds to  610  and includes increasing an amount of power delivered to an exhaust turbine of the turbocharger (e.g., turbine  176  of  FIG. 1 ) to avoid a momentary reduction in compressor mass flow rate that may occur when the VID is adjusted to an open position. For example, during a transition from operating in the low load region  808   b  to the high load region  808   a  shown in  FIG. 8  (or a transition from operating in the first compressor map region  1010  to one of the second compressor map region  1012 , the third compressor map region  1013 , and the fourth compressor map region  1014  of  FIG. 10 ), if the turbine power is maintained during the transition, a momentary loss in compressor efficiency and therefore compressor mass flow rate is expected. Therefore, the controller may perform an anticipatory control action to maintain the compressor efficiency, and thus the mass flow rate, during the transition. 
     Specifically, if the turbine is a VGT, the turbine power may be determined based on a VGT vane position and the pre-turbine exhaust pressure. In order to avoid the loss in mass flow rate, which also reduces the surge margin, the controller may increase the power delivered to the exhaust turbine via a coordinated adjustment of the VGT vane position and an EGR valve position. For example, the controller may input the real-time estimation of the distance from the threshold, which serves as a transition boundary, into one or more look-up tables, algorithms, or maps and output the corresponding VGT vane position and/or EGR valve position. The controller may then send command signals to the VGT and/or the EGR valve to adjust the VGT vanes and/or the EGR valve to the output positions. As an example, decreasing an opening of the EGR valve may increase the pre-turbine exhaust pressure, thereby increasing the compressor speed and maintaining the compressor mass flow rate. As another example, adjusting the VGT vanes to a position that decreases a cross sectional opening of the turbine may increase the pre-turbine exhaust pressure. 
     At  612 , method  600  includes determining if the engine operation crosses the threshold. For example, the engine operation may cross the threshold by going from an operating point below the threshold to an operating point above the threshold, such as by going from an operating point within low load region  808   b  to an operating point in high load region  808   a  shown in  FIG. 8 . As another example, the engine operation may cross the threshold by going from a compressor operating point in the first compressor map region  1010  to a compressor operating point in one of the second compressor map region  1012 , the third compressor map region  1013 , and the fourth compressor map region  1014  shown in  FIG. 10 . 
     If the engine operation does not cross the threshold, method  600  may return to  606  to maintain the VID closed. Furthermore, if the engine operation is no longer approaching the threshold, the controller may reduce the power delivered to the exhaust turbine, such as by reducing the exhaust pressure upstream of the exhaust turbine. For example, the controller may undo the anticipatory control action performed at  610  to revert the VGT vanes and/or the EGR valve to nominal positions for the given operating conditions. The controller may refer to a look-up table having the engine speed and load as the input and output the EGR valve position and/or the VGT vane position corresponding to the input engine speed-load, for example. In another example, the controller may determine the EGR amount (and thus the EGR valve position) and/or VGT vane position through logic rules that directly take into account parameters such as engine load, engine speed, engine temperature, etc. 
     If the engine operation crosses the threshold, method  600  proceeds to  614  and includes opening the VID. Opening the VID may include the controller sending an electronic signal to an actuator of the VID (such as actuator  223  shown in  FIGS. 2A-2B ) to adjust the VID from the closed position to the open position (e.g., as shown in  FIGS. 2B and 3B ). In the open position, flow restriction through the VID is minimized. Adjusting the VID from the closed position to the open position may include pivoting a plurality of adjacently arranged vanes of the VID, via the actuator coupled to an actuation plate (e.g., actuation plate  215  shown in  FIGS. 2A-3B ), in a direction relative to a central axis of the compressor (about which an impeller of the compressor rotates) so that the vanes are parallel to the direction of flow and an effective diameter of the outlet end of the VID is increased. 
     At  616 , method  600  includes decreasing the power delivered to the exhaust turbine. For example, once the threshold has been crossed and the operating condition is established to be out of the low load region  808   b  and/or the first compressor map region  1010 , the controller may revert the VGT vane position and/or the EGR valve position back to nominal positions for the given operating conditions. For example, the EGR valve may be further opened, and the VGT vanes may be adjusted to a position in which the cross sectional opening of the exhaust turbine is increased. In this way, the anticipatory control action at  610  may temporarily increase the power delivered to the exhaust turbine so that the compressor efficiency, and thus mass flow, is maintained while actuating the VID from the closed to the open position. Then, once the VID is in the open position, the power delivered to the exhaust turbine is decreased to provide the desired mass flow rate. Following  616 , method  600  ends. 
     Returning to  604 , if instead the engine is not operating below the threshold (e.g., the current engine speed and load point is in the high load region  808   a  shown in map  800  and to the right of the first threshold  1008  of compressor map  1000 ), method  600  continues to  618  and includes maintaining the VID open. Because the engine is already operating above the threshold, which corresponds to operation with the VID open, it is expected that the VID will already be in the open position. 
     At  620 , method  600  includes determining if the engine operation crosses the threshold. For example, the engine operation may cross the threshold by going from an operating point above the threshold to an operating point below the threshold, such as by going from an operating point within the high load region  808   a  to an operating point in the low load region  808   b  shown in  FIG. 8 . As another example, the engine operation may cross the threshold by going from a compressor operating point outside of the first compressor map region  1010  to a compressor operating point inside of the first compressor map region  1010  shown in  FIG. 10 . 
     If the engine operation does not cross the threshold, method  600  may return to  618  to maintain the VID open. If the engine operation crosses the threshold, method  600  proceeds to  622  and includes closing the VID. Closing the VID may include the controller sending an electronic signal to the actuator of the VID to adjust the VID from the open position to the closed position. Adjusting the VID from the open position to the closed position may include pivoting each vane of the VID, via the actuator coupled to the actuation plate, so a plane of each vane is perpendicular to the direction of flow and the effective diameter of the outlet end of the VID is decreased. Unlike transitioning the VID from a closed to an open position, the controller may transition the VID from the open position to the closed position without an anticipatory control action, as closing the VID may not result in a decreased compressor efficiency and a decreased mass flow rate. With the VID in the closed position and an inlet of the impeller reduced, flow through the impeller is restricted while a surge margin of the compressor is extended, thereby increasing compressor efficiency and reducing fuel economy. Following  622 , method  600  ends. 
     In this way, by varying an inlet diameter of a compressor via a VID based on engine operating conditions, a flow range of the compressor may be increased while compressor efficiency is increased. Furthermore, performing anticipatory control actions when transitioning the VID from a closed position, in which the inlet of the impeller is reduced, to an open position may ensure that the compressor efficiency and mass flow is maintained. Overall, engine fuel economy may be increased. 
     Turning to  FIG. 7 , a flow chart of an example method  700  for controlling operation of an active casing treatment of a compressor is shown. The compressor may be included in an engine system, such as the system of engine  10  shown in  FIG. 1 . The active casing treatment (e.g., active casing treatment  212  shown in  FIGS. 2A and 2B ) may include a recirculation passage and a slidable valve (e.g., slidable valve  234   a  of  FIGS. 2A and 2B ). A controller (e.g., controller  12  of  FIG. 1 ) may control flow through the recirculation passage by adjusting a position of the slidable valve via an actuator (e.g., actuator  209  of  FIGS. 2A and 2B ). As also shown in  FIGS. 2A-2B , the compressor may additionally include a variable inlet device (e.g., VID  240 ) positioned in the compressor inlet. In particular, including the VID selectively restricts flow through the compressor by varying an inlet area of the compressor. However, including a VID alone may not adequately address surge at higher compressor speeds and/or pressure ratios, as the VID may be maintained open at higher compressor speed conditions to deliver a requested boost pressure. Opening the recirculation passage of the active casing treatment enables the surge margin to be extended at higher compressor speeds and/or pressure ratios by allowing air from the compressor outlet to vent and return to the inlet conduit. However, at lower compressor speeds and/or pressure ratios, particularly while the VID is used to restrict flow through the compressor, the compressor efficiency is reduced if the recirculation passage is kept open. Therefore, decreases in the compressor efficiency may be avoided by controlling flow through the recirculation passage based on operating conditions, such as by opening the recirculation passage and using the active casing treatment for surge mitigation during conditions in which the VID is not used (e.g., the VID is open) and closing the recirculation passage (and not using the active casing treatment for surge mitigation) during conditions in which the VID is used for surge mitigation (e.g., the VID is closed) and/or while the compressor is not approaching surge conditions. 
     At  702 , method  700  includes estimating and/or measuring engine operating conditions. Engine operating conditions may include engine speed, engine load, engine temperature (such as inferred from an engine coolant temperature measured by an engine coolant temperature sensor), mass air flow (e.g., as measured by a MAF sensor, such as MAF sensor  122  of  FIG. 1 ), intake manifold pressure (e.g., as measured by a MAP sensor, such as MAP sensor  124  of  FIG. 1 ), a pressure ratio across a compressor, a mass air flow rate through the compressor, a speed of the compressor, a position of the slidable valve of the active casing treatment, a position of the VID, etc. The operating conditions may be measured or inferred based on available data. 
     At  704 , it is determined whether the engine is operating below a first threshold. Operating below the first threshold may include a current (e.g., currently determined) engine speed and engine load being below the first threshold. In one example, the first threshold may be a pre-set threshold stored in a map, such as the threshold  805  in map  800  of  FIG. 8 , or a look-up table in a memory of the controller. When the engine is operating at an engine speed and engine load point that falls to the left of the threshold  805 , the engine is in the low load region  808   b  where peak torque operation of the engine may not be demanded. Then engine operation falls to the right of the threshold  805 , the engine is operating in the high load region  808   a  where peak torque operation and higher boost pressure may be requested. 
     In an alternative example, the first threshold may be a mass flow rate threshold. For example, the mass flow rate into the compressor may be compared to a threshold mass flow rate, such as the first threshold  1008  of compressor map  1000  of  FIG. 10 . When the mass flow rate is greater than the first threshold  1008 , the compressor may be operating in one of the second compressor map region  1012 , the third compressor map region  1013 , and the fourth compressor map region  1014 , corresponding to the high load region  808   a  of  FIG. 8 . When the mass flow rate is lower than the threshold, the compressor may be operating in the first compressor map region  1010 , corresponding to the low load region  808   b  of  FIG. 8 . In some examples, the threshold mass flow rate may vary based on the compressor pressure ratio. A controller (e.g., controller  12  of  FIG. 1 ) may input the pressure ratio into a look-up table or map and output the threshold mass flow rate, for example. 
     If the engine is not operating below the first threshold, method  700  continues to  705  and includes determining if engine operation is below a second threshold. The second threshold, which is different than the first threshold, may be a threshold compressor pressure ratio. The second threshold may correspond to the second threshold  1011  shown in  FIG. 10 , for example. In some examples, the threshold compressor pressure ratio may vary based on the compressor mass flow rate. Therefore, the controller may input the mass flow rate into a look-up table or map and output the second threshold, for example. 
     When engine operation is such that the compressor pressure ratio is above the second threshold, the compressor may be approaching surge conditions. Extending a surge margin of the compressor when the compressor is approaching surge conditions may increase an operating range of the compressor and decrease a likelihood of compressor surge. Therefore, if the engine is not operating below the second threshold, method  700  proceeds to  706  and includes opening (or maintaining open) the casing treatment. Opening the casing treatment may include the controller sending an electronic signal to actuate the slidable valve from a closed position (e.g., shown in  FIG. 2A ) to an open position (e.g., shown in  FIG. 2B ) or maintain the slidable valve in the open position. In the open position, recirculation flow is enabled from an intake passage of the compressor, through a bleed port proximate to an impeller of the compressor, to the recirculation passage of the active casing treatment, and back to the intake passage via a recirculation port. By recirculating air through the active casing treatment, a surge margin may be extended at high compressor speeds and/or high pressure ratios. Following  706 , method  700  ends. 
     Returning to  705 , if the engine is operating below the second threshold, method  700  proceeds to  708  and includes closing (or maintaining closed) the casing treatment. Closing the casing treatment may include the controller sending an electronic signal to actuate the slidable valve from the open position to the closed position or maintain the slidable valve in the closed position. In the closed position, recirculation flow is blocked by the slidable valve, which may be positioned to cover (e.g., block air flow at) the bleed port or the recirculation port. As such, a greater proportion of the air drawn into the compressor intake passage is directed through the impeller and downstream to an intake manifold of the engine. For example, if the engine is operating above the first threshold and below the second threshold, the engine operating conditions may be such that compressor the compressor is operating within one of the third compressor map region  1013  and the fourth compressor map region  1014  shown in  FIG. 10 , which are not approaching the surge limit  1004 . In the fourth compressor map region  1014 , the casing treatment may be closed to avoid a compressor efficiency penalty due to flow loss inside of the casing treatment. Similarly, the third compressor map region  1013  is not near the surge limit, and therefore, surge mitigation is not needed. Following  708 , method  700  ends. 
     It should be noted that in some examples, the casing treatment may be opened while operating in the third compressor map region  1013  in order to extend the choke flow limit  1006  shown in  FIG. 10 . Whether or not the casing treatment is opened while the compressor is operating in the third compressor map region  1013  depends on a wheel design of the compressor. Therefore, variants of method  700  may be used to maximize the compressor map width for a specific wheel design. 
     Returning to  704 , if the engine is operating below the first threshold, method  700  proceeds to  708  and includes closing (or maintaining closed) the casing treatment, as described above. By preventing air recirculation through the active casing treatment at low compressor speeds when the compressor also includes a VID in a closed position that restricts airflow through the compressor, overcompensation for surge mitigation is avoided, and compressor efficiency is increased. Following  708 , method  700  ends. 
     In this way, by controlling air recirculation through an active casing treatment based on compressor operating conditions, a surge margin of the compressor having a VID may be extended at high compressor speeds and engine loads (such as by opening the active casing treatment and enabling the recirculation) while compressor efficiency is increased at low compressor speeds and engine loads (such as by closing the active casing treatment and blocking the recirculation while the VID is closed to mitigate surge or while surge mitigation is not needed). Overall, an air flow range of the compressor may be increased by enabling air recirculation through the active casing treatment at higher compressor speeds and engine loads, and engine fuel economy may be increased by preventing air recirculation through the active casing treatment at lower compressor speeds and engine loads. 
     Next,  FIG. 9  shows an example method  900  for coordinating control of a position of a variable inlet device positioned in an inlet conduit of a compressor and control of an active casing treatment of the compressor. Specifically, the variable inlet device (VID) may be VID  440  shown in  FIGS. 4A-5C . The VID may be positioned in an inlet conduit of a compressor having an active casing treatment, upstream of an impeller. Furthermore, the active casing treatment and the VID may be simultaneously controlled by a single actuation system, such as actuation system  435  shown in  FIGS. 4A-5C . For example, a controller (e.g., controller  12  shown in  FIG. 1 ) may send a signal to the actuation system to move the VID between a smaller radius (e.g., closed) position and a larger radius (e.g., open) position while simultaneously transitioning a recirculation passage of the active casing treatment between a closed position and an open position, as further described below. 
     Method  900  begins at  902  and includes estimating and/or measuring engine operating conditions. Engine operating conditions may include engine speed, engine load, engine temperature (such as inferred from an engine coolant temperature measured by an engine coolant temperature sensor), mass air flow (e.g., as measured by a MAF sensor, such as MAF sensor  122  of  FIG. 1 ), intake manifold pressure (e.g., as measured by a MAP sensor, such as MAP sensor  124  of  FIG. 1 ), a pressure ratio across a compressor, a mass air flow rate through the compressor, a speed of the compressor, a position of a unison ring of the actuation system (e.g., unison ring  415  of  FIGS. 4A-5C ), etc. The operating conditions may be measured or inferred based on available data. 
     At  904 , it is determined whether the engine is operating below an engine load threshold. The engine load threshold may delineate engine operations with relatively high load and high flow from operations with relatively low load and low flow. For example, the controller may input the current engine speed and/or load, including the mass flow rate, into a map or look-up table to determine where engine operations are relative to the threshold  805 , represented by the dashed line, in the engine map  800  of  FIG. 8 . The engine map  800  may be stored in a memory of the controller, and the threshold  805  may define engine speeds and loads at which adjustment of the VID and active casing treatment positions may be desired to either prioritize engine performance or fuel efficiency. 
     In the second area  808  of engine map  800 , the threshold  805  divides the second area  808  into a high load region  808   a  and a low load region  808   b . The high load region  808   a  is to the right of the threshold  805  and comprises engine loads and speeds higher than those defined by the threshold  805 . Peak torque engine operation is included in high load region  808   a , and the VID and the active casing treatment may be adjusted to provide increased flow through the compressor to enable the peak torque engine operation as well as surge mitigation. In the low load region  808   b , engine loads and speeds are lower than those defined by the threshold  805  and may correspond to idling or cruising operations of the vehicle. Thus, in this region, a capacity for peak torque engine operation is not needed, and the VID and the active casing treatment may be adjusted into positions to decrease mass flow into the compressor while increasing compressor efficiency and therefore engine fuel economy. 
     While operating in the low load region  808   b , compressor efficiency (and thus fuel efficiency) may be increased by narrowing an inlet of the compressor using the VID and by preventing recirculation through a casing treatment. While operating in the high load region  808   a , engine power may be increased by widening the inlet of the compressor via the VID, allowing more airflow through the compressor, and by extending the surge margin at higher speeds by enabling recirculation through the casing treatment. Thus, compressor efficiency and fuel economy may be prioritized while operating in the low load region  808   b  while engine performance may be prioritized while operating in the high load region  808   a.    
     In another example, the controller may additionally or alternatively compare a measured compressor pressure ratio and mass flow into the compressor with a compressor map, such as the compressor map  1100  of  FIG. 11 . Compressor map  1100  includes a pressure ratio and mass flow threshold  1108 , represented as a dot-dashed line, that may be analogous to the engine load threshold  805  of the engine map  800  of  FIG. 8 . The pressure ratio and mass flow threshold  1108  defines a boundary between a first compressor map region  1110  and a second compressor map region  1112 . At compressor operating points (e.g., mass flow rates and pressure ratios) below the pressure ratio and mass flow threshold  1108 , the compressor is operating in the first compressor map region  1110 , which corresponds to low compressor pressure ratios and mass flow rates (and lower compressor speeds) and also to the low load region  808   b  of engine map  800 . At compressor operating points at or above the pressure ratio and mass flow threshold  1108 , the compressor is operating in the second compressor map region  1112 , which corresponds to mid-to-high compressor pressure ratios and mass flow rates (and higher compressor speeds) and also to the high load region  808   a  of engine map  800 . 
     Returning to  904  of  FIG. 9 , if the engine is not operating below the engine load threshold, engine operation is, for example, in the high load region  808   a  of engine map  800 , and the method continues to  906  to operate the compressor in a performance mode. While operating in the performance mode, engine power is prioritized, such as by increasing airflow through the compressor. While operating in the engine performance mode, the VID and the casing treatment are maintained open, as indicated at  908 . For example, the VID may be held in the larger radius position by the unison ring, wherein the vanes of the VID are retracted into a wall of the compressor intake passage, as shown in  FIGS. 4B and 5C . Furthermore, maintain the position of the unison ring maintains the casing treatment open, such as by maintaining valves coupled to the unison ring rotated out of the recirculation passage. With the engine already operating above the threshold, it is expected that the VID and the casing treatment will already be in the open position. 
     At  909 , method  900  includes determining if the engine operation crosses the threshold. For example, the controller may monitor the engine operating conditions over time in order to adjust compressor operation in response to the engine load falling below the engine load threshold. The engine operation may cross the threshold by going from an operating point above the threshold to an operating point below the threshold, such as by going from an operating point within the high load region  808   a  to an operating point in the low load region  808   b  shown in  FIG. 8 . As another example, the engine operation may cross the threshold by going from a compressor operating point within the second compressor map region  1112  to a compressor operating point inside of the first compressor map region  1110  shown in  FIG. 11 . 
     If the engine operation does not cross the threshold, method  900  may return to  906  to continue operating the compressor in the performance mode, with the VID open (e.g., in the large trim position) and the casing treatment open to enable high compressor mass flows (via the open VID) with surge mitigation (via the open casing treatment) for increased engine power. If the engine operation crosses the threshold, method  900  proceeds to  911  and includes transitioning the compressor to operating in a fuel economy mode. While operating in the fuel economy mode, engine fuel economy is prioritized over engine power, such as by increasing compressor efficiency while the compressor operates at low mass flow area. Transitioning the compressor to operating in the fuel economy mode includes closing the VID and closing the casing treatment via the single actuation system, as indicated at  913 . For example, closing the VID includes actuating the VID to the smaller radius position, such as by rotating the unison ring to a first, closed position that places vanes of the VID within an intake passage of the compressor. As explained above with reference to  FIGS. 4A and 5A , in the smaller radius position, an inlet diameter/open area of the impeller is reduced, thereby increasing compressor efficiency at low mass flows. In an alternative example, when the VID comprises pivotable vanes, closing the VID may include pivoting each vane of the VID via an actuator coupled to an actuation plate of the vanes so that a plane of each vane is perpendicular to the direction of air flow through the compressor, thereby narrowing the impeller inlet. 
     Due to the single, shared actuation system, actuating the VID to the smaller radius position simultaneously actuates the active casing treatment to the closed position such that airflow through a recirculation passage of the active casing treatment (e.g., recirculation passage  418  of  FIGS. 4A-4B ) is blocked by a valve (e.g., valve  434  of  FIG. 4A  and  FIGS. 5A-5C ). By blocking flow recirculation at lower mass flows and pressure ratios, compressor efficiency is increased, thereby increasing vehicle fuel economy. For example, closing the VID while maintaining the active casing treatment open would result in a compressor efficiency penalty. By closing the active casing treatment while the VID is in the closed position, the compressor efficiency penalty is avoided. Thus, a single signal from the controller results in the actuation of both the VID and the valve, which may move in concert. 
     Other examples may include independent actuation mechanisms for each of the VID and active casing treatment. In such configurations, the VID and active casing treatments may be adjusted simultaneously or at offset timings. Furthermore, the closing of the VID and active casing treatment may occur directly and rapidly from the open position, if previously open, or may close gradually and continuously and pause at any point between the fully open and fully closed positions. 
     At  915 , method  900  includes adjusting engine operations to a low load condition. Engine operations that may be varied include increasing an opening of a throttle valve to maintain a flow of boosted air to the engine intake. Ignition timing may be adjusted, such as by adjusting fuel injection timing or adjusting spark timing in response to the decreased boost pressure delivered to combustion chambers of the engine, and fuel amount may also be adjusted accordingly. However, the actuation of the VID to the smaller radius condition and the casing treatment to the closed position in response to the engine operating below the engine load threshold may be calibrated such that there is minimal change in the compressor mass flow rate, the pressure ratio across the compressor, and the compressor efficiency. In this way, the engine load may smoothly transition between a high load condition and the low load condition. Following  915 , method  900  ends. 
     Returning to  904 , if the engine is operating below the engine load threshold, e.g., in the low load region  808   b  of engine map  800 , method  900  proceeds to  910  and includes operating the compressor in a fuel economy mode. While operating in the fuel economy mode, engine fuel economy is prioritized over engine power, such as by performing surge mitigation with the VID and not with the casing treatment in order to increase compressor efficiency. Operating the compressor in the fuel economy mode may include maintaining the VID and the casing treatment closed, as indicated at  912 . For example, the VID may be held in the smaller radius position by the unison ring, wherein the vanes of the VID are positioned within the intake passage of the compressor, as shown in  FIGS. 4A and 5A . Furthermore, maintaining the position of the unison ring maintains the casing treatment closed, such as by maintaining valves coupled to the unison ring rotated into the recirculation passage. Because the engine is already operating below the threshold, which corresponds to operation with the VID and the casing treatment both closed, it is expected that the VID and the casing treatment will already be in the closed position. Thus, if the VID and the casing treatment are already closed (e.g., the VID is in the smaller radius position and the valve is blocking flow through the active casing treatment), the VID and the casing treatment positions may remain unchanged. With the VID maintained in the smaller radius, closed position, the compressor is operated in a small trim mode that that reduces an inlet diameter/open area of the impeller to increase compressor efficiency at a low flow rate (compared to when the VID is open). At the same time, maintaining the casing treatment in the closed position blocks air recirculation through the casing treatment, thereby avoiding flow loss through the casing treatment to increase compressor efficiency and thereby increase engine fuel economy (compared to when the VID is closed and the casing treatment is open). 
     At  914 , the method includes determining if the engine operation is approaching the threshold. The engine operation approaching the threshold may indicate that a transition from operation below the threshold to operation above the threshold is expected. As one example, the controller may input the compressor mass flow rate, compressor speed, and compressor pressure ratio into one or more look-up tables, algorithms, or maps (such as compressor map  1100  of  FIG. 11 ) to determine a real-time estimation of a distance from the threshold (e.g., threshold  1108 ). Additionally or alternatively, as another example, the controller may input the engine speed and load into one or more look-up tables, algorithms, or maps (such as engine map  800  of  FIG. 8 ) to determine the real-time estimation of the distance from the threshold (e.g., threshold  805 ). It may be determined that the engine operation is approaching the threshold in response to the distance from the threshold being within a predetermined amount and/or the distance from the threshold decreasing at a greater than threshold rate, for example. 
     If the engine operation is not approaching the threshold, a transition across the threshold is not expected, and method  900  may return to  910  to continue operating the compressor in the fuel economy mode, wherein the VID and the casing treatment are maintained closed. If the engine operation is approaching the threshold, an opening of the VID and casing treatment is anticipated. Method  900  proceeds to  916  and includes increasing an amount of power delivered to an exhaust turbine of the turbocharger (e.g., turbine  176  of  FIG. 1 ) to avoid a momentary reduction in compressor mass flow rate. For example, during a transition from operating in the low load region  808   b  to the high load region  808   a  shown in  FIG. 8  (or a transition from operating in the first compressor map region  1110  to the second compressor map region  1112  of  FIG. 11 ), if the turbine power is maintained during the transition, a momentary loss in compressor efficiency and therefore compressor mass flow rate is expected when the VID and the casing treatment are opened. Therefore, the controller may perform an anticipatory control action to maintain the compressor efficiency, and thus the mass flow rate, during the transition. 
     Specifically, if the turbine is a VGT, the turbine power may be determined based on a VGT vane position and a pre-turbine exhaust pressure (e.g., as measured by pressure sensor  158  shown in  FIG. 1 ). In order to avoid the loss in mass flow rate, which also reduces the surge margin, the controller may increase the power delivered to the exhaust turbine via a coordinated adjustment of the VGT vane position and an EGR valve position. For example, the controller may input the real-time estimation of the distance from the threshold, which serves as a transition boundary, into one or more look-up tables, algorithms, or maps and output the corresponding VGT vane position and/or EGR valve position. The controller may then send command signals to the VGT and/or the EGR valve to adjust the VGT vanes and/or the EGR valve to the output positions. As an example, decreasing an opening of the EGR valve may increase the pre-turbine exhaust pressure. 
     At  918 , method  900  includes determining if the engine operation crosses the threshold. For example, the engine operation may cross the threshold by going from an operating point below the threshold to an operating point above the threshold, such as by going from an operating point within low load region  808   b  to an operating point in high load region  808   a  shown in  FIG. 8 . As another example, the engine operation may cross the threshold by going from a compressor operating point in the first compressor map region  1110  to a compressor operating point in the second compressor map region  1112  shown in  FIG. 11 . 
     If the engine operation does not cross the threshold, method  900  may return to  910  to continue operating the compressor in the fuel economy mode, wherein the VID and the casing treatment are maintained closed. Furthermore, if the engine operation is no longer approaching the threshold, the controller may reduce the power delivered to the exhaust turbine, such as by reducing the exhaust pressure upstream of the exhaust turbine. For example, the controller may undo the anticipatory control action performed at  916  to revert the VGT vanes and/or the EGR valve to nominal positions for the given operating conditions. The controller may refer to a look-up table having the engine speed and load as the input and output the EGR valve position and/or VGT vane position corresponding to the input engine speed-load, for example. In another example, the controller may determine the EGR amount (and thus the EGR valve position) and/or the VGT vane position through logic rules that directly take into account parameters such as engine load, engine speed, engine temperature, etc. 
     If the engine operation crosses the threshold, method  900  proceeds to  920  and includes transitioning the compressor to operating in the performance mode. Transitioning the compressor to operating in the performance mode includes opening the VID and opening the casing treatment via the single actuation system, as indicated at  922 . For example, opening the VID includes actuating the VID to the larger radius position, such as by rotating the unison ring to a second, open position that retracts the vanes of the VID into a wall of the compressor intake passage, as shown in  FIGS. 4B and 5C . In an alternative example, when the VID comprises pivotable vanes, opening the VID may include pivoting a plurality of adjacently arranged vanes of the VID via the actuator coupled to the actuation plate of the vanes so that the plane of the vanes is parallel to the direction of air flow through the compressor. In the open, larger radius position, the VID does not restrict flow through the impeller, and the compressor inlet is larger, enabling high compressor flows and pressure ratios at high efficiencies. 
     Due to the single, shared actuation system, actuating the VID to the larger radius position simultaneously transitions the active casing treatment to the open position by rotating the valve out of the recirculation passage. Without the valve positioned in the recirculation passage, airflow through the recirculation passage is enabled, thereby extending the surge margin of the compressor. Thus, a single signal from the controller results in the actuation of both the VID and the valve, which may move in concert. 
     Other examples may include independent actuation mechanisms for each of the VID and active casing treatment. In such configurations, the VID and active casing treatments may be adjusted simultaneously or at offset timings. Furthermore, the opening of the VID and the active casing treatment may occur directly and rapidly from the closed position, if previously closed, or may open gradually and continuously and pause at any point between the fully closed and fully open positions. 
     At  924 , engine operations are adjusted to a high load condition. Engine operations that may be varied include decreasing an opening of a throttle valve to maintain a flow of boosted air to the engine intake. Ignition timing may be adjusted, such as by adjusting fuel injection timing or adjusting spark timing in response to the increased boost pressure delivered to combustion chambers of the engine, and fuel amount may also be adjusted accordingly. However, the actuation of the VID to the larger radius condition and the casing treatment to the open position after the anticipatory control action has been performed at  916  and in response to the engine operating above the engine threshold may be calibrated such that there is minimal change in the compressor mass flow rate, the pressure ratio across the compressor, and the compressor efficiency. In this way, the engine load may smoothly transition between the low load condition and the high load condition. 
     Adjusting engine operations to the high load conditions may further include decreasing the power delivered to the exhaust turbine. For example, once the threshold has been crossed and the operating condition is established to be out of the low load region  808   b  and/or the first compressor map region  1110 , the controller may revert the VGT vane position and/or the EGR valve position back to nominal positions for the given operating conditions. In this way, the anticipatory control action at  916  may temporarily increase the power delivered to the exhaust turbine so that the compressor efficiency, and thus mass flow, is maintained during actuating the VID from the closed to the open position and the casing treatment from the closed position to the open position. Then, once the VID and the casing treatment are in the open position (e.g., the unison ring is in the second, open position), the power delivered to the exhaust turbine is decreased to provide the desired mass flow rate for the given engine load. Following  924 , method  900  ends. 
     In this way, by using a VID and an active casing treatment that are simultaneously actuated via a single actuation system, a turbocharger compressor may be operated in one of two operating modes: a fuel economy mode, wherein the VID and the active casing treatment are closed, and a performance mode, wherein the VID and the active casing treatment are open. The compressor may be transitioned between the two operating modes multiple times throughout a vehicle drive cycle, with the current mode selected based on current operating conditions, to increase an overall airflow range of the compressor. The selected operating mode may increase an efficiency of the compressor at the current operating conditions, resulting in a faster turbocharger response during transient engine conditions. Furthermore, the increased compressor efficiency results in lower fuel consumption for both steady state and transient engine operation. 
       FIG. 12  shows an example timeline  1200  of operating an engine with a compressor having a VID and an active casing treatment that may be independently actuated, such as compressor  202  shown in  FIGS. 2A-2B . The compressor may be included in a turbocharger of a vehicle, such as shown in  FIG. 1 , that also includes a high pressure EGR system. The VID may be adjusted between an open and a closed position based on engine operating conditions, such as according to the method of  FIG. 6 . Similarly, the active casing treatment (CT) may be adjusted between an open and a closed position based on engine operating conditions, such as according to the method of  FIG. 7 . Engine load is shown in plot  1202 , compressor mass flow rate is shown in plot  1204 , compressor pressure ratio is shown in plot  1205 , VID position is shown in plot  1206 , CT position is shown in plot  1208 , and an EGR valve position is shown in plot  1210 . For all of the above, the horizontal axis represents time, with time increasing along the horizontal axis from left to right. The vertical axis represents each labeled parameter. For plots  1202  and  1204 , a value of the labeled parameter increases up the vertical axis from bottom to top. For plots  1206  and  1208 , the vertical axis represents whether the VID and the CT are open or closed, respectively, as labeled. For plot  1210 , the vertical axis shows the EGR valve position from a fully closed position (“closed”) to a fully open position (“open”). Furthermore, a surge limit is shown by dashed line  1201 , which may be similar to the surge threshold  804  of  FIG. 8 , a threshold engine load is shown by dashed line  1203 , which may be similar to the engine load threshold  805  of  FIG. 8 , and a threshold compressor pressure ratio is shown by dashed line  1207 , which may be similar to second threshold  1011  of  FIG. 10 . When engine operation includes loads higher than the threshold engine load  1203 , the engine may be operating in a high load region such as the high load region  808   a  of  FIG. 8 . When engine operation includes loads lower than the threshold engine load  1203 , the engine may be operating in a low load region such as the low load region  808   b  of  FIG. 8 . When the compressor operation includes pressure ratios above the threshold compressor pressure ratio  1207 , the compressor may be approaching surge conditions. While the threshold compressor pressure ratio  1207  is shown having a single value in the example of  FIG. 12 , note that in other examples, the threshold compressor pressure ratio may vary based on the compressor mass flow, such as illustrated in  FIG. 10 . 
     Prior to time t1, the engine load (plot  1202 ) may be much higher than the surge threshold  1201  and also higher than the threshold engine load  1203 , and the compressor mass flow rate (plot  1204 ) is relatively high. With the engine load greater than the threshold engine load, airflow restriction through the compressor is not indicated for surge mitigation. The airflow may include a mixture of fresh intake air and recirculated exhaust gas, for example. As such, the compressor is operated with the VID in the open position (plot  1206 ). Furthermore, the compressor pressure ratio (plot  1205 ) is greater than the threshold compressor pressure ratio  1207 . Therefore, high pressure ratio and/or mass flow surge may be mitigated by the active casing treatment, which is in the open position (plot  1208 ). With the active casing treatment in the open position, airflow is enabled through a recirculation passage of the CT. The open position of the active casing treatment extends the surge margin, enabling higher mass flow rates and pressure ratios of the compressor. With higher mass flow rates and pressure ratios enabled, engine power may be increased. Additionally, due to the high engine load (plot  1202 ), the EGR valve is open to a relatively small degree (plot  1210 ) to provide a relatively small amount of EGR to the engine. 
     At time t1, the compressor pressure ratio (plot  1205 ) decreases below the threshold compressor pressure ratio  1207 . As a result, airflow through the recirculation passage is no longer desired for surge mitigation, and so the CT is actuated to the closed position. For example, a slidable valve (e.g., slidable valve  234   a  or slidable valve  234   b  shown in  FIGS. 2A and 2B ) is moved to the closed position via an actuator (e.g., actuator  209  shown in  FIGS. 2A and 2B ), thereby blocking airflow through the recirculation passage. By closing the CT when the compressor is not approaching a surge limit, compressor efficiency is increased. 
     Between time t1 and time t2, the engine load (plot  1202 ) decreases, such as due to a tip-out of an accelerator pedal by a vehicle operator. As the engine load decreases, the degree of opening of the EGR valve increases (plot  1210 ) in order to increase an amount of EGR provided to the engine. At time t2, the engine load (plot  1202 ) decreases below the threshold engine load (dashed line  1203 ). In response, the VID is actuated to the closed position (plot  1206 ), thereby reducing an effective size of an impeller of the compressor, and the CT is maintained in the closed position (plot  1208 ). With the VID in the closed position, the compressor is operated in a small trim mode, and airflow through the recirculation passage is blocked by the closed CT to increase compressor efficiency. The increased compressor efficiency also increases vehicle fuel economy. 
     Shortly before time t3, the engine load (plot  1202 ) increases, such as due to a tip-in of the accelerator pedal by the vehicle operator. With the engine load (plot  1202 ) approaching the threshold engine load  1203 , the controller adjusts the EGR valve position in anticipation of the engine operation transitioning across the threshold engine load  1203 . Specifically, the controller decreases the opening of the EGR valve (plot  1210 ) in order to increase an exhaust backpressure and therefore an amount of power delivered to an exhaust turbine of the turbocharger. 
     At time t3, the engine load (plot  1202 ) increases above the threshold engine load  1203 . In response, the VID is actuated to the open position (plot  1206 ), thereby enabling higher mass flow rates through the impeller. The compressor mass flow rate (plot  1204 ) transitions smoothly due to the anticipatory control action of decreasing the EGR valve opening. After the engine load (plot  1202 ) increases above the threshold engine load  1203  and the VID is actuated to the open position (plot  1206 ), the EGR valve position is adjusted to a nominal position for the given operating conditions (e.g., engine speed and load). Specifically, the degree of opening of the EGR valve is increased (plot  1210 ) and is thereafter adjusted based on the engine operating conditions to provide a desired engine dilution. Because the compressor pressure ratio (plot  1205 ) remains below the threshold compressor pressure ratio  1207 , the CT remains in the closed position ( 1208 ), thereby blocking airflow through the recirculation passage to increase the compressor efficiency. 
     Next,  FIG. 13  shows an example timeline  1300  of operating an engine with a compressor having a VID and an active casing treatment that may be adjusted via a single actuation system, such as compressor  402  shown in  FIGS. 4A-4B . The compressor may be included in a turbocharger of a vehicle, such as shown in  FIG. 1 , that further includes a high pressure EGR system. The VID and the active casing treatment (CT) may be simultaneously adjusted between an open and a closed position based on engine operating conditions, such as according to the method of  FIG. 9 . Engine load is shown in plot  1302 , compressor mass flow rate is shown in plot  1304 , VID position is shown in plot  1306 , CT position is shown in plot  1308 , and an EGR valve position is shown in plot  1310 . For all of the above, the horizontal axis represents time, with time increasing along the horizontal axis from left to right. The vertical axis represents each labeled parameter. For plots  1302  and  1304 , a value of the labeled parameter increases up the vertical axis from bottom to top. For plots  1306  and  1308 , the vertical axis represents whether the VID and the CT are open or closed, respectively, as labeled. For plot  1310 , the vertical axis shows the EGR valve position from a fully closed position (“closed”) to a fully open position (“open”). Furthermore, a surge limit is shown by dashed line  1301 , which may be similar to the surge threshold  804  of  FIG. 8 , and a threshold engine load is shown by dashed line  1303 , which may be similar to the engine load threshold  805  of  FIG. 8 . When engine operation includes loads higher than the threshold engine load  1303 , the engine may be operating in a high load region such as the high load region  808   a  of  FIG. 8 . When engine operation includes loads lower than the threshold engine load  1303 , the engine may be operating in a low load region such as the low load region  808   b  of  FIG. 8 . 
     Prior to time t1, the engine load (plot  1302 ) may be much higher than the surge threshold  1301  and also higher than the threshold engine load  1303 , and the compressor mass flow rate (plot  1304 ) is relatively high. With the engine load greater than the threshold engine load, airflow restriction through the compressor is not indicated for surge mitigation. The airflow may include a mixture of fresh intake air and recirculated exhaust gas, for example. As such, the compressor is operated with the VID in the open position (plot  1306 ). High pressure ratio and/or mass flow surge may be mitigated by the active casing treatment, which is in the open position (plot  1308 ). With the active casing treatment in the open position, airflow is enabled through a recirculation passage of the CT. The open position of the active casing treatment extends the surge margin, enabling higher mass flow rates and pressure ratios of the compressor. With higher mass flow rates and pressure ratios enabled, engine power may be increased. Therefore, prior to time t1, the compressor is operated in a performance mode. 
     Shortly before time t1, the engine load (plot  1302 ) decreases, such as due to a tip-out of an accelerator pedal by a vehicle operator. At time t1, the engine load (plot  1302 ) decreases below the threshold engine load (dashed line  1303 ). In response, the VID and the CT are simultaneously actuated to their closed positions (plots  1306  and  1308 , respectively), thereby reducing an effective size of an impeller of the compressor (e.g., operating the compressor in a small trim mode) and preventing airflow through the recirculation passage to increase compressor efficiency. The increased compressor efficiency also increases vehicle fuel economy. Therefore, between time t1 and t2, the compressor is operated in a fuel economy mode. 
     Shortly before time t2, the engine load (plot  1302 ) increases, such as due to a tip-in of the accelerator pedal by the vehicle operator. With the engine load (plot  1302 ) approaching the threshold engine load  1303 , the controller adjusts the EGR valve position in anticipation of the engine operation transitioning across the threshold engine load  1303 . Specifically, the controller decreases the opening of the EGR valve (plot  1310 ) in order to increase an exhaust backpressure and therefore an amount of power delivered to an exhaust turbine of the turbocharger. 
     At time t2, the engine load (plot  1302 ) increases above the threshold engine load ( 1303 ). In response, the VID are the CT are simultaneously actuated to their respective open positions (plots  1306  and  1308 , respectively), thereby enabling higher mass flow rates through the impeller and airflow through the recirculation passage. The compressor mass flow rate (plot  1304 ) transitions smoothly due to the anticipatory control action of decreasing the EGR valve opening. After the engine load (plot  1302 ) increases above the threshold engine load  1303  and the VID is actuated to the open position (plot  1306 ), the EGR valve position is adjusted to a nominal position for the given operating conditions (e.g., engine speed and load). Specifically, the degree of opening of the EGR valve is increased (plot  1310 ) and is thereafter adjusted based on the engine operating conditions to provide a desired engine dilution. With the VID in the open position and the CT in the open position, the compressor is again operated in the performance mode after time t2. 
     In this way, by effectively controlling an inlet area of a compressor impeller based on operating conditions using a variable inlet device positioned proximate to a leading edge of the impeller, a flow range of the compressor may be extended, such as by extending a surge margin at lower compressor mass flow rates. By further including an active casing treatment that selectively enables gas flow through a recirculation passage, the flow range of the compressor may be further extended, such as by extending the surge margin at higher compressor mass flow rates. Furthermore, by blocking gas flow through the recirculation passage while the variable inlet device is restricting flow through the impeller, compressor efficiency may be increased, thereby increasing vehicle fuel economy. By independently actuating the variable inlet device and the active casing treatment, the compressor efficiency may be further increased by maintaining the active casing treatment closed until the compressor approaches surge conditions. By actuating the variable inlet device and the active casing treatment through a common actuator, airflow through the compressor may be adjusted with fewer components and a simplified control method. Overall, whether individually actuated or actuated by a common actuator, by including both the variable inlet device and the active casing treatment and adjusting their positions based on compressor operating conditions, high engine power is available at higher engine loads without sacrificing vehicle fuel economy at lower engine loads. 
     The technical effect of positioning a variable inlet device to partially block flow to an impeller of a compressor is that an effective size of the impeller is reduced. 
     The technical effect of closing a recirculation passage of a casing treatment of a compressor while a variable inlet device restricts flow through the compressor is that compressor efficiency is increased, thereby increasing engine fuel economy. 
     As one example, a compressor comprises: a casing forming a recirculation passage surrounding an inlet conduit; an active casing treatment surrounding the inlet conduit and configured to selectively control gas flow through the recirculation passage; an impeller; a volute; and an adjustable device positioned in the inlet conduit upstream of the impeller, at least partially overlapping with a plane of the volute, configured to selectively reduce an effective size of the impeller. In the preceding example, additionally or optionally, the compressor further comprises a bleed port and a recirculation port disposed in the wall, wherein the bleed port fluidically couples the inlet conduit to the recirculation passage downstream of a leading edge of the impeller and the recirculation port fluidically couples the inlet passage to the recirculation passage upstream of the adjustable device. In any or all of the preceding examples, additionally or optionally, an outlet of the adjustable device is proximate to a leading edge of the impeller such that no other components are placed between the outlet of the adjustable device and the leading edge of the impeller. In any or all of the preceding examples, additionally or optionally, the adjustable device includes a plurality of adjacently arranged vanes forming a ring about a central axis of the compressor, an actuation plate coupled to an actuator, and a plurality of actuation arms connecting the plurality of vanes to the actuation plate. In any or all of the preceding examples, additionally or optionally, the impeller is rotatable about the central axis of the compressor, and wherein interior edges of the vanes of the adjustable device form a flow passage through the adjustable device that is aligned along the central axis, each of the vanes being rotatable about an actuation axis arranged radial to the central axis between an open position and a closed position via the actuator, the actuation plate, and the actuation arms. In any or all of the preceding examples, additionally or optionally, each of the plurality of vanes includes a first surface and a second surface separated by a thickness of the vane, the first surface and the second surface perpendicular to the central axis in the closed position and parallel to the central axis in the open position. In any or all of the preceding examples, additionally or optionally, a diameter of the outlet of the adjustable device is smaller in the closed position and larger in the open position. In any or all of the preceding examples, additionally or optionally, gas flow through the impeller is decreased in the closed position relative to the open position, and the effective size of the impeller is reduced in the closed position relative to the open position. In any or all of the preceding examples, additionally or optionally, the active casing treatment includes a slidable valve, and the slidable valve is adjusted between an open position that enables gas flow through the recirculation passage and a closed position that blocks the gas flow through the recirculation passage. 
     As another example, a method comprises: adjusting airflow through a recirculation passage of a casing treatment of a compressor supplying boosted intake air to an engine while also adjusting airflow through an inlet passage of the compressor via a variable inlet device positioned upstream of an impeller of the compressor based on operating conditions. In the preceding example, additionally or optionally, adjusting airflow through the inlet passage of the compressor via the variable inlet device includes adjusting the variable inlet device between a small trim position and a large trim position. In any or all of the preceding examples, additionally or optionally, the variable inlet device is positioned upstream of the impeller at a distance that is less than one third of a diameter of the intake passage, thereby blocking airflow to 20-40% of the impeller in the small trim position in order to adjust airflow through the inlet passage. In any or all of the preceding examples, additionally or optionally, the recirculation passage is fluidically coupled to the inlet passage via a bleed port downstream of a leading edge of the impeller and via a recirculation port upstream of the variable inlet device, and wherein the casing treatment includes a slidable valve positioned at one of the bleed port and the recirculation port in order to adjust airflow through the recirculation passage. In any or all of the preceding examples, additionally or optionally, adjusting airflow through the recirculation passage includes adjusting the slidable valve between an open position that enables airflow through the recirculation passage and a closed position that blocks airflow through the recirculation passage. In any or all of the preceding examples, additionally or optionally, adjusting airflow through the recirculation passage while also adjusting airflow through the inlet passage based on operating conditions comprises: adjusting the slidable valve to the closed position and adjusting the variable inlet device to the small trim position in response to engine load decreasing below a threshold engine load; adjusting the variable inlet device to the large trim position in response to the engine load reaching or exceeding the threshold engine load; adjusting the slidable valve to the open position in response to the engine load reaching or exceeding the threshold engine load and a pressure ratio of the compressor reaching or exceeding a threshold pressure ratio; and maintaining the slidable valve in the closed position in response to the engine load reaching or exceeding the threshold engine load and the pressure ratio of the compressor remaining below the threshold pressure ratio. In any or all of the preceding examples, the method additionally or optionally further comprises, in response to the engine load approaching the threshold engine load from below the threshold engine load, increasing power delivered to an exhaust turbine driving the compressor. 
     As another example, a system comprises: an engine including an engine intake; a compressor coupled to the engine intake, the compressor comprising: a casing forming an intake passage and a recirculation passage surrounding the intake passage, the recirculation passage fluidically coupled with the intake passage via a bleed port and a recirculation port, each of the bleed port and the recirculation port disposed in a wall separating the intake passage and the recirculation passage; a valve positioned between the wall and the casing and configured to selectively block one or more of the bleed port and recirculation port; an impeller contained within the intake passage and rotatable about a central axis; and a variable inlet device (VID) positioned in the intake passage, immediately upstream of the impeller, upstream of the bleed port, and downstream of the recirculation port, the VID including a plurality of adjacently arranged vanes forming a ring around the central axis; and a controller storing executable instructions in non-transitory memory that, when executed, cause the controller to: adjust the plurality of vanes from an open position to a closed position in response to an engine load decreasing below a threshold; and adjust the valve from a first position where the recirculation passage is unblocked to a second position where the recirculation passage is blocked in response the engine load decreasing below the threshold. In the preceding example, additionally or optionally, the VID, when in the closed position, blocks airflow to an outer perimeter of the impeller. In any or all of the preceding examples, additionally or optionally, the VID further comprises an actuation plate and a plurality of actuation arms, each actuation arm coupled to one of the plurality of vanes and the actuation plate, and wherein adjusting the position of the plurality of vanes includes actuating the actuation plate to rotate each vane about an actuation axis via the actuation arms. In any or all of the preceding examples, the system additionally or optionally further comprises an actuator for adjusting the position of the valve, and wherein the second position includes the actuator positioning the valve to block the flow of gas through the recirculation passage at the bleed port or the recirculation port, and the first position includes the actuator positioning the valve to allow the flow of gas through the recirculation passage. 
     In another representation, a method comprises: closing a recirculation passage of a compressor casing treatment and reducing an inlet area of the compressor responsive to engine load decreasing below a threshold; and in response to the engine load reaching or exceeding the threshold, increasing the inlet area of the compressor while selecting between either opening the recirculation passage or maintaining the recirculation passage closed based on operating conditions. In the preceding example, additionally or optionally, the selecting between either opening the recirculation passage or maintaining the recirculation passage closed based on operating conditions includes opening the recirculation passage responsive to a pressure ratio of the compressor reaching or exceeding a threshold pressure ratio; and maintaining the recirculation passage closed responsive to the pressure ratio remaining below the threshold pressure ratio. In any or all of the preceding examples, additionally or optionally, the recirculation passage is coupled to an intake passage of the compressor via a bleed port downstream of a leading edge of an impeller of the compressor and a recirculation port upstream of the impeller. In any or all of the preceding examples, additionally or optionally, closing the recirculation passage includes actuating a valve positioned at one of the bleed port and the recirculation port to a closed position that blocks gas flow through the recirculation passage; and opening the recirculation passage includes actuating the valve to an open position that enables gas flow through the recirculation passage. In any or all of the preceding examples, additionally or optionally, reducing the inlet area of the compressor includes actuating a variable inlet device positioned immediately upstream of the leading edge of the impeller and downstream of the recirculation port to a small trim position; and increasing the inlet area of the compressor includes actuating the variable inlet device to a large trim position. In any or all of the preceding examples, additionally or optionally, actuating the valve includes actuating the valve with a first actuator, and actuating the variable inlet device includes actuating the variable inlet device with a second actuator, which is different than the first actuator. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.