Determining a wastegate valve position

Abstract

Method comprising: Receiving a control to a non-closed position for a wastegate valve (206, 302), wherein the position control occurs in a low-lift (214, 322) or high-lift range with respect to a valve seat (212, 314); and before executing the position control, only temporarily closing the wastegate valve (206, 302) to determine a current fully closed position.

Description

[0001] The invention relates to a control of a wastegate valve in a turbocharger.

[0002] Some internal combustion engines use a compression device, such as a turbocharger, to improve engine torque / power density. In one example, a turbocharger may include a compressor connected to a turbine by a driveshaft, with the turbine coupled to the exhaust manifold side and the compressor coupled to the intake manifold side of an engine. In this way, the exhaust-driven turbine supplies energy to the compressor to increase intake manifold pressure (e.g., boost or boost pressure) and increase airflow into the engine. Boosting may be controlled by adjusting the amount of gas reaching the turbine, for example, with a wastegate. A wastegate valve may be controlled based on operating conditions to achieve the desired boost.In some examples, the wastegate valve is pneumatically actuated, while in other examples the wastegate valve is electrically actuated, for example, by an electric motor.

[0003] DE 10 2008 051 817 A1 is known from the prior art. This describes a method for controlling a wastegate valve using a control unit and a displacement sensor.

[0004] US 7,775,043 B2 discloses a system for controlling the boost pressure supplied to an internal combustion engine by adjusting the position of a wastegate valve in a pneumatic wastegate. A wastegate sensor positioned near the wastegate valve detects the position of the wastegate valve and supplies a signal representative of the position to a controller via a conductor. The controller receives several signals, including indications of engine speed, boost, and barometric pressure, to control the boost pressure supplied to the engine and accordingly adjusts the position of the wastegate valve by controlling the pressure supplied to a chamber acting against a diaphragm of the wastegate. In the event that the wastegate valve is determined to be malfunctioning, the controller may use signals from the wastegate sensor to redetermine the position of the wastegate valve.

[0005] The present inventors have recognized a problem with such approaches. Parts of the wastegate, such as the wastegate valve and the linkage coupling the wastegate valve to the diaphragm (or another actuator in other systems, such as an electric motor), experience high temperatures as the engine warms up and hot exhaust gas is circulated through the engine. Exposure to these components at high temperatures can result in thermal deformation, causing, for example, expansion or shrinkage in the valve actuator linkage and turbine housing deformation. Thus, the accuracy of wastegate valve position detection and the knowledge of the valve lift position relative to a seat contacted by the wastegate valve in a fully closed position are reduced. Compromised accuracy can result in the delivery of inaccurate boost levels to the engine.

[0006] Methods are provided for determining the fully closed position of a wastegate valve.

[0007] In one example, a wastegate valve receives a command to a non-closed position with respect to a valve seat in a low-lift range. Before executing the position control, the wastegate valve is only temporarily closed to determine a fully closed position.

[0008] This avoids inaccurate boost delivery due to uncertainty about the fully closed position. Thus, the technical result of more precise wastegate control is achieved through these actions.

[0009] The above advantages and other advantages and features of the present description will be readily apparent from the following detailed description taken alone or in conjunction with the accompanying drawings.

[0010] It should be understood that the above summary is provided to introduce, in a simplified form, a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any of the disadvantages noted above or in any other part of this disclosure.

[0011] The figures show: Fig. 1 shows a block diagram of a turbocharged engine that includes a wastegate. Fig. 2 shows an example of an electric wastegate according to an embodiment of the present disclosure. Fig. 3 shows an example of a pneumatic wastegate according to an embodiment of the present disclosure. Fig. 4 shows a flowchart illustrating a method for controlling a turbocharger via the wastegate of Fig. 2 or Fig. 3 represents. Fig. 5A and Fig. 5B shows a flowchart illustrating a method for determining the fully closed position of a wastegate valve of the wastegate of Fig. 2 or Fig. 3 represents. Fig. 6 shows an exemplary characteristic map illustrating the determination of the fully closed position of a wastegate valve according to various operating parameters of the engine of Fig. 1 shows. Fig. 7 shows a flowchart illustrating a method for determining the fully closed position of a wastegate valve of the wastegate of Fig. 2 or Fig. 3, when a fully open position is desired. Fig. Figure 8 shows a map of learned fully closed positions as a function of temperature.

[0012] In some internal combustion engines, a compression device, such as a turbocharger, can be used to increase the pressure (e.g., boost pressure) of air supplied to the engine, thereby increasing engine torque / power density. Some approaches use a pneumatic wastegate to control the position of a wastegate valve and thus the amount of exhaust gas delivered to a turbine of the turbocharger, while other approaches use an electric wastegate. In both cases, a linkage coupling an actuator to a wastegate valve and a turbine assembly may be subject to high ambient temperatures and thus thermal deformation (e.g., expansion, shrinkage, etc.).Thus, the accuracy of determining the position of the wastegate valve and the position at which it is fully closed against a valve seat may decrease, resulting in an inaccurate assessment of the valve lift and thus the boost supply to the engine.

[0013] Various methods are provided for determining the fully closed position of a wastegate valve. In one example, a command to a non-closed position is received for a wastegate valve in a low-lift region relative to a valve seat. Before executing the position command, the wastegate valve is only temporarily closed to thereby determine a fully closed position. Fig. 1 is a block diagram of a turbocharged internal combustion engine that includes a wastegate. Fig. 2 shows an example of an electric wastegate according to an embodiment of the present disclosure. Fig. 3 shows an example of a pneumatic wastegate according to an embodiment of the present disclosure. Fig. 4 shows a flowchart illustrating a method for controlling a turbocharger via the wastegate of Fig. 2 or Fig. 3 represents. Fig. 5A and Fig. 5B shows a flowchart illustrating a method for determining the fully closed position of a wastegate valve of the wastegate of Fig. 2 or Fig. 3 represents. Fig. 6 shows an exemplary characteristic map illustrating a determination of the fully closed position of a wastegate valve according to various operating parameters of the engine of Fig. 1. The power machine of Fig. 1 also contains a control system which is used to carry out the Fig. 4, Fig. 5A and Fig. 5B shown method is configured.

[0014] Fig. 1 is a schematic diagram illustrating an exemplary engine 10 that may be included in a propulsion system of a motor vehicle. The engine 10 is shown with four cylinders 30. However, other numbers of cylinders may be used in accordance with the present disclosure. The engine 10 may be at least partially controlled by a control system including a controller 12 and by input from a vehicle operator 132 via an input device 130. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Each combustion chamber (e.g., each cylinder) 30 of the engine 10 may include combustion chamber walls with a piston (not shown) positioned therein. The pistons may be coupled to a crankshaft 40 such that reciprocating motion of the piston is converted into rotary motion of the crankshaft.Crankshaft 40 may be coupled to at least one drive wheel of a vehicle via an intermediate gear system (not shown). Furthermore, a starter motor may be coupled to crankshaft 40 via a flywheel to enable starting operation of engine 10.

[0015] Combustion chambers 30 may receive intake air from intake manifold 44 via intake passage 42 and may exhaust combustion gases via exhaust passage 48. Intake manifold 44 and exhaust manifold 46 may selectively communicate with combustion chamber 30 via intake valves and exhaust valves (not shown), respectively. In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0016] Fuel injectors 50 are shown coupled directly to the combustion chamber 30 for injecting fuel directly therein in proportion to the pulse width of the FPW signal received from the controller 12. In this manner, the fuel injector 50 provides so-called direct injection of fuel into the combustion chamber 30. The fuel injector may be mounted, for example, in the side of the combustion chamber or in the top of the combustion chamber. Fuel may be supplied to the fuel injector 50 by a fuel system (not shown) that includes a fuel tank, a fuel pump, and a fuel rail. In some embodiments, the combustion chambers 30 may alternatively or additionally include a fuel injector disposed in the intake manifold 44 in a configuration providing so-called port injection of fuel into the intake port upstream of each combustion chamber 30.

[0017] The intake passage 42 may include throttles 21 and 23 with throttle plates 22 and 24, respectively. In this particular example, the position of the throttle plates 22 and 24 may be changed by the controller 12 via signals provided to an actuator included with the throttles 21 and 23. In one example, the actuators may be electric actuators (e.g., electric motors), a configuration commonly referred to as electronic throttle control (ETC). In this manner, the throttles 21 and 23 may be actuated to change the intake air supplied to the combustion chamber 30 among other engine cylinders. The position of the throttle plates 22 and 24 may be provided to the controller 12 via the throttle position signal TP.The intake passage 42 may further include a mass airflow sensor 120 and an intake manifold pressure sensor 122 for providing respective MAF (mass airflow) and MAP (manifold air pressure) signals to the controller 12.

[0018] The exhaust passage 48 may receive exhaust gases from the cylinders 30. The exhaust gas sensor 128 is shown coupled to the exhaust passage 48 upstream of the turbine 62 and emission control device 78. The sensor 128 may be selected from various suitable sensors to provide an indication of the exhaust gas air-fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a dual-state oxygen sensor, or an EGO, a NOx, an HC, or a CO sensor. The emission control device 78 may be a three-way catalyst (TWC), a NO x-trap, various other exhaust gas purification devices or combinations thereof.

[0019] The exhaust temperature may be measured by one or more temperature sensors (not shown) positioned in the exhaust passage 48. Alternatively, the exhaust temperature may be inferred based on engine operating conditions, such as speed, load, air-fuel ratio (AFR), spark retard, etc.

[0020] In the presentation of Fig. 1, the controller 12 is a microcomputer that includes a microprocessor unit 102, input / output (I / O) ports 104, an electronic storage medium for executable programs and calibration values, shown in this particular example as a read-only memory (ROM) chip 106, a random access memory (RAM) 108, a keep-alive memory (KAM) 110, and a data bus.The controller 12 may receive various signals from sensors coupled to the engine 10, in addition to the signals previously discussed, including a mass air flow (MAF) measurement from the mass air flow sensor 120; engine coolant temperature (ECT) from the temperature sensor 112, which is schematically shown at a location in the engine 10; a profile ignition pickup (PIP) signal from the Hall sensor 118 (or other type of sensor) coupled to the crankshaft 40; throttle position (TP) from a throttle position sensor, as discussed; and a manifold absolute pressure (MAP) signal from the sensor 122, as discussed. An engine speed signal RPM (revolutions per minute) may be generated by the controller 12 from the PIP signal.The manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum or pressure within the intake manifold 44. It should be noted that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor may provide an indication of engine torque. Furthermore, this sensor, along with the sensed engine speed, may provide an estimate of the charge (including air) introduced into the cylinder. In one example, sensor 118, which is also used as an engine speed sensor, may generate a predetermined number of evenly spaced pulses per revolution of the crankshaft 40.In some examples, the read-only memory storage medium 106 may be programmed with computer-readable data representing instructions executable by the processor 102 to perform the methods described below, as well as other variations that are anticipated but not specifically recited.

[0021] Further, the engine 10 may include a compression device, such as a turbocharger or supercharger, including at least one compressor 60 disposed along the intake manifold 44. With a turbocharger, the compressor 60 may be at least partially driven by a turbine 62, for example, via a shaft or other coupling arrangement. The turbine 62 may be disposed along the exhaust passage 48. Various arrangements for driving the compressor may be provided. With a supercharger, the compressor 60 may be at least partially driven by the engine and / or an electric machine and may not include a turbine. Thus, the amount of compression applied to one or more cylinders of the engine via a turbocharger or supercharger may be varied by the controller 12.In some cases, for example, the turbine 62 may drive an electric generator 64 to supply power to a battery 66 via a turbo driver 68. Power from the battery 66 may then be used to drive the compressor 60 via a motor 70. Furthermore, a sensor 123 may be disposed in the intake manifold 44 to provide a boost signal to the controller 12.

[0022] Further, the exhaust passage 48 may include a wastegate 26 for diverting exhaust gas from the turbine 62. In some embodiments, the wastegate 26 may be a multi-stage wastegate, such as a two-stage wastegate, with a first stage configured to control boost pressure and a second stage configured to increase heat flow to the emission control device 78. The wastegate 26 may be operated by an actuator 150, which may be, for example, an electric actuator. In some embodiments, the actuator 150 may be an electric motor. Additional details and examples regarding the wastegate 26 and actuator 150 are provided below. The intake passage 42 may include a compressor bypass valve 27 configured to bypass the compressor 60.The wastegate 26 and / or the compressor bypass valve 27 can be controlled by the controller 12 via actuators (for example the actuator 150) to open when, for example, a lower boost pressure is desired.

[0023] Intake passage 42 may further include a charge air cooler (CAC) 80 (e.g., an intercooler) to reduce the temperature of the turbocharged or boosted intake gases. In some embodiments, charge air cooler 80 may be an air-to-air heat exchanger. In other embodiments, charge air cooler 80 may be an air-to-liquid heat exchanger.

[0024] Furthermore, in the disclosed embodiments, an exhaust gas recirculation (EGR) system may direct a desired exhaust gas portion from the exhaust passage 48 via an EGR passage 140 to the intake passage 42. The amount of EGR supplied to the intake passage 42 may be varied by the controller 12 via an EGR valve 142. Furthermore, an EGR sensor 144 (not shown) may be disposed in the EGR passage and may provide an indication of pressure, temperature, and / or concentration of the exhaust gas. Alternatively, the EGR may be controlled by a calculated value based on signals from the MAF (upstream), MAP (intake manifold), MAT (manifold air temperature), and crankshaft speed sensors. Further, the EGR may be controlled based on an exhaust O2 sensor and / or an intake manifold oxygen sensor.Under some conditions, the EGR system can be used to control the temperature of the air and fuel mixture in the combustion chamber. Fig. 1 shows a high-pressure EGR system in which EGR is routed from upstream of a turbocharger turbine to downstream of a turbocharger compressor. In other embodiments, the engine may additionally or alternatively utilize a low-pressure EGR system in which EGR is routed from downstream of a turbocharger turbine to upstream of a turbocharger compressor.

[0025] Now on Fig. 2, an exemplary wastegate 200, which is the wastegate 26 of Fig. 1. The wastegate 200 is arranged along a part of the Fig. 1. In the illustrated embodiment, the wastegate 200 is an electric wastegate and is driven by an actuator 150, which in this example is an electric actuator, through various suitable devices that can be used to drive the wastegate. The actuator 150 transmits a drive force via a linkage 204 (e.g., a cylindrical rod) to a wastegate valve 206, which can alternate between a fully closed position and a fully open position and can stop at any point in between. The position of the wastegate valve 206 can thus be continuously adjustable and can be monitored via a position sensor 203, which is configured to send signals to an engine controller, such as the controller 12 of Fig. 1, is configured to be monitored.

[0026] When the wastegate valve 206 is opened from the fully closed position, an opening may be created through which gases flowing through the exhaust manifold 46 may flow into a chamber 207. From the chamber 207, gases may flow to a vent opening 208, which may receive exhaust gas from the exhaust manifold 46 when the wastegate valve 206 is not in the fully closed position. Thus, the boost level delivered to an engine may be controlled by driving the wastegate valve 206 via the actuator 150, thereby controlling the position of a wastegate valve 206 and the amount of gas flowing through an intake manifold and a turbine of a turbocharger (for example, the turbine 62 in Fig. 1). In one example, the valve 206 may be formed by a pintle having a surface facing the flow through the manifold 202. The pressure differential across the pintle may generate forces acting to move the pintle. Although not shown, the wastegate 200 may include an engine and a transmission, with the linkage 204 extending from an output shaft of the transmission to the wastegate valve 206. In some embodiments, the position sensor 203 may measure the orientation of such components as the translational position of the linkage 204, the rotational orientation of the output shaft, or other components within the engine. In this example, such measurements may be used to indirectly determine the position of the wastegate valve 206. Furthermore, in other embodiments, the position of the wastegate valve may be determined based on one or more of the factors discussed above with reference to Fig. 1 described signals (for example BOOST) and sent to the controller 12.

[0027] The wastegate 200 may optionally include a biasing member 210. The biasing member 210 is attached to the wastegate 200 at one end and to the wastegate valve 206 at the other end. In some embodiments, the biasing member 210 is selected to supply a closing force that maintains the wastegate valve 206 in a fully closed position up to a threshold pressure. As a non-limiting example, the biasing member 210 may be selected to allow the wastegate valve 206 to open at an average pressure differential across the turbocharger turbine between 0.75 bar and 1 bar.In the event of wastegate degradation, for example, due to a loss of power to actuator 150, wastegate valve 206 may be held in a fully closed position via spring preload up to a threshold pressure, ensuring that sufficient boost buildup is delivered to the engine. Such a configuration may be particularly advantageous in downsized engines, as the extent of downsizing need not be limited to accommodate the possibility of wastegate actuator degradation. Conversely, at or above the threshold pressure, preload member 210 may allow wastegate valve 206 to move toward a fully open position, thereby limiting maximum boost, particularly at high loads.Furthermore, the size of a wastegate actuator (e.g., actuator 150) and its power consumption can be reduced because the biasing member 210 provides additional closing force to the wastegate 26. Therefore, during unimpaired operation, the actuator can maintain the valve in the fully closed position with a current level less than if the spring preload were zero. The current supplied to the actuator 150 can be selected to account for the closing force of a biasing member, such as the spring. In the illustrated embodiment, the biasing member 210 is shown as a spring in a pre-compressed state, although various other suitable structures may be used to provide additional closing force to the wastegate 26.In the case where a spring is used, the spring constant can be selected to supply a closing force up to a certain threshold pressure and to provide sufficient boost to an engine.

[0028] In the fully closed position, the wastegate valve 206 contacts a valve seat 212, seating against the valve seat, and fluidly seals the wastegate 200 from the exhaust passage 46 so that gases flowing through the exhaust passage do not enter the wastegate. In this position, the engine 10 may, depending on other conditions, such as the positions of the throttles 21 and 23, Fig. 1, maximum charge is supplied. Furthermore, Fig. 2, a low lift range 214, which denotes a range in which the separation between the wastegate valve 206 and the valve seat 212 is considered relatively small for the multiple positions (e.g., lifts) of the wastegate valve in that low lift range. In one example, the low lift range may be less than 25% of the total available lift. In another example, it may be a range of 0-30% of the total available lift. As used herein, "lift" may similarly refer to the position of a wastegate valve relative to the fully closed position. In another example, the low lift range 214 may extend from a top surface 216 of the valve seat 212 to any suitable defined point in the chamber 207 and may be measured from that top surface to the top of the wastegate valve 206.For example, the low-lift region 214 may extend from the top surface 216 of the valve seat 212 to a height of approximately 20% of the total height of the chamber 207. However, it should be understood that suitable low-lift regions may be predetermined based on the physical characteristics of a wastegate or may be dynamically determined based on various operating parameters. The low-lift region 214 will be discussed in more detail below with reference to FIG. Fig. 5, reference is made to the method 500 described for increasing the accuracy of boost control.

[0029] Now on Fig. 3, another example of a wastegate 300 is shown, which is the wastegate 26 of Fig. 1. As with the Fig. 2, the wastegate 300 is arranged along a part of the Fig. 1 and includes a wastegate valve 302 coupled to a linkage 304 (e.g., a cylindrical rod). However, the wastegate 300 is a pneumatic wastegate controlled by pressurized fluid. Thus, the linkage 304 is coupled to a diaphragm 306, which in turn is coupled to a biasing member 308, which is the biasing member 210 of Fig. 2 or any other suitable preloading member. The preloading member 308 can preload the wastegate valve 302 and the diaphragm 306 into any suitable position—for example, a fully closed position, a fully open position, or somewhere in between.

[0030] To enable pneumatic positioning of the wastegate valve 302, a pressurized fluid source 310 supplies various pressurized fluid levels (e.g., compressed air levels) via a first channel 313 to a first chamber 312 of the wastegate 300. Pressurized fluid entering the first chamber 312 acts against the diaphragm 306, thereby adjusting the position of the diaphragm 306 and thus the wastegate valve 302 with sufficient pressures. When the wastegate valve 302 is in a fully closed position (e.g., fully seated on a valve seat 314 and fluidly sealing gases flowing from the first chamber 312 through the exhaust manifold 46), pressurized fluid supplied to the first chamber from the pressurized fluid source 310 provides the mechanism by which the wastegate valve 302 can begin to open.However, in other partially open positions, pressurized fluid supplied from pressurized fluid source 310 may combine with exhaust gases entering first chamber 312 from exhaust manifold 46 to position wastegate valve 302. Pressurized fluid source 310 may be, for example, an air compressor or an intake air source from engine 10 of FIG. Fig. 1. Although not shown, the pressurized fluid source 310 may include a vacuum regulator and / or one or more valves for controlling the supply of pressurized fluid to the first chamber 312. Likewise, the wastegate 300 may optionally include a second pressurized fluid source 316 configured to supply pressurized fluid (e.g., compressed air) to a second chamber 318 in the wastegate 300 via a second channel 320. Pressurized fluid supplied from this source to the second chamber 318 may act against the diaphragm 306 in a direction opposite to that supplied from the first chamber 312. By providing a vacuum regulator and / or one or more valves in the second pressurized fluid source 316 and / or in the second channel 320, precise positioning of the wastegate valve 302 can be achieved via balanced pressurized fluid supply to both the first and second chambers 312 and 318.It is understood that suitable modifications may be made to wastegate 300 without departing from the scope of the disclosure. For example, a vent (not shown) may be provided to further assist pressure regulation within the wastegate. Furthermore, a position sensor (not shown) may be provided within wastegate 300 to enable determination of the position of wastegate valve 302, similar to position sensor 203 in wastegate 200.

[0031] Fig. 3 further shows a low-lift region 322 in which the separation between the wastegate valve 302 and the valve seat 314 is considered to be relatively small for the multiple positions (e.g., strokes) of the wastegate valve in this low-lift region. As with the Fig. 2, the low lift region 322 may extend from a top surface 324 of the valve seat 314 to any suitable defined point in the first chamber 312 and may be measured from that top surface to the top of the wastegate valve 302. As a non-limiting example, the low lift region 322 may extend from the top surface 324 of the valve seat 314 to a height of approximately 15% of the sum of the heights of the first and second chambers 312 and 318. The low lift region 322 may be defined as any suitable portion of the sum of the heights of the first and second chambers 312 and 318 and may be predetermined based on the physical characteristics of the wastegate 300 or dynamically determined based on various desired operating parameters.

[0032] Fig. 4 shows a flowchart illustrating a method 400 that may be performed by an engine controller (e.g., controller 12) for controlling a turbocharger via a wastegate (e.g., wastegates 200 and 300). In one example, a method for controlling an engine turbocharger via a wastegate may include determining a desired boost pressure and an actual boost pressure. The wastegate may be adjusted according to a difference between the desired boost pressure and the actual boost pressure.

[0033] At 410, the method includes determining a desired boost according to engine operating conditions. The evaluated conditions may be directly measured using sensors, such as sensors 112, 118, 120, 122, 123, 124, and 134, and / or the conditions may be estimated from other engine operating conditions. The evaluated conditions may include engine coolant temperature, engine oil temperature, mass air flow (MAF), intake manifold pressure (MAP), boost (e.g., BOOST pressure from sensor 123), engine speed, idle speed, barometric pressure, driver requested torque (e.g., from pedal position sensor 134), air temperature, vehicle speed, etc.

[0034] Next, at 420, an actual boost pressure may be determined. The actual boost pressure may be measured directly by a sensor, such as sensor 123. The measurement may be sent to controller 12 via the BOOST pressure signal and stored in a computer-readable storage medium. In an alternative embodiment, the actual boost pressure may be estimated based on other operating parameters, such as MAP and RPM.

[0035] Next, at 430, atmospheric pressure may be determined. For example, atmospheric pressure may be measured by the MAP sensor at engine start-up and / or estimated based on engine operating conditions, including MAF, MAP, throttle position, etc. The measurement may be sent to controller 12 and stored in a computer-readable storage medium. In an alternative embodiment, atmospheric pressure may be estimated based on other operating parameters.

[0036] Next, at 440, a wastegate actuation force may be calculated based on a pressure differential across the wastegate, exhaust flow, and / or the angle of the wastegate valve. The wastegate may be adjusted according to the wastegate actuation force. The wastegate actuation force may accurately reflect a pressure differential across the wastegate. For example, the wastegate actuation force may be used as an input to wastegate dynamics. The wastegate dynamics may be a map of a desired wastegate pressure or a desired wastegate valve position versus a wastegate duty cycle for a given wastegate actuation force, with the duty cycle signal generated by the controller and sent to the wastegate actuator for adjusting the actuation force. The wastegate actuator can be, for example, actuator 150 in wastegate 200 or a vacuum regulator in wastegate 300.Assignment to a wastegate duty cycle may involve the use of lookup tables or wastegate duty cycle calculations. The wastegate control signal (WGC signal) may include pulse-width modulation across the wastegate duty cycle to adjust the wastegate. The target wastegate pressure or valve position may be achieved, for example, through feedforward, feedback, or other control algorithms.

[0037] A compensation term can account for wastegate actuator delays. Furthermore, the compensation term can further include adjustments based on the movement of independent dual cams, which can affect boost pressure. For example, if the intake cam moves in a manner that would increase boost pressure relative to atmospheric pressure, the magnitude of the compensation term can be reduced. Similarly, if the intake cam moves in a manner that would decrease boost pressure relative to atmospheric pressure, the magnitude of the compensation term can be increased.

[0038] Next, at 450, the position at which the wastegate valve (for example, valves 206, 302) is completely closed can be optionally determined. Fig. 5A and Fig. 5B shows a flowchart illustrating a method 500 for determining the position at which a wastegate valve is fully closed. For example, the method 500 may be used to determine the position at which the wastegate valves 206, 302 are fully closed.

[0039] The use of method 500 is based on the recognition that thermal distortion in a wastegate due to high ambient temperatures adversely affects the control of the wastegate and thus the accurate delivery of boost levels to an engine. In an electric wastegate, such as wastegate 200, thermal distortion can cause expansion and contraction of linkage 204, introducing an error between the determined and actual position of wastegate valve 206. Similarly, in a pneumatic wastegate, such as wastegate 300, thermal distortion in linkage 304 can introduce an error between the determined and actual position of wastegate valve 302.The present inventors have recognized that when a wastegate valve is placed within a certain distance of its corresponding valve seat (e.g., within a low lift region, such as low lift region 214), and under certain conditions described in more detail below, the wastegate valve can be moved to a fully closed position for a short, predetermined period of time without adversely affecting engine performance (e.g., overshooting / undershooting) or endangering the engine and other components, in order to, if desired, determine the position (or the orientation / state of another component) of the fully closed position.

[0040] At 502 of the method, it is determined whether or not the wastegate valve is in a low-lift range. As described above, the low-lift range may refer to a range where the separation between the wastegate valve and its corresponding valve seat (e.g., valve seat 314) is relatively small for the plurality of positions (e.g., lifts) of the wastegate valve in that low-lift range. The low-lift range may be, for example, 20% of the total height of a chamber that the wastegate valve moves. In some embodiments, the low-lift range may be a range that includes positions that are above a lower threshold but below an upper threshold (e.g., between 10-20% of maximum lift).The low lift range may be predetermined based on the physical characteristics of a wastegate and an engine, or dynamically determined so that the maximum lift from which the wastegate valve can be moved to the fully closed position is possible without adversely affecting engine performance. A position sensor corresponding to the wastegate (for example, position sensor 203), if available, may be used to determine whether the wastegate valve is in the low lift range. If it is determined that the wastegate valve is not in the low lift range (NO), normal wastegate operation is resumed by returning to 460 of method 400. If the wastegate valve is in the low lift range (YES), the method proceeds to 504.

[0041] Next, at 504, it is optionally determined whether a threshold duration has elapsed since the previous fully closed position determination. Here, inaccurate boost control due to thermal distortion is mitigated by attempting a periodic fully closed position determination. The threshold duration may be predetermined based on average temperature changes for average drive cycles or may be dynamically determined based on various operating parameters—for example, by tracking temperature changes throughout engine operation. If the threshold duration has not elapsed since the previous fully closed position determination (NO), normal wastegate operation is resumed by returning to 460 from method 400. If the threshold duration has elapsed (YES), the method proceeds to 506.

[0042] Next, at 506, it is optionally determined whether a temperature change has exceeded a threshold since the last fully closed position determination. The threshold may be predetermined based on known thermal expansion coefficients (e.g., corresponding to the wastegate valve linkage), such that temperature changes exceeding this threshold trigger a redetermination of the fully closed position, as a large amount of thermal deformation is likely to have occurred. If the temperature change had not exceeded the threshold since the last fully closed position determination (NO), normal wastegate operation is resumed by returning to 460 of method 400. If the temperature change has exceeded the threshold since the last fully closed position determination (YES), the method proceeds to 508. Fig. 5B, at 508, it is determined whether the rate of change of the desired torque is positive or negative. If the rate of change of the desired torque is positive, the method proceeds to 510. In this case, a greater amount of boost may be supplied to the engine, at which point commands are issued to the wastegate to move the wastegate valve toward the fully closed position. Since the wastegate valve is already moving to the fully closed position in this example, operating conditions may be more suitable for transitioning to the fully closed position. Thus, positive rates of change of desired torque are handled differently by the method than negative rates of change of desired torque, with the method favoring the former over the latter.

[0043] Next, after determining that the rate of change of the desired torque is positive, at 510 it is determined whether the positive rate of change of the desired torque exceeds a first threshold. If the positive rate of change of the desired torque exceeds the first threshold (YES), normal wastegate operation is resumed by returning to 460 of method 400. Here, scenarios in which a driver torque request precludes a fully closed position determination do not trigger such a determination. If, instead, the positive rate of change of the desired torque does not exceed the first threshold (NO), the method proceeds to 514.

[0044] After determining that the target torque rate of change is negative, at 512 it is determined whether the negative target torque rate of change exceeds a second threshold. Unlike the first scenario described above, where the target torque rate of change is positive, commands are issued to the wastegate to move the wastegate valve away from the fully closed position. Thus, negative target torque rates of change may be less conducive to determining the fully closed position, as less time is available for the wastegate valve to deviate from normal operation.Thus, the second threshold may be less than the first threshold, with a larger range of positive rates of change in desired torque conducive to the determination of the fully closed position compared to the range of negative rates of change in desired torque conducive to such a determination. If the second threshold is exceeded (YES), normal wastegate operation is resumed by returning to 460 of method 400. If the second threshold is not exceeded (NO), the method proceeds to 514.

[0045] In some cases, the rate of change of the desired torque may be substantially zero. Here, at least a portion of the desired torque rate of change history may be evaluated to determine a positive or negative net rate of change of the desired torque. Other approaches may predict the desired torque rate of change. In some embodiments, the method may simply proceed to 514 after determining a substantially zero rate of change of the desired torque.

[0046] Next, at 514, it is determined whether the load of the engine (e.g., engine 10) exceeds a threshold load. If the threshold load is exceeded (YES), normal wastegate operation is resumed by returning to 460 of method 400. Here, situations may be avoided where the time required to move the wastegate valve to the fully closed position is unreasonable, as well as situations where further closure of the wastegate valve would pose a danger to the engine and its components. In other embodiments, it may be determined whether an engine rotation rate (e.g., in terms of RPM) exceeds a threshold rate. If the threshold load is not exceeded (NO), the method proceeds to 516.

[0047] At 516, the difference between the actual stroke of the wastegate valve and a value determined by the controller (for example, controller 12 in Fig. 1) commanded lift sent to the wastegate. Since a commanded lift sent by a controller may be encoded as a parameter associated with an actuator of the wastegate valve, the commanded lift may be converted to a wastegate valve position, for example, via a lookup table. While in some scenarios the wastegate valve may be in the low lift range, a commanded lift may be output to the wastegate valve that corresponds to a lift that is far removed from its actual lift. Such a distance may preclude moving the wastegate valve to the fully closed position in the time available to do so and subsequently reaching the commanded lift. Thus, at 518, it is determined whether the difference between the actual lift and the commanded lift exceeds a threshold difference.If the threshold difference is exceeded (YES), normal wastegate operation is resumed by returning to 460 of procedure 400. If the threshold difference is not exceeded (NO), the procedure proceeds to 520.

[0048] At 520, a dwell time for which the wastegate valve may be maintained in the fully closed position is determined. The dwell time may be determined based on at least the actual wastegate valve lift and commanded lift determined at 516 and physical characteristics of the wastegate. The dwell time may be selected such that engine power (e.g., torque) and turbine speed are not overshooted. Such a selection of the dwell time may take into account one or more operating parameters, including the rate of change of desired engine torque, as described in more detail below. For example, the dwell time may decrease as the rate of change of desired torque increases. As another example, the dwell time may be determined based on a difference between a position command and the actual wastegate valve lift.

[0049] Next, at 522, the wastegate valve is moved to the fully closed position for a duration not exceeding the dwell time determined at 520. For certain scenarios, a sufficient determination of the fully closed position may require moving to the fully closed position for a large portion or for the entire duration of the dwell time. For example, the wastegate valve may bounce off its valve seat after being commanded to move to the fully closed position. Thus, more time is required to ensure valve seat contact and thus determine its position.It should be understood that verification that the fully closed position has been achieved may be performed in any suitable manner, including monitoring actuator feedback (e.g., current supplied to a motor in an electric wastegate), feedback from a wastegate valve position sensor, and boost levels. Here, an actual fully closed position may be determined, as the actual fully closed position may differ from a previously determined fully closed position. Furthermore, other data may be associated with a learned fully closed position, including one or more thermal conditions (e.g., exhaust gas temperature) and the time at which the fully closed position is learned.The collective data may be stored in a suitable data structure in the controller 12 to provide an indication of the thoroughness of the fully closed position learning, as described below with reference to FIG. Fig. 8 described in further detail.

[0050] In this way, method 500 provides a mechanism by which inaccurate boost control due to wastegate valve position uncertainty resulting from thermal deformation may be mitigated without adversely impacting engine performance (e.g., torque) or jeopardizing normal operation. In embodiments that utilize inner and outer loop control to control wastegate-delivered boost levels, the relatively fast dynamics of the inner loop control may be exploited to determine the position of a fully closed position (e.g., the valve seat) without adverse effects.As described above, it should be understood that determining the position of the fully closed position may correspond to an orientation or condition of an actuator operatively coupled to a wastegate, such as the orientation of a rotating component in a motor actuating an electric wastegate. Furthermore, method 500 may be configured in various suitable ways to achieve the results described above. For example, the method may be performed without recent delivery of a commanded stroke by an engine controller, but upon exceeding one or more of the thresholds described above (e.g., time, temperature, etc.).

[0051] Method 500 may include additional steps not shown. In particular, the method may indicate degradation of a wastegate valve position detection. If an actual position of a wastegate valve (e.g., indicated by a position sensor) does not match a learned fully closed position by more than a degradation threshold for longer than the duration of a dwell time the wastegate valve is held in the fully closed position, a degradation may be indicated, for example, via a dashboard indicator and / or setting a diagnostic code.

[0052] Now on Fig. 6, a map 600 is shown including an engine load, revolutions per minute (RPM), desired torque (τ D ), rate of change of the target torque (dτ D / dt) and lift of a wastegate valve, all as a function of time. The map 600 may represent an example drive cycle for the engine 10 in embodiments where the engine includes the wastegate 200 or 300 and, for example, implements the method 500 of Fig. 5 executes.

[0053] In particular, Fig. 6 represent times and operating parameter ranges in which a wastegate valve can be activated by executing method 500 of Fig. 5 is moved to its fully closed position to thereby determine the fully closed position position. In a first region 602, operating parameters are conducive to determining the fully closed position. In particular, load, RPM, desired torque, and rate of change of desired torque are within allowable limits for such a determination. Accordingly, as shown by the dashed lines, the wastegate valve lift is reduced to zero (e.g., brought against the valve seat to the fully closed position) for a first dwell time. Conditions such as a command to increase the wastegate valve lift terminate the fully closed position determination. Similarly, operating parameters later in operation of the engine 10 are conducive to redetermining the fully closed position in a second region 604.Here, the time separating the determination of the fully closed position in the first region 602 and the second region 604 exceeds a threshold, prompting a new determination. Furthermore, operating parameters remain conducive to maintaining the wastegate valve in the fully closed position for a second dwell time that is relatively longer than the first dwell time. The termination of the fully closed position determination is also illustrated. Although operating parameters may not require such a termination, the second dwell time is appropriate for a sufficient determination of the fully closed position. In other regions of map 600, operating parameters prevent a fully closed position determination.For example, in regions prior to the first region 602 and between the first and second regions 602 and 604, the valve lift cannot be reduced to zero, for example, due to valve lifts and a high target torque. In region 606, the rate of change of the target torque (dτ) exceeds D / dt) sets an upper limit, preventing application of the fully closed position. In some embodiments, as this rate of change increases, the duration of the dwell time for holding a wastegate valve in a fully closed position decreases. Positioning a wastegate valve in a fully closed state and determining a dwell time for holding the wastegate valve in the fully closed state may take into account one or more of the operating parameters described above (e.g., the rate of change of desired engine torque).

[0054] Again on Fig. 4, the wastegate may be adjusted at 460 according to the desired boost, taking into account adjustments made at 450 when the fully closed position is determined. In some examples, the desired boost pressure may be used as an input to a feedforward control algorithm for adjusting the wastegate position. The feedforward control algorithm may process a target wastegate pressure or a target wastegate valve position, which may be used as an input to internal control loops.

[0055] Finally, at 470, a boost error may be calculated as a difference between the desired boost pressure and the actual boost pressure. The wastegate may be adjusted according to the processed boost pressure error. For example, the boost pressure error may be used as an input to a feedback control algorithm to calculate a target wastegate pressure when pressure control is desired, or a target wastegate valve position in an inner loop. The control algorithm may include a compensation term, as described above.

[0056] Determining the fully closed position of a wastegate valve can be performed under other operating conditions, including those where placement of the wastegate valve in a fully open position is desired. Fig. 7 shows a flowchart illustrating a method 700 for determining the fully closed position of a wastegate valve (e.g., wastegate valves 206, 302) when the fully open position is desired. For example, wastegate valves 206 and 302 may assume fully open positions when positioned in regions above and outside of low-lift regions 214 and 322, respectively. The method 400 of Fig. 4 may be modified to serve as an alternative or in addition to the method 500 of Fig. 5 comprises the method 700.

[0057] At 702 of method 700, it is determined whether the fully open position of a wastegate valve is desired. A wastegate valve controlled by an engine controller (e.g., controller 12 of Fig. 1) The transmitted commanded lift may be evaluated to make such a determination. If the commanded lift corresponds to the fully open position, it is determined that the fully open position is desired (YES), and the method proceeds to 704. If the fully open position is not desired (NO), normal wastegate operation is resumed, for example, by returning to 460 of method 400.

[0058] At 704, it is determined whether fluid flow (e.g., intake air flow) upstream of a turbocharger compressor (e.g., compressor 60) is throttled. Fluid flow upstream of the turbocharger compressor may be determined based on a mass air flow sensor, such as sensor 120 in Fig. 1, are evaluated. If fluid flow is restricted in this region, moving the wastegate valve toward the fully closed position does not increase the boost levels delivered to an engine (e.g., engine 10) or the resulting engine power / torque. Thus, if fluid flow upstream of the compressor is restricted (YES), method 700 proceeds to 708. If fluid flow upstream of the compressor is not restricted (NO), the method proceeds to 706.

[0059] At 706, it is determined whether a deceleration fuel cut-off (DFCO) event is occurring. The evaluation of actual fueling conditions may include, for example, monitoring Fig. 1 output FPW signals. Here, conditions such as vehicle deceleration cause a termination of fuel supply to the cylinders of an engine (for example, cylinders 30 of engine 10 in Fig. 1). In this case, increases in the boost level supplied to the engine do not result in increases in engine power / torque. Thus, the wastegate valve may be moved to the fully closed position without adversely affecting engine operation (e.g., overshooting engine torque). Accordingly, if it is determined that a DFCO event is occurring (YES), the method proceeds to 708. If a DFCO event is not occurring (NO), normal wastegate operation is resumed, for example, by returning to 460 of method 400.

[0060] At 708, a dwell time for which the wastegate valve may be held to learn the fully closed position is determined, as described above.

[0061] Next, at 710, the wastegate valve is moved to the fully closed position and held there for at least the dwell time, or until the wastegate valve position affects engine performance, which in the illustrated embodiment occurs when the DFCO event ends or when fluid flow upstream of the turbocharger compressor is no longer throttled, as described above. Thus, in some scenarios, the wastegate valve is held in the fully closed position for less than the predetermined dwell time.

[0062] Finally, at 712, the fully closed position learned at 710 is associated with one or more thermal conditions and stored, for example, in the RAM 108 and / or KAM 110 of the controller 12 in Fig. 1. The one or more thermal conditions may include readings from a temperature sensor, such as sensor 112 of engine 10, although readings from other sensors, as well as estimates of the temperature near the wastegate valve (e.g., exhaust gas temperature), may also be included. The time at which a fully closed position is learned may be further associated with the learned fully closed position and the associated one or more thermal conditions so that an indication of the frequency of learning the fully closed position for particular thermal conditions may be provided, as described in further detail below. Following 712, normal wastegate operation resumes, for example, by returning to 460 of method 400.

[0063] Now on Fig.8, a map 800 is shown that may be formed based on a plurality of learned fully closed positions and associated data, including one or more thermal conditions, which in this case include a temperature (e.g., exhaust temperature) and the time at which the fully closed positions are learned, shown in this example by shading. Specifically, the map 800 includes a first group 802 of relatively recently learned positions for a relatively high temperature range, a second group 804 of positions learned prior to the first group 802 toward a medium temperature range, and a third group 806 of positions learned prior to the second group 804 toward the beginning of engine operation in a relatively low temperature range.Map 800 provides a structure suitable for storing both current learned fully closed positions and past fully closed positions (e.g., fully closed positions learned prior to a current learned fully closed position). Map 800 may also provide an indication of the frequency of fully closed position learning. For example, by accessing map 800, regions can be determined where a fully closed position learning has not occurred or has not occurred frequently. In the illustrated example, a fully closed position learning has not occurred in regions 808 and 810.To maximize learning of a fully closed position and ensure that learning is performed substantially across various engine operating ranges (e.g., temperatures), an engine controller (e.g., controller 12) may include instructions executable to preferentially schedule learning of a fully closed position for ranges where no or infrequent learning has occurred, such as in ranges 808 and 810. For example, learning of a fully closed position for a particular range may be triggered when a threshold duration has elapsed since the previous learning.

[0064] Furthermore, learning a fully closed position may be performed based on the time elapsed since the last learning. While the third group 806 of positions marks the oldest learning in map 800, relearning the fully closed position in that range may be prioritized. In some approaches, regions 808 and 810 may be populated based on nearby learned positions. For example, these regions may be populated by extrapolating from positions learned in other surrounding regions (for example, region 808 may be populated by extrapolating learned positions in groups 802 and 804). However, it should be understood that the described functionality of map 800 may also be enabled by other suitable data structures. For example, a lookup table may encode data associated with learned positions, including time of learning and temperature.

[0065] It should be appreciated that the example control and estimation methods included herein may be used with various engine and / or vehicle system configurations. The particular methods described herein may represent one or more of a number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Thus, various illustrated acts, operations, or functions may be performed in the order illustrated, in parallel, or in some cases, omitted. Likewise, the processing order may not necessarily achieve the features and advantages of the example embodiments described herein, but is provided for convenience of illustration and description.One or more of the illustrated actions or functions may be performed repeatedly depending on the particular strategy used. Furthermore, the described actions may graphically represent code to be programmed into the computer-readable storage medium in the engine control system.

Claims

[1] Method comprising: Receiving a control to a non-closed position for a wastegate valve (206, 302), wherein the position control occurs in a low-lift (214, 322) or high-lift range with respect to a valve seat (212, 314); and before executing the position control, only temporarily closing the wastegate valve (206, 302) to determine a current fully closed position. [2] The method of claim 1, further comprising adjusting an actuator (150) operatively coupled to the wastegate valve (206, 302) based on the determined current fully closed position while at least partially open, wherein determining the current fully closed position comprises determining an orientation of the actuator (150) operatively coupled to the wastegate valve (206, 302). [3] The method of claim 2, wherein the actuator (150) is a pneumatic actuator (150) or an electric actuator (150), the method further comprising, after only temporarily closing the wastegate (26, 200, 300), adjusting the actuator (150) to move the wastegate (26, 200, 300) to the non-closed position controlled based on the determined current fully closed position, wherein the high lift range control occurs under fuel cut-off conditions. [4] The method of claim 1, further comprising: Receiving a command to the fully open position for the wastegate valve (206, 302), wherein the wastegate valve (206, 302) is arranged in a turbocharger; when fluid flow upstream of a compressor (60) of the turbocharger is throttled, only temporarily closing the wastegate valve (206, 302) to determine the current fully closed positions; and if the fluid flow upstream of the compressor (60) is not throttled, executing the control in the fully open position. [5] The method of claim 1, further comprising: Receiving a command to a fully open position for the wastegate valve (206, 302); when no fuel is supplied to the cylinders (30) of an internal combustion engine (10), only temporarily closing the wastegate valve (206, 302) to determine the current fully closed positions; and when fuel is supplied to the cylinders (30), executing the control to the fully open position. [6] The method of claim 1, further comprising: Assigning a temperature and a time to the current fully closed position; and Storing the fully closed position and the associated temperature and time so that learned fully closed positions are accessible for given temperatures; wherein the temporary closing of the wastegate valve (206, 302) for determining the current fully closed position is preferably set for a selected temperature when a threshold duration since determining a fully closed position for the selected temperature is exceeded. [7] The method of claim 6, further comprising determining the fully closed position for the selected temperature by extrapolating learned fully closed positions for temperatures near the selected temperature. [8] The method of claim 1, further comprising: Determine whether a rate of change of the target torque is positive or negative; if the rate of change of the desired torque is positive and does not exceed a first threshold, only temporarily closing the wastegate valve (206, 302); and if the rate of change of the desired torque is negative and does not exceed a second threshold, only temporarily closing the wastegate valve (206, 302); where the first threshold is greater than the second threshold. [9] The method of claim 1, wherein the wastegate valve (206, 302) is temporarily closed when an engine rotation rate is below a threshold, otherwise the actuator (150) is set to move the wastegate (26, 200, 300) to the commanded non-closed position without temporarily closing the wastegate (26, 200, 300); wherein the wastegate valve (206, 302) is temporarily closed when an engine load is below a threshold, otherwise the actuator (150) is set to move the wastegate (26, 200, 300) to the commanded non-closed position based on the determined current fully closed position. [10] The method of claim 1, wherein the wastegate valve (206, 302) is temporarily closed when a threshold duration has elapsed since the fully closed position was previously determined, otherwise the actuator (150) is set to move the wastegate (26, 200, 300) to the non-closed position commanded without temporarily closing the wastegate (26, 200, 300); and wherein the wastegate valve (206, 302) is temporarily closed when a threshold change in temperature is exceeded, otherwise the actuator (150) is set to move the wastegate (26, 200, 300) to the non-closed position commanded without temporarily closing the wastegate (26, 200, 300). [11] The method of claim 1, further comprising: Determining a dwell time based on a difference between the position command and a current wastegate valve lift; and Maintaining the wastegate valve (206, 302) in the current fully closed position for a majority of the dwell time, wherein the determined dwell time decreases as the difference increases. [12] Method comprising: if a position control for a wastegate valve (206, 302) corresponds to a low-lift (214, 322) or high-lift range, but not a medium-lift range with respect to a valve seat (212, 314), temporarily closing the wastegate valve (206, 302) to determine a current fully closed position before executing the position control; and if the position control does not correspond to the low stroke range (214, 322), execute the position control. [13] The method of claim 10, wherein the current fully closed position corresponds to an orientation of an actuator (150) operatively coupled to the wastegate valve (206, 302). [14] The method of claim 11, wherein the actuator (150) is a pneumatic actuator (150) or an electric actuator (150). [15] The method of claim 10, further comprising: Determine whether a rate of change of the target torque is positive or negative; if the rate of change of the desired torque is positive and does not exceed a first threshold, closing the wastegate valve (206, 302); and if the rate of change of the desired torque is negative and does not exceed a second threshold, closing the wastegate valve (206, 302); where the first threshold is greater than the second threshold. [16] The method of claim 10, wherein the wastegate valve (206, 302) is closed when an engine rotation rate, an engine load, and a rate of change of the desired torque are below respective thresholds. [17] The method of claim 10, further comprising: Determining a dwell time based on a difference between the position command and a current wastegate valve lift; and Maintaining the wastegate valve (206, 302) in the current fully closed position for a majority of the dwell time. [18] Method comprising: Adjusting a wastegate actuator (150) in response to a desired and actual wastegate position, including temporarily moving the wastegate (26, 200, 300) to a fully closed position when commanded to a not fully closed position that is above a lower threshold but below an upper threshold; wherein the adjusting is further based on the actual wastegate position in the fully closed state. [19] The method of claim 16, wherein a duration for which the wastegate (26, 200, 300) is temporarily in the fully closed state is based on a rate of change of the desired engine torque; and wherein the duration decreases as the rate of change increases. [20] The method of claim 18, further comprising indicating a degradation based on the actual wastegate position in the fully closed state not matching the fully closed position by more than a degradation threshold for more than the duration.

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