METHOD AND SYSTEM FOR WASTEGATE CONTROL

Abstract

Method for an engine, comprising: during continuous engine operation, inducing a boost pressure oscillation by actuating a wastegate and compensating for a manifold air pressure with a corresponding throttle oscillation; and updating a gain of a feedback wastegate regulator due to the boost pressure oscillation.

Description

Field of InterestThe present description relates generally to methods and systems for controlling a wastegate with a wastegate feedback controller, wherein parameters of the wastegate feedback controller may be updated by inducing an oscillation in boost pressure during engine operation.Background / SummaryInternal combustion engines may be downsized to improve fuel efficiency. To achieve high peak engine performance, turbochargers may be used to increase boost pressure. In one example, a turbocharger may include a compressor and a turbine connected by a driveshaft, the turbine coupled to an exhaust manifold side of the engine, and the compressor coupled to an intake manifold side of the engine. A throttle may be disposed between the compressor and the intake manifold to regulate airflow into the engine intake manifold. Boost pressure may be regulated by adjusting the amount of exhaust gas reaching the turbine, for example, with a wastegate. In response to a torque demand, an engine control system may calculate a desired throttle inlet pressure and send it to the wastegate feedback controller. In the wastegate feedback controller, a wastegate command may be generated to actuate the wastegate. In one example, the wastegate feedback controller may be a proportional-integral-derivative (PID) feedforward controller. Gains of the proportional, integrating and differentiating term of the PID controller need not be tuned for the engine system. However, determining the gains of the PID controller may be a cumbersome task, as controller gains depend on operating conditions such as engine airflow, turbine speed, and atmospheric pressure.Other attempts to determine the PID controller gain include tuning the controller via relay feedback. An exemplary approach is shown by Boiko et al. in US 8255066B2. There, oscillations are generated corresponding to a selected gain or phase margin, and tuning parameters of the PID controller are calculated based on the amplitude and frequency of the oscillations. Further, the prior art is "non-parametric" because it does not attempt to estimate any rule-route (process) model parameters.From document DE 10 2015 120 372 A1 a further method for controlling the air charge system is known, in which a PID controller is used.However, the present inventors have now recognized the above-mentioned problems as well as other possible problems with such systems. As an example, the procedure for determining PID tuning parameters is complicated and may be time consuming and may not provide a straightforward approach to weighing reaction speed and robustness. Further, controller parameters may need to be updated during a comprehensive vehicle calibration procedure to accommodate subsequent hardware changes or inter-part variability, or after initial factory calibration due to system wear over time.It is therefore an object of the present invention to overcome the above-described problems. This object is achieved by the subject matter of the independent claims. Preferred embodiments of the present invention are the subject matter of the dependent claims.In one example, the issues described above may be overcome using a method for an engine system, comprising: during stable engine operation, inducing a boost pressure vibration by actuating a wastegate and compensating manifold air pressure with a corresponding throttle vibration; and updating a feedback wastegate regulator gain due to the boost pressure vibration. For example, the gains may be updated during engine operation based on parameters describing the measured boost pressure vibration, such as amplitude, frequency, etc. In this way, the gain of the wastegate feedback controller may be updated directly in a process-locked manner while the engine is running.As one example, a wastegate may be controlled using a feedback wastegate controller in the form of a PID controller. During stable engine operation, a low amplitude boost pressure oscillation may be induced by oscillating the position of a wastegate. Boost pressure may be a throttle input pressure or a compressor output pressure. In the case of a diesel engine, boost pressure may be intake manifold pressure. As a non-limiting example, boost pressure is referred to herein as a throttle input pressure (DED). In response to the DED oscillation, a throttle may be vibrated to maintain a constant manifold air pressure. In another embodiment, in hybrid applications, the electric motor or a generator may be used to cancel the effect of the oscillations of the throttle input pressure on the torque delivered. Gains of the PID controller may be updated as a mathematical function of the frequency, amplitude, and phase of the boost pressure swing. By updating the feedback wastegate regulator over time, the boost pressure can be controlled in a robust manner with a tolerance for the wear of vehicle components. By determining the gain of the wastegate feedback controller during steady engine operation, the gain of the wastegate feedback controller may be updated with a reduced disruption in engine operation.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 intended to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely in the claims following the detailed description. Further, the claimed subject matter is not limited to implementations that address the disadvantages mentioned above or in any part of this disclosure.Brief Description of the DrawingsFIG. 1 shows a block diagram of an example boosted engine including a wastegate. FIG. 2 shows a block diagram of an example wastegate feedback controller. FIG. 3 shows a method example for updating parameters of a feedback wastegate regulator. FIG. 4 shows an exemplary internal model control structure. FIG. 5 shows a method example for calibrating a feedback wastegate regulator. FIG. 6 shows timelines representing different engine parameters during implementation of the method example.Detailed DescriptionThe following description relates to systems and methods for controlling a wastegate of a turbo-boosted engine, such as the turbo-boosted engine shown in FIG. 1. The position of the wastegate may be regulated via a wastegate feedback controller. FIG. 2 shows a block diagram of an example wastegate feedback controller. The wastegate feedback controller may include a PID controller, where the controller gain is adjusted via relay feedback. Because the desired controller gain may vary due to vehicle-to-vehicle variations and may vary over time due to system wear, the controller gain may need to be updated after the initial factory calibration. FIG. 3 shows a method example of updating the controller gain via relay feedback. Specifically, during engine operation, a boost pressure swing may be induced by actuating the wastegate with a square wave wastegate command. The feedback wastegate controller gain may be derived from the measured frequency, amplitude, and / or phase of the boost pressure swing based on an internal model control (IMC) loop. FIG. 4 shows an example IMC structure. FIG. 5 demonstrates a method example of factory calibration of the feedback wastegate controller gain. FIG. 6 illustrates the change in engine parameters during updating of the feedback wastegate controller gain during engine operation.FIG. 1 is a schematic diagram showing an example engine 10 that may be included in a propulsion system of a motor vehicle. Engine 10 is shown with four cylinders 30. In this regard, other numbers of cylinders may also be used in accordance with the present disclosure. The engine 10 may be controlled at least in part by a control system including an engine controller 12 and by input by 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 PS. Each combustion chamber (e.g., cylinder) 30 of 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 to rotational motion of the crankshaft. The crankshaft 40 may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system (not shown). Further, a starter motor may be coupled to crankshaft 40 via a flywheel to enable a cranking operation of engine 10.Combustion chamber 30 may receive intake air from intake manifold 44 via intake passage 42 and exhaust combustion exhaust gases via exhaust passage 48. Intake manifold 44 and exhaust manifold 46 may selectively communicate with combustion chamber 30 via respective intake valves and exhaust valves (not shown). In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.Fuel injectors 50 are shown coupled directly to combustion chamber 30 to directly inject fuel therein in proportion to the pulse width of a signal FPW received from engine controller 12. Thus, fuel injection 50 provides a so-called direct injection of fuel into combustion chamber 30. The fuel injection may be mounted in the side of the combustion chamber or in the top of the combustion chamber, for example. Fuel may be delivered to fuel injector 50 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chambers 30 may alternatively or additionally include a fuel injection arranged in intake manifold 44 in a configuration that provides so-called port injection of fuel into the intake port upstream of each combustion chamber 30.The intake passage 42 may include a throttle 23 having a respective throttle 24. In this particular example, the position of throttle 24 may be varied by engine controller 12 via signals provided to an actuator included in throttle 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 way, throttle 23 may be operated to vary the intake air provided to combustion chamber 30 among other engine cylinders. The position of throttle 24 may be provided to engine controller 12 by a throttle position signal DS. Intake passage 42 may further include a mass air sensor 120, a manifold air pressure sensor 122, and a throttle input pressure sensor 123 for providing respective signals LM (mass air) and MAP (manifold air pressure) to engine controller 12.The exhaust passage 48 may receive exhaust gases from the cylinders 30. Exhaust gas sensor 128 is shown coupled to exhaust passage 48, which is downstream of turbine 62 and upstream of emission control device 78. The sensor 128 may be selected from various suitable sensors for providing an indication of exhaust gas air / fuel ratio, such as a linear oxygen sensor or universal exhaust gas oxygen (UEGO) sensor, a two-state lambda sensor or EGO, a NOx, HC, or CO sensor. Emission control device 78 may be a three-way catalyst (DK), NOx trap, various other emission control devices, or combinations thereof.Exhaust temperature may be measured by one or more temperature sensors (not shown) disposed in the exhaust passage 48. Alternatively, exhaust temperature may be inferred based on engine operating conditions such as speed, load, air-fuel ratio (LCV), spark retard, etc.Controller 12 is shown in FIG. 1 as a microcomputer, including microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, shown as read only memory 106 in this particular example, random access memory 108, keep alive memory 110, and a data bus. Controller 12 may receive various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including measurement of inducted mass air flow (LM) from mass air flow sensor 120; engine coolant temperature (MKT) from temperature sensor 112 shown schematically in position with engine 10; throttle input pressure (DED) from sensor 123; a profile ignition pickup signal (PZA) from Hall effect sensor 118 (or other type) coupled to crankshaft 40; throttle position (DS) from a throttle position sensor as discussed; and absolute manifold pressure signal, MAP, from sensor 122 as discussed. The engine speed signal, RPM, may be generated by engine controller 12 from signal PZA. The manifold pressure signal MAP from the manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold 44. It should be noted that various combinations of the above sensors may be used, such as an LM sensor without a MAP sensor, and vice versa. During stoichiometric operation, the MAP sensor may be indicative of engine torque. Further, this sensor, along with the sensed engine speed, may provide an estimate of the charge (including air) introduced to the cylinder. In one example, sensor 118, which may also be used as an engine speed sensor, may produce a predetermined number of equally spaced pulses per revolution of crankshaft 40. In some examples, a storage medium of read-only memory 106 may be programmed with computer readable data representing instructions executable by processor 102 for performing the methods described below, as well as other variants anticipated but not expressly listed.The engine 10 may further include a compression device, such as a turbocharger, including at least one compressor 60 disposed along the intake manifold 44. Compressor 60 may be driven by a turbine 62, for example, via a shaft or other clutch arrangement. The turbine 62 may be disposed along the exhaust passage 48 and may be in communication with exhaust gases passing therethrough. Sensor 123 may be disposed in intake manifold 44 for measuring throttle input pressure and providing a DED signal to engine controller 12.The exhaust passage 48 may include a wastegate 26 coupled to the turbine 62 for directing exhaust gas away from the turbine 62. In some embodiments, wastegate 26 may be a multi-stage wastegate, such as a two-stage wastegate, with a first stage configured to regulate boost pressure and a second stage configured to increase heat flow to emission control device 78. Wastegate 26 may be operated with an actuator 150, which may be an electric actuator such as an electric motor, although pneumatic actuators may also be used. The intake passage 42 may include a compressor bypass valve 27 configured to bypass intake air around the compressor 60. Wastegate 26 and / or compressor bypass valve 27 may be controlled by engine controller 12 via actuators (e.g., actuator 150) such that they open when, e.g., a lower boost pressure is desired.The intake passage 42 may further include the charge air cooler (CAC) 80 (e.g., an intercooler) to reduce the temperature of intake gases boosted with a turbocharger or compressor. In some embodiments, a charge air cooler 80 may be an air-to-air heat exchanger. In other embodiments, the charge air cooler 80 may be an air-liquid heat exchanger.Further, in the disclosed embodiments, an exhaust gas recirculation (EGR) system may route a desired portion of the exhaust gas to a position between throttle 23 and CAC 80 via EGR passage 140. The amount of EGR provided to intake passage 42 may be varied by engine controller 12 via EGR valve 142. Further, an EGR sensor (not shown) may be disposed within the EGR passage and provide an indication of one or more of pressure, temperature, and concentration of the exhaust gas. FIG. 1 shows a high pressure EGR system where EGR is directed from upstream of a turbine of a turbocharger to downstream of a compressor of a turbocharger. In other embodiments, the engine may additionally or alternatively include a low pressure EGR system, where EGR is directed from downstream of a turbine or turbocharger to upstream of a compressor of the turbocharger.The engine controller 12 receives signals from the various sensors of FIG. 1 and uses the various actuators of FIG. 1 to adjust engine operation based on the received signals and instructions stored in a memory of the controller. As one example, adjusting manifold air pressure may include adjusting the actuator of the throttle to adjust throttle opening. As another example, adjusting the throttle input pressure may include adjusting the wastegate actuator to adjust the throttle position.Referring to FIG. 2, an example block diagram of a wastegate feedback controller 200 is demonstrated. The wastegate feedback controller 200 may be part of the engine controller 12. In other words, the wastegate feedback controller mechanism may be implemented via engine controller 12. The wastegate feedback controller has a desired and measured DED as an input and a wastegate command as an output. The DED may be measured via a sensor coupled between a compressor and a throttle (such as pressure sensor 123 in FIG. 1 ). The wastegate feedback controller may include a PID controller 210. The PID controller 210 may take a DED error (i.e., a difference between the desired DED and the measured DED) as input and send a wastegate command to the control path 220. Herein, the loop 220 represents an engine process with input of a wastegate command and output of a throttle input pressure. In the loop 220, the wastegate command may be sent to a wastegate actuator (e.g., wastegate actuator 150 in FIG. 1 ) to adjust wastegate position. The change in wastegate position may cause vibration in the DED. The DED can be measured and fed back to the input to be compared to the desired DED.The PID controller 210 includes three terms: proportional 211, differentiating 212 and integrating 213. Each of these three members has a corresponding reinforcement. The gains are dependent on operating parameters such as engine air mass, turbocharger speed, and ambient pressure. To determine (i.e., tune) the controller gain, the controller 220 may alternatively be connected to a relay function 201. The relay function 201 may take the DED fault as an input and issue a wastegate command in the form of a shifting square wave. Such a wastegate command may induce a vibration in the wastegate position. As a result, the DED may oscillate at the output of the loop 220. The DED oscillation can be used to characterize the dynamics of the controlled system 220. An example method for determining the control gains of the controller 210 is demonstrated in detail in FIGS. 3 and 5.Due to system wear over time, the desired controller gain may vary. FIG. 3 shows a method example 300 of updating the controller gain during engine operation. For example, during steady engine operation, the wastegate actuator may receive a signal from a relay function (e.g., relay function 201 in FIG. 2 ) instead of a PID controller (e.g., PID controller 210 in FIG. 2 ). The method 300 may then determine an updated gain of the PID controller by analyzing the DED sampling signal.Instructions for carrying out method 300 and the remaining methods included herein may be executed by an engine controller based on instructions stored in a memory of the engine 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 engine controller may use engine actuators of the engine system to adjust engine operation according to methods described below.At step 301, vehicle operating conditions are determined by an engine controller (such as engine controller 12 in FIG. 2 ). The engine controller acquires measurements from various sensors in the engine system and estimates operating conditions including engine load, engine speed, DED, MAP, vehicle torque demand, turbocharger speed, wastegate position, and throttle position.At step 302, method 300 loads a look-up table for determining controller gains of a wastegate feedback controller (such as controller 210 in FIG. 1 ). As an example, the look-up table may have been determined in advance and stored in the non-volatile memory of the motor controller (such as motor controller 12 in FIG. 1 ). As another example, the look-up table may be factory calibrated for each vehicle. An example method of factory calibration of the proof table is presented in Fig. 5. In one embodiment, the look-up table stores the speed of the turbocharger and a corresponding gain of the wastegate feedback controller. As one example, based on the turbocharger speed estimated in step 301, method 300 determines gains for each term of a PID controller. As another example, the proportional, differentiating, and integrated gain of the PID controller may decrease with increased speed of the turbocharger. As another example, the feedback wastegate regulator gains may be acquired by interpolating the turbocharger speed stored in the look-up table.At step 303, method 300 determines whether the engine is in steady state engine operation. As one example, the engine may be in steady engine operation when the change in torque demand over a predetermined period of time is within a threshold. In conventional powertrains, the torque variation will be small when the driver demand is relatively constant, such as during stable driving on a low grade. In mild, series, or parallel hybrids, the engine is often operated for long periods of time, regardless of driver demand, at a steady torque demand, which is typically associated with high operating performance. Another example of steady state operation is that the rate of change of the estimated and measured engine air mass is in a predetermined band, which may be achieved by applying a high pass filter to the engine air mass signal and comparing the filtered output to a threshold. If engine operation of the vehicle is not steady, the method may proceed to step 304, where the wastegate is controlled by the wastegate feedback controller, where controller gains are determined based on the lookup table loaded in step 302. Otherwise, if the engine is in steady engine operation, then method 300 proceeds to step 305.At step 305, method 300 may compare the time since the last update of the feedback wastegate regulator gain to a pre-determined time period Th 1. The period Th 1 may be related to the condition of the engine system. For example, Th 1 may be a predicted period of time during which wastegate wear may occur. If the look-up table has not been updated for a time that exceeds Th1, then the method 300 proceeds to step 306. Otherwise, method 300 proceeds to step 304 and uses the controller gains stored in the loaded look-up table for wastegate control. In one embodiment, there may be a timer and a predetermined time period Th 1. In another embodiment, the time during which a subset of the look-up table has not been updated may be a vector of times that each correspond to a subset of engine operating conditions. Thus, the controller cannot update a first subset of the look-up table because its timer has not exceeded the pre-determined time period Th1, but it can update a second subset of the look-up table when these conditions are met because the timer of the second subset has exceeded Th1 due to not being updated as recently as the timer of the first subset. By updating the look-up table over a pre-determined period of time, variation in desired feedback wastegate controller gains may be compensated for improved wastegate control.At step 306, method 300 induces a vibration in the wastegate position by actuating the wastegate via a relay function (such as relay function 201 in FIG. 2 ). The relay function may take the form of a shifting square wave. As a result, the wastegate position may oscillate, resulting in oscillation in the DED. In one example, while the wastegate is actuated via the relay function, EGR flow may be stopped by closing the EGR valve (such as EGR valve 142 in FIG. 2 ). Further, the bypass valve (such as VRV 27 in FIG. 2 ) may be closed. In this way, the DED vibration is induced solely by the vibration of the wastegate position.At step 307, method 300 actuates the throttle (such as throttle 24 in FIG. 1 ) to induce vibration of the throttle position. The throttle may be oscillated to compensate for the change in MAP that would otherwise be induced by the DED oscillation, such that a relatively constant MAP may be achieved. In this way, vehicle drivability may be less degraded during the regulator gain tuning operation. In one example, the throttle opening may increase responsive to an increase in wastegate opening. In one embodiment, the vibration of the throttle may be determined based on the wastegate command. As one example, the throttle may be actuated at a same frequency and phase as the wastegate command. As another example, the throttle may be actuated responsive to a measured wastegate position. In another embodiment, the vibration of the throttle may be determined in response to the DED. For example, engine controller 12 may sense the DED via a sensor and calculate a corresponding throttle position necessary to maintain a constant MAP. In another embodiment, the vibration of the throttle may be determined in response to the MAP. For example, engine controller 12 may sense the MAP via a sensor and determine a corresponding throttle position to compensate for the fluctuation of the MAP. In another embodiment, in hybrid powertrain applications, the vehicle system may use an electric motor or a generator to compensate for the effect of DED vibration on engine torque output. For example, the torque generated by the electric motor or generator may be vibrated to maintain a constant delivered vehicle torque.At step 308, the method 300 determines whether the gain should be tuned by a fast gain tuning operation across steps 310 and 311, or a more time and resource intensive tuning operation across steps 309 and 312. As one example, method 300 may select the fast gain tuning when an engine operating condition is predicted to end in a short time. As another example, method 300 may select the fast gain tuning when the time since the last update of the feedback wastegate regulator gain is less than a threshold Th 2, where Th 2 is greater than the threshold Th 1 of step 305.At step 310, the DED oscillation is sampled at a first frequency. For example, the DED is sensed by a sensor coupled before the throttle (such as sensor 123 in FIG. 1 ). Next, at step 311, the feedback wastegate controller gain may be updated based on the frequency and amplitude of the sampled DED oscillation. In one embodiment, the frequency of the DED oscillation may be determined based on zero crossings of the DED oscillation, and the amplitude of the DED oscillation may be determined based on peaks of the detected DED signal. In another embodiment, as shown in FIG. 6, the peaks 633 and 634 (i.e., the local maximum and minimum) of the DED vibration may be determined. A zero position 631 may be determined based on the peaks. For example, the zero position may be determined by using a sliding means of the tips. The frequency and phase of the DED oscillation may be determined by tracking the zero crossings of the DED signal over time. The amplitude of the DED oscillation may be determined by the difference between peaks and the DED at the zero position (such as the amplitude a between 632 and 631 in FIG. 6 ).Using the information obtained from the DED oscillation, the gain and phase of the system transfer function at the oscillation frequency can be calculated using the equations below derived from the standard analysis of description functions from the control theory: where G is the system transfer function from the wastegate to the DED (i.e., the transfer function of the controller 220 in FIG. 2 ), ω is the frequency of the oscillation, a is the delivered oscillation amplitude, d is the input (relay) amplitude (shown in FIG. 6 ) and ε is the hysteresis quantity. |.| denotes the system gain, denotes the system phase, j denotes the complex variable, and asin is the arcsinus function.As one example, the wastegate feedback controller may include a PID controller as shown in FIG. 2. The feedback wastegate regulator may be configured based on Internal Model Control (IMC). The IMC controller may then be assigned to the PID controller to yield PID controller gains. An example block diagram of the IMC structure is shown in FIG. 4, where r(t) is the input, y(t) is the output, G(s) is the transfer function of the plant (such as plant 220 in FIG. 2 ), Ĝ(s), a model of the plant (i.e., an approximating process model), and Q(s), and a controller block are to be defined. As shown in Figure 4, the closed loop system can be seen as the classic feedback structure by rearranging the blocks, the regulator being given by C(s)=Q / (1-QV).In the procedure of IMC design, block Q may be selected as the inverse of the process model, i.e., Q(s)≈Ĝ -1( s). However, the process model is typically a true transfer function and does not have a causal inversion. Thus, to obtain a causal transfer function, the inverse model is extended with a filter: Q(s)≈G -1( s)F(s), where F(s) is a filter with low pass characteristics. Note that with this choice of Q(s) and the assumption of a perfect process model (Ĝ=G), the closed loop transfer function from r(t) to y(t) is given by F(s); therefore, the bandwidth of F(s) dictates the bandwidth of the closed loop system and can be used as a design parameter for balancing performance and robustness. Once C(s) is designed, it can be assigned to a PID controller by adjusting the coefficients of power of s in the resulting transfer function.During the process of determining the feedback wastegate controller gains, the wastegate command is in the form of a square wave. In other words, the input r(t) to the IMC controller is a square wave. Under this condition, the controlled system behaves like an integrator at the oscillating frequency. In addition, the frequency of relay feedback natural oscillations is close to the desired closed loop bandwidth (1-2 Hz). Thus, the plant may be modeled with a gain-integrator-delay (GID) near the frequency of the relay feedback oscillations. The transmission function of the plant may be in the form: where K is the modeled plant gain and T d is the modeled plant delay. It should be noted that the actual dynamics of the controlled system is inherently a low-pass filter and cannot be described at all frequencies using a GID model. Since the GID model is identified at a frequency close to the closed loop bandwidth, the loop can be approximated here with a GID model. The gain and phase of the transfer function of the controlled system at a frequency ω can be expressed as follows:By equating Equations 1-2 to Equations 4-5 obtained from the relay feedback test, K and T d can be calculated:Since the GID model includes an integrator, it can be shown that the IMC controller will include integral behavior just when F(s) is a second order filter and satisfies: To satisfy these conditions, F(s) may be in the form of: where α is the bandwidth parameter (the IMC tuning knob), and β is selected as β=2α+T d to satisfy the above conditions. Moreover, since the GID model includes a time delay and delays are irreversible, Q(s) is selected to be an approximate inverse of the process model without the time delay:Using the GID process model and the above-mentioned Q(s), and using a pad approximation, the time delay for the plant model yields the following final IMC controller: which includes an integrator, as desired. By equating the coefficients of performance from s to C IMC( s) on top of a PID controller, PID gains can be derived: where K i, K p and K d are gains of the integrating, proportional and differentiating member of the PID controller.In the calibration listed above, the gain of the PID controller may be calculated according to equations 13-15 from a modeled controller gain K and a modeled controller delay T d which may be further determined from the frequency and amplitude of DED oscillations from the relay feedback characterization based on equations 6-7. The parameter α is the tuning knob, which balances the response speed against the robustness of the PID controller. With a lower α, the system reaction may be more aggressive. In other words, with a decreased α, the system response may be fast and exhibit overshoot and oscillation; and with an increased α, the system response may be slower. As an example, α may be 2 or 3.Based on equations 6-7, the modeled plant gain is a function of the amplitude and frequency of the DED oscillation, but not a function of the phase of the DED oscillation. The modeled plant delay, on the other hand, is a function of the amplitude, frequency and phase of the DED oscillation. Due to the variability between parts and system wear over time, the gain and delay of the modeled plant over time must be updated. By experiment, it is found that the modeled controlled system gain is a strong function of the speed of the turbocharger. The modeled plant gain is relatively constant. For this reason, the PID controller gain look-up table is established as a function of the speed of the turbocharger. Further, the modeled link gain may be updated more frequently over time when compared to the modeled link delay. As an example, the lookup table may be created by adjusting 1 / K as a function of the speed of the turbocharger and then calculating the remaining PID gains from equations 13-15. The proportion of increase in the gains of the integrating term, proportional term and differentiating term may be the same.At step 311, back to FIG. 3, only the controlled-path gain K is updated based on the frequency and amplitude of the DED oscillation. Thereafter, the gains of the PID controller may be updated based on the frequency and amplitude of the DED oscillation. For example, gains of the integrating term, proportional term, and differentiating term can be increased with a decreased frequency of the DED vibration and increased with a decreased amplitude of the DED vibration. The proportion of the increase in the gains of the integrating term, proportional term and differentiating term may be the same. As another example, the gain of the PID controller may be calculated based on the frequency and amplitude of the DED oscillation according to Equation 6 and Equations 13-15.If at step 308 it is determined to perform a wide tuning of feedback wastegate controller gains, then the method proceeds to step 309, where the DED is sampled at a second frequency. The second frequency may be higher than the first frequency at step 310. By sampling at a higher frequency, the phase of the DED oscillation can be identified more accurately. The frequency, amplitude, and phase of the DED oscillation may be used to update both the modeled loop gain K and the modeled loop gain T d based on equations 6-7. Subsequently, each PID controller gain is updated according to equations 13-15. In this way, the method 300 may sample the DED signal less often at high frequency only when the modeled plant delay needs to be updated, so that resources of the controller for executing other processes may be saved. At step 312, the modeled plant delay T d is updated based on the frequency, amplitude, and phase of the DED oscillation, and gains of the PID controller are updated accordingly.At step 313, the wastegate is updated based on the updated look-up table.FIG. 5 shows an example method 500 for factory calibration of the look-up table. The look-up table stores gains of the wastegate feedback controller calibrated at each speed of the turbocharger within a predetermined list of speeds of the turbocharger. Similar to step 311 of FIG. 3, the controller gain at each turbocharger speed may be determined by relay feedback.At step 501, the turbocharger is adjusted to run at a predetermined turbocharger speed. Then, at step 502, a vibration of the wastegate position is induced. The DED may oscillate in response to the oscillation of the wastegate position.At step 503, the DED is sampled. As an example, the DED may be sampled at a frequency that is greater than or equal to the second frequency in step 309 of FIG. 3. The feedback wastegate controller gains may then be calculated based on the frequency, amplitude, and phase of the sampled DED oscillation at step 504. As an example, the gains may be calculated as in step 312 of FIG. 3. At step 505, the speed of the turbocharger and the corresponding controller gain may be stored as a look-up table in the non-volatile memory of an engine controller such as engine controller 12 in FIG. 1.FIG. 6 illustrates the change in engine parameters during updating of the feedback wastegate controller gain during engine operation. The x-axes represent time and grow from left to right.From T 0 to T 1 the torque demand 601 remains between the thresholds 610 and 611. Because the change in torque demand during a period between T 0 and T 1 is within a threshold Th, the engine controller (such as controller 12 in FIG. 1 ) may determine that the engine is in steady engine operation. Wastegate command 602 may be the output of a PID controller (such as PID controller 210 in FIG. 2 ). As one example, an increased wastegate command corresponds to an increased wastegate opening. In another example, an increased wastegate command corresponds to a decreased wastegate opening. The throttle opening 604 is adjusted to achieve a MAP corresponding to the requested torque.If the controller determines at T 1 that the feedback wastegate controller gain needs to be updated, then a wastegate command generated from a relay function (such as relay function 201 in FIG. 2 ) is sent to update the wastegate. For example, the wastegate command may be a shifting square wave. As a result, the DED oscillates relative to a zero position 631. To maintain a constant MAP 605, the engine controller adjusts the throttle position by actuating its actuator, causing vibration of the throttle position. As one example, the throttle position may be oscillated at the same phase and frequency as the wastegate command. Due to the oscillation of throttle position, MAP remains relatively constant while DED oscillates from T 1 to T 2.At T 2 the engine controller stops the oscillation of wastegate position and throttle position in response to the engine torque demand 601 increasing to be above the threshold 610. As another example, the engine controller may stop the wastegate position oscillation in response to a change in torque demand being above a threshold. As another example, the engine controller may stop the oscillation of wastegate position in response to a time derivative of torque demand being above a threshold. In another example, the engine controller may stop the oscillation of the wastegate position in response to a high pass filter value of an estimate or measurement of engine air flow being above a positive threshold or below a negative threshold. The wastegate command is the output of the PID controller, and the throttle is actuated to meet a required MAP.In this way, wastegate feedback controller parameters may be adjusted during engine operation to compensate for the change between parts of the engine system and system wear over time. The gain of each PID controller can be directly calculated based on the frequency, amplitude, and phase of the DED oscillation without a complicated tuning process.The technical effect of modeling the engine system as a GID model is that the gains of the PID controller due to the DED vibration may be directly assigned. The technical effect of sampling the DED signal at low frequency when the time since the last update of the look-up table is below a threshold is that regulator resources may be saved and distributed to other operations. The technical effect of updating the look-up table with the frequency and amplitude of the DED oscillation, but not the phase, when the time period since the last update of the look-up table is below a threshold, is that the updated look-up table can be quickly determined. The technical effect of sampling the DED signal at high frequency when the time since the last update of the look-up table is longer than a threshold is that the phase of the DED for calculating a term of model system delay can be accurately determined. The technical effect of updating parameters of the wastegate feedback controller during steady engine operation is that the wastegate feedback controller may be adjusted with minimal effect on vehicle drivability. The technical effect of adjusting throttle position in response to a wastegate command is to reduce variations in manifold air pressure. The technical effect of updating the modeled plant gain more frequently compared to the modeled plant delay is that the PID controller gain can be determined rapidly.As one embodiment, a method for an engine, comprising: during stable engine operation, inducing a boost pressure vibration by actuating a wastegate, and compensating manifold air pressure with a corresponding throttle vibration; and updating a gain of a feedback wastegate regulator due to the boost pressure vibration. In a first example of the method, further comprising updating the gain of the feedback wastegate controller based on the amplitude and frequency of the boost pressure oscillation, wherein the amplitude and frequency of the boost pressure oscillation is determined based on peaks and zeros of the boost pressure oscillation. A second example of the method optionally includes the first example, and further includes increasing the gain of the wastegate feedback controller when an amplitude of the boost pressure decreases. A third example of the method optionally includes one or more of the first and second examples, and further includes calculating the gain of the wastegate feedback controller by modeling an engine process as a gain-integrator delay model. A fourth example of the method optionally includes one or more of the first through third examples, and further includes where the wastegate feedback controller includes a PID controller. A fifth example of the method optionally includes one or more of the first through fourth examples, and further includes updating a proportional gain and a differentiating gain of the PID controller with a tuning knob to balance the response speed against robustness of the PID controller. A sixth example of the method optionally includes one or more of the first through fifth examples, and further includes where steady state engine operation includes a change in torque demand that is below a threshold over a predetermined period of time. A seventh example of the method optionally includes one or more of the first through sixth examples, and further includes stopping the boost pressure vibration and throttle vibration responsive to a change in torque demand being above a threshold. An eighth example of the method optionally includes one or more of the first through seventh examples, and further includes determining throttle vibration based on a wastegate position.As another embodiment, a method for an engine, comprising: determining a boost of a feedback wastegate regulator based on a speed of the turbocharger via a look-up table; during steady engine operation, actuating the wastegate to induce a vibration of wastegate position; and updating the look-up table based on a vibration of boost pressure. In a first example of the method, further comprising decreasing the boost with increased turbocharger speed. A second example of the method optionally includes the first example, and further includes determining the gain based on the amplitude and frequency of the vibration of the boost pressure. A third example of the method optionally includes one or more of the first and second examples, and further includes where the look-up table is updated after a first time period. A fourth example of the method optionally includes one or more of the first through third examples, and further includes where the gain of the wastegate feedback controller is increased with a decreased frequency of the boost pressure oscillation and is increased with a decreased amplitude of the boost pressure oscillation. A fifth example of the method optionally includes one or more of the first through fourth examples, and further includes updating the look-up table based on a phase of the oscillation of boost pressure over a second period of time, and the second period of time is longer than the first period of time.As another embodiment, an engine system, comprising: a turbocharger; a wastegate coupled to a turbine of the turbocharger; a throttle that adjusts the air inlet to an intake manifold of the engine; a sensor upstream of the throttle for sensing boost pressure; a sensor coupled to the intake manifold of the engine for sensing manifold air pressure; and an engine controller configured with computer readable instructions stored in non-transitory memory for: actuating the wastegate via a wastegate feedback controller; during steady state engine operation, actuating the wastegate to induce boost pressure vibration and actuating the throttle in response to the boost pressure vibration; and updating the gain of the wastegate feedback controller due to the boost pressure vibration. In a first example of the system, the engine controller is further configured to update the feedback wastegate regulator gain based on peaks and zeros of the sensed boost pressure. A second example of the system optionally includes the first example, and further includes where the throttle is actuated to maintain a constant manifold air pressure. A third example of the method optionally includes one or more of the first and second examples, and further includes an electric motor, and the engine controller is further configured to use the electric motor to compensate for an effect of the boost pressure vibration on the output torque of the engine. A fourth example of the method optionally includes one or more of the first through third examples, and further includes wherein the engine controller is further configured to oscillate torque generated by a generator to maintain a constant output torque of the engine.It should be appreciated that the example rules and estimation routines included herein may be used with different engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and executed 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 illustrated acts, acts, and / or functions may be performed in the order 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 rather is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be repeatedly performed depending on the particular strategy being employed. 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, in which the described actions are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.It should be understood that the configurations and routines disclosed herein are exemplary in nature and these specific embodiments are not to be interpreted in a limiting sense as numerous variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, 4-cylinder horizontally opposed, 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 characteristics disclosed herein.The following claims particularly set forth certain combinations and sub-combinations which are considered novel and non-obvious. These claims may refer to "a" element or "a first" element or the equivalent thereof. Such claims are to be understood to include inclusion of one or more such elements and neither require nor exclude two or more such elements. Further combinations and sub-combinations of the disclosed features, functions, elements and / or characteristics may be claimed by altering the present claims or by filing novel claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope than the original claims, are also considered to be included within the subject matter of the present disclosure.

Claims

A method for an engine, comprising: during steady engine operation, inducing a boost pressure vibration by actuating a wastegate and compensating a manifold air pressure with a corresponding throttle vibration; and updating a gain of a wastegate feedback controller due to the boost pressure vibration.The method of claim 1, further comprising updating the boost of the wastegate feedback controller based on the amplitude and frequency of the boost pressure oscillation, wherein the frequency of the boost pressure oscillation is determined based on peaks and zeros of the boost pressure oscillation; and adjusting a signal sent to a wastegate actuator based on the updated boost.The method of claim 1, further comprising increasing the gain of the wastegate feedback controller as the amplitude of the boost pressure swing decreases.The method of claim 2, wherein the wastegate is regulated with the updated gain.The method of claim 1, wherein the wastegate feedback controller includes a PID controller.The method of claim 5, further comprising updating a proportional gain, an integrating gain, and a differentiating gain of the PID controller with a tuning knob to balance the response speed against robustness of the PID controller.The method of claim 1, wherein the steady state engine operation includes a change in torque demand over a predetermined period of time being below a threshold.The method of claim 1, further comprising stopping the boost pressure vibration and throttle vibration in response to a change in torque demand being above a threshold.The method of claim 1, further comprising determining the throttle vibration based on a wastegate position.An engine system, comprising: a turbocharger; a wastegate coupled to a turbine of the turbocharger; a throttle regulating air intake to an engine intake manifold; a sensor upstream of the throttle for sensing boost pressure; and an engine controller configured with computer readable instructions stored in non-transitory memory to: actuate the wastegate via a wastegate feedback controller; during steady state engine operation, actuate the wastegate to induce boost pressure vibration and actuate the throttle responsive to the boost pressure vibration; and update a gain of the wastegate feedback controller due to the boost pressure vibration.The system of claim 10, wherein the engine controller is further configured to update the feedback wastegate controller gain based on peaks and zeros of the sensed boost pressure.The system of claim 10, wherein the throttle is actuated to maintain a constant manifold air pressure.The system of claim 10, further including an electric motor, and the engine controller is further configured to use the electric motor to compensate for an effect of the boost pressure vibration on the output torque of the engine.The system of claim 10, wherein the engine controller is further configured to oscillate torque generated by a generator to maintain a constant output torque of the engine.The system of claim 10, wherein the gain of the wastegate feedback controller is increased with a decreased frequency of the boost pressure oscillation and is increased with a decreased amplitude of the boost pressure oscillation.

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