Transient compressor surge response in a turbocharged engine

Abstract

A method for responding to an existing or incipient surge condition of a turbocharger, the turbocharger being coupled to an engine of a motor vehicle and comprising a turbine and a compressor, the method comprising: Receiving a signal in response to an operating condition of the turbocharger; and Adjusting an operating parameter of the motor vehicle when a strength of the signal integrated over a preselected range of non-zero frequencies exceeds a preselected threshold, characterized in that the method further comprises recirculating exhaust gas from downstream of the turbine to upstream of the compressor and adjusting one operating parameter involves opening a pressure relief valve of the turbocharger.

Description

[0001] The invention relates to the field of internal combustion engines and, in particular, to improving the reliability of turbocharged internal combustion engines of motor vehicles.

[0002] A turbocharger can be used to increase the power output of an internal combustion engine. The turbocharger does this by pressurizing the intake air, thereby increasing the mass of air delivered to each of the engine's combustion chambers during the intake stroke. The increased air mass supports the combustion of a correspondingly larger amount of fuel delivered to each combustion chamber, providing increased power relative to a naturally aspirated engine of similar stroke. In a motor vehicle, a turbocharged engine can provide improved fuel economy by maintaining a higher power-to-weight ratio than a naturally aspirated engine of similar power and by recovering internal energy from the exhaust gas to drive the turbocharger compressor.A turbocharger can be advantageously matched to an engine by creating a "working network," which defines suitable pressure and flow conditions for the turbocharger compressor between surge and flow restriction lines. Proper sizing of the working network is necessary to meet the engine's characteristics: oversizing the working network can lead to poor response and emissions characteristics, for example.

[0003] A method according to the preamble of claim 1 is disclosed in EP 1 323 927 A1.

[0004] US Patent No. 7,322,194 B2 teaches determining pressure ratio and mass flow under surge-prone conditions and comparing them with the surge limit. To eliminate surge, the EGR path is used. Opening the EGR valve at a positive purge pressure gradient (i.e., negative exhaust gas recirculation flow) in combination with reducing the turbine inlet pressure allows air from the compressor to bypass the engine, thereby increasing the compressor mass flow.

[0005] WO 2005 / 047 669 A1 also uses the EGR path to eliminate the pumping by closing the EGR valve to reduce the EGR mass flow into the area behind the compressor, so that a higher mass flow can flow from the compressor into the engine.

[0006] JP 2007 - 291 960 A shows the opening of a pressure relief valve as a measure against compressor surge.

[0007] A turbocharger compressor coupled to an internal combustion engine may experience unwanted surge if a pressure ratio within the turbocharger compressor (namely, P, the ratio of the outlet pressure to the inlet pressure) is too large relative to the air flow through the turbocharger compressor. Turbocharger compressor surge (TVS) is a dynamic instability mode that can produce large-amplitude airflow and pressure fluctuations; this condition can induce undesirable mechanical stresses in the turbocharger and inlet, including excessive torsional loading on the turbocharger shaft. Persistent or excessive TVS can reduce the longevity of the turbocharger and / or the engine to which it is connected. Furthermore, TVS in a motor vehicle can negatively impact the satisfaction of the motor vehicle driver by causing undesirable vibration, noise, and power loss.Turbocharged engine systems can therefore be configured to detect certain types of TVS and, upon detection, take measures to suppress TVS.

[0008] For example, a turbocharged engine system may be configured to sense a pressure ratio P and a mass flow rate M of air into the engine intake and indicate TVS when the value of P falls outside a determined interval for the value of M. The converse is also possible—indicating TVS when the value of M falls outside a determined interval for the value of P. However, such approaches may not be the most appropriate for all types of TVS.

[0009] The pressure ratio and mass flow rate intervals mentioned above can be determined based on steady-state engine conditions where engine speed and load are predictably related. Under such conditions, calculations can be used to predict the appropriate P interval for a value of M below which TVS will not occur. However, TVS can also occur during transient engine conditions where speed and load are not related to pressure ratio and mass flow as they are under steady-state conditions. Such transient conditions include, for example, throttle roll-off, rich combustion (intake throttle closed relative to steady-state), and exhaust gas recirculation (intake throttle open relative to steady-state).Under these and other conditions, TVS detection methods based on stationary P or M intervals cannot properly detect TVS.

[0010] To address this problem, some engine systems use P or M intervals derived from steady-state calculations, but incorporate wide safety margins (e.g., 20%) to protect against transient TVS. This approach can significantly limit turbocharger performance and potentially undermine the benefits of the turbocharged engine system.

[0011] The present inventors have recognized the deficiencies of the existing methods outlined above and have provided various approaches directed at a transient TVS response. These approaches include a method for responding to an existing or incipient surge condition of a turbocharger according to claim 1 and systems according to claims 10 and 11. Advantageous further developments are set forth in the subclaims.

[0012] Accordingly, in one embodiment, a method is provided for responding to an existing or incipient surge condition of a turbocharger coupled to an engine of a motor vehicle. The method includes receiving a signal responsive to an operating condition of the turbocharger and adjusting one or more operating parameters of the motor vehicle when a strength of the signal, integrated over a preselected range of non-zero frequencies, exceeds a preselected threshold. Other embodiments provide similar systems for responding to an existing or incipient surge condition of a turbocharger. The systems and methods disclosed herein provide a reliable response to transient TVS while avoiding undue limitations on turbocharger performance.

[0013] It should be understood that the foregoing summary is provided to introduce, in simplified form, a selection of concepts that are further described in the detailed description that follows. It is not intended to identify essential or key features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve the disadvantages noted above or in any part of this disclosure. Brief description of the drawings Fig. 1 shows in schematic detail an exemplary turbocharged engine system according to the present disclosure. Fig. 2 shows a graph of pressure ratio versus corrected air mass flow for various operating conditions of a hypothetical turbocharged engine according to the present disclosure. Fig. 3 shows an exemplary transient TVS observer in schematic detail according to the present disclosure. Fig. 4 shows graphs of engine inlet pressure and TVS flag logic versus time for a hypothetical turbocharged engine system according to the present disclosure. Fig. 5 illustrates an exemplary method for indicating transient TVS in a turbocharged engine system according to the present disclosure. Detailed description

[0014] Fig. 1 shows in schematic detail an exemplary engine system 2 comprising an engine 3, which may be arranged in a motor vehicle. The engine system includes a turbocharger compressor 4 configured to draw air from an air cleaner 6 and supply pressurized air to an intake manifold 8. The turbocharger compressor is mechanically coupled to and driven by a turbocharger turbine 10 by means of a shaft 12. The turbocharger turbine recovers mechanical energy from hot engine exhaust passed therethrough. Accordingly, the turbocharger turbine 10 is configured to admit engine exhaust from an exhaust manifold 14 and direct the engine exhaust (at a lower temperature and pressure) to the exhaust port 16.

[0015] The engine system 2 further includes an exhaust gas recirculation (EGR) valve 18, which is an electronically controllable valve configured to controllably admit engine exhaust gas from the exhaust port to the turbocharger compressor 4. Thus, the illustrated engine system embodies a so-called 'low-pressure EGR' strategy, in which some exhaust gas may be recirculated from the exhaust (downstream of the turbocharger turbine) to the inlet upstream of the turbocharger compressor. Other engine systems fully consistent with this disclosure may embody a so-called 'high-pressure EGR' strategy, in which engine exhaust gas may be controllably admitted from an exhaust manifold (upstream of the turbocharger turbine) to an intake manifold downstream of a turbocharger compressor, also by means of a controllable EGR valve.

[0016] In the configuration shown, at least a portion of the pressurized air passes through the air flow meter 20 on its way to the engine from the turbocharger compressor. The air flow meter may be configured to provide an output (e.g., an electrical voltage or electrical current) in response to the mass flow rate M of air from the turbocharger compressor to the engine intake. In some embodiments, the output of the air flow meter may correspond to a mass flow parameter, e.g., a normalized mass flow rate.

[0017] Fig. 1 also shows a pressure sensor 22 coupled to the intake manifold 8 and configured to provide an output (e.g., an electrical voltage or electrical current) in response to the pressure ratio P. In the configuration shown, the output of the air flow sensor 20 and the output of the pressure sensor 22 are both fed to an electronic control unit 24. The electronic control unit 24 may be any electronic control unit of the engine system 2 or the motor vehicle in which the engine system is located. In some embodiments, the electronic control unit may be part of a larger electronic system, e.g., a diagnostic system of the motor vehicle. The electronic control unit may be configured to indicate when the turbocharger compressor 4 is undergoing a TVS based on the various sensor outputs provided thereto.The electronic control unit may be further configured to adjust one or more operating parameters of the motor vehicle to suppress TVS. In some embodiments, such operating parameters may include engine operating parameters: for example, exhaust gas recirculation, fuel injection quantity, and throttle position. In other embodiments, the operating parameters may include turbocharger operating parameters. Therefore, one or more control signals may be provided by the electronic control unit to, for example, activate or deactivate the turbocharger compressor, to modify the boost pressure and / or speed of the turbocharger, to open or close a wastegate or relief valve of the turbocharger, or to open or close an EGR valve.Thus, the electronic control unit 24 may be configured to indicate when the turbocharger is undergoing TVS and to provide a surge suppressing control signal when TVS is indicated.

[0018] Furthermore, the electronic control unit may include one or more subsystems (e.g., observers) configured to respond to specific variants of TVS. Fig. 1, the electronic control unit 24 includes, for example, a stationary TVS observer 26. The stationary TVS observer may be coupled to an output of the air flow meter 20 and an output of the pressure sensor 22. The stationary TVS observer may be further configured to indicate whether the turbocharger compressor is prone to stationary TVS at the operating point (M, P), as described below with the aid of Fig. 2. For this purpose, the stationary TVS observer may include a set of electronic components configured to indicate the surge condition based on a mass flow rate of air into the engine when an engine inlet pressure exceeds a critical pressure or when, based on an engine inlet pressure, a mass flow rate of air into the engine is below a critical mass flow rate, wherein the critical pressure and / or the critical mass flow rate are based on stationary surge conditions of the turbocharger compressor.

[0019] Fig. Figure 2 shows a graph of pressure ratio P versus corrected mass flow rate M for various operating conditions of a hypothetical turbocharged engine. The graph includes a steady-state TVS limit 28, which is a line below which no TVS can occur under steady-state conditions. Above the line, i.e., at higher P or lower M, the turbocharger compressor may be prone to TVS. The steady-state TVS limit can be derived theoretically based on various characteristics of the turbocharger and engine, or can be derived empirically, e.g., by operating the turbocharger and engine under steady-state conditions and establishing thresholds at which steady-state TVS is likely to occur.

[0020] For any turbocharged engine system, the steady-state TVS observer 26 may be configured to determine whether an observed operating point (M, P) of the turbocharger compressor 4 is above the steady-state limit 28. In doing so, the steady-state TVS observer may employ suitable digital and / or analog electronics—digital-to-analog converters, logic gates, microprocessors, lookup tables, operational amplifiers, analog math processors, etc. In effect, the steady-state TVS observer may establish an interval of allowable P for any observed value of M and may indicate TVS when the observed P lies outside the interval. The converse is also contemplated; i.e., the steady-state TVS observer may establish an interval of allowable M for any observed P and indicate TVS when the observed M lies outside this interval.

[0021] Fig. 2 also shows a location of transient operating points 30, which may correspond to a number of transient operating conditions of the turbocharged engine. In the example shown, the location of transient operating points corresponds to a gas path condition. Even though the overall location of transient operating points lies below the steady-state boundary 28, the turbocharger compressor 4 exhibits TVS at some of the operating points. Specifically, transient TVS is displayed for points in the subset 32 of the location of transient operating points.

[0022] Transient TVS can be triggered by a sudden and significant reduction in the engine fuel delivery rate and / or exhaust airflow rate. Under typical operating conditions, intake pressure may decrease from an initial high value much more slowly than the rate of reduction in turbocharger drive force. Transient TVS can occur when the accumulated pressure at the inlet exceeds the compressor's ability to maintain positive air movement.

[0023] To establish suitable P or M intervals for detecting and suppressing such a transient TVS in the manner described above, it would be necessary to use a boundary line below the steady-state limit 28. For example, a transient-safe limit 34 could be used to establish suitable P or M intervals below which even a transient TVS is unlikely to occur. Fig. 2, a transient-safe limit 34 is derived from the steady-state limit 28 by reducing each pressure value by 20 percent.

[0024] However, it is clear from the graph that the transient-safe boundary approach described above can significantly limit the operating range of the turbocharger compressor. In detail, Fig. 2, a lost region 36 located between the steady-state limit 28 and the transient-safe limit 34. By using the transient-safe limit to set the allowable P or M intervals for the turbocharger compressor, the turbocharger compressor may not be allowed to operate in the lost region, even under steady-state conditions. Thus, the performance advantage of the turbocharged engine relative to its full potential is significantly reduced.

[0025] Back now to Fig. 1, the electronic control unit 24 also includes a transient TVS observer 38. In the configuration shown, the steady-state TVS observer 26 and the transient TVS observer 38 are independently configured to indicate TVS. However, in other embodiments, two or more TVS observers may be configured for different interoperability modes. Through suitable logic circuitry 40, an indicating signal from an observer may trigger an adjustment of one or more operating parameters of the motor vehicle. For example, the indicating signal may invoke a TVS flag 42 in the electronic control unit or in a diagnostic system of the motor vehicle. The indicating signal may further provide a surge suppressing control signal to the turbocharger.

[0026] The surge suppressing control signal may inhibit TVS in various ways depending on the particular configuration of the turbocharged engine system. In some embodiments, the surge suppressing control signal may trigger a reduction in boost pressure and / or turbocharger speed. In the embodiment shown, engine system 2 includes a wastegate 43 configured to controllably bypass a portion of the engine exhaust gas past turbocharger turbine 10, thereby delivering less torque to the turbocharger compressor. The engine system also includes a relief valve 44 configured to vent a portion of the compressed air from the turbocharger compressor away from the intake manifold—e.g., to atmosphere or back to the turbocharger compressor inlet.Thus, the surge suppressing control signal by means of the control device 24 can have the effect of opening the wastegate and / or the relief valve to reduce the boost pressure and / or the speed of the turbocharger.

[0027] In other embodiments, the surge suppressing control signal, via controller 24, may have the effect of adjusting exhaust gas recirculation by at least partially opening or closing low-pressure EGR valve 18. Alternatively or additionally, a high-pressure EGR valve may be adjusted based on the surge suppressing control signal.

[0028] Specifically, some operating conditions of the engine system may be such that TVS is suppressed by further opening the EGR valve, and other (different) operating conditions may be such that TVS is suppressed by further closing the EGR valve. Therefore, the engine system 2 includes an EGR flow sensor 46 coupled to the exhaust passage 16. The EGR flow sensor may be any component responsive to the direction of EGR flow into or out of the exhaust passage. In the illustrated embodiment, an output of the EGR flow sensor is routed to the EGR control module 48 of the electronic control unit 24. The EGR control module may be configured to at least partially close the EGR valve 18 in response to the surge suppressing control signal when the EGR flow sensor 46 indicates a positive exhaust gas recirculation flow.Further, the EGR control module may be configured to at least partially open the EGR valve 18 in response to the surge suppressing control signal when the EGR flow sensor 46 indicates a negative exhaust gas recirculation flow.

[0029] Fig. Figure 3 shows an exemplary transient TVS observer 38 in schematic detail. The transient TVS observer includes first and second frequency-selective modules, a strength-responsive module, and a discriminating module. In the illustrated embodiment, the first frequency-selective module includes a bandpass filter 49. The bandpass filter is configured to receive an output from the pressure sensor 22. The bandpass filter may be an analog filter with a fixed or adjustable lower passband corner frequency and a fixed or adjustable upper passband corner frequency. In one embodiment, the lower passband corner frequency of the bandpass filter may be 30 radians per second, and the upper passband corner frequency may be 80 radians per second. In particular, the bandpass filter may be, for example, a second-order Butterworth filter, a Chebyshev filter, or an elliptic filter. While Fig. 3 shows the filter 49 configured to receive an output from the pressure sensor 22, the bandpass filter or other first frequency-selective module may instead be configured to receive an output from, for example, the air flow sensor 20, or may otherwise be configured to respond to the engine intake pressure and / or the mass flow rate of air into the engine.

[0030] Continue in Fig. 3, the first frequency-selective module is configured to provide an output to a strength-responsive module. The strength-responsive module may be any module responsive to the strength of the sensor output within a band of frequencies selected by the first frequency-selective module. In the embodiment shown, the strength-responsive module includes an absolute value converter 50. The absolute value converter may be an analog circuit configured to accept a positive or negative input (e.g., a voltage input) from the first frequency-selective module and produce a corresponding positive output.

[0031] Continue in Fig. 3, the strength-responsive module is configured to provide an output to a second frequency-selective module. In the illustrated embodiment, the second frequency-selective module includes a low-pass filter 51.

[0032] The low-pass filter may be an analog filter with a fixed or adjustable lower passband corner frequency. In one embodiment, the passband corner frequency of the low-pass filter may be 30 radians per second. In a particular embodiment, the bandpass filter may be a second-order Butterworth filter.

[0033] Continue in Fig. 3, the second frequency-selective module is configured to provide an output to the discriminating module 52. In the embodiment shown, the discriminating module includes a comparator 53, an indication 54, an adder 55, and an increment 56. The comparator may be configured to compare the output of the second frequency-selective module with the indication 54, which may be a fixed or adjustable voltage indication. In one embodiment, the comparator may be configured to change an output voltage state (e.g., negative or positive) when the output of the second frequency-selective module exceeds the indication. The comparator is further configured to provide an output to the adder 55. The adder is configured to add the output of the comparator to an increment 56, which may be, for example, a fixed or adjustable voltage increment.In one embodiment, the increment may be approximately the same order of magnitude as the output voltage swing of comparator 53. Thus, the discriminating module is configured to indicate the surge condition when an output of the second frequency-selective module exceeds a threshold. The discriminating module may further be configured to provide a surge suppressing control signal to the turbocharger when the surge condition is indicated.

[0034] While the above embodiment illustrates the use of analog electronic circuitry in the various modules of the transient TVS observer 38, it should be understood that equivalent functionality may be implemented using digital electronics and digital algorithms. For example, one or more sensor signals may undergo analog-to-digital conversion and be processed by an onboard computer within the electronic control unit. The onboard computer may be configured to implement suitable frequency-selective and magnitude-responsive algorithms to provide the indicated functionality.

[0035] Fig. Figure 4 shows graphs of intake pressure and TVS flag logic versus time for a hypothetical turbocharged engine system. The first graph 58 of Fig. Figure 4 is a graph of boost pressure versus time over a period including a transient TCS event 60. The second graph 62 is a graph of the logic state of the TVS flag 42, by which the electronic control module 24 indicates TVS. In the example shown, the transient TVS observer is triggered approximately 100 milliseconds into the TVS event 60 and indicates the event by changing the TVS flag 42.

[0036] Fig. 5 illustrates an exemplary method 64 for responding to transient TVS in a turbocharged engine system. While the method 64 is explained herein with reference to the exemplary configurations presented above, it should be understood that the method may also be implemented using various other configurations.

[0037] Method 64 begins at 65 where an output signal from a sensor in an electronic control unit of a motor vehicle is received. In some embodiments, the output signal may be responsive to a pressure, for example, downstream of the turbocharger compressor, downstream of an intercooler (not shown in the drawings), and / or upstream of the intake manifold. In another embodiment, the output signal may be responsive to a mass flow rate of air into the engine intake or to a normalized mass flow parameter. The method advances to 66 where bandpass filtering is applied to the signal. Bandpass filtering may be performed using analog circuitry, as described above, or may be performed digitally, for example, using analog-to-digital conversion followed by Fourier filtering.

[0038] The method 64 continues at 68, where the absolute value of the bandpass filtered signal is calculated. The method continues at 70, where low-pass filtering is applied to the absolute value determined at 68. Steps 68 and 70 may be implemented using suitable analog and / or digital electronics, as described hereinabove. Taken together, steps 66-70 of the method may result in an estimate of the strength of the received signal integrated over a preselected range of non-zero frequencies. Further, the preselected range of non-zero frequencies may be determined by the passband applied in step 66. In other embodiments, other estimates of the strength of the signal integrated over the preselected range of non-zero frequencies may be calculated.For example, another estimate of the strength can be calculated according to a modified method that uses the square of the bandpass filtered signal instead of the absolute value.

[0039] Method 64 then proceeds to 72, where it is determined whether the low-pass filtered result calculated at 70 exceeds a threshold. If the low-pass filtered result exceeds the threshold, then at 74 a TVS flag is set in a diagnostic system of the motor vehicle. The method then proceeds to 76, where a relief valve in the turbocharger is opened, venting some of the excess pressure that would normally be delivered to the engine intake. This is the only way the surge condition can be suppressed. In other embodiments, one or more other operating parameters of the motor vehicle may be adjusted if a strength of the signal in the preselected range of non-zero frequencies exceeds a preselected threshold.Adjusting such other operating parameters may include, for example, opening a wastegate in the turbocharger, reducing a boost pressure and / or a speed of the turbocharger, temporarily opening or closing an EGR valve, or taking another action to suppress the surge condition. In one embodiment, adjusting one or more operating parameters may include at least partially closing an exhaust gas recirculation valve when positive exhaust gas recirculation flow is indicated and at least partially opening an exhaust gas recirculation valve when negative exhaust gas recirculation flow is indicated. Following this action, or if it is determined that the low-pass filtered result does not exceed the threshold, the method returns.

[0040] It should be understood that method 64 or similar methods may be used in conjunction with other methods applicable to steady-state TVS detection. Thus, various contemplated methods may further include adjusting the one or more operating parameters when an engine inlet pressure based on a mass flow rate of air into the engine exceeds a critical pressure or when a mass flow rate of air into the engine based on an engine inlet pressure is below a critical mass flow rate, wherein the critical pressure and / or critical mass flow rate are based on steady-state surge conditions of the turbocharger compressor.

[0041] It should be understood that the exemplary control and estimation routines disclosed herein may be used with various system configurations. These routines may represent one or more different processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Therefore, the disclosed process steps may represent code to be programmed into a machine-readable storage medium in an electronic control unit. It should be understood that in some embodiments, some of the process acts described and / or illustrated herein may be omitted without departing from the scope of this disclosure. Similarly, the illustrated order of process steps is not always required to achieve the desired results, but is provided for ease of illustration and description.One or more of the operations, functions or operations shown may be performed repeatedly depending on the strategy used.

[0042] Finally, it should be understood that the systems and methods described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered limiting, as numerous modifications are contemplated. Accordingly, the present disclosure encompasses all novel and non-obvious combinations and subcombinations of the various systems and methods disclosed herein, as well as all equivalents thereof.

Claims

[1] A method for responding to an existing or incipient surge condition of a turbocharger, the turbocharger being coupled to an engine of a motor vehicle and comprising a turbine and a compressor, the method comprising: Receiving a signal in response to an operating condition of the turbocharger; and Adjusting an operating parameter of the motor vehicle when a strength of the signal integrated over a preselected range of non-zero frequencies exceeds a preselected threshold, characterized by , that the method further comprises recirculating exhaust gas from downstream of the turbine to upstream of the compressor and adjusting one operating parameter involves opening a pressure relief valve of the turbocharger. [2] Method according to claim 1, characterized bythat the received signal is responsive to an intake pressure of the engine and / or a mass flow rate of air into the engine, the method further comprising: Performing bandpass filtering on the signal; Calculating an absolute value of the signal subjected to bandpass filtering; Performing a low-pass filter on the absolute value; and Adjusting the operating parameter when the absolute value subjected to low-pass filtering exceeds the preselected threshold. [3] Method according to claim 1, characterized by that the procedure further includes: Performing bandpass filtering on the signal; Calculating an absolute value of the signal subjected to bandpass filtering; Adjust the operating parameter based on the absolute value. [4] Method according to claim 1 or 3, characterized bythat adjusting the operating parameter includes setting a flag in a diagnostic system of the motor vehicle. [5] Method according to claim 1, characterized by that adjusting the operating parameter includes procedures to suppress the surge condition. [6] Method according to claim 1 or 3, characterized by that adjusting the operating parameter includes reducing a boost pressure of the turbocharger and / or a speed of the turbocharger. [7] Method according to claim 1 or 3, characterized by that adjusting the one or more operating parameters further comprises opening a wastegate of the turbocharger. [8] Method according to claim 1 or 3, characterized bythat adjusting the operating parameter comprises at least partially closing an exhaust gas recirculation valve when a positive exhaust gas recirculation flow direction is indicated and at least partially opening the exhaust gas recirculation valve when a negative exhaust gas recirculation flow direction is indicated. [9] The method of claim 1 or 3, further comprising adjusting the operating parameter when an inlet pressure of the engine based on a mass flow rate of air into the engine exceeds a critical pressure or when, based on the inlet pressure of the engine, the mass flow rate of air into the engine is below a critical mass flow rate, wherein the critical pressure and / or the critical mass flow rate are based on steady-state surge conditions of the turbocharger. [10] System comprising: a turbocharger coupled to a motor vehicle engine and comprising a turbine and a compressor, an electronic control unit with a machine-readable storage medium containing a code to carry out the following process steps: Responding to an existing or incipient turbocharger surge condition, comprising: Receiving a signal in response to an operating condition of the turbocharger; and Adjusting an operating parameter of the motor vehicle when a strength of the signal integrated over a preselected range of non-zero frequencies exceeds a preselected threshold, characterized by , that responding to an existing or incipient surge condition of a turbocharger further comprises recirculating exhaust gas from downstream of the turbine to upstream of the compressor, and adjusting one operating parameter involves opening a pressure relief valve of the turbocharger. [11] System which includes: an engine; a turbocharger coupled to the engine; a sensor configured to provide an output in response to an intake pressure of the engine and / or a mass flow rate of air into the engine; an observer having a bandpass filter configured to receive the output, an absolute value converter configured to receive an output of the bandpass filter, a lowpass filter configured to receive an output of the absolute value converter, and a first set of electronic components configured to indicate the surge condition and adjust an operating condition when an output of the lowpass filter exceeds a threshold; and a diagnostic system, characterized by , that the first set of electronic components is further configured to set a flag in the diagnostic system when the surge condition is indicated. [12] The system of claim 11, further comprising a wastegate, wherein the first set of electronic components is further configured to at least partially open the wastegate when the surge condition is indicated. [13] The system of claim 11, further comprising an exhaust gas recirculation valve configured to controllably direct at least some engine exhaust gas to an intake of the engine, wherein the first set of electronic components is further configured to at least partially close the exhaust gas recirculation valve when the output of the low-pass filter exceeds a threshold during a positive exhaust gas recirculation flow, and to at least partially open the exhaust gas recirculation valve when the output of the low-pass filter exceeds a threshold during a negative exhaust gas recirculation flow. [14] The system of claim 11, further comprising a pressure relief valve, wherein the first set of electronic components is further configured to at least partially open the pressure relief valve when the surge condition is indicated. [15] The system of claim 11, wherein the observer further comprises a second set of electronic components configured to indicate the surge condition when an inlet pressure of the engine based on a mass flow rate of air into the engine exceeds a critical pressure or when a mass flow rate of air into the engine based on an inlet pressure of the engine is below a critical mass flow rate, wherein the critical pressure and / or the critical mass flow rate are based on steady-state surge conditions of the turbocharger.

Images