WO2019177597A1

WO2019177597A1 - Detection and mitigation of unintended engine over speed conditions

Info

Publication number: WO2019177597A1
Application number: PCT/US2018/022290
Authority: WO
Inventors: Eric R. THOMPSON
Original assignee: Cummins Inc
Current assignee: Cummins Inc
Priority date: 2018-03-14
Filing date: 2018-03-14
Publication date: 2019-09-19
Anticipated expiration: 2020-09-14

Abstract

One exemplary embodiment is a system including an internal combustion engine operatively coupled with a variable geometry turbocharger, the variable geometry turbocharger including a compressor, a turbine coupled with the compressor and an actuator structured to vary geometry of an exhaust flow passage in flow communication with the turbine between a minimum value and a maximum value, and an electronic control system operatively coupled with the internal combustion engine and the variable geometry turbocharger. The electronic control system may be structured to evaluate operation of the engine to determine whether a runaway engine condition exists, and in response to a determination that the runaway engine condition exists, control the actuator to vary geometry of the exhaust flow passage effective to mitigate the runaway engine condition.

Description

DETECTION AND MITIGATION OF UNINTENDED ENGINE OVER SPEED

CONDITIONS

BACKGROUND

[0001] The present application relates generally detection and mitigation of unintended engine over speed conditions sometimes referred to as runaway engine conditions. Runaway engine conditions can occur in compression ignition engines when combustible matter is unintentionally present in the intake charge, such as when fuel, lubrication oil, or combustible vapor enter the engine air intake system. These conditions can occur in a variety of situation, including but not limited to, operating the engine in an environment where combustible vapors are present, turbocharger malfunction leading to oil passing into the intake air system, and malfunction of the crankcase breather system, including both open and closed type breathers. A number of proposals have been made to mitigate runaway engine conditions; however, existing proposals suffer from a number of drawbacks including the need for operation involvement or judgment and the need to provide ancillary hardware that would not otherwise be present in a given engine system. There remains a significant need for the unique apparatuses, methods and systems disclosed herein.

DISCLOSURE OF ILLUSTRATIVE EMBODIMENTS

[0002] For the purposes of clearly, concisely and exactly describing illustrative embodiments of the present disclosure, the manner and process of making and using the same, and to enable the practice, making and use of the same, reference will now be made to certain exemplary embodiments, including those illustrated in the figures, and specific language will be used to describe the same. It shall nevertheless be understood that no limitation of the scope of the invention is thereby created, and that the invention includes and protects such alterations, modifications, and further applications of the exemplary embodiments as would occur to one skilled in the art.

SUMMARY OF THE DISCLOSURE

[0003] Systems and methods providing mitigation for an internal combustion engine runaway condition are disclosed. Certain exemplary embodiments include unique engine control systems structured to identify and mitigate an unintended engine over speed condition or runaway engine condition. Certain exemplary embodiments include unique engine control methods for determining and mitigating an internal combustion engine runaway condition.

Certain exemplary embodiments include unique engine control apparatuses including a variable geometry turbocharger and one or more electronic control system components structured to determine and mitigate an internal combustion engine runaway condition. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Fig. 1 is a schematic diagram illustrating certain aspects of an exemplary engine.

[0005] Fig. 2 is a flow diagram illustrating certain aspects of an exemplary engine control process.

[0006] Fig. 3 is a flow diagram illustrating certain aspects of an exemplary engine control process.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0007] With reference to Fig. 1 there is illustrated a schematic view of an example engine system 100 including an engine 105, such as an internal combustion engine or a combination of an internal combustion and other prime mover components. Engine 105 is structured to provide an exhaust flow to a variable geometry turbocharger 120. Variable geometry turbocharger 120 is structured to vary geometry of an exhaust flow passage between a minimum value and a maximum value. Engine 105 may be provided in a variety of vehicles including, for example, on-highway and off-highway vehicles. It shall be appreciated that the illustrated embodiment of engine system 100 is but one example of an engine system contemplated by the present disclosure and that a variety of other engine systems including additional or alternate

components and features as well as other engine systems not including one or more of the features of the illustrated embodiment are contemplated.

[0008] In the illustrated embodiment, variable geometry turbocharger 120 is operatively coupled with an intake system 130 and an exhaust system 136 of engine 105. The engine 105 is in fluid communication with the intake system 130 through which charge air enters an intake manifold 110 of the engine 105 and is also in fluid communication with the exhaust system 136, through which exhaust gas resulting from combustion exits by way of an exhaust manifold 112 of the engine 105, it being understood that not all details of these systems are shown. The engine 105 includes a number of cylinders forming combustion chambers into which fuel is injected by fuel injectors to combust with the charge air that has entered through intake manifold 110. The energy released by combustion, powers the engine 105 via pistons connected to a crankshaft. Intake valves control the admission of charge air into the cylinders, and exhaust valves control the outflow of exhaust gas through exhaust manifold 112 and ultimately to the atmosphere.

[0009] The variable geometry turbocharger 120 is operable to compress ambient air and to provide compressed air to intake manifold 110 of the engine 105. The illustrated turbocharger 120 includes a compressor l20c and a variable geometry turbine l20t which are operatively coupled with one another with a shaft l20b supported by a bearing housing. The variable geometry turbine l20t includes a variable geometry flow passage l20v, such as a flow orifice, whose cross sectional area can be varied from a minimum value to a maximum value by an actuator l20a. In some forms the minimum value provides a zero area geometry which blocks flow through the turbine except for leakage flow attributable to components tolerances. In some forms the minimum value provides a non-zero area geometry which restricts flow through the turbine to a sufficiently as to be able to provide an emergency shutdown of engine 105. In the illustrated intake system 130, compressor l20c is in flow communication with a charge air cooler 109 which is in flow communication with intake manifold 110. Compressed intake air from the compressor l20c is pumped through the intake system 130, to the intake manifold 110, and into the cylinders of the engine 105. It is contemplated that the engine system 100 may include other turbocharger or supercharger systems, devices and configurations. The intake system 130 and/or the exhaust system 136 may further include various components not shown, such as coolers, valves, bypasses, an exhaust gas recirculation (EGR) system, intake throttle valves, exhaust throttle valves, EGR valves, and/or compressor bypass valves, for example.

[0010] The engine system 100 further includes an electronic control unit (ECET) 140 structured to perform certain operations and to receive and process signals from any component and/or sensor of the engine system 100. Some of the input signals received by ECU 140 include an engine speed signal received from an engine speed sensor 116, a cruise control target speed received from a cruise control logic 142, and accelerator/throttle position signal received from accelerator position sensor 144. It shall be appreciated that the ECU 140 may be provided in a variety of forms and configurations including one or more computing devices forming a whole or a part of a processing subsystem having non-transitory memory storing computer executable instructions, processing, and communication hardware. The ECU 140 may be a single device or a distributed device, and the functions of the ECU 140 may be performed by hardware or software. The ECU 140 is in communication with any actuators, sensors, datalinks, computing devices, wireless connections, or other devices to be able to perform any described operations.

[0011] The processing logic may be implemented as computer executable instructions, which may be implemented in operating logic as operations by software, hardware, artificial intelligence, fuzzy logic, or any combination thereof, or at least partially performed by a user or operation. The computer executable instructions are stored in a non-transitory computer readable memory medium which may be a single device, distributed across devices, and/or grouped in whole or in part with other media or devices.

[0012] The ECU 140 includes stored data values, constants, and functions, as well as operating instructions stored on computer readable medium. Any of the operations of exemplary procedures described herein may be performed at least partially by the controller. Other groupings that execute similar overall operations are understood within the scope of the present application. Certain embodiments of the ECU 140 and its operations are discussed herein in connection with Figs. 2-3. Operations illustrated are understood to be exemplary only, and operations may be combined or divided, and added or removed, as well as re-ordered in whole or in part.

[0013] The variable geometry turbocharger 120 of engine system 100 includes a turbine housing with an actuator l20a structured to vary geometry of variable geometry flow passage l20v as described above. The ECU 140 is structured to evaluate operation of the internal combustion engine 105 to determine whether a runaway engine condition exists, and in response to a determination that the runaway engine condition exists, controls the actuator to vary geometry of the exhaust flow passage effective to mitigate the runaway engine condition. The ECU 140 is configured to determine that the runaway engine condition exists in response to a sensed engine speed 116 value exceeding a predetermined threshold and/or a difference between a sensed engine speed 116 value and a governed engine speed value exceeding a predetermined threshold. The ECU 140 may determines that the runaway engine condition exists in response to a sensed engine speed value exceeding a first predetermined threshold and/or a difference between the sensed engine speed value and a governed engine speed value exceeding a second predetermined threshold. As further described in the examples below, the governed engine speed value may be a commanded engine speed, an engine speed target or an engine speed reference used by an engine speed governor or a maximum governed engine speed and, in some embodiments, may dynamically vary depending on vehicle or engine operating conditions.

[0014] The controller 105 may be configured to control the actuator of the variable geometry turbocharger to vary geometry of the exhaust flow passage 136 by transitioning immediately to the minimum value in response to a determination that the runaway engine condition exists or by y ramping down geometry of the exhaust flow passage 136 toward the minimum value.

[0015] The ECU 140 is operatively coupled with and configured to store instructions in memory which are readable and executable by the ECU 140 to control operation of engine 105 as described herein. Certain operations described herein include operations to determine one or more parameters. Determining, as utilized herein, includes calculating or computing a value, obtaining a value from a lookup table or using a lookup operation, receiving values from a datalink or network communication, receiving an electronic signal (e.g., a voltage, frequency, current, or pulse-width modulation (PWM) signal) indicative of the value, receiving a software parameter indicative of the value, reading the value from a memory location on a computer readable medium, receiving the value as a run-time parameter by any means known in the art, and/or by receiving a value by which the interpreted parameter can be calculated, and/or by referencing a default value that is interpreted to be the parameter value.

[0016] ECU 140 is one example of a component of an integrated circuit-based electronic control system (ECS) which may be configured to control various operational aspects of vehicle 100 and internal combustion engine 105 as described in further detail herein. An ECS according to the present disclosure may be implemented in a number of forms and may include a number of different elements and configurations of elements. In certain forms an ECS may incorporate one or more microprocessor-based or microcontroller-based electronic control units sometimes referred to as electronic control modules. An ECS according to the present disclosure may be provided in forms having a single processing or computing component, or in forms comprising a plurality of operatively coupled processing or computing components; and may comprise digital circuitry, analog circuitry, or a hybrid combination of both of these types. The integrated circuitry of an ECS and/or any of its constituent processors/controllers or other components may include one or more signal conditioners, modulators, demodulators, arithmetic logic units (ALUs), central processing units (CPUs), limiters, oscillators, control clocks, amplifiers, signal conditioners, filters, format converters, communication ports, clamps, delay devices, memory devices, analog to digital (A/D) converters, digital to analog (D/A) converters, and/or different circuitry or functional components as would occur to those skilled in the art to provide and perform the communication and control aspects disclosed herein.

[0017] With reference to Fig. 2 there is illustrated a flow diagram depicting certain aspects of an exemplary engine control process 200. Process 200 begins at start operation 202 and proceeds to conditional 204 which evaluates whether a sensed engine speed is greater than a governed engine speed plus a margin. The sensed engine speed may be determined by sampling the output of an engine speed sensor such as engine speed sensor 116 at a sampling frequency selected to capture a samples of variation in engine speed attributable to a runaway condition. In some forms the sensed engine speed value may be a filtered engine speed value which takes a moving average of ray engine speed values. [0018] The margin defines a degree of variation above the governed engine speed that defines an engine runaway condition. Conditional 204 may be structured to utilize a number of different margin and commanded speed criteria in response to vehicle operating conditions and may dynamically vary the criteria depending on operation conditions of the engine or vehicle. For example, if the vehicle is below a speed threshold (e.g., zero vehicle speed or a non-zero minimum speed) and the engine is idling under the control of an idle speed governor, the margin may be selected as a number of rpm above the governed idle speed or a percent value above the governed idle speed. In certain forms the margin may be in the range of 50-100 rpm above governed idle speed. In certain forms the margin may be in the range from 2% to 5% above governed idle speed. It shall be appreciated that these rpm values and percentages are exemplary rather than limiting and that the appropriate structure of the margin for idle conditions may vary depending on the inherent stability or variation in governed idle speed such that the margin may be structured to avoid or mitigate the possibility of false positive runaway engine responses by selecting the margin to be outside the expected or empirically observed variation of idle speed relative to a commanded or governed idle speed. It shall be further appreciated that commanded governed idle speed may from a nominal value under certain circumstances, for example, idle speed may be increased relative to a nominal value to provide heat for the vehicle tab or to operate a power take off (PTO) accessory.

[0019] Under operating conditions when the vehicle is in motion, the margin and the governed engine speed may be specified using different criteria relative to when the vehicle is stationary. In some forms, while the vehicle is in motion conditional 204 may be structured to utilize the maximum governed engine speed, which may be an established value for the maximum engine speed value that an ECS will control to in response to operator demand, as the governed engine speed and to provide a margin that is selected as a number of rpm above the maximum governed speed or a percent value above the maximum governed speed. In certain forms the margin may be in the range of 200- 300 rpm above maximum governed speed. In certain forms, the margin may be in the range from 10% to 20% above maximum governed speed. It shall be appreciated that these rpm values and percentages are exemplary rather than limiting and that the appropriate structure of the margin for idle conditions may vary depending on the acceptable excursion above maximum governed speed accounting for safety and failure limits of the engine or vehicle systems. [0020] Under some operating conditions, for example, when the vehicle is in motion, the margin may be specified by predetermine engine speeds per unit time, for example, 10 rpm per second, 20 rpm per second or 25 rpm per second. In some forms, different predetermine engine speeds per unit time may be specified for different operating conditions. For example, different rpm per second margin values may be utilized for idle, partial load and full load conditions. In certain forms a lookup table may be utilized that specifies different rpm per second margin values as a function of engine speed, engine load, degree of change in engine speed and/or degree of change in engine load, among other system operating conditions. In some forms the margin may be a relative value such as a percentage of governed engine speed, for example, 101%, 102% or 102.5% of governed engine speed. The margin values may be implement as one or more calibratible values and may be set based upon empirical data accounting for variation of sensed engine speed from governed engine speed during a variety of non-runaway operating conditions including different steady state and transient operating conditions. In some forms the margin may be set to ensure that it defines variation outside the variation that occurs during a predetermined drive cycle. The predetermined drive cycle may account for a variety of engine loads, engine speeds and acceleration conditions, among other system variables.

[0021] If the sensed engine speed is not greater than the governed engine speed plus the margin, process 200 repeats operation 202. If the sensed engine is greater than the governed engine speed plus the margin process 200 proceeds to conditional 206. Conditional 206 evaluates if the engine over speed condition has been present for longer than a predetermined time, e.g., if the sensed engine speed has remained above the governed engine speed plus the margin for a predetermined time. The predetermined time may be specified based upon the aforementioned empirical data for various non-runaway engine operating conditions.

[0022] If conditional 206 evaluates that the engine over speed condition has not been present for longer than a predetermined time, process 200 returns to operation 204. If conditional 206 evaluates that the engine over speed condition has been present for longer than a predetermined time, process 200 proceeds to operation 208 which commands operation of an actuator associated with a variable geometry turbine, such as actuator l20a of variable geometry turbine l20t. In certain forms, operation 204 may be omitted and the margin may be configured such that an indication that sensed engine speed has exceeded the governed engine speed plus the margin for any duration of time provides an indication of runaway engine conditions. In certain forms the duration evaluation of conditional may be included as part of conditional 202.

[0023] At operation 208, the actuator may be commanded to immediately set the flow passage of the variable geometry turbine to its minimum value, e.g., at the earliest processing event opportunity. The actuator may also be commanded to ramp the flow passage of the variable geometry turbine down to its minimum value. During such ramping operation the evaluations performed by conditionals 204 and 206 may be repeated. The ramp down may provide an opportunity to burn off undesired combustible matter present in the intake system. In the event of ramp down operation a second margin may be implemented to end ramp down operation and immediately set the flow passage of the variable geometry turbine to its minimum value. The second margin is preferably greater than the first margin and provides a safety override limit on the ramp down operation. From operation 208, process 200 proceeds to operation 210 which ends or repeats process 200.

[0024] With reference to Fig. 3 there is illustrated a flow diagram illustrating certain aspects of an exemplary engine control process 300. Process 300 begins at start operation 302 and proceeds to conditional 304 which evaluates whether a sensed engine speed is greater than a first predetermined threshold. The first predetermined threshold may be defined by a governed engine speed plus a margin such as the examples described in connection with operation 202.

The first predetermined threshold may be defined by a governed engine speed plus a margin such as the examples described in connection with conditional 202 such as the examples described in connection with conditional 204. If the sensed engine speed is greater than the predetermined threshold the process proceeds to operation 308.

[0025] Operation 308 commands operation of an actuator associated with a variable geometry turbine, such as actuator l20a of variable geometry turbine l20t. The actuator may be commanded to immediately set the flow passage of the variable geometry turbine to its minimum value, e.g., at the earliest processing event opportunity. The actuator may also be commanded to ramp the flow passage of the variable geometry turbine down to its minimum value. During such ramping operation one or more evaluations performed by conditionals 204 may be repeated. The ramp down may provide an opportunity to bum off undesired combustible matter present in the intake system. In the event of ramp down operation, a second margin may be implemented to end ramp down operation and immediately set the flow passage of the variable geometry turbine to its minimum value. The second margin is preferably greater than the first margin and provides a safety override limit on the ramp down operation. From operation 308, process 300 proceeds to operation 310 which ends or repeats process 300.

[0026] If engine speed is not greater than the predetermined threshold the process proceeds to conditional 306 which evaluates whether a sensed engine speed is greater than a second predetermined threshold. The second predetermined threshold may be defined by a maximum permissible engine speed under given system operating conditions or under any system operating conditions. Maximum permissible engine operating speeds may be specified in a number of different system parameters such as different engine loads or a maximum engine operating speed may be specified or without regard to other variables. If conditional 306 evaluates that the sensed engine speed is not greater than the second predetermined threshold, process 300 returns to conditional 304. If conditional 306 evaluates that the sensed engine speed is greater than the second predetermined threshold, process 300 proceeds to operation 308. From operation 308, process 300 proceeds to operation 310 which ends or repeats process 300.

[0027] A number of exemplary embodiments shall now be further described. A first exemplary embodiment is a system comprising: an internal combustion engine operatively coupled with a variable geometry turbocharger, the variable geometry turbocharger including a compressor, a turbine coupled with the compressor and an actuator structured to vary geometry of an exhaust flow passage in flow communication with the turbine between a minimum value and a maximum value; and an electronic control system operatively coupled with the internal combustion engine and the variable geometry turbocharger, the electronic control system structured to evaluate operation of the engine to determine whether a runaway engine condition exists, and in response to a determination that the runaway engine condition exists, control the actuator to vary geometry of the exhaust flow passage effective to mitigate the runaway engine condition.

[0028] In certain forms of the first exemplary embodiment, the electronic control system is configured to determine that the runaway engine condition exists in response to a sensed engine speed value exceeding a predetermined threshold. In certain forms, the electronic control system is configured to determine that the runaway engine condition exists in response to a difference between a sensed engine speed value and a governed engine speed value exceeding a predetermined threshold. In certain forms, the electronic control system is configured to determine that the runaway engine condition exists in response to either a sensed engine speed value exceeding a first predetermined threshold or a difference between the sensed engine speed value and a governed engine speed value exceeding a second predetermined threshold. In certain forms, the minimum value provides a zero area geometry of the exhaust flow passage. In certain forms, the electronic control system is configured to control the actuator to vary geometry of the exhaust flow passage immediately to the minimum value in response to a determination that the runaway engine condition exists. In certain forms, the electronic control system is configured to control the actuator to ramp down geometry of the exhaust flow passage toward the minimum value in response to a determination that the runaway engine condition exists.

[0029] A second exemplary embodiment is a method comprising: operating an electronic control system to control operation of an internal combustion engine operatively coupled with a variable geometry turbocharger, the variable geometry turbocharger including a compressor, a turbine coupled with the compressor and an actuator structured to vary geometry of an exhaust flow passage in flow communication with the turbine between a minimum value and a maximum value, wherein the operating includes: evaluating operation of the engine to determine whether a runaway engine condition exists, and in response to determining that the runaway engine condition exists, controlling the actuator to vary geometry of the exhaust flow passage effective to mitigate the runaway engine condition.

[0030] In certain forms of the second exemplary embodiment, the operating includes determining that the runaway engine condition exists in response to a sensed engine speed value exceeding a predetermined threshold. In certain forms, the operating includes determining that the runaway engine condition exists in response to a difference between a sensed engine speed value and a governed engine speed value exceeding a predetermined threshold. In certain forms, the operating includes determining that the runaway engine condition exists in response to either a sensed engine speed value exceeding a first predetermined threshold or a difference between the sensed engine speed value and a governed engine speed value exceeding a second predetermined threshold. In certain forms, the controlling the actuator includes commanding the actuator to vary geometry of the exhaust flow passage immediately to the minimum value in response to a determination that the runaway engine condition exists. In certain forms, the controlling the actuator includes commanding the actuator to ramp down geometry of the exhaust flow passage toward the minimum value in response to a determination that the runaway engine condition exists.

[0031] A third exemplary embodiment is an apparatus structured to control operation of an internal combustion engine operatively coupled with a variable geometry turbocharger, the variable geometry turbocharger including a compressor, a turbine coupled with the compressor and an actuator structured to vary geometry of an exhaust flow passage in flow communication with the turbine between a minimum value and a maximum value, the apparatus comprising an electronic control unit structured to execute instructions stored in a non-transitory computer readable memory medium to evaluate operation of the engine to determine whether a runaway engine condition exists and, in response to a determination that the runaway engine condition exists, control the actuator to vary geometry of the exhaust flow passage effective to mitigate the runaway engine condition.

[0032] In certain forms of the third exemplary embodiment, the instructions to evaluate operation of the engine to determine whether a runaway engine condition exists comprise instructions to evaluate a sensed engine speed value relative to a predetermined threshold. In certain forms, the instructions to evaluate operation of the engine to determine whether a runaway engine condition exists comprise instructions to evaluate a difference between a sensed engine speed value and a governed engine speed value exceeding a predetermined threshold. In certain forms, the instructions to evaluate operation of the engine to determine whether a runaway engine condition exists comprise instructions to evaluate a sensed engine speed value relative to first predetermined threshold and instructions to evaluate a difference between the sensed engine speed value and a governed engine speed value relative to a second predetermined threshold. In certain forms, the instructions are configured to control the actuator to vary geometry of the exhaust flow passage immediately to the minimum value in response to a determination that the runaway engine condition exists. In certain forms, the instructions are configured to control the actuator to ramp down geometry of the exhaust flow passage toward the minimum value in response to a determination that the runaway engine condition exists. In certain forms, the minimum value provides a non-zero area geometry of the exhaust flow passage.

[0033] While illustrative embodiments of the disclosure have been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain exemplary embodiments have been shown and described and that all changes and modifications that come within the spirit of the claimed inventions are desired to be protected. It should be understood that while the use of words such as preferable, preferably, preferred or more preferred utilized in the description above indicate that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, the scope being defined by the claims that follow. In reading the claims, it is intended that when words such as“a,”“an,”“at least one,” or“at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language“at least a portion” and/or“a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

1. A system comprising:

an internal combustion engine operatively coupled with a variable geometry

turbocharger, the variable geometry turbocharger including a compressor, a turbine coupled with the compressor and an actuator structured to vary geometry of an exhaust flow passage in flow communication with the turbine between a minimum value and a maximum value; and

an electronic control system operatively coupled with the internal combustion engine and the variable geometry turbocharger, the electronic control system structured to

evaluate operation of the engine to determine whether a runaway engine condition exists, and

in response to a determination that the runaway engine condition exists, control the actuator to vary geometry of the exhaust flow passage effective to mitigate the runaway engine condition.

2. The system of claim 1, wherein the electronic control system is configured to determine that the runaway engine condition exists in response to a sensed engine speed value exceeding a predetermined threshold.

3. The system of claim 1, wherein the electronic control system is configured to determine that the runaway engine condition exists in response to a difference between a sensed engine speed value and a governed engine speed value exceeding a predetermined threshold.

4. The system of claim 1, wherein the electronic control system is configured to determine that the runaway engine condition exists in response to either a sensed engine speed value exceeding a first predetermined threshold or a difference between the sensed engine speed value and a governed engine speed value exceeding a second predetermined threshold.

5. The system of claim 1, wherein the minimum value provides a zero area geometry of the exhaust flow passage.

6. The system of claim 1 wherein the electronic control system is configured to control the actuator to vary geometry of the exhaust flow passage immediately to the minimum value in response to a determination that the runaway engine condition exists.

7. The system of claim 1 wherein the electronic control system is configured to control the actuator to ramp down geometry of the exhaust flow passage toward the minimum value in response to a determination that the runaway engine condition exists.

8. A method comprising:

operating an electronic control system to control operation of an internal combustion engine operatively coupled with a variable geometry turbocharger, the variable geometry turbocharger including a compressor, a turbine coupled with the compressor and an actuator structured to vary geometry of an exhaust flow passage in flow communication with the turbine between a minimum value and a maximum value, wherein the operating includes

evaluating operation of the engine to determine whether a runaway engine condition exists, and

in response to determining that the runaway engine condition exists, controlling the actuator to vary geometry of the exhaust flow passage effective to mitigate the runaway engine condition.

9. The method of claim 8, wherein the operating includes determining that the runaway engine condition exists in response to a sensed engine speed value exceeding a predetermined threshold.

10. The method of claim 8, wherein the operating includes determining that the runaway engine condition exists in response to a difference between a sensed engine speed value and a governed engine speed value exceeding a predetermined threshold.

11. The method of claim 8, wherein the operating includes determining that the runaway engine condition exists in response to either a sensed engine speed value exceeding a first predetermined threshold or a difference between the sensed engine speed value and a governed engine speed value exceeding a second predetermined threshold.

12. The method of claim 8, wherein the controlling the actuator includes commanding the actuator to vary geometry of the exhaust flow passage immediately to the minimum value in response to a determination that the runaway engine condition exists.

13. 12. The method of claim 8, wherein the controlling the actuator includes commanding the actuator to ramp down geometry of the exhaust flow passage toward the minimum value in response to a determination that the runaway engine condition exists.

14. An apparatus structured to control operation of an internal combustion engine operatively coupled with a variable geometry turbocharger, the variable geometry turbocharger including a compressor, a turbine coupled with the compressor and an actuator structured to vary geometry of an exhaust flow passage in flow communication with the turbine between a minimum value and a maximum value, the apparatus comprising an electronic control unit structured to execute instructions stored in a non-transitory computer readable memory medium to evaluate operation of the engine to determine whether a runaway engine condition exists and, in response to a determination that the runaway engine condition exists, control the actuator to vary geometry of the exhaust flow passage effective to mitigate the runaway engine condition.

15. The apparatus of claim 14, wherein the instructions to evaluate operation of the engine to determine whether a runaway engine condition exists comprise instructions to evaluate a sensed engine speed value relative to a predetermined threshold.

16. The apparatus of claim 14, wherein the instructions to evaluate operation of the engine to determine whether a runaway engine condition exists comprise instructions to evaluate a difference between a sensed engine speed value and a governed engine speed value exceeding a predetermined threshold.

17. The apparatus of claim 14, wherein the instructions to evaluate operation of the engine to determine whether a runaway engine condition exists comprise instructions to evaluate a sensed engine speed value relative to first predetermined threshold and instructions to evaluate a difference between the sensed engine speed value and a governed engine speed value relative to a second predetermined threshold.

18. The apparatus of claim 14, wherein the instructions are configured to control the actuator to vary geometry of the exhaust flow passage immediately to the minimum value in response to a determination that the runaway engine condition exists.

19. The apparatus of claim 14, wherein the instructions are configured to control the actuator to ramp down geometry of the exhaust flow passage toward the minimum value in response to a determination that the runaway engine condition exists.

20. The apparatus of claim 14, wherein the minimum value provides a non-zero area geometry of the exhaust flow passage.