Method and internal combustion engine system for boost pressure control

Abstract

Method for an internal combustion engine (10) comprising the following: Adapting an inlet throttle valve (20) to respond to a pre-turbine exhaust pressure of more than a threshold without reducing the boost pressure level by adjusting the boost pressure actuators, while maintaining the valve control of inlet valves (62) and exhaust valves (64), wherein the adjustment includes reducing the opening of the inlet throttle valve (20) until the pre-turbine exhaust pressure is below the threshold, the threshold being based on a pressure required to force open a closed exhaust valve.

Description

Area

[0001] The present application relates to methods and systems for reducing exhaust backpressure problems in a turbocharged internal combustion engine system. Background and brief presentation

[0002] Internal combustion engine systems can be equipped with boosting devices, such as turbochargers or superchargers, to provide a boosted air charge and improve peak power output. Boost pressure can be controlled to a desired setpoint through the actions of one or more boost actuators, including, for example, a wastegate (WG) coupled across an exhaust turbine and a compressor recirculation valve (CRV) coupled across an intake compressor. The wastegate controls boost pressure by controlling exhaust flow across the exhaust turbine, while the compressor recirculation valve is used to manage compressor surge. Each boost actuator can be adjusted based on feedforward and feedback components.

[0003] In such turbocharged internal combustion engine systems, the presence of high exhaust backpressure can cause one or more of the engine's exhaust valves to remain open or be forced open despite commands to close. This inadvertent opening of exhaust valves can lead to abnormal combustion events such as misfire, knock, and / or pre-ignition. This can degrade engine performance and reduce the service life of various engine components. Furthermore, engine exhaust emissions can be adversely affected.

[0004] One approach to controlling exhaust backpressures in turbocharged internal combustion engine systems is presented by Osborn et al. in US 8,621,864 B2.

[0005] Therein, the exhaust gas recirculation (EGR) flow is adjusted to regulate the intake air flow based on an existing exhaust pressure. Specifically, the intake air flow can be modified by varying the EGR flow to regulate the exhaust pressure. The EGR flow can be adjusted by one or more of an EGR valve and a variable geometry turbocharger (VGT). The VGT can be controlled to adjust the EGR flow based on an existing exhaust pressure and a desired exhaust pressure. Further prior art relating to the background of the present invention is provided by the documents DE 102 96 962 T5, DE 10 2010 033 243 A1, and DE 10 2013 217 641 A1.

[0006] However, the inventors herein have recognized potential problems with such an approach to controlling exhaust pressures. As one example, adjusting EGR flows may cause changes in intake airflow at a slower than desired rate. More specifically, intake airflow may respond to variations in EGR flow at a slower rate. Therefore, such higher exhaust backpressures must be reduced quickly to reduce abnormal combustion events and their impact on component degradation. Therefore, EGR flow adjustments may not be able to avert problems resulting in excessive exhaust backpressures in a timely manner.

[0007] In one example, the issues described above may be at least partially addressed by a method for controlling a boosted engine system, including adjusting an intake throttle responsive to a pre-turbine exhaust pressure higher than a threshold without reducing the boost pressure level while maintaining valve timing. In this way, exhaust backpressure in a boosted engine system may be maintained within a range that does not degrade engine hardware and performance.

[0008] As one example, a boosted engine system may include a turbocharger and a particulate filter coupled downstream of an exhaust turbine of the turbocharger. Post-turbine exhaust manifold pressure may be measured by a pressure sensor coupled downstream of the turbine. Pre-turbine exhaust pressure may be estimated (i.e., predicted or modeled) based on various engine operating conditions, including, for example, particulate filter load and / or post-turbine exhaust pressure. In response to pre-turbine pressure becoming higher than a threshold, such as a threshold above which exhaust pressure may hold a cylinder exhaust valve open or bias open, intake airflow to the engine may be restricted without restricting boost output while maintaining exhaust valve control.For example, an intake throttle opening may be reduced to restrict engine intake air. A torque control loop of the engine control system may then use the reduced intake airflow as an input to adjust one or more boost actuators to maintain boost pressure despite reduced intake airflow.

[0009] In this way, excessive exhaust backpressure can be reduced. By adjusting the intake throttle to regulate intake airflow, a faster reduction in intake air charge can be achieved. This can reduce the occurrence of abnormal combustion events due to excessive exhaust backpressure, enabling improved engine performance and increased engine component life. Furthermore, by maintaining boost pressure levels while reducing intake air charge, the vehicle operator experience is not impaired. Overall, drivability and emissions standards can be improved.

[0010] It should be understood that the above summary is provided to introduce, in simplified form, a selection of concepts further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that address any disadvantages noted above or in any part of this disclosure. Short description of the drawings Fig. 1 is a schematic illustration of an exemplary internal combustion engine system in a vehicle. Fig. 2 shows an exemplary control loop for determining an intake air flow restriction and associated torque reduction based on exhaust back pressures. Fig. 3A and Fig. 3B illustrates an example flow diagram for adjusting intake airflow in response to excessive exhaust pressure. Fig. Figure 4 shows an exemplary flow diagram for predicting the exhaust pressure upstream of an exhaust turbine associated with the engine system of Fig. 1 is coupled. Fig. Figure 5 presents example settings of an intake throttle and an exhaust wastegate in response to higher exhaust pressures upstream of the exhaust turbine. Fig. 6 illustrates additional adjustments to airflow via controlling the positive valve overlap and / or position of the intake throttle in response to excessive exhaust pressures. Detailed description

[0011] The following description relates to systems and methods for controlling exhaust back pressures in an internal combustion engine system, such as the internal combustion engine system of Fig. 1. Therefore, the exemplary internal combustion engine may be a turbocharged internal combustion engine in which an exhaust pressure upstream of an exhaust turbine is adjusted based on a plurality of engine operating parameters ( Fig. 4) can be modeled. Excessive exhaust pressure upstream of the exhaust turbine can force open the exhaust valves of the engine cylinders, leading to combustion instabilities and degradation of the engine components. Accordingly, if the exhaust pressure upstream of the exhaust turbine is higher than a threshold, a controller can be configured to activate a routine such as the one described in Fig. 3A-3B to reduce the intake air flow. The intake air flow can be controlled based on a control loop ( Fig. 2) be limited, resulting in a reduction in available torque. Limiting intake airflow can be achieved by reducing and opening an intake throttle valve. Additionally or alternatively, blow-by of boosted intake air into an exhaust manifold upstream of the exhaust turbine (e.g., via positive valve overlap) can be reduced. Simultaneously with reducing intake airflow and available torque, a desired boost pressure can be maintained by actuating various boost actuators such as a wastegate, compressor recirculation valve, etc. If reducing intake airflow does not result in a reduction in exhaust pressure within a predetermined duration, boost levels can be reduced ( Fig. 5). In this way, excessive exhaust backpressure can be quickly reduced.

[0012] With reference to Fig. 1 shows a schematic diagram of a vehicle system 6. The vehicle system 6 includes an internal combustion engine system 100. The internal combustion engine system 100 includes an internal combustion engine 10 having a plurality of cylinders 30. In the illustrated embodiment, the internal combustion engine 10 is a boosted internal combustion engine coupled to a turbocharger 13 including a compressor 14 driven by a turbine 18. Fresh air is introduced into the internal combustion engine 10 along an intake passage 42 via an air cleaner 44 and flows to the compressor 14. A flow rate of ambient air entering the intake passage 42 may be sensed by the mass air flow (MAF) sensor 122.

[0013] Compressor 14 may be any suitable intake air compressor, such as an electric motor-driven or driveshaft-driven supercharger compressor. However, in engine system 10, the compressor is a turbocharger compressor mechanically coupled to turbine 18 via a shaft 19, with turbine 18 driven by expanding engine exhaust. Turbine 18 may therefore be referred to as an exhaust turbine 18. In one embodiment, the compressor and turbine may be coupled within a twin-scroll turbocharger. In another embodiment, the turbocharger may be a variable geometry turbocharger (VGT), with the turbine geometry actively changing as a function of engine speed.

[0014] As in Fig. 1, the compressor 14 is coupled to the intake throttle 20 through the charge air cooler 46. The charge air cooler 46 may cool a temperature of compressed air exiting the compressor 14. The charge air cooler may be, for example, an air-to-air or air-to-water heat exchanger. The intake throttle 20, located downstream of the compressor 14, is fluidly coupled to the intake manifold 22. The intake throttle 20 may include a throttle valve, and in one example, a position of the intake throttle 20 (specifically, a position of the throttle plate) may be varied by a controller 12 using a signal provided to an electric motor or actuator included in the throttle 20, this configuration generally referred to as electronic throttle control (ETC).In this manner, the intake throttle valve 20 may be actuated to vary the amount of intake air provided to the intake manifold 22 of the internal combustion engine 10 and the plurality of cylinders therein.

[0015] In the Fig. 1, the pressure of the air charge within the intake manifold 22 is measured by a manifold air pressure (MAP) sensor 124. Further, a temperature of the air charge within the intake manifold 22 may be measured by the manifold air temperature (MAT) sensor 127. Further, a pressure of compressed air upstream of the intake throttle 20 and downstream of the compressor 14 may be sensed by the throttle inlet pressure (TIP) sensor 129. Specifically, boost pressure levels within the engine system 100 may be measured by the TIP sensor 129 by measuring TIP (also called boost pressure).

[0016] A compressor bypass valve 92 may be coupled in a compressor bypass passage 90 transverse to the compressor 14 (e.g., between the inlet and outlet). The compressor bypass valve 92 may be a normally closed valve configured to open under selected operating conditions to vent excessive boost pressure. For example, the compressor bypass valve may be opened as engine speed decreases to prevent compressor overvoltage. To reduce compressor overvoltage, at least a portion of the air charge compressed by the compressor 14 may be recirculated from the compressor outlet to the compressor inlet via the compressor bypass passage 90. Specifically, in the depicted example, pressurized air may be recirculated from downstream of the charge air cooler 46 to the compressor inlet.In alternative examples, compressed air downstream of the compressor 14 but upstream of the charge air cooler 46 may be redirected to the compressor inlet via the compressor bypass passage 90. The compressor bypass valve 92 (also compressor recirculation valve, CRV 92) may control an amount of compressed air recirculated from the compressor outlet to the compressor inlet. Therefore, the compressor bypass valve (CBV) 92 may then be commanded by the controller 12 to a desired position based on the desired amount of compressor recirculation flow, after which an actuator (e.g., electric, hydraulic, etc.) may actuate the compressor bypass valve 92. It will be appreciated that the CRV 92 may also be controlled to regulate boost pressures. For example, during an engagement event, the CRV 92 may be configured to allow a rapid increase in boost pressure to a more closed (e.g.The CRV can be adjusted to a fully closed position. This can significantly deactivate or reduce compressor bypass flow. Therefore, the CRV can be used as a boost pressure actuator.

[0017] The intake manifold 22 is fluidly coupled to a series of combustion chambers 30 (or a plurality of cylinders 30) through a series of intake valves (the series is not shown). The combustion chambers are further coupled to the exhaust manifold 36 via a series of exhaust valves (not shown). In the illustrated embodiment, a single exhaust manifold 36 is shown. However, in other embodiments, the exhaust manifold may include a plurality of exhaust manifold sections. Configurations with a plurality of exhaust manifold sections may allow effluent from different combustion chambers to be directed to different locations in the engine system.

[0018] The combustion chambers 30 may be supplied with one or more fuels, such as gasoline, alcoholic fuel blends, diesel, biodiesel, compressed natural gas, etc. The fuel may be delivered to the combustion chambers via a fuel injector 66. In the illustrated example, the fuel injector 66 is configured for direct injection, although in other embodiments, the fuel injector 66 may also be configured for port injection or throttle body injection. Further, each combustion chamber may include one or more fuel injectors of various configurations to enable each cylinder to receive fuel via direct injection, port injection, throttle body injection, or combinations thereof. Combustion in the combustion chambers may be initiated via spark ignition and / or compression ignition.

[0019] Exhaust gas from exhaust manifold 36 is directed to turbine 18 to drive the turbine. Exhaust gas sensor 128 is coupled to exhaust manifold 36 upstream of an emission control device 70. Sensor 128 may be any suitable sensor for providing an indication of the exhaust air-fuel ratio, such as a linear oxygen sensor or a wideband oxygen sensor, a two-point oxygen sensor or oxygen sensor, a heated oxygen sensor, a NOx, HC, or CO sensor.

[0020] It will be appreciated that the illustrated example engine system 100 does not include a pressure sensor located upstream of the turbine 18. Alternative example engine systems may include a sensor for measuring pre-turbine exhaust pressure (or exhaust back pressure). However, the engine system 100 does not include a pressure sensor 54 located immediately downstream of the exhaust turbine 18 along the exhaust passage 35. The pressure sensor 54 may measure the exhaust pressure downstream of the exhaust turbine 18 or the post-turbine exhaust pressure.

[0021] Exhaust gases exit combustion chambers 30, and exhaust manifold 36 rotates exhaust turbine 18, which is coupled to compressor 14 via shaft 19. The amount of compression provided to one or more cylinders of the engine via turbocharger 13 can be varied by controller 12. If reduced turbine torque is desired, a portion of the exhaust flow can instead be routed through a wastegate 82 that bypasses the turbine. Wastegate 82 (also called an exhaust wastegate) can be coupled across exhaust turbine 18 in turbocharger 13. More specifically, wastegate 82 can be included in a bypass passage 80 coupled between an inlet and an outlet of exhaust turbine 18. By adjusting a position of wastegate 82 via controller 12, an amount of boost provided by the turbocharger can be controlled. Therefore, the boost pressure control valve can be a boost pressure actuator.Herein, the controller 12 may provide a signal based on the desired boost pressure to adjust an electromechanical actuator coupled to the wastegate 82. The combined flow from the turbine 18 and the wastegate 82 then flows through the exhaust control device 70.

[0022] In general, one or more emission control devices 70 may include one or more exhaust aftertreatment catalysts configured to catalytically treat exhaust gas streams and thereby reduce an amount of one or more substances in the exhaust stream. For example, the emission control device 70 may include a regenerable soot filter 72 (also particulate filter 72) configured to capture and oxidize soot particles in the exhaust stream. The particulate filter 72 may treat exhaust gases and capture soot and ash particles within the particulate filter. In some embodiments, an exhaust aftertreatment catalyst may, for example, be configured to X from the exhaust gas stream when the exhaust gas stream is lean, and the captured NO X reduced when the exhaust flow is rich. In other examples, an exhaust aftertreatment catalyst may be designed to reduce NO Xselectively reduced using a reducing agent. In other examples, an exhaust aftertreatment catalyst may be configured to oxidize residual hydrocarbons and / or residual carbon monoxide in the exhaust stream. Various exhaust aftertreatment catalysts having any such functionality may be disposed in intermediate layers or elsewhere in the exhaust aftertreatment stages, either separately or together. All or a portion of the treated exhaust gas from the emission control device 70 and the particulate filter 72 may be discharged to the environment via the outlet conduit 35.

[0023] The outlet line 35 may also contain the exhaust gas sensor 162 and a temperature sensor 126. Downstream of the exhaust gas sensor 162, any sensor suitable for indicating the concentration of the components of the exhaust gas, such as NO x, NH3, EGO, etc. In the example shown, the sensor 162 may be a particulate matter (PM) sensor. As in Fig. 1, sensor 162 may be disposed downstream of particulate filter 72, while in other embodiments, sensor 162 may be positioned upstream of particulate filter 72. Further, it should be understood that more than one sensor 162 may be provided in any suitable position. Specifically, sensor 162 may measure the mass or concentration of particulate matter downstream of particulate filter 72 and downstream of emission control device 70. Therefore, sensor 162 may be a soot particle sensor. Sensor 162 may be operably coupled to controller 12 and communicate with controller 12 to indicate a concentration of particulate matter in the exhaust exiting particulate filter 72 (and emission control device 70) and flowing through exhaust passage 35. Herein, sensor 162 may also estimate the charge of particulate filter 72.

[0024] Depending on the operating conditions, a portion of the exhaust gases can be recirculated from the exhaust passage 35 downstream of the turbine 18 to the intake passage 42 upstream of the compressor 14 via the exhaust gas recirculation (EGR) passage 50. This portion of the exhaust gases can flow through the EGR passage 50 via the EGR cooler 51 and the LP EGR valve 52. This allows for low-pressure exhaust gas recirculation (LP EGR). In some embodiments, in addition to LP EGR, high-pressure exhaust gas recirculation (HP EGR) may also be enabled, wherein a portion of exhaust gas from the exhaust manifold 36 upstream of the turbine 18 is recirculated to the intake manifold 22 downstream of the compressor 14 via a different and separate high-pressure EGR passage 84 and the EGR cooler 83 and HP EGR valve 86 coupled therein. The LP EGR valve 52 and the HP EGR valve 86 may be opened (e.g.,An opening of the EGR valves may be increased to admit a controlled amount of cooled exhaust gas to the intake port for the desired combustion and emission control performance. Therefore, the EGR valve 52 may be actuated by an actuator (e.g., electrical, mechanical, hydraulic, etc.) based on the commands received from the controller 12.

[0025] Each cylinder 30 may be served by one or more valves. In the present example, each cylinder 30 includes a corresponding intake valve 62 and an exhaust valve 64. Each intake valve 62 and exhaust valve 64 may be held in a desired position via an associated spring. The internal combustion engine system 100 further includes one or more camshafts 57, 68 for actuating the intake valve 62 and / or for operating the exhaust valve 64. In the illustrated example, the intake camshaft 68 is coupled to the intake valve 62 and operable to actuate the intake valve 62. Similarly, the exhaust camshaft 57 is coupled to the exhaust valve 64 and operable to actuate the exhaust valve 64.In some embodiments in which the intake valve of a plurality of cylinders 30 is coupled to a common crankshaft, the intake camshaft 68 may be operated to actuate the intake valves of all coupled cylinders.

[0026] The intake valve 62 can be actuated between an open position, which admits intake air into the corresponding cylinder, and a closed position, which substantially excludes intake air from the cylinder. The intake camshaft 68 can be included in an intake valve actuation system 69. The intake camshaft 68 includes an intake cam 67 having a cam lobe profile for opening the intake valve 62 for a defined intake duration. In some embodiments (not shown), the camshaft can include additional intake lobes with an alternative cam lobe profile that allows the intake valve 62 to be opened for an alternative duration (also referred to herein as a cam profile switching system). Based on the lobe profile of the additional cam, the alternative duration can be longer or shorter than the defined intake duration of the intake cam 67.The cam profile may affect cam lift, cam duration, and / or cam timing. A controller may be capable of switching intake valve duration by moving intake camshaft 68 longitudinally and switching between cam profiles.

[0027] In the same way, each exhaust valve 64 can be actuated between an open position, which allows exhaust gas to flow out of the corresponding cylinder, and a closed position, which substantially retains gas within the cylinder and blocks the exit of exhaust gases from the cylinder. The exhaust camshaft 57 can be included in an exhaust valve actuation system 56. As shown, the exhaust camshaft 57 includes the exhaust cam 53, which has a cam lobe profile for opening the exhaust valve 64 for a defined exhaust duration. In some embodiments in which the exhaust valve of a plurality of cylinders 30 is coupled to a common crankshaft, the exhaust camshaft 57 can be operated to actuate the exhaust valves of all coupled cylinders.In some embodiments, the exhaust camshaft may further include additional exhaust cams with an alternative cam lobe profile that allows the exhaust valve 64 to open for an alternative duration. The lobe profile may affect cam lift height, cam duration, and / or cam timing. A controller may be capable of switching the exhaust valve duration by moving the exhaust camshaft longitudinally and switching between cam profiles.

[0028] It is understood that the intake and / or exhaust camshafts may be coupled to subsets of cylinders, and multiple intake and / or exhaust camshafts may be present. For example, a first intake camshaft may be coupled to the intake valves of a first subset of cylinders, while a second intake camshaft may be coupled to the intake valves of a second subset of cylinders. Similarly, a first exhaust camshaft may be coupled to the exhaust valves of a first subset of cylinders, while a second exhaust camshaft may be coupled to the exhaust valves of a second subset of cylinders. Furthermore, one or more intake valves and exhaust valves may be coupled to each camshaft. The subset of cylinders coupled to the camshaft may be based on its position along an engine block, its firing order, the engine configuration, etc.

[0029] The intake valve actuation system 69 and the exhaust valve actuation system 56 may further include pushrods, rocker arms, lifters, etc. Such devices and features may control the actuation of the intake valve 62 and the exhaust valve 64 by converting the rotational motion of the cams into translational motion of the valves. As previously mentioned, the valves may also be actuated via additional cam lobe profiles on the camshafts, where the cam lobe profiles may provide different cam lift height, cam duration, and / or cam timing between the different valves. However, alternative camshaft arrangements (overhead and / or pushrod) may also be used if desired. In some examples, the cylinders 30 may further each have more than one exhaust valve and / or intake valve.In still further examples, each of the exhaust valve 64 and intake valve 62 of one or more cylinders may be actuated by a common camshaft. Furthermore, in some examples, some of the intake valves 62 and / or exhaust valves 64 may be actuated by their own independent camshaft or other device.

[0030] The internal combustion engine system 100 may include variable valve timing systems, for example, a variable exhaust cam timing (VCT) system 60. It should be noted that the exhaust valve actuation system 56 is also operatively coupled to the VCT system 60, which, for clarity, is shown as a separate block in Fig. 1. Therefore, the VCT system 60 may be operatively and communicatively coupled to the intake valve actuation system 69 and the exhaust valve actuation system 56.

[0031] A variable valve timing system may be configured to open a first valve in a first operating mode for a first duration. The first operating mode may occur at an engine load below an engine part-load threshold. Further, a variable valve timing system may be configured to open the first valve in a second operating mode for a second duration shorter than the first duration. The second operating mode may occur at an engine load above an engine load threshold and an engine speed above an engine speed threshold (e.g., at low to medium engine speeds).

[0032] The VCT system 60 may be an independent dual variable camshaft timing system for independently changing intake valve timing and exhaust valve timing. The VCT system 60 may include an intake camshaft phaser 65 coupled to the common intake camshaft 68 for changing intake valve timing. The VCT system 80 may similarly include an exhaust camshaft phaser 55 coupled to the exhaust camshaft 57 for changing exhaust valve timing. The VCT system 60 may be configured to adjust valve timing by advancing or retarding camshaft timing, and may be controlled by the controller 12. The VCT system 60 may be configured to change the timing of valve opening and closing events by changing the relationship between crankshaft position and camshaft position.For example, the VCT system 60 may be configured to rotate the intake camshaft 68 independently of the crankshaft to advance or retard the valve timing. In some embodiments, the VCT system 60 may be a cam torque-actuated device configured to quickly change cam timing. In some embodiments, valve timing, such as intake valve closing (IVC) and exhaust valve closing (EVC), may be changed by a continuously variable valve lift (CVVL) device.

[0033] The valve / cam control devices and systems described above may be hydraulically driven or electrically actuated, or combinations thereof. In one example, camshaft position may be changed via cam phasing of an electric actuator (e.g., an electrically actuated cam phaser) with an accuracy exceeding that of most hydraulically actuated cam phasers. Signal lines may send control signals to the VCT system 60 and receive a cam timing and / or cam selection measurement therefrom.

[0034] By adjusting the VCT system 60, a position of the intake camshaft 68 can be adjusted to vary an opening and / or closing timing of the intake valve 62. Similarly, a position of the exhaust camshaft 57 can be adjusted by the VCT system 60 to vary an opening and / or closing timing of the exhaust valve 64. Thus, by varying the opening and closing of the intake valve 62, an amount of positive overlap between the intake valve 62 and the exhaust valve 64 can be varied. For example, the VCT system 60 can be adjusted to advance or retard an opening and / or closing of the intake valve 62 with respect to a piston position.

[0035] During internal combustion engine operation, a piston moves gradually downward from TDC, reaching its lowest point at BDC at the end of the power stroke. The piston then returns to its upper end, TDC, at the end of the exhaust stroke. The piston then moves downward again during the intake stroke, finally returning to its upper position at TDC at the end of the compression stroke. During cylinder combustion, an exhaust valve may open when the piston hits the end of the power stroke. The exhaust valve may then close as the piston completes the exhaust stroke and remain open at least until a subsequent intake stroke begins. Similarly, an intake valve may open at or before the start of an intake stroke in any mode and remain open at least until a subsequent compression stroke has begun.

[0036] Based on the timing differences between exhaust valve closing and intake valve opening, the valves may be operated with negative valve overlap, where both the intake and exhaust valves are closed for a brief period after the end of the exhaust stroke and before the start of the intake stroke. This period of both valves being closed is referred to as negative (intake-to-exhaust) valve overlap. In one example, the VCT system may be adjusted such that negative intake-to-exhaust valve overlap timing may be a default engine cam position during cylinder combustion.

[0037] Alternatively, the valves may be operated with positive valve overlap, where both the intake and exhaust valves are open for a short period of time before the end of the exhaust stroke and after the start of the intake stroke. This period, during which both valves (e.g., intake and exhaust valves of a given cylinder) may be open simultaneously, is referred to as positive (intake-to-exhaust) valve overlap. Positive valve overlap may be used to accelerate catalyst warm-up during a cold start. As another example, positive valve overlap may be used in boosted internal combustion engines (e.g., engines coupled with a turbocharger) to reduce turbo lag. Here, boosted air from the compressor can flow through one or more cylinders to the exhaust turbine by increasing the positive valve overlap.

[0038] As described in detail herein, the VCT system 60 may be adjusted to reduce an amount of positive valve overlap during select boosted engine operating conditions, e.g., when exhaust pressures are higher than desired. As one example, a position of the intake camshaft may be adjusted to delay an opening of the intake valve timing. Accordingly, the intake valve may be opened at a later time (before the end of the exhaust stroke) so that a duration of time both valves are open may be reduced, resulting in reduced positive valve overlap. As one example, the positive valve overlap may be reduced by moving the intake camshaft from a position with more positive valve overlap to a position with less positive valve overlap.As another example, positive valve overlap may be reduced by moving the intake camshaft from a position with more positive valve overlap to a position with negative valve overlap.

[0039] It will be appreciated that, although the above example suggests reducing positive valve overlap by retarding the timing of intake opening, in alternative examples, positive valve overlap may be reduced by adjusting an exhaust camshaft to advance exhaust valve closing. Furthermore, each of the intake and exhaust camshafts may be adjusted to vary positive valve overlap by varying both the intake and exhaust valve timings. Furthermore, adjustments to the valve timing may be used to vary intake airflow into an associated cylinder.

[0040] The vehicle system 6 may further include a control system 15. The control system 15 is shown having controller 12 and receives information and signals from a plurality of sensors 16 (various examples of which are described herein) from Fig. 1 and sends control signals to several actuators 81 (various examples of which are described herein). The controller 12 uses various actuators from Fig. 1 to adjust engine operation based on the received signals and instructions stored in a memory of the controller. As one example, the sensors 16 may include an exhaust gas sensor 128 (such as a linear UEGO sensor) located upstream of the emission control device, post-turbine pressure sensor 54, and the downstream exhaust gas sensor 162 (such as a particulate matter sensor). As another example, the actuators may include the fuel injector 66, wastegate 82, EGR valve 52, CRV 92, and intake throttle 20. The controller 12 may receive input data from the various sensors, process the input data, and trigger the various actuators in response to the processed input data based on instructions or code programmed therein according to one or more routines. Example control routines are described herein with reference to Fig. 3A-3B and 4.

[0041] As previously described, excessive exhaust pressure, particularly upstream of the exhaust turbine 18, may force one or more exhaust valves of the plurality of cylinders 30 open from a fully closed position. For example, the exhaust valve may be closed during the compression stroke. In this case, inadvertent opening of the exhaust valve due to exhaust backpressure may reduce the pressure within the associated cylinder housing, resulting in a loss of power and efficiency. Accordingly, if the exhaust pressure upstream of the exhaust turbine is estimated to be higher than a threshold pressure, the controller may command a reduction in intake airflow by adjusting a position of the intake throttle 20. By reducing the intake airflow, the exhaust pressure may be reduced.At the same time, the boost pressure in the internal combustion engine can be maintained by adjusting one or more boost pressure actuators such as CRV and wastegate.

[0042] Fig. 2 shows an example control flow 200 for determining the reduction in intake airflow (e.g., restricted airflow) to assist in mitigating higher than desired exhaust pressures. Furthermore, the example control flow also includes a torque control loop that may use the reduced intake airflow as an input to adjust one or more boost actuators to maintain boost pressure despite reduced intake airflow. A controller such as controller 12 of Fig. 1, may execute the control flow based on the signals received from various sensors of the internal combustion engine system (e.g., internal combustion engine system 100). Furthermore, various actuators related to Fig. 1 are used to make adjustments to the internal combustion engine operation.

[0043] Control flow 200 begins by estimating a desired wheel torque. Controller K1 calculates the desired wheel torque at 202 based on inputs of a vehicle speed and a pedal position (e.g., accelerator pedal position). Based on the calculated desired wheel torque and other additional parameters, such as ambient conditions, emission control device status, etc., as well as a maximum available torque, controller K2 determines a desired engine torque at 204, which is provided to controller K3. Controller K2 further provides an input regarding the desired wheel torque to a transmission at 206. Accordingly, a desired gear may be selected based on the input provided to the transmission. Further, controller K3 uses the desired wheel torque input at 208 to adjust EGR control at 210 and spark timing at 212.Specifically, an amount of EGR flow may be modified in response to the desired engine torque. Therefore, the EGR flow may be LP EGR and / or HP EGR. Likewise, spark timing may be adjusted, e.g., advanced or retarded, to provide the desired engine torque. Although not shown, controller K3 may also provide input to a fuel injection system for a desired air-fuel ratio based on the desired engine torque.

[0044] In addition to adjusting the EGR flow and spark timing, controller K3 determines a desired airflow into the engine. This desired intake airflow into the engine may be passed to controller K5 at 214. Similarly, controller K4 determines a desired restricted airflow at 216 based on the inputs regarding exhaust pressure. As previously mentioned, excessive exhaust pressures in the exhaust manifold upstream of the exhaust turbine may impair engine performance. To reduce exhaust pressures, control flow 200 may effect mitigating actions, such as restricting intake airflow. Controller K4 receives the inputs regarding the pre-turbine exhaust pressure and a post-turbine exhaust pressure. The pre-turbine exhaust pressure is the exhaust pressure upstream of the exhaust turbine, such as turbine 18. Fig. 1. As later with reference to Fig. As described in Figure 4, the pre-turbine exhaust pressure can be modeled based on a variety of engine and vehicle parameters. Therefore, the pre-turbine exhaust pressure cannot be estimated by a pressure sensor. On the other hand, the exhaust pressure downstream of the exhaust turbine can be measured by a pressure sensor, such as sensor 54 of Fig. 1. The pre-turbine exhaust pressure and the post-turbine exhaust pressure are used by control K4 at 216 to determine the desired restricted airflow.

[0045] At 214, controller K5 determines the intake airflow restriction based on the desired airflow and the desired restricted airflow. The restricted airflow is compared to an existing actual airflow at 220 to determine the intake throttle position 222 and the desired valve timing 221. Therefore, intake airflow may be restricted by varying an input throttle position and / or by adjusting the valve timing. The actual airflow at 218 may be based on readings from the MAF sensor and MAP sensor. At 224, the actual engine torque is determined based on the intake throttle position, valve timing, EGR flow, spark timing, and other parameters. The actual engine torque is compared to the desired engine torque at 226 to determine the maximum available torque at 230.Furthermore, the maximum available torque also determines adjustments to one or more of the boost actuators at 228. For example, the boost actuators may be adjusted to maintain the desired boost pressures. Still further, the maximum available torque serves as an input to controller K2 to determine the desired engine torque. Based on whether the limited torque is available, additional strategies may be incorporated by the engine controller. For example, the transmission shift strategies may be modified based on the maximum available torque.

[0046] It will be appreciated that the various controls introduced above into the control flow, e.g., controls K1, K2, etc., may be part of the controller 12. Furthermore, the limited intake air flow may also be obtained by adjusting the intake valve controls and / or intake cam controls.

[0047] The Fig. 3A and Fig. 3B show an example routine 300 illustrating intake airflow adjustments in response to excessive exhaust pressure upstream of the exhaust turbine in an internal combustion engine. Specifically, intake airflow may be reduced by adjusting a position of an input throttle. Simultaneously, boost pressure levels in the internal combustion engine may be maintained by modifying the positions of one or more boost actuators. Therefore, routine 300 (and routine 400 of Fig. 4) with regard to the internal combustion engine system Fig. 1, however, it is understood that similar routines may be used with other systems without departing from the scope of the present disclosure. Instructions for executing routine 300 and routine 400 contained herein may be executed by the controller, such as a controller 12 of the Fig. 1, based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the internal combustion engine system, such as the sensors described above with reference to Fig. 1. The controller can control engine actuators of the engine system, such as the actuators of the Fig. 1, to adjust engine operation according to the routines described below.

[0048] At 302, routine 300 estimates and / or measures the existing engine operating conditions. The engine operating conditions may include engine speed, torque request, air-fuel ratio, absolute manifold pressure (MAP), mass airflow, engine temperature, etc. For example, engine speed may be estimated based on an output from a crankshaft sensor. At 304, routine 300 determines a desired boost pressure based on the existing engine conditions. For example, if the torque request is higher than a torque threshold, such as during an engagement event, higher boost pressure may be requested. In another example, lower (or no) boost pressure levels may be desired during deceleration events.

[0049] In response to the desired boost pressure, one or more boost actuators such as the wastegate and / or CRV may be adjusted at 308. For example, if higher boost pressure is desired, an opening of the wastegate may be decreased so that a greater portion of the exhaust gases may be directed to the exhaust turbine. As one example, the controller may send a control signal to an electromechanical actuator coupled to the wastegate to rotate the wastegate to a more closed position from a more open position. Similarly, the CRV may be adjusted from a more open position to a more closed position to decrease an opening of the CRV. Here, the controller may send a control signal to an electromechanical actuator coupled to the CRV to switch the CRV to a more closed position.By closing the CRV, the flow of compressed air through the compressor bypass passage can be significantly obstructed, allowing an increase in boost pressure. Conversely, if lower boost pressure is desired, the wastegate opening can be increased to allow a greater amount of exhaust gases to bypass the exhaust turbine. Additionally, or alternatively, the CRV can be adjusted to a more open position from a more closed position to allow a higher flow of compressed air through the compressor bypass passage. In doing so, a greater amount of boosted air can be diverted away from the intake throttle and the engine cylinders, resulting in a reduction in boost pressure.

[0050] In addition to adjusting the boost actuators 310, valve timing may be altered to enable or disable boosted air blowby. As one example, when higher boost levels are requested, the positive valve overlap between an intake valve and an exhaust valve of a given cylinder (or multiple cylinders) may be increased. For example, a cylinder intake cam and / or intake valve timing may be adjusted from a current timing (e.g., timing corresponding to negative valve overlap) to a timing that enables positive valve overlap. In another example, a higher amount of positive valve overlap may be provided.The controller may communicate with a valve timing system of the internal combustion engine to utilize cams, camshafts, and other actuators coupled to one or more intake valves (and / or exhaust valves) to activate positive valve overlap. By increasing positive valve overlap, boosted air from downstream of the compressor may be delivered through the given cylinder to the exhaust manifold and exhaust turbine without being burned. In doing so, turbine spin-up may be accelerated to allow for higher boost pressures. In another example, if lower boost pressure is desired, negative valve overlap may be provided by adjusting the valve timing. In doing so, the overlap between the intake valve(s) and the exhaust valve(s) may be reduced, e.g.minimized, so that the charged air is not provided via the given cylinder by blowing to the exhaust turbine.

[0051] Then, at step 312, routine 300 estimates the pre-turbine exhaust pressure. Therefore, routine 400 may Fig. 4 to model the exhaust pressure upstream of the exhaust turbine. It will be appreciated that the pre-turbine exhaust pressure is a predicted pressure. Specifically, the pre-turbine exhaust pressure cannot be estimated or measured by a pressure sensor. Instead, the pre-turbine exhaust pressure can be modeled based on a variety of engine and vehicle parameters such as airflow, ignition timing, vehicle speed, air-fuel ratio, etc., as described below with reference to Fig. 4 described in detail.

[0052] Routine 300 then proceeds to 314 to determine if the predicted pre-turbine exhaust pressure is greater than a threshold Thr_P. The threshold Thr_P, in one example, may be based on a pressure that pushes open (and holds open) one or more exhaust valves of the plurality of cylinders in the engine when the one or more exhaust valves would otherwise be closed. Therefore, the exhaust valves, when closed, may include an exhaust cam on the base circle while an associated spring(s) of the exhaust valve(s) holds the exhaust valve(s) closed. More specifically, the threshold may be based on an exhaust pressure upstream of the exhaust turbine that would push the exhaust valve(s) open from its closed position. As one example, during a power stroke in a cylinder of the engine, the intake valve(s) and the exhaust valve(s) may be closed.The exhaust valve(s) must be fully closed. An estimate of the exhaust pressure that may force the exhaust valve(s) open during the power stroke can be used to determine Thr_P.

[0053] In another example, Thr_P may additionally or alternatively be based on wear of a spring of the one or more exhaust valves of the plurality of cylinders over the life of the engine. As one example, springs coupled to the one or more exhaust valves may deteriorate over the life of the engine, affecting a degree of exhaust valve closure. For example, the exhaust valve springs in an older engine may exhibit greater wear and a lower spring rate than the exhaust valve springs in a relatively newer engine. Herein, low exhaust pressure may force open the exhaust valves coupled to the springs that exhibit greater wear. Accordingly, the Thr_P threshold is related to the deterioration of the springs coupled to the exhaust valves.

[0054] Furthermore, the Thr_P threshold may be based on an engine speed. In another example, the Thr_P threshold may be based on intake manifold pressure (MAP). Additionally, the Thr_P threshold may be based on a position of the cams associated with the intake and / or exhaust valves. Changes in cam timing may result in variations in internal cylinder pressure. Specifically, cam timing may affect minimum and maximum cylinder pressures. Consequently, unintended exhaust valve opening may be influenced by varying cam timing.

[0055] If it is determined at 314 that the exhaust pressure upstream of the exhaust turbine is less than the threshold Thr_P, routine 300 proceeds to 316 to maintain existing engine operation. For example, one or more actuators may be held in their positions. Alternatively, one or more actuators may be adjusted to maintain engine operation. Routine 300 then ends.

[0056] However, if the modeled pre-turbine exhaust pressure is determined to be equal to or greater than a threshold, routine 300 proceeds to 318 to reduce airflow into the engine. By reducing intake airflow into the engine, the pre-turbine exhaust pressure may be reduced. Intake airflow into the engine may be reduced by adjusting the intake throttle while maintaining valve timing (e.g., without adjusting valve timing). For example, intake airflow may be reduced by reducing an opening of the intake throttle at 320. In one example, the intake throttle may be adjusted to a largely closed position (e.g., a less open position) from a largely open position.Here, the controller may send a control signal to an electromechanical actuator coupled to the intake throttle in the intake system to rotate the intake throttle to the largely closed position from the largely open position. In another example, the intake throttle opening may be reduced by switching the intake throttle from a fully open position to a position midway between fully closed and fully open. Therefore, the intake throttle opening may be reduced without actuating the VCT system to change the valve timing. Here, the position of the intake throttle may be changed without adjusting the existing valve overlap.

[0057] Optionally, at 322, the VCT system may be adjusted to reduce intake airflow into the engine. Herein, the VCT system may be modified to reduce positive valve overlap, thereby reducing an amount of boosted blowby air flowing through one or more cylinders into the exhaust turbine. Therefore, the VCT system may be adjusted when engine conditions do not allow a change in throttle position to a more closed position when reducing intake airflow to the engine. For example, the engine may be operated at lower speeds (e.g., less than a speed threshold) and at higher engine loads (e.g., higher than a load threshold). Herein, the throttle position may be limited or restricted.As a non-limiting example, when the vehicle is operating at lower engine speeds and the intake throttle is in a largely closed position, the throttle may not be moved to a more closed position. Instead, the valve timing may be changed to achieve the reduced intake airflow. Specifically, the intake valve and / or intake cam timing of one or more cylinders may be adjusted by the VCT system to reduce intake airflow in the associated cylinders. Furthermore, the blowby of boosted air through the cylinder(s) may also be reduced. In doing so, the positive (intake and exhaust) valve overlap between the intake valve and the exhaust valve of one or more cylinders may be modified (e.g.,reduced) to reduce intake air flow into the cylinders and reduce blow-by of boosted air.

[0058] Although not shown in routine 300, HG-EGR may also be reduced in response to the detection of excessive exhaust pressures in the pre-turbine region. In this case, HP-EGR flow may be reduced (e.g., by reducing an opening of the HP-EGR valve 86 from Fig. 1) and / or in addition to adjusting the intake throttle position. It will be appreciated that reducing HP EGR flow may have a slower effect on pre-turbine exhaust pressure relative to reducing intake air flow via closing the inlet throttle.

[0059] Further, at 324, routine 300 includes maintaining boost pressure levels. Therefore, boost pressure levels may be maintained while reducing intake airflow. At 326, wastegate opening may be reduced to maintain boost pressure. As one example, the wastegate may be adjusted to a fully closed position from a largely open position, allowing a higher amount of exhaust gas to spin the exhaust turbine. Alternatively, the wastegate may be moved to the fully closed position from a largely closed position. In another example, the wastegate may be switched to the largely closed position from a less closed position. Additionally or alternatively, the CRV may be adjusted to a position that decreases the opening of the CRV at 328.For example, the CRV may be adjusted to the fully closed position from a mostly closed position. In another example, the CRV may transition to the fully closed position from a mostly closed position, so that a smaller amount of compressed air from the intake throttle is diverted via the compressor bypass passage. In yet another example, the CRV may be switched from a less closed position to the mostly closed position.

[0060] Next, at 330, a timer is started to monitor a time period from which airflow is reduced. Specifically, the time period since the intake throttle opening was reduced may be monitored. Optionally, a duration since intake airflow was reduced may be tracked by adjusting valve timing. The timer may monitor a number of combustion events since the intake throttle opening was reduced. In another example, the timer may monitor a duration of vehicle travel since the intake airflow was reduced. In yet another example, the timer may monitor a vehicle travel distance. At 332, routine 300 may determine whether a threshold duration Thr_D has elapsed.In one example, the threshold duration may be a threshold number of combustion events since adjusting the intake throttle opening in response to the pre-turbine exhaust pressure exceeding the Thr_P threshold. In another example, the threshold duration Thr_D may be a threshold duration of vehicle travel after reducing intake airflow. For example, a threshold duration of vehicle travel may be 60 seconds. In another example, a threshold duration of vehicle travel may be 30 seconds. In yet another example, the threshold duration Thr_D may be a threshold distance of vehicle travel. For example, Thr_D may be 500 ft. In another example, the threshold duration of vehicle travel after reducing the intake throttle opening in response to the pre-turbine exhaust pressure exceeding the Thr_P threshold may be 200 ft.

[0061] If it is determined at 332 that the threshold duration has not passed since reducing the intake throttle opening in response to the pre-turbine exhaust pressure exceeding the threshold Thr_P, routine 300 may proceed to 334 to maintain the reduced intake throttle opening. Therefore, control may send a signal to the electromechanical actuator coupled to the intake throttle to maintain the intake throttle at its position assumed at 320. Routine 300 then returns to 332.

[0062] On the other hand, if it is determined at 332 that the threshold duration Thr_D has elapsed, routine 300 proceeds to 336 to confirm whether the pre-turbine exhaust pressure has been reduced below the threshold Thr_P. If so, routine 300 proceeds to 338 to adjust the intake throttle position based on existing operating conditions and then ends. In other words, the intake throttle is maintained at a position that reduces intake airflow until the pre-turbine exhaust pressure is reduced below the threshold Thr_P. Once the pre-turbine exhaust pressure is less than the threshold, the intake throttle is restored to a position desired for the existing engine operating conditions. In one example, when the engine is operating at higher boost levels, the intake throttle opening may be increased at 338.In another example, when the engine is operating at a lower torque demand, the intake throttle may be adjusted to a more closed position. Therefore, there may be situations where the intake throttle position is not changed at 338 if the intake airflow entering the intake manifold is the desired one based on the existing engine conditions.

[0063] However, if it is determined at 336 that the pre-turbine exhaust pressure remains higher than the threshold (Thr_P), routine 300 proceeds to 340 to reduce boost levels. Therefore, boost levels may only be reduced after the threshold duration of reduced intake airflow has been exceeded. Accordingly, at 342, an opening of the wastegate is increased to allow a greater portion of the exhaust gases to bypass the exhaust turbine. In one example, the controller may communicate a control signal to the electromechanical actuator coupled to the wastegate to adjust the position of the wastegate from a largely closed position to a largely open position. In another example, the wastegate may be adjusted from a fully closed position to a largely open position.In yet another example, the wastegate may be switched to a fully open position from a fully closed position. Further, at 344, an opening of the CRV is also increased to divert a greater portion of pressurized air from downstream of the compressor to upstream of the compressor. Therefore, in addition to opening the wastegate in response to the pre-turbine exhaust pressure remaining higher than the threshold, the CRV may be opened even after the threshold duration has passed. The controller may communicate a control signal to the electromechanical actuator coupled to the CRV to adjust the position of the CRV from a largely closed position to a largely open position. It should be noted that in other examples, the CRV may be opened as an alternative to opening the wastegate to reduce the pre-turbine exhaust pressure and boost pressure levels.By opening (e.g. increasing the opening) one or more of the wastegate and CRV, the boost pressure levels can be reduced.

[0064] Thereafter, at 346, routine 300 maintains the reduced boost levels until the pre-turbine exhaust pressure is less than the threshold Thr_P. Maintaining the reduced boost levels may include maintaining the increased wastegate and CRV opening. Specifically, the wastegate and CRV positions assumed at 342 and 344 may be maintained until the exhaust flow upstream of the exhaust turbine is less than the threshold. Therefore, once the pre-turbine exhaust pressure is below the threshold, the boost levels may be adjusted (e.g., restored) based on existing engine conditions. Furthermore, once the pre-turbine exhaust pressure is less than the threshold, the intake throttle (and valve timing) may be adjusted based on existing engine conditions. Thereafter, routine 300 ends.

[0065] In this way, excessive pre-turbine exhaust pressures can be reduced and at the same time the likelihood of misfire, knock, etc. in the engine can be reduced. Intake air flow can be reduced in response to detecting higher than desired pre-turbine exhaust pressures. The intake throttle can first be adjusted to a more closed position to reduce intake air flow into the engine. If an intake throttle opening cannot be reduced, the valve timing can selectively be adjusted to reduce intake air flow. At the same time, boost pressure levels can be maintained by closing the wastegate and / or CRV. If the pre-turbine exhaust pressure does not decrease within a threshold period after reducing intake air flow (e.g.by adjusting the intake throttle), boost pressure levels can be reduced in addition to reducing intake airflow.

[0066] It will be appreciated that intake airflow control via the intake throttle can establish a target intake manifold pressure. Furthermore, intake throttle adjustments can serve as a primary remedy for excessive exhaust pressures because the intake throttle can quickly control intake airflow. Meanwhile, changes in valve timing and boost pressure levels can serve as secondary remedies because these changes cause slower changes in intake airflow. In other words, valve timing adjustments via the VCT system and / or modifying boost pressure levels via the boost actuators do not cause rapid changes in intake airflow.

[0067] Fig. 4 shows the exemplary routine 400 for modeling the pre-turbine exhaust pressure based on a plurality of engine and vehicle parameters. Specifically, a controller, e.g., controller 12, may predict a pre-turbine exhaust pressure based on a model rather than measuring the pre-turbine exhaust pressure via a sensor. Therefore, costs can be reduced by reducing components. Routine 400 is described with respect to the engine system of Fig. 1, however, it is understood that similar routines may be used with other systems without departing from the scope of the present disclosure. Instructions for executing routine 400 may be provided by the controller, such as a controller 12 of the Fig. 1, based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the internal combustion engine system, such as the sensors described above with reference to Fig. 1 are described.

[0068] At 404, routine 400 includes obtaining data regarding engine airflow (e.g., intake airflow), exhaust flow, e.g., exhaust gas flow rate, ignition timing, air-fuel ratio, cam timing, intake manifold pressure (e.g., MAP), intake manifold temperature, and vehicle speed. Specifically, the controller may receive output from various sensors. For example, a measurement of intake airflow may be received from the MAF sensor. As another example, measurements of intake manifold temperature may be received from a sensor such as a MAT sensor 127. Fig. 1 can be received.

[0069] Thereafter, an additional output regarding the post-turbine exhaust pressure is received at 406. A pressure sensor such as pressure sensor 54 from Fig. 1 measure the exhaust pressure prevailing downstream of the exhaust turbine. Routine 400 further includes receiving data regarding the soot load of the particulate filter in the exhaust line at 408. For example, a particulate matter sensor such as sensor 162 of Fig. 1 transmit an estimate of the charge of the particulate filter, e.g. from particulate filter 72 Fig. 1. Therefore, higher exhaust backpressure upstream of the exhaust turbine can be generated by a higher particulate filter charge. As previously described, the particulate filter can trap soot and / or ash particles, which can increase the particulate filter charge.

[0070] At 410, routine 400 includes receiving estimates or measurements of boost pressure levels. For example, the controller may receive the output from a throttle inlet pressure (TIP) sensor, such as TIP sensor 129 of Fig. 1, as a measurement of existing boost pressure levels. At 412, routine 400 includes modeling the pre-turbine exhaust pressure based on data obtained at 404, 406, 408, and 410. Therefore, the pre-turbine exhaust pressure is predicted based on the particulate filter soot load, boost pressure levels, post-turbine exhaust pressure, engine airflow, intake manifold pressure, intake manifold temperature, vehicle speed, air-fuel ratio, exhaust flow, cam timing, and spark timing.

[0071] Accordingly, an example method for an internal combustion engine may include adjusting an intake throttle in response to the pre-turbine exhaust pressure being greater than a threshold, such as Thr_P from routine 300, without reducing the boost pressure level and while maintaining valve timing. Therefore, the pre-turbine exhaust pressure may be a predicted pressure, and the pre-turbine exhaust pressure may be modeled based on a post-turbine exhaust manifold pressure. Further, the post-turbine exhaust manifold pressure may be estimated from an exhaust pressure sensor. The internal combustion engine may include a soot filter coupled downstream of a turbocharger turbine, and the pre-turbine exhaust pressure may be further modeled based on the soot filter's soot load and the boost pressure level.Furthermore, the pre-turbine exhaust pressure may be further modeled based on one or more of engine air flow, exhaust flow, ignition timing, air-fuel ratio, cam timing, manifold temperature, manifold pressure, and vehicle speed.

[0072] It should be noted that adjusting includes reducing an opening of the intake throttle until the pre-turbine exhaust pressure is below the threshold, where the threshold is based on a pressure needed to force open a closed exhaust valve. Adjusting may include reducing an opening of the intake throttle for a threshold duration and may be performed in response to the pre-turbine exhaust pressure remaining greater than the threshold after the threshold duration, thereby reducing the boost pressure level by adjusting an exhaust wastegate. Alternatively or additionally, a compressor recirculation valve (CRV) may also be adjusted. Adjusting may further include reducing the opening of the intake throttle during closing of the exhaust wastegate.Adjusting may also include reducing the intake throttle opening during closing of the CRV to maintain boost pressure levels. The internal combustion engine may be coupled in a vehicle, such as a vehicle system 6 of FIG. Fig. 1, and the threshold duration may include a threshold number of engine combustion events, a threshold duration of vehicle travel, and a time taken for a threshold distance of vehicle travel. Reducing the boost pressure level by adjusting the exhaust wastegate may include increasing an opening of the exhaust wastegate to reduce the boost pressure level until the pre-turbine exhaust pressure is less than the threshold. As shown in routine 300, boost pressure levels may also be reduced by increasing the opening of the CRV in addition to, or as an alternative to, increasing the opening of the wastegate.

[0073] In Fig. 5 is an exemplary Fig. depicting adjustments to an intake throttle valve of an internal combustion engine in response to excessive exhaust pressures, such as an internal combustion engine system 100 of Fig. 1 contained in a vehicle. Therefore, the Fig. regarding the system Fig. 1. The Fig. shows the pre-turbine exhaust pressure at plot 502, loading of a soot filter, such as soot filter 72 from Fig. 1 at plot 504, intake air flow at plot 506, intake throttle position at plot 508, boost pressure at plot 510, wastegate status (e.g., open, closed, or in between) at plot 512, and pedal position (PP) at plot 514. Line 501 represents the pre-turbine exhaust pressure threshold Thr_P, while line 503 represents a soot filter charge threshold. Therefore, line 503 is shown to illustrate an increase in pre-turbine exhaust pressure, and the charge threshold may or may not be used without departing from the scope of the present disclosure. All plots are shown as a function of time along the x-axis. Further, time increases from the left of the x-axis to the right. It should be noted that elements aligned with a common time on the curve, e.g., the throttle body, are plotted as follows: B. time t1, take place simultaneously, including e.g.that one parameter increases while another parameter decreases.

[0074] Before t1 (e.g., between t0 and t1), the engine may be operating unboosted with the throttle released (plot 514). For example, the engine may be idling. The wastegate may be largely open (e.g., fully open position), allowing a significant amount of exhaust gases to bypass the exhaust turbine. The intake throttle may be substantially closed (e.g., within 1% of fully closed), and nominal intake airflow may be present. Therefore, at engine idle, a significantly lower intake airflow rate may be present (plot 506). The exhaust pressure upstream of the exhaust turbine (plot 502) may be lower, while the soot filter charge may be moderately high.

[0075] At t1, the pedal is fully depressed while an engagement event is initiated by the vehicle operator. The torque demand (not shown) may increase abruptly due to and in response to the engagement; the intake throttle is adjusted from the largely closed position prior to t1 to a more open position. As an example, the intake throttle may be adjusted to the fully open position at t1, allowing a significant increase in intake air flow into the engine. Additionally, the wastegate is adjusted from the more open position at t0 to a largely closed position at t1 in response to an engagement event. Accordingly, boost pressure increases steadily after t1, producing a stepwise increase in pre-turbine exhaust pressure. As previously discussed with respect to Fig. As described in Figure 4, a pre-turbine exhaust pressure can be based on boost pressure levels, soot filter charge, and other parameters. The additional exhaust flow into the soot filter between t1 and t2 causes the soot filter charge to increase. As the soot filter charge increases, the pre-turbine exhaust pressure simultaneously increases and crosses the threshold (line 501) at t2. Therefore, the soot filter charge also exceeds the charge threshold (line 503) at t2.

[0076] Therefore, at t2, in response to the increase in pre-turbine exhaust pressure above the threshold (line 501), intake air flow may be reduced. To reduce intake air flow at t2, an intake throttle opening is reduced by switching the intake throttle from a more open position at t1 to a less open position at t2. Reducing the intake throttle opening may decrease intake air flow relatively quickly, as illustrated at t2 on plot 506. Therefore, as the intake throttle opening decreases, intake air flow immediately reduces. At the same time, desired boost pressures are maintained by decreasing the wastegate opening at t2. For example, the wastegate may be adjusted from a largely closed position at t1 to a fully open position at t2.In another example, the wastegate valve may transition from a position halfway between fully open and fully closed to a relatively more closed position. Therefore, exhaust gas from the engine may be directed to the exhaust turbine. Although not shown, a compressor bypass valve (or compressor recirculation valve) may also be adjusted to a more closed position to maintain boost pressures. Accordingly, boost pressure may not vary between t2 and t3.

[0077] The intake throttle valve may be held at its more closed position of t2 for a threshold duration T_D, which is Fig. T_D may correspond to Thr_D of routine 300. The threshold duration may be the duration between t2 and t3. Furthermore, the threshold duration may be a threshold number of engine combustion events, a threshold duration of vehicle travel, and a time taken for a threshold distance of vehicle travel.

[0078] Reducing intake airflow may reduce pre-turbine exhaust pressure, as illustrated between t2 and t3. Further, pre-turbine exhaust pressure reduces below the threshold at t3. As pre-turbine exhaust pressure decreases below the threshold within the threshold duration T_D, boost pressure levels may be maintained at desired levels. Further, in response to pre-turbine exhaust pressure decreasing below the threshold at t3, the intake throttle is adjusted from its more closed position at t2 to a position based on existing operating conditions at t3. As illustrated, the pedal remains fully depressed at t3. Accordingly, the intake throttle may be adjusted to the fully open position at t3, allowing an increase in intake throttle opening and achieving a corresponding increase in intake airflow.Furthermore, the wastegate opening can be increased by switching the wastegate from the fully closed position assumed at t2 to the largely closed position. In other words, the wastegate can be adjusted from a less open position to a more open position. Therefore, the wastegate position at t1 can be restored because the existing engine conditions continue to include high boost pressure.

[0079] At t4, the current engine cycle ends (e.g., from t0 to t4). A number of different engine cycles may occur between t4 and t5. Therefore, the engine cycle between t5 and t8 may occur after a significant period since t4. The soot filter may be regenerated between t4 and t5, so that the load at t5 is approximately the same as at t0. Furthermore, the engine may operate at moderately high boost pressure levels with the pedal largely depressed. Specifically, the desired boost pressure at t5 may be slightly lower than the desired boost pressure between t1 and t4. Similarly, the pedal position may be more depressed at t1 than at t5. The wastegate may be in a more closed position to accommodate the moderately higher boost pressure levels. Furthermore, the intake throttle may be largely open to accommodate higher intake airflow.Since the desired boost pressure level is lower than between t1 and t4, the intake air flow may be slightly lower than that provided from t1 to t2.

[0080] Between t5 and t6, the soot sensor charge increases toward the charge threshold, reaching the charge threshold at t6. The moderately higher boost pressures and higher soot filter charge may cause the pre-turbine exhaust pressure to increase above the threshold (line 501) at t6. Other engine parameters may also affect the increase in pre-turbine exhaust pressure. In response to the pre-turbine exhaust pressure being higher than the threshold, the intake throttle is adjusted to a more closed position at t6 relative to the intake throttle position at t5. Reducing the intake throttle opening creates a reduction in intake airflow at t6. Further, boost pressure may be maintained at desired levels by adjusting the wastegate to a more closed position at t6 relative to t5.

[0081] Between t6 and t7, the threshold duration may elapse. However, the pre-turbine exhaust pressure remains higher than the threshold even after the threshold duration T_D has elapsed at t7. Accordingly, boost levels are reduced at t7 by adjusting the wastegate. Specifically, boost levels may be reduced by increasing the wastegate opening. As illustrated, the wastegate is adjusted from the more closed position to a more open position (or a less closed position). In another example, the wastegate may transition from a fully closed position to a more open position. In addition (or as an alternative) to adjusting the wastegate, the opening of the CRV may also be increased to reduce boost levels.The subsequent reduction in boost levels helps reduce pre-turbine exhaust pressure, and at t8, the pre-turbine exhaust pressure drops below the threshold (line 501). Consequently, the intake throttle, wastegate, and CRV may each be adjusted to different positions based on the existing engine conditions. As shown, because the pedal position is mostly depressed, the intake throttle is restored to its largely open position from t5 at t8. Further, the wastegate is adjusted to a more closed position at t8 by decreasing the wastegate opening. Although not shown, the CRV opening may also be decreased in response to the pre-turbine exhaust pressure decreasing below the threshold and the pedal position decreasing at t8. Therefore, decreased boost levels may be maintained until the pre-turbine exhaust pressure is less than the threshold.The boost pressure actuators are then adjusted according to existing engine conditions.

[0082] Fig. 6 shows Fig. , which represents adjustments to intake air flow via one or more changes in intake throttle position and positive valve overlap between an intake valve and an exhaust valve. Therefore, the Fig. regarding the system Fig. 1. The Fig. shows the pre-turbine exhaust pressure at plot 602, the loading of a soot filter, such as soot filter 72 from Fig. 1 at plot 604, the intake air flow at plot 606, the intake throttle position at plot 610, the positive valve overlap at plot 614, the engine load at plot 616, the engine speed (Ne) at plot 618, and the pedal position (PP) at plot 620. Line 601 represents the pre-turbine exhaust pressure threshold Thr_P, while line 603 represents a soot filter loading threshold. Therefore, line 603 is shown for illustrative purposes of an increase in pre-turbine exhaust pressure, and the loading threshold may or may not be used without departing from the scope of the present disclosure. Line 613 represents a threshold load, line 615 represents a first speed threshold, and line 617 represents a second speed threshold. Accordingly, the second speed threshold may be higher than the first speed threshold.All plots are shown as a function of time along the x-axis. Furthermore, time increases from the left of the x-axis to the right. Note that elements aligned with a common time on the curve, such as time t1, occur simultaneously, including, for example, one parameter increasing while another decreases.

[0083] It should also be noted that the positive valve overlap at plot 614 represents the positive intake to exhaust valve overlap as discussed earlier with respect to Fig. 1. Therefore, a positive valve overlap between an intake valve and an exhaust valve of a given cylinder may be higher when the intake valve and the exhaust valve are open simultaneously and for a longer period of time. The positive valve overlap between the intake valve and the exhaust valve may be lower when the intake valve and the exhaust valve are open simultaneously and for a shorter period of time. In some examples, a lower positive valve overlap may also indicate a negative valve overlap.

[0084] At t0, the pedal position (e.g., accelerator pedal) may be fully released and the engine may be idling (as indicated at plot 618 at idle). For example, an engine cold start has occurred. During engine idle between t0 and t1, intake air flow may be lower with the intake throttle at a more closed position, and engine load may be lower. Positive valve overlap may be higher to accelerate catalyst shutdown temperature achievement. Therefore, the engine may be operated such that the intake valve(s) and exhaust valve(s) in one or more cylinders are open simultaneously (e.g., between the exhaust stroke and the following intake stroke), allowing intake air to be blown through the one or more cylinders to the exhaust port.The soot filter charge may be relatively high at t0 and the pre-turbine exhaust pressure may be lower than during engine idle.

[0085] At t1, the pedal is fully depressed while the engagement event occurs. In response to the engagement event, engine speed increases sharply, and there is an increase in engine load. Therefore, engine speed may now be higher than the first speed threshold (line 615). However, engine load remains below the threshold load (line 613). To provide a desired torque request, the intake throttle is switched to a more open position relative to idle. For example, the intake throttle may now be fully open (from a largely closed position) to allow for a higher intake airflow rate. Accordingly, as plot 606 shows, intake airflow into the engine rapidly increases in response to the increased intake throttle opening.The positive valve overlap is maintained at its higher setting (via control signals from a controller to the VCT system) to accelerate turbine ramp-up for the engagement event, as well as catalyst deactivation. The higher positive valve overlap may allow pressurized intake air to be routed across the cylinders from downstream of the compressor to upstream of the exhaust turbine to provide additional mass flow to ramp up the exhaust turbine at t1. Once turbocharger ramp-up is achieved, the positive valve overlap may be reduced, as shown at 609. However, a higher torque demand may still exist due to pedal position and higher engine speed. The higher torque demand may create a stepwise increase in pre-turbine exhaust pressure between t1 and t2.As engine operation continues between t1 and t2, the soot filter load steadily increases until t2, where the load threshold is reached. Furthermore, as the soot filter load increases, the pre-turbine exhaust pressure simultaneously increases and crosses the threshold Thr_P, represented by line 601, at t2.

[0086] In response to the pre-turbine exhaust pressure being higher than the threshold, intake airflow may be reduced. To reduce intake airflow at a faster rate, the intake throttle may be adjusted to provide a reduced opening for the intake air. Specifically, the intake throttle is switched from an open position at t1 to a more closed position at t2. As one example, the intake throttle may be adjusted from a less closed position to the more closed position. As another example, the intake throttle may be moved from a fully open position to a position halfway between fully open and fully closed at t2. Here, because the engine speed is higher than the first speed threshold, only the intake throttle may be adjusted to resist excessive exhaust pressure.Furthermore, the positive valve overlap may be less after turbocharger ramp-up is complete. Accordingly, the positive valve overlap (at the overlap at 609) is maintained, and therefore neither intake valve timing nor intake cam timing can be changed at t2. As previously stated, the valve timing changes may have a slower response to intake airflow and may accordingly be used as a secondary remedial action (e.g., only when engine conditions do not permit a change in intake throttle position).

[0087] The pre-turbine exhaust pressure gradually decreases in response to the reduction in intake airflow between t2 and t3, such that the pre-turbine exhaust pressure decreases below the threshold at t3. Accordingly, at t3, the intake throttle may be reset to its previous position, e.g., that of t1, while the positive valve overlap may be decreased if the catalyst may have reached shutdown temperatures. The intake throttle may be adjusted to a different position based on existing engine conditions after the pre-turbine exhaust pressure has decreased below the threshold. At t4, the engine drive cycle that began at t0 ends.

[0088] A long duration may follow between t4 and t5, during which several different engine drive cycles may occur. At t5, another engine cycle may occur where the pedal position is pressed but not fully depressed, as between t1 and t4. Here, the engine speed may be less than a second speed threshold (line 617), but the engine load may be higher than the load threshold (line 613). For example, an air conditioning system may be activated. Further, the valve overlap may be moderate. Even further, the intake airflow may be at a medium level (plot 610) while the intake throttle is approximately half-open (or half-closed), e.g., halfway between the fully open and fully closed positions to enable the desired engine speed and load.The soot load in the soot filter is higher, and the exhaust pressure upstream of the exhaust turbine is lower. Between t5 and t6, the pedal and intake throttle positions remain constant (e.g., no change), but the soot load continues to increase during engine operation. Accordingly, the pre-turbine exhaust pressure rises and exceeds the threshold at t6.

[0089] The intake throttle, positioned at half-open, may provide a desired intake airflow into the engine based on, respectively, pedal position, engine load greater than the load threshold (line 613), and engine speed below the second speed threshold (line 617) at t6. Here, engine conditions (e.g., pedal position) may not allow a reduction in the intake throttle opening. Therefore, the intake throttle may not be adjusted to a more closed position to reduce intake airflow in response to pre-turbine exhaust pressure exceeding the threshold. Accordingly, a second remedial action to reduce positive valve overlap may be initiated at t6 to reduce intake airflow.As shown at plot 614, positive valve overlap is reduced at t6 by adjusting one or more of intake valve timing, intake cam timing, exhaust valve timing, and exhaust cam timing. Consequently, the amount of blow-by of pressurized (or boosted) air from downstream of the compressor to the exhaust passage may be reduced, enabling a reduction in intake airflow into the engine. It is understood that adjustments to positive valve overlap are incidental to intake throttle adjustments in response to pre-turbine exhaust pressures exceeding the threshold.

[0090] It will be appreciated that if engine conditions permit a change in intake throttle position at t6, intake airflow may be reduced through a combination of adjustments to the intake throttle and positive valve overlap. For example, positive valve overlap may be reduced by a lesser amount, as illustrated by dashed line 615 (relative to solid line 614) between t6 and t7. At the same time, the intake throttle opening may be reduced by a lesser amount (relative to the reduction in opening at t2), as illustrated by dashed line 613 between t6 and t7. Here, the intake throttle may be adjusted from a more open position, e.g., a fully open position, to a more closed position.The combination of modifications may reduce intake air flow more than shown by the dashed line 607 between t6 and t7.

[0091] In another example, when the engine speed is higher than the second speed threshold but less than the first speed threshold prior to t6, as shown at plot 619 (small dashed lines), and when the engine load is higher than the load threshold, the intake throttle may have a slightly more open position between t5 and t6, as shown at plot 611 (small dashed lines). Therefore, plot 611 shows the position variation of the intake throttle when the engine speed is between the first speed threshold and the second speed threshold, as shown by plot 619. Plot 605 (small dashes) shows the variation in intake airflow when the intake throttle position is that shown at plot 611.Since the engine speed is between the first speed threshold and the second speed threshold, the intake airflow into the engine may be higher than that (plot 610 between t5 and t7) when the engine speed is less than the second threshold (plot 618 between t5 and t7). In this case, the intake throttle and the positive valve overlap may each be adjusted in parallel to mitigate the excessive exhaust pressure observed at t6. Accordingly, at t6, the intake airflow may be reduced by adjusting the intake throttle at t6 to a more closed position relative to that at t5 (plot 611). At the same time, the positive valve overlap may be reduced to reduce intake airflow (as shown at plot 614).

[0092] Accordingly, during a first condition (e.g., when the engine speed is higher than the first threshold), only the intake throttle may be adjusted to reduce intake airflow in response to the pre-turbine exhaust pressure being higher than Thr_P. During a second condition, such as when an engine speed is less than the second threshold and the engine load is higher than the load threshold, only the positive valve overlap may be used to reduce intake airflow. During a third condition, such as when an engine speed is between the first speed threshold and the second speed threshold while the engine load is higher than the load threshold, both the intake throttle and the positive valve overlap may be used in combination to reduce intake airflow. Referring again to Fig. In response to the reduction in positive valve overlap at t6, intake airflow may gradually reduce (e.g., versus a faster response to intake throttle opening adjustments at t2), as illustrated at plot 606 between t6 and t7. Further, pre-turbine exhaust pressure may also decrease or fall below the threshold at t7. Therefore, at t7, various actuators may be adjusted based on existing engine conditions. As an example, positive valve overlap may be slightly increased from that between t6 and t7 (solid line). In response to the increase in positive valve overlap, intake airflow may increase (albeit gradually) at t7.

[0093] Therefore, an internal combustion engine system includes an internal combustion engine having an inlet and an outlet, an engine cylinder having an intake valve and an exhaust valve, a turbocharger for providing a boosted intake airflow, the turbocharger having an exhaust turbine, an intake throttle, an exhaust wastegate, an intake cam for adjusting intake valve timing, a particulate filter coupled downstream of the turbine, and a pressure sensor coupled downstream of the turbine.The engine system also includes a controller with computer-readable instructions stored in non-transitory memory for operating the engine with boost enabled and with positive valve overlap for blowing an amount of boosted air from the engine intake to the engine exhaust via an engine cylinder, wherein the exhaust pressure upstream of the turbocharger turbine is estimated based on the soot load of the particulate filter, and wherein, when the estimated exhaust pressure is greater than a threshold, one or more of the intake airflows is reduced using the intake throttle and the amount of boosted air blown.Reducing includes only reducing intake airflow via the intake throttle when the engine speed is higher than a first speed threshold, only reducing the amount of blown-by boosted air when the engine speed is less than a second speed threshold and the engine load is higher than a load threshold, and reducing each intake airflow via the intake throttle and the amount of blown-by boosted air when the engine speed is between the first speed threshold and the second speed threshold and the engine load is higher than the load threshold. Reducing the amount of blown-by boosted air includes adjusting timing of the intake cam to reduce positive valve overlap between the intake valve and the exhaust valve.

[0094] In another embodiment, a method for an internal combustion engine may include treating engine exhaust with a particulate filter, wherein the particulate filter is disposed downstream of a turbocharger turbine, estimating exhaust pressure downstream of the turbocharger turbine based on the soot load on the particulate filter, and reducing intake airflow when the estimated exhaust pressure is greater than a threshold. The threshold is based on a pressure that forces an exhaust valve open when the exhaust valve would otherwise be closed. Further, in any of the above examples, the threshold may additionally or optionally be based on exhaust valve spring wear over a lifetime of the internal combustion engine. Furthermore, in any or all of the above examples, the threshold may additionally or optionally be based on one or more of engine speed and intake manifold pressure.Still further, in any or all of the above examples, the threshold may additionally or optionally be based on cam timing. Therefore, in any or all of the above examples, reducing intake airflow during a first condition may additionally or optionally include reducing intake airflow via adjustments to an intake throttle opening and, during a second condition, reducing intake airflow via adjustments to an intake valve and / or intake cam timing.

[0095] An example method for an internal combustion engine may include adjusting an intake throttle in response to pre-turbine exhaust pressure being greater than a threshold, without reducing the boost pressure level and while maintaining valve timing. In the above example, the pre-turbine exhaust pressure may additionally or optionally be a predicted pressure. In any or all of the above examples, the pre-turbine exhaust pressure may additionally or optionally be modeled based on a post-turbine exhaust manifold pressure. In any or all of the above examples, the internal combustion engine may additionally or optionally include a soot filter coupled downstream of a turbocharger turbine, wherein the pre-turbine exhaust pressure may further be additionally or optionally modeled based on the soot filter's soot load and the boost pressure level.In any or all of the above examples, the pre-turbine exhaust pressure may additionally or optionally be modeled based on one or more of engine airflow, exhaust flow, ignition timing, air-fuel ratio, cam timing, manifold temperature, vehicle speed, and manifold pressure. In any or all of the above examples, the post-turbine exhaust manifold pressure may additionally or optionally be estimated from an exhaust pressure sensor. In any or all of the above examples, adjusting may additionally or optionally include reducing an opening of the intake throttle until the pre-turbine exhaust pressure is below the threshold, where the threshold is based on a pressure needed to force open a closed exhaust valve.In any or all of the above examples, adjusting may additionally or optionally include reducing an intake throttle opening for a threshold duration and may occur in response to the pre-turbine exhaust pressure remaining greater than the threshold after the threshold duration, thereby additionally or optionally reducing the boost pressure level by adjusting an exhaust wastegate. In any or all of the above examples, adjusting may additionally or optionally further include reducing the intake throttle opening during the closing of the exhaust wastegate.In any or all of the above examples, the engine may additionally or optionally be coupled to a vehicle, and the threshold duration may additionally or optionally include one of a threshold number of engine combustion events, a threshold duration of vehicle travel, and a time taken for a threshold distance of vehicle travel. In any or all of the above examples, reducing the boost pressure level by adjusting the exhaust wastegate may additionally or optionally include increasing an opening of the exhaust wastegate to reduce the boost pressure level until the pre-turbine exhaust pressure is less than the threshold.

[0096] In this way, exhaust pressures that are higher than desired can be reduced. The technical effect of reducing excessive exhaust pressures is that the cylinders' exhaust valves are not forced open when the exhaust valves are fully closed. Accordingly, problems such as misfire, pre-ignition, etc. can be reduced. By adjusting the intake throttle to reduce intake airflow in response to excessive exhaust pressures, a faster mitigation action can be initiated. Even further, boost pressure levels can be maintained by operating one of the boost pressure actuators while reducing intake airflow. By maintaining boost pressures at desired levels, drivability can be improved without degrading the vehicle operator experience.

[0097] It should be appreciated that the exemplary control and estimation routines contained herein may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-volatile memory and may be executed by the control system, including the controller in combination with the various sensors, actuators, and other engine hardware. The particular routines described herein may represent one or more of a number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Thus, various illustrated acts, operations, 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 exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy used. Furthermore, the described acts, operations, and / or functions may graphically represent code to be programmed into the non-transitory memory of the computer-readable storage medium in the internal combustion engine control system, wherein the described acts are implemented by executing the instructions in a system including the various engine hardware components along with the electronic controller.

[0098] It is understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered limiting, as numerous variations are possible. The above technology is applicable, for example, to V6, I4, I6, V12, horizontally opposed 4-cylinder, and other internal combustion 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.

[0099] The following claims particularly point out certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims should be construed as encompassing the inclusion of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application. Such claims, whether their scope is broader, narrower, the same, or different from that of the original claims, are also considered to be included within the subject matter of the present disclosure.

Claims

[1] Method for an internal combustion engine (10), comprising: Adjusting an intake throttle valve (20) that responds to a pre-turbine exhaust pressure of more than a threshold without reducing the boost pressure level by adjusting the boost pressure actuators, while maintaining the valve timing of intake valves (62) and exhaust valves (64), wherein adjusting includes reducing an opening of the intake throttle (20) until the pre-turbine exhaust pressure is below the threshold, the threshold being based on a pressure required to force open a closed exhaust valve. [2] The method of claim 1, wherein the pre-turbine exhaust pressure is a predicted pressure. [3] The method of claim 2, wherein the pre-turbine exhaust pressure is modeled based on a post-turbine exhaust manifold pressure. [4] The method of claim 3, wherein the internal combustion engine (10) includes a soot filter (72) coupled downstream of a turbocharger turbine (18), and wherein the pre-turbine exhaust pressure is further modeled based on the soot load of the soot filter (72) and the boost pressure level. [5] The method of claim 4, wherein the pre-turbine exhaust pressure is further modeled based on one or more of engine airflow, exhaust flow, ignition timing, air-fuel ratio, cam timing, manifold temperature, vehicle speed, and manifold pressure. [6] The method of any of claims 3-5, wherein the post-turbine exhaust manifold pressure is estimated from an exhaust pressure sensor (54). [7] A method according to any preceding claim, wherein adjusting includes reducing an opening of the intake throttle (20) for a threshold duration, and the boost pressure level is reduced by adjusting an exhaust wastegate if the pre-turbine exhaust pressure remains greater than the threshold after the threshold duration. [8] The method of claim 7, wherein adjusting further comprises reducing the opening of the intake throttle (20) during closing of the exhaust wastegate. [9] The method of claim 7 or 8, wherein the internal combustion engine (10) is arranged in a vehicle and wherein the threshold duration includes a threshold number of internal combustion engine combustion events, a threshold duration of the vehicle travel, and a time required for a threshold distance of the vehicle travel. [10] The method of claim 9, wherein reducing the boost pressure level by adjusting the exhaust wastegate includes increasing an opening of the exhaust wastegate to reduce the boost pressure level until the pre-turbine exhaust pressure is less than the threshold. [11] Method for an internal combustion engine (10), comprising: Treating internal combustion engine exhaust with a particulate filter (72), wherein the particulate filter (72) is arranged downstream of a turbocharger turbine (18); Estimating the exhaust pressure upstream of the turbocharger turbine (18) based on a soot load of the particulate filter (72); and Reducing the intake air flow when the estimated exhaust pressure is greater than a threshold, wherein the threshold is based on a pressure that forces an exhaust valve open when the exhaust valve would otherwise be closed. [12] The method of claim 11, wherein the threshold is further based on spring wear of the exhaust valve over a lifetime of the internal combustion engine (10). [13] The method of any of claims 11 or 12, wherein the threshold is further based on one or more of engine speed and intake manifold pressure. [14] The method of any of claims 11-13, wherein the threshold is further based on cam control. [15] The method of claim 14, wherein reducing intake air flow during a first condition includes reducing intake air flow via adjustments to an intake throttle opening and, during a second condition, reducing intake air flow via adjustments to an intake valve and / or an intake cam timing. [16] An internal combustion engine system (100) comprising: an internal combustion engine (10) having an inlet and an outlet, an internal combustion engine cylinder having an inlet valve (62) and an exhaust valve (64); a turbocharger (13) for providing a supercharged intake air flow, the turbocharger (13) having an exhaust turbine (18); an intake throttle valve (20); an exhaust gas boost pressure control valve (82); an intake cam (67) for adjusting an intake valve timing; a particulate filter (72) coupled downstream of the exhaust turbine (18); a pressure sensor (54) coupled downstream of the exhaust turbine (18); and a control device having computer-readable instructions stored on the non-volatile memory for: Operating the internal combustion engine (10) with boost pressure activated and with a positive valve overlap to blow a quantity of boosted air from the inlet to the outlet via the internal combustion engine cylinder; Estimating the exhaust pressure upstream of the exhaust turbine (18) based on a soot load of the particulate filter (72); and if the estimated exhaust pressure is greater than a threshold, reducing one or more of intake air flow via the intake throttle valve (20) and amount of blown-through boosted air, wherein reducing the amount of blown-through boosted air includes adjusting a control of the intake cam (67) to reduce a positive valve overlap between the intake valve (62) and the exhaust valve (64), characterized by , that the reducing comprises: only reducing the intake air flow via the intake throttle valve (20) when the engine speed is higher than a first speed threshold; only reducing the amount of blown-through boosted air when the engine speed is lower than a second speed threshold and the engine load is higher than a load threshold, and reducing the intake air flow via the intake throttle valve (20) and the amount of blown-through boosted air, when the engine speed is between the first speed threshold and the second speed threshold, and the engine load is higher than the load threshold.

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