CHARGING CONTROL METHODS AND SYSTEMS

Abstract

A method for a boosted engine system comprising: Adjusting a variable geometry turbine (VGT) based on a difference between an exhaust pressure and an intake pressure to reduce the difference; further comprising adjusting, via a closed loop control, the VGT based on each of the engine speed, the exhaust pressure, and the difference between the exhaust pressure and the intake pressure, as well as based on a desired boost pressure compared to an actual boost pressure; wherein operating via a closed loop control comprises scheduling a gain to adjust a VGT geometry based on each of the engine speed and the exhaust pressure, wherein adjusting further comprises changing an aspect ratio of the VGT based on the scheduled gain.

Description

Field of InterestThe present description relates generally to methods and systems for pressure control in a boosted engine system.STATE OF THE ART / SUMMARYEngine systems may be configured with superchargers, such as turbochargers or superchargers, for providing boosted air charge and improving peak power outputs, fuel economy, and emissions. Turbochargers may include a variable geometry turbine (variable geometry turbine= VGT), where the turbine runner blades (or blades) are regulated to vary boost pressure and exhaust pressure. A position of the VGT impeller vanes may be varied based on a number of factors including engine speed, torque demand, desired reaction time, fuel economy, intake and exhaust manifold pressure, and emissions demand. By varying an aspect ratio of the turbocharger, the VGT adjustment enables the reduction of pumping losses.An exemplary approach to adjusting a VGT geometry is shown by Buckland et al. in U.S. Pat. No. 6,672,060 B1. Therein, a VGT geometry is adjusted by a feedback control loop in consideration of a difference between an actual intake manifold pressure and a desired intake manifold pressure.DE 195 31 871 C1 discloses a method for regulating the charge pressure in an internal combustion engine which is charged by means of an exhaust gas turbocharger with adjustable turbine geometry to a predefined operating point-dependent setpoint value.However, the inventors have recognized potential issues with the above approach. For example, it may not be sufficient to optimize the pumping work and the occurrence of exhaust pressure spikes. More specifically, during transient and idle engine operation, for example during tip-in and tip-out events, there may be exhaust pressure spikes caused by rapid changes in the flow of gases into the exhaust manifold without a corresponding change in the flow of gases out of the exhaust manifold, resulting in an increase in the exhaust manifold pressure. Accordingly, an increase in pressure difference between the exhaust and intake manifolds may be detected. Typically, pressure control in the intake and exhaust manifolds is performed based on the intake manifold pressure, which responds to changes and disturbances slower than the exhaust manifold pressure (due to the larger intake manifold volume compared to a smaller exhaust manifold volume, and because disturbances such as fueling changes will first affect the exhaust manifold and only then reach the intake manifold). In such circumstances, the VGT (or exhaust gas recirculation) actuator is not adjusted to increase exhaust manifold outflow until the increase in intake pressure is detected, during which time the exhaust pressure may have rapidly increased to undesirable levels. During this time, high exhaust manifold pressure and exhaust pressure peaks result in an increase in delta pressure in an engine, so engine pumping work is increased, which may negatively impact engine efficiency, performance, emissions, and fuel economy. Further, during this time, the expansion ratios of the turbine may be excessively increased, which may cause damage to the turbocharger hardware. In addition, such exhaust pressure peaks and high expansion ratios may result in high material fatigue and, ultimately, wear of various engine components such as seals, seals, exhaust valves, and cylinder components.Proceeding from this prior art, the invention proposes methods according to Claim 1 or 8 and an engine system according to Claim 15. Advantageous embodiments of the invention are evident from the dependent claims and the following description.The present inventors have identified an approach by which the above-described problems may be at least partially addressed. An example method for exhaust pressure control includes a method for a boosted engine system, comprising: adjusting a variable geometry turbine (VGT) based on each of an engine speed, an exhaust pressure, and a difference between the exhaust pressure and an intake pressure to maintain a desired delta pressure and boost pressure. The present inventors have recognized that by monitoring the pressure differential (delta pressure) between an exhaust and intake manifold and adjusting VGT geometry based on the pressure differential, VGT adjustments may be more effectively scheduled to reduce the occurrence of high delta pressure in the engine and correspondingly high exhaust pressure and exhaust pressure spikes.Additionally, EGR may be efficiently utilized to reduce pumping work by adjusting the opening of the EGR valve to increase EGR flow from the exhaust manifold to the intake manifold such that exhaust manifold pressure and engine pumping work are reduced.In one example, during transient operation of the engine, at least one of a VGT vane actuator, a wastegate valve, and an EGR valve may be adjusted to control the pressure differential in an engine such that engine pumping work, exhaust pressure peaks, and excessive expansion ratios are controlled / reduced. For example, the position of a VGT vane, wastegate valve opening, and / or an EGR valve opening may be continuously adjusted based on an actual pressure difference between exhaust and intake manifolds to reduce a pressure difference across the engine between the intake and exhaust pressures. More specifically, in addition to an existing proportional-integral (PI) control (e.g., control based on a boost pressure error from a desired boost pressure or exhaust pressure error from a desired exhaust pressure and other signals), a proportional-derivative (PD) control (control based on a difference between exhaust and intake manifold pressures) may be used to adjust at least one of VGT vanes, EGR valve, and wastegate valve opening such that an optimal pressure difference is maintained between the exhaust and intake manifolds (or excessive pressure differences are reduced). The PD controller may receive signals including a pressure difference between the exhaust and intake manifolds, intake and exhaust manifold pressures, flow, and engine speed from the respective sensors, which signals may be used to adjust the VGT vane actuator, wastegate valve, and / or EGR valve position. In one example, gains may be increased based on an increase in engine speed and / or an increase in exhaust pressure, resulting in an increase (both the amount and rate of increase) in opening the VGT vanes, wastegate valve, and / or EGR valve. Similarly, gains may be decreased based on a decrease in engine speed and / or a decrease in exhaust pressure, resulting in a decrease in opening of the VGT vanes, wastegate valve, and / or EGR valve. Because the VGT is coupled to the exhaust manifold, by increasing the opening of the VGT vanes by actuation of a VGT actuator, the VGT aspect ratio may be varied and thereby the exhaust pressure and peaks of the exhaust pressure may be reduced with little impact on the intake manifold pressure.Similarly, since the EGR valve opening is at the exhaust manifold, an exhaust pressure may be effectively reduced by increasing the EGR valve opening. Similarly, by directing exhaust through a wastegate passage (whose opening is controlled by a wastegate valve), exhaust pressure spikes may be decreased. In alternative examples, a relationship between exhaust and intake pressures may be used by the control system to simultaneously adjust VGT and EGR ports.In this way, VGT geometry (vanes), wastegate valve position, and / or EGR valve position may be operatively adjusted by their respective actuators to reduce the difference between exhaust manifold pressure and intake manifold pressure of a boosted engine. Engine pumping losses may be optimized by adjusting based on an engine speed, pressure difference between the exhaust and intake manifolds (delta pressure), and exhaust pressure to control the difference between the exhaust and intake manifold pressures. Additionally, exhaust surge pressures and excessive expansion ratios may be avoided, improving engine performance and fuel efficiency. By varying the gains as a function of engine speed and exhaust pressure along with the difference between exhaust and intake manifolds as a control input, the controller may more aggressively control VGT geometry, wastegate valve position, and EGR valve positions while increasing or decreasing the pressure difference. In one example, if the pressure differential is low, the controller may provide slight adjustments to the VGT and EGR actuators. In another example, if the pressure differential is increased beyond a threshold, the controller may aggressively adjust the actuators to reduce the pressure differential, such as with a higher gain tuning. The technical effect of controlling delta pressure across the engine is reduced engine pumping losses, reduced / reduced exhaust pressure peaks, and reduced excessive expansion ratios, and damage to the turbocharger and other hardware components due to fatigue may be reduced and emissions, performance, and fuel economy may be further improved.It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that address any disadvantages listed above or in any part of the present disclosure.Brief Description of the DrawingsFIG. 1 shows a schematic illustration of an example engine system including a variable geometry turbocharger and an exhaust gas recirculation system. FIG. 2 shows a block diagram of two example control systems that may be used to adjust each of the VGT vane position and EGR valve opening. FIG. 3 shows a block diagram of an example control system that may be used for adjusting VGT vanes, wastegate valve, and / or EGR valve positions. FIG. 4 shows a flow chart depicting a method that may be implemented for boost control and reducing a pressure differential between the exhaust and intake manifolds. FIG. 5 shows example control of a pressure differential between exhaust and intake manifolds through VGT and / or EGR valve position adjustment.Detailed DescriptionThe following description relates to systems and methods for pressure control in a boosted engine system. An example boosted engine system including a variable geometry turbine (VGT) and an exhaust gas recirculation (EGR) system is shown in FIG. 1. Opening of the VGR and EGR valves may be controlled by an engine controller based on a plurality of input signals including intake and exhaust manifold pressure, engine speed, and a fueling schedule via feedback, as shown in the example control system of FIG. 2. In addition to PI (proportional-integral) control, gain scheduled PD (proportional-derivative) control as shown in FIG. 3 may be used to further adjust at least one of VGT vane position, wastegate valve position, and EGR valve openings based on an engine speed, an exhaust manifold pressure, and a difference between exhaust and intake manifold pressures (delta pressure). An engine controller may be configured to execute a control routine, such as the example routine of FIG. 4, to reduce a pressure difference between exhaust and intake manifolds by adjustments to VGT and / or EGR valve positions. Example adjustments to VGT and EGR valve positions in response to an increase in pressure difference between the exhaust and intake manifolds are shown in FIG. 5.FIG. 1 schematically illustrates aspects of an example engine system 100 including an engine 10. In the illustrated embodiment, engine 10 is a boosted engine coupled to a turbocharger 13 that includes a compressor 114 driven by a turbine 116. Specifically, fresh air is introduced into the engine 10 along an intake passage 42 via the air cleaner 112 and flows to the compressor 114. The compressor may be any suitable intake air compressor, such as an electric motor driven or driveshaft driven supercharger compressor. In engine system 10, the compressor is a turbocharger compressor mechanically coupled to turbine 116 via shaft 19, turbine 116 being driven by expanding engine exhaust.The compressor 114 may be coupled to the throttle plate 20 through the charge air cooler (CAC) 17. The throttle 20 is coupled to the engine intake manifold 22. From the compressor, the compressed air charge flows through the charge air cooler 17 and the throttle to the intake manifold. A compressor recirculation passage (not shown) may be provided for compressor surge control. More specifically, boost pressure may be drawn from the intake manifold downstream of CAC 17 and upstream of throttle 20 into intake passage 42 for reducing compressor surge, such as during driver tip-out. By flowing boosted air from upstream of an intake throttle inlet to upstream of the compressor inlets, boost pressure may be rapidly decreased, accelerating boost control. Flow through the compressor recirculation passage may be regulated by adjusting the position of a compressor recirculation valve (not shown) positioned therein. The compressor recirculation valve may be a continuously variable valve whose position may be adjusted to a fully open position, a fully closed position, or any position therebetween. The recirculation valve may therefore also be referred to herein as a continuously variable compressor recirculation valve or CCRV.The exhaust turbine 116 may be configured as a variable geometry turbine (VGT). The VGT may include a valve 117 that may be adjusted to vary the aspect ratio and position of the impeller blades (vanes) of the VGT. As one example, the aspect ratio of the VGT may be increased by opening the VGT vanes by a VGT actuator such that the surface area of the VGT exposed to exhaust flow is increased. Therefore, by varying the opening of valve 117, engine controller 12 may obtain the energy level obtained from the exhaust flow and provided to the corresponding compressor. A wastegate actuator 92 may be actuated to open to release at least some exhaust pressure from upstream of the turbine to a location downstream of the turbine via wastegate 90. By reducing exhaust pressure upstream of the turbine, turbine speed may be decreased, which in turn may contribute to a decrease in compressor surge and excessive boost issues.One or more sensors may be coupled to an inlet of a compressor 114. For example, a temperature sensor 55 may be coupled to the inlet to estimate a compressor inlet temperature and a pressure sensor 56 may be coupled to the inlet to estimate a compressor inlet pressure. As another example, a humidity sensor 57 for estimating a humidity of the air charge entering the compressor may be coupled to the inlet. Still other sensors may include, for example, air-fuel ratio sensors, etc. In other examples, one or more intake conditions of the compressor (such as humidity, temperature, pressure, etc.) may be inferred based on engine operating conditions. Additionally, when exhaust gas recirculation (EGR) is enabled, the sensors may estimate a temperature, pressure, humidity, and air-fuel ratio of the air charge mixture including fresh air, recirculated compressed air, and exhaust residuals received at the compressor inlet.In some examples, intake manifold 22 may include an intake manifold pressure sensor 124 for estimating a manifold pressure (MAP) and / or an intake air flow sensor 125 for estimating a mass air flow (MAF) into intake manifold 22. The intake manifold 22 is coupled to a series of combustion chambers 30 through a series of intake valves (not shown). The combustion chambers are further coupled to the exhaust manifold 36 via a series of exhaust valves (not shown). In the depicted embodiment, a single exhaust manifold 36 is shown. However, in other embodiments, the exhaust manifold may include a plurality of exhaust manifold portions. Configurations with multiple exhaust manifold sections may enable directing effluent from different combustion chambers to different locations in the engine system.In one embodiment, both exhaust and intake valves may be electronically actuated or controlled. In another embodiment, both exhaust and intake valves may be cam actuated or controlled. Whether electronically or cam-actuated, the timing of opening and closing the exhaust and intake valves may be adjusted as desired for desired combustion and emission control performance.The combustion chambers 30 may be supplied with one or more fuels, for example, gasoline, alcoholic fuel mixtures, diesel, biodiesel, pressurized natural gas, etc., by an injector 66. Fuel may be delivered to the combustion chambers via direct injection, port injection, throttle valve body injection, or any combination thereof. In the combustion chambers, combustion may be initiated via spark ignition and / or compression ignition.As shown in FIG. 1, exhaust gas is directed from the one or more exhaust manifold sections to the turbine 116 to drive the turbine. The combined flow from the turbine and wastegate then flows through emission control device 170. In general, one or more emission control devices 170 may include one or more exhaust aftertreatment catalysts configured to catalytically treat the exhaust stream, thereby reducing an amount of one or more substances in the exhaust stream. For example, an exhaust aftertreatment catalyst may be configured to trap NO X from the exhaust flow when the exhaust flow is lean and reduce the trapped NO X when the exhaust flow is rich. In other examples, an exhaust aftertreatment catalyst may be configured to disproportionate NO X or selectively reduce NO X using a reductant. 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. In some embodiments, the exhaust aftertreatment stages may include a regeneratable soot filter configured to trap and oxidize soot particles in the exhaust stream.All or a portion of the treated exhaust gas from the emission controller 170 may be discharged to the environment via the exhaust passage 102 after passing through a muffler 172. A low pressure exhaust gas recirculation (LP-EGR) delivery passage 180 may be coupled to exhaust passage 102 at a location upstream of emission control device 170. A portion of the exhaust gas from the exhaust pipe 102 may be delivered from downstream of the turbocharger turbine 116 to the engine intake manifold 22, upstream of a turbocharger compressor 114 as LP-EGR. Opening of an EGR valve 52 may be regulated to control exhaust flow from the exhaust passage 102 to the intake manifold 22 via the EGR passage 180. The EGR valve 52 may be opened to introduce a controlled amount of exhaust gas into the compressor inlet for desired combustion and emission control performance. The engine may further include a high pressure EGR (HP-EGR) system, wherein a portion of the exhaust gas from the exhaust pipe 102 may be supplied from upstream of a turbocharger turbine 116 to the engine intake manifold 22 downstream of a turbocharger compressor 114 via the HP-EGR passage 182. HP-EGR flow may be regulated by adjusting the opening of an HP-EGR valve 53. The EGR valves 52 and 53 may be configured as continuously variable valves. However, in an alternative example, the EGR valves 52 and 53 may be configured as an on / off valve.One or more sensors may be coupled to EGR passages 180 and 182 to provide details regarding the composition and condition of EGR. For example, a temperature sensor may be provided for determining a temperature of the EGR, a pressure sensor may be provided for determining a pressure of the EGR, a humidity sensor may be provided for determining a humidity or water content of the EGR, and an air-fuel ratio sensor may be provided for estimating an air / fuel ratio of the EGR. Alternatively, EGR conditions may be inferred by the one or more temperature, pressure, humidity, and air-fuel ratio sensors 55- 57 coupled to the compressor inlet. In one example, the air-fuel ratio sensor 57 is an oxygen sensor.The engine system 100 may further include a control system 14. The control system 14 is shown to receive information from a plurality of sensors 16 (various examples of which are described herein) and to send control signals to a plurality of actuators 18 (various examples of which are described herein). As one example, sensors 16 may include a MAP sensor 124, MAF sensor 126, exhaust temperature sensor 128, exhaust pressure sensor 129, compressor inlet temperature sensor 55, compressor inlet pressure sensor 56, compressor inlet humidity sensor 57, crankshaft sensor, and EGR sensor. Other sensors, such as additional pressure, temperature, air / fuel ratio, and composition sensors, may be coupled to various locations in engine system 100. Actuators 81 may include, for example, throttle valve 20, EGR valve 52, VGT actuators 117, wastegate 92, and fuel injector 66.The control system 14 may include a controller 12. The controller 12 may receive input data from the various sensors, process the input data, and trigger various actuators in response to the processed input data based on instructions or code programmed therein corresponding to one or more routines. The controller 12 may be a proportional-integral (PI) or proportional-integral-derivative (PID) controller. For example, the controller may receive an indication of exhaust and intake manifold pressure and engine speed from respective sensors, and based on these signals, the controller may adjust at least one of VGT vane position, wastegate valve, and EGR valve opening via the respective actuators. By making adjustments to VGT geometry and EGR flow rate, boost may be controlled, exhaust pressure peaks may be reduced, and a pressure difference between the exhaust and intake manifolds (also referred to herein as the delta pressure) may be reduced. In addition to the PI control, a proportional derivative (PD) control (or a proportional control) may be used to adjust at least one of the VGT geometry, wastegate valve, and EGR valve opening to reduce engine pumping work and limit a turbine expansion ratio. A detailed description of the mentioned controls will be explained with reference to FIGS. 2, 3 and 4.FIG. 1 shows an example configuration of an internal combustion engine with relative positioning of the various components. If shown directly contacting or directly coupled to each other, such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Likewise, elements shown as contiguous or adjacent to each other may be contiguous or adjacent to each other, at least in one example. As an example, components that are in face contact with each other may be referred to as being in face contact with each other. As another example, elements positioned apart, with only a space and no other components therebetween may be referred to as such in at least one example.FIG. 2 shows an example proportional-integral (PI) control scheme 200 that may be implemented by a controller (e.g., controller 12 as shown in FIG. 1 ) to adjust each of a valve that controls the geometry of a variable geometry turbine (e.g., valve 117 for controlling VGT 116 as shown in FIG. 1 ) and an EGR valve (e.g., EGR valve 52 coupled to LP-EGR passage 180 as shown in FIG. 1 and EGR valve 53 coupled to HP-EGR passage 182) that controls air flow through an exhaust gas recirculation (EGR) passage. It will be appreciated that in the present description, a signal (duty cycle) may refer to an electrical signal, such as an electrical current, and that the modification of a signal may refer to a change in voltage corresponding to the electrical current.The control scheme 200 includes two separate control loops, namely a VGT control loop 210 and an EGR control loop 220. The two control loops may use one or more common inputs including engine speed, fueling, and exhaust pressure to control VGT and EGR valves, respectively. In addition, each control loop may have different, non-overlapping inputs.The VGT loop 210 may include a feed-forward segment. In the feedforward segment, a first signal corresponding to an engine speed obtained from a crankshaft sensor and a second signal corresponding to a fueling schedule may be used as inputs to a look-up table 202. In a first control segment, a signal 203 indicative of a desired VGT geometry may be output based on the look-up table 202. In one example, for a given fuel schedule, the desired VGT opening may increase / decrease as engine speed increases. In another example, for a given engine speed, the desired VGT opening may increase / decrease as the amount of fuel required increases. The VGT loop may further include a second control segment for scheduling gains for VGT adjustment. For gain planning, in addition to engine speed and fuel planning, an exhaust pressure obtained from an exhaust pressure sensor (e.g., exhaust pressure sensor 129 in FIG. 1 ) may be used as input to a look-up table 204. Based on the input parameters, a signal 205 may be generated that indicates control gains. This signal 205 can then be fed to a controller 212. The controller 212 may be a proportional-integral (PI) controller, a proportional-integral-derivative (PID) controller, or a proportional-derivative (PD) controller.Further, a feedback segment (or a closed loop segment) may be included in the VGT loop. A subtractor 208 may receive as inputs a desired (desired) intake manifold pressure and an estimate of the actual intake manifold pressure from a MAP sensor (such as MAP sensor 124 in FIG. 1 ). The subtractor 208 may calculate a difference between the target intake manifold pressure and the actual intake manifold pressure. Based on this difference, the subtractor 208 may calculate a MAP error 211. At PI control, the MAP error 211 may be processed with the control gain signal 205. The signals may be processed and / or modified by a proportional gain (K pv) and / or an integral gain (K iv). In one example, the controller 212 is a PD controller or a derivative (D) controller, where the signals may be processed by a derivative gain (K dv).Adder 214 may receive the proportional term and / or the integral term via signal 213 and receive the feed-forward term (e.g., a duty cycle) via signal 203. Based on the received signals, the adder 214 may output a signal 215 to an actuator coupled to the VGT vanes. The signal 215 may be used to adjust the VGT geometry via adjustments to the positions of the VGT vane. Accordingly, signal 215 may correspond to the power to be provided to the actuator coupled to the VGT vanes for adjusting the vanes. For a VGT coupled to the exhaust manifold, an exhaust pressure may be regulated by varying the geometry of the VGT vane. For example, by opening the VGT vanes, the aspect ratio of the VGT may be increased and, thus, an exhaust pressure may be decreased. Similarly, by closing the VGT vanes, the aspect ratio of the VGT may be decreased and, thus, an exhaust pressure may be increased. In this way, exhaust pressure peaks may be constrained by adjusting the geometry of the VGT vane and an optimal pressure difference between intake and exhaust manifolds may be maintained such that engine pumping work is reduced. The efficiency of the compressor coupled to the VGT is high within a certain window in the compressor characteristic plot. The compressor may plug or pump when operated beyond the surge limit. Adjustments to the VGT geometry may also be made taking into account compressor surge and surge limits. In one example, if a current compressor pressure ratio is close to the surge line, the VGT vanes may not be opened further, thus reducing the possibility of compressor surge. In another example, if a current compressor pressure ratio is near surge line during a tip-out event, the VGT vanes and EGR valve position may be opened simultaneously to provide a series path for exhaust flow (back through EGR) to both reduce the compressor pressure ratio and increase flow through the compressor.Similar to the VGT control loop 210, the EGR control loop 220 may also include a feedforward segment. In the feedforward segment, a first signal corresponding to an engine speed obtained from a crankshaft sensor and a second signal corresponding to a fueling schedule may be used as inputs to a look-up table 222. In a first control segment, a signal 223 indicative of a desired EGR valve position (determining an EGR flow rate) may be output based on the look-up table 222. In one example, for a given fuel schedule, the desired EGR valve opening may increase / decrease as engine speed increases. In another example, for a given engine speed, the desired EGR valve opening may increase / decrease as the amount of fuel required increases. The EGR control loop may further include a second control segment for scheduling gains for adjusting the EGR flow rate. The EGR control loop may further include a second control segment for scheduling gains for EGR flow rate adjustments through adjustments to the EGR valve. To schedule gains, in addition to engine speed and fuel scheduling, an exhaust pressure obtained from an exhaust pressure sensor (e.g., exhaust pressure sensor 129 in FIG. 1 ) may be used as input to a lookup table 224. Based on the input parameters, a signal 225 may be generated that indicates control gains. This signal 225 can then be supplied to a controller 230. The controller 230 may be a proportional-integral (PI) controller, a proportional-integral-derivative (PID) controller, or a proportional-derivative (PD) controller.Further, a feedback segment (or a closed loop segment) may be included in the EGR loop. A subtractor 228 may receive as inputs a desired (desired) EGR flow rate and intake manifold pressure and an estimate of the actual EGR flow rate and intake manifold pressure from a MAF sensor (such as MAF sensor 126 in FIG. 1 ) and / or a MAP sensor (such as MAP sensor 124 in FIG. 1 ). The subtractor 228 may calculate a difference between the target EGR flow rate (and / or pressure) and the actual EGR flow rate (and / or target and actual intake manifold pressures). Based on this difference, subtractor 228 may calculate a MAF error 231. At the PI control, the MAF error 231 may be processed with the control gain signal 225. The signals may be processed and / or modified by a proportional gain (K pv) and / or by an integral gain (K iv) and / or by a derivative gain (K dv).Adder 232 may receive the proportional term and / or integral term via signal 233 and receive the feed-forward term (duty cycle) via signal 223. Based on the received signals, the adder 232 may output a signal 235 to an actuator coupled to the EGR valve. Signal 235 may be used to adjust airflow in the EGR system via adjustments to EGR valve opening. Accordingly, signal 235 may correspond to the power to be provided to the actuator coupled to the EGR valve for adjusting the opening of the valve. As EGR is delivered from the exhaust manifold to the intake manifold, an exhaust pressure may be regulated by varying the opening of the EGR valve (varying the EGR flow rate). As an example, by increasing the opening of the EGR valve, a higher volume of exhaust gas may be recirculated such that the exhaust pressure is reduced. In this way, the EGR flow rate may be adjusted by adjusting the EGR valve opening to limit exhaust pressure peaks and maintain an optimal pressure differential between intake and exhaust manifolds, thus reducing engine pumping work. Exhaust pressure regulation may be performed by adjusting the EGR valve of at least one of an LP-EGR and an HP-EGR system. However, higher than desired levels of EGR flow may cause excessive dilution of intake manifold air flow and cause unstable combustion. Therefore, EGR flow rate adjustments may be further performed in consideration of other engine operating parameters such as engine load, engine temperature, etc. Similar to VGT loop 210 and EGR loop 220, a third loop may regulate opening of a wastegate valve coupled to a wastegate passage of an exhaust turbine. Wastegate valve opening may be adjusted based on boost pressure and boost error, where wastegate valve opening is decreased as boost pressure is requested.FIG. 3 shows an example control scheme 300 that may be used by a vehicle controller (such as controller 12 in FIG. 1 ) to adjust VGT vanes and / or EGR valve positions in response to a change in at least one of a difference between an exhaust manifold and intake manifold pressure, an engine speed, an exhaust manifold and intake manifold pressure. Control scheme 300 may be a modified version of control scheme 200 in FIG. 2, which is optimized for controlling VGT and EGR valve positions, particularly for boost control and reducing engine pumping work (by reducing the pressure differential between exhaust and intake manifolds). Therefore, in addition to a proportional-integral (PI) control of FIG. 2, a proportional-derivative (PD) control may be used to further adjust at least one of a VGT vane actuator, a wastegate valve opening, and an EGR valve opening based on a difference between an exhaust manifold and intake manifold pressure, an engine speed, and an exhaust manifold pressure. Adjusting a VGT vane actuator, wastegate valve, and / or EGR valve includes determining a first term via a proportional-integral (PI) control based on an engine speed, an intake manifold pressure, and an exhaust manifold pressure, and determining a second term via a proportional-derivative (PD) control based on a difference between an exhaust manifold and an intake manifold pressure, an engine speed, and an exhaust manifold pressure. Similar to FIG. 2, in the present specification, a signal may refer to an electric signal such as an electric current, and the modification of a signal may refer to a change in voltage corresponding to the electric current.The control scheme 300 may include two parts, namely a first part 310 and a second part 320. The first portion 310 may be the VGT or EGR control loop 210 (or 220) used to schedule the first term, as described in FIG. 2A. The PI controller 312 may receive a difference (P int- error) 311 in terms of a desired (desired) intake pressure and an actual measured intake pressure obtained from a manifold air pressure (MAP) sensor (such as the MAP sensor 124 in FIG. 1 ). In one example, the PI controller 312 may be the VGT loop 210 or the EGR loop 220 in FIG. 2. In the PI controller 312, the P int- error 311 may be processed and / or modified (scaled) by a proportional gain (K pi). The integral of the P int- error 311 may be similarly processed and / or modified (scaled) by an integral gain (K ii). One of these terms or their sum is then output to signal 313. The boost pressure (or EGR flow rate) control term 313 is then added with the proposed delta pressure control term 339 to generate the final control signal to be sent to the VGT or EGR actuator. In one example, the PI controller 312 may be a proportional-integral-derivative (PID) controller and may process the P int- error 311 using a derivative gain as well as a proportional gain and an integral gain. However, instead of using the signal generated by the PI controller 312 directly to adjust a VGT and / or EGR valve position, a second portion 320 of the control scheme may be used to calculate a second term to optimize the control process.To optimize the pressure difference between an exhaust manifold pressure and an intake manifold pressure, a first signal 315 including an actual measured exhaust manifold pressure (P exh) obtained from an exhaust pressure sensor (such as exhaust pressure sensor 129 in FIG. 1 ) and a second signal 317 including an actual measured intake pressure obtained from a manifold air pressure (MAP) sensor may be used as input to a controller (subtractor) 324 (for calculating a fault). Each of these signals may instead be estimated based on other measurements. The subtractor 324 may calculate a difference between the exhaust and intake manifold pressures. The signals (319 and 325) corresponding to the difference calculated by the subtractor 324 may be processed and / or modified separately from a proportional gain (K p) 326. Signal 319 may generate a proportional term 323 after modification by a proportional gain (K p) 326. In parallel, the signal 319 may be differentiated by a differentiator block (DT1) 328 and a derivative gain (K d) 330 and derivative term 329 may be generated.The adder 332 may receive the proportional term 323 and the derivative term 329. Based on the received signals, the adder 332 may further calculate a signal 331. In addition, gain planning may be performed in consideration of the engine speed and the exhaust pressure. A first signal 335 including an actual measured exhaust manifold pressure (P exh) obtained from an exhaust pressure sensor and a second signal 333 including an engine speed (Ne) obtained from a crankshaft sensor may be used as inputs to a look-up table K 1 334. Based on the input signals, the look-up table may plan a gain 337. In one example, the scheduled boost may be increased based on an increase in engine speed and / or an increase in exhaust pressure. Similarly, the scheduled boost may be decreased based on a decrease in engine speed and / or a decrease in exhaust pressure. The multiplier 322 receives the designed gain 337 and the signal 331 (calculated by the adder 332) as input signals. In one example, increasing the gain 337 when the outlet pressure 335 increases above a threshold allows the controller to more aggressively respond to larger (potentially problematic / harmful) pressure peaks. Engine systems are non-linear and may have different response speeds at different engine operating ranges, particularly based on engine speed. At higher engine speeds, the system responds more quickly to changes. Therefore, a less aggressive (smaller) boost 337 may be sufficient when the engine speed is high.Based on the two input signals 331 and 337, the multiplier 322 may calculate a signal 339 that may be used as a second input to the adder 314. As described above, the first input to adder 314 may be signal 313, which includes the proportional and integral terms from PI controller 312. The controller calculates a signal 316, which may be used to adjust at least one of VGT vane position, wastegate valve opening, and EGR valve opening. An example representation of signal 316 is shown in Equation 1. where VGT is signal 316 corresponding to power to be supplied to an actuator coupled to at least one of VGT (or the EGR valve) to adjust the position of the valve, VGT from boost control is signal 313 received from PI controller 312, K p( p exhaust manifold- p intake manifold) is proportional term 323 received from the PD controller is derivative term 329 received from the PD controller, and K gain is signal 337, which is determined based on the look-up table(s) 334.The second part 320 comprises a PD control (no integral control) and is therefore only effective under transient conditions. The integral effect of the basic boost (PI) control 312) restores the mapped setpoint. In this way, a first term determined by a PI controller and a second term determined by a PD controller may be added to selectively adjust each of the VGT vane actuator (during the first condition), the EGR valve (during the second condition), and the wastegate valve opening (during the third condition). A calculation of the first term is based on inputs (such as those in 210 or 220 in FIG. 2 ) including an engine speed, an intake manifold pressure, and an exhaust manifold pressure. Further, the second term includes first and second components, the first component depending on an intake manifold pressure and an exhaust manifold pressure, and the second component depending on an engine speed and an exhaust manifold pressure. Selectively adjusting during the first condition includes actuating the VGT vane actuator to increase an opening of the VGT vanes based on each of the first and second terms to increase an aspect ratio of the VGT, and wherein selectively adjusting during the second condition includes opening the EGR valve based on each of the first and second terms to increase an opening of an EGR passage, and selectively adjusting during the third condition includes opening the wastegate valve based on each of the first and second gains to increase an opening of a wastegate passage.For example, by opening the VGT vanes, an outlet pressure may be decreased and by closing the VGT vanes, an outlet pressure may be increased. Similarly, by increasing the opening of the EGR valve (LP-EGR and / or HP-EGR), a higher volume of exhaust gas may be recirculated such that exhaust pressure is reduced. By adjusting at least one of the VGT vane position, wastegate valve opening, and EGR valve opening, exhaust pressure peaks may be limited and an optimal pressure difference between the intake and exhaust manifolds may be maintained such that engine pumping work is reduced. FIG. 4 shows an example method 400 for boost control and reducing a pressure difference between exhaust and intake manifolds by adjustments to VGT and / or EGR valve positions. Instructions for executing method 400 and the remaining ones of the methods included herein may be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference to FIG. 1. The controller may employ engine actuators of the engine system according to methods described below for adjusting engine operation.At 402, engine operating conditions may be determined by the controller. Engine operating conditions may include engine load, engine temperature, engine speed, operator torque request, etc. Depending on the estimated operating conditions, multiple engine parameters including a rate of exhaust gas recirculation (EGR) flow, boost pressure, etc. may be determined. At 404, a present value of exhaust manifold pressure may be estimated from an exhaust pressure sensor (such as exhaust pressure sensor 129 in FIG. 1 ) coupled to the exhaust manifold of the engine. Exhaust pressure may vary based on engine operating conditions and further based on parameters such as EGR flow rate, turbine geometry (in the case of a variable geometry turbine), etc. At 404, a present value of intake manifold pressure may be determined by an intake manifold air pressure sensor (such as MAP sensor 124 in FIG. 1 ) coupled to the engine intake manifold downstream of the compressor inlet.At 408, a difference (ΔP) between the exhaust and intake manifold pressures may be calculated by the controller. The pressure difference ΔP may be minimized to ensure optimal pumping work for the engine. The pressure difference ΔP may substantially increase due to exhaust pressure peaks causing engine pumping losses. Increasing engine pumping work beyond a desired level may negatively affect engine efficiency, performance, and fuel economy. Further, during this time, the expansion ratios of the turbine may be excessively increased, which may cause damage to the turbocharger hardware. In addition, such high exhaust pressure, exhaust pressure peaks, and high expansion ratios may result in high material fatigue and ultimately degradation of various engine components. As described above, at least one of the EGR flow rate (EGR valve opening), wastegate valve opening, and the VGT geometry (VGT vane position) may be adjusted to regulate an exhaust pressure and in turn reduce the pressure difference ΔP to the desired level (near zero).At 410, the routine includes determining if the pressure difference (ΔP) between the exhaust and intake manifolds is higher than a threshold pressure difference level. If it is determined that the pressure difference ΔP is lower than the threshold pressure difference, it may be inferred that the engine pumping work is at a desired level. To maintain the pressure difference ΔP below the threshold pressure difference, at 412, a VGT geometry (aspect ratio) and EGR valve position may be maintained at the present state.If it is determined at 410 that the pressure difference ΔP is higher than the threshold, adjustments may be made to at least one of the VGT geometry and the EGR valve opening to reduce the pressure difference to a desired level. An increase in the pressure difference ΔP may occur during transient events (e.g., during tip-in and tip-out events) of the vehicle that may cause exhaust pressure spikes. The pressure difference ΔP may be decreased by further opening the VGT vanes and / or by increasing the opening of the wastegate valve or the EGR valve. It may be appreciated that a change in pressure by changing VGT geometry is a slower process compared to a change in pressure achieved by a change in EGR valve opening.At 414, the routine includes determining whether to make adjustments only to the VGT geometry or the boost set point to regulate the pressure difference ΔP. By varying the aspect ratio of the VGT, the flow area of the VGT exposed to the exhaust gas may be increased, causing a variation in exhaust pressure. Further, by changing the charge set point, an outlet pressure may be effectively reduced so that the pressure difference ΔP is reduced. It is to be considered that the efficiency of a compressor coupled to the VGT is high within a certain acceptable window in the compressor map. The compressor may plug or pump when operating beyond the surge limit (outside the acceptable window). Further adjustments to the VGT geometry are only possible when the updated corresponding compressor operation is estimated within the acceptable window in the compressor characteristic plot to reduce possible compressor plugging or surge. During current operation, if compressor operation is near either surge or surge limit in the characteristic plot, the VGT geometry for regulating the pressure difference ΔP cannot be adjusted further. Further, in some circumstances, when the pressure difference ΔP is greater than a second threshold, adjustments to only the VGT geometry may not be sufficient to reduce the pressure difference ΔP.If it is determined that only the VGT cannot be adjusted to regulate the pressure difference ΔP, at 416, the routine includes determining whether to make adjustments to only one of the EGR valve opening and the EGR target to reduce the pressure difference ΔP. By increasing the opening of the EGR valve, the pressure difference ΔP may be regulated in a shorter time as compared to regulating the pressure difference ΔP by changes in VGT geometry. Similarly, by changing the EGR target value, the exhaust pressure can be effectively reduced so that the pressure difference ΔP is reduced. However, based on engine operating parameters such as engine load, engine temperature, etc., an EGR flow rate may be increased only to a threshold limit. Higher than desired levels of EGR flow may cause excessive dilution of intake manifold air flow, causing unstable combustion. Thus, if the current EGR levels are near the upper threshold limit, the EGR valve opening for regulating the pressure difference ΔP may not be increased further. Further, in some circumstances, when the pressure difference ΔP is higher than a second threshold, adjustment of only the EGR valve opening may not be sufficient to decrease the pressure difference ΔP.If it is determined that adjustments to one of a VGT geometry (or boost set point) and an EGR valve opening (or an EGR set point) is not sufficient to regulate the current pressure difference ΔP, at 418, the routine includes determining if adjustments to each of the VGT geometry and the EGR opening are desired to reduce the pressure difference ΔP. Alternatively, it may be determined whether adjustments to each of the boost target value and the EGR target value are desired to reduce the pressure difference ΔP. In one example, adjustments to both the VGT and the EGR valves (or boost target and EGR target) are desired if the pressure difference ΔP is higher than the second threshold, where adjustments to one of the VGT geometry and the EGR valve opening may not be sufficient to reduce the pressure difference ΔP. In another example, at least one of VGT and EGR may be operated near its limit (compressor surge and surge limit for VGT and combustion stability for EGR) due to engine operating parameters, with margin for further adjustments to the respective valves being limited. It may be determined that based on current engine conditions, current VGT, and EGR valve positions, none of the VGT geometry and EGR valve opening may be adjusted to reduce pressure difference ΔP. In such circumstances, the VGT geometry and EGR valve position may be maintained at 412 in the current state. In one example, adjustments to wastegate valve opening may also be made to regulate the current pressure difference ΔP.If it is determined at 414 that adjustments can be made only to the VGT geometry or the boost set point for the regulation of the pressure difference ΔP, the routine continues to 420, where a difference of a desired pressure difference and an actual pressure difference (error in ΔP) may be estimated by the controller. From each of steps 416 and 418, the routine proceeds to step 420. At 420, the controller may include proportional-integral (PI) or proportional-integral-derivative (PID) control. The PI (or PID) controller may receive signals including an engine speed, fueling schedule, intake, and exhaust pressure from the respective sensors as input parameters. Based on the input parameters and a difference (error) between desired and actual estimates of intake pressure and / or intake manifold air flow, the PI controller may schedule required adjustments to a VGT vane position, wastegate valve opening, and / or EGR valve opening to reduce the pressure difference ΔP to a desired level (near zero). The operation of the PI controller has been explained with reference to FIG. 2. In addition to PI control, a proportional derivative (PD) control may be used to adjust at least one of a VGT vane actuator, a wastegate valve opening, and an EGR valve opening. The PD controller may utilize a difference between exhaust and intake manifold pressures to reduce engine pumping work and limit a turbine expansion ratio. The operation of the PD controller together with the PI controller has been explained with reference to FIG. 3.At 422, the PD controller, along with the PI controller, may adjust a VGT geometry, a wastegate valve position, and / or an EGR valve position based on inputs including the error in ΔP (estimated by the controller in step 420), intake and exhaust manifold pressure, and an engine speed received from the respective engine sensors. In one example, in a first mode, the aspect ratio of the VGT may be increased with at least one of a decrease in engine speed and an increase in exhaust pressure, and the aspect ratio of the VGT may be decreased with at least one of an increase in engine speed and a decrease in exhaust pressure. In a second mode, the aspect ratio of the VGT may be increased with an increase in at least one of the engine speed and the exhaust pressure, and the aspect ratio of the VGT may be decreased with a decrease in at least one of the engine speed and the exhaust pressure.At 424, at least one of VGT geometry, wastegate valve position, and EGR valve positions may be adjusted based on the control output. By increasing the opening of the VGT vanes, a VGT aspect ratio may be increased, causing a reduction in exhaust pressure peaks (more surface area for exhaust expansion) with little effect on intake manifold pressure. By increasing the EGR opening, exhaust flow from the exhaust manifold to the intake manifold may be increased so that an exhaust pressure is reduced. Similarly, by increasing wastegate valve opening, exhaust flow to the tailpipe may be increased bypassing the turbine such that exhaust pressure is reduced.During a first boosted engine operating condition, a VGT vane actuator may be adjusted responsive to greater than a first threshold pressure difference between exhaust and intake manifolds; during a second boosted engine operating condition, an EGR valve may be adjusted responsive to greater than a first threshold pressure difference between the exhaust and intake manifolds; and during a third boosted engine operating condition, a wastegate valve may be adjusted responsive to the pressure difference exceeding the first threshold; wherein boost pressure may be maintained during each of the first, second, and third conditions. Further, each of the VGT vane actuator, the EGR valve, and the wastegate valve may be adjusted responsive to greater than a second threshold pressure difference between the exhaust and intake manifolds. Alternatively, the adjustment may be adjusted during all four engine operating conditions, where the adjustment may be based on a ratio of exhaust manifold pressure to intake manifold pressure. In one example, the first condition includes engine operation near a combustion stability limit, the second condition includes operation of a compressor coupled to the VGT at a compressor surge or surge limit, and the third condition includes the pressure difference between an exhaust and an intake manifold being increased above the second threshold.In this way, a control system may regulate (reduce) the pressure difference between the exhaust and intake manifolds by adjusting a VGT geometry and / or EGR valve position such that engine pumping work and hardware wear are reduced. Instead of using a difference between exhaust and intake pressures to schedule a VGT vane position, wastegate valve opening, and / or EGR valve opening, a relationship between exhaust and intake pressures may be used by the control system in one example. In another example, only the outlet pressure may be used to control outlet pressure peaks.FIG. 5 shows an example operating sequence 500 depicting example control of the pressure difference between exhaust and intake manifolds based on variable geometry turbine (VGT) setting and exhaust gas recirculation (EGR) valve position. Accordingly, this sequence of operations may be executed during engine transient operation to reduce a pressure differential between exhaust and intake manifold pressures caused by exhaust pressure spikes. By reducing the pressure differential, engine pumping work may be reduced. The horizontal axis (x-axis) indicates time, and the vertical markers t1-t9 identify significant times during operation of the sequence 500.The first plot, line 502, from above shows the variation in accelerator pedal position over time. The second plot, line 504, shows a difference (ΔP) between exhaust and intake manifold pressures. An estimate of intake pressure may be obtained from an intake manifold pressure sensor and an estimate of exhaust pressure may be obtained from an exhaust manifold pressure sensor, wherein the difference between the two estimates may be calculated by an engine controller. Dotted lines 505 and 507 show a first and a second lower threshold value of the pressure difference ΔP, respectively. In order for the engine to operate optimally without excessive pumping losses, the pressure difference ΔP may be maintained at a level that is lower than the first threshold 505 (near zero). The third plot, line 506, shows the variation in exhaust pressure over time. During engine transient operation, there may be exhaust pressure peaks that also affect the pressure difference ΔP. The fourth plot, line 508, shows a position of a VGT vane and the fifth plot, line 510, shows a position of an EGR valve (EGR valve opening).Prior to time t 1, the pedal position is determined to be constant without significant fluctuation. During this time, the outlet pressure and the pressure difference ΔP are also maintained at a steady level, with the pressure difference ΔP being well below the first threshold 505. The VGT vane is maintained at a constant position based on boost pressure desired for engine operation. Further, during this time, the EGR valve opening is maintained constant based on the EGR level desired for current engine operation.At time t 1, a tip-in event is detected by the change in the accelerator pedal position. During such transient operation of the engine as during the tip-in event, the exhaust pressure is increased within a short time, causing exhaust pressure spikes. However, an increase in intake pressure (due to the large volume of the intake manifold compared to the exhaust manifold) may take longer. Further, intake pressure peaks may be smaller compared to exhaust pressure peaks occurring due to the same tip-in event. Due to the tip-in event, a peak in exhaust pressure is detected at time t2. As a result, the pressure difference ΔP may be increased to a level above the first threshold 505 (but below the second threshold 507). Higher than the threshold pressure difference ΔP may result in an increase in engine pumping work, which in turn may negatively affect engine efficiency, performance, and fuel economy. Further, during this time, the expansion ratios of the turbine may be excessively increased, which may cause damage to the turbocharger hardware. In addition, such exhaust pressure peaks and high expansion ratios can result in high material fatigue and eventual wear of turbocharger hardware.Therefore, to decrease the exhaust pressure peak and decrease the pressure difference ΔP at time t 2, the VGT vane actuator may be adjusted. In this example, the VGT vanes may be further opened to increase the VGT aspect ratio such that there is a reduction in exhaust pressure as exhaust gas flows through an increased surface area of the VGT vanes. Proportional-integral (PI) control and proportional-derivative (PD) control may be used in combination to determine a desired VGT vane opening setting to reduce the pressure differential between the exhaust and intake manifolds. The controller may send a signal to an actuator coupled to the VGT vanes to adjust the VGT geometry.The PI controller may receive signals including an engine speed, fueling schedule, intake and exhaust manifold pressure, and the PD controller may receive signals including a pressure difference ΔP, intake and exhaust manifold pressure, and engine speed from the respective sensors, which signals may be used to schedule a setting for the VGT vane position. Further adjustments to the VGT geometry may further be made while considering the corresponding compressor surge and surge line. Based on engine operating parameters, the amount of exhaust pressure reduction requested, a VGT vane position, and an EGR valve position, it may be determined by the controller that the EGR valve opening may be maintained at the same position and only VGT vane actuator adjustments may be sufficient to reduce the exhaust pressure peak and the pressure difference ΔP. Accordingly, EGR levels depend on engine operating parameters, and a higher than desired EGR flow rate may result in excessive intake air dilution, causing unstable combustion. Further, since the pressure difference ΔP is less than the second threshold 507, the pressure variation required to reduce the outlet peak and the pressure difference ΔP can be provided solely by adjusting the VGT geometry.Between time t 2 and t 3, the VGT vane opening may be maintained at the increased level. Further, based on the adjustments made to the VGT geometry, there is a reduction in the outlet pressure and the pressure difference ΔP during this time. Due to the change in VGT geometry, intake pressure also decreases at a lower rate compared to the decrease rate of the corresponding exhaust pressure. At time t 3, it may be determined that the tip-in event has ended and the pedal position has returned to a stable value. Further, there is a reduction in the outlet pressure and the pressure difference ΔP to a level higher than the first threshold 505. In response to the reduction in exhaust pressure and pressure difference ΔP, the VGT geometry may be further adjusted in consideration of current pressure levels (intake and exhaust manifold pressures) and other engine operating conditions. In this example, the VGT vanes may be closed at this time to an extent (as compared to VGT geometry during periods t 2 and t 3) such that there is a reduction in surface area of the VGT vanes exposed to the exhaust gas.Between time t 3 and t 4, there is no significant variation in pedal position. During this time, the outlet pressure and the pressure difference ΔP are also maintained at a steady level, with the pressure difference ΔP being well below the first threshold 505. Therefore, each of the VGT and EGR valves is maintained at a constant position based on current engine operating parameters.At time t 4, a second tip-in event is detected by the change in the accelerator pedal position. As a result, a peak of the outlet pressure may be detected and the pressure difference ΔP may be increased to a level above the first threshold 505 (but below the second threshold 507). Therefore, to decrease the exhaust pressure peak and decrease the pressure difference ΔP at time t 5, the EGR valve opening may be adjusted. In this example, by increasing EGR valve opening, air flow from the exhaust manifold to the intake manifold may be increased, causing a reduction in exhaust pressure. The proportional integral (PI) control and the proportional derivative (PD) control may be used together to determine the required adjustment of the EGR valve opening to reduce the pressure differential between the exhaust and intake manifolds. The controller may send a signal to an actuator coupled to the EGR valve to increase valve opening.The PI controller may receive signals including an engine speed, fueling schedule, an EGR flow rate, an intake and exhaust manifold pressure, and the PD controller may receive signals including a pressure difference ΔP, an intake and exhaust manifold pressure, and an engine speed from the respective sensors, which signals may be used to schedule an adjustment for the EGR valve position. Based on engine operating parameters, the amount of exhaust pressure reduction requested, a VGT geometry, and an EGR valve position, it may be determined by the controller that at this time, the VGT vanes may be maintained at the same position and only EGR valve adjustments may be sufficient to reduce the exhaust pressure peak and the pressure difference ΔP. Further, since the pressure difference ΔP is less than the second threshold 507, the pressure variation required to reduce the exhaust peak and the pressure difference ΔP can be provided solely by adjusting the EGR opening. It may be considered that a change in pressure by changing the EGR opening is a more rapid process as compared to a change in pressure achieved by changing the VGT vane position.Between time t 5 and t 6, the EGR valve opening may be maintained at the increased level. Further, based on the adjustments made to the EGR valve opening, during this time there is a reduction in the exhaust pressure and the pressure difference ΔP. In response to the change in EGR valve opening, the intake pressure may increase slightly first and decrease thereafter. This behavior depends on the operating range, and the intake pressure response may be monotone in some ranges. At time t 6, it may be determined that the tip-in event has ended and the pedal position has returned to a stable value. Further, there is a reduction in the discharge pressure, and therefore a reduction in the pressure difference ΔP to a level higher than the first threshold 505 is observed. In response to the reduction in exhaust pressure and pressure difference ΔP, the EGR opening may be further adjusted in consideration of current pressure levels (intake and exhaust manifold pressures) and other engine operating conditions. In this example, at this time, the opening of the EGR valve may be reduced to a smaller amount (as compared to EGR valve opening during time periods t 5 and t 6) to reduce exhaust flow from the exhaust manifold to the intake manifold.Between time t6 and t7 the pedal is held at a constant position without significant fluctuation. During this time, the outlet pressure and the pressure difference ΔP are also maintained at a steady level, with the pressure difference ΔP being well below the first threshold 505. Each of the VGT and EGR valves is maintained at a constant position based on current engine operation.At time t 7, a tip-out event is detected by the change in the accelerator pedal position. During the tip-out event, an exhaust pressure peak may be detected at time t 8. As a result, the pressure difference ΔP may increase to a level even above the second threshold 507. A large value of the pressure difference ΔP (higher than the second threshold 507) may result in a substantial increase in engine pumping work, which in turn may negatively affect the efficiency, performance, and fuel economy of the engine. In addition, such exhaust surge pressures may result in high material fatigue and, ultimately, wear of various engine components.Therefore, to reduce the exhaust pressure peak and pressure difference ΔP at time t 8, each of the VGT geometry and the EGR valve opening may be adjusted. At this time, since the pressure difference ΔP is higher than the second threshold 507, adjustment at one of the VGT geometry and the EGR opening may be insufficient to increase the pressure difference ΔP. Therefore, adjustments may be made to each of the VGT geometry and the EGR opening at this time. As before, the proportional integral (PI) control and the proportional derivative (PD) control may be used together to determine the required setting at each of the VGT vane actuator and the EGR valve to increase the pressure difference between the exhaust and intake manifolds to an optimal level. The controller may send a signal to respective actuators coupled to each of the VGT vanes and the EGR valve to increase valve openings.Between time t 8 and t 9, the VGT geometry and EGR valve opening may be maintained at the elevated levels. Further, based on the adjustments made to both the VGT geometry and the EGR valve opening, during this time there is a reduction in exhaust pressure and pressure difference ΔP. At time t 9, it may be determined that the tip-out event has ended and the pedal position has returned to a stable level. There is also a reduction in the outlet pressure, and consequently a reduction in the pressure difference ΔP is detected. The pressure difference ΔP may be decreased to a level lower than both the second (507) and first thresholds (505). Responsive to the reduction in exhaust pressure and pressure difference ΔP, at time t 9, the opening of the VGT vanes and EGR valve (as compared to VGT and EGR valve opening during periods t 8 and t 9) may be reduced to the level desired based on current engine operating parameters.After time t9, no further change in the pedal is detected. Further, the outlet pressure and the pressure difference ΔP are maintained at a steady level well within the desired limits. Each of the VGT and EGR valves is maintained at a constant position based on current engine operation. In addition to VGT geometry and EGR valve opening, wastegate valve opening may also be adjusted to reduce the difference between exhaust and intake manifold pressures. In this way, during engine transient operation, a pressure differential between the exhaust and intake manifolds may be reduced to an optimal level by appropriate adjustments made to at least one of the VGT geometry and EGR valve position, such that engine pumping work is controlled.In one example, a method for a boosted engine system includes adjusting a variable geometry turbine (VGT) based on a difference between an exhaust pressure and an intake pressure to reduce the difference below a threshold. The above example method further comprises, additionally or optionally, during the adjusting, maintaining a desired boost pressure, and wherein the adjusting is further based on one or more of an air flow, an exhaust flow, an engine speed, an engine speed combined with load, a turbocharger speed, a fuel supply, a torque (load), an exhaust pressure, and ambient conditions including an ambient temperature and an ambient pressure. In any or all of the preceding examples, additionally or optionally, operating in a closed loop includes scheduling a gain to adjust a VGT geometry based on each of engine speed and exhaust pressure. In any or all of the preceding examples, the adjusting further additionally or optionally includes changing an aspect ratio of the VGT based on the scheduled gain. In any or all of the preceding examples, additionally or optionally, the adjusting includes, based on the scheduled boost, in a first mode, increasing the aspect ratio of the VGT with at least one of a decrease in engine speed and an increase in exhaust pressure and decreasing the aspect ratio of the VGT with at least one of an increase in engine speed and a decrease in exhaust pressure; and in a second mode, increasing the aspect ratio of the VGT with an increase in at least one of engine speed and exhaust pressure and decreasing the aspect ratio of the VGT with a decrease in at least one of engine speed and exhaust pressure. In any or all of the preceding examples, additionally or optionally, the adjusting is responsive to the difference between the exhaust pressure and the intake pressure exceeding a first threshold. Any or all of the preceding examples further include, additionally or optionally, adjusting an exhaust gas recirculation (EGR) valve coupled to an EGR system based on the difference between the exhaust pressure and the intake pressure to reduce the difference below the threshold, the adjusting further based on each of the engine speed and the exhaust pressure, wherein adjusting the EGR valve includes increasing the EGR valve opening with at least one of a decrease in the engine speed and an increase in the exhaust pressure; and decreasing the valve opening with at least one of an increase in the engine speed and a decrease in the exhaust pressure. Any or all of the preceding examples further include, additionally or optionally, adjusting a wastegate valve coupled to a wastegate passage based on the difference between the exhaust pressure and the intake pressure to reduce the difference below the threshold, wherein the adjusting is further based on each of the engine speed and the exhaust pressure, and wherein adjusting the wastegate valve includes increasing the wastegate valve opening with at least one of a decrease in the engine speed and an increase in the exhaust pressure; and decreasing the wastegate valve opening with at least one of an increase in the engine speed and a decrease in the exhaust pressure. Any or all of the preceding examples further include, additionally or optionally, adjusting each of the VGT geometry and the EGR valve in response to the difference between the exhaust pressure and the intake pressure exceeding a second threshold, the second threshold being higher than the first threshold. In any or all of the preceding examples, additionally or optionally, adjusting the EGR valve includes increasing the EGR valve opening with at least one of a decrease in engine speed and an increase in exhaust pressure; and decreasing the valve opening with at least one of an increase in engine speed and a decrease in exhaust pressure.Another example method for an engine includes, during a first boosted engine operating condition, selectively adjusting a vane actuator of the variable geometry turbine (VGT) responsive to a pressure difference between an exhaust manifold and an intake manifold exceeding a first threshold; during a second boosted engine operating condition, selectively adjusting an exhaust gas recirculation (EGR) valve responsive to the pressure difference exceeding the first threshold; and during each of the first and second conditions, maintaining boost pressure during a third boosted engine operating condition, selectively adjusting a wastegate valve responsive to the pressure difference exceeding the first threshold; and during each of the first, second, and third conditions, maintaining boost pressure. The above example method may additionally or optionally further comprise, during a fourth boosted engine operating condition, adjusting each of the VGT vane actuator, the EGR valve, and the wastegate valve responsive to the pressure difference exceeding a second threshold, the second threshold being higher than the first threshold, wherein during each of the first, second, and third conditions, the adjusting is further based on a ratio of the exhaust manifold pressure to the intake manifold pressure. In any or all of the preceding examples, additionally or optionally, the engine includes an intake compressor, wherein the first condition includes engine operation at or within a threshold distance of a combustion stability limit, and wherein the second condition includes compressor operation at or within the threshold distance of a compressor surge limit. In any or all of the preceding examples, additionally or optionally, adjusting the VGT vane actuator during the first condition and adjusting the EGR valve during the second condition includes adjusting with a gain, the gain based on each of an engine speed and an exhaust manifold pressure, the gain increased with at least one of a decrease in engine speed and an increase in exhaust manifold pressure.In any or all of the preceding examples, additionally or optionally, adjusting the VGT, EGR, or wastegate actuator includes adjusting with a first term based on a proportional-integral (PI) control, the first term based on an engine speed, an estimated intake manifold pressure, a target intake manifold pressure, and an estimated exhaust manifold pressure, and thereafter adjusting with a second term based on a proportional-derivative (PD) control, the second term based on an engine speed and a difference between the estimated exhaust manifold and the estimated intake manifold pressure. In any or all of the preceding examples, additionally or optionally, the selectively adjusting during the first condition includes actuating the VGT vane actuator to increase an opening of the VGT vanes based on each of the first and second terms to increase an aspect ratio of the VGT, and wherein the selectively adjusting during the second condition includes opening the EGR valve based on each of the first and second terms to increase an opening of an EGR passage. In any or all of the preceding examples, additionally or optionally, the pressure difference between the exhaust manifold and the intake manifold is calculated based on an intake pressure estimate obtained from an intake manifold pressure sensor and an exhaust pressure estimate obtained from an exhaust manifold pressure sensor.In yet another example, an engine including an intake manifold and an exhaust manifold; a turbocharger to provide a boosted air charge to the engine, the turbocharger including a variable geometry exhaust turbine (VGT) driving an intake compressor, the exhaust turbine including vanes to vary an aspect ratio of the turbine; a wastegate passage coupled via the exhaust turbine, the wastegate passage including a wastegate valve; an exhaust gas recirculation (EGR) system including an exhaust gas recirculation passage including an EGR valve, the EGR passage recirculating exhaust gases from the exhaust manifold to the intake manifold; a first pressure sensor coupled to the intake manifold; a second pressure sensor coupled to the exhaust manifold; a controller having computer readable instructions stored in the non-transitory memory to: during operation of the engine with boost enabled, reduce a difference between an exhaust manifold pressure and an intake manifold pressure via adjustments to at least one of an aspect ratio of the exhaust turbine, an opening of the wastegate valve, and an opening of the exhaust gas recirculation valve. The above example further includes, additionally or optionally, wherein reducing the difference between the exhaust manifold pressure and the intake manifold pressure includes increasing at least one of a VGT vane opening, wastegate valve opening, and EGR valve opening in response to an increase in the pressure difference between the exhaust manifold pressure and the intake manifold above the threshold. In the preceding example, additionally or optionally, maintaining a difference above a threshold includes increasing an opening of at least one of the VGT vanes and the EGR valve in response to a pressure difference below a threshold. In the preceding example, additionally or optionally, reducing the difference between the exhaust manifold pressure and the intake manifold pressure includes increasing at least one of the VGT vanes and the EGR valve responsive to an increase in the pressure difference between the exhaust manifold pressure and the intake manifold above the threshold. In any or all of the preceding examples, additionally or optionally, increasing at least one of VGT vane opening, wastegate valve opening, and EGR valve opening includes calculating one or more control terms (e.g., gains) via at least one of a proportional-integral (PI) control, a proportional-derivative (PD) control, and a proportional-integral-derivative (PID) control based on an engine speed, an intake and an exhaust manifold pressure, and actuating at least one of the VGT valve opening, wastegate valve opening, and EGR valve opening in accordance with the calculated gain. In any or all of the preceding examples, additionally or optionally, maintaining a difference above a threshold includes adjusting at least one of the VGT vanes and the EGR valve based on engine speed and exhaust pressure, wherein the opening of at least one of the VGT vanes and the EGR valve is increased while the engine speed is decreased or the exhaust manifold pressure is increased, and wherein the opening of at least one of the VGT vanes and the EGR valve is decreased while the engine speed is increased or the exhaust manifold pressure is decreased. In any or all of the preceding examples, additionally or optionally, reducing the difference between the exhaust manifold pressure and the intake manifold pressure includes adjusting at least one of the VGT vanes, the wastegate valve, and the EGR valve based on the engine speed and the exhaust pressure, wherein at least one of the VGT vane position, the wastegate valve opening, and the EGR valve opening is increased while the engine speed is decreased or the exhaust manifold pressure is increased, and wherein at least one of the VGT vane position, the wastegate valve opening, and the EGR valve opening is decreased while the engine speed or the exhaust manifold pressure is decreased.In another illustration, a method for an engine includes adjusting a variable geometry turbine (VGT) based on a difference between an exhaust pressure and an intake pressure to maintain a desired boost pressure. In the preceding example, the adjusting is additionally or optionally based on each of an engine speed and an exhaust pressure. Any or all of the preceding examples further include, additionally or optionally, adjusting an exhaust gas recirculation (EGR) valve coupled to an EGR system based on the difference between the exhaust pressure and the intake pressure to maintain the desired boost pressure, the adjusting further based on each of the engine speed and the exhaust pressure, wherein adjusting the EGR valve includes increasing the EGR valve opening with at least one of a decrease in engine speed and an increase in exhaust pressure; and decreasing the valve opening with at least one of an increase in engine speed and a decrease in exhaust pressure. Any or all of the preceding examples further include, additionally or optionally, adjusting a wastegate valve coupled to a wastegate passage based on the difference between the exhaust pressure and the intake pressure to maintain the desired boost pressure, wherein the adjusting is further based on each of the engine speed and the exhaust pressure, and wherein adjusting the wastegate valve includes increasing the wastegate valve opening with at least one of a decrease in the engine speed and an increase in the exhaust pressure; and decreasing the wastegate valve opening with at least one of an increase in the engine speed and a decrease in the exhaust pressure. In another example, adjusting each of a VGT vane geometry, an EGR valve opening, and a wastegate valve position with the gain includes adjusting with a first term based on a proportional-integral (PI) control, the first term based on an engine speed, an estimated intake manifold pressure, and exhaust manifold pressure, and thereafter adjusting with a second term based on a proportional-derivative (PD) control, the second term based on an engine speed and exhaust manifold pressure. In yet another example, increasing at least one of the VGT vane opening, wastegate valve opening, and EGR valve opening may include scheduling a gain via at least one of a proportional-integral (PI) control, a proportional-derivative (PD) control, and a proportional-integral-derivative (PID) control based on an engine speed, an intake, and an exhaust manifold pressure. In this way, each of a VGT geometry and an EGR valve opening may be operatively adjusted to maintain an optimal pressure difference between an intake and an exhaust manifold of the engine. By maintaining the pressure differential at an optimal level, engine pumping losses may be reduced. Additionally, exhaust surge pressures and excessive expansion ratios may be avoided, improving engine performance and fuel efficiency. The technical effect of reducing engine pumping losses, exhaust surge pressures, and excessive expansion ratios is to reduce damage to the turbocharger or other hardware components due to fatigue.It should be appreciated that the example control and estimation routines included 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-transitory memory and may be executed by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. Thus, various operations, operations, and / or functions may be performed in the illustrated order, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated operations, operations, and / or functions may be repeatedly performed depending on the particular strategy being used. Furthermore, the described operations, operations, and / or functions may graphically represent code to be programmed into the non-transitory memory of the computer readable storage medium in the engine control system, where the described operations are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.It should be understood that the configurations and routines disclosed herein are exemplary in nature and that these specific embodiments are not to be interpreted in a limiting sense as numerous variations are possible. The above technology can be applied to, for example, V-6, I-4, I-6, V-12, Boxer-4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.The following claims particularly point out certain combinations and sub-combinations which are considered novel and non-obvious. These claims may refer to "a" element or "a first" element or the equivalent thereof. Such claims should be understood to include inclusion of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or characteristics may be claimed by altering the present claims or by providing novel claims in this or a related application. These claims, whether broader, narrower, equal or different in scope than the original claims, are also intended to be included within the scope of the present disclosure.

Claims

A method for a boosted engine system, comprising: adjusting a variable geometry turbine (VGT) based on a difference between an exhaust pressure and an intake pressure to reduce the difference; further comprising adjusting, via a closed loop, the VGT based on each of the engine speed, the exhaust pressure, and the difference between the exhaust pressure and the intake pressure, and based on a target boost pressure compared to an actual boost pressure; wherein operating, via a closed loop, includes scheduling a gain to adjust a VGT geometry based on each of the engine speed and the exhaust pressure, wherein the adjusting further includes changing an aspect ratio of the VGT based on the scheduled gain.The method of claim 1, further comprising, during the adjusting, maintaining a desired boost pressure, and wherein the adjusting is further based on one or more of an air flow, an exhaust flow, an engine speed, an engine speed combined with load, a turbocharger speed, a fueling, a torque (load), an exhaust pressure, and ambient conditions including an ambient temperature and an ambient pressure.The method of claim 1, wherein the adjusting based on the boost includes, in a first mode, increasing the aspect ratio of the VGT with at least one of a decrease in engine speed and an increase in exhaust pressure and decreasing the aspect ratio of the VGT with at least one of an increase in engine speed and a decrease in exhaust pressure; and in a second mode, increasing the aspect ratio of the VGT with an increase in at least one of engine speed and exhaust pressure and decreasing the aspect ratio of the VGT with a decrease in at least one of engine speed and exhaust pressure.The method of claim 1, wherein the adjusting is responsive to the difference between the outlet pressure and the intake pressure exceeding a first threshold.The method of claim 4, further comprising adjusting an exhaust gas recirculation (EGR) valve coupled to an EGR system based on the difference between the exhaust pressure and the intake pressure to reduce the difference, wherein the adjusting is further based on each of the engine speed and the exhaust pressure, wherein adjusting the EGR valve includes increasing the EGR valve opening with at least one of a decrease in the engine speed and an increase in the exhaust pressure; and decreasing the valve opening with at least one of an increase in the engine speed and a decrease in the exhaust pressure.The method of claim 4, further comprising adjusting a wastegate valve coupled to a wastegate passage based on the difference between the exhaust pressure and the intake pressure to reduce the difference, wherein the adjusting is further based on each of the engine speed and the exhaust pressure, and wherein adjusting the wastegate valve includes increasing the wastegate valve opening with at least one of a decrease in the engine speed and an increase in the exhaust pressure; and decreasing the wastegate valve opening with at least one of an increase in the engine speed and a decrease in the exhaust pressure.The method of claim 5, further comprising adjusting each of the VGT geometry and the EGR valve in response to the difference between the exhaust pressure and the intake pressure exceeding a second threshold, the second threshold being higher than the first threshold.A method for an engine, comprising: during a first boosted engine operating condition, selectively adjusting a vane actuator of the variable geometry turbine (VGT) responsive to a pressure difference between an exhaust manifold and an intake manifold exceeding a first threshold; during a second boosted engine operating condition, selectively adjusting an exhaust gas recirculation (EGR) valve responsive to the pressure difference exceeding the first threshold; during a third boosted engine operating condition, selectively adjusting a wastegate valve responsive to the pressure difference exceeding the first threshold; and during each of the first, second, and third conditions, maintaining a boost pressure.The method of claim 8, further comprising, during a fourth boosted engine operating condition, adjusting each of the VGT vane actuator, the EGR valve, and the wastegate valve in response to the pressure difference exceeding a second threshold, the second threshold being higher than the first threshold, wherein during each of the first, second, and third conditions, the adjusting is further based on a ratio of the exhaust manifold pressure to the intake manifold pressure.The method of claim 9, wherein the engine includes an intake compressor, wherein the first condition includes engine operation at or within a threshold distance of a combustion stability limit, and wherein the second condition includes compressor operation at or within the threshold distance of a compressor surge limit.The method of claim 8, wherein adjusting the VGT vane actuator during the first condition and adjusting the EGR valve during the second condition includes adjusting with a gain, the gain based on each of an engine speed and an exhaust manifold pressure, the gain increased with at least one of a decrease in engine speed and an increase in exhaust manifold pressure.The method of claim 8, wherein adjusting each of the VGT vane actuator and the EGR valve includes adjusting with a first term based on a proportional-integral (PI) controller, the first term based on an engine speed, an estimated intake manifold pressure, a target intake manifold pressure, and an estimated exhaust manifold pressure, and thereafter adjusting with a second term based on a proportional-derivative (PD) controller, the second term based on an engine speed, an estimated exhaust pressure, and a difference between the estimated exhaust manifold and the estimated intake manifold pressure.The method of claim 12, wherein selectively adjusting during the first condition includes actuating the VGT vane actuator to increase an opening of the VGT vanes based on each of the first and second terms to increase an aspect ratio of the VGT, and wherein selectively adjusting during the second condition includes opening the EGR valve based on each of the first and second terms to increase an opening of an EGR passage.The method of claim 8, wherein the pressure difference between the exhaust manifold and the intake manifold is calculated based on an intake pressure estimate obtained from an intake manifold pressure sensor and an exhaust pressure estimate obtained from an exhaust manifold pressure sensor.An engine system comprising: an engine having an intake manifold and an exhaust manifold; a turbocharger to provide a boosted air charge to the engine, the turbocharger having a variable geometry exhaust turbine (VGT) driving an intake compressor, the exhaust turbine having vanes to vary an aspect ratio of the turbine; a wastegate passage coupled via the exhaust turbine, the wastegate passage having a wastegate valve; an exhaust gas recirculation (EGR) system having an exhaust gas recirculation passage with an EGR valve, the EGR passage recirculating exhaust gases from the exhaust manifold to the intake manifold; a first pressure sensor coupled to the intake manifold; a second pressure sensor coupled to the exhaust manifold; a controller having computer readable instructions stored in non-transitory memory for: during operation of the engine with boost enabled, reducing a difference between an exhaust manifold pressure and an intake manifold pressure via adjustments to at least one of an aspect ratio of the exhaust turbine, an opening of the wastegate valve, and an opening of the exhaust gas recirculation valve; wherein reducing the difference between the exhaust manifold pressure and the intake manifold pressure includes increasing at least one of a VGT vane opening, wastegate valve opening, and EGR valve opening responsive to an increase in the pressure difference between the exhaust manifold pressure and the intake manifold above the threshold; wherein increasing at least one of a VGT vane opening, wastegate valve opening, and EGR valve opening includes calculating one or more control terms via at least one of a proportional integral (PI) control, a proportional derivative (PD) control, and a proportional integral derivative (PID) control based on an engine speed, an intake, and an exhaust manifold pressure, and actuating at least one of a VGT vane opening, wastegate valve opening, and EGR valve opening in accordance with the calculated gain.The system of claim 15, wherein reducing the difference between the exhaust manifold pressure and the intake manifold pressure includes adjusting at least one of the VGT vanes, the wastegate valve, and the EGR valve based on the engine speed and the exhaust pressure, wherein at least one of the VGT vane position, the wastegate valve opening, and the EGR valve opening is increased while the engine speed is decreased or the exhaust manifold pressure is increased, and wherein at least one of the VGT vane position, the wastegate valve opening, and the EGR valve opening is decreased while the engine speed or the exhaust manifold pressure is decreased.

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