METHOD FOR OPERATING AN ENGINE

Abstract

Engine operating procedure, comprising: determining that the regeneration of a particulate filter should be terminated; and increasing the boost pressure in an engine air intake via a control in response to the termination of the particulate filter regeneration in order to increase SCR efficiency by cooling a temperature of the SCR below a first threshold, while a driver-demand torque is substantially constant.

Description

TECHNICAL AREA The present invention relates to vehicle engines and in particular to a method for operating a vehicle engine. GENERAL STATE OF THE ART / BRIEF OVERVIEW A diesel engine can incorporate a selective catalytic reduction (SCR) catalyst to convert NOx into N2, H2O, and CO2. The diesel engine can also include a particulate filter to capture carbonaceous soot. This soot can be stored until the particulate filter is full; then, it can be burned off to regenerate the filter. Regeneration occurs when exhaust gases are heated in an oxidation catalyst and fed back into the particulate filter. There, the heated exhaust gases continue to heat the soot until it begins to burn in an oxygen-rich environment. The corresponding state of the art is known from publications DE 10 2015 012 736 A1 , DE 10 2010 063 425 A1 , DE 10 2008 032 332 A1 , US 2008 / 0 295 486 A1 and US 2005 / 0 060 989 A1. However, the SCR unit heats up when the particulate filter heats up, and this heating reduces the SCR unit's efficiency. The SCR unit can also remain above a desired temperature for a period of time after the particulate filter has regenerated. Therefore, it may be desirable to provide a way to reduce the period that the SCR unit remains above a temperature higher than a threshold temperature, at which point the SCR unit's efficiency may fall below that threshold. The object of the present invention is therefore to provide improved engine operating methods and an improved engine system. This problem is solved by the subject matter of the independent claims. Preferred embodiments of the present invention are the subject matter of the dependent claims. The inventors of the present invention have recognized the aforementioned disadvantages and have developed a method for operating an engine which comprises: determining that the regeneration of a particulate filter should be terminated; and increasing the turbocharger boost pressure via a control at a substantially constant driver demand torque in response to the end of the particulate filter regeneration in order to increase SCR efficiency by cooling the temperature of the SCR below a first threshold. By increasing the boost pressure in response to the end of particulate filter regeneration at a substantially constant driver demand torque, it may be possible to cool the SCR system after regeneration to such an extent that SCR efficiency can be increased within a short time. The boost pressure can be increased, and an intercooler bypass valve can be closed to increase the exhaust flow and reduce the exhaust temperature, thereby cooling the SCR system. The exhaust flow rate can be reduced to a first flow rate when the SCR temperature falls below a first threshold, and to a second flow rate when the SCR temperature falls below a second threshold. Reducing the exhaust flow allows the SCR system to be cooled while simultaneously increasing engine efficiency. The present description offers several advantages. In particular, the approach can reduce engine emissions by increasing SCR efficiency in a shorter timeframe. Additionally, the approach can enable increased engine efficiency while further reducing the SCR temperature. Furthermore, the approach can be applied to both four-stroke and two-stroke diesel engines. The aforementioned advantages, as well as other advantages and features of the present description, are readily apparent from the following detailed description, whether considered on its own or in conjunction with the accompanying drawings. It is understood that the foregoing summary is provided to present, in simplified form, a selection of concepts that are described in more detail in the detailed description. It is not intended to identify important or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that overcome any of the disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 shows a schematic representation of a first exemplary motor; Fig. 2 shows a schematic representation of a second exemplary motor; Figs. 3A-3B show an exemplary motor operating sequence; Fig. 4 shows a method for operating a motor. DETAILED DESCRIPTION This description concerns the operation of a diesel engine incorporating a particulate filter and an SCR system. Fig. 1 shows an example of a turbocharged diesel engine. Fig. 2 shows a second example of a turbocharged diesel engine. Figs. 3A and 3B show an exemplary engine operating sequence for improving SCR efficiency after particulate filter regeneration. Fig. 4 shows an exemplary method for operating an engine to improve SCR efficiency. With reference to Fig. 1, an internal combustion engine 10, comprising a plurality of cylinders, one of which is shown in Fig. 1, is controlled by an electronic engine control unit 12. The control unit 12 receives signals from the various sensors shown in Fig. 1 and uses the various actuators shown in Fig. 1 to adjust the engine operation based on the received signals and instructions stored in a memory of the control unit. The engine 10 comprises a combustion chamber 30 and cylinder walls 32 with a piston 36 positioned therein and connected to a crankshaft 40. A cylinder head 13 is attached to an engine block 14. The combustion chamber 30 is shown communicating with an intake manifold 44 and an exhaust manifold 48 via an intake valve 52 and an exhaust valve 54, respectively. Each intake and exhaust valve can be actuated by an intake cam 51 and an exhaust cam 53, respectively. However, in other examples, the engine can actuate the valves via a single camshaft or pushrods. The position of the intake cam 51 can be determined by an intake cam sensor 55. The position of the exhaust cam 53 can be determined by an exhaust cam sensor 57. A fuel injection device 68 is shown positioned in the cylinder head 13 to inject fuel directly into the combustion chamber 30, a process known to those skilled in the art as direct injection. Fuel is supplied to the fuel injection device 68 via a fuel system comprising a fuel tank 95, a fuel pump 91, a fuel pump control valve 93, and a fuel distribution line (not shown). The fuel pressure supplied by the fuel system can be adjusted by varying a position valve that regulates the flow to a fuel pump (not shown). Furthermore, a metering valve for a closed-loop fuel control system may be located in or near the fuel distribution line. Additionally, a pump metering valve may regulate the fuel flow to the fuel pump, thereby reducing the amount of fuel pumped to a high-pressure fuel pump. The intake manifold 44 is shown communicating with an optional electronic throttle 62, which sets the position of the throttle valve 64 to control the airflow from an intake charge chamber 46. A compressor 162 draws air from the air inlet 42 to supply it to the charge chamber 46. Exhaust gases cause a turbine 164 to rotate, which is coupled to the compressor 162 via a shaft 161. In some examples, an intercooler may be provided. The compressor speed can be adjusted by setting the position of a variable guide vane control 72 or a compressor bypass valve 158. In alternative examples, a wastegate 79 can replace or be used in addition to the variable guide vane control 78. The variable guide vane control 78 sets the position of variable-geometry turbine guide vanes 77.Exhaust gases can be directed through turbine 164, supplying a small amount of energy to rotate the turbine 164 when the guide vanes are in an open position. Exhaust gases can be directed through turbine 164, transferring increased power to the turbine 164 when the guide vanes are in a closed position. Alternatively, the wastegate 79 or a bypass valve allows the exhaust gases to flow around turbine 164, thus reducing the amount of energy supplied to the turbine. The compressor bypass valve 158 allows compressed air at the compressor 162 outlet to be recirculated to the compressor 162 inlet. In this way, the efficiency of the compressor 162 can be reduced, thereby influencing the compressor 162 flow rate and reducing the possibility of compressor pumping. Combustion is initiated in the combustion chamber 30 when fuel ignites automatically as the piston 36 is near top dead center of the compression stroke. In some examples, a wideband lambda sensor (Universal Exhaust Gas Oxygen Sensor - UEGO sensor) 126 may be coupled to the exhaust manifold 48 upstream of an emission control device 71. In other examples, the UEGO sensor may be located downstream of one or more exhaust aftertreatment devices. Furthermore, in some examples, the UEGO sensor may be replaced by a NOx sensor that incorporates both NOx and oxygen sensing elements. At lower engine temperatures, a glow plug 66 can convert electrical energy into heat energy to increase the temperature in the combustion chamber 30. By increasing the temperature of the combustion chamber 30, it may be easier to ignite a cylinder-air-fuel mixture via compression. The emission device 71 can, in one example, include an oxidation catalyst, followed by an SCR 72 and a diesel particulate filter (DPF) 73. In another example, the DPF 73 can be positioned upstream of the SCR 72. A temperature sensor 75 provides information about the SCR temperature. High-pressure exhaust gas recirculation (EGR) can be supplied to the engine via a high-pressure EGR valve 80 and a high-pressure EGR channel 81. The high-pressure EGR valve 80 is a valve that closes or allows exhaust gas to flow from upstream of the emission device 71 to a point in the engine air intake system located upstream of the compressor 162. The high-pressure EGR can bypass an EGR cooler 85, or alternatively, the high-pressure EGR can be cooled by passing through the EGR cooler 85. Low-pressure EGR can be supplied to the engine via a low-pressure EGR valve 84 and a low-pressure EGR channel 83. The controller 12 is shown in Fig. 1 as a conventional microcomputer comprising: a microprocessor unit 102, input / output ports 104, a read-only memory (e.g., non-volatile memory) 106, a random access memory 108, a keep-alive memory 110, and a conventional data bus.According to the diagram, in addition to the signals discussed previously, the control unit 12 receives various signals from the sensors coupled to the engine 10, including: an engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling sleeve 114; a position sensor 134 coupled to an accelerator pedal 130 to detect the accelerator pedal position set by a human foot 132; a measurement of the engine manifold pressure (MAP) from a pressure sensor 121 coupled to the intake manifold 44; a boost pressure from a pressure sensor 122; an exhaust oxygen concentration from a lambda sensor 126; an engine position sensor from a Hall effect sensor 118 detecting the position of the crankshaft 40; and a measurement of the mass of air flowing into the engine from a sensor 120 (e.g.,a hot-wire air mass meter); and a measurement of the throttle position from a sensor 58. Atmospheric pressure can also be acquired for processing by the controller 12 (sensor not shown). In a preferred aspect of the present description, the engine position sensor 118 generates a predetermined number of evenly spaced pulses at each revolution of the crankshaft, from which the engine speed (rpm) can be determined. During operation, each cylinder in the engine 10 typically undergoes a four-stroke cycle: The cycle includes the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, the exhaust valve 54 generally closes and the intake valve 52 opens. Air is drawn into the combustion chamber 30 via the intake manifold 44, and the piston 36 moves toward the bottom of the cylinder, thus increasing the volume within the combustion chamber 30. The position at which the piston 36 is near the bottom of the cylinder and at the end of its stroke (e.g., when the combustion chamber 30 has reached its maximum volume) is typically referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, the intake valve 52 and the exhaust valve 54 are closed. The piston 36 moves toward the cylinder head, thus compressing the air in the combustion chamber 30.The point at which the piston 36 is closest to the cylinder head at the end of its stroke (e.g., when the combustion chamber 30 has its smallest volume) is typically referred to by those skilled in the art as top dead center (TDC). In a process subsequently referred to as injection, fuel is introduced into the combustion chamber. In some examples, fuel can be injected into a cylinder a multitude of times during a single cylinder cycle. In a process subsequently referred to as ignition, the injected fuel is ignited by auto-ignition, resulting in combustion. During the power stroke, the expanding gases push the piston 36 back to bottom dead center (BDC). The crankshaft 40 converts piston movements into torque of the rotating shaft. Finally, during the exhaust stroke, the exhaust valve 54 opens to release the burnt air-fuel mixture to the exhaust manifold 48, and the piston returns to top dead center (TDC). It should be noted that the foregoing is merely an example and that the timing of the opening and / or closing of the intake and exhaust valves may vary, for example, to provide positive or negative valve overlap, late closing of the intake valve, or various other examples. Furthermore, a two-stroke cycle may be used instead of a four-stroke cycle in some examples. With reference to Fig. 2, an alternative engine is now shown. The engine 20 is an opposed-piston internal combustion engine comprising a plurality of cylinders, one of which is shown in Fig. 2, and is controlled by an electronic engine control unit 212. The control unit 212 receives signals from the various sensors shown in Fig. 2 and uses the various actuators shown in Fig. 2 to adjust the engine operation based on the received signals and the instructions stored in a memory of the control unit. The engine 20 comprises a cylinder 230 and cylinder walls 232, with an intake piston 236a and an exhaust piston 236b positioned within it and each connected to a crankshaft 240a and 240b, respectively. The crankshafts 240a and 240b can be coupled to each other via belts, chains, or gears. The crankshafts 240a and 240b can be rotated by the electric machine 27 (e.g., a starter motor) to crank the engine 20. The cylinder 230 is shown communicating with an intake manifold 244 and an exhaust manifold 248 via intake ports 244a and 244b and exhaust ports 248a and 248b. A first fuel injection device 269 and a second fuel injection device 268 are shown positioned in the cylinder walls 232, and they can inject fuel directly into the cylinder 230, a process known to those skilled in the art as direct injection. Fuel is supplied to the first fuel injection device 269 and the second fuel injection device 268 via a fuel system comprising a fuel tank 295, a fuel pump 291, a fuel pump control valve 293, and a fuel distribution line (not shown). The fuel pressure supplied by the fuel system can be adjusted by varying a position valve that regulates the flow to a fuel pump (not shown). Furthermore, a metering valve for a closed-loop fuel control system may be located in or near the fuel distribution line.In addition, a pump metering valve can regulate the fuel flow to the fuel pump, thereby reducing the amount of fuel pumped to a high-pressure fuel pump. The intake manifold 244 is shown communicating with an optional electronic throttle 262, which sets the position of the throttle valve 264 to control the airflow from an intake charge chamber 246. A mechanically driven compressor 262 draws air from downstream of a turbocharger compressor 235. The turbocharger compressor 235 draws air from an air inlet 242. The compressor 262 supplies air to the charge chamber 246. Exhaust gases cause a variable geometry turbocharger turbine 237 to rotate, which is coupled to the turbocharger compressor 235 via a shaft 236. The compressor 262 is mechanically driven via the crankshaft 240b through a shaft 261 and a gearbox 263, which can be coupled to the crankshaft 240b via a mechanism 264 (e.g. gears, a chain or a belt).The compressor gearbox 263 incorporates a variety of gear ratios to change the speed of the compressor 262 relative to the speed of the crankshaft 240b. The speed of the compressor can be adjusted by selecting and engaging gears 263a of the gearbox 263. For example, the compressor 262 can be rotated at a given speed of the engine crankshaft at a first speed and a second speed by switching between a first and a second gear ratio in the gearbox 263. The compressor bypass valve 258 can be selectively opened to reduce the air pressure in the charge chamber 246 and recirculate air and exhaust gas (EGR) upstream of the compressor 262. In some examples, an intercooler 256 may be provided downstream of the compressor 262 to cool the air charge entering the cylinder 230. An intercooler bypass valve 257 can be selectively opened to bypass the intercooler 256. The position of a swivel motor 237a can be adjusted via the control 212 to increase or decrease the rotational speed of the turbine 237. In alternative examples, a wastegate 237b may replace or be used in addition to the swivel motor 237a. The swivel motor 237a adjusts the position of variable geometry turbine guide vanes.Exhaust gases can be directed through the turbine 237, supplying a small amount of energy to rotate the turbine 237 when the guide vanes are in an open position. Exhaust gases can be directed through the turbine 237, transferring increased power to the turbine 237 when the guide vanes are in a closed position. Alternatively, the wastegate 237b or a bypass valve allows the exhaust gases to flow around the turbine 237, thus reducing the amount of energy supplied to the turbine. In an alternative example, the compressor 262 can be positioned upstream of the turbocharger compressor 235. Furthermore, an intercooler (not shown) can be positioned downstream of the point where an EGR channel 282 between the compressor 262 and the turbocharger compressor 235 meets the inlet 243. The intercooler eliminates the need for an EGR cooler. Exhaust gases can be recirculated to cylinder 230 via the EGR system 281. The EGR system includes an optional EGR cooler 285, an EGR valve 280, an EGR duct 282, an EGR cooler bypass 284, and a cooled EGR duct 283. Exhaust gases can flow from the exhaust manifold 248 to the engine air intake 243 between the supercharger compressor 262 and the turbocharger compressor 235. EGR can flow to the engine air intake when the pressure in the exhaust manifold 248 is greater than the pressure between the turbocharger compressor 235 and the supercharger compressor 262. The EGR can flow through the EGR cooler 285 to reduce engine exhaust gas temperatures. The EGR can bypass the EGR cooler 285 when the engine exhaust temperatures are low. Fuel can be injected into cylinder 230 when pistons 236a and 236b approach each other, after the intake piston 236a covers the intake ports 244a and 244b and the exhaust piston 236b covers the exhaust ports 248a and 248b. The fuel can then be combusted with air in cylinder 230 when piston 236 is near top dead center of the compression stroke. The fuel and air are ignited by auto-ignition. In some examples, a wideband lambda sensor (UEGO sensor) 226 can be coupled to the exhaust manifold 248 upstream of an emission device 271. In other examples, the UEGO sensor can be located downstream of one or more exhaust aftertreatment devices. Furthermore, in some examples the UEGO probe can be replaced by a NOx sensor that has both NOx and oxygen detection elements. Engine 20 does not include glow plugs or spark plugs, as it is a compression-ignition engine and does not have a cylinder head. Furthermore, engine 20 does not include poppet valves for regulating the air and exhaust flow into and out of cylinder 230. The exhaust system 231 transports exhaust gas away from the engine 20 and processes it. An exhaust valve 240 is shown positioned in an exhaust channel 249 downstream of the turbine 237a and upstream of the emission device 271. Alternatively, the exhaust valve 240 can be positioned downstream of the emission device 271. The exhaust valve 240 can be opened and closed to control the pressure in the exhaust manifold 48. Closing the exhaust valve 240 limits the flow through it, thereby increasing the pressure in the exhaust manifold 248. Opening the exhaust valve 240 increases the flow and reduces the pressure in the exhaust manifold 248. The emission device 271 can, in one example, be an oxidation catalyst and can be positioned upstream of the SCR 272 and the particulate filter 273. A temperature sensor 275 provides a temperature reading for the SCR. The controller 212 is shown in Fig. 2 as a conventional microcomputer comprising: a microprocessor unit 202, input / output terminals 204, a read-only memory (e.g., non-volatile memory) 206, a random access memory 208, a keep-alive memory 210, and a conventional data bus.According to the illustration, in addition to the signals discussed previously, the control unit 212 receives various signals from sensors coupled to the engine 20, including: an engine coolant temperature (ECT) from a temperature sensor 212 coupled to a cooling sleeve 214; a position sensor 234 coupled to an accelerator pedal 230 to detect the accelerator pedal position set by a human foot 232; a manifold absolute pressure (MAP) measurement from a pressure sensor 221 coupled to the intake manifold 244; a boost pressure from a pressure sensor 222; an exhaust oxygen concentration from a lambda sensor 226; an engine position sensor from a Hall effect sensor 218 detecting the position of the crankshaft 240b; and a measurement of the mass of air flowing into the engine from a sensor 220 (e.g., a hot-wire air mass meter). and a measurement of the throttle position from a sensor 258.Atmospheric pressure can also be detected for processing by the controller 212 (sensor not shown). In a preferred aspect of the present description, the engine position sensor 218 generates a predetermined number of evenly spaced pulses at each revolution of the crankshaft, from which the engine speed (rpm) can be determined. During operation, each cylinder in engine 20 is typically subjected to a two-stroke cycle: The cycle includes a first stroke in which the intake piston 236a moves towards the exhaust piston 236b and the exhaust piston 236b moves towards the intake piston 236a. In the second stroke, the intake piston 236a moves away from the exhaust piston 236b and the exhaust piston 236b moves away from the intake piston 236a. The intake piston 236a controls the flow through the intake ports 244a and 244b. The exhaust piston 236b controls the flow through the exhaust ports 248a and 248b. In this example, the exhaust piston 236b precedes the intake piston 236a by reaching a top dead center position (e.g., a maximum distance of the exhaust piston 236b from the crankshaft 240b) a few crankshaft degrees (e.g.,The difference (which can be between 0 and 20 crankshaft degrees depending on the configuration) is reached before the intake piston 236a reaches its top dead center position (e.g., the maximum distance of the intake piston 236a from the crankshaft 240a). Thus, the movement of the exhaust piston is offset from the movement of the intake piston by a few crankshaft degrees. During the first stroke, the intake piston 236a and the exhaust piston 236b generally move towards each other to compress the air that has entered cylinder 230. The stroke begins for the intake piston 236a at bottom dead center (BDC) (the intake piston 236a is at its closest point to the crankshaft 240a) and ends for the intake piston 236a at top dead center (the intake piston 236a is at its farthest point from the crankshaft 240a). As mentioned earlier, the exhaust piston 236b precedes the intake piston 236a by a few degrees, so it is already moving towards its top dead center (TDC) position when the intake piston is at BDC. Furthermore, the exhaust piston 236b reaches its TDC position shortly before the intake piston 236a reaches its TDC position. The exhaust piston 236b is located directly after its TDC position when the intake piston 36a reaches its TDC position.The cylinder volume is at its smallest when the intake piston 236a and the exhaust piston 236b are near their respective top dead center (TDC) positions. Air and fuel are compressed in cylinder 230 as the intake piston 236a and the exhaust piston 236b move towards their respective TDC positions. The intake ports 244a and 244b are open and compressed air flows into cylinder 230 when the intake piston 236a and the exhaust piston 236b are near their respective bottom dead center (BDC) positions. The exhaust ports 248a and 248b are also open when the intake piston 236a and the exhaust piston 236b are near BDC. The compressor 262 and the turbocharger 235 supply compressed air to the intake manifold 244, which can flow into cylinder 230 when the intake ports 244a and 244b are open. As the intake piston 236a and the exhaust piston 236b move towards their respective top dead center (TDC) positions, the exhaust ports 248a and 248b close. A few crankshaft degrees later, the intake ports 244a and 244b are closed to prevent additional air from entering cylinder 236.Fuel is injected into cylinder 230 after the exhaust ports 244a and 244b have closed; the fuel-air mixture is then ignited when the intake piston 236a and the exhaust piston 236b are near their respective top dead center (TDC) positions. The fuel-air mixture is ignited by auto-ignition, not by a spark plug or glow plug energy. The fuel can be injected into cylinder 230 via a variety of injection methods, including pre-injection, main injection, and post-injection. During the second stroke, the intake piston 236a and the exhaust piston 236b generally move away from each other after combustion has occurred in cylinder 230. The second stroke begins at top dead center (TDC) of the intake piston 236a and ends at bottom dead center (BDC) of the intake piston 236a. The intake piston 236a and the exhaust piston 236b approach their respective BDC positions, near which the volume of cylinder 230 is greatest. Expanding gases in cylinder 230 push the intake piston 236a and the exhaust piston 236b away from each other toward their respective BDC positions. The exhaust piston 236b passes the exhaust ports 248a and 248b as it moves toward its BDC. The exhaust ports 248a and 248b are exposed when the top of the exhaust piston 236d moves past the exhaust ports 248a and 248b as the exhaust piston 236b moves towards the crankshaft 240b.Exhaust gases exit cylinder 230 after the exhaust piston 236b has passed exhaust ports 248a and 248b as it moves towards bottom dead center. The intake piston 236a and exhaust piston 236b continue to move towards their respective bottom dead center positions, and after a predetermined total number of crankshaft degrees, the intake piston 236a exposes intake ports 244a and 244b. The intake ports 244a and 244b are exposed when the top of the intake piston 236c moves past them as the intake piston 236a moves toward the crankshaft 240a. Fresh air flows into cylinder 230 through the intake ports 244a and 244b once they are exposed. The intake piston 236a and exhaust piston 236b continue moving toward their respective bottom dead center (BDC) positions. After the intake piston reaches BDC, the cylinder cycle repeats. Thus, the engine cycle consists of two strokes, and one engine cycle corresponds to one engine revolution. Other engine cylinders operate similarly, but these other cylinders may burn air and fuel out of phase with the cylinder shown. For example, the top dead center of the compression stroke of one engine cylinder may be at zero crankshaft degrees, while the top dead center of another cylinder may be at one hundred and eighty crankshaft degrees. The systems shown in Figures 1 and 2 provide an engine system comprising: a two-stroke opposed-piston diesel engine containing at least one cylinder; an exhaust system coupled to the two-stroke engine, comprising an oxidation catalyst, a selective catalytic reduction (SCR) system, and a particulate filter; and a control system containing executable instructions stored in non-volatile memory to increase the exhaust flow to the SCR system in response to the end of particulate filter regeneration and the SCR temperature exceeding a first threshold temperature. The engine system includes the first threshold temperature being the temperature above which SCR efficiency falls below a certain threshold. The engine system further includes additional instructions to increase the exhaust flow to the SCR system by increasing the boost pressure in response to the end of particulate filter regeneration.The engine system also includes additional instructions to close an intercooler bypass valve and a compressor bypass valve in response to the end of particulate filter regeneration. The engine system also includes additional instructions to close an EGR cooler bypass valve in response to the end of particulate filter regeneration. The engine system also includes additional instructions to reduce the exhaust gas flow to the SCR in response to the SCR temperature falling below the first threshold. The engine system also includes additional instructions to reduce the exhaust gas flow to the SCR in response to the SCR temperature falling below a second threshold. The engine system also includes the injection of urea into the SCR in response to the end of particulate filter regeneration and the SCR temperature falling below the first threshold. With reference to Figures 3A and 3B, an exemplary motor operating sequence according to the method shown in Figure 4 is now presented. The sequence can be provided via the systems shown in Figures 1 and 2, and their respective controllers can incorporate the method shown in Figure 4. Vertical lines represent relevant time points (e.g., t1-t3) during the respective sequence progressions. The sequences in the progressions occur simultaneously, and the progressions are temporally aligned. The first curve from the top in Fig. 3A represents a particulate filter (PF) regeneration request over time. Line 302 represents the particulate filter's regeneration request state. The vertical axis represents the particulate filter's regeneration state, and regeneration is requested when line 302 is near the vertical axis arrow at a higher level. Particulate filter regeneration is not requested when line 302 is near the horizontal axis. The horizontal axis represents time, and time increases from the left to the right side of the figure. The second line from the top in Fig. 3A represents the position of the guide vanes of a variable geometry turbocharger (VGT) over time. Line 304 represents the guide vane position. The vertical axis represents the guide vane position, and the guide vanes open in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. The third line from the top in Fig. 3A represents the position of the engine intake throttle in relation to time. Line 306 represents the throttle position. The vertical axis represents the throttle position, and the throttle opens in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. The fourth line from the top in Fig. 3A represents the position of the exhaust throttle in relation to time. Line 308 represents the throttle position. The vertical axis represents the exhaust throttle position, and the exhaust throttle opens in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. The fifth curve from the top in Fig. 3A represents the state of the EGR cooler bypass valve over time. Line 310 represents the state of the EGR cooler bypass valve. The vertical axis represents the state of the EGR cooler bypass valve, and the EGR bypass valve is open to bypass the EGR cooler when line 310 is near the vertical axis arrow at a higher level. The EGR cooler bypass valve is closed, so the EGR cooler is not bypassed, when line 310 is at a lower level near the horizontal axis. The horizontal axis represents time, and time increases from the left to the right side of the figure. The sixth line from the top in Fig. 3A represents the state of the charge air cooler (CAC) bypass valve over time. Line 312 represents the position of the CAC bypass valve. The vertical axis represents the state of the CAC bypass valve, and the CAC bypass valve is open to bypass the CAC when line 312 is near the vertical axis arrow at a higher level. The CAC bypass valve is closed, so the CAC is not bypassed, when line 312 is at a lower level near the horizontal axis. The horizontal axis represents time, and time increases from the left to the right side of the figure. The seventh curve from the top in Fig. 3A represents the state of the compressor bypass valve over time. Line 314 represents the position of the compressor bypass valve. The vertical axis represents the state of the compressor bypass valve, and the compressor bypass valve is open to bypass the compressor when line 314 is near the vertical axis arrow at a higher level. The compressor bypass valve is closed, so the compressor cooler is not bypassed, when line 314 is at a lower level near the horizontal axis. The horizontal axis represents time, and time increases from the left to the right side of the figure. The first curve from the top in Fig. 3B represents the urea injection quantity over time. Line 318 represents the urea injection quantity. The vertical axis represents the urea injection quantity, and the urea injection quantity increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. The second curve from the top in Fig. 3B represents the SCR temperature over time. Line 320 represents the SCR temperature. The vertical axis represents the SCR temperature, and the SCR temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. Horizontal line 350 is a threshold value above which the SCR efficiency falls below a certain threshold (e.g., 30%). Horizontal lines 352 and 354 represent the upper and lower limits of a desired SCR temperature range, within which the SCR efficiency can exceed a certain threshold (e.g., 90%). The third curve from the top in Fig. 3B represents the engine boost pressure (e.g., the pressure in boost chamber 46 or boost chamber 246) as a function of time. Line 322 represents the boost pressure. The vertical axis represents the boost pressure, and the boost pressure increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. The fourth curve from the top in Fig. 3B represents the low-pressure EGR flow over time. Line 324 represents the low-pressure EGR flow. The vertical axis represents the low-pressure EGR flow, and the low-pressure EGR flow increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. The fifth curve from the top in Fig. 3B represents the drive ratio of the compressor compressor with respect to time. Line 326 represents the drive ratio of the compressor compressor. The vertical axis represents the drive ratio of the compressor compressor, and this ratio increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. The sixth curve from the top in Fig. 3B represents the high-pressure EGR flow over time. Line 328 represents the high-pressure EGR flow. The vertical axis represents the high-pressure EGR flow, and the high-pressure EGR flow increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left to the right side of the figure. Although not shown, the driver-request torque is essentially constant (e.g., it changes by less than +5% of the desired value) and the engine speed is essentially constant throughout the sequence of Fig. 3A and Fig. 3B. At time t0, the engine is running and burning air and fuel (not shown). The particulate filter is regenerating, as indicated by the PF state line, which is at a higher level. The VGT guide vanes are partially closed, and the intake throttle is in a mid-position. The exhaust throttle is partially open, and the EGR cooler bypass valve is fully open to bypass the EGR cooler. The CAC valve is fully open, and the compressor bypass valve is partially open. The EGR valve is partially open, and no urea is injected. The SCR temperature is above the threshold of 350°C, so its efficiency is low. The boost pressure is at an upper mid-level. The low-pressure EGR flow is at a mid-level, and the high-pressure EGR flow is at a higher mid-level. The compressor drive ratio is at a lower drive ratio.At time t1, the particulate filter regeneration is complete, as indicated by the particulate filter regeneration request, which transitions from a higher to a lower level. The VGT guide vanes are fully closed, and the intake throttle is fully open in response to the completion of particulate filter regeneration. The exhaust throttle is also fully open, and the EGR cooler bypass valve is closed in response to the completion of particulate filter regeneration. The CAC valve is also closed, and the compressor bypass valve is fully closed in response to the completion of particulate filter regeneration. The EGR valve opens in response to engine speed and driver demand torque to control the engine's NOx output while SCR conversion is low.No urea is injected while the SCR temperature is high, thus conserving urea until SCR efficiency can be improved. The SCR temperature remains above the threshold of 350°C. The boost pressure increases in response to the end of the particulate filter regeneration. The low-pressure EGR flow is increased, and the high-pressure EGR flow is decreased. Furthermore, the compressor drive ratio is increased. By increasing boost pressure and closing the CAC (Compressor Acceleration Control Valve), the exhaust gas flow to the SCR (Selective Catalytic Reduction) can be increased. Furthermore, closing the CAC can help reduce exhaust gas temperature, allowing cooler exhaust gases to flow to the SCR, thus cooling it. Closing the compressor bypass increases compressor efficiency to increase exhaust gas flow, and closing the EGR cooler bypass cools the EGR, thereby cooling the engine exhaust gases routed to the SCR. Opening the engine throttle and / or exhaust throttle can increase engine airflow, allowing the SCR to cool more quickly. Increasing the compressor drive ratio increases airflow through the engine. Increasing the low-pressure EGR also increases flow through the engine, which can be particularly beneficial at engine idle speed, as engine boost pressure may be limited by low engine speed.The high-pressure EGR quantity is reduced so that the EGR flow is not too strong. Between time t1 and time t2, the SCR temperature decreases, and exhaust gas continues to flow to the SCR at a higher flow rate than if the boost pressure and exhaust flow were adjusted solely in response to driver demand torque and engine speed. Particulate filter regeneration is not requested, and the VGT guide vanes are fully closed. The intake and exhaust throttles are fully open, and the EGR cooler bypass valve is fully closed. The CAC bypass valve and the compressor bypass valve are fully closed. No urea is injected, and the boost pressure increases and then stabilizes at a higher level. The low-pressure EGR flow increases and then stabilizes. The high-pressure EGR decreases and then stabilizes at a constant value. The compressor drive ratio remains elevated. At time t2, the SCR temperature is below the threshold of 350°C, so the boost pressure is reduced to decrease the exhaust gas flow and increase engine efficiency. Additionally, urea injection begins in response to the SCR temperature falling below the 350°C threshold. A small amount of urea is injected to further enhance SCR efficiency. The VGT guide vane position is opened to reduce boost pressure, and the engine's intake and exhaust throttles remain fully open. The EGR cooler bypass valve remains closed, and the CAC cooler bypass valve is also fully closed. The compressor bypass valve remains closed, and the SCR temperature continues to decrease after time t2, further increasing SCR efficiency (not shown). The compressor drive ratio remains constant, and the low- and high-pressure EGR flows remain at their respective previous values. At time t3, the SCR temperature is reduced below the threshold of 352°C. The SCR NOx conversion efficiency is increased (not shown) when the SCR temperature falls below the threshold of 352°C. The boost pressure is further reduced to a level corresponding to the current engine speed and driver demand torque. The injected amount of urea also increases to further enhance SCR efficiency. Particulate filter regeneration is not requested, and the VGT guide vanes open to reduce boost pressure in response to the SCR temperature. The exhaust and intake throttles are partially closed, and the EGR cooler bypass valve opens in response to the SCR temperature falling below the threshold of 350°C. The CAC and compressor bypass valves are also closed in response to the SCR temperature falling below the threshold of 350.The EGR valve position remains constant. The compressor drive ratio is reduced, increasing the high-pressure EGR flow. The low-pressure EGR flow is decreased. In this way, SCR efficiency can be increased after particulate filter regeneration to reduce engine emissions. The exhaust gas flow to the SCR can be increased and the exhaust gas flow temperature can be decreased to lower the SCR temperature. If the SCR temperature is reduced below an initial threshold temperature, the SCR cooling rate can be further reduced to increase engine efficiency, even while SCR cooling continues. With reference to Fig. 4, a method for operating an engine is now shown. In particular, a flowchart of a method for operating an internal combustion engine is shown. The method from Fig. 4 can be stored as executable instructions in non-volatile memory in a system as shown in Figs. 1 and 2. The method from Fig. 4 can be integrated into and interact with the systems from Figs. 1 and 2. Furthermore, at least sections of the method from Fig. 4 can be integrated as executable instructions stored in non-volatile memory, while other sections of the method can be carried out via a controller that converts operating states of devices and actuators in the physical world. The controller can use motor actuators of the engine system to adjust the engine operation according to the methods described below. In procedure 402, procedure 400 determines engine operating conditions. These conditions can include, among other things, engine temperature, accelerator pedal position, particulate filter soot load, ambient temperature, ambient pressure, driver-demanded torque, and engine speed. The engine operating conditions can be determined via engine sensors and the engine control unit. Procedure 400 then transitions to 404. In procedure 404, procedure 400 determines whether diesel particulate filter (DPF) regeneration is desired. In one example, procedure 400 determines whether DPF regeneration is desired in response to a pressure drop across the DPF. In other examples, procedure 400 may determine that DPF regeneration is desired after a vehicle has driven more than a threshold distance. If procedure 400 determines that DPF regeneration is desired, the answer is yes, and procedure 400 proceeds to 406. Otherwise, the answer is no, and procedure 400 proceeds to 424. In procedure 406, procedure 400 increases a boost pressure (e.g., the pressure in an engine air intake) compared to a boost pressure for the same engine speed and driver-demanded torque when the diesel particulate filter is not regenerating. Furthermore, the engine's intake throttle is partially closed to increase the exhaust gas temperature. Procedure 400 then transitions to procedure 408. At 408, process 400 begins with the post-injection of fuel into the engine cylinders. Post-injected fuel is injected after the main fuel injections, and at least a portion of the fuel injected into the intake manifold is expelled from the engine cylinders to be oxidized in an oxidation catalyst. This oxidation raises the exhaust gas temperature, thereby facilitating the regeneration of the particulate filter. After the start of the post-injection of fuel, process 400 transitions to 410. At step 410, procedure 400 assesses whether diesel particulate filter regeneration is complete. For example, procedure 400 judges that particulate filter regeneration is complete if the pressure drop across the diesel particulate filter is below a threshold. If procedure 400 judges that particulate filter regeneration is complete, the answer is yes, and procedure 400 proceeds to step 412. Otherwise, procedure 400 returns to step 408. At 412, procedure 400 stops the post-injection of fuel and terminates the particulate filter regeneration. Furthermore, procedure 400 increases the boost pressure or, alternatively, maintains the boost pressure after the particulate filter regeneration is complete. The boost pressure can be increased while the driver demand torque remains substantially constant (e.g., by changing by less than +5% of the desired value). Furthermore, the boost pressure can be increased even if the driver demand decreases or increases. The boost pressure can be increased via a turbocharger compressor or a supercharger. Procedure 400 also opens the intake and / or exhaust throttle. By increasing the boost pressure and opening the intake and / or exhaust throttle, the exhaust flow to the SCR can be increased to cool the SCR. Procedure 400 then transitions to 414. Procedure 400, at 414, closes the CAC bypass valve, the EGR cooler bypass valve, and the compressor bypass valve. The CAC bypass, EGR bypass, and compressor bypass are closed to cool the exhaust gases. Furthermore, Procedure 400 can increase the compressor drive ratio to increase the flow through the engine and SCR system. Increasing the compressor drive ratio increases the compressor speed relative to the crankshaft speed. The variable geometry turbocharger (VGT) guide vanes and a supercharger (SC) bypass valve can also be closed to increase engine airflow. In some cases, the VGT guide vanes can be partially closed to a position that provides an upper threshold boost pressure (e.g., maximum boost pressure) in response to the end of particulate filter regeneration and other engine operating conditions.Procedure 400 transitions to 416. In procedure 400, part 416 adjusts the EGR valve in response to engine speed and driver demand torque. When engine speed and load are constant, the EGR valve position remains constant. However, if the engine incorporates high- and low-pressure EGR channels, the low-pressure EGR flow can be increased, and the high-pressure EGR flow can be decreased, to increase engine airflow while reducing engine NOx emissions. The positions of the low- and high-pressure EGR valves can be adjusted in response to engine speed and load after increasing the ratio of low-pressure to high-pressure EGR (e.g., low-pressure EGR quantity or flow / high-pressure EGR quantity or flow). Increasing the low-pressure EGR flow and decreasing the high-pressure EGR flow can improve engine efficiency while maintaining engine NOx emissions. At step 418, procedure 400 assesses whether the SCR temperature is below a first threshold temperature. The first threshold temperature can be a temperature (e.g., 380 °C) above which the NOx conversion efficiency of the SCR falls below a threshold (e.g., below 30%). If procedure 400 determines that the SCR temperature is below the first threshold temperature, the answer is yes, and procedure 400 proceeds to step 420. Otherwise, procedure 400 returns to step 418, and SCR cooling continues. At 420, procedure 400 reduces the boost pressure. The boost pressure can be reduced as a function of the driver-demand torque and the SCR temperature. In one example, the desired boost pressure is determined empirically and stored in a table or function referenced or indexed by the SCR temperature and the driver-demand torque. In another example, the boost pressure is reduced to provide a desired level of engine efficiency improvement for a desired reduction in SCR cooling. Procedure 400 reduces the boost pressure by opening a wastegate or opening variable-position turbocharger guide vanes and proceeds to 422. In procedure 422, procedure 400 assesses whether the SCR temperature is below a second threshold temperature. In one example, the second threshold temperature is a temperature above which the NOx conversion efficiency falls below a threshold efficiency (e.g., 90%). If procedure 400 determines that the SCR temperature is below the second threshold temperature, the answer is yes, and procedure 400 proceeds to 424. Otherwise, the answer is no, and procedure 400 returns to 422. At 424, procedure 400 adjusts the CAC bypass valve, the EGR valve, the EGR cooler bypass valve, the boost pressure, the low-pressure EGR, the high-pressure EGR, the compressor drive ratio, and the compressor bypass valve in response to driver demand torque and engine speed. In other words, the SCR operates within a desired temperature range, and the aforementioned actuators are therefore not adjusted to cool the SCR, but rather to provide a desired demand torque while the engine operates efficiently. Procedure 400 then terminates. Accordingly, Method 400 provides an engine operating method that includes: increasing the boost pressure in an engine air intake via a control system in response to the end of particulate filter regeneration while a driver-demand torque is substantially constant. The engine method involves increasing the boost pressure by at least partially closing the guide vanes of a turbocharger and further includes increasing the low-pressure exhaust gas recirculation flow and decreasing the high-pressure exhaust gas recirculation flow in response to the end of particulate filter regeneration. The engine method further includes opening an intake throttle in response to the end of particulate filter regeneration and increasing a compressor drive ratio to increase the boost pressure. The engine method further includes closing an EGR cooler bypass valve in response to the end of particulate filter regeneration.The engine procedure further includes closing an intercooler bypass valve in response to the end of the particulate filter regeneration. The engine procedure further includes closing a compressor bypass valve in response to the end of the particulate filter regeneration. The engine procedure further includes opening an exhaust throttle in response to the end of the particulate filter regeneration. The method shown in Fig. 4 also provides an engine operating procedure that includes: increasing the boost pressure in an engine air intake via a control system in response to the end of particulate filter regeneration while a driver-demand torque is substantially constant; and adjusting an EGR valve position based on the driver-demand torque and engine speed in response to the end of particulate filter regeneration and before the SCR temperature falls below a first threshold temperature. The engine procedure involves the EGR valve being a low-pressure EGR valve and further includes adjusting the low-pressure EGR valve to increase the low-pressure EGR flow and thus the exhaust gas flow to an SCR in response to the end of particulate filter regeneration and before the SCR temperature falls below the first threshold temperature.The engine procedure further includes reducing the exhaust gas flow to the SCR in response to the SCR temperature falling below the first threshold. The engine procedure further includes injecting urea into the SCR in response to the SCR temperature falling below the first threshold. The engine procedure further includes reducing the exhaust gas flow to the SCR in response to the SCR temperature falling below a second threshold temperature. It should be noted that the exemplary control and estimation routines contained herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in non-transient memory and can be executed by the control system, which includes the control unit in combination with the various sensors, actuators, and other engine hardware. Furthermore, parts of the methods can be physical actions performed in the real world to change the state of a device. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like.Accordingly, various illustrated actions, operations, and / or functions can be performed in the illustrated sequence or in parallel, or in some cases, omitted. Likewise, the processing order is not strictly necessary to achieve the features and benefits of the examples described here, but is provided to facilitate illustration and description. One or more of the illustrated actions, operations, and / or functions can be performed repeatedly, depending on the specific strategy employed.Furthermore, the described actions, operations, and / or functions can graphically represent code to be programmed into the non-transient memory of the computer-readable storage medium in the engine control system. The described actions are performed by executing the instructions in a system that includes the various engine hardware components in combination with the electronic control unit. One or more of the procedure steps described here can be omitted if desired. It is understood that the configurations and routines disclosed herein are exemplary and that these specific examples are not to be interpreted restrictively, as numerous variations are possible. For example, the foregoing technique can be applied to V-6, I-4, I-6, V-12, 4-cylinder boxer, and other engine types. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or properties disclosed herein. The following claims highlight certain combinations and subcombinations that are considered novel and not obvious. These claims may refer to "one" element, "a first" element, or the equivalent thereof. Such claims are to be understood as including one or more such elements, without requiring or excluding two or more. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by filing new claims in this or a related application.Such patent claims shall also be considered as included in the subject matter of the present disclosure, irrespective of whether they have a broader, narrower, the same or a different scope compared to the original patent claims. According to the present invention, an engine operating method includes increasing the boost pressure in an engine air intake via a control system in response to the end of the regeneration of a particulate filter, while a driver-demand torque is essentially constant. According to one embodiment, the boost pressure is increased by at least partially closing the guide vanes of a turbocharger, and the following is further included: increasing the low-pressure exhaust gas recirculation flow and decreasing the high-pressure exhaust gas recirculation flow in response to the end of the particulate filter regeneration. According to one embodiment, the invention is further characterized by opening an intake throttle in response to the end of the regeneration of the particulate filter and increasing a drive ratio of a compressor in order to increase the boost pressure. According to one embodiment, the invention is further characterized by the closing of an EGR cooler bypass valve in response to the end of the regeneration of the particulate filter. According to one embodiment, the invention is further characterized by the closing of a charge air cooler bypass valve in response to the end of the regeneration of the particulate filter. According to one embodiment, the invention is further characterized by the closing of a compressor bypass valve in response to the end of the regeneration of the particulate filter. According to one embodiment, the invention is further characterized by the opening of an exhaust gas throttle in response to the end of the regeneration of the particulate filter. According to the present invention, an engine operating method includes increasing the boost pressure in an engine air intake via a control system in response to the end of the regeneration of a particulate filter while a driver demand torque is substantially constant; and adjusting an EGR valve position based on the driver demand torque and the engine speed in response to the end of the regeneration of the particulate filter and before the SCR temperature falls below a first threshold temperature. According to the present invention, the EGR valve is a low-pressure EGR valve and further comprises: further adjusting the low-pressure EGR valve to increase the low-pressure EGR flow; and increasing the exhaust gas flow to an SCR in response to the end of the regeneration of the particulate filter, wherein the exhaust gas flow is increased before the SCR temperature falls below the first threshold temperature. According to one embodiment, the above invention is further characterized by reducing the exhaust gas flow to the SCR in response to the SCR temperature being below the first threshold temperature. According to one embodiment, the above invention is further characterized by the injection of urea into the SCR in response to the SCR temperature being below the first threshold temperature. According to one embodiment, the above invention is further characterized by reducing the exhaust gas flow to the SCR in response to the SCR temperature being below a second threshold temperature. According to the present invention, an engine system is provided comprising: a two-stroke opposed-piston diesel engine comprising at least one cylinder; an exhaust system coupled to the two-stroke engine comprising an oxidation catalyst, an SCR and a particulate filter; and a control system comprising executable instructions stored in a non-volatile memory to increase the exhaust flow to the SCR in response to the end of the particulate filter regeneration and to the SCR temperature being above a first threshold temperature. According to one embodiment, the first threshold temperature is a temperature above which the SCR efficiency falls below a threshold value. According to one embodiment, the invention is further characterized by additional instructions to increase the exhaust gas flow to the SCR by increasing the boost pressure in response to the end of the regeneration of the particulate filter. According to one embodiment, the invention is further characterized by additional instructions to close a charge air cooler bypass valve and a compressor bypass valve in response to the end of the particulate filter regeneration. According to one embodiment, the invention is further characterized by additional instructions to close an EGR cooler bypass valve in response to the end of the regeneration of the particulate filter. According to one embodiment, the invention is further characterized by additional instructions to reduce the exhaust gas flow to the SCR in response to the SCR temperature being below the first threshold. According to one embodiment, the invention is further characterized by additional instructions to reduce the exhaust gas flow to the SCR in response to the SCR temperature falling below a second threshold. According to one embodiment, the invention is further characterized by the injection of urea into the SCR in response to the end of the regeneration of the particulate filter and to the fact that the SCR temperature is below the first threshold value.

Claims

Engine operating procedure, comprising: determining that the regeneration of a particulate filter should be terminated; and increasing the boost pressure in an engine air intake via a control in response to the termination of the particulate filter regeneration in order to increase SCR efficiency by cooling a temperature of the SCR below a first threshold, while a driver-demand torque is substantially constant. Engine method according to claim 1, wherein the boost pressure is increased by at least partially closing the guide vanes of a turbocharger, and further comprising: increasing the low-pressure exhaust gas recirculation flow and decreasing the high-pressure exhaust gas recirculation flow in response to the end of the regeneration of the particulate filter. Motor method according to claim 1, further comprising opening an intake throttle in response to the end of the regeneration of the particulate filter and increasing a drive ratio of a compressor compressor to increase the boost pressure. Engine method according to claim 3, further comprising closing an EGR cooler bypass valve in response to the end of the regeneration of the particulate filter. Engine method according to claim 4, further comprising closing a charge air cooler bypass valve in response to the end of the regeneration of the particulate filter. Motor method according to claim 5, further comprising closing a compressor bypass valve in response to the end of the regeneration of the particulate filter. Engine method according to claim 1, further comprising opening an exhaust gas throttle in response to the end of the regeneration of the particulate filter. Method for operating an engine, further comprising: determining that the regeneration of a particulate filter should be terminated; increasing the boost pressure in an engine air intake via a control in response to the end of the particulate filter regeneration in order to increase SCR efficiency by cooling a temperature of the SCR below a first threshold while a driver-demand torque is substantially constant; and adjusting an EGR valve position based on the driver-demand torque and engine speed in response to the end of the particulate filter regeneration and before the SCR temperature falls below the first threshold temperature. Engine method according to claim 8, wherein the EGR valve is a low-pressure EGR valve, and further comprising: further adjusting the low-pressure EGR valve to increase the low-pressure EGR flow; and increasing the exhaust gas flow to an SCR in response to the end of the particulate filter regeneration, wherein the exhaust gas flow is increased before the SCR temperature falls below the first threshold temperature. Engine method according to claim 9, further comprising reducing the exhaust gas flow to the SCR in response to the SCR temperature being below the first threshold temperature. Engine system comprising: a two-stroke opposed-piston diesel engine incorporating at least one cylinder; an exhaust system coupled to the two-stroke engine, comprising an oxidation catalyst, a selective catalytic reduction (SCR) catalyst, and a particulate filter; and a control system comprising executable instructions stored in non-volatile memory to increase the exhaust flow to the SCR by increasing the boost pressure while the driver-demand torque remains essentially constant, in response to the end of particulate filter regeneration and to the SCR temperature exceeding a first threshold temperature, the first threshold temperature being a temperature above which the SCR efficiency falls below a threshold. Engine system according to claim 11, further comprising additional instructions to close an intercooler bypass valve and a compressor bypass valve in response to the end of the particulate filter regeneration. Engine system according to claim 12, further comprising additional instructions to close an EGR cooler bypass valve in response to the end of the particulate filter regeneration. Engine system according to claim 11, further comprising additional instructions to reduce the exhaust gas flow to the SCR in response to the SCR temperature being below a first threshold temperature. Engine system according to claim 14, further comprising additional instructions to reduce the exhaust gas flow to the SCR in response to the SCR temperature falling below a second threshold temperature.

Images