METHOD AND SYSTEM FOR REGENERATION OF A PARTICULATE FILTER

Abstract

Engine operating procedure comprising: Supplying an ignition spark for combusting an air-fuel mixture in an engine (10); Storing particles generated by combustion of the air-fuel mixture in a particle filter (71); Heating the particulate filter (71) to enable particulate filter regeneration while the engine load is less than a threshold value and while the engine (10) is rotating via a torque supplied by vehicle wheels, characterized in that the heating of the particulate filter (71) takes place by terminating the delivery of an ignition spark to a cylinder, and the method further comprises injecting fuel into the cylinder during an exhaust stroke of the cylinder in response to an increase in engine load.

Description

BACKGROUND / SUMMARYDirect injection gasoline engines may provide increased performance so that engine efficiency may be improved. Direct injection of fuel into a cylinder may reduce temperature in a cylinder so that more air and fuel may be drawn into the cylinder. However, the air-fuel mixture within the cylinder may not be fully vaporized at the time of ignition at higher engine speeds and loads because less time is available to mix the air with the fuel. As a result, a portion of the injected fuel may not fully oxidize, thereby forming carbonaceous soot within the cylinder. After the soot is expelled from the engine, the soot may be stored in a particulate filter for subsequent oxidation; however, it may be a challenge to initiate combustion in the particulate filter. One possible way to initiate regeneration in the particulate filter (e.g., reduce an amount of soot stored in the particulate filter) is to retard engine spark timing to increase cylinder exhaust port temperature. However, it may take longer than desired for the temperatures in the slot to reach the particulate filter so that regeneration may begin.DE 103 15 476 B4 describes a method for heating exhaust gas aftertreatment systems having the features of the preambles of claims 1 and 7.Further prior art relevant to the invention include DE 10 2008 036 127 A1 and DE 10 2010 046 896 A1, from the latter known to retard the ignition in order to achieve additional heating of the particle filter and to increase a time-varying amplitude of an air-fuel ratio in order to regenerate the particle filter in a first operating mode.The inventors have recognized the above-mentioned limitations and developed an engine operating method having the features of claim 1 and systems for controlling an engine having the features of claims 7-9. Advantageous refinements of the invention are described in the dependent claims.Thus, the method comprises: supplying a spark for combusting an air-fuel mixture in an engine; storing particulates generated by combustion of the air-fuel mixture in a particulate filter; and regenerating the particulate filter while the engine load is less than a threshold and responsive to a pedal removal condition, terminating delivery of the spark to one or more cylinders and supplying fuel to the one or more cylinders.By terminating or stopping spark delivery to one or more cylinders, fuel may be delivered to the cylinder such that fuel is expelled from the cylinders into the exhaust system where it may oxidize closer to the particulate filter. In one example, fuel supplied to a cylinder where spark is suppressed may increase a temperature of a three-way catalyst positioned downstream of the particulate filter such that heat may be transferred from the three-way catalyst to the particulate filter. In this way, regeneration of a particulate filter may be initiated during low engine load conditions. For example, during vehicle deceleration after pedal removal (i.e., releasing an accelerator pedal or decreasing engine torque demand), spark supplied to a cylinder may be stopped as the engine continues to rotate via torque supplied by vehicle wheels. Those cylinders where spark has been stopped may be injected with fuel and then ejected shortly thereafter to a three-way catalyst in an exhaust system. The oxidizing fuel heats the particulate filter, so that soot held within the particulate filter may be oxidized.The present description may provide several advantages. More specifically, the approach may use fuel to regenerate a particulate filter more efficiently. Additionally, the approach may provide improved emissions after particulate filter regeneration by improving catalyst chemistry. Further, the approach may provide increased opportunities to regenerate a particulate filter.The above advantages and other advantages and features of the present specification will be readily apparent from the following detailed description, taken alone or in conjunction with the accompanying drawings.Of course, the summary above has been 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 clearly defined by the claims that follow the detailed description. Moreover, the claimed subject matter is not limited to implementations that solve any disadvantages mentioned above or in any part of this disclosure.BRIEF DESCRIPTION OF THE FIGURESFIG. 1 is a schematic illustration of an engine; FIG. 2 shows an example predictive engine and exhaust operation; FIGS. 3 and 4 show a flow chart of an example method for operating an engine; and FIG. 5 shows an example vehicle in which the engine of FIG. 1 is operating.DETAILED DESCRIPTIONThe present invention relates to the operation of a spark-ignition engine that includes a particulate filter in its exhaust system. An exemplary system is shown in FIG. 1. The engine and exhaust system may be operated to provide the flow in FIG. 2 via the method shown in FIGS. 3 and 4. The method includes ways to regenerate the particulate filter at higher engine loads and at lower engine loads. In one example, the particulate filter may be regenerated while a vehicle is coasting or decelerating from a higher speed to a lower speed. The engine may operate in a vehicle as shown in FIG. 5.Referring to FIG. 1, an internal combustion engine 10 including a plurality of cylinders, one cylinder of which is shown in FIG. 1, is controlled by an electronic engine controller 12. The engine 10 includes a combustion chamber 30 and cylinder walls 32 with a piston 36 positioned therein and connected to the crankshaft 40. Combustion chamber 30 is shown in communication with intake manifold 44 and exhaust manifold 48 via respective intake valve 52 and exhaust valve 54. Each intake and exhaust valve may be operated by an intake cam 51 and an exhaust cam 53. The position of the intake cam 51 may be determined by an intake cam sensor 55. The position of the exhaust cam 53 may be determined by an exhaust cam sensor 57.Fuel injector 66 is shown positioned to directly inject fuel into cylinder 30, as known to those skilled in the art as direct injection. Alternatively, fuel may be injected into an intake port, known to those skilled in the art as single injection. Fuel injector 66 delivers liquid fuel in proportion to a pulse width provided by controller 12. Fuel is delivered to fuel injector 66 through a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail (not shown).Air is supplied to intake manifold 44 by compressor 162. Exhaust gases rotate turbine wheel 164 coupled to shaft 161, thereby driving compressor 162. In some examples, a bypass passage is included such that exhaust gases may bypass turbine wheel 164 during selected operating conditions. Further, in some examples, a compressor bypass passage may be provided to limit the pressure provided by compressor 162. Intake manifold 44 is also shown in communication with a central throttle 62 that adjusts a position of a throttle plate 64 to control airflow from engine air inlet 42. The central throttle 62 is operable electrically.A manifoldless ignition system 88 provides spark to the combustion chamber 30 via a spark plug 92 in response to the controller 12 A universal exhaust gas oxygen (UEGO) sensor 126 is shown coupled to the exhaust manifold 48 at the intake side of the catalyst 70. Alternatively, a two-state exhaust oxygen sensor may be substituted for the UEGO sensor 126.In one example, catalyst 70 may include multiple catalyst bricks. In another example, multiple emission control devices, each with multiple bricks, may be used. In one example, catalyst 70 may be a three-way catalyst. On the outlet side of the catalyst 70, a particulate filter 71 is positioned. Downstream of the catalyst 70, a second UEGO 125 is positioned to provide an indication of the oxygen storage state of the catalyst 70.Controller 12 is shown in FIG. 1 as a conventional microcomputer including: microprocessor unit 102, input / output ports 104, read-only memory 106, random access memory 108, error memory 110, and a conventional data bus. Controller 12 is shown receiving various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including: an engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; a position sensor 134 coupled to an accelerator pedal 130 for sensing the accelerator pedal position adjusted by foot 132; a measurement of engine manifold pressure (MAP) from pressure sensor 122 coupled to intake manifold 44; an engine position sensor from a Hall effect sensor 118 sensing the position of crankshaft 40; a measurement of mass air entering the engine from sensor 120 (e.g., a hot wire airflow meter) and a measurement of throttle position from sensor 58. In a preferred aspect of the present description, the engine position sensor 118 generates a predetermined number of equidistant pulses each revolution of the crankshaft from which the engine speed (RPM) can be determined.In some examples, the engine may be coupled to an electric motor / battery system in a hybrid vehicle. The hybrid vehicle may have a parallel configuration, a series configuration, or a variation or combinations thereof. Further, in some embodiments, other engine configurations, e.g., a diesel engine, may be utilized.During operation, each cylinder within engine 10 typically undergoes a four stroke cycle: the cycle includes the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke. During the intake stroke, generally, the exhaust valve 54 closes and opens the intake valve 52 Air is introduced into the combustion chamber 30 via the intake manifold 44, with the piston 36 moving toward the bottom of the cylinder to increase 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 is at its largest volume) is commonly 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 to compress the air within 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 is at its smallest volume) is commonly referred to by those of skill in the art as top dead center (TDC). In a process referred to as injection hereinafter, fuel is introduced into the combustion chamber. In a process referred to as ignition hereinafter, the injected fuel is ignited by known igniting means such as a spark plug 92, resulting in combustion. During the power stroke, the expanding gases push the piston 36 back to BDC. The crankshaft 40 converts the piston motion into a rotational motion of the rotating shaft. Finally, during the exhaust stroke, the exhaust valve 54 opens to release the combusted air-fuel mixture to the exhaust manifold 48, and the piston returns to TDC. It is noted that the above has been described as an example only and that intake and exhaust valve opening and / or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples.Thus, the system of FIG. 1 provides for a system comprising: an engine; an ignition system that supplies spark to the engine; a particulate filter in an exhaust system of the engine; and a controller including executable instructions stored in non-transitory memory to retard spark timing and to increase a time-varying amplitude of the air-fuel ratio to regenerate the particulate filter in a first mode of operation and executable instructions to cease spark delivery to regenerate the particulate filter in a second mode of operation. Further, the system includes additional executable instructions to additionally retard spark when the air-fuel ratio is lean in the first mode.In one example, the system further comprises a three-way catalyst and additional executable instructions to adjust oxygen stored in the three-way catalyst in response to a regeneration state of the particulate filter. Further, the system includes additional executable instructions to deliver fuel to a cylinder during an exhaust stroke in response to an increase in engine load and an engine load request during the second mode. Further, the system includes additional executable instructions to decrease an air-fuel ratio responsive to a lean state of a catalyst during an increase in engine load demand during the second mode. The system also includes where the time-varying amplitude varies between rich and lean from stoichiometry.Turning now to FIG. 2, an example predictive engine and exhaust system operation sequence is shown. The flow may be provided by the system of FIG. 1 executing instructions of the method shown in FIGS. 3 and 4. The vertical markers represent specific points of interest in the process.The first plot from the top of FIG. 2 is a plot of particulate filter (PF) temperature versus time. The X axis represents time and the Y axis represents PF temperature. The time increases from the left side of the figure to the right side of the figure. The PF temperature increases in the direction of the Y-axis arrow. The signal curve 306 represents PF temperature in accordance with the methods of FIGS. 3 and 4. the signal curve 306 represents PF temperature during pedal removal conditions without the method of FIGS. 3 and 4. an interruption of the time line between time T 3 and time T 4 is indicated by a double SS. The time interval between time T 3 and time T 4 may be measured in minutes or hours. The time lines of the second to eighth graphs also include the time line interrupt. Further, the time lines of the first to eighth plots are aligned in time.The second plot from the top of FIG. 2 is a plot of requested engine load versus time. The X axis represents time and the Y axis represents engine load. The requested engine load may be determined via the accelerator pedal 130 shown in FIG. 1. The time increases from the left side of the figure to the right side of the figure. The requested engine load increases in the direction of the Y-axis arrow. The requested engine load may be characterized as an engine torque or, in some examples, as an amount of air supplied to the engine.The third plot from the top of FIG. 2 is a plot of engine throttle position versus time. The X axis represents time and the Y axis represents engine throttle position. The time increases from the left side of the figure to the right side of the figure. The throttle position increases in the direction of the Y-axis arrow representing an increased throttle opening amount.The fourth plot from the top of FIG. 2 is a plot of an amount of particulates stored within a particulate filter at a location downstream of an engine (e.g., 71 of FIG. 1 ) as a function of time. The X axis represents time and the Y axis represents an amount of particulates stored in a particulate filter. The amount of particulates may be determined via the exhaust pressure upstream and downstream of the particulate filter as known in the art. The time increases from the left side of the figure to the right side of the figure. The amount of the stored particles increases in the direction of the Y-axis arrow. The horizontal marker 302 represents a threshold level of particulates at which it is desired to regenerate the particulate filter.The fifth plot from the top of FIG. 2 is a plot of engine air-fuel ratio versus time. Depending on the engine and exhaust modes, a cylinder air-fuel mixture may be burned or not burned in the engine. The X axis represents time and the Y axis represents engine air-fuel ratio. The time increases from the left side of the figure to the right side of the figure. The engine air-fuel ratio becomes leaner in the direction of the Y-axis arrow. A stoichiometric air-fuel ratio is indicated by horizontal mark 304.The sixth plot from the top of FIG. 2 is a plot of engine spark advance versus time. The X axis represents time and the Y axis represents engine spark advance. The time increases from the left side of the figure to the right side of the figure. Engine spark timing is advanced in the direction of the Y-axis arrow.The seventh plot from the top of FIG. 2 is a plot of state of the three-way catalyst versus time. In one example, the state of the three-way catalyst is determined based on an oxygen sensor positioned in the exhaust flow downstream of the three-way catalyst (e.g., 125 of FIG. 1 ). The state of the three-way catalyst indicates a richer condition (e.g., less oxygen stored within the catalyst) in the direction of the Y-axis arrow. The state of the three-way catalyst indicates a leaner condition (e.g., more oxygen stored within the catalyst) when the curve is near the X axis. The X axis represents time and the Y axis represents the state of the three-way catalyst. The time increases from the left side of the figure to the right side of the figure.The eighth plot from the top of FIG. 2 is a plot of the particulate filter regeneration flag versus time. The X axis represents time and the Y axis represents the state of particulate filter regeneration. The time increases from the left side of the figure to the right side of the figure. When the curve is near the X axis, the particulate filter is not regenerated. When the curve is at a higher level away from the X axis, the particulate filter is regenerated.At time T 0 the engine load is at a higher level indicating a relatively high engine load. The particulate filter temperature is at a medium level. The throttle opening is also open to a higher amount. The amount of particulates stored in the particulate filter is less than the threshold level 302 at which it is desired to regenerate the particulate filter. The engine air-fuel ratio is shown with a smaller alternating amplitude oscillating around stoichiometric conditions. The spark advance is at a mid-level (e.g., 25 degrees advance after top dead center compression stroke). The state of the three-way catalyst is slightly rich, indicating that oxygen storage locations may be available. The particulate filter regeneration state flag is at a low level indicating that the particulate filter is not being regenerated.At time T 1 the engine load and throttle opening amount are still relatively high and have increased 0 since time T. The amount of particulates stored in the particulate filter has increased to the level 302 at which it is desired to regenerate the particulate filter. However, regeneration is delayed for a short time until the operating conditions for particulate filter regeneration are at desired conditions. The engine air-fuel ratio is enriched to maintain the temperature of a three-way catalyst coupled to the engine below a threshold temperature. The spark advance is maintained at a relatively advanced level. As oxygen stored in the catalyst is consumed in the combustion of hydrocarbons, the state of the three-way catalyst starts to shift toward a richer state. The particulate filter regeneration state flag is at a low level indicating that the particulate filter is not being regenerated.At time T 2 the engine load is decreased as is the engine throttle opening amount. In this example, the engine throttle opening amount is closed in response to a pedal removal condition, enabling particulate filter regeneration. Thus, there is a transition from a higher engine load to a lower engine load, e.g., a pedal removal or an accelerator pedal release. In one example, the transition represents conditions of vehicle deceleration where vehicle brakes may or may not be applied. The particulates stored within the particulate filter have increased by a small amount since time T 1. A short time after the transition is started, the engine air-fuel ratio is controlled to a leaner air-fuel ratio to increase the temperature in the three-way catalyst and thereby promote the oxidation of the particulates in the particulate filter. The regeneration state flag also changes state from a low value to a higher value to indicate that particulate filter regeneration has started. Shortly thereafter, spark delivery to one or more engine cylinders is terminated. For example, spark delivery to all six cylinders of a six cylinder engine may stop. Alternatively, spark delivery to three or another subset of the engine cylinders may be terminated. Thus, the combustion in the cylinders in which the spark has been stopped is ended. Throttle position is also shown open to a small amount in response to particulate filter regeneration. Opening the throttle allows air and fuel that have not been burned to reach the three-way catalyst where they may be oxidized to increase the temperature of the three-way catalyst and the particulate filter. The engine air-fuel ratio amplitude is increased to provide additional amounts of fuel and air to the three-way catalyst. The cyclical rate of change of engine air-fuel may be low enough to change the state of the three-way catalyst as indicated in the sixth plot from the top of FIG. 2. In other words, the engine air-fuel rate of change may be low enough to cause a breakthrough of air and / or hydrocarbons in the three-way catalyst. Alternatively, the engine air-fuel rate of change may be high enough to increase the three-way catalyst temperature without causing a breakthrough. The engine continues to rotate via torque provided to the engine by vehicle wheels while transmitting vehicle inertia to the engine, such that the engine may continue to rotate even though spark delivery has been completed in one or more engine cylinders.Between time T 2 and time T 3 the engine load remains low and the throttle position is adjusted to provide a desired oxidation rate within the catalyst and the particulate filter. Since the operator demand is zero, throttle position is not adjusted in response to the operator demand. If the particulate filter oxidation rate is higher than desired, the throttle opening amount is closed. If the particulate filter oxidation rate is lower than desired, the throttle opening amount may be opened. The engine air-fuel ratio is commanded between lean and rich from stoichiometry. In some examples, fuel injection to engine cylinders not receiving spark is deactivated in response to an oxidation rate within the particulate filter, so fuel may be conserved. For example, injection of fuel into cylinders not receiving spark is stopped when the particulate filter reaches a threshold temperature. Between time T 2 and time T 3 the temperature of the particulate filter increases. When the present method is not used, the temperature of the particulate filter decreases.At time T 3 the engine load is still at a low level and the amount of particulates stored in the particulate filter has reached a level at which it is desired to stop particulate filter regeneration. Thus, as indicated by the particulate regeneration flag transitioning from a higher level to a lower level, particulate filter regeneration is halted. The particulate filter temperature begins to decrease. Spark delivery to engine cylinders where spark is deactivated is also resumed at time T 3. In addition, in order to improve the efficiency of the three-way catalyst, the engine air-fuel ratio amplitude is decreased. The state of the three-way catalyst is also driven back to a level between a rich state and a lean state.Between time T 3 and time T 4 the amount of particulates stored in the particulate filter increases as fuel is burned within the engine. When the engine is operated at higher engine speeds and loads, the particulates may accumulate more quickly. Between the braking time interval, the particles stored in the particle filter increase considerably.At time T 4 the amount of particulates stored in the particulate filter reaches the level 302 at which it is desired to regenerate the particulate filter. The engine operates at a higher engine load and the throttle is opened to a relatively large amount. The particulate regeneration flag is set to a higher level to indicate that the particulate filter regeneration is in progress. To increase particulate filter temperature, spark advance is retarded. When the engine is operated lean, spark advance is additionally retarded to reduce engine NOx output. Spark retard may be compensated for by increasing engine airflow via increasing throttle opening area or valve timing. The amplitude of the engine air-fuel ratio between rich and lean operation is also increased compared to when the engine is not operated in a particulate filter regeneration mode. After the particulate filter regeneration starts, the amount of particulates starts to decrease.Thus, during different operating conditions, regeneration of the particulate filter may occur at different times. When engine load is low or at higher engine loads, when spark timing is retarded, the particulate filter may be regenerated without applying spark to one or more cylinders.Referring now to FIGS. 3 and 4, a method for regenerating a particulate filter is shown. The method of FIGS. 3 and 4 may be stored as executable instructions in the non-transitory memory of the controller 12 of FIG. 1. The method of FIGS. 3 and 4 may also provide the flow shown in FIG. 2.At 302, method 300 judges if the vehicle is in an operating state. The vehicle may be judged to be in an operating state when a command to operate the vehicle (e.g., via an ignition switch or remote control signal) has been given. If method 300 judges that the vehicle is in an operating state, the answer is yes and method 300 proceeds to 304. Otherwise, the answer is no and method 300 proceeds to exit.At 304, method 300 provides spark ignition for engine air-fuel mixtures and particulates that may be formed during combustion are stored in a particulate filter in an exhaust system coupled to the engine. The engine rotates via combustion torque provided by spark igniting the engine air-fuel mixtures. After spark ignition is provided to the engine cylinders, method 300 proceeds to 306.At 306, method 300 judges if the particulates stored in a particulate filter are more than a threshold amount. In one example, the amount of particulates stored in a particulate filter may be estimated based on a pressure drop across the particulate filter at a given flow rate through the particulate filter. The pressure drop may be monitored via pressure sensors located in the exhaust at locations upstream and downstream of the particulate filter. The higher the pressure drop, the more particulate accumulation within the particulate filter. If it is judged that more than a threshold amount of particulates have been stored in the particulate filter, the answer is yes and method 300 proceeds to 308. Otherwise, the answer is no and method 300 proceeds to exit.At 308, method 300 judges if there are transitions from a higher engine load to a lower engine load. In some examples, method 300 simply judges whether the engine is operating at a lower engine load and whether the vehicle is moving. Additionally, method 300 may judge if pedal removal is present and if engine load tends to be lower or lower than a threshold level. If so, the answer is yes and method 300 proceeds to 310. Otherwise, the answer is no and method 300 proceeds to 340.If the particulates stored in the particulate filter are less than a threshold level and pedal removal occurs at a low engine load, no fuel is delivered to the engine cylinders and spark is deactivated or may remain active such that the engine enters a deceleration fuel cut mode at low engine loads where torque is provided to rotate the engine via vehicle wheels to conserve fuel.At 310, method 300 ceases or stops delivering spark to one or more engine cylinders with the engine continuing to rotate via torque supplied by vehicle wheels. The vehicle wheels transfer the kinetic energy of the vehicle to the engine to maintain engine rotation. Thus, engine rotational energy immediately after the rotational energy is provided from the combustion is dissipated from the vehicle wheels so that the engine rotation does not stop. In some examples, spark delivery to all engine cylinders is stopped. In other examples, spark delivery is adjusted to less than the total number of engine cylinders. After spark delivery to selected cylinders is stopped, method 300 proceeds to 312.At 312, method 300 adjusts engine air flow via throttle and / or valve timing adjustments. In one example, the throttle is opened to an amount at which an exothermic reaction occurs in a three-way catalyst positioned downstream of the engine. The throttle opening amount may be adjusted in response to a temperature of the three-way catalyst and / or the temperature of the particulate filter. If the catalyst or particulate filter temperature is lower than desired, the throttle opening amount may be increased by a predetermined amount based on a temperature difference between the actual catalyst / particulate filter temperature and the desired catalyst / particulate filter temperature. After the air flow through the engine has been adjusted, method 300 proceeds to 314.At 314, method 300 provides fuel to the cylinders where spark delivery has been stopped. On the other hand, if the three-way catalyst temperature is less than a threshold temperature (e.g., a temperature at which the injected fuel burns), fuel is not injected into the engine while spark has been stopped. Further, fuel flow may be provided to cylinders where spark is provided to keep the engine rotating. In some examples, vehicle inertia during vehicle deceleration allows the engine to continue rotating while not providing spark to engine cylinders. Fuel is provided to cylinders that do not receive spark based on a desired catalyst temperature and engine air flow. After fuel is delivered to engine cylinders, method 300 proceeds to 316.Thus, particulate filter regeneration is initiated by terminating spark delivery and injection of fuel into cylinders where spark delivery has been stopped during low load conditions in response to an amount of particulates stored within a catalyst and in response to a pedal removal condition where the vehicle continues to move on a road.At 316, method 300 initially controls engine air-fuel ratio to a lean level to provide oxygen for oxidizing hydrocarbons that may be stored within the three-way catalyst. In addition, method 300 increases the amplitude of the air-fuel ratio by the stoichiometric conditions to further promote particulate filter regeneration. The engine air-fuel ratio may include fuel and air that are burned together with fuel and air that are not burned before flowing out of the engine. After the engine air-fuel ratio adjustments are provided, method 300 proceeds to 318.At 318, method 300 judges if particulate filter regeneration is complete. In one example, it may be determined that particulate filter regeneration is complete when a pressure drop across the particulate filter at a given flow through the particulate filter is less than a threshold. If so, the answer is yes and method 300 proceeds to 320. Otherwise, the answer is no and method 300 returns to 308.At 320, method 300 resumes delivering spark to engine cylinders where spark has been ceased. In one example, spark is activated by flowing a current to an ignition coil.At 322, method 300 judges if there is an increase in engine load. In one example, an increase in engine load may be indicated via a position of an accelerator pedal operated by a vehicle driver. In some examples, it may be judged that there is an increase in engine load when engine load is increased by more than a threshold amount. If method 300 judges that there is an increase in engine load, the answer is yes and method 300 proceeds to 324. Otherwise, the answer is no and method 300 proceeds to 330.At 324, method 300 judges if a three-way catalyst located downstream of the engine and upstream of the particulate filter is in a lean state. In one example, an oxygen sensor positioned downstream of the three-way catalyst may be judged to be in a lean condition. If method 300 judges that the three-way catalyst is in a lean state, the answer is yes and method 300 proceeds to 328. Otherwise, the answer is no and method 300 proceeds to 326.At 328, method 300 injects additional fuel into the engine cylinders to drive the three-way catalyst to a state between rich and lean. In one example, fuel is injected during an exhaust stroke of a cylinder receiving fuel so that fuel may be delivered to the three-way catalyst as soon as possible after the change in engine load is detected. Because cylinder contents may be purged to the exhaust system during the exhaust stroke, injecting fuel to the cylinder during the exhaust stroke may reduce a time period taken to drive the three-way catalyst to a state between rich and lean. In this way, the state of the catalyst may be adjusted such that during the increase in engine load, NOx may be better processed by the three-way catalyst. After the fuel injected to the engine cylinders has been adjusted, method 300 proceeds to exit.At 326, method 300 reduces an amount of fuel to a first cylinder to receive fuel after an increase in engine load. By reducing a quantity of fuel delivered to the engine cylinders, it may be possible to shift the state of the three-way catalyst to an equilibrium condition between rich and lean conditions. In particular, more oxygen may flow through the first cylinder such that oxygen may be stored at the three-way catalyst. After the amount of fuel injected to the engine has decreased, method 300 proceeds to exit.At 330, method 300 adjusts an amount of oxygen stored within the three-way catalyst responsive to the state of regeneration of the particulate filter via combustion of a rich and lean air-fuel mixture by stoichiometry within engine cylinders. For example, the engine air-fuel ratio may be adjusted with more tendency to a rich side from stoichiometry or to a lean side from stoichiometry such that oxygen storage within the three-way catalyst is balanced (e.g., 50% of the available oxygen storage of the three-way catalyst may be utilized) after particulate filter regeneration is complete. The state of the catalyst may be adjusted over time when engine load is not increasing so that a sudden change in engine fueling is not required. In an example where the state of the three-way catalyst after regeneration is rich, a lean tendency is applied to the engine air-fuel ratio. When the state of the three-way catalyst after regeneration is lean, a rich tendency is applied to the engine air-fuel ratio. In this way, the oxygen storage state of the three-way catalyst is adjusted after the particulate filter is regenerated. After the amount of oxygen stored in the three-way catalyst has been adjusted, method 300 proceeds to exit.At 340, method 300 retards spark timing in selected cylinders from the spark baseline timing to increase temperatures in the exhaust system. Increasing exhaust temperatures at higher engine loads may facilitate particulate oxidation within the particulate filter because the higher mass flow rate at the higher engine load may drive the temperatures downstream of the three-way catalyst higher. The amount of air flowing through the engine may be increased as spark is retarded so that an equivalent engine torque is provided while spark is retarded. After the spark timing is retarded, method 300 proceeds to 342.At 342, method 300 increases the engine air-fuel ratio amplitude change by stoichiometric conditions. In one example, the peak-to-peak change in engine air-fuel ratio is increased by stoichiometric conditions. After adjusting the engine air-fuel ratio, method 300 proceeds to 344.At 344, method 300 breaks through the three-way catalyst with rich and lean combustion products for threshold durations. For example, the lean condition is maintained for a predetermined period if a lean condition is determined at the three-way catalyst outlet. The amount of the lean cut-off time may be adjusted by decreasing an amount of fuel injected into engine cylinders for a desired duration. In this way, the amount of oxygen supplied to the particulate filter during particulate filter regeneration may be controlled. After the rich and lean breakthrough conditions are adjusted, method 300 proceeds to 346.At 346, method 300 provides for additional retarding spark to engine cylinders when the cylinders are operated lean so that NOx output of the cylinders may be decreased. The amount of spark retard may be proportional to the excess air of the engine air-fuel ratio. For example, if the engine is operated leaner, more spark retard may be provided. After spark timing is additionally retarded during lean engine operation, method 300 proceeds to 348.At 348, method 300 increases the amount of engine air flow while the engine is operating lean. The torque reduction that occurs while the cylinders are operating late lean with spark timing may be counteracted via the increase in engine air flow via opening the engine throttle. In this way, engine torque may be more uniform. After the engine air flow is adjusted, method 300 proceeds to 350.At 350, method 300 judges if particulate filter regeneration is complete. Particulate filter regeneration may be considered complete when a pressure drop across the particulate filter at a given flow through the particulate filter is less than a desired amount. If so, the answer is yes and method 300 proceeds to 352. Otherwise, the answer is no and method 300 returns to 340.At 352, method 300 advances spark timing to the baseline spark timing and decreases the engine peak-to-peak air-fuel ratio such that the catalyst's lean and rich breakthrough is decreased. The peak-to-peak air-fuel ratio may be decreased by operating the engine closer to stoichiometric conditions. After the engine spark and fuel are returned to baseline operation, method 300 proceeds to exit.Thus, the method of FIG. 3 provides for an engine operating method comprising: supplying a spark for combusting an air-fuel mixture in an engine; storing particulates generated by combustion of the air-fuel mixture in a particulate filter; and regenerating the particulate filter while the engine load is less than a threshold and responsive to a pedal removal condition, via ceasing supply of the spark to one or more cylinders and supplying fuel to the one or more cylinders.In this way, a particulate filter may be regenerated via generation of heat in a three-way catalyst that is closer to the particulate filter than the engine.The engine operating method includes positioning the particulate filter downstream of a three-way catalyst and rotating the engine via torque supplied by vehicle wheels while spark delivery has been terminated. Further, the engine operating method includes adjusting an amount of air flowing through the engine when the particulate filter is regenerated. In some examples, the engine operating method includes adjusting the amount of air flowing through the engine via a throttle or valve timing. The engine operating method also includes initiating regeneration via supplying a lean air-fuel mixture from the engine to a three-way catalyst positioned upstream of the particulate filter. In one example, the engine operating method includes terminating combustion in the one or more cylinders during regeneration of the particulate filter and the engine has rotated immediately prior to regenerating the particulate filter and stopping spark delivery via combustion in their cylinders. The engine operating method includes combusting fuel injected into the one or more cylinders in a three-way catalyst positioned upstream of the particulate filter. Further, the engine operating method includes where the engine is a direct injection turbocharger engine and where an amount of fuel supplied to the one or more cylinders is changed to provide rich and lean air-fuel mixtures to the one or more cylinders.In another example, the method of FIGS. 3 and 4 provides for an engine operating method comprising: supplying a spark for combusting an air-fuel mixture in an engine; storing particulates generated by combustion of the air-fuel mixture in a particulate filter; regenerating the particulate filter while the engine load is less than a threshold by terminating delivery of a spark to a cylinder while the engine load is less than a threshold and while the engine is rotating via torque supplied by vehicle wheels; and injecting fuel into the cylinder during an exhaust stroke of the cylinder in response to an increase in the engine load. Further, the engine operating method includes supplying fuel to the cylinder while delivery of spark to the cylinder has been terminated. Further, the engine operating method includes not supplying fuel to the cylinder while delivery of spark to the cylinder has been terminated in response to the engine load being less than a threshold and an amount of particulates stored in the particulate filter being less than a threshold.In some examples, the engine operating method includes where the engine is in a deceleration fuel cut mode when fuel is not supplied to the cylinder. The engine operating method also includes injecting fuel during the exhaust stroke of the cylinder in response to a state of a catalyst being lean. Further, the engine operating method includes terminating injecting fuel into the cylinder when a temperature of a three-way catalyst is less than a threshold.Turning now to FIG. 5, an example vehicle is shown in which the engine 10 of FIG. 1 is operating. The vehicle 500 includes an engine 10, a transmission 502, a differential 504, and wheels 506. When engine torque is positive, engine 10 supplies torque to rotate vehicle wheels 506 via a gear arrangement (not shown) in transmission 502. The differential 504 transfers torque from the transmission 502 to the wheels 506. When the engine torque is negative, the wheels 506 may supply torque to rotate the engine 10 via the transmission 502. The wheels 506 transfer the kinetic energy of the vehicle to the engine 10.As will be appreciated by one of ordinary skill in the art, the method described in FIGS. 3 and 4 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 illustrated steps or functions may be performed in the illustrated flow, performed in parallel, or omitted in some cases. Likewise, the order of processing is not necessarily required to achieve the objects described herein, as well as features and advantages, but is provided for ease of illustration and description. Although not explicitly illustrated, those of ordinary skill in the art will appreciate that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used.Thus, the description is completed. As those skilled in the art read, many changes and modifications will occur to them without departing from the spirit and scope of the specification. For example, single cylinder, I2, I3, I4, I5, V6, V8, V10, V12, and V16 engines operating on natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.REFERENCE NUMERALS10 (Internal combustion) Engine 12 Controller 30 Combustion chamber 32 Cylinder walls 36 Piston 40 Crankshaft 42 Engine air inlet 44 Intake manifold 48 Exhaust manifold 51 Intake cam 52 Intake valve 53 Exhaust cam 54 Exhaust valve 55 Intake cam sensor 57 Exhaust cam sensor 58 Sensor (for throttle position) 62 Throttle 64 Throttle 66 Fuel injector 70 Catalyst 71 Particulate filter 88 Ignition system 92 Spark plug 102 Microprocessor unit 104 Input / output ports 106 Read-only memory 108 Random-access memory 112 Temperature sensor 114 Cooling sleeve 118 Hall effect sensor 120 Sensor (for air mass) 122 Pressure sensor (on the intake manifold) 125 Second UEGO 126 UEGO sensor (exhaust gas oxygen sensor) 130 Accelerator pedal 132 Foot 134 Position sensor 161 Shaft 162 Compressor 164 Turbine wheel

Claims

An engine operating method comprising: supplying a spark for combusting an air-fuel mixture in an engine (10); storing particulates generated by combustion of the air-fuel mixture in a particulate filter (71); heating the particulate filter (71) to enable particulate filter regeneration while the engine load is less than a threshold and while the engine (10) is rotating via torque supplied by vehicle wheels, characterized in that heating the particulate filter (71) is via delivery of a spark to a cylinder is stopped, and the method further comprises injecting fuel into the cylinder during an exhaust stroke of the cylinder in response to an increase in engine load.The engine operating method of claim 1, further comprising supplying fuel to the cylinder while the supply of the spark to the cylinder has been terminated.The engine operating method according to claim 1, further comprising failing to supply fuel to the cylinder while the supply of spark to the cylinder has been ended, in response to the engine load being less than a threshold and an amount of the particulates stored in the particulate filter (71) being less than a threshold.The engine operating method of claim 3, wherein the engine (10) is in a deceleration fuel cut mode when no fuel is supplied to the cylinder.The engine operating method according to claim 1, wherein fuel is injected during the exhaust stroke of the cylinder in response to a state of a catalyst (70) being lean.The engine operating method of claim 1, further comprising ceasing to inject fuel into the cylinder when a temperature of a three-way catalyst is less than a threshold temperature.A system for controlling an engine, the system comprising: an engine (10); a particulate filter (71) in an exhaust system of the engine (10); and a controller (12) including executable instructions stored in non-transitory memory to regenerate the particulate filter (71) in a first mode and executable instructions to regenerate the particulate filter (71) in a second mode in response to pedal removal and engine load being below a threshold, characterized in that the system further includes a three way catalyst; an ignition system (88) supplying spark to the engine (10); and additional executable instructions to retard spark timing and increase a time varying amplitude of an air-fuel ratio in the first mode; stopping the spark supply in the second mode and adjusting oxygen stored in the three-way catalyst in response to a regeneration state of the particulate filter ( 71).The system of the preamble of claim 7, characterized in that the system further comprises additional executable instructions for supplying fuel to a cylinder during an exhaust stroke in response to an increase in engine load and an engine load request during the second mode.The system of the preamble of claim 7, characterized in that the system further comprises additional executable instructions for enriching an engine air-fuel ratio in response to a lean state of a catalyst (70) during an increase in an engine load requirement during the second mode.The system of any of claims 7-9, further comprising additional executable instructions for additionally retarding spark when the air-fuel ratio is lean in the first mode.The system of any of claims 7-9, wherein the time varying amplitude varies between rich and lean from stoichiometry.

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