Method for controlling ignition for particulate filter regeneration

Abstract

Method for controlling a spark-ignition engine having an exhaust aftertreatment system with a particulate filter and a catalyst located downstream of the particulate filter, comprising: Adjusting the ignition timing, at which at least one cylinder of a spark-ignition engine (10, 200, 300) receives a spark, to a retarded setting. when the amount of soot retained by a particulate filter (230, 240, 252) exceeds a threshold value and if the engine load is less than a threshold value, wherein a quantity of fuel supplied to at least one cylinder provides rich or stoichiometric exhaust gases which are fed to the exhaust aftertreatment system, while the ignition angle at which a spark is supplied to the at least one cylinder is retarded, and whereupon the engine's air / fuel mixture is subsequently controlled to be lean in order to oxidize the soot held by the particulate filter, where the amount of oxygen stored in the catalyst is monitored and, if this exceeds a first threshold, the air / fuel mixture of the engine is increased to a richer mixture until the amount of oxygen stored in the catalyst is less than a second threshold, whereupon the air / fuel mixture is controlled to a leaner mixture.

Description

Cross-reference to related registrations

[0001] This application claims priority from the preliminary US patent application No. 611246,939, entitled “PARTICULATE FILTER SYSTEM AND METHOD FOR REGENERATING”, filed on September 29, 2009, the disclosure of which is incorporated herein in full and for all purposes by reference. Technical field

[0002] The present application concerns the field of motor vehicle emission control systems and procedures. Background and Summary

[0003] Direct-injection gasoline engines offer improved efficiency because fuel injected directly into a cylinder can lower the cylinder charge temperature. This allows more air to enter the cylinder compared to an equivalent cylinder using port-injected fuel. Consequently, the engine's power output and efficiency can be improved. Furthermore, direct-injection gasoline engines can exhibit improved transient fuel control because there is less tendency for fuel to accumulate in a cylinder's intake port than in a port-injected engine. However, direct-injection engines can produce soot at higher engine speeds and loads because less time is available to atomize the fuel within the cylinder.Therefore, integrating a particulate filter into the exhaust system of a direct-injection engine can be helpful. Gasoline engines include those that run on pure gasoline, gasoline mixtures, or other fuels such as alcohols. This category also includes other fuels used in spark-ignition engines, such as liquefied petroleum gas (LPG) or compressed natural gas (CNG).

[0004] US patent application 2009 / 0193796 describes a system for treating the exhaust gases of a gasoline engine. In several embodiments, a particulate filter follows a three-way catalytic converter. The particulate filter can be coated with various combinations of platinum, palladium, and rhodium. The coated particulate filter can promote the oxidation of soot trapped within it. While filtering gasoline engine emissions with a particulate filter can be advantageous, over time a particulate filter can accumulate so much soot that it reduces engine efficiency by increasing back pressure in the exhaust system. The application appears to provide little guidance on how to remove soot from a particulate filter. Therefore, the system described in the application may cause a deterioration in engine performance over time.Furthermore, the three-way catalytic converters described in the document operate at higher efficiencies when the gases entering the three-way converter are close to stoichiometric conditions. However, there may be some engine operating conditions where the particulate filter temperature is suboptimal for achieving the target soot oxidation rate. The document appears to offer little guidance on overcoming low particulate filter temperatures.

[0005] German patent application DE 10 2007 057 507 A1 discloses a method for regenerating an exhaust gas purification device located in the exhaust system of an internal combustion engine, in which, upon a regeneration request, the target idle speed of the internal combustion engine is increased from a baseline target idle speed, and a device for carrying out the method. The method provides that the engine speed is displayed and that an underlying speed signal is modified during the increase of the target idle speed such that the increase in the target idle speed does not, at least approximately, change the displayed speed signal. The increase in the engine's idle speed occurring during the regeneration of the exhaust gas purification device is therefore not reflected in a corresponding display.This prevents the operator of the internal combustion engine from being made aware of the regeneration process.

[0006] Paragraph

[0006] of the patent in suit shall be worded as follows: The present inventors have developed methods for controlling a spark-ignition engine having an exhaust aftertreatment system with a particulate filter according to the features of independent claims 1, 7 and 13.

[0007] The oxidation of soot held by a particulate filter can be improved by controlling the filter's temperature through retarding ignition timing from minimum ignition for best torque (MBT). For example, when an engine is idling at low speed and load, it may not generate enough heat to achieve a target rate of soot oxidation for soot held by a particulate filter. According to the invention, however, the crankshaft angle at which a spark is delivered to a cylinder is retarded, causing the cylinder's air / fuel mixture to burn later in the cylinder cycle. This reduces engine work and increases the amount of heat transferred from the cylinder to the exhaust system. In this way, the engine ignition can be adjusted to deliver additional heat to a particulate filter in the engine's exhaust system.This allows the particle filter temperature to be raised in order to improve the soot oxidation rate.

[0008] The present description offers several advantages. Specifically, it provides a method for increasing the soot oxidation rate of soot held by a particulate filter. Furthermore, the present method responds to the driver's torque demand, so that the engine torque increases when the driver demands more torque. Finally, the present method can reduce the time required to regenerate a particulate filter, as regeneration can also be performed during low engine loads.

[0009] The aforementioned advantages, as well as other advantages and features of the present invention, will become readily apparent from the following detailed description, either alone or in conjunction with the accompanying drawings.

[0010] It is understood that the foregoing summary is intended to present, in simplified form, a selection of concepts that are further described in the detailed description. It is not intended to identify any essential or key features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that address the disadvantages mentioned above or in any part of this disclosure. Brief description of the drawing Fig. Figure 1 shows a schematic view of an exemplary embodiment of a gasoline engine with direct injection; Fig. 2a shows a diagram of an exemplary exhaust system configuration; Fig. 2b shows a diagram of an exemplary exhaust system configuration; Fig. 2c shows a diagram of an exemplary exhaust system configuration; Fig. Figure 3 shows a diagram of an exemplary exhaust system configuration; Fig. Figure 4 shows a flowchart of a fuel control procedure for regenerating a particulate filter for a gasoline engine; Fig. Figure 5 shows a flowchart of the remaining part of a process in Fig. 4 fuel tax procedure shown; Fig. Figure 6 shows a flowchart of a procedure for increasing the temperature of a particulate filter for a gasoline engine; Fig. Figure 7 shows a flowchart of a procedure for regenerating a particulate filter while operating a gasoline engine in a deceleration cut-off mode or in a variable displacement mode; Fig. Figure 8 shows a flowchart of a procedure for operating a gasoline engine while regenerating a particulate filter; and Fig. Figure 9 shows an exemplary graphical representation of cylinder air / fuel adjustments and exhaust gas oxygen concentration downstream of a particulate filter. Detailed description of the depicted embodiments

[0011] Fig. Figure 1 shows an exemplary embodiment of a gasoline engine system with direct injection, generally at 10. In detail, the internal combustion engine 10 comprises several cylinders, one of which is in Fig. Figure 1 shows the engine 10 being controlled by an electronic engine control unit 12. The engine 10 comprises a combustion chamber 14 and cylinder walls 16 with a piston 18 positioned therein and connected to a crankshaft 20. The combustion chamber 14 is connected to an intake manifold 22 and an exhaust manifold 24 by means of an intake valve 26 and an exhaust valve 28, respectively.

[0012] The intake manifold 22 is connected to a throttle port 30 via a throttle valve 32. In one embodiment, an electronically controlled throttle can be used. In one embodiment, the throttle is electronically controlled to maintain a specified vacuum value in the intake manifold 22 regularly or continuously. It should be noted that in some applications, the throttle port 30 and the throttle valve 32 can be located downstream of a compression device 90. Alternatively, a throttle port 30 and a throttle valve 32 can be omitted.

[0013] The combustion chamber 14 is also shown with an associated fuel injection device 37 for supplying fuel proportional to the pulse width (fpw) of the signal from the control unit 12. Fuel is supplied to the fuel injection device 37 by a conventional fuel system (not shown) comprising a fuel tank, a fuel pump, and a fuel distribution pipe (not shown). In the case of direct injection engines, as in Fig. Figure 1 shows a high-pressure fuel system, for example a common rail system.

[0014] A spark plug 34 provides an ignition source for the contents of the combustion chamber 14. Energy to generate a spark is provided by the ignition system 35. The control unit 12 adjusts the charging of the ignition coil, which supplies electrical voltage to the spark plug 34.

[0015] In the embodiment shown, the control unit 12 is a conventional microcomputer and comprises a microprocessor 40, input / output ports 42, an electronic memory 44, which in this particular example may be an electronically programmable memory, a working memory 46 and a conventional data bus.

[0016] The control unit 12 receives various signals from sensors connected to the engine 10, including but not limited to: measurements of the intake air mass flow (MAF) from an air flow meter 50 connected to the air filter [A in Fig. 1] is coupled; engine coolant temperature (ECT) from a temperature sensor 52 connected to a cooling jacket 54; a manifold pressure (MAP) measurement from a manifold pressure sensor 56 coupled to the intake manifold 22; a throttle position (TP) measurement from a throttle position sensor 58 coupled to the throttle valve 32; and an ignition profile sensor signal (PIP) from a Hall sensor 60 (or variable magnetic resistance sensor) connected to the crankshaft 20, indicating engine speed.

[0017] Engine 10 may include an exhaust gas recirculation (EGR) system to reduce NOₓ. xand contribute to other emissions. The engine 10 can, for example, include a high-pressure EGR system in which exhaust gas is supplied to the intake manifold 22 through a high-pressure EGR pipe 70, which is connected to the exhaust manifold 24 at a point upstream of an exhaust turbine 90a of a compression device 90 and to the intake manifold 22 at a point downstream of an inlet compressor 90b of the compression device 90. The high-pressure EGR system shown includes a high-pressure EGR valve assembly 72 located in the high-pressure EGR pipe 70. Exhaust gas flows from the exhaust manifold 24 first through the high-pressure EGR valve assembly 72 and then to the intake manifold 22. An EGR cooler [in Fig. [1 shown at Y] can be arranged in the high-pressure EGR pipe 70 to cool recirculated exhaust gases before they enter the intake manifold. Cooling is typically achieved using engine water, but an air-to-air heat exchanger can also be used.

[0018] The engine 10 can also include a low-pressure EGR system. The illustrated low-pressure EGR system comprises a low-pressure EGR pipe 170, which connects to the exhaust manifold 24 at a point downstream of the exhaust turbine 90a and to the intake manifold 22 at a point upstream of the intake compressor 90b. A low-pressure valve assembly 172 is arranged in the low-pressure EGR pipe 170. Exhaust gas in the low-pressure EGR circuit flows from the turbine 90a through an aftertreatment device 82 (for example, a particulate filter comprising a three-way catalyst, which may consist of a washcoat comprising platinum, palladium, and rhodium) and an aftertreatment device 80 before entering the low-pressure EGR pipe 170. The aftertreatment device 82 processes engine exhaust gases to, for example, retain soot and oxidize exhaust gas components.Further exhaust system configurations are described in the following description and figures. A low-pressure EGR cooler Ya can be positioned along the low-pressure EGR pipe 170.

[0019] It should be noted that, in the context of this description, an aftertreatment device may include various types of catalysts, including oxidation catalysts, SCR catalysts, a catalyzed particulate filter (e.g., a uniform, zone-coated, or layered catalyzed filter), three-way catalysts, and furthermore, particulate filters, hydrocarbon traps, and NOx traps, but does not include sensors and actuators such as oxygen sensors, NOx sensors, or particulate sensors. Some specific examples of aftertreatment configurations can be explicitly stated by way of example.

[0020] The high-pressure EGR valve assembly 72 and the low-pressure EGR valve assembly 172 each have a (not shown) valve for controlling a variable area restriction in the high-pressure EGR pipe 70 and low-pressure EGR pipe 170, which thereby controls the flow of high-pressure or low-pressure EGR.

[0021] Vacuum regulators 74 and 174 are connected to the high-pressure EGR valve assembly 72 and the low-pressure EGR valve assembly 172, respectively. The vacuum regulators 74 and 174 receive actuation signals from the control unit 12 to control the valve positions of the high-pressure EGR valve assembly 72 and the low-pressure EGR valve assembly 172. In a preferred embodiment, the high-pressure EGR valve assembly 72 and the low-pressure EGR valve assembly 172 are vacuum-actuated valves. However, any type of flow control valve or flow control valves can be used, for example, an electric solenoid-operated valve or a valve operated by a stepper motor.

[0022] The compression device 90 can be a turbocharger or any other such device. The illustrated compression device 90 has a turbine 90a installed in the exhaust manifold 24 and a compressor 90b, which is located in the intake manifold 22 by means of an intercooler [in Fig. [1 shown at X] is connected, which is typically an air-to-air heat exchanger, but could be water-cooled. The turbine 90a is typically connected to the compressor 90b by means of a drive shaft 92. (This could also be a sequential turbocharger arrangement, a single VGT, twin VGTs, or any other arrangement of turbochargers that could be used).

[0023] The oxygen concentration present in the exhaust system can be assessed by oxygen sensors 175, 178, and 176. Furthermore, additional oxygen sensors (not shown) or fewer oxygen sensors can be placed at various locations in the exhaust system, as described herein. Oxygen sensor 175 detects the engine exhaust oxygen concentration, while oxygen sensor 178 detects exhaust oxygen downstream of the aftertreatment device 82. Oxygen sensors can be wide-range sensors exhibiting a linearized output, or they can be sensors indicating a high-gain signal under near-stoichiometric conditions.

[0024] Furthermore, an accelerator pedal 94 is shown along a driver's foot 95. A pedal position sensor (pps) 96 measures the angular position of the pedal actuated by the driver. It is understood that the illustrated engine 10 is shown only as an example and that the systems and methods described herein can be implemented or applied in any other suitable engine that has suitable components and / or a suitable arrangement of components.

[0025] With reference to now Fig. Figure 2a shows a diagram of an exemplary exhaust system configuration. The exhaust system 201 consists of an aftertreatment device 230, which comprises an oxidation catalyst and a particulate filter without an oxygen storage medium (e.g., cerium oxide). Alternatively, in some applications, the aftertreatment device 230 may consist of a particulate filter or a uniform, zoned, or layered catalyzed particulate filter, in which the filter lacks an oxygen storage medium. The aftertreatment device 230 is shown at the furthest upstream position 230, downstream of the engine 200. An oxygen sensor 202 is located downstream of the aftertreatment device 230 and upstream of the aftertreatment device 232. The aftertreatment device 232 may, for example, consist of a three-way catalyst. An oxygen sensor 204 is located downstream of the aftertreatment device 232.

[0026] In the embodiment of Fig. 2a Advantageously, the oxygen sensor 202 takes into account engine exhaust oxygen consumed when soot is burned in the particulate filter 230. When the particulate filter 230 is below the oxidation temperature of soot, the oxygen sensor 202 indicates the raw exhaust oxygen concentration. In contrast, the oxygen sensor 202 indicates the oxygen concentration entering the aftertreatment device 232, regardless of whether soot held by the particulate filter 230 is being burned or not.

[0027] By measuring the oxygen in engine exhaust, it is possible to determine whether an engine is burning a rich or lean air / fuel mixture. Furthermore, by measuring exhaust gases entering an aftertreatment system, it is possible to estimate and control the operation of the aftertreatment system. In the specific configuration of Fig. 2a An oxygen sensor 202 provides an indication of oxygen entering the aftertreatment device 232. Furthermore, the oxygen sensor 202 detects oxygen in engine exhaust gases when soot held in the aftertreatment device 230 is not oxidized. However, if soot is oxidized by the aftertreatment device 230, no estimation of oxidized soot is required to determine the amount of oxygen entering the downstream aftertreatment device 232. Therefore, the amount of fuel supplied to the engine 200 can be adjusted so that the aftertreatment device is exposed to nearly stoichiometric exhaust gases without having to estimate how much oxygen is consumed by soot oxidation.For example, if soot is oxidized and the oxygen sensor 202 indicates a lean air / fuel mixture, the engine fuel can be increased so that the oxygen concentration entering the downstream aftertreatment device is at a stoichiometric value. Conversely, if soot is oxidized and the oxygen sensor 202 indicates a rich air / fuel mixture, the engine fuel can be reduced. Thus, if oxygen from the engine exhaust is involved in the oxidation of soot held by the aftertreatment device 230, the engine fuel can be adjusted so that the downstream aftertreatment device 232 is exposed to a desired amount of oxygen.

[0028] It should also be noted that the oxygen sensor 202 can be used to determine whether other exhaust gas components are increasing or decreasing. Near stoichiometric conditions, for example, an increasing amount of oxygen can indicate increasing NOx, while a decreasing oxygen concentration can indicate increased HC and CO emissions.

[0029] The downstream oxygen sensor 204 can be used to indicate or infer the condition of the aftertreatment device. In one example, if the oxygen sensor 204 indicates a lean condition, the air / fuel mixture supplied to the engine 200 can be enriched so that the aftertreatment device 232 can be returned to stoichiometric conditions. In another example, if the oxygen sensor 204 indicates a rich condition, the air / fuel mixture supplied to the engine 200 can be leaned out so that the aftertreatment device 232 can be returned to stoichiometric conditions. In this way, an air / fuel mixture supplied to an engine can be adjusted to optimize the performance of an aftertreatment device (e.g.,to improve and take into account the upstream operation of a particulate filter in an exhaust system, while maintaining efficient operation of a downstream aftertreatment device (e.g., a three-way catalytic converter).

[0030] With reference to now Fig. Figure 2b shows a diagram of an exemplary exhaust system configuration. An upstream oxygen sensor 206 directly detects the engine exhaust gases from engine 200. The most upstream aftertreatment device 240 can consist of a particulate filter and a three-way catalyst. An oxygen sensor 208 detects exhaust gases that have been treated by the aftertreatment device 240. By providing an oxygen sensor downstream of the aftertreatment device 240, advantages can be realized compared to a system that provides a single oxygen sensor at 206 or a system that provides a single oxygen sensor at 208. For example, engine exhaust emissions can be directly detected by oxygen sensor 206, while oxygen that is used or stored in the three-way catalyst section of the aftertreatment device 240 is observable by oxygen sensor 208.Furthermore, the oxygen sensor 208 detects the reduction in exhaust oxygen when soot is burned in the particulate filter section of the aftertreatment device 240. This allows the outputs of sensors 206 and 208 to be compared to determine when the catalyst section of the aftertreatment device activates (e.g., activation can be indicated by the catalyst's ability to convert oxygen) and when soot oxidation begins in the particulate filter. The oxygen concentration passing through the upstream aftertreatment device can, for example, be subtracted from the amount of oxygen entering the upstream aftertreatment device. If the oxygen concentration deviates from a baseline value of oxygen utilization, it can be determined whether the catalyst has been activated (e.g., catalyst activation has occurred) or whether soot is being burned in the particulate filter.Since the catalyst begins to activate at a lower temperature than the temperature at which soot begins to oxidize, it is possible to monitor oxygen concentrations upstream and downstream of a device acting as both a catalyst and a particulate filter, and to determine when catalyst activation occurs and when soot oxidation begins. For example, in a first temperature range of the particulate filter, the oxygen concentration downstream of an aftertreatment device can be subtracted from the oxygen concentration upstream of the aftertreatment device, and the difference can indicate catalyst activation by detecting oxygen storage.In a second temperature range, which is higher than the first temperature range, the oxygen concentration downstream of a post-treatment device can be subtracted from the oxygen concentration upstream of the post-treatment device, and the difference can indicate when soot begins to oxidize in a post-treatment device.

[0031] The downstream aftertreatment device 242 can consist of a three-way catalyst in the configuration shown. The downstream oxygen sensor 212 can be used to indicate the status of the downstream aftertreatment device 242. Furthermore, the combination of oxygen sensors 208 and 212 can provide even more information regarding the status of the aftertreatment device 242. For example, the output of oxygen sensor 212 can be subtracted from the output of oxygen sensor 208 to determine the oxygen storage capacity of the aftertreatment device 242.In particular, the difference in oxygen detected by oxygen sensor 208 and oxygen sensor 212 when the state of the after-treatment device 242 changes from rich to lean, the difference in oxygen concentration detected by oxygen sensors 212 and 208, provides an indication of the oxygen storage capacity of the after-treatment device 242.

[0032] In one embodiment, portions of the soot held by the aftertreatment device 240 can be oxidized by repeatedly switching the aftertreatment device 240 between rich and lean exhaust gas conditions, while oxygen is depleted and replenished in the aftertreatment device 240, without substantially reducing or replenishing the overall storage capacity of the aftertreatment device 242. For example, the fuel supplied to an engine can be modulated around the stoichiometry so that at least one cylinder of the engine burns an air / fuel mixture that is sub- or super-stoichiometric. The frequency, duty cycle, and degree of richness or leanness can be varied to modulate the burned air / fuel mixture, thereby modulating the oxygen concentration of the exhaust gas. The configuration of Fig. 2b enables the state of the aftertreatment device 204 to be switched between an oxygen concentration above stoichiometric conditions and an oxygen concentration below stoichiometric conditions. Simultaneously, the state of the aftertreatment device 242 can be monitored so that the fuel supplied to the engine is adjusted to ensure that the oxygen storage capacity of the aftertreatment device 242 is neither substantially depleted nor significantly filled. For example, the oxygen storage quantity can be maintained close to 50% of the oxygen storage capacity of the aftertreatment device 242; or the oxygen storage quantity can be maintained in a range of 20% to 80%, preferably 40% to 60%, of the oxygen storage capacity.

[0033] In another embodiment, the oxygen sensor 208 can be removed from the system of Fig. 2b removed. If the oxygen sensor 208 is removed, the engine fuel adjustments can be based on the oxygen sensors 206 and 212. In one embodiment, the amount of oxygen entering the aftertreatment device 242 can be estimated by a model that estimates soot accumulation and soot oxidation. Soot accumulation can be modeled as a mass from empirically determined test results. For example, the amount of soot emitted by an engine at different engine speeds and loads can be stored in a table or function. When the engine is running, the table can be queried based on the current engine speed and load to determine the amount of soot directed to a particulate filter in the exhaust system. Analogously, the oxidation rate of soot can be similarly estimated from the oxygen concentration of the engine exhaust and the particulate filter temperature.By knowing the oxygen concentration of exhaust gases entering the aftertreatment device 240, the oxygen storage capacity of the aftertreatment device 240, the oxidation rate of soot in the aftertreatment device 240, the amount of soot stored by the aftertreatment device 240, and the amount of oxygen entering the aftertreatment device 242 can be estimated. If the estimated amount of oxygen stored in the aftertreatment device 242 is below or above a threshold, the engine fuel can be adjusted to be richer or leaner to return the aftertreatment device 242 to a desired amount of stored oxygen.

[0034] The oxygen sensor 212 receives oxygen concentration information from downstream of the aftertreatment device 242, allowing engine fuel to be adjusted in response to an observed oxygen concentration. For example, if the oxygen sensor 212 indicates a lean condition, the fuel supply to the engine is increased to reduce oxygen in the exhaust gases. If the oxygen sensor 212 indicates a rich condition, the fuel supply to the engine is reduced to increase oxygen in the exhaust gases.

[0035] With reference to now Fig. Figure 2c shows a diagram of an exemplary exhaust system configuration. An oxygen sensor 220 detects exhaust gases directly from the engine 200. A three-way catalyst 250 oxidizes and reduces exhaust gas components before the exhaust gases flow to a particulate filter 252. An oxygen sensor 222 detects exhaust gases that have passed through the three-way catalyst 250 and the particulate filter 252. A three-way catalyst 254 further treats unwanted exhaust gases that have passed through the three-way catalyst 250 and the particulate filter 252. A downstream oxygen sensor 224 detects oxygen that has passed through the upstream catalysts and the particulate filter.

[0036] The system of Fig. 2c works similarly to the one in Fig. The system shown in Figure 2b is different. However, the three-way catalyst 250 and the particulate filter 252 are separate components, so the volumes of each component can be changed without necessarily changing the volume of the other. In one example, the volume of the three-way catalyst is less than half the volume of the particulate filter 252 or the three-way catalyst 254. By reducing the volume of the three-way catalyst, the catalyst can start up more quickly because less mass needs to be heated before the three-way catalyst reaches operating temperature. The oxygen sensor 220 provides the same functions and is used similarly to the oxygen sensor 206. The oxygen sensor 222 provides oxygen concentration information for the exhaust gases that have been treated by the three-way catalyst 250. The oxygen sensor 224 provides oxygen concentration information for the exhaust gases that have been used in the oxidation of soot.By providing oxygen sensors upstream and downstream of the particulate filter, a measured distinction is made between the oxygen storage capacity of the catalyst located furthest upstream and the oxygen utilization during soot oxidation. Finally, the oxygen sensor 226 offers the same function and is used in a similar manner to the oxygen sensor 212 described above.

[0037] With reference to now Fig. Figure 3 shows a diagram of an exemplary exhaust system configuration. Upstream sensors 302 and 304 detect engine exhaust gases directly from different cylinder banks of the engine 300. The three-way catalysts 320 and 322, located furthest upstream, are situated upstream of the particulate filter 324. An oxygen sensor 306 detects exhaust gases that have been treated by the three-way catalysts 320 and 322. Specifically, exhaust gases from two cylinder banks are combined and fed to the particulate filter 324 before reaching the oxygen sensor 306. The oxygen sensor 306 is located downstream of the particulate filter 324 and upstream of the three-way catalyst 326. The oxygen sensor 306 provides an indication of the oxygen concentration associated with both cylinder banks of the engine 300.For example, if oxygen sensor 306 detects a higher oxygen concentration in the exhaust system, the cylinder bank indicating a leaner air / fuel mixture is enriched to bring the exhaust gas concentration closer to a stoichiometric mixture. This is analogous to sensor 224. Fig. 2c A downstream oxygen sensor 308 can be used to adjust the amount of fuel supplied to the cylinders of the engine 300. In particular, the oxygen sensor 308 provides oxygen concentration information from downstream of the aftertreatment device 326, so that engine fuel to each cylinder bank is adjusted in response to an oxygen concentration observed by the downstream sensor 308. For example, if the oxygen sensor 308 indicates a lean condition, the fuel to the engine cylinder bank with the leanest mixture, as detected by oxygen sensor 302 or 304, is increased. If the oxygen sensor 308 indicates a rich condition, the fuel to the engine cylinder bank with the richest mixture, as detected by oxygen sensor 302 or 304, is decreased.

[0038] With reference to now Fig. Figure 4 shows a flowchart of part of a fuel control procedure for regenerating a particulate filter for a gasoline engine. At 402, engine operating conditions are determined by sensors and actuators. In one example, routine 400 determines engine temperature, ambient temperature, the pressure drop across a particulate filter or aftertreatment device, the time since engine start, engine load, engine torque demand, the temperature of a catalyst downstream of a particulate filter, engine speed, and the amount of air supplied to the engine. In other exemplary embodiments, additional or fewer operating conditions can be determined based on specific tasks. After determining engine operating conditions, routine 400 advances to 404.

[0039] In the 404 embodiment, the amount of soot retained by a particulate filter and the soot oxidation rate are determined. As explained above, the soot accumulation can be modeled as a mass from empirically determined test results. In this embodiment, the amount of soot emitted by an engine at different engine speeds and loads can be stored in a table or function. When the engine is running, the table can be queried based on the current engine speed and load to determine the amount of soot directed to a particulate filter in the exhaust system. Similarly, the oxidation rate of soot can be estimated from the engine exhaust oxygen concentration and the particulate filter temperature. For example, a table containing soot oxidation rates can be indexed by particulate filter temperature and the mass flow rate of oxygen to the filter.If the soot oxidation rate exceeds the soot storage rate, the particulate filter is considered to be undergoing a continuous regeneration, as some of the soot storage capacity is released through soot oxidation. Then routine 400 advances to 406.

[0040] In system 406, routine 400 decides whether or not to trigger particulate filter regeneration. In one embodiment, routine 400 makes this decision based on the pressure drop across the particulate filter. In another embodiment, routine 400 can decide to regenerate the particulate filter in response to a model. For example, a soot accumulation model that estimates the amount of soot produced by an engine can be the basis for regenerating a particulate filter. If the estimated soot amount exceeds a threshold, particulate filter regeneration is triggered. Conversely, if a pressure across the particulate filter is determined by a sensor or an estimation model, particulate filter regeneration can be triggered after the observed or estimated pressure exceeds a threshold.

[0041] Furthermore, other conditions can be included to determine when the particulate filter needs to regenerate. For example, filter regeneration must not occur if the engine temperature is above or below a threshold temperature. Additionally, in one example, filter regeneration must not occur if the filter temperature is below a threshold value. However, if soot has accumulated on the filter, the control unit 12 can raise the filter temperature by retarding the ignition timing and increasing the engine airflow, as described in [reference to relevant section]. Fig. As described in section 6, the regeneration process continues until a filter threshold temperature is reached. In this example, particulate filter regeneration can occur after the threshold temperature is reached. In yet another example, particulate filter regeneration must not occur for a certain period after the engine starts. For example, particulate filter regeneration must not be triggered until sufficient time has elapsed for the engine speed to stabilize after starting. In another embodiment, particulate filter regeneration can be triggered during overrun fuel cut-off.In yet another embodiment, particulate filter regeneration must not be triggered unless the engine load exceeds a threshold value (for example, the engine load could be the engine's rated torque divided by the total torque available from the engine; in other applications, the load could be the cylinder air charge divided by the total theoretical cylinder air charge), for example, a load of 0.3. In another example, particulate filter regeneration must not proceed until a catalyst located downstream of a particulate filter reaches a threshold temperature.

[0042] It should be noted that a particulate filter can be regenerated actively or passively. During active regeneration, engine operating conditions can be adjusted to specifically facilitate or improve particulate filter regeneration. For example, engine ignition timing can be adjusted to raise the temperature of a particulate filter, thereby increasing soot oxidation. Conversely, passive particulate filter regeneration is possible if, for example, engine operating conditions cause soot held by the particulate filter to oxidize without a particulate filter regeneration request. In one embodiment, a particulate filter can be passively regenerated when the engine is operated at higher engine speeds and loads.Regeneration can be passive, even if the engine's air / fuel mixture is adjusted in response to an oxygen concentration in the exhaust system, where the oxygen concentration is influenced by the oxidation of particles held by the particulate filter.

[0043] If particulate filter regeneration is desired and conditions are met, routine 400 advances to 408. Otherwise, routine 400 advances to 418.

[0044] At 418, routine 400 returns to operating the engine with a stoichiometric baseline fuel control. It should be noted that the baseline fuel control allows the engine to run above- or below-stoichiometrically under certain conditions. For example, during a cold start, an engine may run lean with baseline fuel control to reduce hydrocarbon emissions. Conversely, during high-load conditions, an engine may run rich with baseline fuel control to reduce the possibility of engine degradation. Furthermore, the engine may operate under various cyclic lean and rich conditions that maintain the time-averaged net stoichiometric conditions.

[0045] At 408, routine 400 determines whether the particulate filter has a temperature that allows the oxidation of soot and other materials that can be retained by a particulate filter. If routine 400 determines that a particulate filter has a temperature that allows regeneration and oxidation, routine 400 advances to 410. Otherwise, routine 400 advances to 414.

[0046] At 414, routine 400 begins to raise the particulate filter temperature to promote filter regeneration. This is particularly important because of... Fig. The six described procedures are used to raise the particulate filter temperature. Then, routine 400 returns to 408 to assess whether the particulate filter temperature is sufficient to proceed to 410 or not.

[0047] At 410, routine 400 decides whether particulate filter regeneration should begin with products of lean or rich combustion. In one embodiment, regeneration begins during a first operating condition by increasing the fuel mixture from substantially stoichiometric combustion (e.g., ± 0.04 lambda, where lambda is the air / fuel ratio at stoichiometry) to rich combustion. Specifically, the engine air / fuel mixture is increased to rich until substantially all oxygen storage (e.g., more than 75% of the available oxygen storage capacity) has been depleted in an aftertreatment device upstream of and including the particulate filter. Then, the engine air / fuel mixture is controlled to be lean by leaning the fuel mixture or by a stepwise change in the cylinder air / fuel mixture (e.g., by jumping from 0.95 λ to 1.05 λ in response to oxygen depletion).By reducing oxygen in upstream aftertreatment devices, it is possible to increase the oxygen flow rate to the particulate filter while reducing the possibility of oxygen slip through the particulate filter and oxygen and / or NOx slip through aftertreatment devices located downstream of the particulate filter. In this way, the oxidation rate can be improved because the kinetic interaction between soot and oxygen increases with higher oxygen flow rates. In another embodiment, or during a second operating condition that differs from the first, regeneration begins by adjusting the engine's air / fuel mixtures under superstoichiometric conditions. In one example, the engine air / fuel mixture is gradually leaned out, so that soot oxidation gradually increases.In this way, the oxidation rate can be controlled so that the particle filter temperature gradually increases and the air / fuel mixture is optimized. -The engine's fuel mixture can be used to control the particulate filter temperature. For example, routine 400 decides, in response to the particulate filter temperature, whether to start the oxidation process with a lean or rich mixture. If the particulate filter temperature is close to the oxidation threshold temperature, routine 400 starts the particulate filter regeneration process by going rich. Conversely, if the particulate filter temperature is higher than the oxidation threshold temperature, routine 400 starts the particulate filter oxidation process by going lean. If routine 400 decides to start the particulate filter oxidation process with a rich mixture, it advances to step 412. Otherwise, routine 400 advances to step 416. Thus, routine 400 provides the option to always start the particulate filter oxidation process with either a rich or lean mixture.However, routine 400 also provides for the initiation of the particulate filter oxidation process depending on the conditions, either rich or lean. For example, the particulate filter oxidation process can begin under one condition, either lean or rich, and under a second condition, the particulate filter oxidation process can begin in the other state, either rich or lean.

[0048] At 412, routine 400 begins particulate filter oxidation by increasing the engine air / fuel mixture to a richer state until it is determined that the exhaust gases downstream of the particulate filter contain a threshold amount less oxygen than a stoichiometric exhaust mixture. In one embodiment, an oxygen sensor downstream of the particulate filter provides data indicating when the oxygen upstream of the oxygen sensor is substantially depleted. In another embodiment, the extent to which the engine's air / fuel mixture can be enriched is limited to a threshold amount. Once the engine's air / fuel ratio has shifted to richer, routine 400 proceeds to the remainder of the routine, which is performed by Fig. 5 is described, and before routine 500.

[0049] At step 416, routine 400 begins particulate filter oxidation by leaning out the engine air / fuel mixture until it is determined that the exhaust gases downstream of the particulate filter contain a threshold amount more oxygen than a stoichiometric exhaust mixture. In one embodiment, an oxygen sensor downstream of the particulate filter provides data indicating when the oxygen begins to break through the aftertreatment devices located upstream of the oxygen sensor. In another embodiment, the extent to which the engine's air / fuel mixture can be leaned out is limited to a threshold amount. Once the engine's air / fuel ratio has shifted to lean, routine 400 proceeds to the remainder of the routine, which is performed by Fig. 5 is described, and before routine 500.

[0050] With reference to now Fig. 5 is the remainder of the in Fig. The routine shown in Figure 4 demonstrates this. At 502, routine 500 determines whether an oxygen sensor is located upstream of a catalyst and whether this oxygen sensor is the one used to determine the oxygen concentration of the engine exhaust. Routine 500 can determine the location of the oxygen sensors, for example, based on system configuration information stored in the memory of an engine control unit. If routine 500 determines that the most upstream oxygen sensor is located upstream of a catalyst, routine 500 advances to 504; otherwise, routine 500 advances to 506.

[0051] In 504, routine 500 takes into account the amount of accumulated soot that is oxidized in the particulate filter. Specifically, in one embodiment, routine 500 adjusts the stoichiometric air / fuel ratio to be leaner, so that the oxygen concentration of the engine exhaust indicates the stoichiometric air / fuel ratio of the engine after the exhaust gases pass through the particulate filter and some of the engine exhaust oxygen oxidizes the soot held by the particulate filter. Then routine 500 advances to 506.

[0052] At 506, routine 500 determines whether a catalyst is located upstream of a particulate filter and whether the catalyst has oxygen storage capacity. Alternatively, the catalyst may be included with the particulate filter. Routine 500 can, for example, use system configuration information stored in the memory of an engine control unit to determine whether a catalyst is located upstream of the particulate filter and whether the catalyst has oxygen storage capacity. If routine 500 determines that a catalyst with oxygen storage capacity is present, it advances to 508. If no catalyst is present, or if the catalyst does not include oxygen storage media, routine 500 advances to 510.

[0053] At 508, routine 500 determines the oxygen storage capacity of the upstream catalyst. In one embodiment, the oxygen storage capacity is determined from a table containing oxygen storage data, which may be indexed by catalyst temperature. Furthermore, the oxygen storage capacity taken from the table can be adjusted to account for catalyst degradation that may occur over time. In another embodiment, the oxygen storage capacity is adjusted based on switching the catalyst between lean and rich conditions and detecting, using data from oxygen sensors located upstream and downstream of the catalyst, when the catalyst's condition changes. After determining the catalyst's oxygen storage capacity, routine 500 advances to 510.

[0054] At 510, the engine's air / fuel ratio is adjusted to modify the exhaust gas components entering the upstream catalyst, if one is present. In one embodiment, where the upstream oxygen catalyst is positioned between the engine and a catalyst, the upstream oxygen sensor provides feedback on the oxygen concentration of the engine exhaust. Furthermore, the upstream oxygen sensor indicates the oxygen concentration entering the upstream catalyst. By multiplying the oxygen concentration by the mass flow rate through the engine, the mass of oxygen entering the upstream catalyst can be determined. In one embodiment, an oxygen sensor located upstream of a catalyst determines how much oxygen (e.g.,Oxygen (mass of oxygen) is supplied to the catalyst over a time interval. In one embodiment, the rate at which oxygen is supplied to the upstream catalyst can be adjusted based on operating conditions. For example, the rate at which oxygen is supplied to the upstream catalyst and particulate filter can be increased when the particulate filter temperature exceeds the oxidation threshold temperature by a certain amount, while the particulate filter temperature is below another threshold temperature. When the particulate filter temperature decreases or is close to the oxidation threshold temperature, the rate at which oxygen is supplied to the upstream catalyst and particulate filter can be decreased.

[0055] In one embodiment, during particulate filter regeneration, the fuel supplied to the engine is controlled by fuel control parameters that differ from those used to control the engine fuel supply when the engine is operating under similar conditions while a particulate filter is not regenerating. For example, the rate at which oxygen is supplied to the exhaust system and the degree of leanness or richness of stoichiometric conditions may differ when a particulate filter is regenerating compared to when a particulate filter is not regenerating while the engine is operating under similar conditions. In another embodiment, additional oxygen is added to the exhaust gas components by leaning out the cylinder's air / fuel mixture during particulate filter regeneration.

[0056] If an upstream catalyst is absent in a particular configuration, the engine's air / fuel ratio can be adjusted to promote soot oxidation. In one embodiment, an oxygen sensor located upstream of a particulate filter can control the amount of oxygen supplied to the filter. For example, an oxygen quantity exceeding the stoichiometric exhaust gas concentration can be supplied in response to the amount of soot retained by the particulate filter or in response to the rate of soot oxidation. Higher amounts of soot retained by the particulate filter allow for higher oxygen quantities to be supplied. Conversely, lower amounts of oxygen can be supplied to the particulate filter when soot retention is lower.In this way, the amount of oxygen in the engine exhaust gases can be controlled so that the excess oxygen in the exhaust gas is used to oxidize the soot held in the particulate filter, and so that the condition of a catalyst located downstream of the particulate filter is not disturbed to such an extent that NOx breaks through a catalyst located downstream of the particulate filter. Fig. Section 8 provides more details on how the engine air / fuel mixture is adjusted during particulate filter regeneration.

[0057] At 512, the engine's air / fuel ratio is adjusted to modify the exhaust gas components entering the downstream catalyst. In one embodiment, the engine's air / fuel ratio determined at 510 is adjusted to change the state of a catalyst downstream of the particulate filter. For example, the air / fuel mixture of a cylinder can be adjusted to be leaner or richer than the air / fuel mixture adjustment determined at 510. By changing the engine's air / fuel mixture, the state of the downstream catalyst is adjusted to convert efficiently while in a particulate filter regeneration mode.

[0058] The engine air / fuel mixture can be adjusted to control the condition of a catalyst downstream of a particulate filter by means of an oxygen sensor located upstream of the downstream catalyst, an oxygen sensor located downstream of the downstream catalyst, or a combination of both. For example, the air / fuel mixture entering a cylinder can be adjusted to be richer than it would be if an oxygen sensor located downstream of the downstream catalyst were indicating a lean condition.If the oxygen sensor located downstream of the catalytic converter indicates a rich condition, the cylinder's air / fuel ratio can be leaned out. Conversely, the oxygen sensor located upstream of the catalytic converter can be used to richen the cylinder's air / fuel mixture if a threshold amount of lean exhaust gas has entered the downstream catalytic converter. If the oxygen sensor located upstream of the catalytic converter indicates a rich condition, the cylinder's air / fuel mixture can be leaned out. In this way, the amount of oxygen present in the downstream catalytic converter can be controlled to oxidize hydrocarbons (HC) and carbon monoxide (CO) while reducing nitrogen oxides (NOx).

[0059] In 514, routine 500 can adjust the engine's air / fuel mixture to control the soot oxidation rate. For example, oxygen can be introduced to the particulate filter by means of a lean air / fuel mixture in the cylinder, so that excess oxygen is present at the particulate filter to oxidize soot. If the oxidation rate is higher than desired, or if the particulate filter temperature rises above a threshold temperature, the engine cylinder's air / fuel mixture can be enriched, so that less oxygen is available to participate in the oxidation of soot held by the particulate filter. The particulate filter temperature can be measured by a sensor, for example, or inferred from engine operating conditions. Furthermore, the rate at which oxygen is delivered to the particulate filter can be varied depending on operating conditions.For example, if the particulate filter temperature is higher than an oxidation threshold temperature but lower than an oxidation setpoint temperature, the amount of oxygen supplied to the particulate filter can be increased by leaning out the air / fuel mixture in the cylinder. Conversely, if the particulate filter temperature is higher than an oxidation threshold temperature but close to an oxidation setpoint temperature, the amount of oxygen supplied to the particulate filter can be decreased by enriching the air / fuel mixture in the cylinder.

[0060] In system 516, routine 500 determines whether the particulate filter has been sufficiently regenerated. In other words, the routine determines whether a target amount of soot held by a particulate filter has been oxidized. Routine 500 determines whether filter regeneration is complete or not, or whether the conditions for regeneration no longer exist. In one embodiment, regeneration is determined to be complete when the pressure differential across the particulate filter is less than a predetermined amount. In another example, regeneration is determined to be complete when the exhaust gas downstream of the particulate filter shows an increase in the oxygen concentration in the exhaust gases passing through the particulate filter. The increased oxygen concentration can be an indicator that soot in the filter has been oxidized and that the amount of soot is reduced, so that less oxygen is consumed to oxidize the soot remaining in the filter.If routine 500 determines that regeneration is complete, routine 500 advances to 518. Otherwise, routine 500 advances to 510.

[0061] At 518, routine 500 returns the fuel control to the base fuel control. In one exemplary embodiment, fuel is adjusted so that, over a time interval, less oxygen is present in the exhaust gases when the particulate filter regeneration has ended than when particulate filter regeneration is ongoing. Of course, there are many ways to achieve this result. For example, the amount of time or the number of cylinder cycles during which the engine runs lean can be reduced. In another example, the degree to which cylinders run lean can be reduced. For example, a cylinder can be run with a stoichiometric air / fuel mixture instead of a mixture that is 0.5 air / fuel ratio lean.These possibilities allow the engine's air / fuel ratio to be reset to a base fuel mixture, in which the engine, for example, burns an essentially stoichiometric air / fuel mixture.

[0062] With reference to now Fig. Figure 6 shows a flowchart of a procedure for raising the temperature of a particulate filter for a gasoline engine. At step 602, routine 600 determines whether a particulate filter has a desired oxidation threshold temperature. If so, routine 600 advances to step 610, where the ignition timing is advanced to minimum ignition for best torque (MBT) or to knock-limited ignition. If the particulate filter does not have a desired temperature, routine 600 advances to step 604. Note that the desired oxidation threshold temperature may be set above the temperature at which soot oxidation begins. For example, a desired threshold temperature may be set at 40°C above the temperature at which soot begins to oxidize.

[0063] In system 604, routine 600 determines whether the engine is operating in a range where retarded ignition timing is desired. For example, the ignition timing cannot be retarded if the engine load exceeds a threshold. Furthermore, this threshold can be modified for different engine speeds. For instance, at an engine speed of 1,200 rpm, the ignition timing must not be retarded for engine loads above 0.6, whereas at an engine speed of 5,000 rpm, the ignition timing must not be retarded for engine loads above 0.45. In another embodiment, during the regeneration of a particulate filter in a spark-ignition engine, the timing of at least one cylinder can be adjusted to control the particulate filter temperature above a threshold. Additionally, the ignition timing can be advanced in response to increasing torque demanded by the driver.For example, if the ignition timing is retarded by 10 degrees to raise the temperature of a particulate filter, the ignition timing can be advanced when the driver demands more torque, ensuring the engine produces the target torque and responds accordingly. Conversely, if the driver then reduces the torque demand, the ignition timing can be retarded to achieve the desired particulate filter temperature.

[0064] If the engine is operating under conditions where retarding the ignition timing is desired, routine 600 advances to 606, where the ignition timing is retarded. Otherwise, routine 600 advances to 610.

[0065] At 606, the engine ignition timing is retarded by MBT or knock-limited ignition. In one example, the ignition timing can be gradually retarded over a number of engine combustion cycles, making it less noticeable to the driver. The amount of ignition retardation can be determined empirically and stored in a table or function indexed by particulate filter temperature, engine speed, and engine load.

[0066] In program 608, routine 600 increases the cylinder air charge so that the engine can produce equivalent torque while the ignition timing is retarded to heat the particulate filter. In one example, the amount of additional air is stored in a table indexed by MBT ignition retard, engine speed, and engine load. Thus, the engine ignition advance and the cylinder air volume are adjusted simultaneously, allowing the engine to deliver the desired torque while increasing the particulate filter temperature.

[0067] With reference to now Fig. Figure 7 shows a flowchart of a method for regenerating a particulate filter while operating a gasoline engine in a fuel cut-off mode (DSFO) or during a variable displacement mode (VDE). During DSFO, fuel is cut off to at least one cylinder or reduced to a level at which combustion with the lean fuel mixture is not possible. During VDE mode, the number of active cylinders generating torque is less than the total number of engine cylinders. Lean-mode VDE or DSFO can be triggered in one embodiment when the temperature of a particulate filter exceeds a threshold value and when it is desirable to operate the engine cylinders in a lean mode, for example, at 416 of Fig. 4 or at 510-514 of Fig. 5. Furthermore, the VDE mode can be activated if the cylinder load is low and the particle filter temperature exceeds a threshold value.

[0068] At step 702, routine 700 determines whether a lean particulate filter regeneration is required or desired. If so, routine 700 advances to step 704. If not, routine 700 proceeds to the end. During a lean particulate filter regeneration, the particulate filter is regenerated by supplying excess oxygen to the filter, allowing soot to be oxidized by the excess oxygen.

[0069] At 704, routine 700 determines whether conditions for VDE or DSFO particulate filter regeneration are met. In one example, the engine can operate within a predetermined threshold range of engine speed / load for VDE. DSFO particulate filter regeneration can be activated when the driver's foot is released from the accelerator while the vehicle is above a threshold speed. If VDE or DSFO conditions are not met, routine 700 advances to 714, where lean particulate filter regeneration can be achieved by adjusting the air / fuel ratios of the engine cylinders without deactivating any engine cylinders. Fig. Section 8 provides details on particulate filter regeneration using this procedure. If the conditions for DSFO or VDE lean-mode particulate filter regeneration are met, routine 700 advances to 706.

[0070] At 706, routine 700 determines whether the particulate filter has reached a target temperature for regeneration. In one example, the particulate filter must be above a threshold temperature. This threshold temperature can be above the temperature at which soot oxidizes, but it doesn't have to be. If the particulate filter is above the threshold temperature, routine 700 advances to 712. If the particulate filter is not above the threshold temperature, routine 700 advances to 708.

[0071] At 708, the engine ignition timing is retarded by MBT or knock-limited ignition. In one example, the ignition timing can be gradually retarded over a number of engine combustion cycles, making it less noticeable to the driver. The amount of ignition retardation can be determined empirically and stored in a table or function indexed by particulate filter temperature, engine speed, and engine load.

[0072] In routine 700, operation 710 increases the cylinder air charge so that the engine can produce equivalent torque while the ignition timing is retarded to heat the particulate filter. In one example, the amount of additional air is stored in a table indexed by MBT ignition retard, engine speed, and engine load. Thus, the engine ignition advance and the cylinder air charge are adjusted simultaneously, allowing the engine to deliver the desired driver torque while increasing the particulate filter temperature. Note that routines 708 and 710 cannot retard the ignition timing or increase the engine air charge if the engine load is below a threshold that can be adjusted for different engine speeds.

[0073] On the 712, engine cylinders can be deactivated to support VDE or DSFO modes. In one example, cylinders are deactivated in response to desired engine load and speed. In VDE or DSFO, the deactivated cylinders can supply oxygen to the particulate filter by pumping a lean air / fuel mixture through the engine and to the exhaust system. Alternatively, engine cylinders can pump intake system gases through the engine and to the particulate filter. While the deactivated cylinders are pumping oxygen to the particulate filter, active cylinders can operate with a rich air / fuel mixture and / or retarded ignition timing. If a catalytic converter is located upstream of the particulate filter, the rich cylinder mixture and the contents of the inactive cylinders can combine at the upstream catalyst to provide additional heat to raise the particulate filter temperature.In one embodiment, the air / fuel mixtures burned in active cylinders can be alternated between lean and rich mixtures. For example, a particulate filter can burn a rich air / fuel mixture for one cylinder cycle and then burn a lean air / fuel mixture for one or more cylinder cycles. In this way, rich and lean air / fuel mixtures can be alternated regularly, so that the particulate filter is exposed to excess fuel while a downstream catalyst is kept close to stoichiometric conditions.

[0074] With reference to now Fig. Figure 8 shows a flowchart for a process for operating a gasoline engine and regenerating a particulate filter. The process allows for the maintenance of near-stoichiometric conditions in a downstream catalyst.

[0075] At 802, routine 800 determines whether particulate filter regeneration is complete. If so, routine 800 advances to the end. If not, routine 800 advances to 804. This occurs at 516 of Fig. The procedure described in section 5 can be used at 802 to determine whether particulate filter regeneration is complete, and is therefore omitted for brevity. And if the procedure of Fig. 8 at 510 and 512 of Fig. If 5 is used, 802 can be omitted, as this function is executed at 516.

[0076] In procedure 804, routine 800 determines the oxygen storage capacity of all catalysts in the exhaust system. In one example, the oxygen storage capacity can be determined as described above by switching the system catalysts between lean and rich conditions and observing the time it takes for the catalyst to change state. In another example, the oxygen storage capacity can be determined while switching system catalysts between rich and lean states, while recording the mass of oxygen supplied to the catalyst (e.g., oxygen concentration multiplied by engine mass flow rate).In yet another embodiment, the oxygen storage of each catalyst can be stored in a table indexed by catalyst temperature and modified by observations of switching times between oxygen sensors located upstream and downstream of catalysts.

[0077] At 806, the amount of soot retained by the particulate filter is determined. As described above, the amount of soot can be determined by measuring the pressure drop across the particle trap. Alternatively, the accumulated soot and the soot oxidation rate can be determined from a model that describes the amount of soot produced by the engine (e.g., a table indexed by engine speed and load) and the soot oxidation rate (e.g., the soot oxidation rate can be related to the particulate filter temperature and the amount of oxygen available in the engine exhaust).

[0078] In 808, routine 800 determines the amount of oxygen stored in each catalyst of the system. As exhaust gases pass through an exhaust system, oxygen can be extracted from the gas and used to oxidize HC or CO at system catalysts or in the particulate filter; therefore, routine 800 monitors where oxygen is stored and used in the exhaust system. In one embodiment, for example, the mass of oxygen contained in engine exhaust gases is observed by an upstream oxygen sensor before the exhaust gases pass through a catalyst or particulate filter. As the exhaust gases pass through a catalyst or particulate filter, some of the oxygen can be used to oxidize HC, CO, and soot. The amount of oxygen consumed by the exhaust gas can be estimated by multiplying the mass of oxygen in the engine exhaust gas by a utilization factor for each catalyst or particulate filter.The utilization factor for each post-treatment device can be adjusted based on factors such as temperature and mass flow rate. Oxygen not involved in oxidation and not detected by a downstream sensor can be considered stored in a catalyst. If an oxygen sensor detects an unexpected oxygen concentration that is inconsistent with the estimated amount of stored oxygen, the oxygen storage capacity of each catalyst can be reset or adjusted. In this way, the amount of oxygen stored in each oxygen storage catalyst can be estimated.

[0079] At 810, routine 800 determines the particulate filter temperature. In one embodiment, a temperature sensor can be used to determine the particulate filter temperature. In another embodiment, the particulate filter temperature can be estimated based on engine speed, engine load, ignition advance, and the engine's air / fuel mixture. For example, a table of empirically determined exhaust gas temperatures can be stored and retrieved at a later time, allowing an engine control unit to estimate the particulate filter temperature.

[0080] At 812, routine 800 determines whether or not a soot oxidation rate should be increased. In one embodiment, a target soot oxidation rate can be based on the amount of soot retained by a particulate filter and the engine load. For example, if the desired soot oxidation rate is 0.1 mg / s and the actual soot oxidation rate is 0.05 mg / s, the cylinder's air / fuel ratio can be leaned out by 0.01 λ based on 50 mg of retained soot.

[0081] In another example, if the desired soot oxidation rate is 0.1 mg / s and the actual soot oxidation rate is 0.05 mg / s, the cylinder air / fuel ratio can be leaned out by 0.05 λ based on 20 mg of retained soot. Thus, during a first condition, the cylinder air / fuel ratio can be adjusted to change the soot oxidation rate in response to an initial amount of soot held by a particulate filter, and during a second condition, the cylinder air / fuel ratio can be adjusted to change the soot oxidation rate in response to a second amount of soot held by the particulate filter. If the estimated soot oxidation rate is less than a desired oxidation rate, routine 800 advances to 814. If the estimated soot oxidation rate is greater than a desired rate, routine 800 advances to 826.

[0082] At step 814, routine 800 determines whether the cylinder's air / fuel mixture is at a lean limit. If so, routine 800 advances to step 818. If not, routine 800 advances to step 816, where the cylinder's air / fuel mixture is leaned out. At step 816, the engine or a cylinder must be gradually leaned out, or it must be leaned out stepwise to a predetermined amount. For example, a small amount of oxygen can be supplied to the exhaust system by leaning out a cylinder's air / fuel mixture from λ = 1 to λ = 1.01. Over time (e.g., 5 seconds) and a number of combustion cycles (e.g., 500 cycles), oxygen is slowly added to the exhaust system. Alternatively, the same amount of oxygen can be added to the exhaust system over a shorter time by leaning out a cylinder to λ = 1.1.The leaning rate, or fuel reduction, of a cylinder can be based on the target oxidation rate or the amount of soot held by the particulate filter. For example, a cylinder might be leaned out at 0.001 λ per minute when the particulate filter is half full, and at a rate of 0.002 λ per minute when the particulate filter is full. Thus, under a first condition, fuel to a cylinder might be leaned out at a first rate, and under a second condition, fuel to a cylinder might be leaned out at a second rate, the second rate being different from the first.

[0083] At 818, routine 800 determines whether a downstream catalyst is operating at a lean limit or not. In the illustrated configuration of Fig. 2a - 2c and Fig. 3. The downstream catalysts serve as a buffer in which exhaust gas components are treated, even when excess oxygen is supplied to the particulate filter and the upstream catalysts. However, it is desirable to maintain the downstream catalysts above a threshold temperature and in a state where between 20% and 80% (preferably between 40% and 60%) of the catalyst's oxygen storage capacity is utilized. If the catalyst temperature falls below the threshold temperature or if excess oxygen is stored in the catalyst, tailpipe emissions of HC, CO, and NOx may increase. Therefore, Routine 800 determines, based on the downstream catalyst's oxygen storage capacity and the amount of oxygen stored in the catalyst, whether the downstream catalyst is operating at a lean limit.If the stored oxygen level exceeds a threshold, the routine advances from 800 to 820. Otherwise, the routine advances from 800 to 824.

[0084] At 820, routine 800 increases the fuel mixture to a richer consistency, even if a higher oxidation rate might be desirable. Routine 800 increases the mixture to a richer consistency so that a downstream catalyst can continue to operate efficiently. The fuel mixture is increased to a richer consistency until the downstream catalyst reaches its rich limit, at which point lean operation can resume for soot reduction in the particulate filter. When the engine is emitting lean combustion products, some of the oxygen in the exhaust gases is consumed by oxidizing soot held by the particulate filter. Therefore, the engine can operate lean for a longer period because less oxygen reaches the downstream catalyst.

[0085] At step 824, routine 800 determines whether a downstream catalyst is operating at a rich limit. As mentioned above, it is desirable to maintain the downstream catalyst in a state where between 20% and 80% (preferably between 40% and 60%) of its oxygen storage capacity is utilized. In this state, the catalyst retains components for oxidation and exhaust gas reduction. Therefore, routine 800 determines whether the downstream catalyst is operating at a rich limit based on the amount of oxygen capacity and the amount of oxygen stored in the catalyst. If the amount of oxygen stored in the downstream catalyst is less than a threshold amount, routine 800 advances to step 822. Otherwise, routine 800 advances to step 802.

[0086] At 822, routine 800 leans out the engine fuel mixture. Routine 800 reduces the mixture to lean so that a downstream catalyst can continue to operate efficiently. In one example, the fuel mixture is leaned out until the desired oxygen level stored in the downstream catalyst is reached. During lean operation, the fuel mixture can be leaned out until a desired air / fuel mixture is achieved in the cylinder, then the engine can continue to run on the lean air / fuel mixture until the downstream catalyst reaches the desired oxygen storage level.

[0087] In 826, routine 800 determines whether particulate filter oxidation should be reduced by enriching the air / fuel ratio of the engine cylinder. As described above, in one embodiment, a soot oxidation rate can be based on the amount of soot retained by a particulate filter and the engine load. For example, if the desired soot oxidation rate is 0.05 mg / s and the actual soot oxidation rate is 0.1 mg / s, the cylinder's air / fuel ratio can be enriched by 0.02 λ based on 5 mg of retained soot. In another example, if the desired soot oxidation rate is 0.05 mg / s and the actual soot oxidation rate is 0.15 mg / s, the cylinder's air / fuel ratio can be enriched by 0.05 λ based on 2 mg of retained soot.Thus, a cylinder air / fuel mixture can be adjusted during a first condition to change the rate of soot oxidation in response to an initial amount of soot held by a particulate filter, and during a second condition, a cylinder air / fuel mixture can be adjusted to change the rate of soot oxidation in response to a second amount of soot held by the particulate filter. If the estimated rate of soot oxidation is greater than a target oxidation rate, routine 800 advances to 828. Otherwise, routine 800 advances to 818.

[0088] At step 828, routine 800 determines whether the engine cylinder's air / fuel mixture is at a rich limit. If so, routine 800 advances to step 818. Otherwise, routine 800 advances to step 830, where the air / fuel mixture is enriched. The engine or a single cylinder can be enriched gradually at step 830, or it can be enriched stepwise to a predetermined amount. For example, a small amount of oxygen can be removed from the exhaust gases by enriching a cylinder's air / fuel mixture from λ = 1 to λ = 0.98. Over time (e.g., 5 seconds) and a number of combustion cycles (e.g., 500 cycles), oxygen is slowly removed from the exhaust system. Alternatively, the same amount of oxygen can be removed from the exhaust system over a shorter time by enriching a cylinder to λ = 0.9.

[0089] At 830, the air / fuel ratio of the engine cylinder is enriched. The engine or a cylinder can be enriched gradually at 830, or it can be enriched stepwise to a predetermined amount. For example, a small amount of oxygen can be removed from the exhaust gases by enriching the cylinder's air / fuel mixture from λ = 1 to λ = 0.98. Over time (e.g., 5 seconds) and a number of combustion cycles (e.g., 500 cycles), oxygen is removed from the aftertreatment devices because the stored oxygen is used to oxidize increasing HC and CO. The same amount of oxygen can, however, be removed from the aftertreatment devices over a shorter time by enriching a cylinder to λ = 0.9. The rate of enrichment of a cylinder can be related to the target oxidation rate or the amount of soot held by the particulate filter, similar to what is described in 816.

[0090] In this way, the procedure of Fig. 8. A cylinder's air / fuel mixture is adjusted during particulate filter regeneration, causing the average or integrated air / fuel mixture to become leaner over a number of cylinder cycles. Simultaneously, the oxygen concentration in the exhaust gases downstream of the particulate filter is reduced, resulting in the average or integrated exhaust gas mixture remaining at essentially stoichiometric conditions over a number of cylinder cycles.

[0091] It should be noted that all routines 4-8 can be executed by a single control unit, or alternatively, an engine control unit can execute only some of the procedures 4-8. Therefore, routines 4-8 can be used for different system configurations.

[0092] With reference to now Fig. Figure 9 is an exemplary graphical representation of cylinder air / fuel ratio adjustments and exhaust oxygen concentration downstream of a particulate filter. The upper graph shows an example of a cylinder's air / fuel ratio over a number of cylinder cycles. The air / fuel ratio fluctuates around an x-axis, which represents a stoichiometric air / fuel ratio. Time increases from left to right. Before T1, the cylinder's air / fuel ratio is symmetrical around stoichiometry, and the particulate filter is not regenerating. Between T1 and T2, particulate filter regeneration begins, and the cylinder's air / fuel ratio shifts towards lean to accommodate the oxygen involved in soot combustion within the particulate filter. Note that the entire fluctuating air / fuel ratio shifts towards lean.Between T2 and T3, the cylinder's air / fuel ratio is shifted further towards lean to further increase the oxidation rate in the particulate filter. The rich side of the air / fuel mixture entering a cylinder is also increased to maintain a balanced and efficient operation of the rear three-way catalytic converter. After T3, the cylinder's air / fuel ratio is shifted towards richer and is again stoichiometrically symmetrical once soot oxidation is complete.

[0093] It should be noted that the in Fig.The air / fuel mixture shown in Figure 9 is for illustrative purposes only and is not intended to limit the description in any way. For example, the engine's air / fuel mixture can be controlled by a triangular air / fuel distribution or by a stochastic distribution around stoichiometric conditions. Furthermore, the duration and degree of richness or leanness of the air / fuel mixture can be adjusted to maintain a downstream three-way catalytic converter at stoichiometric conditions.

[0094] The diagram below illustrates the oxygen concentration in the exhaust system at a point downstream of the particulate filter. It is important to note that the oxygen concentration remains symmetrical around the stoichiometry when the cylinder's air / fuel mixture becomes leaner, as soot is oxidized during particulate filter regeneration. When lean exhaust gases pass through the particulate filter between T1 and T3, oxygen participates in the oxidation of soot to CO and / or CO2. The partial oxidation of soot to CO can provide a reducing agent for NOx reduction. This results in the oxygen concentration exiting the particulate filter remaining symmetrical around stoichiometric conditions. Consequently, stoichiometric conditions are maintained in a downstream catalyst. In this way, a particulate filter can be regenerated upstream while stoichiometric conditions are maintained in a downstream catalyst.Thus, a downstream catalyst can efficiently convert exhaust gases, while soot is oxidized in the particulate filter.

[0095] It is understood that the configurations and routines disclosed herein are exemplary and that these specific descriptions should not be considered restrictive, as numerous modifications are possible. For example, the above procedures can be applied to V-6, I-4, I-6, V-12, opposed-piston, and other engine designs.

[0096] The subject matter of the present disclosure thus includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, as well as other features, functions and / or properties disclosed herein.

[0097] The following claims specifically identify certain combinations and subcombinations which are considered novel and not obvious. These claims may refer to "one" element, "a first" element, or an equivalent thereof. These claims are to be understood as encompassing the integration of one or more such elements, without requiring or excluding two or more of these elements. 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 claims, whether broader, narrower, the same, or different from the scope of protection of the original claims, are also considered to be included in the subject matter of the present disclosure. Reference sign 10 Motor 12 electronic engine control unit 14 Combustion chamber 16 cylinder walls 18 pistons 20 Crankshaft 22 Intake manifold 24 exhaust manifolds 26 Inlet valve 28 Exhaust valve 30 throttle bodies 32 Throttle valve 34 Spark plug 35 Ignition system 37 Fuel injection device 40 microprocessor 42 Input / Output ports 44 electronic storage 46 GB RAM 50 air flow meters 52 temperature sensors 54 Cooling jacket 56 Manifold pressure sensor 58 Throttle position sensor 60 Hall effect sensors 70 High-pressure EGR pipe 72 High-pressure EGR valve assembly 74 Vacuum regulator 80 Post-treatment device 82 Post-treatment device 90 Compression device 90a Exhaust gas turbine 90b Inlet compressor 92 Drive shaft 94 Accelerator pedal 95 driver's foot 96 Pedal position sensor 170 Low-pressure EGR pipe 172 Low-pressure EGR valve assembly 174 Vacuum regulator 175 Oxygen sensor for engine exhaust 176 Oxygen sensor 178 Oxygen sensor downstream of the aftertreatment device 82 200 engine 201 Exhaust system 202 Oxygen sensor between the post-treatment devices 230 and 232 204 Oxygen sensor downstream of the aftertreatment device 232 206 Oxygen sensor downstream of the engine 200 208 Oxygen sensor downstream of the aftertreatment device 240 212 Oxygen sensor downstream of the aftertreatment device 242 220 Oxygen sensor downstream of the engine 200 222 Oxygen sensor downstream of the particulate filter 252 224 oxygen sensor downstream of the three-way catalytic converter 254 230 Aftertreatment device, particle filter 232 Post-treatment device 240 Post-treatment device 242 Post-treatment device 250 Three-way catalytic converter 252 particulate filters 254 three-way catalytic converter downstream of the particulate filter 252 300 engine 302 Oxygen sensor downstream of the engine 300 for one cylinder bank 304 Oxygen sensor downstream of the engine 300 for another cylinder bank 306 Oxygen sensor downstream of the particulate filter 324 308 oxygen sensor downstream of the three-way catalytic converter 326 320 Three-way catalytic converter 322 Three-way catalytic converter 324 Particulate filter downstream of the three-way catalytic converters 320 and 322 326 three-way catalytic converter downstream of the oxygen sensor 306 400 Flowchart for part of the routine for regenerating a particulate filter 500 Flowchart for the remaining part of the routine of flowchart 400 600 Flowchart for raising the temperature of a particle filter 700 Flowchart for regeneration during DSFO or VDE modes 800 Flowchart for regeneration under near-stoichiometric conditions in the catalyst An air filter X Intercooler Y EGR cooler Yes, low-pressure EGR cooler

Claims

[1] Method for controlling a spark-ignition engine having an exhaust aftertreatment system with a particulate filter and a catalyst located downstream of the particulate filter, comprising: Adjusting the ignition timing, at which at least one cylinder of a spark-ignition engine (10, 200, 300) receives a spark, to a retarded setting. when the amount of soot retained by a particulate filter (230, 240, 252) exceeds a threshold value and if the engine load is less than a threshold value, wherein a quantity of fuel supplied to at least one cylinder provides rich or stoichiometric exhaust gases which are fed to the exhaust aftertreatment system, while the ignition angle at which a spark is supplied to the at least one cylinder is retarded, and whereupon the engine's air / fuel mixture is subsequently controlled to be lean in order to oxidize the soot held by the particulate filter, where the amount of oxygen stored in the catalyst is monitored and, if this exceeds a first threshold, the air / fuel mixture of the engine is increased to a richer mixture until the amount of oxygen stored in the catalyst is less than a second threshold, whereupon the air / fuel mixture is controlled to a leaner mixture. [2] Method according to claim 1, characterized by , that the ignition angle, at which a spark is delivered to at least one cylinder, is advanced from a retarded condition (minimal ignition for best torque) to an advanced condition as the engine speed increases. [3] Method according to claim 1, characterized by , that the ignition timing is advanced when the temperature of the particulate filter (230, 240, 252) reaches a threshold temperature. [4] Method according to claim 1, characterized by , that a rate at which air mass flows through the spark-ignition engine (10, 200, 300) is increased in response to the retardation of the ignition timing. [5] Method according to claim 4, characterized by , that increasing the air mass flow rate is achieved by adjusting a throttle position or cam timing. [6] Method according to claim 1, which further comprises advancing an ignition angle, whereby a spark is supplied to the at least one cylinder of a spark-ignition engine (10, 200, 300) when a temperature of the particulate filter (230, 240, 252) exceeds a threshold temperature. [7] Method for controlling a spark-ignition engine having an exhaust aftertreatment system with a particulate filter and a catalyst located downstream of the particulate filter, comprising: Regenerating a particulate filter (230, 240, 252) of a spark-ignition engine (10, 200, 300); and Adjusting at least the ignition timing of at least one cylinder of the spark-ignition engine (10, 200, 300) to control the temperature of the particulate filter (230, 240, 252) above a threshold temperature, wherein a fuel quantity supplied to at least one cylinder provides rich or stoichiometric exhaust gases which are fed to the exhaust aftertreatment system, while the ignition timing at which a spark is supplied to the at least one cylinder is retarded, and whereupon the engine's air / fuel mixture is subsequently controlled to be lean in order to oxidize the soot held by the particulate filter, where the amount of oxygen stored in the catalyst is monitored and, if this exceeds a first threshold, the air / fuel mixture of the engine is increased to a richer mixture until the amount of oxygen stored in the catalyst is less than a second threshold, whereupon the air / fuel mixture is controlled to a leaner mixture. [8] Method according to claim 7, characterized by , that the ignition timing, at which a spark is supplied to at least one cylinder, is advanced from a retarded condition to minimum ignition for best torque when the speed of the spark-ignition engine (10, 200, 300) increases. [9] Method according to claim 7, characterized by , that the ignition timing is advanced when the temperature of the particulate filter (230, 240, 252) reaches a threshold temperature. [10] Method according to claim 7, characterized by, that the rate at which air mass flow through the spark-ignition engine (10, 200, 300) is increased when the ignition timing is retarded. [11] Method according to claim 10, characterized by , that increasing the air mass flow rate is achieved by adjusting a throttle position or cam timing. [12] Method according to claim 7, characterized by , that the adjustment of at least the ignition timing of at least one cylinder of the spark-ignition engine (10, 200, 300) includes advancing the ignition angle at which a spark is supplied to at least one cylinder of a spark-ignition engine (10, 200, 300) when the temperature of the particulate filter (230, 240, 252) exceeds a threshold temperature. [13] Method for controlling a spark-ignition engine having an exhaust aftertreatment system with a particulate filter, comprising: Regenerating a particulate filter (230, 240, 252) of a spark-ignition engine (10, 200, 300); Adjusting at least the ignition timing of at least one cylinder of the spark-ignition engine (10, 200, 300) to control the temperature of the particulate filter (230, 240, 252) above a threshold temperature; and Advancement of at least the ignition timing of at least one cylinder of the spark-ignition engine (10, 200, 300) in response to an increase in the torque demanded by the driver, wherein a quantity of fuel supplied to at least one cylinder provides rich or stoichiometric exhaust gases which are fed to the exhaust aftertreatment system, while the ignition timings at which a spark is supplied to the at least one cylinder are retarded, repeatedly switching between rich and lean exhaust gases to selectively modulate the oxygen concentration of the exhaust gas, shifting the overall fluctuating air / fuel ratio to lean in order to oxidize the soot held by the particulate filter. [14] Method according to claim 13, characterized by , that the ignition timing is advanced when the temperature of the particulate filter (230, 240, 252) reaches a threshold temperature. [15] Method according to claim 13, characterized by , that the rate at which air mass flows through the spark-ignition engine (10, 200, 300) is increased when the ignition timing is retarded.

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