Patent Publication Number: US-10767526-B2

Title: Gasoline particle filter temperature control

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a divisional of U.S. Non-Provisional patent application Ser. No. 15/000,930, entitled “GASOLINE PARTICLE FILTER TEMPERATURE CONTROL,” and filed on Jan. 19, 2016. The entire contents of the above-referenced application are hereby incorporated by reference for all purposes. 
    
    
     FIELD 
     The present description relates generally to methods and systems for reducing airflow to a gasoline particle filter while extending deceleration fuel shut-off time of an engine. 
     BACKGROUND/SUMMARY 
     The fuel consumption of automotive engines may be improved by shutting off fuel delivery into an engine when a vehicle is decelerating. This is known as deceleration fuel shut-off (DFSO). However, during DFSO the delivery of oxygen into an emissions control device of the vehicle increases. In vehicles that include a particulate filter, this increased oxygen delivery may result in degradation of the filter due to the overheating of the filter. 
     U.S. Pat. No. 8,407,988 offers a method to reduce the flow of oxygen to the particle filter during non-combustion conditions by closing an intake throttle valve. However, the inventors herein have recognized an issue with the above approach. As the engine continues to rotate with the intake throttle valve closed, the intake manifold air pressure (MAP) begins to drop. If the MAP gets too low, engine degradation may occur, e.g., lubricants may be drawn into the combustion chamber. 
     Accordingly, the inventors herein provide an approach to at least partially address these issues. In one example, a method includes, in response to a determination that a particle filter has reached a temperature above a threshold while an engine is operating with deceleration fuel shut-off (DFSO), fully closing a throttle valve configured to regulate flow of intake air to the engine, and responsive to intake manifold pressure dropping below a threshold pressure while the throttle valve is fully closed, adjusting a position of the throttle valve based on the particulate filter temperature. 
     In this way, particulate filter temperature during DFSO may be maintained below a threshold temperature, thus preventing filter degradation and extending the length of operation of DFSO. If the MAP drops below a threshold pressure while the throttle valve is closed, the throttle valve position may be adjusted based on filter temperature. For example, if the filter temperature is above the threshold temperature yet below an upper limit threshold, the throttle valve may be open by a small, preset amount. However, if the temperature of the particle filter increases above the upper limit threshold to the throttle may be maintained fully closed and MAP may be controlled by adjusting intake and/or exhaust valve timing to increase the overlap between the intake and exhaust valves of an engine&#39;s cylinders in order to increase the manifold pressure. In doing so, the MAP may be increased while maintaining restricted airflow into the particle filter, and in this way help decrease the temperature of the particle filter, while the engine remains in DFSO mode. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of a combustion chamber of an internal combustion engine. 
         FIG. 2  shows a flowchart illustrating a method for controlling the decelerating fuel shut-off parameters of an engine. 
         FIG. 3  shows a flowchart illustrating a method for keeping a gasoline particle filter from overheating while an engine is in decelerating fuel shut-off mode. 
         FIG. 4  shows an example timeline for controlling the temperature of a gasoline particle filter according to the methods of  FIGS. 2 and 3 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems and methods for maintaining an engine in decelerating fuel shut-off (DFSO) mode while keeping a gasoline particle filter from overheating. Some internal combustion engines employ a particulate filter in an exhaust system to trap particulate matter flowing through the exhaust system and thereby meet emission standards. For example, a direct-injection spark-ignition engine may include a particle filter to trap soot. As particulate matter accumulates in a particulate filter, exhaust backpressure will increase, which can adversely affect fuel economy. Accordingly, a particulate filter may be periodically regenerated by oxidizing stored particulate matter. A regeneration reaction typically includes increased oxygen concentration at the filter and suitable temperature conditions. As more oxygen is supplied to the filter, the heat produced by the combustion of the soot particles trapped by the filter may increase the temperature of the filter. Eventually, the filter may overheat. 
     When the temperature of the particle filter approaches a point at which the filter may be at risk of degradation, the filter may be cooled down by inhibiting the combustion reaction. This reaction may be inhibited by interrupting the supply of oxygen to the particle filter. Normally, an engine utilizes a significant amount of oxygen during the combustion of fuel at the engine&#39;s cylinders. However, when an engine is in DFSO mode fuel delivery to the engine is suspended, therefore no oxygen is consumed at the cylinders and it is eventually routed to the particle filter. Under these circumstances it is more difficult to control the temperature of the filter. In some examples, DFSO may be suspended and fuel delivery to the engine may be resumed, resulting in the reduction of oxygen supply to the particle filter and the subsequent decrease in the temperature of the filter. However, premature suspension of DFSO may decrease fuel efficiency. 
     The disclosed method attempts to extend the time an engine operates in DFSO mode while keeping the particle filter from overheating. In one embodiment, once an engine controller determines that the gasoline particle filter may have reached a threshold temperature, the intake throttle may be adjusted to a minimum position, which in one example may be fully closed. The effect of completely closing the throttle is to suspend the flow of additional oxygen into the particle filter in order to inhibit the soot combustion reaction, which may then result in the lowering of the temperature of the filter. Further, if the air pressure of the intake manifold decreases below a threshold while the throttle is at its minimum position, the timing of the intake and exhaust valves of the engine&#39;s cylinders may be adjusted to increase valve overlap. In this way, the manifold pressure may be increased while maintaining the engine operation in DFSO conditions. 
       FIG. 1  displays a schematic diagram showing one cylinder of a multi-cylinder engine fitted with an emissions control device that includes a gasoline particle filter. The flowchart presented in  FIG. 2  illustrates a method for controlling the decelerating fuel shut-off (DFSO) operation of an engine. A flowchart illustrating a method to control the temperature of the gasoline particle filter is shown in  FIG. 3  that describes the adjustment of the throttle valve and the degree of overlap of the intake and exhaust valves while an engine is operating in decelerating fuel shut-off mode.  FIG. 4  shows an example timeline for several engine operating parameters under a variety of engine conditions, including operation at times under normal conditions and at others under DFSO conditions. While the engine is under DFSO conditions, in one example, the engine throttle valve is adjusted in response to overheating of the particle filter, and in a second example, both the throttle valve and the cam timing valve overlap are adjusted to control the temperature of the particle filter. 
     The schematic diagram in  FIG. 1  illustrates one cylinder of multi-cylinder engine  10 , which may be included in a propulsion system of an automobile. Engine  10  may be controlled at least partially by a control system including controller  12  and by input from a vehicle operator  132  via an input device  130 . In this example, input device  130  includes an accelerator pedal and a pedal position sensor  134  for generating a proportional pedal position signal PP. Combustion chamber (i.e., cylinder)  30  of engine  10  may include combustion chamber walls  32  with piston  36  positioned therein. In some embodiments, the face of piston  36  inside cylinder  30  may have a bowl. Piston  36  may be coupled to crankshaft  40  so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft  40  may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system. Further, a starter motor may be coupled to crankshaft  40  via a flywheel to enable a starting operation of engine  10 . 
     Combustion chamber  30  may receive intake air from intake manifold  44  via intake passage  42  and may exhaust combustion gases via exhaust passage  48 . Intake manifold  44  and exhaust passage  48  can selectively communicate with combustion chamber  30  via a respective intake valve  52  and exhaust valve  54 . In some embodiments, combustion chamber  30  may include two or more intake valves and/or two or more exhaust valves. 
     In this example, intake valve  52  and exhaust valves  54  may be controlled by cam actuation via respective cam actuation systems  51  and  53 . Cam actuation systems  51  and  53  may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by controller  12  to vary valve operation. The position of intake valve  52  and exhaust valve  54  may be determined by position sensors  55  and  57 , respectively. In alternative embodiments, intake valve  52  and/or exhaust valve  54  may be controlled by electric valve actuation. For example, cylinder  30  may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems. 
     Fuel injector  66  is shown coupled directly to combustion chamber  30  for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller  12 . In this manner, fuel injector  66  provides what is known as direct injection of fuel into combustion chamber  30 . The fuel injector may be mounted in the side of the combustion chamber or in the top of the combustion chamber, for example. Fuel may be delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. 
     Ignition system  88  can provide an ignition spark to combustion chamber  30  via spark plug  92  in response to spark advance signal SA from controller  12 , under select operating modes. Though spark ignition components are shown, in some embodiments, combustion chamber  30  or one or more other combustion chambers of engine  10  may be operated in a compression ignition mode, with or without an ignition spark. 
     Intake passage  42  or intake manifold  44  may include a throttle  62  having a throttle plate  64 . In this particular example, the position of throttle plate  64 , or a throttle opening, may be varied by controller  12  via a signal provided to an electric motor or actuator included with throttle  62 , a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle  62  may be operated to vary the intake air provided to combustion chamber  30  among other engine cylinders. The position of throttle plate  64  may be provided to controller  12  by throttle position signal TP. Intake passage  42  may include a mass airflow sensor  120  and a manifold air pressure sensor  122  for providing respective signals MAF and MAP to controller  12 . 
     Further, in the disclosed embodiments, an exhaust gas recirculation (EGR) system may route a desired portion of exhaust gas from exhaust passage  48  to intake manifold  44 . In this example, high pressure (HP) EGR passage  140  is illustrated. The amount of EGR provided to intake manifold  44  may be varied by controller  12  via HP EGR valve  142 . Further, an EGR sensor  144  may be arranged within the HP EGR passage  140  and may provide an indication of one or more of pressure, temperature, and concentration of the exhaust gas. Alternatively, the EGR flow may be controlled through a calculated value based on signals from the MAF sensor (upstream), MAP (intake manifold), MAT (manifold gas temperature) and the crank speed sensor. Further, the EGR flow may be controlled based on an exhaust O 2  sensor and/or an intake oxygen sensor (intake manifold). Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture within the combustion chamber and/or the temperature proximate PF  72 . While  FIG. 1  shows a high pressure EGR system, a low pressure EGR system may additionally, or alternatively, be used. In a low pressure EGR system, EGR may be routed from downstream of a turbine of a turbocharger to upstream of a compressor of the turbocharger. 
     As such, engine  10  may further include a compression device such as a turbocharger or supercharger including at least a compressor  162  arranged along intake manifold  44 . For a turbocharger, compressor  162  may be at least partially driven by a turbine  164  (e.g., via a shaft) arranged along exhaust passage  48 . For a supercharger, compressor  162  may be at least partially driven by the engine  10  and/or an electric machine, and may not include a turbine. Thus, the amount of compression provided to one or more cylinders of the engine via a turbocharger or supercharger may be varied by controller  12 . 
     Exhaust gas sensor  126  is shown coupled to exhaust passage  48  upstream of emission control device (ECD)  70 . Exhaust gas sensor  126  may be any suitable sensor for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. Although oxygen sensor  14  and temperature sensor  16  are shown in addition to exhaust gas sensor  126  in  FIG. 1 , one or more of these sensors may be omitted and/or moved. 
     ECD  70  is shown arranged along exhaust passage  48  downstream of exhaust gas sensor  126 . In this example, ECD  70  includes a three-way catalyst (TWC)  71  and a particulate filter (PF)  72 . In some embodiments, PF  72  may be located downstream of the TWC  71  (as shown in  FIG. 1 ), while in other embodiments, PF  72  may be positioned upstream of the catalyst (not shown in  FIG. 1 ). Further, PF  72  may be arranged between two or more three-way catalysts, or other emission control devices (e.g., selective catalytic reduction system, NOx trap) or combinations thereof. In other embodiments, TWC  71  and PF  72  may be integrated in a unitary housing. Further, while PF  72  is shown in  FIG. 1  as being positioned downstream of the turbine  164  and HP-EGR passage inlet, in some examples PF  72  may be positioned upstream of one or both of the turbine EGR passage inlet. In still further examples, the engine may not include a turbocharger or an EGR system. 
     Controller  12  is shown in  FIG. 1  as a microcomputer, including microprocessor  102 , input/output ports  104 , an electronic storage medium (e.g., computer-readable) for executable programs and calibration values shown as read-only memory  106  in this particular example, random access memory  108 , keep alive memory  110 , and a data bus. Controller  12  may receive various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including measurement of inducted mass airflow (MAF) from mass airflow sensor  120 ; engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a profile ignition pickup signal (PIP) from Hall effect sensor  118  (or other type) coupled to crankshaft  40 ; throttle position (TP), or throttle opening, from a throttle position sensor; and absolute manifold pressure signal, MAP, from sensor  122 . Engine speed signal, RPM, may be generated by controller  12  from signal PIP. Manifold pressure signal MAP from the manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Note that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor can give an indication of engine torque. Further, this sensor, along with the detected engine speed, can provide an estimate of charge (including air) inducted into the cylinder. In one example, sensor  118 , which is also used as an engine speed sensor, may produce a predetermined number of equally spaced pulses every revolution of the crankshaft. 
     Storage medium read-only memory  106  can be programmed with computer readable data representing instructions executable by microprocessor  102  for performing the methods described herein, as well as other variants that are anticipated but not specifically listed. The controller  12  receives signals from the various sensors (e.g., manifold air pressure sensor  122 , valve position sensors  55  and  57 , temperature sensor  16 ) of  FIG. 1  and employs the various actuators (e.g., throttle plate  64 , cam actuation systems  51  and  53 ) of  FIG. 1  to adjust engine operation based on the received signals and instructions stored on a memory of the controller. 
     An engine may shift to deceleration fuel shut-off (DFSO) under a variety of circumstances, such as when the operator reduces vehicle speed, or when the vehicle is coasting. The disclosed method incorporates existing mechanisms that determine the suitability of shifting an engine to DFSO mode. When in DFSO mode, the delivery of fuel to the engine is deactivated, resulting in increased fuel economy, while the engine continues to rotate as it transmits torque to the wheels. The intake and exhaust valves of the cylinders may continue to be actuated with normal timing (e.g. the same timing used prior to entry into DFSO). The disclosed method monitors the temperature of the gasoline particle filter and may adjust the throttle to a minimum position if the temperature of the filter reaches a first threshold. In another example, if the manifold air pressure (MAP) falls below a threshold and the temperature of the filter is above a second threshold, the method may adjust intake and/or exhaust valve timing (e.g., the cam timing mechanism may be adjusted) to increase the overlap of the intake and exhaust valves, thus increasing MAP. 
       FIG. 2  illustrates a method  200  for controlling DFSO operation of an engine, such as engine  10  of  FIG. 1 . Instructions for carrying out method  200  and the rest of the methods included herein may be executed by a controller (e.g., controller  12 ) based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors (e.g., sensor  122 ) described above with reference to  FIG. 1 . The controller may employ engine actuators (e.g., throttle  62 ) of the engine system to adjust engine operation, according to the methods described below. 
     Method  200  includes, at  202 , determining engine operating parameters including engine speed and load, MAP and MAF, engine and/or manifold temperature, driver requested torque, particulate filter temperature and/or load, etc. At  206 , method  200  determines if the conditions are met for the engine to be adjusted into DFSO mode. This estimation may include conditions such as an operator requested deceleration, e.g., speed reduction, or the operator ceasing to depress the accelerator pedal to allow the vehicle to coast at the attained speed. If at  206  method  200  determines that DFSO conditions have not been met, it may proceed to  210 . At  210 , current engine operating parameters are maintained, e.g., fuel injection, throttle position, engine torque transmission to the wheels, and valve timing may be maintained at current settings as determined by the engine controller and/or the request of an operator. Method  200  may return. 
     If at  206 , method  200  determines that DFSO is indicated, a DFSO event may be initiated at  214 . Fuel injectors (such as fuel injector  66 ) may be deactivated at  216  and a throttle (e.g., throttle  62 ) may be adjusted to a preset position at  218 . The preset position may be a suitable position the throttle is positioned to when DFSO is activated, and may include at least partially open in one example. In other examples, the preset position of the throttle may be fully closed. At  220  the engine may continue to transmit torque to the wheels, while at  222  the overlap timing of an intake valve (e.g., intake valve  52 ) and a corresponding exhaust valve (e.g., exhaust valve  54 ) may be maintained at a first amount of overlap, which may be the amount of overlap before the engine entered into DFSO mode. While in DFSO mode an engine may continue to rotate and flow air out of the cylinders (e.g., cylinder  30 ) through an exhaust manifold (such as exhaust manifold  48 ). This air may flow into a particle filter (such as particle filter  72 ). 
     At  224 , method  200  maintains the temperature of the particle filter and the air pressure of an intake manifold (e.g., intake manifold  44 ) at respective designated levels, as will be explained in more detail below with respect to  FIG. 3 . Briefly, the particulate filter may be maintained below a threshold temperature by closing the throttle valve during DFSO, and if the closure of the throttle valve causes MAP to drop below a threshold pressure, the throttle valve may be adjusted and/or valve timing may be adjusted. 
     At  228 , method  200  determines if DFSO exit conditions are met. DFSO exit conditions may include the accelerator pedal being depressed and/or other conditions. If DFSO exit conditions have not been met, method  200  may proceed back to  224 , in which case method  200  may continue to operate in DFSO and maintain particulate filter temperature and MAP at designated levels until DFSO exit conditions have been met, e.g., the operator of the vehicle resumes acceleration. If at  228  method  200  determines that DFSO exit is indicated, method  200  proceeds to  232 . At  232  a DFSO exit event may be initiated, and the pertinent parameters may be returned to normal operating conditions, including activating fuel injection at  234  and adjusting the throttle valve based on requested torque at  236 . In one example, the requested torque may include operator-requested torque. Additionally or alternatively, the requested torque may include vehicle-requested torque, such as an alternator load applied to the engine. At  238  the engine may continue to transmit torque to the wheels, a torque that may be adjusted according to the request of the vehicle operator. At  240 , while the engine is rotating the timing of the intake and exhaust valves may be maintained at or resumed to the first amount of overlap, e.g., the overlap the valves had before they entered into DFSO mode. Method  200  may return. 
       FIG. 3  illustrates a method  300  for maintaining the temperature of a particle filter (such as particle filter  72 ) and the air pressure of an intake manifold (e.g., intake manifold  44 ) while an engine is operating in DFSO mode. Method  300  may be executed as part of method  200 , for example in response to operation in DFSO. At  302 , method  300  determines engine operating parameters, which may include engine speed and load, MAP, particle filter temperature, throttle valve position, etc. At  306  method  300  determines if the particle filter temperature is above a first threshold temperature T 1  based on output from a particulate filter temperature sensor, such as sensor  16  of  FIG. 1 , or based on an estimated particulate filter temperature. The threshold temperature T 1  may be as suitable temperature that indicates particulate filter degradation is likely to occur if relatively high levels of oxygen are provided to the filter. In one example, the threshold T 1  may be the temperature at which soot typically burns, such as 500° C. In some examples, the first threshold temperature T 1  may vary based on the soot load of the particulate filter, e.g., the threshold temperature may increase with decreasing soot load. 
     If it is determined that the temperature is below T 1 , method  300  may proceed to  310 . At  310  a throttle valve (such as throttle  62 ) position and the amount of overlap of an intake valve (such as intake valve  52 ) and a corresponding exhaust valve (e.g., exhaust valve  54 ) may be maintained at their current DFSO levels, e.g., those corresponding to  214  of method  200  of  FIG. 2 . In such a case, the engine may loop back to  228  of  FIG. 2  to continue operating in DFSO mode, as described above for method  200 . 
     If at  306  method  300  determines that the particle filter temperature has exceeded temperature T 1 , it may proceed to  314 . At  314 , method  300  may adjust the throttle to a minimum position, in one example, to a fully closed position. By fully closing the throttle the flow of oxygen to the particle filter may be interrupted, which in turn may result in its temperature decreasing or may prevent the temperature from increasing. 
     At  318 , method  300  determines if the intake manifold pressure is below a threshold pressure, based on output from a MAP sensor, such as sensor  122  of  FIG. 1 . The threshold pressure may be a pressure below which engine degradation may occur due to lubricating fluid being pulled into the combustion chambers, for example. In one example, the threshold MAP may be 30 kPa absolute, although other threshold pressures are possible. If the MAP is not below the threshold pressure, method  300  loops back to  228  of  FIG. 2  to continue to operate in DFSO and monitor for DFSO exit conditions. 
     If the MAP is less than the threshold pressure, method  300  proceeds to  322  to determine if the particulate filter temperature is less than a second threshold temperature, T 2 . The second threshold temperature may be greater than the first threshold temperature, and may represent an upper limit temperature at which degradation of the particulate filter may occur. In one example, the second threshold temperature may be 600° C. If the particulate filter temperature is not below the second threshold temperature, method  300  proceeds to  326  to adjust intake and/or exhaust valve timing to increase the amount of valve overlap. By increasing valve overlap, the MAP may be increased. To increase valve overlap, the timing of the closing the exhaust valves may be adjusted, the timing of the opening of the intake valves may be adjusted, or both the timing of the exhaust valves and the timing of the intake valves may be adjusted. The valve timing may be adjusted by adjusting a variable camshaft timing system, variable valve lift system, or other suitable mechanism. Method  300  then proceeds back to  318  to continue to assess the MAP and particulate filter temperature. 
     If it is determined at  322  that the particulate filter temperature is below the second threshold temperature, method  300  proceeds to  330  to open the throttle valve by a preset amount. In one example, the preset amount may be one degree, although other amounts are possible. By opening the throttle by a relatively small amount, the MAP may be increased without directing too much oxygen to the particulate filter. Method  300  then loops back to  318  to continue to monitor MAP and particulate filter temperature. 
     Thus, method  300  monitors particulate filter temperature during DFSO or other non-combustion operation. If the DFSO temperature is relatively high, the throttle valve is closed to prevent the flow of oxygen to the particulate filter, and thus prevent the combustion of the soot in the particulate filter. However, closing of the throttle valve during DFSO may cause intake manifold pressure to drop below a threshold pressure, which may result in engine degradation. To prevent intake manifold pressure from becoming too low, the temperature of the particulate filter may be assessed. If the particulate filter temperature is below an upper limit temperature at which degradation to the filter may occur, the throttle valve may be opened slightly (e.g., by one degree) to increase MAP without directing excess oxygen to the particulate filter. However, if the particulate filter is at or above the upper limit temperature, even a small amount of oxygen may cause filter degradation. Thus, to increase MAP, the intake and/or exhaust valves may adjusted to increase valve overlap, while the throttle valve remains fully closed. Once conditions for exiting out of DFSO are met, the throttle valve may be returned to a position based on operator-requested torque and valve timing may revert back to pre-DFSO valve timing. 
     Turning now to  FIG. 4 , a diagram  400  illustrating operating plots of interest during execution of the methods  200  and/or  300  described above is illustrated. Diagram  400  illustrates fuel injection status (as shown by curve  404 ), throttle position (as shown by curve  410 ), particulate filter temperature (as shown by curve  416 ), intake and exhaust valve overlap (as shown by curve  422 ), intake manifold pressure (as shown by curve  428 ), accelerator pedal position (as shown by curve  434 ), and vehicle speed (as shown by curve  440 ). For each operating plot, time is depicted along the horizontal axis and respective values for each parameter are depicted along the vertical axis. 
     Prior to time t 1 , the vehicle is operating under standard, non-DFSO conditions. As such, fuel injection is on, the throttle is controlled based on operator-requested torque and is kept partially open, the particulate filter temperature is relatively low (below the first threshold temperature T 1 ), valve overlap is at an amount based on operating parameters (as shown, valve overlap is relatively low), MAP is above the threshold pressure P 1 , the accelerator pedal is partially depressed, and the vehicle speed is maintained at a desired speed. At time t 1 , the operator releases the accelerator pedal, as shown by curve  434 , due to traversal of a declined road surface, for example, and vehicle speed starts to moderately decelerate. Due to the deceleration, combustion is not indicated to maintain desired vehicle speed, and thus fuel injection is shut off, as shown by curve  404 . 
     Once the fuel injection is disabled, the throttle may initially assume a predetermined position, such as partially open. However, due to the particulate filter reaching the first threshold temperature at time t 1 , the throttle is subsequently fully closed to prevent particulate filter degradation. Because MAP is maintained above the threshold pressure P 1 , the throttle is kept fully closed and valve overlap is not adjusted for the duration of the DFSO event. 
     At time t 2 , the operator depresses the accelerator pedal, and thus the vehicle exits out of DFSO by resuming fuel injection. The throttle is controlled based on operator requested torque and as such moves out of the fully closed position. Due to the lack of hot exhaust and oxygen being supplied to the particulate filter during DFSO, the particulate filter temperature has dropped below the first threshold temperature, although it beings to rise again following time t 2 . 
     At time t 3 , another DFSO event is initiated, where fuel injection is disabled due to vehicle deceleration/release of the accelerator pedal. The throttle is moved to the fully closed position due to the particulate filter temperature being at the first threshold temperature. However, unlike the first DFSO event, at time t 4  the MAP drops to below the threshold pressure. To increase MAP, because the particulate filter temperature is below the second threshold temperature, the throttle is opened by a small amount. However, the opening of the throttle results in the particulate filter temperature increasing to the second threshold temperature at time t 5 . Further, while the opening of the throttle valve at time t 4  caused an increase in MAP initially, the MAP again drops to below the threshold pressure at time t 5 . Thus, to increase MAP, the valve timing is adjusted to increase the amount of valve overlap at time t 5 . 
     At time t 6 , the operator again depresses the accelerator pedal, and as a result the vehicle exits out of DFSO by activating fuel injection, opening the throttle and controlling throttle position based on requested torque, and reducing the amount of valve overlap back to the pre-DFSO amount of overlap. 
     In this way, by hard closing of the throttle in DFSO, a much slower rise in particulate filter temperature occurs, allowing for longer DFSO events, thus increasing fuel economy. MAP may be controlled based on particulate filter temperature, such that MAP is increased by slightly opening the throttle if particulate temperature is not too high or MAP is increased by increasing valve overlap if particulate temperature is too high. While closing the throttle during DFSO may prevent particulate filter overtemperature events, in some conditions the particulate filter may still reach the threshold temperature. In such circumstances, the vehicle may exit out of DFSO to prevent filter degradation. 
     Closing the throttle during DFSO may also improve consistency for fuel-off exhaust flow. The throttle flow may not be impacted by other strategy features that might be enacted to increase the airflow in anticipation of the fuel being restored, such as A/C and alternator loads. For example, when it is predicted that the vehicle will exit out of DFSO, auxiliary loads may be applied to the engine to increase engine power. If the throttle is closed when the loads are applied, the throttle may be opened to allow airflow increase in order to generate the additional engine power. 
     The technical effect of closing the throttle during DFSO and controlling MAP based on particulate filter temperature is to prevent particulate filter degradation during DFSO while extending the duration of DFSO, thus improving fuel economy while maintaining MAP above a threshold pressure. 
     As one embodiment, a method for an engine includes, responsive to a particulate filter temperature above a threshold temperature and while operating the engine with deceleration fuel shut-off (DFSO), fully closing a throttle valve configured to regulate flow of intake air to the engine; and responsive to intake manifold pressure dropping below a threshold pressure while the throttle valve is fully closed, adjusting a position of the throttle valve based on the particulate filter temperature. In a first example of the method, adjusting the position of the throttle valve based on the particulate filter temperature comprises, when the particulate filter temperature is above the threshold temperature and below a second, higher threshold temperature, opening the throttle valve by a predetermined amount to increase intake manifold pressure. A second example of the method optionally includes the first example and further includes wherein adjusting the position of the throttle valve based on the particulate filter temperature comprises, when the particulate filter temperature is above the second threshold temperature, maintaining the throttle valve fully closed and adjusting intake and exhaust valve timing to increase intake manifold pressure. A third example of the method optionally includes one or both of the first and second examples and further includes wherein adjusting intake and exhaust valve timing comprises increasing intake and exhaust valve overlap. A fourth example of the method optionally includes one or more or each of the first through third examples and further includes wherein operating the engine with DFSO comprises transmitting engine output to vehicle wheels via a transmission, and deactivating fuel injection to the engine during a deceleration condition of a vehicle in which the engine is installed. A fifth example of the method optionally includes one or more or each of the first through fourth examples and further includes responsive to the particulate filter temperature being below the threshold temperature while the engine is operating in DFSO, maintaining the throttle valve at a fully open or partially open position. A sixth example of the method optionally includes one or more or each of the first through fifth examples and further includes responsive to a request to exit out of operation with DFSO, activating fuel injection to the engine and adjusting a position of the throttle valve based on requested torque. A seventh example of the method optionally includes one or more or each of the first through sixth examples and further includes wherein adjusting a position of the throttle valve based on requested torque comprises adjusting a position of the throttle valve based on operator-requested torque. An eighth example of the method optionally includes one or more or each of the first through seventh examples and further includes wherein adjusting a position of the throttle valve based on requested torque comprises adjusting a position of the throttle valve based on vehicle-requested torque including one or more auxiliary loads placed on the engine. A ninth example of the method optionally includes one or more or each of the first through eighth examples and further includes, prior to exiting out of operation with DFSO, increasing one or more auxiliary loads placed on the engine and opening the throttle valve responsive to a predicted subsequent exit out of operation with DFSO. 
     An embodiment of a system includes an engine including a plurality of cylinders, each cylinder including at least one intake valve and at least one exhaust valve; a throttle valve controlling flow of intake air to the engine; a particulate filter coupled to the engine via an exhaust passage; and a controller having computer readable instructions stored on non-transitory memory for: initiating a deceleration fuel shut-off (DFSO) event during a vehicle deceleration event by deactivating a fuel supply to the plurality of cylinders of the engine; closing the throttle valve responsive to initiating the DFSO event; and when an intake manifold pressure of the engine drops below a threshold pressure, adjusting intake and/or exhaust valve timing based on a temperature of the particulate filter. In a first example of the system, adjusting intake and/or exhaust valve timing based on a temperature of the particulate filter comprises adjusting intake and/or exhaust valve timing to increase valve overlap when the temperature of the particulate filter is above a threshold temperature. A second example of the system optionally includes the first example and further includes wherein the valve overlap is increased relative to an amount of valve overlap prior to initiating of the DFSO event. A third example of the system optionally includes one or more or each of the first and second examples and further includes wherein the controller has further instructions for opening the throttle valve by a predetermined amount when the intake manifold pressure is below the threshold pressure and the temperature of the particulate filter is below the threshold temperature. A fourth example of the system optionally includes one or more or each of the first through third examples and further includes wherein the controller has further instructions for, responsive to a request to exit of DFSO, opening the throttle valve and reactivating the fuel supply. A fifth example of the system optionally includes one or more or each of the first through third examples and further includes wherein the fuel supply to the plurality of cylinders of the engine comprises a direct-injection gasoline fuel supply. 
     An embodiment of a method for an engine includes initiating a deceleration fuel shut-off (DFSO) event by deactivating fuel injection to the engine and moving a throttle valve coupled upstream of the engine to a preset, at least partially open position; responsive to a particulate filter temperature above a threshold temperature, fully closing the throttle valve; and maintaining intake manifold pressure above a threshold pressure by adjusting intake and/or exhaust valve timing. In a first example of the method, the method further comprises prior to initiating the DFSO event, operating with a first amount of intake and exhaust valve overlap, and wherein adjusting intake and/or exhaust valve timing comprises adjusting intake and/or exhaust valve timing to operate with a second amount of intake and exhaust valve overlap. A second example of the method optionally includes the first example and further includes wherein fully closing the throttle valve comprises fully closing the throttle valve while maintaining operation with the first amount of intake and exhaust valve overlap. A third example of the method optionally includes one or more or each of the first and second examples and further includes responsive to a request to exit out of the DFSO event, activating fuel injection, adjusting the throttle valve based on operator requested torque, and adjusting intake and/or exhaust valve timing to operate with the first amount of intake and exhaust valve overlap. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.