METHOD AND SYSTEM FOR CENTRAL FUEL INJECTION

Abstract

Procedure, comprehensive: Estimating the oxygen content of an exhaust catalyst immediately after a fuel shut-off event and Adjusting a first proportion of fuel supplied to an engine via manifold injection relative to a second proportion of fuel supplied to the engine via one or more of port and direct injection, based on the estimated oxygen content of the exhaust catalyst.

Description

Area

[0001] The present description generally concerns methods and systems for adjusting manifold fuel injection to reduce NOx emissions. General state of the art / Summary

[0002] Internal combustion engines can incorporate central fuel injection (CFI) systems, which inject fuel into an intake manifold. When fuel is injected into the engine intake, heat is transferred from the intake air and / or engine components to the fuel, and this heat transfer causes some of the fuel to atomize, resulting in cooling of the engine components. Injecting fuel into the intake air (e.g., into the intake manifold, intake ports, etc.) lowers both the intake air temperature and the combustion temperature in the engine cylinders. By cooling the intake air charge, NOx production can be reduced. NOx is stored in an exhaust catalyst, which is regenerated periodically or opportunistically during operation with a richer than stoichiometric air-fuel ratio.In addition to CFI, fuel can be injected into intake manifolds via port fuel injection systems and / or directly into cylinders via direct injection systems.

[0003] Several approaches are provided to reduce NOx production during engine operation. One exemplary approach is presented by Mulye in US 8,935,996 B2, where liquid water is injected into engine cylinders during the compression and power strokes to reduce the combustion temperature. A reduced combustion temperature leads to a reduction in NOx emissions. The water is supplied to the cylinders via dedicated water injection devices connected to an onboard water source.

[0004] The inventors of the present invention have, however, recognized potential problems with such systems. For example, an increase in the amount of evaporated water in the combustion chambers due to water injection can lead to combustion instability. There may also be conditions in which water is not always available for injection on board a vehicle, such as due to environmental or engine operating conditions that are not conducive to water generation on board the vehicle, or due to water consumption during a previous drive cycle that exceeded water generation. This water shortage can lead to increased NOx levels in the exhaust gas during engine operation.As another example, during cold-start conditions, before an exhaust catalyst reaches its operating temperature, exhaust NOx may not be effectively captured, and consequently, NOx emission levels may rise. Only after the exhaust catalyst reaches its operating temperature is it able to adsorb oxidizing agents such as NOx and oxygen passing through it. As yet another example, during conditions such as deceleration fuel shut-off (DFSO), when the cylinder fuel supply is shut off while air flows through the engine, the exhaust catalyst can become saturated with oxygen. Therefore, when the cylinder fuel supply is resumed, further NOx adsorption may be limited until the engine is run with a richer than stoichiometric air-fuel ratio to purge the catalyst.As a result, emission quality can be negatively affected. Furthermore, the need for additional fuel to flush the catalytic converter negatively impacts fuel efficiency.

[0005] US 7 426 918 B2 and DE 693 14 611 T2 describe methods and systems for central fuel injection.

[0006] The object of the present invention is to address at least some of the problems described above and to advantageously advance the prior art. This object is achieved by the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0007] Accordingly, one method comprises: adjusting a first proportion of fuel supplied to an engine via manifold injection relative to a second proportion of fuel supplied to the engine via one or more port and direct injection systems, based on an estimated oxygen content from an exhaust catalyst, the estimated oxygen content being determined immediately after a fuel cut-off event. In this way, by injecting a proportion of the total fuel mass for injection via the central fuel injection system, combustion temperatures can be reduced, thereby reducing NOx generation.

[0008] During cold starts, an engine control unit can determine an initial fuel injection profile based on engine operating conditions such as engine speed and load. This initial profile may include a fuel quantity to be supplied via manifold fuel injection (e.g., a central manifold fuel injection device, or CFI) and a remaining fuel quantity to be supplied via one or more port and direct fuel injection points. When the fuel injected via CFI atomizes in the intake manifold, it can cool the manifold, creating a local charge cooling effect. During periods when engine intake temperatures exceed a threshold, the proportion of fuel supplied via CFI can be increased until the intake temperature falls below the threshold.Upon exiting a DFSO event, a richer than stoichiometric air-fuel ratio can be maintained to desorb the NOx trapped in the exhaust catalyst and then convert the NOx to water and nitrogen under the richer conditions. A portion of the fuel supplied during this richer-than-stoichiometric engine operation can be provided via CFI. Additionally, if the catalyst is saturated with fuel during the DFSO event, the amount of fuel supplied via CFI can be increased until the oxygen content in the catalyst falls below the threshold level.

[0009] In this way, during conditions conducive to higher NOx production, opportunistic fuel injection via CFI can increase charge cooling and thus reduce NOx generation. Using manifold-injected fuel for charge cooling reduces reliance on the variable availability of onboard water. Increasing manifold charge cooling during a cold start can reduce NOx generation during conditions where the catalytic converter is inactive and unable to optimally capture NOx. The technical benefit of injecting fuel via CFI while operating at a richer-than-stoichiometric air-fuel ratio upon exiting a DFSO condition is that further NOx generation can be reduced.Emission quality can be improved by increasing charge cooling and reducing NOx production during conditions where the catalyst is saturated with oxygen.

[0010] It is understood that the foregoing summary is provided to introduce, in simplified form, a selection of concepts that are further described in the detailed description. It is not intended to identify important or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that address the disadvantages mentioned above or in any part of this disclosure. Brief description of the drawings Fig. Figure 1 shows an exemplary embodiment of an engine system designed with manifold, direct and port fuel injection capabilities. Fig. Figure 2 shows a flowchart illustrating an exemplary procedure for setting a fuel injection schedule during a cold engine start. Fig. Figure 3 shows a flowchart illustrating an exemplary procedure for setting a fuel injection schedule during exit from a fuel cut-off event. Fig. Figure 4 shows exemplary settings for a fuel injection plan, including a manifold fuel injection quantity based on a desired charge cooling effect. Fig. Figure 5 shows a flowchart illustrating an exemplary procedure for setting a fuel injection schedule when cylinder pre-ignition is specified. Fig. Figure 6 shows a first example of fuel split ratios selected based on engine operating conditions. Fig. Figure 7 shows a second example of fuel split ratios selected based on engine operating conditions. Fig. Figure 8 shows exemplary fuel settings that mitigate pre-ignition. Detailed description

[0011] The following description relates to systems and methods for utilizing manifold fuel injection for increased charge air cooling, reduced NOx emissions, and mitigation of ignition advance. The methods of the present invention can be applied to an engine system that has manifold, direct, and port fuel injection capabilities, such as the engine system from Fig. 1. An engine control unit can be configured to perform a control routine, such as the example routines from Fig. 2, Fig. 3 and Fig. 5, to set a fuel injection schedule, including adjusting the amount of fuel supplied via manifold injection relative to the amount of fuel supplied via port injection and / or direct injection to reduce NOx generation and mitigate pre-ignition.

[0012] Exemplary fuel supply plan settings to achieve the desired charge cooling for NOx reduction and mitigation of pre-ignition are described in Fig. 4 and Fig. Figure 8 shows examples of fuel split ratios between manifold injection and port injection (and / or direct injection). Fig. 6 and Fig. 7 shown.

[0013] Fig. Figure 1 shows an exemplary embodiment of an engine system 100 in a motor vehicle 102, which is illustrated schematically. In the illustrated embodiment, the engine 10 is a turbocharged engine coupled to a turbocharger 13, including a compressor 14, which is driven by a turbine 16. Specifically, fresh air is introduced into the engine 10 along the intake duct 142 via an air cleaner 11 and flows to the compressor 14. The compressor can be a suitable intake air compressor, such as a compressor driven by an engine or a drive shaft. In the engine system 100, the compressor is shown as a turbocharger compressor, which is mechanically coupled to the turbine 16 via a shaft 19, with the turbine 16 being driven by expanding engine exhaust gases. In one embodiment, the compressor and the turbine can be coupled within a twin-scroll turbocharger.In another embodiment, the turbocharger can be a variable geometry turbocharger (VGT), in which the turbine geometry is actively varied depending on the engine speed and other operating conditions.

[0014] As in Fig. As shown in Figure 1, the compressor 14 is coupled via the charge air cooler (CAC) 18 to a throttle valve (e.g., an intake throttle) 20. The CAC can be, for example, an air-to-air or air-to-coolant heat exchanger. The throttle valve 20 is coupled to an engine intake manifold 22. From the compressor 14, the warm, compressed air charge enters the inlet of the CAC 18, cools as it flows through the CAC, and then exits to reach the intake manifold 22 via the throttle valve 20. In the Fig. In the embodiment shown in Figure 1, the pressure of the air charge within the intake manifold is detected by a manifold air pressure sensor (MAP sensor) 24, and the boost pressure is detected by a boost pressure sensor 124. A compressor bypass valve (not shown) can be coupled in series between the inlet and outlet of the compressor 14. The compressor bypass valve can be a normally closed valve designed to open under selected operating conditions to release excess boost pressure. For example, the compressor bypass valve can open under conditions of decreasing engine speed to prevent compressor surging.

[0015] The intake manifold 22 is coupled to a series of combustion chambers or cylinders 180 by a series of intake valves (not shown) and intake pipes (e.g., intake ports) 185. As shown in Fig. As shown in Figure 1, the intake manifold 22 is arranged upstream of all combustion chambers 180 of the engine 10. Sensors, such as a manifold charge temperature sensor (MCT sensor) 23 and an air charge temperature sensor (ACT sensor) 125, can be included to determine the intake air temperature at their respective locations in the intake duct. In some examples, the MCT and ACT sensors can be thermistors, and the thermistor output can be used to determine the intake air temperature in the duct 142. The MCT sensor 23 can be positioned between the throttle 20 and the intake valves of the combustion chambers 180. The ACT sensor 125 can be arranged upstream of the CAC 18 as shown; however, in alternative embodiments, the ACT sensor 125 can be positioned upstream of the compressor 14. Each combustion chamber can also include a knock sensor 183.The combustion chambers are further coupled to the exhaust manifold 136 via a series of exhaust valves (not shown).

[0016] The engine system 100 is coupled to a fuel system 60. The fuel system 60 includes a fuel tank 63, which is coupled to a fuel pump 62, the fuel tank supplying fuel to an engine 10 that powers a vehicle. During a refueling event, fuel can be pumped into the vehicle from an external source through a refueling inlet 65. The fuel tank 63 can hold a variety of fuel mixtures, including fuels with a range of alcohol concentrations, such as various gasoline-ethanol blends, including E10, E85, gasoline, etc., and combinations thereof. A fuel level sensor 67, located in the fuel tank 63, can provide the controller 12 with an indication of the fuel level (“fuel level input”). As shown, the level sensor 67 can include a float connected to a control resistor.Alternatively, other types of level sensors can be used. The fuel pump 221 is designed to pressurize fuel supplied to a variety of injection devices of the engine 10, such as the exemplary injection devices 46-48.

[0017] The combustion chambers 180 are covered by a cylinder head 182 and coupled to a first direct fuel injector (DI) 47, which injects fuel directly into one or more combustion chambers 180. A second port fuel injector (PFI) 48 is arranged in the intake manifolds to inject fuel directly onto the intake valve. In one example, the injector 48 can be angled toward and facing the intake valve of the cylinder to which the intake manifold is attached, causing fuel to be injected in the same direction as the intake airflow into the cylinder. In another embodiment, the injector 48 can be angled away from the intake valve and arranged to inject fuel against the direction of intake airflow through the intake manifold. Although in Fig. While only one representative injection device 47 and injection device 48 are shown, each combustion chamber 180 and each intake manifold 185 can include its own injection device. A third central fuel injector (CFI) 46, also referred to in this document as the manifold fuel injector, can be coupled downstream of the throttle 20 to the engine intake manifold 22 to inject fuel directly into the intake manifold. For example, the manifold fuel injector 46 can inject fuel onto a surface of the intake manifold.

[0018] In embodiments incorporating multiple injection devices, the fuel supply channel 61 may contain one or more valves to select between different fuel injection devices. As shown in Fig. As shown in Figure 1, fuel stored in the fuel tank 63 is supplied to the fuel injection devices 46-48, for example, via a common fuel supply channel 61, which branches into the fuel channels 92, 94, and 96. In the illustrated embodiment, fuel from the fuel channel 61 can be diverted by one or more of the valve 93 and the channel 92 to supply fuel to the CFI 46, by the valve 95 and the channel 94 to supply fuel to the PFI 48, and / or by the valve 97 and the channel 96 to supply fuel to the DI 47.

[0019] When fuel is injected into the engine intake, heat is transferred from the intake air and / or engine components to the fuel, and this heat transfer causes a portion of the fuel to atomize, thus cooling the engine components. The same effect occurs when fuel is injected directly into a cylinder, drawing heat from the cylinder charge, cylinder walls, and cylinder surface. Based on engine operating conditions, engine dilution requirements, and engine cooling requirements, fuel can be injected through one or more of the DI, PFI, and CFI injectors. Based on the fuel distribution between the injectors (the amount of fuel supplied by each injector), valves 93, 95, and 97 can be adjusted to direct fuel through one or more fuel lines 92, 94, and 96.

[0020] In one example, in response to increased intake manifold cooling requirements, a higher proportion of the total fuel injection can be supplied via CFI 46, with the remaining portion supplied via one or more of PFI 48 and DI 47. The increased fuel volume can be injected via CFI 46 by increasing the opening of valve 93, while correspondingly decreasing the openings of valve 95 (to provide a smaller volume of fuel injected via PFI) and / or valve 97 (to provide a smaller volume of fuel injected via DI). The increased volume of fuel injected via CFI can enhance charge cooling in the intake manifold.In one example, a manifold charge temperature measured by the MCT sensor 23 before fuel injection via the CFI 46 can be compared with a manifold charge temperature measured by the MCT sensor 23 after fuel injection via the CFI 46. The actual charge cooling effect can then be determined based on the difference between the measured manifold charge temperatures. During engine operation at higher temperatures, NOx production can increase due to the combustion of hydrocarbons at the elevated engine temperature. By increasing the fuel supply via the CFI during such conditions, the resulting charge cooling effect can be utilized to reduce NOx production.In this way, in response to an engine intake manifold temperature that is higher than a threshold, the engine intake manifold temperature can be reduced below the threshold engine intake manifold temperature by increasing a first proportion of fuel supplied to the engine via manifold injection, while correspondingly reducing a second proportion of fuel supplied via one or more of port and direct injection.

[0021] The combustion chamber 180 can also draw in water and / or steam, which can be injected into the engine intake or the combustion chambers 180 themselves by one or more water injection devices. In the illustrated embodiment, a water injection system is designed to inject water upstream of the throttle 20 via the water injection device 45. In an alternative embodiment, water injection devices can be located downstream of the throttle, in intake pipes (e.g., intake ports), and directly in one or more combustion chambers. For example, each combustion chamber 180 and each intake pipe 185 can contain its own injection device. Water can be supplied to each of the injection devices from a water tank 82 via a water line 90. The water tank 82 can be refilled manually via a water filling channel and / or automatically by an onboard collection system.The onboard collection system can be coupled to one or more vehicle components, allowing the onboard water tank 82 to be refilled with condensate collected from various engine or vehicle systems. For example, the collection system can be coupled to an EGR system to collect water condensed from exhaust gas flowing through the EGR system. In another example, the collection system can be coupled to an air conditioning system for water collected from refrigerant condensing through a condenser.

[0022] In the illustrated embodiment, a single exhaust manifold 136 is shown. In other embodiments, however, the exhaust manifold can include a plurality of exhaust manifold sections. Designs featuring a plurality of exhaust manifold sections can allow wastewater from different combustion chambers to be routed to different locations in the engine system. A wideband lambda sensor (Universal Exhaust Gas Oxygen sensor - UEGO sensor) 126 is shown coupled to the exhaust manifold 136 upstream of the turbine 16. Alternatively, the UEGO sensor 126 can be replaced by a binary lambda sensor.

[0023] As in Fig. As shown in Figure 1, exhaust gas from one or more exhaust manifold sections is directed to the turbine 16 to drive the turbine. If reduced turbine torque is desired, some exhaust gas can instead be directed through a wastegate (not shown), thus bypassing the turbine. The combined flow from the turbine and the wastegate then flows through one or more exhaust catalysts 70. The one or more exhaust catalysts 70 can include one or more exhaust aftertreatment catalysts configured to catalytically treat the exhaust flow and reduce the amount of one or more substances in the exhaust flow, such as a NOx trap, oxidation catalysts, reduction catalysts, etc.During lean (relative to stoichiometry) engine operating conditions, NOx can be stored in the exhaust catalyst 70, and during rich (relative to stoichiometry) engine operating conditions, the stored NOx can be desorbed and then converted into water and nitrogen, which can be released into the atmosphere. In this way, NOx emissions can be reduced during engine operation.

[0024] During fuel cut-off events, such as during a deceleration fuel cut-off condition, the cylinder fuel supply can be selectively shut off while cylinder valves continue to operate and air continues to be pumped through the cylinder. Due to fresh air flowing through the cylinder and onward to the exhaust catalyst 70, the exhaust catalyst 70 can become saturated with oxygen, thereby reducing its ability to further adsorb and treat NOx.To reactivate the catalyst upon resumption of fuel supply at one end of the fuel cut-off event in response to an oxygen content in the exhaust catalyst exceeding a threshold, an initial fuel quantity can be injected via the CFI 46, and the remaining fuel quantity can be injected via one or more port and direct injection devices until the oxygen content in the exhaust catalyst falls below the threshold, with the initial fuel quantity being higher than the subsequent fuel quantity. Injecting a larger proportion of the total fuel mass via the CFI 46 can increase charge cooling, further reducing NOx generation until the catalyst's oxygen content decreases and the catalyst regains its ability to treat NOx.The increased initial fuel quantity supplied to the engine via manifold injection can also be based on the estimated oxygen content of the exhaust catalyst, with the initial quantity being increased when the estimated oxygen content of the exhaust catalyst exceeds the threshold oxygen content. Thus, the increased initial fuel quantity can be supplied until the estimated oxygen content of the exhaust catalyst falls below the threshold oxygen content, at which point the initial fuel quantity supplied to the engine via manifold injection can be reduced, while the second fuel quantity supplied via one or more port and direct injection systems can be increased accordingly.

[0025] The treated exhaust gas from the exhaust catalyst 70 can be discharged wholly or partially into the atmosphere via an exhaust gas channel 35. Depending on the operating conditions, however, some exhaust gas can instead be diverted to an exhaust gas recirculation (EGR) channel 151, through an EGR cooler 50 and an EGR valve 152 to the compressor inlet 14. In this way, the compressor is configured to draw in exhaust gas extracted downstream of the turbine 16. The EGR valve 152 can be opened to allow a controlled amount of cooled exhaust gas to flow to the compressor inlet for desired combustion and emission control performance. In this way, the engine system 100 is configured to provide external low-pressure (LP) EGR. The rotation of the compressor, in addition to the relatively long ND-EGR flow path in the engine system 100, provides excellent homogenization of the exhaust gas into the intake air charge.Furthermore, the arrangement of the EGR take-off and mixing points provides effective cooling of the exhaust gas for increased available EGR mass and improved performance. In other embodiments, the EGR system can be a high-pressure EGR system with an EGR channel 151 that provides a connection from upstream of the turbine 16 to downstream of the compressor 14. In some embodiments, the MCT sensor 23 can be positioned to determine the manifold charge temperature and include recirculated air and exhaust gas through the EGR channel 151.

[0026] The engine 100 can include one or more knock sensors 183, distributed along an engine block or coupled to individual cylinders (as shown). If included, the plurality of knock sensors can be distributed symmetrically or asymmetrically along the engine block. The knock sensor 183 can be an accelerometer, an ionization sensor, or a cylinder pressure sensor. An engine control unit can be configured to detect abnormal combustion events due to cylinder knock and to distinguish them from those indicating cylinder pre-ignition, based on the output (e.g., signal timing, amplitude, intensity, frequency, etc.) of the knock sensor 183 and further based on the output of a crankshaft accelerometer.For example, a cylinder pre-ignition event can be determined based on a cylinder knock signal estimated in a first, earlier window (such as a first window before an ignition event in the cylinder) being greater than a first, higher threshold, while a cylinder knock event can be determined based on a cylinder knock signal estimated in a second, later window (such as a second window after an ignition event in the cylinder) being greater than a second, lower threshold. In one example, the windows in which the knock signals are estimated could be crank angle windows.

[0027] Furthermore, mitigating actions taken by the engine control unit to address knocking can differ from those taken by the control unit to address ignition advance. For example, knocking can be addressed by applying spark ignition timing adjustments (e.g., retarded ignition) and EGR, while ignition advance can be addressed by applying load limiting, fuel delivery plan adjustment, fuel enrichment, or a combination thereof.

[0028] The inventors of the present invention have recognized that by utilizing the charge cooling of fuel injected via CFI, pre-ignition can be mitigated without fuel enrichment. For example, in response to a report of pre-ignition in a cylinder, the ratio of fuel supplied to the cylinder affected by the pre-ignition via the central fuel injection system, relative to direct injection, can be selectively increased for a first period while the cylinder is operating at a stoichiometric air-fuel ratio. By increasing the ratio of fuel supplied via the central fuel injection system, manifold charge cooling can be enhanced to mitigate the occurrence of pre-ignition without the need for fuel enrichment.The initial portion of fuel supplied via manifold injection can be increased by increasing the pulse width of a central fuel injector coupled to an engine intake manifold, while simultaneously reducing the pulse width of one or more direct and port fuel injectors to supply the remaining (second) portion of the total fuel mass. Thus, increasing the initial portion of fuel supplied by the central fuel injector can be limited by the operating limit of the central fuel injector. For example, the initial portion can be increased by increasing the pulse width of the central fuel injector until its operating limit is reached.Further charge cooling can then be provided by maintaining the pulse width of the central fuel injection system at the operating limit, while increasing the pulse width of the direct injection system relative to the port injection system. The supply of the increased initial fuel fraction via manifold injection, relative to the subsequent fuel fraction via one or more port and direct injection systems, can be carried out for an initial duration, such as an initial number of engine cycles, immediately after the occurrence of pre-ignition, without any intervening engine cycles. By increasing charge cooling immediately after the occurrence of pre-ignition, the possibility of further occurrence of pre-ignition in the pre-ignited cylinder and in any of the other engine cylinders can be reduced.If, after the completion of the first number of engine cycles, a subsequent pre-ignition event is detected in the previously pre-igniting cylinder or in any of the engine cylinders, then the first proportion of fuel supplied to the engine via manifold injection can be further increased, if possible, relative to the second proportion of fuel supplied to the engine via one or more port and direct injection systems, in order to further enhance the charge cooling effect. Furthermore, in response to a persistent indication of pre-ignition (e.g., persistent pre-ignition), the engine can switch from stoichiometric operation to operation at a richer than stoichiometric exhaust-air-fuel ratio for a second number of engine cycles following the subsequent detection of pre-ignition.By increasing the total mass of fuel supplied during richer-than-stoichiometric engine operation, a greater amount of heat can be dissipated from the engine components during fuel vaporization, thus anticipating further ignition advance. Exemplary fuel supply settings that can be used to mitigate cylinder advance are described with reference to [reference to be inserted here]. Fig. 5 discussed.

[0029] Fig. Figure 1 further shows a control system 28. The control system 28 can be communicatively coupled with various components of the motor system 100 in order to execute the control routines and processes described here. As in Fig. As shown in Figure 1, the control system 28 can, for example, include an electronic digital controller 12. The controller 12 can be a microcomputer, including a microprocessor unit, input / output ports, an electronic storage medium for executable programs and calibration values, direct access memory, keep-alive memory, and a data bus. As shown in the figure, the controller 12 can receive inputs from a variety of sensors 30, which may include user inputs and / or sensors (such as gear position, accelerator pedal input (e.g., pedal position), brake input, gear selector position, vehicle speed, engine speed, mass airflow through the engine, boost pressure, ambient temperature, ambient humidity, intake air temperature, fan speed, etc.), cooling system sensors (such as ECT sensor, fan speed, passenger compartment temperature, ambient humidity, etc.).), intake manifold sensors such as MCT sensor 23, MAP sensor 24, CAC sensors 18 such as CAC intake air temperature, ACT sensor 125 and pressure, CAC exhaust air temperature and pressure, etc., knock sensors 183 for determining ignition timing and knocking and / or water distribution to cylinders, and others. Furthermore, the control unit 12 can communicate with various actuators 32, which may include engine actuators such as the fuel injectors 46-48, an electronically controlled intake air throttle 20, spark plugs 184, the water injector 45, etc. In some examples, the storage medium may be programmed with computer-readable data representing instructions that can be executed by the processor to perform the procedures described below, as well as other variations that are provided for but not specifically listed.

[0030] The controller 12 receives signals from the various sensors. Fig. 1 and suspends the various actuators Fig. 1. The controller is used to adjust engine operation based on received signals and instructions stored in a memory of the controller. In one example, during exit from a DFSO event, the controller can send a pulse width signal to the manifold fuel injector 46 based on an oxygen level in the exhaust catalyst 70 to inject a quantity of fuel into the intake manifold to reduce the manifold temperature and thereby control NOx generation. In another example, the controller can estimate the intake manifold temperature based on inputs from the MCT sensor 23 and, in response to a manifold cooling requirement that exceeds a threshold, send a pulse width signal to the manifold fuel injector 46 to inject a quantity of fuel into the intake manifold to provide a charge cooling effect.

[0031] In some examples, the vehicle 102 may be a hybrid vehicle with multiple torque sources available to one or more vehicle wheels 55. In other examples, the vehicle 102 is a conventional vehicle with only one engine or an electric vehicle with only one electric machine. In the example shown, the vehicle 102 includes the engine 10 and an electric machine 52. The electric machine 52 may be an electric motor or an electric motor / generator. The engine 10 and the electric machine 52 are connected to the vehicle wheels 55 via a transmission 54 when one or more clutches 53 are engaged. In the illustrated example, a first clutch 53 is provided between the engine 10 and the electric machine 52, and a second clutch 53 is provided between the electric machine 52 and the transmission 54.A control unit 12 can send a signal to an actuator of the respective clutch 53 to engage or disengage the clutch, thereby connecting or disconnecting the motor 10 from the electric machine 52 and its associated components, and / or connecting or disconnecting the electric machine 52 from the transmission 54 and its associated components. The transmission 54 can be a manual transmission, a planetary gear system, or another type of transmission. The powertrain can be configured in various ways, including as a parallel, series, or series-parallel hybrid vehicle. The electric machine 52 receives electrical power from a traction battery 58 to provide torque to the vehicle wheels 55. The electric machine 52 can also operate as a generator to provide electrical power for charging the battery 58, for example, during braking.

[0032] In this way, the components from Fig. 1. A system for an engine, comprising an intake system, an engine intake manifold with a manifold air temperature sensor, a plurality of engine cylinders, one or more direct injection devices configured to inject fuel directly into one or more of the plurality of cylinders, one or more port injection devices configured to inject fuel via intake manifold into one or more of the plurality of cylinders, a central fuel injection device for injecting fuel into the engine intake manifold, an engine exhaust manifold with an exhaust port, an exhaust catalyst coupled to the exhaust port and an exhaust oxygen sensor coupled to the exhaust port upstream of the exhaust catalyst, and a control unit with computer-readable instructions.which are stored in non-volatile memory for the following: in response to an oxygen content in the exhaust catalyst that is higher than a threshold and an engine intake manifold temperature that is higher than a threshold, selectively increasing the ratio of fuel supplied via the central fuel injection device relative to fuel supplied via each of the direct injection devices and port injection devices, wherein the oxygen content is estimated via the exhaust oxygen sensor and the engine intake manifold temperature via the manifold air temperature sensor.

[0033] Fig. Figure 2 illustrates an exemplary method 200 that can be implemented to adjust the ratio of fuel supplied to an engine via manifold injection with respect to port and / or direct injection during cold-start engine conditions. Instructions for executing method 200 and the other methods contained herein can be provided by a controller based on instructions stored in a memory of the controller and in conjunction with sensors of the engine system, such as those referred to above. Fig. The control system can execute the signals received from the sensors described in section 1. The system can use motor actuators of the motor system to adjust the motor operation according to the procedures described below.

[0034] At 202, the routine involves estimating and / or measuring engine operating conditions. Conditions assessed may include, for example, driver demand, engine temperature, engine load, engine speed, manifold charge temperature, exhaust gas temperature, environmental conditions including ambient temperature, pressure and humidity, manifold pressure and airflow, boost pressure, exhaust-air-fuel ratio, EGR flow, etc.

[0035] At 204, the routine involves determining whether the vehicle engine is operating under cold-start conditions. A cold-start condition can be confirmed if the engine is started after a prolonged period of inactivity, when the engine temperature is lower than a threshold (such as below the catalyst activation temperature), and while ambient temperatures are below a threshold. During cold-start conditions, when the emission control device temperature is lower than its activation temperature, the device cannot be activated and therefore cannot function optimally. Before reaching the activation temperature, NOx generated by hydrocarbon combustion in the engine cylinders can be directed at the catalyst (such as catalyst 70 in ). Fig. 1) cannot be effectively contained. To reduce cold-start emissions during such conditions, it may be desirable to keep the peak combustion temperature below a threshold temperature to reduce NOx generation during cold-start conditions.

[0036] Accordingly, in section 206, if engine cold-start conditions are confirmed, an initial fuel supply schedule can be determined based on these conditions. For example, based on the torque demand during a cold start, engine dilution and cooling requirements can be determined, and a fuel supply schedule can be determined that meets the torque demand while also meeting the engine dilution and cooling requirements. Determining the initial fuel supply in section 207 involves determining the total amount of fuel to be injected (total fuel mass) to meet the torque demand.

[0037] As the torque demand increases, the total amount of fuel injected can be increased. For example, the control unit can use a lookup table to determine the amount of fuel to inject. A variety of engine operating conditions, such as engine speed and load, can be determined based on the torque demand (or pedal position) and used as inputs to the lookup table. The total amount of fuel to inject can be the output of the table. Alternatively, the control unit can make a logical determination of the total amount of fuel to inject based on logic rules that depend on engine speed, load, and torque demand.

[0038] Determining the initial fuel supply also involves selecting one or more fuel injection points and corresponding fuel injectors to inject at least a portion of the total fuel mass. Fuel injection at different points offers distinct advantages. For example, manifold fuel injection can provide charge cooling in the intake manifold as fuel vaporizes by absorbing heat from the manifold. Additionally, manifold fuel injection can effectively reduce pumping losses. As another example, direct fuel injection into the engine cylinders can provide additional charge cooling within the cylinders. The fuel injection devices to be used can be selected based on the intake manifold cooling requirements, dilution requirements, and charge cooling requirements in relation to each other.The total amount of fuel to be injected may include an initial ratio of fuel supplied via one or more direct injection devices (such as the DI 47 from . Fig. 1), a port fuel injection device (such as the PFI 48 from Fig. 1) and a central fuel injection system (such as the CFI 46 from Fig. 1) is to be injected. The control unit can generate pulse width signals which are sent to one or more fuel injection devices based on the specified initial ratio.

[0039] For example, during cold start conditions, there may be a higher demand for manifold cooling to increase charge cooling, thus keeping the peak combustion temperature below a threshold temperature and reducing NOx production (cold start conditions are reduced). At 208, at least a portion of the total fuel quantity can be supplied via the CFI as manifold injection. Similarly, to increase cylinder internal charge cooling, a portion of the total fuel quantity can be supplied as direct injection via the DI. Two or more fuel injectors (e.g., all fuel injectors) can be selected to simultaneously inject a portion of the total fuel at different points in the engine.The control unit can determine the initial fuel delivery via CFI and a subsequent fuel delivery via DI during cold start conditions based on manifold and cylinder cooling requirements. For example, in response to an increase in manifold temperature, as estimated by a manifold charge temperature (MCT) sensor, the initial fuel delivery via CFI can be increased, while the subsequent fuel delivery via DI can be reduced accordingly. Similarly, in response to an increase in cylinder internal temperature, as estimated by an engine coolant temperature sensor, the subsequent fuel delivery via DI can be increased, while the initial fuel delivery via CFI can be reduced accordingly.Similarly, in response to a drop in manifold temperature following CFI fuel injection, the initial proportion of fuel supplied via CFI can be reduced, while the second proportion supplied via DI can be increased. Likewise, in response to a drop in cylinder internal temperature following DI fuel injection, the second proportion of fuel supplied via DI can be reduced, while the initial proportion supplied via CFI can be increased. By coordinating the CFI and DI fuel injection in this way, manifold and cylinder internal temperatures can be reduced, and the peak combustion temperature can be maintained within a threshold temperature. As a result, NOx emissions during cold starts are reduced.In this way, during cold start conditions, when the exhaust catalyst may not be effective in NOx adsorption, emission quality can be improved by reducing NOx production.

[0040] Determining the injection ratio can also involve determining the number of fuel injections as the fuel is to be supplied. For example, each of the fuel quantities injected via direct injection, port injection, and manifold injection can be supplied as a single injection (of the specified quantity) or as a multitude of injections (which together yield the specified quantity). For example, the fuel injected via direct injection can be supplied as a single intake stroke injection, a single compression stroke injection, multiple intake stroke injections, multiple compression stroke injections, or a combination of intake stroke and compression stroke injections.For example, if the amount of fuel to be injected by a given injection device exceeds a threshold quantity (such as a threshold value based on the pulse width limit of the injection device), the number of injections via the given injection device can be reduced.

[0041] Due to the location of the manifold injection point, the amount of fuel supplied via the central fuel injection (CFI) is distributed to each cylinder, and misdistribution of fuel between cylinders can occur due to cylinder geometry. To address this misdistribution, the fuel supply can be adjusted via one or more port and direct injection devices to compensate for the misdistribution of fuel between cylinders. Misdistribution of fuel injected via the central fuel injection system among a multitude of cylinders can be estimated based on the amount of fuel injected via the CFI and the geometry of the multitude of cylinders, and can be learned based on the knock profile of each cylinder. As an example, an increased knock tendency (as learned from the profile) in one or more engine cylinders indicates misdistribution of fuel between cylinders.In one example, the control unit can use a lookup table to determine the fuel distribution among each of the many cylinders. The amount of fuel injected via CFI can be the input, and the amount of manifold-injected fuel received by each cylinder can be the output of the lookup table. For instance, the first cylinder in the many cylinders might receive a smaller proportion of the fuel supplied via CFI, relative to a larger proportion of fuel received by each of the remaining cylinders in the many cylinders.In one example, if a first cylinder receives a smaller amount of fuel following manifold fuel injection relative to the amount received by the other cylinders, the amount of fuel supplied to the first cylinder via one or more port and direct injection devices can be increased to maintain the total amount of fuel to be supplied to each cylinder. In another example, if a second cylinder receives a larger amount of fuel following manifold fuel injection relative to the amount received by the other cylinders, the amount of fuel supplied to the second cylinder via one or more port and direct injection devices can be reduced to maintain the total amount of fuel to be supplied to each cylinder.The amount of fuel supplied via one or more port and direct injection systems can also be adjusted to maintain an exhaust-air-fuel ratio at or approximately at a target ratio. For example, if a richer than stoichiometric air-fuel ratio is desired, the amount of fuel supplied via one or more port and direct injection systems can be increased relative to the amount of fuel supplied before enrichment, while maintaining the amount of airflow to provide the richer air-fuel ratio.While one or more port and direct injection systems are used to adjust the exhaust-air-fuel ratio and compensate for misdistribution of fuel injected via the central fuel injection system, the amount of fuel injected via a combination of port and direct injection cannot be reduced below a first threshold percentage. Similarly, the amount of fuel injected via the central fuel injection system must not exceed a second threshold percentage. For example, the amount of fuel injected via a combination of port and direct injection may be limited to not less than 20% of the total amount of fuel to be injected, and the amount of fuel injected via the central fuel injection system may be limited so that it does not exceed 80% of the total amount of fuel to be injected.

[0042] Based on the specified pitch ratio, the control unit can determine a control signal to send to each of the fuel injector actuators, such as a pulse width signal. The control unit can make a logical determination (e.g., regarding a pulse width signal to be sent to each fuel injector) based on logic rules that depend on torque demand, engine dilution requirements, and engine cooling requirements. The control unit can then send the control signals to the actuators of the corresponding fuel injectors. Therefore, fuel can be injected simultaneously through two or more fuel injectors, or even all injectors. Consequently, a time gap can exist between fuel injections across the multiple injectors.

[0043] In this way, in response to an exhaust catalyst temperature that is lower than a threshold, the first proportion of fuel supplied to the engine via manifold injection can be increased, while the second proportion of fuel supplied via one or more intake manifold and direct injection systems can be reduced until the exhaust catalyst temperature rises above the threshold quantity exhaust catalyst temperature.

[0044] At step 210, the routine includes determining whether the exhaust catalyst is active. A catalyst can achieve its optimal functionality when it reaches its activation temperature. Once fully activated, the catalyst can effectively adsorb NOx from the exhaust gas, thereby improving emission quality. If it is determined that the exhaust catalyst has not reached its activation temperature and is not fully switched on, at step 212, a portion of the fuel can be further supplied via CFI for increased charge air cooling and the consequent reduction of peak combustion temperature and NOx production.

[0045] If it is determined that the exhaust catalyst is active, the routine at 214 involves determining whether the engine intake manifold temperature, as estimated by an MCT sensor, is higher than a threshold temperature. If the intake manifold temperature rises above the threshold, there may be an increase in the peak combustion temperature, leading to an increase in NOx production due to the elevated combustion temperature. If it is determined that the engine intake manifold temperature is lower than the threshold temperature, at 216 the fuel supply can be adjusted based on engine operating conditions, including torque demand, engine dilution demand, and engine cooling demand. As discussed in step 206, the total amount of injected fuel and the fuel split between the three injection devices (CFI, PI, and DI) can be determined based on the engine operating conditions.If it is determined that the engine intake manifold temperature is lower than the threshold, manifold charge cooling may no longer be desired and the proportion of fuel supplied via CFI can be reduced accordingly.

[0046] However, if the engine intake manifold temperature is determined to be higher than the threshold temperature, the proportion of fuel injected via CFI can be further increased at 218. In one example, the routine adjusts the amount of fuel injected via CFI based on the intake manifold temperature. For instance, the controller can determine a control signal to send to the CFI actuator, such as a pulse width of the signal determined based on a measurement of the intake manifold temperature. The controller can determine the pulse width by a measurement that directly considers a specific intake manifold temperature, such as an increase in pulse width with increasing intake manifold temperature. Alternatively, the controller can determine the pulse width based on a calculation using a lookup table, where the input is the intake manifold temperature and the output is the pulse width.The increased manifold fuel injection can continue until the intake manifold temperature drops below the threshold temperature, thereby reducing NOx production.

[0047] In one example, the amount of fuel delivered via the CFI is determined empirically and stored in predefined lookup tables or functions. For instance, one table might correspond to determining intake manifold injection quantities, while additional tables might correspond to determining direct injection and port injection quantities. The tables can be indexed to engine operating conditions, such as engine speed and engine load.

[0048] In this way, during engine operating conditions that include a cold start condition, the total fuel mass can be provided as a first larger quantity of fuel injected via the central fuel injection device, and a second, smaller (remaining) quantity of fuel injected via one or more of the intake manifold and direct injection devices, until an exhaust catalyst start-up temperature is reached.Also, in response to an intake manifold temperature that is higher than a threshold, the first amount of fuel injected via the central fuel injection device can be increased relative to the second remaining amount of fuel injected via one or more of the port and direct injection devices until the intake manifold temperature falls below the threshold temperature, and then the first and second fuel quantities can be adjusted based on engine speed and engine load.

[0049] If step 204 determines that the engine is not operating under cold start conditions, such as during a warm start condition when the exhaust catalyst may be active (step 205), the fuel delivery schedule, including the total amount of fuel to be injected and the fuel distribution between the various injectors, can be determined based on engine operating conditions during a warm start. The fuel delivery schedule can be optimized to improve engine performance and does not need to be specifically adjusted to reduce NOx production, as the exhaust catalyst is already active and capable of handling the exhaust NOx. The routine can then proceed to step 214, where it can be determined whether the engine intake manifold temperature is higher than a threshold temperature, and further adjustments to the fuel delivery schedule can be made based on the detected intake manifold temperature.

[0050] Fig. Figure 3 illustrates an exemplary method 300 that can be implemented to adjust the proportion of fuel supplied to an engine via manifold injection during exit from a fuel cutoff event. This method allows the exploitation of the increased charge cooling effect achieved by increasing manifold injection to control NOx generation.

[0051] For 302, the routine involves determining and / or recording engine operating conditions, including, for example, driver torque demand, engine temperature, engine load, engine speed, manifold charge temperature, exhaust gas temperature, ambient conditions including ambient temperature, pressure and humidity, manifold pressure and airflow, boost pressure, exhaust air-fuel ratio, EGR flow, etc.

[0052] In section 304, the procedure involves determining whether no-fuel-supply conditions are met. In one example, the fuel supply may be suspended during a deceleration fuel shutdown (DFSO) event. The DFSO entry conditions may be determined based on various vehicle and internal combustion engine operating conditions, such as a combination of one or more of operator torque demand, vehicle speed, internal combustion engine speed, and internal combustion engine load. In one example, the DFSO entry conditions may be considered met in response to the operator torque demand being lower than a threshold. In another example, the DFSO entry conditions may be considered met in response to an operator removing their foot from the accelerator pedal without applying the brake pedal (e.g., during a coasting maneuver).In yet another example, the DFSO entry conditions can be considered fulfilled in response to the vehicle speed falling below a threshold or the vehicle traveling downhill. In yet another example, fuel may be temporarily cut off during transmission gear changes, such as when the transmission gear ratio is reduced from a higher to a lower ratio to accelerate a drop in engine speed.

[0053] If fuel cutoff conditions are not confirmed, fuel may continue to be supplied to the engine at 306 based on estimated engine operating conditions such as engine speed, engine load, operator torque requirement, etc. For example, the amount of fuel to be injected and the fuel distribution between different injection devices, including a central fuel injection (CFI), direct fuel injection (DI), and port fuel injection (PFI), may be determined based on engine operating conditions. The control unit can then send a pulse width corresponding to the determined fuel quantity to actuators coupled to one or more appropriate fuel injection devices to inject the determined amount of fuel into the cylinders.

[0054] If fuel shut-off conditions are confirmed, Procedure 300 proceeds to 308 to slow the engine by shutting off the fuel supply. As an example, the fuel supply can be shut off by disabling all fuel injectors (each of CFI, DI, and PFI) while maintaining cylinder valve operation. During the fuel shut-off, the engine runs without fuel injection while rotating and pumping air through the cylinders. Thus, if an oxidizing agent such as oxygen and NOx passes through the exhaust catalyst, the oxidizing agent will be adsorbed by the catalyst. Therefore, while air is pumped through the engine without combustion, the oxygen content of the exhaust catalyst can increase. Increased oxygen content in the exhaust catalyst can lead to a reduced NOx treatment capacity (conversion to water and nitrogen) at the exhaust catalyst.

[0055] In procedure 310, the routine includes determining whether fuel supply conditions are met. It can also include determining whether DFSO exit conditions are met. For example, fuel supply might be restarted after an upshift is completed, once the engine speed has dropped to the desired speed. Another example is that fuel supply conditions might be met once DFSO exit conditions are confirmed, such as in response to an increase in the operator torque command, which requires cylinder fuel injection to resume as a result of the operator depressing the accelerator pedal, or an anticipated increase in torque demand, such as while the vehicle is traveling uphill.In yet another example, the DFSO exit conditions can be confirmed if the engine slows down without fuel supply to below a threshold speed at which the engine might shut down. If the fuel supply conditions are not met, the engine may continue to slow down at 312 with fuel cut off and cylinder valve operation maintained. The engine then remains in the DFSO state until the DFSO exit conditions are met.

[0056] If the fuel supply conditions are met, then procedure 300 proceeds to 314 to resume fuel supply to the engine. Resuming fuel supply to the engine may involve turning on or activating the fuel injection devices that were previously turned off at 308. Upon resumption of fuel supply, the fuel supply schedule, including the fuel quantity and the fuel supply split ratio between manifold fuel injection, port fuel injection, and direct fuel injection, may be determined based on the engine operating conditions. For example, a fuel supply schedule may be determined that meets the engine torque requirement while also satisfying the engine dilution and cooling requirements.Upon exiting a non-fuel-supply phase, such as a DFSO condition, a rich air-fuel ratio (relative to stoichiometry) may be required to desorb the NOx trapped in the exhaust catalyst. The NOx can then react with hydrocarbons under the richer conditions to produce water and nitrogen. Richer-than-stoichiometric operation can continue until the NOx load in the catalyst reduces below a threshold load. Once the NOx load has reduced below the threshold load, the engine can operate under stoichiometric (or leaner-than-stoichiometric) conditions. During richer operation, while NOx is being converted at the catalyst, the catalyst's further NOx adsorption capacity may be temporarily reduced.Therefore, it may be desirable to further reduce NOx production until the NOx level in the catalyst falls below the threshold charge. To further reduce NOx production, the peak combustion temperature can be kept below a threshold temperature. This allows at least a portion of the total fuel to be delivered for combustion to be injected via the central fuel injection (CFI) system. As the fuel injected via the CFI atomizes in the intake manifold, charge air cooling can be achieved, which reduces the peak combustion temperature. The control unit can determine the amount of fuel to be injected via the CFI based on the peak combustion temperature. For example, the control unit can determine a control signal to send to the CFI actuator, such as a pulse width of the signal, which is determined based on a measurement of the peak combustion temperature.The control unit can determine the pulse width by directly considering a specific or calculated peak combustion temperature, such as increasing the pulse width with increasing peak combustion temperature. Alternatively, the control unit can determine the pulse width based on a calculation using a lookup table, where the peak combustion temperature is the input and the pulse width is the output. The increased manifold fuel injection can continue until the NOx load in the catalyst is reduced below the threshold load and the engine can be operated at a leaner than stoichiometric air-fuel ratio.

[0057] At 316, the routine involves determining whether the oxygen content of the catalyst has risen above a threshold level. During engine fuel cut-off conditions, while air flows through the engine exhaust system, oxygen can accumulate in the catalyst. Once the oxygen content of the catalyst rises above a threshold, it can be concluded that the catalyst is saturated with oxygen and is no longer able to adsorb NOx.

[0058] If the oxygen content in the catalyst is determined to be higher than the threshold, it may be desirable to reduce further NOx production. To reduce NOx production, the peak combustion temperature can be reduced by increasing charge cooling. At 318, the proportion of fuel supplied via CFI can be increased to achieve a higher level of charge cooling. In one example, the control unit can determine a control signal to send to the CFI actuator, such as a pulse width of the signal (indicating the amount of fuel to be injected via CFI), which is determined based on a determination of the catalyst's oxygen content. In another example, the amount of manifold fuel injection can be increased as the catalyst's oxygen content increases, while fuel injection via PFI and DI is reduced accordingly.Fuel supply via CFI can be reduced once the oxygen content in the catalyst drops below the threshold.

[0059] With the 320, the engine fuel supply can be adjusted based on estimated engine operating conditions such as engine speed, engine load, operator speed requirement, etc. For example, the amount of fuel to be injected and the fuel distribution between different injectors, including CFI, DI, and PI, can be determined based on engine operating conditions. The controller can then send a pulse width corresponding to the determined fuel quantity to actuators coupled to one or more appropriate fuel injectors to inject that specific amount of fuel into the cylinders.

[0060] If step 316 determines that the catalyst oxygen content is lower than the threshold, the routine can proceed directly to step 320 to adjust the fuel supply schedule based on engine operating conditions, regardless of the level of NOx production.

[0061] In this way, a control system, in response to an exhaust NOx value downstream of a catalyst exceeding a threshold, predicted based on engine operating conditions, can provide a total fuel mass as a first, larger quantity injected into an engine intake manifold via a central fuel injection device, and a second, remaining, smaller quantity injected via one or more port and direct fuel injection devices, with the first fuel quantity being higher than the second. The charge cooling effect of the manifold injection can be used to keep the peak combustion temperature below a threshold temperature and reduce NOx generation.

[0062] Now, with reference to Fig. Figure 4 shows an example chart 400 for setting a fuel injection schedule, including manifold fuel injection quantity, based on a desired charge cooling effect. To reduce NOx generation and improve emission quality, a higher degree of charge cooling may be desired during certain engine operating conditions. For example, at higher combustion temperatures, when there is an increase in the amount of NOx generated due to hydrocarbon combustion, more charge cooling may be desired. The horizontal (x-axis) represents time, and the vertical markers t1-t6 represent significant points in time during the operation of the heat exchange system.

[0063] The first curve, line 402, shows variations in engine load when the driver requests changes, with the driver request estimated over time via a pedal position sensor. The dotted line 403 indicates a threshold engine load below which fuel can be cut off and a deceleration fuel shut-off (DFSO) event can be initiated. The second curve, line 404, shows a change in exhaust catalyst temperature as estimated by an exhaust gas temperature sensor. The dotted line 405 shows a start-up temperature below which the catalyst cannot be fully functional. The third curve, line 406, shows an engine intake manifold temperature as estimated by a manifold charge temperature sensor. The dotted line 407 shows an intake temperature above which a higher amount of NOx can be produced due to the combustion of hydrocarbons at an elevated combustion temperature.The fourth curve, line 408, shows a DFSO event during engine operation. The fifth curve, line 410, shows the oxygen content in the catalyst as estimated by an exhaust gas oxygen sensor. The dotted line 409 indicates an oxygen threshold above which (due to the catalyst's oxygen saturation) no further NOx adsorption can occur. The sixth curve, line 412, shows the total amount of fuel to be injected using a combination of central fuel injection (CFI), direct injection (DI), and port fuel injection (PFI). The seventh curve, line 414, shows the amount of fuel supplied via CFI. The amount of fuel supplied via CFI is a fraction of the total amount of fuel to be supplied.

[0064] Before time t1, the engine is switched off and the vehicle is not driven using engine torque. At time t1, the engine starts from rest after a period of inactivity in response to an operator torque request. At the time of engine start, the exhaust catalyst temperature may be lower than the threshold temperature 403. The engine cold-start conditions are inferred based on the exhaust catalyst temperature being below a threshold. Between times t1 and t2, the catalyst temperature steadily increases, but the temperature remains below the catalyst's activation temperature, and the catalyst is not fully activated for effective NOx adsorption. To improve emission quality during cold-start conditions, reducing NOx production is desirable so that NOx not captured by the catalyst is not released into the atmosphere.To reduce NOx production, a portion of the total fuel to be injected is administered via CFI (Cold Fuel Injection), while the remainder is injected via port fuel injection (PFI). During port fuel injection, as the fuel atomizes, it removes heat energy from the intake manifold, creating a charge cooling effect. This charge cooling reduces the peak combustion temperature, thereby lowering NOx production.

[0065] At time t2, based on the rise in catalyst temperature to its activation temperature of 405°C, it can be concluded that the exhaust catalyst is active. Once the catalyst is active, oxidizing agents such as NOx and oxygen are effectively trapped within it, and no further adjustment of the fuel delivery schedule to reduce NOx production may be necessary. Between times t2 and t3, the intake manifold temperature remains below the threshold temperature of 407°C, indicating a lower rate of NOx production. Since charge cooling is not required at this time, manifold fuel injection via CFI is reduced, for example, suspended, between t2 and t3, as shown. The total fuel quantity is supplied via one or both direct injection and port injection.The fuel delivery ratio between DI and PFI is determined based on engine operating conditions, including engine speed, engine load, and engine temperature. Therefore, under higher engine load conditions, the proportion of the total fuel delivered via DI is increased, while the proportion delivered via PFI is reduced.

[0066] At time t3, based on an increase in the engine intake temperature above the threshold temperature of 407, it is inferred that the peak combustion temperature has risen, resulting in increased NOx production. Therefore, to reduce the intake manifold temperature and thus NOx production, a larger proportion of the total injected fuel is supplied via CFI, while a smaller, remaining proportion is supplied via PFI. Between times t3 and t4, when manifold injection resumes, fuel evaporates at the intake manifold and extracts heat from the manifold walls, thereby reducing the manifold temperature. The amount of fuel supplied via CFI is adjusted based on the intake temperature, decreasing as the intake temperature decreases.

[0067] At time t4, the engine load drops below the threshold load of 403, and to increase engine fuel efficiency, a deceleration fuel shutdown (DFSO) event is initiated by shutting off the fuel supply to the engine cylinders. Therefore, the fuel supply is suspended via each of the CFI, DI, and PFI cylinders. During the DFSO event, while air flows through the engine system, a higher amount of oxygen is adsorbed by the catalyst. Between times t4 and t5, the oxygen content of the catalyst increases progressively. During the DFSO event, while combustion is suspended, no NOx is produced, but the catalyst's capacity may be full due to the oxygen charge.

[0068] At time t5, the DFSO event is exited in response to an increase in engine load, and fuel supply to the cylinders resumes. Based on the oxygen level in the exhaust catalyst being higher than a threshold, it is inferred that the catalyst is saturated and unable to adsorb further NOx from the exhaust gas flowing through it. Therefore, it is desirable to reduce NOx production until at least a portion of the NOx and oxygen stored in the catalyst is desorbed and treated under richer-than-stoichiometric fuel supply conditions. Between times t5 and t6, a portion of the total injected fuel is supplied via CFI. Due to the manifold fuel injection, the fuel evaporates in the intake manifold, thereby reducing the intake manifold temperature and further reducing NOx production.The amount of fuel injected via CFI is adjusted based on the catalyst oxygen content, decreasing as the oxygen content decreases. Fuel injection via CFI continues until, at time t6, the catalyst oxygen content falls below the threshold and further NOx adsorption by the catalyst is possible.

[0069] After time t6, the total fuel quantity is injected via one or both direct injection (DI) and power fuel injection (PFI), depending on engine operating conditions. Thus, during lower engine load conditions, the proportion of the total fuel quantity supplied via PFI is increased, while the proportion supplied via DI is reduced. Similarly, if the soot load in the particulate filter exceeds a threshold value, the proportion of the total fuel quantity supplied via PFI is increased, while the proportion supplied via DI is reduced. Since the catalyst temperature is above the activation temperature (405), the intake air temperature is below the threshold temperature (407), and the catalyst oxygen content is below the threshold (409), further reduction of NOx production through increased charge air cooling is no longer desirable.

[0070] In this way, during engine operating conditions, when a predicted exhaust NOx level may rise above a threshold, charge cooling can be achieved by opportunistically injecting at least a portion of the total fuel quantity via a central fuel injection device. This reduces NOx generation and keeps the actual exhaust NOx level below the threshold. By increasing the manifold fuel injection, the corresponding charge cooling effect can be utilized to reduce NOx generation during cold-start conditions, when the exhaust catalyst cannot optimally adsorb and treat NOx.The technical effect of injecting fuel via CFI upon exiting a fuel cut-off event, when the catalyst may be saturated with oxygen, is that the level of NOx production can be reduced until the oxygen charge in the catalyst decreases and further NOx adsorption can resume. Overall, by providing manifold cooling and regulating NOx production, engine performance, fuel efficiency, and emissions quality can be improved.

[0071] Fig. Figure 5 illustrates an exemplary method 500 that can be implemented to adjust a fuel injection schedule when cylinder advance is specified. The method enables the use of the increased charge cooling of the manifold fuel injection to reduce the combustion temperature and mitigate the advance.

[0072] For 502, the routine involves determining and / or recording engine operating conditions, including, for example, driver torque demand, engine temperature, engine load, engine speed, manifold charge temperature, exhaust gas temperature, ambient conditions including ambient temperature, pressure and humidity, manifold pressure and airflow, boost pressure, exhaust air-fuel ratio, EGR flow, etc.

[0073] In some embodiments, an engine pre-ignition history can also be retrieved from a lookup table stored in the control unit's memory. The lookup table can be updated at regular intervals (e.g., at each engine cycle, every 50 miles, every hour, etc.) or in response to a cylinder pre-ignition event. The engine pre-ignition (PI) count can include a PI number for each cylinder and can contain details such as an estimate of the total number of pre-ignition events in the cylinder during the current drive or engine cycle (e.g., a cylinder drive PI number). The engine PI count can further include an estimate of the total number of pre-ignition events in the cylinder over the lifetime of engine operation (e.g., a cylinder lifetime PI number).Thus, the PI number of each cylinder can represent the pre-ignition profile of the given cylinder and can correlate with the tendency for further pre-ignition events of each cylinder.

[0074] At 504, it can be determined whether an ignition advance indication exists. In one example, an ignition advance indication involves the detection of an actual ignition advance event, although in other examples, the indication may involve determining a probability of ignition advance (before the ignition advance event actually occurs). An engine control unit can detect abnormal combustion events related to ignition advance and differentiate them from cylinder knock events based on the outputs from one or more engine knock sensors. As an example, an ignition advance indication may be confirmed in response to the knock sensor output, estimated in a window before an ignition event, exceeding a threshold value.

[0075] If it is determined that no ignition advance is specified, a fuel delivery schedule can be determined at 506 based on engine operating conditions such as engine load, engine speed, engine temperature, etc. For example, a total amount of fuel to be injected into the engine to meet the torque demand can be determined. If the torque demand increases, the total amount of fuel to be injected can be increased. In one example, the control unit can use a lookup table to determine the amount of fuel to be injected. A variety of engine operating conditions, such as engine speed, engine load, and torque demand, can be used as input, and the total amount of fuel to be injected can be the output.As another example, the control unit can logically determine the total amount of fuel to be injected based on logic rules that depend on engine speed, engine load, and torque demand. The total amount of fuel to be injected can include fuel delivered via one or more injectors from a direct injection device (such as the DI 47 from...). Fig. 1), a port fuel injection device (such as the PFI 48 from Fig. 1) and a central fuel injection system (such as the CFI 46 from Fig. 1) to be injected. The control unit can generate pulse width signals that are sent to one or more fuel injection devices. Based on engine speed / load conditions, there can be a threshold percentage of the proportion of fuel supplied via CFI relative to the proportion of fuel supplied via port injection and / or direct injection. Therefore, the proportion of fuel supplied via CFI can be limited to within the threshold percentage. In one example, during high engine speed and engine load conditions exceeding a threshold, a maximum of 80% of the total fuel supplied can be delivered via CFI, while the remaining 20% ​​of the total fuel supply can be delivered via DI and / or PFI. Details regarding the threshold percentage of fuel supplied via CFI based on engine speed / load conditions are provided in Fig. 6 discussed.

[0076] At 508, if it is determined that there is an ignition advance specification, at 509 the initial amount of fuel supplied via CFI can be increased relative to the amount of fuel supplied via DI and / or PFI. In one example, increasing the amount of manifold injection involves increasing the pulse width of the CFI. The control unit can determine the pulse width based on a calculation using a lookup table, where the input is engine operating conditions and the output is the pulse width. The proportion of fuel supplied via CFI can be limited so that it does not exceed a threshold percentage determined based on engine operating conditions. Due to the upstream location of the injection, the amount of fuel supplied via CFI is distributed substantially evenly among all engine cylinders. Increasing manifold injection can result in increased charge cooling.Therefore, increasing manifold charge cooling can reduce the pre-ignition tendency of each engine cylinder. By injecting an increased amount of fuel via CFI, the charge cooling properties of the manifold injection can be better utilized to mitigate pre-ignition without increasing the total amount of fuel supplied, thereby improving fuel efficiency. After a pre-ignition indication, the increased fuel supply via CFI can continue for an initial number of engine cycles or for an initial duration immediately after the pre-ignition indication, without any intervening engine cycles or durations. In one example, the initial number of engine cycles or the initial duration can be based on the knock sensor output, with the initial number of engine cycles or the initial duration increasing as the knock sensor output increases above the threshold output.In another example, the initial number of engine cycles or the initial duration can be reduced if the knock sensor output falls below the threshold output.

[0077] At 510, during the first number of engine cycles or during the initial duration following a specified ignition advance, a second, remaining quantity of fuel can be supplied via port fuel injection and / or direct injection. The amount of fuel supplied via port fuel injection and / or direct injection can be adjusted to maintain a target air-fuel ratio (such as stoichiometric). Also, when the fuel injected via CFI is distributed to each of the engine cylinders, misdistribution among cylinders can occur due to geometric differences between them. Misdistribution of fuel injected via the central fuel injection system among a multitude of cylinders, including the advance cylinder, can be estimated based on the amount of fuel injected via CFI and the geometry of the multitude of cylinders.In one example, the control unit can use a lookup table to determine the fuel distribution among each of the many cylinders. Since fuel misdistribution can lead to an increased tendency to knock, fuel misdistribution can also be learned based on the knock profile of each cylinder. The amount of fuel injected via CFI can be the input, and the amount of manifold-injected fuel received by each cylinder can be the output of the lookup table. In one example, the first cylinder in the many cylinders might receive a smaller proportion of the fuel delivered via CFI relative to a larger proportion of fuel received by each of the remaining cylinders in the many cylinders.The amount of fuel injected via one or more of the port fuel injection and direct injection devices can be adjusted based on the estimated misdistribution. For example, in response to the first cylinder receiving a smaller proportion of fuel, the direct (and / or port) injection of fuel to the first cylinder can be increased relative to the direct (and / or port) injection of fuel to each of the remaining cylinders.

[0078] The amount of fuel supplied via PFI relative to the amount supplied via DI can also be determined based on the particulate matter (PM) load in a particulate filter. Direct fuel injection produces more particulate matter (or soot) due to diffuse flame propagation, as the fuel cannot mix adequately with air before combustion. Therefore, if the PM load at the particulate filter exceeds a certain threshold, the amount of fuel supplied via DI can be reduced, and the amount supplied via CFI can be increased accordingly. This improves emission quality while increasing charge cooling and mitigating ignition advance.

[0079] At 512, upon completion of the first number of engine cycles with increased manifold fuel injection or after the first duration, it is determined whether there is a further indication of pre-ignition. For example, a further indication of pre-ignition can be detected during the first number of engine cycles or during the first duration. The further indication of pre-ignition can be detected in the previously pre-igniting cylinder or in any of the other engine cylinders. For example, it can be determined whether there is a surge of pre-ignition events that were not sufficiently mitigated by the initial increase in manifold injection and the adjustment of the fuel injection. If no further pre-ignition is detected, at 506, the nominal cylinder fuel supply can be resumed based on engine operating conditions.Additionally, the split fuel injection ratio applied during the previous ignition advance mitigation can be learned, and the split fuel ratio lookup table can be updated. If further ignition advance is detected, enrichment to mitigate the advance can be determined at 514. Specifically, a fuel quantity required to enrich the advance-firing cylinder and mitigate the advance indication is determined. The enrichment can include a degree of enrichment as well as a number of enrichment cycles. The enrichment can be increased if the advance indication increases. For example, the enrichment degree and / or the number of enrichment cycles applied can be increased if the knock sensor output exceeds the advance threshold.

[0080] At 516, it can be determined whether at least a portion of the enrichment in the engine cycle immediately following the engine cycle in which the ignition advance was detected can be provided via manifold injection. Specifically, it can be determined whether the pulse width of the CFI (Continuous Fuel Injection) can be increased during the immediately following engine cycle. The pulse width of the CFI can be determined based on a pulse width limit for the CFI at a current engine speed / load condition. For example, if the pulse width of the CFI is not already at the limit (based on current engine speed / load conditions), then further manifold injection may be possible. Otherwise, if the CFI pulse width is at the limit, no further manifold injection is possible.

[0081] If further manifold injection is possible, then the routine at 518 in response to the indication of advance ignition involves enriching the fuel injection by adjusting the air-fuel ratio so that it is richer than stoichiometry and then increasing the amount of fuel supplied via CFI relative to the amount of fuel supplied via PFI / DI following the detection of advance ignition.As further explained below, the amount of fuel supplied via manifold injection, port injection and direct injection can be increased, the increase can be adjusted so that the effective increase of the manifold injection for the engine cycle immediately following the detection of the advance ignition is higher than the effective increase for the port injection / direct injection for this engine cycle, and thus the distribution ratio for the manifold injection relative to the port injection / direct injection is increased for at least this engine cycle.

[0082] In one example, increasing the amount of manifold fuel injection involves increasing the pulse width of the CFI (Cooled Fuel Injection). For instance, to take maximum advantage of manifold charge cooling, the CFI can be operated at its upper limit based on engine speed / load conditions. A remainder of the specified enrichment for the given engine cycle can be provided via PFI (Pulsed Fuel Injection) or DI (Direct Injection). The fuel supply via PFI and / or DI can be adjusted to compensate for fuel misdistribution following manifold fuel injection. In another example, the operation of the enriched fuel supply can continue for a second set of engine cycles following the detection of pre-ignition. Each of the degrees of fuel enrichment over this second set of engine cycles can be based on the knock sensor output relative to the threshold output.In one example, both the enrichment level and the number of engine cycles can be increased if the knock sensor output exceeds the threshold. In another example, both the enrichment level and the number of engine cycles can be decreased if the knock sensor output falls below the threshold.

[0083] If, at 516, it is determined that the CFI pulse width cannot be increased further, the routine can proceed to 520, whereby the manifold injection pulse width can be maintained at the highest possible limit (based on current engine speed / load conditions), and the enrichment of the pre-ignition cylinder can be performed by increasing the split ratio of fuel supplied to the cylinder via a port fuel injector at an open intake valve, relative to fuel supplied to the cylinder via a direct injection device, for the second number of engine cycles immediately following the detection of pre-ignition.The amount of fuel supplied via both port and direct injection can be increased, and this increase can be adjusted so that the effective increase for port injection for the engine cycle immediately following the detection of pre-ignition is higher than the effective increase for direct injection for that engine cycle. Furthermore, the ratio of fuel supplied via port injection to fuel supplied via direct injection can be based on the particulate matter load at a particulate filter coupled to an exhaust manifold. Since direct fuel injection can increase particulate matter generation, the ratio of fuel supplied via port injection to direct injection can be increased if the particulate matter load at the particulate filter exceeds a threshold.In one example, increasing the intake manifold injection ratio involves increasing the pulse width of the intake manifold injection and supplying the intake manifold-injected fuel to an open intake valve. Any remaining enrichment required for the given engine cycle can be provided via the direct injection system during the intake stroke.

[0084] From steps 518 and 520, the routine proceeds to step 522, where, after the second set of engine enrichment cycles has elapsed, it determines whether there is a further indication of ignition advance. If no further advance is detected, the nominal cylinder fuel supply can be resumed at step 506 based on engine operating conditions. If further advance is detected, the routine at step 524 involves further adjusting the split fuel injection ratio to further increase cylinder charge cooling. Since the CFI pulse width cannot be increased further beyond the threshold limit, the amount of fuel supplied via port and direct injection can be adjusted. In one example, direct injection can be increased while the amount of fuel supplied via port injection can be reduced accordingly.In addition, the revised split fuel injection ratio can be learned and the split fuel ratio lookup table can be updated.

[0085] In this way, the engine can be operated in response to a first indication of advance in a cylinder at a stoichiometric air-fuel ratio for a first number of engine cycles; and in response to a second indication of advance in the cylinder following the first indication of advance, the engine can be operated at a richer than stoichiometric air-fuel ratio for a second number of engine cycles, wherein operating in response to both the first and the second indication of advance involves providing a total fuel mass as a first quantity of fuel injected into an engine intake manifold via a central fuel injection device, and a second, remaining quantity of fuel injected via one or more port and direct injection devices, the first quantity being greater than the second quantity.

[0086] It will be understood that the procedure consists of Fig. Although described in section 5 with reference to mitigating pre-ignition, it can also be applied, with modifications, to utilize the charge cooling of a manifold injection system for knock mitigation. A cylinder knock event can be detected based on input from a knock sensor during a window following the spark ignition event. In one example, the windows in which knock signals are estimated can be crank angle windows. In response to a knock event, the pulse width of the central fuel injection system can be increased to enhance charge cooling until the tendency for further knocking is reduced. In one example, the pulse width of the central fuel injection system can be increased to the threshold pulse width (corresponding to engine speed and load conditions).Thus, increasing manifold injection in response to an advance event can be greater than increasing manifold injection in response to a knock event. Increasing the manifold injection ratio can be used in addition to, or instead of, using retarded ignition. For example, increasing the ratio of fuel delivered via manifold injection in response to a knock indication can reduce the amount of retard required to mitigate the knock. Alternatively, in response to a knock indication, manifold injection can be increased to the limit while maintaining the ignition timing, and then, while still maintaining manifold injection at the limit, the ignition timing can be retarded to mitigate the knock.

[0087] Fig. Figure 6 shows a first example map 600 of a desired ratio of fuel injected via central fuel injection (CFI) to fuel injected via a combination of port fuel injection (PFI) and direct injection (DI), based on engine operating conditions. The x-axis of the map represents the engine load (in percent) and the y-axis of the map represents the engine speed (in revolutions per minute).

[0088] At any given engine speed and load, a threshold amount (or percentage) of fuel can be injected via CFI, while the remaining amount (or percentage) of the total fuel quantity can be injected via a combination of PFI and DI. The maximum percentage of fuel supplied via CFI can be further affected by conditions such as engine temperature and dilution requirements. The threshold amount of fuel to be injected via CFI can be based on the volatility and vapor pressure characteristics of the injected fuel. The volatility and vapor pressure characteristics of a fuel can be based on the manifold charging temperature and the fuel composition, such as the amount of ethanol (alcohol) present in the fuel. For example, as the ethanol content in the fuel increases, the fuel's volatility decreases.In another example, a decrease in the ethanol content of the fuel increases its volatility. The fuel ethanol level can be estimated based on inputs from an alcohol level sensor coupled to the fuel system. The controller can determine the fuel's evaporation behavior (such as the evaporation rate) using a lookup table, where the input is a fuel ethanol content (fuel composition) and a manifold charging temperature, and the output is the fuel evaporation rate. Additionally, the change in manifold charging temperature after a CFI fuel injection can be used as a feedback signal to estimate the amount of fuel that has evaporated after injection.

[0089] The amount of fuel supplied via CFI is distributed to each cylinder. The amount of fuel supplied via PFI and DI can be adjusted to maintain a desired air-fuel ratio. The amount of fuel supplied to each cylinder via PFI and DI can also be adjusted to compensate for misdistribution of fuel injected via CFI due to geometric differences between cylinders. For a given engine speed and load, it is desirable to keep the percentage of fuel injected via CFI within a defined threshold so that the remaining percentage of fuel supplied via PFI and DI can be effectively used to maintain a desired air-fuel ratio and to balance fuel distribution among all engine cylinders for each engine cycle.

[0090] In one example, during lower engine speed and lower engine load conditions, designated by item 602, a maximum of 20% of the total amount of fuel supplied for combustion during each engine cycle can be supplied via CFI, while the remaining 80% of the total amount of injected fuel can be supplied via a combination of PFI and DI. At medium engine speed and lower engine load conditions, designated by item 604, a maximum of 30% of the total amount of injected fuel can be supplied via CFI, while the remaining 70% of the total amount of injected fuel can be supplied via a combination of PFI and DI.At higher engine speeds and lower engine load conditions, as indicated by point 606, a maximum of 40% of the total amount of injected fuel can be supplied via CFI, while the remaining 60% of the total amount of injected fuel can be supplied via a combination of PFI and DI.

[0091] In another example, during lower engine speed and medium engine load conditions, designated by item 608, a maximum of 50% of the total amount of fuel supplied for combustion during each engine cycle can be supplied via CFI, while the remaining 50% of the total amount of injected fuel can be supplied via a combination of PFI and DI. At medium engine speed and medium engine load conditions, designated by item 610, a maximum of 60% of the total amount of injected fuel can be supplied via CFI, while the remaining 40% of the total amount of injected fuel can be supplied via a combination of PFI and DI.At higher engine speeds and medium engine load conditions, as indicated by point 612, a maximum of 70% of the total amount of injected fuel can be supplied via CFI, while the remaining 30% of the total amount of injected fuel can be supplied via a combination of PFI and DI.

[0092] In yet another example, at lower engine speed and higher engine load conditions, as described in point 614, a maximum of 70% of the total amount of fuel supplied for combustion during each engine cycle can be supplied via CFI, while the remaining 30% of the total amount of injected fuel can be supplied via a combination of PFI and DI. At medium engine speed and higher engine load conditions, as described in point 616, a maximum of 75% of the total amount of injected fuel can be supplied via CFI, while the remaining 25% of the total amount of injected fuel can be supplied via a combination of PFI and DI.At higher engine speeds and higher engine load conditions, as indicated by point 618, a maximum of 80% of the total amount of injected fuel can be supplied via CFI, while the remaining 20% ​​of the total amount of injected fuel can be supplied via a combination of PFI and DI.

[0093] Fig. Figure 7 shows a second example chart 700 of a desired ratio of fuel injected via central fuel injection (CFI) to fuel injected via a combination of port fuel injection (PFI) and direct injection (DI), based on engine operating conditions. The x-axis of chart 700 represents the engine speed (in rpm) and the y-axis represents the brake mean effective pressure (BMEP in bar). The brake mean effective pressure can be an indication of the engine load.

[0094] At each engine speed and BMEP, a first quantity (or percentage) of a threshold (e.g., maximum) of fuel can be injected via DI, a second quantity (or percentage) of a threshold (e.g., maximum) of fuel can be injected via PFI, and a third quantity (or percentage) of a threshold (e.g., maximum) of fuel can be injected via CFI. The maximum percentage of fuel supplied via CFI can be affected by conditions such as engine temperature, dilution requirements, and the volatility and vapor pressure characteristics of the injected fuel. As described above, the volatility and vapor pressure characteristics of the fuel can be based on the fuel composition, such as the amount of ethanol (alcohol) present in the fuel, and the manifold charging temperature.

[0095] In one example, under conditions with lower engine speed (such as below 3000 rpm) and lower BMEP (such as below 7 bar), in a first region designated by 702, a maximum of 2% of the total amount of fuel injected for combustion during each engine cycle can be supplied via CFI, while 98% of the total amount of injected fuel can be supplied via PFI and 0% of the total amount of injected fuel can be supplied via DI. At higher engine speed (such as above 3000 rpm) and lower BMEP (such as below 7 bar), in a second region designated by 704, a maximum of 2% of the total amount of fuel injected for combustion during each engine cycle can be supplied via CFI, while 80% of the total amount of injected fuel can be supplied via PFI and 18% of the total amount of injected fuel can be supplied via DI.

[0096] In another example, under conditions with all engine speeds and medium engine BMEP (such as between 7 bar and 17 bar), in a third region designated by 706, a maximum of 5% of the total amount of fuel injected for combustion during each engine cycle can be supplied via CFI, while 50% of the total amount of injected fuel can be supplied via PFI and 45% of the total amount of injected fuel can be supplied via DI.

[0097] In yet another example, under conditions with lower engine speed (such as below 3000 rpm) and higher BMEP (such as above 17 bar), in a fourth region designated by 708, a maximum of 5% of the total amount of fuel injected for combustion during each engine cycle can be supplied via CFI, while 50% of the total amount of injected fuel can be supplied via PFI and 45% of the total amount of injected fuel can be supplied via DI. At higher engine speed (such as above 3000 rpm) and higher engine BMEP (such as above 17 bar), in a fifth region designated by 710, a maximum of 10% of the total amount of fuel injected for combustion during each engine cycle can be supplied via CFI, while 20% of the total amount of injected fuel can be supplied via PFI and 80% of the total amount of injected fuel can be supplied via DI.

[0098] In this way, the total amount of fuel to be injected can be divided among the three injection devices based on the engine operating conditions.

[0099] Fig. Figure 8 shows an example map 800 of the ignition advance, which mitigates the fuel supply settings. Fig.This illustrates an engine position along the x-axis in crankshaft degrees (CAD). Diagram 808 depicts piston positions (along the y-axis) relative to their position from top dead center (TDC) and / or bottom dead center (BDC), and further, relative to their position within the four strokes (intake, compression, power, and exhaust) of an internal combustion engine cycle. As indicated by the sinusoidal curve 808, a piston moves gradually downward from TDC, flattening out at BDC at the end of the power stroke. The piston then returns upward to TDC at the end of the exhaust stroke. The piston then moves back downward to BDC again during the intake stroke, returning to its original upper position at TDC at the end of the compression stroke.

[0100] Curves 802 and 408 depict valve timing for an exhaust valve (dashed curve 802) and an intake valve (solid curve 804) during engine operation. As illustrated, an exhaust valve can open precisely when the piston flattens at the end of the power stroke. The exhaust valve can then close when the piston completes the exhaust stroke, remaining open at least until a subsequent intake stroke has begun. In the same way, an intake valve can open at the beginning of an intake stroke or before, and remain open at least until a subsequent compression stroke has begun.

[0101] As a consequence of the differences in the timing of the exhaust valve closing and the intake valve opening, both the intake and exhaust valves can be open briefly before the end of the exhaust stroke and after the beginning of the intake stroke. This period during which both valves can be open is referred to as positive overlap 806 from the intake to the exhaust valve (or simply as positive valve overlap), which is represented by a hatched area at the intersection of curves 802 and 804. For example, positive overlap 806 from the intake to the exhaust valve can correspond to a standard cam position of the internal combustion engine during a cold start.

[0102] Fuel injection profile 810 represents an exemplary fuel injection profile that can be used in response to no specified ignition advance. It sets a fuel split ratio based on nominal engine operating conditions. An engine control unit is configured to deliver the total fuel quantity to the cylinders as a first manifold injection via a central fuel injector (CF1, hatched block) and a second port injection via a port fuel injector (PF2, diagonally striped block). The first manifold injection includes an initial portion of fuel (CFI1) injected through the manifold at a first time CAD1. Specifically, the initial portion of fuel is injected through the port during an intake valve closing event (i.e., during the exhaust stroke).Then, a remaining portion of the fuel is injected as an intake stroke injection at CAD2 via the intake manifold (P2). It will be understood that in other examples, a portion of the total fuel quantity can be injected directly as a single compression stroke injection, as multiple intake stroke injections, as multiple compression stroke injections, or as a combination of at least one intake and at least one compression stroke injection. The ignition spark (star spark) is provided during the compression stroke. The fuel quantity P2 is adjusted based on the intake airflow so that the air-fuel ratio of the combustion is at or approximately at stoichiometry. As an example, fuel is supplied at a ratio of 30% manifold injection (CFI1):70% port injection (P2).

[0103] Fuel injection profile 820 represents an exemplary fuel injection profile that can be used in response to an initial indication of pre-ignition 822. In this profile, pre-ignition can be detected during the preceding combustion cycle as an abnormal combustion event (or series of abnormal combustion events) occurring prior to a cylinder spark event. In response to the detection of pre-ignition 822 in combustion cycle 1, fuel injection in combustion cycle 2 is adjusted to increase charge cooling. Charge cooling can be utilized by increasing the amount of fuel supplied via CFI. In the illustrated example, the CFI pulse width may not be limited, and further increases in the CFI pulse width may be possible.Accordingly, the fuel split ratio in combustion cycle 2 is adjusted to increase the amount of fuel supplied via manifold injection during an intake valve closing event (i.e., during the exhaust stroke), while reducing the amount of fuel supplied via port injection during an intake stroke, so that the total amount of fuel supplied during the engine cycle is not increased. An engine control unit is configured to provide the total fuel quantity (without enrichment) as a first manifold injection (CFI11, hatched block) and a second port injection (P12, diagonally striped block). The total fuel supplied via enrichment (CFI11+P12) can be equal to the amount of fuel supplied before the ignition advance (CFI1+P2).The first intake manifold injection involves an initial portion of fuel (CFI11) injected through the exhaust manifold at a specific point in time (CAD11). Then, the remaining fuel is injected through the intake manifold as a secondary injection (P12) at CAD12. The ignition spark (star spark) is provided during the compression stroke. The fuel quantity (P12) is adjusted based on the intake airflow so that the air-fuel ratio during combustion is at or approximately stoichiometric. For example, fuel is supplied at a ratio of 70% intake manifold injection (CFI11) to 30% intake manifold injection (P12).

[0104] Fuel injection profile 830 represents an exemplary fuel injection profile that can be used in response to a second indication of pre-ignition 832. This profile allows for the detection of pre-ignition for a second time during two consecutive engine cycles, occurring before a cylinder ignition event. In response to the detection of pre-ignition 832 in combustion cycle 1, the fuel injection in combustion cycle 2 is adjusted to enrich the cylinder. Additionally, a fuel split ratio is immediately set. Specifically, an enrichment that mitigates pre-ignition (e.g., enrichment level) can be determined based on the intensity of the pre-ignition event. For example, as the intensity increases, the enrichment level of the mitigating enrichment can be increased.At least a portion of the enrichment can then be provided via the CFI, thus utilizing the charge-cooling properties of the manifold injection. The pulse width of the CFI can be increased to the maximum threshold. Accordingly, the fuel split ratio in combustion cycle 2 is adjusted to increase the amount of fuel supplied via manifold injection during an exhaust stroke, while also increasing the amount of fuel supplied via port injection during an intake stroke. An engine control unit is configured to provide the total amount of fuel enrichment to the cylinder as a first manifold injection (CFI21, hatched block) and a second port injection (P22, diagonally striped block). The total fuel supplied via enrichment (CFI21+P22) can be twice the amount of fuel supplied after the first advance (CFI11+P12).The first manifold injection includes an initial portion of fuel (CFI21) injected through the manifold at a specific time point (CAD21). Then, the remaining fuel is injected as an intake stroke injection (P22) at CAD22 through the intake manifold. For example, fuel enrichment is applied at a ratio of 33% manifold injection (CFI21) to 67% intake manifold injection (P22). In this scenario, the change in the amount of intake manifold injection (P12 to P21) is greater than the change in the amount of manifold injection (CFI11 to CFI22). In this example, at CFI11, the CFI operates below the (upper) limit of the pulse width, while at CFI21, the CFI operates at the (upper) limit of the pulse width. The ignition spark (star) is provided during the compression stroke.The fuel-air ratio of CFI22 and P22 is then further adjusted over a number of subsequent combustion cycles to provide charge cooling, while maintaining a richer combustion air-fuel ratio than stoichiometric. In this way, ignition advance is specified in a first engine cycle, and a mitigating enrichment with an increased manifold fuel injection ratio is implemented in a second engine cycle immediately following the first.

[0105] In this way, in response to a first and subsequent second indication of pre-ignition in a cylinder, the ratio of fuel supplied via the central fuel injection device to the direct injection device can be increased towards a threshold pulse width, while a pulse width of the direct injection device is reduced accordingly, and after the pulse width of the central fuel injection device is at the threshold pulse width, the pulse width of the central fuel injection device is maintained at the threshold pulse width and the pulse width of one of the intake manifold and direct injection devices is increased.

[0106] In this way, the charge cooling properties of manifold fuel injection can be used to mitigate ignition advance and reduce NOx formation under selected engine operating conditions. The technical effect of increasing the amount of fuel supplied in response to an ignition advance signal via central fuel injection is that the charge cooling provided by the manifold injection can be used to mitigate the ignition advance, thereby reducing the need for cylinder enrichment and improving fuel efficiency. By reducing the reliance on cylinder enrichment and charge cooling provided by direct injection, the generation of unwanted particulate matter due to increased direct injection can be reduced.The manifold charge cooling effect can also be utilized by each engine cylinder, including one affected by pre-ignition, thereby reducing the likelihood of pre-ignition occurring in all engine cylinders. Overall, when pre-ignition is specified, increasing the amount of fuel injected via manifold injection relative to port injection and / or direct injection can achieve total charge cooling with improved fuel efficiency and emissions.

[0107] An exemplary procedure comprises: in response to a specified ignition advance, selectively increasing a first proportion of fuel supplied to the engine via manifold injection, relative to a second proportion of fuel supplied to the engine via one or more port and direct injection systems, while maintaining an air-fuel ratio prior to the specified ignition advance. In a preceding example, maintaining the air-fuel ratio additionally or optionally includes maintaining the air-fuel ratio at or approximately at stoichiometry.In any or all of the preceding examples, selectively increasing the first proportion of manifold-injected fuel additionally or optionally includes selectively increasing a pulse width of a central fuel injection device coupled to an engine intake manifold, while reducing a pulse width of one or more of a direct injection device and a port injection device accordingly.In any or all of the preceding examples, reducing the pulse width of one or more of the direct injection devices and the port injection in the second portion of fuel additionally or optionally involves adjusting the ratio of fuel supplied via port injection relative to fuel supplied via direct injection, based on a particulate matter load in a particulate filter coupled to an exhaust duct, wherein the adjustment involves increasing the ratio of fuel supplied via port injection relative to direct injection when the particulate matter load in the particulate filter is higher than a threshold value.In any or all of the preceding examples, increasing the pulse width of the central fuel injection device additionally or optionally includes increasing the pulse width of the central fuel injection device until an operating limit of the central fuel injection device is reached, and thereafter maintaining the pulse width of the central fuel injection device at the operating limit while the pulse width of one or more of the port fuel injection devices and the direct fuel injection devices is increased. In any or all of the preceding examples, specifying the ignition advance additionally or optionally includes an output from a cylinder-coupled knock sensor that is higher than a threshold value, estimated in a first crankshaft angle window before a spark ignition event of the cylinder.In any or all of the preceding examples, selective boosting additionally or optionally involves increasing the first proportion of fuel supplied to the engine via manifold injection, relative to the second proportion of fuel supplied to the engine via one or more of port and direct injection, for an initial number of engine cycles immediately following the ignition advance indication, without any intervening engine cycles, and maintaining the air-fuel ratio at or approximately at stoichiometry during the initial number of engine cycles. In any or all of the preceding examples, the initial number of engine cycles is additionally or optionally based on the knock sensor output, with the initial number of engine cycles increasing as the knock sensor output increases above the threshold output.Any or all of the preceding examples, further comprising, additionally or optionally, in response to a further specification of advance ignition after completion of the first number of engine cycles, a further increase in the first proportion of fuel supplied to the engine via manifold injection relative to the second proportion of fuel supplied to the engine via one or more of port and direct injection, and running the engine for a second number of engine cycles at an exhaust-air-fuel ratio richer than stoichiometry.In any or all of the preceding examples, running the engine richer than stoichiometry additionally or optionally involves adjusting a degree of fuel enrichment over the second number of engine cycles based on the knock sensor output relative to the threshold output, with the degree of enrichment increasing as the knock sensor output exceeds the threshold output.

[0108] Another exemplary method comprises: in response to a first indication of advance in a cylinder, operating the engine at a stoichiometric air-fuel ratio for a first number of engine cycles; and in response to a second indication of advance in the cylinder following the first indication of advance, operating the engine at a richer than stoichiometric air-fuel ratio for a second number of engine cycles, wherein operating in response to both the first and the second indication of advance includes providing a total fuel mass as a first quantity of fuel injected into an engine intake manifold via a central fuel injection device and a second, remaining quantity of fuel injected via one or more port and direct injection devices, the first quantity being greater than the second quantity.In any one of the preceding examples, the second indication of advance ignition occurs additionally or optionally within the first number of engine cycles. In any or all of the preceding examples, providing a total fuel mass as a first quantity injected via a central fuel injection device additionally or optionally involves increasing a pulse width of the central fuel injection device to supply the first quantity of fuel, wherein the first quantity of fuel is determined as a function of a pulse width limit of the central fuel injection device at a current engine speed / load condition.In any or all of the preceding examples, additionally or optionally, providing fuel in response to each of the first and second indications of advance ignition involves increasing the first fuel quantity until the pulse width of the central fuel injector reaches the limit, and then maintaining the pulse width of the central fuel injector and increasing a pulse width from one or more of the port fuel injector and direct fuel injector to supply the second, remaining fuel quantity.In any or all of the preceding examples, operating the engine with a richer than stoichiometric air-fuel ratio additionally or optionally involves enriching a total fuel injection during the second number of engine cycles based on a difference between an output from a knock sensor and an advance ignition threshold, with a degree of enrichment increasing as the difference increases.Any or all of the preceding examples, further comprising, additionally or optionally, estimating a misdistribution of the first quantity of fuel injected by the central fuel injection device among a plurality of cylinders, including the early-firing cylinder, wherein the misdistribution includes a first cylinder from the plurality of cylinders which receives a smaller proportion of the first quantity of fuel, relative to a larger proportion of fuel received by each of the other cylinders from the plurality of cylinders.In any or all of the preceding examples, the second quantity of fuel injected via one or more of the port fuel injectors and the direct fuel injectors is additionally or optionally adjusted based on the estimated misdistribution, the adjustment involving increasing the direct injection of fuel to the first cylinder relative to the direct injection of fuel to each of the remaining cylinders from the plurality of cylinders.

[0109] In yet another example, an engine system comprises the following: an engine intake manifold; an engine cylinder; a direct injection device configured to inject fuel directly into the cylinder; a port fuel injection device configured to inject fuel into the cylinder via an intake manifold; a central fuel injection device for injecting fuel into the engine intake manifold upstream of the cylinder; a knock sensor coupled to the cylinder; and a controller with computer-readable instructions stored in non-volatile memory to: indicate an ignition advance, other than knocking, in the cylinder in response to a knock sensor output in a first crankshaft angle window prior to a spark-ignition event in the cylinder exceeding an ignition advance threshold; and, in response to the ignition advance indication, selectively increase a fuel-air ratio,which is supplied to the cylinder via the central fuel injection device, relative to the direct injection device, for a first duration while the cylinder is operated at a stoichiometric fuel ratio. In any of the preceding examples, the specification of an ignition advance is additionally or optionally a first specification, and wherein the control includes further instructions for the following: in response to a second specification of an ignition advance in the cylinder, detected after the first duration, further increasing the ratio of fuel supplied via the central fuel injection device, relative to the direct injection device, while the cylinder is operated for a second duration at a richer than stoichiometric air-fuel ratio. In any or all of the preceding examples, the further increasing of the fuel ratio additionally or optionally includes,which is supplied via the central fuel injection device, increasing a pulse width of the central fuel injection device towards a threshold pulse width, while a pulse width of the direct injection device is reduced accordingly, and after the pulse width of the central fuel injection device is at the threshold pulse width, maintaining the pulse width of the central fuel injection device at the threshold pulse width and increasing the pulse width of the direct injection device.

[0110] It should be noted that the control and estimation routines contained herein can be used with various engine and / or vehicle system configurations. The control procedures and routines disclosed herein can be stored as executable instructions in non-volatile memory and can be executed by the control system, which includes the control unit in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Accordingly, various illustrated actions, operations, and / or functions can be performed in the illustrated sequence or in parallel, or in some cases, omitted.Likewise, the processing sequence is not strictly necessary to achieve the features and advantages of the exemplary embodiments described here, but is provided for easier illustration and description. One or more of the illustrated actions, operations, and / or functions can be performed repeatedly, depending on the specific strategy employed. Furthermore, the described actions, operations, and / or functions can graphically represent code to be programmed in the non-volatile memory of the computer-readable storage medium in the engine control system, whereby the described actions are carried out by executing the instructions in a system that includes the various engine hardware components in combination with the electronic control unit.

[0111] Another exemplary procedure comprises adjusting a first proportion of fuel supplied to an engine via manifold injection relative to a second proportion of fuel supplied to the engine via one or more of port and direct injection, based on an estimated oxygen content of an exhaust catalyst, wherein the estimated oxygen content is determined immediately after a fuel cut-off event. In any of the preceding examples, the adjustment additionally or optionally involves increasing the first proportion of fuel supplied to the engine via manifold injection while correspondingly reducing the second proportion of fuel supplied via one or more of port and direct injection, in response to the estimated oxygen content of the exhaust catalyst rising above a threshold oxygen content.In any or all of the preceding examples, the adjustment further includes, additionally or optionally, maintaining engine operation with the increased first proportion of fuel and the reduced second proportion of fuel until the estimated oxygen content of the exhaust catalyst falls below the threshold oxygen content, and then reducing the first proportion of fuel supplied to the engine via manifold injection while increasing the second proportion of fuel supplied via one or more of port and direct injection accordingly.In any or all of the preceding examples, the first proportion of fuel supplied to the engine via manifold injection is additionally or optionally based on the estimated oxygen content of the exhaust catalyst, with the first proportion being increased if the estimated oxygen content of the exhaust catalyst exceeds the threshold oxygen content. In any or all of the preceding examples, the second proportion of fuel supplied via one or more port and direct injection systems is additionally or optionally adjusted based on the first proportion to maintain an exhaust-air-fuel ratio.In any or all of the preceding examples, the adjustment further includes, additionally or optionally, in the second fuel fraction, the adjustment of a ratio of fuel supplied by port injection relative to fuel supplied by direct injection, based on a particulate matter load in a particulate filter coupled upstream / downstream of the exhaust catalyst, wherein the adjustment includes increasing the ratio of fuel supplied by direct injection relative to port injection when the particulate matter load in the particulate filter is less than a threshold value.In any or all of the preceding examples, increasing the first fuel fraction additionally or optionally involves increasing the first fuel fraction supplied to an engine via manifold injection relative to the second fuel fraction supplied via one or more port and direct injection systems for an initial number of engine cycles immediately following the fuel cutoff event, and during the initial number of engine cycles, operating the engine with a richer than stoichiometric exhaust-air-fuel ratio. In any or all of the preceding examples, the initial number of engine cycles is additionally or optionally based on an exhaust catalyst oxygen charge, with the initial number of cycles increasing as the exhaust catalyst oxygen charge increases.In any or all of the preceding examples, the fuel cutoff event additionally or optionally includes a deceleration fuel cutoff event in response to an operator torque demand that is less than a threshold. In any or all of the preceding examples, the fuel cutoff event additionally or optionally includes a transient fuel cutoff event in response to a transmission upshift.Any or all of the preceding examples, further comprising additionally or optionally, in response to an engine intake manifold temperature exceeding a threshold, increasing the first proportion of fuel supplied to the engine via manifold injection, while correspondingly reducing the second proportion of fuel supplied via one or more of port and direct injection, until the engine intake manifold temperature falls below the threshold engine intake manifold temperature.Any or all of the preceding examples, further comprising additionally or optionally, in response to an exhaust catalyst temperature that is lower than a threshold, increasing the first proportion of fuel supplied to the catalyst via manifold injection, while correspondingly reducing the second proportion of fuel supplied via one or more of port and direct injection, until the exhaust catalyst temperature rises above the threshold exhaust catalyst temperature.

[0112] Another exemplary procedure includes: in response to an exhaust NOx value downstream of an exhaust catalyst, predicted on the basis of engine operating conditions, being higher than a threshold, providing a total fuel mass as a first fuel quantity injected into an engine intake manifold via a central fuel injection device, and a second, remaining fuel quantity injected via one or more of port and direct fuel injection devices, the first fuel quantity being higher than the second fuel quantity.In any one of the preceding examples, the engine operating conditions additionally or optionally include a cold start condition, and wherein the total fuel mass, provided as the first quantity of fuel injected via the central fuel injection device and the second remaining quantity of fuel injected via the one or more of port and direct fuel injection devices, is maintained until an exhaust catalyst start-up temperature is reached.In any or all of the preceding examples, the engine operating conditions additionally or optionally include a fuel cut-off event, the method further comprising, upon resumption of fuel supply at one end of the fuel cut-off event in response to an oxygen content in the exhaust catalyst exceeding a threshold, injecting the first quantity of fuel injected via the central fuel injection device and injecting the second remaining quantity of fuel injected via one or more of port and direct injection devices until the oxygen content in the exhaust catalyst is reduced below the threshold.In any or all of the preceding examples, the engine operating conditions additionally or optionally include an intake manifold temperature that is higher than a threshold, and wherein the first quantity of fuel injected via the central fuel injection device and the second remaining quantity of fuel injected via one or more of port and direct fuel injection devices are maintained until the intake manifold temperature falls below the threshold temperature.In any or all of the preceding examples, the second quantity of fuel injected via one or more of port and direct injection devices is additionally or optionally adjusted based on misdistribution of the first quantity of fuel injected via the central fuel injection device among a plurality of engine cylinders, the adjustment involving increasing the direct injection of fuel to a first cylinder in response to the first cylinder receiving a smaller proportion of the first quantity of fuel relative to the fuel received by other engine cylinders.

[0113] In yet another example, an engine system comprises: an engine intake manifold with an intake air temperature sensor; a plurality of engine cylinders; one or more direct injection devices configured to direct fuel into one or more of the plurality of cylinders; one or more port fuel injection devices configured to inject fuel through an intake manifold into one or more of the plurality of cylinders; a central fuel injection device for injecting fuel into the engine intake manifold; an engine exhaust manifold with an exhaust port, an exhaust catalyst coupled to the exhaust port, and an exhaust oxygen sensor coupled to the exhaust port upstream of the exhaust catalyst; and a controller with computer-readable instructions stored in non-volatile memory for: selectively increasing,In response to an oxygen content in the exhaust catalyst that is higher than a threshold and an engine intake manifold temperature that is higher than a threshold, a ratio of fuel supplied via the central fuel injection device relative to fuel supplied via each of the direct injection devices and the port injection devices is determined, with the oxygen content being estimated via the exhaust oxygen sensor and the engine intake manifold temperature being estimated via the manifold air temperature sensor. In any preceding example, the control unit additionally or optionally includes further instructions for the following: maintaining the engine fuel supply with the increased ratio of manifold injection supplied via the central fuel injection device relative to each of the direct injection devices and port injection devices.until each of the oxygen content in the exhaust catalyst falls below the threshold oxygen content and the engine intake manifold temperature falls below the threshold temperature, and then the ratio is adjusted based on engine speed and engine load. In any or all of the preceding examples, selectively increasing the ratio of manifold-injected fuel additionally or optionally involves selectively increasing a pulse width of the central fuel injection device while reducing a pulse width of the port fuel injection device and the direct fuel injection device, wherein the pulse width of the central fuel injection device is based on each of the oxygen content of the exhaust catalyst and the engine intake manifold temperature, with the pulse width of the central fuel injection device increasing,if one or more of the oxygen content of the exhaust catalyst rises above the threshold oxygen content and the engine intake manifold temperature rises above the threshold temperature.

[0114] In another representation, the vehicle is a hybrid vehicle.

[0115] It will be understood that the configurations and routines disclosed herein are exemplary in nature and that these specific embodiments are not to be interpreted in a restrictive sense, as numerous variations are possible. For example, the foregoing technology can be applied to V-6, I-4, I-6, V-12, 4-cylinder boxer, and other engine types. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of the different systems and designs, and other features, functions, and / or properties disclosed herein.

[0116] The following claims, in particular, describe certain combinations and subcombinations that are considered novel and not obvious. These claims may refer to "one" element or "a first" element, or the equivalent thereof. Such claims are to be understood as including one or more such elements and neither requiring nor excluding two or more such 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 they have a broader, narrower, identical, or different scope of protection compared to the original claims, are also considered to be included in the subject matter of the present disclosure.

Claims

[1] Procedure, encompassing: Estimating the oxygen content of an exhaust catalyst immediately after a fuel shut-off event and Adjusting a first proportion of fuel supplied to an engine via manifold injection relative to a second proportion of fuel supplied to the engine via one or more of port and direct injection, based on the estimated oxygen content of the exhaust catalyst. [2] Method according to claim 1, wherein the adjustment includes increasing the first proportion of fuel supplied to the engine via manifold injection, while the second proportion of fuel supplied via one or more of port and direct injection is reduced accordingly, in response to the estimated oxygen content of the exhaust catalyst rising above a threshold oxygen content. [3] Method according to claim 2, wherein the adjustment further comprises maintaining engine operation with the increased first proportion of fuel and the reduced second proportion of fuel until the estimated oxygen content of the exhaust catalyst falls below the threshold oxygen content, and then reducing the first proportion of fuel supplied to the engine via manifold injection, while increasing the second proportion of fuel supplied via one or more of port and direct injection accordingly. [4] Method according to claim 2, wherein the set first proportion of fuel supplied to the engine via manifold injection is based on the estimated oxygen content of the exhaust catalyst, wherein the first proportion is increased when the estimated oxygen content of the exhaust catalyst increases above the threshold oxygen content. [5] Method according to claim 4, wherein the second proportion of fuel supplied via one or more of port and direct injection is adjusted on the basis of the first proportion to maintain an exhaust-air-fuel ratio. [6] Method according to claim 1, wherein one or more of the port and direct injection is both direct injection and port injection, and the adjustment further comprises in the second proportion of fuel adjusting a ratio of fuel supplied via port injection relative to fuel supplied via direct injection, based on a particulate matter load of a particulate filter coupled upstream and downstream of the exhaust catalyst, wherein the adjustment comprises increasing the ratio of fuel supplied via direct injection relative to port injection when the particulate matter load in the particulate filter is less than a threshold value. [7] Method according to claim 2, wherein increasing the first proportion of fuel includes increasing the first proportion of fuel supplied to an engine via manifold injection relative to the second proportion of fuel supplied via one or more of port and direct injection, for a first number of engine cycles immediately after the fuel cut-off event and during the first number of engine cycles operating the engine with a richer than stoichiometric exhaust-air-fuel ratio. [8] Method according to claim 7, wherein the first number of engine cycles is based on an exhaust catalyst oxygen charge, wherein the first number of cycles increases as the exhaust catalyst oxygen charge increases. [9] Method according to claim 1, wherein the fuel cut-off event includes a deceleration fuel cut-off event in response to an operator torque requirement that is less than a threshold. [10] Method according to claim 1, wherein the fuel cut-off event includes a temporary fuel cut-off event in response to a transmission gear shift up. [11] Method according to claim 1, further comprising, in response to an engine intake manifold temperature that is greater than a threshold, increasing the first proportion of fuel supplied to the engine via manifold injection, while reducing the second proportion of fuel supplied via one or more of port and direct injection accordingly, until the engine intake manifold temperature falls below the threshold engine intake manifold temperature. [12] Method according to claim 1, further comprising, in response to an exhaust catalyst temperature that is lower than a threshold value, increasing the first proportion of fuel supplied to the engine via manifold injection, while reducing the second proportion of fuel supplied via one or more of port and direct injection accordingly, until the exhaust catalyst temperature rises above the threshold exhaust catalyst temperature. [13] Engine system, comprising: an engine intake manifold with a manifold air temperature sensor configured to estimate an engine intake manifold temperature; a large number of engine cylinders; one or more direct injection devices configured to direct fuel into one or more of the plurality of cylinders; one or more intake manifold injection devices configured to inject fuel through an intake manifold into one or more of the plurality of cylinders; a central fuel injection device for injecting fuel into the engine intake manifold; an engine exhaust manifold with an exhaust channel, an exhaust catalyst coupled to the exhaust channel, and an exhaust oxygen sensor coupled to the exhaust channel upstream of the exhaust catalyst and configured to estimate an oxygen content; and a controller with computer-readable instructions stored in non-volatile memory for the following: Selective increase, in response to one of the oxygen content in the exhaust catalyst being greater than an oxygen content threshold and the engine intake manifold temperature being greater than a Engine intake manifold temperature threshold, a ratio of fuel supplied via the central fuel injection device relative to fuel supplied via each of the one or more direct injection devices and the one or more port injection devices. [14] System according to claim 13, wherein the control further includes instructions for: maintaining the engine fuel supply with the increased ratio of manifold injection supplied via the central fuel injection device, relative to each of the one or more direct injection devices and the one or more port injection devices, until each of the oxygen content in the exhaust catalyst falls below the threshold oxygen content and the engine intake manifold temperature falls below the threshold temperature, and then adjusting the ratio based on engine speed and engine load. [15] System according to claim 13, wherein the selective increase of the ratio of fuel injected via manifold and fuel supplied via the central fuel injection device includes the selective increase of a pulse width of the central fuel injection device, while a pulse width of one or more port fuel injection devices and one or more direct fuel injection devices is reduced, wherein the pulse width of the central fuel injection device is based on each of the oxygen content of the exhaust catalyst and the engine intake manifold temperature, wherein the pulse width of the central fuel injection device is increased when one or more of the oxygen content of the exhaust catalyst rises above the threshold oxygen content and the engine intake manifold temperature rises above the threshold temperature.

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