Methods and systems for dual fuel injection

Abstract

Methods for an engine, including: for a first number of successive combustion events, counted from the first combustion event when starting the engine from a standstill, supplying fuel to an engine with both port and direct injection; and Maintaining a ratio of fuel injected via port fuel injection relative to fuel injected via direct fuel injection during the first number of combustion events, even if the fuel mass changes.

Description

Area

[0001] This description generally relates to methods and systems for an engine configured with both port fuel injection and direct fuel injection capabilities. General state of the art and brief description

[0002] Engines can use various forms of fuel delivery to deliver a desired amount of fuel to each cylinder for combustion. One type of fuel delivery uses a port fuel injector for each cylinder to deliver fuel to the respective cylinders. Another type of fuel delivery further uses a direct fuel injector for each cylinder. Direct fuel injection (DI) systems can improve cylinder charge cooling, allowing engine cylinders to operate at higher compression ratios without causing unwanted engine knock. Port fuel injection (PFI) systems can reduce particulate emissions and improve fuel vaporization. Port fuel injection can also reduce pumping losses at low loads.To utilize the advantages of both fuel injection methods, engines can also be configured with both port and direct injection. Depending on engine operating conditions, such as engine speed and load ranges, fuel can be delivered via direct injection only, port injection only, or a combination of both. Upon restarting the engine, for example, the engine can be supplied with fuel using both port and direct injection, with the split ratio adjusted based on one or more engine operating conditions.

[0003] An example of an approach for operating an engine with dual fueling options is presented by Bidner et al. in US Pat. No. 8,100,107 B2. Therein, the split ratio for fueling the engine includes a larger portion of the fuel mass commanded during engine cold start and delivered via port fuel injection, with a remaining smaller portion delivered via direct fuel injection. By increasing the ratio of port fuel injected during fuel splitting, particulate emissions are reduced.

[0004] Furthermore, US 9 284 906 B2 and US 7 726 277 B2 describe methods and systems for controlling and regulating dual fuel injection of an engine system.

[0005] However, the inventors of the present invention have recognized potential problems with an approach such as that of Bidner et al. in US Pat. No. 8,100,107 B2. For example, during engine startup, when combustion occurs at several initial events, counting from the engine's first combustion event, the engine speed may or may not increase predictably. The speed profile can be altered by numerous factors, including engine temperature, component wear leading to friction changes, spark plug degradation, fuel quality, low battery voltage leading to slow startup speeds, etc. Engines may be calibrated to start with larger fuel masses at the initial fueling events / engine strokes until the engine completes startup speeds.If the threshold for ending launch engine speed is exceeded midway through the fueling stroke for one or more cylinders, and if the desired fuel mass decreases during that fueling stroke, the dual-fueled engine may decide to maintain the desired lower fuel mass by trimming the fuel pulse commanded to the DI fuel injector. As a result, a target split ratio between the PFI and DI injectors is not maintained during that combustion event. In particular, the DI fuel mass may be decreased (or eliminated) if the desired fuel mass decreases by a large amount as the engine exits launch speeds, or if the decrease is commanded late in the port fueling window (when port injection adjustments are not possible).Deviation from a calibrated fuel delivery split ratio can have a significant impact on mixture formation. Furthermore, deviation from the calibrated split ratio can have cascading effects on other engine operating parameters, such as a deviation from a calibrated ignition timing. As a result, combustion stability and robustness during engine start-up may be altered. Furthermore, the reliability and repeatability of engine start-up may be reduced.

[0006] Against the above background, the object of the present invention is to improve combustion stability and robustness during engine starting and / or the reliability and repeatability of engine starting compared to the prior art. This object is achieved by the features of the independent patent claims. Advantageous developments of the invention are described in the subclaims.

[0007] In one example, some of the problems described above may be addressed by a method for an engine comprising: for a first number of consecutive combustion events, counting from a first combustion event upon engine startup from a rest state, fueling an engine with both port and direct injection; and maintaining a ratio of port-injected fuel relative to direct injection fuel over the first number of combustion events, even when fuel mass changes. In this way, the calibrated split ratio may be given priority during engine startup until the startup speed is reached, and then the calibrated fuel mass may be given priority.

[0008] As one example, during engine startup from a rest state, the engine may be fueled via both port and direct injection. A calibrated split ratio of fuel delivered via port injection relative to fuel delivered via direct injection may be determined based on engine conditions during engine startup (such as engine temperature). For the first combustion event at startup, as well as for a first number of combustion events counted as occurring consecutively after the first combustion event (with no intervening combustion events), the calibrated fuel split ratio may be maintained even if the fuel mass changes.For example, if a decrease in fuel mass is commanded, the fuel mass is decreased by proportionally trimming both the port injection (PFI) fuel pulse and the direct injection (DI) fuel pulse so that the split ratio is maintained. For example, the end of injection timing of both the PFI and DI fuel pulses may be advanced. Thus, this may be possible if the commanded decrease in fuel mass is received earlier in the port injection fuel delivery window (e.g., before a port injection window cutoff angle is reached). If the commanded decrease in fuel mass is received later in the port injection fuel delivery window (e.g., after the cutoff angle is reached), trimming the port injection pulse may no longer be possible.In this case, instead of trimming the DI fuel pulse to provide the commanded fuel mass at the expense of the commanded split ratio, the DI fuel pulse is maintained to maintain the commanded split ratio at the expense of the commanded fuel mass. This means that the actual delivered fuel mass may be higher than the commanded fuel mass. After the first number of combustion events have elapsed, the commanded split ratio may be modified to allow for changes in the commanded fuel mass.

[0009] In this way, a more robust engine calibration can be provided across engine starts, even when factors that could affect start-up change. By selectively disregarding a commanded reduction in fuel mass received midway through a combustion event during engine start-up, a calibrated fuel split ratio can be maintained for a defined number of combustion events, counting from engine start-up. Thus, variability in mixture formation and deviations from a calibrated spark timing are reduced. By prioritizing the commanded split ratio over the commanded fuel mass for the defined number of combustion events from start-up, engine start-up variability due to sudden changes in fuel mass can be reduced.Overall, combustion stability during engine starting is improved. Engine starting is also made more reliable and repeatable.

[0010] It should be understood that the foregoing Summary is provided to introduce, in a simplified manner, a selection of concepts that are further described in the Detailed Description. It is not intended to identify important or crucial features of the claimed subject matter, the scope of which is defined solely in the claims following the Detailed Description. Furthermore, the claimed subject matter is not limited to implementations that overcome the disadvantages noted above or in any part of this disclosure. Short description of the drawings Fig. 1 schematically shows an embodiment of a cylinder of an internal combustion engine configured with dual fuel injection capabilities. Fig. 2 shows a high-level flow diagram of a method for adjusting one each of direct and port injection fuel pulses during engine cranking in response to a commanded change in fuel mass. Fig. 3 shows example settings of each of a direct and port injection fuel pulse during engine cranking according to the present disclosure. Detailed description

[0011] The following detailed description provides information about adjusting fuel delivery to a vehicle engine during an initial number of combustion events at engine start-up to improve combustion stability until the engine completes starting speeds. An embodiment of a cylinder in an internal combustion engine configured for both port and direct injection is described in Fig. 1. A controller may be configured to execute a control routine, such as the example routine from Fig. 2, to selectively trim a port and direct injection fuel pulse in response to a reduction in fuel mass commanded during an initial number of combustion events at engine start-up. Example fuel injection settings of direct and port injection fuel pulses during engine start-up are shown in Fig. 3 shown.

[0012] Regarding the terminology used in this detailed description, port fuel injection can be abbreviated as PFI, while direct fuel injection can be abbreviated as DI.

[0013] Fig. 1 illustrates an example of a combustion chamber or cylinder of internal combustion engine 10. Engine 10 may be controlled at least in part by a control system including controller 12 and by input from a vehicle operator 130 via input device 132. In this example, input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinder (herein also "combustion chamber") 14 of engine 10 may include combustion chamber walls 136 in which a piston 138 is disposed. Piston 138 may be coupled to a crankshaft 140 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system.Furthermore, a starter (not shown) may be coupled to the crankshaft 140 via a flywheel to enable a starting operation of the engine 10.

[0014] Cylinder 14 may receive intake air via a series of intake air passages 142, 144, and 146. In addition to cylinder 14, intake air passage 146 may communicate with other cylinders of engine 10. In some examples, one or more of the intake passages may include a boost device such as a turbocharger or a supercharger. For example, Fig. 1 shows the engine 10 configured with a turbocharger including a compressor 174 disposed between the intake passages 142 and 144 and an exhaust turbine 176 disposed along an exhaust passage 148. The compressor 174 may be powered at least partially via a shaft 180 by the exhaust turbine 176, wherein the boosting device is configured as a turbocharger. However, in other examples, such as when the engine 10 is provided with a mechanical supercharger, the exhaust turbine 176 may be omitted, where the compressor 174 may be powered by mechanical inputs from an electric motor or the internal combustion engine. A throttle 162 including a throttle plate 164 may be provided along an intake passage of the engine for varying the flow rate and / or pressure of intake air provided to the cylinders of the engine.For example, the throttle 162 may be positioned downstream of the compressor 174, as shown in FIG. Fig. 1, or alternatively it may be provided upstream of the compressor 174.

[0015] The exhaust passage 148 may receive exhaust gases from other cylinders of the engine 10 in addition to cylinder 14. An exhaust gas sensor 128 is shown coupled to the exhaust passage 148 upstream of the emissions control device 178. The sensor 128 may be selected from various suitable sensors for providing an indication of an exhaust air / fuel ratio, such as a linear oxygen sensor or UEGO (Universal Exhaust Gas Oxygen Sensor), a dual-state oxygen sensor or EGO (as shown), a HEGO (Heated EGO), a NOx, HC, or CO sensor. The emissions control device 178 may be a three-way catalyst (TWC), a NOx trap, various other emissions control devices, or combinations thereof.

[0016] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown as including at least one intake poppet valve 150 and at least one exhaust poppet valve 156 located in an upper region of cylinder 14. In some examples, each cylinder of engine 10, including cylinder 14, may include at least two intake poppet valves and at least two exhaust poppet valves located in an upper region of the cylinder.

[0017] The intake valve 150 may be controlled by the controller 12 via actuator 152. Similarly, the exhaust valve 156 may be controlled by the controller 12 via actuator 154. Under some conditions, the controller 12 may vary the signals provided to actuators 152 and 154 to control the opening and closing of the respective intake and exhaust valves. The position of the intake valve 150 and exhaust valve 156 may be determined by respective valve position sensors (not shown). The valve actuators may be of the electric valve actuation type or the cam actuation type, or a combination thereof. The intake and exhaust valve actuation may be controlled simultaneously, or any of variable intake cam actuation, variable exhaust cam actuation, dual independent variable cam actuation, or fixed cam actuation may be used.Each cam actuation system may include one or more cams and utilize one or more of the following: cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems, which may be operated by controller 12 to vary valve operation. For example, cylinder 14 may alternatively include an electronic valve actuation-controlled intake valve and an exhaust valve controlled by cam actuation systems that include CPS and / or VCT. In other examples, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or a variable valve actuation actuator or actuation system.

[0018] Cylinder 14 may have a compression ratio that is the ratio of the volumes when piston 138 is at bottom dead center to top dead center. In one example, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where other fuels are used, the compression ratio may be increased. This may occur, for example, when using fuels with a higher octane rating or fuels with a higher latent heat of vaporization. The compression ratio may also be increased when using direct injection due to its effect on engine knock.

[0019] In some examples, each cylinder of engine 10 may include a spark plug 192 to initiate combustion. Ignition system 190 may provide an ignition spark to combustion chamber 14 via spark plug 192 in response to an ignition pre-ignition signal SA from controller 12 under selected operating modes. However, in some embodiments, spark plug 192 may be omitted, such as when engine 10 can initiate combustion through auto-ignition or by injecting fuel, which may be the case with some diesel engines.

[0020] In some examples, each cylinder of engine 10 may be configured with one or more injectors for providing fuel thereto. As a non-limiting example, cylinder 14 is illustrated as including two injectors 166 and 170. Fuel injectors 166 and 170 may be configured to provide fuel received from fuel system 8. Fuel system 8 may include one or more fuel tanks, fuel pumps, and fuel rails. Injector 166 is illustrated as being directly coupled to cylinder 14 for injecting fuel directly thereto in proportion to the pulse width of a signal FPW-1 received from controller 12 via electronic driver 168.Thus, the fuel injector 166 provides what is known as direct injection (hereinafter referred to as "DI") of fuel into the combustion cylinder 14. Although . Fig. 1 shows the injector 166 positioned on one side of the cylinder 14, it may alternatively be located above the piston, such as near the position of the spark plug 192. Such a position may improve mixing and combustion when the engine is operating on an alcohol-based fuel, as some alcohol-based fuels have lower volatility. Alternatively, the injector may be located above and near the intake valve to improve mixing. The fuel may be supplied to the injector 166 from a fuel tank of the fuel system 8 via a high-pressure fuel pump and a fuel rail. Additionally, the fuel tank may include a pressure transducer that provides a signal to the controller 12.

[0021] The fuel injector 170 is shown disposed in the intake port 146 rather than in the cylinder 14 in a configuration that provides so-called port fuel injection (hereinafter referred to as "PFT") into the intake port downstream of the cylinder 14. The injector 170 can inject fuel received from the fuel system 8 proportional to the pulse width of a signal FPW-2 received from the controller 12 via the electronic driver 171. It should be noted that, as shown, a single driver 168 or 171 can be used for both fuel injection systems, or multiple drivers, for example, driver 168 for the fuel injector 166 and driver 171 for the fuel injector 170, can be used.

[0022] In an alternative example, each of fuel injectors 166 and 170 may be configured as a direct fuel injector for injecting fuel directly into cylinder 14. In yet another example, each of fuel injectors 166 and 170 may be configured as a port fuel injector for injecting fuel upstream of intake valve 150. In still other examples, cylinder 14 may include only a single fuel injector configured to receive various fuels from the fuel systems in varying relative amounts as a fuel mixture, and further configured to inject this fuel mixture either directly into the cylinder as a direct fuel injector or upstream of the intake valves as a port fuel injector.It should therefore be understood that the fuel systems described herein should not be limited by the particular fuel injector configurations described herein as examples.

[0023] Fuel may be delivered to the cylinder by both injectors during a single cylinder stroke. For example, each injector may provide a portion of a total fuel injection combusted in cylinder 14 according to a calibrated split ratio. Further, the distribution and / or relative amount of fuel delivered by each injector (i.e., the split ratio) may vary depending on operating conditions, such as engine load, engine temperature, knock, exhaust temperature, and the combustion event count counted from a first combustion event upon engine start. Port-injected fuel may be delivered during an intake valve open event, an intake valve closed event (e.g., substantially prior to the intake stroke), and during both intake valve open and closed operation.Thus, by delivering fuel via the port during a closed intake valve event, air-fuel mixture formation is improved (compared to during open intake valve operation). Similarly, directly injected fuel may be delivered, for example, during an intake stroke, as well as partially during a preceding exhaust stroke, during the intake stroke, and partially during the compression stroke. Thus, even for a single combustion event, injected fuel may be injected at different times from the port and direct fuel injectors. Furthermore, for a single combustion event, multiple injections of the delivered fuel may be performed per stroke. The multiple injections may be performed during the compression stroke, intake stroke, or suitable combinations thereof.

[0024] As described above, Fig. 1 merely one cylinder of a multi-cylinder engine. Thus, each cylinder may equally include its own set of intake / exhaust valves, fuel injector(s), spark plug, etc. It will be understood that the engine 10 may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each of these cylinders may include some or all of the various components described in Fig. 1 with reference to cylinder 14.

[0025] Fuel injectors 166 and 170 may have different characteristics. This includes differences in size; for example, one injector may have a larger injection orifice than the other. Other differences include, among others, different spray angles, different operating temperatures, different targets, different injection timing, different spray characteristics, different positions, etc. Furthermore, depending on the distribution ratio of the injected fuel among injectors 170 and 166, different effects may be achieved.

[0026] Fuel tanks in the fuel system 8 may contain different types of fuels, such as fuels with different fuel properties and different fuel compositions. These differences may include differences in alcohol content, water content, octane rating, latent heats, fuel blends, and / or combinations thereof, etc. An example of fuels with different latent heats could include gasoline as a first fuel type with lower latent heats of vaporization and ethanol as a second fuel type with higher latent heats of vaporization. In another example, the engine may use gasoline as a first fuel type and an alcohol-containing blended fuel, such as E85 (which is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline), as a second fuel type.Other possible substances include water, methanol, a mixture of alcohol and water, a mixture of water and methanol, a mixture of alcohols, etc.

[0027] Furthermore, in another example, both fuels may be alcohol blends with different alcohol compositions, where the first fuel type may be a gasoline-alcohol blend with a lower alcohol concentration, such as E10 (which is approximately 10% ethanol), while the second fuel type may be a gasoline-alcohol blend with a higher alcohol concentration, such as E85 (which is approximately 85% ethanol). In addition, the first and second fuels may also differ in terms of other fuel properties, such as a difference in temperature, viscosity, octane number, etc. Furthermore, the fuel properties of one or both fuel tanks may change frequently, for example, due to daily fluctuations in tank refilling.

[0028] Control 12 is in Fig. 1 as a microcomputer including a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values, shown in this specific example as non-volatile read-only memory 110 for storing executable instructions, random access memory 112, keep-alive memory 114, and a data bus.The controller 12 may receive various signals from sensors coupled to the engine 10, in addition to the signals previously discussed, including measurements of inducted mass air flow (MAF) from mass air flow sensor 122; engine coolant temperature (ECT) from temperature sensor 116 coupled to cooling sleeve 118; a profile ignition pickup (PIP) signal from Hall effect sensor 120 (or other type) coupled to the crankshaft 140; throttle position (TP) from a throttle position sensor; and an absolute manifold pressure (MAP) signal from sensor 124. The engine speed signal RPM may be generated by the controller 12 from the PIP signal. The manifold pressure signal (MAP) from the manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold.The controller 12 receives signals from the various sensors. Fig. 1 and exposes the various actuators Fig. 1 to adjust engine operation based on the received signals and instructions stored in a memory of the controller. Adjusting may include, for example, the controller sending a signal to the port injector in response to a commanded decrease in fuel mass to advance an end of the injection timing of a port injection fuel pulse. The controller may also send a signal to the direct injector in response to a change in the port injection fuel pulse to advance an end of the injection timing of a direct injection fuel pulse to maintain a calibrated fuel split ratio even when the commanded fuel mass changes. An example control routine is described herein with reference to Fig. 2 described.

[0029] In this way, the system enables Fig. 1 an engine fuel system comprising: an engine cylinder, a direct fuel injector coupled to the cylinder; a port fuel injector coupled to the cylinder; and a controller. The controller may be configured with computer-readable instructions stored in non-transitory memory for: restarting an engine with fuel provided to the cylinder at a first combustion event from the idle state by each of the port fuel injector and the direct fuel injector; adjusting a fuel mass commanded to the cylinder based on a combustion event count from the first combustion event until a threshold number of combustion events has elapsed; when a commanded decrease in fuel mass is received within a threshold number of crank angle degrees of a port fuel injection window,Setting one port injection fuel pulse and one direct injection fuel pulse, respectively, to provide the commanded reduction in fuel mass while adjusting the ratio; and if the commanded reduction in fuel mass is received outside the threshold number of crank angle degrees of the port injection window, maintaining one port injection fuel pulse and one direct injection fuel pulse, respectively, to maintain the ratio while providing an actual fuel mass,which is greater than a commanded fuel mass. In the above exemplary system, adjusting each of the port injection fuel pulse and the direct injection fuel pulse includes advancing an end of the injection timing of each of the port injection fuel pulse and the direct injection fuel pulse. In the above exemplary system, maintaining each of the port injection fuel pulse and the direct injection fuel pulse includes maintaining the end of the injection timing of each of the port injection fuel pulse and the direct injection fuel pulse. The ratio is based on an engine temperature estimated before the first combustion event at engine start-up, wherein the ratio includes a higher proportion of port injected fuel relative to direct injected fuel.when the engine temperature decreases.

[0030] Now, with reference to Fig. 2, a method 200 is described for increasing the robustness of engine starting by maintaining a calibrated split ratio of fuel delivered via port injection relative to fuel delivered via direct injection over each defined number of combustion events counted from engine start-up, even if the fuel mass changes. Instructions for performing method 200 and the other methods included herein may be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the engine system, such as those described above with reference to Fig. 1. The controller may use motor actuators of the engine system to adjust engine operation according to the methods described below.

[0031] At 202, the method includes estimating and / or measuring vehicle operating conditions. These include, for example, engine temperature, environmental conditions (such as ambient temperature, pressure, and humidity), engine load, driver demand, etc.

[0032] At 204, it may be determined whether the engine is being cranked from a rest state. In one example, an engine restart may be confirmed in response to an ignition key turn-on event or an alternative vehicle turn-on event. As another example, in engines configured with start-stop systems, an engine restart may be confirmed in response to an increase in driver demand following an engine idle shutdown.

[0033] An engine start may not be confirmed if the engine has already exceeded the engine start speed (or has exceeded a first number of combustion events since a last engine start) and nominal engine operation continues. If an engine start is not confirmed, the routine includes, at 206, fueling the engine with a fuel mass and a split ratio of port-injected fuel to direct-injected fuel based on one or more of the estimated engine operating conditions. In particular, the split ratio may be adjusted based on engine operating parameters while maintaining a commanded fuel mass even if the fuel mass changes. The split ratio may be determined based on, for example, engine load, engine temperature, exhaust temperature, and / or knock probability.As another example, the split ratio of port injected fuel relative to direct injected fuel may be based on driver torque demand, with the ratio of port injected fuel relative to direct injected fuel being decreased as driver demand increases.

[0034] If engine start is confirmed, the engine may be fueled via port injection and direct injection, respectively, at 208. A ratio of port injected fuel relative to direct injected fuel may be selected based on engine conditions at engine start (e.g., engine conditions before any fueling is initiated), such as engine temperature. As an example, the ratio of port injected fuel to direct injected fuel may be increased as engine temperature decreases during an initial combustion event at start-up. Therefore, a larger proportion of the total fuel mass may be delivered as port injection during a cold engine start compared to a warm engine start.Furthermore, the ratio may be selected based on an alcohol content or an octane number of the fuel injected by the port and direct injection device.

[0035] At 210, the method includes calculating PFI and DI fuel masses for an upcoming combustion event (such as a first combustion event at engine start, as well as a first number of consecutive combustion events counted from the first combustion event at engine start) based on the selected ratio. Here, for each combustion event, control may calculate a total fuel mass to be delivered to a cylinder, and then, based on the selected split ratio, control may calculate the total fuel mass to be delivered to the cylinder via the port fuel injector and via the direct fuel injector.

[0036] At 212, the method includes scheduling PFI and DI fuel pulses based on the determined fuel masses. Here, a start and end injection timing may be determined based on the relative fuel mass to be delivered via each injector, allowing the determined fuel mass to be delivered via each injector at an average target injection timing. The controller may send a signal to actuate a solenoid valve of the corresponding fuel injectors to open and close the valves, thereby beginning and ending fuel injection at the determined start and end injection timing.

[0037] During fuel injection according to the scheduled fuel pulses, a counter may be set at 214 to count each number of combustion events during engine startup. Therefore, a first combustion event may be defined as a combustion event that occurs after fuel is delivered to a first cylinder during engine startup from idle, where the engine was idle and not receiving fuel prior to the first combustion event, and where the engine begins to crank as a result of the first combustion event.

[0038] At 216, it may be determined whether a decrease in fuel mass has been commanded. Thus, the engine may be supplied with a higher fuel mass during initial combustion events at engine start-up, and a decrease in fuel mass may be commanded when or after the engine exits a launch speed. In one example, the decrease in commanded fuel mass may occur in response to the engine launch speed exceeding the launch speed. In another example, the decrease in commanded fuel mass may occur in response to a decrease in air charge. If a decrease in fuel mass is not commanded, fuel continues to be injected as scheduled at 218.

[0039] If a decrease in fuel mass is commanded, a determination may be made at 220 as to whether the number of combustion events at which the decrease in fuel mass was commanded is less than a threshold number. The threshold number may be a predefined number corresponding to a first number of combustion events since engine start. That is, a determination is made as to whether the engine is still within the first number of combustion events since start. As discussed above, combustion events may be counted from an engine start where the engine speed is at zero (at rest), with an initial combustion event at which fueling to the engine is initiated being counted as a first combustion event (e.g., denoted as number 1).Each subsequent combustion event is counted as a single combustion event, and the combustion event count is incremented by one for each event (e.g., designated number 2, 3, 4, and so on until fuel supply to the engine is interrupted). For an initial number of consecutive combustion events since the first combustion event (e.g., for combustion events numbered 1 through n), a ratio of fuel injected via port injection relative to direct injection may be maintained, even as the fuel mass changes, to improve air-fuel mixture formation during engine start-up and overall engine start-up robustness.

[0040] Therefore, if the fuel mass decrease is commanded before the first number of combustion events have occurred, a timing for the fuel mass decrease command relative to a port injection window is determined at 222. In particular, it may be determined whether the command is received when (or after) the PFI abort angle has been reached. In one example, the PFI abort angle may not yet have been reached if the command is received earlier in the port injection window, for example, when there are more than a threshold number of crank angle degrees until an end of the port injection window. In another example, the PFI abort angle may be reached if the command is received later in the port injection window, for example, when there are fewer than a threshold number of crank angle degrees until an end of the port injection window.Thus, if a fuel command is received after the abort angle is reached, adjustments to a PFI fuel pulse may no longer be possible.

[0041] If the abort angle has not been reached, at 224, in response to a decrease in fuel mass previously commanded during the port injection window of a combustion event within the first number of combustion events, the method includes trimming the port injection fuel pulse (of the given combustion event) based on the commanded decrease in fuel mass. Additionally, a direct injection fuel pulse (of the given combustion event) is trimmed based on the trimming of the port injection fuel pulse while maintaining the previously selected split ratio of port injected fuel relative to direct injected fuel. Trimming the port injection fuel pulse includes advancing an end of the port injection injection timing / angle.Likewise, trimming the direct injection fuel pulse involves advancing one end of the direct injection injection timing / angle. As a result of the trim, the commanded fuel mass reduction is met while maintaining the initially selected split ratio.

[0042] If the abort angle has been reached, at 226, in response to a fuel mass decrease later commanded during the port injection window of a combustion event within the first number of combustion events, the method includes maintaining the port injection fuel pulse (of the given combustion event). Additionally, a direct injection fuel pulse (of the given combustion event) is not trimmed to maintain the previously selected split ratio of port injected fuel relative to direct injected fuel. Here, due to the inability to adjust the port injection pulse because the abort angle has been reached or exceeded, the direct injector pulse is maintained, thereby prioritizing maintaining the split ratio over meeting the commanded fuel mass decrease.As a result of the port or direct injection fuel pulse not being trimmed, the actual fuel mass injected into the engine cylinder (when the fuel mass reduction is commanded later in the port injection window) is higher than the commanded fuel mass. As a result of both pulses not being trimmed, the commanded fuel mass reduction is not met to allow the initially selected split ratio to be maintained.

[0043] Additionally, one or more parameters may be adjusted in response to the delivery of fuel in excess of the commanded fuel quantity. For example, intake manifold fuel puddle model dynamics for a subsequent combustion event may be adjusted in response to (and dependent upon) the actual injected fuel mass being greater than the commanded fuel mass.

[0044] In both cases, maintaining the split ratio while the fuel mass changes within an initial number of combustion events from engine start improves combustion stability during the combustion events and makes engine start more repeatable.

[0045] In further examples, it may be further determined at 216 whether an increase in fuel mass has been commanded. In one example, a higher fuel mass may be supplied to the engine during the initial combustion events at engine start-up. For example, the increase in commanded fuel mass may occur in response to the engine speed being below the start-up speed. In another example, the increase in commanded fuel mass may occur in response to an increase in air charge. If an increase in fuel mass is commanded and the combustion event number at which the increase in fuel mass was commanded is less than the threshold number (e.g.,less than a predefined number corresponding to a first number of combustion events counted since engine start), then the ratio of fuel injected via port injection relative to direct injection may be maintained even as fuel mass changes to improve air-fuel mixture formation during engine start-up and overall engine start-up robustness. Specifically, in response to the commanded increase in fuel mass before the first number of combustion events has occurred, a timing of the fuel mass increase relative to a port injection window is determined to determine whether the command was received before or after the PFI abort angle is reached.If the command to increase fuel mass was received earlier in the port injection window before the PFI cutoff angle was reached, the port injection fuel pulse (of the given combustion event) may be extended based on the commanded increase in fuel mass, for example, by delaying an end of the port injection injection timing / angle. In addition, a direct injection fuel pulse (of the given combustion event) is extended, for example, by delaying an end of the direct injection injection timing / angle, based on the port injection fuel pulse adjustment, to maintain the previously selected split ratio of port-injected fuel relative to direct-injected fuel while meeting the increased fuel demand.However, if the command to increase fuel mass is received after the cutoff angle has been reached, the port injection fuel pulse (of the given combustion event) is maintained, and further, the direct injection fuel pulse (of the given combustion event) is also maintained to maintain the previously selected split ratio of port injected fuel relative to direct injected fuel. Here, due to the inability to adjust the port injection pulse because the cutoff angle has been reached or exceeded, the direct injector pulse is maintained, thereby giving priority to maintaining the split ratio over meeting the commanded fuel mass increase.As a result, the actual fuel mass injected into the engine cylinder (when the fuel mass increase is commanded later in the port injection window) is lower than the commanded fuel mass. Furthermore, in response to delivering fuel at a deficit relative to the requested fuel, one or more parameters may be adjusted. For example, a port fuel pool model dynamics for a subsequent combustion event may be adjusted in response to (and dependent upon) the actual injected fuel mass being less than the commanded fuel mass. Furthermore, a port and direct injection fuel pulse may be extended for a subsequent combustion event to compensate for the fuel deficit while maintaining the split ratio for that combustion event.

[0046] Returning to 220, if the decrease (or increase) in fuel mass is commanded after the first number of combustion events has elapsed, at 230, as at 222, a timing for the decrease in fuel mass command relative to the port injection window is determined. In particular, it may be determined whether the command is received when (or after) the PFI abort angle has been reached. Thus, after the first number of combustion events has elapsed, control may again prioritize the commanded fuel mass over the commanded split ratio. This is because the effect of changing the split ratio on engine crankability may be less pronounced after the first number of combustion events have elapsed and when the engine has completed the start-up speed.

[0047] If the abort angle has not been reached, at 232, in response to a decrease in fuel mass commanded earlier during the port injection window of a combustion event after the first number of combustion events, the method includes trimming one or both of the port injection fuel pulse and the direct injection fuel pulse (of the given combustion event) based on the commanded decrease in fuel mass. As an example, the PFI fuel pulse may be trimmed while maintaining the DI fuel pulse. Trimming the port injection fuel pulse may include advancing an end of the port injection injection timing / angle.Trimming can be performed so that the actual fuel mass delivered to the cylinder equals the commanded (reduced) fuel mass without having to maintain the initially selected split ratio for that combustion event.

[0048] Likewise, in response to an increase in fuel mass previously commanded during the port injection window of a combustion event after the first number of combustion events, the method includes extending one or both of the port injection fuel pulse and the direct injection fuel pulse (of the given combustion event) based on the commanded increase in fuel mass. As an example, the PFI fuel pulse may be extended while maintaining the DI fuel pulse by delaying an end of the port injection injection timing / angle. The extending may be performed such that the actual fuel mass delivered to the cylinder equals the commanded (increased) fuel mass without needing to maintain the initially selected split ratio for that combustion event.As another example, the DI fuel pulse may be extended while maintaining the PFI fuel pulse by delaying an end of the direct injection injection timing / angle. The extending may be performed such that the actual fuel mass delivered to the cylinder equals the commanded (increased) fuel mass without requiring the initial selection of the split ratio for that combustion event. As another example, the PFI and DI fuel pulses may each be extended by delaying an end of the direct injection injection timing / angle such that the actual fuel mass delivered to the cylinder equals the commanded (increased) fuel mass without requiring the initial selection of the split ratio for that combustion event.In one example, as the commanded fuel mass increases (after the threshold number of combustion events has elapsed), the DI and PFI fuel pulse may be adjusted to either maintain or decrease the split ratio of port injected fuel to direct injected fuel.

[0049] If the abort angle has been reached, at 234, in response to a decrease in fuel mass later commanded during the port injection window of a combustion event after the first number of combustion events, the method includes maintaining the port injection fuel pulse (of the given combustion event) while trimming the direct injection fuel pulse (of the given combustion event) to provide the commanded fuel mass. Trimming the direct injection fuel pulse may include advancing an end of the direct injection injection timing / angle.Here, due to the inability to adjust the port injection pulse because the cutoff angle is reached or exceeded, the direct injector pulse is trimmed, thereby giving priority to meeting the commanded fuel mass reduction over maintaining the split ratio.

[0050] Additionally, one or more parameters may be adjusted in response to the delivery of fuel in excess of the commanded fuel quantity. For example, intake manifold fuel puddle model dynamics for a subsequent combustion event may be adjusted in response to (and dependent upon) the actual injected fuel mass being greater than the commanded fuel mass.

[0051] Likewise, in response to a fuel mass increase commanded later during the port injection window of a combustion event after the first number of combustion events, the port injection fuel pulse (of the given combustion event) is maintained while the direct injection fuel pulse (of the given combustion event) is extended by delaying an end of the direct injection injection timing / angle. Here, due to the inability to adjust the port injection pulse because the cutoff angle is reached or exceeded, the direct injector pulse is extended, thereby prioritizing meeting the commanded fuel mass increase over maintaining the split ratio. Specifically, this results in the port injected:direct injected fuel split ratio being reduced.

[0052] Additionally, in response to the delivery of fuel with a deficit relative to the requested fuel, one or more parameters may be adjusted. For example, a manifold fuel puddle model dynamics for a subsequent combustion event may be adjusted in response to (and dependent upon) the actual injected fuel mass being less than the commanded fuel mass. Additionally, a manifold and direct injection fuel pulse for a subsequent combustion event may be extended to compensate for the fuel deficit while maintaining the split ratio for that combustion event.

[0053] In both cases, by meeting the commanded fuel mass regardless of the split ratio, as the fuel mass changes after the first number of combustion events since engine start, engine performance is improved and the driver demand is better met.

[0054] Thus, due to trimming of the port and / or direct injection pulse, the actual fuel mass injected into the engine cylinder when the decrease in fuel mass is commanded later in the port injection window after the first number of combustion events is higher than the actual fuel mass injected when the decrease in fuel mass is commanded later in the port injection window within the first number of combustion events.

[0055] Examples of fuel pulse settings are now shown with reference to Fig. 3 shown. Fig. represents changes in engine speed in plot 302, a commanded fuel mass in plot 304, and a delivered fuel pulse in plot 306. In plot 306, for each combustion event, a portion of the total fuel mass delivered as a port injection fuel pulse is represented by a solid bar, while the portion of the total fuel mass delivered as a direct injection fuel pulse is represented by a hatched bar. All plots are plotted over a number of combustion events that increase from left to right along the x-axis. The numbering of consecutive combustion events after an initial engine start is represented as starting with n1, where n1 represents a first combustion event of the initial engine start from rest.A numbering of consecutive combustion events after a second subsequent engine start is represented as starting with m1, where m1 represents a first combustion event of the second engine start from rest.

[0056] Diagram 302 shows an increase in engine speed from zero in response to an initial engine start. Here, the initial engine start is a cold start, where the engine is started while the engine temperature is lower. A first combustion event n1 of the initial engine start from rest is initiated by injecting fuel into the cylinder at a first split ratio of port-injected fuel to direct-injected fuel. Since the initial start is a cold start, the first split ratio includes a higher proportion of port-injected fuel relative to direct-injected fuel to reduce cold-start exhaust emissions. In one example, the first split ratio includes 60% PFI: 40% DI.

[0057] The commanded fuel mass (plot 304) is adjusted at each subsequent combustion event to provide the depicted engine speed profile (plot 302). Specifically, the commanded fuel mass is increased during an initial portion of engine cranking while the engine is being started, and then decreased. After a threshold number of combustion events, depicted here as a non-limiting example at combustion event n21, the engine reaches the starting speed and cranking is terminated. Therefore, between n1 and n21, the engine controller prioritizes maintaining the selected split ratio over ensuring that the actual fuel mass meets the commanded fuel mass.

[0058] At combustion event n14, an initial reduction in fuel mass is commanded. The command for n14 is received during the port injection window, before the cutoff angle is reached. Consequently, the controller meets both the split ratio and the commanded fuel mass by advancing one end of injection of each of the PFI fuel pulse (solid bar) and the DI fuel pulse (hatched bar).

[0059] At combustion event n15, a second reduction in fuel mass is commanded. The command for n15 is received during the port injection window, after the abort angle is reached. Because this reduction in fuel mass is received before the threshold number of combustion events has elapsed (before n21), the controller first aims to maintain the split ratio. Because the command is received too late in the port injection window and adjustments to the PFI pulse are not possible, the PFI fuel pulse is maintained while the DI pulse is also maintained to maintain the selected split ratio. As a result, more fuel is delivered than commanded (shown at dashed line 307).The same occurs for combustion event n16, with a resulting addition of excess fuel (shown at dashed line 308) while maintaining the split ratio. In this way, the selected split ratio is maintained until n21 is reached, even if the fuel mass changes, enabling improved engine startability.

[0060] After n21, the split ratio can be changed as engine operating conditions change. For example, a higher proportion of DI can be applied at higher engine speeds and higher load. Furthermore, after n21, even if the fuel mass changes, the fuel pulses are adjusted so that the actual fuel mass meets the commanded fuel mass while allowing deviations from the target split ratio. For example, after n21, in response to a decrease in the commanded fuel mass, the end of injection of each of the PFI and DI fuel pulses is brought forward if the command is earlier in the port injection window, and the end of injection of only the DI fuel pulse is brought forward if the command is later in the port injection window. At n56, a final combustion event occurs before fueling is interrupted and the engine coasts to idle.

[0061] Diagram 302 shows a subsequent increase in engine speed from zero in response to a second engine cranking after the first engine cranking. Because a short period of time has elapsed since the engine was shut down after n56, the second engine cranking is a warm start, with the engine being cranked while the engine temperature is higher. A first combustion event m1 upon initial engine cranking from rest is initiated by injecting fuel into the cylinder at a second split ratio of port-injected fuel to direct-injected fuel. Because the second cranking is a warm start, the second split ratio includes a smaller proportion of port-injected fuel relative to direct-injected fuel. In one example, the first split ratio includes 30% PFI: 70% DI.

[0062] The commanded fuel mass (plot 304) is adjusted at each subsequent combustion event to provide the depicted engine speed profile (plot 302). Specifically, the commanded fuel mass is increased during an initial portion of engine cranking while the engine is being started, and then decreased. After a threshold number of combustion events, depicted here as a non-limiting example at combustion event m21, the engine reaches the starting speed and cranking is terminated. Therefore, between m1 and m21, the engine controller prioritizes maintaining the selected split ratio over ensuring that the actual fuel mass meets the commanded fuel mass.It is understood that in alternative examples, the threshold number of combustion events over which the split ratio is maintained may differ for a warm start versus a cold start of the engine.

[0063] At combustion event m14, an initial reduction in fuel mass is commanded. The command for m14 is received during the port injection window, before the cutoff angle is reached. Consequently, the controller meets both the split ratio and the commanded fuel mass by advancing one end of injection of each of the PFI fuel pulse (solid bar) and the DI fuel pulse (hatched bar).

[0064] At combustion event m15, a second reduction in fuel mass is commanded. The command for m15 is received during the port injection window, after the abort angle is reached. Because this reduction in fuel mass is received before the threshold number of combustion events has elapsed (before n21), the controller first aims to maintain the split ratio. Because the command is received too late in the port injection window and adjustments to the PFI pulse are not possible, the PFI fuel pulse is maintained while the DI pulse is also maintained to maintain the selected split ratio. As a result, more fuel is delivered than commanded (shown at dashed line 309).The same occurs for combustion event n16, with a resulting addition of excess fuel (shown at dashed line 310) while maintaining the split ratio. In this way, the selected (second) split ratio is maintained until m21 is reached, even if the fuel mass changes, enabling improved engine startability.

[0065] After m21, the split ratio can be changed as engine operating conditions change. For example, a higher proportion of DI can be applied at higher engine speeds and higher load. Furthermore, after m21, even if the fuel mass changes, the fuel pulses are adjusted so that the actual fuel mass meets the commanded fuel mass while allowing deviations from the target split ratio. For example, after m21, in response to a decrease in the commanded fuel mass, the end of injection of each of the PFI and DI fuel pulses is brought forward if the command is earlier in the port injection window, and the end of injection of only the DI fuel pulse is brought forward if the command is later in the port injection window.

[0066] In an alternative example, during cold start, for the threshold number of combustion events that occur consecutively since an initial combustion event, the controller may maintain the selected ratio of fuel delivered via port injection relative to direct injection as the commanded fuel mass decreases. This may cause the actual delivered fuel mass to differ from the commanded fuel mass. In comparison, during warm start, for the threshold number of combustion events that occur consecutively since an initial combustion event, the controller may maintain the actual fuel mass equal to the commanded fuel mass as the commanded fuel mass decreases. This may cause the actual delivered fuel split ratio to differ from the selected / commanded fuel split ratio.

[0067] For example, over a number of combustion events occurring consecutively since a first combustion event at a first engine start-up from rest, a controller may maintain a ratio of port-injected relative to direct-injected fuel as a commanded fuel mass decreases. In comparison, over the number of combustion events occurring consecutively since the first combustion event at a second engine start-up from rest, adjusting the ratio of port-injected relative to direct-injected fuel while maintaining the actual fuel mass at the commanded fuel mass as the commanded fuel mass decreases.During the initial engine start, the actual fuel mass may not be maintained at the commanded fuel mass if the commanded fuel mass decreases. Specifically, during the initial engine start, the actual fuel mass injected into an engine cylinder may be higher than the commanded fuel mass. Furthermore, during the initial engine start, a decrease in the commanded fuel mass is commanded earlier in a port injection window compared to the decrease in the commanded fuel mass commanded during the second engine start.Maintaining the ratio during engine cranking may include advancing an end of the port injection fuel pulse based on the commanded fuel mass reduction and advancing an end of a direct injection fuel pulse based on advancing the end of the port injection fuel pulse. Adjusting the ratio while maintaining the actual fuel mass may include maintaining the end of the port injection fuel pulse and maintaining the direct injection fuel pulse while disregarding the commanded fuel mass reduction.

[0068] It will be understood that while the example in Fig.3 with reference to a commanded decrease in fuel mass, similar adjustments may be performed in response to a commanded increase in fuel mass. For example, in response to a commanded increase in fuel mass received before a threshold number of combustion events, the DI and PFI fuel pulses are adjusted to maintain the split ratio even if the commanded fuel mass is not provided (e.g., the fuel mass may be less than desired). In response to a commanded increase in fuel mass received after a threshold number of combustion events, the DI and PFI fuel pulses are adjusted to provide the commanded fuel mass even if the commanded split ratio is not met (e.g., the split ratio may be less than desired).

[0069] This improves the quality of engine starting. The technical effect of maintaining a constant fuel split ratio for a defined number of consecutive combustion events since the initial combustion event during engine start-up from idle (zero engine speed) is that the air-fuel mixture formation during engine start-up can be improved, enabling greater combustion stability. By reducing the variability of the fuel split ratio, deviations from a calibrated ignition timing are reduced, thereby improving engine start-up performance.By allowing a split ratio commanded for the defined number of combustion events since an initial combustion event at engine start-up to be maintained, while allowing deviations in the actual fuel mass from the commanded fuel mass, engine start-up variability can be reduced by reducing fuel mass during engine ramp-up and start-up. Overall, engine start-up becomes more repeatable.

[0070] An example method for an engine includes: for a first number of consecutive combustion events, counted from a first combustion event upon engine startup from a rest state, supplying fuel to each of a port-injected and direct-injected engine; and maintaining a ratio of fuel injected via port injection relative to direct injection during the first number of combustion events, even as the fuel mass changes. The above example further includes, additionally or optionally, after the first number of consecutive combustion events have elapsed, adjusting the ratio of fuel injected via port injection relative to direct injection based on driver demand while maintaining a commanded fuel mass, even as the fuel mass changes.Additionally or optionally, in any or all of the above examples, the ratio of fuel injected via port injection relative to direct injection is maintained or decreased as the commanded fuel mass increases. Additionally or optionally, in any or all of the above examples, maintaining includes, in response to a decrease in fuel mass previously commanded during a port injection window of a combustion event of the first number of combustion events, trimming a port injection fuel pulse based on the decrease in fuel mass and trimming a direct injection fuel pulse of the combustion event based on the trimming of the port injection fuel pulse while maintaining the ratio.Additionally or optionally, in any or all of the above examples, maintaining further includes, in response to the decrease in fuel mass commanded later during the port injection window of the combustion event, maintaining the port injection fuel pulse and not trimming the direct injection fuel pulse to maintain the ratio. Additionally or optionally, in any or all of the above examples, earlier during the port injection window includes the period of time while there are more than a threshold number of crank angle degrees to an end of the port injection window, and later during the port injection window includes the period of time while there are fewer than the threshold number of crank angle degrees to the end of the port injection window.Additionally or optionally, in any or all of the above examples, the fuel mass actually injected when the decrease in fuel mass is commanded later during the port injection window is greater than a commanded fuel mass. Additionally or optionally, in any or all of the above examples, the method further comprises adjusting intake manifold fuel pool model dynamics for a subsequent combustion event in response to the actual injected fuel mass being greater than the commanded fuel mass. Additionally or optionally, in any or all of the above examples, trimming the direct injection fuel pulse includes advancing an end of the injection angle of the direct injection fuel pulse.Additionally or optionally, in any or all of the above examples, the ratio is based on an engine temperature at engine start-up, wherein the ratio includes a higher ratio of port injected fuel to direct injected fuel as the engine temperature decreases during the first combustion event at engine start-up.

[0071] Another example of an engine method includes: over a number of combustion events occurring sequentially since a first combustion event at a first engine start-up from rest, maintaining a ratio of fuel delivered via port injection relative to direct injection as a commanded fuel mass decreases; and over the number of combustion events occurring sequentially since the first combustion event at a second engine start-up from rest, adjusting the ratio of fuel delivered via port injection relative to direct injection while maintaining the actual fuel mass equal to the commanded fuel mass as the commanded fuel mass decreases.Additionally or optionally, in the above example, during the first engine start, the actual fuel mass is not maintained at the commanded fuel mass as the commanded fuel mass decreases. Additionally or optionally, in any or all of the above examples, during the first engine start, a decrease in the commanded fuel mass is commanded earlier in a port injection window compared to the decrease in the commanded fuel mass commanded during the second engine start.Additionally or optionally, in any or all of the above examples, maintaining the ratio during engine cranking includes advancing an end of the port injection fuel pulse based on the commanded fuel mass reduction and advancing an end of a direct injection fuel pulse based on advancing the end of the port injection fuel pulse. Additionally or optionally, in any or all of the above examples, adjusting the ratio while maintaining the actual fuel mass includes maintaining the end of the port injection fuel pulse and maintaining the direct injection fuel pulse while disregarding the commanded fuel mass reduction.Additionally or optionally, in any or all of the above examples, upon initial engine start-up, the actual fuel mass injected into an engine cylinder is higher than the commanded fuel mass.

[0072] Another example of an engine fuel system includes: an engine cylinder; a direct fuel injection device coupled to the cylinder; a port fuel injection device coupled to the cylinder; and a controller configured with computer-readable instructions stored in non-transitory memory to: restart an engine with fuel provided to the cylinder at a first combustion event from the idle state of each of the port fuel injection device and the direct fuel injection device in a ratio; adjusting a fuel mass commanded to the cylinder based on a combustion event number from the first combustion event until a threshold number of combustion events have elapsed; when a commanded decrease in fuel mass is received within a threshold number of crank angle degrees of a port fuel injection window,Adjusting each of a port injection fuel pulse and a direct injection fuel pulse to provide the commanded reduction in fuel mass while simultaneously adjusting the ratio; and if the commanded reduction in fuel mass is received outside the threshold number of crank angle degrees of the port injection window, maintaining each of the port injection fuel pulse and the direct injection fuel pulse to maintain the ratio while simultaneously providing an actual fuel mass,which is greater than the commanded fuel mass. Additionally or optionally, in the above example, adjusting each of the port injection fuel pulse and the direct injection fuel pulse includes advancing an end of the injection timing of each of the port injection fuel pulse and the direct injection fuel pulse. Additionally or optionally, in any or all of the above examples, maintaining each of the port injection fuel pulse and the direct injection fuel pulse includes maintaining the end of the injection timing of each of the port injection fuel pulse and the direct injection fuel pulse. In any or all of the above examples, the ratio is additionally or optionally based on an engine temperature estimated prior to the first combustion event at engine start-up.wherein the ratio includes a higher proportion of manifold injected fuel relative to directly injected fuel as engine temperature decreases.

[0073] It should be noted that the exemplary control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and executed by the control system, including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. Thus, various illustrated acts, operations, and / or functions may be performed in the illustrated order, in parallel, or in some cases, omitted.Likewise, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but rather is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy employed. Further, the described acts, operations, and / or functions may graphically represent code to be programmed into non-transitory memory of the computer-readable storage medium in the engine control system, in which the described acts are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.

[0074] It is understood that the configurations and routines disclosed herein are exemplary in nature and that these specific embodiments are not to be considered limiting, as numerous variations are possible. For example, the above technology may be applied to V6, I4, I6, V12, horizontally opposed 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.

[0075] The following claims particularly set forth certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims are to be construed as including the inclusion of one or more such elements and neither requiring nor excluding two or more such elements. Further combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by filing new claims in this or a related application.Such claims, whether broader, narrower, equal, or different in scope than the original claims, are further considered to be included within the subject matter of the present disclosure.

Claims

[1] A method for an engine, comprising: for a first number of consecutive combustion events, counted from a first combustion event when starting the engine from a rest state, supplying fuel to an engine with both port and direct injection; and Maintaining a ratio of fuel injected via port injection relative to fuel injected via direct injection during the first number of combustion events, even if the fuel mass changes. [2] The method of claim 1, further comprising, after the first number of consecutive combustion events have elapsed, adjusting the ratio of fuel injected via port injection relative to direct injection based on driver demand while maintaining a commanded fuel mass even as the fuel quantity changes. [3] The method of claim 2, wherein the ratio of fuel injected via port injection relative to direct injection is maintained or decreased as the commanded fuel mass increases. [4] The method of claim 1, wherein maintaining includes, in response to a decrease in fuel mass previously commanded during a port injection window of a combustion event of the first number of combustion events, trimming a port injection fuel pulse based on the decrease in fuel mass and trimming a direct injection fuel pulse of the combustion event based on the trimming of the port injection fuel pulse while maintaining the ratio. [5] The method of claim 4, wherein maintaining further comprises, in response to the decrease in fuel mass later commanded during the port injection window of the combustion event, maintaining the port injection fuel pulse and not trimming the direct injection fuel pulse to maintain the ratio. [6] The method of claim 5, wherein earlier during the port injection window includes the period of time while there are more than a threshold number of crank angle degrees until an end of the port injection window, and wherein later during the port injection window includes the period of time while there are fewer than the threshold number of crank angle degrees until the end of the port injection window. [7] The method of claim 5, wherein the fuel mass actually injected when the decrease in fuel mass is commanded later during the port injection window is greater than a commanded fuel mass. [8] The method of claim 7, further comprising adjusting the intake manifold fuel pool model dynamics for a subsequent combustion event in response to the actual injected fuel mass being greater than the commanded fuel mass. [9] The method of claim 4, wherein trimming the direct injection fuel pulse includes advancing an end of an injection angle of the direct injection fuel pulse. [10] The method of claim 1, wherein the ratio is based on an engine temperature at engine start-up, the ratio including a higher ratio of port injected fuel to direct injected fuel as the engine temperature decreases during the first combustion event at engine start-up. [11] An engine fuel system comprising: an engine cylinder, a direct injection device coupled to the cylinder; a port fuel injector coupled to the cylinder; and a controller having computer-readable instructions stored in non-volatile memory for the following: restarting an engine with fuel supplied to the cylinder in a first combustion event from the rest state by each of the port fuel injector and the direct fuel injector in a ratio; Setting a fuel mass commanded to the cylinder based on a combustion event count from the first combustion event until a threshold number of combustion events has elapsed; when a commanded reduction in fuel mass is received within a threshold number of crank angle degrees of a port injection window, adjusting one port injection fuel pulse and one direct injection fuel pulse, respectively, to provide the commanded reduction in fuel mass while simultaneously adjusting the ratio; and if the commanded decrease in fuel mass is received outside the threshold number of crank angle degrees of the port injection window, maintaining each of the port injection fuel pulse and the direct injection fuel pulse to maintain the ratio while providing an actual fuel mass greater than the commanded fuel mass. [12] The system of claim 11, wherein adjusting each of the port injection fuel pulse and the direct injection fuel pulse includes advancing an end of the injection timing of each of the port injection fuel pulse and the direct injection fuel pulse. [13] The system of claim 12, wherein maintaining each of the port injection fuel pulse and the direct injection fuel pulse includes maintaining the end of injection timing of each of the port injection fuel pulse and the direct injection fuel pulse. [14] The method of claim 11, wherein maintaining the ratio includes advancing an end of the port injection fuel pulse based on the commanded fuel mass reduction and advancing an end of the direct injection fuel pulse based on advancing the end of the port injection fuel pulse. [15] The system of claim 11, wherein the ratio is based on an engine temperature estimated prior to the first combustion event at engine start-up, the ratio including a higher proportion of port injected fuel relative to direct injected fuel as the engine temperature decreases.

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