FUEL INJECTION PROCESS

Abstract

Method comprising: during an engine cold start, injecting, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the direct injectors reaching a minimum direct injection pulse width, reducing a port-to-direct fuel injection ratio.

Description

Area

[0001] The present description generally relates to methods and systems for controlling a multi-injector per cylinder system associated with an internal combustion engine. Background and brief description

[0002] Engines may be configured with various fuel systems to deliver a desired amount of fuel to a combustion chamber. Example fuel systems may include port fuel injectors for delivering fuel into an intake passage upstream of a combustion chamber and direct fuel injectors for delivering fuel directly into the combustion chamber. Still other engines may be configured with a multi-fuel injection system, including, for example, each of a port fuel injector and a direct fuel injector for each engine cylinder.

[0003] An exemplary approach to using both port and direct injection during engine cranking involves using port and split direct injection, as described, for example, by Surnilla et al. in US 2014 / 0297159 A1. Split fuel injection is applied during cranking and starting, such that fuel with a lower alcohol content is injected through a port and fuel with a higher alcohol content is injected directly as one or more injections.

[0004] US 2015 / 0 204 266 A1 and US 2009 / 0 308 367 A1 describe further methods and systems for controlling an engine, in particular during cold starting of the engine.

[0005] However, the inventors of the present invention have recognized potential problems with an approach such as that in US 2014 / 0 297 159 A1. For example, as operating conditions change, the desired relative amounts of the port-to-direct injection ratio, as well as the ratio of the multiple direct injections, also change. It can be difficult to predict such variations under all operating conditions, particularly when an operator intervenes with pedal adjustments during cranking or not. As a result, one or more of the injections may reach a minimum pulse width limit of the injector, unexpectedly causing undesirable enrichment. And even if such situations can be detected, it can be difficult to adequately schedule adjustments to compensate with the least amount of disruption to vehicle operation and emissions.

[0006] The object of the present invention is to improve the cold-start behavior of an internal combustion engine 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, the issues described above may be addressed by a method comprising: during an engine cold start, injecting, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the direct injections reaching a minimum direct injection pulse width, reducing a ratio of the port to direct fuel injection.

[0008] In this way, it is possible to appropriately control not only the port-to-direct fuel injection ratio, but also the ratio of the split direct injections. For example, if multiple direct injections reach the minimum direct injection pulse width, the method can reduce the port-to-direct fuel injection ratio while adjusting a ratio of the direct injections to bring an amount of each of the direct injections closer together while maintaining a total fuel injection amount for the cycle. This allows the effectiveness of the split direct injections in engine start-up performance to be maintained.In contrast, if only one of the direct injections reaches the minimum direct injection pulse width, the method can reduce the port-to-direct fuel injection ratio while maintaining a relative ratio of the direct injections and a total fuel injection quantity for the cycle. The longer the relative ratio of the direct injections can be maintained, the better engine emissions can be managed during the transition, as the unadjusted ratios may have been determined to provide the optimal balance of emissions and fuel economy.Such operation may be particularly relevant when the port fuel injector is connected to a high pressure port fuel injection rail that is at least partially pressurized by the high pressure fuel pump that is also used to pressurize the direct injection fuel rail, although it is also relevant for lower pressure port fuel injection rails that are pressurized solely by a low pressure lift pump driven by an electric motor.

[0009] A technical effect of controlling the port-to-direct injection ratio and / or the split direct injection ratio may be to enable control of engine emissions and stable engine operation even when varying conditions unexpectedly cause one of the fuel injections to reach a minimum allowable pulse width.

[0010] It should be 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 in the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve disadvantages mentioned above or in any part of this disclosure. Brief description of the drawings Fig. 1 schematically illustrates an exemplary embodiment of a cylinder of an internal combustion engine. Fig. 2 schematically illustrates an exemplary embodiment of a fuel system associated with an engine having dual fuel injection capabilities. Fig. 3 shows a high-level exemplary flow diagram for operating an internal combustion engine with an intake pipe fuel injection system and a direct fuel injection system according to the present disclosure. Fig. 4-5 show exemplary flow diagrams for reducing minimum pulse width problems. Fig. 6 shows an exemplary table of empirically determined intake pipe and direct fuel fractions (DI / PFI split ratio). Fig. 7 shows a graphical representation of an exemplary opening and closing of a direct fuel injection device to maintain a minimum fuel injection mass from the direct injection device within a range according to the present disclosure. Detailed Description

[0011] The present invention relates to systems and methods for operating port and direct fuel injectors in an engine system configured with a multi-fuel injection system, such as a dual injection system with only one port and one direct fuel injector per cylinder.

[0012] In a non-limiting example, the engine may be as in Fig. 1. Furthermore, additional components of a connected fuel system are shown in Fig. 2. A motor controller may be configured to perform a control routine in combination with sensors and actuators such as those in Fig. 1-2, including routines like in Fig. 3-5. For example, the routine from Fig. 3 an overall method for controlling fuel injection using an additional operation such as compensation to achieve minimum pulse widths in Fig. 4-5 and in the table in Fig. 6. The routines make various adjustments, where necessary, to a desired ratio not only of the port-to-direct injection, but also of the direct injection ratio. An example timeline for operating in accordance with the above methods and systems is shown in Fig. 7 shown.

[0013] Now, with reference to Fig. 1 shows a schematic diagram of a cylinder of the multi-cylinder engine 10, which may be included in a propulsion system of an automobile. The engine 10 may be controlled at least in part by a control system including the controller 12 and by input from a vehicle operator 132 via an input device 130. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The combustion chamber (i.e., cylinder) 30 of the engine 10 may include the combustion chamber walls 32 with the piston 36 positioned therein. In some embodiments, the face of the piston 36 within the cylinder 30 may include a bowl. The piston 36 may be coupled to the crankshaft 40 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft.The crankshaft 40 may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system. Furthermore, a starter motor may be coupled to the crankshaft 40 via a flywheel to enable a starting operation of the engine 10.

[0014] Combustion chamber 30 may receive intake air from intake manifold 44 via intake passage 42 and exhaust combustion exhaust gases via exhaust passage 48. Intake manifold 44 and exhaust passage 48 may be selectively communicated with combustion chamber 30 via a respective intake valve 52 and exhaust valve 54. In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0015] The intake valve 52 may be controlled by the controller 12 via the intake cam 51. Similarly, the exhaust valve 54 may be controlled by the controller 12 via the exhaust cam 53. Alternatively, the variable valve actuator may be electric, electro-hydraulic, or any other conceivable mechanism to enable valve actuation. Under some conditions, the controller 12 may vary the signals provided to the actuators 51 and 53 to control the opening and closing of the corresponding intake and exhaust valves. The position of the intake valve 52 and exhaust valve 54 may be determined by valve position sensors 55 and 57, respectively.In alternative embodiments, one or more of the intake and exhaust valves may be actuated by one or more cams, and may utilize one or more of the cam profile adjustment (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems to vary valve operation. For example, cylinder 30 may alternatively include an electronic valve timing controlled intake valve and an exhaust valve controlled by cam timing systems that include CPS and / or VCT.

[0016] In some embodiments, each cylinder of the internal combustion engine 10 may be configured with one or more fuel injectors to provide fuel thereto. As a non-limiting example, cylinder 30 is shown as including two injectors 166 and 170. Injector 166 is shown as being directly coupled to cylinder 30 to inject fuel directly therein proportional to the pulse width of a signal FPW-1 received from controller 12 via an electronic driver 168. Thus, injector 166 provides direct injection (hereinafter referred to as "DI") of fuel into combustion cylinder 30. Thus, fuel injector 166 is a direct fuel injector in communication with cylinder 30. While FIG. Fig. 1 illustrates the injector 166 as a side injector, however, it may also be located above the piston, such as near the position of the spark plug 92. 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. Fuel may be delivered to the fuel injector 166 via the high-pressure fuel system 172, including a fuel tank, fuel pumps, a fuel rail, and a driver 168.Alternatively, the fuel may be delivered at a lower pressure by a single-stage fuel pump, in which case the timing of the direct fuel injection during the compression stroke may be more limited than when using a high-pressure fuel system. Further, although not shown, the fuel tank may include a pressure transducer that provides a signal to the controller 12. The injectors are driven by signals that cause the injector pintle to open and close via solenoids. The pulse signal sent to the injector controls its opening time, closing time, etc. The width of the opening is generally associated with a desired amount of fuel and may be referred to as a pulse width.Injectors may have minimum pulse widths below which the injector will not open properly or fully, thereby reducing control of the fuel injection quantity.

[0017] The fuel injector 170 is shown disposed in the intake passage 42 (e.g., in the intake manifold 44) ​​rather than in the cylinder 30 in a configuration that provides so-called port fuel injection (hereinafter referred to as "PFI") into the intake passage downstream of the cylinder 30. Fuel may be delivered from the intake passage to the cylinder 30. Thus, the fuel injector 170 is a port fuel injector in communication with the cylinder 30. The injector 170 may inject fuel proportional to the pulse width of a signal FPW-2 received from the controller 12 via the electronic driver 171. Fuel may be delivered to the fuel injector 170 through the fuel system 172.

[0018] Fuel may be delivered to the cylinder by both injectors during a single cylinder stroke. For example, each injector may provide a portion of the total fuel injection combusted in cylinder 30. Further, the distribution and / or relative amount of fuel provided by each injector may vary with operating conditions as described below. The relative distribution of the total injected fuel among injectors 166 and 170 may be referred to as a first injection ratio.For example, injecting a larger amount of fuel for a combustion event via the (port) injector 170 may be an example of a higher first port-to-direct injection ratio, whereas injecting a larger amount of fuel for a combustion event via the (direct) injector 166 may be a lower first port-to-direct injection ratio. It should be noted that these are merely examples of different injection ratios, and various other injection ratios may be used. Furthermore, it should be understood that the port-injected fuel may be injected during an open intake valve event, a closed intake valve event (e.g.,substantially before an intake stroke, for example, during an exhaust stroke) and during both open and closed intake valve operation. Similarly, directly injected fuel may be delivered, for example, during an intake stroke and partly during a preceding exhaust stroke, during the intake stroke, and partly during the compression stroke. Furthermore, directly injected fuel may be delivered in the form of a single injection or multiple injections. These may include multiple injections during the compression stroke, multiple injections during the intake stroke, or a combination of some direct injections during the compression stroke and some during the intake stroke.When multiple direct injections are performed, the relative distribution of the total injected fuel conducted between an intake stroke (direct) injection and a compression stroke (direct) injection can be referred to as a second injection ratio, also referred to herein as a division ratio. For example, a division ratio (or second injection ratio) of 1 can include all of the directly injected fuel that is delivered during the intake stroke and none of the directly injected fuel that is delivered during the compression stroke. As another example, a division ratio (or second injection ratio) of 0 can include all of the directly injected fuel that is delivered during the compression stroke and none of the directly injected fuel that is delivered during the intake stroke.As yet another example, a split ratio (or second injection ratio) of 0.5 may include 50% of the direct injected fuel delivered on the intake stroke and the remaining 50% of the direct injected fuel delivered on the compression stroke. For example, injecting a larger amount of the direct injected fuel for a combustion event during an intake stroke may be an example of a higher second intake stroke direct injection ratio, while injecting a larger amount of the fuel for a combustion event during a compression stroke may be an example of a lower second intake stroke direct injection ratio. Note that these are merely examples of different injection ratios, and various other injection ratios may be used.

[0019] In principle, even during a single combustion event, injected fuel can be injected at different times from a port and direct fuel injector. Furthermore, for a single combustion event, multiple injections of the supplied fuel can be performed per stroke. The multiple injections can be performed during the compression stroke, intake stroke, or any suitable combination thereof.

[0020] As described above, Fig. 1 represents only one cylinder of a multi-cylinder engine. In principle, each cylinder can equally include its own set of intake / exhaust valves, fuel injector(s), spark plug, etc.

[0021] 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.

[0022] The fuel system 172 may include one or more fuel tanks. In embodiments where the fuel system 172 includes multiple fuel tanks, the fuel tanks may hold fuel with the same fuel qualities or may hold fuel with different fuel qualities, such as different fuel compositions. These differences may include different alcohol content, different octane rating, different heat of vaporization, different fuel blends, and / or combinations thereof, etc. In one example, fuels with different alcohol content could include gasoline, ethanol, methanol, or alcohol blends such as E85 (consisting of approximately 85% ethanol and 15% gasoline) or M85 (consisting of approximately 85% methanol and 15% gasoline).Other alcohol-containing fuels could be a mixture of alcohol and water, a mixture of alcohol, water, and gasoline, etc. In some examples, the fuel system 172 may include a fuel tank holding a liquid fuel, such as gasoline, and also include a fuel tank holding a gaseous fuel, such as CNG. The fuel injectors 166 and 170 may be configured to inject fuel from the same fuel tank, from different fuel tanks, from a plurality of the same fuel tanks, or from an overlapping set of fuel tanks. The fuel system 172 may include a lower pressure fuel pump 175 (such as a lift pump) and a higher pressure fuel pump 173. As described with reference to the fuel system of FIG. Fig. 2, the lower pressure fuel pump 175 may lift fuel from a fuel tank, which fuel is then further pressurized by the higher pressure fuel pump 173. Additionally, the lower pressure fuel pump 175 may provide fuel to a port injection fuel rail, while the higher pressure fuel pump 173 delivers fuel to a direct injection fuel rail.

[0023] The ignition system 88 may provide an ignition spark to the combustion chamber 30 via the spark plug 92 in response to an ignition advance signal SA from the controller 12 under selected operating modes. Although spark-ignition components are shown, in some embodiments, the combustion chamber 30 or one or more other combustion chambers of the engine 10 may be operated in a compression-ignition mode with or without an ignition spark.

[0024] The intake passage 42 may include throttles 62 and 63 with respective throttle bodies 64, 65. In this particular example, the positions of the throttle bodies 64 and 65 may be varied by the controller 12 via signals provided to an electric motor or actuator included in the throttles 62 and 63, a configuration commonly referred to as an electronic throttle control (ETC). In this manner, the throttles 62 and 63 may be operated to vary the intake air provided to different engine cylinders of the combustion chamber 30. The positions of the throttle bodies 64 and 65 may be communicated to the controller 12 via the throttle position signals TP. Pressure, temperature, and mass airflow may be measured at various points along the intake passage 42 and the intake manifold 44.For example, intake passage 42 may include a mass airflow sensor 120 for measuring the clean air mass flow entering through throttle 63. The clean air mass flow may be communicated to controller 12 via the MAF signal.

[0025] The engine 10 may further include a compression device, such as a turbocharger or a supercharger, comprising at least one compressor 162 disposed upstream of the intake manifold 44. In the case of a turbocharger, the compressor 162 may be driven at least partially by a turbine 164 (e.g., via a shaft) disposed along an exhaust passage 48. In the case of a supercharger, the compressor 162 may be driven at least partially by the engine and / or an electric machine and may not include a turbine. Therefore, the amount of compression provided to one or more cylinders of the engine via a turbocharger or supercharger may be varied by the controller 12. A charge air cooler 154 may be included downstream of the compressor 162 and upstream of the intake valve 52.The charge air cooler 154 may be configured, for example, to cool gases that have been heated by compression via the compressor 162. In one embodiment, the charge air cooler 154 may be located upstream of the throttle 62. Pressure, temperature, and mass airflow may be measured downstream of the compressor 162, such as with sensor 145 or 147. The measured results may be communicated to the controller 12 from sensors 145 and 147 via signals 148 and 149, respectively. Pressure and temperature may be measured upstream of the compressor 162, such as with sensor 153, and communicated to the controller 12 via signal 155.

[0026] Further, in the disclosed embodiments, an exhaust gas recirculation (EGR) system may direct a desired portion of the exhaust gas from the exhaust passage 48 to the intake manifold 44. Fig. 1 shows a high-pressure EGR (HP-EGR) system and a low-pressure EGR (LP-EGR) system, but it is possible that an alternative embodiment includes only an LP-EGR system. The HP-EGR is routed through the HP-EGR passage 140, located upstream of the turbine 164, to locations downstream of the compressor 162. The amount of HP-EGR provided to the intake manifold 44 can be varied by the controller 12 via the HP-EGR valve 142. The LP-EGR is routed through the LP-EGR passage 150, located downstream of the turbine 164, to locations upstream of the compressor 162. The amount of LP-EGR provided to the intake manifold 44 can be varied by the controller 12 via the LP-EGR valve 152. The HP EGR system may include the HP EGR cooler 146 and the LP EGR system may include the LP EGR cooler 158 to, for example, reject heat from the EGR gases to engine coolant.Thus, the engine 10 may include both an HP EGR and an LP EGR system for directing exhaust gases back to the intake.

[0027] Under some conditions, the EGR system may be used to regulate the temperature of the air-fuel mixture in the combustion chamber 30. Thus, it may be desirable to measure or estimate the EGR mass flow. EGR sensors may be located within EGR passages and may provide an indication of one or more of mass flow, pressure, temperature, O concentration, and 2 and concentration of the exhaust gas. For example, an HP-EGR sensor 144 may be disposed in the HP-EGR passage 140.

[0028] In some embodiments, one or more sensors may be positioned within the LP-EGR passage 150 to provide an indication of one or more of a pressure, a temperature, and an air-fuel ratio of exhaust gas recirculated through the LP-EGR passage. Exhaust gas redirected through the LP-EGR passage 150 may be diluted with fresh intake air at a mixing point located at the junction of the LP-EGR passage 150 and the intake passage 42. In particular, by adjusting the LP-EGR valve 152 in coordination with the first air intake throttle 63 (positioned within the engine intake air intake passage, upstream of the compressor), dilution of the EGR flow may be adjusted.

[0029] A percentage dilution of the LP EGR flow may be inferred from the output of a sensor 145 in the engine intake gas stream. Specifically, the sensor 145 may be positioned downstream of the first intake throttle 63, downstream of the LP EGR valve 152, and upstream of the second main intake throttle 62 so that the LP EGR dilution can be accurately determined at or near the main intake throttle. The sensor 145 may, for example, be an oxygen sensor such as a UEGO sensor.

[0030] The exhaust gas sensor 126 is shown coupled to the exhaust passage 48 downstream of the turbine 164. The sensor 126 may be any suitable sensor for providing an indication of an exhaust air-fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a dual-state oxygen sensor or EGO, a HEGO (heated EGO), a NO x -, HC or CO sensor.

[0031] As shown, emission control devices 71 and 72 are arranged downstream of exhaust gas sensor 126 along exhaust passage 48. Devices 71 and 72 may include a selective catalytic reduction (SCR) system, a three-way catalyst (TWC), a NO x trap, various other emission control devices, or combinations thereof. For example, device 71 may be a TWC and device 72 may be a particulate filter (PF). In some embodiments, PF 72 may be downstream of TWC 71 (as in Fig. 1), while in other embodiments the PF 72 may be located upstream of TWC 72 (in Fig. 1 not shown). The PF 72 may include a soot load sensor 198 that can communicate a particulate matter load level to the controller 12 via the FS signal.

[0032] The control 12 is in Fig. 1 as a microcomputer, including a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, shown in this particular example as a read-only memory chip 106, random access memory 108, keep-alive memory 110, and a data bus. The controller 12, in addition to the signals previously discussed, may receive various signals from sensors coupled to the engine 10, including measurements of inducted mass air flow (MAF) from a mass air flow sensor 120; engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling sleeve 114; a profile ignition pickup (PIP) signal from a Hall-effect sensor 118 (or other type) coupled to a crankshaft 40; throttle position (TP) from a throttle position sensor; and an intake manifold absolute pressure (MAP) signal from sensor 122.The engine speed signal, RPM, may be generated by the controller 12 from the PIP signal. The manifold pressure signal, MAP, from a manifold pressure sensor may be used to provide an indication of the vacuum or pressure in the intake manifold. It should be noted that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor may be indicative of engine torque. Further, this sensor, along with the sensed engine speed, may provide an estimate of the charge (including air) being introduced into the cylinder. In one example, sensor 118, which may also be used as an engine speed sensor, may produce a predetermined number of evenly spaced pulses per revolution of the crankshaft. The controller 12 receives signals from the various sensors. Fig. 1 (and those described below from Fig. 2) and sets the various actuators Fig. 1 (and those described below from Fig. 2) to adjust the motor operation based on the received signals and instructions stored in a memory of the controller.

[0033] A storage medium of a read-only memory 106 may be programmed with computer-readable data representing instructions executable by the processor 102 for performing the methods described below, as well as other variations that are assumed but not explicitly enumerated. An exemplary routine that may be performed by the controller is shown in Fig. 3 described.

[0034] Fig. 2 schematically illustrates an exemplary embodiment 200 of a fuel system, such as the fuel system 172 of Fig. 1. The fuel system 200 is operable to deliver fuel to an engine, such as the engine 10 of Fig. 1. The fuel system 200 may be operated by a controller to perform some or all of the processes described with reference to the process sequences of Fig. 3 described procedures.

[0035] The fuel system 200 includes a fuel storage tank 210 for storing fuel onboard the vehicle, a lower pressure fuel pump (LPP) 212 (also referred to herein as fuel lift pump 212), and a higher pressure fuel pump (HPP) 214 (also referred to herein as fuel injection pump 214). Fuel may be provided to the fuel tank 210 via a fuel fill passage 204. In one example, the LPP 212 may be an electrically operated lower pressure fuel pump disposed at least partially within the fuel tank 210. The LPP 212 may be controlled by a controller 222 (e.g., the controller 12 of Fig. 1) to provide fuel to the HPP 214 via the fuel passage 218. The LPP 212 may be configured as a so-called fuel lift pump. As one example, the LPP 212 may be a turbine pump (e.g., centrifugal) that includes an electric (e.g., DC) pump motor, wherein the pressure increase in the pump and / or the volumetric flow rate through the pump may be controlled by varying the electrical power provided to the pump motor, thereby increasing or reducing the motor speed. For example, the increase in the volumetric flow rate and / or pressure in the lift pump may be reduced if the controller reduces the electrical power provided to the lift pump 212. The increase in the volumetric flow rate and / or pressure in the pump may be increased by increasing the electrical power provided to the lift pump 212.As one example, the electrical power supplied to the lower pressure pump motor may be obtained from an alternator or other energy storage device onboard the vehicle (not shown), and the control system may control the electrical load used to drive the lower pressure pump. Thus, by varying the voltage and / or current supplied to the lower pressure fuel pump, the flow rate and pressure of the fuel supplied at the inlet of the higher pressure fuel pump 214 are adjusted.

[0036] The LPP 212 may be fluidly connected to a filter 217, which can remove small impurities contained in the fuel that could potentially damage fuel handling components. A check valve 213, which can facilitate fuel dispensing and maintain fuel line pressure, may be fluidly positioned upstream of the filter 217. With the check valve 213 positioned upstream of the filter 217, the compliance of the low-pressure passage 218 may be increased because the filter may have a physically larger volume. Furthermore, a pressure relief valve 219 may be employed to limit the fuel pressure in the low-pressure passage 218 (e.g., the output from the lift pump 212). The check valve 219 may include a ball and spring mechanism that, for example, sits at and seals against a specified pressure differential.The setpoint pressure differential at which check valve 219 may be configured to open may take on various suitable values; as a non-limiting example, the setpoint may be 6.4 bar or 5 bar(g). An orifice 223 may be used to allow air and / or fuel vapor to drain from lift pump 212. This vent at 223 may also be used to drive a jet pump used to transfer fuel from one location to another in tank 210. In one example, an orifice check valve (not shown) may be placed in series with orifice 223. In some embodiments, fuel system 8 may include one or more (e.g., a series) check valves fluidly connected to low-pressure fuel pump 212 to prevent fuel from backing upstream of the valves.In this context, upflow refers to fuel flow moving from the fuel rails 250, 260 toward the LPP 212, while downflow refers to the nominal fuel flow direction from the LPP toward the HPP 214 and thence to the fuel rails.

[0037] Fuel lifted by the LPP 212 may be delivered at a lower pressure into a fuel passage 218 leading to an inlet 203 of the HPP 214. The HPP 214 may then deliver fuel to a first fuel rail 250 connected to one or more fuel injectors of a first group of direct injectors 252 (also referred to herein as a first injector group). Thus, the fuel rail 250 is in communication with a direct injector. Fuel lifted by the LPP 212 may also be delivered to a second fuel rail 260 connected to one or more fuel injectors of a second group of port injectors 262 (also referred to herein as a second injector group). Thus, the fuel rail 260 is in communication with a port injector.As elaborated below, the HPP 214 may be operated to raise the pressure of the fuel delivered to each of the first and second fuel rails above the lift pump pressure, with the first fuel rail connected to the direct injector group operating at a variable high pressure, while the second fuel rail is connected to the port injector group operating at a fixed high pressure. Thus, the high-pressure fuel pump 214 is in communication with each of the fuel rail 260 and the fuel rail 250. As a result, high-pressure port and direct fuel injection may be activated. The high-pressure fuel pump is connected downstream of the low-pressure fuel pump, with no additional pump positioned between the high-pressure fuel pump and the low-pressure fuel pump.

[0038] While each of the first fuel rail 250 and the second fuel rail 260 is illustrated as delivering fuel to four fuel injectors of the respective injector group 252, 262, it should be noted that each fuel rail 250, 260 may deliver fuel to any suitable number of fuel injectors. As an example, the first fuel rail 250 may deliver fuel to one fuel injector of the first injector group 252 for each cylinder of the engine, while the second fuel rail 260 may deliver fuel to one fuel injector of the second injector group 262 for each cylinder of the engine. The controller 222 may individually actuate each of the port injectors 262 via a port injection driver 237 and actuate each of the direct injectors 252 via a direct injection driver 238.The controller 222, the drivers 237, 238, and other suitable engine system controls may comprise a control system. While the drivers 237, 238 are shown external to the controller 222, it should be noted that in other examples, the controller 222 may include the drivers 237, 238 or may be configured to provide the functionality of the drivers 237, 238. The controller 222 may include additional components not shown, such as those included in the controller 12 of FIG. Fig. 1 are included.

[0039] The HPP 214 may be an engine-driven positive displacement pump. As a non-limiting example, the HPP 214 may be a BOSCH HDP5 high-pressure pump that uses a solenoid-activated control valve (e.g., fuel volume regulator, magnetic solenoid valve, etc.) 236 to vary the effective pumping volume for each pumping stroke. The HPP's outlet check valve is mechanically controlled rather than electronically controlled by an external controller. The HPP 214 may be mechanically driven by the engine, unlike the engine-driven LPP 212. The HPP 214 includes a pump piston 228, a pump compression chamber 205 (also referred to herein as the compression chamber), and a stepper chamber 227. The pump piston 228 receives mechanical input from the engine crankshaft or camshaft via the cam lobe 230, thereby operating the HPP according to the principles of a cam-driven single-cylinder pump. A sensor (in Fig. 2 not shown) may be positioned near the cam 230 to enable the determination of the angular position of the cam (e.g., between 0 and 360 degrees), which may be passed to the controller 222.

[0040] The fuel system 200 may optionally further include an accumulator 215. If included, the accumulator 215 may be positioned downstream of the lower pressure fuel pump 212 and upstream of the higher pressure fuel pump 214 and may be configured to hold a volume of fuel that reduces the rate of fuel pressure increase or decrease between the fuel pumps 212 and 214. For example, the accumulator 215 may be connected in the fuel passage 218, as shown, or in a bypass passage 211 connecting the fuel passage 218 to the step space 227 of the HPP 214. The volume of the accumulator 215 may be sized to allow the engine to operate under idle conditions for a predetermined period of time between operating intervals of the lower pressure fuel pump 212.For example, accumulator 215 may be sized such that, when the engine is idling, it takes one or more minutes to reduce pressure in the accumulator to a level at which the higher pressure fuel pump 214 is unable to maintain a sufficiently high fuel pressure for the fuel injectors 252, 262. Thus, accumulator 215 may enable an intermediate (or pulsed) mode of operation of the lower pressure fuel pump 212. By reducing the frequency of LPP operation, power consumption is reduced. In other embodiments, accumulator 215 may be inherently present in the conformity of fuel filter 217 and fuel passage 218 and thus may not be present as a standalone element.

[0041] A lift pump fuel pressure sensor 231 may be positioned along the fuel passage 218 between the lift pump 212 and the higher pressure fuel pump 214. In this configuration, readings from the sensor 231 may be interpreted as indicating the fuel pressure of the lift pump 212 (e.g., the lift pump outlet fuel pressure) and / or the inlet pressure of the higher pressure fuel pump. Readings from the sensor 231 may be used to evaluate the operation of various components in the fuel system 200, to determine whether sufficient fuel pressure is being provided to the higher pressure fuel pump 214 such that the higher pressure fuel pump receives liquid fuel and not fuel vapor, and / or to minimize the average electrical power delivered to the lift pump 212.While the lift pump fuel pressure sensor 231 is shown positioned downstream of the accumulator 215, in other embodiments the sensor may be positioned upstream of the accumulator.

[0042] The first fuel rail 250 includes a first fuel rail pressure sensor 248 for providing an indication of direct injection fuel rail pressure to the controller 222. Likewise, the second fuel rail 260 includes a second fuel rail pressure sensor 258 for providing an indication of port injection fuel rail pressure to the controller 222. An engine speed sensor 233 may be used to provide an indication of engine speed to the controller 222. The engine speed indication may be used to identify the speed of the higher pressure fuel pump 214, since the pump 214 is mechanically driven by the engine 202, for example, via the crankshaft or camshaft.

[0043] The first fuel rail 250 is connected to an outlet 208 of the HPP 214 along the fuel passage 278. In comparison, the second fuel rail 260 is connected to an inlet 203 of the HPP 214 via the fuel passage 288. A check valve and a pressure relief valve may be positioned between the outlet 208 of the HPP 214 and the first fuel rail. Additionally, the pressure relief valve 272, disposed parallel to the check valve 274 in the bypass passage 279, may limit the pressure in the fuel passage 278 located downstream of the HPP 214 and upstream of the first fuel rail 250. For example, the pressure relief valve 272 may limit the pressure in the fuel passage 278 to an upper threshold pressure (e.g., 200 bar).Thus, the pressure relief valve 272 may limit the pressure that would otherwise be generated in the fuel passage 278 if the control valve 236 were open (intentionally or unintentionally) and while the high pressure fuel pump 214 were pumping.

[0044] One or more check valves and pressure relief valves may also be connected to the fuel passage 218 downstream of the LPP 212 and upstream of the HPP 214. For example, the check valve 234 may be provided in the fuel passage 218 to reduce or prevent the backflow of fuel from the high-pressure pump 214 to the low-pressure pump 212 and into the fuel tank 210. Additionally, the pressure relief valve 232 may be provided in a bypass passage positioned parallel to the check valve 234. The pressure relief valve 232 may limit the pressure to its left to 100 bar higher than the pressure at the sensor 231.

[0045] The controller 222 may be configured to regulate the flow of fuel into the HPP 214 through the control valve 236 by energizing or de-energizing the solenoid valve (based on the solenoid valve configuration) in synchronization with the drive cam. Accordingly, the solenoid-activated control valve 236 may be operated in a first mode in which the valve 236 is positioned within the HPP inlet 203 to limit (e.g., prevent) the amount of fuel moving through the solenoid-operated control valve 236. Depending on the timing of the solenoid valve actuation, the volume transferred to the fuel rail 250 is varied. The solenoid valve may also be operated in a second mode in which the solenoid-activated control valve 236 is effectively deactivated, allowing fuel to move upstream and downstream of the valve and into and out of the HPP 214.

[0046] Thus, the solenoid-activated control valve 236 may be configured to regulate the mass (or volume) of fuel compressed into the direct injection fuel pump. In one example, the controller 222 may adjust a closing timing of the solenoid pressure control check valve to regulate the mass of compressed fuel. For example, late closing of the pressure control valve may reduce the amount of fuel mass taken into the compression chamber 205. The opening and closing timing of the solenoid-activated check valve may be coordinated with respect to stroke timing of the direct injection fuel pump.

[0047] The pressure relief valve 232 allows fuel flow from the solenoid-activated control valve 236 toward the LPP 212 when pressure between the pressure relief valve 232 and the solenoid-operated control valve 236 is greater than a predetermined pressure (e.g., 10 bar). When the solenoid-operated control valve 236 is deactivated (e.g., not electrically energized), the solenoid-operated control valve operates in a passthrough mode, and the pressure relief valve 232 regulates the pressure in the compression chamber 205 to the single pressure relief setpoint of the pressure relief valve 232 (e.g., 10 bar above the pressure at sensor 231). Regulating the pressure in the compression chamber 205 allows a pressure differential to develop from the piston tip to the piston crown. The pressure in the step chamber 227 is at the outlet pressure of the low pressure pump (e.g. 5 bar), while the pressure at the piston tip is at the regulating pressure of the pressure relief valve (e.g. 15 bar).The pressure difference allows fuel to seep through the gap between the piston and the pump cylinder wall from the piston tip to the piston crown, lubricating the HPP 214.

[0048] Piston 228 moves up and down. HPP 214 is in a compression stroke when piston 228 moves in a direction that reduces the volume of compression chamber 205. HPP 214 is in an intake stroke when piston 228 moves in a direction that increases the volume of compression chamber 205.

[0049] A forward flow outlet check valve 274 may be connected downstream of an outlet 208 of the compression chamber 205. The outlet check valve 274 opens to allow fuel to flow from the high pressure pump outlet 208 into a fuel rail only when a pressure at the outlet of the direct injection fuel pump 214 (e.g., a compression chamber outlet pressure) is higher than the fuel rail pressure. Thus, under conditions where direct injection fuel pump operation is not called for, the controller 222 may deactivate the solenoid-activated control valve 236, and the pressure relief valve 232 regulates the pressure in the compression chamber 205 to a single, substantially constant pressure during most of the compression stroke. On the intake stroke, the pressure in the compression chamber 205 drops to a pressure near the lift pump (212) pressure.Lubrication of the DI pump 214 may occur when the pressure in the compression chamber 205 exceeds the pressure in the step chamber 227. This pressure differential may also contribute to pump lubrication when the controller 222 deactivates the solenoid-activated control valve 236. One result of this regulation method is that the fuel rail is regulated to a minimum pressure, approximately the pressure relief of the pressure relief valve 232. Thus, if the pressure relief valve 232 has a pressure relief setting of 10 bar, the fuel rail pressure becomes 15 bar, as these 10 bar are added to the 5 bar of lift pump pressure. In particular, the fuel pressure in the compression chamber 205 is regulated during the compression stroke of the direct injection fuel pump 214. Thus, lubrication is provided to the pump at least during the compression stroke of the direct injection fuel pump 214.When the direct fuel injection pump enters a suction stroke, the fuel pressure in the compression chamber can be reduced while still providing some lubrication as long as the pressure differential is present. Another pressure relief valve 272 can be placed in parallel with the check valve 274. The pressure relief valve 272 allows fuel to flow from the DI fuel rail 250 toward the pump outlet 208 when the fuel rail pressure is greater than a predetermined upper threshold pressure. Thus, as the direct injection fuel pump reciprocates, the flow of fuel between the piston and the bore provides sufficient pump lubrication and cooling.

[0050] The lift pump can be temporarily operated in a pulsed mode, in which lift pump operation is adjusted based on a pressure estimated at the lift pump outlet and the high-pressure pump inlet. Specifically, in response to the high-pressure pump inlet pressure falling below a fuel vapor pressure, the lift pump can be operated until the inlet pressure is at or above the fuel vapor pressure. This reduces the risk of the high-pressure fuel pump ingesting fuel vapors (instead of fuel) and resulting engine stall events.

[0051] It is noted here that the high pressure pump 214 from Fig. 2 is shown as an illustrative example of a possible configuration of a high-pressure pump. In Fig. 2 may be removed and / or modified, while additional components not currently shown may be added to pump 214 while still maintaining the ability to deliver high pressure fuel to a direct injection fuel rail and a port injection fuel rail.

[0052] The solenoid-activated control valve 236 can also be operated to direct fuel return flow from the high-pressure pump to one of the pressure relief valve 232 and the accumulator 215. For example, the control valve 236 can be operated to generate fuel pressure and store it in the accumulator 215 for later use. One use of the accumulator 215 is to absorb fuel volume flow resulting from the opening of the discharge pressure relief valve 232. The accumulator 227 draws fuel while the check valve 234 opens during the intake stroke of the pump 214. Another use of the accumulator 215 is to absorb / draw the volume changes in the step chamber 227. Yet another use of the accumulator 215 is to enable intermediate operation of the lift pump 212 to maintain an average pump input power reduction over continuous operation.

[0053] While the first direct injection fuel rail 250 is connected to the outlet 208 of the HPP 214 (and not to the inlet of the HPP 214), the second port injection fuel rail 260 is connected to the inlet 203 of the HPP 214 (and not to the outlet of the HPP 214). Although inlets, outlets, and the like are described herein with respect to the compression chamber 205, it can be noted that there may be a single conduit into the compression chamber 205. The single conduit may serve as both an inlet and an outlet. In particular, the second fuel rail 260 is connected to the HPP inlet 203 at a location upstream of the solenoid-activated control valve 236 and downstream of the check valve 234 and the pressure relief valve 232. Furthermore, it may be possible that no additional pump is required between the lift pump 212 and the port injection fuel rail 260.As elaborated below, the specific configuration of the fuel system, with the port-injection fuel rail connected to the high-pressure pump inlet via a pressure relief valve and a check, allows the pressure at the secondary fuel rail to be raised via the high-pressure pump to a fixed standard pressure that is higher than the standard pressure of the lift pump. This means that the fixed high pressure at the port-injection fuel rail is derived from the high-pressure piston pump.

[0054] When the high-pressure pump 214 is not moving up and down, such as when turning the key before starting, the check valve 244 allows the second fuel rail to fill at 5 bar. As the pump chamber displacement decreases due to the piston moving forward, fuel flows in one of two directions. If the spill valve 236 is closed, the fuel goes into the high-pressure fuel rail 250 via the high-pressure fuel pump outlet 208. If the spill valve 236 is open, the fuel goes either into the low-pressure fuel rail 250 or through the compression relief valve 232 via the high-pressure fuel pump inlet 203.In this manner, the high-pressure fuel pump is operated to deliver fuel at a variable high pressure (such as between 15-200 bar) to the direct fuel injectors 252 via the first fuel rail 250, while also delivering fuel at a fixed high pressure (such as 15 bar) to the port fuel injectors 262 via the second fuel rail 260. The variable pressure may include a minimum pressure that is at the fixed pressure.

[0055] Thus, the spill valve 236 may be operated to control a mass fuel flow from the high-pressure fuel pump outlet to the DI fuel rail 250 to be substantially equal to zero and to control a mass fuel flow from the high-pressure fuel pump inlet to the PFI fuel rail 260. As an example, when one or more direct injectors 252 are deactivated, the spill valve 236 may be operated to control the mass fuel flow from the HPP outlet 208 to the DI fuel rail 250 to be substantially equal to zero. Additionally, the mass fuel flow from the HPP outlet 208 to the DI fuel rail 250 may be controlled to be substantially zero if the direct injectors 252 are activated while the pressure in the DI fuel rail 250 is above a minimum pressure threshold (e.g., 15 bar).Under both conditions, the mass fuel flow from the HPP inlet 203 to the PFI fuel distributor 260 can be controlled such that it is substantially greater than zero. If the fuel flow to one of the fuel distributors 250 or 260 is controlled such that it is substantially equal to zero, the fuel flow thereto may be referred to herein as deactivated.

[0056] In the in Fig. In the configuration shown in Figure 2, the fixed pressure at the port injection fuel rail is the same as the minimum pressure for the direct injection fuel rail, both of which are higher than the standard lift pump pressure. Herein, the fuel supply from the high-pressure pump is controlled via the upstream (solenoid-activated) control valve and further via the various check valves and pressure relief valves connected to the high-pressure pump inlet. By adjusting the operation of the solenoid-activated control valve, the fuel pressure at the first fuel rail is increased from the fixed pressure to the variable pressure while maintaining the fixed pressure at the second fuel rail. Valves 244 and 242 cooperate to maintain the low-pressure fuel rail 260 pressurized at 15 bar during the pump prime stroke.The pressure relief valve 242 simply limits the pressure that can build up in the fuel rail 250 due to thermal expansion of the fuel. A typical pressure relief setting might be 20 bar.

[0057] Controller 222 may also control the operation of each of fuel pumps 212 and 214 to adjust an amount, pressure, flow rate, etc., of fuel provided to the engine. As one example, controller 222 may vary a pressure setting, pump stroke amount, pump duty cycle command, and / or fuel flow rate of the fuel pumps to provide fuel to different locations in the fuel system. A driver (not shown) electronically coupled to controller 222 may be used to send a control signal to the low-pressure pump, as needed, to adjust the output (e.g., speed) of the low-pressure pump.In some examples, the solenoid valve may be configured such that the high pressure fuel pump 214 delivers fuel only to the first fuel rail 250, and in such a configuration, fuel may be delivered to the second fuel rail 260 at the lower outlet pressure of the lift pump 212.

[0058] The controller 222 may control the operation of each of the injector groups 252 and 262. For example, the controller 222 may control the distribution and / or relative amount of fuel provided by each injector, which may vary with operating conditions such as engine load, knock, and exhaust temperature. In particular, the controller 222 may adjust a direct injection fuel ratio by sending appropriate signals to the port injection driver 237 and the direct injection 238, which in turn may actuate the respective port fuel injectors 262 and direct injectors 252 with desired pulse widths to achieve the desired injection ratios. Additionally, the controller 222 may cycle and deactivate one or more of the injector groups based on the fuel pressure in each rail as well as minimum pulse width triggers (i.e.,enable or disable).

[0059] In this way, the components from Fig. 1-2 a system comprising: an engine having a cylinder; a port fuel injector mounted in an intake manifold of the cylinder; a direct fuel injector mounted directly in the cylinder; a temperature sensor for sensing engine temperature; and a controller having instructions stored in memory that, when executed, cause the injector to inject, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the direct injections reaching a minimum direct injection pulse width, adjust a ratio of the port to direct fuel injection.

[0060] Fig. 3 shows an exemplary method 300 for operating an engine configured with multi-fuel injection capabilities, such as the internal combustion engine 10 of Fig. 1, which is connected to the fuel system 200 from Fig. 2. In particular, method 300 enables control of each cylinder's direct and port fuel injectors while monitoring and compensating for potential operation approaching the minimum fuel injection pulse width.

[0061] Instructions for performing method 300 and the other methods included herein may 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 described above with reference to Fig. 1-2. The controller can use motor actuators of the motor system to adjust motor operation according to the procedures described below.

[0062] It should be noted that the adjustment of the port-to-direct injection ratio for a given cylinder and / or the direct injection split for a given cylinder may be adjusted differently depending on the situation, including whether engine hot restart conditions are present or engine cold start conditions are present. Furthermore, differences in handling of minimum pulse width triggers may be provided depending on whether retain fuel (e.g., degraded fuel quality) is present. If retain fuel is detected, then the total fuel mass for the engine may be adjusted while maintaining the port-to-direct injection ratio within the limits of the fuel injector's minimum and maximum pulse widths. Engine start conditions may be based on engine coolant temperature at start-up, intake air temperature, ambient temperature, and / or combinations thereof.In one example, the method may distinguish between a hot restart and a cold restart based on the engine coolant temperature relative to the air temperature at startup, where the cold restart is at a lower initial engine temperature than the hot restart. Also, the hot restart may include automatic engine start-stop restarts if the engine was automatically shut down upon a vehicle stop independent of a driver-off request (e.g., push-button engine stop).

[0063] At 302, the method includes estimating and / or measuring vehicle operating conditions. These may include, for example, engine coolant temperature, intake air temperature, ambient temperature, atmospheric pressure, driver torque demand, etc.

[0064] At 304, the method includes confirming whether an engine start condition exists. In one example, an engine start condition may be confirmed in response to a driver key-on event or a vehicle power-on event, such as via an active or passive key. Alternatively, an engine start may be confirmed in response to automatic engine restart conditions being met, such as when a battery state of charge falls below a threshold or there is an air conditioning demand.

[0065] If an engine start condition is not confirmed, the method proceeds to 324, where engine fuel injection systems are adjusted with a fuel split ratio (which may include a ratio of port-injected fuel to direct-injected fuel, as well as a ratio of direct-injected fuel on the intake stroke relative to direct-injected fuel on the compression stroke) based on engine speed / load conditions. For example, control may rely on the engine speed / load map from Fig. 6 to determine an amount of fuel to be injected, a fuel injection type (or types), and a number of injections. In one example, at lower engine speed / load and cooler engine conditions, all injected fuel may be delivered via a single port injection in an exhaust stroke or an intake stroke. As another example, at higher engine speed / load and warmer engine conditions, all injected fuel may be delivered via multiple direct injections in an intake stroke and / or a compression stroke. As yet another example, at medium speed / load, a portion of the fuel may be delivered via port injection and a remainder of the fuel may be delivered via (single or multiple) direct injections.

[0066] If an engine start is confirmed, a determination may be made at 306 as to whether split fuel injection operation is desired at engine start. As used herein, split injection operation may include a portion of the total fuel of a given cylinder cycle delivered via port fuel injection and a remainder of the total fuel of the given cylinder cycle delivered via (single or multiple) direct fuel injection. Controller may refer to a lookup table stored as a function of engine start parameters, such as engine temperature at start and fuel alcohol content, to determine whether to enable split injection for the current engine start.In one example, split fuel injection may be activated at engine start in response to the engine temperature being less than a threshold or the alcohol content of the injected fuel being higher than a threshold. The split ratio may be further determined based on the number of combustion events since an initial combustion event of engine start.

[0067] If split injection is determined, a split injection ratio of PFI to DI fuel is determined at 308. In one example, split fuel injection may be enabled for both cold engine starts (where the engine temperature is lower at engine start) and hot engine starts (where the engine temperature is higher at engine start), however, the split ratio of port-injected fuel to direct-injected fuel may be different for the starts. As one example, during cold engine starts, the split ratio may include a higher ratio of port-injected fuel to direct-injected fuel for a given cylinder (due to the higher particulate emissions of direct-injected cold fuel).As another example, during engine hot starts, the split ratio may include a lower ratio of port-injected fuel to direct-injected fuel for a given cylinder (due to the higher efficiency of the direct-injected hot fuel). In one example, the desired split ratio at 308 may be a base number determined from a controller lookup table, such as the example table of FIG. Fig. 6.

[0068] With reference to Fig. 6, a table 600 is shown for determining port and direct fuel injection fuel fractions for a total amount of fuel delivered to an engine during an engine cycle. The table from Fig. 6 may provide a basis for determining a direct fuel injector fuel fraction as in the method of Fig. 3. The vertical axis represents engine speed, and engine speed is identified along the vertical axis. The horizontal axis represents engine load, and engine load values ​​are identified along the horizontal axis. In this example, table cells 602 contain two values ​​separated by a comma. Values ​​to the left of the commas represent port fuel injector fuel fractions, and values ​​to the right of the commas represent direct fuel injector fuel fractions. For example, for the table value corresponding to 2000 rpm and a load of 0.2, the empirically determined values ​​are 0.4 and 0.6. The value of 0.4, or 40%, is the port fuel injector fuel fraction, and the value of 0.6, or 60%, is the direct fuel injector fuel fraction.Thus, if the desired fuel injection mass is 1 gram of fuel during an engine cycle, 0.4 grams of fuel will be port-injected fuel and 0.6 grams of fuel will be direct-injected fuel. In other examples, the table may contain only a single value in each table cell, and the corresponding value may be determined by subtracting the value in the table from a value of one. For example, if the 2000 rpm and 0.2 load table cell contains a single value of 0.6 for a direct injector fuel fraction, then the port-injector fuel fraction is 1 - 0.6 = 0.4.

[0069] In this example, it can be observed that the port fuel injection fraction is highest at lower engine speeds and loads. The direct fuel injection fraction is highest at intermediate engine speeds and loads. The port fuel injection fraction increases at higher engine speeds when the timing for directly injecting fuel into a cylinder can be reduced due to a shortening of the time between cylinder combustion events. It can be observed that if the engine speed changes without a change in engine load, the port and direct fuel injection fractions may change.

[0070] With further reference to Fig. 3, at 310, it may be determined whether the direct-injected fuel is to be delivered as a single injection or multiple injections during a given cylinder cycle. The number of DI injections per cycle may be determined based on conditions such as engine temperature, the alcohol content of the injected fuel, the engine soot load, and the total amount of fuel to be delivered via direct injection relative to a minimum pulse width of the direct injector.

[0071] If split DI is desired, the method includes determining at 312 the DI / PFI split ratio (i.e., the portion of the total fuel delivered as port fuel injection relative to direct injection) and the split DI ratio (i.e., the portion of the total direct injected fuel delivered on the intake stroke relative to the compression stroke). Split DI may include multiple direct injections of fuel delivered on a given cycle, including multiple intake stroke injections, multiple compression stroke injections, or a combination of intake stroke and compression stroke injections. As one example, split DI may be enabled when the fuel alcohol content is higher or the engine FS load is higher, with split DI including a greater number of injections per cycle and / or a higher portion of the direct injected fuel delivered on the compression stroke.As another example, split DI may be enabled when the total amount of fuel to be delivered via direct injection increases for a given cylinder cycle, the number of DI injections increases when the total amount of fuel delivered via DI exceeds a minimum amount, where the minimum amount is based on the minimum pulse width of the direct injector.

[0072] Thus, the DI fuel quantity is divided at 312. In one example, the controller may take the base value (of the fuel ratio) determined at 308 (from table 600 in Fig. 6) and modify the base fuel value in a first manner (e.g., based on the total amount of DI). For example, the base value may be modified with a correction factor applied to the based DI / PFI ratio determined at 308, and then the DI ratio may be modified based on a DI split ratio determined as a function of engine speed / load as well as temperature (engine temperature and catalyst temperature). As a result of the split DI and split DI / PFI fuel ratios, an amount of the total fuel is delivered as a single port injection, and a remaining amount of fuel is delivered as multiple intake and / or compression stroke direct injections. As an example, during an engine cold start, more fuel mass may be required than the DI system alone can provide.This may be due to a static fuel injector flow rate limitation or high pressure fuel pump displacement. In this case, fuel mass is delivered from both systems to meet the total fuel mass demand. As another example, the DI fuel injector may be required for catalyst warm-up or combustion stability. If the total fuel mass demand changes, DI injection is still required. In this case, control may continue with DI injection even though the total fuel mass may be rich.

[0073] At 316, while the fuel is being delivered according to the scheduled DI / PFI split ratio, fuel injector pulse widths (for both the DI and PFI injectors) may be monitored and compensated for in the event of minimum pulse width violations. Therein, as described with reference to Fig. 4, in response to one of a cylinder's plurality of direct injectors reaching a minimum direct injection pulse width, a port-to-direct fuel injection ratio may be updated (e.g., reduced) to move injector operation away from the minimum pulse width region.

[0074] If split DI is not confirmed, the method includes determining a desired DI / PFI split ratio at 314 with an amount of fuel to deliver as a single port injection and a remaining amount of fuel to deliver as a single intake or compression stroke direct injection. Thus, the split ratio at 314 when split DI is disabled may be determined differently compared to the split ratio determined at 312 when split DI is enabled. As one example, the split ratio determined when split DI is disabled may include a higher ratio of port injected fuel compared to direct injected fuel.As another example, the split ratio determined when split DI is enabled may include a higher ratio of direct injected fuel compared to port-injected fuel. Thus, two DI injections (including an intake DI injection and a compression DI injection) may have a higher minimum fuel mass than a single injection (intake or compression stroke). Therefore, more fuel may be needed in the DI system to account for the minimum fuel masses. At 314, the DI amount is not further split (as occurs at 312 and 316). Thus, the base value determined at 308 is applied without the use of an additional correction factor.

[0075] At 318, while the fuel is being delivered according to the scheduled DI / PFI split ratio, fuel injector pulse widths (for both the DI and PFI injectors) may be monitored and compensated for in the event of minimum pulse width violations. Therein, as described with reference to Fig. 5, in response to any of a cylinder's port or direct injection reaching a minimum direct injection pulse width, a port-to-direct fuel injection ratio may be updated such that all fuel is delivered exclusively via direct injection while port fuel injection is disabled. As described with reference to Fig. 4-5, the compensation for minimum pulse width violations may differ when split DI is enabled compared to when split DI is disabled. The controller may provide sufficient fuel mass for multiple DI injection pulse widths to meet the minimum pulse width constraint. Thus, if a pulse is requested that is less than the minimum pulse width, the DI fuel injector may not open, or the delivered fuel mass may be very inaccurate.

[0076] From each of 316 and 318, the method moves to 320 to actuate the fuel injectors to deliver the determined fuel injection amounts with the determined compensations, if any are required. Delivering the fuel with the determined injection amounts and the determined compensations may include adjusting injection timing based on the determined adjustments for the DI / PFI split ratio and the DI split ratio. As one example, a start timing of the port and direct fuel injections may be adjusted (e.g., advanced) depending on a reduction in port-to-direct fuel injection.

[0077] Now, with reference to Fig. 4 shows an exemplary method 400 for adjusting a split fuel injection ratio in response to one of a plurality of direct injectors reaching a minimum direct injection pulse width. The method enables compensation for minimum pulse width violations of a fuel injector when split direct injection is enabled. As a result, fuel injection is maintained above the minimum fuel mass of the direct injectors, thereby reducing engine operating and emissions variation.

[0078] At 402, the method includes retrieving a particular split fuel injection ratio (including a fuel split ratio between port fuel injection and direct fuel injection, and the fuel split ratio between intake stroke direct fuel injection and compression stroke direct fuel injection). Upon retrieving the ratio, control may determine whether any of the injections are below the minimum pulse width of the corresponding fuel injector (e.g., whether the port fuel injection amount is below the minimum pulse width of the port fuel injector or whether any of the plurality of direct fuel injection amounts is below the minimum pulse width of the direct fuel injector).If not, at 420, in response to all split fuel injection amounts being above the minimum pulse width of their respective injectors, the determined DI / PFI split ratio is maintained. Additionally, the intake DI / compression DI split ratio is maintained.

[0079] If any of the injections are below the minimum pulse width of the corresponding injector, it may be determined at 404 whether engine cold start conditions exist. For example, it may be determined whether engine restart conditions are met when the ambient temperature is below a threshold. Alternatively, it may be determined whether engine restart conditions are confirmed after a threshold duration has elapsed since a last engine shutdown. Thus, more fuel mass is required during engine cold starts. A single fuel system may not always be able to provide the entire requested fuel mass. Additionally, if all of the fuel mass is injected from one system, there could be a huge PFI fuel puddle or significant cylinder wall wetting. Therefore, such issues are avoided by splitting the injection among the various fuel systems.Thus, during engine cold start, the controller may inject port fuel injection, intake stroke direct fuel injection, and compression stroke direct fuel injection during a single cylinder cycle of the hot restart. Herein, the amount of fuel injected via PFI relative to DI defines the PFI / DI split ratio, while the amount of fuel injected on the intake stroke relative to the compression stroke determines the DI split ratio. Additionally, the port fuel injection is injected from a port fuel rail pressurized at least partially by a high-pressure direct injection fuel pump.

[0080] If an engine cold start is confirmed, then at 406, it may be determined whether any of the cold start's plurality of direct injections is below the direct injector minimum pulse width (PW). If not, it may be concluded that the port fuel injection is below the minimum port fuel injection pulse width (PW). In response to the port fuel injection reaching the minimum direct injection pulse width, the method includes, at 409, disabling the port fuel injection and maintaining a ratio of the plurality of split direct injections relative to one another while maintaining a total fuel injection amount for the cycle.In one example, the port fuel injection may be disabled while the pulse width of each of the plurality of direct injections may be increased evenly (based on a signal sent from the controller to the fuel injector) such that the port fuel injection amount is evenly distributed between the plurality of direct fuel injections. The method then ends.

[0081] If it is determined that one of the split direct injections is below the minimum pulse width (PW) of the direct injector, it may be further determined at 408 whether multiple (e.g., two or more, or all) of the split direct injections are below the minimum pulse width (PW) of the direct injector. If not, it may be concluded that only one of the split direct injections is below the minimum fuel injection mass, while all remaining direct injections are above the minimum fuel injection mass.Accordingly, at 412, in response to only one of the direct injections meeting the minimum direct injection pulse width during the cold start, the method includes reducing the ratio of port-to-direct injected fuel (i.e., increasing the ratio of DI to PFI fuel) while maintaining a ratio of the direct injections relative to each other and while also maintaining a total fuel injection amount for the cycle. The controller may reduce the PFI:DI ratio (or increase the DI:PFI ratio) by increasing the pulse width of the direct injections while correspondingly reducing the port injection pulse width based on a signal sent from the controller to the fuel injector. In one example, reducing the PFI:DI ratio includes transitioning from a 50% PFI:DI ratio to 25% PFI:DI.Such a change may be necessary to ensure the DI injection is delivered. The DI injection timing can remain unchanged unless the updated pulse width is not appropriate. In this case, the timing can be advanced to ensure the updated pulse can fit within the injection window.

[0082] Otherwise, at 410, in response to multiple direct injections reaching the minimum direct injection pulse width, the method includes reducing the port-to-direct fuel injection ratio (i.e., increasing the DI-to-PFI fuel ratio) while adjusting a ratio of the split direct injections to bring an amount of each of the direct injections closer to each other and while maintaining a total fuel injection amount for the cycle. In one example, reducing the PFI:DI ratio and adjusting the split direct injection ratio includes transitioning from an 80% intake:compression direct injection ratio to 50% intake:compression direct injection ratio to reduce the likelihood that the compression injection pulse width is less than the minimum pulse width allowed on the fuel injector.The controller may reduce the PFI:DI ratio (or increase the DI:PFI ratio) and adjust the split DI ratio by increasing the pulse width of the direct injections while correspondingly reducing the pulse width of the port fuel injection based on a signal sent from the controller to the fuel injector. In one example, the pulse width of each of the direct injections may be increased by different amounts based on the relative ratio. For example, the direct injection with the larger fuel ratio may be increased by a smaller amount while the direct injection with the smaller fuel ratio may be increased by a larger amount to bring the amount of the direct injections closer together.

[0083] In this way, during an engine cold start, during a single cylinder cycle, a controller may inject port fuel injection, intake stroke direct fuel injection, and compression stroke direct fuel injection; and in response to one of the direct injections reaching a minimum direct injection pulse width, the controller may reduce a ratio of port to direct fuel injection.

[0084] Referring again to 404, if cold start conditions are not confirmed, then an engine hot restart may be inferred. Thus, during the engine hot start, during a single cylinder cycle of the hot restart, the controller may inject port fuel injection, intake stroke direct fuel injection, and compression stroke direct fuel injection. Herein, the amount of fuel injected via PFI relative to DI defines the PFI / DI split ratio, while the amount of fuel injected on the intake stroke relative to the compression stroke determines the DI split ratio. Additionally, the port fuel injection is injected from a port fuel rail pressurized at least in part by a high-pressure direct injection fuel pump.

[0085] At 430, it may be determined whether any of the multiple hot-start direct injections are below the minimum pulse width (PW) of the direct injector. If not, it may be concluded that the port fuel injection is below the minimum pulse width (PW) of the port fuel injection. In response to the port fuel injection reaching the minimum direct injection pulse width, the method includes, at 438, disabling the port fuel injection and maintaining a ratio of the multiple split direct injections relative to one another while maintaining a total fuel injection amount for the cycle.In one example, the port fuel injection may be disabled while the pulse width of each of the plurality of direct injections may be increased evenly (based on a signal sent from the controller to the fuel injector) such that the port fuel injection amount is evenly distributed between the plurality of direct fuel injections. The method then ends.

[0086] If it is determined that one of the hot start split direct injections is below the minimum pulse width (PW) of the direct injector, at 432 it may be further determined whether multiple (e.g., two or more or all) of the split direct injections are below the minimum pulse width (PW) of the direct injector. If not, it may be concluded that only one of the split direct injection amounts is below the minimum fuel injection mass, while all remaining direct injections are above the minimum fuel injection mass. Accordingly, at 436, in response to only one of the hot start direct injections meeting the minimum direct injection pulse width, the method includes deactivating a smaller one of the hot start direct injections while maintaining a ratio of the hot start direct injection to port injection fuel amount and while maintaining a total fuel injection amount for the cycle.In one example, after disabling the smaller of the hot-start direct injections, the controller may send a signal to the port and direct fuel injectors to uniformly increase the pulse width of the port and the remaining direct injections, thereby evenly distributing the fuel mass contained in the disabled direct injection among the remaining port and direct injections. Additionally, multiple DI injections may be combined into a single injection if the DI injections are too close to (e.g., within a threshold of) the minimum pulse width. For example, the ratio may transition from 40% PFI:DI to 100%DI to reduce the likelihood that the DI injection pulse width is too close to the minimum pulse width.

[0087] Otherwise, at 434, in response to multiple hot-start direct injections reaching the minimum direct injection pulse width, the method includes disabling one of the hot-start direct injections while maintaining a ratio of hot-start port direct injection to direct injection and while maintaining a total fuel injection amount for the cycle. In one example, compression stroke direct injection is disabled. Thereafter, the controller may send a signal to the port and direct fuel injectors to uniformly increase the pulse width of the port and remaining (port) direct injection to evenly distribute the fuel mass contained in the disabled compression stroke direct injection among the remaining port and intake stroke direct injection.Additionally, multiple DI injections can be combined into a single injection if the DI injections are too close to the minimum pulse width (e.g., within a threshold of it). For example, the ratio can transition from 40% PFI:DI to 100%DI to reduce the likelihood that the DI injection pulse width is too close to the minimum pulse width.

[0088] If after deactivating compression direct injection the remaining direct injection is still below the minimum pulse width, only then may the method further include increasing the ratio of DI to PFI fuel.

[0089] In this way, during a single cylinder cycle of the hot restart, a controller may inject a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the hot start direct injections reaching the minimum direct injection pulse width, the controller may deactivate a smaller one of the hot start direct injections while maintaining a ratio of the hot start direct injection to the port injection fuel amount and while maintaining a total fuel injection amount for the cycle.

[0090] It is noted that in situations where the port-to-direct fuel injection ratio is reduced, the port-to-direct fuel injection ratio is reduced relative to a desired port-to-direct fuel injection ratio determined based on temperature and a number of combustion events counted from start. It is further noted that a start timing of the port and direct fuel injections may be adjusted depending on the reduction in port-to-direct fuel injection. As one example, the earlier injections may be retarded more than the later injections. This may improve start timing because the more retarded injection timing allows an earlier first cylinder to be targeted for combustion.Also, less fuel mass is required as the engine begins to start, allowing the port-to-direct injection ratio to be changed as one fuel system may be able to provide all the required fuel mass.

[0091] Now, with reference to Fig. 5 shows an exemplary method 500 for compensating for minimum pulse width violations of a fuel injector when split direct injection is not enabled.

[0092] At 502, the method includes retrieving a particular split fuel injection ratio (including a ratio of fuel split between single port fuel injection and single direct fuel injection). When retrieving the ratio, control may determine whether any of the port and direct fuel injection amounts are below the minimum pulse width of the corresponding fuel injector (e.g., whether the port fuel injection amount is below the minimum pulse width of the port fuel injector or whether the direct fuel injection amount is below the minimum pulse width of the direct fuel injector). If not, at 504, in response to all of the split fuel injection amounts being above the minimum pulse width of their respective injectors, the particular DI / PFI split ratio is maintained.

[0093] If any of the injections are below the minimum pulse width of the corresponding injector, the method includes, at 506, disabling port injection and injecting via direct injection only. For example, the direct injection pulse width may be increased to account for the fuel that would have otherwise been delivered via the port injector. Additionally, a direct injection timing (e.g., a start timing) may be advanced to accommodate the overall fuel pulse width. Further, if the direct injection amount exceeds a threshold amount after updating to account for the port injection disabling, the direct injection may be split into multiple injections.For example, if multiple injections are desired and the fuel mass is sufficient for multiple injections because the PFI fuel mass has been shifted to DI, the direct injection can then be divided into multiple DI injections.

[0094] Now, with reference to Fig.7 shows an example fuel injection adjustment. Map 700 shows engine speed at trace 702, a PFI / DI split ratio at trace 704, a compression DI to intake DI split ratio (DIc / DIi) at trace 706, engine temperature at trace 708, a direct injection pulse width (relative to a minimum pulse width) at traces 710-711 (including a compression DI pulse width at solid trace 711 and an intake DI pulse width at dashed trace 710), a port injection pulse width (relative to a minimum pulse width) at trace 712, and engine load at trace 714. All traces are plotted over time along the x-axis.

[0095] Before t1, the engine may be shut down. The engine temperature may be low at this time. At t1, an engine restart is confirmed in response to an increase in engine load. Due to the lower engine temperature at the time of engine restart, an engine cold start is determined. In response to the engine restart condition, the engine may be started, and engine firing and fuel combustion resume.

[0096] Specifically, at t1, a lookup table is referenced to determine a baseline DI / PFI split ratio based on engine operating conditions, including engine load and engine temperature. In the illustrated example, the split ratio includes a relatively higher proportion of port-injected fuel and a relatively lower proportion of direct-injected fuel (e.g., 0.8 PFI and 0.2 DI). Furthermore, due to the lower engine temperature at start-up, the direct-injected fuel quantity is delivered as a split DI injection with a relatively higher proportion of direct-injected fuel on the compression stroke and a relatively lower proportion of direct-injected fuel on the intake stroke.

[0097] Between t1 and t2, the PFI / DI ratio is varied as engine speed and load vary, while the split DI ratio is also varied. In the present example, as engine speed increases, the ratio of direct fuel injected on the intake stroke is reduced, while the ratio of direct fuel injected on the compression stroke is proportionally increased.

[0098] Between t2 and t3, (only) one of the multiple direct injection pulse widths (herein, the pulse width for the fuel directly injected during the intake stroke) begins to approach the minimum pulse width (dashed line Min). To reduce minimum pulse width violations while approaching the minimum DI pulse width, the DI / PFI split ratio is increased, as indicated by the stepwise reduction of the port injection pulse width and the corresponding increase of the direct injection pulse width. At the same time, the DI split ratio is maintained by proportionally increasing the compression stroke and intake stroke DI pulse widths.

[0099] Another engine restart is shown after t4. At t5, an engine restart request is received. This determines that an engine hot start is occurring due to the higher engine temperature at the time of the engine restart. In response to the engine restart condition, the engine may be started, and engine firing and fuel combustion resume. Based on engine operating conditions, including engine load and engine temperature, a lookup table is referenced to determine a baseline DI / PFI split ratio. In the example shown, due to the hot start conditions, the entire fuel mass is delivered through the DI system to provide the fastest and most robust start timing. Thus, the PFI system is kept deactivated, and the split ratio includes a higher proportion of direct injected fuel.In addition, due to the higher engine temperature at the time of start-up, the direct injected fuel quantity is delivered as a split DI injection with a relatively higher proportion of direct injected fuel during the compression stroke and a relatively lower proportion of direct injected fuel during the intake stroke.

[0100] Between t5 and t6, as start-up and initial engine combustion progress, the proportion of direct injection fuel mass delivered on the intake stroke is reduced while the fuel mass injected on the compression stroke is increased, optionally with an increase in the number of compression stroke DI injections.

[0101] At t6, once a threshold number of combustion events has elapsed, port fuel injection is activated, and then the PFI / DI ratio is varied based on engine load and engine speed, while the split DI ratio is further varied. In the present example, as engine speed increases, the intake stroke direct fuel ratio is reduced, while the compression stroke direct fuel ratio is proportionally increased, and the port fuel ratio is increased.

[0102] Between t6 and t7, (only) one of the multiple direct injection pulse widths (herein, the pulse width for the fuel directly injected on the intake stroke) begins to approach the minimum pulse width (dashed line Min). At t7, to reduce minimum pulse width violations while approaching the DI minimum pulse width, the smaller of the DI injections, here, the intake stroke injection, is deactivated, while the pulse width of the compression stroke DI injection is increased accordingly while maintaining the DI / PFI split ratio. The number of compression DI injections may also be increased. Thus, if multiple DI injections have begun to approach the minimum pulse width, then the compression stroke DI injection may have been deactivated, while the DI / PFI ratio is increased by adjustments (e.g., increasing) the intake stroke DI pulse width.

[0103] At t8, minimum pulse width violations due to a change in engine operating conditions should no longer be a problem. Therefore, firing with split DI use and split PFI / DI use resumes, with the DP / PFI and split DI ratios determined based on contributions from a lookup table stored as a function of engine speed and load.

[0104] In this way, fuel injection ratios can be controlled to reduce excursions of the port and direct injectors below their respective minimum pulse widths due to changes in engine operating conditions. In particular, fuel injection ratios can be controlled while delivering fuel as a split DI / PFI, regardless of whether the DI fuel is delivered as a single or split injection. By reducing the port-to-direct fuel injection ratio while adjusting a ratio of the direct injections to bring an amount of each of the direct injections closer together when multiple direct injections reach the minimum direct injection pulse width, the effectiveness of the split direct injections during engine starts can be improved while maintaining the total fuel injection amount for each cycle.In comparison, by reducing the port-to-direct fuel injection ratio while maintaining a ratio of the direct injections relative to each other when only one of the direct injections reaches the minimum direct injection pulse width, the DI split ratio can be maintained while maintaining a total fuel injection amount for the cycle. Additionally, engine emissions during a fuel injection transient can be better managed, particularly when the port fuel injector is connected to a high-pressure port fuel injection rail that is at least partially pressurized by the high-pressure fuel pump, which is also used to pressurize the direct injection fuel rail.By reducing the excursions of the port and direct fuel injectors to the minimum allowable pulse width regions, engine emissions and combustion stability can be improved even when DI / PFI ratios fluctuate in response to varying engine conditions. Overall engine performance is improved.

[0105] An example method includes: during an engine cold start, injecting, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the direct injections reaching a minimum direct injection pulse width, reducing a ratio of the port-to-direct fuel injection. In the preceding example, additionally or optionally, in response to multiple of the direct injections reaching the minimum direct injection pulse width, reducing the port-to-direct fuel injection ratio while adjusting a ratio of the direct injections to bring an amount of each of the direct injections closer to each other and while maintaining a total fuel injection amount for the cycle.In any or all of the preceding examples, additionally or optionally, in response to only one of the direct injections reaching the minimum direct injection pulse width, the port-to-direct fuel injection ratio is reduced while maintaining a ratio of the direct injections with respect to one another and while maintaining a total fuel injection amount for the cycle. In any or all of the preceding examples, additionally or optionally, the method further comprises, in response to the port fuel injection reaching a minimum port fuel injection pulse width, the port fuel injection is deactivated and a ratio of the direct injections with respect to one another and while maintaining a total fuel injection amount for the cycle.In any or all of the preceding examples, additionally or optionally, the method further comprises, during an engine hot restart, injecting, during a single cylinder cycle of the hot restart, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the hot start direct injections reaching the minimum direct injection pulse width, deactivating a smaller one of the hot start direct injections while maintaining a ratio of the hot start direct injection to the port injection fuel amount and while maintaining a total fuel injection amount for the cycle.In any or all of the preceding examples, additionally or optionally, the method further comprises, in response to the hot start port fuel injection reaching the minimum port fuel injection pulse width, deactivating the port fuel injection and maintaining a ratio of the direct injections with respect to one another and while maintaining a total fuel injection amount for the cycle. In any or all of the preceding examples, additionally or optionally, the method further comprises, in response to a plurality of the hot start direct injections reaching the minimum direct injection pulse width, deactivating one of the hot start direct injections while maintaining a ratio of the hot start port fuel injection to the direct injection and while maintaining a total fuel injection amount for the cycle.In any or all of the preceding examples, additionally or optionally, the port-to-direct fuel injection ratio is reduced relative to a desired port-to-direct fuel injection ratio determined based on temperature and a number of combustion events counted from start. In any or all of the preceding examples, additionally or optionally, the port fuel injection is injected from a port fuel rail pressurized at least in part by a high-pressure direct injection fuel pump. In any or all of the preceding examples, additionally or optionally, a start timing of the port and direct fuel injections is adjusted depending on the reduction in the port-to-direct fuel injection ratio.

[0106] Another example method includes: during startup, injecting, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; in response to cold start conditions and one of the direct injectors reaching a minimum direct injection pulse width, reducing a port-to-direct fuel injection ratio; and in response to hot restart conditions and one of the direct injectors reaching the minimum direct injection pulse width, deactivating a smaller one of the direct injectors while maintaining a port-to-port direct injection ratio.In the preceding example, additionally or optionally, in response to cold start conditions and multiple of the direct injections reaching the minimum direct injection pulse width, the port-to-direct fuel injection ratio is reduced while adjusting a ratio of the direct injections to bring an amount of each of the direct injections closer to each other and while maintaining a total fuel injection amount for the cycle. In any or all of the preceding examples, additionally or optionally, in response to cold start conditions and only one of the direct injections reaching the minimum direct injection pulse width, the port-to-direct fuel injection ratio is reduced while maintaining a ratio of the direct injections with respect to each other.In any or all of the preceding examples, additionally or optionally, in response to cold start conditions and port fuel injection reaching a minimum port fuel injection pulse width, disabling port fuel injection and maintaining a ratio of direct injections with respect to one another. In any or all of the preceding examples, the method further additionally or optionally includes, in response to hot start conditions and port fuel injection reaching the minimum port fuel injection pulse width, disabling port fuel injection and maintaining a ratio of direct injections with respect to one another.In any or all of the preceding examples, the method further additionally or optionally includes, in response to hot start conditions and multiple direct injections reaching the minimum direct injection pulse width, deactivating the direct injections while maintaining a port-to-direct fuel injection ratio. In any or all of the preceding examples, additionally or optionally, the port fuel injection is injected from a port fuel rail pressurized at least in part by a high-pressure direct injection fuel pump. In any or all of the preceding examples, additionally or optionally, a start timing of the port and direct fuel injections is adjusted depending on the reduction in the port-to-direct fuel injection ratio.In any or all of the preceding examples, the method further additionally or optionally comprises, in response to warmed engine running conditions after start-up, determining a port-to-direct fuel injection ratio as a function of speed load, wherein the engine is a boosted engine that compresses intake air with a turbine-driven compressor.

[0107] Another example includes: an engine having a cylinder; a port fuel injector mounted in an intake manifold of the cylinder; a direct fuel injector mounted directly in the cylinder; a temperature sensor for sensing engine temperature; and a controller having instructions stored in memory that, when executed, cause the injector to inject, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the direct injections reaching a minimum direct injection pulse width, adjust a ratio of the port to direct fuel injection.

[0108] 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 also to be considered included within the subject matter of the present disclosure.

Claims

[1] Method comprising: during an engine cold start, injecting, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the direct injectors reaching a minimum direct injection pulse width, reducing a port-to-direct fuel injection ratio. [2] The method of claim 1, wherein in response to a plurality of the direct injections reaching the minimum direct injection pulse width, the port-to-direct fuel injection ratio is reduced while adjusting a ratio of the direct injections to bring an amount of each of the direct injections closer to each other and while maintaining a total fuel injection amount for the cycle. [3] The method of claim 1, wherein in response to only one of the direct injections reaching the minimum direct injection pulse width, the port-to-direct fuel injection ratio is reduced while maintaining a ratio of the direct injections with respect to one another and while maintaining a total fuel injection amount for the cycle. [4] The method of claim 1, further comprising, in response to the port fuel injection reaching a minimum port fuel injection pulse width, disabling the port fuel injection and maintaining a ratio of the direct injections with respect to one another and while maintaining a total fuel injection amount for the cycle. [5] The method of claim 1, further comprising, during an engine hot restart, injecting, during a single cylinder cycle of the hot restart, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and in response to one of the hot start direct injections reaching the minimum direct injection pulse width, deactivating a smaller one of the hot start direct injections while maintaining a ratio of the hot start direct injection to the port injection fuel amount and while maintaining a total fuel injection amount for the cycle. [6] The method of claim 5, further comprising, in response to the hot start port fuel injection reaching the minimum port fuel injection pulse width, disabling port fuel injection and maintaining a ratio of the direct injections with respect to one another and while maintaining a total fuel injection amount for the cycle. [7] The method of claim 5, further comprising, in response to a plurality of the hot start direct injections reaching the minimum direct injection pulse width, disabling one of the hot start direct injections while maintaining a ratio of the hot start port injection to the direct injection and while maintaining a total fuel injection amount for the cycle. [8] The method of claim 1, wherein the port-to-direct fuel injection ratio is reduced relative to a desired port-to-direct fuel injection ratio determined based on temperature and a number of combustion events counted from start. [9] The method of claim 1, wherein the port fuel injection is injected from a port fuel injection rail that is at least partially pressurized by a high pressure direct injection fuel pump, and wherein a start timing of the port and direct fuel injections is adjusted in response to the reduction in the port to direct fuel injection ratio. [10] System comprising: an engine having one cylinder; a direct fuel injector mounted directly in the cylinder, the direct fuel injector being connected to a direct fuel injection manifold, which is pressurized by a high-pressure direct injection fuel pump; a manifold fuel injector mounted in an intake manifold of the cylinder, the manifold fuel injector being provided with a port fuel injection manifold which is at least partially pressurized by the high pressure direct injection fuel pump; a temperature sensor for detecting the engine temperature; and a controller having computer-readable instructions stored in non-volatile memory for the following: during a start, the injection, by the injector, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection and a compression stroke direct fuel injection; and in response to one of the direct injection systems Minimum direct injection pulse width is reached, adjusting a port-to-direct fuel injection ratio. [11] The system of claim 10, wherein the controller includes further instructions for: in response to cold start conditions and one of the direct injectors reaching a minimum direct injection pulse width, reducing the port-to-direct fuel injection ratio; and in response to hot restart conditions and one of the intake stroke and compression stroke direct injection reaching the minimum direct injection pulse width, disabling a smaller one of the intake stroke and Compression stroke direct injection while maintaining the port-to-direct fuel injection ratio. [12] The system of claim 11, wherein the controller includes further instructions for: in response to cold start conditions and that each of the intake stroke and Compression stroke direct injection reaches the minimum direct injection pulse width, reducing the port-to-direct fuel injection ratio while adjusting a ratio of intake stroke direct injection with respect to compression stroke direct injection to bring an amount of each of the intake stroke and compression stroke direct injection closer to each other and while maintaining a total fuel injection amount for the cycle. [13] The system of claim 12, wherein the controller includes further instructions for: in response to cold start conditions and that only one of the intake stroke and Compression stroke direct injection reaches the minimum direct injection pulse width, reducing the port-to-direct fuel injection ratio while maintaining a ratio of intake stroke and compression stroke direct injection with respect to each other. [14] The system of claim 13, wherein the controller includes further instructions for: in response to cold start conditions and the port fuel injection reaching a minimum port fuel injection pulse width, disabling the port fuel injection and maintaining the ratio of the intake stroke and compression stroke direct injection with respect to each other. [15] The system of claim 14, wherein the controller includes further instructions for: in response to hot start conditions and the port fuel injection reaching the minimum port fuel injection pulse width, disabling the port fuel injection and maintaining a ratio of the direct injections with respect to one another; and in response to hot start conditions and each of the intake stroke and compression stroke direct injection reaching the minimum direct injection pulse width, disabling one of the intake stroke and compression stroke direct injection while maintaining the port-to-direct fuel injection ratio.

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