METHODS AND SYSTEMS FOR CONTROLLING FUEL INJECTION

Abstract

Engine process, which includes the following: Estimating a temperature at the direct injection device tip other than a fuel temperature based on cylinder conditions, including cylinder combustion conditions and cylinder valve operation; and in response to the deactivation or reactivation of a direct injection device, setting one or more of a direct injection fuel pulse and a port injection fuel pulse based on each of the estimated temperature at the direct injection device tip and the fuel temperature.

Description

AREA

[0001] The present application generally relates to systems and methods for adjusting the operation of fuel injectors of an internal combustion engine to compensate for temperature variations. GENERAL STATE OF THE ART / SUMMARY

[0002] Engines can be designed to deliver fuel to an engine cylinder using one or more of port fuel injection and direct fuel injection. Port Fuel Direct Injection (PFDI) engines are capable of utilizing both fuel injection systems. For example, at high engine loads, fuel can be injected directly into an engine cylinder via a direct fuel injector, exploiting the charge air cooling characteristics of direct fuel injection (DI). At lower engine loads and during engine start-ups, fuel can be injected into an intake manifold of the engine cylinder via a port fuel injector, reducing particulate matter emissions. Under still other conditions, a portion of the fuel can be delivered to the cylinder via the port fuel injector, while a remainder of the fuel is delivered to the cylinder via the direct fuel injector.

[0003] While direct injection is enabled during engine operation, fuel flow through the direct injector nozzle maintains temperatures at the direct injector tip substantially lower (e.g., approximately 100°C). In comparison, during periods of engine operation when direct fuel injection is disabled and no fuel is being delivered via the direct injector (e.g., under conditions where only port fuel injection is scheduled), the temperature at the direct injector tip may rise substantially (e.g., approximately 260°C). When fuel is subsequently injected from the fuel injector, the fuel may have the elevated temperature and thus a lower density than expected, resulting in unintended fueling errors.For example, due to less fuel being delivered than intended, direct injection can result in a lean air-fuel ratio error. In one example, if the temperature rises by 80°C, a lean error of 4% is generated.

[0004] An exemplary approach for compensating for an elevated temperature at the direct injector tip is presented in US Pat. No. 9,322,340 B2. There, an injection pulse width is adjusted in response to an elevated temperature of a knock control fluid at the time of release from a direct injector. Specifically, a longer direct injection pulse width is applied as the predicted temperature of the fuel at the time of release from the direct injector increases. A similar approach for controlling injection pulses at elevated temperatures is also shown in US Pat. Nos. 4,945,880 A and US Pat. No. 2013 / 0054115 A1.

[0005] However, the present inventors have recognized potential problems with the above approach. For example, even with the '340 setting, fueling errors may persist due to differences in fuel temperature and tip temperature behavior during the period of direct injection deactivation, as well as during the subsequent direct injection.For example, heat transfer to the direct injector during the deactivation period may differ based on whether cylinder combustion continued via port fuel injection, the average cylinder load when cylinder combustion continued, whether any cylinder combustion was stopped, whether air continued to be pumped through the cylinder when combustion was stopped due to selective fuel deactivation without valve deactivation, whether both the fuel injector and valves were deactivated when combustion was stopped, whether the engine was still running when combustion was stopped, etc. Some of the factors may also affect fuel temperature, although the effect is different from that on the direct injector tip temperature.In yet another example, when the direct injector is reactivated and fuel is released from it, the temperature at the injector tip may cool at a faster rate than the fuel temperature. As a result of these fluctuations, if the direct injection of knock control fluid is corrected to compensate for the increased temperature of the fuel at the time of release, the change in density may be overestimated. The direct injection pulse width may be increased more than necessary (or longer than necessary), resulting in an error that is a rich air-fuel ratio. Alternatively, if the direct injection pulse width is increased less than necessary (or shorter than necessary), the change in density may be underestimated, resulting in an error that is a lean air-fuel ratio.As yet another example, the '340 approach calculates fuel temperature based on a derived fuel rail temperature. However, the fuel rail temperature can remain stable during engine transients. This results in the calculated fuel temperature remaining essentially constant while the actual fuel temperature increases.

[0006] It is therefore an object of the present invention to provide an improved engine method and system which avoids the aforementioned disadvantages and can maintain the desired air-fuel ratio even under fluctuating temperatures.

[0007] According to the invention, the stated object is achieved by an engine method according to claim 1 and an engine system according to claim 10. Preferred embodiments of the invention are the subject of the dependent claims.

[0008] The method for an engine thus includes: in response to deactivation of a direct injector, estimating a direct injector tip temperature different from the fuel temperature based on cylinder conditions, including cylinder combustion conditions, cylinder valve operation, and port injector operation during deactivation; and in response to reactivation of the direct injector, adjusting a direct injection fuel pulse based on each of the estimated direct injector tip temperature and the fuel temperature. In this way, direct injection fuel delivery errors may be reduced.

[0009] The engine may be configured with both port and direct fuel injection capability. During engine operation, including under in-cylinder combustion and in-cylinder non-combustion conditions, an engine controller may continuously estimate a direct injector tip temperature different from a fuel temperature. The fuel temperature may be estimated via a fuel rail temperature sensor. The direct injector tip temperature may be determined as a function of heat flow into the direct injector (such as due to combustion heat when in-cylinder combustion is enabled) and cooling flow into the direct injector (such as due to fuel being refilled at the injector).Therefore, the heat flow and cooling flow estimates may vary based on several combustion parameters, such as whether the direct injector is enabled or not, whether cylinder combustion via port injection continues or not when the direct injector is disabled, whether the cylinder valves are operated or not when the direct injector is disabled and the cylinder is not performing combustion, the average cylinder load when the direct injector is disabled and the cylinder is not performing combustion, the duration of the direct injector deactivation, etc. The controller may determine a steady-state temperature at the direct injector tip when direct injection is enabled and subsequently monitor a transient change in the temperature at the direct injector tip while direct injection is disabled.Therefore, the fuel temperature may fluctuate less drastically than the tip temperature. The controller may simultaneously determine a fuel density correction factor based on the tip temperature relative to the fuel temperature and apply the correction factor to an estimate of a nominal fuel density so that fluctuations in fuel density can be monitored in real time. At the time of direct injector reactivation, the controller may adjust a direct injection pulse width based on the corrected fuel density estimate. For example, at a time of direct injector reactivation following a period of DI deactivation where cylinders continued to receive and combust fuel from the port injectors, the DI tip temperature may have risen above the steady-state temperature.Accordingly, the controller may compensate for a decrease in fuel density by increasing the fuel pulse width by a larger amount. In comparison, at the time of reactivation of the direct injector after a period of DI deactivation where cylinders were not performing combustion but continued to pump air through the valves (e.g., a DFSO event), the temperature at the DI tip may have dropped below the steady-state temperature. Accordingly, the controller may compensate for an increase in fuel density by increasing the DI fuel pulse width by a smaller amount or by decreasing the DI fuel pulse width. Additionally, the pulse width may be varied over a duration since reactivation with a time constant based on the transient change in the tip temperature.

[0010] In this way, the fuel injection settings of a direct injector can be adjusted to compensate for changes in fuel density due to different fuel heating levels and injector peaks during a direct injector deactivation period. The technical effect of differently compensating the rate of change in fuel temperature and the rate of change in peak temperature is to account for the different temperature profiles when direct injection is reactivated.By continuously estimating the temperature at the direct injector tip based on fluctuations in heat flow and cooling flow to the injector, temperature-induced changes in fuel density can be more accurately estimated, and the injection pulse width can be adjusted accordingly without causing (lean or rich) air-fuel ratio excursions. Furthermore, the charge air cooling effect of the directly injected fuel can be better utilized. Furthermore, direct injector fouling and thermal degradation can be reduced.

[0011] It should be understood that the foregoing summary is provided to introduce, in a simplified form, a selection of concepts further described in the detailed description. It is not intended to identify important or significant features of the claimed subject matter, the scope of which is defined solely in the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that overcome any disadvantages noted 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 coupled in a hybrid vehicle system. Fig. Figure 2 depicts an exemplary embodiment of a fuel system configured for port injection and direct injection and associated with the engine of Fig. 1 can be used. Fig. 3 provides a flowchart illustrating an example method that may be implemented to adjust a direct injection pulse width at the time of injector reactivation. Fig. 4 illustrates an example model that may be used by an engine controller to estimate a change in DI fuel system temperature during a period of DI deactivation and at the time of DI reactivation. Fig. Figure 5 shows an example table of empirically determined manifold and direct fuel fractions (DI / PFI split ratio). Fig. 6 illustrates an exemplary graph for deriving a direct injector tip temperature based on heat flow and cooling flow to the injector under engine combustion and non-combustion conditions. Fig. 7 illustrates an exemplary diagram of balancing direct injection and port injection fuel pulse width according to the present disclosure. DETAILED DESCRIPTION

[0012] The following description relates to systems and methods for adjusting the operation of a direct fuel injector of an internal combustion engine after a period of deactivation to compensate for a change in injected fuel density with temperature. An exemplary embodiment of a hybrid vehicle system having an engine cylinder configured with each of a direct fuel injector and a port fuel injector is described in Fig. 1 shown. Fig. 2 shows an example fuel system that is compatible with the engine system of Fig. 1 can be used. A split ratio of fuel to be supplied via port injection relative to direct injection can be determined based on engine operating conditions, such as the engine speed / load table from Fig. 5. During certain engine operating conditions, fuel may only be delivered to the engine via port fuel injection, and the direct injectors may be deactivated. During an extended period of deactivation of the direct injectors, a temperature may increase at the direct injector, the direct injection fuel rail, and consequently, the fuel to be delivered via the direct injector. An engine controller may execute a routine, such as the example routine of Fig. 3, to continuously estimate a direct injector tip temperature different from a fuel temperature and correct a fuel density based on the estimates. The controller may rely on a model, such as the example model of Fig. 4 to estimate the temperature change at the DI tip. For example, the controller may compare the heat flow and the cooling flow to the direct injector across engine combustion conditions and non-combustion conditions to determine a net heat flow to the injector tip, as described with reference to the example of Fig. 6. Subsequently, a fuel injection pulse width may be corrected to compensate for a change in fuel density induced by the net heat flow to the injector, as described with reference to Fig. 7. In this way, fuel delivery errors during activation of the direct injector after a period of deactivation of the direct injector can be reduced and thermal damage to the fuel system components can be prevented.

[0013] Regarding the terminology used in this detailed description, a high-pressure pump or direct injection pump can be abbreviated as HPP (High Pressure Pump). Similarly, a low-pressure pump or lift pump can be abbreviated as LPP (Low Pressure Pump). Port fuel injection can be abbreviated as PFI (Port Fuel Injection), while direct fuel injection can be abbreviated as DI. Furthermore, fuel rail pressure, or the value of the pressure of fuel within a fuel rail, can be abbreviated as FRP (Fuel Rail Pressure).

[0014] Fig. 1 depicts an example of a combustion chamber or cylinder of an internal combustion engine 10. The engine 10 may be coupled in a propulsion system for traveling on a road, such as a vehicle system 5. In one example, the vehicle system 5 may be a hybrid electric vehicle system.

[0015] The engine 10 may be controlled at least partially by a control system including the controller 12 and by input from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinder (also referred to herein as the "combustion chamber") 14 of the engine 10 may include combustion chamber walls 136 in which a piston 138 is disposed. The piston 138 may be coupled to a crankshaft 140 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. The crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a gear system. Further, a starter motor (not shown) may be coupled to the crankshaft 140 via a flywheel to enable a starting operation of the engine 10.

[0016] Cylinder 14 may receive intake air through a series of intake air passages 142, 144, and 146. Intake air passage 146 may communicate with other cylinders of engine 10 in addition to cylinder 14. In some examples, one or more of the intake passages may include a boost device, such as a turbocharger or a supercharger. As shown in Fig. 1, the engine 10 is configured with a turbocharger including a compressor 174 disposed between the intake passages 142 and 144 and an exhaust turbine 176 disposed along an exhaust passage 148. The compressor 174 may be driven at least partially via a shaft 180 by the exhaust turbine 176 when the boosting device is configured as a turbocharger. However, in other examples, such as when the engine 10 is provided with a supercharger, the exhaust turbine 176 may optionally be omitted, wherein the compressor 174 may be driven by mechanical inputs from an electric motor or the engine. A throttle 162, including a throttle plate 164, may be provided along an intake passage of the engine to vary the flow rate and / or pressure of the intake air provided to the engine cylinders.For example, the throttle 162 may be positioned downstream of the compressor 174, as shown in FIG. Fig. 1, or alternatively it may be provided upstream of the compressor 174.

[0017] The exhaust passage 148 may receive exhaust gases from other cylinders of the engine 10 in addition to cylinder 14. An exhaust gas sensor 128 is shown coupled to the exhaust passage 148 upstream of an emissions control device 178. The sensor 128 may be selected from various suitable sensors for providing an indication of an exhaust air-fuel ratio, such as a linear oxygen sensor or UEGO (Universal Exhaust Gas Oxygen Sensor; broadband or wide-range oxygen sensor), a dual-state oxygen sensor or EGO (as shown), a HEGO (Heated EGO) sensor, a NOx, HC, or CO sensor. The emissions control device 178 may be a three-way catalyst (TWC), a NOx trap, various other emissions control devices, or combinations thereof.

[0018] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown including at least one intake poppet valve 150 and at least one exhaust poppet valve 156 located in an upper region of cylinder 14. In some examples, each cylinder of engine 10, including cylinder 14, may include at least two intake poppet valves and at least two exhaust poppet valves located in an upper region of the cylinder.

[0019] The intake valve 150 may be controlled by the controller 12 via an actuator 152. Similarly, the exhaust valve 156 may be controlled by the controller 12 via an actuator 154. Under some conditions, the controller 12 may vary the signals provided to the actuators 152 and 154 to control the opening and closing of the respective intake and exhaust valves. The position of the intake valve 150 and the exhaust valve 156 may be determined by respective valve position sensors (not shown). The valve actuators may be of the electric valve actuation type, the cam actuation type, or a combination thereof. The intake and exhaust valve actuation may be controlled simultaneously, or any of variable intake cam actuation, variable exhaust cam actuation, dual independent variable cam actuation, or fixed cam actuation may be used.Each cam actuation system may include one or more cams, and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems operable by controller 12 to vary valve operation. For example, cylinder 14 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation, including CPS and / or VCT. In other examples, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or a variable valve timing actuator or actuation system.

[0020] Cylinder 14 may have a compression ratio that is the ratio of the volume when piston 138 is at bottom dead center to the volume at top dead center. In one example, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where other fuels are used, the compression ratio may be increased. This may occur, for example, when using fuels with a higher octane rating or fuels with a higher latent heat of vaporization. The compression ratio may also be increased when using direct injection due to its effect on engine knock.

[0021] In some examples, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. Ignition system 190 may provide an ignition spark to combustion chamber 14 via spark plug 192 in response to an ignition pre-ignition signal SA from controller 12 under selected operating modes. However, in some embodiments, spark plug 192 may be omitted, such as when engine 10 can initiate combustion through auto-ignition or by injecting fuel, which may be the case with some diesel engines.

[0022] In some examples, each cylinder of engine 10 may be configured with one or more fuel injectors to provide fuel thereto. As a non-limiting example, cylinder 14 is shown including two fuel injectors 166 and 170. Fuel injectors 166 and 170 may be configured to deliver fuel received from fuel system 8. As described with reference to Fig. 2, the fuel system 8 may include one or more fuel tanks, fuel pumps, and fuel rails. As shown, the fuel injector 166 is directly coupled to the cylinder 14 for injecting fuel directly therein in proportion to the pulse width of the signal FPW-1 received from the controller 12 via an electronic driver 168. In this manner, the fuel injector 166 provides what is known as direct injection (hereinafter referred to as "DI") of fuel into the combustion cylinder 14. While the injector 166 of the illustration of Fig. 1 is positioned on one side of the cylinder 14, it may alternatively be located above the piston, such as near the position of the spark plug 192. Such a position may improve mixing and combustion when the engine is operating on an alcohol-containing fuel, since some alcohol-containing fuels have lower volatility. Alternatively, the injector may be located above and near the intake valve to improve mixing. Fuel may be supplied to the fuel injector 166 from a fuel tank of the fuel system 8 via a high-pressure fuel pump and a fuel rail. Further, the fuel tank may include a pressure transducer that provides a signal to the controller 12.

[0023] The fuel injector 170 is shown disposed in the intake passage 146 rather than in the cylinder 14 in a configuration that provides so-called port fuel injection (hereinafter referred to as "PFT") into the intake manifold upstream of the cylinder 14. The fuel injector 170 can inject fuel taken from the fuel system 8 in proportion to the pulse width of the FPW-2 signal received from the controller 12 via the electronic driver 171. It should be noted that, as shown, a single driver 168 or 171 can be used for both fuel injection systems, or multiple drivers, for example, driver 168 for the fuel injector 166 and driver 171 for the fuel injector 170, can be used.

[0024] In an alternative example, each of fuel injectors 166 and 170 may be configured as a direct fuel injector for injecting fuel directly into cylinder 14. In yet another example, each of fuel injectors 166 and 170 may be configured as a port fuel injector for injecting fuel upstream of intake valve 150. In still further examples, cylinder 14 may include only a single fuel injector configured to receive different fuels in varying relative amounts as a fuel mixture from the fuel systems and further configured to inject this fuel mixture either as a direct fuel injector directly into the cylinder or as a port fuel injector upstream of the intake valves.Accordingly, it is understood that the fuel systems described herein are not intended to be limited by the specific fuel injector configurations described herein as examples.

[0025] Fuel may be delivered to the cylinder by both injectors during a single cylinder cycle. For example, each injector may provide a portion of a total fuel injection that is combusted within cylinder 14. Further, the distribution and / or relative amount of fuel delivered by each injector may vary with operating conditions, such as engine load, knock, and exhaust temperature, as described below. Fuel injected into the intake manifold may be delivered during an intake valve open event, a closed intake valve event (e.g., substantially prior to the intake stroke), and during both intake valve open and closed operation.Likewise, directly injected fuel may be delivered, for example, during an intake stroke, as well as partially during a preceding exhaust stroke, during the intake stroke, and partially during the compression stroke. Thus, even during a single combustion event, injected fuel may be injected at different times from the port and direct fuel injectors. Furthermore, during a single combustion event, multiple injections of the delivered fuel may be performed per cycle. The multiple injections may be performed during the compression stroke, intake stroke, or any suitable combination thereof.

[0026] Fuel injectors 166 and 170 may have different characteristics. These include 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 objectives, 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.

[0027] Fuel tanks in the fuel system 8 may contain different types of fuels, such as fuels with different fuel properties and different fuel compositions. These differences may include differences in alcohol content, water content, octane rating, latent heats, fuel blends, and / or combinations thereof, etc. An example of fuels with different latent heats could include gasoline as the first fuel type with lower latent heats of vaporization and ethanol as the second fuel type with higher latent heats of vaporization. In another example, the engine may use gasoline as the first fuel type and an alcohol-containing fuel blend, such as E85 (which is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline), as the second fuel type.Other possible substances include water, methanol, a mixture of alcohol and water, a mixture of water and methanol, a mixture of alcohols, etc.

[0028] In yet another example, both fuels may be alcohol blends with different alcohol compositions, where the first fuel type may be a gasoline-alcohol blend with a lower alcohol concentration, such as E10 (which is approximately 10% ethanol), while the second fuel type may be a gasoline-alcohol blend with a higher alcohol concentration, such as E85 (which is approximately 85% ethanol). Furthermore, the first and second fuels may also differ in other fuel properties, such as a difference in temperature, viscosity, octane number, etc. Furthermore, the fuel properties of one or both fuel tanks may change frequently, for example, due to daily fluctuations in tank refilling.

[0029] The control 12 is in Fig. 1 as a microcomputer including a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values, which in this specific example is shown as a non-volatile read-only memory 110 for storing executable instructions, a random access memory 112, a keep-alive memory 114, and a data bus.The controller 12 may receive various signals from sensors coupled to the engine 10, in addition to the signals previously discussed, including measurements of the inducted mass air flow (MAF) from a mass air flow sensor 122; engine coolant temperature (ECT) from a temperature sensor 116 coupled to a cooling sleeve 118; a profile ignition pickup (PIP) signal from a Hall effect sensor 120 (or other type) coupled to the crankshaft 140; throttle position (TP) from a throttle position sensor; and a manifold absolute pressure (MAP) signal from a sensor 124. An 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 can be used to provide an indication of vacuum or pressure in the intake manifold.The controller 12 receives signals from the various sensors. Fig. 1 and exposes the various actuators Fig. 1 to adjust engine operation based on the received signals and instructions stored in a memory of the controller. For example, based on a pulse width signal commanded by the controller to a driver coupled to the direct injector, a fuel pulse from the direct injector may be delivered to a corresponding cylinder.

[0030] As described above, Fig. 1 merely represents one cylinder of a multi-cylinder engine. Thus, each cylinder may equally include its own set of intake / exhaust valves, fuel injector(s), spark plug, etc. It is understood that the engine 10 may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Furthermore, each of these cylinders may include some or all of the various components described in Fig. 1 with reference to the cylinder 14.

[0031] In some examples, vehicle 5 may be a hybrid vehicle with multiple torque sources available to one or more vehicle wheels 55. In other examples, vehicle 5 may be a conventional vehicle with only an internal combustion engine or an electric vehicle with only electric machine(s). In the depicted example, vehicle 5 includes an engine 10 and an electric machine 52. Electric machine 52 may be an electric motor or an electric motor / generator. Crankshaft 140 of engine 10 and electric machine 52 are connected to vehicle wheels 55 via transmission 54 when one or more clutches 56 are engaged. In the depicted example, a first clutch 56 is provided between crankshaft 140 and electric machine 52, and a second clutch 56 is provided between electric machine 52 and transmission 54.The controller 12 may send a signal to an actuator of each clutch 56 to engage or disengage the clutch to connect or disconnect the crankshaft 140 to or from the electric machine 52 and its associated components and / or to connect or disconnect the electric machine 52 to or from the transmission 54 and its associated components. The transmission 54 may be a manual transmission, a planetary gear system, or another type of transmission. The powertrain may be configured in a variety of ways, including as a parallel, series, or series-parallel hybrid vehicle.

[0032] The electric machine 52 receives electrical power from a traction battery 58 to provide torque to the vehicle wheels 55. The electric machine 52 can also be operated as a generator, for example, to provide electrical power to charge the battery 58 during braking.

[0033] Fig. 2 forms an exemplary embodiment 200 of a fuel system, such as the fuel system 8 of Fig. 1, schematically. The fuel system 200 may be operated to supply 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 functions described with reference to Fig. 3 described procedures.

[0034] The fuel system 200 includes a fuel storage tank 210 for storing fuel on board the vehicle, a low-pressure fuel pump (LPP) 212 (also referred to herein as a fuel lift pump 212), and a high-pressure fuel pump (HPP) 214 (also referred to herein as a fuel injection pump 214). The 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 low-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 pump) having an electric (e.g., DC) pump motor, wherein the pressure increase in the pump and / or the flow rate through the pump can be controlled by varying the electrical power provided to the pump motor, thereby increasing or decreasing the motor speed. For example, the increase in flow rate and / or pressure in the lift pump may be reduced if the controller decreases the electrical power provided to the lift pump 212. The increase in 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 low-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 power the low-pressure pump. Thus, by varying the voltage and / or current supplied to the low-pressure fuel pump, the flow rate and pressure of the fuel supplied at the inlet of the high-pressure fuel pump 214 are adjusted.

[0035] The LPP 212 may be fluidly coupled to a filter 217, which can remove minor contaminants contained in the fuel that could potentially damage fuel handling components. A check valve 213, which can enable fuel delivery and maintain fuel rail 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 can 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 relief valve 219 may include a ball-and-spring mechanism that engages and seals, for example, at a predetermined pressure differential.The target pressure differential at which the relief valve 219 is designed to open may take on various suitable values; as a non-limiting example, the target value may be 6.4 bar or 5 bar(g). An orifice 223 may be used to allow air and / or fuel vapor to escape from the lift pump 212. This escape via the orifice 223 may further be used to drive a jet pump used to transfer fuel from one location to another within the tank 210. In one example, an orifice check valve (not shown) may be arranged in series with the orifice 223. In some embodiments, the fuel system 8 may include one or more (e.g., a series of) check valves fluidly coupled to the low-pressure fuel pump 212 to prevent fuel from backing up to the valves.In this context, upflow refers to a 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 from there to the fuel rails.

[0036] Fuel drawn through the LPP 212 may be delivered at a lower pressure into a fuel passage 218 leading to an inlet 203 of the HPP 214. A solenoid valve 281 upstream of the inlet 203 regulates the amount of fuel that is compressed. The HPP 214 may then deliver fuel to a first fuel rail 250 coupled to one or more fuel injectors of a first group of direct injectors 252 (also referred to herein as a first injector group). Fuel drawn through the LPP 212 may further be delivered to a second fuel rail 260 coupled to one or more fuel injectors of a second group of port injectors 262 (also referred to herein as a second injector group).The HPP 214 can be operated to raise the pressure of fuel supplied to the first fuel rail above the lift pump pressure, with the first fuel rail coupled to the high-pressure direct injection group. As a result, high-pressure DI may be possible while PFI may operate at a lower pressure.

[0037] While each of the first fuel rail 250 and the second fuel rail 260 is illustrated delivering fuel to four fuel injectors of the respective injector group 252, 262, it should be understood 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 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 depicted external to the controller 222, it should be understood 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 depicted, such as those included in the controller 12 of FIG. Fig. 1 are included.

[0038] 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, which utilizes a solenoid-activated control valve (e.g., fuel volume controller, solenoid valve, etc.) 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, unlike the engine-driven LPP 212, may be mechanically driven by the engine. The HPP 214 includes a pump piston 228, a pump compression chamber 205 (also referred to herein as the compression chamber), and a step 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 single-cylinder, cam-driven pump. A (in Fig. A sensor (not shown in Figure 2) may be positioned near cam 230 to enable determination of the cam's angular position (e.g., between 0 and 360 degrees), which may be communicated to controller 222. Step chamber 227 may also be coupled to fuel passage 218 via a fuel line 282. An accumulator 284 may be coupled to the node.

[0039] A lift pump fuel pressure sensor 231 may be positioned along the fuel passage 218 between the lift pump 212 and the high-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 high-pressure fuel pump inlet pressure. 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 high-pressure fuel pump 214 so that the high-pressure fuel pump receives liquid fuel and not fuel vapor, and / or to minimize the average electrical power delivered to the lift pump 212.

[0040] The first fuel rail 250 includes a first fuel rail pressure sensor 248 for providing an indication of the 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 the port injection fuel rail pressure to the controller 222. An engine speed sensor 233 may be used to provide an indication of the engine speed to the controller 222. The engine speed indication may be used to identify the speed of the high-pressure fuel pump 214, since the pump 214 is mechanically driven by the engine 202, for example, via the crankshaft or camshaft.

[0041] The first fuel rail 250 is coupled to an outlet 208 of the HPP 214 along the fuel passage 278. A check valve 274 and a pressure relief valve (also referred to as a pump relief valve) 272 may be positioned between the outlet 208 of the HPP 214 and the first (DI) fuel rail 250. The pump relief valve 272 may be coupled to a bypass passage 279 of the fuel passage 278. 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. The pump relief valve 272 may limit the pressure in the fuel passage 278 downstream of the HPP 214 and upstream of the first fuel rail 250.For example, the pump relief valve 272 may limit the pressure in the fuel passage 278 to 200 bar. The pump relief valve 272 allows fuel flow from the DI fuel rail 250 toward the pump outlet 208 when the fuel rail pressure is greater than a predetermined pressure. The valves 244 and 242 cooperate to maintain the low-pressure fuel rail 260 pressurized at a predetermined low pressure. The pressure relief valve 242 helps limit the pressure that may develop in the fuel rail 260 due to thermal expansion of the fuel.

[0042] Based on engine operating conditions, fuel may be delivered via one or more port injectors 262 and direct injectors 252. For example, under high load conditions, fuel may be delivered to a cylinder at a respective engine stroke only via direct injection, with the port injectors 262 deactivated. In another example, during medium load conditions, fuel may be delivered to a cylinder at a respective engine stroke only via direct injection. As yet another example, during low load conditions, engine starts, and warm idle conditions, fuel may be delivered to a cylinder at a respective engine stroke only via port injection, with the direct injectors 252 deactivated.

[0043] It should be noted 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.

[0044] The controller 12 may further control the operation of each of the fuel pumps 212 and 214 to adjust an amount, pressure, flow rate, etc., of fuel delivered to the engine. As one example, the controller 12 may vary a pressure setting, a pump stroke amount, a pump duty cycle command, and / or a fuel flow rate of the fuel pumps to deliver fuel to different locations in the fuel system. A driver (not shown) electronically coupled to the controller 222 may be used to send a control signal to the low-pressure pump, if desired, to adjust the output (e.g., speed, flow rate, and / or pressure) of the low-pressure pump.

[0045] Because fuel injection from the direct injectors results in cooling of the injectors, after a period of inactivity, pressure may build up due to fuel trapped at the DI fuel rail 250, resulting in increased temperature and pressure acting on the DI fuel rail 250. Furthermore, temperatures at the direct injector tips may begin to rise. If the DI injector tip temperature rises above a threshold where thermal degradation and fouling of the injector (also known as corking) may occur, the direct injector may need to be cooled to prevent damage to the fuel system components.While in one example only port injection is possible, the direct injector may be temporarily operated to release an amount of fuel sufficient to cool the temperature at the direct injector tip to within an allowable temperature range. The increase in temperature at the direct injector tip may also affect the density of the fuel released during direct injection. If direct injection is performed for knock control or charge air cooling (such as when a fuel is injected immediately after a period of direct injection-only operation), the charge air cooling efficiency of the direct injection may be reduced at the elevated fuel and tip temperature due to the decrease in the latent heat of vaporization of the fuel with increasing temperature.In addition, due to the change in fuel density, the mass of fuel released with a given fuel pulse width may decrease, resulting in a lean excursion of the air-fuel ratio.

[0046] The inventors recognized that the temperature at the DI tip can vary based on several parameters. In particular, the net heat transferred to the injector tip varies depending on the presence or absence of combustion heat, fuel flow cooling, air flow cooling, etc. As one example, if direct injection is disabled but cylinder combustion continues, more combustion heat may be transferred to the injector tip than to the cooling flow from the fuel refill, resulting in a higher tip temperature. As another example, if direct injection is disabled and cylinder combustion is interrupted but valve operation is not suspended, less combustion heat is transferred to the injector tip, while more cooling flow is transferred due to injector refill as well as air being pumped through the cylinders.This can lead to a lower tip temperature. As yet another example, if direct injection is disabled, interrupting cylinder combustion and suspending valve operation, less cooling flow is transferred, resulting in net heating of the injector tip. In either situation, the fuel temperature at the fuel rail may remain essentially stable or change differently than the tip temperature.

[0047] To more accurately compensate for temperature drifts at the DI tip and the temperature-dependent change in fuel density, the controller may continuously estimate the temperature at the DI tip based on various operating conditions, including heat transfer to the direct injector in the presence and absence of combustion, cooling flow to the direct injector due to the presence or absence of fuel flow, and fuel temperature and cooling flow to the direct injector due to airflow through the cylinder. As a result, the controller may estimate a more accurate estimate of an instantaneous temperature at the direct injector tip. As described herein with reference to Fig. 3, to reduce the occurrence of air-fuel ratio excursions when direct injection is activated after a period of deactivation, a pulse width commanded to the direct injector may be adjusted based on the instantaneous estimate of the temperature at the direct injector tip. In one example, the change in DI fuel system temperature and the corresponding change in fuel density may be calculated by the engine controller using an algorithm or model, such as the exemplary model of Fig. 4, or via the diagrams from Fig. 6 can be estimated. In particular, by adjusting a DI fuel pulse after DI reactivation to compensate for the difference in the change in injector tip temperature to the change in fuel temperature over the period of DI deactivation, the charge air cooling benefits of DI injection can be provided without inadvertently leaning or richening the air-fuel ratio.

[0048] In this way, the system enables Fig. 1 - 2 an engine system comprising an engine cylinder, including an intake valve and an exhaust valve; a direct fuel injector for supplying fuel directly into the engine cylinder; a port fuel injector for supplying fuel into an intake manifold upstream of the intake valve of the engine cylinder; a fuel rail providing fuel to each of the direct and port fuel injectors, a temperature sensor coupled to the fuel rail, and a controller.The controller may be configured with computer-readable instructions stored on non-transitory memory to: deactivate the direct fuel injector; increase a commanded direct injection fuel pulse width in response to reactivating the direct fuel injector after a period of fueling the engine only via port injection; and decrease the commanded direct injection fuel pulse width in response to reactivating the direct fuel injector after a period of no fueling. In one example, a rate of the increase may be increased as one or more of engine speed, engine load, spark retard, estimated fuel rail temperature, and duration of increases in fueling to the engine.In another example, a rate of decrease may be increased in response to one or more of the intake and exhaust valves remaining active during the engine defueling period and an increase in the engine defueling period. The controller may further include instructions to estimate a fuel flow rate into the deactivated direct injector; and, as the estimated fuel flow rate increases, decrease the increase rate in response to reactivating the direct injector after the engine defueling period only via port injection; and increase the decrease rate in response to reactivating the direct injector after the engine defueling period.

[0049] With reference to Fig. 3, an exemplary method 300 is illustrated for reducing air-fuel ratio excursions due to changes in fuel density with increasing temperature when a direct injection system is deactivated. Instructions for performing method 300 and the other methods included herein may be performed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the engine system, such as those described above with reference to Fig. 1 and Fig. 2. The controller may use motor actuators of the engine system to adjust engine operation according to the methods described below.

[0050] At 302, engine operating conditions may be determined by the controller. The engine operating conditions may include engine load, engine temperature, engine speed, driver torque demand, etc. Depending on the estimated operating conditions, a variety of engine parameters may be determined. For example, at 304, a fuel injection schedule may be determined. This includes determining an amount of fuel to be delivered to a cylinder (e.g., based on torque demand) and a fuel injection timing. Furthermore, a fuel injection mode and a split ratio between port fuel injection and direct fuel injection may be determined for the current engine operating conditions.In one example, at high engine loads, direct injection (DI) of fuel into an engine cylinder via a direct fuel injector may be selected to utilize the charge air cooling characteristics of DI, allowing engine cylinders to operate at higher compression ratios without experiencing undesirable engine knock. When direct injection is selected, the controller may determine whether to deliver the fuel as a single injection or split into multiple injections, and further whether to deliver the injection(s) on an intake stroke and / or a compression stroke. In another example, at lower engine loads (low engine speed) and during engine starts (particularly cold starts), port fuel injection (PFI) of fuel into an intake manifold of the engine cylinder via a port fuel injector may be selected to reduce particulate matter emissions.When port fuel injection is selected, the controller may determine whether to deliver fuel during a closed intake valve event or an open intake valve event. Other conditions may exist under which a portion of the fuel may be delivered to the cylinder via the port fuel injector while a remainder of the fuel is delivered to the cylinder via the direct fuel injector. Determining the fuel injection schedule may further include, per injector, determining a pulse width for the fuel injector and a duration between injection pulses based on the estimated engine operating conditions.

[0051] In one example, the determined fuel plan may include a split ratio between fuel to be delivered via port injection and direct injection, wherein the split ratio is determined from a lookup table of the controller, such as the example table of Fig. 5, is determined. With reference to Fig. 5, a table 500 for determining port and direct fuel injection fuel fractions for a total amount of fuel delivered to an engine during an engine cycle is shown. The table from Fig. 5 may be a basis for determining a mode of fuel system operation (DI only, PFI only, or PFI and DI combined (PFDI)) as in the method of Fig. 3. The vertical axis represents engine speed, and engine speeds are specified along the vertical axis. The horizontal axis represents engine load, and engine load values ​​are specified along the horizontal axis. In this example, table cells 502 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 0.6, or 60%, is the direct fuel injector fuel fraction.Thus, if the desired fuel injection mass is 1 gram of fuel during one engine cycle, 0.4 grams of fuel is port-injected fuel and 0.6 grams of fuel is 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 table cell contains a single value of 0.6 for a direct injector fuel fraction of 2000 rpm and a load of 0.2, then the port-injector fuel fraction is 1 - 0.6 = 0.4.

[0052] In this example, it can be observed that the port fuel injection fraction is highest at lower engine speeds and loads. In the depicted example, table cell 504 represents an engine speed / load condition where all fuel is delivered via port fuel injection only. At this speed / load condition, direct fuel injection is disabled. The direct fuel injection fraction is highest at mid-level engine speeds and loads. In the depicted example, table cell 506 represents an engine speed / load condition where all fuel is delivered via direct fuel injection only. At this speed / load condition, port fuel injection is disabled.The port fuel injection fraction increases at higher engine speeds when the timing for direct fuel injection 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.

[0053] With further reference to Fig. 3, the routine includes determining at 306 whether the conditions for deactivating the direct injector have been met. In one example, the DI deactivation conditions are asserted when a port fuel injection only (PFI only) fueling mode has been selected based on the current engine operating conditions. For example, PFI only fueling may be requested during low engine load and low engine temperature conditions, as well as during engine starts. In another example, the DI deactivation conditions are asserted when combustion is interrupted, such as during a fuel shutoff event, during an engine idle stop, and during an engine shutdown where the engine coasts to a stop without fuel.

[0054] If the DI deactivation conditions are not met, such as when a direct injection only (DI only) fueling mode or a dual fueling mode (with both port and direct injection, PFDI) has been selected, the method proceeds to 308, where the routine includes keeping the direct injectors enabled. At 310, the method includes estimating and monitoring a steady-state temperature at the DI tip based on combustion conditions. As described with reference to Fig. 6, the controller may continuously monitor conditions at the DI tip to estimate a steady-state temperature at the DI tip based on the heat flow and cooling flow to the injector. The steady-state estimate provides the controller with a reference temperature relative to which the temperature drifts, and corresponding fuel density drifts may be estimated during transient engine operation without direct injection.

[0055] Thus, the injector tip temperature model may run continuously while the vehicle is in use. In particular, it may run regardless of whether the DI injectors are currently in use. The temperature model may be initiated at vehicle start-up. In some examples, the temperature may continue to be modeled even after the vehicle is shut down. For example, the controller may track a vehicle shutdown time and use it as a factor in estimating an initial tip temperature on subsequent vehicle starts.

[0056] If the DI deactivation conditions are met, the method includes deactivating the direct injectors at 312. At 314, it may be determined whether the engine is still combusting. That is, it may be determined whether the engine is operating using only port fuel injection while direct injection is deactivated, or whether all engine combustion has been temporarily suspended. Control may then proceed to estimate a direct injector tip temperature different from a fuel temperature at the direct injector based on cylinder conditions, including cylinder combustion conditions and cylinder valve operation. Control may compare the combustion heat flow with respect to a fuel replenishment cooling flow into the direct injector over a period of deactivation to derive a current direct injector temperature.

[0057] Specifically, at 316 and 320, the controller may estimate a combustion heat flux into the direct injector based on whether cylinder combustion is present or absent while the direct injector is deactivated. This heat flux represents the heating power transferred from the combustion chamber to the direct injector tip. The transferred combustion heat flux depends on whether fuel is delivered to the cylinder and ignited. The temperature at the direct injector tip is increased above the fuel temperature when cylinder combustion is present; the temperature at the direct injector tip is decreased below the fuel temperature when cylinder combustion is absent.

[0058] When cylinder combustion is absent, a heat flow into the direct injection device can be estimated at 320 as a function of engine speed, average cylinder load, and cylinder head temperature (CHT). The controller can rely on a lookup table, an algorithm, or a model (such as the example model from Fig. 4) that takes engine speed, average cylinder load, and cylinder head temperature (CHT) as inputs, and provides a DI peak temperature (or an increase in DI peak temperature from a steady-state temperature) as the output. The controller may increase the DI peak temperature as engine speed increases, as average cylinder load increases, and / or as the sensed CHT increases.

[0059] If cylinder combustion is present, a heat flow into the direct injector may be estimated at 316 as a function of engine speed, average cylinder load, cylinder head temperature (CHT), and spark timing. The controller may rely on a lookup table, an algorithm, or a model (such as the example model shown in Fig. 4) that uses engine speed, average cylinder load, cylinder head temperature (CHT), and spark timing as inputs, and provides DI peak temperature (or an increase in DI peak temperature from a steady-state temperature) as the output. The controller may increase DI peak temperature as engine speed increases, as average cylinder load increases, as sensed CHT increases, and / or as spark timing is retarded from MBT. The increase in direct injector tip temperature may be increased relative to the increase in fuel temperature as average cylinder load increases. Additionally, the heat flow may be based on cylinder combustion air-fuel ratio when cylinder combustion is present.For example, if the actual injector tip temperature is hotter than the estimated tip temperature, less fuel may be injected than commanded, resulting in a leaner-than-designed air-fuel ratio. Alternatively, heat flow into the injector may be determined depending on the difference between the steady-state injector tip temperature (calculated at 320 when combustion is absent) and the combustion-induced injector tip temperature (calculated at 316 when combustion is present).

[0060] The injector tip temperature estimate is further based on whether port fuel injection is enabled (and the cylinders are combusting) or disabled (and the cylinders are not combusting) while the direct injector is disabled. The direct injector temperature is increased above the fuel temperature when port fuel injection is enabled. The direct injector temperature is decreased below the fuel temperature when port fuel injection is disabled. In another example, the baseline engine system is a DI engine. When the engine is not combusting, the DI injectors have a reduced heat flow rate and are cooling. When the DI injectors are not flowing fuel, the DI injector tip cooling is reduced and the DI injector tip temperature increases.

[0061] Next, at 318 and 322, the controller may estimate a cooling flow into the direct injector based on the injector refueling. The cooling flow into the direct injector may be determined as a function of the sensed or mapped fuel rail temperature (FRT) (e.g., sensed via a fuel rail temperature sensor) and may be further based on a fuel flow rate (into the direct injector). The fuel flow rate may be determined by the controller because the engine controller injects a known volume of fuel into the cylinder. When the injected mass is multiplied by the number of injection events per unit time (proportional to engine speed), it yields the volumetric flow rate.The cooling flow can be increased as the flow rate of the cooler fuel entering the injector tip increases and as the temperature of the fuel in the fuel rail drops.

[0062] While the above model describes two heat sources / sinks, namely fuel flow and combustion heat, it should be understood that this is not intended to be limiting, and additional heat sources and sinks (e.g., airflow, etc.) may be included in the injector tip temperature model. From 318, the method proceeds directly to 328.

[0063] If the cylinder is not combusting, the method proceeds from 322 to 324 where it may further determine if there is cooling flow due to the cylinder valves operating while the cylinder is not combusting. Thus, at 324, it may be determined whether the valves are active. In one example, fueling to the cylinder may be selectively disabled during DFSO while one or more cylinder valves (e.g., at least one intake and one exhaust valve) continue to operate and pump air through the cylinder. In still further examples, both fueling to the cylinder and valve operation may be selectively disabled during DFSO. Control may estimate the direct injector tip temperature, different from fuel temperature, based on whether cylinder valve operation is enabled or disabled while the direct injector is disabled.If valve operation is present at 326, the controller may update (e.g., increase) the net cooling flow into the direct injector based on airflow through the cylinder via the cylinder valves while the direct injector is deactivated. The temperature at the direct injector tip may be decreased more than the fuel temperature when cylinder valve operation is enabled, and the temperature at the direct injector tip may be increased more than the fuel temperature when cylinder valve operation is deactivated. The method then proceeds to 328. If cylinder deactivation valve operation is not present, the method proceeds directly to 328.

[0064] At 328, the method includes estimating a net heat transferred to the direct injector based on the (combustion) heat flow relative to the cooling (fuel replenishment) flow. In one example, the net heat transfer may be determined as follows: Net heating power = heating power from the combustion chamber to the injector tip − cooling power due to the cool fuel entering the injector nozzle.

[0065] It is understood that in the examples where the control algorithm automatically assigns a negative sign to the heat transfer from the fuel stream to account for cooling and automatically assigns a positive sign to the heat transfer from combustion to account for heating, the net heating power can be determined as the sum of the heat transfer from the cooling stream and the heat transfer from combustion.

[0066] It should be understood that the direct injector tip temperature may also be estimated differently than the fuel temperature based on a duration of direct injector deactivation. The tip temperature may increase faster and to a greater extent than the fuel temperature over the duration of direct injector deactivation. Particularly during transients, the fuel rail temperature may remain relatively stable due to the large volume (40 to 60 ml relative to a 0.02 to 0.5 ml injection event).

[0067] At 330, the method includes estimating a fuel density based on each of the estimated DI tip temperature and the estimated fuel temperature. The controller may use a lookup table or algorithm that uses the mapped DI tip temperature as the input and the fuel density (or a change in fuel density from a nominal density) as the output. As the DI tip temperature increases above a steady-state temperature, the estimated fuel density may decrease. In an example model, the change in tip temperature is proportional to the change in fuel density in the injector tip.

[0068] At 332, it may be determined whether the conditions for DI reactivation have been met. The conditions for DI reactivation may be considered met in response to, among other things, the end of a DFSO event, an increase in the vehicle operator's torque demand, the tip temperature reaching an upper limit, etc. If the conditions for DI reactivation are not met, the method includes, at 334, continuing to monitor the heat flow and cooling flow to the direct injector and updating an estimated value of the DI tip temperature and fuel density accordingly.

[0069] If the conditions for DI reactivation are met, then at 336, the method includes adjusting one or more of a direct injection fuel pulse and a port injection fuel pulse based on each of the estimated direct injector tip temperature and the fuel temperature. The powertrain control module (PCM) of the engine controller may calculate an initial fuel pulse width for the direct injector based on the engine operating conditions at the time of direct injector reactivation and subsequently update the initial fuel pulse width based on the estimated fuel density.As one example, the initial fuel pulse width for the direct injector may be increased while the estimated fuel density falls below a nominal fuel density (due to an increase in peak temperature or fuel temperature), and the initial fuel pulse width for the direct injector may be decreased while the estimated fuel density drop exceeds the nominal fuel density (due to a drop in peak temperature or fuel temperature). The port injection fuel pulse width may be adjusted based on the change in the direct injection fuel pulse width to maintain a combustion air-fuel ratio.

[0070] At 338, the updated fuel pulse width may be commanded to the respective direct and / or port fuel injectors. In this way, the initial settings of at least the DI fuel pulse may be adjusted to compensate for the change in fuel density due to the variation in the temperature at the DI tip. For example, a control signal corresponding to the updated DI fuel pulse width may be sent from the controller to an actuator coupled to the DI fuel injector to deliver fuel from the DI injector according to the updated pulse width. The routine then ends.

[0071] In an alternative example, the controller may determine a first correction factor to apply to the fuel density estimated based on the predicted increase in fuel temperature over the previous period of DI deactivation relative to the predicted decrease in fuel temperature at the time of reactivation due to fuel flow. Similarly, a second correction factor may be determined based on the predicted increase in injector tip temperature over the previous period of DI deactivation relative to the predicted decrease in injector tip temperature at the time of reactivation due to fuel flow.By applying each of the first and second correction factors, a net change in fuel temperature with each DI pulse following reactivation can be determined, and a corresponding change in fuel density can be estimated. By applying each of the first and second correction factors to the initially determined DI fuel pulse, an updated DI fuel pulse profile can be determined that compensates for the temperature-dependent change in fuel density.Thus, if the change in fuel density were estimated based only on the estimated increase in fuel temperature during the previous DI deactivation, without taking into account the predicted drop in fuel temperature due to the rapid drop in injector tip temperature following fuel flow through the DI injector, the estimated fuel density could be underestimated and overcompensated, resulting in a richer-than-designed injection.

[0072] Updating the DI fuel pulse width with the correction factors may include adjusting one or more injection parameters, such as a DI injection pulse width, an injection pressure, and an injection amount. In a particular example, during a first pulse after DI reactivation, a direct injection pulse width may be increased above the initial fuel pulse width, and over subsequent pulses, the direct injection pulse width may be gradually decreased toward the initial pulse width. Thus, the pulse width adjustments (including a magnitude of the adjustment and a speed of the adjustment) may be performed on a fueling event-by-fueling event basis, accounting for the change in fuel temperature due to fuel conditions and DI injector conditions at each fueling event.For example, the settings may account for the change in fuel density due to the slower rise in fuel temperature during the DI deactivation period and the slower fall in fuel temperature after reactivation, as well as the faster rise in injector tip temperature during the DI deactivation period and the faster fall in injector tip temperature after reactivation. Therefore, the increase in pulse width for the first pulse after DI reactivation may be greater than the decrease in pulse width for subsequent DI fuel pulses. In yet another example, the updated fuel system temperature may be fed into a DI slope correction calculation to compensate for the change in fuel density with fuel system temperature.

[0073] While the routine of Fig. 3 describes a DI fuel pulse adjustment for the case where DI is reactivated after a period of fueling the engine only via port injection, it should be understood that in alternative examples, the same routine may be used to predict changes in fuel density when a DI-only fuel system is reactivated after a period of deactivation. For example, changes in the temperature at the DI injector tip due to changes in the valve stem temperature over a period of DI deactivation in a DI-only fuel system may be detected and used to compensate for DI fuel pulses until DI fueling is reactivated. This allows lambda drifts due to the change in fuel system temperature to be reduced.

[0074] An exemplary model or algorithm that may be used by the controller to estimate heat transfer and heat loss from the injector tip and the resulting change in fuel temperature at the time (and after) DI reactivation is described with reference to Fig. 4. There, a map 400 depicts an exemplary model for deriving a mapped temperature at the direct injector tip (inj_tip_mdl_inf_temp).

[0075] The heat capacity of the concentrated thermal mass representing the injector tip (Inj_tip_mdl_inj_hc) is used to determine a heat capacity value (HC). The unit of heat capacity is joules / degree Celsius. Its dimension is energy / temperature difference.

[0076] The cooling of the direct injector tip from the fuel flow is determined by a controller K1 depending on the derived or measured temperature of the fuel in the fuel rail cooling the injector tip when the DI injectors are active (Inj_tip_mdl_frt, which has the unit degrees Celsius and the dimension of temperature), the fuel flow rate through a DI injector (Inj_tip_mdl_di_fuel_flow, which has the unit g / s and the dimension mass / time), and a mapped version of the temperature at the injector tip corresponding to a time step in the past (Inj_tip_mdl_inf_temp). The output of controller K1 is a heat flow rate from the fuel to the direct injector tip (Inj_tip_mdl_dt_hout_net, which has the unit watts and the dimension power).

[0077] A controller K2 calculates the conductive heat transfer to the direct injector tip as a function of the mapped version of the injector tip temperature corresponding to a time step in the past (Inj_tip_mdl_inf_temp), the mean effective temperature generated by the combustion process, which transfers heat to the injector tip through a fixed thermal resistance (Inj_tip_mdl_pfi_temp), and the injector heat capacity (HC). The output of controller K2 is a heat flow rate from the combustion chamber to the injector tip (Inj_tip_mdl_dt_hin_inj, which has the unit watts and the dimension of power).

[0078] The heat flow rate from the combustion chamber and the heat flow rate from the fuel to the direct injector tip are then input to a controller K3 (e.g., a comparator), which calculates the net heat flow rate to the injector tip (Inj_tip_mdl_del_heat, which has the unit watts and the dimension power). Next, a controller K4 (e.g., a multiplier) uses the calculated net heat flow rate in addition to the heat capacity of the direct injector (HC) and the time period over which this discrete time model is executed (Inj_tip_mdl_per, with the unit second and the dimension time difference), to calculate the change in temperature at the injector tip over the time period (Inj_tip_mdl_del_temp, with the unit degrees Celsius). In one example, the model is executed every 0.1 seconds.

[0079] The change in tip temperature is used by a controller K5 (e.g., an adder) in conjunction with the mapped version of the injector tip temperature corresponding to a time step in the past (Inj_tip_mdl_inf_temp) to provide a current estimate of the injector tip temperature (Inj_tip_mdl_inf_temp, with units of degrees Celsius and dimensions of temperature). A controller K6 is used to provide a delay such that a mapped version of the injector tip temperature corresponding to a time step in the past is provided. The mapped version of the injector tip temperature is then updated for the next iteration of the routine based on the current estimate of the injector tip temperature.If no prior estimate of the injector tip temperature is available, the routine is initiated using the cylinder head temperature (cht_degc, with units of degrees Celsius) on the first iteration of the routine. Thereafter, the injector tip temperature model is prepared with the updated mapped injector tip temperature on each iteration of the routine. This allows for a better estimate of the injector tip temperature and allows for better accounting for tip temperature-induced fuel density changes.

[0080] With reference to Fig. 6, a map 600 illustrates an exemplary determination of an effective temperature at the direct injector tip. The map continuously monitors a change in the temperature at the tip over a period of engine operation by comparing changes in heat flow and cooling flow to the direct injector and without cylinder combustion.

[0081] In the example shown, cylinder combustion occurs between t0 and t1 and after t2. Between t1 and t2, all cylinder combustion is temporarily disabled. A DFSO event, for example, can occur between t1 and t2.

[0082] Graph 602 depicts the mapping of a DI tip temperature when cylinder combustion is present. This includes the case where cylinder combustion is present after fueling via direct or port injection. Graph 604 depicts the mapping of a DI tip temperature when cylinder combustion is absent. Graph 606 depicts times when cylinder combustion is present or absent. Using graphs 602-606, the controller may calculate a resulting heat flux to the direct injector tip due to the heat of combustion, as illustrated at graph 608. The heat flux from combustion drops during the periods when cylinder combustion is not present (between t1 and t2).

[0083] The fuel rail temperature over the same period of time is shown at graph 610. Thus, the fuel rail temperature indicates the fuel temperature, which remains stable even when cylinder combustion is turned off or on. The fuel flow rate into the injector is shown at graph 612. The flow rate drops when combustion is disabled and increases when combustion is enabled. When fuel flow is disabled due to combustion being disabled, the heat flow from the refill immediately drops and there is no heat flow to the injector tip. When combustion is disabled, there is also an immediate drop in combustion heat flow to the direct injector, but there is still some combustion heat transferred to the injector tip.When fuel flow resumes at t2 due to combustion being reactivated, the heat flow from the fuel refill immediately resumes. Similarly, the combustion heat flow resumes when combustion is reactivated. However, there is a transient spike in the combustion heat flow due to the sudden influx of combustion heat into the cylinder. Using graphs 610 and 612, the controller may calculate a resulting heat transfer (or cooling flow) to the injector tip due to the refill heat, as illustrated at graph 614.

[0084] A net heat flow into the injector is determined relative to a zero flow (dashed line) as a function of (e.g., as a sum) the heat flow from combustion and the heat of refueling, as illustrated by graph 616 (i.e., graph 616 is a sum of graphs 614 and 608). Specifically, the net heat flow drops sharply when combustion is deactivated but then gradually increases over the duration of the direct injectors' deactivation without cylinder combustion. The net flow then rises sharply again when combustion is reactivated.

[0085] The effective injector tip temperature is then determined as a function of the net heat flow and a heat capacity of the injector tip, as shown in graph 618. The effective injector tip temperature decreases over the period of deactivation without cylinder combustion. When the direct injector is reactivated at the time of combustion reactivation, a fuel density estimate can be updated based on the instantaneous tip temperature.

[0086] An example setting of the fuel pulse width is shown in Fig.7. Map 700 depicts fuel delivery to a cylinder via port injection at graph 702 and fuel delivery to the same cylinder via direct injection at graph 704. The derived temperature at the direct injector tip is continuously estimated and monitored and is depicted at graph 708. Engine speed is depicted at graph 701.

[0087] In the depicted example, prior to t1, the engine cylinder may receive fuel via either direct or port fuel injection (graphs 702, 704) based on engine operating conditions (e.g., mid-range engine speed / load range), with a ratio of injections adjusted based on engine conditions to maintain exhaust stoichiometric. That is, both port and direct fuel injection may be enabled. The inferred temperature at the DI injector tip is estimated at this time based on the higher heat flow transferred to the injector tip due to cylinder combustion relative to the lower cooling flow transferred to the injector tip due to fuel flow through the injector nozzle. During combustion, the inferred temperature at the DI injector nozzle stabilizes to a steady-state temperature.

[0088] At t1, there is an increase in driver demand, and the engine moves to a higher speed / load range where the likelihood of knock is higher. In response to the increase in driver demand, the amount of fuel injected directly into the cylinder via the direct injector is increased, while the amount of fuel injected into the intake manifold via port fuel injection is correspondingly decreased to maintain the combustion air-fuel ratio stoichiometric. At this time, the inferred temperature at the DI injector tip continues to be estimated. There is a slight decrease in temperature due to an increase in cooling flow transferred to the injector tip as a result of the increase in fuel flow through the direct injector nozzle.The derived temperature is essentially at or around the steady-state temperature, and therefore the fuel density remains essentially at or around a nominal density. Therefore, the DI fuel pulse width does not need to be adjusted to compensate for the temperature change.

[0089] Due to a change in engine operating conditions (e.g., a change in engine speed and load conditions for a lower speed / load range), direct fuel injection is deactivated at t2. For example, the engine may be operating at low loads where knocking is rare and where port fuel injection provides higher engine power benefits. At t2, the port fuel injector remains activated, and cylinder combustion continues with fuel injected into the intake manifold, while the direct fuel injector is operated at idle or deactivated. The direct fuel injector may remain deactivated or continue to operate at idle for a duration between t2 and t3.

[0090] The inferred temperature at the DI injector tip continues to be estimated while the direct injector is deactivated. There is a gradual increase in the tip temperature due to a net heat flow into the injector tip. The net heat flow is due to the combustion heat that continues to flow from cylinder combustion into the injector tip, while the cooling flow transferred to the injector tip decreases due to the decrease in fuel flow through the direct injector nozzle. The inferred temperature gradually increases above the steady-state temperature, and therefore the fuel density begins to decrease with respect to the nominal density.

[0091] At t3, there is a further change in engine speed / load to medium to high engine speed / load conditions. At this time, direct fuel injection is reactivated to increase the benefits of charge air cooling. An initial fuel pulse width (shown in dashed segment 703) is determined based on engine operating conditions. However, due to the increase in temperature at the injector tip over the duration during which the direct injector was deactivated but cylinder combustion continued (between t2 and t3), the density of the fuel released by the direct injector drops.If the fuel is directly injected according to the initially determined fuel pulse width 703 without compensating for the temperature-induced change in fuel density, the fuel mass would be lower than intended, resulting in a lean air-fuel ratio error. To correct this, at t3, the direct injection pulse width is adjusted by an amount based on the inferred injector tip temperature, in this case, increased. Specifically, the direct injection pulse width is increased by an amount dependent on the increase in tip temperature above the steady-state injector tip temperature. The increased pulse width includes a larger and longer pulse width than the initial pulse width. In addition, a port injection fuel pulse width is adjusted, in this case, decreased.Thus, the fuel pulse width can continuously change based on the amount of fuel the controller is injecting. However, this base pulse width is set based on the fuel density at the injector tip, which varies depending on the mapped injector tip temperature.

[0092] The pulse width of direct injection of fuel from the direct injector into the engine cylinder is temporarily increased based on the fact that the direct injector was previously deactivated, but cylinder combustion continued. For example, direct injection may continue at the increased pulse width from t3 for a number of engine cycles until the derived DI peak temperature returns to a steady-state temperature at t4. After that, the increase may be discontinued, and a specific nominal fuel pulse width is resumed based on engine speed / load conditions during operation at a nominal fuel density at the steady-state peak temperature.

[0093] Between t4 and t5, fuel is injected directly into the cylinder via the direct injector and injected into the intake manifold via the port injector, with amounts selected based on engine speed / load conditions and driver rpm demand. The inferred temperature at the DI injector tip continues to be estimated. There is a slight drop in temperature due to an increase in cooling flow transferred to the injector tip as a result of fuel flow through the direct injector nozzle.

[0094] At t5, due to a change in engine operating conditions (e.g., a decrease in driver torque demand), a DFSO event is confirmed, and all fueling to the cylinder (including fueling via direct injection and port injection) is disabled. The engine begins to coast. The direct injector and port injection may remain disabled for a duration between t5 and t6, or continue to idle. While fueling to the cylinder is disabled between t5 and t6, cylinder valve operation is not disabled, and air continues to be pumped into the cylinder through the intake and exhaust valves. This increases cooling flow to the direct injector while reducing the combustion heat transferred to the direct injector.The derived temperature at the DI injector tip continues to be estimated while the direct injector and port injector are deactivated. There is a gradual decrease in tip temperature due to a net cooling flow into the injector tip. (In other words, the combustion temperature is lower than the current tip temperature, fuel cooling is zero, and the tip temperature is cooling toward the combustion temperature.) The net cooling flow is due to the reduced combustion heat flowing from cylinder combustion into the injector tip and the increased cooling flow transferred to the injector tip as a result of cylinder valve operation and fuel flow through the direct injector nozzle.The derived temperature gradually falls below the steady-state temperature and therefore the fuel density begins to increase with respect to the nominal density.

[0095] At t6, DFSO conditions cease, and there is a change in engine speed / load conditions to medium to high engine speed / load conditions. At this time, fueling to the cylinder resumes. Direct and port fuel injection are reactivated. An initial fuel pulse width (shown in dashed segment 705) is determined based on the engine operating conditions. However, due to the decrease in injector tip temperature over the duration that the direct and port fuel injection were deactivated and cylinder combustion was interrupted, but cylinder valve operation continued (between t2 and t3), the density of the fuel released by the direct injector increases.If the fuel is directly injected according to the initially determined fuel pulse width 705 without compensating for the temperature-induced change in fuel density, the fuel mass would be higher than intended, resulting in a rich air-fuel ratio error. To correct this, at t6, the direct injection pulse width is adjusted by an amount based on the inferred injector tip temperature, in this case, decreased. Specifically, the direct injection pulse width is decreased by an amount dependent on the decrease in tip temperature beyond the steady-state injector tip temperature. The decreased pulse width includes a smaller and shorter pulse width than the initial pulse width. In addition, a port injection fuel pulse width is adjusted, in this case, increased.In one example, if the tip temperature is colder than the steady-state value, the fueling to an open circuit may tend toward over-fueling, resulting in a rich fault (if the temperature is not compensated). If the actual tip temperature is higher than the assumed tip temperature, this may cause a lean fault.

[0096] The pulse width of the direct injection of fuel from the direct injector into the engine cylinder is temporarily reduced based on the fact that the direct injector was previously deactivated and cylinder combustion was interrupted. For example, direct injection may continue at the reduced pulse width from t6 for a number of engine cycles until the derived DI peak temperature returns to a steady-state temperature. After that, the reduction may be discontinued and a specific nominal fuel pulse width is resumed based on the engine speed / load conditions during operation at a nominal fuel density at the steady-state peak temperature.

[0097] If cylinder valve operation also discontinued during fuel deactivation at t5-t6, it is understood that the inferred temperature at the direct injector tip may have increased above steady-state temperature (or decreased by a lesser amount). This would be due to the higher heat flow and lower cooling flow, resulting in net heating of the injector. Consequently, the direct injection pulse width would have been increased after reactivation at t6 for a number of engine cycles until the inferred temperature at the DI tip returned to steady-state temperature, after which the increase would cease and a specific nominal fuel pulse width would resume based on engine speed / load conditions.In this way, the fuel density is continuously updated based on the continuously updated temperature at the tip and a direct injection fuel pulse width is adjusted accordingly to compensate for the change in fuel density.

[0098] In this way, a temperature-induced change in fuel density at the time of release from a previously deactivated direct injector can be better accounted for. By continuously estimating heat flow to the direct injector in the presence and absence of cylinder combustion, changes in the temperature at the DI injector tip can be more accurately monitored based on combustion heat transfer, cylinder valve operation, port injector operation, cylinder load changes, etc. By adjusting the settings of a direct injection fuel pulse based on the instantaneous temperature at the direct injector tip, changes in fuel density due to temperature can be better determined and compensated for, reducing unintended air-force excursions. Furthermore, the charge air cooling effect of direct injection can be better utilized.In addition, contamination of the direct injection device and thermal degradation can be reduced.

[0099] An example method includes estimating a direct injector tip temperature other than a fuel temperature based on cylinder conditions, including cylinder combustion conditions and cylinder valve operation; and, in response to deactivation or reactivation of a direct injector, adjusting one or more of a direct injection fuel pulse and a port injection fuel pulse based on each of the estimated direct injector tip temperature and the fuel temperature.In the preceding example, additionally or optionally, estimating based on cylinder combustion conditions includes estimating based on whether cylinder combustion is present or absent while the direct injector is deactivated, wherein the direct injector tip temperature is increased higher than the fuel temperature when cylinder combustion is present, and wherein the direct injector tip temperature is decreased below the fuel temperature when cylinder combustion is absent. In any or all of the preceding examples, additionally or optionally, an increase in the direct injector tip temperature is increased relative to an increase in fuel temperature while an average cylinder load increases when cylinder combustion is present.In any or all of the preceding examples, additionally or optionally, an increase in temperature at the direct injector tip is increased relative to an increase in fuel temperature while an air-fuel ratio becomes leaner than stoichiometry when cylinder combustion is present. In any or all of the preceding examples, additionally or optionally, estimating based on cylinder valve operation includes estimating based on whether cylinder valve operation is enabled or disabled while the direct injector is disabled, wherein the temperature at the direct injector tip is decreased more than the fuel temperature when cylinder valve operation is enabled, wherein the temperature at the direct injector tip is decreased more than the fuel temperature when cylinder valve operation is disabled.In any or all of the preceding examples, the estimating is further additionally or optionally based on whether port injection is enabled or disabled while the direct injector is disabled, wherein the direct injector tip temperature is increased above the fuel temperature when port injection is enabled, and wherein the direct injector tip temperature is decreased below the fuel temperature when port injection is disabled. In any or all of the preceding examples, the method further additionally or optionally includes adjusting the estimated direct injector tip temperature, different from the fuel temperature, based on a duration of direct injector deactivation.In any or all of the preceding examples, adjusting the direct injection fuel pulse additionally or optionally includes: estimating a fuel density based on each of the estimated direct injector tip temperature and the fuel temperature; calculating an initial fuel pulse width based on engine operating conditions upon reactivation of the direct injector; and updating the initial fuel pulse width based on the estimated fuel density. In any or all of the preceding examples, the initial fuel pulse width is additionally or optionally increased while the estimated fuel density falls below a nominal fuel density and is decreased while the estimated fuel density exceeds the nominal fuel density.

[0100] Another exemplary method includes comparing a combustion heat flow with respect to a fuel replenishment cooling flow into a direct injector over a period of injector deactivation, the combustion heat flow based on cylinder conditions, the fuel replenishment cooling flow based on a fuel flow rate and a fuel rail temperature; and adjusting a direct injection fuel pulse width after reactivation of the direct injector based on the comparison.In the preceding example, the heat flow is additionally or optionally increased in response to one or more of cylinder combustion continuing via port fuel injection over the period of direct injector deactivation, increasing engine speed or load, increasing spark retard, increasing cylinder head temperature, and increasing the period of cylinder combustion with port fuel injection only, and wherein the combustion heat flow is decreased in response to one or more of port fuel injection deactivation and cylinder valve deactivation over the period of direct injector deactivation and increasing the period of direct injector deactivation without cylinder combustion.In any or all of the preceding examples, the fuel replenishment cooling flow is additionally or optionally increased in response to one or more of decreasing the fuel rail temperature and increasing the fuel flow rate to the direct injector. In any or all of the preceding examples, the adjusting additionally or optionally includes updating an initial temperature at the direct injector tip, estimated immediately prior to deactivation of the direct injector, with a correction factor based on comparing the combustion heat flow to the fuel replenishment cooling flow and further based on a thermal mass of the direct injector tip.In any or all of the preceding examples, adjusting further additionally or optionally includes: estimating a fuel density based on the updated direct injector tip temperature; and adjusting an initial direct injection fuel pulse width based on the estimated fuel density relative to a nominal fuel density, wherein the initial direct injection fuel pulse width is based on engine operating conditions upon reactivation of the direct injector. In any or all of the preceding examples, the direct injection fuel pulse width is further additionally or optionally based on an indication of engine knock, wherein the indication includes detecting knock via a knock sensor or anticipating knock based on engine operating conditions.In any or all of the preceding examples, adjusting additionally or optionally includes increasing an initial direct injection fuel pulse width while the combustion heat flow exceeds the fuel replenishment cooling flow and decreasing the initial direct injection fuel pulse width while the fuel replenishment cooling flow exceeds the combustion heat flow, wherein the initial direct injection fuel pulse width is based on engine operating conditions upon reactivation of the direct injector.

[0101] Another exemplary method for an engine includes: increasing a direct injection fuel pulse width at a time of reactivation of the direct injector during a first condition in response to deactivation of the direct injector without deactivation of combustion; and decreasing the direct injection fuel pulse width at a time of reactivation of the direct injector during a second condition in response to deactivation of the direct injector with deactivation of combustion. In the preceding example, additionally or optionally, during the first condition, a rate of increase is increased while one or more of engine speed, engine load, spark retard, estimated fuel rail temperature, and duration of fueling to the engine increases, and the decrease has a first rate during the second condition,when the cylinder valves are deactivated, and a second speed when the cylinder valves are active, wherein the second speed is higher than the first speed. In any or all of the preceding examples, the method further additionally or optionally comprises estimating a steady-state, different from a steady-state fuel temperature, temperature at the direct injector tip based on cylinder conditions prior to deactivation of the direct injector; and estimating a transition temperature at the direct injector tip based on the steady-state temperature at the direct injector tip,the steady-state fuel temperature and the cylinder conditions after deactivation of the direct injector; wherein the increasing during the first condition is based on the steady-state temperature at the direct injector tip relative to the transition temperature at the direct injector tip, and the decreasing during the second condition is based on the steady-state temperature at the direct injector tip relative to the transition temperature at the direct injector tip. In any or all of the preceding examples, the method further additionally or optionally includes adjusting a port injection fuel pulse width at the time of reactivation of the direct injector during each of the first and second conditions.

[0102] In another embodiment, the engine method includes calculating a direct injector tip temperature based on a sum of combustion heat flow and fuel refill cooling flow to a direct injector over a period of injector deactivation, wherein the combustion heat flow is based on cylinder conditions, wherein the fuel refill cooling flow is based on a fuel flow rate and a fuel rail temperature; and adjusting a direct injection fuel pulse width based on the calculated tip temperature after reactivation of the direct injector. In the preceding example, additionally or optionally, the direct injection fuel pulse width that is increased or decreased is a nominal fuel pulse width based on each of engine speed, engine load, knock intensity, and a nominal fuel density.In any or all of the preceding examples, additionally or optionally, a rate of reduction is increased in response to one or more of the intake and exhaust valves remaining active during the engine defueling period and an increase in the engine defueling period.In any or all of the preceding examples, the method additionally or optionally includes estimating a direct injector tip temperature other than a fuel temperature based on cylinder conditions, including cylinder combustion conditions and cylinder valve operation; and, in response to deactivation or reactivation of a direct injector, adjusting one or more of a direct injection fuel pulse and a manifold injected fuel pulse based on each of the estimated direct injector tip temperature and the fuel temperature.

[0103] In another representation, an engine system comprises an engine cylinder including an intake valve and an exhaust valve; a direct fuel injector for directly delivering fuel to the engine cylinder; a port fuel injector for delivering fuel to an intake manifold upstream of the intake valve of the engine cylinder; a fuel rail that provides fuel to each of the direct and port fuel injectors; a temperature sensor coupled to the fuel rail; and a controller.The controller is configured with computer-readable instructions stored on non-transitory memory to: deactivate the direct fuel injector; increase a commanded direct injection fuel pulse width in response to reactivating the direct fuel injector after a period of fueling the engine only via port fuel injection; and decrease the commanded direct injection fuel pulse width in response to reactivating the direct fuel injector after a period of no fueling. In the preceding example, a rate of the increase is additionally or optionally increased as one or more of engine speed, engine load, spark retard, estimated fuel rail temperature, and duration of increases in fueling to the engine.In any or all of the preceding examples, additionally or optionally, a rate of reduction is increased in response to one or more of the intake and exhaust valves remaining active during the engine defueling period and an increase in the engine defueling period.In any or all of the preceding examples, the controller additionally or optionally includes further instructions to: estimate a fuel flow rate into the deactivated direct injector; and, as the estimated fuel flow rate increases, decrease the increase rate in response to reactivating the direct injector after the period of fueling the engine only via port injection; and increase the decrease rate in response to reactivating the direct injector after the period of no fueling the engine.

[0104] It should be noted that the example control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-volatile memory and executed by the control system, including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Accordingly, various illustrated acts, operations, and / or functions may be performed in the illustrated order, in parallel, or in some cases, may be omitted.Likewise, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but rather is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy employed. Further, the described acts, operations, and / or functions may graphically represent code programmed into non-transitory memory of the computer-readable storage medium in the engine control system, wherein the described acts are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.

[0105] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments are not to be considered limiting, as numerous variations are possible. For example, the above technique may be applied to V-6, I-4, I-6, V-12, horizontally opposed 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems and arrangements, and other features, functions, and / or characteristics disclosed herein.

[0106] 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. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by filing new claims in this or a related application.Such claims, whether broader, narrower, equal, or different in scope than the original claims, are also considered to be included within the subject matter of the present disclosure.

Claims

[1] Engine procedure which includes: Estimating a direct injector tip temperature different from a fuel temperature based on cylinder conditions, including cylinder combustion conditions and cylinder valve operation; and in response to deactivation or reactivation of a direct injector, adjusting one or more of a direct injection fuel pulse and a port injection fuel pulse based on each of the estimated direct injector tip temperature and the fuel temperature. [2] The method of claim 1, wherein estimating based on cylinder combustion conditions includes estimating based on whether cylinder combustion is present or absent while the direct injector is deactivated, wherein the temperature at the direct injector tip is increased higher than the fuel temperature when cylinder combustion is present, wherein the temperature at the direct injector tip is decreased below the fuel temperature when cylinder combustion is absent. [3] The method of claim 2, wherein an increase in temperature at the direct injector tip is increased relative to an increase in fuel temperature as an average cylinder load increases when cylinder combustion is present. [4] The method of claim 2, wherein an increase in temperature at the direct injector tip is increased relative to an increase in fuel temperature while an air-fuel ratio of cylinder combustion becomes leaner than stoichiometry when cylinder combustion is present. [5] The method of claim 1, wherein estimating based on cylinder valve operation includes estimating based on whether cylinder valve operation is enabled or disabled while the direct injector is disabled, wherein the temperature at the direct injector tip is decreased more than the fuel temperature when cylinder valve operation is enabled, wherein the temperature at the direct injector tip is increased more than the fuel temperature when cylinder valve operation is disabled. [6] The method of claim 5, wherein the estimating is further based on whether port injection is enabled or disabled while the direct injector is disabled, wherein the temperature at the direct injector tip is increased above the fuel temperature when port injection is enabled, wherein the temperature at the direct injector tip is decreased below the fuel temperature when port injection is disabled. [7] The method of claim 1, further comprising adjusting the estimated non-fuel temperature at the direct injector tip based on a duration of deactivation of the direct injector. [8] The method of claim 1, wherein adjusting the direct injection fuel pulse includes: estimating a fuel density based on each of the estimated direct injector tip temperature and the fuel temperature; Calculating an initial fuel pulse width based on engine operating conditions upon reactivation of the direct injector; and Update the initial fuel pulse width based on the estimated fuel density. [9] The method of claim 8, wherein the initial fuel pulse width is increased while the estimated fuel density falls below a nominal fuel density and is decreased while the estimated fuel density exceeds the nominal fuel density. [10] Engine system comprising: an engine cylinder; a direct fuel injection device; a direct injection fuel rail coupled to the direct injection device; and a controller with computer-readable instructions stored in non-volatile memory for: Comparing a combustion heat flow with respect to a fuel refill cooling flow into the direct injector over a period of injector deactivation, wherein the combustion heat flow is based on cylinder conditions, wherein the fuel refill cooling flow is based on a fuel flow rate and a fuel rail temperature; and Setting a direct injection fuel pulse width after reactivation of the direct injector based on the comparison. [11] The system of claim 10, further comprising a port fuel injector, wherein the controller includes further instructions for: Increasing combustion heat flow in response to one or more of cylinder combustion continued via port fuel injection over the period of direct injection device deactivation, increasing engine speed or load, increasing spark retard, increasing cylinder head temperature, and increasing the period of cylinder combustion with port fuel injection only; and Decreasing combustion heat flux in response to one or more of port fuel injection deactivation and cylinder valve deactivation over the direct injector deactivation period and increasing the direct injector deactivation period without cylinder combustion. [12] The system of claim 11, wherein the controller further includes instructions to increase the fuel refill cooling flow in response to one or more of decreasing the fuel rail temperature and increasing the fuel flow rate to the direct injector. [13] The system of claim 10, wherein adjusting includes updating an initial direct injector tip temperature estimated immediately prior to direct injector deactivation with a correction factor based on comparing combustion heat flow to fuel refill cooling flow and further based on a thermal mass of the direct injector tip. [14] The system of claim 13, wherein the setting further includes: Estimating a fuel density based on the updated direct injector temperature; and Setting an initial direct injection fuel pulse width based on the estimated fuel density relative to a nominal fuel density, wherein the initial direct injection fuel pulse width is based on engine operating conditions upon reactivation of the direct injection device. [15] The system of claim 14, further comprising a knock sensor, wherein the controller includes further instructions for: Determining the initial direct injection fuel pulse width further based on an indication of engine knock, detected via a knock sensor, or expected based on engine operating conditions.

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