Methods for the direct injection of supercritical fuels

Abstract

Method for a fuel system, wherein the method comprises the following: Setting a fuel injector control parameter based on an air-fuel ratio of the exhaust gas, selective adjustment of the fuel injector control parameter further based on a fuel pump gain; Operating a fuel injector based on the fuel injector control parameter; and wherein the selective adjustment includes: adjusting the fuel injector control parameter further based on the fuel pump gain in response to a determination that the fuel at the fuel pump is subcritical; and Furthermore, the fuel injector control parameter is not adjusted based on the fuel pump gain in response to a determination that the fuel at the fuel pump is supercritical.

Description

[0001] The present invention generally relates to methods and systems for controlling a vehicle engine to directly inject fuels, such as liquefied petroleum gas, into the combustion chamber based on conditions.

[0002] DE 10 2015 117 794 A1 discloses a method for supplying fuel to a direct fuel injection pump of an internal combustion engine. The pressure and / or temperature of a fuel supplied to the direct fuel injection pump can be adjusted to ensure that liquid fuel is supplied to the direct fuel injection pump, thus reducing the possibility of engine air / fuel supply deviations.

[0003] Furthermore, DE 10 2006 000 238 A1 discloses a fuel supply system comprising a common rail that stores high-pressure fuel to be injected into and supplied to an engine. Furthermore, the system comprises a high-pressure pump driven by engine power to pressurize the fuel into the common rail. An electronic control unit calculates a characteristic deviation of the high-pressure pump in an idle operating state of the engine and calculates the characteristic deviation in a cruise control driving state. The control unit controls a fuel discharge amount of the high-pressure pump by reflecting the characteristic deviations at the two points therein.Thus, the characteristic deviation of the high-pressure pump is appropriately reflected and the fuel discharge amount of the high-pressure pump is accurately controlled, thereby improving exhaust emission and drivability.

[0004] In an internal combustion engine, the air-fuel ratio of the combusted gases may be controlled to manage emissions. One source of air-fuel ratio errors may be an actual fuel injector flow rate that differs from an expected fuel injector flow rate. One way to adjust a fuel injector flow rate is described by Thomas et al. in US 7,765,991 B2. Therein, an output of an exhaust gas sensor is used in a feedback path to evaluate the error between an actual air-fuel ratio and a desired air-fuel ratio, and a fuel injector pulse width is adjusted based on this error, thereby adjusting the fuel injector flow rate.

[0005] However, the inventors have recognized potential problems for such systems. For example, when direct injection is used with fuels that are supercritical during at least some engine operating conditions, adjusting the fuel injection rate based on exhaust gas measurements may be unreliable. This is because, in the supercritical state, the density of the fuel within a sample can vary significantly and in a complex manner, which can lead to unreliable exhaust gas measurements and, consequently, inaccurate air-fuel ratio estimates. Supercritical fuels can effectively clean soot deposits from engine components, and direct injection of supercritical fuels can maintain engine cleanliness despite unpredictable injection characteristics.

[0006] In one approach, the above problems can be addressed by a method for a fuel system, the method comprising: setting a fuel injector control parameter based on an exhaust air-fuel ratio, selectively setting the fuel injector control parameter further based on a fuel pump gain, and operating the fuel injector based on the fuel injector control parameter. In this way, a desired amount of injected fuel can be precisely controlled over a wide range of engine temperatures and pump pressures, thereby ensuring the desired air-fuel ratios. Furthermore, the advantages of supercritical fuels, such asthe cleanliness of the injector components and low soot emissions, while also achieving the target air-fuel ratio by allowing the fuel to be in a supercritical state at the fuel injector.

[0007] As one example, a relationship may be determined between a volume of fuel delivered to the fuel rail by the direct injection fuel pump and a resulting increase in fuel rail pressure. This relationship may be referred to herein as a fuel pump gain, and may be based on an average of fuel pump gain estimates during multiple commanded pump strokes. In this manner, a magnitude of pressure in the fuel rail may be associated with a fuel mass. A change in pressure at an injection event may be measured and associated with an injected fuel mass based on the fuel pump gain. In response, an injector control parameter, such as an injection gain, may be increased, thereby increasing the commanded injection volume.By adjusting injector gain based on fuel pump gain when pumping subcritical fuel, a desired injection mass can be delivered even when fuel density at the injection point is unpredictable. For example, supercritical or subcritical fuel determinations at the pump can be used to adjust operation and maintain improved engine air-fuel ratio control.

[0008] It should be understood that the above summary is provided to introduce, in simplified form, a selection of the concepts further described in the detailed description. It is not intended to identify the key or essential features of the claimed subject matter, the scope of which is clearly defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that eliminate any disadvantages noted above or in any part of this disclosure.

[0009] Further embodiments of the invention are disclosed in the figures. They show: Fig. 1 shows an engine system including a direct fuel injector and a port fuel injector and configured to operate with fuels that are supercritical during at least some engine operating conditions; Fig. 2 shows a schematic diagram of an example fuel system coupled to an engine; Fig. Figure 3 shows a graphical representation of temperature and pressure when a fuel becomes supercritical; Fig. 4 shows the graphical representations of a gain of a direct injection fuel pump and a relationship between a change in fuel rail pressure at injection and the rated injection volume; Fig. 5 shows an exemplary prophetic flow for adjusting an injector control parameter based on a fuel pump gain; Fig. 6 shows an exemplary method for adjusting an injector control parameter based on a change in fuel rail pressure; and Fig. 7 shows an exemplary method for adjusting an injector control parameter based on fuel pump gain.

[0010] This description relates to setting the control parameters of a direct fuel injector configured to supply liquefied petroleum gas (LPG) or similar fuels to an internal combustion engine. The engine may be a direct fuel injection engine, wherein the fuel is injected directly into the engine cylinders, as described in the Fig. 1-2. The injected fuel may have properties as shown in Fig. 3. The fuel pump configured to supply high-pressure fuel to the direct fuel injector may operate according to a transfer function, wherein a transfer function gain relates an opening duration of a spill valve to an injected fuel mass, as shown in Fig. 4. Under some conditions, a fuel injector control parameter may be adjusted based on the fuel pump gain, as shown in Fig. 5. Finally, the Fig. 6-7 Procedures by which the fuel injector control parameters can be adjusted to deliver a desired amount of fuel.

[0011] Fig. 1 illustrates an exemplary embodiment of a combustion chamber or cylinder of an internal combustion engine 10. The engine 10 may be controlled at least in part by a control system including a 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 (i.e., combustion chamber) 14 of the engine 10 may include combustion chamber walls 136 with a piston 138 positioned therein. 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 a passenger vehicle via a transmission system.Furthermore, a starter motor may be coupled to the crankshaft 140 via a flywheel to enable a starting operation of the engine 10.

[0012] Cylinder 14 may receive intake air via 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 embodiments, one or more of the intake passages may include a boost device, such as a turbocharger or a supercharger. Fig. For example, Figure 1 shows engine 10 configured with a turbocharger including a compressor 174 disposed between intake passages 142 and 144 and an exhaust turbine 176 disposed along exhaust passage 148. Compressor 174 may be driven at least partially via a shaft 180 by exhaust turbine 176, with the boost device configured as a turbocharger. However, in other examples, such as when engine 10 is provided with a supercharger, exhaust turbine 176 may optionally be omitted, with compressor 174 driven by a mechanical input from an engine or the engine. A throttle valve 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 intake air provided to the engine cylinders. The throttle valve 162 can, for example,be arranged downstream of the compressor 174, as in . Fig. 1, or may alternatively be provided upstream of the compressor 174.

[0013] Exhaust passage 148 may receive exhaust gases from other cylinders of engine 10 in addition to cylinder 14. Exhaust gas sensor 128 is shown coupled to exhaust passage 148 upstream of an emission control device 178. Sensor 128 may be any suitable sensor to provide an indication of the exhaust air / fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide range exhaust oxygen), a dual-state oxygen sensor or EGO (as shown), a HEGO (heated EGO), a NOx, an HC, or a CO sensor. Emission control device 178 may be a three-way catalyst (TWC), a NOx trap, various other emission control devices, or combinations thereof.

[0014] 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 embodiments, 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.

[0015] 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. During 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 positions of the intake valve 150 and the exhaust valve 156 may be determined by respective position sensors (not shown). The valve actuators may be of the electric valve actuation type or the cam actuation type, or a combination thereof. The timing of the intake and exhaust valves may be controlled simultaneously, or any of variable intake cam timing, variable exhaust cam timing, dual independent variable cam timing, or fixed cam timing may be used.Each cam actuation system may include one or more cams and may utilize a cam profile shifting (CPS) system, a variable cam timing (VCT) system, a variable valve timing (VVT) system, and / or a variable valve lift (VVL) system, which may be actuated 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 a CPS and / or a VCT. In other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or valve actuation system or a variable timing valve actuator or valve actuation system.

[0016] Cylinder 14 may have a compression ratio that is the ratio of the volumes when piston 138 is at the bottom center to the top center. Typically, 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 higher octane fuels or fuels with a higher latent heat of vaporization. If direct injection is used, the compression ratio may also be increased due to its effect on engine knock.

[0017] In some embodiments, 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 advance signal SA from controller 12 under selected operating modes. However, in some embodiments, spark plug 192 may be omitted, such as when engine 10 may initiate combustion through auto-ignition or through fuel injection, as may be the case with some diesel engines.

[0018] In some embodiments, 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 to include two fuel injectors 166 and 170. Fuel injector 166 is shown to be directly coupled to cylinder 14 to inject fuel directly thereto in proportion to the pulse width of a signal FPW-1 received from controller 12 via an electronic driver 168. In this manner, fuel injector 166 provides what is known as direct injection (hereinafter referred to as "DI") of fuel into combustion cylinder 14. While Fig. 1 depicts the injector 166 as a side-mounted injector, it may also be located above the piston, such as near the position of the spark plug 192. Such a location may improve mixing and combustion when the engine is operating on an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located above and near the intake valve to improve mixing. Fuel may be delivered to the fuel injector 166 from a high-pressure fuel system 172, including a fuel tank, fuel pumps, a fuel rail, and a driver 168. Further, the fuel tank may include a pressure sensor to provide a signal to the controller 12, although not shown.

[0019] Fuel injector 170 is shown disposed in intake port 146, rather than in cylinder 14, in a configuration that provides what is known as port fuel injection (hereinafter referred to as "PFI") into the intake port upstream of cylinder 14. Fuel injector 170 may inject fuel proportional to the pulse width of a signal FPW-2 received from controller 12 via electronic driver 171. The fuel may be delivered to fuel injector 170 through fuel system 172.

[0020] Fuel may be delivered to the cylinder by both injectors during a single cylinder cycle. For example, each injector may deliver a portion of the total fuel injection combusted in cylinder 14. Further, the distribution and / or relative amount of fuel delivered by each injector may vary with operating conditions, such as described below. The relative distribution of the total injected fuel between injectors 166 and 170 may be referred to as a first injection ratio.Injecting a larger amount of fuel for a combustion event via the (port) injector 170 may be an example of a higher first port-to-direct injection ratio, while injecting a larger amount of fuel for a combustion event via the (direct) injector 166 may be a lower first port-to-direct injection ratio. It is noted that these are merely examples of different injection ratios, and that various other injection ratios may be used. Additionally, it should be appreciated that the port-injected fuel may be delivered during an open intake valve event, a closed intake valve event (e.g., substantially prior to an intake stroke, such as during an exhaust stroke), or during operation with both open and closed intake valves.Similarly, the directly injected fuel may, for example, be delivered during an intake stroke, as well as partially during a preceding exhaust stroke, during the intake stroke, and partially during the compression stroke. Furthermore, the directly injected fuel may be delivered as a single injection or as multiple injections. These may include multiple injections during the compression stroke, multiple injections during the intake stroke, or a combination of some direct injections during the compression stroke and some during the intake stroke. When multiple direct injections are performed, the relative distribution of the total directly injected fuel between an intake stroke (direct) injection and a compression stroke (direct) injection may be referred to as a second injection ratio.Injecting a larger amount of direct-injected fuel for a combustion event during an intake stroke may be an example of a higher second intake-stroke direct injection ratio, while injecting a larger amount of fuel for a combustion event during a compression stroke may be an example of a lower second intake-stroke direct injection ratio. It is noted that these are merely examples of different injection ratios, and various other injection ratios may be used.

[0021] Even for a single combustion event, the injected fuel can be injected with different timings from a port and a direct injector. Furthermore, for a single combustion event, multiple injections of the supplied fuel can be performed per cycle. The multiple injections can be performed during the compression stroke, the intake stroke, or any suitable combination thereof.

[0022] As described above, Fig. 1 only one cylinder of a multi-cylinder engine. Each cylinder as such may contain its own set of intake / exhaust valves, fuel injector(s), spark plug, etc.

[0023] Fuel injectors 166 and 170 may have various characteristics. These include differences in size; for example, one injector may have a larger injection hole than the other. Other differences include, but are not limited to, different spray angles, different operating temperatures, different targeting, different injection timing, different spray characteristics, different locations, etc. Furthermore, depending on the distribution ratio of the injected fuel between injectors 170 and 166, different effects may be achieved.

[0024] The fuel system 172 may include one or more fuel tanks. In embodiments where the fuel system 172 includes multiple fuel tanks, the fuel tanks may contain fuel with the same fuel qualities or may contain fuel with different fuel qualities, such as different fuel compositions. These differences may include different alcohol content, different octane rating, different heats of vaporization, different fuel blends, and / or combinations thereof, etc. In some examples, the fuel system 172 may include a fuel tank containing a liquid fuel, such as liquefied petroleum gas (LPG), and may also include a fuel tank containing a gaseous fuel, such as compressed natural gas (CNG).In other examples, fuel system 172 may include a fuel tank containing a first liquid fuel, such as LPG, and a fuel tank containing a second liquid fuel, such as gasoline. Fuel injectors 166 and 170 may be configured to inject fuel from the same fuel tank, from different fuel tanks, from multiple tanks containing the same fuel, or from an overlapping set of fuel tanks. In one example, injector 166 may be configured to inject LPG from a first fuel tank, while fuel injector 170 may be configured to inject gasoline from a second fuel tank. In another example, fuel injector 166 may be configured to inject LPG from a first fuel tank, while fuel injector 170 may be configured to inject gasoline from a second fuel tank.In yet another example, each of fuel injectors 166 and 170 may be configured to inject LPG from a common fuel tank. In other examples, fuel injector 166 and / or fuel injector 170 may be configured to inject CNG.

[0025] The controller 12 is in Fig. 1 as a microcomputer including a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values, shown in this particular example as a read-only memory chip 110, a random access memory 112, a latch 114, and a data bus.The controller 12 may receive various signals from sensors coupled to the engine 10, in addition to those signals previously discussed, including measurements of inducted mass air flow (MAF) from a mass air flow sensor 122; an engine coolant temperature (ECT) from a temperature sensor 116 coupled to a cooling sleeve 118; a profile ignition response (PIP) signal from a Hall effect sensor 120 (or other type) coupled to the crankshaft 140; a throttle position (TP) from a throttle position sensor; and a manifold absolute pressure (MAP) signal from a sensor 124. The engine speed signal, RPM, may be generated by the controller 12 from the PIP signal. The manifold pressure signal MAP from a manifold pressure sensor can be used to provide an indication of the vacuum or pressure in the intake manifold.

[0026] The read-only memory 110 of the storage medium may be programmed with computer-readable data representing instructions executable by the processor 106 for performing both the methods described below and other variations that are anticipated but not specifically listed. An exemplary routine that may be executed by the controller is shown in the Fig. 6 and Fig. 7 described.

[0027] Fig. 2 shows a direct injection fuel system 200 coupled to an internal combustion engine 10, which may be configured as a propulsion system for a vehicle. The internal combustion engine 10 may include multiple combustion chambers or cylinders 14. LPG fuel may be provided to the cylinders 14 via in-cylinder direct fuel injectors 166. As shown in Fig. 2, the engine 10 can receive intake air, whereby it can discharge the products of the burned fuel and air.

[0028] The fuel may be provided to the engine 10 via a fuel system, generally indicated at 172, via the fuel injectors 166. In this particular example, the fuel system 172 includes a fuel storage tank 252 for storing the fuel onboard the vehicle, a lower pressure fuel pump 230 (e.g., a fuel lift pump), a higher pressure fuel pump or direct injection fuel pump 240, a fuel rail 258, and various fuel passages 254, 255, and 256. In the Fig. 2, fuel passage 254 carries fuel from the lower pressure pump 230 to the fuel filter 206. Fuel passage 255 carries fuel from the fuel filter 206 to the fuel cooling chamber 237 before reaching the direct injection fuel pump 240. Fuel passage 256 carries the fuel from the fuel injection pump 240 to the fuel rail 258.

[0029] The fuel cooling chamber 237 contains a fuel injector 223 to which fuel is supplied from the fuel passage 255. The fuel injector can inject fuel into the fuel cooling chamber 237, where the pressurized fuel expands into vapor and cools the liquid fuel flowing into the direct injection fuel pump 240. The expanded fuel can be injected into the engine 10 via the fuel passage injector 170, which injects the vaporized fuel into the engine's intake manifold or into the cylinder intake ports. Alternatively, the expanded fuel can exit the fuel cooling chamber 237 and be returned to the fuel tank 252 via the passage 233. The fuel injector 223 is opened and closed via the pulse-width modulated voltage supplied by the controller 12.This gaseous fuel may also be routed to the fuel vapor purge system located on-site for the gasoline fuel system if the vehicle is equipped with a gasoline auxiliary system. In this manner, by injecting the expanded fuel into the fuel cooling chamber 237, the fuel entering the inlet of the direct injection pump may be maintained below an upper threshold temperature.

[0030] The fuel rail 258 may distribute fuel to each of a plurality of fuel injectors 166. Each of the plurality of fuel injectors 166 may be positioned within a corresponding cylinder 14 of the engine 10 such that, during operation of the fuel injectors 166, fuel is injected directly into each corresponding cylinder 14. Alternatively (or additionally), the engine 10 may include fuel injectors positioned at the intake port of each cylinder such that, during operation of the fuel injectors, fuel is injected into the intake port of each cylinder. In the illustrated example, the engine 10 includes four cylinders. However, it is recognized that the engine may include a different number of cylinders.

[0031] The lower pressure fuel pump 230 may be operated by a controller 12 to provide fuel via the fuel passage 254 to the fuel injection pump 240. The lower pressure fuel pump 230 may be configured as what may be referred to as a fuel lift pump. As one example, the lower pressure fuel pump 230 may include a pump electric motor, whereby the pressure gain across the pump and / or the volumetric flow rate through the pump may be controlled by varying the electrical power provided to the pump motor, thereby increasing or decreasing the motor speed. For example, if the controller 12 decreases the electrical power provided to the pump 230, the volumetric flow rate and / or the pressure gain across the pump 230 may be decreased.The volumetric flow rate and / or pressure increase across the pump may be increased by increasing the electrical power provided to pump 230. As one example, the electrical power supplied to the lower-pressure pump motor may be obtained from an alternator or other on-board energy storage device (not shown), allowing the control system to control the electrical load used to drive the lower-pressure pump 230. Thus, by varying the voltage and / or current provided to the lower-pressure fuel pump 230 via conductor 282, the flow rate and pressure of fuel provided to the fuel injection pump 240 and ultimately to the fuel rail may be adjusted by the controller 12.

[0032] The low-pressure fuel pump 230 may be in fluid communication with a check valve 204 to promote fuel delivery, prevent fuel backflow, and maintain fuel rail pressure. Specifically, the check valve 204 includes a ball and spring mechanism that mates and seals at a specified pressure differential to deliver fuel downstream of the check valve 204. In some examples, the fuel system 250 may include a series of check valves in communication with the low-pressure fuel pump 230 to further prevent fuel from backflowing upstream of the valves. The check valve 204 is in fluid communication with the fuel filter 206. The fuel filter 206 may remove small contaminants that may be present in the fuel and that could potentially restrict fuel flow.The fuel may be delivered from the filter 206 to the fuel injector 223 and the high-pressure fuel pump (e.g., a fuel injection pump) 240. The fuel injection pump 240 may increase the fuel pressure received by the fuel filter from a first pressure level generated by the low-pressure fuel pump 230 to a second pressure level higher than the first level. The fuel injection pump 240 may deliver the high-pressure fuel to the fuel rail 258 via a fuel line 256. The fuel injection pump 240 may be a positive displacement pump. The operation of the direct injection fuel pump 240 may be adjusted based on vehicle operating conditions to ensure that the delivered fuel is in a liquid state at the fuel injection pump 240.

[0033] The direct injection fuel pump 240 may be controlled by the controller 12 to provide fuel to the fuel rail 258 via the fuel passage 256. As a non-limiting example, the fuel injection pump 240 may utilize a flow control valve, a solenoid-actuated spill valve (SV), or a fuel volume regulator (FVR), indicated at 242, to allow the control system to vary the effective pumping volume of each pumping stroke. In one example, the control system may be configured to vary the duration that the spill valve 242 is open during a pumping stroke of the fuel injection pump 240, and consequently vary the mass of fuel delivered to the fuel rail 258 for each pumping stroke. The fuel injection pump 240 may be mechanically driven by the engine 10, unlike the engine-driven lower pressure fuel pump or the fuel lift pump 230.A pump plunger 244 of the direct injection fuel pump 240 may receive mechanical input from the engine's crankshaft or camshaft via a cam 246. In this manner, the fuel injection pump 240 may be operated according to the principle of a cam-driven single-cylinder pump.

[0034] As in Fig. 2, a fuel sensor 248 is disposed in a channel 254 downstream of the fuel lift pump 230. The fuel sensor 248 can measure the fuel composition and can operate based on the fuel capacity or the number of moles of a dielectric fluid within its sensing volume. For example, an amount of ethanol (e.g., liquid ethanol) in the fuel can be determined based on the capacity of the fuel (e.g., when a fuel-alcohol mixture is used). The fuel sensor 248 can be used to determine a level of fuel vaporization, since fuel vapor has a smaller number of moles than liquid fuel within the sensing volume. Fuel vaporization, as such, can be indicated when the fuel capacity drops. As discussed with respect to the Fig. 4 and Fig. 5, the fuel sensor 248 may be used to determine the level of fuel vaporization of the fuel so that the controller 12 may adjust the lift pump output pressure to reduce fuel vaporization within the fuel lift pump 230.

[0035] Furthermore, in some examples, the direct injection fuel pump 240 may be operated as the fuel sensor 248 to determine the level of fuel vaporization. For example, a piston-cylinder assembly of the fuel injection pump 240 forms a fluid-filled capacitor. As such, the piston-cylinder assembly allows the fuel injection pump 240 to be the capacitive element in the fuel composition sensor. In some examples, the piston-cylinder assembly of the fuel injector 240 may be the warmest point in the system, so that fuel vapor forms there first. In such an example, the direct injection fuel pump 240 may be used as the sensor to detect fuel vaporization because fuel vaporization may occur at the piston-cylinder assembly before occurring anywhere else in the system.

[0036] As in Fig. 2, the fuel rail 258 includes a fuel rail pressure sensor 262 to provide the controller 12 with an indication of the fuel rail pressure. An engine speed sensor 264 may be used to provide the controller 12 with an indication of the engine speed. The engine speed indication may be used to identify the speed of the fuel injection pump 240 because the pump 240 is mechanically driven by the engine 10, for example, via the crankshaft or the camshaft. An exhaust gas sensor 128 may be used to provide the controller 12 with an indication of the exhaust gas composition. As one example, the gas sensor 128 may include a universal exhaust gas (UEGO) sensor. The exhaust gas sensor 128 may be used as feedback by the controller to adjust the amount of fuel delivered to the engine via the injectors 166.In this manner, the controller 12 may control the air-fuel ratio supplied to the engine to a desired air-fuel ratio.

[0037] In addition, the controller 12 may receive other engine / exhaust parameter signals from other engine sensors, such as engine coolant temperature, engine speed, throttle position, manifold absolute pressure, emission control device temperature, etc. Even further, the controller 12 may provide closed-loop control based on the signals received from, among others, the fuel sensor 248, the pressure sensor 262, and the engine speed sensor 264. For example, the controller 12 maySend signals to adjust a current level, a current ramp rate, a pulse width of a fuel injection pump solenoid valve (SV) 242, and the like to adjust operation of the fuel injection pump 240, a fuel pressure setpoint of the fuel pump controller, and / or a fuel injection amount and / or fuel injection timing based on the signals from the fuel sensor 248, the pressure sensor 262, the engine speed sensor 264, and the like.

[0038] The controller 12 may individually actuate each of the injectors 166 and the injector 170. The controller 12 and other suitable controllers of the engine system may comprise a control system. The controller 12, in this particular example, includes an electronic control unit that includes an input / output device 108 and / or a central processing unit (CPU) 106 and / or a read-only memory (ROM) 110 or a non-volatile memory and / or a random access memory (RAM) 112 and / or a hold memory (KAM) 114. The ROM 110 of the storage medium may be programmed with computer-readable data representing non-transitory instructions executable by the processor 106 for performing both the methods described below and other variations that are anticipated but not specifically listed.

[0039] As shown, the direct injection fuel system 200 is a returnless fuel system, and it may be a mechanical returnless fuel system (MRFS) or an electronic returnless fuel system (ERFS). In the case of an MRFS, the fuel rail pressure may be controlled via a pressure regulator (not shown) positioned on the fuel tank 252. In an ERFS, a pressure sensor 262 may be attached to the fuel rail 258 to measure the fuel rail pressure relative to the manifold pressure. The signal from the pressure sensor 262 may be fed back to the controller 12, which modulates the voltage to the fuel injection pump 240 to deliver the desired fuel pressure and fuel flow rate to the injectors.

[0040] Although this is Fig. 2, in other examples, the direct-injection fuel system 200 may include a return line through which excess fuel is returned from the engine to the fuel tank via a fuel pressure regulator via a return line. A fuel pressure regulator may be coupled in series with a return line to regulate the fuel supplied to the fuel rail 258 to a desired pressure. To regulate the fuel pressure to the desired level, the fuel pressure regulator may return excess fuel to the fuel tank 252 via the return line. It will be appreciated that the operation of the fuel pressure regulator may be adjusted to change the desired fuel pressure to suit operating conditions.

[0041] Consequently, the system Fig. 2 provides a vehicle system comprising: an engine; a direct injection fuel pump that supplies fuel to the engine, the direct injection fuel pump including a fuel cooling chamber; a fuel injector in fluid communication with the cooling chamber; a lift pump that supplies fuel to the direct injection fuel pump; and a controller including instructions stored in non-volatile memory for increasing fuel flow to the fuel cooling chamber in response to a volumetric efficiency of the direct injection fuel pump. The vehicle system further includes instructions for increasing the output pressure of the lift pump in response to the volumetric efficiency of the direct injection fuel pump.The vehicle system includes the volumetric efficiency of the direct injection fuel pump being a basis for determining that liquid fuel is being delivered to the direct injection fuel pump. The vehicle system further includes a port fuel injector in fluid communication with the fuel cooling chamber. The vehicle system further includes a fuel port providing fluid communication between the fuel cooling chamber and a fuel tank. The vehicle system includes the controller including additional instructions for determining a direct injection fuel pump volumetric efficiency error.

[0042] The graphical representation according to Fig. 3 has a Y-axis representing pressure, with pressure increasing in the direction of the Y-axis arrow. The graphical representation according to Fig. 3 also includes an X-axis representing temperature, with temperature increasing in the direction of the X-axis arrow.

[0043] Curve 302 represents a phase line that separates where propane is liquid or gaseous. Propane is in a liquid state when it is at conditions above curve 302, while it is in a gaseous state when it is at conditions below curve 302. Propane reaches a supercritical state at temperatures and pressures above 306. The horizontal line 326 represents a temperature where propane becomes supercritical. The vertical line 320 represents a temperature where propane becomes supercritical.

[0044] Curve 304 represents a phase line that separates where butane is a liquid or a gas. Butane is in a liquid state when it is at conditions above curve 304, while it is in a gas state when it is at conditions below curve 304. Butane reaches a supercritical state at temperatures and pressures above 308. The horizontal line 324 represents a temperature at which butane becomes supercritical. The vertical line 322 represents a temperature at which butane becomes supercritical. At temperatures greater than 322, butane is supercritical. At pressures greater than 324, butane is supercritical.

[0045] Liquefied petroleum gas sold for motor vehicles, sometimes sold under the name LPG, is often a mixture of propane and butane. Consequently, when operating a vehicle configured with LPG as a fuel source, it may be desirable to maintain the propane at temperatures less than 320°C and pressures less than 326°C so that the mass of propane delivered to the engine can be accurately determined and controlled. Similarly, it may be desirable to maintain the butane at temperatures less than 322°C and pressures less than 324°C so that the mass of butane delivered to the engine can be accurately determined and controlled. However, during at least some engine operating conditions, temperatures at the direct fuel injector may exceed temperatures 320°C or 322°C, at which point a fuel containing propane or butane may become supercritical.In this case, the density of such a fuel becomes less predictable, and accordingly the relationship between the injection mass and an injection pulse width becomes less reliable.

[0046] Fig. Figure 4 provides two plots 410 and 420 illustrating fuel pump gain and a relationship between a measured decrease in fuel pressure for an injection event and a nominal injected volume, respectively. Each plot uses a curve 412 based on volume and pressure measurements taken at the fuel pump inlet with subcritical fuel.

[0047] First, in the graph 410, the Y-axis represents a change in pressure in the fuel rail during one pump stroke from the direct injection fuel pump, with the change in pressure increasing in the direction of the Y-axis arrow. The X-axis represents a volume of fuel pumped by the direct injection fuel pump, with the volume increasing in the direction of the X-axis arrow. Each data point 414 may represent a measurement of a change in fuel rail pressure resulting from pumping a known volume of fuel into the fuel rail. Thus, each data point 414 represents a single estimate of a fuel pump gain. The data points 414 may only be recorded during conditions where the fuel is determined to be liquid or subcritical at the fuel pump inlet.Determining a volume of fuel to be pumped during a particular pump stroke may be based on a target fuel mass to be pumped and an estimated fuel density. If the fuel at the fuel pump inlet is maintained at subcritical conditions, the estimated fuel density may be a predictable quantity (e.g., based on a measured or estimated DI pump inlet temperature). Based on a number of data points 414, a curve 412 may be generated via a statistical method. In one example, linear regression may be performed on the data points 414 to generate the curve 412. In another example, recursive least squares may be performed on the data points 414 to generate the curve 412, as it is more suitable for continuous processing than regressing a batch of data.Additionally, curve 412 may be repeatedly updated based on the collection of additional data points 414, thereby providing a real-time estimate of fuel pump gain based on an average of the fuel pump gain estimates. In this way, the relationship between the mass entering via the pump and the increase in fuel rail pressure may be recovered in real time if the fuel density in the fuel rail fluctuates in any unknown manner.

[0048] Because the pump pumps subcritical fuel, its added mass per pump stroke can be accurately calculated. This calculation can establish an actual relationship between the pressure change versus the fuel mass change in the fuel rail. This calculated relationship, along with a measured change in pressure resulting from a fuel injection event, can be used to determine an injected fuel mass without information regarding the density or bulk modulus of the supercritical fuel in the fuel rail. In this way, an injected mass of supercritical fuel can be determined in real time based on both a change in fuel rail pressure from pumping subcritical fuel and a change in fuel rail pressure from injecting supercritical fuel.

[0049] Now, in the graphical representation 420, the Y-axis represents a change in pressure in the fuel rail pump resulting from an injection event, with the pressure change decreasing in the direction of the Y-axis arrow. The X-axis represents a fuel volume associated with the pressure change represented by the Y-axis, with the volume increasing in the direction of the X-axis arrow and representing a volume of fuel pumped into the fuel rail. Curve 412, as generated from data points 414 in the graphical representation 410, may be fitted by the graphical representation 420 to translate a decrease in fuel rail pressure at an injection event into an estimate of the volume of fuel pumped into the intake.Because the relationship between fuel rail pressures and fuel volumes described by curve 412 was determined based on measurements of a subcritical fuel, it provides an accurate estimate of the fuel volume in the fuel rail. Consequently, the pressure change resulting from the fuel injection event can be translated into a pumped fuel volume, whether the fuel at the fuel injector is supercritical or not. Furthermore, because the fuel was pumped at subcritical conditions, a nominal subcritical density can be used to accurately relate the drop in fuel rail pressure to an injected fuel mass.

[0050] For example, a drop in fuel rail pressure dP1 may be measured during an injection event. This injection event may have an associated nominal injection volume (not shown) determined based on a desired injection mass and a nominal fuel density. The desired injection mass may also be referred to herein as a nominal injection mass. The drop in fuel rail pressure dP1 may be associated with a pumped fuel volume dV1 via curve 412. The associated pumped fuel volume dV1 may be multiplied by a nominal fuel density to determine an actual injected fuel mass. In this way, a change in fuel rail pressure may be related to an injected fuel mass via the nominal fuel density and the pressure and volume measurements taken at a fuel pump.

[0051] In some examples, this injected mass may be compared to a nominal injected mass, and an injector control parameter may be adjusted based on this comparison. For example, an injector gain may be adjusted to adjust the relationship between a desired injection mass and a commanded injection volume. For example, the nominal injected mass may be greater than the actual injected fuel mass, indicating that the density of the fuel within the fuel rail is lower than predicted. Accordingly, an injector gain may be increased to increase the nominal injection volume associated with a desired injection mass. In one embodiment, the injector gain may be a factor by which a nominal injection volume, determined based on a subcritical fluid density, is multiplied to determine a commanded injection volume.In an alternative embodiment, injector gain may be a factor that adjusts the relationship between an injector pulse width and a desired injection mass.

[0052] In this way, the injector gain may be at or near 1 when the fuel is subcritical, where the injector gain may be adjusted in response to a change in fuel density at the injection location, the change in density being detected based on a comparison of the nominal injection mass to an actual injected fuel mass. For example, during a first condition, the injector gain may be increased, thereby increasing a commanded injection volume, where during a second condition, the injector gain may be decreased, thereby decreasing a commanded injection volume. In one example, the first condition may include an actual injection mass being less than a desired injection mass, while the second condition may include an actual injection mass being greater than a desired injection mass.In this example, the fuel injector gain is adjusted in the signed direction of the difference between a desired injection mass and an actual injection mass. In a second example, the first condition may include the fuel density at the fuel rail becoming less than the subcritical fuel density estimate, while the second condition may include the fuel density at the fuel rail becoming greater than the subcritical fuel density estimate. In this example, the fuel injector gain is adjusted in the signed direction of the difference between a subcritical fuel density and an actual fuel rail density in the fuel rail.

[0053] The Fig. 5 and Fig. 6 provides the flowcharts for routines 500 and 600, which illustrate routines for adjusting fuel injector control parameters based on a change in fuel rail pressure and an injected fuel mass, respectively. In one example, the fuel injector control parameter may be a fuel injector gain. In another example, the fuel injector control parameter may be a transfer function gain of a fuel injector. It is recognized that these examples are not limiting, and the injector control parameter being adjusted may be a parameter other than the injector gain or the transfer function gain.

[0054] Fig. 5 provides a routine 500 for adjusting a fuel injector control parameter based on a change in fuel rail pressure and further based on determinations of whether the fuel at the fuel pump is either subcritical or supercritical.

[0055] Routine 500 may include adjusting the injector control parameter based on the difference between a measured change in fuel rail pressure and a predicted or nominal change in fuel rail pressure. In this example, the measured pressure change results from a commanded volume injection event. The commanded injection volume may be based on a desired injection mass and / or a nominal fuel density and / or an injector control parameter. The fuel injector may deliver a fuel that is supercritical during at least some engine operating conditions, such as LPG.

[0056] At 502, the engine controller determines whether the fuel at the fuel pump is subcritical or supercritical. In one example, determining whether the fuel at the fuel pump is subcritical or supercritical may be based on a comparison of a temperature measurement at the fuel pump with a phase diagram for the fuel (e.g., the diagram shown in Fig. 3) stored in the engine controller's memory. In another example, 502 may include determining whether a direct injection fuel pump gain is below a lower threshold, where the lower threshold is determined based on either a measured or inferred fuel rail temperature. If it is determined that the fuel at the fuel pump is supercritical, or if the fuel pump gain is below the lower threshold, routine 500 proceeds to 503.

[0057] In some examples, 502 may further include determining whether injector overlap is currently present. Determining whether injector cycles currently overlap may be based on comparing the injection pulse signals for each injector on a fuel rail. In such examples, if there is one or more injector cycle overlaps, routine 500 proceeds to 530 and then to 532, as described in more detail below. However, if injector overlap is not present, routine 500 proceeds to 506. In this manner, the changes in fuel rail pressure may be the result of only one fuel injector and one injection event, and the control parameter for only that fuel injector may be adjusted based on the change in fuel rail pressure.

[0058] Continuing at 503, either the cooling or the pressure of the fuel delivered to the fuel pump is increased to change the fuel condition from supercritical to subcritical or to increase fuel pump gain. Routine 500 proceeds from 503 to 530, where the injector control parameter is not adjusted based on a change in fuel rail pressure, and then to 532, where the injector parameter may be adjusted based on an estimated exhaust air-fuel ratio. Further, the fuel injector control parameter may be adjusted based on an exhaust air-fuel ratio, and may further be selectively adjusted based on a change in fuel rail pressure if the fuel at the fuel pump inlet is subcritical.In this way, the fuel injector control parameter can be adjusted when the fuel is liquid at the fuel pump, providing a reliable metering device with which to calibrate the fuel injector.

[0059] If, returning to 502, the fuel at the fuel pump inlet is subcritical, an adjustment of the fuel injector control parameter may occur, with routine 500 continuing to 506. At 506, a full pumping stroke of the fuel injection pump is commanded. The full pumping stroke may have an associated pump stroke volume based on the length of the stroke and the physical parameters of the fuel injection pump piston. Also, at 506, the change in pressure within the fuel pump resulting from the full pumping stroke is measured, e.g., via a pressure sensor within the fuel rail. The adjustment is based on a difference between a measured change in fuel rail pressure and a predicted change in fuel rail pressure.

[0060] At 508, a fuel pump gain is determined based on the commanded pump stroke volume and the resulting pressure increase measured at 506. The fuel pump gain may be Fig. 4. As described therein, the fuel pump gain may be determined based on a number of pumping events, with a linear regression being performed on the number of measurements from the events to determine a slope of pressure increase versus pumped fuel volume.

[0061] Continuing at 510, fuel is injected via a direct fuel injector, with the resulting change in pressure within the fuel rail measured via a pressure sensor. In some examples, 510 may include injecting fuel via a direct fuel injector while also injecting fuel via one or more port fuel injectors. However, injections referred to herein occur via the direct fuel injectors unless otherwise noted. Injecting the fuel includes injecting a commanded fuel volume. The commanded fuel injection volume may be based on a fuel injection control parameter applied to a nominal injection volume. The nominal fuel volume may be determined via a transfer function based on a desired fuel mass.As an example, a nominal injection volume may be determined based on a target injection mass and a nominal fuel density, where the nominal fuel density is based on the properties of the subcritical fuel.

[0062] In an alternative example, injecting the fuel includes injecting the fuel for a commanded duration to inject a nominal fuel mass. The duration may be a pulse width and may be related to the nominal mass via one or more transfer functions. As an example, the nominal injection volume may be determined based on a desired injection mass and a nominal fuel density via a first transfer function. The nominal volume may be adjusted by the injector control parameter to determine a commanded injection volume, where a transfer function may relate the commanded injection volume to an injection pulse width based on injector characterization performed during the injector manufacturing process.As another example, the transfer function may directly relate a desired injection mass to a nominal injector pulse width, where the injector control parameter may adjust the nominal injector pulse width to a commanded injector pulse width. Additionally, at 510, the change in fuel rail pressure is measured.

[0063] At 512, the change in fuel rail pressure measured at 510 is compared to an expected change in fuel rail pressure. Based on this comparison, a fuel injector control parameter may be adjusted later in routine 500. An expected pressure change may be determined based on the fuel pump gain determined at 508 and the injection volume commanded from 510 based on the injector control parameter. The expected pressure change due to the injection event may be determined, for example, via the Fig. 4. In some examples, the comparison at 512 may include comparing an average of a predetermined number of measured pressure changes with an average of the corresponding expected pressure changes. For example, the measured pressure changes and the expected pressure changes may be compared over a predetermined number of injection events of a specific injector and may be averaged to form a more reliable estimate of the difference. In an alternative example, the comparison at 512 may be performed for each pumping and injection event, and adjusting the injector control parameter later in the routine may include adjusting based on each comparison performed at 512.In other words, the injector control parameter can be adjusted after each injection event or, alternatively, can be adjusted periodically after a predetermined number of injection events have occurred.

[0064] In an alternative embodiment, an expected pressure change may be based on a constant fuel pump gain determined based only on subcritical fuel. In other words, this alternative fuel pump gain is a fixed value that describes the slope of the fuel rail pressure change against the commanded pump displacement for fuel maintained throughout subcritical conditions. In this embodiment, the comparison may be constructing the ratio of the measured fuel rail pressure change to the fixed, subcritical expected fuel rail pressure change and applying this ratio as a fuel injector control parameter to set a nominal injection volume or nominal injection pulse width.

[0065] At 514, a decision is made to adjust or maintain the injector control parameter based on the comparison performed at 512. The injector control parameter may be adjusted in response to the measured pressure drop being significantly different from the expected pressure drop, while it may be maintained if the two are not significantly different. The comparison may include determining the difference between the measured and expected pressure changes, or alternatively, may include determining the ratio of the two pressure changes.

[0066] In one example, the fuel at the injector may be supercritical, where its density at the injector may have changed from a first density to a second density. The injector control parameter may have been calibrated to accurately inject a desired fuel mass of the first density, and therefore the controller may expect a pressure change related to the desired injection mass. However, because the density of the fuel has fluctuated, a different amount of pressure may be released from the fuel rail upon injection. Consequently, the measured pressure change may differ from the expected pressure change due to a fluctuation in fuel density at the injector. In response to this difference in expected pressures, the injector control parameter may be adjusted to accurately deliver a desired fuel amount of the second fuel density.However, if the measured pressure change is within a threshold difference of the expected value, the injector control parameters can be maintained. This allows the fuel injector control parameters to be calibrated in real time to maintain a desired air-fuel ratio.

[0067] Specifically, at 514, if the measured pressure change differs from the expected pressure change by more than a threshold difference, routine 500 proceeds to 516 to adjust the injector control parameter. Adjusting the injector control parameter may include decreasing the injector control parameter if the measured pressure change was greater than the expected pressure change by a threshold amount, and increasing the injector control parameter if the measured pressure change is less than the expected pressure change by a threshold amount. The threshold differences may be determined based on the magnitude of the difference in numbers (e.g., whether the difference is greater than a threshold percentage of the expected pressure change).The amount by which the injector control parameter is adjusted may be determined based on a gradual increase in a correction gain to drive the difference between the measured and corrected nominal values ​​to zero. After adjusting the injector control parameter, routine 500 ends. In this manner, an injector control parameter may control a command for the injected volume to be larger when less fuel was injected than desired and control the command for the injected volume to be smaller when more fuel was injected than desired.

[0068] In an alternative embodiment where the injector control parameter controls an injector pulse width, adjusting the injector control parameter may further include increasing the fuel injector control parameter when the measured change in fuel rail pressure is less than a predicted change in fuel rail pressure and decreasing the fuel injector control parameter when the measured change in fuel rail pressure is greater than the predicted change in fuel rail pressure. The control parameter may be directly proportional to the pulse width, thereby increasing the pulse width when the injected fuel mass is greater than the desired injection mass and decreasing the pulse width when the injected fuel mass is greater than the desired injection mass.

[0069] If, returning to 514, the measured pressure change (or an average of the measured pressure changes) is within the threshold difference of the predicted pressure change (or the average of the expected pressure changes), routine 500 proceeds to 518, where the current value for the injector control parameter may be maintained. After maintaining the current injector control parameter, routine 500 ends. The injector control parameter may continue to be adjusted based on an exhaust air-fuel ratio if the parameter is not adjusted based on a change in fuel rail pressure.In this manner, if the amount of fuel delivered to a combustion chamber differs from a desired amount by more than a threshold amount, an injector control parameter may be adjusted to adjust the amount of fuel injected and thereby provide a desired air-fuel ratio. Routine 500 ends after 518.

[0070] A specific embodiment of routine 500 for adjusting the fuel injector control parameter based on a change in fuel rail pressure after each injection event, wherein the measured fuel pumping gain is compared to a fixed pumping gain at subcritical fuel to determine an injector control parameter, is as follows: a pumping event may be executed based on a target pumped mass of 0.100 g of fuel. Based on a nominal (liquid) fuel density of 0.580 g / cm 3The target pump mass can be converted into a pump displacement of 0.172 cm 3 The change in fuel rail pressure resulting from the pumping event can be measured as 0.13 bar, therefore determining that the fuel pumping gain is 0.726 bar / cm 3 A fuel injector control parameter can be adjusted based on the 0.13 bar change in fuel rail pressure. Specifically, a ratio of a constant fuel pump gain and the measured fuel pump gain of 0.726 bar / cm 3 designed and applied as the fuel injector control parameter. A pump stroke of 1 cm 3For example, a pressure increase of 1 bar in the fuel rail can occur if the fuel in the rail is liquid. Consequently, the injector control parameter would be the (unitless) ratio 1.32. It is stated that if the fuel in the fuel is subcritical, the fuel injector control parameter would, in theory, be 1, because the pumping gain for subcritical fuel would be an accurate estimate of the fuel's behavior.

[0071] Continuing the example, a subsequent injection event may have a target injection mass of 0.100 g. Again, based on the nominal fuel density of 0.580 g / cm 3The nominal injection mass can be converted into a nominal injection volume of 0.172. However, the nominal injection volume can be converted into a commanded injection volume by applying the injector control parameter. The nominal injection volume can be specifically converted into 0.228 cm by applying the fuel injector control parameter of 1.32. 3 In this way, an injected fuel quantity can be adjusted based on a change in fuel rail pressure to deliver a more precise amount of fuel to the combustion chamber.

[0072] Fig. 6 provides a routine 600 for adjusting a fuel injector control parameter based on an estimated injected fuel mass and further based on determinations of whether the fuel at the fuel pump is either subcritical or supercritical. In the depicted example, the fuel mass is estimated based on a change in fuel rail pressure. A drop in fuel rail pressure resulting from an injection event may be used with a current factor relating a pumped fuel volume and a resulting increase in fuel rail pressure to determine a fuel mass injected during the injection event.In some examples, routine 600 may be executed in an engine system that includes only a direct injector, while other examples may include executing routine 600 in an engine system that includes both a direct injector and a port injector. In other examples, adjusting an injector control parameter via routine 600 may only include adjusting via the routine when fuel is delivered via only a direct injector. In each of the above examples, the injectors may inject a fuel that is supercritical during at least some engine operating conditions, such as LPG.

[0073] At 602, the engine controller determines whether the fuel at the fuel pump is subcritical, as described below with respect to Fig. 7. In one example, determining the condition of the fuel at 602 may include determining whether a gain of the direct injection fuel pump is above or below a lower threshold, where the lower threshold is determined based on a derived or measured fuel rail temperature. If it is determined that the fuel at the fuel pump is supercritical, routine 600 proceeds to 603. Otherwise, routine 600 proceeds to 606.

[0074] In some examples, 602 may further include determining whether injector overlap is currently present. Determining whether injector cycles currently overlap may be based on comparing the injection pulse signals for each injector on a fuel rail. In such examples, if there is one or more injector cycle overlaps, routine 600 proceeds from 604 to 630 and then to 632, as described in more detail below. However, if injector overlap is not present, routine 600 proceeds to 606. In this manner, the changes in fuel rail pressure may be the result of only one fuel injector and one injection event, and the control parameter for only that fuel injector may be adjusted based on the pressure change.

[0075] At 603, either the cooling or the pressure of the fuel delivered to the fuel pump is increased to change the fuel condition from supercritical to subcritical or to increase fuel pump gain. Routine 600 proceeds from 603 to 630, where the injector control parameter is not adjusted based on fuel injection mass, and then to 632, where the injector parameter may be adjusted based on an estimated exhaust air-fuel ratio. Further, the fuel injector control parameter may be adjusted based on an exhaust air-fuel ratio and may be selectively adjusted based on injection mass if the fuel at the fuel pump inlet is subcritical.In this way, the fuel injector control parameter can only be adjusted when the fuel is liquid at the fuel pump, providing a more reliable metering device with which to calibrate the fuel injector.

[0076] At 606, a current factor relating a pumped fuel volume and an increase in fuel pressure is determined. In one example, estimating the current factor includes pumping a commanded fuel volume into the fuel rail and measuring the resulting increase in fuel rail pressure via a pressure sensor. The relationship may be estimated for a number of pumping events, where the current factor may be based on an average of the measurements. In an alternative embodiment, the current factor is a fuel pump gain, as described with respect to Fig. 4, and the relationship is a slope determined via linear regression of the number of pumping events. In this way, by determining the relationship between a pumped fuel volume and a resulting pressure rise based on a number of pumping events, the reliability of the factor relating the two variables can be more reliable.

[0077] At 607, fuel is injected into the combustion chamber by the fuel injector based on the current injector control parameter. Injecting fuel based on the injector control parameter may include activating the fuel injector for a specified duration to inject a nominal fuel mass. The duration may be a pulse width and may be related to the nominal mass via one or more transfer functions. As one example, a nominal injection volume may be determined based on a desired injection mass and a nominal fuel density via a first transfer function.The nominal volume may be adjusted by the injector control parameter to determine a commanded injection volume, where a transfer function may relate the commanded injection volume to an injection pulse width based on an a priori relationship determined in the laboratory. As another example, a transfer function may directly relate a desired injection mass to a nominal injector pulse width, where the injector control parameter may translate the nominal injector pulse width into a commanded injector pulse width. Additionally, at 607, the change in fuel rail pressure is measured.

[0078] At 608, an injected fuel mass is determined based on the change in fuel rail pressure measured at 607. Specifically, the change in fuel rail pressure is related to a pumped volume via the current factor, or fuel pump gain, determined at 606, which relates a pumped fuel volume to a fuel rail pressure. Because the fuel pumped into the fuel rail was subcritical, the pumped fuel volume is well known. Additionally, a nominal fuel density is used to relate the pumped fuel volume to a pumped fuel mass. In this manner, an injected fuel mass is estimated based on a comparison of a change in fuel rail pressure to a fuel pump gain.

[0079] At 610, the injected fuel mass estimated at 608 is compared to the nominal injected mass. As one example, the nominal injected mass may have been determined based on a desired air-fuel ratio. At 614, a decision to adjust or maintain the injector control parameter is made based on the comparison performed at 610. The injector control parameter may be adjusted in response to the injected fuel mass differing by more than a threshold amount from the nominal or desired injection mass, and may be maintained if the two are not significantly different. In one example, the fuel at the injector may be supercritical, where its density at the injector may have changed from a first density to a second density.The injector control parameter may have been calibrated to accurately inject a desired fuel mass of the first density. However, because the density of the fuel has fluctuated, a fuel mass different from the nominal mass may be released from the fuel rail upon injection. This difference may be detected by the pressure change measured at 607. In response to this difference in expected pressures, the injector control parameter may be adjusted to accurately deliver the fuel of the second fuel density. However, if the measured pressure change is within a threshold difference from the expected value, the injector control parameters may be maintained. In this manner, the fuel injector control parameters may be calibrated in real time to maintain a desired air-fuel ratio.

[0080] Specifically, at 614, if the change in the estimated injected fuel mass differs from the nominal injected fuel mass by more than a threshold difference, routine 600 proceeds to 616 to adjust the injector control parameter. Adjusting the injector control parameter may include increasing the fuel injector control parameter when the injected fuel mass is less than a nominal injected fuel mass and decreasing the fuel injector control parameter when the injected fuel mass is greater than the nominal injected fuel mass. The threshold differences may be determined based on the significance of the difference between corrected nominal and actual (e.g., whether the difference is greater than a threshold percentage of the expected value).The amount by which the injector control parameter is adjusted may be determined based on the stability of the gain term, with the adjusted amount chosen to ensure that the injected fuel masses converge toward the desired values ​​without excessive oscillations. After adjusting the injector control parameter, routine 600 ends. In this manner, an injector control parameter may control an injected volume command to be larger when less mass than desired was injected and control the injected volume command to be smaller when more mass than desired was injected.

[0081] In an alternative embodiment where the injector control parameter controls an injector pulse width, adjusting the injector control parameter may further include increasing the fuel injector control parameter when the injected fuel mass is less than a nominal injected fuel mass and decreasing the fuel injector control parameter when the injected fuel mass is greater than the nominal injected fuel mass. The control parameter may be directly proportional to the pulse width, thereby increasing the pulse width when the injected fuel mass is greater than the desired injection mass and decreasing the pulse width when the injected fuel mass is greater than the desired injection mass.

[0082] Returning to 614, if the injected fuel mass (or the average of the injected fuel masses) is within the threshold difference of the commanded injection mass (or the average of the commanded injection masses), routine 600 proceeds to 618, where the current value for the injector control parameter may be maintained. After maintaining the current injector control parameter, routine 600 ends. The injector control parameter may continue to be adjusted based on the exhaust air-fuel ratio if the parameter is not adjusted based on the injected fuel mass, with the estimated fuel mass based on a change in fuel rail pressure.In this manner, if the mass of fuel delivered to a combustion chamber differs from a desired amount by more than a threshold amount, an injector control parameter may be adjusted to adjust the amount of fuel injected and thereby provide a desired air-fuel ratio. Routine 600 ends after 618.

[0083] In Fig. 7 is an exemplary prophetic flow for adjusting a fuel injector control parameter based on an exhaust air-fuel ratio, selectively adjusting the fuel injector control parameter further based on a fuel pump gain, and operating a fuel injector control parameter based on the fuel injector control parameter. Adjusting the fuel injector control parameter further based on the fuel pump gain may be performed in response to a determination that the fuel at the fuel pump is subcritical and not performed in response to a determination that the fuel at the fuel pump is supercritical. The injector control parameter is adjusted based on an estimated exhaust air-fuel ratio (e.g.,The fuel pressure is adjusted (e.g., via long-term and short-term fuel trim procedures) during the duration of the run, although this is not explicitly shown. However, the fuel changing from a subcritical state to a supercritical state represents a significant (and immediate) change in the injection masses. Relying on exhaust gas measurements to correct injector errors can lead to inefficient response times to the change in fuel state. Consequently, adjusting the injector control parameters in an open-loop manner (e.g., based on measurements of pressure changes resulting from injection) provides improved response time to large fluctuations in the injector calibration.

[0084] The injector control parameter can be set for a direct injector (e.g. 166 after Fig. 1), while the fuel pump gain from a direct injection fuel pump (e.g. 240 after Fig. 2). The process according to Fig. 7 can be used by the system after Fig. 1 in accordance with the procedures laid down in Fig. 5 and Fig. 6. The fuel supplied to the direct injection nozzle 166 after Fig. 1 may be subcritical during at least some engine operating conditions, e.g., LPG. The vertical markers T0-T2 represent the times of interest during the operating sequence.

[0085] The first graphic representation after Fig. Figure 7 is a graphical representation of fuel pump gain (e.g., the increase in fuel rail pressure versus a commanded pump volume, as described with respect to Fig. 4) versus time. The fuel pump gain may be based on the pump's volumetric efficiency. In one example, the fuel pump gain may increase as the pump's volumetric efficiency increases and decrease as the pump's volumetric efficiency decreases. The Y-axis represents the direct injection fuel pump gain (e.g., 240 after Fig. 2), with the gain increasing in the direction of the Y-axis arrow. Alternatively, the Y-axis may represent the ratio of the factor relating a drop in fuel rail pressure to a commanded injection volume and the fuel pump gain described above, with the ratio increasing in the direction of the Y-axis. The X-axis represents time, with time increasing in the direction of the X-axis arrow. The horizontal line 712 represents a lower threshold gain. It may be determined that the fuel at the fuel pump is subcritical when the fuel pump gain is above the horizontal line 712, and that the fuel at the fuel pump is supercritical when the fuel pump gain is below the horizontal line 712.

[0086] In the example where the Y-axis represents the relationship described above, the horizontal line 712 represents a 1:1 ratio. For a given volume of fuel leaving the fuel rail, the pressure drop may be smaller if the fuel is supercritical and larger if it is subcritical. If subcritical, the density may not change appreciably, in which case the relationship between the pumped fuel and the injected fuel may be 1:1. However, supercritical fuel may be less dense than subcritical fuel, and consequently, for a given injection volume, less mass may leave the fuel rail, and the ratio represented along the Y-axis may be less than 1:1 if subcritical fuel is pumped but supercritical fuel is injected.In this way, determining whether the fuel is supercritical at the injection location can be performed without knowledge of the fuel composition. In response to a fuel pump gain below horizontal line 712, either the cooling or the pressure of the fuel at the fuel pump can be increased.

[0087] The second graphical representation after Fig. 7 is a graphical representation of the fuel injector control parameter versus time. In one example, the fuel injector may be a direct fuel injector (e.g., injector 166 after Fig. 1), while the injector control parameter may be an injector gain that controls a commanded injection volume. Controlling the commanded injection volume may include setting a nominal injection volume. Thus, in one example, the Y-axis represents the direct fuel injector gain for a single injector, with gain increasing in the direction of the Y-axis arrow. The X-axis represents time, with time increasing in the direction of the X-axis arrow.

[0088] The horizontal line 722 may represent a predetermined level of the injector control parameter or may represent a desired level for the injector control parameter. For example, the injector control parameter may be a unitless injector gain that sets a commanded injection volume, where the commanded injection volume is based on the properties of the subcritical fuel. In this case, the horizontal line 722 may be one, the predetermined level of injector gain, allowing the injector to operate with an injection gain of one. The injector gain may be set from one to a different value during conditions where the properties of the injected fuel are not those of the subcritical fuel (such as when the fuel at the injection location is supercritical).It will be appreciated that in other examples, the injector control parameter may be a parameter other than injector gain. For example, the injector control parameter adjusted based on fuel pump gain may instead be a parameter for controlling injector pulse width rather than a commanded injection volume.

[0089] The third graphical representation after Fig. Figure 7 is a graphical representation of the fuel condition in a direct injector versus time. Specifically, the fuel condition within the fuel rail at the injector inlet is shown. The Y-axis represents the fuel condition at a direct injector (e.g., 166 after Fig. 2). The fuel is supercritical when the trace is at a higher level near the Y-axis arrow. The fuel is subcritical when the trace is at a lower level near the X-axis. The X-axis represents time, with time increasing in the direction of the X-axis arrow.

[0090] At time T0, the fuel condition at the injector is subcritical. The fuel pump gain is above the lower threshold 712, with the fuel injector control parameter within a threshold level of the predetermined value 722. Between times T0 and T1, the fuel condition at the fuel injector remains subcritical. During this period, minor adjustments to the fuel injector control parameter may be made based on the exhaust air-fuel ratios estimated via UEGO measurements. In addition, during this period, the fuel pump gain estimation (i.e., the plot 410 after Fig.4) are monitored, but due to the subcritical conditions within the fuel rail, the value remains consistent. The fuel injector control parameter cannot be adjusted based on fuel pump gain because the measured gain may be within the expected gain. In this way, a fuel injector control parameter can be adjusted based on feedback from an exhaust gas sensor, and during some conditions, it can also be adjusted based on fuel pump gain.

[0091] At time T1, the fuel condition at the injector becomes supercritical. Determining whether the fuel condition is subcritical or supercritical may be based on the fuel pump gain falling below the lower threshold 712 (as illustrated), and / or an inferred or measured fuel rail temperature, and / or the exhaust gas sensor readings, and / or the temperature measurements at the fuel injector. During this period, fuel pump gain estimates may differ from the fuel pump gain estimates during the subcritical conditions, where the fuel pump gain values ​​may be adjusted based on an average of the fuel pump gain estimates.However, in the illustrated example, the lower density of the supercritical fuel results in a lower fuel pump gain due to less mass being pumped into the fuel rail for a given pump stroke volume, thereby resulting in a lower pressure gain per unit volume of pumped fuel.

[0092] Further, between times T1 and T2, an injector control parameter is adjusted in response to the change in fuel rail pressure that differs from an expected change in fuel rail pressure. In the illustrated example, the injector control parameter is increased in response to a decrease in fuel pump gain, and consequently, the injector delivers a larger volume of fuel per injection event when operating with the updated control parameter. In this manner, an injection mass can be maintained at a desired value throughout a wide range of engine operating conditions.

[0093] After the initial adjustment of the injector control parameter based on a pressure change, the injector control parameter is further adjusted based on feedback from an exhaust gas sensor, as illustrated by the slight fluctuations of the injector control parameter after a more pronounced increase from the predetermined level.

[0094] At time T2, the fuel condition at the injector changes from supercritical to subcritical. The fuel density in the fuel rail may increase due to its subcritical condition. Accordingly, the fuel pump gain may increase. In response to the increase in fuel pump gain, the injector control parameter is decreased, thereby delivering a smaller volume of fuel per injection event. Specifically, the injector control parameter is gradually decremented to a value near the predetermined value 722, and is further adjusted based on feedback from an exhaust gas sensor.In this manner, a fuel injector control parameter operates at a predetermined value when the fuel is subcritical at the injection site, being adjusted based on an exhaust air-fuel ratio, and being further adjusted based on a fuel pump gain when the fuel is supercritical at the injection site and subcritical at the fuel pump inlet.

[0095] The technical effect of adjusting an injector control parameter based on fuel pump gain in addition to injector control corrections based on exhaust air-fuel ratio feedback can improve response times for adjusting injector control parameters. By adjusting injector control parameters only when the fuel is subcritical at the fuel pump, measurements in the fuel pump can be considered reliable and can be used to estimate conditions at the injection point where the fuel is supercritical. Overall, fuel injection masses can be better monitored, allowing supercritical fuel to be injected more accurately, improving air-fuel ratios and providing the purification benefits of supercritical fuel.

[0096] It should be noted that the exemplary control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be 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. As such, the various acts, operations, and / or functions illustrated may be performed in the illustrated order, executed in parallel, or, in some cases, omitted.Likewise, the order of processing is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy employed. Further, the described acts, operations, and / or functions may graphically represent code to be programmed into the 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 components of the engine hardware in combination with the electronic controller.

[0097] It is understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, as numerous variations are possible. For example, the above technique may be applied to V-6, I-4, I-6, V-12, horizontally opposed four, and other engine types.

[0098] The claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims should be understood to include the inclusion of one or more such elements and neither require nor exclude two or more such elements.

Claims

[1] A method for a fuel system, the method comprising: Setting a fuel injector control parameter based on an exhaust air-fuel ratio, selectively adjusting the fuel injector control parameter further based on a fuel pump gain; Operating a fuel injector based on the fuel injector control parameter; and wherein the selectively adjusting includes: adjusting the fuel injector control parameter further based on the fuel pump gain in response to a determination that the fuel at the fuel pump is subcritical; and not adjusting the fuel injector control parameter further based on the fuel pump gain in response to a determination that the fuel at the fuel pump is supercritical. [2] The method of claim 1, wherein the fuel injector control parameter is applied to a direct fuel injector (166) and wherein the fuel pump gain is from a direct injector fuel pump (240). [3] A method according to claim 1 or 2, wherein the fuel is LPG. [4] A method according to any preceding claim, wherein the fuel pump gain is estimated a plurality of times and wherein the fuel injector control parameter is further adjusted based on an average of the estimated fuel pump gain. [5] The method of claim 1, wherein the fuel injector control parameter controls an injection pulse width. [6] A method according to any preceding claim, wherein the fuel pump gain is an increase in the ramp of fuel rail pressure against a commanded pump volume. [7] The method of claim 5, wherein the adjusting further includes, based on the fuel pump gain: when the fuel pump gain decreases, increasing the fuel injector control parameter, and as the fuel pump gain increases, decrease the fuel injector control parameter. [8] A method for a fuel injection system, the method comprising: Adjusting a fuel injector control parameter based on a change in fuel rail pressure and further based on determinations of whether the fuel at the fuel pump is either subcritical or supercritical. [9] The method of claim 8, wherein the fuel injector control parameter sets an injection volume command. [10] A method according to claim 8 or 9, wherein: the adjustment is based on a difference between a measured change in fuel rail pressure and a predicted change in fuel rail pressure. [11] A method according to any one of claims 8 to 10, wherein the fuel injector control parameter is adjusted after each injection event. [12] A method according to any one of claims 8 to 11, wherein: the adjustment is based on a difference between a measured change in fuel rail pressure and a predicted change in fuel rail pressure, and the change in fuel rail pressure is estimated multiple times and wherein the fuel injector control parameter is adjusted based on an average of the estimated changes in fuel rail pressure. [13] A method according to any one of claims 8 to 12, wherein the setting includes: Increasing the fuel injector control parameter if the measured change in fuel rail pressure is less than the predicted change in fuel rail pressure, and Decrease the fuel injector control parameter when the measured fuel rail pressure change is greater than the predicted fuel rail pressure change. [14] A method according to any one of claims 8 to 13, wherein the fuel is LPG. [15] A method for a fuel injection system, the method comprising: Setting a fuel injector control parameter based on an estimated injected fuel mass and further based on determinations of whether the fuel at the fuel pump is either subcritical or supercritical. [16] The method of claim 15, wherein: an injected fuel mass is estimated based on a comparison of a change in fuel rail pressure with a fuel pump gain, the fuel injector control parameter is set based on the difference between the estimated injected fuel mass and a nominal injected fuel mass, and the fuel injector control parameter controls a command for the injected volume. [17] The method of claim 15, wherein the setting includes: Increasing the fuel injector control parameter when the injected fuel mass is less than a nominal injected fuel mass, and Decrease the fuel injector control parameter when the injected fuel mass is greater than the nominal injected fuel mass. [18] A method according to any one of claims 15 to 17, wherein the fuel pump gain is estimated a plurality of times and wherein the fuel injector control parameter is adjusted based on an average of the comparisons of the changes in fuel rail pressure with an average of the fuel pump gain. [19] A method according to any one of claims 15 to 18, wherein the fuel is LPG.

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