Methods for fuel system control

Abstract

Procedure that includes the following: Increasing a suction pump voltage to a high threshold voltage in response to a direct injection pump efficiency (DI pump efficiency) being below a threshold efficiency, and Increasing the suction pump voltage to a first threshold voltage that is lower than the high threshold voltage in response to a main jet pump fuel level being lower than a first threshold level.

Description

Area

[0001] The field of the disclosure generally relates to fuel systems in internal combustion engines. State of the art and brief description

[0002] Lift pump control systems can be used for a variety of fuel system control purposes. These can include, for example, fuel injection vapor management, injection pressure control, temperature control, and lubrication. In one example, a lift pump supplies fuel to a higher-pressure fuel pump (DI pump), which provides high injection pressure to direct fuel injectors in an internal combustion engine. The DI pump can provide the high injection pressure by supplying high-pressure fuel to a fuel rail to which the direct fuel injectors are coupled. A fuel pressure sensor can be disposed in the fuel rail to enable measurement of the fuel rail pressure, upon which various aspects of engine operation, such as fuel injection, can be based.Furthermore, a lift pump can be operated to apply just enough fuel pressure to the high pressure pump to maintain the efficiency of the DI pump while maintaining fuel economy.

[0003] From DE 10 2015 120 577 A1 a method for operating a fuel system is known, which comprises controlling or increasing a suction pump voltage to a high threshold voltage in response to a DI pump efficiency being below a threshold efficiency.

[0004] From DE 11 2015 000 620 T5 a method for operating a fuel system is known, which comprises controlling or increasing a lift pump voltage to an increased threshold voltage in response to a main jet pump fuel level being lower than a first threshold level.

[0005] However, the inventors have identified potential problems with such systems. The lift pump pressures applied to maintain DI pump efficiency can be low, particularly during cold fuel conditions, reducing the performance of the jet pumps within the fuel tank, which can cause low fuel tank and jet pump fuel levels. Low fuel tank and jet pump fuel levels can lead to low fuel rail pressures, fuel atomization within the fuel system, and a rapid drop in DI fuel rail pressure, causing engine stalling.

[0006] In one example, the above problems may be addressed by a method comprising: increasing a lift pump voltage to a high threshold voltage in response to a DI pump efficiency well below a threshold efficiency; and increasing a lift pump voltage to a first threshold voltage lower than the high threshold voltage in response to a main jet pump fuel level being lower than a first threshold level. Thus, the technical result of maintaining jet pump fuel flow and performance while achieving DI pump efficiency may be achieved. A risk of fuel atomization within the liquid fuel delivery system and severe DI fuel rail pressure drops may be reduced, and the stability of engine operation may be increased while maintaining fuel economy.

[0007] In one example, if the DI pump efficiency drops below a threshold efficiency, the lift pump voltage is increased to a high threshold voltage to mitigate the drop in DI pump efficiency and return the DI pump efficiency to the threshold efficiency. Further, in response to a fuel level dropping below a first threshold fuel level, the lift pump voltage may be increased to a second threshold voltage lower than the high threshold voltage. Thus, both engine operation with low high-pressure fuel pump efficiency and fuel atomization resulting from low fuel levels and low jet pump flow may be mitigated while maintaining fuel economy.

[0008] It is understood that the foregoing summary is provided to introduce, in simplified form, a selection of concepts that are described in more detail in the detailed description. It is not intended to reveal critical or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any disadvantages identified above or in any part of this disclosure. Short description of the drawings Fig. 1 is a sketch showing an example machine. Fig. 2 shows an example of a direct injection engine system having a fuel tank system. Fig. 3 shows another exemplary fuel tank system. Fig. 4 shows an example of a jet pump. Fig. Figure 5 shows an example of a main jet pump configuration of a fuel tank system. Fig. Figure 6 shows a graph illustrating jet pump flow versus suction pump pressure. Fig. Figure 7 shows a plot of the time for the fuel rail pressure to drop by 50 bar as a function of DI pump control (duty cycle) and engine speed. The Fig. 8 through 10 show a flowchart illustrating a method for adjusting pump timing in a fuel system lift pump to maintain DI pump efficiency and fuel system jet pump flow. Fig. 11 shows an example timeline for operating a lift pump in a fuel system. Fig. 12 shows an example timeline for operating a suction pump in pulse and increment mode. Fig. 13 shows a table of exemplary control modes for operating a lift pump in a fuel system. Detailed description

[0009] Methods and systems are provided for increasing the consistency of engine operation while maintaining fuel economy by adjusting lift pump pressure operation to maintain jet pump fuel flow and performance in fuel systems used in the Fig. 1 and Fig. 2. One or more jet pumps, such as the exemplary jet pump in Fig. 4, can be used in conjunction with a suction pump, as in the exemplary fuel tank system of Fig. 3, and as shown by the exemplary main jet pump supplying fuel to a main jet pump fuel supply in Fig. 5. The influence of the suction pump pressure (or suction pump voltage) and the duty cycle on the jet pump flow, fuel rail pressure and volume fuel flow as a function of the engine speed are shown in the Fig. 6 and Fig. 7. A suction pump voltage can be controlled to provide a desired suction pump pressure, as shown in the Fig. 11 and Fig. 12. For example, a controller may be configured to execute instructions contained therein, such as the method of Fig. 8 to 10, to increase the lift pump pressure or lift pump voltage in response to a fuel tank level condition or DI pump efficiency level in order to maintain jet pump fuel flow and jet pump performance and mitigate engine shutdown hazards while maintaining DI pump efficiency. The controller-executable instructions of the procedure of Fig. 8 to 10 are in a table of control modes in Fig. 13. Examples of the lift pump settings in response to low fuel tank levels and low DI pump efficiencies are shown in the Fig. 11 and Fig. 12. In this way, jet pump flow and power can be maintained, and engine stalling can be reduced while maintaining fuel economy.

[0010] Fig. 1 is a schematic diagram illustrating an engine 10 that may be included in a propulsion system of a motor vehicle. The engine 10 is shown with four cylinders 30. However, other numbers of cylinders may be used in accordance with the present disclosure. The engine 10 may be controlled at least in part by a control system including a controller 12 and by input from a vehicle driver 132 via an input device 130. The controller 12 receives signals from the various sensors of the Fig. 1 and uses the various actuators of the Fig. 1, to adjust engine operation based on the received signals and instructions stored in a memory of the controller. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Each combustion chamber (e.g., each cylinder) 30 of the engine 10 may have combustion chamber walls with a piston (not shown) positioned therein. The pistons may be coupled to a crankshaft 40 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. The crankshaft 40 may be coupled to at least one drive wheel of a vehicle via an intermediate gear system (not shown). Further, a starter motor may be coupled to the crankshaft 40 via a flywheel to enable starting operation of the engine 10.

[0011] Combustion chambers 30 may receive intake air via an intake manifold 44 through intake passage 42 and exhaust combustion gases via exhaust passage 48. Intake manifold 44 and exhaust manifold 46 may selectively communicate with combustion chamber 30 via respective intake valves and exhaust valves (not shown). In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0012] Fuel injectors 50 are shown coupled directly to the combustion chamber 30 to inject fuel therein in proportion to the pulse width of the signal FPW received from the controller 12. In this manner, the fuel injector 50 provides what is known as direct fuel injection into the combustion chamber 30. The fuel injector may be installed, for example, in the side of the combustion chamber or in the top of the combustion chamber. The fuel may be delivered to the fuel injector 50 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. An exemplary fuel system that may be used in conjunction with the engine 10 is described below with reference to Fig. 2. In some embodiments, the combustion chambers 30 may alternatively or additionally include a fuel injector disposed in the intake manifold 44 in a configuration that provides what is known as port fuel injection into the intake port upstream of each combustion chamber 30.

[0013] The intake passage 42 may include throttles 21 and 23 having throttle bodies 22 and 24. In this particular example, the positions of the throttle bodies 22 and 24 may be varied by the controller 12 via signals sent to an actuator included in the throttle bodies 21 and 23. In one example, the actuators may be electric actuators (e.g., electric motors), a configuration commonly called electronic throttle control (ETC). In this manner, the throttles 21 and 23 may be operated to vary the intake air supplied to the combustion chamber 30 among other engine cylinders. The position of the throttle bodies 22 and 24 may be supplied to the controller 12 via a throttle position signal TP.The intake passage 42 may further include a mass air flow sensor 120, a manifold air pressure sensor 122, and a throttle intake pressure sensor 123 to provide respective MAF (mass air flow) and MAP (manifold air pressure) signals to the controller 12.

[0014] Exhaust passage 48 may receive exhaust gases from cylinders 30. Exhaust sensor 128 is shown coupled to exhaust passage 48 upstream of turbine 62 and an emissions control device 78. Sensor 128 may be selected from a variety of suitable sensors to provide an indication of the exhaust air / fuel ratio, such as a linear oxygen sensor or UEGO (Universal or Wide-Range Exhaust Gas Oxygen), a dual-state oxygen sensor or EGO, a NOx, HC, or CO sensor. Emissions control device 78 may be a three-way catalyst (TWC), a NOx trap, various other emissions control devices, or combinations thereof.

[0015] The exhaust gas temperature may be measured by one or more temperature sensors (not shown) located in the exhaust passage 48. Alternatively, the exhaust gas temperature may be inferred based on engine operating conditions, such as engine speed, load, AFR, spark retard, etc.

[0016] The controller 12 is in Fig. 1 as a microcomputer having a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, shown in this particular example as a read-only memory chip 106, a random access memory 108, a latch 110, and a data bus.The controller 12 may receive various signals from sensors coupled to the engine 10, in addition to the signals discussed above, including the inducted mass air flow (MAF) measurement from the mass air flow sensor 120; the engine coolant temperature (ECT) from a temperature sensor 112, shown schematically at a location within the engine 10; a profile ignition response (PIP) signal from a Hall effect sensor 118 (or other type) coupled to the crankshaft 40; the throttle position (TP) from a throttle position sensor, as discussed; and an absolute manifold pressure signal, MAP, from a sensor 122, as previously discussed. The engine speed signal, RPM, may be generated by the controller 12 from the PIP signal. The manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold 44.It should be noted that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor may provide an indication of engine torque. Further, this sensor, along with the sensed engine speed, may provide an estimate of the load (including air) drawn into the cylinder. In one example, sensor 118, which is also used as an engine speed sensor, may generate a predetermined number of evenly spaced pulses during each revolution of crankshaft 40. In some examples, storage medium read-only memory 106 may be programmed with computer-readable data representing instructions executable by processor 102 to perform the methods described below, as well as other variations anticipated but not specifically listed.

[0017] The engine 10 may further include a compression device, such as a turbocharger or a supercharger having at least one compressor 60 disposed along the intake manifold 44. For a turbocharger, the compressor 60 may be at least partially driven by a turbine 62, for example, via a shaft or other coupling arrangement. The turbine 62 may be disposed along the exhaust passage 48 and communicate with the exhaust gases flowing therethrough. Various arrangements may be provided to drive the compressor. For a supercharger, the compressor 60 may be at least partially driven by the engine and / or an electric motor and may not include a turbine. Therefore, the amount of compression applied to one or more cylinders of the engine via a turbocharger or supercharger may be varied by the controller 12.In some cases, for example, the turbine 62 may drive an electric generator 64 to provide power to an accumulator 66 via a turbo driver 68. Power from the accumulator 66 may then be used to drive the compressor 60 via a motor 70. Further, a sensor 123 may be disposed in the intake manifold 44 to provide a BOOST signal to the controller 12.

[0018] Further, the exhaust passage 48 may include a wastegate 26 to divert exhaust gas away from the turbine 62. In some embodiments, the wastegate 26 may be a multi-stage wastegate, such as a two-stage wastegate, with a first stage configured to control boost pressure and a second stage configured to increase heat flow to the emissions control device 78. The wastegate 26 may be actuated with an actuator 150, which may be, for example, an electric actuator such as an electric motor, although pneumatic actuators are also contemplated. The intake passage 42 may include a compressor bypass valve 27 configured to bypass the compressor 60.The wastegate control valve 26 and / or the compressor bypass valve 27 may be controlled by the controller 12, for example via actuators (for example via the actuator 150), to be opened when, for example, a lower boost pressure is desired.

[0019] The intake passage 42 may further include a charge air cooler (CAC) 80 (e.g., an intercooler) to reduce the temperature of the intake gases charged by the turbocharger. In some embodiments, the charge air cooler 80 may be an air-to-air heat exchanger. In other embodiments, the charge air cooler 80 may be an air-to-liquid heat exchanger.

[0020] Furthermore, in the disclosed embodiments, an exhaust gas recirculation (EGR) system may route a desired portion of exhaust gas from the exhaust passage 48 via the EGR passage 140 to the intake passage 42. The amount of EGR provided to the intake passage 42 may be varied by the controller 12 via the EGR valve 142. Further, an EGR sensor (not shown) may be disposed within the EGR passage and may provide an indication of the pressure, temperature, and / or concentration of the exhaust gas. Alternatively, EGR may be controlled by a calculated value based on signals from the MAF sensor (upstream), MAP sensor (intake manifold), MAT sensor (manifold gas temperature), and the crank speed sensor. Further, EGR may be controlled based on an exhaust O2 sensor and / or an intake manifold oxygen sensor.Under some conditions, the EGR system can be used to regulate the temperature of the air and fuel mixture within the combustion chamber. Fig. 1 shows a high-pressure EGR system, where the EGR is routed from upstream of a turbocharger turbine to downstream of a turbocharger compressor. In other embodiments, the engine may additionally or alternatively include a low-pressure EGR system, where the EGR is routed from downstream of a turbocharger turbine to upstream of a turbocharger compressor.

[0021] Fig. 2 shows a direct injection engine system 200 that may be configured as a propulsion system for a vehicle. The engine system 200 includes an internal combustion engine 202 having a plurality of combustion chambers or cylinders 204. The engine 202 may, for example, be the engine 10 according to Fig. 1. Fuel may be provided directly to the cylinders 204 via the direct injectors 206 within the cylinders. As shown in Fig. As schematically indicated in Figure 2, the engine 202 may receive intake air and exhaust the products of combusted fuel. The engine 202 may be of any suitable type, including a gasoline or diesel engine.

[0022] Fuel may be provided to the engine 202 via the injectors 206 through a fuel system generally indicated at 208. In this particular example, the fuel system 208 includes a fuel storage tank 260 for storing the fuel on board the vehicle, a lower pressure fuel pump 282 (e.g., a fuel lift pump), a higher pressure fuel pump 214, an accumulator 215, a fuel rail 216, and various fuel passages 218 and 220. In the Fig. 2, the fuel passage 218 supplies the fuel from the lower pressure pump 282 to the higher pressure fuel pump 214, while the fuel passage 220 supplies the fuel from the higher pressure fuel pump 214 to the fuel rail 216.

[0023] As in Fig. 2, the fuel storage tank 260 may comprise a saddle-type fuel tank, wherein a partition 276 within the fuel storage tank 260 at least partially fluidically isolates a fuel chamber from the fuel lift pump. As shown in Fig. 2, the partition 276 may include any type of barrier, wall, or barrier, including other types of projections from the bottom of the fuel storage tank 260. The partition 276 may therefore divide the fuel storage tank 260 into two storage sumps, a main fuel sump 280 and an auxiliary storage sump 270. Although in Fig. 2, the auxiliary fuel sump 270 and the main fuel sump 280 may be refilled using standard fuel tank procedures. In one example, fuel may fill the main fuel sump 280 before the auxiliary fuel sump 270 is filled. The main fuel sump 280 is in Fig. 2 with a larger volume than the auxiliary fuel sump 270, however, in other examples they may have the same volume, or the auxiliary fuel sump 270 may have a larger volume than the main fuel sump 280. The fuel storage tank 260 may include a fuel level sensor 262 that measures the fuel level in one or more fuel sumps (e.g., main fuel sump fuel level 281, auxiliary fuel sump fuel level 271) and transmits it to the controller 222 via a signal 264.

[0024] The lower pressure fuel pump 282 may be submerged in liquid fuel within the fuel reservoir 285 (which may also be called the main jet pump fuel reservoir), which may be positioned within the main fuel sump 280. The fuel reservoir 285 may comprise a small fraction of the total volume of the main fuel sump 280. Thus, the lower pressure fuel pump 282 may be maintained submerged with a smaller volume of fuel compared to when the lower pressure fuel pump 282 is positioned within the main fuel sump 280 without the fuel reservoir 285. Maintaining the lower pressure fuel pump 282 submerged in fuel within the fuel reservoir 285 helps reduce suction loss of the lower pressure fuel pump 282 (e.g., cavitation) and maintain DI pump performance and fuel flow to the engine.For example, if the fuel reservoir fuel level 291 falls below the fuel pump suction port at the lower pressure 282, air may be drawn into the fuel line and destabilize engine operation. The fuel reservoir 285 may also mitigate cavitation or suction loss to the lower pressure fuel pump 282 caused by fuel sloshing during vehicle start-up.

[0025] A fuel reservoir fuel level sensor 266 may be used to measure the fuel reservoir fuel level 291 and may communicate the fuel reservoir fuel level 291 to the controller 222 via signal 268. The fuel reservoir 285 is full when the fuel level within the reservoir is at the level of the tank lip, the full fuel reservoir level 287. When the fuel reservoir fuel level 291 is at the full fuel reservoir level 287, additional fuel overflows the fuel reservoir 285 to the main fuel sump 280. Further, when the main fuel sump level 281 is higher than the full fuel reservoir level 287, the fuel reservoir is full, and the fuel reservoir fuel level 291 is the full fuel reservoir level 287. In one example, the full fuel reservoir level 287 may be 100 mm. In other words, the fuel tank can be 285,100 mm deep.In some examples, the fuel supply fuel level 291 may be estimated via a supply fill model that considers a fuel injection control rate, fuel consumption rate, engine load, air / fuel ratio, and other engine operating variables. If the fuel supply fuel level 291 is measured or estimated to be low, various control actions, as described in more detail below, may be performed to mitigate cavitation of the low-pressure fuel pump to reduce the risk of dropping fuel rail pressure, resulting in engine stall.

[0026] The lower pressure fuel pump 282 may be controlled by a controller 222 (for example, the controller 12 of the Fig. 1) to provide fuel to the fuel pump 214 at a higher pressure via the fuel passage 218. The lower pressure fuel pump 282 may be configured as what may be referred to as a fuel lift pump. As one example, the lower pressure fuel pump 282 may be a turbine pump (e.g., a centrifugal pump) having a pump electric motor (e.g., a DC pump motor), whereby the pressure at the pump increases and / or the volumetric flow rate through the pump can be controlled by varying the electrical power (e.g., current and / or voltage) supplied to the pump motor, thereby increasing or decreasing the motor speed. For example, if the controller 222 decreases the electrical power provided to the pump 282, the volumetric flow rate and / or the pressure increase at the pump 282 may be decreased.The volumetric flow rate and / or pressure rise at the pump may be increased by increasing the electrical power provided to pump 282. As one example, the electrical power supplied to the lower pressure pump may be obtained from an alternator or other energy storage device onboard the vehicle (not shown), allowing the control system to control the electrical load used to drive the lower pressure pump 282. Thus, by varying the voltage and / or current provided to the lower pressure fuel pump 282, as indicated at 224, the flow rate and pressure of fuel provided to the higher pressure fuel pump 214 and ultimately to the fuel rail 216 may be adjusted by the controller 222.In addition to providing injection pressure to the direct injectors 206, in some implementations the pump 282 may provide injection pressure to one or more (in . Fig. 2 port injectors (not shown).

[0027] The lower-pressure fuel pump 282 may be fluidly coupled to a filter 286, which may remove small contaminants that may be present in the fuel and could potentially damage fuel-handling components. One or more check valves 295 may prevent fuel from leaking back upstream of the valves. In this context, upstream flow refers to fuel flow from the fuel rail 216 to the low-pressure pump 282, while downstream flow refers to a nominal fuel flow direction from the low-pressure pump to the fuel rail.

[0028] A portion of the fuel pumped by the lower-pressure fuel pump 282 may pass through the check valve 295 and be delivered to the accumulator 215 via the low-pressure fuel passage 218. A remaining portion of the fuel pumped by the lower-pressure fuel pump 282 may remain in the fuel tank 260, flow to the main fuel sump 280 via the opening 290 and fuel passage 292, or may flow back to the fuel reservoir 285 via the opening 254 positioned in the fuel passage 250. The opening 290 may act as an ejector or jet pump, whereby fuel flowing through the opening 290 (e.g., transfer jet pump 290) to the fuel passage 292 is accelerated through the opening, creating a vacuum in the fuel passage 274.Consequently, if the fuel flow rate through orifice 290 is sufficiently high, fuel may be drawn from auxiliary fuel sump 270 via filter 272 and fuel passage 274 to fuel passage 292. Fuel passage 274 may also include a check valve 275 (e.g., an anti-siphon check valve) to direct fuel flow from fuel passage 274 to orifice 290 and fuel passage 292. As shown in FIG. Fig. 2, the fuel passage 292 directs the fuel flow to the fuel supply 285.

[0029] The opening 254 may act as an ejector or jet pump, whereby fuel flowing through the opening 254 (e.g., main jet pump 254) to the fuel passage 250 is accelerated through the opening, creating a vacuum in the fuel passage 256. Consequently, if the fuel flow rate through the opening 254 is sufficiently high, fuel may be drawn from the main fuel sump 280 via the fuel passage 256 to the fuel passage 250. The fuel passage 256 may also include a check valve 258 (e.g., an anti-siphon check valve) to limit fuel flow in the direction from the fuel passage 250 to the opening 254 and to the fuel passage 292.

[0030] Fuel flow through the transfer jet pump 290 and through the main jet pump 254 can help keep the fuel reservoir 285 filled by drawing fuel from the main fuel sump 280. The transfer jet pump 290 can be called a pull-type transfer jet pump because fuel flow through the jet pump 290 "pulls" fuel from the auxiliary fuel sump 270 to the fuel reservoir 285.

[0031] The higher pressure fuel pump 214 may be controlled by the controller 222 to provide fuel to the fuel rail 216 via the fuel passage 220. As a non-limiting example, the higher pressure fuel pump 214 may be a BOSCH HDP5 high pressure pump that utilizes a flow control valve (e.g., a fuel volume regulator, a solenoid valve, etc.) 226 to allow the control system to vary the effective pumping volume of each pump stroke, as indicated at 227. However, it should be recognized that other suitable higher pressure fuel pumps may be used. The higher pressure fuel pump 214 may be driven by the engine 202, unlike the engine-driven lower pressure fuel pump 282.A higher-pressure pump plunger 228 of the fuel pump 214 can receive mechanical input from the engine's crankshaft or camshaft via a cam 230. In this manner, the pump 214 can be operated according to the principle of a single-cylinder, cam-driven, higher-pressure pump. A sensor (in . Fig. 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 relayed to controller 222. In some examples, higher pressure fuel pump 214 may supply sufficiently high fuel pressure to injectors 206. Because injectors 206 may be configured as direct fuel injectors, higher pressure fuel pump 214 may be called a direct fuel injection (DI) pump.

[0032] As described above, maintaining the lower pressure fuel pump 282 submerged in fuel within the fuel reservoir 285 helps reduce suction loss of the lower pressure fuel pump 282 (e.g., cavitation) and maintain DI pump performance and fuel flow to the engine. For example, if the fuel reservoir fuel level 291 falls below the suction port of the lower pressure fuel pump 282, air may be drawn into the fuel line and destabilize engine operation. DI pump performance may be monitored by estimating and measuring DI pump efficiency. For example, a DI pump model may calculate an expected DI pump volumetric flow rate and compare the expected DI pump efficiency rate to the controlled pump volumetric flow rate.A difference between the expected DI pump volumetric flow rate and the controlled pump volumetric flow rate can be calculated as the lost DI pump volumetric fuel flow rate. A DI pump efficiency can then be calculated by normalizing the lost DI pump volumetric fuel flow rate by the DI pump volumetric fuel flow rate when the DI pump is controlled at 100% and has 100% efficiency (for example, 100% rated DI pump flow). The DI pump efficiency can therefore be a measure of DI pump efficiency loss. Consequently, at lower DI pump efficiencies, the DI pump may exhibit cavitation, drawing fuel vapor and / or air instead of liquid fuel.Lower DI pump efficiencies may be increased by increasing the fuel line pressure to the DI pump, for example, by increasing the electrical power delivered to the lift pump (for example, increasing the lift pump voltage). If the DI pump efficiency deviates by more than 15% from the 100% rated DI pump current, for example, the DI pump may be determined to be operating at low DI pump efficiency. In response to the low DI pump efficiency, the lift pump voltage may be increased. In response to the low DI pump efficiency, the lift pump voltage may be increased to a high threshold voltage V. High,TH . be increased. As another example, in response to low DI pump efficiency, the suction pump voltage may be pulsed to a higher threshold voltage and then incremented by incremental threshold voltage, as described herein.

[0033] Fig. 2 depicts the optional inclusion of a top-loaded accumulator 215. If included, accumulator 215 may be positioned downstream of the lower pressure fuel pump 282 and upstream of the higher pressure fuel pump 214, and may be configured to contain a volume of fuel that reduces the rate of increase or decrease in fuel pressure between fuel pumps 282 and 214. The volume of accumulator 215 may be sized to allow engine 202 to operate at idle conditions for a predetermined period of time between operating intervals of lower pressure fuel pump 282.For example, the accumulator 215 may be sized such that, when the engine 202 is idling, it takes 15 seconds to reduce the pressure in the accumulator to a level at which the higher-pressure fuel pump 214 is unable to maintain a sufficiently high fuel pressure for the fuel injectors 206. The accumulator 215 may therefore enable an intermittent, lower-pressure mode of operation of the fuel pump 282, described below. In other embodiments, the accumulator 215 may be inherently present in correspondence with the fuel filter 286 and the fuel passage 218, and thus may not be present as a separate element.

[0034] The controller 222 may individually actuate each of the injectors 206 via a fuel injection driver 236. The controller 222, the driver 236, and other suitable controllers of the engine system may comprise a control system. Although the driver 236 is shown external to the controller 222, it is understood that in other examples, the controller 222 may include the driver 236 or be configured to provide the functionality of the driver 236. The controller 222 may include additional components not shown, such as those included in the controller 12 according to Fig. 1 are included.

[0035] The fuel system 208 includes a low-pressure (LP) fuel pressure sensor 231 positioned between the fuel lift pump 282 and the higher-pressure fuel pump 214 along the fuel passage 218. In this configuration, the readings from the sensor 231 can be interpreted as indicating the fuel pressure of the fuel lift pump 282 (e.g., the fuel outlet pressure of the lift pump) and / or the intake pressure of the higher-pressure fuel pump 214. Signals from the sensor 231 can be used to control the voltage applied to the lift pump in a closed-loop manner.Specifically, the LP fuel pressure sensor 231 may be used to determine whether sufficient fuel pressure is being provided to the higher pressure fuel pump 214 so that the higher pressure fuel pump 214 receives liquid fuel rather than fuel vapor, and / or to minimize the average electrical power supplied to the fuel lift pump 282. It is understood that in other embodiments that utilize a port fuel injection system rather than a direct injection system, the LP fuel pressure sensor 231 may sense both lift pump pressure and fuel injection. Although the LP fuel pressure sensor 231 is shown positioned upstream of the accumulator 215, in other embodiments, the LP sensor may be positioned further downstream of the accumulator.

[0036] As in Fig. 2, the fuel rail 216 includes a fuel rail pressure sensor 232 for providing an indication of the fuel rail pressure to the controller 222. An engine speed sensor 234 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 higher pressure fuel pump 214, since the higher pressure fuel pump 214 is mechanically driven by the engine 202, for example, via the crankshaft or the camshaft.

[0037] The controller 222 may determine a voltage to be applied to the lift pump based on the controlled fuel pressure, and the controlled fuel pressure may depend on a derived or measured fuel temperature. The derived or measured fuel temperature may indicate the fuel pressure above which fuel atomization Pfuel,novap in the fuel system 208 can be prevented. P fuel,novap can, for example, be a threshold pressure differential P diff,fuelvap be greater than the calculated fuel vapor pressure P fuel,vap . In addition, the controller can calculate a lift pump voltage to be applied based on the controlled lift pump pressure and the fuel flow rate. During idle engine conditions, when a lift pump pressure to be applied based on the fuel flow rate may be lower than P fuel,novap , the controller 12 can set a suction pump pressure P fuel,novap to reduce a risk of fuel atomization in the fuel system 208. As another example, the controller 12 may, during high engine load conditions, when the lift pump pressure to be applied based on the fuel flow rate may be higher than P fuelnovap , control the lift pump pressure based on the fuel flow rate. P fuel,vapdepends on the fuel temperature, so that at low fuel temperatures P fuel,vap and consequently P fuel,novap may be lower than compared to high fuel temperatures, where P fuel,vap and consequently P fuel,novap may be higher. Consequently, in another example, during cold fuel conditions, a lift pump pressure to be applied based on the fuel flow rate may be lower than P fuelnovap . The controller 12 can therefore set a suction pump pressure P fuel,novap to reduce the risk of fuel atomization in the fuel system 208. Thus, the lift pump operation can be controlled in a base mode, wherein the lift pump voltage (or pressure) is calculated based on the fuel flow rate, and wherein the controlled lift pump pressure is greater than P fuel,novap based on a derived or measured fuel temperature.

[0038] As used here, fuel pump pressure is used synonymously with high pressure (DI) pump inlet pressure. The controller can use test data or modeled data, such as the Fig. 5 and Fig. 6 to help determine the suction pump voltage. The relationship between the suction pump voltage and other operating conditions, such as the suction pump pressure or test and / or modeled data, can also be stored in a lookup table and retrieved on demand.

[0039] As described with reference to the suction pump control system of the Fig. 8 to 10, in response to a DI pump efficiency being lower than a threshold efficiency, the controller 222 may cancel or disable the base mode control of the suction pump and operate the suction pump in a pulse and increment mode by increasing a suction pump voltage from the base mode controlled suction pump voltage to a V High,TH In one example, increasing the suction pump voltage to V High,TH pulsing the suction pump voltage to the V High,TH The pulse may be applied to the V High,TH Following pulsing of the suction pump voltage to V High,TH, the suction pump voltage can be increased by a threshold incremental voltage relative to the controlled base mode suction pump voltage prior to pulsing. In this way, opportunities for DI pump operation below the threshold efficiency can be reduced and consistent machine operation can be increased.

[0040] Further, as explained in more detail below, the controller 222 may operate the lift pump in a first control mode in response to a main sump fuel level being lower than a first threshold reservoir fuel level. For example, the lift pump may be operated in a first control mode in response to a fuel reservoir fuel level 291 being below a first threshold reservoir level or in response to a fuel tank level (e.g., the main sump fuel level 281) being below a first threshold reservoir level. The first control mode may include maintaining a lift pump voltage above a first threshold voltage.

[0041] Furthermore, in a second control mode, the lift pump may be operated in response to a fuel tank level (e.g., the main fuel sump level 281 or the auxiliary fuel sump fuel level 271) being lower than a threshold fuel sump level, or in response to a fuel storage fuel level 291 being lower than a second threshold fuel storage level. The second control mode may include maintaining a lift pump voltage above a second threshold voltage that is higher than the first threshold voltage and lower than the high threshold voltage V High,TH include.

[0042] Additionally, the controller 222 may cancel or disable the pulse and increment mode and enable a third control mode in response to engine operating conditions that exceed threshold conditions that cause the fuel rail pressure drop detection time to fall below a threshold detection time. Further, the controller 222 may cancel or disable the pulse and increment mode and enable a third control mode in response to engine operating conditions that cause the fuel rail pressure drop detection time to fall below a threshold detection time. The third control mode may include increasing a lift pump voltage to a third threshold voltage that is higher than the second threshold voltage and lower than the high threshold voltage V High,TH. In addition, the controller 222 may cancel or disable the first or second control mode and enable the pulse and increment modes in response to the DI pump efficiency being lower than the threshold efficiency.

[0043] When the fuel reservoir fuel level or the fuel tank fuel levels are lower, the controller 222 may thus reduce a risk of fuel atomization in the fuel system by maintaining the lift pump voltage (and a lift pump pressure) above a threshold level, thereby maintaining or increasing the fuel flow rate through the fuel system jet pumps (e.g., the main jet pump and transfer jet pump). Increased fuel flow rates through the fuel system jet pumps help replenish and maintain the fuel levels in the fuel reservoir and the fuel tank. Furthermore, when the DI efficiency is lower, the controller 222 may reduce a cavitation risk at the DI pump by increasing the lift pump voltage V High,THincreases or pulses and increments the lift pump voltage relative to the base control mode voltage. Further, if the fuel rail pressure drop sensing time is below a threshold sensing time, the controller 222 may reduce a cavitation risk at the DI pump by increasing the lift pump voltage to a third threshold voltage.

[0044] In some cases, controller 222 may also determine an expected or estimated fuel rail pressure and compare the expected fuel rail pressure to the measured fuel rail pressure measured by fuel rail pressure sensor 232. In other cases, controller 222 may determine an expected or estimated lift pump pressure (e.g., the outlet fuel pressure from lift pump 282 and / or the fuel intake pressure into the higher pressure fuel pump 214) and compare the expected lift pump pressure to the measured lift pump pressure measured by LP fuel pressure sensor 231. Determining and comparing expected fuel pressures to the corresponding measured fuel pressures may be performed periodically on a time basis at a suitable frequency or on an event basis.Although the outputs of controller 222 related to lift pump operation are described in terms of controlling lift pump voltage, controller 222 may also issue commands based on lift pump pressure, either alternatively or in combination with lift pump voltage. Lift pump voltage and lift pump pressure are generally affinely correlated (for centrifugal lift pumps), and this affinely correlated pump characterization can be precisely determined a priori. Further, lift pump voltage and lift pump pressure increase with increasing lift pump fuel flow rate. Lift pump characterization data correlating lift pump pressure, lift pump voltage, and lift pump fuel flow rate may be obtained from controller 222. Fig. 2, which accesses them to inform the controller of the fuel system 208. For example, a desired lift pump pressure may be provided to the function 304 as an input so that the minimum lift pump voltage, the application of which to the fuel lift pump 282 results in the desired lift pump pressure, can be obtained. It will also be understood that the minimums and maximums of the lift pump pressure may be limited, respectively, by the fuel vapor pressure and a pressure relief valve setpoint pressure. Furthermore, analog data sets and functions relating the lift pump pressure to the lift pump voltage may be obtained and accessed for lift pump types other than turbine lift pumps driven by DC electric motors, including, but not limited to, positive displacement pumps, and pumps driven by brushless motors.Such functions can take linear or nonlinear forms.

[0045] Determining the expected lift pump pressure may also account for the higher pressure operation of the fuel injectors 206 and / or the fuel pump 214. In particular, the effects of these components on the lift pump pressure may be parameterized by the fuel flow rate, for example, the rate at which fuel is injected through the injectors 206, which under steady-state conditions may be equal to the lift pump flow rate. In some implementations, a linear relationship may be formed between the lift pump voltage, the lift pump pressure, and the fuel flow rate. As a non-limiting example, the relationship may take the following form: V LP = C1 * P LP + C2 * F + C3, where V LP the suction pump voltage is, P LPis the lift pump pressure, F is the fuel flow rate, and C1, C2, and C3 are constants that can take the values ​​1.481, 0.026, and 2.147, respectively. In this example, the relationship can be accessed to determine a lift pump supply voltage, the application of which results in a desired lift pump pressure and fuel flow rate. The relationship can be stored (e.g., via a lookup table), for example, in controller 222, and accessed by controller 222.

[0046] The expected fuel rail pressure in the fuel rail 216 may be determined based on one or more operating parameters, for example, an assessment of fuel consumption (e.g., fuel flow rate, fuel injection rate) and / or fuel temperature (e.g., via a measurement of engine coolant temperature) and / or lift pump pressure (e.g., as measured by the LP fuel pressure sensor 231) may be used.

[0047] As indicated above, the inclusion of accumulator 215 in fuel system 208 may enable intermittent operation of fuel lift pump 282 during at least selected conditions. Intermittent operation of lift pump 282 may include cycling the pump on and off, with the pump speed dropping to zero during off periods, for example. Intermittent lift pump operation may be used to maintain the efficiency of higher pressure lift pump 214 at a desired level, to maintain the efficiency of lift pump 282 at a desired level, and / or to reduce unnecessary energy consumption of lift pump 282.The efficiency (e.g., volumetric efficiency) of the higher pressure fuel pump 214 may be parameterized at least in part by the fuel pressure at its intake; therefore, intermittent lift pump operation may be selected according to this intake pressure, as this pressure may partially determine the efficiency of the higher pressure fuel pump 214. The intake pressure of the higher pressure fuel pump 214 may be determined via the LP fuel pressure sensor 231 or may be inferred based on various operating parameters. The efficiency of the higher pressure fuel pump 214 may be calculated based on the fuel consumption rate by the engine 202, the change in fuel rail pressure, and a fraction of the pump volume to be pumped.The duration during which the fuel lift pump 282 is driven may, for example, be related to maintaining the intake pressure of the higher pressure fuel pump 214 above the fuel vapor pressure. On the other hand, the fuel lift pump 282 may be deactivated according to the amount of fuel (e.g., the volume of fuel) pumped to the accumulator 215. For example, the lift pump may be deactivated when the amount of fuel pumped to the accumulator exceeds the volume of the accumulator by a predetermined amount (e.g., 20%). In other examples, the fuel lift pump 282 may be deactivated when the pressure in the accumulator 215 or the intake pressure of the higher pressure fuel pump 214 exceeds respective threshold pressures. In some implementations, the operating mode of the fuel lift pump 282 may be selected according to the current speed and / or load of the engine 202.A suitable data structure, such as in . Fig. 7, or a lookup table, may store the operating modes, which may be accessed using the engine speed and / or the engine load as indices into the data structure, which may be stored, for example, in the controller 222 and accessed by the controller 222. The intermittent operating mode may be selected, in particular, for relatively lower engine speeds and / or loads. During these conditions, the fuel flow to the engine 202 is relatively low, and the fuel lift pump 282 has capacity to supply fuel at a rate that is higher than the engine's fuel consumption rate. Therefore, the fuel lift pump 282 may fill the accumulator 215 and then be shut down while the engine 202 continues to operate (e.g., combusting air-fuel mixtures) for a period of time before the lift pump is restarted.Restarting the fuel lift pump 282 replenishes the fuel in the accumulator 215 that was fed into the engine 202 while the lift pump was off.

[0048] Fig. 3 illustrates another fuel tank system 360 that includes a transfer jet pump 378 for pumping fuel from the auxiliary fuel sump 270 to the main fuel sump 280 and a main jet pump 394 for pumping fuel from the main fuel sump 280 to the fuel reservoir 285. Thus, the main jet pump 394 and the transfer jet pump 378 help maintain the fuel reservoir fuel level 291. Although in Fig. 3, a controller 222 may send and receive signals to and from the fuel lift pump 282 and one or more fuel level sensors, 262 and 266, respectively, for controlling the fuel reservoir fuel level 291.

[0049] In the fuel tank system 360, fuel may be pumped by the fuel lift pump 282, flow through the lift pump outlet 284, the check valve 285, and the filter 286, after which at least a portion of the fuel flow may be directed through the fuel passage 218 to the fuel injection system (e.g., to the higher pressure fuel pump 214). Another portion of the fuel flow may be directed to the fuel passage connection 380, where fuel may then flow through the fuel passage 372 to the auxiliary fuel sump 270, through the fuel passage 392 to the main fuel sump 280, or via the pressure relief valve 396 to the fuel passage 398. The fuel passage connection 380 may be structured to redirect fuel flow to the fuel passage connection 380 to one or more of the fuel passages 372, 392, or 398.Additionally, additional check valves and pressure relief valves (e.g., in addition to pressure relief valve 396) may be used in fluid communication with fuel passage connection 380 to redirect fuel flow into one or more of fuel passages 372, 392, and 398. The relative orientation and sizing of the fuel passages in . Fig. 3 are for illustrative purposes only, and the actual relative orientation and dimension of the fuel passage may vary.

[0050] Fuel flowing through fuel passage 372 is directed to auxiliary fuel sump 270 and through the orifice of transfer jet pump 378. Thus, the fuel flow through fuel passage 372 may entrain fuel from auxiliary fuel sump 270. Fuel entrained by transfer jet pump 378 may first pass through a fuel filter 272 before entering the orifice of transfer jet pump 378 and being directed to fuel passage 374. As the fuel flow rate through fuel passage 372 increases, transfer jet pump 378 entrains higher fuel flow rates from auxiliary fuel sump 270. Fuel from the fuel passage 374 flows to the fuel reservoir 285 in the main fuel sump 280. The check valve 375 prevents the siphoning or reverse flow of fuel from the fuel reservoir 285 back to the fuel passage 374 and the jet pump 378.In this way, the main jet pump 378 helps maintain the fuel reservoir fuel level 291. As the fuel flow rate in the fuel passage 372 decreases, the pressure drop created by flowing through the orifice of the transfer jet pump 378 decreases such that for very low flow rates, there may not be enough suction through the fuel filter 272 to entrain fuel from the auxiliary fuel sump 270. In other words, the performance of the transfer jet pump may degrade at very low fuel flow rates in the fuel passage 372. The transfer jet pump 378 may be called a push-type transfer jet pump because fuel flow "pushes" fuel from the auxiliary fuel sump 270 to the fuel reservoir 285.

[0051] Fuel flowing through fuel passage 392 is directed to the main fuel sump 280 and through the orifice of main jet pump 394. Thus, the fuel flow through fuel passage 392 may entrain fuel from the main fuel sump 280. Fuel is entrained by main jet pump 394 via fuel passage 395, which may include a fuel filter, before entering the orifice of main jet pump 394 and being directed to fuel reserve 285. As the fuel flow rate through fuel passage 392 increases, main jet pump 394 entrains higher fuel flow rates from main fuel sump 280. Thus, main jet pump 394 assists in maintaining fuel reservoir fuel level 291.As the fuel flow rate in the fuel passage 392 decreases, the pressure drop created by flow through the orifice of the main jet pump 394 decreases such that, for very low flow rates, there may not be enough suction through the fuel filter 395 to entrain fuel from the auxiliary fuel sump 280. In other words, the performance of the main jet pump may degrade at very low fuel flow rates in the fuel passage 392. The check valve 393 prevents the siphoning or reverse flow of fuel from the fuel reservoir 285 back to the fuel passage 292.

[0052] Thus, the transfer jet pump 378 and the main jet pump 394 can transfer fuel from the auxiliary fuel sump 270 and the main fuel sump 280, respectively, to the fuel reservoir 285, making fuel from both sumps available for pumping by the lift pump 282. The transfer jet pump 378 and the main jet pump 394 are each capable of transferring all of the fuel in the auxiliary fuel sump 270 and the main fuel sump 280. For example, when the jet pump pressure (e.g., the lift pump pressure) is sufficiently high, the jet pumps (main jet pump 394 and transfer jet pump 378) may pump fuel at a flow rate greater than the engine fuel consumption rate (e.g., the fuel injection flow rate), thereby keeping the fuel reservoir 285 filled (e.g., the fuel reservoir fuel level 291 is at the filled fuel reservoir level 287).As one example, sufficient jet pump and lift pump pressures may include the jet pump and lift pump pressures being greater than a threshold pressure. In one example, the threshold pressure may be 200 kPa. At jet pump pressures lower than the threshold pressure, the jet pump fuel flow rate may be lower than the engine fuel consumption rate (e.g., the fuel injection flow rate), and the fuel reservoir fuel level 291 may decrease and not be maintained at the full fuel reservoir level 287. Consequently, under certain operating conditions, such as cold fuel conditions, the lift pump pressure and the jet pump pressures may no longer be sufficient to maintain the fuel reservoir fuel level (e.g., jet pump performance may degrade at low lift pump pressures).Under conditions where pump performance may degrade, and when the fuel tank (e.g., main sump) fuel level or fuel reservoir fuel levels are lower (thereby increasing a risk of lift pump cavitation and reduced engine stability), lift pump control modes as described herein may be activated to increase the electrical power supplied to the lift pump. By increasing the electrical power to the lift pump, the lift pump pressure may be increased to a sufficiently high level (e.g., higher than a threshold pressure) so that jet pump performance is restored and the fuel levels in the fuel tank and fuel reservoir can be replenished. Thus, the risk of lift pump cavitation may be reduced, thereby increasing engine stability.

[0053] At higher lift pump pressures, a portion of the returning fuel at fuel passage connection 380 may be directed through fuel passages 372 and 392 and through pressure relief valve 396. Fuel flowing through pressure relief valve 396 is directed to fuel passage 398 and then back to fuel reservoir 285. Thus, higher lift pump pressures can be used to replenish fuel reservoir 285 more quickly because fuel flow via fuel passage connection 380 activates both the main and transfer jet pumps 394 and 378, respectively, transferring fuel from both the main and auxiliary fuel sumps to fuel reservoir 285. Additionally, excess fuel flow (e.g., fuel not directed to fuel passage 218 or by the jet pumps) is returned to fuel reservoir 285.

[0054] Fig. 4 shows an exemplary configuration of a jet pump 400. Jet pumps used in the Fig. 2, Fig. 3 and Fig. 5 and described herein may include the structural features of the jet pump 400. Arrows 440 indicate the direction of fuel flow through the jet pump 400. As described above in connection with the Fig. 2 and Fig. 3, a portion of the fuel flow directed by the fuel lift pump 282 may be directed to jet pumps (e.g., the main jet pumps 394 and 594, or the transfer jet pumps 378 and 290) in the fuel tank fuel sumps. The fuel directed by the fuel lift pump 282 may enter the jet pumps at the intake fuel passage 410, from where it is diverted to the orifice inlet 412. Upstream of the orifice inlet 412, a pressure relief valve 404 may be used to vent fuel flow in the event that the fuel pressure in the jet pump (or the fuel pressure in the lift pump feeding the jet pump) should be very high. Fuel at the orifice inlet 412 is accelerated as it flows through the orifice nozzle 450 into the orifice outlet fuel passage 418, creating a vacuum in the fuel passage 416.This suction, created by accelerating the fuel through the jet pump orifice, entrains and "pumps" fuel fluidly connected to the fuel passage 416 into the jet pump fuel passage 418. As fuel flow rates through the intake fuel passage 410 are increased, a higher pressure differential (e.g., a vacuum) may be created in the fuel passage 416, thereby entraining higher fuel flow rates fluidly connected to the fuel passage 416 into the lift pump fuel passage 418. At very low fuel flow rates through the intake fuel passage 410, a very low pressure differential (e.g., a vacuum) may be created in the fuel passage 416, thereby entraining lower or no fuel flow fluidly connected to the fuel passage 416 into the jet pump fuel passage 418.The fuel passage 416 may be fluidly connected to a fuel source, such as the main fuel sump 280 or the auxiliary fuel sump 270. Fuel flow through the jet pump orifice nozzle 450 may be greater for larger nozzles and less for smaller nozzles at the same fuel flow pressure (e.g., given the same lift pump pressure).

[0055] Fig. 5 illustrates another exemplary configuration of a main jet pump 594 of a fuel tank system 500 that includes the main fuel sump 280 and the fuel reservoir 285 (e.g., the main jet pump fuel reservoir). Although not shown, the fuel tank system may include an auxiliary fuel sump separated from the main fuel sump 280 by a partition 276, as shown in Fig. 2. Fuel may enter the fuel reservoir 285 by overflow from the main fuel sump 280 when the main fuel sump fuel level 281 is higher than the filled fuel reservoir fuel level 287. Fuel may enter the fuel reservoir 285 via the check valve 503 from the head pressure differential between the main fuel sump 280 and the fuel reservoir 285. When the fuel reservoir fuel level 291 is lower than the main fuel sump fuel level 281, this head pressure equalization between the main fuel sump 280 and the fuel reservoir 285 may fill the fuel reservoir 285 to the main fuel sump fuel level 281.

[0056] Fuel pumped by the lift pump 282 may also flow to the fuel passage 528 and through the opening 594 (e.g., the main jet pump). As fuel flow is accelerated through the opening 594, suction is created in the fuel passage 526, and fuel is pumped from the main fuel sump 280 through the fuel passage 526 to the fuel reservoir 285. An anti-siphon check valve 529 may be positioned in the fuel passage 526 to prevent siphoning of fuel from the reservoir back to the main fuel sump 280, for example, when the lift pump is off.

[0057] Fuel pumped from the fuel reservoir 285 may flow through the filter 534 and through the outlet check valve 295 via the fuel passage 284. In the event of overpressure, fuel is diverted through the pressure relief valve 510 and returns to the fuel reservoir via the fuel passage 504. During overpressure, some fuel may also be forced through the jet pump, creating suction that may draw fuel from the main fuel sump 280 into the fuel reservoir 285. The main jet pump intake fuel passage 526 may draw from the bottom of the main fuel sump 280. In other examples, the main jet pump intake fuel passage 526 may draw fuel from other sumps within the fuel tank or from another fuel tank.

[0058] The fuel passage 524 is fluidly coupled to the fuel reservoir 285. Thus, the fuel flow induced by the lift pump pressure can be used to induce the main jet pump 594 to transfer fuel from the main fuel sump 280 to the fuel reservoir 285. As described above for the jet pump operation in the Fig. 2-3, the fuel flow from the main fuel sump 280 to the fuel reservoir 285 via the main jet pump 594 is increased while increasing the lift pump pressure and the resulting fuel flow. If the lift pump pressure is very low, the resulting fuel flow may be low, so the fuel flow from the main fuel sump 280 to the fuel reservoir 285 via the main jet pump 594 is very small, or there may not be enough vacuum to transfer fuel to the fuel reservoir 285 from the main fuel sump 280.

[0059] Fig. 6 illustrates a graph with trend lines 610 showing the relationship between the jet pump net flow rate (e.g., jet pump suction flow rate) and the lift pump pressure, which is typically the jet pump pressure. As described above, the jet pump flow decreases as the lift pump pressure increases. To maintain fuel levels in the fuel supply, the jet pump flow rate may be kept higher than the fuel injection flow rate. For example, if the fuel injection flow rate is 10 cm 3 / s, the jet pump pressure (e.g., the lift pump pressure) is maintained at at least 100 kPa gauge to maintain the fuel supply fuel level, particularly when the fuel supply fuel level is low. Therefore, during periods when the lift pump is off or when the lift pump duty cycle is low (e.g., low lift pump voltage, low lift pump pressure, long time between lift pump pulses, and the like), the pump flow may be reduced. If this pump flow is further reduced, the jet pump intake flow rate may be less than the fuel injection flow rate. The fuel supply fuel level 291 may therefore drop, resulting in lift pump cavitation, drastic drops in fuel rail pressure, and engine stalling.Therefore, as described herein, increasing the lift pump voltage in response to a fuel tank or fuel reservoir fuel level being below a threshold fuel level may help mitigate lift pump cavitation and reduce engine stalling by increasing fuel flow through the jet pumps (e.g., fuel flow transferred from the fuel tank fuel sumps to the fuel reservoir).

[0060] Fig. Figure 7 illustrates a plot 700 of fuel rail pressure (FRP) drop time data by 50 bar, and a plot 702 of volumetric fuel injection flow rate data versus DI pump timing (or DI pump duty cycle) and engine speed. 710 and 740 are constant DI pump timing data lines at 80% DI pump duty cycle, and 730 and 760 are constant engine speed data lines at 3000 rpm. Therefore, areas of plots 700 and 702 above data lines 710 and 740 are areas where the DI pump duty cycle is greater than 80%, and areas of plots 700 and 702 to the right of data lines 730 and 760 are areas where the engine speed is greater than 3000 rpm.720 represents a data boundary where the time for the FRP to drop by a threshold pressure drop (for example, 50 bar) is 100 ms, and 750 represents a data boundary where the fuel injection flow rate is 4 cm. 3 / s. Areas above the data limit 720 therefore represent regions in which the time for the FRP to drop by 50 bar is less than 100 ms, and areas above the data limit 750 represent areas in which the volumetric fuel injection flow rate is greater than 4 cm 3 / s. When the volume fuel injection flow rate is greater than 4 cm 3 / s, the FRP can drop by 50 bar in less than 100 ms.

[0061] A time to detect and respond to fuel atomization within the fuel system (for example, detecting and responding to a DI pump efficiency being lower than a threshold efficiency) may not be instantaneous and may occur after a threshold time interval t FRP due to the non-instantaneous fuel pressure dynamics in the fuel system fuel passages, fuel pressure sensor response time, controller computing speed and response times, and the like. In one example, t FRP100 ms. For example, in a case where the DI pump efficiency is zero, a 50 bar fuel pressure drop may not be detected until a threshold time interval of 100 ms has elapsed following the fuel pressure drop. In other examples, the threshold pressure drop may be greater than 50 bar or less than 50 bar. For vehicle systems where the threshold time interval is less than 100 ms, the threshold pressure drop may be greater than 50 bar, while for vehicle systems where the threshold time interval is greater than 100 ms, the threshold pressure drop may be less than 50 bar. The controller 222 may thus control the lift pump in a third control mode by increasing a lift pump voltage to a third threshold voltage in response to engine operating conditions during which a 50 bar drop in FRP may occur in less than the threshold time interval.By increasing the suction pump voltage to the third threshold voltage, the risk of FRP dropping by 50 bar in less than 100 ms can be reduced.

[0062] The DI pump duty cycle at 80% corresponds to a threshold DI pump duty cycle at which FRP can be maintained or increased by raising a lift pump voltage to a third threshold voltage to mitigate the risk of FRP dropping (e.g., from 50 bar in less than 100 ms). Above the threshold DI pump duty cycle, the available control action to mitigate an FRP drop of 50 bar is less than 100 ms because the DI pump duty cycle cannot be increased above 100%. The engine speed of 3000 rpm corresponds to a threshold engine speed above which engine operation is exceptional. Thus, fuel economy and jet pump operation can be maintained at engine speeds below 3000 rpm, while engine stability takes priority at engine speeds above 3000 rpm. by increasing the suction pump voltage to a third threshold voltage.

[0063] Thus, the shaded area 770 of the plotter representation 700 illustrates engine operating conditions in which the DI pump duty cycle is greater than 80%, the engine speed is greater than 3000 rpm, or the time to drop the FRP by 50 bar is less than 100 ms, while the shaded area 780 of the plotter representation 702 illustrates engine operating conditions in which the DI pump duty cycle is greater than 80%, the engine speed is greater than 3000 rpm, or the volumetric fuel injection flow rate is greater than 4 cm 3 / s. The data of plots 700 and 702 may be stored in controller 222 in the form of a lookup table, a set of equations, or other suitable form. Controller 222 may therefore reference the data during engine operation and perform actions based on current, past, or predicted future operating conditions. For example, controller 222 may increase a fuel lift pump voltage above a third threshold voltage in response to engine speed greater than 3000 rpm or in response to engine operating conditions falling within shaded area 770 to mitigate a 50 bar drop in FRP that occurs in less than 100 ms, thereby increasing engine stability and reducing engine stalling.Similarly, the controller 222 may increase a fuel lift pump voltage above a third threshold voltage in response to engine speed being greater than 3000 rpm or in response to engine operating conditions falling within the shaded area 780 to prevent the volumetric fuel injection flow rate from decreasing below 4 cm. 3 / s, thereby increasing machine stability and reducing machine stalling.

[0064] The Fig. 8 through 10 illustrate flowcharts for methods 800, 900, 902, and 1000 for operating a fuel lift pump to reduce engine stalls while maintaining or increasing DI pump efficiency. Instructions for performing methods 800, 900, 902, 1000, as well as other instructions included herein, may be executed by a controller (e.g., controller 12 or 222) based on instructions stored in a memory of the controller and associated with signals received from sensors of the engine system, such as the sensors described above with reference to the Fig. 1 to 3 and 5, as well as signals sent to various actuators of the machine system, such as signal 224 for operating suction pump 282. The controller may use machine actuators of the machine system according to the methods described below to adjust machine operation.

[0065] Method 800 begins at 810 when vehicle operating conditions, such as engine speed, DI pump duty cycle, fuel injection flow rate, vehicle speed, fuel tank level, fuel sump levels, and the like, are estimated and / or measured. At 822, method 800 begins a third lift pump control mode 826 by determining whether an FRP detection time condition is met.

[0066] With brief reference to Fig. 10 illustrates a method 1000 for assessing whether an FRP detection time condition is met. The FRP detection time condition relates to engine operating conditions where the risk of rapid FRP decay leading to engine stalling may be high, such that the time to detect and respond to low DI pump efficiency or low fuel tank levels (e.g., first or second fuel level conditions), which can cause low DI pump efficiencies and engine stalling, may be greater than the time for FRP to decay. In other words, when the FRP detection time condition is met, the controller 222 may proactively respond by actuating the lift pump in a manner that mitigates the risk of rapid FRP decay.The method 1000 may refer to a lookup table, equation, or other data structure, as illustrated in plotter representations 700 and 702, in determining whether an FRP acquisition time condition is met according to machine operating conditions.

[0067] The procedure 1000 begins at 1010 where it determines whether a DI pump duty cycle DC DI is greater than a threshold DI pump duty cycle DC DI,TH . DC DI,TH can the DC DI above which the DI pump may not be able to respond to a rapid FRP drop that causes engine stalling. As described above with reference to Fig. 7, DC DI,TH 80% (0.8 suction pump control). In other words, if the DI pump duty cycle is greater than DC DI,TH , an FRP acquisition time condition is met. If DC DI < DC DI,TH, the method 1000 continues to 1020 where it determines whether the engine speed is greater than a threshold engine speed Engine Speed TH . The engine speed TH may correspond to the engine speed above which a rapid FRP drop may cause an engine stall. As described above with reference to Fig. 7, the engine speed Engine Speed TH 3000 rpm. If the engine speed < Engine Speed TH , method 1000 continues at 1030 where it determines whether a fuel injection flow rate Q inj,fuel is greater than a threshold fuel injection flow rate Q inj,ruel,TH . Q inj,fuel,TH can the above Q inj,ruel where rapid FRP degradation can cause engine stalling. As described above with reference to Fig. 7, Q inj,fuel,TH 4 cm 3 / s. In other words, if the fuel injection flow rate is greater than Q inj,fuel,TH , an FRP acquisition time condition is met. If Q inj,fuel < Q inj,ruel,TH , the method 1000 continues at 1040 where it determines whether a time t FRP for the FRP to drop by 50 bar is lower than a threshold time for the FRP to drop t FRP,TH around 50 bar, t FRP,TH may correspond to a period of time during which the controller 222 cannot reactively actuate the lift pump quickly enough to mitigate a rapid drop in fuel rail pressure (e.g., 50 bar pressure drop) to avert an engine stall. As described above with reference to Fig. 7, t FRP,TH 100 ms. In other words, if the machine operating conditions are such that t FRPis less than 100 ms (for example, when a machine operating condition falls within the shaded area 770), an FRP capture time condition is met.

[0068] Therefore, if at 1010 DC DI > DCDI TH , at 1020 Engine Speed ​​> Engine Speed TH , at 1030 Q inj,fuel > Q inj,fuel,TH or at 1040 t FRP > t FRP,TH , the method 1000 continues to 1050 where the FRP capture time condition is met before returning to the method 800 at 824. If at 1010 DC DI < DCDI TH , at 1020 engine speed < Engine Speed TH , at 1030 Q inj,fuel < Q inj,fuel,TH and at 1040 t FRP < t FRP,TH , method 1000 continues at 1060 where the FRP capture time condition is not met before returning to method 800 at 830.

[0069] Under Return to Fig. 8, at 824, in response to the FRP acquisition time condition being met, the method 800 sets V LiftPump on V LiftPump,TH3 . In an example, V LiftPump,TH3 a suction pump voltage higher than V LiftPump,TH2 , but lower than a high threshold voltage V High,TH , as described below. V LiftPump,TH3 can be, for example, 11 V. As an example, V LiftPump,TH3 include a lift pump voltage high enough to increase fuel flow rates through the jet pumps to maintain the fuel reservoir and main fuel sump fuel levels and to supply sufficient fuel to the DI pump and fuel rail to reduce the risk of stalling the vehicle engine due to a drop in FRP. Consequently, operating the lift pump at V LiftPump,TH3preventively reduce a rapid FRP drop (for example, a pressure drop of 50 bar) by increasing the flow rates of the fuel transferred to the main fuel sump and / or fuel reservoir via jet pumps, and by increasing the fuel flow rates to the DI pump and the fuel rail. In this way, the fuel pressure in the fuel rail can be maintained under current engine operating conditions, and a rapid FRP drop can be reduced. The controller 222 can LiftPump to V LiftPump,TH3 maintained until the FRP acquisition time condition is no longer met. After executing 824, the method 800 completes executing the third control mode 826, and the method ends.

[0070] Returning to 822, if the FRP capture time condition is not met, method 800 continues at 830 where it determines or estimates a DI pump efficiency based on engine operating conditions. As described above with reference to Fig. 2, the efficiency (e.g., efficiency) of the DI pump (e.g., the higher pressure fuel pump 214) may be parameterized at least in part by the fuel pressure at its intake; therefore, intermittent lift pump operation may be selected according to this intake pressure, as this pressure may partially determine the efficiency of the higher pressure fuel pump 214. In other examples, the efficiency of the higher pressure fuel pump 214 may be predicted based on the fuel consumption rate by the engine 202, as well as one or more DI pump characteristics, such as DI pump piston leakage, DI pump compression ratio, and fluid compression modulus and DI pump check valve actuation model.The DI pump efficiency may also be based at least in part on the difference between the fuel volume flow to the DI pump (e.g., from the fuel lift pump) and the fuel consumption rate by the engine 202. In addition, the DI pump efficiency may also decrease due to fuel atomization and the suction or pumping of fuel vapor and / or air instead of liquid fuel by the DI pump. For example, a DI pump model may calculate an expected DI pump volume flow rate and compare the expected DI pump efficiency rate to the controlled pump volume flow rate. A difference between the expected DI pump volume flow rate and the controlled pump volume flow rate may be calculated as a lost DI pump volume fuel flow rate. A DI pump efficiency. DI, can then be calculated by normalizing the lost DI pump volumetric fuel flow rate by the DI pump volumetric fuel flow rate when the DI pump is controlled at 100% and has 100% efficiency (for example, 100% rated DI pump flow).

[0071] At 832, the method 800 begins executing a fourth control mode 836 of the lift pump by determining whether the efficiency DI , is lower than a threshold DI pump efficiency, Efficiency DI,TH . In one example, the efficiency DI,TH a DI pump efficiency below which there is a high risk of fuel atomization, which can cause engine stalling. In another example, the efficiency DI,TH a DI pump efficiency below which fuel economy is degraded by more than a permissible amount. As an example, Efficiency DI 85%. If Efficiency DI< Efficiency DI,TH , the method 800 continues at 834. If Efficienc DI , is not lower than Efficiency DI,TH , the method 800 completes the execution of the fourth control mode 836, and the method 800 continues at 840.

[0072] At 834, the controller 222 may, in response to Efficiency DI < Efficiency DI,TH operate the fuel pump in a pulse and increment mode, with the controller 222 V LiftPump to a high threshold voltage V High,TH Pulses. By pulsing V LiftPump on V High,TH , the fuel flow from the lift pump to the DI pump can be increased to a flow rate sufficient to increase the DI pump efficiency via Efficiency DI,TH to lift and hold. In an example, V High,TH 12 V. In one example, the controller can be 222 V LiftPump on V High,TH pulse until the efficiency DI about EfficiencyDI,TH increases. In another example, the controller can supply 222 V LiftPump for at least one threshold period on V High,TH hold before V LiftPump In any case, once the pulsing of V LiftPump on V High,TH ends, V LiftPump back to its pre-pulse value plus a threshold increment voltage (ΔV INC,TH ). By incrementing V LiftPump by the threshold increment voltage y (ΔV INC,TH ) in addition to pulsing V LiftPump , there is a risk that Efficienc DI , under Efficiency DI,TH decreases, and therefore reduces the risk of degrading fuel economy and risking significant fuel atomization, which can lead to engine stalling. In one example, the threshold increment voltage may be 0.2 V.

[0073] With a brief return to Fig. 12, this shows a timeline 1200, which uses the pulse and increment mode described above to increase the efficiency DI , which shows trend lines showing efficiency DI < Efficiency DI,TH 1210, suction pump voltage 1220 and suction pump pressure 1230. V LiftPump,TH 1228 is also entered with the suction pump voltage 1220. The timeline 1200 shows a series of suction pump voltage pulses to V LiftPump,TH , which are measured at times t11, t13 and t15 in response to the decrease in efficiency DI under Efficiency DI,TH occur at these respective times. Each pulse that begins at times t11, t13 and t15 is held until after the efficiency DI is no longer lower than the efficiency DI,TH at times t12, t14 and t16, respectively. In the example of timeline 1200, the pulsing of V LiftPump on V LiftPump,TH in response to the decline in efficiency DIunder Efficiency DI,TH held until the efficiency DI is no longer lower than the efficiency DI,TH , so that each of the pulses can have different durations. However, as described above, each pulse can be triggered in response to the decrease in efficiency DI under Efficiency DI,TH Alternatively, in another example, be maintained for a threshold duration. After the completion of each pulse at times t12, t14, and t16, V LiftPump back to its original voltage level plus an incremental voltage, as shown by 1226, 1224, and 1222, respectively. In another example, the pulse and increment mode may include the controller 222 controlling the suction pump based on the suction pump pressure 1230, P LiftPump , instead of the suction pump voltage 1200. In response to the drop in efficiency DI under Efficiency DI,TH, the controller 222 can, for example, analog P LiftPump to a threshold suction pump pressure P LiftPump,TH pulse and then P LiftPump increase by a threshold increment pressure.

[0074] Under Return to Fig. 8, after executing 834, the method 800 ends executing the fourth control mode 836, and the method 800 ends. Returning to 832, if the Efficiency DI is not lower than the efficiency DI,TH , the method 800 completes the execution of the fourth control mode, and the method 800 continues at 840 where it V LiftPump (and the suction pump pressure P LiftPump ). In one example, the method can be 800 V LiftPump (and P LiftPump) based on the fuel temperature and the fuel flow rate. At 842, method 800 begins execution of the lift pump basic control mode 846 by determining whether a fuel atomization condition is met (e.g., V LiftPump < V fuel,novap ). If V LiftPump < V fuel,novap , the method 800 continues at 844 where V LiftPump on V fuel,novap To reduce fuel consumption, the electrical power supplied to the lift pump may be reduced when the lift pump demand is low (for example, at engine idle, very low fuel flow rates, and the like). Consequently, when the lift pump demand is low, the lift pump pressure and fuel passage pressure upstream of the DI pump may be lower. At cold fuel temperatures, the controlled lower lift pump voltages may be below V fuel,novapresult in suction pump pressures below the fuel atomization pressure. By keeping V LiftPump to V fuel,novap or above, the basic control mode of the lift pump can reduce fuel atomization in the fuel system and increase engine durability. After executing 844 or if V LiftPump at 842 is not lower than V fuel,novap , the method 800 ends execution of the basic control mode 846, and the method 800 continues at 860.

[0075] At 860, the method 800 determines whether V LiftPump is lower than V LiftPump,TH2 . If V LiftPump < V LiftPump,TH2 , the method 800 does not execute the second control mode 866, and the method 800 continues at 870. If V LiftPump < V LiftPump,TH2, method 800 continues at 862 by beginning execution of a second lift pump control mode 866. At 862, method 800 determines whether a first fuel level condition is met. Briefly returning to Fig. 9, method 900 illustrates how the first fuel level condition may be estimated. At 910, method 900 determines whether a fuel tank level FuelTank is lower than a threshold swamp level Sump,TH. As a non-limiting example, the threshold sump level may be 10% of a full fuel tank level. For example, the fuel tank level may include the main fuel sump level, and the threshold fuel level may include 10% of the full level of the main fuel sump 280. In one example, 10% of the full level of the main fuel sump 280 may correspond to the main fuel sump fuel level below which, if the fuel reservoir fuel level 291 is at the same level as the main fuel sump fuel level 281, fuel cannot be reliably transferred to the fuel reservoir from the main fuel sump by the main or transfer jet pump. As shown in the Fig. 2 and Fig. 3, the fuel tank level may be measured by fuel level sensors 262. In other examples, fuel tank levels may be estimated using fuel consumption data, fuel refill volume, fuel line compliance, fuel system storage volume, fuel tank dimensions, and the like.

[0076] In one example, an algorithm for determining the fuel storage fuel level may be based on a net fuel flow rate pumped by the fuel system jet pumps, which is directly proportional to the lift pump pressure. Estimating the fuel storage level changes may include integrating the difference between the jet pump fuel flow rate and the injection fuel flow rate. The integrated difference between the jet pump fuel flow rate and the injection fuel flow rate could be multiplied by the storage volume (e.g., 800 cm3 ) to avoid overaccumulation of the error signal. The fuel level at engine start-up can be used to initialize the fuel tank fill volume for the algorithm.

[0077] If the controller 222 determines that the main fuel sump level is FuelTank is not less than 10% of the full level of the main fuel sump (for example, level Sump,TH ), method 900 continues at 912. At 912, method 900 determines whether the estimated or measured fuel supply fuel level 291 Level Reservoir is lower than a second threshold fuel level Reservoir,TH2. In some fuel systems, the fuel level may be measured by a fuel level sensor 266. In other examples, the fuel level may be estimated based on various engine operating conditions, such as lift pump pressure, duration until a lift pump pressure is below a threshold pressure, main fuel sump level, auxiliary fuel sump level, fuel injection flow rate, and the like. For example, if the lift pump pressure is above a threshold Δt for an extended period of time TH below the lower threshold pressure P low,TH is operated, and the fuel tank level (for example, the main fuel sump fuel level 281) is below level Sump,TH the stock level can fall below the level Reservoir,TH2fallen because the fuel flow rates transferred from the main and transfer jet pumps to the fuel reservoir 285 may be very low. Thus, the controller 222 may determine at 912 that the level Reservoir is not lower than the level Reservoir,TH2 , after which method 900 continues at 914 because a first fuel level condition is not met, and method 900 returns to method 800 at 870. If controller 222 determines that at 910 either the level FuelTank < Level Sump,TH or at 912 the level Reservoir < Level Reservoir,TH2 , method 900 continues from 910 or 912 to 916, respectively, because the first fuel level condition is met, and method 900 then returns to method 800 at 864. The level Reservoir,TH2may correspond to a low fuel level that is less than the filled fuel level 287. In other words, if the fuel level is below the level Reservoir,TH2 There may be an increased risk that jet pump performance degradation may cause an increased risk of suction pump cavitation, rapid FRP degradation, and engine stalling.

[0078] Under Return to Fig. 8, in response to the first fuel level condition being met, method 800 continues at 864 where the lift pump voltage V LiftPump to a second threshold suction pump voltage V LiftPump,TH2 is increased. Raising V LiftPump on V LiftPump,THhelps increase jet pump performance, which can increase the flow rates of fuel transferred from the transfer and / or main jet pump to the fuel reservoir and main fuel sump. In one example, the V LiftPump,TH higher than 5 V, but lower than 11 V (for example, lower than V LiftPump,TH3 ). As mentioned above with reference to Fig. 2 in connection with suction pump control methods, the response controller action at 864 may be analogously based on suction pump pressures instead of suction pump voltages. Operating the suction pump with V LiftPump,TH2 (for example V LiftPump > 5 V) can, for example, be used to operate the suction pump with a second threshold suction pump pressure P LiftPump,TH2, of > 200 kPa. For example, at 864, the controller 222 may alternatively increase a lift pump pressure to a second threshold lift pump pressure in response to a low fuel level or a low main fuel sump level. In this way, a fuel level below Level Reservoir,TH2 and a main fuel sump level below level Sump,TH be increased quickly to reduce cavitation of the fuel lift pump 282, which can cause rapid drops in fuel rail pressure and engine stalling. The controller 222 can V LiftPump on V LiftPump,TH2 until the first fuel level condition is not met. Since the second control mode 866 is only executed when V LiftPump < V LiftPump,TH2 , the second control mode 866 can be set as V LiftPump ≥ V LiftPump,TH2 be understood as forcing. In other words, if V LiftPump > V LiftPump,TH2and the engine conditions are such that a first fuel level condition is met, the second control mode 866 does not intervene because the lift pump pressure and the resulting jet pump flows may be sufficient to maintain the fuel reservoir and main sump fuel levels at levels Reservoir,TH2 and levels Sump,TH After executing 864, method 800 completes second control mode 866, and method 800 ends.

[0079] Returning to 862, if the first fuel level condition is not met, method 800 completes the second control mode 866 and continues at 870 where it determines whether V LiftPump lower than V LiftPump,TH1 If V LiftPump is not lower than V LiftPump,TH1 , the procedure ends 800. If V LiftPump is lower than V LiftPump,TH1, the method 800 continues at 872, begins the first control mode 876, where it determines whether a second fuel level condition is met. Briefly returning to Fig. 9, method 902 illustrates how the second fuel level condition may be estimated. At 920, method 902 determines whether a main fuel sump fuel level 281 level Sump is lower than a first fuel supply fuel level level Reservoir,TH1 As an example, level Reservoir,TH1 the level of the fuel tank lip or the filled fuel tank level 287. As described above, Level Sump measured using a fuel level sensor 262 and / or estimated using various machine operating parameters. If level Sump is not lower than level Reservoir,TH1 , the method 902 continues at 922 where it determines whether a fuel level in the fuel supply 285, LevelReservoir , is lower than a first threshold fuel level Reservoir,TH1 As described above, the level Reservoir measured by a fuel level sensor 266 and / or estimated based on various machine operating parameters. If the level Reservoir is not lower than the level Reservoir,TH1 , method 902 continues at 924 because a second fuel level condition is not met before returning to method 800, at which point method 800 ends. If at 920 the level Sump < Level Reservoir,TH1 , or if at 922 level Reservoir < Level Reservoir,TH1 , method 902 continues at 926 because a second fuel level condition is met before returning to method 800 at 874.

[0080] Under Return to Fig. 8 In response to the second fuel condition being met, method 800 continues at 874 where the lift pump voltage V LiftPumpto a first threshold voltage V LiftPump,TH1 is increased. In an example, V LiftPump,TH1 correspond to a lift pump voltage of 5 V, where 5 V may correspond to the generation of a lift pump pressure of 200 kPa by the lift pump, which ensures sufficient transfer flow rate of fuel from the main fuel sump 280 to the fuel reservoir 285 via the main jet pump (e.g., 394, 594) to raise the fuel reservoir fuel level 291 to the filled fuel reservoir level 287. Furthermore, V LiftPump,TH1correspond to a lift pump voltage that ensures that the transfer flow rate of fuel from the auxiliary fuel sump 270 to the main fuel sump 280 via the transfer jet pump (e.g., 290, 378) is sufficiently high to raise the main fuel sump fuel level 281 to the full fuel reservoir level 291. Thus, the lift pump operation can respond to reduce a fuel reservoir fuel level 291 or a main sump fuel level 281 that is below a full fuel reservoir level 291, thereby reducing lift pump cavitation and engine stalling. Since the first control mode 866 is only executed when V LiftPump < V LiftPump,TH1 , the first control mode 876 can be defined as forcing V LiftPump ≥ V LiftPump,TH1 be understood. In other words, if V LiftPump > V LiftPump,TH1and the engine conditions are such that a second fuel level condition is met, the first control mode 876 does not intervene because the lift pump pressure and the resulting jet pump flows may be sufficient to maintain the fuel supply and fuel tank fuel levels at levels Reservoir,TH1 to hold and refill. After executing 874, method 800 closes the first control mode 876 and ends.

[0081] The first threshold voltage V LiftPump,TH1 may be lower than the second threshold voltage V LiftPump,TH2 , and consequently, the flow rate of fuel transferred by the main and transfer jet pumps may be smaller when the lift pump is operated in response to the first fuel level condition being met than when the fuel pump is operated in response to the second fuel level condition being met. In other words, since the level Reservoir,TH1(for example, filled fuel level 287) is higher than the level Reservoir,TH2 and levels Sump,TH , the risk of fuel depletion at the lift pump causing lift pump cavitation and the risk of reduced lift pump performance may be lower, so the lift pump voltage response may be lower (and slower) when the first fuel level condition is met than when the second fuel level condition is met. In this way, the degradation of jet pump performance and lift pump cavitation can be reduced while still maintaining fuel economy because excessive electrical energy is not supplied. The controller 222 may V LiftPump on V LiftPump,TH1 until the second fuel level condition is no longer met, or until the first fuel level condition at 862 is met.

[0082] In addition to the above description, it can be understood that methods 800, 900, 902, and 1000 include various lift pump control modes that can be enabled and disabled in response to various machine operating conditions. As in Fig. 8, the third control mode 826, the fourth control mode 836, the basic control mode 846, the second control mode 866 and the first control mode 876 may include the executable instructions of the methods 800, 900, 902 and 1000 shown within each dashed box of the Fig. 8. As shown in Table 1300 in the Fig. 8 and Fig. 13, in response to an FRP detection time condition being met, a third control method 826 may be activated; a fourth control mode 836 (e.g., pulse and increment mode) may be activated in response to the DI pump efficiency condition being met; a base control mode 846 may be activated in response to a fuel atomization condition being met (e.g., V LiftPump < V fuel,novap ); a second control mode 866 may be activated in response to a first fuel level condition being met, and a first control mode 876 may be activated in response to a second fuel level condition being met.

[0083] As in the Fig. 8 and Fig. As shown in Figure 13, the pulse and increment mode (e.g., the fourth control mode 836) may be deactivated in response to an FRP detection time condition being met. In this manner, the third control mode 826 may operate the lift pump in an open-loop fashion, wherein, in response to an FRP detection time condition being met, the lift pump voltage is increased to V LiftPump,TH3 is increased. In other words, during the third control mode 826, the controller 222 may perform the action of the fourth control mode of pulsing and incrementing V LiftPumpin response to a DI pump efficiency being lower than a threshold efficiency. Similarly, the base control mode 846, the second control mode 866, and the first control mode 876 may be disabled in response to an FRP capture time condition being met. In this way, when the third control mode 826 is activated, the method 800 may end before actions from any other lift pump control modes included in the Fig. 8 to 10 are shown. Since V LiftPump,TH3 is higher than V High,TH , V LiftPump,TH2 and V LiftPump,TH1 , during the third control mode, more than sufficient electrical energy is supplied to the lift pump to fill and maintain the fuel tank and fuel reservoir fuel levels at their full levels, and to Eff DI at or above Eff DI,THIn this way, method 800 may prioritize lift pump control to respond to reduce a risk of a drastic drop in FRP that may cause engine stall, rather than responding to low DI pump efficiency (e.g., when a DI pump efficiency condition is met), a risk of fuel atomization in the fuel passages (e.g., when a fuel atomization condition is met), or low fuel reservoir levels and low jet pump flows (e.g., when a first or second fuel level condition is met).

[0084] As in the Fig. 8 and Fig. 13, the base control mode 846, the second control mode 866, and the first control mode 876 may be disabled in response to a DI pump efficiency condition being met. As shown in Fig. 8, the method 800 may end after executing the action of the fourth control mode 834 before any instructions from the base control mode 846, the second control mode 866, or the first control mode 876 are executed, thereby disabling the base control mode 846, the second control mode 866, and the first control mode 876. Since V High,TH is higher than V LiftPump,TH2 and V LiftPump,TH1 , more than sufficient electrical energy is supplied to the lift pump during the fourth control mode to replenish and maintain the fuel tank and fuel reservoir fuel levels at their full levels. Thus, when the fourth control mode 836 is activated, method 800 may prioritize the lift pump control to respond to achieve a DI pump efficiency greater than Eff DI,TH, thereby reducing a risk of DI pump cavitation and increasing engine durability, rather than responding to a risk of fuel atomization in the fuel passages (for example, when a fuel atomization condition is met), or low fuel levels and low jet pump flows (for example, when a first or second fuel level condition is met).

[0085] Furthermore, as in the Fig. 8 and Fig. 13, the basic control mode 846 may be canceled in response to a second control mode 866 being activated (for example, V LiftPump < V LiftPump,TH2 and a first fuel level condition is met). For example, the base control mode 846 V LiftPump on V fuel,novap However, if V fuel,novap < V LiftPump,TH2 and if the first fuel level condition is met, the second control mode can be activated, and V LiftPumpwill be on V LiftPump,TH2 set, thereby canceling the control action of the basic control mode 846. In addition, the first control mode 876 may be deactivated in response to a second control mode 866 being activated (for example, V LiftPump < V LiftPump,TH2 and when a first fuel level condition is met). As in Fig. 8, the method 800 may end after executing the action of the second control mode 864 before any instruction from the first control mode 876 is executed, thereby disabling the first control mode 876. Thus, when the second control mode 866 is activated, the method 800 may prioritize the suction pump controller to respond to level FuelTank > Level Sump,TH and levels Reservoir > Level Reservoir,TH2 to maintain (for example by forcing V LiftPump ≥ V LiftPump,TH2), thereby reducing the risk of suction pump cavitation and increasing engine durability, rather than reacting to the risk of fuel atomization in the fuel passages (for example, when a fuel atomization condition is met).

[0086] Furthermore, as in the Fig. 8 and Fig. 13, the basic control mode 846 may be canceled in response to a first control mode 876 being activated (for example, V LiftPump < V LiftPump,TH1 and a second fuel level condition is met). For example, the base control mode 846 V LiftPump on V fuel,novap However, if V fuel,novap < V LiftPump,TH1 and the second fuel level condition is met, the first control mode can be activated, and V LiftPump will be on V LiftPump,TH1, thereby canceling the control action of the base control mode 846. Thus, when the first control mode 876 is activated, the method 800 may prioritize the lift pump control to respond to level MainSump > Level Reservoir,TH1 and levels Reservoir > Level Reservoir,TH1 to maintain (for example by forcing V LiftPump ≥ V LiftPump,TH1 ), thereby reducing the risk of suction pump cavitation and increasing engine durability, rather than reacting to the risk of fuel atomization in the fuel passages (for example, when a fuel atomization condition is met).

[0087] Fig. 11 illustrates a timeline 1100 of fuel lift pump operation according to method 800. The timeline 1100 includes trend lines for Efficiency DI < Efficiency DI,TH 1102, V LiftPump 1110, P LiftPump 1120, Level Sump1130, auxiliary fuel sump level 1138, fuel tank fuel level 1140 and engine speed 1150. Furthermore, V LiftPump,TH3 1112, V LiftPump,TH2 1114, V LiftPump,TH1 1116, V High,TH 1118, P LiftPump,TH3 1122, P LiftPump,TH2 1124, P LiftPump,TH1 1126, P Pulse,TH 1128, P low,TH 1125, Level Sump,TH 1134, Level Reservoir,TH1 1142, Level Reservoir,TH2 1144 and Engine Speed TH 1152 shown.

[0088] Between times t1 and t2, it can be seen that the suction pump is operating in a fourth control mode (for example, pulse and increment mode). In response to the occurrence of the events Efficiency DI < Efficiency DI,TH At times t1, t1a and t1b, the controller 222 executes instructions to pulse V LiftPump on V High,TH , by holding the pulses temporarily (for example, long enough for the efficiency DI about the efficiency DI,THincreases). Furthermore, after pulsing at times t1, t1a and t1b, the controller 222 increments V LiftPump by a threshold increment voltage. P LiftPump pulses and sounds at times t1, t1a and t1b in response to the pulsing of V LiftPump at these times. Furthermore, the main fuel sump level 1130 slowly decreases as fuel is slowly transferred from the main sump via the main transfer pump to replenish the fuel supply. Thus, DI pump efficiency can be maintained while preserving fuel economy.

[0089] Between times t1b and t2, the main fuel sump level 1130 drops below level Sump,TH 1134, thereby satisfying a first fuel level condition. In response, the controller 222 activates a second control mode 866. The controller 222 consequently increases V LiftPump on V LiftPump,TH2by maintaining the increase for a period until the main fuel sump level 1130 is above level Sump,TH increases at time t2a, whereby the first fuel level condition is no longer met. While the first fuel level condition is met between times t2 and t2a, the controller 222 maintains the increase in V LiftPump on V LiftPump,TH2 Furthermore, in response to increasing V LiftPump also P LiftPump , and then subsides as soon as the first fuel level condition is no longer met. As a result of the operation of the fuel lift pump in the second control mode, fuel is transferred by the transfer jet pump from the auxiliary fuel sump to the main fuel sump. The auxiliary fuel sump level 1138 consequently decreases, while the level Sump about the level Sump,TH is raised.

[0090] At time t3, level Reservoir 1140 drops below level Reservoir,TH1, thereby satisfying a second fuel level condition. In response, the controller 222 activates a third control mode 876 and increases V LiftPump on V LiftPump,TH1 by holding the increase for a duration until level Reservoir at a time t3a over level Reservoir,TH1 increases, which means that the second fuel level condition is no longer met. Furthermore, in response to increasing V LiftPump also P LiftPump higher and then begins to decay at time t3a as soon as the second fuel level condition is no longer met. As a result of the operation of the fuel lift pump in the third control mode, fuel is transferred by the main jet pump from the main fuel sump to fill the fuel reservoir.

[0091] Before time t4, P decreases LiftPump below a low threshold pressure P Low,TH during a threshold period Δt TH. During the long period at low suction pump pressure, the fuel flow rate transmitted by the jet pumps is low, and the fuel reservoir fuel level 1140 therefore drops below level Reservoir,TH2 , and the main fuel sump level drops below level t4 Sump,TH . Consequently, at t4, the first fuel level condition is met. In response, the controller 222 activates a second control mode 866 and increases V LiftPump on V LiftPump,TH2 for a period until level Reservoir again over level Reservoir,TH2 is manufactured. While V LiftPump on V LiftPump,TH2 is increased, the fuel flow rate from the transfer and main jet pump increases, so that both the fuel reservoir and main fuel sump fuel levels are raised. Furthermore, in response to increasing V LiftPump also P LiftPump , higher and then subsides as soon as the first fuel level condition is no longer met.

[0092] At time t5 the engine speed increases above Engine Speed TH and thereby fulfills an FRP capture time condition. In response, the controller 222 activates a third control mode 826. The controller 222 consequently increases V LiftPump on V LiftPump,TH3 by maintaining the increase for a period until the engine speed at time t5a falls below Engine Speed TH decreases, whereby the FRP acquisition time condition is no longer met. Although the FRP acquisition time condition is met between times t5 and t5a, the controller 222 maintains the increase in V LiftPump on V LiftPump,TH3 despite efficiency DI < Efficiency DI,THevents and despite the fulfillment of the second fuel level condition, which occurs immediately after time t5, as shown in timeline 1100. In other words, the fourth control mode and the first control mode are deactivated, while the third control mode is activated. In the example of timeline 1100, since V LiftPump,TH3 > V High,TH , however, the DI pump efficiency can be maintained while the third control mode is active. Furthermore, since V LiftPump,TH3 > V LiftPump,TH2 , the fuel levels in the fuel reservoir and the fuel tank can be replenished and maintained while the third control mode is active. Furthermore, in response to increasing V LiftPump also P LiftPumphigher and then subsides once the FRP detection time condition is no longer met. As a result of the fuel lift pump operating in the third control mode, fuel is transferred by the transfer jet pump from the auxiliary fuel sump to the main fuel sump and by the main jet pump from the main sump to the fuel reservoir. Consequently, shortly after time t5, the main fuel sump level 1130 begins to gradually rise, and the fuel reservoir level is brought to the full fuel reservoir level. Thus, the controller 222 can reduce the risk of a rapid FRP drop while the FRP detection time condition is met.

[0093] After time t6, the fuel lift pump is seen to return to intermittent operation in a pulse and increment mode. In response to Efficienc DI , < Efficiency DI,TH-Events that occur at times t6 and t6a (and because the FRP acquisition time condition is not met), the controller 222 activates the pulse and increment mode (for example, the fourth control mode) and executes instructions to V LiftPump on V High,TH to pulse by holding the pulses temporarily each time (for example, long enough for Efficiency DI about Efficiency DI,TH increases). Furthermore, after pulsing at t6 and t6a, the controller 222 increments V LiftPump by a threshold increment voltage. P LiftPump pulses and sounds at times t6 and t6a in response to the pulsing of V LiftPump at these times. Furthermore, the main fuel sump level 1130 slowly decreases as fuel is slowly transferred from the main sump via the main transfer pump to replenish the fuel supply. Thus, DI pump efficiency can be maintained while preserving fuel economy.

[0094] Thus, the methods of operating a lift pump disclosed herein can achieve the technical effect of reducing the risks of fuel atomization, rapid FRP pressure drops, and engine stalls while maintaining DI pump efficiency and fuel economy even in cold fuel conditions. Furthermore, the degradation of jet pump performance due to low lift pump pressures can be reduced by operating the lift pump in response to low fuel tank levels, low jet pump fuel levels, or when there is a high risk of FRP drop leading to engine stall.

[0095] Thus, a vehicle fuel system may include a fuel tank having a transfer jet pump and a main jet pump fuel supply including a main jet pump, a fuel lift pump, a fuel injection pump that receives fuel from the lift pump and delivers fuel to a fuel rail, and a controller having computer-readable instructions stored in non-transitory memory for executing methods and routines for operating a lift pump.

[0096] In one example, a method of operating the lift pump may include: a method comprising: increasing a lift pump voltage to a high threshold voltage in response to a DI pump efficiency being below a threshold efficiency, and increasing a lift pump voltage to a first threshold voltage lower than the high threshold voltage in response to a main jet pump fuel tank level being lower than a first threshold tank level. Additionally or alternatively, the method may further include increasing the lift pump voltage to a first threshold voltage in response to a fuel tank level being lower than the first threshold tank level.Additionally or alternatively, the method may further comprise increasing the lift pump voltage to a second threshold voltage in response to the main jet pump fuel supply level being lower than a second threshold supply level, wherein the second threshold supply level is lower than the first threshold supply level, and wherein the second threshold voltage is higher than the first threshold voltage. Additionally or alternatively, the method may further comprise increasing the lift pump voltage to the second threshold voltage in response to a lift pump pressure being lower than a low threshold pressure during a threshold duration, and the fuel tank level being lower than a threshold sump level, wherein the threshold sump level is lower than the first threshold supply level.Additionally or alternatively, the method may further comprise increasing the lift pump voltage to the second threshold voltage in response to the fuel tank level being lower than a threshold sump level, wherein the threshold sump level is lower than the first threshold reservoir level. Additionally or alternatively, the method may further comprise increasing the lift pump voltage to a third threshold voltage in response to an engine speed being higher than a threshold engine speed, wherein the third threshold voltage is higher than the second threshold voltage. Additionally or alternatively, the method may further comprise increasing the lift pump voltage to a third threshold voltage in response to a fuel injection flow rate being higher than a threshold fuel injection flow rate, wherein the third threshold voltage is higher than the second threshold voltage.Additionally or alternatively, the method may further comprise increasing the lift pump voltage to a third threshold voltage in response to a DI pump duty cycle being greater than a threshold duty cycle, wherein the third threshold voltage is higher than the second threshold voltage. Additionally or alternatively, the method may further comprise operating a lift pump voltage at a third threshold voltage when an estimated time for a fuel rail pressure to decrease by a threshold pressure drop is greater than a threshold time interval, wherein the third threshold voltage is higher than the second threshold voltage.

[0097] In another representation, the method may include operating a lift pump in a first mode in response to a fuel tank level falling below a first threshold supply level, the first mode comprising reducing a lift pump voltage to a first threshold voltage, and in response to a DI pump efficiency falling below a threshold efficiency, deactivating the first mode and pulsing a lift pump voltage to a high threshold voltage that is higher than the first threshold voltage.Additionally or alternatively, the method may further comprise deactivating the first mode and operating the lift pump in a second mode in response to a main jet pump fuel level falling below a second threshold fuel level, the second threshold fuel level being below the first threshold fuel level, and the second mode comprising increasing the lift pump voltage to a second threshold voltage that is higher than the first threshold voltage and lower than the high threshold voltage. Additionally or alternatively, the method may comprise incrementing the lift pump voltage by a threshold increment voltage in response to the DI pump efficiency falling below the threshold fuel efficiency.Additionally or alternatively, the method may further comprise deactivating the first mode and operating the lift pump in the second mode in response to the fuel tank level falling below a threshold sump level, wherein the threshold sump level is lower than the first threshold reservoir level. Additionally and alternatively, the method may further comprise deactivating the first mode and operating the lift pump in a third mode in response to a fuel injection flow rate increasing above a threshold flow rate, wherein the third mode comprises increasing the lift pump voltage to a third threshold voltage that is higher than the second threshold voltage and lower than the high threshold voltage.Additionally or alternatively, the method may further include deactivating the first mode and operating the lift pump in a third mode in response to an engine speed increasing above a threshold engine speed. Additionally or alternatively, the method may further include deactivating the first mode and operating the lift pump in a third mode in response to a DI pump duty cycle increasing above a threshold DI pump duty cycle.

[0098] In another representation, a method may include, in response to a DI pump efficiency decreasing below a threshold efficiency, increasing a lift pump pressure to a high threshold pressure, and, in response to a main jet pump fuel tank level being lower than a first threshold tank level, increasing a lift pump pressure to a first threshold pressure that is lower than the high threshold pressure. Additionally or alternatively, the method may further include, in response to a fuel tank level being lower than the first threshold tank level, increasing the lift pump pressure to the first threshold pressure.Additionally or alternatively, the method may further comprise, in response to the main jet pump fuel level falling below a second threshold fuel level that is lower than the first threshold fuel level, increasing the lift pump pressure to a second threshold pressure that is higher than the first threshold pressure. Additionally or alternatively, the method may further comprise, in response to the fuel tank level being below a threshold fuel tank level that is lower than the threshold fuel level, increasing the lift pump pressure to the second threshold pressure.

[0099] It should be appreciated that the exemplary control and estimation routines included herein may be used with various machine 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 machine hardware. The particular routines described herein may represent one or more of a number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Thus, various illustrated acts, operations, and / or functions may be performed in the illustrated order, in parallel, or in some cases, omitted.Likewise, the 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. Furthermore, the described acts, operations, and / or functions may graphically represent code to be programmed into the non-volatile 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 machine hardware components in combination with the electronic controller.

[0100] It is understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be interpreted in a limiting sense, as numerous variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, horizontally opposed four-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or characteristics disclosed herein.

[0101] The following claims particularly point out 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 should be construed as encompassing the inclusion of one or more such elements, 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 presenting new claims in this or a related application. Such claims, whether their scope is broader, narrower, the same, or different from the original claims, are also considered to be included within the subject matter of the present disclosure.

Claims

[1] Procedure comprising: Increasing a lift pump voltage to a high threshold voltage in response to a direct injection (DI) pump efficiency being below a threshold efficiency, and Increasing the lift pump voltage to a first threshold voltage lower than the high threshold voltage in response to a main jet pump fuel level being lower than a first threshold fuel level. [2] The method of claim 1, further comprising: Increasing the lift pump voltage to the first threshold voltage in response to a fuel tank level being lower than the first threshold reservoir level. [3] The method of claim 2, further comprising: Increasing the lift pump voltage to a second threshold voltage in response to the main jet pump fuel supply level being lower than a second threshold supply level, wherein the second threshold supply level is lower than the first threshold supply level, and wherein the second threshold voltage is higher than the first threshold voltage. [4] The method of claim 3, further comprising increasing the lift pump voltage to the second threshold voltage in response to a lift pump pressure being lower than a low threshold pressure during a threshold duration and the fuel tank level being lower than a threshold sump level, wherein the threshold sump level is lower than the first threshold reservoir level. [5] The method of claim 3, further comprising increasing the lift pump voltage to the second threshold voltage in response to the fuel tank level being lower than a threshold sump level, the threshold sump level being lower than the first threshold reservoir level. [6] The method of claim 5, further comprising increasing the lift pump voltage to a third threshold voltage in response to an engine speed being greater than a threshold engine speed, the third threshold voltage being higher than the second threshold voltage. [7] The method of claim 5, further comprising increasing the lift pump voltage to a third threshold voltage in response to a fuel injection flow rate being greater than a threshold fuel injection flow rate, wherein the third threshold voltage is higher than the second threshold voltage. [8] The method of claim 5, further comprising increasing the lift pump voltage to a third threshold voltage in response to a DI pump duty cycle being greater than a threshold duty cycle, wherein the third threshold voltage is higher than the second threshold voltage. [9] The method of claim 5, further comprising operating a lift pump voltage at a third threshold voltage when an estimated time for a fuel rail pressure to decrease by a threshold pressure drop is greater than a threshold time interval, wherein the third threshold voltage is higher than the second threshold voltage. [10] Procedure comprising: Operating a lift pump in a first mode in response to a fuel tank level falling below a first threshold supply level, the first mode comprising increasing a lift pump voltage to a first threshold voltage, and in response to a direct injection (DI) pump efficiency decreasing below a threshold efficiency, deactivating the first mode and pulsing a lift pump voltage to a high threshold voltage higher than the first threshold voltage. [11] The method of claim 10, further comprising: Deactivating the first mode and operating the lift pump in a second mode in response to a main jet pump fuel supply level falling below a second threshold supply level, wherein the second threshold supply level is lower than the first threshold supply level, and wherein the second mode comprises increasing the lift pump voltage to a second threshold voltage that is higher than the first threshold voltage and lower than the high threshold voltage. [12] The method of claim 11, further comprising, in response to the DI pump efficiency decreasing below the threshold efficiency, incrementing the lift pump voltage by a threshold increment voltage. [13] The method of claim 12, further comprising: Deactivating the first mode and operating the lift pump in the second mode in response to the fuel tank level falling below a threshold sump level, the threshold sump level being lower than the first threshold reservoir level. [14] The method of claim 13, further comprising deactivating the first mode and operating the lift pump in a third mode in response to a fuel injection flow rate increasing above a threshold flow rate, the third mode comprising increasing the lift pump voltage to a third threshold voltage that is higher than the second threshold voltage and lower than the high threshold voltage. [15] The method of claim 13, further comprising deactivating the first mode and operating the lift pump in a third mode in response to an engine speed increasing above a threshold engine speed. [16] The method of claim 13, further comprising deactivating the first mode and operating the lift pump in a third mode in response to a DI pump duty cycle increasing above a threshold DI pump duty cycle. [17] Procedure comprising: in response to a direct injection (DI) pump efficiency decreasing below a threshold efficiency, increasing the lift pump pressure to a high threshold pressure, and in response to a main jet pump fuel level being lower than a first threshold fuel level, increasing a lift pump pressure to a first threshold pressure that is lower than the high threshold pressure. [18] The method of claim 17, further comprising: in response to a fuel tank level being lower than the first threshold reservoir level, increasing the lift pump pressure to the first threshold pressure. [19] The method of claim 18, further comprising: in response to the main jet pump fuel level falling below a second threshold fuel level that is lower than the first threshold fuel level, increasing the lift pump pressure to a second threshold pressure that is higher than the first threshold pressure. [20] The method of claim 19, further comprising: in response to the fuel tank level being below a threshold fuel tank level that is lower than the threshold reservoir level, increasing the lift pump pressure to the second threshold pressure.

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