Method for operating an electric fuel pump

Abstract

A method is described for operating an electric fuel pump constituting a low-pressure pump in a fuel supply system for an internal combustion engine, having a high-pressure reservoir and a high-pressure pump, of a motor vehicle. The electric fuel pump is operated at least temporarily, during a time period during which the internal combustion engine is switched off during operation of the motor vehicle, with a minimum value for a control application variable for the electric fuel pump.

Claims

1. A method for operating an electric fuel pump constituting a low-pressure pump in a fuel supply system for an internal combustion engine of a motor vehicle, the fuel supply system including a high-pressure reservoir and a high-pressure pump, the method comprising: ascertaining a minimum value for a control application variable for the electric fuel pump, the minimum value being a value for the control application variable at which the electric fuel pump draws in fuel but does not convey any fuel toward the high-pressure pump; and operating the electric fuel pump at least temporarily, during a time period during which the internal combustion engine is switched off during operation of the motor vehicle, with the ascertained minimum value for the control application variable for the electric fuel pump; wherein the method further comprises determining a value for the control application variable at which zero delivery by the electric pump occurs, wherein the minimum value for the control application variable is ascertained in the ascertaining step using the value for the control application variable at which the zero delivery by the electric pump occurs; wherein the fuel supply system further includes at least one suction jet pump, and wherein the minimum value for the control application variable is also ascertained based on a characteristic curve of the at least one suction jet pump.

2. The method as recited in claim 1, wherein the electric fuel pump is operated for the time period at the minimum value only upon exceedance of a threshold value for at least one of a pressure and a temperature in a fuel tank in which the electric fuel pump is disposed.

3. The method as recited in claim 2, further comprising: ascertaining the at least one of the pressure and the temperature by way of a model and by way of at least one of the following variables: a temperature outside the motor vehicle, a speed of the motor vehicle, a fill level of the fuel tank, a control application current to the electric fuel pump, a delivery volume of the electric fuel pump, an exhaust gas mass flow, a temperature of the exhaust gas, a detection of a fueling operation, a duration of a most recent complete shutoff of the motor vehicle, a pressure outside the motor vehicle, and a composition of a fuel in the fuel tank.

4. The method as recited in claim 1, wherein the electric fuel pump is operated at the minimum value for the time period only when at least one triggering condition is met.

5. The method as recited in claim 1, wherein the value for the control application variable at which zero delivery occurs is determined by elevating the control application variable one of continuously, quasi-continuously, and stepwise until a pressure rise in at least one of the high-pressure reservoir and a low-pressure region of the fuel supply system is detectable.

6. The method as recited in claim 1, wherein the minimum value for the control application variable is ascertained during a pre-running mode of the electric fuel pump before starting of the internal combustion engine.

7. The method as recited in claim 1, wherein the minimum value for the control application variable is ascertained during a pre-running mode of the electric fuel pump before a cold starting of the internal combustion engine.

8. The method as recited in claim 1, wherein the electric fuel pump is an electric fuel pump that is disposed in an in-tank unit that in turn is disposed in the fuel tank.

9. The method as recited in claim 1, wherein the electric fuel pump conveys fuel to the high-pressure pump while the internal combustion engine operates.

10. A computation unit configured to operate an electric fuel pump constituting a low-pressure pump in a fuel supply system for an internal combustion engine of a motor vehicle, the fuel supply system including a high-pressure reservoir and a high-pressure pump, the computation unit configured to: ascertain a minimum value for a control application variable for the electric fuel pump, the minimum value being a value for the control application variable at which the electric fuel pump draws in fuel but does not convey any fuel toward the high-pressure pump; and operate the electric fuel pump at least temporarily, during a time period during which the internal combustion engine is switched off during operation of the motor vehicle, with the ascertained minimum value for the control application variable for the electric fuel pump; wherein the computation unit is further configured to: determine a value for the control application variable at which zero delivery by the electric pump occurs, wherein the minimum value for the control application variable is ascertained in the ascertaining step using the value for the control application variable at which the zero delivery by the electric pump occurs; wherein the fuel supply system further includes at least one suction jet pump, and wherein the minimum value for the control application variable is also ascertained based on a characteristic curve of the at least one suction jet pump.

11. The computation unit as recited in claim 10, wherein computation unit determines the value for the control application variable at which zero delivery by elevating the control application variable one of continuously, quasi-continuously, and stepwise until a pressure rise in at least one of the high-pressure reservoir and a low-pressure region of the fuel supply system is detectable.

12. A non-transitory machine-readable memory medium that stores a computer program for operating an electric fuel pump constituting a low-pressure pump in a fuel supply system for an internal combustion engine of a motor vehicle, the fuel supply system including a high-pressure reservoir and a high-pressure pump, the computer program, when executed by a computation unit, causing the computation unit to perform the following steps: ascertaining a minimum value for a control application variable for the electric fuel pump, the minimum value being a value for the control application variable at which the electric fuel pump draws in fuel but does not convey any fuel toward the high-pressure pump; and operating the electric fuel pump at least temporarily, during a time period during which the internal combustion engine is switched off during operation of the motor vehicle, with the ascertained minimum value for the control application variable for the electric fuel pump; wherein the computer program, when executed by the computation unit, causes the computation unit to perform the following addition step: determining a value for the control application variable at which zero delivery by the electric pump occurs, wherein the minimum value for the control application variable is ascertained in the ascertaining step using the value for the control application variable at which the zero delivery by the electric pump occurs; wherein the fuel supply system further includes at least one suction jet pump, and wherein the minimum value for the control application variable is also ascertained based on a characteristic curve of the at least one suction jet pump.

13. The non-transitory machine-readable memory medium as recited in claim 12, wherein the value for the control application variable at which zero delivery occurs is determined by elevating the control application variable one of continuously, quasi-continuously, and stepwise until a pressure rise in at least one of the high-pressure reservoir and a low-pressure region of the fuel supply system is detectable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically depicts a fuel supply system for an internal combustion engine which can be used for a method according to the present invention.

(2) FIG. 2 schematically shows an execution sequence for ascertaining a minimum value for a control application variable in the context of a method according to the present invention in a preferred embodiment.

(3) FIG. 3 schematically shows profiles of the pressure in the high-pressure reservoir and of the control application variable upon execution of a method according to the present invention in a preferred embodiment.

(4) FIG. 4 schematically shows an execution sequence for operating the electric fuel pump with the minimum value in the context of a method according to the present invention in a preferred embodiment.

DETAILED DESCRIPTION

(5) FIG. 1 schematically depicts a fuel supply system 100 for an internal combustion engine 180, which can be used for a method according to the present invention.

(6) Fuel supply system 100 encompasses a fuel tank 110 that is filled with fuel 111. Located in fuel tank 110 is an in-tank unit 115 that in turn has a pre-supply cup 116 in which an electric fuel pump 125, operating as a low-pressure pump, is disposed.

(7) Pre-supply cup 115 can be filled with fuel from fuel tank 110 via a suction jet pump 120 (or, if applicable, also several suction jet pumps) disposed in fuel tank 110 outside the pre-supply cup. Electric fuel pump 125 can have control applied to it via a computation unit 140 embodied here as a pump control device, so that fuel is delivered out of pre-supply cup 115 via a filter 130 to a high-pressure pump 150. A pressure limiting valve 117 is provided in the low-pressure line.

(8) A pressure sensor 135 for detecting the pressure in the low-pressure line is provided here by way of example in the low-pressure line, i.e. before high-pressure pump 150. As already explained, however, a pressure sensor of this kind in the low-pressure region is not necessary for execution of the proposed method.

(9) High-pressure pump 150 as a rule is driven via internal combustion engine 180 or its camshaft. Fuel is then conveyed from high-pressure pump 150 into a high-pressure reservoir 160, from which fuel can be delivered via fuel injectors 170 to internal combustion engine 180. A pressure sensor 165, with which a pressure in the high-pressure reservoir can be detected, is furthermore provided on high-pressure reservoir 160.

(10) Control can be applied to internal combustion engine 180 or to fuel injectors 170 via an engine control device different from pump control device 140, in which context the control devices can then communicate with one another. It is also conceivable, however, to use one shared control device.

(11) FIG. 2 schematically depicts an execution sequence for ascertaining a minimum value for a control application variable in the context of a method according to the present invention in a preferred embodiment.

(12) FIG. 3 schematically shows profiles, respectively as a function of time t, for the pressure P in the high-pressure reservoir and for the control application variable, here a pulse duty factor TV, upon execution of a method according to the present invention in a preferred embodiment. The execution sequence for ascertaining a minimum value as shown in FIG. 2 will be explained in further detail below with reference to FIG. 3.

(13) Ascertainment of the minimum value can firstly begin in a step 200. In a step 205 a check can then be made as to whether the electric fuel pump is in the EKP pre-running mode, and whether it is possible to begin ascertainment, which in particular encompasses a pressure buildup in the high-pressure reservoir. Usually the electric fuel pump is operated as soon as the driver's door is opened or the ignition key is turned (terminal 15), in order to build up the necessary pressure in the low-pressure system. This phase of EKP pre-running can be used to determine the minimum value of the control application for zero delivery. If not, for example because the electric fuel pump is not in the EKP pre-running mode, execution branches back to step 200.

(14) If the electric fuel pump is in EKP pre-running mode, a check can be made in a step 210 as to whether the elapsed time during which the internal combustion engine was shut off was sufficiently long that the pressure in the high-pressure reservoir has dissipated. If this is not the case, execution can branch immediately to step 245, and the electric fuel pump can be operated normally without ascertaining the minimum value.

(15) If the pressure in the high-pressure reservoir has dissipated, in a step 215 a minimum possible pulse duty factor TV.sub.min, as shown in FIG. 3, can be established. The minimum possible pulse duty factor TV.sub.min can be a pulse duty factor or voltage at which a control application current at which the electric fuel pump can still just be operated is generated.

(16) If applicable, the present pressure P.sub.0 in the high-pressure reservoir, as also depicted in FIG. 3, can furthermore also be ascertained in a step 220 simultaneously with or shortly before step 215.

(17) In a step 225, while control is applied to the electric fuel pump, the pulse duty factor TV can then be elevated, for example in ramped fashion, i.e. linearly and quasi-continuously, or stepwise, as shown in FIG. 3 starting at time t.sub.0.

(18) As soon as a pressure rise is then detected in the high-pressure reservoir, i.e., for example, as soon as the pressure P in the high-pressure reservoir is higher than the pressure P.sub.0 by an amount equal to a threshold P, the elevation of the pulse duty factor can be halted in accordance with a step 230, as is the case at time t.sub.1 in FIG. 3. Conversely, in accordance with step 225 the pulse duty factor can continue to be elevated as long as no pressure rise is detected.

(19) The result here is to ascertain a pulse duty factor TV.sub.0 at which zero delivery occurs. That pulse duty factor TV.sub.0 can then, for example in a step 235, be saved in the associated pump control device.

(20) But because, as already mentioned, the suction jet pump may not yet be delivering sufficiently at the pulse duty factor TV.sub.0, an offset TV can then be ascertained in a step 240 and added, thus yielding the minimum value TV.sub.1. The minimum value TV.sub.1 can also be saved in the pump control device.

(21) The regular EKP pre-running mode of the electric fuel pump can then, in a step 245, be continued in order to convey fuel to the high-pressure pump, so that ascertainment of the minimum value is terminated in a step 250.

(22) FIG. 4 schematically shows an execution sequence for operating the electric fuel pump with the minimum value in the context of a method according to the present invention in a preferred embodiment.

(23) The method can firstly begin in a step 400. A check can then be made in a step 405 as to whether a stop phase of the internal combustion engine exists, i.e. whether the internal combustion engine is shut off. A check can also be made in this context as to the reason why the internal combustion engine is shut off, i.e. whether the stop phase exists, for example, due to an electrical propulsion phase in the context of hybrid operation or due to a stoppage in the context of a start/stop mode.

(24) If the stop phase is not occurring for a reason such that the electric fuel pump is to be operated during the stop phase, execution can then branch back to step 400.

(25) Otherwise, in a step 410 a pressure and/or a temperature in the fuel tank can be ascertained by way of a model and using suitable variables that have been mentioned previously.

(26) In a step 415 it is then possible to ascertain whether the pressure and/or the temperature are above a threshold value such that without operation of the electric fuel pump, the electric fuel pump would be emptied because of the vapor pressure in the fuel tank.

(27) In a step 420 it is then possible to decide whether the electric fuel pump is to be operated. If not, the method can be terminated by branching directly to step 435 (termination).

(28) Otherwise, in a step 425 the minimum valuewhich, as explained above, has been saved e.g. in the pump control deviceis retrieved. According to a step 430 the electric fuel pump can then be operated during the stop phase, if applicable only temporarily, using the minimum value for the pulse duty factor; the method is then terminated in accordance with step 435, i.e. when the stop phase has ended and the internal combustion engine is restarted.