Method for ascertaining a setpoint value for a manipulated variable for activating a low-pressure pump

Abstract

A method for ascertaining a setpoint value for a manipulated variable for activating a low-pressure pump in a fuel supply system for an internal combustion engine, including a high-pressure accumulator and a high-pressure pump including a volume control valve, the low-pressure pump being activated in such a way that a pressure provided by the low-pressure pump is reduced across multiple intake phases, in which fuel delivered by the low-pressure pump is sucked in by the high-pressure pump via the volume control valve, the volume control valve being at least temporarily held in a closed position during each of the multiple intake phases, in which it may be opened from a side facing the low-pressure pump, and the setpoint value being ascertained, taking into account an activating value of the manipulated variable, in which a drop in the delivery rate of the high-pressure pump is detected.

Claims

1. A method for ascertaining a setpoint value for a manipulated variable for activating a low-pressure pump in a fuel supply system for an internal combustion engine, including a high-pressure accumulator and a high-pressure pump including a volume control valve, the method comprising: activating the low-pressure pump by varying a value of the manipulated variable in such a way that a pressure provided by the low-pressure pump is reduced across multiple intake phases, in which fuel delivered by the low-pressure pump is sucked in by the high-pressure pump via the volume control valve; during each of the multiple intake phases: (i) at least temporarily holding the volume control valve in a closed position, and then (ii) opening the volume control valve, from the temporarily held closed position, by applying pressure to the volume control valve from a side of the volume control valve facing the low-pressure pump, the pressure being applied to open the volume control valve by a fuel flow from the low-pressure pump; and ascertaining the setpoint value, based on an activating value of the manipulated variable at which a drop in a delivery rate of the high-pressure pump is detected.

2. The method as recited in claim 1, wherein the volume control valve is held in the closed position, starting at a delivery phase preceding the intake phase, in which fuel is delivered by the high-pressure pump into the high-pressure accumulator.

3. The method as recited in claim 1, wherein the drop in the delivery rate of the high-pressure pump is detected, taking into account a change during the course of a regulation of a pressure in the high-pressure accumulator.

4. The method as recited in claim 3, wherein the change during the course of the regulation of the pressure in the high-pressure accumulator includes a change in a control variable.

5. The method as recited in claim 1, wherein the drop in the delivery rate of the high-pressure pump is detected, taking into account a change in a pressure increase in the high-pressure accumulator.

6. The method as recited in claim 5, wherein the high-pressure pump is operated at full delivery to detect the drop in the delivery rate using a two-point regulation.

7. The method as recited in claim 5, wherein the volume control valve is held in the closed position, starting at an intake phase preceding a particular delivery phase up until after the start of a delivery phase, in which fuel is delivered by the high-pressure pump into the high-pressure accumulator.

8. The method as recited in claim 1, wherein the low-pressure pump is activated using the ascertained setpoint value for the manipulated variable.

9. The method as recited in claim 1, wherein the setpoint value is ascertained as a function of a fuel temperature.

10. The method as recited in claim 1, wherein a currentless closed or currentless open volume control valve is used as the volume control valve.

11. The method as recited in claim 1, wherein during each of the multiple intake phases, the at least temporarily holding of the volume control valve in the closed position includes at least temporarily holding the volume control valve in the closed position using a closing spring.

12. The method as recited in claim 11, wherein during each of the multiple intake phases, the volume control valve is opened from the temporarily held closed position only by applying the pressure to the volume control valve from the side of the volume control valve facing the low-pressure pump by the fuel flow from the low-pressure pump.

13. A processing unit, which is configured to ascertain a setpoint value for a manipulated variable for activating a low-pressure pump in a fuel supply system for an internal combustion engine, including a high-pressure accumulator and a high-pressure pump including a volume control valve, the processing unit configured to: activate the low-pressure pump by varying a value of the manipulated variable in such a way that a pressure provided by the low-pressure pump is reduced across multiple intake phases, in which fuel delivered by the low-pressure pump is sucked in by the high-pressure pump via the volume control valve; during each of the multiple intake phases: (i) at least temporarily hold the volume control valve in a closed position, and then (ii) open the volume control valve, from the temporarily held closed position, by applying pressure to the volume control valve from a side of the volume control valve facing the low-pressure pump, the pressure being applied to open the volume control valve by a fuel flow from the low-pressure pump; and ascertain the setpoint value, based on an activating value of the manipulated variable at which a drop in a delivery rate of the high-pressure pump is detected.

14. The processing unit as recited in claim 13, wherein during each of the multiple intake phases, the at least temporarily holding of the volume control valve in the closed position includes at least temporarily holding the volume control valve in the closed position using a closing spring.

15. The processing unit as recited in claim 14, wherein during each of the multiple intake phases, the volume control valve is opened from the temporarily held closed position only by applying the pressure to the volume control valve from the side of the volume control valve facing the low-pressure pump by the fuel flow from the low-pressure pump.

16. A non-transitory computer-readable medium on which is stored a computer program for ascertaining a setpoint value for a manipulated variable for activating a low-pressure pump in a fuel supply system for an internal combustion engine, including a high-pressure accumulator and a high-pressure pump including a volume control valve, the computer program, when executed by a processing unit, causing the processing unit to perform: activating the low-pressure pump by varying the value of the manipulated variable in such a way that a pressure provided by the low-pressure pump is reduced across multiple intake phases, in which fuel delivered by the low-pressure pump is sucked in by the high-pressure pump via the volume control valve; during each of the multiple intake phases: (i) at least temporarily holding the volume control valve in a closed position, and then (i) opening the volume control valve, from the temporarily held closed position, by applying pressure to the volume control valve from a side of the volume control valve facing the low-pressure pump, the pressure being applied to open the volume control valve by a fuel flow from the low-pressure pump; and ascertaining the setpoint value, based on an activating value of the manipulated variable at which a drop in a delivery rate of the high-pressure pump is detected.

17. The non-transitory computer-readable medium as recited in claim 16, wherein during each of the multiple intake phases, the at least temporarily holding of the volume control valve in the closed position includes at least temporarily holding the volume control valve in the closed position using a closing spring.

18. The non-transitory computer-readable medium as recited in claim 17, wherein during each of the multiple intake phases, the volume control valve is opened from the temporarily held closed position only by applying the pressure to the volume control valve from the side of the volume control valve facing the low-pressure pump by the fuel flow from the low-pressure pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 2 schematically shows a high-pressure pump, including a volume control valve.

(3) FIG. 3 shows profiles of a lift of a piston of the high-pressure pump and a current of an associated volume control valve in a method not according to the present invention.

(4) FIG. 4 shows profiles of valve lifts and pressures in a volume control valve in the method illustrated in FIG. 3.

(5) FIG. 5 shows profiles of a lift of a piston of the high-pressure pump and a current of an associated volume control valve in a method according to the present invention in a preferred specific embodiment.

(6) FIG. 6 shows profiles of valve lifts and pressures in a volume control valve in the method illustrated in FIG. 5.

(7) FIG. 7 schematically shows a sequence of a method according to the present invention in a preferred specific embodiment, based on different variables.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(8) A fuel supply system 100 for an internal combustion engine 180, which may be used for a method according to the present invention, is schematically shown in FIG. 1.

(9) Fuel supply system 100 includes a fuel tank 110, which is filled with fuel 111. An in-tank unit 115 is situated in fuel tank 110, which, in turn, includes a pre-supply vessel 116, in which a low-pressure pump 125 is situated, for example in the form of an electric fuel pump.

(10) Pre-supply vessel 115 may be filled with fuel from fuel tank 110 via a suction jet pump 120 (or possibly also multiple suction jet pumps) situated outside the pre-supply vessel in fuel tank 110. Electric fuel pump 125 may be activated via a processing unit 140, designed as a pump control unit in this case, so that fuel is delivered from pre-supply vessel 115 to a high-pressure pump 150 via a filter 130.

(11) Reference is made at this point to FIG. 2 for a more detailed description of high-pressure pump 150, which is activated in this case via a processing unit 145 designed as another pump control unit. In addition, a pressure limiting valve 117 is provided in the low-pressure line.

(12) High-pressure pump 150 is generally driven via internal combustion engine 180 and its camshaft. The fuel is then delivered by high-pressure pump 150 to a high-pressure accumulator 160, from where the fuel may be fed to internal combustion engine 180 via fuel injectors 170. A pressure sensor 165 is furthermore provided on high-pressure accumulator 160, with the aid of which a pressure in the high-pressure accumulator may be detected.

(13) An activation of internal combustion engine 180 and fuel injectors 170 may take place via an engine control unit 195, which is different from pump control units 140 and 145, the control units then being able to communicate with each other. However, it is also possible to use a shared control unit.

(14) FIG. 2 schematically shows a high-pressure pump 150, including a volume control valve 200, in greater detail than in FIG. 1. High-pressure pump 150 includes a piston 190, which is moved up and down via a cam 186 on a camshaft 185 of the internal combustion engine. A delivery volume 250 is decreased or increased in this way.

(15) Volume control valve 200 has an inlet opening 235, via which fuel provided by the low-pressure pump may enter delivery volume 250. An opening which follows inlet opening 235 may be closed with the aid of an inlet valve 230, using a closing spring 231, which is part of volume control valve 200.

(16) A solenoid coil 210, which may be part of an electromagnet, is also provided, which may be supplied with a voltage U and energized with a current I. Voltage U and current I may be provided, for example, via corresponding pump control unit 145.

(17) A spring 220 is furthermore shown, which presses a bolt 225, on whose end facing the solenoid coil an armature 215 is fastened, in the direction of inlet valve 230. When solenoid coil 210 is not energized, inlet valve 230 is thus continuously held open. It is thus a currentless open volume control valve. It should be noted in this regard that the spring force of spring 220 is greater than that of closing spring 231.

(18) If solenoid coil 210 is now energized with a sufficiently high current, bolt 225 is moved against spring 220 with the aid of armature 215. In this way, inlet valve 225 is closed by closing spring 231; however, it may be opened by the application of pressure.

(19) An outlet valve 240 is furthermore provided with a closing spring 241, via which fuel may be delivered from delivery volume 250 to the high-pressure accumulator via an outlet opening 245.

(20) FIG. 3 shows profiles of a lift h.sub.K of the piston of the high-pressure pump and current I of the associated volume control valve, in a method not according to the present invention, over a camshaft angle or angle in each case. The high-pressure pump, including a volume control valve, as described in greater detail with reference to FIG. 2, is also shown in a particular position for different angles.

(21) The piston of the high-pressure pump is initially in a downward movement, due to the rotation of the cam, as is illustrated by way of example by the position of the high-pressure pump for angle .sub.1. This is an intake phase, i.e. fuel provided by the low-pressure pump is sucked into the delivery volume of the high-pressure pump. The volume control valve is not energized for this purpose and is thus continuously open. In this way, fuel may flow into the delivery volume unhindered. The outlet valve is closed.

(22) At angle .sub.2, the bottom dead center of the piston is reached, and the intake phase is ended. The piston then moves again upward in the direction of the top dead center, as is illustrated by way of example by the position of the high-pressure pump for angle .sub.3. The volume control valve is still continuously open, which means that fuel from the delivery volume is initially pressed back again into the low-pressure area via the inlet opening.

(23) Only during the upward movement of the piston is the solenoid coil energized with a current I, so that the armature releases the inlet valve using the bolt, and it may close, as is illustrated by way of example by the position of the high-pressure pump for angle .sub.4. As is apparent in the area around angle .sub.4, the current may initially include a pull-in current and then a slightly lower holding current, so that the armature may continue to be held pulled after the pulling.

(24) As soon as the volume control valve or the inlet valve is able to close, the fuel is now no longer delivered from the delivery volume back into the low-pressure area but into the high-pressure accumulator via the outlet valve and the outlet opening, as is illustrated by way of example by the position of the high-pressure pump for angle .sub.5. The delivery is ended only when the piston reaches the top dead center at angle .sub.6.

(25) It should be noted in this regard that current I may already be canceled before reaching the top dead center, since the inlet valve also remains closed against the opening force of the spring, due to the high pressure in the delivery volume. The delivery rate and thus the pressure buildup in the high-pressure accumulator may be set or regulated by suitably selecting the point in time or the corresponding angle at which the volume control valve is closed.

(26) FIG. 4 shows profiles of valve lifts h and pressures P in bar in the volume control valve in the method illustrated in FIG. 3, in ms over time t in each case. While h.sub.M shows the lift of the armature, the lift of the inlet valve is illustrated by h.sub.E. P.sub.E shows an associated pressure at the inlet valve, and P.sub.F shows an associated pressure in the delivery volume. The profiles over time between approximately 3 ms and approximately 11 ms more or less correspond to the situations illustrated in FIG. 3 between angles .sub.4 and .sub.6, which correspond to the delivery phase starting at the closure of the volume control valve, due to the energization. The profiles between approximately 11 ms and approximately 26 ms, however, more or less correspond to the situations illustrated in FIG. 3 between angles .sub.6 and .sub.4, which correspond to the intake phase and the delivery phase up to prior to the closure of the volume control valve.

(27) It is apparent from the profiles of the pressures during the intake phase that pressure P.sub.E at the inlet valve and pressure P.sub.F in the delivery volume are nearly identical. At the most, a very slight pressure drop is apparent from the inlet valve in the direction of the delivery volume. This means that almost no steam formation is able to take place at the inlet valve, for which reason a drop in the delivery rate is also difficult to detect, as was explained at the outset.

(28) FIG. 5 shows profiles of lift h.sub.K of the piston of the high-pressure pump and current I of the associated volume control valve, in a method according to the present invention, in a preferred specific embodiment, over a camshaft angle or angle in each case.

(29) The high-pressure pump, including a volume control valve, as described in greater detail with reference to FIG. 2, is also shown in a particular position for different angles. In this case, the profile corresponds to the one illustrated in FIG. 3, but with the difference that the activating current, which sets in shortly before angle .sub.4, is not yet ended during the delivery phase, i.e., the upward movement of the piston, but rather continues to be maintained.

(30) This results in the fact that current I is still present in the subsequent intake phase, as is apparent here on the left side of the profile. The activating current is canceled in this case only shortly before the end of the intake phase, i.e. shortly before reaching the bottom dead center at angle .sub.2.

(31) During the intake phase, the volume control valve is thus in a closed position, in which it may be opened by applying pressure on the part of the low-pressure pump, as is illustrated by way of example by the position of the high-pressure pump for angle .sub.1.

(32) FIG. 6 shows the associated profiles of valve lifts h and pressures P in the volume control valve, in ms over time t in each case. As in FIG. 4, h.sub.M in this case also shows the lift of the armature and h.sub.E shows the lift of the inlet valve. P.sub.E shows an associated pressure at the inlet valve, and P.sub.F shows an associated pressure in the delivery volume.

(33) The profiles over time between approximately 3 ms and approximately 20 ms more or less correspond to the situations illustrated in FIG. 3 between angles .sub.4 and .sub.2. Compared to FIG. 4, it is apparent that lift h.sub.E of the inlet valve according to FIG. 6 is much smaller in the time between approximately 11 ms and approximately 20 ms, i.e., in the intake phase. This is due to the fact that the inlet valve is not held open continuously but is only opened by the fuel flow during the intake phase, thus resulting in a pressure drop.

(34) This furthermore results in the fact that pressure P.sub.E at the inlet valve and pressure P.sub.F in the delivery volume are significantly different during the intake phase, i.e., in the time between approximately 11 ms and approximately 20 ms. A pressure drop of approximately 0.5 bar is apparent here, whereby the steam formation in the delivery volume is favored. As already explained in detail at the outset, this results in a much easier and better detection of the drop in the delivery rate in other operating ranges. The setpoint value for the manipulated variable for activating the low-pressure pump may thus be very easily ascertained.

(35) The profile of activating current I illustrated in FIG. 5 may also be used, in particular, only during a time period in which the setpoint value is to be ascertained. Otherwise, i.e. during regular operation, the profile illustrated in FIG. 3 may continue to be used. It should furthermore be noted that the profile of the activating current is more or less the opposite, i.e., when using a currentless closed volume control valve.

(36) FIG. 7 schematically shows a sequence of a method according to the present invention in a preferred specific embodiment, based on different variables. Profiles of a manipulated variable of the low-pressure pump, in this case an activating current I.sub.A, an associated pressure P.sub.N provided by the low-pressure pump, a delivery rate M of the high-pressure pump and a pressure P.sub.H in the high-pressure accumulator, are illustrated for this purpose, over time t in each case.

(37) Activating current I.sub.A of the low-pressure pump may now be reduced when a setpoint value is to be ascertained, for example continuously across multiple intake phases of the high-pressure pump. Accordingly, pressure P.sub.N provided thereby is reduced, which, however, does not have to be measured. Delivery rate M initially still remains constant, so that pressure P.sub.H in the high-pressure accumulator may be well regulated and maintained.

(38) At point in time to, the point should now be reached, at which the steam formation in the delivery volume of the high-pressure pump has decreased so much, due to further decreasing pressure P.sub.N, that the delivery rate drops. The drop in delivery rate M now results, for example, in a short-term reduction of pressure P.sub.H in the high-pressure accumulator, which, on the one hand, may be measured directly, but which, on the other hand, may also be detected during the course of the regulation of this pressure, based on controller variables.

(39) Activating value I.sub.A used for the activating current at point in time to may now be used to ascertain setpoint value I.sub.V. For example, a suitable offset may be easily added for this purpose.

(40) Setpoint values for different fuel temperatures are preferably ascertained, so that a suitable setpoint value for the manipulated variable, the activating current in this case, may be used for each fuel temperature (e.g. by interpolation or extrapolation) in such a way that a desired admission pressure is present at the high-pressure pump. A desired admission pressure is characterized, in particular, in that it is as low as possible and as high as necessary.