EP2643582B1 - Method for operating a fuel system of an internal combustion engine - Google Patents

Description

State of the art

The invention relates to a method according to the preamble of claim 1, and a computer program and a control and / or regulating device according to the independent claims.

In modern direct-injection internal combustion engines with demand-controlled fuel delivery, the required high-pressure piston pump (HDP) is occasionally operated temporarily depending on an operating condition of a motor vehicle without promotion. This is done in conventional systems, especially in the phases with overrun fuel cutoff, in which the internal combustion engine requires no fuel and therefore no fuel must be promoted. Since these phases are often relatively short (for example, less than five minutes), the HDP can sustain these phases without damage.

A possible damage mechanism of a piston pump used as HDP can be described as follows: If the HDP usually upstream quantity control valve for controlling the amount of fuel supplied for a longer period is not driven, so is due to the lack of pressure difference (between a high-pressure delivery chamber to a pre-pressurized so no significant fuel exchange in the gap between the piston and the piston sleeve of the HDP instead. However, the replacement of fuel is important for the lubrication of the piston as well as for a centering of the piston in the piston sleeve. Additionally, as a result of the lack of or low pressure, the fuel may be at the comparatively high temperature in the HDP if necessary, evaporate already. Due to the lack of lubrication at the contact points between the piston and the piston bushing, the HDP can be permanently damaged ("piston seizure").

Particularly critical in this regard may be bivalent propulsion systems in which the internal combustion engine is operated for longer intervals instead of with liquid fuel (gasoline or diesel) with gas (CNG). During this time, the high-pressure pump (HDP) usually runs without promotion, whereby it can become comparatively hot. This results in the above-mentioned damage mechanism.

Also critical in this regard are hybrid systems where the HDP is subjected to similar conditions during electrical operation as in combined fuel-gas operation.

Both cases described above can have long phases without HDP production at high fuel temperatures. In particular, during normal operation, the cooling of the HDP resulting from the fuel flow is eliminated.

Specialist publications from this area are, for example, the DE 198 34 121 A1 , the US 20080208439 A1 , the US 20070163536 A1 , the US 20060037583 A1 , the US 20060196475 A1 , the US 20060102149 A1 and the US 20050098155 Al ,

Disclosure of the invention

The problem underlying the invention is achieved by a method according to claim 1 and by a computer program and a control and / or regulating device according to the independent claims. Advantageous developments are specified in subclaims. Features which are important for the invention can also be found in the following description and in the drawings, wherein the features, both alone and in different combinations, can be important for the invention, without being explicitly referred to again.

The invention has the advantage that in an operating case of a fuel system in which a fuel pump does not deliver fuel into a pressure range of the fuel system, fuel may flow into a delivery space of the fuel pump, with movable elements of the fuel pump, such as a piston, from the flowing fuel be lubricated. As a result, the fatigue strength of the fuel pump can be increased. In particular, the method according to the invention can be carried out solely by means of a modified actuation of a valve device of the fuel pump, that is to say by means of software.

The invention is based on the consideration that during operation of an internal combustion engine operating cases occur in which no fuel is burned in combustion chambers of the internal combustion engine and accordingly no fuel is conveyed by the fuel pump. This can be the case, for example, in so-called "fuel cut-off" phases, or in such internal combustion engines, which are alternatively operated with liquid fuel or with gas, as well as in motor vehicles with hybrid drive. A first operating case of the fuel system may be defined in which a normal delivery of fuel into the pressure range takes place, and a second operating case in which no fuel is to be conveyed into the pressure range.

According to the invention, a valve device which meters an amount of fuel supplied to the fuel pump is at least temporarily actuated in the second operating mode such that fuel is drawn in from the upstream low-pressure region in a first phase of the working movement of the fuel pump, almost completely back into the low-pressure region in a second phase is conveyed, and in a third phase, a residual amount of fuel between movable elements of the fuel pump and the guide or storage is pressed to lubricate this.

The three phases, in particular the transition from the second to the third or the third to the second phase, are controlled according to the invention by means of the valve device. For example, a controllable inlet valve is the Valve device opened during the first two phases, and closed during the third phase. Preferably, the third phase begins shortly before reaching the top dead center of the piston and ends with the reaching of the top dead center. The three phases can be repeated cyclically with the movement of the piston.

An embodiment of the method provides that the activation of the valve device takes place in the second operating case periodically with each stroke of the fuel pump. This maximum lubrication, for example, the piston can be achieved, whereby the fatigue strength of the fuel pump can be significantly increased.

A further embodiment of the method provides that the control of the valve device takes place occasionally or periodically in the second operating case, and that no activation takes place in intervening intervals. This can - depending on a specific embodiment of the fuel pump - a sufficient lubrication are made possible, at the same time an unwanted promotion of fuel in the pressure range of the fuel system - and thus a possible exceeding of a limit pressure - is unlikely.

A further embodiment of the method provides that the control of the valve device in the second operating case is carried out continuously over in each case a first number of strokes of the fuel pump, and thereafter no activation of the valve device takes place over a second number of strokes of the fuel pump. Thus, the inventive method can be carried out alternately over several strokes of the fuel pump and then not performed over several strokes. In this way, a large number of possibilities for carrying out the method are given, which can be flexibly adapted to operating states or operating variables of the fuel pump and / or the internal combustion engine.

The method works better when the angle of a drive shaft of the fuel pump, in which a compression by a corresponding adjustment of the valve device starts without fuel in the pressure range is promoted (zero conveying angle), taking into account at least one operating variable of the internal combustion engine is determined. This can be achieved depending on the at least one operating variable, on the one hand sufficiently lubricated the fuel pump and on the other hand, an unwanted promotion of fuel is avoided.

The method can be performed more precisely if the zero-feed angle is determined taking into account a plurality of operating variables using at least one characteristic map. As a result, a large number of operating variables can be used to control the valve device, with further information being available without the additional computational outlay of a control and / or regulating device of the internal combustion engine or of the motor vehicle through the use of one or more characteristic maps. This generally improves the performance of the method, saves computing time and reduces costs.

• Drehzahl der Brennkraftmaschine;
• Drehmoment der Brennkraftmaschine;
• Temperatur der Brennkraftmaschine;
• Temperatur des Kraftstoffs;
• Kraftstoffdruck im Druckbereich; und/oder
• Betriebszustand der Brennkraftmaschine, insbesondere eine Schubabschaltung.

In particular, it is provided that the zero-feed angle is determined taking into account at least one of the following variables:

• Speed of the internal combustion engine;
• Torque of the internal combustion engine;
• Temperature of the internal combustion engine;
• Temperature of the fuel;
• Fuel pressure in the pressure range; and or
• Operating state of the internal combustion engine, in particular a fuel cut-off.

Among other things, the first operating case can be distinguished from the second operating case by means of these variables, and thus a "switch-on condition" for the method can be derived. In particular, these quantities are used to precisely determine the time for the transition from the second to the third phase, so that a sufficient lubrication of the fuel pump can be achieved and at the same time the unwanted promotion of fuel in the pressure range can be prevented.

It is further provided that, when the pressure in the pressure range increases at a rate which is greater than a limit value, the zero-feed angle is changed so far that the rate remains below the limit value. So that can so to speak "anticipatory" the zero conveying angle can be adjusted, so that the security against an unwanted delivery of fuel can be reduced and the probability of exceeding a limit pressure in the pressure range can be minimized.

The control of the valve device for carrying out the method is further improved if a pressure increase due to heating of the fuel in the pressure range with increasing operating time is taken into account. This makes it easier to distinguish whether the pressure increase has arisen or arises as a result of an unwanted delivery of fuel or as a result of the heating of the fuel. As far as the pressure increase is due to the heating of the fuel, the zero feed angle need not be further reduced, whereby an optimal lubrication of the fuel pump can be maintained.

Figur 1

ein vereinfachtes Schema eines Kraftstoffsystems einer Brennkraftmaschine;

Figur 2

ein Schema einer Kraftstoffpumpe des Kraftstoffsystems von Figur 1;

Figur 3

ein Zeitdiagramm mit verschiedenen Phasen der Arbeitsbewegung der Kraftstoffpumpe; und

Figur 4

ein Flussdiagramm für ein Computerprogramm zur Abarbeitung in einer Steuer- und/oder Regeleinrichtung der Brennkraftmaschine.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show:

FIG. 1

a simplified diagram of a fuel system of an internal combustion engine;

FIG. 2

a schematic of a fuel pump of the fuel system of FIG. 1 ;

FIG. 3

a time chart with different phases of the working movement of the fuel pump; and

FIG. 4

a flowchart for a computer program for processing in a control and / or regulating device of the internal combustion engine.

The same reference numerals are used for functionally equivalent elements and sizes in all figures, even in different embodiments.

FIG. 1 shows a fuel system 1 of an internal combustion engine in a highly simplified schematic representation. A fuel tank 9 is connected via a suction line 4, a prefeed pump 5 and a low pressure line 7 with a Fuel pump 3 connected. To the fuel pump 3, a high-pressure accumulator 13 ("common rail") is connected via a high-pressure line 11. An electromagnetically operated switching valve 14 - hereinafter referred to as valve means 14 - with an electromagnetic actuator 15 - hereinafter referred to as solenoid 15 - is hydraulically in the course of the low pressure line 7 between the prefeed pump 5 and the fuel pump 3 is arranged. The electromagnet 15 is controlled by a computer program 8 of a control and / or regulating device 19 using maps 6. Furthermore, the fuel pump 3 comprises a cam 17 arranged on a drive shaft 10, which can vertically move a piston 18 in the drawing. Other elements, such as an exhaust valve of the fuel pump 3, are in the FIG. 1 not drawn. It is understood that the valve device 14 may be formed as a unit with the fuel pump 3. For example, the valve device 14 may be designed as a forcibly openable inlet valve of the fuel pump 3 in the sense of a so-called "quantity control valve".

During operation of the fuel system 1, the prefeed pump 5 conveys fuel from the fuel tank 9 into the low-pressure line 7. The valve device 14 determines the fuel quantity supplied to a delivery chamber 36 of the fuel pump 3.

FIG. 2 shows the fuel pump 3 of the FIG. 1 in a somewhat more detailed, but also schematic representation. The fuel pump 3 has a housing 20, in whose left portion in the drawing, the electromagnet 15 with a coil 22, an armature 24 and an armature spring 26 is arranged. Furthermore, the fuel pump 3 comprises an inlet 28 connected to the low-pressure line 7 with an inlet valve 30, and an outlet 32 connected to the high-pressure line 11 with an outlet valve 34. The inlet valve 30 comprises a valve spring 31 and a valve body 33. The valve body 33 can by means of a in the drawing horizontally displaceable and coupled to the armature 24 valve needle 35 are moved. If the electromagnet 15 is energized, the inlet valve 30 can be closed by the force of the valve spring 31. If the electromagnet 15 is not energized, the inlet valve 30 can be forced by the force of the armature spring 26 be opened. In the delivery chamber 36, the piston 18 is arranged vertically movable in the drawing. The piston 18 can be moved by means of a roller 40 of the - in this case elliptical - cam 17 in a cylinder 37. The cylinder 37 is formed in a portion of the housing 20. The inlet valve 30 is hydraulically connected via an opening 38 with the delivery chamber 36.

In a first operating case of the fuel system 1, the fuel pump 3 delivers fuel from the inlet 28 to the outlet 32, wherein the outlet valve 34 opens or closes according to a respective pressure difference between the delivery chamber 36 and the outlet 32. The inlet valve 30 is acted upon by full delivery of a respective pressure difference between the inlet 28 and the delivery chamber 36, but also through the valve needle 35 and the electromagnet 15. In a desired partial delivery of the electromagnet 15 is energized during a delivery stroke from a certain time, whereby the intake valve 30 can close and the fuel still present in the delivery chamber 36 is not conveyed back into the low-pressure line 7, but into the high-pressure accumulator 13 ("rail"). The arranged within the housing 20 volumes of the fuel pump 3 are substantially filled with fuel.

FIG. 3 shows a second case of operation of the fuel system 1, in which the fuel pump 3 does not promote or promote fuel in the pressure range 16. The lower part of the drawing shows a time diagram with two coordinate systems. In the lower coordinate system, a current I flowing in the coil 22 is plotted against the ordinate over a time t. In the upper coordinate system, a stroke 44 of the piston 18 between a bottom dead center UT and a top dead center OT is plotted on the ordinate in the same time scale over the time t.

Furthermore, three phases of the working movement of the piston 18 are delimited by dashed lines, namely a suction phase PH1, a Rückströmphase PH2 and a delivery phase PH3. The delivery phase PH3 corresponds to a delivery angle 46 of the drive shaft 10, which is defined starting from the upper right in the drawing top dead center OT in time negative direction. The transition from the Rückströmphase PH2 in the delivery phase PH3 is too a time t1. The sum of in the FIG. 3 Phases PH1 to PH3 between the two illustrated top dead centers OT corresponds to a period of the working movement of the piston 18, which in this case corresponds to half a rotation of the cam 17 and the drive shaft 10. A hatched area 48 additionally illustrates the delivery phase PH3.

In the upper part of the drawing of FIG. 3 are the three phases PH1 to PH3 corresponding states of the fuel pump 3 - as shown in FIG FIG. 2 - symbolically assigned.

In the second operating case of the fuel system 1 starts from the left in the drawing top dead center OT, the suction phase PH1. The coil 22 of the electromagnet 15 is not energized. The inlet valve 30 is opened under pressure control and the outlet valve 34 is closed. Along an arrow 50, fuel may flow from the inlet 28 through the opened inlet valve 30 and through the opening 38 into the delivery chamber 36. By the downward movement of the piston 18 in the direction of arrow 52, the delivery chamber 36 is simultaneously increased. The arranged within the housing 20 volumes of the fuel pump 3 are also filled in the second operating case substantially with fuel. The suction phase PH1 ends at bottom dead center UT.

In the Rückströmphase PH2, which begins at bottom dead center UT, the inlet valve 30 remain open and the exhaust valve 34 is closed. The coil 22 is still not energized. By the upward movement of the piston 18 in the direction of arrow 54, the volume of the delivery chamber 36 is reduced. In this case, the fuel located in the delivery chamber 36 is at least partially pushed out through the opening 38 and the inlet valve 30 along an arrow 56 and into the low-pressure line 7. The Rückströmphase PH2 ends at time t1.

The transition from the Rückströmphase PH2 in the subsequent delivery phase PH3 is triggered by the coil 22 is energized. The current I has, for example, in the FIG. 3 History displayed in the lower coordinate system. The piston 18 is located shortly before the top dead center OT continues in the upward movement. The armature 24 and the valve needle 35 are moved in the drawing by magnetic force to the left. By the power of Valve spring 31, the valve body 33 - possibly supported by flow forces - also moves to the left and the inlet valve 30 thus closed. The outlet valve 34 remains closed. As a result of the closed intake valve 30 and the closed exhaust valve 34, the fuel is compressed in the delivery chamber 36 and a hydraulic pressure is built up in the delivery chamber 36 due to the remaining stroke movement of the piston 18 up to the top dead center OT. As a result of the hydraulic pressure or a pressure difference to areas outside the housing 20, a small amount of fuel in the direction of arrows 58 in the drawing is pressed down between the peripheral surface of the piston 18 and the cylinder 37. By thus resulting leakage flow of the piston 18 is lubricated.

The delivery angle 46 is so dimensioned that the exhaust valve 34 remains closed in all phases PH1 to PH3 and thus just no fuel is conveyed into the pressure region 16, provided that the pressure prevailing in the pressure chamber 16 hydraulic pressure is not exceeded in the delivery chamber 36. This conveying angle 46 is also referred to as "zero conveying angle", below which there is no delivery of fuel. This is achieved by a suitable control of the electromagnet 15 by the control and / or regulating device 19. As a result, on the one hand, maximum lubrication of the fuel pump 3 can be effected and, on the other hand, an undesired delivery of fuel into the pressure region 16 can be avoided. The zero-feed angle may be based on the angle of the drive shaft 10 of the fuel pump 3.

The control of the electromagnet 15 can be done for example with each stroke 44 of the fuel pump 3. Alternatively, the drive may only be occasional or periodic, with no drive at intervening intervals. Yet another alternative is to perform the control of the valve device 14 over a first limited number of strokes 44 with each stroke 44, and thereafter to make no activation over a second limited number of strokes 44.

• eine Drehzahl der Brennkraftmaschine;
• ein Drehmoment der Brennkraftmaschine;
• eine Temperatur der Brennkraftmaschine;
• eine Temperatur des Kraftstoffs;
• einen Kraftstoffdruck im Druckbereich 16; und/oder
• einen Betriebszustand der Brennkraftmaschine, insbesondere eine Schubabschaltung.

For optimal control of the electromagnet 15 takes into account the control and / or regulating device 19 - using at least one map 6 - When determining the zero feed angle at least one of the following variables, which represent operating variables of the internal combustion engine:

• a rotational speed of the internal combustion engine;
• a torque of the internal combustion engine;
• a temperature of the internal combustion engine;
• a temperature of the fuel;
• a fuel pressure in the pressure region 16; and or
• an operating state of the internal combustion engine, in particular a fuel cut.

FIG. 4 shows a flowchart for processing the method in the computer program 8 of the control and / or regulating device 19. Starting from a start block 70, it is decided in a query block 72 whether a switch-on condition for carrying out the method is present. For this purpose, the first operating case is distinguished from the second operating case by means of the above-mentioned operating variables. This is in the FIG. 4 but not shown in detail. If the engine is currently in the first operating condition, there is no power-on condition and the program branches back to the start block 70.

On the other hand, if there is a switch-on condition, the delivery angle 46 (zero-conveying angle) is determined in a subsequent block 74 from a characteristic diagram 6 and also taking into account the above-mentioned operating variables. According to the thus determined conveying angle 46 of the solenoid 15 is driven in the second operating case and the fuel pump 3 thus in a to the FIG. 3 operated in a comparable manner.

Subsequently, in a block 76, a pressure in the pressure region 16 is detected, from which a rate or a gradient of the pressure is determined. In this case, a possible pressure increase due to heating of the fuel in the pressure region 16 can be taken into account in addition with increasing duration of the second operating case.

Thereafter, it is checked in a query block 78, whether the determined rate is greater than a threshold value 80. If this is not the case, then in turn is branched to the start block 70 and the program continues there.

If, however, the determined rate is greater than the limit value 80, then in a following block 82 the conveying angle 46 is reduced stepwise by first one step. This safety function causes the delivery phase PH3 or the delivery angle 46 (zero conveying angle) to be shortened, whereby correspondingly less pressure is built up in the delivery chamber 36 and the outlet valve 34 is thus acted upon more strongly in the closed position. The risk that unintentionally fuel is conveyed into the pressure region 16, thus becomes smaller. Thereafter, the program branches back to the start block 70 and the program continues there.

Claims (8)

1. Method for operating a fuel system (1) of an internal combustion engine, in which method, in at least a first operating situation, by means of a corresponding setting of a valve device (14), a fuel pump (3) compresses fuel in a delivery chamber (36) and delivers said fuel into a pressure region (16), and in which method, in at least a second operating situation, by means of a corresponding setting of the valve device (14), the fuel pump (3) delivers no fuel into the pressure region (16), characterized in that, in the second operating situation, the valve device (14) is occasionally or periodically activated with a zero-delivery angle such that, in a first phase of the working movement of the fuel pump, the fuel is drawn in from a low-pressure region, in a second phase, said fuel is delivered almost entirely back into the low-pressure region, and in a third phase, a residual quantity of the fuel is forced between movable elements of the fuel pump and the guide or bearing arrangement thereof, and in that no activation occurs in intervening intervals.
2. Method according to at least one of the preceding claims, characterized in that the zero-delivery angle of a drive shaft (10) of the fuel pump (3), at which a compression begins by means of a corresponding setting of the valve device (14) without fuel being delivered into the pressure region (16), is determined taking into consideration at least one operating variable of the internal combustion engine.
3. Method according to Claim 1, characterized in that the zero-delivery angle is determined taking into consideration multiple operating variables using at least one characteristic map (6).
4. Method according to Claim 2 or 3, characterized in that the zero-delivery angle is determined taking into consideration at least one of the following variables:

   - rotational speed of the internal combustion engine;

   - torque of the internal combustion engine;

   - temperature of the internal combustion engine;

   - temperature of the fuel;

   - fuel pressure in the pressure region (16); and/or

   - operating state of the internal combustion engine, in particular an overrun cut-off state.
5. Method according to any of Claims 2 to 4, characterized in that, if the pressure in the pressure region (16) rises at a rate greater than a threshold value (80), the zero-delivery angle is changed to such an extent that the rate remains below the threshold value (80).
6. Method according to Claim 5, characterized in that a pressure increase as a result of warming of the fuel in the pressure region (16) with progressive operating duration is taken into consideration.
7. Computer program (8), characterized in that it is programmed to carry out a method according to at least one of the preceding claims.
8. Open-loop and/or closed-loop control device (19) of an internal combustion engine, characterized in that it comprises a memory on which a computer program (8) according to Claim 7 is stored.

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