Method for operating a high-pressure fuel pump of a fuel injection system of an internal combustion engine

Abstract

Method for operating a high-pressure fuel pump of a fuel injection system of an internal combustion engine, wherein the high-pressure fuel pump (16) has at least one pump element (24), wherein the pump element (24) has a pump piston (26) driven at least indirectly by the internal combustion engine (10) in a stroke motion via a plunger (32), which defines a pump working chamber (46) which can be connected to an inlet or a relief area by an electrically controlled valve (48), wherein fuel is delivered by the high-pressure fuel pump (16) into a high-pressure fuel reservoir (18) to which at least one fuel injector (20) is connected, and wherein the fuel injection system has an electronic control unit (22) by which the valve (48) and the at least one fuel injector (20) are controlled, characterized in thatthat when the internal combustion engine (10) is started, during a first delivery stroke or during a first delivery stroke and at least one subsequent initial delivery stroke of the pump piston (26) of the at least one pump element (24), no fuel delivery takes place through the pump piston (26) into the high-pressure fuel accumulator (18).

Description

State of the art

[0001] The invention is based on a method for operating a high-pressure fuel pump of a fuel injection device of an internal combustion engine according to the preamble of claim 1.

[0002] Such a method is known from EP 0 840 009 A2. The fuel injection device of an internal combustion engine according to this document comprises a high-pressure fuel pump with a pump element having a pump piston driven at least indirectly by the internal combustion engine, for example, via a tappet in a reciprocating motion. The pump piston delimits a pump working chamber that can be connected to an inlet by an electrically controlled valve. The electrically controlled valve allows the delivery rate of the high-pressure fuel pump to be variably adjusted. The fuel injection device comprises a high-pressure fuel accumulator into which fuel is pumped by the high-pressure fuel pump. At least one injector, through which fuel is injected into a combustion chamber of the internal combustion engine, is connected to the high-pressure fuel accumulator.The high-pressure fuel pump is operated in such a way that the electrically controlled valve remains open during the pump piston's delivery stroke until the amount of fuel to be delivered under high pressure into the high-pressure accumulator is present in the pump working chamber. The electrically controlled valve is then closed, and fuel is pumped into the high-pressure fuel accumulator by the pump piston. Typically, when the internal combustion engine is started, the pump element is designed to pump a large amount of fuel into the high-pressure accumulator, so the electrically controlled valve is closed at the beginning of the pump piston's delivery stroke, and high pressure is generated in the pump working chamber by the pump piston.

[0003] From DE 10 2011 082 642 A1 it is known that the pump piston is supported on a cam of a drive shaft via a roller tappet, wherein the drive shaft is driven by the internal combustion engine. The roller tappet comprises a roller shoe in which a roller is rotatably mounted in a recess like a plain bearing, which roller runs on the cam. It is advantageous if hydrodynamic lubrication is present between the roller and the recess in the roller shoe in order to keep friction and wear on the roller and the roller shoe to a minimum. When starting the internal combustion engine, hydrodynamic lubrication cannot initially be achieved because, due to the mechanical drive of the high-pressure fuel pump by the internal combustion engine, the roller must first be accelerated from a standstill.If the pump piston generates high pressure in the pump working chamber during engine start-up, this results in significant stress on the roller and roller shoe, as the roller is not yet sufficiently lubricated in the roller shoe recess. This causes significant wear on the roller and / or roller shoe.

[0004] To reduce fuel consumption in internal combustion engines, it is also known from DE 10 2011 082 642 A1 to provide a so-called start-stop system for these engines. This system shuts off the engine during a brief standstill of a motor vehicle equipped with the engine, for example, at a red light, and restarts it when the vehicle is moving off. This leads to a sharp increase in the number of engine start-ups, which further exacerbates the above-mentioned problem regarding the load and wear on the high-pressure fuel pump.

[0005] WO 02 / 042 626 A1 discloses a method for operating an internal combustion engine, in particular a motor vehicle, wherein fuel is delivered under pressure into a fuel rail. The fuel is supplied to at least one combustion chamber via at least one injection valve. If the fuel pressure in the fuel rail is above a certain value, a control signal is generated, which corresponds to an interruption of the fuel delivery into the fuel rail.

[0006] DE 10 2010 061 081 A1 discloses a method for operating a fuel system of an internal combustion engine, in which, in at least one first operating case, a fuel pump compresses fuel in a delivery chamber and delivers it into a pressure region by means of a corresponding setting of a valve device, and in which, in at least one second operating case, the fuel pump does not deliver any fuel into the pressure region by means of a corresponding setting of the valve device, wherein, in the second operating case, the valve device is at least temporarily controlled in such a way that fuel is compressed in the delivery chamber but is not delivered into the pressure region. Disclosure of the inventionAdvantages of the invention

[0007] The method according to the invention for operating a high-pressure fuel pump with the features of claim 1 has the advantage that the load on the high-pressure fuel pump, in particular on its tappet, is reduced when starting the internal combustion engine.

[0008] Advantageous embodiments and further developments of the method according to the invention are specified in the dependent claims. The application of the method to a high-pressure fuel pump of a fuel injection device with the features of claim 5 has the advantage that reliable starting of the internal combustion engine is possible even without fuel delivery by the high-pressure fuel pump. The application of the method to a high-pressure fuel pump with a roller tappet according to claim 6 enables sufficient lubrication to build up between the roller and the recess during start-up of the internal combustion engine. The application of the method to a high-pressure fuel pump with multiple pump elements according to claim 7 enables partial fuel delivery by the high-pressure fuel pump into the high-pressure fuel accumulator and a distribution of the load among the various pump elements. drawing

[0009] An embodiment of the invention is illustrated in the drawing and explained in more detail in the following description. Fig. 1 shows a simplified representation of a fuel injection device for an internal combustion engine with a high-pressure fuel pump and Fig. 2 A section of the high-pressure fuel pump in a longitudinal section. Description of the embodiment

[0010] In Fig. Figure 1 shows a simplified representation of a fuel injection system for an internal combustion engine 10. The fuel injection system comprises a feed pump 12, through which fuel is drawn from a reservoir 14 and delivered to a high-pressure fuel pump 16 of the fuel injection system. The high-pressure fuel pump 16 delivers fuel under high pressure into a high-pressure fuel accumulator 18 of the fuel injection system. At least one fuel injector 20 of the fuel injection system is connected to the high-pressure fuel accumulator 18, through which fuel is injected into the combustion chamber of a cylinder of the internal combustion engine 10.The fuel injection device also comprises an electronic control device 22, by which the fuel injection of the at least one fuel injector 20 and the amount of fuel delivered by the high-pressure fuel pump 16 into the high-pressure fuel reservoir 18 are controlled or regulated.

[0011] The high-pressure fuel pump 16 is in Fig.2 is shown in an enlarged detail. The high-pressure fuel pump 16 has at least one pump element 24, which in turn has a pump piston 26 which is driven at least indirectly by a drive shaft 28 in a reciprocating movement. The drive shaft 28 has one or more cams 30 or eccentrics, via which the rotary movement of the drive shaft 28 is converted into the reciprocating movement of the pump piston 26. The pump piston 26 is supported via a tappet 32 ​​on the cam 30 or eccentric of the drive shaft 28. The tappet 32 ​​is a roller tappet which comprises a roller shoe 34 which has a recess 36 facing the cam 30, in which a roller 38 is rotatably mounted. The tappet 32 ​​and the pump piston 26 are urged towards the cam 30 by a spring 40.The tappet 32 ​​is arranged in a fuel-filled interior of the high-pressure fuel pump 16, and the fuel lubricates the bearing of the roller 38 in the recess 36. During operation of the high-pressure fuel pump 16, hydrodynamic lubrication conditions preferably arise between the roller 38 and the recess 36, so that there is no direct contact between the roller 38 and the recess 36, but rather a fuel lubricating film is present between them.

[0012] The pump piston 26 is tightly guided in a cylinder bore 42 of a housing part 44 of the high-pressure fuel pump 16 and, with its end facing away from the cam 30, delimits a pump working chamber 46 in the cylinder bore 42. The pump working chamber 46 has a connection to an inlet from the feed pump 12 via an inlet valve 48, via which the pump working chamber 46 is filled with fuel during the suction stroke of the pump piston 26 directed radially inward towards the drive shaft 28. The pump working chamber 46 also has a connection, via an outlet valve 50, which is, for example, an outlet check valve opening out of the pump working chamber 46, to an outlet 52 which leads to the high-pressure fuel accumulator 18 and via which fuel is displaced from the pump working chamber 46 during the delivery stroke of the pump piston 26 directed radially outward away from the drive shaft 28.

[0013] The inlet valve 48 is electrically controlled by the control device 22 in order to variably adjust the amount of fuel pumped into the high-pressure fuel reservoir 18 by the high-pressure fuel pump 16. The inlet valve 48 has a movable valve member 54 that interacts with a valve seat 56. The valve member 54 is, for example, piston-shaped and is urged in the closing direction by a valve spring 58. Furthermore, an electric actuator 60 is provided, by which the movement of the valve member 54 can be influenced and which is controlled by the control device 22. The electric actuator 60 can, for example, be an electromagnet having a stationary magnetic coil 61 and a movable magnetic armature 62 connected to the valve member 54.

[0014] Various methods are possible for implementing a variable delivery rate of the high-pressure fuel pump 16 using the inlet valve 48. In a first method, the inlet valve 48 is constantly open during the suction stroke of the pump piston 26, so that the pump working chamber 46 is fully filled with fuel. During the delivery stroke of the pump piston 26, the inlet valve 48 is closed at a time when the amount of fuel to be delivered by the high-pressure fuel pump 16 into the high-pressure fuel accumulator 18 is present in the pump working chamber 46. If only a small amount of fuel is to be delivered by the high-pressure fuel pump 16, the inlet valve 48 is opened or held open at the beginning of the delivery stroke of the pump piston 26, so that the pump piston 26 initially pumps fuel from the pump working chamber 46 back into the inlet and not into the high-pressure fuel accumulator 18.Only when the inlet valve 48 is closed does fuel flow through the pump piston 26 into the high-pressure fuel reservoir 18. If a large amount of fuel is to be delivered by the high-pressure fuel pump 16, the inlet valve 48 is closed at the beginning of the delivery stroke of the pump piston 26, so that fuel is delivered by the pump piston 26 into the high-pressure fuel reservoir 18. The start of delivery by the pump piston 26 and thus the fuel delivery rate is controlled by the inlet valve 48. Alternatively, it can also be provided that the delivery end of the pump piston 26 is controlled by the inlet valve 48, in that it is opened when the required amount of fuel has been delivered by the pump piston 26.

[0015] In a second method, the filling of the pump working chamber 46 with fuel is varied by the inlet valve 48 during the suction stroke of the pump piston 26. It can be provided that the inlet valve 48 is open during the entire suction stroke or only during part of the suction stroke of the pump piston 26, whereby the filling of the pump working chamber 46 and thus the fuel delivery rate of the high-pressure fuel pump 16 can be varied. If a large amount of fuel is to be delivered by the high-pressure fuel pump 16, the inlet valve 48 is open during the entire suction stroke of the pump piston 26, and if only a small amount of fuel is to be delivered, the inlet valve 48 is only open during part of the suction stroke of the pump piston 26.If no fuel is to be delivered by the high-pressure fuel pump 16, the inlet valve 48 remains closed during the suction stroke of the pump piston 26. Alternatively, it can also be provided that the inlet valve 48 can be opened with a variable opening cross-section. A variable opening cross-section of the inlet valve 48 can be achieved in particular by a variable opening stroke of the valve member 54. If a large amount of fuel is to be delivered by the high-pressure fuel pump 16, the inlet valve 48 is opened with a large opening cross-section; if a small amount of fuel is to be delivered by the high-pressure fuel pump 16, the inlet valve 48 is opened with a small opening cross-section; and if no fuel is to be delivered by the high-pressure fuel pump 16, the inlet valve 48 remains closed.

[0016] In the method according to the invention for operating the high-pressure fuel pump 16, it is provided that when the internal combustion engine is started, at least substantially no fuel is delivered into the high-pressure fuel accumulator 18, at least during the first delivery stroke of the pump piston 26 or during the first delivery stroke and at least one further subsequent delivery stroke of the pump piston 26 of the at least one pump element 24. This is achieved in that the inlet valve 48 is open in the first method described above, at least during part of the first delivery stroke or during at least part of the first delivery stroke and at least one further subsequent delivery stroke of the pump piston 26, so that fuel is only delivered back into the inlet by the pump piston 26 under pressure.

[0017] In the second method described above, during the starting of the internal combustion engine during the first intake stroke or during the first intake stroke and at least one following intake stroke of the pump piston 26 of the at least one pump element 24, the inlet valve 48 is closed at least over part of the intake stroke or is opened only with a small opening cross-section, so that the pump working chamber 46 is not filled or is only filled to a small extent and during the following first delivery stroke or during the following first delivery stroke and at least one further following delivery stroke of the pump piston 26, no fuel is delivered by the latter into the high-pressure fuel accumulator 18.

[0018] When the internal combustion engine 10 is started, a lubricating film can form between the roller 38 and the recess 36 due to the low load caused by the lack of delivery pressure, thus minimizing friction and wear on these parts. After the internal combustion engine 10 is started, when sufficient lubrication has developed between the roller 38 and the recess 36, fuel is delivered by the high-pressure fuel pump 16.

[0019] It can be provided that after the internal combustion engine 10 is switched off, the pressure prevailing in the high-pressure fuel reservoir 18 is kept high enough to be sufficient for fuel injection by the at least one fuel injector 20. The at least one fuel injector 20 connected to the high-pressure fuel reservoir 18 preferably has no leaks, so that no fuel can escape from the high-pressure fuel reservoir 18. When the internal combustion engine 10 is subsequently started, fuel is injected by the at least one fuel injector 20 using the fuel stored in the high-pressure fuel reservoir 18. After one or more delivery strokes after the internal combustion engine 10 has been started, the high-pressure fuel pump 16 again delivers fuel to the high-pressure fuel reservoir 18, so that a sufficiently high pressure is generated in the high-pressure fuel reservoir 18.It may be provided that the pressure in the high-pressure fuel reservoir 18 is maintained sufficiently high for fuel injection only during a relatively brief shutdown of the internal combustion engine 10, as is effected by a so-called start-stop system when the motor vehicle is stationary. If the internal combustion engine 10 is shut down using the ignition key or another shutdown device, it may be provided that the pressure in the high-pressure fuel reservoir 18 is reduced. This may be necessary to enable safe removal of the high-pressure fuel reservoir 18 during servicing or repair work.

[0020] It can be provided that the high-pressure fuel pump 16 has a plurality of pump elements 24, in which the pump pistons 26 execute their delivery and suction strokes one after the other and in which an electrically operated valve 48 is present for each pump element 24. The methods described above for reducing the load on the high-pressure fuel pump 16 when starting the internal combustion engine 10 can be carried out on each pump element 24, or it can be provided that the methods are carried out only on one of the pump elements 24 or alternately on a different one of the pump elements 24 in order to distribute the load evenly and still enable fuel to be pumped into the high-pressure fuel reservoir 18.

Claims

[1] A method for operating a high-pressure fuel pump of a fuel injection device of an internal combustion engine, wherein the high-pressure fuel pump (16) has at least one pump element (24), wherein the pump element (24) has a pump piston (26) which is driven in a reciprocating movement at least indirectly by the internal combustion engine (10) via a tappet (32), which pump piston delimits a pump working chamber (46) which can be connected to an inlet or a relief region by an electrically controlled valve (48), wherein fuel is pumped by the high-pressure fuel pump (16) into a high-pressure fuel reservoir (18) to which at least one fuel injector (20) is connected, and wherein the fuel injection device has an electronic control device (22) by which the valve (48) and the at least one fuel injector (20) are controlled, characterized bythat when starting the internal combustion engine (10) during a first delivery stroke or during a first delivery stroke and at least one subsequent initial delivery stroke of the pump piston (26) of the at least one pump element (24), no fuel is delivered by the pump piston (26) into the high-pressure fuel reservoir (18). [2] Method according to claim 1, characterized by that the valve (48) is opened by the control device (22) when the internal combustion engine (10) is started, at least during a part of the first delivery stroke or at least during a part of the first delivery stroke and at least one following initial delivery stroke of the pump piston (26). [3] Method according to claim 1, characterized bythat the valve (48) is closed by the control device (22) when starting the internal combustion engine (10) at least during a part of a first intake stroke or at least during a part of the first intake stroke and at least one following initial intake stroke of the pump piston (26). [4] Method according to claim 1, characterized by that the valve (48) is opened by the control device (22) with a small opening cross-section at least during part of a first intake stroke or at least during part of a first intake stroke and at least one subsequent initial intake stroke of the pump piston (26) when the internal combustion engine (10) is started. [5] Method according to one of claims 1 to 4, characterized bythat when the internal combustion engine (10) is switched off or at least switched off briefly, a pressure sufficient for fuel injection by the at least one fuel injector (20) is maintained in the high-pressure fuel accumulator (18). [6] Method according to one of the preceding claims, characterized by that the tappet (32) is a roller tappet which comprises a roller shoe (34) and a roller (38) rotatably mounted in a recess (36) of the roller shoe (34). [7] Method according to one of the preceding claims, characterized bythat the high-pressure fuel pump (16) has a plurality of pump elements (24), each with a pump piston (26) and an electrically controlled valve (48), that the pump pistons (26) of the pump elements (24) carry out their delivery and suction strokes one after the other, and that only in one of the pump elements (24) or in all of the pump elements (24) or alternately in different ones of the pump elements (24) when the internal combustion engine (10) is started during a first delivery stroke or during a first delivery stroke and at least one following initial delivery stroke of the pump piston (26) no fuel is delivered by the pump piston (26) into the high-pressure fuel reservoir (18).

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