Method for operating a fuel injection system of an internal combustion engine

Abstract

A method for operating a fuel injection system of an internal combustion engine is disclosed. The fuel injection system comprises a high pressure accumulator (rail) and a high-pressure fuel pump with a digital inlet valve and which guides fuel into the high pressure accumulator. The number of the control pulses for the digital inlet valve and thus the number of the pump delivery strokes is reduced with respect to the number of the injection steps of an injector of the injection system, in order to thereby reduce the noise and the energy consumption of the high-pressure pump.

Claims

1. A method for operating a fuel injection system of an internal combustion engine, which fuel injection system has at least one fuel injector coupled to a high pressure rail and a high pressure fuel pump which feeds fuel into the high pressure rail and has a digital inlet valve, the method comprising: operating the fuel injection system according to a first control protocol, comprising: controlling the at least one fuel injector to perform a first plurality of injection processes, and activating the digital inlet valve of the high pressure fuel pump using a number of first actuation pulses corresponding to the number of the first plurality of injection processes, wherein each first actuation pulse opens the digital inlet valve to permit a pump feed by the high pressure fuel pump, automatically switching over to a rail pressure control protocol for the fuel injection system in response to a predefined engine operation event, and operating the fuel injection system according to the rail pressure control protocol, comprising: controlling the at least one fuel injector to perform a second series of injection processes, and activating the digital inlet valve of the high pressure fuel pump using a number of second actuation pulses that is less than the number of the second plurality of injection processes, wherein each second actuation pulse opens the digital inlet valve to permit a pump feed by the high pressure fuel pump.

2. The method of claim 1, wherein the number of second actuation pulses is reduced as a function of a predefined minimum rail pressure limiting value or rail pressure range corresponding to emission limiting values of the internal combustion engine.

3. The method of claim 2, wherein the predefined minimum rail pressure limiting value or rail pressure range is determined by trials in an engine development phase.

4. The method of claim 1, wherein the number of second actuation pulses is reduced as a function of an operating state of the internal combustion engine.

5. The method of claim 1, wherein according to the rail pressure control protocol, the high pressure pump is actuated such that after one or more injection processes without a corresponding activation of the digital inlet valve, a subsequent actuation pulse is generated that causes a pump feed having an increased quantity of fuel to compensate for a pressure loss resulting from the one or more injection processes without a corresponding activation of the digital inlet valve.

6. The method of claim 1, wherein the method is performed only during operation of the engine in specific areas of an engine characteristic diagram.

7. The method of claim 6, wherein a corresponding engine characteristic diagram is implemented in an engine control device in order to switch the rail pressure control protocol from the first control protocol to the rail pressure control protocol.

8. The method of claim 1, further comprising: calculating a pressure drop associated with a representative injection process, and reducing the number of second actuation pulses as a function of (a) the predefined rail pressure limiting value or rail pressure range and (b) the calculated pressure drop.

9. The method of claim 1, wherein: the high pressure fuel pump has a digital outlet valve in addition to the digital inlet valve, and the method comprises activating—the digital outlet valve in a manner analogous to the activation of the digital inlet valve.

10. A fuel injection system of an internal combustion engine, the fuel injection system comprising: at least one fuel injector coupled to a high pressure rail, a high pressure fuel pump which feeds fuel into the high pressure rail and has a digital inlet valve, and a control device configured to: operate the fuel injection system according to a first control protocol, comprising: controlling the at least one fuel injector to perform a first plurality of injection processes, and activating the digital inlet valve of the high pressure fuel pump using a number of first actuation pulses corresponding to the number of the first plurality of injection processes, wherein each first actuation pulse opens the digital inlet valve to permit a pump feed by the high pressure fuel pump, automatically switch over to a rail pressure control protocol for the fuel injection system in response to a predefined engine operation event, and operate the fuel injection system according to the rail pressure control protocol, comprising: controlling the at least one fuel injector to perform a second series of injection processes, and activating the digital inlet valve of the high pressure fuel pump using a number of second actuation pulses that is less than the number of the second plurality of injection processes, wherein each second actuation pulse opens the digital inlet valve to permit a pump feed by the high pressure fuel pump.

11. The fuel injection system of claim 10, wherein the number of second actuation pulses is reduced as a function of a predefined minimum rail pressure limiting value or rail pressure range corresponding to emission limiting values of the internal combustion engine.

12. The fuel injection system of claim 11, wherein the predefined minimum rail pressure limiting value or rail pressure range is determined by trials in an engine development phase.

13. The fuel injection system of claim 10, wherein the number of second actuation pulses is reduced as a function of an operating state of the internal combustion engine.

14. The fuel injection system of claim 10, wherein according to the rail pressure control protocol, the control device is configured activate the high pressure pump such that after one or more injection processes without a corresponding activation of the digital inlet valve, a subsequent actuation pulse is generated that causes a pump feed having an increased quantity of fuel to compensate for a pressure loss resulting from the one or more injection processes without a corresponding activation of the digital inlet valve.

15. The fuel injection system of claim 10, wherein the control device is configured to switch to the rail pressure control protocol only during operation of the engine in specific areas of an engine characteristic diagram.

16. The fuel injection system of claim 15, wherein the control device implements a corresponding engine characteristic diagram in order to switch the rail pressure control protocol from the first control protocol to the rail pressure control protocol.

17. The fuel injection system of claim 10, wherein the control device is further configured to: calculate a pressure drop associated with a representative injection process, and reduce the number of second actuation pulses as a function of (a) the predefined rail pressure limiting value or rail pressure range and (b) the calculated pressure drop.

18. The fuel injection system of claim 10, wherein: the high pressure fuel pump has a digital outlet valve in addition to the digital inlet valve, and the control device is further configured to activate the digital outlet valve in a manner analogous to the activation of the digital inlet valve.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) An example embodiment of the disclosed method is described below with reference to FIG. 1, which shows a schematic block diagram of the individual method steps.

DETAILED DESCRIPTION

(2) Embodiments of the invention provide a method for operating a fuel injection system of the type described at the beginning, which method permits particularly low-noise operation of the high pressure fuel pump with simple means.

(3) In the fuel injection systems described above, the high pressure fuel pump usually feeds synchronously with the injection, i.e. a pump feed stroke, which compensates the quantity lost by the injection and possibly present leakages, occurs at each injection or proceeds simultaneously.

(4) The presently disclosed method departs from this. According to the disclosed method, a non-injection-synchronous pump feed is carried out in a targeted fashion. In other words, the number of actuation pulses for the digital inlet valve at the high pressure pump is reduced compared to the number of injection processes, which gives rise to a reduction in the noise emission by the digital inlet valve and leads to a reduction in the energy required by the actuation. As a result of the reduction of the switching frequency, the number of load cycles (number of valve movements plotted over the service life) is decreased, which also has a positive effect on the durability of the high pressure pump or of the inlet valve. It was determined by trials that a reduction in noise of approximately 4 dB (A) is already achieved by dispensing with a switching process compared to the known injection-synchronous activation of the inlet valve.

(5) The number of actuation pulses is preferably reduced taking into account a rail pressure limiting value or rail pressure range which is to be complied with as a function of emission limiting values of the internal combustion engine.

(6) In this variant of the method according to the invention, it is taken into account that the number of actuation pulses for the digital inlet valve and therefore the number of pump feed strokes is reduced compared to the number of injection processes only to such an extent that as a result a rail pressure limiting value or rail pressure range which results from emission limiting values of the internal combustion engine is complied with. Such emission limiting values, for example those from exhaust gas legislation (EU4, EU5, EU6 etc.), and the resulting rail pressure limiting values or rail pressure ranges are known or can be calculated or determined by trials. For example, combustion testing with diesel common rail injection systems shows that a motor-dependent deviation of up to 16% from the pressure setpoint for reaching the current emission limit (EU6) can be permissible. If such a rail pressure limiting value or rail pressure range has been determined, according to the invention it is possible to proceed in such a way that the number of saved actuation pulses is increased successively during the operation of the internal combustion engine until the corresponding rail pressure limiting value or the lower limit of the rail pressure range is reached, after which the inlet valve is actuated again in order to start the feeding again.

(7) In this context, the number of actuation pulses is preferably reduced as a function of the operating state of the internal combustion engine and therefore of the requested injection quantity and/or possibly present leakage. For example, the number of actuation pulses is reduced during idling or under partial load.

(8) The high pressure pump is actuated in such a way that after the reduction of the number of actuation pulses a quantity of fuel is fed which is larger in comparison, in order to compensate for the pressure loss.

(9) In one specific embodiment of the method according to the invention, the rail pressure limiting value or rail pressure range which is to be complied with is determined by trials for each internal combustion engine in the development phase thereof. During subsequent operation of the internal combustion engine, the digital inlet valve of the high pressure pump is then actuated in such a way that at least one switching process of the inlet valve is saved, without the rail pressure limiting value which is determined by trials or the corresponding rail pressure range being undershot or exited.

(10) As already mentioned, the method according to the invention is preferably carried out only in specific parts of the engine characteristic diagram such as during idling or under partial load.

(11) In order to provide a switching facility with which it is possible to switch from injection-synchronous actuation of the inlet valve to non-injection-synchronous actuation, a corresponding engine characteristic diagram is expediently implemented in the engine control device. In this way, the rail pressure control strategy according to the invention can be carried out.

(12) In another variant of the method according to the invention, a pressure drop which is brought about by the injection is calculated in advance, and as a result a rail pressure limiting value or rail pressure range which is to be complied with and above which or within which the feeding by the pump is deactivated temporarily by reducing the actuation pulses is defined. In this context, the pressure reduction as a result of the injection can be calculated in advance by means of the injection quantity calculated by the engine control device, using the physical relationship
Pressure drop=compression modulus of the fuel×change in volume at high pressure/total high pressure volume.
the corresponding engine-specific data such as high pressure volume and fuel-specific data are stored in the engine control device here.

(13) Through the corresponding deactivation of the digital inlet valve, the noise emissions are reduced in correspondingly relevant operating states, in particular during idling. In addition, this contributes to reducing the energy requirement. The number of valve switching operations over the service life also decreases.

(14) The method according to the invention can also be applied in an injection system in which the high pressure fuel pump has a digital outlet valve in addition to the digital inlet valve. In this context, the digital outlet valve is actuated in a way which is analogous to the digital inlet valve.

(15) A combination of the method according to the invention with existing noise reducing measures, for example the whispering function, for actuating the digital inlet valve of the high pressure pump is possible.

(16) In step 1 of the method according to the invention, a limiting value for the rail pressure as far as which the rail pressure can drop is determined by trials, without corresponding emission limiting values from the exhaust gas legislation, for example EU6, being exceeded as a result. The corresponding limiting value or limiting range for the rail pressure is stored in the engine control device. In addition, in step 2 a corresponding characteristic diagram is implemented as a function of, for example, the engine speed and the injection quantity etc., in order to permit switching to the rail pressure control strategy according to the invention.

(17) During the operation of the fuel injection system or of the corresponding vehicle, in step 3 of the method according to the invention switching over is performed to the rail pressure control strategy according to the invention if the engine is, for example, in the idling mode.

(18) In this context, the feeding of fuel by the high pressure pump, i.e. the actuation of the digital inlet valve of the high pressure pump, is not implemented until the stored rail pressure limiting value is reached. This may involve, for example, one, two or more feed strokes, with the result that one, two or more switching processes for the inlet valve are dispensed with. The implementation of the rail pressure strategy according to the invention by deactivating the inlet valve until the rail pressure limiting value is reached takes place in step 4.

(19) If the stored limiting value for the rail pressure is reached, the digital inlet valve of the high pressure pump is activated again, and a quantity of fuel which is larger in comparison is fed into the rail in order to compensate more quickly for the pressure loss which has occurred. This is illustrated in step 5.