Method for operating an injection system for fuel

Abstract

The invention relates to a method for operating an injection system (1) for injecting fuel into the combustion chamber (4) of an internal combustion engine (2), wherein the injection system (1) has a number of high-pressure injectors (11) for direct injection of fuel, and also has a number of low-pressure injectors (10) for indirect injection, wherein the injection system (1) can be operated selectively in a direct injection mode in which the fuel is metered by means of the high-pressure injectors (11), or in an indirect injection mode in which the fuel is metered by means of the low-pressure injectors (10), the method for operating the injection system (1) comprising the following steps: - checking, at specified times, the injection mode in which the injection system (1) is operating, and - if the injection system (1) is operating in the indirect injection mode, applying at least one test pulse to an electric drive of at least one high-pressure injector (11) and analyzing a response pulse in the control line.

Description

[0001] Description

[0002] Method for operating a fuel injection system

[0003] The present invention relates to a method for operating an injection system for injecting fuel into the combustion chamber of an internal combustion engine.

[0004] In internal combustion engines whose cylinders are supplied with fuel via a high-pressure line, such as common rail systems, the injected fuel quantity is controlled by the opening duration of the respective injector. Since even small variations in the opening duration have a significant impact on the injected fuel quantity, especially in the case of high-pressure lines, precise knowledge of the injector's opening behavior is important for precise control of the injection process.

[0005] It is therefore known, for example from WO 2015 / 176858 A1, to carry out test controls of the injector from time to time during operation of the combustion engine.

[0006] To do this, the injector, especially an electromagnetic injector, is triggered with a test pulse so short that the opening process is not completed and, in particular, no fuel is injected. The response pulse from the control line is then evaluated to determine the opening point. For particularly precise fuel metering using a high-pressure injector, it is advantageous to know its exact opening point.

[0007] Applying test pulses to the system is therefore advantageous for precise control of the injection system. A problem can be that the pressure at the high-pressure injector is subject to strong fluctuations, which reduces the informative value of test pulses. Furthermore, controlling and evaluating the test pulse requires system capacity. Furthermore, it can be problematic to accommodate test pulses in addition to the injection pulses within the available time window. Therefore, it is an object of the present invention to provide a method for operating a fuel injection system of an internal combustion engine, with which the injection process can be controlled as precisely as possible.

[0008] This problem is solved by the subject matter of the independent claim. Advantageous embodiments and further developments are the subject matter of the dependent claims.

[0009] According to one aspect of the invention, a method is provided for operating an injection system for injecting fuel into the combustion chamber of an internal combustion engine, wherein the injection system has a number of high-pressure injectors for direct fuel injection and a number of low-pressure injectors for intake manifold injection. The injection system can be operated selectively in a direct injection mode, in which the fuel is metered by means of the high-pressure injectors, or in an intake manifold injection mode, in which the fuel is metered by means of the low-pressure injectors.

[0010] The method for operating the injection system includes checking at predetermined times which injection mode the injection system is in. Furthermore, it includes applying at least one test pulse to an electric drive of at least one high-pressure injector and evaluating a response pulse from the control line if the injection system is in intake manifold injection mode.

[0011] Injector test activation is understood here and below to mean an event in which the injector is activated to open in order to test the injector's opening behavior, but not to perform an injection. The injector is therefore only activated for a very short time interval with the intention of testing the injector's opening behavior, but not to move the needle far enough to inject fuel. A test pulse is understood to be the signal sent to the injector's drive for test activation.

[0012] The method has the advantage that test activations of the high-pressure injectors are only performed, or preferably, when the injection system is in intake manifold injection mode, i.e., the actual fuel metering is performed using the low-pressure injectors of the intake manifold injection. This has the advantage that constant pressure conditions prevail at the high-pressure injector during the test activations. Furthermore, the test activations are performed at a time when both the high-pressure injectors themselves and the control system have sufficient capacity, because they are not currently being used for fuel metering.

[0013] The test pulse also does not adversely affect the actual injection process, as there is sufficient time after the test pulse to dissipate any residual magnetization on the injector coil. The test pulse therefore does not compete with control pulses used for fuel metering.

[0014] For injection systems that also allow combinations of intake manifold injection and direct injection, ie simultaneous injection by both low-pressure injectors into the intake manifold and by high-pressure injectors directly into the combustion chamber, the condition for test activation that the system is in intake manifold injection mode is considered to be fulfilled if injection takes place exclusively into the intake manifold.

[0015] According to one embodiment, the response pulse of the control line is evaluated to determine an opening time of the high-pressure injector.

[0016] A test pulse can have a duration of, for example, 150 ps or slightly more. Typical durations are 150 to 330 microseconds, often less than 350 microseconds. The duration is preferably chosen so short that no fuel is injected. Thus, the test pulse does not affect the combustion process.

[0017] According to one embodiment, the application of at least one test pulse to the electric drive of at least one high-pressure injector is aborted if the pressure at the high-pressure injector changes beyond a predetermined level. In this embodiment, a significant change in the pressure conditions at the high-pressure injector is responded to by initially not sending any further test pulses to the electric drive, as their significance would be limited anyway due to the pressure fluctuations.

[0018] The injection system can, in particular, have a multi-point injection system in which each cylinder is supplied with fuel by its own injection valve. The invention utilizes the fact that in systems that can operate in both direct injection mode and intake manifold injection mode, advantageous conditions for performing test activations of the high-pressure injector are available during intake manifold injection.

[0019] According to a further aspect of the invention, a computer program product is provided, comprising instructions that, when executed by a computer, cause the computer to perform the described method. The computer may, in particular, be a control unit of a vehicle, in particular a control device for controlling the injection system, which may, for example, be integrated into an engine control unit.

[0020] According to a further aspect of the invention, a computer-readable medium is provided, comprising instructions which, when executed by a computer, cause the computer to perform the described action.

[0021] Embodiments of the invention are described below by way of example with reference to schematic drawings.

[0022] Figure 1 shows an injection system that can be operated with the method according to an embodiment of the invention and

[0023] Figure 2 shows a diagram of the pressure curve at high-pressure injectors of the injection system according to Figure 1.

[0024] Figure 1 shows an injection system 1 for an internal combustion engine 2 (not shown in detail). The injection system 1 serves to inject fuel into the combustion chamber 4 of the internal combustion engine 2. Figure 1 shows, by way of example only, a cylinder 3 of the internal combustion engine 2 with a combustion chamber 4 and a piston 5 movable within the combustion chamber 4. Thus, only a section of the internal combustion engine 2 is shown.

[0025] Connected to cylinder 3 are an intake manifold 6 and an exhaust pipe 7. The intake manifold 6 communicates with the combustion chamber 4 of cylinder 3 via an intake valve 8. The exhaust pipe 7 communicates with the combustion chamber 4 via an exhaust valve 9. During operation, fuel and combustion air are drawn into the combustion chamber 4, and the mixture is ignited by an ignition device 12. Two different options are available for metering fuel in the injection system 1 shown in Figure 1:

[0026] In a manifold injection mode, the fuel is injected into the intake manifold 6 by a low-pressure injector 10. In a direct injection mode, however, the fuel is injected directly into the combustion chamber 4 by a high-pressure injector 11. The injection system 1 therefore has both low-pressure injectors 10 for injecting fuel into the intake manifold 6 and high-pressure injectors 11 for injecting fuel into the combustion chamber 4.

[0027] A control device 13 controls both the low-pressure injector 10 and the high-pressure injector 11 and, in addition, the ignition device 12 as well as the inlet valve 8 and the outlet valve 9.

[0028] A motor vehicle with the injection system 1 shown in Figure 1 can be operated in both a manifold injection mode and a direct injection mode. The selected injection mode depends, in particular, on the currently required power. In particular, manifold injection exhibits better emission values ​​than direct injection in the medium load range, while direct injection can reduce knocking of the internal combustion engine 2 in the full load range.

[0029] Figure 2 shows the pressure curve at the high-pressure injector 11 over time. The dashed curve represents the pressure curve in a manifold injection mode, and the solid curve represents the pressure curve in a direct injection mode.

[0030] As can be seen in Figure 2, the pressure at the high-pressure injector 11 exhibits strong temporal fluctuations in direct injection mode. In contrast, in the intake manifold injection mode, the pressure at the high-pressure injector 11 increases gradually and remains constant for a calculable period of time.

[0031] Therefore, periods in which the injection system 1 is operated in the intake manifold injection mode are particularly well suited for performing test activations of the high-pressure injector 11. Accordingly, it is provided that the control device 13 checks which injection mode the injection system 1 is currently in.

[0032] If it is in intake manifold injection mode, the electric drive of the high-pressure injector 11 can be subjected to a test pulse to perform a test control of the high-pressure injector 11. A response pulse from the control line is then evaluated by the control device 13 to obtain information about the opening behavior of the high-pressure injector 11, in particular the exact opening time.

[0033] List of reference symbols

[0034] 1 injection system

[0035] 2 internal combustion engines 3 cylinders

[0036] 4 combustion chamber

[0037] 5 pistons

[0038] 6 intake manifold

[0039] 7 Exhaust pipe 8 Inlet valve

[0040] 9 Exhaust valve

[0041] 10 Low pressure injector

[0042] 11 High-pressure injector

[0043] 12 Ignition device 13 Control device

Claims

Patent claims 1. A method for operating an injection system (1) for injecting fuel into the combustion chamber (4) of an internal combustion engine (2), wherein the injection system (1) comprises a number of high-pressure injectors (11) for direct injection of fuel and further a number of low-pressure injectors (10) for intake manifold injection, wherein the injection system (1) is selectively operable in a direct injection mode in which the fuel metering is effected by means of the high-pressure injectors (11), or in an intake manifold injection mode in which the fuel metering is effected by means of the low-pressure injectors (10), wherein the method for operating the injection system (1) comprises the following: - Check at specified times which injection mode the injection system (1 ) is in and - Actuating an electric drive of at least one high-pressure injector (11 ) with at least one test pulse and evaluating a response pulse of the control line if the injection system (1 ) is in the intake manifold injection mode.

2. Method according to claim 1, wherein the response pulse of the control line is evaluated in order to determine an opening time of the high-pressure injector (11).

3. The method according to claim 1 or 2, wherein the at least one test pulse has a duration of at most 350 microseconds, in particular from 150 to 330 microseconds.

4. Method according to one of claims 1 to 3, wherein the application of at least one test pulse to the electric drive of at least one high-pressure injector (11) is interrupted if the pressure at the high-pressure injector (11) changes beyond a predetermined amount.

5. Method according to one of claims 1 to 4, wherein the injection system (1) has a multi-point injection.

6. A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 5.

7. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 5.

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