Method for testing an injection system of an internal combustion engine

Abstract

The invention relates to a method for testing an injection system (1) of an internal combustion engine, wherein the injection system (1) has a collective pressure line (2) which is designed to allow flow through an injector (3), wherein - in a first step, a build-up pressure (p A ) in the injection system (1) using a test medium which is introduced into the injection system (1), - in a second step, after the build-up pressure (p A ) is applied, the injection system (1) is closed pressure-tight, - in a third step within a time interval (PI), which is between a start time (t S ) a measurement and an end time (t E ) the measurement is located, a desired number of injections (E) of the injector (3) are carried out, whereby a pressure (p) in the injection system (1) is measured, - in a fourth step, a result of the measurement is analyzed, and if a pressure increase (Δp) is detected, this is factored out to obtain a corrected result without this pressure increase (Δp), - in a fifth step, if no pressure increase (Δp) was detected, the result is compared, or if a pressure increase (Δp) was detected, the adjusted result is compared with a limit value.

Description

[0001] The invention relates to a method for testing an injection system of an internal combustion engine according to the preamble of claim 1.

[0002] Fuel injection systems for internal combustion engines with a manifold for fuel injection are known. Each cylinder of the internal combustion engine is assigned one injector, which is connected to the manifold, generally referred to as the fuel rail or fuel pressure line, and the manifold has at least two injectors. A fluid to be supplied to the cylinder for combustion is pressurized in the manifold and is fed to the cylinder via the injector according to a corresponding injection timing.

[0003] To achieve legally mandated current and future emission limits, measures are required in the operation of the internal combustion engine, which can be implemented using fuel injection. One example is extending stoichiometric operation of the internal combustion engine across its entire operating range. This means that substoichiometric operation, also known as "rich" operation, should no longer be used to enrich the mixture for component protection. To this end, water is introduced into the combustion chamber of the internal combustion engine, instead of the previous fuel cooling method, particularly in the high-load and / or high-speed range, to cool the mixture and reduce knocking.

[0004] For example, water can be injected into the combustion chamber, with the water and fuel only mixing within the combustion chamber. In this process, the fuel and water are supplied to the combustion chamber via injection systems. The problem is that both fuel and water injection systems can become dirty or clogged, or injectors can be damaged. This leads to insufficient operation of the internal combustion engine.

[0005] German patent application DE 10 2018 204 551 A1 discloses a method for verifying the correct function of injectors in a water injection system of an internal combustion engine, in which pressure is built up in the water injection system and injectors inject a defined quantity of water, with the pressure drop in the rail being measured. The result is compared against a threshold value.

[0006] German patent application DE 10 2013 214 910 A1 describes a fuel injection system in which a fuel leakage quantity is calculated using a temperature in the area of ​​the injector.

[0007] German patent application DE 10 2018 203 542 A1 discloses a method for checking for leaks in water injection injectors. In this method, the injection system is filled with water and then sealed. Pressure and temperature are measured at a first time point and again at a second time point, and the leakage quantity is determined from these measurements.

[0008] German patent application DE 10 2020 213 389 A1 discloses a method for diagnosing a water injection system, wherein the water injection system has a pressure chamber for water, which is connected to a pump for generating water pressure and several injection valves. With the pump switched off, the several injection valves are actuated sequentially and a pressure drop resulting from the actuation of the injection valves is measured.

[0009] German patent application DE 10 2016 200 694 A1 discloses a method for calibrating a water pressure sensor of a water injection system for an internal combustion engine, wherein the water injection system comprises a pumping element and at least one water injector. Water located in the water injector and the pipework is drawn in by the pumping element, and then the water injector is opened, allowing air to enter the water injector and the pipework. Subsequently, the pumping element is switched off and the water injector is closed. Finally, the actual pressure of the air drawn in by the water injector is determined using the water pressure sensor and compared with a target pressure. The water pressure sensor is then calibrated if a measurement inaccuracy is detected, specifically if the pressure deviation between the measured actual pressure and the target pressure is less than or greater than zero.

[0010] The object of the present invention is to provide an improved method for testing an injection system of an internal combustion engine.

[0011] The object of the invention is achieved by a method for testing an injection system of an internal combustion engine with the features of claim 1. Advantageous embodiments with expedient and non-trivial further developments of the invention are specified in the respective dependent claims.

[0012] A method according to the invention for testing an injection system of an internal combustion engine, wherein the injection system has a manifold pressure line which is designed to allow flow through an injector, is characterized in that - In a first step, a build-up pressure is carried out in the injection system using a test medium which is introduced into the injection system, - in a second step, after the pressure build-up has occurred, the collecting pressure line is closed pressure-tight, - in a third step, within a time interval between the start time of a measurement and the end time of the measurement, a desired number of injector injections are carried out, whereby a pressure in the manifold pressure line is measured, - in a fourth step, a measurement result is analyzed, and if a pressure increase is detected, this is factored out to produce a corrected result without this pressure increase, - in a fifth step, if no pressure increase was detected, the result is compared, or if a pressure increase was detected, the adjusted result is compared with a limit value.

[0013] The advantage of the method according to the invention lies in the fact that it eliminates the heating of the injection system, which is detectable in the pressure curve measured during the test interval by a pressure increase, thus ensuring an unadulterated test result. For example, if the internal combustion engine is switched off during the test while idling, and it was previously operated in such a way that it became "hot," the injection system also heats up and the pressure in the injection system rises. This pressure increase leads to an incorrect test result.

[0014] The injection system can comprise one or more injectors. If it comprises more than one injector, steps one, two, three, and four are repeated sequentially according to the number of injectors to measure each injector. In the fifth step, a relative analysis of the results for each injector is additionally performed. In other words, all injectors in the injection system are tested individually, and the measurement results are compared relative to each other. This allows for a more accurate diagnosis of which injectors are contaminated or damaged.

[0015] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. The figures show: Fig. 1. In a schematic diagram, an injection system according to the state of the art, and Fig. 2 in a pressure-time diagram a pressure profile in the injection system over a test period of a method according to the invention.

[0016] An injection system 1 for an internal combustion engine not shown in detail, which in the present embodiment is designed in the form of an injection system 1 for water injection, comprising a manifold pressure line 2 and injectors 3 which are connected to the manifold pressure line 2 in a flow-through manner, is according to Fig. Figure 1, in which the injection system 1 is shown in a schematic diagram, is constructed. Typically, the number of injectors 3 corresponds to the number of cylinders of the internal combustion engine, whereby in the present schematic embodiment, the internal combustion engine would have three cylinders. Likewise, the manifold pressure line 2 could also be configured to supply a different number of injectors.

[0017] The manifold pressure line 2, as a central hydraulic component, connects a conveying medium 4 for conveying an injection medium, which in this exemplary embodiment is water. However, the injection system 1 could also be a fuel injection system, in which case the injection medium would be fuel.

[0018] The manifold pressure line 2 is hollow to allow flow through it, whereby the injection medium is pumped into the manifold pressure line 2 and thus builds up a specific pressure, which is referred to below as the build-up pressure pA. A pressure line 5, which connects the manifold pressure line 2 to the conveying medium 4, is also hollow to allow flow through it.

[0019] The manifold pressure line 2 is closed at its first end 6 and at its second end 7, which is located away from the first end 6, it is designed to allow flow through it to the pressure line 5. The pressure line 5 could also be connected to the manifold pressure line 2 at another point, allowing flow through it.

[0020] To test the mass flow rate of the injectors 3, or in other words, to test for possible contamination or clogging of the injectors 3, or any other defect of the injectors 3, such as damage that prevents the mass flow rate to be achieved, the following procedure for testing the injection system 1 of the internal combustion engine is proposed.

[0021] The method according to the invention is carried out in a so-called running internal combustion engine, or in other words, the internal combustion engine is in operation.

[0022] In Fig. 2 is a pressure curve D over a time t in a pressure-time diagram within a test interval PI of the test of one of the injectors 3, which begins at a start time ts and ends at an end time t E ends, applied.

[0023] At the beginning of the inventive method, water, which is intended for testing and can therefore be referred to as the test medium, is injected into the collecting pressure line 2 of the injection system 1 until the build-up pressure p A in the collective pressure line 2. This build-up pressure p A This typically corresponds to a pressure at the start time ts, which is also known as the start pressure p. S can be described.

[0024] A shut-off device 8 of the injection system 1, which is designed in the form of a conventional shut-off valve and is designed upstream of the injectors 3 to close the manifold pressure line 2 in a pressure-tight manner, is closed, which means in other words that a further supply of the manifold pressure line 2 with the test medium is prevented, thus making it impossible during the testing of the respective injector 3.

[0025] Subsequently, the injector under test injects a specific quantity of water three times into an injection chamber associated with the internal combustion engine, whereby a pressure drop in the manifold pressure line 2 is measured. In the present embodiment, the injector 3 under test has a first injection E1 with a first injection quantity, a second injection E2 with a second injection quantity, a third injection E3 with a third injection quantity, and a fourth injection E4 with a fourth injection quantity. This means that, in the present embodiment, the injector 3 under test injects a specific quantity of water into the injection chamber four times.

[0026] The injection quantities can be the same, but they can also be configured differently. It should be noted that with the method according to the invention, each injector 3 is tested individually. That is, each injector 3 undergoes its test independently of the other injectors 3 within the test interval PI, which lies between the start time ts and the end time t. E , including these time points. The injectors 3 are tested one after the other, and then compared relative to each other and absolutely with a limit value.

[0027] During the test interval PI of injector 3, after the first injection E1, a pressure p1 was established in the manifold pressure line 2, which was lower than the starting pressure ps, thus resulting in a pressure drop in manifold pressure line 2. After the second injection E2, a pressure p2 was established in manifold pressure line 2, which was lower than the first pressure p1, thus resulting in a further pressure drop in manifold pressure line 2.

[0028] The pressure curve D shows that the second pressure p2, however, is measured over a measurement interval that starts from a measurement time t. M2 the second injection E2 is assumed up to a measurement time t M3The pressure at the start of the third injection E3 cannot be maintained. The pressure p2 increases by a pressure rise Δp, thus rising from the second pressure p2. This pressure increase indicates a temperature increase in injection system 1.

[0029] After the end time t E Once this is reached, thus completing the test of injector 3, the shut-off device 8 is reopened and the build-up pressure p is restored. A or the starting pressure p S is brought about again and the test interval PI of the test, starting from the start time ts to the end time t E , starts again. This process is repeated until all three injectors have been tested.

[0030] Thus, the method according to the invention comprises the following steps: - In a first step, the build-up pressure p is established. Ain the injection system 1 using the test medium which is introduced into the injection system 1, - in a second step, after the build-up pressure p A Once this is achieved, the collecting pressure line 2 is closed pressure-tight, in particular with the aid of a shut-off device, - in a third step, within the test interval, which is between the start time ts and the end time t, E A desired number of injections E of injector 3 are carried out, whereby the pressure p in the injection system 1 is measured, - In a fourth step, the result is analyzed and, if a pressure increase Δp is detected, this is factored out to obtain a corrected result without this pressure increase Δp. - in a fifth step, if no pressure increase Δp was detected, the result was compared, or if a pressure increase Δp was detected, the adjusted result was compared with a limit value.

[0031] If the injection system 1 comprises more than one injector 3, the first, second, third, and fourth steps are performed sequentially according to the number of injectors. The fifth step then additionally includes a relative analysis of the results of the individual injectors 3 in relation to each other. Reference symbol list 1 Injection system 2 Collective pressure line 3 injectors 4 Funding opportunities 5 Pressure line 6 First End 7 Second Ending 8 barrier devices Pressure profile E-injection E1 First injection E2 Second injection E3 Third Injection E4 Fourth Injection PI test interval p print p A Building pressure p S Starting pressure p E Final pressure p1 First print p2 Second Print p3 Third Print p4 Fourth Print t time t E End time t M2 Measurement time E2 t M3 Measurement time E3 t S Start time Δp pressure increase

Claims

[1] Method for testing an injection system (1) of an internal combustion engine, wherein the injection system (1) has a collecting pressure line (2) through which an injector (3) can flow, wherein - in a first step, a build-up of pressure (p A ) in the injection system (1) with the aid of a test medium which is fed into the injection system (1), - in a second step, after the build-up pressure (p A ), the collective pressure line (2) is closed pressure-tight, - in a third step within a time interval (PI) between a start time (t S ) a measurement and an end time (t E ) of the measurement, a desired number of injections (E) of the injector (3) are carried out, whereby a pressure (p) in the collecting pressure line (2) is measured, - in a fourth step, a result of the measurement is analyzed and, if a pressure increase (Δp) is detected, this is subtracted to produce an adjusted result without this pressure increase (Δp), - in a fifth step, if no pressure increase (Δp) was detected, the result, or if a pressure increase (Δp) was detected, the adjusted result is compared with a limit value. [2] Method according to claim 1, characterized by , that - if the injection system (1) comprises more than one injector (3), the first step, the second step, the third step and the fourth step are carried out according to the number of injectors (3), and in the fifth step, a relative analysis of the results of the individual injectors (3) to one another is additionally carried out. [3] Method according to claim 1 or 2, characterized by that the injection system (1) is supplied with pressure to generate the build-up pressure (p A) in the collective pressure line (2) the test medium is supplied by means of a conveyor (4). [4] Method according to one of the preceding claims, characterized by that the collecting pressure line (2) is closed by means of a shut-off device (8). [5] Method according to one of the preceding claims, characterized by that the process is carried out during operation of the internal combustion engine. [6] Method according to one of the preceding claims, characterized by that the injection system (1) is a water injection system.

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