Method for testing the tightness of one or more combustion chambers of an internal combustion engine

Abstract

The invention relates to a method for testing the tightness of one or more combustion chambers of an internal combustion engine, using a fuel injector with which fuel can be introduced into one or each of the several combustion chambers, comprising for the one or each of the several combustion chambers: controlling (406) the fuel injector in order to introduce fuel into the combustion chamber at a first crankshaft angle of the internal combustion engine in a first injection or blow-in process, determining (408) a characteristic time duration of the first injection or blow-in process, controlling (410) the fuel injector in order to introduce fuel into the combustion chamber at a second crankshaft angle of the internal combustion engine in a second injection or blow-in process, determining (412) a characteristic time duration of the second injection or blow-in process,Determining (414) a difference between the characteristic duration of the first injection or blow-in process and the characteristic duration of the second injection or blow-in process, determining (418) whether the combustion chamber is assumed to be tight based on a comparison of the difference with a reference value.

Description

[0001] The present invention relates to a method for testing the tightness of one or more combustion chambers of an internal combustion engine as well as a computing unit and a computer program for carrying out the method. Background of the invention

[0002] For clean, i.e., low-emission operation of internal combustion engines such as reciprocating piston engines, air or gas mixtures trapped in the combustion chambers or cylinders of the internal combustion engine should be prevented from escaping as much as possible. Therefore, the tightness of the combustion chambers of an internal combustion engine is crucial. Disclosure of the invention

[0003] According to the invention, a method for testing the leak tightness of one or more combustion chambers of an internal combustion engine, as well as a computing unit and a computer program for carrying out the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0004] The invention concerns internal combustion engines such as reciprocating piston engines and their clean operation. As mentioned, this generally requires that the air trapped in the cylinder or combustion chamber does not escape uncontrollably. This can occur primarily in the case of leaks at various valves (intake, exhaust, injection, or blow-in valves), between the piston and the cylinder wall, or in the seals on other components extending into the combustion chamber (lambda sensor, spark plug, etc.). Causes of such leaks include wear and damage to the cylinder, piston, or the various seals.

[0005] In a workshop, for example, the leaks in individual cylinders or combustion chambers can be measured using special measuring devices that measure the pressure during the cylinder's compression phase. However, this requires extensive preparation of the internal combustion engine for such measurements.

[0006] There are fuel injectors, injection valves or blow-in valves that open via an electrically excited magnetic field; these are referred to as solenoid injectors or solenoid valve injectors. In the following, injection and blow-in processes are summarized under the term "injection". In general, however, they can also be referred to as introduction processes, for example. With this type of injector, the movement of the injector needle can be detected based on the current curve and / or the voltage curve when actuated to carry out an injection process, e.g. by measuring the voltage during and after actuation. The measurement can be carried out, for example, using a special electrical component in an engine control unit.

[0007] This movement depends on the current balance of the forces acting on the injector needle, in particular the magnetic and spring force, as well as the forces caused by the pressures from the fuel supply (rail) and the cylinder or combustion chamber.

[0008] Other options for measuring injector dynamics include current curve analyses to detect the injector opening time or detailed rail pressure analyses.

[0009] The underlying principle is always similar or comparable in that a suitable measurable substitute value is sought in order to obtain more precise information about the needle dynamics and thus about the injected fuel mass.

[0010] This can now, as it turns out, be used to detect a leak in the cylinder or combustion chamber by indirectly measuring the cylinder pressure during the compression phase and comparing it with a reference value. A leak generally occurs when the air pressure in the cylinder is lower than expected during compression.

[0011] For this purpose, the fuel injector of a combustion chamber or cylinder is controlled to inject fuel into the combustion chamber in a first injection event at a first crankshaft angle of the internal combustion engine. A characteristic duration of the first injection event, e.g., a closing delay time (or simply referred to as the closing delay time), is then determined. In the case of a solenoid valve injector as a fuel injector, for example, this can be done, as mentioned, by taking into account a current and / or voltage curve during control.

[0012] The fuel injector is then controlled to inject fuel into the combustion chamber in a second injection event at a second crankshaft angle of the internal combustion engine. The second crankshaft angle is different from the first crankshaft angle. A characteristic duration of the second injection event, e.g., a closing delay time, is then determined. This can be done in the same way as for the first injection event. The first and second injection events should be comparable, e.g., they should involve identical control.

[0013] A difference between the characteristic duration of the first injection event and the characteristic duration of the second injection event is then determined, and based on a comparison of the difference with a reference value, it is then determined whether the combustion chamber is assumed to be tight.

[0014] For example, the combustion chamber can be assumed to be leak-tight if the difference from the reference value deviates by less than a predefined first value, and the combustion chamber can be assumed to be leak-tight if the difference from the reference value deviates by more than a predefined second value. The first and second values ​​can, but do not have to, be identical. By selecting the first and / or second values ​​appropriately, any measurement inaccuracies can be taken into account.

[0015] This can be done individually for each of the engine's several combustion chambers, for example, regularly to check for leaks. If a leak is detected in one or more combustion chambers, an error message can be generated, including a request for repair.

[0016] This allows for a defined control of a fuel injector, particularly a direct injection valve, during the compression phase of each cylinder, and a measurement of its actual behavior. By evaluating the closing and opening behavior of the fuel injector, the pressure within the cylinder at this crankshaft angle can be indirectly determined. This is possible due to the interrelationships between the various acting pressures and forces, which will be explained in more detail in the accompanying figures.

[0017] By comparing the closing or opening behavior with a reference value for the respective crankshaft angle, a deviating pressure change and thus a possible leak can be determined.

[0018] A particular advantage is that such an examination can be performed without requiring any special preparations and / or measuring devices on the internal combustion engine. For example, all that is needed is an OBD diagnostic tool that requests the aforementioned test or examination. The completed examination procedure, including its evaluation, can be requested via a program on the engine control unit.

[0019] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0020] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

[0021] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0022] The invention is illustrated schematically in the drawing using an embodiment and is described below with reference to the drawing. Short description of the drawings Fig. 1 schematically shows an internal combustion engine with a common rail system, which is suitable for carrying out a method according to the invention. Fig. 2 and Fig. 3 show diagrams to explain the invention. Fig. 4 schematically shows a method according to the invention in a preferred embodiment. Embodiment(s) of the invention

[0023] In Fig. 1 schematically shows an arrangement 100 with an internal combustion engine 160, which is suitable for carrying out a method according to the invention. By way of example, the internal combustion engine 160 comprises three combustion chambers or associated cylinders 165. Each combustion chamber 165 is assigned a fuel injector 170 designed as a solenoid valve injector, which in turn is connected to a high-pressure accumulator 175, a so-called (common) rail, via which it is supplied with fuel. It is understood that a method according to the invention can also be carried out in an internal combustion engine with any other number of cylinders, for example, one, two, four, five, six, eight, ten, or twelve cylinders, etc.

[0024] Furthermore, the high-pressure accumulator 175 is fed with fuel 197 from a fuel tank 195 via a high-pressure pump 161. The high-pressure pump 161 is coupled to the internal combustion engine 160, for example, in such a way that the high-pressure pump is driven by the internal combustion engine.

[0025] The fuel injectors 170 are controlled to meter or inject fuel into the respective combustion chambers 165 via a computing unit embodied as an engine control unit 180. For the sake of clarity, only the connection from the engine control unit 180 to one fuel injector 170 is shown; however, it is understood that each fuel injector 170 is connected to the engine control unit accordingly. Each fuel injector 170 can be specifically controlled. Furthermore, the engine control unit 180 is configured, for example, to detect the fuel pressure in the high-pressure accumulator 175 using a pressure sensor 190.

[0026] As mentioned, there are various ways to detect characteristic points of needle movement (e.g. upper stop when injector opens or impact when injector closes) in a fuel injector.

[0027] The movement of the injector needle depends on the force ratio described above. The total force is calculated as follows (regardless of the signs of the forces): Fges=FM(I)+FF(c)+FR(pRail)+FZ(pZyl)

[0028] Where F M The magnetic force. This is proportional to the current profile I(t) used to control the injector. This is specified, for example, by the engine control system, so the resulting force is known or at least easily determined. For this purpose, the necessary parameters of the magnet, the current profile, etc., can be taken into account.

[0029] With F Fis the spring force. The compression spring in the injector serves to tightly close the injector needle when no current is applied. The spring force depends on the spring hardness c and is proportional to the deflection. The spring hardness is constant but can vary from injector to injector.

[0030] With F R is the pressure force through the fuel supply (rail pressure). Depending on the design of the injector, the rail pressure acts to open or close the injector needle. A pressure sensor is usually connected to the rail (as in Fig. 1), so that its pressure and thus the acting force are known or can be determined. A special case are pressure-balanced injectors, in which the rail pressure has no influence on the needle movement.

[0031] Fz denotes the pressure force from the cylinder. This depends on the current cylinder pressure, which varies significantly over time and is dependent on various design and control-related factors of the internal combustion engine. Whether this force component has an opening or closing effect also depends on the engine's design.

[0032] The pressure force Fz is the force that receives particular attention in the context of the present invention. The influences of the other forces can be eliminated by performing two, particularly identical, pilot-controlled injections in the same cylinder or combustion chamber. Fges1−Fges2=(FM(I)+FF(c)+FR(pRail)+FZ(pZyl(ϕ1)))−(FM(I)+FF(c)+FR(pR ail)+FZ(pZyl(ϕ2)))=FZ(pZyl(ϕ1))−FZ(pZyl(ϕ1))=ΔFZ(pZyl(ϕ1),pZyl(ϕ2))

[0033] F ges1 , F ges2The total forces mentioned for a first and a second injection event are denoted by ϕ1 and ϕ1, respectively. The first and second crankshaft angles at which the first and second injection events occur are denoted by ϕ1. In simplified terms, the force can be converted directly into pressure: FZ=pCyl(ϕ)∗ANeedle

[0034] A Nadel denotes the cross-sectional area of ​​the injector needle, which is also known or can be determined. Combined with the above equation, the following expression for a differential force results: ΔFtot=ANeedle∗(ΔpCyl)→ΔFtot∝ΔpCyl

[0035] Measuring this differential force directly is generally not possible, as most internal combustion engines do not have a cylinder pressure sensor. Therefore, in the present invention, the pressure is determined indirectly via the movement of the injector needle. For this purpose, a method can be used that describes this movement using a surrogate variable.

[0036] In the following, an embodiment is described in which the delay time when closing the fuel injector is measured or determined as a characteristic time duration of an injection process.

[0037] For this purpose, Fig. 2 shows a diagram in which a stroke h of the injector needle (solid line, reference numeral 200) and the armature of the solenoid valve injector (dashed line, reference numeral 210) are plotted in µm over a time t in ms.

[0038] When the solenoid valve injector is activated for an injection process, the magnet is energized, starting at time t=0, for a control duration ti. After a time tan or tot, the injector needle is raised, so that the solenoid valve injector opens, thus introducing fuel into the combustion chamber. However, the energization is not yet complete. A time period tab after the injector has opened, the injector closes again. The total open time is designated as t_open. The delay time or delay period mentioned is the time period tab.

[0039] The delay time can be measured using a conventional method. For example, the current and / or voltage curve can be analyzed.

[0040] Depending on whether the injector opens inward or outward, the delay time tab increases or decreases as the backpressure increases. However, the following applies: Fz(pzyl(ϕ))∝tab(ϕ)

[0041] Since force and pressure are also proportional to each other, the above equations result in: ΔpZyl(ϕ1,ϕ2)∝Δtab(ϕ1,ϕ2)

[0042] This means that the pressure difference in the combustion chamber can be directly determined from the difference between the measured delay times during closing; any conversion factors between the pressure in the cylinder and the delay time play no role in the difference.

[0043] This is in Fig. 3 is illustrated in a diagram. Here, a pressure p in bar and a delay time tab in µs are plotted against a crankshaft angle ϕ in °CA. Curve 300 shows values ​​for a sealed combustion chamber, while curve 310 shows values ​​for a leaky combustion chamber.

[0044] While at, for example, 50°CA the cylinder or combustion chamber still has approximately the same pressure in both cases, a leaky compression leads to a weaker pressure increase, as shown by curve 310 compared to curve 300. For an outward-opening injector in this example, this results in a greater closing delay at, for example, 150°CA and thus in a smaller difference between 50°CA and 150°CA. If the difference in tab falls below a certain value, this means that the compression is too weak and there may be a leak.

[0045] In general, for example, the difference ΔtabR can be used as a reference value for the case of a dense combustion chamber, which would be expected; the difference Δtab then represents the currently determined difference between the delay time during a first and a second injection process, for example at the crankshaft angles 50°CA and 150°CA shown here as examples.

[0046] In Fig. 4 schematically shows a method according to the invention in a preferred embodiment. For this purpose, in a step 400, the reference value, for example an at least expected value of the difference between the delay time in a first and a second injection process, can first be determined. In step 402, for example, a steady-state or otherwise suitable operating point of the internal combustion engine for carrying out the further steps can then be determined, for example with regard to load and speed. In particular, an injection duration and the desired first and second crankshaft angles can also be determined here.

[0047] In step 404, a combustion chamber or cylinder for which the leak test is to be carried out can first be selected. In step 406, the fuel injector is then controlled in order to inject fuel into the combustion chamber in a first injection process at the first crankshaft angle of the internal combustion engine. In step 408, the characteristic duration of the first injection process, for example the delay time, is determined. In step 410, the fuel injector is then controlled in order to inject fuel into the combustion chamber in a second injection process at the second crankshaft angle of the internal combustion engine. In step 412, the characteristic duration of the first second injection process, for example also the delay time, is determined.

[0048] In step 414, the difference between the characteristic duration of the first injection event and the characteristic duration of the second injection event is determined or calculated. In step 416, a comparison is then made between the determined difference and the previously defined reference value. Depending on the result, the combustion chamber or cylinder can then be determined to be leaky or tight (step 418).

[0049] This can be repeated for all combustion chambers, ie, in step 420, for example, a check can be made to determine whether all combustion chambers have already been checked. If not, the next combustion chamber can be selected in step 422, and the process can continue with step 406. Once all combustion chambers have been checked, the process can be terminated.

Claims

[1] Method for testing the tightness of one or more combustion chambers (165) of an internal combustion engine (160), using a fuel injector (170) with which fuel can be introduced into one or each of the several combustion chambers, comprising for the one or each of the several combustion chambers: Controlling (406) the fuel injector (170) in order to introduce fuel into the combustion chamber in a first injection or blow-in process at a first crankshaft angle of the internal combustion engine, Determining (408) a characteristic time duration (tab) of the first injection or blow-in process, Controlling (410) the fuel injector to introduce fuel into the combustion chamber in a second injection or blow-in process at a second crankshaft angle of the internal combustion engine, Determining (412) a characteristic time duration (tab) of the second injection or blow-in process, Determining (414) a difference (Δtab) between the characteristic time duration of the first injection or blow-in process and the characteristic time duration of the second injection or blow-in process, Determining (418), based on a comparison of the difference with a reference value (ΔtabR), whether the combustion chamber is assumed to be tight. [2] Method according to claim 1, wherein the combustion chamber is assumed to be tight if the difference with the reference value differs by less than a predetermined first value. [3] Method according to claim 1 or 2, wherein the combustion chamber is assumed to be leak-tight if the difference with the reference value differs by more than a predetermined second value. [4] Method according to one of the preceding claims, wherein the fuel injector is designed as a solenoid valve injector, [5] Method according to claim 4, wherein the characteristic time duration of the first injection process and the characteristic time duration of the second injection process are each determined taking into account a current profile and / or a voltage profile when controlling to carry out the first injection process or the second injection process. [6] Method according to one of the preceding claims, wherein the characteristic time duration of the first injection event and the characteristic time duration of the second injection event each comprise a closing delay time duration. [7] Method according to one of the preceding claims, wherein the first injection process and / or the second injection process take place in a compression phase of the internal combustion engine. [8] Method according to one of the preceding claims, wherein the tightness of all of the plurality of combustion chambers is tested. [9] Computing unit (180) which is configured to carry out all method steps of a method according to one of the preceding claims. [10] Computer program which causes a computing unit to carry out all the method steps of a method according to one of claims 1 to 8 when it is executed on the computing unit. [11] A machine-readable storage medium having stored thereon a computer program according to claim 10.

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