Method for testing sealing of one or more combustion chambers of internal combustion engine

Abstract

The invention relates to a method for checking the sealing of one or more combustion chambers of an internal combustion engine using a fuel injector, by means of which fuel can be introduced into the one or more combustion chambers, the method comprises the following steps for each combustion chamber of the one or more combustion chambers: triggering the fuel injector to introduce fuel into the combustion chamber during a first injection or scavenging with the internal combustion engine at a first crankshaft angle; determining a characteristic time period of the first injection or scavenging process; controlling the fuel injector in order to introduce fuel into the combustion chamber during a second injection or scavenging with the internal combustion engine at a second crankshaft angle; determining a characteristic time period of the second injection or scavenging process; determining a difference between a characteristic time period of the first injection or injection process and a characteristic time period of the second injection or scavenging process; it is determined whether the combustion chamber is sealed based on a comparison of the difference to a reference value.

Description

Technical Field

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

[0002] For the clean, i.e. low-emission operation of an internal combustion engine, for example a reciprocating piston engine, the gas or general gas mixture contained in the combustion chamber or cylinder of the internal combustion engine should not escape as much as possible. In this respect, it depends on the tightness of the combustion chamber of the internal combustion engine. Summary of the invention

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

[0004] The present invention relates to internal combustion engines (e.g. reciprocating piston engines) and their clean operation. As mentioned above, this generally requires that the gases contained in the cylinder or combustion chamber cannot escape uncontrollably. This may be the case in particular for leaks at the various valves (intake valves, exhaust valves, injection valves or scavenging valves), at seals between the piston and the cylinder wall or other components extending into the combustion chamber (oxygen content sensors, spark plugs, etc.). Causes of such leaks are, for example, wear and damage to the cylinder, the piston or the various seals.

[0005] In the workshop, for example, the leakage of individual cylinders or combustion chambers can be measured by measuring the pressure in the compression phase of the cylinder with the aid of special measuring equipment. However, the internal combustion engine must be prepared in a complex manner for such measurements.

[0006] There are fuel injectors or injection valves or scavenging valves which are opened by means of an electrically excited magnetic field; these are referred to as solenoid injectors or solenoid valve injectors. The injection process and the scavenging process are summarized below under the term "injection". In general, it can also be referred to as a lead-in process, for example. For this type of injector, the movement of the injector needle can be identified based on the current curve and / or voltage curve used to perform the injection process during triggering, for example by measuring the voltage during and after triggering. The measurement can be performed, for example, using special electrical components in the engine control unit.

[0007] This movement is dependent on the currently effective balance of the forces acting on the injector needle (in particular magnetic and spring forces) and the forces resulting from the fuel supply (rail) and the pressure of the cylinder or combustion chamber.

[0008] Other possibilities for measuring the injector dynamics are, for example, an analysis of the current curve or a detailed rail pressure analysis to identify the injector opening time.

[0009] The principle on which the present application is based is always similar or comparable in this respect, namely the search for suitable measurable surrogate variables in order to thereby obtain more precise information about the needle valve dynamics and thus about the injected fuel mass.

[0010] It turns out that it is now possible to identify leaks in a cylinder or combustion chamber by indirectly measuring the cylinder pressure during the compression phase and comparing it to a reference value. When the gas pressure in the cylinder during compression is lower than expected, a leak is usually present.

[0011] For this purpose, the fuel injector of the combustion chamber or cylinder is activated so that fuel is introduced into the combustion chamber in a first injection process when the internal combustion engine is at a first crankshaft angle. A characteristic time period of the first injection process is then determined, for example a closing delay time period (or simply closing delay time). In the case of a solenoid valve injector as a fuel injector, this can be done, for example, by taking into account the current curve and / or voltage curve during the activation period as described above.

[0012] The fuel injector is then triggered so that fuel is introduced into the combustion chamber in a second injection process when the internal combustion engine is at a second crankshaft angle. The second crankshaft angle is different from the first crankshaft angle. A characteristic time period of the second injection process is then determined, such as a closing delay time period. This can be done like the first injection process. In this case, the first injection process and the second injection process should be comparable, i.e., for example, include the same triggering.

[0013] Then, a difference between a characteristic time period of the first injection event and a characteristic time period of the second injection event is determined, and based on a comparison of the difference with a reference value, it is determined whether the combustion chamber is sealed.

[0014] For example, if the difference and the reference value deviate from each other by less than a first predetermined value, the combustion chamber may be considered to be sealed, whereas if the difference and the reference value deviate from each other by more than a second predetermined value, the combustion chamber may be considered to be unsealed. The first predetermined value and the second predetermined value may, but need not, be the same. By appropriately selecting the first predetermined value and / or the second predetermined value, any measurement errors, for example, may be taken into account.

[0015] This can be done individually for each of the multiple combustion chambers of the internal combustion engine, for example, also regularly, in order to check the tightness. If a leak is detected in one or more combustion chambers, an error message may appear, for example, which includes a maintenance request.

[0016] A defined triggering of the fuel injectors, in particular the direct injection valves, can be performed during the compression phase of the individual cylinders and a measurement of their actual behavior can be performed. By evaluating the closing or opening behavior of the fuel injectors, the pressure in the cylinder at this crankshaft angle can be indirectly determined. This is possible due to the relationship of the various pressures and forces to one another, which will be explained in more detail in the description of the figures.

[0017] By comparison with reference values ​​for the closing or opening behavior at the corresponding crankshaft angle, different pressure changes can be derived and thus conclusions can be drawn about possible leaks.

[0018] A particular advantage is that such a check can be performed without special preparations and / or measuring devices on the internal combustion engine. For example, only an OBD diagnostic device is required to request the aforementioned inspection or test. The performed inspection program plus the evaluation can be requested via a program on the engine control unit.

[0019] A computing unit according to the invention, for example a control device of a motor vehicle, carries out the method according to the invention, in particular in terms of programming.

[0020] It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product with a program code for executing all method steps, because this leads to particularly low costs, in particular if the control device executed is also used for other tasks and therefore exists anyway. Finally, a machine-readable storage medium is provided on which a computer program as described above is stored. Suitable storage media or data carriers for providing computer programs are especially magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. The program can also be downloaded via a computer network (the Internet, intranet, etc.). Here, this download can be carried out in a wired or wireless manner (for example, via a WLAN network, 3G, 4G, 5G or 6G connection, etc.).

[0021] Further advantages and developments of the invention are apparent from the description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention is schematically illustrated in the drawings by means of exemplary embodiments and is described below with reference to the drawings.

[0023] Figure 1 An internal combustion engine having a common rail system is schematically shown, which is suitable for carrying out the method according to the invention.

[0024] Figure 2 and Figure 3 A diagram for explaining the present invention is shown.

[0025] Figure 4The method according to the invention is schematically illustrated in a preferred embodiment. DETAILED DESCRIPTION

[0026] Figure 1 Schematically, an arrangement 100 with an internal combustion engine 160 is shown, which is suitable for carrying out the method according to the invention. As an example, the internal combustion engine 160 comprises three combustion chambers or associated cylinders 165. Each combustion chamber 165 is assigned a fuel injector 170 configured as a solenoid valve injector, which is in turn connected to a high-pressure reservoir 175, the so-called (common) rail, and is supplied with fuel through it. It should be understood that the method according to the invention can also be carried out in an internal combustion engine with any other number of cylinders (e.g., one, two, four, five, six, eight, ten or twelve cylinders, etc.).

[0027] In addition, fuel 197 is supplied from a fuel tank 195 to the high-pressure accumulator 175 via a high-pressure pump 161. The high-pressure pump 161 is coupled to the internal combustion engine 160, for example, in such a manner that the high-pressure pump is driven by the internal combustion engine.

[0028] The fuel injectors 170 are triggered by a computing unit configured as an engine control 180 to meter or inject fuel into the respective combustion chambers 165. For the sake of clarity, only the connections from the engine control 180 to the fuel injectors 170 are shown, but it should be understood that each fuel injector 170 is connected to the engine control accordingly. Each fuel injector 170 can be specifically triggered here. In addition, the engine control 180 detects the fuel pressure in the high-pressure accumulator 175, for example, via a pressure sensor 190.

[0029] As already mentioned, there are various possibilities for identifying characteristic points of the needle movement in a fuel injector (eg, the top dead center when opening the fuel injector or the bottom dead center when closing the fuel injector).

[0030] The movement of the injector needle is determined by the force ratios described. The resultant forces are as follows (regardless of the force signs):

[0031] F ges =F M (I)+F F (c)+F R (p Rail )+F Z (p Zyl )

[0032] where F Mis the magnetic force. This magnetic force is proportional to the current curve I(t) that controls the injector. This magnetic force is specified, for example, by the engine control device, which is why the resultant force is known or can at least be easily determined. For this purpose, for example, the necessary parameters of the magnet and the current curve, etc., can be considered.

[0033] F F represents the spring force. The compression spring in the fuel injector is used to seal the injector needle valve when there is no current. The spring force depends on the spring stiffness c and is proportional to the deflection. The spring stiffness is constant but varies depending on the fuel injector.

[0034] F R represents the pressure of the fuel supply (rail pressure). Depending on the structural design of the fuel injector, the rail pressure has an opening or closing effect on the injector needle valve. A pressure sensor is usually connected to the rail (as Figure 1 shown) in order to know or determine its pressure and the acting force. A pressure-balanced fuel injector is a special case where the rail pressure has no structural effect on the needle valve movement.

[0035] F Z represents the pressure from the cylinder. This depends on the current cylinder pressure, which varies greatly over time and depends on various structural and control factors of the internal combustion engine. Whether this force component has an opening or closing effect also depends on its structural design.

[0036] where the compressive force F Z is the force that is of particular interest in the context of the present invention. The influence of other forces can be calculated by performing two particularly identical pilot control injections on the same cylinder or combustion chamber.

[0037] F ges1 -F ges2 =(F M (I)+F F (c)+F R (p Rail )+F Z (p Zyl (φ 1 )))

[0038] -(F M (I)+F F (c)+F R (p Rail )+F Z (p Zyl (φ 2 )))

[0039] =F Z (p Zyl (φ 1 ))-F Z(p Zyl (φ 1 ))

[0040] =ΔF Z (p Zyl (φ 1 ), p Zyl (φ 2 ))

[0041] Here, F ges1 、F ges2 represents the resultant force mentioned for the first and second injection processes. φ 1 or φ 2 Indicates the first crankshaft angle or the second crankshaft angle when the first injection process or the second injection process is performed. In simple terms, force can be directly converted into pressure:

[0042] F Z =p Zyl (φ)*A Nadel

[0043] Here, A Nadel represents the cross-sectional area of ​​the injector needle, which is also known or can be determined. Together with the above equation, the following differential force expression can be derived:

[0044] ΔF ges =A Nadel *(Δp Zyl )→ΔF ges ∝Δp Zyl

[0045] It is usually not possible to measure this differential force directly, because most internal combustion engines do not have cylinder pressure sensors. Therefore, in the context of the present invention, the pressure is determined indirectly by the movement of the injector needle. For this purpose, a method that describes this movement by a substitute variable can be used.

[0046] An embodiment is described below in which the delay time when closing the fuel injector is measured or determined as a characteristic time period of the injection event.

[0047] to this end, Figure 2 2 shows a diagram in which the stroke h of the injector needle and the stroke h of the armature of the solenoid valve injector in μm are plotted against the time in ms.

[0048] When the solenoid valve injector is triggered for the injection process, the magnet is energized starting at time t=0 and continues for the triggering period ti. After a period of time tan or tot, the injector needle rises so that the solenoid valve injector opens, i.e., the fuel is introduced into the combustion chamber. However, the energization is not over yet. After the injector is open for a period of time tab, the injector is closed again. The entire opening duration is denoted here by t_offen. The delay time or delay time period mentioned is here the time period tab.

[0049] The delay time can be measured by methods known per se. For example, current and / or voltage curves can be analyzed for this purpose.

[0050] Depending on whether the injector opens inwards or outwards, the delay time tab will increase or decrease as the back pressure increases. However, if:

[0051] F Z (p Zyl (φ))∝tab(φ)

[0052] Since force and pressure are also proportional to each other, the above equation yields:

[0053] Δp Zyl (φ 1 ,φ 2 )∝Δtab(φ 1 ,φ 2 )

[0054] This means that the pressure difference in the combustion chamber can be directly derived from the difference in the delay time measured during closing; any conversion factor between the pressure in the cylinder and the delay period has no effect on the difference.

[0055] Figure 3 This is illustrated in a diagram in . Here, the pressure p in bar and the delay time period tab in μs are plotted against the crankshaft angle φ in °KW. In this case, curve 300 shows the values ​​for a sealed combustion chamber, while curve 310 shows the values ​​for an unsealed combustion chamber.

[0056] Although at 50°KW, for example, the cylinder or combustion chamber still has approximately the same pressure in both cases, the unsealed compression results in a weaker pressure increase, as shown by curve 310 compared to curve 300. In the case of the injector opening outwards in this example, this manifests as a higher closing delay at, for example, 150°KW, and therefore as a smaller difference between 50°KW and 150°KW. If the difference in tab is below a certain value, it means that the compression is too weak and there may be a leak.

[0057] In general, a difference ΔtabR, for example for the case of combustion chamber sealing, can be used as a reference value, which is expected to be a difference Δtab representing the difference between the currently determined delay time periods in the first injection process and the second injection process, for example the crankshaft angles of 50°KW and 150°KW shown in this example.

[0058] Figure 4 The method according to the invention is schematically shown in a preferred embodiment. For this purpose, in step 400, a reference value, i.e. a minimum expected value for the difference between the delay times in the first injection process and the second injection process, can first be determined. In step 402, a fixed or otherwise suitable operating point of the internal combustion engine can then be determined, for example, in dependence on load and speed, for carrying out the further steps. In particular, the injection duration and the expected first and second crankshaft angles can also be determined here.

[0059] In step 404, the combustion chamber or cylinder to be tested for leaks can first be selected. In step 406, the fuel injector is then activated so that fuel is introduced into the combustion chamber in a first injection process when the internal combustion engine is at a first crankshaft angle. In step 408, a characteristic time period of the first injection process is determined, i.e., for example, a delay time period. In step 410, the fuel injector is then activated so that fuel is introduced into the combustion chamber in a second injection process when the internal combustion engine is at a second crankshaft angle. In step 412, a characteristic time period of the second injection process is determined, i.e., likewise, for example, a delay time period.

[0060] In step 414, the difference between the characteristic time period of the first injection event and the characteristic time period of the second injection event is then determined or calculated. In step 416, a comparison is then made between the determined difference and a previously determined reference value. Based on the result of step 418, it can be determined whether the combustion chamber or cylinder is sealed or unsealed.

[0061] These steps can be repeated for all combustion chambers, i.e., it can be checked, for example, in step 420 whether all combustion chambers have been checked. If not, the next combustion chamber can be selected in step 422 and step 406 can be continued. When all combustion chambers have been checked, the method ends.

Claims

1. A method for testing the tightness of a combustion chamber or a plurality of combustion chambers (165) of an internal combustion engine (160) using a fuel injector (170) respectively, wherein the fuel can be introduced into the combustion chamber or each of the plurality of combustion chambers, the method comprising the following steps for each of the combustion chamber or the plurality of combustion chambers: triggering (406) the fuel injector (170) to introduce fuel into the combustion chamber during a first injection process or a first scavenging process when the internal combustion engine is at a first crankshaft angle, determining (408) a characteristic time period (tab) of the first injection process or the first scavenging process, triggering (410) the fuel injector to introduce fuel into the combustion chamber in a second injection process or a second scavenging process when the internal combustion engine is at a second crankshaft angle, determining (412) a characteristic time period (tab) of the second injection process or the second scavenging process, determining (414) a difference (Δtab) between a characteristic time period of the first injection process or the first scavenging process and a characteristic time period of the second injection process or the second scavenging process, Based on a comparison of the difference with a reference value (ΔtabR), it is determined ( 418 ) whether the combustion chamber is sealed.

2. The method according to claim 1, wherein: If the difference value and the reference value deviate from each other by less than a first predetermined value, the combustion chamber is considered to be sealed.

3. The method according to claim 1 or 2, wherein: If the difference value and the reference value deviate from each other by more than a second predetermined value, the combustion chamber is deemed to be leaky.

4. A method according to any one of the preceding claims, wherein: The fuel injectors are each designed as solenoid valve injectors.

5. The method according to claim 4, wherein: The characteristic time period of the first injection process and the characteristic time period of the second injection process are determined taking into account a current curve and / or a voltage curve for carrying out the first injection process or the second injection process during the activation.

6. A method according to any one of the preceding claims, wherein: The characteristic time period of the first injection process and the characteristic time period of the second injection process respectively include a closing delay time period.

7. A method according to any one of the preceding claims, wherein: The first injection event and / or the second injection event takes place during a compression phase of the internal combustion engine.

8. A method according to any one of the preceding claims, wherein: All of the plurality of combustion chambers are tested for leak tightness.

9. A computing unit (180) which executes all method steps of the method according to any of the preceding claims. 10 . A computer program which, when executed on a computing unit, causes the computing unit to execute all method steps of the method according to claim 1 .

11. A machine-readable storage medium on which the computer program according to claim 10 is stored.

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