Method for Detecting Coking in the Inlet Section of an Internal Combustion Engine With a Variable Inlet Valve Lift Controller

Abstract

A method detects coking in the inlet section of an internal combustion engine with direct fuel injection, a throttle valve and a variable inlet valve lift controller. A correction value calculated by the inlet valve lift controller as an offset value with a preset valve lift is determined. In parallel, a first quantity deviation test is carried out by which a first air ratio value is determined, which is formed from a first lambda value measured during the first quantity deviation test and a desired lambda value of the fuel combustion in the combustion chambers of the internal combustion engine, wherein, in the first quantity deviation test a load control process is carried out by way of the variable inlet valve lift controller. In a second quantity deviation test, a second air ratio value is determined which is formed from a lambda value measured during the second quantity deviation test and a desired lambda value of the fuel combustion. In the second quantity deviation test a load control process is carried out by way of the throttle valve. A comparison value is formed from the first air ratio value and the second air ratio value. Whether coking is present in the inlet section of the internal combustion engine is determined by combined evaluation of the comparison result and of the correction value.

Claims

1.-14. (canceled)

15. A method for detecting coking in an inlet section of an internal combustion engine with direct fuel injection, a throttle flap and a variable inlet valve lift controller, comprising: ascertaining a correction value which is offset as an offset value against a preset valve lift by the inlet valve lift controller; carrying out a first quantity deviation test by way of which a first air ratio value is ascertained which is formed from a lambda value measured during the first quantity deviation test and a desired lambda value of a fuel combustion in combustion chambers of the internal combustion engine, wherein, in the first quantity deviation test, load control is performed by way of the variable inlet valve lift controller; carrying out a second quantity deviation test by way of which a second air ratio value is ascertained which is formed from a lambda value measured during the second quantity deviation test and a desired lambda value of the fuel combustion in the combustion chambers of the internal combustion engine, wherein, in the second quantity deviation test, load control is performed by way of the throttle flap; determining a comparison result from the first air ratio value and the second air ratio value; and determining whether coking is present in the inlet section of the internal combustion engine by combined evaluation of the comparison result and the correction value.

16. The method according to claim 15, wherein the correction value is read out of an engine controller.

17. The method according to claim 15, wherein the correction value is a value ascertained in relation to a running time of the internal combustion engine by the engine controller.

18. The method according to claim 17, wherein the correction value is a value adapted in relation to the running time of the internal combustion engine by the engine controller, wherein an adaptation is performed from a theoretically calculated air mass value of air flowing into the combustion chambers of the internal combustion engine and a measured air mass value.

19. The method according to claim 15, wherein the correction value is compared with a predefined limit value, and a presence of a fault in the inlet section is inferred when the correction value exceeds the predefined limit value.

20. The method according to claim 19, wherein a fault signal which represents coking is output when, additionally, the first air ratio value and the second air ratio value are different.

21. The method according to claim 15, wherein the first and/or the second quantity deviation test are carried out during idling operation of the internal combustion engine.

22. The method according to claim 15, wherein the first quantity deviation test is carried out with a small or minimal lift of the inlet valve and with the throttle flap open.

23. The method according to claim 22, wherein the second quantity deviation test is carried out with a maximum lift of the inlet valve and with the throttle flap substantially closed.

24. The method according to claim 15, wherein the second quantity deviation test is carried out with a maximum lift of the inlet valve and with the throttle flap substantially closed.

25. The method according to claim 15, wherein the first air ratio value and the second air ratio value are ascertained on a cylinder-specific basis, and the comparison result is determined on a cylinder-specific basis.

26. The method according to claim 15, wherein the first air ratio value is formed by the quotient of the lambda value measured during the first quantity deviation test and the desired lambda value, and the second air ratio value is formed by the quotient of the lambda value measured during the second quantity deviation test and the desired lambda value.

27. The method according to claim 15, wherein the presence of coking in the inlet section is inferred when the first air ratio value is lower than a predefined first threshold value and the second air ratio value is higher than the predefined first threshold value.

28. A computer product comprising a non-transitory computer readable medium having stored thereon program code which, when executed on a processor, carries out the acts of: ascertaining a correction value which is offset as an offset value against a preset valve lift by the inlet valve lift controller; carrying out a first quantity deviation test by way of which a first air ratio value is ascertained which is formed from a lambda value measured during the first quantity deviation test and a desired lambda value of a fuel combustion in combustion chambers of the internal combustion engine, wherein, in the first quantity deviation test, load control is performed by way of the variable inlet valve lift controller; carrying out a second quantity deviation test by way of which a second air ratio value is ascertained which is formed from a lambda value measured during the second quantity deviation test and a desired lambda value of the fuel combustion in the combustion chambers of the internal combustion engine, wherein, in the second quantity deviation test, load control is performed by way of the throttle flap; determining a comparison result from the first air ratio value and the second air ratio value; and determining whether coking is present in the inlet section of the internal combustion engine by combined evaluation of the comparison result and the correction value.

29. An apparatus, comprising: an engine test unit that detects faults in an inlet section of an internal combustion engine, wherein the engine test unit is operatively configured to: ascertain a correction value which is offset as an offset value against a preset valve lift by the inlet valve lift controller; carry out a first quantity deviation test by way of which a first air ratio value is ascertained which is formed from a lambda value measured during the first quantity deviation test and a desired lambda value of a fuel combustion in combustion chambers of the internal combustion engine, wherein, in the first quantity deviation test, load control is performed by way of the variable inlet valve lift controller; carry out a second quantity deviation test by way of which a second air ratio value is ascertained which is formed from a lambda value measured during the second quantity deviation test and a desired lambda value of the fuel combustion in the combustion chambers of the internal combustion engine, wherein, in the second quantity deviation test, load control is performed by way of the throttle flap; determine a comparison result from the first air ratio value and the second air ratio value; and determine whether coking is present in the inlet section of the internal combustion engine by combined evaluation of the comparison result and the correction value.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0036] FIG. 1 is an exemplary flow diagram of a method for detecting coking in the inlet section of an internal combustion engine.

DETAILED DESCRIPTION OF THE DRAWING

[0037] FIG. 1 shows an exemplary flow diagram of the method for detecting coking in the inlet section of an internal combustion engine. The internal combustion engine has one or more cylinder banks, wherein a respective cylinder bank comprises multiple cylinders with in each case one combustion chamber formed therein and at least one injection nozzle. In particular, exactly one injection nozzle is provided in each combustion chamber. A common air mass flow is fed to the combustion chambers of a respective cylinder bank. Likewise, a common exhaust-gas flow is discharged from the combustion chambers of a respective cylinder bank. The internal combustion engine has direct fuel injection, and is in particular an Otto-cycle engine with gasoline direct injection and fully variable valve controller. The control of the internal combustion engine is performed by means of various control parameters stored in an engine controller.

[0038] The internal combustion engine comprises a variable inlet valve lift controller in addition to a conventional throttle flap in the inlet section. Said variable inlet valve lift controller is a fully variable mechanical valve controller. By means of this system, the load control is regulated not by means of the throttle flap but by means of a valve lift curve of the inlet valves, as is well known to a person skilled in the art, for which reason this will not be discussed in any more detail. With the variable valve lift, the quantity of air admitted into a combustion chamber of the internal combustion engine can be regulated, such that the throttle flap positioned upstream of a cylinder bank is no longer required during normal operation. The throttle flap is used only in particular operating states, for example in an emergency operating mode. In this way, the charge exchange losses during part-load operation of the internal combustion engine can be considerably reduced, and thus a consumption advantage can be attained.

[0039] In the internal combustion engine with variable valve lift controller, a correction value KW provided by the engine controller is processed by the inlet valve lift controller. The correction value KW is offset as an offset value against a preset valve lift by the inlet valve lift controller. The correction value KW makes allowance for the fact that deposits can form on the inlet valves inter alia owing to contaminated inflowing gas masses (from the environment, the exhaust-gas recirculation, the crankcase ventilation, etc.). As a result, the cross section narrows, and less air can pass into the associated combustion chamber in the case of the same valve lift. During idling, these deposits are particularly critical, because the cross sections are at their smallest here. This can in the worst case lead to rough idling and to misfiring. To avoid this, a valve lift correction is ascertained by means of the correction value. In this way, the adverse effects of the deposits can be compensated to a certain degree.

[0040] The correction value KW is a value which is ascertained in relation to the running time of the internal combustion engine by the engine controller and which is commonly adapted by the engine controller over time, wherein an adaptation is performed from a theoretically calculated air mass value of air flowing into the combustion chambers of the internal combustion engine. The determination of the correction value KW is performed in accordance with the following approach: a theoretical air mass flow m_theo into the cylinders is calculated with the aid of an operation model of the intake air guide taking into consideration all mass flows and operating states involved. An actual air mass flow m_real is measured either directly or indirectly, wherein, for this purpose, use may for example be made of a hot film air mass sensor HFM. From the ascertained air mass flows, a ratio characteristic number V=m_real/m_theo is formed. The ratio characteristic number V is hereinafter the reference variable of the adaptive regulation, wherein a value of V_ziel=1 is sought, such that the real and the theoretical air mass flow are identical. Said adaptive regulation (so-called adaptation function) varies, as controlled variable, the elements for air mass control, in this case the inlet valve lift EV_hub_offset, wherein a difference resulting from the adaptation corresponds to the correction value KW. A positive value of the inlet valve lift EV_hub_offset describes an additional opening of the inlet valve by x [mm]. For the carrying-out of the method according to the invention, the currently present correction value KW is processed.

[0041] The correction value KW is ascertained in a step S11 by being read out of the engine controller. In general: the higher the absolute value of the correction value, the more likely it is that there are extensive deposits on the inlet valves. The correction value KW is determined as follows:

KW=(EV_hub_offset/EV_hub_offset_Grenz)*(V_Grenz/V)

[0042] Here, “EV_hub_offset_Grenz” is a limit value for the monitoring of the valve lift adaptation, and “V_Grenz” is a limit value for the monitoring of the remaining regulation error of the air masses. The correction value KW is utilized in accordance with the following logic:

[0043] In step S12, the correction value KW is compared with a predefined limit value GW. The limit value GW may, for example after the manufacture of the internal combustion engine, be written into a memory, for example of the engine controller or of a database, on a vehicle-specific basis or uniformly for an internal combustion engine type. The limit value GW may in particular be a limit value which takes into consideration manufacturing tolerances of the internal combustion engine. The limit value GW is selected for example to be GW=1, and it is then the case that: if the correction value KW is higher than or equal to 1 (KW≥1), then a critical situation is present. There is the suspicion that coking is present. This suspicion can be validated by means of further checks, which will be described below in steps S21, S22 and S23. Said checks are referred to as quantity deviation tests. If the correction value KW is less than 1 (KW<1), then a non-critical situation is present. It is not to be assumed that coking is present.

[0044] In step S12, it is thus ascertained whether the correction value KW exceeds the limit value GW (that is to say KW>=GW) or not (that is to say KW<GW). The result of the comparison is processed further in step S30. The exceedance of the predefined limit value (that is to say KW>=GW) alone constitutes an indication of the presence of coking, which is subsequently verified by carrying out the steps S21, S22 and S23 described below.

[0045] The steps S21, S22 and S23 may be carried out at a time before or at a time after the steps S11 and S12. The steps S21, S22 and S23 may likewise be carried out in parallel with the steps S11 and S12, as shown in FIG. 1.

[0046] In step S21, a first quantity deviation test is carried out, by means of which a first air ratio value w.sub.1 is ascertained. The air ratio value w.sub.1 is formed from the quotient of the lambda value λ.sub.real, 1 measured during the first quantity deviation test and the desired lambda value λ.sub.des, 1 (that is to say the setpoint lambda value) of the fuel combustion in the combustion chambers of the internal combustion engine. In the first quantity deviation test, load control of the internal combustion engine is performed by means of a variable inlet valve lift controller (VVT).

[0047] In step S22, a second quantity deviation test is carried out, by means of which a second air ratio value w.sub.2 is ascertained. The second air ratio value w.sub.2 is formed from the quotient of the lambda value λ.sub.real, 2 measured during the second quantity deviation test and the desired lambda value λ.sub.des, 2 (that is to say a setpoint lambda value) of the fuel combustion in the combustion chambers of the internal combustion engine. In the second quantity deviation test, the load control of the internal combustion engine is performed by means of the throttle flap in the inlet section of the internal combustion engine.

[0048] In step S23, a comparison of the previously ascertained first and second air ratio values w.sub.1 and w.sub.2 is performed. On the basis of the comparison result VE (that is to say w.sub.1<w.sub.2 or w.sub.1=w.sub.2 or w.sub.1>w.sub.2), the presence of a fault, in particular the presence of coking, in the inlet section of the internal combustion engine can be inferred. The comparison result VE is processed further in step S30.

[0049] The first and the second quantity deviation test are performed in succession during idling operation of the internal combustion engine.

[0050] The first quantity deviation test carried out in step S21 is carried out with a small or minimal lift of the inlet valve, wherein the throttle flap that is arranged in the inlet section of the internal combustion engine is open. In other words, the first quantity deviation test is carried out in a conventional operating mode of an internal combustion engine which has a variable inlet valve lift controller.

[0051] By contrast the second quantity deviation test in step S22 is carried out with a maximum lift of the inlet valve (that is to say the inlet valve is open to a maximum extent) and with the throttle valve substantially closed. This operating mode corresponds to an emergency operating mode in which, in engines with a non-operational variable inlet valve lift controller, the load control is carried out by means of the throttle flap.

[0052] Characteristic first and second air ratio values w.sub.1, w.sub.2 (that is to say w.sub.1<w.sub.2 or w.sub.1=w.sub.2 or w.sub.1>w.sub.2) arise in a manner dependent on whether coking is present, wherein the ratio of said air ratio values to one another is an indication of the presence of coking.

[0053] A general fault in the inlet section can be inferred if the first air ratio value w.sub.1, which was ascertained in step S21, and the second air ratio value w.sub.2, which was ascertained in step S22, are different (that is to say w.sub.1<>w.sub.2). This results from the fact that the air ratio values w.sub.1, w.sub.2 would have to have the same value if the lambda values λ.sub.real, 1 and λ.sub.real, 2 respectively measured in step S21 and S22 introduce the same air quantity into the combustion chambers with different load control, which would have to be manifest in a respectively equal measured lambda value. By contrast, if the air quantities introduced into the combustion chambers in the steps S21 and S22 differ from one another, then this leads to differences in the lambda values λ.sub.real, 1 and λ.sub.real, 2 measured in the steps S21 and S22, whilst the desired lambda values λ.sub.des, 1, λ.sub.des, 2 remain unchanged.

[0054] Coking has the effect that a carbon-like mass is deposited in the inlet, in particular in the inlet channel and/or on the inlet valve. The gradual growth of the carbon has the effect, in particular in step S21, in which the valve is only minimally open, that the air flow cross section that is otherwise present is reduced to a disproportionately great extent. As a result, a lesser air quantity can flow into the combustion chamber, whereby the measured lambda value λ.sub.real, 1 becomes smaller. This is manifest in a decrease of the first air ratio value w.sub.1. Thus, if the first air ratio value w.sub.1 is lower than the second air ratio value w.sub.2 (that is to say w.sub.1<w.sub.2), then coking can be inferred. The comparison may be performed in particular in relation to a predefined threshold value, which is selected to be 1, because the respective air ratio characteristic values w.sub.1, w.sub.2 corresponds to the value 1 if no fault is present, because then the measured and the desired lambda value are approximately equal.

[0055] The reverse situation, in which the first air ratio value w.sub.1 is higher than the predefined threshold value and higher than the second air ratio value w.sub.2 (that is to say w.sub.1>w.sub.2), gives grounds for suspicion that there is a leak in the inlet section, because here, owing to the flow conditions in the second step S22, in which the internal combustion engine is operated with throttling, a smaller air quantity passes into the combustion chambers.

[0056] It is in particular expedient if the above-described check is performed on a cylinder-specific basis. For this purpose, the first air ratio value w.sub.1 and the second air ratio value w.sub.2 are ascertained on a cylinder-specific basis, and a comparison is likewise determined on a cylinder-specific basis. In this way, it is possible not only to make an authoritative statement regarding the presence of a fault or of coking, but even to determine the cylinder that has the fault, or demonstrate a fault intensity per cylinder.

[0057] The manner in which the measured lambda values λ.sub.real, 1 and λ.sub.real, 2 and the desired lambda values λ.sub.des, 1 and λ.sub.des, 2 are ascertained in the first step S21 and the second step S22 is well known to a person skilled in the art. One possible approach is described for example in the applicant's WO 2016/041742 A1.

[0058] Furthermore, a person skilled in the art is familiar with further approaches for the cylinder-specific determination of a measured and of a desired lambda value, such that a detailed description of the determination will not be given in the present description.

[0059] If it is identified in step S30 that the correction value KW is higher than the limit value GW (KW>GW) and, at the same time, the comparison result VE has the result that w.sub.1<w.sub.2, then coking is inferred because two mutually independent methods each provide an indication of coking. In this case, a fault message can be output via the engine test unit. In all other cases, a fault message can be suppressed, and a warning may be output if necessary.

LIST OF REFERENCE DESIGNATIONS

[0060] S11 Method step
S12 Method step
S21 Method step
S22 Method step
S23 Method step
S30 Method step
λ.sub.real, 1 Measured lambda value in the first quantity deviation test
λ.sub.real, 2 Measured lambda value in the second quantity deviation test
λ.sub.des, 1 Desired (setpoint) lambda value in the first quantity deviation test
λ.sub.des, 2 Desired (setpoint) lambda value in the second quantity deviation test
w.sub.1 First air ratio characteristic value
w.sub.2 Second air ratio characteristic value
KW Correction value
VE Comparison result
GW Limit value