Method for detecting coking in the intake tract of an internal combustion engine

Abstract

A method detects a fault, in particular coking, in the intake tract of an internal combustion engine with direct fuel injection, a throttle valve, and a variable intake valve lift controller. The method has the steps of a) carrying out a first quantity deviation test, by which a first air ratio value is ascertained that is formed from a lambda value, which is measured during the first quantity deviation test, and a desired lambda value of the fuel combustion in the fuel chambers of the internal combustion engine, wherein in the first quantity deviation test, a load control is carried out by the variable intake valve lift controller; b) carrying out a second quantity deviation test, by which a second air ratio value is ascertained that is formed from a lambda value, which is measured during the second quantity deviation test, and a desired lambda value of the fuel combustion in the fuel chambers of the internal combustion engine, wherein in the second quantity deviation test, a load control is carried out by the throttle valve; and lastly c) determining a comparison result from the first air ratio value and the second air ratio value, the presence of a fault in the intake tract of the internal combustion engine being detectable using the comparison result.

Claims

1. A method for detecting a fault in an inlet section of an internal combustion engine with direct fuel injection, a throttle flap and a variable inlet valve lift controller, the method comprising the steps of: a) carrying out a first quantity deviation test by which a first air ratio value is ascertained which is formed from a lambda value measured during the first quantity deviation test and a first desired lambda value of fuel combustion in combustion chambers of the internal combustion engine, wherein, in the first quantity deviation test, load control is performed by the variable inlet valve lift controller; b) carrying out a second quantity deviation test by which a second air ratio value is ascertained which is formed from a lambda value measured during the second quantity deviation test and a second 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 the throttle flap; and c) determining a comparison result from the first air ratio value and the second air ratio value, wherein a presence of a fault in the inlet section of the internal combustion engine is detectable on the basis of the comparison result.

2. The method according to claim 1, wherein the fault is coking in the inlet section.

3. The method according to claim 1, wherein the first and/or the second quantity deviation test are carried out during idling operation of the internal combustion engine.

4. The method according to claim 1, wherein the first quantity deviation test is carried out with a small or minimal lift of an inlet valve controlled by the variable inlet valve lift controller and with the throttle flap open.

5. The method according to claim 4, wherein the second quantity deviation test is carried out with a maximum lift of the inlet valve and with the throttle flap substantially closed.

6. The method according to claim 1, 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.

7. The method according to claim 1, wherein the first air ratio value is formed by the quotient of the lambda value measured during the first quantity deviation test and the first 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 second desired lambda value.

8. The method according to claim 1, wherein the presence of a fault in the inlet section is inferred if the first air ratio value and the second air ratio value are different.

9. The method according to claim 1, wherein the presence of coking in the inlet section is inferred if 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.

10. The method according to claim 9, wherein the presence of a leak in the inlet section is inferred if the first air ratio value is higher than a predefined second threshold value and the second air ratio value is even further increased in relation to the predefined second threshold value.

11. The method according to claim 10, wherein the predefined first and the predefined second threshold values are equal.

12. The method according to claim 11, wherein the predefined first and the predefined second threshold values are 1.

13. The method according to claim 9, wherein the predefined first and the predefined second threshold values are equal.

14. 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: a) carrying out a first quantity deviation test by which a first air ratio value is ascertained which is formed from a lambda value measured during the first quantity deviation test and a first desired lambda value of fuel combustion in combustion chambers of the internal combustion engine, wherein, in the first quantity deviation test, load control is performed by the variable inlet valve lift controller; b) carrying out a second quantity deviation test by which a second air ratio value is ascertained which is formed from a lambda value measured during the second quantity deviation test and a second 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 the throttle flap; and c) determining a comparison result from the first air ratio value and the second air ratio value, wherein a presence of a fault in an inlet section of the internal combustion engine is detectable on the basis of the comparison result.

15. An engine test unit for detecting faults in an inlet section of an internal combustion engine, which engine test unit is operatively configured to: a) carry out a first quantity deviation test by which a first air ratio value is ascertained which is formed from a lambda value measured during the first quantity deviation test and a first desired lambda value of fuel combustion in combustion chambers of the internal combustion engine, wherein, in the first quantity deviation test, load control is performed by the variable inlet valve lift controller; b) carry out a second quantity deviation test by which a second air ratio value is ascertained which is formed from a lambda value measured during the second quantity deviation test and a second 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 the throttle flap; and c) determine a comparison result from the first air ratio value and the second air ratio value, wherein a presence of a fault in the inlet section of the internal combustion engine is detectable on the basis of the comparison result.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is an exemplary flow diagram of a method according to the invention for detecting a fault, in particular coking, in the inlet section of an internal combustion engine.

DETAILED DESCRIPTION OF THE DRAWING

(2) FIG. 1 shows an exemplary flow diagram of the method according to the invention 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.

(3) In step S1, 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).

(4) In step S2, 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.

(5) In step S3, 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, the presence of a fault, in particular the presence of coking, in the inlet section of the internal combustion engine can be inferred.

(6) The first and the second quantity deviation test are performed in succession during idling operation of the internal combustion engine.

(7) The first quantity deviation test carried out in step S1 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.

(8) By contrast the second quantity deviation test in step S2 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 variable inlet valve lift controller, the load control is carried out by means of the throttle flap.

(9) Characteristic first and second air ratio values w.sub.1, w.sub.2 arise in a manner dependent on whether a fault is present in the inlet section and in particular coking is present, wherein the ratio of said air ratio values to one another makes it possible to detect the presence of a fault in the inlet section and in particular the presence of coking.

(10) A general fault in the inlet section can be inferred if the first air ratio value w.sub.1, which was ascertained in step S1, and the second air ratio value w.sub.2, which was ascertained in step S2, are different. 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 S1 and S2 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 S1 and S2 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 S1 and S2, whilst the desired lambda values λ.sub.des, 1, λ.sub.des, 2 remain unchanged.

(11) 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 S1 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, 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. 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, gives grounds for suspicion that there is a leak in the inlet section, because here, owing to the flow conditions in the second step S2, in which the internal combustion engine is operated with throttling, a smaller air quantity passes into the combustion chambers.

(12) 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.

(13) 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 S1 and the second step S2 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.

(14) 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.

LIST OF REFERENCE DESIGNATIONS

(15) S1 Method step S2 Method step S3 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