Method for the Robust Identification of Knocking in an Internal Combustion Engine, Control Device, and Motor Vehicle

Abstract

A method and control device for automatically identifying knocking in an internal combustion engine, wherein, in a predefined measurement time frame, a signal of the knocking sensor is received and evaluated with respect to a criterion for detecting knocking. A basic threshold value predefined for the identification of knocking is modified by a predefined variable interference factor, which depends on a relative point in time at which an inlet valve of at least one of the cylinders closes in relation to a predefined reference point. A signal based on the sensor signal is only identified as knocking if it reaches at least the modified basic threshold value.

Claims

1-10. (canceled)

11. A method for automatic knocking identification in an internal combustion engine with a plurality of cylinders, a variable inlet valve stroke, and a knocking sensor, the method comprising: operating the internal combustion engine with an inlet valve closure before an end of an induction cycle; acquiring a sensor signal in a predetermined measurement time window by the knocking sensor; evaluating the sensor signal with regard to a predetermined criterion for detecting knocking, the evaluating further comprising determining that a signal based on the sensor signal reaches at least a predetermined basic threshold value to be identified as knocking; modifying the basic threshold value to create a modified basic threshold value using a predetermined variable interference factor that is dependent on a relative time of a closure of an inlet valve of at least one of the plurality of cylinders relative to a predetermined reference point; and identifying the signal as knocking only if it at least reaches the modified basic threshold value.

12. The method according to claim 11, further comprising: filtering the sensor signal using a predefined bandpass filter to create a filtered sensor signal; integrating the filtered sensor signal over the measurement time window to create an integral value; and comparing the integral value with the modified basic threshold value.

13. The method according to claim 11, further comprising: using an individual interference factor specified for each cylinder of the plurality of cylinders for the evaluation.

14. The method according to claim 11, further comprising: using an adaptive mechanism for the identification of a signal as knocking, wherein the adaptive mechanism learns, over time, external signals that are produced by something other than knocking and disregards the external signals for the identification of knocking.

15. The method according to claim 14, further comprising: reducing the variable interference factor in a predetermined way with increasing adaptation of the adaptive mechanism.

16. The method according to claim 15, further comprising: varying a rate of reducing the interference factor as a function of a revolution rate of the internal combustion engine.

17. The method according to claim 11, further comprising: modifying the variable interference factor by a predetermined run time factor, wherein the predetermined run time factor increases with increasing operating time of the internal combustion engine and reduces the interference factor accordingly.

18. The method according to claim 11, further comprising: using, as part of the evaluating, a hysteresis factor that takes into account that an interference signal caused by a closure of an inlet valve of one of the plurality of cylinders, which affects the sensor signal received by the knocking sensor, covers an interference period that can be shifted relative to the measurement time window for knocking identification, and defines the subregion of the measurement time window for which the interference factor is to be used.

19. A control device for an internal combustion engine for automatic detection of knocking, comprising: an input interface for acquiring a sensor signal of a knocking sensor; a data memory; an output interface for outputting a detection signal indicating a detection of knocking; and at least one processor device configured to: receive the sensor signal from the input interface in a predetermined measurement time window; evaluate the sensor signal with regard to a predetermined criterion for detecting knocking at least by determining that a signal based on the sensor signal reaches at least a predetermined basic threshold value to be identified as knocking; modify the basic threshold value to create a modified basic threshold value using a predetermined variable interference factor that is dependent on a relative time of a closure of an inlet valve of at least one of a plurality of cylinders relative to a predetermined reference point, wherein the closure of an inlet valve occurs before an end of an induction cycle; and identify the signal as knocking only if it at least reaches the modified basic threshold value.

20. The control device according to claim 19, wherein the at least one processor device is further configured to: filter the sensor signal using a predefined bandpass filter to create a filtered sensor signal; integrate the filtered sensor signal over the measurement time window to create an integral value; and compare the integral value with the modified basic threshold value.

21. The control device according to claim 19, wherein the at least one processor device is further configured to: use an individual interference factor specified for each cylinder of the plurality of cylinders for the evaluation.

22. The control device according to claim 19, wherein the at least one processor device is further configured to: use an adaptive mechanism for the identification of a signal as knocking, wherein the adaptive mechanism learns, over time, external signals that are produced by something other than knocking and disregards the external signals for the identification of knocking.

23. The control device according to claim 22, wherein the at least one processor device is further configured to: reduce the variable interference factor in a predetermined way with increasing adaptation of the adaptive mechanism.

24. The control device according to claim 23, wherein the at least one processor device is further configured to: vary a rate of reducing the interference factor as a function of a revolution rate of the internal combustion engine.

25. The control device according to claim 19, wherein the at least one processor device is further configured to: modify the variable interference factor by a predetermined run time factor, wherein the predetermined run time factor increases with increasing operating time of the internal combustion engine and reduces the interference factor accordingly.

26. The control device according to claim 19, wherein the at least one processor device is further configured to: use, as part of the evaluation, a hysteresis factor that takes into account that an interference signal caused by a closure of an inlet valve of one of the plurality of cylinders, which affects the sensor signal received by the knocking sensor, covers an interference period that can be shifted relative to the measurement time window for knocking identification, and defines the subregion of the measurement time window for which the interference factor is to be used.

27. A motor vehicle, comprising: an internal combustion engine having a plurality of cylinders; an inlet valve configured to operate with a variable inlet valve stroke; a knocking sensor; and the control device according to claim 19.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0027] FIG. 1 shows a schematic representation of a motor vehicle with knocking identification in the single figure.

DETAILED DESCRIPTION

[0028] FIG. 1 shows a schematic representation of a motor vehicle 10 with an internal combustion engine 12, which may be in particular a gasoline engine which operates or can be operated with an inlet valve closure before the end of the induction stroke in each cycle, i.e. in particular in the Miller cycle or in Miller mode. The internal combustion engine 12 comprises several, for example four or six, cylinders 14, two of which are indicated here by way of example. Specifically, these are a first cylinder 16 with a first piston 18 and a second cylinder 20 with a second piston 22. The pistons 18, 22 are connected here to a schematically indicated crankshaft 24. By way of example, the first piston 18 is near an ignition position here, while the second piston 22 is on its way to its bottom dead center.

[0029] The cylinders 14 each have an inlet valve 26 with a controlled variable valve train 28. The variable valve trains 28 are connected to a control device 30 for control.

[0030] The control device 30 schematically indicated here comprises a data memory 32 and a connected processor 34 for executing an operating or control program stored in the data memory 32. The processor 34 may, for example, be and/or comprise a microchip, a microprocessor, a microcontroller, a hardware circuit and/or the like. The control device 30 further comprises an input interface 36, via which a knocking sensor 38 of the internal combustion engine 12 is connected. Via the input interface 36, therefore, the control device can acquire a sensor signal received or provided by the knocking sensor 38 for processing by means of the processor 34 and the data memory 32.

[0031] The control device 30 is set up for knocking identification based on the detected sensor signal of the knocking sensor 38. If knocking is identified, the control device 30 may, for example, control the inlet valves 26 or the variable valve trains 28 thereof via an output interface 40 in order to avoid or reduce further knocking.

[0032] Especially in the case of turbocharged gasoline engines, a significant disturbance of the identification or detection of gasoline engine knocking can occur in conjunction with the Miller cycle, i.e. in the Miller combustion process, due to the premature inlet valve closure. The inlet valve closure, in the present case, for example, the closing of the inlet valve 26 of the second cylinder 20, can cause structure-borne sound. This structure-borne sound due to seating of the inlet valve 26 in its valve seat and/or to mechanical relaxation of the variable valve train 28 during closing of the inlet valve 26 can lead to a corresponding interference signal in the sensor signal of the knocking sensor 38, since the structure-borne sound or an acoustic signal originating from the inlet valve 26 can reach the knocking sensor 38, for example by appropriate propagation or transport in a housing or component of the internal combustion engine 12 on which the knocking sensor 38 is arranged. Such an interference signal can have a significant negative influence on knocking identification, so that such interference signals should be largely eliminated or filtered out for accurate, reliable and robust knocking identification. In the present case, this is achieved by the suitably set up control device 30 by automatic processing of the sensor signal of the knocking sensor 38.

[0033] In the present case, a command variable may be predetermined for this purpose, which results in a respective time of inlet valve closure of the inlet valves 26 based on the profile of a camshaft of the internal combustion engine 12 and a respective current spread by means of which a basic position of the camshaft is defined. This can be carried out, for example, by means of a current angular position of the crankshaft 24 relative to a respective top dead center. Depending on this command variable, i.e. a respective point in time at which the intake valve closes, a cylinder-specific interference factor can be applied to a predefined basic threshold value, i.e. a knocking threshold for knocking identification in a predefined measurement time window, for example in a main measurement time window and in a pre-ignition measurement time window. For this purpose, for example, a corresponding characteristic map regarding a relative cylinder filling and a revolution rate of the internal combustion engine 12 may be predetermined, for example stored in the data memory 32. That pre-ignition measurement time window can begin, for example, approximately at the top dead center at a crankshaft angle of 0° and can extend for example over a crankshaft movement of 20°. Following or overlapping this, the main measurement time window can extend, for example, up to a crankshaft angle of 60° to 70°.

[0034] By means of a hysteresis value, a respective time of the inlet valve closure or a migration of the interference signal caused by the inlet valve closure relative to the measurement window can be taken into account. The hysteresis value can be interpreted as a characteristic value for an angular position of the crankshaft 24, which defines or takes into account where the interference signal extends or how this occurs or moves in time relative to the measurement time window. In this way, it can be taken into account that the inlet valve closure is never completely constant, but ultimately only the region defined by the predetermined measurement time window is taken into account for knocking identification.

[0035] The initially applied cylinder-specific interference factor can be reduced depending on time, i.e. can be ramped down out of the signal processing, especially if an adaptive or learning mechanism is used for the knocking identification. Such a mechanism can, in the course of time, learn and filter out secondary noise and noise not caused by actual knocking or an effectively unavoidable background noise in the operation of the internal combustion engine 12 or can leave them unconsidered during the actual knocking identification. Such ramping down, i.e. gradual or stepwise reduction, can take place, for example, over some 100 work cycles of the internal combustion engine 12. Here the ramping down of the interference factor can be varied depending on a current revolution rate of the internal combustion engine 12, i.e. it can be slowed down or accelerated. For example, a corresponding characteristic curve against the revolution rate can be predetermined, in particular can be deposited in the data memory 32.

[0036] Likewise, the interference factor can be modified, for example multiplied, by means of a predetermined run time factor which takes aging into account, i.e. a temporal change, and increasingly reduces the interference factor with increasing operating time or aging of the internal combustion engine 12. An actual operating time or an actual number of completed cycles of the internal combustion engine 12 is relevant here and not an operating time of the motor vehicle 10. The run time factor could thus be reset for the motor vehicle 10, for example in the event of replacement of the internal combustion engine 12 or the inlet valves 26.

[0037] Overall, the examples described show how a reduction of an influence of a mechanical interference variable—here the inlet valve closure—on knocking identification during the evaluation of gasoline engine combustion can be realized.

LIST OF REFERENCE SIGNS

[0038] 10 motor vehicle [0039] 12 internal combustion engine [0040] 14 cylinder [0041] 16 first cylinder [0042] 18 first piston [0043] 20 second cylinder [0044] 22 second piston [0045] 24 crankshaft [0046] 26 inlet valve [0047] 28 variable valve train [0048] 30 control device [0049] 32 data memory [0050] 34 processor [0051] 36 input interface [0052] 38 knocking sensor [0053] 40 output interface