WO2010037588A1

WO2010037588A1 - Method and device for detecting a knocking occurrence during a switching process between operating modes of an internal combustion engine

Info

Publication number: WO2010037588A1
Application number: PCT/EP2009/060434
Authority: WO
Inventors: Stefan Kempf; Jochen Goebels; Simon Zorn; Oliver Robert Bodo; Pascal Foermer; Ulrich Lang; Timo Jahn; Anton Kantschar; Robert Sloboda; Rudi Eichhorn
Original assignee: Robert Bosch Gmbh
Priority date: 2008-09-30
Filing date: 2009-08-12
Publication date: 2010-04-08
Also published as: CN102171428B; RU2011116932A; CN102171428A; RU2528780C2; DE102008042475B4; DE102008042475A1

Abstract

The invention relates to a method for detecting a knocking occurrence during a switching process between operating modes of an internal combustion engine (2). The method comprises the following steps: - recording a course of an acoustic signal (ikr) of an internal combustion engine (2); - determining a reference level (rkr) of the acoustic signal which corresponds to a specification of a basic engine noise according to the course of the acoustic signal (ikr); and - detecting a knocking occurrence according to the reference level (rkr); wherein the reference level (rkr) of the acoustic signal is determined according to the switching process between the operating modes of the internal combustion engine (2).

Description

description

title

Method and device for determining a knocking event during a switching operation between operating modes of an internal combustion engine

Technical area

The invention relates to a knock detection of internal combustion engines, in particular in internal combustion engines, which can be operated optionally with different fuel types.

State of the art

For knock detection sound sensors are usually provided in internal combustion engines that detect structure-borne sound signals of the engine block. The knock detection is based on the integration or averaging of the filtered and rectified structure-borne sound signals and the reference levels calculated therefrom. The integration of structure-borne noise signals is usually only during a knock-relevant time range, which is determined by one or more measuring windows within a working cycle of the internal combustion engine. The structure-borne sound signals and the reference level are evaluated in the knock control for detecting a knock.

Modern internal combustion engines can be operated with several types of fuel, whereby the operation, ie the control of the combustion which is adapted to the respective type of fuel. If the type of fuel is switched during operation of the internal combustion engine, this leads to a rapidly changing noise behavior of the internal combustion engine. Although an abrupt changeover of the measurement windows, whose position changes significantly during the switchover due to other ignition times, is generally carried out, the reference level, with which the current structure-borne sound signal for knock detection is related, can only adapt to the rapidly changing noise behavior with a delay because the reference level is determined by integration or averaging. This may lead to misrecognition or non-recognition of knocking.

In addition, the knocking tendency may increase significantly just after mode switching, e.g. when switching from natural gas operation (CNG: Compressed Natural Gas) to gasoline operation. At the momentary switching between modes, it is assumed that the knock tendency immediately after switching from natural gas to gasoline operation does not differ from the tendency to knock in gasoline-only operation. In fact, however, strong knocking events could be detected shortly after the changeover, which should be avoided.

It is therefore an object of the present invention to provide a method and a device with which a non-recognition or false recognition of knocking events when switching between operating modes in an internal combustion engine can be avoided.

Disclosure of the invention

This object is achieved by the method according to claim 1 and by the device according to the independent claim. In one aspect, a method is provided for determining a knocking event during a switching operation between operating modes of an internal combustion engine. The method comprises the following steps:

Detecting a course of a sound signal of an internal combustion engine; - Determining a reference level of the sound signal corresponding to an indication of a motor noise, depending on the course of the sound signal; and

- Detecting a knocking event depending on the reference level. The reference level of the sound signal is determined depending on the switching operation between the operating modes of the internal combustion engine, i. e.g. depending on whether a switching process is taking place or not.

For a knock detection, a reference level is derived from the structure-borne noise signal of the engine block of the internal combustion engine, which represents an indication of the engine noise. The currently detected sound signal of the sound sensor is related to this reference level and from this a knock is detected. When switching the operating mode of the internal combustion engine, there is often a rapid change in the engine noise, so that the reference level must be adjusted accordingly.

In conventional methods for determining the reference level, the reference level generally changes only slowly when the operating mode is switched, and therefore the reference level only gradually adapts to the changed noise behavior. The current sound signal then differs during the switching process to a greater extent from the reference level and it can therefore be falsely detected a non-existing knock or an existing knocking can not be detected. Therefore, it is provided during the switching process, the reference level to the faster monnentane engine noise to adapt than is the case during an operating mode of the internal combustion engine.

Furthermore, the determination of the knocking event may be performed in response to a threshold value, wherein the threshold value is adjusted during the switching operation between the operating modes. In this way, it is possible to increase or decrease the sensitivity of knock detection during the switching between the modes, which is particularly associated with a noise change of the internal combustion engine.

Specifically, the reference level may be determined during a switching period depending on the history of the sound signal during a second time period that is less than a first time period, the reference level being determined outside the switching period depending on the history of the sound signal during the first time period. That while before or after the switching operation, the reference level is formed by e.g. is averaged over the first time period, the reference level during the switching operation is averaged over the second shorter time period.

According to a further embodiment, the reference level may be determined as an average of levels of the sound signal within the relevant time period or as an integration value of the course of the detected sound signal within the relevant time period.

Furthermore, to determine the reference level of the sound signal, the profile of the reference level can be low-pass filtered according to an indication of a filter time constant, the indication of the filter time constant indicating a time constant of the low-pass filtering, wherein the time constant of the low-pass filtering is selected to be smaller during the switchover period than outside the switchover period. The operating modes of the internal combustion engine may each correspond to an operation of the internal combustion engine with different fuel types, wherein the beginning of the switching period corresponds to a time that depends on leaving a first mode. The operation of the combustion engine with different types of fuel usually requires a change in the control of the internal combustion engine, so that already from or shortly after the start of the switching operation, a change in the engine noise occurs.

In particular, the switching operation can provide a mixing operation in which the internal combustion engine is operated with both types of fuel, wherein the beginning of the switching period corresponds to a time corresponding to the time of leaving the first mode or a time at which the first mode a predetermined proportion on the operation of the internal combustion engine.

The duration of the switching period may be fixed or depend on the complete achievement of the second mode.

During the switching period, a Zündwinkelvorhalt can be adjusted to delay the current one, set for operation of the internal combustion engine retardation, wherein the Zündwinkelvorhalt after a certain period of time is reduced continuously or stepwise. The retardation of the firing angle significantly reduces the likelihood of knock events occurring during the switchover process and shortly thereafter.

Furthermore, the Zündwinkelvorhalt can be adjusted in dependence on a temperature of the internal combustion engine and / or the intake air.

In order to check only relevant time periods with regard to the occurrence of knocking events, it may be provided that the course of the sound signal is checked. nals only during time windows during which knock events can occur in the internal combustion engine.

According to a further aspect, an apparatus for detecting a knocking event during a switching operation between operating modes of an internal combustion engine is provided. The device comprises:

- A sound detection unit for detecting the course of a sound signal in an internal combustion engine;

a knock detection unit which is designed to detect the course of the sound signal;

- To determine a reference level of the sound signal corresponding to an indication of a motor noise, depending on the course of the sound signal; and

- To determine a knock event depending on the reference level, characterized in that the knock detection unit is adapted to determine the reference level of the sound signal depending on the switching operation between the operating modes of the internal combustion engine.

In another aspect, an engine system is provided that includes an internal combustion engine and the above apparatus.

In another aspect, a computer program product is provided that includes program code that, when executed on a data processing unit, performs the above method.

Brief description of the drawings

Preferred embodiments of the invention are explained below with reference to the accompanying drawings. Show it: Fig. 1 is a schematic representation of an engine system with a knock detection;

Fig. 2 is a more detailed illustration of a knock detection unit of the engine system of Fig. 1; 3a to 3c signal-time diagrams for showing the profiles of the Zündwinkelvorhalts, the reference level for the knock detection and operating mode signals.

Description of embodiments

1 shows an engine system 1 with an internal combustion engine 2, which is controlled by a control unit 3. The control unit 3 is included, for example, in a conventional engine control unit, and can control all or some of the functions required for operating the engine 2.

The internal combustion engine 2 is designed to handle different types of fuels, e.g. Natural gas (CNG) or gasoline, the engine control unit 3 operating automatically or manually, i. predetermined by the driver, can adjust. The control unit 3 controls the engine 2 by means of engine control signals MS, which can for example indicate the position of a throttle valve, injection quantities (for example, by adjusting the opening and closing timings of the injectors), ignition timings and the like.

Furthermore, a knock detection unit 4 is provided, which receives sound signals SS, which are given for example in the form of an electrical variable, from a sound sensor 5 arranged on the engine 2, for example on its engine block, and can deduce therefrom whether or not knocking occurs in the internal combustion engine 2 Not. The occurrence of knocking is indicated to the control unit 3 in the form of a knock signal KS. When switching the operating modes (switching operation), which is determined by the control unit 3 or predetermined by an external signal, the control unit 3 of the knock detection unit 4, a switching signal US is available, so that the knock detection unit 4 can recognize when a change of modes occurs ,

The knock detection unit 4 basically performs a knock detection by relating the sound signals detected by the sound sensor 5 to a reference level rkr. The reference level rkr is intended to indicate a basic engine noise in the current operating state of the internal combustion engine (2).

The determination of the reference level rkr is carried out by averaging or integrating the sound signals over a certain period of time, taking into account only time windows for measurement (measurement windows) in which knocking is to be expected, ie the sound signals are only in the time windows evaluated during which an air-fuel mixture is in the cylinders, which can lead to a knocking sound (explosion) by a self-igniting combustion. The averaging or integration usually takes place over a plurality of such time windows, usually during one or more operating cycles of the internal combustion engine 2.

The mean value of the sound signals corresponds to an assumed engine noise, which may change depending on Bethebszuständen the internal combustion engine 2. Usually, during operation with a fuel type, changes in the engine noise occur only relatively slowly, so that the averaging takes place during a period in which the reference level rkr can adapt to the possible changes in the basic engine noise. The averaging is usually done using an integrator or a low-pass filter whose low-pass behavior contributes to For example, it can be set using a low-pass factor TPF. The reference level rkr can be determined in a calculation cycle from the instantaneous sound signal ikr in a discrete manner as follows:

rkr (k + 1) = ikr (k + 1) ^■ TPF + rkr (k) ^■ (1-TPF),

where k is the number of the cycle. The time constant of the low-pass filter is predetermined by the cycle time and corresponds approximately to the cycle time divided by the low-pass factor.

The above calculation for determining the reference level rkr is carried out continuously, so that the reference level rkr usually adapts to a change in the sound signal. As a result, the reference level always reflects the current engine noise.

When switching between operating modes, the tendency to knock of the internal combustion engine can increase considerably. This is especially the case when switching from a natural gas operation to a gasoline operation. Further, the engine noise changes relatively abruptly in the switching, so that, based on the above-mentioned low-pass factor or low-pass behavior, the reference level only gradually reproduces the changed engine noise. In the transition phase between the operating modes can thus occur the case that the reference level rkr and the current sound signal SS can differ significantly from each other, causing u.U. erroneously, a non-existent knocking event can be recognized as such or a knocking event can not be detected incorrectly.

The knock detection unit 4 therefore changes the low-pass factor TPF used for the calculation of the reference level when switching between modes of operation occurs. In other words, the reference level rkr during the switching indicated by the switching signal US between The operating modes quickly track the changed sound signal (engine noise). This is done by increasing the low-pass factor TPF or changing the time constant or the like. The low-pass factor TPF can be changed in the knock detection unit 4 based on the switching signal US or the corresponding low-pass factor can be provided by the control unit 3 of the knock detection unit 4.

FIG. 2 shows a block diagram for carrying out the recognition of a knocking event carried out in the knock detection unit 4. The reference level calculation described above with the aid of a first multiplication element 13, a summing element 14 and a second multiplication element 11 is performed as a function of the low-pass factor TPF. The value of the sound signal ikr is multiplied in the first multiplication element 13 by the low-pass factor TPF and the result is then added in the summing element 14 to the value of the last calculated reference level rkr multiplied by (1-LPF) in the second multiplication element 11 by the updated reference level to get rkr.

The calculated reference level rkr and as actual sound signal ikr are supplied to a threshold value comparison block 12.

The threshold value comparison block 12 receives a threshold value SW, which can be set permanently or varied depending on the operating mode of the internal combustion engine 2, for example, by the control unit 3. If the difference or the ratio between the current sound signal ikr (current noise) and the reference level rkr (engine noise) deviates too much from one another, ie the result exceeds the threshold value SW, then a knock event is detected, which is indicated by the knock signal KS. Instead of the difference or the ratio, other relationships between the reference level and the current sound signal can also be used. In particular, the threshold value SW can be adjusted during the switching operation between the operating modes. For example, the threshold SW may be increased if switching between a first mode in which the engine is quieter to a second mode in which the engine 2 is louder is the threshold SW over the threshold SW assumed during the first mode was increased and vice versa.

The length of time during which the fast reference level tracking is activated may be fixed or dependent on the type of control mode switching, i. their direction (from CNG operation to gasoline operation or vice versa) dependent. In particular, the switchover period for the activation of the fast reference level tracking can be selected so as to ensure that the reference level reached after completion of the switchover operation maps the changed engine base noise. For this purpose, it may be provided, for example, that the switching period ends after a predetermined period of time after the gasoline operating mode (second operating mode) has been completely reached.

Further, the fast reference level tracking can be started as soon as the natural gas mode (first mode) is exited, or when the proportion of the total operation of the internal combustion engine 2 determined by the natural gas mode has fallen below a certain threshold.

During the switching, a firing angle bias can be set which serves to retard the firing angle, whereby knocking events during the mixing operation can be prevented. The Zündwinkelvorhalt corresponds to an offset, which is added to the calculated ignition angle. This significantly reduces the tendency to knock. In this way, the trouble-free sequence of the changeover of the operating mode can be guaranteed. In addition, it is possible to initialize the Zündwinkelvorhalt depending on the engine and intake air temperature.

Shown in FIGS. 3 a to 3 c are signal-time diagrams for illustrating the profile of the firing angle ZV when switching the operating modes from a natural gas operation to a gasoline operation.

When switching, the pure CNG operation is first deactivated, which is indicated by the transition from a high level to a low level by the operating mode signal B_cng. After a phase of the mixing operation, the pure gasoline operation is activated, which is indicated by the mode signal B_bz in the same way (see Fig. 3c).

In the phase of mixing operation MB, i. both B_cng and B_bz are at low level, the ignition advance ZV is set by shifting the ignition point ZZP, which is indicated in ° (degrees) of the crankshaft angle, and either immediately after the mixing operation has ended (B_bz to high level) or a certain time t_del the Zündwinkelvorhalt ZV is continuously or gradually withdrawn, so that after resetting the Zündwinkelvorhalts the internal combustion engine 2 is operated with the optimum operating angle for the selected operating mode. The resulting ramp can vary in pitch and time according to the operating parameters of the engine, i. the operating conditions of the engine to be adjusted.

The diagram of FIG. 3b shows the tracking of the reference level rkr during the mixing operation. The curve K1 shows, for example, the fast reference level tracking while the curve K2 indicates the reference level course that conventionally takes place without changing the low-pass behavior.

Claims

claims

1. A method for determining a knocking event during a switching operation between operating modes of an internal combustion engine (2), comprising the following steps:

- Detecting a course of a sound signal (ikr) of an internal combustion engine

(2);

- Determining a reference level (rkr) of the sound signal corresponding to an indication of a motor noise, depending on the course of the sound signal (ikr); and

- detecting a knocking event as a function of the reference level (rkr); characterized in that the reference level (rkr) of the sound signal is determined depending on the switching operation between the operating modes of the internal combustion engine (2).

2. The method of claim 1, wherein the determination of the knocking event is performed depending on the threshold value (SW), wherein the threshold value (SW) is adjusted during the switching operation between the operating modes.

3. The method of claim 1 or 2, wherein the reference level (rkr) during a switching period is determined depending on the course of the sound signal during a second time period which is smaller than a first time period, wherein the reference level (rkr) outside the switching period dependent is determined by the course of the sound signal (ikr) during the first time period.

4. The method of claim 3, wherein the reference level as an average of levels of the sound signal within the time period or as Integration value of the course of the detected sound signal (ikr) is determined within the relevant period of time.

5. The method of claim 3, wherein for determining the reference level (rkr) of the sound signal, the profile of the reference level (rkr) is low-pass filtered according to an indication of a filter time constant (TPF), wherein the indication of the filter time constant (LPF) indicates a time constant of the low-pass filtering, the time constant of the low-pass filtering during the switching period is set smaller than outside the switching period.

6. The method according to any one of claims 3 to 5, wherein the modes of the

Combustion engine (2) each correspond to an operation of the internal combustion engine (2) with different fuel types, wherein the beginning of the switching period corresponds to a time that depends on leaving a first mode.

7. The method of claim 6, wherein the switching operation provides a mixing operation in which the internal combustion engine (2) is operated with both fuel types, the start of the switching period corresponding to a time corresponding to the time of leaving the first mode or a time, in which the first operating mode makes up a predetermined proportion of the operation of the internal combustion engine (2).

8. The method of claim 6 or 7, wherein the switching period has a duration that is fixed or depends on the complete achievement of the second mode.

9. The method according to any one of claims 3 to 8, wherein during the switching period, a Zündwinkelvorhalt is set to a current, for the operation of the internal combustion engine (2) fixed ignition is delayed, the Zündwinkelvorhalt after a certain period of time continuously or stepwise is reduced.

10. The method of claim 9, wherein the Zündwinkelvorhalt in dependence on a temperature of the internal combustion engine (2) and / or the intake air is adjusted.

11. The method according to any one of claims 1 to 10, wherein the course of the sound signal is detected only during time windows during which knock events in the internal combustion engine (2) may occur.

12. A device for determining a knocking event during a switching operation between operating modes of an internal combustion engine (2), comprising:

- A sound detection unit (5) for detecting the course of a sound signal (ikr) in an internal combustion engine (2);

- A knock detection unit (4) which is designed to - to detect the course of the sound signal;

- To a reference level (rkr) of the sound signal (ikr), which corresponds to an indication of a motor noise, depending on the course of the sound signal (ikr) to determine; and

- To determine a knock event depending on the reference level (rkr), characterized in that the knock detection unit (4) is adapted to determine the reference level (rkr) of the sound signal depending on the switching operation between the operating modes of the internal combustion engine (2).

13. Motor system comprising:

an internal combustion engine (2); and

- The device according to claim 12.

A computer program product containing program code which, when executed on a data processing unit, executes a method according to any one of claims 1 to 11.