The invention relates to a method according to the precharacterizing part of the independent claim.

For analysis of combustion methods in internal combustion engines, it is known to pick up combustion chamber signals via sensors and to evaluate them subsequently. In measurements performed on internal combustion engines, however, it is nearly unavoidable that the combustion chamber signal is disturbed by interferences so that an interference suppression has to be performed on the picked-up signal or on the data generated from it.

For analysis and optimization of the combustion methods of internal combustion engines and, as the case may be, also for control device calibration, it is customary, for instance, to record the pressure developments in the interior of the cylinders by means of suited pressure pick-ups, charge amplifiers and fast data acquisition systems. As a consequence of the not always ideal conditions for installation of the pressure sensors and due to external influences such as structure-borne noise signals or structure-borne noise vibrations as caused e.g. by the closing of the valves, the measured pressure curve is afflicted by various disturbing influences which will affect the accuracy of the evaluations. For this reason, it is known to subject the cylinder pressure signal to filtration.

By such a filtration, however, also possible pulsating vibrations superimposed on the cylinder pressure as well as high pressure gradients such as occurring in cases of pre-ignition, will be filtered and thus be reduced in amplitude. Incorrect detection of such phenomena entails the danger that the engine may be overloaded and thus be damaged. Also a reduction of the pressure gradient will prevent a correct determination of the combustion noise.

Since these phenomena occur in the range around the maximal pressure, one possibility for avoidance of the above mentioned side effects resides in not filtering the signal in a uniform manner across the entire crankshaft angle range.

It is known, for instance, that the cylinder pressure signal can be first digitized in a temporally synchronous manner, then be transformed to an angular basis and then be smoothed by weighted averaging wherein, for this sliding averaging, the weight function as well as the window width can be varied via the crankshaft angle.

Since, however, the above is a smoothing method that is applied on a signal which is transformed to a crankshaft angle, it will have the significant disadvantage of being ill-suited to indicate an exact filter characteristic line or an exact limiting frequency because the temporal distance between the crankshaft angle positions is changing with the rotary speed.

According to a further known method, there is performed a crankshaft-dependent filtration of the cylinder pressure development that is adapted to specific disturbance variables, wherein, however, the crankshaft information is in turn derived from the cylinder pressure curve. This has the disadvantage that the crankshaft information at a given point of time is known only approximately and that the current changes of the rotary speed caused by the individual cylinders are left entirely unconsidered.

Since, further, the sample frequency on the time basis is normally considerably higher than on the crankshaft basis, the detected combustion chamber signal will lose information as a consequence of the angle-synchronous smoothing. Further, also the determination of the crankshaft position from an analysis of the cylinder pressure development is massively restricted in its accuracy and is not useful for high-quality evaluation of data.

It is, now, an object of the invention to provide an improved method for at least partial interference suppression in a combustion chamber signal by which the disadvantages of the state of the art are overcome. Particularly, it is an object of the invention to allow for a high-quality evaluation of data of cylinder pressure signals measured in an indication system if the cylinder pressure signals are affected by interferences.

The object of the invention is achieved particularly by the feature defined in the independent claim.

The invention preferably relates to a method for producing an output data stream with at least partial interference suppression by detecting and selectively filtering a combustion chamber signal picked up at an internal combustion engine, comprising the following steps:

- picking up a combustion chamber signal by a combustion chamber sensor and producing a combustion chamber signal data stream by temporally synchronized digitation of the combustion chamber signal,
- simultaneously picking up a crankshaft angle signal and producing a crankshaft signal data stream by temporally synchronized digitation of the crankshaft angle signal,
- splitting or duplicating the combustion chamber signal data stream into a first combustion chamber signal data flow and a second combustion chamber signal data flow,
- producing a first filtered combustion chamber signal data stream by filtering the first combustion chamber signal data flow in a first filter,
- if appropriate, producing a second filtered combustion chamber signal data stream by filtering the second combustion chamber signal data flow in a second filter,
- producing a first transformed combustion chamber signal data stream by transforming the first filtered combustion chamber signal data stream from a time basis to a crankshaft angle basis by use of the picked-up crankshaft signal data stream, and producing a second transformed combustion chamber signal data stream by transforming the second, if appropriate filtered, combustion chamber signal data stream from a time basis to a crankshaft angle basis by use of the picked-up crankshaft signal data stream,
- combining the transformed combustion chamber signal data streams so that the output data stream comprises the first transformed combustion chamber signal data stream in a first crankshaft angle range and the second transformed combustion chamber signal data stream in a second crankshaft angle range.

Optionally, it can be provided that the first transformed combustion chamber signal data stream serves as a base signal and, between specific or selectable crankshaft angles, is replaced by the second transformed combustion chamber signal data stream.

Optionally, it can be provided that the crankshaft angles between which the first transformed combustion chamber signal data stream is replaced by the second transformed combustion chamber signal data stream are freely selectable and/or that the first transformed combustion chamber signal data stream serves as a base signal and, between freely selectable crankshaft angles, values from the second transformed combustion chamber signal data stream are taken over into the base signal.

Optionally, it can be provided that, prior to transformation to a crankshaft angle basis, the first combustion chamber signal data stream is filtered and/or numerically smoothed in a first filter, and/or that, prior to transformation to a crankshaft angle basis, the second combustion chamber signal data stream is filtered and/or numerically smoothed in a second filter.

Optionally, it can be provided that, in the first crankshaft angle range, particularly in the low pressure part of the combustion method between 100° and 50° before the top dead center, a thermodynamic zero adjustment is performed.

Optionally, it can be provided that the second crankshaft angle range comprises at least a part of the high pressure part or the entire high pressure part of the combustion method, and/or that the second crankshaft angle range comprises a range from 30° before the upper dead center of the high pressure part to 120° after the upper dead center of the high pressure part of the combustion method.

Optionally, it can be provided that, in the transition range between the first crankshaft angle range and the second crankshaft angle range, the output data flow comprises a transition data flow or is formed by the transition data flow by which a steady and/or smooth transition is generated between the first transformed combustion chamber signal data stream and the second transformed combustion chamber signal data stream, wherein the transition data flow is formed by a crossfading function such as particularly a Gaussian integral curve or a linear function.

Optionally, it can be provided that the first filter and the second filter can be parametrized independently from each other and freely.

Optionally, it can be provided that the first filter is designed to perform, in the low pressure part of the combustion method, a basic smoothing of the combustion chamber signal or of the first combustion chamber signal data stream, and/or that the first filter is designed to filter relevant interferences such as mechanical interferences or structure-borne noise vibrations caused by the closing of the valves.

Optionally, it can be provided that the second filter is designed to be able, in the high pressure part of the combustion method, to filter particularly interferences caused by the sensor mounting but to allow passage of other vibrations such as e.g. pulsed vibrations.

Optionally, it can be provided that the filter or the filters is/are designed as low-pass filters, bandpass filters, band-stop filters or as filters for numerical smoothing.

Optionally, it can be provided that the first filter is a low-pass filter or that the first filter is a low-pass filter having a limit frequency of 1 kHz to 5 kHz.

Optionally, it can be provided that the second filter is a low-pass filter or that the second filter is a low-pass filter having a limit frequency of 20 kHz to 100 kHz.

Optionally, it can be provided that the filter or the filters is/are designed to filter the respective combustion chamber signal data stream in real time.

Optionally, it can be provided that the combustion chamber signal is a cylinder pressure signal of the combustion chamber or a pressure signal of a combustion chamber pressure sensor of an indexed motor.

Optionally, it can be provided that the filtering times of the filtered combustion chamber signal data stream or of the filtered combustion chamber signal data streams are compensated, and/or that the transformation to a crankshaft angle basis and the transformation of the filtering times are performed in one step, particularly simultaneously.

Optionally, it can be provided that the crankshaft angle signal corresponds to a crankshaft angle development which is picked up by a crankshaft angle pickup device.

Optionally, it can be provided that the temporally synchronous digitization is each time performed by an A/D converter wherein the A/D converter particularly is an 18-bit converter having a sample rate of 2 MHz.

Optionally, it can be provided that the filter or the filters are digital filter stages, particularly digital filter stages of the FIR type (Finite Impulse Response Filter).

Optionally, it can be provided that the producing of the output data stream is performed in real time, particularly in real time but delayed by the filtering time to be compensated.

Optionally, it can be provided that the producing of the output data stream is performed in real time, particularly in real time but delayed by the filtering time to be compensated, and that, for combining the transformed combustion chamber signal data streams into the output data stream, use is made of a digital signal processor or an FPGA (“Free Programmable Gate Array”).

Optionally, it can be provided that the method comprises the following steps:

- splitting or multiplying the combustion chamber signal data stream into a first combustion chamber signal data flow, in a second combustion chamber signal data flow, and in a third or further combustion chamber signal data flow,
- optionally, filtering the third or further combustion chamber signal data flow in a third or further filter,
- producing a third or further transformed combustion chamber signal data stream by transforming the third or further optionally filtered combustion chamber signal data stream from a time basis to a crankshaft angle basis by use of the picked-up crankshaft signal data stream,
- combining the transformed combustion chamber signal data streams so that the output data stream is formed by the first transformed combustion chamber signal data stream in a first crankshaft angle range, by the second transformed combustion chamber signal data stream in a second crankshaft angle range, and by the third or further combustion chamber signal data stream in a third or further combustion chamber signal data stream.

Optionally, it can be provided that the transition between the first transformed combustion chamber signal data stream (P1(phi)) and the values of at least one further transformed combustion chamber signal data stream (Pn(phi)) is defined by a freely adjustable crankshaft angle window (z), wherein the transition is performed according to the following rule:

phi 21 phi1: pr(phi)=p1(phi)

phi1<=phi<=phi1+z: pr(phi)=p1(phi)*(1−u(phi−phi1))+pn(phi)*u(phi−phi 1)

phi1+z<phi<phin: pr(phi)=pn(phi)

phin<=phi <=phin+m: pr(phi)=pn(phi)*(1−u(phi−phin))+p1(phi)*(u(phi−phin))

phi>phin+m: pr(phi)=p1(phi)

wherein phi is the crankshaft angle, phi1 is the first freely settable crankshaft angle, phin is a further freely settable crankshaft angle, p1(phi) is the first transformed combustion chamber signal data stream, pn(phi) is a further transformed combustion chamber signal data stream, u is the crossfading function forming the transition data stream, and z is a first freely settable crankshaft angle window, and m is a further freely settable crankshaft angle window, and pr is the output data stream.

According to a first exemplary embodiment, there is proposed the use of a filter, particularly a digital filter, which is applied only in a specific predefinable crankshaft angle range. The interfering vibrations caused by the closing of the valves are generated roughly in a range of 120° before the TDC (top dead center). For a thermodynamic zero adjustment which requires interference-free data, use is typically made of a range of 100° to 50° before the TDC. The maximum pressure gradient and pulsed vibrations, however, will occur only around the TDC and after it. Thus, it is advantageous to let the low-pass filter be effective only up to about 30″ before the TDC and then to switch it off. The sudden deactivation of a filter, however, typically leads to irregularities in the signal development. To avoid these, a steady or sliding transition between the filtered signal and the unfiltered signal is provided. For this purpose, use is made of a so-called crossfading function (e.g. a Gaussian integral curve), and there is defined a crankshaft range for the transition:

If the pressure is given by the function p(phi)), and the low-pass-filtered pressure curve by pfilt(phi), and the crossfading function is given by u(x); wherein it is required that u(0)=0 and u(z)=1; there will thus apply, for the corrected pressure curve pk(phi):

For phi<phi1: pk(phi)=pfilt(phi)

For phi1<=phi<=phi1+z: pk(phi)=pfilt(phi)*(1−u(phi−phi1))+p(phi)*u(phi−phi1)

For phi>phi1+z: pk(phi)=p(phi)

According to the first or a further exemplary embodiment, the high-frequency data stream supplied by an A/D converter (e.g. 18 Bits with a 2 MHz sample rate) is conducted into two mutually independent digital filter stages (e.g. of the FIR type) whose types and limiting frequencies can be freely defined by the end user of the measurement system. These can be e.g. low-pass filters or band-stop filters. The latter are of advantage e.g. in case that, in the high-pressure part of the cylinder pressure curve, there will occur narrow-band resonances dependent on the sensor mounting. Subsequent to these filtrations, the data are transformed to the crankshaft angle by use of the signals of a crankshaft angle pick-up device. In this step, the filtering times which are unavoidable due to the real-time computation of the digital filters will be considered and compensated so that the filters will cause no signal shifting over the crankshaft angle axis even in case of different rotary speeds. Subsequent thereto, the two generated crankshaft-angle-dependent filtered signal developments are again combined into a single development. Preferably, as a basic pattern herein, use is made of the curve filtered by the first filter, preferably the basic filter. Starting from a specific crankshaft angle phi1 which is freely definable by the user, the values of the second curve are taken over for the result signal and, starting from a further crankshaft angle phi2 which again is freely definable, the values from the first curve will be taken over again.

However, in order to avoid discontinuities at the transition sites, it is preferable not to perform a hard switching but a sliding transition between the curve filtered by the first filter and the curve filtered by the second filter. For this purpose, a crossfading function (e.g. a Gaussian integral curve) is used, and there is defined a crankshaft angle window (n) for the transition:

If the pressure curve filtered by filter 1 is given by the function p1(phi) and the pressure curve filtered by filter 2 is by the function p2(phi) and the crossfading function is given by u(x), wherein it is required that u(0)=0 and u(z)=1, the following applies for the resulting pressure curve pr(phi):

For phi<phi1: pr(phi)=p1(phi)

For phi1<=phi<=phi1+z: pr(phi)=p1(phi)*(1−u(phi−phi1))+p2(phi)*u(phi−phi1)

For phi1+z<phi<phi2: pr(phi)=p2(phi)

For phi2<=phi<=phi2+z: pr(phi)=p2(phi)*(1−u(phi−phi2))+p1(phi)*(u(phi−phi2))

For phi>phi2+z: pr(phi)=p1(phi)

Examples of a possible crossfading function u(phi) could be e.g. a linear function or a Gaussian integral curve.

The method for generating the filtered development of a cylinder pressure curve optionally comprises steps in which the digitized pressure curve is passed through digital filter stages which can be freely parameterized in their type and limiting frequency and whose output developments will then be combined again into a resultant new pressure curve, wherein, before a definable crankshaft angle, there are used the values of the output development of the first filter, then the values of the output development of the second filter and then again the values of the output development of the first filter.

Preferably, it is provided that a sliding switch-over between the output curves of the digital filters is performed with the aid of a crossfading function. Herein, it is preferred that the digital filtration, the transformation of the filtered data from a time basis to a crankshaft angle and the combining of the output curves into a resulting crankshaft-angle-dependent development are performed in real time in a digital signal processor or FPGA (“Free Programmable Gate Array”).

Hereunder, an exemplary embodiment of the invention will be described in greater detail with reference to the FIGURE.

FIG. 1 shows a schematic representation of the process involved in a method for producing a combustion chamber signal data stream with interference suppression or at least partial interference suppression.

Unless indicated otherwise, the reference numerals correspond to the following features: combustion chamber signal 1, combustion chamber signal data stream 2, crankshaft signal 3, crankshaft signal data stream 4, first filter 5, second filter 6, third filter 7, transformation (of the first combustion chamber signal data stream) 8, transformation (of the second combustion chamber signal data stream) 9, transformation (of the third combustion chamber signal data stream) 10, parameter 11, combining (of the output data stream) 12, disturbed signal 12, high-frequency change of the combustion chamber signal data stream at ignition 14, interference-suppressed output data flow 15, transition data stream 16, first crankshaft angle range 17, transition range 18, second crankshaft angle range 19, first transformed combustion chamber signal data stream 20, second transformed combustion chamber signal data stream 21, third transformed combustion chamber signal data stream 22, first filtered combustion chamber signal data stream 23, second optionally filtered combustion chamber signal data stream 24, third optionally filtered combustion chamber signal data stream 25, first combustion chamber signal data stream 26, second combustion chamber signal data stream 27, third combustion chamber signal data stream 28.

According to FIG. 1, in a first step, a combustion chamber signal 1 is picked up. This combustion chamber signal 1 can be e.g. a signal picked up via a pressure sensor, or another signal. Further possibilities would consist in the output signal of a knock sensor or the output sensor of a temperature sensor. In the present preferred embodiment, the invention is realized, by way of example, in connection with a pressure signal, particularly a pressure signal of the combustion chamber pressure sensor of an indexed motor.

The picked-up combustion chamber signal 1 is transformed to a combustion chamber signal data stream 2. This transformation is performed particularly by digitizing, preferably by temporally synchronous digitizing, e.g. in an A/D converter.

At the same time, e.g. via a crankshaft angle pick-up device, a crankshaft signal 3 is picked up and then is digitized. This transformation of the crankshaft signal 3 to a crankshaft signal data stream 4 is carried out particularly by temporally synchronous digitizing with high-frequency, e.g. by scanning, counting and interpolating in an A/D converter.

For the further processing of the combustion chamber signal data stream 2, this stream will be split and/or duplicated into a first combustion chamber signal data stream 26 and a second combustion chamber signal data stream 27. The splitting into a first combustion chamber signal data stream 26 and a second combustion chamber signal data stream 27 allows for an independent processing of the combustion chamber signal data stream in two different method steps. Thus, the first combustion chamber signal data stream 26 is filtered in a first filter 5 without influencing the second combustion chamber signal data stream 27 in the process.

The first filter can be e.g. a low-pass filter, a bandpass filter or a band-stop filter. In the present embodiment, the first filter 5 is designed as a low-pass filter, preferably a low-pass filter having a limit frequency of 1 kHz to 5 kHz. Further, the first filter 5 serves for basis interference suppression. Particularly, in the present embodiment, the purpose of the first filter resides in filtering the interferences of the combustion chamber signal 1 that are caused by the closing of the valves of the internal combustion motor. These are relatively high-frequent interferences which can be removed from the combustion chamber signal 1 or from the combustion chamber signal data stream 2 by the lowpass filter.

Subsequently, a transformation 8 of the first filtered combustion chamber signal data stream 23 from a time basis to a crankshaft angle basis is performed, wherein the crankshaft signal data stream 4 used for this purpose consists in the data of the crankshaft signal 3. According to the present embodiment, also the equalization of the filtering times will take place during the transformation 8. These filtering times are caused particularly by the real-time computation of the—particularly digital—filters. By this equalization, no signal shifts will occur over the crankshaft angle axis also in case of different rotary speeds.

Further, according to a preferred embodiment, also the second combustion chamber signal data stream 27 can be filtered and/or numerically smoothed in a second filter 6. This filtering or smoothing in the second filter 6 is preferably performed in parallel and thus independently from the filtration of the first combustion chamber signal data stream 26 in the first filter 5. Optionally, according to a further embodiment, the second combustion chamber signal data stream 27 can also be passed on without filtration. In the present embodiment, the second filter 6 is designed as a low-pass filter, particularly a low-pass filter having a limit frequency of 20 kHz to 100 kHz. Further, the second filter 6 serves for possible additional interference suppression.

Subsequently, a transformation 9 of the second optionally filtered combustion chamber signal data stream 24 from a time basis to a crankshaft angle basis is performed. In the transformation 9, there is preferably also performed the equalization of the filtering times.

The same is performed during the transformation 8 of the first filtered combustion chamber signal data stream 23 from a time base to a crankshaft angle base.

If required, there is provided a third optionally filtered combustion chamber signal data stream 25 which is produced by filtration of a third combustion chamber signal data stream 28 in a third filter 7. Also this third optionally filtered combustion chamber signal data stream 25 is transformed, in a transformation 10, from a time base to a crankshaft angle base. In the transformation 10, there is preferably also performed the equalization of the filtering times.

In a further step, an output data flow 15 is formed by means of combining 12. According to the present embodiment, this output data flow comprises parts or a part of the first transformed combustion chamber signal data stream 20 and the second transformed combustion chamber signal data stream 21. Particularly, the output data flow 15 comprises at least a part of the first transformed combustion chamber signal data stream 20 and at least a part of the second transformed combustion chamber signal data stream 21. According to the method, there is provided a first crankshaft angle range 17 in which the output data flow 15 corresponds to the first transformed combustion chamber signal data stream 20. Further, a second crankshaft angle range 19 is provided in which the output data flow 15 corresponds to the second transformed combustion chamber signal data stream 21. The first crankshaft angle range 17 preferably comprises that range where an interference occurs which has to be filtered or to be eliminated. In the present case, the first crankshaft angle range 17 comprises the low-pressure part of the combustion method and that range where the valves of the corresponding cylinder of the internal combustion engine are closed. According to the present method, the disturbed signal 13, being illustrated merely for better understanding, is replaced by the first transformed combustion chamber signal data stream 20 which has been filtered in the first filter 5, so that interferences will be eliminated and the output data flow 15 will be, or have been, interference-suppressed. In the second crankshaft angle range 19, on the other hand, the output data flow 15 is formed by the second transformed combustion chamber signal data stream 21 which also reproduces high-frequency changes of the combustion chamber signal data stream caused by pulsed combustion, and/or possible interferences caused by the sensor mounting. In the present case, the second crankshaft angle range 19 comprises the high-pressure part of the combustion method.

As a result of the above combining 12, a different filtering or smoothing is performed in dependence on the crankshaft angle range, wherein the crankshaft angle ranges can be determined or selected by parameters 11.

For avoidance of discontinuities in the output data flow 15, a transition range 18 with a transition data stream 16 is arranged between two lined-up transformed combustion chamber signal data streams 20, 21. Particularly, the transition data stream 16 is suited or designed to bring about a steady development of the output data flow 15 between the two lined-up transformed combustion chamber signal data streams 20, 21. The transition data stream 16 can be e.g. a Gaussian integral curve whose boundary conditions correspond to the boundary conditions of the lined-up combustion chamber signal data streams.

In all embodiments, it can be provided that the filters are designed to filter and/or numerically smoothen the combustion chamber signal data streams in a filter prior to transformation to a crankshaft angle basis.

In all embodiments, it can be provided that the first transformed combustion chamber signal data stream corresponds to a first filtered and/or smoothed and transformed combustion chamber signal data stream.

In all embodiments, it can be provided that the second, third and further transformed combustion chamber signal data streams corresponds to a second, third and further optionally filtered and/or optionally smoothed and transformed combustion chamber signal data stream.

In all embodiments, it can be provided that the high-pressure part of the combustion method corresponds to the high-pressure range of the combustion method.

In all embodiments, it can be provided that the low-pressure part of the combustion method corresponds to the low-pressure range of the combustion method.

In all embodiments, it can be provided that the output data stream is formed, in a first crankshaft angle range, by the first transformed combustion chamber signal data stream and, in a second crankshaft angle range, by the second transformed combustion chamber signal data stream.

According to a further embodiment of the method, the combustion chamber signal data stream is split or multiplied into two, three, four, five, six or more combustion chamber signal data streams.

According to a further embodiment of the method, the first, second, third, fourth, fifth, sixth or further combustion chamber signal data streams that have been split or multiplied from the combustion chamber signal data stream are filtered or smoothed in an associated first, second, third, fourth, fifth, sixth or further filter.

According to a further embodiment of the method, the filtered or optionally filtered first, second, third, fourth, fifth, sixth or further combustion chamber signal data streams are transformed from a time basis to a crankshaft angle basis in an associated first, second, third, fourth, fifth, sixth or further transformation.

According to a further embodiment of the method, the output data stream comprises parts or a part of a first, second, third, fourth, fifth, sixth or further transformed combustion chamber signal data stream or is generated by these/it.