EP3707359A1

EP3707359A1 - Charge amplifier and measurement system for compensating drift, and a method therefor

Info

Publication number: EP3707359A1
Application number: EP18807551.9A
Authority: EP
Inventors: Josef Moik
Original assignee: AVL List GmbH
Current assignee: AVL List GmbH
Priority date: 2017-11-06
Filing date: 2018-11-05
Publication date: 2020-09-16
Also published as: AT520762A1; CN111433447A; WO2019084589A1; JP2021501849A; AT520762B1

Abstract

The invention relates to a method for compensating drift, in particular for compensating the zero-point drift of a combustion chamber pressure signal recorded in an internal combustion engine, a charge amplifier (1) comprising a computing unit (3) for compensating drift and a measurement system comprising said charge amplifier (1), the deviation between a second calculated combustion chamber pressure value p_2,CALCULATED and the second recorded combustion chamber pressure value p_2,RECORDED is determined, inter alia, at the second crank angle position and the deviation determined in the output voltage signal of the charge amplifier (1) is compensated by the generation of a drift compensation current that is additively or subtractively fed to the input of the charge-/voltage transformer stage of the charge amplifier (1), thus generating a drift-compensated combustion chamber pressure signal, so that the deviation is compensated by a specific time constant, which corresponds, in particular, to the actual duration of one or more working cycles or a defined or definable time.

Description

Charge amplifier and measuring system for drift compensation and a method for this purpose

The invention relates to a method for drift compensation, in particular for compensating the zero-point drift of a recorded on an internal combustion engine

Combustion chamber pressure signal, according to the preamble of the independent claim. Furthermore, the invention relates to a charge amplifier with a computation unit for drift compensation and a measuring system comprising a charge amplifier.

For accurate measurement of combustion chamber pressures in internal combustion engines are - in a known manner - piezoelectric sensors together with

Charge amplifiers used. These sensors are characterized by their

Precision, but have the disadvantage that they can detect only pressure changes but no absolute pressure. The amount of charge generated by the sensors under pressure loading is converted by charge amplifiers into a more easily processed voltage signal. Due to the not ideal isolation of the real one

Measurement structure - sensor + cable + charge amplifier - but flows continuously a small amount of charge already before their conversion in the charge amplifier through the insulation. This causes a zero-point drift of the output signal of the charge amplifier, which can only be counteracted with a corresponding drift compensation control loop in order to prevent the signal zero point from slowly saturating and thus making further detection of the charge signal impossible. Likewise, a change in the thermal condition of the sensor, e.g. at a load change of the internal combustion engine, the generation of an additional amount of charge, which also shifts the signal zero point of the output signal.

As described in the introduction, the drift compensation represents an essential one

Challenge in the design of piezoelectric charge amplifiers

Combustion chamber pressure sensors. From the prior art, two methods for drift compensation are known.

a. The so-called "continuous drift compensation" is also called

In principle, the signal filtered via a low-pass filter is used as the control deviation of the drift compensation control loop and "continuous drift compensation" from this generates a corresponding compensation current, which is added in an inverted form to the input current of the charge amplifier. This causes the mean value of the output signal of the charge amplifier to settle to the value zero. Over the time constant of the low pass the aggressiveness of the regulation can be determined - "long" vs. "short". A disadvantage of this method is that the low pass varies depending on the speed of the engine and especially at slower speeds affects the signal itself in a mitigating manner. b. The so-called "cyclic drift compensation" is described, inter alia, in EP 0 325 903. The device is known from US Pat

Charge amplifier circuit fed to a trigger signal which a specific crankshaft position - and thus piston position - in the working cycle of the

Internal combustion engine defined. Preferably, this position is in the intake phase, where the pressure is not affected by the combustion. This trigger position may be derived from a crank angle sensor or from the pressure curve itself, e.g. be generated by appropriately tracked thresholds. The

Drift compensation control now takes at the trigger position a value from the output waveform of the charge amplifier, which can be done in accordance with EP 0 325 903 by a sample and hold circuit. This value now serves as a control deviation for the drift compensation loop, i. from it, a corresponding inverted compensation current is obtained, as in the

Dauerdriftverfahren, the input of the charge amplifier is guided additively. Since the value only changes once per working cycle, a constant current for a working cycle is added as compensation. That way, one becomes

speed-dependent amplitude influencing of the signal as in the first method excluded.

However, both types of drift compensation also have a significant disadvantage for precise measurements, as described below.

As mentioned earlier, due to the non-ideal isolation of the structure, the zero point of a real charge amplifier is subject to drift, which must be compensated to avoid slowly drifting into saturation. Moreover, one can additional drift in a change in the temperature level of the piezoelectric sensor occur because, for example, the pressure membrane of the sensor expands or contracts and thus results in an additional positive or negative charge amount at the sensor output. These unwanted zero point changes must be distinguished from real zero point changes. The latter are in particular due to the operating point-dependent change in the boost pressure through the turbocharger. Furthermore, rapid changes in throttle position can contribute

Otto engines cause very dynamic changes in the absolute pressure level and thus the zero point position of the charge amplifier output signal. While now

Changes due to non-ideal isolation and due to thermal

Changes should be compensated, should real changes in the pressure level correctly not be compensated. However, the above-mentioned drift compensation circuits can not distinguish between the various causes of a zero point change and thus also regulate true pressure level changes to zero.

Although in the software of the data acquisition and evaluation systems, the so-called indexing systems - indicating systems - which the output signals of

Furthermore, a logic for determining the absolute pressure level by means of thermodynamic processes or by reference to a sensor in the intake manifold is present. However, due to the erroneous correction of real pressure level changes by the drift compensation circuit, a certain skew of the cylinder pressure curves is effected, since the supply of a constant correction current leads to a ramped output signal change. Although this distortion of the cylinder pressure curve could at the following

However, it can be corrected mathematically, but it is for rapid evaluations in real time, for example, for the determination of parameters for the control of the following combustion cycle, and for highly accurate further evaluations such as

Charge change analysis of great disadvantage. It would therefore be useful to avoid this effect.

In AT 396 634 is a method for correcting the output level of a

Charge amplifier described on the correction of the output signal of Charge amplifier is based on a correction voltage. This correction voltage is determined by comparing the current value of the charge amplifier signal at a particular crank angle position at which the absolute pressure level is known to it. The difference gives a correction voltage with which the output signal is corrected. However, since the absolute pressure level is known only in uncharged diesel engines - it corresponds approximately during the intake phase to the ambient pressure - must be derived in other engine types, the known pressure of another sensor which is mounted in the intake manifold near the intake valve. As a result, the necessary effort is increased considerably. In addition, the method has the great disadvantage that a correction voltage that once per

Working game is adapted to jump-shaped and therefore not physical

Changes in the output signal leads. Although a slow change, in the form of a ramp, can be considered instead of a sudden change - as suggested by AT 396 634 - it still results in a just ground voltage change, which does not correspond to reality. Regardless of such a correction of the output voltage is definitely one

Drift compensation required, otherwise the output signal of the charge amplifier slowly drifts into saturation and thus makes a level correction at the output no sense.

The object of the invention is now to overcome the disadvantages of the prior art

overcome. In particular, it is an object of the invention to provide a method for

To provide drift compensation, in which the output signal of

Charge amplifier adjusts itself to approximately the absolute

Combustion chamber pressure corresponds and which does not require additional pressure sensors, such as a suction tube pressure sensor. Furthermore, it is a particular object of the invention to provide a charge amplifier for the measurement of the cylinder pressure, whose output is based on the absolute pressure, right

Has output voltage level and which overcomes the above-mentioned disadvantages of the prior art in the correction of the output voltage.

In particular, this charge amplifier in contrast to the aforementioned AT 396 634 need no additional pressure sensor and no known pressure value. The object of the invention is achieved in particular by the features of the independent claim.

In particular, the invention relates to a method for drift compensation, in particular for compensating the zero-point drift of a combustion chamber pressure signal recorded on an internal combustion engine, the method comprising the following steps:

- Conversion of arranged in and / or on the cylinder

piezoelectric pressure transducer generated amount of charge in a

Output voltage signal in a, a substantially real-time computation unit comprising charge amplifier,

- Recording a first crank angle value and a first

Combustion chamber pressure value PI, recorded ^at a first crank angle position within the compression phase ^of a first work cycle,

- Recording a second crank angle value and a second

Combustion chamber pressure value P2, recorded ^at a second crank angle position within the compression phase of the first work cycle,

- Calculation of a pressure difference ^ CALCULATED, ₂ - \ between the second

recorded combustion chamber pressure value P ₂ , RECORDED and the first recorded combustion chamber pressure value

Calculation of a first cylinder volume V at the first

Crank angle position by means of the first recorded crank angle value,

- Calculation of a second cylinder volume V ₂ at the second

Crank angle position by means of the second recorded crank angle value,

Calculation of a second combustion chamber pressure value P ₂ , CALCULATED according to the following

rule:

Pl .BERECHNET ^~

in which the calculated pressure difference, V ₂ the cylinder volume at the second crank angle position, V the cylinder volume at the first

Crank angle position, and kappa is the polytropic exponent, - Determination of the deviation between the second calculated

Combustion chamber pressure P ₂ , CALCULATED and the second recorded

Combustion chamber pressure value P2, taken ^at the second crank angle position,

Compensating the detected deviation in the output voltage signal of the charge amplifier by generating a drift compensation current which is supplied to the input of the charge / voltage converter stage of the charge amplifier additively or subtractively, whereby a drift compensated

Combustion chamber pressure signal is generated so that the deviation with a certain time constant, which corresponds in particular to the current duration of one or more cycles or a defined or definable time is compensated.

Optionally, it is provided that the charge amplifier is adapted to convert the amount of charge generated by the pressure transducer into a voltage signal.

Optionally, it is provided that the charge quantity generated by a pressure transducer, the charge quantity being generated in particular by pressure loading of the pressure transducer, is converted into an output voltage signal in a charge amplifier comprising a computing unit which essentially calculates in real time.

If appropriate, it is provided that the method comprises the following further steps:

- Recording a third crank angle value and a third

Combustion chamber pressure value P ₃ , _A taken ^at a third crank angle position within the compression phase of the first work cycle,

and or

Receiving a plurality of further first crank angle values and a plurality of further first combustion chamber pressure values ^at several other first crank angle positions within the compression phase of the first cycle,

- Recording a fourth crank angle value and a fourth

Combustion chamber pressure value P ₄ , recorded ^at a fourth crank angle position within the compression phase of the first work cycle, and or

Picking up a plurality of further second crank angle values and a plurality of further second combustion chamber pressure values ^at several other second crank angle positions within the compression phase of the first cycle,

Calculation of a further pressure difference Δρ CALCULATED, 4 - 3 between the fourth recorded combustion chamber _pressure value P _4IA UFGENOMMEN ^and the third recorded combustion chamber pressure value P3, RECORDED,

and or

Calculation of a further pressure difference B CALCULATED, nm between the respectively further second recorded combustion chamber pressure value

and the respective further first recorded combustion chamber pressure value

Pm.COMED>

- Calculation of a third cylinder volume V ₃ at the third

Crank angle position by means of the third recorded crank angle value, and / or

Calculating a plurality of further first cylinder volumes V _m at a plurality of further first crank angle positions by means of the respective further first crank angle value,

Calculation of a fourth cylinder volume V ₄ at the fourth

Crank angle position by means of the fourth recorded crank angle value, and / or

Calculating a plurality of further second cylinder volumes V _n at a plurality of further second crank angle positions by means of the respective further second crank angle value,

- Calculation of a fourth combustion chamber pressure value ^NaCN following

rule:

where CALCULATE, 4-3 the further calculated pressure difference, V ₃ the

Cylinder volume at the third crank angle position, V _{4 is} the cylinder volume at the fourth crank angle position and kappa is the polytropic exponent, and or

Calculation of a further second combustion chamber pressure value P _U , BERECHNET according to the following rule:

Pn.BERECHNET ^~

where Δρ CALCULATE, nm the further calculated pressure difference, V _m the

Cylinder volume at the respectively further first crank angle position, V _{n is} the cylinder volume at the respectively further second crank angle position, and kappa is the polytropic exponent,

- Determination of the deviation between the fourth calculated

Combustion chamber pressure value ^{ur |} d the fourth recorded

Combustion chamber pressure value P ₄ , ATTAED ^at the fourth crank angle position, and / or

Determining the deviation between the respectively further second calculated combustion chamber pressure value P _U , CALCULATED ^{ur |} d the other second

recorded combustion chamber pressure value P _U ATTAED ^at the respectively further second crank angle position,

- averaging the determined deviation or deviations,

in particular by using a method for minimizing the

Least square sums and / or by linear or quadratic averaging,

Compensating for the averaged deviation in the output voltage signal of the charge amplifier by generating a drift compensation current which is fed additively or subtractively to the input of the charge / voltage converter stage of the charge amplifier, whereby a drift compensated

Combustion chamber pressure signal is generated, so that the deviation with a certain time constant, which corresponds in particular to the current duration of one or more cycles or a defined or definable time,

is compensated.

If appropriate, it is provided that a least square fit method is used for averaging the determined deviation or the deviations determined. If necessary, it is provided that the calculation of the pressure difference / s

CALCULATES, 2 l and / or ^ CALCULATES AI and / or ^ CALCULATES, nm and thus the calculation of the second combustion chamber pressure value P ₂ , CALCULATED and / or of the fourth combustion chamber pressure value P ₄ , CALCULATED and / or of the respectively further second one

Combustion chamber pressure value P _U , CALCULATED with a filtered combustion chamber pressure value or with filtered combustion chamber pressure values, and that the filtered combustion chamber pressure value or the filtered combustion chamber pressure values P2, RECORDED, Fiiter,

P3, RECORDED, Filter P4.REFOMMENTS, Filter> Pn, RECORDED, Filter And / or

Pm, Taken, filter by filtering the pressure curve by an analog or a digital low-pass filter, in particular a FIR filter is formed and / or generated or will be.

If necessary, it is provided that the calculation of the pressure difference / s

^ p CALCULATED, 2- l and / or ^ CALCULATES AI and / or ^ CALCULATED nm, and thus the calculation of the second combustion chamber pressure value P ₂ , CALCULATED and / or of the fourth combustion chamber pressure value P ₄ , CALCULATED and / or of the respectively further second one

Combustion chamber pressure value P _U , CALCULATED with an averaged combustion chamber pressure value or with averaged combustion chamber pressure values, and in that the averaged combustion chamber pressure value P _U , CALCULATED

Combustion chamber _pressure value or the averaged combustion chamber _pressure values P _1IA UFGENOMMEN, Mittel,

P2, RECORDED, means i P3, RECORDED, means P4, RECEIVED, means Pn, RECEIVED, Means and / or p _{MEASURING means} , are performed by averaging a plurality of combustion chamber _{pressure values} , wherein the combustion chamber _{pressure values} used for averaging are in particular -5 degrees to +5 degrees crank angle of the recorded combustion chamber pressure value or deviated from the recorded combustion chamber pressure values or deviate.

Optionally, it is provided that the first crank angle value and the first

Combustion chamber pressure value P _{1ia V} FGENOMMEN i ^m the range of 90 ° to 120 ° are added before top dead center BTDC, in particular 100 °, and / or that the second crank angle value and the second combustion chamber pressure value P2.AUFGENOMMEN i ^m the range of 40 ° be taken up to 70 ° before top dead center, in particular 50 ° before top dead center, and / or that the third

Crank angle value and the third combustion chamber pressure value P ₃ , _AU taken i ^m range of 90 ° to 120 ° before top dead center, in particular 100 ° before top dead center, and / or that the fourth crank angle value and the fourth combustion chamber pressure value i ^m range from 40 ° to 70 ° before top dead center, in particular 50 ° before top dead center, are recorded, and / or that the respective further first crank angle value and the respective further first combustion chamber pressure value i ^m range from 90 ° to 120 ° before top dead center, in particular 100 ° before top dead center, are recorded, and / or that the respective second crank angle value and the respective second

Combustion chamber pressure value P _U , INCLUDED i ^m range from 40 ° to 70 ° before top dead center, in particular 50 ° before top dead center recorded.

If necessary, it is thereby possible to record the various values, in particular the combustion chamber pressure values, in areas in which the real world

Combustion chamber pressure values approximately correspond to the calculated combustion chamber pressure values. Optionally occur in these areas the least interference, z. B. by the valve closing, and if necessary, the

Heat transfer losses still small, so the physical laws as

may be accepted largely valid.

Optionally, it is provided that the crank angle values of a

Kurbelwinkelaufnehmervorrichtung, in particular from a crank angle sensor, recorded.

Optionally, it is provided that the method comprises the following further steps: determination of the temperature change of the sensor and / or the cylinder and the associated additional sensor pressure, in particular by determining

Energy values and putting the energy values into a model function,

Compensation of the detected temperature change in the output voltage signal of the charge amplifier by generating a modified

Driftkompensationsstroms, which takes into account the detected temperature change, which is supplied to the input of the charge / voltage converter stage of the charge amplifier additive or subtractive, whereby a modified drift-compensated combustion chamber pressure signal is generated, so that the deviation with a certain Time constant, which corresponds in particular to the current duration of one or more cycles or a defined or definable time is compensated.

If appropriate, it is provided that a modified drift compensation current is generated, so that not only the deviation between the calculated pressure level and the measured pressure level can be compensated, but also the additional deviation to be expected due to the temperature change can be compensated for in a predictive manner.

If appropriate, it is provided that the method for determining the

Temperature change includes the following steps: Calculation of a

Temperature characteristic value by means of an energy value difference AE _y _ _x between a

Energy value E _{x of} a first cycle and an energy value E _y of another cycle, the temperature characteristic conclusions on the

Temperature change in the cylinder and possibly also the temperature change of the sensor allows or the temperature characteristic of the temperature change in the cylinder and / or possibly also corresponds to the change in temperature of the sensor.

Optionally, it is provided that the method for calculating the energy value E _{x of} the first work cycle comprises the following steps: picking up a

Combustion chamber _{pressure value} p _V0 R, _x at a crank angle position within the

Compression phase of a first cycle before the onset of combustion of a fuel mixture introduced into the cylinder, in particular at a crank angle position before the injection of the fuel mixture into the cylinder, wherein the crank angle position in particular corresponds to the first crank angle position, receiving a combustion chamber pressure value p _NAC H, x ^at a crank angle position within the working cycle, wherein the crank angle position of the combustion chamber pressure value p _NAC H, x, in particular a mirror image of the position of the crank angle position of

Combustion chamber _{pressure value} p _V0RiX after top dead center,

Calculation of a pressure difference & p _{ENERGY x} between the recorded

Combustion chamber _{pressure value} p _V0RiX and the recorded combustion chamber _{pressure value} p _NACH _{, x} , Determining the energy value E _x by means of the determined pressure difference & p _{ENERGY x} , wherein the determined energy value E _x allows conclusions to be drawn on the amount of energy released by the combustion of the working cycle or the determined energy value E _x corresponds to the released energy amount of the working cycle.

Optionally, it is provided that the combustion chamber pressure value p _NAC H, x ^at a

Crank angle position is taken within the first cycle after the combustion of the fuel mixture is substantially complete.

If necessary, it is provided that the method for calculating the energy value E _{y of} the further working cycle comprises the following steps: picking up a

Combustion chamber _{pressure value} p _V0 R, _y at a crank angle position within the

Compression phase of another cycle before the onset of combustion of a fuel mixture introduced into the cylinder, in particular at a crank angle position before the injection of the fuel mixture into the cylinder, wherein the crank angle position corresponds in particular to the first crank angle position, receiving a combustion chamber pressure value p _NAC H, _y ^at a crank angle position within the further working cycle, wherein the crank angle position of the combustion chamber pressure value PNACH.y, in particular a mirror image of the position of the crank angle position of

Combustion chamber _{pressure value} p _V0Rv after top dead center,

Calculation of a pressure difference p _{ENERGY y} between the recorded

Combustion chamber _{pressure value} p _V0Rv and the recorded combustion chamber pressure value p _NAC H, _y , determination of the energy value E _y by means of the determined pressure difference & p _{ENERGIE i} , wherein the determined energy value E _y provides conclusions on the energy released by the combustion energy of the further cycle or the determined energy value E _y corresponds to the released energy amount of the further working cycle.

Optionally, it is provided that the combustion chamber pressure value p _NAC H, _y ^at a

Crank angle position is taken within the further cycle after the combustion of the fuel mixture is substantially complete. If appropriate, it is provided that the calculation of the pressure difference (s) and thus of the energy value (s) takes place with a filtered combustion chamber pressure value or with filtered combustion chamber pressure values, and that the filtered combustion chamber pressure value or the filtered combustion chamber pressure values p _V oR, x, FUter, PNACH, x, Fiiter, PvoR.y.FUter, and / or

PN ACH, y, Füter by filtering the pressure curve by an analog or a digital low-pass filter, in particular a FIR filter, formed and / or generated or will be.

If necessary, it is provided that the calculation of the pressure difference / s and / or the p _{ENERGY y} and thus the energy value (s) with an averaged combustion chamber pressure value or averaged combustion chamber pressure values,

and that the averaged combustion chamber pressure value or the averaged one

Combustion chamber pressure values PVOR, X, means n PN -ACH, X, means n PvoR.y, means n and / or p _NAC H, y means by averaging a plurality of combustion chamber pressure values, wherein the combustion chamber pressure values used for averaging in particular -5 degrees to +5 degrees Crank angle deviates from the recorded combustion chamber pressure value or from the recorded combustion chamber pressure values or deviate.

If appropriate, it is provided that the determined energy values are used for the identification of working cycles with similar combustion,

and that the identification of the identical work cycles, the intrinsic drift of the measurement setup of pressure transducer, cable and / or charge amplifier is determined, so that even when the engine is a motor to the opposite drift

Driftkompensationsstrom is generated and thus a drifting away of the output signal of the charge amplifier is prevented.

In particular, the invention relates to a charge amplifier with a computation unit for drift compensation, in particular for compensating the zero drift of a recorded on an internal combustion engine combustion chamber pressure signal, wherein the

Charge amplifier is arranged for converting the amount of charge generated by a pressure transducer in an output voltage signal, comprising:

a connection for the pressure transducer, in particular a connection for a piezoelectric pressure sensor, optionally a connection for a Kurbelwinkelaufnehmervorrichtung, in particular a connection for a crank angle sensor.

Optionally, it is provided that the charge amplifier receives only the signal of a Kurbelwinkelaufnehmervorrichtung, in particular a crank angle sensor supplied. Optionally, it is provided that the charge amplifier no

Connection for a Kurbelwinkelaufnehmervorrichtung, in particular a connection for a crank angle sensor comprises.

Optionally, it is provided that the arithmetic unit for executing the

inventive method is arranged for drift compensation.

Optionally, it is provided that the arithmetic unit is an essentially real-time-capable arithmetic unit, and that the arithmetic unit is a part of the

Charge amplifier is.

Optionally, it is provided that the charge amplifier and / or the

Computing unit is connected to an analog / digital converter or connectable, and that the analog / digital converter detects the pressure values.

Optionally, it is provided that the charge amplifier and / or the

Computing unit is connected to a digital / analog converter or connectable, and that the digital / analog converter generates the control voltage and above the required drift compensation current.

In particular, the invention relates to a measuring system which comprises a charge amplifier according to the invention.

Optionally, the invention relates to a charge amplifier for piezoelectric combustion chamber pressure sensors in internal combustion engines, wherein the output signal of the charge amplifier at the same time corresponds to the absolute combustion chamber pressure and that for this purpose in addition to the charge signal only real-time information about at least two crank angle positions, but no other signals Sensors or no other information about otherwise determined or

estimated absolute pressure values e.g. be supplied in the intake phase.

Optionally, it is provided that the charge amplifier from a unit for detecting the crank angle position trigger signals for at least two

Crank angle positions are communicated in the compression phase of the internal combustion engine and that in one connected to the charge amplifier

Real-time computation unit from the relative pressure values detected at these times, the absolute pressure level at at least one of the two trigger times is determined thermodynamically and the deviation of the

Output signal of the charge amplifier from the thus determined absolute level at the corresponding trigger time as a control variable for the

Drift compensation loop of the charge amplifier is used, so that sets the output voltage of the charge amplifier to the absolute level.

Optionally, it is provided that the detection of the pressure values via an ADC and the generation of the control voltage by a DAC, which are connected to a real-time processor unit, which may also be part of an FPGA.

Optionally, it is provided that at least one further trigger signal on

From the end of combustion is supplied, resulting in an estimate of the energy released during combustion and from the comparison with the energy released in the previous cycle, a conclusion on a change in the temperature level of the cylinder pressure sensor is made, it is concluded by a stored model function on an expected higher drift and accordingly the

Drift compensation current is already anticipated adjusted at this time.

Optionally, it is provided that from consecutive cycles with the same energy release in the engine, the intrinsic drift of the measurement structure of piezoelectric pressure transducer, cable and charge amplifier is determined and at a motor stop a corresponding drift compensation current is impressed, so that the intrinsic drift is canceled out and even in real, transient measurements in driving operation over stop - start phases absolutely correct pressure levels result.

To achieve the object of the invention, inter alia, a thermodynamic determination of the absolute pressure level can be linked to the drift compensation control loop.

These can be a real-time capable, contained in the charge amplifier structure

Arithmetic unit trigger signals are supplied for at least two crank angle positions in the compression phase of the internal combustion engine. Optionally, the arithmetic unit can extract the signal value at these points and can calculate it with the aid of the total scaling factor, known from the sensor sensitivity and the charge amplifier transfer factor, e.g. kPa / V, convert to relative pressures.

From the adiabatic state equation for the ideal gas: p · V ⁿ = const. where p denotes the absolute pressure, V the volume and n the polytropic exponent, for the values at two crank angle positions 1 and 2 the relationship is obtained:

From this one obtains the relationship by transformation:

This equation means that the absolute pressure becomes a second

Crank angle position from the independent of a common offset of the pressure values pressure difference between the pressure at the second position and the pressure at the first position and with a combustion independent of the factor can be determined. This factor results from the respective cylinder volumes to the two positions as well as the so-called polytropic exponent. For a given engine, the cylinder volumes can be assumed to be known, since they are based on the cylinder displacement, the compression ratio and the

Push rod ratio of the crank mechanism in dependence on the crank angle can be calculated. Optionally, as the first position, a crank angle at 90 ° to 120 °, in particular at about 100 °, before top dead center [TDC] and as a second position, a crank angle at 40 ° to 70 °, in particular at about 50 ° before top dead center [OT], since in this range the real conditions approximate the ideal adiabatic equation.

Of course, the calculation may work for more than just two

Crank angle positions occur, and there may be different

mathematical methods are used for the suppression of signal interference, for example, the known method for minimizing the least square

[Least Square Fit] or even simple averaging.

If necessary, it is provided that this method in one with a

Charge amplifier linked real-time computation unit that real that occurs at a certain crank angle and scaled to pressure relative

Output signal of the charge amplifier with the associated from the

thermodynamic calculation, and that the pressure difference resulting from the comparison is used as a control deviation for the drift compensation control loop and is regulated by this to zero.

The value of the output signal of the charge amplifier at a certain

Crank angle position is thus - in contrast to the prior art - not be controlled to zero, but preferably to the approximately physically correct value of the absolute pressure. The charge amplifier can thus be between physical

Pressure changes that should be preserved, and the disturbing drift phenomena that are to be corrected differ.

If necessary, the target value of the control loop is continuously adapted in accordance with the thermodynamic calculation, and since the determined from it Compensating current for the entire cycle can be kept constant, a deviation caused by drift can be compensated in the form of over the entire next working cycle continuous ramp. Thus, an undesirable skew of the output signal waveform due to a false adjustment of real pressure changes can be avoided. Inclinations of the

However, output waveform due to drifting phenomena may also be ramped and thus optimally balanced and any hard transitions as in the prior art can be avoided. Optionally, in contrast to the prior art, neither the knowledge of the ambient pressure, nor an additional pressure sensor necessary.

In one embodiment of the subject invention, an analog / digital converter is used to determine the relative pressure values at least the first and the second crank angle position, which is connected to the real-time computing unit and at least the first and the second position

Conditioning unit receives from a Kurbelwinkelgebersignal corresponding derived trigger signals.

In this embodiment, the generation of the drift compensation current takes place via a digital / analog converter which is controlled by the real-time computation unit and from whose output voltage the compensation current is generated via a correspondingly large series resistor which corresponds to the inverting signal input of the

Charge amplifier is supplied.

As already stated above, there are, inter alia, two causes which lead to the occurrence of a drift in the output signal of a charge amplifier. On the one hand, this is the charge amplifier circuit - including sensor and cable - itself, which leads to so-called self-drifting. On the other hand, the heating or cooling of the piezoelectric sensor can cause a drift, these so-called

Discharge drift in case of sudden temperature changes for some cycles of the internal combustion engine can be quite pronounced. Therefore, in an advanced embodiment of this method, it may be particularly advantageous to anticipate an impending load change and to proactively set an increased drift compensation current to virtually completely eliminate the effect. If appropriate, this can succeed with a model function stored in the real-time computing unit and with a load determination carried out in the real-time computing unit.

The load can be determined exactly by known methods, but for the present purpose an approximate determination is sufficient. Advantageously, the real-time computing unit can trigger another trigger at a third

Crank angle position supplied at the end of combustion. If necessary, this is the same position as a first position of the compression phase, not just before, but after top dead center [TDC]. If necessary, it is provided that the

Combustion chamber _{pressure value} p _V0 R, _{x is recorded} at a first crank angle position within a first cycle before top dead center and the

Combustion chamber pressure value p _NAC H, x is recorded ^at a second crank angle position within the first cycle after top dead center. Optionally, it is provided that the combustion chamber _pressure p _V0R , _{x is recorded} in the range of 90 ° to 120 ° before top dead center, in particular 100 ° before top dead center, and the combustion chamber _{pressure value} p _NAC H, xi ^m range from 90 ° to 120 ° after the upper one

Dead center, in particular 100 ° after top dead center is recorded.

Optionally, it is provided that the combustion chamber _pressure p _V0RiX and the

Combustion chamber pressure value p _NAC H, x ^De i are recorded the same crank angle degrees before and after the top dead center and are thus arranged mirrored in particular mirror image or in particular about an axis or around the dead center.

Optionally, it is provided that the combustion chamber _{pressure value} p _V0R , _{y is recorded} at a first crank angle position within a further working _cycle before top dead center and the combustion chamber _{pressure value} p _NAC H, _y ^at a second

Crank angle position is recorded within the further cycle after top dead center. Optionally, it is provided that the combustion chamber _pressure p _V0R , _{y is recorded} in the range from 90 ° to 120 ° before top dead center, in particular 100 ° before top dead center, and the combustion chamber _{pressure value} p _NAC H, _y i ^m range from 90 ° to 120 ° after top dead center, in particular 100 ° after top dead center. If necessary, it is provided that the

Combustion chamber _pressure p _V0R , _y and the combustion chamber _{pressure value} p _NAC H, _y ^De i the same

Crank angle degrees are recorded before and after the top dead center and are thus arranged mirrored in particular mirror image or in particular about an axis or around the dead center.

By taking a pressure value also at this point, the pressure difference to the pressure at the first position can be determined and thus roughly the amount of energy released during combustion can be estimated. By comparing this amount of energy with that of the previous work cycle can on a change of the

Temperature levels in the cylinder and thus also of the sensor are closed, and can be concluded about a stored in the real-time computing model function model on an expected increased drift. Accordingly, the

Real-time computing unit already at the third time, where this is known, generate a correspondingly increased drift compensation current and thus prevent an increased drift of the sensor signal quasi simultaneously with the cause. The remaining difference can then be compensated by determining the real absolute level from the first and second positions of the following cycle and by generating a compensated compensation current.

In this way, drifting phenomena within a working cycle, such as occur particularly in a cold start operation or a run-up - Tipp-In - cold engine can be mastered.

On the basis of the properties of the method described above, a further advantageous embodiment may be possible. By determining the absolute

Pressure levels, the sensor between real, physical pressure changes and apparent pressure changes, which are caused by the intrinsic drift of the measurement setup consisting of piezoelectric pressure sensor, connecting cable and charge amplifier, distinguish. By the above-described estimation of energy released per cycle, the arithmetic unit can consecutively identify the following work cycles with similar combustion. In a sequence of such If necessary, working cycles remain for the drift control then exactly that compensation current that is necessary to compensate only for the internal drift. The size of this stream can now be stored by the processing unit in a memory.

If the motor stops during the measuring operation, then no further

Crank angle triggers are delivered. Charge booster assemblies customary today switch over to continuous drift compensation in this case. The structure proposed here, however, can muster such a compensation current by the above-described identification of the inherent drift of the system that the absolutely correct output level is maintained after a motor stop.

If necessary, there is the great advantage that the behavior of the

Cylinder pressure during stop-start phases, as they occur on vehicles with automatic start-stop automatic in city running, can be analyzed correctly and thus important information on the design of such systems are possible, especially in hybrid drives, where the internal combustion engine to enable a rapid Restart is turned by the electric motor when stopping in a specific position is of great importance.

Other features of the invention will become apparent from the claims, the

Description of the embodiment and the figure.

FIG. 1 shows a schematic representation of a first embodiment.

Unless otherwise indicated, the reference numerals correspond to the following

components:

Charge amplifier 1, analog / digital converter 2, arithmetic unit 3, trigger signals 4, digital / analog converter 5, series resistor 6, input signal 7 and output signal 8.

In this figure, the structure of a charge amplifier stage, in particular a charge amplifier 1, is shown schematically. The output signal 8 is digitized via an analog / digital converter 2 and these values are fed to the arithmetic unit 3. This unit receives trigger signals 4 from a crank angle conditioning unit defined, necessary for the thermodynamic zero correction crank angles. These represent the reference times. Alternatively, this conditioning unit can also be integrated into the arithmetic unit. The arithmetic unit compares the pressure scaled output signal 8 of the charge amplifier with that from the

thermodynamic zero point calculation calculated correct pressure value to one of the two reference times and generated according to the difference between the two

Pressure values - = control deviation - via the digital / analog converter 5 on

corresponding output signal 8, which is converted via the high-impedance series resistor 6 in a corresponding drift compensation current, the aim of which is to compensate for the deviation in the sequence to zero. The

Drift compensation current is supplied in this embodiment, the input of the charge / voltage converter stage of the charge amplifier 1, the so-called input signal 7 additively or subtractively, whereby a driftkompensiertes

Combustion chamber pressure signal is generated so that the deviation with a certain

Time constant, which corresponds in particular to the current duration of one or more cycles or a defined or definable time is compensated.

The invention is defined by the features of the claims and is not limited to the specific embodiment shown, but includes all

Charge boosters and / or measuring systems which themselves or which parts are suitable or arranged for carrying out the method according to the invention.

Claims

Method for drift compensation, in particular for compensating the zero drift of a combustion chamber pressure signal recorded on an internal combustion engine, the method comprising the following steps:

- Conversion of arranged in and / or on the cylinder

piezoelectric pressure transducer generated amount of charge in a

Output voltage signal in a, a substantially real-time computing computing unit (3) comprising charge amplifier (1),

- Recording a first crank angle value and a first

- Recording a second crank angle value and a second

- Calculation of a pressure difference & p _{CALCULATES 2} _ ₁ between the second

Calculation of a first cylinder volume V at the first

Crank angle position by means of the first recorded crank angle value,

- Calculation of a second cylinder volume V ₂ at the second

Crank angle position by means of the second recorded crank angle value,

rule:

in which the calculated pressure difference, V _{2 is} the cylinder volume at the second crank angle position, V is the cylinder volume at the first crank angle position, and kappa is the polytropic exponent,

- Determination of the deviation between the second calculated

Combustion chamber pressure P ₂ , CALCULATED and the second recorded

Combustion chamber pressure value P2, taken ^at the second crank angle position, Compensation of the detected deviation in the output voltage signal of the charge amplifier (1) by generating a drift compensation current corresponding to the input of the charge / voltage converter stage of the charge amplifier

Charge amplifier (1) is supplied additive or subtractive, whereby a drift-compensated combustion chamber pressure signal is generated, so that the

Deviation with a certain time constant, in particular the current duration of one or more work cycles or a defined or

definable time is compensated.

2. The method of claim 1 comprising further following steps:

- Recording a third crank angle value and a third

and or

- Recording a fourth crank angle value and a fourth

Combustion chamber pressure value P ₄ , recorded ^at a fourth crank angle position within the compression phase of the first work cycle,

and or

- Calculation of another pressure difference ^ p CALCULATED, 4 - 3 between the

fourth recorded combustion chamber pressure value P4, _AU taken and the third recorded combustion chamber pressure value P3, recorded,

and or

Calculating a further pressure difference P is _{calculated n} _ _m the respective further second picked combustion chamber pressure value between Pn, recorded ^and the other first recorded

Combustion chamber pressure value p _m, _A uFGENOMMEN,

- Calculation of a third cylinder volume V ₃ at the third

Crank angle position by means of the third recorded crank angle value, and / or

Calculation of a fourth cylinder volume V ₄ at the fourth

- Calculation of a fourth combustion chamber pressure value ^NaCN following

rule:

where CALCULATE, 4-3 the further calculated pressure difference, V ₃ the

Cylinder volume at the third crank angle position, V _{4 is} the cylinder volume at the fourth crank angle position, and kappa is the polytropic exponent, and / or

Calculation of a respective further second combustion chamber pressure value

P _U. ^{REQUIRE the} following rule:

Pn, CALCULATED ~

where Δρ CALCULATE, nm the further calculated pressure difference, V _m the

Cylinder volume at the respectively further first crank angle position, V _{n is} the cylinder volume at the respectively further second crank angle position, and kappa is the polytropic exponent, - Determination of the deviation between the fourth calculated

Combustion chamber pressure value ^and the fourth recorded

Determining the deviation between the respective second second

calculated combustion chamber pressure value P _U , CALCULATED ^and the respectively further second recorded combustion chamber pressure value P _U ATTAED ^to the respectively further second crank angle position,

Averaging the determined deviation or the deviations determined, in particular by using a method for minimizing the least squares of errors and / or by linear or quadratic averaging,

Compensating the averaged deviation in the output voltage signal of the charge amplifier (1) by generating a drift compensation current corresponding to the input of the charge / voltage converter stage of the charge amplifier

definable time is compensated.

3. The method according to claim 1 or 2, characterized

- that the calculation of the pressure difference / en & p _{CALCULATE 2} - \ and / or

Δρ CALCULATE, 4-3 and / or pBERECHNET, nm and thus the calculation of the second combustion chamber pressure value P ₂ , CALCULATED and / or the fourth

Combustion chamber pressure value P ₄ , CALCULATED and / or of the respectively further second combustion chamber pressure value P _U , CALCULATED with a filtered combustion chamber pressure value or with filtered combustion chamber pressure values,

- and that the filtered combustion chamber pressure value or the filtered

B re nn rough md R ckwe rte p _{1 A} UFGENOMMEN.FU ter, PIA UFGENOMMEN.FU ter _>

P3 RECORDED, Filter PUBLISHED .Filter> PUBLISHED, Filter And / or

PmAUGHT, filter by filtering the pressure curve by an analog or a digital low-pass filter, in particular a FIR filter is formed and / or generated or will be. Method according to one of claims 1 to 3, characterized

CALCULATED, 4-3 and / or ^ CALCULATED, nm and thus the calculation of the second combustion chamber pressure value P ₂ , CALCULATED and / or the fourth

Combustion chamber pressure value P ₄ , CALCULATED and / or the respective other second combustion chamber pressure value P _U , CALCULATED with an averaged

Combustion chamber pressure value or with averaged combustion chamber pressure values,

- and that the averaged combustion chamber pressure value or the averaged

Combustion chamber pressures PI UFGENOMMEN mean n PIAUFGENOMMEN means n

P3, RECEIVED, Means P4COMPOSE, Means Pn, RECEIVED, Means And / or

Pm, Taken, means by averaging a plurality of combustion chamber pressure values, wherein the combustion chamber pressure values used for averaging, in particular -5 degrees to +5 degrees crank angle deviates from the recorded combustion chamber pressure value or from the recorded combustion chamber pressure values or deviate.

Method according to one of claims 1 to 4, characterized

- That the first crank angle value and the first combustion chamber pressure value

PIAUFGENOMMEN i ^m range from 90 ° to 120 ° before top dead center, in particular 100 ° before top dead center recorded,

- And / or that the second crank angle value and the second

Combustion chamber pressure value P ₂ taken i ^m the range of 40 ° to 70 ° before top dead center, in particular 50 °, are added before top dead center,

- and / or that the third crank angle value and the third combustion chamber pressure value P3 added i ^m the range of 90 ° to 120 ° are added before top dead center BTDC, in particular 100 °,

and / or that the fourth crank angle value and the fourth combustion chamber pressure value P MEUFGENOMMEN i ^{m in the} range of 40 ° to 70 ° before top dead center, in particular 50 ° before top dead center recorded, - and / or that the respective further first crank angle value and the respective further first combustion chamber pressure value i ^m range from 90 ° to 120 ° before top dead center, in particular 100 ° before top dead center, are added,

- and / or that the respective second crank angle value and the respective second combustion chamber pressure value P _U was added i ^m the range of 40 ° to 70 ° will be added before top dead center BTDC, in particular 50 °.

6. The method according to any one of claims 1 to 5, characterized in that the

Crank angle values are recorded by a Kurbelwinkelaufnehmervorrichtung, in particular by a crank angle sensor.

7. The method according to any one of claims 1 to 6, comprising the following further

Steps:

- Determining the change in temperature of the sensor and / or the cylinder and the associated additional sensor pressure, in particular by

Determination of energy values and use of energy values in one

Model function,

Compensation of the detected temperature change in the

Output voltage signal of the charge amplifier (1) by generating a modified Driftkompensationsstroms, which determined the

Temperature change taking into account the input of the charge /

Voltage converter stage of the charge amplifier (1) is fed additive or subtractive, whereby a modified driftkompensiertes

8. The method of claim 7, wherein the determination of the temperature change

following steps include: Calculation of a temperature characteristic value by means of an energy value difference E _y _ _x between an energy value E _{x of} a first working cycle and an energy value E _y of another working cycle,

wherein the temperature characteristic conclusions on the temperature change in the cylinder and possibly also the temperature change of the sensor allows or the temperature characteristic of the temperature change in the cylinder and / or possibly also the temperature change of the sensor corresponds.

9. The method of claim 7 or 8, wherein the calculation of the energy value E _{x of} the first cycle comprises the steps of:

- Recording a combustion chamber pressure _value p _V0 R, _X at a crank angle position within the compression phase of a first cycle before the

Onset of combustion of an introduced into the cylinder

Fuel mixture, in particular at a crank angle position before the injection of the fuel mixture into the cylinder, wherein the

Crank angle position corresponds in particular to the first crank angle position,

- Recording a combustion chamber pressure value p _NAC H, x ^at a crank angle position within the working cycle, wherein the crank angle position of the

Combustion chamber _{pressure value} p _NAC H, x, in particular a mirror image of the position of the crank angle position of the combustion chamber _{pressure value} p _{V0R, x} after top dead center,

- Calculation of a pressure difference & p _{ENERGY x} between the recorded combustion chamber _{pressure value} p _V0RiX and the recorded combustion chamber _{pressure value}

PNACH, X I

- Determination of the energy value E _x by means of the determined pressure difference

& PENERGIE, X, where the determined energy value E _x allows conclusions about the amount of energy released by the combustion of the working cycle or the determined energy value E _{x of} the energy released

Working game corresponds.

10. The method according to any one of claims 7 to 9, wherein the calculation of the

Energy value E _{Y of} the further working cycle comprises the following steps:

- Recording a combustion chamber pressure _value p _V0 R, _y at a crank angle position within the compression phase of another cycle before the

Onset of combustion of an introduced into the cylinder

- Recording a combustion chamber _{pressure value} p _NAC H, _y ^at a crank angle position within the further cycle, wherein the crank angle position of the combustion chamber _{pressure value} p _NAC H, _Y , in particular is mirror image of the position of the crank angle position of the combustion chamber _{pressure value} p _V0R , _y after top dead center,

Calculation of a pressure difference & _{pEERGY y} between the recorded combustion chamber _{pressure value} p _V0Rv and the recorded combustion chamber _{pressure value}

PNACHy i

- Determining the energy value E _Y by means of the determined pressure difference pENERGiE.i, wherein the determined energy value E _Y provides conclusions about the energy released by the combustion energy of the further cycle or the determined energy value E _Y corresponds to the released energy amount of the other working cycle.

1 1. Method according to one of claims 7 to 10, characterized

that the calculation of the pressure difference (s) and thus of the energy value (s) with a filtered combustion chamber pressure value or with filtered

Combustion chamber pressure values,

- and that the filtered combustion chamber pressure value or the filtered

Combustion chamber _{pressure values} p _{0Rj jFiiter} , p _NAC H, x, Füter, PvoR.y.Feet, and / or

PN ACH, _y , Füter by filtering the pressure curve by an analog or a digital low-pass filter, in particular a FIR filter, formed and / or generated or will be.

12. The method according to any one of claims 7 to 1 1, characterized

- that the calculation of the pressure difference / en & p _{ENERGY x} and / or the pENERGiE.y ^{ur |} d thus the energy value (s) is / are calculated with an averaged combustion chamber pressure value or averaged combustion chamber pressure values,

- and that the averaged combustion chamber pressure value or the averaged

Combustion chamber pressure values p _V0 R, x, center, PN ACH, x, average, PvoR, _y , mean, and / or

PNACH.y.Mittei done by averaging a plurality of combustion chamber pressure values, wherein the combustion chamber pressure values used for averaging in particular -5 degrees to +5 degrees crank angle deviates from the recorded combustion chamber pressure value or from the recorded combustion chamber pressure values or deviate.

13. The method according to any one of claims 7 to 12, characterized

- that the determined energy values are used for the identification of cycles with similar combustion,

- And that is determined by the identification of the same work cycles, the intrinsic drift of the measurement setup of pressure transducer, cable and / or charge amplifier (1), so that even when the motor is stopped to the driving drift compensation current is generated and thus a drifting away of the output signal (8) of the charge amplifier (1) is prevented.

14. charge amplifier (1) having a computing unit (3) for drift compensation,

in particular to compensate for the zero drift of one on one

Combustion engine recorded combustion chamber pressure signal,

wherein the charge amplifier (1) for converting from a

Pressure transducer generated amount of charge is arranged in an output voltage signal, comprising:

a connection for the pressure sensor, in particular a connection for a piezoelectric pressure sensor,

optionally a connection for a crank angle sensor device, in particular a connection for a crank angle sensor,

characterized in that the arithmetic unit (3) is arranged for carrying out the method according to one of claims 1 to 13.

15. charge amplifier (1) according to claim 14, characterized in that

- that the arithmetic unit (3) is a substantially real-time capable arithmetic unit (3),

- And that the arithmetic unit (3) is part of the charge amplifier (1).

16. charge amplifier (1) according to claim 14 or 15, characterized

- That the charge amplifier (1) and / or the arithmetic unit (3) with a

Analog / digital converter (2) is connected or connectable,

- And that the analog / digital converter (2) detects the pressure values.

17. charge amplifier (1) according to one of claims 14 to 16, characterized

in

- That the charge amplifier (1) and / or the arithmetic unit (3) with a

Digital / analog converter (5) is connected or connectable,

- And that the digital / analog converter (5) generates the control voltage and above the required drift compensation current.

18. Measuring system, comprising a charge amplifier (1), according to one of

Claims 14 to 17.