阅读说明：本技术 用于漂移补偿的电荷放大器和测量系统以及漂移补偿方法 (Charge amplifier and measurement system for drift compensation and drift compensation method ) 是由 约瑟夫·莫依克 于 2018-11-05 设计创作，主要内容包括：本发明涉及一种用于漂移补偿的方法,特别是用于补偿在内燃机上接收到的燃烧室压力信号的零点漂移的方法,涉及带有用于漂移补偿的计算单元(3)的电荷放大器(1),并且涉及包括此电荷放大器(1)的测量系统,其中确定在第二曲柄角位置处所计算出的第二燃烧室压力p<Sub>2,计算</Sub>和所接收的第二燃烧室压力p<Sub>2,接收</Sub>之间的偏差等,并且在所述电荷放大器(1)的输出电压信号中通过产生漂移补偿电流来补偿所确定的偏差,所述漂移补偿电流以加或减的方式被供给到所述电荷放大器(1)的电荷/电压变换器级的输入,以此产生被漂移补偿的燃烧室压力信号,使得以一定的时间常数补偿所述偏差,所述时间常数尤其是等于一个或多个工作循环的当前的持续时间或等于一个限定的或可限定的时间。(The invention relates to a method for drift compensation, in particular for compensating for zero point drifts of combustion chamber pressure signals received at an internal combustion engine, to a charge amplifier (1) having a computing unit (3) for drift compensation, and to a measuring system comprising such a charge amplifier (1), wherein a second combustion chamber pressure p calculated at a second crank angle position is determined 2, calculating And the received second combustion chamber pressure p 2, receiving And compensating the determined deviation in the output voltage signal of the charge amplifier (1) by generating a drift compensation current which is supplied to the input of the charge/voltage converter stage of the charge amplifier (1) in an additive or subtractive manner, thereby generating a drift compensated The compensated combustion chamber pressure signal is such that the deviation is compensated with a time constant, which is in particular equal to the current duration of one or more operating cycles or to a defined or definable time.)

1. Method for drift compensation, in particular for compensating for a zero drift of a combustion chamber pressure signal received at an internal combustion engine, wherein the method comprises the following steps:

-converting, in a charge amplifier (1) comprising a calculation unit (3) performing substantially real-time calculations, an amount of charge generated from a piezoelectric pressure sensor arranged in and/or on the cylinder into an output voltage signal,

-receiving a first crank angle value and a first combustion chamber pressure value p at a first crank angle position within a compression phase of a first working cycle _{1, receiving} ，

-receiving a second crank angle value and a second combustion chamber pressure value p at a second crank angle position within the compression phase of the first work cycle _{2, receiving} ，

-calculating the received second combustion chamber pressure value p _{2, receiving} And the received first combustion chamber pressure value p _{1, receiving} Pressure difference Δ p therebetween _{Calculation, 2-1} ，

-calculating a first cylinder volume V at a first crank angle position from the received first crank angle value ₁，

-calculating a second cylinder volume V at a second crank angle position from the received second crank angle value ₂，

-calculating a second combustion chamber pressure value p according to the following formula _{2, calculating} ：

Wherein Δ p _{Calculation, 2-1} Is the calculated pressure difference, V ₂Is the cylinder volume at said second crank angle position, V ₁Is the cylinder volume at the first crank angle position, and kappa is the polytropic exponent,

-determining a second combustion chamber pressure p calculated at said second crank angle position _{2, calculating} And the received second combustion chamber pressure p _{2, receiving} In between The deviation is a function of the time of day,

-compensating the determined deviation in the output voltage signal of the charge amplifier (1) by generating a drift compensation current which is supplied in an additive or subtractive manner to the input of the charge/voltage converter stage of the charge amplifier (1), thereby generating a drift compensated combustion chamber pressure signal such that the deviation is compensated with a time constant which is in particular equal to the current duration of one or more operating cycles or to a defined or definable time.

2. The method of claim 1, further comprising the steps of:

-receiving a third crank angle value and a third combustion chamber pressure value p at a third crank angle position within a compression phase of the first working cycle _{3, receiving} ，

And/or

-receiving a plurality of further first crank angle values and a plurality of further first combustion chamber pressure values p at a plurality of further first crank angle positions within a compression phase of the first working cycle _{m, receiving} ，

-receiving a fourth crank angle value and a fourth combustion chamber pressure value p at a fourth crank angle position within a compression phase of the first working cycle _{4, receiving} ，

And/or

-receiving a plurality of further second crank angle position values and a plurality of further second combustion chamber pressure values p at a plurality of further second crank angle positions within the compression phase of the first working cycle _{n, receiving} ，

-calculating the received fourth combustion chamber pressure p _{4, receiving} And the received third combustion chamber pressure p _{3, receiving} With a further pressure difference ap between _{Calculation, 4-3} ，

And/or

-calculating each further second combustion chamber pressure value p received _{n, receiving} And each received further first combustion chamber pressure value p _{m, receiving} With a further pressure difference ap between _{Calculation of n-m} ，

-calculating a third cylinder volume V at a third crank angle position from the received third crank angle value ₃，

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

-calculating a fourth cylinder volume V at a fourth crank angle position from the received fourth crank angle value ₄，

And/or

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

-calculating a fourth combustion chamber pressure value p according to the following formula _{4, calculating} ：

Wherein Δ p _{Calculation, 4-3} Is the calculated additional pressure difference, V ₃Is the cylinder volume at the third crank angle position, V ₄Is the cylinder volume at the fourth crank angle position, and kappa is the polytropic exponent,

And/or

-calculating each further second combustion chamber pressure value p according to the following formula _{n, calculating} ：

Wherein Δ p _{Calculation of n-m} Is the calculated additional pressure difference, V _mIs the cylinder volume, V, at each other first crank angle position _nIs the cylinder volume at each of the additional second crank angle positions, and kappa is the polytropic exponent,

-determining a fourth combustion chamber pressure value p calculated at a fourth crank angle position _{4, calculating} And the received fourth combustion chamber pressure value p _{4, receiving} The deviation between the two or more of them,

And/or

-determining the respective calculated second combustion chamber pressure value p at the respective second further crank angle position _{n, calculating} And each received additional second combustion chamber pressure value p _{n, receiving} The deviation between the two or more of them,

Averaging the determined deviation or the determined deviations, in particular by using a method for minimizing the sum of squared errors and/or by linear averaging or square averaging,

-compensating for the average deviation in the output voltage signal of the charge amplifier (1) by generating a drift compensation current which is supplied to the input of the charge/voltage converter stage of the charge amplifier (1) in an additive or subtractive manner, thereby generating a drift compensated combustion chamber pressure signal such that the deviation is compensated for with a time constant which is in particular equal to the current duration of one or more operating cycles or to a defined or definable time.

3. The method according to claim 1 or 2,

-said pressure difference/differences Δ p _{Calculation, 2-1} And/or Δ p _{Calculation, 4-3} And/or Δ p _{Calculation of n-m} And thus the second combustion chamber pressure value p _{2, calculating} And/or the fourth combustion chamber pressure value p _{4, calculating} And/or respective additional second combustion chamber pressure values p _{n, calculating} Is calculated at the filtered value of the combustion chamber pressure or at a plurality of filtered values of the combustion chamber pressure,

And the filtered value or values of the combustion chamber pressure p are filtered _{1, receiving, filtering} 、p_{2, receiving, filtering} 、p_{3, receiving and filtering} 、p_{4, receiving and filtering} 、p_{n, receiving, filtering} And/or p _{m, receiving, filtering} Formed and/or generated by filtering the pressure curve by an analog or digital low-pass filter, in particular Which is a FIR filter.

4. The method according to any one of claims 1 to 3,

-said pressure difference/differences Δ p _{Calculation, 2-1} And/or Δ p _{Calculation, 4-3} And/or Δ p _{Calculation of n-m} And thus the second combustion chamber pressure value p _{2, calculating} And/or the fourth combustion chamber pressure value p _{4, calculating} And/or respective additional second combustion chamber pressure values p _{n, calculating} Is calculated as an average combustion chamber pressure value or as a plurality of average combustion chamber pressure values,

And said mean combustion chamber pressure value p _{1, receiving, averaging} 、p_{2, receiving, averaging} 、p_{3, receiving, averaging} 、p_{4, receiving, averaging} 、p_{n, receiving, averaging} And/or p _{m, receiving, averaging} By averaging a plurality of combustion chamber pressure values, wherein the combustion chamber pressure value used for averaging is offset by-5 to +5 degrees, in particular from the received combustion chamber pressure value or the crank angle of the received combustion chamber pressure values.

5. The method according to any one of claims 1 to 4,

-said first crank angle value and said first combustion chamber pressure value p _{1, receiving} Is received in the range of 90 deg. to 120 deg. before top dead center, in particular 100 deg. before top dead center,

-and/or said second crank angle value and said second combustion chamber pressure value p _{2, receiving} In the range 40 deg. to 70 deg. before top dead center, in particular 50 deg. before top dead center,

-and/or said third crank angle value and said third combustion chamber pressure value p _{3, receiving} Is received in the range of 90 deg. to 120 deg. before top dead center, in particular 100 deg. before top dead center,

-and/or said fourth crank angle value and said fourth combustion chamber pressure value p _{4, receiving} In the range from 40 DEG to 70 DEG before top dead center, in particular 50 DEG before top dead center The receiving unit is used for receiving the data,

And/or each further first crank angle degree and each further first combustion chamber pressure value p _{m, receiving} Is received in the range of 90 deg. to 120 deg. before top dead center, in particular 100 deg. before top dead center,

And/or each further second crank angle value and each further second combustion chamber pressure value p _{n, receiving} In the range from 40 ° to 70 ° before top dead center, in particular 50 ° before top dead center.

6. Method according to any one of claims 1 to 5, characterized in that the crank angle value is received by a crank angle receiving device, in particular by a crank angle sensor.

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

Determining a temperature change of the sensor and/or the cylinder and an additional sensor drift associated therewith, in particular by determining an energy value and using the energy value in a model function,

-compensating the determined temperature change within the output voltage signal of the charge amplifier (1) by generating a modified drift compensation current taking into account the determined temperature change, which drift compensation current is supplied to the input of the charge/voltage converter stage of the charge amplifier (1) in an additive or subtractive manner, thereby generating a drift compensated combustion chamber pressure signal such that deviations are compensated with a time constant, in particular equal to the current duration of one or more working cycles or to a defined or definable time.

8. The method of claim 7, wherein determining a temperature change comprises the steps of:

-an energy value E through said first work cycle _xAnd an energy value E of said second working cycle _yEnergy value difference Δ E therebetween _y-xThe temperature characteristic value is calculated, and the temperature characteristic value is calculated,

In this case, the temperature characteristic value enables an inference of a temperature change in the cylinder and, if applicable, also of a temperature change of the sensor, or the temperature characteristic value is equal to a temperature change in the cylinder and/or, if applicable, also of the sensor.

9. Method according to claim 7 or 8, wherein the energy value E of the first duty cycle is calculated _xThe method comprises the following steps:

-receiving a combustion chamber pressure value p at a crank angle position before combustion of a fuel mixture introduced into the cylinder is started, in particular at a crank angle position before injection of the fuel mixture into the cylinder, within a compression phase of said first working cycle _{Front, x} Wherein the crank angle position is in particular equal to the first crank angle position,

-receiving a combustion chamber pressure value p at a crank angle position within a working cycle _{After, x} Wherein the combustion chamber pressure value p _{After, x} After top dead center, in particular with respect to the received combustion chamber pressure value p _{Front, x} Is located in mirror symmetry with respect to the crank angle position,

-calculating the received combustion chamber pressure value p _{Front, x} And the received combustion chamber pressure value p _{After, x} Pressure difference Δ p therebetween _{Energy, x} ，

By the determined pressure difference Δ p _{Energy, x} Determination of the energy value E _xWherein the determined energy value E _xAn inference is made about the amount of energy of the working cycle released as a result of combustion, or the determined energy value E _xAn amount of energy released equal to the duty cycle.

10. Method according to any one of claims 7 to 9, wherein an energy value E of another work cycle is calculated _yThe method comprises the following steps:

At the crank angle position before the start of combustion of the fuel mixture introduced into the cylinder in the compression phase of another working cycle, in particular during the mixing of the fuel Receiving a combustion chamber pressure value p at a crank angle position before the compound is injected into the cylinder _{Front, y} Wherein the crank angle position is in particular equal to the first crank angle position,

-receiving the combustion chamber pressure value p at a crank angle position within another working cycle _{After, y} Wherein the combustion chamber pressure value p _{After, y} After top dead center, in particular with respect to the combustion chamber pressure value p _{Front, y} Is located in mirror symmetry with respect to the crank angle position,

-calculating the received combustion chamber pressure value p _{Front, y} And the received combustion chamber pressure value p _{After, y} Pressure difference Δ p therebetween _{Energy, y} ，

By the determined pressure difference Δ p _{Energy, y} Determination of the energy value E _yWherein the determined energy value E _yAn inference is made about the amount of energy released by the combustion for another working cycle, or the determined energy value E _yAn amount of energy released equal to the further duty cycle.

11. The method according to any one of claims 7 to 10,

-the calculation of the pressure difference/differences and thus of the energy value/values is/are carried out with a filtered value of the combustion chamber pressure or with a filtered plurality of values of the combustion chamber pressure,

And the filtered combustion chamber pressure value or filtered plurality of combustion chamber pressure values p _{Front, x, filtering} 、p_{Post, x, filtering} 、p_{Front, y, filtering} And/or p _{Then, y, filtering} The pressure curve is formed and/or generated by filtering the pressure curve by an analog or digital low-pass filter, in particular an FIR filter.

12. The method according to any one of claims 7 to 11,

-said pressure difference/differences Δ p _{Energy, x} And/or Δ p _{Energy, y} And thus the calculation of the energy value/values is/are carried out with an average combustion chamber pressure value or with a plurality of average combustion chamber pressure values,

And the mean combustion chamber pressure value or values p _{Front, x, filtering} 、p_{Post, x, filtering} 、p_{Front, y, filtering} And/or p _{Then, y, filtering} This is achieved by averaging a plurality of combustion chamber pressure values, wherein the combustion chamber pressure value used for averaging is in particular deviated from the received combustion chamber pressure value or the received combustion chamber pressure values by-5 degrees to +5 degrees in crank angle.

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

The determined energy values are used to identify the work cycles with the same type of combustion,

-and determining, by the recognition of said same type of working cycle, a characteristic drift of a measuring structure consisting of a pressure sensor, a cable and/or the charge amplifier (1), so that a drift compensation current can be generated that counteracts said characteristic drift even when the engine is stationary, and thus prevents the output signal (8) of the charge amplifier (1) from drifting away.

14. Charge amplifier (1) having a computing unit (3), the computing unit (3) being used for drift compensation, in particular for compensating for zero point drifts of combustion chamber pressure signals received at an internal combustion engine, wherein the charge amplifier (1) is arranged to convert an amount of charge generated by a pressure sensor into an output voltage signal, the charge amplifier (1) comprising:

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

A connection for a crank angle receiving device, in particular for a crank angle sensor, if necessary,

Characterized in that the calculation unit (3) is arranged for implementing the method according to any one of claims 1 to 13.

15. The charge amplifier (1) of claim 14,

-the computing unit (3) is a substantially real-time computing unit (3),

-and the calculation unit (3) is part of the charge amplifier (1).

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

-the charge amplifier (1) and/or the calculation unit (3) are or can be connected with an analog/digital converter (2),

-and the analog/digital converter (2) detects a pressure value.

17. Charge amplifier (1) according to one of the claims 14 to 16,

-the charge amplifier (1) and/or the calculation unit (3) are or can be connected with a digital/analog converter (5),

-and the digital/analog converter (5) generates a regulation voltage and thereby a required drift compensation current.

18. A measurement system comprising a charge amplifier (1) according to any one of claims 14 to 17.

Technical Field

The invention relates to a method for drift compensation, in particular for compensating for zero point drifts of combustion chamber pressure signals received at an internal combustion engine, according to the preambles of the independent claims. The invention further relates to a charge amplifier with a calculation unit for drift compensation and a measuring system comprising a charge amplifier.

Background

In order to measure the combustion chamber pressure of an internal combustion engine accurately, piezoelectric sensors and charge amplifiers are used in a known manner. This sensor is characterized by its accuracy, but it has the disadvantage that only pressure changes can be detected and not absolute pressures. The amount of charge generated by the sensor under pressure load is converted by a charge amplifier into a voltage signal that can be easily further processed. Due to the non-ideal insulation of the real measuring structure comprising sensor, cable, charge amplifier, the small charge amount has continuously flowed out through the insulation before it is converted within the charge amplifier. This results in a drift of the zero point of the output signal of the charge amplifier, which can only be counteracted by a corresponding drift compensation regulation loop, in order to avoid that the signal zero point moves slowly into saturation and thus the charge signal cannot be detected further. A change in the thermal state of the sensor, for example in the case of a change in the load of the internal combustion engine, also leads to an additional charge quantity which also moves the signal zero point of the output signal.

As previously mentioned, drift compensation is a key challenge in designing charge amplifiers for piezoelectric combustor sensors. Two methods for drift compensation are known from the prior art.

a. So-called "continuous drift compensation", which is also known as "continuous drift compensation". In principle, the signal filtered by the low-pass filter is used as a control deviation of the drift compensation control loop, and a corresponding compensation current is generated as a result, which compensation current is added in the reverse form to the input current of the charge amplifier. Thereby causing the center value of the output signal of the charge amplifier to reach a zero value. The aggressiveness of the regulation, i.e. "long" and "short", can be determined by the time constant of the low-pass filter. In this method, the disadvantage is that the low-pass filter acts differently depending on the rotational speed of the engine and influences the signal itself in a decreasing manner, in particular at slower rotational speeds.

b. Furthermore, so-called "periodic drift compensation" is described in EP 0325903. The charge amplifier is supplied with a trigger signal by a corresponding device, which defines a certain crankshaft position and thus a piston position in a working cycle of the internal combustion engine. Preferably, this position is in the intake phase, where the pressure is not affected by combustion. The trigger position can be derived from a crank angle sensor or from the pressure curve itself, for example, by means of correspondingly tracked threshold values. The drift compensation regulation device now takes a value from the output signal history of the charge amplifier in the trigger position, which can be implemented by a sample and hold circuit according to EP 0325903. This value is now used as the control deviation for the drift compensation control loop, i.e. from this value a corresponding inverted compensation current is obtained, which is supplied in an additive manner to the input of the charge amplifier as in the continuous drift compensation method. Since the value is added only once per operating cycle, a current which is constant for the operating cycle is thus added to the operating cycle as a compensation. In this way, the rotational speed-dependent amplitude influence on the signal as in the first method is excluded.

However, as described below, both types of drift compensation also have significant disadvantages for accurate measurements.

As mentioned before, the zero of a real charge amplifier drifts due to the non-ideal insulation of the structure, which drift must be compensated to avoid slow drift to saturation. In addition, an additional drift occurs when the temperature level of the piezoelectric sensor changes, since in this case, for example, the pressure membrane of the sensor expands or collapses and thus an additional positive or negative charge quantity is generated at the sensor output. This unwanted zero point change must be distinguished from the true zero point change. The actual zero point change occurs in particular as a result of a change in the operating point-dependent charge pressure caused by the turbocharger. Furthermore, in the case of gasoline engines, rapid changes in throttle position may result in highly dynamic changes in absolute pressure levels and, therefore, in zero positions of the charge amplifier output signal. While changes due to non-ideal insulation and due to thermal variations should now be compensated, it is true that the actual changes in the pressure level should not be compensated. However, the drift compensation circuit described above cannot distinguish between the various causes of the zero point change and therefore also level the true pressure level change to zero.

Although there is always logic also in the software of the data detection and evaluation system (i.e. the so-called indication system) which further processes the output signal of the charge amplifier to determine the absolute pressure level by means of thermodynamic methods or by reference to sensors in the intake pipe, a certain inclination of the cylinder pressure curve is caused due to the incorrect leveling of the actual pressure level change by means of the drift compensation circuit, since the feeding of a constant correction current causes a ramp-shaped output signal change. Although this distortion of the cylinder pressure curve may be computationally eliminated in subsequent evaluations, it has significant disadvantages for rapid evaluation in real time, e.g., for determination of parameters used to control subsequent combustion cycles, and for highly accurate further evaluation, e.g., charge variation analysis. It is therefore of interest to avoid this effect.

A method for correcting the output level of a charge amplifier is described in AT 396634, which is based on the correction of the output signal of the charge amplifier by a correction voltage. This correction voltage is determined by: at a certain crankshaft angular position at which the absolute pressure level is known, the current value of the charge amplifier signal is compared with this absolute pressure level. The difference gives a correction pressure with which the output signal is corrected. However, since the absolute pressure level is known only in the case of non-supercharged diesel engines, i.e. approximately equal to the ambient pressure during the intake phase, in other engine types the known pressure must be derived from a further sensor arranged in the intake pipe in the vicinity of the intake valve. Thereby significantly increasing the required cost. Furthermore, this method has the obvious disadvantage that the correction voltage, which is matched once per duty cycle, leads to a jump-shaped and therefore physically insignificant change of the output signal. Although slow changes with a ramp shape can be considered as an alternative to sudden changes, as also suggested in AT 396634, there are still gradual voltage changes that do not correspond to reality. Regardless of this correction of the output signal, drift compensation is required anyway, since otherwise the output signal of the charge amplifier drifts slowly to saturation and therefore horizontal correction at the output is of no significance either.

Disclosure of Invention

The significance of the invention is now to overcome the disadvantages of the prior art. In particular, the object of the invention is to provide a method for drift compensation, in which the output signal of the charge amplifier is adjusted such that it is approximately equal to the absolute combustion chamber pressure, and no additional pressure sensor, such as an intake manifold pressure sensor, is required. The object of the invention is, furthermore, to provide a charge amplifier for measuring the cylinder pressure, the output signal of which has the correct output signal level with reference to the absolute pressure and which overcomes the aforementioned disadvantages of the prior art when correcting the output voltage.

In particular, this charge amplifier should not require an additional pressure sensor and no pre-known pressure value compared to the AT 396634.

The object of the invention is achieved by the features of the independent claims.

In particular, the invention relates to a method for drift compensation, in particular for compensating for a zero drift of a combustion chamber pressure signal received at an internal combustion engine, wherein the method comprises the following steps:

-converting, in a charge amplifier comprising a calculation unit performing substantially real-time calculations, an amount of charge generated from a piezoelectric pressure sensor arranged in and/or on the cylinder into an output voltage signal,

-receiving a first crank angle value and a first combustion chamber pressure value p at a first crank angle position within a compression phase of a first working cycle _{1, receiving} ，

-receiving a second crank angle value and a second combustion chamber pressure value p at a second crank angle position within the compression phase of the first work cycle _{2, receiving} ，

-calculating the received second combustion chamber pressure value p _{2, receiving} And the received first combustion chamber pressure value p _{1, receiving} Pressure difference Δ p therebetween _{Calculation, 2-1} ，

-calculating a first cylinder volume V at a first crank angle position from the received first crank angle value ₁，

-calculating a second cylinder volume V at a second crank angle position from the received second crank angle value ₂，

-calculating a second combustion chamber pressure value p according to the following formula _{2, calculating} ：

Wherein Δ p _{Calculation, 2-1} Is the calculated pressure difference, V ₂Is the cylinder volume at the second crank angle position, V ₁Is the cylinder volume at the first crank angle position, and kappa is the polytropic exponent,

Determining the calculated second combustion chamber pressure p at the second crank angle position _{2, calculating} And the received second combustion chamber pressure p _{2, receiving} The deviation between the two or more of them,

-compensating the determined 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 in an additive or subtractive manner, thereby generating a drift compensated combustion chamber pressure signal such that the deviation is compensated with a time constant which is in particular equal to the current duration of one or more operating cycles or to a defined or definable time.

If necessary, the charge amplifier is provided to convert the charge quantity generated by the pressure sensor into a voltage signal.

If necessary, it is provided that the charge quantity generated by the pressure sensor, in particular by the pressure load of the pressure sensor, is converted into an output voltage signal in a charge amplifier comprising a computing unit which performs substantially real-time calculations.

If necessary, the method further comprises the following steps:

-receiving a third crank angle value and a third combustion chamber pressure value p at a third crank angle position within a compression phase of the first working cycle _{3, receiving} ，

And/or

Receiving an additional plurality of first crank angle values and an additional plurality of first combustion chamber pressure values p at an additional plurality of first crank angle positions within a compression phase of a first working cycle _{m, receiving} ，

-receiving a fourth crank angle value and a fourth combustion chamber pressure value p at a fourth crank angle position within a compression phase of the first working cycle _{4, receiving} ，

And/or

Receiving an additional plurality of second crank angle values and an additional plurality of second combustion chamber pressure values p at an additional plurality of second crank angle positions within a compression phase of the first duty cycle _{n, receiving} ，

-calculating the received fourth combustion chamber pressure p _{4, receiving} And the received third combustion chamber pressure p _{3, receiving} With a further pressure difference ap between _{Calculation, 4-3} ，

And/or

Calculating respective additional second combustion chamber pressure values p _{n, receiving} And respective additional first combustion chamber pressure values p _{m, receiving} With a further pressure difference ap between _{Calculation of n-m} ，

-passing the received third crank angle Value calculation of the third Cylinder volume V at the third crank Angle position ₃，

-calculating a further plurality of first cylinder volumes V at a further plurality of first crank angle positions by each further first crank angle value _m，

-calculating a fourth cylinder volume V at a fourth crank angle position from the received fourth crank angle value ₄，

And/or

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

-calculating a fourth combustion chamber pressure value p according to the following formula _{4, calculating} ：

Wherein Δ p _{Calculation, 4-3} Is the calculated additional pressure difference, V ₃Is the cylinder volume at the third crank angle position, V ₄Is the cylinder volume at the fourth crank angle position, and kappa is the polytropic exponent,

And/or

-calculating each further second combustion chamber pressure value p according to the following formula _{n, calculating} ：

Wherein Δ p _{Calculation of n-m} Is the calculated additional pressure difference, V _mIs the cylinder volume, V, at each other first crank angle position _nIs the cylinder volume at each of the additional second crank angle positions, and kappa is the polytropic exponent,

-determining a fourth combustion chamber pressure value p calculated at a fourth crank angle position _{4, calculating} And the received fourth combustion chamber pressure value p _{4, receiving} The deviation between the two or more of them,

And/or

Determining The calculated respective further second combustion chamber pressure value p at the respective further second crank angle position _{n, calculating} And each received additional second combustion chamber pressure value p _{n, receiving} The deviation between the two or more of them,

Averaging the determined deviation or the determined deviations, in particular by using a method for minimizing the sum of squared errors and/or by linear averaging or square averaging,

-compensating for the average 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 in an additive or subtractive manner, thereby generating a drift compensated combustion chamber pressure signal such that the deviation is compensated with a time constant which is in particular equal to the current duration of one or more operating cycles or to a defined or definable time.

If necessary, a least squares fit is used to average the determined deviation or the determined deviations.

If necessary, a pressure difference/pressure differences Δ p _{Calculation, 2-1} And/or Δ p _{Calculation, 4-3} And/or Δ p _{Calculation of n-m} And thus the second combustion chamber pressure value p _{2, calculating} And/or a fourth combustion chamber pressure value p _{4, calculating} And/or respective additional second combustion chamber pressure values p _{n, calculating} Is calculated with a filtered value of the combustion chamber pressure or with a plurality of filtered values of the combustion chamber pressure, and the filtered value of the combustion chamber pressure or with a plurality of filtered values of the combustion chamber pressure p _{1, receiving, filtering} 、p_{2, receiving, filtering} 、p_{3, receiving and filtering} 、p_{4, receiving and filtering} 、p_{n, receiving, filtering} And/or p _{m, receiving, filtering} Formed and/or generated by filtering the pressure curve by an analog or digital low-pass filter, in particular a FIR filter.

If necessary, a pressure difference/pressure differences Δ p _{Calculation, 2-1} And/or Δ p _{Calculation, 4-3} And/or Δ p _{Calculation of n-m} And thus the second combustion Value of the room pressure p _{2, calculating} And/or a fourth combustion chamber pressure value p _{4, calculating} And/or respective additional second combustion chamber pressure values p _{n, calculating} Is calculated as an average combustion chamber pressure value or a plurality of average combustion chamber pressure values, and the average combustion chamber pressure value p _{1, receiving, averaging} 、p_{2, receiving, averaging} 、p_{3, receiving, averaging} 、p_{4, receiving, averaging} 、p_{n, receiving, averaging} And/or p _{m, receiving, averaging} By averaging a plurality of combustion chamber pressure values, wherein the combustion chamber pressure value used for averaging is in particular deviated from the received combustion chamber pressure value or from the crank angle of the received combustion chamber pressure values by-5 degrees to +5 degrees.

If necessary, a first crank angle value and a first combustion chamber pressure value p _{1, receiving} Is received in the range of 90 DEG to 120 DEG before top dead center, in particular 100 DEG before top dead center, and/or a second crank angle value and a second combustion chamber pressure value p _{2, receiving} Is received in the range of 40 DEG to 70 DEG before top dead center, in particular 50 DEG before top dead center, and/or a third crank angle value and a third combustion chamber pressure value p _{3, receiving} Is received in the range of 90 DEG to 120 DEG before top dead center, in particular 100 DEG before top dead center, and/or a fourth crank angle value and a fourth combustion chamber pressure value p _{4, receiving} Is received in the range 40 DEG to 70 DEG before top dead center, in particular 50 DEG before top dead center, and/or each further first crank angle value and each further first combustion chamber pressure value p _{m, receiving} Is received in the range of 90 DEG to 120 DEG before top dead center, in particular 100 DEG before top dead center, and/or each further second crank angle value and each further second combustion chamber pressure value p _{n, receiving} In the range from 40 ° to 70 ° before top dead center, in particular 50 ° before top dead center.

If necessary, it is thereby possible to receive different values, in particular combustion chamber pressure values, within a range in which the actual combustion chamber pressure value approximately equals the calculated combustion chamber pressure value. If necessary, minimal disturbing influences, for example due to valve closure, occur in this range, and if necessary the heat transfer losses are still small, so that the physical laws should be regarded as valid to a large extent.

If necessary, it is provided that the crank angle value is received by a crank angle receiving device, in particular by a crank angle sensor.

If necessary, the method comprises the following further steps: the temperature change of the sensor and/or the cylinder and the additional sensor drift associated therewith are determined, in particular by determining an energy value and using the energy value in a model function,

The determined temperature change is compensated for in the output voltage signal of the charge amplifier by generating a corrected drift compensation current which takes account of the determined temperature change and which is supplied to the input of the charge/voltage converter stage of the charge amplifier in an additive or subtractive manner, whereby a drift compensated combustion chamber pressure signal is generated such that deviations are compensated for with a time constant which is in particular equal to the current duration of one or more operating cycles or to a defined or definable time.

If necessary, it is provided that a corrected drift compensation current is generated, so that not only deviations between the calculated pressure level and the measured pressure level can be compensated for, but also additional deviations expected due to temperature changes can be predictively compensated for.

If necessary, the method for determining a temperature change comprises the following steps: energy value E by first duty cycle _xAnd energy value E of another working cycle _yEnergy value difference Δ E therebetween _y-xA temperature characteristic value is calculated, wherein the temperature characteristic value enables an inference of a temperature change in the cylinder and, if necessary, also of a sensor, or the temperature characteristic value is equal to the temperature change in the cylinder and/or, if necessary, also of a sensor.

If necessary, the energy value E for the first working cycle is calculated _xThe method comprises the following steps: introduced into the gas during the compression phase of the first working cycle Receiving a combustion chamber pressure value p at a crank angle position before combustion of a fuel mixture in a cylinder is started, in particular, at a crank angle position before injection of the fuel mixture into the cylinder _{Front, x} Wherein the crank angle position is in particular equal to the first crank angle position,

Receiving a combustion chamber pressure value p at a crank angle position within a working cycle _{After, x} Wherein the combustion chamber pressure value p _{After, x} After top dead center, in particular with respect to the combustion chamber pressure value p _{Front, x} Is located in mirror symmetry with respect to the crank angle position,

Calculating the received combustion chamber pressure value p _{Front, x} And the received combustion chamber pressure value p _{After, x} Pressure difference Δ p therebetween _{Energy, x} ，

By means of the determined pressure difference Δ p _{Energy, x} Determination of the energy value E _xWherein the determined energy value E _xAn inference is made about the amount of energy of the working cycle released as a result of the combustion, or the determined energy value E _xEqual to the amount of energy released for the duty cycle.

If necessary, provision is made for the combustion chamber pressure value p to be received in the first operating cycle at a crank angle position after combustion of the fuel mixture has substantially ended _{After, x} 。

If necessary, an energy value E for calculating a further work cycle _yThe method comprises the following steps: receiving a combustion chamber pressure value p at a crank angle position before combustion of a fuel mixture introduced into a cylinder is started, in particular, at a crank angle position before injection of the fuel mixture into the cylinder, within a compression phase of another working cycle _{Front, y} Wherein the crank angle position is in particular equal to the first crank angle position,

Receiving a combustion chamber pressure value p at one crank angle position within another working cycle _{After, y} Wherein the combustion chamber pressure value p _{After, y} After top dead center with respect to a combustion chamber pressure value p _{Front, y} Is located in mirror symmetry with respect to the crank angle position,

Computing reception To combustion chamber pressure value p _{Front, y} And the received combustion chamber pressure value p _{After, y} Pressure difference Δ p therebetween _{Energy, y} ，

By means of the determined pressure difference Δ p _{Energy, i} Determination of the energy value E _yWherein the determined energy value E _yAn inference is made about the amount of energy released as a result of combustion for another working cycle, or the determined energy value E _yEqual to the amount of energy released for another duty cycle.

If necessary, provision is made for the combustion chamber pressure value p to be received in a further operating cycle at a crank angle position after combustion of the fuel mixture has substantially ended _{After, y} 。

If necessary, it is provided that the calculation of the pressure difference/pressure differences and thus of the energy value/energy values is carried out with a filtered combustion chamber pressure value or with a filtered combustion chamber pressure values, and that the filtered combustion chamber pressure value or the filtered combustion chamber pressure values p are _{Front, x, filtering} 、p_{Post, x, filtering} 、p_{Front, y, filtering} And/or p _{Then, y, filtering} Formed and/or generated by filtering the pressure curve by an analog low-pass filter or a digital low-pass filter, in particular a FIR filter.

If necessary, a pressure difference/pressure differences Δ p _{Energy, x} And/or Δ p _{Energy, y} And therefore the calculation of the energy value/values is/are carried out with a mean combustion chamber pressure value or with a plurality of mean combustion chamber pressure values, and the mean combustion chamber pressure value or the plurality of mean combustion chamber pressure values p _{Front, x, filtering} 、p_{Post, x, filtering} 、p_{Front, y, filtering} And/or p _{Then, y, filtering} This is achieved by averaging a plurality of combustion chamber pressure values, wherein the crank angle for the averaged combustion chamber pressure value deviates in particular by-5 to +5 degrees from the received combustion chamber pressure value or the received combustion chamber pressure values.

If necessary, the determined energy value is used to detect a working cycle with the same type of combustion, and a characteristic drift of the measuring arrangement consisting of the pressure sensor, the cable and/or the charge amplifier is detected by detecting the same type of working cycle, so that a drift compensation current can be generated which counteracts the characteristic drift even when the engine is stationary, and thus the output signal of the charge amplifier is prevented from drifting away.

The invention relates in particular to a charge amplifier with a computing unit for drift compensation, in particular for compensating for zero drift of a combustion chamber pressure signal received at an internal combustion engine, wherein the charge amplifier is configured to convert an amount of charge generated by a pressure sensor into a voltage signal, the charge amplifier comprising: the connection for the pressure sensor, in particular for the piezoelectric pressure sensor, if necessary comprises a connection for a crank angle receiving device, in particular for a crank angle sensor.

If necessary, it is provided that the charge amplifier is supplied only with the signal of the crank angle receiving device, in particular the signal of the crank angle sensor. If necessary, it is provided that the charge amplifier has no connection for the crank angle receiving device, in particular for the crank angle sensor.

If necessary, the computation unit is provided for carrying out the method for drift compensation according to the invention.

If necessary, the calculation unit is a substantially real-time calculation unit and the calculation unit is part of a charge amplifier.

If necessary, it is provided that the charge amplifier and/or the evaluation unit is connected or connectable to an analog/digital converter, and that the analog/digital converter detects the pressure value.

If necessary, it is provided that the charge amplifier and/or the computation unit is or can be connected to a digital/analog converter, and that the digital/analog converter generates the control voltage and thus the required drift compensation current.

The invention relates in particular to a measurement system comprising a charge amplifier according to the invention.

The invention also relates to a charge amplifier for a piezoelectric combustion chamber pressure sensor in an internal combustion engine, wherein the output signal of the charge amplifier is simultaneously equal to the absolute combustion chamber pressure, and for this purpose only real-time information about at least two crank angle positions is required in addition to the charge signal, but no further signals of other sensors or further information about further determined or estimated absolute pressure values, for example provided in the intake phase, are required.

If necessary, it is provided that the unit for detecting the crank angle position transmits a trigger signal for at least two crank angle positions in the compression phase of the internal combustion engine to the charge amplifier, and the associated pressure value detected from this time in a real-time computing unit connected to the charge amplifier thermodynamically determines the absolute pressure level at least one of the two trigger times, and the deviation of the output signal of the charge amplifier from this determined absolute level at the corresponding trigger time is used as a control variable for a drift compensation control loop of the charge amplifier, so that the output voltage of the charge amplifier is regulated to the absolute level.

If necessary, it is provided that the pressure value is detected by an ADC and the control voltage is generated by a DAC, which is connected to a real-time processor unit, which may also be part of an FPGA.

If necessary, at least one further trigger signal is supplied at the end of combustion, from which an estimate of the energy released during combustion is made and a change in the temperature level of the cylinder pressure sensor is inferred from a comparison with the energy released in the preceding operating cycle, whereby the expected higher drift is ascertained by means of the stored model function and the drift compensation current is correspondingly already adapted at this time in advance.

If necessary, it is provided that a characteristic drift of the measuring arrangement consisting of the piezoelectric pressure sensor, the cable and the charge amplifier is determined from successive cycles with identical energy release in the engine, and a corresponding drift compensation current is applied when the engine is stopped, so that the characteristic drift is eliminated and the correct absolute pressure level is also obtained in the stop-start phase during real, transient measurements during driving operation.

To solve the technical problem to be solved by the present invention, thermodynamic determination of absolute pressure level and the like may be associated with the drift compensation regulation loop.

For this purpose, the trigger signals for at least two crank angle positions in the compression phase of the internal combustion engine can be supplied to a real-time operable computing unit contained in the charge amplifier configuration. If necessary, the calculation unit can acquire the signal value at this location and can convert it into a relative pressure value by means of an overall scaling factor (for example kPa/V) which is foreseen from the sensor sensitivity and the charge amplifier transfer factor.

From the ideal gas adiabatic equation of state:

p·VⁿIs constant

Where p is absolute pressure, V is volume and n is a polytropic exponent, the following relationship is found for the values at two crank angle positions 1 and 2:

The following relationships are thus obtained by means of the deformation:

This equation means that the absolute pressure at the second crank angle position can be determined from the pressure difference between the pressure at the second position and the pressure at the first position, which is independent of the common deviation of the pressure values, and from a factor which is independent of the combustion history. This factor is derived from the corresponding cylinder volume at the two positions and the so-called polytropic exponent. For certain engines, the cylinder volume may be considered known because it may be calculated from the displacement of the cylinder, the compression ratio, and the pushrod ratio of the crank-link mechanism, as a function of crank angle. If necessary, a crank angle of 90 ° to 120 °, in particular of approximately 100 °, before top dead center [ OT ] can be used as the first position, and a crank angle of 40 ° to 70 °, in particular of approximately 50 °, before top dead center [ OT ] can be used as the second position, since the real ratio in this range corresponds approximately to the ideal adiabatic equation.

Of course, the calculation can also be carried out for more than just two crank angle positions, and different mathematical methods can also be used here to suppress signal interference, for example the known method for minimizing the sum of squares of errors [ least squares ] or also simple averaging methods.

If necessary, it is provided that the method is implemented in a real-time computing unit associated with the charge amplifier, such that the relative output signal of the charge amplifier, which is actually present at a certain crank angle and is scaled according to the pressure, is compared with the associated value of the absolute pressure determined by thermodynamic calculations, and the pressure difference resulting from the comparison is used as a control deviation for the drift compensation control loop, and the pressure difference is thereby controlled to zero.

In contrast to the prior art, the value of the output signal of the charge amplifier at a certain crank angle position will therefore not be regulated to zero, but preferably to an approximately physically correct value of the absolute pressure. The charge amplifier can thus distinguish between physical pressure changes that should be maintained and drift phenomena that should level disturbances.

The target values of the control cycles are adapted continuously to thermodynamic calculations if necessary, and deviations due to drift in the form of a slope that continues over the next complete operating cycle can be leveled out, since the compensation current determined in this way can be kept constant for all operating cycles. Thus, an undesired tilting position of the output signal history due to misleveling of the real pressure changes can be avoided. However, the inclination of the output signal path due to the drift phenomenon can also be leveled in a sloping and thus optimal manner, and all hard transitions, such as those of the prior art, can be avoided. Unlike the prior art, neither ambient pressure nor an additional pressure sensor is required if necessary.

In one embodiment of the invention, an analog/digital converter is used for determining the relative pressure values at the at least first and second crank angle positions, said analog/digital converter being connected to the real-time calculation unit and obtaining trigger signals at the at least first and second positions, which are correspondingly derived from the crank angle sensor signals by the preparation unit.

In this embodiment, the generation of the drift compensation current is carried out by a digital/analog converter controlled by a real-time computing unit, from whose output voltage the compensation current is generated by a correspondingly large series resistance, which is supplied to the inverting signal input of the charge amplifier.

As already discussed above, there are two reasons, among others, for the drift of the output signal of the charge amplifier to occur. The reason for one is the charge amplifier circuit (including the sensor and cable) itself, which leads to so-called characteristic drift; on the other hand, the reason for this is that heating and cooling of the piezoelectric sensor can also lead to drift, wherein this so-called load change drift can be noticeable in the event of sudden temperature changes for some operating cycles of the internal combustion engine.

It may therefore be particularly advantageous in the case of an extended embodiment of this method to anticipate the above-mentioned load changes and to adjust the increased drift compensation current predictively, in order to virtually completely prevent this effect. This may be achieved, if necessary, with model functions stored within the real-time calculation unit and with load determinations performed within the real-time calculation unit.

The load can be determined accurately in a known manner, but an approximate determination is sufficient for this purpose. For this purpose, a further trigger at a third crank angle position at the end of combustion can advantageously be supplied to the real-time calculation unit. If necessary, the further trigger has the same position as the first position of the compression phase, only not at top dead center [ OT ] ]Before but at top dead center [ OT ]And then. If necessary, combustion chamber pressure p is received in a first operating cycle at a first crank angle position before top dead center _{Front, x} And receiving combustion chamber pressure p at a second crank angle location after top dead center for a first working cycle _{After, x} . If necessary, combustion Value of the room pressure p _{Front, x} Is received in the range from 90 DEG to 120 DEG before top dead center, in particular 100 DEG before top dead center, and a combustion chamber pressure value p _{After, x} In the range from 90 ° to 120 ° after top dead center, in particular 100 ° after top dead center. If necessary, a combustion chamber pressure value p _{Front, x} And a combustion chamber pressure value p _{After, x} Are received at the same crank angle before and after top dead center and are therefore arranged in particular mirror-symmetrical fashion, or in particular mirror-symmetrical fashion about an axis or dead center.

If necessary, a combustion chamber pressure value p _{Front, y} Is received at a first crank angle position before top dead center in another working cycle, and a combustion chamber pressure value p _{After, y} Is received at a second crank angle position after top dead center for another work cycle. If necessary, a combustion chamber pressure value p _{Front, y} Is received in the range from 90 DEG to 120 DEG before top dead center, in particular 100 DEG before top dead center, and a combustion chamber pressure value p _{After, y} In the range from 90 ° to 120 ° after top dead center, in particular 100 ° after top dead center. If necessary, a combustion chamber pressure value p _{Front, y} And a combustion chamber pressure value p _{After, y} Are received at the same crank angle before and after top dead center and are thus arranged in particular mirror-symmetrical fashion, or in particular mirror-symmetrical fashion about an axis or dead center.

By taking the pressure value also at this location, the pressure difference from the pressure at the first location can be determined, and thus the amount of energy released upon combustion can be roughly estimated. By comparing this amount of energy with the amount of energy of the previous working cycle, a change in the temperature level in the cylinder, and thus also of the sensor, can be inferred, and the expected rising drift can be inferred by means of a model function stored in the real-time calculation unit. The real-time calculation unit is therefore already able to generate a corresponding increased drift compensation current at the third point in time (which it knows at the third point in time), and thus prevent an increased drift of the sensor signal almost at the same time as it is induced. The remaining difference can then be compensated for by determining the true absolute level from the first and second positions of the next duty cycle and by generating a matching compensation current.

In this way, drift phenomena within the working cycle, such as those occurring to a certain extent during cold start or cold engine acceleration (i.e. depression of the throttle), can also be controlled.

Based on the features of the method described above, a further advantageous embodiment is possible. By determining the absolute pressure level, the sensor can distinguish between real, physical pressure changes and apparent pressure changes caused by characteristic drift of the measurement structure consisting of the piezoelectric pressure sensor, the connecting cable and the charge amplifier. By means of the above-described estimation of the energy released for each working cycle, the calculation unit can identify successive working cycles with the same type of combustion. In the case of a series of such duty cycles, only the necessary compensation current is precisely retained for drift control, if necessary, in order to compensate only for the characteristic drift. The parameters of this current can be saved in a memory from a computing unit.

If the engine is stopped during the measurement, no crank angle trigger can be provided anymore. In this case, the currently usual charge amplifier structure switches to continuous drift compensation. However, the structure proposed here can apply this compensation current by the aforementioned recognition of the characteristic drift of the system, so that the correct absolute output level remains obtained after the engine has stopped. If necessary, the great advantage is that the behavior of the cylinder pressure can also be evaluated correctly during the stop-start phase, which occurs continuously in city operation, as in the case of vehicles with automatic start-stop, and therefore critical information for designing this system is achieved, which is of great significance in particular also in the case of hybrid drives, in which the internal combustion engine is rotated by the electric motor when it is stopped in a certain position in order to achieve a rapid restart.

Drawings

Further features according to the invention emerge from the claims, the description of the embodiments and the drawing.

Fig. 1 shows a schematic view of a first embodiment.

When not otherwise described, corresponding reference numerals indicate the following components.

1 charge amplifier, 2A/D converter, 3 computing unit, 4 trigger signal, 5D/A converter, 6 series resistance, 7 input signal, 8 output signal

Detailed Description

The structure of the charge amplifier stage, in particular the structure of the charge amplifier 1, is schematically shown in this figure. The output signal 8 is digitized by the analog/digital converter 2 and this value is supplied to the calculation unit 3. This unit obtains from the crank angle processing unit a trigger signal 4 regarding the defined crank angle required for the thermodynamic zero point correction. This trigger signal 4 represents a reference time. Alternatively, the processing unit can also be integrated into the computing unit. The calculation unit compares the output signal 8 of the charge amplifier scaled according to the pressure with the correct pressure value calculated from the thermodynamic zero at one of the two reference moments and generates, according to the difference of the two pressure values (i.e. equal to the regulation deviation), a corresponding output signal 8 by means of the digital/analog converter 5, said output signal 8 being converted into a corresponding drift compensation current by means of the series resistor 6 of high resistance, with the aim of further compensating the regulation deviation to zero. In this embodiment, the drift compensation current is supplied in an additive or subtractive manner to the input of the charge/voltage converter stage of the charge amplifier 1 (i.e. the so-called input signal 7), in order to generate a drift-compensated combustion chamber pressure signal such that the deviation is compensated with a time constant which is in particular equal to the current duration of one or more operating cycles or to a defined or definable time.

The invention is defined by the features of the claims and is not limited to the specifically illustrated embodiments, but comprises all charge amplifiers and/or measurement systems, which per se or parts thereof comprise means adapted or arranged for performing the method according to the invention.