DE102009028492A1 - Method for determining pressure values in cylinder of e.g. internal combustion engine, involves determining correction values in dependent upon pressure measuring values, and utilizing correction values to find pressure values - Google Patents

Abstract

The method involves measuring pressure measuring values i.e. pressure curves, using pressure sensors (24). Correction values are determined in dependent upon the pressure measuring values and an operating cycle condition and/or a combustion condition of a combustion chamber (12) i.e. cylinder, of an internal combustion engine (10). The correction values are utilized for determining the pressure values. A correction function is provided for assigning the correction values in dependent upon the course of the operating cycle and/or the combustion condition of the combustion chamber. Independent claims are also included for the following: (1) a computer program that is programmed for execution of the method for determining pressure values in the combustion chamber of the internal combustion engine (2) a control device for controlling the internal combustion engine.

Description

State of the art

The The invention relates to a method for determining pressure values in a combustion chamber of an internal combustion engine, in which means a pressure sensor pressure readings are measured.

The The invention further relates to a computer program and a control unit for an internal combustion engine.

pressure sensors for determining a pressure in a combustion chamber of an internal combustion engine are used in diesel and petrol engines to produce a improved feedback on the in the combustion chambers get the internal combustion engine running combustion processes. This is especially true with regard to newer operating methods Internal combustion engine relevant, for example, the homogeneous compression ignition (also designated HCCI).

It it turned out that for a sufficient accuracy of pressure readings pressure sensors with a high signal quality should be used. With regard to mass production However, it is desirable, even pressure sensors with a lower signal quality to be able to use.

Disclosure of the invention

The Invention proposes before, that in dependence the pressure readings on the one hand and a Arbeitsspieltage and / or a combustion position of the combustion chamber of the internal combustion engine on the other Correction values are determined which are used to determine the pressure values be used.

advantageous Further developments are specified in the subclaims. Furthermore find themselves for the Invention important features in the following description and in the drawing, the features both in isolation and also be important in different combinations for the invention can, without being explicitly mentioned again.

The inventive method allows it to correct the pressure readings of a pressure sensor. These Correction takes place with the help of correction values, which depend on the pressure readings and a working spin position of the internal combustion engine be determined. In the context of the method according to the invention, it was recognized that the deviation of a measured pressure reading from an actual pressure value from the working game position of each considered combustion chamber of the Internal combustion engine is dependent. Dependent From the working disk position of a combustion chamber, certain disturbing factors occur only for a short time. For example, it increases with the onset of combustion the temperature of the combustion chamber strong. This temperature increase causes a momentary disturbance of the pressure sensor. This disorder can also be referred to as a "thermal shock" or "short-term drift" become.

in the Framework of the present invention is under a working game understood a cycle, after which a combustion chamber of the internal combustion engine goes through another working cycle. In a four-stroke reciprocating internal combustion engine corresponds to a work cycle with a double turn of a crankshaft of the internal combustion engine and a run of four phases (suck in, compress, expand, Ejecting). The phases of different combustion chambers of Internal combustion engine are each offset from each other. In a two-stroke reciprocating internal combustion engine corresponds to a work cycle with a simple turn of a Crankshaft of the internal combustion engine.

The Working game position indicates how far a working cycle of a combustion chamber (In particular, a cylinder) of the internal combustion engine advanced is. For example, a work cycle may be over a crankshaft angle interval of 0 ° and 720 °. A working game position can then be specified by specifying an angle from the be determined interval.

The Combustion indicates how far a conversion from into the combustion chamber (especially in the cylinder) introduced fuel into heat advanced is. For example, a combustion position can be characterized be that a predetermined amount of fuel completely burned is.

The inventive compensation of faulty pressure measurements makes it possible to use pressure sensors with a lower signal quality. Alternatively or in addition to this but can also using pressure sensors with high signal quality more accurate pressure values are determined.

There the correction values depending on the current working game position and / or combustion position of a combustion chamber of the internal combustion engine and depending the pressure readings can be determined, the correction for each Working cycle or each cycle of the combustion chamber to be redetermined. this makes possible a timely compensation of faulty pressure signals.

in the In the simplest case, the correction values correspond to those for a specific one Working platform / combustion position and a measured pressure reading expected error, which with opposite sign to the measured pressure reading can be added.

Advantageous It is when different correction values different layers be assigned within a working cycle of the combustion chamber, by erroneous pressure measured values as a function of the combustion process to compensate for the internal combustion engine.

Especially It is advantageous if a correction function for the assignment of Correction values depending on the course of a work cycle and / or the combustion position of the Combustion chamber is provided. Such a correction function allows a particularly easy and precise specification of correction values over the Course of a work game away.

In Advantageously, the correction function is different Defined functional sections. This allows a correction function provide, which in their different functional sections optimally adapted to the combustion process. At the same time it is possible that the different functional sections are not continuously differentiable merge can, ensuring an exact and fast compensation even in the area of these transitions and is reached adjacent thereto.

Especially it is preferred if at least a first functional section with an increase in the amount of the correction values with a temperature rise correlated within the combustion chamber.

In Accordingly, it is advantageous if at least a second Functional section with a decrease in the amount of the correction values correlated with a temperature drop within the combustion chamber.

Around the beginning and / or the end of at least one functional section the correction function, it is advantageous if this at least a size used which is a given combustion state of the combustion chamber characterized. An example for such a size is one Combustion focus position in which a certain proportion (for example 50%) of fuel that has been introduced into the combustion chamber, completely burned is. Another example of a size to use is the maximum pressure measured within a working cycle. This maximum pressure can also be used to determine a focal point of combustion become. Here, in particular, by the combustion (and not by the compression) conditional maximum pressure used.

If a due to a combustion process pressure increase in the combustion chamber is assigned a first correction value maximum is a particularly accurate error compensation in the area of the focal point of combustion allows.

If a caused by a gas change pressure increase in the combustion chamber a second correction value maximum is assigned, is also in this critical area an accurate error compensation possible.

From Of particular importance is the realization of the method according to the invention in the form of a computer program stored on an electronic storage medium can be stored and in this form a the internal combustion engine controlling controller can be assigned.

Further Advantages, features and details of the invention will become apparent in the following description, with reference to FIGS Drawing various embodiments the invention are shown. It can in the claims and mentioned in the description Features individually for each itself or in any combination essential to the invention.

following becomes an embodiment of the invention with reference to the accompanying drawings explained. In the drawings show:

1 a schematic representation of an embodiment of an internal combustion engine with a combustion chamber and a pressure sensor for detecting a pressure in the combustion chamber;

2 a schematic representation of an embodiment of a procedure for the compensation of errors of the pressure sensor;

3 an embodiment of a correction function;

4 a diagram with over a cycle of the internal combustion engine applied pressure values of the pressure sensor according to 1 with and without error compensation and reference values of a reference pressure sensor;

5 a diagram in which the difference of the pressure values of the pressure sensor is shown in each case with and without error compensation relative to the reference values of the reference pressure sensor;

6 one in 4 With VI marked section on an enlarged scale; and

7 one of the 5 corresponding representation for the section according to 6 ,

In the 1 an internal combustion engine is shown schematically and in total by the reference numeral 10 designated. The internal combustion engine 10 has several combustion chambers, of which in the drawing a combustion chamber 12 is shown.

In the internal combustion engine 10 it is in particular a piston internal combustion engine with a piston 14 , which has a connecting rod 16 on a crankshaft 18 acts.

In the internal combustion engine 10 it is in particular a four-stroke internal combustion engine, in which a working cycle with a double turn of the crankshaft 18 goes hand in hand, causing the piston 14 at each cycle (also called cycle) is reciprocated twice between a bottom dead center and a top dead center. During the four working strokes of the internal combustion engine 10 Starting from a bottom dead center, a Ausschiebetakt, an intake stroke, a compression stroke and an expansion stroke to go through.

It is possible, to operate the internal combustion engine in the so-called HCCI method, in which optional also in the gas exchange phase in the transition take place between Ausschiebetakt and intake stroke combustion can.

The internal combustion engine 10 shows every combustion chamber 12 associated with a schematically illustrated inlet 20 on, through which combustion air, possibly also fuel, in the combustion chamber 12 is insertable. Direct injection is advantageous in the HCCI method, but additionally or alternatively, intake manifold injection is also possible.

Furthermore, the internal combustion engine 10 every combustion chamber 12 assigned an outlet 22 on, by means of which exhaust gas from the combustion chamber 12 can be dissipated.

To monitor the pressure of the combustion chamber 12 is a pressure sensor 24 provided, which, if necessary, can also be used for knock detection. The pressure sensor 24 is via a data line 26 with a control unit 28 connected. Preferably, the controller is used 28 also for controlling a fuel injection device (not shown) of the internal combustion engine 10 , an optionally existing ignition device of the internal combustion engine 10 , An optionally variable controllable valve system, at least one controllable turbocharger and / or a possibly existing device for controlling a to the internal combustion engine 10 recirculated exhaust gas flow.

By means of the pressure sensor 24 Pressure readings are measured by means of the control unit 28 can be read. The reading of the pressure readings corresponds to a in 2 illustrated step 30 a procedure for the compensation of erroneous pressure measured values.

The step 30 follow optional data processing steps 32 . 34 and 36 in which the pressure measurement data is filtered, sensitivity errors are corrected and offset compensation can be performed. Following one of the above steps 30 to 36 takes place in one phase 38 a correction of measured pressure values. In particular, so-called "thermal shock errors" are corrected as part of the correction.

The correction of the measured pressure measured values takes place with the aid of a correction model 40 which is in 3 is shown. As part of the phase 38 can in 2 illustrated steps 42 . 44 . 46 and 48 or a subset of these steps.

For example, in one step 42 fixed parameters of the correction model 40 be determined. In one step 44 can be within a working cycle (with two turns of the crankshaft 18 ) measured maximum pressure reading pMax and a focal point of combustion φMFB50 be determined. The combustion center position φMFB50 indicates the position within the working cycle, in which 50% of the combustion chamber 12 introduced fuel are completely burned.

In one step 46 the actual correction values K can be calculated.

In one step 48 the calculated correction values K and the measured pressure measured values can be added. In one step 50 can then be calculated combustion characteristics, which for controlling the internal combustion engine 10 be used.

The correction model 40 includes a correction function 52 with different functional sections. The functional sections merge, but not continuously differentiable.

The correction function 52 has in particular four or five functional sections. So is a first functional section 54 with a steep correction value increase, a second functional section 56 with a slowly decreasing correction value, a third functional section 60 with a correction value increase, a fourth functional section 62 with a falling correction value and a fifth functional section 64 provided with a constant correction value of in particular equal to zero. The functional sections 54 to 64 are each a subsection of a working cycle of the internal combustion engine 10 assigned. A work cycle extends as explained above about a double turn of the crankshaft 18 and thus over 720 ° crankshaft angle. In the in the 3 to 7 The indication 0 ° crankshaft angle (° CA = ° Crankshaft Angle) corresponds to a top dead center of the piston 14 in which an ignition takes place (ignition TDC) or in which at least the expansion stroke is initiated.

In case of a negative or positive thermal shock error, the measured pressure readings of the pressure sensor 24 From the time of the effect of temperature until the end of the decrease of the temperature to normal level too small or too large. With the help of the illustrated correction function 52 these errors can be compensated. The functional sections 54 . 56 . 60 and 62 can each increase or decrease linearly or exponentially. However, it is particularly preferred if for the definition of the functional sections 54 . 56 . 60 and 62 the following relationships are taken into account.

In particular, applies to the definition of the functional sections 54 and 56 , which the compression and expansion stroke of the internal combustion engine 10 are assigned, the following:
The thermal shock error is directly dependent on the temperature prevailing in the combustion chamber and thus the time of combustion. Based on the start of combustion, the error occurs slightly delayed. Once the temperature of combustion the sensitive components of the pressure sensor 24 has reached, the pressure signal within a few degrees crank angle of the crankshaft 18 falsified by the maximum error height. This is followed by an exponential decay of the thermal shock error until the end of the exhaust stroke.

The correction model 40 is redetermined for each cycle. It forms - in the embodiment described here - the negative shape of the expected thermal shock error and is added to the measured pressure reading. The maximum correction height Thermos _HD (Cycl) depends on the temperature in the combustion chamber, which in turn depends on the intensity of the combustion. The maximum pressure pMax (Cycl) of the respective working cycle provides a good indication for the estimation of the intensity of the combustion and thus the maximum error height. The correction values of the function section 54 are determined, for example, on the basis of a straight line equation as a function of the maximum pressure (alternatively, the correction values can also be determined as a function of a maximum pressure rise and / or as a function of a plurality of parameters). Thermos _HD (Cycl) = pMax (Cycl) · increase _HD + offset _HD

The slope of the straight line equation is defined by rising _HD and can be set like an offset offset _HD due to the sensor behavior.

The beginning of the correction is fixed or depends on the combustion time. Since the combustion center position (.phi.MFB50) already has a good accuracy with the uncorrected pressure signal, this is used as a reference for the beginning. The beginning of the correction relative to the reference point is defined by a parameter offset _HD and may be due to the behavior of the sensor 24 be determined: φ _{start_HD} = φ _MFB50 + offset _HD

Alternatively, other features may be used instead of the combustion centroid location (φMFB50) or in addition to the combustion centroid location (φMFB50), for example, other revenue positions (eg, a position where 10% of that into the combustion chamber 12 introduced fuel), the position of a maximum pressure gradient or features that are calculated from a plurality of individual features.

In order to calculate the linear increase up to the maximum correction value, the following applies to the angles from φ = φ _{start_HD} to φ = φ _{start_HD} + Δφ _{increase_HD} :

By changing the factor Δφ _{increase_HD} , the slope of the slope can be influenced.

The exponential decay of the thermal shock error extends into the next working cycle. For the end φ _{Ende_HD} either a fixed point or a point depending on φ _{Anfang_HD} or φ _{Anfang_ND_Cycl + 1} can be selected, for example φ _{End_HD} = φ _{Start_ND_Cycl + 1} + 720 ° _CA , where φ _{start_ND} can be defined as described below.

If the correction model for the low-pressure loop (function sections 60 . 62 and 64 ) is not used (for example, during SI operation of the internal combustion engine 10 ), φ _{Ende_HD is} in the range of the gas exchange TDC of the subsequent cycle or cycle. Depending on requirements and application, φ _{Ende_HD may} deviate from this, for example depending on the _timing of a variable valve system.

The exponential decay (function section 56 ) after the maximum correction value is calculated for the angles of φ = φ _{start_HD} + Δφ _{increase_HD} to φ = φ _{end_HD} as follows:

The shape of the falling curve is described by the shape _HD factor. However, it is also possible to use another monotone falling waveform, for example in a memory of the control unit 28 is filed.

A further distortion of the measurement signal results when the pressure sensor 24 is used for a HCCI combustion process, in which for the purpose of exhaust gas retention at the gas exchange TDC, an intermediate compression takes place. Due to the high proportion of exhaust gas and the intermediate compression, the temperature in the combustion chamber rises 12 during gas exchange OT and also causes a thermal shock error. The shape of the gas exchange TDC error differs in pitch rate and maximum error level with respect to the TDC. Due to the slower and lower temperature rise both the slope rate and the maximum error height are smaller than the ignition TDC. The exponential decay of the fault ends shortly after the inlet valve of the inlet closes 20 ,

The functional sections 60 and 62 which preferably also be new for each working cycle are correct, thus form the negative shape of the expected thermal shock error and are added to the measured pressure reading. The maximum correction height Thermos _ND (Cycl) is determined by the temperature in the combustion chamber 12 These in turn depend on the intensity of the combustion of the previous working cycle and the operating strategy (valve strategy, operating mode, etc.). The maximum pressure pMax (Cycl - 1) of the previous working cycle provides a good indication for the estimation of the intensity of the combustion and thus the maximum error level (in this case, the calculation of the maximum pressure is carried out in such a way that the maximum pressure caused by the combustion itself and not by the compression is determined becomes). It is true that the temperature of the gas in the gas exchange TDC is determined by the residual gas of the previous combustion and in particular by the combustion position and the injected amount and the work done. The correction values are determined on the basis of a straight line equation as a function of the maximum pressure which has proved suitable: Thermos _ND (Cycl) = pMax (Cycl - 1) · asc _nd + offset _ND

The slope of the straight-line equation is defined by rising _ND , is normally negative and can be offset as the offset _ND due to the behavior of the pressure sensor 24 be determined.

For the beginning of the correction, the closing time of the outlet valve of the outlet 22 be used as a reference. If the data of the valve opening times are not available, the beginning of the correction can also be fixed, since the intermediate compression always takes place at least in the area of the gas exchange TDC. φ _{start_ND} = φ _{AV_close} + offset _ND

The beginning of the correction relative to the reference point is defined by offset _ND and may be due to the behavior of the pressure sensor 24 be determined.

To calculate the increase up to the maximum correction value, the functional section applies 60 for the angles from φ = φ _{start_ND} to φ = φ _{start_ND} + Δφ _{rise_ND} .

By changing the factor Δφ _{increase_ND} , the slope of the rise can be influenced.

For the end φ _{Ende_ND} can a fixed point or an event or a point (for example, the opening of an intake valve of the combustion chamber 12 ) depending on φ _{start_HD} or φ _{start_ND} , for example: φ _{End_ND} = φ _{Start_ND} + Δφ _{Rise_ND} + Δφ _{Drop_ND} .

wobei die Form der abfallenden Kurve durch den Faktor shape_ND beschrieben wird.The exponential decrease in the functional section 62 after the maximum correction value is calculated for the angles of φ = φ _{start_ND} + Δφ _{increase_ND} to φ = φ _{end_ND} as follows:

the shape of the falling curve being described by the factor shape _ND .

If the correction value _korr (φ) is calculated, it is added from φ _{start_ND} to φ = 719 ° _CA to the pressure signal p _Cycl (φ) of the current cycle. The correction _value from φ = 720 ° _CA to φ _{End_HD} is added to the next cycle P _{Cycl + 1} (φ) (0 ° _CA to φ _{End_HD} - 720 ° _CA ) so that corrected pressure values are obtained. Alternatively, the correction is performed in time so that a cycle-synchronous control of combustion depending on the circumstances of the control unit 28 done in real time.

The described correction model 40 refers to a negative thermal shock error. After adjusting the corresponding sign (corresponds to the mirroring of the course of the correction function 52 around the X-axis), however, applies correspondingly to a positive thermal shock error.

The height of the thermal shock to be compensated may additionally or alternatively also dependent on the injection quantity, the pressure increase gradient, the operating point (characterized by load, speed and / or temperature of the internal combustion engine 10 ), the control variables of the air system and in particular the valve system are calculated. The dependency can be mapped, for example, via maps.

In the 4 and 6 three pressure curves are shown, which over a working cycle of 720 ° KW of the internal combustion engine 10 are applied. A first pressure curve 66 corresponds to the course of using the pressure sensor 24 measured pressure readings, which are not compensated. A second course 68 indicates the course of the corrected pressure values. A third course 70 indicates the course of a reference pressure sensor.

Out 4 It can be seen that, in particular in areas of the working cycle which follow a pressure maximum, the measured pressure measured values 66 from the reference values 70 differ from the reference pressure sensor. This deviation is in the 5 and 7 based on the curve " 70 - 66 "Presented.

The pressure values of the corrected course 68 By contrast, they largely correspond to the reference values 70 of the reference pressure sensor. This will be in the 5 and 7 based on the curve " 70 - 68 "Clarifies. This curve has very little variation around zero deviation and illustrates the significant improvement over the curve. " 70 - 66 ".

Claims (12)

Method for determining pressure values ( 68 ) in a combustion chamber ( 12 ) an internal combustion engine ( 10 ), in which by means of a pressure sensor ( 24 ) Pressure readings ( 66 ), characterized in that, depending on the pressure readings ( 66 ) on the one hand and a working foil position and / or a combustion position of the combustion chamber ( 12 ) of the internal combustion engine ( 10 ) On the other hand, correction values (K) are determined which are used to determine the pressure values ( 68 ) be used. Method according to Claim 1, characterized in that different correction values (K) of different positions within a working cycle of the combustion chamber ( 12 ) be assigned. Method according to one of the preceding claims, characterized by a correction function ( 52 ) for the assignment of correction values (K) as a function of the course of a working cycle and / or the combustion position of the combustion chamber ( 12 ), Method according to one of the preceding claims, characterized in that the correction function ( 52 ) by different functional sections ( 54 . 56 . 60 . 62 . 64 ) is defined. Method according to Claim 4, characterized in that different functional sections ( 54 . 56 . 60 . 62 . 64 ) different sections of a working cycle of the combustion chamber ( 12 ) be assigned. Method according to one of claims 4 or 5, characterized in that at least a first functional section ( 54 ) with an increase in the amount of the correction values (K) with a temperature increase within the combustion chamber ( 12 ) correlates. Method according to one of claims 4 to 6, characterized in that at least one second functional section ( 56 ) with a decrease in the amount of the correction values (K) with a temperature drop within the combustion chamber ( 12 ) correlates. Method according to one of claims 4 to 7, characterized in that for determining a beginning and / or the end of at least one functional section ( 54 ) of the correction function ( 52 ) at least one size is used, which a predetermined combustion state of the combustion chamber ( 12 Characterized. Method according to one of the preceding claims, characterized in that a pressure increase in the combustion chamber caused by a combustion process ( 12 ) is assigned a first correction value maximum (Thermos _HD (Cycl)). Method according to one of the preceding claims, characterized in that a pressure increase in the combustion chamber ( 12 ) a second correction value maximum (Thermos _ND (Cycl)) is assigned. Computer program, characterized in that it for execution the method according to one of the preceding claims programmed is. Control unit ( 28 ) for an internal combustion engine ( 10 ), characterized in that the control unit ( 28 ) is configured to carry out the method according to one of claims 1 to 10.

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