DE102005035092A1 - Pressure sensor signal evaluating method for fuel injection system, involves correcting measurement value depending up on estimated value, if pressure sensor is evaluated as functional - Google Patents

Abstract

The method involves recording a measurement value of a pressure in a fuel pressure accumulator (24). An estimated value for the pressure is determined depending up on operating characteristics of the accumulator. A deviation of the estimated value from the measurement value is generated. A pressure sensor (30) is evaluated as functional or non-functional on the basis of the deviation. The measurement value is corrected depending up on the estimated value, if the pressure sensor is evaluated as functional. Independent claims are also included for the following: (1) a control device for a combustion engine including a pressure sensor (2) a computer program for use in a method of evaluating a signal of a pressure sensor (3) a storage medium of a control device for storing a computer program for use in a method of evaluating a signal of a pressure sensor.

Description

The The invention relates to a method for evaluating a signal of a Pressure sensor, which is a reading of a pressure in a fuel pressure accumulator taking an estimate for the Pressure in dependence of operating characteristics of the Fuel pressure accumulator is determined, at least one deviation of the estimate is formed by the measured value, and the pressure sensor on the base at least one deviation is considered to be functional or non-functional becomes.

The Invention further relates to a control unit of an internal combustion engine, having a fuel pressure accumulator and a pressure sensor, the one measured value of a ruling in the fuel pressure accumulator Pressure, which is an estimate for the Pressure in dependence from a fuel extraction from the fuel pressure accumulator and a Fuel supply to the fuel pressure accumulator determines, at least a deviation of the estimated value from the measured value, and the pressure sensor based at least a deviation as functional or not working assessed. About that In addition, the invention relates to a computer program and a storage medium.

Such a method, such a control device, such a computer program and such a storage medium is in each case from the EP 975 942 B1 known.

at modern injection systems is the correct and highly accurate fuel metering central. This dosage occurs in so-called Common rail systems over Injectors, which together serve as a fuel pressure accumulator Rail are connected and at opening control by an injection pulse width signal fuel from the fuel pressure accumulator in combustion chambers inject an internal combustion engine. The injection quantity is through the activation duration and the pressure prevailing in the fuel pressure accumulator Pressure determined. For a correct dosage, the pressure must therefore in the formation of the Injection pulse width considered become.

The Activation time can be specified very accurately and is therefore in Regarding a correct dosage unproblematic. She must, in particular can not be checked by a separate sensor. The pressure in the fuel pressure accumulator on the other hand, in rule over its own pressure sensor, the rail pressure sensor (RDS) directly on the fuel pressure accumulator measured. This sensor generally provides an analog signal, that in the control unit of the internal combustion engine is processed. Due to diverse influences, in particular by a drift behavior during operation and over the life of the pressure sensor, can the actual Pressure in the fuel pressure accumulator from the measured pressure in the individual case clearly differ. By significantly wrong pressure readings will either clearly too much or significantly too little fuel injected, what raises of pollutant emissions and increases in mechanical stress of the internal combustion engine and the drive train can lead.

The aforementioned EP 975 942 allows in this context a digital distinction between a functional and a non-functional pressure sensor, regardless of whether a malfunction was caused by a sudden damage or by slow drift effects in the pressure sensor.

at a pressure sensor whose malfunction has been detected becomes usually switched to a limp-home, with limitations the function of the internal combustion engine is connected. In the mentioned Digital differentiation, the switching is also digital, which is usually an additional Workshop visit and other inconveniences leads.

The inventive method is characterized by the fact that the measured value is judged to be functional Pressure sensor depending from the estimate is corrected.

Analogous characterized the inventive control unit characterized that it measures the reading with the pressure sensor judged to be functional dependent on from the estimate corrected.

The The aforementioned computer program is characterized in that to use the method or any of the embodiments mentioned below is programmed. The storage medium is characterized accordingly characterized in that stored on it such a computer program is.

Advantages of invention

By these features, drift effects in the signal behavior of the pressure sensor can be compensated to some extent. Firstly, this has the advantage that the pressure sensor can continue to be used despite already limited functionality, without having to activate an emergency function. In the case of a steadily deteriorating pressure sensor, replacement may therefore be delayed until the next routine workshop visit. Furthermore, the steady deterioration can nevertheless be detected and a corresponding error message are stored in the control unit, so that the error in a routine workshop visit by reading a fault memory and replacement of the pressure sensor without any impairment of vehicle availability for the customer can be solved.

With Looking at embodiments of the method is preferred that initially a Initial value of the deviation formed at a new pressure sensor and stored in a memory.

Of the Initial value allowed when installing a new pressure sensor, its reading as reliable assuming a calibration of the model so that later occurring Deviations between estimated value and measured value associated with a drift of characteristics of the pressure sensor can be.

Further is preferred that over the life of the pressure sensor further deviations are formed from the other deviations and the initial value of the deviation corrected deviations are formed, and the measured value is corrected again if the corrected deviations are within a predetermined range Intervals lie.

These Design allows a gradual compensation of drift effects in the pressure reading, with the step size defined by the lower Limit of the interval is given. The determination of the lower Boundary hangs from the accuracy of the estimation from. The upper limit preferably marks a boundary between one Pressure sensor whose functionality although restricted, but still correctable, and a pressure sensor whose reading already so unreliable is that must be switched to an emergency operation.

Prefers is also that a renewed correction of the measured value in each case on End of an operating phase of the pressure sensor is done.

By this embodiment will be the rest Functions of the control unit not impaired, because such an off-line correction for example in a so-called ECU overrun can occur in which the controller in the case of an already stopped combustion engine still unfinished tasks and another Start prepared.

alternative or in addition it is preferred that a renewed correction, possibly also several times, while an operating phase of the pressure sensor takes place.

A Such on-line correction offers the advantage, possibly faster to respond to a deterioration of the pressure sensor.

A Another embodiment is characterized in that the pressure sensor as not working is judged when an absolute value of a corrected deviation greater than is a first predetermined threshold.

These Alternative improves the reliability of a detection of a inoperative pressure sensor. The disadvantage here is that a non-functioning pressure sensor comparatively recognized late becomes.

alternative or in addition is therefore preferred that the pressure sensor judged to be non-functional when a difference of two corrected deviations is greater than a second predetermined threshold.

The Difference can be, for example, two in different operating phases the pressure sensor corrected deviations are formed, wherein an operating phase, for example a driving cycle of a motor vehicle equivalent. In this respect, this configuration is recommended as a supplement to the above mentioned off-line correction. In an on-line correction, the Difference of course also be formed within a Fahrzyklusses. in both cases will so to speak evaluated the time behavior of a deterioration of the pressure sensor, so that even with still functioning pressure sensor on a later Can be extrapolated at the time of complete inoperability is to be expected. In this case, the driver can therefore go to a workshop visit be prompted without immediately activating a run-flat mode must become.

With Looking at embodiments of the control unit is preferred that it performs at least one of the above embodiments of the method.

Further Advantages will be apparent from the description and the attached figures.

It it is understood that the above and the following yet to be explained features not only in the specified combination, but also in other combinations or alone, without to leave the scope of the present invention.

drawings

Embodiments of the invention are illustrated in the drawings and in the following description explained in more detail. In each case, in schematic form:

1 a technical environment of the invention;

2 an initial value of a deviation of an estimated value from a measured value;

3 such a deviation in an aged pressure sensor together with a threshold limited interval for distinguishing a correctably aged pressure sensor from a non-functioning pressure sensor;

4 a generalization of the representation from the 3 ; and

5 an alternative or supplementary possibility of detection of an inoperative pressure sensor.

Description of the embodiments

In detail shows 1 a fuel injection system 10 with a fuel tank 12 , Fuel filters 14 and 16 , a low-pressure pump 18 , a metering unit 20 , a high pressure pump 22 , a fuel pressure accumulator 24 , an injection valve assembly 26 , a pressure control valve 28 , a pressure sensor 30 , a speed sensor 32 , a temperature sensor 34 and a controller 36 , The control unit 36 controls the injection system 10 via control signals TV_20 for the metering unit 20 , Injection pulse widths ti for the injection valve assembly 26 and TV_28 for the pressure control valve 28 , Fuel from the tank 12 is from the low pressure pump 18 over the filters 14 and 16 as well as the metering unit 20 to an input of the high pressure pump 22 delivered.

The low-pressure pump generates 18 , which is driven as mechanically by the internal combustion engine or by an electric motor, a delivery pressure in the order of a few bar. The high pressure pump 22 , which is usually realized as a piston pump mechanically driven by the internal combustion engine, increases this pressure to over 1,000 bar and supplies a standing under this pressure high-pressure delivery QHDP to the fuel pressure accumulator 24 , The high-pressure fuel delivery QHDP depends on the speed of the high-pressure pump drive 22 from the speed of the internal combustion engine and in addition from the duty cycle TV_20, with which the control unit 36 the metering unit 20 controls and thus at the low pressure input of the high pressure pump 22 available amount of fuel.

From the fuel pressure accumulator 24 an injection quantity QI flows via the injection valve arrangement 26 and a pressure control amount QDRV via the pressure regulating valve 28 from. The stated quantities QHDP, QI and QDRV represent operating parameters of the fuel pressure accumulator 24 These operating parameters are in the control unit 36 known or may be from others, in the control unit 36 present sizes are determined. For example, the injection quantity QI results from the geometry of the injection valves of the injection valve arrangement 26 , the injection pulse widths ti and the pressure sensor 30 measured fuel pressure p_mess in the fuel pressure accumulator 24 , Analogously, the pressure control quantity QDRV results from the geometry of the pressure regulating valve 28 and its drive duty ratio TV_28. In this case, the geometry of the various components flowed through by fuel in each case by the control unit 36 stored flowcharts, which indicate a flow depending on the respective fuel pressure, are taken into account. The low pressure pump 18 , the fuel filter 14 and 16 as well as the metering unit 20 also represent fuel-carrying components, so that their pressure-dependent flow characteristics in the control unit 36 can be stored.

The high-pressure fuel delivery QHDP can with these and possibly further information from the control unit 36 in particular the duty cycle TV_20 for the metering unit 20 optionally from that of the speed sensor 32 provided engine speed N certain speed of the high-pressure pump 22 and from the coolant or lubricant temperature T of the internal combustion engine received from the temperature sensor 34 is taken into account. From the known and constant geometry of the fuel pressure accumulator 24 and the inflow QHDP and the outflows QI and QDRV determined by the controller 36 an estimated value p_sch for the pressure in the fuel pressure accumulator 24 and compares the estimated value p_sch with that of the pressure sensor 30 provided measured value p_mess.

2 shows a plane spanned by possible estimated values p_sch and measured values p_mess, in which the straight line 38 the ideal case of matching estimated values p_sch and measured values p_mess marked. The point 40 represents a real pair of an estimate p_sch and a measurement p_mess in an initial state as determined, for example, at a band end calibration. The estimated value p_sch in this case is greater than the corresponding measured value p_mess. The distance between the two values represents an initial value of a deviation dpi. This initial value dpi of the deviation is stored in a storage medium of the control unit 36 stored.

3 shows the plane from the 2 with an aged pressure sensor 30 , The same measured value p_mess now corresponds to a larger estimated value p_sch, where the larger estimated value p_sch together with the same measured value p_mess the point 42 Are defined. Correspondingly results for the point 42 a larger deviation dpn. From the larger deviation dpn and the initial value of the deviation dpi, a corrected deviation dpn_korr is formed, for example as dpn_korr = dpn-dpi. The extent of this corrected deviation dpn_korr is an aging of the pressure sensor 30 assigned. In the in the 3 shown ratios is the corrected deviation dpn_korr within an interval defined by thresholds S1 and S2 I = (S2, S1). For such corrected deviations dpn_korr which lie in the interval I, the measured value p_mess is corrected with the value of the corrected deviation dpn_korr or a value dependent thereon.

In the circumstances, as in the subject matter of 3 that is to the point 42 associated measured value p_mess, measured at the associated estimated value p_sch too small, so that a correction of the measured value p_mess can be done by adding the amount of the corrected deviation dpn_korr. Below, the controller works 36 then with a correspondingly corrected measured value, that is to say the sum of the measured value p_mess and the amount of the correction dpn_korr, and forms, in particular, control signals TV_28 for the pressure regulating valve 28 and the injection pulse widths ti for the injection valve assembly 26 based on the corrected value.

The threshold value S1 and S2 and thus the width of the interval I can be selected depending on the magnitude of the measured value p_mess and / or the estimated value p_sch. An embodiment of such a dependency is in the 4 in which said interval limits S1 and S2 as well as further interval limits S1 ', S2' for the cases in which the measured value p_mess is greater than the estimated value p_sch are respectively proportional to measured values p_mess in the new state of the pressure sensor 30 are predetermined. The point 40 in the 4 again corresponds to a value pair of estimated value p_sch and measured value p_mess in a new condition of the pressure sensor 30 , Straight 44 that through the point 40 and the origin of the coordinates, then supplies the position of all further value pairs from estimated values p_sch and measured values p_mess on the assumption that the percentage deviation between estimated value p_sch and measured value p_mess is proportional to the measured value p_mess.

The area 46 in the 4 that is the area between the hatched areas 48 and 50 , then corresponds to the set of all pairs of estimated values p_sch and measured values p_mess, for which the measured value p_mess is not corrected.

At the subject of 4 these are for example the points 52 and 54 , In contrast, the point lies 56 in the hatched area 48 , which represents the set of all value pairs from estimated value p_sch and measured values p_mess, at which the respectively associated measured value p_mess lags behind the estimated value p_sch, ie is smaller than the estimated value p_sch, but is still considered correctable. Accordingly, the point lies 58 in the hatched area 50 which represents the set of all value pairs from estimated values p_sch and measured values p_mess, for which the associated measured value p_mess is too large, but is still considered correctable. The points 59 and 60 on the other hand lie outside the areas 46 . 48 and 50 and therefore represent a defective pressure sensor 30 which is to be assessed as inoperative.

At the subject of 4 the distinction was made between functional and inoperative pressure sensors 30 by comparing deviations of the points 52 . 54 . 56 . 58 . 59 . 60 from the straight 44 with thresholds S1, S2, S1 ', S2'.

Alternatively or additionally, a rapid deterioration of the pressure sensor 30 can also be detected from a time behavior of the deviation between estimated value p_sch and measured value p_mess. In detail, the shows 5 a first deviation dp_n-1, as it occurs at a first time t_n-1 at a certain p_mess or p_sch, and a further deviation dp_n, as it occurs at a later time t_n at the same p_mess or p_sch. The pitch angle α of the straight line 62 , by the points formed by these value pairs 64 and 66 goes, therefore provides a measure of the deterioration of the pressure sensor 30 in the period between the times t_n and t_n-1. The larger the pitch angle α, the faster the pressure sensor degrades 30 , Therefore, a pressure sensor that deteriorates too quickly may be damaged 30 be detected by comparing the pitch angle α with a threshold α_S.

Claims (11)

Method for evaluating a signal of a pressure sensor ( 30 ), which measures a measured value (p_mess) of a pressure in a fuel pressure accumulator ( 24 ), wherein an estimated value (p_sch) for the pressure as a function of operating parameters of the fuel pressure accumulator ( 24 ), at least one deviation (dpi, dpn) of the estimated value (p_sch) from the measured value (P_mess) is formed, and the pressure sensor is judged to be functional or non-functional based on at least one deviation (dpi, dpn), characterized in that the reading (p_mess) is considered functional assessed pressure sensor ( 30 ) is corrected as a function of the estimated value (p_sch). A method according to claim 1, characterized in that initially an initial value (dpi) of the deviation in a new pressure sensor ( 30 ) is formed and stored in a memory. A method according to claim 2, characterized in that over the life of the pressure sensor ( 30 ) further deviations (dpn) are formed, deviations (dpa_korr) corrected from the further deviations (dpa) and the initial value (dpi) of the deviation are formed, and the measured value (p_mess) is corrected when the corrected deviations (dpa_korr) within one predetermined interval ([S2, S1]) are. A method according to claim 3, characterized in that a correction of the measured value (p_mess) in each case at the end of an operating phase of the pressure sensor ( 30 ) he follows. A method according to claim 3, characterized in that a correction, optionally also several times, during an operating phase of the pressure sensor ( 30 ) he follows. Method according to claim 3, characterized in that the pressure sensor ( 30 ) is judged to be inoperative when an absolute value of a corrected deviation (dpa_korr) is greater than a first predetermined threshold. Method according to claim 3, characterized that the pressure sensor is judged to be non-functional if a Difference from two corrected deviations greater than a second predetermined Threshold is. control unit 36 an internal combustion engine having a fuel pressure accumulator ( 24 ) and a pressure sensor ( 30 ) having a measured value (p_mess) of a in the fuel pressure accumulator ( 24 ) receives an estimated value (p_sch) for the pressure as a function of a fuel extraction (QI, QDRV) from the fuel pressure accumulator ( 24 ) and a fuel supply (QHDP) to the fuel pressure accumulator ( 24 ), at least one deviation (dpi, dpa) of the estimated value (p_sch) from the measured value (p_mess) forms, and the pressure sensor ( 30 ) is judged to be functional or non-functional on the basis of at least one deviation (dpi, dpa), characterized in that the control unit ( 36 ) the measured value (p_mess) when the pressure sensor is judged to be functional ( 30 ) is corrected as a function of the estimated value (p_sch). Control unit ( 36 ) according to claim 8, characterized in that it carries out at least one of the methods according to claims 2 to 7. Computer program, characterized in that it for use in one of the methods according to claims 1 to 7 is programmed. Storage medium of a control device ( 36 ) according to claim 8 or 9, characterized in that a computer program for use in one of the methods of claims 1 to 7 is stored on the storage medium.