DE10137871C1 - Procedure for calibrating a pressure sensor - Google Patents

Abstract

Method for calibrating a pressure sensor (8) of an injection system for an internal combustion engine with the following steps: acquisition of a reference measured value for the fuel pressure in a defined first operating state of the injection system, calculation of a theoretical value for the fuel pressure in the defined first operating state on the basis of a predetermined, known dependence of the fuel pressure on the operating state of the injection system, determination of the deviation between the reference measured value and the theoretical value for the fuel pressure in the defined first operating state, detection of at least one further measured value for the fuel pressure in a further operating state of the injection system, correction of the further measured value as a function of the deviation determined in the first operating state.

Description

The invention relates to a method for calibrating a Pressure sensor of an injection system for an internal combustion engine ne according to claim 1.

Conventional injection systems for internal combustion engines have usually a low pressure pump that runs out of fuel sucks a fuel tank and ge to a downstream high-pressure pump, which forwards the injection the fuel into the combustion chambers of the internal combustion engine required fuel pressure generated. In the low pressure range between the low pressure pump and the high pressure pump Here, a low pressure control valve is arranged, the over a predetermined fuel pressure in the low pressure range part of the low pressure pump branched fuel flow and in the fuel tank ter returns. The high pressure pump is on the output side a pressure accumulator (common rail) connected, from which the individual combustion chambers of the internal combustion engine eject the fuel to be injected. The tax eration of the fuel pressure in the pressure accumulator can for example, by a high-pressure control valve that the Exceeding a predetermined fuel pressure in the Part of the pressure accumulator required by the high pressure pump branches fuel flow and in the low pressure range or returns to the fuel tank. However, it is Control of the fuel pressure in the pressure accumulator also possible to use a volume flow controlled high pressure pump the, their delivery rate to adjust the fuel pressure can be adjusted. In both cases, however, the ak actual fuel pressure can be measured in the pressure accumulator, around the high pressure control valve or the volume flow controlled To be able to regulate the high pressure pump accordingly. For this, a  pressure sensor connected to the pressure accumulator, which outputs a pressure-dependent voltage signal.

The disadvantage of this is that the pressure sensor is a component-specific fish and usually temperature-dependent fault tolerance has, which leads to incorrect control of the fuel pressure in the pressure accumulator. Of special importance interpretation here is the fact that the range of errors of the pressure sensor as an absolute error on the sensor end value the pressure sensor is related, so that at low force Press cloth for example during the start of the burning considerable relative error deviations occur can. Especially when starting the internal combustion engine machine therefore leads to the fault tolerance of the pressure sensor considerable misregistration of fuel pressure in the accumulator.

From the post-published publication DE 100 03 906 A1 a method for calibrating a pressure sensor is known, which takes advantage of the fact that the fuel pressure in the high pressure area shortly after starting the firing engine by the target control pressure of the low pressure control valve is specified. The well-known calibration method therefore detects the fuel pressure shortly after starting the Internal combustion engine as a reference measured value and determines the Measurement error from the deviation between the reference measured value and the target control pressure of the low pressure control valve. While the normal operation of the internal combustion engine are those of the measured values then recorded according to the pressure sensor corrected measurement error.

The disadvantage of this known calibration method is that Fact that the fuel pressure after starting the Internal combustion engine not always exactly the same as the target Control pressure of the low pressure control valve is what leads to a learnable determination of the measurement error.  

Another method for calibration is known from DE 199 59 678 A1 ren of a pressure sensor, in which also the Tatsa che is exploited that the fuel pressure in a pre given reference point is known. The well-known calibration The method of measurement therefore measures the fuel pressure in the ref limit point and compares this with the specified known fuel pressure to determine the measurement error. The reference point for determining the measurement error can be at This calibration procedure, for example, by printing loose condition of the high-pressure accumulator.

Another disadvantage of this calibration method is that that the actual fuel pressure in the reference point of the theoretical fuel assumed to be known pressure can deviate, leading to an incorrect determination of the measurement error.

Finally, DE 199 08 411 A1 describes a method for calibers rieren a pressure sensor known, in which also the deed thing exploited wid that the target control pressure of the Nieder pressure control valve is known. It therefore becomes the force shortly after starting the internal combustion engine measure and with the known target pressure of the low pressure control valve compared to determine the measurement error.

A disadvantage of this method is that it did Real fuel pressure during the calibration measurement deviate from the presumed fuel pressure can, which leads to an incorrect determination of the measurement error.

The invention is therefore based on the object of a method to calibrate a pressure sensor in which a incorrect determination of the measurement error is avoided.

The object is achieved by a method according to the invention Claim 1 solved.  

The invention encompasses the general technical teaching Automatically calibrate the pressure sensor to determine the component spec to compensate for errors in the pressure sensor.

To this end, the fact that the Fuel pressure in the pressure accumulator in a certain loading operating state of the injection system even without a measurement of the Fuel pressure is known. The injection system is the half in the context of the inventive method first in brought the operating state in which the theoretical value the fuel pressure is known. In addition, in the  a reference measurement value from the pressure sensor detected. Then the difference between the Reference measured value for the fuel pressure and the theoreti determined value for the fuel pressure. With a wrong The pressure sensor must function without this deviation be approximately zero if you can assume that the theoretical value for fuel pressure is correct is. In the further operation of the injection system, the by the measured values then recorded as a function of the previously determined deviation between the reference Corrected the measured value and the theoretical measured value.

In the defined operating state described above the injection system is preferably the Be drive state in which the injection system becomes one given dead time after switching on the low pressure force material pump is located, the dead time that of the Nieder Pressurized fuel pump time required to build up pressure is. This is because the low pressure is in this operating state pump in the low pressure area between the low pressure fuel pump and the high pressure fuel pump already the Setpoint of fuel pressure is reached, whereas the high pressure pump a greater time delay for the pressure has structure and therefore still no significant contribution to the fuel pressure in the pressure accumulator. Demzu consequence is essentially the fuel pressure in the pressure accumulator Lichen equal to the known pressure in the low pressure area minus the losses from the high pressure pump that between the low pressure fuel pump and the pressure accumulator is not.

However, in the preferred embodiment of the invention before the reference value is recorded by the pressure sensor First, a test measured value is recorded by the pressure sensor and checked against specified conditions, the Subsequent acquisition of the reference measured value only then is released when the test of the test measured value posi  tiv has progressed. For example, it can be checked whether the test measured value is within the theoretically possible error bandwidth, whereby the theoretically possible error bandwidth from the initial pressure (ambient pressure) and the maximum error tolerance of the pressure sensor results. if the Checking the test measured value shows that it is not internal is half the theoretically possible range of errors, he says there is also no measurement of the reference measured value, as a such measurement with probability bordering on certainty would be incorrect and therefore not to correct the Measured values and used to calibrate the pressure sensor can be.

In addition, the preferred embodiment is pre the acquisition of the reference measured value first checks whether the internal combustion engine before turning on the low pressure fuel pump has been idle for a sufficiently long time the fuel pressure in the pressure accumulator up to approximately the ambient pressure could drop. This is important since otherwise the residual pressure still remaining in the pressure accumulator lead to incorrect calibration of the pressure sensor would. The calibration of the pressure sensor according to the invention therefore preferably follows only if between the last ten shutdown of the internal combustion engine and follow it switching on the low pressure fuel pump at least one ne predetermined time has passed that is enough for you corresponding drop in the fuel pressure in the pressure accumulator guaranteed.

The measurement values are corrected as before mentioned - depending on the deviation between the Re reference measured value and the theoretical value of the fuel pressure in the defined first operating state. In the be preferred embodiment, the further measured values of the Pressure sensor corrected by a correction value, the Correction value from the theoretical value of the fuel pressure in the first operating state, the reference measured value for the  Fuel pressure in the first operating state and / or the further measurement value may depend. In the preferred embodiment tion of the invention, the correction value is also beyond retracted with increasing fuel pressure until closing Lich in the normal operation of the injection system no correction of the Measured values of the pressure sensor more done. For one thing, this is possible because the absolute error of the pressure sensor in the normal drove the injection system due to the prevailing re relatively large fuel pressures only insignificant effects kungen. On the other hand, after starting the distiller engine the fuel temperature, so the calibration tion in normal operation of the injection system due to the then prevailing relatively high fuel temperatures no longer leads to completely satisfactory results.

Developments of the invention are in the Subclaims marked. The invention is summarized below men with the description of the preferred embodiment explained in more detail with reference to the figures. Show it:

Fig. 1 is a process of the invention processing tends injection system as a block diagram,

FIGS. 2a-2c method as a flow diagram according to the invention, and

Fig. 3 is a characteristic diagram of the pressure sensor.

The injection system shown in Fig. 1 is largely conventional and has a low-pressure fuel pump 1 , which sucks fuel from a fuel tank 2 and forwards to a downstream high-pressure pump 3 , which generates the fuel pressure required to inject the fuel into the combustion chambers of the internal combustion engine ,

In the low-pressure area between the low-pressure fuel pump 1 and the high-pressure fuel pump 3 , a low-pressure control valve 4 is arranged, which branches off a portion of the fuel flow delivered by the low-fuel pump 1 when a predetermined fuel pressure is exceeded and leads back into the fuel tank 2 , so that Fuel pressure in the low pressure region between the low pressure fuel pump 1 and the high pressure fuel pump 3 remains approximately constant in normal operation of the injection system.

The low-pressure fuel pump 1 is driven by an electric motor (not shown), whereas the high-pressure fuel pump 3 is driven by a camshaft 5 , but a common drive by the camshaft 5 is also possible.

On the output side, the high-pressure fuel pump 3 is connected via a check valve 6 to a pressure accumulator 7 , from which the injectors assigned to the individual combustion chambers of the internal combustion engine and shown here only schematically show the fuel for injection into the combustion chambers of the internal combustion engine.

The pressure accumulator 7 is connected in a conventional manner to a pressure sensor 8 , which generates a voltage signal which reproduces the fuel pressure in the pressure accumulator 7 , the voltage signal from the pressure sensor 8 being forwarded to an electronic engine control 9 .

The electronic engine control 9 has, inter alia, the task of controlling the volume flow-controlled high-pressure fuel pump 3 in such a way that the delivery capacity of the high-pressure fuel pump 3 is adapted to the respective fuel requirement, so that the fuel pressure in the pressure accumulator remains approximately constant. Thus, the control signal output from the electronic engine controller 9 to the high-pressure fuel pump 3 determines the delivery rate of the high-pressure fuel pump 3 and the fuel pressure in the pressure accumulator. 7

However, it is also possible to use a continuously promoting high-pressure fuel pump in conjunction with a proportional control valve instead of the volume-flow-controlled high-pressure fuel pump 3 . With this technology, the proportional control valve is subjected to a pulse-width-modulated voltage, the voltage causing a current to flow that causes a proportional fuel pressure.

The electronic motor controller 9 performs the inventive method described in the fol lowing in order to calibrate the pressure sensor 8 and thereby to compensate for the component-specific error of the pressure sensor 8 .

The mode of operation of the method according to the invention will now be explained with reference to the flowchart shown in FIGS. 2a to 2c.

After a start step 10 , the low-pressure pump 1 is first switched on in a step 11 and then it is determined in a step 12 whether the internal combustion engine has stood still for a sufficiently long period of time in step 11 before the low-pressure pump 1 is switched on, so that the fuel pressure in the Pressure accumulator 7 has dropped to ambient pressure. This is important since otherwise the residual pressure remaining in the pressure accumulator 7 interferes with the calibration in the context of the method according to the invention. If the standstill time T _{OFF is} not greater than the minimum predetermined standstill time T _MIN , then the process _moves on to step 13 and the signal generated by the pressure sensor 8 is not corrected since the calibration would be falsified by the residual pressure in the pressure accumulator 7 .

Otherwise, the process proceeds to step 14 and the first voltage value U ₁ delivered by the pressure sensor 8 is measured, which essentially corresponds to the ambient pressure of approx. Corresponds to 1 bar. The process then proceeds to step 15 , where the range of errors in the current operating state of the injection system is determined. For this purpose, the theoretically possible maximum value U _{1, MAX} and the theoretically possible minimum value U _{1, MIN are} calculated on the basis of the voltage-pressure characteristic curve f (P) of the pressure sensor 8 and the likewise known error ΔU _{ERROR of} the pressure sensor 8 .

A plausibility check of the measured value U ₁ is then then carried out in a step 16 by comparing this measured value with the maximum or minimum value calculated in step 15 . If the measured value U ₁ lies outside the theoretically possible range of errors, this indicates a malfunction and the process proceeds to step 13 , so that the pressure sensor 8 is not corrected or calibrated. Otherwise, it can be assumed that there is no malfunction, so that in a first step 17 nachfol constricting the dead time T _TOT of the low pressure fuel pump is awaited. 1 This is important because the low-pressure fuel pump 1 takes a certain amount of time to build up pressure in the low-pressure region. The dead time T _TOT is therefore dimensioned such that the low-pressure fuel pump 1 has sufficient time to build up the stationary pressure in the low-pressure region, whereas the dead time T _{TOT is} sufficiently short so that the high-pressure fuel pump 3 does not contribute to the fuel pressure due to its delayed pressure build-up supplies in the pressure accumulator 7 .

After the dead time T _TOT , the fuel pressure in the pressure accumulator 7 is essentially the same as the known stationary fuel pressure P _VOR in the low pressure range, less the pressure _losses P _LOSSES caused by the high pressure fuel pump 3 .

In a next step 18 , therefore, the voltage U _{2 is} detected after the dead time T _TOT , which corresponds to the fuel pressure in the pressure accumulator 7 at this time.

In a next step 19, the measured tension nungshub .DELTA.U _MESS = U ₂ is then - U ₁ calculated.

Furthermore, the theoretical voltage swing is calculated in a next step 20 , which is based on the known voltage-pressure characteristic curve of the pressure sensor 8 from the initial ambient pressure of approx. 1 bar and the subsequent pressure P ₂ = P _VOR - P _LOSSES .

In a next step 21 , a start adaptation value for the voltage correction is then calculated using the following formula:

U _{AD, START} = f (P _VOR - P _LOSSES ) - U ₂ .

This start adaptation value corresponds to the deviation between the reference measured value U ₂ and the theoretical value f (P _VOR - P _LOSSES ) of the fuel pressure after the pressure _build-up by the low-pressure fuel pump 1 .

In a next step 22 , a stop value for the voltage adaptation is then calculated using the following formula:

U _{AD, STOP} = U _MAX + U _{AD, START}

This is important because the correction according to the invention of the voltage values supplied by the pressure sensor 8 should only take place up to a predetermined voltage or pressure value, as will be described in detail. In the subsequent starting operation of the internal combustion engine, further measured values from the pressure sensor 8 are then detected in a loop in a step 23 , with a next step 24 first checking whether the respective measured value already exceeds the stop value for the voltage adaptation calculated in step 22 .

In such a case, proceed to step 25 and there is no correction of the voltage, since the injection system is obviously already in the normal operating state.

However, if the voltage value U _MESS supplied by the pressure sensor 8 is still below the stop value U _{AD, STOP} calculated in step 22 , a correction value U _AD for the measured voltage is calculated in a next step 26 according to the following formula:

In the following step 27, the measured value of the tension is then voltage U _MEAS can be rigiert kor to the step 26, the calculated correction value U _AD, so that then used in the following step 28, the Corridor alloyed voltage value U _CORR for controlling the entire An injection system.

In a next step 29 it is then checked whether the internal combustion engine has been switched off, which would lead to an abort and an end of the method according to the invention. If the internal combustion engine continues to operate, step 23 is followed in a loop and a further measured value is detected by the pressure sensor 8 .

In the following, the calibration will now be explained on the basis of the characteristic diagram shown in FIG. 3.

Thus, FIG. 3 shows a first component-specific theo specific voltage pressure characteristic curve 30 of the pressure sensor 8.

Furthermore, the characteristic diagram shows the reference measured value U ₂ , which corresponds to the fuel pressure that has built up in the pressure accumulator after the low-pressure fuel pump 1 has set the steady-state fuel pressure in the low-pressure region and before the high-pressure pump 3 makes a contribution to the fuel pressure , In this loading operation state of the fuel pressure corresponds to the pressure accumulator 7 to the known stationary fuel pressure P _VOR in the low pressure area minus the fuel pump through the high-pressure fuel 3 caused pressure loss P _LOSS.

The characteristic diagram also shows the correction values U _AD , it being recognizable that the correction values decrease linearly to zero as the fuel pressure rises as the fuel pressure rises in accordance with a predetermined envelope curve 31 .

LIST OF REFERENCE NUMBERS

1

Low-pressure fuel pump

2

Fuel tank

3

High pressure fuel pump

4

Low pressure control valve

5

camshaft

6

check valve

7

accumulator

8th

pressure sensor

9

Electronic engine control

10-29

Steps of the method according to the invention

30

Theoretical voltage-pressure characteristic
U _AD

correction values

31

Envelope for correction values

Claims (8)

1. Method for calibrating a pressure sensor ( 8 ) of an injection system for an internal combustion engine with the following steps:

• Detection of a reference measured value (U ₂ ) for the fuel pressure in a defined first operating state of the injection system,
• Calculation of a theoretical value for the fuel pressure in the defined first operating state on the basis of a predetermined, known dependence of the fuel pressure on the operating state of the injection system,
• Determination of the deviation (U _{AD, START} ) between the reference measured value and the theoretical value for the fuel pressure in the defined first operating state,
• Detection of at least one further measured value for the fuel pressure in a further operating state of the injection system,
• Correction of the further measured value as a function of the deviation determined in the first operating state,

characterized by
that before the detection of the reference measured value, a test measured value (U ₁ ) for the fuel pressure is first recorded and checked on the basis of predetermined conditions, the reference measured value (U ₂ ) being recorded only when the test of the test Measured value was positive,
and or
that the time span (T _AUS ) between the last shutdown of the internal combustion engine and the subsequent turn-on of the low-pressure fuel pump is measured, the acquisition of the reference measured value and the correction of the measured values only taking place if this time span a predetermined minimum time period (T _MIN ) exceeds. 2. The method according to claim 1, characterized,  that the further measured value is corrected by a correction value rigig, the correction value from the theoretical Value of the fuel pressure in the first operating state, the Reference measured value for the fuel pressure in the first loading drive state and / or the further measured value depends. 3. The method according to claim 1 or 2, characterized, that the first operating state of the injection system for the Detection of the reference measured value is the state in which it is the injection system at a predetermined dead time after the on switching a low pressure fuel pump is located the dead time being that of the low pressure fuel pump Pressure build-up is required. 4. The method according to at least one of the preceding claims, characterized in that the test measured value (U ₁ ) is compared with a predetermined lower threshold value and a predetermined upper threshold value, the detection of the reference measured value only taking place when the test -Measured value lies between the lower threshold and the upper threshold. 5. The method according to at least one of the preceding claims, characterized in that the predetermined minimum time period between the last shutdown of the internal combustion engine and the subsequent switch-on of the low-pressure fuel pump is so great that the fuel pressure in a pressure accumulator ( 8 ) approximately up to the ambient pressure has dropped. 6. The method according to at least one of the preceding claims che, characterized,  that the further measured values to be corrected for the force fabric pressure compared with a predetermined maximum value the, the correction of the further measured values only then follows when the respective measured value is below the specified value Maximum value. 7. The method according to claim 6, characterized, that for the further measured values the difference to the Maximum value is determined, with the correction of the measured values depending on the difference to the maximum value he follows. 8. The method according to claim 2 and 9, characterized, that the correction value with the difference between the respective current measured value and the maximum value decreases to zero.