DE102016204867A1 - Method and device for monitoring an air mass sensor of an internal combustion engine with low-pressure exhaust gas recirculation - Google Patents

Abstract

The invention relates to a method, a device, a computer program and a storage medium for monitoring an air mass sensor of an internal combustion engine with high-pressure and low-pressure exhaust gas recirculation, in which a release for the monitoring of the air mass sensor is issued when the high-pressure exhaust gas recirculation valve is closed and the low-pressure exhaust gas recirculation valve is open.

Description

The invention relates to a method and a device for monitoring an air mass sensor of an internal combustion engine with high-pressure and low-pressure exhaust gas recirculation, wherein a release for the monitoring of the air mass sensor is issued when the high-pressure exhaust gas recirculation valve is closed and the low-pressure exhaust gas recirculation valve open is.

State of the art

From the state of the art, about the DE 10 2013 200 536 B3 , a method and a device for diagnosing a low-pressure exhaust gas recirculation of an internal combustion engine is known. By means of the difference between a determined low-pressure exhaust gas recirculation mass flow and an associated estimated value, a fault diagnosis can be carried out in the event of a deviation and it is possible to draw conclusions about a closed, clamping low-pressure exhaust gas recirculation valve.

Disclosure of the invention

The invention relates to a method and a device for monitoring an air mass sensor of an internal combustion engine and a computer program on a storage medium for carrying out the method, which enables low-emission monitoring of the air mass sensor.

The procedure according to the invention for monitoring an air mass sensor of an internal combustion engine with high-pressure (HP-EGR) and low-pressure exhaust gas recirculation (ND-EGR) assumes that a release for the monitoring of the air mass sensor is issued when the HP-EGR valve the HP-EGR is closed and the ND-EGR valve of the LP-EGR is open. This has the particular advantage that, in contrast to the monitoring of the air mass sensor with closed HP-EGR valve and closed LP EGR valve, exhaust gases can continue to be supplied via the low-pressure exhaust gas recirculation of the combustion air and thus continue to reduce nitrogen oxides and CO ₂ emissions can be ensured. This is particularly advantageous in dynamic operating points where high exhaust emissions are generated.

For monitoring the air mass sensor, a value for a first deviation between a signal of the air mass sensor and a first comparison value representing an air mass is formed. The first deviation can z. B. are formed as a relative deviation between the signal of the air mass sensor and the first comparison value.

If the value of the first deviation exceeds a first threshold value, the air mass sensor is detected as defective and a corresponding first signal is output.

If the first value of the deviation falls below the first threshold value, the air mass sensor is recognized as intact and a corresponding second signal is transmitted.

The first and the second signal may, for. B. as a status signal (Diagnostic Fault Check) are stored in a control unit. This has the advantage that z. B. for a driving cycle and / or for a later diagnosis request a history of the state of the air mass sensor is traceable and appropriate error responses can be performed. Since the signal of the LP EGR mass flow is subject to tolerances, the tolerances of the differential pressure sensor of the LP EGR, the tolerances of the pressure and temperature sensors used, as well as the cross-sectional area of the LP EGR valve can be taken into consideration for the first threshold value. The tolerances can z. B. calculated as standard deviation.

In an advantageous development, a value for a second deviation between the signal of the air mass sensor and a second comparison value representing an air mass is formed. Again, z. B. a relative deviation for the second deviation between the signal of the air mass sensor and the second comparison value are formed.

If the value of the first deviation exceeds a second threshold value, a further release for a second monitoring of the air mass sensor is advantageously issued as soon as the low-pressure EGR valve is also closed. For the formation of the second threshold, z. B. the tolerance of the LP EGR mass flow may be included or a tighter tolerance without the consideration of the tolerance of the LP EGR mass flow, since advantageously a second monitoring is performed.

If the value of the second deviation exceeds the second threshold value, the air mass sensor is preferably detected as defective and a corresponding first signal is output.

If the value for the second deviation falls below the second threshold value, the air mass sensor is preferably recognized as intact and a corresponding second signal is output.

If the value of the first deviation falls below the second threshold, then Advantageously, the air mass sensor detected intact, with a corresponding second signal is issued only when a predetermined time has expired.

In an advantageous embodiment, the air mass sensor is a hot film air mass sensor. The thus determined fresh air mass flow can be determined by known methods.

The first comparison value is preferably determined on the basis of a first model. The first model is determined as a function of the following variables, the model value of the mass flow into the engine, the mass storage effect of the charge air cooler and the mass flow balance via the LP EGR. This is particularly advantageous since, with an open LP EGR valve, exhaust gases can continue to be supplied to the combustion air via the LP EGR and thus a reduction of nitrogen oxide and CO ₂ emissions can be ensured.

The second comparison value is preferably determined on the basis of a second model. The second model is determined as a function of the following variables, the model value of the mass flow into the engine and the mass storage effect of the intercooler. This has the particular advantage that monitoring of the air mass sensor is possible in dynamic operating points.

In other aspects, the invention relates to a device, in particular a control device and a computer program, which are set up for executing one of the methods, in particular programmed. In yet another aspect, the invention relates to a machine-readable storage medium on which the computer program is stored.

drawing

The invention is described in more detail below with reference to the accompanying drawings and to exemplary embodiments. Show

1 a schematic representation of an internal combustion engine with high-pressure and low-pressure exhaust gas recirculation and an air supply,

2 the exemplary sequence of a method for releasing the monitoring in a first embodiment,

3 the exemplary sequence of a method for releasing the monitoring in a second embodiment.

Description of the embodiments

The sometimes stricter emissions legislation requires new ways of improving vehicle components, especially in the area of the air system. Therefore, z. B. the components of the air system are monitored due to emissions legislation. For hot film air mass sensors (HFM) z. For example, the measurement signal is compared with a reference signal formed from the mass flow into the engine, the intake manifold pressure, the temperature in front of the intake valve, and other engine sizes. An attempt is made to keep the tolerance thresholds for monitoring the HFM sensor small in that the monitoring is performed as an intrusive test, ie, that the high-pressure exhaust gas recirculation valve (HP-EGR valve) and the low-pressure exhaust gas recirculation valve (ND AGR valve) must be completely closed. This has the disadvantage that in these test cycles by the complete closing of both EGR valve no efficient exhaust aftertreatment can be carried out and thus it can lead to increased nitrogen oxide or CO ₂ emissions.

Therefore, it is now proposed to grant the release for a first monitoring, ie to start monitoring only when an HP-EGR valve is closed and an LP EGR valve is open, or perform such monitoring only under this condition , The background is that with the HD EGR closed (ie non-operational) the diagnosis can continue to be carried out more reliably than when both exhaust gas recirculations are open. However, the open (ie operational) LP EGR can be regulated, so that a reduction of the nitrogen oxide and CO ₂ emissions can be carried out. This monitoring can be performed in several embodiments, e.g. In a single-stage embodiment, for example, which always operates under the conditions mentioned, or in a two-stage embodiment in which, if an error in the first stage is suspected under the stated conditions, a second closed-loop monitoring system can again be used for confirmation. EGR and closed LP EGR takes place. These and other embodiments will be explained in more detail below.

1 shows a schematic representation of an internal combustion engine 25 with a fresh air system 48 , via which the internal combustion engine combustion air is supplied, and an exhaust system 49 , via the exhaust gases in the flow direction 51 from the internal combustion engine 25 be dissipated. The representation is limited to relevant parts for the following presentation.

In the fresh air system 48 is in the flow direction of the fresh air 50 seen arranged: A pressure sensor 1 , which determines a pressure p ₀ , a temperature sensor 2 , which determines a temperature T ₀ , an air filter 3 , an air mass sensor (HFM) 5 , a temperature sensor 6 , which determines a temperature T ₁₀ , a pressure sensor 7 , which determines a pressure p ₁₀ , a low pressure exhaust gas recirculation throttle 8th , a pressure sensor 9 , which determines a pressure p ₁₁ , a temperature sensor 10 , which determines a temperature T ₁₁ , a compressor 13 an exhaust gas turbocharger 47 , a charge air cooler 14 with a volume V ₂₁ 15 , a temperature sensor 16 , which determines a temperature T ₂₁ , a pressure sensor 17 , which determines a pressure p ₂₁ , a throttle valve 19 , a pressure sensor 20 , which determines a pressure p ₂₂ , and a temperature sensor 21 which determines a temperature T ₂₂ . The described values can, for. B. as sensor values or as model values. In a preferred embodiment, the pressure sensor determines 1 the ambient pressure and the temperature sensor 2 the outside temperature.

At appropriate measuring points, the air mass values mf ₁₀ 4 , ₁₁ m 11 , mf ₂₁ 18 , mf ₂₂ 22 , mf ₃₀ 28 determined by means of a sensor or by means of a model value. Alternatively, instead of the low-pressure exhaust gas recirculation throttle 8th an exhaust flap 36 for throttling the mass flow via the low-pressure exhaust gas recirculation line 41 be installed.

In the exhaust system 49 is starting from the internal combustion engine 25 in the flow direction of the exhaust gas 51 arranged: a pressure sensor 26 , which determines a pressure p ₃₀ , a temperature sensor 27 , which determines a temperature T ₃₀ , an exhaust gas turbine 30 , an oxidation catalyst (DOC) 31 , a nitrogen oxide storage catalyst 32 , a diesel particulate filter (DPF) 33 , a temperature sensor 34 determining a temperature T ₅₀ , a pressure sensor 35 , which determines a pressure p ₅₀ , an exhaust flap 36 and a silencer 53 , Furthermore, the values of the engine speed are n _Eng 23 and the supplied fuel mass m _Fuel 24 as sensor values or model values provided, for example, by a controller.

Downstream of the DPF 33 , ie on a low-pressure side of the exhaust system 49 , branches off the exhaust system 49 a low-pressure exhaust gas recirculation (ND-EGR) line 41 off, the upstream of the compressor 13 and downstream of the air filter 3 or the air mass sensor 5 back to the fresh air system 48 empties. Along the LP EGR line 41 is starting from the diversion of the exhaust system 49 arranged in the flow direction of a mass flow: a LP EGR cooler 37 with LP EGR bypass 38 , a temperature sensor 39 determining a temperature T _EGRLP and an _LP EGR valve 40 , Via a differential pressure sensor 42 Can the pressure drop over the LP EGR cooler 37 and the LP EGR valve 40 be determined. The described values can, for. B. as sensor values or as model values.

Upstream of the exhaust gas turbine 30 ie on a high pressure side of the exhaust system 49 , branches off the exhaust system 49 a high-pressure exhaust gas recirculation line (HD EGR line) 46 off, the upstream of the engine 25 and the downstream of the throttle 19 in the fresh air system 48 empties. Downstream of the internal combustion engine 25 are located along the HD-AGR line 46 an HD EGR cooler 43 with HD-EGR bypass 44 and an HD EGR valve 45 , The recirculation of exhaust gas serves to reduce the emission of the internal combustion engine 25 ,

In the 2 the exemplary procedure of the method is shown in a first embodiment. In one step 200 becomes the enable for monitoring the air mass sensor 5 issued when the high pressure EGR valve 45 closed and the low pressure EGR valve 40 is open. Under the release can z. B. a waiting period are understood until the HD-EGR valve 45 closed and the LP EGR valve 40 is open. Or it is z. B. a signal to control the HP-EGR valve 45 and the LP EGR valve 40 executed when the enable for monitoring the air mass sensor 5 is requested.

In a particularly preferred embodiment, the following parameters are determined by means of sensors: The pressure p ₀ , the temperature T ₀ , the air mass at location mf ₁₀ , the temperature T ₂₁ , the pressure p ₂₂ and the pressure difference via the LP EGR line 41 , The other variables can z. B. be determined using models.

Subsequently, a value for a first deviation between the signal of the air mass sensor 5 and a first comparison value. The first comparison value may in a preferred embodiment by means of a first model, which in dependence on a value for an air mass at the location in front of the engine mf ₂₂ 22 , corrected for the influence of the mass storage effect of the intercooler 14 with the volume V ₂₁ 15 and a model _{value of} the mass flow _{balance of the LP} EGR mf _EGRLP considered. This model _value mf _{10mod of} the mass flow is to the location of the air mass sensor 5 customized:

, Luftmassenwert mf₁₀ 4 am Ort des Luftmassensensors 5. Alternatively, the first comparison value can also be determined by means of a model in which the model _value mf _{22mod of} the mass flow at the location in front of the inlet valve is adapted:

, Air mass mf ₁₀ 4 at the location of the air mass sensor 5 ,

In the further course of the calculation for the variant is described, in which the model value to the location of the air mass sensor 5 is adjusted.

, wobei A_EGRLP der Querschnittsfläche des ND-AGR-Ventils 40, R die universelle Gaskonstante ist.The ND-EGR mass flow mf _ECRLP can be determined in a preferred embodiment using a throttle _equation . Here, the absolute pressures p ₅₀ before the ND-EGR valve 40 and p ₁₁ before the compressor 13 the exhaust gas turbocharger 47 used. The ND-EGR mass flow can be determined by means of the following equalizers:

where A _{EGRLP is} the cross-sectional area of the _LP EGR valve 40 , R is the universal gas constant.

A calculation of the ND-EGR mass flow via the Bernoulli equation or via map-based approaches is also possible.

Due to the high sensitivity between pressure and mass flow especially at throttling via the exhaust flap 36 or via the low pressure throttle 8th is the following calculation of the absolute pressures before and after the LP EGR valve 40 carried out.

One of the pressures p ₁₁ and p ₅₀ can be modeled in a known manner, the other pressure is then using the differential pressure sensor 42 via the LP EGR line 41 determined.

Depending on the embodiment, in a system with an exhaust flap 36 the absolute pressures are determined as follows: p ₅₀ = p _{11 Mod} + Δp _DiffEGRLP p ₁₁ = p _{11 mod} , where p _{11Mod is} the modeled absolute pressure before the compressor 13 and Δp _DiffEGRLP the differential _pressure across the _LP EGR line 41 is.

Alternatively, the absolute pressures result in a system in which a low-pressure exhaust gas recirculation throttle 8th is installed to: p ₅₀ = p _50Mod p ₁₁ = p _{50 Mod} - Δp _DiffEGRLP where p _{50mod is} the modeled absolute pressure before the ND-EGR valve 40 and Δp _DiffEGRLP the differential _pressure across the _LP EGR line 41 is.

• • die Toleranzen des Differenzdrucksensors 42
• • die Toleranzen der Absolutdrücke p₁₁ und p₅₀
• • die Toleranzen der Temperatur T_EGRLP 39 zwischen dem ND-AGR-Kühler 37 und dem ND-AGR-Ventil 40
• • die Toleranz der Querschnittsfläche A_EGRLP des ND-AGR-Ventils 40

In addition to the calculation of the modeled fresh air _{mass flow} mf _10mod at the location of the sensor, it is advantageous that the min. and max. To calculate tolerances of the individual mass flow components depending on the operating point and to use as a basis for the formation of thresholds. The main influencing factors on the tolerances of the _LP EGR mass flow mf _EGRLP are:

• • the tolerances of the differential pressure sensor 42
• • the tolerances of the absolute pressures p ₁₁ and p ₅₀
• • the tolerances of the temperature T _EGRLP 39 between the LP EGR cooler 37 and the LP EGR valve 40
• • the tolerance of the cross-sectional area A _{EGRLP of} the _LP EGR valve 40

In one step 210 the value of the first deviation is compared with a first threshold value, and if the threshold value is exceeded by the value of the deviation, the air mass sensor is compared 5 recognized as faulty. The value of the first deviation can z. B. as a relative deviation between the value of the air mass sensor 5 and the model _{value of} the air mass flow mf _10mod . In one step 220 then a corresponding first signal is output. The corresponding first signal can be z. B. indicate that the air mass sensor 5 has been detected as defective.

In the event that the first value of the deviation falls below the first threshold, the air mass sensor 5 recognized as intact. In one step 230 then a corresponding second signal is output. The corresponding second signal can be z. B. indicate that the air mass sensor 5 has been recognized as intact.

The first and the second signal may, for. B. transmitted to a controller, and / or stored in the memory of a controller. In a preferred embodiment, this can be done as a diagnostic fault check (DFC).

The 3 shows an exemplary course for the method in a second embodiment. In a first step 300 becomes the enable for monitoring the air mass sensor 5 granted if the HD EGR valve 45 closed and the LP EGR valve 40 is open. Subsequently, a value for a first deviation between the signal of the air mass sensor 5 and a first comparison value.

In one step 310 the value of the first deviation is compared with a second threshold value. In this case, the second threshold z. B. without taking into account the tolerances of the LP-EGR mass flow, so that there is a narrower tolerance range from the first threshold.

If the value of the first deviation exceeds the second threshold, it is done in one step 320 another release for a second monitoring of the air mass sensor 5 , as soon as the LP EGR valve 40 closed is. In one step 330 Then the value for the second deviation is compared with a second threshold value. The value for the second deviation is between the signal of the air mass sensor 5 and a second comparison value. The second comparison value can be determined in a preferred embodiment by means of a second model, which contains the model value of the mass flow into the engine mf ₂₂ 22 and the mass storage effect of the intercooler 14 with volume V ₂₁ 15 considered. The second deviation can z. B. as a relative deviation between the value of the air mass sensor 5 and the model value for the mass air flow.

If in step 330 the value of the second deviation exceeds the second threshold, the air mass sensor 5 recognized as defective. In one step 340 then a corresponding first signal is output.
In an alternative embodiment

If in step 330 the second comparison value falls below the second threshold, the air mass sensor 5 recognized as intact. In one step 350 then a corresponding second signal is output.

The first and the second signal, as already described above, z. B. transmitted to a controller, and / or stored in the memory of a controller. In a preferred embodiment, this can be done as a diagnostic fault check (DFC).

Below in one step 310 the value of the first deviation is the second threshold, the air mass sensor is detected as intact. In one step 370 Then, a corresponding second signal is output, or the second signal is output only after the lapse of a predetermined time, or if z. B. a predetermined number of Intakt measurements of the air mass sensor 5 was carried out.

In an alternative embodiment, in step 370 also a repetition of the release for monitoring the air mass sensor 5 be carried out. This is the step again 300 returned and counted the number of passes in which the air mass sensor 5 in step 310 was recognized as intact. Exceeds the number of intact tested runs a predetermined number, so in step 370 a corresponding second signal is output.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102013200536 B3 [0002]

Claims (17)

Method for monitoring an air mass sensor ( 5 ) an internal combustion engine ( 25 ) with high-pressure and low-pressure exhaust gas recirculation, characterized in that a release for the monitoring of the air mass sensor ( 5 ) is issued when the high pressure exhaust gas recirculation valve ( 45 ) is closed and the low-pressure exhaust gas recirculation valve ( 40 ) is open. A method according to claim 1, characterized in that a value for a first deviation between a signal of the air mass sensor ( 5 ) and a first comparison value representing an air mass is formed. A method according to claim 2, characterized in that when the value of the first deviation exceeds a first threshold, the air mass sensor ( 5 ) is detected as faulty and a corresponding first signal is output. A method according to claim 3, characterized in that when the value of the first deviation falls below a first threshold, the air mass sensor ( 5 ) is recognized as intact and a corresponding second signal is output. Method according to claim 1 or 2, characterized in that the value for a second deviation between the signal of the air mass sensor ( 5 ) and a second comparison value representing an air mass is formed. A method according to claim 5, characterized in that when the value of the first deviation exceeds a second threshold, another release for a second monitoring of the air mass sensor ( 5 ) is issued as soon as the low-pressure exhaust gas recirculation valve 40 also closed. A method according to claim 6, characterized in that when the value for the second deviation exceeds the second threshold, the air mass sensor ( 5 ) is detected as defective and a corresponding first signal is output. A method according to claim 7, characterized in that when the value for the second deviation is less than the second threshold, the air mass sensor ( 5 ) is recognized as intact and a corresponding second signal is output. Method according to one of claims 5 to 8, characterized in that when the value of the first deviation falls below the second threshold value, the air mass sensor ( 5 ) is recognized as intact, wherein a corresponding second signal is issued only when a predetermined time has elapsed. Method according to one of the preceding claims, characterized in that the air mass sensor ( 5 ) is a hot film air mass sensor. A method according to claim 1 to 10, characterized in that the first comparison value is determined based on a first model. A method according to claim 11, characterized in that the first model is determined as a function of the following variables: a. Model value of the mass flow into the engine mf ₂₂ ( 22 b. Mass storage effect of the intercooler ( 14 ) with the volume V ₂₁ ( 15 c. Mass flow via the low-pressure exhaust gas recirculation line ( 40 ) mf _EGRLP A method according to claim 1 to 11, characterized in that the second comparison value is determined based on a second model. A method according to claim 13, characterized in that the second model is determined as a function of the following variables: a. Model value of the mass flow into the engine mf ₂₂ ( 22 b. Mass storage effect of the intercooler ( 14 ) with the volume V ₂₁ ( 15 ) Computer program adapted to carry out the method according to one of Claims 1 to 14. An electronic storage medium with a computer program according to claim 15. Device, in particular control device, with an electronic storage medium according to claim 16.

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