Leak diagnosis for an intake system

Abstract

A vehicle drive has an internal combustion engine, an air conduit system, an exhaust system and a diagnostic unit for identifying a leak in the air conduit system of the internal combustion engine. The diagnostic unit is designed to carry out a method for diagnosing a leak in an internal combustion engine, including by determining mass flows in the air conduit system, and identifying a leakage mass flow.

Claims

1. A method for diagnosing a leakage of an internal combustion engine, comprising: determining regular mass flows ({dot over (m)}.sub.EGR, {dot over (m)}.sub.charge, {dot over (m)}.sub.ThrVlv) of an air conduit of the internal combustion engine; establishing a mass flow balance on the basis of the determined regular mass flows; ascertaining a leakage mass flow ({dot over (m)}.sub.leak) on the basis of the established mass flow balance; ascertaining a position and/or a size (A.sub.leak, d.sub.leak) of a leak depending on the ascertained leakage mass flow; (i) ascertaining a positive-pressure leakage mass flow ({dot over (m)}.sub.leak) and a positive-pressure size characteristic value (A.sub.leak,pos, d.sub.leak,pos) depending on an ascertained positive-pressure leakage mass flow; and/or (ii) ascertaining a negative-pressure leakage mass flow (?{dot over (m)}.sub.leak) and a negative-pressure size characteristic value (A.sub.leak,neg, d.sub.leak,neg) depending on an ascertained negative-pressure leakage mass flow; and determining a position of the leak depending on a ratio of the ascertained positive-pressure size characteristic value to the ascertained negative-pressure size characteristic value.

2. The method according to claim 1, wherein the leakage mass flow is ascertained during regular operation of the internal combustion engine.

3. The method according to claim 1, wherein the size of the leak is determined depending on the ascertained leakage mass flow or flows.

4. The method according to claim 1, wherein a fallback reaction to the leakage mass flow is ascertained depending on the ascertained position, size and/or a flow direction of the leakage mass flow.

5. The method according to claim 1, wherein the leakage mass flow is ascertained depending on an ambient pressure (p.sub.0) of the intake system.

6. The method according to claim 1, wherein the regular, mass flows are determined depending on at least one pressure (p.sub.0, p.sub.12, p.sub.22, p.sub.31), at least one temperature (T.sub.10, T.sub.21, T.sub.22), and/or an interface cross section.

7. An apparatus, comprising: a diagnostic unit for identifying a leakage of an air conduit of an internal combustion engine, wherein the diagnostic unit is operatively configured to: determine regular mass flows ({dot over (m)}.sub.EGR, {dot over (m)}.sub.charge, {dot over (m)}.sub.ThrVlv) of an air conduit of the internal combustion engine; establish a mass flow balance on the basis of the determined regular mass flows; ascertain a leakage mass flow ({dot over (m)}.sub.leak) on the basis of the established mass flow balance; ascertain a position and/or a size (A.sub.leak, d.sub.leak) of a leak depending on the ascertained leakage mass flow; (i) ascertain a positive-pressure leakage mass flow ({dot over (m)}.sub.leak) and a positive-pressure size characteristic value (A.sub.leak,pos, d.sub.leak,pos) depending on an ascertained positive-pressure leakage mass flow; and/or (ii) ascertain a negative-pressure leakage mass flow (?{dot over (m)}.sub.leak) and a negative-pressure size characteristic value (A.sub.leak,neg, d.sub.leak,neg) depending on an ascertained negative-pressure leakage mass flow; and determine a position of the leak depending on a ratio of the ascertained positive-pressure size characteristic value to the ascertained negative-pressure size characteristic value.

8. A vehicle drive, comprising: an internal combustion engine; an air conduit; an exhaust system, and a diagnostic unit according to claim 7.

9. The vehicle drive according to claim 8, further comprising: an exhaust gas recirculation line which connects the exhaust system to an intake system in a manner conducting exhaust gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a vehicle drive with a diagnostic unit according to one exemplary embodiment of the invention.

(2) FIG. 2 shows mass flows at an intake system of an air conduit of the vehicle drive from FIG. 1, with consideration of which a method according to an exemplary embodiment of the invention can be carried out.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) FIG. 1 shows a vehicle drive 1 having an internal combustion engine 2. The internal combustion engine 2 is designed in the exemplary embodiment as a four-cylinder diesel engine. The internal combustion engine 2 is connected to an air conduit 4 for supply with oxygen, and to an exhaust system 6 for conducting and optionally purifying the exhaust gases.

(4) The air conduit 4 has a charge air conduit 8, a charge air cooler 10, a throttle valve 12 and an intake system 14.

(5) Along an exhaust gas conduit 16, the exhaust system 6 has an exhaust gas manifold 18 and an exhaust gas after-treatment arrangement 20 which has at least one oxidation catalytic converter, but in particular further aftertreatment devices such as at least one particulate filter and/or at least one SCR catalytic converter.

(6) To increase the power of the internal combustion engine 2, a two-stage exhaust gas turbocharger 22 is arranged in the charge air conduit 8 of the air conduit 4 and in the exhaust gas conduit 16 of the exhaust system 6, wherein the compressors of the exhaust gas turbocharger 22 are arranged in the charge air conduit 8 and the turbines of the exhaust gas turbocharger 22 are arranged in the exhaust gas conduit 16. In the exemplary embodiment, an engine topology with two series-arranged turbochargers is illustrated. It is self-evident per se that the invention and also the exemplary embodiment described here can also be used in different engine topologies, for example with a single turbocharger.

(7) The high-pressure compressor and the high-pressure turbine of the exhaust gas turbocharger 22 are each designed in the exemplary embodiment such that they can be circumvented by way of a switchable bypass.

(8) The air conduit 4 and the exhaust system 6 are connectable by means of a switchable high-pressure EGR line 24 such that hot exhaust gas can be conducted from the exhaust gas manifold 18 into the air manifold 14 and mixed there with the fresh air. In the exemplary embodiment, the exhaust gases in the EGR line 24 can be switchably guided through an EGR cooler and/or past same.

(9) A hot film air mass meter HFM for measuring an air mass flow mHFM, and a temperature sensor for measuring a fresh air temperature T10, are arranged at a fresh air inlet 7 of the charge air conduit 8.

(10) A pressure sensor for measuring a compressor pressure p12 in the charge air conduit 8 is arranged between the two compressors.

(11) A temperature sensor for measuring a pre-throttle temperature T21 in the fresh air conduit is arranged between the charge air cooler 10 and the throttle valve 12.

(12) A pressure sensor for measuring a charge pressure p22 is arranged in the air manifold 14.

(13) A temperature sensor for measuring an EGR mixture temperature T-nEGR at the inlet into the air manifold 14 is arranged in the EGR line 24.

(14) A pressure sensor for measuring a pre-turbine pressure p31 is arranged in the exhaust gas manifold 18.

(15) A lambda probe for measuring a mixture composition of the exhaust gases before they enter the exhaust gas aftertreatment arrangement 20 is arranged between the low-pressure turbine of the exhaust gas turbocharger 22 and the exhaust gas aftertreatment arrangement 20.

(16) The vehicle drive 1 furthermore has an engine controller 30 that is configured to actuate the vehicle drive 1, and all components thereof, in accordance with the operating requirements of the motor vehicle. For optimum actuation of the vehicle drive and of the components thereof, the engine controller 30 is also configured to take into consideration measured values from all of the abovementioned sensors and to access conventional operation models, lookup tables, etc., optionally using the detected and/or processed sensor values.

(17) The engine controller 30 has a diagnostic unit 32 that is configured to carry out an exemplary method for diagnosing a leakage 40 of the air conduit 4 of the vehicle drive 1, and thus to ascertain a leakage mass flow. The engine controller may be processor, software and/or hardware based.

(18) The execution of the exemplary method together with a number of variants will be described in detail below on the basis of explanations relating to the illustration of FIG. 2.

(19) FIG. 2 shows schematically the regular mass flows at the air manifold 14: a throttle mass flow {dot over (m)}.sub.ThrVLv and an EGR mass flow {dot over (m)}.sub.EGR into the air manifold, and a charge mass flow {dot over (m)}.sub.charge from the air manifold into the cylinders.

(20) In addition, a possible leakage mass flow {dot over (m)}.sub.leak which is to be diagnosed or to be ascertained is indicated. The leakage mass flow {dot over (m)}.sub.leak is indicated without anticipation of the flow direction; both flow directions of a leakage mass flow {dot over (m)}.sub.leak are possible, depending on whether an ambient pressure p.sub.0 is higher or lower than the charge pressure p.sub.22hence the illustration using the double arrow.

(21) Using the temperature value T.sub.22, which is additionally indicated in FIG. 2, in the air manifold 14 and with recourse to operating models and lookup tables stored in the engine controller 30 (optionally in conjunction with further measurement values of the above-described sensors), the diagnostic unit 32 is configured to carry out a method for diagnosing a leakage 40 of the air conduit 4 and here in particular of the air manifold 14.

(22) For this purpose, first of all the regular mass flows (throttle mass flow {dot over (m)}.sub.ThrVlv, EGR mass flow {dot over (m)}.sub.EGR and charge mass flow {dot over (m)}.sub.charge) of the intake system 4 with respect to the air manifold 14 are determined.

(23) Subsequently, a mass flow balance is established on the basis of the determined mass flows by means of the diagnostic unit 30. The mass flow balance of an optimally tight intake system is produced by:
{dot over (m)}.sub.charge?{dot over (m)}.sub.ThrVlv?{dot over (m)}.sub.EGR=0

(24) For an intake system which is not optimally tight, an initially unascertained leakage mass flow {dot over (m)}.sub.leak is produced, for the ascertaining of which on the basis of the established mass flow balance the following applies:
{dot over (m)}.sub.charge?{dot over (m)}.sub.ThrVlv?{dot over (m)}.sub.EGR+{dot over (m)}.sub.leak=0?{dot over (m)}.sub.leak={dot over (m)}.sub.EGR+{dot over (m)}.sub.ThrVLv?{dot over (m)}.sub.charge(1) where p.sub.22>0.Math.{dot over (m)}.sub.leak>0 and p.sub.22<0.Math.{dot over (m)}.sub.leak<0

(25) In this way, during regular operation of the internal combustion engine, the leakage mass flow {dot over (m)}.sub.leak is ascertained on the basis of the established mass flow balance.

(26) Via the general throttle equation of fluid flows

(27) $\begin{array}{cc}\stackrel{.}{m}=\frac{d^2\mathrm{pi}}{4}{p}_{\mathrm{before}}\sqrt{\frac{2}{{\mathrm{RT}}_{\mathrm{before}}}}?& \left(2\right)\end{array}$ a size, here a diameter d.sub.leak of a leak 40, can be ascertained depending on the ascertained leakage mass flow {dot over (m)}.sub.leak.

(28) The calculation of d.sub.leak is based on the fact that d.sub.leak is equal to zero in a leak-free intake system or is at least virtually precisely zero if relatively minor calculation errors are taken into consideration.

(29) In the exemplary method, both a positive-pressure leakage mass flow is ascertained (i.e. in an operating range in which the charge pressure p.sub.22 is greater than the ambient pressure p.sub.0, for example in a normal driving mode) and a negative-pressure leakage mass flow is ascertained (i.e. in an operating range in which the charge pressure p.sub.22 is lower than the ambient pressure p.sub.0, for example in a regeneration operation of a storage catalytic converter or a particulate filter). Depending on the ascertained positive-pressure leakage mass flow, a positive-pressure size characteristic variable (here a positive-pressure leakage cross section) is ascertained. Depending on the ascertained negative-pressure leakage mass flow, a negative-pressure size characteristic variable (here a negative-pressure leakage cross section) is ascertained.

(30) A position of the leak 40 is then determined depending on a ratio of the positive-pressure leakage cross section to the negative-pressure leakage cross section.

(31) If the two leakage cross sections (as a size characteristic value for the leakage) when sign-corrected are approximately identical in size, i.e. in a ratio of approx. 1 to each other, it should be assumed that the leak 40 is present in that region of the air conduit 4 for which the mass flow balancing has been established, here in the air manifold 14. By contrast, it should be assumed that the leak 40 is present in a different region of the air conduit 4 if said ratio significantly differs from 1.

(32) The ratio can also be determined indirectly, for example by both for the ascertained positive-pressure leakage cross section and for the ascertained negative-pressure leakage cross section a respective comparison being carried out with a pre-ascertained threshold value for a relevant leakage cross section.

(33) It can optionally be taken into consideration here that relatively minor errors in the calculations of the regular mass flows by means of the engine controller 30 may lead to errors in the estimation of the leakage diameter d.sub.leak. The estimated value for A.sub.leak can then be taken into consideration, for example, as follows:

(34) Taking into consideration a mass flow error
A.sub.eff+A.sub.err=({dot over (m)}+{dot over (m)}.sub.err)*f(p,T)
and assuming that the area error for p.sub.22>0 and p.sub.22<0 behaves identically, the result is
A.sub.pos+A.sub.err=({dot over (m)}.sub.pos+{dot over (m)}.sub.err,pos)*f(p,T) and
A.sub.neg+A.sub.err=({dot over (m)}.sub.neg+{dot over (m)}.sub.err,neg)*f(p,T),
and thus a mean area

(35) $A_{\mathrm{Avg}}=\frac{A_{\mathrm{pos}}+A_{\mathrm{err}}+A_{\mathrm{neg}}-A_{\mathrm{err}}}{2}=\frac{A_{\mathrm{pos}}+A_{\mathrm{neg}}}{2},$
and, for the leakage diameter

(36) $\frac{d_{\mathrm{Avg}}^2\mathrm{pi}}{4}=\frac{1}{2}\left(\frac{d_{\mathrm{pos}}^2\mathrm{pi}}{4}+\frac{d_{\mathrm{neg}}^2\mathrm{pi}}{4}\right)$
a mean leakage diameter

(37) $d_{\mathrm{Avg}}=\sqrt{\frac{d_{\mathrm{pos}}^2+d_{\mathrm{neg}}^2}{2}}.$

(38) To calculate a leakage area A.sub.leak, equation 2 is used for the leakage mass flow {dot over (m)}.sub.leak in equation 1 for:

(39) ${\stackrel{.}{m}}_{\mathrm{EGR}}+{\stackrel{.}{m}}_{\mathrm{ThrVlv}}-{\stackrel{.}{m}}_{\mathrm{charge}}=A_{\mathrm{leak}}{p}_{\mathrm{before}}\sqrt{\frac{2}{{\mathrm{RT}}_{\mathrm{before}}}}?\mathrm{where}$$\begin{array}{cc}?=\sqrt{\frac{?}{?-1}}\left({\left(\frac{p_{\mathrm{after}}}{p_{\mathrm{before}}}\right)}^{\frac{2}{?}}-{\left(\frac{p_{\mathrm{after}}}{p_{\mathrm{before}}}\right)}^{?+\frac{1}{?}}\right)& \left(3\right)\end{array}$$A_{\mathrm{leak}}=\frac{d_{\mathrm{leak}}^2?}{4}$$R\mathrm{gas}\mathrm{constant}$$?\mathrm{isentropic}\mathrm{exponent}$

(40) For a positive-pressure operating point where p22>p0 (charge pressure is greater than ambient pressure), in equation 3 p.sub.before should be equated to the charge pressure p.sub.22; p.sub.after to the ambient pressure p.sub.0. Both values are present in the engine controller 30 and therefore in the diagnostic unit 32 as sensor measurement values. In addition, T.sub.before should be equated to the temperature T.sub.22 in the intake system 14. T.sub.22 can be gathered by the engine controller 30 from an operating model and/or a lookup table. The EGR mass flow can be gathered from an operating model taking into consideration the measurement values of the pressure sensors which are present. The throttle valve mass flow can be gathered, with dynamic adaptation, from the values of the air mass sensor HFM. The mass flow into the combustion chambers can be gathered from an operating model taking into consideration measured pressure values and a measured engine rotational speed N. The required calculations are each undertaken by the engine controller 30 and/or the diagnostic unit 32.

(41) For a negative-pressure operating point where p.sub.22<p.sub.0 (charge pressure is lower than ambient pressure), in equation 3 p.sub.after should be equated to the charge pressure p.sub.22; p.sub.before to the ambient pressure p.sub.0. Both values are present in the engine controller 30 and therefore in the diagnostic unit 32 as sensor measurement values. In addition, approximately for T.sub.before, a temperature value from the surroundings can be used, or, for example, a weighted combinationin particular by means of a prefilled characteristic mapof ambient temperature and engine temperature, which has the aim of sufficiently precisely depicting a real temperature depending on the operating point. T.sub.22 can be gathered by the engine controller 30 from an operating model and/or a lookup table. The EGR mass flow can be gathered from an operating model taking into consideration the measurement values of the pressure sensors which are present. The throttle valve mass flow can be gathered, with dynamic adaptation, from the values of the air mass sensor HFM. The mass flow into the combustion chambers can be gathered from an operating model taking into consideration measured pressure values and a measured engine rotational speed N. The required calculations are respectively undertaken by the engine controller 30 and/or the diagnostic unit 32.

(42) Both for positive-pressure operating points and for negative-pressure operating points the following applies: if, for A.sub.leak, a value only differing slightly from zero is produced, an at least substantially tight air conduit 4 should nevertheless be assumed. In these cases, the value is normally not equal to zero only because of model and/or sensor tolerances. Determined values for A.sub.leak of, depending on the application, up to approx. 10 to 15 mm.sup.2 therefore result in a diagnosis of tight system. In general, determined values for A.sub.leak that are in proportion substantially smaller than the leakages to be anticipated in the event of an error therefore result in a diagnosis of tight system. The limit for an assumed precision of the diagnosis depends in particular on the system tolerances which are present.

(43) If higher values result for A.sub.leak, a leakage 40 should be assumed within the meaning of the pre-ascertained threshold value which has already been mentioned (optionally analogously estimated for a leakage diameter).

(44) If the determined values for A.sub.leak correspond to a certain extent for a positive-pressure operating point and for a negative-pressure operating point, i.e. said values are of a size ratio of in particular between 0.75 and 1.25, for example between 0.9 and 1.1 to one another, the diagnosis carried out also permits the following statements:

(45) The diagnosed leak 40 is located at that part of the air conduit 4 for which the mass flow balance has been established, here at the air manifold 14.

(46) It should be assumed that the leak 40 arranged there has a size which corresponds at least substantially to the mean value of the two determined values for A.sub.leak.

(47) In accordance with the position and the size of the leak 40 diagnosed in such a manner, suitable measures can be undertaken (i.e. fallback reactions) to compensate for and/or eliminate the leak 40even during the regular driving operation and/or at a possibly necessary garage visit.

LIST OF REFERENCE SIGNS

(48) 1 Vehicle drive 2 Internal combustion engine 4 Air conduit 6 Exhaust system 8 Charge air conduit 10 Charge air cooler 12 Throttle valve 14 Intake system 16 Exhaust gas conduit 20 Exhaust gas aftertreatment arrangement 22 Exhaust gas turbocharger 24 High-pressure EGR line 30 Engine controller 32 Diagnostic unit 40 Leak or leakage A.sub.leak Leakage area d.sub.leak Diameter of the leakage HFM Hot film air mass meter {dot over (m)}.sub.EGR EGR mass flow {dot over (m)}.sub.charge Charge mass flow {dot over (m)}.sub.leak Leakage mass flow {dot over (m)}.sub.ThrVLv Throttle mass flow p.sub.0 Ambient pressure p.sub.12 Compressor pressure p.sub.22 Charge pressure p.sub.31 Pre-turbine pressure T.sub.10 Fresh air temperature T.sub.21 Pre-throttle temperature T.sub.22 Air manifold temperature T-nEGR EGR mixture temperature ? Fuel/air ratio