WO2019149506A1

WO2019149506A1 - Method for detecting a leak in an air intake duct of an internal combustion engine

Info

Publication number: WO2019149506A1
Application number: PCT/EP2019/050734
Authority: WO
Inventors: Sebastian GRASREINER; Michail PALMAN
Original assignee: Bayerische Motoren Werke Aktiengesellschaft
Priority date: 2018-02-05
Filing date: 2019-01-14
Publication date: 2019-08-08
Also published as: DE102018201680A1

Abstract

The invention relates to a method for detecting a leak in an air intake duct of an internal combustion engine with at least one combustion chamber, said air intake duct being split into at least two sections, with a section (A1, A2) upstream of a throttle valve (12) and a section (A3) downstream of the throttle valve (12). In the claimed method, an air mass modelled in the control device, representing the air mass flowing out of the air intake duct and into the at least one combustion chamber, is compared to an air mass that is measured at the inlet of the air intake duct. From the result of this comparison, a correction factor (ev_korr_fak) is determined which is a measurement for alignment between the modelled air mass and the air mass that was measured. Lastly, the value of the correction factor (ev_korr_fak) makes it possible to indicate a leak in the air intake duct.

Description

Method for determining a leak in an intake air duct of a

internal combustion engine

The invention relates to a method for determining a leakage in a Ansaugluftfüh- tion of an internal combustion engine with at least one combustion chamber. The intake air duct is divided into at least two sections, comprising a section in front of a throttle flap and a section downstream of the throttle flap.

A leak in the intake air duct of an internal combustion engine leads to deficiencies in the driving behavior of the vehicle and can lead to various fault memory entries which are MIL (Malfunction Indicator Light) -relevant. Since a review of MIL-relevant functions is required by law, the leakage of the intake air guide, which leads to a change in the air mass-fuel mixture ratio of a predetermined setpoint, to avoid at all costs.

A leak in the intake air duct may e.g. arise during assembly of the vehicle, since the intake air guide is composed of a plurality of different, complex shaped components, which are individual for each vehicle type. Vehicles with leaking intake air ducts will then cause problems for the customer even after a low mileage, which must be remedied during a workshop visit.

Finding leaks, both when installing a new vehicle and in the workshop, is difficult and involves a lot of effort. If leaks are not found or supposedly localized in the wrong places, a repair will not be carried out properly, so that the problems described above can continue to occur. This can lead to unacceptably high warranty costs.

It is an object of the invention to provide a method which enables the determination of leakage in an intake air duct of an internal combustion engine in a simple and robust manner. This object is achieved by a method according to the features of patent claim 1. Advantageous embodiments result from the dependent patent claims.

A method is proposed for determining a leakage in an intake air duct of an internal combustion engine having at least one combustion chamber. The intake air guide is divided into at least two sections, comprising a section in front of a throttle flap and a section downstream of the throttle flap. If the intake air duct comprises a compressor, e.g. a turbocharger, the intake air duct is divided into at least three sections, namely a first section between the (mass air) sensor and the compressor, a second section downstream between the compressor and the throttle and a third section after the throttle.

In the method, a comparison of an air mass modeled in the control unit, which represents the air mass flowing out of the intake air duct into at least one combustion chamber, is performed with a mass of air detected by measurement at the inlet of the intake air duct. From the result of the comparison, a correction factor is determined, which is a measure for the comparison between the modeled air mass and the measured air mass. From the value (i.e., the magnitude of the value) of the correction factor, a leak in the intake air guide is inferred.

The inventive method allows a targeted and rapid diagnosis of whether there is a leak in an intake air or not. The diagnosis can be carried out automatically so that a quick and robust repair procedure is possible. Due to the short time required to carry out the method, this can be used both in existing processes during the manufacture of the vehicle and in stationary operation in a workshop.

In the context of a conventional test procedure, which primarily relates to the functionality of the internal combustion engine, the information determined and evaluated in the method arises anyway and is evaluated in the scope of the method according to the invention in order to infer a leak in the intake air duct. The method can thereby be used, for example, in the context of the production of the vehicle at the end of the belt in order to satisfactorily and simply verify the tightness of the intake air duct. The leak location for the rework can be roughly specified. Depending on the leak location it is possible to reliably detect leak sizes from 2 mm. The method thus makes it possible to increase the delivery quality of newly manufactured vehicles and the probability of a successful repair attempt.

According to an expedient embodiment, the method is carried out on a roller test stand during a pushing phase (towed drive train). This allows the process to be easily incorporated into the manufacture of the vehicle, e.g. at the end of the band. In principle, both acceleration phases and shear phases are suitable for obtaining a primary indication of a leak during a chassis dynamometer test. In the charged operation of acceleration, in the event of a leak, air would escape from the intake air duct and the measured air mass would fall below the expected air mass accordingly. In the overrun phase on the chassis dynamometer, a mixture regulator that adjusts the ratio of fuel to air mass reacts to deviations from the acceleration phase and alters the quality of the mixture. Due to the reaction already made by the mixture controller to deviations from the acceleration phase, a more accurate indication of the presence of a leak is possible in the overrun phase on the chassis dynamometer.

In particular, it is provided to conclude from the value of the correction factor to a leakage in the intake air duct when this exceeds a first predetermined threshold value. The first predetermined threshold can be determined, for example, by experiments.

A further expedient embodiment provides that the method is carried out during an engine test of the internal combustion engine, in which the internal combustion engine is operated idling. Carrying out the method during an engine test of the internal combustion engine, in which the internal combustion engine is operated at idle, allows more accurate statements for the intake engine operation. In particular, this approach allows a distinction between good and bad conditions in the Ansaugluftfüh- tion after the throttle. The implementation of the method can, for example, on End of the engine test carried out during the manufacture of the vehicle. In particular, it is possible to carry out the method proposed according to the invention in parallel to other vehicle checks, so that the cycle time of the production of the vehicle is not adversely affected.

It is expedient if, from the value of the correction factor, a leak in the section in front of the throttle flap of the intake air guide, in particular the second section of the intake air guide, if this has a compressor, is closed if this exceeds the first predetermined threshold value. A leak in the section in front of the throttle valve, in particular the first section in front of an optional compressor, or the section downstream of the throttle valve (third section) of the intake air guide can be inferred if the value of the correction factor is a second predetermined threshold value , which is smaller than the first predetermined threshold, falls below. The second threshold value can also be determined by tests.

In particular, it is expedient to perform an intake manifold pressure reduction during the engine test and to determine a weighting factor from the value of a Lambda adaptation in which slow mixture control values are processed as the long-term tendency of a fuel / air mixture and the value of a lambda control. factor indicates a deviation from a determined desired lambda value of the lambda probe in front of a catalytic converter, and from the value (ie the height of the value) of the evaluation factor, a leak in the intake air guide is concluded. By inserting an additional intake manifold pressure drop, which is e.g. is generated by closing the throttle and / or by increasing an intake valve lift, a positive pressure differential is created from the environment to the intake manifold. In the case of a leak, this leads to an increase in the air mass in the third section. The simultaneous evaluation of the slow and fast mixture regulator output then permits the delimitation of good and bad states in the air guidance to be determined in the third section.

From the value of the weighting factor, a leak in the section in front of the throttle valve, in particular the first section before an optional compressor, or the section after the throttle flap (third section) of the intake air guide is closed. sen, if this exceeds a third predetermined threshold. Leakage in the second section of the intake air guide is inferred if the value of the evaluation factor falls short of a fourth predefined threshold value, which is smaller than the third preset threshold value. The third and the fourth threshold can be determined by experiments.

The first and second thresholds as well as the third and fourth thresholds may be determined by experiments by determining the correction factor and weighting factor as described above. Depending on the evaluation as to whether or not the vehicle just measured has a leak in the intake air duct, if the number of "observed" vehicles is sufficiently large, a statement about the suitable height of the relevant threshold values results.

The invention further proposes a computer program product that can be loaded directly into the internal memory of a digital computer and includes software code portions that perform the steps of the method described herein when the product is run on a computer. The computer program product may, for example, be embodied on a CD-ROM, a DVD, a USB stick or a signal that can be loaded via a network.

The invention will be explained in more detail below with reference to an exemplary embodiment in the drawing. Show it:

Fig. 1 is a schematic representation of an internal combustion engine, in which the Ansaugluft- leadership is illustrated;

FIG. 2 shows a speed-time diagram which is used for carrying out a roller test drive and for determining a leak in an intake air guide; FIG. and

3 shows a table which indicates the determination of a leakage in the intake air duct of the internal combustion engine in various sections and with different checks. 1 shows a schematic illustration of an intake air guide in an internal combustion engine, which has four cylinders as combustion chambers by way of example. 1 shows an intercooler, 2 a recirculating air valve, 3 an intake silencer (filter), 4 a hot-film air mass meter (sensor), the air mass flowing into the internal combustion engine in kg / h immediately after the intake silencer 4 5, an exhaust gas turbocharger, 6 a wastegate valve, 7 a lambda probe in front of a catalytic converter 8, 8 the catalytic converter, 9 a lambda probe after the catalytic converter 8, 10 digital engine electronics (DME), 11 an intake manifold pressure sensor, which inputs as a signal For throttling, 12 a throttle and 13 a charge air temperature / pressure sensor. The intake air duct of the internal combustion engine shown in FIG. 1 essentially comprises three sections: a first section A1 is formed between the hot-film air mass meter 4 or intake silencer (filter) 3 and the compressor 5. A second section A2 is formed between the compressor 5 and the throttle valve 12. A third section A3 is formed between the throttle valve 12 and a respective inlet of the combustion chamber of the internal combustion engine. If the combustion engine has no compressor, the intake air duct only includes sections before and after the throttle valve.

The intake air guide formed from these three sections represents a complex structure of various individual parts, various plug / hose connections and sealing surfaces, which serves to supply filtered fresh air to the combustion chambers in the internal combustion engine. In a supercharged internal combustion engine as shown in FIG. 1, the intake air duct is exposed to a wide pressure range. This ranges from ambient pressure conditions in the first section A1 (ie between the hot-film air mass sensor 4 / intake silencer (filter) 3 and the compressor (exhaust gas turbocharger) 5) to negative pressure during intake engine operation in the third section A3 behind the throttle valve 12 or an overpressure in boosted operation downstream of the compressor (exhaust gas turbocharger) 5. Insufficient installation of the intake air duct risks a potential leak.

Such leakage may have different directions depending on the pressure gradient.

Suction. "False air" can enter the intake air duct and increase the air mass in the intake air duct. So-called "air leakage" may leak from the intake air duct and reduce the air mass in the intake air duct. Both mass flows generate one Deviation from a desired combustion air ratio with corresponding negative effects. In particular, this may result in a fault memory entry which, unless the fault is detected during manufacturing, may result in a motor control lamp (MIL) lighting up.

The complex assembly of the parts of the intake air duct necessitates a detailed inspection of the tightness during the production of the vehicle. A purely optical inspection does not always lead to success, at least in the case of small leaks, even with a so-called leak detection spray and is also time-consuming and prone to errors. The procedure described below enables an automatic check of the airflow tightness of the intake air duct, which is simple and has a high degree of robustness. The result of the method allows a classification into "good" and "bad" as well as a delimitation of the location of the leak in one of the sections A1, A2 or A3.

The method for determining a leakage in the intake air duct of the internal combustion engine preferably comprises a ride on a chassis dynamometer and a model test in which the internal combustion engine is operated at idle (so-called idling test). It may also be sufficient to carry out a chassis dynamometer test if only the statement is to be made as to whether there is leakage or not. Alternatively, only one idle test could be performed.

During the roller test bench test RPT, in which a speed course RT comprising, for example, the six sections I-VI shown in FIG. 2 is moved over time, both acceleration phases (sections I and III) and thrust phases (sections V and B) are suitable VI negative acceleration) to obtain a first indication of leakage. For this purpose, the air mass modeled in the digital engine electronics 10, which represents the air mass flowing out of the intake air duct into a combustion chamber, is compared with the air mass of the hot-film air mass meter 4 measured in parallel thereto. For this purpose, the correction factors ev_korr_fak described in more detail below are determined in sections V and VI. The parameter P1 determined in section I and the parameters P2 determined in section III are recorded and evaluated for other purposes. Controlling the air mass in a combustion chamber controls the desired power requested by a driver based on the accelerator pedal position. The air mass flow flowing into the intake air duct is detected at the beginning of the intake air duct (ie at the entrance of the first section A1) with the hot-film air mass meter 4. However, it only coincides in the stationary load state with the air mass flow actually arriving in the combustion chamber (ie at the outlet of the third section A3). In the dynamic driving range, the value detected by the hot-film air mass meter reacts only with delay to changes in load due to its thermal inertia and pulsations in the intake tract. This is additionally reinforced by the long path that the air flow has to travel from the hot-film air mass meter 4 to the combustion chamber of the internal combustion engine. Since the mass air flow in a combustion chamber can not be measured, it is modeled.

This is done by means of an air mass model, which includes models of the throttle 12, the third section A3 of the intake air guide and the intake valves (not shown in FIG. 1). The latter includes the relationship between the pressure in the third section A3 and the relative filling (the so-called swallowing curve). The relative filling here is the ratio of the actually filled with fresh air combustion chamber volume unthrottled under atmospheric conditions combustor mass.

The most important quantities used to calculate the intake valve model are intake manifold pressure, engine speed, valves intake and exhaust spread, intake valve lift, throttle angle, exhaust gas pressure, estimated combustion chamber temperature and Model correction factor used in the present method. From the mentioned input quantities and the model, the actual air mass in the combustion chamber is calculated in real time, as a result of which inaccuracies of the hot-film air mass measured value can be bypassed. The air mass value determined by the hot film air mass meter is used to match the modeled air mass value in the combustor to the measured value of the hot film air mass meter during steady state operation. This is expressed by the correction factor ev_korr_fak, which is used to diagnose leakage in the intake air duct. In the event of a leak, air would escape from the intake air duct in the boosted mode of acceleration. The measured air mass would fall below the expected air mass which was modeled accordingly. In the coasting phase on the roller test stand (sections V and VI in FIG. 2), a mixture controller reacts to deviations from the acceleration phase and changes the fuel-air mixture. This effect is used to determine a leak, especially in the idle test MT.

The lambda value reflects the ratio of air mass to stoichiometric air consumption during combustion in the combustion chamber, by measuring the residual oxygen content in the exhaust gas and comparing it with the ambient air. The output of the lambda controller, which is supposed to compensate for a different mixture ratio, is called frm. The value of the controller is written over time in the so-called lambda adaptation, which can be found as fra in digital engine electronics. The lambda adaptation is initially not available after the engine is started and usually begins to adapt after a maximum of 100 s. The use of these two values for the leakage test results from the fact that the leakage air changes the ratio of air to fuel and this change in the lambda value and lambda controller becomes visible in the short term or lambda adaptation in the long term. This circumstance is exploited in the idling test MT, which is e.g. can be used in a workshop, since the lambda adaptation (fra) is already present. In this more accurate statements for the intake engine operation are possible.

The evaluation is improved in the idling test MT by inserting an additional intake manifold pressure reduction by closing the throttle valve 12 (so-called throttling) and increasing an intake valve lift, since then a positive pressure gradient is created from the environment to the intake manifold. In the event of a leak, this leads to an increase in the air mass in the third section of the intake air duct. The evaluation of slower mixture regulator output fra and fast mixture regulator output frm (fra x frm) at intake manifold pressure reduction allows a distinction between good and bad conditions in the intake air duct after the throttle valve, i. the third section.

From the procedures and experiments described above for determining suitable threshold values SW1-SW4, a determination of the leakage, an assignment to one of the three sections A1, A2, A3 of the air duct and the size of the leak can be found in the table of FIG. 3 result shown. With the aid of the correction factor determined on the chassis dynamometer, which is determined at the end of the overrun phase and the specification of a first threshold SW1 determined by tests (selected here for SW 1 = 1, 2), leakages of more than 15 mm in the first section can be achieved A1 between the hot-film air mass meter 4 and the compressor (exhaust gas turbocharger) 5 find. If the correction factor ev_korr_fak> SW1, ie ev_korr_fak> 1, 2, the leakage may also be present in the second section A2 between the compressor (turbocharger) 5 and the throttle valve 12, which has a size of at least 6 mm. Alternatively, if the correction factor ev_korr_fak> SW1, ie ev_korr_fak> 1, 2, is exceeded, the leakage may also be present in the third section A3 downstream of the throttle flap 12, which has a size of more than 8 mm.

If the correction factor of the air mass is ev_korr_fak <SW2, i. ev_korr_fak <0.9 (ie the second threshold value SW2 determined by tests is to be determined to be 0.9) and if this is determined during an idling test MT, this indicates a leakage in the third section A3 with a size of approximately 4 mm or more out. The correction factor ev_korr_fak is determined in the idling test MT with a lowering of the intake manifold pressure. If, in addition, the evaluation from the slow and fast mixture regulator output is determined to determine the evaluation factor, this value lies at fra x frm> SW3, i. fra x frm> 1, 2 (whereby the third threshold value SW3 determined to be 1, 2 was determined by tests), it can be concluded with high probability of a leakage in the third section A3 downstream of the throttle flap 12. In this case, leaks in the order of 2 mm can be detected.

If the evaluation factor fra x frm is greater than the third threshold value SW3 (ie greater than 1, 2) and the correction factor ev_korr_fak is less than the second threshold value SW2 (ie ev_korr_fak <0.9), both values being included in the idle test MT with additional cher pressure reduction were determined, it can be concluded that a leak in the first section A1 between the hot-film air mass meter 5 and the compressor (exhaust gas turbocharger) 5. This leakage of a size of more than 15 mm can be determined.

If the weighting factor fra x frm is smaller than a fourth threshold value SW4 (ie fra x frm <SW4, where SW4 was determined to be 0.95), which was determined during idle test MT without intake manifold pressure drop, and at the same time the correction factor ev_korr_fak is greater than As the first threshold value SW1 (ie, ev_korr_fak> 1, 2), wherein the value was determined in the idling test MT with intake manifold pressure reduction, a leakage in the second section A2 between the compressor (turbocharger) 5 and the throttle valve 12 may occur be closed, with leakages of 4 mm and larger are detectable.

The proposed procedure can be carried out automatically during production at the end of the tape or as part of a workshop visit (in the workshop, a test drive on the road is usually carried out instead of a roller ride). By analyzing charged and naturally aspirated operation, the location of the leak can be limited for rework. Depending on the leak location, leak sizes from 2 mm can be reliably detected. As a result, the delivery quality of a moving vehicle in the assembly plant is increased. It also makes it easier to find errors during a workshop visit.

LIST OF REFERENCE NUMBERS

1 intercooler

2 diverter valve

3 intake silencer

4 hot-film air mass meter (sensor)

5 exhaust gas turbocharger

6 wastegate valve

7 Lambda probe in front of the catalytic converter

8 catalyst

9 Lambda probe after the catalyst

10 digital engine electronics (DME)

1 1 intake manifold pressure sensor

12 throttle

13 Charge air temperature pressure sensor

RT speed history

RPT chassis dynamometer test

MT idle

A1 first section of the intake air duct

A2 second section of the intake air duct

A3 third section of the intake air duct

SW1 first threshold

SW2 second threshold

SW3 third threshold

SW4 fourth threshold

Claims

claims

1. A method for determining a leakage in an intake air duct of an internal combustion engine having at least one combustion chamber, the intake air duct being divided into at least two sections, comprising a section (A1, A2) in front of a throttle flap (12), and a section (A3) after the throttle valve (12) is divided, at the

a) a comparison of an air mass modeled in the control unit (10), which represents the air mass flowing out of the intake air duct into the at least one combustion chamber, is performed with an air mass measured at the inlet of the intake air duct;

b) determining from the result of the comparison a correction factor (ev_korr_fak) which is a measure of the balance between the modeled air mass and the measured air mass due to the inertia of the measurement of the measured air mass;

c) is concluded from the value of the correction factor (ev_korr_fak) on a leakage in the intake air duct.

2. The method of claim 1, wherein this is carried out on a chassis dynamometer during a coasting phase.

3. The method of claim 2, wherein from the value of the correction factor

(ev_korr_fak) is closed to a leak in the intake air duct when this exceeds a first predetermined threshold (SW1).

4. The method according to any one of the preceding claims, wherein this during an engine test (MT) of the internal combustion engine, in which the internal combustion engine is operated at idle, is performed.

5. The method of claim 4, wherein from the value of the correction factor

(ev_korr_fak) is closed to a leakage in the section (A2) in front of the throttle flap (12) of the intake air guide, in particular a section between an optional compressor (5) and the throttle flap (12) of the intake air guide, if this the first predetermined threshold ( SW1).

6. The method of claim 4, wherein from the value of the correction factor

(ev_korr_fak) is closed to a leak in the section in front of the throttle valve (12), in particular a section (A1) before an optional compressor (5), or the section (A3) after the throttle valve (12) of the intake air guide, if this one second predetermined threshold value (SW2), which is smaller than the first predetermined threshold value (SW1), falls below.

7. The method according to any one of claims 4 to 6, wherein carried out during the engine test, a Saugrohrdruckabsenkung and a weighting factor (fra x frm) from the value (fra) a Lambdaadaption and the value (frm) of a Lambda- is determined, the Assessment factor (fra x frm) indicates a deviation from a determined desired lambda value of the lambda probe in front of a catalytic converter (7) and wherein a value of the evaluation factor (fra x frm) indicates a leakage in the intake air guide.

8. The method of claim 7, wherein from the value of the evaluation factor (fra x frm) on a leak in the section in front of the throttle valve (12), in particular a section (A1) before an optional compressor (5), or the section ( A3) is closed after the throttle valve (12) of the intake air guide, if this exceeds a third predetermined threshold (SW3).

9. The method of claim 7, wherein, when the intake air guide includes a compressor (5), from the value of the weighting factor to leakage in the portion (A2) between the compressor (5) and the throttle valve (12) - Is closed intake duct when it falls below a fourth predetermined threshold (SW4), which is smaller than the third predetermined threshold (SW3).

10. The method according to any one of claims 7 to 9, wherein the Saugrohrdruckabsk- kung by closing the throttle valve (12) is generated.

11. A method according to any one of claims 7 to 10, wherein the intake manifold pressure drop is generated by an increase in an intake valve lift.

12. Computer program product directly into the internal memory of a digital

Computers can be loaded and includes software code sections, with which the steps are carried out according to one of the preceding claims, when the product is running on a computer.