DE102016217921A1 - Method for detecting a leak in a suction pipe - Google Patents

Abstract

The invention relates to a method for detecting a leakage in a suction pipe (1) via which an internal combustion engine (2) can be supplied with air. According to the invention, a negative pressure is generated in the intake manifold (1) downstream of a throttle valve (3), so that the pressure in the intake manifold (1) is below ambient pressure. The pressure in the intake manifold (1) is measured and the measured value is compared with a model value that is stored in a control unit (8) or a workshop tester. Furthermore, the invention relates to a computer program with a program code for carrying out the method.

Description

The invention relates to a method for detecting a leak in a suction pipe with the features of the preamble of claim 1. The suction pipe is used to supply an internal combustion engine with air. Furthermore, the invention relates to a computer program with a program code for carrying out the method.

State of the art

The optimum operation of an internal combustion engine in terms of performance and emissions requires, among other things, accurate knowledge of the amount of air present in the cylinder of the internal combustion engine. This not only applies to gasoline engines, but increasingly also diesel engines, especially diesel engines with exhaust gas recirculation. In this case, a leakage that occurs in an intake tract or a suction pipe of the intake, lead to false air, which - depending on the specific position of the leakage - has an excess or shortfall result.

Leakage in the fresh air path can also be the cause of a restless engine run, a reduced engine power and / or a poor brake booster.

From the publication DE 10 2005 019 807 A1 a method for the localization of leaks in the intake tract of an internal combustion engine is known in which signals of different sensors are used. The detection of a leak is carried out by a comparison between the determined using an air mass or Saugrohrabsolutdrucksensors load of the internal combustion engine and the determined using the position of a throttle load. For the localization of the leakage, a comparison is made between the value measured using a lambda probe located in the exhaust tract of the internal combustion engine and the lambda desired value. A further limitation can be carried out by a comparison between the air mass measured with the air mass sensor and the air mass determined on the basis of the measured values of the Saugrohrabsolutdrucksensors.

Based on the above-mentioned prior art, the present invention has the object to provide a simple as possible method for detecting a leak in a suction pipe.

To solve the problem, the method with the features of claim 1 is given. Advantageous developments of the invention can be found in the dependent claims. Furthermore, a computer program with a program code for carrying out the method is proposed.

Disclosure of the invention

In the proposed method for detecting a leakage in a suction pipe according to the invention, a negative pressure is generated in the intake manifold downstream of a throttle valve, so that the pressure in the intake manifold is below ambient pressure. The pressure in the intake manifold is measured and the measured value is compared with a model value stored in a control unit or a workshop tester. If the measured value deviates from the model value, a leak or leakage can be deduced therefrom. Because in the event of a leak, pressure equalization takes place, which prevents the pressure or negative pressure in the intake manifold from reaching the model value.

The proposed method thus enables the detection of a leakage in the intake manifold in a simple manner. A manual intervention is not required, so that a high degree of automation is possible. Furthermore, existing components for pressure measurement and / or for the evaluation of the measurement results can be used, so that the implementation is simple and inexpensive.

The negative pressure in the intake manifold is preferably generated by starting the internal combustion engine with closed air passages, in particular with the throttle valve closed. This means that the intake manifold is approximately hermetically sealed when the engine is started and aspirates air from the intake manifold. Since no air can flow in via the closed air passages, a negative pressure or a pressure which is below ambient pressure arises in the intake manifold.

Normally, the intake manifold is at ambient pressure, ie. H. 1 bar. If the combustion engine is started when the airways are closed, the intake manifold pressure falls below ambient pressure. The degree of pressure drop depends on the particular vehicle model. These model-specific data can be stored in an on-board control unit or a workshop tester, so that they are available as a reference size.

Provided that the suction pipe is tight, the pressure can drop to 350 mbar, just to give an example. This value then serves as a model value or reference size. However, if the suction pipe has a leak or a leak, a pressure arises in the suction pipe which, depending on the size of the leak, is somewhere between 350 mbar and ambient pressure. In the case of massive leakage, the pressure can even be approximately ambient pressure.

In order to be able to reliably detect a leakage in the intake manifold by means of the method according to the invention, the air supply into the intake manifold must be interrupted. For this purpose, initially the throttle valve is closed, which serves in normal operation of the control of the amount of air supplied. If, in addition, further air paths are provided through which air enters the intake manifold, these too are to be closed. The further air paths may include, for example, an exhaust gas recirculation line, which can be shut off via a valve. Alternatively or additionally, a tank vent line may be connected to the suction pipe. Then it is necessary to close this additional airway.

When the throttle is closed, the amount of air for the operation of the internal combustion engine is not sufficient, so that it would stall. In a further development of the invention, it is therefore proposed that an injection device which serves to inject fuel be deactivated. This has the consequence that the injection of fuel is omitted when the internal combustion engine is started.

Furthermore, the internal combustion engine is preferably towed during the start, so that a pump action is generated via the stroke movement of a piston of the internal combustion engine accommodated in a cylinder. Finally, the pump action causes air to be sucked out of the suction pipe and a vacuum to be created in the suction pipe.

Advantageously, the pressure measurement in the intake manifold is carried out by means of a pressure sensor arranged in the intake manifold. In this case, an already existing pressure sensor can be used, so that the implementation is particularly cost-effective.

Since a normal operation of the internal combustion engine is not possible with a closed throttle valve and / or deactivated injection device, the method according to the invention for off-board diagnosis, for example in a workshop, is preferably used. Here, the conditions required to carry out the method can be easily created.

Furthermore, it is proposed that a workshop tester be used in carrying out the method, in which at least one vehicle model-specific model value is stored. This then serves as a reference for the pressure measured in the intake manifold. In case of a significant deviation, this can be concluded that a leak.

This applies analogously when a control device, in particular an engine control unit, is used in carrying out the method, in which the at least one vehicle model-specific model value is stored. Such a control device is usually present and possibly already connected to the pressure sensor arranged in the intake manifold. The control unit receives at least one measured value via the pressure sensor, which it then compares with the stored model value. The implementation of the method thus requires no manual intervention. The evaluation takes place automatically via the control unit.

It is also proposed that the method be used to determine the leakage at engine start and engine stop. When the engine is started, the leak can be checked by first closing the throttle valve and then reopening after the leakage test has been carried out. When the engine stops, a closed throttle valve helps stop the engine and allows leakage testing. Thus, the method can be carried out in the context of typical use and used in the so-called on-board diagnosis.

In addition, a computer program with a program code is proposed, which executes the inventive method when it runs in a control unit or in a workshop tester.

The inventive method will be explained in more detail with reference to the accompanying drawings. These show:

1 a system image of an internal combustion engine including intake and exhaust tract and

2 a diagram showing different pressure curves over time with the same starter control.

Detailed description of the drawings

Of the 1 is an internal combustion engine 2 can be seen in a sectional view. The cut is through a cylinder 5 of the internal combustion engine 2 placed in which a piston 6 is received, which is driven via a crankshaft (not shown) in a lifting movement. The piston 6 limited within the cylinder 5 a combustion chamber, the one injection device 4 assigned to the injection of fuel. The air required for combustion of the fuel is the combustion chamber via a suction pipe 1 an intake tract 9 fed. Further, an exhaust tract 10 provided, via which the exhaust gas produced during the combustion is discharged from the combustion chamber.

To control the internal combustion engine 2 over the suction pipe 1 amount of air supplied is in the intake system 9 a throttle 3 The scheme is subject to a ECU 8th he follows. The control unit 8th is further provided with a first pressure sensor 7 connected to the suction pipe 1 is assigned, as well as with a second pressure sensor 11 , which serves to detect the ambient pressure. In the control unit 8th are thus those of the pressure sensors 7 . 11 recorded measured values and can via the control unit 8th be evaluated.

In the control unit 8th is a computer program with a program code for performing the method according to the invention deposited to make a leak test or to detect leakage in the intake manifold. In addition, in the control unit 8th stored a model value, which is the pressure drop in the intake manifold 1 indicates in the absence of leakage.

To a leakage in the intake manifold 1 can be seen, according to the inventive method first, the throttle valve 3 closed, so that the air supply is interrupted. To close all available airways connected to the intake manifold 1 must be in the in the 1 illustrated example, a tank vent line 12 getting closed. Thereafter, the suction tube forms 1 an at least approximately hermetically sealed volume. Furthermore, the injector 4 deactivated, so that no injection of fuel into the combustion chamber of the internal combustion engine 2 he follows. Subsequently, the internal combustion engine 2 started, wherein the engine is towed over the starter to a rotation of the crankshaft and thus a stroke of the piston 6 to effect. Because about the stroke movement of the piston 6 the desired pumping effect is achieved, which causes air to escape from the suction tube 1 is sucked. There is no air in the intake manifold 1 can flow, arises in the intake manifold 1 a negative pressure, that is, a pressure that is below ambient pressure. This is done by the pressure sensor 7 recorded and in the control unit 8th compared with the stored model value. If the measured value deviates from the model value, it can be concluded that there is a leak or leakage. The degree of deviation also allows a conclusion about the size of the leak.

In the 2 exemplary pressure curves are shown (upper three graphs a to c), which were measured at the same starter setting (lower three graphs d-f). The pressure curve a shows a dense intake manifold 1 because the expected pressure drop occurs. Has the same intake manifold 1 leakage or leakage, the pressure drops significantly less (Graph b). If the leak is of a size, it can supply as much air as it does from the combustion engine 2 is sucked, there is no pressure drop to record (graph c).

The inventive method thus allows a reliable statement about the tightness of the suction pipe 1 or its connections too. Another advantage is that all steps automatically, that is, without manual intervention, expire, in accordance with the in the control unit 8th deposited computer program.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102005019807 A1 [0004]

Claims (10)

Method for detecting a leak in a suction tube ( 1 ) via which an internal combustion engine ( 2 ) can be supplied with air, characterized in that in the intake manifold ( 1 ) downstream of a throttle valve ( 3 ) a negative pressure is generated, so that the pressure in the intake manifold ( 1 ) is below ambient pressure, the pressure in the intake manifold is measured and the measured value is compared with a model value which is stored in a control unit ( 8th ) or a workshop tester is deposited. A method according to claim 1, characterized in that the negative pressure in the suction pipe ( 1 ) by starting the internal combustion engine ( 2 ) with closed airways, especially with the throttle closed ( 3 ), is produced. Method according to claim 1 or 2, characterized in that an injection device ( 4 ), which serves to inject fuel, is deactivated, so that the injection of fuel is omitted when the internal combustion engine ( 2 ) is started. Method according to one of the preceding claims, characterized in that the internal combustion engine ( 2 ) is towed during takeoff, so that about the lifting movement of a in a cylinder ( 5 ) received piston ( 6 ) of the internal combustion engine ( 2 ) a pump action is generated. Method according to one of the preceding claims, characterized in that the measurement of the pressure in the intake manifold ( 1 ) by means of a suction tube ( 1 ) arranged pressure sensor ( 7 ) is carried out. Method according to one of the preceding claims, characterized in that the method is used for off-board diagnosis. Method according to one of the preceding claims, characterized in that in the implementation of the method, a workshop tester is used in which at least one vehicle model-specific model value is stored. Method according to one of the preceding claims, characterized in that in carrying out the method, a control device ( 8th ), in particular an engine control unit, is used in which at least one vehicle model-specific model value is stored. Method according to one of the preceding claims, characterized in that the method is used for on-board diagnosis. Computer program with a program code which carries out the method according to one of claims 1 to 8, when the computer program is stored in a control unit ( 8th ) or workshop tester expires.

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