DE102015007513B4 - Method for detecting leaks in a crankcase ventilation system - Google Patents

Abstract

Method for detecting leaks in a crankcase ventilation (16) of an internal combustion engine (10), in which a gaseous medium is fed from a crankcase (12) of the internal combustion engine (10) to an engine intake line (18) of the internal combustion engine (10) at a feed point (30) and upstream an air mass value (mf_air_flow_sensor) is detected at the feed point (30) with an air mass sensor (20), characterized in that in a first step (100) it is detected whether the internal combustion engine (10) is in a leak detection state (mf_engine = const.) , in a further step (200) a value indicative of a vent line mass flow (mf_blow-by) is monitored for a change when the internal combustion engine (10) is in the leakage detection state (mf_engine = const.), and in an additional Step (300) the air mass value (mf_air_flow_sensor) is monitored for a change when the indicative value changes, to infer a leak in the crankcase ventilation (16), a pressure in the crankcase (12) being varied with a switchover valve (24).

Description

The invention relates to a method for detecting leaks in a crankcase ventilation of an internal combustion engine according to the preamble of claim 1.

In internal combustion engines designed as naturally aspirated engines with a throttle valve, brake boosters for such motor vehicles, such as passenger cars, obtain their operating negative pressure from a tapping point of an intake manifold, in which negative pressure prevails during operation of the internal combustion engine. On the other hand, in an internal combustion engine without a throttle valve, such as a gasoline engine with direct injection, a diesel engine with an open throttle valve, or a supercharged internal combustion engine such as an internal combustion engine charged by means of an exhaust gas turbocharger, a vacuum pump is provided that generates the operating vacuum required for the brake booster. The vacuum pump can be coupled to the internal combustion engine so that the internal combustion engine also drives the vacuum pump, or the vacuum pump has its own drive, e.g. in the form of an electric motor.

The air conveyed by the vacuum pump during operation is fed into a crankcase of the internal combustion engine via a vent line. A leak detection of a crankcase ventilation of an internal combustion engine is possible with a pressure sensor in the crankcase and possibly with a shut-off valve in the crankcase ventilation.

From the DE 10 2007 050 087 B3 a method for monitoring the ventilation of a crankcase of an internal combustion engine without such a pressure sensor is known. For this purpose, according to the DE 10 2007 050 087 B3 the respective mass flows upstream and downstream of a feed point of the ventilation line and the respective enthalpies are determined and evaluated using the recorded respective mass flows.

US 2008/058 994 A1 discloses a fault determination device and a generic method for operating a blow-up gas recirculation device for recirculating a blow-up gas to an intake system of an internal combustion engine, the gas recirculation device of which blows gas out of the crankcase leads back into the intake line and has a gas return passage that connects a cylinder head cover and the intake line to one another. A ventilation passage establishes a connection from the cylinder block to the cylinder head. An air mass sensor is arranged upstream of a feed point in the direction of flow.

Furthermore describes the DE 100 26 492 A1 a method for the functional diagnosis of a ventilation system of a crankcase of an internal combustion engine. A clock valve is arranged in the vent line, which is controlled as a function of the pressure in the crankcase. The pressure curve shows whether there is a leak in the closed ventilation system.

From the DE 197 57 345 A1 There is known a blow-by gas passage abnormality detection system for an internal combustion engine in which leakage of blow-by gas coming from a blow-by gas passage is detected only under the condition that the engine is idling. The blow-by gas duct returns the blow-by gas that is generated in the engine to an intake duct.

the EP 2 426 324 A1 describes an engine intake system having a controller for calculating an idle intake air amount based on an air flow rate measured by an air flow meter. A separation of a blow-by gas recirculation line is determined when a value is present which exceeds a limit value for the difference between an idle intake air amount and a stored normal intake air amount.

A method and a device for diagnosing a crankcase ventilation of internal combustion engines are known from WO 2012/034 907 A1. The pressure difference between an ambient pressure and a pressure in the crankcase is determined and a fault in the ventilation device is determined as a function thereof if an air mass flow in the air supply system, filtered by a low-pass filter, exceeds a first threshold value.

The invention is based on the object of showing a simpler way of detecting leaks in a crankcase ventilation system without additional sensors.

This object is achieved according to the invention by a method for detecting leaks in a crankcase ventilation of an internal combustion engine of the above-mentioned type with the features characterized in claim 1. Advantageous embodiments of the invention are described in the further claims.

For this purpose, it is provided according to the invention in a method of the above type that it is detected in a first step whether the internal combustion engine is in a leak detection state, in a further step a value indicative of a vent line mass flow is monitored for a change if there is the internal combustion engine in the leakage detection state is located, and in an additional step, an air mass value is monitored for a change when the indicative value changes in order to conclude a leak in the crankcase ventilation, a pressure in the crankcase being varied with a switchover valve.

This has the advantage that a leak in a crankshaft ventilation system can be detected with simpler means, since a leak detection, in departure from the known prior art, is only possible in a leak detection state by monitoring for a change in the air mass value. For example, there is no need for a second air mass measurement in the direction of flow behind the feed point or a pressure sensor in the crankcase. A leak detection state is understood to mean an operating state of the internal combustion engine in which the air requirement of the internal combustion engines is essentially constant within a time interval during which the leakage detection is carried out, e.g. when idling or during an overrun phase. An essentially constant air requirement is understood here to mean that fluctuations in the air requirement do not impair the leak detection. This is the case, for example, when the leakage loss is greater than the fluctuations in the air requirement. A leak in the crankcase ventilation is concluded if there is no change in the air mass value.

According to one embodiment, it is detected whether a request signal changing the indicative value is present, and if the request signal is present, a change in the vent line mass flow is concluded. The request signal can be a binary logic signal with the logic states one and zero. The request signal then has the value logical one, for example, if the actuating and / or control parameters of the motor vehicle indicate a change in the ventilation line mass flow. Otherwise the request signal is logic zero. The request signal is generated, for example, when there is a particularly high vacuum requirement, e.g. due to multiple actuation of the service brake of the motor vehicle. For example, a control unit of the motor vehicle monitors whether the service brake has been actuated several times. This is a passive monitoring, in which a leakage detection is carried out when suitable states are present, but these states are not actively brought about, e.g. by the control unit.

According to a further embodiment, a control device generates a switchover signal, and the switchover signal controls the switchover valve that changes the vent line mass flow and changes the indicative value. By activating the switchover valve, the switchover valve is opened and a suitable state for leak detection is actively brought about by generating negative pressure. A check valve can be provided so that there is no negative pressure in the entire system and thus a pressure that is below a necessary minimum operating pressure that is required for the operation of, for example, brake boosters. A pressure accumulator, for example, can also be provided to maintain the minimum operating pressure.

According to a further embodiment, a speed of the internal combustion engine is detected, the detected speed is compared with a speed limit value, and a leakage detection state is deduced if the detected speed is less than the speed limit value. The different system characteristics of a vacuum pump for generating negative pressure and the internal combustion engine (absorption behavior) can be used to detect the leakage at a low speed of the internal combustion engine, e.g. when idling, where the internal combustion engine's air requirement is particularly low due to the low speed and the low load requirement . In this case, the speed limit value is the idling speed or less than the idling speed.

According to a further embodiment, when the leakage detection state is present, an air supply to the internal combustion engine is throttled. This can be done by changing the degree of opening of a throttle valve of the internal combustion engine, such as a gasoline engine with direct injection or a diesel engine with a normally open throttle valve, in order to minimize the air supply and thus also fluctuations in the air supply.

According to a further embodiment, when the leakage detection state is present, an exhaust gas recirculation of the internal combustion engine is deactivated, or an exhaust gas recirculation rate of the exhaust gas recirculation is reduced or a variation in the exhaust gas recirculation rate by controlling or regulating the exhaust gas recirculation is prevented. Deactivating the exhaust gas recirculation prevents the exhaust gas recirculation from compensating for a leakage loss by increasing the exhaust gas recirculation rate and thus there is no detectable leakage loss. The alternative reduction in the exhaust gas recirculation rate can also prevent the leakage loss from being compensated for by increasing the exhaust gas recirculation rate. Furthermore, this can also be achieved by deactivating a control or regulation that would otherwise compensate for a leakage loss in the active state by increasing the exhaust gas recirculation rate.

According to a further embodiment, an overrun state parameter of the internal combustion engine is recorded, which is recorded Overrun condition parameter is compared with an overrun condition parameter limit value, and a leakage detection condition is concluded if the detected overrun condition parameter is greater than the overrun condition parameter limit value. A leak detection is therefore only carried out if the air requirement of the internal combustion engine is reduced due to the overrun condition, for example by partially or completely closing a throttle valve of the internal combustion engine. In the case of a vacuum pump that is permanently coupled to the internal combustion engine, the delivery rate of the vacuum pump is increased during an overrun phase due to the higher speed of the internal combustion engine and thus the negative pressure is increased, which facilitates leak detection.

According to a further embodiment, the step “monitoring the indicative value for a change” comprises recording at least one first indicative value, determining a limit value for the indicative value, comparing the limit value with a second, recorded indicative value and inferring a change when the limit value is exceeded by the second recorded indicative value. The limit value for the indicative value is therefore determined on the basis of the first indicative value recorded during an initialization phase, e.g. by defining deviations of 3%, 5% or 10% of the recorded first indicative value as the limit value. Alternatively, the first indicative value can also be an average value of a plurality of values acquired during the initialization phase.

According to a further embodiment, the step of “monitoring the air mass value for a change” comprises detecting at least one first air mass value, determining an air mass limit value for the air mass value, comparing the air mass limit value with a second detected air mass value and inferring a change the second recorded air mass value falling below the air mass limit value. The air mass limit value is therefore determined on the basis of the first air mass value recorded during a further, second initialization phase, e.g. by defining deviations of 3%, 5% or 10% of the first air mass value recorded as the air mass limit value. Alternatively, the first air mass value can also be an average value of a plurality of air mass values acquired during the further, second initialization phase.

The invention also includes an internal combustion engine with a crankcase, a crankcase ventilation, an engine intake line and an air mass sensor, wherein a gaseous medium can be fed from the crankcase via the crankcase ventilation to a feed point downstream of the air mass sensor of the engine intake line, the internal combustion engine being designed to detect whether the internal combustion engine is in a leakage detection state, to monitor a value indicative of a vent line mass flow for a change when the internal combustion engine is in the leakage detection state, and to monitor the air mass value for a change when the pressure measurement value changes to to close a leak in the crankcase ventilation, whereby a pressure in the crankcase is varied with a switching valve. The internal combustion engine can be an internal combustion engine without a throttle valve, such as a gasoline engine with direct injection, a diesel engine with an open throttle valve, or a supercharged internal combustion engine, such as an internal combustion engine charged by means of an exhaust gas turbocharger.

The invention also includes a method for carrying out a motor vehicle diagnosis of a motor vehicle with an internal combustion engine, in which a gaseous medium is fed from a crankcase of the internal combustion engine to an engine intake line of the internal combustion engine at a feed point and an air mass value is recorded upstream of the feed point with an air mass sensor. In a first step, the internal combustion engine is brought into a leak detection state, in a further step a value indicative of a vent line mass flow is monitored for a change when the internal combustion engine is in the leak detection state, and in an additional step the air mass value is set to a Change monitored when the indicative value changes in order to infer a leak in a crankcase ventilation of an internal combustion engine, a pressure in the crankcase being varied with a switchover valve. For this purpose, a diagnostic device for motor vehicle diagnosis can be used as part of an off-board diagnosis, which - connected to the motor vehicle to transmit control and / or actuating signals - initiates the individual steps and, for example, changes the vent line mass flow after setting the leak detection state, e.g. by generating a diagnostic signal. Alternatively, the procedure can also be carried out as part of an on-board diagnosis (OBD). In this case, all the systems of the motor vehicle that affect the exhaust gas are monitored while the vehicle is in motion, as are other important control units, the data of which are accessible through their software. Any errors that occur are brought to the attention of the motor vehicle driver, for example by means of a control lamp, and are permanently stored in the respective control unit of the motor vehicle. Error messages can then be queried later by a specialist workshop via standardized interfaces.

Finally, the invention also includes a diagnostic device (also called a diagnostic tester) for carrying out a motor vehicle diagnosis of a motor vehicle, which is designed to carry out the steps of the method for carrying out a motor vehicle diagnosis of a motor vehicle. The diagnostic device is designed as an external test device.

A motor vehicle diagnosis is understood to mean a precise assignment of findings to errors in, for example, mechanical, electrical and electronic components of a motor vehicle, for example in the error analysis in the event of an inspection or repair. Motor vehicle diagnosis, including off-board diagnosis, thus differs from on-board diagnosis, including vehicle self-diagnosis.

• 1 in schematischer Darstellung ein Ausführungsbeispiel einer erfindungsgemäßen Brennkraftmaschine, und
• 2 ein Ablaufdiagramm eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens zur Leckageerfassung einer Kurbelgehäuseentlüftung der in 1 dargestellten Brennkraftmaschine.

The invention is explained in more detail below with reference to the drawing. This shows in

• 1 in a schematic representation an embodiment of an internal combustion engine according to the invention, and
• 2 a flowchart of an embodiment of a method according to the invention for leak detection of a crankcase ventilation of the in 1 internal combustion engine shown.

the 1 shows an internal combustion engine 10 . In the present exemplary embodiment, the internal combustion engine is 10 a gasoline or diesel engine for driving a motor vehicle, for example a car.

The internal combustion engine 10 is in the present embodiment with the help of a turbocharger 22nd charged by the in 1 the compressor is shown. The compressor of the turbocharger 22nd is driven in the present embodiment by an exhaust gas turbine (not shown). However, it can also be an internal combustion engine 10 act without a throttle valve, such as a gasoline engine with direct injection, or a diesel engine with a throttle valve open in normal operation.

To the internal combustion engine 10 is a vacuum pump 14th directly coupled. The vacuum pump 14th serves to provide an operating vacuum for operating a brake booster (not shown) of the motor vehicle. Alternatively, the vacuum pump 14th also have their own drive, such as an electric motor.

One from the vacuum pump 14th sucked in gaseous medium, eg air, is in a crankcase 12th the internal combustion engine 10 feeds. For venting the crankcase 12th is a crankcase ventilation 16 provided that a vent line 32 having on the crankcase 12th begins and at a feed point 30th an engine intake line 18th ends. The engine intake line 18th serves the internal combustion engine 10 To supply combustion air, the combustion air from the compressor of the turbocharger 22nd is compressed to increase the performance of the internal combustion engine 10 to effect.

The feed point 30th is in the present exemplary embodiment in the flow direction of the combustion air upstream of the compressor of the turbocharger 22nd arranged. In the direction of flow of the combustion air in front of the feed point 30th is an air mass sensor 20th (also mass air flow meter - MAF) intended to record the mass of air flowing through per unit of time. The measured mass flow of air is proportional to the molar amount of oxygen it contains and is therefore used to control combustion processes, especially in diesel and Otto engines to control the amount of fuel injected. Only when the exact air mass is known can the ratio between air and fuel mass, which is decisive for the combustion process, be precisely set (lambda value = 1). In the case of diesel engines, the lambda value also provides a manipulated variable for exhaust gas recirculation. The air mass sensor 20th works in the present embodiment according to the principle of a hot wire anemometer with characteristic curve correction.

There is now an embodiment of a method for leak detection of a crankcase ventilation 16 an internal combustion engine 10 with additional reference to the 2 explained to a leak, for example due to a non-formed plug connection or a leaky vent line 32 capture.

In the first step 100 it is detected whether the internal combustion engine 10 in a leak detection state mf_engine = const . is located. The leak detection state mf_engine = const . occurs when there is a demand for air within a time interval during which the leakage detection is carried out mf_engine the internal combustion engine 10 is essentially constant, such as when idling or during an overrun phase of the internal combustion engine 10 : $$\text{mf\_engine}=\text{const}.$$

For this purpose, for example, one detects the internal combustion engine 10 associated control unit a speed of the internal combustion engine 10 and compares the detected speed with a speed limit value. That The control unit determines a leakage detection status if the detected speed is less than the speed limit value. In the present exemplary embodiment, the speed limit value is, for example, 5% to 10% smaller than the idling speed of the internal combustion engine 10 so that during operation of the internal combustion engine 10 at idle, the leak detection state mf_engine = const . given is.

Additionally or alternatively, it can be provided that the control device detects an overrun state parameter of the internal combustion engine which is characteristic of an overrun phase, for example by detecting and evaluating an accelerator pedal position. The detected overrun condition parameter is compared by the control unit with an overrun condition parameter limit value. A leakage detection state is concluded if the detected thrust state parameter is greater than the thrust state parameter limit value. This means that leakage detection is only carried out if the air requirement is due to the overrun condition mf_engine the internal combustion engine 10 is reduced, for example by partially or completely closing a throttle valve of the internal combustion engine 10 . Because the vacuum pump 14th firmly to the internal combustion engine 10 is coupled, is during an overrun phase due to the higher speed of the internal combustion engine 10 the delivery rate of the vacuum pump 14th increased and thus the negative pressure increases, which facilitates the leak detection.

When the control unit has determined that the internal combustion engine 10 in the leak detection state mf_engine = const . is located in a further, second step 200 one for the vent line mass flow mf_blow-by Indicative value of the mass flow flowing through the vent line monitored for a change.

The indicative value is a measure of the pressure prevailing in the crankcase 12th and the crankcase ventilation 16 .

For this purpose, the control device uses passive monitoring to determine whether there is a request signal that changes the indicative value. A request signal that changes the indicative value can be generated, for example, on the basis of multiple actuation of the service brake of the motor vehicle, since there is then a particularly high vacuum requirement. When the request signal is present, the control unit then concludes that there has been a change.

As an alternative or in addition, it can be provided that the control device generates a switchover signal, which is a switchover valve, as part of active monitoring 24 controls to the indicative value by changing the pressure in the crankcase 12th and the crankcase ventilation 16 to vary. The switching valve is activated by the control signal 24 opened and thus the vent line mass flow ( mf_blow-by ) varies. A check valve 26th prevents pressure equalization with the result that a minimum operating pressure, which is required for the operation of, for example, brake boosters, is not undershot. A pressure accumulator is also used to maintain the minimum operating pressure 28 intended.

Detecting whether there is a request signal changing the indicative value, for example, comprises in the present exemplary embodiment detecting a first indicative value, determining a limit value for the indicative value, comparing the limit value with a second detected indicative value and inferring a change an exceeding of the limit value by the second recorded indicative value. Thus, in the present exemplary embodiment, the request signal has the value logic one if the second detected indicative value is greater than the limit value. Otherwise the request signal is logic zero. In the present exemplary embodiment, the limit value is zero: $$\Delta \text{mf}\_\text{blow}-\text{by}>0$$

These steps are also carried out by the control unit.

If the control unit has determined that the indicative value has changed, an additional, third step takes place 300 one with the air mass sensor 20th recorded air mass value mf_air_flow_sensor monitored for a change.

Since the internal combustion engine 10 itself in the leak detection state mf_engine = const . and therefore a constant air requirement mf_engine as soon as there is a change in the vent line mass flow rate mf_blow-by> 0, this occurs with an intact vent line 32 a lowering of the output signal for the air mass value mf_air_flow_sensor of the air mass sensor 20th one, because the change in the negative pressure leads to an increased delivery rate of the vacuum pump 14th leads, which in turn increases the pressure in the crankcase 12th causes less air to pass through the air mass sensor 20th must flow. In other words, the following applies: $$\text{mf\_air\_flow\_sensor}=\text{mf\_engine}-\text{mf\_blow}-\text{by}$$

A leak, for example due to a non-formed plug connection in the vent line 32 or due to a leaking vent line 32 however, it does not lead to a lowering of the output signal for the air mass value mf_air_flow_sensor of the air mass sensor 20th because the vent line is not plugged in or is leaking 32 there is no pressure increase in the crankcase 12th comes (mf_blow-by = 0). An unchanged air mass thus flows through the air mass sensor 20th . In other words, it is due to a crankcase ventilation leak 16 then closed when there is a change in the air mass value mf_air_flow_sensor fails to appear.

Detecting whether there is a change in the air mass value mf_air_flow_sensor is present, includes in the present embodiment a detection of a first air mass value mf_air_flow_sensor with the air mass sensor 20th , a determination of an air mass limit value for the air mass value mf_air_flow_sensor , a comparison of the air mass limit value with a second recorded air mass value mf_air_flow_sensor and inferring a change in the event that the air mass limit value is exceeded by the second detected air mass value mf_air_flow_sensor to check for a crankcase ventilation leak 16 close.

When the internal combustion engine 10 If a system for exhaust gas recirculation is assigned, the control unit deactivates the exhaust gas recirculation in order to prevent the exhaust gas recirculation from compensating for a leakage loss by increasing the exhaust gas recirculation rate and thus there is no detectable leakage loss. Alternatively, the control unit can reduce the exhaust gas recirculation rate of the exhaust gas recirculation or prevent a variation in the exhaust gas recirculation rate by controlling or regulating the exhaust gas recirculation.

The procedure can be carried out as part of an on-board diagnosis (OBD). In this case, all the systems of the motor vehicle that affect the exhaust gas are monitored while the vehicle is in motion, as are other important control units, the data of which are accessible through their software. Any errors that occur are brought to the attention of the motor vehicle driver, e.g. by means of a control lamp, and are permanently stored in the respective control unit of the motor vehicle. Error messages can then be queried later by a specialist workshop via standardized interfaces.

Alternatively, the method can be used in the context of an off-board diagnosis for carrying out a motor vehicle diagnosis of a motor vehicle with an internal combustion engine 10 serve, in which a diagnostic device (not shown) is used for motor vehicle diagnosis, which is connected to the motor vehicle for transmission of control and / or actuating signals and initiates and monitors the individual steps as well as the vent line mass flow mf_blow-by after setting the leak detection state mf_engine = const . changed, for example by generating a diagnostic signal that the vent line mass flow mf_blow-by changes.

A method is thus provided with which there is no pressure sensor in the crankcase 12th the internal combustion engine 10 , so a pressure sensor-free design of the crankcase 12th can be reached. Furthermore, with the method, only a single air mass sensor instead of two air mass sensors can cause a leak in a crankcase ventilation 16 are recorded.

List of reference symbols

10

Internal combustion engine

12th

Crankcase

14th

Vacuum pump

16

Crankcase ventilation

18th

Engine intake line

20th

Air mass sensor

22nd

turbocharger

24

Changeover valve

26th

check valve

28

Pressure accumulator

30th

Feed point

32

Vent line

100

step

200

step

300

step

mf_engine = const.

Leak detection status

mf_air_flow_sensor

Air mass value

mf_blow-by

Vent line mass flow

mf_engine

Air requirement

Claims (12)

Method for detecting leaks in a crankcase ventilation (16) of an internal combustion engine (10), in which a gaseous medium is fed from a crankcase (12) of the internal combustion engine (10) to an engine intake line (18) of the internal combustion engine (10) at a feed point (30) and upstream an air mass value (mf_air_flow_sensor) is detected at the feed point (30) with an air mass sensor (20), characterized in that in a first step (100) it is detected whether If the internal combustion engine (10) is in a leakage detection state (mf_engine = const.), in a further step (200) a value indicative of a vent line mass flow (mf_blow-by) is monitored for a change when the internal combustion engine (10 ) is in the leak detection state (mf_engine = const.), and in an additional step (300) the air mass value (mf_air_flow_sensor) is monitored for a change when the indicative value changes in order to conclude that there is a leak in the crankcase ventilation (16) , wherein a pressure in the crankcase (12) is varied with a switching valve (24). Procedure according to Claim 1 , characterized in that it is detected whether a request signal changing the indicative value is present, and if the request signal is present, a change in the vent line mass flow (Δ mf_blow-by> 0) is concluded. Procedure according to Claim 1 or 2 , characterized in that a control unit generates a switchover signal, and the switchover signal controls the switchover valve (24) which changes the vent line mass flow (mf_blow-by) and changes the indicative value. Procedure according to Claim 1 , 2 or 3 , characterized in that a speed of the internal combustion engine (10) is detected, the detected speed is compared with a speed limit value, and a leakage detection state (mf_engine = const.) is inferred if the detected speed is less than the speed limit value . Method according to at least one of the preceding claims, characterized in that when the leakage detection state (mf_engine = const.) Is present, an air supply to the internal combustion engine (10) is throttled. Method according to at least one of the preceding claims, characterized in that when the leakage detection state (mf_engine = const.) Is present, an exhaust gas recirculation of the internal combustion engine (10) is deactivated or an exhaust gas recirculation rate of the exhaust gas recirculation is reduced or a variation in the exhaust gas recirculation rate by controlling or regulating the exhaust gas recirculation is prevented. Method according to at least one of the preceding claims, characterized in that a thrust state parameter of the internal combustion engine (10) is detected, the detected thrust state parameter is compared with a thrust state parameter limit value, and a leakage detection state (mf_engine = const.) Is inferred if the detected thrust state parameter is greater than the thrust condition parameter limit value. The method according to at least one of the preceding claims, characterized in that the further step (200) comprises detecting at least one first indicative value, determining a limit value for the indicative value, comparing the limit value with a second detected indicative value and inferring a change when the limit value is exceeded by the second recorded indicative value. The method as claimed in at least one of the preceding claims, characterized in that the additional step (300) includes recording a first air mass value (mf_air_flow_sensor), determining an air mass limit value for the air mass value (mf_air_flow_sensor), comparing the air mass limit value with a second one Air mass value (mf_air_flow_sensor) and an inference to a change when the air mass limit value is undershot by the second recorded air mass value (mf_air_flow_sensor). Internal combustion engine (10) with a crankcase (12), a crankcase ventilation (16), an engine intake line (18) and an air mass sensor (20) for detecting an air mass value (mf_air_flow_sensor), whereby a gaseous medium from the crankcase (12) via the crankcase ventilation ( 16) can be fed to the engine intake line (18) at a feed point (30) downstream of the air mass sensor (20), characterized in that the internal combustion engine (10) is designed to detect whether the internal combustion engine (10) is in a leakage detection state (mf_engine = const.) is to monitor a value indicative of a vent line mass flow (mf_blow-by) for a change when the internal combustion engine (10) is in the leak detection state (mf_engine = const.), and the air mass value (mf_air_flow_sensor) monitor for a change when the indicative value changes to check for crankcase ventilation leakage (16) to close, wherein a pressure in the crankcase (12) is varied with a switch valve (24). Method for carrying out a motor vehicle diagnosis of a motor vehicle with an internal combustion engine (10), in which a gaseous medium is fed from a crankcase (12) of the internal combustion engine (10) to an engine intake line (18) of the internal combustion engine (10) at a feed point (30) and upstream an air mass value (mf_air_flow_sensor) is detected at the feed point (30) with an air mass sensor (20), characterized in that in a first step the internal combustion engine (10) is brought into a leak detection state (mf_engine = const.), in a further step a value indicative of a vent line mass flow (mf_blow-by) is monitored for a change when the internal combustion engine (10) is in the Leak detection state (mf_engine = const.) Is, and in an additional step the air mass value (mf_air_flow_sensor) is monitored for a change when the indicative value changes in order to conclude that there is a leak in a crankcase ventilation (16) of an internal combustion engine (10), wherein a pressure in the crankcase (12) is varied with a switching valve (24). Diagnostic device for carrying out a motor vehicle diagnosis of a motor vehicle with an internal combustion engine (10), in which a gaseous medium is supplied from a crankcase (12) of the internal combustion engine (10) to an engine intake line (18) of the internal combustion engine (10) at a feed point (30) and upstream an air mass value (mf_air_flow_sensor) is detected at the feed point (30) with an air mass sensor (20), characterized in that the diagnostic device is designed to bring the internal combustion engine (10) into a leak detection state (mf_engine = const.) in a first step, in a further step to monitor a value indicative of a vent line mass flow (mf_blow-by) for a change when the internal combustion engine (10) is in the leak detection state (mf_engine = const.), and in an additional step the air mass value ( mf_air_flow_sensor) to monitor a change if the indik ative value changes in order to infer a leak in a crankcase ventilation (16) of an internal combustion engine (10), a pressure in the crankcase (12) being varied with a switching valve (24).

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