Method and device for inspecting the functionality of a crankcase ventilation system of an internal combustion engine

Abstract

The disclosure relates to a method and a device for checking the functionality of a crankcase ventilation system of an internal combustion engine. The crankcase ventilation system includes two crankcase ventilation lines arranged between a crankcase outlet of a crankcase and an associated introduction point into an air path of the internal combustion engine, via which crankcase ventilation lines gas can be introduced from the crankcase into the air path. The method includes measuring a pressure in the crankcase, supplying the measured pressure values to a control unit, and calculating the gradient of the measured pressure. The method also includes performing a gradient check, checking whether the gradient satisfies a specified criterion, and returning to the measurement of the pressure if the gradient satisfies the specified criterion. The method also includes recording an entry in a fault memory if the gradient does not satisfy the specified criterion.

Claims

1. A method for checking functionality of a crankcase ventilation system of an internal combustion engine, the method comprising: measuring a crankcase pressure in a crankcase of the internal combustion engine by a crankcase pressure sensor positioned in the crankcase, the crankcase having an outlet in fluid communication with two crankcase ventilation lines and a pressure control valve in fluid communication with the two crankcase ventilation lines of the crankcase ventilation system, the two crankcase ventilation lines and the pressure control valve are arranged between a crankcase outlet and an associated introduction point into an air path of the internal combustion engine, via which crankcase ventilation lines gas may be introduced from the crankcase into the air path, supplying the measured pressure values to a control unit, detecting a change in an operating point of the internal combustion engine, wherein the change of the operating point includes a negative load change or a positive load change, calculating a gradient with respect to time of the measured crankcase pressure based on the change in the operating point, performing a gradient check of the calculated gradient, checking whether the gradient satisfies a specified criterion to determine whether a leak is present in the two crankcase ventilation lines, wherein the specified criterion depends on whether a positive or a negative load change was detected, returning to the measurement of the crankcase pressure when the gradient satisfies the specified criterion, recording an entry in a fault memory when the gradient does not satisfy the specified criterion, and if the presence of a leak is determined, determining which of the two crankcase ventilation lines is defective by evaluating the gradient during the detected positive or negative load change.

2. The method as claimed in claim 1, wherein the change in the operating point includes a starting or stopping of the internal combustion engine.

3. The method as claimed in claim 2, further comprising: ascertaining and using admissible limit values for the gradient when the change in the operating point is the starting or stopping of the internal combustion engine.

4. The method as claimed in claim 2, further comprising: ascertaining and using a threshold value for the gradient when the change in the operating point change is the negative or positive load change.

5. A device for checking functionality of a crankcase ventilation system of an internal combustion engine, the crankcase ventilation system comprising: a crankcase having a crankcase outlet, two crankcase ventilation lines arranged between the crankcase outlet and an associated introduction point into an air path of the internal combustion engine, the crankcase outlet in fluid communication with the two crankcase ventilation lines of the crankcase ventilation system, the two crankcase ventilation lines introduce gas from the crankcase into the air path, and a pressure control valve in fluid communication with the two crankcase ventilation lines in a location downstream from the crankcase outlet and upstream from each associated introduction point, a control unit configured to: measure a pressure in the crankcase by a crankcase pressure sensor positioned in the crankcase, supply the measured pressure values to a control unit, detect a change in an operating point of the internal combustion engine, wherein the change of the operating point includes a negative load change or a positive load change, calculate a gradient with respect to time of the measured crankcase pressure, perform a gradient check of the calculated gradient, check whether the gradient satisfies a specified criterion to determine whether a leak is present in the two crankcase ventilation lines, wherein the specified criterion depends on whether a positive or a negative load change was detected, return to the measurement of the crankcase pressure when the gradient satisfies the specified criterion, recording an entry in a fault memory when the gradient does not satisfy the specified criterion, and if the presence of a leak is determined, determining which of the two crankcase ventilation lines is defective by evaluating the gradient during the detected positive or negative load change.

6. The device as claimed in claim 5, wherein the change of the operating point includes a starting or stopping of the internal combustion engine.

7. The device as claimed in claim 6, wherein the control unit is further configured to: ascertain and use admissible limit values for the gradient when the change in the operating point is the starting or stopping of the internal combustion engine.

8. The device as claimed in claim 6, wherein the control unit is further configured to: ascertain and use a threshold value for the gradient when the change in operating point is the negative or positive load change.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a schematic sketch for illustrating a device for checking the functionality of a crankcase ventilation system of an internal combustion engine.

(2) FIG. 2 shows sketches for explaining a first example of the disclosure.

(3) FIG. 3 shows diagrams for illustrating measurement results.

(4) FIG. 4 shows sketches for explaining a second example of the disclosure.

(5) FIG. 5 shows sketches for explaining a third example of the disclosure.

(6) FIG. 6 shows sketches for explaining a fourth example of the disclosure.

(7) FIG. 7 shows sketches for explaining a fifth example of the disclosure.

(8) FIG. 8 shows sketches for explaining a sixth example of the disclosure.

(9) FIG. 9 shows diagrams for illustrating measurement results.

(10) FIG. 10 shows a flow diagram for a first exemplary method for checking the functionality of a crankcase ventilation system of an internal combustion engine.

(11) FIG. 11 shows a flow diagram for explaining a second exemplary method for checking the functionality of a crankcase ventilation system of an internal combustion engine.

(12) Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

(13) FIG. 1 shows a schematic sketch for illustrating a device for checking the functionality of a crankcase ventilation system 2 of an internal combustion engine 1.

(14) The illustrated internal combustion engine 1 includes a crankcase 3 from which gases are discharged via a crankcase outlet 4. Gases are introduced via crankcase ventilation lines 7 and 20 into an air path 6 of the internal combustion engine 1 at introduction points 5 and 30 respectively. As shown, an oil separator 13 and a pressure control valve 14 are arranged in these crankcase ventilation lines 7, 20 between the crankcase outlet 4 and the introduction points 5 and 30 respectively. Downstream of the pressure control valve 14, the crankcase ventilation line 7 separates from the crankcase ventilation line 20. The crankcase ventilation line 7 opens into the air path 6 via a suction jet pump 8 at the introduction point 5 upstream of a compressor 17. The motive mass flow is provided here from the high-pressure side of the compressor 17 and fed to the suction jet pump 8 via a motive jet line 25. The crankcase ventilation line 20 opens into the air path 6 downstream of a throttle flap 19 at the introduction point 30.

(15) In naturally aspirated operation of the internal combustion engine 1, the throttle flap 19 is closed and the gas pressure within the air path 6 downstream of the throttle flap 19 is lower than the ambient air pressure. Consequently, gas discharged from the crankcase 3 is introduced via the oil separator 13, the pressure control valve 14 and the crankcase ventilation line 20 into the air path 6 downstream of the throttle flap 19.

(16) In supercharged operation of the internal combustion engine 1, the throttle flap 19 is opened, such that fresh air fed to the air path 6 via a fresh-air inlet 15 is fed via an air filter 16, the compressor 17, a charge-air cooler 18 and the opened throttle flap 19 to the combustion chamber, arranged within the crankcase 3, of the internal combustion engine 1. In this supercharged operation of the internal combustion engine 1, the air pressure in the air path 6 in the region downstream of the throttle flap 19 is higher than the ambient air pressure. Consequently, gas discharged from the crankcase 3 is introduced via the oil separator 13 and the pressure control valve 14 into the air path 6 not downstream of the throttle flap 19 but at the introduction point 5. This introduction point 5 is positioned in the air path 6 downstream of the air filter 16 but upstream of the compressor 17, the charge-air cooler 18 and the throttle flap 19.

(17) The device illustrated in FIG. 1 furthermore has a crankcase pressure sensor 26 which is arranged in the crankcase 3 and by way of which the pressure prevailing in the crankcase 3 is measured. Furthermore, an ambient pressure sensor 9 is arranged in the region of the fresh-air inlet 15 of the air path 6, a first intake pipe pressure sensor 29, which is not imperatively necessary for the method presented, is arranged between the air filter 16 and the compressor 17, and a second intake pipe pressure sensor 28 is arranged between the throttle flap 19 and the crankcase 3.

(18) The output signals provided by the pressure sensors 26, 9, 29 and 28 are supplied as sensor signals s1, s2, s3 and s4 to a control unit 10 and evaluated therein in order to perform a check of the functionality of the crankcase ventilation system 2 of the internal combustion engine 1, as will be discussed in more detail below.

(19) It can also be seen from FIG. 1 that the illustrated device has a fresh-air line 21 which branches off from the air path 6 and which is connected via a check valve 22 to a fresh-air inlet of the crankcase 3. This fresh air is used to improve the air flow through the crankcase 3.

(20) Also illustrated in FIG. 1 is a turbine 24 which, together with the compressor 17, is a constituent part of an exhaust-gas turbocharger of the internal combustion engine 1. Hot exhaust gas from the internal combustion engine is fed to the turbine 24 and sets the turbine wheel of the turbine in rotation. The turbine wheel is connected via a shaft of the exhaust-gas turbocharger to a compressor wheel, which is likewise fixedly connected to the shaft, of the compressor 17, such that the compressor wheel is also set in rotational motion and the fresh air fed to the compressor 17 is compressed. This compressed fresh air is fed to the combustion chambers of the internal combustion engine 1 in order to increase the performance thereof.

(21) The oil separator 13 is provided for separating off oil that is contained in the gases discharged via the crankcase outlet 4, and for returning the oil to the crankcase 3.

(22) Furthermore, as shown in FIG. 1, an additional channel bypassing the oil separator 13 via a safety valve 12 is provided between the crankcase outlet 4 and the pressure control valve 14. In the event of a blockage of the oil separator 13, the gas discharged via the crankcase outlet 4 is conducted via this additional channel into the crankcase ventilation line 7 downstream of the oil separator.

(23) Furthermore, the device illustrated in FIG. 1 has an oil cap 27 that closes off the crankcase 3.

(24) It is furthermore illustrated in FIG. 1 that the control unit 10 interacts with memories 11 and 23. The memory 11 is a memory in which the working programs of the control unit are stored. The memory 23 is a data memory in which data are stored which the control unit 10 requires inter alia for checking the functionality of the crankcase ventilation system. These data include for example specified, empirically ascertained data, data stored in one or more characteristic maps, or data corresponding to a pressure model. The control unit 10 evaluates sensor signals s1-sx supplied to it, which sensor signals include the sensor signals S1, S2, S3, S4 provided by the pressure sensors, using data stored in the memory 23 in order to provide control signals stl-sty for various components of the internal combustion engine and inter alia to check the functionality of the crankcase ventilation system 2 of the internal combustion engine 1 and to identify whether or not the crankcase ventilation system is functional.

(25) The device illustrated in FIG. 1 accordingly shows a crankcase ventilation system of a supercharged internal combustion engine, in the case of which two crankcase ventilation lines lead from the crankcase outlet into the air path of the internal combustion engine, which crankcase ventilation lines conduct gases from the crankcase into the air path. Here, the crankcase ventilation line 20 is connected to the air path 6 downstream of a throttle flap 27 which controls the air mass flow, and the crankcase ventilation line is active during throttled operation, in which the pressure prevailing between the throttle flap 19 and the inlet of the crankcase 3 is lower than the ambient pressure. By contrast, the crankcase ventilation line 7 is active, and conducts gas discharged from the crankcase 3 back into the air path 6 of the internal combustion engine via the introduction point 5, in supercharged operation of the internal combustion engine, in which the pressure prevailing between the throttle flap 19 and the inlet of the crankcase 3 is higher than the ambient pressure. In order to ensure that effective ventilation of the crankcase can take place even during supercharged operation of the internal combustion engine, the suction jet pump 8 described above, to which the crankcase ventilation line 7 is connected, is used. For an intact crankcase ventilation system, the use of this suction jet pump 8 results in a significant negative pressure in the crankcase in relation to the ambient pressure, even in supercharged operation. This makes the identification of a malfunction considerably easier.

(26) If use is not made of a suction jet pump, then the ventilation of the crankcase can however also be promoted through evaluation of the slight negative pressure that prevails downstream of the air filter 16.

(27) Below, with reference to the further figures, examples of the disclosure will be explained in the case of which, for various dynamic changes in the operating point, qualitative pressure profiles for the pressure prevailing in the crankcase and the pressure prevailing in the air path between the throttle flap 19 and the inlet of the crankcase are illustrated in each case for an intact system (OK) and a faulty system. In all of these cases, the gradient of the pressure prevailing in the crankcase 3 is used as a diagnostic criterion.

(28) FIG. 2 shows sketches for explaining a first example of the disclosure. In this example, a leak has occurred at the point denoted by the letter F in the crankcase ventilation line 7.

(29) A leak in the ventilation line 7 leads to an impairment of the crankcase ventilation, because the pressure in the crankcase ventilation line is significantly higher in this case than in the intact state of the crankcase ventilation system. Consequently, the pressure P_kgh measured by the crankcase pressure sensor 26 during supercharged operation, in which the pressure P_im prevailing between the throttle flap 19 and the inlet of the crankcase 3 is higher than the ambient pressure P_amb, is also higher and, depending on the magnitude of the leak, may also be almost ambient pressure, as illustrated in the lower right-hand diagram of FIG. 2.

(30) If the driver of the vehicle powered by the internal combustion engine actuates the accelerator pedal to a lesser degree or takes their foot off the accelerator pedal entirely, then the intake pipe pressure P_im is abruptly reduced and the internal combustion engine switches to throttled operation, in which the following relationship applies:
P_im<P_amb

(31) During this negative load change, a change from crankcase ventilation line 7 to crankcase ventilation line 20 also occurs. If the crankcase ventilation line 20 is intact, then the regular crankcase pressure is set again by the pressure control valve 14. However, since, in the event of a fault, ventilation is performed from a considerably higher pressure P_kgh in the air path 6 or the intake pipe, the pressure gradient of P_kgh has large negative values. From this, it can be inferred that the crankcase ventilation line 7 is defective, because otherwise effective ventilation would have to have taken place during supercharged operation.

(32) A leak or blockage within the motive jet line 25 results in a loss of crankcase ventilation performance 7. Therefore, for such a fault, the same statements as those for a defective crankcase ventilation line 7 are applicable.

(33) As a proof of concept for leak identification in the crankcase ventilation line 7, FIG. 3 shows diagrams for illustrating measurement results. The curves denoted by K1 and shown with dashed lines each represent an intact crankcase ventilation system, and the curves denoted by K2 each represent a faulty crankcase ventilation system. Here, the fault situation was simulated by unplugging the crankcase ventilation line 7. Here, the measured value P_kgh_rel represents the relative pressure in relation to the ambient pressure. The respective gradients P_kgh_grd show the behavior described above with reference to FIG. 2. On the basis of a simple comparison of the gradient with a threshold value, the leak present in the crankcase ventilation line 7 can be identified and a corresponding entry can be recorded in a fault memory of the control unit 10.

(34) FIG. 4 shows sketches for explaining a second example of the disclosure. In this example, a leak has again occurred at the point denoted by the letter F in the crankcase ventilation line 7.

(35) In the event of a leak in the crankcase ventilation line 7, the crankcase pressure P_kgh behaves in a correspondingly reversed manner in the presence of a positive load change. Consequently, the pressure gradient is positive over a longer period of time in the case of a positive load change than in the presence of an intact crankcase ventilation system. This is evident from a comparison of the two lower diagrams of FIG. 4, where the lower left-hand diagram shows the profile of the crankcase pressure P_kgh over time in the presence of an intact crankcase ventilation system, and the lower right-hand diagram shows the profile of the crankcase pressure P_kgh in the presence of a leak in the crankcase ventilation line 7.

(36) A leak or blockage within the motive jet line 25 results in a loss of crankcase ventilation performance 7. Therefore, for such a fault, too, the same statements as those for a defective crankcase ventilation line 7 are applicable.

(37) FIG. 5 shows sketches for explaining a third example of the disclosure. In this example, a leak has occurred at the point denoted by the letter F, where, by contrast to the examples shown in FIGS. 2 and 4, this point lies in the crankcase ventilation line 20.

(38) If the crankcase ventilation line 20 has a leak, this may be detected through an evaluation of the gradient of the crankcase pressure P_kgh during a negative load change. In this case, the crankcase pressure rises over a longer period of time to approximately ambient pressure. This is evident from a comparison of the two lower diagrams of FIG. 5, where the lower left-hand diagram shows the profile of the crankcase pressure P_kgh over time in the presence of an intact crankcase ventilation system, and the lower right-hand diagram shows the profile of the crankcase pressure P_kgh in the presence of a leak in the crankcase ventilation line 20.

(39) FIG. 6 shows sketches for explaining a fourth example of the disclosure. If the gradient of the crankcase pressure P_kgh has excessively low negative values during starting-up of the engine, this indicates either that a leak is present in the ventilation line 20 or that the oil cap 27 is not closed. These two error cases are illustrated in the upper illustration of FIG. 6 by the letter F and can also be seen from the two lower diagrams of FIG. 6. The lower left-hand diagram of FIG. 6 shows the profile of the crankcase pressure P_kgh in the case of an intact system, and the lower right-hand diagram of FIG. 6 shows the profile of the crankcase pressure P_kgh in the presence of a leak in the crankcase ventilation line 20 or in the absence of an oil cap 27.

(40) A quantitative evaluation of the gradient of the crankcase pressure P_kgh allows conclusions to be drawn regarding the magnitude of the leak and the actual location of the fault.

(41) In the case of an internal combustion engine with start/stop function, starting-up of the engine occurs frequently, such that frequent checking of the crankcase ventilation line 20 can also be ensured. Consequently, it can also be checked just as frequently whether or not the oil cap 27 is sealingly closing the crankcase 3.

(42) FIG. 7 shows sketches for explaining a fifth example of the disclosure. If the gradient of the crankcase pressure P_kgh has excessively low positive values during stopping of the engine, this indicates either that a leak is present in the ventilation line 20 or that the oil cap 27 is not sealingly closed. These two error cases are illustrated in the upper illustration of FIG. 7 by the letter F and can also be seen from the two lower diagrams of FIG. 7. The lower left-hand diagram of FIG. 7 shows the profile of the crankcase pressure P_kgh in the case of an intact system, and the lower right-hand diagram of FIG. 7 shows the profile of the crankcase pressure P_kgh in the presence of a leak in the crankcase ventilation line 20 or in the absence of an oil cap 27.

(43) A quantitative evaluation of the gradient of the crankcase pressure P_kgh allows conclusions to be drawn regarding the magnitude of the leak and the actual location of the fault.

(44) In the case of an internal combustion engine with start/stop function, stopping of the engine occurs frequently, such that frequent checking of the crankcase ventilation line 20 can also be ensured. Consequently, it can also be checked just as frequently whether or not the oil cap 27 is closed.

(45) FIG. 8 shows sketches for explaining a sixth example of the disclosure. In this case, a blocked ventilation line 21 is present, as indicated in the upper illustration of FIG. by the letter F. In this case, the gradient of the crankcase pressure P_kgh during starting of the engine is considered. The crankcase volume is evacuated in a shorter time if the ventilation line 21 is blocked than in the presence of an intact ventilation line 21, because in this case no replenishing flow or only a lesser replenishing flow of fresh air is possible. This leads to a higher negative gradient of the crankcase pressure P_kgh during the starting-up of the engine over a long period of time. This is evident from a comparison of the two lower diagrams of FIG. 8. The profile of the crankcase pressure P_kgh in the case of an intact system is illustrated in the lower left-hand diagram of FIG. 8. The profile of the gradient of the crankcase pressure P_kgh in the presence of a blocked ventilation line 21 is illustrated in the lower right-hand diagram of FIG. 8.

(46) FIG. 9 shows diagrams for illustrating measurement results that were obtained on a real vehicle in which the above-described fault was present. In this figure, the curves denoted by K1 and shown with dashed lines each represent an intact ventilation line 21, and the curves denoted by K2 each represent a faulty ventilation line 21.

(47) FIG. 10 shows a flow diagram for explaining a method for checking the functionality of a crankcase ventilation system of an internal combustion engine according to a first example for the disclosure.

(48) This method begins with a step S1. This is followed, in a step S2, by a measurement of the crankcase pressure P_kgh by the crankcase pressure sensor 26, a transmission of the measured pressure value to the control unit 10, and a calculation of the gradient of the crankcase pressure by the control unit 10. In a subsequent step S3, a gradient check is performed in the control unit 10.

(49) For the purposes of this gradient check, a detection of a change in the operating point is performed in a step S7. In a subsequent step S8, it is checked whether starting of the engine or stopping of the engine has been performed. If starting of the engine or stopping of the engine is identified, then a transition is made to a step S9, in which limit values for the gradient of the crankcase pressure P_kgh are ascertained. These limit values are used in step S3 for the abovementioned gradient check.

(50) In a subsequent step S4, it is queried whether or not the ascertained gradient lies within the ascertained limit values. If the ascertained gradient lies within these limit values, then a return to step S2 is performed. If the ascertained gradient does not lie within the ascertained limit values, then a transition is made to step S5. In this step S5, an entry is recorded in a fault memory. Subsequently, a transition is made to a step S6, with which the method is ended.

(51) If, by contrast, the query in step S8 yields that neither starting of the engine nor stopping of the engine is present, then a transition is made to a step S10. In this step S10, a check is performed as to whether a positive or a negative step change in load is present.

(52) If this is not the case, then a return to step S7 is performed. If, by contrast, it is identified in step S10 that a positive or a negative step change in load is present, then a transition is made to a step S11. In this step S11, an ascertainment of a threshold value for the gradient of the crankcase pressure P_kgh measured by the crankcase sensor 26 is performed. This threshold value is used in step S3 for the abovementioned gradient check.

(53) In a subsequent step S4, it is queried whether or not the ascertained gradient exceeds the ascertained threshold value. If the ascertained gradient does not exceed the abovementioned threshold value, then a return to step S2 is performed. If, by contrast, the ascertained gradient exceeds the abovementioned threshold value, then a transition is made to step S5. In this step S5, an entry is recorded in a fault memory. Subsequently, a transition is made to a step S6, with which the method is ended.

(54) FIG. 11 shows a flow diagram for explaining a method for checking the functionality of a crankcase ventilation system of an internal combustion engine according to a second exemplary example for the disclosure.

(55) In this second exemplary example, the method likewise begins with a step S1. This is followed, in a step S2, by a measurement of the crankcase pressure P_kgh by the crankcase pressure sensor 26, a transmission of the measured pressure value to the control unit 10, and a calculation of the gradient of the crankcase pressure by the control unit 10. In a subsequent step S3, a gradient check is performed in the control unit 10.

(56) For the purposes of this gradient check, by contrast to the method shown in FIG. 10, an ascertainment of a model pressure P_kgh_mdl is performed in a step S12. This ascertained model pressure is used in step S3 for the gradient check. For the purposes of the gradient check, a gradient with respect to time is also formed from this model pressure. By way of a now continuous comparison of the modeled and measured pressure, the method may be performed taking into consideration any tolerances.

(57) In a subsequent step S4, it is queried whether the ascertained gradients of the sensor and model have similar profiles. If the ascertained gradient of the measured value accordingly lies within a range around the model gradient, then a return to step S2 is performed. If the ascertained gradient does not lie within the ascertained range, then a transition is made to step S5. In this step S5, an entry is recorded in a fault memory. Subsequently, a transition is made to a step S6, with which the method is ended. Aside from the continuous performance of this gradient comparison, the method may be performed in accordance with the approach above, that is to say only upon certain changes in operating point. Here, the gradient of the model pressure is used as a reference value in steps S9 and S11 in FIG. 10.

(58) Overall, the diagnostic concept described above is based on the use of a pressure sensor which is positioned such that it can measure the pressure within the crankcase. To identify a leak in the crankcase ventilation system, an evaluation of the gradient with respect to time of the measured crankcase pressure is performed during various changes in the engine operating point. An implementation of this diagnostic concept is substantially independent of the engine configuration and the ventilation concept, because, instead of absolute pressure values, an evaluation of the pressure gradient is performed in order to identify leaks in the crankcase ventilation system. Furthermore, the entire crankcase ventilation system may be diagnosed through the use of a single, suitably positioned pressure sensor.

(59) An evaluation of the gradient of the crankcase pressure during different dynamic changes in the operating point, for example in the case of negative load changes, positive load changes, starting of the engine or stopping of the engine, furthermore allows reliable identification of the possible fault locations/states of the crankcase ventilation system. For example, it is possible to diagnose which of the crankcase ventilation lines has a defect and whether an oil cap is missing. Active control of other engine components in order to bring about a certain operating state is also eliminated with this method.

(60) An additional advantage that results from the use of a crankcase pressure sensor consists in the possibility of using the measured pressure value within a physical model for the crankcase ventilation arrangement. The mass flow that flows from the crankcase into the air path or the intake pipe can thus be modeled much more precisely. This is beneficial for a preliminary determination of the cylinder gas composition, which ultimately has a positive influence on the emissions of the engine, for example during highly transient engine operation.

(61) Overall, in the above-described diagnosis of a crankcase ventilation system, the crankcase pressure is measured by a crankcase sensor. An ascertainment of the gradient with respect to time of the measured crankcase pressure is subsequently performed. Furthermore, an identification of a change in the operating point is performed. Suitable variables for the ascertainment and identification of a change in the operating point are, for example, the air path pressure and its gradient, the engine rotational speed, the ambient pressure and the throttle flap position. Depending on the identified change in the operating point, limit values for the crankcase pressure gradient are subsequently determined and used for a gradient check. A faulty system can be diagnosed by a comparison of the limit values with the ascertained gradient of the measured crankcase pressure after the identification of a change in the operating point. Based on the evaluation during individual changes in the operating point, which can be easily distinguished from one another, authoritative information regarding a respectively identified fault can be stored in the fault memory of the engine control unit of the respective vehicle, which allows fast and targeted exchange of defective components in a workshop.

(62) A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

LIST OF REFERENCE SIGNS

(63) 1 Internal combustion engine 2 Crankcase ventilation system 3 Crankcase 4 Crankcase outlet 5 Introduction point 6 Air path 7 Crankcase ventilation line 8 Suction jet pump 9 Ambient pressure sensor 10 Control unit 11 Memory 12 Safety valve 13 Oil separator 14 Pressure control valve 15 Fresh-air inlet 16 Air filter 17 Compressor 18 Charge-air cooler 19 Throttle flap 20 Crankcase ventilation line 21 Fresh-air line 22 Check valve 23 Memory 24 Turbine 25 Motive jet line 26 Crankcase pressure sensor 27 Oil cap 28 Intake pipe pressure sensor 29 Intake pipe pressure sensor 30 Introduction point