EP3443207B1 - Method for controlling a pressure in a crankcase - Google Patents

Description

The invention relates to a method for regulating a pressure to a target pressure in a crankcase of an internal combustion engine with a crankcase ventilation device, the crankcase ventilation device being a suction line through which blow-by gas can be discharged from the crankcase, a pump device driven by an electric drive, and an oil mist separating device comprises, and wherein the pump device and the oil mist separator are arranged in the suction line. The invention further relates to an internal combustion engine with a crankcase ventilation device, such a method being carried out.

In internal combustion engines, in particular reciprocating piston internal combustion engines, a so-called blow-by gas flow occurs due to the imperfect seal between the piston and the cylinder wall. As a result, these blow-by gases enter the crankcase and must therefore be drained out of the crankcase again. It is crucial that the pressure in the crankcase remains within certain limits. Excessive pressure in the crankcase can cause oil to leak out of the crankcase through seals from the engine block. If the pressure is too low, oil can be drawn out of the crankcase by the crankcase ventilation device. Both cases are undesirable, so the pressure in the crankcase must be kept within certain limits.

The blow-by gases derived from the crankcase usually contain an oil mist, which must be separated in an oil mist separator if the oil loss through the crankcase ventilation device is to be minimized. A certain differential pressure is used for the oil mist separator needed, which is given in non-supercharged internal combustion engines by the pressure difference between the crankcase and an intake tract of the internal combustion engine behind a throttle, in which a negative pressure usually prevails. This low pressure is insufficiently available in supercharged internal combustion engines. Crankcase ventilation devices with additional pump devices are therefore known.

From the DE 10 2006 024 816 A1 Such a crankcase ventilation device with an additional pump device is known, for example. However, the performance of the pump device must be regulated so that the pressure in the crankcase does not run out of the permitted limits. Therefore, a pressure measuring device is usually provided in the crankcase. The DE20302824 U1 discloses another exemplary crankcase ventilation device with an additional pumping device.

The present invention is based on the object of providing an improved or at least another embodiment of a method for regulating a pressure to a target pressure in a crankcase, which is distinguished in particular by the fact that a pressure measuring device in the crankcase can be dispensed with.

This object is achieved according to the invention by the subject matter of the independent claims. Advantageous further developments are the subject of the dependent claims.

The invention is based on the general idea of inferring the pressure in the crankcase from parameters of the electric drive which drives the pump device. As a result, the pressure in the crankcase can be kept in a specific target range without an additional pressure measurement in the crankcase. According to the invention it is therefore provided that a speed of the electric drive is regulated and / or controlled, that the speed of the electric drive as Control variable is used for regulating the pressure in the crankcase, and that at least one performance parameter of the electric drive is evaluated in order to infer the pressure in the crankcase. The pressure in the crankcase has a strong influence on the work that the pumping device has to do, therefore the performance parameters of the electric drive can be used to draw conclusions about the pressure in the crankcase. This in turn can be used to keep the pressure in the crankcase at a target pressure or at least within a target pressure range. No pressure sensor in the crankcase is expressly required. It is not necessary to determine an absolute exact value of the pressure in the crankcase. For example, it is sufficient if the performance parameters of the electric drive identify whether the pressure in the crankcase is too high or too low.

In the description and the appended claims, a performance parameter of the electric drive is understood to mean a parameter which at least also determines the power output or received by the electric drive. In particular, such power parameters of the electric drive are a current supplied to the electric drive, preferably a time-averaged electric current, an electric voltage applied to the electric drive, preferably a time-averaged electric voltage, an electric power consumption of the electric drive, preferably a time-averaged electric power consumption, a speed of the electric drive and a torque of the electric drive.

An advantageous solution provides that a current actual value, which corresponds to a current supplied to the electric drive, is compared with a current setpoint and a speed correction value for the speed of the electric drive is determined if there is a discrepancy between the current actual value and the current setpoint. From the actual current value, which is required, to the speed of the electric drive keeping at a speed can be inferred from the pressure difference that the pump device has to overcome. If the pressure difference is small, the pump device has to do less than if the pressure difference is higher. The electrical power consumption of the electric drive also behaves accordingly. Therefore, from the comparison of the actual current value and a current setpoint, it can be recognized whether the speed of the electric drive has to be adjusted.

In the description and the appended claims, an actual current value is understood as a measured value of the current supplied to the electric drive.

Another advantageous solution provides that the current setpoint corresponds to a value for the current supplied to the electric drive, which would be required to maintain the speed of the electric drive given the speed of the electric drive and a pressure in the crankcase corresponding to the target pressure. A deviation of the actual current value from the current setpoint value can therefore be used to identify when the pressure in the crankcase does not correspond to the target pressure. In this way it can be decided that the speed of the electric drive must be adjusted in order to get the pressure in the crankcase back towards the target pressure.

A particularly advantageous solution provides that the current setpoint is determined from the characteristic curves of the electric drive and the pump device. In this way, a theoretical current setpoint can be determined, alternatively or additionally, the current setpoint can also be determined experimentally.

A favorable variant provides that a torque applied to the pump device by the electric drive is determined, that an actual speed value of the pump device, which corresponds to the speed of the pump device, it is determined that a pressure difference generated by the pump device and a volume flow flowing through the pump device are determined from the torque applied to the pump device and the actual speed value of the pump device, in particular with the aid of a characteristic curve of the pump device. The pressure difference in the crankcase can be inferred from the pressure difference generated and the volume flow delivered, so that regulation of the pressure in the crankcase is possible.

An advantageous possibility provides that the actual current value which corresponds to a current supplied to the electric drive is taken into account when determining the torque generated by the electric drive, and that if a gear is present via which the electric drive is coupled to the pump device, a gear ratio is taken into account. The actual current value is technically easy to measure, so that the actual current value can be used to easily infer the torque.

A further advantageous possibility provides that when determining the speed of the pump device, the speed of the pump device is measured on the pump device or that the speed of the electric drive is measured, wherein, if a transmission is present, via which the electric drive is coupled to the pump device , a gear ratio is taken into account. Speed measurements can be carried out in a very simple manner. The speed of the electric drive can also be read out, for example, from a control device of the electric drive.

Another particularly advantageous possibility provides that a pressure drop at the oil mist separating device is determined from the volume flow, that from the pressure drop at the oil mist separating device and that of the Pump device generated pressure difference is closed on the pressure in the crankcase. One end of the suction line is usually open to the intake tract, in which essentially the ambient pressure prevails. As a result, when all pressure differences generated in the suction line are known, the pressure in the crankcase can be inferred, so that the pressure in the crankcase can be regulated.

A favorable solution provides that a control deviation for the pressure in the crankcase is determined, and that a speed correction value for the speed of the electric drive is determined on the basis of the control deviation for the pressure in the crankcase. The speed of the electric drive determines the pumping capacity of the pump device and thus the volume flow of blow-by gas that is derived from the crankcase. As a result, the pressure in the crankcase can be influenced by varying the speed of the electric drive. The speed correction value is preferably determined using a proportional-integral, proportional-differential or proportional-integral-differential control method (PI, PD or PID).

Another inexpensive solution provides that a blow-by gas volume flow presumably generated by the internal combustion engine is determined from a rotational speed of the internal combustion engine and a torque generated by the internal combustion engine, that an estimated speed value is determined which is based on the blow generated by the internal combustion engine. by-gas volume flow is determined so that the volume flow presumably conveyed by the pump device corresponds to the blow-by gas volume flow presumably generated by the internal combustion engine. This allows rough control of the speed of the electric drive. The resulting pressure in the crankcase will be close to the desired target pressure. The regulation ultimately serves Compensate for deviations that arise due to manufacturing tolerances, aging and wear.

A particularly favorable solution provides that the estimated speed value is determined from the blow-by gas volume flow taking into account the characteristics of the pump device and the oil mist separator. The characteristic curve of the oil mist separator can be used to determine how large the pressure drop at the oil mist separator is for the given blow-by gas volume flow. If the pressure drop at the oil mist separator is known, it can be determined how large the pressure difference must be that is to be generated by the pump device. Together with the blow-by gas volume flow to be conveyed, the speed at which the pumping device would have to rotate can thus be determined. The control system compensates for deviations between the real characteristics of the pumping device and the oil mist separator from the theoretical characteristics, which arise, for example, from aging and production tolerances. Furthermore, the control system compensates for deviations in the actual volume flow in the internal combustion engine, which can result from manufacturing tolerances and aging of the internal combustion engine.

An advantageous variant provides that a control device that controls and / or regulates the speed of the electric drive is supplied with a speed setpoint that includes a speed correction value. Due to the speed correction value, the pressure control can use the speed of the electric drive to regulate the pressure in the crankcase.

Another advantageous variant provides that the speed setpoint is composed of the speed estimate and the speed correction value. Because the speed setpoint also includes the speed estimate, the previously described determination of the speed estimate allows the Regulation of the pressure can be accelerated, since the speed can be corrected by the speed estimate if the speed or the generated torque of the internal combustion engine change. As a result, the pressure in the crankcase can be regulated faster than would be possible using the regulation alone.

A favorable possibility provides that the crankcase ventilation device has a pressure control valve which is arranged in the suction line and which is recognized with the aid of a performance parameter of the electric drive when the pressure control valve switches, that the switching behavior of the pressure control valve is taken into account when determining the speed correction value. When regulating the speed, an attempt can be made to get the pressure control valve to trigger regularly. This can ensure that there is sufficient pumping capacity. Furthermore, the pressure control valve can be prevented from being closed for too long. This would waste energy unnecessarily. The switching behavior of the pressure control valve can be recognized by monitoring a performance parameter of the electric drive, since the volume flow is stopped when the pressure control valve is closed. This places a greater strain on the electric drive. As a result, the current actual value increases and an actual speed value decreases. When the pressure control valve is opened, the actual current value and actual speed value behave accordingly in opposite directions.

The invention is further based on the general idea of an internal combustion engine having a crankcase ventilation device and a control device, which is designed such that it carries out a method according to the above description. The advantages of the method described above are thus transferred to the internal combustion engine, to the above description of which reference is made in this respect.

Further important features and advantages of the invention result from the subclaims, from the drawings and from the associated description of the figures with reference to the drawings.

Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, the same reference numerals referring to the same or similar or functionally identical components.

Fig. 1

eine Prinzipskizze einer Brennkraftmaschine mit einer Kurbelgehäuseentlüftungseinrichtung,

Fig. 2

eine Prinzipskizze einer Drehzahlregelung eines Elektroantriebs,

Fig. 3

eine Prinzipskizze einer Regelung eines Druckes in einem Kurbelgehäuse der Brennkraftmaschine gemäß der ersten Ausführungsform der Erfindung,

Fig. 4

eine Prinzipskizze einer Bestimmung einer Druckdifferenz in der Kurbelgehäuseentlüftungseinrichtung anhand von Leistungsparametern des Elektroantriebs,

Fig. 5

eine Prinzipskizze einer Regelung des Druckes im Kurbelgehäuse gemäß einer zweiten Ausführungsform der Erfindung,

Fig. 6

eine Prinzipskizze einer Regelung des Druckes in dem Kurbelgehäuse gemäß einer dritten Ausführungsform der Erfindung, wobei ein Betriebspunkt der Brennkraftmaschine berücksichtigt wird,

Fig. 7

eine Prinzipskizze einer Brennkraftmaschine mit einer Kurbelgehäuseentlüftungseinrichtung gemäß einer vierten Ausführungsform der Erfindung,

Fig. 8

eine Prinzipskizze einer Steuerung der Antriebsleistung eines Elektroantriebes unter Berücksichtigung des Betriebspunktes der Brennkraftmaschine, gemäß der vierten Ausführungsform der Erfindung,

Fig. 9

eine Prinzipskizze einer Regelung eines Druckes im Kurbelgehäuse der Brennkraftmaschine gemäß einer fünften Ausführungsform der Erfindung, wobei Schaltvorgänge eines Druckregelventils berücksichtigt werden, und

Fig. 10

eine Prinzipskizze einer Regelung eines Druckes im Kurbelgehäuse der Brennkraftmaschine gemäß einer sechsten Ausführungsform der Erfindung, wobei Schaltvorgänge eines Druckregelventils und Betriebspunkte der Brennkraftmaschine berücksichtigt werden.

It shows, each schematically

Fig. 1

a schematic diagram of an internal combustion engine with a crankcase ventilation device,

Fig. 2

a schematic diagram of a speed control of an electric drive,

Fig. 3

1 shows a schematic diagram of a regulation of a pressure in a crankcase of the internal combustion engine according to the first embodiment of the invention,

Fig. 4

a schematic diagram of a determination of a pressure difference in the crankcase ventilation device on the basis of performance parameters of the electric drive,

Fig. 5

1 shows a schematic diagram of a regulation of the pressure in the crankcase according to a second embodiment of the invention,

Fig. 6

1 shows a schematic diagram of a regulation of the pressure in the crankcase according to a third embodiment of the invention, an operating point of the internal combustion engine being taken into account,

Fig. 7

1 shows a schematic diagram of an internal combustion engine with a crankcase ventilation device according to a fourth embodiment of the invention,

Fig. 8

1 shows a schematic diagram of a control of the drive power of an electric drive, taking into account the operating point of the internal combustion engine, according to the fourth embodiment of the invention,

Fig. 9

a schematic diagram of a control of a pressure in the crankcase of the internal combustion engine according to a fifth embodiment of the invention, wherein switching operations of a pressure control valve are taken into account, and

Fig. 10

a schematic diagram of a control of a pressure in the crankcase of the internal combustion engine according to a sixth embodiment of the invention, wherein switching operations of a pressure control valve and operating points of the internal combustion engine are taken into account.

One in Figure 1 The internal combustion engine 10 shown has a supercharger 12, in particular a turbocharger. Furthermore, the internal combustion engine 10 has a crankcase 14 in which blow-by gases 16 accumulate during the operation of the internal combustion engine 10. To blow-by gases 16 from the crankcase 14, the internal combustion engine 10 has a crankcase ventilation device 18.

The crankcase ventilation device 18 has a suction line 20, through which blow-by gases 16 can be discharged from the crankcase 14. Furthermore, the crankcase ventilation device 18 has a pump device 22 and an oil mist separating device 24, which is designed, for example, as an impactor. The pump device 22 and the oil mist separating device 24 are arranged in the suction line 20, so that the blow-by gases 16 discharged through the suction line 20 can be freed of oil mist and driven by the pump device 22.

A pressure 26 in the crankcase 14 of the internal combustion engine 10 should be in a certain range. Faults in the operation of internal combustion engine 10 can occur both when this range is exceeded and when it falls below. A regulation 25 of the pressure 26 to a target pressure 27, hereinafter also referred to as pressure regulation 25, is therefore provided. A first embodiment of the pressure control 25 is shown in FIGS Figures 1 to 3 shown.

The pump device 22 is preferably designed as a side channel compressor and driven by an electric drive 28. The electric drive 28 has a speed control 30, as for example in FIG Figure 2 is shown. The speed control 30 has a conventional control scheme 32, for example a proportional-integral (PI), or proportional-differential (PD) or a proportional-integral-differential (PID) control scheme 32. The speed control 30 of the electric drive 28 takes place as follows. First, an actual speed value 34 of the electric drive 28 is determined, which corresponds to the value of the speed of the electric drive 28. The actual speed value 34 is preferably measured. The actual speed value 34 is compared with a desired speed value 36, which as Input value for the speed control 30 is used. A control deviation 38 is determined from the difference between the actual speed value 34 and the desired speed value 36. A new value for a manipulated variable 40 is determined from the control deviation 38 with the aid of the control scheme 32 and is fed to a motor controller 42, which in turn controls the electric drive 28. For example, pulse width modulation, an electrical voltage or the like can be used as manipulated variables 40.

For the actual pressure control 25 of the pressure 26 in the crankcase 14, the speed setpoint 36 serves as a manipulated variable 41. The pressure control 25 according to the first embodiment takes place as follows. A current setpoint 44 is determined on the basis of the present speed setpoint 36. The current setpoint 44 corresponds to a current value that must typically be supplied to the electric drive in order to maintain the speed setpoint 36 under normal operating conditions of the internal combustion engine 10. This is based on the consideration that with a certain blow-by gas volume flow 46 that has to be discharged, a speed of rotation of the pump device 22 is sufficient to discharge this blow-by gas volume flow 46. As long as the pump device 22 must always overcome the same pressure difference when discharging the blow-by gas volume flow 46, the current required to drive the pump device 22, that is to say the actual current value 48, should be constant. If the desired target pressure 27 is present in the crankcase 14, the current setpoint 44 should be set. If the pressure 26 in the crankcase 14 deviates from the target pressure 27, the current actual value 48 should also differ from the current setpoint 44.

The current setpoint 44 can be determined either from theoretical characteristic curves 45 of the electric drive 28, the pump device 22 and the oil mist separating device 24. As an alternative or in addition to this, the relationship between the speed setpoint 36 and the current setpoint 44 can also be determined experimentally.

For the pressure control 25 of the pressure 26, the current actual value 48 is now compared with the current setpoint 44 and thus a control deviation 50 is determined. From the control deviation 50, a speed correction value 52 is determined 53, which is added to the speed setpoint 36 in order to determine a new speed setpoint 36, which is fed to the speed control 30 of the electric drive 28. As a result, the control loop is closed and pressure control 25 is achieved.

One in the Figures 4 and 5 The illustrated second embodiment of the method for pressure control 25 differs from that in FIGS Fig. 1-3 First embodiment of the method for pressure control 25 shown, in that a pressure difference 51, which extends over the crankcase ventilation device 18, is estimated on the basis of performance parameters of the electric drive 28, in order to infer the pressure 26 in the crankcase 14 and thus to determine a control deviation 64.

For example in Figure 4 Determination of the pressure difference 51 shown, which is applied to the crankcase ventilation device 18, the current actual value 48 and the speed actual value 34 of the electric drive 28 are first evaluated. A torque 54 generated by the electric drive 28 can be determined from the current actual value 48. Together with the actual speed value 34 of the electric drive 28, from which the speed of the pump device 22 can be deduced, a pressure difference 56 generated by the pump device 22 can be determined with the aid of a characteristic curve 47 of the pump device 22.

From the pressure difference 56 generated by the pump device 22 and the actual speed value 34 of the electric drive 28 and thus the speed of the pump device 22, a volume flow 58 conveyed by the pump device 22 can be estimated.

From the volume flow 58 conveyed by the pump device 22, it can be concluded with the aid of characteristic curves 60 of the oil mist separating device 24 that the pressure drop 62 drops at the oil mist separating device 24.

From the pressure difference 56 generated by the pump device 22 and the pressure drop 62 applied to the oil mist separating device 24, the pressure difference 51 applied via the crankcase ventilation device 18 can be concluded. Since the suction line 20 usually opens into a region of an intake tract of the internal combustion engine 10 in which ambient pressure prevails, the pressure 26 in the crankcase 14 can be inferred thereby. Thus, a determination 49 of the pressure 26 in the crankcase 14 is carried out with the help of performance parameters of the electric drive 28.

At the in Figure 5 The pressure control 25 shown is determined to determine the control deviation 64, the determination 49 of the pressure 26 from the performance parameters of the electric drive 28 by comparison with the desired target pressure 27. Alternatively, instead of specifying a target pressure 27, a target pressure difference 66 can also be specified, which is determined from the target pressure 27 and compared with the pressure difference 51 applied to the crankcase ventilation device 18, which was determined by the determination 49.

A correction value for the manipulated variable 41, namely a speed correction value 52, from which a new speed setpoint 36 is derived, is determined from the control deviation 64 with the aid of a conventional control scheme 68, which works, for example, according to a proportional-integral, proportional-differential or proportional-integral-differential method it is determined which of the speed control 30 of the electric drive 28 is supplied. The change in the speed setpoint 36 finally also changes the speed actual value 34, as a result of which the volume flow 58 conveyed by the pump device 22 is adjusted, so that the pressure 26 in the crankcase 14 should change, in particular should approach the target pressure 27. This controlled system 70 thus results in a new pressure 26 in the crankcase 14.

Incidentally, that is correct in the Figures 4 and 5 illustrated second embodiment of the method for pressure control 25 with the in the Figures 1-3 illustrated first embodiment of the method for pressure control 25 in terms of structure and function, to the above description of which reference is made.

One in Figure 6 The third embodiment of the method for pressure control 25 shown differs from that in FIGS Figures 4 and 5 illustrated second embodiment of the method for pressure control 25 in that a determination 72 of a speed estimate 74 is made in order to accelerate the pressure control 25. A determination 80 of a typical blow-by gas volume flow 46 can be made from a speed 76 of the internal combustion engine 10 and a torque 78 from the internal combustion engine 10. From the blow-by gas volume flow 46, with the aid of the characteristic curves 47 of the pump device 22 of the oil mist separating device 24 and the electric drive 28, the speed estimate 74 which would be necessary to promote the blow-by gas volume flow 46 can be determined. The speed estimate 74 is fed to the speed control 30 of the electric drive 28. As a result, the speed control 30 can react very quickly to expected changes in the blow-by gas volume flow 46, so that the fluctuations in the blow-by gas 16 caused by a change in load of the internal combustion engine 10 occur and the associated pressure fluctuations in the crankcase 14 can be reduced.

However, since the speed estimate 74 is only based on theoretical considerations, it can deviate from the blow-by gas volume flow 46 that actually occurs. An additional regulation of the pressure 26 in the crankcase 14 is therefore necessary. The speed correction value 52 is determined analogously to the pressure control 25 as described in the second embodiment.

The speed setpoint 36 supplied to the speed control 30 is thus composed of a sum of the speed estimated value 74 and the speed correction value 52.

Incidentally, the in Figure 6 illustrated third embodiment of the method for pressure control 25 with the in the Figures 4 and 5 illustrated second embodiment of the method for pressure control 25 in terms of structure and function, to the above description of which reference is made.

One in the Figures 7 and 8th The fourth embodiment of the method for pressure control 25 shown differs from that in FIGS Figures 1 to 3 illustrated first embodiment of the method for pressure control 25 in that a pressure control valve 82 is used for pressure control 25 of the pressure 26, which is arranged in the suction line 20 between the crankcase 14 and the pump device 22. In addition, a rotational speed estimate 74 is determined analogously to the third embodiment from the operating point of the internal combustion engine 10, in particular from the rotational speed 76 of the internal combustion engine 10 and the torque 78 generated by the internal combustion engine 10. This Speed estimate 74 is increased with an offset in order to be able to intercept deviations from the expected blow-by gas volume flow 46. If the blow-by gas volume flow 46 is too small, the pressure 26 in the crankcase 14 drops, so that the pressure control valve 82 closes and thus temporarily interrupts the suction process of blow-by gas 16 from the crankcase 14. This can effectively prevent the pressure 26 in the crankcase 14 from becoming too low.

Exceeding a permissible pressure 26 in the crankcase 14 is prevented by adding the offset to the speed estimate 74.

Incidentally, the in Figure 7 and 8th Fourth embodiment of the method for pressure control 25 shown with the in the Figures 1-3 illustrated first embodiment of the method for pressure control 25 in terms of structure and function, to the above description of which reference is made.

One in Figure 9 Fifth embodiment of the method for pressure control 25 shown differs from that in FIGS Figures 7 and 8th Fourth embodiment of the method for pressure control 25 shown in that an algorithm 86 for detecting switching operations 84 of the pressure control valve 82 is used in the pressure control 25.

When the pressure control valve 82 opens or closes, the pressure conditions on the inlet side on the pump device 22 change. This also changes the load on the pump device 22, so that the power required to drive the pump device 22 changes. This is also reflected in the performance parameters of the electric drive 28.

For example, when the pressure control valve 82 closes, the volume flow stops and the pressure difference that the pump device 22 has to overcome increases, so that the load increases. This would reduce the actual speed value 34 of the electric drive 28 if no speed control 30 is provided. If a speed control 30 is provided, the actual current value 48 thereby increases. When the pressure control valve 82 is opened, the effects are opposite, so that the opening of the pressure control valve 82 can also be recognized.

The pressure 26 in the crankcase 14 is preferably controlled in such a way that the speed of the electric drive 28 is used as the manipulated variable 41 by supplying a speed setpoint 36 to the speed control 30 of the electric drive 28. The desired speed setpoint 36 is determined on the basis that the pressure control valve 82 opens and closes regularly. This can ensure that the pressure 26 in the crankcase 14 does not increase too much. Furthermore, this can ensure that the power of the electric drive 28 is not too high and therefore no unnecessary energy is wasted.

The speed setpoint 36 is preferably adjusted such that the pressure control valve 82 opens and / or closes at least once every 10 seconds, preferably at least once every 5 seconds, particularly preferably at least once per second.

In addition, when determining the speed setpoint 36, care is taken to ensure that a ratio between opening times and closing times of the pressure control valve 82 is greater than 50%, particularly preferably greater than 80%, the pressure control valve 82 being permanently open at a ratio of 100%. However, it should be noted that there should still be closing times. Therefore, the relationship between opening hours and closing times of the Pressure control valve 82 may be less than 100%. This can ensure that the pressure 26 in the crankcase 14 does not exceed the permissible value.

Incidentally, the in Figure 9 Fifth embodiment of the method for pressure control 25 shown in FIG Figures 7 and 8th Fourth embodiment of the method for pressure control 25 shown illustrated in terms of structure and function, to the above description of which reference is made.

One in Figure 10 The sixth embodiment of the method for pressure control 25 shown differs from that in FIG Figure 9 fifth embodiment of the method for pressure control 25 shown in that the speed setpoint 36 is composed of a speed estimate 74 and a speed correction value 52. The speed estimate 74 is determined as in embodiments three and four. The speed correction value 52 is determined with the aid of the algorithm 86 for the detection of switching operations 84 of the pressure control valve 82.

Incidentally, the in Figure 10 shown sixth embodiment of the method for pressure control 25 with the in Figure 9 shown fifth embodiment of the method for pressure control 25 in terms of structure and function, to the above description of which reference is made.

Claims (11)

1. Method for controlling a pressure (26) to a target pressure (27) in a crankcase (14) of an internal combustion engine (10) with a crankcase venting device (18), wherein the crankcase venting device (18) comprises a suction line (20), by means of which blow-by gas (16) can be removed from the crankcase (14), a pumping device (22) driven by an electric drive (28) and an oil mist separating device (24), and wherein the pumping device (22) and the oil mist separating device (24) are arranged in the suction line (20),
   characterized in that

   - a rotational speed of the electric drive (28) is controlled in a closed-loop and/or open-loop manner,

   - the rotational speed of the electric drive (28) is used as a manipulated variable (41) for the control (25) of the pressure (26) in the crankcase (14), and

   - that at least one performance parameter of the electric drive (28) is evaluated in order to infer the pressure (26) in the crankcase (14).
2. Method according to Claim 1, characterized in that an actual current value (48) corresponding to a current supplied to the electric drive (28) is compared with a current setpoint (44) and a rotational speed correction value (52) is determined for the rotational speed of the electric drive (28) is determined when there is a deviation between the actual current value (48) and the current setpoint (44).
3. Method according to Claim 2, characterized in that the current setpoint (44) corresponds to a value for the current supplied to the electric drive (28), which would be necessary in order to maintain the rotational speed of the electric drive (28) at a given rotational speed of the electric drive (28) and a pressure (26) in the crankcase (14) that corresponds to the target pressure (27).
4. Method according to Claim 1, characterized in that

   - a torque (54) generated by the electric drive (28) and acting on the pumping device (22) is determined,

   - an actual rotational speed value (34) of the pumping device (22), which corresponds to the rotational speed of the pumping device (22) is determined,

   - a pressure differential (56) generated by the pumping device (22) and a volume flow (58) flowing through the pumping device (22) are determined from the torque (54) acting on the pumping device (22) and the actual rotational speed value (34) of the pumping device (22), particularly with the aid of a characteristic curve (47) of the pumping device (22).
5. Method according to Claim 1, characterized in that

   - a drop in pressure (62) at the oil mist separating device (24) is determined from the volume flow (58),

   - the pressure (26) in the crankcase (14) is inferred from the drop in pressure (62) at the oil mist separating device (24) and from the pressure differential (56) generated by the pumping device (22).
6. Method according to Claim 4 or 5, characterized in that a control deviation (64) is determined for the pressure (26) in the crankcase (14), a rotational speed correction value (52) for the rotational speed of the electric drive (28) is determined on the basis of the control deviation (64) for the pressure (26) in the crankcase (14).
7. Method according to any one of Claims 4 to 6, characterized in that

   - a notional Blow-by- gas volume flow (46) generated by the internal combustion engine (10) is determined from a rotational speed (76) of the internal combustion engine (10) and a torque (78) generated by the internal combustion engine (10),

   - an estimated rotational speed value (74) is determined, which is determined on the basis of the notional blow-by gas volume flow (46) generated by the combustion engine (10), so that the notional volume flow (58) displaced by the pumping device (22) matches the notional blow-by gas volume flow (46) generated by the combustion engine (10).
8. Method according to any one of Claims 1 to 7, characterized in that a rotational speed setpoint (36) comprising a rotational speed correction value (52) is supplied to a control device which controls the rotational speed of the electric drive (28) in open-loop and/or closed-loop manner.
9. Method according to Claims 7 and 8, characterized in that the rotational speed setpoint (36) is compiled from the estimated rotational speed value (74) and the rotational speed correction value (52).
10. Method according to Claims 8 or 9, characterized in that

    - the crankcase venting device (18) includes a pressure control valve (82) which is arranged in the suction line (20),

    - a performance parameter of the electric drive (28) is used to detect when the pressure control valve (82) switches,

    - the switching behaviour (84) of the pressure control valve (82) is taken into account in a determination of the rotational speed correction value (52).
11. Internal combustion engine with a crankcase venting device (18) and a control device which is constructed in such manner that it carries out a method according to any one of Claims 1 to 10.

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