Abstract:
The invention relates to a device ( 1 ), for the ventilation of the crankcase ( 20 ) of an internal combustion engine ( 2 ), with a breather tube ( 3 ), running from the crankcase ( 20 ) to an inlet manifold ( 22 ) on the internal combustion engine ( 2 ), in the course of which an oil-mist separator ( 30 ) is arranged. The novel device is characterized in that in the course of the breather line ( 3 ), a pump device is arranged, by means of which a reduced pressure may be generated in the crankcase ( 20 ) relative to ambient pressure.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an apparatus for ventilating the crankcase of a combustion engine, comprising a vent line running from the crankcase to an intake pipe of the combustion engine and an oil-mist separator that is arranged in the course of the vent line. 
   An apparatus of the said type is known from the practice of engine construction, in particular for automobiles. This apparatus aims at maintaining in the crankcase of the combustion engine a vacuum pressure that is required for technical and legal reasons by ventilating the crankcase; to achieve this, gases or, in particular, blow-by gases are conducted out of the crankcase or the combustion chambers of the combustion engine to the intake pipe of the engine. Any oil contents carried in the crankcase ventilation gas are separated in an oil-mist separator; preferably, the separated oil is supplied to the lubricating oil circuit of the combustion engine again. The gas that has been freed from the oil enters the intake pipe of the combustion engine and is then running through the combustion that takes place in the engine. 
   Known apparatuses of the said type have various operational drawbacks that are, in particular, incurred in certain operating states. A drawback of spark-ignition engines is that the drop in pressure above the oil-mist separator is relatively high and causes the danger of an excess pressure developing in the crankcase if the difference between the vacuum pressure in the intake pipe and the atmospheric pressure is inadequate. Moreover, this results in a reduced efficiency of the oil-mist separator because in spark-ignition engines, use is normally made of separators that are operated by the principle of inertia and require a high efficiency to ensure an adequately high volume flow. Another drawback is incurred whenever the combustion engine is in its no-load range because, in this state, the pressure developing in the crankcase may become too high. This problem is, in particular, arising in case of advanced combustion engine wear because this may lead to high blow-by volume flows at high speed and no-load. 
   For that reason, the present invention aims at creating an apparatus of the aforementioned type, which obviates the drawbacks disclosed and which, in particular, permits to maintain a vacuum pressure in the crankcase of the combustion engine in any and all possible operating states of the combustion engine, with the vacuum pressure being negative in comparison with the atmospheric pressure, and, at the same time, to ensure a high efficiency of the oil-mist separator. 
   SUMMARY OF THE INVENTION 
   This problem is solved by the invention by an apparatus of the aforementioned type, characterized in that a pump unit permitting the generation of vacuum pressure in the crankcase as compared with the atmospheric pressure is provided in the course of the vent line. 
   In case of the apparatus according to the invention, the pump unit ensures, to its advantage, that there is always a desired vacuum pressure in the crankcase of the combustion engine, with this vacuum pressure being maintained even in such operating states of the combustion engine that do not permit generation of the appropriate vacuum pressure only via the intake pipe. At the same time, the pump unit ensures an adequately high volume flow at the crankcase ventilation gas through the oil-mist separator, so that the latter has a high efficiency in any operating state of the combustion engine. 
   In addition, the invention preferably provides that the pump unit is arranged between the oil-mist separator and the point where the vent line ends in the intake pipe. This arrangement of the pump unit ensures that the oil mist is already separated before the gases are flowing through the pump unit, so that the pump unit cannot be contaminated by any oil mist nor be impaired in its function. 
   Furthermore, the pump unit is, preferably, a suction pump or an injector. Either pump unit ensures that the desired effects, that is to say the generation of vacuum pressure in the crankcase and the delivery of the crankcase ventilation gases to the intake pipe, are achieved in a reliable manner. 
   Moreover, the invention proposes that the pump unit is non-power-controlled and that either a pressure regulating valve is arranged in the vent line upstream of the oil-mist separator or a bypass line with controllable opening is conducted out of the vent line downstream of the pump unit and to the crankcase. The technical requirements for this apparatus that comprises a pump unit whose power is not controlled are relatively low so that it can be manufactured at low cost. Since the pump unit itself is not controlled with regard to its power, a different method must be used to ensure that the vacuum pressure developing in the crankcase will not become too high. This is achieved by the optionally provided pressure regulating valve or by the bypass line with controllable opening. Actually, a pressure regulating valve of known design may be used here, because it must only fulfill the requirement of closing the vent line once a specified lower pressure limit has been reached, as is the case with pertinent apparatuses that do not comprise any pump unit. 
   To realize the aforementioned controllable opening of the bypass line, a regulating valve that is adjustable according to the pressure in the crankcase is, preferably, arranged in this bypass line. This regulating valve can be used to limit the vacuum pressure in the crankcase both upwards and downwards, thus ensuring that a specified range of vacuum pressure is maintained in the crankcase. 
   To optimize the ventilation of the crankcase and the separation of the oil mist from the crankcase ventilation gas, it is proposed that the regulating valve can, in addition, be adjusted according to the crankshaft speed of the combustion engine and according to the position of a throttle valve, if any is provided in the intake pipe. 
   Where spark-ignition engines are concerned, a long motor life can only be achieved if any fuel that might have entered the lubricating oil in the oil pan as condensate is quickly and completely discharged therefrom, in order to prevent sludge formation and, thus, any resulting damage to the engine. For such a combustion engine that comprises a throttle valve arranged in the intake pipe, the invention proposes an embodiment of the apparatus where a vent line with check valve is coming out of the intake pipe upstream of the throttle valve and is running into the crankcase. Through this vent line, fresh air can be passed into the crankcase, from where it can be removed together with the other crankcase ventilation gases, after having taken up fuel vapors. 
   In a further embodiment, the invention proposes that the vent line ends in the intake pipe upstream of the throttle valve and that a branch line comprising a regulating valve in its course branches off from the vent line at a point between the oil-mist separator and the pump unit, with this branch line ending in the intake pipe downstream of the throttle valve. This branch line can be used to ventilate the crankcase as long as there is an adequate vacuum pressure in the intake pipe. The pump unit must only be used for ventilation in those operating states where the vacuum pressure in the intake pipe is inadequate for ventilation of the crankcase. 
   Appropriately, the regulating valve arranged in the branch line can be adjusted according to the pressure in the crankcase, so as to keep the vacuum pressure in the crankcase within specifiable limits. 
   To optimize the ventilation of the crankcase and the separation of oil mist from the ventilation gas, the regulating valve arranged in the branch line can, in addition, be adjustable according to the crankshaft speed of the combustion engine and according to the position of the throttle valve. 
   In certain operating states of a combustion engine, in particular in the idle state of the combustion engine, it is not favorable to supply the crankcase with fresh air because, then, the supplied fresh air might cause unmetered air to be supplied around the throttle valve, thus impairing the idle quality of the combustion engine. To solve this problem, the invention proposes that, in addition to the check valve, a remote-controllable shut-off valve be arranged in the vent line, either separately or in combination with the check valve. 
   Appropriately, this shut-off valve in the vent line can be adjusted according to the crankshaft speed of the combustion engine; particularly, it can be set to the closed position at idle speed. In the idle state of the combustion engine, this excludes any supply of fresh air through the vent line, past the closed throttle valve and into the intake pipe, thus preventing the idle quality from being impaired. 
   As an alternative to using a non-power-controlled pump unit, a further embodiment of the apparatus proposes that the power of the pump unit can be controlled according to the pressure in the crankcase. Here, it is appropriate to achieve the control in such a manner that the power of the pump unit is just generating the vacuum pressure desired in the crankcase, wherein the pump power required is dependent on the current operating state and, thus, the respective associated amount of crankcase gases. 
   In addition, it can be provided that, at a point downstream of the pump unit, a return line is conducted from the vent line to the crankcase, that is to say via a branching valve that can be switched over according to the position of the throttle valve or according to the intake pipe pressure upstream of the throttle valve. Through this return line, crankcase ventilation gas can be returned into the crankcase, unless the intake pipe is able to take up the gas supplied by the pump unit. In this manner, crankcase ventilation gas is reliably prevented from entering the environment through the intake pipe and the air filter in opposition to the flow direction provided. 
   A further embodiment of the apparatus proposes that the suction pump that forms the pump unit is a radial-flow blower or a side-channel blower with a mechanical drive derived from the combustion engine or with an electric motor as drive. Owing to the fact that the pump power required is only low, the suction pump of the said embodiment may be very compact, thus requiring only little free space. If the suction pump concerned is designed with a mechanical drive derived from the combustion engine, it is appropriate that the suction pump can be driven with a speed whose ratio to the particular crankshaft speed is fixed. In this case, the vacuum pressure in the crankcase is appropriately controlled via the corresponding regulating valves, as has been described above. If the suction pump is provided with an electric motor as drive, control of the vacuum pressure is less restricted. 
   If the apparatus is provided with an electric motor for driving the suction pump, an electric switch or a voltage regulator is preferably connected in series with the electric motor, with this switch or regulator being adjustable according to the crankcase pressure. This ensures that the suction pump and the electric motor driving it are running only if the pump power is really required, thus reducing the load on the suction pump and the drive motor. 
   In embodiments of the apparatus with an injector as pump unit, it is provided that the injector can be driven by compressed air from the outlet side of a turbocharger arranged in the course of the intake pipe and forming a part of the combustion engine that is equipped with the apparatus or by compressed air from a compressed air system of a motor vehicle that is equipped with the apparatus. The injector as pump unit has the particular advantage that it does not comprise any moving parts, thus having a practically unlimited service life and being absolutely maintenance-free. Since compressed air is required for operation of the injector, the use of an injector as pump unit is particularly reasonable in apparatuses that are used on combustion engines or in motor vehicles where compressed air is anyhow available, for example by virtue of the aforementioned turbocharger or the compressed air system that is always provided in commercial vehicles. 
   To ensure that the power of the injector can be controlled as required, it is preferably provided that a regulating valve is incorporated in the compressed air supply line running to the injector, with this regulating valve being adjustable according to the crankcase pressure. The regulating valve will then ensure that the pump power generated by the injector always maintains a vacuum pressure in the crankcase that remains within a specifiable range. 
   As an alternative to controlling the effective power of the pump unit, a bypass duct can be connected to a regulating valve together with the vent line, with this bypass duct short-circuiting the pump unit and this regulating valve being adjustable according to the crankcase pressure. This ensures that closed-circuit delivery of the ventilation gas through the pump unit and the associated bypass duct can be achieved if required, whereby the effective power of the pump unit can be controlled as desired with regard to the crankcase ventilation gas delivered from the crankcase into the intake pipe. The wider open the regulating valve, the lower the effective power of the pump unit, and vice versa. 
   To ensure operation of the apparatus with as few own electric and electronic components as possible, the invention finally and preferably proposes that the adjustable and switchable components of the apparatus, that are particularly its valves, can be actuated and monitored by the existing motor electrics associated with the combustion engine. Modern combustion engines are, in general, provided with motor electronics for controlling and regulating operation of the combustion engine, which can also be used for the apparatus according to the invention by expanding its programming and its inputs and outputs to a minor degree only. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Exemplary forms of the invention will be described below by means of a drawing, wherein: 
       FIG. 1  is a schematic view of an apparatus for ventilation and simultaneous aeration of the crankcase of a combustion engine, preferably an internal combustion engine, in a first embodiment; 
       FIG. 2  is the same view of the apparatus in a second embodiment; 
       FIG. 3  is also the same view of the apparatus in a third embodiment; 
       FIG. 4  is a schematic view of an apparatus for ventilating the crankcase of a combustion engine, preferably a Diesel engine, in a first embodiment; 
       FIG. 5  is the same view of the apparatus according to  FIG. 4  in a second embodiment; 
       FIG. 6  is the same view of the apparatus according to  FIG. 4  in a third embodiment; and 
       FIG. 7  is also the same view of the apparatus according to  FIG. 4  in a fourth embodiment. 
   

   At its extreme left,  FIG. 1  of the drawing shows an air filter  23 , from where an intake pipe  22  is running to the combustion engine  2 , which is indicated to the right of  FIG. 1 . A throttle valve  24  is arranged in the course of the intake pipe  22 . 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A crankcase ventilation line  3  is running from the crankcase  20 , that forms a part of the combustion engine  2 , to the intake pipe  22 , and is ending in the latter upstream of the throttle valve. (Here and below, “upstream” and “downstream” refer to the particular flow direction, as usual.) Initially, an oil-mist separator  30  is arranged in the course of the vent line  3 , as viewed in flow direction of the crankcase ventilation gases. The oil-mist separator  30  is preferably provided as a separator that is operated by the principle of inertia, for example a cyclone. Any oil contents that have been separated from the ventilation gas in the separator  30  can be returned to the oil pan in the crankcase  20  via a line that is not shown here. The gases that have been freed from any oil mist are further delivered through the vent line  3  and to a pump unit  31 , here a suction pump drivable by an electric motor  32 , whose outlet is connected to the intake pipe  22  upstream of the throttle valve  24 . In the embodiment shown here, the pump unit  31  has a permanent drive, that is to say its pump power is constant. In order to be able to adjust the volume of the crankcase ventilation gas delivered to the intake pipe  22  as required, a bypass line  37  is, in addition, connected to the outlet of the pump unit  31 , with the bypass line  37  being returned to the crankcase  20 . The bypass line  37  is provided with an adjustable opening that can, here, be adjusted by means of a regulating valve  37 ′. 
   Here, the regulating valve  37 ′, which is arranged in the bypass line  37 , is adjusted via a regulator  35 , which is, appropriately, a part of the existing motor electrics or electronics of the associated combustion engine  2 , wherein the motor electrics or electronics receive control signals via corresponding sensors, such as, via the pressure sensor  34 , the pressure p inside the crankcase  20 , the crankshaft speed n of the combustion engine and the position a of the throttle valve  24 . Using these measured values and according to a specifiable characteristic map or program, the regulator  35  calculates control signals for the regulating valve  37 ′ that is arranged in the bypass line and adjusts the flow area of the regulating valve  37 ′ according to the particular operating states of the combustion engine  2  such that the vacuum pressure in the crankcase  20  remains within specifiable limit values. 
   A vent line  4 , that branches off from the intake pipe  22  upstream of the throttle valve  24  and ends in the crankcase  20 , is provided for ventilation of the crankcase  20 . A check valve  40 , that permits a flow direction only from the intake pipe  22  to the crankcase  20 , is arranged in the course of the vent line  4 . 
   During operation of this apparatus  1 , the regulating valve  37 ′ in the bypass line  37  is adjusted such that a vacuum pressure of a specified value is always maintained in the crankcase  20 . In this embodiment, the apparatus  1  has the advantage that its design is relatively simple; on the other hand, the pump unit  31 , owing to its permanent operation, is subject to increased wear so that a construction with a correspondingly long life must be selected in this case. To ensure proper functioning of this apparatus  1 , it is irrelevant whether a throttle valve  24  is arranged in the intake pipe  22  or not; hence, this embodiment of the apparatus  1  is suitable for all internal combustion engines with or without throttle valve  24 . This apparatus  1  is even suitable for supercharged engines. In addition to maintaining the desired vacuum pressure in the crankcase  20 , the pump unit  31  ensures that the volume flow through the oil-mist separator  30  is always sufficiently high, so that the latter permanently achieves its optimum efficiency. 
   In case of this apparatus  1 , any supply of unmetered air to the combustion chambers  21  of the combustion engine  2  around the throttle valve  24  is excluded, thus preventing any disturbances in the idle state. 
   The embodiment of the apparatus  1  illustrated in  FIG. 2  of the drawing is different from the apparatus  1  according to  FIG. 1  in that: 
   The bypass line  37  running from the pump  31  to the crankcase  20  in the first embodiment of the apparatus  1  is not applicable; instead, a branch line  38  branches off from the vent line  3  to the pump unit  31  at a point upstream of the oil-mist separator  30  and, via a regulating valve  38 ′, ends in the intake pipe  22  at a point downstream of the throttle valve  24 . A further difference is that, in this case, the check valve  40  in the vent line  4  is combined with a remote-controllable shut-off valve  41 . 
   In its remaining parts, the apparatus according to  FIG. 2  is identical with the embodiment shown in  FIG. 1 . 
   The regulating valve  38 ′ in the branch line  38  running from the outlet of the oil-mist separator  30  to the intake pipe  22  downstream of the throttle valve  24  is adjusted by the regulator  35  according to the pressure p in the crankcase, the crankshaft speed n and the throttle valve position α. Herein, the position of the valve  38 ′ is adjusted such that the valve  38 ′ is in the open position when the vacuum pressure in the intake pipe  22  is adequate. In this case, the crankcase is, in substance, ventilated via the vacuum pressure present in the intake pipe  22 . If the vacuum pressure in the intake pipe  22  is not sufficient for maintaining an adequate vacuum pressure in the crankcase  20 , the regulating valve  38 ′ is closed and the vacuum pressure in the crankcase  20  is adjusted via the pump unit  31 . 
   Moreover, the shut-off valve  41  in the vent line  4  is closed when the combustion engine  2  is in the idle state so that, in this operating state of the combustion engine  2 , unmetered air is prevented from passing the throttle valve  24 . In this embodiment of the apparatus  1  as well, the vacuum pressure required in the crankcase  20  is maintained in all operating states of the combustion engine  2 . At the same time, first-rate oil separation is ensured in the oil-mist separator  30  because the volume flow in the latter is always adequate. Furthermore, smooth idle run of the combustion engine  2  is ensured, without any disturbances caused by unmetered air. 
     FIG. 3  of the drawing shows a third embodiment of the apparatus  1 , differing from the embodiment according to  FIG. 2  in two additional elements. These additional elements are, on the one hand, a branching valve  39 ′ that is incorporated downstream of the pump unit  31  in that section of the vent line  3  that is running to the intake pipe  22 . A return line  39  is running from the branch outlet of the branching valve  39 ′ to the crankcase  20 . 
   The second additional element is the fact that, in this embodiment, the pump unit  31  is power-controlled. To achieve this, the regulator  35  is likewise designed as an electric switch or voltage regulator that is adjusted according to the pressure p in the crankcase, the crankshaft speed n and the throttle valve position α. The regulator  35  acts upon the performance of the engine in a controlling manner, thus regulating the power of the pump unit  31 . 
   In its basic operating state, the apparatus  1  according to  FIG. 3  is operated in the same ways as is the apparatus  1  according to  FIG. 2 . Additionally, in the apparatus  1  according to  FIG. 3  the outlet of the pump unit  31  can, instead of being connected to the intake pipe  22  upstream of the throttle valve  24 , alternatively be connected via the branching valve  39 ′ and the return line  39  to the crankcase. This provides the possibility that, if the volume of crankcase ventilation gas delivered by the pump unit  31  cannot be taken up by the intake pipe  22  upstream of the throttle valve  24 , the crankcase ventilation gas is delivered in recirculation between the crankcase  20  and the pump unit  31 . This case can be determined by measuring the pressure in the intake pipe  22  or by evaluating the parameters that are anyhow registered, such as the throttle valve position α, the pressure p in the crankcase and the crankshaft speed n. In this manner, the crankcase ventilation gas is prevented from entering the environment through the air filter  23 , in opposition to the flow direction provided in the intake pipe  22 . Since operating states of the combustion engine  2  where this working method of the apparatus  1  is incurred are only rare, this additional operating mode does not cause any noticeable additional load. 
   By readjusting the power of the pump unit  31 , the vacuum pressure in the crankcase  20  can be set to the appropriate value. As long as the vacuum pressure present in the intake pipe  22  is adequate, it is even possible to turn off the pump unit  31 . 
     FIG. 4  of the drawing shows an apparatus  1  for ventilating the crankcase  20  of a combustion engine  2 , wherein this apparatus  1  is, to its advantage, combined with a combustion engine  2  that is designed as a Diesel engine. Here as well, the combustion engine  2  is provided with an intake pipe  22 , in the course of which an air filter  23  is arranged. A throttle valve, as it is provided in the embodiment shown in  FIGS. 1 to 2 , is not provided here. Furthermore, a turbocharger  26  may be provided in the course of the intake pipe  22 ; this, however, is not essential for the apparatus  1  according to  FIG. 4  to function properly. Here as well, a vent line  3  that is running from the crankcase  20  to the intake pipe  22  downstream of the air filter  23  is provided for ventilation of the crankcase  20  of the combustion engine  2 . As usual, an oil-mist separator  30  is incorporated in the course of the vent line  3  here as well. A pump unit  31  that is, in this case, formed by a suction pump and can be driven via an electric motor  32  is provided downstream of the oil-mist separator  30 , as viewed in flow direction. Here, the motor  32  is designed without power control, so that the pump unit  31  is always operated with a constant driving power. In order to exclude that the permanently operated pump unit  31  causes a vacuum pressure in the crankcase  20  that is too high, a normal pressure regulating valve  30 ′ is incorporated in the course of the vent line  3 , between the crankcase  20  and the oil-mist separator  30 . This pressure regulating valve  30 ′ is operated in the known manner, that is to say such that the flow area of the vent line  3  is reduced or completely closed once the pressure in the crankcase  20  reaches a lower limit value. Only if the pressure in the crankcase  20  is rising again will the pressure regulating valve  30 ′ open the ventilation duct  3  so that, then, the crankcase ventilation gas is discharged again. The pump power of the pump unit  31  must be rated such that discharge of the crankcase ventilation gas is ensured without the risk that an excess pressure might be developing, even if the crankcase ventilation incurred is at its maximum and the intake vacuum is at its minimum. Since it does not require any active regulating elements whatsoever, the apparatus  1  according to  FIG. 4  is characterized by a particularly simple design. The drive motor  32  of the pump unit  31  is operated with constant power and is supplied from the electric supply system of the combustion engine or of the associated motor vehicle, as soon as the combustion engine  2  is in the operating state. As an alternative, it is also possible to simply derive the drive from the combustion engine in a mechanical manner. The pressure regulating valve  30 ′ is also operated absolutely automatically and in particular without any external regulators or energy sources, so that, here as well, a simple technical solution and a simple mode of operation have been achieved. 
     FIG. 5  of the drawing shows a variation of the apparatus  1  according to  FIG. 4  that is different from the apparatus  1  according to  FIG. 4 , in that the power of the pump unit  31  can be altered. This alteration of the power of the pump unit  31  can be achieved in two different ways. The first way, which is represented by solid lines in  FIG. 5 , provides a pressure sensor  34  that registers the pressure p in the crankcase  20  of the combustion engine  2  in comparison with the environment and supplies a signal corresponding to the pressure p to a regulator  35 . The regulator  35  is an electric switch or voltage regulator whose output is connected to the drive motor  32  and either activates or deactivates the latter or, by changing the supply voltage, takes an effect on the performance of the motor. As a result, the pump power of the pump unit  31  is changed accordingly and is controlled as required, so that the pressure p in the crankcase  20  remains within the limits specified. 
   The alternative possibility of taking effect on the pump power of the pump unit  31  is represented by broken lines and provides a bypass line  36  that is connected to the vent line  3 , with the bypass line  36  bypassing the pump unit  31 . A regulating valve  36 ′ is incorporated in the course of the bypass line that is now supplied with control signals from the regulator  35  instead of the drive motor  32 . If the regulating valve  36 ′ is open, the pump unit  31  is short-circuited, so that gas is practically only delivered in recirculation through the pump unit  31  and the bypass line  36 , whereby the effective pump power of the pump unit  31  is reduced to a minimum with regard to the crankcase ventilation gas delivered from the crankcase  20  into the intake pipe  22 . The more the regulating valve  36 ′ is closed, the larger the effective pump power of the pump unit  31  with regard to the delivery of crankcase ventilation gas from the crankcase  20  into the intake pipe  22 . 
   Here as well, the oil-mist separator  30  is arranged upstream of the pump unit  31 , in order to keep oil mist that might be detrimental to the function of the pump unit  31  away from the latter. Finally, it is also possible in the apparatus  1  according to  FIG. 5  to provide an optional turbocharger  25  in the intake pipe  22 , with the turbocharger  25  neither having any effect on the function of the apparatus  1 . 
     FIG. 6  of the drawing shows an embodiment of the apparatus  1  that is provided with an injector as pump unit  31  instead of a suction pump. The injector  31  is incorporated in the vent line  3  at the same point where the suction pump is arranged as pump unit  31  in the apparatus  1  according to  FIGS. 4 and 5 . The compressed air required for operation of the injector  31  is supplied to the injector  31  through a compressed air line  33 . This compressed air line  33  branches off from the intake pipe  22  on the outlet side of the turbocharger  25  that is provided obligatorily in this case. Since the injector  31  has to generate only a relatively low pump power, only a very small portion of the charge air compressed by the turbocharger  25  is diverted through the compressed air line  33  for operation of the injector  31 ; in practice, this portion amounts to approximately a quarter of a percent of the entire charge air volume. 
   In its remaining parts, the apparatus  1  according to  FIG. 6  is identical with the apparatus according to  FIG. 4 ; as regards the function of the apparatus  1  according to  FIG. 6 , reference is made to the corresponding passages in the description of  FIG. 4 . 
   As a final point,  FIG. 7  of the drawing shows an embodiment of the apparatus  1  that is, in substance, identical with the apparatus  1  according to  FIG. 5 , and is different in that an injector is provided as pump unit  31  instead of the suction pump in the apparatus  1  according to  FIG. 7 . In analogy to the apparatus  1  according to  FIG. 5 , the pump power of the injector  31  in the apparatus  1  according to  FIG. 7  is also controllable. Here as well, there are two preferred ways of control. The first way that is represented by solid lines provides that the volume of the compressed air supplied to the injector  31  through the compressed air line  33  is controlled by a regulating valve  33 ′ incorporated in the line  33 , according to the pressure p present in the crankcase  20 . To achieve this, the pressure p in the crankcase  20  is registered by a pressure sensor  34  and transmitted to the regulator  35  as measurement signal, with the regulator  35  adjusting the regulating valve  33 ′ as required. As a result, the compressed air volume supplied to the injector  31  is always such that the pump effect generated by the injector  31  ensures a vacuum pressure p in the crankcase  20  ranging within specifiable limits. Here as well, the compressed air required for generation of the pump effect of the injector  31  is taken from the intake pipe  22  downstream of the turbocharger  25 . 
   As an alternative, the compressed air required for operation of the injector  31  can also be taken from a compressed air system, that is part of a motor vehicle not shown in the drawings, in particular of a commercial vehicle, provided with a combustion engine  2  and an apparatus  1 . 
   The alternative possibility of taking effect on the pump power of the injector  31  that is represented by broken lines provides that the crankcase gas is enabled to flow through the bypass line  36  via the regulating valve  36 ′, whereby the injector  31  is short-circuited either as a whole or in part. The regulator  35  then acts upon the regulating valve  36 ′ in the bypass line  36 ; the regulating valve  33 ′ in the compressed air line  33  is not required any longer. In its mode of operation, the apparatus  1  according to  FIG. 7  is, otherwise, identical with the apparatus  1  according to  FIG. 5 ; reference is made to the corresponding passages in the description of  FIG. 5 . 
   As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.