Patent Publication Number: US-8991365-B2

Title: Blowby gas returning apparatus for engine with supercharger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2011-082051, filed on Apr. 1, 2011, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a blowby gas returning apparatus for engine with supercharger, the apparatus being provided in an engine including a supercharger or turbocharger in an intake passage and arranged to return blowby gas generated in the engine to the engine through the intake passage. 
     BACKGROUND ART 
     This type of technique is conventionally known as disclosed for example in Patent documents 1 to 4 listed below. In particular, in an engine provided with a supercharger in an intake passage, a blowby gas returning apparatus disclosed in Patent document 1 includes a fresh-air introduction passage to introduce fresh air from the intake passage into a head cover, a first blowby gas returning passage to return the blowby gas accumulated in a crank case to the engine during operation of the supercharger, and a second blowby gas returning apparatus to return the blowby gas accumulated in the head cover to the engine during non-operation of the supercharger. An inlet of the first blowby gas returning passage and an inlet of the second blowby gas returning passage are connected individually to blowby-gas accumulation parts (the crank case, the head cover). 
     In the apparatus disclosed in Patent document 1, since the inlet of the first blowby gas returning passage and the inlet of the second blowby gas returning passage are connected to the different accumulation parts (the crank case, the head cover) placed apart from each other, any problem with backflow of gas between the inlets does not occur. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     JP 2009-299645 A 
     JP 2004-60475 A 
     JP 2008-95528 A 
     JP 2008-184935 A 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     Meanwhile, in the case where the inlet of the first blowby gas returning passage and the inlet of the second blowby gas returning passage are disposed adjacent to each other in a common accumulation part (e.g., the head cover), the apparatus in Patent document 1 may cause the following problems. Specifically, during operation of the engine but non-operation of the supercharger, a negative pressure generated in the intake passage acts on the head cover through the second blowby gas returning passage, and further the negative pressure acts on the inlet of the first blowby gas returning passage. Accordingly, the negative pressure may cause air to flow back from the first blowby gas returning passage to the head cover, and such back-flowing air may directly flow in the intake passage through the second blowby gas returning passage. Consequently, there is a possibility that the blowby gas in the head cover could not flow in the intake passage through the second blowby gas returning passage nor return to the engine. 
     The present invention has been made in view of the above circumstances and has a purpose to provide a blowby gas returning apparatus for engine with supercharger, the apparatus being configured such that an inlet of a first blowby gas returning passage to be used during operation of the supercharger and an inlet of a second blowby gas returning passage to be used during non-operation of the supercharger are placed adjacent to each other in a common accumulation part, so that blowby gas is effectively returned to the engine during operation of the engine and irrespective of whether during operation or non-operation of the supercharger. 
     Means of Solving the Problems 
     To achieve the above object, one aspect of the invention provides a blowby gas returning apparatus for engine with supercharger, provided in an engine including a supercharger in an intake passage and a throttle valve in the intake passage downstream of the supercharger, to allow blowby gas generated in the engine to flow to the intake passage to return to the engine, the blowby gas returning apparatus comprising: a bypass passage that connects an upstream side and a downstream side of the supercharger in the intake passage; an ejector for generating a negative pressure in the bypass passage; a first blowby gas returning passage for allowing the blowby gas to flow to the intake passage during operation of the supercharger, the first blowby gas returning passage including an outlet connected to the bypass passage through the ejector; and a second blowby gas returning passage for allowing the blowby gas to flow to the intake passage during non-operation of the supercharger, the second blowby gas returning passage including an outlet connected to the intake passage downstream of the throttle valve, wherein an inlet of the first blowby gas returning passage and an inlet of the second blowby gas returning passage are placed adjacent to each other in a common accumulation part for accumulating the blowby gas, and the blowby gas returning apparatus further includes a backflow preventing unit placed in the first blowby gas returning passage to prevent a flow of air in a direction opposite to a direction of allowing the blowby gas to flow. 
     Further, another aspect of the invention provides a blowby gas returning apparatus for engine with supercharger, provided in an engine including a supercharger in an intake passage and a throttle valve in the intake passage downstream of the supercharger, to allow blowby gas generated in the engine to flow to the intake passage to return to the engine, the blowby gas returning apparatus comprising: a bypass passage that connects an upstream side and a downstream side of the supercharger in the intake passage; an ejector for generating a negative pressure in the bypass passage; a first blowby gas returning passage for allowing the blowby gas to flow to the intake passage during operation of the supercharger, the first blowby gas returning passage including an outlet connected to the bypass passage through the ejector; and a second blowby gas returning passage for allowing the blowby gas to flow to the intake passage during non-operation of the supercharger, the second blowby gas returning passage including an outlet connected to the intake passage downstream of the throttle valve, wherein an inlet of the first blowby gas returning passage and an inlet of the second blowby gas returning passage are placed adjacent to each other in a common accumulation part for accumulating the blowby gas, and the blowby gas returning apparatus further includes an isolating unit for separating the inlet of the first blowby gas returning passage and the inlet of the second blowby gas returning passage from each other. 
     Effects of Invention 
     According to the invention configured such that an inlet of a first blowby gas returning passage to be used during operation of a supercharger and an inlet of a second blowby gas returning passage to be used during non-operation of the supercharger are placed adjacent to each other in a common accumulation part, so that a blowby gas is effectively returned to an engine during operation of the engine and irrespective of whether during operation or non-operation of the supercharger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration view showing an engine system including a blowby gas returning apparatus for engine with supercharger in a first embodiment; 
         FIG. 2  is a cross-sectional view showing a schematic configuration of an ejector in the first embodiment; 
         FIG. 3  is a perspective view of a head cover in the first embodiment; 
         FIG. 4  is a schematic perspective diagram of the head cover in the first embodiment; 
         FIG. 5  is a schematic diagram showing a separator section in the head cover in the first embodiment; 
         FIG. 6  is a schematic configuration view showing an engine system including a blowby gas returning apparatus for engine with supercharger in a second embodiment; 
         FIG. 7  is a flowchart showing details of a control program to be executed by an ECU in the second embodiment; 
         FIG. 8  is a schematic configuration view showing an engine system including a blowby gas returning apparatus for engine with supercharger in a third embodiment; 
         FIG. 9  is a schematic diagram showing two separator sections in a head cover in the third embodiment; 
         FIG. 10  is a schematic configuration view showing an engine system including a blowby gas returning apparatus for engine with supercharger in a fourth embodiment; and 
         FIG. 11  is a schematic diagram showing an engine system including a blowby gas returning apparatus for engine with supercharger in a fifth embodiment. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     &lt;First Embodiment&gt; 
     A detailed description of a first preferred embodiment of a blowby gas returning apparatus for engine with supercharger embodying the present invention will now be given referring to the accompanying drawings. 
       FIG. 1  is a schematic configuration view showing an engine system including a blowby gas returning apparatus for engine with supercharger in the present embodiment. This engine system includes a reciprocal engine  1 . This engine  1  includes an intake port  2  connected to an intake passage  3  and an exhaust port  4  connected to an exhaust passage  5 . In an inlet of the intake passage  3 , an air cleaner  6  is provided. A supercharger  7  is placed in a position downstream of the air cleaner  6  in the intake passage  3  and between the intake passage  3  and the exhaust passage  5  to increase the pressure of intake air in the intake passage  3 . 
     The supercharger  7  includes a compressor  8  placed in the intake passage  3 , a turbine  9  placed in the exhaust passage  5 , and a rotary shaft  10  that connects the compressor  8  and the turbine  9  so that they are rotatable together. The supercharger  7  is configured to rotate the turbine  9  with exhaust gas flowing in the exhaust passage  5  and integrally rotate the compressor  8  through the rotary shaft  10  in order to increase the pressure of intake air in the intake passage  3 , that is, perform supercharging. 
     In the exhaust passage  5 , adjacent to the supercharger  7 , an exhaust bypass passage  11  is provided to detour the turbine  9 . This bypass passage  11  is internally provided with a wastegate valve  12 . This valve  12  is controlled by a diaphragm actuator  13  to adjust an opening degree. When the exhaust gas flowing in the exhaust bypass passage  11  is regulated by the wastegate valve  12 , adjusting the flow rate of exhaust gas to be supplied to the turbine  9 , thereby adjusting the rotational speeds of the turbine  9  and the compressor  8  to control the charging pressure by the supercharger  7 . 
     In the intake passage  3 , an intercooler  14  is placed between the compressor  8  of the supercharger  7  and the engine  1 . This intercooler  14  is to cool the air whose pressure has been increased by the compressor  8  to an appropriate temperature. A surge tank  3   a  is provided in the intake passage  3 , located between the intercooler  14  and the engine  1 . A throttle valve  15  is placed on the upstream side of the surge tank  3   a.    
     An upstream side and a downstream side of the supercharger  7  in the intake passage  3  are connected to each other through an intake bypass passage  16 . Specifically, this bypass passage  16  is placed to connect a part of the intake passage  3  just downstream of the compressor  8 , in which the charging pressure is increased, and another part of the intake passage  3  upstream of the compressor  8 , so as to detour the compressor  8 . In the bypass passage  16 , an ejector  17  is placed to generate a negative pressure by the air flowing in this bypass passage  16 . 
       FIG. 2  is a cross-sectional view showing a schematic configuration of the ejector  17 . As shown in  FIG. 2 , the ejector  17  includes a nozzle  17   a  provided on an air inlet side, a diffuser  17   b  provided on an air outlet side, and a decompression chamber  17   c  provided between the nozzle  17   a  and the diffuser  17   b . The ejector  17  is arranged to generate a negative pressure in the decompression chamber  17   c  by the air ejected from the nozzle  17   a.    
     Specifically, when air pressure is increased by the compressor  8  during operation of the supercharger  7 , a pressure difference occurs between an upstream part of the intake passage  3  from the compressor  8  and a downstream part of the intake passage  3  from the compressor  8 . Thus, different intake pressures act between the nozzle  17   a  and the diffuser  17   b  in the ejector  17  through the intake bypass passage  16 . Due to this pressure difference, air is ejected from the nozzle  17   a  into the diffuser  17   b , thereby generating a negative pressure in the decompression chamber  17   c . The magnitude of this negative pressure will be changed depending on the magnitude of charging pressure generated by the supercharger  7 . 
     As shown in  FIG. 1 , the decompression chamber  17   c  of the ejector  17  (see  FIG. 2 ) is connected to an outlet of a first blowby gas returning passage  18  to be used during operation of the supercharger  7 . An inlet of the first blowby gas returning passage  18  is connected to a head cover  19  of the engine  1 . The first blowby gas returning passage  18  is arranged to allow the blowby gas leaking from a combustion chamber  20  of the engine  1  into a crank case  21  to return to the combustion chamber  20  again by passing through the head cover  19  and the intake passage  3 . In the present embodiment, the head cover  19  and the crank case  21  are examples of an accumulation part of the invention in which the blowby gas is accumulated. 
     During operation of the engine  1  and operation of the supercharger  7 , a negative pressure is generated in the decompression chamber  17   c  of the ejector  17 , and the generated negative pressure acts on the inside of the head cover  19  through the first blowby gas returning passage  18 . By this action of the negative pressure, the blowby gas is introduced from the head cover  19  to the returning passage  18 , and then this blowby gas flows to the intake passage  3  via the ejector  17  and the intake bypass passage  16 . The blowby gas flowing in the intake passage  3  is returned to the combustion chamber  20  of the engine  1  via the compressor  8 , the intake passage  3 , and others. 
     In the present embodiment, an inlet of a second blowby gas returning passage  22  is connected to the head cover  19  to allow the blowby gas leaking from the combustion chamber  20  to return to the combustion chamber  20  again via the intake passage  3 . An outlet of the second blowby gas returning passage  22  is connected to the surge tank  3   a  of the intake passage  3 . Further, the head cover  19  is provided with a PCV valve  23  at the inlet of the second blowby gas returning passage  22 . 
     Accordingly, during operation of the engine  1  but non-operation of the supercharger  7 , the internal pressure of the surge tank  3   a  is negative, and this negative pressure acts on the inside of the head cover  19  through the second blowby gas returning passage  22 . By this action of the negative pressure, the blowby gas is introduced from the head cover  19  to the returning passage  22 . The blowby gas then flows in the intake passage  3  (the surge tank  3   a ) to return to the combustion chamber  20  of the engine  1 . The PCV valve  23  is arranged to adjust a flow rate of blowby gas to be introduced from the head cover  19  to the second blowby gas returning passage  22 . 
     In the present embodiment, a fresh-air introduction passage  24  is provided between the engine  1  and the intake passage  3  to introduce fresh air into the head cover  19  and the crank case  21 . An inlet of this fresh-air introduction passage  24  is connected to the intake passage  3  near the air cleaner  6  while an outlet of the introduction passage  24  is connected to the head cover  19 . The inside of the head cover  19  and the inside of the crank case  21  are communicated with each other through a communication passage  1   a  provided in the engine  1 . 
       FIG. 3  is a perspective view of the head cover  19 . This head cover  19  includes a raised part  25  having an approximately U-like shape in plan view and providing an interior space for accumulating blowby gas. In one ridge portion  25   a  of the raised part  25 , a PCV valve  23  is attached. This PCV valve  23  is connected to the inlet of the second blowby gas returning passage  22 . The same ridge portion  25   a  is provided with a pipe joint  26  for blowby gas. This pipe joint  26  is connected to the inlet of the first blowby gas returning passage  18 . On the other hand, the other ridge portion  25   b  of the raised part  25  is provided with a pipe joint  27  for fresh air. This pipe joint  27  is connected to an outlet of the fresh-air introduction passage  24 . 
       FIG. 4  is a schematic perspective diagram showing the head cover  19 . As shown in  FIG. 4 , the head cover  19  is internally formed with a separator section  28  partitioned from the other section to separate gases and liquids. In this separator section  28 , the PCV valve  23  and the pipe joint  26  for blowby gas are placed. In the other section of the head cover  19  than the separator section  28 , the pipe joint  27  for fresh air is placed. 
       FIG. 5  is a schematic diagram showing the separator section  28  in the head cover  19 . As shown in  FIG. 5 . the separator section  28  includes an inlet  28   a  and is internally formed with a plurality of fins  28   b  alternately different in orientation and arranged in a labyrinth-like pattern. The pipe joint  26  for blowby gas and the PCV valve  23  are placed adjacent to each other in the same compartment in the separator section  28 . 
     However, the following matter is conceivable from the above configuration that the pipe joint  26  and the PCV valve  23  are placed adjacently in the same compartment. Specifically, during operation of the engine  1  but non-operation of the supercharger  7 , a negative pressure generated in the surge tank  3   a  acts on the inside of the head cover  19  through the second blowby gas returning passage  22  and the PCV valve  23 . At that time, the negative pressure also acts on the pipe joint  26 . Thus, atmospheric air flowing from the ejector  17  side flows in the head cover  19  through the first blowby gas returning passage  18  and the pipe joint  26 . Such air flowing in the head cover  19  passes through the PCV valve  23  under negative pressure into the second blowby gas returning passage  22  and thus no blowby gas enters in the separator section  28  through the inlet  28   a . This may result in a possibility that the interior space of the head cover  19  and the interior space of the crank case  21  cannot be ventilated. 
     In the present embodiment, therefore, as shown in  FIG. 1 , a check valve  29  serving as a backflow preventing unit is placed in the first blowby gas returning passage  18 , near the ejector  17 , to stop a flow of gas in an opposite direction to a direction of allowing the blowby gas to flow. This check valve  29  permits the flow of blowby gas that attempts to flow from the head cover  19  toward the ejector  17  but blocks the flow of air in the opposite direction thereto. 
     According to the blowby gas returning apparatus for engine with supercharger in the present embodiment, during operation of the engine  1  and non-operation of the supercharger  7 , a negative pressure generated in the intake passage  3  (the surge tank  3   a ) downstream of the throttle valve  15  acts on the second blowby gas returning passage  22 . By this action of negative pressure, the blowby gas accumulated in the head cover  19  is caused to flow to the intake passage  3  through the PCV valve  23  and the second blowby gas returning passage  22 . As a result, during non-operation of the supercharger  7 , the blowby gas in the head cover  19  can be returned to the combustion chamber  20  through the intake passage  3 . At that time, an amount of the blowby gas allowed to flow from the head cover  19  to the second blowby gas returning passage  22  is regulated to an appropriate amount by the PCV valve  23 . 
     In the present embodiment, the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  are placed adjacent to each other in the common head cover  19 . In other words, the pipe joint  26  connected to the inlet of the first blowby gas returning passage  18  and the PCV valve  23  connected to the inlet of the second blowby gas returning passage  22  are placed adjacently in the common space in the separator section  28  of the head cover  19 . Accordingly, the negative pressure applied from the intake passage  3  (the surge tank  3   a ) acts on the inside of the head cover  19  through the second blowby gas returning passage  22  and others and also on the first blowby gas returning passage  18 . In the present embodiment, however, in the first blowby gas returning passage  18 , the flow of air in the direction opposite to the direction of permitting the flow of blowby gas is blocked by the check valve  29 . Thus, no air flows from the ejector  17  side to the head cover  19  through the first blowby gas returning passage  18  and others. Therefore, the atmospheric air does not directly flow to the inlet of the second blowby gas returning passage  22  via the inlet of the first blowby gas returning passage  18 . This ensures the flow of blowby gas toward the second blowby gas returning passage  22 . 
     When the blowby gas flows from the head cover  19  to the intake passage  3  through the second blowby gas returning passage  22  and others, fresh air (atmospheric air) is introduced into the head cover  19  through the fresh-air introduction passage  24  and the pipe joint  27 . This makes it possible to ventilate the inside of the head cover  19  with the fresh air. Further, since the inside of the head cover  19  is ventilated, the blowby gas accumulated in the crank case  21  is introduced into the head cover  19  through the communication passage  1   a . Thus, the inside of the crank case  21  can also be ventilated. 
     In the present embodiment, the PCV valve  23  is placed in the inlet of the second blowby gas returning passage  22 , so that the flow rate of blowby gas allowed to flow to the second blowby gas returning passage  22  is regulated to an appropriate amount by the PCV valve  23 . This can prevent returning of an excessive amount of blowby gas to the combustion chamber  20  through the second blowby gas returning passage  22 . 
     On the other hand, during operation of the engine  1  and operation of the supercharger  7 , the internal pressure of the intake passage  3  downstream of the supercharger  7  is high. The negative pressure does not act on the outlet of the second blowby gas returning passage  22 . Accordingly, the blowby gas does not flow from the head cover  19  to the intake passage  3  through the PCV valve  23  and the second blowby gas returning passage  22 . 
     At that time, a pressure difference in intake air occurs between the upstream side and the downstream side of the supercharger  7  in the intake passage  3 , and similarly a pressure difference occurs between both ends of the intake bypass passage  16 . Due to this pressure differences, air is caused to flow in the intake bypass passage  16 , thereby generating a negative pressure in the ejector  17 . Accordingly, this negative pressure acts on the outlet of the first blowby gas returning passage  18 , causing the blowby gas accumulated in the head cover  19  to flow to the intake passage  3  through the first blowby gas returning passage  18 , the ejector  17 , and the intake bypass passage  16 . In this way, during operation of the supercharger  7 , the blowby gas in the head cover  19  can be returned to the combustion chamber  20  through the intake passage  3 . 
     When charging pressure provided by the supercharger  7  increases, the pressure difference between both ends of the intake bypass passage  16  increases, and accordingly a larger negative pressure is generated in the ejector  17 . Therefore, the flow rate of blowby gas allowed to flow from the head cover  19  to the intake passage  3  through the first blowby gas returning passage  18  and others is increased, so that a large amount of blowby gas is returned to the combustion chamber  20 . 
     Since the intake bypass passage  16  is provided by detouring a part of the intake passage  3 , the bypass passage  16  and the ejector  17  will not affect intake resistance in the intake passage  3 . During operation of the supercharger  7 , accordingly, it is possible to return the blowby gas to the combustion chamber  20  without increasing intake resistance in the intake passage  3 . 
     Further, when the blowby gas flows from the head cover  19  to the intake passage  3  through the first blowby gas returning passage  18  and others, fresh air (atmospheric air) is introduced from outside into the head cover  19  through the fresh-air introduction passage  24  and the pipe joint  27 . Accordingly, the inside of the head cover  19  can be ventilated with this fresh air. Further, when the inside of the head cover  19  is ventilated, the blowby gas accumulated in the crank case  21  is introduced into the head cover  19  through the communication passage  1   a . Thus, the inside of the crank case  21  can also be ventilated. 
     In the present embodiment, as explained above, in which the inlet of the first blowby gas returning passage  18  to be used during operation of the supercharger  7  and the inlet of the second blowby gas returning passage  22  to be used during non-operation of the supercharger  7  are placed adjacent to each other in the common head cover  19 , the blowby gas in the head cover  19  and the blowby gas in the crank case  21  can be effectively returned to the combustion chamber  20  of the engine  1  during operation of the engine  1  and irrespective of whether during operation or non-operation of the supercharger  7 . 
     In the present embodiment, when the blowby gas accumulated in the head cover  19  flows from the inlet of the first blowby gas returning passage  18  or the inlet of the second blowby gas returning passage  22  toward the intake passage  3 , fresh air is introduced from outside into the head cover  19  through the fresh-air introduction passage  24 . Therefore, the fresh air introduced in the head cover  19  allows ventilation of the inside of the head cover  19  and simultaneously the inside of the crank case  21 . 
     In the present embodiment, the outlet of the fresh-air introduction passage  24 , the inlet of the first blowby gas returning passage  18 , and the inlet of the second blowby gas returning passage  22  are connected to the single head cover  19 , so that those three passages  24 ,  18 , and  22  are easily arranged. Accordingly, an easier piping work is achieved. 
     &lt;Second Embodiment&gt; 
     A second embodiment of the blowby gas returning apparatus for engine with supercharger according to the present invention will be explained in detail referring to accompanying drawings. 
     In each of the embodiments described below, similar or identical components or parts to those in the first embodiment are given the same reference signs and their details are not repeated below. Differences from the first embodiment are focused on. 
       FIG. 6  is a schematic configuration view of an engine system including the blowby gas returning apparatus for engine with supercharger of the present embodiment. In this embodiment, instead of the check valve  29  in the first embodiment, a vacuum switching valve (VSV)  31  is placed near the ejector  17  in the first blowby gas returning passage  18 . This VSV  31  is configured to be controlled by an electronic control unit (ECU)  32  according to an operating status of the engine  1 . The present embodiment differs in such a configuration from the first embodiment. 
     Herein, the ECU  32  is configured to receive detection values such as engine rotational speed and intake pressure from various sensors (not shown) provided in the engine  1  and control the VSV  31  based on those detection values. In the present embodiment, the VSV  31  and the ECU  32  constitute one example of a backflow preventing unit of the present invention. 
       FIG. 7  is a flowchart showing the details of a control program to be executed by the ECU  32 . When the processing advances to this routine, the ECU  32  determines first at step  100  whether or not a predetermined time has elapsed from engine start. If this determination result is negative, the engine  1  is identified as being in a state before completion of warm-up, and the ECU  32  closes the VSV  31  at step  130 . With this VSV  31 , the first blowby gas returning passage  18  is thus closed, intercepting a flow of air in the passage  18 . 
     On the other hand, if the determination result at step  100  is affirmative, the ECU  32  then determines at step  110  whether the intake pressure is a predetermined value or more. If this determination result is negative, the supercharger  7  is considered to be non-operational after completion of warm-up of the engine  1 , and the ECU  32  closes the VSV  31  as in the above case. 
     If an affirmative result is obtained at step  110 , on the other hand, the supercharger  7  is considered to be operational after completion of warm-up of the engine  1 , the ECU  32  opens the VSV  31  at step  120 . Thus, with the VSV  31 , the first blowby gas returning passage  18  is opened, thereby allowing air to flow in the intake bypass passage  16  according to the charging pressure. This generates a negative pressure in the ejector  17  according to the magnitude of the charging pressure. Accordingly, the negative pressure generated in the ejector  17  acts on the inside of the head cover  19  through the first blowby gas returning passage  18 , thus causing blowby gas to flow out of the head cover  19  into the first blowby gas returning passage  18  according to the magnitude of charging pressure. Consequently, the blowby gas is returned to the combustion chamber  20  through the ejector  17 , intake bypass passage  16 , intake passage  3 , and others. 
     According to the blowby gas returning apparatus for engine with supercharger in the present embodiment explained above, the VSV  31  is controlled according to the operating status of the engine  1 , the first blowby gas returning passage  18  can be opened by the VSV  31  during operation of the supercharger  7 . Accordingly, during operation of the supercharger  7 , the ejector  17  is actuated to cause the blowby gas in the head cover  19  to flow to the intake passage  3  through the first blowby gas returning passage  18  and others and thus return to the combustion chamber  20 . 
     On the other hand, the VSV  31  is controlled according to the operating status of the engine  1 , the first blowby gas returning passage  18  is closed by the VSV  31  during non-operation of the supercharger  7 . This can prevent the air in the ejector  17  side to flow back to the head cover  19  through the first blowby gas returning passage  18 . When the negative pressure applied from the intake passage  3  (surge tank  3   a ) acts on the inside of the head cover  19  through the second blowby gas returning passage  22  and the PCV valve  23 , the blowby gas in the separator section  28  is caused to flow toward the PCV valve  23  through the inlet  28   a . During non-operation of the supercharger  7 , therefore, the blowby gas in the head cover  19  is allowed to flow to the intake passage  3  (surge tank  3   a ) and thus return to the combustion chamber  20 . 
     In the present embodiment, as above, the first blowby gas returning passage  18  can be opened and closed by the VSV  31  according to the operating status of the engine  1 , that is, whether during operation or non-operation of the supercharger  7 . Accordingly, in the configuration that the inlet of the first blowby gas returning passage  18  to be used during operation of the supercharger  7  and the inlet of the second blowby gas returning passage  22  to be used during non-operation of the supercharger  7  are placed adjacent to each other in the common head cover  19 , the blowby gas can be efficiently returned to the combustion chamber  20  of the engine  1  during operation of the engine  1  and irrespective of whether operation or non-operation of the supercharger. Other operations and effects are substantially the same as those in the first embodiment. 
     &lt;Third Embodiment&gt; 
     A third embodiment of the blowby gas returning apparatus for engine with supercharger according to the present invention will be explained in detail below referring to the accompanying drawings. 
       FIG. 8  is a schematic configuration view showing an engine system including the blowby gas returning apparatus for engine with supercharger of the present embodiment. This embodiment does not include the check valve  29  provided in the first blowby gas returning passage  18  in the first embodiment. Instead, the present embodiment differs from the first embodiment in the configuration of separator sections  28 A and  28 B (see  FIG. 9 ) of the head cover  19 . 
       FIG. 9  is a schematic diagram showing two separator sections  28 A and  28 B in the head cover  19 . As shown in  FIG. 9 , the head cover  19  is internally provided with two separator sections  28 A and  28 B separated or isolated from each other. Each of the separator sections  28 A and  28 B includes an inlet  28   a  and a plurality of fins  28   b  arranged in a labyrinth-like pattern. The first separator section  28 A is provided with the pipe joint  26 . This pipe joint  26  is connected to an inlet of the first blowby gas returning passage  18 . The second separator section  28 B is provided with the PCV valve  23 . This PCV valve  23  is connected to an inlet of the second blowby gas returning passage  22 . Specifically, the separator sections  28 A and  28 B are provided respectively at the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  to separate liquids from the blowby gas. Those two separator sections  28 A and  28 B correspond to one example of an isolating unit of the present invention to separate or isolate the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  from each other. 
     According to the blowby gas returning apparatus for engine with supercharger in the present embodiment described above, the head cover  19  is provided with the two separator sections  28 A and  28 B separated from each other. Further, the first separator section  28 A is provided with the pipe joint  26  connected to the inlet of the first blowby gas returning passage  18 . The second separator section  28 B is provided with the PCV valve  23  connected to the inlet of the second blowby gas returning passage  22 . 
     Accordingly, during operation of the engine  1  and operation of the supercharger  7 , a negative pressure acts on the first blowby gas returning passage  18  by the action of the ejector  17 , thereby causing the blowby gas in the head cover  19  to flow to the intake passage  3  through the first separator section  28 A, first blowby gas returning passage  18 , ejector  17 , and intake bypass passage  16 . Thus, the blowby gas flowing in the intake passage  3  can be returned to the combustion chamber  20  of the engine  1 . 
     On the other hand, during operation of the engine  1  but non-operation of the supercharger  7 , the negative pressure generated in the intake passage  3  (surge tank  3   a ) causes the blowby gas in the head cover  19  to flow to the intake passage  3  (surge tank  3   a ) through the second separator section  28 B, PCV valve  23 , and second blowby gas returning passage  22 . Thus, the blowby gas flowing in the intake passage  3  can be returned to the combustion chamber  20  of the engine  1 . 
     Herein, although the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  are placed adjacent to each other in the common head cover  19 , the inlets of the blowby gas returning passages  18  and  22  are isolated from each other by the separator sections  28 A and  28 B. Accordingly, this configuration prevents direct introduction of air from the ejector  17  side to the inlet of the second blowby gas returning passage  22  through the first blowby gas returning passage  18  and others. 
     Specifically, during non-operation of the supercharger  7 , the negative pressure acting on the second blowby gas returning passage  22  acts on the second separator section  28 B through the PCV valve  23 , but does not directly act on the first separator section  28 A. Therefore, the air is not drawn from the ejector  17  side to the first separator section  28 A through the first blowby gas returning passage  18 . Also, this air is not allowed to flow to the second blowby gas returning passage  22  through the second separator section  28 B and the PCV valve  23 . This ensures the flow of blowby gas from the second separator section  28 B toward the PCV valve  23  and the second blowby gas returning passage  22 . 
     Consequently, in the configuration that the inlet of the first blowby gas returning passage  18  to be used during operation of the supercharger  7  and the inlet of the second blowby gas returning passage  22  to be used during non-operation of the supercharger  7  are placed adjacent to each other in the common head cover  19 , the blowby gas can be efficiently returned to the combustion chamber  20  of the engine  1  during operation of the engine  1  and irrespective of during operation or non-operation of the supercharger  7 . Other operations and effects are substantially the same as those in the first embodiment. 
     &lt;Fourth Embodiment&gt; 
     A fourth embodiment of the blowby gas returning apparatus for engine with supercharger according to the present invention will be explained in detail below referring to the accompanying drawings. 
       FIG. 10  is a schematic configuration view showing an engine system including the blowby gas returning apparatus for engine with supercharger of the present embodiment. In this embodiment, the inlet of the first blowby gas returning passage  18  is connected to the crank case  21 , not to the head cover  19 , and the inlet of the second blowby gas returning passage  22  is connected to the crank case  21 , not to the head cover  19 , through the PCV valve  23 . Further, a pipe joint (not shown) connected to the inlet of the first blowby gas returning passage  18  and the PCV valve  23  connected to the inlet of the second blowby gas returning passage  22  are placed adjacent to each other in the crank case  21  serving as a common accumulation part of the invention. The above configuration of the present embodiment differs from the first embodiment. 
     According to the blowby gas returning apparatus for engine with supercharger in the present embodiment described as above, a negative pressure generated by the action of the ejector  17  acts on the first blowby gas returning passage  18  during operation of the engine  1  and operation of the supercharger  7 , thereby causing the blowby gas accumulated in the crank case  21  to flow to the intake passage  3  through the first blowby gas returning passage  18 , ejector  17 , and intake bypass passage  16 . Consequently, the blowby gas flowing in the intake passage  3  can be returned to the combustion chamber  20  of the engine  1 . 
     On the other hand, during operation of the engine  1  but non-operation of the supercharger  7 , a negative pressure generated in the intake passage  3  (surge tank  3   a ) causes the blowby gas in the crank case  21  to flow to the intake passage  3  (surge tank  3   a ) through the PCV valve  23  and second blowby gas returning passage  22 . Consequently, the blowby gas flowing in the intake passage  3  can be returned to the combustion chamber  20  of the engine  1 . 
     Herein, the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  are placed adjacently in the common crank case  21  that stores the blowby gas. Thus, the negative pressure acting on the crank case  21  through the second blowby gas returning passage  22  also attempts to act on the first blowby gas returning passage  18 . In the present embodiment, however, the check valve  29  blocks the flow of air in an opposite direction to a direction of allowing the flow of blowby gas in the first blowby gas returning passage  18 , so that no air is allowed to flow from the ejector  17  side to the crank case  21  through the first blowby gas returning passage  18 . Accordingly, no atmospheric air directly flows to the second blowby gas returning passage  22  via the first blowby gas returning passage  18 . This ensures the flow of blowby gas toward the second blowby gas returning passage  22 . 
     In the present embodiment, consequently, in the configuration that the inlet of the first blowby gas returning passage  18  to be used during operation of the supercharger  7  and the inlet of the second blowby gas returning passage  22  to be used during non-operation of the supercharger  7  are placed adjacently in the common crank case  21 , the blowby gas can be efficiently returned to the combustion chamber  20  during operation of the engine  1  and irrespective of whether operation or non-operation of the supercharger  7 . 
     In the present embodiment, furthermore, when the blowby gas accumulated in the crank case  21  flows toward the intake passage  3  through the inlet of the first blowby gas returning passage  18  or the inlet of the second blowby gas returning passage  22 , fresh air is introduced into the head cover  19  from outside through the fresh-air introduction passage  24 . Fresh air introduced in the head cover is also introduced into the crank case  21  through the communication passage  1   a . Therefore, the inside of the head cover  19  can be ventilated with the fresh air introduced in the head cover  19  and further the inside of the crank case  21  can be ventilated with the fresh air introduced in the crank case  21 . 
     Since the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  are connected to the same crank case  21 , the aforementioned two blowby gas returning passages  19  and  22  can be easily arranged. Accordingly, an easier piping work is achieved. Other operations and effects are substantially the same as those in the first embodiment. 
     &lt;Fifth Embodiment&gt; 
     A fifth embodiment of the blowby gas returning apparatus for engine with supercharger according to the present invention will be explained in detail below referring to the accompanying drawings. 
       FIG. 11  is a schematic configuration view showing an engine system including the blowby gas returning apparatus for engine with supercharger of the present embodiment. This embodiment does not include the check valve  29  provided in the first blowby gas returning passage  18  in the fourth embodiment. Instead, the present embodiment is different from the fourth embodiment in that the crank case  21  is provided with two separator sections  30 A and  30 B. 
     Specifically, as shown in  FIG. 11 , the crank case  21  is internally provided with two separate separator sections  30 A and  30 B isolated from each other. Each of the separator sections  30 A and  30 B has the same configurations as the aforementioned two separator sections  28 A and  28 B. The first separator section  30 A is connected to the inlet of the first blowby gas returning passage  18 . The second separator section  30 B is connected to the inlet of the second blowby gas returning passage  22  through the PCV valve  23 . Specifically, the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  are provided respectively with the separator sections  30 A and  30 B. Those two separator sections  30 A and  30 B correspond to one example of the isolating unit of the present invention to separate or isolate the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  from each other. 
     According to the blowby gas returning apparatus for engine with supercharger in the present embodiment described as above, a negative pressure generated by the action of the ejector  17  acts on the first blowby gas returning passage  18  during operation of the engine  1  and operation of the supercharger  7 , thereby causing the blowby gas accumulated in the crank case  21  to flow to the intake passage  3  through the first separator section  30 A, first blowby gas returning passage  18 , ejector  17 , and intake bypass passage  16 . Consequently, the blowby gas flowing in the intake passage  3  can be returned to the combustion chamber  20  of the engine  1 . 
     On the other hand, during operation of the engine  1  but non-operation of the supercharger  7 , a negative pressure generated in the intake passage  3  (surge tank  3   a ) causes the blowby gas in the crank case  21  to flow to the intake passage  3  (surge tank  3   a ) through the second separator section  30 B, PCV valve  23 , and second blowby gas returning passage  22 . Consequently, the blowby gas flowing in the intake passage  3  can be returned to the combustion chamber  20  of the engine  1 . 
     Herein, the inlet of the first blowby gas returning passage  18  and the inlet of the second blowby gas returning passage  22  are placed adjacently in the common crank case  21 , while the inlets of the blowby gas returning passages  18  and  22  are separated or isolated from each other by the corresponding separator sections  30 A and  30 B. Accordingly, no air is introduced from the ejector  17  side to the inlet of the second blowby gas returning passage  22  through the first blowby gas returning passage  18 . Thus, the air is not drawn from the ejector  17  to the first separator section  30 A through the first blowby gas returning passage  18 . Also, this air is not allowed to flow in the second blowby gas returning passage  22  through the second separator section  30 B and the PCV valve  23 . Accordingly, no atmospheric air directly flows to the second blowby gas returning passage  22  via the first blowby gas returning passage  18 . This ensures the flow of blowby gas toward the second blowby gas returning passage  22 . 
     In the present embodiment, consequently, in the configuration that the inlet of the first blowby gas returning passage  18  to be used during operation of the supercharger  7  and the inlet of the second blowby gas returning passage  22  to be used during non-operation of the supercharger  7  are placed adjacently in the common crank case  21 , the blowby gas can be efficiently returned to the combustion chamber  20  of the engine  1  during operation of the engine  1  and irrespective of during operation or non-operation of the supercharger  7 . Other operations and effects are substantially the same as those in the fourth embodiment. 
     The present invention is not limited to the above embodiments and may be embodied in other specific forms without departing from the essential characteristics thereof, as mentioned below. 
     In the fourth embodiment, the check valve  29  is placed in the first blowby gas returning passage  18 . Instead of this check valve  29 , the VSV  31  to be controlled by the ECU  32  may be placed in the first blowby gas returning passage  18  as in the second embodiment. 
     In the third and fifth embodiments, the first separator sections  28 A and  30 A and the second separator sections  28 B and  30 B are provided as the isolating unit of the present invention. The isolating unit is not limited to the above separator sections and has only to have a function of isolating the inlet of the first blowby gas returning passage and the inlet of the second blowby gas returning passage from each other. For instance, the inlet of each blowby gas returning passage may be configured as a simple compartment having a vent hole. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be utilized in for example an engine with supercharger for vehicle. 
     DESCRIPTION OF THE REFERENCE SIGNS 
     
         
           1  Engine 
           3  Intake passage 
           3   a  Surge tank 
           7  Supercharger 
           15  Throttle valve 
           16  Intake bypass passage 
           17  Ejector 
           18  First blowby gas returning passage 
           19  Head cover 
           21  Crank case 
           22  Second blowby gas returning passage 
           24  Fresh-air introduction passage 
           28 A First separator section 
           28 B Second separator section 
           29  Check valve 
           30 A First separator section 
           30 B Second separator section 
           31  VSV 
           32  ECU