Blowby gas returning device

A blowby gas returning device is arranged to allow blowby gas leaking from a combustion chamber of an engine to flow in an intake passage through a returning passage and return to the combustion chamber, and arranged to regulate a flow rate of the blowby gas by a PCV valve provided in the returning passage. This blowby gas returning device comprises an outside-air passage for mixing outside air into the blowby gas before being introduced into the PCV valve; and an open-close valve for opening and closing the outside-air passage. An electronic control unit controls the open-close valve to open when the operating state detected by sensors is an idle state.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a blowby gas returning device for returning blowby gas leaking from a combustion chamber of an engine to the combustion chamber by allowing the blowby gas to flow in a returning passage and an intake passage via a PCV valve.

2. Description of Related Art

Heretofore, some techniques of this type have been known as disclosed in for example JP2005-240605A, JP53-148639(1978)A, JP60-171915(1985)U, and JP2-3038(1990)U. Particularly, a device disclosed in JP2005-240605A is provided with a blowby gas passage between a crank case and an intake passage in an engine, and a PCV valve is placed in this blowby gas passage. This PCV valve is arranged to control a flow rate of blowby gas by a differential pressure between an inlet port side and an outlet port side of the valve. Here, the blowby gas contains unburned fuel constituent. When this blowby gas is returned to the combustion chamber of the engine, therefore, the fuel constituent contained in the blowby gas is burned together with the fuel normally supplied to the engine.

In the device of JP2005-240605A, however, the fuel constituent contained in the blowby gas may increase in concentration suddenly. In this case, when the blowby gas is returned to the combustion chamber, an air-fuel ratio in the engine may fluctuate to an over-rich side, causing disorder of air-fuel ratio control of the engine. During idling of this engine, especially, the blowby gas would significantly affect the air-fuel ratio. This may cause a change in engine rotational speed and deterioration in exhaust emission. Further, in a direct-injection engine arranged to directly inject fuel into engine cylinders, unburned fuel droplets sticking to a bore wall surface due to fuel injection may flow down along the wall surface and is mixed into a lubricant in an oil pan or receiver. This unburned fuel begins to vaporize when the temperature of the lubricant (oil temperature) rises to “40° C.” or more. When such gas is returned to the combustion chamber, accordingly, the air-fuel ratio may fluctuate, causing disorder of the air-fuel ratio control. Here, as to the engine air-fuel ratio control, learning control configured to learn an air-fuel ratio correction value according to an operating state of an engine and reflect it in the control. This type of learning control can deal with the influence of blowby gas returned to the combustion chamber to some extent. However, when the concentration and the volume of the fuel constituent of the blowby gas exceed permissible ranges in the learning control, the learning control could not appropriately respond thereto, thus causing the air-fuel ratio to fluctuate to an over-rich side, leading to disorder of the air-fuel ratio control.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances and has an object to provide a blowby gas returning device capable of preventing an air-fuel ratio from fluctuating due to blowby gas returned to a combustion chamber.

To achieve the purpose of the invention, there is provided A blowby gas returning device including a returning passage and a PCV valve placed in the returning passage, the device being arranged to allow blowby gas leaking from a combustion chamber of an engine to flow in an intake passage through the returning passage and return to the combustion chamber, and arranged to regulate a flow rate of the blowby gas by the PCV valve, wherein the blowby gas returning device comprises: an outside-air passage for mixing outside air into the blowby gas before being introduced into the PCV valve; and an open-close valve for opening and closing the outside-air passage.

According to another aspect, the invention provides a blowby gas returning device including a returning passage and a PCV valve placed in the returning passage, the device being arranged to allow blowby gas leaking from a combustion chamber of a direct injection engine configured to directly inject fuel in the combustion chamber to flow in an intake passage through the returning passage and return to the combustion chamber, and arranged to regulate a flow rate of the blowby gas by a PCV valve provided in the returning passage, wherein the blowby gas returning device comprises: an outside-air passage for mixing outside air into the blowby gas before being introduced into the PCV valve; an open-close valve for opening and closing the outside-air passage; an oil trapping device for trapping oil from the blowby gas before being introduced into the PCV valve; a scavenging passage for introducing outside air into the engine to scavenge the blowby gas from the engine; an operating state detection device for detecting an operating state of the engine; and a valve control device for controlling the open-close valve based on the detected operating state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A detailed description of a first preferred embodiment of an engine system embodying a blowby gas returning device of the present invention will now be given referring to the accompanying drawings.

FIG. 1is a schematic configuration view of the engine system including the blowby gas returning device of the present embodiment. An engine1constituting this engine system is a direct-injection multicylinder spark-ignition engine arranged to directly inject fuel into a combustion chamber2. An engine block3of this engine1is formed with a plurality of cylinder bores4in each of which a piston5is placed to be movable up and down. The engine block3includes a crank case3aas a lower part of the engine block3, and an oil pan6combined with the crank case3a. Those crank case3aand oil pan6form a crank chamber7. In the crank chamber7, a crank shaft8is rotatably supported, to which each of the piston5is connected through a connecting rod9.

The combustion chamber2formed above the piston5in each cylinder bore4has a pent roof shape slant to be highest at its upper center. In each combustion chamber2, the engine block3is formed at an upper part thereof with an intake port10and an exhaust port11. An intake valve12is set in the intake port10while an exhaust valve13is set in the exhaust port11. The intake valve12and the exhaust valve13are opened and closed in association with rotation of the crank shaft8by a well known valve operating mechanism14. By opening and closing of the intake valve12and the exhaust valve13, outside air is introduced in the combustion chamber2through the intake port10and exhaust gas is discharged after combustion from the combustion chamber2to the exhaust port11. An engine cover15is provided on the engine block3to cover the valve operating mechanism14and others.

The intake port10is connected to an intake passage21including an intake manifold. An inlet port of this intake passage21is connected to an air cleaner22. A throttle body24including a throttle valve23is mounted in a predetermined portion of the intake passage21. The throttle valve23is opened and closed in synchronization with operation of an accelerator pedal (not shown) mounted on a driver's side floor. The air purified by the air cleaner22is sucked in the combustion chamber2via the intake passage21, the throttle body24, and the intake port10. An amount of this sucked air is regulated by an opening degree of the throttle valve23. To the engine block3, an injector25is attached to directly inject fuel into each combustion chamber2. The fuel injected from the injector25into the combustion chamber2is mixed with the air sucked in the combustion chamber2through the intake port10, forming an air-fuel mixture. An ignition plug26is also provided at the top of the engine block3to ignite the air-fuel mixture in each combustion chamber2.

The exhaust port11is connected with an exhaust passage27including the exhaust manifold. The exhaust gas generated in each combustion chamber2after combustion is exhausted to the outside through the exhaust port11and the exhaust passage27.

The aforementioned engine1is provided with a blowby as returning device for allowing blowby gas leaking from each combustion chamber2to flow in the intake passage21and return to each combustion chamber2. Specifically, the crank case3ais provided with an oil separator31communicated with the crank chamber7. This oil separator31has a function for separating oil such as lubricant mixed with the blowby gas in the crank chamber7from the blowby gas, and trapping the separated oil. Thus, the oil separator31corresponds to an oil trapping device of the invention. A returning passage32is arranged between the oil separator31and the intake passage21downstream of the throttle valve23to allow the blowby gas to flow from the crank chamber7into the intake passage21. In a predetermined portion of the returning passage32, a PCV valve33is mounted for regulating a flow rate of the blowby gas. The configuration of the PCV valve33will be mentioned later in detail. Between the intake passage21near the air cleaner22and the engine cover15, a scavenging passage34is arranged to introduce outside air into the crank chamber7in order to scavenge the blowby gas from the crank chamber7of the engine1. The engine block3is formed with vent holes35for providing communication between the crank chamber7and the inside of the engine cover15. Through each vent hole35, the outside air taken in the engine cover15is allowed to flow in the crank chamber7. Each vent hole35also constitutes part of the scavenging passage34. Further, one end of an outside-air passage36is connected to the PCV valve33to mix outside air with the blowby gas to be introduced into the PCV valve33. The other end of the outside-air passage36is connected to the scavenging passage34via a three-way valve37. This three-way valve37is operated to provide communication between the scavenging passage34and the outside-air passage36in a three way configuration. In a predetermined portion of the outside-air passage36, an electromagnetic open-close valve38is mounted, whereby the passage36is opened and closed.

Here, a detail explanation will be given to the configuration of the PCV valve33.FIG. 2is a sectional view of a valve unit41including the PCV valve33. The valve unit41is constituted by the PCV valve33and an adaptor42fit on the valve33. This PCV valve33includes a hollow housing43. The housing43is constituted by a main housing44and a sub housing45which are cylindrical and assembled together. The main housing44is internally provided with a valve seat46, a valve element47, and a spring48. The sub housing45is internally provided with a spring49. The sub housing45is fixed to the main housing44in such a way that a proximal end of the sub housing45is fit in an open end of the main housing44. A distal end of the sub housing45is provided with a pipe joint45a. An open end of this pipe joint45aserves as an outlet port33aof the PCV valve33. This pipe joint45ais connected to the returning passage32connected to the intake passage21. A hollow of the main housing44forms a valve chamber50in which the valve element47and the spring48are housed. One end wall (a bottom wall inFIG. 2) of the main housing44is formed with an inlet port33bof the PCV valve33so as to communicate with the valve chamber50. The sub housing45includes a hollow45bcommunicated with the valve chamber50of the main housing44. The annular valve seat46is placed between the main housing44and the sub housing45. The valve chamber50and the hollow45bare communicated with each other through the valve seat46. In the valve chamber50, the valve element47is disposed to be axially movable relative to the valve seat46. The valve element47has a nearly columnar shape and insertable through the valve seat46. The valve element47is shaped so that its distal end is gradually decreased in diameter. Accordingly, when the valve element47is moved axially, a clearance (an opening degree) between the valve seat46and the valve element47is changed. By changing this clearance (the opening degree), a flow rate of blowby gas allowed to flow in the PCV valve33is regulated. The proximal end of the valve element47located near the inlet port33bis formed with a flange47a. The flange47ahas a shape permitting passage of the blowby gas. The spring48is mounted between the valve seat46and the flange47ato urge the valve element47toward the inlet port33b.

The adaptor42is fit on the main housing44to cover the outer periphery thereof. The adaptor42is of a nearly cylindrical shape having a hollow42aand internally formed, at a part under the hollow42a, with a mixing chamber42bfor mixing blowby gas with outside air. The adaptor42is formed, at its proximal end, with a pipe joint42ccommunicated to the mixing chamber42b. This pipe joint42cis connected to the outside-air passage36. The mixing chamber42bof the adaptor42is communicated to the inlet port33bof the PCV valve33through a vent hole42d. The adaptor42is formed, at its bottom, with an inlet port42eopening into the mixing chamber42b. This inlet port42eis connected to the oil separator31.

In the valve unit41shown inFIG. 2, intake negative pressure in the intake passage21acts on the outlet port33aof the PCV valve33through the returning passage32. Further, the blowby gas introduced in the inlet port42eof the adaptor42is then introduced in the inlet port33bof the PCV valve33via the mixing chamber42b. In the valve chamber50of the PCV valve33, the intake negative pressure, blowby gas pressure, and the urging force (pressure) of the spring48act on the valve element47. By a balance between those pressures, the valve element47is moved toward the valve seat46, thereby changing the clearance (the opening degree) between the valve seat46and the valve element47. This regulates the flow rate of blowby gas to be allowed to flow from the valve chamber50of the main housing44to the hollow45bof the sub housing45, that is, to be dispensed by the PCV valve33. When the distal end of the valve element47comes into contact with the spring49placed in the hollow45b, the valve element47is restricted in movement.

To control the engine system shown inFIG. 1, an electronic control unit (ECU)60is provided. An air flow-meter61is installed on an upstream side of the intake passage21to measure an intake air amount QA. The throttle body24is provided with a throttle sensor62for detecting an opening degree (a throttle opening degree) TA of the throttle valve23. The engine block3is provided with a crank angle sensor63for detecting a rotation angle (a crank angle) of the crank shaft8as engine rotation speed NE. The engine block3is provided with a water temperature sensor64for detecting cooling water temperature THW. The oil pan6is provided with an oil temperature sensor65for detecting lubricant temperature (oil temperature) THO. In the exhaust passage27, an oxygen sensor66is installed for detecting oxygen concentration Ox in exhaust gas. The above sensors61to66correspond to an operating state detection device of the invention. The ECU60is configured to determine intake, compression, expansion (explosion), and exhaust strokes in each cylinder based on the crank angle detected by the crank angle sensor63and to calculate the engine rotation speed NE. The ECU60is further arranged to execute fuel injection control, ignition timing control, blowby gas returning control, and others based on the intake air amount QA, the throttle opening degree TA, the engine rotation speed NE, the cooling water temperature THW, the oil temperature THO, and the oxygen concentration Ox which are detected by the above sensors61to66. The ECU60conducts the fuel injection control to control the injector25. The ECU60executes the ignition timing control to control the ignition plug26. The ECU60executes the blowby gas returning control to control the open-close valve38. In the present embodiment, the ECU60corresponds to a valve control device of the invention.

In the present embodiment, the ECU60executes the air-fuel ratio control including the learning control as part of the fuel injection control. Specifically, in injecting fuel from the injector25, the ECU60conducts the air-fuel ratio control so that the amount of fuel to be injected by the injector25is regulated to meet a required air-fuel ratio of the engine1that changes according to the operating state such as the engine rotation speed NE, an engine load state, and an engine warm-up state. To have the actual air-fuel ratio coincide with the required air-fuel ratio, the ECU60calculates an actual air-fuel ratio from the oxygen concentration Ox detected by the oxygen sensor66and executes air-fuel ratio feedback control so that the actual air-fuel ratio coincides with the required air-fuel ratio. As the air-fuel ratio learning control, the ECU60evaluates and stores past control results and, based on the evaluation, stores and corrects an air-fuel ratio correction amount for the air-fuel ratio control. In other words, in response to individual difference of the engine1, deterioration thereof with age, or use environment condition, the ECU60corrects and stores in advance the air-fuel ratio correction amount in various operating regions of the engine1so that the stored air-fuel ratio correction amount is read according to the operating regions and reflected in the air-fuel ratio control at next startup even after the engine1is stopped. Accordingly, in the engine system of the present embodiment, in addition to the fuel injection amount by the injector25, the fuel constituent concentration in the blowby gas which will be returned to the combustion chamber2can be reflected in the air-fuel ratio control including the learning control. In the present embodiment, the air-fuel ratio control including the learning control adopts well known control details and thus its specific explanation is omitted here.

However, even in the engine system that executes the air-fuel ratio control including this type of learning control, the fuel constituent concentration in the blowby gas to be returned to the combustion chamber2may exceed a permissible range in the learning control. In the present embodiment, therefore, the ECU60executes the blowby gas returning control in order to restrain the influence of blowby gas returned to the combustion chamber2on the air-fuel ratio control.

FIG. 3is a flowchart showing the details of the blowby gas returning control. The ECU60executes this control after the start of the engine1.

Specifically, at step100, the ECU60reads the engine rotation speed NE calculated based on the crank angle detected by the crank angle sensor63and the throttle opening degree TA detected by the throttle sensor62respectively. The ECU60then determines at step110whether or not the engine1is in an idle state based on the read engine rotation speed NE and throttle opening degree TA. For instance, if the throttle opening degree TA indicates a full closed state and the engine rotation speed NE is a predetermined value (an idle rotation speed range), the ECU60determines that the engine1is in the idle state. Here, it is determined whether or not the engine1is in the idle state because the blowby gas strongly affects the air-fuel ratio during the idle state.

If an affirmative result is obtained at step110, the ECU60opens the open-close valve38at step120and advances the process to step100. If a negative result is obtained at step110, on the other hand, the ECU60closes the open-close valve38at step130and advances the process to step100. In this blowby gas returning control, specifically, the open-close valve38is opened during the idle state of the engine1to mix outside air supplied through the outside-air passage36into the blowby gas introduced into the inlet port33bof the PCV valve33.

According to the blowby gas returning device in the engine system of the present embodiment explained above, the blowby gas leaking from the combustion chamber2to the crank chamber7during operation of the engine1is allowed to flow from the crank chamber7to the intake passage21via the oil separator31, the PCV valve33, and the returning passage32, and be returned to the combustion chamber2, the blowby gas will be burned. The flow rate of blowby gas in the returning passage32is regulated by the PCV valve33.

In the present embodiment, the blowby gas introduced into the inlet port33bof the PCV valve33is mixed with the outside air introduced through the outside-air passage36which is opened and closed by the open-close valve38. Accordingly, when the open-close valve38is opened, allowing the outside air to be mixed into the blowby gas introduced into the inlet port33bof the PCV valve33, thereby diluting the blowby gas allowed to flow from the PCV valve33to the intake passage21via the returning passage32. This makes it possible to prevent the air-fuel ratio from fluctuating to an over-rich side by the blowby gas returned to the combustion chamber2and hence avoid disorder of the air-fuel ratio control.

Especially, in the present embodiment, the ECU60is arranged to specify the idle state in which the blowby gas tends to largely affect the air-fuel ratio of the engine1, and open the open-close valve38when the operating state of the engine1detected by the sensors61to66comes to the idle state. Thus, during the idle state in which the blowby gas adversely affects the air-fuel ratio, the blowby gas can be diluted by the outside air. This makes it possible to prevent fluctuation of air-fuel ratio due to the blowby gas according to the operating state of the engine1, particularly, during the idle state.

FIGS. 4A to 4Care graphs showing changes with time of the air-fuel ratio correction amount, water temperature and oil temperature, and engine rotation speed of the engine1which is started at “−10° C.” and remains in the idle state. InFIG. 4A, a solid line represents changes in the air-fuel ratio correction value in the present embodiment and a broken line represents changes in the air-fuel ratio correction value in the prior art where the outside-air passage36and the open-close valve38are not mounted. As is found from this graph, in the case of the present embodiment, when the engine1comes to the idle state after startup, the open-close valve38is opened, causing mixture of the outside air into the blowby gas introduced into the PCV valve33. Accordingly, the fuel constituent concentration of the blowby gas is reduced and kept at that level. As shown inFIG. 4A, therefore, the air-fuel ratio correction amount varies in a range of “−10 to −20” relatively close to “0”. This shows that the influence of the blowby gas on the air-fuel ratio is restrained. As shown inFIGS. 4B and 4C, it is also found that the water temperature (cooling water temperature THW), oil temperature THO, intake pressure, and engine rotation speed NE vary relatively stably without particularly sharp change. In the prior art in which no outside air is mixed into the blowby gas, on the other hand, it is found as indicated by the broken line inFIG. 4Athat the air-fuel ratio correction amount gradually goes away from “0” and finally reaches “−40” which is an abnormal level (MIL lighting-up level). This graph reveals that the blowby gas returning device of the present embodiment is effective in the air-fuel ratio control.

In the present embodiment, furthermore, the oil separator31is provided for trapping oil such as lubricant from the blowby gas before being introduced into the PCV valve33. The oil is thus trapped from the blowby gas by the oil separator31before the blowby gas is introduced into the PCV valve33, so that unnecessary oil is unlikely to flow in the PCV valve33. This makes it possible to prevent the oil from sticking to the valve seat46and the valve element47and avoid a stuck state of the valve element47, hence prevent malfunction of the PCV valve33.

In the present embodiment, the scavenging passage34and the vent hole35are provided for introducing outside air into the crank chamber7in order to scavenge the blowby gas from the crank chamber7. Accordingly, the blowby gas is scavenged out of the crank chamber7by the outside air introduced into the crank chamber7. The blowby gas leaking from the combustion chamber2to the crank chamber7at that time is also diluted by the outside air for scavenging. In this regard, the effect of preventing fluctuation of the air-fuel ratio due to the blowby gas can be enhanced.

In the direct injection engine1of the present embodiment, the fuel is directly injected from the injector25into the combustion chamber2. Thus, unburned fuel droplets may flow down along the wall surface of the cylinder bore4and into the crank chamber7, and mix into the lubricant in the oil pan6. The present embodiment is therefore advantageous in achieving the above operations and effects related to the blowby gas, particularly, in the direct injection engine1.

Second Embodiment

Next, a second embodiment embodying an engine system embodying a blowby gas returning device of the present invention will now be given referring to the accompanying drawings.

In the second and subsequent embodiments explained below, identical components or parts to those in the first embodiment are given the same reference signs as in the first embodiment. The following explanation is made with a focus on differences from the first embodiment.

The second embodiment differs from the first embodiment in the details of the blowby gas returning control to be executed by the ECU60.FIG. 5is a flowchart showing the details of the blowby gas returning control. The ECU60executes this control after the start of the engine1.

Specifically, at step200, the ECU60reads the air-fuel ratio calculated from the oxygen concentration Ox detected by the oxygen sensor66. The ECU60determines at step210whether or not the read air-fuel ratio is shifting to rich side. This determination is made to judge whether or not the air-fuel ratio of the engine1is becoming rich due to the blowby gas.

If an affirmative result is obtained at step210, the ECU60opens the open-close valve38at step220and advances the process to step200. If a negative result is obtained at step210, on the other hand, the ECU60closes the open-close valve38at step230and advances the process to step200. In this blowby gas returning control, specifically, the open-close valve38is opened when the air-fuel ratio of the engine1is actually shifting to the rich side due to the blowby gas, thereby mixing the outside air supplied through the outside-air passage36into the blowby gas introduced into the PCV valve33.

According to the second embodiment, as explained above, the ECU60opens the open-close valve38based on a detection result of the oxygen sensor66showing that the operating state of the engine1corresponds to the air-fuel ratio that is shifting to the rich side. This opening of the open-close valve38causes the blowby gas to be diluted by the outside air, thereby preventing the air-fuel ratio from becoming rich. During operation of the engine1, particularly, when the air-fuel ratio is shifting to the rich side, it is possible to prevent the air-fuel ratio from fluctuating to an over-rich side due to the blowby gas returned to the combustion chamber2, and hence avoid disorder of the air-fuel ratio control. The other operations and effects in the present embodiment are equal to those in the first embodiment.

Third Embodiment

Next, a third embodiment of an engine system embodying a blowby gas returning device of the present invention will now be given referring to the accompanying drawings.

The third embodiment differs from the first and second embodiments in the details of the blowby gas returning control to be executed by the60.FIG. 6is a flowchart showing the details of the blowby gas returning control. The ECU60executes this control after the start of the engine1.

Specifically, at step300, the ECU60reads the oil temperature THO detected by the oil temperature sensor65. The ECU60determines at step310whether or not the read oil temperature THO is higher than a predetermined value T1(e.g. “−40° C.”). This determination is made to check that the blowby gas mixed in the lubricant in the oil pan6begins to vaporize when the oil temperature THO exceeds the predetermined value T1, leading to an increase in fuel constituent concentration of the blowby gas in the crank chamber7.

If a negative result is obtained at step310, the ECU60closes the open-close valve38at step340. If an affirmative result is obtained at step310, on the other hand, the ECU60opens the open-close valve38at step320. At step330, the ECU60successively determines whether or not a predetermined time elapses from the opening of the open-close valve38. This determination is conducted because the opening of the open-close valve38for a predetermined time allows the outside air to be mixed into the blowby gas, thereby sufficiently reducing the fuel constituent concentration. Until the predetermined time elapses at step330, the ECU60continuously holds the open-close valve38in an open state at step320. When the predetermined time elapses at step330, the ECU60closes the open-close valve38at step340.

In other words, this blowby gas returning control is configured to open the open-close valve38for the predetermined time when the oil temperature THO in the oil pan6exceeds the predetermined value T1during operation of the engine1, thereby mixing the outside air supplied through the outside-air passage36into the blowby gas introduced into the PCV valve33.

In the present embodiment, as explained above, when the oil temperature THO detected by the oil temperature sensor65exceeds the predetermined vale, the ECU60opens the open-close valve38only for the predetermined time to admit outside air into the PCV valve33. This outside air dilutes the blowby gas, preventing the air-fuel ratio of the engine1from becoming rich. Accordingly, during operation of the engine1, particularly, in an operating state that causes an increase in the oil temperature THO, it is possible to prevent the air-fuel ratio from fluctuating to an over-rich side due to the blowby gas, hence avoid disorder of the air-fuel ratio control. The other operations and effects in the present embodiment are equal to those in the first embodiment.

The present invention is not limited to the aforementioned embodiments and may be embodied in other specific forms without departing from the essential characteristics thereof.

In each of the above embodiments, inFIG. 1, the inlet port of the outside-air passage36is connected to the scavenging passage34through the three-way valve37. As an alternate, the inlet port of this outside-air passage36may be opened directly into the atmosphere or connected to the air cleaner22.

In each of the above embodiments, the mixing chamber42bformed in the adopter42constituting the PCV valve33and the valve unit41is designed to be hollow, but an oil filter or the like may be set in the mixing chamber42bto provide an oil trapping function. In this case, residual oil in the blowby gas can efficiently be trapped and removed by the oil filter or the like.

In each of the above embodiments, the open-close valve38of the outside-air passage36may be controlled to open at a decelerated operation of the engine1(at an interruption of fuel supply or at a rapid deceleration). In this case, the open-close valve38is opened when it is unnecessary to deal with a large amount of blowby gas to dilute the blowby gas. Thus, an amount of oil mist contained in the blowby gas and carried away therewith can be reduced.