Ventilation system and method for supercharge engine

Abstract

In ventilation system and method for a supercharge engine, in a middle load driving region of the engine in which the boost pressure of position of an intake air passage located at the downstream side with respect to a throttle valve is positive and is lower than a set pressure (P 1 ), with importance placed on the ventilation of a crank chamber, a relatively large quantity of fresh air is introduced into the crank chamber and, on the other hand, in a high load driving region in which the boost pressure is equal to or higher than the set pressure (P 1 ), with importance placed on the engine output, the large quantity of fresh air is supplied to the engine so that, while the deterioration of engine oil within the crank chamber suppressed, the output reduction of the engine in the high load driving region can be suppressed.

1 . A ventilation system for a supercharge engine, comprising:
 a blowby gas reduction passage provided for communicating position of an intake air passage of the engine which is located at a downstream side with respect to a throttle valve with a crank chamber of the engine;   a fresh air introduction passage provided for communicating position of the intake air passage which is located at an upstream side with respect to the throttle valve and the crank chamber;   a PCV valve provided in the blowby gas reduction passage for controlling a flow quantity of blowby gas directed toward the intake air passage side in a case where a boost pressure at position of intake air passage located at downstream side with respect to the throttle valve indicates negative; and   a fresh air flow quantity control section configured to operatively introduce fresh air into the crank chamber from position of intake air passage which is located at the downstream side with respect to the throttle valve in a case where the boost pressure at position of the intake air passage which is located at the downstream side with respect to the throttle valve is positive,   
       wherein the fresh air flow quantity control section is configured to introduce fresh air into the crank chamber, in a middle load driving region in which the boost pressure at position of the intake air passage which is located at the downstream side with respect to the throttle valve is positive and the boost pressure is lower than a set pressure, and, in a high load driving region in which the boost pressure at part of the intake air passage which is located at the downstream side with respect to the throttle valve is equal to or higher than the set pressure, is configured to stop an introduction of fresh air from position of the intake air passage which is located at a downstream side with respect to the throttle valve or is configured to make a flow quantity of introduced fresh air at least smaller than a maximum flow quantity in the middle load driving region. 
     
     
         2 . The ventilation system for the supercharge engine as claimed in  claim 1 , wherein a variable orifice functioning as the fresh air flow quantity control section is installed in the blowby gas reduction passage and, in the high load driving region, a flow passage cross sectional area of the variable orifice which functions as the fresh air flow quantity control section is at least made smaller than the flow passage cross sectional area in the middle load driving region. 
     
     
         3 . The ventilation system for the supercharge engine as claimed in  claim 2 , wherein the PCV valve includes a variable orifice functioning as the fresh air flow quantity control section apart from another variable orifice for a blowby gas flow quantity control that the PCV valve naturally has. 
     
     
         4 . The engine ventilation system as claimed in  claim 1 , wherein a variable orifice functioning as the fresh air flow quantity control section is juxtaposed to the PCV valve and, in the high load driving region, a flow passage cross sectional area of the variable orifice is made smaller than at least the flow passage cross sectional area in the middle load driving region. 
     
     
         5 . The engine ventilation system as claimed in  claim 2 , wherein the variable orifice functioning as the fresh air flow quantity control section is closed in the high load driving region. 
     
     
         6 . The ventilation system for the supercharge engine as claimed in  claim 1 , wherein a flow quantity of fresh air from position of the intake air passage which is located at the downstream side with respect to the throttle valve to the crank chamber, in the middle load driving region (A 2 ), is constant and, in the high load driving region (A 3 ), the flow quantity of fresh air from position of the intake air passage which is located at the downstream side with respect to the throttle valve is made equal to the flow quantity in the middle load driving region. 
     
     
         7 . A ventilation system for a supercharge engine, comprising:
 blowby gas reduction passage means for communicating position of an intake air passage of the engine which is located at a downstream side with respect to a throttle valve with a crank chamber of the engine;   fresh air introduction passage means for communicating position of the intake air passage which is located at an upstream side with respect to the throttle valve and the crank chamber;   PCV valve means provided in the blowby gas reduction passage means for controlling a flow quantity of blowby gas directed toward the intake air passage side in a case where a boost pressure at position of intake air passage located at downstream side with respect to the throttle valve indicates negative; and   fresh air flow quantity control means for operatively introducing fresh air into the crank chamber from position of intake air passage which is located at the downstream side with respect to the throttle valve in a case where the boost pressure at position of the intake air passage which is located at the downstream side with respect to the throttle valve is positive, wherein the fresh air flow quantity control means introduces fresh air into the crank chamber, in a middle load driving region in which the boost pressure at position of the intake air passage which is located at the downstream side with respect to the throttle valve is positive and the boost pressure is lower than a set pressure, and, in a high load driving region in which the boost pressure at part of the intake air passage which is located at the downstream side with respect to the throttle valve is equal to or higher than the set pressure, stops an introduction of fresh air from position of the intake air passage which is located at a downstream side with respect to the throttle valve or makes a flow quantity of introduced fresh air at least smaller than a maximum flow quantity in the middle load driving region.   
     
     
         8 . A ventilation method for a supercharge engine, comprising:
 providing a blowby gas reduction passage for communicating position of an intake air passage of the engine which is located at a downstream side with respect to a throttle valve with a crank chamber of the engine;   providing a fresh air introduction passage provided for communicating position of the intake air passage which is located at an upstream side with respect to the throttle valve and the crank chamber;   providing a PCV valve in the blowby gas reduction passage for controlling a flow quantity of blowby gas directed toward the intake air passage side in a case where a boost pressure at position of intake air passage located at downstream side with respect to the throttle valve indicates negative; and   providing fresh air flow quantity control means for operatively introducing fresh air into the crank chamber from position of intake air passage which is located at the downstream side with respect to the throttle valve in a case where the boost pressure at position of the intake air passage which is located at the downstream side with respect to the throttle valve is positive, wherein fresh air is introduced into the crank chamber through fresh air flow quantity control means, in a middle load driving region in which the boost pressure at position of the intake air passage which is located at the downstream side with respect to the throttle valve is positive and the boost pressure is lower than a set pressure, and, in a high load driving region in which the boost pressure at part of the intake air passage which is located at the downstream side with respect to the throttle valve is equal to or higher than the set pressure, an introduction of fresh air from position of the intake air passage which is located at a downstream side with respect to the throttle valve is stopped or a flow quantity of introduced fresh air is at least made smaller than a maximum flow quantity in the middle load driving region.