Patent Publication Number: US-6338329-B2

Title: Blow-by gas passage abnormality detecting system for internal combustion engines

Description:
This is a Divisional of Application Ser. No. 09/593,818, filed Jun. 15, 2000, which was a Divisional of Application Ser. No. 08/988,608 filed Dec. 11,1997, now U.S. Pat. No. 6,098,603, the entire contents of each of which is hereby incorporated by reference in this application. 
    
    
     CROSS REFERENCE TO RELATED APPLICATION 
     This application is related to and incorporates herein by reference Japanese Patent Application No. 8-343013 filed on Dec. 24, 1996 and No. 8-344776 filed on Dec. 25, 1996. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a blow-by gas passage abnormality detecting system for detecting an abnormality in a blow-by gas passage for recirculating the blow-by gas, as will leak from the combustion chamber of an internal combustion engine to a crankcase, to the intake passage. 
     2. Related Art 
     A blow-by gas recirculating system for preventing blow-by gas from being released into the atmosphere is known in which a blow-by gas passage for recirculating the blow-by gas, as will leak from the combustion chamber of an internal combustion engine to the crankcase, to the intake passage is provided. 
     When an abnormality such as breakage in or detachment of the blow-by gas passage occurs, the blow-by gas may be released, contrary to the desired prevention of environmental pollution. 
     SUMMARY OF THE INVENTION 
     Thus, the present invention has an object to provide a blow-by gas passage abnormality detecting system for an internal combustion engine, as can minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine, by detecting an abnormality in the blow-by gas passage properly. 
     In a blow-by gas passage abnormality detecting system for an internal combustion engine, according to a first aspect of the invention, the abnormality of the blow-by gas passage for returning the blow-by gas in the internal combustion engine to the side of the intake passage is decided on the basis of the amount of load when the running state of the internal combustion engine is idle. By thus grasping the load amount at the idling time of the internal combustion engine, the abnormality of the blow-by gas passage can be properly detected to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine. 
     In a blow-by gas passage abnormality detecting system of the internal combustion engine, according to the second aspect of the invention, the abnormality in the blow-by gas passage is decided on the basis of the pressure in the blow-by gas passage. By the simple and inexpensive construction for detecting the pressure in the blow-by gas passage, the abnormality of the blow-by gas passage can be properly detected to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read with reference to the accompanying drawings. In the drawings: 
     FIG. 1 is a schematic diagram showing the entire construction of a blow-by gas passage abnormality detecting system for an internal combustion engine according to a first embodiment of the invention; 
     FIG. 2 is a flow chart showing a procedure for processing an abnormality decision in an ECU used in the blow-by gas passage abnormality detecting system according to the first embodiment; 
     FIG. 3 is a graph showing a change in a decision value used in the routine of FIG. 2 against an engine RPM in the first embodiment; 
     FIG. 4 is a flow chart showing a procedure for processing after an abnormality decision in the ECU used in the blow-by gas passage abnormality detecting system according to the first to third embodiments of the present invention; 
     FIG. 5 is a flow chart showing a procedure for processing an abnormality decision in the ECU used in the blow-by gas passage abnormality detecting system according to the second embodiment of the present invention; 
     FIG. 6 is a graph showing a change in a decision value used in the routine of FIG. 5 against an engine RPM in the second embodiment; 
     FIG. 7 is a flow chart showing a procedure for processing an abnormality decision in the ECU used in the blow-by gas passage abnormality detecting system according to the third embodiment of the invention; 
     FIG. 8 is a graph showing a change in a decision value of the routine of FIG. 7 against an engine RPM in the third embodiment; 
     FIG. 9 is a flow chart showing a procedure for deciding the normality/abnormality of an intake line device or the like to be added to the blow-by gas passage abnormality detecting systems of an internal combustion engine according to the first to third embodiments of the invention; 
     FIG. 10A is a flow chart showing a procedure for deciding the normality/abnormality of a combustion system device to be added to the blow-by gas passage abnormality detecting systems of an internal combustion engine according to the first to third embodiments of the invention; 
     FIG. 10B is a flow chart showing a procedure for allowing/inhibiting diagnoses at an electric load fluctuation to be added to the blow-by gas passage abnormality detecting systems of an internal combustion engine according to the first to third embodiments of the invention; 
     FIG. 11 is a schematic diagram showing the entire construction of a blow-by gas passage abnormality detecting system for an internal combustion engine according to the fourth embodiment of the invention; 
     FIG. 12 is a flow chart showing a procedure for processing an abnormality decision in an ECU used in the blow-by gas passage abnormality detecting system according to the fourth embodiment of the invention; 
     FIG. 13 is an abnormality decision table showing a decision value of a negative pressure against a blow-by gas pressure level of FIG. 12; 
     FIG. 14 is a graph showing changes in the decision value of the negative pressure of FIG. 13 against the load fluctuation of the internal combustion engine in the fourth embodiment; 
     FIG. 15 is a schematic diagram showing a modification of an arrangement construction of a gas pressure sensor, as used in the blow-by gas passage abnormality detecting system of an internal combustion engine according to the fourth embodiment of the invention, with respect to a blow-by gas passage; 
     FIG. 16 is a flow chart showing a processing procedure after an abnormality decision in an ECU used in the blow-by gas passage abnormality detecting system according to the fourth embodiment of the invention; 
     FIG. 17 is a flow chart showing a procedure for processing an abnormality decision in an ECU used in the blow-by gas passage abnormality detecting system according to the fifth embodiment of the invention; 
     FIG. 18 is an abnormality decision table showing a decision value against the negative pressure difference of FIG. 17 in the fifth embodiment; and 
     FIG. 19 is a flow chart showing a procedure for deciding the normality/abnormality of an intake line device or the like to be added to the blow-by gas passage abnormality detecting systems of an internal combustion engine according to the fourth and fifth embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be described in detail with reference to its various embodiments. 
     &lt;Embodiment 1&gt; 
     In an intake system of an internal combustion engine  1 , as shown in FIG. 1, the air, as introduced from an air cleaner  11  at an upstream side, flows through an air flow meter  33 , as arranged in an intake passage  12 , a throttle valve  13 , as arranged in the intake passage  12 , and a surge tank  14  at a downstream side and is mixed with fuel, as injected into an intake manifold  15  by an injector  16 , until the mixture is introduced from an intake port  17  through an intake valve  18  into a combustion chamber  21  of each engine cylinder. Midway of a bypass passage  19  connected bypassing the throttle valve  13 , on the other hand, there is arranged an ISC (Idle Speed Control) valve  20  for controlling the engine RPM (rotational speed) at an idle time to a predetermined idle RPM. In an exhaust system of the internal combustion engine  1 , the exhaust gas from the combustion chamber  21  is discharged from an exhaust valve  22  through an exhaust port  23  and an exhaust passage  24  by the notshown three-way catalytic converter, until it is discharged into the atmosphere. Here, the air flow meter  33  detects the flow amount of intake air passing through the intake passage  12 . Upstream of the catalytic converter in the exhaust passage  24 , on the other hand, there is arranged an oxygen concentration sensor  25  for detecting the oxygen (O 2 ) concentration in the exhaust gas. 
     On the other hand, the blow-by gas, as will leak out of the combustion chamber  21  through the clearance between a piston  2  and a cylinder wall  3  into a crankcase  4 , is introduced from the upper portion of the crankcase  4  via a communication passage  5  into a head cover  6  of the internal combustion engine  1 . The upper portion of the head cover  6  is connected through a communication passage  26  to the intake passage  12  and through a blow-by gas passage  27  to the surge tank  14  downstream of the throttle valve  13 . Midway of the blow-by gas passage  27 , there is arranged a PCV (Positive Crankcase Ventilation) valve  28  acting as a flow rate control valve having the well-known construction and driven pneumatically by the negative pressure (or the differential pressure). 
     This PCV valve  28  is so opened/closed by the negative pressure in the surge tank  14  that its air passing area is reduced, when the negative pressure as the intake pressure is high as at the idle time, to reduce the blow-by gas flow from the head cover  6  into the surge tank  14 , and that its air passing area is enlarged, when the negative pressure as the intake pressure is enlarged at an acceleration time to increase the blow-by gas flow from the head cover  6  into the surge tank  14 . 
     That is, as the inside of the surge tank  14  takes a negative pressure, the inside of the head cover  6  is ventilated with the fresh air which is introduced out of the intake passage  12  via the communication passage  26 , so that the blow-by gas in the head cover  6  is returned, while its flow rate being regulated by the PCV valve  28 , via the blow-by gas passage  27  into the surge tank  14 . 
     An ECU (Electronic Control Unit)  40  is constructed as a logical operation circuit including: the not-shown well-known central processing unit CPU; a ROM storing a control program; a RAM for storing various data; a B/U (backup) RAM; an input/output circuit; and bus lines for connecting the foregoing components. To this ECU  40 , there are individually inputted a signal on the oxygen concentration in the exhaust passage  24  from the oxygen concentration sensor  25 , a signal on the intake air flow to pass through the intake passage  12  from the air flow meter  33 , and so on. From the ECU  40 , there are individually outputted drive signals to the injector  16  arranged in the intake manifold  15 , the ISC valve  20  arranged in the bypass passage  19 , and the like. 
     The ECU  40 , more particularly the CPU, is programmed to perform processes of FIG. 2 showing a procedure for processing an abnormality decision in the ECU  40  used in the blow-by gas passage abnormality detecting system. 
     In FIG. 2, at step S 101 , it is decided whether or not the running state of the internal combustion engine  1  is idle. When the decision of step S 101  is NO indication that the running state is other than the idle time, the present routine is ended without any operation. On the other hand, when the decision of step S 101  is YES, that is, when the throttle opening of the throttle valve  13  is less than a predetermined value to indicate that the running state is idle, the routine advances to step S 102 , at which it is decided whether or not the prevailing ISC opening of the ISC valve  20  is less than a decision value or reference A. This decision value A is set to the ISC opening for the idle time, as cannot occur if the blow-by gas passage  27  is normal. 
     The setting of this decision value A is based on the fact that the control duty ratio of the ISC valve  20  is ordinarily 20 to 30%, for example, when the blow-by gas passage  27  is normal, whereas an unlikely excess intake supply is made from the side of the blow-by gas passage  27 , when this passage  27  causes the leakage or disengagement, so that the control duty ratio of the ISC valve  20  drops as low as 0%. Here, the decision value A may be so set at each engine RPM as to rise according to the rise in the engine RPM, as illustrated by the graph of FIG.  3 . 
     When the decision of step S 102  is NO indicating that the ISC opening is no less than the decision value A, the routine advances to step S 103 , at which it is ended by determining the normality of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . On the other hand, when the decision of step S 102  is YES indicating that the ISC opening is less than the decision value A, it is determined that the blow-by gas passage  27  has some leakage or disengagement, the routine advances to step S 104 , at which an abnormality is determined in the leakage or disengagement of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . Then, the routine advances to step S 105 , at which it is ended by executing an after-abnormality processing. Thus, it is possible to properly detect the abnormality (i.e., the leakage or the disengagement) of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . 
     Step S 105 , that is a procedure for processing after an abnormality decision in the ECU  40  used in the blow-by gas passage abnormality detecting system of an internal combustion engine according to first embodiment is shown in FIG.  4 . Here, when it is decided that the blow-by gas passage  27  has the abnormality (i.e., the leakage or the disengagement), the reliabilities in the various detection steps and the control steps, as follows, cannot be kept so that these steps are inhibited. 
     In FIG. 4, at first step S 201 , the trouble detection of the air flow meter  33  for detecting the intake flow in the intake passage  12  is inhibited; at next step S 202 , the trouble detection of the ISC valve  20  is inhibited; at next step S 203 , the trouble detection of the ISC system; at next step S 204 , the trouble detection of an EGR (Exhaust Gas Recirculation) system (although not shown in FIG. 1) is inhibited; and at next step S 205 , the trouble detection of the fuel system (such as a fuel injection time control system) is inhibited. 
     The routine advances to step S 206 , at which a misfire detection is inhibited; at next step S 207 , the F/B (i.e., feedback) control of the idle RPM in the ISC system is inhibited (or to lower the gain); at next step S 208 , an A/F (i.e., air/fuel ratio) learning control is inhibited (or to inhibit the main A/F or to lower the gain); at next step S 209 , the EGR control is inhibited (or to lower the gain); and at next step S 210 , the purge control of an evaporated fuel is inhibited (or to lower the gain), and the present routine is ended. 
     Thus, the blow-by gas passage abnormality detecting system of the present embodiment performs deciding the abnormality of the blow-by gas passage  27  to return the blow-by gas, which is produced in the internal combustion engine  1  on the basis of the load amount when the running state of the internal combustion engine  1  is idle, to the side of the intake passage  12  of the internal combustion engine  1 . By taking into consideration the load amount when the running state of the internal combustion engine  1  is idle, therefore, the abnormality of the blow-by gas passage  27  can be properly detected to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine  1 . 
     Moreover, the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment is enabled, by the simple and inexpensive construction for measuring the load amount by using the intake flow amount, to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine  1 . 
     Moreover, the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment measures the ISC opening as the control amount of the ISC valve  20  for controlling the engine RPM at the idle time of the internal combustion engine  1 , by the intake air amount, and decides that the blow-by gas passage  27  has the leakage or disengagement, by the abnormality decision achieved by the ECU  40 , when the ISC opening is smaller than the decision value A or the predetermined value. As a result, it can be decided from the more intake flow coming from the others than the ordinary one that the control of the ISC value  20  at the idle time of the internal combustion engine  1 , that is, the ISC opening is smaller than the predetermined value, and it can be deemed that the leakage or disengagement occurs in the blow-by gas passage  27 . By thus taking into consideration the ISC opening of the ISC valve  20  at the idle time, the abnormality of the blow-by gas passage  27  can be properly detected to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine  1 . 
     Moreover, the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment sets the decision value A corresponding to the ISC opening as the control amount for each engine RPM. As a result, the abnormality decision of the blow-by gas passage  27  is accurately made even if the engine RPM is changed by the load fluctuations. 
     In the present embodiment, moreover, whether or not the abnormality exists is decided at the idle time. If the engine RPM of the internal combustion engine  1  is added to the operational condition so that the decision on whether or not the abnormality exists may be made at an idle time nor more than a predetermined RPM (e.g., 1,000 RPM), an erroneous determination is prevented in a transient state such as at a deceleration to improve the accuracy of the abnormality decision. 
     &lt;Embodiment 2&gt; 
     In the second embodiment shown in FIG. 5, the entire construction of the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment is identical to that of the schematic diagram of FIG. 1 in the aforementioned first embodiment. 
     In FIG. 5, at step S 301 , it is decided whether or not the running state of the internal combustion engine  1  is idle. When the decision of step S 301  is NO indicating that the running state is other than the idle time, the present routine is ended without any operation. On the other hand, when the decision of step S 301  is YES, that is, when the throttle opening of the throttle valve  13  is less than a predetermined value to indicate that the running state is idle, the routine advances to step S 302 , at which it is decided whether or not the prevailing A/F (air/fuel ratio) F/B (feedback) amount on the basis of the output coming from the oxygen concentration sensor  25  are more than a decision value B. This decision value B is set to the A/F F/B amount for the idle time, as cannot occur if the blow-by gas passage  27  is normal. 
     The setting of this decision value B is based on the fact that the A/F F/B amount is not highly fluctuated, when the blow-by gas passage  27  is normal, whereas an unlikely excess intake supply is made from the side of the blow-by gas passage  27 , when this passage  27  causes the leakage or disengagement, so that the A/F F/B amount is highly fluctuated. Here, the decision value B may be so set at each engine RPM as to rise according to the rise in the engine RPM, as illustrated in the graph of FIG.  6 . In the abnormality decision of the present embodiment, moreover, the A/F F/B amount is compared with the decision value B, but similar effects can be expected even if either the learned A/F F/B value or the sum of the A/F F/B value and the learned A/F F/B value are compared with the decision value. 
     When the decision of step S 302  is NO indicating that the A/F F/B amount is no more than the decision value B, the routine advances to step S 303 , at which it is ended by determining the normality in the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . On the other hand, when the decision of step S 302  is YES indicating that the A/F F/B amount is more than the decision value B, it is deemed that the blow-by gas passage  27  has the leakage or disengagement, the routine advances to step S 304 , at which an abnormality is determined in the leakage or disengagement of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . Then, the routine advances to step S 305 , at which it is ended by executing an after-processing of the abnormality decision similar to that of FIG.  4 . Thus, it is possible to properly detect the abnormality (i.e., the leakage or the disengagement) of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . 
     Thus, the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment measures the A/F F/B amount of the internal combustion engine  1  and decides that the blow-by gas passage  27  has the leakage or disengagement, by the abnormality decision achieved by the ECU  40 , when the A/F F/B amount is higher than the decision value B or the predetermined value. As a result, it can be decided from the more intake flow coming from the others than the ordinary one that the A/F F/B amount of the internal combustion engine  1  in the ECU  40  for achieving the abnormality decision is higher than a predetermined value, and it can be deemed that the leakage or disengagement occurs in the blow-by gas passage  27 . By thus taking into consideration the A/F F/B amount of the internal combustion engine  1 , the abnormality of the blow-by gas passage  27  can be properly detected to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine  1 . 
     Moreover, the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment sets the decision value B corresponding to the A/F F/B for each engine RPM. As a result, the abnormality decision of the blow-by gas passage  27  is accurately made even if the engine RPM is changed by the load fluctuations. 
     &lt;Embodiment 3&gt; 
     In the third embodiment shown in FIG. 7, the entire construction of the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment is modified from the schematic diagram of FIG. 1 of the first embodiment by arranging additionally an intake pressure sensor for detecting the intake pressure in the surge tank leading from the intake passage  12 . 
     In FIG. 7, at step S 401 , it is decided whether or not the running state of the internal combustion engine  1  is idle. When the decision of step S 401  is NO indicating that the running state is other than the idle time, the present routine is ended without any operation. On the other hand, when the decision of step S 401  is YES, that is, when the throttle opening of the throttle valve  13  is less than a predetermined value to indicate that the running state is idle, the routine advances to step S 402 , at which it is decided whether or not the prevailing intake pressure detected by the intake pressure sensor is more than a decision value C. This decision value C is set to the intake pressure for the idle time, as cannot occur if the blow-by gas passage  27  is normal. 
     The setting of this decision value C is based on the fact that the intake pressure is within a predetermined negative pressure range, when the blow-by gas passage  27  is normal, whereas a positive pressure near the atmospheric level from the side of the blow-by gas passage  27  is supplied as the suction amount, when this passage  27  causes the leakage or disengagement, so that the intake pressure highly exceeds a predetermined negative pressure range. Here, the decision value C may be so set at each engine RPM as to rise according to the rise in the engine RPM, as illustrated in the graph of FIG.  8 . 
     When the decision of step  402  is NO indicating that the intake pressure is no more than the decision value C, the routine advances to step  403 , at which it is ended by determining the normality in the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . On the other hand, when the decision of step  402  is YES to indicate that the intake pressure is more than the decision value C, it is deemed that the blow-by gas passage  27  has the leakage or disengagement, the routine advances to step  404 , at which an abnormality is determined in the leakage or disengagement of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . Then, the routine advances to step  405 , at which it is ended by executing an after-processing of the abnormality decision similar to that of FIG.  4 . Thus, it is possible to properly detect the abnormality (i.e., the leakage or the disengagement) of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . 
     Thus, the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment decides that the blow-by gas passage  27  causes the leakage or disengagement, by the abnormality decision achieved by the ECU  40 , when the load amount represented by the intake pressure detected by the pressure sensor is higher than the decision value C or the predetermined value. By the simple and inexpensive construction for detecting the intake pressure corresponding to the load amount by using the intake pressure sensor, it can be decided that the intake pressure is influenced by a pressure (e.g., the atmospheric pressure) coming from others if it is higher than a predetermined level, and it can be deemed that the leakage or disengagement occurs in the blow-by gas passage  27 . By thus taking into consideration the intake pressure corresponding to the load amount of the internal combustion engine  1 , the abnormality of the blow-by gas passage  27  can be properly detected to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine  1 . 
     Moreover, the blow-by gas passage abnormality detecting system for an internal combustion engine according to the present embodiment sets the decision value C corresponding to the intake pressure for each engine RPM. As a result, the abnormality decision of the blow-by gas passage  27  is accurately made even if the engine RPM is changed by the load fluctuations. Moreover, the accuracy of the abnormality decision is further improved by correcting the decision value C with the atmospheric pressure. 
     In the above first to third embodiments, before performing the abnormality decision of the blow-by gas passage  27 , a normality/abnormality deciding routine of the intake system device or the like can be added, as shown in FIG.  9 . Specifically, the decisions of the normality/abnormality are executed on the air flow meter  33  at step S 501 , on the ISC valve at step S 502 , on the (not-shown) throttle sensor for detecting the throttle opening of the throttle valve  13  at step S 503 , on the (not-shown) atmospheric sensor for detecting the atmospheric pressure at step S 504 . When all these devices are normal, the diagnosis for executing the abnormality decision of the blow-by gas passage  27  is allowed at step S 505 . When at least one device is abnormal, the diagnosis is inhibited at step S 506 . Then, the present routine is ended. This makes it possible to decide the abnormality of the blow-by gas passage  27  highly accurately. 
     Moreover, the foregoing embodiments are constructed by premising the internal combustion engine (i.e., the so-called “L-J engine”) in which the fuel injection is controlled by measuring the intake amount of air flow into the intake passage and which is equipped with the air flow meter  33 . The application of the invention should not be limited thereto but may employ the intake pressure, as detected in the (not-shown) intake pressure sensor, for the abnormality decision of the blow-by gas passage  27  in the internal combustion engine (i.e., the “D-J engine”) in which the fuel injection is controlled by measuring the pressure in the intake passage. 
     In the foregoing embodiments, moreover, there can be added a normality/abnormality deciding routine of the combustion system device or the like, as shown in FIG.  10 A. The normality/abnormality decisions are executed on the injector  16  at step S 601 , on an (not-shown) ignition coil at step S 602 , and on a (not-shown) pressure regulator at step S 603 . When all these devices are normal, the diagnosis for executing the abnormality decision of the blow-by gas passage  27  is allowed at step S 604 . When at least one device is abnormal, the diagnosis is inhibited at step S 605 . Then, the present routine is ended. This makes it possible to improve the abnormality decision of the blow-by gas passage  27 . 
     Further, in the foregoing embodiments, there can be added a diagnosis allowing/inhibiting routine at an electric load fluctuating time, as shown in FIG.  10 B. Specifically, when it is decided at step S 701  that the electric load is fluctuated from ON to OFF or from OFF to ON, a timer T is set with an initial valve at step S 702 . When no electric load fluctuation is at step S 701 , the value of timer T is decremented at step S 703 . It is decided at step S 704  whether or not the timer T is decremented to zero. When the timer value is zero, the diagnosis to execute the abnormality decision of the blow-by gas passage  27  is allowed at step S 705 . When the timer value is not zero so that a predetermined time has not elapsed from the electric load fluctuation, the diagnosis is inhibited at step S 706 . Then, the present routine is ended. This makes it possible to improve the abnormality decision of the blow-by gas passage  27 . 
     Moreover, the foregoing embodiments employ the PCV valve  28  which is arranged midway of the blow-by gas passage  27  and acts as the flow rate regulating valve to be driven by the negative pressure. It may be an electromagnetically driven valve, the flow rate of which can be controlled from the side of the ECU  40 . In this modification, the decision value in the abnormality decision of the blow-by gas passage  27  may be made variable by the controlled flow rate. 
     Thus, in the blow-by gas passage abnormality detecting system for an internal combustion engine, the abnormality decision of the blow-by gas passage  27  by the ECU  40  is executed when the various devices of the intake system of the internal combustion engine  1  including the air flow meter  33 , the ISC valve  20 , the throttle sensor and the atmospheric sensor are normal. As a result, the abnormality of the blow-by gas passage  27  is properly detected. 
     Moreover, the blow-by gas passage abnormality detecting system for an internal combustion engine executes the abnormality decision of the blow-by gas passage  27  by the ECU  40  when the various devices relating to the combustion of the internal combustion engine  1  including the injector  16 , the ignition coil and the pressure regulator are normal. As a result, the abnormality of the blow-by gas passage  27  is properly detected. 
     &lt;Embodiment 4&gt; 
     In a blow-by gas passage abnormality detecting system for an internal combustion engine according to the fourth embodiment of the invention shown in FIG. 11, in addition to the foregoing embodiments, an intake pressure sensor  31  for detecting the intake pressure in the intake passage  12  downstream of the throttle valve  13  is arranged in the surge tank  14 , and a gas pressure sensor  32  for detecting the blow-by gas pressure is arranged in the blow-by gas passage  27  connecting the PCV valve  28  and the surge tank  14 . These sensors  31  and  32  are also connected to the ECU  40 . 
     The ECU  40  is programmed to perform blow-by gas passage abnormality detecting processing shown in FIG. 12 by the use of an abnormality decision table shown in FIG. 13 which shows decision values X, Y and Z of a negative pressure, as determined in advance by experiments, against a blow-by gas pressure level PBG which is detected by the gas pressure sensor  32  arranged between the PCV valve  28  arranged midway of the blow-by gas passage  27  and the surge tank  14  downstream of the former. 
     In this embodiment, when the blow-by gas passage  27  shown in FIG. 11 clogs at point a (inlet side of the passage  27 ), the inside of the blow-by gas passage  27  takes an intake pressure substantially equal to that in the surge tank  14  so that the blow-by gas pressure level PBG by the gas pressure sensor  32  shifts to the side of a larger negative pressure than at the normal time (i.e., to the side of a larger negative pressure than the decision value X). When the blow-by gas passage  27  leaks at point a (as exemplified by the disengagement of the hose of the passage), the blow-by gas pressure level PBG detected by the gas pressure sensor  32  approaches the atmospheric pressure but slightly the side of the negative pressure (at the side where the negative pressure is smaller than the decision value Y but higher than the decision value Z) because of the pressure loss in the midway PCV valve  28 . When the blow-by gas passage  27  leaks or clogs at point b, the blow-by gas pressure level PBG by the gas pressure sensor  32  is not influenced by the intake pressure in the surge tank  14  so that it takes a substantially atmospheric pressure (at the side where the negative pressure is smaller than the decision value Z). Here, as the negative pressure of the blow-by gas pressure PBG rises in a manner to correspond to the load fluctuation of the internal combustion engine  1 , as shown in the graph of FIG. 14, the decision values x and Y of the negative pressure, as illustrated in FIG. 13, are shifted to the larger side. The parameters of this load fluctuation are exemplified by the engine RPM, the engine coolant temperature, the intake air temperature, the ignition timing and so on of the internal combustion engine  1 . 
     In FIG. 12, it is decided at step S 111  whether or not the running state of the internal combustion engine  1  is idle. When the decision of step S 111  is NO indicating that the running state is not idle, the present routine is ended without any further operation. On the other hand, when the decision of step S 111  is YES indicating that the running state is idle, the routine advances to step S 112 , at which it is decided whether or not the blow-by gas pressure level PBG from the gas pressure sensor  32  is larger than the negative pressure of the decision value X, as illustrated in FIG.  13 . When the decision of step S 112  is NO indicating that the blow-by gas pressure level PBG is smaller than the negative pressure of the decision value X, the routine advances to step S 113 , at which it is decided whether or not the blow-by gas pressure level PBG is smaller than the negative pressure of the decision value Y, as illustrated in FIG.  13 . When the decision of step S 113  is NO indicating that the blow-by gas pressure level PBG is larger than the negative pressure of the decision value Y, that is, when the blow-by gas pressure level PBG is smaller than the negative pressure of the decision value X and larger than the negative pressure of the decision value Y, the routine advances to step S 114 , at which a normality of the blow-by gas passage  27  from the head cover  6  to the surge tank  14  is decided to end the present routine. 
     On the other hand, when the decision of step S 113  is YES indicating that the blow-by gas pressure level PBG is at a smaller side than the negative pressure of the decision value Y, the routine advances to step S 115 , at which it is decided whether or not the blow-by gas pressure level PBG is at a smaller side than the negative pressure of the decision value Z which is set at a smaller side than the negative pressure of the decision value Y, as illustrated in FIG.  13 . When the decision of step S 115  is NO indicating that the blow-by gas pressure level PBG is at a larger side than the negative pressure of the decision value Z, that is, when the blow-by gas pressure level PBG is smaller than the negative pressure of the decision value Y and larger than the negative pressure of the decision value Z, as illustrated in FIG. 13, the routine advances to step S 116 , at which an abnormality of leakage at point a (as should be referred to FIG. 11) of the blow-by gas passage  27  between the PCV valve  28  arranged midway of the blow-by gas passage  27  and the head cover  6  upstream of the former is decided. 
     On the other hand, when the decision of step S 115  is YES indicating that the blow-by gas pressure level PBG is at a smaller side than the negative pressure of the decision value Z, the routine advances to step S 117 , at which an abnormality of clogging or leaking at point b (as should be referred to FIG. 11) of the blow-by gas passage  27  between the PCV valve  28  arranged midway of the blow-by gas passage  27  and the surge tank  14  downstream of the former is decided. On the other hand, when the decision condition of step S 112  is YES indicating that the blow-by gas pressure level PBG is at a larger side than the negative pressure of the decision value X, the routine advances to step S 118 , at which a clogging at point a (as should be referred to FIG. 11) of the blow-by gas passage  27  between the PCV valve  28  arranged midway of the blow-by gas passage  27  and the head cover  6  upstream of the former is decided. When an abnormality is decided at step S 116 , step S 117  or step S 118 , the routine advances to step S 119 , at which the after-processing of the abnormality decision is executed, and the present routine is ended. Thus, it is possible to properly detect the abnormal state (e.g., leakage or clogging) at the individual points of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . 
     In this embodiment, as shown in FIG. 11, the gas pressure sensor  32  for detecting the negative pressure in the blow-by gas passage  27  is arranged between the PCV valve  28  and the surge tank  14  downstream of the former. As modified in FIG. 15, however, the gas pressure sensor  32  can be arranged between the PCV valve  28  and the head cover  6  upstream of the former. In this modification, too, the decision of normality/abnormality may be made in the similar manner as in the fourth embodiment, based upon the negative pressure state detected by the gas pressure sensor  32 . 
     The processing procedure after the abnormality decision of step S 119  of FIG. 12 in the ECU  40  is shown in FIG. 16 which is similar to the after-abnormality processing of the first to third embodiments shown in FIG.  4 . Once it is decided that an abnormality (e.g., leakage or clogging) occurs in the blow-by gas passage  27 , the following various detections and controls are inhibited because the reliabilities will not be maintained. 
     At first step S 211 , there is inhibited the trouble detection of the intake pressure sensor  31  for detecting the intake pressure in the surge tank  14  downstream in the intake passage  12  downstream of the throttle valve  13 . At next step S 212 , the trouble detection of the ISC valve  20  is inhibited. At next step S 213 , the trouble detection of the ISC system is inhibited. At next step S 214 , the trouble detection of the EGR is inhibited. At next step S 215 , the trouble detection of the fuel line (for controlling the fuel injection time or the like) system is inhibited. Next, the routine advances to step S 216 , at which the misfire detection is inhibited. At next step S 217 , the F/B (feedback) control of the idle RPM in the ISC system is inhibited (or to lower its control gain). At next step S 218 , the A/F (air/fuel ratio) learning control is inhibited. At nest step S 219 , the EGR control is inhibited (or to lower its control gain). At next step S 220 , the control of the purge of the evaporated fuel is inhibited (or to lower its control gain). Then, the present routine is ended. 
     Thus, in the blow-by gas passage abnormality detecting system for an internal combustion engine of the fourth embodiment, the abnormality of the blow-by gas passage  27  is decided by the gas pressure sensor  32  for detecting the blow-by gas pressure level PBG in the blow-by gas passage  27  to return the blow-by gas produced in the internal combustion engine  1  to the side of the intake passage  12  of the internal combustion engine  1  and by the ECU  40  on the basis of the blow-by gas pressure level PBG detected by the gas pressure sensor  32 . By the simple and inexpensive construction for detecting the blow-by gas pressure level PBG in the blow-by gas passage  27 , therefore, the abnormality of the blow-by gas passage  27  is properly detected. This makes it possible to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine  1 . 
     &lt;Embodiment 5&gt; 
     In the fifth embodiment also, the intake pressure sensor  31  is arranged in the surge tank  14  in addition to the gas pressure sensor  32  as used in the fourth embodiment and arranged midway of the blow-by gas passage  27 , so that a negative pressure difference ΔP or the difference between the intake pressure level from the intake pressure sensor  31  and the blow-by gas pressure level from the gas pressure sensor  32  is used for detecting the blow-by gas passage abnormality. 
     This detection processing is shown in FIG.  17  and uses an abnormality decision table of decision values D, E and F shown in FIG.  18 . Those values are determined in advance from experiments or the like and correspond to the negative pressure difference ΔP between the intake pressure level from the intake pressure sensor  31  and the blow-by gas pressure level from the gas pressure sensor  32 . 
     In this embodiment, similarly to the fourth embodiment (FIG.  11 ), when the blow-by gas passage  27  clogs at point a, the inside of the blow-by gas passage  27  approaches the intake pressure in the surge tank  14  so that the negative pressure difference ΔP between the intake pressure level by the intake pressure sensor  31  and the blow-by gas pressure level by the gas pressure sensor  32  shifts to the negative (−) side (i.e., to the negative side from the decision value D) from the normal one. On the other hand, when the blow-by gas passage  27  leaks (to cause an disengagement of the passage, for example) at point a, the inside of the blow-by gas passage  27  approaches the atmospheric pressure so that the negative pressure difference ΔP shifts to the positive (+) side (i.e., closer to the positive side than the decision value E and to the negative side than the decision value F) from the normal one because of the pressure loss in the midway PCV valve  28 . Moreover, when the blow-by gas passage  27  leaks or clogs at point b, the blow-by gas pressure level by the gas pressure sensor  32  takes a substantially atmospheric level without being influenced by the intake pressure level in the surge tank  14 , so that the negative pressure difference ΔP between the intake pressure level by the intake pressure sensor  31  and the blow-by gas pressure level by the gas pressure sensor  32  highly shifts to the positive side (i.e., closer to the positive side than the decision value F). 
     In FIG. 17, it is decided at step S 311  whether or not the running state of the internal combustion engine  1  is idle. When the decision of step S 311  is NO indicating that the running condition is not idle, the present routine is ended without any operation. On the other hand, when the decision of step S 311  is YES indicating that the running state is idle, the routine advances to step S 312 , at which it is decided whether or not the negative pressure difference ΔP or the difference between the intake pressure level from the intake pressure sensor  31  and the blow-by gas pressure level from the gas pressure sensor  32  is less than the decision value D and highly at the negative side. When the decision of step S 312  is NO indicating the negative pressure difference ΔP is at the positive side no less than the decision value D, the routine advances to step S 313 , at which it is decided whether or not the negative pressure difference ΔP is over the decision value E and at the positive side, as illustrated in FIG.  18 . When the decision of step S 313  is NO indicating that the negative pressure difference ΔP is no more than the decision value E, that is, when the negative pressure difference ΔP is no less than the decision value D and no more than the decision value E, as illustrated in FIG. 18, the routine advances to step S 314 , at which the normality of the blow-by gas passage  27  from the head cover  6  to the surge tank  14  is decided to end the present routine. 
     On the other hand, when the decision of step S 313  is YES indicating that the negative pressure difference ΔP is over the decision value E and at the positive side, the routine advances to step S 315 , at which it is decided whether or not the negative pressure difference ΔP is over and highly at the positive side of the decision value F set at the positive side of the decision value E, as illustrated in FIG.  18 . When the decision of step S 315  is NO indicating that the negative pressure difference ΔP is below the decision value F and at the negative side, when the negative pressure difference ΔP is over the decision value E and no more than the decision value F, as illustrated in FIG. 18, the routine advances to step S 316 , at which the abnormality (leakage) at point a of the blow-by gas passage  27  between the PCV valve  28  arranged midway of the blow-by gas passage  27  and the head cover  6  upstream of the former is decided. 
     On the other hand, when the decision of step S 315  is YES indicating that the negative pressure difference ΔP is over the decision value F and at the positive side, the routine advances to step S 317 , at which an abnormality (leakage or clogging) at point b of the blow-by gas passage  27  between the PCV valve  28  arranged midway of the blow-by gas passage  27  and the surge tank  14  downstream of the former is decided. On the other hand, when the decision of step S 312  is YES indicating that the negative pressure difference ΔP is at the negative side no less than the decision value D, the routine advances to step S 318 , at which an abnormality (clogging) at point a of the blow-by gas passage  27  between the PCV valve  28  arranged midway of the blow-by gas passage  27  and the head cover  6  upstream of the former is decide. When the abnormality is decided at step S 316 , at step S 317  or at step S 318 , the routine advances to step S 319 , at which the after-processing of the abnormality decision similar to that shown in FIG. 16 is executed to end the present routine. Thus, it is possible to properly detect the abnormal state (leakage or clogging) at each point of the blow-by gas passage  27  from the head cover  6  to the surge tank  14 . 
     Thus in the blow-by gas passage abnormality detecting system for an internal combustion engine according to the fifth embodiment, an abnormality of the blow-by gas passage  27  is decided in the ECU  40  by the gas pressure sensor  32  for detecting the pressure in the blow-by gas passage  27  between the PCV valve  28  acting as the flow rate control valve for controlling the flow rate to pass through the blow-by gas passage  27  to return the blow-by gas produced in the internal combustion engine  1  to the side of the intake passage  12  of the internal combustion engine  1  and the side of the intake passage  12  downstream of the PCV valve  28 , and by the intake pressure sensor  31  for detecting the pressure in the intake passage  12 , such that the differential pressure ΔP between the pressure detected by the gas pressure sensor  32  and the pressure detected by the intake pressure sensor  31  is compared with the decision values D, E and F at the predetermined values. By the simple and inexpensive construction for detecting the differential pressure ΔP between the pressure in the blow-by gas passage  27  downstream of the PCV valve  28  and the pressure in the intake passage  12 , therefore, an abnormality (leakage or clogging) of the blow-by gas passage  27  upstream or downstream of the PCV valve  28  can be properly detected in view of the differential pressure ΔP over the decision values D, E and F thereby to minimize the release of the blow-by gas into the atmosphere and the adverse effect on the internal combustion engine  1 . Here, the abnormality of the blow-by gas passage  27  can likewise be decided, too, by arranging the gas pressure sensor  32  between the upstream of the PCV valve  28  and the side of the internal combustion engine  1  and by detecting the pressure in the blow-by gas passage  27  inbetween. 
     In the fourth and fifth embodiments, the abnormality decision of the blow-by gas passage  27  is executed only at the idle time. However, it should not be limited thereto, but a similar detection can be executed in operations other than the idle time if the decision values are set to correspond to the running state. 
     Before the abnormality decision of the blow-by gas passage  27  in the fourth and fifth embodiments, moreover, there can be added a normality/abnormality deciding routine of the intake system device and so on, as shown in FIG.  19 . The normality/abnormality decisions are executed in the intake pressure sensor  31  at step S 411 , in the ISC valve  20  at step S 412 , in the throttle sensor for detecting the throttle opening  10  of the throttle valve  13  at step S 413 , and in the atmospheric sensor for detecting the atmospheric pressure at step S 414 . When all the devices are normal, the diagnosis for executing the abnormality decision of the blow-by gas passage  27  is allowed at step S 415 . When any of the devices is abnormal, the diagnosis is inhibited at step S 416 . Then, the present routine is ended. This makes it possible to perform the abnormality decision of the blow-by gas passage  27  highly accurately. 
     Moreover, the fourth and fifth embodiments are constructed by premising the internal combustion engine (i.e., the so-called “D-J engine”) in which the fuel injection is controlled by measuring the pressure into the intake passage and which is equipped with the intake pressure sensor  31 . It may employ the intake flow, as detected by an air flow meter and converted into the intake pressure at that time, for the abnormality decision of the blow-by gas passage  27  in the internal combustion engine (i.e., the “L-J engine”) in which the fuel injection is controlled by measuring the intake flow into the intake passage. 
     Moreover, there can be added to the fourth and fifth embodiments a normality/abnormality deciding routine of the combustion system device or the like, as shown in FIGS. 10A and 10B. 
     The present invention having been described with reference to the first to fifth embodiments may be modified or altered further without departing from the spirit and scope of the invention.