Abstract:
An abnormality-determining device for a turbo-supercharger, which is capable of detecting abnormalities, including response delay of a movable member, with accuracy. A turbo-supercharger provided in an internal combustion engine has variable vanes  8   c  arranged in an exhaust turbine, for changing an area of a nozzle thereof. An abnormality-determining device stops supply of fuel to the engine, when the engine is in a predetermined operating condition, actuates the variable vanes, after actuating the same toward one of an open side and a closed side, toward the other of the sides, during the stoppage of fuel supply, detects a supercharging parameter indicative of a degree of supercharging by the turbo-supercharger, and determines abnormality of the turbo-supercharger based on a change in the supercharging parameter detected during the actuation of the movable vanes.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an abnormality-determining device and method for a turbo-supercharger that is provided in an internal combustion engine and has a movable member provided in an exhaust turbine thereof, for changing the area of a nozzle thereof, and an engine control unit. 
     2. Description of the Related Art 
     Conventionally, there has been proposed an abnormality-determining device of this kind in Japanese Laid-Open Patent Publication (Kokai) No. 2006-46246. This turbo-supercharger has an exhaust turbine provided in an exhaust passage of an internal combustion engine, and an intake air compressor provided in an intake passage and coaxially connected to the exhaust turbine. The exhaust turbine has a nozzle having a variable nozzle provided as a movable member. The boost pressure is controlled by actuating the variable nozzle e.g. by an actuator to vary the opening of the variable nozzle. 
     Further, the abnormality-determining device holds the variable nozzle at a predetermined opening degree e.g. at a fully-closed opening degree, during stoppage of the fuel supply to the engine, and determines whether or not the boost pressure detected in this state is within a predetermined pressure range. Then, if the detected boost pressure continues to be outside the predetermined pressure range for not shorter than a predetermined time period, the abnormality-determining device determines that the variable nozzle is faulty. 
     As described above, the conventional abnormality-determining device determines abnormality of the variable nozzle depending on whether the boost pressure detected with the variable nozzle held at the predetermined opening degree, e.g. the fully-closed opening, has turned out to be outside the predetermined pressure range. Although this makes it possible to determine abnormality of the variable nozzle when the variable nozzle is at the predetermined opening degree, e.g. at the fully-closed opening, if the variable nozzle suffers from the abnormality of the response delay, for example, the boost pressure turns out to reach the predetermined pressure range, and hence it is impossible to determine the abnormality of the response delay which the variable nozzle suffers from. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an abnormality-determining device and method for a turbo-supercharger and an engine control unit which are capable of detecting abnormalities, including response delay of a movable member, with accuracy. 
     To attain the above object, in a first aspect of the present invention, there is provided an abnormality-determining device for a turbo-supercharger that is provided in an internal combustion engine and has a variable member provided in an exhaust turbine, for changing an area of a nozzle thereof, comprising fuel supply-stopping means for stopping supply of fuel to the engine, when the engine is in a predetermined operating condition, movable member-actuating means for actuating the movable member toward one of an open side and a closed side, and then toward the other of the open side and the closed side, during the stoppage of the fuel supply by the fuel supply-stopping means, supercharging parameter-detecting means for detecting a supercharging parameter indicative of a degree of supercharging by the turbo-supercharger, and abnormality-determining means for determining abnormality of the turbo-supercharger based on a change in the supercharging parameter detected during actuation of the movable member by the movable member-actuating means. 
     The turbo-supercharge has a movable member in an exhaust turbine, for changing the area of a nozzle, and by varying the opening degree of the movable member, the degree of supercharging is varied to thereby control the supercharging pressure. With the configuration of the abnormality-determining device according to the first aspect of the present invention, during stoppage of fuel supply to the engine, the movable member-actuating means forcibly actuates the movable member toward one of the open side and the closed side, and then forcibly actuates the movable member toward the other of the sides. Further, the supercharging parameter-detecting means detects the supercharging parameter indicative of a degree of supercharging by the turbo-supercharger. Then, based on a change in the supercharging parameter detected during the actuation of the movable member, an abnormality of the turbo-supercharger is determined. 
     As described above, the abnormality determination of the turbo-supercharger is carried out based on a change in the supercharging parameter detected when the movable member is first actuated toward one of the open side and the closed side, and then switched to the other of the sides, it is possible to accurately determine the abnormality of the turbo-charger, including the response delay of the movable member, based on an actual change in the degree of supercharging occurring upon switching of the direction of the actuation. Further, since the abnormality determination is executed during stoppage of the fuel supply to the engine, it is possible to eliminate influence of a disturbance caused by combustion of the engine on the boost pressure, which makes it possible to enhance the accuracy of the determination. 
     Preferably, the supercharging parameter is at least one of an exhaust pressure on an upstream side of the exhaust turbine, an intake air pressure on a downstream side of an intake air compressor driven by the exhaust turbine, and an intake air amount. 
     As the degree of supercharging by the turbo-supercharger is higher, all of the exhaust pressure on the upstream side of the exhaust turbine, the intake air pressure on the downstream side of the intake air compressor, and the intake air amount become higher. That is, these three parameters serve as excellent indexes indicative of the degree of supercharging by the turbo-supercharger. Therefore, by using at least one of these parameters, it is possible to properly carry out the abnormality determination of the turbo-supercharger. 
     Preferably, the engine is provided with an exhaust gas recirculation device that recirculates exhaust gases from an exhaust system to an intake system, and the abnormality-determining device further comprising exhaust gas recirculation-stopping means for stopping an operation of the exhaust gas recirculation device during abnormality determination of the turbo-supercharger by the abnormality-determining means. 
     With the configuration of the preferred embodiment, the recirculation of exhaust gases by the exhaust gas recirculation device is stopped during abnormality determination, and therefore, it is possible to prevent fluctuation of boost pressure caused by recirculation of exhaust gases, which makes it possible to enhance the accuracy of the abnormality determination. 
     To attain the above object, in a second aspect of the present invention, there is provided a method of determining an abnormality of a turbo-supercharger that is provided in an internal combustion engine and has a variable member provided in an exhaust turbine, for changing an area of a nozzle thereof, comprising a fuel supply stoppage step of stopping supply of fuel to the engine, when the engine is in a predetermined operating condition, a movable member-actuating step of actuating the movable member toward one of an open side and a closed side, and then toward the other of the open side and the closed side, during the stoppage of the fuel supply in the fuel supply stoppage step, a supercharging parameter-detecting step of detecting a supercharging parameter indicative of a degree of supercharging by the turbo-supercharger, and an abnormality-determining step of determining abnormality of the turbo-supercharger based on a change in the supercharging parameter detected during actuation of the movable member in the movable member-actuating step. 
     With the configuration of the method according to the second aspect of the present invention, it is possible to obtain the same advantageous effects as provided by the first aspect of the present invention. 
     Preferably, the supercharging parameter is at least one of an exhaust pressure on an upstream side of the exhaust turbine, an intake air pressure on a downstream side of an intake air compressor driven by the exhaust turbine, and an intake air amount. 
     Preferably, the engine is provided with an exhaust gas recirculation device that recirculates exhaust gases from an exhaust system to an intake system, and the method further comprises an exhaust gas recirculation-stopping step of stopping an operation of the exhaust gas recirculation device during abnormality determination of the turbo-supercharger in the abnormality-determining step. 
     With the configurations of these preferred embodiments, it is possible to obtain the same advantageous effects as provided by the respective corresponding preferred embodiments of the first aspect of the present invention. 
     To attain the above object, in a third aspect of the present invention, there is provided an engine control unit including a control program for causing a compute to execute a method of determining an abnormality of a turbo-supercharger that is provided in an internal combustion engine and has a variable member provided in an exhaust turbine, for changing an area of a nozzle thereof, wherein the method comprises a fuel supply stoppage step of stopping supply of fuel to the engine, when the engine is in a predetermined operating condition, a movable member-actuating step of actuating the movable member toward one of an open side and a closed side, and then toward the other of the open side and the closed side, during the stoppage of the fuel supply in the fuel supply stoppage step, a supercharging parameter-detecting step of detecting a supercharging parameter indicative of a degree of supercharging by the turbo-supercharger, and an abnormality-determining step of determining abnormality of the turbo-supercharger based on a change in the supercharging parameter detected during actuation of the movable member in the movable member-actuating step. 
     With the configuration of the engine control unit according to the third aspect of the present invention, it is possible to obtain the same advantageous effects as provided by the first aspect of the present invention. 
     Preferably, the supercharging parameter is at least one of an exhaust pressure on an upstream side of the exhaust turbine, an intake air pressure on a downstream side of an intake air compressor driven by the exhaust turbine, and an intake air amount. 
     Preferably, the engine is provided with an exhaust gas recirculation device that recirculates exhaust gases from an exhaust system to an intake system, and the method further comprises an exhaust gas recirculation-stopping step of stopping an operation of the exhaust gas recirculation device during abnormality determination of the turbo-supercharger in the abnormality-determining step. 
     With the configurations of these preferred embodiments, it is possible to obtain the same advantageous effects as provided by the respective corresponding preferred embodiments of the first aspect of the present invention. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an internal combustion engine to which the present invention is applied; 
         FIG. 2  is a block diagram showing signals input to and output from an ECU: 
         FIG. 3  is a flowchart of a process for determining abnormality of a turbo-supercharger; 
         FIG. 4  is a continuation of the  FIG. 3  flowchart; and 
         FIG. 5  is a timing diagram showing an example of operation of the abnormality-determining device obtained by execution of the abnormality-determining process. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention will now be described in detail with reference to the drawings showing preferred embodiment thereof.  FIG. 1  shows an internal combustion engine to which the present invention is applied. The internal combustion engine (hereinafter simply referred to as “the engine”)  3  is a diesel engine that has e.g. four cylinders (only one of which is shown), and is installed on a vehicle, not shown. 
     A combustion chamber  3   c  is defined between a piston  3   a  and a cylinder head  3   b  for each cylinder of the engine  3 . The cylinder head  3   b  has an intake pipe  4  and an exhaust pipe  5  connected thereto, with a fuel injection valve (hereinafter referred to as “the injector”)  6  mounted therethrough such that it faces the combustion chamber  3   c.    
     The injector  6  is inserted into the combustion chamber  3   c  through a central portion of the top wall thereof, and is connected to a high-pressure pump and a fuel tank, neither of which is shown, in the mentioned order via a common rail. A fuel injection amount TOUT of fuel injected from the injector  6  is controlled by controlling a time period over which the injector  6  is opened by a drive signal from the ECU  2  (see  FIG. 2 ). 
     A magnet rotor  30   a  is mounted on a crankshaft  3   d  of the engine  3 . The magnet rotor  30   a  and an MRE pickup  30   b  form a crank angle sensor  30  which delivers a CRK signal and a TDC signal, which are both pulse signals, to the ECU  2  along with rotation of the crankshaft  3   d.    
     Each pulse of the CRK signal is generated whenever the crankshaft  3   d  rotates through a predetermined crank angle (e.g. 30°). The ECU  2  calculates rotational speed (hereinafter referred to as “the engine speed”) NE of the engine  3  based on the CRK signal. The TDC signal indicates that the piston  3   a  of each cylinder is at a predetermined crank angle position in the vicinity of the top dead center (TDC) at the start of the suction stroke thereof, and in the case of the four-cylinder engine of the illustrated example, it is delivered whenever the crankshaft  3   d  rotates through 180 degrees. 
     The engine  3  has a turbo-supercharger  7  disposed therein. The turbo-supercharger  7  (hereinafter referred to as “supercharger  7 ”) is comprised of a supercharger main unit  8 , an actuator  9  connected to the supercharger main unit  8 , and a vane opening control valve  10  connected to the actuator  9 . 
     The supercharger main unit  8  includes an intake compressor  8   a  rotatably mounted in the intake pipe  4 , a rotatable exhaust turbine  8   b  provided in the exhaust pipe  5 , and a shaft  8   d  integrally formed with the two  8   a  and  8   b  such that the shaft  8   d  connects them. In the supercharger main unit  8 , as the exhaust turbine  8   b  is driven for rotation by exhaust gases flowing through the exhaust pipe  5 , the intake compressor  8   a  integrally formed with the exhaust turbine  8   b  is also rotated, whereby the supercharger main unit  8  is caused to perform a supercharging operation for pressurizing intake air in the intake pipe  4 . 
     Further, a plurality of variable vanes  8   c  (only two of which are shown) are provided in a nozzle (not shown) of the exhaust turbine  8   b , and these variable vanes  8   c  are connected to the actuator  9 . 
     The actuator  9  is of a diaphragm type which is operated by negative pressure. The actuator  9  has negative pressure supplied from a negative pressure pump, not shown, through a negative pressure supply passage, not shown. The vane opening control valve  10  is disposed in an intermediate portion of the negative pressure supply passage. The vane opening control valve  10  is formed by an electromagnetic valve, and the degree of opening thereof is controlled by a drive signal from the ECU  2 , whereby negative pressure to be supplied to the actuator  9  is changed to change the degree of opening of each variable vane  8   c . Thus, by varying the area of the nozzle of the exhaust turbine  8   b , the degree of supercharging by the supercharger  7  is varied, whereby the boost pressure is controlled. 
     An intercooler  11  of a water cooling type, and a throttle valve  12  are inserted into the intake pipe  4  at respective locations downstream of the intake compressor  8   a  from upstream to downstream in the mentioned order. The intercooler  11  is provided for cooling intake air e.g. when the temperature of the intake air is made higher by the supercharging operation of the supercharger  7 . An actuator  12   a  comprised e.g. of a DC motor is connected to the throttle valve  12 . The opening of the throttle valve  12  is controlled by controlling the duty factor of electric current supplied to the actuator  12   a  by the ECU  2 . 
     Further, the intake pipe  4  has an air flow sensor  31  inserted therein at a location upstream of the intake compressor  8   a , and a boost pressure sensor  32  inserted therein between the intercooler  11  and the throttle valve  12 . The air flow sensor  31  detects the intake air amount QAIR, to deliver a signal indicative of the sensed intake air amount QAIR to the ECU  2 , while the boost pressure sensor  32  detects intake pressure on the downstream side of the intake compressor  8   a  as boost pressure PSCHG, to deliver a signal indicative of the sensed boost pressure PSCHG to the ECU  2 . 
     Further, the engine  3  is provided with an EGR device  14  that has an EGR pipe  14   a  and an EGR control valve  14   b . The EGR pipe  14   a  connects between a portion of the intake pipe  4  at a location downstream of the throttle valve  12  and a portion of the exhaust pipe  5  at a location upstream of the exhaust turbine  8   b . Part of exhaust gases exhausted from the engine  3  is recirculated into the intake pipe  4  via the EGR pipe  14   a  as EGR gases. 
     The EGR control valve  14   b  is implemented by a linear solenoid valve inserted into the EGR pipe  14   a , and the valve lift amount thereof is controlled by a duty-controlled drive signal from the ECU  2 , whereby the amount of EGR gases is controlled. 
     A three-way catalyst  16  and a NOx catalyst  17  are provided in the exhaust pipe  5  at respective locations downstream of the exhaust turbine  8   b  from upstream to downstream in the mentioned order. The three-way catalyst  16  oxidizes HC and CO and performs reduction of NOx in exhaust gases under a stoichiometric atmosphere, to thereby purify i.e. reduce exhaust emissions. The NOx catalyst  17  traps NOx contained in exhaust gases under an oxidizing atmosphere in which the concentration of oxygen is high, and under a reducing atmosphere in which large amounts of reducing agents are contained in the exhaust gases, the NOx catalyst  17  performs reduction of the trapped NOx, to thereby purify exhaust emissions. 
     Furthermore, an exhaust pressure sensor  33  is provided in the exhaust pipe  5  at a location upstream of the exhaust turbine  8   b . The exhaust pressure sensor  33  detects pressure of exhaust gases on the upstream side of the exhaust turbine  8   b  as exhaust pressure PEX, and delivers a signal indicative of the detected exhaust pressure PEX to the ECU  2 . Further, an accelerator pedal opening sensor  34  detects the amount AP of operation (stepped-on amount) of an accelerator pedal, not shown (hereinafter referred to as “the accelerator pedal opening AP”), and delivers a signal indicative of the sensed accelerator pedal opening AP to the ECU  2 . 
     The ECU  2  forms fuel supply-stopping means, variable member-actuating means, abnormality-determining means, and exhaust gas recirculation-stopping means, and is implemented by a microcomputer comprised of an I/O interface, a CPU, a RAM, and a ROM (none of which are specifically shown). The detection signals from the aforementioned sensors  30  to  34  are input to the CPU after the I/O interface performs A/D conversion and waveform shaping thereon. 
     Further, in response to these input signals, the CPU determines an operating condition of the engine  3 , and based on the determined operating condition of the engine, performs engine control, such as control of the fuel injection amount and the intake air amount, in accordance with control programs read from the ROM. Further, the CPU executes a decelerating fuel cut-off (F/C) operation in which the supply of fuel to the engine  3  is stopped, when the engine  3  is in a predetermined deceleration condition e.g. in which the accelerator opening AP is approximately equal to 0, and at the same time, the engine speed NE is not lower than a predetermined rotational speed (e.g. 1000 rpm), and executes abnormality determination of the supercharger  7  (hereinafter simply referred to as “the abnormality determination”) during the decelerating F/C operation. 
       FIGS. 3 and 4  are flowcharts showing a process for determining abnormality of the supercharger  7 . This process is executed whenever a predetermined time period elapses. In the present process, first, it is determined in a step  1  (shown as S 1  in abbreviated form in  FIG. 3 ; the following steps are also shown in abbreviated form) whether or not a fuel cut-off flag F_FC is equal to 1. If the answer to this question is negative (NO), i.e. if the engine  3  is not in decelerating F/C operation, a determination completion flag F_DONE, referred to hereinafter, is set to 0 (step  2 ), and at the same time, a vane fully-opening flag F_OPEN and a vane fully-closing flag F_CLOSE are both set to 0 (steps  3  and  4 ), followed by terminating the present process. 
     If the answer to the question of the step  1  is affirmative (YES), i.e. the engine  3  is in decelerating F/C operation, it is determined whether or not the determination completion flag F_DONE is equal to 1 (step  5 ). If the answer to this question is affirmative (YES), i.e. if the abnormality determination has been completed during the present decelerating F/C operation, it is judged that the abnormality determination should not be executed any further, and hence the steps  3  and  4  are carried out, followed by terminating the present process. 
     If the answer to the question of the step  5  is negative (NO), i.e. if the abnormality determination has not been completed during the present decelerating F/C operation, it is determined whether or not the engine speed NE is within a range defined by a predetermined lower limit value NLMTL (e.g. 1000 rpm) and a predetermined upper limit value NLMTH (e.g. 1500 rpm) (step  6 ). If the answer to this question is negative (NO), i.e. the engine speed NE is not within the predetermined range, it is judged that the abnormality-executing conditions are not satisfied, so that the steps  3  and  4  are executed, followed by terminating the present process. 
     If the answer to the question of the step  6  is affirmative (YES), i.e. if the engine speed is within the predetermined range/it is judged that the abnormality determination-executing conditions are satisfied, so that the abnormality determination is executed in a step  7  and the following. 
     First, in the step  7 , by actuating the EGR control valve  14   b  to a fully-closed opening degree, whereby the recirculation of EGR gases by the EGR device  14  is stopped. Then, it is determined whether or not the vane fully-closing flag F_CLOSE and the vane fully-opening flag F_OPEN are equal to 1 (steps  8  and  9 ). If both of the answers to these questions are negative (NO), the vane fully-closing flag F_OPEN is set to 1 (step  10 ), and a timer value TMOPEN of an upcount fully-open state timer (hereinafter referred to as “the fully-open state timer”) is set to 0 (step  11 ). Further, the variable vanes  8   c  of the supercharger  7  are actuated to a substantially fully-open degree (step  12 ). 
     After the step  10  is executed, the answer to the question of the step  9  becomes affirmative (YES). Therefore, in this case, the steps  10  and  11  are skipped, and the process proceeds to the step  12  to continue the fully-opening control of the variable vanes  8   c.    
     In a step  13  following the step  12 , it is determined whether or not the fully-open state timer TMOPEN is equal to a predetermined time period TDLY (e.g. two seconds), if the answer to this question is negative (NO), the present process is immediately terminated. On the other hand, if the answer to the question of the step S 13  is affirmative (YES), i.e. if the predetermined time period TDLY has elapsed after the start of the fully-opening control of the variable vanes  8   c , it is judged that the exhaust pressure PEX by the fully-opening control has been stabilized, so that the vane fully-open state flag F_OPEN is rest to 0 (step  14 ), and the fully-closing control of the variable vanes  8   c  is executed in a step  15  and the following. 
     More specifically, the vane fully-closing flag F_CLOSE is set to 1 (step  15 ), and a time value TMCLOSE of an upcount fully-closed state timer (hereinafter referred to as “the fully-closed state timer”) is rest to 0 (step  16 ). At the same time, the exhaust pressure PEX at this time is stores as an initial pressure P 0  at the start of the fully-closing control (step  17 ), and the variable vanes  8   c  are actuated to a substantially fully-closed opening degree (step  18 ). 
     After execution of the step  15 , the answer to the question of the step  8  becomes affirmative (YES). Therefore, in this case, the steps  9  to  17  are skipped, and the process proceeds to the step  18 , to continue the fully-closing control of the variable vanes  8   c.    
     In a step  19  following the step  18 , it is determined whether or not the differential pressure (PEX−P 0 ) between the initial pressure P 0  of the exhaust pressure stored in the step  17  and the exhaust pressure PEX at the present time is equal to not lower than a predetermined value PREF. 
     If the answer to the question of the step  19  is affirmative (YES), the fully-closed state timer value TMCLOSE is set as a required time period TVRY which the differential pressure (PEX−P 0 ) took to reach the predetermined value PREF (step  20 ), and it is determined whether or not the set required time period TVRY is smaller than a first predetermined time period TREF 1  (e.g. two seconds) (step S 21 ). 
     If the answer to this question is affirmative (YES), i.e. if TVRY&lt;TREF 1  holds, the exhaust pressure PEX is fast in rising after the start of the fully-closing control of the variable vanes  8   c , and hence it is judged that the supercharger  7  is normal, so that an abnormality flag F_NG is set to 0 (step  22 ). 
     On the other hand, if the answer to the question of the step  21  is negative (NO), i.e. if TVRY≧TREF 1  holds, the exhaust pressure PEX is slow in rising after the start of the fully-closing control of the variable vanes  8   c , and hence it is judged that the supercharger  7  suffers from abnormality of the response delay, so that the abnormality flag F_NG is set to 1 (step  23 ). 
     In a step  24  following the step  22  or  23 , to indicate that the abnormality determination is completed, the abnormality determination completion flag F_DONE is set to 1, followed by terminating the present process. 
     On the other hand, if the answer to the question of the step  19  is negative (NO), i.e. if the differential pressure (PEX−P 0 ) has not reached the predetermined value PREF, the fully-closed state timer value TMCLOSE at the time is set to an elapsed time TOVR after the start of the fully-closing control of the variable vanes  8   c  (step  25 ). Then, it is determined whether or not the set elapsed time TOVR is larger than a second predetermined time period TREF 2  (e.g. six seconds) longer than the first predetermined time period TREF 1  (step  26 ). 
     If the answer to the question of the step  26  is negative (NO), the present process is immediately terminated, whereas if the same is affirmative (YES), i.e. even after the lapse of the second predetermined period TREF 2 , the differential pressure (PEX−P 0 ) has not reached the predetermined value PREF, it is judged that the variable vanes  8   c  suffer from abnormality of fully-open state fixation, so that the process proceeds to the step  23 , wherein the abnormality flag F_NG is set to 1, and after execution of the step  24 , the present process is terminated. 
       FIG. 5  is a timing diagram showing an example of operation of the abnormality-determining device obtained by the abnormality-determining process described above. At a time t 1  in  FIG. 5 , when the decelerating operation-executing conditions are satisfied, the fuel cut-off flag F_FC is set to 1, to start the decelerating F/C operation. If the abnormality determination-executing conditions are satisfied at this time, the EGR control valve  14   b  is actuated to a fully closed opening degree, to stop the recirculation of EGR gases (step  7 ). Further, the vane fully-opening flag F_OPEN is set to 1 (step  10 ), whereby the variable vanes  8   c  are actuated from the normally controlled state to the substantially fully-closed opening degree (step  12 ), thereby starting the fully-opening control. The fully-opening control increases the area of the nozzle of the exhaust turbine  8   b , to reduce the degree of supercharging, thereby reducing the exhaust pressure PEX. 
     After the start of the fully-opening control, upon the lapse of the predetermined time period TDLY (t 2 ), the vane fully-opening flag F_OPEN is reset to 0 (step  14 ), and at the same time, the vane fully-closing flag F_CLOSE is set to 1 (step  15 ), to thereby actuating the variable vanes  8   c  to the substantially fully-closed opening (step  18 ), whereby the fully-closing control is started. The fully-closing control narrows the nozzle of the exhaust turbine  8   b , to increase the degree of supercharging, thereby increasing the exhaust pressure PEX. 
     With a rise in the exhaust pressure PEX, when the differential pressure (PEX−P 0 ) between the exhaust pressure PEX and the initial pressure P 0  at the start of the fully-closing control reaches the predetermined value PREF (YES to the step  19 : t 3 ), the fully-closed state timer TMCLOSE at the time is set to the required time TVRY which the exhaust pressure PEX takes to rise by the predetermined value PREF after the start of the fully-closing control (step  20 ). 
     If the variable vanes  8   c  of the supercharger  7  are operating without response delay, as indicated by a solid line in (f) of  FIG. 5 , the exhaust pressure PEX is fast in rising after the start of the fully-closing control, so that the required time TVRY calculated as described above becomes short. On the other hand, if the variable vanes  8   c  suffer from abnormality of the response delay, as indicated by a broken line in (f) of  FIG. 5 , the exhaust pressure PEX is slow in rising, so that the required time TVRY becomes longer (t 3 ′ in  FIG. 5 ; TVRY′). Therefore, by comparing the required time TVRY with the predetermined time period TREV 1 , if TVRY&lt;TREF 1  holds (YES to the step  21 ), it can be judged that the variable vanes  8   c  do not suffer from the response delay, and the supercharger  7  is normal, whereas when TVRY≧TREV 1  holds (NO to the step  21 ), it can be judged that the variable vanes  8   c  suffer from abnormality of the response delay. 
     Further, if the variable vanes  8   c  suffer from abnormality, such as fully-open state fixation, as indicated by a one-dot-chain line in (f) of  FIG. 5 , the exhaust pressure PEX does not rise or is difficult to rise, so that when TOVR&gt;TREF 2  holds (YES to the step  26 ), it can be judged that this kind of abnormality has occurred. 
     As described heretofore, according to the present embodiment, based on a manner of change in the exhaust pressure PEX occurring when fully closing the variable vanes  8   c  of the supercharger after executing the fully-opening control of thereof, more specifically, by comparing the required time TVRY which the exhaust pressure PEX takes to rise by the predetermined value PREF from the start of the fully-closing control with the predetermined time period TREF, it is possible to accurately determine abnormality of the supercharger  7 , including the response delay of the variable vanes  8   c.    
     Further, since the abnormality determination is executed in a state where the recirculation of EGR gases is stopped during decelerating F/C operation, it is possible to eliminating the influence of a disturbance caused by combustion of the engine or EGR gases on the boost pressure, whereby it is possible to enhance the accuracy of the determination. Further, since the fully-opening control of the variable vanes  8   c  is continued over the predetermined time period TDLY, and after waiting for the exhaust pressure PEX to become stable in this state, the control is shifted to the fully-closing control. Therefore, it is possible to properly determining the required time TVRY, thereby further enhancing the accuracy of the determination. 
     It should be noted that the present invention is by no means limited to the above-described embodiment, but it can be practices in various forms. For example, although in the embodiment, after executing the fully-opening control of the variable vanes  8   c , the fully-closing control of the same is executed, the order of these controls may be reversed. In this case, by comparing the required time which the exhaust pressure PEX takes to be reduced by a predetermined value from the start of the fully-opening control with a predetermined time period, it is possible to perform abnormality determination with accuracy. Further, in the embodiment, as the control for opening the variable vanes  8   c , the variable vanes  8   c  are actuated to be substantially fully opened, and as the control for closing the same, they are actuated to be substantially fully closed. However, insofar as the opening degree of the variable vanes  8   c  can cause the difference between the boost pressure on the vane-open side and that on the vane-closed side to be made clearly apparent, the variable vanes  8   c  may be actuated to respective opening degrees other than the fully-open opening degree and the fully-closed opening degree. 
     Further, in the embodiment, the abnormality determination is carried out based on the required time TVRY which the exhaust pressure PEX takes to rise after the start of the fully-closing control, any suitable manner of the abnormality determination may be employed as desired. For example, the determination may be made based on the absolute value of the exhaust pressure PEX detected when a predetermined time period has elapsed after the start of the fully-closing control or a slope of rise of the exhaust pressure PEX occurring over a predetermined time period after the start of the fully-closing control. 
     Further, although in the present embodiment, as supercharging parameters indicative of a degree of supercharging by the supercharger  7 , the exhaust pressure PEX as pressure of exhaust gases on the upstream side of the exhaust turbine  8   b  is employed, instead of this, boost pressure PSCHG as pressure of intake air on the downstream side of the intake compressor  8   a  or the intake air amount QAIR may be employed. The boost pressure PSCHG and the intake air amount QAIR take larger values as the degree of supercharging by the supercharger  7  is higher, thereby serving as excellent indexes of the degree of supercharging. Therefore, by using them as supercharging parameters, it is possible to similarly perform the abnormality determination with accuracy. Alternatively, two or more combinations of the exhaust pressure PEX, the boost pressure PSCHG, and the intake air amount QAIR may be used, whereby it is possible to further enhance the accuracy of the abnormality determination. 
     Furthermore, although the supercharger  7  in the embodiment is a type using the variable vanes  8   c  as movable members, it is to be understood that the present invention is applicable to superchargers in which variable flaps or on-off valves disposed in a plurality of divided nozzle passages, respectively, are used as variable members. 
     Furthermore, the present invention may be applied not only to the diesel engine installed on a vehicle but also to a gasoline engine, such as a lean burn engine. Further, the present invention can be applied to various types of industrial internal combustion engines including engines for ship propulsion machines, such as an outboard motor having a vertically-disposed crankshaft. 
     It is further understood by those skilled in the art that the foregoing are preferred embodiments of the invention, and that various changes and modifications may be made without departing from the spirit and scope thereof.