Patent Publication Number: US-9410508-B2

Title: Controlling apparatus for an engine

Description:
CROSS-REFERENCE TO THE RELATED APPLICATION 
     This application incorporates by references the subject matter of Application No. 2012-242880 filed in Japan on Nov. 2, 2012 on which a priority claim is based under 35 U.S.C. S119(a). 
     FIELD 
     The present invention relates to a controlling apparatus for an engine for introducing purge gas containing evaporated fuel from a sealing-type fuel tank into an intake system. 
     BACKGROUND 
     Conventionally, a technology for introducing fuel gas (evaporated fuel) evaporated in a fuel tank of a vehicle into a cylinder of an engine to prevent leakage of fuel components to the outside of the vehicle is known. Evaporated fuel in the fuel tank is temporarily recovered by a canister, and purge gas containing the evaporated fuel desorbed from the canister is introduced into an intake path. A purge valve for adjusting the flow rate of the purge gas is placed on a purge path for connecting the canister and the intake path, and the degree of opening of the purge valve is controlled in response to an operation state of the engine. 
     For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2000-45886), a method for purging evaporated fuel absorbed to absorbent in the canister to an intake path of an engine is disclosed. In the technology, the evaporated fuel absorbed to the absorbent is vaporized by introducing a negative pressure of the intake path into the canister in a closed state with respect to the atmosphere, and the evaporated fuel vaporized in the canister is purged to the intake system by a difference between the pressure in the canister stepped up by the vaporization and the pressure in the intake path. The flow rate of the evaporated fuel purged to the intake path is grasped based on the magnitude of the pressure difference between the canister and the intake path and the magnitude of the absolute pressure in the canister. 
     It is to be noted that, in Patent Document 1, the canister is placed between the fuel tank in a sealed state and the intake path, and a vacuum control valve is placed between the fuel tank and the canister. The vacuum control valve is opened when the pressure in the fuel tank becomes higher than a predetermined pressure. Consequently, the evaporated fuel in the fuel tank is recovered by the canister, and the pressure in the fuel tank drops. Such purge of the evaporated fuel performed for the object of reduction of the pressure in the fuel tank as described above is referred to as high-pressure purge, reduced pressure purge or the like. 
     However, in the method disclosed in Patent Document 1 described above, it is necessary to acquire in advance a relationship between the magnitude of the pressure difference between the canister and the intake path and the flow rate of evaporated fuel to be purged in response to the magnitude of the absolute pressure in the canister. Further, it is necessary to store all of the acquired data in an electronic controlling apparatus. In addition, complicated working for acquiring all data is additionally performed. As a result, it is necessary to provide a ROM having a great capacity in the electronic controlling apparatus and there is the possibility that the cost may increase. 
     Further, in the high-pressure purge performed when the pressure in the fuel tank is high, the pressure on the upstream side of a valve for purge (purge valve) such as vacuum control valve as that in Patent Document 1 becomes higher than the atmospheric pressure. Therefore, where the degree of opening of the purge valve is controlled similarly as upon normal purge in which evaporated fuel recovered by the canister is purged, there is a high possibility that the flow rate of the purge gas may increase from an intended introduction ratio of purge gas. 
     That is, in the high-pressure purge, it is difficult to obtain an intended flow rate of purge gas, and there is the possibility that a rich air-fuel mixture may be introduced in the cylinder of the engine. Further, in such a case as just described, there is a concern that the control may be complicated in that the control for adjusting the amount of fuel to be injected from an injector is required separately and so forth. Accordingly, it is desired to introduce, also in the high-pressure purge, purge gas into the intake system with an intended introduction ratio of purge gas without complicated control. 
     SUMMARY 
     Technical Problems 
     The present technology disclosed herein has been worked out in view of such subjects as described above, and it is an object of the present technology to provide a controlling apparatus for an engine that can secure an appropriate flow rage of purge gas in high-pressure purge by a simple configuration. 
     It is to be noted that, in addition to the object just described, it can be positioned as another object of the present technology to achieve a working-effect that is derived from configurations indicated by an embodiment of the present invention hereinafter described but cannot be achieved by the known technologies. 
     Solution to Problems 
     (1) The controlling apparatus for an engine disclosed herein includes a purge path connected to a sealing-type fuel tank and an intake system of an engine and configured to allow purge gas containing evaporated fuel from the fuel tank to flow therethrough and a purge valve placed in the purge path and configured to adjust a flow rate of the purge gas. The controlling apparatus for an engine further includes a calculation unit that calculates a degree of opening of the purge valve based on a target introduction ratio of the purge gas, and a controlling unit that controls the purge valve so as to establish the degree of opening calculated by the calculation unit. The calculation unit corrects, in high-pressure purge performed when a pressure in the fuel tank increases exceeding a predetermined pressure, the degree of opening at least using a tank pressure flow velocity correction coefficient corresponding to an upstream pressure of the purge valve. 
     (2) Preferably, the calculation unit corrects, in the high-pressure purge, the degree of opening using a flow velocity ratio correction coefficient corresponding to a ratio between a flow velocity of intake air that passes a throttle valve of the intake system and a flow velocity of the purge gas that passes the purge valve. 
     (3) Preferably, the calculation unit corrects, in the high-pressure purge, the degree of opening using a pipe resistance flow velocity correction coefficient taking a ventilation resistance until the purge gas is introduced into the intake system into consideration. 
     (4) Preferably, the controlling apparatus for an engine further includes a correction coefficient map set such that the tank pressure flow velocity correction coefficient has a proportional relationship to the upstream pressure of the purge valve. At this time, preferably the calculation unit applies the upstream pressure to the correction coefficient map to acquire the tank pressure flow velocity correction coefficient. 
     Advantageous Effects 
     With the controlling apparatus for an engine disclosed herein, when the degree of opening of the purge valve is calculated based on the target introduction ratio of purge gas, in the high-pressure purge, the degree of opening is corrected at least using the tank pressure flow velocity correction coefficient corresponding to the upstream pressure of the purge valve. Therefore, an appropriate flow rate of purge gas can be secured by the simple configuration. Further, since complicated calculation is not required, the capacity of the ROM can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein: 
         FIG. 1  is a view exemplifying a block configuration of a controlling apparatus for an engine according to an embodiment and a configuration of an engine to which the controlling apparatus is applied and depicting the configurations in a high pressure state of a fuel tank; 
         FIG. 2  is a pipe resistance flow velocity correction coefficient map depicting a relationship between a pressure ratio and a pipe resistance flow velocity correction coefficient K 1 ; 
         FIG. 3  is a tank pressure flow velocity correction coefficient map depicting a relationship between an upstream pressure and a tank pressure flow velocity correction coefficient K 2 ; 
         FIG. 4  is a flow velocity map depicting a relationship between a pressure ratio and a flow velocity; 
         FIGS. 5( a ) to 5( c )  are views depicting a configuration extracted from the configuration of  FIG. 1 , wherein  FIGS. 5( a ), 5( b ) and 5( c )  depict a state of valves and a flow of gas during engine operating, during engine stopping and during filling of oil, respectively; 
         FIG. 6  is a flow chart exemplifying a decision procedure performed by the present controlling apparatus; 
         FIG. 7  is a flow chart exemplifying a controlling procedure upon high-pressure purge control by the present controlling apparatus; and 
         FIGS. 8( a ) and 8( b )  are views depicting modifications to the tank pressure flow velocity correction coefficient map of  FIG. 3 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, an embodiment is described with reference to the drawings. It is to be noted that the embodiment hereinafter described is merely illustrative to the end and there is no intention to eliminate various modifications and applications of the technology not explicitly specified in the embodiment described below. 
     [1. Apparatus Configuration] 
     A controlling apparatus for an engine of the present embodiment is applied to a vehicle-carried gasoline engine  10  depicted in  FIG. 1 . Here, one of a plurality of cylinders provided in the engine  10  of the multi-cylinder type is described. A piston  16  is fitted for back and forth sliding movement along an inner peripheral face of a cylinder  19  formed in a hollow cylindrical shape. A space surrounded by an upper face of the piston  16  and the inner peripheral face and a top face of the cylinder  19  functions as a combustion chamber  26  of the engine  10 . The piston  16  is connected to a crankshaft  17  through a connecting rod. 
     An intake port  11  for supplying intake air into the combustion chamber  26  therethrough and an exhaust port  12  for exhausting exhaust air after burning in the combustion chamber  26  therethrough are bored on the top face of the cylinder  19 . Further, an intake valve  14  and an exhaust valve  15  are provided at an end portion of the intake port  11  and the exhaust port  12  on the combustion chamber  26  side, respectively. Further, an ignition plug  13  is provided on the top end of the cylinder  19  in a state in which a tip end thereof projects to the combustion chamber  26  side. An ignition timing by the ignition plug  13  is controlled by the engine controlling apparatus  1  hereinafter described. 
     An injector  18  for injecting fuel is provided in the intake port  11 . The amount of fuel to be injected from the injector  18  is controlled by the engine controlling apparatus  1  hereinafter described. Further, an intake manifold  20  is provided on the upstream side of the intake flow with respect to the injector  18 . A surge tank  21  for temporarily storing air to flow to the intake port  11  side is provided at an upstream portion of the intake manifold  20 . A portion of the intake manifold  20  on the downstream side with respect to the surge tank  21  is formed so as to branch toward the intake ports  11  of the cylinders  19 , and the surge tank  21  is positioned at the branching point. The surge tank  21  functions so as to relax intake pulsation or intake interference that may possibly occur in each cylinder  19 . 
     A throttle body  22  is connected to the upstream side of the intake manifold  20 . An electronically-controlled throttle valve  23  is built in the throttle body  22  so that the amount of air to flow to the intake manifold  20  side is adjusted in response to the degree of opening (throttle opening degree) of the throttle valve  23 . The throttle opening degree is controlled by the engine controlling apparatus  1 . An intake path  24  is connected to the upstream side of the throttle body  22 , and an air filter is placed on the upstream side of the intake path  24 . Consequently, fresh air filtered by the air filter is supplied to the cylinders  19  of the engine  10  through the intake path  24  and the intake manifold  20 . 
     A purge path  28  for introducing purge gas containing evaporated fuel vaporized in the fuel tank  27  into the intake system of the engine  10  is connected to the surge tank  21 . The fuel tank  27  is a sealing-type tank and assumes a closed state with respect to the atmosphere in a state in which a cap  27   b  is fitted with an oil filling entrance  27   a . When fuel is to be supplied into the fuel tank  27 , the cap  27   b  is removed and a nozzle of an oil filling machine  50  [refer to  FIG. 5( c ) ] is inserted into the oil filling entrance  27   a.    
     A tank pressure sensor  36  for detecting the pressure (tank pressure) P T  in the fuel tank  27  is provided on the fuel tank  27 . The tank pressure P T  detected by the tank pressure sensor  36  is transmitted to the engine controlling apparatus  1 . Further, a switch not shown is provided on the cap  27   b , and a state of the cap  27   b  (whether or not the cap  27   b  is fitted) is detected by the switch and a result of the detection is transmitted to the engine controlling apparatus  1 . It is to be noted that the state of the cap  27   b  may be decided otherwise using information detected, for example, by a stroke sensor provided on a filler door not shown. 
     An electromagnetic purge valve  29  for controlling the flow rate (hereinafter referred to as purge gas flow rate Qp) of the purge gas to be introduced into the surge tank  21  is placed on the purge path  28 . The purge gas flow rate Qp increases as the opening degree of the purge valve  29  is controlled so as to increase. The purge gas flow rate Qp decreases as the opening degree is controlled so as to decrease. When the opening degree is zero, the purge gas flow rate Qp is zero (in other words, the purge gas is not introduced into the intake system). 
     Further, an electromagnetic bypass valve  30  is placed on the purge path  28  between the fuel tank  27  and the purge valve  29 . A canister  31  for temporarily recovering the evaporated fuel is connected to the bypass valve  30 . If the bypass valve  30  is opened, then the purge path  28  and the canister  31  are placed into a communicated state with each other, but, if the bypass valve  30  is closed, then the canister  31  is placed into an isolated state from the purge path  28 . 
     An atmospheric air path  32  for taking in external fresh air is connected to the canister  31  and the canister  31  is placed in an opened state with respect to the atmosphere. Activated carbon  31   a  for sorbing the evaporated fuel is built in the canister  31 . Here, the canister  31  is dedicated for oil-filling for temporarily recovering the evaporated fuel generated in the fuel tank  27  when the fuel is supplied into the fuel tank  27  (hereinafter referred to as upon filling oil). It is to be noted that the evaporated fuel recovered by the canister  31  is not desorbed from the activated carbon  31   a  when the pressure thereof is close to the atmospheric pressure P A  but is desorbed when a negative pressure higher than a predefined value is introduced into the canister  31 . 
     An electromagnetic sealed valve  33  is placed on the purge path  28  between the fuel tank  27  and the bypass valve  30 . Further, a bypass path  34  for bypassing the sealed valve  33  is connected to the purge path  28  between the fuel tank  27  and the bypass valve  30 , and a relief valve  35  is placed on the bypass path  34 . The relief valve  35  is a safety valve for a case in which opening and closing control of the sealed valve  33  is disabled by some cause. The relief valve  35  is automatically opened when the tank pressure P T  of the fuel tank  27  rises excessively high, but is normally placed in a closed state when the sealed valve  33  is in a normal state. 
     If the sealed valve  33  is opened, then the fuel tank  27  and the purge path  28  up to the bypass valve  30  are placed into a communicated state with each other. If the sealed valve  33  is closed, then the fuel tank  27  is isolated, in a sealed state thereof, from the purge path  28  on the intake system side with respect to the sealed valve  33 . Here, all of the purge valve  29 , bypass valve  30  and sealed valve  33  are needle valves and are used so that fine adjustment of the purge gas flow rate Qp can be performed. The opening degree of the purge valve  29 , bypass valve  30  and sealed valve  33  is controlled by the engine controlling apparatus  1 . 
     An exhaust manifold  25  is provided on the downstream side of the exhaust port  12 . The exhaust manifold  25  is formed in a shape for merging exhaust air from the cylinders  19  and is connected on the downstream side thereof to an exhaust path, an exhaust catalyst apparatus or the like not shown. An air fuel ratio sensor  37  for grasping air fuel ratio information (A/F) of mixture air burned in the combustion chamber  26  is provided on the exhaust path on the downstream side with respect to the exhaust manifold  25 . The air fuel ratio sensor  37  is, for example, an O 2  sensor, an LAFS (linear air fuel ratio sensor) or the like. 
     An air flow sensor  38  for detecting an intake flow rate Q is provided in the intake path  24 . The intake flow rate Q is a parameter corresponding to a flow rate (throttle flow rate Qth) of air (intake air) passing the throttle valve  23 . An intake manifold pressure sensor  39  for detecting the pressure (intake manifold pressure) P IM  in the intake manifold  20  is provided on the surge tank  21 . An engine rotation speed sensor  40  for detecting the rotational angle of the crankshaft  17  to acquire a rotational speed Ne of the engine  10  is provided for the crankshaft  17 . 
     Further, an accelerator position sensor  41  for detecting the operation amount (accelerator operation amount A PS ) of an accelerator pedal is provided on the vehicle. The accelerator operation amount A ps  is a parameter corresponding to an acceleration request or a starting intention of a driver, and, in other words, the accelerator operation amount A PS  correlates to the load to the engine  10  (output request to the engine  10 ). The air fuel ratio information, intake flow rate Q, intake manifold pressure P IM , engine rotation speed Ne and accelerator operation amount A PS  acquired by the sensors  37  to  41  are transmitted to the engine controlling apparatus  1 . 
     The engine controlling apparatus  1  (Engine Electronic Control Unit) is provided on the vehicle in which the engine  10  is equipped. The engine controlling apparatus  1  is a computer including a CPU for executing various calculation processes, a ROM in which a program and data necessary for the control of the CPU are stored, a RAM in which a result of calculation by the CPU or the like is temporarily stored, input and output ports for inputting and outputting a signal to and from the outside therethrough, and so forth. The engine controlling apparatus  1  is an electronic controller for totally controlling various systems including an ignition system, a fuel system, an intake and exhausting system and a valve gear system for the engine  10 . 
     To the input side of the engine controlling apparatus  1 , the tank pressure sensor  36 , air fuel ratio sensor  37 , air flow sensor  38 , intake manifold pressure sensor  39 , engine rotation speed sensor  40  and accelerator position sensor  41  are connected. On the other hand, to the output side of the engine controlling apparatus  1 , the injector  18 , throttle valve  23 , purge valve  29 , bypass valve  30  and sealed valve  33  are connected. As a particular controlling target by the engine controlling apparatus  1 , the amount of fuel to be injected from the injector  18 , the injection time period, the ignition time period by the ignition plug  13  and the degree of opening of the throttle valve  23 , purge valve  29 , bypass valve  30  and sealed valve  33  are applied. 
     It is to be noted that, in the engine controlling apparatus  1 , an opening degree controlling unit (not shown) for calculating a target degree of opening of the throttle valve  23  and outputting a controlling signal to the throttle valve  23  so that an actual opening degree of the valve coincides with the target opening degree is provided. The target opening degree is calculated, for example, based on the accelerator operation amount A PS  detected by the accelerator position sensor  41 . Here, the target opening degree of the throttle valve  23  calculated by the opening degree controlling unit corresponds to the current opening degree S 1  of the throttle valve  23 . In other words, the opening degree S 1  of the throttle valve  23  that is a controlling value is used as a detection value for control by the engine controlling apparatus  1 . It is to be noted that, in place of such a configuration as described above, a configuration may be applied in which a throttle position sensor for detecting the throttle opening degree S 1  is provided and a sensor value thereof is used for control. 
     Further, in the engine controlling apparatus  1 , a target purge ratio acquisition unit (not shown) for acquiring a target purge ratio R TGT  corresponding to a target introduction ratio of purge gas is provided. In the present embodiment, the ratio of the flow rate Qp of purge gas that passes the purge valve  29  to the flow rate Q of intake air that passes the throttle valve  23  (namely, the throttle flow rate Qth) is defined as purge ratio R. In particular, the purge ratio R is defined by the following expression (1):
 
 R=Qp/Qth   (1)
 
     The target purge ratio R TGT  is acquired, for example, based on the air fuel ratio information detected by the air fuel ratio sensor  37 , the intake flow rate Q detected by the air flow sensor  38  and so forth. The target purge ratio R TGT  acquired by the target purge ratio acquisition unit is transmitted to a calculation unit  3  in the engine controlling apparatus  1  hereinafter described. 
     [2. Controlling Configuration] 
     [2-1. Outline of Control] 
     In the engine controlling apparatus  1 , the opening degree control of the purge valve  29 , bypass valve  30  and sealed valve  33  placed on the purge path  28  is performed. Since the purge valve  29  is disposed at a position nearest to the intake system, fine adjustment of the purge gas flow rate Qp can be performed by controlling the opening degree S 2  of the purge valve  29 . The opening degree S 2  of the purge valve  29  is calculated by the calculation unit  3  hereinafter described. It is to be noted that the opening degree here corresponds to the magnitude of a flow path sectional area at a position (referred to as valve location) at which the valve is provided. For example, when the opening degree of the valve is zero (in a closed state of the valve), the flow path sectional area at the valve location is zero. Meanwhile, when the opening degree of the valve is not zero (in an open state of the valve), the magnitude of the flow path sectional area of the valve location increases as the opening degree increases. Accordingly, the opening degree of the valve can be calculated from the flow path sectional area at the valve location. 
     On the other hand, the bypass valve  30  and the sealed valve  33  are controlled to a state in which the opening degree thereof is zero (in a closed state of the valves) or to a fully open state (an open state of the valves) depending upon whether the engine  10  is operating or stopping or oil is being filled or else the fuel tank  27  is in a high-pressure state. In short, the opening degree of the bypass valve  30  and the opening degree of the sealed valve  33  are not calculated here but are controlled to one of the fully closed state and the fully open state. 
     The engine controlling apparatus  1  controls the opening degree of the purge valve  29 , bypass valve  30  and sealed valve  33  depending upon whether the engine  10  is operating or stopping or oil is being filled or else the fuel tank  27  is in a high-pressure state. When the engine  10  is operating, control is performed so that the evaporated fuel recovered by the canister  31  is desorbed and the purge gas containing the evaporated fuel is introduced into the surge tank  21 . The control is hereinafter referred to as normal purge control. 
     When the engine  10  is stopping or oil is being filled, control is performed so that the introduction of the purge gas is cut off. The control is hereinafter referred to as purge cut control. Further, when the fuel tank  27  is in a high-pressure state, control is performed so that the purge gas containing the evaporated fuel evaporated in the fuel tank  27  is introduced into the surge tank  21 . The control is hereinafter referred to as high-pressure purge control. The engine controlling apparatus  1  is characterized in the high-pressure purge control. 
     [2-2. Controlling Block Configuration] 
     In order to perform the control described above, the engine controlling apparatus  1  includes functional elements as a decision unit  2 , a calculation unit  3  and a controlling unit  4 . The elements mentioned may be implemented by electronic circuitry (hardware) or may be programed as software. Or else, some of the functions may be provided as hardware while the remaining one or ones of the functions are implemented by software. 
     The decision unit  2  decides which one of the normal purge control, purge cut control and high-pressure purge control is to be performed. The decision unit  2  decides which one of the following conditions (A) to (D) is satisfied from the engine rotation speed Ne detected by the engine rotation speed sensor  40 , tank pressure P T  detected by the tank pressure sensor  36  and state of the cap  37   b  of the oil filling entrance  37   a:    
     (A) that the engine rotation speed Ne is not zero (Ne≠0) and the tank pressure P T  is lower than a predetermined pressure P 0  (P T &lt;P 0 ); 
     (B) that the engine rotation speed Ne is zero (Ne=0) and the tank pressure P T  is lower than the predetermined pressure P 0  (P T &lt;P 0 ) and besides the cap  27   b  is in a fitted state; 
     (C) that the cap  27   b  is in a removed state; and 
     (D) that the tank pressure P T  is equal to or higher than the predetermined pressure P 0  (P T ≧P 0 ). 
     The decision unit  2  decides, when the condition (A) is satisfied, that the engine  10  is operating but decides, when the condition (B) is satisfied, that the engine  10  is stopping. Further, the decision unit  2  decides, when the condition (C) is satisfied, that oil is being filled but decides, when the condition (D) is satisfied, that the fuel tank  27  is in a high-pressure state. It is to be noted that the predetermined pressure P 0  is set in advance to a lower value than that of a permissible pressure of the fuel tank  27 . 
     When it is decided by the decision unit  2  that the engine  10  is operating and when it is decided that the fuel tank  27  is in a high-pressure state, the result of the decision is transmitted to the calculation unit  3  and the controlling unit  4 . On the other hand, when it is decided by the decision unit  2  that the engine  10  is stopping and when it is decided that oil is being filled, the result of the decision is transmitted to the controlling unit  4 . 
     The calculation unit  3  calculates, in the normal purge control, the flow path sectional area A 2  (hereinafter referred to as purge area A 2 ) at location of the purge valve  29  corresponding to the opening degree S 2  of the purge valve  29  based on the target purge ratio R TGT . If a result of the decision that the engine  10  is operating is transmitted from the decision unit  2 , then the calculation unit  3  calculates the purge area A 2  of the purge valve  29  for performing the normal purge control. 
     The purge ratio R is defined by the expression (1) given hereinabove. Here, since the throttle flow rate Qth and the purge gas flow rate Qp are represented by the following expressions (2) and (3), respectively, the purge ratio R is rewritten into the following expression (4):
 
 Qth=Vth×A   1   (2)
 
 Qp=Vp×A   2   =Vth×A   2   ×K 1  (3)
 
 R =( Vth×A   2   ×K 1)/( Vth×A   1 )  (4)
 
where A 1  is the flow path sectional area of the throttle valve  23  corresponding to the throttle opening degree S 1  and is hereinafter referred to as throttle area A 1 . Further, Vth is the flow velocity of intake air that passes the throttle valve  23 , and Vp is the flow velocity of purge gas that passes the purge valve  29 , respectively. Further, K 1  is the pipe resistance flow velocity correction coefficient for taking the ventilation resistance (pressure loss) until the purge gas is introduced into the surge tank  21  into account. Since the purge path  28  in which the purge gas flows is thinner than the path of the intake system (intake path  24  or intake manifold  20 ), the ventilation resistance of the purge path  28  is higher than that of the intake path in which intake air flows. Further, since the purge gas passes through the activated carbon  31   a  when it flows in the canister  31 , the ventilation resistance increases further.
 
     Where the ventilation resistance to the purge gas is ignored, since the pressure ratio across the throttle valve  23  and the pressure ratio across the purge valve  29  are equal to each other because the upstream pressure and the downstream pressure are equal to the atmospheric pressure P A  and the intake manifold pressure P IM , respectively, it is supposed that the flow velocity Vth of the intake air and the flow velocity Vp of the purge gas are equal to each other. However, actually since the ventilation resistance to the purge gas is high, the upstream pressure of the purge valve  29  is lower than the atmospheric pressure P A . Therefore, the flow velocity Vp of the purge gas decreases and the purge gas flows but by a flow rate lower than the flow rate of the purge gas that is to flow originally. 
     Therefore, the pipe resistance flow velocity correction coefficient K 1  is a correction coefficient used to increase, taking a pressure loss (decreasing amount of the purge gas flow rate) when the purge gas is introduced into the surge tank  21  into consideration, the purge area A 2  as much. The pipe resistance flow velocity correction coefficient K 1  is acquired, for example, by storing such a pipe resistance flow velocity correction coefficient map as depicted in  FIG. 2  in advance and applying a pressure ratio (intake manifold pressure P IM /atmospheric pressure P A ) to the pipe resistance flow velocity correction coefficient map. 
     By multiplying the purge area A 2  by the pipe resistance flow velocity correction coefficient K 1 , it can be considered that the flow velocity Vth of the intake air and the flow velocity Vp of the purge gas are equal to each other. Accordingly, the purge area A 2  necessary for securing the target purge ratio R TGT  is represented by the following expression (5):
 
 A   2   =A   1   ×R   TGT   /K 1  (5)
 
     In short, in the normal purge control, the calculation unit  3  calculates the purge area A 2  by the expression (5) given above based on the throttle area A 1 , target purge ratio R TGT  and pipe resistance flow velocity correction coefficient K 1 . The purge area A 2  calculated by the calculation unit  3  is transmitted to the controlling unit  4 . 
     The calculation unit  3  further calculates, in the high-pressure purge control, a high-pressure purge area A 2 ′ corresponding to the opening degree S 2 ′ of the purge valve  29  based on the target purge ratio R TGT . If a result of the decision that the fuel tank  27  is in a high-pressure state is transmitted from the decision unit  2 , then the calculation unit  3  calculates the high-pressure purge area A 2 ′ of the purge valve  29  used for performing the high-pressure purge control. 
     While the purge ratio R is defined by the expression (1) given hereinabove and the throttle flow rate Qth and the purge gas flow rate Qp are represented by the expressions (2) and (3) given hereinabove, respectively, since the upstream pressure of the purge valve  29  in the high-pressure purge control is higher than the atmospheric pressure P A , a high pressure is taken into consideration when the flow velocity Vp of the purge gas is calculated. Accordingly, the purge gas flow rate Qp′ in the high-pressure purge is represented by the following expression (6):
 
 Qp′=Vp (taking high pressure into consideration)× A   2 ′=(flow velocity map [ P   IM   /P   T   ]/K 2 ×K 1)× A   2 ′  (6)
 
where the flow velocity map [P IM /P T ] is the flow velocity Vp of purge gas acquired by applying the pressure ratio across the purge valve  29  (downstream pressure/upstream pressure) to the flow velocity map depicted in  FIG. 4 . The flow velocity map is stored in advance in the engine controlling apparatus  1 . It is to be noted that, since the upstream pressure of the purge valve  29  in the high-pressure purge control can be considered as the tank pressure P T  and the downstream pressure of the purge valve  29  is equal to the intake manifold pressure P IM , the pressure ratio across the purge valve  29  is intake manifold pressure P IM /tank pressure P T .
 
     Further, K 2  is a correction coefficient corresponding to the upstream pressure of the purge valve  29  (hereinafter referred to as tank pressure flow velocity correction coefficient K 2 ). The tank pressure flow velocity correction coefficient K 2  is acquired, for example, from such a tank pressure flow velocity correction coefficient map as depicted in  FIG. 3 . The correction coefficient map is stored in advance in the engine controlling apparatus  1  and is set here such that the tank pressure flow velocity correction coefficient K 2  has a proportional relationship to the upstream pressure of the purge valve  29 . As depicted in  FIG. 3 , the tank pressure flow velocity correction coefficient K 2  is set to 1 when the upstream pressure of the purge valve  29  is equal to the atmospheric pressure P A  and is set such that it decreases linearly as the upstream pressure increases with respect to the atmospheric pressure P A . 
     The flow rate Qp of the purge gas that passes the purge valve  29  varies if the upstream pressure varies with respect to the pressure ratio across the purge valve  29 . In particular, even where the pressure ratio across the purge valve  29  is equal, the purge gas flow rate Qp increases as the upstream pressure becomes higher than the atmospheric pressure P A . Therefore, in the high-pressure purge control in which the upstream pressure is equal to or higher than the atmospheric pressure P A , the purge gas flow rate Qp′ is acquired by dividing the purge gas flow velocity Vp in the high-pressure purge control acquired from the flow velocity map by the tank pressure flow velocity correction coefficient K 2 . 
     If the expressions (2) and (6) given hereinabove are substituted into the expression (1) and the resulting expression is solved for the high-pressure purge area A 2 ′, then the high-pressure purge area A 2 ′ is represented by the expression (7) given below. It is to be noted that, since the flow velocity Vth of intake air in the expression (2) is acquired by applying the pressure ratio across the throttle valve  23  (downstream pressure/upstream pressure) to the flow velocity map depicted in  FIG. 4 , in the expression (7), the flow velocity Vth of the intake air is represented as the flow velocity map [P IM /P A ]:
 
 A   2   ′=A   1   ×R   TGT   ×K 2 /K 1×(flow velocity map [ P   IM   /P   A ]/flow velocity map [ P   IM   /P   T ])  (7)
 
     If the ratio of the flow velocity Vth of intake air to the flow velocity Vp (taking a high pressure into consideration) of the purge gas in the expression (7) is placed as the coefficient (flow velocity ratio correction coefficient) K 3 , then the expression (7) can be rewritten into the following expression (8):
 
 A   2   ′=A   1   ×R   TGT   ×K 2 /K 1 ×K 3  (8)
 
     That is, in the high-pressure purge control, the calculation unit  3  calculates the high-pressure purge area A 2 ′ using the expression (8) given above based on the throttle area A 1 , target purge ratio R TGT , pipe resistance flow velocity correction coefficient K 1 , tank pressure flow velocity correction coefficient K 2  and flow velocity ratio correction coefficient K 3 . It is to be noted that, by solving the expression (8) for the high-pressure purge area A 2 ′ in such a manner as described, then it can be considered that the tank pressure flow velocity correction coefficient K 2  is a coefficient for correcting the high-pressure purge area A 2 ′ so as to be smaller than the purge area A 2  in the normal purge control. In other words, it can be considered that the tank pressure flow velocity correction coefficient K 2  is a coefficient for correcting the purge gas flow rate Qp in a decreasing direction taking increase of the purge gas flow rate Qp arising from that the upstream pressure (namely, the tank pressure P T ) of the purge valve  29  has a high pressure into consideration. 
     It is to be noted that, if the purge area A 2  calculated in the normal purge control is used (namely, if it is replaced into the expression (5) given hereinabove), the expression (8) given hereinabove is represented as the following expression (9):
 
 A   2   ′=A   2   ×K 2 ×K 3  (9)
 
     That is, it can be considered that the calculation unit  3  corrects the purge area A 2  calculated in the normal purge control using the tank pressure flow velocity correction coefficient K 2  and the flow velocity ratio correction coefficient K 3  to calculate the high-pressure purge area A 2 ′. The high-pressure purge area A 2 ′ calculated by the calculation unit  3  is transmitted to the controlling unit  4 . 
     The controlling unit  4  performs opening degree control of the purge valve  29 , bypass valve  30  and sealed valve  33  based on a result of the decision by the decision unit  2 . If the result of the decision that the engine  10  is operating is transmitted from the decision unit  2 , then the controlling unit  4  performs the normal purge control. In this case, the controlling unit  4  controls the purge valve  29  and the bypass valve  30  to an open state and controls the sealed valve  33  to a closed state as depicted in  FIG. 5( a ) . 
     In particular, in the normal purge control, the fuel tank  27  is isolated by the sealed valve  33  and purge gas containing evaporated fuel recovered by the canister  31  is introduced suitably into the surge tank  21  of the intake manifold  20 . Consequently, the capacity of the evaporated fuel capable of being recovered by the canister  31  is secured. At this time, the controlling unit  4  controls the opening degree S 2  of the purge valve  29  so as to correspond to the purge area A 2  calculated by the calculation unit  3 . Consequently, purge gas corresponding to the target purge ratio R TGT  is introduced into the intake system. 
     If the result of the decision that the engine  10  is stopping is transmitted from the decision unit  2 , then the controlling unit  4  performs the purge cut control. In this case, as depicted in  FIG. 5( b ) , the controlling unit  4  controls the opening degree S 2  of the purge valve  29  to zero to place the purge valve  29  into a closed state. It is to be noted that, in this case, the state of the bypass valve  30  and the sealed valve  33  where the engine  10  is operating is maintained, and the bypass valve  30  and the sealed valve  33  are placed into an open state and a closed state, respectively. In particular, if the result of the decision that the engine  10  is placed from an operating state into a stopping state is received, then the controlling unit  4  controls only the purge valve  29  into a closed state. It is to be noted that, if the engine  10  is placed into an operating state again, then the normal purge control is performed. 
     If the result of the decision that filling of oil is being performed is transmitted from the decision unit  2 , then the controlling unit  4  performs the purge cut control for oil-filling. In this case, as depicted in  FIG. 5( c ) , the controlling unit  4  controls the opening degree S 2  of the purge valve  29  to zero to place the purge valve  29  into a closed state. Further, the controlling unit  4  controls the bypass valve  30  and the sealed valve  33  into an open state. By placing the bypass valve  30  and the sealed valve  33  into the open state, the tank pressure P T  decreases to a pressure with which oil filling can be performed and the evaporated fuel vaporized upon oil-filling is recovered by the canister  31  so that leakage of the evaporated fuel into the atmosphere is prevented. It is to be noted that, since the purge valve  29  is in a closed state at this time, the purge gas is not introduced into the intake system. 
     If the result of the decision that the fuel tank  27  is in a high-pressure state is transmitted from the decision unit  2 , then the controlling unit  4  performs the high-pressure purge control. In this case, as depicted in  FIG. 1 , the controlling unit  4  controls the purge valve  29  and the sealed valve  33  into an open state and controls the bypass valve  30  into a closed state. In particular, in the high-pressure purge control, the canister  31  is isolated by the bypass valve  30  and purge gas containing the evaporated fuel accumulated in the fuel tank  27  is introduced into the surge tank  21 . Consequently, the tank pressure P T  in the fuel tank  27  is reduced. At this time, the controlling unit  4  controls the opening degree S 2  of the purge valve  29  so as to correspond to the high-pressure purge area A 2 ′ calculated by the calculation unit  3 . Consequently, the purge gas corresponding to the target purge ratio R TGT  is introduced into the intake system. 
     [3. Flow Chart] 
       FIG. 6  is a flow chart exemplifying a decision procedure performed by the decision unit  2  of the engine controlling apparatus  1 , and  FIG. 7  is a flow chart exemplifying a controlling procedure upon high-pressure purge control by the engine controlling apparatus  1 . The procedures depicted in the flow charts operate in dependently of each other in a predetermined controlling cycle usually within a period within which energization to the engine controlling apparatus  1  is performed. Further, when the processes of the flow charts are performed, information of a result of the processes is transmitted to each other. 
     As depicted in  FIG. 6 , various kinds of sensor information including the tank pressure P T , intake manifold pressure P IM , engine rotation speed Ne and so forth are acquired at step S 10 . At step S 20 , it is decided whether or not the cap  27   b  of the fuel tank  27  is in a fitted state, and, if the cap  27   b  is in a fitted state, then the processing advances to step S 30 , at which it is decided whether or not the tank pressure P T  is lower than the predetermined pressure P 0 . On the other hand, if the cap  27   b  is in a removed state, then the processing advances to step S 40 , at which it is decided that oil filling is being performed, and then the controlling cycle ends. 
     If the tank pressure P T  is lower than the predetermined pressure P 0  at step S 30 , then the processing advances to step S 50 , at which it is decided whether or not the engine rotation speed Ne is higher than zero. On the other hand, if the tank pressure P T  is equal to or higher than the predetermined pressure P 0 , then the processing advances to step S 60 , at which it is decided that the fuel tank  27  is in a high-pressure state, and the controlling cycle ends. If the engine rotation speed Ne is higher than zero at step S 50 , then the processing advances to step S 70 , at which it is decided that the engine  10  is operating, and the controlling cycle ends. On the other hand, if the engine rotation speed Ne is zero, then the processing advances to step S 80 , at which it is decided that the engine  10  is stopping, and the controlling cycle ends. 
     Further, as depicted in  FIG. 7 , it is decided at step T 10  whether or not it is decided in the flow chart of  FIG. 6  that the fuel tank  27  is in a high-pressure state. If the fuel tank  27  is in a high-pressure state, then processes at steps T 20  to T 80  are performed. However, if the fuel tank  27  is not in a high-pressure state, then the controlling cycle ends. At step T 20 , various kinds of sensor information are acquired. Next at step T 30 , the pipe resistance flow velocity correction coefficient K 1  corresponding to the pressure ratio (intake manifold pressure P IM /atmospheric pressure P A ) is acquired from the pipe resistance flow velocity correction coefficient map of  FIG. 2 . 
     At step T 40 , the tank pressure flow velocity correction coefficient K 2  corresponding to the tank pressure P T  is acquired from the correction coefficient map of  FIG. 3 . Further, at step T 50 , the flow velocity Vth of the intake air and the flow velocity Vp of the purge gas taking a high pressure into consideration are acquired from the flow velocity map of  FIG. 4  and the flow velocity ratio correction coefficient K 3  is acquired. Then, at step T 60 , the high-pressure purge area A 2 ′ of the purge valve  29  is calculated using the information and the coefficients acquired at steps T 20  to T 50 . 
     At step T 70 , the opening degree control for the purge valve  29  is performed so as to establish an opening degree corresponding to the high-pressure purge area A 2 ′ calculated at the preceding step. Then, at step T 80 , the bypass valve  30  is controlled to a closed state and the sealed valve  33  is controlled to an open state, and then the controlling cycle ends. The processes of the flow chart of  FIG. 7  are repetitively performed where the tank pressure P T  of the fuel tank  27  is equal to or higher than the predetermined pressure P 0 . It is to be noted that, since the tank pressure P T  of the fuel tank  27  gradually decreases by the high-pressure purge control, the pipe resistance flow velocity correction coefficient K 1 , tank pressure flow velocity correction coefficient K 2  and flow velocity ratio correction coefficient K 3  are acquired every time (for each controlling cycle), and also the high-pressure purge area A 2 ′ varies in accordance with the decrease of the tank pressure P T . 
     [4. Effect] 
     Accordingly, with the present engine controlling apparatus  1 , when the opening degree S 2  of the purge valve  29  is calculated based on the introduction ratio (target purge ratio R TGT ) of the target purge gas, the opening degree S 2  of the purge valve  29  is corrected, in the high-pressure purge control, at least using the tank pressure flow velocity correction coefficient K 2  corresponding to the upstream pressure of the purge valve  29 . Therefore, a suitable purge gas flow rate Qp′ can be secured by a simple configuration. Further, since complicated calculation is not required, the capacity of the ROM can be reduced. 
     Further, the opening degree S 2  of the purge valve  29  is corrected using the flow velocity ratio correction coefficient K 3  corresponding to the ratio between the flow velocity Vth of intake air that passes the throttle valve  23  and the flow velocity Vp of the purge gas that passes the purge valve  29  so that an appropriate purge gas flow rate Qp′ can be secured taking it into consideration that the upstream pressure of the purge valve  29  is higher than the atmospheric pressure P A . Therefore, the calculation accuracy of the opening degree S 2  of the purge valve  29  in the high-pressure purge control can be enhanced. 
     Further, the opening degree S 2  of the purge valve  29  is corrected using the pipe resistance flow velocity correction coefficient K 1  taking the ventilation resistance (pressure loss) until purge gas is introduced into the intake system into consideration so that the calculation accuracy for the opening degree S 2  of the purge valve  29  in the high-pressure purge control can be enhanced further. 
     Further, the correction coefficient map set such that the tank pressure flow velocity correction coefficient K 2  has a proportional relationship to the upstream pressure of the purge valve  29  is provided and the calculation unit  3  can acquire the tank pressure flow velocity correction coefficient K 2  using the correction coefficient map. Therefore, the opening degree S 2  of the purge valve  29  can be calculated with a simple configuration. 
     In the present embodiment, the canister  31  is dedicated for filling of oil isolated from the purge path  28  in the high-pressure purge control while recovering evaporated fuel only upon oil-filling, and the normal purge control is suitably performed while the engine  10  is operating. Therefore, the capacity of evaporated fuel capable of being absorbed by the activated carbon  31   a  of the canister  31  can be secured constantly. Consequently, for example, where the engine  10  of  FIG. 1  is equipped in a hybrid electric vehicle, the necessity to operate the engine  10  in order only to desorb the evaporated fuel recovered by the canister  31  is eliminated, and improvement of fuel efficiency can be implemented. 
     In particular, since the hybrid electric vehicle frequently travels only with a motor while the engine  10  is kept stopped, the opportunity is limited in which the evaporated fuel recovered by the canister  31  can be purged. Therefore, where a canister for always recovering the evaporated fuel not only upon filling of oil is provided, a case occurs in which the engine  10  is obliged to be driven only for the purge control when the absorption capacity of the canister becomes poor, and the possibility that mileage may be deteriorated is high. With the engine  10  according to the present embodiment, such a situation as just described does not occur, and therefore, improvement of fuel efficiency can be implemented as described above. 
     [5. Others] 
     While the embodiment of the present invention is described above, the present invention is not limited to the embodiment specifically described above, and variations and modifications can be made without departing from the scope of the present invention. 
     While, in the embodiment described above, it is exemplified that the correction coefficient map for acquiring the tank pressure flow velocity correction coefficient K 2  is set such that the tank pressure flow velocity correction coefficient K 2  linearly reduces as the upstream pressure (tank pressure P T ) of the purge valve  29  increases, the correction coefficient map is not limited to this. For example, such a correction coefficient map may be applied that, as indicated by a solid line in  FIGS. 8( a ) and 8( b ) , the tank pressure flow velocity correction coefficient K 2  where the upstream pressure of the purge valve  29  is equal to or higher than the predetermined value P 1  is low in comparison with that in a case in which the upstream pressure varies with a variation ratio equal to that where the upstream pressure is lower than the predetermined value P 1  (graphs of a broken line in  FIGS. 8( a ) and 8( b ) ). 
     Further, while, in the embodiment described above, the pipe resistance flow velocity correction coefficient K 1 , tank pressure flow velocity correction coefficient K 2  and flow velocity ratio correction coefficient K 3  are used in the calculation of the high-pressure purge area A 2 ′, a configuration may be applied in which, in the high-pressure purge control, the purge area A 2  is corrected using at least the tank pressure flow velocity correction coefficient K 2 . For example, if the ventilation resistance until the purge gas is introduced into the surge tank  21  is so low that it can be ignored, then the pipe resistance flow velocity correction coefficient K 1  may be omitted. Further, since the flow velocity with respect to the pressure ratio does not vary where the pressure ratio is lower than the critical pressure ratio, the flow velocity ratio correction coefficient K 3  may be omitted in response to the magnitude of the pressure ratio. In other words, the purge area A 2  maybe corrected only with the tank pressure flow velocity correction coefficient K 2  or may be corrected with the pipe resistance flow velocity correction coefficient K 1  or the flow velocity ratio correction coefficient K 3  in addition to the tank pressure flow velocity correction coefficient K 2 . 
     Further, the engine  10  is not limited to that depicted in  FIG. 1 . Further, the configuration of the fuel tank  27 , purge path  28 , purge valve  30 , canister  31  and so forth described hereinabove is an example and is not limited to that described above. For example, the canister  31  may not be configured from a canister dedicated for oil filling or may be placed between the fuel tank  27  and the purge valve  29  without through the bypass valve  30 . Further, the purge valve  29 , bypass valve  30  and sealed valve  33  may be individually configured from a valve other than a needle valve. 
     REFERENCE SIGNS LIST 
       1  engine controlling apparatus 
       2  decision unit 
       3  calculation unit 
       4  controlling unit 
       10  engine 
       20  intake manifold 
       21  surge tank 
       23  throttle valve 
       24  intake path 
       27  fuel tank 
       28  purge path 
       29  purge valve 
       30  bypass valve 
       31  canister 
       33  sealed valve 
       36  tank pressure sensor 
       39  intake manifold pressure sensor 
     The invention thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.