Patent Publication Number: US-6910467-B2

Title: Evaporated fuel processing apparatuses for engines with supercharger

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an evaporated fuel processing apparatus adapted to collect evaporated fuel generated in a fuel tank into a canister and then purge the collected evaporated fuel into an intake passage of an engine and, more particularly, to an evaporated fuel processing apparatus provided for an engine with a supercharger. 
   2. Description of Related Art 
   Some conventional arts related to an evaporated fuel processing apparatus for an engine with a supercharger are disclosed in for example the following patent documents; Patent document 1 (Japanese patent unexamined publication No. Sho 62-18747, particularly, pages 1-2 and FIG. 2), Patent document 2 (Japanese patent publication No. Sho 59-563, particularly, pages 1-3 and FIG. 2), and Patent document 3 (Japanese patent publication No. Hei 5-10216, particularly, pages 2-7 and FIGS. 1 and 5). 
   Patent Document 1 discloses an apparatus constructed to purge evaporated fuel collected in a canister into an intake passage by utilizing purge passages configured in a double purging system in response to operation/nonoperation of a supercharger. During supercharging that the pressure in an intake passage positioned downstream of a throttle valve (a restriction valve) is a positive pressure, a change-over valve is opened to purge evaporated fuel from the canister into the intake passage located upstream of a supercharging impeller. The change-over valve is a diaphragm type valve which opens when senses pressure in the intake passage located downstream of the throttle valve during supercharging. 
   Patent document 2 discloses an apparatus using purge passages configured in a double purging system, as with the apparatus in the document 1. Specifically, This apparatus is provided with a first purge passage (a purge line) for purging evaporated fuel from a canister into an intake passage located downstream of a throttle valve (an intake air restriction valve) and a second purge passage for purging the evaporated fuel from the canister into an intake passage located upstream of a compressor in a turbocharger. In an operating condition of the turbocharger, the compressor feeds supercharged air into the canister to thereby force the evaporated fuel out of the canister into the purge passage, thus purging the evaporated fuel into the intake passage upstream of the compressor. The second purge passage is provided with no valve or the like to control the flow of evaporated fuel. 
   Patent document 3 discloses an apparatus using purge passages configured in a double purging system, as with the apparatus in the documents 1 and 2. This apparatus is constructed, differently from that in the document 2, to take in air for purging evaporated fuel from an intake passage positioned upstream of a compressor in a turbocharger through an intake air introducing passage and introduce the air into a canister. In this apparatus, the purge passage for purging evaporated fuel into the intake passage located upstream of the compressor is provided with no valve or the like to control the flow of evaporated fuel. 
   In the apparatus of the document 1, however, since the change-over valve is a diaphragm type valve, a response delay in opening and closing the change-over valve would become problems as below. For example, when an engine is in a decelerating condition, fuel cut is generally performed in the engine. However, there may be cases where a supercharger operates by inertia even just after deceleration, causing a delay in opening the change-over valve. Accordingly, the evaporated fuel is caused to flow in the intake passage upstream of the supercharging impeller. The evaporated fuel at this time would not burn or incompletely burn in a combustion chamber, which results in a deterioration in exhaust gas. To avoid such problems, it is conceivable to provide a check-over valve in the purge passage. Since a negative pressure produced in the intake passage upstream of the supercharging impeller is relatively small, the pressure to open the check valve has to be set at a relatively small pressure. Consequently, the check valve tends to close later during deceleration of the engine and the evaporated fuel also may be caused to flow in the intake passage. 
   In the above documents 2 and 3, any valve or the like is not provided in the purge passage connected in communication with the intake passage upstream of the compressor. Accordingly, when the supercharger operates by inertia just after deceleration of the engine, the evaporated fuel is also caused to flow in the intake passage, leading to a deterioration in exhaust gas. To avoid such problems, a check valve may be provided in the purge passage. However, it can be hardly said that there is no possibility of causing a delay in closing the check valve during deceleration of the engine. This also may cause the evaporated fuel to flow in the intake passage. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide an evaporated fuel processing apparatus for an engine with a supercharger, adapted to allow purging of evaporated fuel into an intake passage through the use of a negative pressure or supercharging pressure produced in the intake passage in association with operation of a supercharger and adapted to allow control of the purging in good response to operating conditions of the engine. 
   Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
   To achieve the purpose of the invention, there is provided an evaporated fuel processing apparatus for an engine with a supercharger, for collecting evaporated fuel generated in a fuel tank into a canister and purging the collected evaporated fuel from the canister to an intake passage of the engine, the supercharger including a compressor provided in the intake passage, the evaporated fuel processing apparatus comprising: a purge passage through which the evaporated fuel is purged from the canister into the intake passage located upstream of the compressor; an electromagnetic valve for opening and closing the purge passage; operating condition detection means which detects an operating condition of the engine; and control means which controls the opening and closing operations of the electromagnetic valve so that the electromagnetic valve is opened when the control means determines that intake pressure of the engine is an atmospheric pressure or more on the basis of the detected operating condition of the engine and the electromagnetic valve is closed when the control means determines that the intake pressure of the engine is less than the atmospheric pressure. 
   According to another aspect, the invention provides an evaporated fuel processing apparatus for an engine with a supercharger, for collecting evaporated fuel generated in a fuel tank into a canister and purging the collected evaporated fuel from the canister into an intake passage of the engine, the supercharger including a compressor provided in the intake passage, the evaporated fuel processing apparatus comprising: a first purge passage through which the evaporated fuel is purged from the canister into the intake passage located upstream of the compressor; a first electromagnetic valve for opening and closing the first purge passage; operating condition detection means which detects an operating condition of the engine; a throttle valve provided in the intake passage located downstream of the compressor; a second purge passage through which the evaporated fuel is purged from the canister into the intake passage located downstream of the throttle valve; a second electromagnetic valve for opening and closing the second purge passage; and control means which controls the opening and closing operations of the first and second electromagnetic valves so that the second electromagnetic valve is closed when the control means determines that intake pressure of the engine is an atmospheric pressure or more on the basis of the detected operating condition of the engine and then the first electromagnetic valve is opened, and the first and second electromagnetic valves are closed when the control means determines that the intake pressure of the engine is less than the atmospheric pressure. 
   According to another aspect, the invention provides an evaporated fuel processing apparatus for an engine with a supercharger, for collecting evaporated fuel generated in a fuel tank into a canister and purging the collected evaporated fuel from the canister to an intake passage of the engine, the supercharger including a compressor provided in the intake passage, the evaporated fuel processing apparatus comprising: a purge passage through which the evaporated fuel is purged from the canister into the intake passage located upstream of the compressor; a supercharging pressure passage through which a supercharging pressure in the intake passage downstream of the compressor is supplied to the canister as a back pressure; an electromagnetic valve for opening and closing the purge passage; operating condition detection means for detecting an operating condition of the engine; and control means which controls the opening and closing operations of the electromagnetic valve on the basis of the detected operating condition of the engine. 
   According to another aspect, the invention provides an evaporated fuel processing apparatus for an engine with a supercharger, for collecting evaporated fuel generated in a fuel tank into a canister and purging the collected evaporated fuel from the canister into an intake passage of the engine, the supercharger including a compressor provided in the intake passage, the evaporated fuel processing apparatus comprising: a purge passage through which the evaporated fuel is purged from the canister into the intake passage located upstream of the compressor; an aspirator, provided in the purge passage, for drawing in the evaporated fuel flowing through the purge passage by allowing working gas to flow; a supercharged air passage through which supercharged air in the intake passage downstream of the compressor is allowed to flow in the aspirator as the working gas; an electromagnetic valve for opening and closing the purge passage; operating condition detection means which detects an operating condition of the engine; and control means for controlling the opening and closing operations of the electromagnetic valve on the basis of the detected operating condition of the engine. 
   According to another aspect, the invention provides an evaporated fuel processing apparatus for an engine with a supercharger, for collecting evaporated fuel generated in a fuel tank into a canister and purging the collected evaporated fuel from the canister to an intake passage of the engine, the supercharger including a compressor provided in the intake passage, the evaporated fuel processing apparatus comprising: a purge passage through which the evaporated fuel is purged from the canister into the intake passage located downstream of the compressor; an aspirator, provided in the purge passage, for drawing in the evaporated fuel flowing through the purge passage by allowing working gas to flow; a supercharged air passage through which supercharged air in the intake passage downstream of the compressor is allowed to flow in the aspirator as the working gas; an electromagnetic valve for opening and closing the purge passage; operating condition detection means which detects an operating condition of the engine; and control means which controls the opening and closing operations of the electromagnetic valve on the basis of the detected operating condition of the engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification illustrate an embodiment of the invention and, together with the description, serve to explain the objects, advantages and principles of the invention. 
     In the drawings, 
       FIG. 1  is a schematic perspective view of an engine system with a supercharger in a first embodiment; 
       FIG. 2  is a flowchart showing a purge control program; 
       FIG. 3  is a schematic perspective view of an engine system with a supercharger in a second embodiment; 
       FIG. 4  is a flowchart showing a purge control program; 
       FIG. 5  is a schematic perspective view of an engine system with a supercharger in a third embodiment; 
       FIG. 6  is a schematic perspective view of an engine system with a supercharger in a fourth embodiment; 
       FIG. 7  is a flowchart showing a purge control program; and 
       FIG. 8  is a schematic perspective view of an engine system with a supercharger in a fifth embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   [First Embodiment] 
   A detailed description of a first preferred embodiment of an evaporated fuel processing apparatus for an engine with a supercharger embodying the present invention will now be given referring to the accompanying drawings. 
     FIG. 1  is a schematic perspective view of an engine system with a supercharger in the present embodiment. An engine  1  is provided with an intake passage  2  for taking in outside air and an exhaust passage  3  for discharging exhaust gas. Fuel stored in a fuel tank  5  is supplied for combustion to a combustion chamber  4  of the engine  1  by a predetermined fuel supply device (not shown). 
   A turbocharger  6  serving as a supercharger is provided at a position of the intake passage  2  and the exhaust passage  3 . More specifically, a compressor  7  constituting the turbocharger  6  is disposed in the intake passage  2  and a turbine  8  also constituting the turbocharger  6  is disposed in the exhaust passage  3 . As it is generally known, the turbocharger  6  is constructed such that the turbine  8  is rotated by power of exhaust gas, thereby rotating the compressor  7  disposed coaxially with the turbine  8 , thus pressurizing (supercharging) the air in the intake passage  2 . This supercharging causes the air of high density to be supplied to the combustion chamber  4  to burn a large amount of fuel, increasing power of the engine  1 . 
   An air cleaner  9  is provided in the intake passage  2  upstream of the compressor  7 . In the intake passage  2  downstream of the compressor  7 , on the other hand, there are provided an intercooler  10 , a throttle valve  11 , and a surge tank  12 . The intercooler  10  is used to cool supercharged air supplied via the compressor  7 . The throttle valve  11  is opened and closed to control the amount of intake air. The throttle valve  11  is operated in interlocked relation with the operation of an accelerator pedal (not shown) by a driver. The surge tank  12  is used to smooth intake air involving pulsation. 
   The engine  1  is provided with a rotational speed sensor  31  for detecting the rotational speed (or engine rotational speed) NE of the engine  1 . The surge tank  12  is provided with an intake pressure sensor  32  for detecting the pressure of intake air (or intake air pressure) PM. The throttle valve  11  is provided with a throttle sensor  33  for detecting an opening degree (throttle position) TA of the throttle valve  11 . The throttle sensor  33  is also used as a switch for detecting a full closed position of the throttle valve  11 . The rotational speed sensor  31 , intake pressure sensor  32 , and throttle sensor  33  constitute operating condition detection means of the present invention to detect an operating condition of the engine  1 . 
   The evaporated fuel processing apparatus in the present embodiment is used to collect and process evaporated fuel (vapor) generated in the fuel tank  5  without discharging the vapor into atmosphere. The evaporated fuel processing apparatus includes a canister  14  for collecting or adsorbing the vapor generated in the fuel tank  5  through a vapor line  13 . The canister  14  contains an adsorbent  15  made of activated charcoal. 
   The canister  14  has an atmospheric port  16  through which atmospheric air is allowed to enter the canister  14 . A purge line  17  extending from the canister  14  branches at a point into a first purge line  18  and a second purge line  19 . The first purge line  18  is connected in communication with the intake passage  2  upstream of the compressor  7 . The second surge line  19  is connected with the surge tank  12 . The purge line  17  and the first purge line  18  constitute a purge passage of the present invention to purge the vapor from the canister  14  into the intake passage  2  upstream of the compressor  7 . The purge line  17  and the second purge line  19  constitute another purge passage of the present invention to purge the vapor from the canister  14  into the intake passage  2  downstream of the throttle valve  11 . In the first purge line  18 , a first electromagnetic valve  20  is provided as an electromagnetic valve of the present invention for opening and closing the line  18 . In the second purge line  19 , a second electromagnetic valve  21  is provided as another electromagnetic valve of the present invention for opening and closing the line  19 . 
   The above evaporated fuel processing apparatus is constructed to collect the vapor generated in the fuel tank  5  into the canister  14  through the vapor line  13 , and purge the collected vapor into the intake passage  2  through the purge line  17  and the first purge line  18  or the second purge line  19 . 
   In the present embodiment, an electronic control unit (ECU)  30  is provided to control the engine  1  and the evaporated fuel processing apparatus. The rotational speed sensor  31 , the intake pressure sensor  32 , and the throttle sensor  33  are individually connected to the ECU  30 . Similarly, the first and second electromagnetic valves  20  and  21  are individually connected to the ECU  30 . To control the evaporated fuel processing apparatus in response to the operating condition of the engine  1 , the ECU  30  controls the electromagnetic valves  20  and  21  respectively based on detection signals from the various sensors  31 - 33 . The ECU  30  in the present embodiment corresponds to control means of the present invention. 
   The ECU  30  includes, as is generally known, a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), a backup RAM, an external input circuit and an external output circuit. The ROM previously stores a predetermined control program related to various controls including the purging control. The RAM temporarily stores calculation results from the CPU. The backup RAM saves the previously stored data. The CPU controls the electromagnetic valves  20  and  21  to execute the purging control using the evaporated fuel processing apparatus in response to detection signals that the CPU receives from the various sensors  31 - 33  through the input circuit. 
   Next, explanation is made on processing details of the purging control that the ECU  30  executes.  FIG. 2  is a flowchart of the purging control program. The ECU  30  periodically executes this routine at predetermined time intervals. 
   In step  100 , the ECU  30  reads each detection value of the engine rotational speed NE, intake pressure PM, and throttle opening degree TA from the corresponding sensors  31  to  33 . 
   In step  110 , the ECU  30  determines whether the read intake pressure PM is an atmospheric pressure P 1  or more. If a negative decision is made, the ECU  30  determined that the turbocharger  6  is not in operation and advances the flow to step  120 . 
   In step  120 , the ECU  30  stops the application of an electric current to the first electromagnetic valve  20  to close the valve  20 , thereby closing the first purge line  18 . This processing stops the mutual flow between the intake passage  2  upstream of the compressor  7  and the first purge line  18 . 
   In step  130 , the ECU  30  determines whether the engine  1  is in a decelerating condition. When the throttle sensor  33  detects a full closed position of the throttle valve  11 , the ECU  30  determines that the engine  1  is in deceleration. 
   If a negative decision is made in step  130 , the ECU  30  applies an electric current to the second electromagnetic valve  21  to open the valve  21 , thereby opening the second purge line  19 . The subsequent processing is temporarily terminated. When the purge line  19  is opened in this way, the vapor is purged from the canister  14  into the surge tank  12  by the negative pressure produced in the surge tank  12  during nonoperation of the turbocharger  6 . In the present embodiment, for example, the second electromagnetic valve  21  may be operated under a duty control to differences in the intake pressure PM. This control makes it possible to control the amount of vapor to be purged into the surge tank  12 . 
   If an affirmative decision is made in step  130 , further, the ECU  30  stops the application of an electric current to the second electromagnetic valve  21  to close the valve  21 , thereby closing the second purge line  19 . This processing stops the purging of the vapor from the canister  14  into the surge tank  12 . 
   If an affirmative decision is made in step  110 , on the other hand, it is determined that the turbocharger  6  is in operation. Thus, the ECU  30  advances the flow to step  160  to purge the vapor through the use of negative pressure produced in the intake passage  2  upstream of the compressor  7 . 
   In step  160 , the ECU  30  stops the application of an electric current to the second electromagnetic valve  21  to close the valve  21 , thereby closing the second purge line  19 . This processing makes it possible to stop the mutual flow between the surge tank  12  and the second purge line  19 . 
   In step  170 , the ECU  30  applies an electric current to the first electromagnetic valve  20  to open the valve  20 , thereby opening the first purge line  18 . When the purge line  18  is opened in this way, the vapor is purged from the canister  14  into the intake passage  2  upstream of the compressor  7  by the negative pressure produced in the intake passage  2  upstream of the compressor  7  during operation of the turbocharger  6 . 
   According to the above structure in the present embodiment explained above, the pressure in the surge tank  12  becomes positive due to a supercharging pressure (the intake pressure PM becomes equal to or more than atmospheric pressure P 1 ) during operation of the turbocharger  6 . At this time, a negative pressure is caused in the intake passage  2  upstream of the compressor  7 . 
   The opening/closing of the second electromagnetic valve  21  in the present embodiment is controlled by the ECU  30  according to the intake pressure PM representing the operating condition of the engine  1 . In other words, when the intake pressure PM becomes less than the atmospheric pressure P 1  in association with the operation of the turbocharger  6 , the second electromagnetic valve  21  is immediately closed, thereby promptly interrupting the purging of vapor through the purge line  17  and the second purge line  19 . Accordingly, during operation of the turbocharger  6 , the supercharging pressure in the intake passage  2  downstream of the compressor  7  is prevented from improperly acting on the canister  14  through the second purge line  19  and others. It is thus possible to prevent a reduction in the efficiency of the vapor purging simultaneously executed with respect to the intake passage  2  upstream of the compressor  7 . 
   At this time, the opening/closing of the first electromagnetic valve  20  is controlled by the ECU  30  on the basis of the intake pressure PM as above. In other words, when the intake pressure PM becomes equal to or more than the atmospheric pressure P 1  in association with the operation of the turbocharger  6 , the first electromagnetic valve  20  is opened immediately after the second electromagnetic valve  21  is closed. The vapor is thus drawn and promptly purged by the negative pressure from the canister  14  into the intake passage  2  upstream of the compressor  7  through the purge line  17  and the first purge line  18 . In association with the operation of the turbocharger  6 , accordingly, the vapor collected in the canister  14  can efficiently be purged into the intake passage  2  upstream of the compressor  7  by the negative pressure produced in the intake passage  2  upstream of the compressor  7 . 
   During nonoperation of the turbocharger  6 , on the other hand, a negative pressure is caused in the surge tank  12  (the intake pressure PM becomes less than the atmospheric pressure P 1 ), and a slight negative pressure resulting from the flow of a small amount of intake air is produced in the intake passage  2  upstream of the compressor  7 . 
   At this time, the first electromagnetic valve  20  is immediately closed, thereby promptly interrupting the purging of vapor through the first purge line  18  and others. Accordingly, during nonoperation of the turbocharger  6 , the positive pressure in the intake passage  2  upstream of the compressor  7  is prevented from improperly acting on the canister  14  through the first purge line  18  and etc. It is therefore possible to prevent a reduction in the efficiency of the vapor purging simultaneously executed with respect to the surge tank  12 . 
   During deceleration of the engine  1 , a negative pressure is produced in the surge tank  12 . At this time, the second electromagnetic valve  21  is immediately closed, thus promptly interrupting the vapor purging through the second purge line  19  and others. During deceleration of the engine  1 , therefore, the collected vapor in the canister  14  will not improperly be purged into the intake passage  2  or drawn into the combustion chamber  4 . This makes it possible to prevent the unburned vapor from deteriorating exhaust gas of the engine  1 . 
   When the engine  1  is not during deceleration, on the other hand, the second electromagnetic valve  21  is immediately opened, promptly allowing the vapor purging through the second purge line  19  and others. During nonoperation of the turbocharger  6 , the collected vapor in the canister  14  can efficiently purged by the negative pressure produced in the surge tank  12 . 
   According to the evaporated fuel processing apparatus in the present embodiment, in association with the operation of the turbocharger  6 , the vapor can be purged into the intake pressure  2  upstream of the compressor  7  by the action of the negative pressure produced in the intake pressure  2  upstream of the compressor  7 . Further, the purging operation can be controlled in good response to the operating condition of the engine  1 . 
   According to the evaporated fuel processing apparatus in the present embodiment, during nonoperation of the turbocharger  6 , a negative pressure is produced in the surge tank  12 . At this time, the second electromagnetic valve  21  is opened and the vapor collected in the canister  14  is drawn by the action of the above negative pressure into the surge tank  12  through the second purge line  19  and others. Thus, the vapor is purged from the canister  14 . During operation of the turbocharger  6 , on the other hand, a negative pressure is produced in the intake passage  2  upstream of the compressor  7 . At this time, the first electromagnetic valve  20  is opened and, by the above negative pressure, the vapor collected in the canister  14  can be drawn and purged into the intake passage  2  upstream of the compressor  7  through the first purge line  18  and others. Accordingly, the vapor purging can be achieved through two purge lines, that is, through the second purge line  19  and others during nonoperation of the turbocharger  6  and through the first purge line  18  and others during operation of the turbocharger  6 , respectively. Thus, the above apparatus can be used as an evaporated fuel processing apparatus equipped in an engine system with the turbocharger  6  to purge the vapor collected in the canister  14  regardless of operation/nonoperation of the turbocharger  6 . It is therefore possible to increase the number of purgings, thereby increasing the capacity of the canister  14  to collect vapor. In proportion to the increase in the vapor collecting capacity, the canister  14  can be made smaller in size correspondingly. 
   According to the evaporated fuel processing apparatus in the present embodiment, on the basis of the intake pressure PM and the operating condition of the engine  1 , i.e., whether the engine  1  is in deceleration or not, the purging is performed through the above two purge lines  18  and  19  and others. Consequently, regardless of operation/nonoperation of the turbocharger  6 , the vapor can be efficiently burned in the combustion chamber  4 . Furthermore, it is possible to prevent the unburned vapor from deteriorating exhaust gas during deceleration of the engine  1 . 
   [Second Embodiment] 
   Next, a second preferred embodiment of the evaporated fuel processing apparatus for an engine with a supercharger will be described with reference to attached drawings. 
   It is to be noted that in the second and subsequent embodiments, like elements corresponding to those in the first embodiment are indicated by like numerals and their explanations are omitted. The following embodiments will be explained with a focus on different structures from those in the first embodiment. 
     FIG. 3  is a schematic perspective view of an engine system with a supercharger in the second embodiment. The evaporated fuel processing apparatus in this embodiment differs from that in the first embodiment in that the apparatus in the second embodiment further includes a supercharging pressure passage  22  through which a supercharging pressure in the intake passage  2  downstream of the compressor  7  is supplied as a back pressure to the canister  14  and a third electromagnetic valve  23  in the passage  22 . 
   More specifically, an end of the supercharging pressure passage  22  is connected in communication with the intake passage  2  downstream of the compressor  7  and the other end is connected with the atmospheric port  16  of the canister  14 . The third electromagnetic valve  23  is constructed of a three-way change-over valve, which can be switched between a supercharging pressure introducing state for bringing the canister  14  into communication with the supercharging pressure passage  22  and an atmospheric discharging state for bringing the canister  14  in communication with atmospheric air. 
     FIG. 4  is a flowchart of a purging control program in the second embodiment. The flowchart of  FIG. 4  are different from that of  FIG. 2  in that step  125  and step  175  are added after step  120  and steps  175  respectively. 
   In this routine, specifically, the ECU  30  closes the first electromagnetic valve  20  in step  120  and, after that, switches the third electromagnetic valve  23  into the atmospheric discharging state in step  125  to open the atmospheric port  16  of the canister  14  to atmospheric air. 
   Further, in this routine, the ECU  30  opens the first electromagnetic valve  20  in step  170  and, after that, switches the third electromagnetic valve  23  into the supercharging pressure introducing state to introduce the supercharging pressure as a back pressure into the canister  14 . 
   According to the evaporated fuel processing apparatus in the second embodiment described above, a supercharging pressure is formed in the intake passage  2  downstream of the compressor  7  during operation of the turbocharger  6 . At this time, when the first electromagnetic valve  20  is opened, the vapor collected in the canister  14  is drawn by the action of the above negative pressure into the intake passage  2  upstream of the compressor  7  through the first purge line  18  and others. Simultaneously, the third electromagnetic valve  23  is switched into the supercharging pressure introducing state to supply the supercharging pressure produced in the intake passage  2  downstream of the compressor  7 , as a back pressure, to the canister  14  through the supercharging pressure passage  22 . This back pressure forces the vapor out of the canister  14  into the first purge line  18  and others. In this way, by cooperation of the drawing by the negative pressure produced in the intake passage upstream of the compressor and the forced flow by the supercharging pressure, the vapor collected in the canister  14  is purged into the intake passage upstream of the compressor. Thus, as compared with the apparatus in the first embodiment, the apparatus in the second embodiment can more efficiently achieve the vapor purging to the intake passage upstream of the compressor by the amount of vapor forced out of the canister  14  by the supercharging pressure. 
   In the second embodiment, on the other hand, during nonoperation of the turbocharger  6 , the third electromagnetic valve  23  is switched into the atmospheric discharging state. Accordingly, unnecessary intake pressure and supercharging pressure will not act on the canister  14  while the vapor is purged into the surge tank  12 . 
   Other functions and effects that the evaporated fuel processing apparatus in the present embodiment can bring about are similar to those in the first embodiment. 
   [Third Embodiment] 
   Next, a third preferred embodiment of the evaporated fuel processing apparatus for an engine with a supercharger will be described with reference to attached drawings. 
     FIG. 5  is a schematic perspective view of an engine system with a supercharger in the present embodiment, which differs from that in the first embodiment in that the system in the third embodiment includes an aspirator  24  which allows working gas to flow to thereby draw in the vapor flowing through the first purge line  18 , and a passage  25  for supplying supercharged air from the intake passage  2  downstream of the compressor  7  to the aspirator  24  as the working gas. 
   Specifically, one end (i.e., an upstream end) of the supercharged air passage  25  is connected in communication with the intake passage  2  downstream of the compressor  7  and the other end (i.e., a downstream end) is connected in communication with the aspirator  24 . The aspirator  24  is adapted to allow the supercharged air to flow in from the passage  25  and thereby draw in the vapor from the first purge line  18  upstream of the aspirator  24  to cause the drawn vapor to flow in the line  18  downstream of the same. 
   In the present embodiment, the purge control program that the ECU  30  executes is the same as that shown in FIG.  2 . 
   According to the evaporated fuel processing apparatus in the present embodiment, consequently, a supercharging pressure is produced in the intake passage  2  on the downstream side of the compressor  7  during operation of the turbocharger  6 . At this time, the first electromagnetic valve  20  is opened, so that the vapor collected in the canister  14  is drawn by the above mentioned negative pressure into the intake passage  2  downstream of the compressor  7  via the first purge line  18 . Simultaneously, the supercharged air in the intake passage  2  on the downstream side of the compressor  7  is caused to flow as the working gas in the aspirator  24  through the passage  25 . The vapor flowing through the first purge line  18  is thus drawn in by the aspirator  24 . In this manner, drawing by the negative pressure in the intake passage  2  on the upstream side of the compressor  7  and drawing by the aspirator  24  cooperate to purge the vapor collected in the canister  14  into the intake passage  2  upstream of the compressor  7 . Accordingly, as compared with the apparatus in the first embodiment, the apparatus in the present embodiment can purge the vapor more efficiently into the intake passage  2  upstream of the compressor  7  by an amount of the vapor drawn in by the aspirator  24  from the first purge line  18 . 
   Other functions and effects that the evaporated fuel processing apparatus in the present embodiment can bring about are similar to those in the first embodiment. 
   [Fourth Embodiment] 
   Next, a fourth preferred embodiment of the evaporated fuel processing apparatus for an engine with a supercharger will be described with reference to attached drawings. 
     FIG. 6  is a schematic perspective view of an engine system with a supercharger in the present embodiment, which differs from that in the first embodiment in that the system in the fourth embodiment includes the first purge line  18  whose leading end (i.e., downstream end) is directly connected with the surge tank  12 , an aspirator  24  which draws in the vapor flowing through the first purge line  18 , a supercharged air passage  25  through which supercharged air is introduced from the intake passage  2  downstream of the compressor  7  into the aspirator  24 , and a fourth electromagnetic valve  26  provided near the downstream end of the first purge line  18 . 
   Specifically, one end of the supercharged air passage  25  is connected in communication with the intake passage  2  located downstream of the compressor  7  and the other end is connected in communication with the aspirator  24 . The aspirator  24  is adapted to allow the supercharged air to flow in from the passage  25  and thereby draw in the vapor from the first purge line  18  upstream of the aspirator  24  to allow the drawn vapor to flow in the line  18  downstream of the same. 
     FIG. 7  is a flowchart of the purge control program in the present embodiment. The flowchart in  FIG. 7  differs from that in  FIG. 2  in that step  126  and step  176  are added after step  120  and step  170  respectively. 
   In this routine, the ECU  30  closes the first electromagnetic valve  20  in step  120  and stops the application of an electric current to the fourth electromagnetic valve  26  in step  126  to close the valve  26 , thereby closing the first purge line  18 . 
   In this routine, furthermore, the ECU  30  opens the first electromagnetic valve  20  in step  170  and applies an electric current to the fourth electromagnetic valve  26  in step  176  to open the valve  26 , thereby opening the first purge line  18 . 
   According to the evaporated fuel processing apparatus in the fourth embodiment described above, the supercharging pressure is produced in the intake passage  2  on the downstream side of the compressor  7  during operation of the turbocharger  6 . When this supercharged air is caused to flow as working gas in the aspirator  24  through the supercharged air passage  25 , a negative pressure acts on the first purge line  18 . At this time, the first electromagnetic valve  20  and the fourth electromagnetic valve  26  are opened. By the above mentioned negative pressure, the vapor collected in the canister  14  is purged into the surge tank  12  through the first purge line  18 . Thus, the apparatus in the present embodiment can purge the vapor to the surge tank  12  by utilizing the supercharging pressure (positive pressure) produced in the intake passage  2  downstream of the compressor  7  in association with the operation of the turbocharger  6 . 
   In the present embodiment, on the other hand, the fourth electromagnetic valve  26  is closed during nonoperation of the turbocharger  6 . Accordingly, when the vapor is purged to the surge tank  12  through the second purge line  19  and others, unnecessary intake pressure does not act on the surge tank through the first purge line  18  and others. 
   Other functions and effects that the evaporated fuel processing apparatus in the fourth embodiment can bring about are similar to those in the first embodiment. 
   [Fifth Embodiment] 
   Next, a fifth preferred embodiment of the evaporated fuel processing apparatus for an engine with a supercharger will be described with reference to attached drawings. 
     FIG. 8  is a schematic perspective view of an engine system with a supercharger in the present embodiment, which differs from that in the first embodiment in that the system in the fifth embodiment includes a venturi  27  at a connected portion of the intake passage  2  with the first purge line  18 . 
   According to the evaporated fuel processing apparatus in the fifth embodiment, consequently, the venturi  27  disposed in the connected portion between the intake passage  2  and the first purge line  18  serves to increase the negative pressure in the intake passage  2  upstream of the compressor  7 . This makes it possible to enhance the power of drawing the vapor from the first purge line  18  into the intake passage  2  upstream of the compressor  7 . Accordingly, as compared with the apparatus in the first embodiment, the apparatus in the present embodiment can purge the vapor more efficiently to the intake passage  2  upstream of the compressor  7  by an amount corresponding to the enhanced drawing power. 
   The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For instance, the following designs may be adopted. 
   In each of the above embodiments, the evaporated fuel processing apparatus is provided with the purge passages configured in the double purging system including the second purge line  19  to be used during nonoperation of the turbocharger  6  and the first purge line  18  to be used during operation of the turbocharger  6 . Instead of this configuration, a single purging system using only the first purge line  18  may be adopted. In this case, the second purge line  19  for nonoperation of the turbocharger  6  is omitted. 
   In each of the above embodiments, although the second electromagnetic valve  21  is disposed in the second purge line  19 , this valve  21  may be omitted. 
   While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.