Patent Publication Number: US-10787999-B2

Title: Evaporated fuel processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2018-063677 filed on Mar. 29, 2018, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The technique disclosed in this specification relates to an evaporated fuel processing apparatus configured such that evaporated fuel generated in a fuel tank is once collected in a canister and purged into an intake passage through a purge passage provided with a purge valve and a purge pump so that the evaporated fuel is processed. 
     Related Art 
     Heretofore, an “evaporated fuel processing apparatus” described in JP2017-180320A has been known as one example of this technique. This apparatus is provided with an aim of preferably estimating a flow rate of purge gas (evaporated fuel or vapor) fed out by a pump. To be more specific, the apparatus includes a canister for absorbing (collecting) vapor generated in a fuel tank, a purge channel (purge passage) for purging the vapor from the canister to an intake passage of the engine, a pump (purge pump) for feeding the vapor from the canister to the intake passage, a control valve (purge valve) for controlling vapor flow in the purge passage, a branch passage (bypass passage) detouring a part of the purge passage, a pressure specification part for specifying a pressure difference between front and rear of a small diameter part on the bypass passage, an air-fuel ratio sensor of the engine, and an estimation unit for estimating a flow rate of the vapor fed out of the purge pump based on a vapor concentration that is estimated by a detection value detected by the air-fuel ratio sensor and a pressure difference (corresponding to a discharge pressure of the purge pump) specified by the pressure specification part. 
     SUMMARY 
     Technical Problems 
     The apparatus described in JP2017-180320A however has a tendency of increase in pressure pulsation on a downstream side of the purge pump. Accordingly, in order to obtain a stable pressure difference between an upstream side and the downstream side of the purge pump for estimating a flow rate of the vapor, pressure sensors need to be provided on both sides of the upstream side and the downstream side of the purge pump. In this case, two pressure sensors need to be provided and the pressure difference from the atmospheric pressure needs to be calculated from detection values detected by the two pressure sensors. This tends to make the apparatus structure complicated and to increase costs. 
     Herein, the vapor concentration is estimated by a discharge pressure of the purge pump when the purge pump is under operation and the purge valve is closed. Accordingly, stable detection of the discharge pressure of the purge pump leads to highly accurate estimation of the vapor concentration. 
     The present disclosure has been made in view of the above circumstances and has an aim of providing an evaporated fuel processing apparatus achieving stable detection of the discharge pressure of the purge pump with a simple configuration to estimate the concentration of the evaporated fuel. 
     Means of Solving the Problems 
     One aspect of the present disclosure to solve the above problem is to provide an evaporated fuel processing apparatus configured to process evaporated fuel generated in a fuel tank without discharging the evaporated fuel into the atmosphere, wherein the evaporated fuel processing apparatus includes: a canister configured to collect the evaporated fuel generated in the fuel tank; a purge passage configured to purge the evaporated fuel collected in the canister to an intake passage of an engine; a purge valve provided in the purge passage to regulate a purge flow rate of the evaporated fuel; a purge pump provided in the purge passage between the canister and the purge valve to pressure-feed the evaporated fuel into the purge passage from the canister; and a pressure detection member configured to detect the pressure of the evaporated fuel in the purge passage, an inside of the canister communicates with the atmosphere, a capacity chamber having a predetermined capacity is provided upstream of the purge pump, and the pressure detection member is provided in the purge passage between the purge valve and the purge pump. 
     According to the above technique, in estimating the concentration of the evaporated fuel, the discharge pressure of the purge pump can be stably detected with a simple configuration configured with a single pressure detection member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configurational view of an engine system including an evaporated fuel processing apparatus in a first embodiment; 
         FIG. 2  is a time chart showing behavior of each parameter during purge control in the first embodiment; 
         FIG. 3  is a time chart showing behavior of each parameter during the purge control in a comparative example; and 
         FIG. 4  a schematic configurational view of an engine system including an evaporated fuel processing apparatus in a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     &lt;First Embodiment&gt; 
     A first embodiment embodying an evaporated fuel processing apparatus in a gasoline engine system is now explained below with reference to the accompanying drawings. 
     (Overview of Engine System) 
       FIG. 1  is a schematic configurational view of an engine system including an evaporated fuel processing apparatus. An engine  1  is provided with an intake passage  3  to take air and others into a combustion chamber  2  and an exhaust passage  4  to discharge exhaust gas from the combustion chamber  2 . To the combustion chamber  2 , fuel stored in a fuel tank  5  is supplied. Specifically, the fuel in the fuel tank  5  is discharged to a fuel passage  7  by a fuel pump  6  embedded in the fuel tank  5  and then pressure-fed to an injector  8  provided in an intake port of the engine  1 . The thus fed fuel is injected through the injector  8  and introduced in the combustion chamber  2  with air having been flowing through the intake passage  3  to form combustible air-fuel mixture used for combustion. The engine  1  is provided with an ignition device  9  for igniting the combustible air-fuel mixture. 
     In the intake passage  3 , there are provided an air cleaner  10 , a throttle device  11 , and a surge tank  12  in this order from an inlet side of the passage  3  toward the engine  1 . The throttle device  11  is provided with a throttle valve  11   a  which is opened or closed to regulate an intake flow rate of intake air flowing in the intake passage  3 . Opening and closing operation of the throttle valve  11   a  is associated with operation of an accelerator pedal (not shown) operated by a driver. The surge tank  12  smoothens intake pulsation in the intake passage  3 . 
     (Configuration of Evaporated Fuel Processing Apparatus) 
     An evaporated fuel processing apparatus of the present embodiment is configured to process the evaporated fuel (vapor) generated in the fuel tank  5  without discharging the fuel into the air. This apparatus is provided with a canister  21  to collect the vapor generated in the fuel tank  5 , a vapor passage  22  to introduce the vapor into the canister  21  from the fuel tank  5 , a purge passage  23  to purge the vapor collected in the canister  21  into the intake passage  3 , a purge valve  24  provided in the purge passage  23  to adjust a purge flow rate of the vapor, a purge pump  25  provided between the canister  21  and the purge valve  24  to pressure-feed the vapor from the canister  21  to the purge passage  23 , and a vapor pressure sensor  30  to detect a pressure of the vapor (a vapor pressure or a discharge pressure of the purge pump  25 ) in the purge passage  23 . The vapor pressure sensor  30  corresponds to one example of a pressure detection member of the present disclosure. 
     The canister has an inner space with a predetermined capacity internally provided with an absorbent such as an activated charcoal. The canister  21  includes an atmospheric port  21   a  to introduce the atmosphere, an inflow port  21   b  to introduce the vapor, and an outflow port  21   c  to discharge the vapor. The inner space of the canister  21  is communicated with the atmosphere. In other words, a leading end of an atmospheric passage  26  extending from this atmospheric port  21   a  is communicated with an inlet of a fuel-supply cylinder  5   a  of the fuel tank  5 . The atmospheric passage  26  is provided with a filter  27  for capturing mine dust in the air. A leading end of the vapor passage  22  extending from the inflow port  21   b  of the canister  21  is communicated with an inside of the fuel tank  5 . A leading end of the purge passage  23  provided between the canister  21  and the intake passage  3  is communicated with the intake passage  3  between the throttle device  11  and the surge tank  12 . 
     In the present embodiment, the purge valve  24  is constituted of a motor-operated valve (VSV) and is variable in its opening degree for adjusting the vapor flow rate. The purge pump  25  is configured to be variable in a discharge amount of the vapor which is to be pressure-fed from the canister  21  to the purge passage  23 . As an example of the purge pump  25 , a turbopump may be adopted. The purge pump  25  includes an intake port  25   a  to intake the vapor and an exhaust port  25   b  to exhaust the vapor. A capacity chamber having a predetermined capacity is provided upstream of the purge pump  25 . In the present embodiment, the capacity chamber is constituted of the inner space of the canister  21 . The purge pump  25  is directly provided in the canister  21  and the intake port  25   a  of the pump  25  is connected to the outflow port  21   c  of the canister  21 . Further, a vapor pressure sensor  30  is provided in the purge passage  23  downstream of the purge pump  25 . 
     The evaporated fuel processing apparatus configured as above introduces the vapor generated in the fuel tank  5  to the canister  21  through the vapor passage  22  and once collects the vapor in the canister  21 . During operation of the engine  1 , the throttle device  11  (the throttle valve  11   a ) is opened, the purge valve  24  is opened, and the purge pump  25  is operated. Thus, the vapor captured in the canister  21  is purged into the intake passage  3  from the canister  21  through the purge passage  23 . 
     In the present embodiment, a cutoff valve  28  for controlling air flow between the fuel tank  5  and the canister  21  is provided in the vapor passage  22 . This cutoff valve  28  is made to open when an inner pressure of the fuel tank  5  is positive at a predetermined value or more and is made to close by negative pressure generated when the vapor captured in the canister  21  is purged into the intake passage  3 . 
     (Electrical Configuration of Engine System) 
     In the present embodiment, various sensors  41  to  46  for detecting an operation state of the engine  1  are provided. An air flow meter  41  provided near the air cleaner  10  detects an amount of air taken in the intake passage  3  as an intake air flow rate and outputs an electrical signal corresponding to the detected value. A throttle sensor  42  provided in the throttle device  11  detects an open degree of the throttle valve  11   a  as a throttle opening degree and outputs an electrical signal corresponding to the detected value. An intake air pressure sensor  43  provided in the surge tank  12  detects pressure in the surge tank  12  as an intake air pressure and outputs an electrical signal corresponding to the detected value. A water temperature sensor  44  provided in the engine  1  detects a temperature of a cooling water flowing inside the engine  1  as a cooling-water temperature and outputs an electrical signal corresponding to the detected value. A rotation speed sensor  45  provided in the engine  1  detects rotation angular speed of a crank shaft (not shown) of the engine  1  as an engine rotation speed and outputs an electrical signal corresponding to the detected value. An oxygen sensor  46  provided in the exhaust passage  4  detects oxygen concentration in the exhaust gas and outputs an electrical signal corresponding to the detected value. Further, in the purge passage  23  between the purge valve  24  and the purge pump  25 , the vapor pressure sensor  30  to detect the discharge pressure (vapor pressure) of the vapor discharged from the purge pump  25  is provided. The vapor pressure detected by the vapor pressure sensor  30  is used for estimating a vapor concentration as explained below. 
     In the present embodiment, an electronic control unit (ECU) taking in charge of various control inputs or receives various signals which are output from the respective sensors  30  and  41  to  46 . The ECU  50  controls the injector  8 , the ignition device  9 , the purge valve  24 , and the purge pump  25  based on these input signals to carry out fuel injection control, ignition timing control, purge control, vapor-concentration estimation control, and others. 
     The fuel injection control is to control a fuel injection amount and a fuel injection timing by controlling the injector  8  according to an operation state of the engine  1 . The ignition timing control is to control a timing for igniting the combustible air-fuel mixture by controlling the ignition device  9  according to the operation state of the engine  1 . The purge control is to control the purge flow rate of the vapor purged from the canister  21  to the intake passage  3  by controlling the purge valve  24  and the purge pump  25  according to the operation state of the engine  1 . Further, the vapor concentration estimation control is to estimate the vapor concentration in the purge passage  23  based on detected values of the vapor pressure or the like. Detailed explanation for a method of estimating the vapor concentration is omitted in the present disclosure. 
     In the present embodiment, the ECU  50  corresponds to one example of a control member of the present disclosure. The ECU  50  is provided with a known configuration including a central processing unit (CPU), a read-only memory (ROM), a random-access memory (RAM), and a back-up RAM. The ROM stores in advance predetermined control programs related to the above-mentioned various control operation. The ECU (CPU)  50  is made to carry out the above-mentioned various control operation according to these control programs. 
     (Operations and Effects of Evaporated Fuel Processing Apparatus) 
     In the evaporated fuel processing apparatus of the above-mentioned present embodiment, detection values of the vapor pressure sensor  30  need to be sampled in order to detect pressure of the vapor discharged out of the purge pump  25  during operation of the pump  25  while the purge valve is closed. This apparatus is configured such that an inside of the canister  21  is communicated with the atmosphere and that a capacity chamber (the canister  21 ) having a predetermined capacity is provided upstream of the purge pump  25 . Accordingly, during operation of the purge pump  25 , pressure pulsation of the vapor pressure on an upstream side of the pump  25  is attenuated and the vapor pressure on the upstream side has less influence on a downstream side of the pump  25 , thus restraining the pressure pulsation of the vapor pressure on the downstream side. Therefore, providing the single vapor pressure sensor  30  for estimating the vapor concentration is enough to achieve stable detection of the discharge pressure of the purge pump  25  with a simple configuration of the evaporated fuel processing apparatus. As a result, the vapor concentration can be accurately estimated based on the vapor pressure and others. 
     Detection results detected by the vapor pressure sensor  30  in purge control operation of the present embodiment are explained below.  FIG. 2  is a time chart indicating behavior of respective parameters in the purge control of the present embodiment. In  FIG. 2 , a graph indicated with an annotated sign (a) represents the purge control, a graph with a sign (b) represents duty control of the purge valve, and a graph with a sign (c) represents the vapor pressure on the downstream side of the purge pump (a downstream-side vapor pressure).  FIG. 3  is a time chart indicating behavior of respective parameters in a conventional purge control operation as a comparative example. In  FIG. 3 , a graph indicated with an annotated sign (a) represents the purge control, a graph with a sign (b) represents the duty control of the purge valve, a graph with a sign (c) represents the downstream-side vapor pressure detected by a vapor pressure sensor on the downstream side of the purge pump, a graph with a sign (d) represents the upstream-side vapor pressure detected by the vapor pressure sensor on the upstream-side of the purge pump, and a graph with a sign (e) represents a purge-pump front-rear differential pressure (a pressure difference between the upstream-side vapor pressure and the downstream-side vapor pressure). 
     In the present embodiment, as shown in (a) of  FIG. 2 , the purge control is carried out during a term between a time t 1  to t 2  to operate the purge pump  25 , and the purge valve  24  is switched on or off at a predetermined duty ratio as shown in (b), so that the downstream-side vapor pressure indicated in (c) is obtained. In this operation, the downstream-side vapor pressure detected by a single vapor pressure sensor  30  reaches a pressure P 1  that is a pressure before carrying out the purge control, a certain lower limit at a time when the purge valve  24  is on (opened), or a certain upper limit, which is almost the same with the pressure P 1 , at a time when the purge valve  24  is off (closed). Thus, according to the present embodiment, providing only the single vapor pressure sensor  30  can achieve obtention of the stable downstream-side vapor pressure from the value detected by the sensor  30 . 
     On the other hand, in the conventional example, as shown in (a) of  FIG. 3 , the purge control is carried out during a term between a time t 1  to t 2  to operate the purge pump, and as shown in (b), the purge valve  24  is switched to be on or off at a predetermined duty ratio, causing pressure pulsation of the upstream-side vapor pressure as shown in (d). This pulsation has influence on increase in the pressure pulsation of the downstream-side vapor pressure indicated in (c). As indicated in (e), a pressure waveform as similar to that of (c) of  FIG. 2  is obtained by calculating the pressure difference between the upstream-side vapor pressure and the downstream-side vapor pressure, but there needs to provide the purge pressure sensor on each of the upstream side and the downstream side of the purge pump in this conventional example, and further, the pressure difference between the upstream-side vapor pressure and the downstream-side vapor pressure needs to be obtained from the detected values. 
     Further, in the present embodiment, the capacity chamber is constituted of an inner space of the canister  21 . The purge pump  25  is directly provided in the canister  21  and the intake port  25   a  is connected to the outflow port  21   c  of the canister  21 . Therefore, there is no need to separately provide a capacity chamber. This achieves further simplification of the configuration of the evaporated fuel processing apparatus and size reduction of the apparatus. 
     &lt;Second Embodiment&gt; 
     A second embodiment embodying an evaporated fuel processing apparatus in a gasoline engine system is now explained in detail with reference to the accompanying drawings. 
     In the following explanation, similar or identical parts or components to those of the first embodiment are assigned with the same reference signs as those in the first embodiment and their explanations are omitted as appropriate. Therefore, the following explanation is made with a focus on the differences from the first embodiment. 
     (Configuration of Evaporated Fuel Processing Apparatus) 
       FIG. 4  is a schematic configurational view of an engine system including an evaporated fuel processing apparatus. In the present embodiment, arrangement of the purge pump  25  and the capacity chamber is different from that of the first embodiment. Specifically, the purge pump  25  of the present embodiment is provided in the purge passage  23  between the canister  21  and the purge valve  24 . Further, a capacity chamber  31  separately provided from the canister  21  is placed in the purge passage  23  upstream of the purge pump  25 . Herein, a capacity of the capacity chamber  31  may be set about “1000 cc”. The capacity chamber  31  can be provided by increasing an inner diameter of the purge passage  23  between the canister  21  and the purge pump  25 . 
     Accordingly, the evaporated fuel processing apparatus of the present embodiment can also achieve the configuration of communicating the inside of the canister  21  with the atmosphere and the apparatus is provided with the capacity chamber  31  having a predetermined capacity on an upstream side of the purge pump  25 . Thus, the pressure pulsation of the vapor pressure on the upstream side of the purge pump  25  is attenuated during operation of the purge pump  25  and the vapor pressure on the upstream side has less influence on the downstream-side of the pump  25 , thus restraining the pressure pulsation of the vapor pressure on the downstream side. Therefore, providing the single vapor pressure sensor  30  to estimate the vapor concentration can achieve simplification of the configuration of the evaporated fuel processing apparatus and stable detection of the discharge pressure of the purge pump  25 . This results in accurate estimation of the vapor concentration based on the vapor pressure and others. 
     The present disclosure is not limited to each of the above embodiments and may be applied with various changes in its part of configuration without departing from the scope of the disclosure. 
     In the above embodiments, an engine system with no supercharger being provided is configured such that the vapor is purged into the intake passage  3  downstream of the throttle device  11  from the purge passage  23 . Alternatively, an engine system may be provided with a supercharger and configured such that the vapor is purged into the intake passage upstream of the throttle device and downstream of the air flow meter from the purge passage. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure may be applied to an engine system provided with an evaporated fuel processing apparatus. 
     REFERENCE SIGNS LIST 
       1  Engine 
       3  Intake passage 
       5  Fuel tank 
       21  Canister 
       21   a  Atmospheric port 
       21   b  Inflow port 
       21   c  Outflow port 
       22  Vapor passage 
       23  Purge passage 
       24  Purge valve 
       25  Purge pump 
       25   a  Intake port 
       25   b  Exhaust port 
       30  Vapor pressure sensor (Pressure detection member) 
       31  Capacity chamber