Patent Publication Number: US-2021172391-A1

Title: Evaporative emission control system

Description:
FIELD 
     The present disclosure relates to an evaporative emission control system, and more particularly relates to an evaporative fuel vapor emission control system for reducing the discharge of evaporative fuel vapor in an automotive vehicle with a combustion engine. 
     BACKGROUND 
     An evaporative emission control system is well known, for example in a motor vehicle having an internal combustion engine, to prevent fuel vapor from being emitted from the fuel tank into the atmosphere during rest time. The fuel vapor is a major potential source of hydrocarbon (HC) air pollution. Such emissions can be controlled by the evaporative emission control system in the vehicle. The control system typically includes a carbon canister system for adsorbing the fuel vapor. The adsorbed fuel vapor is periodically purged from the activated carbon while the vehicle engine is running by drawing ambient air through the canister system to desorb the fuel vapor from the activated carbon. 
     When a motor vehicle is parked in a warm environment during the daytime, the temperature in a fuel tank of the motor vehicle increases, resulting in an increased vapor pressure in the fuel tank. In addition, when the motor vehicle stops at an intersection or is driven by an electric motor in a hybrid system that selectively utilizes either or both the internal combustion engine and the electric motor, the amount of the fuel vapor in the fuel tank is increased. As a result, there is a possibility that the fuel vapor generated in the fuel tank will exceed the absorption-storage capability of the canister system, and the excessive fuel vapor in the fuel tank may be vented improperly, resulting in reduced engine performance and the possibility of impermissibly increased fuel vapor emissions into the atmosphere. 
     To reduce the discharge of the fuel vapor into the atmosphere, a variety of the evaporative emission control systems are continuously developed. However, it is difficult to comply with developing legal requirements with increasingly strict limits. 
     SUMMARY 
     It is the object of the present application to provide an evaporative emission control system meeting strict emission standards. 
     According to one aspect of the present disclosure, the evaporative emission control system in a vehicle having an internal combustion engine and a fuel tank includes a membrane module disposed and connected between the fuel tank and the engine in the vehicle. The membrane module includes a first passage and a second passage separated by a membrane and is configured for allowing fuel vapor generated from the fuel tank to permeate the membrane. The evaporative emission control system further includes a buffer-volume housing connected to the membrane module by an additional passage and configured for storing fuel-rich vapor that has permeated the membrane. 
     The buffer-volume housing is connected to the second passage in the membrane module for transmitting the fuel-rich vapor via the additional passage. 
     The buffer-volume housing in the evaporative emission control system is configured to increase a partial-pressure difference of the fuel vapor between the first passage and the second passage inside the membrane module. 
     Furthermore, the fuel-rich vapor flows into the buffer-volume housing when the engine of the vehicle is an idle state or the vehicle is parked at a warm environment. A purge valve is configured to allow the fuel-rich vapor stored in the second passage of the membrane module and the buffer-volume housing to flow into the engine when the engine of the vehicle is running above an idle speed. 
     The buffer-volume housing is formed of a plastic material. 
     According to a further aspect of the present disclosure, the membrane module includes a membrane inlet for receiving the generated fuel vapor from the fuel tank, an atmosphere outlet for discharging air including the fuel vapor that has not permeated, an atmosphere inlet for receiving atmospheric air from the atmosphere, and a membrane outlet for allowing the fuel-rich vapor to flow into the engine. 
     According to a further aspect of the present disclosure, the membrane inlet and the atmosphere outlet communicate with each other through the first passage in the membrane module, and the atmosphere inlet and the membrane outlet communicate with each other through the second passage in the membrane module. 
     According to a further aspect of the present disclosure, the membrane inlet is connected to a fuel vapor inlet line for communicating with the fuel tank and the membrane outlet is connected to a fuel vapor outlet line for communicating with the engine. 
     According to a further aspect of the present disclosure, a relief valve disposed between the fuel tank and the membrane module is configured to control flow of the fuel vapor generated from the fuel tank. 
     According to a further aspect of the present disclosure, an activated carbon filter disposed between the relief valve and the membrane module is configured to adsorb hydrocarbon (HC) in the generated fuel vapor before entering the membrane module. 
     According to a further aspect of the present disclosure, a purge valve disposed between the membrane module and the engine is configured to control flow of the fuel-rich vapor entering the engine. 
     According to a further aspect of the present disclosure, the membrane formed as a flat shape includes a main body and a plurality of support elements formed with the main body. The main body of the membrane is formed of a silicon material as an active layer. 
     Further details and benefits will become apparent from the following detailed description of the appended drawings. The drawings are provided herewith purely for illustrative purposes and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  shows a schematic view of a vehicle having an evaporative emission control system in accordance with an exemplary form of the present disclosure; 
         FIG. 2  shows a membrane module of the evaporative emission control system of  FIG. 1 ; 
         FIG. 3  shows a diffusion mechanism of a membrane in the membrane module of  FIG. 2 ; and 
         FIG. 4  shows a buffer-volume housing connected to the membrane module of the evaporative emission control system of  FIG. 1 . 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
       FIG. 1  illustrates an evaporative emission control system  100  for an automotive vehicle  10 . In the example of  FIG. 1 , the evaporative emission control system  100  is shown in the vehicle  10  having an internal combustion engine  12  and a fuel tank  14 . In addition, the evaporative emission control system  100  may be used to a hybrid vehicle that selectively utilizes two power systems such as the internal combustion engine  12  and an electric motor (not shown). As shown in  FIG. 1 , the fuel tank  14  includes a fuel pump assembly  16  used in the vehicle  10  for delivering fuel from the fuel tank  14  to the engine  12  for combustion within the engine  12 . A fuel line  18  connected between the engine  12  and the fuel tank  14  communicates with the fuel pump assembly  16  for delivering the fuel to the engine  12 . 
     A throttle valve  20  is disposed in an air inlet line  22  of the internal combustion engine  12  to control the engine&#39;s power by regulating the amount of fuel (such as fuel vapor) or air entering the engine  12 . In the vehicle  10 , for example, the control of the throttle valve  20  is performed by an operator (or a driver) to regulate the power with an accelerator or gas pedal. Furthermore, a compressor  24  disposed in the air inlet line  22  upstream of the throttle valve  20  controls the engine&#39;s power by compressing the air entering the engine  12 . 
     As shown in  FIG. 1 , the evaporative emission control system  100  is installed in the vehicle  10  for preventing fuel vapor from being emitted from the fuel tank  14  into the atmosphere during rest time. The evaporative emission control system  100  includes a relief (or check) valve  102 , a purge valve  104 , a fuel vapor inlet line  106 , a fuel vapor outlet line  108 , a purge outlet line  110  including a first purge outlet line  100   a  and a second purge outlet line  110   b,  and a membrane module  200 . The relief valve  102  is disposed in the fuel vapor inlet line  106  connected between the fuel tank  14  and the membrane module  200  for controlling the amount of the fuel vapor entering the membrane module  200 . 
     The evaporative emission control system  100  further includes an activated carbon filter  112  disposed in the fuel vapor inlet line  106 . The activated carbon filter  112  may be provided upstream of the membrane module  200  as viewed along the vapor path from the fuel tank  14 . As shown in  FIG. 1 , the activated carbon filter  112  is installed between the fuel tank  14  and the membrane module  200 , so that the fuel vapor flows into the carbon filter  112  before entering the membrane module  200 . Alternatively, however, the evaporative emission control system  100  may be modified to place the carbon filter  112  downstream of the membrane module  200 . Accordingly, the activated carbon filter  112  may be installed between the membrane module  200  and the internal combustion engine  12  (not shown), so that the fuel vapor enters the membrane module  200  before entering the carbon filter  112 . 
     As shown in  FIG. 1 , the evaporative emission control system  100  includes the membrane module  200  for selectively separating hydrocarbon (HC) vapor from other air constituents in the fuel vapor generated in the fuel tank  14 . The membrane module  200  is disposed between the internal combustion engine  12  and the fuel tank  14 , and communicates with the relief valve  102  for receiving the fuel vapor generated from the fuel tank  14  via the fuel vapor inlet line  106 . The membrane module  200  includes a membrane inlet  202  connected to the fuel vapor inlet line  106  for communicating with the fuel tank  14 , and a membrane outlet  204  connected to the fuel vapor outlet line  108  for communicating with the internal combustion engine  12 . For example, when the carbon filter  112  is installed between the membrane module  200  and the relief valve  102 , the membrane inlet  202  communicates with the carbon filter  112 . When the carbon filter  112  is alternatively installed between the membrane module  200  and the purge valve  104 , the membrane outlet  204  communicates with the carbon filter  112 . 
     In  FIG. 1 , the purge valve  104  between the membrane module  200  and the internal combustion engine  12  is provided to control the fuel vapor entering the internal combustion engine  12 . The membrane outlet  204  is connected to the fuel vapor outlet line  108  which leads the fuel vapor to the engine  12  of the vehicle  10 . The purge valve  104  is disposed in the fuel vapor outlet line  108  for controlling the purge cycle of the fuel vapor from the membrane module  200  such that the purge valve  104  activates and deactivates flow of the fuel vapor entering the engine  12  from the membrane module  200 . 
     As shown in  FIG. 1 , the purge valve  104  is preferably a solenoid operated valve controlled by an electronic controller unit (ECU) of the vehicle  10  (not shown). The purge valve  104  is normally closed when the vehicle  10  is not running (for example, the vehicle  10  is parked or the engine  12  of the vehicle  10  is running in its idle speed). The purge valve  104  is typically opened and activates the flow of the fuel vapor from the membrane module  200  when the engine  12  is running above its idle speed. When the purge valve  104  is opened, atmospheric air drawn through the air inlet line  22  and the purged fuel vapor flown through the purge outlet line  110  are mixed, and the mixed fuel vapor and the air enter the engine  12 . For example, the purged fuel vapor may be mixed with the air just before entering the engine  12  via the first purge outlet line  110   a  or the purged fuel vapor may be mixed with the air before entering the compressor  24  via the second purge outlet line  110   b.    
       FIG. 2  illustrates the membrane module  200  including the membrane inlet  202 , the membrane outlet  204 , an atmosphere inlet  206 , an atmosphere outlet  208 , and a membrane  210 . In the membrane module  200 , the membrane inlet  202  is connected to the fuel vapor inlet line  106  for receiving fuel vapor FV generated from the fuel tank  14 , and the membrane outlet  204  is connected to the fuel vapor outlet line  108  for allowing fuel-rich vapor FVr that has permeated the membrane  210  to flow into the engine  12  by the purge valve  104 . In addition, an atmosphere inlet valve  216  is connected to the atmosphere inlet  206  for controlling to receive the atmosphere air entering the membrane module  200 , and an atmosphere outlet valve  218  is connected to the atmosphere outlet  208  for controlling to discharge air including fuel vapor FV that has not permeated the membrane  210 , to the atmosphere. 
     In  FIG. 2 , as described above, the membrane module  200  further includes the membrane  210  for allowing the fuel vapor FV generated from the fuel tank  14  to permeate the membrane  210 , and the membrane module  200  is also structurally separated by the membrane  210  as a physical layer even though the fuel vapor FV permeates the membrane  210 . Accordingly, the membrane module  200  forms a first passage  212  including the membrane inlet  202  and the atmosphere outlet  208 , and a second passage  214  including the membrane outlet  204  and the atmosphere inlet  206 . The membrane  210  is formed as a flat shape and/or an asymmetric structure. However, various shapes or structures of the membrane  210  may be implemented in modifications of the shown evaporative emission control system  100 . 
     Referring to  FIG. 3 , the membrane  210  of the membrane module  200  includes a main body  210   a  formed as an active layer and a plurality of support elements  210   b  formed with the main body  210   a.  The material of the main body  210   a  may be an organic material such a silicon.  FIG. 3  illustrates a solution-diffusion mechanism of the membrane  210  such that the fuel vapor FV generated from the fuel tank  14  permeates the membrane  210  in the membrane module  200 . The generated fuel vapor FV from the fuel tank  14  passes through the carbon filter  112 , and the fuel vapor FV exiting the carbon filter  112  enters the membrane module  200  via the membrane inlet  202 , which is called “Feed” process. The entered fuel vapor FV adsorbs to the surface of the membrane  210  in the first passage  212 , and then the fuel vapor FV diffuses across the membrane  210  through micro-channels of the main body  210   a  and the support elements  210   b.  Finally, the fuel vapor FV desorbs from the opposite surface of the membrane  210  in the second passage  214  of the membrane module  200 , which is called “Permeate” process. The driving force for the permeation of the fuel vapor FV across the membrane  210  lies the partial pressure difference of the fuel vapor FV between both sides (the first passage  212  and the second passage  214 ) of the membrane  210 . In particular, the partial pressure difference of the fuel vapor FV may be high near the membrane inlet  202  in the first passage  212 , while in the second passage  214  of the membrane module  200  may have a comparatively low fuel vapor FV partial pressure. Accordingly, the solution-diffusion mechanism drives the permeation of the fuel vapor FV across the membrane  210 . As noted above, the separated fuel vapor FV in the second passage  214  is defined as the fuel-rich vapor FVr. 
     After the Permeate process, in the first passage  212  of the membrane module  200 , air including the fuel vapor FV that has not permeated the membrane  210  is discharged to the atmosphere via the atmosphere outlet  208 , which is called “Retentate” process. In addition, atmospheric air flows into the second passage  214  of the membrane module  200  via the atmosphere inlet  206  for sweeping the fuel-rich vapor FVr away from the opposite surface of the membrane  210 , which is called “Sweep” process. Due to the Sweep process, the fuel-rich vapor FVr is separated from the opposite surface of the membrane  210 . 
     Referring back to  FIG. 1 , the evaporative emission control system  100  further includes a buffer-volume housing  300 . In the evaporative emission control system  100 , the membrane module  200  includes an additional passage  220  connected to the buffer-volume housing  300 . In particular, the additional passage  220  is connected to the second passage  214  of the membrane module  200 . For example, as shown in  FIG. 1 , the additional passage  220  may be a tube connection. Alternatively, however, an integrated version of the tube into the membrane module  200  may be implemented as the additional passage  22  (not shown). The buffer-volume housing  300  is made from a plastic material inert to fuel vapor, such as polyethylene, polymerizing vinyl chloride (PVC), nylon, etc., and also formed as any type of shape such as a box shape or a cylindrical shape for fitting into a limited space of the vehicle  10 . 
     Referring to  FIG. 4 , the buffer-volume housing  300  connected to the membrane module  200  is configured to store the fuel-rich vapor FVr such that the buffer-volume housing  300  is used as an additional storage of the fuel-rich vapor FVr. In the membrane module  200 , as described above, as more fuel vapor FV permeates the membrane  210 , the partial-pressure difference of the fuel vapor FV between both sides of the membrane  210  is decreased so that the driving force for the permeation of the fuel vapor FV across the membrane  210  is reduced. However, due to the buffer-volume housing  300  connected to the second passage  214  of the membrane module  200 , the partial pressure difference of the fuel vapor FV between both sides of the membrane  210  is maintained and more fuel vapor FV generated from the fuel tank  14  permeates the membrane  210 . The fuel-rich vapor FVr that has permeated the membrane  210  is freely transmitted via the additional passage  220  (e.g. a tube) between the membrane module  200  and the buffer-volume housing  300 . 
     As shown in  FIG. 4 , due to the buffer-volume housing  300  as the additional storage, the space for storing the fuel-rich vapor FVr is increased so that the partial pressure difference of the fuel vapor FV between both sides of the membrane  210  remains large. Accordingly, more fuel vapor FV is able to permeate the membrane  210  and is stored in the second passage  214  of the membrane module  200  and the buffer-volume housing  300 . The evaporative emission control system  100  with the buffer-volume housing  300  reduces the discharge of the fuel vapor FV that has not permeated to the atmosphere. 
     In addition, as long as the vehicle  10  remains in the idle state of the engine  12 , fuel vapor FV is generated from the fuel tank  14 . For example, when a hybrid vehicle is driven by an electric motor for a long time or the vehicle  10  is parked in a warm environment for a long time, more fuel vapor FV evaporates from the fuel tank  14 . During the idle state of the engine  12  in the vehicle  10 , the fuel-rich vapor FVr (that has permeated the membrane  210 ) accumulates in the membrane module  200  and the buffer-volume housing  300  instead of flowing into the engine  12 . Accordingly, due to the buffer-volume housing  300  as the additional storage for storing the fuel-rich vapor FVr, more fuel vapor FV generated from the fuel tank  14  permeates the membrane  210  in the membrane module  200 . 
     In addition, the buffer-volume housing  300  is an additional structure for storing the fuel-rich vapor FVr before being sucked into the engine  12 . Accordingly, the evaporative emission control system  100  with both the membrane module  200  and the buffer-volume housing  300  enables the vehicle  10  to install the evaporative emission control system  100  with flexibility in the limited space of the vehicle  10  having surrounding components. For example, the evaporative emission control system  100  may utilize a smaller membrane module  200  combined with a bigger buffer-volume housing  300  or vice versa. Also, due to the additional storage for the fuel-rich vapor FVr in the evaporative emission control system  100  having the buffer-volume housing  300 , the condensate produced above the membrane  210  during the Permeate process in the membrane module  200  may be reduced. 
     While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.