Patent Publication Number: US-7214258-B2

Title: Evaporated fuel processing device

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to an evaporated fuel processing device, in particular for an internal combustion engine of an automotive vehicle, comprising an evaporative canister. 
   BACKGROUND OF THE INVENTION 
   There are three main sources of polluting gasses from an internal combustion engine: engine exhaust, crankcase, fuel supply systems. In the fuel tank, the hydrocarbons that are continually evaporating from the fuel constitute a significant contributing factor to air pollution. 
   To control the air pollution resulting from these emissions, governments establish quality standards and perform inspections to ensure that standards are met. Standards have become progressively more stringent, and the equipment necessary to meet them has become more complex. Emissions from the fuel tank are reduced by an evaporated fuel processing device, the heart of which is an evaporative canister of activated carbon capable of holding fuel vapour. In operation, the fuel tank vapours flow from the fuel tank to a liquid-vapour separator that returns the raw fuel to the tank and channels the fuel vapour to the canister. The evaporative canister acts as a storehouse; when the engine is running, the vapours are purged from the evaporative canister through the purge port into the combustion chamber, where they are burnt. 
   An evaporative canister is e.g. known from US patent application US-A-2002/0007826. The evaporative canister is a typically vertical-placed type integrated canister connected to a fuel tank. Evaporated fuel from the fuel tank is led to the evaporative canister via an evaporated fuel passage and, optionally, a liquid-vapour separator. The latter traps the fuel in a liquid phase. The fuel in the vapour phase only is fed into the canister via a tank port. The air/fuel vapour mixture first flows through a first adsorbent chamber comprising an adsorbent material and then through a second adsorbent chamber also comprising an adsorbent material. As the air/fuel vapour mixture flows through the first and second adsorbent chambers, the fuel component of the mixture is adsorbed by the adsorbent material and purified air exits the canister via an atmospheric port. During operation of the engine, air is drawn through the canister from the atmospheric port, through the second and first adsorbent chambers, and out via a purge port. As the air passes through the second and first adsorbent chambers the air desorbs the fuel component from the adsorbent material, whereby the latter is regenerated. The purge port is connected to the internal combustion engine, where the fuel component is then burnt. 
   Such evaporative canisters are however not designed to meet new, stricter regulations on fuel evaporating from vehicles. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is hence to provide a more effective evaporated fuel processing device. 
   According to the invention, an evaporated fuel processing device is proposed, the device comprising a tank port and an atmospheric port; a first adsorbent chamber between the tank port and the atmospheric port, and a second absorbent chamber between the first adsorbent chamber and the atmospheric port, the first and second adsorbent chambers being filled with an adsorbent material. According to an important aspect of the invention, at least two elongate flow passages are arranged in parallel between the first adsorbent chamber and the second adsorbent chamber. The at least two elongate flow passages provide a better flow distribution of the vapour through the evaporated fuel processing device. Due to the longer flow passages—as compared to the short passages, i.e. via the compensator chamber, of the prior art devices—the time needed for the air/fuel vapour mixture to flow from the first adsorbent chamber to the second adsorbent chamber is increased. The vapour mixture is thereby homogenised and a better balance of vapour front reaching the second adsorbent chamber is achieved. The efficiency of the evaporated fuel processing device can hence be increased. Alternatively, the volume and/or quality of the adsorbent material can be reduced without losing on efficiency, whereby costs can be saved while maintaining the efficiency of the device. 
   Preferably, the elongate flow passages are substantially free from adsorbent material. The flow of air/fuel vapour mixture through the elongate flow passages is hence not unduly restricted. The flow distribution, and hence the efficiency of the device, is increased. 
   The elongate flow passages can extend substantially parallel to the flow of air/fuel vapour mixture through the first adsorbent chamber. 
   Preferably, a first elongate flow passage has a first cross-section and a second elongate flow passage has a second cross-section, the first cross-section being different from the second cross-section. The different cross-sections allow a faster flow of air/fuel vapour mixture through the flow passage of larger cross-section and an aspiration effect in the flow passage of smaller cross-section. This leads to a better evacuation of the vapour mixture from the first adsorbent chamber and to a better cooling of the vapour mixture. The efficiency of the evaporated fuel processing device is thereby improved. 
   The evaporated fuel processing device advantageously further comprises a third adsorbent chamber between the second adsorbent chamber and the atmospheric port, the third adsorbent chamber being filled with an adsorbent material. The third adsorbent chamber allows reducing bleed emissions by adsorbing any remaining fuel component before the vapour escapes into the atmosphere via the atmospheric port. 
   Advantageously, the third adsorbent chamber has a length of between 40 and 80 mm and a diameter of between 30 and 60 mm. Preferably, the length is between 50 and 70 mm and the diameter is between 42 and 50 mm. Third adsorbent chambers of the prior art devices, to reduce bleed emissions, are often filled with a special kind of activated carbon, designed to reduce flow restriction. Such a special kind of activated carbon is however very expensive. A third adsorbent chamber of dimensions specified above, can be filled with normal activated carbon while still maintaining sufficiently low flow restriction. There is no need to use the expensive special kind activated carbon and cheaper normal activated carbon can instead be used. 
   The first, second and third adsorbent chambers are preferably integrated within a single evaporative canister. A more compact design can thereby be achieved. It is however not excluded to provide a main evaporative canister comprising the first and second adsorbent chambers and to provide the third adsorbent chamber as an auxiliary evaporative canister downstream of the main evaporative canister. 
   The first and/or second and/or third adsorbent chambers and/or the elongate flow passages can have rounded cross-sections, so that a more compact arrangement of flow passages can be obtained. Also, the rounded adsorbent chambers allow a more efficient use of adsorbent material arranged therein. Indeed, only a limited amount of vapour mixture flows through the corners of a rectangular adsorbent chamber so that the adsorbent material in the corners is not efficiently used. 
   The adsorbent material preferably comprises activated carbon. 
   The evaporated fuel processing device advantageously comprises a purge port connected to the first adsorbent chamber, so that fresh air can be drawn from the atmospheric port through the adsorbent chambers to the purge port. By drawing fresh air through the adsorbent chambers, the drawn air desorbs the fuel components from the adsorbent material, i.e. fuel components can be stripped off the adsorbent material trapped therein. The adsorbent material can thereby be regenerated during engine operation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic lateral section view through an evaporated fuel processing device according to the invention; and 
       FIG. 2  is a top section view through the evaporative fuel processing device of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
   A preferred embodiment of an evaporative canister according to the invention is shown in  FIG. 1 . The evaporative canister shown in this embodiment is a vertical-placed type integrated canister  10  connected to a fuel tank (not shown). Evaporated fuel from the fuel tank is led to the evaporative canister  10  via an evaporated fuel passage and, optionally, a liquid-vapour separator (not shown). The latter traps the fuel in a liquid phase. The fuel in the vapour phase only is fed into the canister via a tank port  12 . The air/fuel vapour mixture first flows through a first adsorbent chamber  14  comprising an adsorbent material  16 , generally activated carbon, and then through a second adsorbent chamber  18  also comprising an adsorbent material  16 . As the air/fuel vapour mixture flows through the first and second adsorbent chambers  14 ,  18 , the fuel component of the air/fuel vapour mixture is stripped from the vapour mixture and purified air exits the canister  10  into atmosphere via an atmospheric port  22 . During operation of the engine, air can be drawn through the canister  10  from the atmospheric port  22 , through the second and first adsorbent chambers  18 ,  14 , and out via a purge port  24 . As the air passes through the second and first adsorbent chambers  18 ,  14 , the air desorbs the fuel component from the adsorbent material  16 , whereby the latter is regenerated. The purge port  24  is connected to a combustion chamber of an internal combustion engine (not shown), where the fuel component is then burnt. 
   According to an important aspect of the invention, the evaporative canister  10  is provided with at least two elongate flow passages  26 ,  26 ′ (only one of which can be seen on  FIG. 1 ) arranged in parallel between the first adsorbent chamber  14  and the second adsorbent chamber  18 . 
   The elongated flow passages  26 ,  26 ′ are considerably longer than the flow passages of the prior art devices, wherein the flow passages are formed by the compensator chamber  20 . Due to the elongate flow passages  26 ,  26 ′, the air/fuel vapour mixture exiting the first adsorbent chamber  14  must flow through the elongate flow passages  26 ,  26 ′, along substantially the whole length of the first adsorbent chamber  14  to reach the second adsorbent chamber  18 . Due to the longer flow passages the time needed for the air/fuel vapour mixture to flow from the first adsorbent chamber  14  to the second adsorbent chamber  18  is increased. The vapour mixture is thereby homogenised and a better balance of vapour front reaching the second adsorbent chamber  18  is achieved. A better flow distribution of the vapour mixture through the evaporated fuel processing device is hence increased. Alternatively, the volume and/or quality of the adsorbent material can be reduced without losing on efficiency, whereby costs can be saved. The elongate flow passages  26 ,  26 ′ are substantially free from adsorbent material  16 , so that the flow of air/fuel vapour mixture through the elongate flow passages  26 ,  26 ′ is not unduly restricted. The “empty” elongate flow passages  26 ,  26 ′ also increase homogenisation of the vapour mixture in the passages. 
   In order to reduce bleed emissions, a third adsorbent chamber  28  is arranged between the second adsorbent chamber  18  and the atmospheric port  22 . The third adsorbent chamber  28  is also filled with adsorbent material  16  and adsorbs any remaining fuel component from the vapour mixture exiting the second adsorbent chamber  18  before the vapour escapes into the atmosphere via the atmospheric port. The third adsorbent chamber  28  is preferably between 50 and 70 mm in length and between 42 and 50 mm in diameter. A third adsorbent chamber  28  of such dimensions can be filled with normal activated carbon while maintaining sufficiently low flow restriction. There is no need to use an expensive special kind activated carbon as in some prior art devices. 
   Integrating the first, second and third adsorbent chambers  14 ,  18 ,  28  in a single evaporative canister, can achieve a compact design of evaporated fuel processing device  10 . 
   It is further to be noted that it is desirable to compact the adsorbent material  16  in the adsorbent chambers  14 ,  18 ,  28  in order to efficiently adsorb fuel components. The adsorbent material  16  is therefore maintained in a compact state by means of adsorbent holding filters  30  and adsorbent holding springs  32  associated therewith. 
   Further features of the device can be better described by referring to  FIG. 2 , which is a schematic section view from above through the evaporated fuel processing device  10 . 
   Both the first and second elongate flow passages  26 ,  26 ′ can be seen in this Figure. It can also be seen that the first and third adsorbent chambers  14 ,  28  have circular cross-section and that the second adsorbent chamber  18  and the elongate flow passages  26 ,  26 ′ have rounded cross-section. The elongate flow passages  26 ,  26 ′ tightly fit in a space between the first and second adsorbent chambers  14 ,  18 . A compact arrangement of the evaporated fuel processing device  10  is achieved. Also, the rounded adsorbent chambers  14 ,  18 ,  28  allow a more efficient use of the adsorbent material  16  arranged therein. 
   The first and second elongate flow passages  26 ,  26 ′ have different cross-section so as the allow a faster flow of air/fuel vapour mixture through the second flow passage  26 ′ of larger cross-section and an aspiration effect in the first flow passage  26  of smaller cross-section. This leads to a better evacuation of the vapour mixture from the first adsorbent chamber  14  and to a better cooling of the vapour mixture in the elongate flow passages  26 ,  26 ′. The efficiency of the device is thereby improved. 
   It is finally to be noted that, although the above description describes a vertical-placed type integrated canister, a horizontal-placed type integrated canister is not excluded.