JP2012127310A - Evaporation fuel treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress delay of a peak point in which the concentration of an evaporation fuel in purge gas comes to the maximum from the purge initiation while suppressing the abrupt increase of the concentration upon purge.SOLUTION: A purge control valve 37, which is made to be open upon the purge, is disposed on a purge line 20 connecting a purge port 14 of a main canister 11, which is filled with an activated carbon (adsorbent) for adsorbing evaporation fuel produced in a fuel tank 18, with an admission path 22 of an internal combustion engine 21. A buffer line 32, which includes a sub canister 34 with a volume less than the main canister 11, and a bypass line 33, which bypasses the sub canister 34, are arranged side by side on the purge line 20 between the purge port 14 and the purge control valve 37.

Description

  The present invention relates to an evaporated fuel processing apparatus for processing evaporated fuel generated in a fuel tank.

  In a vehicle equipped with an internal combustion engine, an evaporative fuel processing device is provided in order to suppress / prevent the evaporative fuel generated in the fuel tank from being released into the atmosphere. As is well known, this evaporative fuel processing apparatus includes a canister that is filled with an adsorbent such as activated carbon and temporarily adsorbs evaporative fuel introduced from a charge port. The purge port of the canister and the internal combustion engine A purge control valve is provided in the purge line connecting the intake passages. At the time of a predetermined purge during engine operation, the purge control valve is opened so that the evaporated fuel is desorbed (purged) from the canister together with the atmosphere introduced from the atmosphere port using the negative pressure in the intake passage. The air is sucked into an intake passage of the internal combustion engine and is subjected to a combustion process in a combustion chamber of the internal combustion engine.

  Also, when the amount of evaporated fuel adsorbed and collected in the canister is large, such as when the engine is started from a long-term vehicle stop state, immediately after the purge starts, the suction / The concentration of the evaporated fuel in the supplied purge gas may temporarily increase rapidly. In this case, the air-fuel ratio fluctuates inadvertently, and cannot be dealt with by control on the internal combustion engine side such as air-fuel ratio control, which may lead to deterioration of exhaust emission.

  Therefore, in Patent Document 1, in addition to the main canister that temporarily adsorbs the evaporated fuel generated in the fuel tank, a sub-canister is provided in the purge line between the purge port of the main canister and the purge control valve. The canister mitigates the excessive concentration of the evaporated fuel in the purge gas. Also, a plurality of adsorption chambers with different breakthrough times are provided in parallel in the sub-canister so as to gradually increase the fuel vapor concentration from the start of the purge.

JP 2008-69703 A

  As a countermeasure for vehicle exhaust emissions, in addition to the above canister, a catalyst such as a three-way catalyst is provided in the exhaust passage of the internal combustion engine. In order to ensure the purification performance of this catalyst, the air-fuel ratio of the exhaust is set to a predetermined target. Air-fuel ratio control is performed to maintain the air-fuel ratio (for example, the stoichiometric air-fuel ratio). In this air-fuel ratio control, air-fuel ratio feedback control for increasing or decreasing the fuel injection amount is usually performed based on a sensor signal of an air-fuel ratio sensor such as an oxygen sensor that detects the air-fuel ratio of exhaust gas. Here, since the air-fuel ratio of the exhaust also varies depending on the concentration of the evaporated fuel purged from the canister, the concentration of the evaporated fuel in the purge gas is detected at the start of the purge in order to perform the air-fuel ratio feedback control with high accuracy. Then, correction control of the fuel injection amount of the air-fuel ratio feedback control and the opening degree of the purge control valve is performed according to the concentration of the evaporated fuel. The concentration detection of the evaporated fuel is performed using, for example, a sensor signal of an air-fuel ratio sensor (that is, an air-fuel ratio of exhaust gas).

  FIG. 2 shows a change in the concentration of the evaporated fuel contained in the purge gas supplied to the intake passage during the purge. In the figure, L0 indicates a characteristic when the sub-canister is not provided, that is, a characteristic of the concentration of the evaporated fuel in the purge gas discharged from the purge port of the main canister. L1 and L2 indicate the characteristics of the first and second comparative examples in which the sub-canister is provided in the purge line between the purge port of the main canister and the purge control valve, as in the above-mentioned Patent Document 1, and the second comparative example In L2, the capacity of the sub-canister is made larger than that in the first comparative example L1, and the amount of adsorbent (activated carbon) to be filled is increased. Further, reference signs P0 to P2 in the figure represent peak points at which the concentration of the evaporated fuel becomes maximum after the start of purge in the respective characteristics L0 to L2. In the figure, the difference between the density of L1 and L2 and the density of L0 corresponds to the density decrease (or density increase) by the sub-canister.

  As shown in the figure, the concentration of the evaporated fuel in the purge gas rapidly increases immediately after the start of the purge, reaches a peak point (P0), and then gradually decreases as the evaporated fuel remaining in the canister decreases. It becomes a characteristic. Therefore, when detecting the concentration of the evaporated fuel described above, for example, the above peak point is detected, and based on this peak point, a concentration change database in which the concentration change characteristics as shown in FIG. With reference to this, a change in the concentration of the evaporated fuel is predicted.

  Here, as a result of intensive studies by the present inventors, as in Patent Document 1, the first and second comparative examples L1 and L2 provided with a sub-canister in the purge line between the purge port of the main canister and the purge control valve are used. L2 independently discovered the following problems. That is, in the first and second comparative examples L1 and L2, the evaporated fuel having a high concentration is immediately adsorbed and captured in the sub-canister immediately after the start of the purge, and the capacity of the sub-canister (the amount of adsorbent) is the main canister. Therefore, the evaporated fuel adsorbed in the sub-canister is saturated (broken down) at an early stage immediately after the start of the purge, that is, at a stage where the evaporated fuel concentration L0 in the purge gas discharged from the main canister is still high. The concentration-lowering effect of the sub-canister is quickly lost. For this reason, the concentration of the evaporated fuel in the purge gas finally supplied to the intake passage side suddenly rises, and the peak points P1 and P2 at which the concentration becomes maximum are delayed, that is, the peak from the start of the purge. The delay time to the points P1 and P2 becomes longer, and the decrease in the maximum density at the peak points P1 and P2 becomes smaller.

  Further, when the capacity of the sub-canister is increased and the adsorption amount is increased as in the second comparative example L2, the concentration reduction effect immediately after the start of the purge is greatly improved, but the concentration reduction effect does not last long. The concentration lowering effect rapidly decreases when the concentration L0 of the evaporated fuel in the purge gas discharged from the main canister is still high. For this reason, although the maximum density at the peak point P2 slightly decreases, the delay time at the peak point P2 further increases. When the peak point is delayed as described above, the detection time of the concentration (change) of the evaporated fuel described above is also delayed, and as a result, the accurate start timing of the air-fuel ratio control considering the concentration of the evaporated fuel is delayed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a novel evaporative fuel processing apparatus capable of changing the concentration of evaporative fuel at the time of purging to have desirable characteristics.

  The present invention has been made in view of such circumstances. That is, the evaporative fuel processing apparatus of the present invention has a charge port connected to a fuel tank, a main canister filled with an adsorbent that adsorbs evaporative fuel generated in the fuel tank, a purge port of the main canister, and an internal combustion engine A purge control valve that is provided in a purge line connecting the intake passage of the engine and adjusts the flow rate of the purge gas during the purge for supplying the evaporated fuel adsorbed by the main canister to the intake passage, and an adsorbent that adsorbs the evaporated fuel. And a sub-canister having a capacity smaller than that of the main canister. A purge line between the purge port and the purge control valve; a buffer line provided with the sub-canister; and a bypass line provided in parallel with the buffer line so as to bypass the sub-canister; It is characterized by having.

  With this configuration, the purge gas (gas containing fuel vapor) discharged from the purge port of the main canister at the time of purging does not pass through the sub-canister entirely, but partially bypasses the sub-canister through the bypass line. And supplied to the intake passage. Therefore, the flow rate of purge gas that passes through the sub-canister, and hence the amount of evaporated fuel, is suppressed compared to those without a bypass line, and the amount of evaporated fuel that is adsorbed and collected by the sub-canister immediately after the start of the purge is suppressed. can do. As a result, even though a sub-canister with a small capacity is used, the sub-canister is prevented from approaching a saturation / breakthrough state at an early stage immediately after the start of the purge, and a specific period of time is maintained for a relatively long time from the start of the purge. Until the concentration of the evaporated fuel discharged from the main canister becomes sufficiently low, the desired concentration reduction effect by the sub-canister can be maintained.

  As a result, for example, as shown by the characteristic L4 in FIG. 2, the maximum concentration at the peak point of the evaporated fuel concentration at the time of purging is satisfactorily reduced, and the delay of the peak point is also suppressed. Can be made a desirable characteristic.

  Preferably, the bypass line is provided with a flow rate adjusting valve that is opened during a predetermined purge. The flow rate adjusting valve may be a valve that can continuously adjust the flow rate of the bypass line, or may be a two-position switching type switching valve that simply switches between closing and opening of the bypass line.

  Preferably, the flow rate ratio of the bypass line is set larger than the flow rate ratio of the buffer line so that the effect of reducing the concentration of evaporated fuel by the sub-canister can be obtained for a long time.

  As described above, according to the present invention, a change in the concentration of the evaporated fuel in the barge gas supplied to the intake passage at the time of purging can be made a desirable characteristic. Thereby, for example, by suppressing a sudden increase in the concentration of the evaporated fuel at the time of purging, it is possible to suppress inadvertent fluctuations in the air-fuel ratio of the exhaust gas of the internal combustion engine, and to suppress deterioration of exhaust emissions, By preventing the delay in the concentration change, it is possible to start accurate air-fuel ratio control considering the concentration change of the evaporated fuel at an early stage.

The block diagram which shows the evaporative fuel processing apparatus which concerns on 1st Example of this invention. The characteristic view which shows the density | concentration of the fuel vapor in the purge gas supplied to an intake passage at the time of a purge. FIG. 6 is a cross-sectional view showing a sub-canister according to a second embodiment of the present invention. The block diagram which expands and shows the purge line vicinity which concerns on 3rd Example of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a system configuration of a fuel vapor processing apparatus according to a first embodiment of the present invention. This evaporative fuel processing apparatus has a main canister 11 filled with activated carbon as an adsorbent that adsorbs evaporative fuel. A box-shaped casing made of, for example, synthetic resin of the main canister 11 includes a main body 12 having one end opened, and a lid body 13 that closes the open end of the main body 12. A gas passage having a U-turn shape is formed inside the main canister 11, a purge port 14 and a charge port 15 are provided at one end side of the gas passage, and an atmosphere opened to the atmosphere at the other end side of the gas passage. A port 16 is provided. The charge port 15 is connected to a fuel tank 18 of the vehicle via a charge line (charge pipe) 17. The purge port 14 is connected to a position downstream of an intake passage 22 of the internal combustion engine 21, more specifically, a throttle valve 23 that throttles intake air, via a purge line (purge pipe) 20 described later. The purge line 20 is provided with a purge control valve 24 for adjusting the flow rate of the purge gas flowing through the purge line 20, and the operation of the purge control valve 24 is a control capable of storing and executing various engine controls. Controlled by the unit 25.

  In the main canister 11, a first adsorption chamber 26 filled with activated carbon is formed in the vertical passage on the charge / purge port side in the U-turn gas passage, and in the vertical passage on the atmosphere port side. Similarly, a second adsorption chamber 27 filled with activated carbon is formed. Both ends of the first and second adsorption chambers 26 and 27 are partitioned by air-permeable plate-like filter members 28 and 29, and the filter members 28 and 29 prevent the activated carbon from falling off. In addition, two springs 30 are interposed between the inner surface of the lid 13 and a perforated plate 31 having air permeability at the folded portion on the lid 13 side in the U-turn gas passage. The activated carbon in the first and second adsorption chambers 26 and 27 is held in a predetermined filled state by the urging force of 30.

  When manufacturing the main canister 11, the filter member 28, the activated carbon, the filter member 29, the perforated plate 31, and the spring 30 are loaded in this order from the opening end of the main body 12, and finally the lid body 13 opens the opening end of the main body 12. Joined to close.

  The evaporated fuel generated in the fuel tank 18 is introduced into the main canister 11 from the charge port 15 through the charge line 17 and is adsorbed by the activated carbon filled in the main canister 11. Is temporarily captured and charged. When the internal combustion engine is in a predetermined operating state, the purge control valve 24 is opened to start purging the evaporated fuel charged in the main canister 11. At the time of this purge, the atmospheric air is introduced into the main canister 11 from the atmospheric port 16 due to the pressure difference between the negative pressure downstream of the throttle valve 23 in the intake passage 22 and the atmospheric pressure, and is adsorbed in the main canister 11. The evaporated fuel is desorbed, that is, purged, and a purge gas containing the desorbed evaporated fuel is supplied from the purge port 14 to the intake passage 22 through the purge line 20 and is combusted in the combustion chamber of the internal combustion engine 21.

  In this embodiment, the purge line 20 between the purge port 14 and the purge control valve 24 is configured to branch in parallel to the two lines 32 and 33 on the way, and one of the buffer lines 32 is arranged. In addition, a sub-canister 34 filled with activated carbon as an adsorbent for adsorbing evaporated fuel is provided. In the sub-canister 34, similarly to the main canister 11, the third adsorption chamber 35 filled with activated carbon as an adsorbent is formed. Air-permeable filter members 36 are provided at both ends of the third adsorption chamber 35, and the activated carbon is held by these filter members 36 without dropping off.

  This sub-canister 34 is mainly for making the change in the concentration of the evaporated fuel at the time of purging a desirable characteristic, and is much lighter and smaller than the main canister 11. For this reason, the capacity in the sub-canister 34, that is, the amount of activated carbon filled in the sub-canister 34 (adsorption capacity) is sufficiently small with respect to the main canister 11, desirably 1/10 or less, more desirably 1 /. It is set to about 20.

  The other bypass line 33 is arranged in parallel with the buffer line 32 so as to bypass (bypass) the sub-canister 34. The bypass line 33 is provided with a flow rate adjustment valve 37 that is driven and controlled by the control unit 25. By adjusting the opening degree of the flow rate adjusting valve 37 described above, the ratio / ratio of the flow rate flowing through the buffer line 32 and the bypass line 33 can be adjusted.

  The control of the flow rate adjustment valve 37 may be performed when the concentration of the evaporated fuel in the purge gas is expected to change significantly immediately after the start of the purge, such as when the engine is started after a long parking period, When the concentration of the evaporated fuel is detected at the start of the purge for use in control, the flow rate adjustment valve 37 is fully opened so as to optimize the change in the concentration of the evaporated fuel in the purge gas at the time of purging, as will be described later. Alternatively, the opening degree is increased to increase the flow rate ratio on the bypass line 33 side.

  On the other hand, in other engine operating states, basically, the sub-canister 34 is provided by fully closing the flow rate adjusting valve 37 or reducing the opening degree so as to fully utilize the performance and capacity of the sub-canister 34. The flow rate ratio on the buffer line 32 side is increased. For example, depending on the operation state, there may be a so-called vapor charge in which the evaporated fuel enters the main canister 11 from the fuel tank 18 even during the purge. At this time, the main canister 11 is in a high adsorbing state and is excessive. If the adsorption capacity is low, there is a risk of sudden change in the concentration of the purge gas supplied to the intake passage side. Even in such a case, it is possible to obtain a mitigating effect of a rapid change in the purge gas concentration by the sub-canister 34 by restricting the flow rate adjusting valve 37 and sufficiently securing the flow rate passing through the sub-canister 34.

  Next, with reference to FIG. 2, the effect of a present Example is demonstrated. In the figure, L1 and L2 indicate the characteristics of the first and second comparative examples having no bypass line as described above. L3 and L4 show the characteristics of this embodiment in which the bypass line 33 is provided in parallel with the buffer line 32 provided with the sub-canister 34. Here, L3 is a characteristic when the flow rate ratio between the buffer line 32 and the bypass line 33 is equal (1: 1), and L4 is a flow rate ratio of the bypass line 33 from the flow rate ratio of the buffer line 32. The characteristic when the flow rate ratio between the buffer line 32 and the bypass line 33 is about 1: 9 is shown. In Examples L3 and L4, sub-canisters having the same volume and adsorption amount (adsorption capability) as those in the first comparative example L1 are used.

  As shown in the figure, in Examples L3 and L4 in which the bypass line 33 is provided, the concentration of the evaporated fuel in the purge gas is higher than in the first and second comparative examples L1 and L2 without the bypass line 33. The maximum density at the maximum peak points P3 and P4 can be further reduced. Further, in the characteristic L4 of the present embodiment, the delay time from the purge start to the peak point P4 can be sufficiently shortened as compared with the first and second comparative examples L1 and L2.

  These reasons will be described with reference to FIG. The characteristic L0 in FIG. 2 corresponds to the concentration when the sub-canister is not provided as described above, that is, the concentration of the evaporated fuel in the purge gas discharged from the purge port of the main canister. Accordingly, the change in the concentration of the evaporated fuel by the sub-canister (concentration decrease, concentration increase) corresponds to the difference (for example, ΔL in the figure) between the concentration of L0 and the concentrations of L1 to L4.

  Here, as in the first and second comparative examples L1 and L2, when the entire purge gas discharged from the main canister is supplied to the sub-canister, it is included in the purge gas discharged from the main canister immediately after the purge is started. Although most of the evaporated fuel is adsorbed to the sub-canister, the concentration of the evaporated fuel is greatly reduced. However, the sub-canister is smaller than the main canister and has a smaller adsorption capacity. Will be filled with evaporated fuel. For this reason, at the stage where the evaporated fuel concentration L0 from the main canister is still high, the concentration decrease ΔL by the sub-canister rapidly decreases, the evaporated fuel concentrations L1 and L2 rapidly increase, and the concentration peak is delayed. Since the points P1 and P2 are reached, the peak points P1 and P2 are delayed, and the maximum concentration of the evaporated fuel at the peak points P1 and P2 cannot be sufficiently suppressed.

  On the other hand, in the present embodiments L3 and L4, the bypass line 33 is provided, and the amount of purge gas passing through the sub-canister 34 is suppressed, so that it is compared with the first and second comparative examples L1 and L2. Thus, the adsorption of the evaporated fuel to the sub-canister immediately after the start of the purge is suppressed / mitigated, and the rapid concentration decrease immediately after the start of the purge is suppressed, but the concentration L0 of the evaporated fuel discharged from the main canister is The intended concentration lowering effect is maintained over a long time until it decreases, and the maximum concentration at the peak points P3 and P4 can be sufficiently reduced.

  Furthermore, as shown by the characteristic L4 in the present embodiment, by optimizing the flow rate ratio of the bypass line 33, the maximum concentration at the peak point P4 is suppressed, and the delay time from the start of the purge to the peak point P4 is sufficient. Can be shortened. Specifically, in the characteristic L4, the flow rate ratio (90%) of the bypass line 33 is significantly increased as compared with the characteristic L3, thereby greatly increasing the amount of purge gas, that is, evaporated fuel supplied to the sub-canister. Is suppressed. For this reason, the concentration decrease (ΔL) immediately after the start of the purge becomes small, and the concentration L4 of the evaporated fuel rises from an early stage immediately after the start of the purge, and the delay of the peak point P4 is suppressed. Further, by increasing the flow rate ratio on the bypass line 33 side, the adsorption to the evaporated fuel in the sub-canister is further suppressed, and the intended concentration reduction effect can be maintained for a longer time.

  As a result, in the characteristic L4 of the present embodiment, the concentration at the peak point is not significantly delayed with respect to the concentration characteristic L0 of the evaporated fuel in the purge gas discharged from the purge port 14 of the main canister 11 without significant delay of the concentration peak point. It is possible to realize an ideal density characteristic that drastically lowers the maximum density. By suppressing the maximum concentration at the peak point low, inadvertent fluctuations in the air-fuel ratio of the exhaust gas of the internal combustion engine can be suppressed, deterioration of exhaust emission can be suppressed, and the delay of the concentration peak point can be reduced. By suppressing the concentration, the concentration detection of the evaporated fuel using the peak point can be quickly performed. As a result, accurate air-fuel ratio control using the detected concentration can be quickly performed.

  In selecting the activated carbon to be filled in the sub-canister 34, its size (particle size), adsorption performance, holding power, etc. are set so as to optimize the concentration change of the evaporated fuel in the purge gas during the purge. .

  Specifically, the higher the activated carbon adsorption performance, the longer the duration of the concentration reduction effect. Therefore, the activated carbon of the sub-canister 34 is of the same or better adsorption performance as the activated carbon of the main canister 11.

  Further, as the activated carbon of the sub canister 34, one having a lower holding force than the activated carbon of the main canister 11 is used. Here, the “holding force” corresponds to the energy required for purging, and the lower the holding force, the smaller the energy required for purging and promoting neglected diffusion. Therefore, by using activated carbon having a low holding power for the sub-canister 34, the evaporated fuel remaining in the sub-canister 34 can be quickly purged and diffused.

  Further, two or more different activated carbons may be used as the adsorbent filled in the sub-canister 34. For example, in the sub-canister 34A of the second embodiment shown in FIG. 3, activated carbons 39 and 40 having different particle diameters are arranged in series in the flow. Specifically, large activated carbon 39 is filled on the main canister side / upstream side, and small activated carbon 40 superior in rapid adsorption performance than the large activated carbon 39 is filled on the intake passage side / downstream side. In this case, the concentration of the evaporated fuel can be quickly reduced immediately after the purge is started by the small activated carbon 40 on the downstream side, and the desired concentration reduction effect can be secured for a long time by the large activated carbon 39 on the upstream side. It becomes possible.

  FIG. 4 shows a third embodiment of the present invention. In the third embodiment, an on-off valve 37A that can be switched between two positions, “open” and “closed”, is more simply used as a flow rate adjusting valve provided in the bypass line 33. Further, an orifice 38 for limiting the flow rate is provided in the bypass line 33 in series with the on-off valve 37A. Also in the third embodiment, as in the first embodiment, the on-off valve 37A is opened to optimize the change in the concentration of the evaporated fuel during a predetermined purge, and in other engine operating states, the sub valve 37A is opened. In order to fully utilize the capacity and performance of the canister, the on-off valve 37A is closed.

  Alternatively, the flow rate adjusting valve 37 and the on-off valve 37A can be omitted more simply. In this case, the flow rate of the buffer line 32 is always limited by the amount of the bypass gas that always flows through the bypass line 33. For example, the effect of alleviating the concentration change by the sub-canister when the vapor charge described above occurs is reduced. However, similar to the above embodiment, the change in the concentration of the evaporated fuel at the time of purging can be made appropriate.

DESCRIPTION OF SYMBOLS 11 ... Main canister 14 ... Purge port 18 ... Fuel tank 20 ... Purge line 21 ... Internal combustion engine 22 ... Intake passage 24 ... Purge control valve 32 ... Buffer line 33 ... Bypass lines 34, 34A ... Sub-canister 37 ... Flow path adjustment valve

Claims (3)

A main canister having a charge port connected to the fuel tank and filled with an adsorbent for adsorbing the evaporated fuel generated in the fuel tank;
A purge control valve which is provided in a purge line connecting the purge port of the main canister and the intake passage of the internal combustion engine, and adjusts the flow rate of the purge gas at the time of purging to supply the evaporated fuel adsorbed by the main canister to the intake passage;
A sub-canister filled with an adsorbent for adsorbing the evaporated fuel and having a capacity smaller than that of the main canister,
The purge line between the purge port and the purge control valve has a buffer line provided with the sub-canister and a bypass line provided in parallel with the buffer line so as to bypass the sub-canister. The evaporative fuel processing apparatus characterized by the above.   The evaporated fuel processing apparatus according to claim 1, wherein the bypass line is provided with a flow rate adjusting valve that is opened during a predetermined purge.   3. The fuel vapor processing apparatus according to claim 1, wherein a flow rate ratio of the bypass line is set to be larger than a flow rate ratio of the buffer line.

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