JP4135623B2 - Evaporative fuel processing device for internal combustion engine - Google Patents

Description

  The present invention relates to an evaporative fuel processing apparatus for an internal combustion engine, and is particularly suitable for application to an evaporative fuel generated in a fuel tank.

  2. Description of the Related Art Conventionally, there is known an evaporative fuel processing apparatus that prevents vaporized fuel (fuel vapor) generated in a fuel tank from being released into the atmosphere by adsorbing it to a canister. Japanese Patent Application Laid-Open No. 2002-4959 discloses a method of determining a leak in a closed space by applying a predetermined pressure to the evaporated fuel path in such an evaporated fuel processing apparatus.

JP 2002-4959 A JP 2003-155959 A JP-A-6-93932

  However, as described in Japanese Patent Application Laid-Open No. 2002-4959, in an evaporative fuel processing apparatus in which a fuel tank, a canister, and a negative pressure pump are connected in this order, the air in the fuel tank and the canister is evaporated by the negative pressure pump. When the fuel is sucked into the atmosphere, if the amount of evaporated fuel adsorbed by the canister is close to saturation, the problem arises that the evaporated fuel in the evaporated fuel path is released into the atmosphere without being adsorbed by the canister.

  Further, when a predetermined pressure is applied to the evaporated fuel path at the time of leakage determination, the evaporated fuel generated in the evaporated fuel path is adsorbed by the canister. The pressure and flow rate in the closed space of the evaporative fuel path vary depending on the evaporated fuel adsorption state in the canister. For this reason, in the method described in the publication, when pressure is applied to the evaporated fuel path and leakage determination is performed, there is a problem that the actual pressure and flow rate in the evaporated fuel path are different from the measured values.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to prevent the fuel vapor from being released into the atmosphere at the time of leakage determination and to adsorb the evaporated fuel in the canister. It is to accurately determine the leakage of the evaporated fuel path without being affected by the above.

In order to achieve the above object, the first invention provides
A fuel tank,
A canister connected to the fuel tank and adsorbing the evaporated fuel generated in the fuel tank;
A pump connected to the canister and sucking gas in a closed space including the fuel tank through the canister;
Pressure detecting means for detecting a pressure in the closed space on the pump side from the canister;
A leakage determination means for determining a leakage state in the closed space based on the pressure detected by the pressure detection means;
An adsorption capability determination unit that determines the adsorption capability of the evaporated fuel in the canister and a leak determination stop that cancels the determination by the leak determination unit when the adsorption capability is determined to be saturated or nearly saturated Means,
An inflection point detecting means for detecting whether or not an inflection point exists in the pressure characteristic detected by the pressure detecting means,
The adsorption capacity determination means determines that the adsorption capacity is saturated or close to saturation when the inflection point is detected .

According to the first invention, when the adsorption capability of the evaporated fuel in the canister is saturated or close to saturation, the determination of leakage in the closed space is stopped, so that the evaporated fuel is sufficiently adsorbed in the canister. Leakage determination can be made only when possible. Therefore, at the time of leak judgment, all the evaporated fuel in the fuel tank is adsorbed to the canister, and the evaporated fuel does not reach the pressure detecting means. Therefore, the pressure detecting means is measured by the influence of the vapor partial pressure of the evaporated fuel. It is possible to suppress the fluctuation of the applied pressure. Further, according to the present invention, when an inflection point is detected in the pressure characteristic detected by the pressure detecting means, it is determined that the adsorption capacity of the canister is saturated or close to saturation. Is possible. Therefore, the evaporative fuel adsorption capability of the canister can be obtained without directly obtaining the evaporative fuel adsorption state of the canister.

  Several embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining the outline of the evaporated fuel processing apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the apparatus of this embodiment includes a fuel tank 10, a canister 20, and a pump module 36.

  A tank temperature sensor 16 is disposed inside the fuel tank 10. According to the tank temperature sensor 16, the temperature of the gas in the fuel tank 10, that is, the temperature of the fuel vapor can be detected. The fuel tank 10 is provided with a tank internal pressure sensor 11 for detecting the tank internal pressure Ptnk and a liquid level sensor 14 for detecting the liquid level of the fuel.

  A canister 20 communicates with the fuel tank 10 through a vapor passage 18. A VSV valve 56 is provided in the vapor passage 18. A pump module 36 communicates with the fuel tank 10 through a pump passage 38. The canister 20 is filled with activated carbon 30 for adsorbing fuel vapor flowing from the fuel tank 10. Further, the canister 20 is provided with a vapor port 22 connected to the vapor passage 18, a pump side port 24 connected to the pump passage 38, and a purge port 28 communicating with a purge passage 26 described later. As shown in FIG. 1, the vapor port 22 and the purge port 28 are provided on the same side with respect to the activated carbon 30. On the other hand, the pump-side port 24 is provided on the opposite side of the ports 22 and 28 with the activated carbon 30 interposed therebetween.

  The purge passage 26 is a passage communicating with an intake passage (not shown) of the internal combustion engine. A purge VSV 32 for controlling the conduction state is provided in the purge passage 26. During operation of the internal combustion engine, the intake negative pressure of the internal combustion engine is guided into the purge passage 26. Further, during operation of the internal combustion engine, the pump side port 24 is opened to the atmosphere. When the purge VSV 32 is opened in this state, the intake negative pressure reaches the purge port 28 of the canister 20, and as a result, an air flow from the pump side port 24 toward the purge port 28 is generated. When such an air flow occurs, desorption occurs in the fuel adsorbed on the activated carbon 30. Therefore, by appropriately opening the purge VSV 32 during operation of the internal combustion engine, the fuel adsorbed by the canister 20 can be appropriately purged by the internal combustion engine.

  Inside the canister 20, a canister temperature sensor 34 is arranged in the vicinity of the purge port 28. A canister temperature sensor 35 is disposed in the vicinity of the pump-side port 24. According to the canister temperature sensors 34 and 35, the internal temperature of the canister 20 can be measured in the vicinity of the purge port 28 and the pump side port 24.

  As shown in FIG. 1, the evaporated fuel processing apparatus of this embodiment includes an ECU (Electronic Control Unit) 40. The ECU 40 is supplied with output signals from the tank internal pressure sensor 11, the liquid level sensor 14, the tank temperature sensor 16, the canister temperature sensors 34 and 35, the pump module 36 (pressure gauge 44), and the like.

  When the VSV valve 56 is opened at an appropriate timing under the control of the ECU 40, the fuel vapor in the fuel tank 10 is sent to the canister 20. The fuel vapor sent to the canister 20 is adsorbed by the activated carbon 30.

  Further, when the purge VSV 32 is opened at an appropriate timing under the control of the ECU 40, the fuel paper adsorbed in the canister 20 is purged into the intake passage of the internal combustion engine. As a result, the fuel adsorption capacity of the canister 20 is recovered without releasing the fuel vapor to the outside.

  FIG. 2 is a schematic diagram showing the configuration of the pump module 36. The pump module 36 includes a pump 42, a pressure gauge 44, a switching valve 46, and an orifice 48. The pump 42 and the switching valve 46 are connected by a passage 50, and a passage 51 and a passage 52 are connected to the switching valve 46. The passage 51 is connected to the pump passage 38, and the orifice 48 is provided in the passage 52. A passage 54 is connected to the side of the pump 42 opposite to the switching valve 46. The passage 54 is an atmospheric port opened to the atmosphere.

The switching valve 46 functions as a valve that connects either the passage 51 or the passage 52 to the passage 50. The pump 42 generates a flow from the switching valve 46 toward the passage 54 by its operation. As a result, a negative pressure is applied to a region closer to the switching valve 46 than the pump 42. The pressure gauge 44 measures the pressure in the passage 50 at this time. The orifice 48 is a reference hole (for example, φ0.5 mm) provided for measuring the reference pressure P _REF used for leakage determination.

  In the evaporative fuel processing apparatus of the present embodiment configured as described above, a method for performing evaporative fuel path leak determination (leak diagnosis) will be described below. When performing the leak determination, the VSV valve 56 is opened, a negative pressure is applied to the evaporated fuel path including the fuel tank 10 and the canister 20 by the pump module 36, and the leak determination is performed based on the pressure detected by the pressure gauge 44. Do.

When determining leakage, the reference pressure P _REF is first measured. When measuring the reference pressure _PREF , the state of the switching valve 46 is set so that the passage 52 and the passage 50 are connected, and the pump 42 is operated. As a result, a flow from the orifice 48 toward the passage 54 is generated, and a negative pressure is applied to the passage 52. By measuring the pressure in the passage 50 with the pressure gauge 44 in this state, the reference pressure P _REF corresponding to the orifice 48 having a diameter of 0.5 mm can be detected.

When performing leak determination of the evaporated fuel path including the fuel tank 10 and the canister 20, the state of the switching valve 46 is set so that the passage 51 and the passage 50 are connected. Then, the VSV valve 56 is opened, the purge VSV 32 is closed, and the pump 42 is operated. As a result, a flow from the pump passage 38 toward the passage 54 is generated, and a negative pressure is applied to a passage including the fuel tank 10, the canister 20, the vapor passage 18, the purge passage 26, and the pump passage 38. And the pressure P _{actual value} at this time is _measured with the pressure gauge 44. Thereafter, the measured P _{actual value} is compared with the reference pressure P _REF, and the leakage determination of the evaporated fuel path is performed based on the comparison result. In principle, if the pressure P _{measured value} measured is greater than the reference pressure P _REF corresponding to the orifice 48 of 0.5 mm in diameter, leakage from large leakage holes to the outside negative pressure applied to the fuel vapor passage is from 0.5 mm in diameter Can be judged. Therefore, when P _{actual measurement value} > P _REF , it can be determined that a leak hole larger than φ0.5 mm is generated in the evaporated fuel path.

However, depending on the state of fuel vapor adsorption in the canister 20, there may be a problem in accurate leak determination. When the adsorption capability of the fuel vapor in the canister 20 is saturated, the fuel vapor flowing from the fuel tank 10 to the canister 20 flows to the pump module 36 without being adsorbed by the canister 20. In this case, the _actual P _value measured by the pressure gauge 44 includes the vapor pressure of the fuel vapor. On the other hand, not be included vapor pressure of the fuel vapor when measuring the P _REF. Therefore, when the fuel vapor adsorption capacity in the canister 20 is saturated, the _{actual measured value} P is larger than the P _REF by the vapor partial pressure of the fuel vapor, and the evaporated fuel path is obtained from the comparison result between the _actual P _value and the P _REF. It is difficult to accurately perform the leak determination.

FIG. 3 is a schematic diagram for explaining the influence of the vapor pressure of the fuel vapor on the P _{actual measurement value} . In the configuration shown in FIG. 1, the pump module 36 is connected to the evaporated fuel path including the fuel tank 10 and the canister 20 in the configuration shown in FIG. The flow rates of air and fuel vapor in each part when negative pressure is applied are shown.

As shown in FIG. 3, when a leak hole 58 is generated in the fuel tank, if negative pressure is applied to the evaporated fuel path, air flows into the fuel tank 10 from the leak hole 58. The amount of inflow from the leak hole 58 at this time is defined as Q _HOLD . Further, the flow rate (pump discharge amount) discharged from the passage 54 of the pump module 36 is defined as _QPUMP .

When there is no fuel in the fuel tank 10, the flow rate flowing into the evaporated fuel path is only the inflow amount Q _HOLD from the leak hole 58. Further, the flow rate flowing out from the evaporated fuel path is only the pump discharge amount _QPUMP . Therefore, the relationship of the following formula (1) is established.
Q _PUMP = Q _HOLE (1)
Here, when the size of the leak hole is equal to the size of the orifice 48, Q _HOLE is equal to the flow rate of air passing through the orifice 48 when measuring the reference pressure P _REF. In this case, since the fuel vapor flow rate is not included in Q _PUMP ,
Therefore, when there is no fuel in the fuel tank 10, it is possible to accurately determine whether or not the leak hole is φ0.5 mm or more by comparing the reference pressure P _REF with the P _{actual measurement value} .

When fuel is present in the fuel tank 10, fuel vapor is generated in the fuel tank 10 due to evaporation of the fuel. In this case, when a negative pressure is applied to the evaporated fuel path by the pump module 36, both the air flowing in from the leak hole 58 and the fuel vapor generated in the fuel tank 10 flow to the canister 20. If the amount of fuel vapor generated, that is, the flow rate of fuel vapor flowing from the fuel tank 10 to the canister 20 is Q _VAP and the total flow rate of air and fuel vapor flowing from the fuel tank 10 to the canister 20 is Q _OUT , the following (2 ) Is established.
Q _OUT = Q _HOLE + Q _VAP (2)
When the fuel vapor partial pressure reaches the saturated vapor pressure in the fuel tank 10, the fuel vapor does not evaporate any more, but when the fuel vapor in the fuel tank 10 is sucked out by the pump module 36, the fuel tank The fuel vapor corresponding to the flow rate Q _VAP discharged from the fuel 10 evaporates in the fuel tank 10.

When the adsorption capability of the fuel vapor in the canister 20 is saturated, the fuel vapor is not adsorbed by the canister 20, so that the air sent from the fuel tank 10 to the canister 20 and the total flow rate Q _OUT of the fuel vapor are directly _supplied to the pump module 36. Flowing. Accordingly, the relationship of the following expression (3) is established.
Q _PUMP = Q _OUT = Q _HOLE + Q _VAP (3)
In this case, the pump discharge amount Q _PUMP is larger than the inflow amount Q _HOLE by the fuel vapor flow rate (Q _VAP ) as compared with the case of the formula (1) in which no fuel exists in the fuel tank 10. Therefore, even if the size of the leak hole 58 is the same, the pressure in the fuel tank 10 becomes higher by the vapor pressure of the fuel vapor corresponding to the flow rate Q _VAP of the fuel vapor.

In this way, when fuel is present in the fuel tank 10 and the canister 20 is saturated, the _actual pressure P _measured by the pressure gauge 44 is the vapor partial pressure of the fuel vapor as compared to when no fuel is present. It gets higher by the minute. Therefore, the size of the leak hole 58 cannot be accurately determined only by comparing the reference pressure P _REF and the P _{actual measurement value} .

On the other hand, when the adsorption capability of the fuel vapor in the canister 20 is not saturated, the fuel vapor sent from the fuel tank 10 to the canister 20 is adsorbed by the canister 20. In this case, since all of the fuel vapor generated in the fuel tank 10 is adsorbed by the canister 20, the relationship of Q _CANI = Q _VAP is established when the amount of adsorption of the fuel vapor in the canister 20 is Q _CANI . A value obtained by subtracting the adsorption amount Q _CANI from the total flow rate Q _OUT of the air and fuel vapor sent from the fuel tank 10 to the canister 20 flows to the pump module 36. Therefore, the relationship of the following formula (4) is established.
Q _PUMP = Q _OUT -Q _CANI = Q _HOLE (4)
In this case, similarly to the case of the expression (1), the inflow amount Q _HOLD from the leak hole 58 becomes equal to the pump discharge amount Q _PUMP . Accordingly, the vapor partial pressure of the fuel vapor does not affect the _{actual measurement value} of the pressure P _measured by the pressure gauge 44, and the reference pressure _PREF is compared with the _{actual measurement value} P as in the case of the equation (1). Thus, it can be accurately determined whether or not the leakage hole is 0.5 mm or more.

  From the above viewpoint, in the present embodiment, the leakage determination of the evaporated fuel path is performed only when the fuel vapor adsorption capacity of the canister 20 is not saturated, and when the fuel vapor adsorption capacity of the canister 20 is saturated. The leak judgment is not performed.

As a result, the influence of the fuel vapor pressure generated in the fuel tank 10 on the P _{actual measurement value} can be eliminated, and the leakage determination of the evaporated fuel path can be performed with high accuracy. In addition, when the fuel vapor adsorption capacity in the canister 20 is saturated, the leak determination is not performed, and therefore, no negative pressure is applied to the evaporated fuel path by the pump module 36. Accordingly, it is possible to reliably prevent the fuel vapor from passing through the saturated canister 20 and being discharged from the passage 54 into the outside air.

FIG. 4 is a flowchart showing a processing procedure in the evaporated fuel processing apparatus of this embodiment. First, in step S1, to obtain a fuel vapor adsorption amount _{m s} of the canister 20 at the present time. In the next step S2, the adsorption amount m _s acquired in step S1 is compared with a predetermined threshold M _max to determine whether M _max > m _s . Here, the threshold value M _max is the adsorption amount of the fuel vapor that is adsorbed by the canister 20 when the adsorption capability of the fuel vapor of the canister 20 is saturated.

If M _max > M in step S2, the process proceeds to step S3. In this case, since the fuel vapor adsorption amount m _s of the canister 20 at the present time it is smaller than the threshold M _max, adsorption capacity of the fuel vapor in the canister 20 can be determined not to be saturated. Accordingly, the evaporative fuel path leakage determination is performed in the following steps. That is, in step S3, the pump 42 is operated, and in the next step S4, the state of the switching valve 46 is set so that the negative pressure by the pump 42 is applied to the passage 52 where the orifice 48 is provided. The pressure P _REF is detected.

In the next step S5, the VSV valve 56 is opened and the purge VSV 32 is closed. In the next step S6, the state of the switching valve 46 is set so that the negative pressure by the pump 42 is applied to the pump passage 38, and the inside of the fuel tank 10, the canister 20, the vapor passage 18, the purge passage 26, and the vapor port 22 are set. Then, a negative pressure is applied to the evaporated fuel path including the purge port 28. In the next step S7, the pressure P _{actual measurement value} is measured by the pressure gauge 44 in a state where a negative pressure is applied to the evaporated fuel path. When negative pressure is applied in step S6, the fuel vapor and air in the evaporated fuel path are discharged by the pump module 36, and the _actual pressure P _measured by the pressure gauge 44 decreases. In step S7, pressure measurement is performed in which the P _{actual measurement value} is reduced to a steady state.

In the next step S8, the magnitude relationship between the pressure P _{actual measurement value} measured in step S7 and the reference pressure _PREF measured in step S4 is compared. That is, here, it is determined whether or not P _{actual measurement value} ≦ P _REF .

When it is determined in step S8 that P _{actual measurement value} ≦ P _REF , the process proceeds to step S9, and it is determined that the size of the leak hole generated in the evaporated fuel path is φ0.5 mm or less. On the other hand, when it is determined in step S8 that P _{actual measurement value} > P _REF , the process proceeds to step S10, and it is determined that a leak hole larger than φ0.5 mm is generated in the evaporated fuel path.

For _{M max} ≦ _{m s} in step S2 advances to step S11. In this case, since the fuel vapor adsorption amount m _s of the canister 20 at the present time it has reached the threshold value M _max, can be determined that the adsorption capacity of the fuel vapor in the canister 20 is saturated. Therefore, in step S11, the evaporative fuel path leakage determination is not performed. Incidentally, when it reaches the vicinity of the M _max adsorption amount m _s of the canister 20 is increased, because the fuel vapor from the passage 54 of the pump module 36 from being released into the atmosphere, in step S2, on anticipation of predetermined safety factor in it it is preferable to compare the _{M max} and _{m s.} For example, in step _S2, is multiplied by a predetermined coefficient (e.g., 0.9) to _{M max,} it determines whether the 0.9 × _M max> _{m s.} Thereby, although the fuel vapor adsorption capacity of the canister 20 is not completely saturated, it is possible to realize control that does not perform the leakage determination when the canister 20 is in a nearly saturated state. Therefore, the fuel vapor can be reliably prevented from being discharged from the passage 54 of the pump module 36.

According to the process of FIG. 4, since the leakage determination of the evaporated fuel path is performed only when the fuel vapor adsorption capacity in the canister 20 is not saturated, if a negative pressure is applied by the pump module 36 during the leakage determination, the fuel tank The fuel vapor in 10 is surely adsorbed by the canister 20. Therefore, it is possible to reliably prevent the fuel vapor from being released from the passage 54 of the pump module 36 into the atmosphere. Further, since the fuel vapor leakage determination is performed only when the fuel vapor adsorption capacity in the canister 20 is not saturated, the partial pressure of the fuel vapor is not measured by the pressure gauge 44. Therefore, it is possible to partial pressure of fuel vapor to eliminate the influence of the P _{measured value,} it is possible to accurately perform the leakage determination of the evaporative fuel path based on P _Found.

Next, in step S1 in FIG. 4, a method for determining the fuel vapor adsorption amount m _s of the canister 20 at the present time. In the present embodiment, the ECU 40 has a function of accurately estimating the fuel adsorption state (fuel vapor adsorption amount m _s ) corresponding to the absolute amount of fuel vapor adsorbed on the canister 20.

  In the fuel tank 10, fuel vapor is generated by the evaporation of fuel. When the VSV valve 56 is opened, the fuel vapor in the fuel tank 10 flows into the canister 20 and is adsorbed by the canister 20. When the fuel vapor is adsorbed to the canister 20, the internal energy of the canister 20 changes. The amount of change in internal energy at this time varies according to the amount of fuel vapor adsorbed. In the evaporative fuel processing apparatus of this embodiment, the amount of change in the internal energy of the canister 20 while the VSV valve 56 is open is calculated from the adsorption heat generated during the adsorption, and based on this, the fuel vapor of the canister 20 is calculated. The amount of adsorption is calculated.

First, a method for calculating the heat of adsorption will be described. FIG. 5 is a schematic diagram showing how the fuel vapor is adsorbed on the activated carbon 30. As shown in FIG. 5, the fuel vapor before being adsorbed by the activated carbon 30 is in a gas phase. When fuel vapor in a gas phase is adsorbed on the surface of the activated carbon 30, adsorbed molecules are generated. As a result, the fuel vapor is liquefied and becomes an adsorption phase, and heat of adsorption is generated. Here, the following relationship is established between the amount of heat generated by the adsorption of the fuel vapor (adsorption heat), the energy received by the activated carbon 30 and the amount of heat lost by heat conduction.
(Adsorption heat) = (Energy received by activated carbon) + (Amount of heat lost by heat conduction)

  The above relationship can be expressed by the following equation (5) (Tian equation). In equation (5), dq is the heat of adsorption that generates a unit mass of fuel vapor during adsorption. ΔT is a temperature change amount of the fuel vapor (activated carbon 30) at the time of adsorption, and is detected from the canister temperature sensor 34 as a change amount of the internal temperature T of the canister 20 while the VSV valve 56 is opened. Can do. Further, σ is a thermal conductivity coefficient of the activated carbon 30, and c is an effective heat capacity of the activated carbon 30. According to the equation (5), the adsorption heat dq generated by the unit mass of the fuel vapor can be calculated based on the temperature change amount ΔT.

The internal energy E _ads in the canister 20 changes due to the adsorption of the fuel vapor. At this time, if heat does not escape to the outside of the canister 20 due to heat conduction, the following relationship is established.
(Amount of energy change in the canister when the unit mass of the fuel vapor is adsorbed) = (Amount of heat generated by the unit mass of the fuel vapor by adsorption)
That is, the energy change amount dE _ads per unit mass of the fuel vapor and the adsorption heat dq are balanced, and the relationship of the following equation (6) is established.

dE _ads = dq (6)

The internal energy E _ads of the canister 20 can be expressed by the sum of the energy of the activated carbon 30 and the energy E _{S of the} adsorption phase, and the following relationship is established.
(Canister internal energy) = (activated carbon energy) + (adsorption phase energy)
The internal energy of the activated carbon 30 is proportional to the internal temperature T of the activated carbon 30 and can be represented by the product of the internal temperature T and the specific heat C _{VC of the} activated carbon. Accordingly, the relationship of the following expression (7) is established.

E _ads = C _VC · T + E _S (7)

When the equation (7) is differentiated by the amount of adsorption and time, the change amount dE _ads of the internal energy E _ads due to the adsorption of the fuel vapor unit mass while the VSV valve 56 is opened is obtained. Since dE _ads = dq from the equation (6), the relationship of the following equation (8) is established.

dq = dE _ads = C _VC · dT + dE _S (8)

In the equation (8), the change amount dE _S of the adsorption phase energy E _S varies according to the adsorption amount of the fuel vapor. Therefore, by expressing the change amount dE _S as a function of the adsorption amount, the adsorption amount of the fuel vapor can be calculated from the adsorption heat dq based on the equation (8).

A method of expressing the change amount dE _S of the energy E _S of the adsorption phase as a function of the adsorption amount will be described below. FIG. 6 is a characteristic diagram showing how the adsorption phase energy E _S per unit mass fluctuates in accordance with the amount of fuel vapor adsorption M _s per unit activated carbon mass. Figure 6 shows the characteristics in a case where the temperature of the fuel vapor is constant, with the energy E _S of adsorbed per unit mass, the fuel vapor in the gas phase of the energy, heat of adsorption generated during the adsorption, and The latent heat of vaporization of the fuel vapor is shown as a value per unit mass of the fuel vapor. As shown in FIG. 6, the energy of the adsorption phase and the heat of adsorption fluctuate according to the amount of adsorption m _s, and the energy of the gas phase and the latent heat of vaporization are constant regardless of the amount of adsorption m _s .

  As shown in FIG. 6, as the amount of fuel vapor adsorbed on the activated carbon 30 increases, the energy of the adsorption phase increases and the heat of adsorption decreases. As the amount of adsorption of the fuel vapor increases, the energy of the adsorption phase gradually approaches the value obtained by subtracting the latent heat of vaporization from the energy of the gas phase.

The internal energy of the fuel vapor before being adsorbed on the activated carbon 30 is gas-phase energy shown in FIG. When the fuel vapor is adsorbed on the activated carbon 30 and the adsorbed molecules are generated, the internal energy of the fuel vapor becomes the energy of the adsorption phase shown in FIG. 6, and the heat of adsorption is generated. Therefore, the following relationship is established.
(Adsorption phase energy per unit mass of fuel vapor) = (Gas phase energy per unit mass of fuel vapor)-(Adsorption heat per unit mass of fuel vapor)
This relationship can be expressed by the following equation (9).

In the equation (9), C _p · T represents gas phase energy per unit mass of fuel vapor. Here, _Cp is the fuel vapor low pressure specific heat, and T is the temperature of the fuel vapor.

In the equation (9), Δh _vap (T) + f (ν) represents heat of adsorption per unit mass of fuel vapor. Here, Δh _vap (T) is latent heat of vaporization and is a function of the temperature T of the fuel vapor. The latent heat of vaporization Δh _vap (T) can be expressed by, for example, the well-known Clavius Clapeyron equation.

F (ν) represents the adsorption potential of the fuel vapor. The adsorption potential f (ν) is the energy of the fuel vapor generated due to the intermolecular force when the fuel vapor becomes an adsorption phase. The adsorption potential f (ν) is a function of the adsorption volume ν, and ν is the ratio of the adsorption amount m _s to the density ρ _L of the adsorption phase. That is, the relationship of ν = m _s / ρ _L is established. FIG. 7 is a characteristic diagram in which the relationship (adsorption characteristic curve) between the adsorption potential f (ν) and ν (= m _s / ρ _L ) is experimentally determined. As shown in FIG. 7, as ν increases, the adsorption potential f (ν) of the fuel vapor decreases. That is, since ν = m _s / ρ _L , when the adsorption amount m _s increases, the adsorption potential f (ν) decreases. When the adsorption amount _ms further increases, the adsorption potential f (ν) approaches 0, and the heat of adsorption and the latent heat of vaporization become substantially equal as shown in FIG.

As described above, the heat of adsorption per unit mass of the fuel vapor can be represented by the sum of the latent heat of vaporization Δh _vap (T) and the adsorption potential f (ν).

(9) a when integrated between the adsorbed amount _{m s,} equation (10) below is obtained. According to (10), it may represent the energy Es of the adsorption phase as a function of the adsorption amount m _s. In the equation (10), a variable in the adsorption potential f (ν) is indicated as ν ′.

(8) In the equation, the variation dE _S of, per fuel vapor unit mass while opening VSV valve 56 can be calculated by differentiating the equation (10). Here, since the energy E _S of the adsorption phase is a function of the temperature T of the fuel vapor and the adsorption amount m _s , the relationship of the following equation (11) is established. Then, substituting the right side of equation (11) into equation (8) yields the following equation (12). Since it can be considered that the temperature T of the fuel vapor and the internal temperature T of the canister 20 are equal, according to the equation (12), the internal energy change amount dE _ads (= adsorption heat dq) it can be expressed as a function of the amount m _s. Therefore, the adsorption amount m _s can be calculated from the adsorption heat dq and the internal temperature T.

The first term and the second term on the right side of the equation (11) can be obtained by differentiating the equation (10), and can be represented by the following equations (13) and (14). (13) In the formula (14) shows a dT as [Delta] T, also the dm _s as Delta] m _s. In the equations (13) and (14), ΔT is the temperature change amount of the fuel vapor (activated carbon 30) while the VSV valve 56 is opened, that is, while the fuel vapor is adsorbed. T is the temperature of the fuel vapor (activated carbon 30) when the VSV valve 56 is opened. ΔT and T can be detected from the canister temperature sensor 34.

In equation (13), equation (10) is differentiated with respect to internal temperature T. At this time, since f (ν) in equation (10) is not a function of internal temperature T, the term obtained by differentiating f (ν) is 0. In the equation (13), Δ {Δh _vap (T)} is the amount of change in latent heat of evaporation Δh _vap (T) while the VSV valve 56 is open. In addition, since ν = m _s / ρ _L , dν / dm _s = 1 / ρ _L in the equation (14).

Substituting Equations (13) and (14) into Equation (12) yields the following Equation (15). (15) In the formula, Delta] m _s represents the variation of the adsorption amount m _s while opening the VSV valve 56. That is, if the adsorption amount when the VSV valve 56 is opened is m _s (k−1) and the adsorption amount when the VSV valve 56 is closed is m _s (k), Δm _s = m _s (k) −m The relationship of _s (k-1) is established. In the equation (15), m _s represents the adsorption amount m _s (k) when the VSV valve 56 is closed. Therefore, when equation (15) is modified, equation (16) is obtained. According to the equation (16), the heat of adsorption dq can be expressed as a function of m _s (k), m _s (k−1), ΔT.

The following expression (17) is an expression that defines the function f by shifting the left side dq of the expression (16) to the right side. According to the equation (16), it is possible to obtain the current adsorption amount m _s (k) using the adsorption heat dq, the previous adsorption amount m _s (k−1), and the temperature change amount ΔT. since the potential f ([nu) is a function of the adsorption amount m _{s (k),} there is a case where the arithmetic processing directly to be obtained current adsorption amount m _{s (k)} is is complicated from (16) . Therefore, in the present embodiment, the previously acquired adsorption amount m _s (k−1) and the temperature change amount ΔT while the VSV valve 56 is opened are substituted into the equation (17), and the current adsorption amount m _s ( For k), a temporary value is substituted into the equation (17). Then, the expression (17) is iteratively calculated so that f → 0 while changing the value of the temporary adsorption amount m _s (k). Then, the value of m _s (k) when the value of the function f approaches 0 is calculated as the final current adsorption amount m _s (k). Thus, the current adsorption amount m _s (k) can be calculated from the heat of adsorption dq, the previous adsorption amount m _s (k−1), and the temperature change amount ΔT by repeatedly calculating the equation (17). It becomes possible.

  When the adsorption amount in the canister 20 increases and the purge VSV 32 is opened, the fuel vapor adsorbed on the activated carbon 30 is desorbed and flows to the intake passage side. At this time, a reaction opposite to the reaction described with reference to FIG. 5 occurs, and the temperature detected by the canister temperature sensor 34 while the purge VSV 32 is opened decreases with time. Accordingly, the temperature change amount ΔT when the purge VSV 32 is opened is a negative value.

The fuel vapor open for a predetermined time purge VSV32 adsorption m _s after desorbed _(k), like the adsorption amount of After adsorption of the fuel vapor by opening the VSV valve 56 m _{s (k),} (17) It can obtain | require from Formula. At this time, it is possible to obtain the fuel vapor adsorption amount m _s (k) after desorption by substituting the value of ΔT into a negative value in the equation (17).

Therefore, by substituting the adsorption amount m _s (k−1) when the VSV valve 56 or the purge VSV 32 is opened and the temperature change ΔT while the VSV valve 56 or the purge VSV 32 is opened into the equation (17). The adsorption amount m _s (k) when the VSV valve 56 or the purge VSV 32 is closed can be calculated. Then, the adsorption amount m _s (k) is stored, and the calculation of the equation (17) is performed when the VSV valve 56 or the purge VSV 32 is opened next, thereby calculating the absolute amount of the fuel vapor adsorption amount in the canister 20. It is possible to calculate sequentially.

The fuel vapor adsorbed on the canister 20 is completely desorbed by opening the purge VSV 32 for a predetermined time (about several tens of minutes). Accordingly, if the adsorption amount m _s (k−1) at the time when the VSV valve 56 or the purge VSV 32 is opened is unknown, the purge VSV 32 is opened for a predetermined time, the canister 20 is reset to an empty state, and the next calculation is performed. It is preferable to perform the calculation of equation (17) with m _s (k−1) = 0.

  Further, when both the VSV valve 56 and the purge VSV 32 are closed, the fuel vapor adsorption phenomenon and the desorption phenomenon in the canister 20 do not occur, and no temperature change occurs in the canister 20. Therefore, the canister temperature sensor 36 may be activated when one of the VSV valve 56 or the purge VSV 32 is opened.

Next, with reference to the flowchart of FIG. 8, the processing procedure for calculating the fuel vapor adsorption amount m _s is described. Here, processing when the VSV valve 56 is opened and fuel vapor is adsorbed to the canister 20 will be described.

  First, in step S <b> 11, a tank internal pressure valve provided in the fuel tank 10 is closed, and preparations for sending fuel vapor from the fuel tank 10 to the canister 20 are made. In the next step S12, it is determined whether or not preparation for estimating the fuel vapor adsorption amount is completed.

  In the next step S13, it is determined whether or not the internal pressure of the fuel tank 10 is equal to or higher than a predetermined pressure (atmospheric pressure + α). When the internal pressure of the fuel tank 10 is equal to or higher than the predetermined pressure, the fuel vapor is generated in the fuel tank 10, so that the process proceeds to step S14, and the VSV valve 56 is opened for a predetermined time. On the other hand, when the internal pressure of the fuel tank 10 is smaller than the predetermined pressure, the process is terminated (END).

  While the VSV valve 56 is opened in step S14, the fuel vapor in the fuel tank 10 flows into the canister 20. The fuel vapor is adsorbed on the activated carbon 30, and the temperature of the activated carbon 30 rises due to the generation of heat of adsorption. In step S <b> 15, the temperature change amount ΔT while the VSV valve 56 is open is detected from the canister temperature sensor 34.

In the next step S16, the current adsorption amount of fuel vapor (the adsorption amount when the VSV valve 56 is closed) m _s (k) in the activated carbon 30 is obtained using the temperature change ΔT obtained in step S15. After obtaining the fuel vapor adsorption amount m _s (k) in step S16, the process ends (END).

The flowchart of FIG. 9 shows in detail the process of calculating the adsorption amount m _s (k) in step S16 of FIG. First, in step S21, the heat of adsorption dq is calculated from equation (5) using the temperature change ΔT detected in step S15 of FIG. In the next step S22, the adsorption amount m _s (k−1) calculated last time is acquired from the memory of the ECU 40.

In the next step S23, ΔT, m _s (k−1), and the temporarily set value of m _s (k) are substituted into equation (17) to perform iterative calculation. Then, the value of m _s (k) when f in Equation (17) is closest to 0 is calculated as the final current adsorption amount m _s (k). After calculating the current amount of adsorption m _s (k) in step S23, the process ends (END).

  In step S23, if the value of the function f does not converge to a value near 0, after a predetermined time has elapsed, the process returns to step S21 or the process of FIG. 8 and the process is performed again.

Further, in step S13 of FIG. 8, when the VSV valve 56 is opened when (inner pressure of the fuel tank 10) ≦ (atmospheric pressure−α), the fuel vapor adsorbed on the canister 20 is desorbed, and the fuel is removed from the canister 20. Fuel vapor flows into the tank 10. In this case, the temperature change amount ΔT while the VSV valve 56 is open is a negative value. Therefore, even in the case of (inner pressure of the fuel tank 10) ≦ (atmospheric pressure−α), the adsorption amount at the time when the VSV valve 56 is closed after the fuel vapor is desorbed, as in the case where the purge VSV 32 is opened. m _s (k) can be calculated. By opening the VSV valve 56 when (the internal pressure of the fuel tank 10) ≦ (atmospheric pressure−α), it is possible to avoid applying excessive pressure to the fuel tank 10 when the evaporated fuel path is rapidly cooled.

8 and 9, the fuel vapor adsorption amount m _s (k) in the canister 20 at the present time can be calculated sequentially. Therefore, in step S1 of FIG. 4, the fuel vapor adsorption amount m _s (k) that has been sequentially calculated can be acquired as the fuel vapor adsorption amount m _s of the canister 20 at the present time.

Next, a method of calculating the adsorption amount m _s of fuel vapor from the map. FIG. 10 is a characteristic diagram showing how the energy E _S of the adsorbed phase per unit mass fluctuates in accordance with the amount of fuel vapor adsorbed per unit activated carbon mass m _s , as in FIG. 7. Based on FIG. 10, when the temperature change amount ΔT while the VSV valve 56 is open is the same, the difference in the adsorption amount m _s (k−1) at the time when the VSV valve 56 is opened indicates that the VSV valve 56 is open. the impact on the adsorption amount of variation Delta] m _s between and are explained.

When the temperature change amount ΔT while the VSV valve 56 is opened is equal, it can be considered that the energy change amount of the fuel vapor is also equal. As shown in FIG. 10, in two cases where the adsorption amounts m _s (k−1) are different, the energy change amount of the fuel vapor due to the adsorption while the VSV valve 56 is opened is the energy of the adsorption phase per unit mass. Can be represented by areas A ₁ and A ₂ surrounded by a curve 60 representing the gas phase and a straight line 62 representing the energy of the gas phase. Here, in the two cases represented by the areas A ₁ and A ₂ , assuming that the internal temperature T at the start of adsorption is equal and the temperature change ΔT at the time of adsorption is equal, the energy of both fuel vapors since the amount of change is equal, the area A ₁ and the area A ₂ are equal.

Here, the horizontal axis of the area A _1, the width of the area A ₂ can be considered as adsorption amount of variation Delta] m _s while opening the VSV valve 56. As shown in FIG. 10, the widths of the area A ₁ and the area A ₂ in the horizontal axis direction when the temperature change amounts ΔT are equal vary depending on the adsorption amount m _s (k−1) and are compared with the area A ₁ . the horizontal axis direction of the width of the area a ₂ becomes wider Te. Accordingly, as shown in FIG. 10, when the temperature variation ΔT is equal, as the adsorption amount of time you open the VSV valve 56 m _{s (k-1)} is large, the variation Delta] m _s of adsorption increases.

On the other hand, when the adsorption amount m _s (k−1) at the time when the VSV valve 56 is opened is equal, the adsorption reaction of the fuel vapor in the activated carbon 30 is more performed as the temperature change amount ΔT is larger. Therefore, if the adsorption amount m _{s (k-1)} are equal, the greater the temperature variation ΔT is the variation Delta] m _s of adsorption amount increases. This can be explained, for example, from the adsorption characteristic curve of FIG. As shown in FIG. 7, in the two cases variation Delta] m _s of adsorption is different (Δm _s1, Δm _s2), higher the Delta] m _s increases, the amount of change in f (ν) Δ {f ( ν)} is growing. As f (ν) increases, the amount of change in the energy Es of the adsorption phase increases, and as a result, the temperature change amount ΔT also increases. Therefore, if the adsorption amount m _{s (k-1)} are equal, the greater the temperature variation ΔT is the variation Delta] m _s of adsorption amount increases.

From the above viewpoint, the relationship between the temperature change amount ΔT, the adsorption amount m _s (k−1) when the VSV valve 56 is opened, and the adsorption amount change amount Δm _s while the VSV valve 56 is opened is represented by a map. Can be prescribed. Then, it is possible to determine the amount of adsorption of variation Delta] m _s while opening the VSV valve 56 from the map.

Figure 11 is a schematic diagram showing the temperature change amount [Delta] T, adsorption amount m _{s (k-1),} and a map defining the relationship between the variation Delta] m _s of adsorption. The map of FIG. 11 defines a relationship in which, when the temperature change amount ΔT is equal, the adsorption amount change amount Δm _s increases as the adsorption amount m _s (k−1) at the time of opening the VSV valve 56 increases. ing. In addition, when the adsorption amount m _s (k−1) is equal, a relationship is defined in which the change amount Δm _s increases as the temperature change amount ΔT increases. Therefore, by applying the temperature change amount ΔT and the adsorption amount m _s (k−1) to the map of FIG. 11, the adsorption amount change amount Δm _s can be obtained. Then, after obtaining Delta] m _s, by performing the calculation of the _{m s (k) = m s} (k-1) + Δm s, it is possible to determine the current adsorption amount _m s (k). The map of FIG. 11 can be created by experimentally determining the relationship between the temperature change amount ΔT, the adsorption amount m _s (k−1), and the adsorption amount change amount Δm _s .

Similarly, when the purge VSV 32 is opened, the amount of change in adsorption amount (desorption amount) Δm _{s is} obtained by applying the temperature change amount ΔT (<0) and the adsorption amount m _s (k−1) to the map of FIG. Can be requested.

In the map of FIG. 11, the relationship between the temperature change amount ΔT, the adsorption amount m _s (k−1), and the adsorption amount change amount Δm _s is defined, but m _s (k) = m _s (k−1). ) + Δm _s , the relationship between the temperature change amount ΔT, the adsorption amount m _s (k−1), and the adsorption amount m _s (k) may be defined.

According to the map of FIG. 11, the fuel vapor adsorption amount m _s (k) in the canister 20 at the present time can be obtained. Therefore, in step S1 of FIG. 4, the fuel vapor adsorption amount m _s (k) obtained from the map of FIG. 11 can be acquired as the fuel vapor adsorption amount m _s of the canister 20 at the present time.

As described above, according to the first embodiment, it is possible to determine the leakage of the evaporated fuel path only when the fuel vapor adsorption capacity of the canister 20 is not saturated. As a result, since all the fuel vapor in the fuel tank 10 is adsorbed to the canister 20 at the time of leakage determination, the influence of the partial pressure of the fuel vapor on the _actual pressure P _measured by the pressure gauge 44 is affected. Can be eliminated. Therefore, based on the reference pressure P _REF and the _actual pressure P _measured by the pressure gauge 44, it is possible to accurately determine whether or not a leak hole has occurred in the evaporated fuel path. Further, when the fuel vapor adsorbing capacity of the canister 20 is saturated, the leak determination is not performed, so that it is possible to reliably prevent the fuel vapor from being released from the passage 54 of the pump module 36 into the atmosphere. .

Further, according to the first embodiment, the adsorption heat dq can be calculated from the change amount ΔT of the canister internal temperature while the VSV valve 56 is open. Then, it is possible to represent the adsorption heat dq (= internal energy _E variation _{dE Ads} of _ads) in function of the internal temperature T and the adsorption amount _{m s} of the canister 20, the adsorption heat dq, the internal temperature T and the adsorption amount m from _s relationship it is possible to calculate the adsorption amount m _s of time. Further, a map of the current adsorption amount m _s (k) is calculated from the adsorption amount m _s (k−1) when the VSV valve 56 is opened and the temperature change amount ΔT while the VSV valve 56 is opened. It becomes possible. Therefore, it is possible to accurately obtain the fuel vapor adsorption amount of the canister 20 by a simple method.

In the first embodiment, the canister temperature sensors 34 may be provided at a plurality of locations in the canister 20. Thus, it can determine the adsorption amount m _s of fuel vapor per unit activated carbon mass at a plurality of positions in the canister 20, it is possible to determine the adsorption state of the fuel vapor in the canister 20 more accurately.

  In the first embodiment, when calculating the adsorption heat dq, the adsorption heat dq may be calculated in consideration of the amount of heat that escapes to the outside of the canister 20 due to heat transfer. For example, the heat flux sensor 38 is provided on the outer periphery of the canister 20, the heat loss to the outside is detected, and the heat loss is added to the calculated adsorption heat dq, so that the calculation accuracy of the adsorption heat dq can be further increased. It is.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described. In the second embodiment, it is determined whether or not the fuel vapor adsorption capacity of the canister 20 is saturated based on the fluctuation of the _{actual measurement value} of the pressure P _measured by the pressure gauge 44. If the fuel vapor adsorption capacity of the canister 20 is saturated, the evaporative fuel path leakage determination is stopped as in the first embodiment. The configuration of the evaporated fuel processing apparatus of the second embodiment is the same as the configuration described in FIG.

FIG. 12 is a characteristic diagram showing how the _actual pressure P _measured by the pump module 36 varies with time when a negative pressure is applied to the evaporated fuel path. Each of the characteristics A to C shows the fluctuation of the _actual P _{measurement value} from the time when the negative pressure is started to the steady state. Here, the characteristic A indicated by the solid line shows how the _{actual measurement value} of the pressure P fluctuates when negative pressure is applied from the pump module 36 to the evaporated fuel path including the fuel tank 10 and the canister 20 as in the first embodiment. ing.

The characteristic B indicated by the alternate long and short dash line indicates the fluctuation of the _{measured value} of the pressure P when the negative pressure is directly applied from the pump module 36 to the fuel tank 10. That is, the characteristic B shows how the _{actual measurement value} of the pressure P fluctuates when the canister 20 is removed from the configuration of FIG. 1 and the pump module 36 and the fuel tank 10 are directly connected to apply a negative pressure to the evaporated fuel path. ing.

The characteristic C indicated by the broken line is a case where the fuel vapor adsorption capacity of the canister 20 is saturated at the time t when a negative pressure is applied to the evaporated fuel path including the fuel tank 10 and the canister 20 as in the characteristic A. FIG. 9 shows how the _{actual measured value} of pressure P fluctuates thereafter.

As shown in the characteristics A to C, when the negative pressure is started to be applied, the vaporized fuel path is filled with air and fuel vapor, so the pressure until the air and fuel vapor in the path are discharged. The _{actual measurement value} of the pressure P _measured by the total 44 decreases with time. When the air and fuel vapor in the evaporated fuel path are discharged, the pressure measured by the pressure gauge 44 becomes a steady value.

As described in the first embodiment, when the adsorption capability of the fuel vapor in the canister 20 is saturated, the partial pressure of the fuel vapor is measured by the pressure gauge 44. Therefore, the adsorption of the fuel vapor in the canister 20 is performed. The _actual pressure P _measured by the pressure gauge 44 is higher than when the capacity is not saturated. The characteristic B shown in FIG. 12 shows how the _{measured value} of the pressure P fluctuates when the canister 20 is not provided, so the pressure of the characteristic B includes the vapor partial pressure of the fuel vapor. That is, the characteristic B is the same as the characteristic in which the _{actual measurement value} of the pressure P varies when the fuel vapor adsorption capacity in the canister 20 is saturated in the configuration of FIG. Therefore, as shown in FIG. 12, the pressure of the characteristic B is higher than the characteristic A.

In the configuration shown in FIG. 1, when the negative pressure is applied from the pump module 36 to the evaporated fuel path when the fuel vapor adsorption capacity in the canister 20 is not saturated, the _{actually measured} pressure P decreases according to the characteristic A. During this time, the fuel vapor in the fuel tank 10 is sucked out toward the canister 20 and is sequentially adsorbed by the canister 20. Then, when the fuel vapor adsorption capacity of the canister 20 is saturated at the time t shown in FIG. 12, the fuel vapor is not adsorbed to the canister 20 after the time t. Therefore, the _actual pressure P _measured by the pressure gauge 44 is Increases by the vapor partial pressure. Accordingly, the _{actual measurement value} of the pressure P after the time t varies according to the characteristic C and gradually approaches the characteristic B when the canister 20 is not present. The pressure (= Pc) when the steady state is reached is the same as the pressure of the characteristic B in the steady state.

Therefore, if the adsorption capability of the fuel vapor in the canister 20 is saturated while the negative pressure is being applied to the evaporated fuel path, the pressure transition greatly fluctuates at the time t when the canister 20 is saturated, and the pressure P is _{actually measured} at the time t. An inflection point 64 is generated.

For this reason, in the second embodiment, the _{actual measurement value} of the pressure P is monitored while the negative pressure is applied to the evaporated fuel path, and when the inflection point 64 occurs in the _{actual measurement value} of P, the inflection point 64 is generated. At this point, it is determined that the fuel vapor adsorption capacity in the canister 20 is saturated. Then, subsequent leak determination of the evaporated fuel path is stopped. Thereby, it is possible to prevent the leak determination from being performed when the canister 20 is saturated as in the first embodiment. Therefore, the influence of the vapor partial pressure of the fuel vapor on the leakage determination can be eliminated, and the leakage determination of the evaporated fuel path can be performed with high accuracy. Further, by stopping the leak determination after the inflection point 64 is detected, it is possible to prevent the fuel vapor from being released from the pump module 36 into the atmosphere. In the case of detecting the inflection point 64 detects whether or not the P _{measured value} exists is time to turn from a decrease to an increase in the middle of monitoring the P _Found.

FIG. 13 is a characteristic diagram showing how the _actual pressure P _measured by the pump module 36 fluctuates over time, as in FIG. The characteristic C shown in FIG. 13 shows the fluctuation of the P _{actual measurement value} when the canister 20 is saturated before the P _{actual measurement value} reaches Pc. In this case, the P _{actual measurement value} does not change from decreasing to increasing at the inflection point 64, but the rate of change of the P _{actual measurement value} largely changes before and after the inflection point 64. In the present embodiment, as shown in FIG. 13, the timing at which the rate of change in the P _{actual measurement value} changes is also referred to as an inflection point 64. When detecting the inflection point 64 in FIG. 13, for example, the amount of change in the P _{actual measurement value} for each minute time Δt is monitored, and when the change amount for each Δt greatly changes, the change occurs at that timing. It is determined that the music point 64 has occurred. In this case, the case where the difference in change amount for each Δt exceeds a predetermined threshold can be determined as the timing at which the change amount for each Δt greatly changes. Further, the case where the second derivative of the characteristic of the P _{actual measurement value} becomes larger than a predetermined threshold value may be determined as the timing at which the amount of change for each Δt greatly changes.

Next, based on the flowchart of FIG. 14, a processing procedure of the evaporated fuel processing apparatus according to the second embodiment will be described. First, in step S31, the pump 42 is operated. In the next step S32, the state of the switching valve 46 is set so that the negative pressure by the pump 42 is applied to the side of the passage 52 where the orifice 48 is provided, and the reference pressure _PREF is detected.

In the next step S33, the state of the switching valve 46 is set so that negative pressure by the pump 42 is applied to the pump passage 38 side, and the inside of the fuel tank 10, the canister 20, the vapor passage 18, the purge passage 26, and the vapor port 22 are set. Then, a negative pressure is applied to the evaporated fuel path including the purge port 28. In the next step S34, the fluctuation of the _{measured value} of pressure P when negative pressure is applied to the evaporated fuel path is monitored.

In the next step S35, it is determined whether or not the inflection point 64 is generated in the characteristic of the monitored pressure P _{actual measurement value} . If the inflection point 64 does not occur, the fuel vapor adsorption capacity in the canister 20 is not saturated, and thus the process proceeds to step S36, and the leakage determination of the evaporated fuel path is performed in the subsequent steps.

In step S36, the magnitude relationship between the pressure P _{actual measurement value} after reaching the steady state and the reference pressure _PREF measured in step S32 is compared. That is, here, it is determined whether or not P _{actual measurement value} ≦ P _REF .

When it is determined in step S36 that P _{actual measurement value} ≦ P _REF , the process proceeds to step S37, and it is determined that the size of the leak hole generated in the evaporated fuel path is φ0.5 mm or less. On the other hand, if it is determined in step S36 that P _{actual measurement value} > P _REF , the process proceeds to step S38, and it is determined that a leak hole larger than φ0.5 mm is generated in the evaporated fuel path.

  If the inflection point 64 is detected in step S35, the process proceeds to step S39. In this case, since the fuel vapor adsorption capacity in the canister 20 is saturated at the time when the inflection point 64 is detected, the operation of the pump 42 is stopped and the leak determination is stopped.

As described above, according to the second embodiment, the fluctuation of the _actual pressure P _value measured by the pressure gauge 44 is monitored, and when the inflection point 64 occurs in the characteristic of the _actual pressure P _{measurement value} , the inflection point 64 is _detected. When this occurs, it can be determined that the adsorption capability of the fuel vapor in the canister 20 is saturated. Therefore, when the inflection point 64 is detected, it is possible to prevent the fuel vapor from being discharged from the pump module 36 into the outside air by stopping the leak determination.

It is a schematic diagram for demonstrating the outline | summary of the evaporative fuel processing apparatus concerning Embodiment 1 of this invention. It is a schematic diagram which shows the structure of a pump module. It is a schematic diagram for demonstrating the influence which the vapor pressure of a fuel vapor has on P _{actual measurement value} . 3 is a flowchart illustrating a processing procedure in the evaporated fuel processing apparatus according to the first embodiment. It is a schematic diagram which shows a mode that a fuel vapor is adsorbed by activated carbon. Is a characteristic diagram showing how the energy E _S of adsorbed per unit mass varies depending on the adsorbed amount m _s of fuel vapor per unit activated charcoal mass. It is the characteristic figure which calculated | required experimentally the relationship between adsorption potential f ((nu)) and (nu) (= _ms / (rho) _L ). It is a flowchart showing a procedure of a process for calculating the fuel vapor adsorption amount m _s. 9 is a flowchart showing in detail a process for calculating an adsorption amount m _s (k) in step S6 of FIG. 8. When the temperature change ΔT while the VSV valve is open is the same, the difference in the adsorption amount m _s (k−1) when the VSV valve is opened is the change in the adsorption amount while the VSV valve is open. it is a schematic diagram for explaining the effect of the Delta] m _s. It is a schematic diagram showing a map that defines the relationship between the previously calculated adsorption amount m _s (k−1), the temperature change amount ΔT, and the adsorption amount change amount Δm _s while the VSV valve is open. It is a characteristic view which shows a mode that the pressure P _{actual value} measured with the pump module fluctuates with progress of time. It is a characteristic view which shows a mode that the pressure P _{actual value} measured with the pump module fluctuates with progress of time. 6 is a flowchart showing a processing procedure in the evaporated fuel processing apparatus according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel tank 20 Canister 34 Canister temperature sensor 36 Pump module 40 ECU
42 Pump 44 Pressure gauge 64 Inflection point

Claims (1)

A fuel tank,
A canister connected to the fuel tank and adsorbing the evaporated fuel generated in the fuel tank;
A pump connected to the canister and sucking gas in a closed space including the fuel tank through the canister;
Pressure detecting means for detecting a pressure in the closed space on the pump side from the canister;
A leakage determination means for determining a leakage state in the closed space based on the pressure detected by the pressure detection means;
An adsorbing capacity determining means for determining an adsorbing capacity of the evaporated fuel in the canister;
When it is determined that the adsorption capacity is saturated or nearly saturated, leakage determination stopping means for stopping the determination by the leakage determination means;
An inflection point detecting means for detecting whether or not an inflection point exists in the pressure characteristic detected by the pressure detecting means,
The evaporative fuel processing apparatus for an internal combustion engine, wherein the adsorption capacity determination means determines that the adsorption capacity is saturated or nearly saturated when the inflection point is detected .

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