JP6327584B2 - Evaporative fuel processing equipment - Google Patents

Description

  The present invention relates to an evaporative fuel processing apparatus for discharging evaporative fuel in a fuel tank to an intake passage of an engine, and more particularly to an evaporative fuel processing apparatus that estimates the vapor pressure of evaporative fuel.

  Conventionally, it has been known that the relationship between the temperature and the saturated vapor pressure (saturated vapor pressure characteristics) of each fuel differs for each fuel, and attempts have been made to estimate such saturated vapor pressure characteristics for various fuels. Yes. For example, Patent Document 1 discloses a technique for specifying a saturated vapor pressure line of fuel based on a detection result of a fuel property sensor and obtaining a saturated vapor pressure corresponding to the fuel temperature from the saturated vapor pressure line.

JP 2008-232007 A

  By the way, conventionally, the evaporated fuel generated in the fuel tank (hereinafter referred to as “evaporative gas” as appropriate) is once adsorbed to the canister, and in response to a purge request, the evaporated gas adsorbed to the canister is passed to the intake passage of the engine. An evaporative fuel processing apparatus (so-called evaporation purge system) for purging is known. In such an evaporative fuel processing apparatus, it is considered that the vapor pressure of the fuel may be accurately estimated from the viewpoint of accurately executing purge control for purging the evaporation gas. In addition, it is considered that the vapor pressure of the fuel can be estimated using the existing components of the evaporated fuel processing apparatus as much as possible without complicating and increasing the cost of the configuration of the evaporated fuel processing apparatus. In the technique disclosed in Patent Document 1 described above, since the fuel property sensor is used for obtaining the vapor pressure of the fuel, the cost of the apparatus has been increased.

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide an evaporative fuel processing apparatus capable of accurately estimating the vapor pressure of the fuel used with a simple configuration. And

In order to achieve the above object, the present invention is an evaporated fuel processing apparatus for discharging evaporated fuel in a fuel tank to an intake passage of an engine, extending from the fuel tank to the intake passage, and evaporating from the fuel tank. A purge passage for discharging fuel to the intake passage, a canister provided on the purge passage for adsorbing and accumulating evaporated fuel from the fuel tank, and an open air connected to the canister for supplying air to the canister A passage, an air release valve provided on the air release passage for controlling the supply of air to the canister, and a purge valve provided on a purge passage on the downstream side of the canister for controlling the supply of evaporated fuel to the intake passage And a fuel temperature sensor provided in the fuel tank for detecting the fuel temperature and provided on a path through which the evaporated fuel passes from the fuel tank to the purge valve. Is a pressure sensor for detecting the pressure in the path, has a further, based on the pressure detected by the fuel temperature and pressure sensor detected by the fuel temperature sensor, adsorption of fuel vapor in the canister A vapor pressure estimating means for estimating the vapor pressure of the fuel used in the saturated state, and a vapor pressure estimated by the vapor pressure estimating means in a predetermined operating state of the engine, and the vaporized fuel contained in the gas released by the canister Evaporative fuel amount estimation means for estimating the amount of evaporative fuel contained in the gas discharged from the canister using the partial pressure.
According to the present invention thus configured, the vapor pressure of the fuel used is estimated based on the fuel temperature detected by the fuel temperature sensor and the pressure detected by the pressure sensor, and this vapor pressure is released by the canister. The amount of evaporated fuel contained in the gas released by the canister is estimated on the basis of the partial pressure of the evaporated fuel to which the vapor pressure is applied. According to the present invention as described above, the amount of evaporated fuel contained in the gas released from the canister can be accurately estimated with a simple configuration without substantially changing the configuration of the existing evaporated fuel processing apparatus. Further, according to the present invention, since the air-fuel ratio when the evaporated fuel is burned by the engine is not used as in the prior art, it is possible to appropriately estimate the evaporated fuel amount before the evaporated fuel is burned by the engine. It becomes.

In the present invention, it is preferable that the vapor pressure estimation means includes a fuel detected by the fuel temperature sensor based on a relationship between the fuel temperature and the vapor pressure for a plurality of gasolines having different lead vapor pressures obtained in advance. The lead vapor pressure of the used fuel corresponding to the change in temperature and the change in pressure detected by the pressure sensor is obtained, and the vapor pressure of the used fuel is estimated based on this lead vapor pressure.
According to the present invention configured as described above, the vapor pressure of the fuel used can be reduced by appropriately taking into account the difference in the vapor pressure characteristics of the fuel due to the difference in the composition and the like (that is, the difference in the lead vapor pressure of gasoline). It is possible to estimate with higher accuracy.

In the present invention, preferably, the vapor pressure estimating means sets the pressure detected by the pressure sensor before driving the fuel pump to “P ₀ ”, and sets the pressure detected by the pressure sensor after driving the fuel pump to “P ₁ ”. The fuel temperature detected by the fuel temperature sensor before driving the fuel pump is “T _fuel0 ”, and the difference between the fuel temperature T _fuel0 and the fuel temperature detected by the fuel temperature sensor after driving the fuel pump is “ΔT”. _fuel ”, the fuel reed vapor pressure is“ R _VP ”, the function indicating the relationship between the fuel temperature and the vapor pressure for a plurality of gasolines having different reed vapor pressures R _VP is“ f ”, and this function f is The function differentiated by the fuel temperature is “f ′”, the value obtained by substituting the fuel temperature T _fuel0 and the reed vapor pressure R _VP into the function f is “f (T _fuel0 , R _VP )”, and the function f ′ is the fuel temperature T _fuel0 and _Assuming that the value obtained by substituting the _mode vapor pressure R _VP is “f ′ (T _fuel0 , R _VP )”, the lead vapor pressure R _VP of the fuel used is obtained based on the following equation.

  According to the present invention configured as described above, the vapor pressure of the fuel used can be estimated more accurately using the above-described equation.

In the present invention, the vapor pressure estimating means is preferably driven so that the fuel pump operates at the maximum output.
According to the present invention configured as described above, by operating the fuel pump at the maximum output, it is possible to quickly increase the fuel temperature and pressure, and it is possible to quickly estimate the vapor pressure of the fuel used. It becomes.

In the present invention, it is preferable that the vapor pressure estimating means estimates the vapor pressure of the fuel used when starting the engine.
According to the present invention configured as described above, the vapor pressure can be appropriately estimated before the evaporated fuel is burned by the engine.

  According to the evaporated fuel processing apparatus of the present invention, the vapor pressure of the fuel used can be accurately estimated with a simple configuration.

1 is a schematic configuration diagram of a system to which an evaporated fuel processing apparatus according to an embodiment of the present invention is applied. It is explanatory drawing about the relationship between evaporation partial pressure and adsorption | suction evaporation amount. It is explanatory drawing about the saturation state of a canister. It is explanatory drawing about an evaporation density | concentration. It is explanatory drawing about the vapor pressure characteristic of a fuel. It is explanatory drawing about the function f prescribed | regulated by the fuel temperature, the vapor pressure, and the reed vapor pressure, and the function f 'which differentiated this function f by fuel temperature. It is explanatory drawing about the relationship between fuel temperature, the molar weight of a fuel, and reed vapor pressure. It is a flowchart which shows the process of vapor pressure estimation and evaporation weight estimation by embodiment of this invention.

  Hereinafter, an evaporated fuel processing apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[Device configuration]
First, with reference to FIG. 1, the structure of the evaporative fuel processing apparatus by embodiment of this invention is demonstrated. FIG. 1 is a schematic configuration diagram of a system to which an evaporated fuel processing apparatus according to an embodiment of the present invention is applied. This system is mounted on a vehicle.

  As shown in FIG. 1, an evaporative fuel processing apparatus 1 has a fuel tank 2 that stores fuel (specifically, gasoline) supplied to the engine. The fuel tank 2 contains fuel inside the engine. And a fuel temperature sensor 6 for detecting the temperature of the stored fuel (fuel temperature). The fuel tank 2 is connected to one end of a purge passage 8 for discharging evaporated fuel (evaporative gas) generated in the fuel tank 2. The other end of the purge passage 8 is connected to the intake passage 20 on the downstream side of the throttle valve 22 of the engine so that the evaporated fuel can be purged into the intake passage 20.

  A pressure sensor 10 for detecting the pressure in the purge passage 8 (corresponding to the pressure in the fuel tank 2 and hereinafter referred to as “tank internal pressure” as appropriate) on the purge passage 8 in order from the upstream side; An activated carbon that adsorbs the evaporated fuel is provided therein, and a canister 12 that stores the evaporated fuel and a purge valve 18 that controls the supply of the evaporated fuel adsorbed by the canister 12 to the intake passage 20 are provided. The canister 12 is provided with an atmosphere opening port 14 a through which air is supplied from the outside, and is connected to an atmosphere opening passage 14 that supplies air to the canister 12. An atmosphere release valve 16 that controls the supply of air to the canister 12 is provided on the atmosphere release passage 14.

  The evaporated fuel processing apparatus 1 further includes an ECU (Electronic Control Unit) 30 that controls the entire evaporated fuel processing apparatus 1 including the engine. In the present embodiment, the ECU 30 mainly receives a detection signal corresponding to the fuel temperature detected by the fuel temperature sensor 6 and a detection signal corresponding to the tank internal pressure detected by the pressure sensor 10. Based on these detection signals, engine operating conditions, etc., the ECU 30 is connected to the fuel pump 4 in the fuel tank 2 and the atmosphere release valve 16 provided on the atmosphere release passage 14 connected to the canister 12. A control signal is supplied to a purge valve 18 provided on the purge passage 8 downstream of the canister 12 to control these operations. In this case, the ECU 30 opens / closes the atmosphere release valve 16 to control the supply / cutoff of air to the canister 12. Further, the ECU 30 opens / closes the purge valve 18 to control the supply / cutoff of the evaporated fuel adsorbed by the canister 12 to the intake passage 20 and adjust the opening of the purge valve 18 to adjust the intake passage. The amount of evaporated fuel supplied to 20 is controlled. Although details will be described later, the ECU 30 functions as “vapor pressure estimating means”, “evaporated fuel amount estimating means”, and “fuel injection amount reducing means” in the present invention.

[Basic concept of this embodiment]
Next, basic concepts related to estimation of vapor pressure of evaporated fuel (evaporative gas) and estimation of the amount of evaporated fuel (hereinafter referred to as “evaporation weight” as appropriate) executed by the ECU 30 in the present embodiment will be described. In the present specification, “vapor pressure” means “saturated vapor pressure”.

  Conventionally, the evaporation gas adsorbed by the canister 12 is purged into the intake passage 20 of the engine, and this evaporation gas is burned by the engine. In this case, conventionally, when the purge of the evaporation gas from the canister 12 is started, a very small amount of air is supplied from the atmosphere opening passage 14 to release the small amount of the evaporation gas from the canister 12 and the evaporation gas is burned by the engine. Based on the detected air-fuel ratio, the amount of evaporation gas (evaporation weight) released from the canister 12 relative to the amount of air was estimated. Therefore, in such a conventional technique, at the start of the purge, only a small amount of evaporation gas can be supplied to the engine, and the fuel injection amount of the engine can be reduced only slightly (note that the evaporation weight is reduced from the air-fuel ratio). After obtaining the relationship between the fuel injection amount and the fuel injection amount reduction amount, the supply amount of the evaporation gas can be increased).

  Therefore, in the present embodiment, before the evaporation gas is burned by the engine, the evaporation weight released from the canister 12 with respect to the air amount is estimated, and a large amount of air is introduced from the start of the purge. The total purge amount was increased. In order to realize this, the inventors of the present application examined a mechanism for determining the evaporation weight with respect to the air amount with respect to the evaporation gas released from the canister 12. Details thereof will be described with reference to FIGS.

  First, referring to FIG. 2, the gas supplied to adsorb the evaporation gas to the canister 12 (not only the evaporation gas but also a gas containing air, which is hereinafter referred to as “adsorption gas” as appropriate). The relationship between the partial pressure of the evaporation gas (hereinafter simply referred to as “evaporation partial pressure”) and the amount of evaporation gas adsorbed by the canister 12 (hereinafter simply referred to as “adsorption evaporation amount”) will be described. In FIG. 2, the horizontal axis represents the evaporation partial pressure, and the vertical axis represents the adsorption evaporation amount. Note that the evaporation partial pressure is paraphrased as the partial pressure of the evaporation gas contained in the gas released from the canister 12 (a gas including not only the evaporation gas but also air, and hereinafter referred to as “purge gas” as appropriate).

  Specifically, FIG. 2 shows a graph showing the relationship between the evaporation partial pressure and the adsorption evaporation amount for each of a plurality of temperatures, and these graphs correspond to adsorption isotherms. FIG. 2 shows that the amount of adsorption evaporation increases as the evaporation partial pressure increases. It can also be seen that the amount of adsorption evaporation decreases as the temperature increases. This is because the evaporation gas adsorbed by the canister 12 is more likely to desorb when the temperature is higher.

  Here, if the activated carbon in the canister 12 is adsorbed with the evaporation gas over a long time, the evaporation partial pressure in the adsorption gas and the vapor pressure of the evaporation gas adsorbed on the canister 12 (hereinafter referred to as “evaporation vapor pressure” as appropriate). .)) Is equal to the equilibrium state, and the amount of evaporated evaporation is saturated (a constant amount). The adsorption evaporation amount at this time is determined from the evaporation partial pressure and the temperature (that is, determined from the adsorption isotherm) as shown in FIG.

  Next, the saturated state of evaporation gas adsorption by the canister 12 will be described with reference to FIG. FIG. 3 shows the position in the canister 12 in the horizontal direction and the suction evaporation amount in the vertical direction. The position in the canister 12 shown in the horizontal direction corresponds to the position when the activated carbon 12a in the canister 12 is extended in the horizontal direction, the left side is the atmosphere release side, and the right side is the fuel tank side.

  As shown in FIG. 3, since the evaporative gas is supplied to the activated carbon 12a of the canister 12 from the right side of the figure, a saturated state of evaporative gas adsorption occurs from the activated carbon 12a located on the right side of the figure. As the time elapses, the position where the saturated state of the evaporation gas adsorption occurs is gradually shifted to the left, and the shift of the position where the saturated state occurs at a certain position stops. In summer, the evaporation gas is saturated in about one day.

  Next, the concentration of the evaporation gas when the evaporation gas is purged (hereinafter, simply referred to as “evaporation concentration”) will be described with reference to FIG. In FIG. 4, the horizontal axis indicates the amount of air (total purge amount) contained in the purge gas purged into the intake passage 20 of the engine, and the vertical axis indicates the concentration (evaporation concentration) of the evaporation gas in the purge gas. As shown in FIG. 4, the evaporation concentration decreases as the air amount increases.

  Here, the purge of the evaporation gas is performed after the engine is started with the air release valve 16 on the air release passage 14 opened and the purge valve 18 on the purge passage 8 opened. In this case, air is supplied from the atmosphere opening passage 14 into the canister 12, the evaporation gas adsorbed on the activated carbon 12 a of the canister 12 is released, and the purge gas in which the air and the evaporation gas are mixed passes through the purge passage 8 and the engine. Purged into the intake passage 20. In this way, when the evaporation gas is released from the activated carbon 12a of the canister 12 and mixed with air to become the purge gas, the vapor pressure of the evaporation gas (evaporation vapor pressure) adsorbed on the canister 12 and the partial pressure of the evaporation gas (evaporation) contained in the purge gas. Evaporative gas is released from the activated carbon 12a of the canister 12 so that the partial pressure is substantially equal. Therefore, it can be said that the evaporation partial pressure is substantially equal to the evaporation vapor pressure.

  Specifically, the evaporation partial pressure of the evaporation gas generated immediately after the start of the purge execution is determined by the vapor pressure (evaporation vapor pressure) of the evaporation gas adsorbed on the activated carbon 12a in the place near the purge port where the evaporation gas is purged from the canister 12. It is considered to be decided. Therefore, if the evaporation vapor pressure is estimated, this evaporation vapor pressure is used as the evaporation partial pressure, and other parameters such as temperature and air amount are used together, as shown in FIG. The evaporation concentration (initial evaporation concentration) can be estimated. The evaporation concentration uniquely corresponds to the above-described evaporation weight.

Next, with reference to FIG. 5, the vapor pressure characteristic, that is, the vapor pressure characteristic of the evaporated fuel (gasoline) as the vapor gas will be described. FIG. 5 shows the fuel temperature on the horizontal axis and the fuel vapor pressure corresponding to the evaporation vapor pressure on the vertical axis. Specifically, FIG. 5 shows the relationship between the fuel temperature and the fuel vapor pressure (vapor pressure characteristics) for each lead vapor pressure of gasoline as fuel (hereinafter referred to as “RVP” where appropriate). Yes. That is, the vapor pressure characteristics of a plurality of fuels having various reed vapor pressures are shown. As shown in FIG. 5, it can be seen that the fuel vapor pressure increases as the fuel temperature increases. Of course, when the Reed vapor pressure (RVP) increases, the fuel vapor pressure increases.
The Reed vapor pressure is the saturated vapor pressure of gasoline at 37.8 degrees Celsius (100 degrees Fahrenheit), and is an index indicating the ease of evaporation of gasoline. This lead vapor pressure varies depending on the composition of gasoline.

  In this embodiment, based on the fuel temperature detected by the fuel temperature sensor 6, the tank internal pressure detected by the pressure sensor 10 and the like, the lead vapor pressure of the fuel used is obtained, and the present pressure is obtained from the vapor pressure characteristic of the fuel having the lead vapor pressure. The vapor pressure of the fuel used corresponding to the fuel temperature was obtained, and this vapor pressure was used as the evaporation partial pressure as described above. In this case, in this embodiment, vapor pressure characteristics for a plurality of gasolines having different reed vapor pressures are obtained in advance, and the reed vapor pressure of the fuel used is obtained based on these vapor pressure characteristics.

[Estimation of vapor pressure]
Next, the fuel vapor pressure estimation method according to the embodiment of the present invention will be specifically described.

  In the present embodiment, the ECU 30 closes both the air release valve 16 and the purge valve 18 when the engine is started, that is, a path through which the evaporation gas flows through the purge passage 8 from the fuel tank 2 to the intake passage 20. The fuel pump 4 is driven in a sealed state, and the fuel used is based on the change in the fuel temperature detected by the fuel temperature sensor 6 and the change in the tank internal pressure detected by the pressure sensor 10 before and after the fuel pump 4 is driven. Estimate the vapor pressure. That is, the ECU 30 estimates the vapor pressure of the fuel used based on the degree of increase in fuel temperature and the degree of increase in tank internal pressure when the fuel pump 4 is driven to forcibly increase the fuel temperature. For example, the ECU 30 drives the fuel pump 4 to operate at the maximum output (in one example, the fuel pump 4 is driven at the maximum voltage). More specifically, in this embodiment, the relationship between the fuel temperature and the vapor pressure for a plurality of fuels (gasoline) having different lead vapor pressures is obtained in advance and stored in a memory or the like, and the ECU 30 By referring to the relationship between the fuel temperature and the vapor pressure for each different lead vapor pressure stored as described above, the lead vapor pressure corresponding to the detected change in the fuel temperature and the change in the tank internal pressure is obtained, Based on this, the vapor pressure of the fuel used is estimated.

  Next, a specific method for calculating the vapor pressure of the fuel used will be described. The symbols used here are defined as follows.

P ₀ : Tank internal pressure before driving the fuel pump 4 (almost atmospheric pressure)
P ₁ : Tank internal pressure after driving the fuel pump 4 P _B : Fuel vapor pressure before driving the fuel pump 4 (equal to partial pressure of evaporated fuel)
ΔP _B : difference between fuel vapor pressure P _B before driving the fuel pump 4 and fuel vapor pressure after driving the fuel pump T _fuel0 : fuel temperature before driving the fuel pump 4 T _fuel1 : after driving the fuel pump 4 Fuel temperature ΔT _fuel : _Difference between fuel temperature T _fuel0 and fuel temperature T _fuel1 (increase)
V: Space volume of the fuel tank 2, the purge passage 8 (downstream of the purge valve 18), the canister 12, and the air release passage 14 (downstream of the air release valve 16) N _A : number of moles of air N _B : the fuel pump 4 Number of moles of fuel (evaporative gas) before driving ΔN _B : Difference between number of moles of fuel N _B before driving fuel pump 4 and number of moles of fuel after driving fuel pump 4 R: Gas constant R _VP : Fuel ( Evaporative gas) Reed vapor pressure f: Function indicating the relationship between fuel temperature and vapor pressure for a plurality of fuels having different reed vapor pressures f ′: Function f (T _fuel0 , R _VP ) _obtained by differentiating function f with respect to fuel temperature : the value obtained by substituting the fuel temperature T _Fuel0 and Reid vapor pressure R _VP to the function _{f f'(T fuel0, R VP} ): value obtained by substituting the fuel temperature T _Fuel0 and Reid vapor pressure R _VP function f'

  Here, specific examples of the function f and the function f ′ described above are shown in FIG. FIG. 6A is a diagram similar to FIG. 5, wherein the horizontal axis indicates the fuel temperature, the vertical axis indicates the fuel vapor pressure, and the fuel temperature and fuel for a plurality of fuels having different reed vapor pressures. A function f representing the relationship with the vapor pressure is shown. FIG. 6B shows the fuel temperature on the horizontal axis and the value obtained by differentiating the fuel vapor pressure with respect to the fuel temperature on the vertical axis. The function f (FIG. 6 (FIG. 6 (B)) for a plurality of fuels having different reed vapor pressures. A function f ′ obtained by differentiating the one shown in A) with respect to the fuel temperature is shown. These functions f and f ′ are functions having the fuel temperature, fuel vapor pressure, and reed vapor pressure as variables.

  The calculation formula of the fuel vapor pressure is derived by the following procedure. First, before the fuel pump 4 is driven, that is, before the fuel temperature is increased by driving the fuel pump 4, the state of the evaporated fuel is expressed by the following equation (1) and includes evaporated fuel and air. The gas state is represented by the following equation (2). Equations (1) and (2) are ideal gas equations of state.

  Next, after driving the fuel pump 4, that is, after raising the fuel temperature by driving the fuel pump 4, the vapor pressure of the evaporated fuel (equal to the partial pressure of the evaporated fuel) is expressed by the following equation (3). The state of the gas including vaporized fuel and air is expressed by a state equation of the following equation (4). Equations (3) and (4) are also ideal gas equations of state.

_{Let us} consider combining equations (1) to (4) to create an equation consisting of tank internal pressures P ₀ and P ₁ and fuel temperature T _fuel0 , which are physical quantities to be measured, and fuel vapor pressure P _B. First, when the equation (4) is transformed, the following equation (5) is obtained. “ΔT _fuel ” in the equation (5) is “ΔT _fuel = T _fuel1 −T _fuel0 ”.

In Expression (5), if the term of the product of ΔN _B and ΔT _fuel has a smaller value than the other terms, the following Expression (6) is obtained from Expression (5).

  When formula (2) is modified to briefly describe formula (6) by formula (2), the following formula (7) and formula (8) are obtained.

  By substituting Equation (7) and Equation (8) into Equation (6), the following Equation (9) is obtained.

  Next, when the formula (3) is transformed, the following formula (10) is obtained.

In Expression (10), if the term of the product of ΔN _B and ΔT _fuel is neglected as having a smaller value than other terms, the following Expression (11) is obtained from Expression (10).

  Further, when formula (1) is modified so that formula (3) can be simply described by formula (1), the following formula (12) is obtained.

  Next, substituting Equation (1) and Equation (12) into Equation (11) yields the following Equation (13), and further transforming Equation (13) yields Equation (14) below. .

  Next, when the equation (14) is subtracted from the equation (9), the following equation (15) is obtained. When the equation (15) is further modified, the following equation (16) is obtained.

Here, “P _B ” in equation (16) is equal to the value of f (T _fuel0 , R _VP ) for the function f, and “ΔP _B / ΔT _fuel ” in equation (16) is the function f ′. _Is approximately equal to the value of f ′ (T _fuel0 , R _VP ). Therefore, the equation (16) is transformed into the following equation (17).

In the equation (17), the only undetermined variable is the reed vapor pressure _RVP , so the value of the reed vapor pressure _RVP can be obtained from the equation (17). In this embodiment, ECU30 calculates | requires lead vapor pressure _RVP of the fuel used based on Formula (17). Specifically, the ECU 30 substitutes the tank internal pressures P ₀ and P ₁ detected by the pressure sensor 10 and the fuel temperature T _fuel0 and the temperature difference ΔT _fuel detected by the fuel temperature sensor 6 into the equation (17). Then, referring to the data of the function f and the function f ′ stored in advance (for example, those shown in FIGS. 6A and 6B), the equation (17) after substituting the above detection values The lead vapor pressure R _VP that satisfies the above is obtained. Then, the ECU 30 obtains the vapor pressure P _B of the used fuel from the lead vapor pressure R _VP thus obtained. Specifically, the ECU 30 _obtains the vapor pressure P _{B of the} fuel used by substituting the obtained lead vapor pressure R _VP and the fuel temperature T _fuel0 detected by the fuel temperature sensor 6 into the function f. That is, the ECU 30 _obtains the value of f (T _fuel0 , R _VP ) as the vapor pressure P _B of the fuel used. As described above, the ECU 30 uses the vapor pressure P _B as the evaporation partial pressure of the evaporation gas released from the canister 12.

[Evaporation weight estimation]
Next, a method for estimating the evaporation weight according to the embodiment of the present invention will be described in detail.

In the present embodiment, the ECU 30 uses the vapor pressure P _{B of the} fuel estimated as described above as the evaporation partial pressure of the evaporation gas released by the canister 12 (hereinafter, the evaporation partial pressure P _B is appropriately set to “evaporation partial pressure P _B Used to estimate the evaporation weight of the evaporation gas released by the canister 12. Specifically, the ECU 30 obtains the evaporation weight based on the atmospheric pressure, the amount of air supplied from the atmosphere opening passage 14 and the like in addition to the evaporation partial pressure P _B.

  Next, a specific method for calculating the evaporation weight will be described. The symbols used here are defined as follows. In addition, the element which attached | subjected the symbol same as the above-mentioned symbol shall have the same meaning.

P _atm : Atmospheric pressure P _G : Pressure of purge gas released from the canister 12 T _atm : Atmospheric temperature Q _air : Flow rate of air supplied from the air opening passage 14 (volume per unit time)
Q _evap : Flow rate of evaporation _gas released by the canister 12 (volume per unit time)
N _air : Number of moles per unit time of air supplied from the open _air passage 14 N _evap : Number of moles per unit time of the evaporative _gas released by the canister 12 m _evap : Molecular weight of the evaporative gas G _evap : _Evaporated weight per unit time

  First, the air supplied from the air release passage 14 is represented by the following equation (18). Equation (18) is an ideal gas equation of state.

The evaporation partial pressure of the evaporation gas released from the canister 12 is the vapor pressure P _B of the evaporation gas (fuel) estimated as described above. Accordingly, the pressure P _G in the purge gas canister 12 is released, the partial pressure of the air contained in the purge gas canister 12 is discharged is "P _G -P _B". Accordingly, the evaporation gas contained in the purge gas released from the canister 12 is represented by the following equation (19), and the air contained in the purge gas emitted from the canister 12 is represented by the following equation (20). It appears. Equations (19) and (20) are also the ideal gas equation of state.

The expression of “Q _evap ” in the expressions (19) and (20) is obtained. First, since the right sides of Expression (18) and Expression (20) are the same, the following Expression (21) is obtained from Expressions (18) and (20). When this Expression (21) is modified, the following Expression (22) is obtained.

Substituting equation (22) into equation (19) and solving for “N _evap ” yields the following equation (23).

Since “N _evap = G _evap / m _evap ”, the following formula (24), which is a derivation formula for the evaporation weight G _evap per unit time, is obtained by transforming the formula (23) based on this.

In this embodiment, _{ECU30 calculates |} requires evaporation weight _Gevap using Formula (24). In this case, the ECU 30 uses the fuel temperature T _fuel1 after driving the fuel pump 4 detected by the fuel temperature sensor 6 as described above as the atmospheric temperature T _atm in the equation (24). Further, in one example, ECU 30 as the pressure P _G in the purge gas canister 12 in the formula (24) is released, use of pressure and pressure loss by subtracting the canister 12 from the atmospheric pressure P _atm. In this example, the ECU 30 uses the measured value as the pressure loss of the canister 12. In another example, since the canister 12 is generally designed so that the pressure loss is small, the ECU 30 assumes that the pressure loss of the canister 12 is sufficiently smaller than the atmospheric pressure P _atm , and the ECU 30 determines the pressure P _G in the equation (24). As atmospheric pressure P _atm is used.

Further, in one example, the ECU 30 uses a molecular weight of butane of 58 g / mol as the molecular weight m _evap of _{evaporative gas} . This is because the main component of evaporative gas (gasoline) is butane. In another example, the ECU 30 uses the molar weight measured in advance as shown in FIG. 7 as the molecular weight m _evap of _{evaporative gas} . FIG. 7 shows the fuel temperature on the horizontal axis and the molar weight of the fuel on the vertical axis. Show. The ECU 30 refers to such a relationship between the fuel temperature and the molar weight, and the molar weight corresponding to the fuel temperature detected by the fuel temperature sensor 6 and the lead vapor pressure of the fuel used as estimated above. Ask for.

In the present embodiment, when the ECU 30 obtains the evaporation weight G _evap from the equation (24), the ECU 30 _{calculates the} evaporation _gas based on the evaporation weight G _evap with both the atmosphere release valve 16 and the purge valve 18 open. Control to purge the intake passage 20 of the engine is started. Specifically, the ECU 30 obtains a required purge amount, and duty-controls the purge valve 18 based on the required purge amount. Thus, when starting the purge of the evaporation _gas , in this embodiment, the ECU 30 _reduces the fuel injection amount from the fuel injection valve of the engine by the determined evaporation weight G _evap . That is, the ECU 30 applies an amount _obtained by subtracting the evaporation weight G _evap from the original required fuel injection amount as a new fuel injection amount.

[flowchart]
Next, with reference to FIG. 8, the flow of processing of vapor pressure estimation and evaporation weight estimation according to the embodiment of the present invention will be described. FIG. 8 is a flowchart showing processing of vapor pressure estimation and evaporation weight estimation according to the embodiment of the present invention.

  First, in step S1, the ECU 30 determines whether or not the ignition switch of the vehicle is turned on. That is, the ECU 30 determines whether or not the engine is ready to be started. As a result, if it is determined that the ignition switch has been turned on (step S1: Yes), the process proceeds to step S2, and if it is not determined that the ignition switch has been turned on (step S1: No), the flow is exited. The engine is started at any timing after step S2 and after step S2.

  In step S2, the ECU 30 determines whether or not the canister 12 is in a saturated state, that is, whether or not the adsorption evaporation amount of the canister 12 is saturated. For example, the ECU 30 determines that the canister 12 is in a saturated state when a predetermined number of days (for example, 1 day or more, but time may be used instead of the number of days) since the engine stopped. If it is determined that the canister 12 is in a saturated state as a result of the determination in step S2 (step S2: Yes), the process proceeds to step S3, and if the canister 12 is not determined to be in a saturated state (step S2). : No), exit the flow.

In step S _<b> 3, the ECU 30 acquires the tank internal pressure P ₀ detected by the pressure sensor 10 and the fuel temperature T _fuel0 detected by the fuel temperature sensor 6. Next, in step S4, the ECU 30 closes both the atmosphere release valve 16 and the purge valve 18. Incidentally, limited to close the drain valve 16 and the purge valve 18 after the acquisition of the tank internal pressure P ₀ and the fuel temperature T _Fuel0 is not the sole, the air release valve before acquisition tank pressure P ₀ and the fuel temperature T _Fuel0 16 and The purge valve 18 may be closed.

  Next, in step S5, the ECU 30 drives the fuel pump 4. For example, when the voltage of the fuel pump 4 is controlled, the ECU 30 drives the fuel pump 4 with the maximum voltage. When the engine is started at the stage of proceeding to step S5, the fuel pump 4 has already been driven, so that the fuel pump 4 need not be forcibly driven in step S5. Further, when the fuel pump 4 is driven at the maximum voltage as described above, the discharge pressure of the fuel pump 4 tends to exceed a desired pressure. However, excess fuel exceeding the desired pressure is returned to the fuel tank 2. There is no problem in particular.

Next, when a certain amount of time (for example, the time required for the fuel temperature to rise above a predetermined temperature) has elapsed since the fuel pump 4 was driven in step S5, the ECU 30 detects that the tank detected by the pressure sensor 10 in step S6. The fuel temperature T _fuel1 detected by the internal pressure P ₁ and the fuel temperature sensor 6 is acquired.

  Next, in step S7, the ECU 30 opens both the atmosphere release valve 16 and the purge valve 18. In parallel with the process in step S7, the processes in steps S8 to S11 are performed.

First, in step S8, ECU 30 includes a tank internal pressure P ₀ and the fuel temperature T _Fuel0 obtained in step S3, based on the tank internal pressure P ₁ and the fuel temperature T _Fuel1 obtained in step S6, Reid vapor pressure of the fuel used _Find RVP. Specifically, the ECU 30 _substitutes the tank internal pressures P ₀ and P ₁ , the fuel temperature T _fuel0, and the temperature difference ΔT _{fuel obtained} by subtracting the fuel temperature T _fuel0 from the fuel temperature T _fuel1 into the equation (17). Then, referring to the data of the function f and the function f ′ stored in advance (see, for example, FIGS. 6A and 6B), the expression (17) after substituting the pressure and temperature is satisfied. Find the lead vapor pressure _RVP .

Next, in step S9, the ECU 30 obtains the vapor pressure P _{B of the} fuel used based on the reed vapor pressure R _VP obtained in step S8. Specifically, the ECU 30 _obtains the vapor pressure P _{B of the} fuel used by substituting the obtained lead vapor pressure R _VP and the fuel temperature T _fuel0 detected by the fuel temperature sensor 6 into the function f. That is, the ECU 30 _obtains the value of f (T _fuel0 , R _VP ) as the vapor pressure P _B of the fuel used.

Next, in step S10, the ECU 30 uses the vapor pressure P _B obtained in step S9 as the evaporation partial pressure (evaporation partial pressure P _B ) of the evaporation gas released by the canister 12.

Next, in step S11, the ECU 30 obtains an evaporation weight G _evap of the evaporation _gas released from the canister 12 based on the evaporation partial pressure P _B obtained in step S10. Specifically, ECU 30, in addition to the evaporation partial pressure P _B, is supplied and the atmospheric pressure P _atm, and the pressure P _G in the purge gas canister 12 is released, and the ambient temperature T _atm, the atmosphere open passage 14 The evaporation weight G _evap is obtained by substituting the air amount Q _air or the like into the equation (24).

[Function and effect]
Next, an evaporative fuel processing apparatus according to an embodiment of the present invention will be described.

  In the present embodiment, both the atmosphere release valve 16 and the purge valve 18 are closed to drive the fuel pump 4. The change in the fuel temperature detected by the fuel temperature sensor 6 before and after the fuel pump 4 is driven and the pressure sensor. 10 is used to estimate the vapor pressure of the fuel used. That is, in the present embodiment, the fuel temperature rises due to the driving of the fuel pump 4 when the passage through which the evaporated gas flows through the purge passage 8 from the fuel tank 2 to the intake passage 20 (strictly, to the purge valve 18) is sealed. Based on the degree and the degree of increase in pressure in the sealed space, the vapor pressure (vapor pressure characteristic) of the fuel used is estimated. According to this embodiment, since the configuration of the existing evaporated fuel processing apparatus is hardly changed, the vapor pressure of the fuel used can be accurately estimated with a simple configuration.

  In the present embodiment, the vapor pressure estimated as described above is used as the evaporation partial pressure contained in the purge gas released from the canister 12 to estimate the evaporation weight contained in the purge gas released from the canister 12. According to the present embodiment, since the air-fuel ratio when the evaporation gas is burned by the engine is not used as in the prior art, the evaporation weight can be appropriately estimated before the evaporation gas is burned by the engine. As a result, at the start of the purge, the fuel injection amount of the engine can be appropriately reduced by the amount of the evaporation weight. Therefore, a large amount of air can be introduced at the start of purge, and the total amount of purge during traveling can be increased. That is, the required purge amount can be increased, and the purge amount with respect to the travel distance can be increased.

[Modification]
Below, the modification of above-described embodiment is demonstrated.

  In the above-described embodiment, the pressure sensor 10 is provided on the purge passage 8 between the fuel tank 2 and the canister 12, but the pressure sensor 10 is not limited to being provided at this position. The pressure sensor 10 may be provided on a path (including the inside of the fuel tank 2 and the canister 12) through which the evaporation gas from the fuel tank 2 to the purge valve 18 passes.

  In the above-described embodiment (see FIG. 8), when the canister 12 is in a saturated state (step S2: Yes), the vapor pressure estimation and the evaporation weight estimation are performed. However, the determination in step S2 is not performed. In addition, it is possible to uniformly estimate the vapor pressure and the evaporation weight when starting the engine.

  In the above-described embodiment, the evaporation weight (evaporated fuel amount) is estimated. However, the evaporation concentration may be estimated instead. The evaporation weight and the evaporation concentration uniquely correspond to each other. The value obtained by multiplying the amount of purge gas (total purge amount) by the evaporation concentration is the evaporation weight, and the value obtained by dividing the evaporation weight by the amount of purge gas is Evaporation concentration.

DESCRIPTION OF SYMBOLS 1 Evaporative fuel processing apparatus 2 Fuel tank 4 Fuel pump 6 Fuel temperature sensor 8 Purge passage 10 Pressure sensor 12 Canister 14 Atmospheric release passage 16 Atmospheric release valve 18 Purge valve 20 Intake passage 30 ECU

Claims (5)

An evaporative fuel processing device for releasing evaporative fuel in a fuel tank to an intake passage of an engine,
A purge passage that extends from the fuel tank to the intake passage, and discharges evaporated fuel from the fuel tank to the intake passage;
A canister provided on the purge passage for adsorbing and accumulating the evaporated fuel from the fuel tank;
An open air passage communicating with the canister and supplying air to the canister;
An air release valve provided on the air release passage for controlling the supply of air to the canister;
A purge valve provided on the purge passage on the downstream side of the canister for controlling the supply of evaporated fuel to the intake passage;
A fuel pump provided in the fuel tank for pumping fuel to the engine;
A fuel temperature sensor provided in the fuel tank for detecting the fuel temperature;
A pressure sensor provided on a path through which evaporated fuel passes from the fuel tank to the purge valve, and detects a pressure in the path;
Have
Further, in a predetermined operating state of the engine, both the air release valve and the purge valve are closed to drive the fuel pump, and the fuel temperature detected by the fuel temperature sensor before and after the fuel pump is driven. Vapor pressure estimating means for estimating the vapor pressure of the fuel to be used when the adsorption of the evaporated fuel in the canister is saturated based on the change and the change in the pressure detected by the pressure sensor. Evaporative fuel processing device.   The vapor pressure estimating means is configured to determine a change in the fuel temperature detected by the fuel temperature sensor based on the relationship between the fuel temperature and the vapor pressure obtained in advance for a plurality of gasolines having different reed vapor pressures, and The evaporative fuel processing apparatus according to claim 1, wherein a lead vapor pressure of the used fuel corresponding to a change in pressure detected by the pressure sensor is obtained, and a vapor pressure of the used fuel is estimated based on the lead vapor pressure. The vapor pressure estimating means sets the pressure detected by the pressure sensor before driving the fuel pump to “P ₀ ”, sets the pressure detected by the pressure sensor after driving the fuel pump to “P ₁ ”, The fuel temperature detected by the fuel temperature sensor before driving the fuel pump is _defined as “T _fuel0 ”, and the difference between the fuel temperature T _fuel0 and the fuel temperature detected by the fuel temperature sensor after driving the fuel pump is _defined as “T _fuel0 ”. “ΔT _fuel ”, fuel reed vapor pressure “R _VP ”, and a function indicating the relationship between fuel temperature and vapor pressure for a plurality of gasolines having different reed vapor pressures R _VP “f”. A function obtained by differentiating f with respect to the fuel temperature is “f ′”, a value obtained by substituting the fuel temperature T _fuel0 and the reed vapor pressure R _VP into the function f is “f (T _fuel0 , R _VP )”, and the function f ′ is the fuel. Temperature T _fu When _el0 and lead values vapor pressure obtained by substituting R _VP is _"f'(T fuel0, R _VP)", based on the following equation determining the Reid Vapor Pressure R _VP of fuel used, the evaporation of claim 2 Fuel processor.

  The evaporated fuel processing apparatus according to any one of claims 1 to 3, wherein the vapor pressure estimating means is driven so that the fuel pump operates at a maximum output.   The vaporized fuel processing apparatus according to any one of claims 1 to 4, wherein the vapor pressure estimating means estimates a vapor pressure of a fuel used when the engine is started.

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