JP2018155137A - Evaporative fuel treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately change a rotational frequency of a booster pump in accordance with intake air density of an engine in an evaporative fuel treatment device including the booster pump.SOLUTION: An evaporative fuel treatment device 1 includes a purge passage 3, a canister 5, a booster pump 7, a purge valve 9 and an ECU 30. When a predetermined purge condition is satisfied, the ECU 30 drives the booster pump 7 at a first rotational frequency N1 and opens the purge valve 9 to purge evaporative fuel to an intake passage 21. In particular, when the predetermined purge condition is not satisfied, the ECU 30 drives the booster pump 7 at a second rotational frequency N2 lower than the first rotational frequency N1 for pre-rotation of the booster pump 7 while closing the purge valve 9. In the pre-rotation of the booster pump 7, the ECU changes the second rotational frequency N2 in accordance with intake air density of an engine.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an evaporated fuel processing apparatus for releasing evaporated fuel in a fuel tank into an intake passage of an engine.

  2. Description of the Related Art Conventionally, an evaporative fuel processing apparatus is known in which evaporative fuel generated in a fuel tank is once adsorbed to a canister, and evaporative fuel adsorbed on the canister is purged (released) into an engine intake passage through a purge passage. ing. In a general evaporative fuel processing apparatus, the evaporative fuel is purged into the intake passage by utilizing the negative pressure in the intake passage, specifically, the differential pressure between the purge passage and the intake passage. Yes.

  However, in recent years, the negative pressure in the intake passage is reduced as much as possible from the viewpoint of improving the fuel efficiency by reducing the pumping loss of the engine (for example, the negative pressure in the intake passage is reduced by opening the throttle valve). ). For this reason, the fuel vapor tends not to be appropriately purged into the intake passage. A technique has been developed in which evaporated fuel can be purged into the intake passage even when the negative pressure in the intake passage is reduced (see, for example, Patent Document 1). Patent Document 1 discloses a technique in which a pressure pump is provided on a purge passage, and the vaporized fuel is forcibly pumped from the canister toward the intake passage by the pressure pump.

JP, 2006-217172, A

  By the way, in the case where the pressurized pump as described above is used, even when the evaporated fuel purge is not executed, if the pressurized pump is driven in the same manner as when the evaporated fuel purge is executed, an increase in power consumption, Noise due to the operating noise of the pressure pump becomes a problem. In order to cope with this, it is considered that when the evaporated fuel purge is not executed, it is better to reduce the rotation speed of the pressure pump than when the evaporated fuel purge is executed.

  On the other hand, if the intake air density of the engine changes (the intake air density changes when the outside air temperature or atmospheric pressure changes), the characteristics of the pressurizing pump will prevent the pressurizing pump from rotating. Discharge pressure changes. Therefore, when the rotation speed of the pressurization pump is changed between when the purge is not executed and when the purge is executed as described above (in particular, when the purge is not executed and when the purge is executed, the fixed rotation speed is set respectively. When these are set and switched appropriately), the differential pressure of the discharge pressure varies between when the purge is not executed and when the purge is executed. As a result, when a purge request is issued and the rotation speed of the pressure pump is changed (increased), the time required for the discharge pressure of the pressure pump to reach the target discharge pressure for purging depends on the intake air density. Will change. That is, the responsiveness of the pressurization pump for generating a state where purge can be performed changes according to the intake air density. The above-mentioned Patent Document 1 does not disclose any such problems.

  The present invention has been made to solve the above-described problems of the prior art, and in an evaporative fuel processing apparatus including a pressure pump on a purge passage, the number of rotations of the pressure pump according to the intake density of the engine. The purpose of this is to change appropriately.

  In order to achieve the above object, the present invention is an evaporative fuel processing apparatus, comprising: a purge passage extending from a fuel tank toward an intake passage of the engine, and discharging the evaporated fuel in the fuel tank to the intake passage; A canister that is provided on the purge passage and adsorbs and accumulates the evaporated fuel from the fuel tank; a pressure pump that is provided on the purge passage on the downstream side of the canister and pumps the gas in the purge passage; A purge valve that is provided on the purge passage on the downstream side of the pump and controls the release of gas from the purge passage to the intake passage and when a predetermined purge condition for releasing evaporated fuel to the intake passage is satisfied. A purge control means for driving the pressure pump at the first rotation speed and opening the purge valve to release the evaporated fuel to the intake passage; and an intake air density acquisition means for acquiring the intake air density of the engine The purge control means prerotates the pressure pump by driving the pressure pump at a second rotation speed lower than the first rotation speed while closing the purge valve when a predetermined purge condition is not satisfied. The second rotational speed is changed according to the intake density acquired by the intake density acquisition means.

According to the present invention configured as described above, the evaporated fuel processing apparatus drives the pressure pump at the first rotation speed and opens the purge valve when a predetermined purge condition is satisfied, thereby evaporating fuel. When the predetermined purge condition is not satisfied, the pressure pump is driven at a second rotational speed lower than the first rotational speed while the purge valve is closed. Pre-rotate the pressure pump. As a result, it is possible to appropriately ensure the responsiveness of the pressurizing pump when the purge condition is satisfied while suppressing the increase in power consumption and the noise due to the operating sound of the pressurizing pump while the purge condition is not satisfied. it can. That is, when the purge condition is changed from not established to established, the pressurizing pump can be quickly reached the first rotation speed.
In particular, according to the present invention, the evaporative fuel processing apparatus changes the second rotational speed when pre-rotating the pressurizing pump according to the intake density (intake air density). The responsiveness can be made almost constant irrespective of the intake density of the engine. That is, the time from the purge standby state to the start of purge can be made substantially constant regardless of the intake air density of the engine.

In the present invention, it is preferable that the purge control means further changes the first rotation speed in accordance with the intake air density acquired by the intake air density acquisition means.
According to the present invention configured as described above, since the first rotation speed is changed in accordance with the intake air density in addition to the second rotation speed, a change in the response of the pressurizing pump due to the change in the intake air density of the engine is effective. Can be suppressed.

In the present invention, preferably, the purge control means limits the change in the second rotational speed when the change amount of the intake density acquired by the intake density acquisition means is less than a predetermined amount.
According to the present invention configured as described above, it is possible to suppress a decrease in rotational stability of the pressurizing pump due to a minute change in the rotational speed by suppressing a change in the second rotational speed due to a minute environmental change. . That is, it is possible to ensure the rotational stability of the pressurizing pump at the time of a minute environmental change.

In the present invention, preferably, the purge control means increases the second rotational speed as the intake air density acquired by the intake air density acquisition means decreases.
According to the present invention configured as described above, it is possible to effectively ensure the responsiveness of the pressurizing pump when the intake air density is small.

  In the present invention, it is preferable that the intake air density acquisition means obtain the intake air density based on at least one of atmospheric pressure and outside air temperature.

  According to the present invention, in the fuel vapor processing apparatus including a pressure pump on the purge passage, the rotation speed of the pressure pump can be appropriately changed according to the intake air density of the engine.

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 a block diagram which shows the electrical structure of the evaporative fuel processing apparatus by embodiment of this invention. It is a time chart which shows the rotation speed of a pressurization pump applied at the time of purge execution and purge non-execution in embodiment of this invention. It is a time chart for demonstrating the responsiveness of a pressurization pump. It is explanatory drawing about the reason for changing a pump rotation speed according to an intake air density in embodiment of this invention. It is a correction coefficient map according to the intake density by the embodiment of the present invention. It is a flowchart which shows the control by embodiment of this invention. It is a time chart at the time of performing control by the embodiment of the present 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, the configuration of the fuel vapor processing apparatus according to the embodiment of the present invention will be described with reference to FIGS. 1 and 2. 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, and FIG. 2 is a block diagram showing an electrical configuration of the evaporated fuel processing apparatus according to an embodiment of the present invention. .

  As shown in FIG. 1, the evaporated fuel processing apparatus 1 includes a purge passage 3 that extends from a fuel tank 2 that stores fuel to be supplied to an engine toward an intake passage 21 of the engine. The purge passage 3 can purge (discharge) the evaporated fuel (evaporative gas) generated in the fuel tank 2 to the intake passage 21 on the downstream side of the throttle valve 20.

  On the purge passage 3, in order from the upstream side, activated carbon that adsorbs the evaporated fuel is provided inside, a canister 5 that accumulates the evaporated fuel, and a pressure pump 7 that pumps the gas in the purge passage 3 are opened and closed. Thus, a purge valve 9 for controlling the release of gas from the purge passage 3 to the intake passage 21 is provided. The purge passage 3 between the pressurizing pump 7 and the purge valve 9 is provided with a pressure sensor 11 that detects the pressure in the purge passage 3. Further, the canister 5 is provided with an atmosphere opening port 13 a through which air is supplied from the outside, and an atmosphere opening passage 13 for supplying air to the canister 5 is connected thereto. An atmosphere release valve 15 that controls the supply of air to the canister 5 is provided on the atmosphere release passage 13.

  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. As shown in FIG. 2, the ECU 30 detects the pressure detected by the pressure sensor 11, the air-fuel ratio detected by the air-fuel ratio sensor 23 provided on the engine exhaust passage, and the water temperature sensor 24. The engine water temperature, the outside air temperature detected by the outside air temperature sensor 25, and the atmospheric pressure detected by the atmospheric pressure sensor 26 are acquired. The ECU 30 controls the fuel injection valve 28 of the engine in addition to the pressurizing pump 7, the purge valve 9, and the air release valve 15 based on various state values detected by these sensors.

  In particular, the ECU 30 includes an intake density acquisition unit 30a and a purge control unit 30b as functional components. The intake air density acquisition unit 30 a acquires the intake air density (intake air density) of the engine according to the outside air temperature detected by the outside air temperature sensor 25 and / or the atmospheric pressure detected by the atmospheric pressure sensor 26. For example, the intake air density acquisition unit 30a calculates the intake air density based on the outside air temperature and / or the atmospheric pressure. The purge control unit 30b controls to drive the pressurizing pump 7 and open the purge valve 9 to purge the evaporated fuel into the intake passage.

<Control details>
Next, in the embodiment of the present invention, the control content performed by the ECU 30 will be specifically described.

(Basic control)
First, with reference to FIG. 3 and FIG. 4, a basic concept of control contents performed by the ECU 30 in the present embodiment will be described.

  FIG. 3 is a time chart showing the rotation speed of the pressurizing pump 7 applied when the purge of the evaporated fuel is executed and when the purge of the evaporated fuel is not executed in the embodiment of the present invention. The upper part of FIG. 3 shows ON / OFF of the purge execution flag for executing the purge of the evaporated fuel, and the lower part of FIG. 3 shows the rotation speed of the pressurizing pump 7.

The purge execution flag is turned on when a predetermined condition (purge condition) is satisfied. The purge conditions include, for example, the following conditions. When all of these conditions are satisfied, the purge execution flag is turned on.
-The engine water temperature is equal to or higher than a predetermined temperature (for example, 60 ° C), that is, the engine is warmed up.
-The injection amount learning of the fuel injection valve 28 has been completed (this injection amount learning is performed based on the air-fuel ratio detected by the air-fuel ratio sensor 23 so as to realize the target air-fuel ratio. The amount is F / B controlled).
-Evaporated fuel concentration estimation has been completed after IG is turned on (it may be a further condition that evaporative fuel concentration estimation is not in progress).

  Typically, the purge condition described above is established when the engine is stopped or stopped (typically when the engine is idling stopped). Here, the end of injection amount learning is one of the purge conditions. The fuel injection amount control accuracy is ensured in order to reliably realize the target air-fuel ratio from the viewpoint of fuel consumption and emission even during purge of evaporated fuel. This is because it is desirable. The end of the estimation of the concentration of evaporated fuel is one of the purge conditions. This is because the amount of fuel introduced into the engine when purging (the amount depends on the concentration of evaporated fuel) is grasped. This is because the target air-fuel ratio can be reliably realized by combustion combining the fuel amount and the fuel injection amount from the fuel injection valve 28.

  Specifically, FIG. 3 shows that since the purge execution flag is on before time t11, in this embodiment, the ECU 30 opens the purge valve 9 to purge the evaporated fuel into the intake passage 21. At the same time, the pressure pump 7 is driven at the first rotation speed N1 (the rotation speed of the pressure pump 7 is maintained at the first rotation speed N1). At this time, the ECU 30 sets a target purge amount based on the pressure detected by the pressure sensor 11 and controls the purge valve 9 to an opening corresponding to the target purge amount. Further, the ECU 30 refers to the air-fuel ratio detected by the air-fuel ratio sensor 23 in consideration of the estimated concentration of the evaporated fuel so that the target air-fuel ratio is appropriately achieved even when the evaporated fuel is purged. At the same time, the fuel injection amount from the fuel injection valve 28 is controlled.

  Next, at time t11, since the purge execution flag is switched from on to off, in this embodiment, the ECU 30 closes the purge valve 9 and stops the rotation speed of the pressurizing pump 7 to stop purging the evaporated fuel. Is reduced from the first rotational speed N1 to the second rotational speed N2. Then, the ECU 30 maintains the rotation speed of the pressure pump 7 at the second rotation speed N2. Thus, in the present embodiment, the pressurizing pump 7 is pre-rotated while the purge execution flag is off. That is, the pressurizing pump 7 is kept on standby until the purge execution flag is switched from OFF to ON. Next, at time t12, since the purge execution flag is switched from OFF to ON, the ECU 30 opens the purge valve 9 and purges the rotation speed of the pressurizing pump 7 to the second in order to purge the evaporated fuel into the intake passage 21. The rotational speed N2 is increased to the first rotational speed N1.

  Here, the rotation speed of the pressurizing pump 7 that can appropriately introduce the evaporated fuel from the purge passage 3 to the intake passage 21 when the throttle valve 20 is open is applied as the first rotation speed N1. . That is, the first rotation speed N1 is a rotation speed capable of generating a pressure difference between the intake passage 21 and the purge passage 3 so that the evaporated fuel in the purge passage 3 can be appropriately drawn into the intake passage 21. Is done. For example, the first rotation speed N1 is set to about 30,000 rotations. On the other hand, the above-mentioned second rotation speed N2 is preferably such that when the purge execution flag is switched from OFF to ON, the pressurizing pump 7 can be quickly raised to the first rotation speed N1, In addition, the rotation speed of the pressurizing pump 7 is applied so that noise due to the operating sound of the pressurizing pump 7 does not become a problem. For example, the second rotation speed N2 is set to about 10,000 rotations.

  Next, with reference to FIG. 4, the responsiveness of the pressurization pump 7 is demonstrated concretely. FIG. 4 shows the time difference between the time when the pressure pump 7 is raised from the second rotation speed N2 and the time when the pressure pump 7 is raised from almost 0 until the first rotation speed N1 is reached. It is a chart.

  In FIG. 4, the solid line shows a graph when the rotational speed of the pressurizing pump 7 is increased from the second rotational speed N2 to the first rotational speed N1 in the present embodiment. In this embodiment, as described above, when the evaporated fuel is not purged (the purge execution flag is OFF), the rotation speed of the pressurization pump 7 is driven at the second rotation speed N2, and the pressurization pump 7 is pre-rotated. It is something to be made. On the other hand, the broken line shows a graph in the comparative example when the rotation speed of the pressurizing pump 7 is increased from a substantially zero state (a state where driving of the pressurizing pump 7 is stopped) to the first rotation speed N1. ing. In this comparative example, when the evaporated fuel is not purged, the driving of the pressurizing pump 7 is stopped in order to surely suppress the noise due to the increase in power consumption and the operating sound of the pressurizing pump 7. Here, it is assumed that a pressure pump 7 having a brushless motor is used.

  In the present embodiment, when the rotation speed of the pressurization pump 7 is increased from the second rotation speed N2 at time t21, the rotation speed of the pressurization pump 7 reaches the first rotation speed N1 at time t22. On the other hand, in the comparative example, when the rotation speed of the pressure pump 7 is increased from approximately 0 at time t21, the rotation speed of the pressure pump 7 becomes the first rotation speed N1 at time t23 after time t22. To reach. In this case, in the pressurizing pump 7 provided with the brushless motor, since it is necessary to detect the position when the rotational speed starts to increase from almost 0, the rotational speed cannot be increased immediately (indicated by the arrow A1). See the period shown). Then, after this position detection, the rotational speed is increased. At this time, if the speed of change of the rotational speed is increased so that the rotational speed of the pressurizing pump 7 quickly reaches the first rotational speed N1 (see arrow A2), the drive circuit element of the pressurizing pump 7 becomes excessive. There are problems such as an increase in load and cost for high voltage, and an increase in physique.

  From the above, in the present embodiment, the ECU 30 does not stop driving the pressurizing pump 7 when not purging the evaporated fuel, but instead of the second rotation speed N2 lower than the first rotation speed N1 at the time of purging. By driving the pressurizing pump 7, the prepressurizing pump 7 is pre-rotated and kept waiting until the next purge. In this way, when the evaporated fuel is not purged, the responsiveness of the pressurizing pump 7 at the time of the purge request can be ensured while suppressing the increase in power consumption and the noise due to the operating sound of the pressurizing pump 7. In other words, the pressurizing pump 7 can be made to reach the first rotation speed N1 promptly.

  In the present embodiment, the ECU 30 changes the first rotational speed N1 and the second rotational speed N2 according to the intake air density of the engine. Specifically, the ECU 30 increases the first rotation speed N1 and the second rotation speed N2 as the intake air density decreases (the intake air density decreases as the atmospheric pressure decreases, and the intake air density decreases as the outside air temperature increases). To do. In other words, the ECU 30 decreases the first rotation speed N1 and the second rotation speed N2 as the intake air density increases (the intake air density increases as the atmospheric pressure increases, and the intake air density increases as the outside air temperature decreases).

  The reason for changing the rotation speed in accordance with the intake air density will be described with reference to FIG. In FIG. 5, the horizontal axis represents the intake air density, and the vertical axis represents the discharge pressure of the pressurizing pump 7. Graphs G11, G12, and G13 show the characteristics of the discharge pressure according to the intake density at different rotational speeds (the rotational speed of the pressure pump 7 increases in the order of G11 → G12 → G13). As shown in the graphs G11, G12, and G13, the pressurizing pump 7 has a characteristic that the discharge pressure increases as the intake air density increases, and the discharge pressure increases as the rotation speed increases.

  When the intake density is “ρ1”, the rotation speed corresponding to the graph G11 is applied as the second rotation speed N2 when the purge is not executed. In this case, the discharge pressure of the pressurizing pump 7 is increased by “ΔP11” by increasing the number of revolutions of the pressurizing pump 7 in order to reach the target discharge pressure P1 for purging. Become. On the other hand, when the intake density is “ρ2” (ρ2 <ρ1), as in the case where the intake density is “ρ1”, the rotation speed corresponding to the graph G11 when the purge is not executed is the second rotation speed. It shall be applied as N2. In this case, in order to allow the discharge pressure to reach the target discharge pressure P1 for purging, it is necessary to increase the discharge pressure of the pressurization pump 7 by “ΔP12” by increasing the rotation speed of the pressurization pump 7. There is (ΔP12> ΔP11). When the purge execution flag is switched from OFF to ON due to the difference between the differential pressures ΔP11 and ΔP12 with respect to the target discharge pressure P1, the intake density is “ρ1” when the rotation speed of the pressurizing pump 7 is increased. And “ρ2”, the time required for the discharge pressure of the pressurizing pump 7 to reach the target discharge pressure P1 (that is, the time until the purge is started) changes. Specifically, when the intake density is “ρ2”, the start of purging is delayed compared to the case where the intake density is “ρ1”.

  For this reason, when the intake air density of the engine changes, the responsiveness of the pressurizing pump at the time of purging changes. Therefore, in the present embodiment, the ECU 30 changes the first rotation speed N1 and the second rotation speed N2 according to the intake air density in order to suppress the change in the response of the pressurization pump due to the intake air density. Specifically, the ECU 30 decreases the first intake air density so that the differential pressure between the discharge pressure at the first rotation speed N1 and the discharge pressure at the second rotation speed N2 does not change according to the intake air density. The rotational speed N1 and the second rotational speed N2 are increased. For example, in the example shown in FIG. 5, when the intake air density is “ρ2” so that ΔP12 is the same as ΔP11, the rotation speed corresponding to the graph G12 larger than the rotation speed corresponding to the graph G11 is set. The second rotation speed N2 is applied.

  Here, with reference to FIG. 6, the specific method of changing the rotation speed of the pressurizing pump 7 according to the intake air density in the embodiment of the present invention will be described. FIG. 6 shows a correction coefficient map corresponding to the intake air density applied in the embodiment of the present invention. Specifically, in FIG. 6, the horizontal axis indicates the intake air density, and the vertical axis indicates a correction coefficient for correcting the rotation speed of the pressurizing pump 7. This correction coefficient is based on, for example, the first and second rotational speeds N1 and N2 that should be set at a standard intake air density, and the first and second rotational speeds N1 and N2 based on the reference are determined according to the intake air density. This is a correction coefficient for correction. For example, the ECU 30 determines the first and second rotation speeds N1 and N2 to be applied by multiplying the reference first and second rotation speeds N1 and N2 by a correction coefficient. As shown in FIG. 6, the correction coefficient increases as the intake air density decreases. Therefore, as the intake air density decreases, the first and second rotational speeds N1 and N2 corrected by the correction coefficient are increased. Note that the same correction coefficient is not used for the first rotation speed N1 and the second rotation speed N2, and different correction coefficients may be used for the first rotation speed N1 and the second rotation speed N2.

  Further, in the present embodiment, the ECU 30 changes the first and second rotational speeds N1 and N2 according to the intake density last time, so that the intake density has hardly changed, that is, the amount of change in the intake density is predetermined. When it is less than a fixed amount (for example, 10%), the first and second rotational speeds N1 and N2 are not changed. In other words, the ECU 30 changes the first and second rotational speeds N1 and N2 only when the amount of change in the intake air density is greater than or equal to a predetermined amount. By doing so, a change in the rotational speed of the pressurizing pump 7 due to a minute environmental change is suppressed, thereby suppressing a decrease in rotational stability of the pressurizing pump 7 due to a minute change in the rotational speed. That is, the rotational stability of the pressurizing pump 7 is ensured at the time of a minute environmental change.

  Note that the change in the first and second rotational speeds N1 and N2 is not limited to being completely prohibited when the amount of change in the intake air density is less than a predetermined amount, and the first and second rotational speeds N1 and N2 are not limited. Changes may be allowed to some extent. For example, a restriction may be imposed on the amount of change or the rate of change (rate of change) of the first and second rotational speeds N1, N2.

(flowchart)
Next, with reference to FIG. 7, the flowchart which shows the control by embodiment of this invention is demonstrated. This flow is repeatedly executed by the ECU 30.

  First, when IG (ignition) is turned on in step S1, the ECU 30 proceeds to step S2 and starts activation control of the pressurizing pump 7. For example, if the pressurizing pump 7 includes a brushless motor, the ECU 30 first performs position detection control of the motor as the start-up control of the pressurizing pump 7.

  Next, in step S3, the ECU 30 calculates the intake air density based on the outside air temperature detected by the outside air temperature sensor 25 and / or the atmospheric pressure detected by the atmospheric pressure sensor 26, and the correction coefficient map shown in FIG. The correction coefficient corresponding to the calculated intake air density is determined with reference to FIG. Thereafter, in step S4, the ECU 30 drives the pressurization pump 7 using the second rotational speed N2 corrected with the correction coefficient determined in step S3, so that the pressurization pump 7 is pre-rotated and waited. . In this case, the ECU 30 corrects the second rotation speed N2 by multiplying the reference second rotation speed N2 by a correction coefficient.

  Next, in step S5, the ECU 30 determines whether or not a predetermined purge condition is satisfied. The purge conditions are as described in the “Basic Control” section above. If the purge condition is not satisfied as a result of the determination in step S5 (step S5: No), the ECU 30 returns to step S4, and the pressure pump 7 has been described above in order to pre-rotate and pressurize the pressure pump 7. Drive at the second rotation speed N2.

  On the other hand, when the purge condition is satisfied (step S5: Yes), the ECU 30 proceeds to step S6 and drives the pressurizing pump 7 at the first rotational speed N1 in order to purge the evaporated fuel. Specifically, the ECU 30 drives the pressurizing pump 7 using the first rotation speed N1 corrected with the correction coefficient determined in step S3. In this case, the ECU 30 corrects the first rotational speed N1 by multiplying the reference first rotational speed N1 by a correction coefficient.

  Next, in step S <b> 7, the ECU 30 acquires the pressure detected by the pressure sensor 11. In this case, the ECU 30 confirms whether the pressure in the purge passage 3 on the downstream side of the pressure pump 7 has reached a desired pressure by the operation of the pressure pump 7. Next, in step S8, the ECU 30 sets a target purge amount based on the pressure detected by the pressure sensor 11, and controls the purge valve 9 to an opening corresponding to the target purge amount. Further, the ECU 30 refers to the air-fuel ratio detected by the air-fuel ratio sensor 23 in consideration of the estimated concentration of the evaporated fuel so that the target air-fuel ratio is appropriately achieved even when the evaporated fuel is purged. At the same time, the fuel injection amount from the fuel injection valve 28 is controlled.

  Next, in step S9, the ECU 30 determines whether or not the IG is turned off. As a result, when the IG is turned off (step S9: Yes), the ECU 30 proceeds to step S10 and stops driving the pressurizing pump 7. On the other hand, when IG is not turned off (step S9: No), the ECU 30 proceeds to step S11.

  In step S11, the ECU 30 acquires the intake air density of the engine again. Specifically, the ECU 30 calculates the intake air density based on the outside air temperature detected by the outside air temperature sensor 25 and / or the atmospheric pressure detected by the atmospheric pressure sensor 26. In step S12, the ECU 30 determines whether the difference between the intake density acquired last time and the intake density acquired this time, that is, the amount of change in the intake density is equal to or greater than a predetermined amount (for example, 10%).

  If the result of determination in step S12 is that the amount of change in intake air density is greater than or equal to a predetermined amount (step S12: Yes), the ECU 30 returns to step S3 and again determines a correction coefficient corresponding to the intake air density acquired in step S11. . Then, the ECU 30 drives the pressurizing pump 7 using the second rotation speed N2 corrected with the correction coefficient determined in this way (step S4). On the other hand, when the amount of change in the intake air density is less than the predetermined amount (step S12: No), the ECU 30 returns to step S4. In this case, the ECU 30 drives the pressurizing pump 7 using the same second rotational speed N2 as used last time without correcting the second rotational speed N2 (step S4).

(Time chart)
Next, a time chart when the control according to the embodiment of the present invention is performed will be described with reference to FIG. FIG. 8 shows, in order from the top, the vehicle speed, the purge execution flag on / off, the intake density, the pump drive flag on / off of the pressure pump 7, the rotation speed of the pressure pump 7, and the pressure detected by the pressure sensor 11. (Pressure detection value) and the open / close state of the purge valve 9 are shown.

  First, IG is turned on at time t30, and the ECU 30 switches the pump drive flag of the pressure pump 7 from off to on at time t31 immediately after this. Thereafter, at time t32, the ECU 30 starts the activation control of the pressurizing pump 7. Then, the ECU 30 drives the pressurizing pump 7 at the second rotational speed N2 so as to pre-rotate the pressurizing pump 7 to stand by.

  Next, at time t33, because the predetermined purge condition is satisfied due to the vehicle speed increasing from 0, the ECU 30 switches the purge execution flag from OFF to ON, opens the purge valve 9 and The pressure pump 7 is raised from the second rotational speed N2 to the first rotational speed N1, and the evaporated fuel is purged into the intake passage 21. Thereafter, at time t34, the purge condition is not satisfied. Therefore, the ECU 30 switches the purge execution flag from on to off, closes the purge valve 9 and stops the pressurization pump to stop purging the evaporated fuel. In order to pre-rotate 7, the pressure pump 7 is reduced from the first rotation speed N 1 to the second rotation speed N 2.

  Next, at time t35, the intake air density decreases, and the change amount of the intake air density becomes a predetermined amount or more. At this time t35, the ECU 30 corrects the second rotation speed N2 with a correction coefficient (see FIG. 6) corresponding to the intake air density (the corrected second rotation speed N2 is expressed as “second rotation speed N2 ′”). ). Then, the ECU 30 raises the pressure pump 7 from the second rotation speed N2 to the second rotation speed N2 ', and pre-rotates the pressure pump 7.

  Next, at time t36, because the predetermined purge condition is satisfied due to the vehicle speed increasing from 0, the ECU 30 switches the purge execution flag from OFF to ON, opens the purge valve 9 and The pressure pump 7 is raised from the second rotational speed N2 ′ to the first rotational speed N1, and the evaporated fuel is purged into the intake passage 21. Actually, the ECU 30 corrects the first rotation speed N1 with a correction coefficient corresponding to the intake air density in the same manner as the second rotation speed N2 (the corrected first rotation speed N1 is referred to as “first rotation speed”). N1 ′ ”), and the pressurizing pump 7 is increased to the first rotational speed N1 ′. Thereafter, at time t37, since the purge condition is not established, the ECU 30 switches the purge execution flag from on to off, closes the purge valve 9 and stops the purge of the evaporated fuel, and pressurizes the pressure pump. In order to pre-rotate 7, the pressure pump 7 is reduced from the first rotational speed N 1 ′ to the second rotational speed N 2 ′. Thereafter, the vaporized fuel purge is appropriately executed and stopped in the same procedure (time t38, t39).

<Effect>
Next, the effect of the evaporative fuel processing apparatus 1 according to the embodiment of the present invention will be described.

  In the present embodiment, the ECU 30 of the evaporated fuel processing apparatus 1 drives the pressurizing pump 7 at the first rotational speed N1 and opens the purge valve 9 when predetermined purge conditions are satisfied, and supplies the evaporated fuel. When the intake passage 21 is purged and the predetermined purge condition is not satisfied, the pressure pump 7 is driven at the second rotational speed N2 lower than the first rotational speed N1 while the purge valve 9 is closed. Then, the pressurizing pump 7 is pre-rotated. As a result, when the evaporated fuel is not purged, the responsiveness of the pressurizing pump 7 at the time of purging can be ensured while suppressing the noise due to the increase in power consumption and the operating sound of the pressurizing pump 7. The pressure pump 7 can quickly reach the first rotational speed N1.

  In the present embodiment, the ECU 30 changes the first rotational speed N1 and the second rotational speed N2 according to the intake air density of the engine. Thereby, the responsiveness of the pressurizing pump 7 at the start of the purge can be made substantially constant regardless of the intake density of the engine. That is, the time from the purge standby state to the start of purge can be made substantially constant regardless of the intake air density of the engine. In particular, in the present embodiment, the ECU 30 increases the first rotation speed N1 and the second rotation speed N2 as the intake air density decreases, so that the responsiveness of the pressure pump 7 when the intake air density is low is effectively ensured. can do.

  In the present embodiment, the ECU 30 limits the change in the second rotational speed when the amount of change in the intake air density is less than a predetermined amount. Thereby, the rotational stability fall of the pressurization pump 7 by the change of a minute rotation speed can be suppressed by suppressing the change of the rotation speed of the pressurization pump 7 by the minute environmental change. That is, it is possible to ensure the rotational stability of the pressurizing pump 7 at the time of a minute environmental change.

<Modification>
In the above-described embodiment, both the first rotation speed N1 and the second rotation speed N2 are changed according to the intake air density of the engine. However, in another example, the second rotation speed N2 is changed according to the intake air density of the engine. It is good also as changing only. This also can suppress a change in the response of the pressurizing pump 7 due to a change in the intake air density of the engine.

  In the above-described embodiment, the intake air density calculated from the outside air temperature and / or atmospheric pressure is used, but the outside air temperature and / or atmospheric pressure may be directly used instead of using such an intake air density. This is because the outside air temperature and the atmospheric pressure are state values that uniquely reflect the intake air density.

DESCRIPTION OF SYMBOLS 1 Evaporative fuel processing apparatus 2 Fuel tank 3 Purge passage 5 Canister 7 Pressure pump 9 Purge valve 20 Throttle valve 21 Intake passage 25 Outside temperature sensor 26 Atmospheric pressure sensor 28 Fuel injection valve

Claims (5)

An evaporative fuel processing device,
A purge passage extending from the fuel tank toward the intake passage of the engine, and discharging the evaporated fuel in the fuel tank to the intake passage;
A canister that is provided on the purge passage and adsorbs and accumulates the evaporated fuel from the fuel tank;
A pressure pump provided on the purge passage on the downstream side of the canister and pumping gas in the purge passage;
A purge valve provided on the purge passage on the downstream side of the pressurizing pump, for controlling the release of gas from the purge passage to the intake passage;
When a predetermined purge condition for releasing the evaporated fuel into the intake passage is satisfied, the pressure pump is driven at a first rotational speed, and the purge valve is opened so that the evaporated fuel is supplied to the intake air. Purge control means for discharging into the passage;
Intake air density acquisition means for acquiring the intake air density of the engine;
Have
The purge control means includes
When the predetermined purge condition is not satisfied, the pressure pump is driven at a second rotational speed lower than the first rotational speed while the purge valve is closed to pre-rotate the pressure pump. Let
Changing the second rotational speed according to the intake density acquired by the intake density acquisition means;
The evaporative fuel processing apparatus characterized by the above.   2. The evaporated fuel processing apparatus according to claim 1, wherein the purge control unit further changes the first rotation speed in accordance with the intake air density acquired by the intake air density acquisition unit.   3. The evaporation according to claim 1, wherein the purge control unit limits the change in the second rotational speed when the amount of change in the intake density acquired by the intake density acquisition unit is less than a predetermined amount. Fuel processor.   4. The evaporated fuel processing apparatus according to claim 1, wherein the purge control unit increases the second rotational speed as the intake air density acquired by the intake air density acquisition unit decreases. 5.   5. The evaporated fuel processing apparatus according to claim 1, wherein the intake air density acquisition unit obtains the intake air density based on at least one of an atmospheric pressure and an outside air temperature. 6.

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