Fuel vapor processing apparatus

A fuel vapor processing apparatus includes an adsorbent canister, a vapor path connecting the adsorbent canister to a fuel tank, and a flow control valve disposed in the vapor path. The flow control valve is kept closed while a movement distance of a valve body from a predetermined initial position toward a valve opening direction is less than a predetermined distance. A control unit comprising part of the apparatus is configured to set a valve opening speed of the flow control valve to a first speed under a condition where the movement distance of the valve body is less than the predetermined distance, and to set the valve opening speed of the flow control valve to a second speed lower than the first speed under a condition where the movement distance of the valve body is greater than the predetermined distance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese patent application serial number 2015-244328, filed Dec. 15, 2015, the entire contents of which are incorporated herein by reference for all purposes.

Not applicable.

BACKGROUND

This disclosure relates to a fuel vapor processing apparatus.

Japanese Laid-Open Patent Publication No. 2015-102020 discloses a fuel vapor processing apparatus having an adsorbent canister capable of adsorbing fuel vapor. In the fuel vapor processing apparatus, the fuel vapor vaporized in a fuel tank is introduced into the adsorbent canister and is adsorbed therein. Then, the fuel vapor is purged from the adsorbent canister and is supplied to an internal combustion engine (also, referred to as engine) during a purge operation. The fuel vapor processing apparatus further includes a flow control valve in a vapor path connecting the fuel tank to the adsorbent canister. The flow control valve is usually closed and is opened as necessary for controlling a fluid communication through the vapor path.

When the purge operation is performed, the fuel vapor adsorbed in the adsorbent canister is purged and is supplied to the engine. The fuel vapor supplied to the engine may affect an air-fuel ratio in the engine, so a correction of the air-fuel ratio in the engine is performed during the purge operation.

However, when the flow control valve is opened, the fuel vapor flows through the vapor path from the fuel tank toward the adsorbent canister depending on a difference between a pressure in the fuel tank and that in the adsorbent canister. Such flow of the fuel vapor may affect the corrected air-fuel ratio. Accordingly, there has been a need for improved fuel vapor processing apparatuses.

BRIEF SUMMARY

In one aspect of this disclosure, a fuel vapor processing apparatus includes an adsorbent canister, a vapor path connecting the adsorbent canister to a fuel tank, and a flow control valve disposed in the vapor path. The flow control valve is kept closed while a movement distance of a valve body relative to a valve seat from a predetermined initial position toward a valve opening direction is less than a predetermined distance. An opening amount of the flow control valve increases in response to an increase in the movement distance of the valve body under a condition where the movement distance of the valve body is greater than the predetermined distance. A control unit comprising part of the fuel vapor processing apparatus is configured to set a valve opening speed of the flow control valve at a start of valve opening to a first speed under a condition where the movement distance of the valve body from the predetermined initial position is less than the predetermined distance, and to set the valve opening speed of the flow control valve to a second speed lower than the first speed under a condition where the movement distance of the valve body from the predetermined initial position is greater than the predetermined distance.

DETAILED DESCRIPTION

FIG. 1is a schematic view of a fuel vapor processing apparatus according to a first embodiment. In this apparatus, a fuel vapor vaporized in a fuel tank15is introduced into an adsorbent canister21through a vapor path22and is adsorbed in the adsorbent canister21. Then, the fuel vapor adsorbed in the adsorbent canister21is purged and is supplied to an engine body11via a purge path23and a purge valve25. The vapor path22is provided with a closing valve24(also, referred to as “flow control valve”) that is opened and closed by a valve opening means24a. The closing valve24includes a valve seat24band a valve body24cand is configured to be closed while a movement distance of the valve body24crelative to the valve seat24bfrom an initial position toward a valve opening direction is equal to or less than a predetermined value. The closing valve24may be composed of a globe valve having the valve seat24bfacing in a moving direction of the valve body24cas shown inFIG. 1. Alternatively, the closing valve24may be comprised of other types of valves such as a ball valve in which a flow passage is opened and closed by rotating a ball having a through-hole. The valve opening means24ais connected to a control unit16(also referred to as “engine control unit (ECU)”). The control unit16includes a microcomputer composed of various electronic components such as a CPU and a memory where the microcomputer is configured to perform functions as a valve opening speed control means16aand a valve closing speed control means16b, based on specific algorithms and programs stored in the memory.

The valve opening speed control means16acontrols a speed of opening the closing valve24at the time of starting a valve opening operation. Specifically, a valve opening speed of the closing valve24at the time of starting the valve opening is set to a first speed under a closed condition where the movement distance of the valve body24cin the closing valve24is equal to or less than the predetermined value, and is set to a second speed lower than the first speed under an open condition where the movement distance of the valve body24cin the closing valve24is greater than the predetermined value. Furthermore, while the valve opening speed is the second speed, an opening amount of the closing valve24is increased by a predetermined amount at a cycle longer than a control cycle of a feedback control of the air-fuel ratio of the engine.

The valve closing speed control means16bcontrols a valve closing speed of the closing valve24during closing the closing valve24. Specifically, the valve closing speed of the closing valve24is equal to the valve opening speed of the closing valve24under a condition where the closing valve24is in a closed state.

FIG. 2is a schematic view of an engine system10according to the first embodiment. In the engine system10, a gas mixture of air and fuel is supplied to the engine body11via an intake path12. A flow rate of the air is controlled by a throttle valve14, and a flow rate of the fuel is controlled by a fuel injection valve (not shown) that is supplied with the fuel from the fuel tank15. The throttle valve14and the fuel injection valve are connected to the control unit16. The throttle valve14outputs signals relating to an opening amount of the throttle valve14to the control unit16. The control unit16controls an open time of the fuel injection valve.

In the fuel vapor processing apparatus20, the vapor path22connects the fuel tank15to the adsorbent canister21such that the fuel vapor generated during refueling or vaporized in the fuel tank15is introduced into and is adsorbed in the adsorbent canister21. The fuel vapor adsorbed in the adsorbent canister21is purged and is supplied to the intake path12downstream of the throttle valve14via the purge path23. The closing valve24disposed in the vapor path22is composed of a step motor-type valve and is opened and closed by the valve opening means24a, i.e., a step motor. The purge path23has the purge valve25for controlling a fluid communication through the purge path23.

The adsorbent canister21is filled with an activated carbon21aas adsorbent for trapping the fuel vapor flowing into the adsorbent canister21. The adsorbent canister21is connected to an atmospheric path28, which is open to the atmosphere and is configured to suction atmospheric air at a position near a fill opening17of the fuel tank15. When starting the purge operation, negative pressure is applied to the adsorbent canister21via the purge path23, and thus, atmospheric air flows into the adsorbent canister21through the atmospheric path28to compensate for the negative pressure. Consequently, the fuel vapor is purged from the adsorbent canister21and then is supplied to the engine body11via the purge path23and the intake path12.

The control unit16receives various signals, e.g., detection signals from a pressure sensor26, which is configured to detect an inner pressure of the fuel tank15, in order to perform various operations for controlling the fuel vapor processing apparatus20. Such operations include, for example, controlling the open time of the fuel injection valve, opening and closing each of the closing valve24and the purge valve25.

Next, the valve opening control of the closing valve24by the microcomputer of the control unit16will be described in reference toFIGS. 3 and 4. When this control is started, it is determined whether a valve opening control condition of the closing valve24, i.e., a depressurizing control condition of the fuel tank15, is met or not at a step S2. The valve opening control condition of the closing valve24includes whether the purge valve25is opened after a purge start signal is output, whether a purge flow amount is greater than a predetermine value, and whether the inner pressure of the fuel tank15is outside a predetermined range. When at least one of the conditions is met such that the valve opening control condition is met, the step S2is determined as Yes. Then, it is determined whether a current valve opening position (valve opening amount) of the closing valve24is greater than a valve opening start position at a step S4. That is, it is determined whether the closing valve24is in the closed state or an open state at the step S4.

When the closing valve24is in the closed state, i.e., the valve opening position is less than the valve opening start position, the step S4is determined as No, and then the closing valve24is operated to be open at the first speed that is relatively high at a step S10. The opening amount of the closing valve24under this condition varies as shown in a period “T1” inFIG. 4. During this period “T1”, the closing valve24is operated to be open as rapidly as possible from a standby position located on a valve closed side distant from the valve opening start position by a steps toward the valve opening start position. Specifically, the valve opening start position has been previously detected and stored as learning value. While the closing valve24is in the closed state before starting the valve opening control, the closing valve24is kept at the standby position located on the valve closed side distant from the valve opening start position by α steps. Then, the closing valve24is operated from the standby position to the valve opening start position at high speed in response to the valve opening signals for the closing valve24, so it is able to quickly open the closing valve24. Furthermore, because the closing valve24is in the closed state during the period “T1”, such high speed valve opening operation of the closing valve24does not induce a flow of the fuel vapor from the fuel tank15into the adsorbent canister21.

When the closing valve24reaches the valve opening start position after the period “T1”, the step S4is determined as Yes, and the closing valve24is operated to be open at the second speed that is relatively low at a step S8. The opening amount of the closing valve24under this condition varies as shown in a period “T2” inFIG. 4. During the period “T2”, the closing valve24is operated to be open at a low speed, i.e., the second speed, from the valve opening start position toward a target valve opening position. The valve opening speed of the closing valve24under this condition is set such that the opening amount of the closing valve24is increased by the predetermined amount at the cycle longer than the control cycle of the feedback control of the air-fuel ratio of the engine. When the closing valve24is operated to be open at the low speed, the feedback control of the air-fuel ratio can correct the air-fuel ratio in the engine without delay in response to an increase in the fuel vapor supplied to the engine, which is caused by the valve opening of the closing valve24. Accordingly, disturbance of the air-fuel ratio in the engine caused by opening of the closing valve24can be suppressed.

FIG. 4shows changes of the opening amount of the closing valve24in a linear fashion. However, the closing valve24is actually operated by the step motor, so the opening amount of the closing valve24precisely varies in a stepped manner. That is, the closing valve24is operated to be open such that the opening amount of the closing valve24is increased by the predetermined amount at the predetermined cycle.

In the first embodiment, the cycle of the feedback control of the air-fuel ratio is set at 16 milliseconds. An operating cycle of the step motor during the period “T1” (the closing valve24is in the closed state) is set at 6 milliseconds. The operating cycle of the step motor during the period “T2” (the closing valve24is in the open state) is set at 30 milliseconds. These cycles can be changed as necessary, and are not limited to the above-described time periods.

FIG. 5shows changes of the opening amount of the closing valve24according to a prior art for comparison. When an opening operation of the closing valve24is started, the closing valve24is operated to be open from the standby position located on the valve closed side distant from the valve opening start position by a steps toward the target valve opening position at a relatively high speed during a period “Ta”. The period “Ta” from a start of the opening operation of the closing valve24to a time when reaching the target valve opening position in the prior art is substantially equal to a period “T1+T2” in the first embodiment. However, an opening speed of the closing valve24during the period “Ta” in the prior art is lower than the first speed during the period “T1” and is higher than the second speed during the period “T2” in the first embodiment. Thus, until the closing valve24reaches the valve opening start position, the air-fuel ratio may shift toward a fuel lean side. And, while the closing valve24is operated from the valve opening start position toward the target valve opening position, the air-fuel ratio may shift toward a fuel rich side. Specifically, in the former case, the feedback control of the air-fuel ratio is performed to correct the air-fuel ratio toward the fuel lean side under an assumption that the purge operation toward the engine is carried out. However, the flow control valve is actually in the closed state, so the amount of the fuel vapor supplied to the engine is small. Thus, the air-fuel ratio may shift toward the fuel lean side. In the latter case, an increase rate of the fuel vapor supplied to the engine is high, so the feedback control of the air-fuel ratio is delayed with respect to changes of the air-fuel ratio. Thus, the air-fuel ratio may shift toward the fuel rich side.

In the first embodiment, when the valve opening control condition for the closing valve24is not met, the step S2is determined as No, and then the closing valve24is operated to be closed at a constant speed that is relatively high at a step S6. A period “T3” inFIG. 4shows a change of the opening amount of the closing valve24during this closing operation. In this closing operation, the closing valve24is operated to be closed as rapidly as possible from the target valve opening position to the standby position located on the valve closed side distant from the valve opening start position by a steps. Thus, when the valve opening control is stopped, the closing valve24can be closed quickly in order to prevent the fuel vapor in the fuel tank15from flowing toward the adsorbent canister21. A valve closing speed of the closing valve24during this closing operation is equal to the valve opening speed of the closing valve24during the period “T1”.

In a case of a valve closing operation in the prior art, the closing valve24is operated to be closed at a speed equal to the valve opening speed for the closing valve24. Thus, the prior art may need a longer time for closing the closing valve24than the first embodiment, so the fuel vapor may flow into the adsorbent canister21from the fuel tank15unexpectedly.

FIG. 6shows a flowchart according to a second embodiment. The second embodiment is characterized in that the valve opening speed can be changed based on the air-fuel ratio while the closing valve24is operated to be open from the valve opening start position to the target valve opening position, that is, during the period “T2” inFIG. 4. Other configurations of the second embodiment are similar to those of the first embodiment, and thus, will not be described again.

The valve opening control according to the second embodiment includes some steps shown by “A” inFIG. 6instead of the step S8of the first embodiment. Thus, in the second embodiment, when the step S4is determined as Yes after the closing valve24reaches the valve opening start position, it is determined whether the air-fuel ratio detected by an air-fuel ratio sensor (not shown) is in a fuel rich state at a step S12. When the air-fuel ratio is in the fuel rich state as shown by a period “T4” inFIG. 7, a step S12is determined as Yes, and then the closing valve24is operated to be open at a relatively low speed. The valve opening speed of the closing valve24during the period “T4” is set to be slower than a responsiveness of the feedback control of the air-fuel ratio for the engine.

When the closing valve24is operated to be open at the low speed, the amount of the fuel vapor flowing into the adsorbent canister21via the closing valve24is relatively suppressed, so the air-fuel ratio gradually transitions into a fuel lean state. As the result, the step S12is determined as No, and then the closing valve24is operated to be open at a semi-high speed at a step S16. The opening amount of the closing valve24and the air-fuel ratio during this semi-high speed operation are shown at a period “T5” inFIG. 7. The valve opening speed of the closing valve24during this period is set to be equal to or faster than the responsiveness of the feedback control of the air-fuel ratio. Thus, an increase rate of the fuel vapor flowing into the adsorbent canister21from the fuel tank15is raised, so the air-fuel ratio transitions into the fuel rich state. Then, the step S12is determined as Yes again, and the valve opening speed of the closing valve24is changed to be low at a step S14. The opening amount of the closing valve24during this low speed operation is shown at a period “T6” inFIG. 7.

In the second embodiment, the operating cycle of the step motor during the periods of “T4” and “T6” is set at 30 milliseconds. The operating cycle of the step motor during the period “T5” is set at 10 milliseconds. These cycles can be changed as necessary, and are not limited to the above-described time periods.

The above-described operations are continued until the valve opening amount of the closing valve24reaches the target valve opening amount (a target position inFIG. 7). When the valve opening amount of the closing valve24reaches the target valve opening amount, a step S18is determined as Yes, and the valve opening control for the closing valve24is finished.

The closing valve24can be operated to be open quickly to the target opening amount while keeping the air-fuel ratio on or around a theoretical air-fuel ratio by controlling the valve opening speed of the closing valve24at the start of valve opening according to the valve opening control of the second embodiment.

In the first embodiment, the operations of the step S4, the step S8and the step S10are performed by the valve opening speed control means16a. The operation of the step S6is performed by the valve closing speed control means16b. In the second embodiment, the operations of the step S4, the steps S12to S18and the step10are performed by the valve opening speed control means16a. The operation of the step S6is performed by the valve closing speed control means16b.

This disclosure can be modified without departing from the scope of the invention. For example, in the first embodiment, the valve opening speed of the closing valve24in the open state is set such that the opening amount of the closing valve24is increased by the predetermined amount at the cycle longer than the control cycle of the feedback control of the air-fuel ratio of the engine. However, the valve opening speed can be changed in view of a purge amount. That is, when the purge amount is large, the valve opening speed may be corrected to be lower than a case where the purge amount is small.