Abstract:
A fuel vapor treatment system is provided that diagnoses failure of the purge valve using one absolute pressure sensor. The fuel vapor treatment system includes a fuel tank, a canister, a drain cut valve, a purge valve, purge piping and a sensor. The canister adsorbs fuel vapor evaporated from the fuel tank. The drain cut valve controls the introduction of air into the canister. The purge valve is disposed between the canister and an intake passage into which fuel vapor flows from the canister. The purge piping communicates between the fuel tank and the intake passage via the canister. The sensor detects the absolute pressure inside the purge piping. The fuel vapor treatment system is further equipped with an atmospheric pressure setting device that sets the value detected by the sensor when the drain cut valve is open as the atmospheric pressure used for controlling the engine.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to a fuel vapor treatment system. More specifically, the present invention relates an improvement to a fuel vapor treatment system equipped with an absolute pressure sensor.  
           [0003]    2. Background Information  
           [0004]    An example of a fuel vapor treatment system is described in Japanese Laid-Open Patent Publication No. 07-317611. This fuel vapor treatment system has an absolute pressure sensor installed in the evaporation passage that communicates between the fuel tank and the canister. By measuring the atmospheric pressure as a reference pressure, this fuel vapor treatment system diagnoses leaks inside the fuel vapor treatment system based on the difference between the reference pressure and the pressure inside the evaporation passage.  
           [0005]    In view of the above, there exists a need for an improved fuel vapor treatment system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.  
         SUMMARY OF THE INVENTION  
         [0006]    It has been discovered that the aforementioned fuel vapor leak diagnosis device requires the installation of two sensors, i.e., an absolute pressure sensor and an atmospheric pressure sensor. Thus, the installation of the two sensors results in a more costly vapor leak diagnosis device.  
           [0007]    If the atmospheric pressure sensor is eliminated, then the pressure inside the fuel vapor treatment system will fluctuate during the failure diagnosis because the drain cut valve is closed and when the engine is started negative pressure will develop inside the intake manifold. This creates a problem in a control unit that compensates using the atmospheric pressure. For example, an engine control unit 6 is disclosed in Japanese Laid-Open Patent Publication No. 2001-107776, in which atmospheric pressure is used to regulate the fuel injection quantity. Thus, engine control in this system cannot be properly conducted when the pressure inside the fuel vapor treatment system fluctuates.  
           [0008]    Therefore, an object of the present invention is to provide a fuel vapor treatment system that solves the aforementioned problems.  
           [0009]    In accordance with the present invention, a fuel vapor treatment system is provided that basically comprises a fuel tank, a canister, a purge valve, a sensor and an atmospheric pressure setting device. The canister is fluidly coupled to the fuel tank by a first pipe and configured to adsorb fuel vapor evaporated from the fuel tank. The drain cut valve is operatively coupled to the canister to control air flow into the canister. The purge valve is disposed in a second pipe fluidly coupled between the canister and an intake passage of an internal combustion engine into which fuel vapor flows from the canister. The sensor is configured and arranged to detect absolute pressure inside at least one of the first and second pipes. The atmospheric pressure setting device is configured and arranged to set a value detected by the sensor when the drain cut valve is open as atmospheric pressure to control the internal combustion engine.  
           [0010]    These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Referring now to the attached drawings which form a part of this original disclosure:  
         [0012]    [0012]FIG. 1 is a schematic view of a fuel vapor treatment system in accordance with one embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a control flowchart for determining a failure of a purge valve in the fuel vapor treatment system illustrated FIG. 1 in accordance with the present invention;  
         [0014]    [0014]FIG. 3 is a control flowchart for determining a failure of a purge valve in the fuel vapor treatment system illustrated FIG. 1 in accordance with the present invention; and  
         [0015]    [0015]FIG. 4 timing chart indicating an operating state for each component of the fuel vapor treatment system illustrated FIG. 1 in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Selected embodiments of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.  
         [0017]    Referring initially to FIG. 1, a schematic view of a fuel vapor treatment system  20  is illustrated in accordance with a first embodiment of the present invention. The fuel vapor treatment system  20  serves to treat fuel vapor that is generated inside a fuel tank  2  of an engine  1  that is equipped with a canister  3  containing a fuel adsorbing material (e.g., activated carbon). The fuel tank  2  and the canister  3  are fluidly coupled together by a purge pipe  4 . The canister  3  is also fluidly coupled to an intake passage  6  by a pair of purge pipes  7   a  and  7   b  at location that is downstream of a throttle valve  5  of the engine  1 . The purge pipes  4 ,  7   a  and  7   b  together form a purge piping that interconnects the fuel tank  2  to the intake passage  6  via the canister  3 . The purge pipe  4  forms a first purge pipe extending between the fuel tank  2  and the canister  3 , while the purge pipes  7   a  and  7   b  form a second purge pipe extending between the canister  3  and the intake passage  6 .  
         [0018]    A purge valve  8  is provided between the purge pipes  7   a  and  7   b  for opening and closing the connection between the purge pipes  7   a  and  7   b . An absolute pressure sensor  9  measures both the pressure (absolute pressure) inside the purge piping and the atmospheric pressure (absolute pressure), in a manner described later. The absolute pressure sensor  9  is located between the fuel tank  2  and the purge valve  8 . Thus, it is also acceptable to install the absolute pressure sensor  9  anywhere in the first purge pipe  4  such as shown in broken lines in FIG. 1.  
         [0019]    The canister  3  is provided with an atmospheric release port  10 . Preferably, the atmospheric release port  10  is part of a drain cut valve  11 , which closes the atmospheric release port  10 .  
         [0020]    Fuel vapor generated inside the fuel tank  2  is directed to the canister  3  through the first purge pipe  4 . The fuel component of the vapor is adsorbed by the activated carbon inside the canister  3 , while the remaining air is discharged to the outside through the atmospheric release port  10 . Then, in order to treat the fuel adsorbed by the activated carbon, the purge valve  8  opens and fresh air is introduced into the canister  3  through the atmospheric release port  10  by utilizing the negative intake pressure downstream of the throttle valve  5 . This fresh air causes the adsorbed fuel to separate from the activated carbon and be removed together with the fresh air into the intake passage  6  of the engine  1  through the purge pipes  7   a  and  7   b.    
         [0021]    The pressure value detected by the absolute pressure sensor  9  is sent to a controller  15  that functions as an atmospheric pressure setting device. The controller  15  preferably includes a microcomputer with a control program that controls the operation of the engine  1  and the fuel vapor treatment system  20  as discussed below. The controller  15  can also include other conventional components such as an input interface circuit, an output interface circuit, and storage devices such as a ROM (Read Only Memory) device and a RAM (Random Access Memory) device. The memory circuit stores processing results and control programs that are run by the processor circuit. The controller  15  is operatively coupled to the various sensors in a conventional manner. The internal RAM of the controller  15  stores statuses of operational flags and various control data. The internal ROM of the controller  15  stores the signals from the various sensors and the operational states of the purge valve  8  and the drain cut valve  11  for various operations. The controller  15  is capable of selectively controlling any of the components of the control system in accordance with the control program. It will be apparent to those skilled in the art from this disclosure that the precise structure and algorithms for the controller  15  can be any combination of hardware and software that will carry out the functions of the present invention. In other words, “means plus function” clauses as utilized in the specification and claims should include any structure or hardware and/or algorithm or software that can be utilized to carry out the function of the “means plus function” clause.  
         [0022]    The controller  15  receives at least the following signals: an output signal indicating the boost pressure inside the intake passage  6 , an ON-OFF signal from an ignition switch, an ON-OFF signal from a starter switch that starts a starter motor, a battery voltage signal, and an engine speed signal. The controller  15  preferably also receives informational signals from a fuel temperature sensor, and various other sensors that detect the operating conditions of the engine. Based on at least these input values, the engine speed, intake air flow rate, throttle opening, coolant temperature, intake air temperature, vehicle speed, fuel temperature, fuel injection quantity, etc., the controller  15  opens and closes the purge valve  8  and the drain cut valve  11  in response to the operating conditions of the engine  1  and controls the purging of the adsorbed fuel vapor from the canister  3 . In other words, the controller  15  opens and closes the purge valve  8  in specified operating regions (e.g., steady-state travel) and executes purge control (steady-state purge treatment) by controlling the opening and closing of the purge valve  8 . Also based on at least some of these input valves, the controller  15  is configured to control the throttle valve  5  and the fuel injector as seen in FIG. 1 as well as other engine components such as the intake valves, the exhaust valves, and the fuel igniter.  
         [0023]    The controller  15  sets the pressure value detected by the sensor  9  as the true atmospheric pressure PAA when the drain cut valve  11  is open, and uses the resulting atmospheric pressure signal to control, for example, the fuel injection quantity or throttle opening of the internal combustion engine  1 .  
         [0024]    The pressure inside the first or second pipe  4  and  7   a  as detected by the sensor  9  is substantially equal to the atmospheric pressure when the drain cut valve  11  is open. By setting the pressure detected when the drain cut valve  11  is open as the atmospheric pressure, the atmospheric pressure can be detected without using an atmospheric pressure sensor and a separate atmospheric pressure sensor can be omitted.  
         [0025]    When the drain cut valve  11  opens, the engine  1  is controlled as though the substitute atmospheric pressure PA used for controlling the internal combustion engine  1  is the same atmospheric pressure as when the drain cut valve  11  was closed. Consequently, the influence of the negative pressure caused by running the engine  1  can be eliminated and atmospheric pressure control can be executed continuously. In other words, control of an internal combustion engine  1  that involves compensation using the atmospheric pressure can be executed continuously.  
         [0026]    When the drain cut valve  11  switches from the closed state to the open state, the substitute atmospheric pressure PA is revised gradually until the difference between the substitute atmospheric pressure PA and the true atmospheric pressure PAA detected by the sensor  9  is less than or equal to a prescribed pressure PIA. The revised substitute atmospheric pressure PA is set as a new substitute atmospheric pressure and the new substitute atmospheric pressure is used to control the internal combustion engine  1 . Consequently, pressure fluctuations occurring when the drain cut valve  11  is switched can be suppressed effectively so that there is no effect on the operation and exhaust performance of the engine.  
         [0027]    When the difference between the true atmospheric pressure PAA detected by the sensor  9  and the substitute atmospheric pressure PA becomes less than or equal to a prescribed value PIA, the substitute atmospheric pressure is revised such that the pressure difference is zero and the internal combustion engine  1  is controlled using this revised substitute atmospheric pressure. Consequently, when the pressure difference is less than or equal to a prescribed pressure PIA, the substitute atmospheric pressure PA can be controlled so as to immediately become the true atmospheric pressure PAA detected by the sensor  9 .  
         [0028]    The atmospheric pressure control executed by the controller  15  is described using the flowcharts shown in FIGS. 2 and 3. The flowchart shown in FIG. 2 is used to compute the actual (true) absolute pressure (atmospheric pressure) PAA inside the passages of the first and second purge pipes  4  and  7   a . The flowchart shown in FIG. 3 is used for setting the substitute atmospheric pressure when the drain cut valve  11  switches between the open and closed states under conditions where the atmospheric pressure changes.  
         [0029]    First in Step S 1 , the controller  15  determines if the fuel vapor treatment system is operating in a normal manner or not. This determination is preferably accomplished by, for example, comparing the output value of the absolute pressure sensor  9  when the drain cut valve  11  is open with an output value previously obtained by the absolute pressure sensor  9  under atmospheric pressure. If the fuel vapor treatment system is operating in a normal manner, then the controller  15  proceeds to Step S 2  where the controller  15  determines the operating state of the drain cut valve  11 . If the drain cut valve  11  is open, then the controller  15  proceeds to Step S 3  where the controller  15  adopts the weighted average of values VP detected by the absolute pressure sensor  9  as the true absolute pressure PAA. When the drain cut valve  11  is open, the pressure inside the second purge pipe  7   a  is almost the same as atmospheric pressure. Therefore, the true absolute pressure PAA is almost the same value as atmospheric pressure. If drain cut valve  11  is closed, the controller  15  proceeds to Step S 4  where the value of the true absolute pressure PAA is maintained and not changed because the operation of the purge valve  8  might cause the negative pressure inside the intake passage  6  to affect the pressure inside the purge pipes  4 ,  7   a  and  7   b , resulting in a pressure difference between the actual atmospheric pressure and the pressure inside the purge pipes  4 ,  7   a  and  7   b.    
         [0030]    If an abnormality in the fuel vapor treatment system is discovered in Step S 1 , then the controller  15  proceeds to Step S 5  where the controller  15  sets a fixed value as the true absolute pressure PAA. Thus when the drain cut valve  11  is open, the true absolute pressure PAA is calculated based on the actual atmospheric pressure inside the purge pipes  4 ,  7   a  and  7   b  and the internal combustion engine  1  is controlled based on the value of this true absolute pressure.  
         [0031]    Now, the flowchart of FIG. 3 is used to explain how the atmospheric pressure setting is conducted when the drain cut valve  11  switches from the open state to the closed state and when the drain cut valve  11  switches from the closed state to the open state under conditions where the atmospheric pressure changes.  
         [0032]    With the present invention, when the drain cut valve  11  switches from the open state to the closed state, the atmospheric pressure setting is conducted such that the atmospheric pressure from when the drain cut valve  11  was open is held and used to control the internal combustion engine  1  while the drain cut valve  11  is closed. Now, it is feasible that the actual atmospheric pressure will change due to the travel of the vehicle while the drain cut valve  11  is closed. In such a case, when the drain cut valve  11  switches from closed to open, a pressure difference will exist between the pressure detected by the sensor  9  and the actual atmospheric pressure and such trouble as unstable operation of the internal combustion engine  1  could possible result. Therefore, the present invention sets a substitute atmospheric pressure so as to gradually change this pressure difference and executes various controls over the internal combustion engine  1  based on this substitute atmospheric pressure.  
         [0033]    The flowchart shown in FIG. 3 is for setting the substitute atmospheric pressure. The substitute atmospheric pressure PA is set based on the true absolute pressure PAA inside the passages of the first or second purge pipes  4  and  7   a  and can be used in various controls over the internal combustion engine  1 . The control cycle is continuously executed by the controller  15  at a fixed time interval, e.g., every 10 milliseconds.  
         [0034]    First, similarly to Step S 1 , in Step S 11 , the controller  15  determines if the fuel vapor treatment system is operating in a normal manner or not. If the fuel vapor treatment system is operating in a normal manner, then the controller  15  proceeds to Step S 12  where it determines if the pressure difference obtained by subtracting the substitute atmospheric pressure PA from the true absolute pressure PAA is greater than or equal to the dead zone pressure PIA. The controller  15  proceeds to Step S 13  if the pressure difference is less than or equal to the dead zone pressure PIA and to Step S 14  if the pressure difference is greater than or equal to the same.  
         [0035]    In Step S 13 , the controller  15  determines if the pressure difference obtained by subtracting the current true absolute pressure PAA from the substitute atmospheric pressure PA is greater than or equal to the dead zone pressure PIA. If the pressure difference is greater than or equal to the dead zone pressure PIA, then the controller  15  proceeds to Step S 15 . If the pressure difference is smaller than the dead zone pressure PIA, then the controller  15  proceeds to Step S 16 . In Steps S 12  and S 13 , if the difference between the substitute atmospheric pressure PA and the current true absolute pressure PAA is larger than a prescribed pressure (the dead zone pressure PIA), then the control described in the following paragraph is executed so as to reduce this pressure difference.  
         [0036]    In Step S 14 , the controller  15  adds a prescribed pressure change amount PRT to the substitute atmospheric pressure PA and sets the result as a new substitute atmospheric pressure PA. The controller  15  then controls the opening of the drain cut valve  11  based on this new substitute atmospheric pressure PA and holds the new substitute atmospheric pressure PA for one second. In Step S 16 , the controller  15  subtracts prescribed pressure change amount PRT from the substitute atmospheric pressure PA, sets the result as a new substitute atmospheric pressure PA, and holds the new substitute atmospheric pressure PA for one second. After Step S 14  and Step S 16  are completed, the control cycle ends. The pressure difference is reduced by gradually adding or subtracting a fixed amount to or from the substitute atmospheric pressure PA. As a result, abrupt changes in the pressure inside the purge piping are suppressed and stable engine operation and exhaust performance can be maintained.  
         [0037]    In Step S 15 , the controller  15  determines the operating state of the drain cut valve  11 . If the drain cut valve  11  is open, the controller  15  proceeds to Step S 17  and sets the current true absolute pressure PAA as the substitute atmospheric pressure PA. Thus, the substitute atmospheric pressure PA is controlled so as to become the current actual (true) atmospheric pressure immediately and the control time can be reduced. Meanwhile, if the drain cut valve  11  is closed, then the controller  15  proceeds to Step S 18  and maintains the current substitute atmospheric pressure PA.  
         [0038]    If an abnormality is discovered in Step S 11 , then the controller  15  proceeds to Step S 19 , sets a fixed value as the substitute atmospheric pressure PA, and ends the control cycle.  
         [0039]    [0039]FIG. 4 is a timing chart that shows the control content of the previously described flowcharts as a time series. As shown in FIG. 4, the actual (true) atmospheric pressure is assumed to change at a constant rate during the control cycle.  
         [0040]    First at time t 1 , the drain cut valve  11  is closed and a constant value that is equal to the pressure when the drain cut valve  11  was open is set as the atmospheric pressure data (substitute atmospheric pressure) PA for controlling the engine. Thus, the atmospheric pressure data (substitute atmospheric pressure) PA for controlling the engine is different from the true atmospheric pressure.  
         [0041]    At time t 2 , the drain cut valve  11  is opened and a pressure difference exists between the true absolute pressure PAA and the true atmospheric pressure. The true absolute pressure PAA swiftly changes so as to match the true atmospheric pressure. However, the substitute atmospheric pressure PA is changed gradually by a prescribed change amount PRT each time a fixed time period (e.g., one second) elapses such that the difference between the substitute atmospheric pressure and the true absolute pressure PAA slowly diminishes (between time t 3  and time t 4 ). This serves to prevent the control of the fuel injection quantity (or the like) of the internal combustion engine  1  from becoming unstable due to a sudden change in the atmospheric pressure, and thus, prevents the operation and exhaust of the engine  1  from becoming unstable.  
         [0042]    Then at time t 4 , if the difference between the true absolute pressure PAA and the substitute atmospheric pressure PA is smaller than the dead zone pressure PIA, the substitute atmospheric pressure PA is set to the true absolute pressure PAA (i.e., the true atmospheric pressure) such that the pressure difference is quickly canceled. Thus, the time required to compensate for the difference that exists between the true atmospheric pressure and the pressure inside the piping when the drain cut valve  11  is opened (time t 2 ) can be shortened.  
         [0043]    The term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function.  
         [0044]    Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention.  
         [0045]    The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.  
         [0046]    This application claims priority to Japanese Patent Application No. 2001-228962. The entire disclosure of Japanese Patent Application No. 2001-228962 is hereby incorporated herein by reference.  
         [0047]    While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. Thus, the scope of the invention is not limited to the disclosed embodiments.