Abstract:
A method for recovering vapor during an onboard refueling operation comprising the steps of:
       providing a flow path between a fuel tank and a purge canister;   providing a valve in the flow path;   providing a fuel level sensor for indicating the level of fuel in the fuel tank, and a vapor pressure sensor for indicating the pressure of the fuel vapor in the fuel tank; and   actuating the valve to selectively open and close the flow path in response to signals received from the fuel level sensor and the vapor pressure sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage application under 35 U.S.C. §371 of International Application No. PCT/EP2007/050768, filed Jan. 26, 2007, which claims priority to U.S. Application No. 60/763,390, filed on Jan. 31, 2006, and which further claims priority to European Application EP06110657.1, filed Mar. 3, 2006, all of these applications being herein incorporated by reference in their entirety for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method for recovering fuel vapor during an onboard refueling operation, more particularly, a method for operating an onboard refueling vapor recovery (ORVR) system of an automotive vehicle. 
     Increasingly stringent environmental standards have resulted in regulations necessitating a significant reduction in fuel vapors escaping from a vehicle fuel tank during refueling. These regulations generally strive to essentially eliminate fuel vapor escaping into the atmosphere during refueling. The resultant emission control systems are referred to as onboard refueling vapor recovery (ORVR) systems. 
     In such an ORVR system, the filler neck of the fuel system is designed to a diameter to create a seal in the filler neck to prevent vapors from escaping from the fuel tank through the filler neck. During refueling, the fuel volume within the tank increases, thereby reducing the available space for fuel vapors. The pressure created by filling the tank causes the fuel vapors to exit through an exhaust port to a purge canister. The purge canister typically includes a charcoal element to capture hydrocarbons while releasing filtered vapors into the atmosphere. 
     In a typical ORVR system, a control valve is placed in the flow path between the fuel tank and the purge canister. The primary purpose of such a control valve is to enable the transmission of vapor while preventing the transmission of liquid fuel to the purge canister. In case of liquid fuel reaching the purge canister, a situation referred to as carryover, fuel can collect within the purge canister. Because the canister may later be purged to provide fuel to the vehicle via the intake manifold, excessive fuel carryover may cause liquid fuel to exit the fuel system or interfere with engine operation. 
     Typically ORVR control valves are of mechanical nature. They are normally open and thus provide a flow path between the fuel tank and the purge canister. However, these normally open valves must be adaptable to close off the flow path between the fuel tank and the purge canister during conditions such as vibration, slosh, and vehicle tilting which might otherwise result in a carryover condition. Typical valves include a buoyant member with a bias toward an open position. The valve is responsive to slosh, vibration, and tilting conditions to close the vapor passage. However, such valves are often slow to respond and include many moving parts which eventually deteriorate, thereby adversely affecting operation of the valve. 
     U.S. Pat. No. 6,601,617 to Enge proposes to provide the ORVR system with an electronic control valve to selectively enable the passage of fuel vapor from the fuel tank to the purge canister during predetermined conditions. Furthermore, a method is proposed for controlling the electronic control valve which enables vapor to pass from the fuel tank to the purge canister only during predetermined conditions. 
     This invention is also directed to a method for recovering vapor during an onboard refueling operation in a vehicle. The method includes providing a flow path between a fuel tank and a purge canister. The method also includes providing a fueling event sensor for detecting at least one of the introduction of fuel into the fuel tank or the introduction of a filler nozzle into a filler neck of the fuel tank, defined as a fueling event. The method further includes providing an ORVR valve in the flow path and actuating the ORVR valve in accordance with the output of the fueling event sensor to selectively open and close the flow path. 
     A problem associated with electronic ORVR valves controlling the shutoff level, and indeed of the method as disclosed in U.S. Pat. No. 6,601,617, is a fuel spit-back. The closing of all communication to the purge canister at the end of a refueling event will in many cases result in liquid fuel being ejected out of the fill head and, in some cases, onto the operator. It is clear that this is both a safety and an environmental concern and must be avoided. 
     It is therefore an object of the present invention to provide an improved method for recovering fuel vapor during an onboard refueling operation wherein spit-back is prevented. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for recovering vapor during an onboard refueling operation comprising the steps of
         providing a flow path between a fuel tank and a purge canister;   providing a valve in said flow path;   providing a fuel level sensor for indicating the level of fuel in the fuel tank, and a vapor pressure sensor for indicating the pressure of the fuel vapor in the fuel tank; and   actuating the valve to selectively open and close the flow path in response to signals received from the fuel level sensor and the vapor pressure sensor.       

     With such a method, the valve can be controlled so as to avoid spit-back. It is in fact a merit of the present invention to have realized that the spit-back occurs if the flow path between the fuel tank and the purge canister is closed for an extended period of time. By more precisely controlling the opening and closing of the flow path, the spit-back effect can be avoided. 
     In the method of the invention, the valve is preferably an electronic valve. This valve is also preferably a solenoid valve and even more preferably, a solenoid valve according to patent applications WO 2005/059349 and PCT/EP2006/050085 both in the name of INERGY, the content of which is incorporated by reference in the present case. 
     In the method of the invention, the valve is preferably also actuated by a refueling event indicator and even more preferably, it is an electronic valve being actuated that way. 
     The refueling event indicator preferably comprises a device chosen from the group comprising a fill door sensor, a fill pipe sensor, a fill neck check valve sensor, an ignition sensor, a gear shift sensor, a speed sensor, a full level sensor, and any combination thereof. Alternatively, the fuel level sensor can be used as to detect a refueling event. 
     More particularly, the method according to the invention preferably actuates the electronic valve to open the flow path when a start of a refueling event is detected and actuates the electronic valve to close the flow path when the level value received from the fuel level sensor has reached a predetermined fuel level. Upon closure of the flow path, the pressure value received from a vapor pressure sensor associated with the fuel tank is preferably monitored and, depending on the pressure value, the electronic valve is actuated to open and close the flow path. 
     The opening and closing of the flow path, after an end of refueling event has been detected, can comprise the steps of measuring and storing a pressure value; determining a peak pressure value by comparing the measured pressure value to a previously stored pressure value; storing the peak pressure value; monitoring the pressure value until the pressure value has decayed to a predetermined percentage of the peak pressure value; actuating the electronic valve to open the flow path for a predetermined length of time, then actuating the electronic valve to close the flow path. 
     The shutting off of the fuel nozzle occurs shortly after the pressure in the tank peaks and begins to decay. The reason for the decay is that, if the flow path is closed, at certain point, some fuel vapor will escape the fuel tank through the fuel fill neck. Once the venting begins, the vapor begins exiting out the fuel fill neck at a rapid rate, causing decay in tank pressure. If too much flow is allowed out the fuel fill neck, the vehicle fails emissions requirements and in some cases spit-back. By venting the tank to the canister at this point the risk of spit-back is mitigated. 
     The percentage of the peak pressure value, after which the flow path is opened can e.g. be between 50 and 99%. The predetermined length of time at which the flow part remains open can e.g. range from 1 millisecond to 2 seconds. It should however be understood that these values may vary depending on a number of factors such as e.g. vehicle characteristics or climate characteristics. 
     Once the flow path is again closed, the method can further comprise the steps of monitoring the pressure value and determine whether the pressure value is increasing. If the pressure value is increasing, the above steps of detecting the peak pressure value and the decay of the pressure value can be repeated. If, on the other hand, the pressure value is not increasing, it can be concluded that the refueling event is definitely finished and the cycle can be ended. 
     An electronic control unit is preferably provided for receiving signals from the refueling event indicator, the fuel level sensor, and the vapor pressure sensor. The electronic control unit evaluates the received signals and sends a signal to the electronic valve to open and close the flow path accordingly. The electronic control unit of this embodiment may be a stand alone microprocessor, allowing the system to be added to any vehicle with a DC voltage source. Conversely, it can be any processor already on the vehicle, to save cost. This processor could among others be the vehicle&#39;s Engine Control Unit (ECU), or a processor controlling the fuel system functions such as fuel pump speed control . . . (FSCU or Fuel System Control Unit). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings form an integral part of the specification and are to be read in conjunction therewith. The detailed description of the invention is a non-limiting description of one preferred embodiment of the invention. 
         FIG. 1 : is a block diagram of an onboard refueling vapor recovery (ORVR) system arranged in accordance with the principles of the present invention. 
         FIG. 2 : is a flow chart of the method for recovering fuel vapor during an onboard refueling operation according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , an onboard refueling vapor recovery system is indicated generally at  10  and comprises a fuel tank  12  for storing liquid fuel therein. A fuel fill neck  14  is provided with its lower end  16  connected through the wall of the fuel tank  12  and with its upper end  18  being arranged so as to receive a refueling nozzle. A fuel level sensor  20  is arranged in the fuel tank  12  for determining the level of fuel therein. The space occupied by liquid fuel is generally indicated at  22 , whereas the remaining space of the tank, i.e. the space containing fuel vapor, is generally indicated at  24 . The fuel level sensor  20  comprises a floater device  26  swimming on the upper surface of the liquid fuel. The level of liquid fuel in the fuel tank  12  is determined by the vertical position of the floater device  26 . 
     As liquid fuel is poured into the fuel tank  12  though the fuel fill neck  14 , the liquid fuel space  22  increases whereas the fuel vapor space  24  decreases. Excess fuel vapor exits the fuel tank  12  via a flow path  28  and enters a purge canister  30  through an inlet port  32 . Such a purge canister  30  comprises a charcoal element that is used to store the excess fuel vapor from the fuel tank  12 . During operation of the engine, the fuel vapor stored in the purge canister  30  is drawn there from via a purge port  34  and taken to the engine via a purge path  36  for burning. 
     An electronic valve  40  is arranged in the flow path  28  between the fuel tank  12  and the purge canister  30  for opening and closing the flow path  28  as appropriate. Indeed, the flow path  28  should be open during the refueling event so as to allow excess fuel vapor to escape to the purge canister  30 . The flow path  28  should however be closed during operation of the vehicle to avoid liquid fuel from reaching the purge canister  30 . The electronic valve  40  is a solenoid controlled shutoff valve, which is controlled by a signal received from an electronic control unit (ECU)  42 . 
     The ECU  42  evaluates the need for the flow path  28  to be open or closed and controls the electronic valve  40  accordingly. Via a first line  44 , the ECU  42  receives a signal indicative of the level of liquid fuel in the fuel tank, as determined by the fuel level sensor  20 . Via a second line  46 , the ECU  42  receives a signal indicative of the pressure in the fuel vapor space  24  of the fuel tank  12 . 
     The pressure in the fuel vapor space  24  is determined by a pressure sensor  48  mounted in the wall of the fuel tank  12  and in communication with the fuel vapor space  24 . The pressure sensor  48  is preferably a low pressure sensor. 
     Based on the signals received from the fuel level sensor  20  and the pressure sensor  48 , the ECU  42  sends a control signal via a third line  50  to the electronic valve  40  to open or close the flow path  28 . 
     The control algorithm used by the ECU  42  follows the method as described herein, a preferred embodiment of which is explained by referring to  FIG. 2 . 
       FIG. 2  shows a flow chart of the method for recovering fuel vapor during an onboard refueling operation. The method commences at the start of the refueling process, which can be detected by the introduction of a refueling nozzle in the upper end of the fuel fill neck, a flow of fuel in the fuel fill neck or an increase in the liquid fuel level in the fuel tank. Alternatively, other means can be used to detect the start of a refueling process. 
     When the start of a refueling process is detected, the electronic valve is controlled to open  101  the tank to canister communication, i.e. to open the flow path. Excess fuel vapor from the fuel tank can escape from the fuel tank to the purge canister and be stored in the charcoal element thereof. 
     The ECU now monitors  102  the fuel level in the fuel tank by means of the signal received from the fuel level sensor. It is checked  103  if the detected fuel level has reached a predetermined level and, in the affirmative, the tank to canister communication is closed  104 . 
     The ECU now monitors  105  the pressure in the fuel vapor space by means of the signal received from the pressure sensor. The determined pressure is stored  106 . It is checked  107  if the pressure has peaked by comparing the pressure to the previously stored pressure. 
     If it is determined that the pressure has peaked, the pressure is again monitored  108  and stored  109 . It is then checked  110  if the pressure has decayed to a predetermined percentage of the peak pressure. If the pressure has sufficiently decayed, the tank to canister communication is opened  111  and a timer is started  112 . 
     Once the timer has reached a certain value, the timer is again stopped and the tank to canister communication is closed  113 . The pressure in the fuel vapor space is again monitored and it is checked  114  if the pressure is rising. 
     If the pressure is rising, the pressure is again stored at  106  and the pressure peak and decay checks are carried out again before the flow path is again opened for a predetermined period of time. If, on the other hand, the pressure is no longer rising, the end of the refueling process is concluded and the cycle is ended  115 . 
     Such a method controls the electronic valve between the fuel tank and the purge canister in such a way that pressure build-up in the fuel tank and fuel spit-back are avoided. 
     While a specific embodiment has been shown and described in detail to illustrate the principles of the present invention, it will be understood that the invention may be embodied otherwise without departing from such principles. For example, one skilled in the art will readily recognize from the above discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made without departing from the spirit and scope of the invention as described in the following claims.