Patent Publication Number: US-6658923-B2

Title: Leak detection a vapor handling system

Description:
REFERENCE TO RELATED APPLICATION 
     This application expressly claims the benefit of the earlier filing date and right of priority from the following patent application: U.S. Provisional Application Ser. No. 60/184,193, filed on Feb. 22, 2000 in the name of Laurent Fabre and Pierre Calvairac and entitled “Vacuum Detection.” The entirety of that earlier filed co-pending provisional patent application is expressly incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates to leak detection methods and systems, and more particularly, to automotive fuel leak detection in a vapor handling system. 
     BACKGROUND OF INVENTION 
     In a vapor handling system for an automotive vehicle, fuel vapor that escapes from a fuel tank is stored in a canister. If there is a leak in the fuel tank, the canister, or any other component of the vapor handling system, fuel vapor could exit through the leak to escape into the atmosphere. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of leak detection in a closed vapor handling system of an automotive vehicle while an engine is running. This method includes providing a pressure sensing element that obtains at least one pressure signal, closing a control valve and a shut off valve to seal the system from the engine and an atmosphere, generating a vacuum by opening the control valve, analyzing the at least one pressure signal at threshold times, comparing the at least one pressure signal to at least one pressure control value, and determining a leak condition if the at least one pressure signal is not less than the at least one pressure control value. 
     The present invention also provides another method of leak detection in a closed vapor handling system of an automotive vehicle while an engine is running. The method includes providing differential tank pressure sensor that provides pressure, closing a canister purge control valve to seal the system from the engine and an atmosphere, waiting for a first period of time, closing a shut off valve, waiting for a second period of time, determining a pressure sensor offset, estimating a correction value for vapor generation, aborting the leak detection if the correction value is greater than a control correction value, calculating a pressure mean value, dropping the pressure to a first threshold pressure by opening the control valve for a third period of time, detecting a tank cap missing condition if a second threshold pressure is not reached within a third period of time, detecting a large leak condition if the pressure drops below the second threshold pressure and above the first threshold pressure within the third period of time, aborting the leak detection if the speed of the automotive vehicle is greater than zero, ending the leak detection if a fuel volume is not within a control volume range, evaluating a pressure slope over a fourth period of time, calculating a corrected pressure slope using the correction value for vapor generation, and determining a leak diameter by comparing the corrected pressure slope to pressure control values within threshold times. 
     The present invention also provides an automotive evaporative leak detection system. The system includes a pressure sensing element, a control valve, a shut off valve, a processor operatively coupled to the pressure sensing element and the shut off valve and receiving pressure signals from the pressure sensing element and sending signals to the control valve and the shut off valve. The processor closes the control valve and the shut off valve, generates a vacuum, depressurizes the system using the vacuum, controls the vacuum by opening the control valve, analyzes the pressure signal at threshold times, compares the pressure signal to pressure control values, and determines a leak condition. 
     The present invention further provides another automotive evaporative leak detection system. This system includes a differential tank pressure sensor located on a conduit between a fuel tank and a canister, the canister communicating with an engine and an atmosphere, the fuel tank communicating with the engine, a shut off valve located between the canister and the atmosphere, a control valve located between the canister and the engine, and a processor operatively coupled to the pressure sensing element and the shut off valve and receiving pressure signals from the pressure sensing element and sending signals to the control valve and the shut off valve. The processor closes the control valve, waits for a period of time, closes a shut off valve, determines a pressure sensor offset, estimates a correction value for vapor generation, calculates a pressure mean value, drops the pressure to a threshold pressure, detects a tank cap missing condition, detects a large leak condition, aborts the diagnosis, evaluates a pressure slope, calculates a corrected pressure slope, and determines a leak diameter by comparing the corrected pressure slope to pressure control values within threshold times. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiment of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. 
     FIG. 1 is a schematic view of a preferred embodiment of the system of the present invention. 
     FIG. 2 is a graphic illustration of the preferred embodiment of the method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. It is to be understood that the Figures and descriptions of the present invention included herein illustrate and describe elements that are of particular relevance to the present invention, while eliminating, for purposes of clarity, other elements found in typical automotive vehicles and vapor handling systems. 
     As shown in FIG. 1, an evaporative leak detection system  10  in an automotive vehicle includes a pressure sensing element  11 , a shut off valve  25 , a control valve  26 , and a processor  13 . Preferably, the pressure sensing element  11  is in fluid communication with vapor in a fuel tank  16 . In the preferred embodiment, the pressure sensing element  11  is a differential tank pressure sensor (DTP) located on a conduit  15  between the fuel tank  16  and a canister  17 . The differential tank pressure sensor provides a pressure with the system  10  in comparison to an atmosphere  28 . The pressure sensing element  11  may also be a switch that moves at a given relative vacuum, or pressure control value, or a pair of switches that move at different relative vacuums, or pressure control values, having a high vacuum threshold for large leak detection of about 1 mm. 
     The shut off valve  25 , or preferably, a canister purge vent valve, is located on a conduit  27  between the canister  17  and the atmosphere  28 . The shut off valve  25  is normally open. Closing the shut off valve  26  hermetically seals the system  10  from the atmosphere  28 . The control valve  26 , or preferably, a canister purge control valve, is located on a conduit  29  between the canister  17  and an engine  30 . The engine  30  communicates with the fuel tank  16  and the canister  17 . Closing the control valve  26  seals the system  10  from the engine  30 . 
     The processor  13 , or engine management system, is operatively coupled to, or in communication with, the pressure sensing element  11 , the shut off valve  25  and the control valve  26 . The processor  13  receives and processes pressure signals  21  from the pressure sensing element  11  and sends signals  31  and  32 , respectively, to open and close the valves  25  and  26 , respectively. The processor  13  can either include the necessary memory or clock or be coupled to suitable circuits that implement the communication. The processor  13  also waits for a period of time, determines a pressure sensor offset, estimates a correction value for vapor generation, calculates a pressure mean value, drops the pressure to a threshold pressure, detects a tank cap missing condition, detects a large leak condition, aborts the diagnosis, evaluates a pressure slope, calculates a corrected pressure slope, and determines a leak diameter by comparing the corrected pressure slope to pressure control values within threshold times. 
     The system  10  implements a method of leak detection, or leak detection diagnosis, when an automotive vehicle is running. The method is based on vacuum detection and is particularly useful for leak detection during Federal Test Procedure cycles. The method includes leak detection and monitoring for malfunction of components in the system. FIG. 2 illustrates the preferred embodiment of the method by defining the steps by state  40  and showing the DTP value  41 , the control valve and shut off valve status,  42  and  43 , respectively, whether time  44  is involved and whether the canister purge function  45  is active during the steps. The control valve  26  is closed in step  50  to seal the system  10  from the engine  30  and the atmosphere  28 . After a delay of a first period of time, the shut off valve  25  is closed, in step  52 , to generate a vacuum. After a delay of a second period of time in step  54 , the pressure sensor offset is determined in step  56 . To get a reliable monitoring result, the actual sensor offset is necessary to correct the pressure signal. In step  58 , the fuel vapor generation is estimated. The output, B 1 , corresponds to a pressure correction value, which considers the increase of pressure due to unsaturated hydrocarbon vapor. Information about fuel volume may be necessary to determine the pressure correction value. If the vapor generation during steps  58  is too high, where the correction value, B 1 , is greater than a control correction value, B 1  max, the diagnosis may be aborted because excessive evaporation may result in an inaccurate diagnosis. A pressure mean value is then calculated in step  60 . If, however, there is a differential pressure decrease during step  58  due to environmental conditions, there may be a delay until a differential pressure increase. 
     In step  62 , specified as an evacuation step, a vacuum is created where the pressure is dropped to a first threshold pressure, L 1 . The system  10  uses the manifold vacuum by means of the control valve  26  to depressurize the system  10 . If the pressure does not reach a second threshold pressure, L 2 , which is less than L 1 , within a period of time, the system  10  detects that the tank cap is missing. If the pressure drops below L 2 , but does not reach L 1 , then a large leak is detected. If the speed of the automotive vehicle is greater than zero (0), the leak detection diagnosis will be aborted, or ended. In addition, in step  64 , if a fuel volume is not within a control volume range, the diagnosis is aborted because the system  10  is not properly sealed. If the diagnosis is aborted at any time, after a delay time, if all diagnosis conditions exist, or the system  10  stabilizes, the diagnosis may restart at step  56 . 
     Over a period of time, in step  66 , the pressure slope, B 2 , is evaluated. The corrected pressure slope B, may then be calculated using the correction value for vapor generation in the equation, B=B 2 −B 1 . The corrected pressure slope corresponds to the leak magnitude, where a physical relationship exists between B and the leak diameter. The leak diameter may be determined in step  67  by comparing the corrected pressure slope to pressure control values within threshold times, where a leak is determined if the pressure is greater than or equal to the pressure control value. A small leak of about 0.5 millimeter or a large leak of about 1 millimeter may be detected. A no leak detection may also be determined if a pressure is less than the pressure control value. The shut off valve  25  and control valve  26  may then be opened in step  68  and the signals provided by the pressure sensor  11  may become constant. 
     While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the invention, as defined in the appended claims and their equivalents thereof. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims.