Entropy method for leak detection modules in evaporative emission systems

Abstract

A method for detecting a leak in an evaporative emission system includes the following steps: sealing the evaporative emission system; achieving a first target pressure in the evaporative emission system; achieving a second target pressure in the evaporative emission system after achieving the first target pressure; and monitoring the system pressure after the second target pressure achievement step to determine the leakage status of the evaporative emission system.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 078,612, filed September 15, 2020, which is incorporated herein by reference. Technical Field

[0003] This disclosure relates to a method for performing a leak test on the evaporative emission system of a gasoline-powered vehicle, and to a system for performing the method. Background Technology

[0004] For a long time, gasoline-powered vehicles have required evaporative emission systems. During vehicle startup, the system must undergo a leak test to ensure that fuel vapors do not leak into the atmosphere. A pump is used to create a vacuum or pressurize the system. An external filter is used to prevent contamination that could damage the pump or other components of the system during operation. During this test, various valves can be closed to maintain system pressure, and the pressure is monitored to determine if any leaks are present.

[0005] When an evaporative emission system leaks at high ambient temperatures (>35°C), the amount of gasoline vapors (VOCs) emitted through the leak exceeds the design intent for normal operation. Over a 24-hour period, the amount of gas released from the vapor dome of the fuel tank through a 1.0 mm leak can exceed the permissible amount for evaporative emission leaks by more than 10 times. Therefore, a leak test for evaporative emission systems that can quickly and accurately detect leaks in the system is desired. Summary of the Invention

[0006] In one exemplary embodiment, a method for detecting a leak in an evaporative emission system includes the following steps: sealing the evaporative emission system; achieving a first target pressure in the evaporative emission system; achieving a second target pressure in the evaporative emission system after achieving the first target pressure; and monitoring the system pressure after the second target pressure achievement step to determine the leakage status of the evaporative emission system.

[0007] In another embodiment of any of the above, the first target pressure achievement step and the second target pressure achievement step are performed by evacuating the evaporative emission system.

[0008] In another embodiment of any of the above, the first target pressure and the second target pressure are the same as each other.

[0009] In another embodiment of any of the above, the first target pressure realization step and the second target pressure realization step correspond to a first entropy change and a second entropy change, respectively. The second entropy change is essentially smaller than the first entropy change.

[0010] In another embodiment of any of the above, the second target pressure achievement step is performed based on the ambient temperature.

[0011] In another embodiment of any of the above, the leakage condition includes at least one of a no-leakage condition, a very small leakage condition, and a small leakage condition.

[0012] In another embodiment of any of the above, the on-board diagnostic system generates an engine fault code in response to each of the very minor leak conditions and the minor leak conditions.

[0013] In another embodiment of any of the above, the sealed evaporative emission system includes components including a fuel filler and cap, a purge valve, a fresh air side of the charcoal canister, a vapor dome of the fuel tank, and a vapor line connecting the components. The vapor line includes a second fluid passage. A pressure transducer is fluidly connected to the components and the vapor line. The system pressure monitoring step includes measuring the system pressure using the pressure transducer.

[0014] In another embodiment of any of the above, the evaporative emission system sealing step includes: closing the tank valve solenoid to close the first fluid passage to the atmosphere.

[0015] In another embodiment of any of the above, each of the first target pressure achievement step and the second target pressure achievement step includes pumping fluid through a check valve.

[0016] In another exemplary embodiment, the evaporative emission system includes a fuel tank with a fuel filler and a cap. The fuel tank is configured to contain fuel and fuel vapor. The system also includes a charcoal canister configured to store fuel vapor from the fuel tank. The system further includes a purge valve fluidly connected to the charcoal canister and configured to selectively supply fuel vapor to the engine in response to a purge command. The system also includes a leak detection module comprising a canister valve solenoid, a pump, a check valve, and a pressure transducer. A first fluid passage fluidly connects the canister valve solenoid to the atmosphere. A second fluid passage fluidly connects the charcoal canister to the pump via the check valve. The pump is fluidly disposed between the check valve and the atmosphere. A controller communicates with the canister valve solenoid and the pressure transducer. The controller is configured to run a leak test procedure comprising: closing the canister valve solenoid to seal the evaporative emission system; achieving a first target pressure using the pump; achieving a second target pressure using the pump after achieving the first target pressure; and monitoring the system pressure using the pressure transducer after achieving the second target pressure to determine the leakage status of the evaporative emission system.

[0017] In another embodiment of any of the above, the pump evacuates the evaporative discharge system to achieve the first target pressure and the second target pressure.

[0018] In another embodiment of any of the above, the first target pressure and the second target pressure are the same as each other.

[0019] In another embodiment of any of the above, the first target pressure and the second target pressure correspond to a first entropy change and a second entropy change, respectively. The second entropy change is essentially smaller than the first entropy change.

[0020] In another embodiment of any of the above, the second target pressure achievement step is performed based on the ambient temperature.

[0021] In another embodiment of any of the above, the leakage condition includes at least one of a no-leakage condition, a very small leakage condition, and a small leakage condition.

[0022] In another embodiment of any of the above, the on-board diagnostic system generates an engine fault code in response to each of the very minor leak conditions and the minor leak conditions.

[0023] In another embodiment of any of the above, the sealed evaporative emission system includes components including a fuel filler and cap, a purge valve, a fresh air side of the charcoal canister, a vapor dome of the fuel tank, and a vapor line connecting the components. The vapor line includes a second fluid passage. The pressure transducer is fluidly connected to the components and the vapor line.

[0024] In another embodiment of any of the above, the closed tank valve solenoid closes the first fluid passage to the atmosphere.

[0025] In another embodiment of any of the above, each of the first target pressure and the second target pressure is achieved by pumping fluid through a check valve. Attached Figure Description

[0026] This disclosure can be further understood by referring to the following detailed description when considered in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 A portion of an exemplary evaporative fuel system is shown schematically.

[0028] Figure 2 It is used for Figure 1 A schematic diagram of the leak detection module (LDM) of the system shown.

[0029] Figure 2AThis is a schematic diagram of an LDM configured to operate the system under negative pressure (vacuum) during a leak test procedure.

[0030] Figure 2B This is a schematic diagram of an LDM configured to operate the system under positive pressure (pressurization) during a leak test procedure.

[0031] Figure 3A This is a graph showing the entropy curves of fuel vapor in an aluminum fuel tank of the prior art, expressed in kPa vJ.

[0032] Figure 3B It is a graph of fuel vapor in the fuel tank, expressed in kPa vJ, based on the disclosed method and system.

[0033] Figure 4 It is the leakage rate of the fuel tank vacuum relative to the fuel level (no leakage). Very small leak Minor leak The following is a diagram showing the relationships between different relationships.

[0034] Figure 5 This is a flowchart depicting an example leak detection method that minimizes the effect of entropy in the fuel tank.

[0035] The embodiments, examples, and alternatives described in the foregoing paragraphs, claims, or the following description and drawings, including any one or corresponding individual features of their various aspects, can be obtained independently or in any combination. Features described in connection with one embodiment apply to all embodiments unless those features are incompatible. The same reference numerals in the various drawings indicate the same elements. Detailed Implementation

[0036] Figure 1 A portion of an exemplary evaporative fuel system 10 is schematically shown. System 10 includes a fuel tank 12 with a fuel filler 14 having a filler cap 16. A fuel pump 18 supplies gasoline, for example, from the fuel tank 12 to an internal combustion engine 20. A fuel level sensor 15 communicates with a controller 40 and measures the fuel level within the fuel tank 12, which is also related to the amount of fuel vapor within the fuel tank 12.

[0037] System 10 is configured to capture and regulate fuel vapor flow within the system. In one example, a fuel tank isolation valve 24 is fluidly disposed between the fuel tank 12 and the charcoal canister 22, which captures and stores fuel vapor for later use by the engine 20. A purge valve 26 is fluidly connected between the canister 22 and the engine 20. Controller 40 adjusts the position of the purge valve 26 to selectively supply fuel vapor to the engine 20 for utilization during operation.

[0038] The integrity of system 10 must be tested periodically to ensure that fuel vapor does not leak from system 10. One type of system 10 uses a leak detection module (LDM) 28, which can be used, for example, to evacuate and / or pressurize the system using a pressure transducer 52 to determine if a leak is present. In an exemplary leak test procedure, purge valve 26 is closed, and controller 40 operates leak detection module 28 to evacuate or pressurize the system. Another pressure transducer 50 can be used to monitor the pressure of fuel vapor within fuel tank 12 during other conditions. An optional ambient temperature sensor 54 communicates with controller 40. Temperature sensor 54 can be used to quantify the heat transfer characteristics of fuel vapor within fuel tank 12 relative to the ambient atmospheric temperature.

[0039] Figure 2 LDM 28 is schematically shown. LDM 28 includes a pump 30 arranged in a housing. An exemplary pump is disclosed in provisional application No. 62 / 910,708, filed on October 4, 2019, entitled “PUMP FOR EVAPORATIVE EMISSIONS SYSTEM,” which is incorporated herein by reference in its entirety. Some customers prefer to use systems operating under vacuum, while others prefer pressurized systems. Therefore, to provide pressurized evaporative emission system testing, pump 30 draws air from the atmosphere through filter 32 and directs the air to tank 22. Another filter 34 may be provided on the other side of pump 30 to protect the pump from debris. To provide depressurized or negative pressure evaporative emission system testing (i.e., vacuum), pump 30 draws air from tank 22 and expels it into the atmosphere.

[0040] When LDM 28 is not performing a leak check on fuel system 10, tank valve solenoid (CVS) 36 is in the open position to allow air to pass through the first fluid passage 60 between the rest of system 10 and the atmosphere. This allows system 10 to draw air from the atmosphere as needed.

[0041] While LDM 28 is performing a leak test on fuel system 10, CVS 36 is in the closed position, which provides a second fluid passage 62 on the side of tank 22. A CVS check valve 38 is arranged in the second fluid passage 62 and selectively isolates tank 22 from pump 30 and the atmosphere. Pressure transducer 52 is arranged to read the pressure in the second fluid passage 62 when CVS 36 is closed, although the pressure transducer can be used for other purposes.

[0042] LDM 28 contains the hardware necessary to determine whether system 10 has a leak to the atmosphere. During a leak test, depending on how the CVS check valve is used to separate pump 30 from the volume of air being checked for a leak, pump 30 can generate negative pressure (vacuum) or positive pressure in the evaporative discharge system depending on its direction of rotation as described above. Figure 2A The CVS check valve 38 used for negative pressure leakage testing is shown schematically. Figure 2B The CVS check valve 138 used for positive pressure leak testing is schematically shown. The leakage boundary of system 10 includes fuel filler 14 and cap 16, purge valve 26, fresh air side of tank 22 (the side connected to LDM 28), steam dome of fuel tank 12, and steam line connecting all components, including second fluid passage 62.

[0043] During the leak test, pressure transducer 52 is fluidly connected to the second fluid passage 62 and monitors the pressure conditions generated by pump 30 in system 10. Pressure transducer 52 communicates with controller 40, which determines whether there are pressure changes in the evaporative emission system over a predetermined amount of time that may indicate a leak. Any pressure changes detected by pressure transducer 52 and monitored by controller 40 indicate a leak. OBDII diagnostic system 42 communicates with controller 40 and uses the pressure information from pressure transducer to generate engine fault codes, which can be stored and used to illuminate the "Check Engine" light on the vehicle dashboard, indicating that vehicle maintenance is required.

[0044] Controller 40 and OBDII system 42 can be integrated or separated. In terms of hardware architecture, such a controller may include a processor, memory, and one or more input and / or output (I / O) device interfaces communicatively coupled via a local interface. The local interface may include, for example, but not limited to, one or more buses and / or other wired (e.g., CAN, LIN, and / or LAN) or wireless connections. The local interface may have additional components, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communication. Furthermore, the local interface may include address, control, and / or data connections to enable appropriate communication between the aforementioned components.

[0045] A controller can be a hardware device used to execute software, particularly software stored in memory. A processor can be a custom or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the controller, a semiconductor-based microprocessor (in the form of a microchip or chipset), or any device typically used to execute software instructions.

[0046] The memory may include any one or a combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, VRAM, etc.)) and / or non-volatile memory elements (e.g., ROM, etc.). Furthermore, the memory may include electronic, magnetic, optical, and / or other types of storage media. The memory may also have a distributed architecture, in which various components are located remotely to each other but are accessible by a controller.

[0047] Software in memory may include one or more individual programs, each comprising an ordered list of executable instructions for implementing logical functions. System components embodied as software may also be interpreted as source programs, executable programs (object code), scripts, or any other entity including a set of instructions to be executed. When constructed as a source program, the program is translated by a compiler, assembler, interpreter, etc., which may or may not be present in memory.

[0048] When the controller is in operation, the processor can be configured to execute software stored in memory, transfer data to and from memory, and typically control the operation of the computing device based on the software. The software in memory is read, in whole or in part, by the processor, possibly buffered within the processor, and then executed.

[0049] Reference Figure 3A The effect of entropy on system 10 makes rapid and effective leak detection more difficult. A typical leak test is performed by evacuating (shown; or pressurizing) fuel tank 12 to the target pressure. The effect of entropy 80 on the fuel tank wall and fuel vapor within fuel tank 12 is shown by curves 70 and 72, respectively. Heat transfer 82 is also shown.

[0050] Literature indicates that fuel evaporation under vacuum conditions is linear for a given temperature, resulting in a linear change in pressure. However, tests did not provide linear results. This is due to the nonlinear response of entropy and heat transfer changes. After reaching the target vacuum and sealing the system, the pressure initially decays at a nonlinear rate before becoming linear. The magnitude of the nonlinear response depends on the ambient temperature. The slope of the linear response is a consequence of fuel evaporation. For fuels of the same volatility, evaporation increases with temperature. Nonlinear responses are common for both vacuum and pressure systems. System entropy changes with pressure. Evacuating the sealed chamber leads to a decrease in entropy (a decrease in temperature), while pressurizing the sealed chamber leads to an increase in entropy (an increase in temperature).

[0051] The heat transfer rate depends on the fuel tank material and the temperature difference. For a fuel tank in equilibrium, the temperature inside the tank decreases as the vacuum (in the example shown) increases, resulting in a temperature difference between the tank walls and the atmosphere. After the tank is sealed, heat flows back to the vapor space through the tank shell until the air space is in equilibrium again.

[0052] Due to the laws of physics, eliminating entropy changes is impossible, but the effects of undesirable entropy changes can be mitigated. The disclosed method ( Figure 5 The effect of ) Figure 3B The method, illustrated graphically, mitigates the effects of entropy changes by evacuating / pressurizing system 10 to a first target pressure (first curve 80), keeping system 10 sealed to allow heat exchange (second curve 82), and then evacuating / pressurizing system 10 again to a second target pressure (third curve 86). The first and second target pressures correspond to the first and second entropy changes, respectively. The second entropy change is inherently smaller than the first entropy change, for example, 10% or less.

[0053] The ambient temperature measured by temperature sensor 54 can be used to determine, for example, how quickly to rapidly evacuate / pressurize system 10. In one example, the first and second target pressures are the same, for example, within 5% of each other. The duration of the second evacuation (or pressurization) can be significantly shorter than the initial evacuation or the first evacuation (or pressurization), resulting in a smaller entropy change and therefore less heat transfer requirement. In one example, the first and second evacuations of system 10 take a total of 15 to 120 seconds to reach the target pressure, at which point the system pressure is then held to determine if there is a pressure loss indicating a leak. Depending on the vapor space volume, this may take longer or shorter. After this process, a relatively constant pressure is generated due to a leak in the system rather than heat exchange (curve 88, shown as a leak-free condition). Of course, additional evacuation (or pressurization) can be performed, but the benefit will be much smaller compared to the second evacuation (or pressurization).

[0054] The pressure change following the second evacuation (or pressurization) may increase as the fuel level decreases due to greater exposure to the fuel tank wall temperature (infiltration in kPa during negative pressure testing; outfiltration in kPa during positive pressure testing). The fuel level is measured by fuel level sensor 15. This pressure change during the relatively constant pressure curve 88 is... Figure 4 The upward-sloping distribution is shown in the figure.

[0055] Figure 4The graph shows several leakage rates during the holding period (curve 88) of the fuel level test in fuel tank 12. System leakage can be the sum of several small leaks. "No leakage" condition (0.00 inch in system 10) Leakage is indicated by pressure distribution 90, which is sensed by pressure transducer 52. It should be understood that even a "leak-free" condition may not be airtight after about a minute. A very small leak (equivalent to approximately 0.020 inches in system 10) is also considered a leak. The leak lasted until approximately 0.040 inches. The leak (as shown by pressure distribution 92) is very small and can be interpreted by the OBDII diagnostic system 42 as, for example, “very small leak” corresponding to engine fault code P0456. The small leak condition (equivalent to approximately 0.040 inches in system 10) is described by pressure distribution 92. A leak (or larger) is indicated by pressure distribution 94. This small leak condition can be interpreted by the OBDII diagnostic system 42 as, for example, an engine fault code corresponding to P0442, "small leak". Since the system cannot be actually evacuated to the target vacuum within the predetermined time, the concept of "bleed up" may not apply to a total leak, and such a total leak condition may also result in an OBDII code.

[0056] During operation, Figure 5 A method 100 for detecting leaks in an evaporative emission system 10 is illustrated. The system 10 is sealed, and a first target pressure in the system is achieved, for example, by evacuating the system (box 102). After a predetermined time or other measure including the rate of change of a signal (e.g., pressure decay rate), a second target pressure in the system is achieved again by evacuating one or more times (box 104). The system pressure is maintained (box 106) and monitored (box 108) to determine the leakage condition of the evaporative emission system. Since additional evacuation (or pressurization) may be performed, the second target pressure may correspond to the pressure after one or more evacuations of the system. Leakage conditions include at least one of a no-leakage condition, a very small leak condition, and a small leak condition. If an unwanted pressure change (e.g., in time intervals or pressure decay rates) occurs during the system pressure maintenance, a leak is present in the system 10, and the on-board diagnostic system will generate an engine fault code in response to each of the very small leak condition and the small leak condition (box 110).

[0057] This approach mitigates the undesirable effects of entropy in the system, which would otherwise have a longer retention time before pressure monitoring could occur. Monitoring the pressure decay rate rather than the pressure changing over time may be preferable, as pressure monitoring over time depends on the volume of the steam dome, which could require an undesirable long time interval for large gas tanks.

[0058] It should also be understood that while a particular arrangement of components is disclosed in the illustrated embodiment, other arrangements will also benefit from it. Although a particular sequence of steps has been shown, described, and claimed, it should be understood that the steps may be performed, separated, or combined in any order unless otherwise indicated, and will still benefit from the invention.

[0059] While the different examples have specific components shown in the description, embodiments of the invention are not limited to those specific combinations. Parts of a component or feature from one example may be used in combination with components or features from another example. For example, the disclosed pump may be used in applications other than vehicle evaporation systems.

[0060] While exemplary embodiments have been disclosed, those skilled in the art will recognize that certain modifications will fall within the scope of the claims. Therefore, the following claims should be examined to determine their true scope and content.

Claims

1. A method of detecting a leak in an evaporative emission system, the method comprising the steps of: sealing the evaporative emission system; first activating a pump to achieve a first target pressure in the evaporative emission system; after achieving the first target pressure, leaving the evaporative emission system sealed for a predetermined measure that allows heat exchange to occur in the evaporative emission system, then second activating the pump to achieve a second target pressure in the evaporative emission system; and monitoring system pressure after the second target pressure achieving step to determine a leak condition of the evaporative emission system.

2. The method of claim 1, wherein, the first target pressure achieving step and the second target pressure achieving step are performed by drawing a vacuum on the evaporative emission system.

3. The method of claim 1, wherein, the first target pressure and the second target pressure are the same as each other.

4. The method of claim 1, wherein, the first target pressure achieving step and the second target pressure achieving step correspond to a first entropy change and a second entropy change, respectively, and the second entropy change is substantially less than the first entropy change.

5. The method of claim 4, wherein, the second target pressure achieving step is performed based on an ambient temperature.

6. The method of claim 1, wherein, the leak condition includes at least one of a no leak condition, a very small leak condition, and a small leak condition.

7. The method of claim 6, wherein, an on-board diagnostic system generates an engine fault code in response to each of the very small leak condition and the small leak condition.

8. The method of claim 1, wherein, the sealed evaporative emission system includes components including a filler and cap, a purge valve, a fresh air side of a carbon canister, a vapor dome of a fuel tank, and vapor lines connecting the components, the vapor lines including a second fluid passage, a pressure transducer fluidly connected to the components and the vapor lines, the system pressure monitoring step includes measuring system pressure with the pressure transducer.

9. The method of claim 8, wherein, the evaporative emission system sealing step includes closing a canister valve solenoid to close a first fluid passage to atmosphere.

10. The method of claim 9, wherein, each of the first target pressure achieving step and the second target pressure achieving step includes pumping fluid through a check valve.

11. An evaporative emission system, the evaporative emission system comprising: a fuel tank having a filler and cap, the fuel tank configured to contain fuel and fuel vapor; a carbon canister configured to store fuel vapor from the fuel tank; a purge valve in fluid communication with the carbon canister and configured to selectively provide fuel vapor to an engine in response to a purge command; a leak detection module including a canister valve solenoid, a pump, a check valve, and a pressure transducer, a first fluid passage fluidly connecting the canister valve solenoid to atmosphere, a second fluid passage fluidly connecting the carbon canister to the pump through the check valve, the pump fluidly disposed between the check valve and atmosphere; a controller in communication with the canister valve solenoid and the pressure transducer, the controller configured to run a leak test routine, the leak test routine including: closing the canister valve solenoid to seal the evaporative emission system; first activating the pump to achieve a first target pressure in the evaporative emission system; after achieving the first target pressure, maintaining the evaporative emission system sealed for a predetermined measure that allows heat exchange to occur in the evaporative emission system, and then second activating the pump to achieve a second target pressure in the evaporative emission system; and monitoring system pressure with the pressure transducer after achieving the second target pressure to determine a leak condition of the evaporative emission system.

12. The system of claim 11, wherein, the pump evacuates the evaporative emission system to achieve the first target pressure and the second target pressure.

13. The system of claim 12, wherein, the first target pressure and the second target pressure are the same as each other.

14. The system of claim 11, wherein, the first target pressure and the second target pressure respectively correspond to a first entropy change and a second entropy change, and the second entropy change is substantially less than the first entropy change.

15. The system of claim 14, wherein, the second target pressure achieving step is performed based on an ambient temperature.

16. The system of claim 11, wherein, the leak condition includes at least one of a no leak condition, a very small leak condition, and a small leak condition.

17. The system of claim 16, wherein, an on-board diagnostic system generates an engine fault code in response to each of the very small leak condition and the small leak condition.

18. The system of claim 11, wherein, a sealed evaporative emission system includes components including the fuel filler and the cap, the purge valve, a fresh air side of the carbon canister, a vapor dome of the fuel tank, and vapor lines connecting the components, the vapor lines including a second fluid passage, a pressure transducer fluidly connected to the components and the vapor lines.

19. The system of claim 18, wherein, a closed canister valve solenoid closes the first fluid passage to atmosphere.

20. The system of claim 19, wherein, each of the first target pressure and the second target pressure is achieved by pumping fluid through the check valve. the first target pressure and the second target pressure are achieved by pumping fluid through the check valve.

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