Patent Application
20200063697
The present disclosure relates to determining Reid vapor pressure of a fuel system with a bi-directional pump to detect leaks in the fuel system.
This section provides background information related to the present disclosure, which is not necessarily prior art.
Vehicle manufacturers and suppliers are continuously looking for cost effective methods and systems for detecting fuel system leaks. While current methods and systems are suitable for their intended use, they are subject to improvement. The present disclosure advantageously provides for improved methods and systems for detecting fuel system leaks that are more robust compared to current systems and methods for increasingly difficult standards.
This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.
The present disclosure includes a method for determining a Reid vapor pressure of a fuel system using a bi-directional pump located in the fuel system. The method includes: activating the bi-directional pump in a first direction until fuel pressure of the fuel system changes from a base level to a first predetermined fuel pressure, and deactivating the bi-directional pump when the fuel pressure reaches the first predetermined fuel pressure; recording a first rate of fuel pressure decay of the fuel pressure as the fuel pressure changes from the first predetermined fuel pressure to the base level; after the fuel pressure of the fuel system has returned to the base level, or after a predetermined period of time has expired, activating the bi-directional pump in a second direction opposite to the first direction until fuel pressure of the fuel system changes from the base level to a second predetermined fuel pressure, and again deactivating the bi-directional pump when the fuel pressure reaches the second predetermined fuel pressure; recording a second rate of fuel pressure decay of the fuel pressure as the fuel pressure changes from the second predetermined fuel pressure to the base level; and determining the Reid vapor pressure to be calculated by a difference between the first rate of fuel pressure decay and the second rate of fuel pressure decay.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of select embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to the accompanying drawings.
With additional reference to
The fuel system 10 further includes a control module 50. The control module 50 is configured to control at least the bi-directional pump 20, the canister vent solenoid valve 30, the canister purge valve 36, and the fuel tank isolation valve 28. The control module 50 further receives inputs from the pressure sensor 26 identifying the fuel pressure of the fuel system 10. In this application, including the definitions below, the term “control module” may be replaced with the term “circuit.” The term “control module” may refer to, be part of, or include processor hardware (shared, dedicated, or group) that executes code and memory hardware (shared, dedicated, or group) that stores code executed by the processor hardware. The code is configured to provide the features of the modules, controllers, and systems described herein. The term memory hardware is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium is therefore considered tangible and non-transitory. Non-limiting examples of a non-transitory computer-readable medium are nonvolatile memory devices (such as a flash memory device, an erasable programmable read-only memory device, or a mask read-only memory device), volatile memory devices (such as a static random access memory device or a dynamic random access memory device), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).
With reference to
With initial reference to block 212 of the method 210, the control module 50 opens the canister vent valve 30. At block 214, the control module 50 activates the bi-directional pump 20 in a first direction (such as to create positive pressure as illustrated in
After the fuel pressure has returned to the base level (or after a predetermined time interval, for example), the control module 50 reopens the canister vent valve 30 at block 220. Also, the control module 50 activates the bi-directional pump 20 in a second direction (such as to create a vacuum as illustrated in the example of
From blocks 218 and 226 the method 210 proceeds to block 228. At block 228, the control module 50 compares the first rate (slope K1) and second rate (slope K2) of fuel pressure decay. The difference between the first and second rates K1 and K2 can be used by the control module 50 to calculate a current Reid vapor pressure (see block 230), as explained below.
K2-K1 is the decay rate difference in the vacuum pressure check and the positive pressure check (i.e. the pressure rise resultant from vapor generation). The first step in solving K2-K1 is to solve for the air/fuel volume evacuated during the K2 check. This includes determining how much vapor was evacuated from the fuel tank 24 during the vacuum pressure check of block 214 or block 222. The contents of the tank 24 are assumed to be perfectly mixed (fuel vapor and air particles). The volume of air/fuel evacuated is calculated based on the K2 pressure set point (a factor that may be arrived at subsequent to a series of trials) and the vapor space volume of the tank 24 (total fuel space volume—current amount of fuel in the vehicle). P1V1=P2V2 is used to calculate the volume of air+fuel evacuated from the fuel tank 24, where: P1=atmospheric; P2=atmospheric—K2; V1=vapor volume; and V2=solved parameter). The vapor pressure generated while the fuel tank 24 is in vacuum during the K check is assumed to be 0 because the check will be very short in time for a low K2 pressure set point and high flowing pump. The volume from the tank (V1-V2) evacuated is thus known.
In the second step, the fuel vapor portion of the evacuated volume (V1-V2) calculated above is estimated by using an estimated RVP value and the measured fuel temperature. The estimated RVP value can be obtained from a previous leak check RVP calculation, or in any other suitable manner. RVP and temperature are used to obtain the vapor pressure of the fuel vapor using the Antoine Equation. The rule of partial pressures is then used to calculate the percent air/fuel mixture and the corresponding portion of the evacuated volume that belonged to the fuel vapor.
In the third step, the vacuum decay measured in K2 is then predicted using the estimated initial fuel vapor amount in the tank (fuel vapor concentration×V) from step 2 and the new fuel vapor amount (fuel concentration×V2) also calculated in step 2. These parameters are paired with a time that K2 was measured across (determined by the engineer). All of these parameters are included in the following Fick's second law of diffusion calculation:
Boundary conditions are set with the initial vapor concentration (Ci=XX %) and the new vapor concentration (Cf=XX %), where Cf is higher than Ci due to vapor generation. Ci=Initial vapor volume/V1, and Cf=Initial vapor volume +V1-V2/V1. D is a known mass diffusivity coefficient of the fuel. The equation is integrated to determine the rate of vapor evaporation and thus the pressure generation rate K2e. K2e is the estimated K2 based on the estimated RVP from Step 2.
In the fourth and final step, the measured K2 is compared to the estimated K2e. If the values are within a predetermined range of one another, then the estimated RVP is taken to be the real fuel RVP and the solution is found. If the K2 and K2e values are not within the predetermined range (and thus too far apart), RVP is re-estimated based on the difference (i.e. if K2e is greater than K2 then the RVP estimate is lowered by a pre-determined amount) and the process returns to step 2. This process is repeated until an acceptable comparison is made.
Depending on the solved RVP value, different leak check tables can be used, such as the table of
With additional reference to
With reference to
The measured fuel pressure decay rate (arrived at based on determining the Reid vapor pressure using the method 210 a plurality of times over any suitable predetermined period) is compared to the reference fuel pressure decay rates of
The present disclosure thus advantageously provides for the method 210 for identifying a Reid vapor pressure of the fuel system 10 based on use of the bi-directional pump 20. The determined Reid vapor pressure is then compared to reference Reid vapor pressures by the control module 50 associated with a no-leak condition and various leak conditions of different sizes. Based on th comparison, the control module 50 determines whether or not a leak condition is present in the fuel system 10. The use of the bi-directional pump 20 in accordance with the present disclosure to identify the Reid vapor pressure provides cost advantages and various other efficiencies as one skilled in the art will appreciate. Based on the determined Reid vapor pressure, the control module 50 is configured to modify an air-fuel ratio of the engine 12 to increase fuel economy and overall engine performance. One skilled in the art will appreciate that the present disclosure provides numerous additional advantages and unexpected results in addition to those specifically described herein.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
This application claims the benefit of U.S. Provisional Application No. 62/722,503, filed on Aug. 24, 2018, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62722503 | Aug 2018 | US |
