Patent Application
20230258711
The present disclosure relates to a leak testing system. More specifically, the present disclosure relates to a leak testing system for reducing stabilization times.
Leak testing requires accurate measurements of very small flow rates of a gas or liquid within what may in some instances be made for a large volume. Typically, testing results are measured as a flow rate, such as standard cubic centimeters per minute (sccm) or cubic centimeters of helium per second (cc/s He) and millibar liters per second (mbar.1/s) and may, according to application, range from 10−3 to 10−12 mbar.1/s. In some cases, the leak flow rate is correlated to a “virtual pinhole,” to quantify the size of potential defects. For example, to prevent contamination, in small volume leak testing, a sterilized medical package must be sealed such that a “virtual pinhole” in the product is smaller than the size of the smallest microorganism (commonly 0.2 μm in diameter). This theoretical pinhole dimension and the leak flow rate are correlated to each other.
Irrespective of the actual component, device, part, product and/or system being leak tested, the balance of speed, accuracy, and cost of testing exists. While increased speed (reduced time) of leak testing reduces cost per unit, this however may lead to increased costs from yield (as rejections may actually have passed with an increased accuracy test) and/or product failures and customer impact (as products failing at the customer which were incorrectly passed impact yield, customer satisfaction, and in critical cases, may lead directly to damages payable by the manufacturer). Accordingly, there is considerable benefit to manufacturers in increasing accuracy, increasing speed, and increasing defect detection in manufacturing leak testing.
Additionally, some scenarios present further issues, such as, for example, large volume leak testing. Leak testing with large part volumes in, for example, 100 L (approximately 26.4 gallons) and above range, creates additional challenges including temperature sensitivity and pressure sensitivity. For example, in an electric vehicle (EV), one challenge in manufacturing electric vehicles is ensuring the performance of large battery packs which power the vehicles. A leaking battery is more than just an inconvenience, but a safety issue. Specifically, the most common type of EV battery (e.g., lithium ion) can burst into flame or even explode if there is a leak. All components of an EV battery are vulnerable to leaks. For example, the cells, the modules, the cooling components, and the packs themselves that make up the final assembly are all susceptible. In all cases, part size, accepted leak rate, and temperature are key variables. As a first step in ensuring a reliable leak test for EV battery packs, the manufacturer must understand the impact that product design and material selection choices will have on establishing the proper test specification and test method.
There are different pneumatic leak test methods including pressure decay, mass flow and pressure or vacuum each having their own testing strengths and weaknesses as they pertain to the unique physical characteristics of a pack. These test methods are generally governed by the ideal gas law: pressure (P)×volume (V)=amount of gas in moles (n)×universal gas constant (R)×absolute temperature (T) of the gas or PV=nRT.
While the focus of pneumatic leak testing is changes in pressure and flow, changes in temperature and volume have a significant effect on the measurement. For instance, to stimulate a leak the pressure of the gas in a part (e.g., battery pack) or outside the part is changed to create a differential pressure between the inside and outside of the part. This change in pressure creates a temperature change of the gas. This temperature change needs to dissipate, and as this heat transfer occurs the pressure and flow will change independently of the leak. For some leak tests, a significant portion of time is dominated by this thermal heat transfer between the compressed fluid and the part and/or ambient environment. The duration of these thermal effects is affected by surface area and part volume, i.e., typically as the part increase in size, stabilization times get longer.
Some approaches in resolving the stabilization time are to: wait for the thermal stabilization to occur, subtract the thermal effects from the leak estimate as a fixed offset, or measure the thermal effects and compensate for the effect. However, all these approaches are time consuming and can still result in inaccurate measurement readings.
Accordingly, there remains a need to improve leak testing methods and reduce stabilization times in gas-based testing.
In an exemplary embodiment, a system and method for reducing stabilization times are provided. The system includes at least a device-under-test (DUT), a flow generator, and optionally a heat exchanger to accelerate a thermal stabilization of fluid in the DUT during and after it has been filled with test gas. The flow generator increases the rate of heat transfer. The heat exchanger rapidly equilibrates the temperature of the fluid in the DUT to the heat exchange medium, thereby reducing temperature differentials. The reduced magnitude of the temperature differential reduces the flows associated with temperature change of the fluid due to thermal stabilization. As a result, this allows the leak test measurement to be made in less time, or for more of the cycle time to be used for leak measurement and, thus increase the accuracy of the test measurement.
In a further exemplary embodiment, a system for reducing stabilization times in leak testing is provided. The system includes a circulation loop external to the device-under-test (DUT) comprising an isolation valve disposed near an inlet of the loop, a flow generator configured to circulate a fluid through the loop, a heat exchanger configured to regulate the temperature of the fluid received from the flow generator, an isolation valve disposed near the outlet of the loop, and a controller for selectively operating the isolation valves, flow generator and the heat exchanger during various stages of the leak testing.
In yet a further embodiment, a method for reducing stabilization times in leak testing comprises operating a two isolation valves to remove the circulation loop and isolate a device-under-test (DUT), operating a flow generator to ON during a fill stage and a stabilization stage, operating a heat exchanger to ON during the fill stage and the stabilization stage, and operating the flow generator and the heat exchanger to ON or OFF during a test stage and an exhaust stage. The isolation valves can optionally CLOSE remove the loop during the test stage but are OPEN during the fill, stabilize and exhaust stages.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
It should be noted that these Figures are intended to illustrate the general characteristics of methods, structure and/or materials utilized in certain example embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties encompassed by example embodiments. For example, the relative thicknesses and positioning of layers, regions and/or structural elements may be reduced or exaggerated for clarity. The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature.
The present disclosure relates to leak testing, more specifically, leak testing to significantly reduce thermal stabilization times of a gas in a device-under-test (DUT). The present disclosure demonstrates and/or provides the benefits of, such as, effect of increased flow rate on stabilization time reduction, necessity of the heat exchanger in steady state operation, ability to reduce the stabilization time to that of a single air exchange through the heat exchanger, and/or inclusion of isolation valves so as a) to eliminate any leaks from a blower loop, b) to reduce the temperature rise of the blower, and/or c) to eliminate the need for a heat exchanger.
A “device-under-test” (DUT) as used herein and throughout this disclosure, refers to an item being tested for a leak. This includes, but is not limited to, devices, parts, components, packages, packaging, containers, piping systems, individual elements, sub-systems and systems requiring that they isolate the interior from the ambient exterior. A DUT may or may not be intended to form part of a hydraulic, pneumatic, or fluidic system.
A “leak test” as used herein and throughout this disclosure, refers to processes and/or methods of determining whether a DUT has a leak which may, for example, comprise placing the DUT under a positive pressure relative to its environment and determining attributes of the pressure/flow to determine the rate of leakage from the DUT. However, leak test as used herein is not limited to positive pressure testing and may include, but not be limited to, negative pressure leak testing wherein DUTs cannot be placed under positive pressure. Such testing may be performed with a fluid including, for example, air, nitrogen, helium and other gases, as well as water, silicone oil, and other liquids.
One of the longest delays in leak testing is during a stabilization phase. In this phase, the heat that has been added to the gas through the compression of the gas inside the DUT during a fill portion of the leak test is dissipating into an inside surface of the DUT. As this air inside the DUT exchanges heat with the inside surface of the DUT, the pressure in the DUT drops in a pressure decay test (or an increased flow is measured in a flow-based test) or the pressure reaches equilibrium in a mass flow leak test. These processes can take time and are controlled by the physical characteristics of fluid and the inside surface of the DUT including volume of air, velocity of air, inside surface area, inside surface geometry, and inside surface finish.
The system 10 includes the DUT 20 to be tested for leaks. The DUT 20 may be any part to be leak tested with typical volumes ranging from 1 L (0.264 gallons) to 1000 L (264 gallons). System 10 can also be used for leak testing under 1 L, but the severity of the fluid temperature effect increases with volume and test pressure, so there is a cost-benefit aspect to consider when applying this technology. In an example implementation, the DUT 20 is a sealed battery component for an electric vehicle (EV). More specifically, the DUT 20 can be a battery coolant loop, the battery enclosure or tray, a fully assembled battery pack, etc. In another implementation, the DUT 20 can be part of an internal combustion engine, such as, for example, an oil cavity, a fuel rail, etc.
During the fill and stabilization phases of the leak testing, the DUT 20 is filled with fluid (e.g., air) by the leak tester 85, such that the fluid inside the DUT 20 is at a different pressure than that outside the DUT 20. This pressure differential stimulates the leak which is to be measured. The work done on the fluid to change the pressure results in the fluid changing temperature relative to the DUT 20, such that heat transfer between the fluid and the DUT 20 will occur until it reaches equilibrium. When thermal equilibrium is achieved, which means the fluid inside the DUT 20 and the material comprising the DUT 20 are the same temperature, the measured leak can be obtained. If thermal equilibrium is not achieved, the measured leak is influenced by the rate of change of temperature associated with heat transfer. A correction and its associated uncertainty must be applied to compensate for the thermal stabilization, which will decrease repeatability compared to a system where the thermal stabilization is substantially more complete. For instance, while the temperature is stabilizing, the leak can be estimated by subtracting the estimated flow associated with the temperature change from the total flow into the DUT 20. It is difficult to measure the flow associated with the temperature change independently, and so this subtraction is prone to significant error.
In order to advance thermal stabilization, the system 10 includes a flow generator 30 and a heat exchanger 40 connected in series forming a circulation loop with the DUT 20. The flow generator 30 increases the velocity of the fluid and thus the rate of collisions between the fluid and the DUT 20, thereby increasing the rate of heat transfer between the DUT 20 and the fluid. In some implementations, the heat exchanger 40 is positioned after the flow generator 30 to regulate the temperature of a fluid in the DUT 20 to that of the heat exchange medium. More specifically, the heat exchanger 40 can regulate the temperature of the fluid by removing the heat produced by the flow generator 30 in addition to the heat in the fluid medium resulting from the test. Using the ambient environment as the heat exchange medium equilibrates the temperature of the fluid in the DUT 20 and the part itself to the ambient environment, thereby reducing temperature differentials. As a result, this reduces the magnitude of the thermally induced flow and reduces the need for temperature compensation strategies, improving the accuracy of the measurement.
The system 10, including the DUT 20, the flow generator 30, the heat exchanger 40, and tubing 60, is a sealed system. That is, the system 10 has a sealed path from an inlet 23 to an outlet 24 forming a loop. The inlet 23 and the outlet 24 of the loop should be designed to maximize fluid exchange with the DUT 20. Typically, this involves having the inlet 23 and the outlet 24 at different ports. In other implementations, the system 10 can include only one port. When the system 10 includes only one port, efforts should be taken to orient the inlet and outlet paths within the DUT 20 so that the loop has fluid that represents an average fluid temperature in the DUT 20.
If either the flow generator 30 or the heat exchanger 40 or any other part of the circulation loop leak, or substantially increase the test volume, it may be desirable to remove the circulation loop from the leak test during the leak measurement. In one implementation, this can be accomplished by the addition of two optional isolation valves 51 and 52 on the inlet 23 and outlet 24 of the circulation loop.
Referring to
The flow generator 30 facilitates the reduction in stabilization times for thermal equilibrium by increasing the rate of heat transfer between the air and the DUT 20. For example, the graph of
When powered, the flow generator 30 or 30a produces heat due to losses and the work it is doing to accelerate the fluid medium. If significant to the leak test this heat is undesirable and should be removed. In some implementations, a heat exchanger 40 is positioned after the flow generator 30 or 30a to regulate the temperature of the fluid by removing the heat produced by the flow generator 30 or 30a in addition to the heat in the fluid medium resulting from the test. For illustration, as shown in
In other implementations,
Referring to TABLE 1, there is shown resulting stabilization times when operating the flow generator shown in
As depicted in
It should be appreciated that the schematic diagram shown in
In alternative “egress” testing, as shown in
In some implementations, other devices may be employed to further enhance the accuracy of the leak testing. For example, a pressure regulator can be used to keep the fluid pressure at a desired test pressure and/or a flow sensor to measure the flow of fluid to the DUT and/or to other devices. In some implementations, a filter may be coupled to the source to filter the fluid. The filter may also be coupled near the pressure regulator.
In some implementations, control methods can be used to minimize the heat generated by the flow generator, and thereby reduce the need for an active heat exchange. Leak testing is typically broken down into fill, stabilize, test, and exhaust test stages. During the fill and stabilize test stages, the flow generator and heat exchanger should be ON. During all other test and exhaust stages, the flow generator and heat exchanger can be turned OFF to reduce any noise the flow generator and/or heat exchanger introduce into the measurement through turbulence. This approach also saves power and reduces the heat generated by the active devices.
Implementation of the techniques, blocks, steps and means described above may be done in various ways. For example, these techniques, blocks, steps and means may be implemented in some instances as electronic circuits which may comprise hardware, software, or a combination thereof. For a hardware implementation, the processing units may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described above and/or a combination thereof.
Also, it is noted that the embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process is terminated when its operations are completed, but could have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination corresponds to a return of the function to the calling function or the main function.
Furthermore, embodiments may be implemented by hardware, software, scripting languages, firmware, middleware, microcode, hardware description languages and/or any combination thereof. When implemented in software, firmware, middleware, scripting language and/or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine readable medium, such as a storage medium. A code segment or machine-executable instruction may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a script, a class, or any combination of instructions, data structures and/or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters and/or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, etc.
For a firmware and/or software implementation, the methodologies may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. Any machine-readable medium tangibly embodying instructions may be used in implementing the methodologies described herein. For example, software codes may be stored in a memory. Memory may be implemented within the processor or external to the processor and may vary in implementation where the memory is employed in storing software codes for subsequent execution to that when the memory is employed in executing the software codes. As used herein the term “memory” refers to any type of long term, short term, volatile, nonvolatile, or other storage medium and is not to be limited to any particular type of memory or number of memories, or type of media upon which memory is stored.
Moreover, as disclosed herein, the term “storage medium” may represent one or more devices for storing data, including read only memory (ROM), random access memory (RAM), magnetic RAM, core memory, magnetic disk storage mediums, optical storage mediums, flash memory devices and/or other machine readable mediums for storing information. The term “machine-readable medium” includes, but is not limited to portable or fixed storage devices, optical storage devices, wireless channels and/or various other mediums capable of storing, containing or carrying instruction(s) and/or data.
The methodologies described herein are, in one or more embodiments, performable by a machine which includes one or more processors that accept code segments containing instructions. For any of the methods described herein, when the instructions are executed by the machine, the machine performs the method. Any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine are included. Thus, a typical machine may be exemplified by a typical processing system that includes one or more processors. Each processor may include one or more of a CPU, a graphics-processing unit, and a programmable DSP unit. The processing system further may include a memory subsystem including main RAM and/or a static RAM, and/or ROM. A bus subsystem may be included for communicating between the components. If the processing system requires a display, such a display may be included, e.g., a liquid crystal display (LCD). If manual data entry is required, the processing system also includes an input device such as one or more of an alphanumeric input unit such as a keyboard, a pointing control device such as a mouse, and so forth.
The memory includes machine-readable code segments (e.g. software or software code) including instructions for performing, when executed by the processing system, one of more of the methods described herein. The software may reside entirely in the memory, or may also reside, completely or at least partially, within the RAM and/or within the processor during execution thereof by the computer system. Thus, the memory and the processor also constitute a system comprising machine-readable code.
In alternative embodiments, the machine operates as a standalone device or may be connected, e.g., networked to other machines, in a networked deployment, the machine may operate in the capacity of a server or a client machine in server-client network environment, or as a peer machine in a peer-to-peer or distributed network environment. The machine may be, for example, a computer, a server, a cluster of servers, a cluster of computers, a web appliance, a distributed computing environment, a cloud computing environment, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. The term “machine” may also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein.
The aspects and embodiments of the invention can be used alone or in combinations with each other.
The articles “a” and “an,” as used herein, mean one or more when applied to any feature in embodiments of the present disclosure described in the specification and claims. The use of “a” and “an” does not limit the meaning to a single feature unless such a limit is specifically stated. The article “the” preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used. The adjective “any” means one, some, or all indiscriminately of whatever quantity.
“At least one,” as used herein, means one or more and thus includes individual components as well as mixtures/combinations.
The transitional terms “comprising”, “consisting essentially of” and “consisting of”, when used in the appended claims, in original and amended form, define the claim scope with respect to what unrecited additional claim elements or steps, if any, are excluded from the scope of the claim(s). The term “comprising” is intended to be inclusive or open-ended and does not exclude any additional, unrecited element, method, step or material. The term “consisting of” excludes any element, step or material other than those specified in the claim and, in the latter instance, impurities ordinarily associated with the specified material(s). The term “consisting essentially of” limits the scope of a claim to the specified elements, steps or material(s) and those that do not materially affect the basic and novel characteristic(s) of the claimed disclosure. All materials and methods described herein that embody the present disclosure can, in alternate embodiments, be more specifically defined by any of the transitional terms “comprising,” “consisting essentially of,” and “consisting of.”
Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that, if an element is referred to as being “connected” or “coupled” to another element, it can be directly connected, or coupled, to the other element or intervening elements may be present. In contrast, if an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements 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.).
Spatially relative terms (e.g., “beneath,” “below,” “lower,” “above,” “upper” and the like) may be used herein for ease of description to describe one element or a relationship between a feature and another element or feature as illustrated in the figures. It will be understood that the spatially relative terms are 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, for example, the term “below” can encompass both an orientation that is above, as well as, below. The device may be otherwise oriented (rotated 90 degrees or viewed or referenced at other orientations) and the spatially relative descriptors used herein should be interpreted accordingly.
Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, may be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but may include deviations in shapes that result, for example, from manufacturing.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
Specific details are given in the above description to provide a thorough understanding of the embodiments. However, it is understood that the embodiments may be practiced without these specific details. For example, circuits may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments.
| Number | Date | Country | |
|---|---|---|---|
| 63268161 | Feb 2022 | US |
