Thermal Management: Key-Off & Soak

Transcription

1 Thermal Management: Key-Off & Soak A whitepaper discussing the issues automotive engineers face every day attempting to accurately predict thermal conditions during thermal transients Exa Corporation 2015/16

2 CREDITS General Motors US EPA CONTACT Exa Corporation 55 Network Drive Burlington, MA USA Copyright 2015 Exa Corporation

3 THERMAL MANAGEMENT: KEY-OFF & SOAK Introduction One of the biggest concerns for thermal engineers is how to manage thermal transients after the vehicle has stopped running, a situation referred to as keyoff and soak conditions. During the key-off and soak, the underhood surface temperatures usually increase since there is little or no cooling airflow (unlike while the vehicle is operating). The impact of rising surface temperatures increases the risk of underhood component damage, part failures and even fires. Thermal engineers must identify the peak underhood temperatures. Mitigating these high temperatures by relocating sensitive components is extremely difficult due to the competing demands of vehicle safety, packaging, aesthetic design and performance. Achieving underhood thermal design objectives becomes nearly impossible with traditional testing which is time-intensive, expensive and often performed too late in the design process to have an impact. Exa PowerFLOW simulations enables thermal engineers to accurately predict a vehicle s underhood temperature during key-off and soak early in the design cycle, when design changes are more easily accommodated and long before physical prototypes are built. These simulations, coupled with the ability to visualize the flow and component temperatures, help thermal engineers gain insight on how to improve the vehicle design and propose and analyze new designs cheaper and faster Exa Corporation 3

4 Key Drivers Today, there are several key factors driving the automotive industry that affect thermal engineers: 1. Rising fuel economy/co 2 emissions regulations Rapidly increasing fuel economy and CO 2 requirements are driving improvements in aerodynamics that pressure thermal engineers to eliminate any excess cooling airflow into the engine compartment as well as reduce the size of the engine compartment itself. 2. Lightweighting In addition to aerodynamics, fuel economy improvements are driving the industry to reduce the weight of the vehicle. Lightweighting is driving the use of thinner materials and plastics that are less thermal resistant than the materials they are replacing. 3. Increasing vehicle particulate emissions standards Particulate tailpipe emissions impact air quality and cause related health risks. Government regulatory agencies continue to lower the amount of allowable vehicle particulate emissions. This is driving vehicle manufacturers to incorporate additional after-combustion exhaust treatment devices such as close-coupled catalytic converters and particulate filters that run at extremely high temperatures. Key-off and soak challenges are directly related to these key drivers, and engineers must evaluate them early in the design process. Cumbersome late-stage physical testing makes it exceedingly tough for thermal engineers to find the right balance between fuel economy and CO 2 requirements, part costs and particulate emissions standards during vehicle design all while managing the thermal performance of the vehicle. Problem In the traditional design process, thermal engineers use prototype testing in climatic wind tunnels to measure vehicle underhood and underbody temperatures. While prototype testing provides some component temperature data, it remains extremely challenging for thermal engineers to understand heat transfer and fluid flow conditions. Due to these physical test limitations, engineers lack the insights they need to improve the design to meet the temperature requirements.»» Schematic of a vehicle in a climatic wind tunnel

5 THERMAL MANAGEMENT: KEY-OFF & SOAK»» EPA CO 2 and fuel economy charts demonstrate how fast vehicles are changing due to regulations. Credit: US EPA Key-off and soak challenge thermal engineers in several ways, including: Limitation of physical testing Thermal testing on a physical prototype in a wind tunnel is difficult and often performed far too late in the process to make a design impact because it requires a physical prototype. Physical testing also need time-intensive preparation, calibration and proper shielding of thermocouples from radiation when running the tests. Measurements can be inaccurate and range at least ±10 C from the actual underhood part temperatures. Additionally, engineers cannot visualize flow or heat transfer during key-off and soak using a wind tunnel making it hard to understand what is happening. Late-stage design failures Physical prototypes are built late in the development cycle, when design changes are difficult to implement and deploying these modifications is expensive (or even impossible) and time-consuming. Most solutions available in the late development stage add significant cost and (sometimes) weight to the vehicle as thermal engineers are forced to add heat shields or switch components to higher temperature-rated materials. Warranty issues High temperatures during key-off and soak increase the risk that vehicle components degrade or fail faster, causing automakers to spend more on warranty and recall expenses. Edmunds.com reported that roughly 1 million vehicles were recalled in the United States in 2014 due to engine and cooling problems, which represents only a small fraction of the worldwide total. These warranty or recall problems damage an automaker s bottom line and lower their J.D. Power rating. Given that there is increasing pressure from the global automotive marketplace to shorten the vehicle design process and improve vehicle quality, it is clear that a more effective method is required to address the rising thermal challenges presented during key-off and soak situations Exa Corporation 5

6 THERMAL MANAGEMENT: KEY-OFF & SOAK The Exa Solution Thermal engineers use PowerFLOW simulations to accurately predict real world flow problems and find out exactly how underhood components will perform before physical prototypes are built. Unlike physical tests, PowerFLOW (coupled with Exa PowerTHERM ) simulations provide the accuracy and visual insights that thermal engineers can use to learn about key-off and soak early in the design cycle. These insights empower thermal engineers to quickly implement data-driven design changes to verify key-off and soak performance improvements with confidence. The combination of PowerFLOW s transient flow and heat transfer capabilities with PowerTHERM s capabilities to simulate heat conduction in solids and radiation effects, allows thermal engineers to streamline the vehicle design process. Power- FLOW and PowerTHERM together enable thermal engineers to accurately predict the peak underhood temperatures during key-off and soak and visualize the flow and temperature fields for the entire vehicle. PowerFLOW and PowerTHERM ensure that thermal engineers are able to better understand flow and thermal conditions that cause problems related to key-off and soak and take the necessary steps to reduce these issues without significant investments in costly, timeintensive physical prototypes. Post simulation, Exa PowerVIZ provides thermal engineers fast, interactive visualizations of simulation data sets and offers them the ability to easily combine different techniques, all within the same scene. With PowerVIZ, thermal engineers can move slices, point probes and streamline rakes and particle sources throughout the fluid domain to observe how flow patterns evolve and change over extended periods of time. This helps engineers see their simulation data to determine how to thermally optimize their vehicles throughout the design process. This ability to visualize the flow and heat transfer enables cross-team communication and fosters collaboration. Benefits The Exa product suite offers thermal engineers the ability to conduct fully detailed simulations that they can use to identify problems and assess potential solutions of thermal issues during keyoff and soak. The Exa product suite is capable of handing even the most detailed geometries and allows thermal engineers to better understand exactly what is happening. Exa s product suite provides many benefits for engineers, including: Accurate results Thermal engineers run PowerFLOW simulations to calculate fluid flows and heat transfer to get timely answers to important design questions. Accurate simulations (due to PowerFLOW s robust handling of complex geometry details and transient flow solver) help thermal engineers confidently predict thermal behavior relating to key-off and soak. Actionable insights With PowerFLOW, thermal engineers can fully understand (through visualization) a vehicle s powertrain thermal behavior and determine early in the design process whether heat shields, insulating materials or better component placement are viable options to safeguard sensitive components against overheating. Reduced costs The PowerFLOW product suite enables thermal engineers to understand the airflow and temperatures during thermal transients much earlier in the design process, reducing the occurrence of late-stage vehicle design problems that cause added product costs. The product suite helps automakers reduce warranty and recall expenses associated with keyoff and soak that would damage their revenues and reputations Exa Corporation

7 THERMAL MANAGEMENT: KEY-OFF & SOAK Conclusion Elevated temperatures during key-off and soak conditions increase the risk of premature underhood component failures; therefore, thermal engineers must find ways to reduce problems that occur after key-off to improve vehicle design. Physical testing limits thermal engineers ability to assess temperatures during thermal transients early in the design process and requires costly, time-intensive prototypes. Accurate testing is essential for automakers to avoid expensive vehicle warranty and recall issues, significant revenue loss and irreparable reputation damage. The Exa product suite offers thermal engineers the ability to evaluate key-off and soak in an accurate, streamlined manner that is impossible to duplicate with physical testing. Exa simulations enable thermal engineers the ability to collect up front knowledge and make design decisions based on actionable, accurate insights empowering them to produce better vehicle designs.»» Exa key-off and soak simulation: image displays the hot air rising in the engine compartment after the vehicle is parked Exa, PowerFLOW, PowerTHERM and PowerCOOL are registered trademarks of Exa Corporation Exa Corporation 7

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