Materials for thermal management systems in battery electric vehicles Automotive
- The transition to battery electric vehicles is underway
- Thermal management systems and their key functional units
- Battery electric vehicles (BEVs) offer an increasingly ubiquitous alternative to conventional gasoline vehicles. In BEVs, the gasoline engines of conventional vehicles are replaced by three primary modules: a motor, a battery, and an inverter.
- The finite energy-storage capacity of batteries restricts the total distance that BEVs can travel without recharging, and creates a powerful incentive for electric vehicles to use energy as efficiently as possible to achieve adequate travel distances. One important strategy for ensuring energy efficiency is to regulate the operating temperatures of motors, batteries, and other vehicle components, ensuring that these components always remain within their optimal operating-temperature range.
- Consequently, BEVs incorporate specialized functional units responsible for regulating component temperatures; these units are known as thermal management systems. A thermal management system comprises three primary units—an air conditioning, a battery, and a powertrain—and incorporates a variety of cooling and heating mechanisms and various functional components. The structure of these units, and the nature of their interoperation, are chosen carefully in accordance with design objectives regarding travel distance, cost, and other factors, and they play a key role in overall vehicle design.
- Asahi Kasei’s engineering plastics have been used as materials for a wide range of components for thermal management systems. In particular, sophisticated technical support services—which include shape-optimized design proposal and accurate predictions of component performance using Computer-Aided Engineering (CAE) simulations—have helped accelerate product development processes.
The transition to battery electric vehicles is underway—but key challenges remain
All around the world—and especially in Europe and China—the automobile industry is in the midst of a rapid transition from conventional gasoline-fueled vehicles to battery electric vehicles (BEVs). In BEVs, the gasoline engines in conventional vehicles are replaced by three primary modules: a motor, a battery, and an inverter.
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Although BEVs are more energy-efficient than engine-powered vehicles, their batteries can store only limited quantities of energy, and thus the motors and batteries of BEVs must operate with high efficiency to ensure satisfactory performance. The temperature of these components tends to increase when in use, and strategies for offsetting these increases—to maintain each component within its optimal operating temperature range—are crucial for increasing energy efficiency and extending travel distances. Such strategies are known as a thermal management technology. Historically, thermal management systems for BEVs were typically implemented separately for each individual functional unit in isolation—one for the battery, another for the powertrain, and a third for the air conditioning, each operating independently from the others—but more recent vehicle designs have begun to address thermal management as a system-wide challenge demanding unified, comprehensive solutions.
As the following discussion makes clear, thermal management considerations play key roles in all three cases.
A) Extending travel distance
The finite energy storage capacity of vehicle batteries imposes a limit on the total distance a vehicle can travel without recharging. Larger batteries can store more energy, but also weigh more and occupy more space, resulting in heavier vehicles with cramped interiors. Consequently, strategies for reducing power consumption are of primary importance. Aside from the challenges of improving the efficiency of motors and batteries, one major problem is the need for heaters to serve as heat sources. In contrast to gasoline vehicles, whose engines serve as major heat sources due to exhaust-gas emissions, electric vehicles have no intrinsic heat sources and must instead be equipped with external heating elements. For most BEVs, these take the form of Positive Temperature Coefficient (PTC) heaters, but recently some BEVs have instead made use of heat pumps to extract heat from the outside environment.
B) Reducing charging time
Another major challenge for BEV design is to accelerate the battery charging process. Rapid charging requires high power, resulting in heat generation due to electrical resistance. However, the lithium-ion batteries that constitute the heart of BEVs operate properly only within a narrow temperature range—roughly 0 to 45°C—and thus any excess heat generated by rapid charging must be efficiently removed by a well-controlled thermal management system. In particular, batteries operating outside their optimal temperature range tend to charge more slowly and degrade more rapidly. Techniques for cooling/heating batteries include both conventional air-cooling schemes and, more recently, liquid-cooling schemes involving coolant liquids circulating inside cooling plates.
C) Extending battery lifetime
The optimal operating temperature ranges described above are also relevant when considering battery lifetimes: ensuring that batteries remain within their optimal temperature range helps to extend their useful lifetime. Another relevant factor is the temperature distribution in and around the battery; a more uniform distribution leads to higher battery performance and a longer useful lifetime.
Thermal management systems and their key functional units
Vehicle thermal management systems comprise three functional units—an air conditioning, a battery, and a powertrain—and comprehensive control systems, capable of managing heat transfer among these components, are currently being developed. In this section, we describe the techniques and tools commonly used to heat and cool these units.
1) Air conditioning
For heat sources, PTC heaters are one common and inexpensive choice, but heat pumps are an alternative option that can help reduce power consumption. The primary components of heat pumps are electrically actuated compressors, isolation valves, expansion valves, shutoff valves, water pumps, and temperature sensors, together with pipes to connect these functional units.
BEV batteries are accompanied by peripheral components—voltage sensors, current sensors, and a battery-management system (BMS), and are typically cooled (heated) via one of two strategies: air cooling or liquid cooling. The key features of these two approaches are as follows.
Strategies for cooling (heating) batteries
- Air cooling: This approach is simple and inexpensive and boasts an extensive track record in practical application, but is capable of delivering only modest cooling performance. Air cooling schemes may be classified into three categories: natural air cooling, open-circuit forced air cooling, and closed-circuit forced air cooling; the latter two cases involve the installation of air-flow pathways driven by cooling fans and ducts.
- Liquid cooling: The high cooling performance achievable with liquid coolants makes this the most promising strategy for cooling high-power batteries in the near future. Like air-cooling systems, liquid-cooling systems may be implemented in various ways; here we focus on one particular approach, in which coolant water is circulated within a cooling plate. This circulation, driven by an assembly of electric water pumps, chillers, expansion valves, and connecting pipes, is highly effective for cooling vehicle battery packs. In cold-weather conditions, PTC heaters are used to warm the circulating water.
Air-cooling and liquid-cooling strategies are also used to cool electric motors, inverters, and other vehicle components. Air-cooling schemes make use of heat-dispersing fins attached to target components, while liquid-cooling approaches require electric pumps and radiators; because these components must be connected to the vehicle’s battery module, the network of pipes and valves required to connect system components tends to grow to daunting levels of complexity.
As this discussion illustrates, the implementation of thermal management strategies for BEVs is a complex challenge, depending sensitively on design objectives for travel distance, cost, and other factors—and affecting every aspect of vehicle design, manufacture, and sales.
Asahi Kasei’s Recommended Solutions
Asahi Kasei offers both innovative material products and advanced technical support services to assist in developing the broad range of products required for ever-evolving thermal management systems.
Materials for valves with laser-welding and laser-marking characteristics
LEONA™ 14G30 polyamide resin
Asahi Kasei’s LEONA™ polyamide resins are engineering plastics featuring high strength, high rigidity, high heat resistance, and outstanding chemical resistance. These materials may be further strengthened by reinforcing them with glass fibers or similar fillers, which improves their strength, rigidity, durability, and dimensional stability.
As one example, LEONA™ 14G30 is a material with a proven track record of successful adoption for valves in thermal management systems. To help our customers take full advantage of the superior physical properties of this material—including its high strength, resistance to long-life coolants, and excellent laser-welding and laser-marking characteristics—Asahi Kasei offers extensive technical support services: our experienced engineers work together with customers to accelerate product development and achieve innovative solutions.
Typical configuration of valves in thermal management system
Coolant valve system
Materials for cooling-system pipes with excellent resistance to hydrolysis, calcium chloride, and long-life coolants (LLC)
LEONA™ 53G33 polyamide resin
Asahi Kasei offers a variety of materials and processing techniques for pipes used for various purposes. Pipes are typically made from metals (such as aluminum alloys) or from metals in combination with rubber materials. Replacing these metals with resin materials yields lighter-weight products at lower cost.
Below, we review some common techniques for forming materials into pipes.
Water-Injection Technology (WIT)
WIT is a specialized injection molding used to produce pipes and other hollow bodies. The technique begins by filling a mold with molten resin, as in conventional injection molding, but then a stream of water is injected through the center of the mold. Water injection is delayed until the resin near the outer pipe surface has cooled and solidified, while resin near the center of the pipe remains molten and is readily displaced by the water stream to yield a hollow pipe. Although this method is only recommended for relatively short pipes (on the order of 50 cm), it is capable of forming branched pipes and pipes with cross-sectional deformation or non-uniform diameters, making it a good choice for branched and curved pipes in cooling systems.
For WIT applications, Asahi Kasei recommends our LEONA™ 53G33 polyamide resin, which offers outstanding resistance to hydrolysis, calcium chloride, and long-life coolants, even compared to other LEONA™ polyamide resins.
Suction-blow molding is a form of blow molding that is capable of producing long hollow pipes, 3-dimensional shapes, diameters ranging from small to large, and offers good durability and highly uniform wall thicknesses. This approach can also produce pipes with cross-sectional deformations and non-uniform diameters, making it well-suited for pipes and ducts used to connect distinct functional units.
Asahi Kasei offers specific grades of our LEONA™ polyamide resins optimized for use in suction-blow molding; these materials feature excellent resistance to hydrolysis, calcium chloride, and long-life coolants.
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In this method, a resin material is heated beyond its melting point and extruded from a die to yield a contiguous body with a uniform cross-sectional shape.This technique is capable of producing tubes and pipes with small diameters and long lengths. In addition, the extruded bodies can be processed to yield complex configurations of interconnected pipes, with applications including cooling pipes for battery packs and interconnects between functional units such as radiators, battery packs, and motors.
Asahi Kasei offers cooling-liquid-resistant grades of LEONA™ polyamide resins optimized for extrusion molding.
Key features of cooling-liquid-resistant grades of LEONA™ for extrusion molding
- High-speed extrusion molding. Pipes with a diameter of 16 mm and a wall thickness of 1.5 mm can be produced at high extrusion speeds up to 12 m/min.
- Shape flexibility. Modifying the shape of a metal pipe is a cumbersome task that requires working at high temperature and high pressure. In contrast, resin pipes are easily subjected to three-dimensional reshaping simply by heating the resin to a temperature near its melting point.
- Lighter-weight products and three options to consider. Compared to metal pipes (specific gravity: corrosion resistance SUS316=7.98) and rubber hoses, products made from these materials are 30-50% lighter in weight. We offer three material varieties—soft, standard, and hard—to accommodate various specifications regarding bending behavior and pressure tolerance.
|ISO||Soft type||Standard type||Hard type|
Material for smaller, lighter cooling pumps
LEONA™ BG230 biomass plastic polyamide resin
LEONA™ BG230 polyamide resin is a material based on the biomass plastic PA610, which contains 60% plant-based polymers.
PA610 exhibits lower water absorption than PA66, ensuring good dimensional stability even when used in environments subject to water exposure. This material offers excellent chemical and calcium chloride resistance, and exhibits good laser-welding characteristics, making it a suitable choice for cooling pumps with reduced size and weight.
LEONA™ SG104 polyamide resin
LEONA™ SG104 polyamide resin is an alloy grade made from semi-aromatic polyamide and polyamide 66.
This material exhibits low dimensional variation and degradation of physical properties upon water absorption. Its key features include high specific strength, attractive appearance, and excellent fluidity.Compared to polyphenylene sulfide (PPS), a material commonly used for these applications, LEONA™ SG104 generates less gas during injection molding and exhibits better moldability.
Valuable technical assistance based on Asahi Kasei’s advanced simulation capabilities
For customers designing products based on Asahi Kasei’s engineering plastics, we offer a variety of technical support services based on our simulation capabilities.
For example, perhaps you are a designer of metal valves, and you have been tempted to consider switching from metals to resins for your next valve designs—but you are concerned that resin-made valves might lack the strength and rigidity your application demands, or that the reduction in weld-line strength will be problematic.
To assuage your concerns, Asahi Kasei engineers will use our advanced simulation capabilities to investigate a range of shapes and gate positions to minimize the impact of weld lines—and then follow up with design and performance predictions to eliminate any possibility of material failure or leakage for products in use.
Asahi Kasei’s engineering plastics are also useful for a broad range of other applications, including motor end caps, connectors, high-voltage components, and more. For more information, please contact us using the links below.