Revolutionary SIM-WIL electric vehicle benefits from DuPont™ Zytel® HTN polyamide
The SIM-Drive Corporation of Kawasaki City, Japan, has developed SIM-WIL, a new generation electric vehicle (EV) that displays some of the most impressive improvements in range, performance, reliability and comfort yet seen—key features that are expected to boost the appeal of EVs to a broader range of consumers, following the company's intention to start mass production around 2014.
The new in-wheel EV is a technological advance over SIM-LEI, the first generation model, with vehicle range extended from 300 km to 351 km per charge, about 1.5 times that of other electric cars currently on the market. SIM-WIL delivers a maximum speed of 180 km/h, sports car acceleration from 0-100 km/h in 5.4 seconds, and offers a higher level of interior space and comfort.
Collaboration with DuPont
Increased reliability, enhanced motor performance, weight saving and other performance advantages have, in part, been achieved by the use of DuPont™ Zytel® HTN high performance polyamide and a further seven DuPont products in a collaborative development program between the DuPont Automotive Center in Nagoya, Japan, and SIM-Drive.
In addition to Zytel® HTN, SIM-WIL benefits from DuPont™ Corian® solid surfaces, ChromaClear® clearcoat, Cromax® Pro waterborne basecoat, Kapton® polyimide film, Kapton® JP films, Sorona® renewably sourced fiber, and Voltatex® impregnating resins, wire enamels and core sheet varnishes.
"DuPont provides a wide range of products including high performance resin, film, paper and painting materials. Especially in EV applications, these high temperature, chemically resistant products and electrical insulation materials contribute to increased EV car system reliability and performance under severe conditions such as wide ranging temperatures and high voltage," said Mr. Tomoyuki Shinkai, Operating Officer, Vehicle Development Co-ordination Division General Manager, SIM-Drive Corporation.
Paving the way for Zytel®
Zytel® HTN was selected for the key motor bobbin insulator in each in-wheel electric motor in preference to polyphenylene sulfide (PPS) because of its superior toughness at lighter weight, thin-wall moldability, and compatibility with the insulated copper coil wire winding process.
"This project paves the way for Zytel® HTN to further penetrate into the EV and HEV automotive segments, as well as being a great example of 'inclusive innovation' driving advancements in the energy megatrend," said James Hay, regional director for DuPont Performance Polymers, Asia Pacific.
"Participating in this project not only helps enhance our presence in the EV and HEV industries, but also provides opportunities to work with potential customers who are willing to continuously collaborate with us. We have obtained much knowledge through this process and this opportunity will help us accelerate technology development going forward," said Minoru Amoh, President of DuPont Kabushiki Kaisha, Japan.
A better motor bobbin
The four in-wheel motors driving SIM-WIL comprise magnet plates and copper wire. A motor insulator is required between those critical parts to provide the fail-safe electrical insulation now secured by Zytel® HTN51G35EF, a special grade developed for EV/HEV applications combining all the strength, stability and heat resistance of Zytel® with enhanced dielectric properties and minimum moisture absorption.
The new motor is an improvement over the SIM-LEI model in that torque ripples (vibrations due to the uneven revolution of the motor at start-up) have been significantly reduced, enhancing output, efficiency and comfort, and reducing noise level.
PPS has traditionally been used as an electrical insulation material and motor insulator. In the bobbin assembly process, insulated copper wire is wound onto the insulator parts—however, during molding, PPS develops "flash", sharp edges or "thorns" of excess plastic that can cut into the wire insulation layer, necessitating an extra procedure to remove the flash, or risk damaging the sheath material. Also, PPS contains sulfur that can corrode metal injection molds.
Because Zytel® HTN does not generate flash or contain sulfur, and aided by DuPont support in processing and molding, SIM-Drive was able to eliminate two of the processing problems associated with PPS. A third limitation of the PPS part was its tendency to crack as wire winding speeds increased.
No cracking, faster winding
Since Zytel® is 12% lighter and up to 50% stronger than PPS, the weight and wall thickness of the part could be reduced. The more compact unit provides extra wiring space, offering possibilities for increasing motor power. Corner cracking problems of the part during the copper wire winding process were eliminated because of the greater tensile strength of Zytel® versus PPS. This has enabled the company to increase the bobbin wire winding speed, thus increasing productivity.
Benefits of Zytel®
Zytel® HTN51G35EF, the DuPont polymer chosen by SIM-Drive, is one of the EF series of electrical resins specially developed for EV and HEV applications, offering superior electrical insulation and retention of dielectric strength over a wide temperature range, and minimum water absorption. It is a 35% glass reinforced, heat stabilized, lubricated high performance polyamide with the potential to improve parts value and cost reduction in EV, contributing to increased motor performance and cost efficiency.
SIM-Drive will gain three important benefits by switching from PPS to Zytel® HTN:
Opportunities to increase lamination factor—the thin wall moldability of Zytel® HTN, while retaining strength and stiffness in a more compact structure, has resulted in more space for the copper wire winding.
Improved reliability—since Zytel® HTN does not contain sulfur, unlike PPS, any concerns that the bobbin material will attack the copper wire insulation layer have been eliminated.
Cost reduction—the superior strength and rigidity of Zytel® HTN has permitted faster wire winding speeds, resulting in productivity improvements versus PPS which tends to crack as winding speeds increase. Further cost efficiencies are linked to weight reduction and lower specific gravity when the component is molded with Zytel®.
Weight is a critical factor in the performance of electric vehicles, and excess weight imposes a critical drag on electric motors. At 1580 Kg, SIM-WIL is lighter than some other EVs, such as the Chevy Volt. Lightweighting, which was an important consideration when SIM-Drive selected materials for the new car, is one of the key benefits of many DuPont elastomers and plastics used widely by the automotive industry in metals replacement programs.