Swedish steel prize winner 2004
Battery mounting in hybrid cars
2004 | Trim Trends Co Llc | USA Winner 6 min read
US based Trim Trends has developed a crashworthy battery holder manufactured from ultra-high strength steel for the batteries powering the recently launched Ford Escape Hybrid SUV. The battery holder is produced using press tools of advanced design that represent a major technical advance in working high strength steels. This opens the way for regular production of large components made from very high strength steels. The result may be lighter, safer and more environmentally-friendly cars that can be produced at reasonable cost. Trim Trends has now been nominated for the Swedish Steel Prize 2004, which is an annual international design award.
There is growing demand from consumers for more environmentally friendly cars with a hybrid drivetrain, creating new challenges and needs for the designers of such cars. Trim Trends of the US has succeeded in meeting the challenge and has developed a successful design, at the same time achieving a breakthrough in tool design. The product is a new crashworthy battery holder for the large and heavy batteries powering the Ford Escape Hybrid SUV. The battery weighs more than 50 kilograms and is located at the rear of the car, under the luggage compartment. The difficulty lies in making the battery holder strong enough to meet collision safety requirements, while also being light enough to restrict the weight of the vehicle. The battery holder is of crucial importance to the safety of the car, so that the heavy battery will not cause injuries to the vehicle’s passengers in the event of a crash.
"Very high strength steel is needed to hold such heavy batteries in place, while also serving as collision protection," says Engineer Kevin Bilkey at Trim Trends when describing the battery holder. "In a rear-end crash, the energy is transferred from the bumper to the battery holder which will move forward and upwards but without the batteries intruding into the interior."
In the early stages, designers tried to use a conventional steel grade, but the design was not strong enough and turned out to be too heavy.
"We then decided on one of the strongest steel available on the market, which is a martensitic steel with a tensile strength of 1200 N/mm2," continues Kevin Bilkey. "But the problem was that no-one had previously pressed this material into such a large and advanced component. We did not know whether it could actually be produced."
The problem lay in finding a suitable and economical method of production that minimised or eliminated the risk of cracking.
"The component was also very large, and we realised that we faced a serious risk of cracking," explains Kevin Bilkey. "It turned out that the solution lay in allowing the 7-kilo piece of sheet steel freedom to move in the die, so that it would be pressed without restraint."
Once the designers had found the method of pressing the hard steel, a suitable method of welding the securing wedges under the holder had to be found, so that it would be able to slide up the slide rails behind the seat backrests in a rear-end crash.
"Although we have been supplying complicated parts to the large carmakers in Detroit for many years, this turned out to be our most difficult assignment," says David A Crowe, who is the toolmaking specialist at Trim Trends. "We had to forget old theories and preconceived notions, and start from scratch. We managed the welding operation by taking care to lead the heat away when welding the sheet. After solving the problem, we had to be able to make regular deliveries within only one month."
A battery holder is produced in six stages - from punching holes and trimming away excess material, through to welding the wedges for the slide rails. The pressing operation in which the battery holder is given its shape takes place in a single operation. The cut away material is used for the wedges, making material utilisation very efficient.
Production is now in full swing. Sheets for the finished battery holders are pressed at the rate of 150 a day, and these are shipped to Sanyo, where the batteries are mounted in the holders so that Ford receives a complete unit for mounting in the vehicle.
To date, Ford has ordered 30, 000 battery holders. However, interest in the new car from motorists is very high , and provisional orders indicate that many more battery holders will be needed in the future.
"We expect to be delivering battery holders to Sanyo for a long time ahead, and we believe that the Ford Escape Hybrid SUV will be a success," concludes Kevin Bilkey. "To meet the increasingly tough demands of the automotive industry, suppliers must be innovative in finding sound solutions to difficult problems."