The New-Generation Rolling Stock Bogie
Previous bogies were structured of steel side beams in an H pattern and coil springs. efWING achieves a simpler structure by having a CFRP frame serve double duty as a leaf spring.
Conventional, side-beam-and-coil-spring bogies absorb vertical motion from the wheels with coil springs, but the efWING absorbs the vertical motion by having the curved frame serve double duty as a spring. This improves riding comfort by smoothly absorbing vibrations as a whole on turns and junctions, and it also reduces the risk of derailment due to a decrease in wheel load.
The New-Generation Bogie:
A New Standard in Bogies
The CFRP structural material and leaf spring parts have length, thickness, and width determined by the train car placed on them. For a heavy train car, the width is made wide in relation to the spring constant, and, for a light train car, the width is made narrow. Performance and appearance design based on kansei (sense-based) engineering achieves a polished, functional beauty and suggests the powerful, stylish soaring of a race car.
Harsh Running Tests in U.S.
Have Proven a Factor of Safety
Nearly Double the Standard
Before the efWING was commercialized, it was subjected to harsh running tests, starting June 2012, in the United States, by the Transportation Technology Center, Inc. (TTCI). It was tested over a total running distance of 4,500 km, with a maximum speed of 160 km/h. A battery of tests was conducted on its basic performance and running stability according to the standards of the American Public Transportation Association, and it was proven, for instance, in the derailment test that it had a factor of safety nearly double the standard (see fig.). This proves that it reduces the risk of flange climb derailment at turns and junctions.
Kumamoto Introduces efWING,
the World’s First CFRP Bogie!
The Kumamoto Electric Railway took the initiative in introducing efWING before others, equipping one of their train cars with two efWING bogies and putting it into commercial operation starting March 2014 on their line from Fujisakigu-mae Station to Miyoshi Station. Kumamoto Prefecture’s highly popular local mascot Kumamon graces the silver-colored car body. There are even doors on which Kumamon is shown alongside the efWING logo.
Kawasaki is talking to railway companies and others about adopting the efWING as their standard bogie for new rolling stock production.
- By Takehiro Nishimura
Senior Staff Officer
Bogie Engineering Department Rolling Stock Company
Kawasaki Heavy Industries, Ltd.
Innovation in Bogie Technology:
CFRP Used for the First Time in the World
“Could you make a bogie that will make the world go, ‘Wow’?” Imagine if you could put some iron and rubber materials into a machine, push a button, and have a bogie pop out. Like cooking in a microwave.” This was the order from my boss. Our response was: “We couldn’t do it in a microwave, but we managed to make a bogie you can bake in an oven.” This marked the birth of Kawasaki’s new rolling stock bogie, the efWING.
For the first time in the world, carbon fiber-reinforced plastic (CFRP) was used for a bogie frame. CFRP is also used for aircraft fuselages. Its form is cured by heat, explaining the remark about the oven.
Acceleration and deceleration performance, which directly affects rolling stock’s comfort and travel performance, is determined by the performance of the equipment that makes up the bogie, such as the drive unit, control unit, and brakes. In this respect, existing bogie technology was seen as mature and better left alone. This is why our boss gave the microwave order, thinking there might be ground for innovation.
The efWING combines two functions in one: It uses CFRP for part of the bogie frame, which used to be steel, and also incorporates CFRP leaf springs for suspension to replace the conventional coil springs. This allows the bogie to be lighter and simpler in structure. In fact, it is 40% lighter than before, 900 kg lighter per car. This not only contributes to improving fuel efficiency during travel and lowering running costs, but it also helps reduce CO2 emissions. Assuming an annual travel distance of 150,000 km and an electricity cost of ¥12/kW, or approximately ¢11/kW*, it saves about ¥90,000 (approximately $830) per year per car. Looking together at 10 cars with a service life of 40 years, this makes savings of ¥36 million (approximately $331,000).
The CFRP frame not only takes over the suspension role of coil springs, but even radically improves comfort. The leaf springs move complementarily like a seesaw, stabilizing the force between the wheels and the rails.
Based on kansei (sense-based) engineering, a design that balances performance, appearance, and cost was achieved, earning the Japanese Good Design Gold Award in 2013. The relevant review committee had this to say about it: “We highly regard the ingenuity that gave birth to this high-performance bogie endowed with a functional beauty, which was achieved by combing Japan’s advanced new material technology and structural engineering.”
*Calculated at ¥108.7 to the dollar