Technology overview
The GTB-40 was conceived as a “clean sheet of paper” design with the goal of reducing vehicle weight while utilizing affordable, proven manufacturing processes. The mass of the bus was reduced by replacing heavy and traditional carbon steel structures with a lightweight innovative design utilizing stainless steel. As a result, less material is required for the body and chassis structure, with a greater strength to weight ratio, enabling the manufacture of a robust vehicle that weighs one-third less than current hybrid buses in the market.
A special stainless steel alloy is used for the GTB-40 structure. Called Nitronic 30 because the steel is strengthened by exposure to nitrogen gas, the alloy is also corrosion-resistant and durable. Because the high performance material is used for all major chassis and body components of the bus, the service life of the vehicle will be longer than that of today’s 12-year average. Other advantages of Nitronic 30 include excellent mechanical properties at sub-zero and elevated temperatures, low-temperature impact resistance, and superb resistance to high temperature oxidation.
Although this material is more expensive than conventional steel, the incremental cost is offset by design innovation, parts consolidation, and streamlined manufacturing processes. The new steel is also 100% recyclable and environmentally friendlier to produce than aluminum, making the alloy an ideal “green” raw material for vehicle structures. By applying a total vehicle optimization approach, weight was reduced by one-third and the bus was designed to minimize maintenance time and cost.
Advanced vehicle subsystem technologies, such as a 4-wheel independent suspension and brake-by-wire are also incorporated into the bus design. These key innovations enable the bus system to be fully optimized and downsized, further reducing vehicle mass. Additional efficiency improvements have been gained by using an efficient, battery-dominant hybrid electric drive system.
The bus is designed to provide enhanced passenger comfort, improved compliance with the Americans With Disabilities Act, reduced noise, and improved ride dynamics. The major advantage is the reduced total operating expense as a result of significantly lower energy costs and lower maintenance costs.
Nitronic 30 is a registered trademark of AK Steel Corporation
Patented Unibody Architecture
The key building block in the innovation and efficiency of the GTB-40 is our patented unibody architecture, which we refer to as our Hybrid Ultra-Light platform. We also refer to this unique unibody architecture as a hybrid monocoque structure, inspired by the aerospace industry. In such a structure, the exterior walls of the vehicle provide the structural support, not the ladder frames or trusses common in commercial vehicles today. Forming the floor and roof are a series of corrugated panels which are united by vertical structural pillars to form the basic structure. Simple, accurate, repeatable and effective spot welding technology is used throughout. The body is then closed out with outer structural skins; even our solar reflective urethane bonded glass becomes a structural element. It’s truly a unique and effective vehicle architecture.
Lightweight Panel System
The corrugated panels used in our Hybrid Ultra-Light platform are truly unique & proprietary. Formed with low cost, yet very repeatable metal-forming process, each corrugated cross section is sandwiched between unique top and bottom sheets, fixtured and then spot welded with a semi-automated process. The strength to weight ratio of the resultant floor and roof panels is outstanding. Deflection testing on the floor panel under a 30,000 pound load, 2.5 times the anticipated maximum loading (equal to 200 passengers between the front and rear wheel wells), was completed successfully with a maximum elastic deflection of just 3/8” and no measurable permanent set. We have great confidence the structure will be reliable in service.
4-Wheel Independent Suspension
More good news, the innovation does not stop with our structural system. No axles here! We’ve coupled our innovative low-floor, 100% level-floor chassis with an advanced 4-wheel independent suspension resulting in improved ride, reduced harshness and increased passenger comfort. On top of that, the suspension is built entirely of stainless steel, meaning it’s strong and corrosion resistant, which equates to longer life.
Meet the Team
Kevin Wittrup
VP Engineering/Mfg.
On the engineering side the past several months have been focused on refining & developing our core structure & chassis architecture for production release. In support of this, we have developed sophisticated FEA models and have gathered physical test data from a 4-post vehicle simulator to gather valuable information about how this innovative architecture handles inputs characteristic of a durability test.
Our highly capable internal engineering team is working closely with our network of collaborators and key supplier partners in the areas of structural dynamics, driveline, batteries, electric machines, auxiliary power units, and vehicle control systems to bring together all the relevant subsystems and functionality required for a successful product development phase and ultimate launch.
From a manufacturing perspective, we are developing our manufacturing process through the early stages of our pilot builds and have been very pleased with the results. The benefits of scalability and flexibility associated with our low investment manufacturing process are already being recognized.
Speaking for the team as a whole, we look forward to the challenges that 2010 brings and the opportunity to bring this exciting product to market.
