Triax Aims For Low-Cost Hybrid

Automotive Industries, Nov, 1999 by Lindsay Brooke

GM's flexible powertrain concept for global assembly relies on a separate frame and low-cost body.

The program was code-named "Agile," and to the designers, engineers and fabricators who built the car, it was a rapid-fire project -- seven months from idea to the finished concept vehicle. But to General Motors, the program is much more than the metallic-gold compact SUV, currently called the Chevrolet Triax, that surprised show-goers in Tokyo last month.

Triax is really a four-pronged strategy being considered by GM. It's aimed at getting super-efficient "clean" powertrains into production on a global basis. Part one increases GM's technical cooperation with Suzuki Motor Corp., which contributed Triax's internal-combustion engine and would probably be the primary IC engine source, if the program enters production.

Part two is the use of body-on-frame architecture, to create a flexible platform for a variety of drivetrains and body styles. This will allow GM to offer piston engines, hybrid-electrics, pure electrics, and possibly fuel cell-powered vehicles to meet regional environmental regulations and customer needs worldwide. If approved, the Triax platform would support low-to-moderate -volume regional assembly, particularly in developing nations.

Part three is the leveraging of GMs considerable advanced propulsion work, including the electric drives and power controllers developed for the EV-1.

And the fourth part of the Triax strategy is the bottom line. For Triax to be a viable business plan and get the green light, it will have to be cost, efficient to produce, and profitable for GM.

"We learned that we need to work on four different critical elements of the problem at the same time," explains GM President and Chief Operating Officer Rick Waggoner. "These am energy efficiency, mass, power and cost."

Waggoner adds that the Triax concept, if it enters production, has the potential to achieve the long-sought-after goal of "taking the automobile out of the environmental debate."

Adds program manager Mike Kutcher, "From day one, we saw this as a global package. It must be globally accepted. We need to increase the volume of these high-efficiency, advanced drivetrain vehicles and make them capable of regional manufacturing."

Aero, Cooling Were Challenges

The program kicked off last February, the first fruit of the December,1998 agreement between GM and Suzuki to boost their engineering cooperation. "Their (Suzuki) small-displacement internal combustion (IC) engine technology, which comes out of their motorcycle side, is really impressive," notes Brace Zemke, staff development engineer in GMs Advanced Vehicle Technology group. AVT, to which Kutcher also belongs, engineered and managed the Agile program.

A Suzuki 100 hp, 1.0L turbocharged gasoline engine, with variable valve timing, powers the show car's rear wheels through a continuously-variable transmission. That's the basic Triax powertrain. The other planned drivelines would include a hybrid that pairs the Suzuki IC engine with an electric motor, and a pure electric. Both of these utilize GMs latest electric vehicle technologies, including the Gen III 46-hp motor, power control and nickel-metal hydride battery packs.

According to Kutcher, once Agile-Triax got the go ahead from top management, the program was championed by two veteran GM executives. "It was Bob Purcell's vision," he asserts, referring to the executive director of ATV. "He made it happen, and kept our senior execs up to speed on it." GMs Director of Design Jerry Palmer also played a pivotal role, "visiting us every day to check progress and encourage us, as the Tokyo deadline approached."

The enabler for this wide array of driveliness is Triax's body-on-frame construction. The simple ladder frame has proved itself to be the world's most flexible automotive platform, able to be quickly stretched, widened and strengthened to accommodate any body style or drivetrain. For Triax, the frame's front and rear sections will carry the power and drive units, and the center section will hold the energy source. The frame rail section height is sized according to battery pack dimensions, and also would be sized to fit hydrogen or methanol tanks for fuel cells.

"We decided on this clean-sheet approach for three masons," explains Kutcher. "Unibody doesn't lend itself to low-volume, low-cost production or to the platform flexibility we needed for the three drivetrains. Also, converting a conventional unibody IC-powered vehicle to a hybrid or pure electric is high and has too many design and performance compromises. We designed Triax into a single platform, so all the intended vehicles built from it will benefit."

Kutcher also notes that body-on-frame also divorces the flame configuration from the vehicle's body design, which allows a wider model mix at lower cost.' He says the body styles being investigated include the SUV, a pickup track and a small cargo vehicle. To keep tooling costs down, Triax's bodyshell would be produced in plastics -- SMC on the horizontal surfaces, RIM on the vertical panels and TPO for the fascias.