Triax Aims For Low-Cost Hybrid
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.
To execute the program as quickly as possible, Purcell decided to take much of it outside GM. He enlisted the services of Heinz Prechter’s ASC “North” facility in Warren, Mich., close to the GM Tech Center. ASC handled the brunt of the CAD work (done in ALIAS) and the clay models. GMs NAAO Prototype shop did the build.
“Around the Design Center, we nicknamed it the `stealth’ project, because it moved so quickly through the various interations that nobody saw it,” notes Holger Koring, the project’s chief designer.
Koring explains that the SUV’s design theme is based on a wedge. “We wanted to give it good aerodynamics, but with SUV styling cues. And we let the vehicle’s functionality drive the exterior shape, so that the drivetrain packages will fit various body styles. The separate chassis helped us do that” Triax’s coefficient of drag is .27 Cd.
To determine the rough package dimensions, Kutcher and Koring started with a Suzuki J2 Escudo. Their first iteration was a one-box minivan. Mass, aerodynamics and powertrain cooling were the major engineering bogeys, Kutcher says. “We spent half our development time in aerodynamics, the other half in cooling. We relied on our Auto Shape Developer (ASD), a proprietary GM design software program that can automatically develop surface forms and give a drag indicator for them, plus computational fluid dynamics.”
A 1/10-scale model was built first. Then came a 1/3-scale model for the full-scale wind tunnel, to validate the shape. Rear spoiler placement was “a lesson in how to achieve aerodynamic performance of a larger vehicle, without adding overall length (such as a Kamm-type tail) to the vehicle,” recalls Kutcher. He points out that Triax’s use of rear-vision cameras in place of exterior rear-view mirrors gives about 2 mpg at 55 mph, in simulations.
Triax’s rear engine design posed numerous challenges. It compromises the SUV’s rear cargo loading height, but that pushed Koring’s team to innovate. The vehicle’s front mink features a load-through capability, leading straight to a cargo tunnel along the floorpan centerline. Cooling the rear-mounted IC engine and maintaining proper cabin HVAC performance, was also tricky. The solution was in copious heat exchanger surface area, and in the ducts designed into the rear body quarters. These work with the air flow along the body side and don’t interrupt airflow at the rear of car.
Triax also has no traditional cowl, or firewall, up front. Instead, it’s in the rear, above the axle. That layout also changes the interior noise profile, requiring new NVH attenuation tricks.
Early on, Kutcher’s engineers planned for a 60/40% front/rear weight bias, which he claims is achieved on the 2,387-pound show car. Projected weights for the hybrid and EV versions are 2,900 pounds and 3,300 pounds.
Inside, Trix is cleanly functional, with plug-and-play electrics and simple LCD-illuminated gangues. “We wanted no bells and whistles, unlike Toyota’s Prius,” Koring quips. And unlike the first Prius, the Triax is designed for either left- or right-hand drive.
There’s been no dynamic testing, and the other drivetrains have yet to be fitted into operable vehicles. But this program is said to have the blessing of Chairman Jack Smith and Waggoner to continue development. If that happens, the original code name will be an appropriate description of the vehicles Bob Purcell and his AVT team have created.
Living With Triax: Concept Car Hell
`As program leader, all I have to do is be the enabler. But this program consumed me,” admits Mike Kutcher, the straight-shooting 36-year-old engineer who shepherded Triax throughout its seven-month development.
Work was a six-day-per-week whirlwind for Kutcher, who previously spent “a year in the wind tunnel and a year in exterior body development” on the EV-1 program, until moving to GM’s 80-mpg PNGV program, soon to be revealed at the Detroit Auto Show.
It was a grinder. By 6:00 a.m. every day, Mike was on his cell phone driving into work and discussing some facet of Triax with a designer, powertrain engineer, purchasing agent or prototype builder. During the design phase, every work day lasted until at least 8 p.m. Then, when prototype build began April 1, it would be midnight before Mike left the shop every day.
“It was intense for everyone,” he recalls of the 80-person core team. “We really pushed hard. The Tokyo show deadline was set in stone. There was no turning back, no retreat. It wasn’t until September 20 that I really felt comfortable that it would come together.”
The only time he had to do the books was between midnight and 2:00 a.m., when he’d finally turn in with his family. And the chaos was increased when the Kutchers moved into a new home during the project. “You’ve gotta love what you’re doing, or this life will eat you up,” he notes. “Luckily, I love it.”
COPYRIGHT 1999 Cahners Publishing Company
COPYRIGHT 2000 Gale Group