What is Kappa or the Kappa Platform?
The Kappa Platform, or architecture, is a new vehicle
architecture developed by General Motors to enable them to profitably build
low volume production cars. This is the Platform that GM uses to produce
the Pontiac Solstice, Saturn Sky and Opel GT.
A vehicle architecture or platform is the basic running gear of the vehicle.
It includes the chassis, its components, the drivetrain and many of the smaller
items in building the car. The look of the car on the Platform may vary
greatly or contain similar design aspects such as the humps behind the driver
and passenger seats of the Kappa cars. This approach enables car companies such
as GM to utilize the engineering and production capabilities to build multiple
different looking cars aimed at different markets. It also enables
them to leverage the majority of expense in production, design, and validation
of a new car. Automotive companies develop new architectures or platforms
rarely, but introduce new vehicles by using the platform to produce variants or
follow on vehicles.
Twenty-seven months could be considered overnight when it
comes to developing a new vehicle architecture, and that's how long it took a
team of enthusiastic engineers to develop the rear-wheel-drive platform for the
Pontiac Solstice - a concept-to-reality sports car coming in 2005.
The new Kappa architecture is the foundation for the Solstice production model
as well as several exciting concept vehicles that demonstrate its adaptability.
GM introduced the Solstice production model, as well as the Chevrolet Nomad and
Saturn Curve concepts, at the 2004 North American International Auto Show. In
addition to sharing the Kappa architecture, the concept vehicles reflect GM's
global design and engineering resources. With cultural backgrounds from many
corners of the world, designers came together at GM's Advanced Design Studio in
Great Britain, as well as GM Europe's Advanced Design Studio in Sweden to
collaborate on the concept vehicles' designs. Italian coachbuilder Pininfarina
also helped assemble them.
"These vehicles have global appeal that translate well in any language," said
Anne Asensio, executive director, Advanced Vehicles. "From the shape of the
bodywork to the colors and interior materials, they each represent contemporary
design."
Starting from Scratch
The impetus for the Kappa architecture's world-class platform was the Pontiac
Solstice. A strong response to the 2002 Solstice concept car helped green-light
the vehicle for production even though a compact rear-wheel-drive platform for
it did not exist. A core team of engineers was assigned to develop one - and
quickly. This efficient team collaborated globally to develop a flexible
platform that would enable future production work for a distinct set of GM
brands.
"We knew from the start that we would do it right or not do it at all; the
support for that decision came from the very top," said Lori Queen, vehicle line
executive for GM's small cars. "It has been an experience whereby the size and
strength of GM was mobilized on a global scale to get the job done immediately."
To maintain the Solstice concept's aggressive stance, the chassis was developed
to support the vehicle's short overhangs, long wheelbase and wide stance. This
"wheels at the corners" design enhances handling and the overall feeling of
stability. It also allows for a more comfortable interior, with increased
legroom and hip room.
To ensure the lithe proportions of the Solstice were complemented with a firm
foundation, engineers developed a lower-dominant tube structure for the chassis.
Hydroformed frame rails, which run the length of the vehicle, are the basis of
the chassis, while additional stampings form a rigid structure onto which the
bodywork is attached. The hydroforming process uses pressurized fluid to form
each frame rail from a single piece of steel, rather than several pieces of
steel welded together. This creates a stronger frame rail and requires less time
to form it. Additional components and stampings are added to the frame rail
during vehicle assembly. A tunnel at the center of the chassis, which houses the
transmission and driveshaft, is enclosed at the bottom to enhance stiffness.
This built-in strength reduces chassis flex and cowl shake in a vehicle designed
from the outset as a convertible.
"Convertibles typically are less stiff than vehicles with a fixed roof, so we
set out to create the stiffest possible platform for a vehicle this size," said
Queen.
The Kappa architecture's rigid structure also permits more precision when it
comes to tuning the suspension. The Solstice features independent, SLA-type
suspensions in the front and rear, along with coil-over springs wrapped around
Bilstein monotube shock absorbers. The short-long arm suspension designs feature
forged aluminum upper and lower control arms that are both strong and
lightweight. The rear suspension also features a toe control link and the rear
differential housing has an optimized three-point mounting design.
The Kappa's suspension design and geometry are not shared with any other GM
vehicle architecture.
The Solstice also features four-wheel disc brakes, including 11.7-inch
ventilated front rotors and 10.6-inch rear rotors, which combine with optional
ABS with Dynamic Rear Proportioning to provide superior stopping stability.
Eighteen-inch wheels are standard.
Dynamics Perfected
In addition to the robust chassis architecture and suspension components, Kappa
engineers sweated dynamic details to produce a world-class platform, including:
Near 50/50 weight distribution for a balanced handling feel
Hydraulic engine mounts to provide a smoother engine feel
Optimized acoustic barrier and sound absorption package to provide world-class
levels of interior quietness
Exterior components, such as mirrors, wind-tunnel tested to minimize wind noise
Tires selected for handling performance and low noise.
The Kappa chassis also was designed for the all-aluminum Ecotec four-cylinder
engine. In the Solstice, the 2.4-liter version of the sophisticated DOHC
powerplant features twin balance shafts to reduce engine-sourced noise and
vibration. Technologies including intake- and exhaust-cam phasing and electronic
throttle control are employed to maximize volumetric efficiency, boosting the
smoothness and performance of the engine throughout the rpm range.
Clear Mission
Development time and cost were reduced by leveraging existing GM components
where possible. The Solstice's rear differential, for example, is borrowed from
the Cadillac CTS. Other proven component selections also aided Kappa
architecture's development time. "It makes sense to leverage proven parts that
fit the application," said Queen. "The parts are adapted to the Kappa
architecture and do not compromise the vehicle's design or function."
Knowledge that the Solstice would be offered with a version of the Ecotec
four-cylinder engine allowed the chassis team to design for the specific
powertrain from the project's start. Because the Ecotec engine had not
previously been used in a longitudinal layout, several accessory drive
components required redesign to fit the new chassis.
"Knowing these challenges at the beginning helped us design it right the first
time," said Queen. "We had a very clear mission on how to proceed with the
architecture's design."
Although the primary focus of the Kappa architecture was the development of the
Solstice, its platform is adaptable - as demonstrated with the Chevrolet Nomad
sport wagon and Saturn Curve 2+2 coupe concept vehicles. The Nomad rides on a
longer wheelbase than the Solstice for added rear passenger room, while the
expressive Saturn offers a sophisticated, performance-oriented driving
experience with a fixed roof.
"The Kappa architecture is a great platform for sporty, driver-oriented
applications around the globe," said Queen. "Two years ago it didn't exist, but
as the other concepts show, the additional possibilities are tantalizing."
General Motors. January 2004