World-Class Vehicle Dynamics Goal Of New Cadillac CTS

FOR RELEASE: August 16, 2001

World-Class Vehicle Dynamics Goal Of New Cadillac CTS

Nürburg, Germany - Built on General Motors' new rear-drive Sigma architecture, the Cadillac CTS represents a new era of affordable luxury performance sedans for Cadillac. To match its 220 hp V6 powerplant and sporty five-speed manual or automatic transmission, the CTS development team designed a rigid, durable chassis and sophisticated suspension system.

The first step was to construct a suspension that would maximize the platform's outstanding torsional rigidity. The team ensured that the joint attachments, which tie the suspension to the architecture, were sufficiently stiff and robust to allow the suspension to work as intended. Since the rear suspension was to be a multi-link type, such strength was important because the links would experience significant driving loads.

The suspension geometry was optimized through math modeling. Numerous ride evaluations were conducted at various sites, including in Germany on the autobahn and at the legendary Nürburgring racing circuit.

The front suspension of the CTS is a double short/long A-arm design with a high upper control arm. This allows the upper ball joint to move as far outboard as possible, reducing the spindle offset wheel center and minimizing road disturbances or tire/wheel imbalance feedback to the steering. Key components of the front suspension design are:

• Forward-facing lower control arm which isolates passengers from road vibrations
• Hydraulic front lower control arm bushing for good motion control with soft rates for vibration isolation
• Very stiff engine cradle for noise isolation and handling performance
• Engine cradle solid-mounted to motor rails for more precise feel
• Long suspension travel absorbs bumps for smooth ride

Use of aluminum in the upper and lower control arms reduced the total mass of the vehicle as well as the unsprung mass which affects ride smoothness and wheel control. Reduced unsprung mass requires less damping to be tuned into the suspension and holds the road better over driving inputs.

In order to compete on a global level, the CTS' independent rear suspension (IRS) is a no-compromises design. After consideration of multiple options, the team decided that a five-link rear suspension provided excellent suspension kinematics with highly adjustable tuning for ride and handling. With the foundation structure and suspension in place, they built the rest of the car around the selected suspension geometry. The multi-link IRS allows engineers to define exactly where they want the rear wheels to be at any given time. By using rubber isolated upper control arms, front and rear lateral links, and longitudinal links, they can ensure that the rear suspension will react to a given force in a predetermined-and predictable-manner.

The rear suspension is fully isolated from the car by four rubber mounts. The lower links are separated fore and aft for better kinematics and much better compliance behavior. The longitudinal link has been lengthened significantly to allow each bushing in the suspension system to be tuned for specific types of road inputs.

Other keys to the world-class independent rear suspension include extremely high gas-charge shock absorbers, a self-energized hydraulic leveling system, long suspension travel for better bump absorption, hydroformed support assembly for optimum stiffness and mass, and double isolated differential to minimize noise and vibration from the drivetrain. The rear differential, like the upper control arms and suspension knuckles, is aluminum, to reduce mass. Reducing unsprung mass improves the ride and handling and enhances wheel control just as in the front suspension.

Good steering feel is essential to any sports sedan, and a great deal of time was devoted to improving the robustness of the steering gear and decreasing the lash or compliance of the steering system on the CTS. Excessive compliance can make a vehicle's steering feel inaccurate and sloppy. Precise steering feel involves more than the gear. To improve overall steering feel, the CTS' hydraulically assisted rack and pinion steering is mounted forward of the wheel centerline. The steering gear is direct-mounted to the front cradle, eliminating the compliance of rubber bushings between the cradle and gear. Direct-mounting the front engine cradle to the body eliminates compliant mount bushings. An axial rate washer that's added to the front lower control arm rear bushing ensures a pivoting effect rather than a sliding effect to minimize understeer caused by reducing arm translation.

The FE1 suspension (base level) will offer conventional power-assisted steering. The FE3 suspension (uplevel) will offer TRW's Speedpro variable-assist power steering. Both suspensions have a 16.5:1 steering ratio.

The CTS features four-channel ABS, which monitors the speed of each wheel individually, allows individual wheel braking for superior braking control and also allows for backup braking in case one of the two braking circuits fails. The existing ABS software has been refined to enable the system to differentiate between braking in a turn and braking in a straight line for better straight-line braking. It also includes Dynamic Rear Brake Proportioning, which balances the braking pressure front to rear to optimize stopping distances under all possible vehicle load conditions.

The CTS includes electronic grade braking, which uses sensors that monitor the temperature of the brakes and seamlessly shift the automatic transmission to a lower gear to minimize brake overheating when driving downhill. This is especially useful in protecting the brakes when towing a trailer, which is a common practice throughout European markets.

Engine drag control is a part of the ABS system and is on both manual and automatic transmission CTS models. To avoid rear wheel slippage when downshifting in low friction surfaces including ice or wet pavement conditions, the ABS system measures wheel speed versus vehicle speed and applies braking to the rear wheels to provide maximum traction.

Cadillac's stability enhancement system, StabiliTrak, will be standard on the CTS sport model; it will not be available on the base model. The newest version of the system is designed to enhance driver control by helping to maintain the vehicle on its intended path during emergency or hazardous road conditions. Used in conjunction with the standard ABS and traction control systems, StabiliTrak includes four major safety components that help give the driver ultimate control:

• Four-wheel speed sensors to measure wheel speed and direction
• Steering angle sensor that measures the turning of the steering wheel
• Integrated yaw sensor to gauge the turning angle of the car
• Hydraulic control unit that compares the turning angle of the car to the turning angle of the steering wheel.

If the system senses a difference between the two inputs, the hydraulic control unit applies and adjusts braking at any of the four independent brakes to bring the vehicle into alignment with the needs of the driver. The system is fully automatic, requiring no input from the driver, and is designed to help drivers maintain vehicle control when faced with obstacles in the road, adverse pavement conditions or accident avoidance.

Both the traction control and stability control system can be turned off, if the driver desires, via a switch located in the glove compartment.

The four-channel application is a first for StabiliTrak.

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CHASSIS/BODY
Type - unit body construction with one rubber-isolated subframe
Body Material - welded steel stamping

DIMENSIONS AND CAPACITIES
Wheelbase - 113.4 in.
Front Track - 60 in
Rear Track - 60 in.
Length - 190.1 in
Width - 70.7 in
Height - 56. 7 in
Ground Clearance - 5.9 in
Fuel Capacity - 18 gal
Coolant Capacity - 10.4 qts.
Curb Weight - (Manual - 3509 lb.) (Automatic - 3568 lb.)

BASE SUSPENSION
Front - Independent, short/long arm coil over shock, 23mm stabilizer bar (hollow)
Rear - Independent, modified multi-link, coil springs, monotube shock absorbers, 16mm stabilizer bar (solid)

BRAKES
Front - 11.9" x 1.3" vented discs (303mm x 32mm)
Rear - 11.7" x 1.0" vented discs (298mm x 26mm)
Power assist with four channel anti-lock
StabiliTrak and Traction Control available

WHEELS & TIRES
16" x 7" cast aluminum with Goodyear Eagle RS-A 225/55HR16
17" x 7.5" cast aluminum with Goodyear Eagle RS-A 225/50VR 17 (optional)

STEERING
Rack & Pinion, power assisted
Turns lock-to-lock - 3.37
Turning Circle curb-to-curb 35.5 ft.

FUEL ECONOMY (EST.)
EPA City - 18 mpg
EPA Highway - 26 mpg