Cadillac STS

Press Release

Body, safety and security

 

From the inner structure to the architecture of the exterior sheet metal, the all-new Cadillac STS has been meticulously crafted to ensure delivery of the attributes expected of a luxury sedan. The STS features a body frame integral (BFI) structure, based on the premium GM Sigma rear-wheel-drive architecture. With a BFI structure, the upper body structure and sub-frames are engineered as a single unit, enabling a mass efficient, yet stiff, body structure.

 

BFI structures bring an ideal foundation for achieving sports sedan performance, resulting in a particularly rigid base structure with a beaming frequency of approximately 25 Hertz and significant torsional stiffness, some 13 percent greater even than the highly competitive Cadillac CTS. This provides a strong basis for the STS to combine great chassis dynamics with high levels of refinement. Additionally STS is equipped with a host of refinements to ensure a quiet ride and interior environment and impressive wind noise performance.

 

The Cadillac STS joins the CTS and SRX as the first vehicles in GM to be outfitted with a laminated front-of-dash panel – a key to reducing the transfer of engine compartment noise into the cabin. Also called “quiet steel�, the application is found on all Sigma architecture-based vehicles.

 

Noise-damping ‘blanket’

The front-of-dash panel consists of two thin pieces of steel held together by composite adhesive. A sophisticated bonding process ensures the steel will not resonate noise, and damps noise transfer significantly when compared to conventional applications. A front-of-dash mat constructed of a 28-millimeter thick thermal plastic olefin (TPO) cast foam material also reduces powertrain noise transfer into the cabin. The mat, essentially a noise-damping blanket on the engine side of the dash panel, is applied with a glove-like fit and closes out all cavities in the panel.

 

All chassis-to-body structure interfaces (i.e., suspension brackets or cradle attachments) on the STS have been designed to improve stiffness and structure, thus further isolating low-frequency noise from the cabin. Each of the interfaces has essentially been “tuned� through shape or material thickness to ensure a robust, stiff structure that effectively minimizes vibrations and related transfer of noise from road irregularities, engine, prop shaft, and other inputs.

 

In order to add greater reinforcement to the center tunnel of the STS, which serves as the “backbone� of the vehicle, a tubular structured U-shaped “strap� was added for tension and compression, again further improving the vehicle’s overall stiffness. It also helps reduce vibration to the floor pan and rear seats. A constraint layer also is implemented into the tunnel structure – inner and outer steel structures are mated together in a sandwich form. As a result, the two pieces of steel dampen each other, reducing the transfer of noise and vibration into the cockpit.

 

Reducing noise level

To attenuate noise transfer from the shock towers into the passenger compartment, all shock towers are applied with a constraint layer, two pieces of metal that sandwich a rubber viscous material, making up the structure of each shock tower. This application again significantly reduces the noise level in the passenger compartment. Similarly both rear wheelhouses on the STS are constructed of sandwiched steel structures that mate together as inner and outer structures, dampening each other, greatly reducing the resonation of noise into the rear passenger compartment.

 

A front tunnel barrier is applied under the carpet on the STS to ensure superior isolation from driveline acoustics. The barrier, which runs from the dash panel rearward on either side of the tunnel where it meets the floor, is constructed of a lightweight composite with outstanding noise damping characteristics.

 

An acoustic laminated windshield is a key enabler of the Cadillac STS model’s wind noise performance. While the windshield itself is thinner than traditional applications to reduce mass, a four-layer construction allows it to deliver the acoustic performance of thicker glass. Two layers of glass sandwich a safety laminate and an acoustical-grade vinyl sheet laminate, enabling a marked reduction in wind noise. Laminated front side glass also provides significant improvements in wind and external noise performance.

 

Further, typically Cadillac, attention to detail is demonstrated by the use of lightweight damping material throughout the vehicle cabin to address the high- and mid-range frequencies normally requiring heavier deadening materials. The material is a foil/rubber acoustical damping compound that is adhesively applied to the inner sheet metal, a first-time Sigma architecture application, while low weight, high-absorption trunk acoustics effectively damp noise and vibration from the luggage compartment.

 

Lower profile, structure-less windshield wipers deliver a wind noise reduction when compared with conventional applications. Sometimes called “flat blades�, the wipers replace an arm structure, a common source of noise when wind travels through and around it, with a flexible airfoil surface that runs along the top of the blade. The airfoil is “tuned� to the shape of the windshield, ensuring a lower profile and superior contact with the windshield at all positions.

 

The doors-into-roof construction on the STS eliminates the need for molding along the top of side window glass and ensures consistent surfaces around the elements. This door execution, inspired by high-performance aircraft, enables extremely tight gap tolerances, removes a source of wind noise and plays a primary role in the integrated, clean and sleek appearance of the STS. A triple seal architecture around all four doors reduces vehicle interior noise levels. Three seal sets work together to effectively seal the passenger compartment from wind, water, and other elements. 

 

Sculpted surface

The aluminium decklid on the STS luggage compartment is a complex shaped form produced using an advanced superplastic forming (SPF) process, an execution that enables a sculpted surface and outstanding dimensional accuracy. A traditional stamping execution of either steel or aluminium would have resulted in a two-piece execution of the decklid, requiring the use of additional exterior trim.

 

In the superplastic forming process, aluminium is heated to a state of plasticity then formed into a die cavity using air pressure. The final result is a single-piece form, with an integrated pocket for the light emitting diode (LED) CHMSL as well as the backup lamps, which ensures a clean surface throughout the contoured shape of the decklid.

 

The STS maintains Cadillac's long-standing reputation for delivering a safe occupant environment in premium vehicles. Structural enhancements contributing to the excellent crash performance capability of the STS include a two-piece magnesium cross-vehicle structure for side and front crash protection, octagonal engine rails to enhance high-speed offset crash protection and a one-piece hydroformed A-pillar/roof rail structure that brings added upper structural rigidity and enhanced strength during side and frontal impacts.

 

Inner and outer rocker panels are constructed of strong, ultra-high strength steel and longitudinal rails are injected with structural foam to protect and maintain their geometry during an impact. The foam adds to overall body structure stiffness and contributes to preventing intrusion around occupants' feet during high-speed offset impacts. Rear rail inner sections are constructed of high-strength dual phase steel - a first-time application on the Sigma architecture. Dual phase steel brings outstanding characteristics for supporting crashworthiness deformation.

 

Six airbags as standard

The STS has a total of six airbags offered as standard equipment, which help to maximize protection in high-speed crashes while minimizing the risk of injury to out-of-position occupants. Airbags include a dual stage driver's front airbag and a front passenger airbag, driver's and front passenger seat-mounted airbags for thorax protection, along with roof rail side curtain airbags giving head protection with front and second row coverage.

 

In the case of the dual-stage airbags, when the air-bag system's central control unit, the Sensing Diagnostic Module (SDM), detects an impact, it determines whether the crash is severe enough to trigger a deployment, and whether the primary amount of inflation is sufficient or if both primary and secondary stage inflation is required. The primary stage alone will deploy in most frontal impacts requiring the supplemental protection of an airbag, while the secondary stage also will deploy in very severe frontal collisions.

 

The SDM also detects side impacts and determines whether the rail-curtain and side seat-mounted (thorax protection) air bags should deploy. These air bags act like a protective curtain, unfolding from the roof rail between the A and C pillars.  When the bag deploys, it is biased toward the window to help maximize protection.

 

The SDM also activates the safety belt pretensioner, which reduces slack in the safety belt webbing. This helps secure occupants in the seat to better hold them in position so they decelerate at the same rate as the car. The safety belts are equipped with ‘frictionless’ D-rings and low-effort retractors so there is minimum pressure on the occupant, making them more comfortable to wear. The retractors also are energy absorbing.

 

Second row seats have three-point safety belts in all positions. The second-row seats of the STS come equipped with the LATCH system to simplify child seat installation. These anchors, which are secured to the body structure, are provided in all three rear-seat positions.

 

Occupant security features

Occupant security is provided with a number of standard and available features, including child security door locks so a parent can choose to prevent their child from opening the rear doors from the inside and a power window lockout so control of the windows can be limited to the driver controls. An engine immobilizer and theft deterrent system is standard as is delayed entry lighting, which keeps the interior lights on after the driver enters and until the vehicle is started.

 

The Standard Remote Keyless Entry also includes a panic button on the key fob, which turns on all the lights except the headlamps, sounds the horn and activates content theft deterrent and anti-lockout features. Battery rundown protection automatically shuts off any electrical system inadvertently left on after a period of time before the battery runs down. A child entrapment release lever is fitted in the trunk and further peace of mind is offered with the option of a tire pressure monitoring system.

 

Chassis: a perfect balance of ride and handling

A host of chassis refinements ensure that the STS hits the perfect balance of smooth ride and entertaining handling. Road impacts and other harsh inputs are effectively absorbed and dissipated through ride-tuned tires, dampers, suspension components and bushings, as well as improved structure in body-to-chassis interfaces and additional refinements in the engine mounts. The result is a ride that keeps drivers fresh and comfortable without sacrificing the driving experience.

 

Among the many refinements found in the front suspension components is the use of aluminium for both the upper and lower control arms, suspension joints and brake callipers. This reduces unsprung mass, requiring less damping and dynamic wheel control, contributing to more nimble handling and better road-holding ability. Hydraulic control arm front bushings are used to provide optimum motion control while minimizing high-speed road vibration, by damping energy transmitted to the vehicle structure. A hollow front stabilizer bar on all models brings weight savings and added stability. The fully independent multilink rear suspension with fully isolated sub frame is an uncompromising design with excellent suspension kinematics that enables outstanding ride and handling performance.

 

At the same time, the other features of the suspension architecture give it the ability to control loads and maintain stability during dynamic driving situations, striking a balance between ride quality and high-performance handling capability. Other rear suspension features include weight-saving aluminium upper control arms, knuckles and brake callipers, along with hollow rear stabilizer bars. The rear suspension is fully isolated to reduce road and driveline noise.

 

Rear damping is provided by Nivomat load-levelling shocks, a fully automatic hydraulic level-regulating system with integrated shock absorber, adapt automatically to different loads and road conditions.

Front shock absorbers on base models are monotube dampers from Sachs, a leading German producer of high-performance shock absorbers, which provide highly responsive damping of road inputs.

 

The STS V8 model also offers as standard the award-winning Magnetic Ride Control (MR) system which uses electronic control of damping forces in a continuously variable real-time damping system to provide exceptional responsiveness, greatly increased driver control and increased tire contact with the road, regardless of road surface. 

 

The MR system uses valveless damping and magneto-rheological (MR) fluid technology. The fluid is a suspension of iron particles in a synthetic hydrocarbon-base fluid. When the system is activated, the particles are magnetized and aligned into fibrous structures, changing the flow resistance of the fluid. By controlling the current to an electromagnetic coil inside the piston of the damper, the system varies the fluid viscosity continuously in response to road surface conditions over a broad damping range.

 

Increased wheel contact

Damping levels are adjusted up to 1,000 times per second, making the system exceptionally responsive and providing increased wheel contact on even the roughest road. Reduced wheel bounce ensures an even ride by virtually eliminating heave, pitch and roll. It also delivers excellent roll control during transient steering and evasive manoeuvres.

 

A set of wheel-to-body sensors detects changes in the road surface and the system controller adjusts the fluid viscosity to vary the damping force accordingly, providing a flatter ride during cornering and reduced diving or squatting during braking and acceleration.

 

The MR system on the STS is among the first to make available two selectable settings accessed through the infotainment display head – performance or touring modes. The performance mode may be used where road conditions or personal preference demand more control; the setting provides more “feel� or responsiveness to road conditions. The touring mode is available for normal city and highway driving and provides a smoother, more accommodating ride.

 

Enhanced steering input is offered by optional ZF Servotronic II rack-and-pinion speed-sensitive steering gear with 18.2:1 variable ratio and speed-sensitive variable assist. The turning radius of the Cadillac STS is just 11.5 meters. The standard StabiliTrak system on the STS is a sophisticated four-channel (independent control to all four corners of the vehicle) active handling system. It links the vehicle’s dynamic control systems to assist the driver in maintaining control under demanding or adverse conditions such as wet, snow-covered or icy roads, tight turns, and evasive manoeuvres.

 

The STS is equipped with four-wheel-vented disc brakes with standard four-wheel antilock braking system (ABS) and traction control system (TCS). The brakes feature vented rotors consistent with the demands of a luxury performance sedan. Base brake package rotor dimensions are 303 x 32 mm front and 298 x 26 mm rear. Uplevel brake package rotor dimensions measure 323 x 32 mm front and 320 x 26 mm rear.

 

Panic Brake Assist (PBA), which senses emergency braking by detecting the speed or force the driver applies to the brake pedal and boosts the power as needed, is incorporated into the brake system. Under certain conditions, the panic brake assist may activate the ABS more quickly and easily than vehicles without the feature, potentially reducing overall stopping distance by eliminating the delay caused by not braking hard enough and/or soon enough. The system also features Dynamic Rear Brake Proportioning, which regulates braking pressure to optimize stopping distances and control under all vehicle-loading conditions.

 

The Cadillac STS is available with 17- or 18-inch wheels. V6 models use 17 x 7.5 cast aluminium front wheels with P235/50R17 tires and 17 x 8.0 rear wheels with P255/45R17 tires. Cadillac STS V8 models feature 18 x 8.5-inch flow-formed aluminium wheels with high performance 255/45R18 tires on all four corners.