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The 2000 Cadillac DeVille |
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CHASSIS UPGRADES IMPROVE DeVille'S COMFORT, SAFETY, STABILITY & ROAD POISE
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Driver control is improved by two enhanced features of the Northstar System. The first is StabiliTrak 2.0, the next evolution of Cadillac�s world-class stability control system, which is standard on the DTS and optional on the DeVille and DHS. In addition, the DTS comes standard with continuously variable road-sensing suspension (CVRSS) 2.0 with transient roll control, lateral support and enhanced stability. Combined with the G-platform architecture, these Northstar System upgrades deliver major improvements in stability, safety, road poise and ride. Several fundamental design features are carried over in the new chassis design. The engine and transaxle assemblies are still transversely mounted on a rubber-isolated cradle to power the front wheels. The front cradle also provides a lower attachment for the MacPherson strut front suspension and a stable mounting location for the rack-and-pinion steering gear. As before, front and rear suspension systems are independent with coil spring elements. Electronically controlled air shocks at the rear maintain a level attitude with changes in passenger or cargo load. The slightly larger foundation brakes are vented discs in front and solid discs in back.
CLASS II NETWORK
Instead of providing a separate wire for each and every electrical function, messages are digitally coded by an electronic module and then delivered along with thousands of other coded messages via just one wire. This technique, known as multiplexing, permits sharing of the information by various systems and modules. All systems of the vehicle share information along this network, allowing the sharing of key data. The Class II label used to describe this architecture refers to the operating speed of 10,400 bytes of information every second. Since each message is composed of only a few bytes, the system is capable of delivering hundreds of messages per second. DeVille�s five major chassis systems - engine, transaxle, steering, braking and shock absorbers - are interconnected so that one helps the other deliver smooth, safe, surefooted performance.
CHASSIS FEATURES
Magnasteer variable-effort power steering. A magnetic field is generated in the steering gear�s control valve to permit varied steering effort requirements. Low efforts are selected for ease of parking. Higher efforts are specified at higher speeds and when the driver needs a more confident sense of the road. Steering effort also is increased during traction control actuation and during ABS braking events. Using an electrically generated magnetic field instead of the previous permanent magnet design eliminates the chance of audible electrical interference through the entertainment system. The use of cast-aluminum suspension control arms and knuckles, front and rear, minimizes mass. Micro-alloy steel is used to save approximately one pound of mass per coil spring. A "dual-cannon" mounting system for the rack-and-pinion steering gear uses a rigid mount at the driver�s side of the car and a rubber-isolated connection at the opposite side. Attachment fasteners are reduced from five to two. This design significantly reduces car-to-car build variations, thereby improving steering characteristics.
FRONT CHASSIS
An improved engine mounting system minimizes noise and vibration transmitted to the passenger compartment. Two hydraulic mounts between DeVille�s front longitudinal body rails and at each end of the engine-transaxle assembly carry practically all of the powertrain�s mass. These mounts are positioned on the torque axis and are tuned for maximum isolation. The hydraulic feature permits a softer rate without allowing large movements at certain frequencies. Fore-and-aft mounts are tuned to handle the powertrain�s torque reactions. The two fore-and-aft mounts anchor to the cradle. The forward torque-reaction mount is a rubber-hydraulic design while the rear one is conventional rubber and steel composition.
REAR CHASSIS
A welded-steel T-shaped member supports the semi-trailing arms and the rear anti-roll bar. It�s attached to the body through tuned rubber mounts, providing a second level of road isolation. This member also protects the fuel tank. A new composite fuel tank is made of six layers of material to minimize vapor losses.
RIDE AND HANDLING
DTS is equipped with a more active suspension tuned for improved performance. The CVRSS 2.0 system comes with three significant enhancements - transient roll control, lateral support and stability control interaction. CVRSS uses wheel-position sensors to read road conditions and fast-acting dampers at each corner of the car to continuously and instantly adjust ride and handling for any situation. At 65 mph, a damper can shift from full soft to full firm every 6 to 7 inches of road surface traveled. CVRSS manages both body and wheel motion. Damping is adjusted as necessary to control heave (up and down motion over road swells), pitch (front of car lifting while rear of car dives, or vice versa), roll in corners, and front-end lift during acceleration. On very smooth roads, damping forces are minimized to enhance isolation. To maintain ride comfort and stability at high speeds, damping forces are increased with vehicle speed. The extensive use of electronic chassis controls to manage steering, braking, suspension damping and traction functions interactively means that more ideal settings can be provided for every driving circumstance. It is not necessary to make tradeoffs, such as comfort versus performance or agility versus stability. While the car is quiet and smooth during cruising, the driver feels confidently in control during emergency or aggressive handling maneuvers.
CVRSS 2.0 ENHANCEMENTS
Another enhancement uses the lateral acceleration signal to improve vehicle lateral support by stiffening the outside dampers in compression and the inside dampers in rebound, effectively "wedging" the car, or decreasing lateral load transfer in a turn. This means that as the vehicle reaches steady state, the damper settings become optimized to maintain traction with the road. CVRSS 2.0 also features stability control interaction. When StabiliTrak is activated, the front corner with the brake applied is stiffened in compression, while the opposite rear corner damper is stiffened in rebound. This reduces the "dipping" of the body and thus improves handling.
FOUR-STAGE VALVING
Squeeze-cast aluminum road wheels provide the most mass-effective wheels available with superior surface finish. DeVille and DHS are equipped with Michelin blackwall all-season radials - size P225/60SR-16 - which provide very low rolling resistance for excellent fuel economy. White sidewall radials are offered as an option. DTS is equipped with Goodyear Eagle LS P235/55HR-17 blackwall all-season performance radials. DeVille�s anti-lock brake system, traction control and StabiliTrak systems are combined in a new Delco Electronics-Bosch 5.3 design that is smaller and lighter than the 5.0 design it replaces. A significant new feature with this system is electronic brake distribution. In place of a fixed front-to-rear distribution of braking effort for all vehicle loading and operating conditions, the electronic approach uses wheel-speed sensors and hydraulic controls to adjust and optimize distribution dynamically. Stopping distances are shortened, especially in the heavily loaded condition, when more rear brake effort is desired. Electronic brake effort distribution also improves handling during braking-while-turning maneuvers.
STABILITRAK BENEFITS
Introduced on three performance-oriented Cadillac models in the 1997 model year, StabiliTrak provides an important safety advance by helping the driver maintain control during emergency or evasive maneuvers. StabiliTrak works by comparing the driver�s intentions (indicated by steering wheel position) with how the vehicle is responding. Three key sensors keep the ABS and traction control computer informed: one reads steering wheel angle, another reports the vehicle�s lateral acceleration and the third measures yaw rate (rotational velocity about a vertical axis through the car�s center of gravity). Information is also gathered from vehicle speed. If the vehicle�s dynamic response does not agree with the direction the driver is steering, StabiliTrak goes to work by selectively applying the individual front brakes to help keep the car on the intended course. If the car is slipping wide of the desired path in a turn, applying the inside brake helps the DeVille turn tighter. In case of diminished traction at the rear causing the tail of the car to drift wide, activating the outside-front brake gently nudges the car back in line. StabiliTrak is automatic and requires no additional driver action. In most cases, the driver probably won�t even notice the helping hand from this technically sophisticated system. Respected car critics have called StabiliTrak one of the greatest active safety advancements since four-wheel anti-lock brakes. Unlike stability control systems from other manufacturers, Cadillac�s system maintains the driver�s ability to apply throttle in StabiliTrak maneuvers.
STABILITRAK 2.0
Another feature of StabiliTrak 2.0 is active steering effort compensation. Starting in 1998, Cadillac was the first in the industry to coordinate steering assist with stability control. During low-traction or emergency-maneuver situations, StabiliTrak commands the Magnasteer system to adjust the level of power assist in order to achieve a consistent steering feel. With the enhanced version of StabiliTrak on the 2000 DeVille, active steering effort compensation also is triggered by ABS and traction control operation. Combining steering assist level with stability control is unique to Cadillac, and it was achieved solely through software calibrations with no added hardware, cost or mass.
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