CT6 Active Chassis System

The advanced performance chassis system of the Cadillac CT6 is designed to deliver an engaging driving experience — delivering segment-best ride, handling and isolation qualities — with active on-demand all-wheel drive, active rear steering and Magnetic Ride Control on the available Active Chassis System. (Fig. 9)

 

F09 CT6 active chassis image

Fig. 9

 

Active Rear Steering

 

Active Rear Steering (ARS), standard on the Platinum edition and offered as an option on the Luxury and Premium models, improves low-speed maneuverability and increases agility at higher speeds. At low speeds (below 22.3 mph or 36 km/h), the rear wheels turn in the opposite direction of the front wheels in both forward and reverse gears. The system allows the rear wheels to turn in unison with the front wheels at higher speeds (above 22.3 mph or 36 km/h), which helps the vehicle change direction much better. The result is a full-size car that handles like a mid-size sports sedan.

 

Active Rear Steering Smart Actuator

 

The ARS system consists of a smart actuator (Fig. 10, #2) that contains the control module and motor and the linkage that transmits the force from the actuator to the rear steering knuckle and wheels. The ARS system is controlled by the Electronic Brake Control Module (EBCM), which uses inputs including vehicle speed, steering wheel angle sensor, and steering wheel angle rate of change to determine the correct rear wheel steering angle.

 

F10 CT6 actuator

Fig. 10

 

The EBCM uses the Chassis GMLAN bus to command the Rear Wheel Steering Control Module (RWSCM) to turn the rear wheels. The RWSCM provides feedback to the EBCM for the steering position and rate of change. The ARS system can mechanically move 4.6 degrees but the controller limits movement to 3.5 degrees.

 

Active On-Demand AWD

 

Active-on-demand all-wheel drive (AWD) – standard on all CT6 V6 models — is also part of the Active Chassis System, making the most of handling and stability in all weather conditions. The AWD configuration adds an active transfer case after the transmission that splits the power between the one-piece front propeller shaft and the two-piece rear propeller shaft.

 

The AWD system features a Magna model MP 3713G one-speed transfer case. Software calibrations tune an on-demand torque biasing friction clutch. When a driver enters a turn, clutch torque decreases based on the various GM LAN inputs, such as steering angle and vehicle speed, to prevent crow-hopping or driveline binding from occurring at low speeds.

 

The torque split between the front and rear axle is not fixed, which differs from an open center differential transfer case. The active design can transfer 0 to 100 percent of the torque to the front axle. The torque transfer is adjusted based on multiple inputs, including wheel slip, engine speed, throttle position, transmission gear and the selectable driving modes of Tour, Snow/Ice or Sport mode.

 

Torque is moved to the front axle through an active wet clutch within the transfer case. (Fig. 11) The actuator motor turns a worm gear that rotates the shift shaft, which actuates a scissor mechanism and applies the clutch.

 

F11 CT6 transfer case

Fig. 11

 

The selectable driving modes use magneto-rheological technology to independently control each of the shock absorbers and struts and change the characteristics of the suspension system. Magneto-rheological technology independently controls the fluid viscosity in each strut and shock absorber. Front struts and rear shock absorbers contain an internal electrical coil and micron-sized metal particles in the magneto-rheological fluid. The suspension control module uses pulse width modulated (PWM) current to the electric coil within each strut or shock. The PWM current increases the fluid viscosity by aligning the metal particles within it, which increases or decreases the suspension damping force during both compression and rebound.

 

In all types of weather and road conditions, the system allows drivers to tailor the system to deliver a customized ride and precise handling.

 

– Thanks to Sherman Dixon and Blake Streling

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