While the 2013 Cadillac ATS showed the potential of General Motors’ new lightweight Alpha rear-drive/AWD platform for creating strong, mass-efficient passenger cars, the 2014 CTS sedan proves Alpha has plenty of ‘stretch’ for larger, more powerful iterations. When the all-new Alpha-based CTS begins production this fall, Cadillac finally will have two new products aligned directly against the sport-sedan benchmarks, BMW’s 3 Series and 5 Series.
“The previous generation CTS was a ‘tweener’—larger than the 3 Series but smaller than the Five. We were stuck between them,” admitted Dave Leone, GM Executive Chief Engineer―Luxury and Rear-Drive Vehicles. “Now we’ve got the [compact] ATS and [midsize] CTS sized right versus the competitors, and both are the lightest-weight sedans in their segments.”
In moving CTS to the Alpha architecture, the development team lengthened the wheelbase by 1.2 in (31 mm) and added 5 in (127 mm) to the car’s overall length (see table). The roof line and cowl are about an inch (25 mm) lower than those of the outgoing model, which enabled Design Director Mark Adams’ exterior team to “shrink-wrap the vehicle around its mechanicals.” He said the overall “lower, longer, and leaner” form heralds Cadillac’s new design language.
GM's first aluminum doors
In rear-drive configuration, the new CTS sedan equipped with the turbocharged 2.0-L four-cylinder (new for the nameplate) and six-speed automatic, has a mass of about 200 lb (90 kg) less than the BMW 528i, and about 7% less than the previous CTS, according to Leone.
CTS features the first aluminum doors ever on a GM production vehicle in addition to the many lightweight chassis and suspension components carried over from ATS—including cast-magnesium engine mounts, high-pressure die-cast aluminum front strut towers, aluminum crush cans on the frame-rail ends, and aluminum front cradle, suspension links, bumper beam, and hood.
The fully aluminum front and rear door structures save about 17 lb (7.5 kg) per closure—66 lb (30 kg) total—versus a set of comparable steel doors. Leone told AEI that his “every gram every day” mass-reduction mantra that kept the ATS engineering team sweating over their FEA models was carried over into the CTS program.
The body structure also features tailor roll-formed B-pillars that measure 1.4 mm (0.06 in) at their ends, increasing to 1.9 mm (0.08 in) in the center. The design removes unnecessary mass and puts strength where it’s needed most. The pillar structure includes more than 200 spot welds for added stiffness.
The CTS also uses an isolation-mounted fabricated steel cradle similar to that of ATS to support the car’s five-link rear suspension and drive axle. At 54 lb (25 kg), it is 15 lb (7 kg) lighter than the previous CTS’s rear cradle. And being steel, it’s also not overly light as to add unwanted mass in the rear of the vehicle while damping noise more effectively than an aluminum cradle.
The car shares the ATS’s nearly 50/50 front/rear weight balance despite its longer length and overhangs, Leone said. The lighter, longer unibody is approximately 40% stiffer overall than the incumbent CTS and achieves the best torsional stiffness in the luxury D segment, he claimed.
CTS gets premium NVH abatement
The double-ball-joint McPherson strut front suspension and rack-mounted ZF electric variable-assist power steering gear essentially carry over from ATS, with the suspension link geometry and wheel offsets changed for duty on the larger, heavier CTS. The Magnetic Ride Control suspension with real-time damping control pioneered by Delphi and now supplied by Beijing West Industries (BWI) is standard or available with every engine and transmission combination.
GM’s new 3.6-L Twin-Turbo V6 heads the CTS’s engine offerings in the new V-Sport model. For more on the SAE-certified V6 rated at 420 hp (313 kW) and 430 lb·ft (583 N·m), go to http://www.sae.org/mags/aei/11941. The CTS also is available with a naturally aspirated 3.6-L V6 rated at an estimated 321 hp (239 kW) and the aforementioned 2.0-L turbo four-cylinder rated at an estimated 272 hp (203 kW); neither engine was SAE certified at the time of publication.
The V6s are paired with a new Aisin-sourced TL-80SN eight-speed automatic (see http://www.sae.org/mags/aei/11942) with paddle-shift capability for rear-drive models or a GM six-speed automatic with all-wheel drive. The 2.0-L model uses the six-speed transmission. CTS is GM’s first application of an electrically actuated limited-slip rear differential.
CTS passengers will enjoy a placid cabin, Leone promises, that benefits from significant NVH analysis and tuning. Technologies include:
• A custom dash panel featuring strategic applications of laminated steel. This provides sound deadening in key areas rather than on the entire dash, reducing the weight compared to a fully laminated or fully damped panel;
• A double-wall acoustical barrier created by sandwiching the front-of-dash panel between two damping mats. The passenger-side mat is covered with a cast foam and molded barrier that fits tightly over the panel’s contours. The engine-side mat is a 30 mm (1.2 in) thick formed-fiberglass component;
• CTS-specific acoustic material in the transmission tunnel, under the vehicle, in the rear package shelf and other areas;
• Lightweight polypropylene absorption insulation in the trunk trim, under the rear deck, and throughout the interior that enables greater acoustic performance with less mass. It is more than 50% lighter, with greater sound-absorption qualities, than conventional acoustic insulation;
• A GM-first application of vibration damping foam. Similar to the "memory" foam found in premium bedding, it is used on the top layer of the CTS sedan’s front seats to absorb resonance from the lower portion of the vehicle;
• Acoustic-laminated windshield and front side-door glass are standard, with laminated rear-side doors available;
• Engine compartment side curtains made of a sound-absorbing, non-woven polyurethane material that close out the wheel well area down to the chassis to block noise; and
• Active noise cancellation using the Bose audio system that reduces interior noise levels by up to 20 dB under certain conditions.