When discussions began nearly a year ago about what car to bring to Today’s Technology Center booth #W-20 for IMTS 2016, Cadillac’s CT6 was a clear favorite. Not as flashy as the Chevrolet Corvette that we brought to McCormick Place in 2014, or as radical as the Buckeye Bullet electric speed racer from 2012, the CT6 represents where automotive manufacturing needs to be by 2025 to meet fuel economy standards.
A mixed-metal vehicle with extensive use of high-strength steels, sheet aluminum, extruded aluminum, and several exotic alloys, the CT6 is forcing its manufacturer to explore new production techniques and develop entirely new systems.
It’s the role that Cadillac has often played for GM – a nameplate that sells expensive vehicles that stretch the limits of what engineers can accomplish. And as Cadillac perfects those techniques, they flow down to Buick, GMC, and Chevrolet. For example, when the Cadillac CTS launched in 2003, it featured never-before-used welding techniques such as laser-brazed steel sheets to connect vehicle side panels to the roof – creating a smooth, flat seam between the two. The 2016 Chevrolet Malibu uses that technology to create a
, giving the trunk a spoiler-like look without adding plastic trim. sharply raked rear deck lid
The materials and processes enhancements don’t end at the vehicle body. Two redesigned V-6 engines feature specialty alloyed steel crankshafts, rather than cast iron, and use polymer-coated pistons and sintered connecting rods.
On the following pages, we’ll discuss what makes the CT6 special, and how its manufacturing technologies are a glimpse at where the world is heading.
Cadillac – General Motors Co. www.cadillac.com IMTS 2016 Booth #W-20 About the author: Robert Schoenberger is the editor of TMV and can be reached at 216.393.0271 or firstname.lastname@example.org. Multi-metal design
Cadillac engineers like to brag that the CT6 is the size of a BMW 7-Series sedan, with the weight of the 5-Series. It accomplishes this by using aluminum for 62% of its body, saving high-strength steel for critical structural components. Relying mostly on aluminum but using steel strategically, shaves more than 200 lb from the CT6’s weight, compared to steel-bodied vehicles.
However, there’s a tradeoff with aluminum. The material is lighter, but it’s less formable, and not as strong as steel. Creating an A-pillar — the metal bar that connects the roof to the car body and supports the windshield — out of aluminum would require a column so thick that it would create blind spots for drivers.
So, Cadillac engineers use advanced high-strength steels (AHSS) for many critical parts. Connecting those steel parts to aluminum components is a massive challenge – requiring the use of aluminum spot welds, steel spot welds, flow drill screws, self-piercing rivets, laser welding, aluminum arc welding, and hundreds of feet of structural adhesive.
“The structure of the CT6 is one of the most-advanced body systems we’ve ever produced,” says Travis Hester, Cadillac CT6 executive chief engineer. “The innovation surrounding our joining techniques have enabled us to create a vehicle structure with the highest torsional rigidity of any Cadillac while achieving one of the most mass-efficient vehicles in the segment.”
Today’s Motor Vehicles detailed the in the July, 2015 issue. laser-welding techniques used for the CT6 CT6 body Lower structure: 13 complex, high-pressure die-cast components, aluminum sheet construction, aluminum extrusions Underbody: Steel close-out panels to lower cabin noise without adding sound-deadening material B-pillar: High-strength steel structural components to aid vehicle ingress, egress, and visibility Safety structures: High-strength aluminum impact bar added to the rear of the vehicle, high-strength aluminum and steel used for front and side impact zones Advanced transmission
Precision manufacturing allows the 8-speed, paddle-shift automatic in the CT6 to fit into the same space as a 6-speed, yet the transmission is lighter than outgoing 6-speed models. It is based on the 8-speed automatic family introduced on the Corvette Stingray.
Stop/start technology: Shuts down engine to reduce fuel consumption when vehicle comes to a complete stop, automatically restarts engine when driver takes foot off the brake pedal Gear ratio: 7.0 overall improves fuel economy 5% First: 4.62:1 Second: 3.04:1 Third: 2.07:1 Fourth: 1.66:1 Fifth: 1.26:1 Sixth: 1.00:1 Seventh: 0.85:1 Eighth: 0.66:1 Reverse: 3.93:1 Compact, simplified design: Four simple gearsets, five clutches (two brake clutches, three rotating clutches) Friction-reduction: Synthetic fluid, lower spin losses via a powerflow using two open clutches per gear, off-axis binary vane pump Construction: One-piece case with integral bell housing; grounding clutches located rearward of the middle of the structure, outside the gearsets, splined to the case; rotating clutches located near the front of the transmission with short oil feed channels supporting very fast shifts; oil-storage accumulator supports stop/start technology Transmission controller: Mounted externally, processor executes hundreds of calculations and commands every 6.25ms Creative features
The CT6 includes a few bells and whistles to set it apart from mass-market, commodity vehicles.
Surround-view video recording system: Four of the vehicles’ seven exterior cameras – one in each door-mounted rearview mirror, one integrated into the front grille, and one mounted on the rear trunk lid – combine data to create a 360° view of its surroundings and provide video of the CT6’s surroundings. The system can record any tampering attempts when the vehicle is parked, or, when the vehicle is in use, can show how close drivers are to curbs or other vehicles. Captured footage is stored on a standard SD card in the trunk of the vehicle. Owners can choose to save certain captures indefinitely on the SD card or they can view or save the video files onto their personal computers. The three remaining cameras on the CT6 support lane-departure warnings and night vision. : The camera can act as a flat, reflective sheet of glass or as a video monitor for cameras mounted at the rear of the car, avoiding obstructions such as rear-seat passengers. Rear-camera mirror Plug-in hybrid
Lightweighting in the body, engine, and transmission make the CT6 one of the most fuel-efficient gasoline-powered luxury sedans on the market, but late this year or in early 2017, an even more efficient version will become available. The plug-in hybrid electric vehicle (PHEV) will add large batteries and electric motors to the 2L 4-cylinder turbo engine.
30 mile all-electric mode range 65 miles per gallon equivalent (mpge) estimated Two 100hp electric motors 18.4kWh lithium-ion battery pack Three operating modes Normal: Commuting setting for comfort, performance, EV range, fuel economy Sport: More aggressive torque response, stiffer steering response Hold: Owners select when vehicle uses its engine, reserving battery charge for later use
CT6 Engine technology
Cadillac offers three engines, a 2L turbocharged 4-cyliner; a 3.6L V-6; and a 3L two-turbo V-6. Both V-6s debuted on the CT6, while the 2L turbo debuted on the ATS in 2014. The V-6 models include several fuel-saving technologies.
V-6 engines Active fuel management: Deactivates two cylinders at cruising speeds Start-stop technology 3L twin-turbo V-6 400 hp, 400 lb-ft torque Low-inertia turbochargers sustain peak torque from 2,500rpm to 5,000rpm 44MnSiV6 forged-steel crankshaft 9.8:1 compression ratio, turbo-chargers offer 125kPa boost 6% estimated fuel economy improvement 3.6L V-6 335hp, 284 lb-ft torque 1538MV forged-steel crankshaft; friction-reducing polymer-coated pistons; high-copper-content, sinter-forged connecting rods Higher-flow cylinder heads enhance direct injection performance, feature integrated exhaust manifolds 9% estimated fuel economy improvement