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Written by Dan Carney
In developing the Cadillac ATS-V high-performance variant,General Motors" engineers were faced with an unfamiliar problem; a base carthat was a little too light. Not exactly, but that was the gist of the issue. After yearsof developing cars in which mass reduction was a seeming afterthought, GM haswith recently developed models such as the ATS, on its Alpha platform, so thoroughlyoptimized on mass for the base model that the car was left needing a stronger foundation when more powerand traction were added for the ATS-V model. In both its two-door coupe and four-door sedan variants, theATS-V received a raft of needed chassis reinforcements that produce a 25% increase in torsional rigidity, reported Cadillac Chief Engineer DaveLeone. This improvement was achievedthrough the installation of a front shock tower-to-plenum brace along withunderhood V-braces, reinforcement to the rocker bulkhead, stamped steel bolt-onbraces between the rear suspension cradle mount and the floor of the unibody,and (the centerpiece of the upgrades) a large aluminum platform beneath thefront suspension subframe that the company terms a "shear plate" that connectsthe front suspension and its cradle more securely to the car"s unibody. The effect of that huge aluminum reinforcement plate is feltprimarily on corner turn-in, where the ATS-V responds crisply rather than by twistingthe car"s structure, according to Leone. With the platform suitably braced, GM"s engineers beefed upthe suspension components too. That includes replacement of bushings in themulti-link double-pivot MacPherson strut suspension with zero-compliance balljoints, stiffer front springs, and thicker front anti-roll bar that combine toproduce a 50% increase in roll stiffness. The ZF Servotronic II steeringrack is also stiffer than that on the regular ATS, which also contributes toimproved steering feel. At the rear, there are stiffer bushings, springs, andanti-roll bar along with stronger cradle mounts. Revised rear suspensiongeometry incorporates more anti-squat and has less migration of the rear rollcenter. A standard electronic limited-slip differential helps putthe power down on corner exits, while different-diameter halfshafts suppressaxle hop under acceleration by not having the same frequency response totorque. The left side shaft, which is provided by GKN as an assembly with itsconstant velocity joints, is 55 mm (2.2 in) compared to 30 mm (1.2 in) for the standard-issueright shaft, for a 2.6:1 difference in rigidity between the two. Brakes are the same Brembo six-piston one-piece front calipers with14.5-in (368-mm) rotors at the front and four-piston rear calipers with 13.3-in(338-mm) rotors at the rear as were used on the heavier outgoing-generation CTS-V, whichprovided impressive stopping power without fade or increased pedal travelduring track testing at the Circuit of the Americas in Austin, TX. Damping is by the BWI Group"s Magnetic Ride Control thatCadillac brought to market. This latest iteration of the technology providesimproved differentiation between its two modes, according to John Barrick, Program Engineering Manager for the ATS-V. "Now we have two true modes," hesaid. "Before it was more like one and a half modes." The increase in maximumdamping is 40% greater than before. The new system"s quicker response time means that the damper adjusts itself for every inch the ATS-V travels at 60 mph (97 km/h), while theprevious system covered three inches between adjustments to settings, Barrickadded. The 18-inch forged aluminum wheels help reduce mass andmount Michelin Pilot Super Sport tires molded with three distinctly differentzones of compound. The outer shoulder is hardened to withstand the corneringforce of hammering around tracks without burning the rubber off the outside ofthe tires. The middle section is optimized for wet traction, and the innerportion is sticky race-ready rubber. On the track, the tires contributed to an impressive 1.25 glateral acceleration in the turns. Just as engineers attended to every detail under the skin,so did the designers when working on the skin itself. "All of the design elementshave a purpose," said Andrew Smith, Executive Director of Cadillac Global Design."They contribute to lift reduction, enhanced cooling, reduced mass, or all ofthe above." Most obvious is the carbon-fiber hood, with its bare carbon heat extractorvent. The hood saves weight compared to a steel hood, and the extractor notonly helps hold down engine bay temperatures, but the air exiting it atop thehood reduces lift at speed. The enlarged openings in the front fascia feed more air to the variousheat exchangers behind it, and the splitter on the bottom scrapes directs air from theroad surface, minimizing lift. The ATS-V"s fenders are widened to cover thewider wheels and tires, and the rocker panels and rear spoiler provide thefinal touches on overall balance of lift on the car. The optional carbon-fiberpackage provides enlarged splitter, hood air extractor, rear spoiler, rockerpanels, and rear diffuser. Those aren"t the only aerodynamic devices. Under the car, the lower controlarms at the rear are sheathed in plastic covers that Barrick says reduce dragby two counts. Naturally, as a high-performance variant, once the necessarysupporting infrastructure was established, the ATS-V needed a suitably morepowerful powertrain. It is an SAE-certified 464-hp (346-kW), 444-lb ft (601-N m) twin-turbocharged,direct-injected 3.8-L V6 engine matched to a six-speed manual or eight-speedautomatic transmission. The car accelerates to 60 mph in 3.8 s andreaches a top speed of 189 mph (304 km/h). The engine features turbocharges with low-ineria titanium-aluminideturbine and vacuum-actuated wastegates for reduced lag and stronger low-rpm response. The turbos" compressors are matched for peak efficiency atpeak power levels, providing maximum on-track performance. The engine"s response is augmented by a patent-pending low-volumecharge-cooling system that improves packaging efficiency while permittingmaximum boost pressure. The engine itself enjoys some reduced inertiacourtesy of its titanium connecting rods. The Hydra-Matic 8L90 eight-speed automatic is the fasterand more efficient transmission choice. The car features steering-wheel-mounted paddles formanual shift actuation, but when the ATS-V is switched to attack mode, thetransmission"s computer makes flawless shift decisions while the driver hammersthe car around a circuit. In most respects, it is the better way. However, for those drivers who think it is not the fun way, Cadillac offers theTremec TR6060 six-speed manual transmission. We"ve seen automatic rev matchingon downshifts elsewhere, including GM"s own Chevrolet Corvette, but the ATS-V adds tothat no-lift upshifts. The driver depresses the clutch, makes the manualgearchange using the H-pattern shifter, and releases the clutch pedal all asusual. But the accelerator pedal stays on the floor throughout and the carautomatically cuts power just long enough to compete the shift motion. Though this defies the accumulated muscle memory in anyone able tooperate a manual transmission, it makes upshifts shockingly quickly. So, maybecomputer-matched downshifts and automatic power-cut upshifts leave the driverdoing less of the manual shifting job, both ensure that the shifts are smoother and faster. The EPA fuel economy estimates for the automatic transmission-equippedATS-V are 16 mpg city and 24 mpg highway, while the manual gets 17 mpgcity and 23 mpg highway. An electronically controlled limited-slipdifferential helps the power get to the road effectively, with a 3.73:1 finaldrive ratio for the manual transmission and a 2.85:1 for the automatic, thanks toits abundance of gear ratios that permit a very low first gear. Apparently, enthusiasts will have to accustom themselves to both the notion of sporty automatic transmissions and sporty compact Cadillacs.
Date: 05-Jun-2015 01:35 EDT
More of this article on the SAE International website
ID: 1320
In developing the Cadillac ATS-V high-performance variant,General Motors" engineers were faced with an unfamiliar problem; a base carthat was a little too light. Not exactly, but that was the gist of the issue. After yearsof developing cars in which mass reduction was a seeming afterthought, GM haswith recently developed models such as the ATS, on its Alpha platform, so thoroughlyoptimized on mass for the base model that the car was left needing a stronger foundation when more powerand traction were added for the ATS-V model. In both its two-door coupe and four-door sedan variants, theATS-V received a raft of needed chassis reinforcements that produce a 25% increase in torsional rigidity, reported Cadillac Chief Engineer DaveLeone. This improvement was achievedthrough the installation of a front shock tower-to-plenum brace along withunderhood V-braces, reinforcement to the rocker bulkhead, stamped steel bolt-onbraces between the rear suspension cradle mount and the floor of the unibody,and (the centerpiece of the upgrades) a large aluminum platform beneath thefront suspension subframe that the company terms a "shear plate" that connectsthe front suspension and its cradle more securely to the car"s unibody. The effect of that huge aluminum reinforcement plate is feltprimarily on corner turn-in, where the ATS-V responds crisply rather than by twistingthe car"s structure, according to Leone. With the platform suitably braced, GM"s engineers beefed upthe suspension components too. That includes replacement of bushings in themulti-link double-pivot MacPherson strut suspension with zero-compliance balljoints, stiffer front springs, and thicker front anti-roll bar that combine toproduce a 50% increase in roll stiffness. The ZF Servotronic II steeringrack is also stiffer than that on the regular ATS, which also contributes toimproved steering feel. At the rear, there are stiffer bushings, springs, andanti-roll bar along with stronger cradle mounts. Revised rear suspensiongeometry incorporates more anti-squat and has less migration of the rear rollcenter. A standard electronic limited-slip differential helps putthe power down on corner exits, while different-diameter halfshafts suppressaxle hop under acceleration by not having the same frequency response totorque. The left side shaft, which is provided by GKN as an assembly with itsconstant velocity joints, is 55 mm (2.2 in) compared to 30 mm (1.2 in) for the standard-issueright shaft, for a 2.6:1 difference in rigidity between the two. Brakes are the same Brembo six-piston one-piece front calipers with14.5-in (368-mm) rotors at the front and four-piston rear calipers with 13.3-in(338-mm) rotors at the rear as were used on the heavier outgoing-generation CTS-V, whichprovided impressive stopping power without fade or increased pedal travelduring track testing at the Circuit of the Americas in Austin, TX. Damping is by the BWI Group"s Magnetic Ride Control thatCadillac brought to market. This latest iteration of the technology providesimproved differentiation between its two modes, according to John Barrick, Program Engineering Manager for the ATS-V. "Now we have two true modes," hesaid. "Before it was more like one and a half modes." The increase in maximumdamping is 40% greater than before. The new system"s quicker response time means that the damper adjusts itself for every inch the ATS-V travels at 60 mph (97 km/h), while theprevious system covered three inches between adjustments to settings, Barrickadded. The 18-inch forged aluminum wheels help reduce mass andmount Michelin Pilot Super Sport tires molded with three distinctly differentzones of compound. The outer shoulder is hardened to withstand the corneringforce of hammering around tracks without burning the rubber off the outside ofthe tires. The middle section is optimized for wet traction, and the innerportion is sticky race-ready rubber. On the track, the tires contributed to an impressive 1.25 glateral acceleration in the turns. Just as engineers attended to every detail under the skin,so did the designers when working on the skin itself. "All of the design elementshave a purpose," said Andrew Smith, Executive Director of Cadillac Global Design."They contribute to lift reduction, enhanced cooling, reduced mass, or all ofthe above." Most obvious is the carbon-fiber hood, with its bare carbon heat extractorvent. The hood saves weight compared to a steel hood, and the extractor notonly helps hold down engine bay temperatures, but the air exiting it atop thehood reduces lift at speed. The enlarged openings in the front fascia feed more air to the variousheat exchangers behind it, and the splitter on the bottom scrapes directs air from theroad surface, minimizing lift. The ATS-V"s fenders are widened to cover thewider wheels and tires, and the rocker panels and rear spoiler provide thefinal touches on overall balance of lift on the car. The optional carbon-fiberpackage provides enlarged splitter, hood air extractor, rear spoiler, rockerpanels, and rear diffuser. Those aren"t the only aerodynamic devices. Under the car, the lower controlarms at the rear are sheathed in plastic covers that Barrick says reduce dragby two counts. Naturally, as a high-performance variant, once the necessarysupporting infrastructure was established, the ATS-V needed a suitably morepowerful powertrain. It is an SAE-certified 464-hp (346-kW), 444-lb ft (601-N m) twin-turbocharged,direct-injected 3.8-L V6 engine matched to a six-speed manual or eight-speedautomatic transmission. The car accelerates to 60 mph in 3.8 s andreaches a top speed of 189 mph (304 km/h). The engine features turbocharges with low-ineria titanium-aluminideturbine and vacuum-actuated wastegates for reduced lag and stronger low-rpm response. The turbos" compressors are matched for peak efficiency atpeak power levels, providing maximum on-track performance. The engine"s response is augmented by a patent-pending low-volumecharge-cooling system that improves packaging efficiency while permittingmaximum boost pressure. The engine itself enjoys some reduced inertiacourtesy of its titanium connecting rods. The Hydra-Matic 8L90 eight-speed automatic is the fasterand more efficient transmission choice. The car features steering-wheel-mounted paddles formanual shift actuation, but when the ATS-V is switched to attack mode, thetransmission"s computer makes flawless shift decisions while the driver hammersthe car around a circuit. In most respects, it is the better way. However, for those drivers who think it is not the fun way, Cadillac offers theTremec TR6060 six-speed manual transmission. We"ve seen automatic rev matchingon downshifts elsewhere, including GM"s own Chevrolet Corvette, but the ATS-V adds tothat no-lift upshifts. The driver depresses the clutch, makes the manualgearchange using the H-pattern shifter, and releases the clutch pedal all asusual. But the accelerator pedal stays on the floor throughout and the carautomatically cuts power just long enough to compete the shift motion. Though this defies the accumulated muscle memory in anyone able tooperate a manual transmission, it makes upshifts shockingly quickly. So, maybecomputer-matched downshifts and automatic power-cut upshifts leave the driverdoing less of the manual shifting job, both ensure that the shifts are smoother and faster. The EPA fuel economy estimates for the automatic transmission-equippedATS-V are 16 mpg city and 24 mpg highway, while the manual gets 17 mpgcity and 23 mpg highway. An electronically controlled limited-slipdifferential helps the power get to the road effectively, with a 3.73:1 finaldrive ratio for the manual transmission and a 2.85:1 for the automatic, thanks toits abundance of gear ratios that permit a very low first gear. Apparently, enthusiasts will have to accustom themselves to both the notion of sporty automatic transmissions and sporty compact Cadillacs.
Date: 05-Jun-2015 01:35 EDT
More of this article on the SAE International website
ID: 1320
