Cadillac plugs in CT6 for high-value efficiency

  • 25-Sep-2017 03:02 EDT
2018-Cadillac-CT6-Plug-In-Hybrid-036.jpg

Hybrid system layout in the Cadillac CT6 PHEV. The 400-lb lithium battery pack features 192 liquid-cooled cells. GM claims 4.5-h charging time on 220-V Level 2. (GM image)

The badge on the decklid reads ‘2.0E’, with no giveaway that the 2018 Cadillac CT6 we’re driving is a plug-in hybrid. Perhaps a more appropriate nameplate should be CT6 NEV, because this impressively engaging and efficient luxury sedan is mostly aimed at China’s burgeoning New Energy Vehicle market.

In fact, the plug-in version is assembled only in Shanghai and exported to the U.S. Initial stateside volumes will be only 1000 units/year. It would not be surprising to find more American customers who see the CT6 plug-in’s almost ideal balance of EV range (31 mi in optimal thermal conditions), EV top speed (78 mph); acceleration (0 to 60 mph in 5.2 s); EPA rated efficiency (62 mpg-e); total range (442 mi), top speed (150 mph) and retail price ($75,095) as adding up to a compelling value proposition.

“We weren’t trying to make this a super-long-range electric vehicle,” noted Mike Kutcher, the lead vehicle development engineer. “Combining the 335-hp 2.0-L turbo with the plug-in hybrid propulsion system gives V6 twin-turbo performance with pure-electric range that’s equal to about 75% of a typical commute.”

Kutcher, a veteran of GM’s pioneering hybrid and EV development group, added that the 31 mi (50 km) capability is also China’s threshold for NEV purchase incentives.

Kicking off the PHEV development four years ago, the team was fortunate to build upon the most mass-efficient vehicle in its class (thanks to an aluminum-intensive, mixed-materials structure). About 600 lb (272 kg) was added, mainly in the liquid-cooled, 18.4-kW·h lithium battery pack located behind the rear seat bulkhead, plus power electronics, wiring and attendant hardware. The production car’s 4530-lb (2054-kg) curb weight is handily lighter than the Cadillac’s BMW, Mercedes and Porsche PHEV competitors.

Typically the German plug-ins differ from the CT6 in using stepped-gear transmissions with an electric motor located in the P2 (between flywheel and trans) configuration. “This results in the electric motor amplifying the gear changes, up and down through as many as eight ratios multiple times per driving event,” Kutcher observed.

By comparison, the CT6 arrangement that uses GM’s electrically-variable transmission (with two 90-kW/100-hp motors) felt seamless and refined during Automotive Engineering’s 70-mi (112-km) test route on public roads in rural Michigan.

The GRE (Global Rear-drive Electric) unit is unique, noted Jason Mullins, the hybrid propulsion calibration manager that joined Kutcher and me on our test drive. “Having the two motors, three planetary gearsets and five clutches give lots of mechanical advantage,” he said. “We call our approach ‘blended PHEV’ with the automated controls executing all commands in real time. When full, the battery provides primary power and blends in the ICE for supplemental power based on pedal input.”

At 45-50% pedal travel, the system’s electric-only capability ends and the ICE engages smoothly for supplemental torque. When the battery is depleted (at a bit over 31 miles during our summer test drive), the car operates like a conventional HEV. Among the three drive modes, Tour provides the most EV capability; Sport has a more aggressive pedal map and sportier steering, and the Hold mode will save the battery-only operation for when you want it later, such as entering a city after a long interstate trip.

“We were watching the trend for ‘low emission zones’ in urban areas,” Kutcher explained. “The feature may offer opportunity for compliance.” And a regen-on-demand feature is as useful on the luxury-performance Cadillac as it is on the Chevrolet Bolt: paddles on the steering column enable the driver to scrub off speed in increasing levels of deceleration, from .05 g to .18 g.

Fun to drive? You bet. Every electrified vehicle should include this feature — and have it work as effectively as Cadillac’s.

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