As we saw so clearly at this year’s North American International Auto Show in Detroit, any brand that wants to stay competitive in the premium vehicle segments needs to aggressively adopt electrified powertrains. At the Shanghai Motor Show today, Cadillac joined the crowd that already includes Audi, BMW, Mercedes-Benz and Volvo. GM’s top brand already revealed the full-size CT6 luxury sedan with conventional gasoline powertrains a few weeks ago at its new hometown show in New York. In China, Cadillac president Johan de Nysschen is highlighting a new plug-in hybrid powertrain that will in all likelihood find a home throughout most of the brand’s lineup.
So far, Cadillac is being relatively coy with details of its new electrified powertrain but they have revealed some very interesting details. Unlike the system that we’ve already seen for the 2016 Chevrolet Volt and Malibu, the system being shown in China is configured for rear-wheel-drive vehicles but there are some similarities and GM powertrain engineers have probably incorporated many of the same lessons used in designing the front-wheel-drive units.
Like all of the strong hybrid systems produced to date by GM, this one uses two electric motor/generators. However, this version adds a third planetary gear set to the two used in the front-drive system. GM representatives have declined to answer any specific questions about the configuration, but I believe we can make some reasonable deductions based on what we know from previous GM hybrid efforts as well as the tidbits available on this one.
More electric speed range
Starting with GM’s two-mode hybrid system and continuing into the 2016 Volt and Malibu hybrid, the automaker has used a combination of two motor/generators and two planetary gear sets. While electric motors are generally far more efficient than internal combustion engines and have pretty much constant torque output, both of those characteristics can be found from pretty much zero speed up to a maximum speed that depends on the motor design.
Beyond that maximum speed, both efficiency and output begin to fall off. This is part of why most hybrids will only operate electrically up to some maximum speed that started at about 24 mph on early Priuses to about 60 mph on most current models. Adding a second gear set allowed GM to use electric propulsion (either electric only or in blended hybrid mode) at higher speeds while gearing down the motors to keep them within the optimal efficiency range. In the original two-mode hybrid trucks, GM still limited electric only speeds to 24 mph because of the size and weight of the trucks, but they could do blended hybrid operation at higher speeds.
The CT6 is designed to compete against the likes of the Mercedes-Benz S-Class, BMW 7 Series and Audi A8 so that means it needs to be able to be capable of operation at higher speeds. With all of those cars either already available with hybrid or PHEV powertrains, Cadillac will surely want to be able operate electrically at higher speeds and and longer distances. The three planetary gear set configuration probably enables the CT6 to operate with the engine off at speeds approaching triple digits. It probably also enables the powertrain control system to blend operation of the engine and two motors with additional flexibility to maximize overall efficiency.
Speaking of that engine, Cadillac is pairing the hybrid propulsion system with GM’s 2.0-liter direct injected and turbocharged four-cylinder. In the non-hybrid CT6 application, it is rated at 265-horsepower but Cadillac is saying the total system power of the CT6 PHEV will be 335-hp and 432 lb.-ft. of torque. Since the two-motor hybrid likely generates more than 60-hp, the 2.0 will probably be downrated somewhat and calibrated to run on a more efficient Atkinson cycle with the electric propulsion filling the gap.
Storing electrons
Since the chief PHEV competitors to the CT6 are all projected to deliver 20-25 of electric driving range, we can expect the CT6 provide something similar from its battery pack. As an increasing number of major cities around the world consider restricting access to their central cores by vehicles with internal combustion engines, these vehicles are designed to enable drivers get to their offices and then retreat to the suburbs without contributing to urban pollution.
In order for a car as big as the CT6 to achieve these performance goals, it needs quite a bit of battery so Cadillac is packing an 18.4-kWh lithium ion pack between the rear seats and trunk. GM electric vehicle spokesman Kevin Kelly confirmed that the battery is liquid cooled and the cells would be supplied by LG Chem, the same manufacturer that supplies cells for the Volt and Cadillac ELR. With the same overall capacity and 192 cells as the 2016 Volt, the CT6 probably uses the same cells as the Volt although Kelly declined to confirm if the CT6 pack would be assembled in the same Brownstown, Mich. factory as the Volt pack.
The second-generation Chevrolet Volt uses an all-new battery system that maintains its signature t-shape configuration but uses nearly 100 fewer cells. The battery system will provide improved range while weighing 30 lbs. less than the previous battery system.
Since the second-generation Volt is projected to deliver 50 miles of electric driving, it would not be surprising to see 30 miles or more of electric range from the CT6. That’s actually surprisingly close to the slow-selling ELR’s range. However, unlike the ELR which was hurt in part by its high price, customers for the the much larger CT6 are less likely to see a near $100,000 price point for a CT6 PHEV as a problem.
Cadillac plans to launch the CT6 PHEV in China first and then expand it to other markets including North America and Europe. At this time, Cadillac is not saying when this model will launch, but sometime in 2016 seems likely.
