The Cadillac CT6 plug-in hybrid will rip from 0-62 mph in 5.6 seconds but can also deliver 37 miles all-electric range.
Relying on a Chevy Volt-sized battery assembly of 18.4 kilowatt-hours, dual motors, and a 2.0-liter GDI turbo gas engine, the Chinese-built PHEV was highlighted recently at the SAE 2016 Hybrid and Electric Vehicle Technologies Symposium in Anaheim.
There GM’s lead engineers previewed three papers prior to their presentation at the SAE World Congress in April showing GM has learned lessons from the Volt, Cadillac ELR, Chevy Spark EV, and the new flagship Caddy promises fun with frugality, your pick.
Total combined system horsepower for the rear-wheel-drive car is 335 horsepower (250 kW) – not 449 horsepower (335 kW) as published elsewhere in error. All-electric driving may be accomplished up to 78 mph, and GM’s Tim Grewe was quoted by Green Car Congress as saying he thinks they did this one right.
“We have a PHEV system that has incredible efficiency,” said Grewe of the car which will come in conventional all-gas versions as well, “but it is also one of the highest performing vehicles on the road with extraordinarily connected feel to it.”
Speaking of gas, the 2.0-liter itself is rated for up to 266 horsepower and it’s combined with a two-motor hybrid transmission.
This electrically variable transmission is a new design comprised of two electric motors, three planetary gears – two simple and one double-pinion gear – and five clutches. These deliver four continuously variable transmission modes with three fixed gears.
Green Car Congress says GM essentially took the Volt’s drive unit design with two planetary gearsets, two motors, two clutches to make it perform like an EV in all modes, and for more “fun-to-drive” factor added a third planetary gearset and two more clutches.
“Basically, that gives you a Volt on steroids,” said Grewe. “It gives you tremendous launch torque. It’s actually a 6.8 step down in the EVT low. You look at some of the EV effort we have here, you’re almost above 5,000 Nm. You have that EV launch feel.”
GM says also the power delivery is smooth and seamless for the unit that allows for all-electric take-off, selectable regeneration, and power blending with the gas engine.
As for the motors, GM did without rare earth materials in its Motor A induction design, and it as well as the permanent magnet Motor B are designed and manufactured by GM, and use squared-section bar-wound stators, as opposed to round wire coils.
“The induction motor is something we are particularly proud of. We’ve done a great deal of work on interior permanent magnet machines, but we haven’t designed many induction machines. Our eAssist motors are induction type, but they are relatively low power. For the full power capability we went through an elaborate optimization activity to optimize the size of the rotor bars. These would be cast aluminum. We’ve optimized the parameters of the keystone for both power efficiency and torque ripple,” said GM engineer Pete Savagian. “We also examined the number of bars we could put into that rotor. We knew generically we would see a trend toward more and finer bars being better. We explored the limits of that in manufacturing but also in design. This is an eight pole machine, and it is reflected through a 91-bar structure.”
As for the battery pack – using 96 cells in series, its specs mirror the Volt’s with 120 kilowatt maximum power and nominal capacity of 51.8 Ah but it’s packaged in a different housing.
Grewe said GM made a tray to hold the modules that are common with the Volt: electronics, battery state estimator, and so forth.
“Often it is very enticing to say, ‘Well I’m just going to load the battery pack into an existing structure in the car. But basically we cut out the whole back of the CT6,” said Grewe. “We use the tray of the battery pack as the main floor structure. With the ability to handle the weight of the battery in the car structure, it really improved the stiffness. To handle that mass on the rear wheel drive, it actually made driveability better, because it is stiffer and engineered to go together.”
The 0-62 in 5.6-second CT6 PHEV weighs 4,431 pounds, 888 pounds more than the Volt’s nominal 3,543 GM cited which does 0-60 in 8.3 seconds.
Cadillac has also said the Volt-based ELR coupe’s days are numbered, and the ELR which gets comparable 37-mile electric range but with less utility has suffered in the sales arena due in part to high cost and low performance.
While the CT6 is not as quick as the quickest Tesla Model S, it is no slouch either and promises to be engaging, opulently equipped, and part of GM’s efforts to enhance the brand image of its premium nameplate.