Cadillac Introduces New 8-Speed Automatic on CT6

DETROIT – Cadillac advances its legacy of technologically driven performance and luxury with the Hydra-Matic 8L45 paddle-shift eight-speed automatic transmission, which debuts with the all-new 2016 Cadillac CT6.

Matched with the next-generation 3.6L V-6, the 8L45 transmission is based on the same acclaimed General Motors-designed eight-speed automatic family introduced on the Corvette Stingray – with the higher-capacity 8L90 version paired with the CT6’s available 3.0L twin-turbo V-6 engine.

“The shift performance of the new 8L45 paddle-shift eight-speed automatic transmission complements the CT6’s new threshold for efficient luxury to help take it to an even higher level,” said Bill Goodrich, assistant chief engineer for eight-speed automatic transmissions. “The shifts are quick and nearly imperceptible, establishing a benchmark for Cadillac.”

The 8L45 eight-speed shares the architecture and design features of the Hydra-Matic 8L90 transmission, but it is scaled and calibrated for the performance envelope of the new 3.6L V-6. It also incorporates components to support the engine’s stop/start technology.

Stop/start shuts down the engine to reduce fuel consumption when vehicle comes to a complete stop, and it automatically restarts the engine when the driver takes his or her foot off the brake pedal.

In addition to stop/start efficiency, the 8L45 eight-speed’s wide 7.0 overall ratio and numerically lower top gear offer an up to a GM estimated 5 percent fuel economy benefit over a comparable six-speed automatic transmission.

A numerically higher 4.62 first gear ratio also helps drivers start off more confidently, with a greater feeling of immediate performance.

“The 8L45 was designed to enhance the CT6’s driving experience, offering a strong balance between performance and efficiency,” said Goodrich. “Perhaps its best attribute will be that customers really won’t notice it – they’ll simply enjoy the CT6’s seamless, smooth driving experience and on-demand performance.”

Compact, mass-efficient design
With four simple gearsets for optimal efficiency and five clutches (two brake clutches and three rotating clutches), creative packaging enables GM’s eight-speed automatic to fit the same space as the previous six-speed automatic, with a lower weight.

The new 8L45’s smaller package size enables approximately 33 pounds (15 kg) mass saving compared to the 8L90 eight-speed – a transmission that was already lighter than GM’s 6L80 six-speed automatic.

Smaller steps between gears, compared to a six-speed transmission, keep the engine within its optimal rpm range, making the most of its horsepower and torque to optimize performance and efficiency.

Ratios compared: Hydra-Matic 8L45 vs. 8L90

Type: 8L45 eight-speed automatic 8L90 eight-speed automatic
Gear ratios (:1)
     First: 4.62 4.56
     Second: 3.04 2.97
     Third: 2.07 2.08
     Fourth: 1.66 1.69
     Fifth: 1.26 1.27
     Sixth: 1.00 1.00
     Seventh: 0.85 0.85
     Eighth: 0.66 0.65
     Reverse: 3.93 3.82

Additionally, friction-reducing design features – including synthetic fluid – and lower spin losses via a powerflow that uses only two open clutches per gear and an off-axis binary vane pump contribute further to efficiency.

The torque converter design with turbine damper enhances refinement, particularly during low-speed gear changes, for smoother performance.

Architectural features
More than 1,100 computer-aided engineering analyses were made during the development of the Hydra-Matic eight-speed transmission family – resulting in more than two dozen patents – to ensure strength, durability, performance and refinement.

Architectural highlights include:

  • A one-piece case with an integral bell housing for enhanced powertrain stiffness
  • The grounding clutches are located rearward of the middle of the structure, outside the gearsets, and are splined to the case, eliminating the need for a the center support, which reduces weight
  • The rotating clutches are located near the front of the transmission, with short oil feed channels, to support very fast shifts
  • A unique oil-storage accumulator is incorporated to support stop/start technology. It ensures the clutches have oil for immediate take-off when the engine is re-started
  • World-class shift time quickness and responsiveness are accomplished with a Gen II controls system, which works with variable force solenoid technology and three internal Hall Effect speed sensors
  • The transmission controller is mounted externally and its processor executes hundreds of calculations and commands every 6.25 milliseconds.

The Hydra-Matic 8L45 and 8L90 transmissions are built at GM’s Toledo, Ohio, and Silao, Mexico, transmission facilities. They will also be offered in the 2016 Cadillac CTS and ATS, including CTS-V and ATS-V.

8L45 eight-speed automatic 8L90 eight-speed automatic
2016 CT6 2.0L Turbo I-4 and 3.6L V-6 3.0L Twin Turbo V-6
2016 CTS & CTS-V 2.0L Turbo I-4 and 3.6L V-6 6.2L Supercharged V-8
2016 ATS & ATS-V 2.5L, 2.0L Turbo I-4 and 3.6L V-6 3.6L Twin Turbo V-6

 

FAST FACT: In 1941, Cadillac was one of the first major automakers to offer a fully automatic transmission. That early Hydra-Matic transmission was also paired with Cadillac V-8 engines to drive M24 Chaffee tanks during World War II.

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