Transmission Transitions

| May 31, 2018
 

GM transmissions continue to evolve to meet vehicle needs.

When great years for automobiles (think ’57 Chevy and the Muscle Car era) are discussed, model year 1940 doesn’t stand out. It probably should. That was the year Oldsmobile began placing HydraMatic transmissions in its vehicles.

The HydraMatic was the first true, high production fully automatic transmission. Its introduction started a revolution. Over the next decade,
the car driving public used to manual shifting purchased a million HydraMatic automobiles. During WWII, when production of civilian vehicles all but ceased, the HydraMatic found a home in numerous military vehicles, even tanks. A number of other competing brands—Hudson, Nash, Rambler and others—eager for a durable automatic solution turned to the HydraMatic.

Cadillac began pairing the automatic to its vehicles. Even as other GM divisions developed their own versions, the impact of the HydraMatic
could be felt. Its legacy was assured as consumers, at first suspicious of the invention, fully bought in.

Today, more than 97 percent (2016 US vehicle study by Edmunds) of the vehicles sold in the U.S. sport an automatic transmission. This transformation of the automotive industry has its roots in the HydraMatic. This evolution continues with each new generation of GM transmissions. Over the past decade, GM has developed a series of six-, eight-, and 10-speed options (both automatic and manual) with innovations that ramp up performance and efficiency.

Here’s a look at how these transmissions continue to shape the automobile world.

Six-Speed dominance

2014 Hydra-Matic 6T30 Six Speed FWD Automatic Transaxle for Chevrolet Sonic and Chevrolet Cruze

When GM introduced the 2011 Chevrolet Cruze with its six-speed automatic transmissions the automaker established a new landmark. Six-speeds now dominated the Chevrolet product line and, in the process, a large part of the automotive market.

The Cruze became the twelfth Chevrolet model to be offered with the six-speed, which also accounted for fully 75 percent of all gearboxes on Chevrolet cars, trucks, SUVs and crossovers for the year. GM engineers attributed the ascendance of the six-speed over four and five-speeds to its flexibility. GM could fine tune gear ratios to specific engine characteristics and vehicle performance targets. In the case of the Cruze Eco, GM developed a unique combination of speed gear ratios and a final drive ratio that provided a powerful launch and low-speed performance, along with three overdrive speeds (fourth, fifth and sixth) to build excellent efficiency and passing performance.

Other vehicles boasting the ubiquitous six-speed included the Chevrolet Malibu, Equinox, Camaro, Silverado, Suburban and the Corvette—everything from economy models, sedans and SUVs to performance classics. Perhaps just as notable, GM credited the six-speed with boosting sales of each by providing customers who might consider other brands with competitive performance and efficiency.

Eight-speed supremacy

Not long after GM thinking was taking the six-speed into new frontiers, it also produced a revolutionary eight-speed automatic. To prove its
agility, they mated it to the 2015 model of performance icon Corvette Stingray, which had just been named the 2014 North American Car
of the Year.

The 8L90 transmission was based on the same eight-speed automatic offered on the supercharged 2015 Corvette Z06, but with unique clutch
and torque converter specifications matched to the torque capacity of the Stingray’s LT1 6.2L engine.

2015 Hydra-Matic 8L90 Eight Speed RWD Automatic Transmission for Chevrolet Silverado, GMC Sierra, GMC Yukon and Yukon XL, Cadillac Escalade and Escalade ESV

For performance enthusiasts still looking to shift gears, the 8L90provided full manual control via steering wheel paddles. GM declared the combination of a new transmission control system and unique algorithms could deliver shift performance to rival the dual-clutch/semi-automatic transmissions found in many supercars—but with the refinement that comes with a conventional automatic fitted with a torque converter. The controller system accomplished this thanks to its ability to analyze and executes commands 160 times per second.

The 8L90 also made the most of the Stingray’s power output and torque using smaller steps between gears. A 7.0 overall gear ratio spread enhanced off-the line performance with a more aggressive first gear ratio (4.56 vs. 4.03 on a six-speed).

Combined with a new, numerically lower 2.41 rear axle ratio, engine rpm was reduced by eight percent (123 rpm) on the highway at 70 mph, which in turn helped with fuel consumption. The setup allowed the Stingray’s 460 horsepower powerplant to catapult the vehicle from 0-60 mph in better than 3.7 seconds.

Also contributing to efficiency, the 8L90 utilizes a design smaller and lighter than a GM six-speed. Four gearsets and five clutches keep the transmission compact while extensive use of aluminum and magnesium cut weight and reduce friction.

The rise of the 10-speed

For the 2017 model year, GM stayed true to its development path of providing both improved performance and efficiency with another leap
in the evolution of the multi-speed transmission. The 2017 Chevrolet Camaro ZL1 arrived with a newly designed 10-speed automatic, the 10L80, the first-ever application in a car.

2017 Hydra-Matic 10L80 Eight Speed RWD Automatic Transmission for Chevrolet Camaro ZL1

The match between pony car and 10-speed made sense since the 10-speed’s wider, 7.39 overall gear ratio spread enables the ZL1’s supercharged engine to maintain optimal engine speeds during upshifts. The wider ratio enhances off-the-line performance with a more aggressive first gear ratio than GM’s eight-speed automatic. To maintain optimal speed for maximum power at almost all speeds, especially when exiting a corner on a track, GM engineered smaller steps between gears.

The wider overall ratio also enables a lower numerical top gear ratio, reducing engine speed on the highway thereby creating improved fuel
efficiency. Improvements in spin loss, vs. the eight-speed, additionally complement the optimized gearing, further enhancing efficiency.

Much the same way GM’s eight-speed could fit into space for a six-speed, the 10-speed is approximately the same size as the six- and eight-speed transmissions. A unique triple-clutch assembly in the middle of the 10-speed’s architecture is primarily responsible for the reduced size, allowing the 10-speed to be used in multiple vehicle applications.

Other features include:
Reduced spin losses — Two non-applied clutches, the same number as the eight-speed, along with other design features, provide lower friction that helps with fuel efficiency. New ultra-low viscosity transmission fluid reduces friction, while an internal thermal bypass allows the transmission to warm up faster. The 10-speed includes a variable-displacement vane pump to optimizes transmission fluid pressure based on speed and load.

GM-developed controller — The all-new GM-developed control system tailors 10-speed calibrations specifically for different vehicles. And while the Camaro ZL1 was the first GM vehicle to offer the new 10‑speed automatic, designed for rear-wheel drive applications, it’s currently available in eight additional vehicles such as the Yukon, Denali and Silverado.

Looking forward

With so many new transmission innovations arriving in such a short period, gauging what’s on the horizon for the automotive industry isn’t easy. Based on a legacy starting with the HydraMatic 78 years ago up to today’s smaller, lighter, faster and more efficient models, look for GM to continue its leadership in design and production.

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Category: GM Parts News