Chevrolet Silverado Gears Up for 2015

New 8L90 eight-speed automatic 

supports capability, enhances efficiency

DETROIT – The all-new, GM-developed Hydra-Matic 8L90 eight-speed transmission is matched with the available 6.2L EcoTec3 V-8 engine in the 2015 Chevrolet Silverado 1500, supporting the pickup’s capabilities with greater efficiency and refinement.

The all-new Hydra-Matic 8L90 eight-speed automatic transmission provides greater torque capacity
 while being lighter and more efficient than the six-speed automatic it replaces.

It was designed with 11 percent greater torque capacity than GM’s 6L80 six-speed automatic transmission, complementing the output of the 6.2L, which – at 420 horsepower and 460 lb-ft of torque – is the most powerful engine offered in a light-duty pickup.
EPA estimated fuel economy will be announced closer to the start of production in the fourth quarter of 2014.
“The new 8L90 eight-speed is designed tougher to handle the greater power of the Silverado’s powertrains, with great improvements in spin loss to complement that capability with greater efficiency,” said Kavoos Kaveh, global chief engineer for eight-speed automatic transmissions. “It is a marvel of packaging efficiency and driving efficiency that has garnered more than two dozen patents for General Motors.”
With four simple gearsets for optimal efficiency and five clutches (two brake clutches and three rotating clutches), creative packaging enables the new eight-speed automatic to fit the same space as the previous six-speed automatic, with a lower weight. A wider 7.0 overall gear ratio spread provides a numerically higher 4.56 first gear ratio, helping drivers start off more confidently with a heavy load or when trailering.
The 2015 Silverado 1500 equipped with the 6.2L engine and eight-speed automatic transmission will have amaximum available trailer rating of 12,000 pounds, based on SAE J2807 Recommended Practices.
Smaller steps between gears, compared to the 6L80 (see chart below), keep the engine within the sweet spot of the rpm band, making the most of its horsepower and torque to optimize performance and efficiency. They also enable numerically lower rear axle ratios, which reduce engine rpm on the highway for reduced fuel consumption.
Additionally, friction-reducing design features – including all-new synthetic fluid – and lower spin losses via a powerflow that uses only two open clutches contribute further to efficiency. A new torque converter design with turbine damper enhances refinement, particularly during low-speed gear changes, for smoother performance when the truck is loaded or pulling a trailer.
Ratios compared: Hydra-Matic 8L90 vs. 6L80

8L90 eight-speed automatic
6L80 six-speed automatic
Gear ratios (:1)

Architectural and design features
More than 550 computer-aided engineering analysis were made during the development of the 8L90 to ensure strength, durability, performance and refinement. The architecture features a one-piece case with an integral bell housing for enhanced powertrain stiffness.
Similar to GM’s six-speed automatic design, the eight-speed’s architecture locates the grounding clutches rearward of the middle of the structure, outside the gearsets. However, the grounding clutches are splined to the case, eliminating the center support, which reduces weight.
This architecture also features a turbine shaft node that reaches to the outside of the barrel, enabling easy execution of a high-resolution magnetic speed sensor. The turbine shaft itself is very short, keeping oil channel drill lengths to a minimum. The rotating clutches are located near the front of the transmission, with short oil feed channels, supporting very fast shifts.
Additional design and performance features include:
  • Clutch compensators are fed by lubrication oil rather than the dedicated and regulated feed design of the 6L80. There are two benefits of this new design feature: The reduction of one oil channel between the valve body and the rotating clutches, which reduces the number of rotating oil seals and oil channels within the turbine shaft; and secondly, the capability for rapid discharge of oil in the compensators during clutch apply, for greater control.
  • An industry-first off-axis, chain-driven binary vane-type pump – located within the valve body – effectively allows for two pumps in the packaging size of a single, which contributes to lower parasitic losses and optimal priming capability, as well as ideal oil routing to the controls system.
  • The binary pump enables a 60-percent reduction in pump torque at points that represent large portions of the operating duty cycle, compared to the 6L80 six-speed, which is a significant contributor to the overall efficiency gains offered by the 8L90.
  • The binary pump is located very low in the sump, for greater cold prime operation – as low as -40 F (-40 C) and excellent high-speed operation with stable line pressure.
  • Thanks to a new torque converter clutch friction lining and a new control strategy, the 8L90’s squashed torque converter uses conventional dual-path converter feeds.
  • New synthetic fluid with improved cold temperature performance and reduced friction characteristics.
Shift time quickness and improved responsiveness are accomplished with a new Gen II controls system. VFS solenoid technology and three internal speed sensors give the 8L90 the capability for world-class shift performance. The new transmission controller is mounted external to the transmission and has processor that executes hundreds of calculations and commands every 6.25 milliseconds.
The 8L90 is built at GM’s Toledo, Ohio, transmission facility.

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