9-SPEED TRANS­MIS­SION

What’s be­hind IS im­por­tant

Ultimate Diesel Builder's Guide - - Inside Look -

Cou­pled to the new 1.6-liter diesel squeezed into the new GMC Ter­rain, Chevro­let Equinox and Cruze is an all­new 9T50 9-speed au­to­matic trans­mis­sion, a trans­mis­sion that was jointly de­vel­oped with Ford and first used in the 2017 Chevro­let Mal­ibu. It is Chevro­let and GM’S first 9-speed.

Why nine speeds in­stead of six? Fuel econ­omy, launch, pass­ing, and NVH. The new nine-speed has a very wide over­all ra­tio of 7.6:1. That’s far greater than the out­go­ing six-speed’s 6.0:1. A ben­e­fit of­ten over­looked is the first gear launch, now 4.69. With the torque of the new diesel, it should de­liver a very solid stop­light get­away. And the top gear at 0.62, an overdrive gear, cou­pled with the same available torque will make high­way cruis­ing both eco­nom­i­cal and smooth. It will also con­trib­ute to less noise while on the high­way.

With smaller steps be­tween gears the new tranny will have “smooth, al­most im­per­cep­ti­ble up­shifts, for ex­cel­lent re­fine­ment,” said Dan Ni­chol­son, Vice Pres­i­dent Global Propul­sion sys­tems at GM. “No mat­ter the en­gine torque or ve­hi­cle speed, the 9T50 is al­ways in the per­fect gear.”

Development fo­cused on trans­verse-lay­out ve­hi­cles, front-wheel drive—a 10-speed for RWD ve­hi­cles was also co-de­vel­oped—and all gears are lined up with the crank­shaft. The 9T50 also uses GM’S first ap­pli­ca­tion of a se­lectable one-way clutch that can hold torque or free­wheel de­pend­ing on op­er­at­ing mode. Five plan­e­tary gearsets are used, along with four sta­tion­ary clutches and three ro­tat­ing clutches. GM says that saves space and in­creases smooth­ness.

Other fea­tures in­clude new torque con­verter tech­nol­ogy fea­tur­ing a hy­per-el­lip­ti­cal oval cross-sec­tion. This re­duces the thick­ness of the torque con­verter, keep­ing the over­all width nar­row for pack­ag­ing. The trans­mis­sion also em­ploys stop-start tech­nol­ogy and a hy­draulic ac­cu­mu­la­tor keeps the gears ready to go the mo­ment your foot leaves the brake.

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