There’s been a flurry of recent information released about the new 10-speed automatic that rivals GM and Ford have co-developed for longitudinal engines as it gets readied for production in the Chevy Camaro ZL1, Ford F-150 EcoBoost 3.5, and Ford Raptor, but Chevy’s unveiling of the Equinox provided our first real look at that joint venture’stransverse nine-speed, which GM will dub the 9T50 (with those last two digits varying to connote different torque ratings in the future).
According to GM transmission expert Scott Kline, the goal was to package nine ratios in roughly the design envelope of the former six-speed automatic while retaining that transmission’s on-axis design (which keeps all the planetary gears aligned with the engine crankshaft). This design “stacks” the planetary sets in line, whereas the ZF nine-speed nests several of them in a package that is shorter in length but much wider. To help reduce the overall length of the GM/Ford gear train while adding another full planetary gearset, the system of clutching for first and reverse gear was completely redesigned. The six-speed transmissions utilized two clutches—a fat conventional multiplate clutch and a slimmer “sprag”-type one-way clutch that freewheels in one direction but locks up against any effort to spin it the other way. What the team came up with was an ingenious “selectable one-way clutch” that looks like two slim sprag clutches stacked together, one of which gets a control mechanism to keep the little sprag’s feet collapsed when freewheeling in one direction if desired. Releasing these sprag feet allows the clutch to lock like a multiplate clutch resisting motion in both directions. Read more