Transmission makes debut on the 2018 Chevrolet Equinox
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’s transverse 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.
The latest generation of smart torque converter used in this transmission employs both a spring-loaded mass damper to counteract engine vibrations under certain driving conditions when the converter is locked and “micro slip,” tiny bursts of unlocking that permit brief 10–60-rpm speed differentials to eliminate vibrations at engine speeds where the normal mass damper doesn’t work. This greatly broadens the operating conditions under which the transmission can smoothly lock the converter (including much of first gear operation), greatly increasing efficiency.
To support auto start/stop there is a large oil-pressure accumulator that is “powered” by a gigantic coil spring when the engine is off, providing sufficient pressure to the first-gear clutches when restarting. The other various clutches controlling the rest of the gear changes are powered by “linear force solenoids” that power their various valves directly, instead of via a boost valve circuit. And to keep the transmission squeaky clean and free of damaging debris, it includes a second filter on the pressure side of the oil pump; most trannies only filter on the suction side where oil is picked up from the pan. The filters are sized to never need replacing.
The 9T50 is expected to make its first appearance next summer paired with the Chevy Equinox’s 2.0-liter turbo-four and eventually perpetuate throughout the transverse-engine lineup.