|Simplified schematic of different hybrid systems. Click to enlarge.
GM has simplified the two-mode hybrid system for application in front-wheel drive vehicles—the Saturn VUE being the first instance (earlier post)—while retaining its functionality and capability, according to Mark Selogie, Senior Manager Power Electronics, GM Powertrain, speaking at the SAE Hybrid Symposium in San Diego (11-12 Feb).
The RWD version of the two-mode used to power the full-size SUV and pickup hybrid models incorporates two motors, three planetary gearsets and four clutches. The resulting system offers two electric continuously variable transmission (ECVT) modes (low- and high-speed) and also incorporates four fixed-gear ratios for high efficiency and power-handling capabilities in a broad variety of vehicle applications, including towing. (Earlier post.)
The objective was to use the same two-mode architecture and same controls for the same benefits—two EVT modes and four gears. The challenge is to squeeze it into a front-wheel drive transaxle.—Mark Selogie
The powerflow in the new transmission executes two-mode operations with two planetary gearsets instead of three, helping to lower the cost of the system. GM also move to a concentrated-type winding motor construction, and co-axially packages the planetary gears and clutches inside of the motors. The use of the concentrated-type winding motor reduced stator inturns from 62 mm to about 30 mm per machine. The resulting FWD two-mode transmission is 381 mm in length.
The two-mode VUE, which goes on sale later this year, will accelerate from 0-60 mph in 7.5 seconds, and offer a greater than 50% combined fuel economy improvement over a conventional six-cylinder VUE.