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GM Simplifies the Two-Mode Hybrid Transmission, Maintains Functionality for FWD Application

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.



I understood the previous 2-mode transmission (more-or-less) but the diagrams provide no help for this new one.
I wonder what it gives up - range of gearing maybe?
They are elegant in design in that they allow either hybrid (elec/Mech) or totally mechanical drive (with some complexity) while the Prius and, I assume, the Lexus types do not (but with less complexity).
This is great stuff - too bad the world market is dwindling.


Its nice to hear GM did this, too bad they decided to put a V-6 in their 2-Mode Hybrid view. They should have talked to (or just looked at) Honda about how well a big powerful V-6 goes over for the Hybrid target market with their Accord V-6 Hybrid disaster.

Now with that choice of V-6 (instead of say the V-4 in the stop/go View) made they can only shoot for okay mileage, instead of being at the top of the heap. What a wasted opportunity - as oil will be back when the economy starts to warm up (year or so?).

Stan Peterson

There are sizes of vehicles or vehicles that have certain requirements that cannot be met with a conventional Prius type or EREV architecture.

These are vehicles that I would characterize as having towing or hauling requirement or that weighs over 4000 pounds.

For those applications the dual-mode architecture is much better than conventional hybrid designs. The Toyota version for its big 450 hybrid starts along the path, but eventually the dual-mode using a smaller engine and a PHEV battery pack will be the basis of most such vehicles.

Don't forget that GM stated there would be two basic sizes, in both RWD and FWD configurations, for a total of four in the dual-mode family. So far we have seen the big RWD; and now big FWD version coming in the Vue. It will be another year before we see the smaller sized designs for autos, small CVs, Minivans; and not big trucks or SUVs based on them all weighing at least 5000-6000 pounds.

What you'll see in another year or two are FWD I4 or 3.0 liter V6s, mated to the smaller FWD dual-mode drive train with a PHEV sized battery. These will obtain mid-thirties mpg and low forties on the highway, in a Caddy DTS or Chrysler C 300 sized platform on the EPA scale.

When translated ot the CAFE scale, that will Probably 40+ on the CAFE measurements. The minivans wil be a couple of miles lower but still well over the 35 mpg CAFE requirements.

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