In recent months General Motors has rolled-out a compelling hybrid transmission architecture at the heart of the 2016 Volt, 2016 Malibu hybrid and a possibly related transmission for the 2016 RWD Cadillac CT6 plugin hybrid.
This new hybrid system helps the Volt launch to 30 mph like a Tesla after stops at traffic signals and helps the mid-size Malibu sedan get a stunningly good 47 mpg EPA estimate in combined city and highway driving while pumping out up to 182 horsepower.
How did GM get to where it is today?
A Brief History of Power-Split Hybrid Engineering
Thompson Ramo Wooldridge Inc. (TRW)
Although an early hybrid car was designed and sold back in 1900 by Ferdinand Porsche, the modern hybrid era had its stirrings in the late 1960s at an aerospace, credit reporting, and automotive parts conglomerate named TRW. Researchers there invented the modern idea of a power-split hybrid using a planetary gear set, a gasoline engine, and two electric motors. Its 1971 patent, US 3566717, and the closely related US 3732751 issued in 1973 refer to the smaller motor as the “speeder” since it effectively determined the rpm speed of the gas engine and the larger motor is the “torquer” since it added or removed torque going to the wheels of the car.
This was the era of the Apollo moon flights that used spacecraft computers far less capable than today’s Apple wristwatch. Using electric motors and a battery pack to take the place of fixed gears and clutches was an interesting concept but in order to be efficient and useful such a transmission needs to be carefully controlled. A hybrid transmission control computer was not a realistic possibility at that time so its design was not really practical for use in an ordinary consumer vehicle.
Partnership for a New Generation Vehicle
In 1993, shortly after taking office, the PNGV was created by President Bill Clinton and Vice President Al Gore. The program excluded non-U.S. companies and this particularly worried the Japanese car companies like Toyota.
GM, Ford, and Chrysler collaborated on research under PNGV, but each company built its own high mileage prototype car. GM’s car, the Precept, scored the highest EPA mileage estimate at 80 mpg under the more lenient test cycles of that era. It used a 40 kW (54 horsepower) 1.3-liter RWD diesel engine mounted in the back of the car with a 35 kW (47 horsepower) electric motor driving the front wheels using power from a generator hooked off of the engine. They experimented with both NiMH and lithium polymer battery packs. This was a type of approach known as a “through the road” parallel hybrid since the engine powered the rear wheels and the electric motor powered the front wheels.
During this period, GM continued exploring and prototyping other hybrid designs. With the benefit of computer microprocessors, it focused on developing and extending the TRW idea from two decades earlier. It built an awkward prototype and filed a patent in February 1995 titled “One-mode, input-split, parallel, hybrid transmission”. This patent, US 5558595, described many various permutations of how an engine, two motors, and the wheels could be hooked up to one or two planetary gear sets in order to create an Electrically Variable Transmission (EVT or eCVT).
Toyota and the Prius
Meanwhile, in response to the U.S. government’s PNGV effort, Toyota established an internal project code-named G21 that eventually resulted in the design of the Prius. In January, 1995, a team of Toyota engineers began intensive meetings to research and design the transmission for the new car. According to a book titled “The Prius That Shook the World” by Hideshi Itazaki, they carefully studied up to 80 different known approaches. While these meeting were taking place, GM filed its “one-mode” patent which includes as one of its design alternatives the actual approach that Toyota eventually decided on for the Prius. After narrowing the field down to four alternatives, Toyota chose the basic engineering design for the Prius hybrid transmission at a meeting on June 30, 1995. Toyota did not complete the filing of its own Prius hybrid transmission patent, US 5907191, until 1997 although it initiated the filing process on Sept. 24, 1996 which was the day on which the GM one-mode patent was officially issued. The first Prius went on sale in December, 1997 in Japan. A later, modestly updated, version of that model of Prius was first sold in the United States and Europe in the summer of 2000 as a 2001 model
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