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A technical look at parallel axis hybrid transaxles

Monday, January 1, 2018 - 09:00
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The Volt transaxle is an amazing design, but it is heavy, complex, and expensive. The 2017 Chevrolet Malibu Hybrid uses the second-generation Volt transaxle, the 5ET50, which is lighter and more efficient than the previous design. The Malibu hybrid is rated at 49 mpg city! Too bad nobody wants a car anymore. This would be a great pick.

2014 Chevrolet Volt inline axis transaxle (4ET50)

Contender #5:  FCA

FCA’s 2017 Chrysler Pacifica Plug-in Hybrid Mini Van is new to the battle and Chrysler’s first mass produced hybrid vehicle. Their new two motor, series-parallel, parallel axis transaxle, is called the “Single Input Electronic Variable Transaxle” (Si-EVT). It is new to FCA, but it is hardly a new design. I have to chuckle to myself at times when I am talking to Chrysler trainers and technicians because everything hybrid is new to them and they act like it is new to everyone.

I had one trainer tell me about the unique design that Chrysler had developed for the Pacifica hybrid transaxle. I told him it was a modified copy of a 2005 Ford Escape transaxle and took him back to my storage room and showed him. Obviously, he was a little surprised to see and learn this. He said, “But the engineers told us they designed it in-house.” I chuckled a little more inside. The Pacifica transaxle is old school brute force hybrid technology with a few refinements. The cool thing about the Pacifica plug-in hybrid is that it is currently the only plug-in minivan on the market in the US. There are a few others outside the US.

2017-2018 Chrysler Pacifica parallel axis style hybrid transaxle (Si-EVT)

The design trend

Are you seeing the hybrid transaxle trend now? Parallel axis hybrid transaxles in a series-parallel hybrid vehicle seem to be the configuration of choice for efficiency, space utilization, weight reduction, simplicity, and configurability. Let’s look at what is common to all of three transaxles from Ford, Toyota and Chrysler.

They all have a large traction motor that has only two functions: 1. it simply propels the vehicle with or without the assistance of the engine; and 2. it is used as a generator when decelerating to provide regenerative braking when possible. Toyota calls the large motor “MG2,” Ford calls it the “Motor,” Chrysler calls it “Motor B.”

They all have a small motor/generator that has four functions: 1. it starts the engine; 2. it acts as a generator to charge the high voltage battery; 3. it acts as a generator to provide electrical power to the traction motor; and 4. it, along with a power-split planetary gear set, is used to vary how much torque the engine can contribute to traction motor to help propel the vehicle as you drive. Toyota calls the large motor “MG1,” Ford calls it the “Generator,” Chrysler calls it “Motor A.”

Now for some mild humor

China recently announced that they will require 10 percent of all vehicles sold in China (28 million sold last year) by 2019 be plug-in hybrids (PHEV) or Battery Electric Vehicles (BEV). According to what I have read, PHEV and BEV production last year was around 1 million vehicles. About 2.8 million will be needed in China just one year from now.

The required percentage of these vehicles will go up every year until 100 percent is reached. Not many days after China’s announcement, almost every vehicle manufacturer in the world announced that they will produce and sell an all-electric or plug-in lineup by 2020-2025 (yes, that is the humorous part). The auto market in China is almost double what the market is here in the US. What does this mean for you? Expect to see a lot more PHEVs and BEVs available in the U.S.A in the next few years. I expect to see the powertrain types of most PHEVs and BEVs to converge on one or two really efficient designs. The world’s automotive market is changing again, get ready for it by furthering your electrical and hybrid education.

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