Automotive Engineering - January/February 2021 - 18
Gearing EVs
for greater
efficiency
Low Gear
Shift
High Gear
The Ingear low-to-high gear shift process showing 'key segments' sliding out from large sprocket ring, Morse Hy-Vo silent chain and idler mechanism.
Sprocket dynamics
On a typical EV with two helical-cut reduction gears,
the electric machine's output shaft turns about nine
times for each revolution of the wheels. The Ingear replaces the second reduction gear with the Hy-Vo chain
drive and a " morphing " sprocket, as shown in the animation. To execute a Low-High or High-Low shift, an
actuator directs the five interlocking sprocket segments
18 January/February 2021
The differential of
the Ingear unit is
nestled deep within
the gear sprockets.
into place during one revolution of the wheels (about 30 milliseconds).
This changes the size of the sprocket, effectively increasing or decreasing the gear ratio. The segments slide on hardened-steel pins similar to
those used in injection molding equipment, Wong said. When the segments are rigidly locked, they operate exactly like a conventional onepiece sprocket. The system's patented geometry keeps motor and
wheel speeds in sync.
A moving idler (similar in function to a derailleur idler) is used to
take up chain slack as the high- and low-gear sprockets meld. " We
set the geometries so that the 'wrap angles' of the chain are appropriate in both low and high gear, " Wong said. " It took some time to
work out the chain path, but we've got it down pat. " He said Ingear
can transmit continuous torque during the low-to-high gearshift.
" The motor speed comes down very quickly, resulting in a smooth
shift that the passenger doesn't feel, " Bottero explained. Wong's team
has developed torque-fill algorithms to further minimize any perception
of gearchange to the vehicle occupants. In the process, less energy
AUTOMOTIVE ENGINEERING
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" Obviously a bike derailleur would never work in a car;
it would grind itself to pieces very quickly, " Wong noted.
" It's the key segments that enable us to maintain, as the
chain folks say, the 'synchronicity' of the chain with the
sprocket teeth even during a gearshift. These components are really what make the Ingear practical at automotive speeds, under automotive torque loads. " Also patented was a concept called the 'sequencer' which ensures
the key segments always move first during a gearchange.
To commercialize the Ingear technology, Bottero,
Wong and another colleague founded Inmotive in 2010.
" We spent the first five years working on industrial applications - equipment like crushers, conveyors, and
HVAC fans for buildings, " Bottero noted. " These applications proved our core concepts and technology work.
The 2-speed gearing comes into place under peak loads
and allows you to right-size the electric motors. "
The next steps, in 2015, aimed at making Ingear more
robust and durable for automotive. Transitioning from
toothed-belt drive in early iterations to the Hy-Vo chain
- used in the Chevrolet Volt and countless 4wd transfer cases - enabled much higher torque density " with
supreme durability and efficiency, " Wong said.
Added Bottero: " The market was ready for us; we
always thought the best fit for us was EVs. "
Automotive Engineering - January/February 2021
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