Automotive Engineering - May 2021 - 8

TECHNOLOGY REPORT

Counting on cost offsets

Compared with the single-speed transmission typical for most
current EVs, van Spijk concedes the CVT4EV represents increased cost. But using the CVT4EV offers potential for a variety of " system " cost savings that can offset the higher component cost of the new Bosch transmission concept.
" CVT4EV is a more complex system compared to the singlespeed systems, but compensation for the add-on cost is found
in the reduced torque and speed requirements for the electric
motor, resulting in the need for less magnet and copper - and
with that, lower cost, " he asserted.
" Further compensation is in the smaller battery package for
the same range and performance compared to a single-speed
transmission, " van Spijik said.
Bill Visnic

8 May 2021

ADVANCED MANUFACTURING

How 3D printing could add
efficiency to EV power electronics

Additive manufacturing could bring significant benefits to EV inverter
design, noted the U.K. university research team. Without it, the single
piece triangular element in the center of the inverter assembly illustrated,
would be challenging to achieve cost-effectively using conventional
manufacturing techniques, they state.
" Think production! " Perhaps that advice should be posted on
the wall of every design office, R&D lab and advanced technology center in the auto industry. Although obeying that
warning is clearly not cost-effective in some instances, others
are ostensibly perfect to take their place in volume manufacture. An example is 3D printing (aka additive manufacturing,
or AM), but despite a broadening scope that now embraces
rapid prototyping and tooling by entire houses, it could do
better in series production of auto components, particularly in
the new world of EVs.
Prof. Peter Wilson of the U.K.'s newly established Institute
for Advanced Automotive Propulsion Systems (IAAPS) at the
University of Bath, noted the growing adoption of highspeed SiC (silicon carbide) and other wide-band-gap semiconductor devices demonstrates the benefits that 3D printing
could have in the production of EV inverters. " SiC devices offer so much opportunity to improve inverter performance, "
Wilson said. " But system designers are often unable to take
full advantage of their potential because their ideas cannot be
manufactured using conventional techniques. "
AUTOMOTIVE ENGINEERING

UNIVERSITY OF BATH

(0-62 mph) acceleration, a 13% drop in 80-120 km/h (50-75
mph) acceleration and an 11% increase in top speed.
Meanwhile, an overall efficiency gain of up to 4% is projected for a D-segment vehicle.
The potential for improved efficiency is particularly attractive for EVs. Even minor overall gains can translate to the potential to fit a smaller, less-expensive battery pack and/or a
smaller traction motor.
" The advantage of reduced energy consumption is valid at
all speeds, " said van Spijk. " Over a reference cycle like WLTP,
this means an overall advantage in the magnitude of 2 percent to 4 percent, depending on vehicle type. At constantspeed driving, this advantage is even larger since the adaptation to the best [motor] efficiency can be held closer. At
speeds from 40 to 80 km/h, this leads to an advantage in the
magnitude of up to 8 percent, " he explained, depending on
vehicle type.
He said the CVT4EV can handle up to 4,000 Nm (2,950
lb-ft) of wheel torque, which helps make the transmission
viable into the LCV segment. For ICE vehicles, pushbelt CVTs
typically are limited in the amount of engine torque they can
reliably transmit. This has capped their applicability to engines with torque output broadly less than 300 lb-ft (407
Nm). However, van Spijk said the CVT4EV's reduced ratio
spread required for coupling with a traction motor will allow it
to handle more torque than is capable of CVTs coupled to
combustion engines.
" The maximum torque capacity of CVT4EV is higher than in
ICE applications because, technically, ratio-coverage and
torque capacity are exchangeable parameters. Since ratio
coverage is only about half the value of ICE applications, it
enables significantly higher torques for EV, " he said. " This
makes the pushbelt CVT suitable for applications from
C-segment cars to light commercial vehicles.
" Often for a C-segment vehicle, a single speed [transmission] can be sufficient, " he noted. But when the need emerges for towing capacity and improved gradeability; increased
driving range or smaller battery; higher top speed; lower motor revs; motor downsizing and optimized regeneration, the
CVT4EV's value becomes clear, van Spijik asserted.

Automotive Engineering - May 2021

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