Truck & Off-Highway Engineering - December 2021 - 26

MAHLE
Q&
A
Thermal challenges of electric commercial vehicles
Vehicle electrification poses new challenges for thermal management,
driving development of new systems and components
specific to battery and fuel-cell electric vehicles (EVs).
Key components of the cooling circuit that typically were mechanically
driven on an internal combustion engine (ICE) vehicle
also need to be electrified, said Laurent Art, director
pre-development thermal systems and components at Mahle.
This drives the development of new components such as electrical
fans, compressors and pumps.
The solutions developed for passenger EVs
can to some extent be scaled to truck applications,
Art told Truck & Off-Highway
Engineering. " This is, for example, the case for
battery cooling where the same base technology
is used in both cases. " Art's scope of activity
includes air-conditioning and powertrain-cooling
systems for passenger vehicles
and commercial trucks. He recently answered
a few questions for TOHE about the unique
thermal requirements of BEVs and FCEVs.
What are the main thermal-management
challenges with electric commercial
vehicles?
One major challenge is to prevent the fuel cell
stack from overheating. Unlike ICEs, most of
the heat losses of a fuel cell powertrain need
to be rejected via the coolant circuit, and at a
lower temperature level than for an ICE.
Therefore, a fuel cell vehicle requires much
higher cooling performance than an ICE or
even a BEV. To solve this challenge, Mahle has
developed high-performance cooling systems
for such applications.
Another important requirement is to keep
Laurent Art, director pre-development
thermal management at Mahle.
the battery within tight temperature limits to
avoid premature ageing and enable the battery
to always deliver its full capacity. This
means the battery needs to be actively cooled or heated depending
on the operating conditions. Also, due to different
temperature requirements for different subsystems (battery,
e-motor, fuel cell stack), the cooling architecture of electrified
trucks typically includes multiple coolant loops, as well as interaction
between the refrigerant system and coolant circuit for
the battery cooling.
For BEVs, as the temperature of the coolant and the
amount of heat rejected by the powertrain are typically lower
than for ICEs, the cabin heating must be supported by additional
electrical heat.
How can EV driving range be improved?
Mahle is particularly active in the development of heat pump
systems that can warm up the cabin by harvesting, via the
26 December 2021
" A fuel cell vehicle
requires much
higher cooling
performance
than an ICE or
even a BEV. "
refrigerant circuit, the waste heat from the e-powertrain and battery,
as well as energy from the ambient air. This reduces the electrical
power consumed for the cabin heating and therefore improves
the driving range of the vehicle. The benefits of heat
pumps on vehicle driving range are dependent on the ratio of
traction power to cabin heating power. Therefore, while heat
pump systems are very attractive for light vehicles (battery range
can be increased by up to 20% at an outside temperature of
0°C/32°F), we expect a lower penetration on commercial vehicles.
Do off-highway machines require bespoke
solutions or present unique challenges?
Mahle also provides off-highway thermal
management solutions and cooling/HVAC of
agricultural and construction vehicles. There
is a trend towards electrification of small
construction machines, especially on innercity
construction sites. The same applies to
work machines for municipal transport.
There is a need for thermal management for
batteries as pure cooling modules with electric
fan drives or as temperature-controlled
HVAC systems. In addition, there are requirements
for liquid cooling of traction motors
and power electronics in separate cooling
loops due to different temperature levels.
Any specific considerations to enable
effective fast charging?
The amount of heat dissipated in the battery
increases with the charging rate; therefore,
adequate thermal management is a key enabler
for fast charging. Coolant cooled batteries
are currently mainstream on the market. In
this case, the battery cells typically sit on a
cooling plate circulated by cold coolant. It is
critical to provide cold coolant to the cooling
plate, to prevent battery-cell overheating during
charging. For these applications, a high-capacity refrigerant
circuit, based on a high-capacity compressor, high-performance
condenser and chiller, supplies cold water to the battery.
Mahle also develops immersion cooling solutions, whereby the
battery cells are directly cooled by a dielectric fluid. This further
improves the cooling performance of the battery in comparison
with coolant cooled batteries.
In the case of fast charging of trucks, the heat generated under
[the Megawatt Charging System] will further increase.
Therefore, we see an even bigger benefit with our immersion
cooling solution to minimize the risk of derating during the
charging operation. The cooling circuit must also be adapted to
reject the heat out of the vehicle with upsizing or duplication of
some components.
Ryan Gehm
TRUCK & OFF-HIGHWAY ENGINEERING
Truck & Off-Highway Engineering - December 2021

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