Automotive Engineering - September 2023 - 31

SENSORS FEATURE
Regulating EV battery temp
An EV battery can have thousands of
battery cells. Each cell has to be individually
monitored for temperature and
voltage. Voltage sensing is necessary in
large part because batteries operate
better when the load across all the constituent
cells is balanced as evenly as
possible. This data is fed into each EV's
battery management system (BMS). For
temperature sensing, in hot weather the
battery needs to be cooled to avoid battery
degradation that begins to accelerate
at higher than 40° C. That involves
using coolants, as described above, as
well as vents and fans.
During cold weather, the battery
needs to be heated. When Li-ion batteries
get too cold, range is compromised.
Note, too, that the battery must be kept
warm even when the vehicle is not being
driven. This is why EV makers have been
equipping batteries with dedicated heaters.
Keeping the batteries in the optimal
temperature range has to be done anyway
and it helps maintain range when
the weather grows cold - a feature that
EV critics frequently miss.
Sensor rich
The process of heating and cooling the
multiple EV subsystems so that they
remain in their optimal temperature
ranges involves more heat pumps, water
pumps, three-way valves, expansion
valves and other equipment than found in ICE vehicles.
All of these elements must be monitored and controlled.
This requires temperature sensors, pressure-temperature
sensors mounted in various positions and pressure
sensors for the WEG refrigerant.
Many of these sensors need protection from the elements
and so must be mounted in appropriate packaging.
They all need to be positioned and attached with
care, with an awareness that motor vehicles are perpetually
subject to shock and vibration on the road.
TDK, for example, provides many of the required actuators
(HVC 4xyzF) and sensors (HAL 39xy) to extract the
maximum range from a battery at all times.
Effective EV HVAC = safety
Precise measurement is necessary not just for the efficient
operation of the vehicle. It is also an issue of safety.
AUTOMOTIVE ENGINEERING
EV heat-pump function showing related sensors.
Most EVs will rely at least partially on taking an AC source as an
input and converting this into DC to charge the battery. The amount
of power through both AC and DC charge points often is in excess
of 100 kW.
Generating heat as a by-product is inevitable. If not managed, the
accumulated heat could become a potential safety hazard. That
makes temperature sensing even more important at all critical points
throughout the EV power system.
The IEC demands that charging plugs include a temperature sensor
to ensure safe operation. TDK supplies high-voltage-resistant negative
temperature coefficient (NTC) sensors in these hotspots, as they feature
a high operating temperature and high electrical insulation.
The complex HVAC required by EVs depends on
leading-edge sensors, actuators and controllers to assure
that the vehicles operate at peak performance
- including when it's cold outside.
Dr. Jeroen Van Ham oversees the sensor-systems
portfolio at TDK.
September 2023 31
HVAC cool-weather cycle.
ALL IMAGES: TDK-MICRONAS
Automotive Engineering - September 2023

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