Tech Briefs Magazine - February 2022 - MD-5

Discrete Proportional
Valve Technology
The above reon
temperature
feedD
esigns
for electric vehicle (EV)
cooling systems are significantly
more complicated and challenging
than are designs for internal combustion
engine (ICE) vehicles. The cooling
system must accommodate several
points of heat generation in the vehicle
(Figure 1) including:
1. Inverter electronics to control the motors
used for the vehicle's propulsion.
2. Charging electronics
(may or may
not be integrated with inverter electronics).
3.
Motor(s) used for vehicle propulsion
and energy recovery.
4. Vehicle propulsion (high voltage)
battery.
Each of these heat sources may require
maximum flows of eight to ten
liters per minute of coolant in a typical
EV drive train; however, sizing the cooling
system to accommodate maximum
flows for all heat sources would result
in an energy and weight penalty in the
pumping system.
A more efficient scenario would be to
control flow to each heat source based
Motion Design, February 2022
MD Fluid Power Feature 0222_1.indd 5
back. In this scenario,
coolant flow is only delivered to
each heat source as required to maintain
optimal temperature. This would
allow for a pump with somewhat smaller
capacity and would have the added benefit
of providing for different optimal
" setpoints " for the various heat sources.
For example, inverter electronics could
be operated at their optimal temperature
of 40 °C to 65 °C, while motors or
battery could be cooled further,
or allowed to run warmer
for short periods as performance
demands dictate.
The heat generated by
EV components ideally
would not be wasted. In
cold-weather operation,
it would be desirable to
recycle the waste heat
from electronics to provide
cabin heat. Avoiding
electrical resistance
heating for cabin
heat would
reduce parasitic
electrical
loads during
cold-weather
operation.
quirements result in an
optimal cooling system configuration
that is significantly different from
what is required for ICE cooling applications.
The need for independent control
of temperature at multiple points in the
vehicle drive and charging systems and
the desire for efficient management of
heat (reuse when possible) drive a more
complicated system design. Core to this
type of cooling system is a method for
controlling the coolant flow between
components. The key attributes of such
a proportioning method would be:
* Predictable relationship between setting
and flow (lack of hysteresis)'
* Zero steady-state power
at any setpoint
* Capable of fully shutting
off flow (leakfree
off state)
* Failsafe condition
whenpower
is lost,
e.g. full open
Figure 1. Electric vehicle cooling components.
5
Cov
ToC
1/18/22 9:11 AM
http://info.hotims.com/82318-800

Tech Briefs Magazine - February 2022

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