The Oak Ridge National Laboratory (ORNL) Power
Electronics and Electric Machinery Research Center
(PEEMRC) has been developing technologies to address the
thermal concerns associated with hybrid electric vehicles
(HEVs). This work is part of the ongoing FreedomCAR and
Vehicle Technologies program (FCVT), performed for the
Department of Energy (DOE). Removal of the heat generated
from electrical losses in traction motors and their associated
power electronics is essential for the reliable operation of
motors and power electronics. As part of a larger thermal
management project, which includes shrinking inverter size
and direct cooling of electronics, ORNL has developed U.S.
Patent No. 6,772,603 B2, Methods and Apparatus for
Thermal Management of Vehicle Systems and Components
[1], and patent pending Floating Loop System for Cooling
Integrated Motors and Inverters Using Hot Liquid
Refrigerant [2]. The floating-loop system provides a large
coefficient of performance (COP) for hybrid-electric drive
component cooling. This loop (based on R-134a) shares a
vehicle’s existing air-conditioning (AC) condenser, which
dissipates waste heat to the ambient air. Because the
temperature requirements for cooling of power electronics
and electric machines are not as low as that required for
passenger compartment air, this adjoining loop can operate on
the high-pressure side of the existing AC system. This
arrangement also allows for the floating loop to run without
the need for the compressor and only needs a small pump to
move the liquid refrigerant. For the design to be viable, the
loop must not adversely affect the existing system. The loop
would also provide a high COP, a flat temperature profile,
and a low pressure drop.