The Oak Ridge National Laboratory (ORNL) Power
Electronics and Electric Machinery Research Center
(PEEMRC) has been developing technologies to address the
thermal issues associated with hybrid vehicles. This work is
part of the ongoing FreedomCAR and Vehicle Technologies
(FCVT) program, 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 drive component cooling. This loop uses R-134a as a
coolant and shares the vehicle’s existing air-conditioning
(AC) condenser, which dissipates waste heat to the ambient
air. Because temperature requirements for cooling 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 a compressor and requires only 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
should also, ideally, provide a high COP, a flat temperature
profile, and low pressure drop.