Phase change assisted heat sink

Abstract

In an electric vehicle, the traction motor is driven from a battery by way of a controllable electric power switching arrangement. In normal operation of the switches of the switching arrangement, the power losses or heating of the switches depends upon the power being handled; during hard acceleration the power is high, and at constant speed on level ground the power is relatively small. Thus, the power “dissipated” by the switches varies with time. A cooling system transfers heat from the switching arrangement to ambient. During acceleration, the cooling system may not be able to limit the instantaneous temperature of the switches to the desired value. A phase-change heat “sink” coupled to the switches absorbs heat from the switches during hard acceleration, and returns the heat to the cooling system under more constant-speed conditions. In general, any electronic device which experiences transient power surges may use the same principle, thereby allowing the overall cooling system to be sized for average power, with the phase-change sink acting as an “integrator” to average the power by storing heat when the temperature tends to rise, and returning the heat when the temperature tends to fall. In an electric vehicle, braking is accomplished by returning energy to the battery, but when the battery is fully charged and can accept no more charge, braking may be accomplished by coupling the electric power to a cooled phase-change sink. The phase-change material may be iron.