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 AMhttp://info.hotims.com/82318-800