Resolution and Force Increase in Electric Actuator for Thermal Management Expansion Valves

Expansion valves are key components of an automotive thermal management system. Recently electronic expansion valves (EXVs) have been replacing conventional thermostatic valves as they offer a finer degree of control. They are operated by a stepper motor and can be based either on a linear or a rotary motion. However, on one hand, the existing linear EXVs with a leadscrew system are not suitable to manage high-pressure and large-diameter port valves, and on the other hand, rotary EXVs have the main disadvantages of having a high mechanical hysteresis and of requiring a dynamic seal which adds cost to the system. This paper proposes then to solve those issues thanks to a new linear concept that provides a new integration on a classic leadscrew linear EXV using a specific radial flux brushless DC (BLDC) motor, a worm gear, and a sensor integration option. The idea behind this is to stop using the conventional coaxial movements of the reducers and to better use the volume of the metal body where the fluid lines are located. The main benefit is a more compact EXV that can generate more force than the standard solutions. Moreover the integration of a position sensor and a new control scheme led to an increase in the accuracy of the valve positioning and to a global efficiency improvement of the system by being able to adapt the current to the applied load. For comparison purposes, an actuator based on this new concept was then built using two existing EXVs as references. This comparison shows that to reach the same performances, the new linear design needs a much smaller motor and, has an overall height of only 55 mm compared to 80 mm and a theoretical resolution of 0.16 μm.