Design of Valve Body Integrated Direct Acting Control Solenoids

This paper studies the latest trend in transmission hydraulic controls development which involves the integration of the solenoid hydraulic element into the hydraulic valve body and attaching the magnetic part of the solenoid to the assembled valve body. This practice has been adopted by multiple automotive OEMs. Integrated direct acting control solenoids are key enablers for OEMs to meet more stringent fuel economy requirements in competitive environments. In the meantime, there are unique challenges in both integration and packaging due to the limited useful stroke of the armature and the fact that the solenoid armature can only act upon the spool valve in an outward motion. Both normally low and normally high functionality can be achieved with direct acting solenoids, but there are more challenges for the normally high functionality, especially spool valve porting and high hysteresis. This paper uses analytical methods to link the challenges to physical interactions between the magnetic and hydraulic parts of direct acting solenoids, and introduces design principles and best practices to address them in the design phase.