Hartlieb, H., Williams, K., and Hausmann, M., "New Variable Force Solenoid Driver IC with a Unique Controller Design Improves Solenoid Current Regulation," SAE Technical Paper 2010-01-0371, 2010, doi:10.4271/2010-01-0371.
The majority of modern automatic transmissions make use of multiple Variable Force Solenoid (VFS) valves within the hydraulic controls. The requirements for the control of these valves are much more stringent in the latest transmission designs. This leads to challenging requirements for the electronic solenoid driver circuit used to regulate the current flowing through the solenoid valve coil. We have developed a current control method that is fundamentally different than those commonly used in solenoid driver circuits. This unique current control method results in several improvements in the key performance characteristics of the solenoid driver circuit, which in turn improves the performance of the transmission system. In addition, this new control method requires less effort to implement into a specific application than state of the art current control methods.