Abstract: A system for controlling the engagement and disengagement of a viscous type coupling is accomplished by controlling the relative positioning of a spring loaded valve arm relative to a fluid port through the use of an electrically-activated, temperature-sensitive member, such as a NiTi wire. The characteristics of shape memory alloy materials are such that they are hard above a predetermined temperature, but soft and ductile below a predetermined temperature. When engagement or disengagement of the coupling is desired, electrical current is introduced through the member, therein heating it above a predetermined temperature to harden it. This hardening causes the valve arm to either move to either cover or uncover a fluid port, depending upon the design arrangement of the valve arm relative to the fluid port. A controller coupled to a plurality of engine operating sensors and a power source controls the electrical activation as a function of a desired operating condition.

Abstract: A method of controlling a fluid actuated fan drive system (12) for an engine (14) includes determining an engine speed. The speed of a fluid actuated engine-cooling fan (16) is limited when the engine speed is greater than or equal to an engine over-speed level. The fluid controlled fan drive system (12) includes a sensor (31) that generates an engine speed signal. The system (12) also includes the fluid actuated engine-cooling fan (16) and an engagement circuit (36) that is coupled thereto. A controller (28) is coupled to the sensor (31) and the engagement circuit (36) and limits operating speed of the engine-cooling fan (16) to less than a predetermined level when the engine speed signal is indicative of an engine over-speed condition.

Abstract: A system for controlling the engagement and disengagement of a viscous type coupling is accomplished by controlling the relative positioning of a spring loaded valve arm relative to a fluid port through the use of an electrically-activated, temperature-sensitive wire. The characteristics of wire are such that the wire is hard above a predetermined temperature, but soft and ductile below a predetermined temperature. When engagement or disengagement of the coupling is desired, electrical current is introduced through the wire, therein heating the wire above a predetermined temperature to harden the wire. This hardening causes the valve arm to either move to either cover or uncover a fluid port, depending upon the design arrangement of the valve arm relative to the fluid port. A controller coupled to a plurality of engine operating sensors and a power source controls the electrical activation as a function of a desired operating condition.