Dual stage control for viscous fluid coupling

A viscous fluid clutch comprising:

• a first member secured for rotation with a shaft;
• a second member rotatably disposed on said shaft relative to said first member;
• shear surfaces disposed on said first and second members and forming an operating chamber therebetween;
• first and second fluid storage chambers adjacent said operating chamber;
• means operative to generate a circulating flow of viscous fluid between said chambers;
• first valve means operative to modulate flow of viscous fluid between said first storage chamber and said operating chamber as a function of a first sensed fluid temperature;
• and
• second valve means operative to modulate flow of viscous fluid between said second storage chamber and said operating chamber as a function of a second sensed fluid temperature.

A viscous fluid clutch comprising:

• a first member secured for rotation with a shaft;
• a second member rotatably disposed on said shaft relative to said first member;
• shear surfaces disposed on said first and second members and forming an operating chamber therebetween;
• first and second fluid storage chambers serially adjacent said operating chamber;
• pump means operative to circulate viscous fluid between said operating chamber and said storage chambers via a return passageway;
• first valve means operative to modulate the flow of viscous fluid within said return passageway and the flow of viscous fluid between said first storage chamber and said operating chamber as a function of a first sensed fluid temperature;
• and
• second valve means operative to modulate the flow of viscous fluid from said second storage chamber to said first storage chamber as a function of a second sensed fluid temperature.

A viscous fluid clutch comprising:

• a first member secured for rotation with a shaft;
• a second member rotatably disposed on said shaft relative to said first member;
• shear surfaces disposed on said first and second members and forming an operating chamber therebetween;
• first and second fluid storage chambers radially inwardly serially adjacent said operating chamber;
• pump means operative to circulate viscous fluid from said operating chamber to a substantially radially inwardly directed return passageway during relative rotation between said members;
• first valve means operative to modulate the flow of viscous fluid within said return passageway for selective discharge into said storage chambers and the flow of viscous fluid between said first storage chamber and said operating chamber through at least one interconnecting drain port at the radially outwardmost extent of said first storage chamber, as a function of a first sensed fluid temperature;
• and
• second valve means operative to modulate the flow of viscous fluid from said second storage chamber to said first storage chamber through at least one interconnecting drain port at the radially outwardmost extent thereof as a function of a second sensed fluid temperature.