FIGURE 13 Throw-in sprag configuration and spring. (a) Regular engagement. (b) Centrifugal throw-in engagement.

Returning now to the conventional sprag profile, let A and B denote the contact points on the profile of a sprag, as shown in Figure 14, let the line between A and B termed the strut, and let α represent the angle subtended by the strut at the center of the clutch. Let r0 and ri represent the radii of the outer and inner races, respectively, let µ0 and µ denote the corresponding coefficients of friction, and let F0 and Fi refer to the associated normal forces. In these terms,

(4-

is the moment equilibrium equation of the sprag about the axis of rotation of the clutch. Summing forces in the direction of the friction force at A gives

(4-

as the equilibrium condition in that direction. Substitution for F0 in equation (4-2) from equation (4-1) yields