Fig. 28
47. The Differential Lever.—The principle of the operation of the differential lever with which a constantly increasing force can be applied to the brake strap is illustrated in [Fig. 28]. Let a o represent a straight lever whose fulcrum is at o; and let the reach rod be attached at e. In this position, if
| a o | 6 | |
| —— | = | —— |
| e o | 1 |
the effective lever is 6 to 1. If, now, the lever is moved through 30° to the position b o, the force applied at a moves through the distance a b, and the reach rod through the horizontal distance k f, so that the effective leverage is increased a small amount e k and the ratio of the arms becomes
| a o |
| —— . |
| k o |
When the lever is moved another 30° to the position c o, the reach rod moves a distance i g, which is less than k f, so that the effective leverage is increased by the amount k l and the ratio of the arms becomes
| a o |
| —— . |
| l o |
Again, moving the lever 30° more to the position d o, the reach rod moves through the still shorter distance j h, which is less than i g, and the effective leverage becomes very great. It is evident from this that the farther the lever is moved toward d the greater becomes the effective leverage. In practice, it would be impossible to move the lever through the entire quadrant to advantage, and there would also be more movement of the reach rod at the beginning of the stroke and less at the end than is needed to produce the desired effect.
