Patent GB-278711-A (GB)
Title: Improvements in servo brakes
IPC: F16D65/14
Filed: 1927-10-04
Abstract: 278,711. Athimon, F. Oct. 6, 1926, [Convention date]. Actuated or applied by springs.-In a spring relay device for assisting the application of brakes, the point of application of the force of the spring on a lever connected to the brakes shifts when the lever is actuated by the control pedal &c. from an ineffective to an effective position. Means are provided for automatically shortening the effective length of a rod in the connections to the brake when the stroke exceeds a predetermined amount. A lever 4 pivoted to a fixed casing 1 about an axis 7 is connected To the brakes by a rod 3 which passes through the upper end of the lever against which it abuts by means of an adjusting nut 15. A short double-armed lever 16 pivoted at 14 on the lever 4 is connected by the rod 2 to the operating pedal and has limited pivotal movement relative to the lever determined by a pin 17 for actuating aa adjusting nut 15 as described below. The lever 4 is of channel section to receive rollers 6 which ride on the cam surface of the lever and are connected by a link 8 to a sliding rod 10 which is acted upon by an initially compressed spring 13 through the cap 11. The surface of the lever 4 is so shaped that with the parts in the normal position A the axis of the rollers 6 is coaxial with that of the lever and the spring is ineffective. Considering the lever 16 as rigidly connected to the lever 4, if a pull is exerted upon the rod 2 to apply the brakes, the rollers remain in the same position on the lever 4 during its movement from the position A (shown in broken lines in the drawing) to the position B (shown in full lines) at which the braking action commences. When, however, the lever is moved beyond the position B, the rollers 6 travel down the surface of the lever and the force of the spring becomes effective and to an increasing extent. Upon releasing the pedal the tension in the brake connections restores the parts to the initial position. In a modification, Fig. 6, the lever 4 is substituted by a lever 27 upon which the spring 33 acts through a lever 31. The lever 27 has a surface 29 concentric with its axis 28 so that during the initial movement of the lever the spring is ineffective but subsequently applies an increasing force to the brake. Compensating for wear.-The nut 15 on the end of the pull rod 3 which abuts on the end of the lever 4 is engaged by a pawl 18 pivoted at 19 on the lever. The pawl 18 has an arm 18<a> curved about the axis 7 of the lever and adapted for locking engagement with a projection on the end of a lever 20 pivoted to the fixed casing 1 at 22 and having an arm 20a adapted to be engaged by a rod 23 secured to a part 16a carried by the lever 16. A spring 24 extends between the part 69 and a pin 25 on the lever 4. When, during the application of the brakes, the parts reach the position B, the pawl 18 is about to engage the next tooth on the nut 15 but if the brakes are then applied the force on the rod 2 is sufficient to overcome the spring 24 and the movement of the lever 16 about its pivot 14 on the lever 4 and the consequent movement of the lever 20, 20a effects the disengagement of the pawl from the ratchet nut 15 until the end of the operation when the pawl is returned by the engagement of a projection 26 on the lever 4 with the lever 20. If however, the levers 4, 16 move beyond the position B before the braking action commences, the rod 23 becomes disengaged from the arm 20<a> of the lever 20 so that the movement thereof is insufficient to engage the pawl which is thus permitted to engage the next tooth of the nut 15 and during the return movement to turn the nut and thus shorten the effective length of the rod 3.