GB770837A - Improvements in or relating to a pressure-fluid actuating assembly, particularly forhydraulic braking systems - Google Patents

Abstract

770,837. Hydraulic master cylinders. FAWICK, T. L. June 16, 1955 [June 29, 1954], No. 17388/55. Class 103 (1). In a pressure-fluid actuating assembly, particularly for hydraulic braking systems of vehicles, comprising a single fluid impelling member operating in a chamber, means are provided for varying the mechanical advantage of the manually actuated means such that the mechanical advantage gradually increases substantially throughout the working stroke of the fluid impelling member; yielding means being provided between the manually-actuated means and the fluid impelling member. In the embodiment illustrated, an hydraulic master cylinder unit 10 provided with a single piston 13 operable within a cylinder 12, is provided with an L-shaped foot lever 28 fulcrummed at 29 to a pair of bearing brackets 30, 30 which are secured to the casing of the master cylinder unit 10. The short arm 28a of the foot lever 28 is hinged at 32 to one end of a toggle link 33 pivoted at 34 to a sliding guide member 14 which is slidable in cylinder 12. The stem of piston 13 slides in the hollow sliding guide member 14 to a limited extent providing a lostmotion connection between the two parts and a strong compression spring 22 is interposed between the piston and the large diameter part of the sliding guide member 14 to constantly urge the two parts away from each other. In operation, during the first part of the actuating movement of the brake lever 28 the toggle 28a, 33 is at a position of low mechanical advantage such as to impart rapid motion to guide member 14 and piston 13 for quickly moving the brake shoes into contact with the brake drum. When the shoes contact the drum, the spring 22 is further compressed by movement of the guide member 14 closer to the piston, this action being concurrent with movement of the toggle elements to positions of progressively higher mechanical advantage as the braking pressure increases. A modification is described and illustrated in the Specification wherein the toggle mechanism is replaced by a cam and roller arrangement.