Patent GB-294021-A (GB)
Title: Improvements in and relating to hydraulic braking appliances for lifts and the like
IPC: B66D5/02
Filed: 1927-10-03
Abstract: 294,021. Black, G. J. F. Oct. 3, 1927. Brakes and retarding-apparatus for winding and paying-out apparatus; stopping automatically at end of run ; regulating and control-transmitting gear.-In hoisting apparatus for mine cages, &c. a pump driven from the winding-engine through step-up gearing circulates fluid in a closed circuit containing a throttle actuated in accordance with the movement of the cage. When the pressure in the circuit exceeds a predetermined value a trip device is actuated which produces a braking action on the engine. A main shaft a driven by the engine drives a rotary pump b, Fig. 1, through step-up gearing and a clutch d. Coaxial cams c<1>, c<2> are driven by the shaft a so that they turn through approximately three-quarters of a revolution during one journey of the cage. The cam c' closes the clutch d at the ends of a wind, and the cam c<2> actuates through a plunger f which forms a throttle in the circuit through which fluid is circulated by the pump. The pressure in the circuit increases gradually as the plunger is depressed and the engine is slowed down. When the circuit is close, the engine is stopped. This retarding device is used only for slow cage speeds. When the cage is run sometimes at a high speed, the shaft a is arranged to drive an additional retarding device of this character, and the cams are so arranged that one device comes into operation as the other becomes inactive. Alternatively a single retarding device may be used throughout the run by varying the gearing in accordance with the speed of the cage. The plunger cam c<2> is indented slightly for a short distance past the point representing the end of the run in order that the cage may be moved slowly up to the head-pulley for inspection of the rope. At the end of this movement the plunger is forced down quickly. The whole of the pump mechanism is immersed in a liquid kept at a constant temperature by a thermostaticallycontrolled immersion heater n in order that the fluid in the circuit may have a constant viscosity. The channels on either side of the plunger communicate with the opposite sides of a pair of pistons g, h, Fig. 7. A pivot on the rod of the piston g is attached to the free end of a pivoted arm i, Fig. 8, and also to aT-lever j. The arm i is held between springs i', i<2> and the stem of the lever j is held between adjustable screws j<1>, j<2>. A curved block g<1> on the piston rod extension rests on a roller k<1> mounted on a rod k which when depressed actuates brake-mechanism and the throttle of the engine. If during retardation there is a difference of pressure between the fluid on opposite sides of the piston, the spring i<2> will become compressed, and when the difference is sufficiently great, the left-hand arm of the T- lever will slip over the edge of the piston-rod extension, and the rod will move towards the right thereby pulling down the rod k and applying the brake, &c. The movement of the piston rod is assisted by fluid from the cylinder containing the piston h. At the commencement of a run it is necessary to prevent an increase of pressure in the circuit during the period of acceleration. For this purpose the piston h, Fig. 7, co-operates with slidable rods h<1>, h<2> having coned ends which normally are in contact and which seal the central passage through the piston for a certain movement of the piston on either side of its central position. At the commencement of a run, one of the cams c<3>, c<4> will act on an arm h<5>, h<6> to rotate a rod h<3>, h<4> which effects the outward movement of a rod h<1>, h<2>, and as the piston has already been moved slightly in the same direction, there is then a free passage for fluid in the circuit. In a modification the pump is rendered operative only towards the end of the wind by a lever associated with a screwed spindle operated by the winding mechanism. The shape of the cam c<2> is determined by replacing the plunger f by a plunger carrying a scribing point which bears against the circular plate to be cut. The plunger is connected by vertical rods o<1>, o<2>, Fig. 7, to one arm of a bell-crank lever p, the other arm of which is attached to the end of the rod of the piston g. The trip lever i is detached and the plunger is loaded so that there is the same pressure in the circuit as there is towards the end of the wind. Specifications 277,409 and 293,606 are referred to.