Patent GB-439484-A (GB)
Title: Improvements in and relating to devices for applying a predetermined variable torqueto rotatable bodies
IPC: F16H61/02
Filed: 1934-03-08
Abstract: 439,484. Variable speed gearing. BENTLEY, J., and GALLOWAY, H. L., Edenbank, Lenzie, Dumbartonshire. March 8, 1934, Nos. 7389/34 and 6241/35. [Class 80 (i)] [See also Groups XXXIV and XXX] A device for limiting the load in hoisting and winding machinery comprises a device for applying a resisting torque to a member of a differential or epicyclic gearing in the drive, the resisting torque device comprising a piston sliding in a cylinder and connected to a crank connected to the differential gear or regulator motor, a chamber in which air is kept at a constant pressure by a relief valve and into which air is delivered by the piston and means for varying the capacity or clearance volume of the cylinder to vary the load. As applied to a jib crane the motor shaft 1 drives the load shaft 2 through a differential gear 3 the casing 4 of which is geared through wheel 6 and crank 7<1> to a piston 9 in cylinder 10. The cylinder is axially slidable in a fixed ring 11 to vary its capacity or clearance volume, adjustment being effected by a pin 14 on the cylinder engaging a cam slot 15 in a disc 16 mounted freely on the crank-shaft 7. A reservoir space 23 fitted with a relief valve 24 communicates with the cylinder through an outlet valve 22 and the piston 9 carries an inlet valve 25. An auxiliary cylinder 26 carried by the cylinder 10 contains a piston 30<1> connected to a valve 30 controlling communication of the lower part of cylinder 26 with a whistle 32. The upper and lower parts of the cylinder 26 are connected by passage 28, a valve 29 and passage 31 with cylinder 10 and reservoir 23 respectively. When current is supplied to the driving motor the valve 29 is open. The cylinder 26 contains a piston 27 fixed to the ring 11. Pressure at the value determined by valve 24 normally exists in reservoir 23. The maximum resisting torque that the piston 9 can exert on the shaft 7 and casing 4 and thus the maximum permissible load on the shaft 2 is dependent upon the adjustment of the cylinder 10. In order that this maximum load may be made to depend upon the radius or angle of the jib 20 of the crane the jib is connected by link 18 to the disc 16. If this load is exceeded, the shaft 2 remains stationary the casing 4 is driven and air is thus pumped into the cylinder 26 and the warning whistle is sounded. In order that when the shaft 7 rotates a substantially constant resisting torque may be applied to it having regard to the fact that the torque due to the piston tends to decrease as the speed rises, a centrifugal brake is provided which may comprise centrifugal balls 45 in radial slots in spiders 44 secured to shaft 7 and adapted to move a disc 47 with inclined surface, against the force of a spring 48 thus engaging a disc 40 with a fixed part 41. If there is a load on the hook and no current is being supplied to the motor and the jib is derricked out the valve 29 being closed, the air in the upper part of cylinder 26 will be compressed by the relative movement of the piston 27 and thus when the jib reaches an angle at which the load is the permissible maximum the whistle 32 will be blown. The cylinder 26 has a valve 33 normally held closed by the tension in the hoisting rope but when the load is dropped by a free barrel with the motor cut out the valve is free to open so that the pressure in the cylinder cannot increase when the jib is derricked out and the whistle will not therefore sound. The cylinder 26 may be omitted. The crank and piston may be movable instead of the cylinder 10 to vary the clearance volume. According to the first Provisional Specification the device may be used generally to apply a limiting torque.