Patent GB-660281-A (GB)
Title: Improvements in chain hoist
IPC: B66D3/14
Filed: 1948-10-06
Abstract: 660,281. Chain hoists. MANNING, MAXWELL & MOORE, Inc. Oct. 6, 1948. No. 26057/48. Class 78 (v). A hoist includes a load shaft 21 driving a chain sprocket 16, a driving member 26 mounted on said shaft for rotation relative thereto, a brake 36, 37 for braking said shaft: means operated by the relative rotation of said member and said shaft in one direction for rendering said brake effective to prevent rotation of said shaft in a load lowering direction, said brake being released upon relative rotation of said member and said shaft in the opposite direction, and means operable to releasably lock said member and said shaft together in a position to maintain brake release whereby the chain may be pulled freely over the chain sprocket. Raising of the load-Fig. 2 The drive passes from handle 10 through pawl 66 to driving member 26 and from member 26 through friction washers 36 and 37, and ratchet wheel 31 and disc 30 to load shaft 21 which is coupled to the chain sprocket 16 through gears 24 and 25, the latter being integral with the sprocket wheel. The load shaft 21 is formed integrally with the thrust disc 30 and with the threaded extension 28, the latter working within the threaded driving member 26, the friction washers 37 and 36 and the ratchet wheel 39 being carried loosely by the said shaft extension 28. When the driving member 26 is rotated by handle 10 in the clockwise direction the said member moves axially along the threaded extension 28 and compresses the friction washers 36 and 37, thus locking together driving member 26, the ratchet wheel 31 and the disc 30 and the shaft 21 so that the chain sprocket 16 is driven to raise the load. If the load is heavy and tends to drive back the chain sprocket its effect is to rotate the shaft 21 in an anti-clockwise direction whilst member 26 remains stationary so that the member 26 and shaft 21 continue to be locked together and tend to turn in the anticlockwise direction which tendency is checked by the pawl 33 engaging the ratchet wheel 31. In order that the pawl 32 should make a positive and automatic engagement with the ratchet wheel 31 when the shaft 21 is rotated anticlockwise there is provided on the thrust disc 30a spring loop 40 which is fixed at 41 to the pawl 32. Thus the friction of the disc on the wire loop 40 engages or disengages the pawl with the ratchet wheel. Lowering the load. Figs. 2 and 5 When there is a load upon the chain there is a tendency for the shaft 21 to rotate in the anti-clockwise direction locking together the member 26 and the shaft 21. As the handle 10 is moved in the anti-clockwise direction the member 26 unscrews itself along the shaft 21 and momentarily frees the ratchet wheel 31, thus allowing the load to be lowered, which. lowering automatically screws up the shaft and the member so as to lock them together again. Thus the load is lowered under the control of the movement of lever 10. In order that the chain may be lowered when there is no load upon it, there is provided a collar 54 splined on the shaft 21 so as to rotate with it, and the collar is provided with an arm 47 to engage with a lug 48 provided on the member 26. When the handle is moved in the anti-clockwise direction to lower the chain the lug 48 is rotated to engage the arm 47 and then further movement of the handle 10 causes the shaft to move with the member 26 and lower the chain bv a positive drive. Freeing of the chain. Figs. 2 and 5 There is provided a hand-wheel 52 rotatably supported on the end of the member 26. The hand-wheel carries a spring 50 which is secured to the hand-wheel at 51, and is provided with a shoulder 54 and a detent 58. The handwheel 52 is rotated so that a shoulder 54 engages the arm 47 and pushes the arm 47 against the lug 48. At the same time the detent 58 engages in a hollow 59 formed in lug 48, thus locking together the member 26 and the shaft 21. The positions of arm 47 and lug 48 are chosen so that the member 26 is unscrewed along the shaft 21 and the ratchet wheel 31 is free upon the shaft so that the chain sprocket 16 itself is free to move and the chain can be pulled loosely thereover the handle 10 being freed from the member 26. In order to allow for the wear of the friction washers 36 and 37 the collar 45 is, as stated above, formed with splines so that the collar may be removed from the shaft 21, rotated, and replaced, so that the arm 47 thereupon is appropriately positioned to engage the lug 48 and permit the load to be lowered. Handle 10. Fig. 2 Handle 10, which is enlarged to form a casing 62 sliding around member 26, is provided with two springs 71, 72, wound in opposite directions upon the pin 73 and secured at one end to pin 74, the opposite end of each spring engaging with pin 75 formed upon pawl 66 pivoting in bearings 70 formed in the handle 10, the pawl 66 engaging a ratchet wheel 60 formed integral with the member 26. Between the ends of the springs is mounted rotatable cam 79 operated by thumb member 77 so that as the latter is turned the cam engages one spring or the other, thus putting it out of operation and allowing the other spring to influence the pawl and to drive the member 26 through its ratchet wheel 60. The pawl 66 is formed with two ratchet contacting heads so that it can drive the member 26 in either direction or be set neutral.