Patent GB-582998-A (GB)
Title: Improvements in or relating to lifting and pulling mechanism
IPC: B66D3/14
Filed: 1944-07-21
Abstract: 582,998. Brakes. HINCHCLIFFE, S. July 21, 1944, Nos. 14007 and 14930. [Class 103 (i)] [Also in Group XXX] Lifting and pulling mechanism comprises a shaft rotatable in a casing and having rigidly mounted thereon a chain sprocket for carrying the lifting chain and a driving member for turning the said shaft, while interposed between said driving, member and the casing and in resilient rubbing contact with the latter, is a clutch member which is in threaded engagement with the shaft in such manner that when the driving member is turned to take the load, the movement of the shaft tends to retract the clutch member and so relieve pressure between it and the casing, but when the driving member is released from turning effort, and so tends to move in the opposite direction, its movement tends to increase the pressure between the clutch member and the casing so that the shaft is held. In the embodiment shown, the lifting shaft 2 is mounted in a casing 1 and has a chain sprocket 3 for the lifting chain and a ratchet wheel 6 secured to it. Interposed between the wheel 6 and the casing is a clutch member 7 mounted on the threaded portion 2c of the shaft and clutch plates 8. 9 keyed respectively to the shaft and casing. The clutch 7 is connected to the wheel 6 by a spring 25 wrapped around a boss 6b of the wheel and secured at its ends to pins 22, 23 on the clutch member 7 and wheel 6 respectively. The device is operated by a ratchet lever 12 having spring-pressed pawls 13, 14 slidably mounted in casing 15a, 15b and controlled by a locking member 17 to engage with the ratchet wheel and clutch 7 respectively, the teeth on these latter members being oppositely arranged. When a load is to be lifted, the member 17 is turned by an arm 18 to the position shown so chat the lower end of its segmental portion 17g has abutted against a shoulder on the pawl 14 to disengage it from the clutch 7. - At the same time the upper end of the segmental portion 17g has moved inwards beyond the inner limit of the shoulder of the pawl 13 so that this pawl engages the ratchet wheel 6 and the shaft 2 may be rotated. When the lever 12 has completed its stroke, the tendency of the shaft 2 to move in the opposite direction under the load draws the clutch 7 into engagement with the casing 1 through the clutch plates 8, 9 to hold the load during the return movement of the lever. When it is desired to lower the load, the member 17 is operated so that the pawl 13 is withdrawn and the pawl 14 engaged with the teeth 7a on the clutch member 7 which is then moved step by step by the movement of lever 12 in the direction opposite to that for lifting. The chain may be paid-out or in quickly preparatory to carrying a load by hand wheel 21 provided with a slot 21a accommodating pins 22, 23 on the clutch member 7 and ratchet wheel respectively. Angular movement of the arm 18 is restricted by stops 15d, 15e on the casing 15c housing the member 17. Unintentional turning of this member 17 is prevented by nicks 17d, 17e with which the shoulders of the pawls engage, and it is located laterally by a pin 49 engaging in one of of its circumferential grooves provided to accommodate portions of the pawls. According to the first Provisional Specification the clutch member is pressed aigainst the casing by spring-pressed balls in the ratchet wheel, the pins 22, 23 are almost diametrically opposite and the mechanism may be driven by an electric motor or other power source.