Patent GB-790702-A (GB)
Title: Improvements relating to clutches for transmitting rotary motion
Inventor: SHORT PHILIP JOHN
IPC: F16D23/10
Filed: 1955-08-03
Abstract: 790,702. Ratchet clutches. S.S.S. GEARS, Ltd. July 11, 1956 [Aug. 3, 1955], No. 22353/55. Class 80 (2). A clutch of the Legge type, comprising a sleeve 1 with teeth 2 and a shaft 3 having helical splines 5 supporting an intermediate clutch member 4 formed with clutch teeth 7, synchronization of the speeds of the sleeve and shaft 1, 3 allowing pawls 8 or the like on the intermediate member 4 to engage the teeth 2 and thus screw the clutch member 4 along the helical splines 5 to engage the teeth 2, 7, is provided with a dash-pot operative only in the final stages of the screwing motion of the clutch member 4 to cushion the engagement of the clutch teeth. In one form, a sleeve 12, Figs. 1, 2, surrounds a shoulder 11 on the shaft 3 and is formed with an annular flange 13 which co-operates with the shaft shoulder to form a chamber to which oil is continually fed through shaft ducts 14, 15. A further sleeve 17 has flanges 18, 19 at its ends which co-operate with outwardly directed flanges 16, 10 on the sleeve 12 and the intermediate clutch member 4, respectively. A control fork 20 engages between two outwardly directed flanges on the sleeve 17. In the disengaged position of the clutch, the control fork 20 is in the position shown in Fig. 2, when the intermediate clutch member 4 is held to the right. To engage the teeth 2, 7, the control fork 20 is moved to the position shown in Fig. 1. The sleeve 17 is thereby moved to the position shown in the lower half of Fig. 1, and pushes the intermediate clutch member 4 leftwards until the pawls &c. 8 ratchet over the teeth 2. The leftward movement of the sleeve 17 does not effect the dash-pot sleeve 12, due to the lost motion connection between the flanges 16, 18. On synchronization of the sleeve and shaft 1, 3, the sleeve 4 is further screwed to the left, as described above, and the teeth 2, 7 begin to engage. At this moment, the flanges 16, 18 abut, and further leftward movement of the intermediate clutch member 4 expels oil from the dash-pot chamber formed between the flange 13 and shoulder 11 through the annular clearance spaced between the shaft and the flange, and if desired through small escape holes or graduated orifices (not shown) in the shaft or flange. Completion of clutch engagement is thus cushioned. In the final position the pawls lie to the left of the clutch teeth 2. The clutch teeth 2, 7 and the pawl 8 may have their engaging surfaces chamfered as shown in Fig. 3, so that after the initial engaging motion the pawl is relieved of load. Alternatively, the clutch teeth 7 may remain unchamfered, while the nose of the pawl 8 is chamfered across its whole width, Fig. 6 (not shown), or the teeth 7 may be chamfered while the teeth 2 and the noses of the pawl 8 remain unchamfered, Fig. 7 (not shown), or the nose of the pawl 8 may be chamfered across its whole width while the clutch teeth 2, 7 are both chamfered, Fig. 8 (not shown). In a modification, Fig. 9, a dash-pot chamber 23 is formed between the intermediate clutch member 4 and a collar 29 fast on the shaft 3. Oil is continuously fed to the dash-pot chamber through shaft ducts 26 ... 28. An annular piston 25 within the dash-pot chamber is formed with end flanges 32, 33 which co-operate with flanges 31, 34 on the collar 29 and the intermediate clutch member, respectively. The intermediate member 4 is engaged by a control fork 20 which, when moved from the disengaged position shown, first takes up part of the lost motion between the flanges 32, 34 while moving the paws 8 into engagement with the clutch teeth 2. When the speeds of rotation of the sleeve 1 and shaft are synchronized, the pawls 8 screw the intermediate clutch member 4 along the helical splines to cause initial engagement of the clutch teeth 2, 7, this movement engaging the flanges 32, 34. Further screwing of the intermediate clutch member 4, as the clutch teeth 2, 7 move towards full engagement, draws the annular piston 25 into the dash-pot chamber 23 and thus expels oil therefrom, either through small escape holes or graduated orifices (not shown) or past a small clearance space between the piston 25 and the radially outer wall of the dash-pot chamber. Specifications 354,711, 410,083, 513,974 and 534,470 are referred to.