From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Analysis of torsional stress and engine knock related to the crankshaft and slipper wheels.
| Identifier | ExFiles\Box 47\2\ Scan057 | |
| Date | 23th January 1928 guessed | |
| contd :- -3- (up to a certain load) and over run or wind up the crankshaft, until the maximum torsional strain is reached. The speed of the slipper wheels then overcome the friction and slip, thereby releasing the torsional stress with the result that a force acting in the opposite direction to the rotation of the shaft and piston, with the result that the conn. rod is subjected to a compression effect between the crankpin and the gudgeon pin, and the knock is produced. This verifies why the knock is at its maximum when No.3 cyl. is fired, as we have in this case, the increased length of the flexible crankshaft between the slipper wheels and No.3 cyl. which allows a greater winding up of the shaft with a consequent increased reaction when the slipping of the wheels takes place. When we have the slipper wheels solid, the torsional stress is the same but it is max maintained as no sudden release takes place. This explains why no knock is obtained when firing on Nos. 4, 5 and 6 the flywheel maintaining the stress in one direction only. The conditions are made worse when the stickiness of the friction discs brings the load up to 400 in.lbs. approx.before slipping. The use of a more uniform friction material such as cotton duck reduced the effect considerably. We are of the opinion that a progressive load on the slipper wheels would obviate the trouble. Ims/G.W.Hancock. | ||