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).
With diagrams describing the cam and peg mechanism for a gearbox.
| Identifier | ExFiles\Box 136\4\ scan0134 | |
| Date | 9th February 1937 guessed | |
| Locking Wall of Cam -3- Top 2nd Sp.{Mr Spinney} N Cam in Theory Peg Locking Wall of Cam Top Sp.{Mr Spinney} 2nd Sp.{Mr Spinney} N Cam in Practice Peg The Cam and Peg Mechanism. Although the cam and peg provide a simple reliable mechanism for disengaging the gears - putting them into neutral with ease and precision - they are also useful in one or two other ways. In practice the upper wall of the triangular cam is formed with three notches, which hold the peg and gear striking lever in three positions - the middle notch for neutral and the side notches for in-gear positions. The self-change shaft can turn far enough to allow the cam notches to engage the peg and this provides a strong gear lock, for both neutral and in-gear positions- without adding any parts to the mechanism. There is a slight clearance between cam and peg in the side notches. When a gear has fully engaged the self-change shaft is then up against its stop and there is no further load on the coupling pawl. At this point the striking lever has enough free movement to provide a clearance for the coupling pawl and, in consequence, the pawl can uncouple from the striking lever when the selector shaft is turned to preselect another gear - the gear already engaged being held in engagement by the locking action of the cam on the peg. As the self-change spring puts a heavy load on the cam the peg (and with it the striking lever and gear member) is held very securely. As the stop for the self-change shaft is adjustable the clearances are easily provided. Another function of the cam is to keep the gear in use in its correct in-gear position. In traffic, if there is much use of the clutch, most drivers will keep the preselector lever in the notch of the gear in use. This keeps the gear coupled to the self-change shaft, so, if the pedal is depressed beyond the normal limit for clutch operation and partially disengages the gear, the latter is again fully engaged when the pedal is released. But, although ample pedal movement is allowed for clutch operation, there may be occasions - especially by learners - when the normal limit will be exceeded and the gear be partially disengaged. When this happens the cam will push the peg (and the gear member) back into the fully engaged position. In an extreme case the gear would go into neutral. [No.] In any error of this kind the gear must go into full engagement or into neutral before the clutch can re-engage. | ||