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).
Article from 'The Motor' magazine about a novel semi-automatic clutch-pedal gear change mechanism with synchromesh.
| Identifier | ExFiles\Box 136\4\ scan0130 | |
| Date | 9th February 1937 | |
| The Motor February 9, 1937. 55 Novel Clutch-pedal Gear Change Ingenious Adaptation of Synchromesh Which Affords Marked Ease of Control and Semi-automatic Upward Changing During Acceleration NOT long ago, in an editorial published in The Motor, we suggested that the synchromesh form of transmission which is now so widely used is admirably suited to automatic or semi-automatic gear-changing. As a result of this comment Mr. A.{Mr Adams} Alltree, an experienced inventor and designer of transmission mechanisms, has sent us particulars of a novel arrangement which he has evolved to extend the use-fulness of the synchromesh principle. In the accompanying illustration (which is diagrammatic) his ideas are shown as applied to a simple three-speed gearbox, but they can equally well be adapted to suit a four-speed box or extended to include an overdrive. The driver has the choice of two ways of handling his car. The first closely corresponds with the normal control with the important exception that the gear lever, mounted on the steering column, has a preselective action but does not actually shift the gears; the shift is effected by a spring after they have been positively returned to neutral in a way described later. To engage first gear the lever is moved to the appropriate notch and the clutch pedal is fully depressed and released. During acceleration on first the second gear can be preselected and, in the same way, its engagement is delayed until the clutch pedal is once again operated. The same principle applies to the upward change into top and to all downward changes. If, before getting away, the driver flicks the gear lever upwards through a small angle an alternative semi-automatic action is obtained. First gear is engaged, as before, but under these conditions a selector simultaneously prepares the mechanism for the subsequent engagement of second gear. After acceleration on "first," the driver has only to operate the clutch pedal in order to engage "second"; the lever will simultaneously move of itself to the second gear position. A similar sequence of operations engages top gear (and the lever will move, as before) when the clutch pedal is again operated. Driver Concentrates Upon Driving The driver can, therefore, keep both hands on the wheel and his full attention on the road; these are valuable advantages under modern conditions when the multiplicity of traffic lights necessitates frequent stopping and restarting. After reaching top gear the driver has only to flick the lever downwards in order to use it in the normal manner without the semi-automatic action. He cannot forget this because it is not possible to change down until the lever has been restored to its normal position. It is also an advantage that the lever should always remain in the position corresponding to the gear which is in use. The way in which these results are obtained is quite simple and should not prove unduly costly to manufacture. The actual shifting of the gears is accomplished by a powerful spring (not shown) which acts upon one or other of the striking levers according to which one of a series of pawls has been selected by the gear lever. An excellent point is that the gears are moved back into neutral by the positive action of cams and pegs, the spring being used only to shift them into engagement. Synchromesh cones ensure a quiet action and are admirably adapted to operation by a spring. The gear lever is connected to a selector shaft through the lever (A) and a toothed quadrant; a series of flats on this shaft operate a corresponding number of pawls. These pawls in turn are carried by eccentric pins in a second shaft which carries a lever (C) connected to the clutch pedal and to the operating spring. When the pedal is fully depressed the pawls are all withdrawn; upon releasing the pedal the preselected pawl picks up a striking lever and engages the gear which is required. The movement of the eccentric shaft also restores to neutral the gear previously in use by means of the heart-shaped cams and pegs shown in the illustrations. It will be understood that the early part of clutch pedal travel is used simply to withdraw the ordinary clutch placed between the engine and the gearbox, while the second part of the travel keeps the clutch inoperative and also turns the eccentric shaft in the gearbox. The sequence is reversed when the pedal is released, so ensuring that the clutch shall not be engaged until the change has been completed. A Semi-automatic Mechanism To obtain the semi-automatic selection of the gears, as already described, during a get-away, a pawl and ratchet are provided which virtually connect the gear lever to the eccentric shaft. This pawl is kept out of action until the driver lifts the gear lever. It then has the effect of shifting the selector shaft to the second gear position when the clutch pedal is being used to engage first gear. Similarly, the pawl mechanism preselects top gear when the driver is engaging second gear. In order to permit preselection of a gear while an alternative gear is in use the cams and pegs are so arranged as to relieve the pawls of their load when the change is completed. Consequently, the selector shaft can be turned to move one pawl out of its operative position, and to preselect an alternative pawl, without interfering with the gears which are in action. This seems to us to be a neat and practical method for adapting synchromesh to semi-automatic operation and preselection. There are now several well-known cars in which synchromesh is employed for the engagement of every forward gear and it would seem only one further step to provide still greater facility of control. B19 DIAGRAM LABELS: ECCENTRIC SHAFT, TOP, 2ND, 1ST, REV, LOCK, PEG, CAM, STRIKING LEVER, STRIKING LEVERS, CONNECTED TO LEVER A, CONNECTED TO ROD B, PAWLS, Step, SELECTOR SHAFT, LEVER, C, A, B, TO SPRING, TO CLUTCH PEDAL, NORMAL POSITION, POSITION FOR SEMI-AUTOMATIC WORKING, PAWL LIFTED, ECCENTRIC PIN, STRIKING LEVER, SPRING, CLUTCH PEDAL. IMAGE CAPTION: Layout of the Alltree gearbox, in diagrammatic form, showing how the gears are shifted by pawls and rockers. The inset view on the left shows the cam employed to return each gear to neutral before an alternative gear is engaged. HANDWRITTEN NOTES: SELF-CHANGE Preselected Pawl Selector Pawl Coupled to Striking Lever PAWL NOT OPERATIVE Self Adjust is big Correction: When the clutch pedal is pushed down a gear is automatically selected and this same gear is engaged when the pedal returns. From neutral to top each gear in turn is self-selected when the pedal goes down and then engaged when the pedal comes up. This avoids confusion when normal hand control is resumed. | ||