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).
Gearbox design, focusing on alternatives for achieving a 3rd speed using an epicyclic gear unit.
| Identifier | ExFiles\Box 6\4\ 04-page194 | |
| Date | 24th October 1928 guessed | |
| contd :- -2- but not in the side shaft of the gearbox. This we consider the most practical and quickly available way of providing an easily obtainable 3rd. speed. Our gearbox being especially silent by virtue of the spiral side shaft drive, the extra bearing in the centre of the 3rd. motion shaft, and the great accuracy of the ground gears, the usual objection to using the 3rd. speed is greatly reduced. As an alternative to the above scheme we also refer you to an old patent of ours in which we use an epicyclic gear for the 3rd. speed, and a small simple gearbox of the orthodox type comprising a gear equivalent to the 2nd. speed, (.5) and a reverse. With this combination we have 4 speeds available, as the 2nd. speed will become the 1st. if used with a slower driving speed obtained by the epicyclic 3rd. speed unit. Up to this point we believe we have in earlier patents covered the idea, and it has probably been allowed to lapse, but in its simplest form it leaves something to be desired, and we have lately schemed the following combination, which consists of the engine, an ordinary controlling clutch, the epicyclic unit, and the small simple gearbox. The controlling clutch, operated in the usual manner, can be either between the epicyclic unit and the gearbox, or between the epicyclic unit and the engine. The choice of these two positions will be made after some practical experience. To operate this epicyclic unit, which provides a direct drive and a reduction of about .72 in speed, we provide a clutch and brake controlling the sunwheel of the epicyclic. For the top speed the sunwheel is, by the friction clutch, made to revolve with the driving annulus, the unit going round as a solid mass. To obtain the 3rd. speed the sun is declutched from the annulus and brought to rest by a brake of any suitable form. To control this sun unit I arrange that it is spring operated for the direct drive, and to operate the brake, I use one or more cyls. provided with fluid pressure at will, which fluid pressure is taken from the engine oil lubrication or some other source. The sketch shows a simple way in which this can be carried out. Normally the car would be on the direct drive through the gearbox and through the epicyclic unit, when the clutch would be in. When it is desirable to obtain the 3rd. speed it is only necessary to admit the oil pressure by means of a suitable cock or valve to the operating cyls. One need not touch the clutch or take the foot off the accelerator, so that no time is lost, and one is practically always on one gear or the other with the engine when desired giving full max. torque. contd :- | ||