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).
The design and operation of the Spontan automatic transmission gear.
| Identifier | ExFiles\Box 156\4\ scan0024 | |
| Date | 18th November 1927 | |
| [Nov. 18, 1927. THE SPONTAN TRANSMISSION GEAR. THE motor vehicle, whether of the commercial or private passenger type, is becoming more and more essential in daily life, with the result that the more progressive nations are faced with a variety of problems arising from the great increase in the number of vehicles on the roads. Not the least of these is that of public safety, and it is particularly unfortunate that, whereas the increasing intensity of traffic demands a higher degree of skill on the part of the driver, the low first cost, and the confidence inspired by familiarity, tend greatly to increase the number of users who have no natural driving aptitude. While the control of cars has been greatly improved, there is no doubt that many accidents arise through the failure of the average driver to carry out the operations necessary to bring a car to rest in a minimum time in an emergency. Apart altogether from the question of safety, there is also a growing demand for increased manœuvrability under normal conditions on the road, particularly as regards gear changing, and the past year or two have shown a wide recrudescence of interest in devices designed to simplify this operation. A priori, it will be generally admitted that no gain results from complicating the controls, and that every simplification in this respect is a step in the right direction. Simplified control involves an automatic gear change, and more than one such device is now available. The simplification can, however, be carried much farther than this, as exemplified by the new Spontan transmission, designed by Mr. F.{Mr Friese} Ljungström, of Aktiebolaget Spontan, Stockholm, in which every operation necessary for the control of a car, other than that of steering, is performed by the movement of a single pedal. The most important feature of the design is undoubtedly the automatic gear, and this may, with Fig.1. advantage, be described before dealing with such points as the control of the engine and braking. Apart from the difficulty involved in changing the gear, the usual step-down arrangement in a gear box permits of four ratios, as a maximum, being conveniently incorporated in the box, whereas to meet theoretical requirements, an indefinite number of ratios should be available. The simplest solution of the problem, and the only one that has been a practical success for heavy vehicles, is to effect the transmission electrically, but the complication and cost of such an arrangement have militated against its success for cars of medium or light weight. In the latter cases, several exceedingly ingenious mechanical solutions of the problem have already been put forward, of which the best-known are probably those due to Constantinesco and de Lavaud. In both of these, however, the operation of the gear involves the continuous action of some form of mechanical valve, such as a ratchet or one-way clutch. This may be considered as open to certain objections, and it is, therefore, particularly interesting to observe that in the Spontan transmission, the valve only comes into operation when a change of speed is taking place or the car is running on the equivalent of a low gear ratio. The essential feature of the gear will, perhaps, be best understood by a reference to Fig. 1, which, however, is merely diagrammatic, and does not represent the apparatus as now actually constructed. In the figure, the wheel shown, carrying three pins on which planet wheels are mounted, may be assumed to be the flywheel of the engine. The sun wheel is attached to the transmission shaft, and an unbalanced weight is attached to each planet wheel. If it be assumed that the resistance on the transmission shaft is exactly equal to the engine torque, the whole of the elements will rotate together as a solid body, without any rotation of the planet wheels about their own axes. This condition corresponds to the normal direct drive on a car. If now it be assumed that the resistance to rotation of the inner shaft increases, as would be the case if the car commenced to ascend a hill, the flywheel, on the same throttle opening, will tend to rotate faster than the | ||