Patent GB-408510-A (GB)
Title: Improvements in or relating to variable speed gearing and like associated mechanism for the transmission of power
IPC: F16D67/00
Filed: 1932-10-19
Abstract: 408,510. Hydromechanical variable-speed gearing. SWAN, J. G., 14, Old Square, Lincoln's Inn, London. Oct. 19, 1932, No. 25148/33. Divided on 398,861. [Class 80 (ii).] Relates to power transmissions suitable for vehicles which employ coupling units comprising an hydraulic coupling and three-section planetary gearing, one coupling element and one gear section, such as 14, 16, Fig. 1, being rotatable as one with the power input shaft 11 of the unit, another gear section 19 being connected to drive the output shaft 20, the third gear section 15 being rotatable as one with the other hydraulic element 13, all as described in Specifications 393,294, 393,295, and 393,296. The invention consists in a unit of that kind which, by reason of the ratio of its planetary gearing and the relative capacities of its hydraulic elements for creating centrifugal force in the operating liquid, is such that when the input shaft is rotating and the output shaft is not rotating, said hydraulic elements rotate in opposite directions at speeds which are such that the flow, if any, of liquid round the hydraulic working circuit is small and such torque as is transmitted results mainly from viscous drag of liquid between the hydraulic elements. In the bevel-gear arrangement of Fig. 1, when the output shaft 20 is not rotating, the planet gears 18 are turning on stationary arms of the spider 19, and the hydraulic elements 13, 14 are thus rotating at equal speeds in opposite directions. If the elements 13, 14 are such that opposing oil pressures at surfaces 21, 22 are equal, there will be no circulation of oil and the torque imparted to the shaft 20 will be only the viscous drag doubled. Thus a driving internal-combustion engine will be able to run at full throttle without being stalled. Some flow of oil may be allowed, in order to start a vehicle, by adding to the vanes of one element at 25 and cutting away the vanes of the other element at 26. A positive drive at starting may readily be rendered operative by arresting a brake drum rigid with the gear section 15. A friction clutch may be provided for driving the unit solid. Ducts 31, 32 are shown connecting the toric space 30 with the gear space 27 so that froth may escape from the former and excess of oil from the latter. This unit is preferably used in series with mechanical change-speed gearing and there may be a oneway clutch or a friction clutch between. A modification of this bevel-train unit is described in which the gear space does not communicate with the toric space. In a spur-gear form of the invention shown in Fig. 3, an hydraulic element 202 and the planet-carrier 203 rotate with the input shaft 201. A sun gear 211 rotates with the other hydraulic element 212. A sun gear 210 drives the output shaft 213 through a one-way clutch 218. When the shaft 213 is not rotating, planets 207 roll on the stationary sun 210 so that the smaller sun 211 is driven reversely, and the elements 212, 202 thus rotate at equal speeds in opposite directions. Such torque as is transmitted is due to viscous drag as aforesaid. Ducts 223, 224 connect the toric space 225 with the gear space inside the casing 203, and these ducts may be bent back within the toric space so as not to pump too much oil to the gear space. A sun 205 is connected to a brake drum 215 which, in starting, is kept from rotating backwards in order that the shaft 213 may be driven positively through a gear train. A one-way clutch 214 allows the coupling to overrun the drum 215. The shaft 213 is adapted to overrun the driving- gear 210 &c. at 218 and the engine of a vehicle may be used as a brake by the picking up of a one-way clutch at 220, or alternatively at 220<a>. The pair 208, 209 shown with the sun connected rigidly to a second brake drum 219 is provided so that by arresting that drum, the sun 210 may be caused to rotate idly backwards over the one-way clutch 218 so as to relieve the shaft 213 from torque and facilitate gear changing in a mechanical change-speed gear in series, all as described in Specification 399,155. A modification is described with triple instead of quadruple spur planets and having two brake drums for the same purpose as the drums 215, 219, Fig. 3. In this there are two gear-case members with oil between which rotate oppositely when the output shaft is not rotating, so that the residual torque due to viscous drag is considerable. The engine of a stationary vehicle fitted with this invention, in engaged relation, may be accelerated indefinitely without stalling. The Provisional Specification describes arrangements showing parts of Figs. 1 and 2 and an addition to Fig. 4 of Specification 398,861, towards which a disclaimer is directed.