Drive transmission

Abstract: A drive transmission which is particularly suitable for ship propulsion, comprises nested, contra rotating propeller shafts (32,34) which in one example are driven by a single input shaft (4) and which transmits contra rotating drives to the shafts (32,34) via respective planet carriers (24,22). particular advantages are the equal division of torque between the shafts (32,34) and the enabling of location of thrust bearings (122,124) and (126,128) in positions which are easy of access.

Description: This invention relates to drive transmissions for a pair of contra-rotating shafts in particular, although not necessarily exclusively, for contra-rotating marine propellers. Drives for contra-rotating marine propellers have been proposed in various forms, although they have been little used in practice. One excepting is the torpedo drive in which a bevel differential gear divides the output torque equally between two equal diameter contr-rotating propellers. In "Steam Turbine Machiner" , by Professor I K E Jung, Trans. I.MAR.E 1969, Vol 81-5, PP137-161, the merits of a number of drive transmissions for marine propulsion are discussed, including contra-rotating transmissions employing epicyclic gearing. In one example, shown in figure 20 of this reference, the single input shaft is coaxial with the two contra-rotating output shafts emerging from the opposite side of a differential epicyclic gear, ie in which the planet carrier and the annulus rotate in opposite directions to give the two output drives. This configuration provides significant advantages such as the large speed reduction which can be achieved and the facility for reacting axial loads. However one problem with this known configuration is that the transmission would be inherently less efficient because of the poor power distribution between the two propellers. The present invention seeks to provide a drive transmission which will ensure automatic power sharing between the two, contra rotating shafts, either equally or in desired proportions, and whether or not the input drive is contra rotational. According to the present invention a drive transmission by which the contra rotation of concentric propeller shafts is effected and comprising an input drive shaft and first and second epicyclic gears characterised in that said drive shaft drives the first epicyclic gear, said first epicyclic gear drives the second epicyclic gear via an annulus gear and said epicyclic gear drives the contra rotatable propeller shafts via a planet carrier and an annulus gear respectively, and in that at least the second epicyclic gear is a differential gear, thus enabling the relative speeds of the propeller shafts to balance the torque experienced by propellers fitted thereto to the torque experienced by said gears. The invention will now be described, by way of example and with reference to the accompanying drawings in which: Figures 1 and 2 show in axial section alternative forms of drive transmission according to the invention for contra rotating propeller shafts. In Figure 1 a prime mover (not shown) is flange-coupled to an input shaft 2 supported in bearings 4 in the end wall 6 of a gear transmission casing 8. At the other end of the casing, there are coaxial outputs, formed by an outer annular shaft 12 and an inner shaft 14 to drive contra-rotating propellers (not shown), the forward propeller being connected to the annular shaft 12 and the after propeller to the inner shaft 14. The input shaft 2 has secured to it the sun wheel 18 of a star epicyclic gear 20 that functions as a speed reduction stage. Planet wheels 22 meshing with the sun wheel 18 are mounted on a fixed carrier 24 and drive annulus 26 of the gear, the rotational speed of the annulus being very considerably less than that of the input shaft 2. The annulus is connected to a coupling ring 28 which is secured through an end plate 30 to an annular drive shaft 32 carrying a sun wheel 34 of an epicyclic differential gear 36. Planet wheels 38 of the gear 36 are rotatably mounted on a carrier 40 comprising an end disc 42 and collar 44 by means of which the carrier 40 is rotatably supported in a bearing 46 coaxial with the sun wheel 34. A ring 48 carried by the rim of the disc 42 is secured, by two propeller shafts 12, 14 which are apportioned to respective thrust bearings. In addition, the further differential epicyclic gear 90 splits the power input from the shaft 2 between the planet carrier 96 and the annulus 100. A more compact and economic construction results. Whereas the configuration shown in Fig 1 with a single differential epicyclic gear, is able to drive the outer output shaft more slowly than the inner output shaft, a wider choice is obtainable with the double differential epicyclic gear of Fig 2. In that case, it is possible to drive both shafts at substantially the same speed while sharing the power equally between them. Within each epicyclic gear in both examples shown, double helical gearing is employed to eliminate internal end thrusts. The output from each gear is preferably coupled to its associated outer ring in the manner described in GB2136084A.

Claims: A drive transmission by which the contra rotation of concentric propeller shafts is effected and comprising an input drive shaft and first and second epicyclic gears, characterised in that said drive shaft (2) drives the first epicyclic gear (20,90), said first epicyclic gear (20,90) drives the second eipcyclic gear (36) via an annulus gear (26,100) and said second epicyclic gear (36) drives the contra rotatable propeller shafts (12,14) via a planet carrier (40) and an annulus gear (62) respectively, and in that at least the second epicyclic gear (36) is a differential gear, thus enabling the relative speeds of the propeller shafts (12,14) to balance the torque experienced by propellers fitted thereto to the torque experienced by said epicyclic gears (20,90,36). A drive transmission as claimed in claim 1 characterised in that both epicyclic gears (20,90,36) are differential gears.

Inventors: DE VILLE ALAN, LACK GEOFFREY JAMES, YATES DAVID EDWIN, DE VILLE, ALAN, LACK, GEOFFREY, JAMES, YATES, DAVID EDWIN
Applicants: ROLLS ROYCE POWER ENG, ROLLS-ROYCE POWER ENGINEERING PLC
Application year: 1990
Main classification: B63H23
IPC codes: F16H48, F16H37, B63H5