573,528. Variable speed gearing; clutches. HARDY, F. J. May 15, 1941, No. 6300. [Class 80 (ii)] [Also in Group XXXI] In a driving and steering gear for endlesstrack vehicles of the kind in which the tracks are driven in the same direction by a main drive and steering is effected by super-imposing on the main drive a supplementary drive which tends to drive the tracks in opposite directions, the supplementary drive comprises a single slipping clutch 30, 31, a pair of reversing clutches 44, 50, each adapted to drive both tracks in opposite directions, and means for engaging one or other reversing clutch selectively in accordance with the direction of a required turn and for engaging the slipping clutch for a turn in either direction. In the construction shown in Fig. 1 the engine 10 drives the track sprockets 17a, 17b through a main or normal drive comprising a changespeed gear 15, shafts 14, epicyclic.gears 21a, 21b, and reduction gears 18a, 18b. The sun pinions 20a, 20b of the epicyclic gears are fixed to the main driving shafts 14, the planet carriers 22a, 22b are fixed to shafts 16a, 16b driving the track sprockets, and the annuli 23a, 23b of the epicyclic gears are driven or held by shafts 27a, 27b connected to a reversing gear-box 28 of the supplementary drive. This gear-box is driven from the engine shaft through a belt 26, shaft 25, and a clutch 30, 31 which slips under excessive loads. The driven clutch member 31 drives the shafts 27a, 27b through the friction clutches 44, 50 of bevel reversing gear 47, 49. The slipping clutch 30, 31 is normally held. disengaged by springs 39 and the reversing clutches are normally held engaged by a spring 56 so that the reversing gear, the shaft 27a, 27b and the annuli 23a, 23b of the epicyclic gears are all held fast ; thus for straight-driving the engine drives the tracks through the main drive only, the epicyclic gears acting only as reduction gears. To steer the vehicle one of the reversing clutches 44, 50 is first disengaged by means of an air cylinder 60, and the slipping clutch 30, 31 is then engaged by means of a second air cylinder 37 ; the shafts 27a 27b and the annuli 23a, 23b are now driven in opposite directions so that the main drive to one of the tracks is speeded up and the other is slowed down. The radius of the turn is varied by varying the extent to which the slipping clutch slips so as to vary the speed of the shafts 27a, 27b, the minimum radius being obtained when the clutch is fully engaged and does not slip. Brake drums 19a, 19b are provided on the shafts 16a, 16b driving the track sprockets. In a modification, the shaft 14 drives a differential gear, the sun pinions of which are fixed to the shafts 16a, 16b and are geared by two separate gear trains to a supplementary differential gear driven from the bevel wheel 47 of the reversing gear, one of the aforesaid gear trains having an even number of wheels and the other an odd number, so that the supplementary differential tends to drive the shafts 16, 16b in opposite directions as in the construction shown in Figs. 1 and 2 and thus speeds up one track and slows down the other. Clutches, reversing gears. The slipping clutch comprises a driving shaft 25 carrying a driving plate 30, a pressure ring 32 slidably carried by the driving plate by means of three lugs 33 extending through slots in the latter, and a driven plate 31. The clutch is normally held disengaged by springs 39 acting on levers 34 pivoted on the plate 30 at 35 and engaging in slots 33<1> in the lugs on the pressure ring 32. The inner ends of the levers extend through slots in an air cylinder 37 formed in the hub of the driving plate and engage the end of a piston 36, so that when'compressed air is admitted to the cylinder the clutch is engaged to an extent depending on the pressure. The driven plate 31 is slidably splined on a sleeve 40 which carries one driving clutch member 43 and is fixed to a slidable shaft 41. The driven clutch member 44 is fixed to a bevel pinion 45 and is prevented from axial movement. The other end of the shaft 41 is connected by a flexible plate 51<1>, permitting axial movement to a second driving clutch member 51, the driven member 50 being fixed to a bevel pinion 49 and prevented from axial movement. Normally both reversing clutches are held engaged by a spring 56 simultaneously acting through a flange 57 on one clutch member 51 and through a sleeve 53 and the shaft 41 on the other clutch member 43, thus locking the reversing gear and its driven shafts 27a, 27b against rotation. To drive the shafts 27a, 27b in opposite directions one of the clutches is disengaged by compressed air admitted to one or other end of a cylinder 60, the piston 59 of which acts through a thrust bearing 62 either to move the shaft 41 in one direction to disengage the clutch 43, 44, or to move an extension 55 of the clutch member 51 in the other direction to disengage the clutch 51, 50. The reversing gearing and clutches are mounted in bearings in a casing 70.