Patent GB-594362-A (GB)
Title: Improvements in variable speed power transmission mechanism
IPC: F16H47/08
Filed: 1945-03-27
Abstract: 594,362. Hydromechanical variable-speed gear. SALERNI, P. M. March 27, 1945, No. 7732. [Class 80(ii)] [Also in Group XXIX] The direct - drive friction or positive clutch 2d, 4, of a three element epicyclic train 6, 7, 8, arranged behind and driven by a three-element hydrokinetic torqueconverter 1, 2, 3, is automatically disengaged to introduce a geared reduction when the torque delivered to the gear-train by the converter attains a value which lies within a predetermined range the maximum value of which is smaller than the maximum torque-capacity of the converter. Thus ensures that where the direct-drive clutch in the gear-train is of the positive type it is never subjected to torque-loads high enough to render disengagement difficult without special means; and where the clutch is of the friction type its size can be kept small since its torque-capacity need not exceed the maximum of the predetermined range rather than the maximum of the converter. The converter-factors used for disengaging the direct-drive clutch for geared downshift are either (i) the torquereaction acting backwardly on the converter reaction-ring 3 whilst it is stationary; or (ii) the backward component of the torque-reaction acting on the converter reaction-ring 3 whilst it is still rotating forwardly in space; or (iii) the absolute torque delivered by the converter to the gear. The control factors may operate mechanically or through a servomotor, not described. After the geared reduction has been introduced, it persists, notwithstanding subsequent reduction in load below the change-over value, until the sense of the drive is reversed, as by closing the enginethrottle to cause overrun in the case of a motor-vehicle. Manual control of the directdrive is also provided. In the epicyclic train shown, the directdrive friction clutch 2d, 4 is combined with a reduced-drive friction-brake 3e, 4b for the sun 7, and there is a lever 15, Fig. 7, operating the clutch and brake manually when desired, together with a manuallyoperated rockshaft 16, Fig. 7, for changing dog-clutch connections of the planetary train for reverse. The converter reactionring 3 is held by a one-way brake 3d which permits it to rotate forwards for a one-toone coupling drive when load conditions permit. In the forward - drive position shown, the planet-carrier 8 is dog-clutched at 8b to the final driven shaft 9 and the ring-gear 6 is connected to the two-sectioned turbine-ring 2 by a sleeve 6a, dogs 2c, a member 2b and a sleeve 2a. The twosectioned, reaction-ring 3 of the converter is connected by a sleeve 3a to a one-way detent which prevents backward rotation only, and comprises friction discs 3d, 3i, splined respectively to a restrained outer member 3e and an inner member in two parts 3b, 3c, which have opposite screwthreaded connection with the reaction-ring sleeve 3a so as to tighten the discs under backward reaction-torque. The direct-drive clutch of the gear-train comprises axiallymovable plates 2d, secured to the ring-gear connected member 2b, and having friction clutch - facings 2e for engagement with spline connected inner rings 4, which are dog-clutched at 4e to a sleeve 7a of the sun 7, and are pressed apart by internal springs 4f to engage the clutch (position shown), when load conditions permit. The reduceddrive sun - brake is formed by friction facings 4b on outer flanges of the rings 4 which, in the. clutch - engaged position, shown, rotate clear of co-operating brakesurfaces on a pair of spline-connected rings 3e, 3f which have opposite screw-threaded connection with a sleeve 5 splined to the fixed casing. In the form shown in Fig. 1 the outer member of the one-way detent 3d of the converter reaction-ring 3 is also the screwed member 3e of the sun-brake, so that converter torque-reaction is applied to the casing through the screw thread of the member 3b. Thus, increase in load when running in coupling drive and one-to-one clutch drive, first stations the converter reaction-ring 3, giving converter drive, and subsequently reaction-ring torque causes the brake-rings 3e, 3f to screw together, engaging the sun-connected rings 4, and at the same time pushing the rings 4 inwardly off the direct-drive clutch-surfaces 2e, introducing a geared reduction. In this condition the torque-reaction of the sun 7 is passed to the fixed casing through the screw-thread of the brake member 3f, and maintains the brake engaged for geared reduction, even through the converter torquereaction reduces to zero, until the sense of the drive is reversed by closing the enginethrottle whereupon the brake members 3e, 3f screw apart and the springs 4f engage the direct-drive clutch 2e. A stationary spring-loaded detent 9b engages a notch in the screwed brake member 3c to ensure a snap-action downshift. Manual shifts can be effected by directly turning the screwed brake-members 3e, 3f by means of a handlever 15, Fig. 7. For reverse, a manual rockshaft 16, Fig. 7, slides the train axially as a whole at 8c so that the sun 7 is dogclutched to the converter driven member 2b; the planet-carrier dogs 8b are stationed at 17a; and the ring-gear 6, now reversely driven, is dogged to the clutch-member 9a of the driven shaft 9. In a modification, Figs. 3 and 4 (not shown), the outer member of the one-way detent 3d of the converter reaction-ring is connected to one of the sun-connected forward rotating rings 4 by a helical spline, so as to be moved laterally by the backward component of the torque-reaction acting on the reaction-ring 3 while it is still rotating forwardly in space, such movement serving to energise a servomotor (not shown or described) which operates the manual lever 15, Fig. 7, for turning the screwed brake-members 3e, 3f to execute a shift. In a further modification, Figs. 5 and 6 (not shown), the outer member of the oneway detent is fixed to the casing, and the turbo-driven sleeve 2a is connected by opposite helical splines to the two clutchplates 2d, which in this case are separate, so as to cause the plates to separate and disengage the direct-drive clutch when a predetermined turbo-delivered torque is exceeded, the value of the torque being determined by an additional spring-loaded ring having a straight spline connection with one clutch-plate 2d and a helical connection with the turbo-driven member 2a. A spring-ring, engaging grooves in the connected members, provides snap action. The Provisional Specification refers also to clutch-control utilising the speed-difference (slip) between driving and driven members of the torque-converter, and the velocity, of circulation of the fluid therein.