Patent GB-605733-A (GB)
Title: Improvements in or relating to variable-ratio power transmission apparatus
IPC: F16H61/02
Filed: 1945-12-13
Abstract: 605,733. Change-speed epicyclic gear; friction clutches. HOBBS, H. F. Dec. 13, 1945, No. 33765. [Class 80 (ii)] [Also in Group XXXIV] In a change-speed epicyclic gear controlled by friction clutches and brakes, and in which some ratios are obtained by positively connecting alternative elements, e.g. a ring-gear 18 and sun 19, to the output shaft 2, as by dog-clutches 23, 24, or by sliding the respective wheels into and out of mesh with the planets 16, a shift involving operation of the dog-clutch &c. connection is carried out whilst the positive elements to be meshed are held relatively stationary and the gear transmitting power in direct drive. Thus, in the four or five - speed arrangement shown, the only forwardspeed shift involving operation of the dog clutches 23, 24 is that between direct and overdrive, so that, during the upshift, all the parts are rotating at the same speed in direct-drive, and the dog-clutches can be synchronously changed before the friction clutches and brakes. Nested single-plate friction clutches 6, 7, 8, engaged hydraulically through diaphragms 9, selectively connect an input member 1 with a ring-gear 18, planet-carrier 22 and sun 20 respectively, whilst similar hydraulicallyengaged disc-brakes 38, 39 selectively hold the sun 20 and the stepped-planet carrier 22. With the output-shaft 2 dog-clutched at 24 to the sun 19, the various combinations of the friction clutches 6, 7, 8 and brakes 38, 39 give three reduced speeds and direct-drive, the latter by engaging together the clutches 7 and 8 or 6, 7 and 8, and releasing the brakes. For upshift to overdrive, the output shaft 2 is moved axially to release the sun 19 and synchronously dog-clutch the ring-gear 18 at 23. The friction clutch 7 is then left engaged alone to drive the planet-carrier 22 and the brake 38 applied to hold the sun 20. The same dog-clutch engagement gives reverse, using the friction-clutch 8 and brake 39. To avoid shock-loads, the capacity of the reaction-brake 38 is arranged to be insufficient to check high torque-reaction loads on overrun and it is assisted in taking forward torquereactions by a parallel one-way roller detent 44. A dog-detent may be provided to assist the other reaction-brake 39 in reverse. The clutch-disc 6 may be omitted if the lowest speed-ratio is not required. Pressure fluid supplied by a pump 34, reaches the clutch and brake diaphragms through a control-valve 33, and the supplyconduit 27 to each clutch-diaphragm includes a centrifugally-balanced valve 25 opening at a predetermined pressure. Oil for lubrication is supplied through shaft passages, not shown, and reaches the inner periphery of the clutch and brake discs, the oil being allowed to flow over the friction surfaces when disengaged, but being diverted from them, as through grooves 50 in the presser-plates, when engaged, the inner ends of these grooves being blanked by fixed abutments in the disengaged position. Insulator-plates 35 are provided between the diaphragms and presser-plates, and cooling-air circulates centrifugally over one side or the other of the presser-plates according to whether the clutch is engaged or not.