Patent GB-640226-A (GB)
Title: Improvements in or relating to change-speed gears
Inventor: HARDY FREDERICK JAMES
IPC: F16H61/04
Filed: 1946-08-19
Abstract: 640,226. Controlling change-speed gearing. ROLLS-ROYCE, Ltd. Aug. 19, 1946, No. 24598. [Class 80(ii)] Means for facilitating meshing of dog clutches or other coacting rotatable toothed members in change-speed gearing comprises holding means operative to restrain one member from sliding into engagement with the other, said holding means being releasable by a member driven differentially from the toothed members and which releases the holding means periodically for intervals of time inversely proportional to the differential speed, the release being only effective to permit engagement when the differential speed falls below a predetermined value. As shown, the invention is applied tc change-speed gearing of the kind described in Specification 640,228 having alternative third and fourth (direct drive) speeds brought in by operation of the accelerator pedal. A sleeve 25 Fig: 1, rotatable on the output shaft 20 and having a synchro mesh clutch connection 23 thereto is driven from the input shaft 10 through meshing layshaft gear pairs 11, 12 and 14, 17 and a one-way roller clutch for third speed and through a-dog-clutch 31, 32 for direct drive. An accelerator-actuated solenoid armature 46, Fig, 3, operating through a fork 30 the movable member 31 of the dog clutch is additionally controlled by the speed of rotation of the differentially driven cage 37 of a thrust ball race interposed under spring pressure between two gears 34, 35 driven at speeds proportional to those of the members 31, 32 by the gear 12 and by a gear 36 formed on the member 31, respectively. With the solenoid de-energized and the armature in the position shown in Fig. 3 the dog clutch 31, 32 is engaged for direct drive. The solenoid operating coil 48 is in series both with a " kick-down " switch 49 closed by full depression of the accelerator pedal 50 and with a switch 51 opened by a cam 52 on the armature when the latter is moved to the left to disengage the dog clutch 31, 32 upon energization of the coil 48 by accelerator kick-down, the engine ignition being momentarily disabled during the first part of the armature movement to assist clutch disengagement. A holding coil 41, in series with a normally closed switch 40 and a switch 43 closed by a second cam 45 on the armature just prior to the opening of the switch 51, maintains the armature in its attracted position against the pressure of a spring 55 when the switch 51 opens. The switch 40 is held closed by the edge of the cage 37 and is opened for an interval once in each revolution of the cage by a cutaway 39 thereon, such opening only causing release of the armature when the cage 37 is rotating slowly enough to allow the magnetic flux set up by the coil 45 to diminish sufficiently during the interval. Due to engine acceleration, the cage 37 is rotating fast enough to keep the coil 45 energized when the switch 51 is opened upon accelerator kick-down, the drive being then taken up in third gear. Direct drive is re-engaged upon accelerator release, the consequent engine deceleration slowing the cage 37 enough to de-energize the solenoid a sufficient time before actual synchronization of the members 31, 32 to allow the inertia of the clutch-operating mechanism to be overcome. The solenoid may be replaced by a hydraulic circuit.