Patent GB-643499-A (GB)
Title: Improvements in or relating to variable ratio power transmission apparatus
Inventor: HOBBS HOWARD FREDERICK
IPC: F16H61/00
Filed: 1947-10-23
Abstract: 643,499. Change-speed gear. HOBBS TRA NSMISSION, Ltd. Oct. 23, 1947, No. 28344. [Class 80(ii)] [Also in Group XXIX] Two speed-ratio-providing hydraulicallyactuated friction disc clutches 12, 14 mounted on a rotary input member 1. and a similar brake 13, are automatically controlled by a spring and centrifugallyloaded valve 54, carried by the rotary input member 1 and providing speed-responsive control for the liquid pressure delivered by an input driven pump 40 to engage at least one of the friction devices, e.g. the brake 13 for automatic engagement for starting and stopping the drive, the same speed-responsive pressure acting to control automatically one or more two-position selector-valves 57, 58 directing pressure to the other friction devices for selection of other ratios. The engine accelerator-pedal 69 and an independent manual control 70 may provide an opposing pressure to modify ratio-shift speeds in accordance with desired driving conditions on a vehicle. Gear train.-The three-speed gear shown has input and output stepped-planet trains, the former comprising stepped planets 2 carried by the input member 1; a driven sun 3 on an intermediate shaft 5, and a reaction sun 4 on a second intermediate shaft 11. A third intermediate shaft 9 carries the stepped-planets 7 of the output train and is restrained from backward rotation by a one-way roller-detent 10, the planets 7 engaging a final output sun 8 and a sun 6 integral with the intermediate shaft 5 and sun 3 of the input train. Applying the brake 13 alone holds the reaction sun 4 so that the reduction of both trains is effective for first speed. Applying the clutch 12 alone locks the first train, giving the reduction ratio of the second train alone for second speed. Applying both clutches 12, 14 together locks both trains for directdrive top speed. The gear may include also dog-clutches. Fluid circuit.-Input and output driven pumps 40, 42, :independently deliver to a common line 48 through a shut-off valve 47 linked to a control lever 49 for a forward neutral-reverse gear, (not shown), so as to cut off pressure in neutral. Reverse may be by a dog-clutch controlled by the lever 49 or by a friction device controlled by the valve 47. The pump-fed pressure-line 48 branches at a pressure-maintaining valve 50 into two lines, one 51, leading directly to the outer face of the centrifugal valve 54, so that pump-pressure, in opposing the centrifugal and spring-load of the latter causes it to regulate an exhaust-port 56, whereby the pressure in the line 51 is rendered speed-responsive. The other pressure-branch 71 feeds, at full pump-pressure, by virtue of the pressure-maintaining valve 50, the two selector-valves 57, 58 which distribute pump-pressure to ducts 59. 60, 61 leading to diaphragm pressure-spaces engaging the brake 13 and clutches 12, 14 respectively. Centrifugal pressure in the diaphragm pressure spaces assists pump-pressure in the case of the clutches. Initially with both selector-valves 57, 58 in the lower of their ' two positions, centrifugal-valvecontrolled pressure in the branch-line 51 passes to a spring loaded brake-control valve 94, depressing the latter and permitting pump-pressure in the selector-valve supply branch-line 71 to pass through the selector-valve 57 and duct 59 to the diaphragm of the brake 13, causing gradual engagement of the starting ratio with increase in engine-speed. With the selectorvalve 57 alone in its upper position, the brake-line 59 is exhausted through a hole 92 in the valve 57, and pump-pressure is fed from the line 71 to the line 60, leading through a pressure-responsive spring and centrifugally-loaded valve 27 to the diaphragm of the clutch 12, introducing second-speed. With both selector-valves 57, 58, in their upper positions, pump-pressure is supplied to both clutch-lines 60, 61 together to engage both clutches 13. 14 for direct-drive. When the selector-valves 57, 58 return to their lower positions the clutches 13, 14 are self-exhausted by their respective pressure-responsive valves 27, 28. Automatic selection. - The selectorvalves 57, 58, are automatically positioned by the centrifugal-valve-controlled speedresponsive pressure acting through the line 51 on their lower faces, in opposition to the downward pressure of springs 62 and the liquid-pressure in an upper chamber 64, supplied through a restricted passage 65 from the clutch-brake pressure-supply branch 71, and having its magnitude determined by the compression of a spring 68 loading an exhausting-valve 66. Compression of the loading-spring 66 is increased by depression of the accelerator-pedal 69 and also by pulling out the separate manual control 70, so that either of these actions increases the speed at which the speed-responsive pressure, acting below the selector-valves 57, 58, raises them to produce an upshift. In addition, movement of the selector-valves 57, 58 in each direction is opposed by all detents 80, 81 loaded by the liquid-pressure in the upper chamber 64 and also, if desired, by springs. The detents 80, 81 cause the downward selector-valve movement to occur at a speed which is lower than that of its upward movement by an amount which is greater than the input speed change produced by the corresponding ratio-shift, to avoid hunting. The pressure-loading of the detents causes this speed-differential to increase in the same proportion as the increase in shift-speed caused by an increase in the accelerator-controlled loading-pressure in the upper chamber 64. The selector-valves 57, 58 are interlocked by a drift-pin 87 to ensure that outward movement of the second-speed valve 57 precedes that of the high-speed valve 58 and vice versa. Due to the presence of the restrictor-passage 65, the valve-loading pressure in the upper chamber 64 is influenced by the rate of movement of the acceleratorpedal in addition to the absolute position of the pedal so that rapid depression of the pedal produces a rapid downshift. The Provisional Specification describes also a control for a five-speed and reverse gear using five ball-interlocked selector-valves and two centrifugal valves to control two input friction clutches and a reaction friction brake of an output planetary train. and a toothed clutch and balked toothed detent, of an output planetary train. A control for a two-speed gear of a battery electric vehicle is also described, control of a friction clutch and brake being by a single selector-valve controlled by speedresponsive pressure determined by a centrifugal valve as above described, the same control also serving to apply the brake automatically in direct clutch drive to prevent excessive speed.