| 摘要 |
1,175,501. Change-speed gear and control. TWIN DISC Inc. 5 Feb., 1968 [13 Feb., 1967], No. 5681/68. Heading F2D. A variable speed drive for a vehicle such as a tractor comprises constant mesh gearing providing four forward and reverse speeds selected by hydraulically operated duplex clutches, the hydraulic control system including a modulating valve influenced by a flow sensing valve for temporarily reducing the hydraulic pressure during a shift to produce gradual clutch engagement. Gearing.-An input shaft 1, Fig. 1, driven through a torque converter TC drives a gear 18 secured between the casings 6, 7 of a pair of clutches E 1 , Eg either of which may be operated to drive gears 20, 21 freely rotatable on the shaft. Gear 18 is in constant mesh with a gear (28) on a reverse shaft (2), gear 28 being secured to a pair of clutches (A 1 , A 2 ). The gears 20, 21 are in constant mesh respectively with gears 38, 42 on an intermediate shaft 3, freely rotatable reverse gears 30, (31) on the reverse shaft, which may be driven by clutches A 1 , A 2 respectively, also being in constant mesh with these gears, the gear 42 being splined to shaft 3 and gear 38 being secured to clutches S 1 , S 2 also splined to shaft 3 and operable to drive either of gears 40 and 41 freely rotatable on the shaft. Gears 40, 41 are in constant mesh with gears 52, 50 respectively on a pair of output stub shafts 46, 47 coupled to the front and rear wheels respectively of a tractor. Gear 50 is splined to shaft 47 whilst gear 51 is rotatable on shaft 46 but has external splines 53 engaging a shifting collar 54 which also engages splines 56 on shaft 47. As shown, a two wheel drive is provided through shaft 47 but collar 54 may be shifted to the right in the figure so that its splines also engage splines 57 on shaft 46 whereby a four wheel drive is provided through both shafts. Control system.-A pump P, Fig. 2, supplies hydraulic fluid to the clutches through manually operated speed and direction selecting valves SV, DV respectively. Fluid line 68 to the valves incorporates a flow sensing valve FS having a spring loaded spool 72 with a central orifice 77 through which fluid flows to the valves. On operation of a clutch, the rise in pressure shifts spool 72 to the right in the drawing against a stop 79 and opens a line 81 to the sump via an annular groove 73 in the spool and an orifice 82. Line 81 extends from a modulating valve MV connected to the fluid line and on being opened, releases the pressure in a cavity 84 behind a piston 84a, the resulting rightward movement of which fully uncovers a vent 84b and releases fluid in the supply line to a reservoir R. The pump pressure is therefore temporarily reduced and the ensuing gradual build-up of pressure caused by the return of spool 72, closing of line 81 and the return of piston 84a to close-off vent 84b, produces smooth clutch engagement. A brake-pressure operated dump valve 67 is provided. |
