GB945350A - Hydraulic apparatus - Google Patents

Abstract

945,350. Change-speed control. DOWTY HYDRAULIC UNITS Ltd. Sept. 8, 1960 [Sept. 17, 1959], No. 31760/59. Headings F2C and F2D. A hydrostatic transmission comprising a variable-displacement pump 1 driving a motor 2 in series with a two-speed gear unit 9 is so arranged that the pump control-rod 6 is operated to vary the pump output to bring the motor shaft 8 into synchronism upon movement of the gear lever 21. As shown in Fig. 1, rod 6 is operated by a speed control lever 22 connected to a lever 28 rotatable about a pivot 31 on a carrier 32 attached to a link 35 connected to the gear lever 21. Assuming lever 21 to be moved to engage high gear, pivot 31 is moved to the left by link 35, thus moving control-rod 6 to reduce the displacement of pump 1 and the speed of motor shaft 8 to permit engagement of the high gear. In passing through neutral a link 38 connected to link 35 operates an unloading valve 37 between the fluid supply and exhaust lines 3, 4. With high gear engaged the inclination of lever 28 prevents movement of carrier 32 to the right, and thus engagement of low gear, until speed is reduced by adjustment of lever 22. A clamp 39a operated by a cam 40a through links 39, 40 locks control lever 22 during movement of gear lever 21, but is unlocked when lever 21 is at the high or low gear setting. In the embodiment according to Fig. 3 a single control lever 52 operates differential-piston servomotors 54, 74 supplied from a pump 69 and operating pump control-rod 6 and gear change lever 21, respectively. Lever 52 is mounted on a shaft 53 carrying a cam 79 operating a spring-loaded vent valve 65 which, in the position shown, is closed to supply high-pressure liquid to both ends of the cylinders. These conditions obtain when lever 52 is moved forward until a step-in cam 79 allows valve 65 to open, when the pressure in the upper chambers of the cylinders is reduced and both pistons move upwards to operate rod 6 and gear lever 21 to engage high gear. In the further arrangement shown in Fig. 4, lever 21 is connected to a piston valve 92 in a cylinder 88 connected to fluid lines 3, 4 and also to a further cylinder 85 containing a piston 84 attached to a link 82 incorporating a spring 81 and connected to control lever 22. Valve 92 operates in such a way that upon moving gear lever 21 to engage high gear the higher pressure developed in pipe 4 is communicated to the right-hand side of piston 84 to reduce the displacement of lever 22 and thus of the pump control-rod 6. At high forward speed a detent piston 99 is projected forward to prevent the return movement of gear lever 21. Instead of gear unit 9 being of the spur pinion type it may comprise a low-speed epicyclic gear and a friction clutch for establishing direct drive, Fig. 2 (not shown).