AUTOMATIC TRANSMISSION FOR HYDRAULIC DRIVE AUXILIARY SPEED CHANGE GEAR

摘要

PCT No. PCT/JP89/01284 Sec. 371 Date Jul. 1, 1991 Sec. 102(e) Date Jul. 1, 1991 PCT Filed Dec. 21, 1989 PCT Pub. No. WO90/07661 PCT Pub. Date Jul. 12, 1990.An automatic transmission for a hydraulic excavator or the like has an auxiliary speed change gear, capable of changing between high and low speeds, and an automatic change-over valve in a hydraulic circuit which connects the high and low speed clutches and a clutch operating hydraulic pump. One end of the automatic change-over valve is connected to the discharge side of the pump by a conduit containing an automatic speed changing valve. A rotation sensing hydraulic source is coupled to a shaft of the auxiliary speed change gear. A hydraulic circuit connects the discharge side of the rotation sensing hydraulic source to one end of the automatic speed changing valve. The automatic speed changing valve changes over the clutches automatically, without damaging the hydraulic motor driving the clutches.