Hydraulic continuously variable speed transmission with direct clutch valve

摘要

A hydraulic continuously variable speed transmission (T) with a direct clutch valve (DC) comprises a hydraulic pump (P), a hydraulic motor (M), a hydraulic closed circuit (La,Lb) for hydraulically connecting the two (P,M), a direct clutch valve (DC) placed in the closed circuit (La,Lb), a speed reduction ratio control actuator (30), and a direct clutch valve controlling device (40) for controlling operations of said direct clutch valve (DC) to block the closed circuit (La) when the speed reduction ratio becomes substantially "1". The direct clutch valve controlling device (40) maintains direct connecting state when an actual engine (E) speed is higher than a direct clutch (DC) disconnecting reference engine speed at the speed reduction ratio of approximately "1". Then, the direct clutch valve control device (40) releases the blocking of the closed circuit (LA) by the direct valve (DC) when a drop of the actual engine speed from the direct clutch (DC) disconnecting reference engine speed exceeds a predetermined amount corresponding to the vehicle speed.