초록 ▼

A hydraulic drive system is equipped with an engine, a plurality of hydraulic pumps adapted to be driven by the engine and including a variable displacement hydraulic pump provided with a displacement varying mechanism, a hydraulic motor connected to the variable displacement pump, a hydraulic actua

A hydraulic drive system is equipped with an engine, a plurality of hydraulic pumps adapted to be driven by the engine and including a variable displacement hydraulic pump provided with a displacement varying mechanism, a hydraulic motor connected to the variable displacement pump, a hydraulic actuator for actuating the displacement varying mechanism of the variable displacement hydraulic pump, a working fluid feeding means for feeding the hydraulic actuator with a hydraulic fluid of a pressure according to the degree of control of an accelerator lever which is adapted to instruct a target revolution number of the engine, and a low-pressure circuit for allowing the hydraulic fluid to be discharged therethrough from the hydraulic actuator. The system is provided with a maximum pressure limiting means for guiding the hydraulic fluid of the hydraulic fluid feeding means to the low-pressure circuit depending on the degree of control of the accelerator lever, thereby limiting the maximum pressure of the hydraulic fluid and a means for selectively actuating the maximum pressure limiting means.

대표청구항 ▼

A hydraulic drive system for a vehicle having hydraulically powered wheels and a hydraulically powered work means, said hydraulic drive system comprising: (a) an engine; (b) a first hydraulic pump for running the wheels, said first hydraulic pump being provided with a displacement varying mechanism;

A hydraulic drive system for a vehicle having hydraulically powered wheels and a hydraulically powered work means, said hydraulic drive system comprising: (a) an engine; (b) a first hydraulic pump for running the wheels, said first hydraulic pump being provided with a displacement varying mechanism; (c) a second hydraulic pump for running the work means, said second hydraulic pump being operatively connected to said engine; (d) a hydraulic motor operatively connected to said first hydraulic pump; (e) a hydraulic actuator for actuating said displacement varying mechanism; (f) an accelerator lever which is under the control of the operator of said hydraulic drive system and which is operatively connected to said engine so that the operator can set a target revolution number for said engine; (g) a third hydraulic pump for feeding hydraulic fluid to said hydraulic actuator, said third hydraulic pump being operatively connected to said engine; (h) a hydraulic fluid feeding means operatively connected between said third hydraulic pump and said hydraulic actuator so that a pressure increased responsive to an increase in the degree of operation of said accelerator lever can be transmitted together with hydraulic fluid to said hydraulic actuator; (i) a low-pressure circuit operatively connected to said hydraulic actuator and to said hydraulic fluid feeding means and adapted to allow the hydraulic fluid from said third hydraulic pump to be discharged therethrough; (j) a maximum pressure limiting means for bypassing the hydraulic fluid from said hydraulic fluid feeding means to said low-pressure circuit at a pressure value less than the maximum pressure value that said hydraulic fluid feeding means can output to said hydraulic actuator, whereby the maximum value of pressure to be fed to said hydraulic actuator can be limited; and (k) actuating means under the control of the operator of said hydraulic drive system for selectively actuating said maximum pressure limiting means, (l) whereby, when actuation of said maximum pressure limiting means is selected by said actuating means and the revolution number of each of said first and second hydraulic pumps is increased based on an increase in the revolution number of said engine by an operation of said accelerator lever, the delivery rate of said second hydraulic pump increases responsive to the increase in the revolution number of said engine, but the delivery rate of said first hydraulic pump is limited to a value less than the maximum pressure value that would otherwise be outputted responsive to a value set by said maximum pressure limiting means.