Hydraulic control system

In a hydraulic control system provided with a plurality of directional control valves connected in parallel with a variable displacement hydraulic pump equipped with a discharge rate control means, a hydraulic actuator connected to each of said directional control valves, a tank for oil return from each of said directional control valves, a pilot operated valve for operating said directional control valves so as to cause pressure oil discharged from said variable displacement hydraulic pump to be supplied to said hydraulic actuator and cause oil return from the hydraulic actuator to be discharged to the tank, and a flow dividing compensation valve located between each of said directional control valves and said hydraulic actuator, said hydraulic control system further comprises:

• a first control signal generating means for generating a discharge rate control signal X to control the discharge rate of said variable displacement hydraulic pump with respect to an operation signal to said directional control valve,
• a first pressure detecting means for detecting pressure Pd in pressure oil discharged from said variable displacement hydraulic pump,
• a second pressure detecting means for detecting pressure Pu at upstream of said flow dividing compensation valve, which locates at downstream of a variable aperture portion formed between a supplying line for the pressure oil and a cylinder port in said directional control valve,
• a hydraulic circuit for applying said pressure Pu detected by said first pressure detecting means to said flow dividing compensation valve concerned so as to operate in the direction of open, and for applying a maximum pressure Ps to said flow dividing compensation valve concerned so as to operate in the direction of close, said maximum pressure Ps being selected as the highest pressure among said detected pressure Pu corresponding to said each directional control valve, and
• a second control signal generating means for generating a discharge rate control signal Y to control the discharge rate of said variable displacement hydraulic pump so that the differential pressure (Pd-Ps) between said maximum pressure Ps and said pressure Pd is held within a predetermined value,
• said discharge rate control means being controlled by said discharge rate control signals X and Y, thereby controlling the discharge rate of said variable displacement hydraulic pump.

In a hydraulic control system provided with a plurality of directional control valves connected in parallel with a variable displacement hydraulic pump equipped with a discharge rate control means, a hydraulic actuator connected to each directional control valve, a tank for oil return from each directional control valve, a pilot operated valve for operating the directional control valves so as to cause pressure oil discharged from the variable displacement hydraulic pump to be supplied to the hydraulic actuator and cause oil return from the hydraulic actuator to be discharged to the tank, and a flow dividing compensation valve located between each directional control valve and hydraulic actuator, said hydraulic control system further comprises:

• a first control signal generating means for generating a discharge rate control signal X to control the discharge rate of the variable displacement hydraulic pump with respect to an operation signal to the directional control valve,
• a second control signal generating means for generating a discharge rate control signal Y to control the discharge rate of the variable displacement hydraulic pump so that the differential pressure (Pd-Ps) between the maximum pressure Ps and the pressure Pd is held within a predetermined value, the discharge rate control means being controlled by the discharge rate control signals X and Y to control the discharge rate of the variable displacement hydraulic pump,
• a first pressure detecting means for detecting pressure Pd in pressure oil discharged from the variable displacement hydraulic pump,
• a second pressure detecting means for detecting pressure Pu at upstream of the flow dividing compensation valve, which locates at downstream of a variable aperture portion formed between a supplying line for the pressure oil and a cylinder port of each directional control valve,
• a hydraulic circuit for applying the pressure Pu detected by the first pressure detecting means to the flow dividing compensation valve concerned so as to operate in the direction of open, and for applying a maximum pressure Ps to the flow dividing compensation valve concerned so as to operate in the direction of close, said maximum pressure Ps being selected as the highest pressure among said detected pressure Pu corresponding to each directional control valve,
• a flow control valve with pressure compensation located at a bypass line branched out from a pump supplying line of said variable displacement hydraulic pump for receiving said detected pressure Pd in the direction of open, and for receiving said detected maximum pressure Ps and spring force in the direction of close,
• a pressure generating means located at said bypass line and connected to said flow control valve with pressure compensation,
• a third pressure detecting means for detecting pressure at a location between said flow control valve with pressure compensation and said pressure generating means, and
• a variable reducing valve that reduces its secondary pressure in accordance with increase of the pressure detected by said third pressure detecting means,
• whereby said discharge rate control signal Y is applied to said variable reducing valve, and said discharge rate control signal X is applied as a primary pressure to said variable reducing valve.