摘要:
A hydraulic drive unit is provided with a boom cylinder, an arm cylinder, a communication line communicating a rod chamber of the boom cylinder and a bottom chamber of the arm cylinder with each other, and a switching valve arranged on the communication line for communicating or shutting off the communication line in accordance with a rod pressure of the boom cylinder. When an arm-crowding single operation is performed and by its digging counterforce, a rod pressure of the boom cylinder rises to a high pressure of at least a predetermined pressure, the switching valve is changed over from a shut-off position to a communicating position to feed pressure oil from the rod chamber to the bottom chamber. The boom cylinder is hence caused to automatically extend, thereby avoiding lifting of a hydraulic excavator body.
摘要:
To permit releasing an excessive rod pressure from a first hydraulic cylinder and also effectively using pressure oil of its rod chamber upon performing such an operation that pressure oil is fed to a bottom chamber of a second hydraulic cylinder, a hydraulic drive unit is provided with a boom cylinder, an arm cylinder, a communication line communicating a rod chamber of the boom cylinder and a bottom chamber of the arm cylinder with each other, and a switching valve arranged on the communication line for communicating or shutting off the communication line in accordance with a rod pressure of the boom cylinder. When an arm-crowding single operation is performed and by its digging counterforce, a rod pressure of the boom cylinder rises to a high pressure of at least a predetermined pressure, the switching valve is changed over from a shut-off position to a communicating position to feed pressure oil from the rod chamber of the boom cylinder to the bottom chamber of the arm cylinder. The boom cylinder is hence caused to automatically extend, thereby avoiding lifting of a body of a hydraulic excavator.
摘要:
A hydraulic drive system has a hydraulic pump (1), an actuator (2), a flow control valve (5) disposed between the hydraulic pump and the actuator, a pressure compensating valve (8; 8A; 8B) having a valve spool (23; 23A; 23B) that controls the differential pressure (Pz-PLS) across the flow control valve, and a pump delivery rate control device (9) for controlling a flow rate of the hydraulic fluid delivered from the hydraulic pump dependent on a differential pressure (Pd-PLS) between a pump pressure and a load pressure of the actuator. The pressure compensating valve has a first control chamber (30; 30A) subjected to the load pressure (PLS) of the actuator such that the load pressure acts on a first pressure receiving section (28; 28A) of the valve spool to urge the valve spool in the valve-opening direction, a second control chamber (29; 29A) subjected to the inlet pressure (Pz) of the flow control valve such that the inlet pressure acts on a second pressure receiving section (27; 27A) of the valve spool to urge the valve spool in the valve-closing direction, and a target differential pressure setting arrangement (31, 50, 51; 31B, 51) for urging the valve spool in the valve-opening direction. A damping capability to the actuator (2) is provided by setting pressure receiving area (Az) of the second pressure receiving section (27; 27A) to be greater than a pressure receiving area (ALS) of the first pressure receiving section (28; 28A).
摘要:
In a controller (229) of a hydraulic control system for construction machines, a valve control signal calculating function (301) works such that when an operation pattern signal (A-I) for actuators (201, 202 . . . ) is outputted, it selects corresponding one of plural output patterns for an auxiliary valve control pressure stored, as a function of a differential pressure signal between a pump delivery pressure and a maximum load pressure, in relation to the operation pattern signals, followed by calculating an auxiliary valve control pressure (Pc) dependent upon the differential pressure signal based on the selected output pattern, and also selects corresponding one of plural sets of rates of change (K . . . , K . . . ) for the auxiliary valve control pressure stored in relation to the operation pattern signals, followed by combining the calculated auxiliary valve control amount with the selected set of speed changes to calculate each of valve control signals (S21-S26).
摘要:
A hydraulic drive system comprising a prime mover (21), a hydraulic pump (22) driven by the prime mover, a plurality of hydraulic actuators (23-28) driven by hydraulic fluid supplied from the hydraulic pump, a plurality of flow control valves (29-34) for controlling flow of the hydraulic fluid supplied to the actuators, and a plurality of pressure compensating valve (35-40) for controlling respective differential pressures across the respective flow control valves, in which each of the pressure compensating valves applies a control force (f-F.sub.c) in a valve opening direction for setting a target value of the differential pressure across the flow control valve. There are provided a first detector (60) for detecting the target rotational speed (N.sub.0) of the prime mover (21), and controllers (61, 62, 63) for controlling the control force on the basis of the target rotational speed detected by at least the first detector such that the control force (f-F.sub.c) decreases in accordance with a decrease in the target rotational speed.
摘要:
A hydraulic system for a construction machine comprising plural hydraulic actuators (23-28) driven by fluid supplied from a pump (22), first and second flow control valves (29-34) for controlling flows of fluid supplied to the first and second actuators, and first and second distribution compensating valves (35-40) for controlling first differential pressure (.DELTA.P v1-.DELTA.P v6) produced between inlets and outlets of the first and second flow control valves. The first and second distribution compensating valves have respective drives (45-50, 35c-40c) for applying control forces (Fc1-Fc2) in accordance with the second differential pressure to the associated distribution compensating valves, to thereby set target values of the first differential pressures. The hydraulic system includes first means (59) for detecting the second differential pressure (.DELTA.P LS) from the discharge pressure (P s) of the pump (22) and the maximum load pressure (P amax) out of the first and second actuators; second means (61) for calculating individual values (Fc1-Fc6), as values of the control forces applied from the drives (45-50, 35C-40C) of the first and second distribution compensating valves (35-40), in accordance with at least the second differential pressure detected by the first means; and first and second control pressure generators (62a-62f) provided in association with the first and second distribution compensating valves. The first and second control pressure generators (62a-62f) produce control pressures (P c1-P c6) dependent on the individual values obtained by the second means and output the control pressures to the drives (35c-40c) of the first and second distribution compensating valves.
摘要:
A valve apparatus has a flow control valve having a supply passage communicating with a hydraulic fluid supply source, a load passage communicating with an actuator, and a first meter-in variable restrictor disposed between the supply passage and the load passage and opened dependent on an operation amount there; a first signal passage located downstream of the first variable restrictor and having a passage section for detecting load pressure of the actuator; a tank passage communicating with a reservoir tank; a discharge passage for communicating the first signal passage with the tank passage; and a second variable restrictor provided in the discharge passage and having its opening variable dependent on the operation amount of the flow control valve to produce in the first signal passage a control pressure different from the load pressure, the control pressure in the first signal passage being led to the hydraulic fluid supply source though a second signal passage. An auxiliary restrictor is disposed in the first signal passage to reduce the load pressure detected in the passage section of the first signal passage so that a pressure lower than the detected load pressure is produced in the first signal passage as the control pressure.
摘要:
There is disclosed a direction selector valve having function of detecting load. The valve is used in a hydraulic system. A spool has two passage holes extending axially partially through the spool from both side ends. These two passage holes have their respective high-pressure holes. When the spool is in its neutral position, the high-pressure holes are closed off by spool hole walls between bridge ports and actuator ports. The two passage holes further include low-pressure holes which are in communication with tank ports via load check valves mounted in the passage holes, respectively. Guide holes are formed near the front end of one passage hole and in communication with a load-sensing port. A restriction portion is formed on the outer surface of the spool adjacently to the guide holes to control the flow from the load-sensing port to the tank ports. First guide holes and second guide holes which are close to each other are formed near the front end of the other passage hole. The first guide holes are in communication with the load-sensing port even when the spool is in its neutral position. The second guide holes are placed in communication with the load-sensing port after the spool has shifted from its neutral position, connecting the high-pressure holes with the bridge ports. This structure smoothly responds to the load pressure in the actuator.
摘要:
A hydraulic drive system for a construction machine has a flow control valve (5) disposed between a hydraulic pump and an acutator, a pressure compensating valve for controlling a differential pressure across the flow control valve, and a pump delivery rate regulator for controlling a flow rate of the hydraulic fluid delivered from the hydraulic pump dependent on a differential pressure (Pd-PLS) between a pump pressure and a load pressure of the actuator. The pressure compensating valve has a valve body subjected to control forces. A first control force based on the differential pressure across the flow control valve to the valve body urges the valve body in the valve-closing direction. A second predetermined control force urges the valve body in the valve-operating direction; and a third control force based on the differential pressure (Pd-PLS) between the pump pressure and the load pressure of the actuator urges the valve body in the valve-opening direction.
摘要:
A hydraulic drive system for a crawler-mounted construction vehicle includes: a hydraulic pump (1); a plurality of hydraulic actuators including traveling hydraulic motors (2, 3) driven by the hydraulic pump; a plurality of flow control valve means including first and second flow control valve means (15, 16; 35, 36) for respectively controlling the flow rates of the hydraulic fluid supplied from the pump to motors; pump controlling means (11) for effecting control during the driving of the motors in such a manner that the discharge pressure of the pump becomes higher by a fixed value than the higher one of load pressures of the motors; and first and second pressure balance valve means (17, 18; 37, 38) for respectively controlling the rates of flow through the flow control valve means during the driving of the motors in such a manner that the load pressures of the motors do not affect the rates of flow through the first and second flow control valve means. The first and second pressure balance valve means (17, 18; 37, 38) are respectively provided with valve control means (62, 63; 66, 67 ) which do not cause the associated pressure balance valve means to be actuated until the differential pressure between the load pressure generated in a first motor (2) and the load pressure generated in a second motor (3) reaches a predetermined value (.DELTA.P.sub.0), and causes the pressure balance valve means to be actuated when the differential pressure exceeds the predetermined value.