Abstract: A relief pressure control system is provided with a controller for outputting, responsive to an adjustment signal output from a dial switch, a control signal to control a relief pressure of a variable solenoid relief valve, a display unit for displaying, responsive to display signals outputted from the controller, a relationship between a circuit pressure output from a pressure sensor and a pressure required by a hydraulic cylinder, and a control device constituting a start instruction unit for instructing a start of control of the variable solenoid relief valve. Stop valves are arranged in sections of main lines, which communicate a directional control valve and the hydraulic cylinder with each other, to open or close the section. The sections are located between positions on the main lines, where the variable solenoid relief valves are connected to the main lines, respectively, and the hydraulic cylinder.

Abstract: A hydraulic drive device for a hydraulic excavator, includes: a first hydraulic pump; a first boom directional control valve and a second arm directional control valve which are connected in parallel to the first pump; a second hydraulic pump; and a second boom directional control valve and a first arm directional control valve which are connected in parallel to the second pump; wherein: the hydraulic drive device also includes: a third hydraulic pump; a third boom directional control valve connected to the third pump and controlling the flow of pressure oil supplied to a boom cylinder; and a third arm directional control valve connected in tandem with the third boom directional control valve and controlling the flow of pressure oil supplied to an arm cylinder.

Abstract: During a swing start, a pump torque calculating section associated with pump delivery pressure, a pump torque calculating section associated with swing operation pressure, and a maximum value selecting section of a controller perform control to change a maximum absorption torque of a second hydraulic pump between Tb and Tc in accordance with a delivery pressure of the second hydraulic pump. In an operation combining swing with other motion, a subtraction section performs a calculation to subtract a maximum absorption torque Tp2 of the second hydraulic pump from a total pump torque Tr0 to thereby distribute an amount of torque reduced in the second hydraulic pump to a first hydraulic pump associated with an actuator other than a swing motor. Further, a required flow rate can be supplied to the swing motor, thus achieving a smooth shift to a constant speed swing.

Abstract: The operability when performing a combined arm-crowd and bucket operation can be improved. A hydraulic drive device for a hydraulic excavator includes: a bucket directional control valve and a second arm directional control valve, which are connected in parallel tandem with a first hydraulic pump; a first arm directional control valve that is connected to a second hydraulic pump; and a flow rate restriction device that restricts the flow rate of pressure oil supplied to the second arm directional control valve, during crowd operation of a bucket. This flow rate restriction device includes a variable throttle whose opening is controlled so as to become smaller as a bucket operating device is operated to the crowd side, the variable throttle being provided in a bypass path connecting to the supply port of the second arm directional control valve.

Abstract: A hydraulic driving device for a working machine surely prevents behavior of a single rod double acting cylinder not intended by an operator when discharge pressure of a main pump is raised to raise exhaust gas temperature to temperature required for burning particulate matter. A selector valve 160 interposed between a spool valve 61 and a rod chamber of a single rod double acting cylinder 51 and a section (a filter regeneration time actuation valve 122, a vehicle body controller 150) controlling the selector valve, are provided. A switch control section prevents a flow of oil directed from the rod chamber of the cylinder toward the spool valve by actuating the selector valve by a poppet of the selector valve when a by-pass cut valve 110 is controlled to increase a load of an engine 21 to a degree exhaust gas temperature reaches temperature required for burning particulate matter.

Abstract: A hydraulic drive device for a construction machine includes an engine stopping unit and a discharge rate control unit. The engine stopping unit stops the engine when a predetermined state of the construction machine has continued for a predetermined period of time. The discharge rate control unit controls a discharge rate control pressure being input to the regulator, when an exhaust emission control device performs regeneration control, or performs warm-up control, and the gate lock lever is in the open position.

Abstract: A hydraulic drive device for a hydraulic excavator, includes: a first hydraulic pump; a first boom directional control valve and a second arm directional control valve which are connected in parallel to the first pump; a second hydraulic pump; and a second boom directional control valve and a first arm directional control valve which are connected in parallel to the second pump; wherein: the hydraulic drive device also includes: a third hydraulic pump; a third boom directional control valve connected to the third pump and controlling the flow of pressure oil supplied to a boom cylinder; and a third arm directional control valve connected in tandem with the third boom directional control valve and controlling the flow of pressure oil supplied to an arm cylinder.

Abstract: A hydraulic drive system realizes a jack-up operation without arrangement of a flow rate control valve and center bypass selector valve. The hydraulic drive system has first and second hydraulic pumps, first and second directional control valves for controlling boom cylinders, a third directional control valve for controlling the boom cylinders, and a third hydraulic pump for feeding pressure oil to the third directional control valve. A jack-up selector valve has a second select position where, when a pressure in bottom chambers of the boom cylinders is not higher than a predetermined pressure, feeding of pressure oil, which is delivered from the first hydraulic pump and second hydraulic pump, to rod chambers of the boom cylinders, is held permissible in association with switching of the second directional control valve and third directional control valve by a manipulation of a control device.

Abstract: A hydraulic drive system for a working machine provides improved safety during forced regeneration. Upon input of a forced regeneration command signal from a forced regeneration switch, a controller detects non-operated states of all hydraulic actuators such as an arm cylinder arranged on a hydraulic excavator based on a lock detection signal from a gate lock detection switch, and also an attitude of a front working mechanism. The attitude is proper from the standpoint of safety. The detection is based on an arm angle signal from an arm angle sensor, a bucket angle signal from a bucket angle sensor and a boom pressure signal from a boom pressure sensor. Taking the detection of the non-operated states and proper attitude as conditions, the controller outputs control signals to a boosting proportional solenoid valve and flow-rate controlling, proportional solenoid valve to make a forced regenerator conduct forced regeneration.

Abstract: A prime mover revolution speed control system for a hydraulic construction machine sets the revolution speed of the prime mover in accordance with the operating state invoked by an operating command and as a result of a determination of an excavation state so that that the revolution speed of the engine can be increased for a heavy load (speedup) in the excavation state. When the control lever is fully operated in the direction of arm crowding, the control lever 43 is also operated, and first judgment conditions are all met to conclude that an excavation state has begun. During excavation work, when the control lever 44 is subjected to a half or greater operation in the arm crowding direction, second judgment conditions are all met to conclude that the excavation state persists, and the speedup sequence is continued.

Abstract: A relief pressure control system is provided with a controller for outputting, responsive to an adjustment signal output from a dial switch, a control signal to control a relief pressure of a variable solenoid relief valve, a display unit for displaying, responsive to display signals outputted from the controller, a relationship between a circuit pressure output from a pressure sensor and a pressure required by a hydraulic cylinder, and a control device constituting a start instruction unit for instructing a start of control of the variable solenoid relief valve. Stop valves are arranged in sections of main lines, which communicate a directional control valve and the hydraulic cylinder with each other, to open or close the section. The sections are located between positions on the main lines, where the variable solenoid relief valves are connected to the main lines, respectively, and the hydraulic cylinder.

Abstract: Disclosed is a hydraulic drive system for a working machine, which enables to conduct forced regeneration continuously for a sufficient time. Based on an input of a lock detection signal S1 from a gate lock detection switch 40, a controller 50 detects that a gate lock lever 32 for controlling a gate lock on/off valve 33 is in a locked state, in other words, hydraulic actuators such as an arm cylinder 12 arranged on a hydraulic excavator 1 are all in non-operated states. Upon an input of a forced regeneration command signal So from a forced regeneration switch 53 in this detected state, control signals Cp,Cf are outputted to a boosting control valve 51 and regulator 52 to make a forced regeneration means (an arm cylinder control valve 27 and the regulator 52) conduct forced regeneration.

Abstract: A pump torque control system is capable of preventing hunting due to interference between speed sensing control and control of an engine speed of a prime mover when the temperature of a hydraulic fluid is low. A maximum absorption torque is set in a regulator 31 that controls displacement volumes of hydraulic pumps 2 and 3 based on a deviation between target and actual engine speeds of a prime mover 1. A second modification factor calculating section 45 and a control gain modifying section 49, which are included in a controller 23 that performs speed sensing control to ensure that the maximum absorption torque of the hydraulic pumps 2 and 3 is reduced, change a control gain of the speed sensing control based on a value detected by the hydraulic temperature sensor 34 to ensure that the control gain is reduced as the temperature of the hydraulic fluid is reduced.

Abstract: To provide an engine control system for a construction machine, which can decrease a consumption of energy to be required for the reduction of an engine lag-down that occurs upon a sudden increase in load, such as upon quick manipulation of a control device, is provided with a load condition detecting unit, a charge amount detecting unit, a boost pressure sensor, and a determination processing unit. The load condition detecting unit includes a manipulation stroke detector for detecting that a control device has been fully manipulated, and also, a first computation unit of a controller. The charge amount detecting unit can detect an amount of charge in a capacitor. The determination processing unit includes a determination processing unit of the controller.

Abstract: In an attachment control apparatus for a hydraulic excavator having a hydraulic circuit that includes a hydraulic pump, a plurality of actuators having a breaker which is an attachment actuator, and a plurality of flow control valves having an attachment flow control valve that is switched by operation pilot pressure from a control pedal device to supply delivery fluid of the hydraulic pump to the attachment actuator, if the control pedal device is operated in a state where an attachment mode is not selected by an attachment selection device, the movement of the attachment actuator is limited. Thus, failure and reduced life of the attachment and other hydraulic devices can be prevented in the event that an operator has forgotten to switch from a normal mode to an attachment mode and has operated the attachment.

Abstract: During a swing start, a pump torque calculating section associated with pump delivery pressure, a pump torque calculating section associated with swing operation pressure, and a maximum value selecting section of a controller perform control to change a maximum absorption torque of a second hydraulic pump between Tb and Tc in accordance with a delivery pressure of the second hydraulic pump. In an operation combining swing with other motion, a subtraction section performs a calculation to subtract a maximum absorption torque Tp2 of the second hydraulic pump from a total pump torque Tr0 to thereby distribute an amount of torque reduced in the second hydraulic pump to a first hydraulic pump associated with an actuator other than a swing motor. Further, a required flow rate can be supplied to the swing motor, thus achieving a smooth shift to a constant speed swing.

Abstract: A hydraulic driving device for a working machine surely prevents behavior of a single rod double acting cylinder not intended by an operator when discharge pressure of a main pump is raised to raise exhaust gas temperature to temperature required for burning particulate matter. A selector valve 160 interposed between a spool valve 61 and a rod chamber of a single rod double acting cylinder 51 and a section (a filter regeneration time actuation valve 122, a vehicle body controller 150) controlling the selector valve, are provided. A switch control section prevents a flow of oil directed from the rod chamber of the cylinder toward the spool valve by actuating the selector valve by a poppet of the selector valve when a by-pass cut valve 110 is controlled to increase a load of an engine 21 to a degree exhaust gas temperature reaches temperature required for burning particulate matter.

Abstract: A hydraulic drive system realizes a jack-up operation without arrangement of a flow rate control valve and center bypass selector valve. The hydraulic drive system has first and second hydraulic pumps, first and second directional control valves for controlling boom cylinders, a third directional control valve for controlling the boom cylinders, and a third hydraulic pump for feeding pressure oil to the third directional control valve. A jack-up selector valve has a second select position where, when a pressure in bottom chambers of the boom cylinders is not higher than a predetermined pressure, feeding of pressure oil, which is delivered from the first hydraulic pump and second hydraulic pump, to rod chambers of the boom cylinders, is held permissible in association with switching of the second directional control valve and third directional control valve by a manipulation of a control device.

Abstract: A hydraulic drive system for a working machine provides improved safety during forced regeneration. Upon input of a forced regeneration command signal from a forced regeneration switch, a controller detects non-operated states of all hydraulic actuators such as an arm cylinder arranged on a hydraulic excavator based on a lock detection signal from a gate lock detection switch, and also an attitude of a front working mechanism. The attitude is proper from the standpoint of safety. The detection is based on an arm angle signal from an arm angle sensor, a bucket angle signal from a bucket angle sensor and a boom pressure signal from a boom pressure sensor. Taking the detection of the non-operated states and proper attitude as conditions, the controller outputs control signals to a boosting proportional solenoid valve and flow-rate controlling, proportional solenoid valve to make a forced regenerator conduct forced regeneration.

Abstract: Disclosed is a hydraulic drive system for a working machine, which enables to conduct forced regeneration continuously for a sufficient time. Based on an input of a lock detection signal S1 from a gate lock detection switch 40, a controller 50 detects that a gate lock lever 32 for controlling a gate lock on/off valve 33 is in a locked state, in other words, hydraulic actuators such as an arm cylinder 12 arranged on a hydraulic excavator 1 are all in non-operated states. Upon an input of a forced regeneration command signal So from a forced regeneration switch 53 in this detected state, control signals Cp,Cf are outputted to a boosting control valve 51 and regulator 52 to make a forced regeneration means (an arm cylinder control valve 27 and the regulator 52) conduct forced regeneration.