Abstract: A hydraulic drive system is provided with a signal guide system for guiding a delivery pressure of a pump as a command pressure via a line and a port, another signal guide system for guiding a pilot pressure of a pilot pump as another command pressure via a line and a port, a tilting control unit for controlling the displacement of the pump by the command pressures guided to the ports, a controller having a command current-setting unit for setting a relationship between a target engine speed and a command current, a target engine speed-indicating unit for an engine, and a solenoid-operated proportional valve for allowing the pilot pressure of the line to pass as is while no drive signal is outputted from the controller but for being reduced in opening to change the pilot pressure to a smaller value when a drive signal is outputted from the controller.

Abstract: A hydraulic drive system includes a closed center directional control valve connected to a hydraulic pump through a hydraulic fluid supply line and controlling a flow of a hydraulic fluid supplied to an actuator. A throttle and cutoff means for throttling and cutting off an unloading circuit depending on a operation amount of the directional control valve is installed in the unloading circuit interconnecting the hydraulic fluid supply line and a reservoir. The throttle and cutoff means comprises a logic valve including a feedback slit of which an opening area is increased and decreased depending on an amount by which a valve body is moved, and a pilot variable throttle for controlling a rate of a pilot flow passing the feedback slit depending on the operation amount of the directional control valve.

Abstract: An operator's cab in a construction machine in which hollow pillar portions are formed each with an outer panel and an inner panel bonded to each other and the hollow pillar portions constitute an operator's cab frame, includes at least one reinforcement member constituted of thin plate that is bonded to the outer panel and/or the inner panel to divide an internal space of each of the hollow pillar portions.

Abstract: An operator's cab in a construction machine, which has pillars standing at a left side surface and a right side surface, includes a frame reinforcement member that extends between the pillars and meets at a near right angle to the pillars so as to create a resistance against a bending load applied to the pillars.

Abstract: A tournament oil path constituting apparatus in which while a laminated block is constituted by laminating a number of oil path plates, a number of shuttle valve holes and connection grooves made continuous to the shuttle valve holes are formed at overlap faces of the oil path plates, shuttle valves are integrated to the shuttle valve holes, introductory oil paths communicating with the shuttle valve holes are formed at both of the oil path plates formed with the shuttle valve holes and the oil path plates having match faces on sides of the shuttle valve holes and a high pressure oil is selected by the shuttle valves from pressure oils conducted both of the introductory oil paths and conducted to the connection grooves. The tournament oil path constituting apparatus also including a number of main paths penetrating the number of laminated oil path plates and branch grooves branched from the main paths.

Abstract: A control system wherein a reverse characteristic having a reverse input/output relationship to a target input/output characteristic of a control object, is preset, and a target value for an output of the control object is calculated. A command signal corresponding to the target value then is determined based on the preset reverse characteristic, and the command signal is output to the control object. The control system includes first means for calculating a command signal corresponding to a given target value for the output of the control object based on the preset reverse characteristic, outputting the command signal to the control object, measuring an output of the control object and estimating a deviation between an actual input/output characteristic of the control object and the target input/output characteristic therefor, and storing data on the deviation between the input/output characteristics as learning correction data.

Abstract: A pump controller (40) calculates a pump maximum absorbing horsepower and a pump required horsepower based on an accelerator signal, a pump delivery pressure and an operation signal, determines an engine required horsepower (PN) by selecting minimum one of both horsepower values, and calculates a pump required revolution speed based on the accelerator signal, the operation signal and an engine revolution speed signal to determine an engine required revolution speed (NN). The engine controller (40) determines, from the engine required horsepower (PN), a required-horsepower-referenced target engine revolution speed (NK) at which a fuel consumption rate is minimized, and selects larger one of the engine required revolution speed (NN) and the target engine revolution speed (NK) as an engine target revolution speed (NZ) to control an injected fuel amount and fuel injection timing, thereby controlling an engine torque and an engine output revolution speed.

Abstract: An excavation area setting system for area limiting excavation control in construction machines, with the excavation control being performed to calculate a target speed vector for control of a front device on the basis of a body, modify the target speed vector to limit a moving speed of the front device in the direction toward a boundary of a preset excavation area when the front device comes close to the boundary of the excavation area, and move the front device along the boundary of the excavation area. To set the excavation area, an external reference is installed horizontally outside the hydraulic excavator and a depth from the external reference to the boundary of the excavation area is set by using a setting device. The excavation area is set in a manner matched with the excavation control in which calculation is executed based on the position of the body.

Abstract: A hydraulic circuit system includes a shuttle block, and shuttle valves are arranged and connected within the shuttle block. The maximum pressure in a predetermined operation signal pressure group selected from operation signal pressures generated by pilot operating units is selected to produce a control signal pressure within the shuttle block. The control signal pressure is output to control devices such as a track communicating valve, a swing brake cylinder, and regulators for hydraulic pumps.

Abstract: An engine torque, which corresponds to a target engine speed inputted in a controller, is determined by a functional computing function unit. A torque correction value is added to the engine torque, followed by the multiplication with a constant. The product is divided by a pump delivery pressure to determine a pump displacement. A target tilting corresponding to this value is determined by another functional computing function unit, and is then compared with another target tilting which has been determined from a negative control pressure. The smaller one is selected and is outputted as a target tilting. The torque correction value is set at an EEPROM through an input device as desired. Selection of a negative value as the torque correction value makes it possible to prevent occurrence of stalling.

Abstract: In the arm-crowding or track operation, a calculating portion (700d2 or 700d4) calculates a modification gain (KAC or KTR) depending on an operation pilot pressure and a calculating portion (700g) calculates a decrease modification (DND) based on the KAC or KTR, while a calculating portion (700m or 700p) calculates a modification gain (KACH or KTRH) depending on an operation pilot pressure and calculating portions (700q-700s) calculate an increase modification (DNH) based on the KACH or KTRH. A reference target engine revolution speed NR0 is modified using the DND and DNH. In other operations than the arm-crowding and track operations, NR0 is modified using only the decrease modification (DND) calculated from the modification gain just depending on the operation pilot pressure. In the operation where an engine revolution speed is desired to become higher as an actuator load increases, the engine revolution speed can be controlled in accordance with change of the actuator load as well.

Abstract: A reference pump-delivery-rate calculating portion calculates a reference delivery rate of a hydraulic pump by referring to a table stored in a memory based on a control pilot pressure for the hydraulic pump. A target pump-delivery-rate calculating portion divides the reference delivery rate by a ratio of a maximum revolution speed to a target engine revolution speed, thereby calculating a target delivery rate. A target pump tilting calculating portion divides the target delivery rate by an actual engine revolution speed and a constant, thereby calculating a target tilting. A solenoid output current calculating portion calculates a drive current to provide the target tilting and outputs the drive current to a solenoid control valve. The pump delivery rate is thereby controlled with good response following input change of an operation instructing device.

Abstract: A hydraulic control system according to the present invention for a construction machine is provided with a directional control valve switchable by a pilot control valve, a hydraulic cylinder, a pilot pump, a selector valve for selecting one of a maximum value out of pilot pressures of the pilot control valve, a flow control unit for controlling the flow rate of a variable displacement hydraulic pump, a pressure-reducing valve for converting a delivery pressure of the pilot pump to a pump control signal, which controls driving of the flow control unit, in accordance with a pilot pressure guided to a first signal line connected to the selector valve, a branch line connecting the pilot pump and the pressure-reducing valve with each other, and a second signal line for guiding the pump control signal, which has been converted at the pressure-reducing valve, to the flow control unit.

Abstract: A pilot pressure sensor detects a pilot pressure from an arm operating unit and outputs a pilot pressure signal. A drive signal corresponding to the pilot pressure signal is then outputted from a controller to a solenoid-operated proportional valve. Through the solenoid-operated proportional valve, a pilot pressure is fed to an auxiliary selector valve so that an opening of said auxiliary selector valve becomes greater. Of pressure oil delivered from a first hydraulic pump, a flow rate of the pressure oil to be branched to a side of a by-pass circuit is hence increased. The pressure oil fed through the by-pass circuit passes through a merging directional control valve and is caused to merge with pressure oil fed from a second hydraulic pump. The thus-merged pressure oil is then fed to a hydraulic arm cylinder.

Abstract: A hydraulic system for a construction machine includes a hydraulic pump driven by a prime mover, actuators driven by a hydraulic fluid delivered from the hydraulic pump, flow control valves for controlling flow of the hydraulic fluid to the actuators and operation means for operating the flow control valves. A relief value sets a relief pressure for limiting the maximum delivery pressure of the hydraulic pump and relief pressure change means increase or decrease the relief pressure set by the relief valve. The relief pressure change means automatically increase or decrease the relief pressure in accordance with the input amount of the operation means.

Abstract: In a region limiting excavation control system for a construction machine, a region where a front attachment (1A) is movable is set beforehand. A control unit (9) calculates the position and posture of the front attachment based on signals from angle sensors (8a-8c), calculates a target speed vector (Vc) of the front attachment based on signals from control lever units (4a, 4b), and modifies the target speed vector such that the target speed vector is maintained as it is when the front attachment is within the set region but not near the boundary thereof. A vector component (Vcy) of the target speed vector in the direction toward the boundary of the set region is reduced when the front attachment is within the set region near the boundary thereof, and the front attachment is returned to the set region and when the front attachment is outside the set region. As a result, the excavation within a limited region can be implemented efficiently and smoothly.

Abstract: Pump ports 9p, 10p, 11p, 13p of boom, arm, bucket and first travel directional control valves 9-11, 13 are connected to first and second hydraulic pumps 1a, 1b through feeder lines 93a, 93b; 103a, 103b; 113a, 113b; 133a, 133b. Auxiliary valves 91a, 91b; 101a, 101b; 111a, 101b; 131a, 131b controlled respectively by proportional solenoid valves 31a, 31b; 32a, 32b; 33a, 33b; 34a, 34b are disposed in those feeder lines. The auxiliary valves each have a function as a reverse-flow preventing function and a variable resisting function including a flow cutoff function, whereby a joining circuit and a preference circuit can be realized in the closed center circuit with a simple structure and further, a preference degree and metering characteristics can be set independently of each other during the combined operation of plural actuators.

Abstract: A controller 520 has a data portion 520c in which the relationship between a pump delivery pressure and a target opening area of a variable throttle 300a of a control valve 300 is set such that the target opening area is large when the pump delivery pressure is low, and small when the pump delivery pressure is high. An input portion 520a takes in a detection signal from a pump pressure sensor 700, a processing portion 520b reads the data from the data portion 520c and calculates a signal output to a solenoid proportional valve 590, and an output portion 520d converts the calculated signal into a command signal for the solenoid proportional valve 590 and outputs the command signal. Upon receiving the command signal from the controller 520, the solenoid proportional valve 590 produces a command pilot pressure for the control valve 300 corresponding to the input signal and controls the opening area of the variable throttle 300a.

Abstract: A hydraulic control system is intended to easily hydraulically back up a trouble caused in an electric system, while employing a control unit (13) to utilize the advantage of electric control, when the displacement of a hydraulic pump (1) is controlled in accordance with a status variable of a hydraulic driving system. To this end, a pump regulator (16) is constructed so as to increase the tilting amount .theta. of a swash plate (1a) with a reduction in pressure of a second hydraulic signal Pc. A characteristic of the pump regulator is set such that a negative control pressure Pco can be employed to operate the pump regulator in place of the second hydraulic signal, and characteristics of a fixed throttle (10) and a spring (18d) in the pump regulator are set such that the pump regulator can be operated in the working range of the negative control pressure.