Abstract: A working machine is provided with a revolving upperstructure, working equipment, an engine compartment, a counterweight, a muffler, and an exhaust path for releasing exhaust gas, which has been discharged from the muffler, to an outer side of the revolving upperstructure. The exhaust path includes a tailpipe connected to the muffler and an exhaust pipe for releasing exhaust gas, which has been discharged from the tailpipe, to the outer side of the revolving upperstructure. The counterweight is utilized for the formation of the exhaust path. The exhaust path includes a passage formed in the counterweight and accommodating an upper end portion of the tailpipe inserted therein with a predetermined clearance formed around the upper end portion such that the exhaust gas discharged from the tailpipe can be guided to the exhaust pipe.

Abstract: A working machine is provided with a revolving upperstructure, working equipment, an engine compartment, a counterweight, a muffler, and an exhaust path for releasing exhaust gas, which has been discharged from the muffler, to an outer side of the revolving upperstructure. The exhaust path includes a tailpipe connected to the muffler and an exhaust pipe for releasing exhaust gas, which has been discharged from the tailpipe, to the outer side of the revolving upperstructure. The counterweight is utilized for the formation of the exhaust path. The exhaust path includes a passage formed in the counterweight and accommodating an upper end portion of the tailpipe inserted therein with a predetermined clearance formed around the upper end portion such that the exhaust gas discharged from the tailpipe can be guided to the exhaust pipe.

Abstract: A swivel joint for a construction machine is mounted to an upper track frame, and a body is rotatable together with a swing structure main frame in an opening through engagement between a stopper projection and a stopper plate. Tubes on the swing structure side are connected to an upper end surface of the body by using fittings in concentrated layout, and tubes on the travel structure side are connected to a lower portion of the spindle by using fittings. The body has thicker wall portions in sidewalls thereof, and a plurality of axial passages communicating with a plurality of circumferential grooves are formed inside the thicker wall portions. The plurality of axial passages are opened at the upper end surface of the body, and the tubes on the swing structure side are connected to the upper end surface of the body in concentrated layout.

Abstract: To permit driving a tilt cylinder and an angle cylinder at relatively low speed and also to permit driving an additional actuator at high speed. Provided are a tilt cylinder 9 and angle cylinder 10 for pivotally tilting a blade 7 selectively leftward and rightward and for pivotally angling the blade 7 selectively forward and rearward, respectively, and an additional actuator for actuating an additional attachment. Also provided are a tilting/angling pressure oil feed means comprising a tilting/angling directional control valve 19 for controlling a flow of pressure oil to be fed to one of the cylinders 9,10 and a selector valve 20 for selectively feeding pressure oil, which flows out of the directional control valve 19, to one of the cylinders 9,10. An additional pressure oil feed means for feeding pressure oil to the additional actuator 27 is provided independently of the tilting/angling directional control valve, and the additional pressure oil feed means has an additional directional control valve 29.

Abstract: The hydraulic drive system comprises an engine 1, a pump unit 100, a plurality of actuators 5a, 5b and 5c, a control valve unit 4, and engine revolution speed detecting means 4f. The pump unit 100 includes a pump tilting control mechanism 8 for load sensing control, and the control valve unit 4 includes a plurality of flow control valves 15a, 15b and 15c and pressure compensation valves 10a, 10b and 10c. The engine revolution speed detecting means 4f includes a first differential pressure reducing valve 14 for outputting, as an absolute value, a pressure depending on an engine revolution speed. The output pressure of the first differential pressure reducing valve 14 is introduced, as a target load-sensing differential pressure, to the pump tilting mechanism 8 via a line 127.

Abstract: A swivel joint for a construction machine, is mounted to an upper track frame, and a body is rotatable together with a swing structure main frame in an opening through engagement between a stopper projection and a stopper plate. Tubes on the swing structure side are connected to an upper end surface of the body by using fittings in concentrated layout, and tubes on the travel structure side are connected to a lower portion of the spindle by using fittings. The body has thicker wall portions in sidewalls thereof, and a plurality of axial passages communicating with a plurality of circumferential grooves are formed inside the thicker wall portions. The plurality of axial passages are opened at the upper end surface of the body, and the tubes on the swing structure side are connected to the upper end surface of the body in concentrated layout.

Abstract: A differential pressure between a delivery pressure of a fixed displacement hydraulic pump 2 and a maximum load pressure among a plurality of actuators 3a to 3c is maintained at a target differential pressure by an unloading valve 5. A setting pressure of the unloading valve 5 is changed depending on an engine revolution speed by introducing a differential pressure &Dgr;Pp across a throttle 50, which is disposed in a delivery line of a fixed pump 30, to a pressure bearing sector 5d of the unloading valve. With such an arrangement, in a hydraulic drive system including an LS system, it is possible to ensure fine operability based on setting of the engine revolution speed, to perform flow rate control at a good response, and to realize superior operability.

Abstract: Differential pressures across flow control valves 6a, 6b and 6c are controlled by pressure compensating valves 7a, 7b and 7c to be held at the same value, i.e., a differential pressure &Dgr;PLS, and the differential pressure &Dgr;PLS is maintained at a target differential pressure &Dgr;PLSref by a pump displacement control unit 5. For changing the target differential pressure depending on change in revolution speed of an engine 1, a flow detecting valve 31 is disposed in a delivery line 30a, 30b of a fixed displacement hydraulic pump 30, and a differential pressure &Dgr;Pp across a variable throttle portion 31a of the flow detecting valve 31 is introduced to a setting controller 32. A selector valve 50 operable to shift between a fully closed position and a throttle position is disposed in parallel to the flow detecting valve 31 and is shifted by a control lever 51.

Abstract: In a hydraulic drive system in which a target compensated differential pressure for each of pressure compensating valves 21a, 21b is set in accordance with a differential pressure between a pump delivery pressure and a maximum load pressure, and a target LS differential pressure is set as a variable value depending on a revolution speed of an engine 1, a fixed throttle 32 and a signal pressure variable relief valve 33 are disposed in a maximum load pressure line 35. A relief setting pressure PLMAXO of the signal pressure variable relief valve 33 is set so as to satisfy PLMAXO=PR−PGR+a (where a is a value smaller than PGR) with respect to a target LS differential pressure PGR and a setting pressure PR of the main relief valve 30.

Abstract: Differential pressures across flow control valves 6a, 6b and 6c are controlled by pressure compensating valves 7a, 7b and 7c to be held at the same value, i.e., a differential pressure &Dgr;PLS, and the differential pressure &Dgr;PLS is maintained at a target differential pressure &Dgr;PLSref by a pump displacement control unit 5. For changing the target differential pressure depending on change in revolution speed of an engine 1, a flow detecting valve 31 is disposed in a delivery line 30a, 30b of a fixed displacement hydraulic pump 30, and a differential pressure &Dgr;Pp across a variable throttle portion 31a of the flow detecting valve 31 is introduced to a setting controller 32. A selector valve 50 operable to shift between a fully closed position and a throttle position is disposed in parallel to the flow detecting valve 31 and is shifted by a control lever 51.

Abstract: An actuator lock switching valve 50 is provided which communicates a drain line 52 and a pilot line 53 with each other when the valve 50 is in a position C, and which communicates pilot lines 51, 53 with each other when it is shifted to a position D. The pilot line 51 is connected to a delivery line 7 of a hydraulic pump 10, and the pilot line 53 is connected to pressure receiving sections 28a, 28b provided at ends of the pressure compensating valves 21a, 21b on the side acting in the closing direction. The actuator lock switching valve 50 has a pressure receiving section 55 connected to the output side of a pilot lock switching valve 43, and is switched over in interlock with shifting of the switching valve 43.

Abstract: A differential pressure between a delivery pressure of a fixed displacement hydraulic pump 2 and a maximum load pressure among a plurality of actuators 3a to 3c is maintained at a target differential pressure by an unloading valve 5. A setting pressure of the unloading valve 5 is changed depending on an engine revolution speed by introducing a differential pressure &Dgr;Pp across a throttle 50, which is disposed in a delivery line of a fixed pump 30, to a pressure bearing sector 5d of the unloading valve. With such an arrangement, in a hydraulic drive system including an LS system, it is possible to ensure fine operability based on setting of the engine revolution speed, to perform flow rate control at a good response, and to realize superior operability.

Abstract: In a hydraulic drive system in which a target compensated differential pressure for each of pressure compensating valves 21a, 21b is set in accordance with a differential pressure between a pump delivery pressure and a maximum load pressure, and a target LS differential pressure is set as a variable value depending on a revolution speed of an engine 1, a fixed throttle 32 and a signal pressure variable relief valve 33 are disposed in a maximum load pressure line 35. A relief setting pressure PLMAX′ of the signal pressure variable relief valve 33 is set so as to satisfy PLMAX′=PR−PGR+&agr; (where &agr; is a value smaller than PGR) with respect to a target LS differential pressure PGR and a setting pressure PR of the main relief valve 30.

Abstract: An actuator lock switching valve 50 is provided which communicates a drain line 52 and a pilot line 53 with each other when the valve 50 is in a position C, and which communicates pilot lines 51, 53 with each other when it is shifted to a position D. The pilot line 51 is connected to a delivery line 7 of a hydraulic pump 10, and the pilot line 53 is connected to pressure receiving sections 28a, 28b provided at ends of the pressure compensating valves 21a, 21b on the side acting in the closing direction. The actuator lock switching valve 50 has a pressure receiving section 55 connected to the output side of a pilot lock switching valve 43, and is switched over in interlock with shifting of the switching valve 43.

Abstract: A hydraulic drive system having a swing control system, includes a pump control unit for controlling a pump delivery rate such that a pump delivery pressure is held a predetermined value higher than a maximum load pressure among a plurality of actuators. Pressure compensating valves are each constructed to set, as a target compensation differential pressure, a differential pressure between a delivery pressure of a hydraulic pump and a maximum load pressure among the actuators. A pressure compensating valve for a swing section is given such a load dependent characteristic that when the load pressure rises, the target compensation differential pressure is reduced, the load dependent characteristic being set so as to provide a flow rate characteristic simulating constant-horsepower control of a swing motor.

Abstract: A hydraulic drive system includes a pump control unit 18 for controlling a pump delivery rate such that a pump delivery pressure is held at a predetermined value higher than a maximum load pressure among actuators 2-6. Pressure compensating valves 12-16 are each constructed to set, as a target compensation differential pressure, a differential pressure between the delivery pressure of a hydraulic pump 1 and the maximum load pressure among the actuators 2-6. The pressure compensating valve 12 is given such a load dependent characteristic that the target compensation differential pressure is reduced when a load pressure rises. A lower limit setting spring 55 for limiting the target compensation differential pressure from becoming smaller than a predetermined value is provided in the pressure compensating valve 12 for the swing section.

Abstract: A differential pressure &Dgr;PLS between a delivery pressure of a hydraulic pump 2 and a maximum load pressure among a plurality of actuators 3a-3c is maintained at a target differential pressure &Dgr;PLSref by pump displacement control means 5. The target differential pressure &Dgr;PLSref is modified depending on an engine rotational speed by introducing a differential pressure &Dgr;Pp across a throttle 50 disposed in a delivery line of a fixed pump 30. An unloading valve 80 has first and second auxiliary control pressure chambers 80e, 80f to which the differential pressure p across the throttle 50 is introduced, and a target differential pressure &Dgr;Pun of the unloading valve is also modified in match with change in the target differential pressure &Dgr;PLSref modified by the operation driver 32. Stable load sensing control is thereby achieved without being affected by the engine rotational speed.

Abstract: An engine speed control system for a construction machine is arranged in association with its hydraulic circuit, which has main pumps, a communication line through which input ports of travel-controlling directional control valves are connected with each other, and a travel-controlling communication valve arranged in the communication line.

Abstract: A hydraulic drive system wherein differential pressures across flow control valves are controlled by pressure compensating valves to become the same value, i.e., a differential pressure .DELTA.PLS, and the differential pressure .DELTA.PLS is maintained at a target differential pressure .DELTA.PLSref by a pump displacement control system. For modifying the target differential pressure .DELTA.PLSref depending on change in rotational speed of an engine, a flow rate detecting valve is disposed intermediate between delivery lines of a fixed displacement hydraulic pump and a differential pressure .DELTA.Pp across a variable throttle of the flow rate detecting valve is introduced to a setting modifying unit to thereby modify the target differential pressure .DELTA.PLSref. The flow rate detecting valve changes an opening area of the variable throttle depending on the differential pressure .DELTA.Pp depending on the rotational speed of the engine.