Abstract: A construction machine including: a swivel motor; a working attachment having a boom, a boom cylinder, an arm and an arm cylinder; a hydraulic actuator circuit having a first circuit including the boom cylinder and a boom control valve, a second circuit including the arm cylinder and an arm control valve, and a third circuit including the swivel motor and a swivel control valve; first to third pumps for the first to third circuits; a merge valve having a first position for merge of third pump fluid into the first circuit and connection of an unload line of the third circuit to a tank, and a second position for prohibiting the merge; and a merge selecting control section which holds the merge valve at the first position either of when only a swivel operation is performed and when a boom raising operation is performed.

Abstract: A construction machine includes a hydraulic actuator circuit including: a first circuit connected to one of travel motors and a boom cylinder; a second circuit connected to the other travel motor and arm cylinder; and a third circuit connected to a slewing motor; control valves for hydraulic actuators; and a merging valve having a first position for unloading hydraulic fluid discharged from a third pump upon no operation except for two travel motors; a second position for merging the hydraulic fluid into the first and second circuits upon a simultaneous operation of the travel motors and an operation of at least one remaining hydraulic actuator except for a boom raising operation; and a third position for merging the hydraulic fluid into the first circuit while blocking it from the second circuit upon the boom raising operation.

Abstract: Provided is a construction machine including a first circuit with a boom cylinder, a second circuit with an arm cylinder and a third circuit with a slewing motor, first to third pumps discharging respective first to third pump fluids, a first flow combining valve having a first combining position for the third and first pump fluids and a first combination limiting position, a second flow combining valve having a second combining position for the third and second pump fluids and a first combination and a second combination limiting position, and a flow combination switching control section which switches the flow combining valves to their respective combination limiting positions during an arm attracting operation and switches the combining valves to their respective combination limiting positions during a single slewing operation or during a boom raising operation with no arm operation.

Abstract: A construction machine including: a swivel motor; a working attachment having a boom, a boom cylinder, an arm and an arm cylinder; a hydraulic actuator circuit having a first circuit including the boom cylinder and a boom control valve, a second circuit including the arm cylinder and an arm control valve, and a third circuit including the swivel motor and a swivel control valve; first to third pumps for the first to third circuits; a merge valve having a first position for merge of third pump fluid into the first circuit and connection of an unload line of the third circuit to a tank, and a second position for prohibiting the merge; and a merge selecting control section which holds the merge valve at the first position either of when only a swivel operation is performed and when a boom raising operation is performed.

Abstract: A construction machine includes a hydraulic actuator circuit including: a first circuit connected to one of travel motors and a boom cylinder; a second circuit connected to the other travel motor and arm cylinder; and a third circuit connected to a slewing motor; control valves for hydraulic actuators; and a merging valve having a first position for unloading hydraulic fluid discharged from a third pump upon no operation except for two travel motors; a second position for merging the hydraulic fluid into the first and second circuits upon a simultaneous operation of the travel motors and an operation of at least one remaining hydraulic actuator except for a boom raising operation; and a third position for merging the hydraulic fluid into the first circuit while blocking it from the second circuit upon the boom raising operation.

Abstract: A throttle path for returning a part of pilot oil to a tank is formed by a tank path provided in a valve block of a control valve and a notch provided in a spool thereof. The above path is opened within a section from a vicinity of a stroke where a hydraulic actuator starts moving to right before a stroke end among a spool stroke of the control valve. An opening area of the above path is slowly reduced in accordance with an increase in the stroke at a final phase of the section.

Abstract: A throttle path for returning a part of pilot oil to a tank is formed by a tank path provided in a valve block of a control valve and a notch provided in a spool thereof. The above path is opened within a section from a vicinity of a stroke where a hydraulic actuator starts moving to right before a stroke end among a spool stroke of the control valve. An opening area of the above path is slowly reduced in accordance with an increase in the stroke at a final phase of the section.

Abstract: A controlling system for a cooling fan according to the present invention includes a fluid-pressure motor for driving the cooling fan; a fluid-pressure pump functioning as a driving source for the fluid-pressure motor; and a controller. The controller determines a target motor speed value by selecting a higher one of required motor speed values respectively corresponding to multiple kinds of fluids to be cooled and controls the fluid-pressure motor so that the motor speed thereof reaches the target motor speed value, each of the required motor speed values being determined from a temperature value of the corresponding fluid detected by a corresponding one of temperature sensors on the basis of a characteristic preliminarily determined by a temperature-versus-motor-speed relationship for the corresponding fluids the characteristic being set for each kind of fluid.

Abstract: An apparatus for suppressing vibratory or quaky movements in travel of mobile type cranes, which facilitates the operation of re-starting the vehicle after temporarily stopping the engine, for example, at a gas station for fuel replenishment as well as operations for switching the mode of operation between vehicle travel and working modes. The apparatus includes for this purpose a memory means for storing at least information as to the mode of operation under engine working conditions before an engine cut-off, and a controller adapted to reproduce automatically the mode of operation before the engine cut-off, by setting a mode selector means in a reproducing position upon re-starting the engine based on the information stored in the memory means.

Abstract: According to the displacement suppressing mechanism for a travelling crane of the present invention, when a mode selection switch selects an operation mode and a detected value by a boom position detecting means is smaller than a lower limit value of an appropriate travelling range, a change-over valve for replenishment capable of changing over the position of an auxiliary pressure oil source selectively to a communicating position for communication of the auxiliary pressure oil source with a first oil chamber of a boom raising and lowering hydraulic cylinder and a communication cutting-off position is shifted to the communicating position by a control means to supply a predetermined amount of pressure oil to the first oil chamber of the hydraulic cylinder.

Abstract: A mechanism for effectively suppressing vibrations in travel of mobile type crane includes; a boom lifting hydraulic cylinder connected between a vehicle body of the mobile crane and a boom; a main hydraulic pump; a direction control valve for supplying the discharge oil of the main hydraulic pump selectively to and from a first load-supporting oil chamber and an opposingly located second oil chamber of the boom lifting cylinder.

Abstract: An apparatus for supressing vibration and quaky movements of a pivotally mounted boom on a mobile crane. The boom is supported for pivotal movement by a hydraulic cylinder which is subjected to abrupt forces when the crane is in motion. A hydraulic circuit is constructed to prevent such forces from damaging the hydraulic cylinder and vehicle body of the crane. The circuit is selectively operative to place the hydraulic cylinder in either a working or travel made. The circuit includes an accumulator and three change-over valves to control the flow of fluid in the hydraulic cylinder during the work and travel modes of operation.

Abstract: An apparatus for damping quaky movements of a mobile type crane includes the prohibition of the formation of a closed damping circuit through the opposing oil chambers of a boom uplifting cylinder in working mode or a crane operation in travel mode of the crane, enhancing safety in crane operation while ensuring effective quake damping action in vehicle travel.