Abstract:
When simultaneous operation of rotating and arm pulling is detected by a detector, a switching controller recognizes that both signals are output simultaneously, and switches a switching valve to a second position, so that oil flows discharged from a plurality of hydraulic pumps are united and supplied to a rotating motor and an arm cylinder. A meter-in flow controller restricts a quantity of oil supplied to the arm cylinder. Thereby, even where rotating and arm pulling are operated simultaneously, each of operations can be done quickly, and the delay of the rotating operation is overcome, to enable proper rotating and arm pulling operations.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is based on Japanese patent application 2000-112340 filed on Apr. 13, 2000, which is herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a construction machine such as a hydraulic excavator. Particularly, the invention relates to a hydraulic control circuit provided in the construction machine. 
     2. Description of the Background 
     In the past, where excavation work is carried out by a hydraulic excavator, earth and sand scooped by a bucket are loaded on a dump truck waiting behind the hydraulic excavator by rotating an upper rotating body of the excavator. The operation is carried such that when loading onto the dump truck is terminated, an excavator arm is turned while elevated, and returned to an excavation point. 
     The conventional hydraulic control circuit is designed so that oil is supplied from a common pump to a control valve for an arm and a control valve for rotating. Because of this, the arm, which has the smaller load, is first operated, so that the rotating operation is delayed. 
     In this case, an operator has to carry out a complicated operation in which an arm operating lever is operated moderately, to provide sufficient oil pressure for the rotating operation. The complicated operation is difficult to do unless an operator is a skilled person. However, when pulling and rotating of the arm are carried out while adjusting an operating lever, there occurs a problem that rerotating to the excavation point is delayed to lower the work efficiency. 
     To cope with the foregoing, control has been carried out so that a valve for throttling a quantity of oil discharged from an arm cylinder at the time of an arm pulling operation is provided to overcome the delay of the rotating operation during the arm pulling operation. However, in this hydraulic control circuit, since the valve is provided in a circuit on the rod side of an arm cylinder, even if throttling is done relatively strongly, a sufficient throttling effect could not be a obtained. The digging equipment herein denoted in simplified manner as an “excavator arm,” as a rule comprises an integral single boom or a boom in two parts, plus a shovel stem and an excavating implement. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a construction machine capable of carrying out a rotating operation and an excavator arm operation properly even if both the rotating and the arm pulling are operated simultaneously. 
     In accordance with at least an aspect of the invention, the above and other objects are addressed by a rotating motor for causing a rotating operation such as a rotating operation of an upper rotating body. The arm operation comprises an operating such as arm pulling and arm-in, wherein “arm-in” means bringing in the excavator arm. Actuators include an arm cylinder for causing an excavator arm operation. Control valves control supply and discharge of oil between each of hydraulic pumps and each of the actuators. The control valves incline a control valve for a rotating motor and a control valve for an arm cylinder. A switching valve is switched between a first position for separately supplying oil from the hydraulic pumps to the control valve for the rotating motor and the control valve for the arm cylinder, and a second position for uniting and supplying oil from the hydraulic pumps. A detector outputs signals responsive to the rotating operation and the arm pulling operation respectively when those operations are carried out. A switching controller switches the switching valve to the second position when the signals are output substantially simultaneously. A meter-in flow-controller such as meter-in flow-control valve restricts a quantity of oil supplied to the arm cylinder when the switching valve is switched to the second position. 
     In this case, when rotating and arm pulling are operated simultaneously, signals are respectively output from the detector and applied to the switching controller. The switching controller recognizes that the signals are output simultaneously, and switches the switching valve to the second position. When the switching valve is switched to the second position, oil flows discharged from the plurality of hydraulic pumps are united and supplied to the rotating motor and the arm cylinder through a specific control valve. Accordingly, the quantity of oil supplied to the rotating motor and the arm cylinder is increased. Thereby, the quantity of oil necessary for quickly carrying out the rotating and arm pulling operations is secured. 
     In this state, the meter-in flow-controller restricts the quantity of oil supplied to the arm cylinder, so that the arm pulling speed can be suppressed. Accordingly, even if the rotating and arm pulling are operated simultaneously, respective operations of the rotating and the arm pulling can be done quickly, the delay of the rotating operation can be overcome, and the rotating and arm pulling operations can be realized properly. 
     Preferably, the meter-out flow controller is provided for restricting a quantity of oil discharged from the arm cylinder when the switching valve is switched to the second position. 
     In this case, when the quantity of oil supplied to the arm cylinder is throttled, the meter-out flow controller also simultaneously throttles the quantity of oil from the arm cylinder. Accordingly, cavitation can be prevented when, for example, the arm descends by its own weight without any operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a hydraulic circuit view of a construction machine according to one embodiment of the present invention; 
     FIG. 2 is a meter-in throttle characteristic view of an arm cylinder shown in FIG. 1; 
     FIG. 3 is likewise a meter-out throttle characteristic view; and 
     FIG. 4 is a sectional view showing the constitution in which an adjusting valve for adjusting a meter-in flow rate is housed in an arm spool. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in detail hereinafter on the basis of one embodiment of the invention shown in the drawings. 
     FIG. 1 shows one embodiment where a hydraulic control circuit of the construction machine according to the present invention is applied to a hydraulic excavator. 
     In the figure, when an engine  1  is driven, a first hydraulic pump  2 , a second hydraulic pump  3  and a pilot pump  4  are driven, respectively. The first and second hydraulic pumps  2  and  3 , as plural pumps, are variable capacity type hydraulic pumps. These pumps are swash plate type axial piston pumps whose discharge flow rate changes on the basis of a displacement of an angle of inclination of a swash plate. 
     Oil discharged from the first and second hydraulic pumps  2  and  3  is supplied to direction control valves arranged in a left center bypass line (sometimes abbreviated as LCB), and to direction control valves arranged in a right center bypass line (sometimes abbreviated as RCB). The control valves arranged in the LCB include a control valve  5  for a right traveling motor, a control valve  6  for a bucket cylinder and a control valve  7  for a boom cylinder. The control valves arranged in the RCB include a control valve for a left traveling motor  8 , a control valve  9  for a rotating motor and a control valve  10  for an arm cylinder. 
     Further, pilot pressure discharged from the pilot pump  4  is utilized as a pressure source Pa for various controls. 
     A travel straight valve  11  as a switching valve is interposed in an upstream oil path L 1  of the control valve for the right traveling motor  5 . The travel straight valve  11  has a position a as a first position and a position b as a second position. Normally, it is held at the position a. 
     At the position a, oil discharged from the first hydraulic pump  2  is supplied to the LCB side through the oil path L 1 . On the other hand, oil discharged from the second hydraulic pump  3  is supplied to the RCB side through the oil path L 2 . Accordingly, oil is supplied respectively from the first hydraulic pump  2  and the second hydraulic pump  3  to the control valve for a right traveling motor  5  and the control valve for a left traveling motor  8 . 
     For example, when the boom or the arm is operated in the state that the left and right operating levers (not shown in the figure) are operated to the same position, the travel straight valve  11  is switched from the position a to the position b. Oil discharged from the first hydraulic pump  2  is distributed and supplied to the control valve for a rotating motor  9 , and the control valve for an arm cylinder  10  through the oil path L 3 . 
     At that time, oil discharged from the second hydraulic pump  3  flows to the oil paths L 1  and L 2  in parallel, and is supplied to the left and right control valves for a traveling motor  5  and  8 . Thereby, for example, even where a composite operation such that the boom is risen and fallen while driving the traveling motor, oil discharged from the second hydraulic pump  3  is equally supplied to the left and right traveling motors. Accordingly, the travel straightness can be held. 
     Further, a cut valve  12  is provided downstream of the control valve for a boom cylinder  7  in the LCB. On the other hand, a cut valve  13  is provided downstream of the control valve for an arm cylinder  10  in the RCB. 
     The cut valve  12  performs a closing operation when the control valve on the RCB side is operated. On the other hand, the cut valve  13  performs a closing operation when the control valves on the LCB side are operated. The reason is as follows: When the travel straight valve  11  is switched to the position a, oil discharged from the second hydraulic pump  3  is branched to the oil paths L 1  and L 2 . This is because when either of control valves on the RCB side is operated, pump pressure is not created unless the cut valve  12  on the LCB side is closed. On the other hand, when either of control valves on the LCB side is operated, pump pressure is not created unless the cut valve  13  on the RCB side is closed. 
     The oil path L 3  is connected, at a united point P, to united oil path L 4  branched from downstream end of the control valve for a traveling motor  8  in the RCB. Oil is supplied to the control valve for a rotating motor  9  through an oil path L 5  extended from the united point P. Further, oil is supplied to the control valve for an arm cylinder  10  through oil paths L 6  and L 7  extended from the united point P. Numerals  14  and  15  in the oil paths L 3  and L 4  denote check valves. In the figure, numeral  9   a  denotes a rotating motor for rotating an upper rotating body. 
     In the oil path L 7 , there is provided a flow rate control valve  16  as meter-in flow-control valve for restricting or throttling a quantity of oil in a meter-in circuit in the control valve for an arm cylinder  10 . The flow rate control valve  16  is controlled by a controller  17  as a switching control means. 
     Further, in an oil path L 8  downstream of the control valve for an arm cylinder  10 , there is provided a flow rate control valve  18  as meter-out flow-control valve for throttling a quantity of oil in a meter-out circuit in the control valve for an arm cylinder  10 . It is likewise controlled by the controller  17 . An oil path L 9  downstream of the flow rate control valve  18  is fed back to a head-side oil chamber of an arm cylinder  19  through a check valve  18   a . This constitutes a reproducing circuit for increasing an arm speed. In the figure, numeral  20  denotes an arm-push united valve for accelerating arm-pushing. Likewise, numeral  50  denotes a boom-lift united valve for accelerating boom-lifting. 
     The meter-in circuit and the meter-out circuit are so designed as to be throttled or restricted respectively when the rotating and the arm-pulling are operated simultaneously. The throttling effect depends on an inflow flow rate of oil. The inflow flow rate depends on a rotational frequency of an engine. Accordingly, when the rotational frequency of the engine falls to lower the quantity of discharge of the pump, the throttling effect lowers. Therefore, where a solenoid proportional valve  27  for applying a meter-in throttle hydraulic signal P in  to the flow rate control valve  16  and a solenoid proportional valve  28  for applying a meter-out throttle signal P out  to the flow rate control valve  18  are controlled, throttle signals P 6  and P 7  according to the rotational frequency of the engine are commanded from the controller  17 . 
     FIG. 2 shows a characteristic view of the meter-in throttle hydraulic signal P in . In the operating range in which rotating remote control pressure P 1  of a remote control valve for rotating  22  changes from P 1a  to P 1b , when the engine is rated-operated, the meter-in throttle hydraulic signal P in  output from the solenoid proportional valve  21 , that is, the so called proportional valve secondary pressure, increases from P a1  to P amax . As the rotational frequency of the engine falls, the characteristics is lowered from M 1  to M 5  stepwise until the maximum secondary pressure assumes a pressure P a2  according to the decrease of the rotational frequency of the engine. Thereby, the throttling effect is relieved stepwise. 
     FIG. 3 shows a characteristic view of a meter-out throttle hydraulic signal P out . In the operating range in which remote control pressure P 1  changes from P 1a  to P 1b , when the engine is rated-operated, the meter-out throttle hydraulic signal P out  output from the solenoid proportional valve  28 , that is, the so called proportional valve secondary pressure, increases from P a1  to P a2 . As the rotational frequency of the engine falls, the characteristic pressure is increased from S 1  to S 3  stepwise till the maximum secondary pressure assumes a value according to decrease of the rotational frequency of the engine, conversely to the characteristics shown in FIG.  2 . Thereby, cavitations can be prevented. 
     In the above-described constitution, when the remote control pressure rises, the proportional secondary pressure rises in proportion thereto and the flow rate control valve  16  is throttled. Alternatively, an inverse proportion may be made in which when the rotating remote control pressure rises, the proportional secondary pressure falls and the flow rate control valve  16  is throttled. 
     FIG. 4 shows the constitution in which the flow rate control valve  16  is housed in the control valve  10  for an arm cylinder. 
     In the figure, a bore  31  extends through a housing  30 . An arm spool  32  and an auxiliary arm spool for throttling  41  constituting a flow rate control valve  16  are slidably inserted into the bore  31  and in the outer periphery of the arm spool  32 , respectively. The housing  30  is internally formed with pump ports  33   a ,  33   b  connected to the hydraulic pump, bleed-off ports  34 ,  35  constituting the center bypass passage RCB, and a tank port  36 . Oil introduced from the pump port  33   a  is discharged from the head port  37  and supplied to a head-side oil chamber  19   a  of the arm cylinder  19 . Oil discharged from a rod-side oil chamber  19   b  of the arm cylinder  19  is introduced into the rod port  38  and discharged from a reproducing port  39 . Then the oil is supplied to the head-side oil chamber  19   a  through the flow rate control valve  18 . 
     On the right hand side of the housing  30 , there is provided a pilot port  40  into which is introduced a meter-in throttle hydraulic signal P in  from the solenoid proportional valve  27 . The auxiliary spool  41  is operated by the signal P in  so as to throttle the meter-in flow rate of the inflow flow rate. Alternately, remote control pressure of the remote control valve for rotating  22  in place of a hydraulic signal from the solenoid proportional valve  27  may be input into the port  40  directly. 
     As described above, according to the constitution in which the flow rate control valve  16  for throttling a meter-in circuit is housed in the control valve for an arm cylinder  10 , the hydraulic circuit becomes simple, and the space is also saved. 
     In the following, the operation of the hydraulic control circuit having the above-described constitution will be described. In the following description of operation, a description will be made of a case where after earth and sand are loaded on the dump truck, the arm is rotated while being elevated, and returned to the excavation point. 
     An operator simultaneous operates the remote control valve  21  for an arm  19  and the remote control valve  22  for rotating simultaneously start arm pulling and rotating. At that time, an arm pulling signal P 1  and a rotating signal P 2  are respectively output from a pressure sensor  23  and a pressure sensor  24  as detection means for detecting remote control pressure and applied to the controller  17 . 
     The controller  17  judges if both the signals P 1  and P 2  are input, to thereby recognize simultaneous operation of arm pulling and rotating. When the simultaneous operation is recognized, a united signal P 3  is output to the solenoid proportional valve  25 . The solenoid proportional valve  25  applies a switching hydraulic signal P 4  to the control port of the travel straight valve  11  to switch the travel straight valve  11  from the position a to the position b. 
     At the same time, a united signal P 5  is output to the solenoid proportional valve  26 . The solenoid proportional valve  26  switches the cut valve  12  from a position c (open) to a position d (closed). 
     At that time, oil discharged from the first hydraulic pump  2  is supplied to the RCB through the passage L 3 . On the other hand, oil discharged from the second hydraulic pump  3  is supplied to the LCB through the passage L 1 . 
     The oil discharged from the second hydraulic pump  3  is branched to the oil path L 2  also. The oil further flows into the united oil path L 4  through the center bypass of the control valve for a left traveling motor  8 . Accordingly, oil flows of both the hydraulic pumps  2  and  3  are united at the united point P. However, it is assumed that the control valves on the LCB are not operated. 
     In this state, the operating levers of the remote control valve for an arm  21  and the remote control valve for rotating  22  are deeply operated. At that time, an increase in operating pressure in the remote control valve for rotating  22  is detected by the pressure sensor  24  and applied to the controller  17 . The controller  17  outputs throttle signals P 6  and P 7  according to operating pressures detected to the solenoid proportional valves  27  and  28 , respectively. Thereby, opening degrees of the low rate control valves  16  and  18  are respectively throttled. As a result, the meter-in circuit and the meter-out circuit of the control valve for an arm cylinder  10  are throttled to prevent the oil united at the united point P from preferentially flowing to the control valve for an arm cylinder  10 . Accordingly, the control valve for a rotating motor  9  and the control valve for an arm cylinder  10  can be operated properly. 
     Further, where the rotational frequency of the engine falls to lower the discharge quantity of the pump, the following operation for preventing the lowering of the throttling effect is carried out, as mentioned above. That is, the throttling of the meter-in circuit is relieved according to the rotational frequency of the engine, and the throttling of he meter-out circuit is increased. Thereby, cavitation is prevented. 
     According to the embodiments of the present invention, the meter-in flow controller and the meter-out flow controller are designed so that the quantity of oil supplied to the arm cylinder is restricted according to the amplitude of a signal output by the rotating operation. Therefore, the quantity of oil supplied to the rotating motor and the arm cylinder in the simultaneous operation of rotating and arm pulling can be kept to the desired ratio. Accordingly, even an unskilled person can perform the rotating and arm pulling operations simply. 
     Further, the meter-in flow-controller and the meter-out flow-controller are designed so that the restriction characteristics can be changed according to the rotational frequency of the engine. Therefore, the fixed restricting effect corresponding to the variation of the rotational frequency of the engine is obtained. Thereby, cavitation can be prevented. 
     In the present embodiment, in realizing a circuit capable of simultaneously operating the rotating and arm pulling, the travel straight valve  11  is utilized. However, the effect of the present invention is exhibited even with a different circuit for providing the united oil path L 4 . The flow rate control valve  16  for throttling the meter-in circuit of the arm cylinder  19  can be constituted by changing a land shape of an arm spool. 
     That is, in the present embodiment, there are left and right traveling motors as actuators, and both traveling control valves for controlling both traveling motors as control valves. Further, there is provided a hydraulic control circuit of a construction machine using, as a switching valve, a traveling control valve which is switched between a first position for independently supplying oil from separate hydraulic pumps to both traveling control valves and a second position for supplying oil from a singe hydraulic pump in parallel. 
     While in the present embodiment, the hydraulic control circuit of the present invention has been described taking a hydraulic excavator as an example, the invention is not limited thereto. The invention can be applied to a suitable construction machine, which is provided with an arm and turns an upper rotating body. 
     While one embodiment of the present invention has been disclosed, the scope of protection of the present invention is not limited thereto. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.