Work machine

Abstract

To suppress shock caused by frequent switching of pressure oil, in a work machine comprising: a hydraulic drive device; an operation member; and a controller, the controller is configured to: until the operation member reaches a first position from an initial position, control a flow combiner valve so as to supply the pressure oil from a first hydraulic pump to a first hydraulic actuator; in a case where the operation member is operated in a direction of increasing the operation amount beyond the first position, control the flow combiner valve so as to supply the combined pressure oil to the first hydraulic actuator; and in a case where the operation member reaches a second position closer to the initial position than the first position from any position beyond the first position, control the flow combiner valve so as to supply the pressure oil from the first hydraulic pump to the first hydraulic actuator.

Description

TECHNICAL FIELD

[0001] The present invention relates to work machines such hydraulic excavators.BACKGROUND ART

[0002] For a typical hydraulic system used in a work machine such as a hydraulic excavator, there have been an actuator that is powered by one of two hydraulic pumps to work and an actuator that is powered by both the hydraulic pumps to work. For the purpose of reducing throttling losses due to flow dividing, a priority order of the two hydraulic pumps is often set in advance for an actuator which is supplied with the power from both the hydraulic pumps to work.

[0003] In the hydraulic system of the type as described above, for example, one of the hydraulic pumps to which the first priority is assigned is set as a primary pump and the other one of the hydraulic pumps to which the second priority is assigned is set as a secondary pump, and when a target flow rate falls within the range of the flow rate that can be supplied by the primary pump, the hydraulic oil is supplied from only the primary pump to the actuator, while the hydraulic oil is supplied from the secondary pump to the actuator only when the target flow rate exceeds the flow rate that can be supplied by the primary pump.

[0004] In this system, the discharge pressure of the secondary pump varies depending on the presence or absence of flow combining, and accordingly, in the case where the pressure of an actuator which is a flow-combining target is greater than the pressure of other actuators, if a target flow rate increases or decreases around an upper limit of the suppliable flow rate of the primary pump, repeated fluctuation in the discharge pressure caused by switching between the flow-combining state and the non-flow-combining state may cause operational shock, discomfort during operations, instable control, and the like.

[0005] For this problem, in Patent Literature 1, when the drive pressure, which is a difference between the rod-side pressure and the cap-side pressure of the hydraulic cylinder (actuator), is equal to or less than a specified value, the first hydraulic pump and the second hydraulic pump are controlled to be in a connected state so as to suppress operational shock caused by switching between the connected state (flow-combining state) and a disconnected state (non-flow-combining state).CITATION LISTPATENT LITERATURE

[0006] Patent Literature 1: JP-B-6145229SUMMARY OF INVENTIONTECHNICAL PROBLEM

[0007] In Patent Literature 1, however, the controller controls the connection state of the pumps depending on whether a request flow rate is equal to or more than a threshold value, or whether the drive pressure is equal to or more than a threshold value, and in this configuration, increase and decrease in the request flow rate and the drive pressure around the threshold values may cause repeated switching between the flow-combining state and the non-flow-combining state. This repeated switching between the flow-combining state and the non-flow-combining state in the state where the drive pressure is high may lead to a risk that the operator feels discomfort during operations, or a risk of instable control. Furthermore, even in a flow rate condition not requiring flow combining, the flow-combining state is maintained if the drive pressure is equal to or less than the specified value. This may lead to a risk of unnecessary throttling losses while a combined operation (for example, the boom and arm are operated in the air at the same time) is performed in an aerial operation of the work machine, and thus a further risk of deterioration in the fuel efficiency.

[0008] An object of the present invention is to provide a work machine capable of suppressing shock caused by frequent switching between a non-flow-combining state and a flow-combining state of pressure oil from two hydraulic pumps, while reducing throttling losses due to flow dividing.SOLUTION TO PROBLEM

[0009] In order to achieve the object described above, an aspect of the present invention provides a work machine comprising: a hydraulic drive device including a first hydraulic pump, a second hydraulic pump, a first hydraulic actuator driven by a pressure oil supplied from the first hydraulic pump, and a flow combiner valve for combining the pressure oil supplied from the first hydraulic pump and a pressure oil supplied from the second hydraulic pump to communicate a pressured oil thus combined to the first hydraulic actuator; an operation member to be operated by an operator; and a controller configured to control the hydraulic drive device based on an operation amount of the operation member, the controller being configured to: in a case where the operation member is operated in a direction of increasing the operation amount, until the operation member reaches a first position from an initial position, control the flow combiner valve so as to supply the pressure oil from the first hydraulic pump to the first hydraulic actuator (non-flow-combining state); in a case where the operation member is operated in a direction of increasing the operation amount beyond the first position, control the flow combiner valve so as to combine the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump and supply the pressure oil thus combined to the first hydraulic actuator in response to increase in the operation amount (flow-combining state); and in a case where the operation member is operated in a direction of decreasing the operation amount from any position beyond the first position and the operation amount reaches a second position closer to the initial position than the first position, control the flow combiner valve so as to cancel a flow-combining state in which the pressure oil from the first hydraulic pump is combined with the pressure oil from the second hydraulic pump, and supply the pressure oil from the first hydraulic pump to the first hydraulic actuator in response to decrease in the operation amount (non-flow-combining state).ADVANTAGEOUS EFFECTS OF INVENTION

[0010] According to the work machine of the present invention, it is possible to suppress shock caused by frequent switching between a non-flow-combining state and a flow-combining state of pressure oil from two hydraulic pumps while reducing throttling losses due to flow dividing. The problems, configurations, and advantageous effects other than those described above will be clarified by explanation of the embodiments below.BRIEF DESCRIPTION OF DRAWINGS

[0011] [FIG. 1] FIG. 1 is a side view illustrating the appearance of a hydraulic excavator. [FIG. 2] FIG. 2 is a hydraulic circuit diagram of a hydraulic system. [FIG. 3] FIG. 3 is a functional block diagram of a controller. [FIG. 4] FIG. 4 illustrates how a flow rate, pressure, and throttling losses due to flow dividing change relative to a boom operation amount in a conventional technique. [FIG. 5] FIG. 5 illustrates how a flow rate changes relative to a boom operation amount in the first embodiment. [FIG. 6] FIG. 6 illustrates a flowchart of a procedure of control processing to be executed by a controller. [FIG. 7] FIG. 7 illustrates how a flow rate changes relative to a boom operation amount in a modified example. [FIG. 8] FIG. 8 illustrates a flowchart of a procedure of control processing to be executed by a controller according to the second embodiment. [FIG. 9] FIG. 9 illustrates a flowchart of a procedure of control processing to be executed by a controller according to the third embodiment. DESCRIPTION OF EMBODIMENTS(First embodiment)

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] FIG. 1 is a side view illustrating an appearance of a hydraulic excavator which is an example of a work machine according to the present invention. In FIG. 1, a hydraulic excavator 1 includes an undercarriage 3, an upperstructure 2 that is provided to the undercarriage 3 so as to swing, and an operator's cab 10. The upperstructure 2 is provided with a front working device including a boom 4, an arm 6, and a bucket 8. The boom 4, the arm 6, and the bucket 8 are driven by a boom cylinder 5, an arm cylinder 7, and a bucket cylinder 9, respectively, which are hydraulic actuators. Although not illustrated, an attachment may be mounted to the hydraulic excavator 1.

[0014] Here, the boom cylinder 5 corresponds to a first hydraulic actuator according to the present invention, and the arm cylinder 7 corresponds to a second hydraulic actuator according to the present invention.

[0015] FIG. 2 is a hydraulic circuit diagram of a hydraulic drive device HD to be mounted to the hydraulic excavator 1. In the following, a circuit of a hydraulic system for driving the boom cylinder 5, the arm cylinder 7, a first-attachment cylinder 24, and a second-attachment cylinder 25 will be described.

[0016] The hydraulic drive device HD includes a controller 20 for controlling the operations of the hydraulic actuators 5, 7, 24, 25, an operation lever 21 for transmitting an electric signal to the controller 20, a first hydraulic pump 17 for supplying the hydraulic oil to the hydraulic actuators 5, 7, 24, 25, a second hydraulic pump 18, a pilot pump 19 for supplying the hydraulic oil to drive the switching valves, respectively, an engine 52 for driving the first hydraulic pump 17, the second hydraulic pump 18, and the pilot pump 19, a control valve 16 for controlling the flow rate and direction of the hydraulic oil to be supplied to the hydraulic actuators 5, 7, 24, 25, and a hydraulic oil tank 26 for storing therein the hydraulic oil.

[0017] The operation lever (operation member) 21 is mounted in the operator's cab 10 where an operator gets on board, and includes an operation lever that can be tilted toward front, rear, left, and right, and a detection device configured to electrically detect an operation signal corresponding to the amount of tilting of the operation lever (lever operation amount). The operation lever 21 outputs the lever operation amount detected by the detection device to the controller 20 through an electrical wiring. That is, in the operation lever 21, the operations of the hydraulic actuators 5, 7, 24, 25 are made associated with the front and rear direction or the left-right direction of each of the levers, respectively.

[0018] The first hydraulic pump 17 and the second hydraulic pump 18 are driven by the engine 52, and discharge the hydraulic oil stored in the hydraulic oil tank 26 as the pressure oil toward the hydraulic actuators 5, 7, 24, 25.

[0019] Together with the first hydraulic pump 17 and the second hydraulic pump 18, the pilot pump 19 is driven by the engine 52 and discharges the hydraulic oil stored in the hydraulic oil tank 26 as the pressure oil toward switching valves 41, 42, 43.

[0020] In the present embodiment, solenoid proportional valves are exemplified as the switching valves 41, 42, 43, however, other types of valves may be used for them. Although not illustrated, the solenoid proportional valves are also used to switch the hydraulic actuators other than the boom cylinder 5, that is, the switching valves and the bleed-off valves for the arm cylinder 7, the first-attachment cylinder 24, and the second-attachment cylinder 25.

[0021] The control valve 16 is provided between the first hydraulic pump 17 and the second hydraulic pump 18 and the boom cylinder 5, the arm cylinder 7, the first-attachment cylinder 24, and the second-attachment cylinder 25. Upon receiving a command signal based on the operation lever 21 from the controller 20, the control valve 16 controls supply and discharge of the pressure oil to and from the boom cylinder 5, the arm cylinder 7, the first-attachment cylinder 24, and the second-attachment cylinder 25 or stop thereof.

[0022] The control valve 16 includes pump flow combiner valves 28, 29, 31, 32, 34, 35, 37, 38 for controlling the flow rate of the pressure oil supplied from each of the hydraulic pumps 17, 18, direction switching valves 27, 30, 33, 36 for switching the direction of the pressure oil supplied from the pump flow combiner valves 28, 29, 31, 32, 34, 35, 37, 38 to the cylinders 5, 7, 24, 25 and the pressure oil discharged from the cylinders 5, 7, 24, 25 to the hydraulic oil tank 26, and bleed-off valves 39, 40 for controlling the flow rate of the pressure oil discharged from the hydraulic pumps 17, 18 to the hydraulic oil tank 26.

[0023] In the control valve 16, a first pump line 53 connected to the first hydraulic pump 17 and a second pump line 54 connected to the second hydraulic pump 18 are formed. From the first pump line 53, a boom first-pump flow combiner valve 28, an arm first-pump flow combiner valve 31, a first-attachment first-pump flow combiner valve 34, and a second-attachment second-pump flow combiner valve 37 are connected in parallel. In the same manner, from the second pump line 54, a boom second-pump flow combiner valve 29, an arm second-pump flow combiner valve 32, an attachment second-pump flow combiner valve 35, and an attachment second-pump flow combiner valve 38 are connected in parallel.

[0024] The operations of the cylinders 5, 7, 24, 25 are basically the same from each other, and thus, in the following, an example where the boom cylinder 5 is operated will be described.

[0025] The boom first-pump flow combiner valve 28 is pilot-operated by the solenoid proportional valve 42, and controls the flow rate of the pressure oil supplied from the first hydraulic pump 17 and then let the pressure oil to flow to the direction switching valve 27 at the downstream. The boom second-pump flow combiner valve 29 is pilot-operated by the solenoid proportional valve 43, and controls the flow rate of the pressure oil supplied from the second hydraulic pump 18 and then let the pressure oil to flow to the direction switching valve 27 at the downstream. The controller 20 controls the flow rate of the pressure oil which passes through each of the pump flow combiner valves 28, 29, so as to control whether the pressure oil is to be supplied to the boom cylinder 5 only from the first hydraulic pump 17, the pressure oil is to be supplied thereto only from the second hydraulic pump 18, or the pressure oil from the first hydraulic pump 17 and that from the second hydraulic pump 18 are to be combined and supplied (switching control of a flow-combining state and a non-flow-combining state).

[0026] The hydraulic oil supplied from the hydraulic pumps 17, 18 through the pump flow combiner valves 28, 29 is supplied to the bottom side and the rod side of the boom cylinder 5 through the boom direction switching valve 27. Furthermore, the hydraulic oil discharged from the bottom side and the hydraulic oil discharged from the rod side are discharged to the hydraulic oil tank 26 through the boom direction switching valve 27. Thus, the boom cylinder 5 performs an extension and contraction operation.

[0027] The solenoid proportional valve 41 is connected to the pilot pump 19 by a pilot primary pressure pipe 55. Furthermore, the solenoid proportional valve 41 is connected to a pilot oil chamber provided on one end side of the boom direction switching valve 27 by a pilot secondary pressure pipe 56. In the same manner, the solenoid proportional valve 42 is connected to a pilot oil chamber provided at one end side of the boom first-pump flow combiner valve 28, and the solenoid proportional valve 43 is connected to a pilot oil chamber provided at one end side of the boom second-pump flow combiner valve 29.

[0028] In response to an operation made by the operator to tilt the operation lever 21 from the initial position (neutral position) to the operation position, the controller 20 outputs a command signal corresponding to the operation amount to the solenoid proportional valve 41 through a solenoid proportional valve command circuit 57. Then, in response to the command signal, the solenoid proportional valve 41 controls the pressure of the pilot pressure oil supplied from the pilot primary pressure pipe 55. Furthermore, the pilot pressure oil with its pressure having been controlled by the solenoid proportional valve 41 is supplied to or discharged from the pilot oil chamber of the boom direction switching valve 27 through the pilot secondary pressure pipe 56. In the same manner, the pilot pressure oil is supplied to or discharged from the pilot oil chamber of the boom first-pump flow combiner valve 28 and that of the boom second-pump flow combiner valve 29.

[0029] Thus, the boom first-pump flow combiner valve 28, the boom second-pump flow combiner valve 29, and the boom direction switching valve 27 are driven, whereby the pressure oil of the boom cylinder 5 is supplied or discharged.

[0030] Next, the functions of the controller 20 will be described. FIG. 3 is a functional block diagram of the controller 20. As illustrated in FIG. 3, the controller 20 includes a request flow rate calculation section 61, a pump dischargeable flow rate calculation section 63, and a valve control section 60.

[0031] The request flow rate calculation section 61 is configured to calculate an actuator request flow rate using a lever operation amount of the operation lever 21 as input, and outputs the actuator request flow rate to the valve control section 60. Specifically, the request flow rate calculation section 61 calculates the actuator request speed based on the lever operation amount, and calculates the actuator request flow rate based on the actuator request speed.

[0032] The pump dischargeable flow rate calculation section 63 is configured to calculate a pump dischargeable flow rate using the pump pressure received from pump pressure sensors 49, 50 as input, and outputs the pump dischargeable flow rate to the valve control section 60. Specifically, the pump dischargeable flow rate calculation section 63 calculates the maximum flow rate that the hydraulic pump can discharge within a torque limit value set based on the pump pressure.

[0033] The valve control section 60 is configured to calculate a command current to a solenoid proportional valve for each spool valve, using the actuator request flow rate, the pump dischargeable flow rate, and the boom pressure (actuator load pressure) from boom pressure sensors 44A, 44B as input, and outputs the command current to each solenoid proportional valve.

[0034] The valve control section 60 includes a priority pump recording section 64, a direction switching valve control section 66, a pump flow combiner valve control section 67, and a bleed-off valve control section 68.

[0035] In the priority pump recording section 64, primary pumps (first priority pumps) of the actuators 5, 7, 24, 25 are set, respectively. The primary pumps are set so as not to cause discomfort in a normal usage. For example, the primary pumps are set as follows. (1) Primary pumps are separately set for two frequently used actuators (ex. setting the first hydraulic pump 17 for the primary pump of the boom cylinder 5 and setting the second hydraulic pump 18 for the primary pump of the arm cylinder 7). (2) Primary pumps are separately set for two actuators frequently used in combined operations (ex. setting the first hydraulic pump 17 for the primary pump of the bucket cylinder 9 and setting the second hydraulic pump 18 for the primary pump of the arm cylinder 7). (3) An actuator which tends to have a high load pressure band during combined operations is not connected to a primary pump side of an actuator frequently used in operations which require the large flow rate (ex. not using the same hydraulic pump for a boom raising operation and a swinging operation). (4) The same hydraulic pump is used for actuators having mutually close load pressure bands (ex. using the first hydraulic pump 17 for a boom lowering operation and a bucket dumping operation).

[0036] The direction switching valve control section 66 is configured to determine which of a bottom side and a rod side of a cylinder is to be communicated with a pump line, based on the result of detection of the lever operation amount, and output a command signal to a solenoid proportional valve for a direction switching valve.

[0037] The pump flow combiner valve control section 67 is configured to calculate an actuator target flow rate, and a first-pump flow combiner valve target flow rate and a second-pump flow combiner valve target flow rate, respectively, which are details of the actuator target flow rate, based on the actuator request flow rate, the priority pump data, and the pump dischargeable flow rate. Then, the pump flow combiner valve control section 67 outputs a command signal to a solenoid proportional valve for a flow combiner valve so as to cause it to open in accordance with the target flow rate.

[0038] The bleed-off valve control section 68 is configured to output a command signal to a solenoid proportional valve for a bleed-off valve so as to discharge, if any, a pump flow rate of the pressure oil which is excessive relative to the actuator target flow rate.

[0039] Next, the control in the actual operations will be described as below.

[0040] In response to an operation of the operation lever 21 in the boom operation direction, the request flow rate calculation section 61 calculates a boom request flow rate (actuator request flow rate), and outputs the boom request flow rate to the valve control section 60.

[0041] The pump dischargeable flow rate calculation section 63 calculates a pump dischargeable flow rate of the first hydraulic pump 17 based on the value from the pump pressure sensor 49 and a pump dischargeable flow rate of the second hydraulic pump 18 based on the value from the pump pressure sensor 50, respectively, and outputs the pump dischargeable flow rates thus calculated to the valve control section 60.

[0042] The pump flow combiner valve control section 67 calculates a target flow rate of an actuator by the following method. (1) Calculate the total value of the actuator request flow rates of the actuators receiving the operation command signals. (2) Calculate the total value of the pump dischargeable flow rate of the first hydraulic pump 17 and that of the second hydraulic pump 18. (3) Divide the total value of the pump dischargeable flow rates by the total value of the actuator request flow rates to calculate a flow rate reduction rate. (4) Multiply the actuator request flow rate by the flow rate reduction rate to calculate an actuator target flow rate.

[0043] Next, the pump flow combiner valve control section 67 reads out the record of a boom primary pump from the priority pump recording section 64. The primary pump of the boom cylinder 5 recorded therein is the first hydraulic pump 17, and thus, firstly, the pump flow combiner valve control section 67 assigns the boom target flow rate to the boom first-pump flow combiner valve 28.

[0044] In the case where the operation lever 21 is operated in the arm operation direction as well, the pump flow combiner valve control section 67 calculates a target flow rate of the arm cylinder 7 in the same manner as the boom cylinder 5.

[0045] The pump flow combiner valve control section 67 reads out the record of an arm primary pump from the priority pump recording section 64. The primary pump of the arm cylinder 7 recorded therein is the second hydraulic pump 18, and thus, firstly, the pump flow combiner valve control section 67 assigns an arm target flow rate to the arm second-pump flow combiner valve 32.

[0046] Next, the pump flow combiner valve control section 67 calculates a primary pump suppliable flow rate for each of the boom cylinder 5 and the arm cylinder 7. Here, a boom primary pump suppliable flow rate is equal to the pump dischargeable flow rate of the first hydraulic pump 17, and an arm primary pump suppliable flow rate is equal to the pump dischargeable flow rate of the second hydraulic pump 18. In the case where the actuators having the records of the primary pumps which overlap from each other are operated at the same time, the target flow rates of the actuators having the higher priority is sequentially subtracted from the pump dischargeable flow rate in accordance with a predetermined priority order of the actuators, so as to calculate the primary pump suppliable flow rate of each actuator.

[0047] Next, in comparison with a conventional technique, how the flow rate, pressure, and throttling losses due to flow dividing change relative to the boom operation amount in the present invention will be described below.

[0048] Firstly, an example according to a conventional technique will be described. FIG. 4 illustrates how the flow rate, pressure, and throttling losses due to flow dividing change relative to a boom operation amount in a conventional technique. In the following, it is presupposed that the operation amount of both the arm 6 and the target flow rate of the arm cylinder 7 are constant.

[0049] FIG. 4(a) illustrates a boom target flow rate, a supply flow rate of a primary pump P1 (supply flow rate of the first hydraulic pump 17), and a supply flow rate of a secondary pump P2 (supply flow rate of the second hydraulic pump 18) relative to the boom operation amount. In the direction of increasing the boom operation amount, the boom target flow rate is zero until the boom operation amount reaches a certain operation amount. That is, no flow rate of the pressure oil is supplied to the boom cylinder 5 from the first hydraulic pump 17 nor the second hydraulic pump 18. When the boom operation amount reaches a certain operation amount (B1), the boom target flow rate starts to increase. At this point, the boom target flow rate is less than the primary pump suppliable flow rate, and thus all the pressure oil of the boom target flow rate can be supplied from the first hydraulic pump 17, which is the primary pump. Accordingly, the target flow rate of the boom first-pump flow combiner valve 28 is equal to the boom target flow rate while the target flow rate of the boom second-pump flow combiner valve 29 is set to zero. This causes the boom first-pump flow combiner valve 28 to open depending on the target flow rate, so that the pressure oil is supplied to the boom cylinder 5 through the boom direction switching valve 27.

[0050] FIG. 4(b) illustrates an arm target flow rate and an arm supply flow rate of the second hydraulic pump 18 relative to the boom operation amount. The arm target flow rate is less than the primary pump suppliable flow rate for the arm cylinder 7 which is not illustrated, and thus all the pressure oil of the arm target flow rate can be supplied from the second hydraulic pump 18 which is the primary pump. Accordingly, the target flow rate of the arm second-pump flow combiner valve 32 is equal to the arm target flow rate, and the target flow rate of the arm first-pump flow combiner valve 31 is set to zero. This cases the arm second-pump flow combiner valve 32 to open depending on the target flow rate, so that the pressure oil is supplied to the arm cylinder 7 through the arm direction switching valve 30.

[0051] FIG. 4(c) illustrates the first-pump pressure (pressure of the first hydraulic pump 17), the second-pump pressure (pressure of the second hydraulic pump 18), the boom pressure (pressure of the boom cylinder 5), and the arm pressure (pressure of the arm cylinder 7) relative to the boom operation amount. In this example, the boom pressure and the arm pressure are constant. In the state in which the boom cylinder 5 is supplied with the pressure oil from the first hydraulic pump 17 and the arm cylinder 7 is supplied with the pressure oil from the second hydraulic pump 18, that is, in a non-flow-combining state, the first-pump pressure is substantially equal to the boom pressure and the second-pump pressure is substantially equal to the arm pressure.

[0052] FIG. 4(d) illustrates throttling losses due to flow dividing relative to the boom operation amount. In the non-flow-combining state described above, no flow dividing occurs in each pump line, and thus a throttling loss due to flow dividing is zero.

[0053] When the boom operation amount increases to an operation amount B2, the flow rate supplied from the first hydraulic pump 17 becomes insufficient, and accordingly, a target flow rate by the amount of an insufficient flow rate is set in the boom second-pump flow combiner valve 29. This causes the boom second-pump flow combiner valve 29 to open depending on the target flow rate, so that the pressure oil thereof is combined with the one which has passed through the boom first-pump flow combiner valve 28 and supplied to the boom cylinder 5. At this time, as illustrated in FIG. 4(c), the second-pump pressure increases until it becomes equal to the first-pump pressure in order to supply the pressure oil to the boom cylinder 5. Furthermore, the opening of the arm second-pump flow combiner valve 32 is throttled so as to divide the flow into that for the boom cylinder 5 and that for the arm cylinder 7 in the second pump line 54. This causes throttling losses at the point where the boom operation amount reaches B2, as illustrated in FIG. 4(d).

[0054] As described above, in the conventional technique, when the flow state is switched from the non-flow-combining state to the flow-combining state or switched from the flow-combining state to the non-flow-combining state, there are cases where the control for changing the opening of a flow combiner valve has to be performed during the fluctuation of the pump discharge pressure, which may cause the change in the actual flow rates supplied to the actuators. For example, while an operation for increasing and decreasing the lever operation amount little by little is being performed and if the target flow rate at that time is close to the primary pump suppliable flow rate, the non-flow-combining state and the flow-combining state are frequently switched and thus the pump discharge pressure fluctuates repeatedly. This may cause operational shock, discomfort during operations, instable control, and the like. Here, the operation for increasing and decreasing the lever operation amount little by little refers to an operation such as sieving the sand placed in the bucket 8.

[0055] Next, the first embodiment of the present invention will be described with reference to FIG. 5 and FIG. 6. FIG. 5 illustrates how a boom target flow rate, a supply flow rate of the primary pump P1 (first hydraulic pump 17), and a supply flow rate of the secondary pump P2 (second hydraulic pump 18) change relative to the boom operation amount. For the changes in the arm flow rate, pressure, and throttling losses which are not illustrated in FIG. 5, in the same manner as those illustrated in FIG. 4(b), FIG. 4(c), and FIG. (d), respectively, an example in which the arm flow rate, the first-pump pressure, the boom pressure, and the arm pressure are constant and the second-pump pressure and the throttling losses vary depending on the switching between the non-flow-combining state and the flow-combining state will be described.

[0056] FIG. 6 illustrates a flowchart of a procedure of the control processing to be executed by the controller 20. The processing illustrated in FIG. 6 is started, for example, upon start of an engine, and is repeatedly executed at predetermined intervals (for example, every one millisecond). In FIG. 6, the processes (S1 to S5) for sequentially calculating a request flow rate, a target flow rate, and a primary pump suppliable flow rate based on an actuator (Act) operation amount has been described above, and thus the details thereof will not be referred below. In the following, the processes after S6, which are the features of the present invention, will be explained in detail.

[0057] In S6, the pump flow combiner valve control section 67 determines an ON / OFF state of a primary pump dischargeable flow rate correction flag. The state of the correction flag is set in S13, S14, which will be described later. An initial value of the correction flag is set to OFF. In the state of the correction flag being OFF, a primary pump suppliable flow rate is not corrected (S8), and in the state of the correction flag being ON, the primary pump suppliable flow rate is corrected to be lowered by a certain amount (predetermined amount) (S7 / flow rate adjustment control).

[0058] In S9, the pump flow combiner valve control section 67 determines whether a target flow rate exceeds the primary pump suppliable flow rate. If it does not exceed, for bringing the state to the non-flow-combining state, the pump flow combiner valve on the secondary pump side is closed (S11). If it exceeds, for bringing the state to the flow-combining state, the pump flow combiner valve on the secondary pump side is opened (S10). In S9, Yes is determined when the boom operation amount in FIG. 5(a) exceeds X1.

[0059] In the flow-combining state, in S12, whether a primary pump insufficient flow rate falls within a range of a secondary pump suppliable flow rate is determined. If it falls within the range, in S13, the correction flag is turned ON. If it is not within the range or if the non-flow-combining state is determined, the correction flag is turned OFF.

[0060] Referring to FIG. 5, how a flow rate changes relative to a boom operation amount in the case where the control flow described above is applied will be described. FIG. 5(a) illustrates an example in which the boom operation amount increases, and FIG. 5(b) illustrates an example in which the boom operation amount decreases. In FIG. 5, Q1 represents a primary pump suppliable flow rate and Q0 represents a primary pump suppliable flow rate after correction.

[0061] In FIG. 5(a), the boom operation amount increases from zero (initial position of the operation lever 21), but a boom target flow rate does not exceed the primary pump suppliable flow rate Q1 until the operation amount reaches X1 (first position of the operation lever 21), during which No is determined in S9 of the control flow and a non-flow-combining state is established. When the boom operation amount exceeds X1, the boom target flow rate exceeds the primary pump suppliable flow rate Q1 (maximum flow rate of the primary pump), at which Yes is determined in S9 of the control flow and the state is switched to the flow-combining state. Furthermore, the correction flag is turned ON and the primary pump suppliable flow rate is lowered to Q0 apparently. As a result, the first-pump supply flow rate (supply flow rate of the first hydraulic pump 17) once decreases when the boom operation amount exceeds X1, and then becomes constant, while the second-pump supply flow rate (supply flow rate of the second hydraulic pump 18) increases as the target flow rate increases. The value obtained by Q1-Q0(=ΔQ) illustrated in in FIG. 5(a) corresponds to the "predetermined amount" according to the present invention.

[0062] Apparently lowering the primary pump suppliable flow rate causes the primary pump insufficient flow rate to increase apparently. If the insufficient flow rate falls within the range of the secondary pump suppliable flow rate, the correction flag ON state is maintained. On the other hand, when the boom operation amount reaches X2, the insufficient flow rate exceeds the range of the secondary pump suppliable flow rate, at which NO is determined in S12 of the control flow and the correction flag is turned OFF. As a result, the primary pump suppliable flow rate returns to Q1 so as to increase the first-pump suppliable flow rate, and also the second-pump suppliable flow rate decreases as the insufficient flow rate decreases. At this point of time, the secondary pump suppliable flow rate becomes ample, which allows the second-pump supply amount to also increase as the boom operation amount further increases. With the configuration described above, the correction for reducing the primary pump suppliable flow rate is cancelled when the target flow rate becomes close to the limit of the total value of the pump suppliable flow rates. This enables the total flow rate that could be originally supplied to the boom cylinder 5 to be reliably supplied thereto from the first hydraulic pump 17 and the second hydraulic pump 18.

[0063] Next, an example in which the boom operation amount decreases as illustrated in FIG. 5(b) will be described. When the boom operation amount decreases from the maximum (any position beyond X1 at which the operation lever 21 is in the first position) and then reaches X2, the insufficient flow rate falls within the range of the secondary pump suppliable flow rate, and thus the correction flag is turned ON. Even if the boom operation amount further decreases and falls below X1 (first position), the flow-combining state is maintained. When the boom operation amount further decreases and reaches X0 (second position at which the operation lever 21 is closer to the initial position than the first position) and falls below X0, the boom target flow rate falls below the primary pump suppliable flow rate Q0 after correction, at which No is determined in S9 of the control flow and the flow state is switched to the non-flow-combining state. At the same time, the correction flag is switched to OFF.

[0064] As described above, in the case of increase in the boom operation amount, the flow state is switched from the non-flow-combining state to the flow-combining state when the boom operation amount reaches X1, on the other hand, in the case of decrease in the boom operation amount, it is switched when the boom operation amount returns to X0. For example, even if an operation of increasing and decreasing the boom operation amount little by little when the boom operation amount is around X1, the flow-combining state is maintained without being switched between the non-flow-combining state and the flow-combining state as long as the boom operation amount does not return to X0. This can prevent operational shock, discomfort during operations, instable control, and the like which are caused by repeated fluctuation in the pump discharge pressure.

[0065] The correction amount (predetermined amount) of the primary suppliable flow rate is set within a range of the secondary suppliable flow rate. The smaller the correction amount is, the more the frequency of switching between the non-flow-combining state and the flow-combining state increases, which enables reduction in throttling losses due to flow dividing. On the other hand, the larger the correction amount is, the more the frequency of switching between the non-flow-combining state and the flow-combining state decreased, which enables improvement in the operability. Preferably, for example, the correction amount is set to any amount in a range between about 1 / 4 to 1 / 2 of the secondary suppliable flow rate (maximum suppliable flow rate of the second hydraulic pump 18).(Modified example)

[0066] FIG. 7 illustrates a relation between a boom operation amount and a flow rate according to a modified example. As illustrated in FIG. 7, in the modified example, the correction amount for the boom operation amount is not made constant but varied. Specifically, the first-pump supply flow rate gradually decreases from a point beyond the boom operation volume X1, and at the same time, the second-pump supply flow rate gradually increases. Furthermore, when the boom operation amount reaches X2, the insufficient flow rate becomes equal to the secondary pump suppliable flow rate, and thereafter, the correction amount gradually decreases so as to prevent the insufficient flow rate from increasing even if the target flow rate increases. As a result, both the first-pump supply flow rate and the second-pump supply flow rate increase. With this configuration, the supply flow rate from each pump changes smoothly so that the operability can be further improved. Here, it is obvious that, in the case of making a correction amount vary, the primary pump insufficient flow rate calculated in accordance with the correction falls within the secondary pump suppliable flow rate.(Second embodiment)

[0067] Next, the second embodiment of the present invention will be described with reference to FIG. 8. FIG. 8 illustrates a flowchart of a procedure of the processing to be executed by the controller according to the second embodiment. FIG. 8 does not illustrate the details of the processes in S102 to S108 as they are the same as those in S2 to S8 of FIG. 6.

[0068] In the second embodiment, in S110, whether the load pressure on a target actuator (Act) is greater than the load pressure on all the other actuators (Act) which are supplied with the pressure oil from the secondary pump of the target actuator. For example, in the first embodiment, in the case where the boom cylinder 5 is the target actuator, the other actuator which is supplied with the pressure oil from the second hydraulic pump 18 (second-pump) which is the secondary pump of the boom cylinder 5 is the arm cylinder 7. In this example, Yes is determined in S110 as the load pressure on the boom cylinder 5 is greater than the load pressure on the arm cylinder 7. After S111, the same processes as those in S10, S12, and S13 according to the first embodiment are carried out in this order. That is, the primary pump suppliable flow rate is corrected to be reduced by a certain amount (predetermined amount) (flow rate adjustment control).

[0069] On the other hand, if No is determined in S110, in other words, when the load pressure on the boom cylinder 5 is smaller than the load pressure on the arm cylinder 7, the discharge pressure of the second hydraulic pump 18 (second-pump) does not change even while the boom cylinder 5 is in a flow-combining state. In this case, setting the correction flag of the primary pump suppliable flow rate to OFF (S116) allow the non-flow-combining state and the flow-combining state to be positively switched, which results in the reduction in throttling losses due to flow dividing.(Third embodiment)

[0070] Next, the third embodiment of the present invention will be described with reference to FIG. 9. FIG. 9 illustrates a flowchart of a procedure of the processing to be executed by the controller according to the third embodiment. FIG. 9 does not illustrate the details of the processes in S202 to S208 as they are the same as those in S2 to S8 of FIG. 6.

[0071] In the third embodiment, in the case where it is determined in S210 that the load pressure on a target actuator (Act) is greater than the load pressure on all the other actuators (Act) which are supplied with the pressure oil from the secondary pump of the target actuator, whether the load pressure on the target actuator (in this example, boom cylinder 5) is more than a certain threshold is determined in S211. The certain threshold (limit value) is a value at which a pump displacement is reduced by horsepower control when the first hydraulic pump 17 (first-pump) and the second hydraulic pump 18 (second-pump) have the same pressure, and in the present embodiment, for example, it is set to 15MPa. That is, when the flow-combining state is established with the load pressure exceeding this threshold value and the first-pump and the second-pump having the same pressure, the pump dischargeable flow rate decreases and thus the supply flow rate to the actuator decreases.

[0072] If the load pressure on the boom cylinder 5 is equal to or less than this threshold, Yes is determined in S211, and the processes after S212 are the same as those in the first embodiment. If the load pressure is more than this threshold, No is determined in S211 and the flow-combining state for the boom is not established (S212). Increasing the operation amount to increase the supply flow rate to the actuator may lead to decrease in the supply flow rate on the contrary, which, however, can be prevented in the configuration described above, and thus discomfort during operations can be prevented.

[0073] In the embodiments described above, the pump flow combiner valves are provided separately from the direction switching valves, however, the direction switching valves (as the pump flow combiner valves in the present invention) may be provided in the pump lines, respectively, to control the supply flow rates from the pumps and combine them at the downstream of the direction switching valves. That is, the flow combiner valves 28, 29 may be used as the direction switching valves, without providing the direction switching valve 27 separately.

[0074] Furthermore, in each of the embodiments described above, the examples in which the target flow rate varies depending on the operation amount have been described, however, the present invention can be also advantageously applied in the case where the target flow rate changes for other factors. For example, in the autonomous control, the request flow rate is calculated directly based on the request speed of the actuator rather than the operation amount, and the target flow rate is calculated based on the request flow rate. Even in the case where the request flow rate does not change, change in the total value of the pump dischargeable flow rates may cause change in the target flow rate.

[0075] Still further, in each of the embodiments described above, the example of a combined operation, in which two or more actuators are driven, has been described, however, the present invention is also advantageous even in the case of a single operation, in which a single actuator is driven. The present invention is particularly advantageous in a situation involving a half-lever operation for, such as finishing, regardless of whether a single operation is performed or a combine operation is performed.

[0076] The embodiments described above are examples for explaining the present invention, and are not intended to limit the scope of the present invention only thereto. Those skilled in the art exploit the present invention in various ways within the scope of the concept of the present invention without departing from it.REFERENCE SIGNS LIST

[0077] 1... construction machine (work machine) 2... upperstructure 3... undercarriage 4... boom 5... boom cylinder (first hydraulic actuator) 6... arm 7... arm cylinder (second hydraulic actuator) 8... bucket 9... bucket cylinder 10... operator's cab 16... control valve 17... first hydraulic pump 18... second hydraulic pump 19... pilot pump 20... controller 21... operation lever (operation member) 24... first-attachment cylinder 25... second-attachment cylinder 26... hydraulic oil tank 27... boom direction switching valve 28... boom first-pump flow combiner valve (flow combiner valve) 29... boom second-pump flow combiner valve (flow combiner valve) 30... arm direction switching valve 31... arm first-pump flow combiner valve 32... arm second-pump flow combiner valve 33... first-attachment direction switching valve 34... first-attachment first-pump flow combiner valve 35... first-attachment second-pump flow combiner valve 36... second-attachment direction switching valve 37... second-attachment first-pump flow combiner valve 38... second-attachment second-pump flow combiner valve 39... first-pump bleed-off valve 40... second-pump bleed-off valve 41... solenoid proportional valve for boom direction switching valve 42... solenoid proportional valve for boom first-pump flow combiner valve 43... solenoid proportional valve for boom second-pump flow combiner valve 44A...boom rod pressure sensor 44B... boom bottom pressure sensor 45A...arm rod pressure sensor 45B...arm bottom pressure sensor 46A...first-attachment rod pressure sensor 46B...first-attachment bottom pressure sensor 47A...second-attachment rod pressure sensor 47B...second-attachment bottom pressure sensor 48... mode selection dial 49... first pump pressure sensor 50... second pump pressure sensor 52... engine 53... first pump line 54... second pump line 55... pilot primary pressure pipe 56... pilot secondary pressure pipe 57... solenoid proportional valve command circuit 60... valve control section 61... request flow rate calculation section 63... pump dischargeable flow rate calculation section 64... priority pump recording section 66... direction switching valve control section 67... pump flow combiner valve control section 68... bleed-off valve control section HD... hydraulic drive device

Examples

first embodiment

(First embodiment)

[0012]Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013]FIG. 1 is a side view illustrating an appearance of a hydraulic excavator which is an example of a work machine according to the present invention. In FIG. 1, a hydraulic excavator 1 includes an undercarriage 3, an upperstructure 2 that is provided to the undercarriage 3 so as to swing, and an operator's cab 10. The upperstructure 2 is provided with a front working device including a boom 4, an arm 6, and a bucket 8. The boom 4, the arm 6, and the bucket 8 are driven by a boom cylinder 5, an arm cylinder 7, and a bucket cylinder 9, respectively, which are hydraulic actuators. Although not illustrated, an attachment may be mounted to the hydraulic excavator 1.

[0014]Here, the boom cylinder 5 corresponds to a first hydraulic actuator according to the present invention, and the arm cylinder 7 corresponds to a second hydraulic actuator according to the present ...

second embodiment

(Second embodiment)

[0067]Next, the second embodiment of the present invention will be described with reference to FIG. 8. FIG. 8 illustrates a flowchart of a procedure of the processing to be executed by the controller according to the second embodiment. FIG. 8 does not illustrate the details of the processes in S102 to S108 as they are the same as those in S2 to S8 of FIG. 6.

[0068]In the second embodiment, in S110, whether the load pressure on a target actuator (Act) is greater than the load pressure on all the other actuators (Act) which are supplied with the pressure oil from the secondary pump of the target actuator. For example, in the first embodiment, in the case where the boom cylinder 5 is the target actuator, the other actuator which is supplied with the pressure oil from the second hydraulic pump 18 (second-pump) which is the secondary pump of the boom cylinder 5 is the arm cylinder 7. In this example, Yes is determined in S110 as the load pressure on the boom cylinder 5 ...

third embodiment

(Third embodiment)

[0070]Next, the third embodiment of the present invention will be described with reference to FIG. 9. FIG. 9 illustrates a flowchart of a procedure of the processing to be executed by the controller according to the third embodiment. FIG. 9 does not illustrate the details of the processes in S202 to S208 as they are the same as those in S2 to S8 of FIG. 6.

[0071]In the third embodiment, in the case where it is determined in S210 that the load pressure on a target actuator (Act) is greater than the load pressure on all the other actuators (Act) which are supplied with the pressure oil from the secondary pump of the target actuator, whether the load pressure on the target actuator (in this example, boom cylinder 5) is more than a certain threshold is determined in S211. The certain threshold (limit value) is a value at which a pump displacement is reduced by horsepower control when the first hydraulic pump 17 (first-pump) and the second hydraulic pump 18 (second-pump)...

TECHNICAL FIELD

[0001] The present invention relates to work machines such hydraulic excavators.BACKGROUND ART

[0002] For a typical hydraulic system used in a work machine such as a hydraulic excavator, there have been an actuator that is powered by one of two hydraulic pumps to work and an actuator that is powered by both the hydraulic pumps to work. For the purpose of reducing throttling losses due to flow dividing, a priority order of the two hydraulic pumps is often set in advance for an actuator which is supplied with the power from both the hydraulic pumps to work.

[0003] In the hydraulic system of the type as described above, for example, one of the hydraulic pumps to which the first priority is assigned is set as a primary pump and the other one of the hydraulic pumps to which the second priority is assigned is set as a secondary pump, and when a target flow rate falls within the range of the flow rate that can be supplied by the primary pump, the hydraulic oil is supplied from only the primary pump to the actuator, while the hydraulic oil is supplied from the secondary pump to the actuator only when the target flow rate exceeds the flow rate that can be supplied by the primary pump.

[0004] In this system, the discharge pressure of the secondary pump varies depending on the presence or absence of flow combining, and accordingly, in the case where the pressure of an actuator which is a flow-combining target is greater than the pressure of other actuators, if a target flow rate increases or decreases around an upper limit of the suppliable flow rate of the primary pump, repeated fluctuation in the discharge pressure caused by switching between the flow-combining state and the non-flow-combining state may cause operational shock, discomfort during operations, instable control, and the like.

[0005] For this problem, in Patent Literature 1, when the drive pressure, which is a difference between the rod-side pressure and the cap-side pressure of the hydraulic cylinder (actuator), is equal to or less than a specified value, the first hydraulic pump and the second hydraulic pump are controlled to be in a connected state so as to suppress operational shock caused by switching between the connected state (flow-combining state) and a disconnected state (non-flow-combining state).CITATION LISTPATENT LITERATURE

[0006] Patent Literature 1: JP-B-6145229SUMMARY OF INVENTIONTECHNICAL PROBLEM

[0007] In Patent Literature 1, however, the controller controls the connection state of the pumps depending on whether a request flow rate is equal to or more than a threshold value, or whether the drive pressure is equal to or more than a threshold value, and in this configuration, increase and decrease in the request flow rate and the drive pressure around the threshold values may cause repeated switching between the flow-combining state and the non-flow-combining state. This repeated switching between the flow-combining state and the non-flow-combining state in the state where the drive pressure is high may lead to a risk that the operator feels discomfort during operations, or a risk of instable control. Furthermore, even in a flow rate condition not requiring flow combining, the flow-combining state is maintained if the drive pressure is equal to or less than the specified value. This may lead to a risk of unnecessary throttling losses while a combined operation (for example, the boom and arm are operated in the air at the same time) is performed in an aerial operation of the work machine, and thus a further risk of deterioration in the fuel efficiency.

[0008] An object of the present invention is to provide a work machine capable of suppressing shock caused by frequent switching between a non-flow-combining state and a flow-combining state of pressure oil from two hydraulic pumps, while reducing throttling losses due to flow dividing.SOLUTION TO PROBLEM

[0009] In order to achieve the object described above, an aspect of the present invention provides a work machine comprising: a hydraulic drive device including a first hydraulic pump, a second hydraulic pump, a first hydraulic actuator driven by a pressure oil supplied from the first hydraulic pump, and a flow combiner valve for combining the pressure oil supplied from the first hydraulic pump and a pressure oil supplied from the second hydraulic pump to communicate a pressured oil thus combined to the first hydraulic actuator; an operation member to be operated by an operator; and a controller configured to control the hydraulic drive device based on an operation amount of the operation member, the controller being configured to: in a case where the operation member is operated in a direction of increasing the operation amount, until the operation member reaches a first position from an initial position, control the flow combiner valve so as to supply the pressure oil from the first hydraulic pump to the first hydraulic actuator (non-flow-combining state); in a case where the operation member is operated in a direction of increasing the operation amount beyond the first position, control the flow combiner valve so as to combine the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump and supply the pressure oil thus combined to the first hydraulic actuator in response to increase in the operation amount (flow-combining state); and in a case where the operation member is operated in a direction of decreasing the operation amount from any position beyond the first position and the operation amount reaches a second position closer to the initial position than the first position, control the flow combiner valve so as to cancel a flow-combining state in which the pressure oil from the first hydraulic pump is combined with the pressure oil from the second hydraulic pump, and supply the pressure oil from the first hydraulic pump to the first hydraulic actuator in response to decrease in the operation amount (non-flow-combining state).ADVANTAGEOUS EFFECTS OF INVENTION

[0010] According to the work machine of the present invention, it is possible to suppress shock caused by frequent switching between a non-flow-combining state and a flow-combining state of pressure oil from two hydraulic pumps while reducing throttling losses due to flow dividing. The problems, configurations, and advantageous effects other than those described above will be clarified by explanation of the embodiments below.BRIEF DESCRIPTION OF DRAWINGS

[0011] [FIG. 1] FIG. 1 is a side view illustrating the appearance of a hydraulic excavator. [FIG. 2] FIG. 2 is a hydraulic circuit diagram of a hydraulic system. [FIG. 3] FIG. 3 is a functional block diagram of a controller. [FIG. 4] FIG. 4 illustrates how a flow rate, pressure, and throttling losses due to flow dividing change relative to a boom operation amount in a conventional technique. [FIG. 5] FIG. 5 illustrates how a flow rate changes relative to a boom operation amount in the first embodiment. [FIG. 6] FIG. 6 illustrates a flowchart of a procedure of control processing to be executed by a controller. [FIG. 7] FIG. 7 illustrates how a flow rate changes relative to a boom operation amount in a modified example. [FIG. 8] FIG. 8 illustrates a flowchart of a procedure of control processing to be executed by a controller according to the second embodiment. [FIG. 9] FIG. 9 illustrates a flowchart of a procedure of control processing to be executed by a controller according to the third embodiment. DESCRIPTION OF EMBODIMENTS(First embodiment)

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] FIG. 1 is a side view illustrating an appearance of a hydraulic excavator which is an example of a work machine according to the present invention. In FIG. 1, a hydraulic excavator 1 includes an undercarriage 3, an upperstructure 2 that is provided to the undercarriage 3 so as to swing, and an operator's cab 10. The upperstructure 2 is provided with a front working device including a boom 4, an arm 6, and a bucket 8. The boom 4, the arm 6, and the bucket 8 are driven by a boom cylinder 5, an arm cylinder 7, and a bucket cylinder 9, respectively, which are hydraulic actuators. Although not illustrated, an attachment may be mounted to the hydraulic excavator 1.

[0014] Here, the boom cylinder 5 corresponds to a first hydraulic actuator according to the present invention, and the arm cylinder 7 corresponds to a second hydraulic actuator according to the present invention.

[0015] FIG. 2 is a hydraulic circuit diagram of a hydraulic drive device HD to be mounted to the hydraulic excavator 1. In the following, a circuit of a hydraulic system for driving the boom cylinder 5, the arm cylinder 7, a first-attachment cylinder 24, and a second-attachment cylinder 25 will be described.

[0016] The hydraulic drive device HD includes a controller 20 for controlling the operations of the hydraulic actuators 5, 7, 24, 25, an operation lever 21 for transmitting an electric signal to the controller 20, a first hydraulic pump 17 for supplying the hydraulic oil to the hydraulic actuators 5, 7, 24, 25, a second hydraulic pump 18, a pilot pump 19 for supplying the hydraulic oil to drive the switching valves, respectively, an engine 52 for driving the first hydraulic pump 17, the second hydraulic pump 18, and the pilot pump 19, a control valve 16 for controlling the flow rate and direction of the hydraulic oil to be supplied to the hydraulic actuators 5, 7, 24, 25, and a hydraulic oil tank 26 for storing therein the hydraulic oil.

[0017] The operation lever (operation member) 21 is mounted in the operator's cab 10 where an operator gets on board, and includes an operation lever that can be tilted toward front, rear, left, and right, and a detection device configured to electrically detect an operation signal corresponding to the amount of tilting of the operation lever (lever operation amount). The operation lever 21 outputs the lever operation amount detected by the detection device to the controller 20 through an electrical wiring. That is, in the operation lever 21, the operations of the hydraulic actuators 5, 7, 24, 25 are made associated with the front and rear direction or the left-right direction of each of the levers, respectively.

[0018] The first hydraulic pump 17 and the second hydraulic pump 18 are driven by the engine 52, and discharge the hydraulic oil stored in the hydraulic oil tank 26 as the pressure oil toward the hydraulic actuators 5, 7, 24, 25.

[0019] Together with the first hydraulic pump 17 and the second hydraulic pump 18, the pilot pump 19 is driven by the engine 52 and discharges the hydraulic oil stored in the hydraulic oil tank 26 as the pressure oil toward switching valves 41, 42, 43.

[0020] In the present embodiment, solenoid proportional valves are exemplified as the switching valves 41, 42, 43, however, other types of valves may be used for them. Although not illustrated, the solenoid proportional valves are also used to switch the hydraulic actuators other than the boom cylinder 5, that is, the switching valves and the bleed-off valves for the arm cylinder 7, the first-attachment cylinder 24, and the second-attachment cylinder 25.

[0021] The control valve 16 is provided between the first hydraulic pump 17 and the second hydraulic pump 18 and the boom cylinder 5, the arm cylinder 7, the first-attachment cylinder 24, and the second-attachment cylinder 25. Upon receiving a command signal based on the operation lever 21 from the controller 20, the control valve 16 controls supply and discharge of the pressure oil to and from the boom cylinder 5, the arm cylinder 7, the first-attachment cylinder 24, and the second-attachment cylinder 25 or stop thereof.

[0022] The control valve 16 includes pump flow combiner valves 28, 29, 31, 32, 34, 35, 37, 38 for controlling the flow rate of the pressure oil supplied from each of the hydraulic pumps 17, 18, direction switching valves 27, 30, 33, 36 for switching the direction of the pressure oil supplied from the pump flow combiner valves 28, 29, 31, 32, 34, 35, 37, 38 to the cylinders 5, 7, 24, 25 and the pressure oil discharged from the cylinders 5, 7, 24, 25 to the hydraulic oil tank 26, and bleed-off valves 39, 40 for controlling the flow rate of the pressure oil discharged from the hydraulic pumps 17, 18 to the hydraulic oil tank 26.

[0023] In the control valve 16, a first pump line 53 connected to the first hydraulic pump 17 and a second pump line 54 connected to the second hydraulic pump 18 are formed. From the first pump line 53, a boom first-pump flow combiner valve 28, an arm first-pump flow combiner valve 31, a first-attachment first-pump flow combiner valve 34, and a second-attachment second-pump flow combiner valve 37 are connected in parallel. In the same manner, from the second pump line 54, a boom second-pump flow combiner valve 29, an arm second-pump flow combiner valve 32, an attachment second-pump flow combiner valve 35, and an attachment second-pump flow combiner valve 38 are connected in parallel.

[0024] The operations of the cylinders 5, 7, 24, 25 are basically the same from each other, and thus, in the following, an example where the boom cylinder 5 is operated will be described.

[0025] The boom first-pump flow combiner valve 28 is pilot-operated by the solenoid proportional valve 42, and controls the flow rate of the pressure oil supplied from the first hydraulic pump 17 and then let the pressure oil to flow to the direction switching valve 27 at the downstream. The boom second-pump flow combiner valve 29 is pilot-operated by the solenoid proportional valve 43, and controls the flow rate of the pressure oil supplied from the second hydraulic pump 18 and then let the pressure oil to flow to the direction switching valve 27 at the downstream. The controller 20 controls the flow rate of the pressure oil which passes through each of the pump flow combiner valves 28, 29, so as to control whether the pressure oil is to be supplied to the boom cylinder 5 only from the first hydraulic pump 17, the pressure oil is to be supplied thereto only from the second hydraulic pump 18, or the pressure oil from the first hydraulic pump 17 and that from the second hydraulic pump 18 are to be combined and supplied (switching control of a flow-combining state and a non-flow-combining state).

[0026] The hydraulic oil supplied from the hydraulic pumps 17, 18 through the pump flow combiner valves 28, 29 is supplied to the bottom side and the rod side of the boom cylinder 5 through the boom direction switching valve 27. Furthermore, the hydraulic oil discharged from the bottom side and the hydraulic oil discharged from the rod side are discharged to the hydraulic oil tank 26 through the boom direction switching valve 27. Thus, the boom cylinder 5 performs an extension and contraction operation.

[0027] The solenoid proportional valve 41 is connected to the pilot pump 19 by a pilot primary pressure pipe 55. Furthermore, the solenoid proportional valve 41 is connected to a pilot oil chamber provided on one end side of the boom direction switching valve 27 by a pilot secondary pressure pipe 56. In the same manner, the solenoid proportional valve 42 is connected to a pilot oil chamber provided at one end side of the boom first-pump flow combiner valve 28, and the solenoid proportional valve 43 is connected to a pilot oil chamber provided at one end side of the boom second-pump flow combiner valve 29.

[0028] In response to an operation made by the operator to tilt the operation lever 21 from the initial position (neutral position) to the operation position, the controller 20 outputs a command signal corresponding to the operation amount to the solenoid proportional valve 41 through a solenoid proportional valve command circuit 57. Then, in response to the command signal, the solenoid proportional valve 41 controls the pressure of the pilot pressure oil supplied from the pilot primary pressure pipe 55. Furthermore, the pilot pressure oil with its pressure having been controlled by the solenoid proportional valve 41 is supplied to or discharged from the pilot oil chamber of the boom direction switching valve 27 through the pilot secondary pressure pipe 56. In the same manner, the pilot pressure oil is supplied to or discharged from the pilot oil chamber of the boom first-pump flow combiner valve 28 and that of the boom second-pump flow combiner valve 29.

[0029] Thus, the boom first-pump flow combiner valve 28, the boom second-pump flow combiner valve 29, and the boom direction switching valve 27 are driven, whereby the pressure oil of the boom cylinder 5 is supplied or discharged.

[0030] Next, the functions of the controller 20 will be described. FIG. 3 is a functional block diagram of the controller 20. As illustrated in FIG. 3, the controller 20 includes a request flow rate calculation section 61, a pump dischargeable flow rate calculation section 63, and a valve control section 60.

[0031] The request flow rate calculation section 61 is configured to calculate an actuator request flow rate using a lever operation amount of the operation lever 21 as input, and outputs the actuator request flow rate to the valve control section 60. Specifically, the request flow rate calculation section 61 calculates the actuator request speed based on the lever operation amount, and calculates the actuator request flow rate based on the actuator request speed.

[0032] The pump dischargeable flow rate calculation section 63 is configured to calculate a pump dischargeable flow rate using the pump pressure received from pump pressure sensors 49, 50 as input, and outputs the pump dischargeable flow rate to the valve control section 60. Specifically, the pump dischargeable flow rate calculation section 63 calculates the maximum flow rate that the hydraulic pump can discharge within a torque limit value set based on the pump pressure.

[0033] The valve control section 60 is configured to calculate a command current to a solenoid proportional valve for each spool valve, using the actuator request flow rate, the pump dischargeable flow rate, and the boom pressure (actuator load pressure) from boom pressure sensors 44A, 44B as input, and outputs the command current to each solenoid proportional valve.

[0034] The valve control section 60 includes a priority pump recording section 64, a direction switching valve control section 66, a pump flow combiner valve control section 67, and a bleed-off valve control section 68.

[0035] In the priority pump recording section 64, primary pumps (first priority pumps) of the actuators 5, 7, 24, 25 are set, respectively. The primary pumps are set so as not to cause discomfort in a normal usage. For example, the primary pumps are set as follows. (1) Primary pumps are separately set for two frequently used actuators (ex. setting the first hydraulic pump 17 for the primary pump of the boom cylinder 5 and setting the second hydraulic pump 18 for the primary pump of the arm cylinder 7). (2) Primary pumps are separately set for two actuators frequently used in combined operations (ex. setting the first hydraulic pump 17 for the primary pump of the bucket cylinder 9 and setting the second hydraulic pump 18 for the primary pump of the arm cylinder 7). (3) An actuator which tends to have a high load pressure band during combined operations is not connected to a primary pump side of an actuator frequently used in operations which require the large flow rate (ex. not using the same hydraulic pump for a boom raising operation and a swinging operation). (4) The same hydraulic pump is used for actuators having mutually close load pressure bands (ex. using the first hydraulic pump 17 for a boom lowering operation and a bucket dumping operation).

[0036] The direction switching valve control section 66 is configured to determine which of a bottom side and a rod side of a cylinder is to be communicated with a pump line, based on the result of detection of the lever operation amount, and output a command signal to a solenoid proportional valve for a direction switching valve.

[0037] The pump flow combiner valve control section 67 is configured to calculate an actuator target flow rate, and a first-pump flow combiner valve target flow rate and a second-pump flow combiner valve target flow rate, respectively, which are details of the actuator target flow rate, based on the actuator request flow rate, the priority pump data, and the pump dischargeable flow rate. Then, the pump flow combiner valve control section 67 outputs a command signal to a solenoid proportional valve for a flow combiner valve so as to cause it to open in accordance with the target flow rate.

[0038] The bleed-off valve control section 68 is configured to output a command signal to a solenoid proportional valve for a bleed-off valve so as to discharge, if any, a pump flow rate of the pressure oil which is excessive relative to the actuator target flow rate.

[0039] Next, the control in the actual operations will be described as below.

[0040] In response to an operation of the operation lever 21 in the boom operation direction, the request flow rate calculation section 61 calculates a boom request flow rate (actuator request flow rate), and outputs the boom request flow rate to the valve control section 60.

[0041] The pump dischargeable flow rate calculation section 63 calculates a pump dischargeable flow rate of the first hydraulic pump 17 based on the value from the pump pressure sensor 49 and a pump dischargeable flow rate of the second hydraulic pump 18 based on the value from the pump pressure sensor 50, respectively, and outputs the pump dischargeable flow rates thus calculated to the valve control section 60.

[0042] The pump flow combiner valve control section 67 calculates a target flow rate of an actuator by the following method. (1) Calculate the total value of the actuator request flow rates of the actuators receiving the operation command signals. (2) Calculate the total value of the pump dischargeable flow rate of the first hydraulic pump 17 and that of the second hydraulic pump 18. (3) Divide the total value of the pump dischargeable flow rates by the total value of the actuator request flow rates to calculate a flow rate reduction rate. (4) Multiply the actuator request flow rate by the flow rate reduction rate to calculate an actuator target flow rate.

[0043] Next, the pump flow combiner valve control section 67 reads out the record of a boom primary pump from the priority pump recording section 64. The primary pump of the boom cylinder 5 recorded therein is the first hydraulic pump 17, and thus, firstly, the pump flow combiner valve control section 67 assigns the boom target flow rate to the boom first-pump flow combiner valve 28.

[0044] In the case where the operation lever 21 is operated in the arm operation direction as well, the pump flow combiner valve control section 67 calculates a target flow rate of the arm cylinder 7 in the same manner as the boom cylinder 5.

[0045] The pump flow combiner valve control section 67 reads out the record of an arm primary pump from the priority pump recording section 64. The primary pump of the arm cylinder 7 recorded therein is the second hydraulic pump 18, and thus, firstly, the pump flow combiner valve control section 67 assigns an arm target flow rate to the arm second-pump flow combiner valve 32.

[0046] Next, the pump flow combiner valve control section 67 calculates a primary pump suppliable flow rate for each of the boom cylinder 5 and the arm cylinder 7. Here, a boom primary pump suppliable flow rate is equal to the pump dischargeable flow rate of the first hydraulic pump 17, and an arm primary pump suppliable flow rate is equal to the pump dischargeable flow rate of the second hydraulic pump 18. In the case where the actuators having the records of the primary pumps which overlap from each other are operated at the same time, the target flow rates of the actuators having the higher priority is sequentially subtracted from the pump dischargeable flow rate in accordance with a predetermined priority order of the actuators, so as to calculate the primary pump suppliable flow rate of each actuator.

[0047] Next, in comparison with a conventional technique, how the flow rate, pressure, and throttling losses due to flow dividing change relative to the boom operation amount in the present invention will be described below.

[0048] Firstly, an example according to a conventional technique will be described. FIG. 4 illustrates how the flow rate, pressure, and throttling losses due to flow dividing change relative to a boom operation amount in a conventional technique. In the following, it is presupposed that the operation amount of both the arm 6 and the target flow rate of the arm cylinder 7 are constant.

[0049] FIG. 4(a) illustrates a boom target flow rate, a supply flow rate of a primary pump P1 (supply flow rate of the first hydraulic pump 17), and a supply flow rate of a secondary pump P2 (supply flow rate of the second hydraulic pump 18) relative to the boom operation amount. In the direction of increasing the boom operation amount, the boom target flow rate is zero until the boom operation amount reaches a certain operation amount. That is, no flow rate of the pressure oil is supplied to the boom cylinder 5 from the first hydraulic pump 17 nor the second hydraulic pump 18. When the boom operation amount reaches a certain operation amount (B1), the boom target flow rate starts to increase. At this point, the boom target flow rate is less than the primary pump suppliable flow rate, and thus all the pressure oil of the boom target flow rate can be supplied from the first hydraulic pump 17, which is the primary pump. Accordingly, the target flow rate of the boom first-pump flow combiner valve 28 is equal to the boom target flow rate while the target flow rate of the boom second-pump flow combiner valve 29 is set to zero. This causes the boom first-pump flow combiner valve 28 to open depending on the target flow rate, so that the pressure oil is supplied to the boom cylinder 5 through the boom direction switching valve 27.

[0050] FIG. 4(b) illustrates an arm target flow rate and an arm supply flow rate of the second hydraulic pump 18 relative to the boom operation amount. The arm target flow rate is less than the primary pump suppliable flow rate for the arm cylinder 7 which is not illustrated, and thus all the pressure oil of the arm target flow rate can be supplied from the second hydraulic pump 18 which is the primary pump. Accordingly, the target flow rate of the arm second-pump flow combiner valve 32 is equal to the arm target flow rate, and the target flow rate of the arm first-pump flow combiner valve 31 is set to zero. This cases the arm second-pump flow combiner valve 32 to open depending on the target flow rate, so that the pressure oil is supplied to the arm cylinder 7 through the arm direction switching valve 30.

[0051] FIG. 4(c) illustrates the first-pump pressure (pressure of the first hydraulic pump 17), the second-pump pressure (pressure of the second hydraulic pump 18), the boom pressure (pressure of the boom cylinder 5), and the arm pressure (pressure of the arm cylinder 7) relative to the boom operation amount. In this example, the boom pressure and the arm pressure are constant. In the state in which the boom cylinder 5 is supplied with the pressure oil from the first hydraulic pump 17 and the arm cylinder 7 is supplied with the pressure oil from the second hydraulic pump 18, that is, in a non-flow-combining state, the first-pump pressure is substantially equal to the boom pressure and the second-pump pressure is substantially equal to the arm pressure.

[0052] FIG. 4(d) illustrates throttling losses due to flow dividing relative to the boom operation amount. In the non-flow-combining state described above, no flow dividing occurs in each pump line, and thus a throttling loss due to flow dividing is zero.

[0053] When the boom operation amount increases to an operation amount B2, the flow rate supplied from the first hydraulic pump 17 becomes insufficient, and accordingly, a target flow rate by the amount of an insufficient flow rate is set in the boom second-pump flow combiner valve 29. This causes the boom second-pump flow combiner valve 29 to open depending on the target flow rate, so that the pressure oil thereof is combined with the one which has passed through the boom first-pump flow combiner valve 28 and supplied to the boom cylinder 5. At this time, as illustrated in FIG. 4(c), the second-pump pressure increases until it becomes equal to the first-pump pressure in order to supply the pressure oil to the boom cylinder 5. Furthermore, the opening of the arm second-pump flow combiner valve 32 is throttled so as to divide the flow into that for the boom cylinder 5 and that for the arm cylinder 7 in the second pump line 54. This causes throttling losses at the point where the boom operation amount reaches B2, as illustrated in FIG. 4(d).

[0054] As described above, in the conventional technique, when the flow state is switched from the non-flow-combining state to the flow-combining state or switched from the flow-combining state to the non-flow-combining state, there are cases where the control for changing the opening of a flow combiner valve has to be performed during the fluctuation of the pump discharge pressure, which may cause the change in the actual flow rates supplied to the actuators. For example, while an operation for increasing and decreasing the lever operation amount little by little is being performed and if the target flow rate at that time is close to the primary pump suppliable flow rate, the non-flow-combining state and the flow-combining state are frequently switched and thus the pump discharge pressure fluctuates repeatedly. This may cause operational shock, discomfort during operations, instable control, and the like. Here, the operation for increasing and decreasing the lever operation amount little by little refers to an operation such as sieving the sand placed in the bucket 8.

[0055] Next, the first embodiment of the present invention will be described with reference to FIG. 5 and FIG. 6. FIG. 5 illustrates how a boom target flow rate, a supply flow rate of the primary pump P1 (first hydraulic pump 17), and a supply flow rate of the secondary pump P2 (second hydraulic pump 18) change relative to the boom operation amount. For the changes in the arm flow rate, pressure, and throttling losses which are not illustrated in FIG. 5, in the same manner as those illustrated in FIG. 4(b), FIG. 4(c), and FIG. (d), respectively, an example in which the arm flow rate, the first-pump pressure, the boom pressure, and the arm pressure are constant and the second-pump pressure and the throttling losses vary depending on the switching between the non-flow-combining state and the flow-combining state will be described.

[0056] FIG. 6 illustrates a flowchart of a procedure of the control processing to be executed by the controller 20. The processing illustrated in FIG. 6 is started, for example, upon start of an engine, and is repeatedly executed at predetermined intervals (for example, every one millisecond). In FIG. 6, the processes (S1 to S5) for sequentially calculating a request flow rate, a target flow rate, and a primary pump suppliable flow rate based on an actuator (Act) operation amount has been described above, and thus the details thereof will not be referred below. In the following, the processes after S6, which are the features of the present invention, will be explained in detail.

[0057] In S6, the pump flow combiner valve control section 67 determines an ON / OFF state of a primary pump dischargeable flow rate correction flag. The state of the correction flag is set in S13, S14, which will be described later. An initial value of the correction flag is set to OFF. In the state of the correction flag being OFF, a primary pump suppliable flow rate is not corrected (S8), and in the state of the correction flag being ON, the primary pump suppliable flow rate is corrected to be lowered by a certain amount (predetermined amount) (S7 / flow rate adjustment control).

[0058] In S9, the pump flow combiner valve control section 67 determines whether a target flow rate exceeds the primary pump suppliable flow rate. If it does not exceed, for bringing the state to the non-flow-combining state, the pump flow combiner valve on the secondary pump side is closed (S11). If it exceeds, for bringing the state to the flow-combining state, the pump flow combiner valve on the secondary pump side is opened (S10). In S9, Yes is determined when the boom operation amount in FIG. 5(a) exceeds X1.

[0059] In the flow-combining state, in S12, whether a primary pump insufficient flow rate falls within a range of a secondary pump suppliable flow rate is determined. If it falls within the range, in S13, the correction flag is turned ON. If it is not within the range or if the non-flow-combining state is determined, the correction flag is turned OFF.

[0060] Referring to FIG. 5, how a flow rate changes relative to a boom operation amount in the case where the control flow described above is applied will be described. FIG. 5(a) illustrates an example in which the boom operation amount increases, and FIG. 5(b) illustrates an example in which the boom operation amount decreases. In FIG. 5, Q1 represents a primary pump suppliable flow rate and Q0 represents a primary pump suppliable flow rate after correction.

[0061] In FIG. 5(a), the boom operation amount increases from zero (initial position of the operation lever 21), but a boom target flow rate does not exceed the primary pump suppliable flow rate Q1 until the operation amount reaches X1 (first position of the operation lever 21), during which No is determined in S9 of the control flow and a non-flow-combining state is established. When the boom operation amount exceeds X1, the boom target flow rate exceeds the primary pump suppliable flow rate Q1 (maximum flow rate of the primary pump), at which Yes is determined in S9 of the control flow and the state is switched to the flow-combining state. Furthermore, the correction flag is turned ON and the primary pump suppliable flow rate is lowered to Q0 apparently. As a result, the first-pump supply flow rate (supply flow rate of the first hydraulic pump 17) once decreases when the boom operation amount exceeds X1, and then becomes constant, while the second-pump supply flow rate (supply flow rate of the second hydraulic pump 18) increases as the target flow rate increases. The value obtained by Q1-Q0(=ΔQ) illustrated in in FIG. 5(a) corresponds to the "predetermined amount" according to the present invention.

[0062] Apparently lowering the primary pump suppliable flow rate causes the primary pump insufficient flow rate to increase apparently. If the insufficient flow rate falls within the range of the secondary pump suppliable flow rate, the correction flag ON state is maintained. On the other hand, when the boom operation amount reaches X2, the insufficient flow rate exceeds the range of the secondary pump suppliable flow rate, at which NO is determined in S12 of the control flow and the correction flag is turned OFF. As a result, the primary pump suppliable flow rate returns to Q1 so as to increase the first-pump suppliable flow rate, and also the second-pump suppliable flow rate decreases as the insufficient flow rate decreases. At this point of time, the secondary pump suppliable flow rate becomes ample, which allows the second-pump supply amount to also increase as the boom operation amount further increases. With the configuration described above, the correction for reducing the primary pump suppliable flow rate is cancelled when the target flow rate becomes close to the limit of the total value of the pump suppliable flow rates. This enables the total flow rate that could be originally supplied to the boom cylinder 5 to be reliably supplied thereto from the first hydraulic pump 17 and the second hydraulic pump 18.

[0063] Next, an example in which the boom operation amount decreases as illustrated in FIG. 5(b) will be described. When the boom operation amount decreases from the maximum (any position beyond X1 at which the operation lever 21 is in the first position) and then reaches X2, the insufficient flow rate falls within the range of the secondary pump suppliable flow rate, and thus the correction flag is turned ON. Even if the boom operation amount further decreases and falls below X1 (first position), the flow-combining state is maintained. When the boom operation amount further decreases and reaches X0 (second position at which the operation lever 21 is closer to the initial position than the first position) and falls below X0, the boom target flow rate falls below the primary pump suppliable flow rate Q0 after correction, at which No is determined in S9 of the control flow and the flow state is switched to the non-flow-combining state. At the same time, the correction flag is switched to OFF.

[0064] As described above, in the case of increase in the boom operation amount, the flow state is switched from the non-flow-combining state to the flow-combining state when the boom operation amount reaches X1, on the other hand, in the case of decrease in the boom operation amount, it is switched when the boom operation amount returns to X0. For example, even if an operation of increasing and decreasing the boom operation amount little by little when the boom operation amount is around X1, the flow-combining state is maintained without being switched between the non-flow-combining state and the flow-combining state as long as the boom operation amount does not return to X0. This can prevent operational shock, discomfort during operations, instable control, and the like which are caused by repeated fluctuation in the pump discharge pressure.

[0065] The correction amount (predetermined amount) of the primary suppliable flow rate is set within a range of the secondary suppliable flow rate. The smaller the correction amount is, the more the frequency of switching between the non-flow-combining state and the flow-combining state increases, which enables reduction in throttling losses due to flow dividing. On the other hand, the larger the correction amount is, the more the frequency of switching between the non-flow-combining state and the flow-combining state decreased, which enables improvement in the operability. Preferably, for example, the correction amount is set to any amount in a range between about 1 / 4 to 1 / 2 of the secondary suppliable flow rate (maximum suppliable flow rate of the second hydraulic pump 18).(Modified example)

[0066] FIG. 7 illustrates a relation between a boom operation amount and a flow rate according to a modified example. As illustrated in FIG. 7, in the modified example, the correction amount for the boom operation amount is not made constant but varied. Specifically, the first-pump supply flow rate gradually decreases from a point beyond the boom operation volume X1, and at the same time, the second-pump supply flow rate gradually increases. Furthermore, when the boom operation amount reaches X2, the insufficient flow rate becomes equal to the secondary pump suppliable flow rate, and thereafter, the correction amount gradually decreases so as to prevent the insufficient flow rate from increasing even if the target flow rate increases. As a result, both the first-pump supply flow rate and the second-pump supply flow rate increase. With this configuration, the supply flow rate from each pump changes smoothly so that the operability can be further improved. Here, it is obvious that, in the case of making a correction amount vary, the primary pump insufficient flow rate calculated in accordance with the correction falls within the secondary pump suppliable flow rate.(Second embodiment)

[0067] Next, the second embodiment of the present invention will be described with reference to FIG. 8. FIG. 8 illustrates a flowchart of a procedure of the processing to be executed by the controller according to the second embodiment. FIG. 8 does not illustrate the details of the processes in S102 to S108 as they are the same as those in S2 to S8 of FIG. 6.

[0068] In the second embodiment, in S110, whether the load pressure on a target actuator (Act) is greater than the load pressure on all the other actuators (Act) which are supplied with the pressure oil from the secondary pump of the target actuator. For example, in the first embodiment, in the case where the boom cylinder 5 is the target actuator, the other actuator which is supplied with the pressure oil from the second hydraulic pump 18 (second-pump) which is the secondary pump of the boom cylinder 5 is the arm cylinder 7. In this example, Yes is determined in S110 as the load pressure on the boom cylinder 5 is greater than the load pressure on the arm cylinder 7. After S111, the same processes as those in S10, S12, and S13 according to the first embodiment are carried out in this order. That is, the primary pump suppliable flow rate is corrected to be reduced by a certain amount (predetermined amount) (flow rate adjustment control).

[0069] On the other hand, if No is determined in S110, in other words, when the load pressure on the boom cylinder 5 is smaller than the load pressure on the arm cylinder 7, the discharge pressure of the second hydraulic pump 18 (second-pump) does not change even while the boom cylinder 5 is in a flow-combining state. In this case, setting the correction flag of the primary pump suppliable flow rate to OFF (S116) allow the non-flow-combining state and the flow-combining state to be positively switched, which results in the reduction in throttling losses due to flow dividing.(Third embodiment)

[0070] Next, the third embodiment of the present invention will be described with reference to FIG. 9. FIG. 9 illustrates a flowchart of a procedure of the processing to be executed by the controller according to the third embodiment. FIG. 9 does not illustrate the details of the processes in S202 to S208 as they are the same as those in S2 to S8 of FIG. 6.

[0071] In the third embodiment, in the case where it is determined in S210 that the load pressure on a target actuator (Act) is greater than the load pressure on all the other actuators (Act) which are supplied with the pressure oil from the secondary pump of the target actuator, whether the load pressure on the target actuator (in this example, boom cylinder 5) is more than a certain threshold is determined in S211. The certain threshold (limit value) is a value at which a pump displacement is reduced by horsepower control when the first hydraulic pump 17 (first-pump) and the second hydraulic pump 18 (second-pump) have the same pressure, and in the present embodiment, for example, it is set to 15MPa. That is, when the flow-combining state is established with the load pressure exceeding this threshold value and the first-pump and the second-pump having the same pressure, the pump dischargeable flow rate decreases and thus the supply flow rate to the actuator decreases.

[0072] If the load pressure on the boom cylinder 5 is equal to or less than this threshold, Yes is determined in S211, and the processes after S212 are the same as those in the first embodiment. If the load pressure is more than this threshold, No is determined in S211 and the flow-combining state for the boom is not established (S212). Increasing the operation amount to increase the supply flow rate to the actuator may lead to decrease in the supply flow rate on the contrary, which, however, can be prevented in the configuration described above, and thus discomfort during operations can be prevented.

[0073] In the embodiments described above, the pump flow combiner valves are provided separately from the direction switching valves, however, the direction switching valves (as the pump flow combiner valves in the present invention) may be provided in the pump lines, respectively, to control the supply flow rates from the pumps and combine them at the downstream of the direction switching valves. That is, the flow combiner valves 28, 29 may be used as the direction switching valves, without providing the direction switching valve 27 separately.

[0074] Furthermore, in each of the embodiments described above, the examples in which the target flow rate varies depending on the operation amount have been described, however, the present invention can be also advantageously applied in the case where the target flow rate changes for other factors. For example, in the autonomous control, the request flow rate is calculated directly based on the request speed of the actuator rather than the operation amount, and the target flow rate is calculated based on the request flow rate. Even in the case where the request flow rate does not change, change in the total value of the pump dischargeable flow rates may cause change in the target flow rate.

[0075] Still further, in each of the embodiments described above, the example of a combined operation, in which two or more actuators are driven, has been described, however, the present invention is also advantageous even in the case of a single operation, in which a single actuator is driven. The present invention is particularly advantageous in a situation involving a half-lever operation for, such as finishing, regardless of whether a single operation is performed or a combine operation is performed.

[0076] The embodiments described above are examples for explaining the present invention, and are not intended to limit the scope of the present invention only thereto. Those skilled in the art exploit the present invention in various ways within the scope of the concept of the present invention without departing from it.REFERENCE SIGNS LIST

[0077] 1... construction machine (work machine) 2... upperstructure 3... undercarriage 4... boom 5... boom cylinder (first hydraulic actuator) 6... arm 7... arm cylinder (second hydraulic actuator) 8... bucket 9... bucket cylinder 10... operator's cab 16... control valve 17... first hydraulic pump 18... second hydraulic pump 19... pilot pump 20... controller 21... operation lever (operation member) 24... first-attachment cylinder 25... second-attachment cylinder 26... hydraulic oil tank 27... boom direction switching valve 28... boom first-pump flow combiner valve (flow combiner valve) 29... boom second-pump flow combiner valve (flow combiner valve) 30... arm direction switching valve 31... arm first-pump flow combiner valve 32... arm second-pump flow combiner valve 33... first-attachment direction switching valve 34... first-attachment first-pump flow combiner valve 35... first-attachment second-pump flow combiner valve 36... second-attachment direction switching valve 37... second-attachment first-pump flow combiner valve 38... second-attachment second-pump flow combiner valve 39... first-pump bleed-off valve 40... second-pump bleed-off valve 41... solenoid proportional valve for boom direction switching valve 42... solenoid proportional valve for boom first-pump flow combiner valve 43... solenoid proportional valve for boom second-pump flow combiner valve 44A...boom rod pressure sensor 44B... boom bottom pressure sensor 45A...arm rod pressure sensor 45B...arm bottom pressure sensor 46A...first-attachment rod pressure sensor 46B...first-attachment bottom pressure sensor 47A...second-attachment rod pressure sensor 47B...second-attachment bottom pressure sensor 48... mode selection dial 49... first pump pressure sensor 50... second pump pressure sensor 52... engine 53... first pump line 54... second pump line 55... pilot primary pressure pipe 56... pilot secondary pressure pipe 57... solenoid proportional valve command circuit 60... valve control section 61... request flow rate calculation section 63... pump dischargeable flow rate calculation section 64... priority pump recording section 66... direction switching valve control section 67... pump flow combiner valve control section 68... bleed-off valve control section HD... hydraulic drive device

Examples

first embodiment

(First embodiment)

[0012]Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013]FIG. 1 is a side view illustrating an appearance of a hydraulic excavator which is an example of a work machine according to the present invention. In FIG. 1, a hydraulic excavator 1 includes an undercarriage 3, an upperstructure 2 that is provided to the undercarriage 3 so as to swing, and an operator's cab 10. The upperstructure 2 is provided with a front working device including a boom 4, an arm 6, and a bucket 8. The boom 4, the arm 6, and the bucket 8 are driven by a boom cylinder 5, an arm cylinder 7, and a bucket cylinder 9, respectively, which are hydraulic actuators. Although not illustrated, an attachment may be mounted to the hydraulic excavator 1.

[0014]Here, the boom cylinder 5 corresponds to a first hydraulic actuator according to the present invention, and the arm cylinder 7 corresponds to a second hydraulic actuator according to the present ...

second embodiment

(Second embodiment)

[0067]Next, the second embodiment of the present invention will be described with reference to FIG. 8. FIG. 8 illustrates a flowchart of a procedure of the processing to be executed by the controller according to the second embodiment. FIG. 8 does not illustrate the details of the processes in S102 to S108 as they are the same as those in S2 to S8 of FIG. 6.

[0068]In the second embodiment, in S110, whether the load pressure on a target actuator (Act) is greater than the load pressure on all the other actuators (Act) which are supplied with the pressure oil from the secondary pump of the target actuator. For example, in the first embodiment, in the case where the boom cylinder 5 is the target actuator, the other actuator which is supplied with the pressure oil from the second hydraulic pump 18 (second-pump) which is the secondary pump of the boom cylinder 5 is the arm cylinder 7. In this example, Yes is determined in S110 as the load pressure on the boom cylinder 5 ...

third embodiment

(Third embodiment)

[0070]Next, the third embodiment of the present invention will be described with reference to FIG. 9. FIG. 9 illustrates a flowchart of a procedure of the processing to be executed by the controller according to the third embodiment. FIG. 9 does not illustrate the details of the processes in S202 to S208 as they are the same as those in S2 to S8 of FIG. 6.

[0071]In the third embodiment, in the case where it is determined in S210 that the load pressure on a target actuator (Act) is greater than the load pressure on all the other actuators (Act) which are supplied with the pressure oil from the secondary pump of the target actuator, whether the load pressure on the target actuator (in this example, boom cylinder 5) is more than a certain threshold is determined in S211. The certain threshold (limit value) is a value at which a pump displacement is reduced by horsepower control when the first hydraulic pump 17 (first-pump) and the second hydraulic pump 18 (second-pump)...

Claims

1. A work machine comprising: a hydraulic drive device including a first hydraulic pump, a second hydraulic pump, a first hydraulic actuator driven by a pressure oil supplied from the first hydraulic pump, and a flow combiner valve for combining the pressure oil supplied from the first hydraulic pump and a pressure oil supplied from the second hydraulic pump to communicate a pressured oil thus combined to the first hydraulic actuator; an operation member to be operated by an operator; and a controller configured to control the hydraulic drive device based on an operation amount of the operation member, the controller being configured to: in a case where the operation member is operated in a direction of increasing the operation amount, until the operation member reaches a first position from an initial position, control the flow combiner valve so as to supply the pressure oil from the first hydraulic pump to the first hydraulic actuator; in a case where the operation member is operated in a direction of increasing the operation amount beyond the first position, control the flow combiner valve so as to combine the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump and supply the pressure oil thus combined to the first hydraulic actuator in response to increase in the operation amount; and in a case where the operation member is operated in a direction of decreasing the operation amount from any position beyond the first position and the operation amount reaches a second position closer to the initial position than the first position, control the flow combiner valve so as to cancel a flow-combining state in which the pressure oil from the first hydraulic pump is combined with the pressure oil from the second hydraulic pump, and supply the pressure oil from the first hydraulic pump to the first hydraulic actuator in response to decrease in the operation amount.

2. The work machine according to claim 1, wherein the first position is set to an operation position of the operation member which corresponds to a maximum flow rate that can be supplied from the first hydraulic pump.

3. The work machine according to claim 2, wherein the controller is configured to: in combining the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump, carry out a flow rate adjustment control for decreasing a supply flow rate of the pressure oil from the first hydraulic pump to the first hydraulic actuator by a predetermined amount and increasing a supply flow rate of the pressure oil from the second hydraulic pump to the first hydraulic actuator by the predetermined amount.

4. The work machine according to claim 3, wherein the predetermined amount is predetermined within a range of a flow rate that can be supplied from the second hydraulic pump.

5. The work machine according to claim 3, further comprising a second hydraulic actuator driven by the pressure oil supplied from the second hydraulic pump, wherein the controller is configured to: in combining the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump, carry out the flow rate adjustment control only in a case where a pressure on the first hydraulic actuator is greater than a pressure on the second hydraulic actuator.

6. The work machine according to claim 5, wherein the controller is configured to: in combining the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump, control the flow combiner valve so as not to combine the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump in a case where the pressure on the first hydraulic actuator exceeds a limit value of a discharge pressure of the first hydraulic pump even in the case where the pressure on the first hydraulic actuator is greater than the pressure on the second hydraulic actuator.

Images